Adaptive robust control of mechanical systems with non-linear dynamic friction compensation

In this paper, an adaptive robust control (ARC) scheme based friction compensation strategy is presented for a class of mechanical systems in the presence of dynamic friction effects. In contrast to existing deterministic robust control (DRC) and adaptive control (AC) schemes, the proposed ARC scheme utilizes both the structural information of the dynamic friction model and the available prior information on a physical system such as the bounds of parameter variations and unmeasurable friction state for high performance. In particular, the physical bound on the unmeasurable dynamic friction state is fully exploited to construct certain projection type modifications to the dynamic friction state observers. By doing so, a controlled dynamic friction state estimation process is achieved even in the presence of disturbances. The resulting controller achieves a guaranteed transient performance and final tracking accuracy. Furthermore, in the absence of uncertain nonlinearities, asymptotic output tracking is achieved.