Abstract:
A rotary die cutter system the amount of scrap between successive blanks cut from web material by holding the web against backward movement at a position spaced upstream from the nip defined by the die and anvil cylinders, retracting the cut leading end of the web through a predetermined distance in response to release of the web by the cut-off knife at the trailing edge of the die on the die cylinder such that on the next cycle, the leading edge of the die will engage the web at a position spaced close to the leading end of the web.

Description:
REFERENCE TO RELATED APPLICATION 
     This is a continuation of co-pending application Ser. No. 817,720, filed Jan. 20, 1986 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a rotary die cutting system which is fed by web stock and more particularly to a system for reducing the scrap material produced by rotary die cutters between successive blanks treated or cut from the web. 
     In conventional rotary die cutter systems, wherein the web stock is fed by powered pull rolls operating in synchronism with the die and anvil cylinders, the web is fed intermittently to maintain approximately the same accumulated loop of web material. 
     One of the problems with this conventional technique is that after the trailing edge of the die, which includes a cut-off knife, has cut off the portion of the web which passed between the die and the anvil cylinders, momentum tends to feed the cut edge of the web forward so that there will be a substantial area of the web lying beyond the point at which the leading end of the die will again strike the web. All of the material in advance of the line where the die will make contact during the next cycle will be scrap. 
     Accordingly, there is a need for a mechanism which when combined with a rotary die cutter, reduces the amount of web material which lies beyond the point where the leading edge of the die, upon rotation of the circular die cutter, strikes the web, and thereby reduces the amount of scrap web material produced. 
     SUMMARY OF THE INVENTION 
     The present invention provides for retracting the severed leading end of the web from a position beyond the nip of the rotary die cutter to a position in such relation to the nip that the leading end of the web will lie just beyond the point at which the web will be engaged by the leading edge of the die on the next cutting cycle. 
     Specifically, the present invention provides a device which includes a floating part so mounted that when the web is pulled forward by the pressure between the die cylinder and the anvil cylinder blanket during a die cutting cycle, the web will be sufficiently tensional to assure an essentially horizontal position with the floating part on top of the web material. As soon as the severing cut across the web is made upon completion of the particular die cycle, this part will return to a position below the line of feed of the web, thereby retracting the severed new leading end of the web by a predetermined amount. 
     This retraction preferably will be such that the new leading end of the web will lie just beyond, in the direction of web feed, the line at which the web will be engaged by the leading edge of the die during the next cycle. Upon engagement of the web by the die, the web loop will then again be pulled straight, which will return the floating part to its raised position during the next die cutting cycle. 
     The primary object of this invention, therefore, is to provide means for reducing the amount of scrap produced during successive cycles of a rotary die cutter operating on web material; and to provide means for precisely controlling the amount of severed web material retracted from a position beyond the nip of the die cylinder and the anvil cylinder to a position in such relation to the nip that the leading edge of the die will engage the web just behind its leading end. 
     Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of a die cutter line embodying the present invention and showing the parts during a die-cutting operation; 
     FIG. 2 is a fragment of FIG. 1 showing the trailing end of the die just after disengagement from the web; 
     FIG. 3 is a view similar to FIG. 2 showing the positions of the parts immediately after the leading edge of the die engages the leading end of the web; and 
     FIG. 4 is a perspective view of the assembly for retracting the leading end of the web after its release by the trailing edge of the die. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in FIG. 1, the web 10 is supplied under tension from a roll or material processor shown schematically as a station 11 by conventional means such as driven pull rolls (not shown). The driving of the pull rolls is controlled in a conventional manner whereby a slack loop 13 is maintained in the web 10 between two idler rollers 15-16. 
     The web 10 drawn from the slack loop 13 is fed over a guide table or material support tray 20 and between a pair of pinch rolls 22-23 to the rotary die cutter 25, which comprises an upper die cylinder 26 and a lower anvil cylinder 27 rotatably mounted in the usual nip defining relation in suitable end frames 28. The anvil cylinder 27 may be a plain metal cylinder or may be provided with a conventional blanket of elastomeric or other protective material. The pinch rolls 22-23 are idler rolls in pressure engagement with the web 10, but they are provided with one-way clutches of any conventional construction which permit them to rotate only in the direction of advance movement of the web so that they hold the web against reverse movement toward the loop 13. 
     The movement of the web through the rotary die cutter 25 is effected by the direct pull applied to the web by the die 30 on the anvil cylinder 27, which grips the leading end portion of the web against the anvil cylinder 27. As illustrated in FIG. 1, the die 30 extends only part way around the circumference of die cylinder 26, so that each of the blanks to be cut from the web 10 by the die cutter 25 is of a length less than the circumferential dimension of the die cylinder 26. There will therefore be a gap 31 on the surface of the die cylinder 26 between the trailing and leading edges of the die 30. 
     The die 30 may be of any steel rule or other conventional type, which will include a cut-off knife 32 on its trailing edge for cutting the completed blank and any scrap material on either side of it free of the web behind it. There will also usually be a cut-off knife 33 at the leading edge of the die for cutting off the scrap material immediately in advance of the line on which this leading cut-off knife strikes the web. As described below in connection with FIGS. 2 and 3, the leading edge knife 33 on the die 30 will engage the web on the surface of anvil cylinder 27 ahead of the nip line 34 of the two cylinders. Similarly, the trailing edge knife 32 will engage the web beyond the nip line 34. Inherently, therefore, unless some provision is made to prevent it, the portion of the web lying between those two positions at the end of the cutting portion of each cycle will become scrap. 
