Technical Field of Invention

This invention relates to a clamping arrangement, or, more particularly, to a way of actuating a clamp so that it can be moved between different configurations and allow coupled elements to be relatively rotated or restrained as required. The invention is particularly suited to tidal turbines which are required to be rotated to face an oncoming stream of water, but the invention is not limited to this application.

Background of Invention

Sub-aquatic power generating apparatuses are generally well known and currently the subject of much research and development. One type of sub-aquatic power generating apparatus is the tidal turbine generator 10 shown in Figure 1. This generator 10 includes a turbine 12 mounted on a support structure 14 which is fixed, either by gravity or some other suitable fixing means, to the sea bed 16. The turbine 12 includes a rotor 18 having a plurality of turbine blades 20 which are arranged to provide rotative force about a principal axis 22 when placed in an appropriate flow of water 24. The rotor 18 is used to drive an electrical machine in the form of an electromagnetic generator (not shown) which is housed within the so-called nacelle or casing 26 of the turbine 12.

As will be appreciated, to take the maximum amount of energy out of a tidal flow, the turbine must be capable of extracting energy from ebb and flood tides and there have been many proposed ways of achieving this.

GB2448710 describes a tidal turbine similar to that shown in Figure 1. The turbine described in GB'710 is rotatable around a vertical axis such that the rotor can be directed towards a particular flow. An important feature of the described tidal turbine is a clamp which couples the turbine to a support structure which is anchored to the sea bed. The described clamp has three configurations. The first is a fixed configuration in which the turbine and support structure are securely attached to each other and no relative rotation is possible. The second is a rotating configuration in which the clamp is loosened slightly so as to allow relative rotation between the turbine and support structure about the vertical axis. The third is a free configuration in which the turbine can be released from the support structure.

The present invention seeks to provide an improved clamp arrangement. Statements of Invention

In a first aspect the present invention provides a clamp arrangement for coupling two components, comprising: a clamp having at least two arms which are operable so as to close around either or both of the first and second components; and, at least two drives, each drive being connected to and configured to move at least one of the arms relative to either or both of the two components. Providing a clamp arrangement with two drives allows for independent actuation of the clamp arms which helps ensure an even clamping pressure is achieved and the separation of the clamp is circumferentially distributed to allow for controlled release of the clamp and structures. The drives may be arranged to move the arms apart from one another. The drives may be arranged to move the arms in opposing directions. The drives may be arranged to move the arms relative to a common point which is located within an anchor zone. The anchor zone may be located between the two arms. Each drive may be attached to the first or second component using a floating anchor which is configured to allow limited movement between the drives and the first or second component.

Each drive may be fixed to the first or second component via a bearing element. The bearing element may be located in the anchor zone towards a mid-portion between the arms.

Each drive may be driveably connected to both arms. Each drive may include a nut and lead screw. The lead screw may be common to both drives and include respective right hand and left hand threaded portions for driving each of the arms apart.

Each drive may include a fluidic actuator. The fluidic actuator may be hydraulic or pneumatic. The fluidic actuator may include a hydraulic or pneumatic ram. The drive may include a motor. The motor may be hydraulic. The actuator may be a linear actuator. Each drive may include a ram having a piston housed within a chamber, the piston being driveable between a first position and a second position within the chamber, wherein the chamber includes: a first port for introducing pressurised fluid to the chamber; and, a travel limiting port located so as to be fluidicly switched as the piston passes from the first to the second position.

The travel limiting port may be exposed by the movement of the piston passing into the second position, thereby removing fluidic pressure from the chamber.

The travel limiting port may be covered by the movement of the piston passing into the second position, thereby blocking the fluidic circuit and preventing further movement of the piston.

The piston may be drivable between a first position, second position and third position.

The travel limiting port may be selectively operable so as to be an inlet, an outlet or closed.

The chamber may include a third port for introducing fluid to the chamber so as to drive the ram from the third position to the second position.

Each arm may be driven by a separate piston.

The drives may be located such that the driving directions of the rams are coaxial to one another.

The two drives may be placed back-to-back so as to displace the arms in opposing directions. The two drives may be anchored to the first or second component with a floating anchor which is configured to allow limited movement between the drives and the first or second components.

