Vertical noncontact positioning H_∞ robust control for magnetically levitated surface motor

To fulfill the stringent requirement, super-precision positioning and ultra cleanness, a surface motor with the integrated chip fabrication equipment is constructed by using permanent magnets and electromagnet coils as primary actuating components. It consists of stator and mover, and the mover is isolated from the stator by the magnetic bearing. The magnetic bearing in the stator is composed of eight air core electromagnet coils, the propulsion in the stator is composed of iron core and electromagnetic coils, and the mover is composed of NdFeB permanent magnets and levitated stage. Based on Lorentz law, some parameters, including permanent magnets dimensions, currents and levitation height, which may affect the stability, are analyzed and optimized. To improve the positioning accuracy in the vertical direction of the magnetic levitation surface motor, a robust controller is proposed using H_∞ mixed sensitivity control theory. The simulation results show that by choosing appropriate weight functions, the controller can ensure the robustness of the closed loop system under the presence of uncertainties, and the H_∞ robust controller is excellent for reducing steady error and increasing response speed.