Tracking Controllers for Robot Manipulators: A High Gain Perspective

We propose a controller for the path tracking problem of robotic manipulators. The proposed controller structure is similar to that of the “computed-torque” scheme widely known in the literature. Unlike the computed-torque scheme, this controller is robust with respect to parameter uncertainty and disturbances. The robustness is given by a high gain mechanism that works in conjunction with a nonlinear precompensator in the control loop. The fundamental action of the high gain is to minimize the effective uncertainty that remains, subsequent to any cancellation by the precompensator. Comparison of the performance of this controller with two other schemes reported in the literature suggests that it performs as effectively. An interesting relationship among the high-gain, the control effort and the accuracy of tracking is identified for a special class of path-tracking that is commensurate with zero tracking error. The synthesis of this controller is easily formulated and its performance is dictated primarily by a single high-gain parameter, making it particularly attractive for on-line tuning. Some guidelines are given for the off-line selection of this high-gain parameter.