Fluid bearing component including thrust bearing groove recesses and disk drive device including same

An example rotating device is a disk drive device that includes a base, a hub on which a recording disk is to be mounted and which rotates relative to the base, and a fluid dynamic bearing unit that allows the hub to rotate relative to the base. The fluid dynamic bearing unit includes a shaft that performs relative rotation and a cylindrical member that encircles the shaft, the cylindrical member includes a thrust dynamic pressure generating groove which is provided in one end face of the cylindrical member and which generates thrust dynamic pressure, and the thrust dynamic pressure generating groove includes a cut-and-machined face.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rotating device having a thrust fluid dynamic pressure bearing, a manufacturing method of the rotating device, and a bearing component thereof.

2. Description of the Related Art

Rotating devices like hard disk drives are becoming compact and increasing the capacity, and loaded in various electronic devices. In particular, loading of disk drive devices in portable electronic devices, such as a laptop computer and a portable music player, is advancing. Rotating devices like disk drive devices loaded in such portable electronic device need thinning and weight saving, and also improvement of the rigidity of the rotating devices in order to withstand against a vibration at the time of carrying in comparison with the rotating devices loaded in a stationary electronic device like a desktop computer. In general, thinning of rotating devices and improvement of the rigidity thereof are in a trade-off relationship.

The inventor of the present invention propose, in JP 2011-153705 A, a rotating device that has an improvement in an efficiency of collecting the lubricant in a thrust dynamic pressure generating part, thereby enhancing the dynamic pressure. The rotating device of JP 2011-153705 A includes thrust dynamic pressure patterns formed by pressing a mold against a patterning target, such as a rotating body or a stationary body. According to such a rotating device, the collapsing of the shapes of the concavities of the formed thrust dynamic pressure pattern and the convexities thereof and the unevenness in height of those concavities and convexities can be suppressed.

In order to downsize the rotating device having a dynamic pressure generation part, a component configuring the dynamic pressure generating part may be downsized. When, however, the dynamic pressure generating part is downsized, the area of the dynamic pressure generating part is reduced, and thus the bearing rigidity decreases. This results in a negative effect to the shock resistance of the rotating device and the vibration resistance thereof. Such rotating devices have a stationary body and a rotating body, and when the bearing rigidity decreases, respective faces of the stationary body and the rotating body in the rotation axis direction may contact with each other when a shock like falling is applied to the rotating devices. When the rotating body contacts the stationary body, the performance is deteriorated, contact sounds are produced, or the contacting portion is worn out, resulting in the reduction of the lifetime of the rotating devices.

In order to compensate such a reduction of the bearing rigidity, a gap with the dynamic pressure generating part may be reduced. When, however, the gap is reduced, the bearing loss increases, and power consumption may increase in some cases. Alternatively, the dynamic pressure generating part may be deformed by processing pressure when the dynamic pressure generating part is processed. For example, when a mold is pressed against an end face of a cylindrical member having an inner circumferential surface that encircles a shaft and retains the shaft therein in the axial direction, a deformation such that the inner circumferential surface of that member expands inwardly may occur. When a radial dynamic pressure generating groove is formed in this inner circumferential surface, the radial dynamic pressure generating groove may be deformed, which may negatively affect the formation of dynamic pressure. Moreover, when the inner circumferential surface is deformed, the inner circumferential surface and the retained shaft highly possibly contact with each other during a relative rotation. When a contact occurs during a rotation, it may be a cause of the deterioration of the performance, a generation of contact sounds, or a worn-out of the contacting portion. Furthermore, when a work is carefully carried out so as not to cause the inner circumferential surface to be deformed, the work efficiency becomes poor.

In order to compensate such a reduction of the bearing rigidity, a groove pattern that can efficiently generate dynamic pressure may be derived through a computer simulation and employed. An example groove pattern derived through a computer simulation has a change in the width of the groove and the depth thereof. Another example groove pattern derived through a computer simulation has the groove pattern miniaturized in comparison with conventional technologies. However, according to the conventional manufacturing technologies, it is difficult to stably produce a groove having a width and a depth changed and a groove employing a miniaturized structure. Alternatively, the processing of the groove in such a shape needs a large labor work, resulting in a decrease of the work efficiency.

Such disadvantage is not only for rotating devices loaded in portable electronic devices, but also for rotating devices loaded in electronic devices of other kinds.

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a rotating device including a thrust dynamic pressure generating groove that can suppress a reduction of a bearing rigidity and a manufacturing method thereof and a bearing component.

SUMMARY OF THE INVENTION

To accomplish the above object, a first aspect of the present invention provides a bearing component that includes: a cylindrical member comprising a thrust dynamic pressure generating groove which is provided in one end face of the cylindrical member and which generates thrust dynamic pressure, and the thrust dynamic pressure generating groove comprising a cut-and-machined face.

To accomplish the above object, a second aspect of the present invention provides a bearing component that includes: a cylindrical member including a thrust dynamic pressure generating groove which is provided in one end face of the cylindrical member and which generates thrust dynamic pressure, the thrust dynamic pressure generating groove including a cut-and-machined face, the cylindrical member further includes a radial dynamic pressure generating groove which is provided in an inner circumferential surface of the cylindrical member, the thrust dynamic pressure generating groove being a set of intermittent recesses formed intermittently continuous from one another along a spiral line that gradually increases a radius for each turn from an inner circumference to an outer circumference, and the adjoining intermittent recesses being disposed so as to partially overlap in a radial direction.

To accomplish the above object, a third aspect of the present invention provides a disk drive device that includes: a base; a hub on which a recording disk is to be mounted and which rotates relative to the base; and a fluid dynamic bearing unit that allows the hub to rotate relative to the base, the fluid dynamic bearing unit including a shaft that performs relative rotation and a cylindrical member that encircles the shaft, the cylindrical member including a thrust dynamic pressure generating groove which is provided in one end face of the cylindrical member and which generates thrust dynamic pressure, and the thrust dynamic pressure generating groove including a cut-and-machined face.

Any combination of the above-explained components and replacement of the component of the present invention and the expression thereof between a method, a device, and a system, etc., are also advantageous as an aspect of the present invention.

According to the present invention, it becomes possible to provide a rotating device including a thrust dynamic pressure generating groove that can suppress a reduction of a bearing rigidity and a manufacturing method thereof and a bearing component.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be explained below with reference to the accompanying drawings. The same or equivalent component illustrated in the respective figures will be denoted by the same reference numeral, and the duplicated explanation thereof will be omitted accordingly. The dimension of a component in each figure is indicated in an enlarged or scale-down manner as needed in order to facilitate understanding to the present invention. A part of a component not important to explain an embodiment of the present invention in each figure will be omitted.

A rotating device according to an embodiment is suitably used as a disk drive device like a hard disk drive on which a magnetic recording disk magnetically recording data is to be mounted and which rotates and drives such a magnetic recording disk. In particular, it is suitably used as a fastened-shaft disk drive device which has a shaft fastened to a base and which has a hub rotating relative to the shaft. It is also suitably used as a shaft-rotating disk drive device which has a shaft fastened to a hub and which allows the shaft to rotate relative to a base.

For example, this rotating device may include a rotating body that is attached to a stationary body in a freely rotatable manner through a bearing unit. The bearing unit may include a thrust bearing unit formed in either one of the stationary body and the rotating body. For example, the thrust bearing unit may include a thrust dynamic pressure generating groove that is a set of intermittent recesses. For example, the bearing unit may produce dynamic pressure to a lubricating medium. For example, the lubricating medium may be a lubrication fluid.

