Abstract:
Stretch band wrapping apparatus having, in cooperative action with a rotary load support platform and film roll supporting spool, a restraining brake on the spindle, and an elongated, controlled-restraint tension roll intermediate the spindle and platform. The tension roll has a friction surface engaging the width of the film stock unrolled from a roll of film on the spindle, and a restraining brake, the film being kept in engagement with the friction surface by a slight braking action on the spindle, such that a constant tension is applied across the width of the film during stretch wrapping of a load rotating on the platform.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to equipment for stretch band wrapping pallet loads with stretch film. 
     Various machines are presently marketed for stretch band wrapping palletized loads with a stretchable polymer. Multiple layers of the polymeric film are wrapped around the load by rotating the load on a platform while restraining the film feed to cause the film to stretch and wrap tightly. The film is supplied from a roll of film initially having a diameter of several inches, typically about 8 to about 20 inches in diameter. The width of the roll or rolls can vary from about 20 inches to 110 inches. The roll is usually positioned on a vertical spindle parallel to the rotational axis of the pallet load. 
     One known technique for restraining the film is to apply a constant torque braking force to the central rotating spindle that mounts the roll of film. But, as the roll of film decreases in diameter, the tension on the film extending from the periphery of the roll to the load increases. This is undesirable. Because of this characteristic, another technique sometimes employed is that of pressing a plurality of spaced braking wheels against the outer surface of the film roll. But the web portions between the wheels are subjected to different tensile forces than those portions engaged by the wheels, thereby applying undesired diagonal tension forces to the film. 
     SUMMARY OF THE INVENTION 
     The present invention constitutes a stretch film wrapping machine which subjects the wrapping film to uniform tension regardless of the diameter of the film roll being unwound, and applies it over the full width of the film stock. A special tension roll is located between the roll support spindle and the load, such having a constant diameter friction surface engaging the width of the unwound film being fed to the revolving load. A braking force applied to the tension roll causes its surface to have a controlled constant braking force applied to the passing film. The film is maintained in engagement with the tension roll friction surface by the support spindle having a restraining brake applying a small constant restraint to prevent excess film unrolling from the roll to maintain the engagement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspecitve view of a preferred form of the novel apparatus viewed from the front and one side; 
     FIG. 2 is a rear elevational view of the apparatus; 
     FIG. 3 is a side elevational view of the apparatus, from the opposite side to that viewed in FIG. 1; 
     FIG. 4 is a plan view of the apparatus; and 
     FIG. 5 is a perspective view showing the apparatus with a palletized load to be wrapped. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now specifically to the drawings, the stretch band wrapping apparatus 10 includes a framework composed of a horizontal base 12 and an upright support 14. The base 12 depicted is basically rectangular, composed of a pair of interconnected parallel legs 13 and 13&#39;. The upright 14 depicted is basically rectangular, having a pair of upright columns 15 and 15&#39; connected by cross beam 17. This can be varied. Mounted on base 12 is a rotational horizontal platform 16. The platform is peripherally supported by a plurality of rollers 24 (FIG. 3) mounted in respective yokes 25. 
     This platform 16 is forcibly rotated by power rotating means 22 therebeneath such as an electric motor or the equivalent. This rotates shaft 18 at the center of the platform. Platform 16 is adapted to receive a pallet P (FIG. 5) having a load L of stacked cartons or the like thereon, both being placed there by a lift truck, a conveyor, or the equivalent, for stretch band wrapping thereof. 
     Mounted laterally adjacent this platform is a vertical spindle or spool 26 for supporting a roll of stretch film. This spindle includes a lower horizontal support plate 28 and a central upstanding shaft 30 preferably having tapered portions 32 and 34 at the lower and upper ends thereof for interfitting with the central sleeve of the roll of film F (FIG. 4). This spindle is rotational on underlying central shaft 36 supported in an upper anti-friction bearing 38 and on a lower thrust bearing 40. At the base of this shaft, functionally cooperative with the spool, is a restraining brake 42 (FIG. 2). This spindle assembly is supported on a cross beam 46, the ends of which are attached to a pair of roller chains 48 and 48&#39; extending around lower sprockets 50 and 50&#39; and upper sprockets 60 and 60&#39;. The upper sprockets are mounted on a rotational shaft 62 interconnected to a reversible drive motor 64 to raise or lower cross beam 46 within guides 66 and 66&#39; and thereby raise and lower the roll of film F. This enables the spool and film to wrap vertically successive portions of the pallet load in helical overlapping fashion in a manner to be understood from the full description hereof. 
