Method and apparatus for the control of a weight suspended from a floating vessel

Claim 2

In an apparatus adapted to be mounted on a vessel subject to heave due to wave action, which apparatus includes a hydraulic cylinder, a first piston and a first piston rod in said cylinder, means to connect a load to said first piston rod, a second hydraulic cylinder and a second piston in said second hydraulic cylinder; said second piston operatively connected to said first piston, separate pneumatic accumulator systems, one each connected to each one of said cylinders for control of the forces exerted on said piston rod, the improvement which comprises means separately to vary the pressure in a first of said accumulator systems, to modulate the pressure in said first accumulator system to compensate for change in pressure in a second accumulator system on imposition of a load on said first piston, whereby the forces on said piston rod are maintained substantially constant.

Claim 3

In the apparatus of claim 1, said means to modulate said pressure including a source of liquid under pressure and a reservoir at a pressure lower than in one of said accumulator systems, control means for selectively opening a first communication between the said one of said accumulator systems and said source and selectively closing a second communication between said one of said accumulator systems and said reservoir when said firSt communication is opened and control means for opening said second communication and closing said first communication.

Claim 4

In the apparatus of claim 2, said control means comprising a signal means responsive to the forces imposed on the first piston rod by said load when said apparatus is mounted on said vessel, during all portions of the heave, means to generate a signal responsive to the forces predetermined to be maintained on the first piston rod by said load, means to generate an error signal responsive to the differences between said first and second-mentioned signals and means selectively to open and selective to close the aforesaid communications responsive to said error signal.

Claim 5

In the apparatus of claim 2, said communications including pipe connections between each of the cylinders and each accumulator system, a gas connection between each of the accumulator systems and a source of gas under pressure, a pipe connected between one of said cylinders and the accumulator system connected thereto and connected to said source, and another pipe connected between said last-named accumulator system and said reservoir, said means to open and close said communications through said pipes including valves in each of said pipes, means to open a first valve in one of said first-mentioned pipes and means to close a second valve in the other of said pipes when the first valve is opened and means to open said second valve when said first valve is closed.

Claim 6

In the apparatus of claim 4, control means to open the first valve in said pipe connected to said first accumulator system and said source and to close a second valve in the pipe connecting said first accumulator system to said reservoir system, when the force imposed on said piston rod by said load when said apparatus is mounted on a vessel, is substantially below a predetermined value and control means to open the second valve and close the first valve when the force exerted on said piston rod is substantially above said predetermined value.

Claim 7

In the apparatus of claim 5, said control means comprising means to generate a signal responsive to the forces imposed on the first piston rod in said first cylinder, during all portions of the heave, means to generate a signal responsive to the forces predetermined to be maintained on the first piston rod, means to generate an error signal responsive to the differences between said first and second-mentioned signals and means to selectively open and selectively close the aforesaid valves responsive to said error signal.

Claim 8

In combination with a drilling vessel, a derrick, drilling lines suspended from said derrick, a hydraulic cylinder and piston-pneumatic accumulator system for control of the forces in said piston rod by a load connected to the piston rod, the improvement which comprises a plurality of accumulators, a plurality of pistons connected to the same piston rod, means to establish pressures separately on said pistons, said means including a cylinder element for each piston, one of said pneumatic accumulators connected to each cylinder, a source of liquid under pressure, a reservoir, a source of gas pressure for each accumulator, a first pipe means to connect to a first one of said accumulators to said source, and a second pipe means to connect said first one of said accumulators to said reservoir, and means opening communication through said pipe means between said source and said first one of said accumulators and closing said communication through said second pipe means, during that portion only of the heave when the volume of the liquid in a second one of said accumulators tends to decrease and means to open communication through said second pipe means and closing communication through said first pipe means during that portion only of the heave when the volume of liquid in the said second one of said accumulators tends to increase.

Claim 9

In combination with a drilling vessel, a derrick, drilling lines suspended from said derrick, a hydraulic cylinder and piston-pneumatic accumulator system for control of the forces in said piston rod by a load connected to the piston rod, the improvement which comprises a plurality of accumulators, a plurality of pistons connected to the same piston rod, means to establish pressures separately on said pistons, said means including a cylinder element for each piston, one of said pneumatic accumulators connected to each cylinder, a source of liquid under pressure, a reservoir, a source of gas pressure for each accumulator, a first pipe means to connect to a first one of said accumulators to said source, and a second pipe means to connect said first one of said accumulators to said reservoir, and means opening communication through said pipe means between said source and said first one of said accumulators and closing said communication through said second pipe means, during that portion only of the heave when the volume of the liquid in a second one of said accumulators tends to decrease and means to open communication through said second pipe means and closing communication through said first pipe means during that portion only of the heave when the volume of liquid in the said second one of said accumulators tends to increase.

