Abstract:
A compound punching apparatus for providing a substrate having half of the perforations formed from one major surface of the substrate and the other half of the perforations formed from the opposite major surface. The arrangement of the punches create equal and opposite stress forces in the substrate that essentially cancel each other out to provide a product meeting exacting planarity requirements. The compound punching apparatus includes two diametrically opposed dies and punching tools, a feed system, a drive system and a frame.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to a compound punching apparatus, and more particularly to a compound punching apparatus for perforating a planar, electrically conductive substrate suitable for use in producing a current collector in an electrochemical cell.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is known to form perforated substrates from a sheet of electrically conductive material wherein the perforations are punched or otherwise introduced from one side only. The problem with this type of punching is that the resultant burrs formed on the opposite side at each of the perforations introduce stress forces into the substrate that cause it to bow. Conventionally, the bow is removed from the perforated substrate by pressing out the burrs. However, as the width of the substrate increases, the difficulty of compensating for the bow is magnified.  
           [0003]    During battery manufacture, it is extremely critical that the substrate current collector be as planar as possible to allow for high speed lamination of the electrode active material onto the substrate. However, it is often difficult to adequately press out the burrs to provide an acceptably planar substrate, and pressing the substrate to remove the bow from a perforated substrate adds an extra step to the manufacturing process. A substrate having perforations formed from opposing major surfaces is disclosed and claimed in U.S. Pat. No. 5,578,398, which is hereby incorporated by reference.  
           [0004]    Coating, laminating and other processes normally limit how fast the substrates can be processed. To increase the throughput while holding the speed constant, wider materials must be passed through the system. Wider materials are more difficult to maintain flat and the chances of cross bow increase with the increased width. Accordingly, there is a need for a punching apparatus that minimizes the risk of crossbow and produces a perforated substrate that conforms to strict planarity requirements.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention meets the above described need by providing a compound punching apparatus that punches the substrate from opposite sides of the substrate in alternating fashion. By uniformly alternating the perforations in this manner, the stress forces produced at each perforation are essentially canceled by the adjacent perforation formed through the opposite major surface of the substrate and the substrate maintains an extremely planar shape.  
           [0006]    The present invention provides a compound punching apparatus for providing a perforated material having first and second major surfaces. The apparatus includes a frame for maintaining all of the elements substantially square relative to the material. A pair of punching tools are mounted to the frame and are disposed opposite from each other. The punching tools include a set of punches mounted to a punch ram. The punching tool is attached to a slide that slides back and forth inside a set of gibs. The gibs maintain the slides and the punches in their proper alignment relative to the material. A pair of dies are mounted to the frame opposite to each other. The dies have openings that correspond to the punching tools such that the punching tools pass through the dies into the substrate on their punching stroke. The first die is stationary and the second dies moves toward and away from the first die such that the dies are disposed in spaced apart relation for a portion of the cycle and are disposed in juxtaposition for another portion of the cycle. In this manner, the moving die acts as a stripper.  
           [0007]    A feed mechanism in the form of a pair of grippers advances the material through the system. Each of the grippers includes a feed bar and a clamp. When the clamp is closed and the feed bar is moving, the gripper conveys the material. During this feed cycle, the other gripper is moving in the opposite direction with its clamp open to reposition prior to its next feed. In this manner, the grippers feed in alternating fashion and are always in position for their next feed. As a result, there is no dead time in the cycle associated with repositioning the feed bars. 
