Abstract:
A cutting apparatus for cutting shrink wrap film residing in a roll. The apparatus includes a first roller pair receiving the film from the roll and carrying the film away from the roll; without the need for a second roller pair to receive the cut sheet of film. Film snap-back is prevented by cutting the film between a shear deck with teeth and a rotating blade with teeth intermeshing with the teeth of the shear deck. A method for cutting a sheet of shrink wrap film, including: feeding the film into a first roller pair; and cutting the film between the first roller pair and the second roller pair using a rotating knife with a number of teeth intermeshing with a shear bar with teeth.

Description:
[0001]     This patent application is a continuation-in-part of co-pending U.S. application Ser. No. 10/960,238, filed Oct. 7, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention generally relates to shrink wrap packaging apparatus and in particular to an apparatus for cutting shrink wrap film prior to the shrink wrapping operation.  
         [0003]     In single roll shrink wrapping, a single sheet of shrink wrap film is wrapped around the product and into a tubular form. The overlapping lateral edges are located beneath the product and are sealed or otherwise joined together. During shrinking in a heat tunnel, the longitudinal edges of the shrink wrap film collapse against the ends of the product creating bullseye-type openings.  
         [0004]     Various deficiencies exist in prior shrink wrap packaging and the methods of its fabrication. The single sheet of shrink wrap film was typically cut from a supply roll of the film. A common manner to cut the sheet from the web of film was to engage the film with a hot iron to melt the film and thus sever the sheet from the film. This hot iron is a high wear component and is always a source of operational problems. Another approach is to utilize a rotary blade which cuts the film. However, this approach experienced problems that the new leading edge of the web of film did not continue to follow the desired path of the film as a result of the velocity of the film and air resistance, the memory of the film, and/or the snap back of the film when the tension was released on the film because of cutting. These problems were overcome by cutting the film while the film is held across the cut and/or by including mechanical devices which grasp and pull the new leading edge, but such approaches unduly complicated the construction of the apparatus. Thus, there continues to be a need for feeding the film after a sheet is cut from the free end thereof which overcomes the deficiencies of the current approaches.  
         [0005]     U.S. Pat. No. 5,771,662 (Struges et. al.), herein incorporated by reference, discloses an apparatus and methods for producing shrink wrap packaging. However, the Struges patent does not fully overcome the deficiencies of prior approaches, particularly in the area of cutting the film. Struges requires a vacuum table at the exit from the nip rollers to hold the film for further processing. The vacuum table is an expensive and complex piece of equipment which is not necessary for lower-speed operation. In addition, Struges requires a cutting blade that cuts tie strips into the film that allow the trailing edge of a single sheet of film which is downstream from the cut to remain connected to a new leading edge for the web of film which is upstream from the cut, so that the single sheet of film remains attached to the web of film thereby pulling the leading edge of the web of film toward and through the downstream pinch rollers  14  and  15  and to maintain tension of film between the upstream pinch rollers  12  and  13  and the downstream pinch rollers  14  and  15  and to ensure that the new leading edge of the web of film follows the desired path to the downstream pinch rollers.  
         [0006]     The present invention overcomes the above deficiencies. It defines novel and non-obvious enhancements over the device described in U.S. patent application Ser. No. 10/960,238. In particular, it needs only a single nip roller pair rather than two roller pairs, it eliminates the need to keep tension on the film with the accompanying required programming complexity, it lessens snap-back of the film, and it eliminates folding-over the film by the second roller pair. Furthermore, the apparatus feeds the film so precisely even after it is cut, that the invention eliminates the need for an air knife to direct the new cut edge of the film into the rollers.  
       SUMMARY OF THE INVENTION  
       [0007]     A cutting apparatus for cutting shrink wrap film residing in a roll. The apparatus includes a first roller pair receiving the film from the roll and carrying the film away from the roll; without the need for a second roller pair to receive the cut sheet of film. Film snap-back is prevented by cutting the film between a shear deck with teeth and a rotating blade with teeth intermeshing with the teeth of the shear deck. A method for cutting a sheet of shrink wrap film, including: feeding the film into a first roller pair; and cutting the film between the first roller pair and the second roller pair using a rotating knife with a number of teeth intermeshing with a shear bar with teeth.  
         [0008]     A principal object and advantage of the present invention is that it eliminates the expense and complication of a vacuum table.  
         [0009]     Another principal object and advantage of the present invention is that it eliminates tie strips cut into some kinds of film to feed the film into the second roller pair and maintain film tension.  
         [0010]     Another principal object and advantage of the present invention is that it uses a single roller pair to pull the film from the roll and to hold the film as it is cut.  
         [0011]     Another principal object and advantage of the present invention is that it eliminates the need for a second roller pair.  
