U.S. patent application number 10/242336 was filed with the patent office on 2003-12-04 for method and apparatus for forming grooved journals.
Invention is credited to Cochran, Dustin Alan.
Application Number | 20030221959 10/242336 |
Document ID | / |
Family ID | 29586445 |
Filed Date | 2003-12-04 |
United States Patent
Application |
20030221959 |
Kind Code |
A1 |
Cochran, Dustin Alan |
December 4, 2003 |
Method and apparatus for forming grooved journals
Abstract
Embodiments of the invention generally provide a method and
apparatus for forming grooves on hydrodynamic bearings used with a
disc drive. In one embodiment, the invention provides a method and
apparatus to align an electrode having a hydrodynamic groove
pattern thereon within a journal bearing. The invention provides a
floating electrode having groove patterns thereon. The floating
electrode is inserted within a hydrodynamic bearing and fluidly
aligned to maintain a uniform gap there between.
Inventors: |
Cochran, Dustin Alan;
(Watsonville, CA) |
Correspondence
Address: |
MOSER, PATTERSON & SHERIDAN, LLP
Suite 250
350 Cambridge Avenue
Palo Alto
CA
94306
US
|
Family ID: |
29586445 |
Appl. No.: |
10/242336 |
Filed: |
September 11, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60383949 |
May 28, 2002 |
|
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Current U.S.
Class: |
204/280 |
Current CPC
Class: |
F16C 33/107 20130101;
F16C 33/14 20130101; B23H 3/04 20130101; F16C 2370/12 20130101;
B23H 2200/10 20130101; F16C 17/102 20130101; B23H 9/00
20130101 |
Class at
Publication: |
204/280 |
International
Class: |
C25C 007/02 |
Claims
1. A method for aligning an electrode having one or more journal
bearing groove patterns thereon within a hydrodynamic bearing,
comprising; positioning the electrode within the hydrodynamic
bearing; and providing a fluid pressurable medium within a gap
formed between the electrode and the journal bearing to align the
electrode and the hydrodynamic bearing, and pressurizing the
medium.
2. The method of claim 1, wherein the medium is a fluid.
3. The method of claim 1, wherein the medium comprises air at
pressure to align the electrode.
4. The method of claim 1, wherein providing a medium comprises
directing a fluid flow from the electrode against at least some
portion of an inner surface of the journal bearing, wherein the
fluid provides a centering force against the inner surface.
5. The method of claim 1, wherein at least a portion of the
electrode comprises fluid jets for directing the fluid flow against
at least some portion of an inner wall of the journal bearing.
6. The method of claim 5, wherein directing the fluid flow provides
a force having a magnitude to form a gap between the electrode and
inner wall.
7. The method of claim 1, wherein positioning comprises providing
air flow within a gap formed between at least a portion of the
electrode and an inner surface of an fluidstatic bearing.
8. The method of claim 7, wherein providing air flow comprises
adjusting the air flow to align the electrode relative an inner
bore defined by the fluidstatic bearing.
9. An apparatus for forming grooves within a journal bearing,
comprising: an fluidstatic bearing configured to support at least a
portion of an electrode having at least one surface carrying a
groove pattern to electrochemically etch on an inner surface of the
journal bearing; a fluid input configured to couple fluid flow
within a gap between at least some of the electrode and an inner
surface of the journal bearing to adjust the width of the gap; and
a source of electrolyte to be pumped within the gap.
10. The apparatus of claim 9, further comprising a power source to
energize the electrode, the electrolyte, and journal bearing.
11. The apparatus of claim 9, wherein the fluid input is configured
to direct fluid flow from the electrode against at least some of
the inner surface of the journal bearing.
12. The apparatus of claim 9, wherein the electrode comprises fluid
jets configured to direct a fluid flow against at least some of the
inner surface of the journal bearing.
13. The apparatus of claim 12, wherein the fluid jets are spaced
radially about the electrode at an angle configured to provide the
fluid flow in a direction to align the electrode with the inner
surface of the journal bearing.
14. The apparatus of claim 13, wherein the angle is selected to
provide an angle between the fluid jets so that the fluid jets are
about equally spaced apart.
15. The apparatus of claim 12, wherein the fluid flow is about 45
degrees relative the inner surface.
16. An apparatus for electrochemically forming grooves on a journal
bearing, comprising: means for fluidly supporting an electrode
having a groove pattern thereon; and means for fluidly aligning the
electrode within a journal bearing.