For example, the rotating body may include a loading unit on which a drive-target medium like a magnetic recording disk is loaded. For example, the bearing unit may include a radial dynamic bearing unit that is provided in either one of the stationary body and the rotating body. For example, the radial dynamic bearing unit may include a radial dynamic pressure generating groove that is a set of intermittent recesses. For example, the radial dynamic pressure generating groove may be formed in a component in which the thrust dynamic pressure generating groove is formed. For example, the thrust bearing unit may be provided at a location encircling the radial bearing unit. For example, the rotating device may include a rotating-driving unit that applies rotation torque to the rotating body. For example, the rotating-driving unit may be a brush-less spindle motor. For example, this rotating-driving unit may include coils and a magnet.

FIG. 1is a perspective view illustrating a rotating device100according to an embodiment of the present invention.FIG. 1illustrates a condition in which a top cover22is detached in order to facilitate understanding to the present invention. The rotating device100includes a base24, an upper shaft member110, a hub26, a magnetic recording disk62, a data reader/writer60, the top cover22, and for example, six screws104.

In the following explanation it is defined that a side where the hub26is mounted on the base24is an upper side. Moreover, a direction along a rotation axis R of a rotating body, an arbitrary direction passing through the rotation axis R on a plane orthogonal to the rotation axis R, and an arbitrary direction on that plane are defined as an axial direction, a radial direction, and a planar direction, respectively.

The magnetic recording disk62is, for example, a 2.5-inch magnetic recording disk formed of glass and having a diameter of 65 mm. The magnetic recording disk62has a center hole with a diameter of, for example, 20 mm, and has a thickness of, for example, 0.65 mm. The hub26carries, for example, one magnetic recording disk62. The magnetic recording disk62is fastened to the hub26by, for example, unillustrated clamper. The magnetic recording disk62may be held between the clamper and the hub26. The clamper may be fastened by, for example, allowing the inner circumferential surface to be engaged with a circumferential groove26G of the hub26to be discussed later.

The base24is formed by performing die-cast molding on an aluminum alloy. The base24includes a bottom plate24A that forms the bottom of the rotating device100, and an outer circumferential wall24B formed along the outer circumference of the bottom plate24A so as to surround an area where the magnetic recording disk62is to be mounted. The outer circumferential wall24B has, for example, six screw holes24C provided in the top face.

The data reader/writer60includes a recording/playing head (unillustrated), a swing arm64, a voice coil motor66, and a pivot assembly68. The recording/playing head is attached to the tip of the swing arm64, records data in the magnetic recording disk62, or reads the data therefrom. The pivot assembly68supports the swing arm64in a swingable manner to the base24around a head rotating shaft S. The voice coil motor66allows the swing arm64to swing around the head rotating shaft S to move the recording/playing head to a desired location over the top face of the magnetic recording disk62. The voice coil motor66and the pivot assembly68are configured by conventionally well-known technologies of controlling the position of a head.

The top cover22is a thin plate formed in a substantially rectangular shape, and has, for example, six screw through-holes22C provided at the periphery of the top cover22, a cover recess22E, and an engagement hole22D provided at the center of the cover recess22E. The top cover22is formed by, for example, pressing an aluminum plate or an iron-steel plate into a predetermined shape. A surface processing like plating may be applied on the top cover22in order to suppress corrosion. The top cover22is fastened to the top face of the outer circumferential wall24B of the base24by, for example, the six screws104. The six screws104correspond to the six screw holes24C, respectively. In particular, the top cover22and the top face of the outer circumferential wall24B are fastened with each other so as to suppress a leak into the interior of the rotating device100from the joined portion of the top cover22and the top face of the outer circumferential wall24B. The interior of the rotating device100is, more specifically, a clean space70surrounded by the bottom plate24A of the base24, the outer circumferential wall24B of the base24, and the top cover22. This clean space70is designed so as to be fully sealed, i.e., so as not to have a leak-in from the exterior and a leak-out to the exterior. The clean space70is filled with clean air having particles eliminated. Hence, foreign materials like the particles are prevented from sticking to the magnetic recording disk62, thereby improving the reliability of the operation of the rotating device100. The engagement hole22D of the top cover22is engaged and joined with a cylindrical convexity110F of the upper shaft member110.

FIG. 2is a cross-sectional view taken along a line A-A inFIG. 1.FIG. 3is an exploded perspective view illustrating the major components of a fluid dynamic bearing unit illustrated inFIG. 2.FIG. 2is symmetrical along the rotation axis R, and either right or left reference numeral for the same component will be omitted in some cases in the figure.

With reference toFIG. 2, a stationary body2includes the upper shaft member110, a lower shaft member112, a stator core32, coils30, and a magnetic ring34. The upper shaft member110includes an upper rod10and an upper flange12. The lower shaft member112includes a lower rod14, a lower flange16, and a flange encircling member18.

A rotating body4includes a shaft encircling member40, a cap48, and a cylindrical magnet28. A lubricant20is continuously present in several spaces between the rotating body4and the stationary body2. The shaft encircling member40includes a sleeve42, a cylindrical member44, and a ring member46.

The base24is formed with an opening24D around the rotation axis R of the rotating body4, and includes an annular protrusion24E encircling the opening24D. The protrusion24E protrudes toward the hub26from the upper face of the base24.

The stator core32includes an annular part and, for example, 12 salient poles running outwardly of the radial direction from the annular part, and is fastened to, for example, an outer circumferential surface of the protrusion24E at the upper-surface side of the base24. The stator core32can be joined with the base24by press-fitting, bonding or a combination thereof. The stator core32is formed by, for example, laminating five electromagnetic steel sheets each with a thickness of 0.2 mm and joining those sheets together by caulking. A skin layer is provided on the surface of the stator core32. Insulation painting, such as electrodeposition coating or a power coating, is applied on the surface of the stator core32. The coil30is wound around each salient pole of the stator core32. When, for example, a three-phase substantially sinusoidal waveform drive current is caused to flow through the coils30, field magnetic field is produced along the respective salient poles.

The magnetic ring34is coaxial with the magnet28along the rotation axis R, and is firmly fastened to the upper face of the base24by, for example, bonding, caulking or a combination thereof. The magnetic ring34is in a hollow ring shape that is thin in the axial direction, and is formed by pressing, for example, a ferrous sheet with soft magnetism. The magnetic ring34has an area facing with a bottom face28D of the magnet28in a non-contact manner therewith in the axial direction, and applies downward suction force to the magnet28. This structure suppresses a floating of the rotating body4in the axial direction when the rotating body4is rotating.

The hub26includes a hollow first annular part26A, a disk part26D extending outwardly of the radial direction from an outer circumferential surface26C of the first annular part26A, a second annular part26E extending downwardly of the axial direction from the outer circumference of the disk part26D, and a mount part26J extending outwardly of the radial direction from a lower outer circumferential surface26F of the second annular part26E. The hub26is formed in a substantially cup shape. The first annular part26A, the disk part26D, the second annular part26E, and the mount part26J are formed coaxially with each other along the rotation axis R. The first annular part26A, the disk part26d, the second annular part26E, and the mount part26J are formed together as a single piece. Any part may be formed separately and joined with the other parts. The hub26is formed of a ferrous material with soft magnetism like SUS 430F. The outer circumferential surface26F of the second annular part26E of the hub26is engaged with the inner circumferential surface of the magnetic recording disk62in a doughnut shape. The magnetic recording disk62is to be mounted on the top of the mount part26J of the hub26. The circumferential groove26G recessed inwardly of the radial direction is formed annularly in the outer circumferential surface26F of the second annular part26E. The circumferential groove26G is located above the top face of the magnetic recording disk62in the axial direction when the magnetic recording disk62is mounted on the hub26. For example, an inner circumference of the clamper may be fitted and fastened to the circumferential groove26G. A protrusion26M protruding downwardly of the axial direction is provided on the lower face of the disk part26D at the outer circumferential side. A recess26I recessed outwardly of the radial direction is provided annularly at the upper part of an inner circumferential surface26B of the first annular part26A.

