Abstract:
A pre-stretched plastic strap is produced for subsequent use in a strapping machine. Two mated pairs of rollers are attached to a drive mechanism causing each roller pair to roll at a predetermined rate. Each roller pair comprises a nip therebetween, one serving as a brake nip and one the other serving as a tensioner nip. The rolling speed of the tensioner nip is controlled higher than the rolling speed of the brake nip. A plastic strap is conducted through the brake nip and tensioner nip, and the rolling speed differential between brake and tensioner nips causes elongation of the strap conducted therethrough, with the strap having a predetermined tendency to return to its original, unstretched length. This abstract is submitted in compliance with USPTO rules, and is not intended to limit or otherwise indicate the scope of the claims.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of The Invention  
         [0002]     This invention relates to a method for securing packages, packaging containers and other articles.  
         [0003]     2. Description of the Related Art  
         [0004]     The commercial use of strapping or banding has existed for decades. Strapping is typically used to bind items into bundles and/or to bind an item(s) onto pallets. A strapping dispenser is normally use to facilitate better speed and efficiency. These dispensers vary in size depending on the application and industry. Strapping is normally measured in width, thickness, break strength, pounds per coil, and coils per pallet. Initially strapping and strapping materials were most commonly made from leather or simple textile materials. Today, the strapping types most commonly used are steel, or polymer-based thermoplastics such as or polypropylene (PP), polyethylene terephthalate (PET), other polyesters or elastomers.  
         [0005]     Strapping is frequently used in the packaging industry to prevent articles from uncontrolled shifting during transport, falling off a pallet, altering a prearranged packaging or pallet configuration or loosening from a packaging container. Productivity now dictates that the speed at which articles are packaged, palletized, and/or shipped is of great importance and the packaging section of a manufacturing process should not become a productivity bottleneck. Further, competitive economics require better utilization of warehouse space, so uniformity and performance demands placed on palletized and/or unitized articles continue to increase as pallets and/or units are stacked higher and in closer proximity than ever before.  
         [0006]     Most manufacturing plants that produce individual articles utilize processes to unitize or palletize a plurality of articles, then wrap loaded pallets or units to prevent individual items from escaping and to preserve the finished dimensions of a palletized or unitized load. A typical strapping technique involves strapping material fed from a supply spool being wrapped around the palletized or unitized articles most commonly, sometimes by means of a rotary turntable in combination with a fixed supply spool, or using a carriage which supports a supply spool that travels around the palletized or unitized load while dispensing the strap.  
         [0007]     Another commonly used system utilizes a fixed perimetric guide frame which provides for a unit or pallet to be positioned inside the frame, a strap is conducted through the frame and about the unit to be palletized, released from the frame, tightened, then crimped or otherwise fastened in place.  
         [0008]     In nearly all strapping systems, strapping material is fed around the unit to form a loop, pulled to the desired tension, then secured. Most strapping system equipment comprises a dispenser which dispenses the strap from a spool, a tensioner which tightens the strap once in place, a crimper which attaches and secures the strap to itself, and a cutter which cleanly cuts the strap.  
         [0009]      FIGS. 5   a - 5   c  illustrate a typical strapping apparatus and application. In  FIG. 5   a , plastic strap  9  is shown supplied from a spool  100  and directed around a tensioner wheel  101 . Strap  9  then proceeds to the drive mechanism  102  which is comprised primarily of two drive/tensioner wheels  103 . After a following a serpentine route through drive/tensioner wheels  103 , plastic strap  9  is directed through welding/cutting mechanism  104  then through perimetric frame  105  where it encircles articles to be strapped, then eventually re-enters welding/cutting mechanism  104 .  
         [0010]     For illustration, said articles may comprise a typical application for PET bottles (e.g. soda pop bottles, product containers, etc.), wherein bottles  107  are regularly stacked in repeating rows, separated by interleaving sheets  108 , capped by a top sheet  109  and placed on a pallet  106 .  
         [0011]      FIG. 5   b  shows strap  9  released from the perimetric frame  105  and pulled tight around subject load by means of reversing the direction of drive/tensioner wheels  103 . Finally,  FIG. 5   c  shows a tightly strapped unit after welding/cutting mechanism  104  welded an overlapping section of strap  9  together, then cut the strap entering from the drive mechanism  102 .  
         [0012]     A problem common to many strapping applications is a shifting, settling or shrinking of the articles being held by the strapping some time after the palletization and strapping operations are complete. This change in the size or volume of the strapped articles causes the strap tension to decrease, thus reducing the effectiveness of the strap.  
