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1. WO2004063001 - PLATE-FORME D'INSTRUMENTS, APPAREIL ET KIT

Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]

INSTRUMENT PLATFORM, APPARATUS AND KIT

BACKGROUND OF THE INVENTION

Field of the invention

The present invention relates to an instrument platform. The platform may be for deployment in water, for example in sea water or in fresh water. The platform may be used for oceanographic deployment . The plat orm may be used in combination with an instrument to form an apparatus. Further, the platform or apparatus may be used in combination with a deployment means to form a kit

Related art

Oceanographic instruments can provide important information about the state of an ocean. This
information in turn is increasingly useful in the wider context of physical data relating to, for example, global environmental and climate change.
Long term measurements on the deep ocean floor are usually made using instruments that are hoisted or allowed to free fall from the surface down through the water column to land on the seabed. The instrument automatically records data for an extended period. This period can be, for example, between one and four years. Long term information from a static location can be very important, since it is more reliable than a series of measurements taken, e.g., by ship. Such a series of measurements taken from a ship cannot be guaranteed to have been taken at exactly the same location.

Known instruments are usually mounted on large bedstead-style frames. These have weights attached at their lower ends in order to help orientate the apparatus during free fall through the water column. Such frames require a team of trained personnel to prepare and deploy them. Usually they require careful deployment using a crane, and thus they require deployment by a ship which is large enough and stable enough to support a crane of sufficient lifting capacity. Typically, the requirements of the deployment are such that only research vessels with a team of trained personnel are capable of deploying the apparatus .
During deployment, because a crane is employed, the deployment vessel must be stopped. The time taken to deploy the apparatus makes the exercise expensive, since research vessels are expensive to run.
Once the apparatus has been deployed and is in position on the seabed, the instrument automatically record data for the measurement period. On completion of the measurement period, the research vessel returns to the deployment area and sends an acoustic command to the apparatus. At this command, the apparatus releases ballast, allowing at least the data logger and sensor section of the instrument to float to the surface. The instrument can then be recovered, e.g. by a research vessel .
Deployment, recovery and redeployment of the
instrument each involves time-consuming research vessel effort, in terms of the number of trained personnel needed and in terms of the need to halt the progress of the vessel itself.

