Axial load carrying magnetic bearing for a rotatable body

• US 6,175,174 B1
• Filed: 12/17/1997
• Issued: 01/16/2001
• Est. Priority Date: 12/25/1996
• Status: Expired due to Fees

• Current Assignee: Fuji Xerox Company Limited (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Xerox Company Limited (Fujifilm Holdings Corporation)
• Inventors: Takahashi, Masahiro
• Primary Examiner(s): Enad, Elvin
• Application Number:
  US08/992,005
• Time in Patent Office: 1,126 Days
• Field of Search: 310/67.R, 310/68.R, 310/90.5, 310/90, 384/100, 384/107, 384/120, 384/123, 350/6.8
• US Class Current: 310/90.5
• CPC Class Codes: F16C 17/02 for radial load only
• CPC Class Codes: F16C 17/026 with helical grooves in the bearing surface to generate hydrodynamic pressure, e.g. herringbone grooves
• CPC Class Codes: F16C 32/0402 combined with other supporting means, e.g. hybrid bearings with both magnetic and fluid supporting means
• CPC Class Codes: F16C 33/107 Grooves for generating pressure
• CPC Class Codes: F16C 39/063 Permanent magnets
• CPC Class Codes: H02K 7/086 radially supporting the rotor around a fixed spindle; radially supporting the rotor directly H02K7/09 takes precedence
• CPC Class Codes: H02K 7/09 with magnetic bearings

Abstract

The present invention has achieved an object of obtaining a magnetic bearing in which a drive motor can be made compact and the number of components can be reduced. The present invention is formed by a magnetic bearing used by a drive motor which includes: (a) a stationary shaft which is fixed to a base; (b) a rotating body which is rotatably provided at the outer peripheral portion of the stationary shaft with a predetermined gap therebetween; (c) a rotational permanent magnet which is fixed to the outer peripheral portion of the rotating body; and (d) a drive coil which is disposed on a circuit board of the base and which generates torque between the drive coil and the rotational permanent magnet; the magnetic bearing, comprising: a levitational permanent magnet which is disposed at the axial direction end portion of the rotating body in an annular shape; and a yoke which forms a magnetic circuit between the yoke and the rotational permanent magnet and which faces the outer peripheral portion of the levitational permanent magnet with a predetermined gap therebetween.

Claims

1. A magnetic bearing for a rotatable body provided about a stationary shaft fixed to a base, the magnetic bearing supporting a load applied axially by the rotatable body, comprising:

an annular levitational permanent magnet having an axial thickness, an inner peripheral surface and an outer peripheral surface, and disposed at an axial end portion of said rotatable body; and

a magnetic substance having an axial thickness, an inner peripheral surface, and being non-saturable by magnetic flux density passing through the inner peripheral surface thereof, the magnetic substance being disposed on the base so that the inner peripheral surface thereof faces the outer peripheral surface of said levitational permanent magnet with a predetermined gap therebetween,

wherein each of the inner peripheral surface and the outer peripheral surface of said levitational permanent magnet is polarized to a single pole of opposite polarity, respectively, thereby to develop maximum flux density midway of the axial thickness thereof, and the axial thickness of said magnetic substance is less than the axial thickness of said levitational permanent magnet so that said levitational permanent magnet is attracted into alignment with the axial thickness of said magnetic substance;

and wherein said rotatable body has a rotational permanent magnet fixed to said rotatable body outwardly from said annular levitational magnet, and said magnetic substance forms a magnetic circuit with said rotational permanent magnet.

2. A magnetic bearing according to claim 1, wherein the base has a circuit board mounted thereon, and said magnetic substance is disposed between the base and the circuit board.

