Patent Document

CROSS-REFERENCES TO RELATED APPLICATIONS 
   This application claims priority from Japanese Patent Application No. JP2004-338665, filed Nov. 24, 2004, the entire disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a technique for fastening a magnetic disk to a hub structure by a clamping mechanism. More specifically, the present invention relates to a technique for fastening a magnetic disk to a hub structure by a clamping mechanism, capable of accurately controlling fastening pressure exerted by the clamping mechanism. 
   In a magnetic disk drive, a magnetic disk, namely, a recording medium, is fastened to a hub, a spindle motor is formed by a coil stator incorporated into the hub and a magnet, and the magnetic disk is driven for rotation by the spindle motor. Generally, the magnetic disk is fastened to the hub by a clamping mechanism. The clamping mechanism fastens the magnetic disk to the hub by pressing the magnetic disk placed on the hub so that the hub is fitted in a circular through hole formed in a central part of the magnetic disk by a thin plate spring, namely, a dished, thin metal plate, and screwing a fastening screw in a threaded hole of the hub so as to apply a proper fastening pressure to the magnetic disk by the thin plate spring. 
   A clamping mechanism for holding a magnetic disk having a magnetic recording surface and provided with a central hole is illustrated in FIG. 6 of Patent document 1 (Japanese Patent Laid-Open 2004-199760). The magnetic recording surface is provided with a clamping boss to be fitted in the central hole of the magnetic disk, a spring member fixed to the clamping boss to press the magnetic disk against the clamping boss, and a spacing ring placed between the magnetic disk and the spring member. The spacing ring engages loosely with a stepped part formed around the central hole of the magnetic disk. 
   When the clamping mechanism fastens the magnetic disk to the clamping boss, the fastening pressure exerted by the spring member on the magnetic disk must be properly managed. The magnetic disk will be dislocated when an external shock is given to the magnetic disk drive and servo data cannot be read if the fastening pressure is excessively low. The magnetic disk will be excessively distorted, the surface of the magnetic disk rises and the accuracy of servo control of the tracking operation of a head slider is deteriorated and the head slider collides against the surface of the magnetic disk if the fastening pressure is excessively high. The relation between the deflection of a conical spring employed in such a clamping mechanism and clamping force or fastening pressure is disclosed in Patent document 2 (Japanese Patent Laid-Open 9-265702). Patent document 2 shows that there is a certain relation between the deflection of the conical spring and the fastening pressure. 
   Generally, a thin plate spring included in a clamping mechanism is provided in its central part with a through hole through which a fastening screw is passed. The thin plate spring is put in place on a magnetic disk mounted on a hub and the fastening screw is screwed through the through hole in a threaded hole formed in a central part of the hub. Then, the thin plate spring is deflected gradually as fastening pressure applied thereto increases. A torque applied to a torque driver to screw the fastening screw in the threaded hole is used for managing the fastening pressure applied by the clamping mechanism to the magnetic disk. Torque necessary for turning the fastening screw increases as an axial force acting on the fastening screw increases due to increase in the deflection of the thin plate spring. Therefore, the conventional magnetic disk drive is able to manage the fastening pressure on the basis of the torque applied to the torque driver. 
   BRIEF SUMMARY OF THE INVENTION 
   Recording density in which magnetic disk drive records data in the magnetic disk has progressively increased and the gap between the head slider and the surface of the magnetic disk has progressively decreased in recent years. Consequently, the importance of the accurate management of the fastening pressure for pressing the magnetic disk has increased for the improvement of the accuracy of servo control. The relation between the torque for turning the fastening screw and the axial force in the clamping mechanism is dependent on many parameters including friction acting between the fastening screw and the thin plate spring, dimensional tolerance for the manufacture of the fastening screw, fastening screw rotating speed at which the fastening screw is rotated for fastening and the accuracy of torque indicated by the fastening tool used for rotating the fastening screw. Thus, it is difficult to press the thin plate spring with the fastening screw so that a recently desired accurately managed fastening pressure may be applied to the thin plate spring. 
   An improved fastening pressure managing method is desired instead of the fastening pressure managing method using the fastening torque applied to the fastening torque for managing the fastening pressure. Accordingly, it is a feature of the present invention to provide a magnetic disk drive producing method of producing a magnetic disk drive provided with a magnetic disk fastened to a hub structure by an accurate fastening pressure. Another feature of the present invention is to provide a magnetic disk fastening method capable of fastening a magnetic disk by a clamping mechanism to a hub structure by accurate fastening pressure. A third feature of the present invention is to provide a magnetic disk drive assembling device capable of fastening a magnetic disk to a hub by an accurate fastening pressure. 
