Design of robust controller for flexible joint robot with nonlinear friction characteristics

A robust controller method for flexible joint robot considering the effect caused by nonlinear friction was presented. The nonlinear friction was denoted as inverse additive output uncertainty relative to the nominal model in our work, based on which the describing function was analyzed in frequency domain, and the weighting function of nonlinear friction was further calculated as well. By combining the friction uncertainty, the mixed sensitivity H_∞ optimization was proposed as the benchmark for controller design, which also leaded to good performance of robustness. Furthermore, unstructured perturbation to the system was analyzed so that the stability was guaranteed. Simulation results show that the proposed controller can provide excellent tracking and regulation performance.