The magnet28is in a hollow ring shape, and has an outer circumferential surface fastened to an inner circumferential surface26H of the hub26by, for example, bonding. An upper face28C contacts the protrusion26M of the hub26. 16 drive magnetic poles are provided at an inner circumferential surface28B in the circumferential direction by magnetization. The magnet28is formed of a material containing, for example, neodymium, iron, or boron. The magnet28may contain a resin at a predetermined percentage. The magnet28may be formed of a material containing a ferrite magnetic material, or may be formed by laminating a layer containing a ferrite magnetic material and another layer containing a rare-earth material like neodymium. A skin layer is provided on the surface of the magnetic layer of the magnet28. For example, electrodeposition coating or spray painting is applied on the surface of the magnet28. The provided skin layer suppresses an oxidization of the magnet, or suppresses a peeling of the surface of the magnet.

An explanation will be given of the fluid dynamic bearing unit with reference toFIG. 4.FIG. 4is an enlarged cross-sectional view illustrating the periphery of an area where the lubricant20is present inFIG. 2in an enlarged manner.FIG. 4illustrates only the left part relative to the rotation axis R.

The lower shaft member112includes a lower rod14in a rod shape having a through-hole14B formed in the center thereof, a lower flange16in a disk shape extending outwardly of the radial direction from the lower end of an outer circumferential surface14A of the lower rod14, and a flange encircling member18in a cylindrical shape protruding upwardly of the axial direction from the outer circumferential edge of the lower flange16. The lower shaft member112is in a cup shape having a rod provided at a center thereof in a standing manner (seeFIG. 3). For example, the lower shaft member112has the lower rod14, the lower flange16, and the flange encircling member18formed together as a single piece. In this case, the production error of the lower shaft member112can be reduced, and the labor work for joining those members can be eliminated. Alternatively, the lower shaft member112can be prevented from being deformed by a shock and a load. For example, the lower shaft member112is formed by cutting and machining a metallic material like SUS 303. The lower shaft member112may be formed of other materials like a resin, and may be formed by other techniques, such as pressing and molding. The lower shaft member112has an outer circumferential surface18B of the flange encircling member18and an outer circumferential surface16B of the lower flange16bonded to the inner circumferential surface of the opening24D, thereby being fastened to the base24. The lower rod14has a passage cover120that covers the lower end of the through-hole14B. For example, the passage cover120is formed by applying a sealant around the lower end of the through-hole14B and the edge thereof, and letting such a sealant to be cured. The passage cover120may be formed by bonding and fastening a sheet formed of, for example, a metallic material or a resin material. For example, an upper end18C of the flange encircling member18is located at or above an area where a first dynamic pressure generating groove50to be discussed later is provided in the axial direction. This structure increases the volume of a space between an inner circumferential surface18A of the flange encircling member18and an outer circumferential surface of the shaft encircling member40to be discussed later, thereby increasing the volume of the retainable lubricant20. The increase of the retained lubricant20reduces the possibility that a failure occurs due to the lack of the lubricant20.

The upper shaft member110includes an upper rod10in a rod shape having a retainer hole10A formed in the center thereof and retaining the lower rod14, and an upper flange12in a substantially disk shape extending outwardly of the radial direction from the upper end of an outer circumferential surface10C of the upper rod10. The upper shaft member is in a substantially mushroom shape (seeFIG. 3). The upper shaft member110includes the cylindrical convexity110F at an upper end of the upper rod10and protruding in a cylindrical shape upwardly of the axial direction. For example, the upper shaft member110has the upper rod10, the upper flange12, and the cylindrical convexity110F formed together as a single piece. For example, the upper shaft member110may have the upper rod10and the cylindrical convexity110F formed together and have the upper flange12formed separately but joined together. For example, the upper shaft member110is formed by cutting and machining a ferrous material like SUS 420 J2. For example, the upper shaft member110may be quenched in order to increase the hardness. For example, the upper shaft member110may have an outer circumferential surface10C of the upper rod10and a lower face12C of the upper flange12polished in order to enhance the dimensional precision. The upper shaft member110may be formed of other materials like a resin, and may be formed by other techniques, such as pressing and molding. The upper shaft member110has an upper end fastened to the top cover22through a method to be discussed later. The lower rod14is encircled by and fastened to the upper rod10. For example, the lower rod14has the outer circumferential surface14A fastened to the retainer hole10A by a combination technique of bonding and press-fitting. InFIG. 4, a lower part of the outer circumferential surface14A is defined as a press-fit surface14AA, while a bonding surface14AB having a smaller diameter than the press-fit surface14AA is provided above the press-fit surface14AA. A bond of, for example, anaerobic is present between the retainer hole10A and the bonding surface14AB.

As will be discussed later, the cylindrical convexity110F is fitted in and bonded to the engagement hole22D of the top cover22, and thus the upper shaft member110is fastened to the top cover22. Moreover, the top cover22is fastened to the base24. According to the rotating device of this type having both ends of the shaft fastened to a chassis including the base24and the top cover22, among the fastened-shaft rotating devices, the shock resistance of the rotating device and the vibration resistance thereof can be enhanced.

The upper end of the upper shaft member110may be fastened to the top cover22by other techniques than bonding, such as caulking and welding. Since no threaded screw hole to which a screw is fastened is formed in the upper end of the upper shaft member110, a deformation of the outer circumferential surface of the upper rod10that occurs in the case of a structure in which a screw is engaged with a screw hole can be suppressed.

The upper rod10has a gas reservoir10B provided at an upper end area of the retainer hole10A and reserving a gas. The gas reservoir10B is formed as a space in a substantially conical or cylindrical shape. The gas reservoir10B is in communication with the through-hole14B of the lower rod14. When an uncured bond is present between the retainer hole10A and the outer circumferential surface14A, this bond is let cured while producing a gas of contained volatile components. However, by providing the gas reservoir10B, the volatile component gas of the bond is efficiently discharged to the exterior through the gas reservoir10B and the through-hole14B. This results in a reduction of a curing time of the bond, and a reduction of a labor hour. Moreover, the passage cover120is provided so as to block off the through-hole14B after a predetermined time has elapsed since such a work completes. This reduces the possibility of a leak-in of foreign materials from the through-hole14B, the gas reservoir10B, and the space between the upper rod10and the lower rod14to the region where the lubricant20is present. Moreover, in a labor work of fitting the lower rod14into the retainer hole10A, air in the retainer hole10A is discharged to the exterior through the gas reservoir10B and the through-hole14B, the efficiency of the fitting work improves.