17. The apparatus of claim 16, wherein means for fluidly supporting
the electrode comprises an fluidstatic bearing coupled to the
electrode configured to support the electrode within the journal
bearing.
18. The apparatus of claim 16, wherein means for fluidly supporting
the electrode comprises an fluidstatic bearing having an air input
configured to direct air flow against at least some of the
electrode of a magnitude to form a gap between the electrode and
fluidstatic bearing.
19. The apparatus of claim 16, wherein means for fluidly aligning
the electrode comprises fluid jets disposed within the electrode
and configured to direct a stream of fluid against an inner wall of
the journal bearing.
20. The apparatus of claim 16, wherein means for fluidly aligning
the electrode comprises a fluid delivery bore axially disposed
within the electrode, the fluid delivery bore includes fluid jets
extending though the electrode and configured to direct a stream of
fluid against an inner wall of the journal bearing.
Description
CROSS-REFERENCE TO A RELATED APPLICATION
[0001] This invention is based on U.S. Provisional Patent
Application Serial No. 60/383,949 filed May 28, 2002, entitled
"Dynamic Machining Gap For Cylindrical ECM Applications" filed in
the name of Dustin Alan Cochran. The priority of this provisional
application is hereby claimed.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates generally to the field of disc drives,
and more particularly to an apparatus and method for forming
hydrodynamic grooves in a disc drive.
[0004] 2. Description of the Related Art
[0005] Disc drives are capable of storing large amounts of digital
data in a relatively small area. Disc drives store information on
one or more recording media. The recording media conventionally
takes the form of a circular storage disc, e.g., media, having a
plurality of concentric circular recording tracks. A typical disc
drive has one or more discs for storing information. This
information is written to and read from the discs using read/write
heads mounted on actuator arms that are moved from track to track
across surfaces of the discs by an actuator mechanism.
[0006] Generally, the discs are mounted on a spindle that is turned
by a spindle motor to pass the surfaces of the discs under the
read/write heads. The spindle motor generally includes a shaft
fixed to a base plate and a hub, to which the spindle is attached,
having a sleeve into which the shaft is inserted. Permanent magnets
attached to the hub interact with a stator winding on the base
plate to rotate the hub relative to the shaft. In order to
facilitate rotation, one or more bearings are usually disposed
between the hub and the shaft.
[0007] Over the years, storage density has tended to increase and
the size of the storage system has tended to decrease. This trend
has lead to greater precision and lower tolerance in the
manufacturing and operating of magnetic storage discs. For example,
to achieve increased storage densities the read/write heads must be
placed increasingly close to the surface of the storage disc. This
proximity requires that the disc rotate substantially in a single
plane. A slight wobble or run-out in disc rotation can cause the
surface of the disc to contact the read/write heads. This is known
as a "crash" and can damage the read/write heads and surface of the
storage disc resulting in loss of data.
[0008] From the foregoing discussion, it can be seen that the
bearing assembly which supports the storage disc is of critical
importance. One typical bearing assembly comprises ball bearings
supported between a pair of races which allow a hub of a storage
disc to rotate relative to a fixed member. However, ball bearing
assemblies have many mechanical problems such as wear, run-out and
manufacturing difficulties. Moreover, resistance to operating shock
and vibration is poor because of low damping.
[0009] One alternative bearing design is a hydrodynamic bearing. In
a hydrodynamic bearing, a lubricating fluid such as air or liquid
provides a bearing surface between a fixed member of the housing
and a rotating member of the disc hub. In addition to air, typical
lubricants include oil or other fluids. Hydrodynamic bearings
spread the bearing interface over a large surface area in
comparison with a ball bearing assembly, which comprises a series
of point interfaces. This is desirable because the increased
bearing surface reduces wobble or run-out between the rotating and
fixed members. Further, the use of fluid in the interface area
imparts damping effects to the bearing which helps to reduce
non-repeat run out.
[0010] Dynamic pressure-generating grooves (i.e., hydrodynamic
grooves) disposed on journals, thrust, and conical hydrodynamic
bearings generate localized area of high fluid pressure and provide
a transport mechanism for fluid or air to more evenly distribute
fluid pressure within the bearing, and between the rotating
surfaces. The shape of the hydrodynamic grooves is dependant on the
pressure uniformity desired. The quality of the fluid displacement
and therefore the pressure uniformity is generally dependant upon
the groove depth and dimensional uniformity. For example, a
hydrodynamic groove having a non-uniform depth may lead to pressure
differentials and subsequent premature hydrodynamic bearing or
journal failure.
