Abstract:
A method and apparatus for removing the lowest workpiece from a stack of a plurality of substantially similar workpieces. A horizontal shuttle has a lip on its edge, and is driven in one direction to remove the lip from a void beneath the stack, thereby permitting the stack to fall. The lowest workpiece drops into the void, and the next higher workpiece rests on the upper surface of the shuttle lip. The shuttle is subsequently reversed to drive the workpiece into a slot in a vertical clamp body. The clamp body is driven downwardly, thereby driving the workpiece downwardly, to be acted upon by a secondary device, such as a conventional degating apparatus.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to devices for removing component parts from a stack and using them in the assembly of an article of manufacture, and more particularly relates to a method and apparatus for removing component parts from the bottom of a stack of parts to permit supplying of the stack from the top. 
     2. Description of the Related Art 
     In the field of microsurgery, a surgical instrument having a cutting blade traverses a specific path through tissue. One feature of the surgical instrument is a single-use cartridge that is a holder for surgical staples. The cartridge is an elongated plastic body with a longitudinal channel that serves as a guide for a surgical blade. The cartridge has rows of small staples on opposite sides of the channel, and these rows are aligned parallel to the guide channel. Drivers are inserted in apertures (also called “pockets”) aligned with the rows in order to push the staples out of the cartridge and through the adjacent tissue. Before the blade has made its cut, each side of the incision is stapled together by displacing the drivers relative to the cartridge. This displacement forces the staples against an anvil on the opposing side of the surgical instrument as the cartridge and the anvil deflect the points of the staples into a clasping position. 
     There may be as many as fifty or more very small staples on each side of a two-inch incision. Each staple can be driven into the tissue to close the incision by the correspondingly small drivers. The task of inserting the drivers into the cartridge is labor-intensive due to the small size and number of the drivers and the apertures. 
     One prior art system for mounting the staple drivers into apertures in the cartridge includes a plastic holder, commonly referred to as a “tree” having aligned “branches” with drivers integrally formed on an end of each of the aligned branches. The conventional cartridge is placed in an apparatus and the tree with drivers is hand-manipulated to place the drivers adjacent the entrance to the pockets. This is normally accomplished by inserting the drivers in funnel-shaped passages that are aligned with the pockets. Each driver is subsequently driven into the associated pocket of the cartridge. The separation of the individual drivers from the branch of the tree on which it is mounted is accomplished by flexing the branches of the tree manually to break the tree away from the staple drivers. Then, a hand-manipulated tool is used to press each staple driver down into the cartridge to near the pocket opening on the opposite side of the cartridge. 
     The finger operation of pressing each driver into a pocket, the flexing of the branches and the subsequent pressing from the hand-operated prongs can misalign some of the drivers within the pockets. Furthermore, the sizes of the pockets and the drivers vary slightly due to the minute structure involved and the fact that both the cartridge and the staple drivers are formed of thermoplastic resin, which does not always result in a perfectly formed structure. This combination of factors can cause some “play” in the assembly, which can result in an alignment problem. In particular, inversion of the cartridge after assembly can result in some of the drivers being displaced from their pockets. If a staple driver is absent, no staple will be driven into the tissue at that point in the incision. 
     Another problem is the imprecision in the process of separating the staple drivers from the branches of the plastic “tree”, a process referred to as “degating.” The drivers are mounted to the tree prior to insertion in the cartridge, but must be removed from the tree before or during the insertion process. Because the separation of a driver from the tree is not precise, it leaves some material on one side of each driver. The remnants of material left on the drivers is not a predictable size, and often the remnants are larger than desired. While it is not practical to remove all of the holder material from the side of each driver in the separation process, it is important that the amount of material left on each driver be relatively consistent between drivers. This is because the material left on the side tends to cause friction when the staple driver is used in surgery. If the amount of material left is consistent, it allows a user of such a staple cartridge to accurately predict the amount of force needed to expel a staple in surgery. In addition, the smaller the volume of material left, the less friction will be generated, and the less the force required to use the staple cartridge. 
     It is known in the prior art to insert drivers mechanically into surgical stapling cartridges, as shown in U.S. Pat. No. 5,836,147 to Schnipke, U.S. Pat. No. 5,653,928 to Schnipke, U.S. Pat. No. 6,158,205 to Schnipke et al., and U.S. Pat. No. 7,207,168 to Doepker et al., all of which are incorporated herein by reference. Workers manually position the cartridges, as well as the holders that contain the drivers and hold them relative to the machine, in the machines disclosed in these patents, and then actuate the machine to insert the tiny drivers into the pockets in the cartridges. After a fraction of the total number of drivers is inserted by one machine, the cartridge is then manually transported to the next machine, which inserts another fraction of the drivers. In U.S. Pat. No. 6,729,119 to Schnipke et al., which is incorporated herein by reference, a robotic loader is described for use in filling the cartridges discussed herein with the use of fewer workers than the prior art. 
