Abstract:
An automatic high speed packaging machine ( 10 ) for wrapping packages (P) in polymer film ( 32 ) is disclosed wherein the film seal at the sides and ends of the packages (P) is made at a high rate of speed as the packages (P) travel through the machine ( 10 ). The packages (P) travel continuously in a straight lien through the machine ( 10 ). The packages (P) are delivered at the input end of the machine ( 10 ) by an in-feed conveyor ( 20 ) into a film inverting head ( 40 ) where the packages (P) are surrounded by longitudinally half-folded polymer film ( 32 ). Thereafter, the packages (P) are transported to a side sealing mechanism ( 50 ) which forms a longitudinal seal in the film ( 32 ) on the side opposite the fold. Finally, the packages (P) are transported to a travelling end sealing mechanism ( 70 ) where a lateral seal is formed at each end of the package (P) and the film web ( 32 ) connecting succeeding packages (P) is severed. The machine ( 10 ) produces packages (P) which have a sealed film wrap around the entire package (P). If desired, the polymer film ( 32 ) may be of heat shrinkable variety and the sealed package (P) may be passed through a shrinking oven to produce a package (P) having a tight “shrink-wrap” film covering.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation-in-part of application Ser. No. 09/752,784 filed Dec. 28, 2000, the contents of which are incorporated fully by reference herein. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates to automatic package wrapping machines and in particular to a machine which wraps packages in polymer film, including heat shrinkable thermoplastic film, and seals the edges of the film to completely encase the packages within the film where the packages move continuously at a high rate of speed through the machine.  
           [0003]    In typical prior art bagging and in-line shrink wrap packaging machines, packages are moved towards a cutting and sealing area by an in-feed conveyor. As the packages are moved towards the cutting and sealing area, the packages are surrounded by center folded polymer or shrink wrap film that has been partially unfolded so that the packages may be conveyed between the film layers. Subsequently, the packages are transferred to an exit conveyor where the packages move to a designated sealing and cutting location. At the sealing and cutting location, it is typical to stop the forward movement of the exit conveyor and use a hot knife or hot wire system to longitudinally and laterally seal the layers of polymer film and to sever the film between adjacent packages at the lateral or cross seal. The end result of the cutting and sealing operations are packages that are securely enclosed or “bagged” within polymer film. After the packages are bagged, the exit conveyor is again activated and the packages are typically either packed for shipping or are further conveyed to a shrink wrap tunnel or oven, where the film is heated causing it to shrink over the packages thereby securely wrapping the packages.  
           [0004]    One typical prior art machine, commonly referred to as an L-sealer, is described in U.S. Pat. No. 3,583,888, issued to Shanklin, entitled “Packaging Wrapping Apparatus and Method.” An L-sealer uses an L-shaped hot knife to contemporaneously cross-seal and side seal the layers of polymer film when the package is stopped at the cutting and sealing location. L-shaped hot knives are typically coated with Teflon, so that melted polymer film will not stick to the knife. An advantage of L-sealers is that the packages they make are neat and attractive having trim seals on three sides and clear film on the fourth side and top and bottom. L-sealers, however, have several disadvantages. The dimensions of L-shaped hot knives must be larger than the size of the packages being wrapped. Thus, L-sealers cannot produce longitudinal seals longer than the length of the knife. In addition, it is important that a Teflon coated hot knife be extremely straight and without nicks. If the knife is improperly adjusted, warped, or nicked, polymer film will not seal properly. For instance, a nick in the knife will create a hole in the seal. Likewise, a warped or improperly adjusted knife will create an incomplete seal.  
           [0005]    More recent machines have overcome some of the limitations of L-sealers by using continuous longitudinal or side sealers. These machines have utilized hot wires and ultrasonic welders to create a continuous side seal. However, most of these machines have used a straight hot knife for cross sealing and require the conveyer system to be stopped while the hot knife makes the cross seal. Thus, these machines still suffer from the intermittent operation typical of L-sealer type machines and therefore have the same limitations regarding package throughput.  
           [0006]    Efforts have also been made with rotary hot knife systems that can cut and side seal polymer film without stopping the forward movement of the film. Such rotary hot knife side sealing systems typically have a circular Teflon coated knife mounted for rotation. However, these systems are typically not compatible with some of the thicker polymer films commonly used in high speed applications because of insufficient contact time between the film and the rotary knife to produce suitable welds.  
           [0007]    What is needed therefore is a high speed package wrapping machine capable of continuous operation during both side and cross sealing functions. The machine should be readily adaptable for use with a wide range of package sizes without requiring the need to replace hot knives or other hardware to accommodate different size packages. Such a machine would thus be simpler and have a quicker setup time than existing machines. Ideally, such a machine would utilize a sealing mechanism that improves on existing hot knife, hot wire, and ultrasonic sealing devices.  
         SUMMARY OF THE INVENTION  
         [0008]    The high speed wrapping machine of the present invention solves many of the above mentioned problems by providing an in-line wrapping machine capable of wrapping a wide range of package sizes through simple on-machine adjustments. The machine is capable of continuously wrapping packages at film velocities of 65 feet per minute. The machine includes a powered film dispenser, an in-feed conveyor, a film inverter, a side sealer and conveyor, and a traveling end sealer and conveyor.  
