U.S. patent application number 12/176360 was filed with the patent office on 2008-11-06 for method and system for withstanding a shock event for a fluid dynamic bearing motor.
Invention is credited to Alan Lyndon Grantz, Lynn Bich-Quy Le.
Application Number | 20080273822 12/176360 |
Document ID | / |
Family ID | 32994782 |
Filed Date | 2008-11-06 |
United States Patent
Application |
20080273822 |
Kind Code |
A1 |
Le; Lynn Bich-Quy ; et
al. |
November 6, 2008 |
Method And System For Withstanding A Shock Event For A Fluid
Dynamic Bearing Motor
Abstract
A system, method and means is provided for withstanding
mechanical shock for use with fluid dynamic bearings. A sealing
system is provided that withstands 1000 G shock events. In an
aspect, a grooved pumping seal employed between a thrust plate and
a shield, a thrust plate having spiral grooves, a fluid
recirculation passageway, and a reservoir creates an asymmetric
pressure gradient. In an aspect, fluid is retained and air is
purged utilizing an enlarged fluid reservoir, axial channels and an
angled fill hole. In an aspect, a shaft is attached to a top cover
supplying radial stiffness, and an enlarged single-sided thrust
plate improves dynamic parallelism.
Inventors: |
Le; Lynn Bich-Quy; (San
Jose, CA) ; Grantz; Alan Lyndon; (Aptos, CA) |
Correspondence
Address: |
WAX LAW GROUP
1017 L STREET #425
SACRAMENTO
CA
95814
US
|
Family ID: |
32994782 |
Appl. No.: |
12/176360 |
Filed: |
July 19, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10632449 |
Jul 31, 2003 |
7407327 |
|
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12176360 |
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60456896 |
Mar 21, 2003 |
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Current U.S.
Class: |
384/107 ;
384/115; G9B/19.029 |
Current CPC
Class: |
F16C 33/1085 20130101;
G11B 19/2018 20130101; F16C 33/745 20130101; F16C 2370/12 20130101;
F16C 17/107 20130101; F16C 32/0629 20130101; F16C 33/107
20130101 |
Class at
Publication: |
384/107 ;
384/115 |
International
Class: |
F16C 32/06 20060101
F16C032/06 |
Claims
1. A method for recirculating fluid, purging air, and withstanding
shock for use with a fluid dynamic bearing motor comprising
creating an asymmetric pressure gradient within an interfacial
region of the fluid dynamic bearing motor, wherein the interfacial
region is defined within an area including a journal bearing, a
first fluid passageway, a second fluid passageway, and a reservoir,
wherein the journal bearing, the first fluid passageway, and the
second fluid passageway are connected for fluid recirculation, and
are in fluid communication with the reservoir, and wherein: i.) the
journal bearing is defined between an inner component and an outer
component, the inner component and the outer component positioned
for relative rotation; ii.) the first fluid passageway is defined
within the outer component; iii.) the second fluid passageway is
defined between the outer component and a radial member extending
from the inner component; and iv.) the reservoir is defined between
a shield and the outer component, the shield connected to one of
the inner component and the outer component.
2. The method as in claim 1, wherein creating an asymmetric
pressure gradient comprises employing grooves on at least one of a
facing surface of the radial member and the outer component, to
generate fluid pumping pressure to pump fluid from the second fluid
passageway toward the inner component and into the journal bearing,
when the inner component and the outer component are relatively
rotating.
3. The method as in claim 1, wherein creating an asymmetric
pressure gradient comprises employing pumping grooves on a facing
surface positioned at an outer diameter gap defined between the
shield and an outer diameter of the radial member, to pump fluid
from the outer diameter gap toward a recirculation plenum when the
inner component and the outer component are relatively rotating,
the recirculation plenum defined by a junction joining the
reservoir, the first fluid passageway and the second fluid
passageway.
4. The method as in claim 1, further comprising utilizing
centrifugal force to act on fluid situated at an outer diameter gap
defined between the shield and an outer diameter of the radial
member, when the inner component and the outer component are
relatively rotating.
5. The method as in claim 1, wherein creating the asymmetric
pressure gradient comprises creating a first pressure area within
the reservoir, and creating a second pressure area within the
journal bearing, wherein the first pressure area has a lower
pressure than the second pressure area.
6. The method as in claim 5, wherein creating the asymmetric
pressure gradient further comprises creating a third pressure area
at an axial end of the journal bearing, and creating a fourth
pressure area at an apex of grooves formed on a facing surface of
the journal bearing, wherein when the inner component and the outer
component are relatively rotating, the third pressure area has a
lower pressure than the fourth pressure area.
7. The method as in claim 1, wherein creating the asymmetric
pressure gradient comprises creating a lower pressure area and a
lower flow resistance in the first fluid passageway as compared to
the journal bearing, wherein the first fluid passageway connects to
substantially an axial center of the journal bearing.
8. The method as in claim 1, wherein creating the asymmetric
pressure gradient comprises creating a lower pressure area within
the reservoir as compared to a recirculation plenum, the
recirculation plenum defined by a junction joining the reservoir,
the first fluid passageway and the second fluid passageway.