Description of Drawings

Embodiments of the invention will now be described with the aid of the following drawings of which: Figure 1 shows the previously described tidal turbine.

Figure 2 shows a clamp arrangement for coupling the first and second components.

Figure 3 shows a drive arrangement for actuator the clamp arrangement.

Figure 4 shows an alternative drive arrangement for actuating the clamp arrangement. Detailed Description of Invention

With reference to Figures 2a-c, there is shown a sub-aquatic structure 210 having a power generating apparatus 212 similar to that shown in Figure 1. The power generating apparatus 212 is in the form of a buoyant turbine which is mounted on a support structure 214 such that it can be rotated to face oncoming flows from different directions. The turbine 212 is mounted on a turbine support in the form of a columnar structure 213 which has a generally circular cross-section and which extends down from the turbine housing 226 to terminate in a tapering flanged portion 230. This flanged portion 230 abuts a corresponding mirrored tapering flanged portion 232 of a seabed support structure 215 at respective mating surfaces 234 of the turbine support and seabed support structures 213, 215. The flanged portions 230, 232 are arranged such that when the mating surfaces 234 are aligned and in intimate contact, the upper and lower flanges 230, 232 of the turbine support 213 and sea bed support structures 215 join to provide a circumferential ring which extends around the unified support structure 214 and projects outwardly therefrom. The tapers of the opposing flanged portions 230, 232 are presented on the upper and lower surfaces of the ringed flange so as to provide it with a truncated isosceles triangle shape in the cross section which diverges from the coincident outer radial edge of the flanges 230, 232. It will be appreciated that other formations and taper angles etc may be implemented whilst retaining the resultant axial compression functionality which is elaborated on below.

In order to couple the turbine column 213 and support structure column 215, a circumferential clamp 250 is provided which extends around the opposing flanged portions 230, 232. The clamp 250 is made up from a plurality of arcuate sections (as best seen in Figure 3) which are movable relative to each other so as to constrict or dilate around mated flanged portions 230, 232 and bear upon and urge the respective flanges 230, 232 together. The clamp 250 achieves the axial compression across the mating surfaces 234 by engaging and constricting around the tapered surfaces of the flanges 230, 232 which act to translate the radial constriction of the clamp 250 into an axial compression across the joint. Using this mechanism, the friction between the mating surfaces 234 is increased or decreased so as to allow the relative rotation or restraint of the two components, as required. In some embodiments, the turbine 212 will be a buoyant unit and partially releasing the clamp 250 will result in the mating surfaces 234 being separated. As shown in Figures 2a to 2c, the clamping arrangement 250 is actuable so as to have three different respective configurations: a free configuration (Figure 2a); a rotatable configuration (Figure 2b); and, a fixed or clamped configuration (Figure 2c). The free configuration is provided by fully opening the clamp 250 so as to allow the support structure 214 and turbine 212 to be coupled and separated during deployment and retrieval operations. The rotatable configuration is provided when the clamp 250 is opened enough to allow the buoyant turbine to lift and reduce the frictional engagement across the mating surface. When in the rotatable configuration, the turbine 212 can be rotated by an appropriate mechanism, such as the thruster described in GB2441769, which is incorporated by reference. Once in the desired orientation, the clamp 250 is tightened so as to place the power generating apparatus 212 in the fixed configuration which is achieved when the clamp 250 is tightened so as to sufficiently axially compress and clamp the tapered portions 230, 232 and provide the associated restraining friction.

Turning to Figure 3, there is shown a clamp arrangement 310 for coupling two components such as the turbine support 213 and the seabed support structure 215. The clamp arrangement 310 includes a clamp 312 which has three arms, or arcuate segments 314a-c, which are linked together to form a segmented open ring; the open ends being formed by the free ends of two of the arms. The arms are actuable relative to one another so as to close around either or both of the first and second components, as required by the particular configuration used. The clamping arrangement also includes two drives 316a,b. Each drive 316a,b is operably connected to one of the arms 314a-c so as to cause it to constrict or dilate around the seabed support structure 215 and turbine support 213 which are generally represented in cross section by the central circular structure 214. Having two drives 316a,b is important as it allows the arms 314a-c of the clamp 312 to be actuated separately, thereby allowing for independent actuation of the arms 314a-c which can help provide an even clamping pressure or opening to partially releasing the turbine for rotation. The two drives 316a,b in this described example include actuators (not shown) which are placed at either end of a lead screw 318. The lead screw 318 is a threaded bar having two portions 318a,b which are oppositely threaded and which are each driveably attached to one of the arms 314a-c. By oppositely threaded it is meant that one side has a left hand thread; the other a right hand thread.

