Abstract:
Embodiments of the invention provide, in a compact magnetic disk drive, a stable structure capable of reducing self-oscillation occurring from disk spinning, while suppressing generation of dust and dirt. In one embodiment, a magnetic disk is mounted on a hub of a spindle motor. A clamp is further attached to secure the magnetic disk in position. A plurality of opening portions are formed in the clamp around an axis. A counterweight formed of an elastic material is mounted in the opening portion by being press-fitted therein. The counterweight is less likely to generate dust and dirt through friction during insertion and looseness. A gap is provided between the clamp and the hub at locations near the opening portions. The counterweight has a protruded portion on a side surface of a circular column portion. The protruded portion slides into the gap between the clamp and the hub, counteracting a tendency of the counterweight to drop out of position.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application claims priority from Japanese Patent Application No. JP2004-354078, filed Dec. 7, 2004, the entire disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates generally to a magnetic disk drive and, more particularly, to an adjustment of a rotational balance after assembly of a disk assembly.  
         [0003]     In recent years, efforts are being made to achieve a higher rotating speed of the disk in order to meet the need for an improved access performance in a 2.5-inch disk drive. Self-oscillation is involved here of the magnetic disk, arising from imbalance of a spindle motor itself or imbalance caused by eccentricity of different members of the magnetic disk after assembly. The self-oscillation tends to increase in proportion to the rotating speed of the disk to the second power. The effort made to increase the disk rotating speed in the 2.5-inch disk drive could make the self-oscillation more pronounced, resulting in inconveniences such as impaired quietness or the like.  
         [0004]     Conventionally, effort has been made to reduce the self-oscillation by improving accuracy in aligning centers of gravity when the magnetic disk or clamps for holding the magnetic disk are assembled onto a hub (motor hub) of the spindle motor.  
         [0005]     In a large-sized disk drive, approaches are taken to reduce the self-oscillation by placing a screw or driving a plastic pin as a counterweight at a position for canceling the imbalance. One patent reference is Japanese Patent Laid-open No. 2000-184678.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     There is a limit to existing accuracy in machining parts for attaching to the spindle motor, and in assembling these parts together. It is difficult to suppress appropriately, by improving this accuracy, the self-oscillation occurring in conjunction with the recent effort made to increase the rotating speed in the 2.5-inch disk drive. Further, it is difficult to adopt the arrangement of placing the screw in a compact disk drive, in which downsizing is at a premium, for the following reason. Specifically, the arrangement requires that a threaded hole be formed by machining the hub of the spindle motor. Moreover, there is a problem that fastening the screw involves generation of dust and dirt. On the other hand, the arrangement, in which the plastic pin is fitted into a hole, presents a problem, in which looseness occurs in the hole into which the pin is driven, causing dust and dirt to be generated.  
         [0007]     It is therefore a feature of the present invention to provide a magnetic disk drive having a stable structure featuring the following. Specifically, the structure can be mounted in a narrow space in a compact magnetic disk drive. The structure suppresses generation of dust and dirt. The structure can reduce self-oscillation more easily than by improving assembly accuracy. The structure is further stable during high-speed spinning.  
         [0008]     A magnetic disk drive according to an embodiment of the present invention includes a motor hub, a clamp board, a magnetic disk, and a counterweight. The clamp board serves as a sheet member mounted on the motor hub. The clamp board has opening portions passing through the sheet member. The opening portions are formed on a plurality of directional lines as viewed from a disk rotary axis. The magnetic disk is clamped by the motor hub and the clamp board. The counterweight is formed of an elastic material and mounted by being press-fitted into part of the plurality of opening portions. The clamp board is disposed by having a gap provided from the motor hub at a location near at least each of the plurality of opening portions. The counterweight includes a protruded portion on a side surface thereof. The protruded portion is to be engaged with the gap when the counterweight is mounted in the opening portion.  
         [0009]     According to the present invention, the counterweight is formed of an elastic material and designed to be press-fitted into a hole. The diameter and depth of the hole can therefore be kept small. Looseness in the hole can also be prevented. Accordingly, space saving and prevention of generation of dust and dirt can be appropriately achieved. Further, the protruded portion provided on the side of the counterweight is designed to be slid into the gap between the clamp board and the motor hub. The counterweight is therefore stably held in position in the hole, opposing to a large acceleration during high-speed spinning.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a plan view showing schematically a 2.5-inch magnetic disk drive according to an embodiment of the present invention.  
         [0011]      FIG. 2  is a plan view showing schematically a clamp.  
         [0012]      FIG. 3  is a cross sectional view showing schematically a disk assembly including a magnetic disk assembled to a spindle motor.  
         [0013]      FIG. 4  is a perspective view showing schematically a counterweight.  
         [0014]      FIG. 5  is a vertical cross sectional view showing schematically the counterweight.  