9. The method as in claim 1, further comprising creating a pressure
differential within the reservoir by employing an axial channel on
at least a portion of an inner surface of the shield, the axial
channel substantially extending from a recirculation plenum, to
allow air within fluid to travel along the channels and be purged
from the fluid, and to retain fluid, wherein the recirculation
plenum is defined by a junction joining the reservoir, the first
fluid passageway and the second fluid passageway.
10. The method as in claim 1, further comprising employing a
capillary seal extending from the shield to the outer component,
the shield and the outer component having surfaces that are
relatively tapered and converge toward a recirculation plenum, the
recirculation plenum defined by a junction joining the reservoir,
the first fluid passageway and the second fluid passageway.
11. The method as in claim 1, further comprising utilizing a single
sided thrustplate with magnetic preload to reduce any power losses,
wherein the radial member is the single sided thrustplate.
12. A method of fluid sealing for use with a data storage device
employing a fluid dynamic bearing motor comprising creating an
asymmetric pressure gradient within an interfacial region of the
fluid dynamic bearing motor, wherein the interfacial region is
defined within an area including a journal bearing, a first fluid
passageway, a second fluid passageway, and a reservoir, wherein the
journal bearing, the first fluid passageway, and the second fluid
passageway are connected for fluid recirculation, and are in fluid
communication with the reservoir, wherein the reservoir maintains a
lowest pressure of the interfacial region, and wherein: i.) the
journal bearing is defined between an inner component and an outer
component, the inner component and the outer component positioned
for relative rotation; ii.) the first fluid passageway is defined
within the outer component; iii.) the second fluid passageway is
defined between the outer component and a radial member extending
from the inner component; iv.) the reservoir is defined between a
shield and the outer component, the shield connected to one of the
inner component and the outer component; and v.) grooves are
situated on at last one of a facing surface of the radial member
and the outer component, to generate fluid pumping pressure to pump
fluid from the second fluid passageway toward the inner component
and into the journal bearing, when the inner component and the
outer component are relatively rotating.
13. The method as in claim 12, wherein creating an asymmetric
pressure gradient comprises employing pumping grooves on a facing
surface positioned at an outer diameter gap defined between the
shield and an outer diameter of the radial member, to pump fluid
from the outer diameter gap toward a recirculation plenum when the
inner component and the outer component are relatively rotating,
the recirculation plenum defined by a junction joining the
reservoir, the first fluid passageway and the second fluid
passageway.
14. The method as in claim 12, further comprising utilizing
centrifugal force to act on fluid situated at an outer diameter gap
defined between the shield and an outer diameter of the radial
member, when the inner component and the outer component are
relatively rotating.
15. The method as in claim 14, wherein creating the asymmetric
pressure gradient further comprises creating a third pressure area
at an axial end of the journal bearing, and creating a fourth
pressure area at an apex of grooves formed on a facing surface of
the journal bearing, wherein when the inner component and the outer
component are relatively rotating, the third pressure area has a
lower pressure than the fourth pressure area.
16. The method as in claim 12, wherein creating the asymmetric
pressure gradient comprises creating a lower pressure area and a
lower flow resistance in the first fluid passageway as compared to
the journal bearing, wherein the first fluid passageway connects to
substantially an axial center of the journal bearing.
17. The method as in claim 12, wherein creating the asymmetric
pressure gradient comprises creating a lower pressure area within
the reservoir as compared to a recirculation plenum, the
recirculation plenum defined by a junction joining the reservoir,
the first fluid passageway and the second fluid passageway.
18. The method as in claim 12, further comprising creating a
pressure differential within the reservoir by employing an axial
channel on at least a portion of an inner surface of the shield,
the axial channel substantially extending from a recirculation
plenum, to allow air within fluid to travel along the channels and
be purged from the fluid, and to retain fluid, wherein the
recirculation plenum is defined by a junction joining the
reservoir, the first fluid passageway and the second fluid
passageway.
19. The method as in claim 12, further comprising employing a
capillary seal extending from the shield to the outer component,
the shield and the outer component having surfaces that are
relatively tapered and converge toward a recirculation plenum, the
recirculation plenum defined by a junction joining the reservoir,
the first fluid passageway and the second fluid passageway.
20. The method as in claim 12, further comprising utilizing a
single sided thrustplate with magnetic preload to reduce any power
losses, wherein the radial member is the single sided thrustplate.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from and benefit under 35
U.S.C. sec. 120 as a Divisional patent application of co-pending
U.S. non-provisional patent application 10/632,449, filed Jul. 31,
2003, entitled "Method And System For Withstanding Shock In A
Spindle Motor Bearing," assigned to the assignee of the present
application and incorporated herein by reference. In the
above-referenced patent application 10/632,449, the method claims
were classified by the U.S. Patent and Trademark Office under class
29, subclass 893. This application is based on a provisional
application Ser. 60/456,896, filed Mar. 21, 2003, attorney docket
STL 3333.01, entitled Top Cover Attach FDB With Inverted Sealing,
and assigned to the Assignee of this application and incorporated
herein by reference.
FIELD
[0002] The invention relates generally to spindle motors, and more
particularly to a sealing system that withstands mechanical shock
events for use with fluid dynamic bearings in disc drive data
storage systems.
