Abstract:
A method of assembling a carriage assembly is capable of suppressing deformation of spacer portions when suspensions are attached to carriage arms. The method of assembling a carriage assembly aligns fitting holes provided in front end portions of carriage arms and spacer holes provided in spacer portions of suspensions and places the suspensions onto the carriage arms, and then presses a ball with a diameter equal to or greater than an inner diameter of the spacer holes with a pressure-applying member to pass the ball through the spacer holes, thereby crimping spacer hole edge portions of the spacer portions and attaching the suspensions to the front end portions of the carriage arms. By applying ultrasonic vibration from two axial directions to the pressure-applying member, the pressure-applying member is caused to vibrate on a two-dimensional movement path on a predetermined plane and passes the ball through the spacer holes while causing the ball to rotate.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method of assembling a carriage assembly for use in a magnetic disk apparatus where suspensions are attached to front end portions of carriage arms, and to an assembling apparatus that uses such method. 
   2. Related Art 
     FIG. 3  is a view showing the external appearance of a carriage assembly used in a magnetic disk apparatus. In  FIG. 3 , reference numeral  10  designates carriage arms and  12  one example of a suspension that is connected to front ends of the carriage arms  10 . A magnetic head  14  is mounted on a front end portion of each suspension  12 . Each magnetic head  14  is electrically connected via a flexible circuit board  16 , which is attached to side surfaces of the carriage arms  10 , to a control unit  18 . Reference numeral  19  designates an actuator shaft that is fixed to a base portion of the carriage arms  10 . The carriage arms  10  rotate about the axis of the actuator shaft  19  to carry out seek operations on flat planes that are parallel to the surfaces of recording media. 
   The carriage assembly is formed by fixing each suspension  12  by crimping to both surfaces of a front end portion of one out of the carriage arms  10  that are attached to the actuator shaft  19  so as to be parallel to one another. 
   A conventional method of fixing the suspensions  12  to the carriage arms  10  is disclosed by Patent Document 1.  FIG. 5  shows the conventional method of fixing the suspensions  12  to the carriage arms  10  disclosed in Patent Document 1. 
   According to this conventional method, after the suspensions  12  have been aligned with and placed upon the front ends of the respective carriage arms  10 , a metal ball  20  formed with a slightly larger diameter than an inner diameter of spacer holes  12   b  provided in the suspensions  12  is passed through the spacer holes  12   b  to fix the suspensions  12  to the carriage arms  10  by crimping. Reference numeral  22  designates a pressing shaft for pressing the metal ball  20  to cause the metal ball  20  to pass through the spacer holes  12   b.    
     FIG. 4  shows an operation that passes the metal ball  20  through the spacer holes  12   b  of the suspensions  12  to fix the suspensions  12  to the carriage arms  10  by crimping. The suspensions  12  are placed on both surfaces of the respective carriage arms  10  with the fitting holes  10   a  and the spacer holes  12   b  in alignment. Since the metal ball  20  is formed with a slightly larger diameter than the spacer holes  12   b , when the metal ball  20  is passed through the spacer holes  12   b , the metal ball  20  acts so as to press open crimping portions  13  formed on inner circumferential edges of the spacer holes  12   b , and as a result, the suspensions  12  are fixed so as to “bite into” the carriage arms  10 . As shown in  FIG. 4 , during a single crimping operation, the metal ball  20  is caused by the pressing shaft  22  to move successively through the spacer holes  12   b.    
   In this way, when assembling a carriage assembly, conventionally the metal ball  20  is used to press open the spacer holes  12   b  to fix the suspensions  12  to the carriage arms  10  by crimping. Accordingly, depending on the balance between the external diameter of the metal ball  20  and the internal diameter of the spacer holes  12   b , a problem can occur where the spacer portions  12   a  deform due to stress that acts thereupon during crimping, resulting in the suspensions  12  becoming displaced from the standard positions. That is, when the suspensions  12  are fixed to the carriage arms  10  by crimping, the spacer portions  12   a  become bent, which can result in the suspensions  12  becoming tilted with respect to the standard angle. Tilting of the suspensions  12  affects the float heights of the magnetic heads  14  above the surfaces of the recording media, resulting in fluctuation in the float heights of the magnetic heads  14  above the surfaces of the recording media. 
