Abstract:
A vehicle restraint includes a hook supported by a carriage that travels vertically along a track, wherein the hook can move to selectively restrain or release a vehicle&#39;s ICC bar at a loading dock. The carriage includes a unique roller arrangement that minimizes friction while maximizing the rolling line contact between a set of rollers and the track. Instead of individual rollers mounted at opposite ends of a shaft extending from the carriage, two or more rollers are mounted to a module, and two such modules are rotatably or otherwise movably attached to the ends of the shaft. Each module includes a shaft-receiving bore having an inner diameter comparable to that of a conventional individual roller, thus the unique roller arrangement lends itself well to retrofit applications.

Description:
FIELD OF THE INVENTION 
     The subject invention generally pertains to a vehicle restraint at a loading dock and more specifically to the restraint&#39;s guide track and track follower. 
     BACKGROUND OF RELATED ART 
     A typical truck loading dock of a building includes an exterior doorway with an elevated platform for loading and unloading vehicles such as trucks and trailers. Many loading docks have a dock leveler to compensate for height differences between the loading dock platform and an adjacent bed of the truck or trailer. A typical dock leveler includes a deck, also known as a ramp or dockboard, which is pivotally hinged along its back edge to vary the height of its front edge. An extension plate, or lip, extends outward from the deck&#39;s front edge to span the gap between the rear of the trailer bed and the front edge of the deck. Extending from the deck&#39;s front edge, the lip rests upon the truck bed to form a bridge between the deck and the bed. This allows personnel and material handling equipment, such as a forklift, to readily move on and off the vehicle during loading and unloading operations. 
     To help hold the vehicle sufficiently close to the dock platform so that the lip of the dock leveler can remain resting upon and supported by the bed of the vehicle, loading docks often include a vehicle restraint that helps prevent the vehicle from accidentally pulling away from the dock. Vehicle restraints, such as those disclosed in U.S. Pat. Nos. 4,443,150 and 4,915,568, usually include a hook or barrier that restrains the vehicle by reaching up in front of the vehicle&#39;s RIG (rear impact guard), also known as an ICC bar. An ICC bar is a beam that extends horizontally across the rear of a truck, just below the truck bed. An ICC bar&#39;s primary purpose is to prevent an automobile from under-riding the truck in a rear-end collision. 
     When a forklift drives over the dock leveler and onto the trailer bed, the weight of the forklift and the cargo it may be carrying can add a significant load to the truck bed. Likewise, when the forklift exits the truck bed, substantial weight is removed from the trailer. Thus, the load carried by the trailer changes repeatedly during the loading/unloading process. The trailer&#39;s suspension may respond to these load changes by allowing the trailer and its ICC bar to rise and fall accordingly. The vertical movement can be particularly pronounced when the vehicle has an air suspension system. 
     As the vehicle moves up and down, the vehicle restraint&#39;s hook preferably moves with it to prevent the ICC bar from rising up and over the hook, and thereby disengaging from the barrier. Many barrier restraints can follow the vertical movement of an ICC bar because the barriers are usually mounted to a carriage or sliding member that can travel along a vertical guide track. Unfortunately, vehicles with air suspension often have a generally equal but horizontal component of movement for every vertical movement. Such horizontal movement can apply a substantial horizontal force between the carriage and the guide track. Repeated vertical and thus horizontal movement of the barrier creates localized wear due to the concentrated horizontal line contact between the guide track and the individual rollers of the carriage. Sliding members without rollers distribute the wear more evenly over a broader contact area; however, friction associated with sliding members is typically greater than that of rolling elements, thus wear is a problem with sliding members as well. 
     Although the vehicle restraint shown in U.S. Pat. No. 4,443,150 has six rollers to help distribute the load, such a design has its drawbacks. If all six rollers are not perfectly parallel to the guide track due to manufacturing tolerances of the size and location of the rollers or nonlinearity of the track, some rollers may carry substantially more load than others. Even if all six rollers are perfectly aligned parallel to a perfectly straight track, an ICC bar pulling the hook forward or pushing the hook down might apply a rotational moment on the carriage such that the upper most rollers push forward on one side of the track while the lowermost rollers press against the rear surface of the track, thereby possibly leaving the rollers of intermediate height only lightly loaded or substantially unloaded. Moreover, if each pair of horizontally displaced rollers is mounted to its own shaft, the added number of shafts can add bulk, weight and cost to a vehicle restraint. 
     Consequently, there is a need for a vehicle restraint that minimizes the wear between the carriage of a vertically movable barrier and the track along which the carriage travels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a conventional vehicle restraint in a lowered release position. 
         FIG. 2  is a side view similar to  FIG. 1  but showing the restraint in a raised blocking position. 
