Abstract:
A dock leveler ramp with a lip that can be latched in an extended position to ensure that the lip comes to rest upon the back end of a vehicle as the ramp descends includes an unlatching mechanism. The mechanism positively unlatches the lip by direct force created by the lip engaging the vehicle or created by the ramp descending upon an internal abutment in the event that a vehicle is not present. Also, the descent of an unlatched lip is dampened to prevent the lip from slamming back down to its pendant position.

Description:
BACKGROUND OF THE INVENTION 
     1. Field Of The Invention 
     The subject invention generally relates to dock levelers, and more specifically, to dock levelers having a lip extension. 
     2. Description Of Related Art 
     Dock levelers are often used to compensate for a height difference that may exist between a loading dock platform and the bed of a truck parked at the dock. A dock leveler typically includes a ramp that is hinged at its back edge to raise or lower its front edge to generally match the height of the truck bed. Often an extension plate or lip is pivotally coupled to the ramp to bridge the gap between the ramp&#39;s front edge and a back edge of the truck bed. The ramp and lip provide a path for forklift trucks to travel from the loading dock platform and onto the truck bed, thus facilitating loading or unloading the truck. 
     For some dock levelers, the operating sequence involves pivoting the ramp upward to a height that allows the lip to pivot outward so it can extend over the back edge of the truck bed without striking it. The extended position of the lip can be latched to the ramp to allow the ramp enough time to descend and thus place the extended lip upon the truck bed. A contact force between the truck bed and the underside of the lip can be used to unlatch it, so when the truck departs, the unlatched lip is free to swing down. 
     An example of a latching-style dock leveler can be found in U.S. Pat. No. 3,997,932. It appears that a ramp pivots upward to its peak height, while the lip remains hanging downward in its pendant position. Then as the ramp pivots back down, a bar 23 forces linkages 14 and 17 to start lifting the lip. As the ramp continues downward, the lip continues to pivot outward and eventually latches as linkages 14 and 17 toggle over-center. The action of the lip engaging the bed of a truck unlatches the lip. When the truck departs, it appears that the lip falls freely. The resulting slamming action could be startling, unsafe, and possibly shorten the life of the dock leveler. Another problem exists when the ramp descends, but the lip misses the bed of the truck (e.g., no truck is present). It appears that the ramp would fully descend while leaving the lip extended. The next truck to arrive at the dock might back into the extended lip to damage both the truck and the dock leveler. 
     The &#39;932, latching device is also incorporated in the dock levelers of U.S. Pat. Nos. 4,398,315 and 5,416,941. However, the &#39;315 dock leveler adds a break-away coupling (FIGS. 3, 4 and 5) that buckles in the event that a truck backs into a lip that was left latched in an extended position. This might minimize damage to the truck and dock leveler in the event of a collision; however, it might be better to avoid the collision entirely. It appears that neither the &#39;315 nor the &#39;941 dock levelers address the problems associated with a lip being able to free-fall. 
     A latching dock leveler described in U.S. Pat. No. 4,091,488 addresses the free-fall problem, but in doing so introduces yet another problem. An additional link (item 54) is added to latch the lip. To unlatch the lip, link 54 needs to swing down away from item 58. It appears that the only force urging link 54 to swing down is its own weight. And that may be insufficient if link 54 were to seize on some dirt, corrosion, or otherwise bind where link 54 pivots on bracket 55 or possibly where link 54 engages item 58. Such binding could create all the problems normally associated with a lip left in its latched extended position after the truck departs. 
     Similarly, U.S. Pat. No. 3,995,342 also includes a separate additional link (item 32) to hold the lip in a latched state. Link 32 would appear to be susceptible to the forementioned problems of link 54 of the &#39;488 device. Moreover, the &#39;342 dock leveler also appears to allow its lip to fall freely without controlled descent. 
     Although some of the above-mentioned dock levelers have latching lips that are unlatched by the lip engaging the vehicle, the lip/vehicle engagement only triggers the unlatching motion as opposed to forcing it. Thus, additional mechanisms are needed, such as springs or weight, to provide the unlatching force. 
     SUMMARY OF THE INVENTION 
     In order to provide a dock leveler with a positive unlatching mechanism for an extended latched lip, the mechanism unlatches by direct force created by the lip engaging the vehicle or created by the dock leveler descending upon an internal abutment in the event that a vehicle is not present. 
