Patent Publication Number: US-2005138897-A1

Title: Low profile conveyor for use in stretch wrapping operations

Description:
This application claims priority under 35 U.S.C. § 119 based on U.S. Provisional Application No. 60/510,083, filed Oct. 10, 2003, the complete disclosure of which is incorporated herein by reference. 
    
    
     DESCRIPTION OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates generally to methods and apparatuses for improving throughput of loads built on and transported with pallet trucks or “pallet jacks,” and more particularly, to providing methods for accumulating and wrapping order-picked loads.  
      2. Background of the Invention  
      High volume distribution warehouses such as WAL-MART®, HOME DEPOT®, and KROGER® utilize a relatively common process to order pick products and load trucks for individual stores. The term “order-picking” refers to the process of assembling one or more loads of products. The process begins with a computer generated “pick list” given to an individual often called a “picker.” The pick list may contain various different types of products, such as bottles, cartons, trays, boxes, bags, plastic totes, drums, yarn spools, or the like. These types of products are typically stacked in rows arranged upon a warehouse floor (see  FIG. 1 ).  
      The picker loads two pallets onto a special battery powered pallet truck. The pallets are normally constructed with a top platform and at least a partial bottom platform, for example, the bottom platform may have spaces between the boards that form the bottom platform. The bottom platform supports the load when stacked on top of another load. The pallets are preferably constructed of wood, but alternatively may be made of plastic. Plastic pallets generally have a series of “legs” rather than a bottom platform (see  FIG. 4 ). The pallets are typically constructed to industry standards, such as GMA standards (see  FIG. 2 ). Alternatively, pallets may be leased from a supplier, such as Chep (see  FIG. 3 ), a well-known pallet supplier.  
      The pallets are positioned on long forks of the pallet truck, one behind the other. The long forks are cantilevered off of the pallet truck, but may include collapsible wheels on their distal ends. The picker maneuvers the forks of the pallet truck through the fork holes (between the top and bottom platforms of the pallet or between the legs of the pallet) with the collapsible wheels in a raised position. After the forks extend through both pallets, the picker raises the pallets off of the ground by hydraulically lowering the collapsible wheels on the forks. The wheels pass through holes in the bottom platform and engage the ground, raising the pallets off of the ground.  
      The picker moves up and down aisles of the warehouse to locate the products on the pick list, pulling each product and placing it on one of the pallets. The process is repeated until the order is finished and a load is built. The resulting load can be homogenous, i.e., contain only one type of product, or non-homogenous, i.e., contain many different types of products of various sizes and shapes. Most often, the pull list requires the formation of non-homogenous loads, which may be very unstable.  
      After the load is built, it must be wrapped to contain the load for shipping. Various packaging techniques have been used to wrap a load of products for transportation, storage, containment and stabilization, protection and waterproofing. One system uses stretch wrapping machines to stretch, dispense, and wrap stretch packaging material around a load. Stretch wrapping can be performed as an inline automated packaging technique which dispenses and wraps packaging material in a stretched condition around a load on a pallet to cover and contain the load. Pallet stretch wrapping, whether accomplished by turntable, rotating arm, or rotating ring typically covers the four vertical sides of the load with a stretchable film such as polyethylene film. In each of these arrangements, relative rotation is provided between the load and a packaging material dispenser to wrap packaging material about the sides of the load.  
      When the load is complete, the picker delivers the load to a stretch wrapping area, typically containing a single stretch wrapping apparatus. Since only one load can be wrapped at a time, the two loads on the pallet truck must be separated. Normally, the picker drops the loads in a staging area or “parking lot” type area, where the load remains until it is picked up and transported to the stretch wrapping apparatus. The transport of the load from the staging area to the wrapping apparatus may be performed by a second worker, often called an “operator.” In addition to transporting the unwrapped load to the wrapping apparatus, the operator must set the unwrapped load aside, remove a wrapped load from the wrapping apparatus and move it to a loading staging area or directly to the truck, then place the unwrapped load on the wrapping apparatus, attach the leading end of the film to the load, and cut the film at the end of the wrapping cycle. This process involves multiple handling of the picked load due to the fact that the picker cannot directly place the load in a wrap zone of the stretch wrapping apparatus. In addition, more than one picker is generally working the warehouse floor, resulting in a large number of unwrapped loads sitting in the staging area, waiting to be transported to the stretch wrapping apparatus. Since typical wrapping stations wrap only one load at a time, the result is a bottleneck at the staging area waiting for the wrapping apparatus, thereby limiting efficiency.  
      While use of a conveyor to feed loads to the stretch wrapping apparatus seems an obvious solution, there have been several failed attempts to do so. Pallet trucks are unable to lift the loads high enough to place the picked loads onto a conventional, above-floor conveyor. Conveyors with lift tables or elevators are available to automate the process. However, such devices require a large amount of space and are mechanically complex and costly to maintain. In addition, conveyors have been placed in pits created in the floor to lower the conveyor to be approximately level with the floor. This requires a large amount of space and the permanent destruction of the floor. In addition, such a process is costly. Due to the widespread use of pallet trucks, manufacturers have not been able to successfully employ either powered or non-powered conveyors to sequence loads around a wrapping operation.  
      In light of these drawbacks, there is a need to reduce the complexity, time, and number of material handling steps necessary to move loads to and from a wrapping station in a simple, reliable, and inexpensive manner.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention is directed to methods and apparatuses for wrapping a palletized load with packaging material which provides advantages and obviates a number of problems in earlier methods and apparatuses for wrapping a load.  
