U.S. patent application number 09/836457 was filed with the patent office on 2001-09-13 for disk drive unit with hydrodynamic fluid bearing unit and disk device with said drive unit.
Invention is credited to Kanamaru, Hisanobu, Kawakami, Kazuhiko, Kouno, Takashi, Kumasaka, Noriyuki, Muranishi, Masaru, Nii, Katsutoshi, Nishida, Hiroshi, Tomida, Kenji, Uefune, Kouki, Yanagase, Yuuichi.
Application Number | 20010021080 09/836457 |
Document ID | / |
Family ID | 13860582 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010021080 |
Kind Code |
A1 |
Nii, Katsutoshi ; et
al. |
September 13, 2001 |
Disk drive unit with hydrodynamic fluid bearing unit and disk
device with said drive unit
Abstract
A disk drive unit includes a rotary member, which has a spindle,
and has an information-recording disk fixedly mounted thereon, and
a bearing unit rotatably supporting the spindle. The bearing unit
includes a radial bearing device, provided in opposed relation to
an outer peripheral surface of the spindle, and a thrust bearing
device provided in opposed relation to a distal end surface of the
spindle. The radial bearing device has a concentric arc-shaped
bearing surface, which is concentric with the circular outer
periphery of the spindle, and a non-concentric arc-shaped bearing
surface which is non-concentric with the circular outer periphery
of the spindle. The disk drive unit further includes a motor for
imparting a rotational force to the spindle, and a lubricating
fluid filled in the bearing unit.
Inventors: |
Nii, Katsutoshi;
(Hitachi-shi, JP) ; Tomida, Kenji; (Odawara-shi,
JP) ; Nishida, Hiroshi; (Kanagawa-ken, JP) ;
Uefune, Kouki; (Odawara-shi, JP) ; Yanagase,
Yuuichi; (Ibaraki-ken, JP) ; Muranishi, Masaru;
(Ibaraki-ken, JP) ; Kouno, Takashi; (Ibaraki-ken,
JP) ; Kawakami, Kazuhiko; (Hitachinaka-shi, JP)
; Kanamaru, Hisanobu; (Hitachinaka-shi, JP) ;
Kumasaka, Noriyuki; (Ome-shi, JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
13860582 |
Appl. No.: |
09/836457 |
Filed: |
April 18, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09836457 |
Apr 18, 2001 |
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09277163 |
Mar 26, 1999 |
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6243230 |
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Current U.S.
Class: |
360/99.08 ;
G9B/19.029 |
Current CPC
Class: |
F16C 17/028 20130101;
F16C 17/18 20130101; F16C 2370/12 20130101; F16C 33/1075 20130101;
H02K 5/1675 20130101; G11B 19/2018 20130101 |
Class at
Publication: |
360/99.08 |
International
Class: |
G11B 017/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 1998 |
JP |
10-085497 |
Claims
What is claimed is:
1. A disk drive unit comprising: a rotary member having a spindle;
an information-recording disk being fixedly mounted on said rotary
member; a bearing unit rotatably supporting said spindle, the
bearing unit including a radial bearing device provided in opposed
relation to an outer peripheral surface of said spindle, the radial
bearing device having a concentric arc-shaped bearing surface that
is concentric with said circular outer periphery of said spindle,
and a non-concentric arc-shaped bearing surface that is
non-concentric with said circular outer periphery of said spindle,
and a thrust bearing device provided in opposed relation to a
distal end surface of said spindle, a motor for imparting a
rotational force to said spindle; and a lubricating fluid filled in
said bearing unit.
2. A disk drive unit according to claim 1, wherein said radial
bearing device comprises a plurality of radial bearings arranged in
a direction of an axis of said spindle; one of said plurality of
radial bearings has only said concentric arc-shaped bearing
surface; and another of said plurality of radial bearings has a
plurality of said non-concentric arc-shaped bearing surfaces.
3. A disk drive unit according to claim 2, wherein said radial
bearing device further comprises axial grooves formed associatedly
adjacent to said non-concentric arc-shaped bearing surfaces.
4. A disk drive unit according to claim 1, wherein said radial
bearing device comprises a plurality of radial bearings arranged in
a direction of an axis of said spindle; each of said plurality of
radial bearings has a plurality of said concentric arc-shaped
bearing surfaces, a plurality of said non-concentric arc-shaped
bearing surfaces, and said plurality of concentric arc-shaped
bearing surfaces of said radial bearing extend 1/6 to 3/4 of an
inner peripheral surface of said radial bearing in a
circumferential direction.
