Patent Publication Number: US-6216303-B1

Title: Dock leveler having an improved support leg mechanism

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to the field of dock levelers, and more particularly to dock levelers having support legs. 
     BACKGROUND OF THE INVENTION 
     Dock levelers are mounted on loading docks and are adapted to bridge the gap between the dock and the end of a vehicle (e.g., a truck) parked in front of the dock. The dock leveler enables material handling equipment, such as a fork lift, to move between the dock and the vehicle bed. 
     The typical dock leveler includes a supporting structure, which is mounted in a pit in the loading dock, and a ramp. The rear end of the ramp is pivotally attached to the supporting structure so that the ramp is movable from a horizontal position to a position within the working range of the ramp (e.g., between an upwardly inclined position and a downwardly declined position). Hinged to the front end of most ramps is an extension lip, which is movable between a downwardly hanging pendent position and an extended position where the lip forms an extension to the ramp. Typically, after a truck is parked in front of the loading dock in preparation for a loading operation, the ramp of the dock leveler is pivoted upwardly to allow the pendent lip to clear the vehicle bed and subsequently lowered. As the ramp is moved, the lip is pivoted outwardly from the pendent position to the extended position. As the ramp is lowered, the extended lip will engage the bed of the truck to provide support to the ramp. 
     Many dock levelers also include support legs that maintain the ramp in a substantially horizontal position when the ramp is not in use (i.e., when the dock leveler is not engaged with a truck bed). These legs can be retracted for servicing truck beds that are below dock level. Typically, a pair of support legs are pivotally attached to the ramp at or around the lip hinge area and extend downwardly to engage a supporting sub-frame. The support legs may be spring biased forwardly toward a supporting position, and may be retracted to a non-supporting position by one of several means. 
     Both manual and automatic mechanisms have been used to retract the support legs. Manual support leg retraction mechanisms require the operator to engage a mechanism, for example by pulling a chain, to retract the support legs as the ramp is being lowered. Automatic support leg retraction mechanisms typically retract the support legs as the lip of the dock leveler is extended. In this way, the support leg is always retracted when the lip engages a truck bed. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improvement in dock levelers. More specifically, the invention relates to a mechanism and a method of controlling the movement of one or more support legs, and incorporates several features and advantages of manual and automatic support leg retraction mechanisms while avoiding some of their respective disadvantages. 
     One feature of the present invention is that the support legs may be automatically retracted to facilitate lowering the ramp for below dock level service. In this way, the dock leveler is less likely to stall at the horizontal position as a result of the operator forgetting to manually retract the support legs. Another feature of the present invention is that the support legs may be positioned in a supporting position when a truck bed is engaged by the lip for above dock level service. This feature limits the descent of the ramp if a truck pulls away unexpectedly. Yet another feature of the present invention is that a means is provided for accomplishing the above function that is relatively simple in construction and does not require, for example, sensor arms or acceleration sensitive mechanisms. 
     In one aspect, a dock leveler is provided having a ramp, a support leg for supporting the ramp, and an extension lip that is movably connected to the ramp. The support leg is capable of movement relative to the ramp from a supporting position to a retracted position, and the lip is movable to an extended position. Movement of the lip toward the extended position results in movement of the support leg from the retracted position to a supporting position. 
     In another aspect, the present invention provides a method of operating a dock leveler having a ramp, a support leg and a lip. The method includes the steps of raising the ramp above a resting position, retracting the support leg to a retracted position, contacting the lip with a vehicle, extending the lip to an extended position, and moving the support leg from the retracted position to a supporting position during the extending step. 
     In yet another aspect, the present invention provides a method of operating a dock leveler having a ramp and a support leg, the method including the steps of raising the ramp above a resting position, retracting the support leg to a retracted position, lowering the ramp into substantial alignment with the vehicle bed, and moving the support leg from the retracted position to a supporting position during the aligning step. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a dock leveler incorporating a support leg mechanism embodying the present invention. 
     FIG. 2 is a side elevation section showing the support legs resting on the supporting subframe and the ramp in a substantially horizontal position. 
     FIG. 3 is a rear elevation of one of the support legs taken along line  3 — 3  in FIG.  2 . 
     FIG. 4 is a side elevation section showing the lip in a partially extended position, the support leg in a retracted position, and the follower in an active position. 
     FIG. 5 is a side elevation showing the lip in a fully extended position and the support leg in a retracted position, but moving toward a supporting position. 
     FIG. 6 is a side elevation showing the lip in a fully extended position and the support leg in a supporting position. 
     FIG. 7 is a side elevation showing the lip falling to a pendent position, the support leg in a supporting position, and the follower in an inactive position. 