      In accordance with an aspect of the present invention, a low profile conveyor includes at least two non-powered conveyor elements, each conveyor element having a longitudinal axis and including an inner side rail, an outer side rail, and a conveying surface formed by a plurality of rolling elements positioned between the side rails, wherein the longitudinal axis of one of the conveyor elements is parallel to the longitudinal axis of the other of the conveyor elements. The low profile conveyor further includes a base surface positioned between the conveyor elements.  
      Another aspect of the present invention includes a stretch wrapping system for wrapping palletized loads. The system includes a dispenser for dispensing packaging material, means for providing relative rotation between the dispenser and a load to wrap packaging material around the load, a low profile conveyor comprising at least two conveyor elements, each conveyor element having a longitudinal axis and including an inner side rail, an outer side rail, and a conveying surface formed by a plurality of rolling elements positioned between the side rails, wherein the longitudinal axis of one of the conveyor elements is parallel to the longitudinal axis of the other of the conveyor elements. The low profile conveyor further includes a base surface positioned between the conveyor elements, and the stretch wrapping system further includes a powered pusher assembly for moving the load on the conveying surfaces of the at least two conveyor elements.  
      Yet another aspect of the present invention includes a method of wrapping a palletized load with packaging material. The method includes placing a palletized load to be wrapped onto a low profile conveyor comprising at least two non-powered conveyor elements, each conveyor element having a longitudinal axis and including an inner side rail, an outer side rail, and a conveying surface formed by a plurality of rolling elements positioned between the side rails, wherein the longitudinal axis of one of the conveyor elements is parallel to the longitudinal axis of the other of the conveyor element. The low profile conveyor further includes a base surface positioned between the conveyor elements, and the method further includes pushing the load with a powered pusher assembly to move the load on the conveying surfaces of the at least two conveyor elements, and providing relative rotation between a packaging material dispenser and the load to wrap packaging material around sides of the loads.  
      A further aspect of the present invention includes a method of wrapping a palletized load with packaging material. The method includes placing a first palletized load of a dual load carried by a pallet truck onto a low profile load conveyor having at least two non-powered conveyor elements, each conveyor element having a longitudinal axis and including an inner side rail, an outer side rail, and a conveying surface formed by a plurality of rolling elements positioned between the side rails, wherein the longitudinal axis of one of the conveyor elements is parallel to the longitudinal axis of the other of the conveyor elements. The low profile load conveyor further includes a base surface positioned between the conveyor elements. The method further includes placing a second palletized load of the dual load carried by the pallet truck onto the low profile load accumulation conveyor, pushing the first palletized load with a powered pusher assembly to move the first palletized load on the conveying surfaces into a wrapping area, and providing relative rotation between a packaging material dispenser and the first palletized load to wrap packaging material around sides of the first palletized load.  
      Another aspect of the present invention includes a low profile conveyor having at least two conveyor elements, each conveyor element having a longitudinal axis and including an inner side rail, an outer side rail, and a conveying surface formed by a plurality of rolling elements positioned between the side rails, wherein the longitudinal axis of one of the conveyor elements is parallel to the longitudinal axis of the other of the conveyor elements, a base surface positioned between the conveyor elements, and a powered pusher assembly for moving the load on the conveying surfaces of the at least two conveyor elements.  
      Yet another aspect of the present invention includes a stretch wrapping system for wrapping palletized loads. The system includes a dispenser for dispensing packaging material, means for providing relative rotation between the dispenser and a load to be wrapped to wrap packaging material around the load, a first low profile conveyor portion comprising first and second conveyor elements, each conveyor element having a longitudinal axis and including an inner side rail, an outer side rail, and a conveying surface formed by a plurality of rolling elements positioned between the side rails, wherein the longitudinal axis of the first conveyor element is parallel to the longitudinal axis of the second conveyor element. The first low profile conveyor further includes a base surface positioned between the first and second conveyor elements. The system further includes a second low profile conveyor portion comprising third and fourth conveyor elements, each conveyor element having a longitudinal axis and including an inner side rail, an outer side rail, and a conveying surface formed by a plurality of rolling elements positioned between the side rails, wherein the longitudinal axis of the third conveyor element is parallel to the longitudinal axis of the fourth conveyor element. The second low profile conveyor also includes a base surface positioned between the third and fourth conveyor elements, and the system further includes at least one powered pusher assembly for moving the load on the conveying surfaces.  
      Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one embodiment of the invention and together with the description, serve to explain the principles of the invention.  
