EP2953884A1

EP2953884A1 - Motion compensation device

Info

Publication number: EP2953884A1
Application number: EP14704183.4A
Authority: EP
Inventors: Eelko Maij
Original assignee: BARGE MASTER IP BV
Current assignee: BARGE MASTER IP BV
Priority date: 2013-02-05
Filing date: 2014-02-05
Publication date: 2015-12-16
Anticipated expiration: 2034-02-05
Also published as: EP2953884B1; WO2014123414A1

Abstract

Pedestal motion compensation device 1) for compensating heave, pitch and roll motion of a carrier frame on board of a vessel. The device comprises: a carrier frame (2); a base (3) for supporting the device on the vessel; a z-translation unit (4); and a xy-rotation unit (5). The z-translation unit allows a z-axis translational movement. The xy-rotation unit allows x-axis rotational movement as well as y-axis rotational movement. A z-axis rotational movement is prevented by a linear guide system (12), and a main universal joint (14) including a blocking element (58), so that the carrier frame and the base are moveable with respect to each other in a translational direction along the z-axis, in a rotational direction around the x-axis and in a rotational direction around the y-axis but restrained from mutual movement in a translational direction along the x-axis, in a translational direction along the y-axis and in a rotational direction around the z-axis.

Description

Title: Motion compensation device. The present invention relates in general to a motion compensation device for compensating for local water motion of a carrier frame - which might for example carry a load transfer device, like a crane or gantry, or a winch - on a vessel.

More specifically, the present invention relates to a motion compensation device for compensating a carrier frame arranged on a vessel for water motion, wherein an imaginary set of three orthogonal axes is defined by an x-axis, an y-axis and an z-axis; wherein the device comprises:

a said carrier frame;

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

· a compensation system allowing z-axis translational, x-axis rotational, and y-axis rotational movement of the carrier frame with respect to the base, whilst preventing x-axis translational, y-axis translational, and z-axis rotational movement of the carrier frame with respect to the base. The invention further relates to an assembly comprising such a motion compensation device according to the invention and a crane or winch, which assembly might further comprise a vessel as well.

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 crane or winch 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 crane as well. 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 Cartesian 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.

The above terms surge, sway, heave, roll, pitch and yaw all are dynamic in the sense that these might vary from moment to moment depending on the movements of the water. On top of this comes that the vessel might not be aligned horizontal - also not in absence of any motion of the water - for example due to uneven load distribution or wind influences. In that situation there might be a static deviation with respect to the x-axis rotation and y-axis rotation. The static deviation with respect rotation around the x-axis is called 'list' and the static deviation with respect to the y-axis rotation is called 'trim'.

WO 2010/1 14359 describes a motion compensation device of the same applicant as the present application. 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 there is an actuator system comprising at least three cylinder-piston-units, which are arranged essentially parallel, especially essentially vertical. In use these cylinder-piston units can be extended 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 same cylinder-piston-units differently with respect to each other. WO

2010/1 14359 describes a 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 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. The concept behind WO 2010/114359 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 general object of the present invention is to at least partially eliminate drawbacks of known devices and/or to provide a useable alternative. More specific, it is an object of the invention to provide a motion compensation device to compensate heave, roll and pitch motion for a pedestal structure on board of a vessel.

Starting with the same concept as WO 2010/114359 (i.e. compensating for x-axis rotational, y-axis rotational and z-axis translational movement whilst not compensating for the other 3 degrees of freedom), the present invention has as its object to provide a motion

compensation device allowing easier control of the compensation system and/or a smaller footprint of the compensation system. This object is achieved by providing a motion compensation device for compensating for water motion of a carrier frame arranged on a vessel, wherein an imaginary set of three orthogonal axes is defined by an x-axis, an y-axis and an z- axis;

wherein the device comprises:

a said carrier frame;

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

a z-translation unit; and

a xy-rotation unit;

wherein the z-translation unit allows z-axis translational movement and prevents x-axis translational movement, y-axis translational movement, z-axis rotational movement, x-axis rotational movement and y-axis rotational movement;

wherein the z-translation unit has, viewed in the direction of the z-axis, a first end and a second end;

wherein the xy-rotation unit allows x-axis rotational movement as well as y-axis rotational movement and prevents z-axis rotational movement, x-axis translational movement, y-axis translational movement, and z-axis translational movement;

wherein the base is provided at a first end of the z-translation unit and the carrier frame at a second end of the z-translation unit wherein the carrier frame and base are:

on the one hand, moveable with respect to each other in a translational direction along the z-axis, in a rotational direction around the x-axis and in a rotational direction around the y-axis; and

on the other hand, restrained from mutual movement in a translational direction along the x-axis, in a translational direction along the y-axis and in a rotational direction around the z-axis;

wherein the z-translation unit is provided with at least one z-actuator arranged to cause, upon actuation of said z-actuator, z-axis translational movement of the carrier frame with respect to the base frame, whilst the xy-rotation unit is provided with at least two xy-actuators arranged to cause, upon actuation of one or more of said xy-actuators, x-axis rotational and/or y-axis rotational movement of the carrier frame with respect to the base frame, the at least one z- actuator and at least two xy-actuators being different actuators.

Advantageously, the functionality of the x-axis, y-axis rotational movement and the z-axis translational movement of the device is carried out by separate actuators. The rotational movement is carried out by the xy-actuators of the xy-rotation unit and the z-translational movement is carried out by the z- actuator of the z-translation unit. The rotational movement can be carried out independent of a translational movement. This arrangement of functional separate actuators may simplify a control system to control the motion compensation device. In an embodiment of the motion compensation device according to the invention, the z- translation unit and the xy-rotation unit are aligned with each other. The alignment of the z- translation unit and the xy-rotation unit means that the central axes of both units are aligned in a neutral position of the device. In the neutral position of the device, the z-translation unit and xy-rotation unit are oriented in upwards direction which corresponds with the z-axis. The alignment of the z-translation unit and the xy-rotation unit contributes to a pedestal type configuration of the device. A pedestal type configuration of a structure has only a single leg for supporting the structure to a ground base.

In particular the z-translation unit and the xy-rotation unit are concentrically positioned. The z- translation unit has a central axis which substantially coincidences with a central axis of the xy-rotation unit. In particular, the z-actuator of the z-translation unit is positioned in a central region of the xy-rotation unit.

In an embodiment of the motion composition device according to the invention the z- translation unit is stacked with the xy-rotation unit.

In an embodiment of the motion compensation device according to the invention, the xy- rotation unit is arranged between the z-translation unit and the carrier frame.