         [0015]     FIGS.  6 ( a ),  6 ( b ), and  6 ( c ) are explanatory views showing schematically a mounting method of the counterweight. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     An exemplary embodiment (hereinafter referred to as the “embodiment”) of the present invention will be described in detail with reference to the accompanying drawings.  
         [0017]      FIG. 1  is a plan view showing schematically a 2.5-inch magnetic disk drive according to the embodiment of the present invention. The magnetic disk drive includes a magnetic disk  4  in a cabinet  2 . The magnetic disk  4  is clamped between a hub of a spindle motor and a clamp (clamp plate)  6 . The magnetic disk  4  is spun at high speed around a rotary axis  8  by the spindle motor. For example, in the magnetic disk drive according to the embodiment of the present invention, the magnetic disk  4  can be spun at about 7500 rpm. The spindle motor is hidden behind the clamp  6  and not visible in  FIG. 1 . The magnetic disk  4  includes concentrically formed tracks. A magnetic head  10  is held in close proximity to a surface of the magnetic disk  4 , performing read/write operations along the track. The position of the magnetic head  10  along and relative to the track moves as the magnetic disk  4  spins. A movement (seek operation) of the magnetic head  10  across tracks is achieved by a voice coil motor  12 . Specifically, the voice coil motor  12  causes a head arm  14  to pivot about a fulcrum  16 .  
         [0018]      FIG. 2  is a plan view showing schematically the clamp. The clamp  6  is a disk having an opening portion  30  formed at a center thereof. The clamp  6  serves as a fixing tool for clamping the magnetic disk  4  mounted on the hub. Formed around the opening portion  30  are, for example, eight equally spaced opening portions  18 . A counterweight  20  to be described later is inserted into part of these opening portions  18 .  FIGS. 1 and 2  show the counterweight  20  inserted in one of these opening portions  18 .  
         [0019]      FIG. 3  is a cross sectional view showing schematically a disk assembly including the magnetic disk  4  assembled to the spindle motor.  FIG. 3  is a cross section taken in a plane passing through the rotary axis  8  and the opening portion  18 . A bearing sleeve  42  is formed integrally with a motor base  40 . The bearing sleeve  42  has a cylindrical shape formed about the rotary axis  8  as its center. A shaft portion  48  integrated with a hub  46  is rotatably supported inside the bearing sleeve  42  via a bearing  44 . The hub  46  includes the shaft portion  48 , a drum portion  50 , and a roof portion  52 . The drum portion  50  is of a cylindrical shape having a central axis in common with the shaft portion  48 . The roof portion  52  is of a disk shape connecting an upper end of the shaft portion  48  and an upper end of the drum portion  50 .  
         [0020]     An edge portion  54  is provided on a lower end of the drum portion  50 . The edge portion  54  protrudes outwardly. The drum portion  50  has an outside diameter corresponding to a diameter of a circular opening portion provided at a center of the magnetic disk  4 . The drum portion  50  is fitted into the circular opening portion in the magnetic disk  4 . The magnetic disk drive according to the embodiment of the present invention is mounted with two magnetic disks  4 . A lower magnetic disk  4 D is locked onto the edge portion  54 . An upper magnetic disk  4 U is attached to the drum portion  50  after a ring-shaped spacer  56  is disposed around the drum portion  50  on top of the lower magnetic disk  4 D.  
         [0021]     Thereafter, the clamp  6  is placed on the roof portion  52  by being centrally aligned with the rotary axis  8 . The clamp  6  is then secured to the hub  46  using a screw  58  screwed into the shaft portion  48  through the opening portion  30 . The clamp  6  has a diameter larger than the outside diameter of the drum portion  50 . An edge portion of the clamp  6  protruding from the drum portion  50  presses an upper surface of the upper magnetic disk  4 U. This results in the two magnetic disks  4 U,  4 D stacked one on top of the other with the spacer  56  interposed therebetween being clamped by the edge portion  54  of the drum portion  50  and the clamp  6 , and thus secured to the hub  46 .  
         [0022]     A plurality of stators  60  composed of electromagnets is arranged on an outer periphery of the bearing sleeve  42 . A plurality of magnets  62  opposing the stators  60  is arranged on an inner peripheral surface of the drum portion  50 .  
         [0023]     As described earlier, the clamp  6  has the plurality of opening portions  18  arranged around the opening portion  30  at the center thereof. The clamp  6  is disposed in a position raised from the roof portion  52  in areas near these opening portions  18 . That is, a gap is provided between the clamp  6  and the hub  46 . The gap may be formed by curving the clamp  6  radially, thereby forming an arch between the opening portion  30  and the outer periphery. Specifically, referring to the cross sectional view shown in  FIG. 3 , a ring-shape plate forming the clamp  6  is bent so as to rise from an edge of the opening portion  30  toward the outer periphery. Further, the clamp  6  is also bent so as to rise from an edge of the outer periphery toward the center. This results in areas between these bends being raised from the roof portion  52 . The areas correspond to portions, at which the opening portions  18  are provided.  
