WO2009132652A1

WO2009132652A1 - A valve with an elastomer based valve structure and control system for controlling the valve

Info

Publication number: WO2009132652A1
Application number: PCT/DK2009/000099
Authority: WO
Inventors: Morten Kjaer Hansen; Benjamin Thomsen; Michael Tryson; Mohamed Benslimane; Hans-Erik Kiil
Original assignee: Danfoss A/S
Priority date: 2008-04-30
Filing date: 2009-04-30
Publication date: 2009-11-05

Abstract

The invention provides a valve with an orifice (6) and a power actuated valve structure (7) for varying a flow area of the orifice. The valve structure provides two way communication so that the orifice may be changed by application of a bias voltage between two conductive layers arranged on opposite sides of a film of a dielectric elastomer material (2), and such that a pressure in the orifice may deflect the film and thereby cause a change in capacitance of the capacitor structure defined by the conductive layers and the film.

Description

A VALVE WITH AN ELASTOMER BASED VALVE STRUCTURE AND A CONTROL SYSTEM FOR CONTROLLING THE VALVE

INTRODUCTION

The invention relates to a valve with an orifice and a power actuated valve structure for varying a flow area of the orifice.

BACKGROUND OF THE INVENTION

Power transducers are available for various kinds of valves used in industry. Known transducers are frequently powered by electric solenoids, by hydraulics, and by pneumatics. Solenoids are simple, cheap and fairly reliable in discrete, stepwise, control of valves to provide different flow characteristics, typically on/off control.

Sometimes, power operated valves are controlled randomly. As an example, the power may be adjusted manually or by very simple control systems capable of operating the valve structure in a certain time-step which thereby provides a certain movement of the valve structure and thus a certain variation of the flow area through the orifice. Since the resistance against changes to the flow area depends on various flow conditions in the valve, e.g. on a pressure difference over the orifice etc. it is difficult or impossible to determine the variation of the flow area except for the situations where the valve structure is moved to a fully open or closed position, and such valves are therefore unsuitable for applications in which an exact setting of a flow resistance through the valve is desired.

To improve controllability of the flow resistance, valves exist in which the positioning of the valve structure and thus the variation of the flow area is guided by various sensors. In such valves, however, the controllability of the flow resistance depends on the precision and reliability of the sensors, and typically the valves becomes expensive and sensitive.

DESCRIPTION OF THE INVENTION

It is an object of the invention to improve the existing power actuated valves and to provide a simple and yet reliable and potentially cheap way of controlling setting of power actuated valves. According to a first aspect, the invention provides a valve of the kind mentioned in the introduction in which the valve structure comprises first and second layers of an electrically conductive material, a control system for applying an electrical potential between the layers, and a film of a dielectric elastomer material arranged between the layers and being elastically deflectable in response to the electrical potential, wherein the film is arranged so that the deflection thereof causes the variation of the flow area and so that it can be deformed by a pressure in the orifice.

Due to the two-way communication provided by the claimed valve, the size of the flow area may be changed and determined by controlling and monitoring the electrical potential between the layers and no additional, separate, sensors are necessary to provide various control information and thus to enable a more exact setting of the valve.

The film and the conductive layers may be provided in various geometries and they may be bonded in various ways. In the following, the film and the conductive layers will be referred to as a laminate.

By deflect is herein meant to bend or to deform under influence of a pressure. The film is deflected as the layers are repelled from each other or attracted towards each other when an electrical potential is 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_r, 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 μm to 0.1 μm, such as in the range of 0.02 μm to 0.09 μm, such as in the range of 0.05 μm to 0.07 μm. 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 μm and 200 μm, such as between 20 μm and 150 μm, such as between 30 μm and 100 μm, such as between 40 μm and 80 μm. 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 10^~2 Ω cm such as in the order of 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 for changing the size of the orifice 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 Ω 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. The laminate may preferably be provided with a structure whereby it achieves an anisotropic deflection characteristic meaning that it deflects mainly in one specific direction - this compliance in one direction is achievable in various ways, e.g. by providing in the film, a surface pattern. The surface pattern may comprise corrugations which render the length of the electrically conductive layer in a lengthwise direction, longer than the length of the composite as such in the lengthwise direction. 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 force which is required to deform the film, the corrugated shaped 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. I.e. the electrically conductive layers may be shaped from the film when applied to 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 neighboring 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 μm and 20 μm, such as between 1 μm and 15 μm, such as between 2 μm and 10 μm, such as between 4 μm and 8 μm.

