Abstract:
A digital die cutting system including at least a first addressable die cutter having a surface carrying a plurality of knives in an array, each of the knives extendable and retractable above and below the surface is presented/provided. A controller is provided for individually addressing, and extending, and retracting the knives above and below the surface. A central processing unit receives an image of a pattern to be cut by selected ones of the knives, processes that image for a controller, which then extends selected ones of the knives to correspond to the shape of the pattern. The die cutter is then presented by conventional apparatus to the surface of a panel to be die cut when at least some of the knives are extended.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to die cutters, and more particularly, to an apparatus for replacing conventional dies for cutting and scoring paper products such as corrugated board used in containerboard packaging.  
       BACKGROUND OF THE INVENTION  
       [0002]     Corrugated cardboard comprises an inner or bottom ply and outer or top ply between which is sandwiched a third ply that is fluted. These plies are adhesively secured to each other to form a finished corrugated board. Normally, the corrugator machine produces a continuous sheet of cardboard, which is cut to produce individual sheets of board of a given size. These cardboard sheets are stacked, transported, and later fed into a box-making machine that performs two key manufacturing steps, printing and die cutting.  
         [0003]     Typical box-making machines include, for example, a one to four color flexographic print station. Each of the stations houses a flexible printing plate and associated hardware for metering and delivering printing ink of a given color to produce text, line art, and graphics. Toward the end of the box-making machine, a die cutting unit is positioned. The purpose of the die cutting unit is to indent (create an indentation in the surface of one of the plies to assist in folding), partially cut or perforate the board, and/or completely cut the board to remove interior or peripheral portions of the board. These indentations and cuts form the finished box of proper shape (for example, tapered, rounded comers, etc.) and dimensions. Also, appropriate sections may be removed at a later time, for example, to create hand-holds and ventilation ports in the sides of the finished box.  
         [0004]     The majority of die cutting equipment used in box plants today is of the rotary type, although a few flatbed die cutters are still in use. In both the rotary and flatbed machines, sharp knives of various shapes and lengths are inserted where needed by wedging them with a mallet into a die template made of laminated sheets of plywood. The template is routed in various places to generate the necessary grooves or channels to receive the various knives according to the box design. In a rotary die cutter, the plywood template is also curved about an axis so that it can be mounted on a steel cylinder, much like a printing plate is attached to a press cylinder. Finally, various sized pieces of foam are placed within the knife cavities or cutting zones to act like springs to provide the necessary force to eject cut pieces of board from the interior of the die cutter and to keep the cardboard panel from sticking to the die.  
         [0005]     The tooling costs of creating a typical cutting die are relatively high, and can serve as a barrier to new product design and introduction. While the cutting die can be reused, some or all of the blades periodically need to be replaced because of wear and/or damage. Setting up the printing plates as well as maintenance and repair are all time-consuming processes that require significant machine shutdown time, thereby limiting the production capability of a line. Moreover, whenever a different box is made, the box-making machine must be stopped so that a different set of printing plates and/or associated cutting dies can be inserted in the machine. Finally, the large amount of manufacturing floor space needed to house the die inventory, die management, and care from damage all add to the cost of the workflow.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention therefore provides a solution to the labor-intensive prior methods for producing dies for cutting, indenting and scoring cardboard boxes and eliminates need for die storage and management and reduces downtime during grade changes. In accordance with the present invention, a digital die cutting system is provided comprising at least a first addressable die cutter having a surface. The die cutter has a plurality of knives arranged in an array on the surface. Each of the knives are extendable above and retractable below the surface. The system also has a controller for individually addressing, extending, setting, and retracting each of the knives above and below the surface. A central processing unit receives an image of a pattern to be cut by selected ones of the knives and processes the image into signals for the controller to extend selected ones of the knives to correspond to the shape of the pattern. Finally, a means is provided for presenting the surface of the die cutter to one surface of the panel to be die cut when at least one of the knives is extended.  