           [0009]    Packages enter the machine on the in-line, in-feed conveyor. Center-folded film is fed from a powered film dispenser mounted at the rear of the machine and passes over the adjustable film inverting head. The inverting head turns the film inside out, leaving an opening into which packages maybe inserted. The in-feed convey or carries packages through the film inverting head where they are wrapped with polymer film. As the product is conveyed onto the side seal conveyor, a side sealer equipped with a hot tapered drag wire, and a hot post cutoff, begins the process of drawing the film through the sealer at about the same rate as packages advance on the conveyor. This permits light and heavy films to be fed through the machine without distorting the film. The side sealer makes a continuous seal and trims the selvage off the packages creating a sealed tube as the film advances through the machine. The side sealer is driven by a main drive motor via a power-take-off shaft which also drives the side seal conveyor. This provides for smooth package and film travel at various speeds. The horizontal package carrying surfaces of the in-feed conveyor, the side seal conveyor, and the traveling end seal conveyor are mounted at the same elevation to ensure that packages are carried smoothly through the machine.  
           [0010]    Since the machine uses a continuous side sealer, package length is not limited by the length of the sealing system, and packages of very long lengths can be wrapped if supported by conveyors. As a package progresses further through the machine, a traveling end seal mechanism seals the trailing edge of the package and simultaneously seals the leading edge of the next package traveling through the machine. The traveling end sealer is equipped with a photocell trigger such that as a package breaks the photocell beam, a unique combination of linear and rotary air cylinders, in combination with a partial revolution clutch, a variable speed transmission, and other drive components, causes the sealing jaws to close, while simultaneously, the end sealer moves forward longitudinally on a traveling carriage assembly. The carriage assembly reciprocates back and forth along one or more linear bearings. At the end of the carriage&#39;s travel the sealing jaws open and the carriage returns to its initial or rest position. The machine includes a discharge conveyor which utilizes a single belt which extends through the traveling end sealer to the end of the machine. Generally, the traveling end sealer moves longitudinally at about the same speed as the packages. However, the traveling carriage assembly&#39;s speed maybe independently controlled by means of the variable speed transmission incorporated in the drive system.  
           [0011]    Other features and advantages of the invention will become more apparent from the following detailed description of the invention, when taken in conjunction with the accompanying exemplary drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a perspective view, from the front, of a high speed film wrapping machine in accordance with the present invention.  
         [0013]    [0013]FIG. 2 is a perspective view of the high speed film wrapping machine shown in FIG. 1, with the traveling end seal mechanism and associated conveyor assembly of the machine longitudinally separated from other subassemblies for clarity, with the supporting structure removed to expose the details of the invention.  
         [0014]    [0014]FIG. 2A is a view, in schematic form, taken along the line B-B, as shown in FIG. 2, of a film inverter according to the present invention.  
         [0015]    [0015]FIG. 3 is a schematic of the power transmission for the entire system for the entire machine shown in FIG. 1.  
         [0016]    [0016]FIG. 4 is a top view of the machine of FIG. 1 showing the packages as they travel through the machine.  
         [0017]    [0017]FIG. 5 is a perspective view of the packages of FIG. 4 showing the state of the film sealing procedure corresponding to package flow through the machine.  
         [0018]    [0018]FIG. 6 is a perspective view of the side sealing mechanism of the present invention.  
         [0019]    [0019]FIG. 7 is a perspective view of the sealing jaw which forms part of the sealing mechanism.  
         [0020]    [0020]FIG. 8 is a top view of the side sealing mechanism of FIG. 7 showing the offset and horizontal spacing of the film feed pulleys of the side seal unit.  
         [0021]    [0021]FIG. 9 is a perspective view of the side sealing mechanism of the present invention, partially cutaway to reveal internal details.  
         [0022]    [0022]FIG. 10 is a side view of the side sealing mechanism shown in FIG. 9.  
         [0023]    [0023]FIG. 11 is a perspective view of the traveling end seal mechanism of the machine of FIG. 1.  
         [0024]    [0024]FIG. 12 is a front view of a portion of the traveling end seal mechanism shown in FIG. 11.  
         [0025]    [0025]FIG. 13 is a perspective view of hot drag wire shown in FIG. 7.  
         [0026]    [0026]FIG. 14 is an enlarged view of Detail B shown in FIG. 13.  
         [0027]    [0027]FIG. 15 is a sectional view taken along the line A-A as shown in FIG. 13, showing the cross section of the tapered drag wire. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    [0028]FIGS. 1 and 2, show perspective views of the high speed wrapping machine of the present invention, generally designated  10 . Designated generally, the machine comprises an in-feed conveyor  20 , a film dispenser  30 , an inverting head  40 , a side sealer  50 , a side seal conveyor  60 , a traveling end sealer  70 , an end seal conveyor unit  80 , a control panel  2 , and a power transmission system  100 .  
         [0029]    Referring now to FIGS.  1 - 2  and  4 - 5 , a general overview of the functioning of the high speed wrapping machine of the present invention is as follows. The machine  10  wraps a package (“P”) in a flexible polymer film  32  in which the direction of package flow through the machine is essentially continuous and in a straight line. The film is supplied to the machine as a center folded web at right angles to the direction  22  of flow of the packages (best shown in FIG. 4) through the machine. The film is provided to the inverting head  40  where the film is redirected and turned inside out to provide film traveling in the same direction as the packages delivered by the in-feed conveyor  20 . The in-feed conveyor  20  pulls the packages (P 6 ) into the inverting head  40  to cause them to be enclosed by the folded film  32  supplied by the film dispenser  30  on the top, and on one side of each package with the other side of each package adjacent to the edges of the folded film. The packages (P 5 ) thus enclosed in the web of film pass from the in-feed conveyor to the side seal conveyor  60 , where a speed differential between the two conveyors uniformly spaces the packages on the side seal conveyor. The speed differential and thus the spacing between packages is adjustable by the machine&#39;s operator. As the packages pass the side sealer  50 , the two free edges of the folded film are sealed to form the continuous tube of film  36  which envelopes the succession of packages which are being fed into the machine by the in-feed conveyor (P 4  and P 5 ). The side sealer also severs the excess width of film from the tube and this scrap film  38  is removed by the take-up wheel assembly  302 . As the packages progress further through the machine, the traveling end sealer  70  seals the trailing edge of each package while simultaneously sealing the leading edge of the succeeding package in the machine  10  (P 2 ). During the sealing operation, the end sealer also severs one package from another while the packages are traveling without stopping the machine. The end seal mechanism is designed so that it travels a short distance with a package at substantially the same velocity as the package for the duration of time required to make the seal. After the seal has been made, the end seal mechanism releases from the film and returns to its original position to repeat the end seal for the next package. The wrapped package may optionally then be conveyed through a shrink tunnel (shown schematically in FIG. 5) if shrinking of the film around the package is desired (P 1 ). The component parts and assembly of the high speed wrapping machine will now be discussed in detail.  
