A New Approach to Adaptive Control of Manipulators

The paper presents a new approach to adaptive control of manipulators to achieve trajectory tracking by the joint angles. The central concept in this approach is the utilization of the manipulator “inverse” as a feedforward controller. The desired trajectory is applied as an input to the feedforward controller which “behaves” as the “inverse” of the manipulator at any operating point; and the controller output is used as the driving torque for the manipulator. The controller gains are then updated by an adaptation algorithm derived from MR AC theory to cope with variations in the manipulator inverse due to changes of the operating point. An adaptive feedback controller and an auxiliary signal are also used to enhance closed-loop stability and to achieve faster adaptation. The proposed control scheme is computationally fast and does not require a priori knowledge of the complex dynamic model or the parameter values of the manipulator or the payload. Simulation results are presented in support of the proposed adaptive control scheme. The results demonstrate that the adaptive controller performs remarkably well for different reference trajectories and despite gross variations in the payload.