5. A disk drive unit according to claim 4, wherein said plurality
of concentric arc-shaped bearing surfaces of said radial bearing
extend about 1/3 of said inner peripheral surface of said radial
bearing in said circumferential direction.
6. A disk drive unit according to claim 4, wherein said radial
bearing device further comprises axial grooves formed associatedly
adjacent to said non-concentric arc-shaped bearing surfaces.
7. A disk drive unit according to claim 6, wherein if viewed in a
direction of an axis of said spindle, each of said plurality of
concentric arc-shaped bearing surfaces is disposed substantially
centrally between said axial grooves.
8. A disk drive unit according to claim 6, wherein if viewed in a
direction of an axis of said spindle, each of said plurality of
concentric arc-shaped bearing surfaces is disposed adjacent to said
axial groove.
9. A disk drive unit according to claim 1, wherein the maximum
distance between said spindle and said non-concentric arc-shaped
bearing surfaces is 1.5 to 3 times larger than the distance between
said spindle and said concentric arc-shaped bearing surfaces.
10. A disk drive unit according to claim 1, wherein said distal end
surface of said spindle is formed into a flat surface, and said
thrust bearing device has a flat surface which is smaller in
diameter than said spindle, and is held in opposed relationship
with said flat distal end surface of said spindle.
11. A disk drive unit according to claim 1, wherein said distal end
surface of said spindle is rounded, and said thrust bearing device
has a flat surface held in opposed relationship with said rounded
distal end surface of said spindle.
12. A disk drive unit according to claim 1, wherein said distal end
surface of said spindle is rounded, and said thrust bearing device
has a concave surface which is substantially complementary to said
rounded distal end surface of said spindle, and is held in opposed
relationship with said rounded distal end surface.
13. A disk device comprising: a rotary member having a spindle; an
information-recording disk being fixedly mounted on said rotary
member; a bearing unit rotatably supporting said spindle, the
bearing unit including a radial bearing device provided in opposed
relation to an outer peripheral surface of said spindle, the radial
bearing device having a concentric arc-shaped bearing surface that
is concentric with said circular outer periphery of said spindle,
and a non-concentric arc-shaped bearing surface that is
non-concentric with said circular outer periphery of said spindle;
and a thrust bearing device provided in opposed relation to a
distal end surface of said spindle; a motor for imparting a
rotational force to said spindle; a lubricating fluid filled in
said bearing unit; a read/write head disposed in opposed relation
to said information-recording disk; and an actuator for positioning
said head on said information-recording disk.
14. A disk device according to claim 13, wherein said radial
bearing device comprises a plurality of radial bearings arranged in
a direction of an axis of said spindle; one of said plurality of
radial bearings has only said concentric arc-shaped bearing
surface; and another of said plurality of radial bearings has a
plurality of said non-concentric arc-shaped bearing surfaces.
15. A disk device according to claim 14, wherein said radial
bearing device further comprises axial grooves formed associatedly
adjacent to said non-concentric arc-shaped bearing surfaces.
16. A disk device according to claim 13, wherein said radial
bearing device comprises a plurality of radial bearings arranged in
a direction of an axis of said spindle; each of said plurality of
radial bearings has a plurality of said concentric arc-shaped
bearing surfaces, a plurality of said non-concentric arc-shaped
bearing surfaces, and said plurality of concentric arc-shaped
bearing surfaces of said radial bearing extend 1/6 to 3/4 of an
inner peripheral surface of said radial bearing in a
circumferential direction.
17. A disk device according to claim 16, wherein said plurality of
concentric arc-shaped bearing surfaces of said radial bearing
extend about 1/3 of said inner peripheral surface of said radial
bearing in said circumferential direction.
18. A disk device according to claim 16, wherein said radial
bearing device further comprises axial grooves formed associatedly
adjacent to said non-concentric arc-shaped bearing surfaces.
19. A disk device according to claim 18, wherein if viewed in a
direction of an axis of said spindle, each of said plurality of
concentric arc-shaped bearing surfaces is disposed substantially
centrally between said axial grooves.
20. A disk device according to claim 18, wherein if viewed in a
direction of an axis of said spindle, each of said plurality of
concentric arc-shaped bearing surfaces is disposed adjacent to said
axial groove.
21. A disk device according to claim 13, wherein the maximum
distance between said spindle and said non-concentric arc-shaped
bearing surfaces is 1.5 to 3 times larger than the distance between
said spindle and said concentric arc-shaped bearing surfaces.
22. A disk device according to claim 13, wherein said distal end
surface of said spindle is formed into a flat surface, and said
thrust bearing device has a flat surface which is smaller in
diameter than said spindle, and is held in opposed relationship
with said flat distal end surface of said spindle.
