U.S. patent application number 09/314486 was filed with the patent office on 2001-12-20 for fluid bearing seal and support structure.
Invention is credited to LEE, CHEN-HSIUNG, NAGARAJ, HOLAVANAHALLY SESHACHAR, SCHIRLE, NEAL BERTRAM.
Application Number | 20010053042 09/314486 |
Document ID | / |
Family ID | 25533600 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010053042 |
Kind Code |
A1 |
LEE, CHEN-HSIUNG ; et
al. |
December 20, 2001 |
FLUID BEARING SEAL AND SUPPORT STRUCTURE
Abstract
A bearing structure for a spindle motor is disclosed. The
bearing structure provides a fluid bearing seal and support
structure that may simultaneously addresses the problems of
preventing oil leakage, of maintaining the bearing integrity under
shock, of reducing oil evaporation and of minimizing distortion of
the active bearing surface. The bearing structure includes a thrust
plate coupled to a shaft and a bearing plate and load plate coupled
to a sleeve, wherein the load plate urges the bearing plate towards
the thrust plate, and wherein an adhesive is interposed between the
load plate and the thrust plate. The adhesive may be an UV epoxy.
The sleeve is operatively coupled to a stator, and the stator
rotates the sleeve upon receiving a drive signal. The bearing
further includes a diffusion barrier disposed between the sleeve
and the stator. A second diffusion barrier is disposed between the
load plate and the shaft. The bearing structure may also include an
O-ring disposed above the bearing plate for sealing a gap between
the bearing plate and the sleeve.
Inventors: |
LEE, CHEN-HSIUNG; (SAN JOSE,
CA) ; NAGARAJ, HOLAVANAHALLY SESHACHAR; (MORGAN HILL,
CA) ; SCHIRLE, NEAL BERTRAM; (MORGAN HILL,
CA) |
Correspondence
Address: |
DAVID W. LYNCH
ALTERA LAW GROUP, LLC
6500 CITY WEST PARKWAY, SUITE 100
MINNEAPOLIS
MN
55344-7701
US
|
Family ID: |
25533600 |
Appl. No.: |
09/314486 |
Filed: |
May 18, 1999 |
Current U.S.
Class: |
360/99.08 ;
G9B/19.029 |
Current CPC
Class: |
H02K 5/124 20130101;
F16C 33/74 20130101; G11B 25/043 20130101; G11B 19/2018 20130101;
F16C 33/107 20130101; F16C 2370/12 20130101; H02K 5/1677
20130101 |
Class at
Publication: |
360/99.08 |
International
Class: |
G11B 017/02 |
Claims
What is claimed is:
1. A dynamic fluid bearing for a spindle motor having a thrust
plate secured to a shaft and a bearing plate and load plate secured
to a sleeve, wherein the load plate urges the bearing plate towards
the thrust plate, and wherein an adhesive is interposed between the
load plate and the thrust plate.
2. The dynamic fluid bearing of claim 1 wherein the adhesive is an
UV epoxy.
3. The dynamic fluid bearing of claim 1 further comprising a
diffusion barrier disposed between the load plate and the
shaft.
4. The dynamic fluid bearing of claim 1 further comprising a
diffusion barrier disposed between the sleeve and the shaft.
5. The dynamic fluid bearing of claim 1 wherein the sleeve is
operatively coupled to a stator, the stator rotating the sleeve
upon receiving a drive signal, the bearing further comprising a
diffusion barrier disposed between the sleeve and the stator.
6. The dynamic fluid bearing of claim 1 further comprising a
diffusion barrier disposed between the load plate and the shaft,
the sleeve being operatively coupled to a stator and the stator
rotating the sleeve upon receiving a drive signal, the bearing
further comprising a diffusion barrier disposed between the sleeve
and the stator.
7. The dynamic fluid bearing of claim 1 wherein the adhesive
maintains integrity between the load plate and the bearing plate
when a shock condition occurs.
8. The dynamic fluid bearing of claim 1 wherein the adhesive
maintains integrity between the load plate and the bearing plate by
absorbing tolerances of the load plate and the bearing plate when
the shock condition occurs.
9. The dynamic fluid bearing of claim 1 further comprising a
diffusion barrier disposed between the load plate and the shaft,
the diffusion barrier preventing bearing lubricant from leaking
between the load plate and the shaft.
10. The dynamic fluid bearing of claim 1 further comprising a
diffusion barrier disposed between the sleeve and the shaft, the
diffusion barrier preventing bearing lubricant from leaking between
the sleeve and the shaft.
