Abstract:
A dockleveler having a lip that can be both moved between a pendent inoperative position and an operative position and moved from a retracted to an extended position. This feature allows the lip to be partially extended during an end load so that the lip engages a portion of the vehicle bed and does not contact the load. The dockleveler further includes a barrier that is resiliently mounted to provide a cushioning effect when impacted by material handling equipment. This feature reduces the likelihood of damage to the barrier and/or dockleveler, and further reduces the chance of disrupting a load carried by the material handling equipment.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to the field of docklevelers that provide a bridge between a loading dock and a vehicle (e.g., a truck or a trailer) positioned at the loading dock. 
     BACKGROUND OF THE INVENTION 
     Docklevelers typically include a deck for bridging the space between a loading dock and a vehicle. The deck commonly is pivotally attached to the loading dock and is movable between a declined lowered position, a horizontal stored position, and an inclined raised position. A lip is usually mounted to the outer end of the deck and is disposed in an pendent inoperative position when the deck is in the stored position. In this stored position, the deck is supported by the pendent lip, which is engaged with a lip support. In operation, the deck is lifted to the raised position, then subsequently lowered while moving the lip from the pendent position to an extended operative position. The deck continues to lower until the lip engages the vehicle, and the lip provides support for the outer end of the deck. 
     In certain loading situations, the lip cannot be moved to the operative position due the positioning of a load on a vehicle. For example, the load may be positioned too close to the end of the vehicle, thereby not providing sufficient space for full extension of the lip. This situation is commonly called an “end load.” In order to remove an end load, the dockleveler must be positioned in either the horizontal stored position or the lowered position with the lip in the pendent inoperative position. A fork lift can then be positioned on the deck and used to lift the end load from the vehicle. After the end load is removed, the dockleveler can be raised an then lowered to rest the lip on the vehicle. 
     Some loading docks include a barrier that inhibits material handling equipment (e.g., fork lifts) from accidentally falling off the end of the deck when the deck is in the stored position. One type of barrier is a lip barrier that is incorporated into the lip of the dockleveler, as disclosed in German Patent Nos. DE2634652 and DE2852888. When the lip is in the extended operative position, the lip barrier is designed to be in a non-blocking position that is below or flush with an upper surface of the deck. When the lip moves to the pendent inoperative position, the lip barrier raises to a blocking position that is above the upper surface of the deck, thereby inhibiting material handling equipment from rolling off the outer end of the deck. 
     SUMMARY OF THE INVENTION 
     Lip barriers are simple, reliable barriers that are raised to the blocking position when the lip is pendent. One problem with this design is that it can prevent unloading an end load. That is, with the lip pendent, the raised lip barrier can impede the ability of a fork lift to access the end load. Another problem with the basic lip barrier design is that it is very rigid and can be easily damaged by even a slight impact of a fork lift. Any bending of or damage to the barrier will require repair of the dockleveler. The rigid barrier can also disrupt a load carried by the fork lift. 
     The dockleveler described herein has several distinct features that provide important advantages over the basic lip barrier design. One such feature is the provision of a lip that can be both moved between a pendent inoperative position and an operative position and moved from a retracted to an extended position. This feature allows the lip to be partially extended during an end load so that the lip engages a portion of the vehicle bed and does not contact the load. 
     Another distinct feature is the provision of a barrier that is resiliently mounted to provide a cushioning effect when impacted by material handling equipment. This feature reduces the likelihood of damage to the barrier and/or dockleveler, and further reduces the chance of disrupting a load carried by the material handling equipment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a loading dock and dockleveler embodying the present invention. 
     FIG. 2 is a side section view of the dockleveler of FIG. 1 in a stored position. 
     FIG. 3 is the section view of FIG. 2 with the deck raised and the lip in an operative and retracted position. 
     FIG. 4 is the section view of FIG. 2 with the lip in an operative and extended position and engaged with a vehicle. 
     FIG. 5 is an enlarged view of the back end of the barrier in a non-blocking position. 
     FIG. 6 is the section view of FIG. 2 with the lip in an operative and partially-extended position and engaged with a vehicle having an end load. 
     FIG. 7 is the section view of FIG. 2 illustrating a fork lift impacting the barrier. 
     FIG. 8 is a schematic of the hydraulic circuit for the illustrated embodiment. 
    
    
     DETAILED DESCRIPTION 
     The drawings illustrate a loading dock  10  and a dockleveler mounted at the loading dock  10 . The dockleveler includes a support structure  12  mounted within a pit  14 , and a deck  16  pivotally connected to the support structure  12 . A deck actuator in the form of a hydraulic deck cylinder  18  is interconnected between the support structure  12  and the deck  16  to facilitate pivoting the deck  16  relative to the support structure  12 . 
     An extension member  20  is slidably connected to the deck  16 , and an extension actuator in the form of a hydraulic extension cylinder  22  is connected between the deck  16  and the extension member  20  to facilitate movement of the extension member  20  relative to the deck  16 . The extension member  20  can be moved between a retracted position (FIG. 3) and an extended position (FIG.  4 ), or to a partially extended position between the retracted position and the extended position (FIG.  6 ). 
