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 mechanical system in the presence of dynamic friction effects. The system may be subjected to both parametric uncertainties (e.g., unknown parameters in the dynamic friction model) and uncertain non-linearities such as external disturbances and modelling errors. In contrast to existing deterministic robust control (DRC) and robust adaptive control (AC) schemes, the proposed ARC scheme utilizes both the structural information of the dynamic friction model and the a priori information of the system, such as the bounds on the parameters and unmeasured internal friction state. In particular, the bounds on the friction state are fully exploited to construct certain projection-type modifications to the state observers. By doing so, a controlled 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 non-linearities, asymptotic position tracking is achieved. Comparative simulation results illustrate the effectiveness of the proposed scheme.