WO2013107453A1

WO2013107453A1 - Transducer activated morphing structure

Info

Publication number: WO2013107453A1
Application number: PCT/DK2013/000005
Authority: WO
Inventors: Mohamed Yahia Benslimane; Andreas BARGUM
Original assignee: Danfoss Polypower A/S
Priority date: 2012-01-17
Filing date: 2013-01-16
Publication date: 2013-07-25

Abstract

The present invention relates to constructions where at least part of the shape is changeable as response to a relative contraction states of transducers. The present invention is for example suitable to make surfaces adapt to the actual conditions wherein they operate, to optimize their operation efficiency, such as e.g. the aerodynamic characteristics of wings in wind mills, fan blades etc.

Description

TRANSDUCER ACTIVATED MORPHING STRUCTURE

BACKGROUND OF THE INVENTION

Constructions operating under dynamic conditions often have reasons to change their shape to keep optimised operation efficiency despite the changing conditions.

Examples include surface of adapted to some aerodynamic conditions, such as for example the blades of wind mills, fans, wings, wing flaps, propellers etc., where the efficiency could be improved by changing the shapes as response to e.g. changing wind conditions etc. However, the present invention would apply to any construction where some adaptation of shape would be required or desired.

A wind turbine produces energy by catching as much wind as possible, and thereby creating maximum lift on the wings, and this is one reason why wind turbines potentially could produce more energy than they actually do. The lift is a force that makes the rotor on a wind turbine rotate being, and this force also causes the blade to bend towards the tower.

If the wind conditions where consistent it would have been easy to calculate the maximum possible allowable lift on the blades that would not cause a bending of the blades such large that there is a risk of a collision with the tower.

Unfortunately nature does not behave very consistent in terms of wind speeds. The tower causes wind turbulences which affect the blade, and considering the large rotor diameters it leads to the fact, that the tip of the blade on many present wind turbines changes its height from the ground by 90 meters as it rotates on the turbine. The wind speed of course changes as you move further away from the ground.

The risk is an oscillation of the blades which may cause a collision with the tower. Besides the danger of collision, the oscillation of the wings stresses the tower construction.

Wind turbines do have the option to pitch the wings. Pitching the wings means turning the whole wing more or less angled into the wind. Although this might deal with some previously mentioned problems, the disadvantage of this system is that it is very slow. The mechanism is not dimensioned for continuous use. Also the system pitches all wings at the same time so no individual control of the wing is possible. Pitching is used to get the most optimal angle of attack and to stop the wind turbine from operating in extreme weather conditions.

Wing flaps are usually mounted on an airplane wing with the purpose o change the aerodynamic behaviour of the wing, which may be advantageous when landing the airplane or taking off. The wing flap change the aerodynamic behaviour of the wing and are usually located at the trailing edge. Implementing a flap on the wing can reduce the noise pollution and enables more energy harvesting without disturbing residents.

A flap changes the overall shape of the wing, and to create a construction able to adapt its shape one may introduce power transducers being available for various kinds of uses in industry. These transducers are frequently powered by electric solenoids, by hydraulics, and by pneumatics, but also include

electroactive transducers as they are well known.

Though the working example of the present invention is related to wind turbines, or mills, it is no manner limited to this use, any other system or construction would also apply, such as systems or constructions having a surface being in some interaction with externals, and there this surface is to change such as due to a change in the external conditions.

This could for example be a vehicle changing a shape or surface to optimize, or at least improve, the aerodynamic conditions for the vehicle.

It could pumps, ventilators changing pars to optimize e.g. to flow conditions.

It could be devices simply changing form due to changing an aesthetic appearance, or any other system.The present invention relates to constructions able to change the shape during operation where the change is related to a state of activation of an electroactive transducer.

SUMMARY OF THE INVENTION

The present invention thus relates to constructions being MORPHING structures in the sense their outer geometry are changeable thus in a way beingstructures without a definite shape. The actual shape in the present invention is related to the state of at least one transducer comprising a laminate with a film of a dielectric polymer material arranged between first and second layers of an electrically conductive material so that it is elastically deformable in response to an electrical field applied between the layers.

The laminate which is arranged to function as a transducer is relatively simple and requires in it self no mechanically interacting, rotating or sliding elements. Since an applied electrical field deforms the film elastically, the elastic property of the film provides a build-in spring-force which pushes the transducer back towards a neutral position when the electrical field disappears.

By transducer is hereby meant that it is capable of converting electrical energy to mechanical energy and reciprocally of converting mechanical energy to electrical energy. This enables the use of the transducer as an actuator which works to change the flow condition through the path when provided with an electrical field between the first and second layers of electrically conductive material, and/or the use of the transducer as a sensor which provides a change of an electrical characteristic, e.g. capacitance between the layers of electrically conductive material, upon a change in the flow condition in the path.

By deflect is herein meant to bend or to deform under influence of a pressure. In case of the film, the deflection is triggered by the pressure from the conductive layers under a force of attraction or repulsion from an electrical field applied between the conductive layers. By laminate is here meant a product made by two or more layers of material, e.g. bonded together. As an example, the laminate may comprise a

nonconductive polymer material and a conductive material on each side, where the two kinds of material are bonded e.g. adhesively, by sintering, or simply arranged in contact with each other. In the following, an electro-active laminate is a laminate with a film of a dielectric polymer material arranged between first and second layers of an electrically conductive material so that it is elastically deformable in response to an electrical field applied between the layers.

The dielectric material could be any material that can sustain an electric field without conducting an electric current, such as a material having a relative permittivity, ε, which is larger than or equal to 2. It could be a polymer, e.g. an elastomer, such as a silicone elastomer, such as a weak adhesive silicone or in general a material which has elatomer like characteristics with respect to elastic deformation. For example, Elastosil RT 625, Elastosil RT 622, Elastosil RT 601 all three from Wacker-Chemie could be used as a dielectric material.

