Compensation device for a crane

A ship-mounted crane is provided with a compensation device for ensuring that its load rope will suspend a load selectively stationary relative to the ship, or stationary relative to a load-receiving surface relative to which the ship moves. For this purpose, the crane is provided with a second rope separate from the load rope, and main and auxiliary pneumatic springs movable independently of each other. The load rope is trained about the main pneumatic spring; while the second rope is trained about both pneumatic springs and is selectively connectible to the load-receiving surface.

The invention relates to a compensation device for a crane or similar 
hoisting machine consisting of a controllable pneumatic main spring in the 
track of the load rope, a measuring rope which can be provided between the 
crane and the surface upon which a load has to be put down or from which 
the load has to be picked up, as well as means which are controlled by 
this measuring rope for controlling the pneumatic spring, such that 
differences in the movement between the load and said surface can be 
compensated. Such compensation devices are known. They serve for providing 
that when a load e.g. is put down from a ship which is moving by the waves 
onto another ship or platform the movements of the load and the load 
receiving surface are equalized. The known devices which serve for 
attaining this object are complicated in construction and in use and 
generally comprise a servo-device which is controlled by the measuring 
rope. 
The invention aims to provide a simple solution for this problem and 
according to the invention this object is attained by the fact that the 
measuring rope not only has its own pneumatic auxiliary spring but also is 
coupled with the controllable pneumatic main spring. 
In case of a crane which is provided with a main hoisting apparatus and a 
top hoisting apparatus, both can be realized in a simple manner by having 
the rope of the top hoisting apparatus run over the auxiliary spring and 
over the main spring and by fixing a fastening rope to its load hook. By 
means of this fastening rope, which together with the top hoisting means 
functions as a measuring rope, the crane can be coupled with the load 
receiving surface. The movements of the crane with respect to the load 
receiving surface remain possible by the presence of the pneumatic 
springs. A load which is suspended by the load rope normally will follow 
the movements of the crane. When now the measuring rope is connected to 
the loading receiving surface and when this rope is stretched until the 
auxiliary spring is moving around its central position, then the load is 
always still moving with the crane. When now the pressure in the pneumatic 
main spring is controlled in such a way that the auxiliary spring is 
brought to a stop then the main spring behaves in the same manner for the 
measuring rope as for the load rope which means that the load is coming to 
a stop with respect to the load receiving surface and so can be put down. 
It is important that on the basis of the movements of the pneumatic 
auxiliary spring it can be decided whether it is justified to start with 
moving the load.

The drawing shows a crane which is disposed on a ship and has a main 
hoisting winch 1 and a top hoisting winch 2. The load rope 3 runs over the 
pulleys 4 and 5 of a pneumatic spring 6 and further via the deflection 
roll 7 in the jib to the load 8. 
The second rope 10, of the top hoisting winch 2, runs over the pulleys 11 
and 12 of a pneumatic auxiliary spring 13 and further over the pulleys 14 
and 15 of the pneumatic main spring 6 and then over the top roll 16 to the 
load hook 17 to which a fastening rope 18 is fixed which can be connected 
to the put down surface 19. When now a load 8 has to be put down from the 
ship onto the surface 19 then the following is done. The pneumatic 
cylinder 6 is brought on its maximum pressure corresponding to its 
extended position. The load 8 which is tilted from the ship now will move 
together with the crane while it is suspended from the latter. 
Now the rope 18 is connected to the surface 19 and the rope 10 is stretched 
by turning the hoisting winch 2 until the auxiliary spring 13 is moving 
around its centre position. So this auxiliary spring then is absorbing the 
movements of the ship with respect to the load receiving surface but the 
load still moves together with the crane. When now the pressure in the 
spring 6 is decreased until the movements of the spring 13 cease, the 
point is reached that the movements of the load rope 3 are equal to those 
of the measuring rope 10, 18 and therefore the load 8 is no longer moving 
with respect to the load receiving surface and so can be put down on this 
surface by means of the main hoisting winch 1. 
When a load has contacted the load receiving surface in the described way 
then the load can be fully put down by further slackening rope 3. By doing 
so the pneumatic main spring 6 again reaches its extreme position and the 
pneumatic auxiliary spring 13 is taking over again the compensation of the 
measuring rope. 
The invention is very simple and can always be applied regardless of the 
relative movements between the ship and the load receiving surface. The 
latter can move also in which case the movements of the load are made 
equal to those of the load receiving surface by the means according to the 
invention. 
Preferably the compensation system described above is situated near the 
deadends of the ropes 3 and 10. Then the mounting of the system in a crane 
is more simple and there is less friction and so less wear when the system 
is not in use because the ropes do not move over additional pulleys.