     A lip member  24  is pivotally mounted to the extension member  20 . The lip member  24  can be moved between a pendent inoperative position (FIG. 2) and an operative position (FIGS. 3,  4  and  6 ). When in the inoperative position, the lip member  24  can be engaged with a lip support  26 , which provides support to the deck  16  and holds the deck  16  in a substantially horizontal position. When in the operative position, the lip will be positioned to engage the bed of a vehicle  28  parked at the loading dock  10 . Movement of the lip member  24  from the inoperative position to the operative position is provided by a lip actuator interconnected between the extension member  20  and the lip member  24 . In the illustrated embodiment, the lip actuator comprises a hydraulic lip cylinder  30 . 
     A barrier member  32  is mounted for a movement relative to the deck  16  between a blocking position (FIGS.  2  and  7 ), where the barrier member  32  extends above an upper surface  34  of the deck  16 , and a non-blocking position (FIGS.  3 - 16 ). In the illustrated embodiment, the barrier member  32  is integrally formed with the lip member  24 . Movement of the illustrated lip member  24  from the inoperative position to the operative position results in movement of the barrier member  32  from the blocking position to the non-blocking position. 
     The standard operation of the dockleveler starts with the dockleveler in the stored position (FIG.  2 ). After a vehicle  28  is properly positioned against at the loading dock  10 , the deck actuator can be activated to lift the deck  16  to a raised position, and the lip actuator can be activated to move the lip member  24  to the operative position (FIG.  3 ). The extension actuator is then activated to extend the lip from the retracted position to the extended position, and the deck  16  is then lowered until the lip engages the vehicle  28  (FIG.  4 ). With the lip in the operative position and fully extended, the tip of the barrier (in the non-blocking position) will fall into a recess  36  in the upper surface  34  of the deck  16  to provide a smooth transition from the deck  16  onto the lip member  24  (FIG.  5 ). After the loading operation is complete, the deck  16  can be raised, and the lip can be moved to the inoperative position and then to the retracted position. Subsequent lowering of the deck  16  will result in the lip engaging the lip support  26  to put the dockleveler back in the stored position (FIG.  2 ). 
     When the illustrated dockleveler is used to service a vehicle  28  having an end load  38 , the operator of the dockleveler can control the extension of the lip so that the lip never reaches its fully extended position (FIG.  6 ). By controlling the extension of the lip, the lip can be extended to a point where it will engage the vehicle  28 , but will not contact the load on the vehicle  28 . 
     With the dockleveler in the stored position (FIGS.  2  and  7 ), it can be appreciated that the barrier member  32  will provide some resilience if impacted by a material handling vehicle  28 . More specifically, if the barrier member  32  is contacted, the extension actuator will allow the extension member  20  (and the barrier member  32  connected to the extension member  20 ) to move outwardly away from the loading dock  10  by virtue of an impact relief valve, described below in more detail. 
     Referring to FIG. 8, the hydraulic circuit of the illustrated embodiment includes a pump  40 , five valves (labelled valve- 1 , valve- 2 , etc.), the deck cylinder  18 , the lip cylinder  30 , and the extension cylinder  22  that is a double-acting cylinder. The system further includes a “raise” button (not shown) that activates the pump  40 , and an “extend” button (not shown) that activates the pump  40  and de-energizes valve- 1 . 
     When the system is provided with power, valve- 1  is energized and moved to the open position. Pushing the raise button activates the pump  40 , which creates pressure in the fluid line and cause valve- 2  to open. Fluid is thereby allowed to enter both the back side of the extension cylinder  22 , to hold the extension member  20  retracted, and the deck cylinder  18 , to raise the deck. When the deck cylinder  18  reaches its limit, the increased pressure causes valve- 3  to open, thereby allowing pressurized fluid to reach the lip cylinder  30 . Once the lip cylinder  30  reaches its limit, the increased pressure causes valve- 4  to open and valve- 5  to shift, thereby allowing pressurized fluid to reach the front side of the extension cylinder  22  and return oil from the backside to pass the reservoir. Once the extension cylinder  22  reaches its limit, the pump  40  is turned off by releasing the raise button, and the deck  16  lowers until the lip contacts the vehicle  28  bed. The pilot pressure from the deck cylinder  18  maintains valve- 3  in its open position until the dockleveler comes to rest on the vehicle  28 , at which time the line pressure falls and pressure-actuated valves return to the resting positions. 
     After the loading operation is completed, the deck  16  can be returned to the stored position by pushing the raise button to lift the deck. The lip will fall since valve- 3  has returned to the closed position, and the lip will also be retracted since valve- 4  and valve- 5  have returned to their resting positions. Once the lip has cleared the vehicle  28  bed, but before the deck reaches its full height, the raise button is released, resulting in the deck slowly descending until the lip engages the lip support  26 . 
     In order to perform an end load, the same sequence of events is performed, except the raise button is released before the extension cylinder  22  reaches its fully-extended position. This will cause the deck to start descending with a partially-extended lip. If the lip needs to be extended further, the extend button can be pushed, which causes valve- 1  to close (thereby stopping the descent of the deck) and starts the pump  40 . This causes the extension cylinder  22  to further extend. Upon release of the extend button, the pump  40  will stop and the deck will continue to fall. This sequence can be repeated until the lip is extended to the desired position. 
     The hydraulic circuit further includes a pressure relief valve  42  that will relive excessive pressure in the extension cylinder. More specifically, when the dockleveler is stored (FIG.  2 ), the barrier member  32  will absorb an impact (FIG. 7) by expelling fluid through the pressure relief valve  42 . 
     The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and the skill or knowledge of the relevant art, are within the scope of the present invention. The embodiments described herein are further intended to explain best modes known for practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with various modifications required by the particular applications or uses of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.