BACKGROUND
[0003] Disc drive memory systems are widely used throughout the
world today. These systems are used by computers and devices
including digital cameras, digital video recorders, laser printers,
photo copiers and personal music players. Disc drive memory systems
store digital information that is recorded on concentric tracks of
a magnetic disc medium. Several discs are rotatably mounted on a
spindle, and the information, which can be stored in the form of
magnetic transitions within the discs, is accessed using read/write
heads or transducers. The read/write heads are located on a
pivoting arm that moves radially over the surface of the disc. The
discs are rotated at high speeds during operation using an electric
motor located inside a hub or below the discs. Magnets on the hub
interact with a stator to cause rotation of the hub relative to the
shaft. One type of motor is known as an in-hub or in-spindle motor,
which typically has a spindle mounted by means of a bearing system
to a motor shaft disposed in the center of the hub. The bearings
permit rotational movement between the shaft and the hub, while
maintaining alignment of the spindle to the shaft. The read/write
heads must be accurately aligned with the storage tracks on the
disc to ensure the proper reading and writing of information.
[0004] Spindle motors have in the past used conventional ball
bearings between the hub and the shaft. However, the demand for
increased storage capacity and smaller disc drives has led to the
read/write head being placed increasingly close to the disc
surface. The close proximity requires that the disc rotate
substantially in a single plane. A slight wobble or run-out in disc
rotation can cause the disc to strike the read/write head, possibly
damaging the disc drive and resulting in loss of data. Further,
resistance to mechanical shock and vibration is poor in the case of
ball bearings, because of low damping. Because this rotational
accuracy cannot be achieved using ball bearings, disc drives
currently utilize a spindle motor having fluid dynamic bearings on
the shaft and a thrust plate to support a hub and the disc for
rotation. One alternative bearing design is a hydrodynamic
bearing.
[0005] In a hydrodynamic bearing, a lubricating fluid such as gas
or liquid or air provides a bearing surface between a fixed member
and a rotating member of the disc drive. Dynamic
pressure-generating grooves formed on a surface of the fixed member
or the rotating member generate a localized area of high pressure
and provide a transport mechanism for fluid or air to more evenly
distribute fluid pressure within the bearing and between the
rotating surfaces, enabling the spindle to rotate with more
accuracy. However, hydrodynamic bearings suffer from disadvantages,
including a low stiffness-to-power ratio and increased sensitivity
of the bearing to external loads or mechanical shock events.
[0006] To increase stiffness, spindle motors have been attached to
both the base and the top cover of the disc drive housing. However,
in order to use top cover attachment, the motor is open on both
ends, which increases the risk of oil leakage. This leakage among
other things is caused by differences in net flow rate created by
differing pumping grooves in the bearing. If the flow rates within
the bearing are not carefully balanced, a net pressure rise toward
one or both ends may force fluid out through a seal. Balancing the
flow rates is difficult because the flow rates created by the
pumping grooves are a function of the gaps defined in the
hydrodynamic bearing, and the gaps, in turn, are a function of
parts tolerances. Proper sealing is also critical. Bearing fluids
give off vaporous components that could diffuse into a disc
chamber. This vapor can transport particles such as material
abraded from bearings or other components. These particles can
deposit on the read/write heads and the surfaces of the discs,
causing damage to the discs and the read/write heads as they pass
over the discs.
[0007] Efforts have been made to address these problems. One design
is a top-cover-attach conical bearing having two independent flow
paths. This design uses asymmetric sealing and includes a
centrifugal seal and a grooved pumping seal. Another existing
design, the exclusion seal (x-seal), is used to seal interfacial
spaces between the hub and shaft (shown in FIG. 4). The x-seal
includes an asymmetric sealing design with a single thrust plate,
wherein one end is pumped inward with thrust spiral grooves and the
other end with a groove pumping seal. At the thrust bearing end, a
centrifugal seal maintains oil level change in the capillary
reservoir during static to dynamic stage, and non-operating shock.
Tests have shown, however, that the centrifugal seal fails at about
500 G shock, and oil leaks through fill holes at about 500 G
shock.
[0008] Mobile applications require higher non-operating shock than
desktop or enterprise products. Laptop computers can be subjected
to large magnitudes of mechanical shock as a result of handling. It
has become essential in the industry to require disc drives to be
able to withstand substantial mechanical shock. A sufficient
sealing system that can withstand 1000 Gs shock is needed for
mobile applications. Further, a need exists to increase shaft
stiffness and dynamic parallelism (alignment of the disc surfaces
to the plane of the actuator arm motion) while simultaneously
lowering bearing power.
SUMMARY
[0009] An improved sealing system is provided that withstands
operating mode and non-operating mode mechanical shock for use with
fluid dynamic bearings, which in turn may be incorporated into a
spindle motor or the like. In an embodiment, the sealing system
withstands at least 1000 G shock. The invention provides an
asymmetric sealing method and system and active recirculation
within a hydrodynamic bearing to retain fluid and purge air.
[0010] Also provided is a system for filling the journal with
fluid, which withstands shock. The invention further provides a
method for consumption of less power in a spindle motor, and a
spindle motor that utilizes smaller size components, yet maintains
necessary stability. Also provided is a method for achieving a
longer operating life for a spindle motor. Further provided is a
method and system for supplying radial stiffness within the
journal. The invention additionally provides a method and system
for increasing dynamic parallelism and shaft to thrust plate bond
strength.
