Decoupled nonlinear three-term controllers for robot trajectory tracking

A simple controller is proposed for independent joint control of a manipulator to enable accurate trajectory tracking without requiring specific knowledge about the robot dynamics. Each joint controller consists of three nonlinear integral terms in the tracking error. Global asymptotic stability of tracking errors is established using the Lyapunov stability theory. The control system is shown to be robust to torque disturbances affecting the system and to a class of unmodeled dynamics. To further improve the robustness of the closed-loop system in situations where measurement noise is present, a simple modification to the controller is proposed. It is shown that exponential convergence of the error to arbitrarily small values is guaranteed with this modification. A systematic procedure for the selection of controller parameters is provided, and simulations results using the complete dynamic model of a six degree of freedom industrial robot are presented to demonstrate the excellent tracking performance of the proposed controller