     The machines disclosed in the patents referenced above, although representing a significant improvement over the prior art, still require parts to be fed in batches to the machines. This requires periods of time in which the machine is not operating in order to supply components to the machines. Thus, there is a need for an apparatus that permits continuous feeding of component parts to the above machines, and to other machines that are unrelated to the above. 
     BRIEF SUMMARY OF THE INVENTION 
     The apparatus and method described herein allow the advantageous ejection of the lowest part or parts from a stack of similar and preferably identical parts. Such a system permits a stack of parts to be continuously filled from above and held in place by the force of gravity. When the stack of parts needs to be refilled, due to falling below a predetermined height, a sensor signals a computer and the computer actuates a robot to refill the stack. Thus, a continuous process, which operates uninterrupted, is realized from the invention. The preferred apparatus includes a plate to which a pair of rigid buffer columns are mounted with grooves inwardly facing one another. Protruding tabs on a part, such as a “tree” that is used to transport drivers to a degating apparatus that inserts the drivers in a surgical cartridge, extend into the grooves for restricting the lateral and longitudinal movement of the trees. A shuttle is slidably mounted to the plate substantially parallel to the plane of the plate. The shuttle has an upper surface that supports the stack of trees, but is withdrawn from beneath the grooves to permit one of the trees to fall downwardly into a slot between the column and the plate. The shuttle then reverses and drives the tree into a slot on a vertically moveable shuttle, such as a clamp body. The clamp body is driven in a path that is transverse, and preferably substantially perpendicular, to the path of the shuttle, although this is not required. This drives the tree downwardly toward a degating machine or other device that acts upon the trees. 
     A clamp bar accompanies the clamp bodies and the tree, and applies a clamping force to the tree while its drivers are being inserted into the cartridge. When the drivers are severed from the tree, the cutting force causes the scrap (i.e., all parts of the tree other than the drivers) to rapidly move away from the degating apparatus. Because the slot into which the protruding tabs on the tree are inserted opens toward the shuttle that drives it thereinto, the opening of the slot faces away from the degating apparatus. Therefore, the rapid movement of the scrap caused by cutting the drivers from the tree causes the scrap to move rapidly out of the slots and toward a scrap collection area. This can be further encouraged by a blast of air or other mechanism. 
     The slots on the clamp bodies that accept the tree&#39;s tabs are displaced as far below the plate at the time the drivers are cut from the tree as is necessary to permit this movement of the scrap away from the degating apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a view in perspective illustrating a preferred embodiment of the present invention in a cooperating configuration with a degating apparatus. 
         FIG. 2  is an exploded view illustrating the embodiment of  FIG. 1 . 
         FIG. 3  is a view in perspective illustrating a preferred embodiment of the present invention. 
         FIG. 4  is an exploded view illustrating the embodiment of  FIG. 3 . 
         FIG. 5  is a magnified view of a portion of the embodiment of  FIG. 3 . 
         FIG. 6  is a further magnified view of a portion of the embodiment of  FIG. 3 . 
         FIG. 7  is a view in perspective illustrating the embodiment of  FIG. 1  in a first step of a preferred process. 
         FIG. 8  is a view in perspective illustrating the embodiment of  FIG. 1  in a second step of a preferred process. 
         FIG. 9  is a view in perspective illustrating the embodiment of  FIG. 1  in a third step of a preferred process. 
         FIG. 10  is a view in perspective illustrating the embodiment of  FIG. 1  in a fourth step of a preferred process. 
         FIG. 11  is a view in perspective illustrating the embodiment of  FIG. 1  in a fifth step of a preferred process. 
         FIG. 12  is a view in perspective illustrating the embodiment of  FIG. 1  in a sixth step of a preferred process. 
         FIG. 13  is a view in perspective illustrating the embodiment of  FIG. 1  in a seventh step of a preferred process. 
         FIG. 14  is a view in perspective illustrating the embodiment of  FIG. 1  in an eighth step of a preferred process. 
         FIG. 15  is a view in perspective illustrating the embodiment of  FIG. 1  in a ninth step of a preferred process. 
         FIG. 16  is a view in perspective illustrating the embodiment of  FIG. 1  in a tenth step of a preferred process. 