   The principle of the present invention is to manage the tightening degree of the fastening screw on the basis of the deflection of the thin plate spring most closely connected with fastening pressure that may be applied to the magnetic disk when the magnetic disk is fastened to the hub structure by the clamping mechanism. A magnetic disk fastening method of fastening a magnetic disk to a hub structure in a first aspect of the present invention comprises the steps of: mounting the magnetic disk on the hub structure; setting a thin plate spring having a pressure-bearing part, a flexible part and a disk holding part at a predetermined position relative to the magnetic disk with the disk holding part in contact with a surface of the magnetic disk; pressing the magnetic disk by the disk holding part by screwing a fastening screw in a threaded hole formed in the hub structure; measuring a deflection by which the flexible part is deflected in the step of pressing the magnetic disk; and stopping pressing the magnetic disk upon the increase of the deflection to a predetermined value. 
   The flexible part of the thin plate spring is deflected when the fastening screw is screwed in the threaded hole to press the disk holding part elastically against the surface of the magnetic disk to fasten the magnetic disk to the hub structure. The step of pressing the pressure-bearing part is stopped upon the increase of the measured deflection of the thin plate spring to a predetermined value. Therefore, the time for stopping screwing the fastening screw to apply a predetermined fastening pressure to the magnetic disk can be controlled on the basis of a direct parameter instead of an indirect parameter such as torque for turning the fastening screw. 
   The pressure-bearing part may surround a through hole formed in a part, with which the head of the fastening screw comes into contact, of the thin plate spring. Fastening pressure may be applied to the pressure-bearing part of the thin plate spring by pressing a different pressing member for pressing the thin plate spring with the fastening screw. The deflection of the thin plate spring may be directly measured. However, the deflection can be easily determined by measuring the position of a probe that changes its position according to the deflection of the thin plate spring. 
   Measurement error in a measured deflection can be reduced by setting a point of measurement in the vicinity of the most greatly deflected pressure-bearing part. When the thin plate spring is a dished thin plate spring provided in its central part with a through hole through which the fastening screw is passed and having a disk holding part in a peripheral part, and a flexible part extending between the through hole and the disk holding part, the clamping mechanism is able to press the magnetic disk against the hub structure by uniformly applying fastening pressure to the magnetic disk with respect to a circumferential direction. 
   A magnetic disk attaching machine in a second aspect of the present invention for attaching a magnetic disk to a hub structure by pressing the magnetic disk against the hub structure with a thin plate spring provided with a through hole and having a flexible part, a pressure-bearing part and a disk holding part includes: a screw driving member supported for rotation and having a holding head holding a screw driving tool suitable for driving a fastening screw; a sleeve internally holding the screw driving member and so elastically pressed against the flexible part as to deflect the elastic part; a deflection measuring unit for measuring the displacement of the sleeve displaced according to the deflection of the defecting part deflected by screwing a fastening screw through the through hole in a threaded hole formed in the hub structure by the screw driving member; and a controller for controlling the screw driving member and the deflection measuring unit. 
   The magnetic disk attaching machine of the present invention includes the screw driving member, the sleeve, the deflection measuring unit and the controller. The position of the sleeve changes according to the deflection of the flexible part when the screw driving member screws the fastening screw in the threaded hole. Therefore, the displacement of the sleeve corresponds to the deflection. The controller is able to determine the time for stopping the screwing operation of the screw driving member on the basis of data on the displacement of the sleeve received from the deflection measuring unit. Thus present invention is capable of adjusting the fastening force more accurately than the method of managing the torque applied to the fastening screw. 
   Measurement of the deflection by a noncontact measuring method that projects a beam of electromagnetic radiation, such as a laser beam or an infrared ray, on a reflecting surface formed on the probe and capable of reflecting a beam of electromagnetic radiation does not need to apply an extra force through the sleeve to the flexible part and hence measurement error in the measured deflection can be reduced. When an end of the sleeve is elastically pressed against a flat region of the flexible part surrounding the through hole, it is possible to prevent producing errors due to the positional change of the sleeve in contact with the flexible part relative to the flexible part during deflection measurement. When a deflection by which the thin spring plate pressed by the sleeve is deflected is not greater than about 5% of a deflection at the completion of fastening the magnetic disk with the fastening screw, the sleeve is able to follow the deflection of the flexible part satisfactorily and measurement error in the measured deflection can be reduced. 
