Development of coarse/fine dual stage using pneumatically driven bellows actuator and cylinder with air bearings

In this paper, a coarse/fine dual positioning stage for single degree of freedom using pneumatic actuators is developed. The coarse movement utilizes a pneumatic cylinder with air bearings. The fine movement utilizes an actuator driven by pneumatic bellows. A high-performance pneumatic servo valve, we have developed, having high dynamics up to 300 Hz is used to control the coarse stage. The fine stage is controlled with a nozzle-flapper type servo valve. The fine stage is mounted on the coarse stage. As the proposed coarse/fine dual stage is pneumatically driven, the stage has advantages of low heat generation and non-magnetic those are suitable for ultra precise positioning. The control method of the dual stage is proposed. The experimental results demonstrated that the steady state error is less than 5 μm for 100 mm stroke with the coarse stage and it is minimize to 20 nm with the fine stage.