       FIG. 1  is a top view of a warehouse floor showing a conventional wrapping staging area, stretch wrapping apparatus, and loading staging area;  
       FIG. 2  is a partial isometric view of a GMS pallet;  
       FIG. 3  is a partial isometric view of a Chep pallet;  
       FIG. 4  is an isometric view of a plastic pallet;  
       FIG. 5  is a top view of a warehouse floor showing a load accumulation area, a stretch wrapping apparatus, and a wrapped load staging area according to one aspect of the present invention;  
       FIG. 6A  is a side view of a pallet truck with an elevated palletized load;  
       FIG. 6B  is a side view of the pallet truck of  FIG. 6A  lowering the palletized load onto a low profile conveyor, according to one aspect of the present invention;  
       FIG. 6C  is a side view of the pallet truck of  FIG. 6A  withdrawing from the palletized load with the leg and support wheel in a retracted position, according to one aspect of the present invention;  
       FIG. 7A  is an end view of a low profile conveyor supporting a pallet mounted on forks of the pallet truck, according to one aspect of the present invention;  
       FIG. 7B  is a top cross-sectional view taken along line B-B of the low profile conveyor supporting a pallet mounted on forks of the pallet truck of  FIG. 7A , according to one aspect of the present invention;  
       FIG. 7C  is a side view of the low profile conveyor supporting a pallet mounted on forks of the pallet truck of  FIG. 7A , according to one aspect of the present invention;  
       FIG. 8A  is a partial isometric view of a low profile accumulation conveyor, according to one aspect of the present invention;  
       FIG. 8B  is an enlarged partial view of a conveying surface of the low profile accumulation conveyor of  FIG. 8A ;  
       FIG. 8C  is an isometric view of a shaft and a roller used to form the conveying surface of  FIG. 8B ;  
       FIG. 9A  is a side view of a palletized load being placed onto the low profile conveyor by a pallet truck, according to one aspect of the invention;  
       FIG. 9B  is an end view of the palletized load of  FIG. 9A  being placed onto the low profile conveyor by the pallet truck, according to one aspect of the invention;  
       FIG. 10A  is an isometric view of a stretch wrapping system including a low profile conveyor according to one aspect of the present invention;  
       FIG. 10B  is an isometric view of a pusher arm of a pusher assembly according to one aspect of the invention;  
       FIGS. 11A-11D  are top views of order-picked loads being processed on a stretch wrapping apparatus including a low profile infeed conveyor and a low profile exit conveyor, according to one aspect of the present invention;  
       FIGS. 12A-12D  are cross-sectional end views of various configurations of a low profile conveyor including various surface types and showing relative heights in the different combinations, according to one aspect of the present invention;  
       FIGS. 13A-13B  are top views of various configurations of a low profile infeed conveyor and a low profile exit conveyor used with a rotatable turntable, according to one aspect of the present invention; and  
       FIG. 13C  is an isometric view of a rotatable turntable and a stretch wrapping system used with a system having the configurations of  FIGS. 13A and 13B , according to one aspect of the present invention. 
    
    
     DESCRIPTION OF THE EMBODIMENTS  
      Reference will now be made in detail to the present exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
      The present invention permits pickers to deliver order-picked loads directly to an accumulation conveyor in front of the stretch wrapping apparatus. The accumulation conveyer of the present invention is “low profile” to permit the order-picked loads to be placed directly onto the conveyor with the pallet truck. As used herein, the term “low profile” means that the height of the conveying surface, above a base surface, is less than the distance between the raised bottom pallet surface of a pallet supported by forks of the pallet truck and the base surface when the forks of the pallet truck are in their “raised” position.  
      The present invention describes various surfaces and their heights relative to one another. These surfaces will now be defined.  
      As used herein, the term “base surface” is intended to define the surface between the conveyor elements upon which the pallet truck drives to position and deposit a palletized load onto the conveying surfaces of the conveyor elements. As shown in  FIGS. 12A-12D , the “base surface” may be the floor ( FIG. 12D ), a base plate upon which the conveyor elements and guide element are mounted ( FIG. 12C ), or one or more rolling plates positioned on top of the base plate ( FIGS. 12A and 12B ). If the base surface comprises one or both of a base plate and a rolling plate, it is preferred that the total height of the base surface does not exceed approximately 2 inches above the ground. This is because the load carried by the pallet truck is very unstable, and to drive up a ramp of more that 2 inches is likely to disturb or shift the load. In a preferred embodiment, the base surface, when comprising one or both of a base plate and a rolling plate, is between 0.5 inch and 0.25 inch in height.  
      As used herein, the term “conveying surface” is intended to define a rolling or movable top surface of a conveyor element upon which the load is placed to be moved into a load wrapping area. As shown in  FIGS. 12A-12D , the distance between the top of the conveying surface and the base surface is always less than the distance between the base surface and the raised bottom pallet surface of a pallet supported on forks of a pallet truck, when the pallet truck is on the base surface. As shown in  FIGS. 12A-12D , the conveying elements may be placed on the floor or on a base plate.  
      As used herein, the “guide element surface” is a top surface of a structure centrally positioned between the two conveyor elements. As shown in  FIGS. 12A-12D , the guide element may be positioned on the same surface as the conveyor elements, or may be positioned on a rolling surface if one is provided. The distance between the guide element surface and the base surface is less than a distance between the base surface and the top of the conveying surface so as to prevent the guide element surface from interfering with conveyance of the load on the conveying surfaces.  
      As used herein, the term “raised bottom pallet surface” is intended to define the base of the bottom deck of a pallet when supported by forks of a pallet truck in a raised position. The distance between the raised bottom pallet surface and the base surface is always larger than the distance between the base surface and the top of the conveying surfaces of the conveyor elements to facilitate positioning of the palletized load on the conveying surfaces.  
      As shown in  FIG. 8B , the conveying surface preferably extends no more than one inch above the base surface. Generally, the distance between a bottom surface of the pallet and the ground when the forks of the pallet truck are in their “raised” position is between about 0.5 inch and 4 inches. Therefore, the conveying surface may extend between approximately 0.5 inch and approximately 3.5 inches above the base surface, but preferably is approximately 1 inch above the base surface. It is important to note that the height of the conveying surfaces cannot be so small that the conveying surfaces cannot support the weight of the load. An example follows.  
