Abstract:
A disk drive unit has a spindle motor for rotating a disk, a magnetic head for processing data, a actuator for seeking the magnetic head with respect to the disk, a voice coil motor for moving the actuator, and a base with an opening and a top cover that seals the opening. A damper is disposed between the voice coil motor and the top cover. The voice coil motor comprises first and second yokes, which are placed opposite each other at a predetermined gap, and a permanent magnet disposed between the first and second yokes. The first and second yokes respectively have an inner perimeter edge facing the pivot axis, an outer perimeter edge facing the base, and a pair of side perimeter edges combining the outer and inner perimeter edges. The damper includes first dampers with a predetermined width along the pair of side perimeter edges.

Description:
[0001]    This application claims the priority of Japanese Patent No. JP2001-343823 (IEBM Docket No. JP920010346JP1), filed on Nov. 8, 2001, and entitled “Disk Drive Unit, Motor Device, and Damper”.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Technical Field  
           [0003]    The present invention relates in general to a disk drive unit and, in particular, to system and method for constraining vibration in a hard disk drive.  
           [0004]    2. Description of the Related Art  
           [0005]    A hard disk drive (hereinafter, a HDD), which is most commonly used as data storage means for computers, comprises a single or multiple magnetic disks on the same shaft, which is rotated by a spindle motor. Reading and writing of data is performed by a magnetic head placed facing the magnetic disk, wherein the magnetic head is driven by an actuator, which is commonly a voice coil motor (hereinafter, a VCM). The magnetic disk, magnetic head and actuator are accommodated in a chassis called disk enclosure. The disk enclosure is composed of a thin box-shaped aluminum alloy base and a top cover for sealing an opening of the base.  
           [0006]    Major technical problems for HDDs include increasing the storage capacity per magnetic disk and increasing the speed of reading data from and writing to the magnetic disk, etc. Concerning the latter, the speed for reading and writing data can be improved by reducing the seek time necessary for the magnetic head to move to a desired track on the magnetic disk. Since the magnetic head is driven by the VCM as described above, the seek speed can be increased by improving the performance of the VCM. In order to improve the performance of the VCM, it may be necessary to increase the magnetic property of the permanent magnet of the VCM or to increase the thickness of the magnet to increase the magnetic field applied to the voice coil. However, the magnetic property of the permanent magnet has been approaching its limit. Besides, it is difficult to increase the thickness of the permanent magnet than at present since the space-saving is strongly required for HDDs. Alternatively, the speed for reading and writing data can be increased by increasing the speed of rotation of the magnetic disk. However, this may cause the problem of acoustic noise or vibrations.  
           [0007]    In the prior art, various countermeasures have been made to overcome acoustic noise and vibrations. For example, Japanese Published Unexamined Patent Application (PUPA) No. 2001-43658 discloses a structure where an adherent visco-elastic material is inserted into a gap between a fixed shaft of the spindle motor and a top cover or a gap between an upper yoke of the VCM and the top cover, etc. Also, PUPA No. 1996-167259 and PUPA No. 1997-213029 disclose structures where an adherent visco-elastic material is inserted between an upper yoke of the VCM and a top cover.  
           [0008]    3. Problems to be Solved by the Invention  
           [0009]    The prior art references described above show that the VCM has a significant influence on acoustic noise or vibrations in HDDs. Unfortunately, in spite of the countermeasures described above, the acoustic noise or vibrations are remarkable at the seek time of the magnetic head. Therefore, it is an object of the present invention to further decrease acoustic noise or vibrations of HDDs.  
         SUMMARY OF THE INVENTION  
         [0010]    The present inventor measured the acoustic level at the seek time for HDD  100  at respective points on the top cover. The results are shown in FIG. 10. In FIG. 10, the acoustic noise is shown by means of shading level where the darker the color is, the higher the acoustic level is. Focusing on the vicinity of VCM  200 , it is seen that the acoustic level is great around the perimeter of VCM  200  while it is small at the center of VCM  200 . This acoustic level is to be regarded as actual vibrations of the top cover. Thus, according to the present invention, a damper is provided along the portions where the vibration is great, i.e., the peak points of vibration. As a result, the acoustic level can be reduced compared with using the damper that covers the whole VCM  200 , as described later.  
