Rotary device

A rotary device includes a fixed body including a shaft; a rotary body including a sleeve being configured to surround the shaft through lubricant; and first and second taper seals provided in a space between the fixed body and the rotary body in which gas-liquid interfaces of the lubricant exist, respectively, when the rotary device is operated, the first and taper seals being configured such that a lower limit of a filling ratio of the second taper seal corresponds to a predetermined range of the filling ratio of the first taper seal including its lower limit of the filling ratio, and an upper limit of the filling ratio of the second taper seal corresponds to a predetermined filling ratio of the first taper seal that is larger than an upper limit of the predetermined range and lower than an upper limit of the first taper seal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to rotary devices.

2. Description of the Related Art

Disk drive devices such as hard-disk drives have been mounted in various electronic devices as a result of miniaturization and capacity enlargement. In particular, disk drive devices have been mounted in portable electronic devices such as notebook computers, portable music players or the like. For disk drive devices that are mounted in such portable electronic devices, it is required to improve resistance against shock and resistance against vibration, in order to resist against shock such as falling down or vibration when carrying such electronic devices, to a greater extent than for stationary electronic devices such as desktop Personal Computers (PCs) or the like.

For example, in Patent Document 1 or Patent Document 2 a motor is proposed in which a shaft is fixed to a base plate and a fluid dynamic bearing mechanism is adopted for a bearing.

When manufacturing a motor adopting the fluid dynamic bearing, lubricant is injected into a space between a rotary body and a fixed body. Then, it is necessary to measure the position of a gas-liquid interface of the lubricant injected into the space between the rotary body and the fixed body and determine whether the position is within a predetermined range. Many of shaft fixed type motors have a plurality of gas-liquid interfaces, respectively, and it takes a long time to measure the positions of the plurality of gas-liquid interfaces, respectively. This reduces production efficiency.

PATENT DOCUMENT

SUMMARY OF THE INVENTION

The present invention is made in light of the above problems, and provides a shaft fixed type rotary device capable of improving production efficiency.

According to an embodiment, there is provided a rotary device including a fixed body that includes a shaft; a rotary body that includes a sleeve being configured to surround an periphery of the shaft through lubricant; and a first taper seal and a second taper seal provided in a space between the fixed body and the rotary body in which gas-liquid interfaces of the lubricant exist, respectively, when the rotary device is operated, the first taper seal and the second taper seal being configured such that a lower limit of a filling ratio, which is a ratio of the volume of the lubricant filled in a taper seal with respect to the volume of the respective taper seal, of the second taper seal corresponds to a predetermined range of the filling ratio of the first taper seal including a lower limit of the filling ratio of the first taper seal, and an upper limit of the filling ratio of the second taper seal corresponds to a predetermined filling ratio of the first taper seal that is larger than an upper limit of the predetermined range and lower than an upper limit of the first taper seal.

According to another embodiment, there is provided a rotary device including a fixed body that includes a shaft; a rotary body that includes a sleeve being configured to surround an periphery of the shaft through lubricant; a first taper seal provided in a space between the fixed body and the rotary body in which a first gas-liquid interface of the lubricant exist when the rotary device is operated, and including a first taper portion in which the space becomes larger by a predetermined first proportion in a first direction of a path of the lubricant away from the second taper seal, and a second taper portion that is positioned further from the second taper seal in the first direction in which the space becomes larger by a predetermined second proportion, which is larger than the first proportion; and a second taper seal provided in a space between the fixed body and the rotary body in which a second gas-liquid interface of the lubricant exist when the rotary device is operated, the first taper seal and the second taper seal being configured such that the first gas-liquid interface exists in the first taper portion of the first taper seal as long as the second gas-liquid interface exists at a lower end of the second taper seal and the first gas-liquid interface of the lubricant exists in the second taper portion of the first taper seal even when the second gas-liquid interface exists at an upper end of the second taper seal.

As such, the filling ratio of the first taper seal and the filling ratio of the second taper seal can be made to correspond.

Note that also arbitrary combinations of the above-described constituents, and any exchanges of expressions in the present invention, made among methods, devices, systems and so forth, are valid as embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is to be noted that, in the explanation of the drawings, the same components are given the same reference numerals, and explanations are not repeated. Further, sizes of components are appropriately enlarged or reduced for explanation purposes. Some parts not particularly related to the structure of the embodiment may be omitted.

A rotary device of the following embodiments is appropriately used as a disk drive device such as a hard-disk drive that mounts a magnetic recording disk and rotates and drives the magnetic recording disk. Specifically, the rotary device of the following embodiments is appropriately used for a shaft fixed type disk drive in which a shaft is fixed to a base while a hub is rotated with respect to the shaft.

First Embodiment

The rotary device of a first embodiment is a shaft fixed type rotary device. A shaft is provided at a fixed body side and a sleeve at a rotary body side surrounds the periphery of the shaft through lubricant. The rotary device adopts fluid dynamic bearing. Specifically, both ends of the shaft are supported and there exist two gas-liquid interfaces of the lubricant between the fixed body and the rotary body. The gas-liquid interfaces exit at corresponding taper seals, respectively.

In this embodiment, the taper seals are configured such that when a gas-liquid interface exists at a second taper seal when injecting the lubricant, a gas-liquid interface also exists at a first taper seal such that the lubricant does not spill out from the first taper seal. With this configuration, by measuring the height of the gas-liquid interface at the second taper seal when injecting the lubricant, the height of the gas-liquid interface at the first taper seal can be recognized without measuring the height. As a result, the process of adjusting the injection amount of the lubricant can be simplified and the production efficiency can be improved.

FIG. 1AtoFIG. 10are views illustrating an example of a rotary device100of the first embodiment.FIG. 1Ais a top view of the rotary device100.FIG. 1Bis a side view of the rotary device100.FIG. 10is a top view of the rotary device100in which a top cover2is removed.

The rotary device100includes a fixed body, a rotary body that rotates with respect to the fixed body and a data read/write unit10. The fixed body includes a base4, a shaft26fixed to the base4, the top cover2, six screws20and a shaft fixing screw6. The rotary body includes a cap12and a clamper154. The cap12and the clamper154are attached to a hub, not shown inFIGS. 1A to 1C. Magnetic recording disks8are attached to the rotary body.

In the following, a side where the hub is mounted with respect to the base4is referred to as an upper side.

Each of the magnetic recording disks8may be a 2.5 inch magnetic recording disk having a diameter of 65 mm, made of glass, provided with a hole having a diameter of 20 mm and having a thickness of 0.65 mm, for example. The rotary body is capable of mounting three of the magnetic recording disks8.

The base4is formed by shaping aluminum alloy by a die-cast. The base4includes a bottom plate portion4athat composes a bottom portion of the rotary device100and an outside periphery wall portion4bthat is formed along an outer periphery of the bottom plate portion4ato surround an area where the magnetic recording disks8are mounted. An upper surface4cof the outside periphery wall portion4bis provided with six screw holes22.

The data read/write unit10includes a recording and playing head (not shown in the drawings), a swing arm14, a voice coil motor16and a pivot assembly18. The recording and playing head is attached to a front end portion of the swing arm14, records data on the magnetic recording disk8and reads data from the magnetic recording disk8. The pivot assembly18oscillatably supports the swing arm14with respect to the base4around a head rotational axis S. The voice coil motor16oscillates the swing arm14around the head rotational axis S and moves the recording and playing head to a desired position above the magnetic recording disk8. The voice coil motor16and the pivot assembly18are configured by known techniques for controlling positioning of the head.

The top cover2is fixed to the upper surface4cof the outside periphery wall portion4bof the base4by the six screws20. The six screws20correspond to the six screw holes22, respectively. Specifically, the top cover2and the upper surface4cof the outside periphery wall portion4bare fixed with each other such that leaking does not occur from the connected portion to inside the rotary device100. Specifically, the inside of the rotary device100is a clean space24surrounded by the bottom plate portion4aof the base4, the outside periphery wall portion4bof the base4and the top cover2. The rotary device100is designed such that the clean space24is sealed, in other words, leak-in from the outside or leak-out to the outside does not occur. The clean space24is filled with clean air from which particles are removed. With this, adhesion of contaminants such as particles or the like to the magnetic recording disks8can be suppressed, and the reliability of the operation of the rotary device100is increased.