[0011] As the result of the above problems, electrochemical
machining (ECM) of grooves in a hydrodynamic bearing has been
developed. Broadly described, ECM is a process of removing material
metal without the use of mechanical or thermal energy. Basically,
electrical energy is combined with a chemical to form an etching
reaction to remove material from the hydrodynamic bearing to form
hydrodynamic grooves thereon. To carry out the method, direct
current is passed between the work piece which serves as an anode
and the electrode, which typically carries the pattern to be formed
and serves as the cathode, the current being passed through a
conductive electrolyte which is between the two surfaces. At the
anode surface, electrons are removed by current flow, and the
metallic bonds of the molecular structure at the surface are
broken. These atoms go into solution, with the electrolyte as metal
ions and form metallic hydroxides. These metallic hydroxide (MOH)
molecules are carried away to be filtered out. However, this
process raises the need to accurate and simultaneously place
grooves on a surface across a gap which must be very accurately
measured, as the setting of the gap will determine the rate and
volume at which the metal ions are carried away. Even in simple
structures, this problem can be difficult to solve. When the
structure is the interior surface of a conical bearing, the setting
of the gap width can be extremely difficult. Manufacturability
issues associated with conical parts often make it difficult to
control the diameter of the cones. Due to mechanical tolerances,
the work piece may be misaligned with the electrode causing an
uneven gap and a correspondingly uneven depth hydrodynamic groove.
Therefore, it is almost impossible to make a tool with fixed
electrodes that will guarantee a continued consistent work piece to
electrode gap to form dimensionally consistent hydrodynamic
grooves.
[0012] Therefore, a need exists for a method and apparatus to
provide a reliable method and apparatus for forming hydrodynamic
grooves that is accurate and cost effective.
SUMMARY OF THE INVENTION
[0013] Embodiments of the present invention relate to a method and
apparatus for electromechanically etching grooves in a surface of a
conical bearing. In one embodiment, the invention provides a method
for aligning an electrode having one or more hydrodynamic bearing
groove patterns thereon within a hydrodynamic bearing. The method
includes positioning the electrode within a hydrodynamic bearing,
and providing a fluid pressure between the electrode and the
hydrodynamic bearing to align the electrode and the hydrodynamic
bearing.
[0014] In another embodiment, the invention provides an apparatus
for forming grooves within a hydrodynamic bearing. The apparatus
includes a fluidstatic bearing configured to support at least a
portion of an electrode having at least one surface carrying a
groove pattern to electrochemically etch on an inner surface of the
hydrodynamic bearing. The fluid static bearing utilizes a
pressurable medium which may comprise liquid or air. The apparatus
includes a fluid input configured to couple a fluid flow in a gap
between at least some of the electrode and an inner surface of the
hydrodynamic bearing to adjust the width of the gap, and a source
of electrolyte to be pumped within the gap.
[0015] In another embodiment, the invention provides an apparatus
for electrochemically forming grooves on a hydrodynamic bearing,
including means for fluidly supporting an electrode having a groove
pattern thereon, and means for fluidly aligning the electrode
within a hydrodynamic bearing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] So that the manner in which the above recited embodiments of
the invention are attained and can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to the embodiments thereof which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0017] FIG. 1 depicts a plan view of one embodiment of a disc drive
for use with aspects of the invention.
[0018] FIG. 2 is a vertical sectional depicting one embodiment of a
dual conical bearing utilized in the disc drive of FIG. 1 for use
with aspects of the invention.
[0019] FIG. 3 depicts a simplified sectional view of an
electrochemical machining system for use with aspects of the
invention.
[0020] FIG. 4 depicts a partial sectional view of an
electrochemical machining system for use with aspects of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] FIG. 1 depicts a plan view of one embodiment of a disc drive
10 for use with embodiments of the invention. Referring to FIG. 1,
the disc drive 10 includes a housing base 12 and a top cover 14.
The housing base 12 is combined with top cover 14 to form a sealed
environment to protect the internal components from contamination
by elements from outside the sealed environment. The base and top
cover arrangement shown in FIG. 1 is well known in the industry.