         [0007]     In an embodiment, the addressable die cutter comprises at least a first rotary member having a cylindrically shaped surface. A plurality of knives is mounted in an array across and around the surface. Each of the knives has a blade that is extendable in a radial direction to at least a first position above the surface and is retractable below the surface. The first rotary member is mounted for rotation adjacent the path of travel for a cardboard panel to be cut or scored. This axis of rotation is oriented laterally relative to the path. In an embodiment, a second cylindrical member similar to the first member is provided. The second member is also mounted for rotation adjacent the path of travel for the panel to be cut and/or scored. The axis of rotation of the second member is oriented laterally relative to the path. The first and second cylindrical members are mounted so that the first member addresses a first side of the panel to be cut and/or scored and the second member is mounted to address the second side of the panel to be cut and/or scored. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0009]      FIG. 1  is a schematic side view of a box-making apparatus including a printing station, a die cutting station, and an indenting station;  
         [0010]      FIG. 2A  is an isometric view of a die cutter constructed in accordance with the present invention showing the knife array with all knives retracted;  
         [0011]      FIG. 2B  shows the die cutter with selected knives extended;  
         [0012]      FIG. 2B ′ shows an indenting die with selected blades extended;  
         [0013]     FIGS.  2 C′,  2 C″ and  2 C′″ are enlarged views of a knife with a cutting blade;  
         [0014]     FIGS.  2 D′ and  2 D″ are enlarged views of a knife with an indenting blade;  
         [0015]      FIG. 3A  is an isometric view of the pattern overlaid on a corrugated panel;  
         [0016]      FIG. 3B  is a corrugated board cut in accordance with the pattern shown in  FIG. 3A ;  
         [0017]      FIG. 4  is a schematic block diagram of a digital die cutting system;  
         [0018]      FIG. 5  is an enlarged schematic view of the die cutting station;  
         [0019]      FIG. 6  is a view similar to  FIG. 5  illustrating one manner of cutting a corrugated board; and  
         [0020]      FIG. 7  is a partial sectional view taken through the axes of the die cutting and indenting cylinders at the die cutting and indenting stations, respectively. 
     
    
     DETAILED DESCRIPTION  
       [0021]     Referring to  FIG. 1 , a schematic diagram of a box-making machine includes a feed station  20 , a printing station  22 , a die cutting station  24 , and an indenting station  25 . A stack of previously cut corrugated boards  26  are shown accumulated at the feeding station. Individual boards  26  are sequentially fed through the printing station  22 , the die cutting station  24 , and the indenting station  25 . In this illustration, the printing station comprises a three-color press including red printing rolls  28 , green rolls  30 , and blue rolls  32 . Red, blue, and green inks, for example, are applied to these three stations to produce a three-color image on the final board issuing from the printing station  22 . The printing station  22  is controlled from a processing unit  34  that controls the ink flows, rotation, and registration of the printing press in a conventional manner. Color separations for each ink appear in each printing plate and are used to reproduce the composite image.  
         [0022]     The board  26 , upon exiting the printing station, enters the die cutting station and is run between juxtaposed digital die cutters  40  and  42  constructed in accordance with the present invention. In an embodiment, die cutters  40  and  42  may be of virtually identical construction. Referring now to  FIG. 2A , a schematic of one of the die cutters  40  is illustrated. In this embodiment, the die cutter  40  comprises a cylinder that may be mounted on its axis of rotation  46 . When mounted, the die cutter  40  is properly positioned at the cutting station  24  so that a surface of the die cutter may be presented to the upper surface of the board  26  as the board traverses the advance path  90 . The die cutter  40  preferably has a cylindrical surface  48  on which are positioned a plurality of openings  50  or channels that house retractable knives. Preferably the openings, and thus the knives, are arranged in a rectangular array that extends longitudinally across the die cutter  40  and is wrapped circumferentially about the cylindrical surface  48  of the die cutter  40 . In an embodiment, these channels or openings would be arrayed at about 8 to 10 per inch (3 to 4 per centimeter), both in the lateral and circumferential direction. The typical length of a die cutting roll  40  would be on the order of 6.3-9.5 feet (1.9-2.9 meters). The typical diameter of a die cutting roll  40  would be on the order of 2-3 feet (0.6-0.9 meters).  
