Abstract:
A lapping machine for lapping a row bar includes a lap plate for providing a lapping surface, a row tool having a plurality of bend cells formed by defining a plurality of slits, a pressure mechanism for pressing the row tool toward the lapping surface of the lap plate, and a bend mechanism for bending the bend cells of the row tool toward the lapping surface of the lap plate. The bend mechanism includes an air cylinder unit having a plurality of double-acting air cylinders, a plurality of racks operatively connected to the double-acting air cylinders, respectively, a plurality of drive pinions arranged coaxially and meshing with the racks, respectively, each drive pinion having a lever for driving the corresponding bend cell, a plurality of support pinions arranged coaxially and meshing with the racks, respectively, and a guide mechanism for guiding each rack, the respective drive pinion, and the respective support pinion in substantially the same plane.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lapping machine for lapping a row bar formed with a plurality of head elements arranged in a line, and a lapping method for lapping such a row bar. 
     2. Description of the Related Art 
     In a manufacturing process for a magnetic head slider, for example, a magnetic head thin film is formed on a substrate and next subjected to lapping, thereby making constant the heights of a magnetoresistive layer and a gap in the magnetic head thin film. The heights of the magnetoresistive layer and the gap are required to have an accuracy on the order of submicrons. Accordingly, a lapping machine for lapping a row bar as a workpiece is also required to have a high accuracy. Thus, the magnetic head slider is lapped so that the height of the magnetoresistive film becomes constant. However, the row bar is very thin, and its thickness is about 0.3 mm, for example. 
     Accordingly, it is difficult to lap the row bar directly by the lapping machine, and the row bar is therefore bonded to a row tool before lapping. That is, the row bar bonded to the row tool is pressed on a lap plate during lapping. As known from U.S. Pat. No. 5,023,991 and Japanese Patent Laid-open. No. Hei 5-123960, for example, the resistances of electrical lapping guide elements (ELG elements) formed integrally with the row bar are always measured during lapping. Then, whether or not the height of the magnetoresistive film of each magnetic head element has become a target height is detected according to the measured resistance of each ELG element. When it is detected that the magnetoresistive film has been lapped up to the target height, according to the measured resistance, the lapping operation is stopped. 
     Thereafter, the lapped surface of the row bar is formed into the shapes of flying surfaces of a plurality of magnetic head sliders, and the row bar is next cut into the plurality of magnetic head sliders in the condition that it is bonded to the row tool. Thereafter, the row tool is heated to melt an adhesive bonding the row bar to the row tool, thereby removing the magnetic head sliders from the row tool to obtain the individual magnetic head sliders. In this manner, a wafer is cut into a plurality of row bars each having the plural magnetic head elements arranged in a line, and each row bar is subjected to lapping by using the row tool. Accordingly, the magnetoresistive films of the plural magnetic head elements can be lapped at a time. 
     However, there are variations in height among the magnetoresistive films of the plural magnetic head elements in the row bar on the order of submicrons, depending on the accuracy of film deposition of the magnetoresistive films, the accuracy of bonding of the row bar to the row tool, etc. It is accordingly necessary to correct for such variations in the lapping operation for mass production of magnetic head sliders uniform in characteristics. There have been proposed various conventional methods for correcting for the above-mentioned variations on the order of submicrons in the lapping operation. For example, U.S. Pat. No. 5,607,346 has proposed a method such that a plurality of holes are formed through the row tool and forces are applied from actuators through these holes to the row tool. 
     However, these actuators are required to have capacities of applying relatively large forces to these holes, in order to obtain a desired pressure distribution, and it is therefore difficult to manufacture such actuators acting on a plurality of load points. As a result, the spacing between any adjacent ones of the plural load points (the plural holes) cannot be greatly reduced, causing a difficulty of improvement in lapping accuracy. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a lapping machine and a lapping method which can improve the accuracy of lapping of a row bar formed with a plurality of head elements arranged in a line. 
