Note: Descriptions are shown in the official language in which they were submitted.
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PIVOTAL AND TRANSLATIONAL DOCK LEVELER LIP
Background Of The Invention
Field Of The Invention
The subject invention generally relates to dock levelers, and more
specifically,
to dock levelers having a lip extension.
Descri~~tion Of Related Art
Dock levelers are used to compensate for height differences between a
loading dock platform and an adjacent bed of a truck or trailer. A typical
dock leveler
includes a deck, also known as a ramp or dockboard, which is pivotally hinged
along
its back edge to vary the height of its front edge. An extension plate, or
lip, extends
outward from the deck's front edge to span the gap between the rear of the
truck bed
and the front edge of the deck. The lip is usually moveable between a
retracted,
stored position (i.e., clear of the truck) to an extended, operative position.
In the
extended, operative position, the lip extends from the deck's front edge and
rests upon
the truck bed to form a bridge between the two. This allows personnel and
material
handling equipment to readily move on and off the vehicle during loading and
unloading operations.
With some dock levelers, the lip moves linearly, as disclosed in U. S. Patent
6,081,954 and German Patent DE2800128A1. The linear movement allows varying
the extent to which the front edge of the lip overlaps the vehicle bed. A
variable overlap
can be useful when cargo rests particularly near the rear edge of the vehicle
bed, and
thus limits the bed's available floor space upon which the front edge of the
lip may
rest. In such cases, the operator may move the lip linearly up against the
cargo. But
this could create dangerously insufficient overlap between the lip and the
truck bed;
as such an approach relies on the operator's judgment. Too small of an overlap
could
result in loss of contact between the lip and the bed - potentially allowing
the deck to
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fall. Another dock leveler, disclosed in German Patent DE19612135A1, has a lip
fixed
relative to its deck with side bumpers that move along a plane. However, all
of these
devices in their stored positions (also known as a cross-traffic position
where an
upper surface of the deck is flush with the adjacent floor) provide no
significant
obstruction to a forklift or other material handling equipment that might
accidentally
drive off the front edge of the deck when a vehicle is not present at the
dock.
However, some dock levelers include a pivotal lip with a rear edge that
protrudes above the deck when the deck is in its cross-traffic position,
thereby
providing an obstruction to material-handling equipment. During loading or
unloading
operations, a front edge of the tip pivots out over the rear edge of the truck
bed, while
the rear edge of the lip pivots down to overlap the deck, thus bridging the
gap
between the deck and the truck bed while removing the obstruction to material-
handling equipment. But the extension of the lip is generally fixed, so the
lip is unable
to adjust to situations where there is limited floor space at the rear of a
vehicle bed.
Another dock leveler, disclosed in U. S. Patent 4,920,598, provides a pivoting
lip with some sliding movement when the tip hangs generally pendant. In the
stored,
cross-traffic position, the sliding movement allows the lip to protrude above
the deck.
The protruding portion of the lip thus creates an obstruction that helps
inhibit
equipment from accidentally driving off the front edge of the deck. When the
deck is
raised from the cross-traffic position, the sliding movement allows the lip 30
to translate
relative to the deck to a position where the rear or top edge of the lip no
longer forms
an obstruction. The lip can then be extended to a position where the rear edge
of the
lip abuts the front edge of the deck, thus preventing the lip from sliding
back. Thus,
cargo at the very back of the truck bed may interfere with a fully extended
lip. So in
such cases, the lip is moved to a substantially pendant position below the
deck, and
the deck is either moved to its cross-traffic position or to a below-dock
position. In the
cross-traffic position the deck is generally flush with the adjacent floor of
the dock
platform, and in the below-dock position, the deck is below the adjacent
floor. In
either case, the lip does not rest on the bed of the truck nor does it
protrude above
the deck. This allows some material-handling equipment, such as fork lift
trucks, to
drive onto the deck and reach out with their forks to place or remove loads
from the
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very rear of the truck bed without interference from the lip. However, the gap
between
the deck and the truck bed (due to the lip being pendant) is generally not
meant to be
driven across. Thus, the gap inhibits some material handling equipment, such
as
pallet jacks, from loading or unloading cargo from the very rear of the
vehicle bed.
Summary Of The Invention
In order to provide a dock leveler with a traffic surface of variable length,
a
dock leveler includes a lip that pivots and translates from a stored, pendant
position to
various operative, extended positions.
In some embodiments, a dock leveler includes a lip moveably coupled to a
deck, such that when the deck is in a cross-traffic position, the lip
protrudes above the
deck to obstruct material handling equipment from accidentally driving over
the edge
of the deck when a vehicle is not parked adjacent the dock leveler.
