Joint stick‐slip friction compensation of robot manipulators by using smooth robust controllers

In this article, two new smooth robust nonlinear compensators have been developed, respectively, for positional regulation and trajectory tracking of rigid robot manipulators with internal joint stick‐slip friction. The proposed controllers can improve not only the positioning accuracy but also the smoothness of motion. No exact knowledge of the friction models is required for the design of the controllers. Furthermore, the tracking controller is also robust with respect to the uncertain link parameters. Using Lyapunov's direct method, we can show that the time‐invariant positional regulation controller guarantees the global boundedness stability of the closed‐loop system, while the time‐varying positional tracking controller guarantees the global asymptotic stability of the closed‐loop system. The numerical simulations of the controllers on a two‐link robot are presented as illustrations. © 1994 John Wiley & Sons, Inc.