WO2012161565A1

WO2012161565A1 - Motion compensation device, method and control system therefor

Info

Publication number: WO2012161565A1
Application number: PCT/NL2011/050346
Authority: WO
Inventors: Pieter Martijn Koppert
Original assignee: Barge Master Ip B.V.
Priority date: 2011-05-20
Filing date: 2011-05-20
Publication date: 2012-11-29
Also published as: EP2709942A1

Abstract

The present invention relates to a motion compensation device (1) for compensating a load carried by a gripper (65) attached to a manipulator (53) on a vessel (3) for water motion. The motion compensation device (1) comprises a carrier frame (2) supported by at least three vertical cylinder- piston units (4,5,6) on the vessel, a sensor system (8), a control system (9), a mechanical constraining system (18, 19, 20) limiting movement of the carrier fame (2) to x-axis rotation, y-axis rotation and optionally z-axis translation; and a heave compensator (60) arranged between the gripper (65) and the manipulator (53).

Description

MOTION COMPENSATION DEVICE, METHOD AND CONTROL SYSTEM THEREFOR

The present invention relates in general to a motion compensation device for

compensating a load carried by a gripper attached to a manipulator on a vessel for water motion.

More specifically, the present invention relates to a motion compensation device for compensating a load carried by a gripper attached to a manipulator on a vessel for water motion;

wherein the motion compensation device comprises:

• a carrier frame for carrying the manipulator;

• an actuator system adapted for translating the load along a z-axis and rotating the carrier frame around an x-axis and an y-axis, wherein the x-axis, y-axis and z-axis define an imaginary set of orthogonal axes, the z-axis extending vertical;

• a sensor system for sensing z-axis translational movement, x-axis rotational movement and y-axis rotational movement of the vessel and/or carrier frame and generating sensor signals representing said sensed movements;

· a control system generating control signals for driving the actuator system in response to said sensor signals such that the position of the load is compensated for said sensed movements; and

• a base for supporting the motion compensation device on the vessel;

• a mechanical constraining system restricting x-axis translational movement, y-axis

translational movement and z-axis rotational movement of the carrier frame with respect to the base

wherein the actuator system comprises at least three cylinder-piston-units each having a vertical longitudinal axis;

wherein each cylinder-piston unit has an upper support for supporting the carrier frame on said cylinder-piston-unit and a lower support for supporting said cylinder-piston-unit on the base;

wherein

• the upper support allows for rotational movement of the respective cylinder-piston-unit relative to the carrier frame around the x-axis as well as the y-axis;

and/or

• the lower support allows for rotational movement of the respective cylinder-piston-unit relative to the base around the x-axis as well as the y-axis. The invention further relates to an assembly comprising such a motion compensation device according to the invention and manipulator and a gripper.

The invention further relates to an assembly comprising such a motion compensation device according to the invention and a vessel, which assembly preferably comprises a manipulator and gripper as well. Worded differently, the present invention thus also relates to a vessel provided with a motion compensation device according to the invention, which vessel preferably is provided with a manipulator and gripper.

When transferring loads from a vessel to another vessel or to some other construction, which might be movable or unmovable relative to the ground, problems arise due to movement of the water on which the vessel floats. Motion of the water subjects the load transfer device, and consequently the load to be transferred, to similar movements. In case the load is carried by a hoisting cable, the water motion will cause a swinging movement of the load as well.

Also when the weather conditions are very calm, the above mentioned problems due to local water movement are present. In this respect it is to be noted that although evidently the water is brought into motion strongly by wind, the effects of wind can lag for weeks in water and have influence on water at large distance away from the location of the wind. Even the water might look like very calm, but still being in motion due to wind weeks ago and/or far away. The effect of this on for example marine building operations is that one has to wait for the water to be almost motionless, in case for example a crane with hoisting cable is to be used safely.

With respect to the motions to which a vessel on water is subjected, it is to be noted that a vessel is in fact subject to 6 degrees of freedom of movement, three translational movements and three rotational movements. Using a mathematical approach based on a carthesian coordinate system having an imaginary set of three orthogonal axes - an x-axis, y- axis and z-axis - these 6 movements can be called x-axis translational movement, y-axis translational movement, z-axis translational movement, x-axis rotational movement, y-axis rotational movement and z-axis rotational movement. It is to be noted, that from a

mathematical point of view there are also other equivalent manners to define the 6-degrees of movement in a space, for example the 3 axes used might not be orthogonal with respect to each other or a so called spherical coordinate system might be used. It is just a matter of mathematical calculation to transfer one definition of 6 degrees of freedom of movement into another definition of 6 degrees of freedom of movement. Using the so called carthesian coordinate system and defining the z-axis as extending vertically, the x-axis as extending in longitudinal direction of a vessel and the y-axis as extending in transverse direction of a vessel,

the x-axis translational movement is in practise called surge

the y-axis translational movement is in practise called sway the z-axis translational movement is in practise called heave

the x-axis rotational movement is in practise called roll

the y-axis rotational movement is in practise called pitch

the z-axis rotational movement is in practise called yaw

GB 2.163.402 discloses an arrangement for open sea transfer of articles between two vessels, which arrangement uses a gantry - having two hingingly connected arms - mounted with one end of the gantry upon a vessel and carrying on the other free end of the gantry a carrying device in the form of a load platform. The load carrying device is space stabilised, it carries a stabilisation sensing arrangement which senses all three rotational and all three translational movements of the load carrying device in space and provides signals so that the gantry can be controlled by jacks and associated control means for compensation of all three rotational movements and all three rotational movements. This arrangement is complex in construction and unable to compensate for local water movements in case the load is carried by a hoisting cable. Also the control for compensation of 6 degrees of freedom of movement is complex. Further, taking into account that the load platform provided with the sensors is due to being carried by a hinging arm (the gantry) at a large distance from the vessel, the rotational movements of the vessel are first increased in magnitude by the arm length and afterwards compensated, which makes the control more difficult.