In the present context the term 'dielectric material' should be interpreted in particular but not exclusively to mean a material having a relative permittivity, ε_Γ, which is larger than or equal to 2. In the case that a dielectric material which is not an elastomer is used, it should be noted that the dielectric material should have elastomer-like properties, e.g. in terms of elasticity. Thus, the dielectric material should be deformable to such an extent that the composite is capable of deflecting and thereby pushing and/or pulling due to deformations of the dielectric material.

The film and the electrically conductive layers may have a relatively uniform thickness, e.g. with a largest thickness which is less than 110 percent of an average thickness of the film, and a smallest thickness which is at least 90 percent of an average thickness of the film. Correspondingly, the first electrically conductive layer may have a largest thickness which is less than 110 percent of an average thickness of the first electrically conductive layer, and a smallest thickness which is at least 90 percent of an average thickness of the first electrically conductive layer. In absolute terms, the electrically conductive layer may have a thickness in the range of 0.01 pm to 0.1 pm, such as in the range of 0.02 pm to 0.09 pm, such as in the range of 0.05 pm to 0.07 pm. Thus, the electrically conductive layer is preferably applied to the film in a very thin layer. This facilitates good performance and facilitates that the electrically conductive layer can follow the corrugated pattern of the surface of the film upon deflection.

The film may have a thickness between 10 pm and 200 pm, such as between 20 pm and 150 pm, such as between 30 pm and 100 pm, such as between 40 pm and 80 pm. In this context, the thickness of the film is defined as the shortest distance from a point on one surface of the film to an intermediate point located halfway between a crest and a trough on a corrugated surface of the film. The electrically conductive layer may have a resistivity which is less than 0^"2 Ω-cm or even less than 10^"4 Ω-cm. By providing an electrically conductive layer having a very low resistivity the total resistance of the electrically conductive layer will not become excessive, even if a very long electrically conductive layer is used. Thereby, the response time for conversion between mechanical and electrical energy can be maintained at an acceptable level while allowing a large surface area of the composite, and thereby obtaining a large influence on the flow conditions in the path. In the prior art, it has not been possible to provide corrugated electrically conductive layers with sufficiently low electrical resistance, mainly because it was necessary to select the material for the prior art electrically conductive layer with due consideration to other properties of the material in order to provide the compliance. By the present invention it is therefore made possible to provide compliant electrically conductive layers from a material with a very low resistivity. This allows a large actuation force to be obtained while an acceptable response time of the transducer is maintained. The electrically conductive layer may preferably be made from a metal or an electrically conductive alloy, e.g. from a metal selected from a group consisting of silver, gold and nickel. Alternatively other suitable metals or electrically conductive alloys may be chosen. Since metals and electrically conductive alloys normally have a very low resistivity, the advantages mentioned above are obtained by making the electrically conductive layer from a metal or an electrically conductive alloy.

The dielectric material may have a resistivity which is larger than 10¹⁰ Q cm. Preferably, the resistivity of the dielectric material is much higher than the resistivity of the electrically conductive layer, preferably at least 10¹⁴-10¹⁸ times higher.

To facilitate increased compliance of the transducer in one direction, to facilitate an improved reaction time and therefore an improved performance and controllability of the valve, or potentially to provide an increased lifetime of the transducer, the film may have a surface pattern e.g. forming corrugations which render the length of the electrically conductive layer in a lengthwise direction, longer than the length of the laminate as such in the lengthwise direction - i.e. the surface pattern makes the surface longer than the laminate as such.

The corrugated shape of the electrically conductive layer thereby facilitates that the laminate can be stretched in the lengthwise direction without having to stretch the electrically conductive layer in that direction, but merely by evening out the corrugated shape of the electrically conductive layer. If it requires a larger force to elastically deform the electrically conductive layers than that which is required to deform the film, the corrugated shaped thereby renders the laminate more compliant in that lengthwise direction than in other directions.

According to the invention, the corrugated shape of the electrically conductive layer may be a replica of the surface pattern of the film.

The corrugated pattern may comprise waves forming crests and troughs extending in one common direction, the waves defining an anisotropic characteristic facilitating movement in a direction which is perpendicular to the common direction. According to this embodiment, the crests and troughs resemble standing waves with essentially parallel wave fronts. However, the waves are not necessarily sinusoidal, but could have any suitable shape as long as crests and troughs are defined. According to this embodiment a crest (or a trough) will define substantially linear contour-lines, i.e. lines along a portion of the corrugation with equal height relative to the composite in general. This at least substantially linear line will be at least substantially parallel to similar contour lines formed by other crest and troughs, and the directions of the at least substantially linear lines define the common direction. The common direction defined in this manner has the consequence that anisotropy occurs, and that movement of the composite in a direction perpendicular to the common direction is facilitated, i.e. the composite, or at least an electrically conductive layer arranged on the corrugated surface, is compliant in a direction

perpendicular to the common direction. The variations of the raised and depressed surface portions may be relatively macroscopic and easily detected by the naked eye of a human being, and they may be the result of a deliberate act by the manufacturer. The periodic variations may include marks or imprints caused by one or more joints formed on a roller used for manufacturing the film. Alternatively or additionally, the periodic variations may occur on a substantially microscopic scale. In this case, the periodic variations may be of the order of magnitude of manufacturing tolerances of the tool, such as a roller, used during manufacture of the film. Even if it is intended and attempted to provide a perfect roller, having a perfect pattern, there will in practice always be small variations in the pattern defined by the roller due to manufacturing tolerances. Regardless of how small such variations are, they will cause periodical variations to occur on a film being produced by repeatedly using the roller. In this way the film may have two kinds of periodic variations, a first being the imprinted surface pattern of structures such as corrugations being shaped perpendicular to the film, this could be called the sub-pattern of variations, and further due to the repeated imprinting of the same roller or a negative plate for imprinting, a super-pattern arises of repeated sub-patterns.

