This application claims priority based on the following Japanese patent applications: 2004-174866, filed Jun. 11, 2004; and 2005-141974, filed May 13, 2005.
1. Field of the Invention
The invention described in this patent application relates to fluid dynamic pressure bearings (bearings) that can be mass-produced at a low cost and with high quality, particularly those bearings suited for use with a spindle motor used for magnetic disk, optical disk or other memory storage devices, for example, a CD or a DVD.
2. Description of the Related Art
In recent years, the demand has been strong for increasingly smaller, thinner, lighter and higher-density magnetic disk, optical disk and other memory storage devices used in computers. For this reason, there is a demand for acceleration of rotation speed and increase of rotational accuracy of the spindle motors used for disk rotation. In order to meet this demand, rotational bearings like fluid dynamic bearing are used to replace conventional ball bearings. In a fluid dynamic bearing, lubricant is used to generate fluid dynamic pressure to support the rotating shaft. The requested volume of the fluid dynamic bearing is increasingly large. However, the problem with these fluid dynamic pressure bearings is that it is difficult to mass-produce them at high quality and low cost due to their high dimensional accuracy and also due to the fact that manufacturing is not easy.
The flange part 04 is sandwiched between the lower end surface 05a of the sleeve 05 and the upper surface 07a of the endplate 07. The lower end surface 05a of the sleeve 05 and the upper surface 04a of the flange part 04, as well as the upper surface 07a of the endplate 07 and the lower surface 04b of the flange part 04, oppose each other via the thrust microgaps.
A first dynamic pressure generating groove 011 is formed between the inner circumferential surface 05b of the sleeve 05 and the facing outer circumferential surface 03a of the rotating shaft body 03 to generate the dynamic pressure that will bear the radial load. A second dynamic pressure generating groove 012 is also formed between the lower end surface 05a of the sleeve 05 and the facing upper surface 04a of the flange part 04 to generate the dynamic pressure that will bear the axial load. A third dynamic pressure generating groove 013 is formed between the upper surface 07a of the endplate 07 and the facing lower surface 04b of the flange part 04 in order to generate the dynamic pressure that will bear the axial load. A lubricant 010 surrounds the rotating shaft 02 with the flange part 04 and fills in the pouch-shaped bearing gap.
This pouch-shaped bearing gap is formed by linking together the radial bearing gap formed between the inner circumferential surface 05b of the sleeve. 05 and the outer circumferential surface 03a of the rotating shaft body 03, the axial bearing gap formed between the lower end surface 05a of the sleeve 05 and the upper surface 04a of the flange part 04, the radial bearing gap formed between the outer circumferential surface of the flange part 04 and the inner circumferential surface of the case 06, and the axial bearing gap formed between the upper surface 07a of the endplate 07 and the lower surface 04b of the flange part 04.
Accordingly, when the rotating shaft 02 rotates, said rotating shaft 02 is supported by the radial and axial fluid dynamic pressure created by the radial dynamic pressure generating grooves 011 and axial dynamic pressure generating grooves 012, 013, and it rotates without contacting the inner circumferential surface 05b of the sleeve 05, the lower end surface 05a of the sleeve 05, the inner circumferential surface of the case 06, or the upper surface 07a of the endplate 07.
Furthermore, in cases where the fluid dynamic pressure bearing 01 has a flange part 04 attached to the other end (the upper end in
A spacer 08 is provided between the lower surface 05a of the sleeve 05 and the bottom surface 06a of the cup-shaped case 06. A fixed space between the lower surface 05a of the sleeve 05 and the bottom surface 06a of the cup-shaped case 06 is provided via this spacer 08, and this maintains the bearing gap adjacent to the upper and lower surfaces of the flange part 04. The remaining features of the example of
All of the main components of the conventional examples above are manufactured by precision machine processing mainly consisting of turning and polishing. Precision machine tools and machining technology is necessary to carry out this precision processing. Also, the machining time required for precision processing presents a problem for mass production. Manufacturing of the cup-shaped case 06 in particular requires long machining time.
Furthermore, there is a problem with the adhesive fastening (
The present invention solves the problems found in the conventional fluid dynamic pressure bearings as described above and reduces unnecessary work such as removal of the adhesive from areas outside the prescribed filling site by preventing the adhesive from adhering to the inner circumferential surface and other areas outside the prescribed filling site, and by preventing the adhesive from flowing out before it hardens completely. In addition, this invention provides a fluid dynamic pressure bearing having a structure that makes it possible to reduce the manufacturing steps required by precision machine processing of the case, which is one of the important components of the fluid dynamic pressure bearing. In this way, the quality of the bearing can be maintained while improving mass production in the manufacturing and achieving much lower costs.
