Abstract:
A pallet clamping device is mounted between forks of a material handling vehicle. The device clamps to a stringer of a pallet using a pair of horizontally moveable jaws. The jaws are resiliently forced toward one another for clamping a stringer so that a clamped pallet will not move off the forks. The jaws are mounted for pivoting and sliding motion relative to mounting pins which, together with links coupling the jaws to a base of the device, tighten jaw closure if a pallet moves away from the forks. The pivoting and sliding motion of the jaws helps align the jaws with pallets not perfectly aligned with the vehicle. Depression of a foot pedal moves the jaws from a closed position to a latched open position for receiving a pallet stringer. The jaws can also be moved to an unlatched open position for receiving a greater width center stringer. Upon release of the operating device from the unlatched open position, the jaws move toward their closed position.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/698,856, filed Jul. 13, 2005, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates in general to material handling vehicles and, more particularly, to a pallet clamping device associated with forks of such vehicles for selectively clamping or grabbing a center rib or stringer of a pallet supported by the forks so that the pallet is effectively locked to the forks and cannot move off the forks.  
         [0003]     A variety of pallet clamps and other pallet locking devices are known in the prior art. In U.S. Pat. No. 2,256,454, a lift truck includes a load pushing frame mounted above its forks and a pair of pallet grippers. Both the grippers and the load pushing frame are actuated to push a piled load of bags off a pallet upon which the load is stacked while the grippers engage a center rib of the pallet to retain the pallet on the truck as the load is pushed off the pallet. The pallet grippers, best shown in  FIGS. 3 and 4 , include a pair of grab hooks that are activated by cam plates and a spread fork by operation of a solenoid or by a double acting hydraulic cylinder. The grab hooks engage hook bars added to the center rib of pallets being used with the truck. An alternate pallet gripper, shown in  FIG. 7 , includes a lug integral with a fork and a socket formed in the underside of the top surface of a pallet being used with the truck.  
         [0004]     Another currently popular form of pallet clamping device includes passive locking clamps wherein either single cam action forces or double cam action forces resulting from movement of a pallet off the forks wedge the cam or cams into a center rib or stringer of the pallet to prevent the pallet from moving off the forks. The structure and operation of such a pallet clamp is illustrated in  FIGS. 1-4  wherein a foot pedal  10  controls extension of a cable  12  to move wedge cams  14  to an open position against the force of torsion springs  16  mounted to move the wedge cams  14  toward a closed position. As shown in  FIGS. 2-4 , the wedge cams  14  accommodate a variety of widths of center ribs or stringers  17  as a pallet is engaged. Once a stringer has been moved into the wedge cams  14 , into which they can freely move, its exit is blocked by the cam action of the wedge cams  14  to firmly grip the stringer.  
         [0005]     Yet another form of pallet clamping device is disclosed in U.S. Pat. No. 6,767,175 wherein lock bars positioned between forks of an order picking truck have tapered portions positioned on upper faces of a top end of the lock bars as shown in  FIGS. 3-5 . When the forks are inserted into a pallet, if the tapered portions come into contact with an end face of an upper deck board of the pallet, the lock bars rotate downward. If not, the lock bars rotate downward upon lifting of the pallet. When a landing sensor is activated by a magnet, see  FIGS. 3 and 7   a - 7   d,  the lock bars are immediately driven and the locking operation is started. The ends of the lock bars push or come into pressure contact with an upper face of a lower deck board of the pallet, and the pallet is locked. A damper provides a resilient force to ensure that the lock bars remain engaged in spite of oscillations due to movement of the truck.  
         [0006]     While known pallet clamping devices each have their own advantages and disadvantages, there is an ongoing need to advance the state of the art and provide new pallet clamping devices that offer alternates to existing designs and produce clamping characteristics that facilitate material handling operations performed by trucks equipped with the new clamping devices.  