Manufacturing the film by repeatedly using the same shape defining element, allows the film to be manufactured in any desired length, merely by using the shape defining element a number of times which results in the desired length. Thereby the size of the composite along a length direction is not limited by the dimensions of the tools used for the manufacturing process. This is very advantageous. The film may be produced and stored on a roll, and afterwards, the film may be unrolled while the electrically conductive layer or layers are applied to the film.

Each wave in the corrugated surface may define a height being a shortest distance between a crest and neighbouring troughs. In this case each wave may define a largest wave having a height of at most 110 percent of an average wave height, and/or each wave may define a smallest wave having a height of at least 90 percent of an average wave height. According to this embodiment, variations in the height of the waves are very small, i.e. a very uniform pattern is obtained

According to one embodiment, an average wave height of the waves may be between 1/3 pm and 20 pm, such as between 1 pm and 15 pm, such as between 2 pm and 10 pm, such as between 4 pm and 8 pm. In one embodiment, the height of the waves are varying e.g. so that the height increases from a small initial height with an increasing height towards a higher end height. In this respect, the laminate may e.g. be rolled so that the wave with the initial height is in the centre of the rolled actuator or at the periphery of the rolled actuator.

Alternatively or additionally, the waves may have a wavelength defined as the shortest distance between two crests, and the ratio between an average height of the waves and an average wavelength may be between 1/30 and 2, such as between 1/20 and 1.5, such as between 1/10 and 1.

The waves may have an average wavelength in the range of 1 μηη to 20 μηι, such as in the range of 2 m to 15 μιη, such as in the range of 5 m to 10 μιτι.

A ratio between an average height of the waves and an average thickness of the film may be between 1/50 and 1/2, such as between 1/40 and 1/3, such as between 1/30 and 1/4, such as between 1/20 and 1/5.

The second electrically conductive layer may, like the first layer, have a surface pattern, e.g. including a corrugated shape which could be provided as a replica of a surface pattern of the film. Alternatively, the second electrically conductive layer is substantially flat. If the second electrically conductive layer is flat, the composite will only have compliance on one of its two surfaces while the second electrically conductive layer tends to prevent elongation of the other surface. This provides a composite which bends when an electrical potential is applied across the two electrically conductive layers.

One way of making the laminate is by combining several composites into a multilayer composite with a laminated structure. Each composite layer may comprise: - a film made of a dielectric material and having a front surface and rear surface, the front surface comprising a surface pattern of raised and depressed surface portions, and

- a first electrically conductive layer being deposited onto the surface pattern, the electrically conductive layer having a corrugated shape which is formed by the surface pattern of the film.

In this structure, an electrode group structure may be defined, such that every second electrically conductive layer becomes an electrode of a first group and every each intermediate electrically conductive layer becomes an electrode of a second group of electrodes. A potential difference between the electrodes of the two groups will cause a deformation of the film layers located there between, and the composite is therefore electro-active. In such a layered configuration, a last layer will remain inactive. Accordingly, a multilayer composite with three layers comprises 2 active layers, a multilayer composite with 10 layers comprises 9 active layers, etc.

According to one embodiment, the raised and depressed surface portions of the surface pattern of the film of each composite layer may have a shape and/or a size which varies periodically along at least one direction of the front surface. This has already been explained above. If the electrically conductive layers are deposited on front surfaces of the films, it may be an advantage to arrange the layers with the rear surfaces towards each other. In this way, the multilayer composite becomes less vulnerable to faults in the film. If the film in one layer has a defect which enables short circuiting of electrodes on opposite surfaces thereof, it would be very unlikely if the layer which is arranged with its rear surface against the film in question has a defect at the same location. In other words, at least one of the two films provides electrical separation of the two electrically conductive layers. The multilayer composite can be made by a multiple layer coating technique wherein each layer is coated directly on top of the previous layer, or it can be made by "dry" lamination of finished film layers on top of each other.

The multilayer composite can be made by arranging the composite layers in a stack and by applying an electrical potential difference between each adjacent electrically conductive layer in the stack so that the layers are biased towards each other while they are simultaneously flattened out. Due to the physical or characteristic properties of the film, the above method may bond the layers together. As an alternative or in addition, the layers may be bonded by an adhesive arranged between each layer. The adhesive should preferably be selected not to dampen the compliance of the multilayer structure. Accordingly, it may be preferred to select the same material for the film and adhesive, or at least to select an adhesive with a modulus of elasticity being less than the modulus of elasticity of the film. The composite layers in the multilayer composite should preferably be identical to ensure a homogeneous deformation of the multilayer composite throughout all layers, when an electrical field is applied. Furthermore, it may be an advantage to provide the corrugated pattern of each layer either in such a way that wave crests of one layer are adjacent to wave crests of the adjacent layer or in such a way that wave crests of one layer are adjacent to troughs of the adjacent layer.

According to a preferred embodiment the laminate may have been rolled to form a coiled pattern of dielectric material and electrodes, the rolled laminate thereby forming the transducer. In the present context, the term 'coiled pattern' should be interpreted to mean that a cross section of the transducer exhibits a flat, spiral-like pattern of electrodes and dielectric material. Thus, the rolled transducer resembles a Swiss roll or part of a Swiss roll.

Traditionally, transducers based on a body of polymer between electrode layers operate with a higher performance when the polymer is pre-strained. The pre- strain can be obtained by stretching the laminate or the rolled structure obtained by rolling of the laminate by use of a spring structure. In the rolled embodiment, the transducer is preferably designed by rolling or spooling of a laminate of potentially unlimited length in a thick-walled column-like self-supporting structure. Such a self-supporting structure may become sufficiently strong to prevent buckling during normal operation of the valve. By rolling of the laminate into a rolled structure, it may be possible to avoid pre-straining of the laminate and the self-supporting structure may therefore become very simple to manufacture. The laminate may be rolled around an axially extending axis to form a transducer of an elongated shape extending in the axial direction. The rolled laminate may form a tubular member. This should be understood in such a manner that the rolled laminate defines an outer surface and an inner surface facing a hollow interior cavity of the rolled laminate. Thus, the transducer in this case forms a 'tube', but the 'tube' may have any suitable shape.

