Abstract:
The present invention provides a magnetic disk device which uses a plurality of screws of different weights for fastening a disk clamp, and which combines the screws of different weights in such a manner to eliminate weight imbalance. Accordingly, the device does not use extra components such as a weight for eliminating the weight imbalance, and thus achieves cost reduction.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a magnetic disk device used as an external storage device of a computer system. 
         [0003]    2. Description of the Related Art 
         [0004]    A magnetic disk device is not only used as an auxiliary storage device of a computer but also mounted on a mobile terminal device, a video device, and so forth. With such expansion of the range of applications, further increase in capacity and improvement in response of the magnetic disk device have been sought. To increase the capacity, the number of disks mounted on the magnetic disk device has been increasing. Further, to improve the response, the rotation speed of a spindle motor has been increasing. 
         [0005]    A plurality of the magnetic disks are stacked through a hub fixed to the shaft of the spindle motor, and a disk clamp is screwed to fix the disks. However, a slight gap exists between the hub of the spindle motor and the magnetic disks. Further, each of the magnetic disks, a disk spacer, and the disk clamp has eccentricity. After the magnetic disks have been fixed, therefore, weight imbalance occurs around the axis of the spindle motor. 
         [0006]    Conventional art documents relating to the elimination of the weight imbalance include Japanese Unexamined Patent Application Publication Nos. 59-210565, 03-230309, and 2001-167554. 
         [0007]    As a conceivable method to eliminate the weight imbalance around the axis of the spindle motor, for example, a balance adjusting weight may be separately prepared and placed at such a position that the weight eliminates the weight imbalance. According to the method, however, an extra component needs to be added, and thus the cost is increased. Further, a process of placing the weight needs to be added. 
       SUMMARY OF THE INVENTION 
       [0008]    One aspect is a magnetic disk device. The magnetic disk device includes at least one magnetic disk for recording information, a motor for rotating the magnetic disk, a disk clamp for fixing the magnetic disk to the motor, and a plurality of fastening members for fixing the disk clamp to the motor, at least one of said fastening members having a different weights from the others to generate an improved weight balance around the rotational axis of the motor. 
         [0009]    According to the present invention, the weight imbalance is eliminated by fastening a disk clamp with screws having such weights that generate torque in the opposite direction to the direction in which the weight imbalance occurs. Therefore, the present invention has the effect of enabling the elimination of the weight imbalance without adding a new type of component. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is an overview diagram of a magnetic disk device according to an embodiment of the present invention; 
           [0011]      FIG. 2  is the first cross-sectional view of a spindle motor; 
           [0012]      FIG. 3  is the first diagram illustrating weight imbalance; 
           [0013]      FIG. 4  is the second diagram illustrating the weight imbalance; 
           [0014]      FIG. 5  is the third diagram illustrating the weight imbalance; 
           [0015]      FIG. 6  is the second cross-sectional view of the spindle motor; 
           [0016]      FIG. 7  is the fourth diagram illustrating the weight imbalance; 
           [0017]      FIG. 8  is the first diagram illustrating an example of a disk clamp; 
           [0018]      FIG. 9  is the first cross-sectional view of the disk clamp; 
           [0019]      FIG. 10  is the second diagram illustrating an example of the disk clamp; 
           [0020]      FIG. 11  is the second cross-sectional view of the disk clamp; and 
           [0021]      FIG. 12  is a cross-section diagram illustrating the spindle motor rotating. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    An embodiment of the present invention will be described below with reference to the drawings. 
         [0023]    Structure of a Hard Disk Drive: 
         [0024]      FIG. 1  schematically illustrates the internal structure of a specific example of a sealed recording disk drive, i.e., a hard disk drive (HDD)  11 . The HDD  11  includes a box-shaped chassis body  7  for defining the internal space of a flat rectangular parallelepiped, for example. The housing space houses at least one magnetic disk  16  which serves as a recording medium. The magnetic disk  16  is mounted on a spindle motor  12 . The spindle motor  12  can be rotated at a high speed, such as 7200 rpm, 10000 rpm, or 15000 rpm, for example. 
         [0025]    The housing space further houses an actuator arm  19 . The actuator arm  19  is provided for each of the front surface and the rear surface of the magnetic disk  16 . The actuator arm  19  is attached with a head suspension  21  at the leading end thereof. The head suspension  21  extends forward from the leading end of the actuator arm  19 . The front end of the head suspension  21  supports a floating head slider  17 . The floating head slider  17  is set to face the surface of the magnetic disk  16 . 
         [0026]    The floating head slider  17  is mounted with a so-called magnetic head. The magnetic head may be formed by, for example, a reading section, such as a tunnel effect-type magnetoresistance effect element, which reads magnetic information from the magnetic disk  16  by using the tunnel effect, and a writing section, such as a thin film magnetic head, which is formed by a thin film coil pattern to write information on the magnetic disk  16  by using a magnetic flux. 
