Abstract:
A perforated palletizing sheet  10  and method for forming such palletizing sheets  10  for receiving, handling, storing and shipping unitized loads. The method includes placing at least one perforation  18  in a upper surface  14  of the palletizing sheet  10 . The size, shape, number, and placement of perforations  18  acting to prevent formation of a vacuum between adjacent sheets such that when an attempt is made to transfer the top palletizing sheet  10  from a stack thereof, only the top sheet is transferred.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority to copending U.S. provisional application entitled, “Fibreboard Sheets With Vacuum Breaking Perforations,” having Ser. No. 60/234,729, filed Sep. 22, 2000, which is incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates to palletizing sheets for receiving, handling, storing and shipping a unitized load product and, more particularly, to an improved palletizing sheet for use in automated palletizing systems.  
         BACKGROUND OF THE INVENTION  
         [0003]    In many applications, product, e.g., cartoned or bagged product, is unitized to achieve economies by receiving, shipping, handling and storing the product in bulk loads. For many years, these unitized loads were carried on conventional hard wood pallets. The wooden pallet system for handling unitized loads was adopted and became the most popular system initially because the wood pallet was low in cost, availability of wood was adequate, and it was easy to handle the product on the wooden pallet with a standard forklift truck. However, the use of wooden pallets has suffered from a number of disadvantages. These include high initial investment cost, problems in inventorying and storage, high cost of pallet maintenance to keep the pallets in service, high cost of pallet replacement, problems of lost pallets, and high weight and volume which add significant cost to shipment and space requirements for storage of the pallets. Because wooden pallets are rather bulky and require large amounts of space for storage, they are often stored in the outside environment between uses. As such, they are susceptible to the elements and infestation by both rodents and insects, which can ultimately lead to infestation of the products to be palletized. As well, wooden pallets can also cause damage to the load during handling and storage, for example, by nails and broken boards rupturing packages mounted on the pallets.  
           [0004]    For these and other various reasons, the palletizing sheet method of handling unitized loads was adopted and its use has continued to expand up to the present day. A palletizing sheet is a thin sheet of material that is of a length and width generally the size of the unit load. Various constructions of palletizing sheets perform different functions within the palletizing process. For example, there are those palletizing sheets upon which an entire unitized load is placed, and there are those sheets that are placed between the various layers of a given load. The former are often referred to as slipsheets, and the latter as tiersheets. Slipsheets typically have one or more “pull tabs” which extend about three or four inches beyond the load, allowing the slipsheet to be gripped and pulled onto the platens of a forklift truck with the aid of a gripper or push-pull attachment mounted to the forklift truck. Typically, the slipsheets are provided with pull tabs on adjacent sides allowing the load to be picked up either from the front or the side for convenience of loading and full utilization of trailer width. However, they can be made with any number of tabs. Tiersheets, on the other hand, typically do not require pull tabs because they are placed between the various layers of a load.  
           [0005]    In the palletizing or unitizing process, a stack of palletizing sheets is typically provided for use in assembling multiple loads. The sheets are sequentially picked up and transferred one by one to a loading area, and the load unitized on the palletizing sheet for shipment. Typically, the top palletizing sheet of the stack is removed from the stack and transferred to the loading area by means of a suction gripping apparatus. This is a device that includes one or more gripping heads to which suction is applied. The suction causes the gripping heads to grip the upper surface of the top palletizing sheet. The gripper with attached palletizing sheet is then transferred to the loading and/or palletizing area where the suction is released, in turn releasing the palletizing sheet. The gripper is then moved back to the stack of palletizing sheets to grip the sheet now at the top of the stack, and the process is repeated. The load to be palletized is placed on the palletizing sheet, which has been transferred, and that load is secured such as by stretch wrapping. As noted above, the palletizing sheet underlying the entire load is the slipsheet, and tiersheets may or may not be used within the load to separate various layers. The palletized load, along with its underlying slipsheet, is then transferred to a storage or transport area. Once this load is removed, the next palletizing sheet is gripped by the transfer apparatus and transferred to the loading and/or palletizing area. This transfer process from the stack of palletizing sheets to the loading area continues until the stack is exhausted.  