In the case that the rolled transducer forms a tubular member, the rolled laminate may form a member of a substantially cylindrical or cylindrical-like shape. In the present context the term 'cylindrical-like shape' should be interpreted to mean a shape defining a longitudinal axis, and where a cross section of the member along a plane which is at least substantially

perpendicular to the longitudinal axis will have a size and a shape which is at least substantially independent of the position along the longitudinal axis. Thus, according to this embodiment the cross section may have an at least

substantially circular shape, thereby defining a tubular member of a

substantially cylindrical shape. However, it is preferred that the cross section has a non-circular shape, such as an elliptical shape, an oval shape, a rectangular shape, or even an unsymmetrical shape. A non-circular shape is preferred because it is desired to change the cross sectional area of the transducer during operation, while maintaining an at least substantially constant circumference of the cross section. In the case that the cross section has a circular shape this is not possible, since a circular shape with a constant circumference is not able to change its area. Accordingly, a non-circular shape is preferred.

The rolled transducer may define a cross sectional area, A, being the area of the part of the cross section of the rolled transducer where the material forming the rolled transducer is positioned, and A may be within the range 10 mm² to 40000 mm², such as within the range 50 mm² to 2000 mm², such as within the range 75 mm² to 1500 mm², such as within the range 100 mm² to 000 mm², such as within the range 200 mm² to 700 mm². Thus, A may be regarded as the size of the part of the total cross sectional area of the rolled transducer, which is Occupied' by the transducer. In other words, A is the cross sectional area which is delimited on one side by the outer surface and on the other side by the inner surface facing the hollow cavity of the rolled structure.

The rolled laminate may define a radius of gyration, r_g, given by r = J , where

I is the area moment of inertia of the rolled transducer, and r_g may be within the range 5 mm to 100 mm, such as within the range 10 mm to 75 mm, such as within the range 25 mm to 50 mm. The radius of gyration, r_g, reflects a distance from a centre axis running along the longitudinal axis of the tubular member which, if the entire cross section of the rolled transducer was located at that distance from the centre axis, it would result in the same moment of inertia, I. Furthermore, the rolled laminate may define a slenderness ratio, λ, given by A=L/r_g, where L is an axial length of the rolled laminate, and λ may be smaller than 20, such as smaller than 10. Thus, the slenderness ratio, λ, reflects the ratio between the axial length of the rolled laminate and the radius defined above. Accordingly, if λ is high the axial length is large as compared to the radius, and the rolled laminate will thereby appear to be a 'slender' object. On the other hand, if λ is low the length is small as compared to the radius, and the rolled transducer will thereby appear to be a 'fat' object, hence the term

'slenderness ratio'. An object having a low slenderness ratio tends to exhibit more stiffness than an object having a high slenderness ratio. Accordingly, in a rolled laminate having a low slenderness ratio buckling during actuation is avoided, or at least reduced considerably.

The rolled laminate may define a wall thickness, t, and the ratio t/r_g may be within the range 1/1000 to 2, such as within the range 1/500-1 , such as within the range 1/300-2/3. This ratio reflects how thin or thick the wall defined by the rolled laminate is as compared to the total size of the rolled laminate. If the ratio is high the wall thickness is large, and the hollow cavity defined by the rolled transducer is relatively small. On the other hand, if the ratio is low the wall thickness is small, and the hollow cavity defined by the rolled laminate is relatively large.

Alternatively or additionally, the rolled laminate may have a wall thickness, t, and may comprise a number of windings, n, being in the range of 5 to 100 windings per mm wall thickness, such as in the range 10 to 50 windings per mm wall thickness. The larger this number is, the thinner the unrolled laminate has to be. A large number of windings of a thin film allows a given actuation force to be achieved with a lower potential difference between the electrodes as compared to similar transducers having a smaller number of windings of a thicker film, i.e. having the same or a similar cross sectional area. This is a great advantage. The mechanical and electrostatic properties of an electro-active web are used as a basis to estimate actuator force per unit area and stroke. Rolled laminates as described above are made by rolling/spooling very thin composite layers, e.g. having a thickness within the micrometers range. A typical transducer of this type can be made of laminate which is wound in thousands of windings. When activated, direct/push transducers convert electrical energy into mechanical energy. Part of this energy is stored in the form of potential energy in the transducer material and is available again for use when the transducer is discharged. The remaining part of mechanical energy is effectively available for actuation. Complete conversion of this remaining part of the mechanical energy into actuation energy is only possible if the support structure is reinforced against mechanical instabilities, such as well known buckling due to axial compression. This can be done by reinforcing the cross sectional area of the transducer on one hand and then optimising the length of the transducer according to Euler's theory.

The optimisation process starts by defining the level of force required for a given valve. Then based on the actuator force per unit area, it is possible to estimate the necessary cross sectional area to reach that level of force.

Stabilisation of the transducer against any mechanical instability requires reinforcing its cross section by increasing its area moment of inertia of the cross section, I. Low values of I result in less stable structures and high values of I result in very stable structures against buckling. The design parameter for reinforcing the structure is the radius of gyration r_g ( r_g = J— ) which relates cross section, A, and area moment of inertia, I. Low values of r_g result in less stable support structures and high values of r_g result in highly stable support structures. After having defined optimum ranges for both area, A, and radius of gyration, r_g, it is possible to define the optimum range for the rolled transducer wall thickness, t, with respect to r_g in the form of t/r_g. Area, A, radius, r_g, and wall thickness, t, are the design parameters for reinforcing the transducer cross section for maximum stability. Low values of t/r_g result in highly stable support structures and high values of t/r_g result in less stable support structures.

