Load clamping apparatus with an increased extent of vertical movement

A load clamping apparatus is provided for use with a forklift truck including a mast having a vertical guide channel, a lift carriage mounted to the mast for elevational movement therealong and a pair of spaced apart forks carried by the lift carriage to support a load to be handled. The load clamping apparatus comprises: a slider member slidably fitted into the vertical guide channel and elevationally movable along the mast, the slider member having a vertical guide groove; a clamp carriage slidably fitted into the vertical guide groove of the slidable member for pressing the load against the pair of spaced apart forks; an actuator pivotally affixed to the mast for causing the slider member to move up and down; upper and lower rotary guide rollers each rotatably mounted to top and bottom ends of the slider member; a first pliable connector having a first end anchored to the mast and a second end fixedly secured to the clamp carriage, the first pliable connector extending upwardly from the first end thereof, turning around the upper rotary guide rollers and then extending downwardly to reach the second end thereof; and a second pliable connector having a first end anchored to the mast and a second end fixedly secured to the clamp carriage, the second pliable connector extending downwardly from the first end thereof, turning around the lower rotary guide rollers and then extending upwardly to reach the second end thereof.

FIELD OF THE INVENTION 
The present invention pertains generally to a forklift truck, and more 
particularly to a load clamping apparatus for use with the forklift truck 
that has a clamp carriage elevationally movable over an increased extent 
of vertical movement to press down the load against tines or forks of a 
lift carriage. 
DESCRIPTION OF THE PRIOR ART 
Extensive use has been made of forklift trucks to lift up loads, cargos, 
freights and the like (hereinbelow referred to as "load") for the purpose 
of their shipment and transportation from one place to another. 
Conventional forklift trucks customarily carry a vertically oriented mast 
assembly to which a carriage assembly is mounted for elevational movement 
therealong to raise the load up to a desired elevation. The carriage 
assembly is provided with a pair of spaced apart, generally parallel forks 
that overhang from the carriage assembly so as to take up the vertically 
exerted force of the load. The up/down movement of the carriage assembly 
may be rendered effective by the combination of a lift jack and a lift 
chain associated therewith. Side shift cylinders are also employed to have 
the carriage assembly move laterally, if appropriate. Lateral movement of 
the carriage assembly makes it possible for the forklift truck to readily 
access to the load even in a narrow working space and to permit unshipment 
of the lifted load on a precise location. 
U.S. Pat. No. 4,392,773 dated Jul. 12, 1983 to Johannson teaches a carriage 
assembly with shiftable forks so designed that all vertical forces are 
taken up by a lower bar to render tile upper portion of tile carriage 
assembly relatively light and small, thus allowing clear forward and 
downward vision for the vehicle operator. A primary feature of the '773 
patent is that substantially only the horizontal forces are transferred to 
an upper bar of a side shifter, with the vertical forces to a lower bar of 
the side shifter. 
U.S. Pat. No. 4,896,748 dated Jan. 30, 1990 to Mikkelsen et al. discloses a 
full free lift mast assembly that can significantly reduce bending of 
carriage lift jacks, fluid leakage, missequencing and like problems. The 
full free lift mast assembly has a first pair of spaced apart uprights, a 
second pair of spaced apart uprights mounted on the first pair of uprights 
and elevationally movable therealong and a carriage mounted on the second 
pair of uprights. A first mast lift jack is connected between the first 
and second pairs of spaced apart uprights, first and second interconnected 
carriage lift jacks being pivotally connected to and between the second 
pair of spaced apart uprights and the carriage. A connecting arrangement 
serves to couple cylinders of the first and second carriage lift jacks and 
maintains them parallel in a preselected overlapping relationship with 
each other. 
The afore-mentioned and other prior art forklift trucks are, however, 
adapted to perform the load lifting and transporting operation with tile 
load simply placed on the forks, which would frequently result in a 
reduced stability or even falling-down of the load from the carriage 
during the course of handling same. This is particularly true for the 
bulky and light weight load which has a higher gravitational center. For 
the reason stated above, it would be desirable to provide a way of 
stabilizing the load when they are lifted up and transported. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a load 
clamping apparatus for use with a forklift truck that substantially 
eliminates the drawbacks inherent in the prior art forklift trucks and 
that can exert a downward clamping force against the load placed on a lift 
carriage to assure a stabilized handling thereof. 
Another object of the invention is to provide a load clamping apparatus 
capable of increasing the vertical movement extent of a clamp carriage 
without the need to use a hydraulic actuator of overly extended stroke 
length. 
