Shielding fluid reservoirs of fluid dynamic bearing motors

In one example, a fluid dynamic bearing motor having a shield member is provided. In one example, the method includes disposing a first member and a second member for relative rotation about an axis of rotation. An annular shield member is attached to the first member, the shield member disposed adjacent a fluid reservoir for containing a bearing fluid. The reservoir is filled through an aperture (e.g., a fill hole) in the shield member. Thereafter, the aperture is at least partially sealed. The aperture may be hermetically sealed via one or more laser pulses. In other examples, a two piece shield is provided for shielding a reservoir without a fill hole.

BACKGROUND

Various examples described herein relate generally to methods and devices for shielding reservoirs of Fluid Dynamic Bearing (FDB) motors, and in particular methods and systems for reducing or preventing the loss of liquid within FDB motors.

2. Description of Related Art

Disk drives are capable of storing large amounts of digital data in a relatively small area. Disk drives store information on one or more recording media, which conventionally take the form of circular storage disks (e.g. media) having a plurality of concentric circular recording tracks. A typical disk drive has one or more disks for storing information. This information is written to and read from the disks using read/write heads mounted on actuator arms that are moved from track to track across the surfaces of the disks by an actuator mechanism.

Generally, the disks are mounted on a spindle that is turned by a spindle motor to pass the surfaces of the disks under the read/write heads. The spindle motor generally includes a shaft and a hub, to which one or more disks are attached, and a sleeve defining a bore for the shaft. Permanent magnets attached to the hub interact with a stator winding to rotate the hub and disk. In order to facilitate rotation, one or more bearings are usually disposed between the sleeve and the shaft.

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 disks. Accordingly, the bearing assembly that supports the hub and storage disk is of increasing importance.

One typical bearing assembly used in such storage systems includes a fluid dynamic bearing system. In a fluid dynamic bearing system, 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 disk hub. In addition to air, typical lubricants include gas, oil, or other fluids. Fluid dynamic bearings spread the bearing surface over a large surface area, as opposed to a ball bearing assembly, which comprises a series of point interfaces. This is desirable because the increased bearing surface reduces wobble or runout between the rotating and fixed members. Further, the use of fluid in the interface area imparts damping effects to the bearing, which helps reduce non-repeatable run-out.

To keep the lubricating liquid in the bearing region, the bearing system generally includes various sealing mechanisms, such as capillary seals for retaining the lubricating liquid in the bearing region during non-operation of the motor. A capillary seal typically comprises two relatively angled surfaces at the end of the fluid dynamic bearing gap containing the bearing region(s) and utilizes capillary forces to bias the fluid toward the bearing region(s).

The fluid dynamic bearing motor, and in particular, the capillary seals, may lose fluid over time to evaporation or if subject to sudden jarring, often referred to as a shock event. Accordingly, motors including fluid dynamic bearings typically include a fluid reservoir adapted to contain additional fluid for the bearings that is lost, e.g., due to evaporation over the life of the motor or during a shock event. Often, the fluid reservoir is part of or at least in fluidic communication with a capillary seal.

Fluid within the capillary seal and reservoir may be contained or sealed within the motor by a shield member that acts to reduce evaporation and contain the oil during a shock event. For example, an annular shaped shield member may be placed adjacent to the capillary seal and reservoir to at least partially seal and protect the capillary seal and reservoir from evaporation or leakage of fluid. Typically, such fluid reservoirs are filled via a needle, which may be inserted through a fill hole located in the shield. The fill hole in the shield, however, allows for evaporation of the fluid and may allow contaminants to enter, thereby limiting the useful life of the FDB motor. In addition to evaporation, fluid may exit the fill hole during a shock event.

Additionally, during injection of fluid into the system, a needle is threaded through the fill hole of the shield to the fluid reservoir. The needle tip may contact surfaces of the shield not associated with the reservoir, thereby depositing fluid on unintended portions of the shield or motor.

Finally, the shield may be placed in close proximity to relatively rotating portions of the FDB motor system and may contact a relatively rotating portion of the FDB motor during an operational shock event or the like. Such contact may lead to possible damage or seizure of the motor.

Accordingly, systems and methods for providing reduced evaporation or escape of fluid from a fluid reservoir of a fluid dynamic bearing motor system are desired.

