Shape recovery from robot contour-tracking with force feedback

In this paper we describe a process for shape recovery from robot contour-tracking operations with force feedback. Shape recovery is an important task for self-teaching robots and for exploratory operations in unknown environments. An algorithm which directs a position-controlled robot around an unknown planar contour using the steady-state contact force information is described in this paper. Shape recovery from planar contouring is not a trivial problem. It was found experimentally that there is significant distortion of the original contour if direct kinematics are used to recover the object's shape, as we are unable to recover the exact position of the robot tool owing to the errors present in the kinematic model of the arm and the non-linearities of the drive train. Drive train errors can consist of the joint compliance, gear backlash, and gear eccentricity. A mathematical model of the errors generated by the drive train has been previously addressed. In this paper a compensation process is explored for purposes of planar shape recovery. It was found through experimentation that the joint compliance is most conveniently compensated for in practice. Improvements in the shapes recovered from robot contouring are seen with our compensations. Experimental details and difficulties are also discussed.