[0011] Features of the invention are achieved in part, in an
embodiment, by utilizing an asymmetric sealing system. An enlarged
fluid reservoir, defined between a shield and a sleeve, having a
lower pressure area than other fluid containing areas is employed.
The invention utilizes a fluid recirculation passageway in fluid
communication with the enlarged reservoir to ensure the pressure
due to the asymmetry in the journal bearing adjacent to the thrust
plate, and inward pumping pressure from the thrust plate are
reduced to about atmospheric pressure. A centrifugal capillary seal
is employed on an end of the reservoir. When the motor is spinning,
centrifugal force acts on the reservoir fluid forcing it into the
bearing, and causing air to be expelled. In an embodiment, channels
are included adjacent to the reservoir on a shield allowing fluid
to be retained rather than leak during a shock event. Due to a
pressure difference in the reservoir between a tight gap
(non-channel portion) and a larger gap (channel portion), fluid is
retained within the reservoir during shock events. The channels
further allow air within the fluid to travel along the channel and
be expelled from the bearing fluid. An angled fill hole is provided
at an end of the reservoir for filling fluid into the bearing and
also serving as a location to expel air.
[0012] A tapered journal gap further provides asymmetric pressure
as well as reduces power consumption at a journal plenum. In an
embodiment, a grooved pumping seal (GPS), defined between a shield
and an outer diameter of a thrust plate, is provided. The shield is
self-aligning (concentric to the hub OD) and acts as a travel
limiter to the hub. The asymmetric sealing method and system
further incorporates spiral grooves. The spiral grooves are defined
on the thrust plate for actively generating pumping pressure to
drive fluid recirculation and to pump fluid from the thrust plate
bearing toward the shaft, into the journal bearing, and beyond a
journal grooving apex, when the shaft and the sleeve are in
relative rotational motion. A single-sided thrust plate bearing is
utilized. In a further embodiment, grooved pumping is utilized
within the journal for providing radial stiffness substantially
focused at an apex of the grooving pattern. Further, in an
embodiment, an unbalanced and asymmetric grooving pattern at an end
of the bearing provides a pressure gradient and establishes a
seal.
[0013] Dynamic parallelism is improved due to a larger surface
contact between the interface of thrush plate OD and the base. A
larger thrust plate improves the bond strength at the interface of
the thrust plate and shaft.
[0014] Reduction of power consumption is achieved, in part, by
utilizing smaller size components, including a smaller diameter
shaft. Stability of the motor is, however, maintained by attaching
the shaft to the top cover. Reduction of power consumption is
further achieved, in part, by employing grooved pumping on the
thrust plate OD, and utilizing a thinner fluid. A larger reservoir
is provided and so a thinner fluid can be utilized, the thinner
fluid typically having a higher evaporation rate than thicker
fluids. The thinner fluid results in less friction and reduces
power consumption by the motor. Further, in an embodiment, a single
sided thrust plate is used with magnetic preload to further reduce
power losses in the thrust region, bearing losses occurring on only
one side of the thrust plate.
[0015] Other features and advantages of this invention will be
apparent to a person of skill in the art who studies the invention
disclosure. Therefore, the scope of the invention will be better
understood by reference to an example of an embodiment, given with
respect to the following figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated by reference
to the following detailed description, when taken in conjunction
with the accompanying drawings, wherein:
[0017] FIG. 1 is a top plan view of a disc drive data storage
system in which the present invention is useful;
[0018] FIG. 2 is a sectional side view of a hydrodynamic bearing
spindle motor illustrating features including a fluid recirculation
passageway, shield, reservoir and fill hole, in accordance with an
embodiment of the present invention;
[0019] FIG. 3 is another sectional side view of a hydrodynamic
bearing spindle motor as in FIG. 2, with FIG. 3 having a shallower
cross section as compared to FIG. 2, and the symmetric and
asymmetric grooves of FIG. 2 shown instead by arrows, in order to
show in FIG. 3 a more detailed view of features including a fluid
recirculation passageway, shield, reservoir, fill hole, thrust
plate pumping grooves, example pressures, fluid flow direction and
pumping direction, and FIG. 3 not illustrating particular features
sufficiently shown in FIG. 2 including a top cover, stator winding,
magnets, and baseplate, in accordance with an embodiment of the
present invention;
[0020] FIG. 4 is a sectional side view of a known spindle motor
design;
[0021] FIG. 5 is a perspective view of a shield sectioned to
illustrate channels and an angled fill hole, in accordance with an
embodiment of the present invention;
[0022] FIG. 6 is another perspective view of a shield illustrating
channels and an angled fill hole, in accordance with an embodiment
of the present invention; and
[0023] FIG. 7 is a sectional side view of a portion of a
hydrodynamic bearing spindle motor illustrating features including
a fluid recirculation passageway, a shield attached to a thrust
plate, a reservoir and a fill hole, in accordance with another
embodiment of the present invention.