The segments 318a,b of the lead screw are separated by a bearing arrangement 320 which is secured to either the turbine support 213 or the support structure 215, preferably the former. In the described embodiment, the arms 314a,b are equidistantly positioned from the bearing element 320 such that there is symmetry along a plane which lies along the longitudinal axis of the turbine support 213 and passes through the bearing element 320.

The attachment of the bearing element 320 to the turbine support 213 is via a floating anchor 321 placed within an anchor zone 323. The floating anchor 321 allows the bearing element 320 to move relatively freely in the circumferential, radial and axial directions but in a limited way. The floating anchor 321 can be any sliding, swivel or toggle connection which provides the necessary limited movement and strength to allow the arms 314a,b to be moved apart from one another and the support structure 214 in the desired way. It will be appreciated that the degree of movement which may be tolerated or desired will be application specific. However, the necessary limited movement will be readily discernable by the skilled man.

Having a floating anchor 321 allows the preloading and axial compression of the flanges 314a,b to be achieved through the hoop stress of the clamp 312, rather than being translated through the anchor 321. That is, the lead screw of the described embodiment becomes part of the clamping loop and carries a portion of the hoop stress when the clamp is constricted which allows a greater degree of axial compression to be achieved without an oversized anchor. Further, the floating anchor helps the two drives to react against each other in equal but opposite amounts to push or pull the free ends of the arms apart or together, rather than driving against a fixed anchor. Thus, the bearing element 320 provides a floating anchor against which the arms 314a-c of the clamp 312 can react so as to prevent differential movement relative to the support 214, but not carrying significant amounts of load. This configuration allows the clamp 312 to be opened more evenly around the turbine support 213 which assists with an even clamping pressure being achieved. In the case where the arms 314a-c react against each other and not the support structure 214, there is a risk of the clamp 312 not opening evenly and not providing the necessary separation between the arms 314a-c and the support structure 214.

Each segment of the lead screw 318 engages with a nut arrangement 322 so as to form a linear actuator or runner arrangement for each arm 314a,b . The purpose of the runner arrangement is to allow the ends of the arms 314a-c to move to allow the constriction and dilation of the clamp 312. Hence, the nuts 322 of the described embodiment is carried by the thread of the lead screw 318 and attached to the arm 314a-c via an appropriate bearing or swivel 324 which allows the arm 314a-c to rotate relative to the direction of travel provided by the lead screw 318. In use, when the drives 316a,b are operated, the lead screw 318 is rotated by the actuator causing the nuts 322 to travel along its length between the bearing element 320 and drive 316a,b. This movement causes the actuated end of the arm 314a,c to move toward the drive 316a,b thereby increasing the radial separation of the arm 314a,c and flanged portion along the length of the arm 314a,c. As the arrangement is substantially symmetrical about the bearing element, operation of the actuator results in the separation of both arms 314a,c from the flanged portion.

The drives 316a,b in the described example include hydraulic motors arranged to rotate the lead screw 318. There is one drive 316a,b at each end of the lead screw 318 and each drive may be individually controlled. Thus, one of the drives 316a,b may be used with the other being redundant, or they can be used in unison. Alternatively, one drive 316a,b could be used to move the clamp 312 between the fixed and rotating configurations with the other being utilised for moving the clamp 312 between the rotating and free configurations, thereby operably separating the actuation required to provide the rotating and free configurations and helping to prevent accidental release of the turbine 212 structure. In another embodiment, the lead screw 318 may not be a single piece but may be separately rotatable for each of the arms. In this case, each actuator would be controlled individually to move each respective arm as required and the need for an oppositely threaded lead screw 318 would be removed.

It will be appreciated that other forms of linear or rotatable drives may be employed as required. For example, the drives 316a, b may include electric motors, or hydraulic rams which do not require the lead screw 318 and nut 322. Further, the runner arrangement may not include the nuts 322 and lead screw 318 but some other form of linear device.