SUMMARY OF THE INVENTION

The present invention aims to address and/or
ameliorate one or more of the above problems.
Accordingly, in one general aspect of a first development, the present invention provides
reconfiguration of an instrument platform between a transport configuration and a landing configuration.
Preferably, in a first aspect of this first
development, the present invention provides an instrument platform, preferably for sea deployment, e.g. for
location on the seabed, having a transport configuration and being reconfigurable to a landing configuration by deployment of a support arrangement for orienting the platform in a preferred orientation on, e.g., the seabed. Preferably, in the case where the platform is for deployment in water, the support arrangement is capable of deployment after the platform enters the water.
Typically, the support arrangement is deployed by an actuator. Suitable forms for the actuator are discussed in more detail below. First, preferred forms for the support arrangement are defined.
During steady-state freefall, the preferred
orientation of the platform is typically upright, with the support arrangement being disposed at the lower end of the platform in the landing configuration. The centre of gravity of the platform should preferably lie above the support arrangement, the weight of the platform thereby being supported on the seabed via the support arrangement .
Typically, the support arrangement should contact the seabed on at least three support points. At least two and preferably three of these support points should be laterally disposed around the intersection point of a plane containing the three support points and the
direction of gravity acting on the centre of gravity (upright direction) . Most preferably, the three support points should be substantially equispaced about the intersection point. This gives rise to a suitably stable support arrangement .
Given the location of the support points, it is possible to define a footprint of the instrument . The footprint may be defined in terms of area or in terms of width. In terms of area, the footprint is the area of the triangle formed by the three support points. In terms of width, the footprint is twice the distance between the intersection point and the most laterally spaced support point .
Typically, the linear footprint is at least equal to and preferably at least twice the distance between the centre of gravity of the platform and the intersection point . Preferably, the centre of gravity is as close as possible to the intersection point. This can provide the platform with greater stability.
Preferably, the support arrangement includes at least three support feet. In that case, a support point is located on each foot. Preferably, the support feet are pivotable with respect to a main body of the platform from the transport configuration to the landing
configuration.
Typically, as mentioned above, the platform includes an actuator. The actuator may drive the movement of the support feet between the transport configuration and the landing configuration. Preferably, the actuator operates automatically due to immersion in water, such as sea water. Most preferably, the actuator operates in
response to water pressure. The actuator may have a threshold pressure above which it is operable, that threshold pressure substantially corresponding to the hydrostatic pressure at a predetermined depth in water such as sea water.
The inventors have realised that such an actuator may have alternate or additional applications in relation to instrument platforms or other devices. Accordingly, in a general aspect of a second development, the present invention provides the operation of an actuator due to hydrostatic pressure at a predetermined depth in, for example, water.
Preferably, in a first aspect of the second
development, the present invention provides a device adapted for immersion in water, the device including an actuator containing a compressible volume, compression of the volume providing a force for operating at least a part of the device, the actuator having a threshold pressure above which it is operable, that threshold pressure substantially corresponding to the hydrostatic pressure at a predetermined depth in water.
The force provided by the actuator may be used for different operations. Typically, the use to which the force is put will depend on the type of device. The force may be used to provide movement of one part of the device relative to another. An example is shown in the first development of the invention, where parts of the support arrangement move relative to one another to reconfigure the platform into the landing configuration. In this way, the first development may be combined with the second development . Any preferred feature of the first development may be combined with the second development, and vice-versa.
However, the second development may be used in applications other than those shown with respect to the first development .
Preferably (as in the first development) , the actuator force is used to provide movement of one part of the device with respect to another. The movement may be harnessed so that the device reconfigures itself from one configuration (e.g. a deployment configuration) to another (e.g. a measurement configuration) . In the case of oceanographic instruments, the movement may be
harnessed in order to move the instrument in relation to an instrument support in order to adopt a more efficient measurement configuration. For example, in the case where an instrument is deployed in one attitude (e.g. vertically) and it is required to take measurements in another attitude (e.g. horizontally), the movement providable by the actuator may be harnessed in order to position the instrument in a desirable orientation.
Alternatively, the force provided by the actuator may be used to store potential energy within the device. The potential energy may be stored in the form of
chemical, electrical or mechanical potential energy. For example, the force may be used to generate electricity which may then be stored in a battery. Preferably, however, the force is used to deform a resilient means such as a spring or a volume of compressible gas. The deformation of the resilient means may subsequently be allowed to be released, allowing release of the energy contained. For example, the energy may be released when the actuator is exposed to a lower hydrostatic pressure than the threshold pressure, such as when the device is in a smaller depth of water.
As will be explained below, the actuator preferably produces a linear force rather than a torque. However, the linear for may be converted to rotary motion, if necessary. The device may include a rack and pinion for this purpose.
The actuator may be used as a switch. For example, the actuator may provide a lock or switch on a more powerful actuator. At the required depth, therefore, the actuator would allow the more powerful actuator to operate. The more powerful actuator may be, for example, a spring or other energy storage means in which energy is stored (but not released) prior to the deployment of the device.
In a second aspect of the second development , the present invention provides a use, in an oceanographic device, of an actuator containing a compressible volume, compression of the volume providing a force for operating at least a part of the device, the actuator having a threshold pressure above which it is operable, that threshold pressure substantially corresponding to the hydrostatic pressure at a predetermined depth in water.
The device may include a sediment trap. In that case, the actuator may be operable to open and/or close the sediment trap.
In what follows, the preferred features of the structure and operation of the actuator are mentioned. These features are applicable to the first and/or second deve1opments .
The actuator may include a cylinder along the axis of which a piston is moveable, typically the piston forming a sealing engagement with an internal surface of the cylinder. The piston typically has a piston shaft attached. The actuator may have an inlet for water, so that ambient water pressure can act on a first surface of the piston. The actuator may also have an outlet in fluid communication with the interior of the cylinder, typically controlled by a valve.
Before actuation, the cylinder typically contains gas (e.g. air) at a pressure below the predetermined pressure. For example, the pressure in the cylinder before deployment may be atmospheric pressure. When the ambient water pressure at the inlet exceeds a
predetermined amount, the piston may be driven to expel gas through the outlet, thereby driving the piston shaft. However, the cylinder may contain gas at sub-atmospheric pressure, or it may contain a vacuum.
In the valve, a valve element may be held against a valve seat by a retaining element. The force with which the valve element is retained by the retaining element, in part, determines the pressure at which the actuator operates. As such it is designated as factor (1)
However, there are also other factors which determine this pressure. These include:
Factor (2) : the pressure of the gas in the cylinder before deployment .
Factor (3) : the surface area of the first surface of the piston.
Factor (4) : the surface area of the valve element on which water pressure can act before operation of the actuator.
Thus, the pressure at which the actuator operates can be tuned to correspond to a particular depth in water (fresh water or sea water) . This constitutes an
independent, further aspect of either development of the invention, i.e. a method of operation of a platform or device according to the first aspect, the method
including the step of selecting a water depth at which the platform reconfigures from the transport
configuration to the landing configuration (first
development) or at which the actuator operates (second development) . Preferably, the selected water depth is matched to the platform by appropriate selection of a combination of factors (1) to (4) .
Preferably, the diameter of the first surface of the piston is at least 15 mm. However, it may be around 25 mm or even up to 50 mm or greater.
In embodiments of the invention in which the force produced by the actuator is stored as potential energy, a similar piston arrangement may be used. However, in this case, the gas in the cylinder is compressed by movement of the piston ram. If the compressed gas is to be allowed to expand later to harness the energy stored in it, the gas must be stored. Thus, the outlet of the actuator may not be present, or it may be sealed. In that case, movement of the piston causes the gas to be compressed with increasing hydrostatic pressure as the depth of the actuator is increased.
Typically, it is the movement of the piston shaft with respect to the cylinder which deploys the support arrangement of the first development. Preferably, the support arrangement is a tripod arrangement. Each support foot may have associated with it at least two legs, so that the support arrangement has two sets of legs . The first set of legs may be pivotably attached to the cylinder. The second set of legs may be pivotably attached to the piston shaft, or to the main body if the main body of the platform is attached to the shaft.
Preferably, stabiliser struts are attached
(typically pivotably) between corresponding first and second legs of a particular support foot .
For each foot, the first leg is typically pivotably attached to the foot, and the second leg is also
pivotably attached to the foot, but at a location
displaced from the first leg. Typically, therefore, the foot is pivotably moveable with respect to the first and second legs by relative movement between the first and second legs .
Preferably, the support feet are formed of a
relatively dense material compared to the material of the remainder of the platform. For example, the support feet may be formed of lead or a lead alloy. In this way, the location of the centre of gravity of the platform in the landing configuration can be kept close to the plane intersection of the three support points. This helps to improve the stability of the platform.
In the transport configuration, preferably the feet are located close to each other. Typically, the outer surface (in the transport configuration) of the feet form a tapering shape at a lower extremity of the platform. This shape can avoid excessive mechanical shock on the platform when it enters the water.
In the transport configuration, the legs may be disposed around and close to the actuator. This can give rise to an advantageous overall shape of the platform by efficient utilisation of space to give a compact form.