23. A disk device according to claim 13, wherein said distal end
surface of said spindle is rounded, and said thrust bearing device
has a flat surface held in opposed relationship with said rounded
distal end surface of said spindle.
24. A disk device according to claim 13, wherein said distal end
surface of said spindle is rounded, and said thrust bearing device
has a concave surface which is substantially complementary to said
rounded distal end surface of said spindle, and is held in opposed
relationship with said rounded distal end surface.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a disk drive unit and a
disk device having this drive unit, and more particularly to a
hydrodynamic fluid bearing unit for the disk drive unit.
[0002] Recently, in order to achieve the high-speed transfer of
data and high-density recording, a motor in a magnetic disk drive
unit has been more and more required to achieve a high-speed,
high-precision rotation. In order to meet this requirement, a motor
(as disclosed in JP-A-5-336696, JP-A-8-189525 and JP-A-9-200998),
having a hydrodynamic bearing, has been proposed.
[0003] A motor in a magnetic disk drive unit is intensely required
to have an improved shock resistance so that the function of the
disk drive unit will not be deteriorated when a personal computer,
incorporating the disk drive unit, is dropped from a desk or is
fallen while it is carried.
[0004] Particularly, a notebook-type personal computer can undergo
an impact force of about 1,000 G while it is used or carried,
depending on the manner of handling it. And besides, since the
notebook-type personal computer is driven by a battery, it requires
a disk drive unit of the low power consumption-type.
[0005] A groove bearing, wherein shallow grooves for producing a
dynamic pressure are formed in a spindle, is proposed in
JP-A-5-336696. Although this groove bearing is excellent in
high-speed operation and in accuracy of the spindle rotation, it
has problems that the production cost is high and that the mass
production can not be easily carried out. The depth of the dynamic
pressure-producing grooves in the groove bearing are several
microns, and when the grooves are deformed by an impact load, the
adequate dynamic pressure cannot be produced, which results in a
possibility that the unstable vibration occurs. A hydrodynamic
three-lobe bearing, disclosed in JP-A-8-189525 and JP-A-9-200998,
can achieve high-speed, high precision rotation equivalent to that
obtained with the above groove bearing. However, when an impact
force of about 1,000 G acts on this bearing, edge portions of the
grooves can be deformed, so that its bearing characteristics are
deteriorated.
[0006] JP-A-8-189525 discloses a groove-type thrust bearing. When a
bearing surface of the groove-type thrust bearing is deformed by an
impact force, it is liable-that a lubricating fluid is not-properly
supplied to the bearing surface.
[0007] The groove-type bearing supports or bears a thrust load at
an end surface of a spindle or bearing, and therefore is subjected
to a larger friction loss as compared with a ball bearing-type, and
it is difficult to achieve a low power consumption design.
SUMMARY OF THE INVENTION
[0008] With the above problems of the prior art in view, it is an
object of this invention to provide a disk drive unit provided with
a bearing unit which has a small friction loss, and is excellent in
shock resistance and mass production efficiency.
[0009] Another object of the invention is to provide a magnetic
disk device provided with the above disk drive unit.
[0010] According to one aspect of the present invention, there is
provided a disk drive unit comprising:
[0011] a rotary member having a spindle;
[0012] an information-recording disk being fixedly mounted on said
rotary member;
[0013] a bearing unit rotatably supporting the spindle, the bearing
unit including
[0014] a radial bearing device provided in opposed relation to an
outer peripheral surface of the spindle, the radial bearing device
having a concentric arc-shaped bearing surface that is concentric
with the circular outer periphery of the spindle, and a
non-concentric arc-shaped bearing surface that is non-concentric
with the circular outer periphery of the spindle, and
[0015] a thrust bearing device provided in opposed relation to a
distal end surface of the spindle;
[0016] a motor for imparting a rotational force to the spindle;
and
[0017] a lubricating fluid filled in the bearing unit.
[0018] The maximum distance between the spindle and each of the
non-concentric arc-shaped bearing surfaces is 1.5 to 3 times larger
than the distance between the spindle and each of the concentric
arc-shaped bearing surfaces.
[0019] The distal end surface of the spindle is formed into a flat
surface, and the thrust bearing device has a flat surface which is
smaller in diameter than the spindle, and is held in opposed
relationship with the flat distal end surface of the spindle.
[0020] In one form of the invention, the distal end surface of the
spindle is rounded, and the thrust bearing device has a flat
surface held in opposed relationship with the rounded distal end
surface of the spindle.