         FIG. 17  is a view in perspective illustrating the embodiment of  FIG. 1  with a stack of trees installed thereon. 
     
    
    
     In describing the preferred embodiment of the invention which is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific term so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the word connected or term similar thereto are often used. They are not limited to direct connection, but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The apparatus  6  shown in  FIG. 1  is the stack feeding apparatus  10  of the invention mounted in cooperation with a conventional degating apparatus  8 , with which the apparatus  10  is designed to cooperate. The combination of the apparatus  10  and the degating apparatus  8  is exploded in  FIG. 2  to provide viewing of details of the configuration. It will be apparent from the description herein that both apparatuses are mounted to a base  20  having a central aperture  22  into which a conventional surgical cartridge (not shown) is disposed during operation. This base is preferably mounted in an assembly operation in which pallets, or other moveable objects, are conveyed along from station to station to have component parts mounted in a surgical cartridge, as is conventionally known. 
     In the preferred operation, “trees” with drivers are placed in the apparatus  10 , and the apparatus  10  mechanically inserts the trees into the degating apparatus  8 . The degating apparatus  8  separates the drivers from the “branches”, inserts the drivers into the apertures or “pockets” of a conventional surgical cartridge in a conventional manner, and the scrap material is ejected out of the apparatus  6 . The driver insertion and degating process is described in detail in the patents incorporated by reference herein. 
     The novel aspects of the apparatus  10  are described in detail herein, with reference to the figures, beginning with  FIG. 3 , which shows the apparatus  10  with the degating apparatus  8  removed. The apparatus  10  is not found in this state during normal operation, but the apparatus  10  is illustrated in this manner for clarity. The plate  30  is mounted rigidly to the base  20 , as shown in  FIG. 1 , and has a central aperture  35  that corresponds with the central aperture  22  of the plate  20 . As noted above, a cartridge mounted in a pallet is raised into precise registration with these apertures  22  and  32 , so that the drivers can be inserted in the cartridge thereof. 
     A pair of upright buffer columns  31  and  32  rigidly mount to the plate  30  with facing grooves  33  and  34 , respectively, that receive trees as described below and form a guide channel for the trees. Most preferably, protruding tabs (not visible) extend laterally from the trees and are inserted in the grooves  33  and  34 , thereby securing the trees from longitudinal movement and lateral movement except as described herein. 
     It should be noted that terms such as “front,” “rear,” “top,” “bottom,” “horizontally,” “vertically,” “above” and “below” are used herein to describe the relative position and orientation of various components of the invention, all with respect to the geometry and orientation of the apparatus  10  in an operable orientation, which is shown in  FIGS. 1 and 2 . Likewise, the terms “laterally,” “longitudinally,” “upstream” and “downstream” relate to the direction of travel of trees during their movement into and out of the degating apparatus  8 , in which the longitudinal direction refers to the direction the trees move when first driven out of the grooves  33  and  34 , and the upstream position is a point from which a tree moving along the longitudinal axis starts and the downstream position is a point to which the tree on moves from the upstream position. This terminology includes the words specifically mentioned, derivatives thereof, and words of similar import, as understood by a person having ordinary skill in the art. 
     Two prime movers, such as the conventional pneumatic rams  36  and  38 , are mounted to the buffer columns  31  and  32 , and are drivingly linked, such as by their drive rods (not visible) to the vertical clamp bodies  40  and  42 . The rams  36  and  38  are connected to the central computer  16 , which is preferably a programmable logic controller (PLC) or equivalent multifunction programmable computer. The clamp bodies  40  and  42  are slidably mounted to the buffer columns  31  and  32 , such as by the roller slide assemblies  40 ′ and  42 ′ or equivalent, respectively, which are illustrated in  FIG. 4 . The clamp bodies  40  and  42  are driven along a substantially vertical, linear path relative to the buffer columns  31  and  32 . A clamp bar  44  is rigidly mounted to each of the clamp bodies  40  and  42 , and moves with the same as described in more detail below. 
     Referring to  FIGS. 1 and 4 , the horizontal shuttle  50  is slidably mounted to the plate  30 , such as by roller slide assemblies  50   a  and  50   b  or equivalent, which are preferably substantially identical to the roller slide assemblies  40 ′ and  42 ′. A prime mover, preferably the conventional pneumatic ram  52 , is mounted to the member  53 , which is rigidly attached to the plate  30 , with its drive rod  54  extending slidably therethrough for attachment to the shuttle  50 , or to other members rigidly attached to the shuttle  50 . The ram  52  is connected to the central computer  16 . The ram  52  and the rams  36  and  38  are controlled by the central computer  16 , and are actuated thereby in a conventional manner. The shuttle  50  is driven along a path substantially parallel to the plane of the plate  30  toward and away from the central aperture  22 , and the clamp bodies  40  and  42  are driven substantially vertically within the central aperture  22 . It is possible for the shuttle to be oriented other than horizontally, and the clamp bodies  40  and  42  to be oriented other than vertically, but because the force due to gravity biases the components when they are in the preferred configuration, mechanical biases would be necessary to compensate for this modification. 
