Observer-based adaptive sliding mode control for pneumatic servo system

In this paper, an extended state observer (ESO) being incorporated with the adaptive sliding mode control theory is proposed to deal with a nonlinear pneumatic servo system characterized with input dead-zone, unknown system function, and external disturbance. The ESO is used to estimate system state variables of the unknown nonlinear system; the adaptive law is employed to compensate for dead-zone system behavior. Positioning experiments based on the derived control strategy were performed. As one example of positioning results, the positioning accuracy with sub-micrometers range was verified for both forward and backward actuations with step commands of 3 mm. The control scheme provided in this paper that can significantly improve the positioning performance of a traditional pneumatic servo system is demonstrated.