DETAILED DESCRIPTION
[0024] Exemplary embodiments are described with reference to
specific configurations. Those of ordinary skill in the art will
appreciate that various changes and modifications can be made while
remaining within the scope of the appended claims. Additionally,
well-known elements, devices, components, methods, process steps
and the like may not be set forth in detail in order to avoid
obscuring the invention.
[0025] A method, system and means of sealing that withstands
operating mode and non-operating mode mechanical shock for use with
fluid dynamic bearings is described herein. In an embodiment, the
sealing system withstands 1000 G shock by way of asymmetric sealing
and pressure gradient. As discussed below, in an embodiment, a
fluid recirculation passageway, an enlarged fluid reservoir defined
between a shield and a sleeve, reservoir channels, grooved pumping,
a tapered journal gap and asymmetric journal grooves provide, in
part, a system and method of employing an asymmetric pressure
gradient. Also as discussed below, in an embodiment, the invention
further utilizes the properties of a grooved pumping seal (low
volume, high stiffness) and a centrifugal capillary seal (high
volume, low stiffness) in the design of the method and system to
withstand shock. Further, in an embodiment, an angled fluid fill
hole avoids fluid leak during shock and is located at an end of the
reservoir.
[0026] Referring to the drawings wherein identical reference
numerals denote the same elements throughout the various views,
FIG. 1 illustrates a typical disc drive data storage device 110 in
which the present invention is useful. Clearly, features of the
discussion and claims are not limited to this particular design,
which is shown only for purposes of the example. It will be readily
apparent that the present invention may be applied to disc drives,
spindle motors, and other motors having a stationary and a
rotatable component. In fact, the designs discussed below can be
used in systems where rotation between components exists, even if
the components rotate in the same direction.
[0027] Disc drive 110 includes housing base 112 that is combined
with cover 114 to form a sealed environment. Disc drive 110 further
includes disc pack 116, which is mounted for rotation on a spindle
motor (not shown) by disc clamp 118. Disc pack 116 includes a
plurality of individual discs, which are mounted for co-rotation
about a central axis. Each disc surface has an associated head 120
(read head and write head), which is mounted to disc drive 110 for
communicating with the disc surface. In the example shown in FIG.
1, heads 120 are supported by flexures 122, which are in turn
attached to head mounting arms 124 of actuator body 126. The
actuator shown in FIG. 1 is a rotary moving coil actuator and
includes a voice coil motor, shown generally at 128. Voice coil
motor 128 rotates actuator body 126 with its attached heads 120
about pivot shaft 130 to position heads 120 over a desired data
track along arcuate path 132. This allows heads 120 to read and
write magnetically encoded information on the surfaces of discs 116
at selected locations.
[0028] FIG. 2 is a sectional side view of a hydrodynamic bearing
spindle motor 255 used in disc drives 110 in which the present
invention is useful. Typically, spindle motor 255 includes a
stationary component and a rotatable component. The stationary
component includes shaft 275 that is fixed and attached to base
210. It is to be appreciated that spindle motor 255 can employ a
fixed shaft as shown in FIG. 2, or a rotating shaft. Further, in an
embodiment of the invention, shaft 275 is attached to top cover
256, providing stability to shaft 275 and improving dynamic
performance. Thus, in a fixed shaft motor, both upper and lower
ends of shaft 275 can be fastened to base 210 and to top cover 256
of the housing, so that the stiffness of the motor and its
resistance to shock as well as its alignment to the rest of the
system is enhanced.
[0029] The rotatable component includes hub 260 having one or more
magnets 265 attached to a periphery thereof. The magnets 265
interact with a stator winding 270 attached to the base 210 to
cause the hub 260 to rotate. Magnet 265 can be formed as a unitary,
annular ring or can be formed of a plurality of individual magnets
that are spaced about the periphery of hub 260. Magnet 265 is
magnetized to form one or more magnetic poles.
[0030] The hub 260 is supported on a shaft 275 having a thrust
plate 283 on one end. Thrust plate 283 can be an integral part of
the shaft 275, or it can be a separate piece that is attached to
the shaft, for example, by a press fit. Further, thrust plate 283
engages with base 210 at interface 290. The invention provides an
enlarged contact surface between thrust plate 283 and base 210,
namely at interface 290. In an embodiment, interface 290 (the
diameter of thrust plate 283 in contact with base 210) is 4.5 mm.
It is to be appreciated that the length of interface 290 may vary,
and in some cases interface 290 ranges from 3 millimeters to 5
millimeters. This is achieved by an enlarged thrust plate OD
contact surface. An improvement in dynamic parallelism results,
dynamic parallelism defined as the parallelism between the spinning
disk and reference features in base 210 that determine a plane. A
three point datum on base 210 is compared with the perpendicularity
of the spin axis. The invention provides an enlarged footprint,
improving the dynamic parallelism of the components.
[0031] Further, due to the longer engagement between thrust plate
283 and shaft 275, bond strength at the interface between thrust
plate 283 and shaft 275 is improved. In an embodiment, the
engagement between thrust plate 283 and shaft 275 is two times the
engagement as compared with conventional motors (i.e., compared to
the x-seal).