In an embodiment of the motion compensation device according to the invention, the xy- rotation unit is arranged between the z-translation unit and base. In an embodiment of the motion compensation device according to the invention, the z- translation unit comprises a linear guide system and the xy-rotation unit comprises a main universal joint, which linear guide system and main universal joint prevent together the z-axis rotational movement of the carrier frame with respect to the base.

The z-axis translation unit thus has one DOF (=degree of freedom) in the z-axis translational direction. The other five DOF of the z-axis translation unit are fixated. Similarly, the xy- rotation unit has two DOF, the x-axis rotation and the y-axis rotation. The other 4 DOF of the xy-rotation unit are fixated. By stacking and coupling the z-axis translation unit and the xy- rotation unit, a motion compensation device is obtained which allows a compensation about 3 DOF. A z-translational movement, a x-axis rotational and y-axis rotational movement can be compensated.

The motion compensation device according to the invention is able to compensate for roll, list, pitch, trim and heave of the carrier frame. This compensation according to the invention might be with respect to the fixed world.

In an embodiment of the motion compensation device according to the invention, the z-axis translation unit is rotationally coupled in a central region to the xy-rotation unit. The main universal joint may have a centrally positioned rotational coupling, like a ball joint of the z- translation unit to allow the z-translation unit to rotate about a rotation point.

By arranging a single z-translation unit and a single xy-rotation unit, from a functional perspective, aligned on the z-axis, it becomes possible to decouple the compensation for z- axis translation from the compensation for xy-axis translation, i.e. movement of the z-actuator can be done without influencing the xy-axis rotation of the carrier frame and movement of the xy-actuators can be done without influencing the z-axis translation. This enables a considerably simpler control of said actuators and allows a design with a much smaller footprint.

In an embodiment of the motion compensation device, -viewed in vertical direction- , the base is arranged at the lower side of the motion compensation device and the carrier frame at the upper side of the motion compensation device, there are, according to the invention, basically two configurations possible:

· a first configuration with, in vertical direction, sequentially: the base, the z-translation unit, the xy-rotation unit and the carrier frame; and

• a second configuration with, in vertical direction, sequentially: the base, the xy-rotation unit, z-translation unit and the carrier frame.

An imaginary set of three orthogonal axes, defined by an x-axis, an y-axis and an z-axis, means that the x-axis and y-axis are mutually perpendicular, and the z-axis being

perpendicular with respect to both the x-axis and y-axis. The z-axis can be defined as a fixed vertical axis immovable with respect to the surrounding, but it can also be defined as another vertical, like a vertical immovable with respect to the vessel. According to an embodiment of the device according to the invention, the z-translation unit comprises a first and second part mutually connected by a linear guide system extending in the z-direction, which linear guide system is arranged to allow the first and second part to shift in z-direction with respect to each other and to prevent x-axis translational movement, y- axis translational movement, x-axis rotational movement, y-axis rotational movement and z- axis rotational movement of the first part with respect to the second part. In contrast to a linked bar mechanism for guiding a carrier frame, the linear guide system contributes advantageously to a compact configuration of the motion compensation device. The first part is also called an outer pedestal. The second part is also called an inner pedestal. Preferably, the outer pedestal is connected to the base or vessel or on top of the xy-rotation unit, wherein the inner pedestal is able to move with respect to the outer pedestal. However, in an inverted embodiment it is also possible to connect the inner pedestal to the base or vessel or on top of the xy-rotation unit, wherein the outer pedestal is able to move with respect to the inner pedestal.

In an embodiment of the motion compensation device according to the invention, the inner part comprises an inner space for receiving said z-actuator. The inner part is hollow. The inner part has a cylindrical shape which is open at a bottom end and closed at a top end. The z-actuator can be positioned inside the inner space of the inner part and connected to the closed top end. According to an embodiment of the device according to the invention, the first and second part are telescopic parts. The first and second part might be tubular having a circular cross section or a cross section with different shape, like square or triangular. Such a telescopic construction can be made very resistant against moments around the x-axis, y-axis and z- axis.

In an embodiment of the motion compensation device according to the invention, the linear guide system comprises at least three guidance units. The guidance units are preferably connected to the outer pedestal to guide the inner pedestal in a translational movement with respect to the outer pedestal. The at least three guidance units are positioned in parallel and spaced from each other. Each guidance unit extends in a longitudinal direction of the outer pedestal. The longitudinal direction corresponds with a z-axis direction of the device in its neutral position. The at least three guidance units enclose the inner pedestal to constrain all rotational movements and two translational movements which result in 1 DOF which is the z- axis translational movement.

In an embodiment of the motion compensation device according to the invention, each guidance unit comprises a pair of an upper and a lower roller box. Each roller box include at least one roller. Each roller has an outer roller surface to contact a running surface provided at a movable counterpart.

In a particular embodiment of the device according to the invention, the linear guide system comprises three guidance units including each a pair of an upper and a lower roller box. The pair of roller boxes define a longitudinal axis of the guidance unit. The guidance units are positioned along an outer circumference of the first or second part. Preferably, the guidance units are equally distributed along the outer circumference under an angle of 120°. The guidance units are in their longitudinal direction arranged in parallel to allow a z-axis translational movement, but to prevent a translational movement in x-and y-direction and to prevent a rotational movement about the x-axis and y-axis. So, in this embodiment, a z-axis rotational movement is still allowed by the three guidance units. An auxiliary roller box is provided to prevent the z-axis rotational movement. The auxiliary roller box is positioned in between the upper and lower roller boxes of the guidance units. Preferably, the auxiliary roller box is positioned in a middle region in between the upper and lower roller boxes. The presence of the auxiliary roller box advantageously contribute to a robust structure of the linear guide system.

In an embodiment of the device according to the invention, the z-translation unit comprises a plurality of rollers which are in a abutting engagement with a running surface of the counterpart. Preferably, all rollers of the z-translation unit are biased. Preferably, each roller is biased by a set of cup springs. Each set of springs may comprise a variety of cup springs, such that a bias force is arranged which increases exponentially over a bias stroke of the set of cup springs. Advantageously, the presence of the guidance units including at least one roller provide a robust structure which is able to withstand heavy workloads.

In an embodiment of the motion compensation device according to the invention, the linear guide system comprises four guidance units. The fourth guidance unit can be arranged to constrain a z-axis rotational movement. The four guidance units include two pairs of guidance units which include two guidance units which are staggered and mated at a distance from each other. The two pairs of guidance units are oriented along their longitudinal axis in perpendicular to each other. Each pair of guidance units constrain 3DOF which include one translational movement and two rotational movements. In combination, the two pairs of guidance units constrain two translational movements and all rotational movements. The guidance units allow a translational movement in parallel with the guidance unit which corresponds with the z-direction in a neutral position of the device.

