Abstract:
Embodiments of the invention provide a retaining ring attaching device capable of improving assembling efficiency and a data storage device fabricating method. In one embodiment, a C ring attaching device included in a hard disk drive assembling apparatus expands a C ring, puts the expanded C ring on a pivot, and contracts the C ring on the pivot. The C ring attaching device moves chuck arms holding the C ring such that the C ring is moved so that a gap in the C ring moves away from the pivot while the C ring is being contracted.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application claims priority from Japanese Patent Application No. JP2004-162472, filed May 31, 2004, the entire disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a retaining ring attaching device and a data storage device fabricating method.  
         [0003]     There are various known data storage devices using various recording mediums, such as optical disks and magnetic tapes. A hard disk drive is used prevalently as a storage device for computers and is one of indispensable storage devices for current computer systems. Uses of the hard disk drive as removable storage devices for motion image storage/reproduction devices, car navigation systems and digital cameras are progressively increasing owing to the excellent characteristics of the hard disk drive.  
         [0004]     Internal contamination of products using a hard disk, such as hard disk drives, with metal powder is extremely detrimental to those products. Accordingly, there is a tendency to avoid using retaining rings (hereinafter, referred to as “C ring(s)”) for assembling a hard disk drive because C rings come into sliding contact with metal members.  
         [0005]     Reduction of the cost of the data storage device is an urgent need in recent years and demands a data storage device of simple construction capable of being assembled with reliability, and an assembling method of assembling the data storage device. The conventional hard disk drive is provided with a head stack assembly (hereinafter, abbreviated to “HSA”) fixedly mounted on a pivot. A slide screw fixing method has been used for fixedly mounting the HSA on the pivot. However, a fixing method that uses a C ring for fixing the HAS to the pivot is used to achieve cost reduction.  FIG. 20  shows a HSA assembled by the fixing method using a C ring in a perspective view.  
         [0006]     Referring to  FIG. 20 , a pivot  903  is fitted in a hole  902  formed in a HSA  901  such that the HSA  901  is seated on a flange  904  formed in the pivot  903 . A wavy washer  905  is put on the HSA  901 , and a C ring  906  is attached to the pivot  903  so as to retain the HSA  901  and the wavy washer  905  on the pivot  903 . The HSA  901  is held between the flange  904  and the wavy washer  905  and is held fixedly on the pivot  903  by the resilience of the wavy washer  905 . Generally, the C ring  906  is attached to the pivot  903  by a manual operation using a hand tool, such as a pair of pliers.  
         [0007]     A C ring attaching device disclosed in Japanese Patent Laid-open JP-A 10-138054 (Patent Document 1) inserts pins in small holes formed at the opposite ends of a C ring, moves the pins away from each other to expand the C ring, and fits the C ring in an annular groove formed in a shaft. This C ring attaching device is capable of forcibly reducing the diameter of the C ring if necessary in attaching the C ring to the shaft. A C ring attaching device disclosed in Japanese Patent Laid-open JP-A 6-304823 (Patent Document 2) is capable of automatically attaching a C ring to a shaft. These two references mention nothing about the application of the C ring attaching devices to attaching a C ring to a shaft in assembling a hard disk drive.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     The conventional hard disk drive assembling method is unable to assemble a hard disk drive efficiently because a C ring needs to be attached to a shaft by an operator.  
         [0009]     The present invention has been made in view of the foregoing circumstances and it is therefore a feature of the present invention to provide a retaining ring attaching device capable of efficiently attaching a retaining ring to a shaft, and to provide a data storage device fabricating method.  
         [0010]     A retaining ring attaching device in a first aspect of the present invention for attaching a retaining ring having an opening to a shaft includes: chucking arms for expanding the retaining ring, putting the retaining ring on the shaft and contracting the retaining ring; and a chucking arm moving mechanism for moving the chuck arms holding the retaining ring so as to move the retaining ring in a first direction in which a gap in the retaining ring moves away from the shaft while the retaining ring is contracting on the shaft.  
         [0011]     The retaining ring attaching device is used for automatically and efficiently assembling a data storage device. Since the retaining ring is contracted while the open end of the retaining ring is shifted away from the shaft, the possibility of the shaft being flawed by the retaining ring can be decreased.  
         [0012]     Preferably, the chucking arm moving mechanism includes: sliders capable of sliding in a second direction in which the retaining ring expands; and a guide mechanism capable of sliding the chucking arms in a third direction inclined to the second direction toward the first direction so that the chucking arms move toward each other, pushing the retaining ring in the first direction.  
         [0013]     The retaining ring attaching device according to an embodiment of the present invention further includes: a motor having a rotating shaft; an eccentric cam having an inner eccentric cam and an outer eccentric cam, and fixedly mounted on the rotating shaft of the motor; and cam followers connected to the sliders so as to move along the inner eccentric cam or the outer eccentric cam to slide the sliders. The retaining ring attaching device further includes slider springs movably connecting the sliders and the cam followers.  
         [0014]     The guide mechanism has an arm cam fixed to the chuck arm, and a guide block having an inclined surface, and fixed to the slider with the inclined surface inclined in the third direction and in contact with the arm cam.  
         [0015]     A retaining ring attaching device in a second aspect of the present invention includes: sliders capable of sliding in a direction in which a retaining ring having a gap expands; chucking arms fixed to the sliders, capable of sliding in the direction in which the retaining ring expands as the sliders slide and of putting the retaining ring on a shaft inserted in the retaining ring; a motor having a rotating shaft; an eccentric cam having an inner eccentric cam and an outer eccentric cam and fixedly mounted on the rotating shaft for rotation together with the rotating shaft; and cam followers connected to the sliders so as to move along the inner eccentric cam or the outer eccentric cam to slide the slider. The retaining ring attaching device is used for automatically and efficiently assembling a data storage device.  
         [0016]     A retaining ring attaching device in a third aspect of the present invention includes: first and second sliders disposed opposite to each other and capable of moving in opposite directions; a first chuck arm to be connected to a first end of a retaining ring having a gap, connected to the first slider, and capable of moving in the opposite directions as the first slider slides; a second chuck arm to be connected to a second end of the retaining ring opposite the first end, connected to the second slider, and capable of sliding in the opposite directions as the second slider slides to expand the retaining ring in cooperation with the first chuck arm so that the retaining ring is attached to a shaft; and a guide mechanism for guiding the first and the second chuck arm for sliding in a direction inclined to the opposite directions toward an outward direction from the center of the retaining ring toward the gap of the retaining ring so that the first and the second chuck arm permit the retaining ring to contract by pressing the retaining ring in the outward direction.  
         [0017]     A data storage device can be automatically and efficiently assembled by using the retaining ring attaching device. Since the retaining ring contracts as the open ends of the retaining ring is separated from the shaft, the possibility of the shaft being flawed by the retaining ring can be decreased.  