    
    
     DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
     FIG. 1 illustrates a dock leveler  10  embodying the present invention. The dock leveler  10  is adapted to bridge the gap between a loading dock and the bed of a truck or carrier parked in front of the loading dock. The dock leveler  10  includes a frame  12  or supporting structure mounted in the rear end of a pit  14 , a ramp  16  pivoted to the frame  12 , and a lip  18  pivotally attached to the ramp  16 . The ramp  16  is movable between a generally horizontal position and upwardly inclined or downwardly declined positions. A dock leveler that may be suitable for application of the present invention is described in U.S. Pat. No. 5,481,774, issued Jan. 9, 1996 to Hodges et al. 
     The illustrated dock leveler  10  also includes a support leg mechanism  20  having two support legs  22 . The support legs  22  are pivotally mounted to the ramp  16  near its front end  24  by means of leg brackets  26 . As shown in FIGS. 2 through 7, the support legs  22  can be rotated between a supporting position (FIG. 2) and a retracted position (FIG.  4 ). When the support legs  22  are in a retracted position, they allow the ramp  16  to fall below a substantially horizontal position to a full below dock position. When the support legs  22  are in the supporting position of FIG. 2, they can support the ramp  16  in a substantially horizontal position (FIG.  2 ). 
     A supporting sub-frame  28  rests within the frame  12  of the dock leveler  10  and engages the support leg  22  in a supporting position. In the illustrated embodiment the supporting sub-frame  28  includes a V-shaped groove configured to receive the V-shaped end of the support leg  22 . In this way, the support leg  22  is positioned on the supporting sub-frame  28 . 
     Support legs  22  can be configured such that they can engage the supporting sub-frame  28  in a variety of positions (e.g., when the ramp  16  is slightly above or below a substantially horizontal position). The illustrated embodiment includes an abutment  29  that can engage the support leg  22  such that the ramp  16  is positioned in an intermediate below dock level position. In particular, the front end  24  of the ramp  16  can descend about four inches when the support leg  22  engages the abutment  29 . This is approximately half of the maximum possible descent of the front end  24  of eight inches. A similar multiple engagement may also be accomplished, for example, by providing the support legs  22  with a series of notches that can engage the supporting sub-frame  28 , as in U.S. Pat. No. 3,858,264 to Kuhns et al. As used herein, the support legs  22  are in a supporting position if they can support the ramp  16  above the full below dock position, and the support legs  22  are otherwise in a retracted position. 
     The support legs  22  are biased toward a supporting position by a leg spring  30 , shown in FIG.  3 . As shown in FIG. 2, the leg spring  30  is mounted to the support leg  22  and to the bracket  26  to spring bias the support leg  22  to the supporting position. In the illustrated embodiment, the leg spring  30  is a torsion spring. 
     The illustrated extension lip  18  is pivotally mounted to the ramp  16  near the front end  24  of the ramp  16 . As shown in FIGS. 2 and 3, the extension lip  18  is mounted onto a plurality of lip brackets  32  that rotate on a shaft  34  attached to the ramp  16 . When the extension lip  18  is rotated outwardly and upwardly, the top surface of the extension lip  18  forms an extension of the surface of the ramp  16  (FIGS.  5  and  6 ). The fully extended lip  18  can be rested upon a vehicle bed  36  to form a continuous surface. Thus, the lip  18  provides a means for bringing the ramp  16  into substantial alignment with the vehicle bed  36 . Engagement of the rear edge of the lip  18  with the front surface of the ramp  16  prevents the lip  18  from moving beyond the fully extended position where it is generally flush with the ramp  16 . When not extended, the illustrated lip  18  hangs in a downwardly pendent position (FIG.  2 ). The pendent position of the lip  18  is an inoperative position because the lip  18  will not engage the vehicle bed  36 . 
     As shown in FIG. 1, the lip  18  can be moved from the pendent position to an extended or operative position, and held such that the lip  18  may engage the vehicle bed  36 , by a lip lifting mechanism  39 . Various mechanical, hydraulic or pneumatic lip lifting mechanisms are well-known in the field. Lip lifting mechanisms may engage the lip  18  upon lifting of the ramp  16 . With such a mechanism, the raising of the ramp  16  causes extension of the lip  18  which may then engage the vehicle bed  36 . An example of such a mechanism is pictured in U.S. Pat. No. 3,858,264 to Kuhns et al. Alternately, extension of the lip  18  may be caused by lowering of the ramp  16  after the ramp  16  is raised to its highest position. An example of such a mechanism is pictured in U.S. Pat. No. 5,475,888 to Massey. By either method, the lip  18  is moved to an extended position in order to engage the vehicle bed  36  surface. 