The upper flange12includes an inclined surface12AA provided at an outer circumferential surface12A and having a distance in the radial direction from the rotation axis R becoming large as becoming close to the base24. The upper flange12has the lower face12C facing with an upper face42C of the sleeve42of the shaft encircling member40to be discussed later with a gap in the axial direction. The upper flange12includes a terrace12D extending inwardly of the radial direction from the upper end of the outer circumferential surface12A, and an uplift12E raised upwardly of the axial direction in a substantially cylindrical shape from the internal end of the terrace12D. The cylindrical convexity110F protrudes upwardly of the axial direction from the middle part of the uplift12E. The cylindrical convexity110F includes a circumferential recess110G provided around the outer circumferential surface of the cylindrical convexity110F. A seat110H with which a lower surface of the top cover22contacts and which extends outwardly of the radial direction is provided around the cylindrical convexity110F.

The shaft encircling member40encircles the upper rod10with a gap, and is rotatable relative to the upper rod10. The shaft encircling member40is present between the upper flange12and the lower flange16with respective gaps. The shaft encircling member40is encircled by and fastened to the hub26. The shaft encircling member40is encircled by the flange encircling member18of the lower shaft member112with a gap. According to such a structure, the hub26is supported in a rotatable manner relative to the base24.

The shaft encircling member40includes the substantially cylindrical sleeve42that encircles the upper rod10, a cylindrical member44in a substantially cylindrical shape that encircles and is joined with the sleeve42, and a ring member46in a ring shape that is joined with an upper end part of the cylindrical member44. The sleeve42and the cylindrical member44are each formed by, for example, cutting and machining a metallic material like brass, and applying electroless nickel plating on the surface thereof. The sleeve42and the cylindrical member44may be formed of other materials like stainless steel. For example, the sleeve42is joined with the cylindrical member44by interference fitting like press-fitting or bonding, or a combination thereof. The sleeve42and the cylindrical member44may be formed together as a single piece.

The sleeve42is in a substantially hollow cylindrical shape (seeFIG. 3), and includes an inner circumferential surface42A, an outer circumferential surface42B, the upper face42C, and a lower face42D. The sleeve42has the inner circumferential surface42A encircling the upper rod10with a gap. The sleeve42has the first dynamic pressure generating groove50and a second dynamic pressure generating groove52for generating radial dynamic pressure and provided in areas of the inner circumferential surface42afacing with the outer circumferential surface10C of the upper rod10in the radial direction. The second dynamic pressure generating groove52is provided above the first dynamic pressure generating groove50so as to be distant therefrom. The first and second dynamic pressure generating grooves50and52may be provided in the outer circumferential surface10C of the upper rod10instead of the sleeve42.

A third dynamic pressure generating groove54for generating thrust dynamic pressure is provided in an area of the upper face42C of the sleeve42facing with the upper flange12in the axial direction. The third dynamic pressure generating groove54may be provided in an area of the lower face12C of the upper flange12facing with the sleeve42in the axial direction instead of the sleeve42. A fourth dynamic pressure generating groove56for generating thrust dynamic pressure is provided in an area of the lower face42D of the sleeve42facing with the lower flange16in the axial direction. The fourth dynamic pressure generating groove56may be provided in an area of an upper face16A of the lower flange16facing with the sleeve42in the axial direction instead of the sleeve42.

For example, the first and second dynamic pressure generating grooves50and52are each formed in a herringbone shape. The first and second dynamic pressure generating grooves50and52may be in other shapes like a spiral shape. For example, the third and fourth dynamic pressure generating grooves54and56are each formed in a herringbone shape. The third and fourth dynamic pressure generating grooves54and56may be formed in other shapes like a spiral shape. The first and second dynamic pressure generating grooves50and52are formed by, for example, pressing, ball-rolling, etching, and cutting and machining. Those dynamic pressure generating grooves may be formed by different techniques from each other. How to form the third and fourth dynamic pressure generating grooves54and56will be explained in detail later.

The cylindrical member44is in a substantially hollow cylindrical shape (seeFIG. 3), and includes an inner circumferential surface44A, an outer circumferential surface44B, an upper face44C, a lower face44D, and a recess44E provided annularly at the upper end side of the inner circumferential surface44A so as to be concaved outwardly of the radial direction. The inner circumferential surface44A is joined with the sleeve42. An upper part of the outer circumferential surface44B is joined with an inner circumferential surface26B of the first annular part26A of the hub26. A part of the outer circumferential surface44B below the area joined with the hub26is encircled by the flange encircling member18with a gap. The outer circumferential surface44B includes an inclined surface44BA provided at an area facing with the inner circumferential surface18A of the flange encircling member18in the radial direction and having a radius becoming small as coming close to the upper end of the outer circumferential surface44B. A gap between the inclined surface44BA and the inner circumferential surface18A gradually becomes widespread toward the upper space in the axial direction. The inclined surface44BA and the inner circumferential surface18A contact a first air-liquid interface122of the lubricant20to be discussed later, and form a capillary seal that prevents the lubricant20from being splashed by capillary force. For example, the first air-liquid interface122is located at or above the area where the first dynamic pressure generating groove50is disposed in the axial direction. This structure enables the rotating device1to retain a larger amount of lubricant20, thereby reducing the possibility of a breakdown due to the lack of the lubricant20. For example, the first air-liquid interface122is provided outwardly of the third and fourth dynamic pressure generating grooves54and56in the radial direction.

The ring member46is in a hollow ring shape (seeFIG. 3), and includes an inner circumferential surface46A, an outer circumferential surface46B, an upper face46C, and a lower face46D. The ring member46is formed by, for example, cutting and machining a stainless-steel material like SUS 303 or SUS 430. The ring member46has the outer circumferential surface46B and the lower face46D fitted in the recess44E of the cylindrical member44, and bonded and fastened thereto. The ring member46includes an inclined surface46AA provided at the inner circumferential surface46A and having a diameter that becomes small as coming close to the upper end of the inner circumferential surface46A. The inclined surface46AA of the ring member46and the inclined surface12AA of the upper flange12contact a second air-liquid interface124of the lubricant20to be discussed later, and form a capillary seal that prevents the lubricant20from being splashed by capillary force.

The cap48is a hollow ring shape thin in the axial direction, and includes an inner circumferential surface48A, an outer circumferential surface48B, an upper face and a lower face48D. For example, the cap48is formed by cutting and machining a stainless-steel material like SUS 303 or SUS 430. The cap48may be formed of other metallic materials or resin materials or may be formed through other techniques, such as pressing and molding. The cap48has the outer circumferential surface48B fitted in the recess26I of the inner circumferential surface26B of the first annular part26A of the hub26, and bonded and joined thereto. The cap48has the lower face48D covering the second air-liquid interface124. The cap48has the inner circumferential surface48A encircling the side face of the uplift12E of the upper flange12in a non-contact manner. The inner circumferential side of the lower face48D of the cap48faces the terrace12D of the upper flange12in a non-contact manner in the axial direction. This structure causes the cap48and the upper flange12to form a labyrinth to the lubricant20, thereby preventing the lubricant20from being splashed.

The lubricating medium is not limited to any particular one, and for example, conventionally well-known lubrication fluid can be applied. A structure having an air-liquid interface only at one side or a so-called partial-fill structure having the lubrication fluid non-continuously present may be employed for the lubrication fluid. In this embodiment, the lubricant20is applied as the lubrication fluid. The lubricant20is present between the rotating body4and the stationary body2continuously from the first air-liquid interface122to the second air-liquid interface124. The lubricant20is present, for example, a space between the inclined surface44BA and the inner circumferential surface18A in the radial direction, a space between the cylindrical member44and the lower flange16in the axial direction, a space between the sleeve42and the lower flange16in the axial direction, a space between the sleeve42and the upper rod10in the radial direction, a space between the upper flange12and the sleeve42in the axial direction, a space between the upper flange12and the cylindrical member44in the radial direction, and a space between the inclined surface12AA and the inclined surface46AA in the radial direction. When the rotating body4rotates relative to the stationary body2, the first, second, third, and fourth dynamic pressure generating grooves50,52,54, and56cause the lubricant20to produce dynamic pressure, respectively. Such dynamic pressure supports the rotating body4in the radial direction and in the axial direction in a non-contact manner with the stationary body2.