           [0006]    A major problem that has been observed with this method of transferring palletizing sheets is that, often, a vacuum exists between the top palletizing sheet and subsequent sheets. Consequently, the vacuum may cause one or more sheets, in addition to the top palletizing sheet, to be transferred to the palletizing area at the same time. Generally, this problem occurs in palletizing sheets having a thickness on the order of between 0.02 inch to 0.120 inch. As a result, there exists a significant problem in handling and transporting palletizing sheets using the suction gripping method of transfer.  
           [0007]    Prior art attempts to solve this problem have included embossing or lightly dusting the surfaces of the palletizing sheets in an effort to allow airflow between adjacent sheets. Although such methods have reduced the problem of multiple palletizing sheet pick-ups, they have not eliminated the problem.  
         SUMMARY OF THE INVENTION  
         [0008]    The problem of multiple palletizing sheet transfer described above is overcome without the use of embossing rollers or the added processing step of applying fine dust to the boards. In accordance with the present invention, the palletizing sheets are provided with at least one perforation that extends from the upper surface to the lower surface of each palletizing sheet. The perforations are such that when the palletizing sheets are stacked upon one another, the perforations form an airflow passage between the upper surface of the top palletizing sheet and the bottom surface of the top sheet, which is in contact with the upper surface of the adjacent palletizing sheet. By so providing, any potential vacuum existing between adjacent palletizing sheets during suction transfer will be negated and the transfer of individual palletizing sheets, one at a time, will be possible. The perforations are normally placed on the palletizing sheet such that it will not be within the area on the palletizing sheet contacted by the suction gripper apparatus.  
           [0009]    Palletizing sheet formation is well known in the prior art. Numerous means may be adequate for forming the perforations required in the present invention. However, a preferred embodiment of the present invention would include palletizing sheets which are cut to the desired size. After the palletizing sheet is the desired size, the desired number of perforations would be die cut at the necessary locations and in the necessary shapes and sizes.  
           [0010]    These and other objects and advantages of the details of construction will become apparent upon reading the following description of the illustrative embodiment describing the principles of the present invention with reference to the attached drawings wherein like reference numerals have been used to refer to like parts throughout the several figures. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    FIGS.  1 A- 1 F are top views of palletizing sheets of the present invention showing various embodiments of perforation shape, number and location.  
         [0012]    [0012]FIG. 2 is a flow chart depicting the process of using palletizing sheets of the present invention in the palletizing/unitizing process.  
         [0013]    [0013]FIG. 3 is a top view of the palletizing sheet as shown in FIG. 1A, showing various placements of a suction gripper apparatus.  
         [0014]    [0014]FIG. 4 is a partial side view of the palletizing sheet as shown in FIG. 1F, along line IV-IV.  
         [0015]    [0015]FIG. 5 is a flow chart depicting a process of producing palletizing sheets of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0016]    Referring now to FIGS.  1 A- 1 F, in the automated palletizing process, a load which is unitized, for example, by taping, tying, gluing, cartoning or stretch wrapping, has a defined unit width and length. A palletizing sheet  10  is the medium upon which the unit load is placed, and is sized in accordance with the size of the load to be placed thereon. Palletizing sheets  10  are often placed between the various layers of the unit load. The underlying palletizing sheet  10  (commonly referred to as a slipsheet) typically has two pull tabs  12 , generally three to four inches in width, on adjacent sides of the palletizing sheet upper surface  14  (defined by edges  16 ) which facilitate transferring the unitized load once it has been placed on the palletizing sheet  10 . However, any shape or number of tabs  12  may be used, and may be configured about the edges  16  of the palletizing sheet  10  as desired. An indentation is often provided consistent with the edge  16  along which a pull tab  12  is attached. Although not necessary, the indentation permits the pull tab  12  to be more readily deflected, thereby allowing a gripper apparatus on a forklift (not shown) to more easily grasp the pull tab. Also, in that the pull tab  12  is more easily deflected, it is less likely to puncture and damage adjacent goods than is a pull tab without the capability to deflect. Those palletizing sheets  10  that are placed between various layers of the unit load (commonly referred to as tiersheets) typically have no pull tabs  12 .  