The present invention provides a fluid dynamic pressure bearing wherein free rotation of a rotating shaft having a flange part on one end (the lower end) is supported via radial microgaps between the shaft and the sleeve having radial dynamic pressure generating grooves on the inner circumference. The flange part is inserted and held sandwiched between the lower end surface of said sleeve where thrust dynamic pressure generating grooves are formed and the upper surface of the endplate where additional thrust dynamic pressure generating grooves are formed. The lower end surface of said sleeve and the upper surface of said flange part, and the upper surface of said endplate and the lower surface of said flange part are respectively made to oppose each other via thrust microgaps. The endplate is fixed onto the lower end part of a case. The upper end surface of the sleeve projects out from the upper end surface of said case. A first reservoir for an adhesive is formed between the case and the sleeve in a position facing the upper end part of said case. The outer circumferential surface of said sleeve is attached onto the inner circumferential surface of the case by the adhesive filling the first reservoir.
Another embodiment of the present invention provides a fluid dynamic pressure bearing wherein free rotation of a rotating shaft having a flange part on another end (the upper end) is supported via radial microgaps next to the sleeve having radial dynamic pressure generating grooves on the inner circumferential surface. The flange part is placed on the upper end surface of the sleeve where thrust dynamic pressure generating grooves are formed. The upper end surface of said sleeve and the lower surface of said flange part oppose each other via thrust microgaps. The upper end surface of said sleeve projects out from the upper end surface of a case. A first reservoir for an adhesive is formed between the case and the sleeve in a position facing the upper end part of the case, and the outer circumferential surface of said sleeve is attached to the inner circumferential surface of said case by the adhesive filling the first reservoir.
When the sleeve is fastened to the case by the adhesive, the outer circumferential surface of the sleeve which projects out from the upper end surface of the case is attached to the upper end part of the case by the adhesive filling the first reservoir. Because of this, it is possible to prevent the adhesive from getting into the inner circumferential surface of the sleeve and adhering to the inner circumferential surface of the sleeve and other areas outside of the prescribed filling site during the filling of the adhesive. The adhesive no longer discharges onto the outer parts before it has completely set due to handling posture or external force, and it is possible to reduce unnecessary work such as removal of the adhesive that has discharged or adhered in an area outside the prescribed filling site. This effect becomes more and more striking as the radial distance between the injection site of the adhesive and the inner circumferential edge of the sleeve becomes smaller, and particularly accompanies the miniaturization of fluid dynamic pressure bearings.
Also, since the axial length of the case is shortened, it is easier to manufacture the case by machining, tube rolling or press processing. The manufacture of the fluid dynamic pressure bearing requires fewer materials, and mass production of the fluid dynamic pressure bearings at lower costs is made possible.
In another embodiment, the upper end part of the case is diametrically expanded, forming a diametrically expanded upper end part. By forming the first reservoir of the adhesive between this diametrically expanded upper end part and the outer circumferential surface of the sleeve, the process of filling is made easier.
This way, during the adhesive filling time, the adhesive is securely retained in the first reservoir formed between the diametrically expanded upper end part of the case and the outer circumferential surface of the sleeve. Not only is adhesion prevented outside this prescribed filling site, but also during the state before the adhesive is completely set, the adhesive no longer discharges to outer areas due to handling posture or from external force, and it is possible to reduce unnecessary work such as removal of adhesive that has discharged or adhered in areas outside the prescribed filling site. Furthermore, the outer circumferential surface of the sleeve is reliably fixed to the inner circumferential surface of the case and the mating gap between the two is completely sealed with adhesive.
In another embodiment, a seal cover that is fitted onto and covers the outer circumferential surface part of the sleeve that projects out from the upper end surface of the case. A second reservoir for an adhesive is formed between the seal cover and the sleeve in a position facing the lower end part of the seal cover. The inner circumferential surface of the seal cover is fixed to the outer circumferential surface of the sleeve by the adhesive filling said second reservoir.
In this way, the outer part of the aperture end of the bearing is sealed, preventing contamination of the bearing part. Also, since the inner circumferential surface of the seal cover is fixed to the outer circumferential surface of the sleeve by the adhesive filling the second reservoir, it is possible to prevent the adhesive from adhering to the inner circumferential surface of the sleeve and other areas outside the prescribed filling site by penetrating into the upper surface of the seal cover and the inner circumferential surface of the sleeve. Also, the adhesive no longer discharges onto the outer parts before it has completely set due to the handling posture or external force, and it is possible to reduce unnecessary work such as removal of the adhesive that has discharged or adhered in an area outside the prescribed filling point.
