Stump out safety leg system for dock levelers

Abstract

A pit dock leveler having a base frame secured to a loading dock pit and a dock platform pivotally connected at one of its ends 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, the dock leveler having at least one safety leg pivotally mounted directly to the underside of the dock platform near its pivotal connection to the dock platform lip, the safety leg manually pivotal between a first position and a second position, until it is substantially not perpendicular to the underside of the dock platform.

Description

BACKGROUND OF INVENTION

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. fork truck traffic). 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. See FIG. 1.

The Loading Dock Equipment Manufacturers Association (LODEM) has devised what it considered to be the minimum safety and performance criteria for dock levelers, which are published in ANSI Standard MH30.1. They describe a dock-leveling device as “a manufactured structure design to span and compensate for space and height differentials between a loading dock and a transport vehicle to facilitate safe and efficient freight transfers.” Later in the standard (4.1.9) it recommends that “safety systems that restrict uncontrolled drop of the platform shall be designed for resistance to loads imposed by loss of support at the lip end of the platform when the dock leveling device carries a load not exceeding its rated capacity.” In other words, when a truck pulls away from the dock while the leveler is in the bridging configuration, the leveler shall include some method of preventing excessive drop of the leveler, thus limiting the risk of injury.

Except for fully hydraulic types, to meet the requirements of the standard, pit dock levelers use pivoting safety legs mounted near the end of the platform, aft of the lip. The legs support the leveler at horizontal when the leveler is stored. When the leveler is in the bridging configuration when the truck bed is above dock level, the legs hang downward. If the truck pulls away from the dock in this configuration, the legs will stop the downward travel of the platform at the horizontal level. See FIG. 2.

For below dock level loading, typically the pivoting safety legs are connected to a pull chain through mechanical linkages. When the chain is pulled, the legs rotate out of the way, allowing the deck to go below dock level. See FIG. 3.

This common safety leg paradigm has a problem associated with it that has plagued the loading dock industry since the pit dock leveler's inception. The problem is known in the industry as stump out.

Stump out occurs when the leveler is at or just above dock level, and the truck is being loaded. A typical stump out scenario follows:

• • 1. The leveler is in the bridging configuration with the truck just above dock level.
  • 2. The load (usually transported by a forklift) is wheeled onto the truck.
  • 3. The greater load on the truck's suspension causes the truck bed height to lower.
  • 4. The hold down mechanism keeps the platform at the higher level, but the lip rotates to rest on the lowered truck bed.
  • 5. When a forklift tries to exit the truck, the lip is positioned at such a severe angle that the forklift cannot exit the truck.

Not only is stump out inconvenient because typically the fork lift driver then exits the truck and recycles the leveler for a below dock level configuration, but it can be dangerous as well.

If the forklift driver does not recognize stump out, he may try to drive up the lip (which is at too steep of an angle) imparting a large impact force onto the lip and the rest of the leveler structure. The safety legs stop the fall of the platform. In severe cases, the safety legs will push through the leveler platform and the lip bent to the point of rendering the leveler damaged and unusable.

Several attempts have been made previously to control stump out in a mechanically activated (non-hydraulic) lip actuation, as disclosed in U.S. Pat. Nos. 3,995,342, 5,440,772, and 6,276,016. All were workable in theory, but proved to be impractical in their execution. All used some variation of a sensor hinged to the lip. In the case of U.S. Pat. No. 6,276,016, the lip is segmented into three parts, with two shorter lip segments serving as the sensors. When the truck is safely in position and the lip extended, the sensors (which are typically under the lip) are engaged. Connected to the sensors are linkages that push or pull the legs 30 away from the stationary legs 40 connected to the base frame. When the truck pulls away from the dock, the shorter sensors disengage before the lip loses its purchase on the truck bed. When the sensors lose purchase, the legs 30 are brought to perpendicular with the platform to minimize platform freefall.

All of these prior art designs suffer from what happens after an initial impact during freefall. The lip and sensors would both rotate erratically and uncontrollably until the impact energy is dissipated. During this time, the sensors pull or push the legs out of their safety, supporting position and the platform falls to its lowest position.

SUMMARY OF THE INVENTION

The present invention described hereinafter is directed to a dock leveler safety leg system wherein the chance of stump out is eliminated while at the same time retaining the safety capabilities of LODEM 4.1.9.

