Low profile fluid dynamic bearing
View Patent ↗The design comprises a shaft and sleeve supported for relative rotation by a journal type fluid dynamic bearing utilizing grooves on one of the shaft or sleeve surfaces. A grooved pattern of a design similar to that usually found on a thrust plate is defined on an axial end surface of the shaft or the counterplate facing the axial end of the shaft, so that thrust is created to maintain separation of the end of the shaft and the facing thrust plate during relative rotation. In one embodiment, to establish and maintain the gap between the shaft end and the facing counterplate, the journal bearing has an asymmetry to pump toward the shaft end having the bearing. In a further refinement, to maintain the shaft and gap within an optimum spacing, a magnet is mounted to provide an axially directed magnetic force on the shaft which works against the axial force created by shaft end thrust bearing. To prevent separation of the shaft and sleeve or hub, the hub which is integrated with a rotating shaft, further incorporates a shoulder which extends axially beneath a cooperating shoulder on the sleeve surrounding the shaft to prevent any more than a limited axially displacement of the hub and shaft relative to the sleeve.
1. A fluid dynamic bearing comprising a shaft supporting a hub at one end, the shaft being adapted to rotate within a sleeve supported from a base, the base including a counterplate facing an end of the shaft distal from the one end on which the hub is mounted, the shaft being supported for rotation within the sleeve by a biased journal bearing comprising fluid in the gap between the shaft and the sleeve, one of the distal end of the shaft or the surface of the counterplate which faces the end face of the shaft having a grooved pattern thereon to maintain fluid in the gap between the shaft and the counterplate, wherein the distal end of the shaft has an outer radial surface at a first radial distance from the center of the shaft and the grooved pattern is disposed within the first radial distance thereby supporting the shaft for rotation relative to the counterplate and sleeve, wherein at least one of the shaft or a center of the counterplate comprises a raised island defining a small touchdown surface for the bottom surface of the shaft, thereby reducing wear on the surfaces of the fluid dynamic bearing defined by the bottom surface of the shaft and the facing surface of the counterplate.
2. A fluid dynamic bearing motor as claimed in claim 1 further comprising a first magnet supported on the hub, the magnet being axially offset from the spindle and more distant from the base supporting the fluid dynamic bearing to establish an electro-magnetic bias working against separation of the base of the shaft from the counterplate.
3. A fluid dynamic bearing as claimed in claim 1 , wherein the hub includes a first shoulder which extends axially beneath a cooperating second shoulder included on an outer surface of the sleeve surrounding the shaft, the first and second shoulders cooperating to limit axial displacement of the hub and the shaft relative to the sleeve.
4. A bearing as claimed in claim 3 further comprising a biasing magnet supported on an end of the sleeve distal from the base across a relatively narrow gap from the hub, the biasing magnet and hub cooperating to limit the gap between the shaft end face and the counterplate.
5. A bearing as claimed in claim 4 wherein the shaft comprises phosphor bronze, and the sleeve comprises stainless steel.
6. A fluid dynamic bearing as claimed in claim 1 further comprising a biasing magnet supported on a shoulder extending axially from the base and supporting on a outer surface thereof the stator of the motor in alignment with the motor magnet supported on the hub, the biasing magnet being located across a gap from a shoulder piece supported from the hub, the biasing magnet and shoulder cooperating to prevent undue displacement of the shaft end face and hub relative to the base.
7. A fluid dynamic bearing as claimed in claim 1 wherein the center region which comprises the raised island faces an ungrooved region in a center of the grooved bottom surface of one of the shaft or counterplate center.
8. A fluid dynamic bearing as claimed in claim 1 wherein the journal bearing is biased to create asymmetric fluid pressure toward the end face of the shaft, thereby supplying fluid to the thrust bearing between the shaft end face and the sleeve.
9. A fluid dynamic bearing as claimed in claim 8 wherein one of the end face of the shaft and the counterplate is coated with a diamond-like coating.
10. A fluid dynamic bearing as claimed in claim 6 wherein one of the counterplate or shaft comprises a ceramic material.
11. A spindle motor for use in a disc drive comprising a shaft rotating in a bore defined by an inner surface of a sleeve, the shaft being supported for rotation by a biased fluid dynamic journal bearing comprising fluid in a gap between the shaft and the sleeve, the shaft supporting a hub at one end, the shaft being adapted to rotate within the sleeve supported from a base, the base including a counterplate facing an end of the shaft distal from the one end on which the hub is mounted, one of the distal end of the shaft or the surface of the counterplate which faces the end face of the shaft having a grooved pattern thereon to maintain fluid in the gap between the shaft and the counterplate, wherein the distal end of the shaft has an outer radial surface at a first radial distance from the center of the shaft and the grooved pattern is disposed within the first radial distance, thereby supporting the shaft for rotation relative to the counterplate and sleeve, wherein at least one of the shaft or a center of the counterplate comprises a raised island defining a small touchdown surface for the bottom surface of the shaft, thereby reducing wear on the, surfaces of the fluid dynamic bearing defined by the bottom surface of the shaft and the facing surface of the counterplate.