      A typical pallet truck may be able to raise its forks approximately 9 inches above the ground. The pallet truck supports a palletized load on its forks. The pallet supporting the load is generally about 6 inches in height, with a top platform and a bottom platform each having approximately 0.5 inch height. The forks of the pallet truck extend between the top and bottom platforms of the pallet to support the load. Therefore, assuming the forks are raised to their maximum height, approximately 5-5.5 inches of pallet hang down from the forks and above the ground, leaving approximately 3.5-4 inches of clearance between the raised bottom pallet surface and the ground. However, it is important to note that it is very rare to transport an order-picked load with the forks raised to their maximum height due to the instability of the order-picked load. Instead, it is common to transport the load with the bottom of the pallet as close to the ground as possible, for example, a 0.5 inch above the ground.  
      The low height of the conveying surfaces is important not only for placing the load onto the conveying surfaces as discussed above, but also for permitting the forks of the pallet truck to be withdrawn from the pallet fork holes after the load is positioned on the conveying surfaces. As noted above, a pallet generally has a height of 6 inches, with top and bottom platforms representing approximately 0.166 of that height. That leaves approximately 5 inches of space for the forks of the fork truck. The forks of the fork truck include a leg with a support wheel to help carry the load. The support wheel extends outward from the bottom of the pallet to the ground. The support wheel is not hydraulically retractable, but instead is “pushed” even with the fork into a retracted position by releasing hydraulic fluid pressure and by the weight of the load.  
      Thus, when the load is positioned on the conveying surfaces, the distance between the raised bottom pallet surface and the base surface cannot be so great that the pallet truck cannot withdraw the forks from the fork holes in the pallet. In addition to overcoming the distance between the top of the conveying surface and the base surface, the leg and support wheel must also be withdrawn over the bottom deck of the pallet. Thus, if the bottom deck of the pallet is 0.5 inch thick, and the top of the conveying surfaces is approximately 1 inch above the base surface, the leg and wheel must be withdrawn upwards 1.5 inches. If the height is greater than this, the leg and wheel will tend to grab the pallet, rather than be pushed up into the forks as the forks are withdrawn, preventing withdrawal of the forks.  
      The present invention also provides a wrapped load accumulation conveyor to convey the wrapped loads away from the stretch wrapper. Both accumulation conveyors are preferably non-powered, thereby providing an inexpensive means for moving the loads. These accumulation conveyors may be incorporated into any stretch wrapping system, but are particularly suited for systems which use pallet trucks or pallet jacks.  
      According to one aspect of the invention, a low profile accumulation conveyor is provided. As embodied herein and shown in  FIGS. 8A-8C , the accumulation conveyor  100  may include two conveyor elements  110 . Each conveyor element  110  includes a non-powered rolling conveying surface  111 . Each conveying surface  111  may be formed by a plurality of non-powered rollers  112 , each roller  112  being mounted on a shaft  114 . In one example, the non-powered rollers have a 0.75 inch diameter and are supported on 0.5 inch diameter shafts. Alternatively, it is possible that the conveying surfaces  111  may not be a roller surface, but instead may be some other low-friction surface. For example, instead of non-powered rollers  112 , the conveying surfaces  111  may use drag chains, belts, transfer ball bearings, or other non-powered low friction elements such as a smooth surface. Each conveyor element  110  includes a pair of side rails, an inner side rail  120  and an outer side rail  118 . The shafts  114  may be mounted in the rails  118 ,  120  in any suitable way, for example, with slots in the rails to support the rollers  112 .  
      Each of the conveyor elements  110  includes a longitudinal axis  110   a  and the conveyor elements  110  are positioned parallel to one another such that their longitudinal axes  110   a  are parallel. The conveyor elements  110  are spaced apart from one another a sufficient distance to permit the forks of a pallet truck to fit between the respective inner side rails  120  of the conveyor elements  110 . The conveyor elements  110  are also positioned close enough to one another that at least a portion of each of the outer side edges of the pallet supporting the load are positioned on the conveying surfaces  111  of the conveyor elements  110 , as shown in  FIG. 9B .  
      The conveyor elements  110  may be positioned on the floor or mounted on a base plate  116 . If mounted on a base plate  116 , the base plate  116  may include a tapered end  117  to facilitate access by the pallet truck. Preferably, the base plate  116  extends no more than approximately 2 inches above the ground to facilitate the pallet truck driving onto the base plate with an unstable load. More preferably, the base plate  116  extends approximately 0.25 inch above the ground. The pallet truck can drive up the tapered end  117  of the base plate  116  to deposit the load(s) onto the conveying surfaces  111  of the conveyor elements  110 . Regardless of whether a base plate  116  is used, it is also possible to utilize one or more rolling plates  113  (see  FIGS. 12A and 12B ). The purpose of the rolling plate  113  is to reduce the distance between the top of the conveying surface  111  of the conveyor elements  110  and the base surface. When rolling plates  113  are used, they become the base surface. Rolling plates  113  may be placed directly on the floor or on top of the base plate  116 .  
      The accumulation conveyor  100  may also include elements for guiding the forks of the pallet truck. As embodied herein and shown in  FIG. 9B , the guide elements for guiding the forks of the pallet truck may include a raised center structure  122 . The raised center structure  122  may be centered between the inner side rails  120  of the conveyor elements  110 . If a base plate  116  is used, the center structure  122  may be positioned on the base plate  116 . If rolling plates  113  are used, the center structure  122  may or may not be positioned on the rolling plates  113  (see  FIGS. 12A and 12B ).  
