High Steady-State Accuracy Pneumatic Servo Positioning System with PVA/PV Control and Friction Compensation

Pneumatic servo actuators have the benefits of lowcost, cleanliness and a high power-to-weight ratio. However, their relatively poor accuracy prevents them from competing with electro-mechanical systems when higher accuracy is needed. The cause of the steady-state error for a pneumatic servo system with an open-center servo valve is investigated. Full nonlinear and linearized plant models are presented. An effective friction compensation method is introduced which can be added to any control strategy. When combined with a novel PVA/PV control approach, a steady-state accuracy of ±0.01mm has been verified in experiments. This is a tenfold improvement over previously reported experimental results for such systems. This performance is achieved for both vertical and horizontal movements with payloads ranging from 0.3 to 11.3 kg, without re-tuning the controller.