         [0013]     One method employed to compensate for this product shifting, settling or shrinkage is to initially over-tighten the strap. This method, howeber, is particularly problematic when the articles are fragile or otherwise crushable as this limits the initial amount of strap tension and results in loose and ineffective strapping after settling, shrinking or shifting has occurred.  
         [0014]     Therefore, what is needed in the art is a strapping method and apparatus which will contract or otherwise draw in at a rate substantially commensurate with the shrinking or settling of articles held thereby. Further, what is needed in the art is an apparatus and lo method for producing a strap that will contract or otherwise draw in at a rate substantially commensurate with the shrinking or settling of held articles.  
       SUMMARY OF THE INVENTION  
       [0015]     The present invention produces pre-stretched strap material for securing arranged or packaged articles prior to handling or shipment. The present invention is also directed to a method of pre-stretching a strap for securing arranged or packaged articles for handling or shipping by stretching an elastically stretchable strapping material immediately prior to use, then wrapping the article or articles and securing the pre-stretched strap.  
         [0016]     The subject invention finds particular application for strapping an article or plurality of articles that tend to shrink individually, pack, or settle over time such that the strapped aggregate parcel becomes smaller over time. The present invention finds even more particular application for strapping an article or plurality of articles that are susceptible to crushing when strapped or banded too tightly.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The following drawings, which considered in conjunction with the description contained herein, provide a disclosure of our invention including one or more illustrative embodiments and methods for use thereof:  
         [0018]      FIG. 1  shows a front view of the elements of subject stretching apparatus that directly interact with a plastic strap.  
         [0019]      FIG. 2  provides a front view of the elements comprising the drive mechanism for subject apparatus.  
         [0020]      FIG. 3   a  is a detailed front view of a nip comprised of two mated drive wheels.  
         [0021]      FIG. 3   b  is a detailed cutaway side view of a nip.  
         [0022]      FIG. 4   a  is a side view of the subject apparatus absent belt elements.  
         [0023]      FIG. 4   b  is a side view of the apparatus with belt elements in place.  
         [0024]      FIG. 5   a - 5   c  provide front views of a typical prior art strapping apparatus.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     The present invention provides a means for pre-stretching a strapping material which has a damped elastic recovery characteristic, such as polyester strapping, for bundling or packaging applications, or for otherwise securing articles wherein the strap is pre-stretched to a predetermined amount immediately before application to the articles to be packaged. The amount of pre-stretching is adjusted to correlate with the amount of shrinkage, settling or shifting of the articles held within the strap over an certain period of time, thereby allowing the strap to shrink in a manner which compensates for load changes without the need for initial over-tensioning, and avoiding eventual strap loosening.  
         [0026]     The present invention comprises a method and an apparatus wherein a elastic-memory strap is conducted in series through a plurality of nips, each nip defined by a pair of opposed rollers and each pair of rollers defining a nip therebetween. Both rollers in a pair rotate at the same speed and in opposite direction. For preferred functionality, nips are grouped in sets of two with the second set of two nips set to rotate at a higher relative speed than the first set of two nips such that when a plastic strap is conducted through entire series of nips, the first pair of nips effectively brake the strap while the second pair of nips effectively stretch the strap.  
         [0027]     The relative speed between the first set of two nips and the second set of two nips is adjustable, thus providing for an adjustable amount of imparted stretch. Upon exiting the first set of nips, the strap is directed around a plurality of idler wheels then directed through the second set of nips. Upon leaving the last set of nips, the stretched strap is immediately fed to a conventional strapping machine or other strapping apparatus wherein the strap is applied to wrap a group of packages or articles, further pulled to a desired tension, then secured in place. Immediately after exiting the second brake nip, the pre-stretched polyester strap begins a process of slow, damped elastic recovery wherein the strap returns to the original unstretched length over a prolonged period of time, thus maintaining a more effective tension as wrapped packages or articles shift, settle or otherwise effectively shrink  
         [0028]     Referring to  FIG. 1 , the path of a plastic strap as it passes through our stretching unit is shown, according to our invention. Our apparatus utilizes and applies plastic strap which is known to have damped elastic recovery characteristics, at least in its lengthwise dimension, such that after being initially stretched, it will return to its original length (or a shorter, predicable length) over a period of time. Many ordinary strap materials, such as polyesters and polypropylene, have such characteristics, and can be used suitably well with our invention.  
         [0029]     For clarification of  FIG. 1 , plastic strap  9  enters from the left and exits to the right of the drawing, a convention which is adopted for better illustration of the invention but in no way represents the only possible configuration of the invention.  
