Active assist device for simultaneous reduction of heat and vibration in precision scanning stages

Scanning stages are used for precise positioning in a variety of advanced manufacturing processes, and must deliver high accelerations/decelerations at motion reversals to achieve high throughput. The resulting inertial forces cause excessive motor heating and residual vibration of the stage, both of which must be mitigated to preserve positioning accuracy. A novel scanning stage, having a permanent magnet based device that actively provides assist forces to the motor to simultaneously reduce motor heating and residual vibration, is presented. The active assist device is optimally designed to be versatile, allowing it to provide adequate assist for scan trajectories involving the widest range of scan strokes/positions. A basis-spline-based method is proposed for optimal control of the device, to maximize the assist it provides for scan trajectories with varying scan strokes/positions. Experiments conducted with a prototype stage involving scanning trajectories commonly employed in silicon wafer processing are used to demonstrate up to 60% and 34% reductions in heat and vibration-induced errors, respectively, when compared to cases without the proposed active assist device.