© Vincent Hayward, 1997,1998,1999,2000,2001,2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2015, 2015. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder such as IEEE's or ACM's . Appropriate credit must be given as to its source and authorship.

Abstracts of Publications by Vincent Hayward


Adams, M., Johnson, S., Lefèvre, Ph., Levesque, V., Hayward, V., André, T., Thonnard, J.-L. 2013.
Finger pad friction and its role in grip and touch.
Journal of the Royal Society Interface, 10(80):20120467, online: doi 10.1098/rsif.2012.0467

Many aspects of both grip function and tactile perception depend on complex frictional interactions occurring in the contact zone of the finger pad, which is the subject of the current review. While it is well established that friction plays a crucial role in grip function, its exact contribution for discriminatory touch involving the sliding of a finger pad is more elusive. For texture discrimination, it is clear that vibrotaction plays an important role in the discriminatory mechanism. Among other factors, friction impacts the nature of the vibrations generated by the relative movement of the fingertip skin against a probed object. Friction also has a major influence on the perceived tactile pleasantness of a surface. The contact mechanics of a finger pad is governed by the fingerprint ridges and the sweat that is exuded from pores located on these ridges. Counter-intuitively, the coefficient of friction can increase by an order of magnitude in tens of seconds when in contact with an impermeably smooth surface, such as glass, whereas the value will decrease for a porous surface, such as paper. The increase in friction is attributed to an occlusion mechanism and can be described by first order kinetics. Surprisingly, the sensitivity of the friction to the normal load and sliding velocity is comparatively second order, yet it provides the main basis for evaluating theoretical models which, to-date, largely ignore the time evolution of the frictional dynamics. One well-known effect on taction is the possibility of inducing stick-slip if the friction decreases with increasing sliding velocity. Moreover, the initial slip of a finger pad occurs by the propagation of an annulus of failure from the perimeter of the contact zone and this phenomenon could be important in tactile perception and grip function.
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André, T., Levesque, V., Hayward, V., Lefèvre, P., and Thonnard, J.-L. 2011.
Effect Of Skin Hydration On The Dynamics Of Fingertip Gripping Contact.
Journal of the Royal Society Interface. 8(64):1574-1583.

The dynamics of fingertip contact manifest themselves in the complex skin movements observed during the transition from a stuck state to a fully developed slip. While investigating this transition, we found that it depended on skin hydration. To quantify this dependency, we asked subjects to slide their index fingertip on a glass surface while keeping the normal component of the interaction force constant with the help of visual feedback. Skin deformation inside the contact region was imaged with an optical apparatus that allowed us to quantify the relative sizes of the slipping and sticking regions. The ratio of the stuck skin area to the total contact area decreased linearly from one to zero when the tangential force component increased from zero to a maximum. The slope of this relationship was inversely correlated to the normal force component. The skin hydration level dramatically affected the dynamics of the contact encapsulated in the course of evolution from sticking to slipping. The specific effect was to reduce the tendency of a contact to slip, regardless of the variations of the coefficient of friction. Since grips were more unstable under dry skin conditions, our results suggest that the nervous system responds to dry skin by exaggerated grip forces that cannot be simply explained by a change in the coefficient of friction.
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Astley, O. and Hayward, V. 2000.
Design Constraints For Haptic Surgery Simulation.
Proc. of the IEEE Int. Conf. on Robotics and Automation, San Francisco, CA, April 2000. pp. 2446-2451.

There are many engineering challenges that must be addressed in order to successfully integrate haptics with the environmental characteristics found in surgery. The most fundamental of these challenges is to achieve update rates of solid nonlinear deformable objects that are acceptable to the human haptic system. This paper presents a software architecture that is designed to meet these challenges by analysing the task, the haptic, and the hardware constraints of surgery simulation.
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Astley, O. and Hayward, V. 1998.
Multirate Haptic Simulation Achieved By Coupling Finite Element Meshes Through Norton Equivalents.
Proc. IEEE Int. Conf. on Robotics and Automation. pp. 989-994.

This paper introduces a methodology to simulate the dynamics of deformable visco-elastic 3-dimensional bodies in real-time for haptic interaction. The method is based upon a finite element approach. The central idea in this scheme is to reduce the computation required in regions which are to the periphery of the region of interaction between the virtual haptic device and the virtual body. This is accomplished by implementing a multi-layer finite element mesh. The top layer, or parent, consists of a coarse mesh of the entire body; child meshes represent sub-regions of the coarse mesh, but have a much finer resolution. By using equivalent impedances to relate the two meshes, it is possible to decouple the coarse and fine regions; this enables the system to not only to have different resolutions in different regions, but also allows the parent and child meshes to be updated at different frequencies. The multi-layer mesh also addresses numerical integration issues.
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Astley, O. and Hayward, V. 1997.
Real-Time Finite-Elements Simulation Of General Visco-Elastic Materials For Haptic Presentation.
Workshop on Dynamic Simulation: Methods and Applications. IROS'97 1997 IEEE/RSJ Int. Conf. on Intelligent Robotics and Systems, Grenoble, France, Sept. 1997. pp. 52-57.

This paper introduces a methodology to simulate the dynamics of visco-elastic 3-dimensional bodies in real-time using a finite element approach. The method is currently being applied to a haptic simulation of a deformable body incorporating mass, damping, and stiffness. The central idea in this scheme is to reduce the computation required in regions which are to the periphery of area of interaction between the virtual haptic device and the virtual body. This is accomplished by implementing a multi-layer mesh; the top layer, or parent mesh, consisting of a coarse mesh, while child meshes represent sub-regions of the coarse mesh but have a much finer resolution. The effective decoupling of regions enables the system not only to have different resolutions in different regions, but also allows the regions of the mesh to be updated at different frequencies. The key to achieving this is by utilizing equivalent impedances.
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Astley, O. and Hayward, V. 1997.
An Experimental Procedure For Autonomous Joint Sensor Estimation Using Adaptive Control.
Proc. IEEE Int. Conf. on Robotics and Automation. Vol. 2, pp. 1743-1748.

The autonomous parameter estimation of a manipulator is considered with respect to both dynamic and joint sensor properties. Using methods based on adaptive control, a new formulation is introduced such that bench calibration of the robot joint sensors and actuators is no longer necessary. This method is unique because estimation is done with respect to invariant forces due to gravity loading. The method also guarantees convergence to the true values from arbitrary initial estimates; consequently, the algorithm can also be used for manipulator self test. Experimental results are presented which were performed on two links of a a six degree of freedom hand-controller. Results show that angles can be recovered to an accuracy of +-1o in the absence of initial estimates.
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Aubry, S. and Hayward, V. 1987a.
Recursive decomposition of free-space from boundary points.
Proc. Workshop on Spatial Reasoning and Multi-Sensor Fusion. pp. 118-126.

Because of the exponential complexity nature of robotic path-planning and collision detection, there has been an increasing trend to approach the problem from a representational point of view as much as from an algorithmic one. The article addresses the issues involved in converting the information given by a collection of surface points such as those made available from a range sensor, into a hierarchical volumetric decomposition. The aim of the representation is to achieve search efficiency, compactness and parallelism while avoiding the creation of an arbitrary coordinate system such as is the case with the octree representation. The authors propose a paradigm for achieving such a goal, they show that surface connectivity is a key element of a valid representation and they present a method to obtain such a connectivity in optimal time. Finally, they suggest that, because of topological considerations, the representation of free-space is often preferable to the representation of obstacles.
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Aubry, S. and Hayward, V. 1995.
Three Dimentional Model Construction From Multiple Sensor View Points.
Proc. Int. IEEE Conference on Robotics and Automation. pp. 2054-2059.

We address the problem of constructing a boundary model of an object when the input consists of a set of points that lie on its surface. We assume that the points are acquired using telemetric techniques. Such data constitute a discrete sampling of the surface: a "cloud" of points. Supplemental connectivity informa- tion between those points is necessary if one is to re- construct an approximation to the underlying object. We use the implicit information provided by the ac- quisition procedure itself to achieve this goal.
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Azar, T. and Hayward, V. 2008.
Estimation of the Fracture Toughness of Soft Tissue From Needle Insertion.
Proc. Biomedical Simulation, 4th International Symposium, ISBMS 2008, Bello, F. and Edwards, E. (Eds.) Lecture Notes in Computer Science, Vol. 5104, Springer Verlag, pp. 166-175.

A fracture mechanics approach was employed to develop a model that can predict the penetration force during quasi-static needle insertion in soft tissue. The model captures a mechanical process where the sharp needle produces a crack that is opened to accommodate the shaft of the needle. This process involves the interchange of energy between four distinct phenomena: the work done by the needle, the irreversible work of fracture, the work of friction, and the change in recoverable strain energy. From measurements made in vivo, porcine liver fracture toughness was estimated from the dierence in penetration force between two consecutive insertions at the same location. The values obtained fall within a reasonable range and conrm the relevance of a computational model of needle insertion based on fracture mechanics.
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Aubry, S. and Hayward, V. 1987b.
Range image analysis using level curves.
Proceedings of the Scandinavian Conference on Image Analysis. pp. 661-668.

Of the many methods for obtaining range images (Jarvis 1983), triangulation techniques are generally believed to offer the best trade-off among the measures of reliability, of accuracy and of implementation costs (Aubry and Hayward 1986). Some of the main techniques published in this field are reviewed. The authors present a new methodology for analysing range images based on level curves, or lines of equal depth. An application of the algorithm on blocks-world polyhedra is given.
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Bergmann Tiest, W. and Hayward, V. 2015.
Inside vs. Outside: Haptic Perception of Object Size.
Proceedings of the IEEE World Haptics Conference, 94-99.

We have performed a psychophysical experiment to investigate differences in perceived object size when exploring the inside or outside of objects. The experiment consisted of five conditions, in which ten blindfolded subjects compared the size of circular disks and holes using either the index finger, two different probes, the finger-span method, or an infinitesimal virtual probe. The result showed significant negative biases for the conditions with the large probe and the finger-span method, meaning that an object felt on the inside should be larger than an object felt on the outside in order to be perceived as the same size. This indicates that subjects are unable to sufficiently correct for the diameter of the probe when exploring objects. At the same time, a general tendency was observed in all conditions that involved movement to feel the inside of objects as larger than the outside. This suggests that, in order to obtain a neutral estimate of object size in a virtual environment, one should use a virtual probe diameter of about 4 % of the size of the object to be explored.
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Berrezag, A. Visell, Y. Hayward, V. 2012.
Compressibility and Crushability Reproduction Through an Amorphous Haptic Interface.
Proceedings of Eurohaptics 2012. (Demonstration). pp. 186-190.

The demonstration involves a new haptic interface intended to reproduce, with high-fidelity, properties of complex materials that are experienced through pressing and squeezing actions, at the detriment of shape.
Proceedings of Eurohaptics 2012, LNCS 7283, Part II, pp. 186-190 (Demonstration) [PDF] [ Back ]

Bochereau, S., Sinclair, S., Hayward, V. 2018.
Perceptual Constancy in the Reproduction of Virtual Tactile Textures With Surface Displays.
ACM Transactions on Applied Perception, 15(2):10.

For very rough surfaces, friction-induced vibrations contain frequencies that change in proportion to sliding speed. Given the poor capacity of the somatosensory system to discriminate frequencies, this fact raises the question of how accurately nger sliding speed must be known during the reproduction of virtual textures with a surface tactile display. During active touch, ten observers were asked to discriminate texture recordings corresponding to di erent speeds. The samples were constructed from a common texture which was resampled at various frequencies to give a set of stimuli of di erent swiping speeds. In trials, they swiped their nger in rapid succession over a glass plate which vibrated to accurately reproduce three texture recordings. Two of these recordings were identical and the third di ered in that the sample represented a texture swiped at a speed di erent from the other two. Observers identi ed which of the three samples felt di erent. For a metal mesh texture recording, seven observers reported di erences when the speed varied by 60, 80 and 100 millimetres per second while the other three did not reach a discrimination threshold. For a ner leather chamois texture recording, thresholds were never reached in the 100 mm/s range. These results show that the need for high-accuracy measurement of swiping speed during texture reproduction may actually be quite limited compared to what is commonly found in the literature.
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Bochereau, S., Dzidek, B., Adams, M., Hayward, V. 2017.
Characterizing and imaging gross and real finger contacts under dynamic loading.
IEEE Transactions on Haptics, 10(4):456--465.

We describe an instrument intended to study finger contacts under tangential dynamic loading. This type of loading is relevant to the natural conditions when touch is used to discriminate and identify the properties of the surfaces of objects  it is also crucial during object manipulation. The system comprises a high performance tribometer able to accurately record in vivo the components of the interfacial forces when a finger interacts with arbitrary surfaces which is combined with a high-speed, high-definition imaging apparatus. Broadband skin excitation reproducing the dynamic contact loads previously identified can be effected while imaging the contact through a transparent window, thus closely approximating the condition when the skin interacts with a non-transparent surface during sliding. As a preliminary example of the type of phenomenon that can be identified with this apparatus, we show that traction in the range from 10 to 1000 Hz tends to decrease faster with excitation frequency for dry fingers than for moist fingers.
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Bochereau, S., Sinclair, S. and Hayward, V. 2015.
Looking for Physical Invariants in the Mechanical Response of a Tactually Scanned Braille Dot.
Proceedings of the IEEE World Haptics Conference, pp. 119-124.

One human finger explored plastic Braille dots using a variety of velocity and force profiles. The fingertip friction forces were measured. Characteristics of the interaction were studied to explore the manifestation of the amplitude/duration interdependence of signals across velocity, normal force and dot height. Both amplitude, defined here as maximum tangential force, and duration, were seen to vary with velocity and normal force, however the integral of the tangential force over time was found to not have a strong dependence on either variable. When three consecutive dots of varying height were examined, the tangential force integral was not constant, but increased in proportion to height. We propose that the nervous system may use the tangential force integral as an invariant to recognise the same spatial asperity explored under different velocity and force conditions.
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Bochereau, S., Terekhov, A. V., and Hayward, V. 2014.
Amplitude and Duration Interdependence in the Perceived Intensity of Complex Tactile Signals
in Haptics: Neuroscience, Devices, Modeling, and Applications, Part-I, Auvray, M. and Duriez, C. (Eds). pp. 93-100

The dependency of the perceived intensity of a short stimulus on its duration is well established in vision and audition. No such phenomenon has been reported for the tactile modality. In this study naive observers were presented with pink noise vibrations enveloped in a Gabor wavelet. Characteristic durations ranging between 100 and 700 ms and intensities ranging from 0.3 and 3.0 10-3 m/s2 were presented to the fingertip. Using a two alternative forced choice staircase procedure, the points of subjective equivalence were estimated for the 400 ms long ref- erence stimulus. Similarly to vision and audition, lower intensities were consistently reported for shorter stimuli. The observed relationship could be interpreted as reflecting a mechanism of haptic constancy with respect to exploration speed.
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Bonneton, E. 1994.
Pantograph Project, Chapter: Implementation of a virtual wall.
Technical Report. McGill Research Center for Intelligent Machines. McGill University, Montreal, Canada.

The purpose of this project, is to continue on the results achieved by Jehangir Choksi, Gonzalo Layin and Angelo Mirarchi in their Project Laboratory (April 13, 1993): the designed pantograph is the master of a teleoperation system whose slave, which has he position of its master, manoeuvres in a virtual environment. The virtual forces aplied to the slave are reflected to the operator by the way of the manipulandum. Knowing position and velocity should allow one to perform any desired force model. The stability problems occuring when one wants to model string or damping forces will be emphasized.
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Boulet, B. and Hayward, V. 2000.
Robust Control Of A Robot Joint With Hydraulic Actuator Redundancy.
Proceedings of 31st International Symposium on Robotics (ISR2000), Montreal, Canada, May 14-17, 2000, pp. 36-41.

A robot joint with two hydraulic actuators, one being redundant, is described. Two methods are proposed for allocating actuation effort in terms of the solutions of minimum-norm problems. In each case, a particular physical interpretation is given. A robust pid controller derived from robust servomechanism theory and a robust controller based on the H-inf-optimal sensitivity minimization method are designed and experimentally tested. Conclusions are drawn comparing the two approaches.
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Boulet, B., Daneshmend, L. K., Hayward, V., and Nemri, C. 1993.
System Identification And Modelling Of A High Performance Hydraulic Actuator.
In Experimental Robotics 2, Chatila, R., Hirzinger, G. (Eds.), Lecture Notes in Control and Information Sciences, Springer Verlag, pp. 505-520.

Detailed knowledge of actuator properties is a prerequisite for advanced manipula- tor design and control. This paper deals with the experimental identification and modelling of the nonlinear dynamics of a high performance hydraulic actuator. Such actuators are of interest for applications which require both high power and high bandwidth. An analytical model of the system is formulated, and a software simulator implementing the force-controlled actuator model including all the nonlinear elements is shown to predict the real system's behavior quite well. The actuator properties and performance are also discussed.
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Boyer, M., Daneshmend, L. K., Hayward, V., and Foisy, A. 1991.
An object-oriented paradigm for the design and implementation of robot planning and programming systems.
Proc. IEEE Int. Conference on Robotics and Automation, pp. 204-209.

Traditional software design methodologies have been shown to have drawbacks in designing and implementing software systems for robotics. A novel dual-hierarchical object-oriented design methodology is presented, which is well suited to problems of this type. A practical example of the application of this methodology is presented, utilizing CLOS as the implementation vehicle. The methodology developed is shown to facilitate the programming and planning of complex robot tasks, and the provision of generic recovery procedures for exception handling.
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Cai, V. A. D., Bidaud, P., Hayward, V., Gosselin, F. 2017.
Self-adjustment mechanisms and their application for orthosis design
Meccanica, 52(3):713-728.

Medical orthoses aim at guiding anatomical joints along their natural trajectories while preventing pathological movements, especially in case of trauma or injuries. The motions that take place between bone surfaces have complex kinematics. These so-called arthrokinematic motions exhibit axes that move both in translation and rotation. Traditionally, orthoses are carefully adjusted and positioned such that their kinematics approximate the arthrokine- matic movements as closely as possible in order to protect the joint. Adjustment procedures are typically long and tedious. We suggest in this paper another approach. We propose mechanisms having intrinsic self-aligning properties. They are designed such that their main axis self-adjusts with respect to the joints physiological axis during motion. When connected to a limb, their movement becomes homokinetic and they have the property of automatically minimizing internal stresses. The study is performed here in the planar case focusing on the most important component of the arthrokinematic motions of a knee joint.
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Cai, V. A. D., Bru, B., Bidaud, P., Hayward, V., and Pasqui, V. 2010.
Experimental Evaluation of a Goniometer For the Identification of Anatomical Joint Motions.
Proc. of the Thirteenth International Conference on Climbing and Walking Robots and the Support Technologies for Mobile Machines, CLAWAR 2010, pp. 1255--1262.

This paper exposes the experimental evaluation of a new technique for the estimation of the instantaneous helical axis of movement of human anatomical joints. The measurement technique, using a six degrees of freedom spatial electro-goniometer, is tested onto a simple revolute joint and onto a subjects knee. A motion capture system with active optical markers is used at the same time in order to validate the measurement results.
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Cai, V. A. D., Bidaud, P., Hayward, V., and Gosselin, F. 2010.
Estimation of Complex Anatomical Joint Motions Using a Spatial Goniometer.
Proc. of the 18th CISM-IFToMM Symposium on Robot Design, Dynamics, and Control, ROMANSY 2010, pp 399-406.

The determination of the instantaneous axis of rotation of human joints has numerous applications. The screw axis can be determined using optical motion capture systems or electromechan- ical goniometers. In this paper, we introduce a new method for the localization of the instantaneous screw axis in human anatomical joints from the data given by a spatial mechanical goniometer.
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Cai, V. A. D., Bidaud, P., Hayward, V., and Gosselin, F. 2009.
Design of Self-Adjusting Orthoses For Rehabilitation.
Proc. of the 14th IASTED International Conference Robotics and Applications, pp. 215-223.

Safety and comfort are primary concerns in rehabil- itation devices and exoskeletons. However, the re- sult of using simplified kinematic arrangements can be discomfort, or even injury, as a result of overcon- straining the joint. In this paper, we describe a self-adjusting mechanism able to overcome misalignment between the rotational axis of the mechanism that is attached to the users limbs and the rotational axis of the anatomical joint. Additional degrees of free- dom are added to the mechanism to eliminate inter- nal residual forces. Furthermore, a new technique for the estimation of the Instantaneous Center of Rotation of the assisted joint based on velocity and position sensors is demonstrated. We illustrate this technique with a mechanism which is able to self-adjust with or without resorting to motorized add-ons. Kinematic analyses are presented and are validated by computer simulation on 2D examples.
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Campion, G. and Hayward, V. 2009.
Fast Calibration Of Haptic Texture Synthesis Algorithms.
IEEE Transactions on Haptics. 2(2):85-93.

Calibrating displays can be a time-consuming process. We describe a fast technique for adjusting the subjective experience of roughness produced by different haptic texture synthesis algorithms. Its efficiency is due to the exponential convergence of the ``modified binary search method'' (MOBS) applied to find points of subjective equivalence between virtual haptic textures synthesized by different algorithms. The method was applied to find the values of the coefficient of friction in a friction-based texture algorithm that yield the same perception of roughness as the normal-force variations of conventional texture synthesis algorithms. Our main result is a table giving the perceptual equivalence between parameters having different physical dimensions. A similar method could be applied to other perceptual dimensions provided that the controlling parameter be monotonically related to a subjective estimate.
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Campion, G. and Hayward, V. 2008.
On the Synthesis of Haptic Textures.
IEEE Transactions on Robotics, 24(3):527-536.

Advanced, synthetic haptic virtual environments require textured virtual surfaces. We found that texturing smooth surfaces often reduces the system passivity margin of a haptic simulation. As a result, a smooth virtual surface that can be rendered in a passive manner may loose this property once textured. We propose that any texture algorithm is associated with a characteristic number that expresses the relative change in loop gain. We further found that a passive virtual interaction can have severe unwanted artifacts if the synthesized force field is not conservative. The energy characteristics of seven algorithms are analyzed. Finally a new texture synthesis algorithm, which operates by modulating a friction force during scanning, is shown to have several advantages over previous ones.
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Castaños, F., Gromov, D., Hayward, V., Michalska, H. 2013.
Implicit and explicit representations of continuous-time port-Hamiltonian systems.
Systems & Control Letters, 62(4):324-330

Implicit and explicit representations of smooth, finite-dimensional port-Hamiltonian systems are studied from the per- spective of their use in numerical simulation and control design. Implicit representations arise when a system is modeled in Cartesian coordinates and when the system constraints are applied in the form of additional algebraic equations. Explicit representations are derived when generalized coordinates are used. By virtue of their selection, they automat- ically provide for the satisfaction of the system constraints. A relationship between the phase spaces for both system representations is derived in this article, justifying the equivalence of the representations in the sense of preserving their Hamiltonian functions as well as their Hamiltonian symplectic forms, ultimately resulting in the same Hamiltonian flow.
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Campion, G., Gosline, A. H. and Hayward, V. 2008b.
Does Judgement of Haptic Virtual Texture Roughness Scale Monotonically With Lateral Force Modulation?
Proc. Eurohaptics 2008, LNCS 5024, Springer-Verlag, pp. 718-723.

We describe experiments that compared the perceived relative roughness of textured virtual walls synthesized with an accurately controlled haptic interface. Texture was modeled as a spatially modulated sinusoidal friction grating. The results indicate that both the modulation depth of the grating (A), and the coefcient of friction (mu) are strongly associated with the perceived roughness when increasing either A or mu. Changing the spatial period of the grating however, did not yield consistent relative roughness judgement results, indicating that there is a weaker association.
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Campion, G., Gosline, A. H. and Hayward, V. 2008a.
Passive Viscous Haptic Textures.
Proc. 16th Symposium on Haptic Interfaces For Virtual Environment And Teleoperator Systems, pp. 379-380.

We describe the use of eddy current brakes for the synthesis haptic textures. Textural effects are achieved through rapid variations of the viscous damping coefcient that these brakes create when activated. We demonstrate that eddy current brakes can be actuated reliably at frequencies typical of haptic texture rendering. Performance is evaluated by measuring the movement of the manipulandum with an accelerometer while modulating the viscous force at high frequency. Key advantages of this technique include guaranteed passivity of the haptic synthesis, accurate results from the linear dynamics of these brakes, and elimination of the need to estimate or observe velocity.
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Campion, G., Gosline, A. H. and Hayward, V. 2006. Initial results using Eddy Current Brakes as Fast Turn-on, Programmable Physical Dampers for Haptic Rendering.
Proc. 14th Symposium on Haptic Interfaces For Virtual Environment And Teleoperator Systems IEEE VR 2006. pp. 73-74.

We demonstrate the use of eddy current braking as programmable, fast turn-on, physical damping to improve both the impedance range and stability of a haptic interface while rendering virtual walls and friction.
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Campion, G., Wang, Q., and Hayward, V. 2005.
The Pantograph Mk-II: A Haptic Instrument.
Proc. IROS 2005, IEEE/RSJ Int. Conf. Intelligent Robots and Systems, pp. 723-728.

We describe the redesign and the performance evaluation of a high-performance haptic device system called the Pantograph. The device is based on a two degree-of-freedom parallel mechanism which was designed for optimized dynamic performance, but which also is well kinematically conditioned. The results show that the system is capable of producing accurate tactile signals in the DC-400 Hz range and can resolve displacements of the order of 10 micrometers. Future improvements are discussed.
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Campion, G. and Hayward, V. 2005.
Fundamental Limits in The Rendering of Virtual Haptic Textures.
Proc. First Joint Eurohaptics Conference and Symposium on Haptic Interfaces for Virtual Environments and Teleoperator Systems WHC'05, pp. 263-270.

We analyze properties that fundamentally limit the ability of a force-feedback haptic simulation system to create periodic gratings. These properties include sampling rate, device resolution, and structural dynamics. Basic sampling limitations are analyzed in terms of the Nyquist and the Courant conditions. The analysis proposes that the sampling noise injected in the system may prevent it to achieve acceptable performance under many circumstances, unless special precautions, such as the use of reconstruction filters, make the closed-loop more robust to noise. The structural response of a PHANTOM 1.0A device was such that no such filter could be found, and the device could introduce heavy distortion in gratings as coarse as 10 mm. The Pantograph Mark-II device having more favorable structural properties could reliably create gratings between 1 and 10 mm.
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Carter, O., Konkle, T., Wang, Q., Hayward, V., Moore, C. I. 2008.
Tactile Rivalry Demonstrated with an Ambiguous Apparent-Motion Quartet.
Current Biology, 18(14):1050-1054.

