Evaluation of Three Nonlinear Control Methods to Reject the Constant Bounded Disturbance for Robotic Manipulators

In this paper, we consider the tracking control problem for robot manipulators which are affected by constant bounded disturbances. Three control schemes are applied for the problem, which are composed of integral action and tracking controllers. The goal is improving the accuracy of tracking procedure for a robot manipulator to track a specified reference signal in the presence of constant bounded disturbances. Inverse dynamics controller, improved Lyapunovbased controller with integral action and discontinuous Lyapunov-based controller are three schemes that are evaluated in this paper. The third one is a novel controller that achieves trajectory following without requiring exact knowledge of the nonlinear dynamics. Based on the disturbance rejection scheme, tracking controllers are constructed which are asymptotically stabilizing in the sense of Lyapunov. Furthermore the closed loop system has strong disturbance rejection property. It is shown that how under proper assumptions, the proposed schemes succeed in achieving disturbance rejection at the input of a nonlinear system. Computer simulation results given for a two degree of freedom manipulator with a large payload and fast maneuver, demonstrate that accurate trajectory tracking can be achieved by using the proposed controllers.