       
    
    
       [0008]    Other features and advantages of the present invention will become apparent upon reading the following detailed description of embodiments of the invention, when taken in conjunction with the accompanying drawings and the appended claims.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The invention is illustrated in the drawings in which like reference characters designate the same or similar parts throughout the figures of which:  
         [0010]    [0010]FIG. 1 is a side elevation view of the apparatus of the present invention;  
         [0011]    [0011]FIG. 2 is a partial side elevation of the apparatus shown in FIG. 1;  
         [0012]    [0012]FIG. 3 is a top plan view of the apparatus;  
         [0013]    [0013]FIG. 4 is a schematic diagram of the drive system of the present invention;  
         [0014]    [0014]FIG. 5 is a side elevation view of the cam shaft and stripper mechanism of the present invention;  
         [0015]    [0015]FIG. 6A is a sectional view taken along line  6 - 6  of FIG. 5;  
         [0016]    [0016]FIG. 6B is a side view of the eccentric, the roller bearing and the collar, that moves the punch plate;  
         [0017]    [0017]FIG. 7 is a sectional view taken along line  7 - 7  of FIG. 3;  
         [0018]    [0018]FIG. 8 is a sectional view taken along line  8 - 8  of FIG. 7;  
         [0019]    [0019]FIG. 9 is a sectional view taken along line  9 - 9  of FIG. 8;  
         [0020]    [0020]FIG. 10 is a top plan view of the feed system;  
         [0021]    [0021]FIG. 11 is a sectional view taken along line  11 - 11  of FIG. 10;  
         [0022]    [0022]FIG. 12 is an enlarged, partial side elevation view of the feed system of the present invention;  
         [0023]    [0023]FIG. 13 is a front elevational view of the feed system of the present invention;  
         [0024]    [0024]FIG. 14 is a partial side elevation view of the present invention;  
         [0025]    [0025]FIG. 15 is a timing diagram for the present invention;  
         [0026]    [0026]FIG. 16 is a partial, plan view of a perforated substrate according to the present invention; and,  
         [0027]    [0027]FIG. 17 is a cross-sectional view taken along line  17 - 17  of FIG. 16. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]    In FIG. 1, a compound punching apparatus  20  perforates a thin sheet of material  23  from opposite sides of the material  23 . Approximately half of the perforations are formed from one major surface  26  of the material  23 , and the other half of the perforations are formed from the other major surface  29 . The material  23  is a planar sheet of thin gauge material that is substantially flat. For example, the sheet may be an electrically conductive, thin metal sheet suitable for use as a current collector in a battery. Accordingly, the thin material is perforated to form a substrate. The perforated substrate is then laminated with an electrode active material. The invention is also suitable for other applications where thin materials susceptible to crossbow need to be perforated and maintained as flat as possible, for example, some components of microcomputers would be suitable.  
         [0029]    The thin material  23  is normally stored in rolls of flat sheets having a predetermined width corresponding to the maximum width suitable for processing in the compound punching apparatus  20 . The material  23  unwinds from the roll (not shown) and a loop control system (not shown) is typically used to isolate the compound punching apparatus  20  from any tension due to the roll. In order to do so, as known by those of ordinary skill in the art, the loop control apparatus controls the unwinding of the material by means of an electric eye such that enough slack is maintained between the roller and the apparatus  20  so that the only tension upstream is due to the weight of the material  23 . The material  23  enters the apparatus  20  across a fixed roller  32  that is made of a material having a minimum frictional effect on the material  23 . The material  23  is provided with edge guidance as it enters the punching apparatus  20  as is known to those of ordinary skill in the art. A coarse adjustment is accomplished by edge guides  35  (FIG. 14) that physically border the edges of the material  23 . Fine adjustment is provided by a lead screw that provides for fine tuning by turning a knob  38  to advance a carriage.  
         [0030]    The material  23  passes between two sets of tooling  41  positioned on opposite sides. Each set of tooling  41  is controlled by a cam shaft  44 . The tooling  41  primarily includes a pair of punch rams  47  (FIG. 9), a pair of die mounting plates  50  and  53  (FIG. 9), and a set of dies  51 ,  54  (FIG. 9). The tooling  41  is mounted to a subframe  56  that is mounted to the main frame  59  by isolation pads  62 . A set of hand wheels  65  provide for manual rotation of the cam shafts  44  for threading the machine and the like. The left side of the tooling  41  has a fixed die mounting plate  50 . Die plate  53  acts as a stripper and moves toward and away from die plate  50  according to the cycle of the apparatus  20 .  
         [0031]    A pair of horizontal slug evacuation tubes  68  attach to a manifold that is connected to a centrifugal blower (not shown) for vacuum conveying the slugs  71  (shown in FIG. 8) for disposal.  
