Abstract:
An elevating load platform comprising a base member and a load supporting member interconnected by a linkage means that facilitates vertical movement of the load supporting member generally parallel to the base member, and a plurality of coil springs positioned to urge the load supporting member upwardly relative to the base member so that when the load supporting member is laden the coil springs are compressed, and as the load is progressively removed the coil springs urge the load supporting member upwards to thereby maintain the load supporting member at a desired height, the linkage means comprising a pair of spaced scissor linkages interconnected by a central cross-member, the plurality of compression springs being positioned in a spaced array interposed between the base member and the cross-member.

Description:
INTRODUCTION  
       [0001]     This invention relates to elevating load platforms, and in particular load platforms for use with palletised loads.  
         [0002]     These days health and safety requirements place considerable emphasis on the need to protect operators from back injuries. The manual loading and unloading of pallets is particularly dangerous from the point of view of back injury, particularly when the operators must lift a load bending down to the base of a pallet.  
         [0003]     There have thus been a number of proposals to ensure that the height of the load that is to be lifted in either a loading or unloading situation is at an optimum level. It is known to use electric or hydraulic means to raise and lower the platform and maintain it at the optimum height.  
         [0004]     In Australian patents 571354 and 582692 it was suggested to use sets of coil springs calibrated in dependence of the load to again ensure that the platform is substantially at the optimum height as the platform is loaded or unloaded.  
         [0005]     An issue with load elevators of the kind described in the earlier patents is the need to have a variety of sets of springs that have to be changed as the load is changed. In situations where the load varies from large, comparatively light produce to small and heavy produce it is clear that the force that the springs have to exert on the platform would vary considerably. Interchanging coil springs can be a difficult procedure and it is this issue that has brought about the present invention.  
       SUMMARY OF THE INVENTION  
       [0006]     According to one aspect of the present invention there is provided an elevating load platform comprising a base member and a load supporting member interconnected by a linkage that facilitates vertical movement of the load supporting member generally parallel to the base member, and a plurality of coil springs positioned to urge the load supporting member upwardly relative to the base member so that when the load supporting member is laden the coil springs are compressed, and as the load is progressively removed the coil springs urge the load supporting member upwards to thereby maintain the load supporting member at a desired height, the linkage means comprising a pair of spaced scissor linkages interconnected by a central cross-member the plurality of compression springs being positioned in a spaced array interposed between the base member and the cross-member.  
         [0007]     Preferably, the cross-member and the base member include spring support means that support the springs in use but facilitate simple removal and replaceability of the springs.  
         [0008]     In a preferred embodiment, up to five coil springs can be used with the size, capacity and number of springs varying in dependence of the load that has to be lifted.  
         [0009]     Preferably, the cross-member is pivotally secured to the linkages so that the member pivots as the load supporting member moves.  
         [0010]     Preferably, a damper is positioned between the load supporting member and the base.  
         [0011]     In a preferred embodiment, the cross-member is coupled to the base via a linkage that causes the cross-member to axially pivot as the load supporting member moves vertically.  
         [0012]     The load supporting member may support a rotatable turntable.  
         [0013]     Preferably, one end of each scissor linkage at the base member and load supporting member is adapted to slide along a rail to facilitate the movement.  
         [0014]     In a preferred embodiment the platform includes means to urge that end of each scissor linkage along the rail to lift the cross-member so that end of the linkage can be released from the rail to allow the load supporting member to be lifted to such a height that the springs become disengaged from the spring support means thereby facilitating replacement. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0015]     An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which:  
         [0016]      FIG. 1  is a perspective view of an elevating load platform viewed from the front,  
         [0017]      FIG. 2  is a perspective view of the load platform viewed from the rear,  
         [0018]      FIG. 3  is a perspective view illustrating the underside of the load supporting platform,  
         [0019]      FIG. 4  is a perspective view illustrating location of springs,  
         [0020]      FIG. 5  is a perspective view taken from the rear of the elevating load platform, and  
         [0021]      FIG. 6  is a plan view of an adjustment jack for use to lift the platform for adjustment purposes. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]     As shown in the accompanying drawings, an elevating load platform  10  comprises a base structure  11  that supports a load supporting platform  12 . The base support and load support platform are interconnected by scissor linkages  13 ,  14  that are mounted to extend along two parallel sides of the platform. The scissor linkages  13 ,  14  are joined by a central cross-member  15  and an array of coil springs  20  are positioned between the base structure  11  and the underside of the cross-member  15  the scissor linkages  13 ,  14  and the coil springs  20  operate to urge the load supporting platform  12  upwardly parallel to the base structure  11 .  
         [0023]     The base structure  11  is fabricated from steel and can provide two elongate parallel spaced bearers  21 ,  22  joined by cross-members  23 ,  24 ,  25 . The elongate bearers  21 ,  22  define forklift tine entry  26  at either end. The elongate bearers also have rectangular cutouts  27 ,  28  along their sides defining forklift tine entry from opposite sides. Thus, the load platform  10  can be lifted by a forklift from either side or either end. Pallet lifters can also be used to lift and transport the platform  10 .  
         [0024]     In an embodiment (not shown) it is understood that the base structure  11  can also be mounted on castors.  