         [0012]     Another principal object and advantage of the present invention is that it does not need a stream of air to guide the leading edge of the film into a second roller pair. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0013]      FIG. 1  is an exploded perspective view of the apparatus of the present invention.  
         [0014]      FIG. 2  is a front elevational view of the apparatus of the present invention.  
         [0015]      FIG. 3  is a top plan view of the apparatus of the present invention.  
         [0016]      FIG. 4  is a schematic cross-section taken at approximately the lines  4  in  FIG. 3 .  
         [0017]      FIG. 5  is a flowchart of the method of the present invention.  
         [0018]      FIG. 6  is a top plan view of a second embodiment of the present invention.  
         [0019]      FIG. 7  is a cross-section taken at approximately the lines  7  of  FIG. 6 .  
         [0020]      FIG. 8  is similar to  FIG. 6  with some structure cut away.  
         [0021]      FIG. 9  is a cross-section taken at approximately the lines  9  of  FIG. 8 .  
         [0022]      FIG. 10  is a perspective view of the embodiment of  FIG. 6 .  
         [0023]      FIG. 11  is a detailed view shown at the dashed circle in  FIG. 10 .  
         [0024]      FIG. 12  is a schematic of the embodiment of  FIG. 6 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]     The present invention is a cutting apparatus and method for cutting shrink wrap film and is generally shown in the drawings as reference numeral  10 .  
         [0026]     In one embodiment, the apparatus  10  comprises a first roller pair  12  adapted to receive the film F from its roll (not shown) and to carry the film F away from the roll. The apparatus  10  further comprises a second roller pair  14  adapted to receive the sheet of film F from the first roller pair  12  and carry the film away from the first roller pair. The apparatus  10  further comprises a mechanism  16  for providing an air stream adapted to direct the leading edge E of the film F into the second roller pair  14 . The apparatus  10  further comprises a mechanism  18  for regulating the pressure exerted by the second roller pair against the sheet of film F thereby maintaining tension on the film between the first roller pair  12  and the second roller pair  14 . The apparatus  10  further comprises a rotating blade  20  adapted to cut the film as the film exits the first roller pair, thereby producing a cut sheet of film.  
         [0027]     In one embodiment, the second roller pair further comprises a driven roller  14 A and a non-driven roller  14 B engaging the driven roller, and further comprises a mechanism  22  pressing the non-driven roller  14 B against the driven roller  14 A and producing a variable pressure between the non-driven roller  14 B and the driven roller  14 A. The first roller pair may also comprise a driven roller  12 A and a non-driven roller  12 B. The driven roller in each pair is preferably belt driven by a servomotor  23 . The first roller pair preferably has the non-driven roller  12 B pressed against the driven roller  12 A by air pressure. This air pressure can be set by the operator to consistently pull the film F from the roll without slippage, depending on the thickness and quality of the film F.  
         [0028]     The apparatus  10  may also preferably comprise a mechanism  24  separating the non-driven roller  14 B from the driven roller  14 A.  
         [0029]     The apparatus  10  may also preferably comprise a means (not shown) for coordinating the mechanism  22  and the mechanism  24  whereby the resultant pressure between the non-driven roller  14 B and the driven roller  14 A can be varied. The means for coordinating may be any programmable means such as a digital computer or a PLC.  
         [0030]     Preferably the mechanism  22  and the mechanism  24  are driven by air pressure, and the air pressure is varied through regulators (not shown) to control air cylinders  22 A and  24 A. It should be noted that a single air cylinder may be used to provide both the mechanism  22  and the mechanism  24 .  
         [0031]     Preferably, the second roller pair  14  is geared to rotate a speed somewhat faster than the rotational speed of the first roller pair, which provides a way of stretching the film to enhance the cutting action of the knife  20 . The second roller pair may rotate 1% to 5% faster. Most preferably, the second roller pair is geared to rotate about 3.6% faster than the first roller pair.  
         [0032]     Operation of the apparatus and a description of the method will now be described, referring to  FIGS. 4 and 5 .  
         [0033]     Optionally, the tension on the film F being fed into the first roller pair may be increased to pre-stretch and flatten the film. For example, this may be done by dancer bars (which are illustrated in the Struges patent).  
         [0034]     The film F enters the first roller pair  12 . The mechanism or air nozzles  16  then directs a stream of air against the leading edge E of the film, guiding the leading edge E into the second roller pair  14 .  
         [0035]     The air pressure applied to the second roller pair  14  is varied during each cutting cycle. Pressurized air is supplied to the air cylinders  22 A and  24 A controlling the force exerted to hold the non-driven roller  14 B against the driven roller  14 A. At the start of the cycle, the air pressure forcing the rollers  14  together (down pressure) is slightly more than the pressure that would move the rollers apart (up pressure). This balance of air pressures allows the rollers  14  to grip the film surface and feed film received from the rollers  12  into the wrapping area W without allowing any slack to develop in the film.  