In some embodiments a dock leveler includes a deck and a lip that together
provide a traffic surface of variable length by having a variable overlap
between the lip
and the deck.
In some embodiments, a dock leveler includes a deck and a lip with the lip
being pivotal relative to the deck about a substantially horizontal axis and
being
further rotatable about a second axis generally perpendicular to the
horizontal axis,
whereby a forward edge of the lip can lie at various angles relative to the
horizontal
axis.
In some embodiments, a dock leveler includes a manually operated switch
installed a significant distance away from a lip of the dock leveler to help
encourage an
operator to stay off the leveler while the lip moves from a pendant position
to an
extended position.
in some embodiments, a dock leveler includes a deck with a recess in which a
lip may lie to help align an upper surface of the lip to an upper surface of
the deck.
Therefore, in accordance with the present invention, there is provided a
dock leveler adapted to engage a vehicle that can have one of several
different
operational circumstances. The dock leveler comprises a ramp and a lip
pivotally
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coupled to the ramp about a substantially horizontal axis, the axis being
fixed
relative to the ramp, the lip being moveable relative to the ramp such that
the lip and
the ramp overlap a variable amount to create a traffic surface of variable
length to
accommodate the different operational circumstances.
Also in accordance with the present invention, there is provided a dock
leveler adapted to engage a vehicle. The dock leveler comprises a ramp having
a
forward edge and a rear edge and a lip adjacent to the forward edge and being
pivotally coupled to the ramp about a substantially horizontal axis, the axis
being
fixed relative to the forward edge, wherein the lip is moveable to place a
distal edge
of the lip upon the vehicle while creating a traffic surface of variable
length
extending from the distal edge to the rear edge.
Further in accordance with the present invention, there is provided a dock
leveler adapted to engage a vehicle. The dock leveler comprises a ramp pivotal
about a first axis and a lip pivotal relative to the ramp about a second axis,
wherein
the lip is pivotal from a pendant orientation to an operative orientation and
is also
selectively moveable to a fully extended position and a partially extended
position,
wherein the lip includes a distal edge adapted to engage the vehicle with a
distance
between the distal edge and the second axis being greater when the lip is in
the
operative orientation while in the fully extended position than when the lip
is in the
operative orientation while in the partially extended position.
Still further in accordance with the present invention, there is provided a
method of operating a dock leveler that includes a ramp rotatable about a
first axis
with a lip coupled to the ramp and being adapted to engage a vehicle, the lip
having
a width substantially the same as a width of the ramp. The method comprises
pivoting the lip about a substantially horizontal axis and simultaneously
providing
relative translation between the lip and the ramp.
Still further in accordance with the present invention, there is provided a
dock leveler adapted to engage a vehicle. The dock leveler comprises a ramp, a
lip
having a front edge and a rear edge with the front edge being adapted to
engage
the vehicle and the lip being pivotally coupled to the ramp to render the lip
moveable between a pendant orientation and an operative orientation, wherein
the
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rear edge of the lip protrudes above the ramp in the pendant orientation and
overlays the ramp in the operative orientation and a switch disposed at a
remote
location relative to the lip, wherein the switch being manually unattended
inhibits the
lip from moving completely from the pendant orientation to the operative
orientation.
5 Still further in accordance with the present invention, there is provided a
dock
leveler adapted to engage a vehicle that can have one of several different
operational circumstances. The dock leveler comprises a ramp, a iip pivotally
coupled
to the ramp about a substantially horizontal axis and slidably coupled to the
ramp
and being moveable relative to the ramp such that the lip and the ramp overlap
a
variable amount to create a traffic surface of variable length to accommodate
the
different operational circumstances and a means for rotating the lip about the
horizontal axis.
Brief Description Of The Drawings
Figure 1 is a side view of one exemplary embodiment of a dock lever in its
standby position with its lip in a stored, pendant position.
Figure 2 shows the dock leveler of Figure 1 with its ramp having risen above
the bed of a vehicle while the leveler's lip hangs in a pendant orientation
relative to
the ramp.
Figure 3 is the same as Figure 2, but with the lip pivoted outward to an
intermediate orientation.
Figure 4 is the dock leveler of Figure 1 touching its lip to a vehicle.
Figure 5 shows the dock leveler of Figure 1 simultaneously resting a portion
of the lip upon the vehicle, pivoting the ramp downward about an axis, and
moving
another portion of the lip toward the axis.