11. The dynamic fluid bearing of claim 1 wherein the sleeve is
operatively coupled to a stator, the stator rotating the sleeve
upon receiving a drive signal, the bearing further comprising a
diffusion barrier disposed between the sleeve and the stator, the
diffusion barrier preventing bearing lubricant from leaking between
the sleeve and the stator.
12. The dynamic fluid bearing of claim 1 further comprising an
O-ring disposed above the bearing plate for sealing a gap between
the bearing plate and the sleeve.
13. A spindle motor, comprising: a shaft; a sleeve having an inner
periphery and an outer periphery, the sleeve defining a disk hub on
the outer periphery; a shaft rotatably supporting the sleeve; a
stator for rotating the sleeve; and a dynamic fluid bearing
disposed between the sleeve and the shaft, the dynamic fluid
bearing further comprising a thrust plate coupled to the shaft, and
a bearing plate and load plate coupled to the sleeve, wherein the
load plate urges the bearing plate towards the thrust plate, and
wherein an adhesive is interposed between the load plate and the
thrust plate to maintain integrity between the load plate and the
bearing plate when a shock condition occurs to the spindle
motor.
14. The spindle motor of claim 13 wherein the adhesive is an UV
epoxy.
15. The spindle motor of claim 13 further comprising a diffusion
barrier disposed between the load plate and the shaft.
16. The spindle motor of claim 15 further comprising a diffusion
barrier disposed between the sleeve and the shaft.
17. The spindle motor of claim 13 further comprising a diffusion
barrier disposed between the sleeve and the shaft.
18. The spindle motor of claim 13 wherein the adhesive maintains
integrity between the load plate and the bearing plate by absorbing
tolerances of the load plate and the bearing plate when the shock
condition occurs.
19. The spindle motor of claim 13 further comprising a diffusion
barrier disposed between the load plate and the shaft, the
diffusion barrier preventing bearing lubricant from leaking between
the load plate and the shaft.
20. The spindle motor of claim 13 further comprising a diffusion
barrier disposed between the sleeve and the shaft, the diffusion
barrier preventing bearing lubricant from leaking between the
sleeve and the shaft.
21. The spindle motor of claim 13 further comprising a diffusion
barrier disposed between the sleeve and the stator, the diffusion
barrier preventing bearing lubricant from leaking between the
sleeve and the stator.
22. The spindle motor of claim 13 further comprising an O-ring
disposed above the bearing plate for sealing a gap between the
bearing plate and the sleeve.
23. A method for providing a dynamic fluid bearing for a spindle
motor having a thrust plate secured to a shaft and a bearing plate
and a load plate secured to a sleeve, wherein the load plate urges
the bearing plate towards the thrust plate, the method comprising
the steps of applying an adhesive between the load plate and the
thrust plate and curing the adhesive to form the seal.
24. The method of claim 23 wherein the adhesive is an UV epoxy.
25. The method of claim 23 wherein the adhesive maintains integrity
between the load plate and the bearing plate when a shock condition
occurs.
26. The method of claim 23 wherein the adhesive maintains integrity
between the load plate and the bearing plate by absorbing
tolerances of the load plate and the bearing plate when the shock
condition occurs.
27. A disk drive, comprising: at least one storage disk; an
actuator assembly including at least one actuator arm having a
sensor disposed at a distal end of the actuator arm for reading and
writing data on the at least one disk; a spindle shaft, coupled to
the at least one storage disk, for rotating the at least one
storage disk; and a spindle motor, coupled to the spindle shaft,
for rotating the spindle shaft; the spindle motor further
comprising: a sleeve having an inner periphery and an outer
periphery, the sleeve defining a disk hub on the outer periphery,
the sleeve being rotatably supported by the spindle shaft; a stator
for rotating the sleeve; and a dynamic fluid bearing disposed
between the sleeve and the shaft, the dynamic fluid bearing further
comprising a thrust plate coupled to the shaft, and a bearing plate
and load plate coupled to the sleeve, wherein the load plate urges
the bearing plate towards the thrust plate, and wherein an adhesive
is interposed between the load plate and the thrust plate to
maintain integrity between the load plate and the bearing plate
when a shock condition occurs to the spindle motor.
28. The disk drive of claim 27 wherein the adhesive is an UV
epoxy.
29. The disk drive of claim 27 further comprising a diffusion
barrier disposed between the load plate and the shaft.
30. The disk drive of claim 29 further comprising a diffusion
barrier disposed between the sleeve and the shaft.