         [0024]     A recessed portion  64  having a circular opening of the same size as the opening portion  18  is disposed in the roof portion  52  at a position corresponding to each of the opening portions  18 . The recessed portions  64  are pre-formed so as to be aligned with the corresponding ones of the opening portions  18  when the center of the clamp  6  is brought into alignment with the center of the hub  46 . Fine-adjustments of the position of the clamp  6  are made as detailed in the following when the clamp  6  is screwed in the hub  46 . Specifically, the clamp  6  is placed on the hub  46  such that the opening portions  18  are aligned with the recessed portions  64 . Then, a bar having a diameter corresponding to the shape of the opening in each of the opening portions  18  and the recessed portions  64  is inserted from each of the opening portions  18  into the corresponding one of the recessed portions  64  thereunder. The recessed portions  64  are used, as such, for ensuring accuracy in alignment between the clamp  6  and the hub  46 . The recessed portions  64  are, accordingly, disposed at positions opposing the opening portions  18 .  
         [0025]     In the magnetic disk drive according to the embodiment of the present invention, the counterweight  20  is inserted until a lower end thereof bottoms in the recessed portion  64 . The counterweight  20  is mounted in position where the magnetic disks  4 U,  4 D, the spacer  56 , the clamp  6 , the screw  58 , and the like have been assembled together to the spindle motor including the hub  46  and the like. Specifically, a spinning part basic assembly completed by including the magnetic disk  4  is spun or otherwise operated by the spindle motor in accordance with actual operating conditions. A balance measuring machine is then used to measure rotating imbalance of the basic assembly. Based on this measurement, an opening portion  18  is selected, in which the counterweight  20  is to be inserted to compensate for the rotating imbalance. The counterweight  20  is then inserted in that particular opening portion  18 . According to the measurement, one or two mutually adjoining opening portions  18  are selected as a rule. It is nonetheless appropriate that more opening portions  18  be selected as appropriately.  
         [0026]      FIG. 4  is a perspective view showing schematically the counterweight  20 .  FIG. 5  is a vertical cross sectional view showing schematically the counterweight  20 . The counterweight  20  has a basic shape of a column corresponding to the shape of the opening in the opening portion  18 , including a protruded portion formed on a side surface thereof. In the magnetic disk drive according to the embodiment of the present invention, the opening portion  18  is circular. Accordingly, the counterweight  20  has an outline combining a circular column portion  70  with a protruded portion  72  annularly surrounding an entire periphery of a side surface thereof. Further, the counterweight  20  has an opening portion  74  formed along a central axis of the circular column portion  70 . The protruded portion  72  may be formed, for example, to have a width h 3 . The width h 3  is a remainder of a total distance between upper and lower end faces of the circular column portion  70  less a distance h 1  and a distance h 2 . The width h 3  of the protruded portion  72  is set in accordance with the gap between the clamp  6  and the roof portion  52 . The protruded portion  72  is designed to slide into the gap when the counterweight  20  is mounted in the opening portion  18 . The distance h 1  between the protruded portion  72  and the upper end of the circular column portion  70  and the distance h 2  between the protruded portion  72  and the lower end of the circular column portion  70  are set, for example, according to a thickness of the clamp  6  or a depth of the recessed portion  64  of the hub  46 . Specifically, for example, the distance hi is set to be smaller than the thickness of the clamp  6  such that the upper end of the circular column portion  70  does not protrude from the opening portion  18  when the counterweight  20  is inserted in the opening portion  18 . Similarly, the distance h 2  and the depth of the recessed portion  64  can be set such that a portion of the circular column portion  70  below the protruded portion  72  fits completely in the recessed portion  64 . In addition to these requirements, the counterweight  20  used with the magnetic disk drive according to the embodiment of the present invention is structured symmetrically about the width h 3  by having a dimension of the distance h 1  identical to that of the distance h 2 . This eliminates the need for ensuring correct up-and-down orientation of the counterweight  20  when mounting the counterweight  20 . Mounting work is thus simplified.  
         [0027]     The counterweight  20  is formed of an elastic material. When the counterweight  20  is inserted into the opening portion  18 , the protruded portion  72  receives stress from an edge or an inner surface of the opening portion  18 . This causes the counterweight  20  to be elastically deformed, allowing the protruded portion  72  to pass through the opening portion  18 . On reaching the gap beneath the gap, the protruded portion  72  restores to original state, sliding into the gap. With a view to ensuring that the protruded portion  72  smoothly passes through the opening portion  18  or suppressing generation of dust and dirt through friction during passage, the protruded portion  72  may be formed into a convex shape as detailed in the following. Specifically, the height of the protruded portion  72  from the side surface of the circular column portion  70  is the maximum at a center of the width h 3 . The height is smaller toward the ends. The protruded portion of the counterweight  20  of the magnetic disk drive according to the embodiment of the present invention has a rounded convex shape as shown in  FIG. 5 .  