Figure 6 shows the dock leveler of Figure 1 with its lip at an operative
orientation and a partially extended position.
Figure 7 shows the dock leveler of Figure 1 with its lip at an operative
orientation and a fully extended position.
Figure 8 is a top view of Figure 6 with the lip having rotated about an axis
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perpendicular to a horizontal axis.
Figure 9 is a hydraulic schematic used in operating the dock leveler of Figure
1.
Figure 10 is an electrical schematic associated with the hydraulic schematic
of Figure 9.
Figure 11 shows the dock leveler of Figure 1 with its lip pivotally fixed to
force
sliding motion between the lip and the deck as the deck descends.
Description of the Preferred Embodiment
To compensate for height differences between a loading dock platform 10
and the bed of a vehicle 12 (e.g., truck, trailer, etc.) and to form a bridge
between the
two, a dock leveler 14 includes a pivotal ramp 16 with a moveable lip
extension 18, as
shown in Figures 1 - 8. Along a rear edge 20 of ramp 16, a hinge 22 allows
ramp 16
to pivot about a generally horizontal axis 24 to adjust the height of a front
edge 26 of
ramp 16. A ramp actuator 28 (e.g., fluid cylinder, diaphragm, bellows, spring,
motor-
driven actuator, etc.) can then move front edge 26 to the same general
elevation as a
rear edge 30 of vehicle 12.
To bridge the gap between rear edge 30 of vehicle 12 and front edge 26 of
ramp 76, lip 18 is moveably coupled to front edge 26. Lip 18 is interconnected
to the
front edge 26 to provide a variety of positions and types of motion relative
to the
ramp. For example, lip 18 is pivotable relative to the ramp 16 between a
stored, or
pendant, orientation (as in Fig. 1 ) wherein the lip 18 is disposed generally
perpendicular to ramp 16; and an operative orientation wherein lip 18 is
pivoted so as
to form a generally co-planar extension of the ramp 16. It is in the operative
orientation that lip 18 forms a bridge between the ramp 16 and the rear edge
30 of
the vehicle 12. Movement of the lip 18 to the operative orientation thus
creates a
traffic surface 32 (Figures 6 and 7) extending from a front edge 34 of lip 18
to rear
edge 20, which allows personnel and material handling equipment to readily
move on
and off the vehicle during loading and unloading operations.
According to one aspect of the invention, the length of traffic surface 32 can
vary. That is, with lip 18 in the operative orientation, the amount of overlap
between
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the rear portion of the lip 18 and the front portion of the ramp 16 may be
different for
different operational circumstances. Indeed, the nature of the interconnection
between lip 18 and ramp 16 is adapted to provide this adjustability of the
length of
traffic surface 32 based on the operational circumstances, as will be
discussed in
detail below.
In some embodiments, lip 18 is coupled to ramp 16 by way of a sliding
connection that includes a series of studs 40 extending through a
corresponding
series of slots 42 in lip 18. Studs 40 are screwed into or otherwise fastened
to a hinge
plate 44 of a hinge 39. Hinge plate 44 can be one continuous plate or a series
of
individual plate segments, with each segment carrying one of studs 40. A slip-
fit
between studs 40 and slots 42 allows the relative sliding motion, while the
heads on
studs 40 prevent lip 18 and hinge plate 44 from separating. Hinge 39, in turn,
pivotally
couples plate 44 to ramp 16 to provide lip 18 with pivotal motion about a
substantially
horizontal axis 48 for certain operational circumstances, and to provide lip
18 with a
fixed reference point for a more complex translating/rotational motion for
other
operational circumstances, as discussed below.
When the lip 18 is in the pendant orientation of Figures 1 and 2, the sliding
connection allows the iip 18 to slide relative to the ramp 16 between a
stored,
pendant position (in which the lip 18 extends above the ramp 16 to form an
obstruction to material handling equipment that might otherwise accidentally
drive of
the front edge of the ramp 16) as in Figure 1, and a retracted, pendant
position in
which the rear edge of the lip 18 does not extend above the upper surface of
the
ramp 16, as in Figure 2. According to the embodiment, movement of lip 16 from
the
stored, pendant position to the retracted, pendant position is caused by
relative
movement between the ramp 16 and lip 18. That is, lip 18 remains substantially
fixed
as ramp 16 is raised to the Figure 2 position. The sliding connection between
the lip
18 and ramp 16 facilitates this movement. In this regard, the sliding
connection
between lip 18 and ramp 16 is similar to the one disclosed in U.S. Patent
4,920,598.