31. The disk drive of claim 27 further comprising a diffusion
barrier disposed between the sleeve and the shaft.
32. The disk drive of claim 27 wherein the adhesive maintains
integrity between the load plate and the bearing plate by absorbing
tolerances of the load plate and the bearing plate when the shock
condition occurs.
33. The disk drive of claim 27 further comprising a diffusion
barrier disposed between the load plate and the shaft, the
diffusion barrier preventing bearing lubricant from leaking between
the load plate and the shaft.
34. The disk drive of claim 27 further comprising a diffusion
barrier disposed between the sleeve and the shaft, the diffusion
barrier preventing bearing lubricant from leaking between the
sleeve and the shaft.
35. The disk drive of claim 27 further comprising a diffusion
barrier disposed between the sleeve and the stator, the diffusion
barrier preventing bearing lubricant from leaking between the
sleeve and the stator.
36. The disk drive of claim 27 further comprising a n O-ring
disposed above the bearing plate for sealing a gap between the
bearing plate and the sleeve.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates in general to a bearing structure for
a spindle motor, and more particularly to a fluid bearing seal and
support structure for use in a spindle motor.
[0003] 2. Description of Related Art
[0004] Disk drives are computer mass storage devices from which
data may be read and/or to which such data may be written. In
general, they comprise one or more randomly accessible rotating
storage media, or disks, on which data is encoded by various means.
In magnetic disk drives, data is encoded as bits of information
including magnetic field reversals grouped in tracks on the
magnetically-hard surface of the rotating disks. The disks are
stacked in a generally parallel and spaced-apart relationship and
affixed at their inner diameter ("ID") to a common hub which is
rotationally coupled to a stationary spindle shaft by a pair of
bearings, typically ball bearings.
[0005] With the growing trend toward even lower height form factor
disk drives, the length of the spindle shaft and spacing between
the upper and lower bearings becomes a significant consideration in
meeting specific drive height constraints. As drive height is
decreased, a proportionately shorter spindle must be accommodated
within the decreased height constraints with a concomitantly
shorter spacing available between the upper and lower bearings
supporting the hub on the spindle.
[0006] Rotary spindle motors having fluid bearings for supporting
the rotary member rather than traditional ball bearings typically
include a shaft having at least one axial thrust plate and a hub,
which may be a rotary hub, having a sleeve portion generally
enclosing the shaft and thrust plate, thus forming a journal
bearing with bearing fluid disposed therein. The bearing fluid will
form capillary seals at one or more ends of the shaft that are
exposed to ambient air pressure.
[0007] The problem with such constructions is that under certain
conditions the capillary seal may break down and fluid may leak
from the bearing. Disruption of the seal may be caused by shock or
vibration. Under certain conditions the rotating portion of the
bearing may be displaced along the axis of the shaft. In the normal
course of events, lubricant flows around the end of the thrust
plate from the side with decreasing clearance to the side with
increasing clearance. If, however, because of sudden shock or
vibration, the lubricant flow around the thrust plate is impeded,
fluid will be pushed toward one end of the shaft or the other,
possibly breaking down the surface tension which holds the seal in
place.
[0008] Leakage may also occur when there are inaccuracies in the
fabrication of the patterned grooves used by the thrust plate's
upper and lower surfaces to maintain a desired net pressure
gradient. The object of the grooves is to create a high pressure
region in the middle of each thrust plate surface and to create
ambient pressure zones at the inner diameter of the thrust plate,
adjacent the shaft, and at the outer diameter in the gap between
the readily outermost edge of the thrust plate and the sleeve. This
type of pressure distribution ordinarily results in no displacement
of bearing fluid, that is, the static pressures will equalize.
However, fabrication inaccuracies do occur, as does tilt in the
bearing, or any other physical phenomena, and these factors can
alter the pressure balance in the bearing fluid resulting in flow
across the bearing. The flow of bearing fluid can overcome the
surface tension seal at either end of the bearing and cause the
fluid to leak. The situation is particularly acute at the thrust
plate end where pressure imbalances between the upper and lower
surfaces of the thrust plate may create a net flow which is near
the capillary seal at the upper surface of the thrust plate.
[0009] Nevertheless, prior axial bearing support structures have
not simultaneously address preventing oil from leaking out,
maintaining the bearing integrity under shock, reducing oil
evaporation and minimizing distortion of the active bearing
surface. Rather, existing designs have addressed only a fraction of
the requirements, e.g., only evaporation and shock induced bearing
separation or distortion and evaporation.
