U.S. patent application number 09/931411 was filed with the patent office on 2002-01-10 for spindle device having a dynamic-pressure-fluid bearing.
Invention is credited to Saeki, Yasuo, Sakuragi, Katsunori.
Application Number | 20020003678 09/931411 |
Document ID | / |
Family ID | 17172266 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020003678 |
Kind Code |
A1 |
Sakuragi, Katsunori ; et
al. |
January 10, 2002 |
Spindle device having a dynamic-pressure-fluid bearing
Abstract
In a spindle device mounted to a disc driving apparatus, a mist
seal which blocks a mist of lubricating fluid, an oil seal which
prevents the lubricating fluid from flowing out, and an oil pool
which prevents surplus fluid from flowing out, are combined and
disposed so that the lubricating fluid from a
dynamic-pressure-fluid bearing is prevented from flowing out or
splashing into a clean space. As a result, inconveniences such as a
head crush or a head absorption can be avoided, and a reliable
spindle device is realized.
Inventors: |
Sakuragi, Katsunori;
(Tottori, JP) ; Saeki, Yasuo; (Tottori,
JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
17172266 |
Appl. No.: |
09/931411 |
Filed: |
August 17, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09931411 |
Aug 17, 2001 |
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09781425 |
Feb 13, 2001 |
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6301074 |
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09781425 |
Feb 13, 2001 |
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09151734 |
Sep 11, 1998 |
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6219199 |
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Current U.S.
Class: |
360/99.08 ;
G9B/17.006; G9B/19.028 |
Current CPC
Class: |
F16C 33/746 20130101;
F16C 2370/12 20130101; G11B 17/0282 20130101; F16C 17/045 20130101;
G11B 19/2009 20130101; F16C 33/107 20130101; F16C 17/10 20130101;
H02K 5/1677 20130101; F16C 17/026 20130101; F16C 17/107
20130101 |
Class at
Publication: |
360/99.08 |
International
Class: |
G11B 017/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 1997 |
JP |
9-248037 |
Claims
What is claimed is:
1. A spindle device comprising: a shaft having a first end and a
second end; a stator; a rotor rotatably supported by said shaft via
lubricating fluid so as to form a radial-dynamic-pressure-fluid
bearing; a magnet opposed to a coiled wire for causing rotation of
said stator relative to said rotor; and a mist-proof seal means to
create a mist-proof seal at least one of adjacent said first end of
said shaft and adjacent said second end of said shaft for
preventing a mist of the lubricating fluid from flowing beyond said
first end of said shaft and said second end of said shaft,
respectively.
2. The spindle device according to claim 1, and further comprising
a bracket, wherein said shaft and said stator are fixed to said
bracket.
3. The spindle device according to claim 2, wherein said rotor
comprises a sleeve rotatably supported by said shaft via the
lubricating fluid so as to form the radial-dynamic-pressure-fluid
bearing, and a hub fixed to said sleeve, with said hub being
adapted to receive discs thereon in a disc space, and wherein said
means to create the mist-proof seal is to create the mist-proof
seal for preventing mist of the lubricating fluid from flowing
beyond at least one of said first end of said shaft into the disc
space and said second end of said shaft into the disc space.
4. The spindle device according to claim 3, wherein said stator
includes a core having said coiled wire thereon, and said magnet is
secured to said hub.
5. The spindle device according to claim 4, wherein said sleeve has
a first end face and a second end face, and further comprising a
first thrust-dynamic-pressure-fluid bearing disposed at said first
end face and a second thrust-dynamic-pressure-fluid bearing
disposed at said second end face, and wherein said means to create
the mist-proof seal is disposed at least one of between said first
thrust-dynamic-pressure-fluid bearing and the disc space and
between said second thrust-dynamic-pressure-fluid bearing and the
disc space.
6. The spindle device according to claim 5, wherein said means to
create the mist-proof seal is to create the mist-proof seal by
creating a viscous seal.
7. The spindle device according to claim 5, and further comprising
an oil-proof seal means to create an oil proof seal at least at one
of between said first thrust-dynamic-pressure-fluid bearing and
said first end of said shaft and between said second
thrust-dynamic-pressure-fluid bearing and said second end of said
shaft for preventing a liquid of the lubricating fluid from flowing
beyond said first end of said shaft and said second end of said
shaft, respectively.