US 5,947,740 discloses a simulator enabling an operator to reproduce or represent under test conditions phenomena likely to occur. This simulator comprises a platform carried by six + one hydraulic units. The lower ends of the six hydraulic units are fixed in pairs of two in a triangular pattern to the fixed world and the upper ends are fixed in different pairs of two to a simulation platform, also in a triangular pattern. In rest position all the six hydraulic units extend obliquely with respect to the vertical - none of the hydraulic units being parallel to each other in the rest position. These six hydraulic units are actively controlled to move the platform for simulation purposes. The other one hydraulic unit is a vertical one, which essentially carries the load of the platform and is passive, i.e. not controlled. Advantage of this passive central hydraulic unit is that the other six hydraulic units are just for control of movements of the platform and do not need to support the load of the platform. The forces to be exerted for control of the movement of this platform are thus reduced. Although the document does not appear to say so, this simulator is of the type which is used for flight simulators for training airplane pilots. It is known, that this simulator of US 5,947,740 is also used to compensate a passenger transfer platform on a vessel against movement of the water, so that the passengers can walk easily to another vessel or a construction with fixed position without movement of the gangway. The difference between simulator and movement compensator application being essentially in the control. In the compensator application, the control is based on measurements of movement sensors to compensate the six degrees of freedom of movement of the platform for the measured movement. This compensator and its control system are relatively complex and consequently also expensive.

A motion compensation device according to the preamble of claim 1 is known from WO 2010/1 14359. In WO 2010/1 14359 the carrier frame is compensated for x-axis rotational movement, y-axis rotational movement as well as z-axis translational movement due to water motion. Taking into account that the load is carried on the carrier frame, this also

compensates the load. According to WO 2010/1 14359 the actuator system comprises at least three cylinder-piston-units, which are arranged essentially parallel, especially essentially vertical (i.e. in the z-axis direction). In use these cylinder-piston units can be extend or shortened simultaneously to adjust the vertical height - in z-axis direction - of the carrier frame with respect to the vessel. During use, when a vessel is essentially stationary on its place this is the dominant vessel movement to be compensated for when the vessel goes up and down with the - often relatively slow and long - wave movement of the water. The less dominant sideways roll of the vessel and aft-front pitch of the vessel are compensated for by adjusting the cylinder-piston-units differently with respect to each other. In order to prevent jamming of the device due to the device being over-determined, the upper and/or lower support of each cylinder-piston-unit is/are arranged to allow for x-axis rotational movement and y-axis rotational movement. The constraining system restricts x-axis translational movement, y-axis translational movement and z-axis rotational movement of the carrier frame with respect to the base to movements necessary to allow for z-axis translational movement, x-axis rotational movement and y-axis rotational movement of the carrier frame with respect to the base by said actuator system. Advantages of the device according to WO 2010/1 14359 are that the control for compensational movements is less complicated - the piston-cylinder- units will essentially stay parallel which simplifies the control -; that three piston-cylinder-units are sufficient, although easily more, in rest position, essentially parallel piston-cylinder-units can be used as well, in case this might be practical for whatever reason, without the control becoming much more complicated; and that relatively little space is needed in order to allow compensational movements of the support frame because the piston-cylinder-units stay essentially parallel during use (with a system like in US 5,947,740 all space below the platform is required to be free from obstacles in order to allow the piston-cylinder-units to move between different slanting positions). The concept behind t WO 2010/1 14359 is that in most cases, it suffices to compensate only for z-axis translational movement, x-axis rotational movement and y-axis rotational movement of the vessel. The other three degrees of freedom of movement of the vessel (i.e. the z-axis rotational movement, the x-axis translational movement and the y-axis translational movement) need not be compensated for because they are under many circumstances negligible. These other three degrees of freedom of movements being negligible can have different reasons. When, for example, the vessel is anchored and/or kept in position by a dynamic positioning control, these other degrees of freedom of movement are already being taken care of.

The present invention has as its object to provide a motion compensation device for compensating a load carried by a gripper attached to a manipulator on a vessel for water motion, which is relatively simple in construction and control. Starting from WO 2010/1 14359, the present invention has as its object to provide an improved motion compensation device for compensating a load carried by a gripper attached to a manipulator on a vessel for water motion.