[0010] For example, U.S. Pat. No. 5,490,021, issued Feb. 6, 1996,
to Johannes C. A. Muller et al., and assigned to U.S. Phillips
Corporation, herein incorporated by reference, disclosed a dynamic
groove bearing for a hard disk drive. The dynamic groove bearing
includes a sleeve-like housing having a locking piece that includes
a bearing disk portion which cooperates with an annular bearing
disk provided on a shaft. A pressure member is adapted to compress
an annular, elastically deformable sealing element to thereby seal
the interface between the housing and the locking piece and to
pretension the locking piece against a seat formed on the housing.
However, Muller et al. does not address evaporation and shock
induced bearing separation.
[0011] It can be seen that there is a need for an axial bearing
support structure that prevents oil from leaking out, maintains the
bearing integrity under shock, reduces oil evaporation and
minimizes distortion of the active bearing surface.
SUMMARY OF THE INVENTION
[0012] To overcome the limitations in the prior art described
above, and to overcome other limitations that will become apparent
upon reading and understanding the present specification, the
present invention discloses a bearing structure for a spindle
motor.
[0013] The present invention provides a fluid bearing seal and
support structure that simultaneously addresses preventing oil
leakage, maintaining the bearing integrity under shock, reducing
oil evaporation and minimizing distortion of the active bearing
surface.
[0014] A system in accordance with the principles of the present
invention includes a dynamic fluid bearing for a spindle motor
having a thrust plate secured to a shaft and a bearing plate and
load plate secured to a sleeve. The load plate urges the bearing
plate towards the thrust plate. An adhesive is interposed between
the load plate and the thrust plate.
[0015] Other embodiments of a system in accordance with the
principles of the invention may include alternative or optional
additional aspects. One such aspect of the present invention is
that the adhesive is an UV epoxy.
[0016] Another aspect of the present invention is that the system
further including a diffusion barrier disposed between the load
plate and the shaft.
[0017] Another aspect of the present invention is that the system
further including a diffusion barrier disposed between the sleeve
and the shaft.
[0018] Another aspect of the present invention is that the adhesive
maintains integrity between the load plate and the bearing plate
when a shock condition occurs.
[0019] Another aspect of the present invention is that the system
further including an O-ring disposed above the bearing plate for
sealing a gap between the bearing plate and the sleeve.
[0020] These and various other advantages and features of novelty
which characterize the invention are pointed out with particularity
in the claims annexed hereto and form a part hereof. However, for a
better understanding of the invention, its advantages, and the
objects obtained by its use, reference should be made to the
drawings which form a further part hereof, and to accompanying
descriptive matter, in which there are illustrated and described
specific examples of an apparatus in accordance with the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Referring now to the drawings in which like reference
numbers represent corresponding parts throughout:
[0022] FIG. 1 illustrates an exploded view of a magnetic storage
system;
[0023] FIG. 2 illustrates the configuration of a fluid bearing seal
for a spindle motor according to the present invention;
[0024] FIG. 3 illustrates the top cross section of the spindle;
and
[0025] FIG. 4 shows the bottom cross section of the spindle.
DETAILED DESCRIPTION OF THE INVENTION
[0026] In the following description of the exemplary embodiment,
reference is made to the accompanying drawings which form a part
hereof, and in which is shown by way of illustration the specific
embodiment in which the invention may be practiced. It is to be
understood that other embodiments may be utilized as structural
changes may be made without departing from the scope of the present
invention.
[0027] The present invention provides a fluid bearing seal and
support structure that may simultaneously prevent oil leakage,
maintain the bearing integrity under shock, reduce oil evaporation
and minimize distortion of the active bearing surface.
[0028] FIG. 1 illustrates an exploded view of a magnetic storage
system 100. The disk drive 100 includes a housing 112 and a housing
cover 114 which, after assembly, is mounted within a frame 116.
Mounted within the housing is a spindle shaft 122. Rotatably
attached to the spindle shaft 122 are a number of magnetic storage
disks 124. In FIG. 1, multiple disks 124 are attached to the
spindle shaft 122 in spaced apart relation. The disks 124 rotate on
spindle shaft 122 which is powered by a motor (not shown).
Information is written on or read from the disks 124 by heads or
magnetic transducers (not shown) which are supported by sliders
126. Preferably, sliders 126 are coupled to the suspensions or load
springs 128. The load springs 128 are attached to separate arms 130
on an E block or comb 132. The E block or comb 132 is attached at
one end of an actuator arm assembly 136. The actuator arm assembly
136 is rotatably attached within the housing 112 on an actuator
shaft 138. The rotary actuator assembly 136 moves the integrated
transducer/suspension assembly in accordance with the present
invention in an arcuate path across the surface of the storage disk
124. However, those skilled in the art will recognize that the
invention is not meant to be limited to use in the particular
storage device described above.