         [0028]     FIGS.  6 ( a ),  6 ( b ), and  6 ( c ) are explanatory views showing schematically a mounting method of the counterweight  20 . Mounting of the counterweight  20  to the disk assembly can be achieved easily by using a barjig  80 . The jig  80  is a shaft having a step formed on its leading end. The jig  80  includes a shaft  82  and a leading end pin  84  formed thinner than the shaft  82 . The leading end pin  84  has a shape to be fit into the opening portion  74  in the counterweight  20 . The leading end pin  84  is inserted into the opening portion  74  ( FIG. 6 ( a )) to make the counterweight  20  held at the leading end of the jig  80 . In this condition, the jig  80  is moved to a position above the opening portion  18  and the counterweight  20  held at the leading end is inserted into the opening portion  18  ( FIG. 6 ( b )). The counterweight  20  has the circular column portion  70 , the diameter of which is determined such that the counterweight  20  exerts an adequate pressure to the opening portion  18  and the recessed portion  64 , and has the protruded portion  72 . The counterweight  20  therefore receives an upward drag from the opening portion  18  and the recessed portion  64  during insertion therein. At this time, a shoulder portion  86  of the jig  80  at a root of the leading end pin  84  and the shaft  82  presses a top surface of the counterweight  20 . This allows the counterweight  20  to be pushed into the opening portion  18  and the recessed portion  64  easily. After the counterweight  20  has been pushed into the opening portion  18  and the recessed portion  64 , the jig  80  is retracted upward. At this time, the counterweight  20  can be left mounted in the opening portion  18  by a friction force produced on surfaces in contact with the opening portion  18  and the recessed portion  64  and a force encountered as the protruded portion  72  fitted in the gap is locked in the opening portion  18 . This allows the jig  80  only to be pulled out ( FIG. 6 ( c )).  
         [0029]     As described earlier, the counterweight  20  is formed of an elastic material. Possible elastic materials to be used include, for example, a synthetic rubber such as styrene-butadience rubber, butadiene rubber, butyl rubber, ethylene propylene rubber, nitrile rubber, chloroprene rubber, fluororubber, silicone rubber, and urethane rubber, and a natural rubber. In addition, an elastomeric material, such as a styrene-based elastomer, an olefin-based elastomer, an urethane-based elastomer, and an ester-based elastomer may be used.  
         [0030]     The material for the counterweight  20  is selected in consideration of the specific gravity thereof, in addition to the requirement that the material be elastic. The counterweight  20  is, as its name implies, highly significant when its weight ensures rotating balance. The weight of the counterweight  20  can be regulated to some extent by the size thereof. Making the counterweight  20  large, however, makes it necessary to enlarge the opening portion  18  and the recessed portion  64 . With the trend in need toward reduction in size of the magnetic disk drive, enlarging the opening portion  18  and the recessed portion  64  could result in a reduction of the strength of the clamp  6  and the hub  46 . There is therefore a limit to regulation of the size of the counterweight  20 . Accordingly, it becomes important to select the specific gravity of the material used for the counterweight  20 . For example, to adjust the specific gravity, any of the aforementioned rubbers and the like may be used as a base material, with which a metal filler or the like is mixed.  
         [0031]     Further, it is preferable that a material or a shape that is less likely to cause dust and dirt be produced during press-fitting in the opening portion  18  and the recessed portion  64  be selected for the counterweight  20 . The aforementioned rubbers and the like meet this requirement, too.  
         [0032]     The counterweight  20  formed of the elastic material as described above is mounted in the disk assembly by being press-fitted into the opening portion  18  and the recessed portion  64 . As a result, there is an increase in the friction force between the counterweight  20  and the inner surfaces of the opening portion  18  and the recessed portion  64 . The counterweight  20  can therefore be appropriately prevented from falling off by a centrifugal force or the like occurring from high-speed spinning of the disk assembly. Further, the protruded portion  72  of the counterweight  20  is locked by the clamp  6 . This prevents the counterweight  20  from coming off even more positively.  
         [0033]     As described in the foregoing, the magnetic disk drive according to the embodiment of the present invention has a stable structure that achieves the following effects. Specifically, the structure reduces self-oscillation by controlling the rotating balance using the counterweight featuring a space-saving body and suppression of production of dust and dirt. The structure also prevents the counterweight from falling off during high-speed spinning.  
         [0034]     It is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims alone with their full scope of equivalents.