       In-Feed Conveyor  
       [0030]    Referring now to FIGS. 2 and 3, as stated earlier, the in-feed conveyor  20  feeds packages into the machine  10 . The in-feed conveyor comprises an endless belt  22  and a conveyor plate  24 . At one end of the conveyer plate is a drive roller  26  and an idler or tension roller  28 . At the conveyor plate&#39;s opposite end, the plate has a rounded nosepiece  210 , which is used in place of a more conventional idler roller. The drive roller is connected to a motor  204  by means of a pulley and belt arrangement, where a pulley  208  is connected to the motor output shaft and a pulley  206  is connected to the drive roller and the two pulleys are coupled by a drive belt  202 . In operation, the endless belt  22  is fitted over the drive roller, idler roller, and conveyor plate. Belt slack is taken up by the idler roller which may be equipped with a biasing feature for automatic belt tension adjustment. Methods of tensioning idler rollers are well known to those skilled in the art.  
         [0031]    By the arrangement described above, the in-feed conveyor is driven at a constant speed. The speed of the motor  204  is electrically controlled by means of the control panel  2 . Control of the in-feed drive motor is electrically coupled to that of the main drive system (to be described). The control logic includes the ability to maintain a speed differential between the in-feed conveyor and the side seal conveyor  60  as the overall system speed is increased or decreased. Typically, the speed of the in-feed drive motor is less than that of side seal conveyor. In general, the slower the in-feed conveyor runs in comparison to the side seal conveyor, the greater will be the spacing between packages. If the in-feed conveyor is run at a speed close the to that of the side seal conveyor the spacing between packages will be quite small. The in-feed/side seal conveyor speed differential is easily controlled by the machine&#39;s operator and the subsequent package spacing may be visually verified.  
         [0032]    Referring now to FIG. 1, the in-feed conveyor further includes package guides  212  and  214 , where guide  214  is a fixed guide, and guide  212  is laterally movable with respect to the fixed guide. The guides allow the machine  10  to be readily adjusted to accommodate packages of varying widths. In addition, the lateral position of the in-feed conveyor is adjustable with respect to the side seal conveyor. In the exemplary embodiment, the in-feed conveyor is laterally adjustable by rotating a control wheel  210 . The lateral adjustment mechanism (not shown) may comprise screw leads, ball slides, or any other suitable adjustment mechanism.  
       Film Inverter  
       [0033]    With reference to FIGS. 1 and 2, the film inverter  40  of the present invention comprises a first movable triangular inverting head  42 A which is positioned above the in-feed conveyor, a second fixed triangular inverting head  42 B (not shown) which is positioned below the in-feed conveyor. The first inverting head is attached to a vertical inverting head adjustment assembly  44  which serves to raise or lower the first inverting head in order to accommodate packages of various heights. The present embodiment of the vertical inverting head adjustment assembly comprises a screw lead  48  which is driven by an adjustment wheel  402  and is guided by twin linear guides  46 . This embodiment is meant to be exemplary only. Those skilled in the art will recognize that alternative means of accomplishing the vertical adjustment of the inverting head are possible.  
         [0034]    For the most efficient operation, elements  404 A and  404 B of the upper and lower inverting heads respectively should be substantially at an angle of 45 degrees with respect to the direction of package flow  22 . Also elements  406 A and  406 B of the upper and lower inverting heads should be at substantially right angles to the flow of film  32  from the film dispenser  30 .  
         [0035]    In operation, one side of the center-folded film  32  from the film dispenser  30  passes under the in-feed conveyor to the lower inverting head  42 B and one side of the film passes over the in-feed conveyor to the upper inverting head  42 A. As the in-feed conveyor pulls the package through the inverter a top layer of film covers the packages. The bottom layer of film is threaded from under the in-feed conveyor to the top of the side seal conveyor  60 . Thus, as each package emerges from the film inverting assembly  40 , and crosses to the side seal conveyor  60  there is a layer of film over the top of the package and a layer between the bottom of each package and the side seal conveyor. On the side of each package facing the film inverter or opposite the side sealer  50 , the film is unbroken around the package. On the side of each package facing the side sealer the free edges of the upper and lower layers of center-folded film rest on top of each other.  
