Bridges – Gangway – ramp – or dock leveler – Attached
Reexamination Certificate
1997-04-15
2001-08-21
Neuder, William (Department: 3673)
Bridges
Gangway, ramp, or dock leveler
Attached
C014S069500, C014S071300
Reexamination Certificate
active
06276016
ABSTRACT:
FIELD OF THE INVENTION
The invention is directed generally to dock levelers, and more particularly to a dock leveler exhibiting enhanced protection against uncontrolled free fall.
BACKGROUND OF THE INVENTION
Dock levelers are commonly used at loading docks for the purpose of bridging the gap between a vehicle parked adjacent the loading dock and the loading dock itself. Typically, the vehicle will back up into a parked position wherein the rear of the vehicle engages bumpers disposed on the face of the building and intended to protect both the building and the rear of the vehicle from impact or defacement. With the vehicle backed against the bumpers, a gap still exists between the loading dock and the truck. The dock leveler is intended to bridge this gap.
Typically, the loading dock will be formed with a pit within which framing for the dock leveler is housed. The leveler itself comprises a deck pivotally attached at its rear end relative to the loading dock, usually to the framing. The deck is movable between a stored or “cross-traffic” position wherein the deck is even with the warehouse or building floor on either side of the pit, and a range of operating positions to accommodate various vehicle elevations. The stored position is referred to as a “cross-traffic” position since traffic moving in the warehouse can move over the deck easily as it forms an extension of the surrounding floor. At the front end of the deck, adjacent the parked truck, is a lip pivotally connected to the front end of the deck for movement between a pendant, or stored position and an extended position wherein the lip bridges the gap between the deck and the bed of the parked vehicle. With the leveler in this bridging configuration, fork trucks or personnel can pass between the loading dock and the bed of the parked vehicle for the purpose of loading and unloading the vehicle. As the vehicle is loaded or unloaded, and as the fork truck passes on and off of the vehicle, differing weights are exerted on the vehicle's suspension. As a result, the vehicle will typically move up and down throughout the loading or unloading procedure. The pivotal connection of the deck of the dock leveler allows the leveler to track this up and down movement of the vehicle.
In operation, the deck is first raised from the cross-traffic position (with the lip pendant) to a raised preparatory position. The power to raise the deck is provided either by springs (in the case of a so-called “mechanical leveler”) or by a hydraulic cylinder or other actuator disposed between the framing and the deck. In a mechanical leveler a “holddown” device normally holds the leveler down against the upward bias of the springs. The holddown may be released to raise the deck by pulling the unit's main pull chain. Once the deck reaches the preparatory position, the lip is extended from its pendant position to an extended position. Subsequent downward rotation of the deck places the lip on the bed of the vehicle so as to bridge the gap between the dock and the vehicle. In a hydraulically-powered leveler, or one powered up by a different actuator, gravity provides the force necessary to rotate the leveler downward, while a mechanical leveler requires the weight of dock personnel to “walk down” the leveler to a position wherein the lip rests on the bed of the vehicle. As the vehicle moves up and down during loading or unloading, the leveler pivots up and down to maintain proper contact with the vehicle.
Since dock levelers are capable of pivoting in this manner, they preferably also include some means for preventing uncontrolled free fall of the deck in the event that the vehicle departs while a fork truck or other load is still disposed on the deck. Departure of the vehicle with a load still on the deck is typically referred to as “premature” or “unscheduled” since proper safety procedures require that the deck be unloaded before a vehicle departs. If premature departure were to occur without any means of free fall protection, such premature departure of the vehicle would mean that the lip was no longer in contact with the vehicle, and thus that the heavily loaded deck was effectively unsupported, and it would thus pivot downwardly through its full range of motion until it engaged the pit below. Given that a typical operating range for dock levelers is from 10 inches above dock height to 10 inches below dock height, it would be possible for a fork truck disposed on the leveler in such a situation to fall as much as 20 inches. The violent contact between the falling deck and the pit, as well as the substantial pitch at which the deck would then be disposed, could lead to undesirable results, such as the fork truck falling off the deck or goods or personnel being damaged or injured.
Different types of levelers may include different types of free fall protection intended to minimize the distance through which the deck may free fall before such downward movement is arrested. In the case of hydraulic levelers, the deck is powered through its range of motion by means of a hydraulic cylinder disposed between the underside of the deck and the pit below. To protect against free fall, the hydraulic cylinder typically includes a velocity fuse. The velocity fuse is intended to lock the hydraulic cylinder against further movement in the event that the deck achieves a certain velocity. Accordingly, if free fall begins to occur and the deck reaches this velocity, the hydraulic cylinder will be locked, and prevent the deck from further downward movement. Mechanical and other types of levelers, on the other hand, typically include so-called safety legs to limit free fall distance. An example of one type of safety leg mechanism is shown in the prior art
FIGS. 2 and 3
. The safety leg SL depends from the bottom of the deck and is adapted to engage a pedestal P disposed in the pit. Contact between the end of the leg SL and the pedestal P will arrest downward movement of the deck indicated as D. Thus, if a vehicle prematurely departs with a load on the deck, the deck will only “free fall” a limited distance—until the legs SL engage pedestal P. The legs SL typically remain in a supporting orientation for this purpose. For situations where the bed of the truck is significantly lower than dock height, the legs may be retracted rearwardly by a retracting mechanism R to allow the deck to angle downwardly below dock without the safety leg engaging the first stop S
1
on the pedestal. To protect against free fall with the deck in a below-dock configuration, a second stop S
2
is provided on the pedestal. The safety leg L is biased by a biasing member B, in this case a spring, toward the vertical position shown in FIG.
2
. Accordingly, if the leveler is initially disposed below dock with the legs retracted and then is raised above dock by virtue of weight being removed from the truck and the vehicle suspension raising the leveler, the safety leg SL will return to the vertical orientation shown in FIG.
2
.
While the safety leg configuration, and other similar safety leg configurations, provide the advantageous function of preventing substantial free fall in the event of premature or unscheduled departure of the vehicle with a load on the deck, they are not without their own limitations. One such limitation to previous safety leg configurations is shown if FIG.
3
. In the circumstance shown in
FIG. 3
, the leveler is in a position wherein the safety leg SL engages the stop S
1
on the pedestal P, thus preventing further downward movement of the leveler. As the fork truck moved onto the vehicle bed, however, the weight of the fork truck pushed the vehicle down further. The lip L was able to track this downward movement of the vehicle, since engagement of the safety leg SL with the stop S
1
does not limit rotational movement of the lip L. The deck D, however, was prevented from moving to a lower position. The steep angle of the lip L may prevent the fork truck from being able to drive back up that slope and onto the deck D, or may at least cause a jarring collision
Marshall O'Toole Gerstein Murray & Borun
Neuder William
Rite-Hite Holding Corporation
Singh Sunil
LandOfFree
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