Model-Based Motion and Force Control for Flexible-Joint Robot Manipulators

Abstract

Two model-based control algorithms to control the motion and force of flexible-joint robot manipulators are presented. Both algorithms are based on the feedback-linearization concept, and utilize a fourth-order feedback-linearizable model of the flexible-joint manipulators. The first algorithm, dynamic hy brid controller, deals with the problem where the flexible-joint robot is constrained by a rigid environment, and aims at di rect control of the contact forces. A constraint frame is derived that enables decoupling of the system into a position subsystem and a force subsystem. A nonlinear feedback-control law is designed to first decouple and linearize the constrained flexible- joint manipulator system, then impose desired closed-loop characteristics in each subsystem independently. The second algorithm, impedance controller, aims at regulating the rela tionship between the contact force and the difference between the commanded and true positions of the end point. A desired target impedance is designed for the end point of the flexible- joint robot manipulator in the reference frame. A nonlinear feedback controller is designed to linearize the system and to impose the target impedance. The same controller is used when the robot is performing compliant and free motions. An experimental two-link, flexible-joint robot manipulator in con tact with a straight wall is used to evaluate and compare the performance of the two controllers.