[cl 1] According to the present invention, the above objects are, according to a first aspect of the invention, achieved by providing a motion compensation device for

compensating a load carried by a gripper attached to a manipulator on a vessel for water motion;

wherein the motion compensation device comprises:

• a carrier frame for carrying the manipulator;

· an actuator system adapted for translating the load along a z-axis and rotating the carrier frame around an x-axis and an y-axis, wherein the x-axis, y-axis and z-axis define an imaginary set of orthogonal axes, the z-axis extending vertical;

• a sensor system for sensing x-axis rotational movement and y-axis rotational movement of the vessel and/or carrier frame and generating sensor signals representing said sensed movements;

• a control system generating control signals for driving the actuator system in response to said sensor signals such that the position of the load is compensated for said sensed movements; and

• a base for supporting the motion compensation device on the vessel;

· a mechanical constraining system restricting x-axis translational movement, y-axis

wherein

and/or • the lower support allows for rotational movement of the respective cylinder-piston-unit relative to the base around the x-axis as well as the y-axis;

wherein the motion compensation device is characterized, in that the actuator system further comprises a heave compensator for compensating z-axis translation of the load by adjustment of the heave compensator, wherein the heave compensator is to be arranged between the gripper and the manipulator, and in that the control system is arranged for compensating the x-axis rotational movement and y-axis rotational movement of the carrier frame by adjusting one or more of said cylinder-piston-units.

The base of the motion compensation device according to the invention will in use be supported on the vessel. In general the base of the motion compensation device will be fixed with respect to the vessel. The base can for example be formed by one or more feet attached to the lower ends of the cylinder piston units, but can also be formed by the deck of the vessel, in which latter case the lower ends of the cylinder-piston units might be mounted directly to the vessel, for example on the deck of the vessel.

When adjusting for z-axis translational movement a mass is to be displaced over a distance. When using a heave compensator arranged between the load -i.e. the gripper for gripping the load - and manipulator, this mass to be displaced is only the mass of the load carried by the gripper of the manipulator. Taking into account that the dominant movement of the vessel due to movement of the water, is the heave (z-axis translational movement), this allows for on the one hand for a considerable reduction in response times when correcting the load for heave (z-axis translational movement) of the vessel and on the other hand for a considerable reduction in energy consumption of the at least three cylinder-piston units, which are according to the present invention preferably hydraulic. With the motion compensation device according to the invention, x-axis rotational movement and y-axis rotational movement of the vessel due to water motion are compensated for by adjusting the carrier frame with respect to the base. As the compensation for z-axis translation takes place, at least partly, in the heave compensator, the stroke required for the cylinder-piston units is reduced.

It is noted, that although, according to the present invention, it is possible that the cylinder-piston-units are fixed with respect to each other in the sense that during use their relative positions remain unchanged (- for example in case they are mutually perfect parallel they will always extend mutually parallel -) , it is in practise more practical to allow them some freedom of rotational movement around the x-axis or y-axis, i.e. during use the longitudinal axis of said cylinder-piston-units undergo some movement relative to each other. Here a vertical longitudinal axis - of a said cylinder-piston-unit - is, according to the present invention, understood to comprise deviations of the longitudinal axis with respect to the vertical of less than 15°, preferably at most 10°, more preferably at most 5°. In rest position - defined as a position in which the carrier frame and base are parallel to each other -, the said piston-cylinder-units will however preferably be mutually parallel. [cl 2] According to a further embodiment, the control system is passive with respect to compensating z-axis translational movement of the carrier frame. The 'control system being passive with respect to compensating z-axis translational movement of the carrier frame' means that z-axis translational movement of the carrier frame is not actively controlled by the control system. Concerning this embodiment one could also say, the control system is not arranged for compensating z-axis translational movement of the carrier frame. The 'control system being passive with respect to compensating z-axis translational movement of the carrier frame' does not mean that z-axis translational movement of the carrier frame is excluded, it might for example occur due to parasitic movement when controlling the x-axis rotational movement and/or y-axis rotational movement of the carrier frame. Another example of z-axis translational movement of the carrier frame which might occur is for example adjustment of the carrier frame from a rest position to a working position, in which case the z- axis translational movement might very well be under control of the control system but is not really a z-axis compensation.

[cl 3] According to a further embodiment of the motion compensation device according to the invention, the control system is arranged to keep the z-axis translational movement of the carrier frame essentially the same as the z-axis translational movement of the base. Keeping the z-axis translational movement of the carrier frame and base essentially the same, means that the carrier frame and base are essentially not translated with respect to each other but - in case required for compensation of water movement- only rotated with respect to each other. This results in maximising the advantages obtainable with the invention as essentially all compensation for z-axis translational movement is taken care of by the heave

compensator and only x-axis rotational movement and y-axis rotational movement is taken care of by the cylinder-piston units.

[cl 4] The heave compensator can according to the invention be a passive heave compensator or an active heave compensator. A passive heave compensator is a heave compensator which compensates passively for heave movement, without the heave compensator being under control of a control system generating steering signals actively driving the heave compensator. In case of an active heave compensator, the sensor system is further arranged for sensing z-axis translational movement, and the control system is further arranged for compensating the z-axis translational movement by adjusting the heave compensator. An active heave compensator will be driven by steering signals generated by the control system in response to a z-axis translational movement sensed by the sensor system. An active heave compensator allows a more accurate control and lower adjustment times than a passive heave compensator. Further, the control of the heave compensator can be performed entirely separate from the control of the cylinder-piston units, which simplifies the control algorithm considerably. [cl 5] According to another further embodiment of the motion compensation device according to the invention, the control system is arranged to keep a centre point at essentially fixed position relative to the base, wherein the centre point is a point fixed relative to the carrier frame.