In a further embodiment of the device according to the invention, the inner pedestal has a first and second opposite positioned corner edge in cross-section. The four guidance units are positioned in abutting engagement with the corner edges. The corner etches are provided with the running surfaces to allow the at least one roller of the guidance unit to run smoothly across the corner edge.

In a further embodiment of the device according to the invention, the first and second opposite positioned corner edges comprise a square angle chamfer edge. The chamfer edge is provided with the running surface. Advantageously, the guidance units of the linear guide system are spaced apart at a large distance which provides a robust structure to compensate occurring heavy workloads.

According to an embodiment of the device according to the invention, the xy-rotation unit comprises a main universal joint attached to the z-translation unit, on the one hand, and to the carrier frame respectively the base, on the other hand. In this application a 'main universal joint' is a joint allowing rotational movement around two perpendicular axes. The two parts joined by the main universal joint thus are allowed to rotate with respect to each other around two perpendicular axes, whilst any translation with respect to each other and rotation with respect to the third rotational axis is prohibited. Three examples of such a joint are a cardan joint, a ball joint and spherical joint with two degrees of freedom. A conventional ball joint allows 3DOF which are three orthogonal rotational movements. The main universal joint of the device according to the invention may comprise such a conventional ball joint, wherein further a blocking element is provided to prevent one orthogonal rotational movement. In particular, this blocking element is spaced apart from the conventional ball joint.

In an embodiment of the device according to the invention, the conventional ball joint and the blocking element of the main universal joint are positioned opposite each other at an outer circumference of the outer part. Advantageously, the conventional ball joint and the blocking element are positioned at a large distance from each other which provides a strong structure to compensate occurring heavy workloads.

In an embodiment of the device according to the invention of the blocking element comprises a raking shore structure. The raking shore structure comprises a push-pull-bar and a raking shore. The push-pull-bar is positioned at an upper connection point on top of the raking shore. The raking shore includes a stander and a shore which are connected to each other at the upper connection point. In a lower region of the raking shore, the stander and sure are connected to the base or vessel. In principle, the stander provides rigidity in a longitudinal direction, but is relatively flexible in radial direction. The shore provides rigidity to the stander in one radial direction and let the remaining radial directions relatively flexible. The stander and shore may be incorporated into a plate shaped item. Advantageously, the raking shore structure is relatively flexible to compensate for parasitic movements in x-direction and y- direction during a rotational movement introduced by the xy-rotational unit.

According to an embodiment of the device according to the invention, said at least one z- actuator and/or said at least two xy-actuators are hydraulically or electrically driven. According to an embodiment of the device according to the invention, said at least one z- actuator and/or said at least two xy-actuators comprise a cylinder-piston assembly and/or a spindle. The cylinder-piston assembly might be of hydraulic type, especially in case of large forces and short response times. A spindle might be driven electrically or otherwise.

According to an embodiment of the device according to the invention, said at least two xy- actuators are linear; wherein the proximal end of each said linear actuator is attached to the z-translation unit by a proximal universal joint, whilst the distal end of each said linear actuator is attached to the carrier frame respectively base by a distal universal joint. The terms proximal and distal are used in relation to the z-translation unit, i.e. the end closest to the z-translation unit is proximal, whilst the other end is distal. According to this embodiment, the linear direction of the linear actuators can - in rest condition - be essentially parallel to the z-axis. But note on the one hand that, as the xy-actuators have at their ends universal joints, it will be clear that during use the angle between the linear direction and the z-direction will vary depending on the condition of the respective actuator, and on the other hand that also in rest condition the linear direction of the linear actuators might slant with respect to the z-axis. For example it is conceivable that the linear direction of the linear actuators extend perpendicular to the z-direction and that the linear movement is transferred by means of a link mechanism. In case the linear xy-actuators comprise one or more actuators having their linear direction in the x-direction and one or more actuators having their linear direction in the y-direction, it becomes possible to control the x-axis rotational movement independently from (i.e. without influencing) the y-axis rotational movement, on the one hand, and to control the y-axis rotational movement independently from (i.e. without influencing) the x-axis rotational movement. For this, the xy-actuators require to set of linear actuators extending

perpendicular with respect to each other in a plane perpendicular to the z-axis.

With respect to the term 'universal joint' it is repeated that, according to this application, this is a joint allowing rotational movement around two perpendicular axes. The two parts joined by the universal joint thus are allowed to rotate with respect to each other around two perpendicular axes, whilst any translation with respect to each other is prohibited. Three examples of such a joint are a cardan joint, a spherical bearing and a ball joint. In relation to the x-axis, y-axis and z-axis as used to define the invention, the two perpendicular axes of the distal/proximal 'universal joint' might be the x-axis and y-axis or any other similar pair of orthogonal axes.

According to an embodiment of the device according to the invention, the maximum stroke of the z-actuators of the z-translation unit is at least 2x, such as at least 4x or at least 10x or at least 15x, as large as the maximum stroke of said linear actuators of the xy-rotation unit. Taking into account that in practise the heave motions - which might be meters - are large with respect to the roll and pitch motions - which typically are up to about 10 degrees for many situations -, this embodiment allows on the one hand effective compensation of both heave and roll/pitch, and on the other hand a slim design with a small footprint.

According to an embodiment of the device according to the invention, the diameter of the base is in the range of 2x to 50x - such as 15x to 50x or 2x to 10x like 2x to 5x - the maximum stroke of said linear actuators of the xy-rotation unit. This ensures a footprint which is relatively small.

According to an embodiment of the device according to the invention, the device further comprises a sensor system for sensing z-axis translational movement, x-axis rotational movement, y-axis rotational movement of the base (vessel) and/or carrier frame and generating sensor signals representing said movements.

According to an embodiment of the device according to the invention, the device further comprises a control system generating control signals for driving the z-actuator and/or one or more of said xy-actuators in response to said sensor signals such that the position of the carrier frame is compensated for said sensed movements.

With respect to the dimensions of the device according to the invention, the following characteristic values are mentioned by way of example for illustrative purposes:

• the diameter of the base is at most 7 m, such as at most 5 m or at most 4 m;

and/or;

• the maximum stroke of the at least one z-actuator is at least 150 cm, such as at least 200 cm;

and/or

• the maximum stroke of the at least two xy-actuators is at most 80 cm, such as at most 40 cm or at most 30 cm or at most 20 cm.