       Powered Film Dispenser  
       [0036]    Referring now to FIGS. 2 and 2A, the wrapping machine  10  of the present invention uses center-folded film  32  from the roll of film  34  supplied by the powered film unwind or dispenser  30 . In the present embodiment, a powered film unwind system is used where a slight tension on the film web  32  raises a dancer roller  314  which in turn activates and rotates a potentiometer  318 , which drives a motor  316 , which drives a drive roller  304 , which turns the roll of film in a direction to provide film to the machine. As shown in FIGS. 2 and 2A, the film roll is supported by rollers  38  and  302 . The drive roller  304  is also paired with a pinch roller  306 , which in combination unwind film from the film roll. Prior to feeding the film into the inverter  40 , the film passes a fixed guide roller  320  and travels upwardly to an adjustable guide roller  313 . The film subsequently travels downwardly around the dancer roller  314  and upwardly to a fixed guide roller  312 . Just prior to being fed into the film inverter  40  the center folded film is separated by a separating bar  315 . The drive motor of the present embodiment of the film dispenser is electrically coupled to the system controls  90 , thus film dispenser speed may be automatically controlled depending upon the machines desired rate of operation.  
         [0037]    An exemplary embodiment of the film dispenser has been described above. However, it should be noted that several powered film unwind systems are known in the art, and the machine  10  of the present invention is designed to be compatible with existing systems. Further, the film  32  referred to throughout this specification is generically termed “polymer” film. It is to be understood that the term “polymer” refers to any heat sealable plastic or thermoplastic or similar film. All such heat sealable films are suitable for use with the wrapping machine of the present invention.  
       Side Seal Mechanism  
       [0038]    Referring now to FIG. 1, the side sealer  50  and the side seal conveyer  60  are shown in relation to the other sub assemblies of the packaging machine. The side sealer may be adjusted vertically with respect to the side seal conveyor by means of adjustment screw  52 . Vertical adjustment of the side sealer is desirable in that it is preferred for esthetic reasons that the sealed seam of film on the side of each package be made at approximately the center of the side of the package. In the present embodiment, vertical adjustment is accomplished by mounting the side sealer on a base plate (not shown) and moving the sealer by means of a lead screw (not shown). Other methods of vertical adjustment such as ball bearing screws are known in the art. The side sealer and the side seal conveyor are, as a unit, laterally movable to accommodate packages of varying widths. Such lateral movement may be accomplished by rotating the lateral positioning screw  54 . In the present embodiment, the side sealer and conveyor unit are mounted on a linear positioning slide (not shown). Many types of linear positioning slides are suitable and known in the art.  
         [0039]    Referring now to FIGS.  6 - 9 , the side seal assembly  50  includes a plurality of shaft mounted front and rear, and inboard and outboard pinch rollers  502 A- 508 B, inboard and outboard pinch belts  512 A and  510 A respectively, inboard and outboard fixed lower runners  58 A and  58 B (best seen in the partial cutaway portion of FIG. 9), inboard and outboard floating upper runners  56 A and  56 B (best seen in the partial cutaway portion of FIG. 9), upper runner biasing arms  514  and biasing springs  516 , and a side sealing jaw assembly  517 . The sealing jaw assembly comprises a sealing jaw  518 , an electrically heated tapered hot wire  520 , and an electrically heated hot post  522 .  
         [0040]    Referring now to FIGS.  13 - 15 , the hot wire  520  and hot post  522  are shown in more detail. The hot wire is formed with a slope angle θ. The slope angle effects the dwell time required to melt the polymer film. In the exemplary embodiment, the hot post is formed as an integral portion of the hot wire.  
         [0041]    Referring again to FIGS.  6 - 9 , in general, the side sealer operates as follows. Power from the packaging machine&#39;s drive system is supplied to the pinch roller  502 B which also functions as a drive roller. By means of a belt and pulley system to be explained later, all four of the pinch rollers are driven at the speed of the side seal conveyer. The film to be sealed  32  enters the side sealer at the front pinch rollers following the direction of film flow as indicated by arrow  22 . The film is squeezed between the upper and lower pinch belts corresponding to the inboard and outboard pinch rollers respectively and is subsequently drawn through the side sealer by the these belts. Between the front and rear pinch rollers, uniform pressure is maintained on the pinch belts by means of the upper and lower runners  58 A-B and  56 A-B. The lower runners  58  are fixed runners within which the pinch belts travel in a guide channel  532 . The guide channel is incorporated into each of the lower and upper runners. The upper runners  56  are movable or floating runners which are biased against the pinch belts by means of the biasing arms  514  and biasing springs  516  (FIG. 6). The pinch belts are biased against the film  32  with sufficient force to prevent slippage or lateral or sideways movement of the film relative to the belts. Disposed between the inboard and outboard runners is the side sealing jaw assembly  517 . As the two layers of film are drawn through the side sealer, a seal is formed as the layers pass over the tapered hot wire  520  of the sealing jaw assembly  517 . The hot wire forms the seal by essentially melting or welding the layers of polymer film together. The “dwell time” or time required for the polymer film to be in contact with the tapered hot wire is primarily a function of the thickness of the film, the thermal conductivity of the film, and the slope angle of the hot wire. The required dwell time for any particular film thickness and composition may be adjusted by: 1) varying the temperature of the tapered hot wire; varying the slope angle of the hot wire; and 3) adjusting the speed of side seal conveyor. Upon reaching the end of the sealing jaw  518 , the now sealed film reaches the hot post cutoff  522 . The hot post cutoff serves to sever the selvage  38  (FIG. 5) at the line of the seal. The term “selvage” refers to that portion of film extending beyond the seal line, i.e., scrap film. The selvage is wound onto the take-up wheel  302  (FIG. 1) as the packages, now enclosed in a tube of film  36  (FIG. 6), leave the side sealer. In the exemplary embodiment, a take-up wheel is shown for removing selvage, however, other means are known in the art and can be used.  
