U.S. patent number 3,646,627 [Application Number 05/042,006] was granted by the patent office on 1972-03-07 for holddown mechanism for the ramp of a dockboard.
This patent grant is currently assigned to Kelley Company, Inc.. Invention is credited to Roderick B. Potter.
United States Patent |
3,646,627 |
Potter |
March 7, 1972 |
HOLDDOWN MECHANISM FOR THE RAMP OF A DOCKBOARD
Abstract
A holddown mechanism for the ramp of a dockboard. The rear edge
of the ramp is hinged to the dock and a counterbalancing member is
connected to the ramp and serves to counterbalance the weight of
the ramp and pivot the ramp upwardly to an inclined position. The
holddown mechanism, which is manually releasable, serves to
restrain the counterbalancing member from raising the ramp and
includes a tubular housing pivotally connected to the dock. A
spring is mounted in the housing and the force of the spring acts
against the end of a concentrically mounted tube and urges the tube
to a retracted or telescoped position with respect to the spring
and housing. A ratchet bar is mounted for sliding movement within
the tube and the outer end of the ratchet bar is connected to the
ramp. To prevent relative movement between the ratchet bar and the
tube, a double-pawl mechanism is associated with the tube and is
engageable with the teeth of the ratchet bar. The pawls are
manually released by a pivotable operating handle which operates
through a lost motion connection to move the pawls out of
engagement with the ratchet bar teeth and enable the force of the
counterbalancing member to elevate the ramp.
Inventors: |
Potter; Roderick B. (Milwaukee,
WI) |
Assignee: |
Kelley Company, Inc.
(Milwaukee, WI)
|
Family
ID: |
21919543 |
Appl.
No.: |
05/042,006 |
Filed: |
June 1, 1970 |
Current U.S.
Class: |
14/71.3 |
Current CPC
Class: |
B65G
69/2841 (20130101) |
Current International
Class: |
B65G
69/28 (20060101); B65G 69/00 (20060101); B65g
011/00 () |
Field of
Search: |
;14/71 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Nackenoff; Jacob L.
Claims
I claim:
1. In a dockboard having a ramp member mounted on a support member
and having counterbalancing means for urging the ramp to an
elevated position, a holddown mechanism for locking the ramp
against movement toward said elevated position, said holddown
mechanism comprising a tubular housing pivotally connected to one
of said members, an elongated element pivotally connected to the
other of said members and having a series of abutments spaced along
its length, a tube disposed within the housing and mounted for
movement with respect to the housing and having resilient means
disposed within the housing and arranged to bias the tube to a
retracted position with respect to said housing, said elongated
element mounted for movement with respect to said tube between a
retracted position and an extended position, a substantial portion
of the length of the elongated element being disposed within the
housing when the element is in the retracted position, locking
means engageable with the elongated member for locking the
elongated member with respect to the tube, and release means for
releasing the locking means to thereby permit said counterbalancing
means to move the ramp to the elevated position with movement of
said ramp to the elevated position serving to move said elongated
element to said extended position.
2. The dockboard of claim 1, and including biasing means for
biasing the locking means into locking engagement with the
abutments on said elongated element.
3. The dockboard of claim 2, wherein said release means includes an
operating member movable between a locking position and a release
position, movement of said operating member from the locking
position to the release position acting against the force of said
biasing means to release the locking means from engagement with
said abutments, said release means also including a lost motion
connection arranged so that initial movement of the operating
member on return from the release position through a predetermined
distance toward said locking position will not release the force of
said biasing means and further movement of said operating means
beyond said predetermined distance toward said locking position
will release the force on said biasing means to permit said biasing
means to move the locking means to the locked position.
4. The dockboard of claim 1, wherein said elongated element is a
ratchet having a series of teeth and said locking means includes a
pawl engageable with the teeth of the ratchet.
5. The dockboard of claim 4, in which the teeth of the ratchet and
the pawl are arranged so that the pawl will lock the ratchet
against outward movement with respect to the tube and will permit
free inward movement of the ratchet with respect to the tube.
6. The dockboard of claim 1, wherein said release means comprises a
lever arm connecting to said locking means, a cable having one end
connected to the lever arm, pulley means disposed on the
undersurface of the ramp, said cable extending over said pulley
means, and handle means connected to the opposite end of the cable
and located on the upper surface of the ramp, pulling upward on
said handle means acting to pivot said lever arm to thereby release
the locking means.