12. A spindle motor as claimed in claim 11 further comprising a magnet supported on the hub, the magnet being axially offset from the spindle, and more distant from the base supporting the fluid dynamic bearing to establish an electromagnetic bias affecting the gap between the base of the shaft and the counterplate.
13. A spindle motor as claimed in claim 11 , wherein the hub includes a first shoulder which extends axially beneath a cooperating second shoulder included on an outer surface of the sleeve surrounding the shaft, the first and second shoulders cooperating to limit axial displacement of the hub and the shaft relative to the sleeve.
14. A spindle motor as claimed in claim 11 further comprising a bias magnet supported on an end of the sleeve across a relatively narrow gap from the hub, the biasing magnet and hub cooperating to affect the gap between the end face of the shaft and the counterplate.
15. A bearing as claimed in claim 11 wherein the shaft comprises phosphor bronze, and the sleeve comprises stainless steel.
16. A fluid dynamic bearing comprising a shaft supporting a hub at one end, the shaft being adapted to rotate within a sleeve supported from a base, the base including a counterplate facing an end of the shaft distal from the one end on which the hub is mounted, the shaft being supported for rotation within the sleeve by fluid in the gap between the shaft and the sleeve, and a biased means associated with the distal end of the shaft and the surface of the counterplate for supporting the shaft for rotation relative to the counterplate and sleeve, wherein the distal end of the shaft has an outer radial surface at a first radial distance from the center of the shaft and the biased means is disposed within the first radial distance and wherein at least one of the shaft or a center of the counterplate comprises a raised island defining a small touchdown surface for the bottom surface of the shaft, thereby reducing wear on the, surfaces of the fluid dynamic bearing defined by the bottom surface of the shaft and the facing surface of the counterplate.
17. A fluid dynamic bearing as claimed in claim 16 , wherein said supporting means further comprising means for magnetically biasing the shaft within the sleeve to maintain the gap between the end face of the shaft and the counterplate.
18. A fluid dynamic bearing is claimed in claim 16 further comprising means associated with the sleeve and the hub for preventing loss of alignment of the draft and the sleeve under shock.
19. A fluid dynamic bearing comprising a shaft supporting a hub at one end, the shaft being adapted to rotate within a sleeve supported from a base, the base including a counterplate facing an end of the shaft distal from the one end on which the hub is mounted, the shaft being supported for rotation within the sleeve by a biased journal bearing comprising fluid in the gap between the shaft and the sleeve, one of the distal end of the shaft or the surface of the counterplate which faces the end face of the shaft having a grooved pattern thereon to maintain fluid in the gap between the shaft and the counterplate, thereby supporting the shaft for rotation relative to the counterplate and sleeve, wherein the journal bearing is biased to create asymmetric fluid pressure toward the end face of the shaft, thereby producing pressure on an end of the shaft to lift the shaft independently of the thrust gap.
20. A fluid dynamic bearing motor as claimed in claim 19 further comprising a first magnet supported on the hub, the magnet being axially offset from the spindle and more distant from the base supporting the fluid dynamic bearing to establish an electro-magnetic bias working against separation of the base of the shaft from the counterplate.
21. A fluid dynamic bearing as claimed in claim 19 , wherein the hub includes a first shoulder which extends axially beneath a cooperating second shoulder included on an outer surface of the sleeve surrounding the shaft, the first and second shoulders cooperating to limit axial displacement of the hub and the shaft relative to the sleeve.
22. A bearing as claimed in claim 19 further comprising a biasing magnet supported on an end of the sleeve distal from the base across a relatively narrow gap from the hub, the biasing magnet and hub cooperating to limit the gap between the shaft end face and the counterplate.
23. A bearing as claimed in claim 19 wherein the shaft comprises phosphor bronze, and the sleeve comprises stainless steel.
24. A fluid dynamic bearing as claimed in claim 19 further comprising a biasing magnet supported on a shoulder extending axially from the base and supporting on a outer surface thereof the stator of the motor is alignment with the motor magnet supported on the hub, the biasing magnet and shoulder cooperating to prevent undue displacement of the shaft end face and hub relative to the base.
25. A fluid dynamic bearing as claimed in claim 19 wherein at least one of the shaft or a center of the counterplate comprises a raised island defining a small touchdown surface for the bottom surface of the shaft, thereby reducing wear on the surfaces of the fluid dynamic bearing defined by the bottom surface of the shaft and the facing surface of the counterplate.
26. A fluid dynamic bearing as claimed in claim 19 wherein the center region which comprises the raised island faces an ungrooved region in a center of the grooved bottom surface of one of the shaft or counterplate center.
27. A fluid dynamic bearing as claimed in claim 19 wherein one of the end face of the shaft and the counterplate is coated with a diamond-like coating.
28. A fluid dynamic bearing as claimed in claim 19 wherein one of the counterplate or shaft comprises a ceramic material.