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.

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 &agr; 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 &THgr; 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.

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.