Magnetic bearing device

A magnetic bearing device comprising:

• a stator;
• a rotor having a rotational axis and rotatable with respect to and in contact-free relation with the stator;
• an annular magnet secured to the stator, coaxial with the rotational axis of the rotor, and magnetized in an axial direction;
• magnetic path forming means including a stator side yoke secured to the stator and magnetically coupled to the annular magnet, at least three control poles magnetically coupled to the stator side yoke and radially extending with respect to the rotational axis of the rotor in a uniformly separated relationship to one another in a circumferential direction, and a rotor side yoke secured to the rotor to face the stator side yoke, said rotor side yoke having an outer cylindrical portion disposed coaxial with the rotational axis of the rotor on an outer side of the magnet facing the magnet, an inner cylindrical portion located on an inner side of the magnet, coaxial with the outer cylindrical portion, and an annular portion coupling the outer and inner cylindrical portions together and coaxial with the rotational axis of the rotor, for forming a first magnetic path for the passage of a magnetic flux from the magnet through the stator side yoke and rotor side yoke to control an axial position of the rotor, and for forming a control magnetic path passing through the stator side yoke, rotor side yoke and one of the control poles, overlapping part of the first magnetic path and extending substantially radially with respect to the rotational axis of the rotor;
• control coils, wound around the control poles, for generating a control flux that flows through the control magnetic path, to control the flux flowing through the first magnetic path;
• detecting means for detecting a radial position of the rotor relative to the stator;
• and
• control means for energizing the control coils, in accordance with the output of the detecting means, to thereby control the radial position of the rotor with respect to the stator.