The shaft encircling member40includes, separately from the gap between the sleeve42and the upper rod10in the radial direction, a communication passage BP of the lubricant20that causes the space between the upper flange12and the sleeve42in the axial direction and the space between the sleeve42and the lower flange16in the axial direction to be in communication with each other. For example, the communication passage BP includes a passage provided in the sleeve42in the axial direction. The communication passage BP may be provided in the cylindrical member44instead of the sleeve42. The communication passage BP reduces a pressure difference between the space between the upper flange12and the sleeve42in the axial direction and the space between the sleeve42and the lower flange16in the axial direction. As a result, a possibility that the lubricant20leaks out can be reduced.

An explanation will now be given of a structure in which the top cover22is joined with the upper shaft member110with reference toFIG. 5.FIG. 5is an enlarged cross-sectional view illustrating a joined portion between the top cover22and the upper shaft member110of the rotating device inFIG. 2.FIG. 5is symmetrical along the rotation axis R, and the reference numeral for the same component at the right or left will be omitted in some cases.

The upper shaft member110has the cylindrical convexity110F fitted in the engagement hole22D of the top cover22, and the tip of the cylindrical convexity110F including the circumferential recess110G protrudes from the top face of the top cover22. A fastener36with a larger diameter than the engagement hole22D is fitted to the circumferential recess110G. For example, a U-shaped or C-shaped snap ring (circlip) as the fastener36is fitted to the circumferential recess110G. The seat110H and the fastener36hold therebetween the circumferential edge of the engagement hole22D, thereby joining the upper shaft member110to the top cover22. A sealant38covers across the circumferential edge of the engagement hole22D, the fastener36, and the cylindrical convexity110F. For example, the sealant38is formed by applying a curable resin with an ultraviolet curable characteristic to a predetermined area, and emitting ultraviolet rays of a predetermined integrated light quantity to such a resin. The sealant38is formed so as not to protrude from the top face of the top cover22. The top cover22has a cover film58applied thereto so as to cover the cylindrical convexity110F. The sealant38or the cover film58suppresses a leak-in of unclean ambient air from the exterior of the rotating device100to the clean space70. In particular, when the sealant38is attached to the side of the engagement hole22D and a space between the bottom face of the top cover22and the seat110H of the upper shaft member110, a leak-in of unclean ambient air can be further suppressed.

FIG. 6is a top view illustrating the top face of the cylindrical member44and that of the sleeve42both illustrated inFIG. 2. The third dynamic pressure generating groove54that produces thrust dynamic pressure is provided in an dispose area610of the upper face42C of the sleeve42which is an end face orthogonal to the rotation axis R. The dispose area610is formed in a substantially hollow circular shape having an inner circumference610A and an outer circumference610B. For example, the third dynamic pressure generating groove54has 12 streaks disposed in the dispose area610in the circumferential direction at a substantially equal pitch. The third dynamic pressure generating groove54runs from the inner circumference610A of the dispose area610toward the outer circumference610B in the circumferential direction and in the radial direction.FIG. 7is an enlarged cross-sectional view illustrating the cylindrical member44and the sleeve42both illustrated in FIG.2. The first and second dynamic pressure generating grooves50and52that produce radial dynamic pressure are provided in the inner circumferential surface42A of the sleeve42.FIG. 8is a bottom view illustrating the bottom face of the cylindrical member44and that of the sleeve42both illustrated inFIG. 2. The fourth dynamic pressure generating groove56that produces thrust dynamic pressure is provided in a dispose area620of the bottom face42D of the sleeve42that is an end face orthogonal to the rotation axis R. The dispose area620is in a substantially hollow circular shape with an inner circumference620A and an outer circumference620B. For example, the fourth dynamic pressure generating groove56has 12 streaks disposed in the dispose area620in the circumferential direction at a substantially equal pitch. The fourth dynamic pressure generating groove56runs from the inner circumference620A of the dispose area620toward the outer circumference620B in the circumferential direction and in the radial direction.

FIG. 9is a top view exemplifying the third dynamic pressure generating groove54inFIG. 6in an enlarged manner. Intermittent recesses630are disposed successively in a non-continuous manner along a spiral line612having a distance from the rotation axis R gradually increasing for each circumference from the inner circumference to the outer circumference. In order to facilitate understanding, inFIG. 9, an adjacent pitch P of the spiral line612in the radial direction is illustrated in an emphasized manner, and the inclination of the third dynamic pressure generating groove54in the circumferential direction is illustrated in a suppressed manner. The third dynamic pressure generating groove54has the intermittent recesses630disposed in such a manner so as to partially overlap in the radial direction, thereby being formed as a set of intermittent recesses630.FIG. 10is a perspective view exemplifying how to process the intermittent recess630inFIG. 6. For example, a machining tool640like a cutting bite is relatively moved in the direction of an arrow616along the spiral line612on the upper face42C, thereby performing non-continuous cutting and machining. The intermittent recess630is formed through such cutting and machining.FIG. 11illustrates a cross-section630A of the intermittent recess630taken along a line B-B inFIG. 10.FIG. 12illustrates a cross-section630B of the intermittent recess630taken along a line C-C inFIG. 10.FIG. 13illustrates a cross-section54A of the third dynamic pressure generating groove54taken along a line D-D inFIG. 9. The cross-section54A includes protrusions54B which is present at the boundary of the adjoining intermittent recess630in the radial direction and which runs in the circumferential direction. When the rotating body4rotates relative to the stationary body2, the protrusions54B arrange the direction of the flow of the lubricant20, thereby suppressing an increase of the rotational resistance.

An explanation will be given of an example shape of the intermittent recess630with reference to mainlyFIGS. 9 to 12. In the cross-section630A of the intermittent recess630, it is preferable if a width W be 0.02 mm to 0.2 mm, and a depth dimension H at the center be 5 μm to 50 μm since this facilitates machining. In the cross-section630B of the intermittent recess630, it is preferable if a dimension L in the circumferential direction be 0.3 mm to 2 mm since this facilitates machining. Moreover, it is preferable if the adjoining pitch (pitch of intermittent recess630adjoining in radial direction) P of the adjoining portions of the spiral line612in the radial direction be 5 μm to 50 μm since this facilitates machining (seeFIG. 9). In this embodiment, the intermittent recess630has the dimension L in the circumferential direction that is from 0.6 mm to 1.2 mm, the width W that is from 0.05 mm to 0.1 mm, the depth dimension H at the center of the width that is from 10 μm to 20 μm, and the pitch P of the spiral line612in the radial direction that is from 7 μm to 14 μm. Moreover, the cross-section630A of the intermittent recess630has a radius that is from 0.03 mm to 0.07 mm. Such setting eliminates variation in machining dimension, or enables a production within a predetermined manufacturing takt time.

