Precise position control of coarse/fine dual stage using pneumatic actuators

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 within 50 nm for 100 mm stroke with the coarse stage using integral controller and it is minimize to 20 nm with the dual stage.