     Above platform 16 and cooperative therewith is an optional upper platen 70 for stabilizing a load on a pallet while being wrapped. This stabilizing unit is vertically shiftable to engage the top of the load as depicted in FIG. 5. When so engaged, it applies a biasing force as a result of a compression coil spring 72 around suspension shaft 76 and between the upper side of platen 70 and the lower side of cantilever beam 75 which extends from cross beam 74 and supports the platen (FIG. 2). Shaft 76 is rotational as well as axially movable in beam 75 to allow the upper platen to rotate with the palletized load during wrapping. The opposite ends of cross beam 74 are supported on a pair of chains 80 and 80&#39; which extend around lower sprockets 82 and 82&#39; and upper sprockets 84 and 84&#39;. The upper sprockets are mounted to a cross shaft 86 suspended in bearings and rotationally driven by a motor and gear box unit 88 which is reversible to raise and lower cross beam 74 within guides 90 and 90&#39;. The cross beam in turn raises and lowers the shaft 76 which supports the depending upper platen. 
     In this novel apparatus, the special tension roll assembly 100 is positioned to be functionally between the film support spindle and the pallet supporting platform. This assembly includes a vertical tension roll 102 positioned generally between the platform and spindle, but laterally offset therefrom so as to cause the advance path of the film to include a bight at the peripheral surface of the vertical tension roll 102. The film engages a substantial portion of this surface. This peripheral surface constitutes a friction surface. It can be coated with any of a variety of films to have the desired amount of friction to suit the particular film stock. This tension roll assembly is physically supported on the same cross beam 46 as the spindle, causing both to be raised and lowered simultaneously during the stretch band wrapping of the load. This tension roll is mounted in a yoke 106 rotationally supporting the upper and lower ends of the roll. The yoke in turn is attached to the cross beam 46. At the upper end of roll 102 is a variable, electromagnetic, restraining brake 108 controllable as to the degree of resistance applied to resist rotation of this roll as the web is pulled therearound during rotation of the load. 
     This equipment may be controlled through control panel 114 of coventional type. The structure may also optionally include a protective screen and frame 116 for personnel safety. 
     In operation, a roll of stretch film stock F is placed on the spool 26 by lowering it down onto the spindle 30 until it rests on plate 28. A palletized load on a pallet P is then placed as by a lift truck on platform 16. If the optional upper platen assembly is employed, it is lowered until platen 70 engages the stacked items and then lowered a small amount more to compress coil spring 76 and thereby apply a controlled bias to the stack. This stabilizer is lowered by operating motor 88 to rotate shaft 86, advance roller chains 84 and 84&#39;, cross beam 74 mounted on the chains and thus shaft 76 that supports platen 70. 
     Film stock is then advanced from the roll on the spindle, around the periphery of tension roll 102 in the manner depicted in FIG. 4, forming a bight to cause maximum engagement of the film stock with the roll for the governing effect described hereinafter. The film is then held in engagement with the palletized load L, e.g. manually, while the load is rotated with motor 22 until at least one complete wrap has been made. During this time, the braking action on the spindle prevents uncontrolled unwinding of the film from the roll of film F. After a complete revolution of the wrapped film on the stack, typically at the bottom, the electromagnetic brake 108 on the tension roll is activated to apply a predetermined restraining force while the platform and palletized load thereon continue to be rotated, using the gear motor 22. 
     The restraining effect of tension roll 102 has a constant restraining force on the stretch film being wrapped around the load. Thus, even though the diameter of the roll from which the film is being taken constantly decreases, the stress applied to the film actually being stretched remains constant. The braking action applied to the spool and thus to the roll of film is just sufficient to prevent uncontrolled unwinding of the film. The combination of these components prevents constantly changing tension being applied to the stretch film. In the form of the apparatus depicted, the stretch banding operation proceeds by causing the spinlde with its roll thereon, and the tension roll, to vertically raise and thereby feed the stretch film to vertically successive portions of the load for band wrapping the entire load from the bottom to the top and then preferably reversing to again wrap from the top to the bottom. 
     When the complete load is wrapped, the brake for the spindle is actuated to stop the spindle completely and thereby cause the stretch film to snap at a controlled location, whereupon the vertical stabilizer 70 is raised and the wrapped palletized load can be removed by a lift truck from the apparatus. 
     It is recognized that the specific physical embodiment of the overall structure may be varied somewhat to suit the particular circumstances and design requirements. Thus, in some instances it is not always necessary to employ the upper stabilizer platen. Further, the pair of upright columns 15 and 15&#39; can be substituted by a single column having a chain to drive the support element for the spindle and tension roll during the vertical movement thereof. It is possible for some operations to have the film spindle and film roll thereon stay vertically stationary. The tension roll can also be kept vertically stationary. There can be more than one film roll spindle, e.g. two, offset vertically of each other, to supply film for wrapping at different vertical levels. These can use the same tension roll by being of a length to overlap both film rolls so that two lengths of film extend around the same tension roll and onto the stacked load of articles on the platform. These are some illustrative variations.