         [0042]    Referring now to FIG. 7, the sealing jaw  518  further includes a radius or semicircular portion  523  over which the tapered hot wire  520  forms a radius portion  521 . When the film to be sealed is within this radiused region of the sealing jaw the film absorbs heat from the tapered hot wire and is thus preheated and softened prior to actually making contact with the hot wire. Preheating of the film also reduces drag on the tapered hot wire and results in a better seal than would otherwise be obtainable. In some embodiments, where very precise temperature control is desired, it may be desirable to place a thermocouple on the tapered hot wire.  
         [0043]    Again, with reference to FIGS.  6 - 9 , more details of the side sealer and its operation are described. The rear pinch rollers comprise, upper inboard and outboard rollers  502 A and  504 A respectively, and lower inboard and outboard rollers  502 B and  504 B respectively. The upper and lower rear rollers are vertically in-line and have a predetermined spacing  524  between the inboard and outboard rollers. The front pinch rollers comprise, upper inboard and outboard rollers  506 A and  508 A respectively, and lower inboard and outboard rollers  506 B and  508 B respectively. Like the rear pinch rollers, the upper and lower front pinch rollers are vertically in-line. However, unlike the rear pinch rollers, the inboard and outboard front pinch rollers are longitudinally spaced or offset by a predetermined distance  528 . The inboard and outboard front pinch rollers are also laterally spaced a predetermined distance  526 . It is particularly important to note that the lateral spacing  524  of the rear pinch rollers is greater than the lateral spacing  526  of the front pinch rollers.  
         [0044]    The front  502 A- 504 B and the rear  506 A- 508 B pinch rollers are coupled by upper and lower and inboard and outboard film pinch belts  512 A-B and  510 A-B respectively, i.e., the upper inboard belt  512 A and the lower inboard belt  512 B form one set of matched pinch belts and upper outboard belt  510 A and the lower outboard belt  510 B form a second set of matched belts. As is best shown in FIG. 8, the outboard set of belts  510 A-B is angled away from the inboard set of belts  512 A-B by a predetermined angle  530 . The offset of the inboard and outboard front pinch rollers and the angled outboard pinch belts provides one of the unique operational advantages of the packaging machine  10  of the present invention. As film to be sealed  32  enters the outboard pair of front pinch rollers, lateral tension is developed in the film. This lateral tension increases as the film enters the inboard front pinch rollers. Once the film has entered the pinch rollers, it is forced to follow the path of the pinch belts. As explained above, due to the pressure maintained on the pinch belts, the film is unable to slip laterally or sideways. Therefore, because the outboard belt set  510  is angled away from the inboard belt set  512 , lateral film tension increases as the film travels through the side sealer. In other words, the film is stretched as it passes through the side sealer and the selvage parts readily due to the film tension, as it is severed by the hot post cutoff  522 . Further the comparatively wide spacing of the rear pinch rollers allows the selvage to be taken up by the take-up wheel  302  (FIG. 1) with little or no possibility of interference with sealed film tube  36  (FIG. 5).  
       Side Seal Conveyer  
       [0045]    Referring now to FIG. 3, the side seal conveyer  60  is similar in design to the in-feed conveyor  20  and includes an endless belt  64 , and a conveyor plate  66 . Disposed off-center from the conveyor plate is a drive roller  62 . Disposed at each end of the conveyor plate is a rounded nosepiece  68 . Like the in-feed conveyor, the rounded nosepiece is used in place of a more conventional idler roller for simplicity. Unlike the in-feed conveyor, the side seal conveyor utilizes two idler or tension rollers  602 . As will be explained below, the side seal conveyor drive roller  62  also drives the side sealer  50 , thus the side seal drive roller experiences higher load and correspondingly increased drag than that of the in-feed conveyor drive roller. For this reason, a pair of idler rollers is preferred in the side seal conveyor in order maintain appropriate tension in the conveyor belt.  
       Side Sealer and Conveyor Drive  
       [0046]    Referring now to FIG. 2, the side sealer  50  is driven by the power transmission system  100  of the packaging machine  10 , as follows. A main drive motor  102  applies power to a pulley  104 , which in turn drives a pulley  114 , by means of a main drive belt  106 . The main drive belt is equipped with an idler pulley  108  to eliminate slack. The pulley  114  is mounted on a power transfer shaft  110 . The power transfer shaft drives a pulley  116  which is mounted to and drives the side seal conveyor drive roller  62 , via a pulley  120  connected to the drive roller  62  and a belt  123  which couples pulley  116  to pulley  120 . The side seal conveyor drive roller rotates the side seal endless conveyor belt  64 . The side seal conveyor drive roller  62  further includes a power-take-off (“PTO”) pulley  122 . PTO pulley  122  is connected to the main side seal drive pulley  530  via a drive belt  121 .  
         [0047]    Referring now to FIG. 10, it may be seen that the drive pulley  530  is mounted on a common shaft with the lower inboard and outboard rear pinch rollers  502 B and  504 B respectively, as well as with a lower side gear  534 . Lower side gear  534  is meshed with upper side gear  532  which itself is on a common shaft with the upper rear inboard and outboard pinch rollers  502 A and  504 A respectively. When power is supplied to the lower rear pinch rollers via drive gear  530  and to the upper rear pinch rollers via the side gears, the rear pinch rollers in turn drive the front pinch rollers  506 A- 508 B (FIG. 8) by means of the upper and lower inboard and outboard belt sets  510 A-B and  512 A-B respectively. Driving of the front rollers causes the film to be sealed  32  (FIGS. 5) to be drawn through the side sealer and whereby the film is sealed and the selvage is trimmed leaving the packages in a sealed tube of film  36 , as shown in FIG. 5  
       Traveling End Seal Mechanism  
       [0048]    Referring now to FIG. 1, the traveling end seal mechanism  70  is shown in relation to the other subassemblies of the machine  10 . As shown, the end seal mechanism comprises a conveyor assembly  80 , a carriage assembly  90  and a cross seal assembly  72 .  