         [0027]    The floating head slider  17  is applied with pressing force by the head suspension  21  toward the surface of the magnetic disk  16 . Further, the floating head slider  17  is applied with buoyancy by the action of an air flow generated by the rotation of the magnetic disk  16 . Due to the balance between the buoyancy and the pressing force applied by the head suspension  21 , the floating head slider  17  can continue to float during the rotation of the magnetic disk  16 . 
         [0028]    The actuator arm  19  is connected to a drive power source, such as a voice coil motor, for example. Due to the operation of the voice coil motor, the actuator arm  19  can rotate around a spindle  18 . When the actuator arm  19  oscillates around the spindle  18  during the flotation of the floating head slider  17 , the floating head slider  17  can traverse over the surface of the magnetic disk  16  in the radial direction. 
         [0029]      FIG. 2  is a cross-sectional view of the position indicated by the dashed line in  FIG. 1 , as viewed in the direction of the arrows. The figure illustrates the structure of the spindle motor  12 . The spindle motor  12  is mainly formed by a stator  23  and a rotor  24  rotatably supported by the stator  23 . 
         [0030]    The stator  23  includes a sleeve  62 . The sleeve  62  may be formed of a metal material, such as brass and stainless steel, for example. The sleeve  62  is formed with an opening at a lower portion thereof, and a thrust plate  67  is pressed into the opening. The stator  23  further includes a core  71  and a coil  70  wound around the core  71 . The core  71  is formed by a plurality of stacked metal thin plates. 
         [0031]    The rotor  24  includes a shaft  61 . The shaft  61  includes a spindle hub  63  attached thereto. The shaft  61  is received by the sleeve  62 . The space between the shaft  61  and the sleeve  62  is filled with oil. Thereby, the shaft  61  is supported by the sleeve  62 . The shaft  61  is fixed with a disk-shaped thrust flange  68 . The bottom surface of the thrust flange  68  is set to face a surface of the thrust plate  67 . The shaft  61  and the thrust flange  68  may be formed of a metal material, such as brass and stainless steel, for example. 
         [0032]    The shaft  61  is inserted in the spindle hub  63 . The shaft  61  is adhered to the spindle hub  63  by an adhesive agent. The inner circumferential surface of the cylinder of the spindle hub  63  is fixed with a permanent magnet  66 . Thereby, the permanent magnet  66  is set to face the coil  70 . When the coil  70  is applied with a current, a magnetic flux generated by the coil  70  rotates the shaft  61  and the spindle hub  63 . The spindle hub  63  is mounted with two magnetic disks  16 , for example. Each of the magnetic disks  16  is pierced with a through hole at the center thereof to be mounted on the spindle hub  63 . The through hole receives the spindle hub  63 . Between the magnetic disks  16 , a spacer  65  is inserted around the spindle hub  63  to be sandwiched by the magnetic disks  16 . The spacer  65  keeps the interval between the magnetic disks  16 . Further, the lower end of the spindle hub  63  is formed with a flange  69 . 
         [0033]    The leading end of the spindle hub  63  is attached with a disk clamp  64 , which forms the first latch member. The disk clamp  64  is fixed to the spindle hub  63  by six screws  36  in a 3.5 inch type HDD, for example. The disk clamp  64  is formed with through holes for receiving the screws  36 , each of which forms the second latch member. The disk clamp  64  has a projection  64   a  projecting from a surface thereof to come in contact with a surface of one of the magnetic disks  16 . Thereby, the magnetic disks  16  and the spacer  65  are sandwiched between the disk clamp  64  and the spindle hub  63 . 
         [0034]    Detailed description will now be made of the mounting of the magnetic disks  16 , the spacer  65 , and the disk clamp  65  on the spindle motor  12 . Firstly, the first magnetic disk  16  is mounted on the flange  69 . In the mounting process, the spindle hub  63  moves into the through hole of the magnetic disk  16 . After the first magnetic disk  16  has been mounted, the spacer  65  is mounted. Thereafter, the remaining magnetic disks  16  and spacers  65  are alternately mounted. After the last magnetic disk  16  has been mounted, the disk clamp  64  is mounted. In the mounting process, the through holes of the disk clamp  64  may be previously positioned to screw holes  57  formed in the spindle hub  63 . Subsequently, the screws  36  are screwed through the through holes into the screw holes  57  with predetermined fastening torque. 