[0021] In another form of the invention, the distal end surface of
the spindle is rounded, and the thrust bearing device has a concave
surface which is substantially complementary to the rounded distal
end surface of the spindle, and is held in opposed relationship
with the rounded distal end surface.
[0022] In one form of the disk drive unit of the invention, the
radial bearing device comprises a plurality of radial bearings
arranged in a direction of an axis of the spindle, and at least one
of the plurality of radial bearings has only the concentric
arc-shaped bearing surface, and each of the other radial bearings
has a plurality of the non-concentric arc-shaped bearing surfaces
and axial grooves each formed between the associated adjacent
non-concentric arc-shaped bearing surfaces.
[0023] In another form of the disk drive unit of the invention, the
radial bearing device comprises a plurality of radial bearings
arranged in a direction of an axis of the spindle, and each of the
plurality of radial bearings has a plurality of the concentric
arc-shaped bearing surfaces, a plurality of the non-concentric
arc-shaped bearing surfaces and axial grooves each formed between
the associated adjacent non-concentric arc-shaped bearing surfaces,
and the plurality of concentric arc-shaped bearing surfaces of the
radial bearing extend 1/6 to 3/4 of an inner peripheral surface of
the radial bearing in a circumferential direction.
[0024] Preferably, the plurality of concentric arc-shaped bearing
surfaces of the radial bearing extend about 1/3 of the inner
peripheral surface of the radial bearing in the circumferential
direction.
[0025] When viewed in a direction of an axis of the spindle, each
of the plurality of concentric arc-shaped bearing surfaces is
disposed substantially centrally between the associated adjacent
axial grooves. Alternatively, each of the plurality of concentric
arc-shaped bearing surfaces is disposed adjacent to the associated
axial groove.
[0026] According to another aspect of the invention, there is
provided a disk device comprising:
[0027] a rotary member having a spindle;
[0028] an information-recording disk being fixedly mounted on the
rotary member;
[0029] a bearing unit rotatably supporting the spindle, the bearing
unit including
[0030] a radial bearing device provided in opposed relation to an
outer peripheral surface of the spindle, the radial bearing device
having a concentric arc-shaped bearing surface that is concentric
with the circular outer periphery of the spindle, and a
non-concentric arc-shaped bearing surface that is non-concentric
with the circular outer periphery of the spindle, and
[0031] a thrust bearing device provided in opposed relation to a
distal end surface of the spindle,
[0032] a motor for imparting a rotational force to the spindle;
[0033] a lubricating fluid filled in the bearing unit;
[0034] a read/write head disposed in opposed relation to the
information-recording disk; and
[0035] an actuator for positioning the head on said
information-recording disk.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 is a vertical cross-sectional view of a first
embodiment of a magnetic disk drive unit of the invention;
[0037] FIG. 2 is an enlarged, vertical cross-sectional view of a
bearing unit of the first embodiment;
[0038] FIGS. 3 and 4 are transverse cross-sectional views of radial
bearings of the first embodiment, respectively;
[0039] FIG. 5 is a vertical cross-sectional view of a second
embodiment of a magnetic disk drive unit of the invention;
[0040] FIG. 6 is an enlarged, vertical cross-sectional view of a
bearing unit of the second embodiment;
[0041] FIG. 7 is a transverse cross-sectional view of a radial
bearing of the second embodiment;
[0042] FIG. 8 is a graph showing the relation between a bearing
stiffness of the radial bearing and concentric arc-shaped bearing
surfaces in the second embodiment;
[0043] FIG. 9 is a plan view of the radial bearing of the second
embodiment;
[0044] FIG. 10 is a plan view of a modified radial bearing of the
second embodiment;
[0045] FIG. 11 is a view explanatory of a hydrodynamic effect of
the modified radial bearing;
[0046] FIG. 12 is a plan view of a modified form of the radial
bearing shown in FIG. 10;
[0047] FIG. 13 is a vertical cross-sectional view of a third
embodiment of a magnetic disk drive unit of the invention;
[0048] FIG. 14 is an enlarged, vertical cross-sectional view of a
bearing unit of the third embodiment;
[0049] FIG. 15 is an enlarged, vertical cross-sectional view of a
bearing unit used in a fourth embodiment of a magnetic disk drive
unit of the invention;
[0050] FIG. 16 is a vertical cross-sectional view of a magnetic
disk device of the invention, taken along line XVI-XVI in FIG. 17;
and
[0051] FIG. 17 is a plan view of the magnetic disk device of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0052] The present invention will now be described with reference
to the drawings.
[0053] FIGS. 1 to 4 show a first embodiment of a magnetic disk
drive unit of the present invention. Although this embodiment is
directed to the magnetic disk drive unit, the present invention can
be applied to any other suitable device for driving or rotating an
information-recording medium.