   The storage capacity of modern magnetic disk apparatuses has been greatly increased, which has led to the float height of magnetic heads above the surfaces of recording media being kept low. This means that fluctuations in the float height of magnetic heads have a large effect on the information reading and writing characteristics, and therefore there are demands for the suppression of fluctuation in the float height of the magnetic heads to produce the required characteristics. 
   Patent Document 1 discloses a method of assembling a carriage assembly that can suppress deformation of the spacer portions  12   a  due to the stress applied during crimping.  FIG. 6  is a diagram useful in explaining a method of assembling a carriage assembly using an ultrasonic horn  32  disclosed in Patent Document 1 as a method of assembling that can suppress deformation. 
   The method of assembling a carriage assembly disclosed in Patent Document 1 is characterized by using the ultrasonic horn  32  to pass the metal ball  20  through the spacer holes  12   b . The metal ball  20  is the same as the metal ball  20  used in the method of assembling a carriage assembly described above.  FIG. 6  shows a state of an assembly where gap maintaining plates  36  are inserted between adjacent carriage arms  10  and pressure applying plates  37   a ,  37   b  are placed in contact with both end surfaces of the carriage arms  10  so that the respective carriage arms  10  are supported by being sandwiched on both sides thereof. 
   The ultrasonic horn  32  applies ultrasonic vibration in the axial direction and due to the action of the ultrasonic horn  32 , the metal ball  20  causes less damage to the spacer portions  12   a  during crimping, so that deformation is prevented when the suspensions  12  are attached to the carriage arms  10  and the suspensions  12  can be fixed to the carriage arms  10  more accurately. The reason for this is thought to be that the stress caused by the ultrasonic vibration of the ultrasonic horn  32  and the static stress due to the metal ball  20  pressing open the crimping portions  13  act so as to be superimposed, which makes it possible to reduce the resistance to deformation, and by reducing the average machining force by using a striking action that is repeated at high speed, it is possible to fix the members while suppressing deformation of the fixed portions of the suspensions  12  and the carriage arms  10 . 
   Patent Document 1 
   Japanese Laid-Open Patent Publication No. 2004-127491 (see paragraphs 0003, 0004, 0015, 0023, and 0024 and FIGS. 3, 5, and 6). 
   However, with the above conventional method of assembling a carriage assembly that uses ultrasonic vibration, it is not possible to completely avoid deformation of the spacer portions  12   a  and therefore it is not possible to completely avoid fluctuations in the float amount of the magnetic head  14  from the surface of the recording medium due to displacement of the suspensions from the standard positions. 
   For this reason, there is much demand for a method of assembling a carriage assembly that can further reduce deformation in the spacer portions when suspensions are attached to carriage arms. 
   SUMMARY OF THE INVENTION 
   The present invention was conceived to solve the problem described above and it is an object of the present invention to provide a method of assembling a carriage assembly that compared to the conventional method can suppress deformation in spacer portions when suspensions are attached to carriage arms and can therefore further suppress fluctuation in the float height of magnetic heads from the surfaces of the recording media, and also an assembling apparatus that uses such method. 
   To solve the above problem, a method of assembling a carriage assembly according to the present invention aligns fitting holes provided in front end portions of carriage arms used in a magnetic disk apparatus and spacer holes provided in spacer portions of suspensions and places the suspensions onto the carriage arms, and then presses a ball with a diameter equal to or greater than an inner diameter of the spacer holes with a pressure-applying member to pass the ball through the spacer holes to crimp spacer hole edge portions of the spacer portions and attach the suspensions to the front end portions of the carriage arms, wherein by applying ultrasonic vibration from two axial directions to the pressure-applying member, the pressure applying member is caused to vibrate on a two dimensional movement path on a predetermined plane and passes the ball through the spacer holes while causing the ball to rotate. 
