U.S. patent application number 12/419579 was filed with the patent office on 2009-11-12 for hydrodynamic bearing and method for manufacturing the same, and spindle motor and method for manufacturing the same.
Invention is credited to Naoshi Kainoh, Kazunori MAEKAWA, Junichi Nakamura, Akihito Shirai, Yosei Yoshikawa.
Application Number | 20090276996 12/419579 |
Document ID | / |
Family ID | 36970081 |
Filed Date | 2009-11-12 |
United States Patent
Application |
20090276996 |
Kind Code |
A1 |
MAEKAWA; Kazunori ; et
al. |
November 12, 2009 |
HYDRODYNAMIC BEARING AND METHOD FOR MANUFACTURING THE SAME, AND
SPINDLE MOTOR AND METHOD FOR MANUFACTURING THE SAME
Abstract
The object of the present invention is to provide a hydrodynamic
bearing, a method for manufacturing the same, and a spindle motor,
with which the gap in the axial direction required for the smooth
operation of a bearing can be sufficiently ensured. A method for
manufacturing a hydrodynamic bearing comprising a shaft 7, a sleeve
8 attached so as to be capable of relative rotation with respect to
the shaft 7, a first flange unit 6 fixed to or integrated with the
shaft 7, and a second flange unit 9 fixed to the shaft 7, the
method comprising at least inserting the shaft 7 into the sleeve 8,
and inserting the shaft 7 into the second flange unit 9, pressing
the top face of the second flange unit 9 in the axial direction,
and fixing the second flange unit 9 to the shaft 7 by welding the
shaft 7 and the second flange unit 9 while maintaining the pressing
state.
Inventors: |
MAEKAWA; Kazunori; (Ozu-shi,
JP) ; Yoshikawa; Yosei; (Tohon-shi, JP) ;
Kainoh; Naoshi; (Ozu-shi, JP) ; Nakamura;
Junichi; (Ozu-shi, JP) ; Shirai; Akihito;
(Ozu-shi, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK L.L.P.
1030 15th Street, N.W., Suite 400 East
Washington
DC
20005-1503
US
|
Family ID: |
36970081 |
Appl. No.: |
12/419579 |
Filed: |
April 7, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11369879 |
Mar 8, 2006 |
|
|
|
12419579 |
|
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|
Current U.S.
Class: |
29/596 |
Current CPC
Class: |
Y10T 29/49636 20150115;
Y10T 29/49009 20150115; H02K 15/14 20130101; F16C 17/107 20130101;
F16C 43/02 20130101; H02K 7/086 20130101 |
Class at
Publication: |
29/596 |
International
Class: |
H02K 15/14 20060101
H02K015/14 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 11, 2005 |
JP |
2005-069162 |
Sep 27, 2005 |
JP |
2005-279705 |
Claims
1. A method for manufacturing a hydrodynamic bearing comprising: a
shaft; a sleeve attached so as to be capable of relative rotation
with respect to the shaft; a first flange unit fixed to or
integrated with the shaft; and a second flange unit fixed to the
shaft, the method comprising: inserting the sleeve into the shaft,
and inserting the second flange unit into the shaft; pressing the
top face of the second flange unit in the axial direction; and
fixing the second flange unit to the shaft by welding the shaft and
the second flange unit while keeping pressing the top face of the
second flange unit.
2. The method for manufacturing a hydrodynamic bearing according to
claim 1, further comprising: coating the welded portion with an
adhesive resin.
3. The method for manufacturing a hydrodynamic bearing according to
claim 1, wherein while pressing the top face of the second flange
unit in the axial direction, the top face of the shaft is also
pressed in the axial direction.
4. The method for manufacturing a hydrodynamic bearing according to
claim 3, wherein the shaft has a threaded hole in its end face, and
while pressing the top face of the second flange unit in the axial
direction, the top face of the shaft is pressed in the axial
direction while the threaded hole is blocked off.
5. The method for manufacturing a hydrodynamic bearing according to
claim 1, wherein while pressing the top face of the second flange
unit in the axial direction, a holding jig is used to press the top
face of the shaft in the axial direction.
6. The method for manufacturing a hydrodynamic bearing according to
claim 5, wherein the holding jig has elasticity.
7. The method for manufacturing a hydrodynamic bearing according to
claim 5, wherein the holding jig has a spherical shape at its
distal end.
8. The method for manufacturing a hydrodynamic bearing according to
claim 1, wherein the first flange unit is fixed to the shaft by
welding.
9. The method for manufacturing a hydrodynamic bearing according to
claim 1, wherein the second flange unit has a concave part on the
inner peripheral side of the top face in the axial direction, and
while fixing the second flange unit to the shaft by welding the
shaft and the second flange unit, the welding is performed near the
boundary between the concave part and the shaft.
Description
[0001] This is a Rule 1.53(b) Divisional of application Ser. No.
11/369,879, filed Mar. 8, 2006
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a hydrodynamic bearing used
in a spindle motor or the like, to a method for manufacturing the
bearing, to a spindle motor, and to a method for manufacturing the
motor.
[0004] 2. Description of the Related Art
[0005] The spindle motors installed in disk drives such as hard
disk drives (hereinafter referred to as HDDs) have in recent years
been hydrodynamic bearing motors, which involve non-contact
rotation and therefore afford reductions in noise and NRRO.
[0006] As to the structure of these hydrodynamic bearing motors,
FIG. 9 shows a conventional hydrodynamic bearing (see Japanese
Utility Model Publication No. 2,525,216, for example), which
comprises from a shaft 103, a tapered portion 106, a sleeve 112,
and a tapered bearing shell 108. The units on the shaft 103 side
are fixed by a screw cramp. In this example, the tapered portion
106 is fitted to the shaft 103 having a similar tapered portion 104
that combines a radial bearing with a thrust bearing, and these are
fixed with a threaded cover 114. The tapered bearing shell 108 is
fitted to the sleeve 112. The space between the tapered portion of
the shaft 103 and the tapered bearing shell is filled with a
lubricating fluid.
[0007] In manufacturing a hydrodynamic bearing such as this, the
required strength is achieved and the size of the product is
reduced by fastening the above-mentioned units together by
press-fitting, using an adhesive, or the like. Specific examples of
fastening methods that have been used include shrink fitting and
using an adhesive agent. All of these methods, however, entail
problems; for example, there is dimensional change in the units, or
the adhesive works its way into the parts and lowers the ultimate
performance of the bearing.
[0008] Accordingly, in more recent hydrodynamic bearings (see
Japanese Unexamined Patent Publication No. 2002-070849, for
example), a large-diameter unit (first flange unit) 6 is formed as
a first sealing unit integrally with part of a shaft 7, this is
inserted into a sleeve 8, and a second flange unit 9 is
press-fitted as a second sealing unit while a specific thrust gap
is maintained (see FIG. 2, for example). FIG. 2 is actually a
diagram of the structure of the hydrodynamic bearing pertaining to
the present invention, but is used here for the sake of describing
the structure of a conventional hydrodynamic bearing. However, even
with this structure, when the second flange unit 9 is press-fitted
to the shaft 7, the press-fitting produces burrs, and these burrs
can find their way into the bearing parts and diminish the
performance of the bearing, although the incidence of this problem
is lower here. It is because of this that welding is the most
commonly used method, since it does not produce any burrs (see
Japanese Unexamined Patent Publication No. 2002-369438, for
example).
[0009] Also, HDDs need to be even thinner and more compact. To
reduce the size and thickness of a HDD, the spindle motor that
rotates the disk must be made smaller and thinner. FIG. 13 is a
cross-sectional view of a spindle motor in a conventional example
(see Japanese Patent No. 3,282,945).
[0010] In FIG. 13, a sleeve 33 is provided in the middle of a
housing 31, and a shaft 34 is inserted rotatably in a bearing hole
of the sleeve 33. The sleeve 33, the shaft 34, and a thrust plate
35 constitute a hydrodynamic bearing that is known in this field of
technology, and the shaft 34 and the sleeve 33 rotate in a
non-contact manner. A rotor hub 32 is attached to the shaft 34. A
magnet 36 is attached to the inner periphery of the rotor hub 32,
and a magnetic disk 39 is attached to the outer periphery. The
shaft 34 has a threaded hole 43, and a clamp screw 42 for fixing a
clamping unit 41 is threaded into the threaded hole 43. The
clamping unit 41 serves to hold the magnetic disk 39 in place. The
magnet 36 rotates the rotor hub 32 and the shaft 34 upon receiving
drive force from a stator core 37 fixed to the housing 31.
