U.S. patent application number 10/926375 was filed with the patent office on 2006-03-02 for stump out safety leg system for dock levelers.
Invention is credited to Robert J. Chirico, Young Z. Yoon.
Application Number | 20060042030 10/926375 |
Document ID | / |
Family ID | 35940921 |
Filed Date | 2006-03-02 |
United States Patent
Application |
20060042030 |
Kind Code |
A1 |
Yoon; Young Z. ; et
al. |
March 2, 2006 |
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.
Inventors: |
Yoon; Young Z.;
(Indianapolis, IN) ; Chirico; Robert J.;
(Indianapolis, IN) |
Correspondence
Address: |
Clifford W. Browning;Bank One Center/Tower
111 Monument Circle, Suite 3700
Indianapolis
IN
46204-5137
US
|
Family ID: |
35940921 |
Appl. No.: |
10/926375 |
Filed: |
August 25, 2004 |
Current U.S.
Class: |
14/71.1 |
Current CPC
Class: |
B65G 69/2841
20130101 |
Class at
Publication: |
014/071.1 |
International
Class: |
E01D 1/00 20060101
E01D001/00 |
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.
Description
BACKGROUND OF INVENTION
[0001] 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.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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: [0011] 1. The leveler is in the bridging configuration
with the truck just above dock level. [0012] 2. The load (usually
transported by a forklift) is wheeled onto the truck. [0013] 3. The
greater load on the truck's suspension causes the truck bed height
to lower. [0014] 4. The hold down mechanism keeps the platform at
the higher level, but the lip rotates to rest on the lowered truck
bed. [0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] Related objects of the invention will be clear from the
following descriptions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The drawings illustrate the best mode presently envisioned
for carrying out the invention.
[0026] FIG. 1 is a prior art pit leveler with extended lip resting
on truck bed.
[0027] FIG. 2 is a prior art pit leveler in above dock level
bridging configuration.
[0028] FIG. 3 is a prior art pit leveler in below dock level
bridging configuration.
[0029] FIG. 4 is a perspective view of a dock leveler with a safety
leg system according to one embodiment of the present
invention.
[0030] FIGS. 5 and 6 are prior art drawings showing dock levelers
with safety leg assemblies that are prone to stump out.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] FIG. 12a is an enlarged partial view of FIG. 12.
[0038] 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.
[0039] FIG. 13a is an enlarged partial view of FIG. 13.
[0040] 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.
[0041] FIG. 14a is an enlarged partial view of FIG. 14.
[0042] 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.
[0043] FIG. 15a is an enlarged partial view of FIG. 15.
[0044] FIG. 15b is a partial front perspective view of FIG. 15.
[0045] 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.
[0046] FIG. 16a is an enlarged partial view of FIG. 16.
[0047] 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.
[0048] FIG. 17a is an enlarged partial view of FIG. 17.
[0049] 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.
[0050] FIG. 18a is an enlarged partial view of FIG. 18.
[0051] FIG. 18b is a partial front perspective view of FIG. 18.
[0052] 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.
[0053] FIG. 19a is an enlarged partial view of FIG. 19.
[0054] 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.
[0055] FIG. 20a is an enlarged partial view of FIG. 20.
[0056] 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.
[0057] FIG. 21a is an enlarged partial view of FIG. 21.
[0058] 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.
[0059] FIG. 22a is an enlarged partial view of FIG. 22.
[0060] 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.
[0061] FIG. 23a is an enlarged partial view of FIG. 23.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0062] 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.
[0063] 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).
[0064] 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).
[0065] 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).
[0066] 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.
[0067] 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).
[0068] 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).
[0069] 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).
[0070] 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.
[0071] 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).
[0072] 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.
[0073] 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).
[0074] 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.
[0075] 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).
[0076] 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).
[0077] 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.
[0078] 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.
[0079] 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.
* * * * *