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 μm to 20 μm, such as in the range of 2 μm to 15 μm, such as in the range of 5 μm to 10 μm.

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, i.e. the composites form together a structure with an elastomer material with dielectric properties between two electrically conductive layers. 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 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.

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 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.

The laminate may have been rolled to form a coiled pattern of dielectric material and electrodes. In the present context, the term 'coiled pattern' should be interpreted to mean that a cross section exhibits a flat, spiral-like pattern of electrodes and dielectric material.

The rolled laminate may form a tubular member so that the rolled laminate defines an outer surface and an inner surface facing a hollow interior cavity of the rolled laminate, and the laminate thereby forms a conduit which may form part of a path through the valve.

By rolling the laminate around an axis which is perpendicular to the crests and troughs of the previously explained waved pattern, the tubular structure becomes deformable mainly in the direction of the axis around which the laminate is rolled. In the following description this will be referred to as a laminate rolled for elongation.

By rolling the laminate around an axis which is parallel to the crests and troughs of the waved pattern, the tubular structure becomes deformable mainly in a direction perpendicular to the axis around which the laminate is rolled. In the following description, this will be referred to as a laminate rolled for expansion.

The 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 laminate, such as at least 75 times, such as at least 100 times. According to the present invention, this increased area moment of inertia is preferably obtained by rolling the laminate with a sufficient number of windings to achieve the desired area moment of inertia of the rolled structure. Thus, even though the unrolled laminate 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 laminate can be obtained simply by rolling the laminate with a sufficient number of windings. The area moment of inertia of the rolled laminate should preferably be sufficient to prevent buckling of the rolled laminate during normal operation.

Thus, the rolled laminate may have a number of windings sufficient to achieve an area moment of inertia of the cross section of the rolled laminate which is at least 50 times an average of an area moment of inertia of the cross section of an unrolled laminate, 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 rolled structure 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 rolled structure 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.

The valve may include a valve housing forming an inlet for entering fluid into the valve, an exit for exit of the fluid from the valve, and a path between the inlet and the exit. The orifice may be formed between an inner surface of the path and the laminate itself. As an example, the laminate may be rolled for elongation or expansion, and it may simply be arranged in the path and thereby provide an orifice of a variable size upon deflection of the film.

Alternatively, the laminate may be arranged to move an element which provides the variation in the size of the orifice. As an example, the valve and movable element may form a ball-valve, a butterfly-valve, a gate-valve, a diaphragm- valve, a rotary-valve, a needle-valve, a pinch-valve, a spool-valve, flapper-nozzle valve, or a seat-valve. The housing may be provided in any kind of material, e.g. in a hard polymeric material, in metal such as brass or aluminum, or even in a soft polymeric material such as silicone etc. The valve may also include micro channels and may e.g. comprise a silicon wafer in which the path and the orifice are made in microscopic scale.

The control system may be adapted to apply a known voltage between the layers. The electrical potential between the two layers creates a force of attraction or repulsion between the layers, and the film therefore deflects. In the following, the voltage which is applied to make the film deflect and thus to make the flow area change, is from now called the actuation voltage. Since the distance between the electrically conductive layers changes when the film deflects, the capacitance of the laminate also changes. By determining the capacitance, the degree of deflection can therefore be determined, and based on the degree of deflection, the area of the orifice can be determined. It may therefore be desired to provide the valve so that there is always a fixed ratio between the deflection of the film and the area of the orifice. To determine the capacitance while the actuation voltage is applied, a measuring AC signal may be injected into the laminate and standard methods for measuring capacitance may be applied. As an example, the capacitance may be determined periodically, e.g. with a fixed frequency, e.g. every second or even more often.

If the control system is adapted for storage of first information relating to a relationship between the area of the orifice and the determined capacitance, it may be a feature of the control system, from the first information and the determined capacitance, to determine the area of the orifice. The control system will be described further with reference to the drawings.