[0011] With the above spindle motor, the rotor hub 32 must be
tightly attached to the shaft 34. With a typical attachment method,
the shaft 34 is press-fitted in the hole of the rotor hub 32.
However, since the inside diameter of the hole of the rotor hub 32
and the outside diameter of the shaft 34 may include a certain
amount of production error, press-fitting alone does not always
provide a secure and tight attachment. In view of this, the shaft
34 is press-fitted into the hole of the rotor hub 32 and the two
are welded together, which affords a tighter and more secure
attachment. The method for attaching the rotor hub 32 and the shaft
34 will be described through reference to FIG. 14.
[0012] FIG. 14a is a detail cross-sectional view of the main
components, and shows a first method for attaching the rotor hub 32
and the shaft 34. A rounded portion 44 or an inside-chamfered
portion 45 has been formed on the square edge of the top face of
the shaft 34. The inside diameter of the hole in the rotor hub 32
is slightly smaller than the outside diameter of the shaft 34, and
when the shaft 34 is press-fitted into the hole of the rotor hub
32, the two are fixed by this tight fit. Next, a V-shaped concave
part 46 formed with the rounded portion 44 and the inside-chamfered
portion 45 is irradiated with a laser beam, which melts the shaft
34 and the rotor hub 32 near the concave part 46 and laser welds
the two.
[0013] FIG. 14b is a detail cross-sectional view of the main
components, and shows a second method for attaching the rotor hub
32 and the shaft 34. First, a concave part 47 is formed around the
hole of the rotor hub 32 so that the top part 34a of the shaft 34
sticks out. When the rotor hub 32 is attached to the shaft 34, the
shaft 34 is press-fitted in the hole of the rotor hub 32, after
which the square edge 48 is irradiated with a laser beam to laser
weld the units.
[0014] With both of the above methods, the rotor hub 32 is fixed to
the shaft 34 by press-fitting and laser welding, so a high fixing
strength is obtained.
[0015] Nevertheless, the following problems are still encountered
with the above conventional structures and methods.
[0016] When units are welded together, the solidification of the
welds is accompanied by a change in the shrinkage stress of the
units, which is a problem in that the specified dimensions of the
units cannot be ensured. In particular, when the shaft and the
flange that constitute the thrust bearing portion are welded, as
disclosed in Japanese Unexamined Patent Publication No.
2002-369438, the welding causes the flange to move in the axial
direction, and the heat imparted during welding also makes the
flange warp in the vertical direction. Consequently, a problem is
that the gap in the axial direction that is required with a thrust
bearing cannot be ensured.
[0017] Also, with the first attachment method, when the rotor hub
32 and the shaft 34 are welded with a laser beam near the concave
part 46, microcracks about 1 to 2 .mu.m long and 1 to 1.5 .mu.m
deep develop in the surface of the welds. These microcracks contain
tiny metal particles that cannot be readily removed by ordinary
cleaning treatments. These tiny metal particles fly out of the
microcracks as a result of vibration and so forth during operation
of the spindle motor, stick to the surface of the magnetic disk,
and adversely affect the recording or reproduction of data by the
magnetic head. Also, welding fumes generated during laser welding
(composed of an oxide micropowder produced from high-temperature
metal during welding) may enter the threaded hole 43 and may cause
contamination in the motor when assembling the HDD.
[0018] With the second attachment method, the flange can be
prevented from going into the threaded hole 43 if the depth L of
the concave part 47 and the length L that the top part 34a of the
shaft 34 sticks out are increased. However, because the thickness
of a spindle motor is restricted, if the length L (see FIG. 14b) of
the top part 34a of the shaft 34 is too long, a fastening power
between the shaft 34 and the rotor hub 32 get decreased, and enough
resistance to shock between them cannot be obtained. To prevent the
problem, it is preferable also to minimize the length L. If the
length L is decreased, though, welding fumes will be more apt to
find their way into the threaded hole 43. Since the generation of
microcracks is unavoidable, the same problems are encountered as
with the first method.
SUMMARY OF THE INVENTION
[0019] In view of the above, it is an object of the present
invention to provide a hydrodynamic bearing and a method for
manufacturing the bearing, and a spindle motor and a method for
manufacturing the motor, with which the above problems can be
solved.
[0020] The method pertaining to the first invention is a method for
manufacturing a hydrodynamic bearing comprising a shaft, a sleeve,
a first flange unit, and a second flange unit, the method
comprising inserting the shaft into the sleeve, and inserting the
shaft into the second flange unit, pressing the top face of the
second flange unit in the axial direction, and fixing the second
flange unit to the shaft by welding the shaft and the second flange
unit while keeping pressing the top face of the second flange unit.
The sleeve here is attached so as to be capable of relative
rotation with respect to the shaft. The first flange unit is fixed
to or integrated with the shaft. The second flange unit is fixed to
the shaft.
[0021] What is indicated here is a method for manufacturing a
hydrodynamic bearing in which the top face of the second flange
unit is pressed in the axial direction in the course of welding the
second flange unit and the shaft.
[0022] Laser welding is usually used as the method for fixing the
second flange unit to the shaft. Laser welding was introduced to
eliminate the drawbacks to conventional methods in which a unit is
fastened by press-fitting or the use of an adhesive agent or the
like, and an advantage of this method is that there is less
decrease in the ultimate performance of the hydrodynamic bearing
than with conventional methods. Nevertheless, a problem is that the
welding causes the second flange unit to move in the axial
direction, and the heat imparted during welding results in
distortion in the form of vertical warping, so the specified gap in
the axial direction cannot be sufficiently maintained. A
lubricating fluid is injected into the gap in the axial direction,
and allows the smooth operation of a hydrodynamic bearing that
rotates in non-contact. Accordingly, the units cannot be
manufactured in their specified dimensions, and this in turn lowers
the performance of the hydrodynamic bearing.
[0023] In view of this, with the method for manufacturing a
hydrodynamic bearing in this application, the top face of the
second flange unit is pressed in the axial direction during
welding. The pressed location may be the top face of the second
flange unit in the axial direction in order to fix the second
flange unit and suppress distortion. When the shrinkage stress at
the welding location is taken into account, it is particularly
favorable to press on the outer peripheral side of the top
face.
[0024] This prevents movement and distortion of the second flange
unit, so when welding is performed, the specified gap in the axial
direction can be sufficiently ensured, and a hydrodynamic bearing
can be manufactured with good precision. Therefore, the desired
performance of the hydrodynamic bearing can be ensured.
[0025] The method pertaining to the second invention is the method
for manufacturing a hydrodynamic bearing pertaining to the first
invention, further comprising, coating the welded portion with an
adhesive resin.
[0026] What is indicated here is a step after fixing the second
flange unit to the shaft.
[0027] At the welded portion, microcracks are produced, and metal
microparticles can fly out of the microcracks and lower the
performance of the spindle motor.
[0028] In view of this, by coating the welded portion with an
adhesive resin after the welding, the resin covers the microcracks
and prevents the metal microparticles from flying out of the
microcracks.
[0029] Therefore, the desired performance of the hydrodynamic
bearing can be ensured.
[0030] The method pertaining to the third invention is the method
for manufacturing a hydrodynamic bearing pertaining to the first or
the second invention, wherein, while pressing the top face of the
second flange unit in the axial direction, the top face of the
shaft is also pressed in the axial direction.
[0031] What is indicated here is a method for manufacturing a
hydrodynamic bearing in which not only the second flange unit, but
also the top face of the shaft is pressed in the axial direction in
the course of welding the second flange unit and the shaft.
[0032] Another problem encountered during welding is that the
effect of shrinkage stress at the weld sites further raises the
shaft. This again, just as above, means that the specified gap in
the axial direction cannot be sufficiently ensured. Accordingly,
units cannot be manufactured in their intended sizes, and this in
turn diminishes the performance of the hydrodynamic bearing.