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 of its ends 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, the dock leveler having at least one safety leg pivotally mounted directly to the underside of the dock platform near its pivotal connection to the dock platform lip, the safety leg manually pivotal between a first position perpendicular to the underside of the dock platform and a second position in which the safety leg is pivotal away from the dock platform lip, until it is substantially not perpendicular to the underside of the dock platform, the safety leg, when in its first position, is of sufficient length to prevent the dock platform from pivoting below horizontal after loss of transport vehicle support for the in-use dock platform lip; wherein the improvement comprises, a first moment arm extending between each safety leg and the safety leg pivotal mounting on the underside of the dock platform, whereby when the dock platform is horizontal the moment of the first moment arm pivots the safety leg away from its first position towards its second position to a position therebetween in which the safety leg is not perpendicular to the underside of the dock platform; a second moment arm for each first moment arm, each second moment arm having a weight at one end and a safety leg contact point at the other end, and each pivotally mounted to the underside of the dock platform about a point between the weight and the contact point, whereby the contact point is pivotal into contact with the safety leg by the moment of the second moment arm from its pivotal mounting to the weight, which is greater than the moment of the first moment arm, whereby when the dock platform is horizontal the safety leg is pivoted by the moment of the second moment arm to the safety leg's first position, perpendicular to the underside of the dock platform; and a linkage pivotally mounted at one end to the dock platform lip and pivotally mounted at the other end to each second moment arm between its pivotal mounting and the weight, whereby when the dock platform lip is in the extended position, or when the dock platform lip is in the downward hanging position, the linkage does not affect the moment of the second moment arm, but when the dock platform lip is therebetween, the linkage pivotally moves the second moment arm against the moment between the pivotal mounting and the weight, reducing the moment of the second moment arm to less than the moment of the first moment arm, whereby the moment of first moment overcomes the moment of the second moment arm and pivots the safety leg from its first position toward its second position to a position therebetween in which the safety leg is not perpendicular to the underside of the dock platform.

Another 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 of its ends 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, the dock leveler having at least one safety leg pivotally mounted directly to the underside of the dock platform near its pivotal connection to the dock platform lip, the safety leg manually pivotal between a first position perpendicular to the underside of the dock platform and a second position in which the safety leg is pivotal away from the dock platform lip until it is substantially not perpendicular to the underside of the dock platform, the safety leg, when in its first position, being of sufficient length to prevent the dock platform from pivoting below horizontal after loss of transport vehicle for the in-use dock platform lip; wherein the improvement comprises, a first movement arm extending between each safety leg and the safety leg pivotal mounting on the underside of the dock platform, whereby when the dock platform is horizontal the first movement arm pivots the safety leg away from its first position towards its second position to a position therebetween in which the safety leg is not perpendicular to the underside of the dock platform; a second movement arm for each first movement arm, each second movement arm having a safety leg contact point at one end thereof, and each pivotally mounted to the underside of the dock platform, whereby the contact point is pivotal into contact with the safety leg by the second movement arm, the force of which upon the safety leg is greater than the force of the first movement arm upon the safety leg, whereby the safety leg is pivoted by the second movement arm to the safety leg's first position, a linkage pivotally mounted at one end to the dock platform lip and pivotally mounted at the other end to each second movement arm, whereby when the dock platform lip is in the extended position, or when the dock platform lip is in the downward hanging position, the linkage does not affect the movement of the second movement arm, but when the dock platform lip is therebetween, the linkage moves the second movement to reduce its force upon the safety leg, reducing the force upon the safety leg of the second movement arm to less than the force upon the safety leg of the first movement arm, whereby the first movement arm overcomes the second movement arm and pivots the safety leg from its first position toward its second position to a position therebetween in which the safety leg is not perpendicular to the underside of the dock platform.

Another 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 of its ends 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, the dock leveler having at least one safety leg pivotally mounted directly to the underside of the dock platform near its pivotal connection to the dock platform lip, the safety leg manually pivotal between a first position perpendicular to the underside of the dock platform and a second position in which the safety leg is pivotal away from the dock platform lip until it is substantially parallel to the underside of the dock platform, the safety leg, when in its first position, being of sufficient length to prevent the dock platform from pivoting below horizontal after loss of transport vehicle support for the in-use dock platform lip; wherein the improvement comprises, apparatus to pivot each safety leg from its first position in which it is positioned when the dock platform lip is in the extended position, or when the dock platform lip is in the downward hanging position, and towards its second position to a position therebetween when the dock platform lip is between the extended and downward hanging positions.