         FIG. 3  is a top view of  FIG. 1 . 
         FIG. 4  is a top view showing one embodiment of a novel vehicle restraint in a lowered release position. 
         FIG. 5  is a side view of the vehicle restraint of  FIG. 4  but showing the restraint in a raised blocking position. 
         FIG. 6  is a perspective view showing a method of retrofitting a vehicle restraint. 
         FIG. 7  is a side view of a vehicle restraint with a pivotal hook. 
         FIGS. 7   a - c  are schematic side views illustrating an operational sequence of the vehicle restraint of  FIG. 7 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIGS. 1-3  show a conventional vehicle restraint  10  for restraining a vehicle  12  (e.g., via the vehicle&#39;s ICC bar) adjacent a loading dock face  14 , and  FIGS. 4 and 5  show an improved vehicle restraint  16  that provides a more effective distribution of load between a guide track  18  and a set of rollers that travel along track  18 . Restraints  10  and  16  are shown in their basic form to more clearly illustrate the subject invention, which can be readily incorporated in a wide variety of more complicated restraint designs such as those disclosed in U.S. Pat. Nos. 6,431,819; 6,322,310; 6,190,109; 5,964,572; 5,297,921 and 4,443,150; all of which are specifically incorporated by reference herein. 
     Vehicle restraints  10  and  16  each include a restraining structure  17  and a track  18  mountable to dock face  14 . Restraining structure  17  comprises a base  20  vertically movable along track  18  and a hook  22  supported by base  20 . As used herein, the term “base” is interchangeable with “track follower” and has been adopted in the interest of brevity and readability. Use of the term “base” is not meant to be limiting in connoting a structure or support that is under something. Rather the base/track follower forms a part of the overall restraining structure  17  along with a “hook”  22 . Hook in this context should also be broadly construed to connote a member coupled to the base and adapted to selectively engage and release a vehicle&#39;s ICC bar—either by being fixed to the base, or coupled for the movement relative thereto. Vehicle restraints  10  and  16  also include an actuator  25  (e.g., piston/cylinder, hydraulic motor, electric motor, linear motor, etc.) for moving hook  22  between a raised position ( FIGS. 2 and 5 ) and a lowered position ( FIGS. 1 ,  3  and  4 ) to respectively block and release the ICC bar of vehicle  12 . 
     The actual construction of hook  22  and base  20  may vary. In some cases, hook  22  is rigidly attached or is an integral extension of base  20 , whereby the two move in unison. In other cases, a hook  22 ′ can pivot or otherwise move relative to a base  20 ′ as is the case with a vehicle restraint  10 ′ shown in  FIGS. 7 and 7   a - c . At least some of the patents that have been incorporated by reference provide additional examples of vehicle restraints with a pivotal hook. 
     To hold hook  22  in relation to dock face  14  and to enable base  20  to travel smoothly along the height of track  18 , vehicle restraint  10  of  FIGS. 1-3  includes an upper set of rollers  24  and a lower set of rollers  26  that are captured by vertical flanges  28  of track  18 . Roller sets  24  and  26  are rotatably coupled to base  20  by way of upper and lower shafts  30  and  32 , respectively. Since each roller of sets  24  and  26  are in virtual horizontal line contact with track  18 , the load between track  18  and roller sets  24  and  26  is concentrated along approximately four rolling lines of contact. 
     To distribute the load more broadly over a greater number of rolling lines of contact, roller sets  24  and  26  can be replaced by roller modules such as modules  34 ,  36  or  38  of  FIG. 6 . This is possible because modules  34 ,  36  and  38  each have a shaft-mounting bore that is approximately the same diameter of a shaft-mounting bore  40  of rollers  24  and  26 . In addition to the benefit of having more rolling lines of contact, the even distribution of load is further improved because modules  34 ,  36  and  38  distribute its rollers both above and below shaft  30 . The roller modules described herein can be provided as factory installed options sold with vehicle restraints, and/or, the roller modules described herein can be retrofit to vehicle restraints already existing in the field. 
     Referring to  FIGS. 4 and 5 , vehicle restraint  16  has four roller modules  34  instead of roller sets  24  and  26  of  FIGS. 1-3 . Restraint  16  can be originally made this way, or restraint  16  can be the result of retrofitting restraint  10  of  FIGS. 1-3 . In either case, the roller module  34  includes a first upper module  34   a , a second upper module  34   b , a first lower module  34   c  and a second lower module (the second lower module is hidden from view underneath module  34   b  and is behind module  34   c  with respect to  FIG. 5 ). Each module  34  includes four relatively small diameter rollers  42  that can each rotate about its own relatively small axle  44 . A shaft-mounting bore  46  allows modules  34   a  and  34   b  to be mounted to upper shaft  30  and allows modules  34   c  and one opposite thereto to be mounted to lower shaft  32 . Limited rotational or translational movement between module  34  and shaft  30 , or similar movement between shaft  30  and base  20  enables modules  34  to align themselves in firm rolling contact with track  18  regardless of some dimensional tolerance of the vehicle restraint&#39;s component parts. 
