Bearingless segment motor with Halbach magnet

Abstract

Today magnetically levitated rotors are mainly used in applications where wearless operation and high life cycle are of importance (e.g. in the pharmaceutical, biomedical, chemical and semiconductor industry). The bearingless slice motor features a very compact design because three degrees of freedom (one translational and two rotatory) are passively stabilized by reluctance forces. Therefore, only two translational degrees of freedom remain to be actively controlled. This paper introduces a new bearingless segment motor (a subtype of the bearingless slice motor) featuring a Halbach magnet ring mounted on the rotor. Thus, no back iron is needed on the rotor and therefore the overall weight of the permanent magnet excited disc-shaped rotor is reduced to a minimum. The bearing forces which can be created by one optimized stator segment are calculated analytically. These results allow conclusions for the total force locus. A prototype is built and measurements verify the results of the analytic considerations.