         [0023]     An indenting station  25  is positioned downstream from the die cutting station  24 . The indenting station has a pair of rolls  41  and  43  of similar construction to die cutter  40 , except the indenting rolls carry blunt knives or blades instead of sharp-edged knives. The array of blades in the indenting rolls  41  and  43  may be similar to the array in the die cutting rolls.  
         [0024]     Referring to  FIG. 2C ′, a segment of the surface  48  of the cylinder  40  is shown surrounding a single opening  50 . A knife  60  is reciprocally mounted in the opening  50 . It is reciprocated by an appropriate actuator  62 , such as a pneumatic or hydraulic cylinder, a solenoid actuator, stepping motor, or other suitable mechanical or electrical actuation mechanism. As shown in  FIG. 2C ″, the knife  60  is shown partially extended to a first position by the actuator  62 . The knife  60  has a sharp cutting edge  64  that is capable of penetrating at least one layer of the board as it traverses the die cutting station. In the partially extended position, the cutting edge is located at a predetermined distance above the surface  48 . Thus, when the surface  48  is presented to the surface of a board  26 , the knife will penetrate the board to the extended depth. It is also contemplated, as shown in  FIG. 2C ′″, that the knife  60  is extendable to a third position beyond the first position shown in  FIG. 2C ″. The purpose of these two different positions will be explained in more detail later.  
         [0025]     Referring to  FIG. 2D ′, a second type of knife or blade  66  having a blunt end  68  is shown retracted below a surface  48  of the indenting roll  41 . In  FIG. 2D ″, the knife  66  is shown in a partially extended position. These knives or blades  66  are actuated in a manner similar to the sharp-edged knives  60  shown in  FIGS. 2 . It is possible that the blunt-edged knife  66  can be actuated so that it is actuated from a retracted position below the surface  48 ′ of roll  41  to first, second, or even more extended positions depending upon the desired indenting function the knife is to perform.  
         [0026]     Referring now to  FIG. 3B , a typical box blank  70  formed from a corrugated board  26  after it exits the die cutting machine is shown. The solid outline  72  shows the outer edge of the blank  70  while the dashed line  74  represents an indented score line.  
         [0027]     Referring to  FIG. 3A , the pattern for the blank  70  is shown overlying a corrugated board  26 . As will be explained in more detail later, the die cutters  40  and  42  of the present invention has its knives arranged so as to cut the periphery  72  of the blank  70 . Referring to  FIG. 2B , this is accomplished by partially or fully extending the knives  60  from the array on the cutter  40  so that the knives  60  extend above the surface, for example, as shown in  FIG. 2C ′″. When the corrugated board is run through the die cutter, the knives  60  will cut along the peripheral portion to form the blank.  
         [0028]     Referring to  FIG. 2B ′, the blades  66  in the indenting roll  41  are similarly extended in a transverse line corresponding to the indented lines  74  in the pattern ( FIG. 3A ). As the board  26  is fed between the rolls  41 , the indented lines will be formed in the board to aid in folding the box into its final shape.  
         [0029]     Referring to  FIG. 4 , the pattern, for example the pattern shown in  FIG. 2B , is in the form of a set of computer instructions  80 . These instructions would normally be in an image format such as a CAD file (.cad), a bitmap file (.bmp), or other graphics files, such as .tiff or .jpg files. The instructions  80  are then fed to the processing unit of a computer  82  where the image is read and a knife map prepared. The knife map may be in the form of a bitmap file as well. The computer then processes this rasterized image and sends appropriate commands to a controller  84 , which in turn addresses the actuators of each knife of the digital die cutters  40  and  42 . Where required, the knives would be extended to a first, second, or other position corresponding to the original instructions, while the remaining knives would remain in a retracted state as shown in  FIG. 2B . The rasterized image would provide sufficient information to the controller so that not only would the knives be extended to the appropriate height, but that the appropriate knives would be extended to provide cutting action, scoring action, or both. The blunt blades  66  in the roll  41  are similarly extended and set by the controller  84 . Alternatively, a completely separate controller may be used.  