Related objects of the invention will be clear from the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the best mode presently envisioned for carrying out the invention.

FIG. 1 is a prior art pit leveler with extended lip resting on truck bed.

FIG. 2 is a prior art pit leveler in above dock level bridging configuration.

FIG. 3 is a prior art pit leveler in below dock level bridging configuration.

FIG. 4 is a perspective view of a dock leveler with a safety leg system according to one embodiment of the present invention.

FIGS. 5 and 6 are prior art drawings showing dock levelers with safety leg assemblies that are prone to stump out.

FIG. 7 is a side view of the safety leg system of the present invention with the lip in a downward hanging position and the deck leveler in a stored position.

FIG. 8 is a side view of the safety leg system of the present invention with the leveler in the bridging configuration, slightly above dock level, and the safety legs perpendicular to the platform.

FIG. 9 is a side view of the safety leg system of the present invention in which the truck bed has been lowered and the safety legs have been rotated rearwards.

FIG. 10 is a side view of the safety leg system of the present invention in which the leveler is in the bridging configuration and slightly below dock level.

FIG. 11 is a side view of the safety leg system of the present invention in which “action” lines have been added to illustrate the movements during platform free fall.

FIG. 12 is a side view of an alternative embodiment of the safety leg system of the present invention with the leveler in the bridging configuration.

FIG. 12a is an enlarged partial view of FIG. 12.

FIG. 13 is a side view of the alternative embodiment of FIG. 12 in which the truck bed would have been lowered and the safety legs have been rotated rearwards.

FIG. 13a is an enlarged partial view of FIG. 13.

FIG. 14 is a side view of the alternative embodiment of FIG. 12 with the lip in a downward hanging position and the deck leveler in a stored position.

FIG. 14a is an enlarged partial view of FIG. 14.

FIG. 15 is a side view of an alternative embodiment of the safety leg system of the present invention with the leveler in the bridging configuration.

FIG. 15a is an enlarged partial view of FIG. 15.

FIG. 15b is a partial front perspective view of FIG. 15.

FIG. 16 is a side view of the alternative embodiment of FIG. 15 in which the truck bed would have been lowered and the safety legs have been rotated rearwards.

FIG. 16a is an enlarged partial view of FIG. 16.

FIG. 17 is a side view of the alternative embodiment of FIG. 15 with the lip in a downward hanging position and the deck leveler in a stored position.

FIG. 17a is an enlarged partial view of FIG. 17.

FIG. 18 is a side view of an alternative embodiment of the safety leg system of the present invention with the leveler in the bridging configuration.

FIG. 18a is an enlarged partial view of FIG. 18.

FIG. 18b is a partial front perspective view of FIG. 18.

FIG. 19 is a side view of the alternative embodiment of FIG. 18 with the lip in a downward hanging position and the deck leveler in a stored position.

FIG. 19a is an enlarged partial view of FIG. 19.

FIG. 20 is a side view of the alternative embodiment of FIG. 18 in which the truck bed would have been lowered and the safety legs have been rotated forward.

FIG. 20a is an enlarged partial view of FIG. 20.

FIG. 21 is a side view of an alternative embodiment of the safety leg system of the present invention with the leveler in the bridging configuration.

FIG. 21a is an enlarged partial view of FIG. 21.

FIG. 22 is a side view of the alternative embodiment of FIG. 21 in which the truck bed would have been lowered and the safety legs have been rotated rearwards.

FIG. 22a is an enlarged partial view of FIG. 22.

FIG. 23 is a side view of the alternative embodiment of FIG. 21 with the lip in a downward hanging position and the deck leveler in a stored position.

FIG. 23a is an enlarged partial view of FIG. 23.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, the safety leg system is a series of linkages and levers. Referring to FIGS. 8-10, the safety legs (10) are hinged about pivot points (16) to the underside of the platform (02) of the dock leveler (01). Also hinged about pivot point (16) to the underside of the deck (02) is a moment arm (15) with a weight (11) at one end thereof and safety leg contact plate (17) at the other end thereof, with the moment arm (15) orientated such that contact plate (17) pushes the safety leg (10) forward when weight (11), moment arm (15) and contact plate (17) are subjected only to the force of gravity.