[0054] A spindle 1 is fixedly secured to a hub 13 having a
cylindrical surface for mounting disks thereon. Magnetic disks 14
and 15 are fixedly secured to the hub 3 by a screw 22 through a
disk clamp 18 and a spacer ring 16. A motor rotor (rotor magnet) 9,
magnetized in a multi-pole pattern, is fixedly secured to an inner
peripheral surface of the hub 13. The spindle 1 is rotatably
supported by radial bearings 2, 3 and 26 and a thrust bearing 8. A
retainer ring 7 is fixedly mounted on an end portion of the spindle
1.
[0055] A cover 17, the radial bearings 2, 3 and 26, the thrust
bearing 8 and the retainer ring 7 are provided in a bearing housing
5 made of a non-magnetic material, and a lubricating fluid 6 is
sealed in the bearing housing 5. The bearing housing 5 and a motor
stator 10, having a motor coil 11, are fixedly mounted on a motor
casing 12.
[0056] The motor of this construction is a DC brushless motor, and
the hub 13 is driven by a rotating magnetic field, produced when
the coil 11 is energized, and a magnetic field possessed by the
motor rotor 9 magnetized in a multi-polar manner.
[0057] The bearing 26, having only a circular (arc-shaped) surface
concentric with the spindle 1, and the bearings 2 and 3, each
having non-concentric, arc-shaped surfaces (see FIG. 4), are
provided in the bearing unit of FIG. 2. A spacer 4 is provided
between the bearings 2 and 3. The distal end of the spindle 1 is
formed into a generally semi-spherical shape, and the flat thrust
bearing 8 is disposed in opposed relation to this distal end.
[0058] The lubricating fluid 6 is sealed in the bearing housing 5,
and the spindle 1 is supported in a non-contact manner by the
radial bearings 26, 2 and 3 through the lubricating fluid 6.
[0059] Ordinary lubricating oil may be used as the lubricating
fluid 6. However, preferably, in order to achieve a sealing effect,
a ring-shaped permanent magnet, made of a rare earth element, is
used as the spacer 4, and a magnetic fluid, having superfine
magnetic powder (having a particle size of about 0.01 .mu.m)
dispersed in lubricating oil, is used as the lubricating fluid 6.
With this construction, the magnetic fluid is attracted by the
spacer 4 comprising the permanent magnet, and will not leak to the
exterior of the bearing unit. The gap between the spindle 1 and the
radial bearings 2, 3 and 26, is very small on the order of several
micron meters, and therefore in a stationary condition, the sliding
surfaces of the spindle and the radial bearings are wetted with the
magnetic fluid 6 because of a capillary phenomenon. Therefore, when
the spindle 1 is driven, the sliding surfaces between the bearing
and the spindle are lubricated from the beginning of the rotation.
And besides, the magnetic fluid 6, overflowing the radial bearing 2
because of the expansion of the volume of the magnetic fluid 6 by a
temperature rise and a hydrodynamic effect of the bearing, is
attracted by the spacer 4 of a permanent magnet via grooves 19, 20
and 21 (FIG. 2) formed in bearing end surfaces and bearing outer
peripheral surfaces of the radial bearings 2 and 3. Therefore,
there is no fear that the magnetic fluid 6 leaks to the exterior of
the bearing unit.
[0060] FIG. 3 shows the configuration of the radial bearing 26
having only the concentric circular (arc-shaped) bearing surface,
and this radial bearing is a cylindrical bearing having a radius r.
FIG. 4 shows the configuration of the radial bearing 2, 3 including
the non-concentric arc-shaped bearing surfaces. More specifically,
the radial bearing 2, 3 has the three arc-shaped bearing surfaces,
which are not concentric or coaxial with the axis of the bearing,
and have a radius (arc radius) R, and axial grooves 20' each formed
between the adjacent bearing surfaces. When an impact force is
applied, the radial bearing 26 and the spindle 1 come substantially
into surface contact with each other since they have substantially
the same curvature. In this case, if the lubricating fluid is
provided on the bearing surface, a damping effect due to a squeeze
action effect is large, and therefore the spindle 1 and the radial
bearing hardly come into direct contact with each other. During the
rotation, in addition to the effect of the radial bearing 26, the
spindle 1 is supported in a non-contact manner by an oil film
because of the hydrodynamic effect of the radial bearings 2 and 3,
and therefore the shock resistance is enhanced. And besides, since
the spindle 1 is supported highly stiff by the oil film, the
precise rotation can always be maintained.