         [0032]    The material  23  is conveyed through the apparatus  20  by a pair of grippers  74 ,  77  that advance the material  23  through the apparatus. A pair of tricoidal cams  80 ,  83  control the positioning of each gripper  74 ,  77 , as will be described in detail with reference to FIGS.  10 - 13 .  
         [0033]    A single electric motor  86  preferably drives all of the shafts. The motor  86  is preferably a 5 HP DC drive, variable speed motor. Other types of motors for driving the shafts known to those of ordinary skill in the art would also be suitable.  
         [0034]    Turning to FIG. 2, the die mounting plates  50  and  53  are mounted to a pair of slides  89 , 92  that move inside a set of stationary gibs  95  that are positioned on both the right and the left hand sides of the apparatus  20 . As shown in FIG. 3, the components shown in FIG. 2 on the left hand side  96  and right hand side  97  are present on both the front side  99  and the back side  100  of the apparatus  20 . Since the components on the back side  100  of the apparatus  20  are the same, they are not described separately.  
         [0035]    The die mounting plate  50  and die  51  on the left side of apparatus  10  are fixed during the operation of the apparatus  20 . A tapered block  98  is removable and provides room for die mounting plate  50  and die  51  to be retracted by moving the slide  89 . The die mounting plates  50 ,  53  are carried by frames  101  that are formed out of H-blocks  104  and cross members  107 .  
         [0036]    Referring to FIG. 7, the frame  101  on the right side moves the die mounting plate  53  toward and away from the die mounting plate  50  to form a stripper. The stripper action is provided by the slide  92 .  
         [0037]    Referring to FIG. 5, the right slide  92  moves between the stationary gibs  95  according to a cam operated block  110  having an eccentric hole  113 . The cam operated block  110  is driven up and down by a cam surface  116  rotated by cam shaft  44  and disposed between a set of rollers  119 . The rotation of the cam surface  116  causes the rollers  119  to move up or down through a portion of each rotation of the cam shaft  44 . Each time the cam surface  116  pushes the top roller  119  upward, the eccentric slot  113  moves upward which causes the pin  122  connected to the slide  92  to move the slide  92  inward to close the stripper. In contrast, when the cam surface  116  pushes down on the lower roller  119 , the eccentric slot  113  moves downward causing the pin  122  and slide  92  to move away to open the stripper. The stripper movement covers a distance of approximately twenty-thousandths of an inch. The timing of the opening and closing of the stripper is thereby linked to the rotation of the cam shaft  44  through the cam surface  116 .  
         [0038]    Returning to FIG. 2, a mechanical interlock  125  ensures registry of the die plates  51  and  54 . The interlock  125  (best shown in FIG. 14) includes a precision fit tab and opening  128 .  
         [0039]    In FIG. 3, a set of tie bars  129 ,  131  connect the two sides of the apparatus  20  to help maintain the apparatus  20  perfectly square with regard to the tooling  41  and the punch rams  47 . A T-shaped bar  134  is fastened to a square plate  137 . The T-shaped bar  134  carries the punches  140  (shown in FIG. 8). The T-shaped bar  134  is driven off of the cam shaft  44  by an eccentric cam  143  mounted on the shaft  44  (best shown in FIG. 6A) that drives a roller bearing  146  (FIG. 6A) with a set of rollers  149  (FIG. 6A).  
         [0040]    Referring to FIG. 6B, the roller bearing  146  is mounted inside a collar  147  that is connected to the plate  137  by suitable fasteners  148 . The centerline  200  for the cam shaft  44  is shown in broken lines and the centerline  210  of the eccentric is also shown in broken lines. The inside of the collar  147  has bearing surfaces  149  that can be replaced if wear grooves are formed. Accordingly, the rotation of the eccentric  143  caused by rotation of the cam shaft  44  causes the roller bearing  146  to transfer the plate  137  horizontally.  