         [0030]     Strap  9  passes through first brake nip  23  as defined by the pinch point between first drive wheel  1  and second drive wheel roller  2 , then passes through second brake nip  24  as defined by the pinch point between third drive wheel  3  and fourth drive wheel  4 . Drive wheels  1 ,  2 ,  3 , and  4  are rotating as indicated in  FIG. 1 , and all four drive wheels are rotating at the same speed such that the linear speed through each nip is equal. Upon exiting second brake nip  24 , strap  9  is preferably routed around a series of idler wheels, such as a first idler wheel  19 , a second idler wheel  20  and a third idler wheel  21 . In alternate embodiment of the invention, the idler wheels may comprise more or fewer wheels, be eliminated altogether, or be replaced in whole or part by other means of direction such as guides and slides.  
         [0031]     Strap  9  is then directed through a second series of nips comprised of first tension nip  25  as defined by the pinch point between fifth drive wheel  5  and sixth drive wheel  6 , and second tension nip  26  as defined by the pinch point between seventh drive wheel  7  and eighth drive wheel  8 . Drive wheels  5 ,  6 ,  7  and  8  are rotating as indicated in is  FIG. 1 . Importantly, drive wheels  5 ,  6 ,  7  and  8  are rotating faster than drive wheels  1 ,  2 ,  3 , and  4  so as to create a higher linear velocity through tension nips  25 ,  26  than through brake nips  23 ,  24 .  
         [0032]     This linear speed differential causes tensional forces in strap  9  as it passes through the series of nips such that first and second brake nips  23 ,  24  effectively brake the strap as first and second tension nips  25 ,  26  effectively stretch the strap so as to impart a measured amount of elastic deformation. As previously stated, drive wheels  1 ,  2 ,  3  and  4 , have a common drive mechanism and rotate at the same speed. Likewise, drive wheels  5 ,  6 ,  7  and  8  also share a common drive mechanism and rotate at the same speed. However, the rotational speed of each set of drive wheels is adjustable so that the amount of stretch imparted to plastic strap  9  is adjustable.  
         [0033]     In the preferred embodiment, strap  9  is pre-stretched between 4% and 8% as it exits second tension nip  26 . Using a polyester strap, we have noted that about ⅓ of the pre-stretch (e.g. 2%-3%) will be recovered within a period of time such as a few hours or few days. Use of other materials with differing stretch recovery characteristics, or strapping of articles with more or less anticipated shrinkage, settling or shifting may require adjustment of our apparatus to produce more or less pre-stretching prior to strapping.  
         [0034]     The nip pressure between each set of opposed drive wheels should be sufficiently high so as to prevent any slippage of strap  9  as it passes therethrough. During normal operation, strap  9  will be under tensile loading and will tend to slip forward as it passes through brake nips  23 ,  24  and backward as it passes through tension nips  25 ,  26 . Upon exiting second tension nip  26 , strap  9  is immediately fed to a conventional strapping machine such as disclosed  FIGS. 5   a - 5   c  herein. In the preferred embodiment, the abutted outer surfaces of drive wheels  1 - 8  which come into contact with strap  9  are smooth, however, these surfaces can be textured such as with a knurled finish or otherwise roughened, or provided with small teeth, cogs, tines or other apparatus that provide for an effective grip between said drive wheels and strap  9 .  
         [0035]     Continuing with  FIG. 1 , the collective mechanism illustrated by  FIG. 1  is mounted to the front side of base plate  50 . Drive wheels  1 ,  2 ,  3 , and  4  are rigidly and concentrically attached to first ends of shafts  11 ,  12 ,  13 , and  14  respectively with each shaft penetrating through base plate  50 . Likewise, drive wheels  5 ,  6 ,  7 , and  8  are rigidly and concentrically attached to first ends of shafts  15 ,  16 ,  17 , and  18  respectively with each shaft also penetrating through base plate  50 . The connections between base plate  50  and shafts  11 - 18  where shafts  11 - 18  penetrate through said base plate  50  provides for free rotation of each shaft relative to base plate  50  and can be accomplished by a number of conventional means including concentrically mounting properly sized housings with bearings on one or both sides of penetration through base plate  50 .  
         [0036]     First, second and third idler wheels  19 ,  20 , and  21  are each concentrically and rotatably attached to base plate  50  such that each idler wheel freely rotates about its center. Said attachment between idler wheels  19 ,  20 , and  21  and base plate  50  can be by any of a number of conventional means such as a rigid axle attached to base plate  50  and fitted with necessary bearings, bushings and collars to provide freely rotatable attachment.  
         [0037]      FIG. 3   a  provides a side view and  FIG. 3   b  a cutaway end view of a typical nip and the components that comprise said nip, specifically, first brake nip  23 . Referring first to  FIG. 3   a , first drive wheel  1  and second drive wheel  2  are shown with a portion of strap  9  located therebetween. The pinch point described as first brake nip  23  is also shown. In  FIG. 3   b , first and second shafts  11 ,  12  are shown with first and second drive wheels  1 ,  2  attached respectively thereon. As illustrated, in the preferred embodiment, drive wheels are sized to be wider than the plastic strap so as to insure adequate traction. As previously described, each drive wheel-shaft attachment should be sufficiently rigid so at to prohibit any relative movement therebetween. Also, the nip pressure between each set of opposed drive wheels must be sufficiently high so as to prevent any slippage of strap  9  as it passes therethrough.  
         [0038]      FIG. 2  provides a side view of the drive mechanism. For reference, the components shown in  FIG. 2  are all located on the back side of base plate  50 . Power for the entire mechanism comes from electric drive motor  10  which is mounted to base plate  50  and coupled to speed reducer  28 . Said speed reducer  28  may be any suitable transmission mechanism equipped with one rotary input and two rotary shaft outputs. The horsepower rating of drive motor  10  and the gear ratio of speed reducer  28  can both be varied to attain a desirable operation.  
         [0039]     In a preferred embodiment, electric drive motor  10  is rated at 3 HP and operates at 1750 RPM, and the gear ratio of speed reducer  28  provide a 5:1 shaft speed reduction. As illustrated, speed reducer  28  has an opposed dual shaft output that is fitted with first V-belt sheave  40  and second V-belt sheave  42 . Two right angle gear boxes are utilized as illustrated by first gear box  29  and second gear box  30 . Input shaft of first gear box  29  is fitted with an input V-belt sheave  41 and coupled to speed reducer  28  by means of V-belt  48 . Input shaft of second gear box  30  is fitted with an input V-belt sheave  43  and coupled to speed reducer  28  by means of V-belt  49 . In the preferred embodiment, V-belts and belt sheaves are used to provide the coupling between speed reducer  28  and gear boxes  29 ,  30 , but cogged V-belts or ribbed V-belts may be used. Further, sprocket and roller-chain couplings or other comparable drive couplings can be used.  
         [0040]     The output shaft of first gear box  30  is fitted with output pulley  47  and associated idler pulley  46  is located adjacent thereto. First drive belt  52  is positioned about pulleys  46  and  47  and serpentined through crank wheels  31 ,  32 ,  33  and  34  as illustrated. Crank wheels  31 ,  32 ,  33  and  34  are rigidly and concentrically attached to the second ends of shafts  11 ,  12 ,  13  and  14  respectively. Further, the output shaft of second gear box  29  is fitted with output pulley  45  and associated idler pulley  44  is located adjacent thereto. Second drive belt  51  is positioned about pulleys  44  and  45  and serpentined through crank wheels  35 ,  36 ,  37  and  38  as illustrated. Crank wheels  35 ,  36 ,  37  and  38  are rigidly and concentrically attached to the second ends of shafts  15 ,  16 ,  17  and  18  respectively. As illustrated, crank wheels  35 ,  36 ,  37  and  38  are all the same size and share a common drive belt, thus rotate at the same speed.  
         [0041]     Likewise, crank wheels  31 ,  32 ,  33  and  34  are identically sized, share a common drive belt, and rotate at the same speed. First gear box  30  and second gear box  29  are identical and in the preferred embodiment produce a 1:1 input to output drive ratio. A speed differential between the first group of crank wheels  31 ,  32 ,  33  and  34  and the second group of crank wheels  35 ,  36 ,  37  and  38  is preferably accomplished by varying the respective sizes of output V-belt sheaves  40  and  42 , or by varying the respective sizes of input V-belt sheaves  41  and  43  such that the second group of crank wheels  35 ,  36 ,  37  and  38  rotate faster than the first group of crank wheels  31 ,  32 ,  33  and  34 .  
         [0042]     With continuing reference to  FIG. 2 , first mounting plate  53  and second mounting plate  54  are illustrated in  FIG. 2  by dotted lines and represent mounting plates attached to and raised above base plate  50 . First mounting plate  53  and second mounting plate  54  are in coplanar relative orientation, and both are attached to and raised above base plate  50  in parallel orientation therewith. Shafts  11 ,  12 ,  13  and  14  penetrate through and are rotatably attached to first mounting plate  53  by means of bearings and housings or comparable. Idler pulley  46  is rotatably attached to mounting plate  53  and output pulley  47  is positioned above mounting plate  53  while associated gear box  30  is positioned below.  