The shaft26is provided with shaft fixing screw holes26aat an upper end surface. The lower end of the shaft26is fixed to the base4as will be explained later. The upper end of the shaft26is fixed to the top cover2by having the shaft fixing screw6penetrate the top cover2to be screwed with the shaft fixing screw holes26a.

With shaft fixed type rotary devices, resistance against shock or resistance against vibration of the rotary device100can be increased, according to the use of the aforementioned type of the rotary device in which both ends of the shaft26are fixed to a chassis such as the base4, the top cover2or the like. In such a type of rotary device, when the fluid dynamic bearing is adopted, generally, there exist two gas-liquid interfaces of the lubricant.

In addition to the cap12and the clamper154, the rotary body includes a hub28, a cylindrical magnet32and a sleeve106. In addition to the base4and the shaft26, the fixed body includes a stacked core40, coils42, a housing102and an overhang surrounding portion104. There exists lubricant92at a part of a space between the rotary body (the sleeve106or the like) and the fixed body (the housing102, the shaft26, the overhang surrounding portion104or the like) in a continuous manner.

When manufacturing the rotary device100, a fluid dynamic bearing unit101including the housing102, the shaft26and the overhang surrounding portion104at the fixed body side, the sleeve106at the rotary body side and the lubricant92is manufactured. Then the rotary device100in which the hub28, the base4or the like are attached to the fluid dynamic bearing unit101is manufactured. The base4rotatably supports the hub28through the fluid dynamic bearing unit101.

The hub28is fixed to an outer periphery side of the sleeve106. The hub28is made of a material having soft magnetic properties such as, for example, a steel material such as SUS430F or the like, or aluminum. For example, the hub28is formed to have a predetermined shape, substantially a cup shape, provided with a center hole28aalong a rotational axis R by performing press working or cutting on a steel plate, for example. For the steel material for the hub28, for example, stainless steel whose product name is DHS1, manufactured by Daido Steel Co., Ltd., may be used as outgassing is small and being easy to be processed. Alternatively, stainless steel whose product name is DHS2, manufactured by Daido Steel Co., Ltd., may be used as having a good corrosion resistance. The hub28may be processed with a surface treatment such as plating, resin coating or the like. The hub28of the embodiment includes a surface layer made of electroless nickel plating. With this structure, peeling of small residue adhered to the processed surface can be suppressed.

The sleeve106engages the hub28in the center hole28a. In other words, an outer circumferential surface106aof the sleeve106at its upper portion is connected to a sidewall of the center hole28aof the hub28. The connected portion is explained later.

The hub28includes a hub protruding portion28bthat engages center holes of the magnetic recording disks8, respectively, and a mounting portion28cthat is provided outside of the hub protruding portion28bin a radial direction (a direction perpendicular to the rotational axis R). The magnetic recording disk8is mounted on a disk mounting surface28jof the mounting portion28c.

An annular spacer152is inserted between the two magnetic recording disks8, which are adjacent from each other in the axial direction, which is a direction parallel to the rotational axis R of the rotary body. The clamper154pushes the three magnetic recording disks8and the two spacers152toward the disk mounting surface28jto be fixed. The magnetic recording disks8are fixed to the hub28by being interposed by the clamper154and the mounting portion28c. The clamper154is fixed to an upper surface28lof the hub28by a plurality of clamp screws156. Specifically, the clamp screws156are screwed with clamp screw holes28mprovided at the hub protruding portion28b, respectively.

The clamp screw holes28mare provided to penetrate the hub protruding portion28b, respectively. A lower end of each of the clamp screw holes28mis blocked by a block member34such as a tape or the like. With this, the clamp screw holes28mcan be easily formed as being through holes and the diffusion of the steam of the lubricant92from the inside to the outside of the hub28can be suppressed.

The cylindrical magnet32is fixed to a cylindrical inner circumferential surface28fof the hub protruding portion28bby bonding. The cylindrical magnet32may be, for example, made of a rare earth magnetic material or a ferrite magnetic material. In this embodiment, the cylindrical magnet32is made of a neodymium system rare earth magnetic material. The cylindrical magnet32is polarized to have 16 poles for driving in a circumferential direction (tangent directions of a circle whose center is the rotational axis R and is perpendicular to the rotational axis R). The cylindrical magnet32is applied with a surface layer forming process, such as by electro deposition, spray coating or the like at its surface, for example, to suppress generation of rust.

The stacked core40includes an annular portion and 12 salient poles that extend outwardly from the annular portion in a radial direction and is fixed to an upper surface side of the base4. The stacked core40is formed by stacking 10 thin electromagnet steel plates and formed to be in an integral body by caulking. The stacked core40is applied with an insulating coating such as by electro deposition, powder coating or the like at its surface. Each of the coils42is wound around the respective salient poles of the stacked core40. When a drive current having a substantially sine wave shape of three phases flows through the coil42, drive magnetic flux is generated along the salient poles.

The cylindrical magnet32faces the 12 salient poles of the stacked core40in a radial direction.

The base4includes a cylindrical protruding portion4ewhose center is the rotational axis R. The protruding portion4eis provided to protrude upward from the upper surface of the base4to surround the periphery of the housing102. The stacked core40is fixed to the base4when an outer circumferential surface of the protruding portion4eengages with the stacked core40in a center hole of the annular portion of the stacked core40. Specifically, the stacked core40and the protruding portion4eof the base4are fixed by press fitting or a running fit with bonding.

The housing102is made of a steel material such as SUS or the like. The housing102includes a flat circular shaft supporting portion110and a cylindrical sleeve surrounding portion112that is fixed to the shaft supporting portion110at an outer periphery side. The shaft supporting portion110and the sleeve surrounding portion112are formed such that the entirety of the outer circumferential surface of the shaft supporting portion110is connected to a lower portion of an inner circumferential surface112aof the sleeve surrounding portion112. Specifically, the shaft supporting portion110and the sleeve surrounding portion112are integrally formed. With this structure, manufacturing error of the housing102can be reduced and the process of connecting the components can be omitted. The sleeve surrounding portion112is surrounded by the protruding portion4eof the base4. Specifically, the sleeve surrounding portion112is fixed to an inner circumferential surface, in other words, a bearing hole4h, whose center is the rotational axis R, provided at the base4, of the protruding portion4e, by bonding.

The lower end of the shaft26is inserted into and fixed to an inner circumferential surface, in other words, a shaft hole110a, whose center is the rotational axis R, provided at the shaft supporting portion110, of the shaft supporting portion110by bonding or pressing.

The overhang surrounding portion104surrounds the periphery of the shaft26at the upper end side to be fixed to the shaft26by, for example, bonding or a combination of bonding and pressing.

The sleeve106is formed by cutting a base material made of brass, aluminum or DHS1 into a desired shape, and performing nickel plating on the obtained object. The sleeve106surrounds the periphery of a part of the shaft26at a middle between a part that engages with the shaft hole110aof the housing102and a part surrounded by the overhang surrounding portion104. The lubricant92is provided between the sleeve106and the shaft26. In other words, the inner circumferential surface106fof the sleeve106and the outer circumferential surface26dof the shaft26at the middle part face each other with a first space, which is filled with the lubricant92, therebetween.

The rotary device100includes a first radial dynamic pressure generator160and a second radial dynamic pressure generator162each generates dynamic pressure in the radial direction in the lubricant92when the rotary body is rotated, in the first space. The first radial dynamic pressure generator160and the second radial dynamic pressure generator162are separated from each other in the axial direction where the first radial dynamic pressure generator160is positioned above the second radial dynamic pressure generator162. The inner circumferential surface106fof the sleeve106is provided with a first radial dynamic pressure generation groove50and a second radial dynamic pressure generation groove52, each having a herringbone shape or a spiral shape, at positions corresponding to the first radial dynamic pressure generator160and the second radial dynamic pressure generator162, respectively. Here, at least one of the first radial dynamic pressure generation groove50and the second radial dynamic pressure generation groove52may be provided at the outer circumferential surface26dat the middle part of the shaft26instead of at the inner circumferential surface106fof the sleeve106. The first and second dynamic pressure generation grooves50and52may be made by piezo processing.

