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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to clamps for the lifting of steel plate and, more
particularly, to a plate lifting clamp without a neutral position which
can be released from gripping the plate and locked open from a position
remote from the clamp.
Hoists are used to lift heavy steel plate in steel warehouses or similar
type operations. A lifting clamp, connected to the hoist, is used to grip
the edge of the steel plate to permit the steel plate to be lifted by the
hoist for transporting the plate in the warehouse. See, for example, U.S.
Pat. Nos. 4,491,358 and 4,702,508.
Many prior art clamps are locked closed and open by lever operation. All
lever operated clamps have a neutral position between the locking and
unlocking positions of the operating lever. Because such prior art lever
operated clamps have a neutral position, the operator is able to place the
clamp into the neutral position while the clamp is suspending a steel
plate from its lifting shackle. Whenever the locking mechanisms on these
prior art clamps are in the neutral position, clamping engagement of the
work piece is dependent on the gravitational force on the work piece. A
sharp blow or bump to the steel plate can cause a temporary loss of
tension on the lifting shackle thereby disengaging the gripping cam from
the plate and causing the clamp to release and drop the plate.
The locking mechanism on most of these clamps is a single device that is
directly connected to the linkage operating the gripping cam. It is this
device that permits the locking mechanism to be shifted into the neutral
position while the clamp is being suspended from its lifting shackle and
carrying a steel plate. Under normal operating conditions, such clamps are
relatively safe if the operator diligently adheres to the safety
instructions that are provided by the manufacturer of the clamp.
Unfortunately, serious accidents occur because the operators ignore these
safety instructions and shift the locking mechanism to the neutral
position while the clamp is under load. One of the principal reasons that
these safety instructions are ignored is that the locking mechanism of the
clamp cannot be unlocked and locked open from a remote location. When the
clamp is used to lift a plate to a high location, often the operator will
place the locking mechanism in the neutral position after lifting the
plate and before raising the plate to the high location, thereby avoiding
having to climb up to the clamp to unlock its locking mechanism. Further,
in some cases, after the worker has climbed up to the clamp's position to
release the clamp, the worker must also lift the clamp off the steel
plate.
Thus, the lifting clamps of the locking and unlocking type have serious
deficiencies. The prior art clamps cannot be locked open or locked closed
from a remote position below the clamp. The locking and unlocking
mechanisms of the clamp are directly connected to each other and, in some
cases, also connected to the linkage operating the gripping cam. Movement
of the cam linkage, such as by a sharp blow, to the open position while
the locking mechanism is in the neutral position, can cause the locking
mechanism to lock the cam in the open position. The locking mechanisms of
the prior art clamps have a neutral position which creates an unsafe
condition.
It is an object of the present invention to overcome these deficiencies of
the prior art. In particular, the present invention eliminates the neutral
position of the locking mechanism of the clamp, the locking and unlocking
mechanisms of the present invention being completely independent. The
clamp of the present invention may be remotely actuated to release the
clamp thereby eliminating the need for operators to climb up to the clamp.
Further, the clamp of the present invention cannot be unlocked or opened
while there is tension on the lifting shackle.
Other objects and advantages of the present invention will appear from the
following description.
SUMMARY OF THE INVENTION
The plate lifting clamp of the present invention includes linkage disposed
on the clamp with one end of the linkage connected to the lifting shackle
and the other end of the linkage connected to a cam rotatably mounted on
the clamp. Upon the application of a force on the lifting shackle by the
hoist, the linkage causes the cam to rotate against the work piece
gripping the work piece between the cam and a swivel pad mounted on the
clamp. An operating handle is rotatably disposed on the clamp whereby when
rotated to the open position, will cause the cam to rotate away from the
work piece and open the clamp. A spring biased locking pin mechanism is
provided on the clamp to lock the operating handle into the open position.
A spring on the linkage maintains the cam in the closed position.
The plate lifting clamp of the present invention includes the following
advantages:
(1) The locking and unlocking mechanisms are completely independent of each
other.
(2) The plate lifting clamp does not have a neutral position in the locking
and unlocking mechanisms.
(3) The clamp can be locked open or locked closed from a remote position.
(4) The clamp unlocking mechanism cannot be placed in neutral or opened
when the clamp is being suspended from its lifting shackle.
(5) The clamp can be released and locked open only when the load and the
clamp body are resting on a solid object and there is no tension on the
clamp lifting shackle.
(6) When the clamp is being suspended from its lifting shackle, the
operating arm cannot be shifted to open the cam linkage or shifted to a
neutral position since there is no neutral position.
