GB2376795A

GB2376795A - Electro-mechanical control using an electro-active device

Info

Publication number: GB2376795A
Application number: GB0115069A
Authority: GB
Inventors: David Pearce; Gareth Mckevitt; Anthony Hooley; Ursula Ruth Lenel
Original assignee: 1 Ltd
Current assignee: 1 Ltd
Priority date: 2001-06-20
Filing date: 2001-06-20
Publication date: 2002-12-24
Anticipated expiration: 2021-06-20
Also published as: GB2376795B; GB0115069D0

Abstract

Various electro-mechanical devices, in particular a valve, a mechanical switch, a relay, a circuit breaker, a transformer, a limiter and an electrical meter, use an electro-active device 11 for operation. The electro-active device 11 comprises an electro-active structure in the form of a continuous electro-active member 12 curving in a helix around a minor axis 13 which is in itself curved for example in a helix around a major axis 14. The continuous member 12 has a bender construction of a plurality of layers 21 and 22 including at least one layer of electro-active material so that it bends, on activation, around the minor axis 13. Concomitantly with the bending, the electro-active structure twist around the minor axis. Concomitantly with that twisting, relative displacement of the ends 16 of the device 11 occurs due to the combination of the twisting around the minor axis 13 and the fact that the minor axis 13 is curved. The electro-active device 11 has the advantage of providing a relatively high displacement which allows its application in the electro-mechanical devices in question, whilst being relatively compact and lightweight as compared to electromagnetic solenoid arrangements which might otherwise be used.

Description

Electro-Mechanical Control Using An Electro-Active Device The present invention relates to various electro-mechanical devices, in particular a valve, a mechanical switch, a relay, a circuit breaker, a transformer and a limiter, which are operated by a particular form of electro-active device.

Electro-mechanical devices are devices in which mechanical operation is driven by an electric current or voltage. Most large-scale, known electro-mechanical devices are based on electro-magnetism using a coil or solenoid, for example to move a magnetisable translator or magnetically linked to another coil to create a transformer. Such devices suffer from the problem that the coils needed are relatively large and bulky. Also the creation of magnetic fields which is inherent in such devices can create problems in some applications.

Electro-active devices using electro-active materials are known. However such electro-active devices have not found practical application in many large-scale devices, principally because the electro-active devices do not create sufficient displacement as compared to that achievable using an electro-magnetic coil.

Electro-active materials are materials which deform in response to applied electrical conditions or, vice versa, have electrical properties which change in response to applied deformation. The best known and most developed type of electro-active material is piezoelectric material, but other types of electro-active material include electrostrictive material and piezoresistive material. Many devices which make use of electro-active properties are known.

The most simple type of piezoelectric device is a block of piezoelectric material activated in an expansion-contraction mode by applying an activation voltage in the direction of poling. However, as the piezoelectric effect is small, of the order 10'' m/V, the change in dimensions is relatively small, typically less than a micron. Therefore, more complicated electro-active structures have been developed to achieve larger displacements.

A known electro-active structure is the bender construction, for example a bimorph bender construction. With a bender construction, the electro-active

structure comprises a plurality of layers at least one of which is of electro-active material. On activation, the layers deform with a differential change in length between the layers for example one layer expanding and another layer contracting.

Due to the layers being constrained by being coupled to one another, the differential change in length causes the bender to bend perpendicular to the layers. Accordingly there is a relative displacement of the ends of the structure. However, the relative displacement does not follow a linear path in space. As the structure bends and the degree of curvature increases, the relative displacement of the ends follows a curve in space. Furthermore, to achieve relatively large displacement, it is necessary to increase the length of the structure which therefore becomes inconvenient. For

example, to achieve a displacement of the order of 0. 1mm with a bimorph bender construction, a structure of length around 5cm is typically needed.

It would therefore be desirable to provide, for use in operating an electromagnetic device, an electro-active device which allows for large linear displacements on activation but which is relatively lightweight and compact.

According to a first aspect of the present invention, there is provided a valve including a valve member which is movable to control fluid flow through the valve and an electro-active device coupled to move the valve member on activation, the electro-active device comprising an electro-active structure extending along a curved minor axis and arranged, on activation, for the structure to twist around the minor axis and concomitantly for relative displacement of the ends of the structure to occur for moving the valve member.

According to a second aspect of the present invention, there is provided a mechanical switch including a switch member having at least one stable position from which the switch member is movable, and an electro-active device coupled to move the switch member, the electro-active device comprising an electro-active structure extending along a curved minor axis and arranged, on activation, for the structure to twist around the minor axis and concomitantly for relative displacement of the ends of the structure to occur for moving the switch member.

According to a third aspect of the present invention, there is provided an

electrical relay including an electrical contact which is movable to open and close a circuit path, and an electro-active device coupled to move the electrical contact, the electro-active device comprising an electro-active structure extending along a curved minor axis and arranged, on activation, for the structure to twist around the minor axis and concomitantly for relative displacement of the ends of the structure to occur for moving the electrical contact.

In the electrical relay the electro-active device is in series with the circuit path so that the electro-active device constitutes a circuit breaker.

According to a fourth aspect of the present invention, there is provided a transformer comprising two electro-active devices comprising an electro-active structure extending along a curved minor axis and arranged, on activation, for the structure to twist around the minor axis and concomitantly for relative displacement of the ends of the structure to occur, the two electro-active devices being coupled together so that displacement of one electro-active device on electrical activation by application of an input alternating voltage mechanically activates the other electroactive device to generate an output alternating voltage.

The transformer may further comprise a mechanical stop for limiting the relative displacement of the ends of the structures of the electro-active devices to limit the magnitude of the output alternating current so that the transformer acts as a limiter.

According to a fifth aspect of the present invention, there is provided an electrical meter comprising an electro-active device and electrical terminals electrically connected to the electro-active device for receiving an electrical signal, the electro-active device comprising an electro-active structure extending along a curved minor axis and arranged, on electrical activation by application of an electrical signal across the electrical terminals, for the structure to twist around the minor axis and concomitantly for relative displacement of the ends of the structure to occur, one end of the electro-active device being fixed relative to a visible scale and the other end of the electro-active device being coupled to a pointer for indicating the relative displacement on the scale.

Thus the electro-active device may be used to form an electrical meter in which the movement of the device provides a visible indication of electrical current or-voltage in a similar manner to the coil in a conventional moving coil meter.