Figure 4 shows another example of a drive arrangement 410 in the form of a dual sided, back to back linear actuator which is operable to drive the arms (not shown) of the clamps 250 apart or together so as to respectively constrict or dilate it around the flanged portion support structure 214. The drive arrangement 410 includes a pair of drives in the form of two hydraulic dual sided or back to back rams 412, 414, each having a cylinder 416a,b which accommodates a piston 418a,b which are coupled to the arms (not shown) of the clamp (not shown) at a distal end 415a,b when in use. The cylinders 416a,b are each fixed relative to either the turbine support structure 213 or seabed support 215 at a midpoint 420 such that the arms are moved relative to the structure when operating. In this instance it will be appreciated that the term fixed relates to a connection between the cylinders 416a,b and the support structure 214 which may or may not be a floating connection which allows limited movement if required. The floating connection may be any suitable type and will be similar in nature to that described in relation to the embodiment of Figure 3.

The pistons 418a,b are located within the cylinders 416a,b so as to divide the internal space of each cylinder 416a,b into two chambers A,B which can be pressurised as required with hydraulic fluid to affect motion. Each hydraulic cylinder 416a,b includes three ports 422, 424, 426 which are arranged along the length of the cylinder 416a,b. Two of the ports 422, 426 are arranged one on either side of the piston 418a,b in each chamber A,B and are selectively operable as inlets or outlets for pressurised fluid so as to drive the piston 418a,b in either direction. Thus, one of the ports relates to an open port 422 for opening the clamp, the other a close port 426 for closing the clamp.

The third of the three ports is a travel limiting port 424 and is located at a mid portion of the cylinder 416a,b. The travel limiting port 424 can be used in different configurations and placed in different locations relative to the piston travel but is generally arranged so as to act as a fluidic switch which is either covered or exposed during the travel of the piston so as to prevent further movement by adjusting the fluidic pressure across the piston. Generally, the travelling limiting port 424 may be selectively operable as an inlet or an outlet, or closed by an appropriate valve so as to be removed from the hydraulic circuit. Thus, the travel limiting port 424 can be used to reduce, maintain or increase the pressure in a chamber as required but is predominantly there to be switched by the travel of the piston 418a,b and alter the pressure across the piston 418a,b.

The drive arrangement 410 is configured such that the travel of the piston 418a,b can be readily controlled to move between first 421, second 423 and third 425 positions which correspond to the free, rotating and fixed positions of the clamp. In one embodiment, when the pistons are in the first position 421, hydraulic fluid is injected into chamber A under pressure via the first port 422 which results in the piston 418a,b moving laterally outwards from the mid-point 420 towards the second position 423. During this movement, the close port 426 of each chamber is opened to allow removal of the hydraulic fluid from Chamber B, thereby accommodating the movement between the first 421 and second positions 423. As the piston 418a,b approaches the second position 423 the travel limiting port 424 will be exposed as shown in Figure 4.

The travel limiting port 424 has three operational settings to allow the three clamp configurations to be achieved. The first setting limits the travel of the piston 418a,b. In this case, the port 424 is configured to act as an outlet which results in an outflow of hydraulic fluid from the chamber A and a resultant pressure drop when exposed in the second position 423. This pressure drop prevents further travel of the piston 418a,b which will remain in second position 423. The second operational setting is that in which the port is closed so as to be ineffectual in the hydraulic circuit and operation of the drive. In this configuration, the first port 422 will continue to drive the piston 418a,b and attached arm whilst pressurised to reach the third position 425. The third operational setting is to use the travel limiting port 424 as a drive, thereby providing additional force to the opening (or clamping) force if required.

Thus, in use and starting in the free configuration, the piston 418a,b would be placed in the third position 425 between the close port 426 and travelling limiting ports 424. The open port 422 would be open circuited to allow the outflow of hydraulic fluid and the travel limiting port 424 would be closed. It will be appreciated that open circuited may include the case in which the hydraulic fluid is returned to the hydraulic pump or an associated reservoir. Pressurising the close port 426 causes the piston 418a,b to travel inwards towards the midpoint of the back-to-back arrangement and the clamp would constrict around the support 214. This actuation stage can continue until the clamp is closed and in the fixed configuration which correlates to the piston being in the first position 421.

