Work machine

A work machine includes a boom which is pivotally connected at one end to the machine and is provided at the other end with a tool carriage which is attached to the boom at a pivot which is fixed with respect to the boom. The tool carriage is associated with a mechanism for maintaining it at a constant attitude when the boom is raised and lowered. The boom further includes an extension for improving the versatility of the machine.

TECHNICAL FIELD 
The present invention relates to a work machine comprising a boom which is 
pivotally connected at one end to the machine body and is provided at the 
other end with a tool carriage attached to the boom at a pivot which is 
fixed with respect to the boom, the carriage being associated with a 
mechanism for keeping it at a constant attitude when the boom is raised 
and lowered. Such a machine is referred to as of the kind described. 
BACKGROUND ART 
If a load which is to be moved by such a work machine is to be picked up 
from or deposited at a location, for example, deep within a container or 
high above the machine, it is possible that the boom may not be long 
enough to reach the location. 
DISCLOSURE OF THE INVENTION 
According to the present invention a machine of the kind described is 
provided with an elongate boom extension comprising a parallelogram 
linkage having a pair of parallel links each pivotally connected at one 
end to a tool, a first one of the links being connected at its other end 
at or adjacent to the pivot of the tool carriage, and the second one of 
the links being pivotally connected to the tool carriage such that the 
tool follows the attitude of the tool carriage when the boom is raised and 
lowered. 
By fitting the extension to the boom of the machine its operating range can 
be increased, thereby improving its versatility. Attaching the boom 
extension in this way allows an operator to control the angle of the tool 
on the extension as though it was a tool which is normally fitted to the 
carriage without the boom extension. 
When the boom is raised and lowered, the first link does not follow the 
rotation of the carriage but rotates relatively to it. Thus, the other 
ends of the first and second links are moved relatively to one another 
thereby cranking the parallelogram linkage in such a way as to maintain 
the tool at a constant attitude. This arrangement ensures that the 
extension always remains substantially parallel to the boom, so that the 
bending moments on the boom are kept to a minimum. 
To stabilize the parallelogram linkage, an additional link may be pivotally 
attached at one end to the tool, and at the other end to the boom at a 
location spaced from the carriage. 
To improve the operating range of the boom, the boom is preferably 
telescopic.

