Multiple-surface sliding controller design for pneumatic servo systems

A multiple-surface sliding controller (MSSC) is proposed for pneumatic servo systems with variable payload and mismatched uncertainties. The system is firstly modeled by a non-autonomous dynamic equation with consideration of the valve dynamics. Various nonlinearities and bounded uncertainties are then lumped into two bounded functions to represent the system equation into a formal form for the design of the MSSC so that the mismatched uncertainties can be properly compensated. The closed loop system is proved to have asymptotically stable performance by using the Lyapunov stability theory. Experimental results show that the proposed algorithm is able to give good performance regardless of the uncertainties and time-varying payload.