     During each portion of a cycle of the die cutter while the gap 31 is opposite the anvil cylinder, the die cutter is not applying a pulling force to the web. However, there will be a tendency for momentum to propel the cut leading end of the web forward. In addition, since this free leading portion of the web is resting on the constantly rotating surface of the anvil cylinder 27, frictional engagement therebetween will also cause forward movement of the leading end of the web. 
     As a result of this combination of forces, it has been found that unless special provision is made to prevent it, a substantial portion of the leading end of the web will travel beyond the nip line 34 of the two cylinders 26-27 before the leading end of the die 30 again engages the web. All this material which lies forward of the line where the knife 33 at the leading end of the die next engages the web will become scrap. The essential purpose of the present invention is to minimize the amount of that scrap by controlled retraction of the leading end of the web during that portion of each cycle of the die cutter when there is no pressure engagement between its two cylinders. 
     As schematically illustrated in FIG. 1, in accordance with the present invention, a retraction or back-up device 35 is provided at a position spaced between the pressure rolls 22-23 and the two cylinders 26-27. The hack-up device 35 functions to retract that portion of the web material which has passed beyond the nip line 34 of the die cylinder 26 and anvil cylinder 27 back toward the pressure rolls 22-23 immediately after the trailing edge knife 32 of the die 30 has severed the latest blank and released the web. 
     This back-up device 35 comprises a cylindrical bar 40 rotatably mounted at one end of each of a pair of pivot arms 41 which are in turn pivotally mounted at 42 on the end frames 28 so that the bar 40 can effectively float in operation as described below. Downward movement of the bar 40 and arms 41 about the pivotal mountings 42 is limited by a tray 44 pivotally mounted at 45 in the end frames 28 below the pivotal mountings 42 and just forward of a fixed support tray 46. Adjustment of the tray 44 is effected by adjusting screws 47 threaded in brackets 48 mounted on the end frames 28. 
     In operation, as illustrated in FIGS. 1-2, the web 10 is threaded below the bar 40, and its tension will cause the bar 40 to float, with the arms 41 horizontal, so long as the web is being pulled forward by engagement between the die 30 and anvil cylinder 27. In the absence of the taut web, gravity would cause the arms 41 to pivot downwardly until the bar 40 rests on the tray 44, and each arm 41 is also provided with a biasing tension spring 50 for augmenting the gravity force. The lower end of each spring 50 is adjustably mounted on the adjacent frame 28 by a screw 51 in a slot 52 in the block 53 to which the lower end of the spring 50 is attached. 
     FIG. 1 illustrates the relative positions of the parts of the system during a die-cutting operation, with the die 30 in pressure engagement with the anvil cylinder 27 to pull the web forward while it is cutting a blank therefrom. As shown, the tension on that portion of the web between the rolls 22-23 and the nip of die 30 with anvil cylinder 27 pulls that web portion essentially straight, thereby raising the bar 40 against the force of springs 50 and gravity to the position wherein its supporting arms 41 are essentially horizontal. 
     FIG. 2 shows the relative positions of the parts immediately following completion of the die-cutting operation. The trailing end of that portion of the web from which a blank has been cut has been cut off, as indicated at 55, and the resulting new leading end of the web is now no longer gripped between opposed portions of the die and anvil cylinders. There is therefore no tension on that part of the web forward of the pressure rolls 22-23, which hold that web length against retraction into the loop 13 by reason of this one-way clutches as previously described. 
     The bar 40 accordingly drops, under the combined forces of gravity and the springs 50, until it is stopped by the tray 44. During this movement, it will carry with it that portion of the web on which it is resting, thereby retracting the leading end of the web as shown in FIG. 2 to produce a corresponding downward loop 60 of web forward of the pivotal mountings 42 for the arms 41. 
     As previously pointed out, and as illustrated in FIG. 2, the trailing edge knife 32 will cut off the blank along a line beyond the nip line 34. Similarly, and as illustrated in FIG. 3, the leading edge knife 33 on the die will engage the web along a line in advance of the nip line 34. The retracted position of the bar 40 is therefore preferably so established, by adjustment of the tray 44 as previously described, that the new leading end of the web will lie just beyond the angular position on the anvil roll 27 which will be engaged by the leading edge knife 33 at the start of the next cutting cycle. 
     FIG. 3 illustrates the relative position of the parts just after that point in the cycle, with the leading end of the web now gripped between the die 30 and the anvil cylinder so that the loop 60 of web previously produced by the bar 40 is being straightened out until the web is restored to the horizontal position shown in FIG. 1. 
     In summary, the complete cycle can be visualized as running from the rest position illustrated in FIG. 2 through the positions illustrated in FIG. 3 and FIG. 1 back to the rest position, which extends for the entire portion of the cycle represented by the space 31 where there is no die on the die cylinder 26. The adjustments provided by the adjusting screws 47, 51 for the tray 44 for the spring mounting blocks 53 may be employed as desired or needed in accordance with properties of the particular web being cut such as thickness, stiffness, flexibilty and friction engagement with the anvil cylinder 27. 
     Thus for a material such as thin plastic film, the extra biasing force of the springs 50 may not be needed, but for relatively heavy web materials, the additional downward biasing force on the bar 40 may be essential to effect adequate retraction of the leading end of the web. Experience with practical applications of the invention has shown that where in the absence of the invention, the scrap material ranged from two inches in the direction of the web length to as high as six inches per cycle, the practice of the invention has made it possible to reduce that dimension to or less than one inch. 
     While the form of apparatus herein described constitutes a preferred embodiment of this invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.