Adaptive friction compensation robust control for permanent magnet spherical actuator under compound disturbance

The permanent magnet spherical actuator (PMSA) is a multi-variable featured and strongly coupled nonlinear system, and its motion control will unavoidably be affected by various factors. In order to reduce the influence of model uncertainty, friction, and external disturbance on the actual control during the position tracking of PMSA, this paper proposes a novel adaptive friction compensation robust control method under compound disturbance to improve the motion stability of PMSA. In this method, an adaptive compensator is designed to compensate for the unmodeled friction with unknown but constant parameters, and a robust compensator is used to deal with friction parameter variation and non-parametric interference factors that cannot be modeled. The combination of the two controllers can achieve better friction compensation and interference suppression with smaller feedback gain, thus reducing the trajectory tracking errors. In addition, in order to add the smoothness of the velocity value during the experiment, a first-order filter is introduced into the controller. Finally, the stability of the designed controller for the closed-loop system is proved by the Lyapunov method. Furthermore, a simulation model is established and experiments are conducted on the research prototype, and the feasibility and effectiveness under compound disturbance of the proposed control method are verified by comparing with the simulation and experimental results of other controllers.