Principle and Experiments of an All-passive-type Magnetic Bearing System

It has been proved by a toy, magnetically levitated spinning top, that magnetic levitation without active control is possible if the body to be levitated has rotational speed. The authors were also trying developing the titled system. AI the first experiments of the system, we could not levitate the rotor due to excessive rotational drag force of eddy currents in the null-flux coil system. That is to say the rotational velocity which was required for levitation could not been attained using air turbines. By stacking many sheets on which many thin coils were printed, an improved null-flux coil system was made and was used in the second experiments. In the second experiments, 6,000 r.p.m. of the rotational speed was attained, and we could levitate the rotor (about 7.5 kg) within ± 0.5mm radial and axial air gaps of the touch-down bearings in Feb. of 1995. In this paper, mainly structural/dynamical fea tures, experimental data and its analysis are given.