[0061] Next, a second embodiment of a magnetic disk drive unit of
the present invention will be described with reference to FIGS. 5
to 8.
[0062] FIG. 6 shows a bearing unit of this disk drive unit which
differs from the bearing unit of FIG. 2 in that the radial bearing
26 is not provided. The radial bearings 2' and 3' are different in
configuration from the radial bearings 2 and 3 of the first
embodiment in that a bearing surface of the radial bearings 2' and
3' has portions for surface contact with a spindle 1 upon being
subjected to an impact load, as shown in FIG. 7.
[0063] More specifically, each of the radial bearings 2' and 3' has
bearing surfaces, which are concentric or coaxial with the axis of
the spindle 1, and have an arc radius r, and bearing surfaces which
are not concentric or coaxial with the axis of the spindle 1, and
have an arc radius R. In the radial bearing 2', 3' shown in FIG. 7,
the concentric arc-shaped bearing surfaces are represented by
.theta., and each of these concentric arc-shaped bearing surfaces
is provided centrally between adjacent axial grooves 20'. When an
external impact force is applied, these concentric arc-shaped
bearing surfaces perform a damping effect.
[0064] Particularly when the concentric bearing surfaces .theta.,
having the arc radius r, are suitably designed, the rigidity of the
oil film for the bearing is about 1.5 times larger as compared with
the conventional hydrodynamic bearing, and therefore the more
enhanced rotation precision can be obtained. With respect to the
optimum dimension of the bearing surfaces .theta. determined by the
bearing stiffness, the sum of the dimensions of the bearing
surfaces .theta. is in the range of about 1/3 of the entire bearing
surface, as shown in FIG. 8. In order to enhance the shock
resistance, the sum of the dimensions of the bearing surfaces
.theta. should be about 3/4 of the entire bearing surface though
this slightly lowers the oil film stiffness of the bearing.
[0065] Even if the sum of the dimensions of the bearing surfaces
.theta. is not more than 1/6 of the entire bearing surface, similar
results can be obtained, and preferably the sum of the dimensions
of the bearing surfaces .theta. is 1/6 to 3/4. If the maximum gap a
between the non-concentric arc-shaped bearing surface and the
spindle is 1.5 to 3 times larger than the gap c between the
concentric arc-shaped bearing surface and the spindle, the
stiffness of the oil film due to the hydrodynamic effect is
increased.
[0066] As shown in FIG. 9, grooves 19 are formed in a bearing end
surface of the radial bearing 2', 3', and grooves 20 are formed in
the outer peripheral surface thereof. With this construction, a
magnetic fluid 6 is drawn by a magnetic attraction force of a
spacer 4, comprising a permanent magnet, as described above.
[0067] The hydrodynamic radial bearing of the present invention can
be formed or shaped using a sintered lubricant-containing bearing
material, and by doing so, the bearing unit, having good
dimensional accuracy and excellent mass production efficiency, can
be provided.
[0068] As shown in FIG. 10, the concentric arc-shaped bearing
surfaces can be provided near to the grooves 20', respectively.
[0069] The hydrodynamic effect of the hydrodynamic bearings, shown
respectively in FIGS. 7 and 10, will be described. The bearing gap
between the spindle 1 and the bearing surface is gently decreasing
or narrowing as shown in the drawings. Therefore, when the spindle
1 rotates in a direction of arrow A, oil film pressures Pa, having
a profile shown in FIG. 11, develop, and serve to hold the spindle
1 at the axis (centerline) of the bearing. In contrast, the gap
between the spindle 1 and the bearing surface at those portions
designated by .alpha. is increasing in the direction of rotation,
and therefore negative oil pressures Pb develop, and serve to lower
the bearing stifness.
[0070] It is desirable for the bearing that the negative oil
pressures Pb are small. However, the negative pressures serve to
return the magnetic fluid from the bearing end surface to the
bearing surface. Thus, the negative pressures serve to draw the
magnetic fluid to the bearing surface, and therefore if the
dimension of a is set to about {fraction (1/10)} of the bearing
surface, the magnetic fluid on the bearing end surface can be
returned to the bearing surface without hardly lowering the
performance of the bearing. In the bearing shown in FIG. 7, each
concentric arc-shaped bearing surface is disposed centrally between
the adjacent axial grooves 20', and therefore this bearing is
designed for supporting the spindle rotating in opposite
directions. On the other hand, the bearing, shown in FIG. 10, is
designed for supporting the spindle rotating in one direction.
[0071] In the above embodiment, although each of the radial
bearings has the three concentric arc-shaped bearing surfaces and
the three non-concentric arc-shaped bearing surfaces, each radial
bearing may have three or more arc-shaped bearing surfaces (for
example, 4 to 5 arc-shaped bearing surfaces as shown in FIG. 12).