However, other arrangements of the housing components have been
frequently used, and aspects of the invention are not limited to
the configuration of the disc drive housing. For example, disc
drives have been manufactured using a vertical split between two
housing members. In such drives, that portion of the housing half
which connects to the lower end of the spindle motor is analogous
to base 12, while the opposite side of the same housing member,
which is connected to or adjacent the top of the spindle motor, is
functionally the same as the top cover 14. Disc drive to further
includes a disc pack 16 which is mounted on a hub 202 (See FIG. 2)
for rotation on a spindle motor (not shown) by a disc clamp 18.
Disc pack 16 includes a plurality of individual discs that are
mounted for co-rotation about a central axis. Each disc surface has
an associated read/write head 20 which is mounted to disc drive 10
for communicating with the disc surface. In the example shown in
FIG. 1, read/write heads 20 are supported by flexures 22 which are
in turn attached to head mounting arms 24 of an actuator body 26.
The actuator shown in FIG. 1 is of the type known as a rotary
moving coil actuator and includes a voice coil motor (VCM), shown
generally at 28. Voice coil motor 28 rotates actuator body 26 with
its attached read/write heads 20 about a pivot shaft 30 to position
read/write heads 20 over a desired data track along a path 32.
[0022] FIG. 2 is a vertical sectional view of a hub 202 supported
by dual conical and journal bearing 200 for rotation about a shaft
not shown. The hub 202 is integrated with the sleeve 204. The
sleeve 204 includes internal surfaces 206 having grooved regions
214, 216 forming the hydrodynamic bearing to support the hub during
rotation. As is well-known in this technology, a shaft (not shown)
is inserted within the sleeve 204 and has dual conical surfaces
which face the conical regions 210, 212 at the upper and lower ends
of the journal bearing 200. The shaft would further include a
smooth center section which would cooperate with a portion of the
journal bearing 200 defined by the grooved regions 214, 216. As is
well-known in this field of fluid dynamic bearings, fluid will fill
the gap between the stationary shaft and the inner grooved surfaces
of the sleeve 204.
[0023] As the sleeve 204 rotates, under the impetus of interaction
between magnets mounted on an inner surface of the hub 202 which
cooperate with windings supported from the base of the hub 202,
pressure is built up in each of the grooved regions 214, 216. In
this way, the shaft easily supports the hub 202 for constant high
speed rotation. Hydrodynamic grooves 222 on the inner surface of
the sleeve 204 can easily be seen FIG. 2. They include, in one
example, two sets of grooves 230, 232 for the upper cone and a
corresponding set 234, 236 for the lower cone. This particular
design also utilizes two journal bearings 240, 242 to further
stabilize the shaft.
[0024] FIG. 3 is a simplified illustration of a groove forming
apparatus 300 and method for making hydrodynamic grooves 222. FIG.
2 may be referenced as needed in the discussion of FIG. 3. For
purposes of clarity, the illustrative apparatus and method are
described in terms of hydrodynamic grooves 222. However, the
present invention is not limited to making this particular
combination of hydrodynamic grooves 222. For example, the apparatus
and method described could be used to make the hydrodynamic grooves
(e.g., grooves) 222 inside a single cone or a single cone
cooperating with a single journal bearing or dual cones cooperating
with one or more journal bearings 200. Further, each of the conical
bearings could have one or more sets of hydrodynamic grooves 222.
The principles of the present invention are applicable in forming
any design of conical or journal bearing. The solution provided by
this invention is especially important in defining conical bearings
because manufacturability issues associated with conical parts
often make it difficult to control the diameter of the cones. Given
this, it is extremely hard to make a tool with fixed electrodes
that will guarantee a consistent work piece to electrode gap. As
described above, this gap distance is paramount to the accuracy of
hydrodynamic groove dimensions. Considering fluid dynamic bearings,
the importance of the accuracy of hydrodynamic grooves is that a
fluid dynamic bearing generally comprises two relatively rotating
members having juxtaposed surfaces between which a layer or film or
fluid is maintained to form a dynamic cushion with an antifriction
medium. To form the dynamic cushion, at least one of the surfaces,
in this case the interior surfaces of sleeve 204, are provided with
the hydrodynamic grooves 222 which induce fluid flow in the
interfacial region and generate a localized region of dynamic high
pressure.