When observers view ambiguous visual stimuli, their perception will often alternate between the possible interpretations, a phenomenon termed perceptual rivalry [1]. To induce perceptual rivalry in the tactile domain, we developed a new tactile illusion, based on the visual apparent motion quartet [2]. Pairs of 200 ms vibrotactile stimuli were applied to the finger pad at intervals separated by 300 ms. The location of each successive stimulus pair alternated between the opposing diagonal corners of the ~1 cm2 stimulation array. This stimulation sequence led all participants to report switches between the perception of motion traveling either up/down or left/right across their fingertip. Adaptation to tactile stimulation biased towards one direction caused subsequent ambiguous stimulation to be experienced in the opposing direction. In contrast, when consecutive trials of ambiguous stimulation were presented, motion was generally perceived in the direction consistent with the motion reported in the previous trial. Voluntary eye movements induced shifts in the tactile perception towards a motion axis aligned along a world-centered coordinate frame. Because the tactile quartet results in switching perceptual states despite unvaried sensory input, it is ideally suited to future studies of the neural processes associated with conscious tactile perception.
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Cruz-Hernandez, J. M. and Hayward, V. 2001.
Phase Control Approach To Hysteresis Reduction.
IEEE T. On Control Systems Technology. Vol. 9, No. 1, pp. 17-26.

This paper describes a method for the design of compensators able to reduce hysteresis in transducers, as well as two measures to quantify and compare controller performance. Rate independent hysteresis, as represented by the Preisach model of hysteresis, is seen as an inputoutput phase lag. The compensation is based on controllers derived from the phaser, a unitary gain operator that shifts a periodic signal by a single phase angle. A variable phaser is shown to be able to handle minor hysteresis loops. Practical implementations of these controllers are given and discussed. Experimental results exemplify the use of these techniques.
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Cruz-Hernandez, J. M. and Hayward, V. 1998b.
Reduction of Major and Minor Hysteresis Loops in a Piezoelectric Actuator.
Proc. 1998. CDC Conference.

This paper addresses the compensation of major and minor hysteresis loops using an operator termed a phaser which shifts the phase of a periodic signal by an amount phi. For periodic inputs, hysteresis can be approximated by a phaser with a negative phase shift opening the possibility of cascade compensation. Since in actual hysteresis the phase shift varies according to the size of the input, giving rise to minor loops, the possibility exists to handle the compensation of minor loops by using phasers which vary the phase shift according to the magnitude of the input in an inverse fashion. In this paper, this technique is applied to the compensation of a piezoelectric actuator.
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Cruz-Hernandez, J. M., and Hayward, V. 1998.
An Approach To Reduction Of Hysteresis In Smart Materials.
Proc. IEEE Int. Conf. on Robotics and Automation. pp. 1510-1515.

This paper addresses the problem of reducing the hysteresis found in the actuation of most smart materials. They are divided in two groups: systems with no saturation (e.g. piezoelectric actuators), and systems with saturation (e.g. Shape Memory Actuators). For the control of the first group the concept of phaser is introduced, an operator which shifts the phase of a periodic signal but keeps its magnitude unchanged. Since it is possible to approximate phasers with linear filters, it is possible to design practical compensators. The design of a phaser requires the knowledge of one parameter phi, easily identified from experimental transfer function estimates. For the second group, two phasers are used in a tandem connection. One phaser is designed as described before, and the second is designed so as to vary with the input. This compensation reduces the hysteresis to a single saturation. To show its effectiveness, simulation results are provided using the hystery model, then the method is applied to an SMA actuator. The effectiveness of a single phaser for non-saturated hysteresis have already been experimentally demonstrated in previous work.
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Cruz-Hernandez, J. M., and Hayward, V. 1997.
On The Linear Compensation Of Hysteresis.
IEEE CDC-97. pp. 1956-1957.

Compensation for hysteresis often relies on a precise system model. This makes controller design complicated and time consuming. In this paper, the Preisach hysteresis model is interpreted in terms of phase shift. This leads to a simple linear compensator design methodology. The closed-loop connection of a compensator that we call a phaser with a nonlinear system with hysteresis is shown to produce an almost linear response in a given operating range. The present method is advantageous for its simplicity and robustness and requires the identification of only one parameter. This result is experimentally applied to the control of a piezoceramic actuator.
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Cruz-Hernandez, M., and Hayward, V. 2005.
Position Stability For Phase Control Of The Preisach Hysteresis Model
Transactions of the CSME (Special Edition), Vol. 29, No. 2, pp. 129--142.

Many systems with hysteresis are adequately represented by the Preisach model. Hysteresis in these systems can be very effectively reduced using the "phaser", an ideal frequency domain operator, in a feedback connection. The position stability of this type of control has not yet been established in spite of the experimental evidence that the resulting systems are stable. This paper shows the dissipativity for the relay operator, for the Preisach model, and then for the lead approximation to the phaser. We then give a proof of stability for the feedback connection of this phaser approximation with systems represented by the Preisach model of hysteresis.
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Delhaye, B., Hayward, V., Lefèvre, Ph., Thonnard, J.-L. 2012.
Texture-induced vibrations in the forearm during tactile exploration.
Frontiers in Behavioral Neuroscience. 6(7):1-10.

Humans can detect and discriminate between fine variations of surface roughness using active touch. It is hitherto believed that roughness perception is mediated mostly by cutaneous and subcutaneous afferents located in the fingertips. However, recent findings have shown that following abolishment of cutaneous afferences resulting from trauma or pharmacological intervention, the ability of subjects to discriminate between textures roughness was not significantly altered. These findings suggest that the somatosensory system is able to collect textural information from other sources than fingertip afference. It follows that signals resulting of the interaction of a finger with a rough surface must be transmitted to stimulate receptor populations in regions far away from the contact. This transmission was characterized by measuring in the wrist vibrations originating at the fingertip and thus propagating through the finger, the hand and the wrist during active exploration of textured surfaces. The spectral analysis of the vibrations taking place in the forearm tissues revealed regularities that were correlated with the scanned surface and the speed of exploration. In the case of periodic textures, the vibration signal contained a fundamental frequency component corresponding to the finger velocity divided by the spatial period of the stimulus. This regularity was found for a wide range of textural length scales and scanning velocities. For non-periodic textures, the spectrum of the vibration did not contain obvious features that would enable discrimination between the different stimuli. However, for both periodic and non-periodic stimuli, the intensity of the vibrations could be related to the microgeometry of the scanned surfaces.
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Deroy, O., Fasiello, I., Hayward, V., Auvray, M. 2016.
Differentiated audio-tactile correspondences in sighted and blind individuals.
Journal of Experimental Psychology: Human Perception and Performance. 42(8):1204-1214.

The aim of the present study is to investigate whether the crossmodal correspondence robustly documented between auditory pitch and visual elevation has analogues in the audio-tactile domain. Across four experiments, the compatibility effects between intuitively congruent pairs of stimuli (i.e., outward tactile movement, going from the inside of the finger toward the fingertip and increasing pitch, or inward tactile movement and decreasing pitch) and incongruent pairs stimuli (i.e., the reverse associations) were measured. Two methods were compared to assess the behavioural effects of such a correspondence: One where participants have to respond to either the auditory or tactile stimulus presented simultaneously, while ignoring the other, and the other where the auditory and tactile stimuli are presented sequentially and associated to different response buttons (IAT). No significant compatibility effect was observed under the speeded classification task. The implicit association task revealed a significant compatibility effect. This effect was similar in the conditions where the finger was placed vertically and horizontally,However this implicit association between pitch and tactile movements was not observed in blind participants. These results have methodological implications for the explanation and testing of crossmodal congruency, and the origin of the widely discussed association between pitch and vertical elevation.
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Dong, C-J. , Swindale, N. V. , Zakarauskas, P., Hayward, V., and Cynader, M. 2000.
The Auditory Motion Aftereffect: Its Tuning And Specificity In The Spatial And Frequency Domains.
Perception and Psychophysics, Vol. 62(5):1099-1111.

In this paper, the auditory motion aftereffect (aMAE) was studied by using real moving sound as both the adapting and test stimulus. The real moving sound was generated by a loudspeaker mounted on a robot arm which was able to move quietly in three dimensional space. Seven subjects with normal hearing were tested. Results from Experiment 1 showed a robust and reliable negative aMAE in all the subjects involved. After listening to a sound source moving repeatedly to the right, a stationary sound source was perceived to be moving to the left. The magnitude of the aMAE tended to increase up to the highest velocity tested (<30/sec). The tuning and specificity of this aftereffect was further studied in the spatial and frequency domains. The strength of the aftereffect depended on matching both the spatial location and the frequency content of the adapting and test stimuli. Offsetting the locations of adapting and test stimuli by 20 reduced the size of the effect by about 50%. A similar decline occurred when the frequency of the adapting and test stimuli differed by one octave.
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Dostmohamed, H. and Hayward, V. 2005.
Trajectory of Contact Region On the Fingerpad Gives the Illusion of Haptic Shape.
Experimental Brain Research. Vol. 164, pp. 387-394.

When one explores a solid object with a fingertip, a contact region is usually defined. When the trajectory of this region on the fingerpad is artificially controlled so as to resemble the trajectory that is normally present while exploring a real object, the experience of shape is created. In order to generate appropriate local deformation trajectories, we built a servo-controlled mechanism that rolled a flat plate on the fingerpad during the manual exploration of virtual surfaces so that the plate was kept tangent to a virtual shape at the point of virtual contact. An experiment was then designed to test which mode of exploration maximized the shape information gain: active versus semi-active exploration, where semi-active exploration is when one hand touches passively and the other moves the target object, and the use of single versus multiple points of contact. We found that subjects were able to perform curvature discrimination at levels comparable to those achieved when using direct manual contact with real objects, and that the highly simplified stimulus provided by the device was a sufficient cue to give the illusion of touching three dimensional surfaces.
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Dostmohamed, H. and Hayward, V. 2005.
Contact Location Trajectory on the Fingertip as a Sufficient Requisite for Illusory Perception of Haptic Shape and Effect of Multiple Contacts
In Multi-point Interaction with Real and Virtual Objects, F. Barbagli, D. Prattichizzo and K. Salisbury (Eds.), Springer Tracts in Advanced Robotics. Volume 18, pp. 189-198.

This paper seeks to demonstrate that haptic curvature perception can result solely from the trajectory of the deformed region of the fingertip due to contact with an object during tactile exploration. To test this hypothesis, we built a servo controlled 2-degree-of-freedom spherical mechanism called a Morpheotron. This device operates by rolling a flat plate on the fingertip during the exploration of a virtual surface while eliminating all other cues that are normally present, including kinesthetic cues. In carrying out the experimental protocols described herein, we found that subjects were able to perform curvature discrimination at levels comparable to those achieved when using direct manual contact with real objects, and that the highly simplified stimulus provided was able to give the illusion of touching three dimensional surfaces.
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Dupin, L., Hayward, V., Wexler, M. 2017.
Generalized movement representation in haptic perception.
Journal of Experimental Psychology: Human Perception and Performance, 43(3):581--595.

The extraction of spatial information by touch often involves exploratory movements, with tactile and kinesthetic signals combined to construct a spatial haptic percept. However, the body has many sensory surfaces that can move independently, giving rise to the source binding problem: when there are multiple tactile signals originating from sensory surfaces with multiple movements, are the tactile and kinesthetic signals bound to one another? We studied haptic signal combination by applying the tactile signal to a stationary fingertip while another body part (the other hand or a foot) or a visual target moves, and using a task that can only be done if the tactile and kinesthetic signals are combined. We found that both direction and speed of movement transfer across limbs, but only direction transfers between visual target motion and the tactile signal. In control experiments, we excluded the role of explicit reasoning or knowledge of motion kinematics in this transfer. These results demonstrate the existence of two motion representations in the haptic systemone of direction and another of speed or amplitude that are both source-free or unbound from their sensory surface of origin. These representations may well underlie our flexibility in haptic perception and sensorimotor control.
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Dupin, L., Hayward, V. Wexler, M. 2015.
Direct Coupling of Haptic Signals Between Hands.
Proceedings of the National Academy of Sciences, 112(2):619-624

Although motor actions can profoundly affect the perceptual interpretation of sensory inputs, it is not known whether the combination of sensory and movement signals occurs only for sensory surfaces undergoing movement or whether it is a more general phenomenon. In the haptic modality, the independent movement of multiple sensory surfaces poses a challenge to the nervous system when combining the tactile and kinesthetic signals into a coherent percept. When exploring a stationary object, the tactile and kinesthetic signals come from the same hand. Here we probe the internal structure of haptic combination by directing the two signal streams to separate hands: one hand moves but receives no tactile stimulation, while the other hand feels the consequences of the first hands movement but remains still. We find that both discrete and continuous tactile and kinesthetic signals are combined as if they came from the same hand. This combination proceeds by direct coupling or transfer of the kinesthetic signal from the moving to the feeling hand, rather than assuming the displacement of a mediating object. The combination of signals is due to perception rather than inference, because a small temporal offset between the signals significantly degrades performance. These results sug- gest that the brain simplifies the complex coordinate transformation task of remapping sensory inputs to take into account the movements of multiple body parts in haptic perception, and they show that the effects of action are not limited to moving sensors.
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Dupont, P., Hayward, V., Armstrong, B., and Altpeter, F. 2002.
Single State Elasto-Plastic Friction Models.
IEEE Transactions on Automatic Control, 47(5):787-792.

For control applications involving small displacements and velocities, friction modeling and compensation can be very important. In particular, the modeling of presliding displacement (motion prior to fully developed slip) can play a pivotal role. In this paper, it is shown that existing single-state friction models exhibit a nonphysical drift phenomenon which results from modeling presliding as a combination of elastic and plastic displacement. A new class of single state models is defined in which presliding is elasto-plastic: under loading, frictional displacement is first purely elastic and then transitions to plastic. The new model class is demonstrated to substantially reduce drift while preserving the favorable properties of existing models (e.g., dissipativity) and to provide a comparable match to experimental data.
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Dupont, P., Armstrong, B., and Hayward, V. 2000.
Elasto-Plastic Friction Model: Contact Compliance and Stiction.
Proc. 2000 American Control Conference, June 28-30, 2000, Chicago, Ill. USA.

The presliding displacement and stiction properties of friction models are investigated. It is found that existing single-state-variable friction models possess either stiction or presliding displacement. Next, those models with continuous states are interpreted as examples of Prandlt's elasto-plastic material model. A class of general one-state models is derived that is stable, dissipative and exhibits both stiction and presliding displacement.
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Doyon, M., Hayward, V., and Pelletier, M. 1994.
Decentralized Impedance Control.
Proc. SY.RO.CO'94, IFAC. Vol. 2, pp. 389-394. USA.

We describe an impedance control method follwoing an independent joint control approach. Simple impedance controllers are set up at each joint and coupling among the joints is cancelled using equally simple compensators. It is possible to program any diagonal visco-elastic impedance matrix in Cartesian task coordinates within the limits of what can be achieved at the joint level. The performance depends on the precise tracking of joint torque specifications which may be achieved by minor feedback loops and co-locate joint torque sensors. This technique takes advantage of the frequency separation of signals describing the dynamics of most serial manipulators to achieve excellent performanceand robustness at a low computational cost. In the described method, we should more appropriately speak of control of the impedance rather than impedance control. Experimental results are reported using the Sarcos redundant manipulators GRLA (General Robotic Large Arm). The method applies equally well to kinematically non-redundant and redundant manipulators.
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Dupuis, E., Papadopoulos, E., and Hayward, V. 2001.
The Singular Vector Algorithm for the Computation of the Loci of Rank-Deficiency Loci of Rectangular Jacobians.
Proc. Int. Conf. on Intelligence Robots and Systems, IROS2001 IEEE/RSJ, pp. 324-329.

This paper presents a novel approach to compute the rank-deficiency locus of non-square Jacobian matrices. This algorithm is based on the computation of the singular vectors associated to zero singular values of the Jacobian. Results are shown for a four degree-of-freedom and a seven degree-of-freedom manipulator.
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Duvernoy, B., Farkhatdinov, I., Topp, S., Hayward, V. 2018.
Electromagnetic Actuator for Tactile Communication.
Proceedings of the Eurohaptics Conference. In press.

Fingerspelling is a tactile code that enables linguistic communication with people who are Deafblind. We describe and undertake initial testing of a crucial component of a device that is designed to perform tactile fingerspelling with the speed and the clarity approaching that of a human signer. The component in question is a tactile actuator, which is based on a conventional electromagnetic motor, but which is carefully configured to meet the requirements of communication by tactile spelling. The actuator is intended to be easy to manufacture, reliable, inexpensive, to be made in many variants and to be safe to use.
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Dzidek, B., Bochereau, S., Johnson, S. A., Hayward, V., Adams, M. J. 2017.
Why pens have rubbery grips.
Proceedings of the National Academy of Sciences. 114(41)10864--10869.

The process by which human fingers gives rise to stable contacts with smooth, hard objects is surprisingly slow. Using high-resolution imaging, we found that, when pressed against glass, the actual contact made by finger pad ridges evolved over time following a first-order kinetics relationship. This evolution was the result of a two-stage coalescence process of microscopic junctions made between the keratin of the stratum corneum of the skin and the glass surface. This process was driven by the secretion of moisture from the sweat glands, since increased hydration in stratum corneum causes it to become softer. Saturation was typically reached within 20 s of loading the contact, regardless of the initial moisture state of the finger and of the normal force applied. Hence, the gross contact area, frequently used as a benchmark quantity in grip and perceptual studies, is a poor reflection of the actual contact mechanics that take place between human fingers and smooth, impermeable surfaces. In contrast, the forma- tion of a steady-state contact area is almost instantaneous if the counter surface is soft relative to keratin in a dry state. It is for this reason that elastomers are commonly used to coat grip surfaces.
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Dzidek, B., Bochereau, S., Johnson, S. A., Hayward, V., and Adams, M. J. 2016.
Frictional dynamics of finger pads are governed by four length-scales and two time-scales.
Proceedings of the Haptic Symposium. 161-166.

The evolution of the contact area of a finger pad against a surface is critical during tactile interaction, whether for gripping or discriminating surfaces. The contact area made by a finger pad is commonly considered at two distinct length scales corresponding to the gross area, A_gross, and to the smaller ridge area, A_ridge, that excludes the interstitial spaces between the ridges. Here, these quantities were obtained from high-resolution imaging of contacts during loading and stress relaxation. While gross rapidly reaches an ultimate value, the contact made by the ridges is initially formed from unconnected junctions with a total contact area, A_junct , which continues to increase for several seconds during the holding period. Thus, the contact area grows in a two-step process where the number of junction made by the ridges first increases, followed by a growth of their size and connectivity. Immediately after contact the stratum corneum is in a glassy state and the individual junctions form a multiple asperity contact. At longer contact times, the asperities soften owing to the occlusion of moisture excreted from the sweat pores in the ridges. Thus, the real area of contact, real, which drives the creation of friction, grows with time at a relatively slow rate. It is concluded that multi-asperity dynamic contact models should be preferred compared with static models in order to describe the physics of finger pad contact mechanics and friction.
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Dzidek, B. M., Adams, M., Zhang, Z., Johnson, S., Bochereau, S., and Hayward, V. 2014.
Role of Occlusion in Non-Coulombic Slip of the Finger Pad
in Haptics: Neuroscience, Devices, Modeling, and Applications, Part-I, Auvray, M. and Duriez, C. (Eds). pp. 109-116

Understanding how fingers slip on surfaces is essential for elucidating the mechanisms of haptic perception. This paper describes an investigation of the relationship between occlusion and the non-Coulombic slip of the finger pad, which results in the frictional force being a power law function of the normal load, with an index n; Coulombic slip corresponds to n= 1. For smooth impermeable surfaces, occlusion of moisture excreted by the sweat glands may cause up to an order of magnitude increase in the coefficient of friction with a characteristic time of ~ 20 s. This arises because the moisture plasticises the asperities on the finger print ridges resulting in an increase in their compliance and hence an increase in the contact area. Under such steady state sliding conditions a finger pad behaves like a Hertzian contact decorated with the valleys between the finger print ridges, which only act to reduce the true but not the nominal contact area. In the limit, at long occlusion times (~ 50 s), it can be shown that the power law index tends to a value in the range. In contrast, measurements against a rough surface demonstrate that the friction is not affected by occlusion and that a finger pad exhibits Coulombic slip.
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Fradet, C., Manfredi, L. R., Bensmaia, S., Hayward, V. 2017.
Fingertip skin as a linear medium for wave propagation.
Proceedings of the World Haptics Conference (WHC), IEEE, pp. 507-510.

The skin is the medium that conveys tactile information arising from mechanical interaction with the environment. Several prior studies have demonstrated that mechanical waves propagating from the region of contact carry significant tactile information far away from the region of contact. It is therefore important to determine whether it is appropriate to consider the skin to be a linear wave propagation medium for since linearity would considerably simplify any analysis related to this phenomenon. For example, linearity would enable the application of the superposition principle, of the reciprocity principle, and others, even if the skin is considered to be anisotropic. The linearity assumption is important for the scientist interested in the physics of the tactile perception and it can also be surmised to be taken into account by the neural circuits processing tactile information. Such property would be important even if much of the other tactile physics, such as friction, are predominantly nonlinear. We found that indeed, the human fingertip skin could be considered to be a linear propagation medium, except in irregular regions such as the folds near the joints where linearity breaks down.
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Foisy, A., Hayward, V., and Aubry, S. 1990.
The use of awareness in collision prediction.
Proc. IEEE International Conference on Robotics and Automation. pp. 338-343.

Consideration is given to a world made up of a collection of objects which are all moving with respect to each other. The goal is to design a system capable of reporting predicting all possible object collisions, given that all relevant information is available in due time. Previous approaches are based on the notion of a distance function that reflects the closest distance between objects in the world at any given instant in time. Explicitly including time in the representation makes it possible to obtain an algorithm based on the shortest possible time before the next possible collision. The algorithm deals with all pairwise interactions between objects, sorts the pairs with respect to their predicted collision time, and maintains the most-likely-to-collide pairs at the top of a stack. A novel kind of hierarchy in the representation of the world is thus introduced. To find the shortest possible time before a collision, the trajectory of objects is constrained by imposing bounds on the object's acceleration and velocity. All interacting pairs are classified into buckets that reflect the imminence of the collision. The computing cost is kept constant by reclassifying only one pair from each bucket at each time sample.
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Foisy, A. and Hayward, V. 1995.
A Safe Swept Volume Method For Collision Detection.
In Robotics Research, the Sixth International Symposium. The International Foundation for Robotics Research. Cambridge, MA. pp. 62-68.

This paper presents a collision detection method based on a swept volume approach. The proposed method computes a convex approximation (CSV) guaranteed to encompass the real swept volume (RSV). It is shown to be robust, which means that small errors in the model result in small errors in the result. It is first shown to be safe, which means that detections can ever be missed. It is then shown reliable, meaning that the exact result can be approached as closely as desired for a known cost.
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Frissen, I., Ziat, M., Campion, G., Hayward, V. and Guastavino, C. 2012.
The effects of voluntary movements on auditoryhaptic and haptichaptic temporal order judgments.
Acta Psychologica, 141:40-148

In two experiments we investigated the effects of voluntary movements on temporal haptic perception. Measures of sensitivity (JND) and temporal alignment (PSS) were obtained from temporal order judgments made on intermodal auditory-haptic (Experiment 1) or intramodal haptic (Experiment 2) stimulus pairs under three movement conditions. In the baseline, static condition, the arm of the participants remained stationary. In the passive condition, the arm was displaced by a servo-controlled motorized device. In the active condition, the participants moved voluntarily. The auditory stimulus was a short, 500 Hz tone presented over headphones and the haptic stimulus was a brief suprathreshold force pulse applied to the tip of the index finger orthogonally to the finger movement. Active movement did not significantly affect discrimination sensitivity on the auditory- haptic stimulus pairs, whereas it significantly improved sensitivity in the case of the haptic stimulus pair, demonstrating a key role for motor command information in temporal sensitivity in the haptic system. Points of subjective simultaneity were by-and-large coincident with physical simultaneity, with one striking exception in the passive condition with the auditory-haptic stimulus pair. In the latter case, the haptic stimulus had to be presented 45 ms before the auditory stimulus in order to obtain subjective simultaneity. A model is proposed to explain the discrimination performance.
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Garroway, D. and Hayward, V. 2004.
A Haptic Interface for Editing Space Trajectories. (Poster)
Proc. ACM SIGGRAPH & EuroGraphics Symposium on Computer Animation. August 27-29. Grenoble France.

Animators working with 3D models and data typically are still bound to 2D interaction. We present a new multimodal interface for editing 3D motion data using a haptic device. In the basic mode, the haptic device guides the hand of the user along a trajectory that was previously recorded or specified. Any signi cant deviation from the initial trajectory instantly results in permanent changes made to this trajectory. This interface provides a simple, intuitive method for the user to actually experience movement other than visually for purposes of creation.
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Gosline, A. H. C., Hayward, V., Michalska, H. 2011.
Ineluctability of Oscillations in Systems With Digital Implementation of Derivative Feedback
Automatica, 47(11):2444-2450

Differentiation in the feedback is common practice in digital control. Yet, the fundamental behavior of the universally employed backward difference of quantized signals has not been studied thus far. We show that velocity always oscillates when this type of feedback is applied to a forced, linear second-order system for any system parameters. We then compute a bound for the oscillation amplitude which can be easily computed given the parameters of the system. Experimental results are in tight agreement with the theory. If the system has dry friction, our study yields a sufficient condition for the quenching of spontaneous oscillations.
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Giordano, B., Visell, Y., Yao, H.-Y., Hayward, V., Cooperstock, J. and McAdams, S. 2012.
Identification Of Walked-Upon Materials In Auditory, Kinesthetic, Haptic And Audio-Haptic Conditions.
Journal of the Acoustical Society of America, 131(5):4002-4012.