   By doing so, by applying ultrasonic vibration from two axial directions to the pressure applying member, the pressure applying member can be caused to move on a predetermined curved movement path on a predetermined plane. Accordingly, although the ball is pressed by a pressure applying member (ultrasonic horn) that vibrates only in the pressing direction (the axial direction of the spacer holes) in the conventional art and therefore the ball hardly rotates, with the invention of Claim  1 , since the pressure applying member that applies pressure to the ball contacts the ball while tracing a two dimensional movement path, the ball can be passed through the spacer holes while rotating. The present inventors discovered that by doing so, excessive force is not applied to the spacer portions when the ball passes through the spacer holes, and therefore there is reduced deformation in the spacer portions. 
   In addition, by applying ultrasonic vibration with frequencies that are integer multiples of a predetermined frequency to the pressure-applying member from the two axial directions, the ball may be caused to pass through the spacer holes while rotating in a predetermined direction. 
   By doing so, the direction of movement of the pressure applying member at the instant when the pressure-applying member contacts the ball is set at a predetermined direction, and therefore the ball can be passed through the spacer holes while rotating in a predetermined direction. The present inventors discovered that by doing so, it is possible to further avoid having an excessive force applied to the spacer portions when the ball passes through the spacer holes and therefore deformation of the spacer portions is reduced. 
   In addition, the movement path of the pressure-applying member due to the ultrasonic vibration may be one of a circle and an oval. 
   By doing so, it is possible to use a simple construction that sets the frequencies of the ultrasonic vibration applied from the two axial directions equally. 
   Also, ultrasonic vibration may be applied to the pressure-applying member from two axial directions that are a pressing direction for the ball and a direction perpendicular to the pressing direction to cause the pressure-applying member to vibrate with a movement path on a plane parallel to the pressing direction and cause the ball to rotate about a rotational axis that is substantially perpendicular to the pressing direction. 
   By doing so, it is possible to cause the ball to rotate about a rotational axis that is substantially perpendicular to the pressing direction. The present inventors discovered that by doing so, it is possible to further avoid having an excessive force applied to the spacer portions when the ball passes through the spacer holes and therefore deformation of the spacer portions is reduced. 
   To solve the above problem, an assembling apparatus for a carriage assembly according to the present invention aligns fitting holes provided in front end portions of carriage arms used in a magnetic disk apparatus and spacer holes provided in spacer portions of suspensions and places the suspensions onto the carriage arms, and then passes a ball with a diameter equal to or greater than an inner diameter of the spacer holes through the spacer holes to crimp spacer hole edge portions of the spacer portions and attach the suspensions to the front end portions of the carriage arms, the assembling apparatus including: a pressure-applying member; a driving device that moves the pressure-applying member so that the pressure-applying member presses the ball to pass the ball through the spacer holes; and ultrasonic vibrating means that causes the pressure-applying member to vibrate on a two dimensional movement path on a predetermined plane by applying ultrasonic vibration to the pressure-applying member from two axial directions to cause the ball that passes through the spacer holes to rotate. 
   With the above construction, by applying ultrasonic vibration from two axial directions to the pressure-applying member, the pressure-applying member can be caused to move on a predetermined curved movement path on a predetermined plane. Accordingly, although the ball is pressed by a pressure-applying member (ultrasonic horn) that vibrates only in the pressing direction (the axial direction of the spacer holes) in the conventional art and therefore the ball hardly rotates, with the invention of claim  5 , since the pressure-applying member that applies pressure to the ball contacts the ball while tracing a two dimensional movement path, the ball can be passed through the spacer holes while rotating. The present inventors discovered that by doing so, excessive force is not applied to the spacer portions when the ball passes through the spacer holes, and therefore there is reduced deformation in the spacer portions. 
   In addition, the ultrasonic vibrating means may apply ultrasonic vibration with frequencies that are integer multiples of a predetermined frequency to the pressure-applying member from two axial directions to cause the ball to pass through the spacer holes while rotating in a predetermined direction. 
   By doing so, the direction of movement of the pressure-applying member at the instant when the pressure-applying member contacts the ball is set at a predetermined direction, and therefore the ball can be passed through the spacer holes while rotating in a predetermined direction. The present inventors discovered that by doing so, it is possible to further avoid having an excessive force applied to the spacer portions when the ball passes through the spacer holes and therefore deformation of the spacer portions is reduced. 
   In addition, the movement path of the pressure-applying member due to the ultrasonic vibration produced by the ultrasonic vibrating means may be one of a circle and an oval. 