7. The dockboard of claim 6, wherein the rear edge of the ramp
member is hinged to the support member and said handle mans is
located adjacent said rear edge, said pulley means including a
first pulley located generally beneath said handle means and
including a second pulley located between the first pulley and the
front edge of the ramp, said cable extending over said first and
second pulleys.
8. In a dockboard having a ramp member mounted on a support member
and having counterbalancing means for urging the ramp to an
inclined elevated position, a holddown mechanism for locking the
ramp against movement toward said elevated position, said holddown
mechanism including a tubular housing pivotally connected to one of
said members, an elongated element pivotally connected to the other
of said members and having a series of abutments spaced along a
length thereof, a second elongated element disposed within the
housing and mounted for movement with respect to the housing and
having an end projecting beyond the housing, resilient means
disposed within the housing for biasing the second element to a
retracted position with respect to said housing, said first element
being mounted for movement with respect to said second element
between a retracted and extended position, a pair of pawls
engageable with the projections on the first element for locking
the first element with respect to said second element, said pawls
and the projections of said first element being arranged so that
only one of the pair of pawls is in full engagement with the
projections at any given position of said first element, and
release means for releasing the pawls from engagement with the
projections to thereby permit said counterbalancing means to move
the ramp to the elevated position, movement of said ramp to the
elevated position serving to move said first element to the
extended position with respect to the second element.
9. The dockboard of claim 8, wherein said pawls are arranged in a
side-by-side relation in the direction of movement of the
ratchet.
10. In a dockboard having a ramp member mounted for movement with
respect to a support member and having counterbalancing means for
urging the ramp from a generally horizontal position to an elevated
inclined position, a holddown mechanism for locking the ramp
against movement toward said elevated position, said holddown
mechanism comprising a tubular housing pivotally connected to one
of said members, an elongated element pivotally connected to the
other of said members and having a series of abutments spaced along
the length thereof, a tube slidably mounted within the housing and
having an end projecting beyond the corresponding end of the
housing, spring means disposed within the housing and located
around the tube and arranged to bias the tube to a retracted
position with respect to the housing, said elongated element being
movably disposed within the tube, said elongated element, said tube
and said housing being disposed in telescoped concentric relation
when the ramp is in the horizontal position, a pair of locking
members supported by the tube and disposed to engage the abutments
of the elongated element, engagement of the locking members with
said abutments preventing outward movement of the elongated element
with respect to the tube, but permitting inward movement of the
elongated element with respect to the tube, an actuating member
carried by the tube and disposed to move the locking members
between a locked and a released position, and operating means
connected to the actuating member for manually operating said
actuating member.
11. The dockboard of claim 10, wherein said operating means
comprises a lever arm mounted for pivotal movement with respect to
the tube between a locking position and a release position and
connected to said actuating member, and a cable connected to the
lever arm and extending to the upper surface of the ramp in
position where it can be actuated by an operator.
12. The dockboard of claim 11, and including resilient means for
urging the locking members into locking engagement with said
abutments, movement of said lever arm from the locking position to
the release position acting against the force of said resilient
means to thereby release the locking members from engagement with
said abutment, and a lost motion connection interconnecting the
lever arm and the actuating member and arranged so that initial
movement of the lever arm on return from the release position
through a predetermined distance toward the locking position will
not release the force of said resilient means, whereby partial loss
of displacement on said cable will not move the locking members
into partial engagement with the abutments, and further movement of
said lever arm beyond said predetermined distance toward the
locking position will release the force of said resilient means to
permit said resilient means to bias the locking members into
engagement with said abutments.
13. The dockboard of claim 12, wherein said lost motion connection
includes a shaft secured to the lever arm, and a projection
extending outwardly from said shaft, said actuating member being
provided with a recess to receive the projection with the recess
being substantially larger than the projection, whereby the
projection can be moved within the boundaries of the recess without
a corresponding movement of said actuating member.
14. The dockboard of claim 13, and including second resilient means
to return the lever arm to the locking position.