First, the operation of the electro-active device will be considered. The relative displacement between the ends of the device occurs concomitantly with the twist of the structure around the minor axis on activation, because of the fact that the device extends along a curved minor axis. The electro-active device uses the physical principal that twisting of a curved object causes displacement perpendicular to the local curve, and vice versa displacement of the ends of a curved object causes twisting along its length. The displacement is equivalent to a change in the orientation of the minor axis of the structure relative to its original orientation.

The device uses an electro-active structure which twists on activation.

Considering any given small section of the structure along the curved minor axis it is easy to visualise how twist of that given section rotates adjacent sections and hence relatively displaces them in opposite directions perpendicular to the local curve of the given section, because the adjacent sections extend at an angle to the given section as a result of the curve of the minor axis. Therefore twisting of the given section is concomitant with a relative displacement of the adjacent sections perpendicular to the plane of the curve. The degree of relative displacement is proportional to the degree of curvature in the given section and the magnitude of the twisting. The overall displacement of the device is the combination of the displacement of each section.

Thus the overall displacement on activation is a relative displacement of the ends of the structure.

For minor axes which extend along a regular curve around a major axis, such as along an arc of a circle or a helix, on activation each section produces displacement in the same direction parallel to the major axis. Therefore, the overall relative displacement of the end of the structure is a linear displacement parallel to the major axis. Therefore an electro-active device in accordance to the present invention can produce displacement which is linear in space.

The degree of displacement is proportional to the length of the structure along

the minor axis, because each section of the structure contributes to the overall displacement. Therefore any desired degree of displacement may be achieved by suitable design of the device, in particular by selection of the length of the structure along the minor axis and of the type of structure which controls the magnitude of the twisting-field response.

In summary, the structure of the electro-active device allows the device to provide a linear displacement between the ends of the structure which may be of any magnitude. In accordance with the present invention the electro-active device is used to operate particular electro-mechanical devices, namely a valve, a mechanical switch, a relay, a circuit breaker, a transformer or a limiter, by being coupled either directly or indirectly through a mechanical linkage to an element of the device to be moved. The large displacement which is achievable with the electro-active device allows use in large scale electro-mechanical devices which might otherwise use an electro-magnetic coil. However, as compared to such an electro-magnetic coil the electro-active device in accordance with the present invention has several advantages. Firstly it has a relatively low weight and size. Secondly it does not produce a significant magnetic field. Although a small magnetic field may be created by the current flowing through the electro-active device this is significantly less than a coil in which magnetic fields are generated to drive displacement.

Considering the electro-active device further, as a result of the structure extending along a minor axis which is curved, a relatively compact device may be produced. In general, the curve along which the minor axis extends may be of any shape.

One possibility is for the curve along which the minor axis extends to be planar, for example as the arc of a circle or a spiral. In this case, the displacement on activation occurs perpendicular to the plane of the curve. The thickness of the device in the direction in which relative displacement occurs is merely the thickness of the electro-active structure so a relatively thin device may be produced.

Another possibility is for the curve along which the minor axis extends to be a helix. In this case, each helical turn of the structure contributes towards

displacement in the direction along the geometrical major axis around which the helix is formed. Therefore a large degree of displacement may be achieved proportional to the number of helical turns, therefore producing relatively high displacement for a relatively compact device.

Preferably, the electro-active structure of the electro-active device comprises electro-active portions disposed successively along the minor axis and arranged to bend, on activation, around the minor axis.

The electro-active structure is arranged with portions which bend on activation around the minor axis concomitantly with twisting of the structure around the minor axis. As a result, the electro-active portion may have any construction which bends on activation. The preferred construction is the known bender construction comprising a plurality of layers including at least one layer of electroactive material, preferably a bimorph bender construction having two layers. Such a construction is well known and understood as applied to a straight bender and particularly easy to manufacture. The same benefits are obtained when the bender construction is applied to the portions of the present invention. However, any other construction which provides bending on activation may be used.

Preferably, the electro-active structure comprises a continuous electro-active member curving around the minor axis, said electro-active portions being adjacent finite portions of the continuous member.

This structure is particularly easy to manufacture, for example by winding a deformable continuous electro-active member into shape.

Preferably wherein the continuous electro-active member curves in a helix around the minor axis.

By using a continuous electro-active member which curves in a helix around the minor axis a number of advantages are achieved. Firstly, it is easy to provide a structure which is regular along the length of the minor axis and hence provide the same degree of twisting along the entire length of the minor axis. Secondly, the helix is easy to manufacture, for example by winding a deformable continuous member into shape or by making a helical cut in a tubular electro-active member. Thirdly, the

device is compact as the helical turns of the member around the minor axis may be packed closely together.

However the electro-active structure may alternatively comprise a continuous electro-active member having a different shape which provides for bending around the minor axis concomitantly with twisting around the minor axis. For example it may comprise a continuous member having the shape of a flat member twisted around the minor axis. Furthermore, instead of comprising a continuous electroactive member, the electro-active structure may comprise a plurality of electro-active portions coupled together.

To allow better understanding, embodiments of the present invention will now be described by way of non-limitative examples with reference to the accompanying drawings in which: Fig. 1 is a plan view of a first electro-active device; Fig. 2 is a side view of a second electro-active device; Fig. 3 is a perspective view of a portion of either the first device of Fig. 1 or the second device of Fig. 2; Fig. 4 is a cross-sectional view of a valve; Fig. 5 is a cross-sectional view of bistable switch; Fig. 6 is schematic of a rotary switch; Fig. 7 is a cross-sectional view of a relay; Fig. 8 is a cross-sectional view of a circuit-breaker; Fig. 9 is a cross-sectional view of a portion of the circuit-breaker of Fig. 8 showing the state of the device after dripping: Fig. 10 is a cross-sectional view of a transformer ; Fig. 11 is a cross-sectional view of a limiter ; and Fig. 12 is a side view of an electrical meter.

For clarity, the electro-active device will first be described before describing electro-mechanical devices in which the electro-active device is used.

In the following description, the electro-active devices are described with reference to minor and major axes which are imaginary, but are nonetheless useful

for visualising and defining the devices.

A first electro-active device 1 in accordance with the present invention is illustrated in Fig. 1. The device 1 comprises a structure consisting of a continuous electro-active member 2 curving in a helix around a minor axis 3 so that the structure extends along the minor axis 3. The minor axis 3 is curved, extending in a curve which is an arc of a circle around a geometrical major axis 4 perpendicular to the plane of the minor axis 3, i. e out of the plane of the paper in Fig. 1. As the minor curve 3 is planar, the thickness of the device parallel to the major axis 4 is merely the thickness of the helical structure of the electro-active member 2.

