Design Study of Air-Core Coil Winding Topologies for Bearingless Axial-Force/Torque Motors

The Bearingless Axial-Force/Torque Motor is a Lorentz-Force-Type actuator featuring a compact and integrated design using a special permanent magnet excitation system and a slotless air gap winding. The end-windings of the concentric air-core stator coils, shaped in circumferential rotor direction, provide active suspension forces in axial direction. The actuator unifies levitation force and drive torque generation in a single device unit sharing one common winding system. Especially for single-phase motor configurations, the resulting drive topology ensures the tilt stabilization of the rotor. In general, only a few air gap winding structures are suitable for proper polyphase drive torque generation without any negative side effects. The present article treats the drive torque and axial force generation mechanisms for Bearingless Axial-Force/Torque Motors and its influences regarding the appearance of tilt torques. As the radial drive stabilization is realized by multiple axial displaced passive magnetic ring bearings, the radial force generation due to a mismatch of the number of rotor pole pairs and the number of stator coils is also significant for drive stability considerations. As conclusion, numerical simulations for different drive configurations will prove for the validity of the presented analytical design framework.