Test and theory of electrodynamic bearings coupled to active magnetic dampers

Electrodynamic bearings exploit repulsive forces due to eddy currents to produce positive stiffness by passive means. Such a feature would make this type of bearing a viable alternative to active and permanent magnet bearings. Although electrodynamic bearings do not violate Earnshaw’s theorem, the open issue remains the stabilization system that is needed to make the rotating body stable, due to the low rotational speeds. Stabilizing solutions proposed in the literature are partially effective and not totally convincing. This limits real industrial applications. The present paper proposes a combination of electrodynamic and active magnetic bearings. At low speed the active part behaves as a conventional active magnetic bearing, while at high speed it provides damping. The readiness of the proposed solution is demonstrated by experimental results obtained using a dedicate test rig.