15. A dockboard, comprising a supporting structure; a ramp having
its rear end hinged to the supporting structure; counterbalancing
means for urging the ramp to an upwardly inclined position; and a
holddown mechanism for locking the ramp against movement toward
said inclined position, said holddown mechanism comprising a
tubular housing pivotally connected to the supporting structure, a
tube movably disposed within the housing and having an end
projecting beyond the upper end of the housing, spring means
disposed within the housing and arranged to urge the tube to a
retracted position with respect to said housing, a ratchet bar
movably mounted within the tube and having a series of teeth
disposed along its length, a pawl connected to the tube and
disposed to engage the ratchet bar teeth to thereby prevent
movement of the ratchet with respect to the tube, a pawl actuating
member operatively connected to said pawl for moving said pawl
between a locked and a released position, operating means connected
to the pawl actuating member and including an operating member
disposed on the upper surface of the ramp in position to be engaged
by an operator and movable between a locking position and a
released position, means responsive to a predetermined initial
amount of movement of said operating member in a direction from the
released position toward said locking position for preventing
actuation of said pawl actuating member, and means responsive to
movement of said operating member beyond said initial amount for
actuating said pawl actuating member to thereby move the pawl into
engagement with the ratchet teeth and lock the ratchet with respect
to the tube.
16. The dockboard of claim 15, and including a pair of pawls, said
pawls being arranged whereby only one of said pawls is in full
locking engagement with the teeth of the ratchet at any position of
said ratchet, and means for urging the pawls to the locked
position.
Description
BACKGROUND OF INVENTION
A common form of dockboard is installed in a shallow depression or
pit and includes a ramp that is hinged at its rear edge to the dock
and an extension lip is hinged to the front edge of the ramp. Due
to the substantial weight of the ramp, a counterbalancing member is
employed to bias the ramp upwardly to an inclined position while a
releasable holddown mechanism interconnects the dock and the ramp
and locks the ramp against upward movement. When not in use, the
ramp is locked or held down by the holddown mechanism in a cross
traffic position in which the ramp is generally flush with the
upper surface of the dock. When a truck or other carrier is located
at the dock, the operator manually releases the holddown mechanism
so that the counterbalancing member will pivot the ramp upwardly to
an inclined position. As a consequence of the upward pivotal
movement of the ramp, a lip lifting mechanism is actuated to pivot
the lip upwardly to an extended position. The operator then walks
outwardly on the inclined ramp and his weight will overbalance the
force of the counterbalancing member to lower the ramp and move the
lip into engagement with the bed of the carrier. The conventional
holddown mechanism is arranged so that the ramp can be moved
downwardly without restraint, yet the holddown mechanism, when
engaged, will prevent upward movement of the ramp.
SUMMARY OF THE INVENTION
The present invention is directed to an improved holddown mechanism
for restraining the counterbalancing means from raising the ramp of
the dockboard to an inclined position. The holddown mechanism
includes a tubular housing having one end pivotally connected to
the supporting structure of dock and a compression spring is
mounted within the housing. A tube is located concentrically within
the spring, and the force of the spring acts against a cap on the
end of the tube to urge the tube into a telescoped position with
respect to the tubular housing.
Mounted for sliding movement within the tube is a ratchet bar and
the outer end of the ratchet bar is pivotally connected to the
ramp. The ratchet bar is locked with respect to the tube by a
differential indexing double pawl mechanism which engages the teeth
of the ratchet. To release the pawls from the ratchet bar teeth the
operator pivots a handle through an operating cable and pivotal
movement of the handle operates through a lost motion connection to
move the pawls out of engagement with the ratchet bar teeth, and
thereby enables the counterbalancing mechanism to elevate the ramp
to an inclined position. Upward pivotal movement of the ramp causes
the ratchet to move outwardly with respect to the tube.
When the ramp is walked downwardly by the operator, the ratchet bar
will move inwardly with respect to the tube to a telescoped or
retracted position, and the pawls and ratchet bar teeth are
arranged so that the ratchet bar can move to the retracted position
without interference from the pawls. When the lip of the dockboard
engages the carrier or truck, the engagement of the pawls with the
ratchet bar teeth will prevent upward movement of the ramp through
the force of the counterbalancing mechanism.
The holddown mechanism of the invention incorporates a lost motion
connection in that the operating handle, when in the released
position, must be moved through a predetermined arc of movement
before the pawls will reengage the ratchet teeth. This lost motion
feature prevents accidental reengagement of the pawls with the
ratchet bar teeth when the operator does not maintain nearly full
angular displacement of the operating handle.
The holddown mechanism, by incorporating the differential indexing
double pawl mechanism, provides double the indexing sensitivity and
enables the ramp to be locked at shorter increments of travel
without reducing the size of the ratchet teeth. The double-pawl
system also provides added security in that the breakage of one of
the pawls will not destroy the holddown capabilities so that the
dockboard can continue to function with a single pawl in
operation.