By selecting appropriate viscosity of the adhesive for filling the mating gap formed between the outer circumferential surface of the sleeve and the inner circumferential surface of the case, the mating gap can be filled in an airtight and secure manner by the adhesive filling the reservoir, which passes over the whole area of the outer circumferential surface of the sleeve and the inner circumferential surface of the case due to the capillary phenomenon. The sleeve is thus fixed securely to the case by the adhesive, and it is thus possible to reliably prevent the lubricant that fills the bearing gap from leaking out onto the outer parts via said mating gap.
Also, since the axial length of the case is shortened, the manufacturing by machining or press processing becomes easier, requires fewer materials, and mass producibility of the fluid dynamic pressure bearings is improved achieving a lower manufacturing costs. Particularly in cases where the case is formed by plastic work like press processing or tube rolling, it is possible to reduce the manufacturing steps required by the precision machining process of the case. Furthermore, the quality can be maintained, and improved mass producibility and much lower costs can be achieved.
Further features and advantages will appear more clearly on a reading of the detailed description, which is given below by way of example only and with reference to the accompanying drawings wherein corresponding reference characters on different drawings indicate corresponding parts.
The endplate 7 is fitted into the lower end part of the case 6, and its lower edge is fixed to inner circumferential surface of the lower end part of the case 6 by an adhesive 21. Also, the upper end surface 5b of the sleeve 5 projects out from the upper end surface of the case 6 when the sleeve is fitted into the case 6. The type of fitting between the sleeve 5 and case 6 may be an interference fit, a clearance fit or a transition fit. In the case of a transition fit, either a clearance or an interference may result when mating parts are assembled depending upon the actual manufactured dimensions of the mating parts.
The circumferential grooves 15 for filling with adhesive are formed in a depressed manner on the outer circumferential surface 5c of the sleeve 5. An adhesive 16 fills the adhesive reservoir (the first reservoir) formed between these circumferential grooves 15 and the inner circumferential surface of the upper end part of the case 6. Adhesive 16 is securely retained in the reservoir and the outer circumferential surface 5c of the sleeve 5 is fixed to the inner circumferential surface of the case 6 by the adhesive 16.
When the sleeve 5 is fastened onto the case 6 by the adhesive 16 using the manner of fastening as described above, it is possible to prevent the adhesive 16 from adhering on the inner circumferential surface of the sleeve 5 and other areas outside the prescribed filling site during the adhesive filling time. Also, during the state before the adhesive is completely set, the adhesive no longer discharges to outer areas due to handling or from external force and it is possible to reduce unnecessary work such as removal of adhesive that has discharged or adhered in areas outside the prescribed filling site.
When the sleeve 5 is inserted into the case 6 by an clearance fit or by transition fit, it is slidable relative to the case 6 and the sleeve 5 is aligned with high precision in the axial direction relative to the case 6 by applying an appropriate load in the axial direction at an arbitrary one end of the sleeve 5 and fixing in the case 6 by the adhesive 16. This is very important issue to achieve a stable and highly efficient mass production of fluid dynamic pressure bearings 1 while maintaining the perpendicularity and the concentricity of the sleeve 5 and the case 6 relative to the axial center of the fluid dynamic pressure bearing 1, the parallelism between the sleeve 5 and the case 6, and the flatness of the sleeve end surface within the desired accuracy. When inserting the sleeve 5 in the case 6, it is also effective in making assembly easier and minimizing deviations in dimensional and geometrical accuracy (dimensions of inner diameter, roundness, etc.) due to press fitting on the sleeve 5 inner peripheral face even if deformation of the sleeve 5 occurs easily due to thin thickness in the radial direction.
In this case, when a viscosity of the adhesive 16 for filling the adhesive reservoir is appropriately selected, the adhesive travels by the capillary phenomenon over the whole area of the mating gap formed between the outer circumferential surface 5c of the sleeve 5 and the inner circumferential surface 6 of the case. After the adhesive has set completely, the outer circumferential surface 5c of the sleeve 5 and the inner circumferential surface of the case 6 are fastened together in a secure and airtight manner by the adhesive passing over the whole circumference. The seal function of said mating gap is thus reliably ensured and it is possible to reliably prevent the lubricant filling the bearing gap from leaking out onto the outer part via said mating gap.
The case 6 is formed of either steel, stainless steel, or other, non-ferrous alloys by press processing or tube rolling. Although the wall thickness of the case 6 is considerably thinner than the case in the conventional fluid dynamic pressure bearings, processing is easy because the axial length is shorter than in conventional models. Consequently, manufacturing the case 6 by the aforementioned processing method is easy, and the manufacturing costs associated with conventional precision machine processing can be reduced. Moreover, since the quality can be maintained, and the cost of materials can be curtailed, the ability to mass-produce and manufacture the fluid dynamic pressure bearings can be boosted, and lower costs can be achieved.