         [0018]     The retaining ring attaching device according to an embodiment of the present invention further includes: a motor having a rotating shaft; an eccentric cam having an inner eccentric cam and an outer eccentric cam and fixedly mounted on the rotating shaft; a first cam follower that moves along the inner or the outer eccentric cam to slide the first slider; a second cam follower that moves along the inner or the outer eccentric cam to slide the second slider in coordination with the first slider; a first slider spring movably connecting the first slider and the first cam follower; a second slider spring movably connecting the second slider and the second cam follower; and a cam follower spring having a spring constant lower than those of the first and the second slider spring and movably connecting the first and the second cam follower.  
         [0019]     The guide mechanism includes a first guide mechanism capable of coming into contact with the first chuck arm in an inclined plane inclined in the outward direction to the opposite directions to guide the first chuck arm along the inclined plane so that the retaining ring is pushed, and a second guide mechanism interlocked with the first chuck arm and capable of guiding the second chuck arm so as to push the retaining ring.  
         [0020]     The second guide mechanism includes: an arm spring movably connecting the first chuck arm and the second chuck arm; and an arm cam fixed to the second chuck arm, and holding the first chuck arm together with the first guide mechanism to operate the second chuck arm substantially symmetrically with the first chuck arm with respect to an axis substantially perpendicular to a line connecting the first and the second end.  
         [0021]     The first guide mechanism is substantially a mechanism that inclines and slides the first and the second chuck arm. Therefore, the first and the second chuck arm can be inclined and slid without excessively increasing parts for inclining and sliding the first and the second chuck arm.  
         [0022]     A data storage device fabricating method in a fourth aspect of the present invention includes the steps of: mounting a head stack assembly on a pivot; expanding a retaining ring; putting the expanded retaining spring on the pivot; and contracting the retaining ring while the retaining ring put on the pivot is pushed to attach the retaining ring to the pivot. The data storage device fabricating method can automatically and efficiently assemble a data storage device. Since the retaining ring is contracted while the same is being pushed, the possibility of the pivot being flawed by the retaining ring can be decreased.  
         [0023]     A data storage device assembling method in a fifth aspect of the present invention includes the steps of: mounting a head stack assembly on a pivot; expanding a retaining ring; putting the expanded retaining ring on the pivot; attaching the retaining ring to the pivot by contracting the retaining ring; re-expanding the retaining ring; and contracting the re-expanded retaining ring. The data storage device fabricating method can automatically and efficiently assemble a data storage device.  
         [0024]     The retaining ring attaching device of the present invention enables efficient assembling work, and the data storage device fabricating method is capable of efficiently assembling a data storage device. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a schematic, typical view of assistance in explaining a hard disk drive assembling operation to be carried out by an assembling apparatus according to embodiments of the present invention.  
         [0026]      FIG. 2  is a schematic, typical view of assistance in explaining the hard disk drive assembling operation to be carried out by the assembling apparatus according to embodiments of the present invention.  
         [0027]      FIG. 3  is a perspective view of a C ring attaching device in a first embodiment according to the present invention.  
         [0028]      FIG. 4  is a perspective view of the C ring attaching device in the first embodiment.  
         [0029]      FIG. 5  is a perspective view of the C ring attaching device in the first embodiment.  
         [0030]      FIG. 6  is a schematic, typical view of assistance in explaining a C ring attaching operation to be carried out by the C ring attaching device according to an embodiment of the present invention.  
         [0031]      FIG. 7  is a schematic, typical view of assistance in explaining the C ring attaching operation to be carried out by the C ring attaching device according to an embodiment of the present invention.  
         [0032]      FIG. 8  is a schematic, typical view of assistance in explaining the C ring attaching operation to be carried out by the C ring attaching device according to an embodiment of the present invention.  
         [0033]      FIG. 9  is a schematic typical view of assistance in explaining another C ring attaching operation to be carried out by the C ring attaching device according to a second embodiment of the present invention.  
         [0034]      FIG. 10  is a schematic typical view of assistance in explaining another C ring attaching operation to be carried out by the C ring attaching device according to an embodiment of the present invention.  
         [0035]      FIG. 11  is a perspective view of a C ring attaching device in a third embodiment according to the present invention.  
         [0036]      FIG. 12  is a schematic, typical view of assistance in explaining a C ring attaching operation to be carried out by the C ring attaching device according to an embodiment of the present invention.  
         [0037]      FIG. 13  is a schematic, typical view of assistance in explaining another C ring attaching operation to be carried out by the C ring attaching device according to an embodiment of the present invention.  
         [0038]      FIG. 14  is a schematic, typical view of assistance in explaining another C ring attaching operation to be carried out by the C ring attaching device according to a fourth embodiment of the present invention.  
         [0039]      FIG. 15  is a schematic, typical view of assistance in explaining another C ring attaching operation to be carried out by the C ring attaching device according to a fifth embodiment of the present invention.  
         [0040]      FIG. 16  is a plan view of a C ring relating to a sixth embodiment of the present invention.  
         [0041]      FIG. 17  is a table showing the results of evaluation of the C ring attaching operation carried out by the C ring attaching devices according to embodiments of the present invention.  
         [0042]      FIG. 18  is a strip film carrying photographs of a C ring in a C ring attaching process carried out by the C ring attaching device according to embodiments of the present invention.  
         [0043]      FIG. 19  is a strip film carrying photographs of a C ring in a C ring attaching process carried out by the C ring attaching device according to embodiments of the present invention.  
         [0044]      FIG. 20  is a perspective view of a HSA and a pivot in a conventional hard disk drive. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0045]     Specific embodiments of the present invention will be described with reference to the accompanying drawings. The present invention will be described as applied to a hard disk drive in an example of a data storage device.  
       First Embodiment  
       [0046]     A hard disk drive assembling apparatus relating to an embodiment of the present invention will be described with reference to  FIGS. 1 and 2  showing steps of hard disk drive assembling operation to be carried out by the hard disk drive assembling apparatus in typical views.  
         [0047]     Referring to  FIG. 1 ( a ), a hard disk drive assembling apparatus  100  embodying the present invention has a C ring attaching device  110  in a first embodiment according to the present invention and an index table  120 . In the following description, the hard disk drive assembling apparatus  100  will be referred to simply as the assembling apparatus  100 .  
         [0048]     The C ring attaching device  110  serves as a pair of pliers for expanding and contracting a C ring. The index table  120  is a turntable that turns in a substantially horizontal plane. The C ring attaching device  110  is fixedly disposed near an inner part of the index table  120 . The index table  120  is fixedly provided with fixtures  121 ,  122 ,  123  and  124 . The fixtures  121  to  124  turn together with the index table  120 .  
         [0049]     A C ring attaching operation of the assembling apparatus  100  will be described. As shown in  FIG. 1 ( a ), a C ring  130  is placed on the fixture  121  of the index table  120 . For example, the C ring  130  is carried by and positioned relative to the fixture  121  by a robot arm, not shown.  
         [0050]     As shown in  FIG. 1 ( b ), the index table  120  turns after the C ring  130  has been placed on the fixture  121 . The index table  120  stops after turning clockwise, as viewed in  FIG. 1 , through an angle of about 90°. Then, a robot arm, not shown, places a HSA  131  on the fixture  124  after the index table  120  has stopped.  