         [0041]    The plate  137  drives the punches  140  on an independent set of slides  150  (shown in FIG. 7). Accordingly, as shown in FIG. 7, the die mounting plate  53  and die  54  are attached to the frame  101  which is moved by slide  92 . The punches  140  are carried by the T-bar  134  which is moved by slide  150 . The punches  140  travel approximately five millimeters during the punch stroke. Accordingly, the stripper movement and the punch stroke both operate off of the cam shaft  44 , but are driven by different cams and different slides.  
         [0042]    Returning to FIG. 3, the cam shafts  44  are driven from the same motor  86  and variable speed drive through a system of precision belts  152 . In FIG. 4, a schematic of the drive system illustrates that belts  152  drive the cam shafts  44  at the same speed, and drive the gripper shafts  155 ,  158  at a second speed. The speed reducers  161  are designed according to the throughput of the line and the timing of the apparatus  20 , as known to those of ordinary skill in the art. FIG. 15 illustrates a timing diagram for the compound punching apparatus which will be described in detail hereinafter.  
         [0043]    In FIG. 8, the punches  140  are shown as they pass through the material  23  and produce a slug  71 . The slugs  71  move in a column through a passageway  164  that leads to a vertical manifold  167  that connects to the evacuation tubes  68 . The dies  51 ,  54  and the die mounting plates  50 ,  53  are shown in the stripper closed position. The stripper is closed during the entry into and removal of the punches  140  from the material  23  to provide support to the material, to maintain the very close tolerances, and to prevent undesirable deformations from occurring. The die  54  and die mounting plate  53  are attached to the H-blocks  104  which move toward and away from the stationary die  51  and die mounting plate  50 .  
         [0044]    Turning to FIG. 9, the punches  140  produce slugs  71  that have to be removed without jamming. When the slugs  71  are punched by the force of the ram  47 , they tend to form a column that sticks together. By having a curved opening  170  with a relatively short radius, the column of slugs  71  is forced to break up as it conforms to the curve, and the curve reduces the likelihood of jamming. From the center outward on the left side, the components include the die  51 , the die mounting plate  50 , a vertical manifold  167 , a punch holder  173 , a punch head spacer  176 , a back-up plate  178 , and a punch ram  47 . The punch ram  47  is mounted to the T-shaped bar  134  that is driven by the cam shaft  44  (FIG. 8).  
         [0045]    Turning to FIGS.  10 - 13 , a pair of grippers  74 ,  77  advance the materials  23  during a portion of each cycle of the apparatus  20 . The material  23  advances through the apparatus  20  on an intermittent basis because the material  23  cannot be advanced when the stripper is closed or when the punches  140  are extending through the material  23  during the punch stroke. The grippers  74 ,  77  have gripper feed bars  179 ,  182  that are disposed one above the other, and they are coordinated with one another, such that they grip and feed in a “hand over hand” fashion. Both gripper feed bars  179 ,  182  move vertically up and down. Also, both gripper feed bars  179 ,  182  have clamps  183 ,  184  that close such that only one gripper feed bar  179 ,  182  is capable of conveying the material  23  at any given time. While one of the grippers  74  is conveying the material  23 , the other gripper  77  is capable of being open and moving upward to get into position for its next cycle. Accordingly, the capability of repositioning one gripper  74  while the other gripper  77  is moving, eliminates dead time.  
         [0046]    In FIG. 12, tricoidal cam  80  rotates on gripper shaft  155  and tricoidal cam  83  rotates on gripper shaft  158 . The cam  80  moves a cam follower  185  by means of a pair of rollers  188 . The rollers  188  are attached to an assembly  191  that moves up and down according to the position of the cam  80  which moves the gripper feed bars  179 ,  182  up and down. The rollers  188  are fixed relative to one another. The gripper shafts  155 ,  158  also control the opening and closing of the grippers clamps  183 ,  184  through a second cam surface  194 . The gripper shaft  155  engages a cam wheel  197  that is attached to a member  200  that pivots about a pivot point  203 . The opposite end  216  of the member  200  moves in and out to activate the clamping of the gripper  74 .  