       SUMMARY OF THE INVENTION  
       [0007]     This need is currently met by a pallet clamping device mounted between forks of a material handling vehicle for grabbing a center stringer of a pallet to be moved using the vehicle. The pallet clamping device comprises a pair of horizontally moveable jaws having a closed position wherein the jaws are resiliently forced toward one another for engagement with a stringer to grab the stringer and thereby clamp the corresponding pallet to the forks. The jaws are pivotally mounted and linked to a clamp base so that attempted movement of a clamped pallet off the forks results in tighter closure of the jaws onto the stringer. An operating device, a foot pedal and associated linkages as illustrated, moves the jaws from their closed position to a latched first open position wherein the jaws are separated by a first distance for receiving a center stringer sized up to the first distance and to an unlatched second open position wherein the jaws are separated by a second distance greater than the first distance, wherein the jaws can receive a center stringer sized up to the second distance and wherein, upon release of the operating device from the unlatched second position, the jaws move to their closed position. By mounted the jaws by means of pinned slots so that the jaws pivot about and slide along the pins, alignment of the jaws with a pallet and hence entrance of the pallet clamp into a pallet is facilitated. The operating device may comprise a foot pedal movable between a fully up position and a fully depressed position with the foot pedal being spring biased to its fully up position.  
         [0008]     In accordance with one aspect of the present invention a material handling vehicle comprises a pair of forks to be inserted into a pallet having a center stringer and a hoisting device for raising the forks. A pallet clamp device is mounted between the forks, the pallet clamp device including a pair of jaws having a closed position wherein the jaws are resiliently forced toward one another for engagement with the center stringer. An operating device is provided for moving the jaws from their closed position to a latched open position wherein the jaws are separated by a first distance and to an unlatched open position wherein the jaws are separated by a second distance greater than the first distance.  
         [0009]     In accordance with another aspect of the present invention a material handling vehicle comprises a pair of forks to be inserted into a pallet having a center stringer and a hoisting device for raising the forks. A pallet clamp device is mounted between the forks, the pallet clamp device including a pair of jaws having a closed position wherein the jaws are resiliently forced toward one another for engagement with the center stringer. Pivot pins are provided for mounting the jaws for pivoting and sliding movement about the pins as the jaws move between the closed and open positions for receiving the center stringer.  
         [0010]     The operating device may comprise a foot pedal movable between a fully up position and a fully depressed position. When a foot pedal is used, the foot pedal may be spring biased to its fully up position. The foot pedal may be held in a partially depressed position, corresponding to a jaws latched open position between the fully up position and the fully depressed position, when the jaws are in the latched open position. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIGS. 1-4  illustrate a passive locking pallet clamping device wherein double cam action forces, resulting from attempted movement of the pallet off the forks, are used to clamp pallet stringers;  
         [0012]      FIGS. 5 and 6  are isometric views of a pallet clamping device in accordance with the present invention with first and second jaws closed taken from opposite sides of the device;  
         [0013]      FIGS. 7 and 8  are isometric views of the first jaw and the second jaw, respectively, of the pallet clamping device of  FIGS. 5 and 6 ;  
         [0014]      FIG. 8A  is a top plan view of the second jaw illustrating pivoting and sliding movement of the second jaw about a pin and a link pivotally mounted to a clamp base for operating the second jaw;  
         [0015]      FIG. 9  is a top plan view of the pallet clamping device of  FIGS. 5 and 6  with the jaws closed;  
         [0016]      FIG. 10  is an isometric view of a portion of the pallet clamping device of  FIGS. 5 and 6  showing a pivoting latch which operates with a link pin to hold the jaws in a latched open position;  