A second electro-active device 11 in accordance with the present invention is illustrated in Fig. 2. The device 2 comprises a structure consisting of a continuous electro-active member 12 to curving in a helix around a minor axis 13 so that the structure extends along the minor axis 13. The minor axis 13 is curved, extending in a curve which is a helix around a geometrical major axis 14. The electro-active device 11 is illustrated in Fig. 2 with a minor axis which extends along of a helix of three turns merely for illustration, any number of turns being possible.

Fig. 3 illustrates a portion 20 of either the continuous member 2 of the first device 1 of Fig. 1 or the continuous member 12 of the second device 11 of Fig. 2.

The construction of the portion 20 being the same for both the first device 1 and the second device 2 the electro-active portion 20 is a finite portion of the continuous member 2 or 12 and hence the electro-active member 2 or 12 may be considered as a plurality of adjacent portions 20 as illustrated in Fig. 3 disposed successively along the minor axis 3 or 13. Hence, the portion 20 extends along part of a helical curve around the minor axis 3 or 13 as shown in Fig. 3.

Fig. 3 illustrates the construction of the electro-active portion 20. This construction is preferably uniform along the entire length of the minor axis 3 or 13 in order to provide uniform properties on activation. Alternatively, the device 1 or 11 may be designed with some variation along the length of the minor axis 3 or 13, either in the construction of the continuous member 2 or 20 or in the shape of the curve of the continuous member 2 or 20 around the minor axis 3 or 13.

The electro-active portion 20 has a bimorph bender construction comprising two layers 21,22 of electro-active material extending along the length of the portion 20. The layers 21,22 of electro-active material both face the minor axis 3 or 13. The electro-active layers 21 or 22 preferably extend, across the width of the portion 20, parallel to the minor axis 3 or 13, although there may be some distortion of the electro-active portion 20 of the continuous member 2 or 12 due to the nature of the curve around the minor axis 3 or 13. Alternatively, the layers 21 or 22 may extend, across the width of the portion 20, at an angle to the minor axis 3 or 13 so that one edge along the electro-active portion 20 is closer to the minor axis 3 or 13 than the opposite edge.

The material of the electro-active layers 21 or 22 is preferably piezoelectric material. The piezoelectric material may be any suitable material, for example a piezoelectric ceramic such as lead zirconate titanate (PZT) or a piezoelectric polymer such as polyvinylidenefluoride (PVDF). However, the material of the electro-active layers 21,22 may be any other type of electro-active material, for example piezoresistive material, in which the electrical resistance changes as the material is deformed or strained, or electrostrictive material, which constricts on application of an electric field.

The electro-active portion 20 further comprises electrodes 23 to 25 extending parallel to the layers 21,22 of piezoelectric material. Outer electrodes 23,24 are provided outside the electro-active layers 21,22 on opposite sides of the electricactive portion 20. A centre electrode 25 is provided between the electro-active layers 21 and 22. The electrodes 23 to 25 are used to apply poling voltages and to operate electro-active portion 20 in a bending mode. On electrical activation, activation voltages are applied to the electrodes 23 to 25. Conversely on mechanical activation voltages are developed on the electrodes 23 to 25. On activation, the electro-active layers 21 and 22 undergo a differential change in length concomitant with bending of the portion 20 due to the constraint of the layers being coupled together at their interface formed by the centre electrode 25. For maximum displacement, on activation one of the electro-active layers 21 or 22 expands and the other one of the

electro-active layers 21 and 22 contracts The relative direction and magnitude of the activation and poling voltages may be selected in the same manner as for known linear electro-active devices having a bender construction. For example, poling voltages of sufficient magnitude to pole the electro-active layers 21 and 22 may be applied in opposite directions across the electro-active layers 21 and 22 by grounding the centre electrode 25 and applying poling voltages of the same polarity to both the outer electrodes 23,24. In this case, the electro-active portion 20 is electrically activated by applying activation voltages in the same direction across the electroactive layers 21 and 22 by applying voltages of opposite polarity to the two outer electrodes 23 and 24.

On activation the electro-active portion 20 bends around the minor axis 3 or 13, either towards or away from the minor axis 3,13 depending on the polarity of the activation voltages. On electrical activation the activation voltages are applied from a circuit 26 through external terminals 27 electrically connected to the electrodes 23 to 25 in the manner known for known straight piezoelectric devices having a bender construction. On mechanical activation, the activation voltages developed at the electrodes 23 to 25 are fed to the circuit 26.

Electrical connection to the electrodes 23 to 25 may be made in the same way as is known for known straight devices having a bender construction, in principle at any point along the length of the device of which the portion 20 forms part but preferably at the end. The preferred technique is to provide the electrodes with fingers (not shown) extending at the end of the device at different lateral positions across the width of the device as known for straight devices having a bender construction.

It will be appreciated that other bender constructions could equally be applied to the portion 20, for example a unimorph bender construction comprising a layer of electro-active material and an inactive layer or a multimorph bender construction comprising a plurality of layers of electro-active material.

Whilst the bender construction illustrated in Fig. 3 is preferred for simplicity and ease of manufacture, it will be appreciated that the continuous numbers 2 or 12

could in fact have any construction which bends around the minor axis 3 or 13 on activation. For example, the continuous members could be electro-active elements of the type described in the application being filed simultaneously with this application entitled"Electro-Active Elements and Devices"in which the elements have two pairs of electrodes extending along the length of the member for bending across the width on activation.

On activation, the electro-active portions 20 of the continuous member 2 or 12 bend around the minor axis 3 or 13. As a result of the continuous electro-active member 2 or 12 curving around the minor axis 3 or 13, in particular in a helix, such bending is concomitant with twisting of the continuous member 2 or 12 around the minor axis 3 or 13. This may be visualised as the turns of the continuous member 2 or 12 as the bending tightening or loosening causing a twist of the structure of the member 2 or 12 along the minor axis 3 or 13. The twist of the continuous member 2 or 12 occurs along the entire length of the minor axis 3 or 13 causing a relative rotation of the ends of the structure labelled 5 and 6 in the first device 1 of Fig. 1 and 15 and 16 in the second device 11 of Fig. 2.

It will be appreciated that the continuous member 2 or 12 could curve around the minor axis 3 or 13 in curves other than a helix to produce such twisting, for example by having the shape as though formed by twisting a flat member round the minor axis. It will also be appreciated that other structures other than a continuous member could be applied to produce twisting around the minor axis. For example the electro-active structure could consist of a plurality of electro-active portion disposed successively along the minor axis and coupled together so that the bending of each individual portion twists the adjacent portion around the minor axis causing twisting of the structure as a whole. Alternatively the electro-active structure could be a device of the type described in the application being filed simultaneously with this application entitled"Piezoelectric Devices"which comprises a plurality of electro-active torsional actuators which may comprise electro-active elements activated in shear mode.