In the fluid dynamic pressure bearing 1 of this second embodiment, the upper end part of the case 6 is diametrically expanded, forming the diametrically expanded upper part 22. The expanded upper part 22 is easier to form as compared to circumferential grooves of the first embodiment. The space formed between this diametrically expanded upper end part 22 and the outer circumferential surface 5c of the sleeve 5 is filled by the adhesive 16 to achieve the same effects as in the first embodiment.
The positioning component 8 allows accurate positioning of the sleeve 5 that is fitted in the case 6. This in turn allows forming accurately the prescribed size of the bearing gap between the upper surface 4a of the flange part 4 and the lower end surface 5a of the sleeve 5, and between the lower surface 4b of the flange part 4 and the upper surface 7a of the endplate 7.
The seal cover 9 is a cap component whose shape combines a disc part and a cylinder part. The disc part has a stepped composition with a large diameter part and a small diameter part, and there is a hole in the center part that the body of the rotating shaft 3 passes through. This seal cover 9 is inserted on the shaft body 3 without coming into contact with it. Also, the open end of the bearing is sealed on the outside, preventing contamination of the bearing.
The lower end part of the seal cover 9 fixed to the outer circumferential surface 5c of the sleeve 5 by an adhesive 17 filling the adhesive reservoir (the second reservoir) formed between said lower end part and the circumferential groove 15′ formed on the outer circumferential surface 5c of the sleeve 5. The circumferential groove 15′ including the first and the second reservoirs is formed by slightly extending the width of the circumferential groove 15 in Embodiment 1.
In this manner, since the lower end part of the seal cover 9 is fixed onto the outer circumferential surface 5c of the sleeve 5 by the adhesive 17 filling the second reservoir, it is possible to prevent the adhesive 17 from adhering to areas outside of the prescribed filling site during the adhesive filling. The adhesive 17 no longer discharges onto the outer parts before it has completely set due to handling or external force, and it is possible to reduce unnecessary work such as removal of the adhesive, which has discharged or adhered in an area outside the prescribed filling site. Also, the two reservoirs (the first and second reservoirs) of the adhesive are both formed in the same groove on the outer circumferential surface 5c of the sleeve 5, and are provided so that they mutually approach each other. Due to their proximity, the injection of the adhesive in the first and second reservoir can be done at the same time to increase the manufacturing efficiency for fluid dynamic pressure bearing 1.
In contrast with the seal cover 9 of Embodiment 4, the seal cover 9′ differs in regard to the lower end part of the seal cover 9′, which is diametrically expanded, forming a diametrically expanded lower end part 23. As a result the second reservoir of the adhesive in Embodiment 5 is formed between this diametrically expanded lower end part 23 and the outer circumferential surface 5c of the sleeve 5. Said second reservoir has the same shape as the first reservoir, and it is desirable that the two are made to approach and face each other. The diametrically expanded lower end part 23 is formed in place of circumferential groove 15′ of embodiment 4.
Since the effects of fitting of this seal cover 9′ are roughly the same as in Embodiment 4, and since the other results and aspects of its composition are the same as in Embodiment 2, a more detailed explanation has been omitted.
The seal cover 9 covers the outer circumferential surface of the sleeve 5 that extends from the upper end surface of the case 6. The seal cover 9 covers the portion of the upper surface of the flange part 4′ including at least the area in the vicinity of the outer circumferential edge of flange part 4′. Microgaps are provided between the seal cover 9 and the flange part 4′. The flange part 4′ smoothly rotates relative to the seal cover 9. The seal cover 9 restricts the upward movement of the area in the vicinity of the outer circumferential edge of the flange part 4′, retaining the rotating shaft 2, as well as seals the lubricant that fills the thrust dynamic pressure generating region and the radial dynamic pressure generating region. Furthermore, although in the present embodiment the endplate 7 is fitted on the lower end part of the tube-shaped case 6 so that it blocks the bottom end of the sleeve 5, a cup-shaped case 6 can be formed by press processing, making it possible to omit the endplate 7. Although this sixth embodiment differs in the aforementioned ways from Embodiment 4 (see
As shown in
The case 6 of the fluid dynamic pressure bearing 1 is installed on the inner peripheral face of the boss portion 32. A thermosetting adhesive is used in order to prevent the formation of a gap between the outer surface of case 6 and the inner surface of the boss portion 32.