The sleeve106is interposed between the overhang surrounding portion104and the shaft supporting portion110in the axial direction. The lubricant92exists between the sleeve106and the overhang surrounding portion104and between the sleeve106and the shaft supporting portion110, respectively. This means that the upper surface106bof the sleeve106and the lower surface104aof the overhang surrounding portion104face each other through a second space, which is filled with the lubricant92. A lower surface106gof the sleeve106and the upper surface110bof the shaft supporting portion110face each other through a third space, which is filled with the lubricant92.

The rotary device100includes a first thrust dynamic pressure generator164that generates dynamic pressure in the axial direction in the lubricant92when the rotary body is rotated, in the third space. The lower surface106gof the sleeve106is provided with a first thrust dynamic pressure generation groove54, having a herringbone shape or a spiral shape, at a position corresponding to the first thrust dynamic pressure generator164. Alternatively, the first thrust dynamic pressure generation groove54may be provided at the upper surface110bof the shaft supporting portion110instead of at the lower surface106gof the sleeve106.

The rotary device100includes a second thrust dynamic pressure generator166that generates dynamic pressure in the axial direction in the lubricant92when the rotary body is rotated, in the second space. The upper surface106bof the sleeve106is provided with a thrust dynamic pressure generation groove56, having a herringbone shape or a spiral shape, at a position corresponding to the second thrust dynamic pressure generator166. Alternatively, the second thrust dynamic pressure generation groove56may be provided at the lower surface104aof the overhang surrounding portion104instead of at the upper surface106bof the sleeve106.

When the rotary body is relatively rotated with respective to the fixed body, the first radial dynamic pressure generation groove50, the second radial dynamic pressure generation groove52, the first thrust dynamic pressure generation groove54and the second thrust dynamic pressure generation groove56generate the dynamic pressure in the lubricant92, respectively. The rotary body is supported in the radial direction and in the axial direction without contacting the fixed body by the dynamic pressure.

For the positional relationship between the sleeve surrounding portion112and the sleeve106, the sleeve surrounding portion112surrounds the periphery of the sleeve106at its lower portion. A first taper seal114is formed between the sleeve surrounding portion112and the sleeve106. The first taper seal114is configured such that a fourth space between the inner circumferential surface112aof the sleeve surrounding portion112and an outer circumferential surface106eof the sleeve106at its lower portion gradually expands upwardly.

As described above, the lubricant92exists between the sleeve106and the overhang surrounding portion104, between the sleeve106and the shaft26and between the sleeve106and the housing102. Then, a first gas-liquid interface116of the lubricant92exists in the first taper seal114when the rotary device100is operated. Here, the spaces between the sleeve106and the overhang surrounding portion104, the shaft26and the housing102where the lubricant92is to be filled is referred to as a “path of the lubricant92” in the following description.

The sleeve106includes an upper taper generation portion106cthat faces the overhang surrounding portion104in the radial direction. The upper taper generation portion106csurrounds the periphery of the overhang surrounding portion104. A second taper seal118is provided between the upper taper generation portion106cand the overhang surrounding portion104in which a fifth space between the inner circumferential surface106dof the upper taper generation portion106cand the outer circumferential surface104bof the overhang surrounding portion104gradually expands upwardly. A second gas-liquid interface120of the lubricant92exits in the second taper seal118while using the rotary device100.

The sleeve106is provided with a bypass connection hole168that bypasses the first radial dynamic pressure generator160and the second radial dynamic pressure generator162. Specifically, the bypass connection hole168connects upstream of the first radial dynamic pressure generator160and downstream of the second radial dynamic pressure generator162when seen from the second taper seal118side. The upper end of the bypass connection hole168exists in the second space while the lower end of the bypass connection hole168exists in the third space. The bypass connection hole168penetrates the sleeve106in the axial direction. The bypass connection hole168is formed such that a ratio of the diameter of the bypass connection hole168with respect to the diameter of the inner circumferential surface106fof the sleeve106becomes more than 0.13. As an example, the diameter of the bypass connection hole168is within a range between 0.35 mm to 0.50 mm, and the diameter of the inner circumferential surface106fof the sleeve106is about 2.5 mm.

When the bypass connection hole is relatively small, if the pressure of the lubricant92is varied drastically by an upward or downward movement of the rotary device100, by the shock to the rotary device100or the like, the lubricant92may show an expected behavior. Thus, in this embodiment, the bypass connection hole168is made relatively large to increase a function of averaging the pressure of the lubricant92to stabilize the behavior of the lubricant92.

The cap12has an annular shape and is fixed to the upper surface28lof the hub28by bonding for covering the second taper seal118and the overhang surrounding portion104. The cap12is made of a metal material such as SUS430, SUS304, brass or the like, or a resin material. The hub28, the sleeve106and the cap12form a steam trap space13. The steam trap space13is in communication with a space15surrounded by the outer circumferential surface104bof the overhang surrounding portion104and the inner circumferential surface106dof the upper taper generation portion106c. The steam trap space13is positioned outside of the space15in the radial direction. When the sleeve106is rotated, at least a part of the steam of the lubricant92evaporated from the second gas-liquid interface120is captured in the steam trap space13by the centrifugal force. With this configuration, the amount of the steam of the lubricant92discharged to the clean space24can be suppressed.

When the space between the cap12and the fixed body is large, the amount of the steam of the lubricant92evaporated from the second gas-liquid interface120and discharged to the clean space24increases. On the other hand, when the space between the cap12and the fixed body is small, there is a possibility that the cap12contacts the fixed body. By the study by the present inventors, it is confirmed that the discharged amount of the steam of the lubricant92is suppressed to a level not causing a trouble in use, as well as the possibility that the cap12contacts the fixed body can be reduced to a level not causing a trouble in use by setting the minimum space between the cap12and the fixed body in the axial direction within a range between 0.06 mm to 0.18 mm. Further, it is confirmed that the discharged amount of the steam of the lubricant92is suppressed to a level not causing a trouble in use, as well as the possibility that the cap12contacts the fixed body can be reduced to a level not causing a trouble in use by setting the minimum space between the cap12and the fixed body in the radial direction within a range between 0.01 mm to 0.15 mm.

FIG. 3AandFIG. 3Bare enlarged cross-sectional views of the taper seals, respectively.FIG. 3Ais an enlarged cross-sectional view of the second taper seal118.FIG. 3Bis an enlarged cross-sectional view of the first taper seal114. In the following, a ratio of the volume of the lubricant92filled in the taper seal with respect to the volume of the taper seal is referred to as “filling ratio”.

First filling ratio F1 of the first taper seal114is a value obtained by dividing the volume OV1 of the lubricant92filled in the first taper seal114by the volume TV1 of the first taper seal114(F1=OV1/TV1). Second filling ratio F2 of the second taper seal118is a value obtained by dividing the volume OV2 of the lubricant92filled in the second taper seal118by the volume TV2 of the second taper seal118(F2=OV2/TV2).

When moving along the path of the lubricant92, in the first taper seal114, the higher the position becomes, the further the distance from the second taper seal118becomes. With reference toFIG. 3B, the first taper seal114includes a first taper portion114aand a second taper portion114bprovided at an upper side of the first taper portion114a. In the first taper portion114a, a space t1 between the housing102and the sleeve106becomes larger upwardly by a predetermined first proportion while in the second taper portion114b, a space t2 between the housing102and the sleeve106becomes larger upwardly by a second proportion, which is larger than the first proportion.

When defining a z coordinate as the axial direction, the space t1 of the first taper portion114abecomes a function of z. The first proportion may be defined as a differential coefficient (dt1/dz) of t1 with respect to z. The second proportion may be similarly defined as a differential coefficient (dt2/dz) of t2 with respect to z.