If the control system is adapted for storage of second information relating to a relationship between an applied bias voltage, a corresponding area of the orifice, and a corresponding differential pressure over the orifice, the control system may determine, from the second information, the applied voltage, and the determined capacitance, a differential pressure over the orifice.

To determine the second information, the control system may be adapted to receive first calibration information describing an actual differential pressure over the orifice, and to determine the second information based on the first calibration information, the applied voltage and the determined capacitance.

The control system may be adapted for storage of third information which describes a characteristic of a fluid which flows through the orifice, and to determine a flow rate of the fluid through the orifice based on the third information, the determined differential pressure over the orifice and the determined area of the orifice. To determine the third information, the control system may be adapted to receive second calibration information describing an actual flow of a fluid through the orifice, and to determine the third information based on the second calibration information, the determined differential pressure over the orifice, and the determined area of the orifice.

In facilitating use of the valve for controlling a flow of a fluid, e.g. in combination with a thermal control system for heating or cooling purposes, the control system may use the second information and the determined capacitance, to determine a voltage which, when applied between the conductive layers, deforms the film to an extend whereby a specific user requested differential pressure over the orifice is achieved. In a corresponding manner, the control system may receive a user requested flow rate of a fluid through the orifice, and by use of the third information and the determined capacitance, the control system may determine a voltage and a time duration in which this voltage must be applied between the conductive layers to obtain the requested flow rate.

DETAILED DESCRIPTION OF THE INVENTION

In the following, a preferred embodiment of the valve and particularly of the control system will be described in further details with reference to the drawing in which:

Figs. 1 and 2 illustrate a valve according to the invention in an open and a closed configuration;

Fig. 3 illustrates a laminate for a transducer;

Figs. 4 and 5 illustrate rolling of the laminate for elongation and expansion, respectively;

Fig. 6 illustrates an alternative way of making a rolled transducer by stacking of two composite structures; Fig. 7 illustrates schematically, a control system for a valve;

Fig. 8 illustrates in a diagram a ratio between capacitance of the transducer and deflection of the film; and

Fig. 9 illustrates in different diagrams each being for a specific pressure, a ratio between a bias voltage and a deflection of the film.

As illustrated in Fig. 1 , the valve 1 , comprises a transducer 2 arranged in a housing 3 which forms an inlet 4 for entering fluid into the valve, and an exit 5 for exit of the fluid from the valve. A path 6 extends between the inlet and the exit, and a valve member 7 is arranged to control flow conditions in the path. The valve member 7 is moved by the transducer 2.

The transducer is made from 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 is rolled and therefore has a tubular shape with wall around an inner cavity 8.

First and second connectors 9, 10 are provided to apply the electrical field to the layers.

A fluid flow through the valve is symbolized by the bolded arrows in Fig. 1 , and the deformation of the dielectric polymer material influences the flow conditions by changing the area of the passage between the inner wall of the housing 3 and the valve member 7.

The valve opens and closes by movement of the valve member 7 in the direction of the path 6. This is enabled in a very simple manner by arrangement of the transducer inside the path, and this is possible due to the very simple and robust structure of the transducer. The laminate is provided so that it is easier to deform in one, compliant, direction than in other directions. The laminate 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. 3, this characteristic can be provided by a waved surface structure by which the laminate can be expanded in the compliant, longitudinal, direction indicated by the bold arrows 11 , 12 by elastic deformation of the polymer material 13, while the electrically conductive material which is applied to the waved surface is straightened out rather than stretched.

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 14, 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.

The laminate structure illustrated in Fig. 3 is rolled to form a tubular actuator. The laminate may be rolled around an axis extending in parallel with the crests and troughs as shown in Fig. 4. This provides radial expansion of the tubular actuator upon deformation of the polymer - herein referred to as "rolled for expansion". The laminate may also be rolled around an axis being perpendicular to the crests and troughs as shown in Fig. 5. This provides axial elongation of the tubular actuator upon deformation of the polymer - herein referred to as "rolled for elongation". When the laminate is rolled, the two opposite layers of a conductive material, in the following referred to as the top and bottom layer, must be electrically separated from each other by an additional film of a non conductive material.