         [0051]     As shown in  FIG. 1 ( c ), the index table  120  fixedly holding the C ring  130  and the HSA  131  thereon turns through an angle of about 90°. At this stage, the fixture  121  is positioned at a back part of the index table  120  such that the C ring  130  is positioned so as to correspond to the C ring attaching device  110 . The C ring attaching device  110  takes up the C ring  130  from the fixture  121 .  
         [0052]     As shown in  FIG. 2 ( d ), the index table  120  turns through an angle of about 90° after the C ring attaching device  110  has held the C ring  130 . At this stage, the HSA  131  held by the fixture  124  is moved to a back part of the index table  120  so as to correspond to the C ring attaching device  110 . The C ring attaching device  110  attaches the C ring  130  to a pivot  132 . An operation for attaching the C ring  130  to the pivot  132  will be described later.  
         [0053]     As shown in  FIG. 2 ( e ), the index table  120  turns clockwise through an angle of about 90° after the C ring  131  has been attached to the pivot  132 . Thus the HSA  131  is separated from the C ring attaching device  110  to enable an assembly  133  of the HSA  131 , and the pivot  132  and the C ring  130  can be removed from the index table  120 . Then, as shown in  FIG. 2 ( f ), the index table  120  turns further through an angle of about 90° to position the assembly  133  at a removing position where a robot arm, not shown, takes up the assembly  133  from the index table  120 . The C ring attaching operation illustrated by FIGS.  2 ( a ) to  2 ( f ) uses the fixtures  121  and  124 . Another assembly  133  can be assembled simultaneously with the assembly  133  assembled by using the fixtures  121  and  124  by using the fixtures  122  and  123 .  
         [0054]     The assembling apparatus  100  is capable of attaching the C ring  130  to the pivot  132 . The assembling apparatus  100  has three working stations, and turns the index table  120  through an angle of about 90° at a time to locate the parts at the working stations. The assembling apparatus  100  assembles one assembly  133  every turn of the index table  120  through an angle of about 180°. The assembling apparatus  100  performs assembling operations simultaneously at the three working stations to reduce time.  
         [0055]     The construction of the C ring attaching device  110  in the first embodiment of the present invention will be described with reference to FIGS.  3  to  5 .  FIG. 3  shows a pick-up mechanism included in the C ring attaching device  110  for taking up the C ring  130  in a bottom view.  FIG. 3  is a view of the C ring attaching device  110  taken from below the C ring attaching device  110  fixed relative to the index table  120 . In  FIG. 3 , a side on the side of the front surface of the paper is an upper side, a side on the side of the back surface of the paper is a lower side, a side on the side of an upper part of the paper is a front side, and a side on the side of a lower part of the paper is a back side.  
         [0056]     Referring to  FIG. 3 , the C ring attaching device  110  is provided with a pick-up mechanism  200 . The pick-up mechanism  200  includes a base plate  210 , a back slide rail  220 , cam followers  231  and  232 , upper slide rails  241  and  242 , back slide rails  251  and  252 , front sliders  261  and  262 , chuck arms  271  and  272 , a C ring guide  280 , a cam follower spring  290 , slider springs  300  and  310 , and arm spring  320 .  
         [0057]     The component members of the C ring attaching device  110  are mounted on the base plate  210 . The base plate  210  is fixedly disposed relative to the index table  120 . The base plate  210  has an upper wall  211 , a back wall  212  and sidewalls  213  and  214 . The C ring attaching device  110  is fixedly installed with the upper wall  211  held substantially horizontally. The upper wall  211  is substantially perpendicular to the back wall  212  and the sidewalls  213  and  214 . The back wall  212  and the side walls  213  and  214  are held substantially vertically when the C ring attaching device  110  is fixedly installed.  
         [0058]     The back slide rail  220  is an elongate member having the shape of a strip. The back slide rail  220  is fixed to the back wall  212  so as to extend substantially parallel to the upper wall  211  of the base plate  210 .  
         [0059]     The cam followers  231  and  232  are substantially L shaped members. The cam followers  231  and  232  are mounted on the base plate  210  such that one of the legs of each of the cam followers  231  and  232  is slidable along the back wall  212  of the base plate  210  and the other leg is slidable along the upper wall  211  of the base plate  210 . Sides, on the side of the upper wall  211 , of the cam followers  231  and  232  are engaged with an eccentric cam, not shown in  FIG. 3 . The cam followers  231  and  232  are symmetrical with respect to a centerline.  
         [0060]     The upper slide rails are elongate members substantially resembling a strip. The upper side rails  241  and  242  are fixed to the upper wall  211  so as to extend substantially parallel to the back wall  212  of the base plate  210 . The upper slide rails  241  and  242  are substantially aligned with a straight line.  
         [0061]     The back sliders  251  and  252  are mounted on the upper slide rails  241  and  242  so as to move straight. The back sliders  251  and  252  are able to slide substantially parallel to the back wall  212  of the base plate  210 . The back sliders  251  and  252  are substantially symmetric with respect to the center line.  
         [0062]     The front sliders  261  and  262  are connected to the back sliders  251  and  252 , respectively. The front sliders  261  and  262  are mounted on the end surface  215  of the back wall  212  of the base plate  210  for sliding along the end surface  215 . The front sliders  261  and  262 , similarly to the back sliders  251  and  252 , are substantially symmetric with respect to the center line.  
         [0063]     The chuck arms  271  and  272  are supported for turning on the front sliders  261  and  262 , respectively. More specifically, the chuck arms  271  and  272  are supported on end parts of the front sliders  261  and  262 , respectively. The chuck arms  271  and  272  are substantially symmetric with respect to the centerline. The chuck arms  271  and  272  extend toward each other. The chuck arms  271  and  272  are provided with chuck pins  273  and  274 , respectively. The chuck pins  273  and  274  are attached to end parts of the chuck arms  271  and  272  so as to project downward.  
         [0064]     The C ring guide  280  positions the C ring  130 . The C ring guide  280  is fixed to the upper wall  211  of the base plate  210  at a position between the extremities of the chuck arms  271  and  272 . The C ring guide  280  is provided with a C-shaped groove  281  resembling the shape of the C ring  130 . The C ring guide  280  is fixed to the upper wall  211  such that the C-shaped groove  281  is substantially horizontal.  
         [0065]     The cam follower spring  290  has opposite ends attached to the cam followers  231  and  232 . More concretely, the cam follower spring  290  is extended between the legs of the L-shaped cam followers  231  and  232  on the back wall  212 .  
         [0066]     The respective spring constants of the slider springs  300  and  310  are greater than that of the cam follower spring  290 . The slider spring  300  has opposite ends attached to the back slider  251  and the cam follower  231 . More concretely, the slide spring  300  is attached to the leg of the substantially L-shaped cam follower  231  on the upper wall  211 . The slider spring  300  extends substantially parallel to the upper wall  211  of the base plate  210 . The slider spring  311 , similarly to the slider spring  300 , has opposite ends attached to the cam follower  232  and the back slider  252 . The arm spring  320  is extended between the chuck arms  271  and  272 .  