When the surface roughness of the bottom of the third dynamic pressure generating groove54in the circumferential direction is large, friction with the lubricant20increases, and thus rotational resistance at the bearing unit when the rotating body4rotates increases. When the rotating body4rotates at a predetermined speed with such a rotational resistance, a large drive current becomes necessary. In order to reduce such rotational resistance, the bottom of the intermittent recess630has a cut face632cut in the circumferential direction using the machining tool640like a cutting bite (seeFIG. 10). By forming the cut face632at the bottom of the intermittent recess630, the surface roughness measured for the bottom in the circumferential direction can be easily reduced. The machining condition to obtain a desired surface roughness can be defined by, for example, a test with parameters that are the relative speed of the machining tool640and that of the sleeve42. In this embodiment, the surface roughness measured in the circumferential direction for the bottom of the third dynamic pressure generating groove54is set to be equal to or smaller than 0.5 μm, and is smaller than the surface roughness measured in the radial direction which is 1 μm.

When the side face of the cross-section630A of the intermittent recess630which is a cross-section along a straight line passing through the rotation axis R has unevenness like concavities and convexities, a turbulence of the lubricant20is caused in accordance with the concavities and convexities when the rotating body4rotates, and thus the rotational resistance is highly possibly increased (seeFIG. 11). In this embodiment, the cross-section630A of the intermittent recess630is formed as a smooth curve that gradually decreases the width of the radial direction inwardly of the axial direction, i.e., toward the deeper part in the depthwise direction. It is preferable since such a curve is not likely to produce a turbulence of the lubricant20. The side face shape of the third dynamic pressure generating groove54can be defined by, for example, a test with a parameter that is the tip shape of the machining tool640.

When the number of turns of the spiral line612is small, a length dimension G of the third dynamic pressure generating groove54in the radial direction becomes short. Accordingly, thrust dynamic pressure to be generated becomes small, and thus a sufficient bearing rigidity cannot be ensured in some cases (seeFIG. 9). In order to address this disadvantage, the intermittent recesses630are formed so as to be successive along the spiral line612that turns equal to or greater than 10 turns from the inner circumference610A of the dispose area610to the outer circumference610B thereof. The number of turns of the spiral line612can be substantially defined by a quotient obtained by dividing the length dimension G of the third dynamic pressure generating groove54in the radial direction by the pitch P of the adjoining intermittent recesses630in the radial direction (seeFIG. 9). When, for example, the length dimension G of the third dynamic pressure generating groove54in the radial direction is 5 mm, and the pitch P of the adjoining intermittent recess630is 20 μn, the number of turns of the spiral line612is 250 turns. If the number of turns of the spiral line612is too large, the machining time for the third dynamic pressure generating groove54becomes long. It is confirmed that when the number of turns of the spiral line612is equal to or smaller than 2000 turns, such machining time does not become a practical problem.

The inventor of the present invention reaches following findings through a keen study.

(1) When the rotating body4rotates relative to the stationary body2, the third dynamic pressure generating groove54gathers the lubricant20toward a predetermined area (hereinafter, referred to as a compression area), thereby generating dynamic pressure at the compression area.

(2) The generated dynamic pressure can be increased by increasing the amount of gathered lubricant20. Moreover, the generated dynamic pressure can be increased by narrowing down the compression area. That is, when the larger amount of lubricant20is gathered at the narrower compression area, the dynamic pressure generated at the compression area can be increased.

Based on the above findings, the third dynamic pressure generating groove54has a width dimension in the circumferential dimension becoming small from the outer circumference610B of the dispose area610toward the inner circumference610A thereof where the compression area is provided (seeFIG. 6). When the compression area is provided at the outer-circumference-610B side, the third dynamic pressure generating groove54may have the width dimension in the circumferential direction becoming small from the inner circumference610A of the dispose area610toward the outer circumference610B where the compression area is provided. When the compression area is provided in the middle portion between the inner circumference610A and the outer circumference610B, the third dynamic pressure generating groove54may have a width dimension in the circumferential direction becoming small from the outer circumference610B of the dispose area610and from the inner circumference610A toward the middle portion where the compression area is provided.

Next, an explanation will be given of a vertex angle A of a sector outwardly contacting the third dynamic pressure generating groove of a streak and having the rotation axis R as a vertex. When this vertex angle8is small, the rotational resistance at a dynamic pressure generating groove portion increases, and thus the efficiency of gathering the lubricant may decrease. It is confirmed through a computer simulation that when the vertex angle8is at least within a range from 60 degrees to 120 degrees, the rotation resistance at the third dynamic pressure generating groove is reduced, and the lubricant20can be efficiently gathered.FIG. 16is a top view illustrating the upper face42C of the sleeve42having a dynamic pressure generating groove254with another example shape according to the embodiment of the present invention. When a point contacting the inner circumference610A of the third dynamic pressure generating groove254is Q, and a point contacting the outer circumference610B is S, the vertex angle θ (=∠QRS) of the sector having the rotation axis R as a vertex is set to be 80 degrees±10 degrees. Moreover, such a sector is disposed in such a manner as to traverse two or three streaks of the third dynamic pressure generating groove254in the radial direction from the inner circumference610A of the dispose area610toward the outer circumference610B thereof. According to such a structure, a variation in the above-explained effect can be canceled and dynamic pressure can be efficiently generated.

FIG. 17is a cross-sectional view illustrating a cross-section of the third dynamic pressure generating groove254inFIG. 16along the center of the circumferential direction. The third dynamic pressure generating groove254has a larger depth dimension in the axial direction at the outer-circumference-610B side of the dispose area610, and has a smaller depth dimension in the axial direction toward the inner-circumference-610A side where the compression area is provided. According to this structure, a larger amount of lubricant20is gathered at the outer-circumference-610B side, the compression area at the inner-circumference-610A side is narrowed down, thereby increasing dynamic pressure in the thrust direction to be generated at such an area. The increase of the dynamic pressure in the thrust direction increases the bearing rigidity or suppresses a reduction of the bearing rigidity when the rotating device is downsized.

When the compression area is provided at the outer circumference side, the third dynamic pressure generating groove may have a larger depth dimension in the axial direction at the inner circumference side of the dispose area, and have a smaller depth dimension in the axial direction toward the outer circumference. Moreover, when the compression area is provided at the middle portion between the inner circumference and the outer circumference, the third dynamic pressure generating groove may have a larger depth dimension in the axial direction at the inner circumference side of the dispose area and at the outer circumference thereof and have a smaller depth dimension in the axial direction toward the middle portion where the compression area is provided.

The third dynamic pressure generating groove54has a boundary with a non-concaved portion where the intermittent recess630is not formed in a wavy shape from the inner circumference610A of the dispose area610toward the outer circumference610B thereof (seeFIG. 9).

The above explanation was given of a case in which the third dynamic pressure generating groove54is in a spiral shape, but the present invention is not limited to this case. For example, the third dynamic pressure generating groove54may be in a herringbone shape, and the same action and advantage can be accomplished.FIG. 18is a top view illustrating the upper face42C of the sleeve42having a dynamic pressure generating groove354in a herringbone shape according to an embodiment of the present invention.

The explanation was mainly given of the structure of the third dynamic pressure generating groove54, but the fourth dynamic pressure generating groove56also employs the same structure as that of the third dynamic pressure generating groove54.

A manufacturing method according to an embodiment of the present invention is a method of manufacturing a rotating device. The rotating device is, for example, a disk drive device, in particular, a hard disk drive on which a magnetic recording disk is loaded. The following explanation will be given of an example case in which the above-explained rotating device100is manufactured.