   A magnetic disk drive manufacturing method in a third aspect of the present invention comprises the steps of: attaching a hub structure to a base; mounting a magnetic disk on the hub structure; setting a thin plate spring having a pressure-bearing part to be pressed by a fastening screw, a flexible part and a disk holding part at a predetermined position relative to the magnetic disk with the disk holding part in contact with a surface of the magnetic disk; pressing the magnetic disk with the pressure-bearing part by screwing a fastening screw in a threaded hole formed in the hub structure; measuring a deflection by which the flexible part is deflected in the step of pressing the magnetic disk; and stopping pressing the magnetic disk upon the increase of the deflection to a predetermined value. 
   The present invention provides the method of producing the magnetic disk drive in which the magnetic disk is fastened to the hub structure by applying an accurate fastening pressure to the clamping mechanism. The present invention provides the magnetic disk fastening method capable of attaching the magnetic disk to the hub structure by applying an accurate fastening pressure to the magnetic disk by the clamping mechanism. The present invention provides the magnetic disk attaching deice capable of attaching the magnetic disk to the hub structure by an accurate fastening pressure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view of a magnetic disk drive in an embodiment according to the present invention. 
       FIG. 2  is a view of a thin plate spring. 
       FIG. 3  is a sectional view of assistance in explaining operations for fastening a magnetic disk to a hub structure with a thin plate spring. 
       FIG. 4  is a block diagram of a magnetic disk attaching machine. 
       FIG. 5  is a perspective view of the magnetic disk attaching machine. 
       FIG. 6  is a flow chart of a magnetic disk drive producing method. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a plan view of an essential part of a magnetic disk drive  10  in an exemplary embodiment according to the present invention.  FIGS. 2(A) and 2(B)  are a sectional view and a plan view, respectively, of a thin plate spring  50 .  FIG. 3  is a sectional view of assistance in explaining operations for fastening a magnetic disk to a hub structure with the thin plate spring  50 . A magnetic disk stack  13  ( 13   a ,  13   b ), a head stack assembly (hereinafter, abbreviated to “HSA”)  19 , a ramp  14 , an external terminal  21  and a voice coil yoke  25  are arranged on a base  11 . The magnetic disk drive  10  includes generally known components, but a process for tightening a fastening screw  17  included in a clamping mechanism is different from generally known ones. 
   As shown in  FIG. 3 , the magnetic disk stack  13  includes two magnetic disks  13   a  and  13   b . The clamping mechanism for holding the magnetic disk stack  13  includes the dished, thin plate spring  50 , the fastening screw  17  and a hub structure. As shown in  FIG. 3 , the hub structure includes a hub  29  and a shaft  27 . The magnetic disk stack  13  clamped by the clamping mechanism is rotated in the direction of the arrow A by a spindle motor. 
     FIGS. 2(A) and 2(B)  are a sectional view and a plan view, respectively, of the dished, thin plate spring  50  which is an essential part of the clamping mechanism. Shown also in  FIG. 2(A)  is the fastening screw  17 . The dished, thin plate spring  50  is formed by processing a stainless spring steel sheet of about 0.5 mm in thickness and is about 20 mm in a diameter. The thin plate spring  50  has a shape resembling a circular dish having a central part curved relative to a peripheral part. The thin spring plate  50  has a depressed part  56  formed in a central part thereof and provided with a through hole  51  in its central part. 
   The depressed part  56  surrounding the through hole  51  has a flat surface. The flat depressed part  56  is used for deflection measurement. Eight through holes  53  of a small diameter are formed around the depressed part  56 . The through holes  53  are used for restraining the thin plate spring  50  from turning when thin plate spring  50  is fastened by the fastening screw  17  and for balancing a rotary structure including the magnetic disks. A circumferential disk holding part  55  is formed in a peripheral part of the thin plate spring  50 . A flexible part extends between the through hole  51  and the disk holding part  55 . 
   The disk holding part  55  applies a fastening pressure to the magnetic disk  13   a  to fasten the magnetic disk stack  13  to the hub structure. When the thin plate spring  50  is placed on a flat surface with the disk holding part  55  in contact with the flat surface, a gap is formed between the central depressed part and the flat surface. Thus the flexible part is deflected elastically when the central depressed part is pressed toward the flat surface. An annular part, surrounding the through hole  51 , of the thin plate spring  50  is a pressure-bearing part. When the fastening screw is screwed in a threaded hole of the hub  29 , the head of the fastening screw pushes the pressure-bearing part and, consequently, the flexible part is deflected to depress the disk holding part  55  elastically. 