         [0067]      FIG. 4  shows a driving mechanism for operating the chuck arms  271  and  272  of the C ring attaching device  110  in a bottom view.  FIG. 4 , similarly to  FIG. 3 , is a bottom view taken from below the C ring attaching device  110  fixedly disposed relative to the index table  120 . In  FIG. 4 , a side on the side of the front surface of the paper is an upper side, a side on the side of the back surface of the paper is a lower side, a side on the side of an upper part of the paper is a front side, and a side on the side of a lower part of the paper is a back side. As shown in  FIG. 4 , the C ring attaching device  110  is provided with a driving mechanism  400  in addition to the members  210  to  320 . The driving mechanism  400  includes an eccentric cam  410 , a motor  420  and a cam base plate  430 .  
         [0068]     The eccentric cam  410  is a grooved cam having a substantially circular shape on a plane. The eccentric cam  410  has an inner eccentric cam  411  and an outer eccentric cam  412  spaced apart from each other by a cam groove  413 . The inner and the outer side surface of the cam groove  413  are the cam surfaces of the inner eccentric cam  411  and the outer eccentric cam  412 , respectively.  
         [0069]     The inner eccentric cam  411  consists of two eccentric curved sections  451  and  452 , and two flat sections  453  and  454 . As shown in  FIG. 4 , the curved sections  451  and  452  and the flat sections  453  and  454  are connected successively and are substantially symmetric with respect to the center of the eccentric cam  410 . Each of the curved sections  451  and  452  has opposite ends connected to the flat sections  453  and  454 . A corner  455  is formed at the joint of the curved section  451  and the flat section  453 , and a corner  456  is formed at the joint of the curved section  452  and the flat section  454 . The incenter of a circle inscribed in the curved sections  451  and  452  and the incenter of a circle inscribed in the flat sections  453  and  454  are at different positions, respectively.  
         [0070]     The outer eccentric cam  412 , similarly to the inner eccentric cam  411 , consists of two eccentric curved sections  461  and  462 , and two flat sections  463  and  464 . The curved sections  461  and  462  and the flat sections  463  and  464  are arranged alternately and are substantially symmetric with respect to the center of the eccentric cam  410 . Corners  466  and  465  are formed at the joint of the curved section  461  and the flat section  463 , and the joint of the curved section  462  and the flat section  464 , respectively.  
         [0071]     The curved sections  461  and  462  of the outer eccentric cam  412  face the curved sections  451  and  452  of the inner eccentric cam  411 , respectively, with the cam groove  413  disposed therebetween. The curved sections  461  and  462  are substantially similar to the curved sections  451  and  452 . The flat sections  463  and  464  face the flat sections  453  and  454  of the inner eccentric cam  411 , respectively, with the cam groove  413  disposed therebetween.  
         [0072]     The outer eccentric cam  412  is greater than the inner eccentric cam  411  and has a shape substantially similar to that of the inner eccentric cam  411 . The outer eccentric cam  412  having the two curved sections  461  and  462  and the flat sections  463  and  464  serves as an eccentric cam surface. Since the sections  461  to  464  of the outer cam surface face the sections  451  to  454  of the inner eccentric cam  411 , respectively, the respective centers of the inner eccentric cam  411  and the outer eccentric cam  412  are at substantially the same position.  
         [0073]     The motor  420  is an electric motor, such as a stepper motor. The motor  420  has a drive shaft  421  connected to a central part of the inner eccentric cam  411  perpendicularly to the inner eccentric cam  411 . The cam base plate  430  supports the drive shaft  421  of the motor  420  connected to the eccentric cam  410 . The cam base plate  430  supports the eccentric cam  410  on the base plate  210 . The eccentric cam  410  is supported substantially parallel to the upper wall  211  of the base plate  210  by the cam base plate  430 . The cam base plate  430  is fixed to the upper surface of the upper wall  211  of the base plate  210 . The eccentric cam  410  is supported on a side of the upper wall  211  of the base plate opposite a side on which the members of the pick-up mechanism  200  are disposed.  
         [0074]     In this driving mechanism  400 , the eccentric cam  410  guides the cam followers  231  and  232  by both the inner eccentric cam  411  and the outer eccentric cam  412 . The chuck arms  271  and  272  can be opened and closed by the motor  420 .  
         [0075]      FIG. 5  shows an arm guide mechanism  500  included in the C ring attaching device  110  in a top view. The arm guide mechanism  500  guides the chuck arms  271  and  272 .  FIG. 5  is a top view of the C ring attaching device  110  fixedly disposed relative to the index table  120 . In  FIG. 5 , a side on the side of the front surface of the paper is a front side, a side on the side of the back surface of the paper is a back side, a side on the side of an upper part of the paper is an upper side, and a side on the side of a lower part of the paper is a lower side. As shown in  FIG. 5 , the C ring attaching device  110  further includes the arm guide mechanism  500  having a guide block  510  and arm cams  520  and  530 .  
         [0076]     The guide block  510  has an inclined surface  511 . The guide block  510  is fixed to the cam base plate  430  with the inclined surface  511  facing the chuck arm  272 . The inclined surface  511  is substantially vertical and is inclined to the upper wall  211  of the base plate  210 . The inclined surface  511  is inclined to the length of the chuck arm  272 ; that is, the inclined surface  511  is inclined to a direction in which the front sliders  261  and  262  slide. The arm cam  520  is a drum cam and is fastened to the chuck arm  272 . The arm cam  520  has a side surface  521  in contact with the inclined surface  511 . The arm cam  520  slides along the inclined surface  511 . The arm cam  530  is fixed to the chuck arm  271  so as to be in contact with the front surface of the chuck arm  272 .  
         [0077]     In this arm guide mechanism  500 , the chuck arm  272  lies between the guide block  510  and the arm cam  530 . The chuck arms  271  and  272  are forced to extend toward each other by the arm spring  320  extended between the chuck arms  271  and  272 . Thus the respective motions of the chuck arms  271  and  272  are substantially symmetric. When the arm cam  520  attached to the chuck arm  272  slides along the inclined surface  511 , the chuck arm  271  moves and inclined similarly to the chuck arm  272 .  
         [0078]     A C ring attaching operation to be carried out by the C ring attaching device  110  will be described with reference to FIGS.  6  to  8 . The C ring attaching operation will be described principally in connection with  FIG. 6  and reference will be made to  FIGS. 7 and 8  when necessary.  
         [0079]      FIG. 6  illustrates the general operation of the C ring attaching device  110  in a schematic view. In  FIG. 6 , two guide blocks  510  and two arm cams  520  are shown hypothetically to facilitate understanding the operation of the chuck arms  271  and  272 .  
         [0080]     As shown in  FIG. 6 ( a ), the cam followers  231  and  232  are in contact with the inner eccentric cam  411  of the eccentric cam  410  when the chuck arms  271  and  272  are opened. The cam followers  231  and  232  slides along the back slide rail  220  so as to separate from each other when the eccentric cam  410  turns.  
