Speed and Stability Limits for High-Speed Bearingless Disc Drives

Increasing material costs and emerging applications have steered research trends towards compacter and therefore faster drives. The arising challenges of miniaturization have made contactless magnetic levitation increasingly attractive, which offer practically zero maintenance necessity as well. Still, magnetic levitation derives in higher overall complexity so efforts have been made to simplify bearing schemes. In this work, so called bearingless slice motors are studied, which offer a compact construction and degrees of freedom which are passively stable. The speed potential, the stability limits and the natural resonances of two high speed topologies is investigated. Various airgap considerations are evaluated, contemplating different application scenarios and the limitations of actual manufacturing techniques. This work serves therefore as a guideline for bearingless disc drive pre-sizing and tracing the limits for the absolute values of their passive stability.