[0033] In view of this, the top face of the shaft in the axial
direction is also pressed at the same during welding to fix the
shaft.
[0034] This prevents the shaft from rising, so when welding is
employed, it is possible to manufacture a hydrodynamic bearing with
good precision while ensuring the specified gap in the axial
direction. Therefore, the performance of the hydrodynamic bearing
can be better ensured.
[0035] The method pertaining to the fourth invention is the method
for manufacturing a hydrodynamic bearing pertaining to the third
invention, wherein the shaft has a threaded hole in its end face,
and while pressing the top face of the second flange unit in the
axial direction, the top face of the shaft is pressed in the axial
direction while the threaded hole is blocked off.
[0036] What is indicated here is a method for manufacturing a
hydrodynamic bearing in which the top face of the shaft is
simultaneously pressed, in a state in which the threaded hole of
the shaft is blocked off, in the course of welding the second
flange unit and the shaft.
[0037] A hydrodynamic bearing is usually structured such that a
threaded hole for fixing a cover that covers the upper side of the
spindle motor is provided to the shaft such that the hole opens on
the top face in the axial direction. With a structure such as this,
in addition to the above-mentioned movement and distortion of the
second flange unit and the rise of the shaft, another problem is
that spatter and other such welding fumes are scattered during
welding and find their way into the threaded hole. Consequently,
the ultimate manufacturing precision of the hydrodynamic bearing
ends up being decreased.
[0038] In view of this, with the manufacturing method of the
present invention, the threaded hole in the shaft is blocked off
during the pressing of the top face of the shaft.
[0039] This prevents welding fumes from scattering and minimizes
the decrease in the manufacturing precision of the hydrodynamic
bearing.
[0040] The method pertaining to the fifth invention is the method
for manufacturing a hydrodynamic bearing pertaining to any of the
first to fourth inventions, wherein while pressing the top face of
the second flange unit in the axial direction, a holding jig is
used to press the top face of the shaft in the axial direction.
[0041] What is indicated here is a unit for pressing on the top
face of the shaft in the axial direction.
[0042] This holding jig may have a shape that allows the pressing
force to be uniformly transferred to the shaft.
[0043] This allows the top face of the shaft to be pressed with
good precision.
[0044] The method pertaining to the sixth invention is the method
for manufacturing a hydrodynamic bearing pertaining to the fifth
invention, wherein the holding jig has elasticity.
[0045] What is indicated here is that the holding jig is an object
that has elasticity.
[0046] The holding jig can be made of a hard rubber, for
example.
[0047] This allows the pressing force to be imparted uniformly, so
the top face of the shaft can be pressed with good precision.
[0048] The method pertaining to the seventh invention is the method
for manufacturing a hydrodynamic bearing pertaining to the fifth or
sixth invention, wherein the holding jig has a spherical shape at
its distal end.
[0049] What is indicated here is that the distal end is spherical
in shape, as an example of the shape of the holding jig.
[0050] The shape of the holding jig is preferably one that will not
scratch the top face of the shaft in the axial direction.
[0051] In view of this, the distal end of the holding jig, that is,
the part that comes into contact with the top face of the shaft in
the axial direction, is spherical in shape.
[0052] This allows the top face of the shaft to be pressed with
good precision without being scratched.
[0053] The method pertaining to the eighth invention is the method
for manufacturing a hydrodynamic bearing pertaining to any of the
first to seventh inventions, wherein the first flange unit is fixed
to the shaft by welding.
[0054] What is indicated here is a method for fixing the first
flange unit to the shaft.
[0055] The first flange unit is sometimes molded integrally with
the shaft, and sometimes fixed to the shaft. Press-fitting and
adhesion are generally employed when fixing is involved. A problem,
however, is that burrs are produced in press-fitting, which can
affect the manufacture of a hydrodynamic bearing.
[0056] In view of this, when fixing is involved, welding is
employed just as when the first flange unit is formed by being
welded to the shaft.
[0057] This allows a hydrodynamic bearing to be manufactured with
good precision and without producing any burrs.
[0058] The welding method may be laser welding, for example.
[0059] The method pertaining to the ninth invention is method for
manufacturing a hydrodynamic bearing pertaining to any of the first
to eighth inventions, wherein the second flange unit has a concave
part on the inner peripheral side of the top face in the axial
direction, and while fixing the second flange unit to the shaft by
welding the shaft and the second flange unit, the welding is
performed near the boundary between the concave part and the
shaft.
[0060] What is indicated here is a structure in which a concave
part is provided to the top face of the second flange unit.
[0061] Usually, in welding the second flange unit and the shaft,
the welding site is near the upper tangent of the flange unit and
the shaft. Nevertheless, if nothing else is done, welding fumes and
so forth may scatter during welding and affect the manufacturing
precision of other units. This means that the ultimate
manufacturing precision of the hydrodynamic bearing ends up being
diminished.
[0062] In view of this, a concave part is provided to the second
flange unit on the inner peripheral side of the top face in the
axial direction, and welding is performed near the boundary between
the bottom of the concave part and the shaft. Any welding fumes
produced in this welding will stay in the concave part.
[0063] This prevents welding fumes from scattering and minimizes
the decrease in the manufacturing precision of the hydrodynamic
bearing.
[0064] The hydrodynamic bearing pertaining to the tenth invention
comprises at least a shaft, a sleeve, a first flange unit, and a
second flange unit. The sleeve is attached so as to be capable of
relative rotation with respect to the shaft. The first flange unit
is fixed to or integrated with the shaft. The second flange unit is
fixed to the shaft. Also, the portion that is welded to fix the
second flange unit to the shaft is coated with an adhesive
resin.
[0065] What is indicated here is an example of a basic structure of
the hydrodynamic bearing of the present invention.
[0066] The portion that is welded to fix the second flange unit to
the shaft is coated with an adhesive resin, for preventing the
metal microparticles from flying out of the microcracks.
[0067] This reduces the metal microparticles from flying, and the
desired performance of the hydrodynamic bearing can be ensured.
[0068] The hydrodynamic bearing pertaining to the eleventh
invention is the hydrodynamic bearing pertaining to the tenth
invention, the second flange unit further has a concave part on the
inner peripheral side of the top face in the axial direction. The
welded portion is near a boundary of a bottom face of the concave
part and the shaft.
[0069] What is indicated here is the basic structure of the
hydrodynamic bearing of the present invention, and an example of
the shape pertaining to the second flange unit, in which a concave
part is provided on the inner peripheral side of the top face in
the axial direction.
[0070] Usually, in welding the second flange unit and the shaft,
the welding site is near the upper tangent of the flange unit and
the shaft. Nevertheless, if nothing else is done, welding fumes and
so forth may scatter during welding and affect the manufacturing
precision of other units. This means that the ultimate
manufacturing precision of the hydrodynamic bearing ends up being
diminished.
[0071] In view of this, a concave part is provided on the inner
peripheral side of the top face in the axial direction, and welding
is performed near the boundary between the bottom of the concave
part and the shaft. Then, any welding fumes produced in this
welding will stay in the concave part.
[0072] Also, by coating near the welded portion with a resin, the
resin covers the microcracks and can prevent the metal
microparticles from flying out of the microcracks.
[0073] This prevents welding fumes from scattering and minimizes
the decrease in the manufacturing precision of the hydrodynamic
bearing.
[0074] The hydrodynamic bearing pertaining to the twelfth invention
is the hydrodynamic bearing pertaining to the eleventh invention,
wherein the second flange unit further has a concave part on the
inner peripheral side of the top face in the axial direction.
[0075] What is indicated here is that the second flange unit has a
concave part on its bottom face as well.
[0076] Usually, when a hydrodynamic bearing is operated, bubbles
are produced from the lubricating fluid injected into the gaps
between units, and these bubbles can impede the smooth operation of
the hydrodynamic bearing.
[0077] In view of this, a concave part is provided on the inner
peripheral side of the bottom face in the axial direction, which is
not used in laser welding, and this concave part serves as a bubble
escape portion.