Considering the first device 1 of Fig. 1, the twisting of the continuous

member 2 around the minor axis 3 is concomitant with relative displacement of the ends of the device 5 and 6 perpendicular to the curve of the minor axis 3, that is parallel to the major axis 4. The relative displacement of the ends 5 and 6 derives from the twisting of the continuous member 2 around the minor axis 3 in combination with the curve of the minor axis 3. It is an inevitable result that twisting of a curved object causes relative displacement of the ends of that object perpendicular to the local curve of the object.

In a similar manner, on activation of the second device of Fig. 2, the twisting of the continuous member 12 around the minor axis 13 is concomitant with displacement of the ends of the device 15 and 16 parallel to the major axis 14.

Again, this relative displacement derives from the rotation of the continuous member 12 around the minor axis 13 in combination with the curve of the minor axis 13. In this case, the relative displacement caused by any given small section of the structure along the minor axis 13 causes relative displacement of the ends of that section perpendicular to the local curve of the minor axis 13. The overall displacement of the ends 15,16 of the device 11 is the sum of the displacements of all the sections which results in an overall relative displacement parallel to the major axis 14.

The exact construction and dimensions of the member 2 or 12 and the form of the electro-active structure may be freely varied to produce the desired response. A suitable member 2 or 12 has a 0.5 mm thickness tape wound as a 4 mm diameter minor helix around the minor axis 3 or 13. When this forms the first device 1 in which the minor curve extends around about three quarters of a circle of 30 mm diameter the observed displacement is about 6mm. Similarly if this structure was used to form the second device 11 in which the minor curve extends along a 20 turn helix of diameter 30mm, this would produce displacement of around 120mm.

In general, the minor axis, along which the structure of devices in accordance with the present invention extend, may follow any curve and the resultant displacement of the ends of the structure will be the sum of the displacement caused by each section of the structure along the curve. However, curves which are regular such as the curve of the minor axis of the first and second devices 1 and 11 are

preferred so that all sections of the device caused relative displacement in a common direction and also because design and manufacture are thereby simplified.

In most applications, the first and second devices 1 and 11 are electrically activated to create mechanical displacement between the ends 5 and 6 or 15 and 16.

Conversely the device may be mechanically activated in which case relative displacement of the ends 5 and 6 or 15 and 16 causes an electrical voltage to be developed across the electrodes 23 to 25. This mode of operation is used in some applications, in particular in the transformer and limiter.

Manufacture of the electro-active devices I and 11 will now be described.

The preferred method of manufacture is to initially form the electro-active structure extending along a straight minor axis and subsequently to bend the straight electro-active structure so that the minor axis along which it extends becomes curved.

To form the continuous member 2 or 12 as an electro-active structure along a straight minor axis there are two preferred techniques.

The first preferred technique is to initially form the continuous member 2 or 12 as a straight member and subsequently to deform it to curve around the straight minor axis. The bender construction of the continuous member 2 or 12 is in itself known and the continuous member 2 or 12 may be formed by applying any of the known techniques for manufacturing a device having a bender construction. For example, the continuous member 12 may be initially manufactured by co-extrusion of the layers 21 and 22 of plasticised material or by co-calendering of the layers 21 and 22. Alternatively, the continuous member 2 or 12 may be made through lamination of thin layers 21 and 22. These thinner layers may be made by any suitable route, such as high shear mixing of a ceramic powder, polymer and solvent mixer followed by co-extrusion and calendering. Alternatively, techniques such as tape casting or the process called the Solutech process known in the field of ceramics may be used.

The electrodes may be formed as an integral part of the manufacture of the continuous member 2 or 12, for example by being in co-extruded or co-calendered.

Further electrodes, which may be activation layers 23 to 25 or may be terminal

electrodes to allow access to the electrodes 23 to 25, may be applied by printing, by electro-less plating, through fired-on silver past or by any other appropriate technique.

The second preferred technique is to initially manufacture the continuous member as a cylinder or other tube with a multi-layered bender construction of electro-active layers 21 and 22 and electrodes 23 to 25 and subsequently to cut the member along the helical line to leave the continuous member 2 or 12 extending in a helix around the axis of the cylinder or tube which then constitutes the minor axis.

Subsequently the straight structure is bent to curve the minor axis along which the structure extends.

To deform the member and structure, there must exist in the initially formed member a sufficient degree of flexibility. Suitably deformable electro-active materials are known, typically including constituent polymers which enhance the defonnability. With such materials after shaping, the constituent polymers are burnt

out, typically at up to 600 C and the material is then densified through further sintering at higher temperature, typically 1000 C to 1200 C. In this case, the electro- active structure is initially formed with enlarged dimensions to allow for linear shrinkage which occurs during sintering, typically of around 12 to 25%.

The curving of the straight member and the bending of the structure may be performed around formers. The formers are subsequently removed either physically or by destruction of the former for example by melting, burning or dissolving.

The electro-active device described above is used in a variety of electromechanical devices, as follows. In the following embodiments, the electro-active device is shown as having a structure like that of the second device 11 described above curving in a helix, but this is merely for illustration and the electro-active device may have any of the types of structure described above.

Fig. 4 illustrates a valve 40 in accordance with the present invention. The valve 40 has a fluid flow passage 41 defined by passage walls 42. Disposed in the fluid flow passage 41 is a valve member 43 and a valve seat 44 against which the

valve member is movable along the axis of the fluid flow passage 41 to control the tn

flow of fluid through the passage 41. The fluid passage 41 and also the valve member 43 and valve seat 44 may have any cross-section axially of the passage 41, preferably circular. The arrangement of the valve member 43 and the valve seat 44 is that of a conventional needle valve.

For moving the valve member 43, the valve 40 further comprises an electroactive device 45 of the type described above. One end 48 of the structure of the electro-active device 45 is coupled to the valve seat 44 and/or the walls 42 of the passage 41. The other end 49 of the structure of the electro-active device 45 is coupled to an extension 46 protruding from the valve member 43. Accordingly, on electrical activation, the relative displacement of the ends 48 and 49 of the structure of the electro-active device 45 drives movement of the valve member 43 relative to the seat 44. This is turn controls the flow of fluid through the fluid passage 41 between the valve member 43 and the seat 44.

The electrodes of the electro-active member 45 are electrically connected to a control circuit 47 for applying activation voltages to activate the electro-active device 45 and hence to control the valve 40.

