Development of a novel magnetically levitated surface motor

To realize high speed and high precision positioning for photolithography, a novel scheme of six degree of freedom magnetically levitated precision positioning stage is designed, where 8 air core solenoid coils and 32 permanent magnets are employed as the stator and mover respectively, and the levitation and linear drive parts of the stage are separated, thus the coupling between them is minimized and the nonlinearity due to the material ferromagnetism is avoided. Based on Lorentz law, some parameters, including permanent magnets length, currents and levitation height are analyzed to determine the equilibrium position. A dynamical model in levitation direction is established and an H infinity robust control algorithm based on the mixed sensitivity control is applied. Lastly, the dynamic response is simulated. The results show that the stage enable to work stably under the conditions with 2A current and 0.5mm levitation height. This validates the design of the system and demonstrates the feasibility of the developed controller.