Locomotion generates multisensory information about walked-upon objects. It remains unexplored how perceptual systems use such information to get to know the environment. The ability to identify solid (e.g., marble) and aggregate (e.g., gravel) walked-upon materials was investigated in auditory, haptic or audio-haptic conditions, and in a kinesthetic condition where tactile information was perturbed with a vibromechanical noise. Overall, identification performance was better than chance in all experimental conditions and for both solids and the better identified aggregates. Despite large mechanical differences between the response of solids and aggregates to locomotion, for both material categories discrimination was at its worst in the auditory and kinesthetic conditions and at its best in the haptic and audio-haptic conditions. An analysis of the dominance of sensory information in the audio-haptic context supported a focus on the most accurate modality, haptics, but only for the identification of solid materials. When identifying aggregates, response biases appeared to produce a focus on the least accurate modality -- kinesthesia. When walking on loose materials such as gravels, individuals do not perceive surfaces by focusing on the most accurate modality, but by focusing on the modality which would most promptly signal postural instabilities.
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Gosline, A. H. C. and Hayward, V. 2009.
Dual-Channel Haptic Synthesis of Viscoelastic Tissue Properties Using Programmable Eddy Current Brakes.
International Journal of Robotics Research, 28(10):1387-1399.

We describe the design of an eddy current brake for use as programmable viscous damper for haptic interfaces. Unlike other types of programmable brakes, eddy current brakes can provide linear, programmable physical damping that can be modulated at high frequency. These properties makes them well suited as dissipative actuators for haptic interfaces. We overview the governing physical relationships, and describe design optimization for inertial constraints. A prototype haptic interface is described, and experimental results are shown that illustrate the improvement in stability when simulating a stiff wall that is made possible using programmable eddy current dampers.
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Gosline, A. H. C. and Hayward, V. 2008.
Eddy Current Brakes for Haptic Interfaces: Design, Identification, and Control.
IEEE/ASME Transactions on Mechatronics. 13(6):669-677.

We describe the design of an eddy current brake for use as programmable viscous damper for haptic interfaces. Unlike other types of programmable brakes, eddy current brakes can provide linear, programmable physical damping that can be modulated at high frequency. These properties makes them well suited as dissipative actuators for haptic interfaces. We overview the governing physical relationships, and describe design optimization for inertial constraints. A prototype haptic interface is described, and experimental results are shown that illustrate the improvement in stability when simulating a stiff wall that is made possible using programmable eddy current dampers.
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Gosline, A. H. C. and Hayward, V. 2007.
Time-Domain Passivity Control of Haptic Interfaces with Tunable Damping Hardware.
Proc. World Haptics 2007 (Second Joint Eurohaptics Conference And Symposium On Haptic Interfaces For Virtual Environment And Teleoperator Systems), pp. 164-169.

We describe a time-domain passivity control methodology that uses programmable eddy current viscous dampers to prevent a user from extracting energy from a haptic interface. A passivity observer monitors the energy flow of the virtual environment, and damping hardware is used to remove any energy contributions from the virtual environment that violate passivity constraints. Experiments illustrate that the programmable physical damper method im- proves the performance of a haptic device that has minimal inherent dissipation.
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Gosline, A. H. C., Campion, G. and Hayward, V. 2006.
On The Use of Eddy Current Brakes as Tunable, Fast Turn-On Viscous Dampers For Haptic Rendering.
Proc. Eurohaptics 2006. pp. 229-234.

We describe the use of eddy current brakes as fast turn-on, tunable, linear dampers for haptic rendering using a prototype haptic device outfitted with eddy current brakes. We show that at the speeds typically required for haptic interaction, eddy-current-induced drag is proportional to velocity. We also show that an modulation rate of approximately 250~Hz can easily be achieved with off the shelf components. A method for decoupling the damping at the end effector is discussed. We discuss the results from haptic experiments for rendering viscosity, virtual walls and virtual friction. Experimental results show that the addition of programmable physical damping improves impedance and stability for rendering with negligible computational cost.
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Grant, D. and Hayward, V. 2000.
Constrained Force Control Of Shape Memory Alloy Actuators.
Proc. of the IEEE Int. Conf. on Robotics and Automation, San Francisco, CA, April 2000. pp. 1320-1314.

Experimental results are presented to show that SMA actuators are able to control forces both rapidly and precisely. An antagonistic pair of constrained actuators is shown to be capable of rapidly changing the setpoint throughout a +7.00 N range. Although the system entered into a limit cycle at the setpoint, the limit cycle magnitude was small. The peak to peak amplitude of the limit cycles was only 0.07 N with a worst case average offset of 0.016 N at high force rates up to 75 N/s. Simulation results also indicate that accuracy could be improved with an increased sampling rate. The SMA actuator pair was also shown to be capable of accurate tracking. The maximum tracking error for a f = 0.5 Hz, 2.00 N sine wave was 0.04 N. For the 2.00 Hz tracking, the maximum error was approximately equal to the boundary layer width which was set at 0.30 N.
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Grant, D. and Hayward, V. 1998.
Vibration Isolation With High Strain Shape Memory Alloy Actuators.
International Mechanical Engineering Congress and Exposition. Vol. 229, Applied Mechanics Division.

Shape Memory Alloys (SMA's) are generally considered to be a slow and imprecise means of actuation. With the SMA actuator designed at McGill University we wish to show the contrary. In this paper, several SMA actuators are used to actively damp an external impulse disturbance on a mass to be isolated from vibrations. The vibration isolation testbed consists of a `strong' actuator to low-pass the system and a `fast' antagonistic pair to attenuate the remaining disturbance. Both damping systems use the same basic actuator architecture. A variable structure controller switching on the acceleration error and the jerk is effectively used to dampen out an impulse disturbance within 360 msec.
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Grant, D. and Hayward, V. 1997b.
Controller for a High Strain Shape Memory Alloy Actuator: Quenching of Limit Cycles.
Proc. IEEE Int. Conf. on Robotics and Automation. Vol. 1, pp. 254-259.

Further development of a three level switching controller is presented. The controller was originally designed to drive a novel Shape Memory Alloy (SMA) actuator consisting of a number of thin NiTi fibers woven in a counter rotating helical pattern around supporting disks. While the original controller performed satisfactorily, it was hampered by the presence of limit cycles at higher gains. By allowing the upper switch- ing level to be proportional to the velocity it is possible to achieve a damped response, analogous to PD control for linear systems, effectively quenching the limit cycle. With this damping, it is possible to decrease the rise time by almost half and maintain the same steady state accuracy.
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Grant, D. and Hayward, V. 1997a.
Variable Structure Control Of Shape Memory Alloy Actuators.
IEEE Systems and Control Magazine. Vol. 17, No. 3, pp. 80-88.

A novel Shape Memory Alloy (SMA) actuator consisting of several thin NiTi fibers woven in a counter rotating helical pattern around supporting disks is first described. This structure accomplishes a highly efficient transformation between force and displacement overcoming the main mechanical drawback of shape memory alloys, that being limited strain. Time domain open loop experiments were then conducted to determine the intrinsic properties of the actuator. From these experiments and from the knowledge of the underlying physics of SMA's, a multi-term model, including linear and nonlinear elements, was proposed. After further investigation and simulation, it was found that most of these complexities did not need to be considered in order to explain the reported results, and that the model could be reduced to that of a single integrator. A variable structure controller was then applied to a pair of antagonist actuators. The feedback switches between the two actuators according to the sign of the displacement error. A further improvement was added to compensate for known gross nonlinearities by modulating the current magnitude in a discrete manner as a function of the state space position. It was therefore possible to realize smooth and robust control with very little cost in complexity.
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Grant, D. and Hayward, V. 1995.
Design of Shape Memory Alloy Actuator with High Strain and Variable Structure Control.
Proc. Int. IEEE Conference on Robotics and Automation.

A novel Shape Memory Alloy (SMA) actuator consisting of a number of thin NiTi fibers woven in a counter rotating helical pattern around supporting disks is first described. This structure can be viewed as a parallel mechanism used to accomplish a highly efficient transformation between force and displacement. The actuator overcomes the main mechanical drawback of shape memory alloys, that being limited strain. Two variable structure controllers are applied to a pair of antagonist actuators. The first involves a switching control input creating a sliding mode in conjunction with a linear control activated within a boundary layer in the vicinity of the set point. The second involves a multi-stage switching control that simplifies amplifier construction. Experimental performance results in the time domain are discussed.
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Greenish, S., Hayward, V., Chial, V., Okamura, A., and Steffen, T. 2002.
Measurement, Analysis and Display of Haptic Signals During Surgical Cutting.
Presence: Teleoperators and Virtual Environments. Vol. 11(6). pp. 626-651.

The forces experienced while surgically cutting anatomical tissues from a sheep and two rats were investigated for three scissor types. Data were collected in situ using instrumented Mayo, Metzenbaum, and Iris scissors immediately after death to minimize post-mortem effects. The force-position relationship, the frequency components present in the signal, the significance of the cutting rate, as well as other invariant properties, were investigated after segmentation of the data into distinct task phases. Measurements were found to be independent of the cutting speed for Mayo and Metzenbaum scissors, but the results for Iris scissors were inconclusive. Sensitivity to cutting tissues longitudinally or transversely depended on both the tissue and on the scissor type. Data from cutting three tissues (rat skin, liver and tendon) with Metzenbaum scissors as well as blank runs were processed and displayed as haptic recordings through a custom designed haptic interface. Experiments demonstrated that human subjects could identify tissues with similar accuracy when performing a real or simulated cutting task. The use of haptic recordings to generate the simulations was simple and efficient, however, it lacked flexibility because only the information obtained during data acquisition could be displayed. Future experiments should account for the user grip, tissue thickness, tissue moisture content, hand orientation, and innate scissor dynamics. A database of the collected signals has been created on the Internet for public use at tissue/data.html).
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Gueorguiev, D., Bochereau, S., Mouraux, A., Hayward, V. and Thonnard, J-L. 2016.
Touch uses frictional cues to discriminate flat materials.
Scientific Reports, 6 :25553.

In a forced-choice task, we asked human participants to discriminate by touch alone glass plates from transparent polymethyl methacrylate (PMMA) plastic plates. While the surfaces were at and did not exhibit geometric features beyond a few tens of nanometres, the materials di ered by their molecular structures. They produced similar coe cients of friction and thermal e ects were controlled. Most participants performed well above chance and participants with dry ngers discriminated the materials especially well. Current models of tactile surface perception appeal to surface topography and cannot explain our results. A correlation analysis between detailed measurements of the interfacial forces and discrimination performance suggested that the perceptual task depended on the transitory contact phase leading to full slip. This result demonstrates that di erences in interfacial mechanics between the nger and a material can be sensed by touch and that the evanescent mechanics that take place before the onset of steady slip have perceptual value.
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Hartcher-O'Brien, J., Auvray, M. and Hayward, V. 2015.
Perception Of Distance-To-Obstacle Through Time-Delayed Tactile Feedback
Proceedings of the IEEE World Haptics Conference, pp. 7-12.

In previous vision-to-touch sensory substitution approaches, including most electronic white canes, typical approaches include mapping space-to-space, space-to-intensity, or space-to-frequency. To our knowledge, however, mapping space to time-delay has not been considered. Yet, because organisms must anticipate impending collisions with obstacles or anticipate being contacted by approaching objects, many organisms have developed computational short-cuts where distance-to-target is assumed to be proportional to a time-span. This short-cut often manifests itself in low-level sensorimotor behaviours and perceptual mechanisms. We studied whether untrained humans would spontaneously employ such a short- cut to estimate distance-to-obstacle in the absence of vision. The observers pressed a push button and a tactile pulse was delivered to the hand with a delay proportional to the distance to an obstacle detected by an optical range finder that they wore. The observers were not informed of the nature of the coding but could freely probe the obstacle while walking toward the target. Upon randomized presentation of obstacle distances, the observers quickly calibrated their judgement of distance-to-obstacle and were able to estimate this distance within a range of four meters for a proportionality factor corresponding to a velocity of one m/s.
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Hartcher-O'Brien, J., Terekhov, A. V., Auvray, M., and Hayward, V. 2014.
Haptic Shape Constancy Across Distance.
in Haptics: Neuroscience, Devices, Modeling, and Applications, Part-I, Auvray, M. and Duriez, C. (Eds). pp. 77-84

To explore haptic shape constancy across distance, we measured perceived curvature thresholds of cylindrical shapes, cut out of acetal resin blocks. On each trial, blindfolded observers used their bare finger to scan the surface of two of the shapes consecutively. One shape was close to the observer and the other positioned further away. This spatial displacement changes the available proprioceptive information about the object shape, and therefore the combined proprio-tactile information may signal different objects at the two distances. The results reveal a perceptual compensation for the change in proprioceptive information. However, two distinct patterns of distance compensation emerged: one groups' data are consistent with predictions from visual object constancy. The other group of observers demonstrate the reverse pattern of response such that objects further away need to have lower curvature to be perceived having equal curvature. We propose that perceived haptic curvature across distance de- pends on observers' differential weighting of the multiple available cues.
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Hayward, V. 2018.
A Brief Overview of the Human Somatosensory System.
in Musical Haptics, Papetti, S. and Saitis, C. (Eds.), pp. 29-48

This chapter provides an overview of the human somatosensory system. It is the system that subserves our sense of touch, which is so essential to our awareness of the world and of our own bodies. Without it, we could not hold and manipulate objects dextrously and securely, let alone musical instruments, and we would not have a body that belongs to us. Tactile sensations, conscious or unconscious, arise from the contact of our skin with objects. It follows that the mechanics of the skin and of the hand its interaction with objects is the source of information that our brain uses to dextrously manipulate objects, as in music playing. This information is collected by vast array of mechanoreceptors that are sensitive to the effects of contacting objects, often with the fingers, even far away for the region of contact. This information is processed by neural circuits in numerous regions of the brain to provide us with extraordinary cognitive and manipulative functions that depend so fundamentally on somatosensation.
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Hayward, V. 2015.
Tactile Illusions.
in Encyclopedia of Touch, Prescott, T. J. and Ahissar, E. (Eds.), Scholarpedia, 10(3):8245.

Tactile illusions are found when the perception of a quality of an object through the sense of touch does not seem to be in agreement with the physical stimulus. They can arise in numerous circumstances and can provide insights into the mechanisms subserving haptic sensations. Many of them can be exploited, or avoided, in order to create efficient haptic display systems or to study the nervous system.
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Hayward, V., Terekhov, A. V., Wong, S.-C., Geborek, P, Bengtsson, F., Jörntell, H. 2014.
Spatio-Temporal Skin Strain Distributions Evoke Low Variability Spike Responses In Cuneate Neurons.
Journal of the Royal Society Interface, 11(93):20131015

A common method to explore the somatosensory function of the brain is to relate skin stimuli to neurophysiological recordings. However, interaction with the skin involves complex mechanical effects. Variability in mechanically induced spike responses is likely to be due in part to mechanical variability of the transformation of stimuli into spiking patterns in the primary sensors located in the skin. This source of variability greatly hampers detailed investigations of the response of the brain to different types of mechanical stimuli. A novel stimulation technique designed to minimize the uncertainty in the strain distributions induced in the skin was applied to evoke responses in single neurons in the cat. We show that exposure to specific spatio-temporal stimuli induced highly reproducible spike responses in the cells of the cuneate nucleus, which represents the first stage of integration of peripheral inputs to the brain. Using precisely controlled spatio-temporal stimuli, we also show that cuneate neurons, as a whole, were selectively sensitive to the spatial and to the temporal aspects of the stimuli. We conclude that the present skin stimulation technique based on localized differential tractions greatly reduces response variability that is exogenous to the information processing of the brain and hence paves the way for substantially more detailed investigations of the brain's somatosensory system.
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Hayward, V. 2011.
Is There a `Plenhaptic' Function?
Philosophical Transactions of the Royal Society B, 366:3115-3122.

One approach to gauge the complexity of the computational problem underlying haptic perception is to determine the number of dimensions needed to describe it. In vision, the number of dimensions can be estimated to be seven. This observation raises the question of what is the number of dimensions needed to describe touch. Only with certain simplified representations of mechanical interactions can this number be estimated, because it is in general infinite. Organisms must be sensitive to considerably reduced subsets of all possible measurements. These reductions are discussed by considering the sensing apparatuses of some animals and the underlying mechanisms of two haptic illusions.
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Hayward, V. 2008.
Physically-Based Haptic Synthesis.
In "Haptic Rendering: Foundations, Algorithms and Applications", M. Lin and M. Otaduy (eds.), A K Peters, Ltd, pp. 297-309.

This chapter discusses a set of algorithms to reconstruct interaction forces between objects in a physically accurate manner. They must be fast enough to minimize the creation of spurious energy resulting from the discrete-time realization of displacement-to-force relationships. The most fundamental is an algorithm to compute the force of friction. Another algorithm is then described for sharp cutting, a close cousin of friction because of its dissipative nature. Synthesis of the nonlinear deformation response of arbitrary bodies is then considered. Textural effect are discussed in terms of small perturbations to the nominal signal and shocks in terms of the Hunt-Crossley collision model.
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Hayward, V. 2008.
A Brief Taxonomy of Tactile Illusions and Demonstrations That Can Be Done In a Hardware Store.
Brain Research Bulletin (special issue on Robotics and Neuroscience), 75:742-752.

This paper surveys more than twenty types of tactile illusions and discusses several of their aspects. These aspects include the ease with which they can be demonstrated and whether they have clear visual analogs. The paper also shows how to construct equipment made of simple supplies able to deliver well controlled tactile signals in order to conveniently demonstrate four different tactile illusions.
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Hayward, V. 2008.
Haptic Shape Cues, Invariants, Priors, and Interface Design.
In "Human Haptic Perception - Basics and Applications", Grunwald, M. (ed.), Birkhauser Verlag, pp. 381-392.

Perception is often discussed by reference to cues as separate sources of information for the perceiver. With vision and audition, the list of such known cues is quite extensive. These cues are tied with the manner in which the sensory apparatus---physically and computationally---has evolved to account for the ambient physics. It is thus natural to propose that for touch, like for vision and audition, such physically and computationally specific cues must exist and can be identified. This chapter is about discussing some putative tactile cues that refer to shape as one of the object attributes that a perceiver could be interested in. The notion of invariants is used to identify a collection of possible tactile shape cues and priors necessary to the processing of haptic shape are suggested from the analysis of experimental evidence. Examples of how these notions can be applied by looking at two specific haptic detection tasks and how stereotypical movements can be interpreted. Displays may be thought to operate like ``mirrors'' of the perceptual system. For haptic interfaces one may adopt a similar view point and examples of how this approach can be applied are discussed.
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Hayward, V. and MacLean, K. E. 2007.
Do It Yourself Haptics, Part-I.
IEEE Robotics and Automation Magazine, Vol. 14, No. 4, pp. 88-104.

This article is the first of a two-part series intended as an introduction to haptic interfaces. Together they provide a general introduction to haptic interfaces, their construction and application design. Haptic interfaces comprise hardware and software components aiming at providing computer-controlled, programmable sensations of mechanical nature, that is, pertaining to the sense of touch. In this article (Part I), we describe methods which have been researched and developed to date to achieve the generation of haptic sensations, the means to construct experimental devices of modest complexity, and the software components needed to drive them. In Part II of this this series, we will describe some basic concepts of haptic interaction design together with several interesting applications based on this technology.
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Hayward, V. 2006.
Haptic Synthesis.
(Keynote Paper.) Proc. SYROCO 2006, 8th International IFAC Symposium on Robot Control. pp. 19-24.

This paper discusses a set of algorithms to reconstruct interaction forces between objects in a physically accurate manner. They must be fast enough to minimize the creation of spurious energy resulting from the discrete-time realization of displacement-to-force relationships. The most fundamental is an algorithm to compute the force of friction. Another algorithm is then described for sharp cutting, a close cousin of friction because of its dissipative nature. Synthesis of the nonlinear deformation response of arbitrary bodies is then considered. Textural effect are discussed in terms of small perturbations to the nominal signal.
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Hayward, V. 2004.
Display of Haptic Shape at Different Scales.
(Keynote Paper.) Proc. Eurohaptics 2004. Munich, Germany, June 5-7. pp. 20-27.

This paper describes three haptic devices which can create the experience of haptic shape, each at a different scale. They operate by causing fingertip deformations that match the scale of the features of the objects being virtually touched. For large objects, shape display is obtained by the movement of the deformed contact area on the skin, for medium objects, display is given by the deformation of the fingertip rolling laterally, and for small objects, by stretching and compressing the skin locally. These display modes can in principle be combined to make complex displays operating at different scales.
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Hayward, V. 2004.
Transduction tactile par champs de contraintes latérales réparties : les dispositifs STReSS.
Proc. Journée "Conception de stimulateurs tactiles orientée utilisateur", Université de Lille 1 (USTL), 23 Mars 2004.

Les afficheurs de type stress tirent parti du fait que des sensations tactiles utiles résultent de champs de contraintes latérales et donc de déformation tangentielle de la peau des doigts. Ceci nous permet de fabriquer des dispositifs d'affichages tactiles miniatures basés sur ce principe.
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Hayward, V., Astley, O. R., Cruz-Hernandez, M., Grant, D. and Robles-De-La-Torre, G. 2004.
Haptic Interfaces and Devices.
Sensor Review. 24(1):16-29.

Haptic interfaces enable person-machine communication through touch, and most commonly, in response to user movements. We comment on a distinct property of haptic interfaces, that of providing for simultaneous information exchange between a user and a machine. We also comment on the fact that, like other kinds of displays, they can take advantage of both the strengths and the limitations of human perception. The paper then proceeds with a description of the components and the modus operandi of haptic interfaces, followed by a list of current and prospective applications and a discussion of a cross-section of current device designs.
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Hayward, V., and Yi, D. 2003.
Change of Height: An Approach to the Haptic Display of Shape and Texture Without Surface Normal.
In Experimental Robotics VIII, Springer Tracts in Advanced Robotics 5, Springer Verlag, New York. pp. 570-579.

Several haptic shape display methods rely on the surface normal to compute a force response. Instead, it is possible to use the change of height of an interaction point to compute a force response when a subject explores the surface of an object. The notion of surface normal is no longer needed, and the diffculties associated with it are eliminated. An experiment is designed to illustrate some differences between this approach and previous ones. Open questions are mentioned.
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Hayward, V. 2001.
Haptics: A Key To Fast Paced Interactivity.
In Human Friendly Mechatronics. Selected Papers of the International Conference on Machine Automation, 25-27 September, 2000, Osaka, Japan, (Opening Talk). Takano, M., Arai E. Arai T., Elsevier Science. ISBN 0-444-50649-7.

The word haptics is now well accepted. Hundreds of papers are published each year on the topic of haptic devices and interfaces. Haptics, as a technological niche, has become rich with opportunities and challenges. The field borrows from, and lends to, many subjects in science and technology. Among these, two are particularly relevant: mechatronics on one hand, and robot-human interaction on the other. Haptic devices belong to the family of mechatronic devices because their fundamental function is to take advantage of mechanical signals to provide for communication between people and machines. It follows that haptic devices must include include transducers to convert mechanical signals to electrical signals and vice-versa used in conjunction with one or several computational or data processing systems. These transducers appeal to a variety of technologies: electromechanical devices, optoelectronics, uids, smart materials, exploiting the possibilities that exist to build highly integrated and cost eective devices. The popularization of haptics as an area of investigation is due to the work of such pioneers as Brooks and Iwata.
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Hayward, V. 2001.
Survey Of Haptic Interface Research At McGill University.
Proc. Workshop on "Advances in Interactive Multimodal Telepresence Systems", March 2001, Munich, Germany (Invited Keynote). Hieronymus Buchreproduktions GmbH, ISBN 3-00-007586-0.

This paper surveys three classes of haptic interface devices that were developed at McGill University since 1993. One class covers devices which output planar forces and explore various ways in which the human hand can input data. Another kind of device is meant to reproduce with fidelity the tasks corresponding to the manipulation of small tools in three dimensions. Lastly, we investigated a new class of tactile display.
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Hayward, V., Armstrong, B. S. R., Altpeter, F., and Dupont P. E. 2009.
Discrete-Time Elasto-Plastic Friction Estimation.
IEEE Transactions on Control Systems Technology. 17(3):688-696.

For control applications involving small displacements and velocities, friction modeling and compensation can be very important, especially around velocity reversal. We previously described single-state friction models that are based on elasto-plastic presliding, something that reduces drift while preserving the favorable properties of existing models (e.g., dissipativity) and that provide a comparable match to experimental data. In this paper, for this class of models, discrete estimation for friction force compensation is derived. The estimator uses only position and velocity (not force) measurements and integrates over space rather than time, yielding a discrete-time implementation that is robust to issues of sample size and sensor noise, reliably renders static friction and is computationally efficient for real-time implementation. Boundedness with respect to all inputs, convergence during steady sliding and dissipativity are established for the discrete-time formulation. [PDF] [ Back ]

Hayward, V. and Cruz-Hernandez, M. 2000.
Tactile Display Device Using Distributed Lateral Skin Stretch.
Proc. Symposium on Haptic Interfaces for Virtual Environments and Teleoperator System (IMECE2000), Orlando, Florida, USA. Proc. ASME Vol. DSC-69-2, pp. 1309-1314.

In the past, tactile displays were of one of two kinds: they were either shape displays, or relied on distributed vibrotactile stimulation. A tactile display device is described in this paper which is distinguished by the fact that it relies exclusively on lateral skin stretch stimulation. It is constructed from an array of 64 closely packed piezoelectric actuators connected to a membrane. The deformations of this membrane cause an array of 112 skin contactors to create programmable lateral stress fields in the skin of the finger pad. Some preliminary observations are reported with respect to the sensations that this kind of display can produce.
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Hayward, V. and Armstrong, B. 2000.
A New Computational Model Of Friction Applied To Haptic Rendering.
In Experimental Robotics VI, Peter Corke and James Trevelyan (Eds), Lecture Notes in Control and Information Sciences, Vol. 250, Springer-Verlag,pp. 403-412.

A time-free, drift-free, multi-dimensional model of friction is introduced. A discrete implementation is developed which exhibits four solution regimes: sticking, creeping, oscillating, and sliding. Its computational solution is ecient to compute online and is robust to noise. It is applied to haptic rendering.
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Hayward, V. Gregorio, P. Astley, O. Greenish, S. Doyon, M. Lessard, L. McDougall, J. Sinclair, I. Boelen, S. Chen, X. Demers, J.-P. Poulin, J. Benguigui, I. Almey, N. Makuc, B. and Zhang, X. 1998.
Freedom-7: A High Fidelity Seven Axis Haptic Device With Application To Surgical Training.
In Experimental Robotics V, Casals, A., de Almeida, A. T. (eds.), Lecture Notes in Control and Information Science 232, pp. 445-456.