Once the ranges of the cross section parameters have been determined, it is necessary to estimate the maximum length, L, of the transducer, for which buckling by axial compression does not occur for the required level of force. Slenderness ratio, λ, as defined above, is the commonly used parameter in relation with Euler's theory. Low values of λ result in highly stable support structures and high values of λ result in less stable support structures against buckling. Once all design parameters for the optimum working direct transducer have been determined, it is possible to estimate the total number of windings that are necessary to build the transducer based on the transducer wall thickness, t, and the number of windings per millimetre, n, for a given electro-active web with a specific thickness in the micrometer range.

The rolled transducer may comprise a centre rod arranged in such a manner that the transducer is rolled around the centre rod, the centre rod having a modulus of elasticity which is lower than a modulus of elasticity of the dielectric material. According to this embodiment the hollow cavity defined by the tubular member may be filled by the centre rod, or the centre rod may be hollow, i.e. it may have a tubular structure. The centre rod may support the rolled transducer. However, it is important that the modulus of elasticity of the centre rod is lower than the modulus of elasticity of the dielectric material in order to prevent that the centre rod inhibits the function of the transducer. Alternatively or additionally, the rolled transducer may comprise a centre rod arranged in such a manner that the transducer is rolled around the centre rod, and the centre rod may have an outer surface abutting the rolled transducer, said outer surface having a friction which allows the rolled transducer to slide along said outer surface during actuation of the transducer. The centre rod could, in this case, e.g. be a spring or similar elastically deformable element. Since the rolled transducer is allowed to slide along the outer surface of the centre rod, the presence of the centre rod will not inhibit elongation of the transducer along a longitudinal direction defined by the centre rod, and the operation of the transducer will thereby not be inhibited by the presence of the centre rod due to the low friction characteristics of the centre rod.

The transducer which comprises a rolled laminate may have an area moment of inertia of the cross section which is at least 50 times an area moment of inertia of the cross section of an un-rolled transducer, such as at least 75 times, such as at least 00 times. According to the present invention, this increased area moment of inertia is preferably obtained by rolling the transducer with a sufficient number of windings to achieve the desired area moment of inertia of the rolled structure. Thus, even though the unrolled transducer is preferably very thin, and therefore must be expected to have a very low area moment of inertia, a desired area moment of inertia of the rolled transducer can be obtained simply by rolling the transducer with a sufficient number of windings. The area moment of inertia of the rolled transducer should preferably be sufficient to prevent buckling of the transducer during normal operation.

Thus, the rolled transducer may have a number of windings sufficient to achieve an area moment of inertia of the cross section of the rolled transducer which is at least 50 times an average of an area moment of inertia of the cross section of an un-rolled transducer, such as at least 75 times, such as at least 100 times.

According to one embodiment, positive and negative electrodes may be arranged on the same surface of the dielectric material in a pattern, and the transducer may be formed by rolling the dielectric material having the

electrodes arranged thereon in such a manner that the rolled transducer defines layers where, in each layer, a positive electrode is arranged opposite a negative electrode with dielectric material there between. According to this embodiment the transducer may preferably be manufactured by providing a long film of dielectric material and depositing the electrodes on one surface of the film. The electrodes may, e.g., be arranged in an alternating manner along a longitudinal direction of the long film. The long film may then be rolled in such a manner that a part of the film having a positive electrode positioned thereon will be arranged adjacent to a part of the film belonging to an immediately previous winding and having a negative electrode thereon. Thereby the positive and the negative electrodes will be arranged opposite each other with a part of the dielectric film there between. Accordingly, a transducer is formed when the film is rolled.

The laminate may e.g. be rolled relative to a surface pattern of at least one of the layers so that the deformation of the film causes radial expansion of the transducer. This could be obtained with a pattern of corrugations extending parallel to an axis around which the laminate is rolled. Alternatively, the laminate could be rolled relative to a surface pattern of at least one of the layers so that the deformation of the film causes axial expansion of the transducer and thus variable distance between axially opposite end faces of the transducer. This could be obtained with a pattern of corrugations extending perpendicularly to the axis around which the laminate is rolled so that the crests and chests of the corrugations extend circumferentially around the transducer.

FIGURES

Fig. 1 shows one example of a film transducer applicable for the present invention. Figs. 2A-C shows the film transducer rolled into direct actuating transducers.

Fig. 3A-B shows a first embodiment of the present invention.

Fig. 4 shows a second embodiment of the present invention.

Figs. 5A&B show a third embodiment of the present invention. Figs. 6A&B show a fourth embodiment of the present invention.

Fig. 7 shows a fifth embodiment of the present invention.

Fig. 8 shows a sixth embodiment of the present invention.

Fig. 9 shows a seventh embodiment of the present invention.

Figs. 10A-B shows an embodiment of the present invention where a

transducer is positioned on the surface of a sheet like support structure. Figs. 11 A-C shows an embodiment with transducers on a sheet like, or plane, support structure giving changing curving of the support structure.

Fig. 12 shows an embodiment with transducers on a sheet like, or plane, support structure giving complex changing curving of the support structure. DETAILED DESCRIPTION

The non-limiting transducers used in the example of description the present description is made as a film-transducer (9) of a dielectric polymer material arranged between first and second layers of an electrically conductive material so that it is elastically deformable in response to an electrical field applied between the layers.

The film (9) is provided so that it is easier to deform in one, compliant, direction than in other directions. The film (9) is further provided with an anisotropic characteristic so that it is less compliant in one specific direction than in other directions. As illustrated in Fig. 1 , this characteristic can be provided by a waved cover skin by which the laminate can be expanded in the compliant,

longitudinal, direction indicated by the bold arrows (1 , 2) by elastic deformation of the polymer material (3), while the electrically conductive material which is applied to the waved surface is straightened out rather than stretched.