In accordance with the invention, a load clamping apparatus is provided for 
use with a forklift truck which includes a mast having a vertical guide 
channel, a lift carriage mounted to the mast for elevational movement 
therealong and a pair of spaced apart forks carried by the lift carriage 
to support a load to be handled. The load clamping apparatus comprises: a 
slider member slidably fitted into the vertical guide channel and 
elevationally movable along the mast, the slider member having a vertical 
guide groove; a clamp carriage slidably fitted into the vertical guide 
groove of the slider member for pressing the load against the pair of 
spaced apart forks; an actuator pivotally affixed to the mast for causing 
the slider member to move up and down; upper and lower rotary guide 
rollers each rotatably mounted to top and bottom ends of the slider 
member; a first pliable connector having a first end anchored to the mast 
and a second end fixedly secured to the clamp carriage, the first pliable 
connector extending upwardly from the first end thereof, turning around 
the upper rotary guide roller and then extending downwardly to reach the 
second end thereof; and a second pliable connector having a first end 
anchored to the mast and a second end fixedly secured to the clamp 
carriage, the second pliable connector extending downwardly from the first 
end thereof, turning around the lower rotary guide means and then 
extending upwardly to reach the second end thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, a forklift truck is shown to include a vehicle 
body 10, a vertically oriented mast 12 in front of the vehicle body 10 and 
a lift carriage 14 slidably mounted to the mast 12 for elevational 
movement therealong. The lift carriage 14 may be laterally shifted by 
means of a suitable hydraulic actuator not shown in the drawings for 
simplicity. 
The lift carriage 14 is provided with a pair of spaced apart, generally "L" 
shaped forks or tines 16, 18 which are movable toward and away from each 
other as by first and second side shift cylinders 20, 22. To raise a load 
of relatively large transverse dimension, the spacing of the individual 
forks 16, 18 should preferably remain broad, while the spacing has to be 
narrowed to lift up a load having relatively small transverse dimension. 
In a typical forklift truck, the lift carriage 14 is adapted to move 
vertically by virtue of a lift cylinder and a lift chain (not shown). 
Turning to FIGS. 2 and 3, the mast 12 includes first and second guide rails 
24, 26 of generally "U" shaped cross-section each disposed in an opposing 
relationship to one another with an appropriate spacing therebetween. 
These guide rails 24, 26 may be mutually connected through the use of top 
and intermediate plate-like brackets 28, 30. A vertical guide channel 32 
is defined between the guide rails 24, 26 to accommodate a slider member 
34 in a vertically movable way. The slider member 34 is composed of first 
and second side frames 36, 38 having generally "U" shaped cross-section, 
each of the side frames 36, 38 being in a opposing relationship to one 
another. The side frames 36, 38 are connected with each other by means of 
uniformly spaced, top, intermediate and bottom cross-bars 40, 42, 44. As a 
result, a vertical guide groove 46 is defined between the side frames 36, 
38 to accommodate the carrier member of a clamp carriage set forth below. 
An upper rotary guide means is mounted on the top cross-bar 40, with a 
lower rotary guide means on the bottom cross-bar 44. As is clearly shown 
in FIG.4, the upper rotary guide means includes a first center roller 50 
carried by the top cross-bar 40 for rotation about a first axis 48 and a 
second center roller 54 carried by the top cross-bar 40 for rotation about 
a second axis 52 which is offset forwardly downwardly from the first axis 
48. Furthermore, the lower rotary guide means includes a pair of parallel 
side rollers 58, 60 that are coaxially disposed on a third axis 56 with an 
appropriate spacing therebetween. It is perferred that the first and third 
axes 48, 56 should lie on a common vertical plane. While, in the 
illustrated embodiment, rollers are used as the upper and lower rotary 
guide means, it would be possible to employ pulleys or other suitable 
rotary bodies in place of the rollers. 
With reference to FIGS. 1 through 4, it can be appreciated that a clamp 
carriage 61 is combined with the slider member 34 for vertical sliding 
movement therealong. The clamp carriage 61 includes a carrier member 62 
slidably fitted into the vertical guide groove 46 of the slider member 34, 
a support bracket 64 protruding forwardly from the carrier member 62 and a 
pressure plate 66 pivotally mounted on the support bracket 64. Since the 
pressure plate 66 is to come into contact with the load placed on the lift 
carriage 14, it may be desirable to attach a compliant pad made of rubber 
or other soft material to the underside of the pressure plate 66. 