         [0035]    The rotation of the magnetic disk  16  will be then described. When the coil  70  is applied with the current, drive force is generated between the coil  70  and the permanent magnet  66 . Then, the shaft  61  starts rotating, and the oil flows along the inner circumferential surface of the sleeve  62 . In this process, the oil generates dynamic pressure. Due to the dynamic pressure, a constant interval is secured between the outer circumferential surface of the shaft  61  and the inner circumferential surface of the sleeve  62 . At the same time, a constant interval is secured between the bottom surface of the thrust flange  68  and the surface of the thrust plate  67 . Accordingly, the magnetic disk  16  can continue to rotate. On the other hand, if the application of the current to the coil  70  is stopped, the rotational force of the shaft  61  is lost. Thereby, the rotation of the magnetic disk  16  stops. 
         [0036]    Conceptual Diagram of Weight Imbalance: 
         [0037]      FIG. 3  is a diagram illustrating the magnetic disk device  11  of  FIG. 1 , as viewed from the above. The figure illustrates the disk clamp  64 . Weight imbalance occurs around the axis of the spindle motor  12  in the directions indicated by the arrows in  FIG. 3 . The weight imbalance is caused by the eccentricity of each of the rotor  24 , the magnetic disk  16 , the disk spacer  65 , and the disk clamp  64 . When faster rotation of the spindle motor  12  is required, the eccentricity cannot be ignored, even if the accuracy of the components is improved. As a result, the weight imbalance occurs. To illustrate the directions in which the weight imbalance occurs, the present example illustrates a case in which the weight imbalance occurs in a direction connecting the center of the spindle motor  12  and the center of one of the screw holes  57  ( 57   f ), i.e., in the direction of A, and a case in which the weight imbalance occurs in a direction other than the above-described direction, i.e., in the direction of B. 
         [0038]    In the present embodiment, the weight imbalance is eliminated by using screws which are formed of the same material but have different lengths. That is, since the distance from the center of the rotational axis of the spindle motor  12  to the center of each of the screw holes  57  is constant, the weight of the screws  36  inserted in the screw holes  57  is changed to generate torque in the opposite direction to the direction in which the weight imbalance occurs, so that the weight imbalance is eliminated.  FIG. 12  is a cross-section diagram of the spindle motor  12  rotating. For simplification, the figure illustrates the occurrence of the weight imbalance by using disk clamp  64  and disk  16 . The weight imbalance of the disk  16  as illustrated in  FIG. 12 , is occurred when the spindle motor  12  is rotating. The weight imbalance is corrected by the weight of screw  36 . The screw hole  57  is arranged to a predetermined position from a center axis of the disk  16  and a distance from the center axis  102  to the screw hole  57  is r. The screw has a weight to correct the weight imbalance at the screw hole  57  when the screw fastens at the screw hole  57 . As the material of the screws  36 , iron or stainless steel is used, for example. The different lengths of the screws  36  include three lengths of 3 mm, 6 mm, and 9 mm, for example. Since the material of the screws  36  is the same, the weight of the screws  36  is substantially proportional to the length thereof. Thus, the different weights of the screws  36  are 140 mg, 200 mg, and 280 mg, for example. 
         [0039]    In fixing the disk clamp  64 , the disk clamp  64  is first screwed by three screws  36   a  having a standard length of 6 mm into positions apart from one another by 120°, i.e., into the screw holes  57   a ,  57   c , and  57   e  illustrated in  FIG. 3 . In this process, the torque generated in the screws  36   a  is such toque that temporarily holds the disk clamp  64  without causing a positional misalignment even if the magnetic disk  16  is rotated. This is because, if the disk clamp  64  is firmly fastened by the three screws  36   a  of the standard length, the effect of reducing the curve of magnetic recording medium is lost, as compared with the case in which the disk clamp  64  is firmly fastened by six screws  36  at the same timing. This is true even if the disk clamp  64  is screwed by the total of six screws  36  including three later-added screws  36  which include a screw  36  of a different length. Subsequently, the amount of imbalance is measured by an imbalance measuring device to detect the direction in which the weight imbalance occurs. And, the amount of imbalance is measured when the spindle motor  12  is rotating. Then, the combination of the screws  36  to be inserted in the three remaining holes  57  is determined such that the weight imbalance is eliminated. 
         [0040]    For example, if the weight imbalance occurs in the direction indicated by the arrow in  FIG. 4  (i.e., in the direction of A 1 ), a screw  36   b  having a longer length than the standard length is inserted in the screw hole  57   f , and the screws  36   a  having the standard length are inserted in the screw holes  57   b  and  57   d . Then, the screw  36   b  and the screws  36   a  inserted in the three remaining positions are fastened, and at the same time, the three previously temporarily fastened screws  36   a  are firmly fastened. Thereby, weight is applied in the opposite direction to the direction of A 1 , and thus the weight imbalance is eliminated.  FIG. 2  illustrates the state in which the screw  36   a  having the standard length and the screw  36   b  having the longer length than the standard length are inserted. 