     In accordance with an aspect of the present invention, there is provided a lapping machine for lapping a row bar formed with a plurality of head elements arranged in a line, comprising a lap plate for providing a lapping surface; a row tool having a plurality of bend cells formed by defining a plurality of slits; a pressure mechanism for pressing the row tool toward the lapping surface of the lap plate; and a bend mechanism for bending the bend cells of the row tool toward the lapping surface of the lap plate; the bend mechanism comprising an air cylinder unit having a plurality of double-acting air cylinders; a plurality of racks operatively connected to the double-acting air cylinders, respectively; a plurality of first pinions arranged coaxially and meshing with the racks, respectively, each of the first pinions being integrally formed with a lever; a plurality of second pinions arranged coaxially and meshing with the racks, respectively, the second pinions being spaced apart from the first pinions; and a guide mechanism for guiding each of the racks, the respective first pinion, and the respective second pinion in substantially the same plane; each of the bend cells of the row tool having an engaging hole for engaging a front end of each lever, whereby each lever engaged with the engaging hole is rotated to bend each bend cell of the row tool toward the lapping surface of the lap plate. 
     Preferably, the bend mechanism further comprises a plurality of electro-pneumatic conversion regulators connected to the double-acting air cylinders, respectively; and a compressed air source connected to the electro-pneumatic conversion regulators. Preferably, the row tool further has first and second ends between which the bend cells are formed; a pair of fixed cells formed at the first and second ends, each of the fixed cells having a width larger than that of each bend cell; and a parallel spring mechanism formed by defining a through hole extending from the first end to the second end. 
     Preferably, the guide mechanism comprises a rack guide having a plurality of guide gaps for guiding the racks, respectively; each of the racks has a first surface formed with a gear and a second surface formed with a projection opposite to the first surface, the projection being in contact with the rack guide; and each of the racks is supported at a first point of contact with the respective first pinion, a second point of contact with the respective second pinion, and a third point of contact with the rack guide at the projection, whereby each rack is linearly reciprocated in a horizontal direction. 
     In accordance with another aspect of the present invention, there is provided a bend mechanism for locally bending a row bar formed with a plurality of head elements arranged in a line, comprising a plurality of racks arranged in a direction perpendicular to a direction of movement of the racks; and a plurality of first pinions arranged coaxially and meshing with the racks, respectively, each of the first pinions being integrally formed with a lever. 
     Preferably, the bend mechanism further comprises an air cylinder unit having a plurality of double-acting air cylinders, each of the double-acting air cylinders having a piston and a piston rod connected to the piston; a plurality of second pinions arranged coaxially and meshing with the racks, respectively, the second pinions being spaced apart from the first pinions; and a guide mechanism for guiding each of the racks, the respective first pinion, and the respective second pinion in substantially the same plane; the racks being connected to the piston rods of the double-acting air cylinders, respectively. 
     Preferably, the guide mechanism comprises a rack guide having a plurality of first guide gaps, and a pinion guide having a plurality of second guide gaps; the racks being guided in the first guide gaps of the rack guide, respectively; the first and second pinions being guided in the second guide gaps of the pinion guide, respectively. 
     In accordance with a further aspect of the present invention, there is provided a lapping method for lapping a row bar formed with a plurality of head elements arranged in a line, comprising the steps of providing a lapping surface by a lap plate; bonding the row bar to a lower surface of a row tool having a plurality of bend cells formed by defining a plurality of slits; pressing the row bar on the lapping surface; and operating a bend mechanism including an air cylinder unit having a plurality of double-acting air cylinders, a plurality of racks operatively connected to the double-acting air cylinders, respectively, and a plurality of pinions arranged coaxially and meshing with the racks, respectively, each of the pinions being integrally formed with a lever, thereby applying an adjustable bending pressure to each of the bend cells; whereby the row bar is bent at a plurality of points to perform lapping of the row bar. 
     In accordance with a still further aspect of the present invention, there is provided a row tool to which a row bar formed with a plurality of head elements arranged in a line is to be bonded, comprising a plurality of bend cells formed by defining a plurality of slits, each of the bend cells having an engaging hole; first and second ends between which the bend cells are formed; a pair of fixed cells formed at the first and second ends, each of the fixed cells having a width larger than that of each bend cell; and a parallel spring mechanism formed by defining a through hole extending from the first end to the second end. 