The valve 40 illustrated in Fig. 4 is exemplary of a valve in which a valve member is movable to control fluid flow through the valve. Many such types of valve are known. It will be appreciated that the electro-active device in accordance with the present invention may be applied to move the valve member in any such valve.

Fig. 5 illustrates a mechanical switch 50 including a switch member 51 which has two stable positions, so the mechanical switch is bistable. In particular, the switch member 51 is slidable along a base 52 between two travel-limiting steps 53.

Between the steps 53, a plate 54 is mounted in a recess 55 in the base 52. The plate 54 is biased outwardly by a spring 56 or any other biassing means out into the path of the switch member 51. The plate 54 has rounded edges 57 to be engaged by the spring plate 51. Accordingly, in order to pass the plate 54, the spring member 51 must deflect the plate 54 against the biassing action of the spring 56. Consequently, the switch member 51 has two stable positions, one on either side of the spring plate

54 adjacent the respective steps 53, due the returning force provided by the spring 56 and plate 54.

To drive movement of the spring member 51 between its stable positions, the switch 50 is provided with an electro-active device 58 of the type described above.

One end 59 of the structure of the electro-active device 58 is coupled to the switch plate 51. The other end 60 of the structure of the electro-active device 58 is coupled to the base 52. Accordingly, on electrical activation the relative displacement of the ends 59 and 60 of the structure of the electro-active device 58 causes movement of the switch plate 51 between its two stable positions. Thus the force provided by the electro-active device 58 overcomes the biassing force provided by string 56 to deflect the plate 54. As a result of the switch member 51 being retained when it is in one of the two stable positions, the electro-active device 58 need only supply sufficient force to move the switch member 51 between the stable positions and does not have to carry the stress of holding the switch member 51 between switching.

The electrodes of the electro-active device 58 are electrically connected to a control circuit 61 which provides activation voltages to control the activation of the electro-active device 58 and hence to control movement of the switch member 51.

Fig. 6 illustrates a rotary mechanical switch 70 having a rotatable switch member 71 mounted on an axle 72. The switch member 71 is an elongate bar which alternately engages and releases a catch 73 as the switch member 71 rotates. While the switch member 71 is in the angular position shown in bold outline in Fig. 6, it is in a locked state where it engages the catch 73 which is held in the position shown in Fig. 6 against a stop 74. When the switch member 71 is in the angular position shown in dotted outline in Fig. 6, it is in an unlocked state where it releases the catch 73 which is thus free to move to the position shown in dotted outline in Fig. 6, thereby releasing the stop 74.

The rotary mechanical switch 70 is driven by an electro-active device 75 of the type described above. One end 76 of the electro-active device 75 is fixed, for example to the body of the mechanical switch 70. The other end 77 of the electroactive device 75 is coupled to the switch member 71 through a ratchet arrangement

consisting of a ratchet wheel 78 mounted on the axle 72 and a pawl 79 coupled to the free end 77 of the electro-active device 75. The pawl 79 engages a tooth 80 on the ratchet wheel 78. The teeth 80 are shaped so that on actuation of the electro-active device 75 which causes its ends 76 and 77 to be displaced away from one another, the extension of the electro-active device 75 drives the pawl 79 to rotate the ratchet wheel 78. This in turn drives rotation of the bar 71 through the axle 72 in the direction of the arrow A.

Subsequently as the electro-active device is activated so that its ends 76 and 77 are displaced back towards one another, the pawl 79 slides over the ratchet wheel 78 to engage the next tooth 80 on the ratchet wheel 78.

The ratchet wheel 78 is illustrated as having four teeth 80 each corresponding to a successive angular position of the switch member 71 where the switch 70 is in one of a locked or unlocked state. Thus each single stroke of the electro-active device 75 rotates the switch member 71 alternately between locked and unlocked states of the switch 70. In these states, the pawl 79 holds the ratchet wheel 78 and catch member 71 in a stable position.

Alternatively, the ratchet wheel 78 may be provided with a larger number of teeth so that plural strokes of the electro-active device 75 are required to rotate switch member 71 between locked and unlocked states.

The rotary mechanical switch 70 further comprises an auxiliary pawl 81 which is fixed, for example to the body of the rotary mechanical switch 70. The auxiliary pawl 81 engages the ratchet wheel 80 in addition to the pawl 79 coupled to the electro-active device 75. The auxiliary pawl 81 engages a tooth 80 on the ratchet wheel 78. Accordingly, the auxiliary pawl 81 holds the ratchet wheel 78, and hence the catch member 71, in a stable position when the pawl 79 coupled to the electroactive device 75 is itself disengaged with the teeth 80 of the ratchet wheel 78. Firstly this ensures that the ratchet wheel 78 is held in position during the reverse stroke of the electro-active device 75 as the pawl 79 coupled to the electro-active device 75 slides over a tooth 80 of the ratchet wheel 78. Secondly, the auxiliary pawl 81 allows the electro-active device 75 to adopt a position in which the pawl 79 is retracted from

engagement with the ratchet wheel 78 altogether when it is deactivated with no activation voltage being applied.

A control circuit 82 is electrically connected to the electrodes of the electroactive device 75 to apply activation voltages to activate the electro-active device 75.

To rotate the switch member 71 between successive states, activation voltages are applied to the electro-active device 75 to cause the electro-active device 75 to undergo a drive stroke during which its ends 76 and 77 are displaced away from each other and a release stroke in which the ends 76 and 77 of the electro-active device are displaced towards one another.

The mechanical switches 50 and 70 are exemplary of mechanical switches having a movable switch member with one or more stable positions in which the switch member is mechanically retained. Many such types of mechanical switch are known, car door locks being one example. The purpose of the switch member having a stable position where it is retained is that the drive mechanism for moving the switch member does not itself need to carry all the stress of holding the switch member in a given position. It will be appreciated that the electro-active device in accordance with the present invention may be applied to the switch member in other such mechanical switches Fig. 7 illustrates an electrical relay 90 having an electrical contact 91 which is movable into and out of contact with a pair of fixed contacts 92 to close and open a circuit path formed between two terminals 93 through the fixed contacts 92 and movable contact 91. An electro-active device 94 of the type described above is coupled to the movable contact 91 to drive its movement.

One end 95 of the electro-active device 94 is coupled to the movable contact 91 indirectly through a member 97 of electrically insulating material, so that the electro-active device 94 is electrically insulated from the movable contact 91. The other end 96 of the electro-active device 94 is coupled to a housing 98 of the electrical relay 90. The housing 98 houses the electro-active device 94 and the movable contact 91 and mounts the fixed contacts 92. The housing 98 is electrically insulating, for example by being made from an insulating material. On activation of

the electro-active device 94, the relative displacement of its ends 95 and 96 drives movement of the movable member 91 into and out of contact with the fixed contacts 92, hence opening and closing the circuit path 93.