[cl 6] According to a further embodiment of the motion compensation device according to the invention, the centre point is defined as the centroid of the polygonal plane defined by the upper supports of the cylinder-piston-units. As known to the skilled man, a centroid is the mathematical centre of a plane. By using the centroid of the polygonal plane defined by the upper supports of the cylinder-piston units, the control algorithm used by the control system can be pre-programmed for a large extent independently from the manipulator to be used with the motion compensation device. This because once having the carrier platform, cylinder piston units and base, the basic parameters for the control algorithm based on this centroid are known.

[cl 7] According to another embodiment of the motion compensation device according to the invention, the centre point is defined as the centre of gravity of the carrier frame. This results in a control algorithm requiring low energy consumption for the cylinder-piston units,

[cl 8-9] According to another embodiment of the motion compensation device according to the invention, the centre point is defined as the centre of gravity of the carrier frame and manipulator carried on the carrier frame. This results in a control algorithm reducing the energy consumption of the cylinder-piston units to almost a minimal. However, this centre of gravity might be at a position relatively high with respect to the vessel, which might be a disadvantage. Further, this requires detailed knowledge of the manipulator in advance in order to be able to program the control algorithm. Although other drawbacks might be introduced, these disadvantages can be reduced by arranging the centre of gravity of the manipulator carried on the carrier frame to lie on the vertical through the centre point, when the carrier frame is in horizontal position.

[cl 10-14] According to another further embodiment of the motion compensation device according to the invention, the constraining system comprises at least three bars, each bar being arranged to function in its longitudinal direction as an essentially rigid push-pull-element having one end attached to the base and the other end attached to the carrier frame. In this embodiment:

^■ said one end of each bar might be attached to the base by means of a ball hinge and the other end of each bar is attached to the carrier frame by means of a ball hinge. These ball hinges allow essentially unconstrained movement of the carrier platform when actuated by the cylinder-piston-units;

and/or

^■ the bars might extend horizontally and at least two bars might be arranged mutually

orthogonal; and/or

^■ at least two of said bars are arranged mutually parallel;

and/or

^■ the constraining system might consists of three of said bars, two of said bars being

arranged mutually parallel and the third of said bars being arranged orthogonal with respect to said two mutually parallel bars,

[cl 15-16] Although according to the invention, the manipulator might be any device for manipulation a load on, especially, a vessel, the manipulator is according to a further embodiment of the invention a manipulator chosen from the group comprising: a crane, a derrick, a gantry, a drilling rig, a backhoe, and dragline. According to this embodiment, the manipulator might further comprise a hoisting cable or arm carrying the gripper.

[cl 17-20] According to a second aspect, the present invention relates to an assembly comprising: a motion compensation device according to the invention; a said manipulator; and a gripper. According to this second aspect, the manipulator might be placed on the carrier frame and the gripper might be attached to the manipulator via the heave

compensator. With this second aspect, the motion compensation device is placed on a vessel, which in turn might be part of the assembly according to this aspect,

[cl 21] According to a third aspect, the present invention relates to a method for

compensation a load, which is carried by gripper attached to a manipulator on a vessel, for local water motion;

wherein the method uses a motion compensation device, comprising:

• a carrier frame carrying the manipulator;

• a base for supporting the motion compensation device on the vessel;

translational movement and z-axis rotational movement of the carrier frame with respect to the base;

wherein the actuator system comprises:

• at least three cylinder-piston-units each having a vertical longitudinal axis; wherein each cylinder-piston unit has an upper support for supporting the carrier frame on said cylinder-piston-unit and a lower support for supporting said cylinder-piston-unit on the base; and

· a heave compensator arranged between the gripper and the manipulator;

wherein • the upper support allows for rotational movement of the respective cylinder-piston-unit relative to the carrier frame around the x-axis as well as the y-axis;

and/or

• the lower support allows for rotational movement of the respective cylinder-piston-unit relative to the base around the x-axis as well as the y-axis;

wherein the method comprises the steps of:

• measuring x-axis rotational movement and y-axis rotational movement; and

• driving the actuator system such that the x-axis rotational movement and y-axis rotational movement is compensated by adjusting one or more of said cylinder-piston-units in response to the measured x-axis rotational movement and y-axis rotational movement; and

• compensating z-axis translational movement by adjusting the heave compensator.

Advantages of this third aspect are already described in relation to the first aspect of this invention.

[cl 22] According to a further embodiment, the z-axis translational movement of the carrier frame is passively allowed. This means that the control system used is 'passive with respect to compensating z-axis translational movement of the carrier frame'. The meaning of this term has been explained earlier above.

[cl 23-25] Although also further embodiments of this third aspect are already described in relation to the first aspect of the invention, claims 23-25 are directed to some specific embodiments of this third aspect.

