Active aerostatic bearings for ultraprecision applications

Abstract

For ultraprecision applications, two types of active control restrictors for aerostatic bearings are evaluated. The first restrictor is called an aerostatically controlled restrictor (ACR), a bearing-pressure-feedback type. The change in the pressure on the bearing surface directly controls the restriction gap, and the stiffness of the aerostatic bearing with the ACR can be infinite. The second restrictor is called an active inherent restrictor (AIR), a bearing-gap-feedback type. The change in the air-gap on the bearing surface is detected by an electric sensor, and then an electric actuator controls the restriction gap. By using the AIR, infinite bearing stiffness and nanometer-order of rotational accuracy of the spindle can be realized. Positioning with subnanometer order of resolution can also be executed by an aerostatic guideway with the AIR.