Adaptive model-based feedforward to compensate Lorentz force variation of voice coil motor for the fine stage of lithographic equipment

Abstract

This paper presents an adaptive model-based feedforward combined with PID feedback controller based on model identification to compensate the variation of the Lorentz force. In the previous work, we applied an analytical model to calculate the magnetic flux density and Lorentz force for the rectangular Voice Coil Motor (VCM) used in ultra-precision motion stage. This analytical model indicates the Lorentz force will change when coil of the VCM moves in the permanent magnet air gap, and the simulation and experiment results verify the effectiveness of this phenomenon. In order to improve the tracking and positioning performance of the fine stage, an adaptive controller is applied to the VCM to compensate the Lorentz force variation, and the step experiment verify it is effective to decrease the positioning error for the fine stage.