         [0081]     Since the back sliders  251  and  252  are connected to the cam followers  231  and  232  by the slider springs  300  and  310 , respectively, the back sliders  251  and  252  slide on the upper slide rails  241  and  242  so as to separate from each other. The strong slider springs  300  and  310  are not stretched, and the weak cam follower spring  290  for removing the back lash is stretched.  
         [0082]     The front sliders  261  and  262  fixed respectively to the back sliders  251  and  252  slide along the end surface  215  of the base plate  210  according to the sliding of the back sliders  251  and  252 . Consequently, the chuck arms  271  and  272  are moved apart from each other, and the distance between the chuck pins  273  and  274  is increased. Upon engagement of the cam followers  231  and  232  with the corners  455  and  456  of the inner eccentric cam  411 , the distance between the chuck pins  273  and  274  of the chuck arms  271  and  272  increases to the maximum. The chuck arms  271  and  272  press the C ring  130  against a wavy washer, not shown, and put the C ring  130  on the pivot  132 .  
         [0083]      FIG. 7 ( a ) shows the C ring  130  put on the pivot  132  in a typical view. The arm guide mechanism  500  shown in  FIG. 5  has the single guide block  510  that slides the chuck arms  271  and  272  in an inclined position.  FIG. 7 , similarly to  FIG. 6 , shows hypothetically two guide blocks  510  and two arm cams  520  to facilitate understanding the operation of the chuck arms  271  and  272 .  
         [0084]     As shown in  FIG. 7 ( a ), the C ring  130  has a gap  141  (see  FIG. 8 ) and chuck holes  142  and  143 . The gap  141  is formed between the opposite ends  144  and  145  of the substantially annular C ring  130 . The chuck holes  142  and  143  are through holes formed in the ends  144  and  145 , respectively.  
         [0085]     When the chuck arms  271  and  272  take up the C ring  130 , the C ring  130  is fitted in the C-shaped groove  281  of the C ring guide  280 . In this state, the chuck pins  273  and  274  are fitted in the chuck holes  142  and  143  of the C ring  130 . The chuck arms  271  and  272  are moved to engage the chuck pins  273  and  274  with the side surfaces of the chuck holes  142  and  143 , respectively, and expand the gap  141 . The chuck arms  271  and  272  slide without inclining in the vicinity of parts of the guide blocks  510  near the side ends of the chuck arms  271  and  272 ; that is, the chuck arms  271  and  272  move straight in directions (lateral directions) in which the front sliders  261  and  262  slide.  
         [0086]     Referring to  FIG. 6 ( b ), the motor  420  continues to operate in the state shown in  FIG. 6 ( a ) and then the cam followers  231  and  232  in engagement with the inner eccentric cam  411  are disengaged gradually from the inner eccentric cam  411 . As the cam followers  231  and  232  are disengaged from the inner eccentric cam  411 , the stretched, weak cam follower spring  290  contracts. The strong slider springs  300  and  310  remain unstretched. The operations of the cam followers  231  and  232  and the chuck arms  271  and  272  are coordinated.  
         [0087]      FIG. 7 ( b ) shows the C ring  130  in this state in a typical view. The separated chuck arms  271  and  272  are moved toward each other. The chuck arms  271  and  272  slide up the slopes of the guide blocks  510 . The chuck arms  271  and  272  slide in both the sliding directions (lateral directions) of the front sliders  261  and  262  and a direction substantially perpendicular to the lateral directions (longitudinal direction); that is, the chuck arms  271  and  272  move so as to push the C ring  130  gradually toward the pivot  132 .  
         [0088]     As shown in  FIG. 6 ( c ), the cam followers  231  and  232  are disengaged from the inner eccentric cam  411  and are engaged with the outer eccentric cam  412 . At this stage, the slider springs  300  and  310  stronger than the cam follower spring  290  start being stretched. As the motor  420  rotates further, the weak cam follower spring  290  is stretched to a necessary and sufficient extent and the resilience of the cam follower spring  290  acts through the sliders  241 ,  242 ,  251  and  252  on the chuck arms  271  and  272 . Consequently, sufficient force for fastening the C ring  130  can be obtained.  
         [0089]      FIG. 7 ( c ) shows the C ring  130  in this state in a typical view. As shown in  FIG. 7 ( c ), the distance between the chuck arms  271  and  272  is shorter than that in the state shown in  FIG. 7 ( b ). The C ring  130  is pushed forward when the C ring  130  is attached to the pivot  132 . As the chuck arms  271  and  272  slide in an inclined position, the expanded C ring  130  contracts by its own resilience and the gap  141  narrows. The resilience of the C ring  130  decreases to zero when the C ring  130  fastens on the pivot  132 .  
         [0090]      FIG. 8  shows the fastening process of the C ring  130  shown in FIGS.  7 ( b ) and  7 ( c ) in an enlarged typical view. The contraction of the C ring  130  from a state shown in  FIG. 7 ( b ) to a state shown in  FIG. 7 ( c ) is indicated by the arrows. As shown in  FIG. 8 , the chuck arms  271  and  272  slide in oblique directions. Consequently, the C ring  130  fastens on the pivot  132  without the edges  146  and  147  of the C ring  130  touching the pivot  132  because the chuck arms  271  and  272  push the C ring  130  forward before the edges  146  and  147  come into contact with the pivot  132 . The chuck arms  271  and  272  move such that the edges  146  and  147  of the C ring  130  do not touch the pivot  132  before the C ring  130  fully contracts. The inclined surface  511  of the guide block  510  is designed so that the edges  146  and  147  of the C ring  130  may not touch the pivot  132 .  
         [0091]     Thus the C ring  130  can be automatically attached to the pivot  132  by the C ring attaching device  110  of the present embodiment. Consequently, a hard disk drive can be efficiently assembled by the assembling apparatus  100  of the present embodiment.  
         [0092]     The chuck arms  271  and  272  of the C ring attaching device  110  achieve simultaneously the operation for contracting the C ring  130  and the operation for pushing the C ring  130  forward. Consequently, scratching the pivot  132  with the edges  146  and  147  of the C ring  130  can be avoided and the production of metal powder by scraping the pivot  132  with the edges  146  and  147  of the C ring can be prevented, which is a greatly advantageous effect on assembling a hard disk drive to which existence of metal powder is extremely detrimental. Since the pivot  132  is scarcely damaged, the C ring  130  can properly contract.  
         [0093]     If an additional actuator, such as a cylinder actuator, is used for pulling the chuck arms  271  and  272 , the design of the C ring attaching device  110  needs to be changed to add wiring and piping to the C ring attaching device  110 . The design of the C ring attaching device  110  does not need to be changed greatly in incorporating the arm guide mechanism  500  into the C ring attaching device  110 . Thus, the chuck arms  271  and  272  can be moved forward by the low-cost mechanism and hence increase of the cost of the C ring attaching device  110  can be avoided.  
       Second Embodiment  
       [0094]     A C ring attaching device  110  in a second embodiment according to the present invention is not provided with any members corresponding to the guide block  510  and the arm cam  520  of the C ring attaching device  110  in the first embodiment. The description of the general construction of the C ring attaching device  110  in the second embodiment will be omitted.  