The electrical relay 90 has a pair of control terminals 99 electrically connected to the electrodes of the electro-active device 94. The control terminals 99 are for receiving an activation voltage to control the relay 90 to open and close the circuit path between the electrodes 93.

The electrical relay 90 illustrated in Fig. 7 is exemplary of a relay including an electrical contact which is movable to open and close a circuit path by application of an electrical input. Many alternative arrangements for an electrical relay are possible. It will be appreciated that the electro-active device in accordance with the present invention may be applied to move the electrical contact of any such electrical relay.

An advantage of relays in accordance with the present invention is that the current required to hold the contacts in position is a small fraction of the current required to change position. The holding current is merely a leakage current through the electro-active material of the electro-active device. This is in stark contrast to electro-magnetic relays which consume considerable power in the holding position.

Fig. 8 illustrates a circuit breaker 100 which is in essence an electrical relay having an electrical contact 101 which is movable driven by an electro-active device 102 in a similar manner to the electrical relay 90 of Fig. 7. However, in the circuit breaker 100, the circuit path formed through the movable contact 101 is in series with the electro-active device 102. The circuit breaker 100 is design so that when the voltage (or current) flowing through the electro-active device 102 exceeds a predetermined level, the movable contact 101 is moved to open the circuit path, hence breaking the current flowing through the circuit breaker 100. The circuit breaker 100 will now be described in more detail.

The circuit breaker 100 has a housing 103 which is electrically insulating, for example by being formed from an insulator. The various elements of the circuit breaker 100 including the movable contact 101 and the electro-active device 102 are

housed inside the housing 103.

The movable contact 101 is a bar 101 extending between two conductive contacts 104 and 105 formed as blocks. In the normal closed state of the circuit breaker 100, the movable contact 101 is in the position shown in Fig. 8 with its ends in electrical contact with the further contact 104 and 105. Thus a circuit path between nodes 106 through the further contacts 104 and 105 and the movable contact 101 is closed. The movable contact 101 is held in this position by a spring 107, or other resilient biassing means, coupled between the movable contact 101 and the housing 103.

The electro-active device 102 is disposed on the opposite side of the movable contact 101 from the spring 107. The electro-active device 102 is coupled at one end 108 to the movable contact 101 and at the other end 109 to the housing 103. The face of the movable contact 101 adjacent the electro-active device 102 is covered by a sheet 110 of electrically insulating material which insulates the electro-active device 102 from the movable contact 101. The electro-active device 102 is arranged so that the force applied on activation to the movable contact 101 counteracts the force applied by the spring 107.

The circuit breaker 100 has a pair of input terminals 111 across which the electro-active device 102 and the circuit path formed between the nodes 106 are connected in series. Thus the voltage applied to the input terminals 111 is applied through the circuit path between the nodes 106, to the electrodes of the electro-active device 102. As this applied voltage increases, the electro-active device 102 is activated applying a force tending to relatively displace the ends 108 and 109 of the electro-active device 102 away from each other and hence tending to move the movable contact 101 out of contact with the further contacts 104 and 105, but opposed by the spring 107. The circuit path between the nodes 106 remains closed until the applied voltage is sufficient to cause the force applied by the electro-active device 102 to overcome the mechanical spring 107. At this point, the electro-active device 102 moves the movable contact 101 out of contact with the further contacts 104 and 105, thereby opening the circuit path between the nodes 106 and hence

breaking the circuit between the input terminals 111 of the circuit breaker 100. The applied voltage (or current) at which the circuit breaker 100 breaks the circuit between the input terminals 111 may be controlled by appropriate selection of the electro-active device 102 as compared to the mechanical systems of the spring 107.

The circuit breaker 100 is further arranged to hold the circuit path 106 open after the operation described above, as follows and as shown in detail in Fig. 9. A first one of the further contacts 104 is fixed to the housing 103. The second further contact 105 is slidably movable in a recess 112 formed in the housing 103 and is biased towards the first further contact 104 by a spring 113 or other resilient means.

When the circuit path between the nodes 106 is closed in the normal state as shown in Fig. 8, the movable contact 101 holds the second further contact 105 in the recess 112 against the action of the biassing spring 113. However, when the movable contact 101 is moved by the retracted device 102 out of contact with the second further contact 105, the biassing spring 113 drives the second further contact 105 towards the first further contact 104. The surface 114 of the second further contact 105 on the side facing the movable contact 101 after it has moved out of contact with the further contacts 104 and 105 extends in a direction parallel to the movable contact 101 and hence engages the movable contact 101 act as a stop preventing the movable contact 101 from moving back. The parallel surface 114 of the second further contact 105, and also the corresponding surface of the first further contact 104 are both covered by pieces of insulating material 115 which, together with the insulating material 110 covering the rear surface of the movable contact 101 insulates the further contacts 104 and 105 from the movable contact 101 after the circuit path between the nodes 106 has been opened.

The second further contact 105 is also provided with a button 116 protruding from the housing 103 to allow manual retraction of the second further contact 105 against the biassing spring 113 in order to reset the circuit breaker 100.

In addition in order to ensure a clean action in opening the circuit path between the nodes 106, the comers of the further contacts 105 and 106 and the comer 117 of the second further contact 105 adjacent the surface 114 slopes at an angle to

the surface 114.

Fig. 10 illustrates a transformer 120 in accordance with the present invention.

The transformer 120 comprises two electro-active devices 121 and 122 of the type described above housed in a housing 123 which is electrically insulating for example by being made from an insulator. The electro-active devices 121 and 122 are both coupled at one end to each other indirectly through a coupling plate 124 which is electrically insulating, for example by being made of an insulator, in order to insulate the two electro-active devices 121 and 122 from each other. The opposite ends of each of the electro-active devices 121 and 122 are coupled to the housing 123 at opposite ends of the housing 123.

Input terminals 125 are electrically connected to the electrodes of the first electro-active device 121. Output terminals 126 are electrically connected to the electrodes of the second electro-active device 122. The electro-active devices 121 and 122 are aligned so that the relative displacement between the ends of each electro-active device 121 and 122 occurs in the same direction.

By coupling the electro-active devices 121 and 122 together in this way, a transformer action is achieved. When an alternating input signal is applied to the input terminals 125, the first electro-active device 121 is electrically activated, thereby causing relative displacement of its ends. As the first electro-active device 121 is mechanically coupled to the second electro-active device 122, the displacement of the first electro-active device 121 mechanically activates the second electro-active device 122, relatively displacing its ends. This mechanical activation of the second electro-active device 122 causes an alternating signal to be generated in the second electro-active device 122 and output to the output terminals 126. Thus a signal input at the input terminals 125 is transformed into an output signal at the output terminals 126 coupled mechanically by the displacement of the two electroactive devices 121 and 122 which are electrically insulated from one another.