FIG. 14is an exemplary diagram for explaining a manufacturing method according to an embodiment of the present invention.FIG. 14illustrates a process of forming the third dynamic pressure generating groove54that generates thrust dynamic pressure in the dispose area610of the upper face42C of the sleeve42retained in and joined with the cylindrical member44inFIG. 2. The third dynamic pressure generating groove54is formed as a set of the intermittent recesses630in the substantially hollow circular dispose area610. More specifically, the sleeve42joined with the cylindrical member44has the outer circumferential surface44B of the cylindrical member44held by an unillustrated clamping mechanism, and is clamped on the spindle of a processing machine. Next, the spindle of the processing machine is rotated to rotate the sleeve42joined with the cylindrical member44in the direction of an arrow658around the rotation axis R of the rotating body. Subsequently, the machining tool640is moved close to the upper face42C of the rotating sleeve42in the direction of an arrow652along the rotation axis R. The machining tool640is caused to perform reciprocal motion that repeats a contacting condition and a non-contacting condition with the upper face42C by moving the machining tool640in the direction of an arrow656along the rotation axis R. The machining tool640is moved in the direction of an arrow654from the inner circumference610A of the dispose area610toward the outer circumference610B. The machining tool640may be moved in the direction of an arrow654from the outer circumference610B of the dispose area610toward the inner circumference610A.

In an example method illustrated inFIG. 14according to the embodiment of the present invention, the machining tool640is joined with a piezoelectric element642. The piezoelectric element642is driven by an unillustrated drive circuit, and generates reciprocal drive force. The reciprocal drive force by the piezoelectric element642causes the machining tool640to perform reciprocal motion along the direction of an arrow656. When a time axis is taken as a horizontal axis and a position of the tip of the machining tool640in the axial direction is taken as a vertical axis, the machining tool640performs reciprocal motion in, for example, a substantially sinusoidal waveform. The machining tool640and the piezoelectric element642are coupled on a movable stage644. The movable stage644moves in the direction of an arrow654by an unillustrated drive unit.

FIG. 15is an exemplary diagram for explaining a relationship between the position of the upper face42C and the range of the reciprocal motion of the machining tool640in the process of forming the third dynamic pressure generating groove54inFIG. 14. InFIG. 15, Mc is a position of the tip of the machining tool640in an undriven condition. The machining tool640has the tip position reciprocate within a range from Ma to Mb. In the method according to this embodiment, the tip position Mc of the machining tool640in an undriven condition is located at the center of the reciprocal motion range that is between Ma and Mb. When it is attempted to set the tip position Mc of the machining tool640in an undriven condition to be inwardly of the upper face42C in the axial direction, a setting work needs a time. Hence, according to this embodiment, the tip position Mc of the machining tool640in an undriven condition is set to be located outwardly of the upper face42C in the axial direction by a distance F. When, for example, it is attempted to obtain a desired groove depth H, the distance F to be set can be easily obtained as a difference between a width X from Ma to Mc and the groove depth H. That is, the groove depth H is set to be smaller than the width X.

The timing of the reciprocal motion is controlled in synchronization with the timing of the rotation of the sleeve42. More specifically, when a repeat cycle of the reciprocal motion is Fa, a number of rotations of the sleeve42is Fs, and the number of streaks of the third dynamic pressure generating groove54is N, it is controlled so as to satisfy a relationship Fa=N·Fs. According to the method of this embodiment, for example, the number of rotations Fs of the sleeve42is set to be 25 Hz (1500 min−1), and the repeat cycle of the reciprocal motion is set to be 300 Hz, and the third dynamic pressure generating groove54having a number of streaks that is 12 is formed. When the number of rotations Fs of the sleeve42or the repeat cycle Fa of the reciprocal motion is too high, the respective shapes of the intermittent recesses630become nonuniform, which may negatively affect the bearing action. Conversely, when Fs or Fa is too low, the labor time becomes long. It is preferable that the number of rotations Fs should be set within a range from 5 Hz to 100 Hz, and the repeat cycle Fa of the reciprocal motion should be within a range from 100 Hz to 2000 Hz. It is confirmed that there is no practical problem in the shapes of the intermittent recesses630and the labor time at least within this range.

When the upper face42C of the sleeve42is inclined against the rotation axis R, an offset in the circumferential direction is caused in the gap with the lower face12C of the upper flange12in the thrust direction. When this gap is offset, dynamic pressure to be produced in the thrust direction is also offset in the circumferential direction, which may negatively affects the rotation of the rotating body4. The method according to this embodiment includes a pre-machining process of letting the squareness of the upper face42C of the sleeve42relative to the rotation axis R to be small. The process of forming the third dynamic pressure generating groove54is executed continuously from the pre-machining process. In the pre-machining process, the sleeve42joined with the cylindrical member42in the process illustrated inFIG. 14is rotated in the direction of the arrow658around the rotation axis R of the rotating body, and the upper face42C of the sleeve42is cut and machined using the machining tool640. The machining tool640is moved in the direction of the arrow652along the rotation axis R, and is moved in the direction of the arrow654from the inner circumference of a pre-machining area in a substantially annular shape including the dispose area610and larger than the dispose area610toward the outer circumference thereof while contacting the upper face42C to cut and machine the pre-machining area. At this time, the machining tool640is not subjected to a reciprocal motion. The machining tool640may be moved in the direction of the arrow654from the outer circumference of the pre-machining area toward the inner circumference thereof. The machining allowance is set to be larger than the depth dimension of the intermittent recess630in the axial direction but is set to be equal to or smaller than 200 μm. Such a setting reduces the manufacturing error, and suppresses an increase of the labor time. The machining allowance of the pre-machining process is set to be within a range from 20 μm to 60 μm in this embodiment. Such a setting eliminates a variation in the dimension at the time of machining or enables a manufacturing within a predetermined manufacturing takt time. The process of forming the third dynamic pressure generating groove54is successively executed while the clamped condition of the cylindrical member44joined with the sleeve42to the processing machine in the pre-machining process is maintained and without releasing such a clamped condition. Accordingly, a labor time associated with clamping can be reduced.

When the third dynamic pressure generating groove54is machined by the machining tool640, a flush or a burr may be present at a boundary between the intermittent recess630and the non-concaved portion through such machining. When such flush or burr is peeled from the sleeve42, it may become a foreign material, enters in a narrow space in the rotating device100, and may cause a performance deterioration or a breakdown. The method according to this embodiment includes a post-machining process that reduces the unevenness of the surface of the non-concaved portion of the third dynamic pressure generating groove54, and the process of forming the third dynamic pressure generating groove54and the post-machining process are successively executed. This can reduce the flush or burr of the non-concaved portion, thereby reducing the possibility of a breakdown. In the post-machining process, the sleeve42joined with the cylindrical member44in the process illustrated inFIG. 14is rotated in the direction of the arrow658around the rotation axis R of the rotating body, and the upper face42C of the sleeve42is cut and machined using the machining tool640. The machining tool640is moved in the direction of the arrow652along the rotation axis R, and is moved in the direction of the arrow654from the inner circumference of a post-machining area in a substantially annular shape including the dispose area610and larger than the dispose area610toward the outer circumference thereof while being contacting the upper face42C to cut and machine the post-machining area. At this time, the machining tool640is not subjected to a reciprocal motion. The machining tool640may be moved in the direction of the arrow654from the outer circumference of the post-machining area toward the inner circumference thereof. The machining allowance of the post-machining process in this embodiment is set to be within a range from 2 μm to 8 μm. This machining allowance is set to be smaller than the depth dimension of the intermittent recess630in the axial direction. Such a setting eliminates a variation in the dimension at the time of machining or enables a manufacturing within a predetermined manufacturing takt time. The post-machining process is successively executed while the clamped condition of the cylindrical member44joined with the sleeve42to the processing machine in the process of forming the third dynamic pressure generating groove54is maintained and without releasing such a clamped condition. Accordingly, a labor time associated with clamping can be reduced.