           [0011]    According to the present invention, a disk drive unit comprises a disk storage medium for storing data; a spindle motor for rotating the disk storage medium; a magnetic head for storing and reproducing data from the disk storage medium; a rotary actuator for seeking the magnetic head with respect to the disk storage medium and rotating on a pivot axis; a voice coil motor for rotatably moving the rotary actuator; a disk enclosure for accommodating the disk storage medium, the spindle motor, the rotary actuator and the voice coil motor and which is comprised of a box-shaped base with an opening and a top cover that seals the opening; and a damper disposed between the voice coil motor and the top cover. The voice coil motor comprises a first yoke (generally an upper yoke) and a second yoke (generally a lower yoke), which are placed opposite each other at a predetermined gap; and a permanent magnet disposed between the first and second yokes, wherein the first and second yokes respectively comprise an inner perimeter edge facing the pivot axis, an outer perimeter edge facing the base, and a pair of side perimeter edges combining the outer and inner perimeter edges, and wherein the damper comprises first dampers with a predetermined width along the pair of side perimeter edges.  
           [0012]    As shown in FIG. 10, the acoustic level in the vicinity of VCM  200  is higher along the side perimeter edge  201  of VCM  200  (first yoke). The present invention provides the first dampers at this portion corresponding to the higher acoustic level. Also as shown in FIG. 10, the acoustic level is higher along the inner perimeter edge  202  of VCM  200 . Accordingly, it is desirable in the disk drive unit of the invention to further provide a second damper with a predetermined width along the inner perimeter edge of the first yoke, the second damper stretching from the first dampers. Furthermore, as seen from FIG. 10, at the outer perimeter edge  203  of VCM  200  (first yoke) is the acoustic level high. Thus, it is also desirable in the disk drive unit of the invention to provide a third damper with a predetermined width along the outer perimeter edge of the first yoke, the third damper stretching from the first dampers.  
           [0013]    In the disk drive unit of the invention, an air gap is formed between the first yoke and the top cover except for regions where the damper is inserted. As described below, the damper covering the entire first yoke has a poor vibration damping capacity compared to the preferred embodiment of the invention where the air gap is formed between the first yoke and the top cover except for the regions where the damper is inserted. The vibration damping capacity can be thoroughly improved by measuring the actual acoustic level and specifying regions where the damper is to be provided based on the results of the measurements.  
           [0014]    For the disk drive unit of the invention, the material of the dampers is not essentially limited. However, for disk drive units for which high cleanness is internally required, a fluorine rubber is preferably used due to its less likelihood of contamination. The dampers of the invention are disposed between the top cover and the first yoke, which causes the dampers to be compressed. Fluorine rubber decreases its vibration damping capacity when being compressed to be deformed. Therefore, when being disposed between the top cover and the first yoke, the damper, especially that made of fluorine rubber, is preferably not to be compressed significantly. However, due to the dimensional tolerances in manufacturing of the top cover and base, it is feared that the damper is significantly compressed. In view of this, the damper of the invention desirably comprises a sheet-shaped base and multiple protrusions formed on this base. When the damper is disposed between the top cover and the first yoke, these protrusions are exclusively compressed to be deformed since their strength is weaker than that of the sheet-shaped base. On the other hand, when being disposed between the top cover and the first yoke, the sheet-shaped base exerts its vibration damping capacity since its deformation degree is smaller than that of the protrusions.  
           [0015]    Hereinabove, there has been described about the disk drive unit including hard disk drives, in which the present invention is applied. However, application of the present invention is not limited only to disk drive units but would be universally extended to devices that have a voice coil motor. Namely, the present invention may be applied to a motor device which comprises an actuator rotating on an axis of rotation; a voice coil motor for driving the actuator; and a chassis for accommodating the actuator and the voice coil motor. For this motor device, the voice coil motor is configured such that it is in a constrained relationship at its perimeter edges with the chassis while being in an unconstrained relationship with the chassis at its central region surrounded by the perimeter edges.  
           [0016]    As described later, the optimum configuration for excellent vibration damping capacity is to dispose a continuous damper capable of constraining the perimeter edges of the voice coil motor between the voice coil motor and the top cover. Therefore, the motor device of the invention is configured such that the voice coil motor is in a constrained relationship at its perimeter edges with the chassis while the region surrounded by the perimeter edges is in an unconstrained relationship with the chassis.  