It is to be noted that the term 'movement' as used in this application is to be understood to encompass displacement and/or velocity and/or acceleration. A sensor sensing a movement thus might sense a displacement, a velocity, an acceleration and/or any combination of two or more of these entities. The invention will be explained in more detail with reference to the appended drawings. The drawings show practical embodiments according to the invention, which may not be interpreted as limiting the scope of the invention. Specific features may also be considered apart from the shown embodiments and may be taken into account in a broader context as a delimiting feature, not only for the shown embodiments but as a common feature for all embodiments falling within the scope of the appended claims, in which:

Figure 1 shows, in perspective view, a device according to the invention;

Figure 2 is, in perspective view, a detail of the device of figure 1 ;

Figure 3A shows, in a perspective view, an embodiment of the device according to the invention which comprises an alternative structure to prevent a rotational movement about a z-axis of a z-translation unit with respect to a base of the device;

Figure 3B shows, in a perspective view, the embodiment of the device as shown in figure 3A;

Figure 3C, 3D and3F show several orthogonal views the device as shown in figure 3A; Figure 3E shows a cross-sectional view of the device over section line E-E as indicated in figure 3C;

Figure 3G shows a cross sectional view similar as the one shown in figure 3E; Figure 3G shows a variant of the embodiment shown in figures 3E and 3C, which variant has three guidance units;

Figure 4A shows, in perspective view, a vessel provided with the device as shown in figure 1 ; and

Fig. 4B shows in a perspective view, a vessel provided with the device as shown in figure 3 which vessel is positioned close to an off shore object In the figures 1-3, a Cartesian coordinate system having an x-axis x, y-axis y and z-axis 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-axis.

Figure 1 shows in perspective view a first embodiment of a motion compensation device 1 according to the invention. The motion compensation device 1 has a pedestal type configuration and is arranged to support a pedestal structure, like a pedestal crane to compensate for heave motion. For that reason, the motion compensation device 1 is also called a pedestal motion compensation device. The motion compensation device 1 is column shaped. Herewith, the motion compensation device 1 has a compact elongated configuration. This motion compensation device 1 has at its lower end L a base 3. When mounted on a vessel 40, this base 3 is rigidly attached to the vessel 40, see fig 4A, 4B. In this embodiment the base 3 has a circular flange 50 with a plurality of bolt passages 51. The base 3 determines the so called 'footprint' of the device 1 on the vessel. In the embodiment shown the footprint is circular with a diameter of about 385 cm. It is however to be noted that the footprint might have a different shape, like square, and that also the diameter of the footprint can have another size. For example a square footprint with a diameter of about 3 or 7 meter is conceivable as well. In case of a non-circular footprint, the diameter of the footprint is to be understood as the diameter of an imaginary circle enclosing the entire footprint.

At its upper end U, the motion compensation device 1 is provided with a carrier frame 2. This carrier frame 2 is intended to support an object which is to be motion compensated. In the embodiment shown this object is a crane 30, in particular a pedestal crane like a knuckle boom crane, having a telescopic or fixed boom 34, a hoisting cable 32, crane hook 31 and winch 33 for operating the cable. However, the carrier frame 2 according to the invention can also be used for supporting other objects, like just a winch, etcetera. In particular, the motion compensation device 1 is arranged to support structures having a pedestal type

configuration. Such structures are also called pedestal structures. The pedestal type configuration is characterised by its one support column which supports the whole pedestal structure. In contrast to a portal structure which includes at least two spaced apart supporting legs which support the portal structure from several spaced apart locations, a pedestal structure having a pedestal type configuration comprises only one supporting leg to support the structure from only one location. As shown in figure 1 , the carrier frame 2 supports the whole pedestal structure. On board of a vessel, the motion compensation device 1 advantageously just requires a minimum working area. Although the carrier frame 2 shown is essentially a plate, it will be clear that the carrier frame can have lots of other configurations as well.

Although, the carrier frame might have dimensions in the x- and y- direction which are larger than the dimensions of the footprint, the carrier frame 2 has in the shown embodiment xy- dimensions smaller than the footprint. In the embodiment as shown, the entire motion compensation device 1 has xy-dimensions within the footprint formed by the base 3. The footprint of the motion compensation device 1 is smaller than the footprint of the base 3. The motion compensation device 1 has according to the invention a z-translation unit 4 and a xy-rotation unit 5. The z-translation unit 4 and the xy-rotation unit 5 are arranged in between the base 3 and the carrier frame 2. The z-translation unit 4 has a first end 6, in this embodiment at the lower side, and a second end 7, in this embodiment at the upper side. The z-translation unit 4 comprises a first part 10, an inner pedestal and a second part 1 1 , an outer pedestal. This first 10 and second 1 1 part are mutually connected by a linear guide system 12 extending in the z-direction. This linear guide system 12, which may be formed by two parallel flanges 13 on one of the first and second part and an intermediate flange (not shown) on the other of the first and second part, is adapted to guide linear movement of the first and second part relative to each other in the z-direction. It will be clear that this linear guide system 12 can also be designed differently. In the embodiment shown, the first 10 and second part 11 are telescopic, tubular parts. Note however that the first 10 and second 1 1 parts neither must be telescopic neither tubular. The first and second part can also be designed differently. Another configuration is for example shown in figure 3. Functionally, the z-translation unit (in this embodiment especially the first and second part of the z-translation unit) is designed such that it allows only z-axis translational movement and prevents all other movements, i.e. x-axis translational movement, y-axis translational movement, z-axis rotational movement, x-axis rotational movement and y- axis rotational movement.

The z-translation unit 4 is further provided with at least one z-actuator 8. This z-actuator is designed to cause upon its actuation a z-axis translational movement of the carrier frame 2 with respect to the base 3. In the embodiment shown, the z-actuator is a hydraulic cylinder- piston unit 8. At its upper end and lower end the z-actuator is attached to the second part 1 1 and first part 10, respectively, by a hinge joint 57. These hinge joints prevent the z-actuator from being subjected to bending moments. The xy-rotation unit 5 as shown in figure 1 , is shown in more detail in figure 2.

In the embodiment of figure 1 and 2, the xy-rotation unit 5 has a proximal side 52 and a distal side 53. Proximal, in relation to the xy-rotation unit, means in this embodiment relatively close to the z-translation unit, whilst distal, in relation to the z-translation unit, means relatively remote from the z-translation unit.

