Tracking control of mechanical systems in the presence of nonlinear dynamic friction effects

In this paper, we design an observer-based exact model knowledge position t racking controller for a second-order mechanical system with nonlinear load dynamics and the nonlinear dynamic friction model proposed in [9], Since t he controller requires an estimate of the unmeasurable friction state. We d emonstrate how the friction dynamics can be exploited to design three diffe rent observers which foster different transient response characteristics fo r the composite closed-loop system. We then present two adaptive controller s which utilize nonlinear observer/filter structures to provide for asympto tic position tracking while compensating for selected parametric uncertaint y. Dynamic simulation and experimental results are utilized to illustrate c ontrol performance.