           [0017]    The motor device of the invention provides for the constrained condition by disposing a vibration damping member between the voice coil motor and the chassis. This vibration damping member is preferably made of fluorine rubber and has a multilayer structure comprising a portion with relatively small compressibility and a portion with relatively large compressibility. The portion with relatively small compressibility is exclusively responsible for vibration damping when lying between the voice coil motor and the chassis. On the other hand, the portion with relatively large compressibility is exclusively compressed to be deformed when lying between the voice coil motor and the chassis.  
           [0018]    The portion with relatively large compressibility may be composed of a member whose density is lower than that of the portion with relatively small compressibility. The collection of protrusions mentioned above is lower in density than the contents of the rubber member. Alternatively, the vibration damping member, which is composed of the base and the protrusions, may have a multilayer structure comprising a portion with a relatively small cross-sectional area and a portion with a relatively large cross-sectional area. Moreover, the vibration damping member of the invention may be composed of a combination of fluorine rubbers whose density differs.  
           [0019]    The vibration damping member should lie in the chassis between a portion with less thickness than the other portion and the voice coil motor in order to achieve an object of the invention, i.e., to decrease vibrations of the chassis due to driving of the voice coil motor since the portion with less thickness is likely to vibrate.  
           [0020]    The present invention proposes a following damper that is effective for use in disk drive units and motor devices mentioned above. This damper is held tight between a source of vibrations and a vibrating member due to this source of vibrations. The damper comprises contents of a sheet-shaped base and multiple protrusions formed on a surface of this base.  
           [0021]    The damper of the invention is preferably made of fluorine rubber because it provides for a predetermined damping capacity and is unlikely to cause contamination compared to other rubbers.  
           [0022]    The damper of the invention is held tight between the source of vibrations and the vibrating member, wherein the sheet-shaped base is exclusively responsible for vibration damping when the source of vibrations is causing vibration. On the other hand, the protrusions are exclusively compressed to be deformed when the damper is held tight between the source of vibrations and the vibrating member.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a perspective view of a disk enclosure for a hard disk drive according to one embodiment of the invention.  
         [0024]    [0024]FIG. 2 is a perspective view showing the inside of a hard disk drive according to the embodiment of the invention.  
         [0025]    [0025]FIG. 3 is a side view of a damper according to the embodiment of the invention.  
         [0026]    [0026]FIG. 4 is a side view of a damper according to the embodiment of the invention being compressed to be deformed.  
         [0027]    [0027]FIG. 5 shows the results of sound power measured over the respective frequency bands when the seek operation was performed using hard disk drives with and without a damper.  
         [0028]    FIGS.  6 A- 6 F depict top plan views of various shapes of dampers prepared to confirm the effects of the present invention.  
         [0029]    [0029]FIG. 7 shows the results of sound power measured over the respective frequency bands when the seek operation was performed using hard disk drives with various shapes of dampers.  
         [0030]    [0030]FIG. 8 shows the results of sound power measured over the respective frequency bands when the seek operation was performed using hard disk drives with various shapes of dampers.  
         [0031]    [0031]FIG. 9 shows the results of sound power measured over the respective frequency bands when the seek operation was performed using hard disk drives with various thickness of dampers.  
         [0032]    [0032]FIG. 10 depicts measured results of the acoustic level at the seek time for HDD at respective points on the top cover.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]    As shown in FIG. 1, a hard disk drive (HDD)  10  comprises a disk enclosure  16  which is comprises of a box-type base  12  with a thin bottom made of aluminum alloy and a top cover  14  that covers an opening of the base  12 . Disk enclosure  16  has a form factor of  3 . 5  inch in size. The top cover  14  is screwed to base  12  through a rectangular frame-like seal member (not shown), thus it is airproofed inside disk enclosure  16 .  
         [0034]    There is provided in disk enclosure  16  a spindle motor  18  with a hub-in structure in nearly the center of the base  12 , as shown in FIG. 2. It is noted that top cover  14  is removed in FIG. 2. On the top surface of the hub (not shown) of spindle motor  18 , there are provided magnetic disks  22  made of glass or aluminum substrates coaxially in lamination through spacers (not shown) and are secured by means of top cramps  26 .  