         [0095]      FIG. 9  is a typical view of assistance in explaining a C ring attaching operation to be carried out by the C ring attaching device  110  in the second embodiment to attach a C ring  130  on a pivot  132 . As shown in  FIG. 9 ( a ), the C ring  130  is expanded so as to expand the gap  141  (see  FIG. 10 ) thereof and is placed so as to surround the pivot  132 . This state is substantially the same as the state shown in  FIG. 7 ( a ).  
         [0096]     Then, the C ring  130  is allowed to contract as shown in  FIG. 9 ( b ). Chuck arms  271  and  272  move laterally toward each other to close the gap  141  of the C ring  130 . In this state, the chuck arms  271  and  272  are spaced a distance A apart from each other. As the chuck arms  271  and  273  move laterally, the edges  146  and  147  of the C ring  130  approach the pivot  132 .  
         [0097]      FIG. 9 ( c ) shows a C ring fastening process of completing fastening the C ring  130  in a state shown in  FIG. 9 ( b ). As shown in  FIG. 9 ( c ), the chuck arms  271  and  272  turn relative to front sliders  261  and  262  to push the C ring  130  forward to permit the C ring  130  contract further. The width of the gap  141  decreases from A to A−α The C ring  130  contracts by its own resilience to close the gap  141  and fastens on the pivot  132 .  
         [0098]     The fastening operation of the C ring  130  explained in connection with  FIG. 9  is illustrated in  FIG. 10  in an enlarged typical view. Movement of the C ring  130  during a fastening process from a state shown in  FIG. 9 ( a ) to a state shown in  FIG. 9 ( c ) is indicated by the arrows. As shown in  FIG. 10 , the C ring  130  approaches the pivot  132  once, and then separates from the pivot  132  and fastens to the pivot  132 .  
         [0099]     Thus the C ring can be automatically attached to the pivot  132  by the C ring attaching device  110  in the second embodiment. Since the chuck arms  271  and  272  of the C ring attaching device  110  are turnable, and hence the chuck arms  271  and  272  are able to move longitudinally as well as laterally. The chuck arms  271  and  272  can move the C ring  130  forward by the lateral and longitudinal movement. Even if the C ring  130  touches the pivot  132 , the C ring  130  can be pulled toward the pivot  132  and can fully contract.  
       Third Embodiment  
       [0100]     A C ring attaching device  600  in a third embodiment according to the present invention is similar to the C ring attaching device  110  in the second embodiment, except that the former is provided with chuck arms  271  and  272  fastened to front sliders  261  and  262 .  
         [0101]     The general construction of the C ring attaching device  600  in the third embodiment will be described with reference to  FIG. 11 . A pick-up mechanism  601  for picking up a C ring  130  included in the C ring attaching device  600  is shown in a bottom view in  FIG. 11 .  FIG. 11 , similarly to  FIG. 3 , is a view taken from below the C ring attaching device  600 .  
         [0102]     As shown in  FIG. 11 , the C ring attaching device  600  is provided with a pick-up mechanism  601 . The pick-up mechanism  601  includes a base plate  610 , a slide rail  620 , sliders  631  and  632 , chuck arms  641  and  642 , a C ring guide  650  and a slider spring  660 . The base plate  610 , similarly to the base plate  210  of the C ring attaching device  110 , has an upper wall  611 , a back wall  612 , and side walls  613  and  614 . The slide rail  620 , similarly to the back slide rail  220  of the C ring attaching device  110 , is an elongate member having the shape of a strip. The slide rail  620  is fixed to the back wall  212  so as to extend parallel to the upper wall  611 . The sliders  631  and  632  are mounted on the slide rail  620  so as to slide parallel to the back wall  612  along the slide rail  620 . The sliders  631  and  632  are symmetric with respect to a centerline.  
         [0103]     The chuck arms  641  and  642  are fixed to the sliders  631  and  632 , respectively. The chuck arms  641  and  642  extend laterally opposite to each other. Chuck pins  643  and  644  similar to the chuck pins  273  and  274  are attached near the free ends of the chuck arms  641  and  642 , respectively.  
         [0104]     The C ring guide  650 , similarly to the C ring guide  280 , positions the C ring  130 . The C ring guide  650  is provided with a C-shaped groove  651  resembling the shape of the C ring  130 . The C ring guide  650  is fixed to the upper wall  611  of the base plate  610  at a position between the chuck arms  641  and  642 .  
         [0105]     The slider spring  660  is extended between the sliders  631  and  632  so as to pull the sliders  631  and  632  toward each other. The slider spring  660  is designed such that the sliders  631  and  632  are able to move symmetrically.  
         [0106]     The C ring attaching device  600  is provided on the upper wall  611  of the base plate  610  with a driving mechanism, not shown in  FIG. 11 , similar to the driving mechanism of the C ring attaching device  110 . The driving mechanism includes an eccentric cam, not shown, and a motor, not shown. The sliders  631  and  632  are interlocked with the eccentric cam of the driving mechanism. The motor drives the eccentric cam for rotation to slide the sliders  631  and  632  along the slide rail  620  toward and away from each other. The chuck arms  641  and  642  move toward and away from each other as the sliders  631  and  632  move toward and away from each other.  
         [0107]     A C ring attaching operation of the C ring attaching device  600  will be described with reference to  FIGS. 12 and 13 . The C ring attaching operation will be described principally in connection with  FIG. 12  and reference will be made to  FIG. 13  when necessary.  
         [0108]      FIG. 12  illustrates the general operation of the C ring attaching device  600 . As shown in  FIG. 12 ( a ), a HSA  131  and a wavy washer  134  are attached to a pivot  132 . The chuck pins  643  and  644  of the chuck arms  641  and  642  are inserted in the chuck holes  142  and  142  of the C ring  130 , and the chuck arms  641  and  642  are moved away from each other to expand a gap  141  in the C ring  130 . The chuck arms  641  and  642  position the C ring  130  directly above the pivot  132 .  
         [0109]     As shown in  FIG. 12 ( b ), the chuck arms  641  and  642  put the C ring  130  on the wavy washer  134  previously put on the HSA  131  mounted on the pivot  132 .  FIG. 13 ( a ) shows the C ring  130  put on the wavy washer  134 . This state is similar to the state of the C rings  130  shown in FIGS.  7 ( a ) and  9 ( a ).  
         [0110]     As shown in  FIG. 12 ( c ), the chuck arms  641  and  642  depress the wavy washer  134  to attach the C ring  130  to the pivot  132 . As shown in  FIG. 12 ( d ), the C ring  130  contracts by its own resilience. The contracted C ring  130  is pushed upward by the wavy washer  134  and is held between the wavy washer  134  and a flange  150  formed on the pivot  132 .  FIG. 13 ( b ) shows the contracted C ring  130 . As shown in  FIG. 13 ( b ), the C ring  130  contracts as the chuck arms  641  and  642  slide laterally toward each other.  
