Other tasks required in the servicing and maintenance of aircrafts are more demanding in terms of accuracy, e.g., stripping, deicing, and painting. Stripping requires more accuracy in the execution of the task, in that the tool is rigid and sharp, positioning errors thus becoming dangerous, for they can lead to damage of the fuselage. Deicing requires a uniform application of the solvent, which calls for moderately accurate positioning but highly accurate velocity control. Painting, in turn, is the most demanding of these tasks, for it requires an accurate velocity control of the painting nozzle with the purpose of guaranteeing a uniform application of the painting, while concurrently requiring a highly accurate positioning control. This requirement becomes critical when the painting involves the tracing of regular geometric shapes on the fuselage, like curves that appear projected either as straight lines or as circles. These requirements motivated the need for a light, and hence, flexible structure, while at the same time capable of executing accurate positioning and velocity control.
Figure 6.11: The three modules of the M System: (a) the 4-dof macro-manipulator; (b) the intermediate 4-dof Cuatro Arm; and (c) the 3-dof Agile Wrist
In this project a modular approach to the design of the mechanical structure of an 11-axis robot to accomplish accurate positioning and velocity-controlled tasks in the presence of a flexible substructure is currently being explored. The manipulator is designed as a cascade of three modules, the proximal one being termed the macromanipulator, and comprising four revolute axes aimed at realizing four-dof positioning tasks proper of what are called SCARA--Selective-Compliance Assembly Robot Arm. The macromanipulator is responsible for a long reach and a high flexibility. The two other modules, comprising the seven-axis micromanipulator, are responsible for the accurate positioning and orientation of the tool attached to the end-effector. Of these, the intermediate module, the Cuatro Arm, developed during Phase I of IRIS, a Canadian network of centres of excellence, is a four-dof architecture responsible for the positioning of a point of its terminal link, which plays the role of the centre of the three-dof spherical wrist. Both the intermediate module and the spherical wrist were designed with an isotropic architecture for highest positioning accuracy. The spherical wrist, that we term the Agile Wrist, owes its name to the architecture adopted, namely, that of the Agile Eye developed by Prof. Clément Gosselin and his team at Université Laval, in Ste.-Foy, Quebec. (Figure 6.11).
A. Morozov, O. Navarro, J. Angeles, R. V. Patel (U. of Western Ontario)