   By doing so, it is possible to use a simple construction that sets the frequencies of the ultrasonic vibration applied from the two axial directions equally. 
   The ultrasonic vibrating means may apply ultrasonic vibration to the pressure-applying member from two axial directions that are a pressing direction for the ball and a direction perpendicular to the pressing direction to cause the pressure-applying member to vibrate with a movement path on a plane parallel to the pressing direction and cause the ball to rotate about a rotational axis that is substantially perpendicular to the pressing direction. 
   By doing so, it is possible to cause the ball to rotate about a rotational axis that is substantially perpendicular to the pressing direction. The present inventors discovered that by doing so, it is possible to further avoid having an excessive force applied to the spacer portions when the ball passes through the spacer holes and therefore deformation of the spacer portions is reduced. 
   With the method of assembling a cartridge assembly and assembling apparatus according to the present invention, it is possible to suppress deformation in the spacer portions of suspensions and therefore keep the spacer portions flat, which makes it possible to attach suspensions to the carriage arms without tilting and with higher accuracy than the conventional art. By doing so, it is possible to suppress fluctuations in the float characteristics of magnetic heads and therefore it is possible to assemble a carriage assembly with favorable information read/write characteristics. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The aforementioned and other objects and advantages of the present invention will become apparent to those skilled in the art upon reading an understanding the following detailed description with reference to the accompanying drawings. 
     In the drawings: 
       FIG. 1  is a diagram useful in explaining a method of assembling a carriage assembly and an assembling apparatus according to the present invention; 
       FIG. 2  is a graph showing one example of a movement path of an ultrasonic horn (pressure-applying member); 
       FIG. 3  is a view showing the appearance of a carriage assembly; 
       FIG. 4  is a diagram useful in explaining the action that crimps and fixes suspensions to carriage arms by passing a metal ball (ball) through spacer holes of the suspensions; 
       FIG. 5  is a diagram useful in explaining a conventional method of assembling a carriage assembly; and 
       FIG. 6  is a diagram useful in explaining a conventional method of assembling a carriage assembly. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The carriage assembly to be assembled by the method of assembling a carriage assembly and assembling apparatus according to an embodiment of the present invention is shown in  FIG. 3 . The overall construction of the carriage assembly shown in  FIG. 3  has been described for the conventional art, and therefore description thereof is omitted here. 
     FIG. 1  is a diagram useful in explaining the method of assembling a carriage assembly and assembling apparatus according to the present embodiment. In  FIG. 1 , the carriage arms  10  and the suspensions  12  have the same forms as in the conventional art described earlier. That is, the fitting holes  10   a  are provided in the front ends of the carriage arms  10  and the spacer holes  12   b  to be fitted into the fitting holes  10   a  are provided in the spacer portions  12   a  provided at the base portions of the suspensions  12 . 
   The assembling apparatus A for a carriage assembly that uses the method of assembling a carriage assembly according to the present embodiment includes an ultrasonic horn  40 , a first ultrasonic vibrating device  42  and a second ultrasonic vibrating device  44  as ultrasonic vibrating means that apply ultrasonic vibration to the ultrasonic horn  40 , and a driving device  46  capable of moving and controlling the ultrasonic horn  40  so that the ultrasonic horn  40  presses the metal ball  20  to pass the metal ball  20  through . the spacer holes  12   b.    
   The ultrasonic horn  40  is cylindrical in form and is provided so as to be capable of being coaxially inserted through the spacer holes  12   b , can transmit ultrasonic vibration produced by the first and second ultrasonic vibrating devices  42 ,  44  and functions as a pressure-applying member that presses the metal ball  20  to pass the metal ball  20  through the spacer holes  12   b.    
   It should be noted that the metal ball  20  is formed with a slightly larger diameter than the inner diameter of the spacer holes  12   b.    
   The first ultrasonic vibrating device  42  applies ultrasonic vibration to the ultrasonic horn  40  in the pressing direction of the metal ball  20  (that is, the axial direction of the spacer holes  12   b ). The second ultrasonic vibrating device  44  applies ultrasonic vibration to the ultrasonic horn  40  in a direction perpendicular to the pressing direction. 