[0078] This allows bubbles to flow into the concave part, and a
hydrodynamic bearing capable of sustained smooth operation can be
obtained.
[0079] The hydrodynamic bearing pertaining to the thirteenth
invention comprises at least a shaft, a sleeve, a first flange
unit, a second flange unit, and at least a first sealing or a
second sealing unit. The sleeve is attached so as to be capable of
relative rotation with respect to the shaft. The first flange unit
is fixed to or integrated with the shaft. The second flange unit is
fixed to the shaft. The hydrodynamic bearing of this invention also
comprises a first sealing unit and/or a second sealing unit. The
first sealing unit is fixed to the sleeve so as to cover the bottom
face of the first flange unit in the axial direction, or the second
sealing unit is fixed to the sleeve so as to cover the top face of
the second flange unit in the axial direction.
[0080] What is indicated here is a structure in which a sealing
unit is provided covering a flange unit.
[0081] A lubricating fluid is injected into the gaps between the
flange units and the sleeve. Foreign matter can find its way into
these gaps from the bottom face in the axial direction, or the
lubricating fluid may leak out from these gaps. Foreign matter may
also find its way in from the top face. As a result, the smooth
operation of the hydrodynamic bearing is impeded.
[0082] In view of this, a sealing unit that has the role of a cover
is formed by being fixed to the shaft in a shape that will cover
the flange unit. Since they are intended to cover the gaps between
the flange units and the sleeve, the sealing units at least span
the outer peripheral sides of the flange units in the axial
direction.
[0083] This prevents contamination by foreign matter and the
leakage of the lubricating fluid, and gives a hydrodynamic bearing
capable of sustained smooth operation.
[0084] The spindle motor pertaining to the fourteenth invention
comprises at least the hydrodynamic bearing pertaining to any of
the ninth to thirteenth inventions, a hub, a magnet, a base plate,
and a stator core. The hub is fixed to the hydrodynamic bearing and
allows the hydrodynamic bearing to rotate. The magnet is fixed to
the hub. The base plate fixes the hydrodynamic bearing. The stator
core is fixed to the base plate so as to be across from the
magnet.
[0085] What is indicated here is the basic structure of a spindle
motor in which the hydrodynamic bearing of this application is
employed.
[0086] A spindle motor usually makes use of a hydrodynamic bearing.
Since hydrodynamic bearings involve non-contact rotation and
therefore afford reductions in noise and NRRO, the performance of
the bearing affects the performance of the spindle motor.
Accordingly, the hydrodynamic bearing must be accurately
manufactured to the required dimensions, and must have good
precision.
[0087] Use of the hydrodynamic bearing of this application affords
stable bearing performance. With this hydrodynamic bearing, a
concave part is provided on the inner peripheral side of the top
face of the second flange unit in the axial direction. The area
near the tangent of the shaft and the bottom corner of this concave
part is welded, which allows welding fumes to be kept inside the
concave part and yields a hydrodynamic bearing with better
operating performance. Also, a bubble escape portion may be formed
in this hydrodynamic bearing by providing a concave part on the
inner peripheral side of the bottom face in the axial direction,
which is not used in laser welding.
[0088] As a result, any bubbles will flow into the concave part,
and a hydrodynamic bearing capable of sustained smooth operation
will be obtained, so a spindle motor with better operating
performance can be obtained.
[0089] The spindle motor pertaining to the fifteenth invention
comprises at least the hydrodynamic bearing pertaining to any of
the ninth to thirteenth inventions, a hub, a magnet, a base plate,
and a stator core. The hub is fixed to the hydrodynamic bearing and
allows the hydrodynamic bearing to rotate. The magnet is fixed to
the hub. The base plate fixes the hydrodynamic bearing. The stator
core is fixed to the base plate so as to be across from the magnet.
Also, the base plate has a concave part, and the bottom face of the
sleeve and the first flange unit in the hydrodynamic bearing is
kept at a specific gap away from the base plate while being
inserted into the concave part.
[0090] What is indicated here is the structural relationship
between the base plate and the hydrodynamic bearing in a spindle
motor.
[0091] It is preferable for a spindle motor to have a structure
that prevents the lubricating fluid from scattering into the motor,
and prevents the admixture of foreign matter from the outside into
the gaps of the hydrodynamic bearing.
[0092] In view of this, a concave part is provided to the base
plate to which the hydrodynamic bearing is attached, and the
hydrodynamic bearing is inserted into this concave part.
[0093] The spindle motor pertaining to the sixteenth invention has
a sleeve, a hub, a resin, and a rotor magnet. The sleeve rotatably
supports a shaft. The hub includes a hole in which the shaft is
press-fitted, has in the end region of the hole a concave part that
is recessed by a specific distance from the surface and an
inside-chamfered portion provided to the inner periphery of the
concave part, and is welded to the shaft that has been press-fitted
in the hole by irradiating the inside-chamfered portion with a
laser beam. The resin is an adhesive resin and coated on the welded
portion The rotor magnet is fixed to the hub and is across from a
stator coil attached to a housing to which the sleeve is fixed.
[0094] What is indicated here is the basic structure of another
spindle motor of the present invention, and the shape of the hub
thereof.
[0095] Ordinarily, welding fumes generated during laser welding can
enter the threaded hole and may cause contamination in the motor
when assembling a HDD.
[0096] In view of this, a concave part that is recessed by a
specific distance from the surface and an inside-chamfered portion
provided to the inner periphery of the concave part are formed in
the end region of the hole in the hub. When the hub and the shaft
are welded by irradiating the V-shaped bottom of the
inside-chamfered portion with a laser beam, any welding fumes
generated during the welding will not readily go into the threaded
hole, and furthermore, even if molten metal from the
inside-chamfered portion should overflow, it will be contained in
the concave part, and therefore will not make it to the surface of
the hub.
[0097] This prevents welding fumes from scattering toward the
threaded hole of the shaft, and yields a spindle motor with better
operating performance.
[0098] The spindle motor pertaining to the seventeenth invention is
the spindle motor pertaining to the sixteenth invention, further
comprises a circular groove to prevent a lubricating fluid from
leaching that is formed at a joint portion of the shaft and the
hub.
[0099] What is indicated here is a further structure of the spindle
motor.
[0100] Ordinarily, when the laser welding is used for manufacturing
the spindle motor, the shaft and the hub are jointed together by
only press-fitting. This is because, for example, an adhesive bond
is burned during the welding when performing press-fitting and
adhesive bonding, and it results in contaminations. However, only
press-fitting cause a problem that a leaching of the lubricating
fluid in the hydrodynamic bearing.
[0101] In view of this, at the joint portion of the shaft and the
hub, the circular groove is formed to prevent the lubricant fluid
from leaching and to make the lubricant fluid remain in the
circular groove. The circular groove can be formed at either the
shaft side or the hub side.
[0102] This yields a spindle motor with better operating
performance.
[0103] The method for manufacturing a spindle motor pertaining to
the eighteenth invention is a method for manufacturing a spindle
motor comprising a cylindrical shaft having a threaded hole in its
end face, a sleeve that rotatably supports a shaft, a hub that has
a hole in which is press-fitted the end of the shaft having the
threaded hole, and has in the end region of the hole a concave part
that is recessed by a specific distance from the surface and an
inside-chamfered portion provided to the inner periphery of the
concave part, and a rotor magnet that is fixed to the hub and is
across from a stator coil attached to a housing to which the sleeve
is fixed, the method comprising, press-fitting in the hole the end
of the shaft having the threaded hole, temporarily blocking the end
face of the shaft having the threaded hole with a sealing jig,
irradiating the inside-chamfered portion with a laser beam to weld
the hub and the shaft, and coating with a resin that will bond to
the welded portion after the welding.
[0104] What is indicated here is a spindle motor manufacturing
method that prevents the scattering of welding fumes and the
like.
[0105] Ordinarily, welding fumes generated during laser welding can
enter the threaded hole and may cause contamination in the motor
when assembling the HDD. Also, metal microparticles can fly out of
microcracks and lower the performance of the spindle motor.