As shown in figure 2, the xy-rotation unit 5 comprises a main universal joint 14 (also called u- joint) extending from the proximal side 52 to the distal side 53. The main universal joint 14 is positioned at a centreline of the xy-rotation unit 5. In figure 2, the universal joint is, in this embodiment, in the form of a ball joint. The ball joint comprises a shaft 54 provided with a ball 55. This ball 55 is moveably received in a flange 56. The flange 56 is rigidly attached to the carrier frame 2. The shaft 54 is carried by two flanges 50, which in turn are rigidly attached to the upper end of the z-translation unit 4. The main universal joint 14 further comprises partly cylindrical blocks 58. The cylindrical blocks 58 are fixedly connected to the flange 56. Only two of these blocks 581 can be seen in figure 2, but at the backside two further blocks 58 can, optionally, be provided. The cylindrical blocks 58 are positioned at a distance from a centre of rotation of the ball 55, such that the cylindrical blocks 58 serve as a blocking element to prevent a rotational movement. Each cylindrical block 58 comprises a cylindrical running surface which is in abutting engagement with the flange 50. Herewith, the cylindrical blocks 58 prevent a rotational movement of the flange 56 with respect to the flange 50 about the ball 55, but allow a rotational movement about the x-axis. The rotational movement about the z-axis is prevented by the blocking element. As rotation of the joint 14 around the z-axis is prevented by the partly cylindrical blocks 581 () and the ball 55 is freely movable in the flange 56, this universal joint has two degrees of freedom, namely rotational freedom around two mutually perpendicular axes. So, the arrangement of the universal joint 14 prevents translational movements in x, y and a z-direction, allows two perpendicular rotational movements about the x- and y-axis, and prevents a rotational movement about the z-axis. It is to be noted that the main universal joint 14 can also be designed differently, for example as shown in figure 3D or like a cardan joint similar to the cardan joints 16 and 18 (to be discussed below). In particular, the blocking element 58 which is in figure 1 configured as comprising partly cylindrical blocks 581 for blocking a rotational movement about the z-axis can be designed differently. The main universal joint 14 ensures that the xy-rotation unit allows x-axis rotational movement as well as y-axis rotational movement, on the one hand, and prevents z-axis rotational movement, x-axis translational movement, y-axis translational movement, and z-axis translational movement, on the other hand. As shown in figure 2, in order to be able to control the xy-rotational movement of the carrier frame 2 with respect to second end 7 of the z-translation unit - and accordingly also with respect to the base 3 -, the xy-rotation unit is provided with at least two xy-actuators 9. In this embodiment there are four xy-actuators provided. In the embodiment shown, the xy-actuators are designed as linear, hydraulic actuators. Note however, that the xy-actuators can also be designed differently, for example using a spindle which is driven electrically.

The xy-actuators 9 each have a proximal end 15 and a distal end 17. At their proximal ends the xy-actuators are attached to the second end 7 of the z-translation unit 4 by a proximal universal joint 16. At their distal ends the xy-actuators are attached to the carrier frame 2 by a distal universal joint 18. In the embodiment as shown, the longitudinal direction of the xy- actuators 9 is, in the neutral position of the xy-actuators 9, parallel to the z-direction. It is however noted, that in the neutral position - in which the carrier frame is parallel to the base - the longitudinal direction of the xy-actuators might also slant with respect to the z-axis.

Further it is to be noted that in the embodiment shown, the longitudinal direction of one or more of the xy-actuators will slant with respect to the z-axis when the carrier frame 2 and base 3 are not parallel. In the embodiment shown the distal and proximal universal joints are cardan joints with two orthogonal shafts 26 and 27. It is however to be noted that these universal joints can also be designed in different manner, for example as a ball joint like the main universal joint 14.

Upon actuation of one or more of the xy-actuators, the carrier frame 2 will rotate around the x-axis and/or y-axis with respect to the upper end 7 of the z-translation unit/with respect to the base 3.

Figure 3A shows in a perspective view an embodiment of the motion compensation device according to the invention. The motion compensation device 1 comprises a base 3 for supporting a z-translation unit 4 and a xy-rotation unit 5. A carrier frame 2 is supported by the z-translation unit 4. The z-translation unit 4 and the xy-rotation unit 5 are positioned in between the base 3 and the carrier frame 2. A crane 30 is mounted on top of the carrier frame 2. The motion compensation device 1 has a pedestal type configuration. The motion compensation device 1 is column shaped. The motion compensation device 1 has a compact elongated configuration.

The z-translation unit 4 has a first end 6 at a lower side and a second end 7 at an upper side. The z-translation unit 4 comprises a first part 10, a so called outer pedestal, and a second part 11 , a so called inner pedestal. The inner pedestal 1 1 is movable in translation with respect to the outer pedestal 10. A relative rotation of the inner pedestal 11 with respect to the outer pedestal 10 is constrained by a linear guide system 12. It is noted that the inner and outer pedestal can also be mutually changed in their position. Fig. 3A shows the crane mounted on the inner pedestal 1 1 , but the crane can also be mounted on the outer pedestal 10.

The linear guide system 12 is arranged to guide the inner pedestal 1 1 in translation with respect to the outer pedestal 10. The linear guide system 12 comprises at least three guidance units, 12.2, 12.3, 12.4 which are positioned along a circumference of the outer pedestal 10. Here, four guidance units 12.1 ,12.2,12.3,12.4, which are shown in cross section in figure 3E, are positioned along an circumference of the outer pedestal 10. The guidance units 12.1 , 12.2, 12.3, 12.4 enclose the inner pedestal 11 , such that the inner pedestal 11 is constrained in rotation about its own central axis with respect to the outer pedestal 10. The guidance units are connected to the outer pedestal. The guidance units are mounted to an outer surface of the outer pedestal. Each guidance unit is elongated and extends z-direction, which corresponds with the z-axis. Figure 3E shows a cross sectional view of the device 1 about section line E-E as indicated in figure 3C. As shown in figure 3E, the inner pedestal 1 1 has a substantially triangular shape in cross section. The inner pedestal 1 1 has a hollow inner space to receive the z-actuator 8. The inner pedestal 11 is guided at an outer surface by the four guidance units

12.1 , 12.2, 12.3, 12.4 at a first and a second opposing corner edge. The first and second corner edge have each a first and second square angled chamfer edge which are provided with a running surface 123. Each guidance unit is in engagement with a corresponding running surface.

As shown in figure 3C, each guidance unit comprises a pair of a lower and upper roller boxes 121. One roller box 121 of said pair is positioned in an upper region of the outer pedestal, the other roller box of said pair is positioned in a lower region of the outer pedestal 10. Each roller box 121 include at least one roller 122 having an outer roller surface which is in abutting engagement via a through hole in the outer pedestal 10 with said running surface 123 of the inner pedestal 1 1 . Herewith, the four guidance units 12.1 ,12.2,12.3,12.4 enclose the inner pedestal 1 1 to constrain all relative rotational movements and traverse translational movements, and to allow a translational movement in longitudinal direction, which corresponds with the z-direction in the neutral position of the device 1.

As shown in figure 3D and 3E, the z-translation unit 4 is provided with at least one z-actuator 8. The z-actuator 8 is a hydraulic cylinder. The z-actuator is received in the hollow inner space of the inner pedestal. One end of the z-actuator 8, the upper end, is connected to the inner pedestal 1 1 while an opposed end, the lower end, of the z-actuator 8 is connected to the base 3 or vessel. By operating the z-actuator 8, the inner pedestal 11 can move in and outwards the outer pedestal 10.