A seven axis haptic device, called the Freedom-7, is described in relation to its application to surgical training. The generality of its concept makes it also relevant to most other haptic applications. The design rationale is driven by a long list of requirements since such a device is meant to interact with the human hand: uniform response, balanced inertial properties, static balancing, low inertia, high frequency response, high resolution, low friction, arbitrary reorientation, and low visual intrusion. Some basic performance figures are also reported.
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Hayward, V. and Cruz-Hernandez, J. M. 1998.
Parameter Sensitivity Analysis For Design And Control Of Force Transmission.
Journal of Dynamic Systems, Measurement, and Control, Transactions of the ASME. Vol 120, No. 2, pp. 241-249.

We apply sensitivity analysis to the design and control of force transmission systems. With this approach, the effect of the values of the system parameters on the response can be investigated: transmission ratio, sensor placement, damping and allowable load variation. It is found that feedback must be applied to reduce the sensitivity of the system response to the load. Based on these observations, a loop shaped feedback compensator design is proposed. Such compensators can compensate for the nonlinear behavior of the transmissions due to friction, while exhibiting good disturbance rejection and robustness. This is achieved without detailed knowledge of friction behavior and without measurement nor estimation of velocity. Experimental results using a test bench are discussed.
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Hayward, V. and Cruz-Hernandez, M. J. 1997.
Parameter Sensitivity Analysis For Design And Control Of Tendon Transmissions.
Experimental Robotics IV, Khatib, O., Salisbury, J. K. (Eds.) Lecture Notes in Control and Information Sciences 223. pp. 241-252.

We apply sensitivity analysis to the design and control of a tendon transmission. With this approach, some prefered values for the system parameters and a feedback compensator can be proposed. The controller has the special characteristic of being designed based on a linear plant using a robust loopshaping technique, yet it compensates also for the nonlinear behavior of the plant, while exhibiting good disturbance rejection and robustness. Experimental results using a test bench are discussed.
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Hayward, V., Janabi-Sharifi, F., and C-S. J. Chen, 1997.
Adaptive Windowing Discrete-Time Velocity Estimation Techniques: Application To Haptic Interfaces.
Symp. on Rob. Control. SY.RO.CO'97, IFAC. Nantes, France, September 1997. pp. 465-472.

A method is described to estimate velocity from discrete and quantized position samples via adaptive windowing. It addresses the shortcomings of previously known methods which necessitate tradeoffs between noise reduction, control delay, estimate accuracy, reliability, computational load, transient preservation, and which cause difficulties with tuning. The method is optimal in the sense that it minimizes the velocity error variance while maximizes the accuracy of the estimates. The design of the estimator requires the selection of only one parameter, namely a bound on the noise. Simulation and experimental results are presented.
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Hayward, V. and Astley, O.R. 1996.
Performance Measures For Haptic Interfaces.
In Robotics Research: The 7th International Symposium. Giralt, G., Hirzinger, G., (Eds.), Springer Verlag. pp. 195-207.

A haptic interface is distinct from other display devices because it is bi-directional; it is capable of both reading and writing input to and from a human user. Due to both the direct human interaction and bi-directionality there has been much ambiguity in describing and evaluating these devices, making evaluation and comparison difficult. The goal of this paper is to set out requirements and guidelines for the performance measures of haptic devices and to hopefully lead towards resolving the current equivocal situation. In particular, performance measures are introduced which have so far not been pertinent in traditional robotics; these include, peak force, peak acceleration and frequency dependent measurements. Performance measures often quoted in traditional robotics are also discussed, however, the focus and relevance of these measures are different in haptic devices. Each of the suggested performance measures in this paper is discussed with respect to its importance, its measurabilty and the condition under which it should be measured.
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Hayward, V. Aubry, S., Foisy, A., and Ghallab, Y. 1995.
Collision Prediction Among Many Moving Objects.
Int. J. Robotics Research. Vol. 14, No. 2, MIT Press. pp. 129-143.

We consider the problem of flagging all collisions between a large number of dynamic objects. Because the number of possible collisions grows quadratically with the number of objects, a brute force approach is not applicable with finite compuational resources. Hence, we propose a scheduling mechanism that reduces the computational load by exploiting the coherence of the world thoughout time. This mechanism has a very simple structure and easiy lends itself to distributed processing. It considers all pairwise interactions between objects and maintaind a structure that reflects the imminence, or urgency, of collision for each pair. Bounds on the urgency of collisions can be computed gievn minimal knowledge of the system dynamics. For example, we represent physical by their position and by bounds on their relative speed and accelerations. These are assumed to be available at all times. If the environment does not change too rapidly, the mechanism flags all collisions. False alarms may also be generated but can be eliminated with a specialized post-processor. We address the question of how often to perform the collision checks while guaranteeing that all collisions will be caught. Given the large number of possible environments and motions, no general optimal answer can be provided. Yet the soundess and the efficiency of the proposed algorithm is experimentally verified in the case of a world consisting of many spheres moving simultaneously and randomly.
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Hayward, V. 1994.
Design Of Hydraulic Robot Shoulder Based On Combinatorial Mechanism.
In Experimental Robotics 3, Yoshikaswa, T., Myiazaki, F (Eds.), Lecture Notes in Control and Information Sciences 200. Springer Verlag. pp. 297-310.

In previous papers, I have argued that while parallel mechanisms are well known for their favorable structural properties, their utility is generally limited by an inherently small workspace. I have also argued that proper use of actuator redundancy can simultaneously increase the workspace, remove singularities, and dramatically improve overall kinematic, structural, and actuator performance, while keeping the complexity low. This paper discusses a prototype shoulder joint more appropriately described as a combinatorial mechanism which exhibits the features. Additional benefits in terms of modularity, self-calibration, reliability, self-test, and degraded modes of operation are briefly discussed in the conclusion.
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Hayward, V., Daneshemend, L. K. Nilakantan, A. 1994.
Trajectory Generation And Control For Automatic Manipulation.
Robotica, (Special issue on Automatic Manipulation), Vol. 12, pp. 115-125.

A method is described to convert information available at manipulator programming level into trajectories which are suitable for tracking by a servo control system. This process generates trajectories in real time which comply with general dynamic and kinematic constraints. Tracking accuracy will depend mainly on the acceleration demand of the nominal trajectory setpoints - the actuator output demands, in particular, must remain bounded. Our scheme takes into consideration at the trajectory computation level the dynamics of the underlying system, dynamically available information acquired through sensors, and various types of constraints, such as manipulators. It has been developed in the context of a multi-manipulator programming and control system called Kali and developed at McGill University.
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Hayward, V., Choksi, J. Lanvin, G. and Ramstein, C. 1994.
Design And Multi-Objective Optimization Of A Linkage For A Haptic Interface.
In Advances in Robot Kinematics. J. Lenarcic and B. Ravani (Eds.). Kluver Academic. pp. 352-359.

A method to carry out the design of linkage for a haptic interface is described. Factors such as size, workspace, intrusion, inertia, response and structural properties are considered in this process. The dependencies of the various criteria are examined and a hierarchical method is applied. The result is a compact device which is easy to manufacture and which fulfills the requirements demanded by its application. Several quantitative measures designed to capture its principal properties are at the heart the process.
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Hayward, V. 1995.
Toward a Seven Axis Haptic Device.
Proc. IEEE/RSJ Int. Conf. on Intelligent Robots and Systems '95. Vol. 3, pp. 133-139.

The development of a haptic interface to address the tasks performed by people with small tools is described. Design issues are considered from the requirements, in terms of actuation, kinematics, motion transmission, sensing, and concept design.
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Hayward, V., Nemri, C., Chen, X., and Duplat, B. 1993.
Kinematic Decoupling In Mechanisms And Application To A Passive HandController.
J. Robotics Systems, Wiley, Vol. 10, No. 5, pp. 767-790.

Observations regarding the kinematics of mechanisms are applied to the synthesis of a passive hand controller. It is argued that stiffness (and damping) properties are central to the effectiveness of such devices and in particular that the simplicity of these properties is crucial. What simple means is analyzed and it is shown that only certain types of manipulators can appropriately be used. In effect, decoupling is shown to be architecture and configuration dependent. The properties of parallel mechanisms are reviewed and found appropriate for restricted-workspace hand controllers. A particular kinematic design is then derived and a practical implementation described.
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Hayward, V., 1993.
Borrowing Some Design Ideas From Biological Manipulators To Design An Artificial One.
In Robots and Biological Systems, NATO Series, P. Dario, P. Aebisher, and G. Sandini, (Eds.), Springer Verlag. pp. 135-148.

The design of robotic manipuators is a difficult question because most traditional disciplines needed for the design of robots, like kinematics and dynamics, are mostly analytic and have little synthetic power. We first discuss seen as a generative process and suggest that analogy is a powerful design method. Then a spherical mechanism actuated in parallel with a large workspace that can be used to construct a complete limb is discussed. The design systhesis is performaed by translating ideas borrowed from the design of biological manipulators.
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Hayward, V., 1992.
Physical Modeling Applies To Physiology, Too.
Open Peer Commentary in Behavior and Brain Sciences, Vol. 15, No. 2, Cambridge University Press. pp. 342-343.

A physical model was utilized to show that the neural system can memorize a target position and is able to cause motor and sensory events that move the arm to a target with more accuracy. However, this cannot indicate in which coordinates the necessary computations are carried out. Turning off the lights causes the error to increase which is accomplished by cutting off one feedback path. The geometrical properties of arm kinematics and the properties of the kinesthetic and visual sensorial systems should be better known before inferences about higher levels of processing can be drawn.
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Hayward, V., Daneshmend, L. K., Foisy, A., Boyer, M., Demers, L. P., Ravindran, R., and Ng, T. 1990.
The evolutionary design of MCPL, the MSS command and programming language.
Int. IEEE International Workshop on Intelligent Robots and Systems IROS. pp. 413-419.

The remote manipulator system system designated by the acronym MSS, which Canada is contributing to the International Space Station, is briefly described. The underlying structure of MSS is analyzed in terms of a collection of hierarchies. Control language design issues are then analyzed and an object-oriented methodology is proposed with a view to define a run-time structure in relation with task planning requirements.
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Hayward, V. and Osorio, A. 1983.
System To Automatically Analyze assembled Programs
IEEE Transactions on Software Engineering, Vol. SE-9, No. 2, pp. 210-213.

An original system to perform an automatic analysis of assembled programs is presented. Executable programs are analyzed from the description of the machine on which they run and are translated into an intermediate language taking into account the particularities of the considered machine. The system was primarily designed as the first step of a project for transferring programs from one machine to another. The final goal of the project is to achieve an even utilization of computer resources for a real-time controlled robot, on the basis of partially dedicated processors. At the present time, the actual implementation provides a tool for studying the theoretical aspect of machine-level program analysis. Nevertheless, other applications can be found in program debugging and assembled program validation.
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Hayward, V., Paul, R. P. 1984.
Introduction to RCCL: A Robot Control `C' Library.
Proc. IEEE Int. Conf. Robotics and Automation, San Fransisco, CA. pp. 1044-1049.

RCCL is a robot programming system that enables a user to specify robot manipulator tasks using a set of primitive system calls similar to those of the UNIX input-output system. The goals addressed in the RCCL system are: manipulator task description; sensor integration; updatable world representation; flexibility; wide range of applications; medium-level robot programming; offline programming; efficiency; manipulator independence; portability; foreground-background programming; Cartesian path programming; arbitrary path specification; tracking; and force control.
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Hayward, V., Paul, R. P. 1986.
Robot Manipulator Control Under Unix: RCCL A Robot Control `C' Library.
Int. J. of Robotics Research, MIT Press, Vol. 5(4). pp. 94-111.

The article presents a general purpose manipulator control system. The system is run under the Unix operating system. Manipulator programs are written in the `C' language making use of the primitive functions included in a library. The manipulator control is thus integrated within the language in the same manner as is input-output. The system includes a world modeler and a trajectory generator that are accessed through two sets of primitive functions. The system's structured world modeler is designed for an easy integration of sensors. The paper reviews the functional organization of the system, through world modeling, trajectory generation, force control, and synchronization. Actual robot programming examples are given.
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Hayward, V., Kurtz, R. 1989.
Preliminary Study of Serial-parallel Redundant Manipulator.
Proc. NASA Conference on Space Telerobotics. Vol. 2, pp. 39-48.

The manipulator design discussed here results from the examination of some of the reasons why redundancy is necessary in general purpose manipulation systems. A spherical joint design actuated in-parallel, having the many advantages of parallel actuation, is described. In addition, the benefits of using redundant actuators are discussed and illustrated in the design by the elimination of loci of singularities from the usable workspace with the addition of only one actuator. Finally, what is known by the authors about space robotics requirements is summarized and the relevance of the proposed design matched against these requirements. The design problems outlined here are viewed as much from the mechanical engineering aspect as from concerns arising from the control and the programming of manipulators.
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Hayward, V. 1989.
A Translation in Artificial Terms of the Design of Biological Manipulators
Proc. IEEE Engineering in Medicine & Biology Society llth Annual International Conference. pp. 898-899.

The design of manipulators is a difficult question in robotics because most of the traditional disciplines, like kinematics and dynamics are analytic and have little synthetic power. Design is a generative process. Powerful design methodologies come from exploiting modularity and analogy. These are used in this paper to create a spherical mechanism actuated in parallel with a large workspace that can be used to construct a complete limb. The design synthesis is performed by translating ideas borrowed from the design of biological manipulators.
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Hayward, V., Daneshmend, L., Hayati, S. 1989.
An Overview of KALI: a System to Program and Control Cooperative Manipulators.
Proc. International Conference on Advanced Robotics, pp. 547-558.

A software and hardware system, called Kali, for programming and controlling coop- erative manipulators is described. It has been designed at McGill University in a collaborative effort with the Jet Propulsion Laboratory. A set of programming primitives which permit a programmer, human or automated, to specify cooperative tasks are first outlined. In the context of cooperative robots, trajectory generation issues are discussed and our implementation briefly described. Software engineering for system integration is also discussed. Finally, the paper describes the allocation of various computational tasks among the elements of a multi-processor computer. Target applications presently envisioned include space robotics, power line maintenance, and other resource industry applications.
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Hayward, V. 1988.
Autonomous Control Issues In a Telerobot.
Proc. IEEE International Conference on Systems Man and Cybernetics. Workshop on Manipulators in Space. pp. 122--125.

We discuss the structure of a possible autonomous control structure for a telerobot, and then establish corespondance with concepts familiar in the field of teleoperation Traded, Thared and supervlsory control systems such as telerobots can be described from various perspectives leading to various system decompositions which each impose constraints on the overall design.
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Hayward, V. 1986.
Fast Collision Detection Scheme By Recursive Decomposition Of A Manipulator Worspace.
Proc. IEEE Int. Conf. Robotics and Automation, San Fransisco, CA. pp. 1044-1049.

This paper explains a simple method fast collision detection in manipulator tasks. We show from examples taken in the literature that solutions to this problem can be chosen among a continuum of schemes, according to the method selected for representing the workspace of the robot, and the amount og performed before testing a particular trajectory. We then describe a methods based on a recursice decomposition of the workspace, also referred ro as an octree model, as a good tradeoff for a class of applications.
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Hudin, C. , Lozada, J., Hayward, V. 2015.
Localized Tactile Feedback on a Transparent Surface Through Time-Reversal Wave Focusing.
IEEE Transactions on Haptics, 8(2):188-198.

This article addresses the problem of producing independent tactile stimuli to multiple fingers exploring a transparent solid surface without the need to track their positions. To this end, wave time-reversal was applied to re- focus displacement impulses in time and in space at one or several locations in a thin glass plate. This result was achieved using ultrasonic bending waves produced by a set of lamellar piezoelectric actuators bonded at the periphery of the plate. Starting from first principles, the relations linking implementation parameters to the performance of the display are developed. The mechanical design of the display, signal processing and driving electronics are described. A set of engineering tradeoffs are made explicit and used for the design of a mock up device comprising a glass plate 148 x 210 x 0.5 mm^3. Tests indicate that a peak amplitude of 7 micron confined to a 20 mm2 region could be obtained for an average power consumption of 45 mW. Simultaneous focusing at several locations was successfully achieved. We showed that a lumped-mass model for the fingertip can effectively describe the effect of an actual fingertip load at the focus point. Lastly, we elucidated a likely stimulation mechanism that involves the transient decoupling of the finger skin from the plate surface. This phenomenon explains the observed tactile effect.
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Hudin, C., Lozada, J., Hayward, V. 2014.
Spatial, temporal, and thermal contributions to focusing contrast by time reversal in a cavity.
Journal of Sound and Vibration. 333(6):1818-1832

The accuracy of wave focusing by time reversal depends on a quantity termed contrast ratio that measures the amplitude of a localized peak of velocity relatively to background noise. A comprehensive expression for the contrast ratio in a lossy cavity is derived by modal decomposition of the wave field. This expression accounts for the effects of the mechanical and the dimensional properties of the cavity, the bandwidth of the excitation signal, the number of sources, and the duration of time reversal window. The expression can predict the characteristics of a given process such as the long-time saturation and the single-channel time reversal limit. The expression also models the effect of temperature variations on focusing accuracy and shows that thermal drift exhibits two regimes. In the first regime, small temperature variations have little effect on contrast. The second regime is characterized by a rapid deterioration of contrast. Experimental measurements show close agreement with the theory.
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Hudin, C., Lozada, J., Hayward, V. 2013.
Localized Tactile Stimulation by Time-Reversal of Flexural Waves: Case Study With a Thin Sheet of Glass.
Proceedings of the IEEE World Haptics Conference 2013. pp. 67-72.

This paper addresses the issue of producing localized tactile stimuli on a transparent surface. An approach based on time reversal of acoustic waves is presented and implemented on a thin glass surface actuated by piezoelectric transducers located at the periphery. The physical performance measurement, completed by a user study demonstrates the ability to provide localised and perceivable tactile stimulation.
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Hudin, C., Lozada, J., Wiertlewski, M., Hayward, V. 2012.
Tradeoffs In The Application of Time-Reversed Acoustics to Tactile Stimulation.
Proceedings of Eurohaptics 2012, LNCS 7283, Part I, pp. 218-226. (Best Paper Honorable Mention)

The creation of active tactile surfaces through electrome- chanical actuation is an important problem. We describe here the appli- cation of time-reversed acoustics to the creation of deformations localized in time and in space in a stretched membrane that can be touched. We discuss the basic physical and engineering tradeoffs of this approach and describe the results obtained from an experimental mock-up device.
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Izaguirre, A., Hashimoto, M., Paul, R. P., and Hayward, V. 1992.
A New Computational Structure For Real-Time Dynamics.
Int. J. of Robotics Research. MIT Press, Vol. 11(4). pp. 346-362..

Presents an efficient structure for the computation of robot dynamics in real time. The fundamental characteristic of this structure is the division of the computation into a high-priority synchronous task and low-priority background tasks, possibly sharing the resources of a conventional computing unit based on commercial microprocessors. The background tasks compute the inertial and gravitational coefficients as well as the forces due to the velocities of the joints. In each control sample period, the high-priority synchronous task computes the product of the inertial coefficients by the accelerations of the joints and performs the summation of the torques due to the velocities and gravitational forces. Kircanski et al. (1986) have shown that the bandwidth of the variation of joint angles and of their velocities is an order of magnitude less than the variation of the joint accelerations. This result agrees with the experiments that the authors have carried out using a PUMA 260 robot.
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Janabi-Sharifi, F., Hayward, V., Wang, Q. Y. 2007.
Design and implementation of a graphic-haptic display system.
Displays, Vol. 28, pp. 118-128. pp. 1003-1009.

Despite current advances in multimedia environments, tracing the geometrical structures of graphical images using force feedback remains a research issue. In this paper, the development and implementation of a Multi-Modal Display System (MMDs) for tracing 2D boundaries in graphic images are discussed. A method is proposed that provides a type of haptic feedback designed to assist a user to trace the contours of objects seen in images. This method is an example of a family of haptic synthesis methods whereby the force field explored by the user is dynamic in the sense that it depends both on movement as well as on the object being haptically represented. The proposed performance-based method provides users with a movement guidance through an active haptic sense rather than the more common impedance technique. The tracing effectiveness of the proposed method is verified experimentally.
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Klöcker, A., Wiertlewski, M., Théate, V., Hayward, V., Thonnard, J.-L. 2013.
Physical factors influencing pleasant touch during tactile exploration.
PloS ONE, 8(11):e79085.

Background: When scanning surfaces, humans perceive some of their physical attributes. These percepts are frequently accompanied by a sensation of (un)pleasantness. We therefore hypothesized that aspects of the mechanical activity induced by scanning surfaces with fingertips could be objectively associated with a pleasantness sensation. Previously, we developed a unidimensional measure of pleasantness, the Pleasant Touch Scale, quantifying the pleasantness level of 37 different materials. Findings of this study suggested that the sensation of pleasantness was influenced by the average magnitude of the frictional forces brought about by sliding the finger on the surface, and by the surface topography. In the present study, we correlated (i) characteristics of the fluctuations of frictional forces resulting from the interaction between the finger and the surface asperities as well as (ii) the average friction with the sensation of pleasantness.

Results: Eight blindfolded participants tactually explored twelve materials of the Pleasant Touch Scale through lateral sliding movements of their index fingertip. During exploration, the normal and tangential interaction force components, fN and fT, as well as the fingertip trajectory were measured. The effect of the frictional force on pleasantness sensation was investigated through the analysis of the ratio fT to fN, i.e. the net coefficient of kinetic friction, µ. The influence of the surface topographies was investigated through analysis of rapid fT fluctuations in the spatial frequency domain. Results showed that high values of were anticorrelated with pleasantness. Furthermore, surfaces associated with fluctuations of fT having higher amplitudes in the low frequency range than in the high one were judged to be less pleasant than the surfaces yielding evenly distributed amplitudes throughout the whole spatial frequency domain.

Conclusion: Characteristics of the frictional force fluctuations and of the net friction taking place during scanning can reliably be correlated with the pleasantness sensation of surfaces.
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Farkhatdinov, I., Ouarti, N., Hayward, V. 2013.
Vibrotactile Inputs To The Feet Can Modulate Vection.
Proceedings of the IEEE World Haptics Conference 2013. pp. 677-681.

Vection refers to the illusion of self-motion when a significant portion of the visual field is stimulated by visual flow, while body is still. Vection is known to be strong for peripheral vision stimulation and relatively weak for central vision. In this paper, the results of an experimental study of central linear vection with and without vibrotactile feet stimulation are presented. Three types of vibratory stimuli were used: a sinusoidal signal, pink noise, and a chirp signal. Six subjects faced a screen looking at a looming visual flow that suggested virtual forward motion. The results showed that the sensation of self-motion happened faster and its intensity was the strongest for sinusoidal vibrations at constant frequency. For some subjects, a vibrotactile stimulus with an increasing frequency (a chirp) elicited as well a stronger vection. The strength of sensation of self-motion was the lowest in the cases when pink noise vibrations and no vibrotactile stimulation accompanied the visual flow stimulation. Possible application areas are mentioned.
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Farkhatdinov, I., Hayward, V. Berthoz, A., Michalska, H. 2012.
Modeling Verticality Estimation During Locomotion.
Proceedings of the 19th CISM-IFToMM Symposium on Robot Design, Dynamics, and Control, Romansy 2012. pp. 651-656

Estimation of the gravitational vertical is a fundamental problem faced by locomoting biological systems and robots alike. A robotic model of a vestibular system is suggested with the purpose of explaining an observed phenomenonhead stabilization during locomotion. The mechanical model of the vestibular system com- prises a damped inclinometer and an inertial measurement unit which are mounted on an actuated orienting platform (a robotic head). Generic linear control is employed to stabilize the head- platform while the vestibular system exercises an extended Kalman filter algorithm to estimate the gravitational direction in space. It is demonstrated that stabilization of the head-platform is essential in achieving accurate verticality estimation as it attenuates the dis- turbances generated by locomotion and simplifies state observation in a non-inertial frame, without the need for fixed external beacons.
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Farkhatdinov, I. and Hayward, V. and Berthoz, A. 2011.
On the Benefits of Head Stabilization with a View to Control Balance and Locomotion in Humanoids.
Proceedings of the 11th IEEE-RAS International Conference on Humanoid Robots. pp. 147-152.

The estimation of the gravitational vertical is a fundamental problem faced by locomoting robots and animals alike. We describe a technique to address this problem that involves a damped inclinometer, an inertial measurement unit mounted on an actuated orienting platform, that is a robot head, so-to-speak. Simulations show that a nonlinear observer based on Newtons method to solve the full dynamics of the system given inertial sensor data gives accurate verticality estimates even in the presence of highly dynamic perturbations that include large fictitious force terms. Moreover, when the sensor platform is servoed to the estimate of the gravitational vertical to provide for horizontal stabilization, the accuracy of the estimate is improved by almost two orders of magnitude. Similar gains of performance are observed even in the presence of noise and parameter uncertainty.
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Janabi-Sharifi, F., Hayward, V., and Chen, C-S. J. 2000.
Discrete-Time Adaptive Windowing For Velocity Estimation.
IEEE T. On Control Systems Technology. Vol. 8, No. 6, pp. 1003-1009.

We present methods for velocity estimation from discrete and quantized position samples using adaptive windowing. Previous methods necessitate tradeoffs between noise reduction, control delay, estimate accuracy, reliability, computational load, transient preservation, and difficulties with tuning. In contrast, a first order adaptive windowing method is shown to be optimal in the sense that it minimizes the velocity error variance while maximizes the accuracy of the estimates, requiring no tradeoffs. Variants of this method are also discussed. The effectiveness of the proposed technique is verified in simulation and by experiments on the control of a haptic device.
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Joly, L. D., Andriot, C., and Hayward, V. 1997.
Mechanical Analogies In Hybrid Position/Force Control.
Proc. IEEE Int. Conf. on Robotics and Automation. Vol. 1, pp. 835-839.

