A smooth robust nonlinear controller for robot manipulators with joint stick-slip friction

The design of a smooth robust nonlinear controller for the regulation of an n-degree-of-freedom rigid robot with internal joint stick-slip friction is presented. It is shown that not only positioning accuracy, but also smoothness of motion is improved through nonlinear feedback. The Lyapunov direct method is employed to prove the global stability of the closed-loop system. The desired accuracy can be achieved by adjusting the parameters of the controller. The nonlinear compensator is robust with respect to the character of the slipping torque. Only the maximum static friction torque of the internal joint is required for controller design. The numerical implementation of this controller on a two-link robot is presented