In this case, similar effects as described above can be achieved,
and besides the higher-precision rotation can be obtained, and this
construction is suited for the type of magnetic disk drive unit
required to have a particularly-high rotation precision.
[0072] FIGS. 13 and 14 show a third embodiment of a disk drive unit
of the present invention. In this embodiment, a distal end of a
spindle 1 is flat, and a bearing surface of a thrust bearing 8 is
flat, and is smaller in diameter than the spindle 1. A bearing unit
of this embodiment differs from the bearing unit of FIG. 6 in that
an impact force, applied in a thrust direction, is supported or
borne by the flat surface of the thrust bearing 8 and the distal
end surface of the spindle 1. This construction has a higher shock
resistance as compared with the thrust bearing of FIG. 6.
[0073] If the diameter of the contact surface of the thrust bearing
8 is 1/2 to 2/3 of the diameter of the spindle 1, the deformation
of the bearing surface, developing upon application of an impact
force of 1,000 G, is on the order of sub-micron meters, and
therefore the precision of the magnetic disk device will not be
deteriorated. Although a friction loss is slightly larger as
compared with the bearing of the first embodiment, the smooth
rotation can be achieved since an oil film is provided on the
sliding surface.
[0074] FIG. 15 shows a fifth embodiment of a magnetic disk drive
unit of the present invention. In this embodiment, a thrust
bearing, having a flat surface, is used in combination of a spindle
1, having a distal end of a generally semi-spherical shape, as
shown in FIG. 2, and a load, corresponding to an impact force of
1,000 G, is beforehand applied to form the bearing surface of the
thrust bearing into a concave surface having substantially the same
semi-spherical shape as that of the distal end of the spindle
1.
[0075] When a load of several tens of kilograms is applied to a
motor, having a conventional ball bearing, in an axial direction, a
dent is formed on a rolling surface of the bearing or balls. As a
result, a rotating sound is increased, and also the rotation
precision is much deteriorated. On the other hand, in the bearing
unit of the present invention, a thrust load is supported or borne
by the surface, that is, by the surface contact. Therefore, even if
the bearing unit is press-fitted into the motor casing 12 while
applying a load of several tens of kilograms to the spindle 1, the
bearing surface of the thrust bearing is hardly deformed, and
therefore the assembling efficiency of the magnetic disk device is
greatly enhanced.
[0076] FIG. 16 shows a magnetic disk device of the present
invention. Although this embodiment is directed to the magnetic
disk device, the present invention can be applied to any other
suitable device or unit designed to store information in a rotating
information-recording medium.
[0077] A magnetic head 104 is provided on one or each side of each
magnetic disk (information-recording medium) 101 in opposed
relation thereto. When the magnetic disk 101 is rotated, the
magnetic head 104 flies a microscopic distance off the magnetic
disk 101, and in this condition the magnetic head 104 reads and
writes magnetic information relative to the magnetic disk 101. The
magnetic head 104 is connected to a carriage 106 through a load arm
105.
[0078] The carriage 106 is pivotally supported by a pivot bearing
107 so as to be pivotally moved about an axis of this pivot bearing
107. With this construction, a desired track on the magnetic disk
101 can be accessed. A voice-coil motor 108 is provided at that
side of the carriage 106 facing away from the magnetic heads 104,
and moves the magnetic head 104 at high speed to a desired track,
and locates it at this track on the magnetic disk 101.
[0079] The load arms 105, the carriage 106, the pivot bearing 107
and the voice-coil motor 108 jointly constitute an actuator.
Generally, the pivot bearing 107 and the voice-coil motor 108 are
pivotally mounted on a base 109 through pivot shafts. The provision
of the load arms 105 may be omitted. In order to protect these
constituent parts from external dirt and dust, a cover 110 is
attached to the base 109, so that the constituent parts are
isolated from the exterior.
[0080] FIG. 17 is a plan view of the magnetic disk device of FIG.
16, with the cover removed.
[0081] A spindle 1 is rotatably mounted on the base 109, and the
magnetic disks 101 are fixedly mounted on the spindle 1 through a
fixing member 18. Each magnetic head 104 is fixedly secured to the
carriage 106, and is disposed in proximity to the associated
magnetic disk 101. The carriage 106 is pivotally supported by the
rotation shaft 107, and is driven by the voice-coil motor 108. A
signal, read by the magnetic head 104, is transmitted to the
exterior of the sealed structure via a flexible connecting
conductor 111. Adhesive members 114 and 115 are provided at an
outlet port (through which the flexible connecting conductor 111
passes) in the sealed structure, and hold the flexible connecting
conductor 111 therebetween. Longer sides of the adhesive member 114
are different in length from the longer sides of the adhesive
member 115. The cover 110 (FIG. 16) is attached to the base 109,
and with this construction the sealed structure is provided.