8. The spindle device according to claim 7, and further comprising
a hub, with said hub being adapted to receive discs thereon in a
disc space, and wherein said means to create the oil-proof seal is
to create the oil-proof seal for preventing liquid of the
lubricating fluid from flowing beyond at least one of said first
end of said shaft into the disc space and said second end of said
shaft into the disc space.
9. The spindle device according to claim 8, wherein said means to
create the oil-proof seal is to create the oil-proof seal by
creating a centrifugal force seal.
10. The spindle device according to claim 8, wherein said means to
create the mist-proof seal is to create the mist-proof seal by
creating a viscous seal, and said means to create the oil-proof
seal is to create the oil-proof seal by creating a centrifugal
force seal.
11. The spindle device according to claim 5, and further comprising
a means to create a centrifugal force seal disposed on an outer
circumferential surface of said sleeve.
12. The spindle device according to claim 5, and further comprising
a labyrinth seal including a small clearance between an inner
circumference of said rotor and an outer circumference of said
stator.
13. The spindle device according to claim 5, and further comprising
a mount collar fixed to said bracket and coaxially surrounding said
second end face of said sleeve.
14. A spindle device comprising: a shaft having a first end and a
second end; a stator; a rotor including a sleeve rotatably
supported by said shaft via lubricating fluid so as to form the
radial-dynamic-pressure-flu- id bearing, with said sleeve having a
first end face and a second end face; a magnet opposed to a coiled
wire for causing rotation of said stator relative to said rotor; a
thrust-dynamic-pressure-fluid bearing disposed at at least one of
said first end face and said second end face; and a mist-proof seal
means to create a mist-proof seal adjacent said first end of said
shaft for preventing a mist of the lubricating fluid from flowing
beyond said first end of said shaft.
15. The spindle device according to claim 14, and further
comprising an oil-proof seal means to create an oil proof seal
between said thrust-dynamic-pressure-fluid bearing and at least one
of said first end of said shaft and said second end of said shaft
for preventing a liquid of the lubricating fluid from flowing
beyond said first end of said shaft and said second end of said
shaft, respectively.
16. The spindle device according to claim 15, and further
comprising an oil pool disposed between said
thrust-dynamic-pressure-fluid bearing and at least one of said
first end of said shaft and said second end of said shaft.
17. The spindle device according to claim 16, and further
comprising a bracket, wherein said shaft and said stator are fixed
to said bracket.
18. The spindle device according to claim 17, wherein said rotor
further includes a hub fixed to said sleeve, with said hub being
adapted to receive discs thereon in a disc space, wherein said
means to create the mist-proof seal is to create the mist-proof
seal for preventing mist of the lubricating fluid from flowing
beyond t least one of said first end of said shaft into the disc
space and said second end of said shaft into the disc space, and
wherein said means to create the oil-proof seal is to create the
oil-proof seal for preventing liquid of the lubricating fluid from
flowing beyond at least one of said first end of said shaft into
the disc space and said second end of said shaft into the disc
space.
19. The spindle device according to claim 18, wherein said stator
includes a core having said coiled wire thereon, and said magnet is
secured to said hub.
20. The spindle device according to claim 19, wherein said means to
create the mist-proof seal is disposed between said
thrust-dynamic-pressure-flui- d bearing and the disc space, and
said means to create the oil-proof seal is disposed between said
thrust-dynamic-pressure-fluid bearing and the disc space.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a spindle device to be
mounted to a disc driving apparatus for driving, e.g., discs, and
more particularly to a structure of a spindle motor of an outer
rotor type, which is formed by fixing rotor magnets within a hub
that clamps magnetic discs.
BACKGROUND OF THE INVENTION
[0002] One of the distinctive trends in computer systems is that
memory capacities are becoming larger and larger due to the
extending of computer networks, popularity of engineering work
stations, utilization of data bases and the like. Further, the most
common magnetic disc driving apparatus built in computer systems as
a memory apparatus has been changed from the 5.25-inch disc drive
to the 3.5-inch disc drive, which proves the demand for memory
apparatus to be made more compact and slim in size. The demands of
magnetic disc driving apparatus, such as the demands for larger
capacity, smaller and slimmer size, naturally lead to demands for a
spindle motor (hereinafter called simply a "motor") mounted to the
disc driving apparatus to be of higher accuracy and smaller size.
The higher accuracy, among others, is strongly demanded.