As shown in figure 3C, in the neutral position of the device 1 , the xy-rotation unit 5 is aligned with the z-translation unit 4. The central axis of the xy-rotation unit 5 is in parallel with the central axis of the z-translation unit 4. The xy-rotation unit 5 has a proximal side 52 and a distal side 53. The proximal side 52 is positioned at a lower region of the device 1 . The xy- rotation unit 5 comprises two xy-actuators 9. In the neutral position of the device 1 , the xy- actuators 9 extent in a longitudinal direction of the device 1. At the distal side 53, the xy- actuators 9 are connected to the outer pedestal 10. At the proximal side, the xy-actuators 9 are connected to the base 3.

In the shown embodiment, the xy-actuators 9 extend away from a lower region of the outer pedestal 10 in a downwards direction. In an alternative column shaped embodiment (not shown), the xy-actuators 9 may extend from a lower region of the outer pedestal 10 in an upwards direction and may extend in parallel with the outer pedestal. The base 3 may include a ring-shaped base body which extend around the outer pedestal 10 to connect the ends of the xy-actuators 9 to the base or vessel.

As shown in figure 3D the motion compensation device 1 comprises a main universal joint 14. The main universal joint 14 comprises a ball joint 54,55 and a blocking element 58. The ball joint 54, 55 is positioned at the outer circumference of the outer pedestal 10. The blocking element 58 is positioned at the outer circumference of the outer pedestal 10 diametrically opposite the ball joint 54, 55. Herewith, a distance in between the 54, 55 and the blocking element 58 is considerably enlarged with respect to the embodiment shown in figure 1 and 2. The enlarged distance contributes to a substantial reduction of occurring forces to withstand on the main universal joint 14. Advantageously, the main universal joint 14 is robust. The ball joint 54,55 is arranged to pivotally connect the outer pedestal 10 with respect to the base or vessel which is formed by the base 3. The ball joint 54, 55 has three degrees of freedom and allows a rotational movement of the outer pedestal 10 about three orthogonal axes. As shown in figure 3A, 3C and 3D, the base 3 is provided with a space frame 310 to provide a rigid structure to mount the main universal joint 14 at a height level which corresponds with a desired height level of the outer pedestal 10. The space frame 31 comprises two flanges 50 for mounting a shaft 54. The shaft is provided with a ball 55 which is locked in a flange 56 which is connected to the outer pedestal 10.

The blocking element 58 is arranged to provide in combination with the ball joint 54, 55 a constraint in a z-axis rotational movement of the ball joint 54, 55. Here, the blocking element is arranged to constrain the z-axis rotational movement of the outer pedestal 10. The blocking element connects the outer pedestal 10 with the base or vessel. The blocking element 58 comprises a push-pull-bar 581 which has one end, the distal end, attached to the outer pedestal and the other end, the proximal end, attached to the base or vessel. The attachment of the proximal end of the push-pull-bar to the base or vessel can, according to a further embodiment, be realised by means of a raking shore structure. The raking shore structure provides - from a functional view - a rigid connection between the proximal end of the push-pull-bar, on the one hand, and the base or vessel, on the other hand. This rigid connection, can, for example, be realised with a raking shore 582. The push-pull-bar 581 is provided with ball joints at both ends. The push-pull-bar 581 has three degrees of freedom. The push-pull-bar has an elongated push-pull-bar body which provides a constraint in a translational direction. The push-pull-bar extends in a substantially horizontal direction in the neutral position of the device 1. One or more shores 5822 are fixedly connected to the stander 5821 which shores 5822 provides rigidity to the stander 5821 in all directions. The stander 5821 and the shore 5822 built the raking shore 582. In an equivalent embodiment, the stander 5821 and the shore 5822 may be integrated as a one piece item into a single plate-shaped piece.

The shore 5822 and stander 5821 serve the purpose of providing rigidity to an upper connection point of the raking shore 582 in at least two translational directions X and Z, like in all three translational directions X, Y and Z. The proximal end of the push-pull-bar is connected to this upper connection point.

As shown in Fig. 3G, in a particular embodiment of the device according to the invention, the linear guide system comprises three guidance units 12.2, 12.3 and 12.4, each including a pair of an upper and a lower roller box 121. The pair of roller boxes define a longitudinal axis of the guidance unit. The guidance units are positioned along an outer circumference of the first or second part. In this example of Fig. 3G, the guidance units are equally distributed along the outer circumference under an angle of 120°. The guidance units are in their longitudinal direction arranged in parallel to allow a z-axis translational movement, but to prevent a translational movement in x-and y-direction and to prevent a rotational movement about the x-axis and y-axis. So, in this embodiment, a z-axis rotational movement is still allowed by the three guidance units. An auxiliary roller box is provided to prevent the z-axis rotational movement. The auxiliary roller box is positioned in between the upper and lower roller boxes of the guidance units. Preferably, the auxiliary roller box is positioned in a middle region in between the upper and lower roller boxes. The presence of the auxiliary roller box advantageously contribute to a robust structure of the linear guide system.

As shown in figure 1 , in order to be able to control the movement of the carrier frame 2 with respect to the base 3, the motion compensation device 1 is according to the invention provided with a sensor system and a control system. The sensor system comprises a sensor 19 for sensing the movements of the base. In addition to sensor 19 or as alternative for sensor 19, the sensor system might further comprise a sensor 20 for sensing the movements of the carrier frame. As the base 19 will be rigidly attached to a vessel 40, the sensor 19 thus senses the movements of the vessel when the motion compensation device 1 has been mounted on a vessel 40.

Although for the present invention the sensors 19 and 20 only need to be able to sense z- translational movement, x-rotational movement and y-rotational movement, it will in practise be practical to use sensors which are capable of sensing also the x-translational movement, y-translational movement and z-rotational movement. This simply because such sensors are commonly available on the market as standard sensor. In practise, most sensors sense in fact the acceleration in x-translational direction, y-translational direction, in z-translational direction, in x-rotational direction, in y-rotational direction and in z-rotational direction.

Knowing these accelerations, the corresponding velocities and displacements can easily be calculated/determined by software.

The sensors 19 and 20 will generate sensor signals representing the sensed movements. These sensor signals are transferred wireless or by wire to a control system 21 as is indicated in figure 1 with sensor lines 22 and 23. In response to these sensor signals, the control system 21 will generate one or more control signals for driving the z-actuator and/or one or more of the xy-actuators. These control signals are transferred wireless or by wire to the z-actuator and xy-actuators as is indicated in figure 1 with control lines 24 and 25. In addition also sensors can be used to sense the movements of the carrier frame and/or at least one z-actuator and/or at least two xy-actuators to provide corresponding sensor signals used as feedback by the control system 21 to increase the accuracy of the control.