         [0035]    Also provided in disk enclosure  16  are actuators  28 , each of which has a magnetic head  30  for reading and writing data at one end and whose intermediate part is supported on base  12  through a pivot axis  32 , whereby the actuators  28  can be rotated on pivot axis  32 . At the other end of actuators  28  are provided coils for a voice coil motor (VCM)  36 , wherein actuators are turned by VCM  36  which is provided in disk enclosure  16  to cooperate with the VCM coils. As is well known in the art, VCM  36  comprises an upper yoke (first yoke)  36   a , a lower yoke (not shown), and a pair of permanent magnets disposed between upper yoke  36   a  and lower yoke. This pair of permanent magnets are spaced apart at a predetermined gap, wherein the magnetic field generated in this gap acts on the VCM coil mounted on actuator  28  to move it.  
         [0036]    On the outer surface (under surface) of base  12  is attached a card for circuit board (not shown), which is rectangular and covers half of the outer surface of base  12 . There are transmitted electric power for driving the motor and control signals between the card and spindle motor  18  while a motive energy for VCM coils and electric power and control signals for read/write operation of magnetic heads  30  are transmitted between the card and actuators  28 . Connections between the card and actuators  28  are achieved using flexible cables (FPC).  
         [0037]    HDD  10  of the embodiment is a disk drive unit called head load/unload type of disk drive unit. This head load/unload type HDD is the one where actuators  28  are held on a ramp block  40  when not operating, whereby the magnetic head  30  is unloaded in a position for evacuation not in contact with the surface of magnetic disk  22 . Upon operation, actuator  28  is driven so that magnetic head  30  seeks over magnetic disk  22 .  
         [0038]    As shown in FIG. 2, a damper  42  is disposed between VCM  36  and top cover  14  of HDD  10 . Upper yoke  36   a  of VCM  36  comprises an inner perimeter edge  36   a   1  facing the pivot axis  32 , an outer perimeter edge  36   a   2  facing the side wall of base  12 , and a pair of side perimeter edges  36   a   3  combining inner perimeter edge  36   a   1  and outer perimeter edge  36   a   2 . On the other hand, damper  42  comprises first dampers  42   a  along the pair of side perimeter edges, which are strip-shaped with a predetermined width. Furthermore, damper  42  comprises a second damper  42   b  with a predetermined width along the inner perimeter edge  36   a   1  of the upper yoke  36   a , the second damper stretching from the first damper  42   a . Moreover, damper  42  comprises a third damper  42   c  with a predetermined width along the outer perimeter edge  36   a   2  of upper yoke  36   a , the third damper stretching from the first dampers. As shown in FIG. 2, the first dampers  42   a , second damper  42   b  and third damper  42   c  are integrated. The perimeter form of damper  42  is quite similar to that of upper yoke  36   a . When first dampers  42   a  are disposed between upper yoke  36   a  and top cover  14 , upper yoke  36   a , i.e., the perimeter edges of VCM  36  are in a constrained relationship with top cover  14 . However, as for the central region surrounded by these perimeter edges, there is formed an air gap between top cover  14  and upper yoke  36   a , wherein upper yoke  36   a , i.e., VCM  36   a  is in an unconstrained relationship with top cover  14 .  
         [0039]    Damper  42  is made of fluorine rubber. HDD  10  requires quite high cleanness internally. Fluorine rubber discharges a quite small amount of contaminants even for a long use compared to urethane rubber, for example, thus it was employed in the embodiment of the invention. However, the present invention does not intend to limit the material for damper  42  only to fluorine rubber while it is preferably used.  
         [0040]    [0040]FIG. 3 depicts a side view of damper  42 . Damper  42  is composed of a sheet-shaped base  421  and multiple hemispheric protrusions  422  formed on the surface of base  421 . On the backside of base  42  is provided an adhesive tape  423  which is used to attach damper  42  to upper yoke  36   a  or top cover  14 . Protrusions  422  are formed integral with base  421  by injection molding, for example. The reason why damper  42  is composed in such a bi-layer structure is the following.  
         [0041]    Damper  42  is disposed between upper yoke  36   a  and top cover  14 . At this time, damper  42  is compressed to be deformed. This deformation due to compression is essential for holding damper  42  tightly. On the other hand, there may exist dimensional tolerances in manufacturing of base  12  on which VCM  36  is mounted and top cover  14 . Since base  12  is manufactured by casting and top cover  14  is made of sheet metal, there is a limit to reducing those dimensional tolerances. Accordingly, there may occur individual differences for amounts of deformation of damper  42 . Major concerns about this would be that the vibration damping capacity decreases when the amount of deformation increases. As a result, the amount of deformation may increase for some of HDDs  10 , whereby a sufficient damping capacity can not be obtained.  