         [0017]      FIGS. 11-13  illustrate the pivoting latch mechanism with the pallet clamping device of  FIGS. 9 and 10  for illustration of operation of the pivoting latch of  FIG. 10 ;  
         [0018]      FIG. 14  is a top plan view of the pallet clamping device of  FIGS. 5 and 6  showing the jaws in the latched open position;  
         [0019]      FIG. 15  is a top plan view of the pallet clamping device of  FIGS. 5 and 6  showing the jaws in their full open position for receiving maximum width pallet stringers and for releasing the jaws from their latched open position;  
         [0020]      FIG. 16  is a perspective view of a material handling vehicle including an illustrative embodiment of the pallet clamping device of the present invention;  
         [0021]      FIG. 17  is a perspective top view of the forks and a portion of an operator&#39;s platform of  FIG. 16  to which the pallet clamping device of the present invention is mounted;  
         [0022]      FIG. 17A  is a perspective top view of the portion of the operator&#39;s platform shown in  FIG. 17  with the floor cover removed to reveal the mounting of the pallet clamping device of the present invention; and  
         [0023]      FIG. 18  is a perspective bottom view of the forks and a portion of an operator&#39;s platform to which the pallet clamping device of the present invention is mounted. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     The pallet clamping device of the present application will now be described with reference to drawing  FIGS. 5-18  which illustrate a currently preferred structure of a pallet clamp  100  that is fitted between forks  202  of a material handling vehicle  200 , with the vehicle  200  including a hoisting device  216  for raising the forks  202  being shown in  FIG. 16 . The pallet clamp  100  includes a first jaw  102 , best shown in  FIG. 7 , including a laterally extending jaw portion  102 C having a slot  104  that receives a pivot pin  106  so that the first jaw  102  is mounted for pivoting about and sliding along the pin  106 . A second jaw  108 , best shown in  FIGS. 8 and 8 A, also includes a laterally extending jaw portion  108 C having a slot  110  that receives a pivot pin  112  so that the second jaw  108  is mounted for pivoting about and sliding along the pin  112 . The pivoting and sliding motion of the jaws  102 ,  108  facilitates engagement of the pallet clamp with pallet stringers when the jaws  102 ,  108  and forks  202  of the vehicle  200  are not perfectly square with a pallet. The jaws  102 ,  108  can be operated to clamp onto pallet stringers ranging in width from approximately 1 inch to approximately 7 inches for a working embodiment, however, the size of the pallet clamping device  100  of the present application can be changed as well as the angles of the slots  104 ,  110  to accommodate other pallet stringer size ranges as required. Also, changes in the illustrated shape of the jaws  102 ,  108 , for example to reduce the weight of the jaws  102 ,  108 , are contemplated for the pallet clamp  100 .  
         [0025]     An operating device, taking the form of a foot pedal  120  in the illustrated embodiment, is depressed to open the jaws  102 ,  108  with depression of the pedal  120  being opposed by a pedal reset spring  121 . When the pedal  120  is depressed, a linkage  140 A ultimately pulls on couplings comprising pins  140  which extend through arcuate slots  140 B of the linkage  140 A and also through holes  102 B and  108 B, see  FIGS. 7 and 8 , of the jaws  102 ,  108 . The pins  140  are fixedly connected, such as by welding, to pivot links  143  which are in turn pivotally mounted to pins  143 A which are fixedly mounted, such as by welding, to and extend from a support frame  142  for the pallet clamp  100 . When the linkage  140 A pulls on the pins  140 , the pivot links  143  swing apart and as they do, the jaws  102 ,  108  are forced to pivot about the pins  106 ,  112 , respectively, and slide in the slots  104 ,  110 , respectively. In the illustrated embodiment, the pivoting of the jaws  102 ,  108  about the pins  106 ,  112  magnifies their movement so that the teeth T defining gripping surfaces on the jaws  102 ,  108  spread apart a greater amount than the pins  140  spread apart within the slots  140 B. For example, in one embodiment of the invention, the teeth T defining gripping surfaces on the jaws  102 ,  108  may spread apart approximately fifteen (15) times as much as the pins  140  spread apart within the slots  140 B. The slots  104 ,  110  allow for the change in distance between the pins  140  and the pins  106 ,  112  as the pins  140  swing through their respective arcs in the slots  140 B, see  FIG. 8A .  