[0106] In view of this, the threaded hole is temporarily blocked
off by the sealing jig during the welding of the shaft and the hub,
which prevents the scattering of welding fumes. Furthermore, the
welds are coated with a resin after welding, so the microcracks are
covered by the resin, and this suppresses the scattering of metal
microparticles.
[0107] This allows a spindle motor to be manufactured with good
precision.
[0108] The method pertaining to the nineteenth invention is the
method for manufacturing a spindle motor pertaining to the
eighteenth invention, wherein the threaded hole is blocked with the
sealing jig only during coating with the resin.
[0109] What is indicated here is a spindle motor manufacturing
method in which the threaded hole is blocked off during coating
with a resin.
[0110] During resin coating, extra resin may find its way into the
threaded hole and lower the performance of the spindle motor.
[0111] In view of this, the resin is prevented from getting into
the threaded hole by blocking the hole during resin coating.
[0112] This allows a spindle motor to be manufactured with good
precision.
[0113] The method pertaining to the twentieth invention is a method
for manufacturing a spindle motor comprising a cylindrical shaft
having a threaded hole in its end face, a sleeve that rotatably
supports a shaft, a hub that has a hole in which is press-fitted
the end of the shaft having the threaded hole, and has in the end
region of the hole a concave part that is recessed by a specific
distance from the surface and an inside-chamfered portion provided
to the inner periphery of the concave part, and a rotor magnet that
is fixed to the hub and is across from a stator coil attached to a
housing to which the sleeve is fixed, the method comprising
press-fitting in the hole the end of the shaft having the threaded
hole, irradiating the inside-chamfered portion with a laser beam to
weld the hub and the shaft, and blocking the threaded hole with a
sealing jig after welding, while coating with a resin that will
bond to the welded portion after the welding.
[0114] What is indicated here is a spindle motor manufacturing
method in which the threaded hole is blocked off during resin
coating.
[0115] During resin coating, extra resin may find its way into the
threaded hole and lower the performance of the spindle motor.
[0116] In view of this, the resin is prevented from getting into
the threaded hole by blocking the hole during resin coating.
[0117] This allows a spindle motor to be manufactured with good
precision.
BRIEF DESCRIPTION OF THE DRAWINGS
[0118] FIG. 1 is a cross-sectional view of the structure of a
spindle motor having a hydrodynamic bearing in an embodiment of the
present invention;
[0119] FIG. 2 is a diagram of the structure of a hydrodynamic
bearing in an embodiment of the present invention;
[0120] FIG. 3 is a diagram of the method for manufacturing a
hydrodynamic bearing in an embodiment of the present invention;
[0121] FIG. 4 is a diagram of weld sites of a hydrodynamic bearing
in an embodiment of the present invention;
[0122] FIG. 5 is a diagram of the oil repellant coating location of
a hydrodynamic bearing in an embodiment of the present
invention;
[0123] FIG. 6a is a diagram of the structure and weld sites of a
hydrodynamic bearing in another embodiment of the present
invention, and FIG. 6b is a detail view of part of the structure of
a hydrodynamic bearing in yet another embodiment;
[0124] FIG. 7 is a diagram of the structure of a spindle motor in
another embodiment of the present invention;
[0125] FIG. 8 is a diagram of the structure of a spindle motor in
another embodiment of the present invention;
[0126] FIG. 9 is a diagram of the structure of a conventional
hydrodynamic bearing;
[0127] FIG. 10 is a cross-sectional view of a spindle motor in yet
another embodiment of the present invention;
[0128] FIG. 11 is a detail cross-sectional view of the main
attachment portions of a shaft and a hub in a spindle motor;
[0129] FIG. 12 is a detail cross-sectional view of the main
components during the welding of a shaft and a hub in a spindle
motor;
[0130] FIG. 13 is a cross-sectional view of a conventional spindle
motor; and
[0131] FIG. 14 is a detail cross-sectional view of the main
attachment portions of a shaft and a hub in a conventional spindle
motor.
[0132] FIG. 15 is an overview of performing a laser welding.
[0133] FIG. 16 is a diagram of an example of a further structure of
a spindle motor of the present invention,
DETAILED DESCRIPTION OF THE INVENTION
[0134] Embodiments of the present invention will now be
described.
Embodiment 1
[0135] A spindle motor 100 that features a bearing unit 101 that is
the hydrodynamic bearing pertaining to this embodiment will now be
described through reference to FIGS. 1 to 5.
Structure of Spindle Motor 100
[0136] In very broad terms, the spindle motor 100 is made up of
stationary units and rotating units.
[0137] Examples of the stationary units include, as shown in FIG.
1, a base plate 1, a stator core 2, a coil 3, an insulating tube 4,
a first flange unit 6, a shaft 7, a second flange unit 9, and a
cylindrical wall 16. The base plate 1 is composed of an aluminum
alloy or the like. Silicon steel plate or the like is used for the
stator core 2, and the coil 3 composed of a cuprous metal or the
like wound around this core to form a stator core assembly. The
stator core assembly is fixed to the base plate 1 by press-fitting
and adhesive bonding, for example. One end of the insulating tube 4
is inserted to coil leads, and the other end is led out to the
outside of the device. A heat-shrinkable tube composed of a
polyolefin resin or the like is often used for the insulating tube
4. The flange units 6 and 9 are dynamic pressure generators, and
are composed of stainless steel or another such material. The role
of the shaft 7 is that of a support that stably bears the bearing
unit 101 and in turn the spindle motor 100. The shaft 7 is composed
of stainless steel or the like, and is press-fitted and adhesively
bonded to the base plate 1. The cylindrical wall 16 forms a concave
part in the base plate 1.
[0138] As shown in FIG. 1, for example, the rotating units include
a sleeve 8, a back yoke 13, an air seal 14, and a magnet 15. The
sleeve is produced by subjecting a copper alloy to electroless
nickel plating, for example. A hub 12 composed of an aluminum alloy
or the like supports a recording medium or the like (not shown),
and is affixed to and rotates integrally with the sleeve 8. The
back yoke 13 is composed, for example of a magnetic material
produced by subjecting a ferrous metal to electroless nickel
plating, and is fixed to the hub 12 by press-fitting or the like.
The magnet 15 is adhesively bonded and fixed to the back yoke 13
and then heated and hardened. An Ne--Fe-Bo-based resin magnet is
usually used for this magnet. The air seal 14 mainly blocks off the
space in which the recording medium is supported and the space in
which the stator core assembly is located. The magnet 15 is
disposed across from the stator core assembly and provides the
motive power for the rotation of the rotating units. The lower ends
of the first flange unit 6 and the sleeve 8 are inserted in this
concave part, resulting in what is called a labyrinth structure.
Here, the gap L3 between the outer periphery of the sleeve 8 and
the inner periphery of the cylindrical wall 16 is 0.25 mm or less,
for example.
[0139] A specific gap L4 is formed between the bottom faces of the
first flange unit 6 and the base plate 1. The gap L4 is necessary
to adjust the height position of the shaft 7 when the shaft 7 is
press-fitted into the base plate 1. At the same time, since the
bottom face of the first flange unit 6 and the base plate 1 is
coated with an oil repellant 24 (discussed in detail below), a gap
large enough to accommodate this must be also be provided. The gap
L4 is usually about 0.2 mm.
[0140] Of the above units, the shaft 7, the flange units 6 and 9,
the sleeve 8, and a lubricating fluid 116 constitute the bearing
unit 101 (a hydrodynamic bearing). The structure of the bearing
unit 101 will now be discussed in detail.
Structure of Bearing Unit 101
[0141] An example of the structure of the bearing unit 101 will be
described through reference to FIG. 2.
[0142] The bearing unit 101 is made up of the shaft 7, the flange
units 6 and 9, the sleeve 8, and the lubricating fluid 116, which
are combined as shown in FIG. 2.
[0143] The shaft 7 is located in the center of the bearing unit
101, and its lower end is inserted in the base plate 1 (see FIG.
