Hoisting device with compensated tackle

A hydraulic or pneumatic cylinder supports a pair of non-circular discs and a circular pulley about which a hoisting cable and a carrying cable are trained. The discs are configured such that a constant force is exerted on a load supported by the hoisting cable independent of the variation in pressure in the cylinder due to displacement of the piston supporting the discs. The carrying cable comprises two runs; one having one end fixed to one of the discs and the other end fixed to the supporting base, and the other having one end fixed to the other disc and the other end fixed to a pulley block supporting the load. The hoisting cable extends from a winch, over the circular pulley, to the pulley block. The arrangement compensates for relative motion between the load and the supporting base.

The invention relates to a hoisting device disposed on a freely movable 
support and mainly comprising one or more hoisting cables adapted to be 
wound on a winch drum or the like connected with said support and leading 
to a freely hanging tackle which carries the load. 
The invention has for its object to construct the hoisting device so that 
despite the freely movable support the lower block of the tackle and hence 
the load remain hanging at the same level. 
The device embodying the invention is distinguished in that the tackle is 
suspended to at least one carrying cable which is directly or indirectly 
fastened to the support via a disc displaceable by a setting member with 
respect to the support. 
Thanks to the setting member it is now possible to move the tackle with 
respect to the displaceable support without the need for paying off or 
hauling the hoisting cable. The setting member takes care of the desired 
displacement of the disc which thus compensates for the movement of the 
support. If the load is an element bearing on the sea bottom, a constant 
ground pressure can thus be maintained. 
In a preferred embodiment the setting member is formed by a hydraulic or 
pneumatic cylinder controlled by a gas buffer. 
In order to enable a compensation of the gas pressure fluctuations in the 
gas buffer, the displaceable disc is designed in the form of a cam or 
eccentric disc so that with a possibly constant load force automatic 
compensation occurs as a function of the displacement of the piston rod in 
the cylinder. 
In a further embodiment a reversing disc can, in addition, be journalled 
for the hoisting cable on the rotary shaft of the displaceable disc so 
that the hoisting cable need not be hauled or payed out. 
The invention will be described more fully with reference to a few 
embodiments.