As an added advantage of this holddown mechanism, the housing, tube
and ratchet are all three telescoped together which provides a
shorter assembly. By providing a shorter assembly, the holddown
mechanism can be connected to the supporting structure at a
location closer to the front of the pit, thereby resulting in a
more favorable working angle with the ramp and increasing the
mechanical advantage.
Other objects and advantages will appear in the course of the
following description.
The drawings illustrate the best mode presently contemplated of
carrying out the invention.
In the drawings:
FIG. 1 is a perspective view of the dockboard incorporating the
holddown mechanism of the invention and showing the ramp in the
elevated position;
FIG. 2 is a side elevation of the dockboard showing the ramp in the
upwardly inclined position.
FIG. 3 is a side elevation of the dockboard with the ramp in the
cross traffic position;
FIG. 4 is a longitudinal section showing the details of the
holddown mechanism with the pawls in the engaged position;
FIG. 5 is an enlarged view, similar to FIG. 4, showing the pawls in
the released position;
FIG. 6 is a view taken along line 6--6 of FIG. 4;
FIG. 7 is a view taken along line 7--7 of FIG. 4; and
FIG. 8 is an enlarged vertical section of the double-pawl locking
mechanism .
The drawings illustrate a loading dock 1 formed with a shallow pit
or depression 2 and the dockboard 3 of the invention is installed
in the pit. Dockboard 3 has a structural mounting frame 4 that is
mounted in the pit with the rear portion of the frame including a
series of vertical channels 5 that carry a horizontal angle 6. The
upper flange of angle 6 is flush with the upper surface of dock
1.
The dockboard 3 includes a ramp 7, and the rear end of the ramp is
hinged to the angle 6 of structural frame 4. Ramp 7 is composed of
a generally flat tread plate 8 which is supported by a series of
channel-shaped, parallel beams 9 and the forward edges of the beams
are welded together by a front plate 10.
To hinge the rear edge of the ramp 7 to the angle 6 two pair of
lugs 11 are welded to the angle 6 and the lugs 11 straddle a
U-shaped member 12 welded to the angle 13 at the rear of the ramp.
Hinge pins 14 extend through the aligned openings in the lugs 11 as
well as through the central slot in the U-shaped member 12. With
the slotted connection provided by the U-shaped member 12, the rear
edge of the ramp can shift vertically to compensate for variations
in level of the bed of the carrier truck, thereby enabling the ramp
to tilt slightly in the event the bed of the carrier is at a slight
angle to the horizontal.
The ramp is biased upwardly to an inclined position by a
counterbalancing mechanism similar to that described in the
copending U.S. Pat. No. 3,528,118. The counterbalancing mechanism
includes a lever arm 15 which is welded to the rear angle 13 and
the lower end of the lever arm is pivotally connected by a pin 16
to the rear end of a rod 17. Rod 17 extends through the coil spring
18 and the forward end of the rod is retained within an opening in
a movable spring retainer 19 by a nut that is threaded on the end
of the rod. Coil spring 18 is retained within an outer tubular
sleeve 20 and the forward end of the sleeve 20 is secured to the
frame 4 of the dockboard by a supporting structure 21, while the
rear end of the sleeve is similarly secured to the frame by a
supporting structure 22. With this construction, the force of the
spring 18 acts to urge the rod 17 forwardly and thereby pivot the
lever arm 15 forwardly to bias the ramp upward to the inclined
position, as shown in FIGS. 1 and 2.
An extension lip 23 is hinged to the forward edge of the ramp 7 and
in the storage or cross traffic position, as illustrated in FIG. 3,
the lip will assume a pendant position in which it hangs downwardly
in front of the ramp. As the ramp is pivoted upwardly to an
inclined position, as shown in FIGS. 1 and 2, the lip 23 will be
automatically pivoted outwardly to an extended position by a lip
lifting and latching mechanism, not shown, which can be similar to
that described in U.S. Pat. No. 3,203,002. The lip lifting and
latching mechanism in itself forms no part of the present
invention.
According to the invention, a holddown mechanism 24 locks the ramp
against upward movement through action of the spring 18 and the
details of the holddown mechanism are best illustrated in FIGS.
4-7. The holddown mechanism includes a tubular housing 25 and end
plates 26 and 27 enclose the ends of the housing. The outer surface
of the lower end plate 27 is provided with a pair of lugs 28 which
are pivotally connected to a bracket 29 mounted on the structural
frame 4 of the dockboard. Thus, the housing 25 is fixed to the
stationary portion or frame of the dockboard although the housing
can pivot with respect to the frame by virtue of the pivotal
connection.
