Patent ID: 6259179
Filing Date: 2001-07-10
Classification: F16C

Abstract:
A magnetic bearing system comprising;a rotor shaft;a stationary electromagnetic pole;a displacement sensor for detecting the position of said rotor shaft with respect to said electromagnetic pole;a permanent magnet disposed in a portion of a magnetic member forming a magnetic circuit between said rotor shaft and said electromagnetic pole; anda controller which supplies a control current to an excitation coil of said electromagnetic pole in accordance with an output from said displacement sensor, to thereby perform a position control of said rotor shaft,said controller comprising;a difference operation circuit which operates a difference signal between an input signal for providing a target position of said rotor shaft and a displacement sensor signal output from said displacement sensor, and outputs said difference signal;a control circuit generating a control signal on the basis of said difference signal, said control signal corresponding to the control current to be supplied to said excitation coil of said electromagnetic pole so as to retain said rotor shaft in the target position;an integration circuit integrating said control current passing through said excitation coil to generate a D.C. component signal of said control signal; anda memory retaining and outputting a balanced position signal obtained by averaging said displacement sensor signals when no load is subject to said rotor shaft,wherein an initial position instruction value providing an initial target position of said rotor shaft is set to a position where a balance exists between an attraction force developed in said permanent magnet and a static force which acts on said rotor shaft when no load is imposed on said rotor shaft, andwherein said difference operation circuit outputs a first difference signal by providing as said input signal, said initial position instruction value,said difference operation circuit outputs a second difference signal by inputting said D.C. component of said control current obtained on the basis of said first difference signal to said difference operation circuit and providing as said input signal, a correction value which subtracts said D.C. component from said initial position instruction value, whereby said rotor shaft is position-controlled on the basis of said second difference signal,said memory retains said balanced position signal of said rotary shaft at the time of the position control on the basis of said second difference signal, and furtherafter the position control on the basis of said second difference signal, said difference operation circuit outputs a third difference signal by providing as said input signal, said balanced position signal, whereby said rotor shaft is position-controlled on the basis of said third difference signal.