It is shown that in hybrid position/force control as well as in multi-robot cooperation, the desired behavior of the system can be defined in terms of a massless mechanism whose joints act as ideal position or source forces. Based on this remark, a simple and robust controller is proposed. Experiments validate this approach.
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Kaneko, S., Kajimoto, H., and Hayward, V. 2018.
A Case of Perceptual Completion in Spatio-Temporal Tactile Space.
Proceedings of the Eurohaptics Conference. In press.

We reproduced a perceptual phenomenon where a tactile stimulus moving on the fingertip jumps instantly over a gap but is felt as if the space of the gap was perceptually obliterated. This phenomenon was recently demonstrated on the forearm using brushes. On the fingertip, we elicited this effect using virtual edges and measured psychometric response curves obtained by varying the time taken by the moving edge to traverse the gap between the first and the third portion of the stimulus. Most people failed to detect 2 mm gaps when the traversal time fell below 0.2 s. The gaps were consistently detected when they were tra- versed at same the speed as that of the moving edge in the first and third portion of the stimulus. We discuss the implications of these findings.
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Kurtz, R. and Hayward, V. 1995.
Dexterity Measures For Mechanisms With Unilateral Constraints: The N+1 Case.
J. of Advanced Robotics. (Special Issue on enveloping grasp and whole-arm manipulation). Vol. 9. No. 5, pp. 561-577.

A new set of measures applicable to unilaterally actuated mechanisms is developed in the case when one biasing force is present. Unilaterally mechanisms are found for example in grasping situations, tendon actuation, jet propulsion, and variable reluctance magnetic servo levitation.
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Kurtz, R. and Hayward, V. 1992.
Multiple-Goal Optimization Of A Parallel Mechanism With Actuator Redundancy.
IEEE Transactions on Robotics and Automation. Vol. RA-8, No. 5. pp. 633-651.

A new kinematic design will be presented that is fully parallel and actuator redundant, Actuator redundancy refers to the use of more actuators than are strictly needed to control the mechanism without increasing the mobility. The ueses of this form of redundancy include the ability to partially control the internal forces, increase the workspace, remove singularities, and augment dexterity. Optimization will take place based on several objective functions. The kinematic dexterity, the forces present at the actutators, and the uniformity of the desterity over the workspace will all be investigated as potential objects, Global measures will be rerived from each of these quantities for optimization purposes. Examining only one single objective may not yield an acceptable design. Instead, optimization of several factors is done simultaneously by specifying a primany objective and minimum performance standards for the secondary objectives.
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Kurtz, R. and Hayward, V. 1991.
Dexterity Measures For Tendon Actuated Parallel Mechanisms.
Int. Conf. on Advanced Robotics, ICAR, pp. 1141-1148.

We look at a class of tendon actuated mechanisms. We show that the conventional dexterity measures used for the analysis of manipulators are not applicable to the tendon case because there are non-linear elements. We then develop a correct dexterity measure for this type of mechanism.
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Hayward, V. and Kurtz, R. 1991.
Modeling of a parallel wrist mechanism with actuator redundancy.
Proc. Symposium on Advances in Robot Kinematics, pp. 444-456.

Parallel mechanisms can lead to high structural rigidity and good inertial properties, however their utility is generally limited by an inherently small workspace. The use of actuator redundancy can simultaneously increase the workspace and overcome the problems associated with a type of kinematic singularity found in parallel mechanisms. In order to substantiate this idea, a parallel spherical mechanism with actuator redundancy id exhibited and modeled in terms of its kinematics, velocities, singular configurations and finally workspace properties.
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Hayward, V., Hayati, S. 1988.
Kali: An Environment For The Programming And Control Of Cooperative Manipulators
Proc. American Control Conference. pp. 473-478.

The paper describes the design of a controler for coopeerative robots designed at McGill University in a colaborative effort with the Jet Propukion Laboratory. The first part of the paper discusses the background and motivation for multiple arm control. Then, a set of programming primnitives, which permit a programmer to specify cooperative tasks are described. Motion primitives specify asynchronous motions, master/slave motions, and cooperative motions. In the context of cooperative robots, trajectory generation issues are discussed and our implementation briefly described. The relations between programming and control in the case of multiple robots are examined. Finally, the paper describes the allocation of various tasks among a multi-processor computer.
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Hayward, V. and Hayati, S. 1987.
Design principles of a cooperative robot controller.
Proc. SPIE - International Society Optical Engineering, 851. pp. 135--140.

Describes the design of a controller for cooperative robots being designed at McGill University in a collaborative effort with the Jet Propulsion Laboratory. The first part of the paper discusses the background and motivation for multiple arm control. Then, a set of programming primitives which are based on the RCCL system and which permit a programmer to specify cooperative tasks are described. The first group of primitives are motion primitives which specify asynchronous motions, master/slave motions, and cooperative motions. In the context of cooperative robots, trajectory generation issues are discussed and a practical implementation described. A second set of primitives provides for the specification of spatial relationships. The relations between programming and control in the case of a multiple robot are examined. The allocation of various tasks among a set of microprocessors sharing a common bus, is described.
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Jörntell, H., Bengtsson, F., Geborek, P., Spanne, A., Terekhov, A. V., Hayward, V. 2014.
Segregation of Tactile Input Features in Neurons of the Cuneate Nucleus.
Neuron. 83:1444-1452

Our tactile perception of external objects depends on skin-object interactions. The mechanics of contact dictates the existence of fundamental spatiotemporal input features - contact initiation and cessation, slip, and rolling contact - that originate from the fact that solid objects do not interpenetrate. However, it is unknown whether these features are represented within the brain. We used a novel haptic interface to deliver such inputs to the glabrous skin of finger/digit pads and recorded from neurons of the cuneate nucleus (the brain's first level of tactile pro- cessing) in the cat. Surprisingly, despite having similar receptive fields and response properties, each cuneate neuron responded to a unique combi- nation of these inputs. Hence, distinct haptic input features are encoded already at subcortical process- ing stages. This organization maps skin-object inter- actions into rich representations provided to higher cortical levels and may call for a re-evaluation of our current understanding of the brain's somatosensory systems.
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Konkle, T., Wang, Q., Hayward, V., Moore, C. I. 2009.
Motion Aftereffects Transfer between Touch and Vision.
Current Biology, 19(9), pp. 745-750.

Current views on multisensory motion integration assume separate substrates where visual motion perceptually dominates tactile motion. However, recent neuroimaging ndings demonstrate strong activation of visual motion pro- cessing areas by tactile stimuli, implying a potentially bidirectional relationship. To test the relationship between visual and tactile motion processing, we examined the transfer of motion aftereffects. In the well-known visual motion aftereffect, adapting to visual motion in one direction causes a subsequently presented stationary stimulus to be perceived as moving in the opposite direction. The existence of motion aftereffects in the tactile domain was debated, though robust tactile motion aftereffects have recently been demonstrated. By using a motion adaptation paradigm, we found that repeated exposure to visual motion in a given direction produced a tactile motion aftereffect, the illusion of motion in the opponent direction across the nger pad. We also observed that repeated expo- sure to tactile motion induces a visual motion aftereffect, biasing the perceived direction of counterphase gratings. These crossmodal aftereffects, operating both from vision to touch and from touch to vision, present strong behavioral evidence that the processing of visual and tactile motion rely on shared representations that dynamically impact modality- specic perception.
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Lee, J. S. and Hayati, S. and Hayward, V. and Lloyd, J. E. 1987.
Implementation of RCCL, a robot control C library on a microVAX II.
Proc. SPIE - International Society Optical Engineering, 726, pp. 472--480.

Describes the design of a controller for cooperative robots being designed at McGill University in a collaborative effort with the Jet Propulsion Laboratory. The first part of the paper discusses the background and motivation for multiple arm control. Then, a set of programming primitives which are based on the RCCL system and which permit a programmer to specify cooperative tasks are described. The first group of primitives are motion primitives which specify asynchronous motions, master/slave motions, and cooperative motions. In the context of cooperative robots, trajectory generation issues are discussed and a practical implementation described. A second set of primitives provides for the specification of spatial relationships. The relations between programming and control in the case of a multiple robot are examined. The allocation of various tasks among a set of microprocessors sharing a common bus, is described.
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Levesque, V. and Hayward, V. 2010.
Laterotactile Rendering of Vector Graphics with the Stroke Pattern. Proc. of Europhaptics 2010, Part II, Kappers, A.M.L. et al. (Eds.), LNSC 6192, Springer-Verlag, pp. 25-30.

This paper presents preliminary work towards the development and evaluation of a practical refreshable tactile graphics system for the display of tactile maps, diagrams and graphs for people with visual impairments. Refreshable tactile graphics were dynamically produced by laterally deforming the skin of a finger using the STReSS2 tactile display. Tactile features were displayed over an 11x6 cm virtual surface by controlling the tactile sensations produced by the ngerpad-sized tactile display as it was moved on a planar carrier. Three tactile rendering methods were used to respectively produce virtual gratings, dots and vibrating patterns. These tactile features were used alone or in combination to display shapes and textures. The ability of the system to produce tactile graphics elements was evaluated in ve experiments, each conducted with 10 sighted subjects. The first four evaluated the perception of simple shapes, grating orientations, and grating spatial frequencies. The fifth experiment combined these elements and showed that tactile icons composed of both vibrating contours and grated textures can be identied. The fith experiment was repeated with 6 visually impaired subjects with results suggesting that similar performance should be expected from that user group.
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Levesque, V. and Hayward, V. 2008.
Tactile Graphics Rendering Using Three Laterotactile Drawing Primitives. Proc. 16th Symposium on Haptic Interfaces For Virtual Environment And Teleoperator Systems, pp. 429-436.

This paper presents preliminary work towards the development and evaluation of a practical refreshable tactile graphics system for the display of tactile maps, diagrams and graphs for people with visual impairments. Refreshable tactile graphics were dynamically produced by laterally deforming the skin of a finger using the STReSS2 tactile display. Tactile features were displayed over an 11x6 cm virtual surface by controlling the tactile sensations produced by the ngerpad-sized tactile display as it was moved on a planar carrier. Three tactile rendering methods were used to respectively produce virtual gratings, dots and vibrating patterns. These tactile features were used alone or in combination to display shapes and textures. The ability of the system to produce tactile graphics elements was evaluated in ve experiments, each conducted with 10 sighted subjects. The first four evaluated the perception of simple shapes, grating orientations, and grating spatial frequencies. The fifth experiment combined these elements and showed that tactile icons composed of both vibrating contours and grated textures can be identied. The fith experiment was repeated with 6 visually impaired subjects with results suggesting that similar performance should be expected from that user group.
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Pasquero, J., and Hayward, V. 2011.
Tactile Feedback Can Assist Vision in Mobile Interaction.
Proceedings of CHI 2011, the International Conference on Human Factors in Computing Systems, pp. 3277--3280.

We evaluated the use of rich tactile feedback in the task of scrolling through a long list of items. We used a hand-held device having a tactile transducer that could provide sensations with temporal and spatial content. These capabilities were put to use in an interaction metaphor where input and tactile feedback were tightly coupled. We measured time-to-target and error rates, but also measured the time spent by participants to look at the screen. We found a 28% decrease of reliance on vision when tactile feedback was enabled.
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Levesque, V., Pasquero, J., and Hayward, V. 2007.
Braille Display by Lateral Skin Deformation with the STReSS^2 Tactile Transducer.
Proc. World Haptics 2007 (Second Joint Eurohaptics Conference And Symposium On Haptic Interfaces For Virtual Environment And Teleoperator Systems), pp. 115-120.

Earlier work with a 1-D tactile transducer demonstrated that lateral skin deformation is sufficient to produce sensations similar to those felt when brushing a finger against a line of Braille dots. Here, we extend this work to the display of complete 6-dot Braille characters using a general pur- pose 2-D tactile transducer called STReSS2 . The legibility of the produced Braille was evaluated by asking seven ex- pert Braille readers to identify meaningless 5-letter strings as well as familiar words. Results indicate that reading was difficult but possible for most individuals. The superposition of texture to the sensation of a dot improved performance. The results contain much information to guide the design of a specialized Braille display operating by lateral skin deformation. They also suggest that rendering for contrast rather than realism may facilitate Braille reading when using a weak tactile transducer.
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Levesque, V. 2005.
Blindness, Technology and Haptics.
Technical Report TR-CIM-05.08. Center for Intelligent Machines, McGill University.

The blind and the visually impaired are in a unique position to appreciate and make functional use of haptic devices. Designing devices for the blind is, however, more arduous than many researchers and inventors expect. It is thus important to fully un- derstand the needs and requirements of that community before attempting to create devices for them. It is also important to learn from past research and development in the application of technology for the blind. This survey provides an overview of current knowledge on blindness and rehabilitation technology relevant for the design of aids for the blind, and more particularly for the use of haptics with the blind. The survey begins with a demystification of blindness and a discussion of the differences between blind and sighted. Follows a broad overview of the many attempts at applying technological solutions to problems encountered by the blind. The survey ends with a discussion of lessons learned from previous failures and successes in rehabilitation technology as well as speculation on the future of haptics and other technologies for people living with blindness.
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Levesque, V., Pasquero, J., Hayward V., and Legault, M. 2005.
Display Of Virtual Braille Dots By Lateral Skin Deformation: Feasibility Study.
ACM Transactions on Applied Perception.Vol. 2, No. 2, pp. 132-149.

When a progressive wave of localized deformations occurs tangentially on the fingerpad skin, one typically experiences the illusion of a small object sliding on it. This effect was investigated because of its potential application to the display of Braille. A device was constructed that could produce such deformation patterns along a line. Blind subjects' ability to read truncated Braille characters ( blank-blank, blank-dot, dot-blank, and dot-dot) using the device was experimentally tested and compared to their performance with a conventional Braille medium. While subjects could identify twocharacter strings with a high rate of success, several factors need to be addressed before a display based on this principle can become practical.
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Levesque, V. and Hayward, V. 2003.
Experimental Evidence of Lateral Skin Strain During Tactile Exploration.
Proc. Eurohaptics 2003. Dublin, Ireland, July 2003.

This paper describes an experimental platform for the study of stretch and compression of the human fingerpad skin during tactile exploration. A digital camera records the sequence of patterns created by a fingertip as it slides over a transparent surface with simple geometrical features. Skin deformation is measured with high temporal and spatial resolution by tracking anatomical landmarks on the fingertip. Techniques adapted from the field of online fingerprinting are used to acquire highcontrast fingerprint images and extract salient features (pores, valley endings, and valley bifurcations). The results of experiments performed with surfaces with a bump or hole and flat surfaces are presented. This work is motivated by the need to provide meaningful tactile movies for a tactile display that uses distributed lateral skin stretch.
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Lloyd, J. E. and Hayward, V. 2001.
Singularity Robust Trajectory Generation.
Int. J. Robotics Research. Vol. 20, No. 1, pp. 38-56.

A singularity-robust trajectory generator is presented which, given a prescribed manipulator path and corresponding kinematic solution, computes a feasible trajectory in the presence of kinematic singularities. The resulting trajectory is close to minimum time, subject to individual bounds on joint velocities and accelerations, and follows the path with precision. The algorithm has complexity O(M log M), where M is the number of robot joints, and works using coordinate pivoting, in which the path timing near singularities is controlled using the fastest changing joint coordinate. This allows the handling of singular situations, including linear self-motions (e.g., wrist singularities), where the speed along the path is zero but some joint velocities are non-zero. To compute the trajectory, knot points are inserted along the path, dividing it into intervals, with the knot density increasing near singularities. An appropriate path velocity is then computed at each knot point, and the resulting knot-velocity sequence is integrated to yield the path timing. Examples involving the PUMA manipulator are shown.
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Lloyd, J. E and Hayward, V. 1993.
Trajectory Generation For Dynamic, Sensor-Driven Environments.
Int. J. Robotics Research, MIT Press, Vol. 12, No. 4. pp. 380-394.

In on-line robot trajectory generation, a connecting polynomial is normally used to remove discontinuities in velocity and acceleration between adjacent path segments. This article presents a new technique for performing such transitions in which adjacent path segments are "blended" together, with excess acceleration being removed using an estimate of the initial path velocities. Because this method requires no advance knowledge of the path segments, it can handle situations where the paths are changing with time (as when tracking sensor or control inputs). The method can also be used to adjust the spatial shape of the transition curve (such as to have it pass around or through the "via point"), which may be necessary to handle constraints imposed by different types of manipulator tasks. When the blended paths are nonlinear, it is possible to set a tight bound on the resulting transition acceleration. The blend technique works directly for vector trajectories and can be modified to handle 3-D rotational trajectories. A simple trajectory generation algorithm is presented as an illustration.
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Lloyd, J. E and Hayward, V. 1993.
Real-Time Trajectory Generation In Multi-RCCL.
J. Robotics Systems, Wiley, Vol. 10, No. 3., pp. 369-390.

This article describes the design of the trajectory generator for a robot programming system called Multi-RCCL, which is a package of C routines for doing real-time manipulator control in a UNIX environment. RCCL has been used successfully in developing robot control applications in numerous research and industry facilities over the last several years. One of its strongest features is the ability to integrate real-time sensor control into the manipulator task specification. RCCL primitives supply the trajectory generator with target points for motions in joint or Cartesian coordinates. Other primitives allow the code developer to specify on-line functions that can modify the target points, or possibly cancel motion requests, in response to various sensor or control inputs. The design requirements of the trajectory generator are that it be able to integrate these on-line modifications into the overall robot motion and provide a smooth path between adjacent motions even when sensor inputs make the future trajectory uncertain.
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Lloyd, J. E and Hayward, V. 1991.
Real-Time Trajectory Generation Using Blend Functions.
Proc. Int. IEEE Conference on Robotics and Automation. pp. 784-789.

A technique for transitioning between path segments is described which is tolerant to dynamic changes arising from sensor inputs. The main idea is to "blend" the segments together in a way that does not require advance knowledge of the paths. It is also possible to decompose the transition into an action which "bings to rest" the motion along the initial path plus an action which "starts up" the motion along the final path. By adjusting the timing of these two components, one may control the shape of the transition, in both time and space, so as satisfy different task constraints.
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Lloyd, J. M. and Hayward, V. 1998.
Generating Robust Trajectories in the Presence of Ordinay and Linear-Self-Motion Singularities.
Proc. IEEE Int. Conf. on Robotics and Automation. pp. 3228-3234.

An algorithm is presented which computes feasible manipulator trajectories along fixed paths in the presence of kinematic singlarities. The resulting trajectories are close to minimum tiem, gievn an inverse kinematic solution for the path and bounds on joint velocities and accelerations. The algorithm has complexity O(M log M) with respect to the number of joint corrdinates M, and works using "coordinate pivoting", in which the path timing is generates locally with respect to whichever joint coordinate is changing the fastest. This allows the handling of singularities, including linear elf-motion (e.g. wrist singularities), where the path speed is zero but other joint velocities are non-zero. Example involving the PUMA manipulator are shown.
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Lloyd, J. M. and Hayward, V. 1998.
A Discrete Algorithm For Fixed-Path Trajectory Generation At Kinematic Singlarities.
Proc. IEEE Int. Conf. on Robotics and Automation, pp. 2743-2748.

An algorithm is presented for computing the necessary time-scaling to allow a non-redundant manipulator to fol- low a fixed Cartesian path containing kinematic singular- ities. The resulting trajectory is close to minimum-time, subject to bounds on joint velocities and accelerations. The algorithm assigns a series of knot points along the path, increasing the knot density in the vicinity of singularities. Appropriate path velocities are then computed for each knot point. Two experiments involving the PUMA manipulator are shown.
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Lloyd, E. J. and Hayward, V. 1988.
Kinematics Of Common Industrial Robots.
Robotics, North-Holland, Vol. 4. pp. 169-191.

An approach to finding the solution equations for simple manipulators is described which enhances the well known method of Paul, Renaud, and Stevenson, by explicitly making use of known decouplings in the manipulator kinematics. This reduces the set of acceptable equations from which we obtain relationships for the joint variables. For analyzing the Jacobian, such decoupling is also useful since it manifests itself as a block of zeros, which makes inversion much easier. This zero lock can be used to obtain a concise representation for the forward and inverse Jacobian computations. The decoupling also simplifies the calculations sufficiently to allow us to make good use of a symbolic algebra program (MACSYMA) in obtaining our results. Techniques for using MACSYMA in this way are described. Examples are given for several industrial manipulators.
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Lu, T., Pacoret, C., Hériban, D., Mohand-Ousaid, A., Régnier, S., and Hayward, V. 2017.
KiloHertz Bandwidth, Dual-Stage Haptic Device Lets You Touch Brownian Motion.
IEEE Transactions on Haptics. In press.

This paper describes a haptic interface that has a uniform response over the entire human tactile frequency range. Structural mechanics makes it very difficult to implement articulated mechanical systems that can transmit high frequency signals. Here, we separated the frequency range into two frequency bands. The lower band is within the first structural mode of the corresponding haptic device while the higher one can be transmitted accurately by a fast actuator operating from conservation of momentum, that is, without reaction forces to the ground. To couple the two systems, we adopted a channel separation approach akin to that employed in the design of acoustic reproduction systems. The two channels are recombined at the tip of the device to give a uniform frequency response from DC to one kHz. In terms of mechanical design, the high-frequency transducer was embedded inside the tip of the main stage so that during operation, the human operator has only to interact with a single finger interface. In order to exemplify the type of application that would benefit from this kind of interface, we applied it to the haptic exploration with microscopic scales objects which are known to behave with very fast dynamics. The novel haptic interface was bilaterally coupled with a micromanipulation platform to demonstrate its capabilities. Operators could feel interaction forces arising from contact as well as those resulting from Brownian motion and could manoeuvre a micro bead in the absence of vision.
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Lu, X., Grant, D., and Hayward, V. 1997.
Design And Comparison Of High Strain Shape Memory Actuators.
Proc. IEEE Int. Conf. on Robotics and Automation. Vol. 1, pp. 260-267.

A simulator is developed to model and design high strain shape memory alloy (SMA) tension actuators. The simulator may be used predict characteristics of a given actuator, or to design its geometry under specifications such as force, speed, stroke and size. The accuracy of the model is verifed experimentally in reference to an existing NiTi shape memory alloy prototype actuator. Having developed some confidence in the model, the performance of the proposed actuation mechanism is compared to other existing technologies. In particular, the force-displacement and speed characteristics of a micro-solenoid electro-magnetic actuator and a muscle-size pneumatic actuator are compared to those of the SMA actuators with same dimensions.
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Luk, J., Pasquero, J., Little, S., MacLean, K. E., Levesque, V. and Hayward, V. 2006.
A Role for Haptics in Mobile Interaction: Initial Design Using a Handheld Tactile Display Prototype.
Proc. of the 2006 ACM Conference on Human Factors in Computing Systems, CHI 2006. pp. 171-180.

Mobile interaction can potentially be enhanced with well- designed haptic control and display. However, advances have been limited by a vicious cycle whereby inadequate haptic technology obstructs inception of vitalizing applications. We present the first stages of a systematic design effort to break that cycle, beginning with specific usage scenarios and a new handheld display platform based on lateral skin stretch. Results of a perceptual device characterization inform mappings between device capabilities and specific roles in mobile interaction, and the next step of hardware re-engineering.
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MacLean, K. E. and Hayward, V. 2008.
Do It Yourself Haptics, Part-II.
IEEE Robotics and Automation Magazine, 15(1):104-119.

This article is the second of a two-part series intended to be an introduction to haptic interfaces, their construction and application design. Haptic interactions employ mechanical, programmed physical devices which can be used for human-computer communication via the sense of touch. In Part I of this series, we focused on the devices themselves: the classes of hardware schemes currently available or envisioned, the software components which drive them, and specific examples which can be built on the kitchen table. Here in Part II, we broach a topic which is coming into its own: between the vision of a particular utility that haptic feedback theoretically should enable, and the hardware capable of delivering the required sensations, is the problem of designing the interaction in a usable way.
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Mahvash, M. and Hayward V. 2005.
High Fidelity Passive Force Reflecting Virtual Environments. IEEE Transactions on Robotics. 21(1):38-46.

Passivity theory is employed to create synthetic, complex multi-dimensional haptic environments. It is shown that sufficiently high rendering rates guarantee the passivity of a simulation produced by a haptic device coupled to a discrete-time realization of a nominally passive environment. The creation of a passive, globally-defined, virtual environment is either analytically complex or computationally costly. A method is described whereby a passive environment is created from transitions between locally-defined force models that encode static conservative force fields. This is applied to the haptic rendering of tool contact with deformable bodies in which sparse force-deflection responses are used to define local models. Passivity, continuity and fidelity are provided by response function interpolation rather than by interpolation of forces as in previous methods. The paper also includes an illustrative example.
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Mahvash, M. and Hayward, V. 2004.
High Fidelity Haptic Synthesis of Contact With Deformable Bodies.
IEEE Computer Graphics and Applications. (Special issue on haptic rendering), Vol. 24(2):48-55.

This article describes an efficient method to synthesize the nonlinear haptic response of deformable objects from data obtained by offline simulation or measurements. This capability is useful to create surgical simulators with high-fidelity haptic feedback, as various effects of contact mechanics can be reproduced accurately and in a passive manner.
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Mahvash, M. and Hayward, V. 2003a.
Passivity-Based High-Fidelity Haptic Rendering of Contact.
Proc. IEEE Int. Conf. on Robotics and Automation. pp. 3722-3728.

A method is described whereby the virtual haptic interaction with deformable elastic objects is created in terms of two processes: a slow process which carries out the simulation, and a fast process to render forces. Passivity theory is used to design an update strategy which reproduces exactly pre-computed responses between a tool and an object. This yields a design procedure for adjustable local models which guarantee the passivity of the interaction while preserving fidelity. Two examples of local models are given and some experimental results are reported. of the operator.
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Mahvash, M. and Hayward, V. 2003b.
Haptic Simulation of a Tool In ContactWith a Nonlinear Deformable Body.
In "IS4TM: International Symposium on Surgery Simulation and Soft Tissue Modelling", N. Ayache, H. Delingette (Eds), Lecture Notes in Computer Science (LNSC 2673), Springer Verlag. pp. 311-320.