The process of forming the third dynamic pressure generating groove54was mainly explained above, but the fourth dynamic pressure generating groove56is also formed through the same processes as those of the third dynamic pressure generating groove54.

Next, with reference toFIGS. 2,4and5, an explanation will be given of an example method of manufacturing the rotating device100.

(1) The outer circumferential surface42B of the sleeve42is, for example, fitted in and fastened to the inner circumferential surface44A of the cylindrical member44. Bonding or press-fit bonding may be applied instead of press-fitting (seeFIG. 4).

(2) The first and second dynamic pressure generating grooves50and52are provided in the inner circumferential surface42A of the sleeve42(seeFIG. 4).

(3) The third dynamic pressure generating groove54is provided in the upper face42C of the sleeve42. The fourth dynamic pressure generating groove56is provided in the lower face42D of the sleeve42(seeFIG. 4).

(4) The upper shaft member110having the upper rod10and the upper flange12already joined together is fitted in the inner circumferential surface42A of the sleeve42, and retained therein (seeFIG. 4).

(5) The lower shaft member112having the lower flange16, the flange encircling member18and the lower rod14already joined together has the lower rod14fitted in the retainer hole10A of the upper rod10, and joined therewith. The lower rod14is joined with the retainer hole10A of the upper rod10by a combination of press-fitting and bonding. For example, the lower rod14is fitted in and fastened to the retainer hole10A at an area near the lower flange16, and is bonded and fastened to the retainer hole10A at an area near the upper flange12. That is, the bonding area of the lower rod14and the retainer hole10A is located above the press-fit area of those lower rod14and retainer hole10A.

Upon joining the upper rod10with the lower rod14, the sleeve42is present in a space where the upper flange12and the lower flange16face with each other in the axial direction (seeFIG. 4).

(6) The ring member46is, for example, press-fitted in and fastened to the cylindrical member44. Bonding or press-fit bonding may be applied instead of press-fitting (seeFIG. 4).

(7) The lubricant20is filled in the predetermined space between the rotating body4and the stationary body2. The fluid dynamic bearing unit is thus produced (seeFIG. 4).

(8) The magnet28is fastened to the inner circumferential surface26H of the second annular part26E of the hub26(seeFIG. 2).

(9) The outer circumferential surface44B of the cylindrical member44is fastened to the inner circumferential surface26B of the first annular part26A of the hub26by, for example, press-fitting. Bonding or press-fit bonding may be applied instead of press-fitting (seeFIG. 4).

(10) The cap48is fastened to the recess26I of the first annular part26A by, for example, press-fitting. Bonding or press-fit bonding may be applied instead of press-fitting (seeFIG. 4).

(11) The stator core32having the coils30wound therearound is fastened to the base24by, for example, press-fitting. Bonding or Press-fit bonding may be applied instead of press-fitting (seeFIG. 2).

(12) The flange encircling member18is fitted in the opening24D of the base24, and is bonded and fastened thereto (seeFIG. 4).

(13) The magnetic recording disk62is mounted on the hub26(seeFIG. 2).

(14) The reader/writer60and other components are attached to the base24.

(15) The cylindrical convexity110F is fitted in the engagement hole22D of the top cover22, and the fastener36is attached. The sealant38is applied across the circumferential edge of the engagement hole22D, the fastener36, and the cylindrical convexity110F, and the cover film58is further applied thereabove (seeFIG. 5).

(16) The top cover22is joined with the base24. The rotating device100is completely manufactured through other processes like a predetermined inspection.

The above-explained manufacturing method of the rotating device100and the procedures thereof are merely examples, and the rotating device100can be manufactured by other methods and procedures.

An explanation will now be given of an operation of the rotating device100employing the above-explained structure. Three-phase drive currents are supplied to the coils30in order to rotate the magnetic recording disk62. The drive currents flowing through the coils30produce field magnetic fluxes along the salient poles of the stator core32. Torque is applied to the magnet28by the mutual action of the field magnetic fluxes and the magnetic fluxes of the drive magnetic poles of the magnet28, and thus the hub26and the magnetic recording disk62engaged therewith are rotated. At the same time, the voice coil motor66causes the swing arm64to swing, thereby causing the recording/playing head to move back and forth within the swingable range over the magnetic recording disk62. The recording/playing head converts magnetic data recorded in the magnetic recording disk62into electric signals, and transmits such electric signals to an unillustrated control substrate, or writes data transmitted from the control circuit in the form of electric signals into the magnetic recording disk62as magnetic data.

The rotating device100according to this embodiment and employing the above-explained structure has following features. The rotating device100has a dynamic pressure generating groove formed as a set of intermittent recesses. This enables production of a dynamic pressure generating groove having a groove width and a groove depth changed and a refined dynamic pressure generating groove which are difficult in the cases of conventional manufacturing technologies. Alternatively, the labor work for processing such a shape of the dynamic pressure generating groove can be reduced, thereby suppressing a reduction of the work efficiency. As a result, the dynamic pressure generating groove can be structured so as to efficiently generate dynamic pressure, and compensates the bearing rigidity. This enables a rotating device suitable for downsizing to be provided.

According to the manufacturing method of the rotating device of the embodiment, the dynamic pressure generating groove is formed by cutting and machining, pressure loading applied to the sleeve in the axial direction can be suppressed, thereby preventing the inner circumference surface of the sleeve from being deformed and expanded due to the pressure loading. This results in a reduction of a possibility that the shaft and sleeve contact with each other, thereby suppressing a deterioration of the performance, a generation of contact sounds, and an occurrence of a worn-out of a contacting portion, etc. Moreover, the shape of the dynamic pressure generating groove to be formed can be easily changed by changing a machining program. As a result, the dynamic pressure generating groove that can efficiently generate dynamic pressure can be formed, and thus a manufacturing method of a rotating device which facilitates downsizing can be provided.

The explanation was given of the structure of the rotating device according to the embodiment, and the operation thereof. The embodiment is merely an example, and it should be understood for those skilled in the art that the combination of the respective components permits various modifications, and such modifications are within the scope and spirit of the present invention.

In the above-explained embodiment, the explanation was given of the example case in which the lower shaft member is directly attached to the base, but the present invention is not limited to this case. For example, a brushless motor including a rotating body and a stationary body may be formed separately, and such a brushless motor may be attached to a chassis.

In the above-explained embodiment, the explanation was given of the example case (a so-called outer rotor structure) in which the stator core is encircled by the magnet, but the present invention is not limited to this case. For example, a structure (a so-called inner rotor structure) in which the magnet is encircled by the stator core may be employed.

In the above-explained embodiment, although a part of the cylindrical convexity of the upper shaft member protrudes from the top face of the top cover, the present invention is not limited to this case. For example, a structure may be employed in which the upper end face of the cylindrical convexity is bonded with and fastened to the bottom face of the top cover.

In the above-explained embodiment, the explanation was given of the example case in which the third and fourth dynamic pressure generating grooves54and56which generate dynamic pressure in the thrust direction are each formed as a set of intermittent recesses. However, the first and second dynamic pressure generating grooves50and52which generate dynamic pressure in the radial direction may be each formed as a set of intermittent recesses. In this case, such recesses may be formed through cutting and machining as explained above.