Patent Application
20050251934
The present invention pertains to a dock leveler construction, generally, and to an improved construction for the platform of a pit dock leveler, in particular.
A dock leveler (dockboard) is a device designed to bridge the gap between a loading dock and the top surface of a truck or trailer bed. Because the truck bed and the top of the loading dock are often not at the same height, most dock levelers can accommodate a range of vertical dock/truck bed mismatches.
Dock levelers come in three primary configurations: edge of dock levelers, vertically stored levelers, and pit dock levelers. The least expensive type of dock leveler, the edge of dock leveler (EOD), attaches to the face of the dock. EOD's require the least amount of concrete work for installation, and provide unobstructed access to the dock, such as for end loading of a truck. EODs' limited extended length relegates them to servicing a relatively narrow vertical range of around ±5 inches. Vertically stored levelers accommodate considerably more dock/truck bed level mismatch than EOD levelers. The vertically stored leveler's shortcoming is a relatively high initial cost and access to the dock face is unobtainable. Pit dock levelers reside in a pit formed in the dock and usually can accommodate a comparatively large dock/truck bed height mismatches of ±12 inches in most models. Pit dock levelers provide unobstructed access to the dock, but tend to cost more than other dock leveler types, both in initial cost and in the cost of the concrete work required for installation of pit levelers in the dock.
Pit dock levelers come in many variations, but those of the existing art have a base frame that is secured to the dock pit and upon which other components of the leveler are attached, either directly or indirectly. Pivotally connected to the base frame is a dock platform capable of supporting a substantial load (i.e., a fork truck traffic). The dock platform is therefore typically reinforced with ribs of C-channel, rolled steel beam, trapezoidal beam, or box beam construction. These reinforcing ribs are typically welded directly to the underside of the dock platform. Pivotally connected to the other end of the platform is a dock platform lip, which hangs substantially downwards when not in use and is extended when in use to rest on a truck bed, creating a bridge between the dock and the truck.
The weight of the platform/lip combination is not trivial, and if the movement of the platform and lip is not motorized by either hydraulics, screw drives, pneumatics, or the like, then a counterbalancing method using springs is used. In most cases, the counterbalancing mechanism is upwardly biased and the counterbalancing moment is slightly more than the moment required to rotate the platform, thus rotating the platform upwards. Preventing the platform from rotating upwards is a hold down mechanism.
The typical operation of mechanical upwardly-biased levelers involves pulling a cable or chain releasing the hold down mechanism and allowing the counterbalance mechanism to raise the platform. Towards the top of the platform travel, a chain or cable connected to a mechanism extends (or rotates away from the platform) the lip in some levelers. In other levelers, the lip extends when an operator walks down the upwardly rotated platform. In either case, an operator releases the chain, re-engaging the hold down. The operator then walks down the platform causing the extended lip to rest on the truck bed. Among the most common failure points in traditional dock leveler construction are the welded joints between the platform and the platform's underside reinforcing ribs. As heavy fork truck traffic repeatedly rolls over the platform, the welds are repeatedly stressed, and eventually fatigue-induced weld failure occurs. Given this deficiency in existing pit dock leveler construction, it is desirable to have a dock platform design in which the number of reinforcing ribs is minimized yet the platform retains sufficient structural support to perform the bridging function of the dock leveler.
This goal is accomplished by forming the dock platform from independent structural segments that are arranged adjacent one another to create a stronger segmented dock platform for the dock leveler with fewer welded joints.
The preferred embodiment of the present invention is a pit dock leveler having a base frame secured to a loading dock pit and a dock platform pivotally connected at one end to the base frame and pivotally connected at its opposite end to a dock platform lip that pivots between a downward hanging position when the dock leveler is not in use and an extended position substantially co-planar with the dock platform when the dock leveler is in use, whereby the dock platform lip spans and compensates for the space and height differentials between the loading dock and a transport vehicle, wherein the improvement comprises, the dock platform having a plurality of independent segments arranged adjacent one another, each segment being formed from a single metallic sheet having two opposing ends and two opposing side edges, with the opposing side edges first bent downwardly at right angles and then bent inwardly in mirror image relationship, forming two opposing C-channels from the single metallic sheet, with each segment being separately and pivotally connected at one end to the loading dock pit and separately and pivotally connected at an opposite end to the dock platform lip.
Referring to
Connected to the dock platform assembly 103 and to the dock pit 102 is a lifting mechanism 108. It will be appreciated that while the illustration of this embodiment of the invention in
Connected to frame 101 is a dock platform lip extension mechanism 109 that mechanically extends the dock platform-lip plate 104 after the dock platform 103 has been raised. It will be appreciated that the dock platform lip extension mechanism 109 illustrated can be replaced with many other types currently on the market and not change the segmented platform for the dock leveler of the present invention.
The dock platform assembly 103 compromises at least two adjacent independent support segments 132 (
Referring now to
A platform deck plate 106 of each support segment 132 is formed from a single metallic sheet that has two opposing ends pivotally attached to rotating joint 125 and pivot joint 105, and two opposing sides that are bent downwardly and inwardly to form two mirror image C channels, and forming platform deck legs 128 by bending the plate 106 at points 126 and 127. The bends at points 126 and 127 position the platform deck legs 128 some distance away from the top of the platform deck plate 106. When bent in this fashion, the platform deck legs 128 of formed platform deck plate 106 become a significant structural component of the platform deck plate 106.
Depending on the width of each support segment 132, the load the dock platform assembly 103 is to support, and the concentration of that load, supporting platform deck rib structures 107 may be required. It will be appreciated that though a box structure for the platform deck supporting rib 107 is depicted in
It will be appreciated that while the shape of the ribs (if any), the length of the platform deck plate bends, and the number of platform deck segments can be modified, the essential scope of the invention is not departed. For example, while the formed legs 128, 132 of