         [0043]     Likewise, shafts  15 ,  16 ,  17  and  18  penetrate through and are rotatably attached to second mounting plate  54  by means of bearings and housings or comparable. Idler pulley  44  is rotatably attached to mounting plate  53  and output pulley  45  is positioned above mounting plate  53  while associated gear box  30  is positioned below. First and second mounting plates  53 ,  54  are used in the preferred embodiment, but can easily be replaced by properly positioned and secured brackets or other apparatus.  
         [0044]      FIG. 4   a  and  4   b  provide end or elevation views of the subject apparatus. For reference, all components located left of base plate  50  are included in  FIG. 2 , while all components located right of base plate  50  are included in  FIG. 1 . Referring first to  FIG. 4   a , drive motor  10  is shown and is attached to speed reducer  28 . Second output belt sheave  42  is shown, while first output belt sheave  40  is located on the opposite side of speed reducer  28  and is hidden from view. Second V-belt  49  is shown attached to second output belt sheave  42  and first V-belt  48  can be partially seen by virtue of first output belt sheave  40  being larger than second output belt sheave  42  in the preferred embodiment.  
         [0045]     As previously disclosed, second V-belt  49  is attached to input belt sheave  43  (not shown) located on gear box  30 , while first V-belt  48  is attached to input belt sheave  41  (not shown) located on gear box  29 . In the preferred embodiment, drive motor  10 , speed reducer  28 , gear box  29 , and gear box  30  are attached to base plate  50  by suitable attachment means such as welds, bolts or comparable. Continuing, first shaft  11  can be seen and is shown connected to first crank wheel  31  on the left, penetrating through base plate  50  and connected to first drive wheel  1  on the right. Second shaft  12  is then shown connected to second crank wheel  32  on the left, penetrating through base plate  50  and connected to second drive wheel  2  on the right. Fifth shaft  15  can partially be seen and is accordingly attached to crank wheel  35  on the left, penetrating through base plate  50 , and connecting to drive wheel  5  on the right.  
         [0046]     Finally, sixth shaft  16  is shown attached to sixth crank wheel  36  on the left, penetrating through base plate  50  and is shown connected to sixth drive wheel  6  on the right. As previously discussed, all shaft ( 11 - 18 ) penetrations through base plate  50  provide for free or otherwise unhindered rotation of each shaft, accomplished by means of a concentrically positioned bearing and housing, bushing or other suitable means. First mounting plate  53  and second mounting plate  54  are shown in the preferred position. Though not shown, attachment means between said mounting plate and base plate  50  may be suitably sized threaded rods, angled or flat members or other suitable apparatus preferably welded or bolted into position.  
         [0047]     With continued reference to  FIG. 4   a , elements comprising the stretching mechanism that contact plastic strap  2 , and those included in  FIG. 2  are shown located to the right of base plate  50 . Beginning at the top, second idler wheel  20 , first idler wheel  19  and third idler wheel  21  are shown. As discussed supra, attachment between said idler wheels  19 ,  20  and  21  and base plate  50  must provide for free rotation of idler wheels and can be accomplished by a number of conventional means including a rigid axle welded or otherwise attached to base plate  50  provided with bearings, bushings or other low friction rotatable connection subsequently attached to subject idler wheels.  
         [0048]     Continuing, first and second drive wheels  1 ,  2  are attached to first and second shafts  11 ,  12  respectively, and further comprise first brake nip  23 . Below, fifth and sixth drive wheels  5 ,  6  are shown attached to fifth and sixth shafts  15 ,  16  respectively are further comprise first tension nip  25 . For reference, first tension nip  25  lies in line with the lower surface of third idler wheel  21 , thus is not readily apparent.  
         [0049]     Referring finally to  FIG. 4   b , second drive belt  51  and first drive belt  52  are shown, as is plastic strap  9 . Though not shown in  FIG. 4   b , plastic strap  9  enters the apparatus through first brake nip  23  and exits the apparatus through second tension nip  26  (not shown) located behind first tension nip  25 .  
         [0050]     The embodiments shown and described herein are exemplary. It is within the skill in the art to vary the details, arrangement, and materials utilized to realize a pre-stretching apparatus according to our invention. Therefore, the scope of the present invention should be determined by the following claims with reference to, but not necessarily limited to these illustrative embodiments.