         [0036]     Because the rollers  14  rotate faster than the rollers  12 , the film slips on the surface of the driven roller  14 A. Prior to cutting the film, the up pressure on the roller  14 B is reduced to zero. This eliminates the slippage between the film and the driven roller  14 A. The film is pulled taut prior to being cut by the knife  20 . As the film is cut and begins to separate, the up pressure to roller  14 B is re-applied. This reduces film tension and minimizes film “snap back.” This enhances the ability of the air knife  16  to guide the film leading edge E into the rollers  14  for the next cutting cycle.  
         [0037]     The knife  20  is positioned just above the film and between the pairs of rollers  12  and  14 . The knife is mounted on a shaft  20 A that rotates in the same direction as the film travel. A clutch  20 B is mounted on the knife shaft  20 A. When the clutch engages, the knife swings in an arc, contacting and cutting the film.  
         [0038]     A steel deck  26  is positioned between the rollers  12  and the knife  20  and just outside the knife arc. This deck provides a shear point to enhance the cutting action of the knife.  
         [0039]     After the film is cut, the leading edge E of the cut film is directed and supported by streams of air from air nozzles  16  located in the deck support structure. These air nozzles are aligned with relief grooves  27  in the downstream driven roller  14 A. The air stream flowing from each nozzle and through a relief groove creates a venturi effect. This venturi effect at each relief groove aids in directing the leading edge of the film between the downstream rollers  14 A and  14 B.  
         [0040]     An air knife  30  mounted downstream of the second rollers  14 , guides the film leading edge into the proper position for wrapping around the product.  
         [0041]     Preferably, the rollers  12  and  14  are supported at intermediate points along their length by supports  28 , thus preventing deflection. This is important in order to allow very light weight rollers to be used to reduce inertia.  
         [0042]     A second embodiment of the present invention is generally shown in the Figures as reference numeral  110 . This embodiment uses a single roller pair with a serrated cutting blade, rather than two roller pairs.  
         [0043]     The apparatus  110  comprises a first roller pair  112  adapted to receive the film F from its roll (not shown) and to carry the film F away from the roll. The apparatus  110  further comprises a rotating blade  120  adapted to cut the film as the film exits the first roller pair, thereby producing a cut sheet of film. The rotating blade  120  has serrated teeth  120   a.  As best seen in  FIG. 11 , the serrated teeth  120   a  mesh with second serrated teeth  121   a  on shear bar  121 , cutting the film between the two sets of teeth and preventing film snap-back.  
         [0044]     The first roller pair may also comprise a driven roller  112 A and a non-driven roller  112 B. The driven roller is preferably belt driven by a servomotor  123  ( FIG. 9 ). The first roller pair preferably has the non-driven roller  112 B pressed against the driven roller  112 A by air pressure provided by cylinder  124 . This air pressure can be set by the operator to allow easy feeding of film into the first roller pair, depending on the thickness and quality of the film F.  
         [0045]     Operation of the apparatus and a description of the method will now be described, referring to  FIGS. 6-12 .  
         [0046]     Optionally, the tension on the film F being fed into the first roller pair  112  may be increased to pre-stretch and flatten the film. For example, this may be done by dancer bars (which are illustrated in the Struges patent). However, the use of the interleaved teeth to cut the film substantially eliminates the need to keep tension on the film.  
         [0047]     The film F enters the first roller pair  112 , then is fed by the first roller pair across the shear deck  121 . The film is pulled taut prior to being cut by the knife  120 . As the teeth  120   a  mesh with the teeth  121   a,  the film is cut cleanly without snapback.  
         [0048]     The knife  120  is positioned just above the film and between the pair of rollers  112 . The knife is mounted on a shaft  120 B that rotates in the same direction as the film travel. A clutch (not shown) may be used to connect the knife shaft to a source of power. When the clutch engages, the knife swings in an arc, contacting and cutting the film. Alternatively, the knife shaft may be driven by a servo motor  125 , suitably by a belt  126  ( FIG. 7 ).  
         [0049]     After the film is cut, the leading edge E of the cut film is directed and supported by streams of air from air nozzles  116  located in the deck support structure, directing the leading edge of the film onto the discharge deck  32 .  
         [0050]     Eliminating the need for a second pair of rollers to receive the leading edge of the cut film prevents folding over of the leading edge by the second pair of rollers. However, in some cases a second roller pair may be used, and such is considered to be within the scope of the present application.  
         [0051]     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar to or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety to the extent allowed by applicable law and regulations. In case of conflict, the present specification, including definitions, will control.  
         [0052]     The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is therefore desired that the present embodiment be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.