     The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical sectional view of a lapping machine; 
     FIG. 2 is a plan view of the lapping machine; 
     FIG. 3 is a schematic view for illustrating the principle of operation of a bend assembly; 
     FIG. 4 is a perspective view of an air cylinder unit; 
     FIG. 5A is a plan view of the air cylinder unit; 
     FIG. 5B is a rear elevation of the air cylinder unit; 
     FIG. 5C is a front elevation of the air cylinder unit; 
     FIG. 6 is a perspective view of a bend unit; 
     FIGS. 7A to  7 D are side views showing four kinds of rack shapes used in the present invention; 
     FIG. 8 is a view taken in the direction of arrow VIII in FIG. 6; 
     FIG. 9A is a partially sectional, side view showing a connection structure between a piston rod and a rack; 
     FIG. 9B is a plan view of the connection structure shown in FIG. 9A; 
     FIG. 10 is a side view for illustrating the transmission of torque by a drive pinion having a lever; 
     FIG. 11 is a perspective view of a row tool; 
     FIG. 12 is a front elevation of the row tool; 
     FIG. 13 is a plan view of the row tool; 
     FIG. 14 is a rear elevation of the row tool; and 
     FIG. 15 is a cross section taken along the line XV—XV in FIG.  14 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the present invention will now be described in detail with reference to the drawings. Referring to FIG. 1, there is shown a sectional view of a lapping machine  10 . FIG. 2 is a plan view of the lapping machine  10 . The lapping machine  10  is composed of a lap plate  12  for providing a lapping surface  12   a,  and a lap unit  14 . The lap unit  14  includes a lap base  20  pivotably supported through an arm  18  to a pivot shaft  16 , and a lap head  24  supported relatively movably to the lap base  20  by a ball joint  22  fixed to the lap base  20 . 
     The lap base  20  has an opening  25 , and the lap head  24  is inserted in the opening  25 . A plurality of (e.g., four) feet  26  are provided on the lower surface of the lap base  20 . The feet  26  slide on the lapping surface  12   a.  A bend assembly  30  to be hereinafter described in detail is fixed to the lap head  24  by means of screws or the like. Three pneumatic cylinders  32  for applying pressure to the lap head  24  are provided above the lap head  24 . Each pneumatic cylinder  32  is connected through pipes  34  and  36  to an electro-pneumatic conversion regulator (not shown) and a compressed air source  38 . 
     The bend assembly  30  includes an air cylinder unit having a plurality of double-acting air cylinders to be hereinafter described. Each double-acting air cylinder is connected through an air tube  40  to an electro-pneumatic conversion regulator  42 . Each electro-pneumatic conversion regulator  42  is connected to the compressed air source  38 . The bend assembly  30  further includes a row tool to be hereinafter described. In lapping a row bar bonded to the row tool, the lap plate  12  is rotated in a direction of arrow R shown in FIG. 2 by a motor (not shown), and the lap unit  14  is swung in opposite directions of arrow S shown in FIG. 2 about the pivot shaft  16  by a drive mechanism (not shown). The lap plate  12  is rotated at about 50 rpm during rough lapping and at about 15 rpm during finish lapping. On the other hand, the lap unit  14  is swung at about 10 cycles per minute both during rough lapping and during finish lapping. 
     Referring to FIG. 3, there is shown a schematic view for illustrating the principle of operation of the bend assembly  30 . Reference numeral  46   a  denotes a rack having a body portion  48  and a head portion  50  formed integrally with the body portion  48 . A gear  52  is formed on the lower surface of the body portion  48 , and an arcuate projection  54  is formed on the upper surface of the body portion  48 . The head portion  50  is formed with an engaging hole  56 . The rack  46   a  is reciprocated by a double-acting air cylinder  62 . The double-acting air cylinder  62  is included in an air cylinder unit  58  shown in FIG.  4 . The air cylinder unit  58  has a cylinder housing  60 , and a plurality of (e.g.,  28 ) double-acting air cylinders  62  are defined in the cylinder housing  60 . Each air cylinder  62  has a piston  64  and a piston rod  66  connected to the piston  64 , whereby a head-side chamber  63  and a rod-side chamber  65  are defined in the air cylinder  62 . The piston rod  66  is connected to the rack  46   a.  Each air cylinder  62  has a bore of 2.5 mm, and the piston rod  66  has a diameter of 1 mm. 