   That is, ultrasonic vibration is applied to the ultrasonic horn  40  by the first ultrasonic vibrating device  42  and the second ultrasonic vibrating device  44  in two directions that are the pressing direction and the direction perpendicular to the pressing direction. By doing so, the ultrasonic horn  40  is caused to vibrate on a movement path on a plane that is parallel to the pressing direction. 
     FIG. 2  shows an example of the movement path of the ultrasonic horn  40 . In  FIG. 2 , the horizontal axis (X axis) shows the displacement of the ultrasonic horn  40  in the pressing direction and the vertical axis (Y axis) shows the displacement of the ultrasonic horn  40  in the direction perpendicular to the pressing direction (i.e., the up down direction in  FIG. 1 ). That is, the amplitude of the ultrasonic horn  40  due to the first ultrasonic vibrating device  42  is expressed by the horizontal axis (X axis) in  FIG. 2  and the amplitude due to the second ultrasonic vibrating device  44  is expressed by the vertical axis (Y axis). 
   In the example shown in  FIG. 2 , when the ranges of the displacements of the ultrasonic vibration due to the first ultrasonic vibrating device  42  and the second ultrasonic vibrating device  44  are expressed as −1 to 1 (i.e., the respective amplitudes are 2), the displacements in the X axis and the Y axis of the ultrasonic horn  40  are expressed by the equations X=sin(2πft), Y=cos(2πft) (where f is the frequency (in Hz) of the ultrasonic vibration and t is elapsed time (in seconds)). 
   By doing so, as shown by the arrow in  FIG. 1  and by  FIG. 2 , the ultrasonic horn  40  is caused to vibrate on a circular movement path on a plane that is parallel to the pressing direction. 
   Next, the method of assembling a carriage assembly according to the present embodiment that uses the assembling apparatus A for a carriage assembly will be described. 
     FIG. 1  shows an operation where the assembling apparatus A for a carriage assembly is used to pass the metal ball  20  through the spacer holes  12   b , of the suspensions  12  to crimp and fix the suspensions  12  to the carriage arms  10 . 
   As shown in  FIG. 1 , in the method of assembling a carriage assembly according to the present embodiment, the suspensions  12  are placed on both surfaces of the respective carriage arms  10  so that the spacer holes  12   b , and the fitting holes  10   a  are aligned. In addition, gap maintaining plates  36  are inserted between adjacent carriage arms  10  and pressure-applying plates  37   a ,  37   b  are placed in contact with both end surfaces of the carriage arms  10  so that the carriage arms  10  are sandwiched from both sides. 
   In this state, the assembling apparatus A for a carriage assembly is used to pass the metal ball  20  through the spacer holes  12   b . That is, first the metal ball  20  is aligned with the spacer holes  12   b , and the ultrasonic horn  40  is moved by the driving device  46  so as to contact the metal ball  20  and to press in the metal ball  20  so that the metal ball  20  is passed through the spacer holes  12   b . When doing so, the first and second ultrasonic vibrating devices  42 ,  44  are driven to apply ultrasonic vibration to the ultrasonic horn  40  from the two axial directions mentioned above. 
   Since the metal ball  20  is formed with a slightly larger diameter than the spacer holes  12   b , when the metal ball  20  passes through the spacer holes  12   b , the metal ball  20  acts so as to press open the crimping portions  13  formed at the inner circumferential edges of the spacer holes  12   b , and as a result, the suspensions  12  are fixed so as to bite into the carriage arms  10 . As shown in  FIGS. 1 and 4 , the metal ball  20  is caused by the ultrasonic horn  40  to move through the successive spacer holes  12   b , from one side of the carriage arms  10  to the other in a single crimping operation. 
   When doing so, as described above, the ultrasonic horn  40  is caused to vibrate on a circular movement path on a plane that is parallel to the pressing direction. As a result, the ultrasonic horn  40  moves toward and away from the metal ball  20  and since the ultrasonic horn  40  moves in a predetermined direction at the instant when the ultrasonic horn  40  contacts the metal ball  20  (upward in  FIG. 1 ), the metal ball  20  is caused to rotate in a predetermined direction about a rotational axis that is substantially perpendicular to the pressing direction (in  FIG. 1 , the metal ball  20  is caused to rotate counterclockwise as shown by the arrow). 
