Magnetic field and forces analysis of precision linear motor with air-bearings

Abstract

Precision linear motor (PLM) with air-bearings is widely used in the optical lithographic manufacturing of wafers to realize nearly zero friction and to reach submicron position accuracy for the motion of stage. The mover of PLM is floated on the stator by three air-bearings in Z (normal)-direction and two air-bearings on the each side in X (lateral)-direction. This design releases the normal and lateral degree of freedom (DOF). To study the relations of airgap length and magnetic field as well as magnetic forces, the 2-dimension (2-D) model of PLM is established by finite element method (FEM). Based on the 2-D model, the distribution of magnetic field, airgap magnetic flux density and magnetic forces are obtained in the case of no-load and load by using Maxwell's equations and virtual work method. The formulations of magnetic forces are then derived from this method. The variation of airgap length which results from different air pressures and flow speeds can change magnetic flux density, distribution of magnetic field and magnetic forces, and the relationships of current, magnetic flux density and magnetic forces are obtained in the research.