1). The shaft 7 has a threaded hole 11 in its top face for fixing a
cover (not shown) that covers the upper face of the spindle motor
100 (see FIG. 1). A radial dynamic pressure generating groove is
formed in the outer peripheral face of the shaft 7 or the inner
peripheral face of the sleeve 8. The first flange unit 6 may be
fixed to or integrated with the shaft 7. A thrust dynamic pressure
generating groove is formed in the face of the sleeve 8 across from
the first flange unit 6, or the face of the first flange unit 6
across from the sleeve 8. The second flange unit 9 is fixed to the
shaft 7. A thrust dynamic pressure generating groove is formed in
the face of the second flange unit 9 across from the sleeve 8, or
the face of the sleeve 8 across from the second flange unit 9. The
lubricating fluid 116 is injected into the space in which these
dynamic pressure generating grooves are formed, that is, the
bearing gap.
[0144] A communicating passage 19 that communicates with the
above-mentioned two thrust dynamic pressure generating grooves is
formed in the sleeve 8, which achieves pressure equilibrium inside
the bearing. The communicating passage 19 may be formed by making a
hole in the sleeve 8, or the sleeve may be divided into outer and
inner sleeves, and part of the outer periphery of the inner sleeve
may be given a D-cut or the like and these two parts fitted
together.
Method for Manufacturing Bearing Unit 101
[0145] Next, an example of the method for manufacturing the bearing
unit 101 will be described through reference to FIG. 3.
[0146] First, as shown in FIG. 3, the lower end of the shaft 7 on
which the first flange unit 6 has been formed is inserted in a
receiving jig 20 whose surface has been polished. The receiving jig
20 serves as a base for stably and horizontally fixing the bearing
unit 101. Next, the sleeve 8 is allowed to fall under its own
weight onto the shaft 7 so that the sleeve 8 is rotatable with
respect to the shaft 7.
[0147] The face (A face) where the first flange unit 6 hits the
receiving jig 20, and the face (B face) where the sleeve 8 hits the
receiving jig 20 lie in the same plane in the receiving jig 20.
However, depending on the size and shape of the first flange unit 6
and the sleeve 8, the A and B faces may lie in different planes in
the receiving jig 20.
[0148] We will let L1 here be the distance from the B face to the
dynamic pressure face on the sleeve 8 side, and L2 be the distance
from the A face to the dynamic pressure face on the first flange
unit 6 side. This gives L1>L2. If we assume that L1-L2=Gs, then
Gs is the distance of the gap between the first flange unit 6 and
the sleeve 8, that is, the thrust bearing gap.
[0149] If Gs here is wide, the dynamic pressure in the axial
direction will be unbalanced, thrust stiffness will decrease, and
motor performance will decline. Conversely, if Gs is narrow,
resistance of the lubricating fluid will rise, bearing loss will
increase, and the motor current will go up. Therefore, when ease of
assembly and thrust stiffness and motor current consumption after
assembly are taken into account, Gs may be a distance from 15 to 25
.mu.m. It is preferably limited to 20 .mu.m.
[0150] In the welding of the second flange unit 9 to the shaft 7,
the top face of the second flange unit 9 is pressed. Accordingly,
the second flange unit 9 is preferably fixed snugly against the
face of the sleeve 8 across from the second flange unit 9 in the
axial direction. The gap between the second flange unit 9 and the
sleeve 8 in the axial direction can be formed by moving the sleeve
8 downward in the axial direction relative to the shaft 7 after
welding.
[0151] The second flange unit 9 is inserted while the distance Gs
is thus restricted.
[0152] Next, a spherical jig 10 (holding jig) is placed on the top
face of the shaft 7 while the outer periphery of the top face of
the second flange unit 9 in the axial direction is pressed. This
spherical jig 10 also serves as a sealing unit. Therefore, the top
face of the shaft 7 in the axial direction is pressed while the
threaded hole 11 is sealed with the spherical jig 10, and either
the entire periphery near the boundary between the shaft 7 and the
second flange unit 9, or a plurality of locations along this
periphery, are laser welded. This laser may be a YAG laser or the
like. FIG. 4 shows the laser welding locations. The spherical jig
10 is capable of sealing the threaded hole 11 of the shaft 7
without scratching it, and allows uniform pressure to be applied to
the shaft 7, so its contact face with the shaft 7 may be
spherical.
[0153] After this, as shown in FIG. 5, on the top side of the
bearing unit 101, the outer periphery of the top face of the second
flange unit 9 and the inner peripheral face of the sleeve 8 near
the opening of the bearing unit 101 are coated with an oil
repellant 24. On the bottom side of the bearing unit 101, the outer
periphery of the bottom face of the first flange unit 6 and either
just the inner periphery or the entire bottom face of the sleeve 8
are coated with the oil repellant 24. A fluorine-based oil
repellant is usually used as the oil repellant 24.
[0154] Once assembled by the above method, the bearing unit 101 is
put in a vacuum chamber (not shown) and placed under a low-pressure
environment, and the lubricating fluid 116 is dropped into the gap
of the bearing. After the entire bearing gap has been filled with
the lubricating fluid 116, the vacuum chamber is returned to
atmospheric pressure and left in that state for a specific length
of time. The lubricating fluid here may be oil, for example.
[0155] After this, a top cover (not shown) may be adhesively fixed
to the top face of the second flange unit 9 as desired.
[0156] With the above method, even when laser welding is employed,
the gap between the flange units 6 and 9 and the sleeve 8 can be
accurately maintained, and the bearing unit 101 can be manufactured
with good precision.
Features of the Manufacturing Method
[0157] (1) The constituent elements of the bearing unit 101
manufactured in this embodiment are the shaft 7, the sleeve 8 that
is attached in a state of being rotatable relative to the shaft 7,
the first flange unit 6 that is fixed to or integrated with the
shaft 7, the second flange unit 9 that is fixed to the shaft 7, and
so forth. The process of manufacturing this bearing unit 101
includes the following steps. (1) Inserting the second flange unit
9 after inserting the sleeve 8 to the shaft 7, (2) pressing on the
top face of the second flange unit 9 in the axial direction, (3)
maintaining this pressing state while the shaft 7 and the second
flange unit 9 are welded, thereby fixing the second flange unit 9
to the shaft 7.
[0158] As a result, the second flange unit moves in the axial
direction during welding, and the heat imparted during welding
results in vertical warping, which therefore avoids the problem of
being unable to ensure the specified gap in the axial
direction.
[0159] Therefore, a hydrodynamic bearing can be manufactured with
good precision while the specified gap is ensured in the axial
direction.
(2) With the method for manufacturing the bearing unit 101 in this
embodiment, the top face of the shaft 7 in the axial direction is
also pressed in the course of pressing the top face of the second
flange unit 9 in the axial direction in the above-mentioned second
step.
[0160] During the welding of the shaft 7 and the second flange unit
9, the effect of shrinkage stress at the weld sites raises even the
shaft, which is a problem in that the specified gap in the axial
direction cannot be sufficiently ensured.
[0161] In view of this, the top face of the shaft 7 in the axial
direction may also be pressed so that the shaft 7 is fixed during
welding.
[0162] This makes it possible to manufacture a hydrodynamic bearing
with good precision while ensuring the specified gap in the axial
direction.
(3) The shaft 7 of the bearing unit 101 in this embodiment has the
threaded hole 11 in its end face, and the method for manufacturing
the bearing unit 101 in this embodiment involves pressing the top
face of the shaft 7 in the axial direction while blocking off the
threaded hole 11 in the above-mentioned second step.
[0163] This avoids the problem whereby welding fumes and the like
scatter during welding and find their way into the threaded
hole.
[0164] Therefore, the decrease in the manufacturing precision of
the hydrodynamic bearing can be minimized.
(4) The method for manufacturing the bearing unit 101 in this
embodiment involves using a holding jig to press on the top face of
the shaft in the axial direction.
[0165] This allows the top face of the shaft to be pressed with
good precision.
(5) In the method for manufacturing the bearing unit 101 in this
embodiment, the holding jig has elasticity.
[0166] This allows the pressing force to be imparted uniformly to
the top face of the shaft 7.
[0167] Therefore, the top of the shaft 7 can be pressed with good
precision.
(6) In the method for manufacturing the bearing unit 101 in this
embodiment, the holding jig has a spherical shape at its distal
end.
[0168] This allows the top face of the shaft 7 to be pressed with
good precision, without being scratched.