         [0030]     Once the arrays of knives have been initialized, production of the die cut corrugated board can be initiated. During operation on a given production run, the knife array would remain static. That is, it would behave like a conventional die cutter with no changes in the knife arrangement during a given run. Once a production run of a particular pattern is finished, the knives are reset (retracted) and a new pattern is introduced into the computer  82 , instructions are generated for the controller, and a new pattern on the digital die cutter is formed. This reset and repatterning process will take on the order of minutes. This is much less time than is required to reset the printing presses for a new run. Previously, resetting of the die cutter with fixed dies was the limiting factor on turnaround time from one production run to another.  
         [0031]     Referring now to  FIG. 5 , an embodiment of the present invention includes a top die cutter  40  and a bottom die cutter  42 . Both of these dies are virtually identical in construction. In  FIG. 5  and the ensuing figures, the knives  60  are shown in exaggerated form extending from the die cutters  40  and  42 . In reality, the diameter of the die cutters  40  and  42  would be relatively large compared with the extension length of the knives. In  FIG. 5 , a corrugated board  26  is fed along the advance path  90  between the dies  40  and  42 . In  FIG. 6 , the corrugated board is shown being cut. In this view, the knives are only partially extended so that a perforation or partial cut is formed through the corrugated board. This would result in a perforated line but no complete severing of material from the corrugated board.  
         [0032]     Referring to  FIG. 7 , different knife sets are shown schematically arranged in different patterns laterally across the two die cutters  40  and  42 . (As used herein, laterally means laterally relative to the machine direction and longitudinally (or in the axial direction) along the surface of the die cutter.) Toward the left-hand side, knives  60 ′″ are shown in a fully extended position. The lateral relationship of the knives on the respective die cutters  40  and  42  are also laterally offset by a distance equal to one-half the distance between the knives in the arrays. This allows the knives  60 ′″ in the upper die cutter  40  to interleave with the knives  60 ′″ from the lower die cutter  42 . This interrelationship will result in an almost complete severance of material from the corrugated board because each of the knife sets extends almost the entire thickness of the board. This configuration would, for example, be utilized to cut the peripheral portion  72  of the pattern shown in  FIG. 3B .  
         [0033]     Toward the left center of the die cutters  40  and  42 , the knives  60 ″ are shown only in partial extension. This configuration will result in a perforation or partial cut through the board at spaced locations. Toward the right center of the indenting rolls  41  and  43 , blunt-edged knives  66  are shown in a partially extended position. In this position, the surface of the corrugated board is deformed or indented by the blunt knives  66  to produce indents, such as line  74  of  FIG. 3A . Toward the right of the cutters  40  and  42 , the knives  60  are deployed continuously around the circumference, corresponding to the deployment in  FIG. 6 . This will provide a continuous perforation, which will allow for easy folding or for later severance by the user of the box.  FIG. 7  is intended to provide representative examples of how the knives may be fully or partially extended and the functions of both a knife with a cutting edge and a blunt edge would perform. The die cutter of the present invention can replace conventional rollers to which dies are currently mounted. Thus, much of the existing equipment in a box making machine can be used, significantly reducing the capital expenditures to change to the present invention. In addition, conventional techniques for ejecting waste pieces may be used by mounting high density neoprene pads to the die cutter face. Alternately, a punch for removing waste pieces may be positioned downstream of the die cutter.  
         [0034]     It is contemplated within the context of the invention that each knife in the array could itself comprise multiple knives. The knives may be arranged in a variety of patterns so that an angled line in the array would achieve the approximation of a straight line without utilizing an unduly complicated or higher resolution array of knives across the cutters  40  and  42 .  
         [0035]     While an embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.