      Preferably, the distance between the top of the raised center structure  122  and the base surface is less than the distance between the tops of the conveying surfaces  111  of the conveyor elements  110  and the base surface. This prevents the palletized load  124  from resting on the raised center structure  122  when the load  124  is placed on the conveying surfaces  111  of conveyor elements  110 , which might create friction resistance to forward movement of the load  124  on the conveying surfaces  111 . Raised center structure  122  may include tapered edges  123 . The raised center structure  122  may have any length suitable. For example, the raised center structure  122  may extend for the entire length of the accumulation conveyor  100 , or it may be the approximate length of the forks of the pallet truck. Raised center structure  122  cooperates with inner side rails  120  of the conveyor elements  110  to guide the forks of the pallet truck, keeping the forks of the pallet truck between the raised center structure  122  and the inner side rails  120 . This prevents the fork truck from moving onto the conveying surfaces  111  of the conveying elements  110  and helps to position the outer side edges of the palletized load  124  with respect to the conveying surfaces  111 .  
      Although less preferred, it is also possible that the low profile conveyor includes only one conveyor element  110 . In such an embodiment, the conveying surface must be wide enough to support the load and narrow enough to permit the forks of the fork truck to move on either side of the conveyor element  110  to deposit the load on the conveying surface  111 . Alternatively, more than two conveying elements  110  may be used to form the low profile conveyor.  
      According to another aspect of the invention, the load accumulation conveyor  100  is provided with a load pusher assembly  150  for moving the load on the conveying surfaces  111  of the conveying elements  110  to a stretch wrapping apparatus. Such a pusher assembly is disclosed in U.S. Patent Application Publication No. 2002/0056253 entitled “Method and Apparatus for Wrapping a Load,” the entire contents of which is incorporated herein by reference. In a preferred embodiment, the pusher assembly  150  includes a pusher bar or arm  151 . Pusher arm  151  is preferably located alongside the load accumulation conveyor  100  and a stretch wrapping apparatus. As shown in  FIG. 10B , pusher arm  151  includes a pusher carrier  154  that rides on a pusher guide  156  and is powered by a pusher drive  158 . In a preferred embodiment, the pusher arm  151  may be a rotating bar mounted to a linear bearing. The pusher arm  151  may have a first travel position where the arm is upright and vertical, and a second pushing position where the arm is lowered and horizontal.  
      Alternatively, a motor with integrated gear box may be attached to pusher carrier  154  to drive pusher arm  151  along the pusher guide  156 . In such an embodiment, the motor drives the rotation of the pusher arm  151  about a center of rotation as determined by the carrier frame  154 . Thus, pusher arm  151  is moveable between an upright travel position and a horizontal pushing position.  
      Referring to  FIG. 10B , pusher arm  151  preferably has an “L” shape, and is configured such that a guiding leg  151   b  of the “L” moves along pusher guide  156  that forms a track for pusher carrier  154  which carries pusher arm and moves it along the guide. Pushing leg  151   a  of pusher arm  151  extends across the conveying surfaces  111  when in the pushing position, i.e., horizontal and lowered position. In a preferred embodiment, the pushing leg  151   a  is of a length greater than or equal to the width of the load to be pushed. However, it is possible to reduce the length of the pushing leg  151   a  while still moving the load in the desired manner. Pusher arm  151  may be made of any material of sufficient strength and rigidity to move loads, such as steel. In addition, when more than one load is to be placed on the accumulation conveyor  100 , it may be desirable or necessary, dependent upon the configuration of the conveyor  100 , to use more than one pusher arm  252   a ,  252   b , to move the load, as shown in  FIGS. 11A-11B . In such a case, it may be desirable to provide one rotatable pusher arm, and one non-rotatable or fixed pusher arm. When two or more pusher arms are used, it may be desirable to link them to one another such that they act in concert.  
      Pusher arm  151  is moveable between an upright, vertical position and a lowered, horizontal pushing position. Pusher arm  151  preferably remains in the upright position unless engaging and moving a load between positions, for example, from an accumulation area to a wrapping area. The movement of pusher arm  151  may be controlled in any suitable way. For example, movement may be controlled by simple logic programming. In addition, it may be preferable to provide a signal or flag to determine whether there is a load already on the wrapping area. If there is a load on the wrapping area, the pusher arm  151  will not move another load the from accumulation area to the wrapping area.  
      According to another aspect of the invention, the accumulation conveyor  100  may be incorporated into a stretch wrapping system  200 . As embodied herein and shown in  FIGS. 11A-11D , the stretch wrapping system  200  may include a low profile conveyor including a load accumulation area and a load wrapping area, a packaging material dispenser, means for providing relative rotation between a load and the dispenser, and a load pusher assembly for moving the load between the load accumulation area and the load wrapping area.  
      According to one aspect of the invention, system  200  includes a low profile conveyor  201  including a load accumulation area  225  and a load wrapping area  230 . As embodied herein and shown in  FIGS. 11A-11D , the accumulation conveyor  201  includes two conveyor elements  210 . As shown in  FIGS. 8A-8C , each conveyor element  210  may include a non-powered conveying surface  211 . Each conveying surface  211  may be formed by a plurality of non-powered rollers  212 , each roller  212  being mounted on a shaft  214 . In one example, the non-powered rollers have a 0.75 inch diameter and are supported on 0.5 inch diameter shafts. Alternatively, it is possible that the conveying surfaces  211  may not be a roller surface, but instead may be some other low-friction surface. For example, instead of non-powered rollers  212 , the conveying surfaces  211  may use drag chains, belts, transfer ball bearings, or other non-powered, low friction elements such as a smooth surface. Each conveyor element  210  includes a pair of side rails, an inner side rail  220 , and an outer side rail  218 . The shafts  214  may be mounted to the rails  218 ,  220  in any suitable way, for example, with slots in the rails  218 ,  220  to receive the shafts  214  that support the rollers  212 .  
