WO2009044041A2

WO2009044041A2 - Actuator device with electro-active membrane

Info

Publication number: WO2009044041A2
Application number: PCT/FR2008/051571
Authority: WO
Inventors: Sébastien GAY; Thierry Planas
Original assignee: Renault S.A.S.
Priority date: 2007-09-04
Filing date: 2008-09-03
Publication date: 2009-04-09
Also published as: WO2009044041A3; FR2920591B1; FR2920591A1; EP2191522A2

Abstract

The invention relates to an electro-active device (10; 10?; 10??) that comprises a member (11) made of an electro-active material and two electrodes (14, 15) in contact with a first surface (12) of the member, characterised in that both electrodes are to be brought to two different electric potentials and in that a means (16) for reflecting the electric field generated between the two electrodes is provided on a second surface (13) of the member.

Description

ELECTROACTIVE MEMBRANE ACTUATOR DEVICE

The present invention relates to an electroactive polymer membrane device.

It is known, for example from document US 2006/01 13878, to produce devices 1 comprising an electroactive polymer membrane 2 as shown in FIG. 1. In such a device, a first face 9 of the membrane has been placed on in contact therewith, a first electrode 3 and, on a second face 8 of the membrane, in contact therewith, a second electrode 4. The electrodes each have means of connection to one of the poles of the same voltage generator. In such a device, when the two electrodes are carried at different electrical potentials, an electric field substantially perpendicular to the faces of the membrane is created in the membrane, this field causing deformation of the membrane as long as it is is applied. The membrane returns to an initial configuration as soon as the field disappears. The deformation is done by crushing the polymer parallel to the electric field lines. Such a phenomenon can be used for the production of actuators (especially diaphragm pumps) but also for the realization of sensor, the polymer being such that the electric field is altered when it is deformed.

It is known from the application US 2006/0208610 a device comprising an electroactive polymer membrane on a first face of which are disposed two first electrodes and on a second face of which is disposed opposite the first two electrodes, a third electrode. In this device, the first two electrodes are alternately connected to a first pole of a voltage generator while the third electrode is connected to the second pole of the voltage generator.

Application US 2005/0256367 discloses an electrically operated sphincter prosthesis using the principle mentioned above. It consists of a ring having an electrical structure as evoked previously and whose diameter increases when an electric potential difference is revealed between two faces of an electroactive polymer.

All the devices described in these documents have a major disadvantage: it is necessary to carry two electrodes on either side of a membrane at different electrical potentials using a voltage generator and, therefore, necessary to provide a passage, in the membrane or around the membrane, for an electric wire connecting an electrode to the generator. This solution poses sealing problems when a fluid, and in particular a pressurized fluid, is retained on one side of the membrane, poses mechanical problems of resistance of the membrane, a hole in it obviously causing a local problem. particularly troublesome stress concentration zone, in particular when the membrane is subjected to fatigue stresses and poses electrical problems, electrical insulation of the two faces of the membrane being necessary. Thus, the possibilities and shapes of the membranes are limited.

However, in some applications, it is possible to apply an electrical potential to one of the electrodes without a wire connection, by using the electrical conduction of the medium with which an electrode is in contact. In the case of the application of US 2005/0256367, the human body serves as an electrical ground in one embodiment.

To remedy some of these drawbacks, EP 1 683 968 discloses a diaphragm pump device comprising a concentric structure of discs of electroactive material separated by electrodes, this structure being bonded to the membrane. This device allows in this precise application not to pierce the membrane. However, this relatively complex solution can not be used in all membrane device applications. The object of the invention is to provide an electroactive device obviating the aforementioned drawbacks and improving the electroactive devices known from the prior art. In particular, the electroactive device according to the invention has a simple structure making it possible to avoid making a hole in an electroactive element in order to connect one of the electrodes to a terminal of a voltage generator. The invention also relates to an actuator comprising such an electroactive device.

