Radial Shear Force Permanent Magnet Bearing System with Zero-Power Axial Control and Passive Radial Damping
The bearing system described was developed starting from the idea of a simple radial magnetic floatation system with axial pin stops, i.e., mechanical contacts, as devised by L.I. Mendelsohn for application in watt hour meters (General Electric Patent, 1953). The Mendelsohn system provides positive radial and, without the stops, negative axial bearing stiffnesses due to magnetic forces acting between cylindrical magnets with axial magnetization. The magnets are mounted to the rotor and stator assemblies in a face-to-face configuration for mutual attraction. A novel stabilization unit has been developed making the Mendelsohn system a non-contacting device. The unit compensates for the axial force instability and additionally provides radial damping forces. Axial stabilization is accomplished by interaction of electric coils with the end faces of two axially spaced, cylindrical permanent magnets fixed to the rotor shaft, while radial damping is provided by interaction of the rotor magnets with a copper disk projecting into the axial flux between the rotor magnets. A high-speed neutron beam chopper cascade (four units) equipped with the new bearing system is running in continuous operation at ILL-Grenoble since 1985. A turbomolecular pump prototype for industrial application was set up in 1987.
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