      Each of the conveyor elements  210  includes a longitudinal axis  210   a  and the conveyor elements  210  are positioned parallel to one another such that their longitudinal axes  210   a  are parallel. The conveyor elements  210  are spaced apart from one another a sufficient distance to permit the forks of a pallet truck to fit between the respective inner side rails  220  of the conveyor elements  210 . The conveyor elements  210  are also positioned close enough to one another that at least a portion of each of the outer side edges of the pallet supporting the load are positioned on the conveying surfaces  211  of the conveyor elements  210 , as shown in  FIG. 9B .  
      The conveyor elements  210  may be positioned on the floor or mounted on a base plate  216  as previously described with respect to  FIGS. 12A-12D . Preferably, the base plate extends no more than approximately 2 inches above the ground to facilitate the pallet truck driving onto the base plate with an unstable load. More preferably, the base plate extends approximately 0.25 inch above the ground. The pallet truck can drive up the tapered end  217  and onto the base plate  216  to deposit the load(s) onto the conveying surfaces of conveyor elements  210  in a load accumulation area  225  of conveyor  201 . Regardless of whether a base plate  216  is used, it is also possible to utilize one or more rolling plates  213  as previously described with respect to  FIGS. 12A and 12B .  
      The accumulation conveyor  201  may also include a guide element for guiding the forks of the pallet truck as previously described with respect to  FIG. 9B .  
      As embodied herein and shown in  FIGS. 11A-11D , the low profile conveyor  201  preferably includes a load accumulation area  225 , a load wrapping area  230 , and a load exit area  235 . The load accumulation area  225  is positioned upstream of the wrapping area  230 . The wrapping area  230  is positioned between the load accumulation area  225  and the load exit area  235 . The load accumulation area  225  is configured to receive loads from pallet trucks and move these loads into the load wrapping area  230 . A load pusher assembly  250   a  is provided for moving loads between the load accumulation area  225  and the load wrapping area  230 . The load pusher assembly  250   a  is substantially the same as load pusher assembly  150  discussed above with respect to  FIG. 10   b . Such a pusher assembly is also disclosed in U.S. Patent Application Publication No. 2002/0056253 entitled “Method and Apparatus for Wrapping a Load,” the entire contents of which is incorporated herein by reference. In a preferred embodiment, the pusher assembly  250   a  includes two pusher bars or arms  252   a . Pusher arms  252   a  are preferably located alongside the load accumulation area  225 . A separate exit pusher assembly  250   b  may be provided to move wrapped loads from the wrapping area  230  to the load exit area  235 . In a preferred embodiment, the exit pusher assembly  250   b  includes a single pusher bar or arm  252   b . Pusher arm  252   b  is preferably located alongside the load wrapping area  230  and load exit area  235 . Alternatively, the load pusher assembly and the exit pusher assembly may be connected to form a single unit.  
      According to another aspect of the invention, system  200  may include a packaging material dispenser. As shown in  FIG. 10A , a dispenser  202  is provided for dispensing packaging material  207 . Packaging material dispenser  202  dispenses a sheet of packaging material  207  in a web form and includes a roll carriage that supports a roll of packaging material. The roll carriage of dispenser  202  is mounted and vertically moveable on an arm  204  to dispense packaging material  207  spirally about load  224  as rotation is provided between load  224  and dispenser  202 . The roll carriage may include a support for the packaging material roll and means for moving on arm  204 .  
      According to one aspect of the present invention, the dispenser  202  may include a prestretch portion configured to prestretch the film. The prestretch portion may be any type of conventional prestretch portion, including either powered roller stretch or unpowered roller stretch.  
      In a preferred embodiment, stretch wrap packaging material is used. In the stretch wrapping art, stretch wrap packaging material is known to have a high yield coefficient to allow the material a large amount of stretch during wrapping. Various other packaging materials, generally not considered to be stretch wrap materials, such as netting, strapping, banding, and tape, can be used as well.  
      According to another aspect of the invention, system  200  includes means for providing relative rotation between the dispenser  202  and the load  224 . As shown in  FIG. 10A , dispenser  202  is mounted on a vertical structure such as a rotary arm  204 . Rotary arm  204  has a first portion secured to a bearing member and a second portion holding the dispenser  202 . The first portion of the arm  204  is rotatable about a vertically extending axis of rotation to wrap packaging material  207  around the sides of the load  224 .  
      A motor drive (not shown) is provided for providing relative rotation around the generally vertical axis between the packaging material dispenser and the load to wrap packaging material about the sides of load. The drive rotates rotatable arm  204  and dispenser  202  about generally vertical axis to wrap packaging material  207  around the sides of load  224 .  
