Pressure Sensor Free Adaptive Controller Design for Pneumatic Servo Systems with Time-Varying Mismatched Uncertainties

Abstract

Control of pneumatic servo systems is well-known to be challenge due to highly nonlinearities in the actuator dynamics and compressibility of the media. Most state feedback based strategies for the pneumatic servo systems require full state feedback to stabilize the closed loop system which implies the need for pressure measurements of the cylinder. Many researchers used state observers to complete the controller design without using actual pressure sensor feedback. In this paper, a transformation is suggested to reformulate the dynamic equation so that the pressure sensor feedback can be avoided without deteriorating the closed loop performance. A function approximation technique (FAT) based adaptive multiple-surface sliding controller (AMSSC) is proposed for the closed loop stabilization. The multiple-surface sliding control is a backstepping-like design which is used to cope with the mismatched structure of the uncertainties, while the time-varying nature of the uncertainties is handled by the FAT. The closed-loop system is proved to be uniformly ultimately bounded by using the Lyapunov stability method. Explicit bounds for the error signals are also derived to ensure feasible transient performance. Experimental results demonstrate the effectiveness of the proposed design.