The relative magnitudes of the input and output signals depend on the relative electro-mechanical responses of the electro-active devices 121, that is the displacement-voltage responses. This is because the relative displacement of each electro-active device 121 and 122 is of the same magnitude (but opposite sign)

because the distance between the ends of the electro-active devices 121 and 122 which are fixed to the housing 123 is fixed.

For the transformer 120 to constitute a step-up or step-down transformer, the - electro-mechanical responses of the two electro-active devices 121 and 122 are different. Different electro-mechanical responses may be achieved by providing the two electro-active devices 121 and 122 with different structures. Any of the parameters of the structures of the electro-active devices 121 and 122 may be varied.

For example, the shape of the minor axis along which the structure of the electro- active devices extends may be varied, for example in the case that the minor axis curves in a helix by varying the number of helical turns. Similarly in the case that the structure of the electro-active devices 121 and 122 comprises a continuous electro-active member curving around the minor axis, the curve of the continuous member around the minor axis may be varied, or where a bender construction is used, the compliance, layer thickness, or number of layers of electro-active material may be varied. This will also affect the impedance of the transformer 120 which is proportional to the area of material between the electrodes of the electro-active devices 121 and 122 and inversely proportional to the thickness of this material.

As an example, when arranged as a step-down transformer, the transformer 120 could be used to step-down a main input signal to a low-level signal for subsequent conversion into a DC signal for use with domestic electronic equipment.

The mechanical responses of the two electro-active devices 121 and 122 may be controlled by selection of the mechanical properties of the structures of the electro-active devices 121 and 122 to control the mechanical resonance frequency to be equal to the expected frequency of the input signal.

As an alternative, to form the transformer 120 as a unitary transformer, the electro-mechanical response of the two electro-active devices 121 and 122 is the same, preferably for ease of manufacture by the electro-active devices 121 and 122 being mechanically identical. Such a unitary transformer is useful to electrically isolate one part of circuit from another, for example to protect a sensitive or critical device from a surge or spike which might occur on a power supply.

The transformer 120 may be designed to operate with input and output signals

of any magnitude by appropriate selection of the properties of the electro-active devices 121 and 122. Accordingly the transformer 120 may replace known electro- magnetic transformers formed by two electrically isolated but magnetically linked coils. As compared to such known electro-magnetic transformers, the transformer 120 is of comparatively low weight, principally because an electro-magnetic transformer has a heavy magnetic core which is not necessary in the transformer 120.

Also, the transformer 120 is of comparatively high efficiency.

In the transformer 120, the two separate devices 121 and 122 form input and output elements. As an alternative, the two separate devices 121 and 122 may be replaced by a single electro-active device of the type described above, but with a split in the electrodes at a position along the length of the device so that the portions of the device on either side of the split are independently operable and form input and output elements which correspond to the separate devices 121 and 122 of the transformer 120 to produce a transformer effect in the same manner, as described

above. Such an alternative may be termed an"auto-transformer".

Fig. 11 illustrates a limiter 130 in accordance with the present invention. The limiter 130 is identical to the transformer 120 except for the provision of a mechanical stop 131 described further below. Therefore the description of the transformer 120 will not be repeated and the same reference numerals will be used to describe the common elements of the limiter 130.

The mechanical stop 131 is fixed inside the housing 123 in a position to engage the coupling plate 124 coupled between the electro-active devices 121 and 122 when the displacement of the electro-active devices 121 and 122 reaches a predetermined magnitude. The mechanical stop 131 is a simple block of any suitable material provided inside the curve of the structure of the second electro-active device 122. Optionally, a mechanical stop may be provided inside the curve of the structure of the first electro-active device 122, in addition to the mechanical stop 131, or as an alternative thereto. Indeed, any suitable mechanical stop for limiting the relative displacement of the ends of the structure of the electro-active devices 121 and 122 may be used.

The mechanical stop 131, by limiting the relative displacement of the ends of

the structures of the two electro-active devices 121 and 122, limits the electrical signal developed within the second electro-active device 122 and hence limits the magnitude of the output alternating signal. If the input signal is of any higher - magnitude, the force produced in the first electro-active device 121 is taken up by the mechanical stop 131 and so no additional stress or strain is produced in the second electro-active device 122.

As an alternative to the simple mechanical stop, any mechanical arrangement which limits the relative displacement of the ends of the structure of the second electro-active device 122 may be used, for example a decoupling mechanism limiting the magnitude of the relative displacement of the second electro-active device 122 without affecting the relative displacement of the ends of the first electro-active device 121. Such a decoupling mechanism would have the advantage that the input impedance of the first electro-active device 121 would not be affected by limiting the magnitude of the displacement of the ends of the first electro-active device 121.

The means for limiting the rates of displacement of the ends of the second electro-active device 122 may be made to be variable, for example by using a mechanical stop with a screw thread to adjust its position.

Fig. 12 illustrates an electrical meter 130 comprising an electro-active device 131 of the type described above. The electrical meter 130 has terminals 132 electrically connected to the electro-active device 131 for connection to an external circuit. The electro-active device 131 is coupled at a first end 133 to a support 134 on which is formed a visible scale 135. The second end 136 of the electro-active device 131 is coupled to a pointer 137 indicating the position of the second end 136 of the electro-active device 131 on the scale 135, and hence indicating the relative displacement of the ends 133 and 136 of the electro-active device 131.

Across the input terminals 132 is arranged a resistance 138 which may be switched in parallel with the electro-active device 131 via a switch 139. By operating the switch 139, the electrical meter 130 may be used as a voltage meter or a current meter.

When the switch 139 is opened so that the terminals 132 are in open circuit across the electro-active device 131, the electrical meter constitutes a voltage meter

and operates as follows. The voltage across the external terminals 132 electrically activates the electro-active device 131 causing a relative displacement of the ends 133 and 136 of the electro-active device 131 which is indicated by the position of the - pointer 137 on the scale 135.

Conversely, when the switch 139 is closed so that the resistance 138 is connected in parallel with the electro-active device 131, a relative displacement of the ends 133 and 136 of the electro-active device 131 indicated by the position of the pointer 137 on the scale 135 changes in accordance with the current flowing through the terminals 132 and the resistance 138. The size of the resistance 138 is selected so that the voltage developed there across for the current range to be measured is appropriate for displacing the electro-active device 131. Thus the electrical meter 130 is equivalent to a moving coil meter of a conventional type.