      According to another aspect of the invention, it may be desirable to provide a system  300  that includes more than one accumulation conveyor  301  feeding a stretch wrapper, or in some instances, a separate exit conveyor  401 . As embodied herein and shown in  FIGS. 13A-13C , the accumulation conveyor  301  and exit conveyor  401  each may include two or more conveyor elements  310 ,  410  respectively, the conveyor elements being similar to conveyor elements  110 ,  210  previously described. Each conveyor element  310 ,  410  may have conveying surfaces  311 ,  411  respectively, the conveying surfaces being similar to conveying surfaces  111 ,  211  previously described. Each conveyor element  310 ,  410  also has a longitudinal axis  310   a ,  410   a , respectively, as described above with regard to conveyor elements  110 ,  210 . In addition, each of the conveyor elements making up a conveyor (e.g., an accumulation conveyor or an exit conveyor) may be positioned parallel to one another such that their longitudinal axes are parallel. For example, conveyor elements  310  making up conveyor  301  are positioned parallel to one another such that their longitudinal axes  310   a  are parallel. However, conveying elements  310 ,  410  making up separate conveyors may or may not be positioned parallel to one another. For example and as shown in  FIG. 13B , conveying elements  310  making up conveyor  301  are positioned parallel to one another, and conveying elements  410  making up conveyor  401  are positioned parallel to one another; however, conveying elements  310  and  410  may be positioned substantially at any angular orientation with respect to each other.  
      In addition, it is also possible to provide more than one accumulation conveyor  301 . For example, a system may include two accumulation conveyors, each conveyor including, for example, two conveyor elements having longitudinal axes which are parallel to the additional conveyor elements making up the individual conveyor. The longitudinal axes of individual accumulation conveyors need not be parallel to one another and preferably are not parallel to one another. The addition of another accumulation conveyor may increase throughput and may provide additional space for holding loads to be wrapped. Alternatively, more than one exit conveyor may be used instead of or in conjunction with additional accumulation conveyors. In an embodiment in which separate accumulation and exit conveyors are provided, it may be necessary to provide a structure to transition the load between the two conveyors. One such structure is a turntable, as described below. Additional structures suitable to move the load from the accumulation conveyor to the exit conveyor may also be used.  
      According to another aspect of the present invention, the means for providing relative rotation may include a rotatable turntable  332  that rotates a load  324  relative to a dispenser  302 , which may be mounted to move vertically on a mast  304 . In such an embodiment, it would be necessary to provide two pairs of conveying elements  310 ,  410 , one to form the low profile conveyor  301  in the load accumulation area and a second pair to form a low profile conveyor  401  in the load exit area, as previously described. The rotatable turntable  332  in conjunction with a pusher assembly  350   b  is capable of moving the load  324  between the accumulation conveyor  301  and the exit conveyor  401 .  
      As shown in  FIG. 13C , packaging material dispenser  302  dispenses a sheet of packaging material  316  in a web form and may include a roll carriage  309  that supports a roll  308  of packaging material  316 . Roll carriage  309  of dispenser  302  is mounted on and vertically moveable on a mast  304  to dispense packaging material  316  spirally about load  324  as rotation is provided between the load and the dispenser  302 .  
      Rotatable turntable  332  may include a non-powered upper conveyor surface  330  with a plurality of non-powered rollers  312  for supporting the load during wrapping. Alternatively, instead of non powered rollers  312 , the non-powered conveyor load wrapping surface  330  may use drag chains, belts, transfer ball bearings, or other non-powered, low friction elements such as a smooth surface. Alternatively, the upper conveyor surface  330  may power rollers  312 .  
      The rollers  312  of the conveyor load wrapping surface  330  are preferably capable of being locked into a non-rolling position during wrapping. That it, when load  324  is being wrapped, the rollers  312  of the load wrapping surface  330  do not move, reducing the chances of a load shifting during wrapping. Prior and subsequent to the wrapping cycle, the rollers  312  of the conveyor load wrapping surface  330  are preferably in an “unlocked” or rolling position. Thus, the rollers  312  are capable of rolling to assist in moving load  324  onto or off of the conveyor load wrapping surface  330 . Alternatively, tabs or pins can be used, projecting through the rollers  312 , to prevent travel of the load.  
      Rotatable turntable  332  may include a packaging material holder assembly  370  for holding a leading end of the packaging material  316  during wrapping of the load. The packaging material holder assembly  370  may be positioned at an end of the load wrapping surface  330  where it will not interfere with the movements of loads onto and off of the rotatable turntable  332 . Alternatively, instead of a packaging material assembly  370 , a clamp or other means may be used to restrain the leading end of the packaging material during wrapping.  
      A method of use of the system  200  will now be described.  
      A picker builds a dual load  24   a ,  24   b . To build the dual load  24   a ,  24   b , the picker moves a pallet truck  40  (sometimes hand operated with the picker walking behind the pallet truck, sometimes operator rides) between rows  10  of products in a warehouse and “picks” the necessary products to form the loads  24   a ,  24   b . (See  FIG. 5 .) Each load  24   a ,  24   b  is built on a pallet  26 . Each pallet  26  includes a top platform  28 , a bottom platform  30 , side supports  32 , fork holes  34 , and bottom holes  36  in the bottom platform  30  (see  FIGS. 2, 3 , and  6 A- 6 C). The pallets  26  are supported on forks  42  of a pallet truck  40  operated by the picker. The forks  42  of the pallet truck  40  extend through the fork holes  34  of the pallets  26  and a support wheel  44  mounted on a leg  46  extends from each fork  42  and through the bottom holes  36  in the bottom platform  30  of the pallet  26 . When the forks  42  are in a raised position, the support wheel  44  is in contact with the ground and the leg  46  extends downwardly from fork  42 .  