     In the illustrated embodiment, the lip lifting mechanism  39  extends the lip  18  only partially, to a partially extended position between its pendent position and its fully extended position. The lip  18  then comes to its fully extended position as it rests upon the surface of the vehicle bed  36  and the weight of the ramp  16  extends the lip  18  to its maximum extension. 
     A cam and follower assembly  38  is operatively positioned between the lip  18  and the support leg  22 . The illustrated cam and follower assembly  38  includes a cam in the form of a striker bar  40  mounted between two lip brackets  32 , and a follower  44  mounted on the support leg  22 . The striker bar  40  will engage the follower  44  as the lip  18  is moved to an extended position. Because the striker bar  40  has effectively a stepped cam profile, it can engage or release the follower  44  in a stepped fashion. 
     The illustrated follower  44  is movably mounted to the support leg  22 . The follower  44  rotates on a follower shaft  46  within the support leg  22 , and is biased to a forward active position by a torsion spring  48  connected between the follower  44  and to the support leg  22 . As seen in FIGS. 2 and 3, the follower  44  extends through an opening  50  in the front surface of the support leg  22 . The striker bar  40  can engage either the top surface  52  of the follower  44 , during retraction of the support leg  22 , or the front surface  54  of the follower  44 , when the lip  18  falls to a pendent position. When the top surface  52  of the follower  44  is acted upon by the striker bar  40  in a downward direction (FIG.  4 ), the follower  44  will not move relative to the support leg  22  and the support leg  22  will be retracted. When the front surface  54  of the follower  44  is acted upon in a rearward direction, the follower  44  will move to an inactive position and allow the lip  18  to return to its resting pendent position without affecting the position of the support leg  22  (FIG.  7 ). 
     The present invention generally relates to the means by which alignment of the ramp  16  with the vehicle bed  36 , and thereby movement of the lip  18 , is related to movement of the support leg  22 . As shown in FIGS. 2 through 7, a mechanism  20  causes movement of the support leg  22  in response to movement of the lip  18 . 
     In operation of the illustrated embodiment, the ramp  16  begins from a substantially horizontal position (i.e., a dock level position) with the lip  18  in a pendent position before any loading occurs, as shown in FIG.  2 . In this resting position, the support legs  22  are in a supporting position. 
     Next, as shown in FIG. 4, the ramp  16  is raised and lowered towards the vehicle bed  36  surface. Simultaneously, the lip  18  is moved to an extended position, here a partially extended position, by a lip lifting mechanism. As the lip  18  rotates to the partially extended position, the support leg  22  is retracted by engagement of the striker bar  40  with the top surface  52  of the follower  44  while the follower  44  is in the active position. Because the support leg  22  is retracted, the ramp  16  of the dock leveler  10  can be lowered to a below dock level position. 
     Next, as shown in FIG. 5, the lip  18  engages the vehicle bed  36  surface and is moved to an extended position, here a fully extended position, by the weight of the ramp  16 . The contacting of the rear edge of the lip  18  with the front surface of the front end  24  of the ramp  16  limits the rotation of the lip  18  past its fully extended position. As the lip  18  rotates to its fully extended position, the striker bar  40  disengages the follower  44 . When this happens, the support leg  22  may rotate forward to a supporting position. Because the support leg  22  is spring biased forwardly, it will automatically move to a supporting position. In this way, extension of the lip  18  from a partially extended position to a fully extended position causes movement of the support leg  22  from the retracted position to a supporting position at substantially the same time. 
     Finally, after the loading operations are completed the vehicle pulls away from the loading dock. Customarily, the dock leveler  10  will be returned to a resting position before the truck leaves the loading dock. This is accomplished by raising the ramp  16  sufficiently for the lip  18  to return to a pendant position, and then lowering the ramp  16  to a substantially horizontal position where the ramp  16  rests on the support legs  22 . The extension lip  18  thus hangs between the dock leveler  10  and the vehicle bed  36  and allows the ramp to descend past the vehicle bed  36  to a resting position. 
     In the event that the vehicle pulls away unexpectedly, the lip  18  can fall to its pendent position without moving the support leg  22 , as shown in FIG.  7 . This is accomplished by actuation of the striker bar  40  with the front surface  54  of the movable follower  44 , and rotation of the follower  44  to an inactive position. The ramp  16  can thereby descend to a resting position (e.g., a substantially horizontal position). 
     Other means of accomplishing the present invention may be possible, for example using chains or other linkages. 
     Various modes of carrying out the invention are contemplated as being within the scope of the following claims, particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.