[cl 26] According to a fourth aspect, the present invention relates to a control system for performing the method according to the invention, the control system comprising:

• one or more sensors for sensing x-axis rotational movement and y-axis rotational

movement and generating sensor signals representing said sensed movements;

• a controller generating control signals for driving the actuator system in response to said sensor signals such that the x-axis rotational movement and y-axis rotational movement is compensated by adjusting the one or more of said cylinder-piston-units and optionally z- axis translational movement is compensated by adjusting the heave compensator.

The present invention will be explained further with reference to the enclosed drawing, in which:

Figure 1 is a perspective view of a first embodiment of a motion compensation device according to the invention;

Figure 2 is a side view of the device of Figure 1 , arranged on a vessel and carrying a crane; Figure 3 is a perspective view of a base unit of the device of Figure 1 ; and Figure 4 is a side view of a second embodiment of a motion compensation device according to the invention.

In the figures 1 -4, a Cartesian coordinate system having axis x, y and z is represented to define the x-direction, y-direction and z-direction. An x-axis rotational movement is a movement having the x-axis as centre of rotation, an x-axis translational movement is a movement in a the direction of arrow x (or opposite direction). The same applies for the y-axis and z-xis.

Figures 1 -3 show a device 1 according to a first embodiment of the invention. The device comprises a carrier frame 2, which is in this case triangular but might have any shape. The device 1 further comprises three hydraulic cylinder-piston-units 4, 5, 6 - four, five or more cylinder-piston units is however also conceivable - . The device further comprises a heave compensator 60. The hydraulic cylinder-piston units 4, 5 and 6 and heave

compensator 60 together form the actuator system. In order to control the cylinder-piston- units 4, 5, 6 a control system 9 is provided, which is connected by means of control lines 1 1 , 12, 13 to each cylinder-piston-unit. This control system 9 generates control signals driving the cylinder-piston units in response to sensor signals 10 which come from a sensor system 8. The sensor system 8 is arranged for sensing x-axis rotational movement and y-axis rotational movement of a vessel. The heave compensator 60 might be a passive heave compensator, in which case it is not controlled by the control system. The heave compensator 60 is however in particular an active heave compensator. In case of an active heave compensator, the sensor system will also be arranged for sensing z-axis translational movement of a vessel and generating a corresponding sensor signal 10. This sensor signal representing the z-axis translation is fed to the control system 9, which in turn is connected via a control line 51 to the heave compensator 60 for transmitting a control signal generated in response to the sensor signal for the sensed z-axis translation. Taking into account that the control of the heave compensator can be performed entirely separate from the control of the cylinder-piston units, it is noted that the control system 9 might be sub-divided into two separate control units, one for the cylinder piston units and one for the heave compensator.

As shown in figure 2, the device 1 is provided on a vessel 3 and carries a manipulator

53, in this case a crane 25 with hoisting cable 26. Instead of a crane, the manipulator can essentially be any kind of manipulator capable of manipulating a load. In order to be able to carry a load, the manipulator is provided by a gripper, which is shown in figure 1 in highly schematic manner as 65. This gripper can for example be a crane hook, like 55 shown in figure 4 or a jaw gripper having two or more jaws which can grasp a load.

Referring to figure 3, each cylinder-piston-unit 4, 5, 6 has an upper support 15 carrying the carrier frame and a lower support 16 supported on a base 17. The upper support 15 is in the form of a ball hinge 21 which supports a downwardly facing bearing surface on the carrier frame 2. The lower support 16 is a cardan joint 22 having two orthogonal hinge axes 23 and 24. The cardan joint 22 allows the cylinder-piston-unit to rotate around hinge 24 (x-axis) and hinge 23 (y-axis) relative to the base 17. The ball hinge 21 allows the cylinder-piston-unit to rotate relative to the carrier frame 2 around the x-axis, indicated by arrow 28, and the y-axis, indicated by arrow 27. It is however noted that the lower support 16 and upper support 15 can also comprise another type of joint. For example, both the lower and upper support might be a cardan joint or ball hinge.

As indicated with arrow 29, the cylinder-piston-units 4, 5, 6 can move along their longitudinal axis 14. When one cylinder-piston-unit is extended or shortened more than one or both others, the ball hinges 21 and cardan joints 16 allow the cylinder-piston-units 4, 5, 6 to be slanted slightly with respect to the z-axis. The angle a between the longitudinal axis 14 and z-axis can vary in a range of [0°, 10°], but a range of [0°, 5°] is in general sufficient.

In order to prevent the carrier frame from drifting away due to the freedom of rotational movements of the cylinder-piston-units 4, 5, 6, there is provided a constraining system which restricts x-axis translational movement, y-axis translational movement and z-axis rotational movement of the carrier frame 2 with respect to the base to movements necessary to allow for x-axis rotational movement and y-axis rotational movement of the carrier frame 2 with respect to the base 17 by said actuator system. In the embodiment of figures 1 -3, the constraining system comprises three bars 18, 19 and 20 of preferably steel. Each bar 18, 19, 20 is hinged at one end 30 to the base and at the other end 31 to the carrier frame 2.

