Abstract:
In one aspect, the present invention contemplates a strapping station that integrates with a machine for wrapping and clamping a strap around a load, particularly a palletized load. The strapping station includes a transfer conveyor and a compression conveyor that is supported to be lowered onto the upper surface of a load to apply pressure to or compress the load during the strapping operation. The compression conveyor is maintained in that position, continuously applying pressure to the load, even as the load is moved for the application of straps at different locations.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to U.S. Provisional Application No. 61/470,749, filed on Apr. 1, 2011, in the name of the same inventors, the entire disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates to conveyor systems and particularly to conveyor systems having a strapping station at which a load is wound with more than one strap to hold the load together. 
         [0003]    Conveyors play a central role in the packaging and transport of sheet products, such as corrugated sheet material. Conveyors carry a newly manufactured sheet to various stations where stacks of sheets are formed and eventually loaded onto pallets for shipment. In some cases, where the sheets are smaller in size, multiple stacks of sheets may be loaded onto a single pallet. Once the sheets have been loaded onto a pallet it is typically necessary to constrain the stacks to retain them on the pallet. Strapping machines are used to automatically wind one or more straps around a palletized load. In most cases, multiple straps are used with the straps spaced uniformly across the length of the load or each stack in a load. The straps are guided through the pallet beams and around the upper surface of the load where they are automatically cinched and clamped in a conventional manner. 
         [0004]    In the strapping operation it is important to squeeze or compress the load as the strap is affixed around the load. Prior art systems drop a platen onto the upper surface of the load, applying the strap while the platen remains on the load. The platen is then lifted and the load is advanced to another location, at which point another strap is applied in the same manner. This process may be repeated two or more times for a given load. One problem that arises is that when the platen is lifted the compression of the load is relieved. Thus, on a load that requires multiple straps, the load will be under an uneven force from the strap during the period when the compression is relieved. This uneven loading can cause damage to the load, particularly on the top sheet. In addition, the first strap applied must be strong enough to hold the entire load under compression while the load is situated to receive additional straps. This requires the straps to be stronger than necessary to constrain the load, requiring more material for the straps than is needed. 
         [0005]    Furthermore, although the load is squeezed again when the platen is dropped for the next strap, the amount of compression is rarely the same. This leads to multiple straps applying varying degrees of compression on the load. In a worst case scenario, greater compression at one strap may lead to loosening and dislodgment of an adjacent strap. Nominally though, the inconsistent compression leads to an uneven load surface which can create problems if loads are stacked or may compromise the quality of the stacked sheets. 
       SUMMARY 
       [0006]    According to aspects illustrated herein, there is provided a strapping station for applying a strap to a load. The strapping station includes a transfer conveyor configured to transport the load to and from a staging area in a travel direction and a compression conveyor above the transfer conveyor in the staging area, including movable conveyor elements configured to apply a compressive force to the load while the load moves in the travel direction. The station contains a strapping machine located in the staging area configured to position the strap around the load while the compression conveyor applies the compressive force to the load. A first conveyor drive system drives at least one of the compression conveyor and the transfer conveyor to move the load in the travel direction while the compression conveyor applies the compressive force to the load. A compression drive system is provided to move the compression conveyor in a compression direction to apply the compressive force to the load. 
         [0007]    In another embodiment, a method of applying a strap to a load comprises positioning a load in a first position on a transfer conveyor in a staging area and engaging a compression conveyor to the load to apply a compressive force to the load. The strap is applied to the load, and the load can then be moved within the staging area while maintaining the compressive force on the load. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a top perspective view a strapping station showing a compression conveyor disengaged from the load. 
           [0009]      FIG. 2  is an end view of the strapping station of  FIG. 1  showing the compression conveyor disengaged from the load. 
           [0010]      FIG. 3  is a side view of the strapping station of  FIG. 1  showing the compression conveyor disengaged from the load. 
           [0011]      FIG. 4  is a top perspective view the strapping station of  FIG. 1  showing the compression conveyor engaged with the load. 
           [0012]      FIG. 5  is an end view of the strapping station of  FIG. 1  showing the compression conveyor engaged with the load. 
           [0013]      FIG. 6  is a side view of the strapping station of  FIG. 1  showing the compression conveyor engaged with the load. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains. 
         [0015]    As shown in the  FIG. 1 , a strapping station  10  is defined by a station frame  12  adjacent a strapping machine S. The strapping machine S includes a frame F that encircles a load L positioned within the station  10 . The strapping machine S and frame F may be any conventional design capable of tightly winding and clamping a strap around a load or a palletized load, such as the automatic strapping machine described in U.S. Pat. No. 4,938,009 to Takami, the contents of which are incorporated herein by reference. 
         [0016]    As shown in  FIG. 1 , the load L is carried by a pallet P. A transfer conveyor  14  is situated at the base of the station frame  12  of the strapping station  10  and integrates into feed and discharge conveyor sections (not shown) to receive and transfer the palletized load to and from the strapping station  10 . As shown in the end and side views of  FIGS. 2 and 3 , respectively, the frame F of the strapping machine passes through the ribs of the pallet P in a conventional manner, as is described by U.S. Pat. No. 2,985,098 to Winkler or U.S. Pat. No. 4,228,733 to Davis et al., the contents of which are incorporated herein by reference. 