[0003] Along with the technology advancement, a memory capacity of
the magnetic disc has increased, and the track density of discs can
be 8000 TPI (tracks per inch)-10000 TPI, which is converted to a
track pitch as fine as 3 .mu.m. The performance required of the
motor mounted to the apparatus is to always accurately trace each
track having such fine track pitch. This kind of motor has employed
ball bearings in general; however, the rotation of ball bearings
inevitably generates vibration. The level of vibration is measured
to be as fine as ca. 0.15 .mu.m based on NRRO (Non Repeatable Run
Out), which is non repeatable sway of the hub of the motor. This
vibration level is the minimum possible value for the ball
bearings. When this vibration occurs, a magnetic head deviates from
a track by the displacement component due to the vibration. This
deviation has a harmful influence on read/write operation, and the
conventional apparatus employing the ball bearings thus allows
almost no margin to meet the required performance.
[0004] Recently, a motor has been proposed in order to improve the
accuracy, lower the noise level, and extend the product life. The
motor comprises a fixed shaft, a sleeve that is supported and
rotated by the shaft and a radial-dynamic-pressure-fluid bearing,
or the motor comprises a fixed sleeve, a rotating shaft that is
supported and rotated by the sleeve and the
radial-dynamic-pressure-fluid bearing.
[0005] The motor employing the dynamic-pressure-fluid bearing is
disclosed in Japanese Patent Application unexamined publication No.
H06-178489.
[0006] FIG. 16 is a cross sectional view of this conventional
motor. In FIG. 16, a shaft 501 is vertically fixed at the center of
a bracket 504, and a stator core 510 with wires wound thereon is
mounted to the bracket 504. A rotor magnet 506 is fixed to a rotor
frame 505 so that the rotor magnet faces the stator core 510. The
rotor frame 505 is mounted to the hub 503. A bushing 511 is fixed
at a lower section of an inner rim of the hub 503, and another
bushing 512 is mounted to an outer rim of the bracket 504. The
bushing 511 faces the bushing 512 with a clearance in-between. The
magnetic discs (not shown) are to be mounted around the hub
503.
[0007] Grooves (not shown) are provided inside of a sleeve 502, the
grooves produce dynamic pressure of lubricating fluid by the
rotation of the sleeve 502, which is rotatively supported by the
fixed shaft 501 via lubricating fluid.
Radial-dynamic-pressure-fluid bearings R501 and R502 are thus
constructed. Axial dynamic pressure bearings A501 and A502 comprise
both end faces of a fixed thrust ring 507, a lower face of rotation
thrust ring 508 and an upper face of the sleeve 502. A groove 541
is provided on an outer circumference of a cap 509, and another
groove 542 is provided on an inner circumference of the rotation
thrust ring 508. The lower rim of groove 541 is disposed at
substantially the center of groove 542, and the upper rim of groove
542 is disposed at substantially the center of groove 541. The
upper and lower rims of each groove 541 and 542 face each other
with some offset.
[0008] The conventional motor employing the above
dynamic-pressure-fluid bearing has a possible problem that the
lubricating fluid might splash into a space where the magnetic
discs are disposed. In this space, a magnetic head reads/writes
data from/to the magnetic disc with little clearance between the
head and disc. The space thus must be kept utmost clean because if
the lubricating fluid splashes or flows into the space, serious
problems such as a head crush, a head absorption, etc. will occur.
(Hereinafter the above space is called the "clean space".)
[0009] The above conventional motor has provided a countermeasure
against lubricating oil splashes by forming an oil pool using the
grooves 541 and 542 to prevent the lubricating fluid from splashing
out from the upper part of the motor; however, this countermeasure
cannot prevent a mist of lubricating fluid from flowing out.
SUMMARY OF THE INVENTION
[0010] The present invention aims to provide a reliable spindle
device which avoids inconvenience such as a head crush or a head
absorption by disposing a mist seal between the
thrust-dynamic-pressure-fluid bearing and the clean space where
magnetic discs are disposed. The mist seal prevents a mist of
lubricating fluid from flowing out into the clean space where
magnetic discs are disposed.
[0011] The spindle device of the present invention comprises the
following elements:
[0012] (a) a bracket comprising a fixed shaft and a stator core on
which wire is wound,
[0013] (b) a hub to which discs are mounted,
[0014] (c) a rotor magnet mounted to the hub and facing the stator
core,
[0015] (d) a sleeve fixed to the hub and rotatively supported by
the fixed shaft via the lubricating fluid,
[0016] (e) thrust-dynamic-pressure-fluid bearings disposed on both
end faces of the sleeve, and
[0017] (f) a mist seal such as a viscous seal, a labyrinth seal, a
magnetic fluid seal or the like disposed between the
thrust-dynamic-pressure-fluid bearing and the clean space where the
discs are disposed, and the mist seal blocks the mist of
lubricating fluid from flowing out.