[0032] The shaft 275 and thrust plate 283 fit into sleeve 280
within hub 260. Hub 260 includes a disc carrier member 214, which
supports disc pack 116 (shown in FIG. 1) for rotation about shaft
275. Disc pack 116 is held on disc carrier member 214 by disc clamp
118 (also shown in FIG. 1). Hub 260 is interconnected with shaft
275 through hydrodynamic bearing 217 for rotation about shaft
275.
[0033] A fluid, such as lubricating oil or a ferromagnetic fluid
fills interfacial regions between shaft 275 and sleeve 280, thrust
plate 283 and sleeve 280, thrust plate 283 and shield 282, and
between shield 282 and sleeve 280. In an embodiment, angled fill
hole 285 is positioned to make a 30 degree angle (or an alternative
angle, as discussed below) with a surface of shield 282. Although
the present figure is described herein with a lubricating fluid,
those skilled in the art will appreciate that a lubricating gas can
be used.
[0034] Typically one of shaft 275 and sleeve 280 includes sections
of pressure generating grooves, including asymmetric grooves 240,
and symmetric grooves 244. The grooving pattern includes one of a
herringbone pattern and a sinusoidal pattern. As shown, asymmetric
grooves 240 are placed on one end of the journal and symmetric
grooves 244 are placed on an opposite end of the journal.
Asymmetric grooves 240 and symmetric grooves 244 induce fluid flow
in the interfacial region and generate a localized region of
dynamic high pressure and radial stiffness. The pressures are
focused at symmetric grooves apex 246 and asymmetric grooves apex
242. As sleeve 280 rotates, pressure is built up in each of its
grooved regions. In this way, shaft 275 easily supports hub 260 for
constant high speed rotation. In an example, the grooves are
separated by raised lands or ribs and have a small depth. In an
embodiment, a diamond-like carbon (DLC) coating is utilized on
shaft 275 in the region of asymmetric grooves 240 to prevent or
minimize particle generation during any contact between shaft 275
and sleeve 280.
[0035] In addition to, or as an alternative to the pressure
generating grooves as discussed in the previous paragraph, an
embodiment of the invention provides fluid flow by other methods
(as discussed in detail below). The other methods include a tapered
or widened journal area 262, an asymmetric pressure gradient, a low
pressure area within reservoir 284 defined between shield 282 and
sleeve 280, a sleeve passageway 286, a grooved pumping seal between
shield 282 and thrust plate 283, and spiral grooves on thrust plate
283.
[0036] In an embodiment of the invention, sleeve passageway 286 is
situated at a point between asymmetric grooves 240, and symmetric
grooves 244. Sleeve passageway 286 is generally positioned at a
midpoint along shaft 275 providing a low pressure area. A low
pressure area in the center of the motor is acceptable since a
bearing in the center of the motor offers little radial stiffness.
Further, positioning sleeve passageway 286 in an angled manner
enables a one-piece hub to be machined.
[0037] The invention further provides a shield 282 that radially
self-aligns into sleeve 280. A light radial interference fit (light
press fit) is employed between shield 282 and sleeve 280 for self
alignment. On one end (adjacent to thrust plate 283) sleeve 280
locates shield 282 radially, and on another end shield 282 is
attached to hub 260 (i.e., laser welded). The invention therefore
provides, in an embodiment, a constant gap of about 20 to 30
microns between thrust plate 283 and shield 282.
[0038] Since thrust plate 283 is single-sided, hub 260 has freedom
of movement in an axial direction. Shield 282 is therefore provided
by the invention as a travel limiter to hub 260, defining a radial
displacement limit to hub 260. Shield 282 also serves as a damper
to hub 260 to dissipate energy caused by mechanical shock.
[0039] FIG. 3 presents a fluid dynamic bearing system illustrating,
in an embodiment of the invention, fluid pumping direction, fluid
direction and example pressures. In an embodiment, an inverted
shield is utilized. Shield 282 is described as inverted since
capillary seal 316 is inverted as compared to an x-shield design
(x-shield shown in FIG. 4). An asymmetric pressure gradient is
created by the invention. The asymmetric pressure is created by
features including a fluid recirculation passageway, an enlarged
fluid reservoir defined between a shield and a sleeve, reservoir
channels, grooved pumping, a tapered journal gap and asymmetric
journal grooves.
[0040] In an embodiment, the fluid capacity of reservoir 284 is 2.5
mg. It is to be appreciated that this capacity is not fixed. The
enlarged fluid reservoir 284 having channels 510 contribute to the
asymmetric pressure gradient (channels 510 shown in FIG. 5). Due to
a lower flow resistance and lower pressure in enlarged reservoir
284, compared with other fluid containing areas, fluid is received
and retained within reservoir 284 during non-operating or operating
shock events. As an example, numerical example pressures are
illustrated in FIG. 3. As shown, reservoir 284 shows a pressure of
0.0 psi while the journal shows pressures of 0.06 psi to 135 psi.
When the motor is spinning and forcing fluid by centrifugal force
from reservoir 284, pumping grooves 324 generate pumping pressure
and drive fluid recirculation through the motor. However, when the
motor is not spinning and centrifugal force subsides, or during
shock events, reservoir 284 can receive fluid from areas including
the outer diameter gap 346 of thrust plate 283 and from the journal
between shaft 275 and sleeve 280.