SUMMARY

In one aspect, a method for manufacturing a Fluid Dynamic Bearing (FDB) motor having a shield member is provided. In one example, the method includes disposing a first member and a second member for relative rotation about an axis of rotation. An annular shield member is attached to the first member, the shield member disposed adjacent a fluid reservoir for containing a bearing fluid. The fluid reservoir is filled with a fluid through an aperture (e.g., a fill hole) in the shield member. The aperture is then at least partially sealed, thereby shielding the fluid reservoir (e.g., by reducing or preventing evaporation or escape of fluid from the fluid reservoir).

The aperture may be laser welded after the fluid is added to at least partially seal the aperture. Further, a plug may be placed over or within the aperture and fixed in place to seal the aperture. The seal may be a hermetic or vacuum seal.

In another example, a fluid dynamic bearing system is provided that includes a first member and a second member disposed for relative rotation about an axis of rotation. A shield member is fixed to the first member, and a fluid reservoir is disposed between a portion of the shield member and a portion of the second member. The shield member further includes an aperture, wherein the aperture is at least partially sealed.

In another aspect, a method for manufacturing an FDB motor having a two piece shield member is provided. In one example, the method includes disposing a first member and a second member for relative rotation about an axis of rotation. A first shield portion is attached to the first member, wherein a surface of the first shield portion opposes a surface of the second member to form a fluid reservoir therebetween. A bearing fluid is added to the reservoir and a second shield portion is positioned to shield the reservoir.

In another example, a fluid dynamic bearing system is provided that includes a first member and a second member disposed for relative rotation about an axis of rotation. An annular shield is spatially fixed with respect to the first member, the shield including a first portion and a second portion, wherein a fluid reservoir is positioned between a surface of the first portion and a surface of the second member, and the second portion of the shield is positioned to shield the reservoir.

In another aspect, a disk drive is provided. The disk drive includes an FDB motor having an exemplary shield as described herein.

The present invention and its various embodiments are better understood upon consideration of the detailed description below in conjunction with the accompanying drawings and claims.

DETAILED DESCRIPTION

The following description is presented to enable a person of ordinary skill in the art to make and use various aspects of the inventions. Descriptions of specific materials, techniques, and applications are provided only as examples. Various modifications to the examples described herein will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the inventions. For example, aspects and examples may be employed in a variety of motors, including motors for use in disk storage drives. Motors for disk storage drives may be designed and may operate in a number of ways. The exemplary motors and other exemplary subject matter provided herein are for illustrating various aspects and are not intended to limit the range of motors and devices in which such examples and aspects may be applied.

In one example described herein, methods and systems for disposing a shield member with a Fluid Dynamic Bearing (FDB) motor are described. The shield member is placed to shield a fluid reservoir and includes an aperture or fill hole for adding fluid to the reservoir. After fluid has been added to the reservoir the fill hole is sealed to prevent or reduce evaporation and escape of fluid through the fill hole. In one example, the fill hole is sealed by a laser weld process. For example, a single laser pulse may be used to melt a plug material disposed adjacent or within the fill hole of the shield member, thereby sealing the fill hole. In one example, the fill hole is hermetically sealed, which may realize lower design and manufacturing cost, improved fluid life, and improved shock performance of an FDB motor.

In another example described herein, methods and systems for including a two piece shield with an FDB motor are provided. As described previously, a conventional shield member is generally welded (or otherwise fixed) to a sleeve portion of the motor and fluid is injected into the fluid reservoir through a fill hole in the shield member. In one example provided herein, the shield includes two portions, a first portion of the shield is fixed (e.g., welded) into place with the motor (e.g., fixed to the sleeve or the like). Fluid is then added to a reservoir portion that may be formed at least partially between the first portion of the shield and an opposing portion of the motor. The fluid is added without having to pass through a fill hole. A second portion of the shield may thereafter be fixed to the first portion of the shield, thereby providing a shield member for the FDB motor (in particular, to the oil reservoir) that does not include a fill hole or other aperture in the shield member. Further, the two portions of the shield may include two different materials, and may be optimized for different characteristics. In one example, the second portion further acts as an axial limiter for the motor and the material of the second portion may be optimized for suitable wear characteristics or the like.

