Fuzzy control for a pneumatic positioning system

Due to the drawbacks of compressibility of air, nonlinear friction force existing on contact surfaces, and nonlinear dead-zone characteristic of servo valve, the pneumatic positioning system usually cannot achieve high precision positioning accuracy. In order to improve the positioning performance of pneumatic positioning systems, the fuzzy control with friction compensation and the combined fuzzy PD and fuzzy PI control schemes are applied to control a nonlinear pneumatic positioning system characterized with friction, unknown system model, and external disturbance. Positioning experiments based on both control strategies were performed to show and validate the positioning control performance. As two experimental examples of positioning results in a total of 30 experimental trials for the stepwise input positioning controls, the positioning accuracy with less than 30nm was verified for both forward and backward actuations with step commands. Hence, the control performance of control schemes provided in this paper that could significantly improve the positioning performance of a traditional pneumatic positioning system is demonstrated.