Variable structure model reference adaptive control of robot manipulators

Abstract

An adaptive control scheme combining the variable structure and model reference methods is presented. With the variable structure technique, all known parameters of the robot system are fully used while the unknown parameters are adaptively adjusted. The overall control system maintains the basic structure of the computer torque controller, but incorporates adaptive components in the system. The method removes the requirement for persistent excitation, essential to traditional adaptive schemes for satisfactory operation. The control algorithm ensures the robustness of the controlled system with respect to disturbance, since the tracking error always converges to zero theoretically, rather than to an ill-defined residual set as in other adaptive schemes. Using this method, the transient response can be prescribed in advance. Thus, all the outstanding issues in adaptive control are directly treated. Simulation analysis for a two-degree-of-freedom robot is conducted to compare the method with the classical model reference method and computed torque method.