Fig. 6 illustrates a laminate which is rolled to form a tubular structure and which comprises a multilayer structure with at least two composites. The composites are identical and each comprises a film 15 made of a dielectric polymer material and having a front surface and a rear surface, the front surface comprising a surface pattern of raised and depressed surface portions, and a first layer 16 of an electrically conductive material being deposited onto the surface pattern. When such two composites are arranged on top of each other, a laminate with a film of a polymer material between two electrically conductive layers is formed. The second film provides isolation between the top and bottom layers.

The transducer in Fig. 1 is rolled for elongation, and an electrical field applied between the two connectors 9, 10 therefore results in a change of the length of the transducer and thus a change of the distance between the valve member 7 and the inner surface of the housing 3. Accordingly, the illustrated valve provides a ratio between deformation of the film and a flow condition, namely a flow resistance, in the path.

In addition to the use of the transducer for controlling the flow through the valve, the transducer may also be used for determining pressure of a fluid which flows in the valve and thus, for a known flow system, for determining flow speed etc. for the system in question. This will be described in further details with reference to Fig. 7 illustrating an electrical diagram of a control system for controlling operation of the transducer in Fig. 1.

The control system utilizes the structure of the transducer to provide a close loop control of the valve with use of no additional sensors. The control process is based on the structure of the laminate where a bias voltage is applied to the conductive layers and the film therefore deflects whereby the capacitance of the laminate changes. The film of the valve is also arranged so that a change to a pressure difference over the orifice changes the deflection of the film and therefore also changes the capacitance. The control system can therefore determine an actually obtained area of the orifice by finding the capacitance.

Fig. 7 illustrates an electrical diagram of a control system with a closed control loop which a ratio between capacitance and orifice effective flow area forms a reference characteristic for the valve in a specific situation, e.g. for a valve which is not subjected to a fluid pressure. The control system is capable of applying a known bias voltage between the layers and simultaneously to determine the capacitance of the laminate. According to the reference characteristic for the valve, the applied bias voltage should provide a theoretical orifice effective flow area and thus a theoretical capacitance of the laminate. By the simultaneous measurement of the capacitance, the control system is capable of deriving an actually obtained orifice effective flow area and to adjust the bias voltage until a desired flow area is obtained.

The control system comprises data storage capacity 17 in which a ratio between an orifice effective flow area versus actuator capacitance is specified. In a most simple embodiment, the ratio is stored as discrete values. A computing device 18 communicates with the data storage 17 and determines based on a desired orifice area, a theoretical bias voltage 19 by which the film is theoretically deflected to cause the desired orifice area. The computing device communicates the theoretical bias voltage to an error correction device 20 from which the bias source 21 receives input for setting a high voltage bias signal to the actuating device 22. The actuating device 22 comprises a laminate of the kind already described, and in the diagram, such a laminate corresponds to a capacitor.

In addition to the bias signal, the bias source 21 provides, via the connection 23, a low voltage test signal which is applied to the laminate simultaneously with the bias signal. The filter 24 extracts the low voltage signal from the high voltage signal, and the capacitance measuring device 25 determines the actual capacitance of the laminate actuating device 22.

The capacitance is determined while the film is deflected by the high voltage bias signal and therefore, the capacitance indicates how much the film was deflected by the bias signal. In the illustrated embodiment, the capacitance is converted into feedback signal 26, in this case in form of a comparative bias voltage, i.e. a bias voltage which, with the reference characteristics of the valve, would have provided that deflection of the film which actually occurred and which was determined by measuring of the capacitance. The comparative bias voltage is subtracted from the determined bias voltage in the correction device 20 and the resulting corrected bias voltage 27 is received by the bias source 21.

In general, the feedback signal 26 can be manipulated in various ways via amplifies and converters of different kind.

The capacitance measuring structure may be implemented in a regular computer system, and it may include, without being limited to, any of the following measuring principles: AC Power, AC Voltage, RMS Power, Peak detectors, Log detectors, RSSI, Impedance, Pulse Measuring circuit or Spectral Measuring circuit.

The setting voltage that provides the high voltage bias signal to the actuator is typically greater than 300 Volts and less than 10 kV. An example would be 500 to 2.5 kV high voltage. The Low voltage test signal would typically be between 1 and 10 V, an example would be 3 to 5V. The High voltage actuator control signal is typically DC to low frequency less than 1 KHz repetition rate, an example would be 50 Hz. The AC test signal is generally at a frequency rate considerably higher than the actuator, usually by a factor of 10 away from the actuator repetition rate. An actuator with a 2.5 kV signal, with a 10 Hz repetition rate, could have an AC test signal of 5V and 1 KHz repetition rate.