[0082] Here, description will be made of effects achieved when
using the bearing unit of the present invention (for example, the
bearing unit of FIG. 14) as the motor bearing unit in the magnetic
disk device, will be described.
[0083] In the magnetic disk device, as many magnetic disks 101 as
possible are packaged or received in the magnetic disk device
having a limited height (vertical dimension) so as to obtain an
increased memory capacity. Therefore, generally, a gap between the
magnetic disk 101 and the load arm 105, or a gap between the
magnetic disk 101 and the carriage 106, is microscopic on the order
of not more than 0.5 mm. When a hydrodynamic bearing is used as a
motor bearing, gaps of radial bearings exist, and if these gaps are
large, the magnetic disk 101 is much tilted upon application of an
impact or the like, so that the magnetic disk 101 is brought into
contact with the load arm 105 or the carriage 106. As a result, the
magnetic disk 101 is damaged, and the magnetic head 104 is damaged
by powder dust produced by such contact. Therefore, in the magnetic
disk device, it is necessary to reduce the gaps of the radial
bearings as much as possible.
[0084] In the case of a groove bearing, an inner peripheral surface
of the bearing is concentric (coaxial) and circular with respect to
the axis of the bearing over an entire circumference thereof.
Therefore, if a bearing gap is reduced, a friction loss increases.
On the other hand, in the bearing unit of the present invention,
the gap between each concentric arc-shaped bearing surface (which
is concentric with respect to the axis of the bearing) and the
outer peripheral surface of the spindle is reduced, and by doing
so, the tilting of the disk due to a gap (play) in the bearing
portion can be suppressed. And besides, the gap between each
non-concentric arc-shaped bearing surface (which is non-concentric
with respect to the axis of the bearing) is increased, and by doing
so, the increase of the friction loss can be suppressed. Therefore,
in the magnetic disk device of this embodiment, not only the
bearing unit but also the magnetic disk device can be enhanced in
shock resistance without increasing the power consumption.
[0085] In the hydrodynamic bearings of the present invention, the
stiffness of the oil film for the bearing is high because of the
above-mentioned effects, and therefore the high-precision rotation
can be maintained, and the excellent shock resistance is achieved.
And besides, the bearing gap can be made larger as compared with a
cylindrical bearing and the above-mentioned conventional groove
bearing, and therefore the viscous friction loss is small, so that
the low-loss design of the motor can be achieved.
[0086] Furthermore, since the thrust bearing has the flat surface,
the shock resistance in the axial direction is excellent. The
surface, bearing the thrust load, is smaller in diameter than the
spindle, and therefore the friction loss is smaller as compared
with a thrust bearing of the hydrodynamic groove type, and there
can be provided the magnetic disk drive motor of a low power
consumption-type suited for the magnetic disk device. And besides,
the hydrodynamic bearings of the present invention can be produced
using a sintered lubricant-containing bearing material excellent in
mass production efficiency, and therefore there can be provided the
bearing unit wherein the dimensional accuracy of the bearing is
high, and is suited for the magnetic disk device even from the
viewpoint of the cost. And, the assembling precision and the
rotation precision are high, and the requirements of the
high-density and high-speed design of the magnetic disk device can
be met.
[0087] By using the radial bearing and the thrust bearing of the
present invention, there can be provided the magnetic disk device
wherein the bearing is hardly deformed even if a large impact force
is applied, and the dimensional precision of the magnetic disk can
be maintained, and the excellent shock resistance is achieved. The
bearing unit of the present invention is designed to bear a thrust
load by the surface, and therefore even if this bearing unit is
press-fitted into the motor casing 12 while applying a load of
several tens of kilograms to the spindle 1, the thrust bearing
surface is hardly deformed, and therefore the assembling efficiency
of the magnetic disk device is greatly enhanced.
[0088] As described above, the bearing unit, the disk drive unit
having this bearing unit, and the magnetic disk device having this
bearing unit, can meet the requirements of the high-density
recording of the magnetic disk medium, the mass production and
low-cost production of the magnetic disk device, and the
long-lifetime and high-reliability design of the disk drive unit.
The bearing units, described and shown in the present specification
and drawings, can be applied to a disk rotating (driving) mechanism
used in a MD device, a CD-ROM device, a DVD-RAM device and the
like.
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