The first taper portion114aand the second taper portion114bare directly connected. When it is assumed that the volume of the first taper portion114ais “TV3” and the volume of the second taper portion114bis “TV4”, the volume TV1 of the first taper seal114becomes, TV1=TV3+TV4.

In the second taper seal118, a space t3 between the upper taper generation portion106cand the overhang surrounding portion104becomes larger upwardly by a third proportion, which is larger than the first proportion and smaller than the second proportion.

FIG. 11AandFIG. 11Bcorrespond toFIG. 3AandFIG. 3B, respectively. With reference toFIG. 11A, the second taper seal118is defined by a lower end122and an upper end132. Similarly, with reference toFIG. 11B, the first taper portion114aof the first taper seal114is defined by a lower end124and an upper end128. The second taper portion114bof the first taper seal114is defined by a lower end128, which is the same as the upper end of the first taper portion114a, and an upper end134.

Referring back toFIG. 3AandFIG. 3B, when the amount of the lubricant92is to fill the path of the lubricant92other than the first taper seal114and the second taper seal118, the second gas-liquid interface120exists at the lower end122of the second taper seal118(FIG. 3A), and the first gas-liquid interface116exists at the lower end124of the first taper portion114a(FIG. 3B).

When the amount of the lubricant92is increased by injecting the lubricant92from the second taper seal118, for example, the first gas-liquid interface116and/or the second gas-liquid interface120is to move upward. According to the rotary device100of the embodiment, as the third proportion of the second taper seal118is larger than the first proportion of the first taper portion114a, the increased amount of the lubricant92is predominantly received in the first taper portion114a. Thus, the first gas-liquid interface116moves upward in the first taper portion114awhile the second gas-liquid interface120stays at the lower end122of the second taper seal118. When the amount of the lubricant92is further increased and the first gas-liquid interface116in the first taper portion114amoves up to a position126, the second gas-liquid interface120starts moving upward from the lower end122of the second taper seal118. Specifically, the first gas-liquid interface116exists within a predetermined positional range RP in the first taper portion114a, which is shown by an arrow inFIG. 3B, under a state that the second gas-liquid interface120substantially exists at the lower end122of the second taper seal118. The lower limit of the positional range RP is the lower end124of the first taper portion114aand the upper limit of the positional range RP is the position126.

The second filling ratio F2 when the second gas-liquid interface120exists at the lower end122of the second taper seal118is the lower limit, in other words, substantially zero. The first filling ratio F1 when the first gas-liquid interface116exists at the lower end124of the first taper portion114ais the lower limit, in other words, substantially zero.

Here, the first filling ratio F1 when the first gas-liquid interface116exists at the position126in the first taper portion114ais referred to as “x1”, where x1 is smaller than TV3/TV1.

Therefore, the lower limit of the second filling ratio F2 corresponds to a range 0 (the lower limit)≦F1≦x1 of the first filling ratio F1. Thus, the first taper seal114and the second taper seal118are configured such that it is ensured that the first filling ratio F1 does not exceed x1 as long as the second filling ratio F2 is at the lower limit.

In other words, the first taper seal114and the second taper seal118are configured such that the first gas-liquid interface116is to exist within the first taper portion114aof the first taper seal114as long as the second gas-liquid interface120exists at the lower end122of the second taper seal118.

FIG. 4AandFIG. 4Bare enlarged cross-sectional views of the taper seals, respectively.FIG. 4Ais an enlarged cross-sectional view of the second taper seal118.FIG. 4Bis an enlarged cross-sectional view of the first taper seal114. When the amount of the lubricant92is further increased from the state shown inFIG. 3AandFIG. 3B, the first gas-liquid interface116reaches the upper end128of the first taper portion114a. At this time, the first filling ratio F1 is substantially equal to TV3/TV1. The upper end128of the first taper portion114ais also the lower end of the second taper portion114b.

At the time when the first gas-liquid interface116reaches the upper end128of the first taper portion114a, the second gas-liquid interface120is already moved upward, away from the lower end122of the second taper seal118, and is at a position130in the second taper seal118.

FIG. 5AandFIG. 5Bare enlarged cross-sectional views of the taper seals, respectively.FIG. 5Ais an enlarged cross-sectional view of the second taper seal118.FIG. 5Bis an enlarged cross-sectional view of the first taper seal114. When the amount of the lubricant92is further increased from the state shown inFIG. 4AandFIG. 4B, as the second proportion of the second taper portion114bis larger than the third proportion of the second taper seal118, the increased amount of the lubricant92is predominantly received in the second taper seal118. Thus, the second gas-liquid interface120moves upward in the second taper seal118while the first gas-liquid interface116exists substantially at the upper end128of the first taper portion114a. When the amount of the lubricant92is further increased, the first gas-liquid interface116starts moving upward from the upper end128of the first taper portion114awhile the second gas-liquid interface120moves upward in the second taper seal118.

When the amount of the lubricant92is further increased, the second gas-liquid interface120reaches the upper end132of the second taper seal118. At this time, the second filling ratio F2 is the upper limit, in other words, 1. According to the embodiment, the first taper seal114and the second taper seal118are configured such that even when the second gas-liquid interface120reaches the upper end132of the second taper seal118, the first gas-liquid interface116does not reach the upper end134of the second taper portion114band exists in the second taper portion114b.

When the second gas-liquid interface120exists at the upper end132of the second taper seal118, the first gas-liquid interface116exists at a position136in the second taper portion114b. The first filling ratio F1 when the first gas-liquid interface116exists at the position136in the second taper portion114bis referred to as “x2”, where TV3/TV1<x2<1 (the upper limit).

Therefore, the upper limit of the second filling ratio F2 corresponds to x2. Thus, the first taper seal114and the second taper seal118are configured such that the first filling ratio F1 does not become lower than the upper limit even when the second filling ratio F2 reaches the upper limit.

In other words, the first taper seal114and the second taper seal118are configured such that the first gas-liquid interface116is to exist within the second taper portion114bof the first taper seal114, not to reach the upper end134, even when the second gas-liquid interface120exists at the upper end132of the second taper seal118.

FIG. 6AandFIG. 6Bare views for explaining a connected portion between the sidewall of the center hole28aprovided in the hub28and the outer circumferential surface106aof the sleeve106at its upper portion.FIG. 6Ashows a status in which the sleeve106(the fluid dynamic bearing unit101) is in the middle of being inserted into the center hole28afrom the lower side andFIG. 6Bshows a status in which the sleeve106is completely inserted into the center hole28a.

The sidewall of the center hole28ais provided with a circular first concave portion138. The outer circumferential surface106aof the sleeve106at its upper portion is provided with a circular second concave portion140. The side wall of the center hole28ahas a first portion28uthat faces the second concave portion140and a second portion28tthat is positioned at the upper side of the first portion28uwhile interposing the first concave portion138therebetween. Specifically, the first portion28uis positioned at the lower side of the first concave portion138while the second portion28tis positioned at the upper side of the first concave portion138of the sidewall of the center hole28a. The sidewall of the center hole28ais formed such that the diameter of the first portion28ubecomes substantially the same as that of the second portion28t.

With reference toFIG. 6B, the first concave portion138corresponds to the first radial dynamic pressure generator160in the axial direction. Specifically, the first concave portion138is formed to surround at least a part of the first radial dynamic pressure generator160. In other words, the area where the first concave portion138exists and the area where the first radial dynamic pressure generator160exists have a common part in the axial direction.

The second concave portion140partially overlaps the first concave portion138in the axial direction. There is a space (142,146and144) between the hub28and the sleeve106. A part of the space between the hub28and the sleeve106where the first concave portion138is formed is referred to as an upper space142. A part of the space between the hub28and the sleeve106where the second concave portion140is formed is referred to as a lower space144. A part of the space between the hub28and the sleeve106where the second concave portion140and the first concave portion138overlap and between the upper space142and the lower space144is referred to as an intermediate space146. The second portion28tis pressed to be in contact with the outer circumferential surface106aof the sleeve106.