       End Seal Assembly  
       [0049]    Referring now to FIG. 11, the details of the end or cross seal assembly  72  and the carriage assembly  90  are shown. The end seal assembly further comprises a housing  74 , which contains an upper horizontal shaft  76 , a lower horizontal shaft  78 , an inboard vertical slide shaft  704  and an outboard vertical slide shaft  702 . Mounted between and attached to the vertical slide&#39;shafts are an upper cross bar  712  and a lower cross bar  714 . The upper and lower cross bars include a linear bearing  710  attached to each end of the bars. In the presently preferred embodiment, the upper and lower cross bars are essentially the same, with the lower cross bar being rotated  180  degrees with respect to the upper bar. The linear bearings  710  sidably couple the upper and lower cross bars to the vertical slide shafts. The upper and lower horizontal shafts are equipped with a side gear  724  at each end of each shaft. Rotatably coupling the upper and lower horizontal shafts, via the gears  724 , are actuating chains  706 . In the present embodiment, a single inboard chain  706  couples the horizontal shafts at their inboard ends and a single outboard chain  726  couples the horizontal shafts at their outboard ends. With particular reference to the upper cross bar  712 , the cross bar is coupled to the front of the inboard actuating chain by means of a tie-plate  708  and is coupled to the front of the outboard actuating chain by another tie-plate  708 . The upper cross bar is not coupled to the rear of the of the actuating chains. The lower cross bar is also coupled to the actuating chains by tie-plates  708 . However, unlike the upper cross bar, the lower cross bar is coupled to the rear of the actuating chains and also unlike the upper cross bar, the lower cross bar is not coupled to the front of the chains. In other words, the means of coupling the upper and lower cross bars to the chains via tie-plates is identical, what is different is that the upper cross bar is only coupled to the front of the chains and lower cross bar is only coupled to the rear of the chains.  
         [0050]    The use of tie-plates  708  to couple the cross bars to the actuating chains provides for the ability to adjust the opening between the upper and lower cross bars to accommodate packages of various heights. To change the spacing or opening between the cross bars, an operator need only remove the tie-plates and adjust the cross bars to the desired vertical spacing and then reattach the tie-plates.  
         [0051]    With continued reference to FIG. 11, the upper cross bar  712  also includes a seal bar  716  which is attached to the upper cross bar via spring loaded guide pins  720 . The seal bar includes a hot wire (not shown) for making a cross seal  39 , as shown in FIG. 6. The lower cross bar  714  includes a seal base  718 , which is attached to the lower cross bar by means of the spring loaded guide pins  720 . The spring loaded seal bar  716  and hot wire and the spring loaded seal base create uniform pressure on the polymer film to be sealed when the seal bar and seal base are brought together during the action of the cross seal assembly. It should be noted that although the upper and lower cross bars are described as being attached to the sealing bar and the seal base respectively by means of spring loaded connections, this method of attachment is meant to be exemplary only. The cross sealer will operate effectively with rigid attachments between the upper and lower cross bars and the sealing bar and seal base respectively, and in some situations rigid attachments may be preferred.  
         [0052]    The driving force for the end seal assembly is provided by a rotary or pneumatic air cylinder  722 . It should be noted that the lower horizontal shaft  78  is an integral component of the rotary air cylinder  722 . The rotary air cylinder is capable of both clockwise and counter-clockwise rotation. The rotary air cylinder is actuated in a clockwise direction in response to a first electrical signal generated by a photocell  154  (FIG. 1). An energizing electrical signal is produced by the photocell when a light beam from a light source  155  (FIG. 1) is interrupted by a package moving along the end seal conveyor. When the rotary air cylinder is actuated in the clockwise direction, the upper and lower cross bars  712  and  714  close causing the spring loaded sealing bar  716  to bear against the spring loaded seal base  718 , between which lies the tube of film  36  (FIG. 5) to be sealed. Heat from the hot wire in the sealing jaw  716  and pressure produced by the jaw bearing against the sealing pad produces a cross seal  39  (FIG. 5) and simultaneously severs the film at the point of the seal. Counter-clockwise movement of the rotary air cylinder causes the sealing bars and consequently the sealing jaw and pad to open. The rotary air cylinder rotates counterclockwise in response to a second electrical signal generated by a cam operated limit switch  152  (FIG. 2). The operation of this switch will be explained in more detail in the section on the traveling end seal drive to be discussed below. The rotary air cylinder and chain drive system of the cross seal mechanism of the present invention are believed to be unique to film wrapping machines and provide the film wrapping machine  10  of the present invention with a degree of simplicity, adjustability, and speed of operation not previously obtainable in such machines.  