[0041] Grooved pumping is employed along the inside diameter (ID)
and the outside diameter (OD) of thrust plate 330. Pumping grooves
are formed on thrust plate 283 for active recirculation. In the
case of the ID, spiral pumping grooves 324 generate sufficient
pumping pressure to drive fluid recirculation and to pump fluid
from thrust plate bearing passageway (adjacent to the thrust plate
ID) toward shaft 275, into the journal bearing, and beyond lower
journal symmetric grooving apex 246, when shaft 275 and sleeve 280
are in relative rotational motion. Asymmetric grooves 242 and
symmetric grooves 244 also create pressure within the journal and
force fluid movement to a groove apex (as described above in FIG.
2). In an embodiment, when the motor is spinning, the fluid flow
direction is inward from the bearing of the thrust plate ID 330,
along the journal bearing to journal plenum 312, through sleeve
passageway 286, to recirculation plenum 332 and then returning to
the bearing of the thrust plate ID 330. The fluid flow direction,
in an example, is illustrated by solid lines shown in FIG. 3. It is
to be appreciated that in other embodiments, the fluid flow
direction may take on another direction. The grooved pumping
direction, in an example, is illustrated by dashed lines shown in
FIG. 3. In another embodiment of the invention, thrust plate 283 is
structured without pumping grooves 324.
[0042] A fluid recirculation passageway includes sleeve passageway
286 and a bearing between thrust plate ID 330 and sleeve 280.
Sleeve passageway 286 is positioned such that one end is placed
generally at a midpoint along shaft 275 and a second end joins
recirculation plenum 332 such that, in one situation, fluid and air
may travel along channels 510 (FIG. 5). Recirculation plenum 332 is
defined by a junction joining reservoir 284, sleeve passageway 286,
thrust plate ID 330 and thrust plate outer diameter gap 346. Sleeve
passageway 286 provides a low pressure area compared to the journal
bearing. A low pressure area in the center of the motor is feasible
for the reason that a bearing in the center of the motor offers
little radial stiffness. The lower pressure area also
advantageously reduces power consumption by journal plenum 312. In
an example, as shown in FIG. 3, 0.06 psi occurs at journal plenum
312, while a higher pressure occurs on either side of journal
plenum 312. A wider or variable journal gap also is provided
adjacent to journal plenum 312 for creating a lower pressure area.
The wider or variable journal gap, adjacent to journal plenum 312,
diverges toward journal plenum 312.
[0043] A recirculation passageway ensures the pressure due to the
asymmetry in lower journal bearing 326 adjacent to the thrust
plate, and inward pumping pressure from pumping grooves 324 of
thrust plate 283 are reduced to about atmospheric pressure. The
flow resistance of sleeve passageway 286 is significantly lower
than the flow resistance of the upper journal 310 and lower journal
326, so a pressure drop occurs across the journal bearing.
[0044] The fluid recirculation passageway is biased for creating an
asymmetric pressure gradient and substantially circulating fluid
from the journal to sleeve passageway 286 and then to the bearing
of thrust plate ID 330, and then returning to the journal.
Capillary attraction fills the journal area, and recirculation of
the fluid purges any air within the journal.
[0045] In an embodiment, the invention utilizes and makes use of
the properties of a grooved pumping seal (low volume, high
stiffness) and a centrifugal capillary seal (high volume, low
stiffness) to withstand mechanical shock.
[0046] In FIG. 3, a grooved pumping seal (GPS) 318 is employed in
outer diameter gap 346 defined between shield 282 and an OD of
thrust plate 283. By way of pumping grooves 324, GPS 318
establishes an outer diameter gap sealing stiffness and generates
pressure substantially equivalent to the pressure located at
recirculation plenum 332, when shaft 275 and sleeve 280 are in
relative rotational motion. GPS 318 is a high stiffness seal and,
in an embodiment, the invention makes use of this characteristic by
utilizing GPS 318 with an end of outer diameter gap 346. GPS 318
pumps fluid from outer diameter gap 346 serving to prevent fluid
leakage from fluid boundary 322. GPS 318 is a low volume seal and
the invention makes use of this characteristic. Pumping fluid from
outer diameter gap 346 serves to reduce power consumption by
establishing air in outer diameter gap 346, thereby reducing
friction since air is present between the OD of thrust plate 283
and shield 282.
[0047] A centrifugal capillary seal (CCS) 316 is defined between
shield 282 and sleeve 280. In an embodiment, the adjacent surfaces
of shield 282 and sleeve 280 have relatively tapered surfaces that
converge toward recirculation plenum 332. A meniscus is formed
between the tapered surfaces, and fluid within reservoir 284 is
forced toward recirculation plenum 332 by centrifugal force when
shaft 275 and sleeve 280 are in relative rotational motion. CCS 316
is a low stiffness seal and, in an embodiment, the invention makes
use of this characteristic by attaching shield 282 to hub 260 by
welding or other means making a fluid barrier above the fluid
meniscus. CCS 316 is a high volume seal and the invention makes use
of this characteristic by utilizing CCS 316 with an enlarged
reservoir 284.
[0048] Asymmetric sealing is also employed at upper journal 310.