(7) In the method for manufacturing the bearing unit 101 in this
embodiment, the second flange unit 9 is fixed to the shaft 7 by
welding.
[0169] Press-fitting and adhesive bonding or another such method is
generally used to fix these units, but this method is not suitable
with the present invention. This is because a gap is provided
between the outer peripheral face of the shaft 7 and adjacent
units, and contamination by burrs and the like produced in
press-fitting and adhesive bonding must be avoided.
[0170] Also, as discussed above, the method for manufacturing the
bearing unit 101 avoids problems encountered in welding.
[0171] Accordingly, the bearing unit 101 can be manufactured with
good precision by welding.
Embodiment 2
[0172] A spindle motor 200 pertaining to this embodiment will be
described through reference to FIGS. 10 to 12.
[0173] FIG. 10 is a cross-sectional view of the spindle motor
200.
[0174] In FIG. 10, a housing 51 has a cylindrical unit 51a in its
middle, and a sleeve 52 is attached to the cylindrical unit 51a. A
shaft 53 is rotatably inserted into a bearing hole 52a of the
sleeve 52. A flange 55 is attached to the bottom of the shaft 53.
An opening at the bottom of the sleeve 52 is sealed off by a thrust
receiving plate 54. A fluid such as oil fills the space between the
shaft 53 and the sleeve 52 and the space between the thrust
receiving plate 54 and the flange 55. This constitutes a
hydrodynamic bearing that is known in this field of technology.
[0175] In this embodiment, an aluminum die-cast material or an iron
material is used for the housing 51. The sleeve 52 is produced by
nickel plating a brass material (copper alloy). A stainless steel
material (such as SUS 420J2) is used for the shaft 53, and a
stainless steel material (such as SUS 304) is used for the flange
55. A stainless steel material (such as SUS 420J2) is used for the
thrust receiving plate 54, and a stainless steel material (such as
DHS1) or an aluminum material is used for a hub 57.
[0176] The hub 57 is attached to the top part of the shaft 53 by a
method that will be described in detail below.
[0177] A threaded hole 61 that is parallel to the axial direction
of the shaft 53 is provided in the center of the shaft 53. A
magnetic disk or the like is supported on a disk receiving face 57g
on the outer periphery of the hub 57 by fixing a screw (not shown)
in the threaded hole 61 by using a threaded clamping unit. A rotor
magnet 67 is provided on the inside of the hub 57. A stator core 59
is attached to the housing 51 so as to be across from the rotor
magnet 67.
[0178] How the shaft 53 and the hub 57 are attached will now be
described.
[0179] FIG. 11 is a detail cross-sectional view of the attachment
parts of the shaft 53 and the hub 57. When the hub 57 is attached
to the shaft 53, first the shaft 53 is press-fitted into the hole
57b of the hub 57. The outside diameter of the shaft 53 is 4 to 11
.mu.m larger than the inside diameter of the hole 57b, so that the
press-fit removal strength is about 10 kgf. The top face 53a of the
shaft 53 and the top face 57a of the hub 57 after press-fitting are
at substantially the same height. A curved surface with a radius of
about 0.1 mm is formed at the corner of the outer periphery of the
shaft 53. The corner on the inner periphery of the attachment hole
57b of the hub 57 is subjected to inside-chamfering of about 0.05
mm, forming an inside-chamfered portion 57c. A flat portion 57d
connected to the inside-chamfered portion 57c is the bottom face of
a concave part 57f with a depth of approximately 0.1 mm from the
top face 57a. With a small spindle motor, the depth of the concave
part 57f may be substantially the same (about 0.1 mm) regardless of
the size of the motor. Since the 0.1 mm depth of the concave part
57f is so small, it will have little effect on reducing the size
and thickness of the spindle motor. A slanted face 57e is formed
between the flat portion 57d and the top face 57a.
[0180] Next, the shaft 53 and the hub 57 are welded with a laser
welding apparatus featuring a YAG laser or the like. As shown in
FIG. 12, prior to welding, a sealing jig 62 provided at its distal
end with a metal sphere or cone having a diameter slightly larger
than the diameter of the threaded hole 61 is placed against the
threaded hole 61 to block off the threaded hole 61. Blocking off
the threaded hole 61 with the sealing jig 62 prevents welding fumes
from entering the threaded hole 61 should such welding fumes be
generated during welding. However, the sealing jig 62 need not be
used if some other welding fume removal means is employed.
[0181] In the welding step, a laser beam is directed toward the
bottom 60 of a valley-shaped concave part formed by the
inside-chamfered portion 57c and the outer peripheral face of the
shaft 53. During the laser welding, as shown in FIG. 15, the hub 57
is rotated and simultaneously irradiated with laser by three laser
welding heads. The rotation speed of the hub 57 is set
approximately 200-300 r/min. The output of the laser is
approximately 1-2 kW, and irradiated by 20-30 pulse/sec. The
intensity of the laser beam and the irradiation time are set so
that the metal material of the hub 57 and the shaft 53 near the
bottom 60 will melt and this molten metal will embed the
valley-shaped concave part including the inside-chamfered portion
57c. Even if the molten metal should overflow from the
valley-shaped concave part, it will just flow into the concave part
57f. Accordingly, this prevents the molten metal from overflowing
the top face 57a of the hub 57.
[0182] Upon completion of the laser welding, the weld including the
flat portion 57d is washed with a brush and a washing solvent.
After the washing solvent has been completely evaporated, the
concave part 57f including the flat portion 57d is coated with a
resin 63. This step is called the "overcoating step." Overcoating
with the resin 63 allows the microcracks produced by laser welding
to be covered up, and therefore prevents microparticles of metal
from flying out of the microcracks during the operation of the
spindle motor. The resin 63 is preferably composed of a material
that will cure in a short time after coating and will not release
gas after curing. A thermosetting epoxy adhesive is a readily
available and inexpensive example of such a resin. A two-liquid
epoxy adhesive may also be used, for instance. The resin 63 coating
amount should be about 0.1 mg for a spindle motor having a shaft
diameter of 2 mm.
[0183] In the overcoating step, excess resin can be prevented from
getting into the threaded hole 61 if the threaded hole 61 is
blocked off with the sealing jig 62 during coating with the resin
63.
[0184] With a spindle motor manufactured by the above method, the
removal strength of the shaft 53 and the hub 57 after laser welding
was approximately 80 kgf, which represents sufficient strength.
Since the threaded hole 61 was blocked off by the sealing jig 62
during welding, no welding fumes got into the threaded hole 61. If
the threaded hole 61 was also blocked off by the sealing jig 62 in
the overcoating step after welding, then no excess resin got into
the threaded hole 61.
[0185] Thus, the manufacturing method of the present invention
greatly increases the spindle motor manufacturing yield, and
increases the reliability and service life of HDDs and so forth
that make use of spindle motors.
Other Embodiments
[0186] (A) In Embodiment 1 above, an example in which the area near
the boundary between the shaft 7 and the second flange unit 9 was
laser welded in order to fix the second flange unit 9 to the shaft
7 was described through reference to FIG. 4. The shape of the
second flange unit 9 here is not limited to this, however. For
instance, as shown in FIG. 6a, the second flange unit may have a
concave part 5 on the inner peripheral side of the top face in the
axial direction, and laser welding may be performed in the area
near the boundary between the bottom of this concave part 5 and the
shaft 7.
[0187] The effect of the concave part 5 is to prevent warpage of
the second flange unit 9 during welding and prevent the scattering
of foreign matter.
[0188] When welding is performed with the configuration shown in
FIG. 4, a load is applied that draws the top face of the second
flange unit 9 toward the inner periphery. Consequently, the second
flange unit 9 may be warped upward in the axial direction (so that
the outer periphery is higher than the inner periphery).
[0189] In the above embodiment, the outer peripheral side of the
top face of the second flange unit 9 in the axial direction was
pressed in order to keep this warpage within a specified range. If,
in addition to this, the concave part 5 shown in FIG. 6a is
provided, the load that draws the second flange unit 9 toward the
inner periphery as a result of melting is instead exerted near the
bottom of the concave part 5, and therefore has less effect on the
top face. This means that the warpage of the second flange unit 9
is ameliorated.
