Multiple-surface sliding mode control of pneumatic actuator with mismatched uncertainties

Abstract

This paper deals with the position control of a servo-pneumatic system in presence of mismatched uncertainties. Pneumatic actuators are used in many industrial applications; such as haptic interfaces, mechatronic systems and robotics. Restriction of control effort, to apply directly on the mismatched uncertainties, causes problem to cope with these kinds of uncertainties. Nonlinearities due to internal and external disturbances such as friction force between piston seal and cylinder wall; make it difficult to control these actuators. Thus modeling and identification of friction parameters is an essential part of the controller design procedure. Using simple model for friction such as stribeck model could help to put more effort on design a controller. Also bounded uncertainty owing to unmodel dynamics of friction is considered. First the system dynamics represented. Then By using multi surface sliding mode control scheme, mismatched uncertainties that appear in state equation of system dynamics are compensated. The simulation results are compared with experimental measured system output. Asymptotic stability of the closed loop system is proven by using Lyapunov method; experimental results show that the proposed controller can deliver good tracking performance and it is robust to uncertainties.