[0025] With continuing reference to FIG. 3, groove-forming
apparatus 300 includes an fluidstatic bearing 306. Fluidstatic
bearing 306 includes an air inlet 308 to receive fluid 310 such as
pressurized air, clean dry air (CDA), liquid and the like. Internal
surfaces 307 of fluidstatic bearing 306 define a longitudinal bore
309. Longitudinal bore 309 inside diameter is sized to hold a
floating electrode 302 therein. Floating electrode 302 has an
outside diameter sized smaller than longitudinal bore 307 to define
a gap 316 there between. Fluid flow through inlet 308 into gap 316
is at sufficient viscosity or pressure provides force FX1 between
internal surfaces 307 and floating electrode 302. FX1 is of a
magnitude capable of supporting floating electrode 302 to maintain
gap 316. In this embodiment, pressure within gap 316 between
internal surfaces 307 and floating electrode 302 center and support
such floating electrode 302 within longitudinal bore 309.
Fluidstatic bearing 306 may include one or more end walls not shown
to prevent floating electrode 306 from moving outside longitudinal
bore 309.
[0026] Floating electrode 302 includes an extension 304 extending
from one end thereof. Extension 304 has an outside diameter sized
to fit within an inside diameter of journal bearing 200 (i.e., work
piece) to form a fluid gap 322 there between. The journal bearing
200 is rigidly held in place by a clamping apparatus not shown.
Extension 304 is configured with a hydrodynamic journal pattern 324
juxtaposed to inside surfaces 206. Hydrodynamic journal pattern 324
may be used to form hydrodynamic grooves 222 on the journal bearing
200, for example. During a hydrodynamic groove forming operation,
electrolyte 320 is pumped through an electrolyte inlet 321 into
fluid gap 322. As electrolyte 320 is generally non-compressible,
electrolyte 320 fills fluid gap 322 centering electrode extension
304 within journal bearing 200. In this embodiment, electrolyte 320
is used to center the extension 304 within journal bearing 200.
[0027] In another aspect of the invention, Floating electrode 302
may further include a fluid delivery bore 315 extending axially
there through, and at least partially through extension 304. Fluid
delivery bore 315 includes a positioning fluid inlet 314 on one end
and a plurality of fluid jets 328A-C coupled to an opposite end of
fluid bore 315. Fluid jets 328A-C are disposed so that positioning
fluid 312 received from fluid inlet 314 exits at least partially
against an inside surfaces 206 of journal bearing 200. To maximize
centering pressure FX2 and holding force FY2, fluid jets 328A-C may
be angled at an angle .alpha. approximately 45 degrees relative the
inside surfaces 206 they contact. Positioning fluid 312 may be any
fluid configured to work with electrolyte 320, and may be an
electrolyte similar to or the same as electrolyte 320.
[0028] As illustrated in FIG. 4, fluid jets 328A-C may be radially
spaced approximately uniformly about extension 304 so that
positioning fluid 312 discharged from fluid jets 328A-C provide
uniform centering forces FX2 and FY2 against the journal bearing
200. Positioning fluid 312 exits from fluid gap 322 via an end of
journal bearing 200. During another alignment operation of
extension 304 within journal bearing 200, positioning fluid 312 is
pumped though fluid inlet 314 and forced through fluid jets 328A-C.
Fluid forces FX2 and FY2 balance force FX1 in an equilibrium
condition so that extension 304 is horizontally and vertically
centered within journal bearing 200. While three fluid jets 328A-C
are illustrated spaced so the angle .THETA. is approximately 120
degrees apart to provide an equal fluid force FX2 to center the
extension 304 within the journal bearing 200, any number or
configuration of fluid jets 328 may be used to provide such
centering and aligning forces.
[0029] The ECM process can then be executed by then applying an
electrical potential to the work piece 200 and floating electrode
302, the work piece receiving the positive potential and the
floating electrode 302 serving as the cathode and receiving the
negative potential. By timing the current flow, an imprint in the
form of the groove patterns 222 shown in FIG. 2 are placed on the
work piece 200. As is well-known, the width and depth of the
resulting hydrodynamic grooves 222 is controlled by the duration
and level of current applied to the work piece 200 and the floating
electrode 302. The current level being modified primarily by the
fluid gap 322 which has now been adjusted by fluidstatic bearing
306, electrolyte 320, and positing fluid 312 via fluid jets
328A-C.
[0030] While the foregoing is directed to embodiments of the
invention, other and further embodiments of the invention may be
devised without departing from the basic scope thereof, and the
scope thereof is determined by the claims that follow.
* * * * *