Preferably, in the transport configuration, the legs are surrounded by one or more covers which may be
breakable from the platform on reconfiguration of the platform from the transport to landing configurations. The cover preferably provides protection of the support arrangement and/or the actuator from accidental damage which might otherwise affect the operation of the support arrangement or actuator.
In a third aspect of the first development, the present invention provides an apparatus which is a combination of an instrument and an instrument platform according to the first aspect. The instrument may, for example, be packaged as an instrument package, which may contain other instruments.
Preferably, the instrument or package is attachable or attached to the platform at, e.g., the main body of the platform. In this way, the instrument is locatable above the support arrangement, so that the instrument does not affect the operation of the support arrangement. Preferably, the instrument or package has net positive buoyancy in water (e.g. fresh water or sea water) . However, the overall combination of the
apparatus should typically have negative buoyancy to aid free fall of the apparatus to the seabed.
Preferably, the instrument or package is detachable from the instrument platform. Typically, this detachment is capable of occurring automatically, e.g. after a predetermined time or after detection of a signal, e.g. an acoustic signal. After detachment, due to its net positive buoyancy, the instrument package will float up to the water surface . The package may include
communications means via which data collected by the instrument may be transmitted to a remote location, e.g. by satellite. This then avoids the need for the
information to be collected from the instrument by physically retrieving the instrument package itself.
This can save time and costs by avoiding the need for a research vessel to find and collect the instrument package .
Preferably, the instrument package includes one or more sensors which are suitable for, e.g., environmental monitoring or physical research. In particular, the sensor (s) may be suitable for measuring data associated with one or more of the following:
(i) water level measurement, waves and tides;
(ii) current measurement;
(iii) water turbidity;
(iv) concentration of dissolved oxygen;
(v) phytoplankton concentration;
(vi) hydrocarbon pollution measurement; and/or
(vii) conductivity, temperature and depth.

