Tracking control in the presence of nonlinear dynamic frictional effects: robot extension

We extend the observer/control strategies previously published by Vedagarbha et al. (1997) to an n-link, serially connected, direct drive, rigid link, revolute robot operating in the presence of nonlinear friction effects modeled by the Lu-Gre model. In addition, we also present a new adaptive control technique for compensating the nonlinear parametrizable Stribeck effects. Specifically, an adaptive observer/controller scheme is developed which contains a feedforward approximation of the Stribeck effects. This feedforward approximation is used in a composite controller/observer strategy which forces the average spare integral of the position tracking error to an arbitrarily small value