         [0111]     As shown in  FIG. 12 ( e ), the gap  141  of the C ring  130  is expanded slightly to extract the chuck pins  643  and  644  of the chuck arms  641  and  642  from the chuck holes  142  and  143 . Consequently, the chuck pins  643  and  644  are separated from the side surfaces of the chuck holes  142  and  143  and can be extracted from the chuck holes  142  and  143 . As shown in  FIG. 12 ( f ), the chuck arms  641  and  642  are raised and are returned to their predetermined home positions in the C ring attaching device  600 .  
         [0112]     The C ring  130  can be automatically attached to the pivot  132  by using the C ring attaching device  600  in the third embodiment. The C ring  130  contracts by its own resilience and fastens on the pivot  132  after the C ring  130  has been placed under the flange  150  of the pivot  132  by the C ring attaching device  600 . Thus the C ring attaching device  600  has only a simple opening and closing function. Therefore, in some cases, the pressure of the wavy washer  134  applied to the C ring  130  restrains the C ring from being freely moved and, consequently, it is possible that the following problem arises.  
         [0113]     There is the possibility that the C ring  130  is unable to contract completely. The C ring  130  is put in place under the flange  150  of the pivot  132  and is allowed to contract resiliently so as to fasten on the pivot  132 . When the C ring  130  is put in place, the wavy washer  134  is compressed to some extent and applies a pressure to the C ring  130 . Consequently, friction acting between the C ring  130  and the wavy washer  134  increases and the C ring  130  is unable to contract against the high friction. The slider spring  600  may be replaced with another stronger slider spring to contract the C ring  130  against a high friction caused by the pressure of the wavy washer  134 .  
         [0114]     There is the possibility that an assembly  133  built by assembling the HSA  131 , the wavy washer  134 , the pivot  132  and the C ring  130  is lifted up together with the chuck pins  643  and  644  when the chuck arms  641  and  642  are raised. Even if the C ring  130  is unable to contract completely, there is no functional problem provided that the C ring  130  is put in place in an annular groove under the flange  150  of the pivot  132 . Thus the C ring  130  does not need necessarily to contract completely. In the C ring attaching device  600 , the chuck arms  641  and  624  keep exerting force on the C ring  130  so as to make the C ring  130  contract completely. Consequently, the assembly  133  is held between the chuck pins  643  and  644  inserted in the chuck holes  142  and  143  of the C ring  130  and is raised by the C ring attaching device  600 . It is possible that the weight of the assembly  133  exceeds the force holding the assembly  133  on the C ring attaching device  600  and the assembly  133  drops. Consequently, shocks that act on the assembly  133  when the assembly  133  drops cause dimple separation.  
         [0115]     When the C ring  130  is attached to the pivot  132  automatically by the C ring attaching device  600 , the chuck pins  643  and  644 , similarly to those of the C ring attaching devices disclosed in Patent documents 1 and 2, move straight. In such a case, the C ring  130  is expanded once by an external force and contracts resiliently in a groove formed in a workpiece (pivot  132 ), so that the C ring  130  is able to fasten on the pivot  132 .  
         [0116]     When a force is applied perpendicularly to the C ring and a high frictional force acts on the C ring  130  as mentioned above, the C ring  130  is unable to contract freely and completely. Although it is desired to apply a force mechanically to make the C ring  130  contract, the C ring  130  is very small as compared with a device capable of exerting a mechanical force necessary to make the C ring  130  contract on the C ring  130 . Therefore, a device capable of exerting a high force on the C ring  130  cannot be used and the C ring attaching device cannot be freely designed.  
         [0117]     When the C ring attaching apparatus  600  in the third embodiment or the known C ring attaching device disclosed in Patent document 1 or 2 is used, it is highly possible that metal powder is produced due to friction between the C ring  130  and the pivot  132  and the assembly  133  and a hard disk drive including the assembly  133  are contaminated with the metal powder. Such a possibility is a serious problem to a hard disk drive to which contamination with metal powder is extremely detrimental.  
         [0118]     Accordingly, the C ring attaching devices  110  in the first embodiment and the second embodiment that turn the chuck pins  273  and  274  is preferable to the C ring attaching device  600  in the third embodiment that moves the chuck pins  643  and  644  straight.  
       Fourth Embodiment  
       [0119]     A C ring attaching device  600  in a fourth embodiment according to the present invention is developed by incorporating improvements relating to operations to be carried out after a C ring  130  has been put in place into the C ring attaching device  600  in the third embodiment.  
         [0120]      FIG. 14  typically illustrates additional operations of the C ring attaching device  600 . As shown in FIGS.  14 ( a ) and  14 ( b ), chuck arms  641  and  642  expand a C ring  130  and put the expanded C ring  130  on a pivot  132 . As shown in  FIG. 14 ( c ), the chuck arms  641  and  642  are moved again so as to expand the C ring  130  after the C ring  130  has contracted. Consequently, chuck pins  643  and  644  are separated from the side surfaces of the chuck holes  142  and  143  of the C ring  130  to release the C ring  130 . Subsequently, the chuck arms  641  and  642  are separated from the C ring  130  and are returned to their home positions.  
         [0121]     Thus the chuck arms  641  and  642  are moved again so as to release the C ring  130  after the C rings  130  have contracted. Since tension acting on the chuck arms  641  and  642  is thus removed, the C ring  130  is able to contract still further.  
       Fifth Embodiment  
       [0122]     A C ring attaching device  600  in the fifth embodiment according to the present invention is developed by incorporating improvements relating to operations to be carried out after a C ring  130  has been put in place into the C ring attaching device  600  in the third embodiment. The C ring attaching operation of the C ring attaching device  600  in the fifth embodiment will be described with reference to  FIG. 15 . Reference will be made to  FIG. 12  when necessary.  
         [0123]      FIG. 15  illustrates additional operations to be performed by the C ring attaching device  600 . As shown in FIGS.  12 ( a ) to  12 ( e ), chuck arms  641  and  642  are moved to make a C ring  130  contract. In this state, the C ring  130  is placed below the flange  150  of a pivot  132  at a sufficient distance from the flange  150 . Then, as shown in  FIG. 15 ( a ), the chuck arms  641  and  642  are moved to expand the C ring  130  again and to lift up the C ring  130  slightly by a distance shorter than that shown in  FIG. 12 ( f ).  
         [0124]     As shown in  FIG. 15 ( b ), the chuck arms  641  and  642  are moved to make the C ring  130  contract again after lifting up the C ring  130 . Then, as shown in FIGS.  15 ( c ) and  15 ( d ), chuck pins  643  and  644  attached to the chuck arms  641  and  642  are separated from the C ring  130  and are returned to their home positions. Operations illustrated by FIGS.  15 ( c ) and  15 ( d ) are the same as releasing operations for releasing the C ring  130  illustrated by FIGS.  12 ( e ) and  12 ( f ).  
         [0125]     Thus the chuck arms  641  and  642  are operated to make the C ring  130  contract in two steps. The C ring  130  is able to contract properly in two steps and to fasten on the pivot  132  even if the wavy washer  134  compressed to some extent applies pressure upward on the C ring  130 .  