         [0042]    The purpose of composing damper  42  of the embodiment in bi-layer structure as shown in FIG. 3 is to constrain a decrease in the damping capacity due to compression of damper  42 . Now there will be described about this function with reference to FIG. 4. FIG. 4 depicts that damper  42  is compressed to be deformed when disposed between upper yoke  36   a  and top cover  14 .  
         [0043]    Damper  42  is composed of a sheet-shaped base  421  and multiple hemispheric protrusions  422  formed on the surface of base  421 . Since protrusions  422  has lower rigidity than base  421 , protrusions  422  are compressed and deformed in preference to base  421  when damper  42  suffers a load to be compressed. Namely, base  421  has a relatively small compressibility while protrusions  422  have a relatively high compressibility. Since the amount of deformation of base  421  is small, its decrease of vibration damping capacity is constrained. As mentioned above, the sheet-shaped base  421  is exclusively responsible for vibration damping when damper  42  is held tight between upper yoke  36   a  and top cover  14 . On the other hand, protrusions  422  are exclusively compressed to be deformed when damper  42  is held tight between upper yoke  36   a  and top cover  14 .  
         [0044]    For damper  42  in the embodiment described above, protrusions  422  are formed integral with base  421 . However, the present invention need only have a portion which is exclusively responsible for vibration damping and a portion which is exclusively compressed to be deformed due to its being held tight. Embodiments satisfying such conditions include that in which a layer with a smaller cross-sectional area than that of base  421  is laminated on base  421  or that in which fluorine rubber that is easily compressed to be deformed due to its lower density than base  421  is laminated on base  421 . It is noted that the lamination is not limited to the case where they are formed integrally. What is only needed is that the laminated structure is formed such that the damper is disposed between upper yoke  26   a  and top cover  14 .  
         [0045]    In order to confirm the effects of damper  42  according to the embodiment of the invention, we measured sound power over the respective frequency bands when the seek operation was performed using hard disk drive  10  with and without damper  42 . The results are shown in FIG. 5. As shown in FIG. 5, it is seen that in the band of  500  Hz to  8  kHz, the sound power decreases significantly with hard disk drive  10  with damper  42  according to the present invention. It is noted that the term “A-wgt” represents the results of measured sounds being weighted in terms of audible frequencies for human beings. With respect to A-wgt, hard disk drive  10  with damper  42  is 1.5 dB lower in sound power than that without damper  42 .  
         [0046]    Furthermore, we made various shapes of dampers  42  and measured sound power over the respective frequency bands in the same manner described above. Top plan views of prepared dampers  42  are shown in FIGS.  6 A- 6 F and measured results are shown in FIG. 7 and FIG. 8.  
         [0047]    Six kinds of dampers  42  are prepared, including type A through type F, as shown in FIGS.  6 A- 6 F. Dampers  42  according to the invention correspond to type A, B and E. Type A is the same type as generalized damper  42  described above. Type B is basically in the same shape as type A except for having no horn prepared in type A. Type C has a shape that corresponds to an air gap of type A and type B. Type D has the same perimeter form as type B, however, it has no air gap. Type E has a shape which lacks the third damper  42   c  of type A. Type F is composed of the second damper  42   b  and third damper  42   c  according to the embodiment of the invention.  
         [0048]    [0048]FIG. 7 and FIG. 8 shows that type A is the lowest in sound pressure followed by type E and type B in order. Comparing type C and type D, it is seen to be effective to dispose damper  42  only at portions where a peak vibration occurs. Further comparing to type F, it should be understood that it is important to provide the second damper  42   b  according to the embodiment of the invention.  
         [0049]    Then, we measured sound power over the respective frequency bands by changing the thickness of damper  42  of type A. The results are shown in FIG. 9. It is noted that dampers  42  with various thickness were obtained by fixing the thickness of protrusions  422  to 0.5 mm and changing the thickness of base  421 . Thus, the thickness shown in FIG. 9 is the total thickness of base  421  and protrusions  422 .  
         [0050]    It is seen from FIG. 9 that damping capacity decreases as the thickness of damper  42  increases. Accordingly, it is useful that damper  42  is composed of a multilayer structure including base  421  and protrusions  422 . Hereinabove, the present invention has been described with respect to HDD  10 , however, it encompasses devices containing voice coil motor  36 . As mentioned above, according to the present invention, it becomes possible to effectively reduce vibration of disk drive units or devices containing a voice coil motor.