[0018] The above structure can prevent the mist of lubricating
fluid from splashing into the clean space by using the mist
seal.
[0019] Further, an oil seal that prevents the lubricating fluid per
se from flowing out, and an oil pool that prevents surplus
lubricating fluid from flowing out are combined, whereby liquid
lubricating fluid is prevented from flowing out into the clean
space. This structure can further enhance a reliability of the
spindle device.
[0020] The spindle device according to the present invention has an
advantageous sealing structure that can prevent the lubricating
fluid of the dynamic-pressure-fluid bearing from splashing out into
the clean space. There are the following sealing mechanisms between
the dynamic-pressure-lubricating-fluid-bearing and the clean space:
oil seal (surface tension seal, centrifugal force seal) and mist
seal (viscous seal, magnetic fluid seal, labyrinth seal). The
dynamic-pressure-lubricat- ing-fluid-bearing holds the lubricating
fluid using the surface tension seal, and the centrifugal force
seal restores the lubricating fluid, further, the mist seal
prevents the mist of lubricating fluid from splashing. This sealing
process effectively prevents the lubricating fluid from flowing and
splashing out into the clean space. A part of this arrangement can
be omitted depending on the motor construction.
[0021] The oil pool and grooves in addition to the above sealing
process contribute to preventing the fluid from flowing as well as
splashing out not only in a continuous operation but also in an
intermittent operation, at rest at a high temperature or with a
change in orientation.
[0022] The thrust-dynamic-pressure-fluid bearings are disposed on
both the upper and lower sections of the
radial-dynamic-pressure-fluid bearing, whereby a longer bearing
span for the radial-dynamic-pressure-fluid bearing can be obtained,
and the rigidity is increased. As a result, the
dynamic-pressure-fluid bearing can be well-balanced.
[0023] Since the spindle device of the present invention allows no
flow-out of the lubricating fluid, the bearing is always filled
with the lubricating fluid, which substantially extends a life span
of the magnetic disc driving apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a cross section of a motor used in a first
exemplary embodiment of the present invention.
[0025] FIG. 2 is an enlarged view of an upper portion of the motor
used in the first exemplary embodiment of the present
invention.
[0026] FIG. 3 is an enlarged view of a lower portion of the motor
used in the first exemplary embodiment of the present
invention.
[0027] FIG. 4 details the inside of a sleeve used in the first
exemplary embodiment of the present invention.
[0028] FIG. 5 details a thrust-dynamic-pressure-fluid bearing used
in the first exemplary of the present invention.
[0029] FIG. 6 is an enlarged view of a lower portion of a motor
used in a second exemplary embodiment of the present invention.
[0030] FIG. 7 is a cross section of a motor used in third exemplary
embodiment of the present invention.
[0031] FIG. 8 is an enlarged view of a lower portion of the motor
used in the third exemplary embodiment of the present
invention.
[0032] FIG. 9 is a cross section of a motor used in a fourth
exemplary embodiment of the present invention.
[0033] FIG. 10 is a cross section of a motor used in a fifth
exemplary embodiment of the present invention.
[0034] FIG. 11 is an enlarged view of an upper portion of the motor
used in the fifth exemplary embodiment of the present
invention.
[0035] FIG. 12 is a cross section of a motor used in a sixth
exemplary embodiment of the present invention.
[0036] FIG. 13 is an enlarged view of an upper portion of the motor
used in the sixth exemplary embodiment of the present
invention.
[0037] FIG. 14 is a cross section of a motor used in a seventh
exemplary embodiment of the present invention.
[0038] FIG. 15 is a cross section of a motor used in an eighth
exemplary embodiment of the present invention.
[0039] FIG. 16 is a cross section of a conventional motor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] Exemplary embodiments of the present invention are detailed
hereinafter by referring to the attached drawings.
[0041] (Exemplary Embodiment 1)
[0042] FIG. 1 is a cross section of a motor used in a first
exemplary embodiment of the present invention. FIG. 2 is an
enlarged view of an upper portion of the motor. FIG. 3 is an
enlarged view of a lower portion of the motor. FIG. 4 details the
inside of sleeve used in the first exemplary embodiment. FIG. 5
details the thrust-dynamic-pressure-fluid bearing used in the first
exemplary embodiment.