The sidewall of the center hole28ais formed such that the second portion28tdoes not overlap the first radial dynamic pressure generator160in the axial direction. Specifically, the first concave portion138is formed such that the upper end of the first concave portion138is positioned upper than or equal to the upper end of the first radial dynamic pressure generator160in the axial direction. As an example, the range where the second portion28texists and the range where the first radial dynamic pressure generator160exists do not overlap in the axial direction.

With reference toFIG. 6A, when inserting the sleeve106into the center hole28aof the hub28, both the first portion28uand the second portion28tare pressed to be in contact with the outer circumferential surface106aof the sleeve106. At this time, the sleeve106is supported at two positions of the hub28, and backlash is hardly generated so that the sleeve106can be positioned vertically with respect to the hub28.

With reference toFIG. 6B, after completely inserting the sleeve106to the center hole28aof the hub28, there is the space between the first portion28uand the outer circumferential surface106aof the sleeve106. Thus, the sidewall of the center hole28aand the outer circumferential surface106aof the sleeve106only contact with each other at the second portion28t. With this, an undesired effect to the first radial dynamic pressure generator160by the pressure caused by the contact between the hub28and the sleeve106can be reduced. Specifically, deformation of the first radial dynamic pressure generator160by the influence of the pressure caused by the contact between the hub28and the sleeve106can be suppressed.

Here, an adhesive material may be partially filled in the intermediate space142, the lower space144or in the overlapped intermediate space146.

Further, the influence on the first radial dynamic pressure generator160can be reduced even when the connected portion of the sidewall of the center hole28aand the outer circumferential surface106aof the sleeve106overlaps the first radial dynamic pressure generator160in the axial direction, the first radial dynamic pressure generator160can be positioned further upper side to spread a bearing span.

Alternatively, the first concave portion (the upper concave portion) may be formed at the outer circumferential surface of the sleeve106while the second concave portion (the lower concave portion) may be formed at the sidewall of the center hole28aof the hub28. At this time, the same advantage as described above can be obtained by inserting the sleeve106into the center hole28aof the hub28from the upper side.

The operation of the rotary device100of the embodiment is explained next.

First, a drive current of three phases is supplied to the coils42for rotating the magnetic recording disks8. When the drive current flows through the coils42, magnetic flux is generated along the 12 salient poles. The rotary body and the magnetic recording disks8that engage the rotary body are rotated by torque applied to the cylindrical magnet32by the magnetic flux. At the same time, the recording and playing head moves within an oscillating range on the magnetic recording disks8when the voice coil motor16oscillates the swing arm14. The recording and playing head converts magnetic data recorded in the magnetic recording disks8to an electric signal and transmits the electric signal to a control substrate (not shown in the drawings) and converts an electric signal sent from the control substrate to magnetic data and writes the magnetic data on the magnetic recording disks8.

According to the rotary device100of the embodiment, by controlling the height of the second gas-liquid interface120of the second taper seal118, the height of the first gas-liquid interface116of the first taper seal114can also be controlled. Specifically, when the second gas-liquid interface120exists at a position higher than the lower end122of the second taper seal118, it can be ensured that the first filling ratio F1 of the first taper seal114is within a range between x1 and x2. Thus, the height of the first gas-liquid interface116can be set within a desired range without directly measuring the height of the first gas-liquid interface116. As a result, it is unnecessary to configure the rotary device100such that the height of the first gas-liquid interface116can be measured so that the degree of freedom in design is improved. Specifically, even when the first gas-liquid interface116of the first taper seal114is hard to be seen, the heights of the first gas-liquid interface116and the second gas-liquid interface120can be grasped so that a life time of the product can be ensured. Further, a step of measuring the height of the first gas-liquid interface116can be omitted to improve production efficiency.

Further, according to the rotary device100of the embodiment, it is ensured that the first gas-liquid interface116exists in the second taper portion114band does not exceed the upper end134of the second taper portion114beven when the second gas-liquid interface120reaches the upper end132of the second taper seal118. Thus, spill out of the lubricant92from the first taper seal114can be suppressed.

Second Embodiment

FIG. 7is a cross-sectional view illustrating an example of a rotary device200of a second embodiment. In the rotary device100of the first embodiment, the overhang surrounding portion104and the shaft26are separately formed. However, in the rotary device200of the second embodiment, the overhang surrounding portion and the shaft are integrally formed as a shaft226. Further, in the rotary device100of the first embodiment, the sleeve106and the hub28are separately formed. However, in the rotary device200of the second embodiment, the sleeve and the hub are integrally formed as a hub228.

According to the rotary device200of the embodiment, the same advantages as those of the rotary device100of the first embodiment can be obtained. In addition, accuracy of run-out, in other words, accuracy of processing or dimensional accuracy, between a disk mounting surface228jand a sleeve inner circumferential surface206fof the hub228is improved.

Third Embodiment

FIG. 8is a cross-sectional view illustrating an example of a rotary device300of a third embodiment.

In this embodiment, the rotary body includes a hub328, a cylindrical magnet332and an outer surrounding member306. The fixed body includes a base304, a stacked core340, coils342, a housing302, a shaft326, an attraction plate386. There exists lubricant392at a part of the space between the rotary body and the fixed body in a continuous manner.

Similar to the first embodiment, magnetic recording disks (not shown in the drawings) are mounted on a disk mounting surface328aof the hub328. The hub328includes a cylindrical shaft surrounding portion328bthat surrounds the periphery of the shaft326. The shaft surrounding portion328bis provided with a radial dynamic pressure generation groove at an inner circumferential surface328c.

The cylindrical magnet332is attached to a cylindrical inner circumferential surface328fof the hub328by bonding. An inner circumferential surface of the cylindrical magnet332faces12salient poles of the stacked core340in the radial direction. The cylindrical magnet332is polarized to have 16 poles for driving in the circumferential direction.

The stacked core340includes an annular portion and 12 salient poles that extend outwardly from the annular portion in the radial direction and is fixed to an upper surface side of the base304. The stacked core340is formed by stacking 10 thin electromagnet steel plates and formed to be in an integral body by caulking. Each of the coils342is wound around the respective salient pole of the stacked core340.

The base304is provided with a through hole304hwhose center is the rotational axis R of the rotary body. The housing302has a substantially L shape in a cross-sectional view and is attached to the base304in the through hole304hby bonding. The housing302surrounds the periphery of the lower portion of the shaft326. This means that the housing302is provided with a shaft hole302awhose center is the rotational axis R of the rotary body, and the lower portion of the shaft326is inserted into the shaft hole302aand fixed therein by bonding or tight fitting. The housing302includes a cylindrical barrel portion302bthat surrounds the periphery of the lower portion of the shaft surrounding portion328b.

The outer surrounding member306is a cylindrical member that surrounds the periphery of the barrel portion302band is fixed to the hub328. A first taper seal310is formed between the outer surrounding member306and the barrel portion302b. The first taper seal310is configured such that a space between the inner circumferential surface306aof the outer surrounding member306and the outer circumferential surface302cof the barrel portion302bbecomes gradually larger downwardly. The first taper seal310has a first gas-liquid interface312of the lubricant392and suppresses leakage of the lubricant392by a capillary action.

The base304includes a cylindrical protruding portion304ewhose center is the rotational axis R of the rotary body. The protruding portion304eis formed to be protruded from the upper surface of the base304to surround the periphery of the outer surrounding member306. The stacked core340is fixed to the base304when the center hole of the annular portion of the stacked core340engages the outer circumferential surface of the protruding portion304e. The protruding portion304eand the outer surrounding member306forms a labyrinth seal for the lubricant392that is evaporated from the first gas-liquid interface312.

The shaft326includes an overhang portion326athat is formed at the upper end side of the shaft326and overhung outwardly in the radial direction. A second taper seal314is formed between the overhang portion326aand the shaft surrounding portion328b. A second gas-liquid interface316of the lubricant392is positioned above the second taper seal314in the space between the overhang portion326aand the shaft surrounding portion328b.

The relationship between the filling ratio of the first taper seal310and the filling ratio of the space between the overhang portion326aand the shaft surrounding portion328b(second taper seal314) are the same as that in the first embodiment.