[0029] FIG. 2 illustrates the configuration of a fluid bearing seal
200 for a spindle motor according to the present invention.
Hydrodynamic pressure is generated at the axial bearing 210 and the
axial bearing plate 214 when the bearing surfaces 216, 218 are
rotating with respect to each other. Therefore, bearing plate 214
must be very flat. Distortion should be minimized during and after
assembly. This is accomplished by placing the O-ring 222 on top of
the axial bearing plate 214. The O-ring 222 is placed at the
interface between the axial bearing plate 214 and sleeve 230 to
prevent oil from leaking out. Compression of the O-ring 222 is
provided by load plate 240 through the fingers 242 or other
means.
[0030] It is important that load plate 240 should not impinge the
bearing plate 214 during the assembly or thereafter. Therefore, a
nominal gap, such as a tenth of a millimeter, is desired. A gap at
the axial bearing 210 can suddenly form during a vertical shock.
The gap at the axial bearing 210 creates a vacuum that pulls air in
because the O-ring 222 is highly compliant. This mechanism is
prevented by applying a few adhesive droplets 250 between the load
plate 240 and the axial bearing plate 214. The adhesive 250 is
applied through a hole, e.g., at least two holes 180 degrees apart
to maintain balance, in the load plate 240. This allows the load
plate 240 to be installed immediately after oil fill and
installation of bearing plate 214 and O-ring 222. The adhesive 250
can then be applied through the a hole 252 in the load plate 240.
The hole 252 allows the use of a UV cure aerobic adhesive 250. This
also allows adhesive 250 application at the same station as
adhesive seal application at location 242. The adhesive 250 may be
an UV epoxy, wherein a UV cure of the adhesive 250 can also be
performed at the same station.
[0031] Diffusion barriers 260, 270 are disposed near the top of the
shaft just outside of the top axial bearing 210 and at the bottom
of the shaft just outside of the bottom radial bearing 272. The
diffusion barriers 260, 270 typically include narrow gaps that
offer significant resistance to flow and mass transfer of lubricant
vapor.
[0032] FIGS. 3 and 4 show details at the top 300 and bottom 400
areas of the spindle respectively. In FIG. 3, the top cross section
300 of the spindle is shown. The load plate 340 which secures the
opposing plate of the axial plate 314 forms a first level of
barrier because of the small radial gap 360 on the inner diameter
near the shaft 380. The second barrier is formed by the narrow
radial gap 382 and the relatively narrow axial gap 390. Radial gap
382 is located between the load plate 340 and the sleeve 330. The
axial gap 390 is located between the axial plate 314 and the load
plate 340.
[0033] FIG. 4 shows the bottom cross section 400 of the spindle. At
the lower radial bearing end, a small axial gap 492 is provided
between end of the sleeve 430 and the top end of the mount flange
496. The mount flange 496 is a press fit on the shaft 480. The
stator mount 494 is a press fit on the mount flange 496 and is used
for mounting the stator lamination stack 498. A long narrow annular
cylindrical gap 470 is formed between the end of the sleeve 430 and
the stator mount 494. Both of the above mentioned axial 492 and
radial 470 gaps form effective labyrinths offering significant
resistance to mass transfer of lubricant vapor.
[0034] These gaps are between rotating and stationary surfaces and
have been shown to be effective in this function in the range of
0.025 to 0.050 mm. Gaps smaller than 0.025 mm could be incorporated
provided manufacturing and assembly level tolerances permit them
without causing surface interference. Gaps larger than 0.05 mm may
be used only if calculated mass transfer rates are acceptable. For
example for a radial gap of 0.025 mm (1 thousandth of an inch) at a
diameter of 5 mm and a length of 2 mm for the barrier, calculated
evaporative loss at 70C amounts to about 3.25 mg over 5 years. To
meet mean time between failure requirements, sufficient reservoir
capacity will have to be provided so that the loss of the lubricant
does not affect the functional performance of the spindle bearing
system.
[0035] The foregoing description of the exemplary embodiment of the
invention has been presented for the purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed. Many modifications and
variations are possible in light of the above teaching. It is
intended that the scope of the invention be limited not with this
detailed description, but rather by the claims appended hereto.
* * * * *