High performance regulator control for mechanical systems subjected to friction

Several control strategies are compared with respect to their performance for regulator tasks on mechanical systems that exhibit friction. For this purpose a classic PID-controller combined with mass and frictional feedforward is compared to (i) a PID-controller combined with a model-based friction compensation using the dynamic LuGre friction model and (ii) a gain-scheduled optimal PD-controller based on a polytopic linear model (PLM). The latter consists of a feedforward part and an optimal nonlinear feedback part. The controllers are compared to the classic PID-controller by means of experiments on a rotating arm subjected to friction. The performance for three third order point to point setpoints shows that the gain-scheduled optimal PD-controller outperforms the other controllers with respect to settling time and maximal error after setpoint. The tracking performance is comparable for the LuGre-based controller and the classic PID-controller where the tracking performance of the gain-scheduled PD-controller is limited.