by Hsin-Yun Yao
Last updated: April 2007

MicroTactus

An instrument designed to magnify the tactile feedback
by detecting acceleration at the tip and amplifying it.

What is it?

MicroTactus is an active probing device which enhances tactile sensations experienced while probing a surface with a tooltip.

It measures the tip acceleration signal resulting from the interaction with the probing surface and actively amplified it at the handle. The same signal could also be transformed into sound to heighten sensitivity to small details even further.

An accelerometer is attached near the tip. Its amplified signal is fed to an inertial actuator embedded in the handle. The actuator has a cylindrical magnet elastically suspended inside the handle. The geometry of the magnet and the coil is such that a Lorentz force is developed between the magnet and the handle when current flows.

The accelerometer picks up acceleration in the axes orthogonal to the handle. The actuator moves in the axial direction. Making the sensing directions orthogonal to the moving direction decouples the sensor from the actuator, thus improving stability.


Processing

The acceleration signals are processed digitally before being sent to a 5W audio amplifier. The amplifier output is connected to both the actuator and an audio speaker. The processor provides enough design headroom for the implementation of advanced features such as digital filters, record or play functions and stability control loops.

Recorded Acceleration

The accelerometer can record very small surface imperfections. The first figure on the left is a recording made when the probe was dragged over a rubbery surface with two cuts. The acceleration valleys and peaks caused by the probe tip "entering" and "leaving' the cuts are clearly visible.

The figure below was recorded while probing a surface with a deeper cut. It shows that if the cut is deeper, the acceleration valley and peak are bigger.


Actuator Fabrication

The actuator consists of one magnet, rubber suspensions and coils. The rare-earth magnet (NeFeB) is suspended by rubber sheets. The coil is separated into two parts, one on each side of the magnet. It has 6 ohm input impedance, like a loudspeaker. This characteristic makes the actuator compatible with audio amplifiers.

Application in Minimally Invasive Surgery

Arthroscopy, the application which first inspired this project, is a minimally invasive surgical procedure performed mostly in joints. An arthroscopic probe is an instrument used during diagnostic arthroscopy operations to detect abnormal tissues. In addition to visual feedback provided by the viewing scope inserted in the joint, tactile feedback from the probe also plays an important role in a number of tasks.

MicroTactus can be used during arthroscopic procedures to enhance the tactile sensations experienced by the surgeons. It can also be used as a texture recording/playing instrument, with considerable potential for use in surgical simulation and training.


Application in Multi-lateral Settings

Because MicroTactus is light-weight, portable and compatible with audio equipments, it can be used directly for network transmission in a multi-lateral configuration, for example, over an existing teleconference network. The haptic data can be transmitted directly over existing audio channel, thus eliminates the need of any additional hardware or software.

Publications

Touch Magnifying Instrument for Minimally Invasive Surgery
Hsin-Yun Yao, Vincent Hayward, Randy E. Ellis
7th International Conference of Medical Image Computing and Computer-Assisted Intervention (MICCAI), September 2004

Touch Magnifying Instrument for Minimally Invasive Surgery
Hsin-Yun Yao
M. Eng. Thesis, McGill University, September 2004

A Tactile Enhancement Instrument for Minimally Invasive Surgery
Hsin-Yun Yao, Vincent Hayward, Randy E. Ellis
Computer Aided Surgery, Vol. 10, No. 4, pp. 233-239. May 2005

Network-ready Multi-lateral High Fidelity Haptic Probe.
Hsin-Yun Yao, Vincent Hayward
14th Symposium on Haptic Interfaces For Virtual Environment And Teleoperator Systems IEEE VR, pp. 81-82. March 2006

Poster and Demonstration

Touch Magnifying Instrument for Minimally Invasive Surgery
Hsin-Yun Yao, Randy E. Ellis, Vincent Hayward
15th Annual Canadian Conference on Intelligent Systems (IRIS), Quebec City, Canada, June 2005

Patent

Tactile Amplification Instrument and Method of Use
Randy Ellis, Vincent Hayward, Hsin-Yun Yao
USPTO Application No. 60/719.564 (pending)
CIPO No. 2,520,942 (pending)