Robust control of a direct drive manipulator

Trajectory control of robotics manipulators is considered. Due to the coupled and nonlinear dynamics, robot control is a challenging problem. The effects of the complicated dynamics are more significant when the payload is large and time varying. Variable structure control methodologies are proposed in the literature to solve the problems encountered. High frequency oscillations in the joint velocities-chattering-may occur if discontinuities are introduced in the control input artificially to generate a sliding mode. A chattering free sliding mode control algorithm design is considered in this paper. Variable structure systems and Lyapunov designs are combined in the algorithm implemented. The controller possesses robustness properties of sliding mode systems. Experiments are carried out on a direct drive SCARA type manipulator for various payload configurations. A comparison of the results obtained with the chattering free sliding mode controller and a well tuned conventional PD control scheme is presented