In the illustration the film is formed by a laminate of two composites (3a, 3b) being

- a film made of a dielectric material and having a front surface and rear surface, the front surface comprising a surface pattern of raised and depressed surface portions, and

- a first electrically conductive layer being deposited onto the surface pattern, the electrically conductive layer having a corrugated shape which is formed by the surface pattern of the film. Composites (3a, 3b) may be laminated front surface to front surface, rear surface to rear surface and / or rear surface to front surface. Films, laminates and transducers may be formed in any combination of laminations.

By selection of a conductive material which requires a larger force to deform elastically than that required to deform the polymer material, and by application of the conductive material throughout the transverse direction indicated by the bold arrows (4, 5), i.e. parallel to the direction in which the crests and troughs of the waves extend, the laminate becomes anisotropic. By anisotropic is meant that the laminate is compliant in the longitudinal direction and non-compliant in the transverse direction.

Film-transducers (9) as illustrated in Fig. 1 may be formed into a number of configurations to make working transducers may laminating a number of layers of film / composites e.g. as a number of individual sheets, by folding a web of films / composites, or by rolling them.

Figs. 2a-2c are perspective views of direct actuating transducers (6) according to embodiments of the invention formed by rolling a laminate e.g. according to Fig. 1. The transducer (6a) of Fig. 2a is solid, whereas the transducer (6b) of Fig. 2b is hollow. The transducers (6) may have any elongated form, e.g.

substantially cylindrical with a cross section which is substantially circular, elliptical or curve formed as illustrated in Fig. 2c.

Accordingly, a laminate of corrugated anisotropic dielectric film layers with electrically conductive electrode layers can be rolled into a tubular shape with a number of windings sufficient to make the resulting structure of the tubular element sufficiently stiff to avoid buckling. In the present context, the term 'buckling' means a situation where an elongated structure deforms by bending due to an applied axial load. It has been found that no additional component such as any stiffening rod or spring inside the elongated structure is necessary to obtain sufficient stiffness to avoid buckling under technically useful levels of axial load. The required stiffness is obtained merely by winding up a sufficient number of windings of the laminate material.

The rolled structures illustrated in Figs. 2a-2c are designed to withstand a specified maximum level of load at which the stiffness is sufficient to avoid buckling. This specified maximum level may, e.g., be a certain level of force at a certain level of elongation, or it may be a maximum level of actuation force, a blocking force, or a higher level of force occurring when the transducer is compressed to a shorter length against the direction of the arrows 7.

Fig. 3A and 3B illustrates a first example design of a construction (1) according to the present invention, where the surface is represented by the transducer (11) material itself. It is swept over the top of a first member (13) to create closed shell. The transducer (11) is inactive at the top of the flap resulting in two individually controllable sub-transducers ( 1a) and (11b). This and many of the following figures are seen as highly illustrative cross sectional looks into the side of the constructions, the constructions to be understood as extending in a 3-D direction into the paper. The transducers (11) in the preferred but not exclusive embodiment are formed of a number of layered or laminated film- transducers (9) of the kind shown in Fig. 1. The transducer (11) preferable is pre-strained such as by stretching it over the first member (13) of the support structure (12).

In the present context 'pre-strain' is to mean that the pre-strained transducer (11) in its relaxed stated in the construction is longer than its relaxed unattached free state.

The support structures (12) comprises at least one first (13) and second (14) member made of a substantially stiff material to form the needed support of the transducers (11), and to be adapted to extend a cover skin (21) (such as e.g. a transducer (11) itself as illustrated in Fig. 3A and B) in mutual different directions. In the illustrated embodiment the first member (13) comprises a flexible segment (20). The flexible segment (20) is a flexible section of the support structure (12), the first (13) and / or second member (14), and may e.g. be a pivot joint / connection etc., only it is to be understood as a section or point where two parts or members are able to form a rotating / bending / leaning / tilting movement relative to each other in or around the flexible segment (20). In Figs. 3A and 3B the flexible segment (20) is a flexible part (20a) of the first member (13) positioned close to the respective second member (14), where the flexible part (20a) is able to bend to change the configuration of the support structure (12) as either the first (13) or the second (14) member changes the tilting relative to the other by the flexible segment (20, 20a) as the equilibrium of the transducers (11 , 11a, 11b) are changed due to e.g. a change of the state of the activation of one or both of the transducers ( 1 , 11a, 11b).

The second member (14) in the illustrated example further operates as a clamp fixing (15).

In this and any following and other embodiments of the present invention the construction (1) would comprise a surface being the interlink, or connection, to the externals, such as one having a surface geometry that is to be changeable such as to adapt the surface geometry to some present conditions of the externals, such as exampled and not limited to the aerodynamics of a wind mill wing adapting to the present wind conditions. The surface geometry then depends on the configuration of the support structure (12) that again depends on the states of activation of the transducers (11), as also described above. This surface may be a cover at least party enclosing the support structure (12) (and optionally transducers (11)) and / or may partly be composed by at least some of the transducers (11) themselves. Fig. 4 illustrates an alternative embodiment where the construction (1) is formed of a plural of support structures (12) connected in succession by flexible segments (20) formed a flexible connections (20b) in a manner as illustrated where a 'rounded' connector (17) of one support structure (12) is supported on a platform (18) of a suitable shape of a neighbouring support structure (12) etc., so that the connector (17) may 'roll' on the platform (18) as a response to the actual states / elongations of the individual transducers (11), or sub-transducers (11a, 11b). This illustrates one example where flexible segment (20) is positioned such that the relative rotation is given by one support structure (12) relative to another support structure (12), the shapes and relative position of each first member (13) to the associated second member (14) being unaffected.

When the lengths of the transducers (11) changes, the equilibrium defined by the states of the transducers (11) are changed and the rotations of the individual supporting structures (12) will change accordingly as they 'roll' on the platforms (18) to tilt relative to the neighbouring supporting structures (12), this not illustrated in Fig. 4.