The safety legs (10) are designed with their own moment arm (21) about pivot point (16) such that when the platform (02) is substantially horizontal, and not under the influence of weight (11), the safety leg (10) would rotate about pivot point (16) rearwards under gravity until it hangs substantially pendant from pivot point (16). Nonetheless, with the safety legs (10) rotated slightly rearwards, short of pendency, they will not make contact with the stationary legs (12), which are part of the leveler base frame (03). The weight (11) imparts through moment arm (15) a greater moment onto the safety leg (10) through contact plate (17) than the safety leg's own moment rearward through moment arm (21), thus ensuring that under the influence of weight (11) the safety leg (10) remains perpendicular to the underside of the platform (02).

Therefore, if the weight (11) is mechanically pushed rearwards, the safety leg (10) will also rotate rearward under its own moment about pivot point (16). Otherwise, the weight (11) will rotate the contact plate (17) through moment arm (15), forward causing the safety leg (10) to rotate forward until its proximate end (20) contacts the bottom of the platform (02), at which point safety leg (10) is perpendicular to the underside of the platform (02).

A linkage (13) is pivotally connected at pivot point (19) to the moment arm (15) at one end and is pivotally connected at pivot point (18) to the dock leveler lip (04) at the other end of moment arm (15).

The linkage (13) and its pivot points (18, 19) are orientated such that when the lip (04) is mostly to fully extended (FIG. 8), the weight (11) is freed to hold the safety leg (10) perpendicular to the platform (02), as described, above. When the lip (04) is in the middle of its downward travel, usually between 15 degrees and 70 degrees below parallel with the platform (02), the linkage (13) mechanically pushes moment arm (15) upward and the weight (11) rearward, allowing the safety leg (10) to pivot rearward against contact plate (17), under gravity. When the lip (04) is mostly hanging downwardly (pendant), such as when the dock leveler (01) is stored (FIG. 7), the moment arm (15) and the weight (11) are again freed to hold the safety leg (10) perpendicular to the deck (02) through the contact plate (17), as described, above.

Referring now to FIGS. 8-11, when the substantially level dock leveler (01) is in the bridging configuration (FIG. 8) and the bridged truck bed (05) lowers, the classic stump out scenario occurs (FIG. 9), the platform (02) maintains its position because of an engaged hold down (06) (FIG. 4). The lip (04) then rotates (falls) to contact the lower truck bed height (FIG. 9). The lowered lip (04) through the pivot point (18) and linkage (13), pushes the moment arm (15) upwards and the weight (11) rearwards freeing the safety leg (10) from the previous influence of contact plate (17) allowing the safety leg (10) to rotate rearwards (FIG. 9).

As a forklift exits the truck, its wheels contact the lip (04). The weight of the forklift, through the lip (04), pushes the platform (02) downwards until the lip (04) is substantially parallel with the deck (02) (FIG. 10). As the deck is lowering, the rearwardly rotated safety leg (10) misses the stationary leg (12) connected to the base frame (03), and the platform (02) descends below dock level bypassing stump out (FIG. 9).

Referring again to FIG. 4, to maintain the requirements of meeting LODEM 1.4.9, connected between the lip (04) and the platform (02) is a damper (14) usually a shock absorber, or dampened gas spring, to slow the descent of the lip (04).

Referring now to FIG. 11, when a truck pulls away from a bridging dock leveler (01) with a load (fork lift, material, etc.) on the platform (02), the platform (02) descends much more quickly than the dampened lip (04) can rotate to the downward hanging position. In this short period of free fall, the lip (04) remains substantially extended. The linkage (13) does not move substantially, allowing the weight (11) to keep the safety leg (10) perpendicular to the platform (02). Thus, under a panic freefall scenario, the safety legs (10) will impact the stationary legs (12) connected to the base frame (03). Under free fall, when the safety legs (10) impact the stationary legs (12) connected to the base frame (03), the platform (02) has a tendency to rebound, but it maintains a substantially horizontal (stored) position. Testing to date has demonstrated that the lip (04) will rotate wildly and unpredictably during rebound. If the safety leg (10) was actuated directly via a direct connection to the linkage (13) instead of being indirectly actuated through the moment arm (15), contact plate (17) and weight (11), the safety leg (10) would be immediately pushed rearwards during a rebound allowing the platform (02) to fall to a below dock level position.

