An Ultraprecision Aerostatic Guideway Controlled by Active Inherent Restrictors

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An active control method for improving the performance of an aerostatic guideway used in an ultraprecision positioning system is proposed. The proposed method employs an Active Inherent Restrictor (AIR) to control pneumatic pressure onthe guideway. The AIR invented by the authors consists of a piezoelectric actuator having a through hole, one end of which is small enough to function as an orificewhen the actuator is embedded in the guideway to be controlled. Six AIRs are incorporated into the table guided by the aerostatic guideway ; four AIRs for compensating the vertical displacement, and two for the horizontal displacement. According to the table displacements detected by sensors, amicro computer changes the length of the piezoelectric actuators for controlling the orifice area of the AIRs, and for compensating the displacements. In both vertical and horizontal directions, it was provedthat the stifness of the guideway can be infinite, and the straightness of motion of the table can beabout 20nm, while the pneumatic hammer did not occur. The effect of the AIR on diamond tuning is also shown ; an aluminum alloy mounted on the table controlled by the AIR was tuned, and the roughness on the machined surface can be improved.