Asymmetric grooves 242 generate pressure within upper journal 310
substantially equivalent to the pressure located at journal plenum
312. Fluid is forced from upper journal 310 generally to groove
apex 242 (as described above in FIG. 2).
[0049] FIG. 4 illustrates an example of a fluid dynamic bearing
utilizing a conventional X-seal. Motor 450 includes shaft 475,
sleeve 455, path 484, thrust plate 480, shield 482, fill hole 485
and capillary seal 420. As can be observed, gap 425 maintains fluid
(about 0.5 mg of fluid) in part by way of capillary seal 420.
Further, fill hole is positioned below capillary seal 420. In an
embodiment, the present invention utilizes an enlarged reservoir
284, channels 510, a grooved pumping seal 318 and an angled fill
hole 285, thereby withstanding greater shock than the X-seal
design, using less power and providing a longer life for the motor.
Further, the present invention provides interface 290, which, in an
embodiment, is a larger surface area than interface 440 of the
X-seal design, effecting greater dynamic parallelism and shaft to
thrust plate bond strength.
[0050] Referring to FIG. 5, in an embodiment, reservoir 284
includes channels 510. Channels 510 run in a generally axial
direction along the walls of shield 282. Channels 510 extend from
recirculation plenum 332 and along reservoir 284. In some cases,
channels 510 are in-line with sleeve passageway 286. In one
embodiment, six channels are employed, and in another embodiment,
two wider channels are employed. It is to be appreciated that the
number, length, width and positioning of channels 510 may vary and
is determined by bearing requirements.
[0051] Channels 510 allow air within the fluid to travel along
channels 510 and be purged from the fluid. Channels 510 further
provide a means for fluid to be retained within reservoir 284.
Fluid is retained within reservoir 284 during shock events due to a
pressure difference between a portion of reservoir 284 having
channels and a portion of reservoir 284 without channels. In
another embodiment of the invention, reservoir 284 serves as a low
pressure area without having channels 510.
[0052] FIG. 6 illustrates an embodiment of the invention that
includes angled fill hole 285. Angled fill hole 285 (or air vent
hole) provides a means to fill a fluid dynamic bearing with fluid.
A predetermined amount of fluid is injected into angled fill hole
285 above capillary seal 316. Angled fill hole 285 is positioned to
make a 30 degree angle or an alternative angle (i.e., 45 degrees)
with a surface of shield 282. It is to be appreciated that angles
beside 30 degree can be used. Further, in an embodiment, two angled
fill holes are employed. It is to be appreciated that other numbers
of angled fill holes can be utilized. Also shown in FIG. 6 is
attachment location 520 wherein shield 282 is attached to sleeve
280, in an embodiment of the invention. Fill hole 285 is positioned
adjacent to a sealed wall at attachment location 520. In an
embodiment, fill hole 285 is positioned between channels 510. In
another embodiment of the invention, the fill hole is positioned
without making an angle with a surface of shield 282 and positioned
on another section of shield 282.
[0053] During a shock event, fluid may travel along channels 510
and collide with sleeve 280, decelerating the traveling fluid.
Frictional drag slows the fluid within reservoir 284 and along
channels 510, due to the viscosity of the fluid. The motion of the
fluid is therefore retarded such that fluid may reach and collect
at pool area 530 without leaking from fill hole 285. In some cases,
pool area 530 fills with fluid slower than the duration of a shock
event. Further, angled fill hole 285 opposes escape of fluid during
shock since the fluid follows a path of least resistance and an
angled fill hole presents greater resistance in comparison to
capillary force gradients.
[0054] Referring to FIG. 7, a further embodiment of the invention
is illustrated. Similar to previously described embodiments, an
inverted shield is employed with spindle motor 700. Also similar to
previously described embodiments, enlarged reservoir 724 and sleeve
passageway 726 contribute to the asymmetric pressure gradient (as
described above) for withstanding shock events. Thrust plate 752
establishes an enlarged interface 762 with base 750.
[0055] In this embodiment of the invention, however, shield 720 is
attached to thrust plate 752 at shield attachment 722 and hub 754
rotates relative to shield 720. A DLC coating is utilized on one of
the relatively rotating adjacent surfaces, namely sleeve 756 and
shield 720 to prevent or minimize particle generation during any
contact. Further, in this embodiment, fill hole 760 is positioned
without making an angle with a surface of shield 282.
[0056] The following specific example is provided for illustrative
purposes and is not intended to be limiting. Results from
experiments conducted showed, in an embodiment, the present
invention utilized within a spindle motor satisfactorily withstands
1000 G shock. The shock was directed over six axes with pulse
duration of two milliseconds, half sine wave. In further testing,
multiple shocks having the same testing conditions were directed
onto a spindle motor incorporating an embodiment of the invention
and the spindle motor withstood the shock events.
[0057] Having disclosed exemplary embodiments, modifications and
variations may be made to the disclosed embodiments while remaining
within the spirit and scope of the invention as defined by the
appended claims. For example, although the present invention has
been described with reference to a sealing system for a disc drive
storage system and a spindle motor assembly, those skilled in the
art will recognize that features of the discussion and claims may
be practiced with other systems having a stationary and a rotatable
component. The components may even rotate in the same direction.
Further, the present invention is useful in many additional systems
requiring shock tolerance.
* * * * *