The present invention allows the lip (04) to rotate wildly during rebound yet not move the safety legs (10) out of position in contact with the stationary legs (12) connected to the base frame (03).

It is to be understood that although the preferred embodiment of the present invention is shown using weight masses and gravity to move the parts in the preferred embodiment of the invention to date, springs could have also been used with the same result.

Referring now to FIGS. 12 to 14a, an alternative embodiment of the safety leg system of the present invention has a deck (02), lip (04), stationary leg (12), and pivoting safety leg (10) about pivot point (16) similar to the previous descriptions. In this embodiment, connected to the lip (04) is a cam (22) that controls the position of the safety leg (10). The safety leg (10), when not under the influence of the cam (22), will swing pendant and out of the way of contacting the stationary leg (12). When the lip (04) is substantially horizontal or pendant (vertical), the cam (22) pushes the safety leg (12) substantially vertical. Otherwise, the cam (22) allows the safety leg (12) to swing out of the way of the stationary leg (12). Referring to FIG. 14, like previous designs, this embodiment preferably uses a damper (114) on the lip (04) for the same reason as previously mentioned. In this embodiment, the damper (114) is connected directly to the safety leg (12) slowing the rearward movement of the safety leg (12). Therefore, under a freefall condition, the damper (114) would maintain the position of the safety leg (12) long enough for the safety leg (12) to make contact with the stationary leg (12).

Referring now to FIGS. 15 to 17a, another alternative embodiment of the safety leg system of the present invention has a deck (02), lip (04), stationary leg (12), and pivoting safety leg (110) about pivot point (116) similar to the previous descriptions. The primary difference is that the safety leg (110) when hanging pendant, is in the vertical, supporting configuration. Pivotally connected to the lip (04) is a control arm assembly (30) that is slidably received within slide tube (34). The slide tube (34) is pivotally connected to the safety leg (110). When the lip (04) is substantially horizontal, the control arm assembly (30) does not impact the movement of the safety leg (110) and the safety leg (28) stays in the vertical supporting orientation in contact with stationary leg (12). When the lip (04) is in the middle of its movement between parallel and perpendicular to the deck (02), the control arm assembly (30), through the slide tube (34) pushes the safety leg (110) rearward, thus missing the stationary leg (12). When the lip (04) is pendant (vertical), the control arm assembly (30) does not impact the slide tube (34) and the safety leg (28) stays in the vertical, supporting orientation. Like previous designs, this alternative embodiment also preferably uses a damper (14) on the lip (04) for the same reasons previously mentioned.

Referring now to FIGS. 18 to 20a, another alternative embodiment of the safety leg system of the present invention has a deck (02), lip (04), stationary leg (12), and pivoting safety leg (210) about pivot point (216) similar to the previous descriptions except that the safety leg (210) pivots forwards toward the lip (04) instead of rearwards. Pivotally connected to the lip (04) is a control arm assembly (42) that is slidably received within slide tube (46). The slide tube (46) is pivotally connected to the safety leg (210). When the lip (04) is substantially horizontal, the safety leg (210) is pushed by the control arm assembly rearwards until substantially vertical. When the lip (04) is in the middle of its movement between horizontal and vertical, the control arm (42), through the slide tube (46) does not push the safety leg (210), allowing the safety leg (210) to rotate about pivot point (216) pendant under gravity, thus missing the stationary leg (12) (FIGS. 20, 20a). When the lip (04) is pendant, the control arm (42), through the slide tube (46), again pushes the safety leg (210) rearwards until substantially vertical. Like previous designs, this alternative embodiment also preferably uses a damper (14) on the lip (04) for the same reasons previously mentioned. In this embodiment, the damper (214) is connected directly to the safety leg (210), as in the previous embodiment, slowing the rearward movement of the safety leg (210). Therefore, under a freefall condition, the damper (14) would maintain the position of the safety leg (210) long enough for the safety leg (210) to make contact with the stationary leg (12).

