Design of a Bearingless Segment Motor

Active magnetic bearings and bearingless motors have begun to be used in industry and medical technology. When the rotor is short with respect to its diameter, it is possible to stabilize three degrees of freedom passively by reluctance forces. For this type of motor a new approach to a mechanical design is presented – the Bearingless Segment Motor. This paper deduces a model of the new motor for current injection. Finite element simulations allow the optimisation of force and torque, the reduction of cogging torque and reluctance forces as well as the consideration of the passive radial and passive axial stiffness. However, the force distribution and the mathematical model are nonlinear. Therefore a suitable nonlinear control scheme is presented. The introduction of a prototype and first measurements complete the paper.