The rotor 34 contains a rotor hub 35 installed at the upper end portion of the rotary shaft 2 and a rotor magnet 37 that is installed on the inner peripheral face of the outer peripheral cylinder portion of the rotor hub 35 via a yoke 36. Rotor magnet 37 generates a rotary magnetic field in coordination with the stator 33. The spindle motor 30 of Embodiment 8 is an outer rotor type motor, but it is not limited to this.
In the middle step portion of the rotor hub 35, multiple screw holes 38 are formed in the axial direction and as will be described later, a clamp member 43 is screwed in the screw holes 38 to fix a hard disk 42. Although it is not illustrated, a flexible wiring circuit board is fixed on the spindle motor 30 and a control current is supplied from the output terminal of the wiring circuit board to the coil in the stator 33 in order to start rotating the rotor assembly (rotor) 34 consisting of a rotor hub 35, a yoke 36 and a rotor magnet 37 and a rotary shaft 2 relative to the stator 33.
In the spindle motor 30 of Embodiment 8, the rotor 34 is stably supported in a non-contact state relative to each bearing surface (inner surface of sleeve 5, lower end surface 5a of the sleeve 5, upper surface 7a of the endplate 7, see
Since the spindle motor 30 of Embodiment 8 has the said configuration, the adhesive does not adhere or flow to the locations other than the specified locations to be filled at the time of assembly of the fluid dynamic pressure bearing 1, and does not contaminate the motor or does not enter into the interior of the bearing so that high precision rotation is not affected and highly reliable spindle motor 30 can be mass produced at a low cost.
A spindle motor 30 is fixed in the housing 41 by screwing installation screws 48 through the multiple through-holes made in the frame 31. The housing 41 is clamped during installation of motor 30. In this way, a main body portion containing a stator 33 and a rotor 34 of the spindle motor 30 is placed inside of the box of the hard disk drive unit 40. As a modification example, a single component housing can be formed by integration of the frame 31 with the housing 41 and the housing can have a structure such that it becomes at the same time a part of the spindle motor and a part of the box of the hard disk drive unit 40.
On the outer peripheral face of the middle cylindrical portion of the rotor hub 35, two sheets of hard disk 42 (recording disks) are installed. The hard disk 42 is fixed at the rotor hub 35 via the clamp 43 by screwing installation screws 49 into multiple screw holes in the middle step of the rotor hub 35. As a result, the hard disk 42 rotates integrally along with the rotor hub 35. In the example shown in
The hard disk drive unit 40 comprises of a magnetic head (recording head) to write and read information for the hard disk 42. A magnetic head 44, an arm 45 for supporting the magnetic head 44 via suspension, and a voice coil motor 46 that moves the magnetic head 44 and the arm 45 to the desirable positions are included in the hard disk drive unit 40. The voice coil motor 46 contains a coil 46a and a magnet 46b facing the coil 46a.
A magnetic head 44 is installed at the tip of the suspension fixed on the arm 45 which is supported rotatably at appropriate positions in the housing 41. A pair of magnetic heads 44 is used for each hard disk so that information can be written or read on both sides of the hard disk 42. In the example shown in
Since the hard disk drive unit 40 of Example of Embodiment 9 has such a configuration described above, the adhesive does not adhere or flow to the locations other than the specified locations to be filled and does not contaminate the interior of the unit during the assembly of the fluid dynamic pressure bearing 1, allowing mass production of a highly reliable hard disk drive unit 40 at a low cost.
In Embodiment 9, a spindle motor 30 is used in the hard disk drive unit 40, but the use of the spindle motor 30 is not limited to this. For example, the hard disk drive unit 40 can be replaced by a recording disk drive unit using optical recording disks such as CDs and DVDs while replacing magnetic head 44 with an optical head. In this case, the same effects can be achieved.
The present invention is not limited to the examples listed above and can be modified in the range not exceeding the objective of the invention. For example, in Examples of Embodiment 1 through 9, the fluid dynamic pressure bearing 1 was assumed to be all the axially rotary type, but the invention is equally applicable to an axially fixed type bearing. In the spindle motor using an axially fixed fluid dynamic pressure bearing, the rotary shaft 2 is fixed in the frame 31 and becomes a fixed shaft and the rotary hub 35 is installed on the case 6. Other configurations of the spindle motor are not basically different from the configuration of the spindle motor 30 of Embodiment 8 and are clear to those in the art so that detailed explanations will be omitted. Various modifications apparent to one skilled in the art are intended to fall within the scope of the appended claims.
Number | Date | Country | Kind |
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2004-174866 | Jun 2004 | JP | national |
2005-141974 | May 2005 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US05/20321 | 6/9/2005 | WO | 00 | 12/11/2006 |