       Sixth Embodiment  
       [0126]     Various types of C rings  130  to be attached by the C ring attaching devices in the first to the fifth embodiment will be described.  FIG. 16  shows C rings  130  by way of example in a plan view. As shown in  FIG. 16 ( a ), the inner circumference of a C ring  130  is terminated by a gap  141 , and edges  146  and  147  enclosed by broken circles in  FIG. 16 ( a ) are formed at the opposite ends of the inner circumference of the C ring  130 . The edges  146  and  147  shown in  FIG. 16 ( a ) have square corners.  
         [0127]     Edges  148  and  149  of the inner circumference of a C ring  130  shown in  FIG. 16 ( b ) have round corners formed by rounding square edges  146  and  147 . The round edges  148  and  149  do not scratch a pivot  132  easily when the C ring  130  is attached to the pivot  132 .  
       EXAMPLE 1  
       [0128]     C rings  130  were attached to pivots  132  by the C ring attaching devices  110  in the first embodiment and the second embodiment and the C ring attaching device  600  in the third embodiment. The respective C ring attaching performances of the C ring attaching devices  110  and  600  were comparatively evaluated in terms of fastening condition, lifting and flaws formed in the pivots  132 .  
         [0129]     The fastening condition of the C ring  130  was evaluated on the basis of the distance D between the chuck holes  142  and  143 . Shorter distance D indicates better fastening condition. An excessively long distance D indicates that the C ring  130  has not properly fastened on the pivot  132 . When the C ring  130  is put on the pivot  132  without the wavy washer  134 , the distance D is on the order of 5.6 mm.  
         [0130]     Lifting of the C ring  130  due to the pressure applied to the C ring  130  by the wavy washer  134  is not a regular occurrence but an accidental occurrence. Some assemblies were formed and the lifting was determined on the basis of the frequency of lifting. Since lifting itself cannot be detected by a machine, a ratio of dimple separation resulting from lifting was used for the evaluation of lifting. C rings  130  attached to the pivots  132  by the C ring attaching devices  110  and  600  were removed carefully with a pair of hand pliers, and the annular grooves of the pivots  132  were observed under a microscope to measure the depth and length of flaws.  
         [0131]      FIG. 17  shows the results of comparative evaluations.  FIGS. 18 and 19  are strip films carrying photographs of a C ring in a C ring expanding process carried out by the C ring attaching device  600  in the third embodiment. Horizontal lines  711  and  712 , vertical lines  721 ,  722  and  723 , and circles  731  and  732  are drawn in those photographs. The upper horizontal line  711  represents the path of the chuck pins, the lower horizontal lines  712  is tangent to the bottom point of the inner edge of the C ring  130  in a state where the C ring  130  was not expanded in  FIGS. 17 and 18 . The vertical lines  721 ,  722  and  723  are a line tangent to the left end of the inner edge of the C ring  130 , a line corresponding to a center pin holding the pivot  132 , and a line tangent to the right end of the inner edge of the C ring  130 , respectively. The circles  731  and  732  correspond to the inner edge of the C ring  130  before expansion and after expansion, respectively.  
         [0132]     The C ring attaching devices  110  in the first embodiment and the second embodiment will be examined with reference to  FIGS. 18 and 19 . The use of the guide block  510  improved the fastening condition of the C ring  130  and reduced flaws in the pivot  132 .  
         [0133]     As obvious from  FIGS. 18 and 19 , the inner edge of the C ring  130  is deformed uniformly when the C ring  130  is expanded. The expanded C ring  130  contracts, reversing the sequential conditions shown in the photographs on the strip films shown in  FIGS. 18 and 19 ; that is, the inside diameter of the C ring decreases gradually.  
         [0134]     The C ring  130  expands and contracts in the foregoing mode under no load thereon. The C ring  130  does not necessarily expand and contract in the foregoing mode under the pressure applied thereto by the wavy washer  134 . More concretely, an end part of the C ring  130  on the side of the gap  141  is held by the chuck pins  273  and  274  of the chuck arms  271  and  272 , and is moved forcibly by the chuck arms  271  and  272  under the pressure applied thereto by the wavy washer  134 .  
         [0135]     A top part of the C ring  130  on the side opposite the gap  141  (a lower part of the C ring  130  in  FIGS. 18 and 19 ) is unable to restore its original shape unless a force is exerted on the C ring  130  to assist the C ring  130  to contract. Therefore, the gap  141  is fixed at a position and the C ring  130  contracts incompletely. The guide block  510  exerts a force on the C ring  130  to pull the C ring  130  toward the pivot  132 . Consequently, the C ring  130  is able to contract completely without flawing the pivot  132 .  
         [0136]     The C ring attaching device  110  provided with the guide block  510  and capable of thus making the C ring expand and contract prevents dimple separation due to the lifting of the C ring and reduces flaws in the pivot. The C ring  130  is often unable to contract completely when an external force, such as a frictional force, acts thereon. When the C ring  130  is put on the pivot  132  in a state where an external force, such as a frictional force, is exerted on the C ring  130 , the top part of the C ring  130  on the side opposite the gap  141  is pulled toward the pivot  132 . The C ring  130  is able to contract completely when the inner edge of the C ring  130  is brought into contact with the pivot  132 .  
         [0137]     The C ring attaching devices  600  in the second embodiment and the third embodiment will be examined with reference to  FIGS. 18 and 19 . The size D of the C ring attaching devices  600  in the second embodiment and the third embodiment was 6.4 mm or above because the edges  146  and  147  of the C ring  130  bit into the surface of the pivot  132 .  
         [0138]     Flaws formed by the C ring attaching device  600  in the second embodiment are larger than those formed by the C ring attaching device  600  in the third embodiment and the flaws start from the outer side. In the C ring attaching device  600  in the second embodiment, the chuck arms  641  and  642  were able to turn and it is considered that the chuck arms  641  and  642  were pulled slightly toward the C ring  130  when the C ring  130  was expanded; that is, the chuck arms  641  and  642  were pulled toward the pivot  132  beyond the blue line shown in  FIGS. 17 and 18 . It is considered that the center of the C ring  130  was dislocated from the center of the pivot  132 , and, consequently, flaws were formed from the outer side in the pivot  132 .  
         [0139]     It is considered that the size D in the C ring attaching device  600  in the third embodiment increases when the center of the C ring  130  is dislocated from the center of the pivot  132 . The chuck arms  641  and  642  of the C ring attaching device  600  in the second embodiment are turnable. Therefore, it is inferred that the C ring  130  did not stop upon contact with the pivot  132  and the chuck arms  641  and  642  could move along the surface of the pivot  132  and, consequently, deep scratches were formed in the pivot  132 .  
         [0140]     When the guide block  510  included in the C ring attaching device  110  in the first embodiment is added to the C ring attaching devices in the second embodiment and the third embodiment, the chuck arms  271  and  272  are restrained from turning toward the C ring  130  beyond the guide block  510 . Thus, it is considered that the C ring attaching device in the first embodiment could thus improve the condition of flaws.  
         [0141]     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 along with their full scope of equivalents.