The data processing structure may further be adapted to use the determined area of the orifice to provide flow specific information. Such information may be based on information in a second data file which describes a ratio between the area of the orifice and pressure drop over the valve, flow speed for a specific fluid etc.

Furthermore, the control system may be adapted to control the valve for dosing purposes. As an example, the control system may be capable of reading a user request with respect to the flow. As an example, this may be a desired pressure drop, a desired flow speed, or a desired dose of a fluid medium which is released through the valve. Based on the request, the control system controls applies a bias voltage to the first and second electrically conductive layers while the capacitance is measured. In this way the area of the orifice is determined and by use of the data in the first and second data files, the request may be fulfilled.

Fig. 8 shows a graph which illustrates a ratio between deflection of the film and thus the size of the aperture along the X-axis and capacitance of the transducer along the Y-axis. The graph is for illustrative purpose only, and the exact ratio depends on details of the transducer.

Fig. 9 shows 4 graphs illustrating four different ratios between bias voltage along the X-axis and deflection of the film along the Y-axis. The graph illustrates the ratio for an unloaded transducer - i.e. a transducer in a situation with no pressure difference across the valve. Graph b illustrates the ratio for a relatively small load, graph c for a larger load, and graph d for an even larger load applied to the transducer.

The graphs in Fig. 8 and 9, and thus the information necessary to control the valve may be determined experimentally by various tests where a bias voltage is applied to a transducer which is loaded by different pressures. The graphs may also be found analytically by simulation flow conditions etc. for a valve. The graphs may represent discrete values of deflection to capacitance or bias voltage to deflection, or a control function may be formed which provides a continuous ratio between the values in question.

For control of the valve, the control system may derive from the measured capacitance, a specific deflection of the film. From the known bias voltage and the specific deflection, the control system may determine which load and thus pressure which is applied on the valve. By use of a model of the flow and pressure conditions for a valve which operate on a specific fluid, the control system may further provide specific flow data such as a flow rate etc.

Claims

1. A valve with an orifice and a power actuated valve structure for varying a flow area of the orifice, the valve structure providing two way communication so that the orifice area may be changed by change of a bias voltage between two conductive layers arranged on opposite sides of a film of a dielectric elastomer material, and such that a pressure in the orifice may deflect the film and thereby cause a change in capacitance of a capacitor structure defined by the conductive layers and the film.

2. A valve according to claim 1 , wherein the control system is adapted to apply a known bias voltage between the layers and to determine a capacitance of the laminate.

3. A valve according to claim 2, wherein the control system is adapted for storage of first information relating to a relationship between the area of the orifice and the determined capacitance, and from the first information and the determined capacitance to determine the area of the orifice.

4. A valve according to claim 2 or 3, wherein the control system is adapted for storage of second information relating to a relationship between an applied voltage, a corresponding area of the orifice, and a corresponding differential pressure over the orifice.

5. A valve according to claim 3 and 4, wherein the control system is adapted to determine from the second information, the applied voltage, and the determined capacitance, a differential pressure over the orifice.

6. A valve according to claim 5, wherein the control system is adapted to receive first calibration information describing an actual differential pressure over the orifice, and to determine the second information based on the first calibration information, the applied voltage and the determined capacitance.

7. A valve according to claim 5 or 6, wherein the control system is adapted for storage of third information which describes a characteristic of a fluid which flows through the orifice, and to determine a flow rate of the fluid through the orifice based on the third information, the determined differential pressure over the orifice and the determined area of the orifice.

8. A valve according to claim 7, wherein the control system is adapted to receive second calibration information describing an actual flow of a fluid through the orifice, and to determine the third information based on the second calibration information, the determined differential pressure over the orifice, and the determined area of the orifice.

9. A valve according to any of claims 5-8, wherein the control system is adapted to receive a user requested differential pressure over the orifice, and to apply a voltage between the first and second layers in accordance therewith.

10. A valve according to any of claims 6-9, wherein the control system is adapted to receive a user requested flow rate of a fluid through the orifice, and to apply a voltage between the first and second layers in accordance therewith.