     If four roller modules  34  replace roller sets  24  and  26 , the rolling line contact with track  18  can at least double. If some horizontal clearance  48  exists between rollers  42  of module  34  and the contact surfaces of track  18  (i.e., the inside surface of flange  28  or a back side  50  of track  18 ), then the rolling line contact with track  18  increases from four rolling line contacts provided by rollers  24  and  26 , to eight rolling line contacts provided by rollers  42 . If, however, module  34  fits tightly within track  18  with no horizontal clearance  48 , then all of rollers  42  will be in rolling line contact with track  18  to provide sixteen rolling line contacts. 
     Alternatively, roller module  36  could be used instead of module  34 , as module  36  has a shaft-mounting bore  52  that also fits the outer diameter of shafts  30  and  32 . If four roller modules  36  replace roller sets  24  and  26 , the rolling line contact with track  18  can double. In this case, some horizontal clearance  48  is particularly beneficial to prevent one side of a roller  54  from dragging against one of the contact surfaces  28  or  50  of track  18  while the opposite side of the same roller  54  is in rolling contact with track  18 . 
     As another alternative, roller module  38  could be used instead of modules  34  or  36 , as module  38  has a shaft-mounting bore  56  that can also fit the outer diameter of shafts  30  and  32  via, for example, a bushing  58 . If four roller modules  38  replace roller sets  24  and  26 , the rolling line contact with track  18  increases from four rolling line contacts provided by roller sets  24  and  26 , to eight rolling line contacts provided by the roller module  38  when some horizontal clearance  48  exists between the rollers of the module  38  and the guide track  18 , or to as many as 24 rolling line contacts when the roller modules  38  fit tightly within guide track  18  (i.e., in the presence of little horizontal clearance between the rollers of the module  38  and the guide track). 
     Any of the roller modules  34 ,  36  and  38  could also be incorporated into a vehicle restraint with a pivotal hook, such as vehicle restraint  10 ′ of  FIGS. 7 and 7   a - c . Roller module  34 , for instance, could couple base  20 ′ to track  18 . In this case, a pin  68  pivotally couples hook  22 ′ to base  20 ′, and an actuator  60  moves hook  22 ′ between a blocking position ( FIGS. 7 and 7   c ) and a retracted position ( FIGS. 7   a  and  7   b ). 
       FIGS. 7   a - c  schematically illustrate an operating sequence of vehicle restraint  10 ′. As vehicle  12  backs into the loading dock, as shown in  FIG. 7   a , the ICC bar of vehicle  12  pushes against an inclined edge  62  of base  20 ′, which forces base  20 ′ down underneath the ICC bar as shown in  FIG. 7   b . A spring  64  holds base  20 ′ solidly up against the ICC bar even if the ICC bar moves up and down in reaction to vehicle  12  being loaded or unloaded of its cargo. Actuator  60  raises hook  22 ′ from its retracted position of  FIG. 7   b  to its blocking position of  FIG. 7   c , thereby restraining vehicle  12  at the loading dock. An optional hydraulic system  66  can be added to help restrict or dampen the vertical movement of the ICC bar. 
     In some embodiments, a vehicle restraint includes “floating” sets of rollers that help evenly distribute the load between a guide track and the rollers. 
     In some embodiments, a vehicle restraint includes a set of rollers that are pivotal or otherwise horizontally movable to compensate for nonlinearity of a guide track or other manufacturing tolerances. 
     In some embodiments, a vehicle restraint includes four or more rollers that are supported by a single main shaft. 
     In some embodiments, a vehicle restraint includes a plurality of rollers supported by a single main shaft, wherein the rollers are distributed both above and below the shaft. 
     In some embodiments, a vehicle restraint includes more than twice as many rollers as shafts for supporting them. 
     In some embodiments, a conventional vehicle restraint with a shaft supporting only two rollers is modified to create an improved retrofit restraint where the original shaft supports more than two rollers. 
     In some embodiments, a vehicle restraint is modified by replacing its original rollers with smaller ones, yet the modified restraint more evenly distributes the load between the guide track and the smaller rollers. 
     Although the invention is described with respect to a preferred embodiment, modifications thereto will be apparent to those of ordinary skill in the art. The scope of the invention, therefore, is to be determined by reference to the following claims: