Saturation effects in high acceleration bearingless motors

Bearingless motors offer contactless levitation and rotation through a hermitically closed process chamber and satisfy the increasing demand for ultra high purity spin processes in chemical, biochemical and semiconductor industry. Most of these processes require a high acceleration capability for minimal process times and a large air gap in order to fit in a mechanical stable chamber wall. The combination of these requirements possibly causes saturation effect issues that may occur depending on the specific drive claw shape. In this paper, saturation effects which reduce the effective torque of the motor are investigated for two commonly known drive claw shapes. The investigations are exemplarily carried out for the Bearingless 2-Level Motor (B2M), since it allows the isolated examination of saturation effects caused by the drive flux due to the axial and circumferential separation of the bearing and drive units. The paper visualizes the flux density distribution and the flux trajectory change at the presence of saturation for the presented drive claw shapes by means of 3D finite element simulations. One drive claw type is found to be the more applicable concept and is subsequently optimized with respect to maximum torque by variation of the drive claw width. Finally, the superior performance of the designed claw is proven by the comparison of simulation results with measurement data of an experimental prototype.