         [0017]    Note that any number of perforations  18  can be used, and that the location of those perforations can also be varied as desired. Any shape (circular, triangular, square, irregular, etc.) can be used for the perforation  18  so long as adequate airflow is allowed therethrough, thereby negating any potential vacuum that may exist between adjacent palletizing sheets  10  during transfer of the top palletizing sheet  10 . Although various shapes, sizes, numbers and locations, of perforations  18  are within the scope of the present invention, in the preferred embodiment represented in FIG. 1A, the palletizing sheet upper surface  14  has three perforations  18 , one being distributed in each of three comers. In the preferred embodiment, predominantly circular perforations  18 , approximately 0.250 inches in diameter, have been found to perform satisfactorily. Note, however, that the required size of the perforations  18  can vary greatly depending on the number of perforations used, as well as the thickness of the palletizing sheet  10  and the material used in its construction. For example, perforations  18  with diameters ranging from 0.1 inch to 3.0 inches have been found to function adequately without jeopardizing the structural integrity of the palletizing sheets  10 . Although the perforations  18  may be formed at any location on the upper surface  14  of the palletizing sheet, placement in the comers approximately three inches from adjacent edges  16  of the upper surface has been found to perform satisfactorily.  
         [0018]    The palletizing or unitizing process is depicted in FIG. 2. First, as shown in block  200 , a stack of palletizing sheets  10  is provided. Typically, the palletizing sheets  10  of the stack are picked up and transferred to a loading station, one at a time. The top palletizing sheet  10  of the stack is picked up and transferred to the loading area by a suction gripping apparatus, (not shown) as is well known in the art. The suction gripping apparatus typically has one or more gripping heads. As described in block  202 , the suction heads are normally positioned on the upper surface  14  of the top palletizing sheet  10 , such that the gripper heads do not encompass any of the perforations  18 . FIG. 3 shows the palletizing sheet  10  of FIG. 1A with potential placements of the gripper head (not shown) depicted as broken circles. Next, the gripper head is used to create a suction, thereby “gripping” the top palletizing sheet  10 , as described in block  204 . This is the point at which prior art systems experience problems. Because of the tendency for a natural vacuum to form between the top palletizing sheet  10  and those subsequent palletizing sheets  10  in the stack, the simultaneous transfer of multiple palletizing sheets  10  often occurs with prior art systems.  
         [0019]    As previously noted, perforations  18  are used to overcome this problem by “breaking” the natural vacuum that may develop between adjacent palletizing sheets  10 , as described in block  206 . As shown in FIG. 4, as the top palletizing sheet  10  is lifted from the stack, air passes through the perforations  18  (as depicted by the arrows) and between the bottom surface  15  of the top palletizing sheet  10  and the upper surface  14 A of the adjacent palletizing sheet  10 A, thereby preventing the formation of a natural vacuum. As such, only the top palletizing sheet  10  will be lifted and transferred to the loading and/or palletizing area, as described in block  208 . Once in the loading and/or palletizing area, the suction is released, in turn releasing the palletizing sheet  10 . As described in block  210 , once a load is placed on the palletizing sheet  10 , the load and associated palletizing sheet  10  are removed to a storage or transport area. Again, palletizing sheets  10  may also be used between various layers of the load when desired.  
         [0020]    Although numerous materials can be used to produce the palletizing sheets  10  of the present invention (i.e., plastic, nylon, polymers, fibreboard, chipboard), the preferred embodiment includes laminating multiple plies of paperboard material, such as kraft paper. One method of manufacturing palletizing sheets  10  in accordance with the present invention is described in FIG. 5. First, as described in block  500 , multiple plies are laminated together, as in a paster. Next, as described in block  502 , the palletizing sheets  10  are cut to the desired size. Frequently, this is dictated by factors such as load size, load weight, or space available in a transport vehicle or storage facility. Finally, as described in block  504 , the desired number and shape of perforations  18  are created in the palletizing sheets  10  at the desired locations. In the preferred embodiment, the perforations are die-cut; however, other methods or means of providing the perforation or perforations can be employed to produce the same result and are considered to be within the scope of the present invention. In its simplest form, the perforation or perforations could be cut by hand. Single ply or multi-ply palletizing sheets  10  are encompassed within the scope of the present invention. Whether single ply or multi-ply sheets are required will depend on factors such as the material, dimensions and weight of load, etc.  
         [0021]    It should be emphasized that the above-described embodiments of the present invention, particularly, any “preferred” embodiments, are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiment(s) of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.