BRIEF DESCRIPTION OF THE DRAWINGS
For a detailed description of a preferred embodiment of the invention,
reference will not be made to the accompanying drawings wherein:
FIG. 1 is a side elevation view of the clamp of the present invention in
the closed position;
FIG. 2 is a side elevation view of the clamp of the present invention in
the open position;
FIG. 3 is a partial end view of the clamp of FIG. 2 showing the spring pin
assembly;
FIG. 4 is an exploded view of the spring assembly shown in FIG. 3;
FIG. 5 is a side view of the operating handle shown in FIGS. 1 and 2;
FIG. 6 is a cross section of the operating handle shown at plane 6--6 in
FIG. 5; and
FIG. 7 is an elevation view of the cam of the clamp shown in FIGS. 1 and 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring initially to FIG. 1, the plate lifting clamp 10 of the present
invention lifts a work piece, such as a steel plate 18, using a hoist hook
14 connected to the shackle 12 of the clamp 10. A spring-biased radius arm
20 pivots around pivot point 16 causing a connecting arm 22 to exert a
downward force on a jaw or gripping cam 30. The spring 72, together with
the gravitational force caused by the weight of the steel plate 18 on the
shackle 12, applies a downward force which causes the cam 30 to rotate
into the steel plate 18 to be lifted by hoist hook 14. This rotation into
the plate 18 forces the plate 18 against another jaw or swiveling pad 32
to grip the steel plate 18 between the cam 30 and the swiveling pad 32.
The force of the cam 30 against the plate 18, which in turn is pressed
against the swiveling pad 32, causes the lifting clamp 10 to grip the
steel plate 18. With the clamp 10 in the closed position, as the hoist
raises the clamp 10 and steel plate 18 on the shackle 12, the weight of
the steel plate 18 causes the cam 30 to rotate further into the steel
plate 18 with a force dependent upon the weight of the steel plate 18. In
this manner, the lifting clamp 10 connects the steel plate 18 to the hoist
hook 14 whereby the hoist (not shown) is used to lift the heavy steel
plate 18 for transport.
An operating arm 40 is engageable with the cam 30 whereby as the operating
arm 40 is rotated counterclockwise from a retracted or relaxed position to
an open locked position, the operating arm 40 will cause the cam 30 to
also rotate counterclockwise away from gripping engagement with the plate
18. After the operating arm 40 and the cam 30 have been rotated into the
open position, the operating arm 40, and thus the clamp 10, is locked into
the open position by a pin mechanism 50.
The body 24 of plate lifting clamp 10 includes two facing shells or sides
26, 28 separated by a plurality of spacers 33, 34, 36, and 38 which are
configured and positioned to also serve as stops to the movement of
various parts of the clamp as hereinafter described. Such spacers,
together with sides 26, 28, form an interior for housing the operating
mechanisms of the clamp 10. The spacers 33, 34, 36 and 38 are forged with
the sides 26, 28 of the clamp body 24, and project from each of the sides
26, 28 for attachment by welding so as to connect the sides 26, 28 of the
clamp body 24.
Plate lifting clamp 10 includes an opening or slot 52 formed by the sides
26, 28 for receiving an edge 54 of work piece or steel plate 18 to be
attached to the hoist nook 14. The plate 18 is affixed to the clamp 10 by
the frictional engagement of the swiveling pad 32, rotatably mounted on a
swivel pad pin 42 located on one side of slot 52, and the cam 30,
rotatably mounted on the cam pin 44 disposed on the other side of slot 52.
The pins 42, 44 extend between the clamp sides 26, 28, passing through
apertures in the swiveling pad 32 and the cam 30, respectively, to permit
a swiveling and rotating movement thereon. The pins 42, 44 project through
the apertures and are held in place by cotter keys (not shown). The
swiveling pad 32 is limited in its rotational movement by the spacer stops
33, 34 which are positioned to engage the swiveling pad 32 so as to
position the swiveling pad 32 for proper gripping engagement with the
steel plate 18. Serrations or teeth 62 are provided on the face of the
swiveling pad 32 to insure frictional engagement of the clamp 10 with the
plate 18. As the cam 30 rotates into engagement with one side of the plate
18, swiveling pad 32 rotates with the movement of the plate 18 within the
slot 52 so as to permit full contact with the work piece 18 at all times.
The cam 30 is rotated into frictional engagement with the plate 18 by means
of linkage 60 connecting the cam 30 with the shackle 12 and the spring 72
biasing linkage 60, and thus the cam 30, toward the closed position
whereby as the weight of the plate 18 is applied to the shackle 12, the
shackle 12, by means of the linkage 60, increases the camming force of the
cam 30 on the plate 18.