According to the invention, the electroactive device comprises an element made of electroactive material and two electrodes in contact with a first surface of the element. It is characterized in that the two electrodes are intended to be carried at two different electrical potentials and in that a means of reflection of the electric field created between the two electrodes is arranged on a second surface of the element.

The electroactive material may be a polymer.

The element can be a membrane.

The first and second surfaces may be opposite or at least substantially parallel.

The reflection means of the electric field may be at least substantially disposed vis-à-vis the electrodes.

The electric field reflection means may comprise an integral electrical conductive element or a set of discrete electrical conductive elements.

The reflection means may be covered by an insulating coating.

The electric field reflection means may comprise electrically conductive grains in an insulating matrix. An insulating coating may cover the assembly formed by the first surface and the electrodes in contact with this surface.

The electrodes may have means for connecting them to the two poles of the same voltage generator.

The element may have an at least substantially flat shape.

The element may have an at least substantially tubular shape, the first surface being the outer surface of this shape and the second surface being the inner surface thereof.

The element may have an at least substantially spherical shape, the first surface being the outer surface of this shape and the second surface being the inner surface thereof.

According to the invention, an actuator comprises at least one device defined previously.

The appended drawing shows, by way of example, several embodiments of an electroactive device according to the invention.

Figure 1 is a diagram of an electroactive device known from the prior art.

Figure 2 is a diagram of a first embodiment of an electroactive device according to the invention.

Figure 3 is a diagram of an actuator comprising an electroactive device according to this first mode.

FIG. 4 is a diagram of an actuator comprising an electroactive device according to a second embodiment. Figure 5 is a diagram of a third embodiment of an electroactive device according to the invention.

A first embodiment of an electroactive device (shown in FIG. 2) mainly comprises an electroactive element 11 such as an electroactive polymer membrane. This membrane has an upper face 12 and a lower face 13, these two faces being opposite and at least substantially parallel. On the upper face 12 are disposed a first electrode 14 and a second electrode 15. The electrodes are directly in contact with the membrane at its upper face. The electrodes are made of an electrically conductive material such as for example a metal or a conductive polymer. Each electrode 14, 15 comprises means 18, 19 making it possible to connect it to a terminal of an electric voltage generator 20. On the lower face 13, there is a means 16 of reflection of the electric field called "floating potential electrode" extending across the electrodes 14 and 15. This element comprises for example a plate or a metal film. The floating potential electrode may also not be uniform and / or be composed of conductive grains isolated from each other. It is thus possible to deposit, by spraying, deposition or other on the lower face of the membrane 11, a film constituting a floating potential electrode composed of metal grains, for example a metal powder, taken in a polymer matrix.

When the electrodes 14 and 15 are brought to different electrical potentials by connecting them to the terminals of the same voltage source

20, there is created between the electrodes in the membrane 1 1, an electric field of which a few field lines have been shown in Figure 2. These field lines are substantially perpendicular to the lower and upper faces of the membrane. This orientation of the field lines is due to the high electrical conductivity of the floating potential electrode (which is not strictly speaking an "electrode" because it is not intended to be connected to the voltage source). Indeed, this high electrical conductivity ensures a Concentration function of electric field or electric field lines and all field lines tend to go through this floating potential electrode. The floating potential electrode thus creates an "electric mirror" effect and the effect on the membrane thus obtained is substantially equivalent to that which would be obtained in a conventional structure with two pairs of electrodes facing each other. and other a membrane, each electrode on the same side of the membrane being connected to the same pole of a voltage source. It is noted in particular that the effect produced is the same whether the floating potential electrode is made in one piece or by a set of conductive grains discrete or isolated from each other.

It should be noted that the electric field is not strictly perpendicular to the membrane at any point. There is, in places, a small parasitic lateral component which causes a slight lateral contraction of the membrane whereas the main field tends to dilate it in this lateral direction. The parasitic field being mainly present in the space between the two electrodes of the upper face, this defect is limited.