Generally, exemplary shield members described herein, whether including a sealed fill hole or a two piece design, are intended to reduce or prevent evaporation and escape of the fluid in the FDB reservoir. The reduction in evaporation or escape of fluid may increase the life and performance of the FDB motor.

Turning briefly toFIG. 1, a plan view of an exemplary disk drive10for use with various aspects described herein is shown. The disk drive10includes a housing base12and a top cover14. The housing base12is combined with top cover14to form a sealed environment to protect the internal components from contamination by elements outside the sealed environment. Disk drive10further includes a disk pack16that is mounted on a hub202(seeFIG. 2a) for rotation on a spindle motor200(seeFIG. 2a) by a disk clamp18. Disk pack16includes one or more individual disks that are mounted for co-rotation about a central axis. Each disk surface has an associated read/write head20that is mounted to the disk drive10for communicating with the disk surface. In the example shown inFIG. 1, read/write heads20are supported by flexures22that are in turn attached to head mounting arms24of an actuator26. The actuator shown inFIG. 1is of the type known as a rotary moving coil actuator and includes a voice coil motor (VCM), shown generally at28. Voice coil motor28rotates actuator26with its attached read/write heads20about a pivot shaft30to position read/write heads20over a desired data track along a path32. The general configuration and arrangement of disk drive10shown inFIG. 1is illustrative only, and other arrangements of the various components have frequently been used, and aspects provided are not limited by the particular configuration of disk drive10shown.

FIGS. 2a-2cillustrate various views of an exemplary shield member250according to a first example and are preferably referenced in combination. In particular,FIG. 2aillustrates an exemplary spindle motor200including shield member250,FIG. 2billustrates a detailed portion of shield member250of motor200, andFIG. 2cillustrates a perspective view of shield member250, according to one example.

In this example, motor200generally includes a stationary shaft portion including shaft220and thrust plate222. Shaft220is further fixed at the lower end with base14and the upper end by screw support226. Screw support226is further fixed with respect to top cover14in a top-cover attached configuration.

Motor200further includes a rotor portion rotatably mounted to the shaft portion, the rotor portion generally including sleeve205and hub202which rotate around stationary shaft220. An inner radial surface of sleeve205and outer radial surface of shaft220form a fluid dynamic bearing gap therebetween, where one or both of the radial surfaces may include circumferentially disposed groove regions215and216. Groove region215and/or groove region216may be asymmetrical and may function as pumping seals and/or to recirculate lubricating liquid through portions of motor200, e.g., recirculation channel207. A groove region217may further be formed between sleeve205and thrust plate222to form a thrust bearing, for example.

Mounted with shaft220and thrust plate222is a stator212that, when energized, communicates with a magnet associated with hub202and induces rotation of hub202and sleeve205about stationary shaft220. Stator212comprises a plurality of “teeth” (not shown) formed of a magnetic material where each of the teeth is wound with a winding or wire (not shown).

This particular example includes an electro-magnetic biased motor. In particular, to establish and maintain pressure in the groove region217, and to bias the rotating assembly, a constant force magnetic circuit may be provided comprising magnet213supported on the rotating assembly (here mounted on hub202), and located across a gap from a magnetically conducting steel ring209supported on the stationary assembly. Other magnetic circuits or configurations are of course possible. Such a configuration recognizes many advantages; however, a significant disadvantage to magnetically biased FDB motors of the prior art is that the axial magnetic force may be overcome by a shock event or the like resulting in relative axial displacement of the rotor portion and shaft portion. Accordingly, shield member250may further act as an axial limiter to restrict axial displacement of hub202relative to shaft220. In particular, a small axial gap224defined between the lower edge of shield member250and thrust plate222may be set to restrict axial movement as desired.

Additionally, a fluid reservoir defined in part by capillary seal260is disposed between shield member250and a portion of motor200, in this example, a portion of thrust plate222. As illustrated more clearly inFIG. 2b, the distance between the outer radial surface of thrust plate222and the inner radial surface of shield member250varies from a narrow gap distance proximate circulation channel207and the bearing regions to a wide gap distance distal therefrom, forming capillary seal260therebetween.FIG. 2bfurther shows fluid between shield member250and thrust plate222forming a meniscus262. In this configuration, capillary forces on liquid within capillary seal260will draw liquid toward bearing regions of motor200. Additionally, capillary seal260serves as a fluid reservoir of lubricating liquid for bearings215,216, and217, for example.