The linkage 60 includes a radius link or arm 20 pivotally mounted on the
radius arm pin 46. The link pin 46 extends between the clamp sides 26, 28
through an aperture in the radius arm 20 and is held in place by cotter
keys (not shown). One end of the radius arm 20 is rotatably connected to
one end of the shackle 12 by a linkage rivet 64 extending through mating
apertures in the shackle 12 and the radius arm 20. The other end of radius
arm 20 is rotatably attached to the connecting link or arm 22. The
connecting arm 22 links radius arm 20 with the cam 30. Linkage rivets 66,
68 extend between mating apertures in connecting arm 22 and radius arm 20
and in connecting arm 22 and the cam 30 to permit relative rotation
therebetween. The linkage rivet 68, affixed to the cam 30, is spaced apart
from the rotation point of cam pin 44 to provide leverage of the cam 30
against the plate 18 as force is applied to the cam 30 through the
connecting arm 22. The cam 30 includes a camming surface 70 which cams
into frictional engagement with the plate 18 as the force is applied to
the cam 30 by linkage 60 thereby biasing the plate 18 between camming face
70 and the teeth 62.
A coiled spring 72 is disposed around radius arm pin 46 with the ends 74,
and 76 of the spring 72 inserted through apertures in the sides 26, 28 of
clamp 10. The spring 72 is wrapped around radius arm 20 so as to apply a
counterclockwise bearing force to the radius arm 20. The spring 72 is
coiled as the radius arm 20 is rotated clockwise and as the clamp is
opened as shown in FIG. 2. Upon unlocking the clamp 10 from the open
position, the spring 72, applying a counterclockwise rotational force on
the radius arm 20, causes radius arm 20 to rotate counterclockwise moving
the linkage 60, and thus the clamp 10, to the closed position shown in
FIG. 1. The spring tension applied by the spring 72 varies with the size
of the clamp 10 but is sufficient to maintain a force on the linkage 60
and thus the cam 30 to maintain the clamp 10 in the closed position. Thus,
in operation, as the spring 72 and the shackle 12 provide a
counterclockwise rotational force on the radius arm 20, the opposite end
of the radius arm 20 applies a clockwise rotational force on the cam 30 by
means of the connecting arm 22 to cause the cam 30 to rotate clockwise
against the plate 18.
The operating arm or handle 40 is provided to disengage the cam 30 from the
plate 18 and open the clamp 10. Referring now to FIGS. 5 and 6, the
operating handle 40 is generally S-shaped with one end having an aperture
80 therethrough and the aperture 80 having a chamfered side 82 riding in a
boss (not shown) projecting from the side 26 of the clamp 10. Cam pin 44
passes through the aperture 80 for rotating the operating arm 40 with
respect to the cam 30. The operating arm 40 includes a projecting
midportion 84 normal to the side of the clamp 10. As shown in FIG. 7, an
ear or dog 86 is provided on cam 30 opposite camming surface 70. The
projecting midportion 84 of operating arm 40 is positioned to engage the
dog 86 as the operating arm 40 is rotated counterclockwise in a direction
opposite the clockwise rotation of the cam 30 as it engages the plate 18.
As midportion 84 engages the dog 86, a counterclockwise force is applied
to the cam 30 such that the cam 30 rotates away from the plate 18 to open
the clamp 10.
A spring 88, shown in FIG. 1, is disposed around cam pin 44 with one end 90
received into bore 92 of the midportion 84 of operating arm 40, and the
other end 94 of the spring 88 affixed to the clamp side 28. As the
operating arm 40 is moved in a counterclockwise direction to open the
clamp 10, the spring 88 is coiled as shown in FIG. 2 to subsequently
assist the return of the operating arm 40 to its relaxed and retracted
position as shown in FIG. 1. Spacer stop 38 limits the movement of the
operating arm 40 to its relaxed or retracted position, and spacer stop 36
limits the movement of the operating arm 40 in the open locked position as
shown in FIG. 2. The thickness of the steel plate 18 may be so great as to
limit the clockwise rotation of the cam 30 and thus the rotation of the
dog 86 against midportion 84 of the operating arm 40. The spring 88
insures that the operating arm 40 fully rotates against the spacer stop 38
to prevent the end of operation arm 40 from projecting away from the clamp
10 in its relaxed or retracted position. The opposite end of operating arm
40 includes an aperture 96 for receiving a pulling ring 98 to assist the
operator in rotating the operating arm 40 to open the clamp 10. The
pulling ring 98 facilitates the engagement of operating arm 40 by a hook
on a pole or extension or lanyard (not shown) to rotate the arm 40 from a
remote position.