[0043] In FIG. 1 through FIG. 5, a shaft 1 is vertically fixed at
the center of a bracket 4, for which screw holes and protruded
sections are provided so that the bracket can be mounted to the
disc driving apparatus. A core holder 12 is also provided in the
bracket 4. A stator core 11 of coiled wires is mounted on the outer
circumference of the core holder 12 so that the stator core 11 is
situated opposite to a cylindrical rotor magnet 6 via a narrow
clearance.
[0044] Magnetic discs (not shown) are mounted on an outer
circumference of a hub 3. On the inner circumference of the hub 3,
the cylindrical rotor magnet 6 is mounted via a cylindrical rotor
frame S. A sleeve 2 is mounted on another circumference of the hub
3. Grooves 17 are provided inside the sleeve 2, the grooves 17
produce dynamic pressure of lubricating fluid (not shown) through
rotation of the sleeve 2. The sleeve 2 is rotatively supported by
the fixed shaft 1 via lubricating fluid, and forms the radial
dynamic-fluid-bearings R1 and R2.
[0045] On the upper end face of sleeve 2, a rotation thrust ring 8
is fixed, and rotatively supported via the lubricating fluid by a
thrust ring 7 which is fixed on the fixed shaft 1, thereby forming
a thrust-dynamic-pressure-fluid bearing A1. The rotation thrust
ring 8 has grooves 18 which produce dynamic pressure in the
lubricating fluid. These grooves 18 can be provided on the fixed
thrust ring 7 instead of on the rotation thrust ring 8. On the
lower end face of sleeve 2, a rotation thrust ring 10 is fixed, and
rotatively supported via the lubricating fluid by a thrust ring 9
which is fixed to an end portion of bracket 4, thereby forming a
thrust-dynamic-pressure-fluid bearing A2. The rotation thrust ring
10 has grooves similar to the grooves 18 of one rotation thrust
ring 8) which produce dynamic pressure in the lubricating fluid.
These grooves can be provided on fixed thrust ring 9 instead of on
the thrust ring 10.
[0046] On the upper side of the rotation thrust ring 8, a seal
member 13 is fixed to the sleeve 2 so as to sandwich the ring 8
between the seal member 13 and the sleeve 2. On the seal member 13,
a tapered centrifugal force seal 16 and an oil pool 30 are
provided. The inner circumference of hub 3 faces the outer
circumference of fixed thrust ring 7 via a small clearance 15, this
small clearance preferably ranging from 0.03 to 0.05 mm. On the
inner circumference of hub 3, a viscous seal 14 is formed. The
viscous seal 14 employs a screw to be rotated for drawing air in
from the clean space 29.
[0047] An example of the viscous seal has the following structure
and mechanism. In a cylindrical space, the screw is provided on an
inner or outer circumference that forms the cylindrical space. The
screw rotates to produce pressure so that air flows from the clean
space where the discs are disposed toward the
thrust-dynamic-pressure-fluid bearing, whereby the mist of the
lubricating fluid is prevented from splashing into the clean space
29.
[0048] On the lower circumference of sleeve 2, a tapered
centrifugal force seal 21 is provided. An example of a mechanism of
the centrifugal force seal is now will be described. The
centrifugal force is proportional to a radius from a rotating
center, and based on this principle, when the motor is driven, the
lubricating fluid flows toward the dynamic-pressure-fluid bearing
by utilizing the taper. A liquid of the lubricating fluid is thus
prevented from flowing out.
[0049] For a better effect, the centrifugal force seal 21 is
disposed on the outer circumference of the rotative sleeve 2.
[0050] The lower outer circumference of sleeve 2 faces the inner
circumference of core holder 12 via a small clearance 20, this
small clearance preferably ranging from 0.03 to 0.05 mm. Another
viscous seal 19 is formed on the lower outer circumference of
sleeve 2. The viscous seal 19 employs a screw that rotates to draw
air in from the clean space 29 through the space where the stator
core 11 and rotor magnet 6 are disposed.
[0051] The above structure allows the centrifugal force seals 16
and 21 to prevent liquid lubricating fluid from flowing out, and
allows the viscous seals 14 and 19 to prevent lubricating fluid
mist from splashing out into the clean space.
[0052] A small annular space is provided between the outer
circumference of the ring 10 and the inner circumference of core
holder 12, whereby a surface tension seal 24 is formed to provide
an oil seal. Further, an oil pool 22 is disposed on the core holder
12. These arrangements reinforce the prevention of the flowing out
of the lubricating fluid.