Figs. 5A and 5B illustrate an alternative setup where surface is not formed of transducers (11). In this example of Fig. 5A the transducer (11) is connected to the first member ( 3) at its first end, and to a spring element (19) at its second end. The spring is further fixed the second member (14) and to a cover skin (21), the cover skin (21) forming a flexible segment (20) as a flexible connection (20c) to the first member (13) in a manner where the cover skin (21) is free to form at least some rotation around a point defined by the flexible connection (20). The spring element ( 9) is biased such that it tends to stretch the transducer ( 1) to a longer length. When activated, Fig. 5B, the elongation of the transducer (11) and the biasing of the spring will form a rotation of the cover skin (21) around the flexible connection (20c).

In this example the rotation defined by the flexible segment (20) is of an external structure, the cover skin (21), relative to the second (14) (and also first (13)) member.

Fig. 6A illustrates a related setup to the one of Fig. 4. Again the construction (1) is formed of support structures (12) connected in succession by flexible segments (20), in this example these being pivot connections (20d) as they are well known in the arts, again the connection is in a manner where two connected neighbouring support structures (12) are free at least to some degree to rotate mutually independently around the pivot.

Each support structure (12) comprises a first member (13) and a second member (14), where the second members (14) again are adapted for holding the transducers (11) at a distance to the respective first members (13).

Transducers (11) are connected to the second members (14) in such a manner that a transducer (1 ) attached at each opposite sides of the first member ( 3) extends to second member (14) of a neighbouring support structure (12) where it is attached too. Since each of the support structures (12) is connected to neighbouring support structures (12) in a pivot (20d) manner and being able to rotate mutually independently around the pivot (20d), then the actual relative rotation of the neighbouring support structures (12) is given by the actual and relative lengths of the individual transducers (11). Fig. 6B illustrates this alternative manner to fix the transducers (11) to the second members (14), where the transducers (11) are formed of film- transducers (9) wrapped, or rolled, a number of times around bars (22) of the second members (14), and where the actuator is adapted for a deflection in directions as given by the arrows. Fig. 7 shows another alternative embodiment of the present invention, where the construction (1) rather than being formed by a number if support structures (12) positioned in succession, then the support structure (12) rather constitutes one first member (13) and a number of second members (14) attached thereto, the first member (13) comprising a number of flexible segments (20e) either in the shape of a number of flexible sections or because the whole of the first member (13) is made of a flexible material, perhaps a shape-memory material. Figs. 8 and 9 illustrate two further alternative embodiments especially suited for transducers (11) formed as the self-supported rolled structured transducers (6a- 6c) illustrated in Figs. 2A - 2C. In the illustrated embodiments the first elements (13) are fixed to at least two second elements (14) in a flexible segment (20) manner, such as by pivot connections (20d), and where the transducers (11) extends from a second element (14) of one support structure (12) to the second element (14) of a neighbouring support structure (12). In these embodiments the transducers themselves forms part of the stiffness of the construction of the construction (1). Any embodiments of the present invention may further comprise any needed means such as further stiff or spring elements and the like to bias and / or to support the construction (1), such as the whole of the structures and / or support and / or basis individual elements, such as support structures (12), first elements (13), second elements (14), the cover skins (21), etc. The construction (1) of the present invention may be covered with one or more layers of surface material, the cover skin (21), wholly or partly covering and / or enclosing the transducers (11) and support structures (12), where such materials are chosen according to the conditions of the environment where the construction is to operate. Such materials will be well known to a craftsman. The surface material(s) naturally would have to be such that they are able to adapt to the changing forms and shapes of the construction (1).

In one embodiment the material(s) of the cover skin (21) comprises sections of the same film materials as used to form the transducers (11), or even is the transducers ( ) attached to the surface structure (12), such as e.g. seen in Figs. 3A and 3B. Since the films forms capacitive elements adapted to deflect when activated, they in the same manner their capacitive constant will change if they are stretched due to e.g. mechanical forces affecting them. This may be measured so that the states of the films are sensed. In this manner a cover may be formed being able to sense external conditions as they affect the

construction over its surface, and the activation states of the transducers (11) may then be changed as response to this. The needed electronics etc. needed as it will be recognized and known by a craftsman naturally would have to be included to the construction (1).

One non-limiting example of use of the present invention, is systems where the surface of the construction is to be adapted to some aerodynamic conditions, such as for example the blades of wind mills, fans, wings, wing flaps, propellers etc. However, the present invention would apply to any construction where some adaptation of its shape would be required or desired.

The present invention is not limited to one of the embodiments, but any number of and combination of embodiments into the same construction would also apply.

Fig. 10A illustrates a different setup of the same invention, where not only the ends of the transducers (11) are attached to the support structure (12), but rather a whole surface (30) of the transducer if fixed to it, or any section of it. In the figure the transducer (1 ) is such that it expands in at least one direction when activated, such as illustrated by arrow (31). If the support structure (12) is such that it is flexible to bend etc. in any manner, but not to contract or expand its length, unlike the transducer (11), then a change of the length in a direction of the transducer (11) will be transferred from the surface (30) to the support structure (12), and since this cannot contract or expand it will react by changing the curvature. This is also illustrated in Fig. 11 A, 11B and 11 C, where Fig. 11A illustrates the system (1) in one configuration of the support structure (12) having a plural transducers (11) such as in parallel as illustrated, but any configuration of placing and shaping the transducers (11) would also apply, and also having transducers (11) at both sides as in Fig. 10B optionally having different shapes and / or orientation. Figs. 11 B and 11 C illustrates the system (1) in one configuration of the support structure (12) for a configuration as in Fig. 11A with the illustrated or any other configuration of transducers (11), where depending to the actual state of activation of the transducer(s) (11) the bending of the support structure (12) has changed from Fig. 11 B to Fig. 11C.

