Discrete-time robust adaptive control for robotic manipulators

This paper deals with a design of discrete-time robust adaptive controllers with fixed compensators for robotic manipulators. Although several adaptive control schemes with fixed compensators for minimum-phase systems have been proposed, they can not be applied for robotic manipulators because their discrete-time models are not of minimum-phase. In this paper, first, we design a direct adaptive controller for robotic manipulators using an existing discrete-time model with unstable zeros. Then a fixed compensator is also designed for improving the robustness of the adaptive control system based on the fact that the stable zeros and poles of the open-loop transfer function improve the feedback properties. The fixed compensator is obtained by solving a convex optimization problem. The proposed method is applied to a two-link manipulator and its effectiveness is experimentally examined.