Additionally or alternatively, the instrument package may provide an acoustic beacon, e.g. for precise underwater navigation.
Preferably, in the transport configuration, the apparatus has a substantially uniform overall outer profile (except for the optional tapered nose portion formed by the feet) . For example, the apparatus may have a substantially cylindrical (e.g. circularly cylindrical) outer profile.
This makes the apparatus particularly suitable for deployment from, e.g., a deployment tube such as a launcher. Accordingly, in a fourth, independent aspect of the first development, the present invention provides a kit including a platform according to the first aspect of the first development, an apparatus according to the third aspect of the first development or a device according to the first aspect of the second development, and a deployment means for containing and deploying the platform, apparatus or device.
The platform or apparatus may in particular be suitable for deployment from a moving craft such as a boat, ship, helicopter, fixed wing aircraft or other aircraft. If the deployment is to be from an aircraft, the platform or apparatus may include a parachute to slow its descent through the atmosphere until the platform or apparatus enters the water.
Typically, the platform has a mass of less than

100 kg, and may have a mass of less than 50 kg. In the transport configuration, the lateral width of the platform may be as small as 500 mm or 200 mm or smaller. In the landing configuration, the lateral width of the footprint may be up to 4 m or smaller, for example up to 2 . In the landing configuration, the height of the platform may be up to about 1 m, but may be less, for example up to about 50 cm. The platform may be operated in substantially any depth of water, for example up to about 6000 m. The apparent weight of the platform in water may be up to about 85 kg, or up to about 40 kg. Typically, the predetermined depth at which the actuator operates is between 1 and 100 m. This depth may be more than 5 m or 10 m but is preferably less than 50 m.
A typical instrument package to be attached to the platform would be, for example, a tide gauge such as the Proudman Oceanographic Laboratory (UK) BPR tide gauge.

Such a tide gauge has an operating depth of up to about 4 m. Such an instrument package (and similar, other, instrument packages) has a mass of about 6 kg but a buoyancy in water of around 1 kg. In the transport configuration, a combination of such an instrument package with a platform as described above would have an overall length of less than 2 m and may be less than 1 m. The instrument package is typically shaped so that the overall lateral width of the combination of instrument and platform is no greater than the lateral width of the platform itself.
In another aspect, the invention provides a method of deployment of a series of platforms or apparatuses according to any of the above aspects, e.g. over a large area of sea. In particular, the devices may be deployed in the case of a pollution event over the suspected area (or larger) of the pollution event in order to monitor the effects of that event.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which: - Fig. 1 shows an embodiment of an instrument package plus platform according to the present invention in the transport configuration.
Fig. 2 shows a schematic view from above of the landing platform of Fig. 1 in a landing configuration.
Fig. 3 shows an enlarged view from the side of the apparatus shown in Fig. 2.

Figs. 4 to 6 show schematic views of the first piston surface of an actuator for use with an embodiment of the present invention. These figures also show rough calculations for the force experienced by the piston at various depth of seawater.
Fig. 7 shows a schematic axial sectional view of an actuator for use in embodiments of the present invention.

