A simple nonlinear proportional-derivative controller for friction compensation

This paper addresses the global asymptotic tracking of one-degree-of-freedom (DOF) uncertain mechanical systems with unknown friction. A very simple variable structure-like nonlinear proportional-derivative (NP-D) controller is proposed. The closed-loop system formed by the controller and the mechanical system is shown to be global asymptotically stable. Advantages of the proposed controller include an absence of modeling parameters in the control law formulation and the control gains are easy tuned according to some simple explicit conditions, and thus it is readily implemented. Even when the proposed scheme is modified to avoid the possible chattering in practical implementation, the overall performance remains appealing. The effectiveness of the proposed approach is illustrated via simulation results.