This paper presents a method to artificially re-create haptic feedback while moving and sliding an arbitrary virtual tool against a virtual deformable body with nonlinear elastic properties. The computation of the response in such general cases is a task which does not yet admit computational solutions suitable for realtime implementation. To address this, we describe an approach based on the bookkeeping of force deflections curves stored at the nodes of a triangulated body surface. For realism, normal and lateral deformations at each node are represented in a range of deflection distances. The response everywhere is synthesized via area interpolation of response curves stored at the nodes of the mesh. The mathematical continuity of the synthetic response is the result of both local coordinates interpolation and of response function interpolation, which previous methods did not account for. This guarantees the absence of haptic clicks and pops which are unacceptable artifacts in high fidelity simulations. Sliding contacts are also considered.
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Mahvash, M., Hayward, V., and Lloyd, J. E. 2002.
Haptic Rendering of Tool Contact.
Eurohaptics 2002. pp. 110-115.

Virtual haptic interaction with simulated deformable bodies requires contact forces to be computed with reasonable approximations in real time. This paper makes use of St. Venants principle on concentrated loads, and Castiglianos theory on deflection to show that when an elastic body is globally deformed, the point-force representation of a tool contact is a good approximation. However, when the deformation of the body is localized in a small region, the contact forces critically depend on the shape of the tool. Previously proposed approaches based on finite element and boundary element methods to predict deformation can not always be used to simulate tool contact. We propose a model for computing tool force-displacement responses which is efficiently calculated at run time by interpolation of pre-calculated force-deflection responses, each representing the response of a contact between a given tool and a body. The interpolation approach ensures the continuity of the rendered force, although this force is obtained from pre-calculated responses at a set of discrete surface points. The paper also describes how sliding contacts can be modeled by computing tangential friction forces in terms of pre-sliding displacements over the surface of the undeformed body. Tests involving two deformation types and various contact forms were performed on samples of rubber and of calf liver. A computer implementation is also described.
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Mahvash, M. and Hayward, V. 2001.
Haptic Rendering of Cutting: A Fracture Mechanics Approach.
Haptics-e,Vol. 2, No. 3.

Cutting a deformable body may be viewed as an interchange between three forms of energy: the elastic energy stored in the deformed body, the work done by a sharp tool as it moves against it, and the irreversible work spent in creating a fracture. Other dissipative phenomena such as friction can optionally also be considered. The force applied can be found by evaluating the work done by a tool which is suciently sharp to cause local deformation only. To evaluate this work, we propose a computational model that reduces cutting to the existence of three modes of interaction: deformation, rupture, and cutting, each of which considers the exchange between two forms of energy. During deformation, the work done by a tool is recoverable. During rupture, this work is zero. During cutting, it is equal to the irreversible work spent by fracture formation. The work spent in separating the sample is a function of its fracture toughness and of the area of a crack extension. It is in principle necessary to compute the deformation caused by a sharp tool in order to recover the force. This is in general an unsolved problem. However, for the case of a sharp interaction, measurements from tests performed on samples used in conjunction with analytical approximations to the contact problem, make it possible to propose a model which is applicable to haptic rendering. The technique is then compared to experimental results which confirms the model hypotheses. An implementation of the model that yields realistic results is also described.
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Michalska, H. and Hayward, V. 2009.
Quantized and Sampled Control of Linear Second Order Systems.
Proc. European Control Conference 2009, pp. 531-536. pp. 273-278.

Continuous systems are today controlled digitally. It is therefore necessary to consider the effects of quantization and sampling. We show that any second-order LTI system can be controlled exactly by fixed quantized feedback independently from the resolution of the sensors. When sampling is considered, only practical stabilization can be achieved and the size of the limit cycle depends on the sampling rate.
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Millet, G., Haliyo, S., Régnier, S., Hayward, V. 2009.
The ultimate haptic device: First step.
Proc. Third Joint Eurohaptics Conference and Symposium on Haptic Interfaces for Virtual Environments and Teleoperator Systems WHC'09. pp. 273-278.

We describe a single-axis haptic interface which is based on a dual-stage actuator technique and which is aimed at achieving perfect transparency to a human user. The paper shows how all parasitic forces arising from inertia and friction can be brought below human detection thresholds, yet, the system is able to output significant torque. It has a stage with a large motor coupled to a distal stage with a smaller motor via a viscous coupler based on the principle of eddy current induction. The paper also describes its control principle and preliminary results.
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Mohand-Ousaid, A., Haliyo, S., Rgnier, S., Hayward, V. 2015. A Stable and Transparent Microscale Force Feedback Teleoperation System. IEEE/ASME Transactions on Mechatronics, 20(5):2593-2603

Scaled force-feedback teleoperation is a promising approach to assist an operator engaged in a micro-scale task. Several systems were previously described to achieve such purpose, but much room was left for improvement, especially with regard to the specificities of bilateral coupling with very large scaling coefficients. Here the objective is to render at human scale haptic information available at the micro-scale, and to provide scaled teleoperation that simultaneously achieves stability and transparency. An active force sensor and a novel haptic interface were interconnected to form a complete teleoperation chain through a direct, two-channel scheme. Stability was ensured by enforcing passivity in the slave and in the master subsystems. Several experiments were carried out to demonstrate the capabilities of the system. The first experiment involved non-contact magnetic interaction.A second set of experiments demonstrated the penetration of a thin glass probe in a water droplet where the operator interactively felt capillary forces.
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Mohand-Ousaid, A. M., Bolopion, A., Haliyo, S., Rgnier, S., and Hayward, V., 2014.
Stability and transparency analysis of a teleoperation chain for microscale interaction.
Proceedings of the 2014 IEEE International Conference onRobotics and Automation, pp. 5946-5951

Microscale teleoperation with haptic feedback re- quires scaling gains in the order of 10^4 10^7. These high gains impose a trade-off between stability and transparency. Due to the conservative approach used in most designs, transparency is reduced since damping is added to the system to guarantee stability. Starting from the fact that series, negative feedback and parallel connection of passive systems is a passive system, a new approach is addressed in this work. We propose here a complete teleoperation chain designed from the ground up for full transparency and stability, including a novel self-sensing probe and a high fidelity force-feedback haptic interface. By guaranteeing the passivity of each device and assuming that the human operator and the environment are passive systems, a homothetic direct coupling can be used without jeopardizing the stability and provides best transparency. The system is experimentally demonstrated in the complex case of a probe interacting with a water droplet under human control, while accurately transcribing the interaction back to operator.
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Mohand-Ousaid, A., Millet, G., Haliyo, S., Rgnier, S., Hayward, V. 2014.
Feeling What An Insect Feels.
PloS ONE, 9(10):e108895

We describe a manually operated, bilateral mechanical scaling instrument that simultaneously magnifies microscopic forces and reduces displacements with quasi-perfect transparency. In contrast with existing micro-teleoperation designs, the system is unconditionally stable for any scaling gains and interaction curves. In the present realization, the work done by the hand is more than a million times that done by a microscopic probe so that one can feel complete interaction cycles with water and compare them to what is felt when an insect leg interacts with a wet surface.
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Mohand-Ousaid, A., Haliyo, S., Régnier, S. and Hayward, V. 2013
H-infinity optimal control for micro-force sensing.
Proceedings of the 3rd International Conference on Systems and Control (ICSC13), pp. 490-495.

This paper describes a micro-force sensing device where a H-infinity control scheme is used to actively balance the external force and provide the measurement. The force sensing principle is based on the active control of the electrostatic bipolar actuator (comb-drive) within the sensor. An external load force acts on the sensor and displaces the probe. The controller is set to balance the applied force and keep the probe at its null position. As a result, the applied force is obtained in real time from the balancing control signal. A meso-scale prototype has been built as proof-of-concept and an especially designed H-infinity control allows for a measurement accuracy of 0.4 μN over a large range [-400 +400] μN.
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Mohand-Ousaid, A., Haliyo, S., Régnier, S. and Hayward, V. 2013.
Micro-Force Sensor by Active Control of a Comb-Drive.
Proceedings of the IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM), pp. 612-617

This article describes an active force sensor with an accuracy of 0.4 μN over a large range [-400 to 400] μN. The mechanical structure, through a fiber suspension arrangement, provides exactly one degree of freedom. This design allows for a precise displacement sensing by a laser optical lever. The force sensing principle is based on the active control of an electrostatic bi-polar actuator. A meso-scale prototype has been built as proof-of-concept and an especially designed controller allows for high precision measurements on a large range. The system is validated by measuring both pull-in and pull-off forces during an approach-retract cycle on water droplet. Both phenomena, although differing by an order of magnitude in amplitude, are correctly assessed.
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Mohand-Ousaid, A., Millet, G., Régnier, S., Haliyo, S., and Hayward, V. 2012.
Haptic Interface Transparency Achieved Through Viscous Coupling.
International Journal of Robotics Research. 31(3):319-329

Electromagnetic drives are subjected to an inherent inertia-torque tradeoff that fundamentally limits transparency: the higher the torque, the higher the inertia. We describe a dual-stage design that is not subjected to this tradeoff and that is able to approach perfect transparency for human users. It comprises a large, proximal motor and a small, distal motor to reproduce the transients. The two stages are coupled by a viscous clutch based on eddy-currents that, without contact, accurately transforms slip velocity into torque. Such a system can, in general, be controlled to achieve a variety of objectives. Here, we show that an advanced, discrete-time, RST polynomial pole-placement controller can achieve near-perfect transparency. Experimental validation evaluated the human ability to detect small haptic details when using this drive and compared it to when using a conventional, single-motor interface.
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Moscatelli, A., Hayward, V., Wexler, M. and Ernst, M. O. 2015
Illusory Tactile Motion Perception: An Analog of the Visual Filehne Illusion.
Scientific Reports, 5:14584.

We continually move our body and our eyes when exploring the world, causing our sensory surfaces, the skin and the retina, to move relative to external objects. In order to estimate object motion consistently, an ideal observer would transform estimates of motion acquired from the sensory surface into fixed, world-centered estimates, by taking the motion of the sensor into account. This ability is referred to as spatial constancy. Human vision does not follow this rule strictly and is therefore subject to perceptual illusions during eye movements, where immobile objects can appear to move. Here, we investigated whether one of these, the Filehne illusion, had a counterpart in touch. To this end, observers estimated the movement of a surface from tactile slip, with a moving or with a stationary finger. We found the perceived movement of the surface to be biased if the surface was sensed while moving. This effect exemplifies a failure of spatial constancy that is similar to the Filehne illusion in vision. We quantified this illusion by using a Bayesian model with a prior for stationarity, applied previously in vision. The analogy between vision and touch points to a modality-independent solution to the spatial constancy problem.
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Moscatelli, A., Bianchi, M., Serio, A., Terekhov, A., Hayward, V., Ernst, M. O., Bicchi, A. 2016.
The Change in Fingertip Contact Area as a Novel Proprioceptive Cue,
Current Biology. 26(9):1159-1163.

Humans, many animals, and certain robotic hands have deformable fingertip pads. Deformable pads have the advantage of conforming to the objects that are being touched, ensuring a stable grasp for a large range of forces and shapes. Pad deformations change with finger displacements during touch. Pushing a finger against an external surface typically provokes an increase of the gross contact area, potentially providing a relative motion cue, a situation comparable to looming in vision [4]. The rate of increase of the area of contact also depends on the compliance of the object [5]. Because objects normally do not suddenly change compliance, participants may interpret an artificially induced variation in compliance, which coincides with a change in the gross contact area, as a change in finger displacement and consequently they may misestimate their finger's position relative to the touched object. To test this, we asked participants to compare the perceived displacements of their finger while contacting an object varying pseudo-randomly in compliance from trial to trial. Results indicate a bias in the perception of finger displacement induced by the change in compliance, hence in contact area, indicating that participants interpreted the altered cutaneous input as a cue to proprioception. This situation highlights the capacity of the brain to take advantage of the knowledge of the mechanical properties of the body and of the external environment.
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Moscatelli, A., Bianchi, M., Serio, A., Al Atassi, O., Fani, S., Terekhov, A. V, Hayward V., Ernst, M. O., and Bicchi, A. 2014.
A Change in the Fingertip Contact Area Induces an Illusory Displacement of the Finger.
in Haptics: Neuroscience, Devices, Modeling, and Applications, Part-II, Auvray, M. and Duriez, C. (Eds). pp. 72-79.

Imagine you are pushing your finger against a compliant object. The change in the area of contact can provide an estimate of the relative displacement of the finger, such that the larger is the area of contact, the larger is the displacement. Does the human haptic system use this as a cue for estimating the displacement of the finger with respect to the external object? Here we conducted a psychophysical experiment to test this hypothesis. Participants compared the passive displacement of the index finger between a reference and a comparison stimulus. The compliance of the contacted object changed between the two stimuli, thus producing a different area-displacement relationship. In accordance with the hypothesis, the modulation of the area-displacement relation- ship produced a bias in the perceived displacement of the finger.
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Mougenet, J.-F., and Hayward, V. 1995.
Limit Cycle Characterization, ExistenceAnd Quenching In The Control Of High Performance Hydraulic Actuator.
Proceedings of the International IEEE Conference on Robotics and Automation. pp. 2218-2223.

The characteristics and the nonlinear dynamics of a high performance hyndraulic actuator produced by ASI Inc. are described and modeled. When a feedback is applied for the regulation of output force, a limit cycle is observed. The existence of the limit cycle can be a priori be attributed to one, or to a combination of the four nonlinear that were identified in these acturators. In order to pinpoint its origin, successive approximations are made to apply the describing function principle, so as to predict the onset of the limit cycles as a function of the feedback gain. Given the experimental data, this method allows us to attribute beyond any doubt its origin to the electromagnetic hysteresis in the valve, which is based on jet-pipe technology. A multiple term lead-lag controller is designed and implemented to quench the limit cycles and improve the rise time of the force control by more than an order of magnitude.
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Mutlu, Ö., Wottrich, V. M., Hayward, V. 2017.
Contaminant resistant pin-based tactile display.
Proceedings of the World Haptics Conference (WHC), IEEE, pp. 165-170.

Pin-based tactile displays have now been in use for more than forty years. One shortcoming, however, is their susceptibility to contaminants that jeopardize the operation of the delicate actuating mechanisms, necessitating costly periodic maintenance. We propose to cover such displays with a Gore-Tex protective layer to block the contaminants from reaching the sliding surfaces. The feel of the dots, however, is affected. We showed the correlation through tribological and perceptual experiments that certain pin shapes could restore the tactile feeling experience of standard braille pins.
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Nahvi, A. Hollerbach, J. M., and Hayward, V. 1994.
Calibration of a Parallel Robot Using Multiple Loops.
Int. IEEE Conference on Robotics and Automation. pp. 407-413.

A method is presented for autonomous kinematic calibration of a 3-DOF redundant parallel robot. Multiple loops are used in a least-square optimization method. Ill-conditioning, columns scaling of the gradient matrix, and observability indices for the best pose set of robot calibration configurations are discussed. Experimental results are presented and compared with the results using an external calibration device.
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Nakatani, M. , Sato, A., Tachi, S. and Hayward, V. 2008.
Tactile Illusion Caused by Tangential Skin Srain and Analysis In Terms of Skin Deformation.
Proc. Eurohaptics 2008, LNCS 5024, Springer-Vergal, pp. 229-237

We describe a new tactile illusion of surface geometry that can be easily produced with simple materials. When the ngertip skin is strained by loading it in traction along a narrow band surrounded by two xed traction surfaces, the sensation of a raised surface is typically experienced. This and other analogous cases are discussed in terms of tissue deformation created at a short distance inside the skin where the target mechanoreceptors are presumably located. A nite element analysis allowed us to propose that the basis of this illusion is connected with the observation that normal loading and tangential loading can create similar strain distribution, thereby creating an instance of an ambiguous stimulus. In the discussion we relate this stimulus to several other ambiguous tactile stimuli.
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Nilakantan, A. and Hayward, V.1989.
The Synchronization Of Multiple Manipulators In Kali.
Robotics and Autonomous Systems, North-Holland. Vol. 5., pp. 345-358.

This paper presents a strategy in multi-manipulator synchroni- zation that treats the motions as finite state machines. We use the concept of a motion-system as a convenient abstraction for programming explicitly coupled motions. Motions, treated as processes, can communicate/affect one another through the use of control signals and the dynamics of the system are taken into account during the transitions between different motion states. Using examples, we show that such a scheme is general enough to cover diverse situations as two cooperating arms in a multi-manipulator environment, synchronizing motion of the feet of a legged robot for simple gaits and synchronizing the fingers of an anthropomorphic end-effector for simple grasping strategies.
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Nordahl, R., Berrezag, A., Dimitrov, S., Turchet, L., Hayward, V. Serafin, S. 2010.
Preliminary Experiment Combining Virtual Reality Haptic Shoes And Audio Synthesis.
Proceedings of Europhaptics 2010, Part II, Kappers, A.M.L. et al. (Eds.), LNSC 6192, Springer-Verlag, pp. 123-129.

We describe a system that can provide combined auditory and haptic sensations that arise while walking on different grounds. The simulation is based on a physical model that drives both haptic transdu- cers embedded in sandals and headphones. The model is able to represent walking interactions with solid surfaces that can creak, be covered with crumpling material. The simulation responds to pressure on the floor by a vibrotactile signal felt by the feet. In a preliminary discrimination expe- riment, 15 participants were asked to recognize four different surfaces in a list of sixteen possibilities and under three different conditions, haptics only, audition only and combined haptic-audition. The results indicate that subjects are able to recognize most of the stimuli in the audition only condition, and some of the material properties such as hardness in the haptics only condition. The combination of auditory and haptic cues does not significantly improve recognition.
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Okamoto, S., Wiertlewski, M., Hayward, V. 2016.
Anticipatory vibrotactile cueing facilitates grip force adjustment during perturbative loading.
IEEE Transactions on Haptics. 9(2):233-242.

Grip force applied to an object held between the thumb and index finger is automatically and unconsciously adjusted upon perception of an external disturbance to the object. Typically, this adjustment occurs within approximately 100 ms. Here, we investigated the effect of anticipatory vibrotactile cues prior to a perturbative force, which the central nervous system may use for rapid grip re-stabilization. We asked participants to grip and hold an instrumented, actuated handle between the thumb and index finger. Under computer control, the handle could suddenly be pulled away from a static grip and could independently provide vibration to the gripping fingers. The mean latency of corrective motor action was 139 ms. When vibrotactile stimulation was applied 50 ms before application of tractive force, the latency was reduced to 117 ms, whereas the mean latency of the conscious response to vibrotactile stimuli alone was 229 ms. This suggests that vibrotactile stimulation can influence reflex-like actions. We also examined the effects of anticipatory cues using a set of perturbative loads with different rising rates. As expected, facilitation of grip force adjustment was observed for moderate loads. In contrast, anticipatory cues had an insignificant effect on rapid loads that evoked an adjustment within 60-80 ms, which approaches the minimum latency of human grip adjustment. Understanding the facilitative effects of anticipatory cues on human reactive grip can aid the development of human-machine interfaces to enhance human behavior.
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Okamoto, S., Wiertlewski, M., Hayward, V. 2013.
Anticipatory vibrotactile cueing facilitates grip force adjustment.
Proceedings of the IEEE World Haptics Conference 2013. pp. 525--530.

Human grip forces are automatically adjusted upon occurrence of an external disturbance experienced by an object that is held by a thumb and index finger. We investigated some of the cues that may be used by the brain to perform rapid grip restabilization. To this end we ask subjects to grip and hold an instrumented and actuated parallelepiped-shaped handle between the index finger and the thumb. Under computer control, the handle could be jerked from the still grip and could independently provided vibration of 250 or 100 Hz to the gripping fingers. We found that the latency of the motor corrective action was 139 ms on average, but when a vibrotactile stimulation was applied 50 ms before the application of the pulling force, the latency was reduced on average to 117 ms. The average latency of the conscious response to the vibrotactile stimuli was 230 ms, suggesting that vibrotactile stimulation was capable of influencing the reflex action.
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Okazaki, R., Hachisu, T., Sato, M., Fukushima, S., Hayward, V., Kajimoto, K. 2013.
Judged Consonance of Tactile and Auditory Frequencies.
Proceedings of the IEEE World Haptics Conference 2013. pp. 663-666.

With the aim of augmenting auditory sensation by tactile stimuli, we investigated cross-modal relationships between the two modalities, focusing on frequency. The results showed that frequency consonance between tactile and audio stimuli depends on the relationship between harmonics, in a manner similar to auditory waves, but with broader peaks.
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Okazaki, R., Kajimoto, H., Hayward, V. 2012.
Vibrotactile Stimulation Can Affect Auditory Loudness: A Pilot Study.
Proceedings of Eurohaptics 2012. LNCS 7283, Part II, pp. 103-108.

Very few cases have been reported where tactile stimulation affects auditory perception. In this pilot study, we asked volunteers to compare the loudness of combinations of vibrotactile and auditory stimuli. A 50-300~Hz band-limited pink noise signal was used as the stimulus in the two modalities, simultaneously heard through headphones and felt in the hands to be compared to when it was heard only. On average, the same auditory stimulus was judged to be about one~dB louder when it was simultaneously heard and felt rather than when it was heard only. This condition could be interpreted as having enhanced the perception of loudness by a whole JND.
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Ortega, A., Weill-Duflos, A., Haliyo, S., Régnier, S., Hayward, V. 2017.
Linear Induction Actuators for a Haptic Interface: A quasi-perfect transparent mechanism.
Proceedings of the World Haptics Conference (WHC), IEEE, pp. 575-580.

This article describes the design of a high-fidelity haptic interface based on a two-axis induction system. Unlike other type of actuators, linear induction motors can provide simultaneously a non-contact drive and a very low inertia. Their integration in a haptic device enables an interface with quasi-perfect mechanical transparency. We detail the conception of linear induction motors for this application and experimental results of a proof of concept are shown.
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Pacchierotti, C., Sinclair, S., Solazzi, M., Frisoli, A., Hayward, V., Prattichizzo, D. 2017.
Wearable Haptic Systems for the Fingertip and the Hand: Taxonomy, Review, and Perspectives.
IEEE Transactions on Haptics, 10(4):580600.

In the last decade, we have witnessed a drastic change in the form factor of audio and vision technologies, from heavy and grounded machines to lightweight devices that naturally fit our bodies. However, only recently, haptic systems have started to be designed with wearability in mind. The wearability of haptic systems enables novel forms of communication, cooperation, and integration between humans and machines. Wearable haptic interfaces are capable of communicating with the human wearers during their interaction with the environment they share, in a natural and yet private way. This paper presents a taxonomy and review of wearable haptic systems for the fingertip and the hand, focusing on those systems directly addressing wearability challenges. The paper also discusses the main technological and design challenges for the development of wearable haptic interfaces, and it reports on the future perspectives of the field. Finally, the paper includes two tables summarizing the characteristics and features of the most representative wearable haptic systems for the fingertip and the hand.
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Pasquero, J., Luk, J., Levesque, V., Wang, Q., Hayward, V., and MacLean, K. E. 2007.
Haptically Enabled Handheld Information Display with Distributed Tactile Transducer.
IEEE Transactions on Multimedia, 9(4):746-753.

This paper describes the design, construction, and initial evaluation of a handheld information device that supports combined tactile and graphical interaction. The design comprises a liquid crystal graphic display co-located with a miniature, low-power, distributed tactile transducer. This transducer can create electronically-controlled lateral skin deformation patterns which give the sensation of sliding over small shapes. It is integrated within a slider mechanism to control scrolling. It also functions as a detent when pushing on it. Tactile feedback and the combination of visual and tactile feedback in a mobile context enable the development of new functions, such as multimodal navigation within large graphic spaces.
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Pasquero, J. 2006.
Survey on communication through touch.
Technical Report TR-CIM-06.04. Center for Intelligent Machines, McGill University.

In this report, we first consider early and recent research on the development of artificial tactile communication. Then, we review current models of the encoding of tactile information in humans before examining the state-of-the-art for tactile displays. While much remains to be discovered, we believe that these findings can guide the design of an artificial language for touch. We conclude with a summary of guidelines and insights collected from the literature on touch.
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Pasquero, J., Luk, J., Little, S. MacLean, K. E. 2006.
Perceptual Analysis of Haptic Icons: an Investigation into the Validity of Cluster Sorted MDS.
Proc. 14th Symposium on Haptic Interfaces For Virtual Environment And Teleoperator Systems IEEE VR 2006, pp. 437-444.

The design of usable haptic icons (brief informational signals de- livered through the sense of touch) requires a tool for measuring perceptual distances between icons that will be used together as a set. Our experiences with one potentially powerful approach, Mul- tidimensional Scaling (MDS) analysis of perceptual data acquired using an efficient cluster sorting technique, raised questions relat- ing to the methodology for data collection. In this paper, we review key issues relating to perceptual data collection method, describe an example data set and present its initial MDS analysis, and then examine the impact of collection method on MDS outcome through a secondary analysis of the data and the inherent structure of the al- gorithm components. Our analysis suggests that an understanding of these issues is important for the methods effective use, but has not exposed any major flaws with the process.
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Pasquero, J., Levesque, V., Hayward V., and Legault, M. 2004.
Display of Virtual Braille Dots by Lateral Skin Deformation: A Pilot Study. Proc. Eurohaptics 2004. Munich, Germany, June 5-7. pp. 96-103.

When a progressive wave of localized deformations occurs tangentially on the fingerpad skin, one typically experiences the illusion of a small object sliding on it. This effect was investigated because of its potential application to the display of Braille. A device was constructed that could produce such deformation patterns along a line. This enabled us to test blind subjects' ability to read the truncated Braille characters ` ', `.4', `a', and `c'. While subjects could identify two-character strings with a high rate of success, several factors need to be addressed before a display based on this principle can become practical.
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Pasquero, J. and Hayward, V. 2003.
STReSS: A Practical Tactile Display System with One Millimeter Spatial Resolution and 700 Hz Refresh Rate.
Proc. Eurohaptics 2003. Dublin, Ireland, July 2003.

A tactile display system is described which can produce tactile movies, that is, rapid sequences of tactile images refreshed at a rate of 700 Hz. The display uses an array of one hundred laterally moving skin contactors designed to create a time-varying programmable strain field at the skin surface. The density of the array is of one contactor per millimeter square, resulting in a device with high spatial and temporal resolution. The paper describes the construction method and the drive electronics. It also reports informally on initial test patterns and on the resulting tactile sensations.
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Paul, R. P. and Hayward, V. 1985.
Robot Control and Computer Languages.
Proc. CISM-IFToM Symposium on Theory and Practice of Robots and Manipulators (RoManSy), pp. 187-193.