         [0041]    Further, if the weight imbalance occurs in the direction indicated by the arrow in  FIG. 5  (i.e., in the direction of A 2 ), a screw  36   c  having a shorter length than the standard length is inserted in the screw hole  57   f , and the screw  36   a  having the standard length are inserted in the screw holes  57   b  and  57   d . Then, the screw  36   c  and the screws  36   a  inserted in the three remaining positions are fastened, and at the same time, the three previously temporarily fastened screws  36   a  are firmly fastened. Thereby, weight is applied in the opposite direction to the direction of A 2 , and thus the weight imbalance is eliminated.  FIG. 6  illustrates the state in which the screw  36   a  having the standard length and the screw  36   c  having the shorter length than the standard length are inserted. 
         [0042]    Furthermore, if the weight imbalance occurs in the direction indicated by the arrow in  FIG. 7  (i.e., in the direction of B 1 ), for example, the weight imbalance is eliminated by applying weight in the direction of C 1 , which is the opposite direction to the direction of B 1 . The weight is applied in the direction of C 1  by combining the lengths of the screws  36  to be inserted in the screw holes  57   b ,  57   d , and  57   f . Specifically, the weight imbalance is eliminated by causing the torque, which corresponds to the product of the distance from the center of the spindle motor  12  to the center of each of the screw holes  57  and the weight of the screw  36  inserted in each of the screw holes  57 , to be generated in the opposite direction to the direction in which the weight imbalance occurs. The centers of the respective screw holes  57  are positioned on the same circumference. Thus, as indicated by the dashed-dotted lines in  FIG. 7 , the distance from the center of the spindle motor  12  to the center of each of the screw holes  57  is constant. Therefore, the lengths of the screws  36  to be inserted in the screw holes  57   b ,  57   d , and  57   f  are determined such that weight is applied in the direction of C 1 . 
         [0043]    As described above, the combination of the screws depends on the direction in which the weight imbalance occurs. The combination of the screws varies depending on the measurement result. For example, screws having the same length as the length of the three previously fastened screws may be used. Further, two of the three screws to be used may be longer length than the previously fastened screws, and the remaining screw may be shorter than the previously fastened screws. Furthermore, two of the three screws to be used may be shorter than the previously fastened screws, and the remaining screw may be longer than the previously fastened screws. In addition, if further varied screw lengths are prepared instead of simply preparing the screws of the long length and the short length with respect to the standard screws, a finer control can be performed to reduce the imbalance. 
         [0044]    Availability of the Present Invention: 
         [0045]    Finally, the availability of the present invention will be described.  FIG. 8  illustrates an example of the disk clamp.  FIG. 9  is a cross-sectional view of the portion indicated by the dashed line in  FIG. 8 , as viewed in the direction of the arrows. As illustrated in  FIG. 9 , the upper surface of the disk clamp is formed with a step  51 . Further, an adjusting balancer weight  9 , which functions as a balancer for keeping the rotational balance of the magnetic disk, is pasted to the step  51  by an adhesive agent along the inner wall of the step  51 . 
         [0046]    Further,  FIG. 10  illustrates an example of the disk clamp.  FIG. 11  is a cross-sectional view of the portion indicated by the dashed line in  FIG. 10 , as viewed in the direction of the arrows. As illustrated in  FIG. 11 , the balance in the circumferential direction of the disk clamp  64  is adjusted by a C-ring balancer  8  attached to the outer circumference of the disk clamp  64 . More specifically, the lateral side of the outer circumference of the disk clamp  64  is formed with a groove  54  in which the C-ring balancer  8  is fitted. 
         [0047]    On the other hand, according to the present invention, the weight imbalance is eliminated solely by the screws, without using extra components such as the weight and the C-ring balancer. Therefore, such processes as the pasting of the weight and the fitting of the C-ring balancer with respect to the disk clamp can be omitted. 
         [0048]    The above-described embodiment has been specifically described for better understanding of the present invention, and thus does not limit other embodiments. Therefore, alternations can be made within a scope not changing the gist of the invention. For example, in  FIG. 8 , the screw having the long length may be inserted in the screw hole located nearest to the position to which the weight is pasted, and the screws having the standard length may be inserted in the other screw holes, to thereby exert a similar effect to the effect obtained by pasting the weight and to eliminate the weight imbalance. Further, the weight imbalance may be eliminated by using screws having the same size but formed of difference materials, i.e., screws having the same size but different weights, for example. Iron or stainless steel may be used as the material of a standard screw, while aluminum and brass may be used as the material of a screw lighter than the standard screw and the material of a screw heavier than the standard screw, respectively.