Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to cranes and more particularly
but not exclusively to tag lines for cranes and cranes employed in
ocean areas to lift loads from boats.
In ocean regions which are subjected to considerable wave action
such as the North Sea, it is very difficult to operate a crane to raise
a load from a boat. This is due to movement of the ship relative to
the crane. Motion of the load will subject the crane to shock loading
while this problem is exacerbated since the weight of the load indicated
to the crane operator may not be consistent with the actual weight of
the load. Additionally the weight may not be fully uncoupled from the
boat or may be caught on a rail and become jammed. In all these
circumstances it is possible for the crane to be damaged and the operator
subjected to danger. Thus, given any one of the above adverse conditions
and the situation that the load is engaged at the crest of a wave, the
crane may be subjected to excessive loading as the boat falls under the
influence of wave action thereby subjecting the crane uncontrollably to
the full load dynamically magnified.
In the use of tag lines on cranes to date, the controls for such
tag lines must be continually manipulated if the tag line is to retain
and support the load at a predetermined location~ That is to say, the
controls are not generally adapted to maintain a constant tension in
the tag line.
It is an object of the present invention to overcome or substant-
ially ameliorate the above disadvantages.
There is disclosed herein a crane hoist drive assembly comprising
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an hydraulic hoist motor to provide a lift force for the crane; a variable
displacement hydraulic pump operatively coupled to said motor to drive
same by pumping hydraulic fluid therethrough, said pump having displace-
ment control means adapated to govern the displacement of said pump;
and an hydraulic control circuit operatively coupled to said displacement
control means to thereby control displacement of said pump and therefore
the lift force generated by said motor, said control circuit including
selectively operable valve means adapted to limit the pressure delivered
by said control circuit to said control means to thereby limit the lift
force generated.
A preferred form of the present invention will now be described by
way of example with reference to the accompanying drawings, wherein:
Figure 1 is an hydraulic control system to control the hoist
hydraulic motor and hydraulic pump of a crane;
Figure 2 is an hydraulic circuit including a main hoist hydraulic
motor and hydraulic pump to be controlled by the circuit of Figure l;
and
Figure 3 is an hydraulic circuit for a tag line control system to
be employed with the circuit of Figure 2.
In Figure 1 there is depicted a control hydraulic circuit 10 for
the hoist motor and pump of a crane to be used in conjunction with the
hydraulic circuit of Figure 2 which includes the hoist hydraulic motor
20 and hydraulic pump 21.
The circuit 10 is adapted to control the maximum output of the
pump 21 so that the force applied to the hoist cable by the motor 20
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has a predetermined maximum. The circuit 10 provides for two modes of
controlling the output of the pump 21. The first mode of operation is
to control the pump 21 when a load is ini-tially being coupled to the
hoist cable. In this first mode the cable will merely follow movement
of the load as in the case of a pitching boat. This is known as a light
line operation. The second mode of control enables the load to be raised
This is known as a normal line operation. However, in both modes of
operation the force applied to the hoist cable is limited at a pre-
determined maximum which, if exceeded, will result in the motor 20
reversing so as to pay out cable to reduce the load.
With reference to Figure 2 in particular, there is schematically
illustrated the hydraulic motor 20 which is driven by the hydraulic
pump 21. The motor 20 is provided with speed control valves 22 which
in the case of a radial piston-type motor, selectively vary the hydraulic
fluid displacement of the motor 20 to thereby regulate the speed and
torque of the motor 20, assuming a given pressure and fluid delivery
to the motor 20. Also provided is a boost extraction valve 23 which
enables hydraulic fluid to be drained from the pump circuit.