A tube 30 is mounted within the housing 25 and the outer end of the
tube extends through an opening in the end plate 26. A cap 31 is
welded to the inner end of the tube 30 and a compression spring 32
is located around the tube and extends between the end plate 26 and
the cap 31. The force of the spring 32 acts to move the cap 31
toward the end plate 27 to thereby move the tube 30 to a retracted
or telescoped position with respect to the outer housing 25.
Mounted for sliding movement within the tube 30 is a ratchet bar 33
having a series of teeth 34. The outer end of the ratchet bar is
attached to a lug 35 which is pivotally connected to the
undersurface of the ramp 7. Thus, the housing 25 is connected to
the stationary structural frame 4 of the dockboard, while the
ratchet bar 33 is connected to the ramp. The ratchet bar 33 is
locked with respect to the tube 30 by a pair of pawls 36 and 37.
The pawls 36 and 37 are arranged such that only one of the pawls is
in full engagement with the teeth 34 of ratchet bar 33 at one time.
As shown in FIG. 4, pawl 36 is in the full engagement with one of
the teeth 34, while the second pawl 37, is halfway between
engagement with succeeding teeth. This arrangement provides even
differential indexing and enables the ratchet bar to be locked at
increments equal to one-half the pitch of the teeth 34.
Pawls 36 and 37 are mounted for sliding movement within a casing 38
that is connected between spaced sideplates 39. Sideplates 39 are
welded to the tube 30 and thus form an integral unit with the tube
30. The lower end of each pawl 36 and 37 is provided with a slot
40, and the nose 41 of a pawl lifter 42 extends within the aligned
slots 40. Pins 43 extend across the bottom of each of the slots 40
and engagement of the nose 41 with the pins 43 will move the pawls
36 and 37 out of engagement with the teeth 34 of the ratchet
33.
The pawls 36 and 37 are urged or biased into engagement with the
ratchet teeth 34 by torsion springs 44. Each torsion spring
includes a coiled section 45 that is mounted around a pin 46, and a
second coiled section 47 which is wound around a pin 48. Pins 46
and 48 extend through aligned openings in the sideplates 39. The
free end 49 of each spring 44 bears against the bottom of the
respective pawls 36 and 37, so that the spring force will urge the
pawls into engagement with the ratchet teeth 34.
In addition to the pins 46 and 48, a third pin 50 extends between
the sideplates 39 and is in alignment with the pins 46 and 48 and
limits downward displacement of the pawls.
The pawl lifter 42 includes a central hub 51 which is mounted on a
shaft 52 that extends through aligned openings in the sideplates
39. The hub 51 is connected to the shaft 52 by pin 53 that extends
through slots 54 in the hub as well as through an opening in the
shaft 52.
To pivot the pawl lifter 42 about the axis of shaft 52, a handle 55
is attached to the shaft and extends outwardly a substantial
distance from the sideplates 39. As shown in FIG. 4, the pawl
lifter 42 and pawls 36 and 37 are in the engaged or inoperative
position. To bias the pawl lifter 42 to the engaged position, a
torsion spring 56 is wound around a sleeve 57 on the end of shaft
52. One end 58 of the spring 56 is secured behind one of the
sideplates 39, while the other bent end 59 of the spring bears
against the handle 55 so that the force of the torsion spring 56
will act to urge the handle in a direction opposite to that of the
arrow in FIG. 4 and maintain the pawl lifter 42 in the position
shown in FIG. 4.
In addition to the torsion spring 56, a second torsion spring 60 is
wound around a sleeve 61 mounted on the opposite end of the shaft
52. One end 62 of spring 60 is secured within a slot in the shaft
52, while the opposite end 63 of spring 60 bears against the
undersurface of an ear 64 of the pawl lifter 42. The torsion spring
60 acts to maintain the pin 63 in engagement with the wall 65 of
the slot 54 as will be hereinafter described.
To pivot the handle 55 and thereby release the pawls 36 and 37 from
locking engagement, a cable 66 is connected to the end of the
handle 55 and travels over a pair of pulleys 67 and 68 mounted on
the beam 9 and ramp 7. The free end of the cable 66 extends through
an opening in the tread plate 8 and is provided with a pull ring
69. The pull ring 69 is normally located within a recess 70 in the
tread plate. By pulling upwardly on the pull ring 69, the handle 55
will be pivoted to the position shown in FIG. 5 to thereby move the
locking pawls 36 and 37 to the released position. Release of the
pawls enables the counterbalancing spring to pivot the ramp
upwardly to the position shown in FIG. 2, and as the ramp pivots
upwardly, the ratchet bar 33, which is connected to the ramp, will
be drawn out of the tube 30.