     The structure of the air cylinder unit  58  will now be described with reference to FIGS. 4 and 5A to  5 C. The double-acting air cylinders  62  are zigzag arranged in the cylinder housing  60  so as to form a 4×7 parallelogram lattice as viewed in elevation. The piston rods  66  project from the front surface of the cylinder housing  60  in such a manner that seven piston rods  66  are aligned in each of rows a, b, c, and d. As shown in FIG. 5A,  14  pull ports  68  respectively corresponding to the piston rods  66  arranged in the rows a and b open to the upper surface of the cylinder housing  60  in such a manner that seven pull ports  68  are aligned in each of the rows a and b. Each pull port  68  communicates with the rod-side chamber  65  of the corresponding air cylinder  62 . Although not shown,  14  pull ports respectively corresponding to the piston rods  66  arranged in the rows c and d open to the lower surface of the cylinder housing  60  like the pull ports  68 . 
     The pull ports  68  for the piston rods  66  arranged in the rows a and b are connected to upward extending air tubes  70  shown in FIG. 4, respectively. Similarly, the pull ports for the piston rods  66  arranged in the rows c and d are connected to downward extending air tubes  70  shown in FIG. 4, respectively. Further, as shown in FIG. 5B,  28  push ports  72  respectively corresponding to the piston rods  66  arranged in the rows a, b, c, and d open to the rear surface of the cylinder housing  60  in such a manner that seven push ports  72  are aligned in each of the rows a, b, c, and d. Each push port  72  communicates with the head-side chamber  63  of the corresponding air cylinder  62 . Although not shown, all of the push ports  72  are connected to air tubes, respectively. The air tubes  70  for the pull ports  68  and the air tubes for the push ports  72  are connected to the electro-pneumatic conversion regulators  42  shown in FIG. 1, respectively. 
     Referring again to FIG. 3, a drive pinion  74  integrally formed with a lever  76  meshes with the gear  52  of the rack  46   a.  The drive pinion  74  has a central mounting hole  75 . Similarly, a support pinion  78  meshes with the gear  52  of the rack  46   a.  The support pinion  78  has a central mounting hole  79 , and is arranged so as to prevent lowering of the rack  46   a  and to allow a linear reciprocating motion of the rack  46   a.    
     Referring to FIG. 6, there is shown a perspective view of a bend unit  80 . The bend unit  80  includes a rack guide  82  having a plurality of first guide gaps  84 , and a pinion guide  86  having a plurality of second guide gaps  88 . The rack guide  82  and the pinion guide  86  are fixed to a pair of side plates  90  and  92 . A shaft  94  extends over the side plate  90 , the pinion guide  86 , and the side plate  92 . The shaft  94  is inserted through the mounting holes  75  of a plurality of drive pinions  74  to rotatably support these drive pinions  74 . Similarly, a shaft  96  extends over the side plate  90 , the pinion guide  86 , and the side plate  92 . The shaft  96  is inserted through the mounting holes  79  of a plurality of support pinions  78  to rotatably support these support pinions  78 . 
     A plurality of racks  46   a,    46   b,    46   c,  and  46   d  respectively shown in FIGS. 7A,  7 B,  7 C, and  7 D are inserted in the first guide gaps  84  of the rack guide  82  sequentially and cyclically. These racks  46   a  to  46   d  are different in height of the engaging hole  56  from the gear  52 , and the other configuration is the same as each other. Each of the racks  46   a  to  46   d  has a thickness of 0.6 mm. Further, each drive pinion  74  has a thickness of 0.4 mm, and each support pinion  78  has a thickness of 0.4 mm. 
