ON THE DECOUPLING OF POSITION AND FORCE CONTROLLERS IN CONSTRAINED ROBOTIC TASKS

In hybrid control of robot manipulators separate controllers are desig ned for force and position errors control. Controllers are designed ei ther in task or joint space and their outputs combine to provide input torque to the manipulator. Position and force controllers performance in a constrained robotic task is affected by their interaction to a d egree dependent on the controller's ability to reject disturbances. Id eally, decoupling of the two control loops is desired to achieve the b est performance in position and force directions. In this article, ana lysis of control loop interactions is performed for contact and noncon tact phases, and controller design requirements are developed to achie ve maximum decoupling. Design requirements involve output subspace of each controller leading to control discontinuities for contact and non contact phases. In the noncontact phase, satisfaction of design requir ements leads to a fully linearized and decoupled system. When in conta ct with the constraining surface, design requirements eliminate distur bances in the farce loop, but minimize disturbances in the position lo op to an extent dependent on force loop performance. Known hybrid cont rol schemes analysis is performed to reveal existence of control loop interactions in these schemes. Confirmation of theoretical analysis is done through simulation of a three revolute planar manipulator. (C) 1 998 John Wiley & Sons, Inc.