Claims

1. A valve including a valve member which is movable to control fluid flow through the valve and an electro-active device coupled to move the valve member on activation, the electro-active device comprising an electro-active structure extending along a curved minor axis and arranged, on activation, for the structure to twist around the minor axis and concomitantly for relative displacement of the ends of the structure to occur for moving the valve member.

2. A valve as claimed in claim 1, wherein the valve includes a fluid flow passage in which the valve member is disposed.

3. A valve as claimed in claim 2, wherein the fluid flow passage has a valve seat against which the valve member is movable to control fluid flow.

4. A mechanical switch including a switch member having at least one stable position from which the switch member is movable, and an electro-active device coupled to move the switch member, the electro-active device comprising an electro-active structure extending along a curved minor axis and arranged, on activation, for the structure to twist around the minor axis and concomitantly for relative displacement of the ends of the structure to occur for moving the switch member.

5. A mechanical switch as claimed in claim 4, wherein the switch member has two stable positions, the electro-active device being coupled to move the switch member between the two stable positions.

6. A mechanical switch as claimed in claim 4, wherein the switch member is rotatable.

7. A mechanical switch as claimed in claim 6, wherein the electro-active

member is coupled to the switch member through a ratchet arrangement.

8. An electrical relay including an electrical contact which is movable to - open and close a circuit path, and an electro-active device coupled to move the electrical contact, the electro-active device comprising an electro-active structure extending along a curved minor axis and arranged, on activation, for the structure to twist around the minor axis and concomitantly for relative displacement of the ends

of the structure to occur for moving the electrical contact. tn

9. An electrical relay as claimed in claim 8, wherein the electro-active device is electrically insulated from the electrical contact.

10. An electrical relay as claimed in claim 8 or 9, wherein the electroactive device and the electrical contact are housed in a housing.

11. An electrical relay as claimed in claim 10, wherein the housing is electrically insulating.

12. An electrical relay as claimed in claim 10 or 11, having at least one fixed contact mounted on the housing to be contactable by the movable contact to open and close the circuit path.

13. An electrical relay as claimed in any one of claims 8 to 12, wherein the electro-active device is in series with the circuit path so that the electrical relay constitutes a circuit breaker.

14. An electrical relay as claimed in claim 13, wherein the contact is mechanically biased to close the circuit path.

15. An electrical relay as claimed in claim 13 or 14, wherein the contact is a conductive bar extending between two further conductive contacts.

16. An electrical relay as claimed in claim 15, wherein at least one of the conductive members is biased against the conductive bar so that, on movement of the contact to open the circuit path, the at least one conductive member is moved to a - position where it prevents return of the conductive bar.

17. A transformer comprising two electro-active elements each comprising an electro-active structure extending along a curved minor axis and arranged, on activation, for the structure to twist around the minor axis and concomitantly for relative displacement of the ends of the structure to occur, the two electro-active elements being coupled together so that displacement of one electro- active device on electrical activation by application of an input alternating signal mechanically activates the other electro-active device to generate an output alternating signal.

18. A transformer as claimed in claim 17, wherein the electro-mechanical response of the two electro-active elements is different so that the transformer is a step-up or step-down transformer.

19. A transformer as claimed in claim 18, wherein the electro-mechanical response of the two electro-active elements is the same so that the transformer is a unitary transformer.

20. A transformer as claimed in any one of claims 17 to 19, wherein the two electro-active elements are electrically insulated from each other.

21. A transformer as claimed in any one of claims 17 to 21, wherein the two electro-active elements are separate electro-active devices.

22. A transformer as claimed in any one of claims 17 to 21, further comprising means for limiting the relative displacement of the ends of the structure of the second electro-active device to limit the magnitude of the output alternating

signal so that the transformer acts as a limiter.

23. An electrical meter comprising an electro-active device and electrical - terminals electrically connected to the electro-active device for receiving an electrical signal, the electro-active device comprising an electro-active structure extending along a curved minor axis and arranged, on electrical activation by application of an electrical signal across the electrical terminals, for the structure to twist around the minor axis and concomitantly for relative displacement of the ends of the structure to occur, one end of the electro-active device being fixed relative to a visible scale and the other end of the electro-active device being coupled to a pointer for indicating the relative displacement on the scale.

24. An electrical meter as claimed in claim 23, wherein the electrical terminals are connected in open circuit across the electro-active device so that the meter constitutes a voltage meter.

25. An electrical meter as claimed in claim 23, wherein a resistance is connected across the electrical terminals in parallel with the electro-active device so that the meter constitutes a current meter.

26. A device as claimed in any one of the preceding claims, wherein the electro-active structure of the electro-active device comprises electro-active portions disposed successively along the minor axis and arranged to bend, on activation, around the minor axis.

27. A device as claimed in claim 26, wherein the electro-active structure comprises a continuous electro-active member curving around the minor axis, said electro-active portions being adjacent finite portions of the continuous member.

28. A device as claimed in claim 27, wherein the continuous electro- active member curves in a helix around the minor axis.

29. A device as claimed in any one of claims 26 to 28, wherein the successive electro-active portions have a bender construction of a plurality of layers including at least one layer of electro-active material.

30. A device as claimed in claim 29, wherein the electro-active portions have a bimorph bender construction of two layers of electro-active material or a multimorph bender construction of more than two layers of electro-active material.

31. A device as claimed in any one of the preceding claims, wherein the electro-active structure includes electrodes for development of an electric potential thereacross on activation of the electro-active structure.

32. A device as claimed in any one of the preceding claims, wherein the minor axis extends in curve which is a helix.

33. A device as claimed in any one of the preceding claims, wherein the minor axis extends in curve which is planar.

34. A device as claimed in any one of the preceding claims, wherein the electro-active structure includes piezoelectric material.

35. A device as claimed in claim 34, wherein the piezoelectric material is a piezoelectric ceramic or a piezoelectric polymer.

36. An electro-active device as claimed in claim 35, wherein the piezoelectric material is lead zirconate titanate (PZT) or polyvinylidenefluoride (PVDF).

37. A valve constructed and arranged to operate substantially as hereinbefore described with reference to the accompanying drawings.

38. A mechanical switch constructed and arranged to operate substantially as hereinbefore described with reference to the accompanying drawings.

39. An electrical relay constructed and arranged to operate substantially as hereinbefore described with reference to the accompanying drawings.

40. A transformer constructed and arranged to operate substantially as hereinbefore described with reference to the accompanying drawings.