BEST MODE FOR CARRYING OUT THE INVENTION 
A machine to which the boom extension can be attached is shown in FIG. 1. 
The machine has a boom 1 which is pivotally mounted at a pivot 2 extending 
transversely to the longitudinal axis of the machine. The boom 1 comprises 
outer 3, intermediate 4 and inner 5 portions telescopically coupled 
together. The inner portion 5 has a depending bracket portion 5A. The 
inner portion 5 is provided at the extremity of the bracket portion 5A 
with a tool carriage 6 which is pivotally mounted to the bracket 5A at 
pivot 7. The angular position of the carriage 6 is adjustable via a 
linkage 8 which is pivotally connected at one end to the carriage 6 and at 
the other end to a hydraulic cylinder 9 which is pivotally mounted to the 
bracket portion 5A of the boom. This hydraulic cylinder 9 is hydraulically 
coupled by a rolling hose coiled within the boom 1 to a compensating 
hydraulic cylinder 10 which is positioned in such a way that the oil 
displaced from the compensating cylinder 10 when the boom is raised and 
lowered changes the length of the cylinder 9 and hence automatically 
adjusts the angle of the carriage 6. Thus, a conventional tool which is 
attached to the carriage can be kept at a constant attitude when the boom 
1 is raised and lowered. 
When the range of operation of the boom is to be increased, the 
conventional tool which is normally mounted on the carriage 6 is removed 
and is replaced by a boom extension B as shown in FIGS. 2 to 4. 
The boom extension B is provided at one end with an attachment 11 which is 
attached to the carriage 6 by a quick hitch device such that it does not 
rotate with respect to the carriage 6. At each side, a first link 12 is 
attached to the pivot 7 so that it can rotate relatively to the boom 1 and 
carriage 6. The opposite end of each first link 12 is pivotally connected 
to the conventional tool such as a fork 13. At each side a second link 14 
is pivotally connected to the attachment 11 at one end and at the opposite 
end to the fork 13. The first 12 and second 14 links are the same length 
so as to provide a parallelogram linkage. 
The parallelogram linkage is stabilized by a third link 15 which is 
pivotally connected at one end to the boom at a location remote from the 
carriage 6, and at the other end to the fork 13 at a position adjacent to 
the pivotal connection for the opposite end of the first link 12. 
The construction of the boom extension is shown in more detail in FIGS. 5 
to 7. Thus the quick hitch device comprises a pair of hooks 16 which hook 
over respective pins 17 carried by the carriage 6. With these hooks 
engaged, pins 18 are inserted through aligned apertures in the attachment 
11 and carriage 6 to secure the attachment to the carriage. 
The linkage 8 interconnecting the hydraulic cylinder 9 with the carriage 6 
comprises a bell crank 8A, which is pivoted at 19 to the bracket 5A and is 
pivoted at one end 20 to the ram and at its other end 21 to one end of a 
link 8B, the other end of which is pivoted at 22 to the carriage 6. It 
will thus be appreciated that as the ram 9 is extended, the bell crank 8A 
is caused to rotate in a clockwise direction as seen in FIGS. 5 and 7 thus 
closing the angle between the bell crank 8A and the link 8B and 
simultaneously rotating the carriage 6 and, when fitted, attachment 11, in 
a clockwise direction as seen in these figures. The fork or other tool 13 
then follows this rotation by virtue of the parallelogram linkage 12,14 
and FIG. 7 shows the fully extended position of the ram 9 in which the 
forks 13 are shown fully rolled back extending at 20.degree. above the 
horizontal, with the boom extending horizontally. Similarly retraction of 
the ram 9 will rotate the parts in the anti-clockwise direction until the 
forks 13 are extending perpendicularly to the boom as shown in the right 
hand part of FIG. 4. 
FIGS. 5 to 7 show the end pivots for the links 12,14 and 15 at 7 and 23,24 
and 25, and 26 and 27, respectively. The pivots 23 and 25 are to webs 28, 
and the pivot 27 to a web 29, the webs 28 and 29 projecting from a back 
frame 30 of the fork tool. 
INDUSTRIAL APPLICABILITY 
In use, when the machine is fitted with the boom extension B, and the boom 
1 is raised from the horizontal position shown in FIG. 2 to the elevated 
position shown in FIG. 3, the boom extension reacts as follows. The 
carriage 6 and attachment 11 are maintained at the same attitude while the 
first link 12 is rotated with respect to the carriage 6 and attachment 11. 
This cranks the parallelogram linkage round in such a way as to maintain 
the fork 13 at a constant attitude as shown in FIGS. 2 to 4. 
If the controller of the machine wishes to adjust the angle of the fork 13, 
he does so in the same way as he would if a tool was attached directly to 
the carriage 6. Thus, a hydraulic force from the compensating cylinder 10 
would adjust the length of hydraulic cylinder 9 which in turn rotates the 
carriage 6 causing the parallel linkage to rotate the fork 13. 
The range of movement attainable by the tool is shown by envelope A in FIG. 
4. The radially innermost corners of this envelope are those positions in 
which the boom 1 is fully telescopically retracted, and the radially 
outermost corners of the envelope are those in which the boom is 
telescopically fully extended. 
In practice, when the boom 1 is raised from the horizontal position shown 
in FIG. 2 to the elevated position shown in FIG. 3, the boom will first be 
telescopically retracted before it is elevated, and will then be 
telescopically extended once it has reached its elevated position. This 
reduces the turning moment necessary to elevate the boom. 
Other aspects, objects and advantages of this invention can be obtained 
from a study of the drawings, the disclosure and the appended claims.