In distinction to the '598 patent, however, the sliding connection according
to
this embodiment also provides for a sliding translation of the lip 18 relative
to the
ramp 16 for the full range of lip orientations between the pendant orientation
and the
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operative orientation. For example, in the operative orientation according to
this
embodiment, rotation of the lip about axis 54 allows lip 18 to adjust to
situations
where vehicle 12 andlor load 36 are disposed at a slight angle to dock face
10, as
shown in Fig. 8. Such movement does not appear to be possible in the context
of the
'598 patent as the rear edge of the lip abuts a vertical surface on the ramp
when the
lip is in the operative orientation (Fig. 3 of '598). Perhaps more
importantly, the
interconnection between the lip 18 and ramp 16 in this embodiment is also
distinct
from that shown in the '598 patent, as the interconnection here provides for
sliding
movement of the lip relative to the ramp 16 at intermediate orientations
between the
pendant and operative orientations. It is this movement that allows the amount
of
overlap between the rear portion of lip 18 and the front portion of deck 16 to
be
different for varying operational circumstances, and thus to adjust the length
of the
traffic surface 32 depending on those circumstances. To provide this enhanced
functionality relative to the '598 patent, the position of slots 42 in lip 18
and the height
of hinge 39 relative to traffic surface 32 are different to allow lip 18 to
slide relative to
ramp 16 throughout the range of lip orientations. More specifically, slots 42
are
shifted further away from a rear edge 62 of lip 18 and hinge 39 is raised to
be closer
to traffic surface 32.
The operational advantages provided by this structure will now be discussed
in greater detail, particularly in regard to the ability of the length traffic
surface 32 to
be adjusted depending on operational circumstances. In one operational
circumstance,
the vehicle being unloaded has ample floor space at the rear to receive the
lip 18. In
this instance, the leveler according to this embodiment would be operated
conventionally. Ramp 16 would be raised until studs 40 engaged the tops of
slots 42
and raised lip 18 out of lip keepers 60. Once the front edge of lip were high
enough
for front edge 34 to clear the bed of the vehicle, the lip would be rotated
fully to the
operative orientation. To pivot lip 18 about axis 48, a lip actuator 50 (e.g.,
fluid
cylinder, diaphragm, bellows, spring, motor-driven actuator, etc.) is coupled
to a lug
52 that rigidly extends from hinge plate 44. As actuator 50 extends, lip 18
pivots
outward. When the lip is fully rotated to the operative orientation, the ramp
16 and now
generally co-planar lip 18 can be lowered onto the bed of vehicle 12, to
facilitate the
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unloading or loading process. In this circumstance, the length 38 of traffic
surface 32
is at its maximum, as the lip in the operative orientation has its most
minimal overlap
with ramp 16 (see Fig. 7). That is, lip 18 is in an extended position in its
operative
orientation.
A hydraulic circuit 64 of Figure 9 and an electrical circuit 66 of Figure 10
can
control the operation of dock leveler 14. A typical operating sequence would
begin
with dock leveler 14 in its standby position of Figure 1. In this position,
ramp 16 is in
its cross-traffic position where an upper surface 58 of ramp 16 is generally
flush with
the adjacent floor of dock 10. Lip 18 is stored in a generally pendant
orientation with
front edge 34 of lip 18 supported by lip keepers 60 and with a rear edge 62 of
lip 18
ramp 16, as ramp 16 descends from its position of Figure 4 to that of Figure
5. To do
this, load 36, being an obstruction to further extension of lip 18, forces
rear edge 62 of
lip 18 to overlap ramp 16 as ramp 16 descends. Varying the amount of overlap
adjusts length 38 of traffic surface 32 or the distance between axis 24 and
the rear of
load 36. In some embodiments, the movement between lip 18 and ramp 16 is, in
part,
a sliding motion guided by studs 40 sliding within slots 42. While rear edge
62 of lip
18 moves toward axis 24, lip 18 continues rotational movement.