Note that this device comprising two electrodes on the same membrane face and a floating potential electrode on the other side allows to have electrical connections on one side of the membrane.

To avoid any electric arc between the two electrodes 14 and 15 in all circumstances, while allowing the deformation of the membrane, an insulator 17 is provided. This insulator is flexible to deform with the membrane. The insulator covers the surfaces of the electrodes not in contact with the upper face of the membrane. It can also cover the upper surface of the membrane not in contact with the electrodes. The insulator has a dielectric permittivity much lower than that of the electroactive material constituting the membrane so as to avoid that electric field lines are concentrated in the insulator between the two electrodes. The insulation may for example be applied in one of the following ways: by gluing: a sheet of insulation is glued to the membrane once the electrodes are in place. The dielectric qualities (avalanche field) and mechanical (fatigue in the presence of cyclic stresses, temperature resistance) are as important as those of insulation itself, by deposition: the insulation is melted and applied in thin layers on the membrane, where it solidifies and settles. This method is more particularly indicated for viscous and / or thick polymer insulators, - by spraying: suitable for very thin and very low viscosity insulators in the liquid phase, by polymerization on the membrane: the reagents for the manufacture of the insulation are mixed on the membrane and stick to it during the formation of the polymer, - by painting: the paint then constitutes the insulator.

The insulator is preferably at least as flexible as the electroactive polymer constituting the membrane on which it is laid. It must also have a relative permittivity much lower than that of the electroactive polymer constituting the membrane otherwise it will deform as much if not more than it. Possible materials include but are not limited to: rubber, neoprene, polytetrafluoroethylene (PTFE or teflon ®), - PVC, polyethylene, ethylene tetrafluoroethylene (ETFE).

The floating potential electrode can also be isolated. For example, it can be insulated in the same way as the electrodes 14 and 15 using the same material to make an insulating film 21. This insulation is recommended when the floating potential electrode is a metal film or a conductive polymer. On the other hand, when the electrode consists of metal grains embedded in an insulating polymer, the electrical insulation is already achieved. Thus, the insulator and the floating potential electrode can constitute a single assembly, which makes the device comprising the membrane and the electrodes finer and eliminates the risk of leakage of electrical current to the medium in contact with the membrane.

The device described with reference to FIG. 2 can be used to produce an actuator 100 comprising multiple electrodes.

For example, as shown in FIG. 3, a plane membrane 11 may be in contact with a linear succession of electrodes 14a, 15a, 14b, 15b, 14c, 15c, 14d intended to be alternately connected to a first pole 18a and to a second pole 19a of a voltage source or several generators to form a succession of devices similar to that of Figure 2. The elements with the elements of Figures 2 and 3 bearing the same references are similar.

This actuator can for example be placed on a conductive surface, in which case, compared to the known devices of the prior art, the absence of contacts on the contact surface avoids electrical faults, including short circuit. It should be noted that if the membrane is placed on a conductive surface, the floating potential electrode is no longer necessary, the conductive surface ensuring its function. It is then necessary to provide means for isolating this conductive surface if necessary. Another advantage of resting the membrane on a surface lies in the uniformity of the mechanical contact with the surface under the floating potential electrode. Prestressing can then be performed by stretching and gluing on the surface in question.

The principle of the device described with reference to Figure 2 can also be used to realize an actuator comprising multiple electrodes and having a tubular shape. Such an actuator 1 10 is described with reference to Figure 4 and comprises a succession of tubular devices 10 'having an electrical structure similar to that of the device of Figure 2 and comprising a tubular membrane 1 1' of electroactive material on the outer face 12 'of which are disposed a first annular electrode 14'a and a second annular electrode 15'a and on the inner face 13' of which is provided a tubular shaped floating potential electrode 16 '. The electrodes 14'a, 15'a, 14'b, 15'b 14'c, 15'c, 14'd, surrounded by an insulator 17 ', are intended to be alternately connected to a first pole 18'a and at a second pole 19'b of a voltage source or at several voltage sources. This structure has a significant advantage: the floating potential electrode is inside a tube and it is therefore not necessary to perforate the tube to pass an electrical conductor. Thus, this structure has the advantage of simplifying the construction of the tube, which can thus contain liquids without risk of electrical contact, leakage or rupture of the tube at son passage points under the effect of pressure.