From the earliest stages of their development, robot manipulators have been tied to computers by robot-control languages. These special languages have endeavoured to deal with the complexities of real-time control, multiple processes, the description of robot-manipulation tasks and the integration of sensors. In every case, these languages have been able to provide only partial solutions to the general problem. We propose a new solution to the problem by integrating the robot control into an existing high-level language. The robot manipulator is integrated in such a manner that conventional programming techniques can be used to solve the special requirements of manipulator control.
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Payette, J. Hayward, V., Ramstein, C., andBergeron, D. 1996.
Evaluation Of A Force-Feedback (Haptic) Computer Pointing Device In Zero Gravity.
Proc. Fifth Annual Symposium on Haptic Interfaces for Virtual Environments and Teleoperated Systems, ASME Dynamic Systems and Control Division, DSC-Vol. 58. pp. 547-553.

Haptic devices and spcecialized force-feedback hand controllers have been proposed as alternative input/output devices for use in challenging operational environments such as space. In the case described here, it is proposed that a pointing device with force feedback (a haptic mouse) be used as a generic cursor device for operating computers in weightlessness. It is believes that such devices will decrease the effective workload of operators while invreasing their efficiency in space. This paper describes an experiment that was designed to measure the effectiveness of haptic device (hereby called the Pantograph) in zero gravity conditions. The Pantograph was compared to a standard trackball pointing device. Both devices were tested on the ground and aboard a NASA reduced-gravity aircraft using a common graphical interface (GUI). Results have shown that in zero gravity, the haptic device has proven more time efficient in performaing standard GUI operations such as clicking, dragging, and selecting.
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Petit, G., Dufresne, A., Levesque, V., Hayward V. 2008.
Exploration multimodale d'images pour des utilisateurs ayant une déficience visuelle
Sciences et Technologies pour le Handicap, 2(2):175-186.

Cet article présente une recherche visant rendre accessibles des images aux usagers ayant une dficience visuelle. Le logiciel MaskGen a été dveloppé afin de transformer interactivement ces images "visuelles" en images multimodales (tactiles et audio). Une méthodologie a été développée pour transposer ces images et les afficher sur le Tactograph, un appareil multimodal dynamique.
This article presents research on making images accessible for people with visual impairment. The MaskGen system was developed to interactively transpose these "visual" images into multimodal images (tactile and audio). A methodology was designed to transpose the images and prepare them to be displayed on the Tactograph, a refreshable multimodal device.
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Petit, G., Dufresne, A., Levesque, V., Hayward V., Trudeau, N. 2008.
Refreshable Tactile Graphics Applied to Schoolbook Illustrations for Students with Visual Impairment.
Proc. 10th International ACM SIGACCESS Conference on Computers and accessibility (ASSETS 2008), pp. 89-96.

This article presents research on making schoolbook illustrations accessible for students with visual impairment. The MaskGen system was developed to interactively transpose illustrations of schoolbooks into tactile graphics. A methodology was designed to transpose the graphics and prepare them to be displayed on the STReSS2, a refreshable tactile device. We experimented different associations of tactile rendering and audio feedbacks to find a model that children with visual impairment could use. We experimented with three scientific graphics (diagram, bar-chart and map) with forty participants: twenty sighted adults, ten adults with visual impairment, and ten children with visual impairment. Results show that the participants with visual impairment liked the tactile graphics and could use them to explore illustrations and answer questions about their content.
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Petit, G., Dufresne, A., Levesque, V., Hayward V., Trudeau, N. 2008.
Graphisme tactile appliqué aux illustrations de manuels scolaires l'usage d'enfants ayant une déficience visuelle.
Proc. Interaction Homme-Machine (IHM'08).

Cet article présente une recherche visant rendre accessible, aux étudiants ayant une déficience visuelle les illustrations de manuels scolaires. Le logiciel MaskGen a été développé afin de transformer interactivement ces illustrations en graphiques tactiles. Une méthodologie a été développée pour transposer ces graphiques et les afficher sur le STReSS2, un appareil tactile dynamique. Nous avons expérimenté différentes associations de rendus tactiles et de retours sonores pour obtenir une version compréhensible pour les étudiants ayant une déficience visuelle. Nous avons testé trois graphiques tactiles (un plan, un histogramme et une carte) avec quarante participants : vingt voyants, dix adultes non-voyants et dix enfants non-voyants. Les résultats de l'expérimentation montrent que les participants ayant une déficience visuelle ont aimé les images tactiles, ont été capables de les explorer correctement et de répondre avec succs aux questions posées sur ces images.
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Pelletier, M., Hayward V. 1989.
Super-Grip: An Expert System For Grasping Boxes.
Proc. IEEE International Conference on Systems Man and Cybernetics. pp. 510-515.

This paper is concerned with the development of an expert system which determines the best grasp configuration to pick up a rectangular box. This two level system first chooses from a predetermined set of grasps, the ones best suited for the task using a set of rules. and then computes a quality index for each possible configuration. The program is written in LISP and was tested for many different objects and situations. The grasps found are not necessarily optimal but are efficient since they are similar to the grasps a human would choose in the same situation. Because the program gives fast results and doesn't perform tedious computations, the best grip found can easily be used as a sub-optimal solution, or as a starting point for an optimizing program.
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Platkiewicz, J., Lipson, H., Hayward, V. 2016.
Haptic Edge Detection Through Shear.
Scientific Reports, 6:23551.

Most tactile sensors are based on the assumption that touch depends on measuring pressure. However, the pressure distribution at the surface of a tactile sensor cannot be acquired directly and must be inferred from the deformation field induced by the touched object in the sensor medium. Currently, there is no consensus as to which components of strain are most informative for tactile sensing. Here, we propose that shape-related tactile information is more suitably recovered from shear strain than normal strain. Based on a contact mechanics analysis, we demonstrate that the elastic behavior of a haptic probe provides a robust edge detection mechanism when shear strain is sensed. We used a jamming-based robot gripper as a tactile sensor to empirically validate that shear strain processing gives accurate edge information that is invariant to changes in pressure, as predicted by the contact mechanics study. This result has implications for the design of effective tactile sensors as well as for the understanding of the early somatosensory processing in mammals.
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Platkiewicz, J., Mansutti, A., Bordegoni, M., Hayward, V. 2014.
Recording Device for Natural Haptic Textures Felt with the Bare Fingertip.
in Haptics: Neuroscience, Devices, Modeling, and Applications, Part-I, Auvray, M. and Duriez, C. (Eds), pp. 521-528

The perception of haptic textures depends on the mechan ical interaction between a surface and a biological sensor. A texture is apprehended by sliding one's fingers over the surface of an object. We describe here an apparatus that makes it possible to record the mechanical fluctuations arising from the friction between a human fingertip and easily interchangeable samples. Using this apparatus, human participants tactually scanned material samples. The analysis of the results indicates that the biomechanical characteristics of individual fingertips clearly af- fected the mechanical fluctuations. Nevertheless, the signals generated for a single material sample under different conditions showed some invariant features. We propose that this apparatus can be a valuable tool for the analysis of natural haptic surfaces.
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Platkiewicz, J., Hayward, V. 2014.
Perception-Action Dissociation Generalizes to the Size-Inertia Illusion.
Journal of Neurophysiology, 111(7):1409-1416

Two objects of similar visual aspects and of equal mass, but of different sizes, generally do not elicit the same percept of heaviness in humans. The larger object is consistently felt to be lighter than the smaller, an effect known as the `size-weight illusion'. We investigated whether the same effect can be observed if the mass of an object is available to participants through inertial rather than gravitational cues. We compared the responses of ten participants in two experimental conditions, where they manipulated objects supported by a frictionless, air bearing slide that could be oriented vertically or horizontally. We also analyzed the participants' anticipatory motor behavior by measuring the grip force prior to motion onset. We found that the perceptual illusory effect was qualitatively the same in the two conditions and observed that both visual size and haptic mass had a negligible effect on the anticipatory gripping control of the participants in the gravitational and inertial conditions, despite the enormous differences in the mechanics of the two conditions.
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Ramstein, C. and Hayward, V. 1994 (April, Boston, MA).
The Pantograph: A Large Workspace Haptic Device For A Multi-Modal Human-Computer Interaction.
CHI'94, Conference on Human Factors in Computing Systems ACM/SIGCHI Companion-4/94. pp. 57-58.

A multi-modal user interface taking advantage of kinesthesia, force display, sound, and graphics, to improve human-computer interaction is described. This design primarily addresses the needs of visually impaired persons working in an office situation, but is presently applied to numerous other instances of human-machine interaction; such as operator workstations in control rooms or cockpits. The main technological item introduced here is the haptic interface itself (nicknamed the ``Pantograph'') which measures position and velocity of a manipulated knob and displays forces in two dimensions over a wide frequency range. Programmed mechanical models are used to kinesthetically describe the features of the interface. These models are analogous to iconic representations in conventional graphic interfaces. Users, acting and perceiving through the haptic channel, simultaneously perceive simulated objects through the visual and auditory channels. Further developments are briefly reported.
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Robles-De-La-Torre, G. and Hayward, V. 2001.
Force Can Overcome Object Geometry In The Perception Of Shape Through Active Touch.
Nature, Vol. 412, pp. 445-448.

Haptic (touch) perception normally entails an active exploration of object surfaces over time. This is called active touch. When exploring the shape of an object, we experience both geometrical and force cues. For example, when sliding a finger across a surface with a rigid bump on it, the finger moves over the bump while being opposed by a force whose direction and magnitude are related to the slope of the bump. The steeper the bump, the stronger the resistance. Geometrical and force cues are correlated, but it has been commonly assumed that shape perception relies on object geometry alone. Here we show that regardless of surface geometry, subjects identified and located shape features on the basis of force cues or their correlates. Using paradoxical stimuli, for example combining the force cues of a bump with the geometry of a hole, we found that subjects perceived a bump. Conversely, when combining the force cues of a hole with the geometry of a bump, subjects typically perceived a hole.
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Robles-De-La-Torre, G. and Hayward, V. 2000.
Virtual Surfaces and Haptic Shape Perception.
Proc. of the Haptic Interfaces for Virtual Environment and Teleoperator Systems Symposium, ASME IMECE2000, Orlando, Florida, USA. Proc. ASME Vol. DSC-69-2, pp. 1081-1087.

Lateral force fields (LFFs) have been used before to generate haptic textures. We propose that LFFs can be used to study haptic shape perception. We present preliminary results of an experiment in which human subjects interact with realistic LFFs. The LFFs encode shape information in the magnitude of unidimensional force vectors. Subjects explore the LFFs and classify them into haptic categories. We found that subjects can consistently perform this classiffication. This and subjects qualitative judgments of the stimuli suggest that haptic interaction with LFFs resembles the experience of touching a real 3D object.
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Rovan, J. and Hayward, V. 2000.
Typology Of Tactile Sounds And Their Synthesis In Gesture-Driven Computer Music Performance.
In "Trends in Gestural Control of Music". Wanderley, M., Battier, M. (eds). Editions IRCAM, Paris, 2000. pp. 297--320.

In this paper we outline the fundamentals for a tactile feedback system to be used in conjunction with openair computer music performance devices. Some underlying physiological and perceptual mechanisms of haptics are examined, some currently available open-air controllers are reviewed, and previous technologies and experiments regarding haptic/tactile feedback are surveyed. Our VR/TX system is proposed as a solution for adding tactile feedback to open-air controllers; experiments show that the VR/TX vibrotactile stimulators provide invaluable perceptually-significant tactile feedback when used in conjunction with an open-air music controller. A typology of tactile sound events is also described, as well as the notion of a tactile simulation event (TSE).
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Shao, Y., Hayward, Visell, Y. 2016.
Spatial Patterns of Cutaneous Vibration During Whole-Hand Haptic Interactions.
Proceedings of the National Academy of Sciences. 113(15) :4188-4193.

We investigated the propagation patterns of cutaneous vibration in the hand during interactions with touched objects. Prior research has highlighted the importance of vibrotactile signals during haptic inter- actions but little is known of how vibrations propagate throughout the hand. Furthermore, the extent to which the patterns of vibrations reflect the nature of the objects that are touched, and how they are touched, is unknown. Using a novel apparatus comprised of an array of accelerometers, we mapped and analyzed spatial distributions of vibrations propagating in the skin of the dorsal region of the hand during active touch, grasping, and manipulation tasks. We found these spatial patterns of vibration to vary systematically with touch interactions, and determined that it is possible to use this data to decode the modes of interaction with touched objects. The observed vibration patterns evolved rapidly in time, peaking in intensity within a few milliseconds, fading within 20 to 30 milliseconds, and yielding interaction-dependent distributions of energy in frequency bands that span the range of vibrotactile sensitivity. These results are consistent with findings in perception research that indicate that vibrotactile information distributed throughout the hand can transmit information regarding explored and manipulated objects. The results may further clarify the role of distributed sensory resources in the perceptual recovery of object attributes during active touch, may guide the development of new approaches to robotic sensing, and could have implications for the rehabilitation of the upper extremity.
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Sidobre, D. and Hayward, V. 2004.
Calibrated Measurement of Mechanical Junctions Behaviour from Micrometer to Subnanometer Scale: the Friction Force Scanner.
J. of Meas. Sci. and Technol. 15(2):451-459.

We describe an instrument called a friction force scanner (FFS) able to perform calibrated measurements of the behaviour of mechanical junctions with more than four orders of magnitude of resolution for both displacement and force. A probe carrier is suspended by fibres in an arrangement that provides exactly two degrees-of-freedom of motion. The suspension makes it possible to measure the carrier displacement by interferometry. A novel differential electrostatic actuator with linear response mounted on the carrier was used to precisely determine the force experienced by a junction. The single stage design is easily calibrated and can be used for force measurement and scanning, allowing the study of friction at multiple length scales. Measurements involving mica-mica and steel-steel junctions are reported while using the instrument in open loop.
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Sinclair, S., Wanderley, M., Hayward, V., Scavone, G.
Noise-Free Haptic Interaction With A Bowed-String Acoustic Model.
Proceedings of World Haptics Conference 2011, pp. pp. 463--468.

Force-feedback interaction with a bowed string model can suffer critically from noise in the velocity signal derived from differenti- ating position measurements. To address this problem, we present a model for bowed string interaction based on a position-constraint friction. We validate the proposed model by comparing to previous work using off-line simulations, and show measurements of inter- action on haptic hardware. This noise-free excitation signal leads to cleaner string motion than previous models, thereby improving the quality of force and audio synthesis.
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Sinclair, S., Wanderley, M. M., Hayward, V. 2014. Velocity Estimation Algorithms For Audio-Haptic Simulations Involving Stick-Slip.
IEEE Transactions on Haptics. 7(4):533-544

With real-time models of friction that take velocity as input, accuracy depends in great part on adequately estimating velocity from position measurements. This process can be sensitive to noise, especially at high sampling rates. In audio-haptic acoustic simulations, often characterized by friction-induced, relaxation-type stick-slip oscillations, this gives a gritty, dry haptic feel and a raspy, unnatural sound. Numerous techniques have been proposed, but each depend on tuning parameters so that they may offer a good trade-off between delay and noise rejection. In an effort to compare fairly, each of thirteen methods considered in the present study was automatically optimized and evaluated; finally a subset of these were compared subjectively. Results suggest that no one method is ideal for all gain levels, though the best general performance was found by using a sliding-mode differentiator as input to a Kalman integrator. An additional conclusion is that estimators do not approach the quality available in physical velocity transduction, and therefore such sensors should be considered in haptic device design. [PDF] [ Back ]

Smith, A. M., Basile, G., Theriault-Groom, J., Fortier-Poisson, P., Campion, G., Hayward, V. 2010.
Roughness of simulated surfaces examined with a haptic tool; effects of spatial period, friction, and resistance amplitude.
Experimental Brain Research, 202(1):33-43.

A computer controlled force-feedback device simulated textures consisting of modulated resistances to lateral motion. The textures were either periodic trapezoidal force fields, or modulated sinusoidal forces spaced at various intervals from 1.5 mm to 8.5 mm. In each of two experiments, ten subjects interacted with the virtual surfaces using the index finger placed on a mobile plate that produced the lateral force fields. The subjects selected their own speed and contact force for exploring the test surface. The apparatus returned force fields as a function of both the finger position and finger normal force allowing full control over the tangential interaction force. In experiment #1, subjects used an integer, numerical scale of their own choosing to rate the roughness of eight identical, varyingly-spaced force ramps superimposed on a background resistance. The results indicated that subjective roughness was significantly, but negatively, correlated with spatial period (mean r = -0.84) of the resistances for all subjects. In a second experiment, subjects evaluated the roughness of 80 different sinusoidal modulated force fields, which included 4 levels of resistance amplitude, 4 levels of baseline friction, and 5 spatial periods. A multiple regression procedure indicated that the coefficient of friction and the tangential force amplitude together produced a combined correlation of 0.70 with subjective roughness. The addition of spatial period only increased the multiple regression correlation to 0.71. The correlation between roughness estimates and the rate of change in tangential force was 0.72 in experiment #1 and 0.57 in experiment #2. The results suggest that the sensation of roughness is strongly influenced by friction and tangential force amplitude, whereas the spatial period of resistance alone makes a negligible contribution.
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Smith, A. M., Chapman, C. E., Donati, F., Fortier-Poisson, P. and Hayward, V. 2009.
Perception of simulated local shapes using active and passive touch.
Journal of Neurophysiology. 102:3519-3529 .

This study re-examined the perceptual equivalence of active and passive touch using a computer-controlled force-feedback device. Nine subjects explored a 6 X 10 cm workspace with the index finger resting upon a mobile flat plate, and experienced simulated Gaussian ridges and troughs (15mm wide; amplitude, 0.5 to 4.5mm). The device simulated shapes by modulating either lateral resistance with no vertical movement or by vertical movement with no lateral forces, as a function of the digit position in the horizontal workspace. The force profiles and displacements recorded during active touch were played back to the stationary finger in the passive condition, ensuring that stimulation conditions were identical. For the passive condition, shapes simulated by vertical displacements of the finger had lower categorization thresholds and higher magnitude estimates compared to active touch. In contrast, the results with the lateral force fields showed that with passive touch, subjects recognized that a stimulus was present but were unable to correctly categorize its shape as convex or concave. This result suggests that feedback from the motor command can play an important role in processing sensory inputs during tactile exploration. Finally, subjects were administered a ring-block anesthesia of the digital nerves of the index finger and subsequently retested. Removing skin sensation significantly increased the categorization threshold for the perception of shapes generated by lateral force fields, but not for those generated by displacement fields.
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Terekhov, A. V., Hayward, V. 2015.
The Brain Uses Extra-Somatic Information To Estimate Limb Displacement.
Proceedings of the Royal Society, B, 282(1814):20151661.

A fundamental problem faced by the brain is to estimate whether a touched object is rigidly attached to a ground reference or is movable. A simple solution to this problem would be for the brain to test whether pushing on the object with a limb is accompanied by limb displacement. The mere act of pushing excites large populations of mechanoreceptors, generating a sensory response that is only weakly sensitive to limb displacement if the movements are small, and thus can hardly be used to determine the mobility of the object. In the mechanical world, displacement or deformation of objects frequently co-occurs with microscopic fluctuations associated with the frictional sliding of surfaces in contact or with micro-failures inside an object. In this study, we provide compelling evidence that the brain relies on these microscopic mechanical events to estimate the displacement of the limb in contact with an object, and hence the mobility of the touched object. We show that when pressing with a finger on a stiff surface, fluctuations that resemble the mechanical response of granular solids provoke a sensation of limb displacement. Our findings suggest that when acting on an external object, prior knowledge about the sensory consequences of interacting with the object contributes to proprioception.
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Terekhov, A. V., Hayward, V. 2011.
Minimal Adhesion Surface Area In Tangentially Loaded Digital Contacts
Journal of Biomechanics, 44(13):2508--2510.

The stick-to-slip transition of a fingertip in contact with a planar surface does not occur instantaneously. As the tangential load increases, portions of the skin adhere while others slip, giving rise to an evolution of the contact state, termed partial slip. We develop a quasi-static model that predicts that if the coefficient of kinetic friction is larger than the coefficient of static friction, then the stuck surface area diminishes as the tangential load increases until reaching a `minimal adhesion surface area' where it vanishes abruptly. This phenomenon was observed in recently measured finger-slip image data (Andre et al., 2011)that were processed by an optic flow detection algorithm. We examined the results of ten trails. Four of them exhibited the minimal adhesion surface area phenomenon, four of them did not, and two were inconclusive.
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Turchet, L., Nordahl, R., Serafin, S., Berrezag, A., Dimitrov, S., and Hayward, V. 2010.
Audio-haptic physically-based simulation of walking on different grounds.
Proceedings of the 2010 the IEEE International Worshop on Multimedia Signal Processing, MMSP10, pp. 269-273.

We describe a system which simulates in real- time the auditory and haptic sensations of walking on different surfaces. The system is based on a pair of sandals enhanced with pressure sensors and actuators. The pressure sensors detect the interaction force during walking, and control several physically based synthesis algorithms, which drive both the auditory and haptic feedback. The different hardware and software components of the system are described, together with possible uses and possibilities for improvements in future design iterations.
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Visell, Y., Duraikkannan, K. A., and Hayward, V. 2014.
A Device and Method for Multimodal Haptic Rendering of Volumetric Stiffness
in Haptics: Neuroscience, Devices, Modeling, and Applications, Part-I, Auvray, M. and Duriez, C. (Eds). pp. 478-486

Vibrotactile signals are produced during haptic exploration of compressible objects through a variety of contact and bulk mechanical processes. Prior studies have found that vibrotactile feedback can influence stiffness perception, but the reason for this is unknown. Here, we investigated the role of vibration in stiffness perception during object squeezing. We propose a physi- cally motivated explanatory model and rendering algorithm relating vibrotactile and force-displacement cues, then present a novel haptic interface that was designed to accurately reproduce these cues. Finally, we present the results of an experiment on the perceptual integration of vibrotactile and force-displacement cues during one- and two-finger stiffness perception. The results indicate that vibration feedback can increase perceived object softness during interaction with one finger, but preclude a similar conclusion for two-finger grasping. We argue that the results support the proposed model once innate differences in one- and two-finger exploration are accounted for.
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Visell, Y., Hayward, V, 2013.
An Asymmetry In Force Perception Contingent On Motion Reversal.
Proceedings of the IEEE World Haptics Conference 2013. pp. 651--656.

We investigated the perception of differences between directiondependent, movement-opposing forces. The magnitude of these forces changed in whenever the direction of motion reversed. They were felt by participants during an experiment that required them to scan a virtual surface, represented by a planar haptic interface, via left-right motions of the index finger. We found that individuals are surprisingly insensitive to changes in opposing force magnitude that are contingent on reversals in direction of motion, despite large contrasts in force magnitude. Forces of 1 N failed consistently to be discriminated from forces of 0 N during sequential presentation at the highest speeds. As the mean scanning speed of the digit was reduced, the effect progressively vanished. The effect we observed is simple and robust enough to be demonstrated on virtually any haptic force-feedback interface. We suggest possible interpretations based on temporal information processing in the nervous system, on physiology and biomechanics, and through inferences that the nervous system may rely on to relate motor commands to sensory input during dynamic haptic interaction. The results obtained raise fundamental questions about the perceptual interpretation of kinesthetic stimuli involving rapid movement, and may also suggest a reconsideration of requirements for haptic interfaces.
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Wang, Q. and Hayward, V. 2010.
Biomechanically Optimized Distributed Tactile Transducer Based on Lateral Skin Deformation.
International Journal of Robotics Research. 29(4):323-335.

This paper describes a tactile transducer device that is optimized from biomechanical data and has a compact, yet modular design. The tactile transducer comprises a 6 x 10 piezoelectric bimorph actuator array with a spatial resolution of 1.8 x 1.2 millimeters and has a wide temporal bandwidth. The actuator mounting method was improved from a conventional cantilever method to a dual-pinned method, giving the actuator the ability to deform the glabrous skin maximally during laterotactile stimulation. The results were validated by asking subjects to detect tactile features under a wide range of operating conditions. The tactile display device is modular, makes use of ordinary fabrication methods, and can be assembled and dismantled in a short time for debugging and maintenance. It weighs 60 g, it is self-contained in a 150 cm3 volume and may be interfaced to most computers, provided that two analog outputs and six digital IO lines are available. Psychophysical experiments were carried out to assess its effectiveness in rendering virtual tactile features.
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Wang, Q. and Hayward V. 2008.
Tactile Synthesis and Perceptual Inverse Problems Seen from the View Point of Contact Mechanics.
ACM Transactions on Applied Perception. 5(2):1-19

A contact mechanics analysis was used to explain a tactile illusion engendered by straining the fingertip skin tangentially in a progressive wave pattern resulting in the perception of a moving undulating surface. We derived the strain tensor field induced by a sinusoidal surface sliding on a finger as well as the field created by a tactile transducer array deforming the fingerpad skin by lateral traction. We found that the first field could be well approximated by the second. Our results have several implications. First, tactile displays using lateral skin deformation can generate tactile sensations similar to those using normal skin deformation. Second, a synthesis approach can achieve this result if some constraints on the design of tactile stimulators are met. Third, the mechanoreceptors embedded in the skin must respond to the deviatoric part of the strain tensor field and not to its volumetric part. Finally, many tactile stimuli might represent for the brain an inverse problem to be solved, such specific examples of `tactile metameres' are given.
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Wang, Q., Hayward, V. 2007.
In Vivo Biomechanics of the Fingerpad Skin Under Local Tangential Traction.
J. of Biomechanics. 40(4):851-860.

Small patches of fingerpad glabrous skin in human subjects were tested in vivo for their biomechanical properties under tangential loading and for large deformations. These conditions included stretching and shearing the skin at a length scale of 0.3~mm using an apparatus comprising a pair of piezoelectric benders arranged to increase the stiffness/free deflection tradeoff when compared to ordinary cantilevered benders. It was then possible to test the skin with up to 80% of tangential strain. With feedback control, it was also possible to create isotonic and isometric testing conditions. The results showed much variability across subjects and it was seen that the glabrous skin exhibited nonlinear stiffening in tangential traction. The skin was consistently more elastic across the ridges than along the ridges regardless of the location of the sample on the fingerpad. The skin behaved visco-elastically but relaxed about twice as fast than it crept. Finally, it was found that under large deformation, there was consistently an 80\% of hysteretic loss for a wide range of loading conditions.
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Wang, Q. and Hayward V. 2006.
Compact, Portable, Modular, High-performance, Distributed Tactile Transducer Device Based on Lateral Skin Deformation.
Proc. 14th Symposium on Haptic Interfaces For Virtual Environment And Teleoperator Systems IEEE VR 2006. pp. 67-72.