Specifically, the first taper seal310includes a first taper portion and a second taper portion similar to the first embodiment. In the first taper portion, a space between the housing302and the outer surrounding member306becomes larger downwardly by a predetermined first proportion while in the second taper portion, a space between the housing302and the outer surrounding member306becomes larger downwardly by a second proportion, which is larger than the first proportion.

The rotary device300includes a first radial dynamic pressure generator360and a second radial dynamic pressure generator362each generates dynamic pressure in the radial direction in the lubricant392when the rotary body is rotated, in the space between the inner circumferential surface328cof the shaft surrounding portion328band the corresponding circumferential surface326bof the shaft326. The first radial dynamic pressure generator360and the second radial dynamic pressure generator362are separated from each other in the axial direction where the first radial dynamic pressure generator360is positioned above the second radial dynamic pressure generator362. The inner circumferential surface328cof the shaft surrounding portion328bis provided with a first radial dynamic pressure generation groove and a second radial dynamic pressure generation groove, each having a herringbone shape or a spiral shape (not shown in the drawings) at positions corresponding to the first radial dynamic pressure generator360and the second radial dynamic pressure generator362, respectively. Here, at least one of the first radial dynamic pressure generation groove and the second radial dynamic pressure generation groove may be provided at the circumferential surface326bof the shaft326instead of the inner circumferential surface328cof the shaft surrounding portion328b.

The rotary device300includes a thrust dynamic pressure generator364that generates dynamic pressure in the axial direction in the lubricant392when the rotary body is rotated, in the space between the upper surface302dof the barrel portion302band the lower surface328dof the shaft surrounding portion328b. The dynamic pressure generated in the thrust dynamic pressure generator364applies an upward force in the axial direction to the hub328. The lower surface328dof the shaft surrounding portion328bat the position corresponding to the thrust dynamic pressure generator364is provided with a thrust dynamic pressure generation groove (not shown in the drawings) having a herringbone shape or a spiral shape. The thrust dynamic pressure generation groove may be formed at the upper surface302dof the barrel portion302binstead of the lower surface328dof the shaft surrounding portion328b.

The attraction plate386is fixed to the upper surface of the base304by caulking or by bonding to face the cylindrical magnet332in the axial direction. As the attraction plate386is made of magnetic material, the attraction plate386and the cylindrical magnet332attract each other by a magnetic force. With this, a force in the lower axial direction is applied to the cylindrical magnet332to suppress the floating of the rotary body while being rotated.

When the rotary body is rotated, the first radial dynamic pressure generation groove, the second radial dynamic pressure generation groove and the thrust dynamic pressure generation groove respectively generate dynamic pressure to the lubricant392. By these dynamic pressures, the rotary body is supported in the radial direction and in the axial direction without directly contacting the fixed body. The distance between the attraction plate386and the cylindrical magnet332and the magnetic force of the attraction plate386are designed such that the attraction force by the attraction plate386to attract the cylindrical magnet332corresponds to the thrust dynamic pressure generated at the thrust dynamic pressure generator364. Specifically, the distance between the attraction plate386and the cylindrical magnet332and the magnetic force of the attraction plate386are designed such that the floating amount of the rotary body becomes within a desired range when the rotary body is rotated.

The space between the rotary body and the fixed body includes the thrust dynamic pressure generator364, the second radial dynamic pressure generator362and the first radial dynamic pressure generator360in this order in the path of the lubricant392from the first taper seal310to the second taper seal314.

The shaft surrounding portion328bis provided with a communication hole370that is formed to connect a portion between the first radial dynamic pressure generator360and the second radial dynamic pressure generator362, and a portion between the second radial dynamic pressure generator362and the thrust dynamic pressure generator364. The communication hole370bypasses the second radial dynamic pressure generator362. The communication hole370is formed as a straight through hole. The shaft surrounding portion328bis further provided with a bypass path372that bypasses the first radial dynamic pressure generator360, the second radial dynamic pressure generator362and the thrust dynamic pressure generator364. The bypass path372is formed as a straight through hole.

According to the rotary device300of the third embodiment, the attraction plate386is provided in order to obtain a necessary lower side force in the axial direction for stabilizing the floating amount of the rotary body when the rotary body is rotated, instead of providing another thrust dynamic pressure generator. Thus, it is not necessary to provide such another thrust dynamic pressure generator, thus, the number of process steps and the difficulties in processing can be reduced. Specifically, as relatively higher process accuracy is required for forming a dynamic pressure generator while such higher process accuracy is not required in providing the attraction plate, the number of process steps or the difficulties in processing can be reduced to improve the production efficiency.

Further, the center of gravity of the rotary body can be positioned between the first radial dynamic pressure generator360and the second radial dynamic pressure generator362, in other words, within the bearing span and the stable rotation can be performed.

Further, according to the rotary device300of the third embodiment, the pressure gradient of the lubricant392within the bearing can be reduced by the functions to average the pressure by the communication hole370and the bypass path372, and leakage of the lubricant392can be suppressed.

Further, according to the rotary device300of the third embodiment, the lower portion of the shaft surrounding portion328bis interposed between the thrust dynamic pressure generator364and the shaft326. Thus, the thrust dynamic pressure generator364can be positioned relatively outside in the radial direction. As a result, rigidity of the bearing is improved and the stability when the rotary body is rotated can be increased.

Further, according to the rotary device300of the third embodiment, the pressure of the lubricant392can be gathered to a thrust surface portion374, which is downstream of the second radial dynamic pressure generator362when seen from the second taper seal314side. Thus, a pump-in force is generated in a direction opposite to the attraction force by the attraction plate386. With this configuration, sufficient floating amount can be retained when the rotary body is rotated. This effect can be increased as the number of the magnetic recording disks increases to 3, 4, 5 and more.

Further, according to the rotary device300of the third embodiment, it is not necessary to form an additional thrust dynamic pressure generator near the second taper seal314. Thus, the second taper seal314can be made to be relatively compact. With this, the bearing span can be enlarged for an amount that the second taper seal314is made to be compact in the axial direction.

Further, according to the rotary device300of the third embodiment, the overhang portion326afunctions as a stopper to stop the hub328from slipping from the shaft326by protruding in the radial direction.

Fourth Embodiment

FIG. 9is a cross-sectional view illustrating an example of a rotary device400of a fourth embodiment. The rotary body includes a hub428, the cylindrical magnet32, the cap12and a clamper154. The fixed body includes the base4, the stacked core40, the coils42, a periphery wall member402, the shaft426, the overhang surrounding portion104and an insulating tape494. There exists lubricant492at a part of the space between the rotary body and the fixed body in a continuous manner.

The hub428includes a shaft surrounding portion428athat surrounds the periphery of the shaft426, a hub protruding portion428bthat is inserted in the center holes of the magnetic recording disks8, respectively, and a mounting portion428cthat is provided outside of the hub protruding portion428bin the radial direction. The magnetic recording disks8are mounted on a disk mounting surface428j, which is an upper surface of the mounting portion428c.

The clamp screws156are screwed with clamp screw holes428mprovided at the hub protruding portion428b, respectively. The protruding portion4eof the base4protrudes upward from the upper surface of the base4to surround the periphery wall member402. The base4is provided with an insulating tape494, which aids insulating the base4from the coils42, is attached at the upper surface of the base4at a portion facing the coils42in the axial direction.

The shaft426includes a cylinder rod portion426athat extends in the rotational axis R and a flat circular flange portion426bthat protrudes outward in the radial direction from the lower end of the rod portion426a. The rod portion426ais be formed by cutting, grinding and quenching. The flange portion426bis formed by cutting. The flange portion426bmay be performed with grinding.

The periphery wall member402is a cylindrical member and fixed to the inner circumferential surface of the protruding portion4e, in other words the bearing hole4h, by bonding. The periphery wall member402is fixed to an outer periphery end of the flange portion426b. The periphery wall member402and the flange portion426bare connected by one of or a combination of either of bonding, press fitting, welding and caulking. When considering a leakage of the lubricant492, the periphery wall member402and the flange portion426bmay be connected by bonding.