         [0026]     The jaws  102 ,  108  can be opened to a latched open position wherein the jaws  102 ,  108  are separated by approximately 5.65 inches for a working embodiment of the pallet clamp  100 , see  FIGS. 12 and 14 , by means of the interaction of a latch link  122  having a pin  124  extending therefrom that engages a pivoting latch  126  biased to a neutral position shown in  FIGS. 10 and 11  by a spring  128 . While the spring  128  is shown as an extension spring, other springs and resilient biasing arrangements can be used. For example, a torsion spring located around the shaft on which the pivoting latch  126  is mounted can be coupled between the pivoting latch  126  and the support frame  142 . With the jaws  102 ,  108  latched open, an operator of a material handling vehicle including the illustrated pallet clamp  100  can approach a pallet having a stringer up to about 5.5 inches in width without having to hold the jaws  102 ,  108  open by keeping his/her foot on the foot pedal  120 . In the latched open position, the pin  124  engages a circular portion of a notch  126 N, see  FIGS. 11-13 , of the latch  126  and, due to the length of the latch link  122  and the orientation of the latch link  122  and the latch  126 , as best shown in  FIG. 12 , the latch link  122  cannot pivot toward the forks  202  so that the jaws  102 ,  108  are held in the latched open position.  
         [0027]     In the illustrated embodiment, the operator is made aware that the pallet clamp  100  is in the latched open position by the foot pedal  120  remaining in a partially depressed position corresponding to the latched open position of the jaws  102 ,  108 . Of course, the pedal  120  could be returned to its fully up position and other indicators, such as visual or audible signaling devices, could be used to indicate the latched open position of the pallet clamp  100  to the operator. Thus, while not required, the described positioning of the foot pedal  120  may provide a simple, inexpensive and convenient way of communicating the operational status of the pallet clamp  100  to the operator. If desired, the shape of the latch  126  can also provide feedback through the foot pedal  120  so that the operator can feel when the foot pedal has been pushed down far enough so as to latch the jaws  102 ,  108  in the latched open position.  
         [0028]     The foot pedal  120  is returned to its fully up position when the jaws  102 ,  108  are in their closed position or are clamping a pallet stringer. As shown in  FIGS. 6 and 11 , for example, a slotted link  144  enables the foot pedal  120  to return to its fully up position. The slotted link  144  receives an extension  124 A of the pin  124  on the side of the latch link  122  opposite to the side from which the pin  124  extends so that it can slide along the extension  124 A of the pin  124  when the jaws  102 ,  108  engage a pallet stringer without impacting the position of the foot pedal  120 .  
         [0029]     To release the jaws  102 ,  108  from the latched open position so that they move to their closed position or close onto a pallet stringer that has been positioned between the jaws  102 ,  108 , the operator depresses the foot pedal  120  further, i.e., beyond the pedal position corresponding to the latched open position. This further depression of the foot pedal  120  moves the jaws  102 ,  108  so that they are opened toward a full opened position, approximately 7 inches for a working embodiment, and releases the jaws  102 ,  108  from the latched open position. Of course other full open widths can be used in the present invention. Since the jaws  102 ,  108  can be opened wider than their latched open position by using the foot pedal  120 , the operator can also engage a pallet having a stringer with a width up to around 7 inches for a working embodiment by using the foot pedal  120  to fully open the jaws  102 ,  108 .  