Under normal conditions the holddown mechanism will be in the
locked position in which the pawls 36 and 37 are in engagement with
the ratchet teeth 34 and the ramp is in the cross traffic position
as shown in FIG. 3. When it is desired to release the holddown
mechanism, the operator will pull upwardly on the pull ring 69,
thereby pivoting the handle 55 in the direction of the arrow in
FIG. 4. As the handle 55 is pivoted, the force of the torsion
spring 60 will maintain the pin 53 in engagement with the walls 65
bordering the slot 54 so that the pawl lifter 42 will be
correspondingly rotated until the nose 41 of pawl lifter 42 engages
the pins 43. With the nose 41 in engagement with the pins 43, there
will be a load on the pin 43 which will overcome the force of
torsion spring 60, so that further pivotal movement of the handle
55 will cause the pin 53 to move out of engagement with the wall 65
and move into engagement with the opposite walls 71 bordering the
slot 54. When this occurs further pivotal movement of the handle 55
and pawl lifter 42 will cause the nose 41 operating against the
pins 43 to move the pawls 36 and 37 out of engagement with the
ratchet teeth 34. With the ratchet teeth disengaged, the force of
the spring 18 acting on the ramp can pivot the ramp upwardly to an
inclined position and the ratchet bar 33, being attached to the
ramp will move outwardly with respect to the tube 30.
The lost motion connection provided by the pin 53 and the segmental
slot 54 enables the pull ring 69 to be partially released without
having an immediate reengagement of the pawls 36 and 37 with the
ratchet teeth 34. In some instances the operator is unable to apply
a continuous uniform pull to the pull ring, and if the tension on
the pull ring is momentarily released, causing the handle 55 to
pivot toward its original position by virtue of the spring 56, this
partial pivotal motion of the handle will not cause reengagement of
the pawls due to the lost motion connection. Thus, the pull ring is
able to move several inches due to the lost motion connection
without providing partial reengagement of the pawls with the
ratchet teeth. When the operator fully releases the pull ring 69,
the handle 55 will be urged to this original position through the
action of the spring 56 and initial pivotal movement of the handle
will cause the pin 53 to move relative to the pawl lifter 42 to
bring the pin into engagement with the wall 65 of the pawl lifter.
Continued pivotal movement of the handle 55, will move nose 41 out
of engagement with pins 43 and permit the springs 44 to return the
pawls to the locked position as shown in FIG. 4.
When the operator walks down on the ramp, after releasing the pull
ring 69, the weight of the operator will overbalance the force of
spring 18 to thereby pivot the ramp downwardly and cause the
ratchet to move inwardly of the tube 30. The pawls 36 and 37 will
ride over the sloping edges of the teeth 34 to permit the ramp to
be walked down. The engagement of the pawls with the ratchet teeth
34 will serve to prevent upward movement of the ramp at any
elevation.
The float spring 32 of the holddown mechanism functions primarily
during loading or unloading of the carrier or truck. DUring loading
and unloading the height of the bed of the truck may vary. For
example, during loading, as a load is moved across the ramp and
onto the bed of the truck the rear springs of the truck will yield
and allow the truck to descend and as it does the ramp 7 and its
extension lip will move down with it due to the weight of the load
moving thereacross and the ratchet bar will move inwardly of the
tube 30 to a further retracted position. As the load is moved
toward the front of the truck so that the weight on its rear
springs becomes less, the truck springs will attempt to restore the
rear end portion of the truck to its approximate previous height.
As this happens the float spring 32 is compressed to allow the ramp
to rise with the carrier bed. The float spring 32 also comes into
play during unloading of the truck and allows the ramp to rise with
the rising truck bed as the load is removed from the truck and thus
holds the ramp down on the truck bed. Thus, float springs 32
cooperates with the holddown mechanism to enable the ramp to float
upward with the truck bed as the truck is loaded or unloaded.
While the drawings illustrate the holddown mechanism associated
with a pit-mounted dockboard, it is contemplated that the holddown
mechanism can be utilized with any type of dockboard employing a
counterbalancing mechanism to bias a ramp to an upward
position.
Various modes of carrying out the invention are contemplated as
being within the scope of the following claims particularly
pointing out and distinctly claiming the subject matter which is
regarded as the invention.
* * * * *