Figure 4A shows a vessel 40 provided with a motion compensation device 1 according to the invention. In particular, the vessel 40 is a vessel of shallow draught which allows the vessel 40 to come close to static objects O at sea. The motion compensation device 1 is positioned at a deck 41 of the vessel 40. In particular, the motion compensation device 1 is positioned close to the hull to enhance lifting operations to be carried out. In particular, the motion compensation device is arranged to compensate for: a roll and pitch up to at most +/-10"; a heave up to 4.0m, in particular 3.5m, more in particular 3.0m; a wave period of at least 4s and at most 20s. The motion compensation device 1 supports a pedestal crane 30. The pedestal crane 30 comprises one base leg which is supported by the motion compensation device 1 and at least one arm for lifting a load 43. In particular, the pedestal crane 30 has a reach of a radius of at most 50m, in particular at most 40m, more in particular at most 35m for lifting a load 43 at a target location 42. In particular, the motion compensation device 1 is arranged to compensate movements of a pedestal crane, in particular a knuckle boom type crane, with a maximum load capacity of at most 50 tons, in particular at most 40tons or at most 30 tons, more in particular is most 20tons. In order to keep an object, like a pedestal crane 30, placed on the carrier frame still relative to the fixed world whilst the vessel below it is moving with respect to the fixed world, the control system will be arranged to neutralize all z-translations and x- and y-rotations of the vessel. As shown in figure 4B, the motion compensation device 1 is in particular advantageous to carry out lifting operations to a static off shore object O which provides little freedom of movement for the crane itself. The off shore object O may be a static positioned object, like a windmill or a platform at sea which has a founding at a water bottom. When the tip of the crane needs to be inserted in an inner space IS of the off shore object O, it is necessary to keep the tip of the crane in position to prevent a collision of the tip with the off shore object O. The motion compensation device 1 compensates movements of the vessel 40 and keeps the crane in a substantially static position. The motion compensation device 1 according to the invention is suitable for lifting operations in such circumstances. In particular, the motion compensation device according to the invention allows the z- translation compensation to be essentially independent from the xy-rotation compensation. This simplifies the control algorithms used by the control system and allows increase in accuracy. Numerous variants are possible in addition to the embodiment shown. Features and aspects described for or in relation with a particular embodiment may be suitably combined with features and aspects of other embodiments, unless explicitly stated otherwise.

It is remarked that aspects according to the invention and in particular mentioned in the dependent claims are considered patentable as such. It is noted that the term "comprising" (and grammatical variations thereof) is used in this specification in the inclusive sense of "having" or "including", and not in the exclusive sense of "consisting only of". Although the invention has been disclosed with reference to particular embodiments, from reading this description those of skilled in the art may appreciate a change or modification that may be possible from a technical point of view but which do not depart from the scope of the invention as described above and claimed hereafter. Modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. It will be understood by those of skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. Therefore, it is intended that the invention is not limited to the particular embodiments disclosed in the above detailed description, but that the invention will include all embodiments falling within the scope of the appended claims.

Further, it is remarked that any feature of the linear guide system and main universal joint according to the invention which is described in the embodiments and/or mentioned in the dependent claims is in itself considered patentable without any dependency to another presented feature. In particular, any measure presented in a dependent claim is also considered patentable without dependency of the independent claim.

Thus, the invention provides a motion compensation device having separate actuators to carry out separate compensating movements. The device according to the invention allows a simple control of a translational movement in length direction which control is independent of an induced rotational movement.

List of references to figures

motion compensation device 40 Vessel

carrier frame 41 Deck

Base 42 Target location

z-translation unit 43 Load

xy-rotation unit 50 Flange

first end of z-translation unit 51 bolt passage

second end of z-translation unit 52 proximal side of xy-rotation unit z-actuator 53 distal side of xy-rotation unit xy-actuator 54 Shaft

first part of z-translation unit 55 Ball

second part of z-translation unit 56 Flange

linear guide system 57 hinge joint

parallel flanges 58 Blocking element

main universal joint 581 push-pull-bar

proximal end of xy-actuator 582 Raking shore

proximal universal joint 5821 stander

distal end of xy-actuator 5822 shore

distal universal joint 60 Switch

sensor for sensing base movements

sensor for sensing carrier frame

movements

control system

sensor signal line

control line

first axis of proximal/distal u-joint

second axis of proximal/distal u-joint

Crane

crane hook

hoisting cable x x-axis

Winch y y-axis

Boom z z-axis

Claims

1] Motion compensation device (1 ) for compensating for water motion of a carrier frame (2) arranged on a vessel,

wherein an imaginary set of three orthogonal axes is defined by an x-axis, an y-axis and an z- axis;

wherein the device (1 ) comprises:

• a said carrier frame (2);

• a base (3) for supporting the motion compensation device (1 ) on the vessel;

· a z-translation unit (4); and

• a xy-rotation unit (5);

wherein the z-translation unit (4) allows z-axis translational movement and prevents x-axis translational movement, y-axis translational movement, z-axis rotational movement, x-axis rotational movement and y-axis rotational movement;

wherein the z-translation unit (4) has, viewed in the direction of the z-axis, a first end (6) and a second end (7);

wherein the xy-rotation unit (5) allows x-axis rotational movement as well as y-axis rotational movement and prevents z-axis rotational movement, x-axis translational movement, y-axis translational movement, and z-axis translational movement;

wherein the base (3) is provided at the first end (6) of the z-translation unit (4) and the carrier frame (2) at the second end (7) of the z-translation unit (4)

wherein the carrier frame (2) and base (3) are:

• on the one hand, moveable with respect to each other in a translational direction

along the z-axis, in a rotational direction around the x-axis and in a rotational direction around the y-axis; and

• on the other hand, restrained from mutual movement in a rotational direction around the z-axis;

wherein the z-translation unit (4) is provided with at least one z-actuator (8) arranged to cause, upon actuation of said z-actuator (8), z-axis translational movement of the carrier frame (2) with respect to the base (3), whilst the xy-rotation unit (5) is provided with at least two xy-actuators (9) arranged to cause, upon actuation of one or more of said xy-actuators (9), x-axis rotational and/or y-axis rotational movement of the carrier frame (2) with respect to the base (3), the at least one z-actuator (8) and at least two xy-actuators (9) being different actuators.

2] Device (1 ) according to claim 1 , wherein the device (1 ) has a pedestal type configuration. 3] Device (1 ) according to claim 1 or 2, wherein the z-translation unit (4) comprises a linear guide system (12) and wherein the xy-rotation unit (5) comprises a main universal joint (14), in which the lineair guide system and main universal joint each prevent the z-axis rotational movement of the carrier frame (2) with respect to the base (3).