Referring now to FIGS. 3 and 4, there is shown the locking pin mechanism 50
for locking the clamp 10 in the open position. The locking pin mechanism
50 includes a housing 102 affixed to the inner surface of the clamp side
28 by welding and aligned with a threaded aperture 104 therethrough.
Housing 102 includes a throughbore 106 for receiving the locking pin 100
and a counterbore 108 for receiving the locking spring 110. As shown in
FIG. 3, the locking pin 100 extends from outside of the clamp side 28
through bore 106 and into the space or clearance 120 between the inner
side of the clamp side 26 and the end of housing 102. The operating arm 40
is positioned on the cam pin 44 between the clamp sides 26, 28 so as to
pass through the space or clearance 120. Thus, when protruding into the
space 120, the locking pin 100 will engage the operating arm 40 as
hereinafter described.
Referring again to FIG. 4, locking pin 100 is assembled within housing 102
with a snap ring 114 disposed in an annular ring groove 116 at a
predetermined position on pin 100 whereby the snap ring 114 will limit the
downward movement of locking pin 100 in counterbore 108 of housing 102.
Thus, snap ring 114 and groove 116 determine the extent to which locking
pin 100 protrudes into the clearance 120. A washer 118 is disposed around
locking pin 100 within counterbore 108 to provide a bearing surface for
one end of the spring 110. A retaining bushing 112, having an aperture 114
therethrough for locking pin 100, threadingly engages the threaded
aperture 104 of the clamp side 28. The inner end of retaining bushing 112
provides the upper bearing surface for the other end of the spring 110.
Spring 110 forces the locking pin 100 through the housing 102 causing it to
protrude into the clearance 120. The protruding end 122 of the pin 100 is
rounded to facilitate engagement with operating arm 40. As best shown in
FIG. 2, the locking pin 100 locks operating arm 40, and thus clamp 10, in
the open position by capturing the arm 40 between pin 100 and spacer stop
36 and preventing the arm 40 from rotating- clockwise into its relaxed or
retracted position. The other opposite end 124 of the locking pin 100
extends out of the aperture 104 and includes a bore 126 therethrough to
receive a pulling ring 128 whereby locking pin 100 can be retracted from
clearance 120 and into the housing 102 to clear the path of movement of
the operating arm 40 through clearance 120. By retracting pin 100 using
pulling ring 128, the spring 88 will move operating arm 40 clockwise to
its upper relaxed or retracted position shown in FIG. 1. Operating arm 40
includes a cam surface 130 which engages the rounded end 122 of locking
pin 100 to automatically retract locking pin 100 as the operating arm 40
is moved from its upper relaxed or retracted position to its lower open
and locked position.
In operation, the clamp 10 is suspended from the hoist hook 14 by the
shackle 12. With its operating arm 40 in its lower open and locked
position, the clamp 10 is maintained in the open position by the locking
pin 100 with the linkage 60 and the cam 30 positioned as shown in FIG. 2.
A steel plate or other work piece 18 is inserted into the slot 52 of the
clamp 10. The clamp 10 is placed over the edge 54 of the plate 10. When
the plate 18 is in position within slot 52, a pulling force is applied to
ring 128 to retract the spring-loaded locking pin 100. This permits the
operating arm 40 to rotate to its upper relaxed or retracted position with
the clamp 10 in the closed position shown in FIGURE 1. A hook (not shown)
may be used to hook the ring 128, located on the end of the spring-loaded
pin 100, and retract the pin 100. This clockwise rotation of the operating
arm 40 into its upper relaxed or retracted position permits the cam 30 to
rotate clockwise against the plate 18 initially due to the bias of the
spring 72 and then further rotate as the weight of the plate 18 is applied
to the shackle 12. The clamp 10 then frictionally engages and grips the
plate 18 between the camming face 70 and the pad 32. The upward force on
the shackle 12 causes, by means of the linkage 60, the cam 30 to rotate
clockwise into the plate 18 with a force dependent upon the weight of the
plate 18.
When the weight of the plate 18 has been taken off the shackle 12 by
putting the plate 18 at rest, a pole and hook (not shown) may be used to
grab the ring 98 on the operating arm 40. A downward force on the
operating arm 40 will cause the cam 30 to rotate and move away from the
plate 18 whereby releasing the frictional engagement between the clamp 10
and the plate 18. After the operating arm 40 has been rotated under the
spring loaded locking pin 100, the clamp 10 is in the open and locked
position as shown in FIG. 2.
While a preferred embodiment of the invention has been shown and described,
modifications thereof can be made by one skilled in the art without
departing from the spirit of the invention.
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