[0053] The lubricating fluid is filled into the
radial-dynamic-pressure-fl- uid bearings R1 and R2 as well as the
thrust-dynamic-pressure-fluid bearings A1 and A2 when the spindle
device is assembled. When the motor is rotated, the lubricating
fluid concentrates on the centers of R1, R2, A1 and A2. However,
surplus fluid does not have a constant flow, and sometimes splashes
due to the centrifugal force. When the spindle device is assembled,
bubbles are incidentally entrapped in the lubricating fluid. The
bubbles grow due to temperature changes, or concentrate and grow in
a lower pressure section in the bearings due to the rotation. The
growth of the bubbles pushes up the fluid to cause splashing. When
the spindle device is left at a high temperature atmosphere for a
long period, the lubricating fluid is more likely to leak. In these
cases, the spindle device of the present invention can prevent the
fluid from flowing and splashing out into the clean space 29 thanks
to a combination of the mist seal, oil seal and oil pool.
[0054] (Exemplary Embodiment 2)
[0055] FIG. 6 is an enlarged view of a lower portion of a motor
used in the second exemplary embodiment of the present invention.
In FIG. 6, grooves (not shown, but similar to the grooves 17 in
FIG. 4) are provided inside the sleeve 52. These grooves generate
dynamic pressure through rotation. The sleeve 52 is rotatively
supported via the lubricating fluid by the fixed shaft 1, thereby
forming the radial-dynamic-pressure-fluid bearing R2. This
embodiment differs from the first exemplary embodiment only in the
following point: a tapered centrifugal force seal 25 has a larger
taper angle than that in the first exemplary embodiment. The
tapered seal 25 is disposed as an oil seal on the lower outer
circumference of the sleeve 52. In the lower part of sleeve 52, in
particular, the fluid is subject to flowing out due to gravity. A
larger taper angle is thus preferably employed for the centrifugal
force seal 25 to expand the space. This structure further assures
the prevention of fluid flow-out.
[0056] (Exemplary Embodiment 3)
[0057] FIG. 7 is a cross section of a motor used in the third
exemplary embodiment of the present invention. FIG. 8 is an
enlarged view of a lower portion of the motor.
[0058] In FIGS. 7 and 8, this embodiment differs from the first and
second exemplary embodiments in the following points: The stator
core 11 of coiled wires is mounted to a bracket 54, and a mount
collar 62 is mounted at the center of an inner circumference of the
bracket 54. The shaft 1 is fixed at the center of the mount collar
62, and a thrust ring 60 is fixed at the end face of the mount
collar 62. Grooves for generating dynamic pressure are provided on
either the thrust ring 60 or a rotating ring 10 mounted to the
sleeve 52. The thrust-dynamic-pressure-fluid bearing A2 is formed
by the fixed thrust ring 60 and the rotation thrust ring 10 via the
lubricating fluid. This structure can also prevent the fluid from
flowing out as already discussed in connection with the first and
second exemplary embodiments.
[0059] (Exemplary Embodiment 4)
[0060] FIG. 9 is a cross section of a motor used in the fourth
exemplary embodiment of the present invention.
[0061] This embodiment differs from the first exemplary embodiment
in the following points: On a bracket 104, an airtight seal 26 is
disposed to seal the screw holes and the like provided on the
bracket 104. A small annular space is provided between the inner
circumference of hub 3 and the outer circumference of bracket 104
whereby a labyrinth seal 27 is formed to provide a mist seal.
[0062] In general, the labyrinth seal thus comprises a small
clearance and an expansion room, this small clearance preferably
ranging from 0.05 to 0.1 mm. Namely, a room 28, where the rotor
core 11 coiled by wires and the rotor magnet 6 are disposed, is the
expansion room, and the annular space between the hub 3 and the
bracket 104 is the small clearance. Air flow energy is consumed in
the expansion room 28, and the air flow rate through the small
clearance decreases substantially, which prohibits the mist of
lubricating fluid from splashing into the clean space 29.
[0063] (Exemplary Embodiment 5)
[0064] FIG. 10 is a cross section of a motor used in the fifth
exemplary embodiment of the present invention. FIG. 11 is an
enlarged view of an upper portion of the motor.
[0065] In FIGS. 10 and 11, a mount collar 212 is mounted to the
inner center of a bracket 204. A shaft 301 is vertically fixed at
the center of the mount collar 212. On the bracket 204, protrusion
sections and screw holes are provided to mount the spindle device
to the disc driving apparatus. On the outer circumference of
bracket 204, a stator core 211 of coiled wires is mounted to face a
rotor magnet 206 via a narrow clearance.