Although not shown in the figures, these hinges at the ends 30 and 31 can be ball hinges. In longitudinal direction these bars function as essentially rigid push-pull elements. Ball hinges at the ends 30 and 31 allow the carrier frame to be moved in x-axis rotational direction, y-axis rotational direction and optionally z-axis rotational direction without generating transverse bending forces in the bars 18, 19 and 20.

It is however noted, that - although not preferred - the cylinder-piston-units might in a rest position extend at an angle of say 5 to 10 degrees with respect to the z-axis (=vertical). According to the invention this is still to be understood as the cylinder-piston-units extending vertical.

As can be seen in figure 3, the base segments 35 have the dimensions of a sea container, in this case a 40 feet one. In order to transport a base segment easily and in compact manner, the cylinder-piston-units 4, 5, 6 can be swivelled 90° around axle 23 as indicated by arrow 32. The lower side 4 of the cylinder-piston-unit can pass through aperture 33 in order to come in a horizontal position inside the 'sea-container' base segment 35.

Figure 4 shows in side view a motion compensation device according to a second embodiment. This second embodiment differs only slightly from the first embodiment. The gripper is shown to be a crane hook 55 and the heave compensator 50 is arranged at a different location and in a little more detail. Further the manipulator is a crane 52 having a crane boom 54. This crane 52 is basically the same as the crane 53 of figure 2.

The heave compensator 50 is arranged at the free end of the hoisting cable 26. In this embodiment the heave compensator 50 comprises a cylinder 56 having a piston 58 moveable in said cylinder 56. The piston carries a rod 57 to which in turn the crane hook 55 is attached.

The present invention can also be worded as represented in the next following clauses:

1 ] Motion compensation device (1 ) for compensating a load carried by a gripper attached to a manipulator on a vessel (3) for water motion;

wherein the motion compensation device comprises:

• a carrier frame (2) for carrying the manipulator;

• an actuator system (4, 5, 6) adapted for translating the load along a z-axis and rotating the carrier frame (2) around an x-axis and an y-axis, wherein the x-axis, y-axis and z-axis define an imaginary set of orthogonal axes, the z-axis extending vertical;

· a sensor system (8) for sensing x-axis rotational movement and y-axis rotational

movement of the vessel and/or carrier frame and generating sensor signals (10) representing said sensed movements;

• a control system (9) generating control signals (1 1 , 12, 13) for driving the actuator system in response to said sensor signals (10) such that the position of the load is compensated for said sensed movements; and

• a base for supporting the motion compensation device on the vessel;

• a mechanical constraining system (18; 19; 20) restricting x-axis translational movement, y-axis translational movement and z-axis rotational movement of the carrier frame (2) with respect to the base

wherein the actuator system comprises at least three cylinder-piston-units (4, 5, 6) each having a vertical longitudinal axis (14);

wherein each cylinder-piston unit (4, 5, 6) has an upper support (15) for supporting the carrier frame (2) on said cylinder-piston-unit (4, 5, 6) and a lower support (16) for supporting said cylinder-piston-unit (4, 5, 6) on the base (17);

wherein

• the upper support (15) allows for rotational movement of the respective cylinder- piston-unit (4, 5, 6) relative to the carrier frame (2) around the x-axis as well as the y- axis;

and/or

· the lower support (16) allows for rotational movement of the respective cylinder- piston-unit (4, 5, 6) relative to the base (17) around the x-axis as well as the y-axis; characterized, in that the actuator system further comprises a heave compensator to be arranged between the gripper and the manipulator for compensating z-axis translation of the load by adjustment of the heave compensator, and

in that the control system is arranged for compensating the x-axis rotational movement and y- axis rotational movement of the carrier frame by adjusting one or more of said cylinder-piston- units.

2] Motion compensation device according to clause 1 , wherein the control system is arranged to be passive with respect to compensating z-axis translational movement of the carrier frame.

3] Motion compensation device according to clause 1 or 2, wherein the control system is arranged to keep the z-axis translational movement of the carrier frame essentially the same as the z-axis translational movement of the base.

4] Motion compensation device according to one of clauses 1 -3, wherein the heave compensator is an active heave compensator, wherein the sensor system is further arranged for sensing z-axis translational movement, and wherein the control system is further arranged for compensating the z-axis translational movement by adjusting the heave compensator. 5] Motion compensation device according to one of clauses 1 -4, wherein the control system is arranged to keep a centre point at essentially fixed position relative to the base, wherein the centre point is a point fixed relative to the carrier frame.

6] Motion compensation device according to clause 5, wherein the centre point is defined as the centroid of the polygonal plane defined by the upper supports of the cylinder-piston- units.

7] Motion compensation device according to one of the clauses 5-6, wherein the centre point is defined as the centre of gravity of the carrier frame.

8] Motion compensation device according to one of clauses 5-7, wherein the centre point is defined as the centre of gravity of the carrier frame and manipulator carried on the carrier frame.

9] Motion compensation device according to one of clauses 5-7, wherein, when the carrier frame is in horizontal position, the centre of gravity of the manipulator carried on the carrier frame lies on the vertical through the centre point.

10] Motion compensation device according to one of the preceding clauses, wherein the constraining system comprises at least three bars, each bar being arranged to function in its longitudinal direction as an essentially rigid push-pull-element having one end attached to the base and the other end attached to the carrier frame.