The hoisting device shown in FIG. 1 is arranged on a freely movable support 
1, which may be a vehicle or a vessel. 
The hoisting device mainly comprises a winch 2 provided with a winch drum 
3, about which a hoisting cable 4 can be wound. The winch drum can be 
rotated by any driving gear 5. 
The hoisting cable 4 leads via a reversing disc 6 to a tackle 7, which 
consists in this embodiment of a one-disc upper block and a double-disc 
lower block. The end of the hoisting cable is fastened at 8 to the upper 
block. The lower block carries a load 9 and may be constructed in any 
manner with a magnet shoe, hoisting eyelet or the like. 
The upper block of the tackle 7 is suspended to a carrying cable 10, the 
first run of which leads to a segment disc 11. This first run 10' is 
guided in a circumferential groove and fastened at 12. The segment disc 11 
is fastened to a rotary shaft 13, on which is journalled the reversing top 
disc 6 of the hoisting cable 4. 
At the side of the segment disc 11 is arranged a second segment disc 14, 
which cannot rotate with respect to the segment disc 11. The second run of 
the carrying cable 10 is fastened to the circumference thereof and also 
guided through a circumferential groove, said second run passing to a 
fixed point 15 of the support 1. 
The rotary shaft 13 is journalled in a fork-like support 16, which is 
arranged at the top side of a piston rod 17. The piston rod 17 is part of 
a hydraulic cylinder 18, which is rigidly secured to the support 1. The 
hydraulic cylinder 18 enables the upward and downward movements of the 
rotary shaft 13 and hence of the top disc 6 and the two segment discs 11 
and 14. 
The device described above operates in general as follows. During a 
downward movement of the support 1, for example, due to swell in the case 
of a vessel, the tackle 7 can be held at its level with respect to the sea 
bottom by energizing the cylinder 18 so that the piston rod 17 moves out 
of the cylinder 18. Thus the hoisting cable 4 as well as the carrying 
cable is moved along the discs so that the segment discs 11 and 14 
respectively will turn around the shaft 13. Also the top disc 6 will turn, 
but with a circumferential speed differing from that of the segment discs. 
When due to pressure fluctuations in the energizing medium of the cylinder 
18 the setting force varies in dependence on the displacement of the 
piston 17' in the cylinder, the circumferential shape of the segment discs 
11 and 13 can be adapted thereto in a manner such that the reactive 
pressure resulting from the load on the piston rod 17 also varies in 
relationship to the setting pressure in the cylinder 18 so that 
compensation is obtained. 
The foregoing is set out in detail in FIGS. 2 and 3. The same parts are 
designated by the same reference numerals and it is assumed that a gas 
buffer controlled cylinder 18 is used. The cylinder itself is a hydraulic 
cylinder fed by a fluid stored in a reservoir 19, which communicates 
through the feed duct 20 with the lower side of the cylinder 18. The 
reservoir 19 is provided with a separation piston 20, on the other side of 
which a pressurized gas is operative. This pressurized gas is stored in 
bottles 21. When the piston rod 17 has to move upwards in the cylinder 18, 
fluid is pressed from the reservoir 19 below the piston 17' by means of 
the gas pressure in the bottles 21. Obviously with an increasing gas 
volume the gas pressure decreases and hence also the force expelling the 
piston rod 17. This can be compensated for by varying the reactive torque 
produced by the run 10" so that a constant force on the lower block of the 
tackle is ensured. 
FIG. 3 illustrates how this is achieved in the embodiment concerned. The 
segment disc 11 has a circumferential groove, which is in this embodiment 
concentric with the rotary shaft 13. The second segment disc 14, however, 
is designed so that, when the piston 17' moves outwards, the distance 
between the second run 10" and the rotary shaft 13 varies. This distance 
variation is indicated by "a" in FIG. 3. Since the tractive forces in the 
runs 4 and 10' will be substantially constant, a reactive torque depending 
on the position of the piston rod 17 will occur as a result of the 
variation of the radius with respect to the rotary shaft 13. Since this 
reactive torque varies in proportion to the decrease and increase of the 
gas pressure in the bottles 21, a constant force is maintained on the 
lower block of the tackle. 
It will be obvious that any other shape of the two segment discs 11 and 14 
is possible, whilst it is also possible to use only one cam disc, that is 
to say, a combination of the segment discs 11, 14 in which the carrying 
cable directly passes on and the friction between cable and disc ensures 
the "connection". 
FIGS. 4 and 5 show two possibilities of use, in which a vessel 25 is 
provided with an implement 26 on the underside thereof. The end of the 
implement 26 may serve for working the bottom, to scan it and the like and 
it will be obvious that the end of the implement 26 has to remain at the 
correct level and the gas pressure has to be constant and low. The 
implement 26 is suspended to the hoisting appliance described with 
reference to FIGS. 1 to 3 on the deck of the vessel 25 so that in the case 
of swell the upward and downward movements of the ship's hull, i.e. the 
support 1 in FIG. 1, are compensated for. 
In the second example of use a drilling derrick is mounted on, for example, 
a floating working platform 28 so that also in this case in the event of 
swell the lower tackle block to which the relatively slender drilling tube 
29 is suspended has to remain at its level since otherwise the drilling 
tube might kink. The weight of the drilling tube can, moreover, be partly 
taken by the tackle block, since the full weight would be too high for the 
desired chisel pressure. 
Therefore, the upper tackle block is suspended to a carrying cable 10' of 
the compensated hoisting device of FIGS. 1 to 3 arranged above in the 
derrick 27. It is indifferent to the effect of the compensated hoisting 
device whether the winch 5 is arranged on the deck of the platform 28 or 
in the derrick 27. The gas buffer system 21 or the fluid reservoir 19 
arranged in this case in the derrick may also be mounted on the deck. 
FIG. 6 shows an alternative embodiment in which the tackle 7 is provided 
with a guide disc 30. Around the guide disc is passed a carrying cable 31, 
which passes along fixed guide wheels 32, 33 to a segment disc 11'. The 
cable is transferred to the adjacent second segment disc 14', whilst the 
free end of the cable is secured to a fixed point of the support. The 
other part of the cable is passed in a similar manner along segment discs 
11" and 14" to a second fixed point of the support. The rotary shaft 13' 
of the discs is supported by a piston rod 17 of a cylinder 18'. 
The hoisting cable 4 of the tackle 7 is passed directly or indirectly 
towards a winch disposed on the support. In this embodiment during an 
upward and downward movement of the support, that is to say, of the 
compensation device, the lower block of the tackle 7 has to be held at its 
level by sliding the piston rod 17 in or out. Thus the distance between 
the discs 11, 14 with respect to the fixed discs 32, 33 is varied so that 
the upper block of the tackle 7 is moved up and down. The compensation of 
the hoisting cable 4 in this embodiment has, however, to be taken over by 
the displacement of the discs 11, 14 so that the lower block of the tackle 
7 remains at the same level. Nevertheless the hoisting cable can be 
compensated through the same or a separate system. Thanks to the double 
structure of the carrying cable 31 it may be thinner than in the 
embodiment shown in FIGS. 1 to 3 so that a more flexible system is 
obtained. Also in this case the segment discs may have any desired shape. 
The invention is not limited to the embodiments depicted above. It is, of 
course, possible to double the embodiment of FIGS. 1 to 3 as well as that 
of FIG. 6.