In this example, capillary seal260is disposed in series (e.g., at similar radial distances and varying axial positions) with sleeve205, but may also be disposed in parallel (e.g., at similar axial positions but varying radial distances), which may reduce the overall height (along the axis of rotation) of motor200. Further, this particular example may increase the volume of fluid reservoir in the motor200. Those of ordinary skill in the art will recognize, however, that various other designs and configurations of capillary seal260and fluid reservoirs are possible (whether used in conjunction with shield member250or otherwise).

FIG. 2cillustrates a perspective view of exemplary shield member250. In this example, shield member250includes an annular shaped member having two fill holes252. In other examples, one or more fill holes252are possible. Additionally, in other examples, various other annular shapes and designs are possible. For example, the cross-sectional shape, as seen inFIGS. 2aand2b, may include one or more ridges, shoulders, curves, and the like, forming L or S shaped cross-sections, for example. Additionally, shield member250may include conical portions and may be fixed with respect to other portions of the motor such as shaft220or the like. Further, shield member250may be formed integral with various portions of the motor such as sleeve205, or the like.

In one aspect described herein, a method for manufacturing an FDB motor such as motor200includes disposing shield member250with an FDB motor, such as motor200, adding fluid through fill hole252into the fluid reservoir of the motor, and sealing fill hole252after the fluid has been added. In particular, shield member250may be fixed to a motor portion, e.g., sleeve205, by any suitable method. Fluid may then be added through one or more fill holes252into the reservoir, e.g., formed in part by capillary seat260. Fill holes252may then be partially or completely sealed to reduce or prevent the loss of fluid.

In one example, fill hole252is sealed by heating a selective portion of shield member250to melt and reflow base material (e.g., steel or other suitable material) of shield member250into fill hole252. For example, a laser source may direct one or more pulses to a portion of shield member250adjacent fill hole252to locally heat and melt material of shield member250surrounding hole252such that the material melts and flows within or over fill hole252. In one example, shield member250may be manufactured with excess material in the vicinity of fill hole252, e.g., a ridge or the like around fill hole252, such that upon heating there is sufficient material to reflow and fill hole252.

In another example, a fill material or plug member is placed in or adjacent fill hole252and fixed in place to at least partially seal fill hole252. For example, a wire may be fed partially into or through fill hole252and a laser pulse directed to a portion of the wire in or adjacent fill hole252with sufficient power, duration, etc., to fuse a portion of the wire to shield member250. In one example, a single laser pulse having characteristics in the range of 3.7-4.0 ms, 300-400 v, and 2.5-4 j is used to weld a plug member such as a wire or the like within fill hole252. The wire may then be trimmed back after fill hole252is sealed. The wire may be comprised of the same or different materials than shield member250, and the wire may have a diameter or cross-sectional shape similar to fill hole252. For example, the diameter of fill hole252may be between 0.3 and 0.5 mm and a wire having a similar diameter of between 0.3 and 0.5 mm may be used.

FIGS. 3aand3billustrate exemplary plugs354aand354bover and/or within fill hole352aand352b, which may be then fixed in place to at least partially seal fill hole352aand352brespectively. With respect toFIG. 3a, an exemplary ball shaped plug354ais placed over a cylindrical shaped fill hole352a. Plug354amay then be fixed in place to seal fill hole352a. In one example, a laser pulse as described above may be used to heat and weld plug354aover hole352a, for example, such that plug354amelts and covers or fills fill hole352a. In other examples, plug354amay be epoxy bonded, press fitted, or otherwise fixed in place with respect to fill hole352a.

With respect toFIG. 3b, an exemplary flush rivet shaped plug354bis placed within a corresponding shaped fill hole352b. In one example, a laser pulse is used to heat and weld plug354bin place within fill hole352b. In other examples, plug354bcould be epoxy bonded, press fitted, or otherwise fixed in place with respect to fill hole352b. The flush rivet shaped plug354band corresponding hole352bmay provide relative smooth surfaces on the upper and lower portion of shield350b.