Fig. 10B illustrates a system as in Fig. 10A only having transducers at both sides of the support structure (12). The transducer (11) may be a laminate of a number of individual film

transducers (9), as also described in relation to Fig.1 , layered together and fixed at least in specific sections, as also illustrated, thus forming a transducer (11) with operating as the added number of individual film transducers (9), this is also referred to as monolithic transducers. The transducer (11) may be one single transducer (e.g. of the laminated kind as described above) or may be a number of individual transducers being connected to the surface of the support structure (12) thus making it possible to have very different characteristics of the bending of it over its extension.

These different transducers (11) may also have very different configurations and / or characteristics. Configurations in the present context means such as being flat, single individual film transducers (9) or transducers (11) laminated by layers of individual film transducers (9), folded, rolled etc.,

Characteristics in the present context means they react differently to being stimulated, where this could be due to having different number of layers, due to having different configurations, different dimensions (length, diameter, width etc.), having different conductive layers (different materials, different sizes / extensions etc.), having different shapes or dimensions of corrugations, different polymer materials etc., and any number and permutation thereof.

Any number of different kinds of transducers having different configurations and / or characteristics may be attached to the support structures (12) of any embodiments. Transducers (11) may also be attached to any support structure (12) of any embodiment with different strains, where this means that the un-activated transducers (11) may be fixed to the support structure (12) in a stretched condition, where they have been stretched to a length longer than their rest un- activated length. This is also referred to the transducers (11) being pre-strained.

One key aspect of one embodiment of the present invention very unlike e.g. the system described in US 2004/0217671 is to attach a plural of individual transducers (11) to the support structure. In US 2004/0217671 an actuator formed of a rolled electroactive polymer and where to a mechanical linkage is connected. These actuators then have separate active areas operating individually as separate actuators. This however has the disadvantage that these active areas are formed within the same electroactive polymer film thus reducing the degrees of freedom design the system in that very different transducers (11) may be introduced with different configurations and / or characteristics, as also described above, but also that transducers ( 1) may be attached with very different stains, or pre-strains. This is not possible when all the actuators are formed within the same rolled sheet of polymer.

This thus also is an embodiment of the present invention relating to any of the previous embodiments, that at least two transducers (11) are attached with different strains, or pre-strains.

It should also be noted that though many of the figures shows 2D-configurations of the constructions (1), but naturally the support structures (12) may extend in any directions in space.

Fig. 12 just illustrates and even more complex change of the configuration of the system of Fig.11 B.

Claims

1. A construction (1) comprising a a support structure (12) that is adapted to change its configuration, and where at least one transducer (11) is connected to the support structure (12) in such a manner that the actual configuration of the support structure (12) relates to the actual activation of the individual transducers (11), and where the transducers ( 1) are made as a laminate of films of a dielectric polymer material arranged between first and second layers of an electrically conductive material so that it is elastically deformable in response to an electrical field applied between the layers and these laminates are arranged such such that a change of the state of activation of a transducer (11 ) induces a change of a dimension of the transducer ( ), characterized in that the support structure (12) is adapted to change a surface geometry.

2. A construction (1) according to claim 1 , where the construction (1) has a cover skin (21) at least partly enclosing a support structure (12), and where the cover skin (21) is connected to the support structure (12) in a manner where the outer geometry of the cover skin (21) at least partly is related to the actual configuration of the support structure (12).

3. A construction (1) according to claim 2, wherein the cover skin (21) at least partly is made of the same film materials as used to form the at least one transducer (11), and where they are adapted to operate as sensors of their own actual length.

4. A construction (1) according to claim 3, wherein at least some of the transducers (11) forms at least part of the cover skin (21).

5. A construction (1) according to one of claims 1 to 4, wherein the surface (30) of at least one transducer (11) is fixed to the surface to a plane support structure (12).

6. A construction (1) according to one of claims 1 to 5, where at least two individual transducers (11) are connected to the support structure (12) in a manner where the configuration of the support structure (12) is related to their relative states to each other.

7. A construction (1) according to claim 6, where the at least two individual transducers (11) are connected to the support structure (12) with different strains.

8. A construction (1) according to any preceeding claim, where the at least two individual transducers (1 ) have different actuation characteristics.

9. A construction (1) according to any of the preceding claims, where the film is provided so that it is easier to deform in one, compliant, direction than in other directions, the activation of the transducers ( 1) being the electrical field, and wherein this one compliant direction can be provided by a waved surface structure by which the laminate can be expanded in the compliant, longitudinal, direction.

10. A construction (1) according to any preceding claim, where the support structure (12) comprises at least one flexible segment (20) being a section, point or joint where the support structure (12) is able to form a rotating, bending, leaning and / or tilting movement.

11. A construction (10) according any of claims 2-10, wherein the support structure (12) comprises at least one first element (13) and at least one second element (14), where the first (13) and (14) elements are adapted to extend the cover skin (21) in mutual different directions.

12. A construction (1) according to any preceding claim, where the construction (1) comprises at least two support structures ( 2) connected by a flexible segment (20) such that two neighbouring support structures (12) are able to change their configuration relative to each other.

13. A construction (1) according to claim 11 or 12, wherein the flexible segment (26) is positioned such that the change of configuration is of a first element (13) relative to a second element ( 4).

14. A construction (1) according to claim 12 or 13, wherein at least one transducer ( ) is connected to two support structures ( 2).

15. A construction (1) according to any of the preceding claims, where the construction (1) comprises one support structure ( 2) with at least two flexible segments (20), the change of configuration being a change of the shape of the support structure ( 2) itself. 6. A construction (1) according to claims 4, wherein at least some of the transducers ( 1) forms at least part of said surface. 7. A construction (1) according to any preceding claim, wherein the outer geometry defined by the cover skin (21) forms an aerodynamic profile.