[0190] Also, it is usually common for welding fumes or soot and
other such foreign matter produced in welding to scatter during
welding, and for these to affect the manufacturing precision of
other units. It is therefore preferable for this foreign matter to
be wiped away, sucked up with air, or otherwise removed after laser
welding, but even then there will be scattering of foreign
matter.
[0191] As shown in FIG. 6a, however, the scattering of foreign
matter can be suppressed by providing the concave part 5 to the
inner peripheral side of the second flange unit 9.
[0192] This provides a bearing unit 101 with better
performance.
(B) In the above Embodiment 1 and the above (A), an example of
using laser welding to fix the second flange unit 9 to the shaft 7
was described. After this, though, the laser welded sites may be
further overcoated with an adhesive resin (adhesive bond) or the
like.
[0193] The purpose of this is to prevent fouling of the interior of
the bearing unit 101 or the spindle motor 100 by contamination that
falls or flies out of microcracks produced at the laser welding
sites.
[0194] This provides a bearing unit 101 with better
performance.
(C) In the above Embodiment 1 and the above (A), the shape of the
second flange unit 9 was described, but the shape is not limited to
this. For instance, as shown in FIG. 6b, the second flange unit 9
may further have a bubble escape portion (a concave part) 21 on the
inner peripheral side of the bottom face in the axial
direction.
[0195] When the bearing unit 101 is operated after its manufacture,
bubbles may be produced in the lubricating fluid 116 injected into
the gaps between the units, and may hamper the smooth operation of
the bearing unit 101. Bubbles that move from the radial bearing
region to the thrust bearing region try to accumulate at the
boundary thereof. This is because centrifugal force acts on the
lubricating fluid while the bearing is operating, and the
lubricating fluid, which has a high specific gravity, moves toward
the outside of the thrust bearing, while bubbles, which have a low
specific gravity, move toward the inside of the thrust bearing.
Also, bubbles produced in the thrust bearing region move toward the
inside of the thrust bearing similarly to the above.
[0196] In view of this, a concave part is provided as a bubble
escape portion 21 on the inner peripheral side of the bottom face
of the second flange unit 9 in the axial direction. The bubbles
flow into and accumulate in this concave part, and do not impede
the smooth operation of the bearing unit 101.
[0197] This makes it possible to sustain the smooth operation of
the bearing unit 101.
[0198] As to the size of the concave part 5 and the bubble escape
portion 21, if, for example, the diameter of the shaft 7 is
approximately 3.5 to 4.5 mm and the thickness of the second flange
unit 9 is approximately 2 to 4 mm, the inside diameter of the
concave part 5 will be approximately 5.5 mm (1.5 to 2 times the
shaft diameter) and the depth approximately 1 mm (less than
one-third the thickness of the second flange unit 9), and the
inside diameter of the bubble escape portion 21 will be
approximately 3.7 mm (less than the minimum inside diameter of the
thrust bearing groove portion and greater than the sleeve inside
diameter) and the depth approximately 1 mm (less than one-third the
thickness of the second flange unit 9 and greater than the thrust
gap).
[0199] Also, a location of the bubble escape portion 21 is not
limited to the above. For instance, the bubble escape portion 21
can be formed on the first flange unit 6 fixed on the shaft 7.
(D) In the above Embodiment 1 and the above (A) through (C), the
bearing unit 101 pertaining to the present invention was described,
but the present invention is not limited to this. For instance, a
bearing unit 101' equipped with a spindle motor 100' may be
configured as shown in FIG. 7. Specifically, the bearing unit 101'
comprises at least the shaft 7, the sleeve 8 that is attached in a
state of being rotatable relative to the shaft 7, the first flange
unit 6 that is fixed to or integrated with the shaft 7, and the
second flange unit 9 that is fixed to the shaft 7, and further has
a first sealing unit 18 fixed to the sleeve 8 so as to cover the
bottom face of the first flange unit 6 in the axial direction,
and/or a second sealing unit 17 fixed to the sleeve 8 so as to
cover the top face of the second flange unit 9 in the axial
direction.
[0200] The lubricating fluid 116 is injected into the gaps between
the flange units 6 and 9 and the sleeve 8. Foreign matter can find
its way into these gaps from the bottom face in the axial
direction, or the lubricating fluid 116 can leak out from these
gaps. Foreign matter may also find its way in from the top face. As
a result, the smooth operation of the bearing unit 101 is
impeded.
[0201] Also, the sleeve 8 and the first flange unit 6 are usually
disposed near the base plate 1, with a specific gap provided
between them and the base plate 1. The distance of this gap is tiny
in order to prevent contamination by foreign matter from the bottom
face in the axial direction and leakage of the lubricating fluid
116. Consequently, high precision is required in the manufacture of
a spindle motor, and this limits the freedom of design of the
spindle motor.
[0202] In view of this, the sleeve 8 is fixed by disposing the
sealing units 17 and 18 so as to cover the faces of the flange
units 6 and 9, respectively, in the axial direction in order to
seal the gap between the flange units 6 and 9 and the sleeve 8. As
long as the above-mentioned gap can be sealed, the sealing units 17
and 18 may be disposed so as to span at least the outer peripheral
sides of the faces of the flange units in the axial direction.
Here, the sealing units 17 and 18 may be fixed to the sleeve 8 with
an adhesive or the like.
[0203] Using a structure such as this no only suppresses the
admixture of foreign matter and the leakage of the lubricating
fluid 116, but also means that the bearing unit 101' does not
necessarily have to be disposed near the base plate 1, which
affords greater design freedom.
[0204] This yields a bearing unit 101' with better operating
performance.
(E) In Embodiment 1 above, an example of using the spherical jig 10
to press on the shaft 7 directly was described, but the present
invention is not limited to this method. For example, the shaft 7
may be pressed via another unit such as a piece of hard rubber
material.
[0205] This allows a bearing unit 101 to be manufactured with good
precision.
(F) In Embodiment 1 above and in the above (A) through (E), an
example in which the shaft 7 was a stationary unit was described,
but the present invention is not limited to this constitution. For
example, as shown in FIG. 8, the present invention may be applied
to what is known as a shaft rotation type of bearing unit 102, in
which a shaft 7' is a rotating unit and a sleeve 8' is a stationary
unit.
[0206] In this bearing unit 102, a hub 12' is affixed to the shaft
7' and rotates integrally with the shaft 7'. The sleeve 8' is
press-fitted and adhesively bonded to the concave part of the base
plate 1, and thereby fixed to the base plate 1. Here, a ventilation
hole 22 as shown in FIG. 8 is preferably formed between the base
plate 1 and the sleeve 8'. The role of the ventilation hole 22 is
to prevent the lubricating fluid from leaking out by means of air
that has nowhere to go when the gap between the bearing unit 102
and the base plate 1 is sealed. The rest of the units are
constituted the same as in the above Embodiment 1 or any of the
above (A) through (E).
[0207] This again has the same effect as the above Embodiment 1 or
any of the above (A) through (E).
(G) Also, according to the spindle motor of the present invention,
the spindle motor may have a structure having a circular groove to
prevent a lubricating fluid from leaching. In particular, as shown
in FIG. 16, the circular groove 320 is formed at a joint portion
between the shaft 353 and the hub 357 of the shaft 353 side of the
spindle motor 300.
[0208] Ordinarily, when the laser welding is used for manufacturing
the spindle motor 300, the shaft 353 and the hub 357 are jointed
together by only press-fitting. However, only press-fitting cause a
problem that a leaching of the lubricating fluid (not shown) in a
bearing unit 302.
[0209] In view of this, at the joint portion of the shaft 353 and
the hub 357, the circular groove 320 is formed to prevent the
lubricant fluid from leaching and to make the lubricant fluid
remain in the circular groove 320.
[0210] This yields a spindle motor 300 with better operating
performance.
[0211] The circular groove 320 may be formed at the hub 357
side.
[0212] The present invention can be applied to any motor having a
hydrodynamic bearing, such as a spindle motor. Furthermore, the
present invention can be applied to spindle motors of the type that
are open at both ends and have a fixed shaft, which are used in
recording medium control devices having a plurality of disks.
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