Theory and Experiment

Abstract

This work describes a control method for the stable accommodation of contact forces! when the robot interacts with the environment. In robotic deburring, for example, the robot endpoint is constrained by the the part to be deburred (7,8). After defming unstructured models (input-output relationships) for both the robotic and environment subsystems, we combine them to obtain a general, nonlinear stability condition for the total system. This prescribes a finite sensitivity (a mapping from forces to displacements) for the robot and the environment. It also states that decreasing the sensitivity of either subsystem reduces the stability range; as both subsystems approach zero sensitivity, stability cannot be guaranteed. We then focus on the robot's rigid body dynamics and an infinitely stiff environment (structured models) to obtain a specific stability condition in terms of the Jacobian and the robot's tracking controller. This condition has been verified via simulation of and experimentation with the Minnesota direct drive robot. 1