     Referring to  FIG. 5 , which is a magnified view of an area adjacent the central aperture  37  of  FIG. 3 , the clamp bodies  40  and  42  are shown having lower lips  46  and  47  (the lip  47  is visible in  FIG. 7 ). The lip  46  is adjacent a shoulder  37  of the plate  30 , and there is a mirror image shoulder (not visible) adjacent the lip  47 . As the clamp body  40  moves vertically, the lip  46  moves relative to, and adjacent, the shoulder  37 . The slot  46 ′, shown in more detail in  FIG. 6 , is shown aligned with the top of the shoulder  37 , and this corresponds with the highest point the clamp bodies  40  and  42  are designed to reach in their path of movement. At this point, the upwardly facing surface of the lip  46  is substantially co-planar with the upwardly facing surface of the shoulder  37 . The lip  46  is illustrated having a slight chamfer to avoid jamming during feeding of the component parts, as described below, but this is not required. The lip can be lowered beneath the plate  30  to a lowest point, at which point a tab in the slot  46 ′ can be ejected as described below. 
     The buffer column  31  is shown in  FIG. 5  mounted to the plate  30 , with the groove  33  directly below the lower end of the buffer column  31  and above the plate  30 . The surface of the buffer column  31  in which the groove  33  is formed is substantially co-planar with the face of the shoulder  37 , and this configuration defines the slot  33 ′ therebetween into which the lip  56  is inserted. The lip  56  is preferably the end of the shuttle  50  and is substantially the same thickness as the slot  33 ′, thereby displacing objects in the slot  33 ′ when the shuttle  50  is driven by the ram  52  through the slot  33 ′. 
     The shuttle  50  is shown in a “dropping” configuration in  FIGS. 5 and 6  with the lip  56  displaced out of the slot  33 ′, thereby permitting objects in the grooves  33  and  34  to drop downwardly under the force of gravity. For example, as shown in  FIG. 17 , there can be a stack of trees in the grooves  33  and  34 , and in the dropping configuration the lowest tree  100  drops into the slot  33 ′ and the higher trees rest upon the shuttle  50 . The higher trees preferably rest upon the upwardly facing surface  57  of the lip during the dropping configuration. 
     As viewed in  FIG. 7 , the ram  52  drives the shuttle  50  toward and away from the buffer columns  31  and  32 , thereby displacing the lip  56 , and a substantially identical lip  58  through the slots between the buffer columns  31  and  32  and the plate  30 . A tree  100  inserted in the space between the buffer columns  31  and  32  is driven by the shuttle  50  as described below, and in relation to  FIG. 8  and following. 
     In  FIG. 8 , the tree  100  is shown in the space directly between the buffer columns  31  and  32 , with its protruding tabs extending laterally into the grooves  33  and  34 . The apparatus  10  is in the starting position, in which the tabs of the tree  100  are resting upon the upwardly facing surface  57  of the shuttle. In this position, the tree  100 , and any other trees which, in a preferred embodiment, rest upon the tree  100 , are above the slot  33 ′ and its corresponding slot on the opposite side of the aperture  32 . The surface  57 , and a corresponding surface on the opposite side of the aperture, are positioned directly beneath the grooves  33  and  34 , thereby preventing any trees from dropping downwardly into the slot  33 ′ and its corresponding slot on the opposite side of the aperture  32 . 
     In  FIG. 9 , the apparatus  10  is shown in the dropping configuration, shown in  FIGS. 5 and 6 , after the shuttle  50  has been driven away from the starting position shown in  FIG. 8 . When the shuttle  50  is pulled to the dropping configuration, the lips in the slots between the lower ends of the buffer columns  31  and  32  and the upwardly facing surface of the plate  30  are moved out of the slots to permit the tabs of the tree  100  to drop downwardly in the grooves  33  and  34 . Thus, the tree  100  tabs are positioned in the slots beneath the grooves  33  and  34 . When the tree  100  drops, the lower surfaces of the tabs of any trees above the tree  100  preferably remain higher than the lip  56 , and preferably higher than the upwardly facing surface  57 . In this manner, when the shuttle  50  is driven toward the aperture  32 , the lip  56 , which is now longitudinally adjacent the tab of the tree  100  (rather than vertically adjacent the tab) is driven into the slot  33 ′ that the tab occupies beneath the next higher tree&#39;s tabs. 