         [0017]    The present embodiment contemplates a compression conveyor  20  that is slidably mounted to the station frame  12 . The compression conveyor  20  includes conveyor components suitable for contacting an upper surface U of the palletized load L. For instance, the compression conveyor  20  includes a conveyor frame  22  supporting a series of belts  35  and a conveyor drive  37 . The belts  35  may be preferred for a load composed of sheet material, although other types of conveyor elements, powered and non-powered, are contemplated, provided that the elements allow the load to translate while continuously compressing the load. 
         [0018]    The compression conveyor  20  includes a slide mount  24  incorporated into each end of the conveyor frame  22 . Each slide mount  24  is slidably engaged to vertical beams  16 ,  17  of the conveyor frame  12  and may also incorporate an end fitting  25  adapted to fit within a slot or channel  18  defined in each vertical beam. In the present embodiment, the compression conveyor includes a slot  40  through which the upper portion of the frame F passes to allow the strap to be placed on the load L through the compression conveyor  20 . It can be appreciated that the slot  40  may be defined by a gap between adjacent sections  35   a ,  35   b  of the compression conveyor  35  spaced along the length of the load L. 
         [0019]    A compression drive mechanism  26  is provided to raise and lower the compression conveyor  20  within the station frame  12 , in a direction orthogonal to a travel direction  50 . In one embodiment, the compression drive mechanism  26  includes a compression drive motor  28  mounted to the station frame  12  and a cable system  30  that is fastened to each corner of the compression conveyor  20 , preferably to the end fittings  25  with the cables of the cable system  30  contained within the channel  18 , as shown in  FIG. 3 . It can thus be appreciated that the compression drive motor  28  is operated to lower the compression conveyor  20  onto the upper surface U of the load L when the palletized load is positioned within the strapping station  10 . As conveyor  20  is lowered it passes along the frame F of the strapping machine S via the slot  40 . A reversible motor and appropriate cabling can be used to raise the compression conveyor  20  to relieve the compressive force on the load once the final strap has been applied. In an alternative embodiment, a chain drive system is used in lieu of the cable system. 
         [0020]      FIGS. 4-6  depict the compression conveyor  20  in the position in which the load L is compressed between the transfer conveyor  14  and the compression conveyor  20 . It can be appreciated that the amount of compression that is applied may be based simply upon the weight of the compression conveyor  20 . Alternatively, the compression drive mechanism  26  may be configured to apply a specific force independent of the conveyor weight such that the compressive force exerted on the load L is different from the weight of the compression conveyor  20 . In one embodiment the cabling system  30  is configured to pull down on the conveyor frame  22  with a predetermined force to apply a known amount of pressure to the upper surface U of the load L. Other drive mechanisms may be provided that are capable of actively compressing the conveyor on the load. The compressive force applied to the load L may be stored in a strapping station controller (not shown), such that multiple types of loads may be strapped under uniform compression. 
         [0021]    The compression conveyor  20  is operable to maintain pressure on the load surface U continuously even as the load L is shifted along the transfer conveyor  14  to apply additional straps. Thus, as shown in the side view of  FIG. 6 , with the load L compressed between the two conveyors  14  and  20 , the load is advanced in the travel direction  50  so that the frame F may be aligned with another location along the length of the load. This movement may be accomplished by the compression conveyor  20  by activating the conveyor drive  37  to rotate the conveyor belts  35 . Thus, even as the compression conveyor  20  is maintaining a constant compressive force on the upper surface U, it is also applying a longitudinal force to push the load L toward the discharge end of the station  10 . Depending upon the strapping convention for the particular load, the conveyor drive  37  may be reversible to move the palletized load backward or forward within the station as needed. 
         [0022]    In one specific embodiment, when compression is applied the load L is transferred under power from the compression conveyor  20  only. The transfer conveyor  14  is, in essence, an idler conveyor. In an alternate configuration, both conveyors are powered to move the load L in a coordinated fashion. In yet another configuration, the compression conveyor  20  acts as an idler conveyor, with only the transfer conveyor  14  being powered to move load L in the travel direction  50  while the load L is under compression. The activation of the powered conveyors (such as conveyor drive  37 ) may be controlled by the strapping station controller. The strapping station controller may be pre-programmed for a specific load and a specific strapping pattern, or may maintain a database of load types and strapping patterns that is accessed based on external data about the load. 
         [0023]    Although the illustrated embodiment contemplates a vertical compression, it can be appreciated that one or more compression or transfer conveyors may be placed to compress the load horizontally when applying a strap. For example, compression and transfer conveyors may be placed transverse to the travel direction to compress the load horizontally. 
         [0024]    It is further contemplated that the compression conveyor  20  reflects the nature of the transfer conveyor with respect to the motion capabilities. In particular, the two conveyors may be configured to not only translate but also to rotate the load to apply straps crosswise and lengthwise on the load. Alternatively, the transfer conveyor  14  may be configured to rotate the load with the compression conveyor retracted. 
         [0025]    The conveyor elements of the illustrated embodiment include conveyor belts to achieve a uniform pressure along the load L. Other conveyor elements are contemplated provided the elements can exert a generally uniform continuous pressure on the load L while the load L is translated along the station  10 .