1 1 ] Motion compensation device according to clause 10, wherein said one end of each bar is attached to the base by means of a ball hinge and wherein the other end of each bar is attached to the carrier frame by means of a ball hinge. 12] Motion compensation device according to one of clauses 10-1 1 , wherein the bars extend horizontally and wherein at least two bars are arranged mutually orthogonal.

13] Motion compensation device according to one of clauses 10-12, wherein at least two of said bars are arranged mutually parallel.

14] Motion compensation device according to one of clauses 10-13, wherein the constraining system consists of three of said bars, two of said bars being arranged mutually parallel and the third of said bars being arranged orthogonal with respect to said two mutually parallel bars.

15] Motion compensation device according to one of the preceding clauses, wherein the manipulator is one of the group comprising: a crane, a derrick, a gantry, a drilling rig, a backhoe, and dragline.

16] Motion compensation device according to clause 15, wherein the manipulator comprises a hoisting cable or arm carrying the gripper.

17] Assembly comprising:

· a motion compensation device according to one of the preceding clauses;

• a said manipulator; and

• a gripper.

18] Assembly according to clause 17, wherein the manipulator is placed on the carrier frame and wherein the gripper is attached to the manipulator via the heave compensator. 19] Assembly according to one of clauses 17-18, wherein the motion compensation device is placed on a vessel.

20] Assembly according to one of clauses 17-19, further comprising a vessel.

21 ] Method for compensation a load, which is carried by gripper attached to a manipulator on a vessel, for local water motion;

wherein the method uses a motion compensation device, comprising:

• a carrier frame carrying the manipulator;

· a base for supporting the motion compensation device on the vessel;

wherein the actuator system comprises:

· at least three cylinder-piston-units each having a vertical longitudinal axis; wherein each cylinder-piston unit has an upper support for supporting the carrier frame on said cylinder-piston-unit and a lower support for supporting said cylinder-piston-unit on the base; and

• a heave compensator arranged between the gripper and the manipulator;

wherein

· the upper support allows for rotational movement of the respective cylinder-piston-unit relative to the carrier frame around the x-axis as well as the y-axis;

and/or

wherein the method comprises the steps of:

• measuring x-axis rotational movement and y-axis rotational movement; and

22] Method according to clause 21 , wherein the z-axis translational movement of the carrier frame is passively allowed.

23] Method according to one of clauses clause 21 -22, wherein the z-axis translational movement of the carrier frame is kept essentially the same as the z-axis translational movement of the base.

24] Method according to one of clauses 21 -23, wherein the heave compensator is an active heave compensator, wherein the z-axis translational movement is measured, and compensating the z-axis translational movement by adjusting the heave compensator in response to the measured z-axis translational movement.

25] Method according to one of clauses 21 -24, wherein a centre point is kept at an essentially fixed position relative to the vessel, and wherein the centre point is defined as:

• the centroid of the polygonal plane defined by the upper supports of the cylinder- piston-units; or

· the centre of gravity of the carrier frame; or

• the centre of gravity of the carrier frame and manipulator carried on the carrier frame. 26] Control system for performing the method according to one of clauses 21 -25, the control system comprises:

movement and generating sensor signals (10) representing said sensed movements;

• a controller generating control signals (1 1 , 12, 13) for driving the actuator system in

response to said sensor signals (10) such that the x-axis rotational movement and y-axis rotational movement is compensated by adjusting the one or more of said cylinder-piston- units and optionally z-axis translational movement is compensated by adjusting the heave compensator.

As a general remark, it is noted that a heave compensator is as such known to the skilled man and that there are many different designs of heave compensator known. Also the heave compensator according to this invention can, within the scope of this invention as determined by the claims, be of another design than the one shown in the figure 4.

As a further general remark, it will be clear to the skilled man, that the sensor system is preferably arranged to measure the x-axis rotational and y-axis rotational movement of the carrier frame with respect to a fixed reference point, which reference point could be called the fixed world. However, in stead of or in addition the sensor system could also be arranged to measure the x-axis rotational and y-axis rotational movement of the vessel with respect to said fixed reference point.

As a still further general remark, it will also be clear to the skilled man, that the sensor system can in addition (optionally) also be arranged to measure the z-axis translational movement of the gripper (or load) and/or of the carrier frame and/or of the vessel with respect to a said fixed reference point. In case of a passive heave compensator, measurement of the z-axis translational movement might not be necessary for adjusting the heave compensator, but it might still be useful for monitoring purposes and/or for allowing additional compensation by adjustment of at least three cylinder-piston units carrying the carrier frame.