   In  FIG. 3 , the magnetic disks  13   a  and  13   b  are fastened to the hub  29  with the magnetic disks  13   a  and  13   b  spaced a predetermined distance apart from each other by a spacer ring  45 . Rotor magnets  43  are attached to the inner surface of a side wall of the hub  29 . The rotor magnets  43  and a stator coil  33  constitute the driving unit of the spindle motor. The stator coil  33  is fastened to the outer circumference of a bracket  35  fixedly held on the base  11 . 
   A bearing  37  is fitted in a bore formed in the bracket  35 . A shaft  27  pressed in the hub  29  is supported in the bearing  37 . A thrust bearing  39  is fixed to the shaft  27  to bear a vertical thrust that acts on the shaft  27 . The magnetic disks  13   a  and  13   b  are provided with central through holes, respectively. The magnetic disks  13   a  and  13   b  are put on the hub  29 . The disk holding part  55  of the thin plate spring  50  is pressed against a part, around the through hole, of the magnetic disk  13   a  to fasten the magnetic disks  13   a  and  13   b  to the hub  29 . The hub  29 , the shaft  27 , the bearing  37 , the thrust bearing  39 , the bracket  35 , the rotor magnets  43  and the stator coil  33  are the component members of the spindle motor. 
   In the construction of the spindle motor shown in  FIG. 3 , the fastening screw  17  is screwed in a threaded hole formed in the shaft  27 , the central part of the thin plate spring  50  is elastically distorted, and the resilience of the elastically distorted central part of the thin plate spring  50  pushes down the magnetic disk holding part  55 . In  FIG. 3 , the threaded hole is formed in the shaft  27 . Since the shaft  27  and the hub  29  are firmly joined together for simultaneous rotation, only the hub  29 , both the hub  29  and the shaft, or only the shaft  27  may be subjected to a tapping process. A screw driving device  103  provided with a screw driving tool suitable for driving the fastening screw  17  at its free end, and a cylindrical sleeve  101  shown in  FIG. 3  will be described later. 
     FIGS. 4(A) and 4(B)  are block diagrams of a magnetic disk attaching machine  100  for fastening the magnetic disk to the hub structure in a state before the fastening screw is tightened and in a state after the fastening screw has been tightened to deflect the thin plate spring  50  by a predetermined deflection, respectively.  FIG. 5  is a perspective view of the magnetic disk attaching machine  100 . The magnetic disk attaching machine  100  includes a sleeve  101  having an open first end on the side of the thin plate spring  50  and a second end through which the screw driving device  103  extends into the sleeve  101 . The screw driving device  103  includes a long shaft provided at its free end with a screw driving tool capable of snugly engaging in the slot of the head of the fastening screw  17 . A driving unit  115  drives the screw driving device  103  for rotation. 
   The magnetic disk attaching machine  100  is provided with a pressing spring  106  for elastically pressing the sleeve  101  in the direction of the arrow B parallel to the axis of the fastening screw  17 . The thin plate spring  50  is deflected in the direction of the arrow B when a fastening pressure is applied to the thin plate spring  50  in the direction of the arrow B. A probe  105  is connected to the sleeve  101  so as to move in the direction of the arrow B together with the sleeve  101 . A reflecting surface  107  is formed in the free end of the probe  105 . An air discharge pipe  117  connected to the sleeve  101  is connected to an evacuating device, not shown. An electromagnetic radiation send-receive device  109  projects a beam of electromagnetic radiation, such as an infrared ray or a laser beam, on the reflecting surface  107 , receives the reflected beam and generates a distance signal representing the distance between the electromagnetic radiation send-receive device  109  and the reflecting surface  107 . A deflection measuring unit  111  determines a displacement by which the reflecting surface  107  is displaced in the direction of the arrow B on the basis of the distance signal provided by the electromagnetic radiation send-receive device  109 . A controller  113  controls general operations of the magnetic disk attaching machine  100 . 
   A magnetic disk drive producing method using the magnetic disk attaching machine  100  for producing the magnetic disk drive  10  will be described with reference to  FIGS. 4 and 6 . The magnetic disk drive producing method embodying the present invention is characterized by a step of fastening the magnetic disk to the hub structure, and the rest of the steps of the magnetic disk drive producing method may be the same as those of the generally known magnetic disk drive producing methods. 