[0066] Magnetic discs (not shown) are to be mounted on the outer
circumference of a hub 203. The cylindrical rotor magnet 206 is
mounted to the inner circumference of hub 203 via a cylindrical
rotor frame 205. On the inner circumference of hub 203, a magnetic
shield panel 210 is mounted for preventing leakage of magnetic
flux. A sleeve 202 is mounted to another inner circumference of hub
203. Grooves (not shown, but similar to grooves 17 in FIG. 4) are
provided inside the sleeve 202 for generating dynamic pressure in
lubricating fluid through rotation. The sleeve 202 is rotatively
supported by the fixed shaft 301 via the lubricating fluid, and
thereby forms radial-dynamic-pressure-fluid bearings R201 and
R202.
[0067] On the upper end of the fixed shaft 301, a thrust ring 207
is mounted to a top screw 201 to be fixed so that the ring 207 can
be kept coaxial with the shaft 301. The fixed thrust ring 207
employs grooves on both sides for generating dynamic pressure in
the lubricating fluid. A thrust bearing A202 is formed and
rotatively supported between the sleeve 202 and a lower face of the
fixed thrust ring 207 via the lubricating fluid. A rotation thrust
ring 208 is mounted to the sleeve 202 above the thrust ring 207. A
thrust-dynamic-pressure-fluid bearing A201 is formed and rotatively
supported between the upper face of thrust ring 207 and the lower
face of thrust ring 208 via the lubricating fluid.
[0068] The outer circumference of top screw 201 faces the inner
circumference of a member 209 for forming a viscous seal 213 via a
small annular space 214. The viscous seal 213 is provided above the
rotation thrust ring 208. A screw is provided inside the member
209, and thereby forms the viscous seal 213. The screw rotates to
draw air in from the clean space 29 so that the viscous seal 213
can prevent the lubricating fluid from splashing.
[0069] A small annular space 219 is formed between the sleeve 202
and the fixed thrust ring 207, and is filled with the lubricating
fluid, which is held by surface tension. Further a small annular
space 220 is formed between the outer circumference of top screw
201 and the inner circumference of rotation thrust ring 208. The
small space 220 is filled with the lubricating fluid, which is held
by surface tension.
[0070] This surface tension prevents the lubricating fluid from
flowing out, and further prevents the mist thereof from splashing
above the rotation thrust ring 208. The outer circumference of top
screw 201 can be that of fixed shaft 301.
[0071] An oil pool 217 is disposed between the thrust ring 208 and
the member 209 so that surplus fluid on the inner circumference of
the ring 208 travels on the surface of the ring 208 to the oil pool
217 due to centrifugal force. A groove 218 facing the oil pool 217
is provided on the top screw 201. If centrifugal force pushes the
surplus fluid on the inner circumference of the ring 208 to flow
out, the groove 218 can prevent the flow from traveling to the
clean space 29. When the motor is kept upside down, the surplus
fluid travels along the top screw 201 and reaches the head thereof.
If the motor is driven in this attitude, the fluid will splash into
the clean space; however, the groove 218 can block the surplus
fluid from travelling down to the head.
[0072] A tapered centrifugal force seal 225 is disposed on the
lower outer circumference of sleeve 202. For better effect, the
seal 225 is disposed on the outer circumference of the rotating
body, i.e., sleeve 202, to prevent the lubricating fluid from
flowing out. An oil pool 221 is disposed between the sleeve 202 and
the magnetic shield plate 210, and another oil pool 226 is disposed
between the rotor frame 205 and the magnetic shield panel 210.
Surplus fluid in the lower part of sleeve 202 flows out to the
outer circumference of sleeve 202; however, the flow is blocked by
the centrifugal force seal 225. If the surplus fluid still travels
on the outer circumference of sleeve 202 to flow out, the oil pool
221 can block the flow-out from the lower part of sleeve 202. And
yet, if the surplus fluid travels on the magnetic shield panel 210
due to centrifugal force accompanied by rotation, the oil pool 226
can block the flow from flowing out to the clean space 29. A narrow
clearance can be provided to the oil pools 221 and 226 so that the
lubricating fluid can be held by surface tension even if the motor
is repeatedly started and stopped.