     The next step in the process is shown in  FIG. 10 , in which the tree  100  is driven farther beyond the grooves  33  and  34  so that its tabs extend into the slots  46 ′ and  47 ′ (not shown) above the lips  46  and  47  on the clamp bodies  40  and  42 . The tabs of the tree  100  are pushed into the slots  46 ′ and  47 ′ until they are preferably displaced by the shuttle  50  to or near the rear wall of the lips  46  and  47 , thereby passing the end of the shoulder  37  and its corresponding shoulder on the opposite side of the aperture  32 . The upwardly facing surface  57  occupies the groove  33 , thereby preventing any other trees from falling downwardly. In this configuration, the entire tab is beyond the shoulder  37 , thereby permitting vertical movement by the clamp bodies  40  and  42  as driven by the rams  36  and  38 . This movement is illustrated in  FIGS. 11 and 12 . 
     The next step includes movement of the clamp bodies  40  and  42  vertically, at which time the horizontal shuttle  50  is maintained stationary. The vertical movement of the tree  100  forces the drivers into the degating apparatus  8 , and proceeds with the clamp bar  44  disposed directly above the branches of the tree  100 , thereby clamping the branches against the degating apparatus  8  in order to maintain the drivers thereon in a known position. In  FIGS. 13 and 14 , the degating apparatus  8  is driven downwardly, thereby removing the drivers from the tree  100  and inserting them in the surgical cartridge. In  FIGS. 15 and 16 , the degating apparatus  8  is shown reversing its plunging motion, after the scrap from the tree  100  is withdrawn through the apertures  22  and  32 . Preferably, an air jet (not shown) blasts air to ensure that the scrap is completely removed. 
     As shown in  FIG. 17 , it is contemplated to stack a plurality of trees between the buffer columns  31  and  32 , as alluded to above, so that after the lowest tree  100  is driven by the clamp bodies  40  and  42  toward the cartridge and degated, the next lowest tree can be fed toward the cartridge in the same manner. Preferably, a sensor connected to the central computer  16  detects when the stack of trees becomes low enough, according to a predetermined minimum, that a conventional robot (not shown) should be actuated to replenish the supply of trees. 
     It should be noted that the tree  100  is not the only structure that can be used in association with the invention. Any body that is desirably stacked with the lowest such body in the stack removed and operated upon prior to removal of the next higher body is a candidate for the invention. For example, and without limitation, the invention contemplates a planar blank, a sphere, a cup-shaped object or any other type of body that can be stacked with other like bodies, located by its outer periphery and a lower part in a stack removed from under the next higher part can be disposed in a version of the apparatus  10  that is modified to function according to the principles described above. 
     It will become apparent that the surface  57  is designed to be as high above the upwardly facing surface of the plate  30  as is needed to ensure that the bottom of the next higher object tab in the grooves  33  and  34  is above the surface  57 . If the tab is the highest part of the object, then the surface  57  can be flush with top of the lip  56 . If not, the surface  57  must be raised to prevent the next higher object from dropping into the opening under the buffer columns  31  and  32 . 
     It should be noted that it is possible to take more than one workpiece at a time from a stack of workpieces, as long as the structure described above is modified to permit this. For example, it is contemplated that if a plurality of stacked parts can be acted upon, such as by a press or other machine, when the parts are still stacked, an alternative embodiment can drive two or more such stacked parts out of a main stack of many more such parts. Likewise, if the machine that acts upon the plurality of parts can separate the stack, then it is considered equivalent to eject a plurality of stacked parts into the machine rather than a single part, as described in association with the preferred embodiment described above. Still further, it is contemplated that some machines that receive parts from the invention can accept a single part or a plurality of parts. In such a situation, it is contemplated that the number of parts stacked in the apparatus can vary from ejection to ejection. Still further, two stacked parts of a first type have the same height as one part of a second type, the number of parts ejected will vary according to the type of part the apparatus encounters. 
     This detailed description in connection with the drawings is intended principally as a description of the presently preferred embodiments of the invention, and is not intended to represent the only form in which the present invention may be constructed or utilized. The description sets forth the designs, functions, means, and methods of implementing the invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions and features may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention and that various modifications may be adopted without departing from the invention or scope of the following claims.