Acceleration Feedback in a Stage Having Paired Reluctance Linear Actuator with Hysteresis

The hysteresis force in the reluctance linear actuator limits its applications in the lithographic equipment for nanometer positioning. Acceleration feedback increases the mass of a system as experienced by disturbance force. In this paper, acceleration feedback is designed for the fine stage having paired reluctance linear actuator with hysteresis. The feature of this method lies in that by treating the hysteresis force as a disturbance force, we can design the acceleration feedback loop to reduce the influence of the hysteresis force. The proposed method can improve the process sensitivity at low frequency. Acceleration feedback implementation in digital controller and control for a fine stage mounted on a coarse stage are discussed. Simulation results show that the proposed method is effective in overcoming the hysteresis force and promising in precision stage control.