To open the clamp, the close ports 426 are opened so as to allow an outflow of hydraulic fluid. The travel limiting port 424, which is located in chamber B, is also open. The open port 422 is pressurised with hydraulic fluid sufficient to cause the piston 418a,b to travel outwards from the mid-point 420. The travel continues until the second position 423 is reached and the travel limiting port 424 is exposed to chamber A which results in a pressure drop in chamber A and a cessation of movement of the piston 418a,b . The positioning of the travelling limiting port 424 coincides with the clamp being placed in the rotational position, hence, there is provided an automatic hydraulic switch to prevent further movement of the clamp until the travel limiting port 424 is closed or pressurised.

To open the clamp further and provide the free configuration, the close port 426 remains open circuited, the travel limiting port 424 is either closed or pressurised and the open port 422 is pressurised to drive the piston 418 a,b until the limit of the travel is reached or sensed in the third position 425 and the hydraulic pressure removed.

In the above described embodiment, the travel limiting port 424 acts to remove hydraulic pressure from the drive when exposed, thereby preventing further movement. However, in other embodiments the ports 422, 424, 426 may be controlled such that the travel limiting port 424 operates to limit the travel when covered by the piston 418a,b rather than by being exposed. In this instance, the close ports 426 will be closed when the piston 418a,b is moving from the first position to the second position, with the travel limiting ports 424 being opened to accommodate the hydraulic flow which results from the movement of the piston. In this case, the movement of the piston 418a,b will be prevented when the travel limiting port 424 is covered by the piston and the differential pressure across the piston would increase and prevent the further movement.

Subsequent opening of the close ports 426 would allow the piston 418a, b to move from the second 423 to third 425 positions.

The control of the clamp and switching of the ports 422, 424, 426 which determine the operating state of the drive may be carried out to some predefined schedule or instructed manually by an operator, as required. To enable this, the clamp arrangement may include sensing equipment to sense the position of either or both of the clamp and drive or associated parts. In one embodiment, the detection of a pressure drop in the driving chamber or fluid flow in the hydraulic circuit of the travel limiting port 424 is advantageously used to provide a control signal for operating the fluid drive or pump. In one embodiment, the travel limiting port 424 is used predominantly as a safety device to prevent accidental opening of the clamp only. In this case, the position of the clamp, or an associated part such as the piston 418a,b which is indicative of the arm position and overall configuration of the clamp, could be monitored and the drive could be switched prior to the exposure or covering of the travel limiting port 424. In this instance, the travel limiting port is only utilised as an emergency fail safe which is preferable from a wear and reliability point of view and also provides some redundancy.

In one embodiment, the drive system relies on the sensory detection of the clamps operational state in accordance with the sensed data only, rather than relying on the travel limiting port 424. In this instance, the travel limiting port 424 is omitted and the operation governed by open and close ports of the actuator only.

It will be understood that the actuators and drives described in the above embodiments may be electrical, pneumatic or hydraulic, despite the description relating predominantly to hydraulic systems. Although the embodiments described above relate predominantly to buoyant turbines, it will be appreciated that the invention may be applicable to non-buoyant or heavy turbines in which the separation is achieved in other ways. For example, the clamping mechanism may be used for structures which are suspended below a float or the like and for which the gravity provides the separation.

Further, drive should be taken to include any mechanism which can be utilised to move the arm in relation to a fixed point on the support. Hence, the term drive may relate to a mechanism such as a lead screw or the piston of a hydraulic ram which connects to the arm and which causes it to move when actuated. In some embodiments it will be possible to have a single actuator which operates the two drives to move the arms so as to constrict or dilate the clamp relative to the support structure. Alternatively, the term drive may collectively refer to a mechanism which connects to the arm and an actuator which drives the mechanism. The two drives may be connected together so as to operated at the same time, potentially by one or more actuating means. Thus, a single lead screw could be used to separately drive the arms in opposing directions.

The drives are generally arranged to push the arms apart relative to a common point. The common point may be anchored to either or both of the first and second components and may be located in a gap which separates the free ends of the arms. However, the anchor may feasibly be anywhere around the clamp provided it allows the necessary movement of the free ends of the arms.

Preferably, the anchor will be at a mid-point between the free ends of the arms such that it can support one or both of the drives.