Design and implementation of an active rectangular aerostatic thrust bearing stage with electromagnetic actuators

Abstract

The design and implementation of an active rectangular aerostatic thrust bearing stage with electromagnetic actuators are presented. The stage is fundamentally precise and simple since the out-of-plane degree-of-freedoms (DOF) of a thrust air bearing are closed-loop controlled by electromagnetic actuators. The design is one-moving-part with mechanical symmetry, and a commercially available air bearing is rigidly attached to the table. The actuators are four independent coils mounted to the guiding surface of the table with iron cores, which are directly machined on the table. A bench level prototype system is developed and out-of-plane axes decoupled models of the system are derived. A control algorithm synthesized by arbitrarily placing closed-loop poles according to the model with air bearing dynamics neglected is implemented by C programming language running on the DOS platform. The stage is capable of vertical direction precision micro-positioning and guiding 3-DOF plane motions without limiting the working range of plane motions. Positioning accuracy of the stage no longer depends upon design and manufacturing of an air bearing, while passive preload of the stage for a flat film aerostatic thrust bearing is eliminated.