   The component parts of the spindle motor including the bearing  37 , the rotor magnet  43 , the stator coil  33 , the hub  29  and the shaft  27  are mounted on the base  11  in step  201 . The magnetic disk  13   b  is put on the hub  29 , the spacer ring  45  is put on the magnetic disk  13   b , and then the magnetic disk  13   a  is put on the spacer ring  45  in step  203 . Subsequently, the thin plate spring  50  put on the magnetic disk  13   a  such that the axis of the through hole  51  is aligned with the axis of the hub  29 . 
   In step  205 , data on magnetic disk fastening conditions including a desired deflection and the rotating speed of the screw driving device  103  are entered into the controller  113 . The thin plate spring  50  is deflected by the sleeve  101  pressed by the pressing spring  106  against the thin plate spring  50  by a very small initial deflection not greater than about 5% of a desired deflection by which the thin plate spring  50  is deflected upon the completion of screwing the fastening screw in the threaded hole. This initial deflection is within a tolerance for a desired deflection of the thin plate spring  50 . Therefore the proper management of the deflection of the thin plate spring  50  is not hindered by the initial deflection. The controller  113  may take into account the modulus of elasticity of the pressing spring  106  and the weight of the sleeve  101  for the management of the deflection. 
   In step  207 , the sleeve  101  is evacuated at a negative pressure to hold the fastening screw  17  on the first end of the sleeve  101 , the fastening screw  17  is aligned with the threaded hole of the shaft  27  and the sleeve  101  is brought into contact with the thin plate spring  50 . The sleeve  101  is pressed lightly against the depressed part  56  of the thin plate spring  50  to depress the depressed part  56  slightly. Since the depressed part  56  has a flat surface, the sleeve  101  can be stably kept in contact with the depressed part  56 . Therefore, the sleeve  101  will not be displaced from its correct position on the thin plate spring  50  and will not cause any measurement error at all while the fastening screw is being screwed in the threaded hole. 
   The sleeve  101  is in contact with a part, which is deflected greatly by the fastening pressure applied by the fastening screw  17  to the thin plate spring  50 , of the thin plate spring  50 , measurement error in the measured deflection is small and a desired fastening pressure can be accurately applied to the thin plate spring  50 . In step  209 , the electromagnetic radiation send-receive device  109  projects a beam of electromagnetic radiation on the reflecting surface  107  and receives the reflected beam of electromagnetic radiation, and the deflection measuring unit  111  determines the position of the reflecting surface  107  with respect to the direction of the arrow B on the basis of an electric signal received from the electromagnetic radiation send-receive device  109 . This position is used as a reference position. In step  211 , the driving unit  115  drives the screw driving device  103  for rotation to rotate the fastening screw  17  at a predetermined rotating speed. In step  213 , the electromagnetic radiation send-receive device  109  continues sending the beam of electromagnetic radiation on the reflecting surface  107 , and the deflection measuring unit  111  calculates the displacement of the reflecting surface  107  from the reference position and sends a signal representing the displacement of the reflecting surface  107  to the controller  113 . 
   In step  215 , the controller  113  monitors the displacement continuously to see if a deflection by which the thin plate spring  50  has been deflected is equal to a predetermined deflection Δx. Upon the coincidence of the deflection of the thin plate spring  50  with the predetermined deflection Δx, step  217  is executed. In step  217 , the controller  113  sends a stop signal to the driving unit  115  to make the driving unit  115  stop driving the screw driving device  103 . In this embodiment, a desired fastening pressure can be produced when the predetermined deflection Δx is on the order of 0.2 mm. After the completion of a magnetic disk attaching operation in step  217 , steps for assembling the rest of the component parts including the HSA  19 , the ramp  14  and the external terminal  21  are carried out in step  219 . Those steps to be carried out in step  219  may be carried out prior to the operations for attaching the magnetic disk to the hub structure. 
   The foregoing magnetic disk drive producing method controls the fastening pressure for pressing the magnetic disk against the hub structure by the clamping mechanism on the basis of the deflection of the thin plate spring directly representing the fastening pressure instead of the torque applied to the fastening screw indirectly representing the fastening pressure. Therefore, parameters affecting the actual fastening pressure are omitted and the magnetic disk can be fastened to the hub structure by a more accurate fastening pressure. Consequently, the magnetic disk will not be dislocated relative to the hub during operation due to the application of an excessively low fastening pressure to the magnetic disk and the magnetic disk will not be distorted due to the application of an excessively high fastening pressure to the magnetic disk. 
   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.

Technology Category: g