Once lip 18 moves upward (relative to ramp 16) beyond its position shown in
Figure 5 and into the operative orientation of Figure 6 (either by powered
movement
or because of deck descent), ramp descent switch 124 can be released. To sense
the
pivoted positions of lip 18, an arm 130 carrying cams 102, 132 and 134 has one
end
fixed to a rod end 136 of lip actuator 50 while an elongated portion of arm
130 slides
within a guide 138 fixed relative to the cylinder of actuator 50. As rod end
136
extends and retracts, arm 130 moves cams i02 and 132 across limit switch 96
and
moves cam 134 across a roller arm actuator 142 of a limit switch 140. As lip
18
moves from its position of Figure 5 to that of Figure 6, cam 132 actuates
limit switch
96. Cam 132 closing limit switch 96 keeps solenoid valve 92 open (regardless
of
switch 124) by energizing solenoid 90 through the closed contacts 94 of limit
switch
96 and the normally closed contacts 98 of lip switch 100. With cam 132 holding
the
contacts of limit switch 96 closed, solenoid valve 92 remains open while dock
leveler
14 is in the position shown in Figure 6. Solenoid valve 92 being open allows
ramp 16
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to "float" with the incidental up and down movement of vehicle 12, as vehicle
12 is
being loaded or unloaded of its cargo.
To minimize any impedance to material handling equipment traveling
between lip 18 and ramp 16, in some embodiments, ramp 16 includes a pocket or
5 recess 144 into which lip 18 lies when in the operative orientation. In
other
embodiments; however, lip 18 simply overlays surface 58 of ramp 16 without a
recess.
After completing the loading or unloading of vehicle 12 and vehicle 12 departs
the dock area, ramp 16 descends under its own weight, as cam 132 actuating
limit
10 switch 96 keeps solenoid valve 92 open. Once ramp 16 bottoms out (e.g.,
ramp 16
abuts some mechanical stop), the pressure in line 112 drops virtually to zero,
as
actuator 28 no longer supports the weight of ramp 16. The absence of
significant
pressure in line 112 allows the hydraulic fluid in line 122 (which is
pressurized by the
weight of lip 18 pushing against lip actuator 50) to release through a
pressure relief
valve 146, thereby pivoting lip 18 downward by the weight of lip 18 and/or by
a
biasing force of compression spring 125 in cylinder 50. Although slight
downward
movement of lip 18 causes cam 132 to release limit switch 96, cam 134 trips
limit
switch 140 just before cam 132 disengages limit switch 96. Cam 134 closing the
contacts of limit switch 140 restarts pump 82 and keeps solenoid valve 92
open.
Thus, ramp 16 begins rising due to pressurized hydraulic fluid entering ramp
actuator
28 upon flowing in series through fluid line 88, line 110, solenoid valve 92,
line 112
and velocity fuse 114.
Meanwhile, lip 18 continues pivoting downward by way of hydraulic fluid
draining from lip actuator 50 to tank 84 upon flowing in series through
normally open
valve 123, line 122, a pilot-operated check valve 150 (held open by a pilot
line 152
being pressurized by line 88), and a flow restrictor 154. The upward movement
of ramp
16 and the relative downward movement of lip 18 continue until lip 18 achieves
the
pendant orientation.
At that point, cam 134 releases limit switch 140 just after cam 102 trips
limit
switch 96. This turns pump 82 off as the contacts of limit switch 140 and pump
switch
70 are open. Yet, cam 102 tripping limit switch 96 continues to energize
solenoid 90
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of valve 92 through closed contacts 98 of lip switch 100 and the closed
contacts 94 of
limit switch 96. Thus, ramp 16 descends to its standby position of Figure 1,
as
hydraulic fluid escapes from ramp actuator 28 by flowing in series through
velocity
fuse 114, line 112, open solenoid valve 92, and flow restriction 128 of
shuttle valve
104.
When wanting to place the last load on the end of vehicle 12, lip 18 may need
to be slid back without the aid of a load already in place to help push lip 18
back. To
do this, ramp 16 and lip 18 are first moved to the position of Figure 3. From
there,
dock leveler 14 can be lowered to the position of Figure 11 by actuating ramp
descent
switch 124 and a lip-lock switch 127 at the same time. Lip-lock switch 127
energizes
a solenoid 129 to close valve 123, which helps prevent lip 18 from pivoting in
either
direction. Thus, as ramp 16 descends due to switch 124 opening solenoid valve
92,
lip 18 is forced to slide back as front edge 34 abuts vehicle 12. Once lip 18
is slid
back, lip-lock switch 127 can be released, so that further downward movement
of
ramp 16 can force rear edge 62 of lip 18 to pivot downward until dock leveler
14 is in
the position of Figure 6 (but without load 36 already in place).
Although the invention is described with respect to a preferred embodiment,
modifications thereto will be apparent to those skilled in the art. For
example, a
pressure relief valve 156, as shown in Figure 9, can be added to line 110 to
limit the
maximum pressure in the hydraulic system. Therefore, the scope of the
invention is to
be determined by reference to the claims that follow.