[0073] The oil pools 221 and 226 are, in addition to other seals,
preventive measures against draining the fluid into the clean space
29, and these oil pools further prevent the lubricating fluid from
flowing out.
[0074] (Exemplary Embodiment 6)
[0075] FIG. 12 is a cross section of a motor used in the sixth
exemplary embodiment of the present invention. FIG. 13 is an
enlarged view of an upper portion of the motor. In FIGS. 12 and 13,
this embodiment differs from the fifth exemplary embodiment in the
following points: Above the rotation thrust ring 208, a magnetic
fluid seal holder 309 is fixed to the sleeve 202. A magnetic fluid
seal 314 is fixed to the holder 309, and the seal 314 holds
magnetic fluid 313 with magnetic force.
[0076] The magnetic fluid seal 314 comprises the following
elements:
[0077] (a) a ring-shape magnet 315 having N and S poles on
respective ends;
[0078] (b) ring-shape magnetic members 316 and 317 sandwiching the
ring-shape magnet 315; and
[0079] (c) magnetic fluid 313.
[0080] The magnetic fluid seal 314 is formed by being encircled
with these elements.
[0081] The magnetic fluid 313, as shown in FIG. 13, completely
clogs a small clearance between the outer circumference of the top
screw 201 and an end face of the magnetic member 316 opposite to
the outer circumference. In this case, the following magnetic path
is formed. Magnetic flux produced by the magnet 315 travels through
the magnetic member 316, magnetic fluid 313 and top screw 201, and
arrives at the magnet 315 again via a small clearance between the
outer circumference of the top screw 201 and an end face of the
magnetic member 317 opposite to the outer circumference. This
magnetic path can hold the magnetic fluid 313, whereby the mist of
the lubricating fluid is prevented from splashing out from the
inner rim of ring 208 into the clean space 29.
[0082] Because a room 318 formed by the seal 314 is substantially
airtight, the magnetic fluid 313 could possibly be blown out due to
a temperature change or a pressure difference. This possible
blow-out can be avoided by the following measures: (a) decreasing
the capacity of the airtight room 318, and (b) providing a small
annular clearance 220 between the ring 208 and the top screw 201 to
obtain surface tension which can hold the lubricating fluid. The
height of the lubricating fluid surface thus changes, which
balances pressures, whereby the blow-out is avoided. The capacity
of the airtight room 318 is preferably less than a capacity
enclosed by the inner circumference of the rotation thrust ring and
the outer circumference of the top screw. The top screw can be
incorporated into the fixed shaft.
[0083] (Exemplary Embodiment 7)
[0084] FIG. 14 is a cross section of a motor used in the seventh
exemplary embodiment of the present invention. In FIG. 14, on a
bracket 304, an airtight seal 222 is disposed to seal the screw
holes and the like provided in the bracket 304. A small annular
space is provided between the inner circumference of hub 203 and
the outer circumference of bracket 304 whereby a labyrinth seal 223
is formed to provide a mist seal. In the same manner as the fourth
exemplary embodiment shows, an expansion room 224, where a stator
core 211 and a rotor magnet 206 are disposed, consumes air flow,
and the air flow rate through the labyrinth seal decreases
substantially, which prevents the mist of lubricating fluid from
splashing into the clean space 29.
[0085] (Exemplary Embodiment 8)
[0086] FIG. 15 is a cross section of a motor used in the eighth
exemplary embodiment of the present invention. In FIG. 15, this
embodiment differs from the seventh exemplary embodiment in the
following point: A magnetic fluid seal 314 is provided, which
reinforces the preventive measures against the splash-out of the
mist fluid from above the motor.
[0087] According to the present invention, combinations of mist
seals, oil seals and oil pools can prevent the lubricating fluid
from flowing out into the clean space, whereby a reliable spindle
device can be realized. The mist seal prevents a mist of the
lubricating fluid from splashing out, the oil seal prohibits the
lubricating fluid per se from flowing out, and the oil pool is a
measure to prevent surplus lubricating fluid from flowing out.
[0088] The spindle device of the present invention can be used not
only in the magnetic disc driving apparatus, but also other disc
driving apparatuses for optical discs, CD-ROMs, MDs, DVDs and
others. Further, the spindle device also can be used in other
apparatuses, and therefore, the spindle device has a great
advantage in industrial applications.
[0089] Although illustrated and described herein with reference to
certain specific embodiments, the present invention is not limited
to the details shown. Rather, various modifications may be made in
the details within the scope and range of equivalents of the claims
and without departing from the spirit of the invention.
* * * * *