         [0025]     The pair of scissor linkages  13 ,  14  are defined by a first rectangular frame  30  of square metal section that has top and bottom cross-members  31 ,  32 . Each end of the bottom cross-member  31  has a downwardly extending flange  35 ,  36  that are each bolted to a pair of upstanding lugs  37 ,  38  that project upwardly from one end of the base structure  11 . The attachment allows the frame  30  to pivot about the lugs  37 ,  38 . The center of the rectangular frame  30  is pivotally coupled on each side to diagonal stays  40 ,  41  that are in turn bolted at their upper ends to the ends of horizontal bearers  43 ,  44 . A cross-member  45  interconnects the upper ends of the stays  40 ,  41  across the bearers  43 ,  44 . The other end of the diagonal stays  40 ,  41 , namely the lower end, is interconnected by a cross-member  47  that in turn supports small rollers  48 ,  49  that run in an open track  50 ,  51  on either side of the base structure  11 . The upper end of the rectangular frame  30  has the cross-member  32  arranged to be a sliding fit with elongate slots  52 ,  53  at either end of horizontal bearers  43 ,  44 . In this way the bearers  43 ,  44  can move up and down vertically as the scissor linkages  13 ,  14  are compressed or expanded with the relative horizontal movement being afforded at one end of the platform  10 .  
         [0026]     The elongate bearers  43 ,  44  at the top of the platform  10  are welded to a circular support structure  60  that has peripherally positioned rollers  61  on which a circular loaded platform  62  with a downwardly extending annular skirt  63  that is arranged to be a running fit to constitute a turntable.  
         [0027]     The cross-member  15  at the center of the scissor linkages  13 ,  14  is a square section tube that is adapted to pivot relative to a shaft  65  that extends across the diagonal struts and through the rectangular frame  30 . The underside of the cross-member  15  is provided with five cylindrical projections  66  that are equally spaced along the cross-member  15 . The cylindrical projections  66  are adapted to fit within a coil spring  70 , the opposite end of which is located in an upstanding enclosure  71  that is welded to the cross-member  24  that extends across the center of the base structure  11 . In this way five coil springs  70  can be held captive by the respective downwardly extending male projections  70  and upwardly extending female recesses  71  defined by the cross-member  15  and cross-member  24  of the base structure respectively. As shown in  FIG. 1 , the cross-member  15  is also coupled to the base structure via a linkage  74  that is bolted to an upstanding web  75  at one end of the base structure  11  and to a smaller web  76  projecting upwardly from the cross-member  15 . The linkage  74  ensures that any movement of the cross-member imparts a pivotal rotation of the cross-member  15  to ensure that the springs  70  remain axially located on the male projection  66 .  
         [0028]     As shown in  FIG. 5 , a gas strut or damper  80  is also bolted with one end coupled to projecting flanges  81  from the interior of one side of the base structure  11  and the other end being bolted to a pair of parallel webs  82  extending downwardly from the support structure  60  of the loading platform  12 .  
         [0029]     The scissor linkage  13 ,  14  of the assembly allows the loading platform to move in a vertical distance of about 300 mm and the coil springs  70  control that movement. By suitable selection of the number and/or the rating of the springs for a particular load, the platform  10  can be designed in a manner that a full palletized load presses the platform  12  fully down allowing ready access to the top of the pallet. As the top layer is removed, springs  70  urge the loading platform  12  upwardly again maintaining the constant height until when the pallet is empty the platform has been raised to its full height shown in the drawings.  
         [0030]     In a preferred embodiment the load capacity of the platform varies in accordance with the number of springs  70 . Five identical springs provide support for the greatest load capacity 1200 kg whilst the number of springs are reduced to four, three, two or even one as the load demand reduces. In other embodiments, springs of differing capacities can be selected or secondary springs can be located within the existing springs to increase the load capacity.  
         [0031]     To remove or replace springs an adjustment or screw jack  100  of the kind shown in  FIG. 6  is placed adjacent one rail. The jack  100  comprises a T bar  101  having a cross head  102  and elongate shank  103  that is welded to a nut  104 . An external threaded drive  105  terminating at one end of an open channel drive  106  is threadedly engaged with the nut  104 . The driver  105  has a turning nut or pair of lock nuts  108  at the opposite end. As shown in  FIG. 5  the T bar  101  is slid under the cross-member  47  flat against the bearer  22  and the cross head  102  is positioned behind a pair of spaced lugs  120 ,  121  that project upwardly from bearer  22 , and the open channel drive  106  is engaged against the cross-member  47 . By turning the lock nuts  108  the driver pushes the cross-member  47  towards the cross head  102  causing the scissor linkages to lift. By further turning of the lock nuts  108  the scissor linkages can be lifted until the springs  70  are released from the cross-member  15 . It is necessary to disconnect the damper  80  before jacking up the scissor linkages.  
         [0032]     The adjustment jack  100  firmly and positively locates the scissor mechanisms in an elevated position facilitating removal and replacement of springs without danger of collapse of the platform  10 . At this height the male downward projections of the cross-member escapes from the end of the spring and it is a simple matter to remove and/or replace the coil springs from the female recesses as necessary. The platform can then be lowered through turning the lock nuts  108  of the jack  100  backwards until the male projections engage within the ends of the coil springs. When the jack  100  is not in use it is removed from the bearer  21  and stored against one of the cross-members of the base structure.  
         [0033]     The gas damper  80  is for the purpose reducing shock loads and controlling the speed of both depression and return of the loading platform. It is further understood that an additional safety feature, preventing collapse of the structure when springs are being replaced, is a stay (not shown) that interconnects the base structure and the mounting platform in an elevated position facilitating spring replacement.  
         [0034]     In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.