     In some embodiments, the descent of an unlatched lip is dampened to provide a smooth, safe operation. 
     In some embodiments, the unlatching mechanism includes one element that not only exerts a force that holds the lip in a latched condition, but also alternately exerts another lower force that allows the lip to descend at a controlled speed. 
     A positive unlatching mechanism, as provided by a preferred embodiment, might be more reliable than having to rely on spring force to pull relatively small linkages into position or relying on their weight alone to unlatch the lip. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cut-away side view of one exemplary embodiment of a dock lever in its standby position. 
     FIG. 2 shows the ramp of a dock leveler beginning to rise. 
     FIG. 3 shows a dock leveler&#39;s subbing cable just as it becomes taut. 
     FIG. 4 shows the dock leveler&#39;s lip in a latched mode. 
     FIG. 5 shows the ramp about to rest the latched lip upon a truck bed. 
     FIG. 6 shows a toggle-over-center mechanism unlatching the lip. 
     FIG. 7 shows the ramp and an unlatched lip descending as the truck departs. 
     FIG. 8 shows a latched lip that missed the truck. 
     FIG. 9 shows the dock leveler itself forcing the toggle mechanism to unlatch the lip. 
     FIG. 10 shows an unlatched lip with the ramp pivoted below the loading dock platform. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     One example of dock leveler that forcibly unlatches its extended lip by the force generated at a distal end of the lip upon engaging the vehicle is shown in FIG.  1 . In this figure, a dock leveler  20  is shown in standby with its pivoting lip  22  stored and its pivoting ramp  24  generally flush with an upper level of a loading dock  26 . 
     When a vehicle  32 , such as a truck, arrives at dock  26 , ramp  24  pivots upward about a hinge  28  connected to a frame  30 . This starts raising a front edge  34  of ramp  24 , as shown in FIG.  2 . In this case, a lifting device  36  is employed to assist the upward pivotal motion of ramp  24 . Examples of lifting device  36  include, but are not limited to, a hydraulic cylinder, a pneumatic cylinder, an air bag or a spring (gas or mechanical). 
     Ramp  24  continues to rise, which tightens an elongated snubbing member  38 , as shown in FIG.  3 . In this example, snubbing member  38  connects a main link  40  to frame  30  and can be any one of a variety of elongated members. Some examples of snubbing member  38  would include, but not be limited to, a cable, a chain, a strap, or even a sliding rod or link with a slot. 
     Once snubbing member  38  is taut, ramp  24  continuing to pivot upward causes snubbing member  38  to pull main link  40  counter clockwise, as shown in FIG.  4 . Main link  40  rotates about an axis  42  whose position is fixed relative to ramp  24  by way of a conventional bracket. Such a bracket is well known by those skilled in the art and is only schematically incorporated in the illustration of axis  42  to more clearly show the operation of dock leveler  20 . Rotational motion of main link  40  drives a lip link  44  by way of a pin  46  engaging the end of a slot  48  of lip link  44 . A second pin  50  couples lip link  44  to a lip lug  52  that rigidly extends from lip  22 . Thus, lip  22  pivots (in relation to ramp  24 ) about a hinge  54  in response to main link  40  rotating. 
     In one exemplary embodiment, main link  40 , in conjunction with lip link  44  provides a toggle-over-center mechanism  56  that latches lip  22  in an extended position prior to ramp  24  descending. In FIG. 3, mechanism  56  is first shown in an unlatched configuration with pin  46  generally above a line  58  that is defined by axis  42  and pin  50 . Then, as main link  40  rotates to the position shown in FIG. 4, pin  46  moves generally below line  58  to place mechanism  56  in an over-toggle, latched configuration. To avoid making it too difficult to unlatch, a stop  60  is fixed relative to ramp  24  to prevent mechanism  56  from over-traveling in its latched configuration. 
     Once latched, the over-toggle position of main link member  40  and lip link member  44  holds lip  22  in a latched mode. Member  44  exerting a holding force  61  against lug  52  holds lip  22  substantially fixed relative to ramp  24 , regardless of any tension in snubbing member  38 . This ensures that lip  22  remains extended over the back edge of the vehicle, as ramp  24  pivots downward, as shown in FIG.  5 . As ramp  22  descends farther, as shown in FIG. 6, the underside of lip  22  engages vehicle  32 . For example, lip  22  might rest upon the back end of a trailer bed of a truck. 