Referring now to FIGS. 21 to 23a, another alternative embodiment of the safety leg system of the present invention has a deck (02), lip (04), stationary leg (12), and pivoting safety leg (310) about pivot point (316) similar to the previous descriptions. Pivotally connected to the lip (04) is a control arm assembly (54) that is slidably received within slide tube (58). The slide tube (58) is pivotally connected to the safety leg (310). When the lip (04) is substantially horizontal, the safety leg (310) is pulled forward until substantially vertical. When the lip (04) is in the middle of its movement between horizontal and vertical, the control arm assembly (54), through the slide tube (58) does not pull the safety leg (310) allowing the safety leg (310) to rotate about pivot point (316) pendant under gravity, thus missing the stationary leg (12). When the lip (04) is pendant, the control arm assembly (54), through the slide tube (58), again pulls the safety leg (310) forward towards the lip (04) and substantially vertical. In this embodiment, the damper (314) is connected directly to the safety leg (310), slowing the rearward movement of the safety leg (310). Therefore, under a freefall condition, the damper (314) would maintain the position of the safety leg (310) long enough for the safety leg (310) to make contact with the stationary leg (12).

Referring again to each of the embodiments of FIGS. 15-23a, each control arm assembly (30, 42, 54) is illustrated having a spring (410, 420, 430). A spring as shown, or some other equivalent means, for eliminating control arm assembly movement of the safety leg (110, 210, 310) in certain circumstances in which movement of the safety leg (110, 210, 310) is not desired is provided for the following reasons.

In the embodiment of FIGS. 15 to 17a, in which the safety leg (110) is perpendicular to the deck (02) under the force of gravity, the spring (410) is operable just after a lip (04) freefall, when the lip (04) is rotating wildly and the safety leg (110) is contacting the stationary leg (12). When the lip (04) is in the middle of its travel, the frictional force between the safety leg (110) and stationary leg (12) is greater than the force imparted onto the safety leg (110) from the lip (04) through control arm assembly (30) and through the spring (410). Thus, the spring (410) will compress instead of the safety leg (110) being rotated rearwards, thus maintaining deck (02) support and meeting LODEM 30.1.

In the embodiments of FIGS. 18-23a in which the safety legs (210, 310) are not perpendicular to the deck (02) under the forces of gravity, the safety legs (210, 310) desirably remain in their supporting configuration, perpendicular to the deck (02), when the lip (04) is approximately between 0 and 15 degrees and 70 to 90 degrees from parallel with the deck (02). When the safety legs (210, 310) are pushed perpendicular to the deck (02), and the lip (04) still has some travel to it, the spring (420, 430) will then compress, allowing the lip (04) to maintain its full range of travel.

Claims

1. A pit dock leveler having a base frame secured to a loading dock pit and a dock platform pivotally connected at one of its ends 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, the dock leveler having at least one safety leg pivotally mounted directly to the underside of the dock platform near its pivotal connection to the dock platform lip, the safety leg manually pivotal between a first position perpendicular to the underside of the dock platform and a second position in which the safety leg is pivotal away from the dock platform lip, until it is substantially not perpendicular to the underside of the dock platform, the safety leg, when in its first position, is of sufficient length to prevent the dock platform from pivoting below horizontal after loss of transport vehicle support for the in-use dock platform lip; wherein the improvement comprises,

a first moment arm extending between each safety leg and the safety leg pivotal mounting on the underside of the dock platform, whereby when the dock platform is horizontal the moment of the first moment arm pivots the safety leg away from its first position towards its second position to a position therebetween in which the safety leg is not perpendicular to the underside of the dock platform;

a second moment arm for each first moment arm, each second moment arm having a weight at one end and a safety leg contact point at the other end, and each pivotally mounted to the underside of the dock platform about a point between the weight and the contact point, whereby the contact point is pivotal into contact with the safety leg by the moment of the second moment arm from its pivotal mounting to the weight, which is greater than the moment of the first moment arm, whereby when the dock platform is horizontal the safety leg is pivoted by the moment of the second moment arm to the safety leg's first position, perpendicular to the underside of the dock platform; and

a linkage pivotally mounted at one end to the dock platform lip and pivotally mounted at the other end to each second moment arm between its pivotal mounting and the weight, whereby when the dock platform lip is in the extended position, or when the dock platform lip is in the downward hanging position, the linkage does not affect the moment of the second moment arm, but when the dock platform lip is therebetween, the linkage pivotally moves the second moment arm against the moment between the pivotal mounting and the weight, reducing the moment of the second moment arm to less than the moment of the first moment arm, whereby the moment of first moment overcomes the moment of the second moment arm and pivots the safety leg from its first position toward its second position to a position therebetween in which the safety leg is not perpendicular to the underside of the dock platform.