It would be possible to obtain the same security with a device according to the prior art, but at the cost of an additional tube inside to contain the fluid.

The principle of the device described with reference to FIG. 2 can also be used to produce an actuator 10 "having a spherical shape and represented in FIG.

The actuator 10 "has an electrical structure similar to that of the device of FIG. 2 and comprises a spherical membrane 11" of electroactive material on the outer face 12 "of which are disposed a first electrode 14" and a second electrode 15 " and on the inner face 13 "of which a spherical floating potential electrode 16" is provided, the electrodes 14 "and 15", surrounded by an insulator 17 ", are intended to be connected to a first pole 18 "and a second pole 19" of a voltage source. This structure has the same advantage as mentioned above: the floating potential electrode is inside a sphere that is not necessary to perforate to pass an electrical conductor.

Thanks to the device according to the invention, it is possible to produce actuators having simplified structures. More exactly, the membrane can be made more freely without any perforation that could affect its sealing and / or its mechanical strength. The floating potential electrode may have various structures and act as a mirror for the electric field created by the electrodes connected to a voltage source. The potential of the floating potential electrode is fixed by itself with reference to the other electrodes and changes with the voltage applied thereto. The device according to the invention has a reduced number of electrical connections and simplifies the control of the electric field in the membrane. In addition, the device according to the invention makes it possible to use only one voltage source.

The device according to the invention can in particular be applied to pumps, in particular membrane or pump hoses and cushions, balloons or surfaces with variable geometric shapes (headrest, seat ...).

Claims

Electroactive device (10; 10 '; 10 ") comprising an element (1 1) of electroactive material and two electrodes (14,15) in contact with a first surface (12) of the element, characterized in that the two electrodes are intended to be carried at two different electrical potentials and in that means (16) for reflection of the electric field created between the two electrodes is arranged on a second surface (13) of the element.

2. Device according to claim 1, characterized in that the electroactive material is a polymer.

3. Device according to one of the preceding claims, characterized in that the element is a membrane.

4. Device according to one of the preceding claims, characterized in that the first and second surfaces are opposite or at least substantially parallel.

5. Device according to one of the preceding claims, characterized in that the means of reflection of the electric field is at least substantially disposed vis-à-vis the electrodes.

6. Device according to one of the preceding claims, characterized in that the means of reflection of the electric field comprises an electrically conductive element in one piece or a set of discrete electrical conductive elements.

7. Device according to the preceding claim, characterized in that the reflection means is covered by an insulating coating (21).

8. Device according to one of the preceding claims, characterized in that the means of reflection of the electric field comprises electrically conductive grains in an insulating matrix.

9. Device according to one of the preceding claims, characterized in that an insulating coating (17; 17 '; 17 ") covers the assembly formed by the first surface and the electrodes in contact with this surface.

10. Device according to one of the preceding claims, characterized in that the electrodes have means (18, 19) for connecting them to the two poles of the same voltage generator (20).

1 1. Device according to one of the preceding claims, characterized in that the element (11) has a shape at least substantially flat.

12. Device (10 ') according to one of the preceding claims, characterized in that the element (11') has a shape at least substantially tubular, the first surface being the outer surface (12 ') of this form and the second surface being the inner surface (13 ') of this form.

13. Device (10 ") according to one of the preceding claims, characterized in that the element (1 1") has a shape at least substantially spherical, the first surface being the outer surface (12 ") of this form and the second surface being the inner surface (13 ") of this form.

14. Actuator (100; 1 10) comprising at least one device according to one of the preceding claims.