   In the conventional method of assembling a carriage assembly, the metal ball is pressed by a pressure-applying member (ultrasonic horn) that vibrates only in the pressing direction (the axial direction of the spacer holes), and therefore the metal ball hardly rotates. However, in the method of assembling a carriage assembly according to the present embodiment, the pressure-applying member (the ultrasonic horn  40 ) that presses the metal ball  20  contacts the metal ball  20  while tracing a two dimensional movement path, and therefore it is possible to cause the metal ball  20  to pass through the spacer holes  12   b , while rotating. 
   The present inventors found that by doing so, excessive force is not applied to the spacer portions  12   a  when the metal ball  20  passes through the spacer holes  12   b , and therefore there is reduced deformation in the spacer portions  12   a.    
   Note that the present inventors suppose that the reason for this is that while static friction is produced between the metal ball  20  and the crimping portions  13  with the conventional method, with the method according to the present embodiment, a dynamic friction that is smaller than the static friction acts between the metal ball  20  and the crimping portions  13  due to the metal ball  20  rotating. 
   With the method of assembling a carriage assembly and the assembling apparatus according to the present embodiment, since deformation of the spacer portions  12   a  of the suspensions  12  is suppressed and the spacer portions  12   a  are kept flat, the suspensions  12  can be attached to the carriage arms  10  without tilting and with higher accuracy than the conventional art. By doing so, it is possible to suppress fluctuations in the float characteristics of the magnetic heads and therefore it is possible to assemble a carriage assembly with favorable information read/write characteristics. 
   In particular, by applying ultrasonic vibration of frequencies that are different integer multiples of a predetermined frequency from the two axial directions, the direction of movement of the ultrasonic horn  40  at the instant when the ultrasonic horn  40  contacts the metal ball  20  can be set at a predetermined direction, and therefore the metal ball  20  can be caused to rotate in a “predetermined direction” (that is, a predetermined direction of rotation). 
   The present inventors discovered that by passing the metal ball  20  through the spacer holes  12   b , while causing the metal ball  20  to rotate in a predetermined direction, it is possible to avoid having an excessive force applied to the spacer portions  12   a  when the metal ball  20  passes through the spacer holes  12   b , and therefore deformation of the spacer portions  12   a  is reduced. 
   It should be noted that in the present embodiment, as should be clear from the f value being the same in the equations expressing the displacements of the ultrasonic horn  40  in the two axial directions, the frequencies of the ultrasonic vibration applied from the two axial directions are equal. However, the present invention is not limited to this and may be constructed so that the ultrasonic vibration is applied in the two axial directions with frequencies that are different integer multiples of a predetermined frequency. For example, the frequency F of the ultrasonic vibration applied in the Y axis direction may be set at double the frequency f of the ultrasonic vibration applied in the X axis direction (i.e., F=2f) and the displacement due to the respective ultrasonic vibrations may be set so as to be expressed by the equations X=sin(2πft) and Y=cos(2πFt). By doing so, since it is possible to set the direction of movement of the ultrasonic horn  40  at a predetermined direction when the ultrasonic horn  40  contacts the metal ball  20 , it is possible to cause the metal ball  20  to rotate in a “predetermined direction” (that is, a predetermined direction of rotation). 
   It is also possible to set the amplitude of the ultrasonic vibration in the X axis direction and the amplitude of the ultrasonic vibration in the Y axis direction differently, that is, to set the respective equations at X=A·sin(2πft) and Y=B·cos(2πft)(where the values A and B are constants such that A≠B) for example, so that the movement path of the ultrasonic horn  40  becomes oval. 
   Also, although the present embodiment is constructed so that ultrasonic vibration is applied to the ultrasonic horn  40  from two axial directions that are the pressing direction for the metal ball  20  and a direction perpendicular to the pressing direction, the two axial directions for the present invention are not limited to such. For example, if the two axial directions are set as directions that are both perpendicular to the pressing direction and are perpendicular to each other, it is possible to cause the ultrasonic horn  40  to move on a movement path on a plane perpendicular to the pressing direction and to cause the metal ball  20  to rotate about a rotational axis that is parallel to the pressing direction.