Claim 10

In the apparatus of claim 7, said means to open and close communication through each of said pipe means, valves In each of said pipe means and means responsive to said error signal to close and open the valves in said pipe means.

Claim 11

In the apparatus of claim 7, said control means comprising a means to generate a signal responsive to the forces imposed on the piston rod during all portions of the heave, means to generate a signal responsive to a predetermined stress to be maintained in the piston rod, means to generate an error signal responsive to the differences between said first and second-mentioned signals, and means to selectively open and selectively close the aforesaid communications responsive to said error signal.

Claim 12

In the apparatus of claim 9, said control means including means selectively to open a first valve in said first pipe means and to close a second valve in said second pipe means when the said force is substantially below a predetermined value and means to close said first valve and open the second valve when the force exerted on said piston is substantially above said predetermined value.

Claim 15

The method of claim 11, the step of advancing the piston spacially downward during each portion of the heave cycle and withdrawing from said first-mentioned said first one of said accumulators to an extraneous point a quantity of liquid responsive to the said spacial advance.

Claim 16

In the process of claim 12, said withdrawal occurring only during that portion of the heave when the volume under the pistons in the cylinders is decreasing.

Claim 17

In the process of claim 13, introducing into the first one of said accumulators a quantity of liquid less than the quantity withdrawn, said introduction occurring only during that portion of the heave when said volume in said cylinders is increasing.

Claim 18

In an apparatus adapted to be mounted on a vessel subject to heave due to wave action, which apparatus includes a first cylinder, a first piston, and a first piston rod in said first cylinder, a second cylinder and a second piston in said second cylinder, said second piston in said second cylinder operatively connected to said first piston rod, a fluid pressure source connected to one of said cylinders for control of the forces exerted on said piston rod, which comprises means separately to vary the pressure in one of said cylinders, to modulate the pressure in one of the cylinders to compensate for change in pressure in another of said cylinders, whereby the forces on said piston rod are maintained substantially constant.

Claim 19

In an apparatus adapted to be mounted on a vessel subject to heave due to wave action, which apparatus includes a first cylinder, a first piston, and a first piston rod in said first cylinder, a second cylinder and a second piston in said second cylinder, said second piston in said second cylinder operatively connected to said first piston rod, a fluid pressure source connected to one of said cylinders for control of the forces exerted on said piston rod, which comprises means separately to vary the pressure in one of said cylinders, to modulate the pressure in one of the cylinders to compensate for change in pressure in another of said cylinders, whereby the forces on said piston rod are maintained substantially constant.

Claim 20

In the apparatus of claim 15, a control means comprising a signal means responsive to the forces imposed on the first piston rod, during all portions of the heave, means to generate a signal responsive to the forces predetermined to be maintained on the first piston rod, means to generate an error signal responsive to the differences between said first and second-mentioned signals and means to adjust the pressure in one of said cylinders responsive to said error signal.

Claim 21

In combination with a drilling vessel, a derrick, drilling lines suspenDed from said derrick, a cylinder, and a gas pressure system for control of the forces in said piston rod, a plurality of pistons connected to the same piston rod, means to establish separate pressures on said pistons, said means including a cylinder element for each piston, a source of pressure connected to each cylinder, means to increase the pressure in one of said cylinders during that portion only of the heave when the volume under the piston on the other of said cylinders tends to decrease and means to decrease the pressure in said one cylinder during that portion only of the heave when the volume under the piston in the other cylinder tends to increase.

Claim 22

In combination with a drilling vessel, a derrick, drilling lines suspenDed from said derrick, a cylinder, and a gas pressure system for control of the forces in said piston rod, a plurality of pistons connected to the same piston rod, means to establish separate pressures on said pistons, said means including a cylinder element for each piston, a source of pressure connected to each cylinder, means to increase the pressure in one of said cylinders during that portion only of the heave when the volume under the piston on the other of said cylinders tends to decrease and means to decrease the pressure in said one cylinder during that portion only of the heave when the volume under the piston in the other cylinder tends to increase.

Claim 23

In the apparatus of claim 17, said means comprising a means to generate a signal responsive to the forces imposed on the piston rod during all portions of the heave, means to generate a signal responsive to a predetermined stress to be maintained in the piston rod, means to generate an error signal responsive to the differences between said first and second-mentioned signals, and means to selectively increase and decrease said pressure responsive to said error signal.

Claim 26

The method of claim 19, the step of advancing the piston rod spacially downward during each portion of the heave cycle.