Claims

1 . Motion compensation device (1 ) for compensating a load carried by a gripper attached to a manipulator on a vessel (3) for water motion;

wherein the motion compensation device comprises:

• a carrier frame (2) for carrying the manipulator;

· an actuator system (4, 5, 6) adapted for translating the load along a z-axis and rotating the carrier frame (2) around an x-axis and an y-axis, wherein the x-axis, y-axis and z-axis define an imaginary set of orthogonal axes, the z-axis extending vertical;

• a sensor system (8) for sensing x-axis rotational movement and y-axis rotational

• a base for supporting the motion compensation device on the vessel;

· a mechanical constraining system (18; 19; 20) restricting x-axis translational movement, y-axis translational movement and z-axis rotational movement of the carrier frame (2) with respect to the base

wherein

and/or

• the lower support (16) allows for rotational movement of the respective cylinder- piston-unit (4, 5, 6) relative to the base (17) around the x-axis as well as the y-axis; characterized,

in that the actuator system further comprises a heave compensator to be arranged between the gripper and the manipulator for compensating z-axis translation of the load by adjustment of the heave compensator, and in that the control system is arranged for compensating the x-axis rotational movement and y- axis rotational movement of the carrier frame by adjusting one or more of said cylinder-piston- units.

2. Motion compensation device according to claim 1 , wherein the control system is arranged to be passive with respect to compensating z-axis translational movement of the carrier frame.

3. Motion compensation device according to claim 1 or 2, wherein the control system is arranged to keep the z-axis translational movement of the carrier frame essentially the same as the z-axis translational movement of the base.

4. Motion compensation device according to one of claims 1 -3, wherein the heave compensator is an active heave compensator, wherein the sensor system is further arranged for sensing z-axis translational movement, and wherein the control system is further arranged for compensating the z-axis translational movement by adjusting the heave compensator.

5. Motion compensation device according to one of claims 1 -4, wherein the control system is arranged to keep a centre point at essentially fixed position relative to the base, wherein the centre point is a point fixed relative to the carrier frame.

6. Motion compensation device according to claim 5, wherein the centre point is defined as the centroid of the polygonal plane defined by the upper supports of the cylinder-piston- units.

7. Motion compensation device according to one of the claims 5-6, wherein the centre point is defined as the centre of gravity of the carrier frame.

8. Motion compensation device according to one of claims 5-7, wherein the centre point is defined as the centre of gravity of the carrier frame and manipulator carried on the carrier frame.

9. Motion compensation device according to one of claims 5-7, wherein, when the carrier frame is in horizontal position, the centre of gravity of the manipulator carried on the carrier frame lies on the vertical through the centre point.

10. Motion compensation device according to one of the preceding claims, wherein the constraining system comprises at least three bars, each bar being arranged to function in its longitudinal direction as an essentially rigid push-pull-element having one end attached to the base and the other end attached to the carrier frame.

1 1 . Motion compensation device according to claim 10, wherein said one end of each bar is attached to the base by means of a ball hinge and wherein the other end of each bar is attached to the carrier frame by means of a ball hinge.

12. Motion compensation device according to one of claims 10-1 1 , wherein the bars extend horizontally and wherein at least two bars are arranged mutually orthogonal.

13. Motion compensation device according to one of claims 10-12, wherein at least two of said bars are arranged mutually parallel.

14. Motion compensation device according to one of claims 10-13, wherein the constraining system consists of three of said bars, two of said bars being arranged mutually parallel and the third of said bars being arranged orthogonal with respect to said two mutually parallel bars.

15. Motion compensation device according to one of the preceding claims, wherein the manipulator is one of the group comprising: a crane, a derrick, a gantry, a drilling rig, a backhoe, and dragline.

16. Motion compensation device according to claim 15, wherein the manipulator comprises a hoisting cable or arm carrying the gripper.

17. Assembly comprising:

• a motion compensation device according to one of the preceding claims;

• a said manipulator; and

• a gripper.

18. Assembly according to claim 17, wherein the manipulator is placed on the carrier frame and wherein the gripper is attached to the manipulator via the heave compensator.

19. Assembly according to one of claims 17-18, wherein the motion compensation device is placed on a vessel.

20. Assembly according to one of claims 17-19, further comprising a vessel.

21 . Method for compensation a load, which is carried by gripper attached to a manipulator on a vessel, for local water motion;

wherein the method uses a motion compensation device, comprising:

• a carrier frame carrying the manipulator;

• a base for supporting the motion compensation device on the vessel;

wherein the actuator system comprises:

• a heave compensator arranged between the gripper and the manipulator;

wherein

and/or

wherein the method comprises the steps of:

· measuring x-axis rotational movement and y-axis rotational movement; and

· compensating z-axis translational movement by adjusting the heave compensator.

22. Method according to claim 21 , wherein the z-axis translational movement of the carrier frame is passively allowed.

23. Method according to one of claims claim 21 -22, wherein the z-axis translational movement of the carrier frame is kept essentially the same as the z-axis translational movement of the base.

24. Method according to one of claims 21 -23, wherein the heave compensator is an active heave compensator, wherein the z-axis translational movement is measured, and

compensating the z-axis translational movement by adjusting the heave compensator in response to the measured z-axis translational movement.

25. Method according to one of claims 21 -24, wherein a centre point is kept at an essentially fixed position relative to the vessel, and wherein the centre point is defined as:

· the centre of gravity of the carrier frame; or

• the centre of gravity of the carrier frame and manipulator carried on the carrier frame.

26. Control system for performing the method according to one of claims 21 -25, the control system comprises:

· one or more sensors for sensing x-axis rotational movement and y-axis rotational

movement and generating sensor signals (10) representing said sensed movements; • a controller generating control signals (1 1 , 12, 13) for driving the actuator system in