     The thicknesses of each of the racks  46   a  to  46   d,  each drive pinion  74 , and each support pinion  78  are preferably set in the range of ¼ to ½ of the pitch of bend cells of the row tool to be hereinafter described in detail. Further, the gear module of each of the racks  46   a  to  46   d,  each drive pinion  74 , and each support pinion  78  is preferably set to ½ or less of the pitch of the bend cells. More preferably, this gear module is set to 0.1 to 0.3 times the pitch of the bend cells. 
     The racks  46   a  shown in FIG. 7A are connected to the piston rods  66  arranged in the row d in the air cylinder unit  58  shown in FIG.  4 . The racks  46   b  shown in FIG. 7B are connected to the piston rods  66  arranged in the row c in the air cylinder unit  58  shown in FIG.  4 . The racks  46   c  shown in FIG. 7C are connected to the piston rods  66  arranged in the row b in the air cylinder unit  58  shown in FIG.  4 . The racks  46   d  shown in FIG. 7D are connected to the piston rods  66  arranged in the row a in the air cylinder unit  58  shown in FIG.  4 . 
     FIG. 8 is a view taken in the direction of arrow VIII in FIG.  6 . Each of the racks  46   a  to  46   d  has a thickness of 0.6 mm as mentioned above, so that each first guide gap  84  of the rack guide  82  has a width slightly larger than 0.6 mm. Further, each drive pinion  74  has a thickness of 0.4 mm, and each support pinion  78  has a thickness of 0.4 mm as mentioned above, so that each second guide gap  88  of the pinion guide  86  has a width slightly larger than 0.4 mm. 
     Further, the pitch of the first guide gaps  84  of the rack guide  82  is the same as the pitch of the second guide gaps  88  of the pinion guide  86 . The racks  46   a  to  46   d,  the drive pinions  74 , and the support pinions  78  are formed of stainless steel, and surface-treated to have wear resistance. The shafts  94  and  96  for rotatably supporting the drive pinions  74  and the support pinions  78  are also formed of stainless steel quenched to improve hardness. 
     Referring to FIG. 9A, there is shown a partially sectional, side view showing a connection structure between the piston rod  66  and the rack  46   a.  FIG. 9B is a plan view of the connection structure shown in FIG.  9 A. Reference numeral  98  denotes a coupling threadedly engaged with the front end of the piston rod  66 . The coupling  98  is integrally formed with a pair of plates  100   a  and  100   b  spaced in parallel relationship with each other. The head portion  50  of the rack  46   a  is inserted between the plates  100   a  and  100   b.  Each of the plates  100   a  and  100   b  has a pin insertion hole. A pin  102  is press-fitted with the pin insertion holes of the plates  100   a  and  100   b  and engaged with the engaging hole  56  of the rack  46   a,  thus connecting the piston rod  66  and the rack  46   a  through the coupling  98 . 
     Each of the racks  46   a  to  46   d  has an arcuate projection  54  on the upper side opposite to the gear  52 , and the projection  54  is in contact with the inner surface of the corresponding first guide gap  84  of the rack guide  82 . Accordingly, each of the racks  46   a  to  46   d  is horizontally supported at three points, i.e., a first point of contact with the corresponding drive pinion  74 , a second point of contact with the corresponding support pinion  78 , and a third point of contact with the rack guide  82  at the projection  54 . When each air cylinder  62  is operated, the corresponding one of the racks  46   a  to  46   d  is linearly reciprocated in the horizontal direction. 
     The transmission of torque F at a front end portion  76   a  of the lever  76  of each drive pinion  74  will now be described with reference to FIG.  10 . Letting F 0  denote the torque on the pitch circle of the drive pinion  74 , the torque F at the front end portion  76   a  of the lever  76  is determined by the following equation because of no speed reducing mechanism. 
     
       
           F=F   0 ×( r/R ) 
       
     
     where r is the radius of the pitch circle of the drive pinion  74 , and R is the distance from the center of the drive pinion  74  to a load point on the front end portion  76   a.  A standard spur gear is used for each of the racks  46   a  to  46   d  and each drive pinion  74 , so that the torque transmission efficiency is about 100%. 