Pivotally mounted on the mast 12 is an actuator 68 that consists of a 
hydraulic cylinder 70 and a piston rod 72 extendibly fitted into the 
hydraulic cylinder 70. The piston rod 72 is connected at its distal end to 
the intermediate cross-bar 42 of the slider member 34, thus enabling the 
actuator 68 to raise and lower the slider member 34 at the vehicle 
operator's will. 
As can be seen in FIGS. 2, 3 and 4, the clamp carriage 61 is coupled to the 
mast 12 by virtue of first and second pliable connecting means. 
Preferably, the first pliable connecting means includes a center rope 74 
having a first end anchored to the top bracket 28 of the mast 12 and a 
second end fixedly secured to the carrier member 62 of the clamp carriage 
61. The center rope 74 extends upwardly from the first end thereof to turn 
around the first and second center rollers 50, 54 and then goes downwardly 
from the rollers 50, 54 to reach the second end thereof. Accordingly, as 
the slide member 34 moves upward by the actuator 68, the second end side 
vertical extension of the center rope 74 will gradually become shorter, 
with the first end side vertical extension longer, so as to cause the 
clamp carriage 61 to be pulled upwardly. 
The second pliable connecting means includes a pair of parallel side ropes 
76, 78, each of which has a first end anchored to the top bracket 28 of 
the mast 12 and a second end fixedly secured to the carrier member 62 of 
the clamp carriage 61. As is apparent from FIG. 4, the respective side 
rope 76 or 78 extends downwardly from the first end thereof to turn around 
each of the side rollers 58, 60 and then goes upwardly toward the second 
end. Thus, as the slider member 34 moves downwardly by the actuator 68, 
the second end side vertical extension of each of the side ropes 76, 78 
will gradually become shorter, with the first end side vertical extension 
longer, thereby causing the clamp carriage 61 to be pulled in the downward 
direction. Alternatively, the ropes 74, 76, 78 may be replaced with chains 
and, therefore, use of the chains as the first and second pliable 
connecting means should fall within the coverage of the invention. 
In the following, description will be given as to the operation of the 
instant load clamping apparatus with reference to FIGS.5A, 5B and 5C. 
FIG. 5A shows a first illustrative operation mode of the load clamping 
apparatus wherein the piston rod 72 of the actuator 68 is fully retracted, 
with the slider member 34 and the clamp carriage 61 brought into the 
lowermost position. Under this state, configuration of the center rope 74 
is such that the second end side vertical extension thereof remains 
longest and the first end side vertical extension is kept shortest. In 
contrast, the second end vertical side extension of the respective side 
rope 76 or 78 becomes shortest and the first end side vertical extension 
thereof is maintained longest. As a consequence, the clamp carriage 61 
would be pulled downwardly along the slider member 34 into the lowermost 
Position whereby the spacing between the forks 16, 18 and the pressure 
plate 66 is minimized to assure positive clamping of a low profile load. 
FIG. 5B depicts a second illustrative operation mode of the load clamping 
apparatus wherein the piston rod 72 of the actuator 68 is in a 
half-extended position. In response to the extending movement of the 
piston rod 72, the slider member 34 is brought into a middle position, 
with the result that the center rope 74 should be pressed by the rollers 
50, 52 in the upward direction. Accordingly, the second end side extension 
of the center rope 74 becomes shorter and the first end side extension 
thereof is rendered longer in proportion to the reduction in length of the 
second end side extension. This means that the clamp carriage 61 is moved 
upwardly twice as far as the extension length of the piston rod 72, as 
readily understood from the comparison of FIGS. 5A and 5B. 
FIG. 5C represents a third illustrative operation mode of the load clamping 
apparatus wherein the piston rod 72 of the actuator 68 is in a fully 
extended position. Responsive to such an extending movement of the piston 
rod 72, the slider member 34 is brought into the uppermost position, which 
in turn cause the rollers 50, 52 to further press the center rope 74 
upwardly. Therefore, the second end side extension of the center rope 74 
becomes shortest and the first end side extension thereof is rendered 
longest. This allows the clamp carriage to be pulled up to the top edge of 
the slider member 34, thereby maximizing the spacing between the forks 16, 
18 and the pressure plate 66 for ready accommodation of a high profile 
load. 
In a case where the piston rod 72 is retracted from the position shown in 
FIG. 5C, the slider member 34 descends in exact proportion to the 
retraction length of the piston rod 72 but the side ropes 76, 78 move 
downwardly twice as far as the retraction length of the piston rod 72 to 
eventually come back to the position illustrated in FIG. 5A. 
While the invention has been shown and described with reference to a 
preferred embodiment, it should be apparent to those skilled in the art 
that many changes and modifications may be made without departing from the 
scope of the invention as defined in the claims.