Integrated passive magnetic bearing system and spindle magnet for use in an axial magnet spindle motor

• US 5,598,048 A
• Filed: 08/12/1994
• Issued: 01/28/1997
• Est. Priority Date: 08/12/1994
• Status: Expired due to Term

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology plc (Seagate Technology Holdings Plc)
• Inventors: Oveyssi, Kamran, Dunfield, John C.
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): Mullins, Burton S.
• Application Number:
  US08/289,949
• Time in Patent Office: 900 Days
• Field of Search: 310/67 R, 310/90, 310/90.5, 310/156, 360/98.07, 360/99.04, 360/99.08
• US Class Current: 310/90.5
• CPC Class Codes: F16C 17/08 for supporting the end face of a shaft or other member, e.g. footstep bearings
• CPC Class Codes: F16C 2370/12 Hard disk drives or the like
• CPC Class Codes: F16C 25/045 with magnetic means to preload the bearing
• CPC Class Codes: F16C 32/0412 for radial load mainly
• CPC Class Codes: F16C 32/0425 for radial load mainly
• CPC Class Codes: F16C 39/063 Permanent magnets
• CPC Class Codes: G11B 19/2009 Turntables, hubs and motors for disk drives; Mounting of motors in the drive means for clamping of disk to turntable G11B17/022 and subgroups
• CPC Class Codes: H02K 5/167 using sliding-contact or spherical cap bearings
• CPC Class Codes: H02K 7/09 with magnetic bearings

Abstract

An apparatus for rotatably journaling a rotor of a flat spindle motor about a stator comprising a spindle magnet disc disposed on the rotor assembly of the flat spindle motor and journaled about the spindle motor shaft having a disc shaped first magnetized region with an outer radius r comprised of a plurality of axial aligned poles, a disc shaped second region having an outer radius r2 (where r2>r) comprised of a single pole, and a disc shaped non-magnetized spacer region disposed there between. The integrated spindle magnet disc is disposed on the inside surface of a rotor over complementary axially aligned electromagnet poles which are disposed on the base of the stator assembly. A like aligned single pole is fixedly attached to the stator and disposed in opposition to the second magnetized region having like aligned pole of the integrated spindle permanent magnet. The single poles are disposed on both the rotor and stator in attraction mode with opposite poles facing one another, or in opposition mode with a complete or partial offset thereby forming a stable magnetic bearing for maintaining rotor displacement about the stator in conjunction with a conventional pivot. The stator base assembly is extended toward the first magnetized region to provide axial pre-load for the motor. The electromagnet poles further include a steel bobbin for increased flux density and added axial stiffness. Finally, eddy current generation means are disposed between the stator base and the like aligned single pole for improved dampening characteristics.

Claims

1. In a reduced height disc drive having a flat spindle motor assembly comprised of a spindle permanent magnet held in opposition to an electromagnet assembly attached to a stator, an apparatus for journaling a rotor having a hub shaft about said stator of said flat spindle motor comprising:

a stator comprising a base portion and a stator well, said stator well comprising a raised centrally disposed cylindrical portion disposed on said base portion, said stator well for receiving said hub shaft;

a pivot, said pivot for pivotally displacing said rotor about said stator, said pivot for engaging said hub shaft at a base portion of said stator well;

a first annular disc, said disc comprising an axially aligned magnetic pole, said disc radially extending from said stator;

a spindle permanent magnet having a first and second end and non-magnetized region disposed there between, said first end comprising a plurality of magnetic poles disposed on said rotor in opposition to said spindle motor electromagnet assembly, said second end comprised of a like axially aligned magnetic pole disposed on said rotor, opposing and offset to the inside of said axially aligned magnetic pole on said first annular disc; and

bearing means disposed between said hub shaft and said stator well, said bearing means for providing additional radial stiffness to said flat spindle motor assembly.

2. The apparatus of claim 1 wherein said first annular disc is disposed 0.25 mm beneath said axially magnetized region.

3. The apparatus of claim 1 wherein said pivot is an axial hydrodynamic bearing.

4. The apparatus of claim 1 wherein said pivot is a conventional ball bearing.

5. The apparatus of claim 1 wherein said pivot is a ruby ball bearing.

6. The apparatus of claim 1 wherein said pivot is a ceramic ball bearing.

7. The apparatus of claim 1 wherein said bearing means is a radial hydrodynamic bearing.

8. The apparatus of claim 1 wherein said bearing means includes a pair of radial hydrodynamic bearings, a first of said pair of hydrodynamic bearings disposed between an inner wall of said stator well and said hub shaft, a second of said pair of radial hydrodynamic bearing disposed between an outer wall of said stator well and an inner shoulder of said rotor, said pair of radial hydrodynamic bearings for increasing the radial stiffness of the said flat spindle motor.

9. In a reduced height disc drive having a flat spindle motor assembly comprised of a spindle permanent magnet held in opposition to an electromagnet assembly, an apparatus for journaling a rotor about a stator in a flat spindle motor of a disc drive comprising:

a shaft centrally disposed on said rotor;

a reservoir in said stator for receiving said shaft;

bearing means comprising means for maintaining radial stiffness of said rotor with respect to said stator while said bearing means is operational;

alignment means for centering said rotor about said stator during non-operational periods, said alignment means comprising a magnetic bearing having one pole integral to said spindle permanent magnet; and

pre-load means for engaging said rotor to said stator comprising;

a first annular disc, said disc comprising an axially aligned magnetic pole, said disc radially extending from said stator; and

a spindle permanent magnet having a first and second end and non-magnetized region disposed therebetween, said first end comprising a plurality of magnetic poles disposed on said rotor in opposition to said spindle motor electromagnet assembly, said second end comprised of a like axially aligned magnetic pole disposed on said rotor and opposing said axially aligned magnetic pole on said first annular disc.

10. The apparatus of claim 9 wherein said bearing means is a hydrodynamic bearing.

11. The apparatus of claim 9 wherein said pre-load means comprises an annular base extension, said annular base extension integral to said stator beginning at an exterior wall of said stator reservoir and extending toward and at a height equal to said electromagnet assembly and directly beneath said first end of said spindle permanent magnet, whereby said rotor is pre-loaded due to the attractive forces developed between said annular base extension and said first end of said spindle permanent magnet.

12. The apparatus of claim 9 wherein said pre-load means comprises said electromagnet assembly having a coil wrapped about a steel bobbin, whereby said rotor is pre-loaded due to the attractive forces developed between said steel bobbin and said first end of said spindle permanent magnet.

13. The apparatus of claim 9 further comprising dampening means for dampening wobble of said rotor about said stator due to shock.

14. The apparatus of claim 13 wherein said dampening means comprises a pair of copper annular rings, said axially aligned magnet pole disposed therebetween, whereby currents are induced in said copper rings in opposition to said shocks thereby dampening their effect.

15. The apparatus of claim 13 wherein said dampening means comprises a L-shaped copper flange disposed in a recess in said stator beneath said first annular disc, said L-shaped copper flange having a head and extended tail portion, said tail portion extending upward along an outside edge of said first annular disc and said head portion disposed beneath said annular disc flush with said stator toward said electromagnet assembly.

16. The apparatus of claim 9 further comprising contamination control means for maintaining the integrity of said flat spindle motor, said contamination control means further comprising a ferro-fluid seal having a retro fluid disposed in a joint formed between said rotor and said stator whereby said axially aligned magnetic pole attracts said ferro fluid to said joint and maintains said fluid in said joint to restrict the flow of contaminants out of said flat spindle motor.