Fig. 8 shows detailed schematic views of different parts of a landing platform according to an embodiment of the present invention in the transport configuration. In Fig. 8, some features are shown as see-through or in cross-section and some details are omitted for clarity. Fig. 8b shows the landing platform in schematic lateral view. Only one leg is shown for clarity. Fig. 8a shows a view of the platform along line A in Fig. 8b. Fig. 8c shows a view of the platform along line B in Fig. 8c.
Fig. 9 shows views of a platform similar to that shown in Fig. 8, but this time in the landing
configuration. Again, some features are shown as see-through or in cross-section and some details are omitted for clarity. Fig. 9a shows a lateral view of the platform. Fig. 9b shows a view of the platform along line A in Fig. 9a.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 shows an oceanographic apparatus 10 having two separable parts. Instrument package 12 is attached to the main body 14 of instrument landing platform 16. Fig. 1 shows the apparatus in a transport configuration where legs (not shown) of the platform are folded
together and feet 18 of the landing platform abut together. The outer profile of feet 18 in the transport configuration is a tapering profile. This can help to reduce the mechanical shock on the apparatus on impact with water.
The legs of the platform are enclosed by a cover 20 in the transport configuration. Cover 20 has a generally uniform cylindrical outer profile which matches the outer profile of instrument package 12. In this way, the apparatus 10 has a substantially uniform outer profile which enables it to be stored in and deployed from a tubular launcher.
The overall length of the apparatus is 1.6m. Its diameter is 127mm. The mass of the apparatus is 36kg. The instrument package 12 has a mass of 6 kg but a buoyancy in water of 1.1 kg. The instrument is a
Proudman Oceanographic Laboratory (U.K.) BPR tide gauge. It has an operating depth of up to 400 m. In the
transport configuration, its axial length is 720 mm. The skilled person will understand that this instrument may be substituted by other oceanographic instruments.
Fig. 2 shows a schematic view of the landing
platform alone from above when the apparatus is in the landing configuration. Feet 18a, 18b, 18c are opened to their full extent in Fig. 2, adjacent feet being oriented 120° apart from each other. The footprint of the
platform shown in Fig. 2 is the diameter of the circle described by the locus of the lateral extremities of feet 18a, 18b, 18c. In Fig. 2, the footprint is 1.4m in diameter. The overall height of the apparatus in the landing configuration is 1.23m.
In seawater, the weight of the apparatus (accounting for the weight of water displaced by the apparatus and any positive buoyancy of the instrument package 12) is 24kg. In this case, the positive buoyancy of the
instrument package is 1.1kg.
Fig. 3 shows an enlarged view of the apparatus 10 shown in Fig. 1 but in the landing configuration. Note that foot 18a is not visible since it is disposed behind foot 18c.
Looking first at the instrument package 12, this is generally cylindrical and is attached at its lower end to main body 14 by attachment means (not shown) . A release mechanism or spooler 22 allows detachment of instrument package 12 from main body 14.
A sensor 24 is shown schematically protruding from the upper end of instrument package 12. Also, a
communications aerial 26 extends from the same end of instrument package 12. The communications aerial is capable of transmitting data to a satellite for
retransmission to a base station.
Looking now at the landing platform in its open configuration, the landing platform has a tripod
mechanism, designated in general by reference numeral 28. For foot 18b, an upper leg 30b is attached to a midpoint of foot 18b by a pivot connection 31b. Leg 30b is attached to main body 14 by another pivot connection 33b. A lower leg 32b is attached to a laterally inward end of foot 18b via pivot connection 34b. The other end of leg 32b is attached via pivot connection 35b to a cylinder of actuator 36, which is described in more detail below. A support strut 39 extends between upper leg 30b and lower leg 32b. The support strut 39 is attached to each leg via a respective pivot connection.

