Modeling and vector control of a planar magnetic levitator

The authors designed and implemented a magnetically levitated stage with large planar motion capability. This positioning system is the first capable of providing all the motions required for photolithography in semiconductor manufacturing with only a single moving part. This planar magnetic levitator employs four novel permanent-magnet linear motors which generate vertical force for suspension against gravity, and horizontal force for drive. In this paper, the authors discuss electromechanical modeling and real-time vector control of such a permanent-magnet levitator. They describe the dynamics in a DQ frame introduced to decouple the forces acting on the stage. A similar transformation to the Blondel-Park transformation is derived for commutation of the phase currents of the levitator. They provide testing results on step responses of the stage. It shows a 5-nm position noise in x and y, which demonstrates the applicability in the next-generation photolithography