     There will now be described a row tool  106  fixed to the bend unit  80  shown in FIG. 6 for locally bending a row bar  126  (see FIG. 3) bonded to the lower end surface of the row tool  106  with reference to FIGS. 11 to  15 . The row tool  106  includes a plurality of bend cells  110  for locally bending the row bar  126 , and a pair of fixed cells  112  formed so as to interpose the bend cells  110 . Each fixed cell  112  has a width larger than that of each bend cell  110 . A slit  108  is defined between any adjacent ones of the bend cells  110  and a slit  108  is defined between each fixed cell  112  and the bend cell  110  adjacent thereto. Each slit  108  has a width of 0.1 mm. 
     As shown in FIGS. 3,  14 , and  15 , each bend cell  110  is formed with an engaging hole  116  for engaging the front end portion  76   a  of the corresponding lever  76 . A through hole  120  is formed in the row tool  106  so as to horizontally extend from one end of the row tool  106  to the other end thereof, and a pair of spring portions  122  and  124  are formed at the lower and upper ends of the row tool  106 , thereby forming a parallel spring mechanism for deformably supporting the bend cells  110 . As best shown in FIG. 14, a horizontally elongated opening  118  is formed on the rear surface of the row tool  106  so as to communicate with the through hole  120  and the engaging holes  116 . Thus, the front end portions  76   a  of all the levers  76  are engaged through the opening  118  and the through hole  120  into the engaging holes  116  of the bend cells  110 . 
     When the front end portion  76   a  of each lever  76  is inserted in the corresponding engaging hole  116 , there are defined upper and lower gaps between the front end portion  76   a  and upper and lower wall surfaces of the corresponding engaging hole  116 . Each of the upper and lower gaps is about 0.1 mm. As shown in FIG. 3, the row bar  126  is bonded to the lower end surface of the row tool  106  by means of a hot-melt wax or adhesive with high accuracy. The row bar  126  is formed with a plurality of magnetic head elements arranged in a line. The row tool  106  is formed of stainless steel. 
     The bending operation of the row bar  126  will now be described with reference to FIG.  3 . The compressed air supplied from the compressed air source  38  is introduced through the electro-pneumatic conversion regulator  42  into the head-side (push-side) chamber  63  or the rod-side (pull-side) chamber  65  of the double-acting air cylinder  62 , thereby moving the piston rod  66  to the right or to the left as viewed in FIG.  3 . By the movement of the piston rod  66 , the rack  46   a  is moved to the right or to the left as viewed in FIG.  3 . As a result, the drive pinion  74  is rotated clockwise or counterclockwise. 
     By the rotation of the drive pinion  74 , the lever  76  engaged with the corresponding bend cell  110  of the row tool  106  is rotated to deform the corresponding bend cell  110  in the vertical direction. The amount of deformation of the bend cell  110  can be controlled by changing the pressure of the compressed air supplied to the double-acting air cylinder  62  in an analog fashion, so that an appropriate amount of deformation can be obtained in each bend cell  110 . Accordingly, the row bar  126  can be minutely displaced with a fine pitch determined by the number of bend cells  110  (e.g., 28 bend cells  110  in this preferred embodiment), thereby realizing high-accuracy ELG lapping. 
     The row bar  126  is formed with a plurality of magnetic head elements and a plurality of ELG elements as resistance elements for monitoring the lapping. These head elements and ELG elements are arranged in a line. In lapping the row bar  126 , a printed wiring board is bonded to the front surface of the row tool  106 , and pads of the printed wiring board and terminals of the ELG elements are connected by wire bonding to measure a change in resistance of each ELG element. 
     A lapping pressure applied to the row bar  126  bonded to the row tool  106  during lapping is determined by the self-weight of the lap head  24  shown in FIG.  1  and the pressure applied to the lap head  24  by the pneumatic cylinders  32 . In the case of rough lapping, this pressure is set to a high value, whereas in the case of finish lapping, this pressure is set to a low value. This pressure can be finely adjusted by operating the bend unit  80  to control a thrust applied to each bend cell  110 . 
     According to the row bar lapping method and machine of the present invention, the displacement of the row bar at multiple points can be controlled, so that a target shape of the row bar can be easily obtained and high-accuracy lapping can be realized. 
     The present invention is not limited to the details of the above described preferred embodiments. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.