     Vehicle  32  abutting lip  22  may, in effect, rotate lip  22  slightly upward relative to ramp  24 . The relative rotational motion could cause a release link  62  (e.g., a slidable bar or a pliable elongated member, such as a chain or a cable) to pull mechanism  56  into its unlatched configuration. In other words, an engagement force  63  created by lip  22  engaging vehicle  32  is used or transmitted to another member (e.g., member  52 ,  44  and/or  40 ) for positively unlatching lip  22 . Of course, the magnitude and direction of force  63  can vary upon being transmitted to other members. The basic concept of using engagement force  63  to positively and directly move member  56  to an unlatched position can be carried out by a variety of structures too numerous to mention. However, as one example, release link  62  connects lip lug  52  to main link  40 , so as lip  22  pivots upward relative to ramp  24 , the resulting rotation of lug  52  pulls on link  62  to force main link  40  to rotate clockwise about pin  42 , thus moving main link  40  and lip link  44  to an under-toggle position. In this example, the action is facilitated by pin  46  being free to slide within slot  48 . With dock leveler  20  in the position shown in FIG. 6, vehicle  32  may now be loaded or unloaded, if desired. 
     When vehicle  32  departs, as shown in FIG. 7, lip  22  drops slightly, as allowed by the travel of pin  46  within slot  48 . This removes the tension in release link  62  and allows lip  22  to descend while in an unlatched mode. Now lip  22  and ramp  24  are both free to pivot downward to the position shown in FIG.  2  and eventually return to its standby position of FIG.  1 . 
     To prevent lip  22  from undergoing rapid descent, a dampener  64  can be added to dampen the motion (i.e., reduce the velocity) of at least one of lip  22 , lip lug  52 , lip link  44 , or main link  40 . For example, in one embodiment, dampener  64  is a piston/cylinder arrangement with an integral spring  66  (FIG. 7) that helps counteract the weight of lip  22 . Spring  66  could be a mechanical compression spring, or dampener  64  could be a gas spring providing both functions of dampening motion and counteracting the weight of lip  22 . In one embodiment, dampener  64  is a fluid-filled piston/cylinder such that compression of the cylinder results in fluid flow through a size-controlled orifice to reduce the velocity of clockwise rotation of link  40 . 
     Returning to FIG. 5, where ramp  24  is descending with lip  22  latched, it is possible that lip  22  may miss vehicle  32 . For example, vehicle  32  may be improperly parked or may not even be present at dock  26 . In such a case, vehicle  32  would not unlatch lip  22 ; thus ramp  24  and latched lip  22  could descend to a predetermined lower limit  70 , as shown in FIGS. 8 and 9. To address this situation, lip  22  is unlatched by a mechanism other than the vehicle. 
     For example, in one embodiment, a travel limiting member  68  obstructs continued downward movement of ramp  24  once ramp  24  reaches its lower limit  70 . In this example, member  68  is situated under ramp  24  to engage mechanism  56  to forcible unlatch it automatically (i.e., without additional intervention from a vehicle  32  or an operator). Obstructing member  68  engaging the underside of links  40  or  44  unlatches lip  22  by forcing main link  40  to rotate clockwise, so mechanism  56  toggles through the center position (toggle position) wherein pivots  50 ,  46  and  42  are collinear to an under-toggle position wherein pivot  46  is above a line connecting pivots  50  and  42  as shown in FIG.  9 . This unlatching operation is illustrated by dock leveler  20  moving from the position shown in FIG. 8 to that of FIG.  9 . 
     When lip  22  is unlatched by obstructing member  68 , dock leveler  20  will eventually reach the position of FIG.  10 . From this extremely low position, ramp  24  can be raised slightly and then re-lowered to its standby position of FIG.  1 . This final operation might be carried out by an operator manipulating some control or performed automatically in response to a limit switch sensing that lip  22  or ramp  24  has reached some predetermined low position with the lip in a pendant or near-pendant position. 
     Although the invention is described with respect to a preferred embodiment, modifications thereto will be apparent to those skilled in the art. Therefore, the scope of the invention is to be determined by reference to the claims that follow.