The thickness T3 of the periphery wall member402in the radial direction is larger than the thickness T4 of the protruding portion4eat a portion facing the center hole of the stacked core40in the radial direction.

The first taper seal414, the first thrust dynamic pressure generator464, the second radial dynamic pressure generator462, the first radial dynamic pressure generator460, the second thrust dynamic pressure generator466and the second taper seal418of the rotary device400of the fourth embodiment correspond to the first taper seal114, the first thrust dynamic pressure generator164, the second radial dynamic pressure generator162, the first radial dynamic pressure generator160, the second thrust dynamic pressure generator166and the second taper seal118of the rotary device100of the first embodiment, respectively.

The shaft surrounding portion428ais provided with a bypass connection hole468that bypasses the first radial dynamic pressure generator460and the second radial dynamic pressure generator462.

There is provided a sixth space482, having a reverse L shape in a cross-sectional view, between an upper portion of the periphery wall member402and the hub428at an upper side of the first taper seal414. The sixth space482functions as a labyrinth for the lubricant492evaporated from the first gas-liquid interface416of the first taper seal414to reduce the evaporated amount of the lubricant492.

The thickness T1 of the flange portion426bat a portion corresponding to the first thrust dynamic pressure generator464, in other words, a portion at a lower side of the first thrust dynamic pressure generator464in the axial direction, is smaller than the thickness T2 of the base4at a portion facing the coils42in the axial direction.

The inner circumferential surface402aof the periphery wall member402is provided with a circular periphery wall concave portion402bin the vicinity of an exit of the first taper seal414. The outer circumferential surface428dthat faces the periphery wall member402is provided with an opposing concave portion428eat a position facing the periphery wall concave portion402bof the shaft surrounding portion428ain the radial direction. A lipophobic material that repels the lubricant492is coated at exit sides of the periphery wall concave portion402band the opposing concave portion428e, respectively.

According to the rotary device400of the embodiment, as the rod portion426aand the flange portion426bare integrally formed as the shaft426, the length in the axial direction can be shortened while maintaining the strength at the connected portion between the rod portion426aand the flange portion426b.

If the rod portion and the flange portion are separately formed, it is necessary to provide the connected portion of the rod portion and the flange portion, in other words, an overlapping range in the axial direction, to be relatively long. In this embodiment, as the rod portion426aand the flange portion426bare integrally formed, a sufficient bonding strength can be obtained even when the overlapping range is relatively short. As a result, the distance between the first radial dynamic pressure generator460and the second radial dynamic pressure generator462, in other words, the bearing span can be enlarged, for the amount that the length of the connected portion is shortened, to increase the rigidity of the bearing.

Further, by separately forming the shaft426and the periphery wall member402while integrally forming the rod portion426aand the flange portion426b, the flange portion426bcan be easily positioned perpendicularly with respect to the rod portion426a. Thus, the perpendicularity between the upper surface of the flange portion426bthat forms the first thrust dynamic pressure generator464and the circumferential surface of the rod portion426athat forms the first radial dynamic pressure generator460and the second radial dynamic pressure generator462can be improved.

Fifth Embodiment

FIG. 10is a cross-sectional view of the rotary device500of a fifth embodiment. The rotary body includes a hub528, a cylindrical magnet32, a cap12and a clamper154. The fixed body includes the base4, the stacked core40, the coil42, a housing502, a shaft526, an overhang surrounding portion504and an insulating tape494. There exists lubricant592at a part of the space between the rotary body and the fixed body in a continuous manner.

The hub528includes a shaft surrounding portion528athat surrounds the periphery of the shaft526, a hub protruding portion528bthat engages the center holes of the magnetic recording disks8, and a mounting portion528cprovided further outside than the hub protruding portion528bin the radial direction. The magnetic recording disks8are mounted on a disk mounting surface528j, which is the upper surface of the mounting portion528c.

The clamp screws156are screwed with the clamp screw holes528mprovided at the hub protruding portion528b, respectively.

The protruding portion4eof the base4is protruded from the upper surface of the base4to surround the periphery of the housing502.

The housing502includes a flat circular housing bottom portion510, a cylindrical base side surrounding portion512fixed to an outer periphery side of the housing bottom portion510and a cylindrical support protruding portion508fixed to an inner periphery side of the housing bottom portion510. The housing502supports the shaft526.

The housing bottom portion510and the base side surrounding portion512are formed such that an outer circumferential surface of the housing bottom portion510contacts an inner circumferential surface of the base side surrounding portion512at its lower side portion. Specifically, the housing bottom portion510and the base side surrounding portion512are integrally formed. The housing bottom portion510and the support protruding portion508are formed such that an inner circumferential surface of the housing bottom portion510contacts an outer circumferential surface of the support protruding portion508at a lower side. Specifically, the housing bottom portion510and the support protruding portion508are integrally formed. The base side surrounding portion512is fixed to the bearing hole4hprovided in the base4by bonding.

The shaft526is provided with a support hole526dat its lower end surface526calong the axial direction. The support protruding portion508is inserted in the support hole526dand is fixed therein. The shaft526includes a rod portion526bthat extends along the rotational axis R, and an overhang portion526athat is provided at the upper end side of the rod portion526band outwardly protrudes in the radial direction.

The overhang surrounding portion504surrounds the periphery of the overhang portion526aand is fixed to the overhang portion526a. The overhang surrounding portion504is fixed to the overhang portion526aby a combination of bonding and press fitting. Alternatively, the overhang surrounding portion504may be fixed to the overhang portion526aby welding. For this case, a curing resin may be coated on a surface of the welded portion. With such a structure, the deposited material can be prevented from pealing from the surface of the welded portion.

The first taper seal514, the first thrust dynamic pressure generator564, the second radial dynamic pressure generator562, the first radial dynamic pressure generator560and the second thrust dynamic pressure generator566of the rotary device500of the fifth embodiment correspond to the first taper seal414, the first thrust dynamic pressure generator464, the second radial dynamic pressure generator462, the first radial dynamic pressure generator460and the second thrust dynamic pressure generator466of the rotary device400of the fourth embodiment, respectively.

The shaft surrounding portion528is provided with a bypass connection hole568that bypasses the first radial dynamic pressure generator560and the second radial dynamic pressure generator562. There is provided a space, having a reverse L shape in a cross-sectional view, between an upper portion of the base side surrounding portion512and the hub528. The space functions as a labyrinth, similar to the sixth space482explained in the fourth embodiment.

In the fifth embodiment, the minimum space between the overhang surrounding portion504and the hub528in the axial direction is made larger than the minimum space between the overhang portion526aand the hub528in the axial direction. Even when the hub528is moved in a direction away from the base4, the movement of the hub528is regulated by colliding with the overhang portion526aso that the overhang surrounding portion504can be maintained not to be in contact with the hub528. With this configuration, even when the rotary device500is applied with a shock, the hub528may collide with the overhang portion526a, however, the hub528does not collide with the overhang surrounding portion504. Thus, the possibility that a connected portion of the overhang surrounding portion504and the overhang portion526ais deformed can be decreased.

The space between the outer circumferential surface504aof the overhang surrounding portion504and a surface of the hub528that faces the outer circumferential surface504ain the radial direction gradually expands upwardly to form the second taper seal518. The second taper seal518is configured such that a second gas-liquid interface520of the lubricant592exists when the rotary device500is being operated.

There is provided a constriction portion in which the space between the overhang surrounding portion504and the hub528gradually decreases toward the second thrust dynamic pressure generator566is provided between the second taper seal518and the second thrust dynamic pressure generator566in the path of the lubricant592. In the constriction portion572, the space becomes narrower as approaching the upper side (as being close to the shaft526). With this, the lubricant592is further prevented from leaking in addition to the function of the second taper seal518.