      To position the dual load  24   a ,  24   b  in the accumulation area  225  on the conveyor  201 , the picker “drives” the pallet truck  40  onto the base surface (floor, base plate  216 , or rolling plate  213 ) with the forks  42  and their respective leg  46  and wheel  44  positioned on either side of the raised center structure  222  (if present). Each fork  42 , leg  46 , and wheel  44  is guided onto the base surface, in this example, base plate  216  between the raised center structure  222  and the inner side rails  220  of the conveyor elements  210 , as shown in  FIGS. 9A and 9B . The pallet truck  40  moves onto the base surface with the palletized loads elevated (see  FIG. 6A ). The forks  42  of the pallet truck  40  are then lowered to lower a first palletized load onto the conveying surfaces  211  of the conveyor elements  210  (see  FIG. 6B ). As the pallet truck  40  backs out of the first pallet, the leg  46  and support wheel  44  are retracted by contact with the base deck boards  30  of the pallet  26  to completely withdraw from the first pallet (see  FIG. 6C ). The forks  42  are then raised to elevate a second palletized load and this process is repeated to position the second palletized load. Preferably, the conveyor  201  includes a mechanism to engage a bottom portion of the pallet to ensure that the load is positioned appropriately. This is particularly useful when placing more than one load. An example of a suitable mechanism is a plate which permits forward movement and prevents reverse movement, as illustrated in  FIG. 9A . After the first palletized load passes over the plate, the plate will engage a back portion of the pallet, preventing backward movement of the load and assisting in withdrawal of the forks from the fork holes of the pallet.  
      As shown in  FIGS. 1A and 11B , the dual loads  24   a ,  24   b  may be positioned on the accumulation area  225  of the conveyor  201  while another load  24   c  is being wrapped in the wrapping area. As shown in  FIG. 11B , a second dual load  24   d ,  24   e  may be positioned behind the first dual load  24   a ,  24   b  in the accumulation area  225  of the conveyor  201  by a different picker.  
      During wrapping, the pusher arms  252   a  remain in an upright position (see  FIG. 11A ). During the last rotation of the wrapping cycle (wrapping load  24   c ), pusher arms  252   a  rotate approximately 90 degrees into the horizontal pushing position (see  FIG. 11B ). Pusher arms  252   a  then begin to move in the downstream direction toward the wrapping area  230  along pusher guide  256  while in the horizontal pushing position. As pusher arms  252   a  move downstream, they engage the first dual load  24   a ,  24   b  on the non-powered conveying surfaces  211  of the conveyor elements  210  in the load accumulation area  225  and simultaneously push the first portion  24   a  of the dual load  24   a ,  24   b  from the load accumulation area  225  into the wrapping area  230  and second portion of the dual load  24   b  to a position closer to the wrapping area  230 .  
      At the same time, pusher arm  252   b  of the exit pusher assembly  250   b  moves along pusher guide  256   b  in an upstream direction. When pusher arm  252   b  reaches a position slightly upstream of the end of the load being wrapped, pusher arm  252   b  rotates approximately 90 degrees into the horizontal pushing position. Pusher arm  252   b  then begins to move in the opposite direction (downstream) along pusher guide  256   b  while in the horizontal pushing position. As pusher arm  252   b  moves, it engages a side of the wrapped load  24   c  on the non-powered conveying surfaces  211  of conveyor elements  210  in the wrapping area  230  and pushes the wrapped load  24   c  from the load wrapping area  230  into load exit area  235  (see  FIG. 11C ).  
      Once the load  24   a  is positioned in the load wrapping area  230 , relative rotation is provided between the load  24   a  and the dispenser  202  by rotating rotatable arm  204  and dispenser  202  around the load  24   a . As the arm  204  and dispenser  202  rotate, packaging material  207  is wrapped around the sides of the load  24   a . The operator picks up the wrapped load  24   c  from the load exit area  235  and transports it to a truck-loading staging area.  
      A method of use of the system  300  will now be described.  
      A picker builds a dual load and positions the dual load on accumulation conveyor  301  in substantially the same manner as described above with respect to  FIGS. 2, 3 ,  5 ,  6 A- 6 C,  9 A and  9 B. If a second accumulation conveyor is provided (not shown), a second picker may position a second dual load on the second accumulation conveyor while the first dual load is being positioned on the accumulation conveyor  301 . A load  324  may or may not be wrapped while the loads are positioned.  
      After the loads are positioned, the pusher arms  352   a  of load pusher assembly  350   a  move along pusher guide  356  and push a load from the accumulation conveyor  301  onto rotatable turntable  332 . If necessary, rotatable turntable may rotate to align its conveyor surface with conveyor  301  in order to facilitate movement of the load onto the turntable. Rotatable turntable  332  rotates load  324  and dispenser  302  dispenses packaging material  316  and moves vertically on mast  304  to wrap packaging material  316  around the sides of the load  324 .  
      After wrapping, load  324  is pushed onto exit conveyor  401  by exit pusher assembly  350   b  as it travels along exit pusher guide  356   b . If the longitudinal axis of load accumulation conveyor  301  is not parallel to the longitudinal axis of the exit conveyor  401 , it may be necessary to rotate turntable  332  to align the load with exit conveyor  401  prior to moving the load  324  onto exit conveyor  401  with pusher arm  352   b.    
      The remainder of the process is substantially as described above. If more than one accumulation conveyor is provided, the process may alternatively take loads from each conveyor. Additionally, if more than one exit conveyor is provided, loads may alternatively be provided to the exit conveyors. In each instance, it may be necessary for the turntable to rotate to align its conveying surface with the conveyor delivering or receiving the load.  
      Embodiments of the invention may be used in conjunction with any packing or loading process, including where products are picked and loaded together for transportation. In addition, at least certain aspects of the aforementioned embodiments may be combined with other aspects of the embodiments, or removed, without departing from the scope of the invention.  
      Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.