Stator design of a multi-consequent-pole bearingless motor with toroidal winding

Multi-consequent-pole bearingless motors have been developed for low rotational speed and swinging stages used in monitoring system and vacuum process chambers. The motor has flat shape and two degrees of freedom are actively controlled in the radial x-y directions. The suspension windings have a novel structure of a toroidal coil wound around the stator yoke. The structure realizes a short axial length with compact coil end-windings. In this paper, the toroidal winding design is compared with conventional distributed winding design. The design process indicates a consideration of magnetic saturation in the stator yoke with three dimensional finite element analysis. A special design consideration for the stator yoke is required because of significant leakage flux caused by the toroidal winding. It is shown that a compact axial length is realized. It is also shown that a wide cross sectional area is required in the stator yoke compared with conventional distributed windings.