The circuit 10 is connected to the pump 21 by hydraulic lines 24,
25 and 26 at points designated Hl, H2 and V. The line 26 is a vent
line. The pump 21 is preferably an axial piston type with a variable
angle swash plate to regulate the pump displacement and direction of
flow through the pump 21. The pump 21 is equipped with a primary dis-
placement control by way of a control piston 31 and cylinder 32 to which
the circuit 10 is connected via lines 24 and 25. The control piston 31
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and cylinder 32 alter the swash plate angle of the pump 21 Additionally,
as the hydraulic control pressure within the pump is proportional to the
pump output the swash pump angle is variable by venting pressure there-
from via line 26. However, it should be appreciated that the piston 31
is moved by varying the pressure between the lines 24 and 25. In this
known type of pump the vent line allows pressure to be bled from within
the pump which in turn allows main pump pressure to be used in controlling
the swash plate angle. Thus the response of the pump is rapid. The
circuit 10 includes a main control panel 15 having two valves 12 and
13 which are manipulatable via an operator to control the main hoist
motor and pump and are coupled to lines 24 and 25. The valves 12 and 13
are coupled via line 16 to a pump which provides hydraulic fluid under
pressure to be used in circuit 10. Circuit 10 further includes a wave
compensation selection valve 17 and a wave compensation valve 18. The
valve 17 is a solenoid actuated valve and merely selects the position of
valve 18. There is also provided a hoist up limit valve 19 which limits
the maximum raised hoist position. Connected to the line 26 is a load
capacity selection valve 27 which adjustably limits the maximum load
force and thus the load lift applied to the main line, by limiting the
pump output pressure. Also connected to the line 26 is a light line
selection valve 28 and a light line limit valve 29. The valve 29 may
also be adjustable. The valve 28 is solenoid actuated and can be simult-
aneously actuated with valve 17 in the light line wave compensation mode
of operation.
In operation the lift force provided by the hoist may he set at a
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predetermined maximum by the valve 27 or by the valve 29 upon selection
of valve 28. If wave compensation is required the valve 17 is actuated.
By doing so main control pressure is connected to the line 25 via
actuation of valve 17 which would bias the pump 21 to maximum output.
This is commonly known as biasing the pump to an "on-stroke" mode of
operation. However, this is modified by venting pressure from vent line
26 when the output of the pump 21 exceeds a predetermined pressure.
Initially the predetermined pressure is adjustably set by valve 29
by actuation of the valve 28.
As mentioned above this is a light line operation. Once the load
has been securely engaged the solenoid valve 28 is operated to isolate
the valve 29, this then places the pump 21 under normal mode of operation.
Under normal load lifting conditions the maximum output of the pump 21
is determined by valve 27.
Accordingly, via lines 24, 25 and 26 the angle of the swash plate
of pump 21 may be automatically caried to determine the pressure and
direction of flow produced by pump 21. Under wave conditions the motor
20 may be actually reversed in rotational direction to maintain a
constant tension in the hoist cable, as for example when the boat is
falling under the influence of wave action. The pressure output may be
varied between a maxiumum set by valve 27 and 0 for the normal hoisting
mode or the predetermined fixed setting of valve 29 in case of light line,
wave compensation mode and the flow may be reversed in direction. In
variable swash plate pumps the flow is reversed by having the pump
operate "over centre". In this "over centre" condition the swash plate
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is positioned so as to reverse the pump flow and thus reverse the motor
20.
An operator may regain manual control of the lifting operation by
again actuating valves 12 and 13, which will cause actuation of sensor
30, which in turn will de-activate solenoid valve 17 and hydraulic
control valve 28 and return circuit 10 to a normal mode of operation with
a maximum tension setting controlled by valve 27. Under wave compensation
mode of operation the operator does not manipulate the valves 12 and 13,
which will remain in a neutral position.
Turning now to Figure 3, there is depicted a tag line control
circuit 50 -to be coupled to the pump 21 of Figure 2. However, in this
example the motor 20 of E~igure 2 is adapted to apply a constant tension
to a tag line. The lines 24, 25 and 26 of Figure 3 correspond to the
lines 24, 25 and 26 of Figure 2 for ease of description.
The circuit 50 includes a control panel 53 which includes spool
valves manipulated by an operator and to which is connected control
pressure via line 55, a variable setting and pilot operated constant
tension control valve 56 connected to vent line 26 and an isolation valve
57 which upon selection of constant tension mode of operation applies
full control pressure to the line 25. There is also provided an over-
ride valve 58.
The valves of control panel 53 are biased to a neutral position
wherein control pressure is permitted to flow through valves 57 and 58
to bias the pump to maximum output. The pump will then maintain a
constant output pressure as dictated by the adjustable setting of valve
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56. For example, if the pressure drops the valve 56 will cause the
pump 21 to increase in stroke, or if the pressure increases to the
setting of the valve 56 the valve 56 will cause a decrease in stroke.
If the control panel 53 is operated to increase tension in the tag
line, the output pressure is increased by increasing the stroke of the
pump 21. The valve 56 is influenced by control pressure proportional
to the tension required, to adjust the pump 21 pressure output.
If tag line tension is to be descreased and the tag line paid out,
then the line 25 is dumped to tank via valve 58 and proportional control
pressure if delivered to the line 24 via panel 53.
If the tag line tension is to be dropped -to zero then panel
57 is operated.
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