       Carriage Assembly  
       [0053]    Referring now to FIGS.  3 , and  11 - 12 , the carriage assembly  90 , of the traveling end sealer  70 , comprises an upper housing  92  and a lower housing  94 . In the exemplary embodiment, the upper housing comprises a base plate  912  and inboard and outboard side plates  914  and  916  respectively. Included within the upper housing are front and rear lower conveyor belt rollers  902  and  904  and front and rear upper conveyor belt rollers  906  and  908 . The upper housing further includes an upper cross member  910  which provides lateral rigidity to the side plates of the upper housing. Attached to the upper housing is a lower housing  94 . Enclosed within the lower housing is linear slide carriage  920 , which in combination with a slide ram  918  forms a complete linear slide bearing assembly  96 . The ends of the slide ram are fixed to the support structure (not shown) of the high speed wrapping machine  10 . The lower housing also includes a fitting  98  for attachment of a first pushrod  126 . In operation the mated carriage and cross seal assemblies reciprocate back and forth over the ram  918  of the linear bearing  96  via reciprocating force applied by the first pushrod  126  to the linear bearing carriage  920 . In the exemplary embodiment, the lower housing serves to provide a connection between the linear bearing carriage  920  and the upper housing  92  of the carriage assembly  90 . The lower housing also provides a connection point for the first pushrod  126 . However, those skilled in the art will realize that the lower housing may take many forms and may be dispensed with entirely as the provisions for connection to the carriage assembly  90  and for attachment to the first pushrod  126  may be incorporated directly into the linear bearing carriage  920 .  
         [0054]    Referring again to FIG. 11, in many situations it is desirable to be able to adjust the height of end sealer  72  such that the cross or end seals are approximately centered with respect to the ends of the packages. To accomplish such adjustment, it is necessary to be able to raise or lower the end sealer with respect to the center line of the packages. In the packaging machine of the present invention  10 , this is accomplished by indexably mating the end sealer to the carriage assembly  90  as follows. The carriage assembly is mated to the end seal assembly by means of holes  915  in the carriage assembly side plates  914  and  916 , which index with matching holes  715  in the housing  74  of the end seal assembly. The means of attachment may be bolts, ball-lock pins, or any other suitable fasteners. If more precise height adjustments are required, those skilled in the art will realize that the indexing method described above may be replaced with simple lead screws, ball screws, or any other suitable linear positioning device.  
         [0055]    Those skilled in the art will realize that simplifications may be made to the exemplary embodiment described above without departing from the scope of the invention. For example the sealing bar  716  and the sealing base  718  may be eliminated and the hot wire, or a hot knife, may be incorporated directly in either one of the cross bars  712  and  714 . In addition, the end seal assembly  72  and the carriage assembly  90  may be constructed as a single unit. This may be readily accomplished by incorporating the features of the carriage assembly directly into the end seal assembly housing or frame  74 . Further, the sealing bars have been described as closing during clockwise rotation of the rotary air cylinder  722  and as opening during counter-clockwise rotation of the rotary air cylinder. However, the end sealer may be easily constructed so that the sealing bars close during counter-clockwise rotation of the rotary air cylinder and open during clockwise rotation of the rotary air cylinder. Other simplifications are also possible.  
       Traveling End Seal Conveyor and Drive  
       [0056]    Referring now to FIGS. 2 and 3, and with particular reference to FIG. 3, the traveling end seal conveyor  80  includes a conveyor belt  81 , which begins at a drive roller  84  and follows the direction of belt travel shown by arrow  804 . The belt path is as follows. From the drive roller  84 , the belt travels upwards past a tension roller  802  to an idler roller  82 . From the idler roller  82  the belt travels in a flat plane, coplaner with the side seal conveyor  60 , to the idler roller  906  mounted on the carriage assembly  90 . The belt proceeds to drop downwards and then upwards to form a U-shape around the cross sealer  72  following the idler rollers on the carriage assembly, which are  902 ,  904 , and  908  respectively. From the idler roller  908  to idler roller  88 , the belt is flat and coplaner with the side seal and the in-feed conveyors,  60  and  20 , of the packaging machine  10 . At idler roller  88 , the packages may optionally be passed into a heat shrinking tunnel or other machine if desired. From the idler roller  88  the path of the belt continues back to the drive roller via another idler roller  86 . It will be noted that because idler rollers  902 ,  906 ,  904 , and  908 , are mounted on the carriage assembly  90 , the “U” formed by the belt will reciprocate back and forth traveling with the carriage assembly  90 . Further, because the aforementioned idler rollers are positioned on the carriage assembly, there is no possibility of the conveyor belt interfering with the operation of the cross sealer  72 , which is also fixed to the carriage assembly.  
         [0057]    Referring now to FIG. 2, the drive system for the conveyor belt of the traveling end sealer  70  is an extension of the system used to drive the side seal conveyer  60 . The main drive motor  102  applies power to the pulley  104 , which in turn drives the pulley  114 , by means of the main drive belt  106 . The main drive belt is equipped with the idler pulley  108  to eliminate slack. The pulley  114  is mounted on the power transfer shaft  110 . The power transfer shaft drives a PTO pulley  112  which in turn drives the traveling end sealer conveyor belt drive roller  84  via a pulley  128  and belt  130 . The pulley  128  is mounted on the shaft of the drive roller  84 . Belt  130  is tensioned by a tension pulley  132 .  
       Carriage Assembly Drive  
       [0058]    Referring now to FIG. 2, the reciprocating operation of the carriage assembly  90  is explained below. The drive motor  102  of the power transmission system  100  operates continuously to drive the side sealer  50  and the side seal and traveling end seal conveyor systems  60  and  80  as explained previously. The same motor  102  is also used to provide forward motion of the carriage assembly. The motor  102  drives a pulley  132 , which in turn drives a pulley  156 , and a belt  134 . Tension is maintained in the belt  134  via a tension pulley  136 . The pulley  156  is on a common shaft with a variable input pulley  160  which in combination with a mating output pulley  162 , and belt coupling the pulleys, forms part of a continuously variable transmission  138 . The reduction ratio of the continuously variable transmission is controlled by a lever  158 . Essentially, for any given input pulley speed the continuously variable transmission allows an operator to selectively control the output pulley speed. Therefore, the speed of the carriage assembly may be synchronized with the conveyor systems.  