When the shaft526and the support protruding portion508are integrally formed, the shape of such an integrally formed member becomes relatively complicated and it is difficult to accurately manufacture such an integrally formed member. For example, it may be difficult to introduce a grinder to grind a circumferential surface of the shaft. As the circumferential surface of the shaft corresponds to the radial dynamic pressure generator, a relatively high dimensional accuracy is required. On the other hand, according to the rotary device500of the embodiment, the shaft526and the support protruding portion508are separately formed. Thus, the circumferential surface of the shaft526can be manufactured with a high dimensional accuracy while fixing the base4to the shaft526.

Further, if the support protruding portion508is separately formed in the housing502, the connected portion of the support protruding portion508and the housing bottom portion510may be formed in a relatively large scale in order to fix then with a sufficient fixing strength. In such a case, the rotary device500cannot be made thinner. Thus, according to the rotary device500of the embodiment, the support protruding portion508is integrally formed with the housing bottom portion510.

According to the rotary device500of the embodiment, the rod portion526band the overhang portion526aare integrally formed as the shaft526. Thus, the connected portion of the overhang portion526aand the rod portion526bcan be formed to be shorter in the axial direction while maintaining the strength in connection.

If the rod portion and the overhang portion are separately formed, it is necessary to provide the connected portion of the rod portion and the overhang portion, in other words, an overlapping range in the axial direction, to be relatively long in order to connect then with a sufficient strength. However, in this embodiment, as the rod portion526band the overhang portion526aare integrally formed, a sufficient bonding strength can be obtained even when the overlapping range is made relatively small. As a result, the distance between the first radial dynamic pressure generator560and the second radial dynamic pressure generator562, in other words, the bearing span can be enlarged, for the amount that the length of the connected portion is shortened, to increase the rigidity of the bearing.

Although a preferred embodiment of the rotary device has been specifically illustrated and described, it is to be understood that minor modifications may be made therein without departing from the spirit and scope of the invention as defined by the claims.

In the first to fifth embodiments, a so-called outer rotor type rotary device in which the cylindrical magnet positions outside the stacked core is explained. However, teachings herein are not so-limited. For example, a so-called inner rotor type rotary device in which the cylindrical magnet is positioned inside the stacked core may be used, for example.

In the first to fifth embodiments, an example in which the housing is directly attached to the base is explained. However, teachings herein are not so-limited. For example, a structure may be obtained by preparing a brushless motor including the rotary body and the fixed body, and then attaching the brushless motor to a chassis.

In the first to fifth embodiments, examples in which the stacked core is used are explained. However, the core may not be the stacked core.

In the first embodiment, an example in which the base4is formed by shaping aluminum alloy by the die-cast is explained. However, it is not limited so and the base4may be formed by press working on a metal plate such as an aluminum plate, an iron plate or the like. At this time, the base4may be formed to have an emboss portion including a protruding portion at one surface and a concave portion at the other surface corresponding to the concave portion by pressing up the base4. By providing the emboss portion at a predetermined position, deformation of the base4can be suppressed. Further, at this time, the base4may be applied with a surface treatment such as plating, resin coating or the like. For example, when the base4is made of an iron plate, a nickel plating layer and a surface layer of epoxy resin may be provided after performing press working.

The base4may be configured by a combination of a sheet metal portion that is formed by performing press working on a metal plate such as an aluminum plate, an iron plate or the like, and a die-cast portion that is formed by shaping the aluminum alloy or the like by the die-cast. For example, the bottom plate portion4amay be configured by the sheet metal portion while the outside periphery wall portion4bmay be configured by the die-cast portion. With this structure, lowering of the rigidity of the screw holes22can be suppressed. A method of manufacturing such a base4may be, a die-cast portion is formed by shaping the aluminum alloy or the like by an aluminum die-cast while a previously formed sheet metal portion is placed in the aluminum die-cast. According to the method, it is not necessary to connect the sheet metal portion and the die-cast portion and the dimensional accuracy of the sheet metal portion and the die-cast portion can be improved. Further, members for connecting the sheet metal portion and the die-cast portion can be made small or omitted. As a result, the base4can be formed to be thinner.

In the first embodiment, the cap12is formed to extend in the direction. However, teachings herein are not so-limited. For example, the cap12may be formed by a portion that extends in the radial direction and a portion that extends in the axial direction. By narrowing the space between the cap12and the fixed body in the radial direction, the diffusion if the steam of the lubricant92can be further reduced.

In the first embodiment, a case in which the overhang surrounding portion104is fixed to the shaft26by bonding, press fitting and bonding, or the like is explained. However, teachings herein are not so-limited. For example, the overhang surrounding portion104may be fixed to the shaft26by welding. At this time, the bonding strength can be increased and the resistance against shock can be improved. Further, as the bonding strength similar to that obtained when bonding is used can be obtained even when the length of the connected portion is short and the rotary device can be made thinner. This structure can be adoptable for other connected portions such as the connected portion between the hub28and the sleeve106, the connected portion between the cap12and the hub, the connected portion between the sleeve surrounding portion112and the base4or the like. When such a structure is provided, the same advantage as described above can be obtained.

When parts are connected by welding, there is a possibility that a removable contaminant is attached to a welded portion. Thus, a surface coat cover may be provided at the surface of the welded portion in order to prevent pealing of such a contaminant. The surface coat cover may be formed by, for example, coating a liquid resin at a surface of the welded portion, and curing the liquid resin by heating or by UV. Further, bonding or press filling and bonding may be combined with welding for such a connected portion. For example, welding is partially performed while bonding or press fitting and bonding is partially performed at other parts. In such a case, as a certain bonding strength can be obtained by a portion where welding is adopted, deformation of the bonding part by a shrinkage on curing of the adhesive material can be suppressed.

In the first embodiment, an example in which each of the taper seals and the taper portions is defined by a proportion by which the respective space becomes larger is explained, however, this is not limited so. For example, each of the taper seals and the taper portions may be defined by a radius of curvature of the respective gas-liquid interface.

Specifically, it is assumed that a radius of curvature of the second gas-liquid interface120at the lower end122of the second taper seal118is “r1”, a radius of curvature of the second gas-liquid interface120at a position upper than the position130in the second taper seal118is “r4”, and a radius of curvature of the second gas-liquid interface120at the upper end132of the second taper seal118is “r5”. Further, it is assumed that a radius of curvature of the first gas-liquid interface116at the lower end124of the first taper portion114ais “r2”, a radius of curvature of the first gas-liquid interface116at the upper end128of the first taper portion114ais “r3”, and a radius of curvature of the first gas-liquid interface116at the upper end134of the second taper portion114bis “r6”. At this time, the first taper seal114and the second taper seal118may be formed to satisfy the following condition: r1<r2<r3<r4<r5<r6.

In the first embodiment, a case where x1 is smaller than TV3/TV1 is explained, however, this is not limited so. For example, x1 may be set substantially equal to TV3/TV1. In other words, the first taper seal114and the second taper seal118may be formed such that the lower limit of the second filling ratio F2 corresponds to a range, 0 (the lower limit)≦F1≦TV3/TV1, of the first filling ratio F1, in other words, the first taper portion114a. At this time, by setting the volume TV3 of the first taper portion114ato be larger than or equal to the minimum value of the lubricant92for which the first taper seal114is to include, it is easier to retain such a minimum amount of the lubricant92in the first taper seal114.

In the third embodiment, an example in which the communication hole370and the bypass path372are provided in the shaft surrounding portion328bis explained. However, this is not limited so, and at least one of the communication hole370and the bypass path372may be provided in the shaft surrounding portion.

In the first to fifth embodiments, an example in which both end surfaces of the cap have flat surfaces, respectively. However, teachings herein are not so-limited. Both end surfaces of the cap may be provided with a protruding portion or a concave portion. For example, the cap12may be provided with a periphery protruding portion or a concave portion at a surface near the base4. By providing the protruding portion or the concave portion, it is easier to recognize front and back surfaces of the cap12and it is easier to attach the cap12in a proper side.

According to the embodiments, production efficiency of the shaft fixed type rotary device can be improved.

The present application is based on and claims the benefit of priority of Japanese Priority Application No. 2012-184302 filed on Aug. 23, 2012, the entire contents of which are hereby incorporated by reference.