         [0030]     As the foot pedal  120  is depressed beyond the latched open position, the pin  124  passes over the latch  126  so that the pin  124  is released from the notch  126 N and the latch  126  moves forward to its spring biased position as shown in  FIG. 13 . Positions of the jaws  102 ,  108  between the position immediately after the pin  124  is released from the notch  126 N and the fully open position of the jaws  102 ,  108  are referred to herein as an unlatched open position. When the foot pedal  120  is then released from the unlatched open position, the latch link  122  passes back to its position shown in  FIG. 11  with the pin  124  passing over the latch  126  as the latch link  122  pivots as shown by an arrow A in  FIG. 13 . Jaw clamping springs  130 ,  132  extend between the support frame  142  and spring receiving extensions  102 A and  108 A of the jaws  102 ,  108  to force the jaws  102 ,  108  closed. The clamping force exerted by the jaw clamping springs  130 ,  132  is increased if a pallet attempts to move away from the pallet clamp  100  due to supplemental forces generated by the pivoting action of the jaws  102 ,  108  and the pivoting action of the pivot links  143 . The operation of the pivot links  143  is best shown in  FIG. 8A  wherein only the jaw  108  is shown since the operation of the pivot link associated with the jaw  102  is substantially the same as should be apparent.  
         [0031]     The pallet clamp  100  is mounted beneath a floor  204  of the truck  200  as shown in  FIGS. 16, 17 ,  17 A and  18 . The rear of the support frame  142  is pivotally mounted to a clamp support  206  by an appropriate connector  208 , such as a bolt/nut combination, while the front of the support frame  142  is supported by a pair of generally horizontal support surfaces  142 A which engage a cross bar  210  extending between first and second clamp support members  212 ,  214 . Alignment of the jaws  102 ,  108  with a pallet which is not perfectly centered on the forks of an associated material handling vehicle is facilitated by the pivoting movement of the support frame  142  about the connector  208 . The flexibility of the jaws  102 ,  108 , provided by the slot and pin connections to the jaws  102 ,  108 , such as at  104 ,  106 ,  110 ,  112  and  140 , also aids with the alignment of the jaws  102 ,  108  with a pallet that is not perfectly centered on the forks.  
         [0032]     While operation of the pallet clamp  100  is apparent from the foregoing description, a brief description of its use will now be provided. For a material handling vehicle, such as the truck  200  of  FIG. 16 , including the pallet clamp  100  of the present application, an operator approaches a pallet to be moved using the vehicle so that forks of the vehicle are aligned to engage openings in the pallet, one on either side of the pallet stringer. Presuming that normal sized pallets, i.e., pallets having stringers which can be engaged with the jaws of the pallet clamp  100  in the latched open position, are being handled, the operator already has the jaws positioned in the latched open position, indicated by a partially depressed foot pedal or otherwise. If not, the operator depresses the foot pedal and places the jaws in the latched open position which can be felt through the foot pedal (or holds the foot pedal down). The pallet is then engaged and the operator depresses the foot pedal to a position beyond the latched position (or releases the foot pedal if not depressed to the latched position), not necessarily the fully depressed position, although depression of the pedal to the fully depressed position will ensure disengagement of the jaws from the latched position if they are latched open. The foot pedal is then released and the jaws close onto the pallet stringer. The pallet is then moved as required and, once repositioned where desired, the foot pedal is again depressed to release the pallet clamp  100  from the pallet.  
         [0033]     To expedite pallet handling operations, the operator can place the pallet clamp  100  in its latched open position so that it is ready to clamp the next pallet to be moved. While the latched open position for the pallet clamp would normally be selected to accommodate most if not all pallets normally used at a facility utilizing a material handling vehicle including the pallet clamp, pallets having stringers with a width exceeding that corresponding to the latched open position of the jaws can still be accommodated. For pallets having oversized stringers, the operator can manually activate the pallet clamp  100  to its fully opened position by fully depressing the foot pedal and holding it down until a pallet is ready to be clamped. The foot pedal is then released to clamp the pallet stringer and the pallet clamped on the forks is then moved as before. When the pallet clamp is to be released, the foot pedal is once again fully depressed to fully open the jaws and release the pallet.  
         [0034]     Having thus described the invention of the present application in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the spirit of the invention.