4] Device (1 ) according to any of the preceding claims, wherein the z-translation unit (4) comprises a first part (10), an outer pedestal, and a second part (1 1 ), an inner

pedestal, mutually connected by the linear guide system (12) extending in the z-direction, which linear guide system (12) is arranged to allow the first part (10) and second part (11 ) to shift in z-direction with respect to each other and to prevent x-axis translational movement, y- axis translational movement, x-axis rotational movement, y-axis rotational movement and z- axis rotational movement of the first part (10) with respect to the second part (11 ).

5] Device (1 ) according to claim 4, wherein the first part (10) and second part (1 1 ) are telescopic parts.

6] Device (1 ) according to claim 4 or 5, wherein the inner part (1 1 ) comprises an inner space for receiving said z-actuator (8). 7] Device (1 ) according to any of the claims 3-6, wherein the linear guide system (12) comprises at least three guidance units (12.1 , 12.2, 12.3, 12.4) which are connected to the outer pedestal (10) to guide the inner pedestal (1 1 ) in a translational movement.

8] Device (1 ) according to claim 7, wherein the linear guide system (12) comprises three guidance units (12.2, 12.3, 12.4) which are arranged at an angular distance of 120° around a central point.

9] Device (1 ) according to claim 7, wherein each guidance unit comprises a pair of an upper and lower roller box (121 ), wherein each roller box include at least one roller (122) having an outer roller surface which is in abutting engagement with a running surface (123) provided at the inner pedestal (11 ).

10] Device (1 ) according to claim 9, wherein an auxiliary roller box is provided to prevent a z-axis rotational movement. 1 1] Device (1 ) according to claim 9, wherein the inner pedestal (1 1 ) has - seen in cross- section- a first and second opposite positioned corner edge which are provided with said running surface (123). 12] Device (1 ) according to claim 11 , wherein the corner edge comprises a square angled chamfer edge which is provided with the running surface (123).

13] Device (1 ) according to one of the preceding claims, wherein the xy-rotation unit (5) comprises the main universal joint (14) attached to the z-translation unit (4), on the one hand, and to the carrier frame (2) respectively the base (3), on the other hand.

14] Device (1 ) according to claim 13, wherein said main universal joint (14) has a cardan joint or ball joint (54,55) or spherical joint. 15] Device (1 ) according to claim 13 or 14, wherein the main universal joint (14) comprises a blocking element (58) to prevent the z-axis rotational movement of the device (1 )-

16] Device (1 ) according to claim 15, wherein the blocking element (58) is spaced apart from the ball joint (54, 55).

17] Device (1 ) according to claim 16, wherein the ball joint (54,55) and the blocking element (58) are positioned opposite each other at an outer circumference of the outer pedestal (10).

18] Device (1 ) according to any of the claims 15-17, wherein the blocking element (58) comprises a raking shore structure including a push-pull-bar (581 ) and a raking shore (582), which raking shore structure is configured such that the blocking element (58) in combination with the ball joint (54, 55) prevents a z-axis rotational movement of the ball joint (55).

19] Device (1 ) according to one of the preceding claims, wherein said at least one z- actuator (8) and/or said at least two xy-actuators (9) are hydraulically or electrically driven.

20] Device (1 ) according to one of the preceding claims, wherein said at least one z- actuator (8) and/or said at least two xy-actuators (9) comprise a cylinder-piston assembly and/or a spindle. 21] Device (1 ) according to one of the preceding claims, wherein said at least two xy- actuators (9) are linear actuators; wherein the proximal end (15) of each said linear actuator is attached to the z-translation unit (4) by a proximal universal joint (16), whilst the distal end (17) of each said linear actuator is attached to the carrier frame (2) respectively base (3) by a 5 distal universal joint (18).

22] Device (1 ) according to claim 21 , wherein all said linear actuators (9) have a linear direction essentially parallel to the z-axis.

10 23] Device (1 ) according to claim 21 or 22, wherein the proximal and/or distal universal joint is a cardan joint (16, 18) or ball joint or spherical bearing.

24] Device (1 ) according to one of the preceding claims, wherein the maximum stroke of the z-actuators (7) of the z-translation unit (4) is at least 4x, such as at least 10x or at least 15 15x, as large as the maximum stroke of said linear actuators of the xy-rotation unit (5).

25] Device (1 ) according to one of the preceding claims, wherein the diameter of the base (3) is in the range of 15x to 50x the maximum stroke of said linear actuators of the xy-rotation unit (5).

20

26] Device (1 ) according to one of the preceding claims, wherein the diameter of the base (3) is at most 7 m, such as at most 5 m or at most 4 m.

27] Device (1 ) according to one of the preceding claims, further comprising a sensor 25 system (19, 20) for sensing z-axis translational movement, x-axis rotational movement, y-axis rotational movement of the base (3) and/or carrier frame (2) and generating sensor signals representing said movements.

28] Device (1 ) according to any of the preceding claims , further comprising a control 30 system generating control signals for driving the z-actuator (8) and/or one or more of said xy- actuators (9) in response to said sensor signals such that the position of the carrier frame (2) is compensated for said sensed movements.

29] Assembly comprising:

35 · a device (1 ) according to one of the preceding claims; and

• a crane (30) or winch. 30] Assembly according to claim 29, further comprising a vessel (40).

31] Assembly comprising:

• a device (1 ) according to one of the claims 1 -28; and

· a vessel (40).

32] Motion compensation device (1 ) for compensating a carrier frame (2) arranged on a vessel for water motion,

wherein the device (1 ) comprises:

• a said carrier frame (2);

• a z-translation unit (4); and

· a xy-rotation unit (5);

wherein the base (3) is provided at the first end (6) of the z-translation unit (4) and the carrier frame (2) at the second end (7) of the z-translation unit (4) with the xy-rotation unit (5) being arranged between

• the z-translation unit (4) and the carrier frame (2)

or

• the z-translation unit (4) and the base (3)

such that the carrier frame (2) and base (3) are:

• on the other hand, restrained from mutual movement in a translational direction along the x-axis, in a translational direction along the y-axis and in a rotational direction around the z-axis; wherein the z-translation unit (4) is provided with at least one z-actuator (8) arranged to cause, upon actuation of said z-actuator (8), z-axis translational movement of the carrier frame (2) with respect to the base (3), whilst the xy-rotation unit (5) is provided with at least two xy-actuators (9) arranged to cause, upon actuation of one or more of said xy-actuators (9), x-axis rotational and/or y-axis rotational movement of the carrier frame (2) with respect to the base (3), the at least one z-actuator (8) and at least two xy-actuators (9) being different actuators.