FIGS. 3c-3gillustrate various exemplary shaped plugs354c-gthat may be placed within or over a fill hole as described. The shape of the corresponding fill hole may also include various exemplary shapes to accommodate the different plug shapes. For example, various shapes including cylindrical, rivet, wedge, plate, annular shim, or the like may be used for the plug, fill hole352, or both. Plug material may be bonded via welding, laser welding, epoxy bonding, or otherwise fixed in place, as well as pressed to form a friction fit within hole352. Further, plug material may include the same or different material than shield member350.

After a fill hole has been sealed adequately, further processing may be desired to remove excess material from the surfaces of the shield member that may cause undesirable surface relief features, for example, a bump or ridge. In one example, an additional laser pulse (or pulses) is used to melt or ablate undesirable surface relief features. Such subsequent laser pulse(s) may include a larger spot diameter, for example, to melt and reflow the excess material. Additionally, various mechanical or chemical polishing processing and the like may be used to remove excess material.

With reference toFIG. 4, a cross-sectional view of an exemplary motor400including a two piece shield according to another aspect provided herein is illustrated. Motor400is similar to motor200; accordingly, only differences will be discussed in detail. In particular, shield member250as illustrated inFIGS. 2a-2cis replaced with a two piece shield member including a first portion, reservoir shield450, and a second portion, shield451.

In one example, a two piece shield member configuration allows for a first portion, reservoir shield450, to be fixed to a portion of the motor and disposed to define a portion of a fluid reservoir and capillary seal260. Fluid may then be added to the reservoir and capillary seal260directly without passing through a fill hole as described previously and held between reservoir shield450and a portion of thrust plate222, at least partially, by capillary forces. A second portion of the shield member, shield451, may then be fixed to the first portion, reservoir shield450, thereby defining a shield member similar to that of shield member250.

Reservoir shield450may be mounted, for example, by press fitting or epoxy bonding reservoir shield450into an annular ridge or shoulder portion of sleeve205. Additionally, reservoir shield450may be formed integral with sleeve205, or other portion spatially fixed with respect to shield451, e.g., a surface opposing thrust plate222may simply be formed as part of a motor element and placed in opposition with an opposing surface to form capillary seal260and fluid reservoir therebetween. In other examples, reservoir shield450may be similarly fixed with respect to the rotor, e.g., fixed to a rotating portion of the motor, and configured to form a capillary seal/reservoir between an opposing surface associated with a stationary portion of the motor.

Shield451may be fixed to reservoir shield450by adhesive480, for example. Reservoir shield450and shield451may be attached by any suitable method including, but not limited to welding, epoxy boding, press fitting, and the like.

Additionally, the cross-sectional shapes of reservoir shield450and shield451may vary similarly as discussed above for shield member250.

In one example, reservoir shield450and shield451include different materials. For example, in instances where shield451provides an axial limiter for motor400, shield451may include different materials, coatings, etc. to improve the wear characteristics relative to reservoir shield450. In particular, shield451may include materials suited for contacting a relatively rotating, opposing surface of thrust plate222across gap424during an axial displacement.

Various motor and FDB aspects have been illustrated and described herein. It should be recognized that exemplary spindle motor200and motor400are shown for illustrative purposes only and other motor designs are contemplated and possible for use with exemplary aspects described. For example, U.S. Pat. Nos. 6,154,339 and 6,828,709, and U.S. patent application Ser. No. 10/600,096, all of which are hereby incorporated by reference as if fully set forth herein, describe additional motor configurations that may be used with various aspects described herein. Also, it would be understood that certain components have been separately identified herein, but such identification does not imply that such components must be separately formed from other components. Similarly, components identified herein may be subdivided into sub-components in other designs. Additionally, illustrated features such as recirculation channels, bearing surfaces, pumping grooves, and the like may be disposed additionally or differently than presented in aspects herein.

Other modifications and variations would also be apparent to those of ordinary skill in the art from the exemplary aspects presented. By example, various exemplary methods and systems described herein may be used alone or in combination with various FDB and capillary seal systems and methods. Additionally, particular examples have been discussed and how these examples are thought to address certain disadvantages in related art. This discussion is not meant, however, to restrict the various examples to methods and/or systems that actually address or solve the disadvantages.