         [0047]    Referring to the timing diagram in FIG. 15, the cycle for the apparatus  20  is shown for two revolutions of the cam shaft  44 . The punch rams  47  are fully retracted at 0 degrees. The cross-hatched region  209  corresponds to the portion of the cycle when the punches  140  have entered the material  23  to punch out the perforation. Next, they travel forward a short distance and then start moving backward out of the material  23 . The point  212  at the front of the region  209  is where the punch  140  enters the material  23 . The point  215  at the back of the region  209  is where the punch  140  exits the material  23 . During the time that the punches  140  are in the material  23 , the material  23  cannot be advanced by the feed system. Accordingly, from a portion of the cycle just prior to the punches  140  entering the material  23  to the time when the punch  140  exits the material  23 , the gripper feed bars  179 ,  182  are “flat lined” in the diagram, indicating that they are not moving. During this still period for the gripper feed bars  179 ,  182 , the clamps  183 ,  184  are alternately opening and closing. For a fractional portion of the cycle while the punches  140  are inserted through the material  23 , both clamps  183 ,  184  release the material  23 . This short period provides a chance for the material  23  to adjust slightly so that if it becomes misaligned it is not locked in to misalignment by constant positive traction from the grippers  74 .  
         [0048]    The stripper closes prior to the punches  140  entering the material  23  and opens shortly after the punches  140  exit the material  23 , such that the stripper is open when the material  23  is being advanced.  
         [0049]    As indicated in the diagram, the gripper feed bars  179 ,  182  move in opposite directions such that while one is feeding (with its corresponding clamp closed), the other is moving upward (with its clamp open) into position for its next feed.  
         [0050]    The timing of all of the movements is synchronized by the drive system which ties all of the shafts to a single motor  86 .  
         [0051]    Turning to FIG. 16, a perforated substrate  250 , preferably of an electrically conductive material, is formed using the compound punching apparatus  20  of the present invention. The perforations  253  are preferably disposed such that the centers  256  of any three adjacent perforations  253  form an equilateral triangle. Accordingly, each of the perforations  253  is equidistant from any adjacent perforation  253 . In FIG. 17, the perforations  253  are formed such that adjacent perforations  253  are punched from opposite major surfaces of the material  23  as indicated by the burrs  259 . In this manner, the adjacent perforations  253  introduce substantially equal and opposite stress forces into the material  23  that essentially cancel each other to provide a planar characteristic to the perforated substrate  250 . The perforations  253  do not have to be made simultaneously to obtain this effect.  
         [0052]    Accordingly, the present invention offers several advantages including a reduction in the amount of crossbow that is normally associated with wider materials. By uniformly alternating the perforations such that adjacent perforations are punched from opposite sides of the material, the stress forces produced at each perforation are essentially canceled by the adjacent perforation formed through the opposite major surface of the material.  
         [0053]    By providing wider, flatter material, the present invention provides for faster production of high quality substrates for use in the production of electrochemical cells. The wider materials facilitate greater production by increasing the throughput without increasing the line speed. The perforated substrates produced by the present invention are suitable for use as current collector substrates that are laminated at high speeds with an electrode-active material to form current collectors.  
         [0054]    It is contemplated that the compound punching apparatus may be suitable for processes outside of the electrochemical area. For example, the present invention would be suitable for any process where a thin substrate must be maintained as planar as possible for downstream coating, laminating or other processes where bowing of the material has to be minimized.  
         [0055]    Another advantage of the present invention is that the hand over hand operation of the grippers provides for smooth operation of the feed system such that after the punches retract from the material, a pair of grippers is always in position to feed material. While the active gripper is feeding the material for the next punch, the inactive gripper is moving simultaneously into position for its next feed.  
         [0056]    The present invention also advantageously provides a slug removal system that prevents clogs that can damage the tooling. The curvilinear entry path into the disposal tube forces the slugs to separate from one another such that they continue to feed into the disposal tube rather than jamming and backing up into the path of the punch.  
         [0057]    The present invention also provides for precision timing of all of the cam movements by linking all of the shafts to a single motor and drive.  
         [0058]    While the invention has been described in connection with certain preferred embodiments, it is not intended to limit the scope of the invention to the particular forms set forth, but, on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.