         [0059]    Continuously variable transmissions utilizing variable pulleys are known to those skilled in transmission design. Variable pulleys of the type used to make the continuously variable transmission incorporated in the film wrapping machine of the present invention are available from Speed Selector Corporation.  
         [0060]    Power from the output pulley  162  of the continuously variable transmission  138  is used to drive the input pulley  160  of an electromagnetic clutch  142 . All components of the carriage drive up to the input pulley  160  of the electromagnetic clutch are continuously driven via the drive motor  102 . All drive system components subsequent to the clutch experience intermittent operation.  
         [0061]    An electromagnetic or partial revolution clutch is a type of clutch that will make a single or partial revolution upon being energized and will automatically de-energize after the single or partial revolution is complete. The partial revolution clutch  142  used in the present invention revolves about  110  degrees before being de-energized by the second electrical signal triggered by the limit switch  152 . Such clutches are available commercially. Borg-Warner Corporation of is one such source.  
         [0062]    The partial revolution clutch  142  is energized to make a mechanical connection between the input pulley of the clutch  160  and a corresponding output pulley  164  in response to the first electrical signal from the photocell  154 . As stated previously, an energizing electrical signal is produced by the photocell when the light beam from the light source  155  is interrupted by a package moving along the end seal conveyor. Once a package breaks the light beam, an electrical signal from the photocell energizes the clutch. (It should be noted that the photocell simultaneously energizes the clutch and the rotary air cylinder  722  (FIG. 11)). The clutch subsequently rotates  110  degrees counterclockwise thereby rotating a bell crank  148 , via a pulley  146  and the output pulley  164 , which are coupled by a drive belt  166 . The drive belt  166  is tensioned by a tension pulley  168 . Counterclockwise rotation of the partial revolution clutch produces counter clockwise rotation of the bell crank  148 , which in turn pushes the first pushrod  126  forward, causing the traveling end sealer  70  to move forward.  
         [0063]    The bell crank  148  and the pulley  146  are mounted on a shaft  144 , which further includes a cam  150 . Rotation of the shaft  144  in response to rotation of the partial revolution clutch causes the cam to rotate and actuate the limit switch  152 . Once the limit switch is actuated it produces the second electrical signal which activates a linear or pneumatic air cylinder  170  which retracts the bell crank via a second pushrod  172 . Retraction of the bell crank in turn causes the traveling end sealer  70  to be retracted or pulled backwards to its original position. The second electrical signal produced by the limit switch simultaneously de-energizes the partial revolution clutch. The clutch remains de-energized until a subsequent package triggers the photocell  154 .  
       Relationship of Cross Seal Motion to Carriage Motion  
       [0064]    Referring now to FIGS. 2 and 11, in the wrapping machine of the present invention  10 , the cross bars  712  and  714  of the cross seal mechanism  72  are caused to close and open in synchronism with the reciprocating longitudinal motion of the carriage assembly  90 . This process occurs as follows. Once a package breaks the light beam to the photocell  154 , the first electrical signal actuates the rotary air cylinder  722  in a clockwise direction causing the sealing bars to close on the film to be sealed. Simultaneously, the first electrical signal from the photocell causes the partial revolution clutch  142  to actuate, which thereby drives the carriage assembly  90  forward. Since the end seal assembly is mounted to the carriage assembly, the now closed jaws travel forward with the carriage, which is synchronized to move at about the same velocity as the film enclosed packages. As the partial revolution clutch completes its 110 degrees of revolution, forward motion of the carriage assembly stops and the cam  150 , which is mechanically linked to the clutch as described in the section on the carriage assembly drive, actuates the limit switch  152 . The second electrical signal generated by the limit switch actuates both the rotary air cylinder of the cross seal assembly and the linear air cylinder  170  of the carriage drive and de-energizes the clutch. The rotary air cylinder is actuated in the counterclockwise direction thereby causing the cross seal bars to open, releasing the now sealed and severed film, and the linear air cylinder is caused to retract thereby moving the carriage assembly back to its initial starting or rest position. This cycle of operation is repeated each time a package breaks the light beam of the photocell.  
       Conclusion  
       [0065]    It is apparent from the foregoing description of the high speed wrapping machine, where reference is made to the control of pneumatic or air cylinders actuating certain devices such as the cross sealer and the carriage assembly, where reference is made to photoelectric cells actuating the air cylinders and an electromagnetic clutch, and where reference is made to the motor controlled feed of film and the driving of various conveyors and the like, that electrical and electronic controls for such devices may be assembled from control devices known to those skilled in the art. Since the function of the various motors, air cylinders, clutch, photocell, and the like have been described in detail, it is believed that those skilled in the art will not need a detailed description of the electrical and pneumatic circuitry whereby these elements are interconnected to practice this invention.  
         [0066]    Also, a photocell has been used to trigger the operation of the cross sealer and carriage assembly in the exemplary embodiment because it has been found that this form of control is most convenient when packages are to be wrapped which change in length from run to run. However, limit switches or other types of mechanical and electro-mechanical switches may also be used. In the event of a single production machine, however, such as machines wrapping video cassettes, it should be understood that the end sealer may be linked to the main drive of the machine and synchronized with the inflow of video cassettes to the machine without requiring photocell initiation of the end sealer.  
         [0067]    While only the presently preferred embodiment has been described in detail, as will be apparent to those skilled in the art, modifications and improvements maybe made to the device disclosed herein without departing from the scope of the invention. Accordingly, it is not intended that the invention be limited except as by the appended claims.