The assembly of the tripod mechanism 28 is such that, on relative displacement of main body 14 and actuator 36, legs 30, 32 are forced apart which in turn forces feet 18 outwardly from each other. The spaced apart location of pivot connection 34b and 31b ensure that relative
movement of legs 30b and 32b gives rise to relative pivoting of foot 18b. This allows the extended lower surface 19b of foot 18b to be presented for contact with the seabed.
Actuator 36 is moved relative to main body 14 by movement of piston shaft 38. Piston shaft 38 is
connected to main body 14 so that, when the actuator operates, actuator 36 is moved relative to main body 14. Fig. 7 shows actuator 36 in more detail. Cylinder 40 has a piston 42 located within it. Piston 42 sealingly engages with inner surface 44 of cylinder 40 via an 0-ring 46. A piston shaft 38 is connected to piston 42 and is axially displaceable with respect to cylinder 40 on operation of the actuator. The interface between the piston shaft 38 and cylinder 40 includes a seal 35.
The cylinder has an inlet 48 in fluid communication with the interior of a first end of the cylinder, in order that water pressure can act against first surface 50 of piston 42. The cylinder has an outlet 52 in fluid communication with the remainder of the interior of the cylinder. Outlet 52 is controlled by one way valve 54 which includes a valve ball 56 held in sealing engagement with a valve seat 58 by a retaining spring 60.
Before deployment, the interior of the cylinder contains air at atmospheric pressure. On immersion into the sea, water pressure builds up against surface 50 of piston 42. When this pressure exceeds the retaining force offered by spring 60 combined with any additional retaining force due to water pressure, valve ball 56 is dislodged from the valve seat 58 and the air in the cylinder is expelled through the valve into the sea.
Consequently, piston shaft 38 is displaced axially along the cylinder in direction R.
The force exerted by the piston shaft 38 acts to push main body 14 and actuator cylinder 40 apart, thereby operating the tripod mechanism 28 from the transport configuration to the landing configuration. The force offered by the piston shaft 38 is dependent, in part, on the surface area of the first surface 50 of the piston. Figs. 4, 5 and 6 illustrate some exemplary sizes for first surface 50 of piston 42. In Fig. 4, a 16mm
diameter piston gives rise to a 2kgf force at a 10m depth in seawater. At 100m, this force is increased to 20kgf . At 1000m, this force is increased to 200kgf . Fig. 6 shows the case where the piston 42 is of diameter 50mm. At a 10m depth in seawater, the piston provides a force of 20kgf. At 100m the piston force is 200kgf . At 1000m, the piston force is 2000kgf . These forces are arrived at on the assumption that a 10 metre depth in seawater gives rise to a change in pressure of 1 bar (about 14.7 psi or 105 Pa) .
In an alternative embodiment of the invention, actuator 36 does not have an outlet 52 or valve 54. In that case, the interior of the cylinder 40 forms a substantially sealed volume due to seals 35 and 46. On immersion into water, the interior of the cylinder contains air at atmospheric pressure. With increasing hydrostatic pressure from the water, due to increasing depth, the piston 42 in forced along cylinder 40, compressing the air within the cylinder to pressures higher than atmospheric pressure. The cylinder itself must be built relatively robustly in order to withstand the pressure built up inside. If the compressed gas is trapped inside the cylinder, it may be used at a later time as a source of energy or buoyancy. In particular, the compressed air (or some of it) may be used to inflate a buoyancy aid for the apparatus to allow it to float back to the surface. As the apparatus decreases in depth, the hydrostatic pressure which has kept the air
compressed decreases. Consequently, the piston 42 moves in the reverse direction, allowing the gas to expand again, thereby driving rod 38 in the reverse direction.
Fig. 8 shows an engineering drawing of different views of a modified embodiment of the landing platform. Fig. 8a shows the landing platform viewed from below, with feet 18a, 18b and 18c abutting each other in the transport configuration. Fig. 8b shows the main body 14 and only one part of the three-part tripod mechanism.
Fig. 8c shows the main body 14 from above.
Fig. 9 shows the platform of Fig. 8 in the landing configuration.
The transport configuration of the apparatus (the combination of the instrument platform and the instrument package) is a convenient elongate, e.g. cylindrical, shape. This allows the apparatus to be assembled into a kit including a deployment container. In a preferred embodiment, the deployment container is substantially cylindrical, its internal shape corresponding to the external shape of the apparatus in the transport
configuration. A cover is removably located at one end of the deployment container. Removal of the cover allows the apparatus to be deployed by sliding out of the container along the direction of the elongate axis of the container, under the influence of the weight of the apparatus . The apparatus then simply falls towards the water surface. If deployment of the apparatus is done from the air, e.g. from an aircraft, then the kit
includes a parachute . The parachute is removably
attached to the apparatus rather than to the deployment container. The parachute is attached to the upper end of the apparatus . The parachute opens to slow the descent of the apparatus through the air, and detaches from the apparatus when the apparatus makes contact with the water surface. Subsequently, the apparatus makes its way to the seabed as has already been described. If the
apparatus is to be deployed from a ship, there may be no need for a parachute, so that in that case the parachute may be dispensed with.
The present invention has been described with reference to preferred embodiments. Modifications of these embodiments, further embodiments and modifications thereof will be apparent to the skilled person and as such are within the scope of the invention.