We describe a tactile transducer system that has a compact, yet modular design. The tactile transducer comprises a 6 10 piezo bimorph actuator array with a spatial resolution of 1.8 1.2 millimeter and a wide temporal bandwidth. The blocked force of individual actuators can be changed (0.15 N, 0.22 N) by adjusting the cantilever mechanics to optimally match skins and/or applications. This tac- tile transducer is modular, appeals to ordinary fabrication methods, and can be assembled and dismantled in a short time for debugging and maintenance. It weighs 60 g, it is self-contained in a 150 cm3 volume and may be interfaced to most computers, provided that two analog outputs and six digital I O lines are available. A pilot test was carried out where subjects were asked to detect a virtual line randomly located on an otherwise smooth virtual surface.
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Wang, Q., Levesque, V., Pasquero, J. and Hayward V. 2006. A Haptic Memory Game using the STRESS2 Tactile Display
Proc. of the 2006 ACM Conference on Human Factors in Computing Systems, CHI 2006. pp. 271-274.

A computer implementation of a classic memory card game was adapted to rely on touch rather than vision. Instead of memorizing pictures on cards, players explore tactile graphics on a computer-generated virtual surface. Tactile sensations are created by controlling dynamic, distributed lateral strain patterns on a fingerpad in contact with an electronic tactile display called STRESS2. The tactile graphics are explored by moving the device within the workspace of a 2D planar carrier. Three tactile rendering methods were developed and used to create distinct tactile memory cards. The haptic memory game showcases the capabilities of this novel tactile display technology.
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Wang, Q., Kong, L., Sprigle, S., Hayward, V. 2006. Portable Gage for Pressure Ulcer Detection.
Proc. IEEE Engineering in Medicine and Biology Society Conference, EMBC06, 5997-6000.

Pressure ulcers are widely considered to be a critical problem in rehabilitation since they result in severe discomfort and high healthcare cost. The prevention of pressure ulcers is a constant preoccupation for every nursing team. This paper introduces a novel handheld instrument that can detect subtle changes in the skin biomechanical properties by measuring its biomechanical response. This could be used to detect stage-I pressure ulcers and deep tissue injury. Its high bandwidth makes it possible to load the skin under wide range of conditions. The instrument is portable, inexpensive, and intrinsically precise. Several experiments were conducted to validate the function of the device. Preliminary results show that the device could effectively measure the difference in the viscoelasticity between human skin of different sites, hence paving the way for the development of clinical protocols and trials.
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Wang, Q., Hayward, V., and Smith, A. M. 2004.
A New Technique for the Controlled Stimulation Of The Skin.
Proc. Canadian Medical and Biological Engineering Society Conference, CMBEC Quebec City, Canada, September 9-11.

Traditional methods of skin stimulation for psychophysical, neurophysiologic studies and other investigations involve the use of indentation. We will describe an apparatus intended to cause skin tangential deformation in a controlled manner, which is motivated by much recent evidence suggesting that such stimulation is both behaviorally and physiologically relevant. What the apparatus does is to contact the skin at two locations separated by a distance of about one millimeter, and stretch and compress it by using piezoelectric benders. The mechanical behavior of the skin at this scale is not quantitatively known. We designed the lateral skin stimulator to have a programmable mechanical impedance. This enables us to test the response of the skin mechanically, behaviorally and neurophysiologically with a wide range of conditions.
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Weill-Duflos, A., Mohand-Ousaid, A., Haliyo, S., Régnier, S., Hayward, V. 2015..
Optimizing Transparency of Haptic Device Through Velocity Estimation.
Proceedings of the 2005 IEEE International Conference on Advanced Intelligent Mechatronics pp. 529-534.

In this paper, the conception and optimization of a new dual-stage haptic device is described. A particular attention is given to the choice of encoder. Compact, consumer grade, but low resolution encoders are particularly used. An issue arising from this particularity is the deterioration of the velocity measurement when Finite Difference method is used. Moreover, when encoders resolution decreases, velocity estimation becomes noisy. From haptic point of view, this noise destroys the realism of the rendered force. To deal with this problem, numerous methods have been proposed to offer a noiseless estimation. Here, advanced methods such as Low-Pass Filter, First Order Adaptive Windowing, Kalman Filter are proposed. Performances of theses methods are verified and experimentally compared to a conventional finite difference method. Here, we show that Kalman filter and First Order Adaptive Windowing offers a good trade-off between estimation and noise rejection.
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Wexler, M. and Hayward V. 2011.
Weak Spatial Constancy In Touch.
Proceedings of World Haptics Conference 2011, pp. 605--607.

We propose extending the concept of spatial constancy to haptic perception. In vision, spatial constancy refers to the conversion of retinotopic signals into spatiotopic representations, allowing the observer to perceive space independently of his or her own eye movements, or at least partly so. The problem would seem at least as important in haptic perception, where sensory surfaces undergo even more complex movements in space. Here we develop a methodology for studying haptic spatial constancy, which involves a tactile display mounted on a mobile platform, and which allows us to decouple movements of the sensory surface in this case the fingertip from movements of objects on the fingertip. Using this apparatus, we find evidence for only weak haptic spatial constancy.
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Wiertlewski, M., Endo, S., Wing, A. M., Hayward, V. 2013.
Slip-Induced Vibration Influences the Grip Reflex: A Pilot Study.
Proceedings of the IEEE World Haptics Conference 2013. pp. 627-632.

Grasping is one of the most common forms of dexterity. So far, most research has focused on slow-varying loads which can be resisted by anticipatory grip adjustments. There are common cases, however, when a rapid, unexpected increase in the load occurs and where the central nervous system must re-adjust the grip dynamically to prevent slippage. During such events, the central nervous system reactively updates the grip force to minimize further escape of an object. While existing theories postulates that the shear strain of thefinger pads caused by the load force is a primary source of information for detecting a new load condition, vibrations induced by even minute object slip in the hand might more effectively signal the occurrence of unwanted movement of the object relatively to the hand. With the help of a high-sensitivity force sensor interposed in the load-path of a fast traction-creating device, we recorded the fluctuations of the force projected onto the fingertip when a rapid perturbation was applied to a grasped object. These fluctuations are indicative of slip. The results highlight the existence of a correlation between the amplitude of the vibrations and the grip force modulation, when textural features are present. The study provides promising evidence that the central nervous system exploits vibrations to detect the onset of unwanted movement of an object relatively to the hand to optimally scale the grip force in response to unexpected, rapid load variations.
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Wiertlewski, M., Hayward, V. 2012.
Mechanical Behavior of the Fingertip In The Range of Frequencies and Displacements Relevant to Touch.
Journal of Biomechanics, 45(11):1869-1874

It was previously suggested that the mechanical properties of the fingertip could be characterized by elasticity from dc to about 100 Hz and by viscosity above this frequency. Using a specifically designed high mobility probe, we accurately measured the impedance of the fingertips of seven participants under a variety of conditions relevant to purposeful touch. Direct measurements vindicated previous indirect observations. We also characterized the dependency of the fingertip impedance upon normal load, orientation, and time.
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Wiertlewski, M., Hayward, V. 2012.
Transducer For Mechanical Impedance Testing over a Wide Frequency Range Through Active Feedback.
Review of Scientific Instruments, 83(2):025001

We describe a feedback-controlled active mechanical probe which can achieve a very low mechanical impedance, uniformly over a wide frequency range. The feedback produces a state of quasi-resonance which transforms the probe into a source of force used to excite an unknown load, resulting in a precise measurement of the real and imaginary components of the load impedance at any frequency. The instrument is applied to the determination of the mechanical impedance of a fingertip.
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Wiertlewski, M., Lozada,J., Hayward, V. 2011.
The Spatial Spectrum Of Tangential Skin Displacement Can Encode Tactual Texture.
IEEE Transactions on Robotics. 27(3):461--472

The tactual scanning of five naturalistic textures was recorded with an apparatus capable of measuring the tangential interaction force with a high degree of temporal and spatial resolution. The resulting signal showed that the transformation from the geometry of a surface to the force of traction, and hence to the skin deformation experienced by a finger is a highly nonlinear process. Participants were asked to identify simulated textures reproduced by stimulating their fingers with rapid, imposed lateral skin displacements as a function of net position. They performed the identification task with a high degree of success, yet not perfectly. The fact that the experimental conditions eliminated many aspects of the interaction, including low-frequency finger deformation, distributed information, as well as normal skin movements, shows that the nervous system is able to rely on only two cues: amplitude and spectral information. The examination of the "spatial spectrograms" of the imposed lateral skin displacement revealed that texture could be repre- sented spatially despite being sensed through time and that these spectrograms were distinctively organized into what could be called "spatial formants". This finding led us to speculate that the mechanical properties of the finger enables spatial information to be used for perceptual purposes in humans without any distributed sensing, a principle that could be applied to robots.
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Wiertlewski, M., Hudin, C., Hayward, V. 2011.
On The 1/F Noise And Non-Integer Harmonic Decay Of The Interaction Of A Finger Sliding On Flat And Sinusoidal Surfaces.
Proceedings of World Haptics Conference 2011. pp. 25-30.

The fluctuations of the frictional force that arise from the stroke of a finger against flat and sinusoidal surfaces were studied. We used a custom-made, high-resolution friction force sensor able to resolve milli-newton forces, we recorded those fluctuations as well as the net, low-frequency components of the interaction force. Measurements showed that the fluctuations of the sliding force were highly non-stationary. Despite their randomness, force spectra averages revealed regularities. With a smooth, flat, but not mirror-finish, surface the background noise followed a 1/f trend. Recordings made with pure-tone sinusoidal gratings revealed complexities in the interaction between a finger and a surface. The fundamental frequency was driven by the periodicity of the gratings and harmon- ics followed a non-integer power-law decay that suggested strong nonlinearities in the fingertip interaction. The results are consistent with the existence of a multiplicity of simultaneous and rapid stick-slip relaxation oscillations. Results have implications for high fidelity haptic rendering and biotribology.
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Wiertlewski, M., Lozada, J., Pissaloux, E., and Hayward, V. 2010.
Causality Inversion in the Reproduction of Roughness.
Proceedings of Europhaptics 2010, Part II, Kappers, A.M.L. et al. (Eds.), LNSC 6192, Springer-Verlag, pp. 17-24.

When a finger scans a non-smooth surface, a sensation of roughness is experienced. A similar sensation is felt when a finger is in contact with a mobile surface vibrating in the tangential direction. Since an actual finger-surface inter- action results in a varying friction force, how can a measured friction force can be converted into skin relative displacement. With a bidirectional apparatus that can measure this force and transform it into displacement with unambiguous causality, such mapping could be experimentally established. A pilot study showed that a subjectively equivalent sensation of roughness can be achieved betweem a fixed real surface and a vibrated mobile surface.
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Wiertlewski, M., Lozada, J., Pissaloux, E., and Hayward, V. 2010.
Tactile interface for stimulation of fingertip via lateral traction.
Proceedings of Actuators 2010, the 12th International Conference on New Actuators, pp. 520-523.

Tactile displays are gaining recognition as new human-machine interfaces. This paper present a low-weight, single-axis tactile interface designed to stimulate the fingertip through lateral traction. It operates with two ultrasonic linear motors able to move a small plate in contact with the users fingertip. This miniature interface is capable of a wide range of stimulation signals due to its high force output (0.6 N), its long throw (3 mm) and its high speed (13 mm/s). This interface is driven under closed loop control employing a Hall-effect sensor for position measurement. A model and experimental results will be presented.
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Wijntjes, M. W. A., Sato, A., Kappers, A. M. L. and Hayward V. 2008.
Haptic Perception of Real and Virtual Curvature.
Proc. Eurohaptics 2008, LNCS 5024, Springer-Verlag, pp. 361-366.

In this study we compared human discrimination performance for real and virtual curved shapes. To simulate a curved shape we used a device that could independently orient and elevate a moving surface that was in contact with an exploring nger. Thus, the geometry was preserved up to the rst order in the virtual shape. In our experiment we found that this preservation was indeed sucient: discrimination thresholds were similar for the real and virtual conditions. Our results were also in line with previous curvature studies performed with real stimuli.
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Wijntjes, M. W. A., Sato, A., Kappers, A. M. L. and Hayward V. 2009.
Local Surface Orientation Dominates Haptic Curvature Discrimination.
IEEE Transactions on Haptics. 2(2):94-102.

Prior studies have shown that local surface orientation is a dominant source of information for haptic curvature perception in static conditions. We show that this dominance holds for dynamic touch, just as was shown earlier for static touch. Using an apparatus specifically developed for this purpose, we tested this hypothesis by providing observers with two independently controlled sources of geometric information. The robotic-like apparatus could accurately control the position of a contact surface independently from its orientation in space, while allowing subjects to freely and actively explore virtual shapes in the lateral direction. In the first experiment, we measured discrimination thresholds for the two types of shape information and compared the discrimination of real shapes to that of virtual shapes. The results confirmed the dominance of local surface orientation. We propose a model that predicts cue dominance for different scales of exploration. In the second experiment we investigated whether a virtual curved surface felt as curved as a real curved surface. We found that observers did not systematically judge either of the two kinds of stimuli to be more curved than the other. More importantly, we found that points of subjective curvedness were not influenced by the availability of height information.
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Xinjilefu, Michalska, H. and Hayward, V. 2010.
Hybrid Stabilizing Control for the Spatial Double Inverted Pendulum.
In "International Symposium on Brain, Body and Machine", Springers series in Advances in Intelligent and Soft Computing, Angeles, J., Boulet, B., Clark, J. J., Kovecses, J. and Siddiqi, K. (Eds.), pp. 201-215.

The spatial double inverted pendulum actuated at the hip, but not at the foot, may be considered to be a model of standing creatures and robots. Moving in-space, as opposed to in-plane, poses new control problems which, for the most part, are still open. In this paper, a hybrid approach where an energy-shaping, passivity-based swing-up controller hands off the control to a linear-quadratic-regulator in the vicinity of the unstable upright equilibrium is proposed. A direct approach and a pre-compensated approach are described, discussed, and illustrated by means of examples in simulation.
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Xinjilefu, Michalska, H. and Hayward, V. 2009.
Stabilization of the spatial double inverted pendulum using stochastic programming seen as a model of standing postural control.
Proc. 9th RAS International Conference on Humanoid Robots (Humanoids09), pp. 367-372.

The stabilization of a double inverted pendulum moving in a three dimensional space may be considered to be a model of a human --- and of other animals --- postural control. Here, we show that postural control is possible by on-line minimization of the system Lagrangian. An stochastic programming procedure proves to be able to find oscillatory inputs that bring the system close to the unstable upright equilibrium position. In conclusion, our study demonstrates that steering complex mechanical systems may in certain cases be actually be simpler than expected.
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Yao, H.-Y. and Hayward, V. 2010.
Design and Analysis of A Recoil-Type Vibrotactile Transducer.
Journal of the Acoustical Society of America. 128(2):619-627.

This article describes the design of a high-bandwidth, iron-less, recoil-based electromagnetic vi- brotactile actuator. Its working principle, the theoretical analysis, the method used to determine its transfer function, its scaling properties and its design constraints are discussed along with its fabrication and possible improvements.
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Yao, H.-Y., Hayward, M. Cruz, D. Grant. V. 2007.
The Effect of Weight on the Perception of Vibrotactile Intensity with Handheld Devices.
Proc. World Haptics 2007 (Second Joint Eurohaptics Conference And Symposium On Haptic Interfaces For Virtual Environment And Teleoperator Systems), pp. 551-552.

The objective of this study was to determine whether the weight of a vibrating handheld object influenced the perceived intensity of its vibrations. Experiments were conducted to determine the subjective equivalence of vibrotactile intensity for objects that had the same size but had different weights. The results suggest that for the same surface acceleration and hence the same movement, the heavier is the device, the stronger is the perceived intensity.
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Yao, H.-Y. and Hayward, V. 2006.
An Experiment on Length Perception with a Virtual Rolling Stone.
Proc. Eurohaptics 2006. pp. 325-330.

When an object rolls or slides inside a hand-held tube, a variety of cues are normally available to estimate its location inside the cavity. These cues are related to the dynamics of an object subjected to the law of physics such as gravity and friction. This may be viewed as a form of sensorymotor coupling which does not involve vision but which links motor output to acoustic and tactile inputs. The theory of sensorymotor contingency posits that humans exploit invariants about the physics of their environment and about their own sensorymotor apparatus to develop the perception of the outside world. We report on the design and the results of an experiment where subjects held an apparatus that simulated the physics of an object rolling or sliding inside a tubular cavity. The apparatus synthesized simple haptic cues resulting from rolling noise or impact on internal walls. Given these cues, subjects were asked to discriminate between the lengths of different virtual tubes. The subjects were not trained at the task and had to make judgments from a single gesture. The results support the idea that the subjects mastered invariants related to the dynamics of objects under the influence of gravity that they were able to use them to perceive the length of invisible cavities.
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Yao, H.-Y. and Hayward, V. 2006.
A Network-ready Multi-lateral High Fidelity Haptic Probe.
Proc. 14th Symposium on Haptic Interfaces For Virtual Environment And Teleoperator Systems IEEE VR 2006, pp. 81-82.

We describe a system comprising two or several haptic probes each having a sensor, an actuator, and circuitry. The inputs and outputs can be connected to audio channels of standard audio equipment and hence be networked via computers. When a user manipulates a probe to scratch and tap surfaces, the other users can share her haptic experience.
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Yao, H.-Y., Hayward, V., and Ellis, R. E. 2005.
Tactile Enhancement Instrument for Minimally Invasive Surgery.
Computer Aided Surgery, Vol. 10, No. 4, pp. 233-239.

Objective: Surgeons use probes during during minimally invasive arthroscopy as diagnostic tools to detect tissues anomalies. Improving tactile sensitivity during this activity would be valuable.
Materials and Methods: We developed an enhanced probe that could heighten the tactile sensations experienced while probing objects. It operated by detecting the acceleration signal resulting from the interaction of the tool tip with surfaces and magnifying it for tactile and auditory reproduction. The instrument consisted of an accelerometer and an actuator arranged such that the sensing direction was orthogonal to the actuating direction so as to decouple input from output. Using the instrument, subjects were asked to detect cuts under four conditions: with no amplification, with enhanced tactile feedback, with sound feedback, and with passive touch.
Results: We found that, for tactile reproduction, the current prototype could amplify the signals by 10 dB on average. Results from statistical methods showed significant improvements of performance in the case of tactile and auditory feedback.
Conclusion: We developed a surgical probe with tactile and auditory feedback. Despite the moderate system gain achievable by the initial prototype, the system could measurably improve users' ability to detect small cuts in cartilage-like elastic surfaces.
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Yao, H.-Y., Hayward, V., and Ellis, R. E. 2004.
A Tactile Magnification Instrument for Minimally Invasive Surgery.
Proc. MICCAI 2004, Barillot, C. Haynor, D.R. and Hellier P. (Eds.), LNCS 3217, pp. 89-96, Springer-Verlag: Berlin, Heidelberg.

The MicroTactus is a family of instruments that we have designed to detect signals arising from the interaction of a tip with soft or hard objects and to magnify them for haptic and auditory reproduction. We constructed an enhanced arthroscopic surgical probe and tested it in detecting surface defects of a cartilage-like material. Elastomeric samples were cut at different depths and mixed with blank samples. Subjects were asked to detect the cuts under four conditions: no amplification, with haptic feedback, with sound feedback, and with passive touch. We found that both haptic and auditory feedback significantly improved detection performance, which demonstrated that an enhanced arthroscopic probe provided useful information for the detection of small cuts in tissue-like materials.
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Yi, D. and Hayward, V., 2006.
Depth Discrimination with 2d Haptics During Static Viewing of 3d Angiograms.
Haptics-e. Vol. 3, No. 8.

We describe a force feedback scheme that is able to provide for haptic depth perception for use during the static 2d viewing of 3d angiograms. The scheme returns 2d horizontal forces that bear some analogy with forces that would be needed to glide a virtual proxy on the vessel centerlines. The display system was evaluated by asking sub jects to determine the relative depth of randomly selected points on vessel segments. The results indicate that sub jects were able to discriminate the relative depth in an average time of 12 seconds and with an accuracy of 95%.
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Yi, D. and Hayward, V., 2002.
Skeletonization of Volumetric Angiograms for Display.
Computer Methods in Biomechanics and Biomedical Engineering. Vol. 5, No. 5, pp. 329-341.

The display of three-dimensional angiograms can benefit from the knowledge of quantitative shape features such as tangent and curvature of the centerline of vessels. These can be obtained from a curve-like skeleton representation. If connectivity and topology are preserved, and if geometrical constraints such as smoothness and centeredness are satisfied, it is possible to estimate length, orientation, curvature, and torsion. It is also required that no part of the original object be left unrepresented. An efficient method for the identification of such shape components is developed. First, a suitable representation is obtained using a voxel coding approach to yield connected and labeled unit-thick paths. The desired features are estimated from a smoothed version of the skeleton produced by a moving average filter. The computational cost is linear, of the order of Nobject, the total number of object voxels contained in the binary volumetric data. The method is also shown to be robust to boundary noise. Examples are discussed.
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Yi, D. and Hayward, V., 2002.
Augmenting Computer Graphics With Haptics For The Visualization Of Vessel Networks.
10th Pacific Conference on Computer Graphics and Applications.

Current visualization methods of volume angiograms are limited in their ability to display vessel connectivity and depth information readily available in the data set. In this work, we introduce a hybrid graphic-haptic display technique that allows visualizing vessel connectivity as well as provides user assistance in tracing vessel branches. Most importantly, our display provides three-dimensional shape cues in both visual and haptic domains that eliminate the need for a rotational display for 3D perception. Issues related to haptic rendering, implementation, and experimental validation of the developed system are reported. This proposed multimodal visualization approach is independent of the devices used and can be applied to current visualization platforms for angiograms due to the small computational load it requires.
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Yi, D. and Hayward, V., 2002.
Linear Cost Reconstruction of Vascular Trees From Intensity Volume Angiograms.
Proc. 2nd International Conference on Image and Graphics, ICIG2002, SPIE. pp. 195-200.

This paper introduces a two-phase algorithm to extract a center-adjusted, one-voxel-thick line representation of cerebral vascular trees from volume angiograms coded in gray-scale intensity. The first stage extracts and arranges the vessel system in the form of a directed graph whose nodes correspond to the cross sections of the vessels and whose node connectivity encodes their adjacency. The manual input reduces to the selection of two thresholds and the designation of a single initial point. In a second stage, each node is replaced by a centered voxel. The locations of the extracted centerlines are insensitive to noise and to the thresholds used. The overall computational cost is linear, of the order of the size of the input image. An example is provided which demonstrates the result of the algorithm applied to actual data. While being developed to reconstruct a line representation of a vessel network, the proposed algorithm can also be used to estimate quantitative features in any and/or intensity images. This technique is sufficiently fast to process large images at interactive rates using commodity computers.
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Ziat, M. and Yao, H.-Y. and Schmitt, R. and Hayward, V. 2016.
FrontPanel: Tangible User Interface for Touch-Screens Dedicated to Elderly.
Proceedings of the 2016 CHI Conference Extended Abstracts on Human Factors in Computing Systems, pp. 3808-3811.

In this paper, we describe FrontPanel, a tangible user interface that enhances accessibility features in an iPad. More specifically, FrontPanel was designed for the senior population who has difficulty interacting with touch-screen tablets because of the lack of tangibility. FrontPanel is a result of one year help sessions with elderly who wished to replace their desktop/laptop computer with a touch-screen tablet that has the advantage of being light and mobile.
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Ziat, M., Frissen, I., Campion, G., Hayward, V., Guastavino, C. 2013.
Plucked String Stiffness Affects Loudness Perception
Proceedings of the Workshop on Haptic and Audio Interaction Design. LNCS 7989, Springer-Verlag Berlin Heidelberg, pp. 79-88

A great variety of interactions between senses, and between motor production and senses, have been reported in previous research. In the present study, we tested whether the mechanics of a plucked string affected how the sound it produced was perceived. To test this hypothesis, we simulated the feel of a plucked string using a high fidelity haptic force-feedback device and simultaneously simulated its acoustic emission. This way, we could independently manipulate the two sensory inputs -- how it felt and how it sounded -- together with physical correct haptic interaction and with accurate synchronization. This arrangement makes it very plausible that the two sensory inputs came from a common source. We used a two-interval forced-choice discrimination procedure to determine the point of subjective equality of the loudness between a stiff and a soft plucked string. When the stiffness of the string was low, the sound was perceived to be softer. Interestingly, this effect was found only when the first string was less stiff than the second string plucked during a comparison. The results are consistent with the inverse effectiveness principle of multisensory integration.
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Ziat, M., Hayward, V., Chapman, C. E., Ernst, M. O., and Lenay, C. 2010.
Tactile Suppression of Displacement.
Experimental Brain Research, 206(3):299-310

In vision, the discovery of the phenomenon of saccadic suppression of displacement has made important contributions to the understanding of the stable world problem. Here we report a similar phenomenon in the tactile modality. When scanning a single Braille dot with two fingers of the same hand, participants were asked to decide whether the dot was stationary or whether it was displaced from one location to another. The stimulus was produced by refreshable Braille devices which have dots that can be swiftly raised and recessed. In some conditions the dot was stationary. In others, a displacement was created by monitoring the participants finger position and by switching the dot activation when it was not touched by either finger. The dot displacement was of either 2.5 mm or 5 mm. We found that in certain cases, displaced dots were felt to be stationary. If the displacement was orthogonal to the finger movements, tactile suppression occurred effectively when it was of 2.5 mm, but when the displacement was of 5 mm, the participants easily detected it. If the displacement was medial-lateral, the suppression effect occurred as well but less often when the apparent movement of the dot opposed the movement of the finger. In such cases, the stimulus appeared sooner than when the brain could predict it from finger movement, supporting a predictive rather than a postdictive differential processing hypothesis.
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