3. A magnetic bearing for a rotatable body provided about a stationary shaft fixed to a base, the magnetic bearing supporting a load applied axially by the rotatable body, comprising:

an annular levitational permanent magnet having an axial thickness, inner and outer peripheral surfaces, and upper and lower end surfaces, the levitational permanent magnet being disposed at an axial end portion of said rotatable body; and

a magnetic substance having an axial thickness, an inner peripheral surface, and being non-saturable by magnetic flux density passing through the inner peripheral surface thereof, the magnetic substance being disposed on the base so that the inner peripheral surface thereof faces the outer peripheral surface of said levitational permanent magnet with a predetermined gap therebetween,

wherein each of the upper end surface and the lower end surface of said levitational permanent magnet is polarized to a single pole, of opposite polarity, respectively, thereby to develop maximum flux density at the upper and lower end surfaces thereof, and the axial thickness of said magnetic substance is slightly larger than the axial thickness of said levitational permanent magnet so that said levitational permanent magnet is attracted into alignment with the axial thickness of said magnetic substance,

and wherein said rotatable body has a rotational permanent magnet fixed to said rotatable body outwardly from said annular levitational magnet, and said magnetic substance forms a magnetic circuit with said rotational permanent magnet.

4. A magnetic bearing according to claim 3, wherein the base has a circuit board mounted thereon, and said magnetic substance is disposed between the base and the circuit board.

5. A magnetic bearing for a drive motor including:

a stationary shaft fixed to a base and having an outer peripheral portion;

a rotatable body having an outer peripheral portion and provided about the outer peripheral portion of said stationary shaft with a predetermined gap therebetween;

a rotational permanent magnet fixed to the outer peripheral portion of said rotatable body;

a circuit board provided on the base; and

a drive coil disposed on the circuit board and for generating torque between said drive coil and said rotational permanent magnet;

said magnetic bearing comprising;

an annular levitational permanent magnet having an axial thickness and disposed at an axial end portion of said rotatable body; and

a magnetic substance having an inner peripheral surface and being non-saturable by magnetic flux density passing through the inner peripheral surface thereof and disposed so that the inner peripheral surface thereof faces an outer peripheral portion of said levitational permanent magnet with a predetermined gap therebetween, the magnetic substance forming a magnetic circuit with said rotational permanent magnet;

wherein each of an inner peripheral surface and an outer peripheral surface of said levitational permanent magnet is polarized to a single pole of opposite polarity, respectively, thereby to develop maximum flux density midway of the axial thickness thereof, said magnetic substance has an axial thickness less than an axial thickness of said levitational permanent magnet so that said levitational permanent magnet is attracted into alignment with the axial thickness of said magnetic substance, and said magnetic substance is disposed between the base and the circuit board.

6. A magnetic bearing for a drive motor including:

a stationary shaft fixed to a base and having an outer peripheral portion;

a rotatable body having an outer peripheral portion and provided about the outer peripheral portion of said stationary shaft with a predetermined gap therebetween;

a rotational permanent magnet fixed to the outer peripheral portion of said rotatable body;

a circuit board provided on the base; and

a drive coil disposed on the circuit board and for generating torque between said drive coil and said rotational permanent magnet;

said magnetic bearing comprising;

an annular levitational permanent magnet disposed at an axial end portion of said rotatable body, said annular levitational permanent magnet having upper and lower end surfances; and

a magnetic substance having an inner peripheral surface and being non-saturable by magnetic flux density passing through the inner peripheral surface thereof and disposed so that the inner peripheral surface thereof faces an outer peripheral portion of said levitational permanent magnet with a predetermined gap therebetween, the magnetic substance forming a magnetic circuit with said rotational permanent magnet;

wherein each of the upper and lower end surfaces of said levitational permanent magnet is polarized to a single pole of opposite polarity, respectively, thereby to develop maximum flux density at the upper and lower end surfaces thereof, said magnetic substance has an axial thickness greater than an axial thickness of said levitational permanent magnet so that said levitational permanent magnet is attracted into alignment with the axial thickness of said magnetic substance, and said magnetic substance is disposed between the base and the circuit board.