Note: Descriptions are shown in the official language in which they were submitted.
~0~969Z
The invention relates to a cargo boom which can be
pivoted about the boom needle by means of two winches which, r
through a system of cables and tackles, also called guys, affect
the boom such that one obtains the moment required to pivot
the boom and its cargo sideways, without slack in any of the
cables.
One previously known system for this purpose utilizes
a winch with two drums, where one drum winds in and the other
pays out simultaneously. This sort of arrangement has several
disadvantages. Owing to the geometric ratios, the sum of the
cable lengths between the two drums has to change during a -
pivoting operation if a slackening or tautening of the cables
is to be avoided. This compensation of cable length cannot
be effected ~hen both drums rotate together, with the result
that one has an alternating slackening or tautening of the
cable system, depending on the boom's angle of swing.
Another problem with this type of system is that wXen
the cables stretch with time, the slack will increase, and
readjustment is very difficult.
Any slack in the guys will result in imprecision in
the control of the boom, and can lead to dangerous situations.
In an attempt to compensate to some degree for slack, -~
springs or other elastic members between the boom and tackles
have been used. However, this is merely a makeshift solutlon;
it is still not possible to avoid slack under certain loading
and heeling conditions, and the tension in the elastic members
will also decrease as the guys gradually stretch with time.
Another system which utilizes two winches is Xnown from
Norwegian Patent No. 124,022. The way in which slack in the
guys is avoided in this system is that "a braking force is
applied to the slacking winch motor such that the slacking guy
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10~969Z
1 wire has to be drawn off the drum against a certain force."
This effect is obtained because the slacking hydraulic winch
motor is pulled around ~y the motor that hauls in, oil from the
- slacking motor being made to pass through a counterpressure valve
which produces a braking moment on the slacking motor. To hold
the guy wires taut when the winch system is not in operation,
a certain pressure is applied to the motors on the drive side.
A decided disadvantage of the latter system is that
the winch motor that pays out cable receives a significant
10 braking moment owing to the counterpressure valve! this in
addition to the friction and resistance already present in the
system. Therefore, in order to be able to effect a certain
moment on the boom about the boom needle, the winch motor that
hauls in must necessarily be dimensioned so large that it can
overcome both the boom-force and the braking force from the
slackening winch. -This means that one is forced to utilize
larger and more expensive winch motors than one really needs
for a specific boom, cargo, heeling angle and the normal friction
conditions.
To obtain the desired pivoting velocity, therefore,
a larger pump and increased applied power are required to over-
come the braking effect caused by the counterpressure valve.
It is obvious that the costs involved in such a system are
dependent on the dimensions and installed power of the machinery
that is utilized. This results in an increase both in the
initial investment for procuring the machinery and in the running
costs during operation, owing to the increased energy consumption.
The present invention is the result of work to find a
solution to the problems of previous systems, as described
30 above.
1079692
1 Briefly, the invention is characterized in that pressure
from a separate pressure source is led into a pipeline which
connects up the respective sides of the two motors which indi-
vidually try to draw the boom to one side or the other,
respectively. By ensuring that the pressure in this pipeline
is always somewhat higher than the highest pressure existing
elsewhere in the system, the guys will always be under tension
without any application of braking force on the motor which is
paylng out cable being necessary, and one thus obtains the
10 desired savings in power consumption.
The supply of pressure medium (oil) from said separate
pressure source is very small. In the non-operational state,
it will merely refill enough oil to compensate for a small inner
leak in the system, and with a pivoting of the boom it will
compensate for the changes in volume which are the result of the
aforementioned geometric ratios which cause the one motor to
pay out more cable than the other motor hauls in, or vice-versa.
The surplus of pressure medium from the two motors when the
total length of cable is shortened is led out of the connective
20 line between the motors through a pressure-regulating valve.
In the ~ollowing, the method of operation will be
explained with reference to the accompanying diagram.
The pivotable boom is symbolically drawn ànd designated
(B). The two winch drums are designated Tl and T2, and the
guys, the cables gl and g2, are attached to the top of the boom
and pull it to either side. In practice, there would normally
be multi-sheaved tackles between the drum and boom in o~der to
obtain the most advantageous ratio, but this simplified drawing
has been chosen merely for the purpose of illustrating the
30 system.
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107969Z
1 Each of the two drums Tl and T2 is driven by its own
hydraulic motor, Ml and M2, respectively. These motors are
coupled to the pipeline 1 in such a way that supplying an over-
pressure in the pipeline 1 produces a moment on each of the
two motors Ml and M2, each of which then tries to pull the boom
to its side via the drums Tl and T2 and the guy wires gl and g2.
Both winches are alike and are supplied the same pressure, and
when the boom is in the position shown on the drawing, the
winches are in equilibrium and the boom is stationary. To make
the boom pivot, the moment on one motor must be reduced such that
the other motor has the upper hand. This is accomplished by
guiding the control lever for the maneuvering valve 2 to the
side toward which one wants the boom to swing. The control slide
~a 4-way valve of known type) is arranged such that it will then
conduct pressure medium from the pump 3 to the motor that is
supposed to pay out cable~ The moment on this motor, which is
approximately proportional to the pressure difference over the
motor, will thus be reduced,and the other motor, which retains
its moment, will draw the boom toward its side.
It is essential that the pressure in the pipeline 1
always be higher than the highest of the two pressures that can
exist in the pipelines 4 and 5. This can be achieved, for example,
by ensuring that the maximum-pressure valve 6 is adjusted
somewhat lower than the pressure in the separate pressure source
12 which is coupled to the pipeline 1.
In a preferred embodiment, the use of a pressure-
regulating valve 7 of a known type has been chosen, as shown on
Fig. 1. As is known, this valve functions such that the
pressure in the line 1 will be higher than the pressure in lines
4 or 5 by an amount equal to the spring force F that
is set. The slide in the valve 7 is in equilibrium when
107969Z
PF A Pl '
where PF = pressure in the spring housing,
F = the spring force,
A = the end cross section of the slide valve, and
Pl = the pressure in the pipeline 1.
The spring housing is automatically coupled via a
relay 8-to whichever of the pipelines 4 or 5 has the highest
pressure at the moment.
To prevent an unnecessarily high pressure build-up in
pipelines 4 and 5 when the maneuvering valve is in the stop ~ -~
position, the pipeline which has the lowest pressure is auto- `
matically coupled to a reservoir tank 9 through a relay 10 and
a choke valve 13. In this way, pressure medium which leaks
from line 1 through the motors Ml and M2 to line 4 or S can
flow back to the return side of the auxiliary pump 12, which
also is connected to the reservoir tank 9. This tank is
dimensioned such that it can refill or receive that volume of ~ .
pressure medium brought about as a result-of temperature changes,
an~ can also compensate for the changes in volume occurring when
the motors Ml and M2, owing to the geometry of the rigging,
are forced to rotate at different speeds during a pivoting `~
operation. The surplus fluid from line 1 is led off through
valves 7 and 13 to the reservoir 9.
Also shown on Fig. 1 is a valve 11 of conventional
design and function. This valve's job is to ensure that the
pressure on the pump's intake side will not be too high if the
cargo pulls the boom to the same side as the one toward which it
is pivoting. This valve also ensures that the pressure on the
pump's outlet side is sufficient to prevent cavitation in the
~0796g2
1 motor that pays out cable in the same situation.
Standard symbols or schematic representations with
which a person skilled in the art will be familiar and whose
functions he will understand have been utilized for the purpose
of illustrating the method of operation for the invention.
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