2. A pit dock leveler having a base frame secured to a loading dock pit and a dock platform pivotally connected at one end of its ends 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, the dock leveler having at least one safety leg pivotally mounted directly to the underside of the dock platform near its pivotal connection to the dock platform lip, the safety leg manually pivotal between a first position perpendicular to the underside of the dock platform and a second position in which the safety leg is pivotal away from the dock platform lip until it is substantially not perpendicular to the underside of the dock platform, the safety leg, when in its first position, is of sufficient length to prevent the dock platform from pivoting below horizontal after loss of transport vehicle for the in-use dock platform lip; wherein the improvement comprises,

a first movement arm extending between each safety leg and the safety leg pivotal mounting on the underside of the dock platform, whereby when the dock platform is horizontal the first movement arm pivots the safety leg away from its first position towards its second position to a position therebetween in which the safety leg is not perpendicular to the underside of the dock platform;

a second movement arm for each first movement arm, each second movement arm having a safety leg contact point at one end thereof, and each pivotally mounted to the underside of the dock platform, whereby the contact point is pivotal into contact with the safety leg by the second movement arm, the force of which upon the safety leg is greater than the force of the first movement arm upon the safety leg, whereby the safety leg is pivoted by the second movement arm to the safety leg's first position, perpendicular to the underside of the dock platform; and

a linkage pivotally mounted at one end to the dock platform lip and pivotally mounted at the other end to each second movement arm, whereby when the dock platform lip is in the extended position, or when the dock platform lip is in the downward hanging position, the linkage does not affect the movement of the second movement arm, but when the dock platform lip is therebetween, the linkage moves the second movement to reduce its force upon the safety leg, reducing the force upon the safety leg of the second movement arm to less than the force upon the safety leg of the first movement arm, whereby the first movement arm overcomes the second movement arm and pivots the safety leg from its first position toward its second position to a position therebetween in which the safety leg is not perpendicular to the underside of the dock platform.

3. The loading dock leveler of claim 1 in which the first moment arm and second moment arm pivot about a common axis.

4. The loading dock leveler of claim 2 in which the first movement arm and second movement arm pivot about a common axis.

5. The loading dock leveler of claim 1 and further comprising a damper connected between the dock platform lip and the dock platform, whereby the pivotal movement of the dock platform lip between the extended position and the downward hanging position is slowed.

6. The loading dock leveler of claim 2 and further comprising a damper connected between the dock platform lip and the dock platform, whereby the pivotal movement of the dock platform lip between the extended position and the downward hanging position is slowed.

7. A pit dock leveler having a base frame secured to a loading dock pit and a dock platform pivotally connected at one of its ends 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, the dock leveler having at least one safety leg pivotally mounted directly to the underside of the dock platform near its pivotal connection to the dock platform lip, the safety leg manually pivotal between a first position perpendicular to the underside of the dock platform and a second position in which the safety leg is pivotal away from the dock platform lip until it is substantially not perpendicular to the underside of the dock platform, the safety leg, when in its first position, is of sufficient length to prevent the dock platform from pivoting below horizontal after loss of transport vehicle support for the in-use dock platform lip; wherein the improvement comprises,

means to pivot each safety leg from its first position in which it is positioned when the dock platform lip is in the extended position, or when the dock platform lip is in the downward hanging position, and towards its second position to a position there between when the dock platform lip is between the extended and downward hanging positions.

8. The loading dock leveler of claim 7 wherein the means to pivot each safety leg includes a cam mounted to the dock platform lip that controls the pivotal movement of each safety leg.

9. The loading dock leveler of claim 7 wherein the means to pivot each safety leg includes a control arm assembly mounted at one end to the dock platform lip and received at its other end within a sliding tube that is pivotally mounted to each safety leg.

10. The loading dock leveler of claim 9 wherein the means to pivot each safety leg pivots the safety leg towards a second position that is forward of its vertical position.

11. The loading dock leveler of one of claims 7-10 and further comprising a damper connected between the dock platform lip and the dock platform, whereby the pivotal movement of the dock platform lip between the extended position and the downward hanging position is slowed.

12. The loading dock leveler of one of claims 9-10 wherein the control arm assembly includes means to dampen its movement.