DIELECTRIC ELASTOMER ACTUATOR

Abstract

A dielectric elastomer actuator comprising: a plurality of polymer layer; a plurality of stretchable electrode layers, each polymer layer being sandwiched between two electrode layers so as to control the electric field within the polymer layer; at least one stretchable charge distribution layer, each charge distribution layer being adjacent to one stretchable electrode layer and/or to one polymer layer.

Claims

1. A dielectric elastomer actuator comprising: a plurality of polymer layers; a plurality of stretchable electrode layers, each polymer layer being sandwiched between two stretchable electrode layers so as to control the electric field within the polymer layer; at least one stretchable charge distribution layer, each charge distribution layer being adjacent to one stretchable electrode layer and/or to one polymer layer.

2. The actuator of claim 1, one charge distribution layer being provided between one stretchable electrode layer and one polymer layer.

3. The actuator of claim 2, one charge distribution layer being provided between each stretchable electrode layer and each polymer layer.

4. The actuator of claim 1, one stretchable charge distribution layer being juxtaposed next to a stretchable electrode layer.

5. The actuator of claim 1, at least one stretchable charge distribution layer surrounding a stretchable electrode layer on at least three sides.

6. The actuator of claim 1, the surface of the stretchable charge distribution layer being larger than the surface of the adjacent stretchable electrode layer.

7. The actuator of claim 1, the thickness of at least one stretchable charge distribution layer being variable over its surface.

8. The actuator of claim 1, the thickness of at least one stretchable electrode layer being variable over its surface.

9. The actuator of claim 1, the resistivity of at least one stretchable charge distribution layer being variable over its surface, so as to reduce the concentration of charges at the edge of an adjacent stretchable electrode layer.

10. The actuator of claim 1, the permittivity of at least one stretchable charge distribution layer being variable over its surface, so as to reduce the field concentration near the edge of an adjacent stretchable electrode layer.

11. The actuator of claim 1, the permittivity of at least one stretchable charge distribution layer being anisotropic.

12. The actuator of claim 1, the charges stretchable distribution layers comprising a silicone composite with carbon particles.

13. The actuator of claim 12, the concentration and/or dimension of the particles within the substrate being non homogeneous.

14. The actuator of claim 1, the stretchable electrode layers comprising a silicone composite with carbon particles.

15. An artificial muscle comprising the actuator of claim 1.

16. The actuator of claim 1, wherein each charge distribution layer has an electric resistivity in a range between 10.sup.10 and 10.sup.13 Ohm.Math.cm, wherein said stretchable electrode layer has an electric resistivity in a range between 1 and 10.sup.4 Ohm.Math.cm and wherein said polymer layer has an electric resistivity in a range between 10.sup.14 and 10.sup.17 Ohm.Math.cm.

17. A dielectric elastomer actuator comprising: a plurality of polymer layers; a plurality of stretchable electrode layers, each polymer layer being sandwiched between two stretchable electrode layers so as to control the electric field within the polymer layer; at least one stretchable charge distribution layer, each charge distribution layer being adjacent to one stretchable electrode layer and/or to one polymer layer, wherein each charge distribution layer has an electric resistivity in a range between 10.sup.10 and 10.sup.13 Ohm.Math.cm, wherein said stretchable electrode layer has an electric resistivity in a range between 1 and 10.sup.4 Ohm.Math.cm and wherein said polymer layer has an electric resistivity in a range between 10.sup.14 and 10.sup.17 Ohm.Math.cm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The invention will be better understood with the aid of the description of an embodiment given by way of example and illustrated by the figures, in which:

[0033] FIG. 1 shows a cross section of a conventional DEA with one single layer of polymer;

[0034] FIG. 2 shows a cross section of a conventional DEA with two layers of polymer;

[0035] FIG. 3 shows a cross section of a DEA according to a first embodiment of the invention;

[0036] FIG. 4 shows a cross section of a DEA according to a second embodiment of the invention;

[0037] FIG. 5 shows a cross section of a DEA according to a third embodiment of the invention;

[0038] FIG. 6 shows a cross section of a DEA according to a fourth embodiment of the invention;

[0039] FIG. 7 shows a cross section of a DEA according to a fifth embodiment of the invention.

[0040] FIG. 8 shows a cross section of a DEA according to a sixth embodiment of the invention.

DETAILED DESCRIPTION OF POSSIBLE EMBODIMENTS OF THE INVENTION

[0041] FIG. 3 shows an example of dielectric elastomer actuator (DEA) according to a first embodiment of the present invention. In the example, the embodiment comprises two layers 2 of dielectric polymer material sandwiched and separated by three conductive electrode layers 3. Application of a voltage difference between the electrode layers 3 create a deformation of the polymer layer 2. The layer 2 deflects with a change in electric field between the electrode layers 3. The polymer layers 2 may be prestrained.

[0042] In order to increase the force or energy for a given voltage and surface, a higher number of polymer layers 2 can be provided, each pair of adjacent layers 2 being separated by an electrode layer 3.

[0043] Intermediate charge distribution layers 4 are provided adjacent to the electrode layers 3, in this example on at least one side of at least one of the electrode layers 3, for controlling the repartition of electric charges around the electrode layers 3. The conductivity and thickness of the charge distribution layers 4 is determined to reduce the accumulation of charges at the edges of the electrode layers 3, thus reducing the risk of breakdown.

[0044] In one preferred embodiment, a charge distribution layer 4 is provided between at least one electrode layer 3 and the adjacent polymer layers.

[0045] In the illustrated example, a charge distribution layer is provided between each side of the intermediate electrode layer 3 and the two adjacent polymer layers 2. In another embodiment (not shown), it would also be possible to provide one charge distribution layer between only one side of the intermediate electrode layer 3 and one of the two adjacent polymer layers 2.

[0046] In order to reduce the thickness of the arrangement, no charge distribution layer is provided between the electrode layer 3 at each end of the stack and the adjacent polymer layers 2. It is also possible to have a charge distribution layer between each electrode layer and each adjacent polymer layer, as in FIG. 4.

[0047] In all embodiments, each of the layers 2,3,4 is stretchable, so that application of a voltage on the electrodes can not only produce a variation of the thickness of the layers 2, but also a deformation, such as for example a bending, of the whole stack. The electrode layers 3 and the charge distribution layers are compliant and conform to the changing shape of the polymer layer while maintaining electrical contact.

[0048] In all embodiments, the polymer layers 2 have preferably a thickness in a range between 5 and 300 μm. The thickness of the layer 2 can vary over its surface, for example in order to control its deformation. The electrode layers 3 have preferably a thickness in a range between 0.1 and 20 μm, for example between 5 and 10 μm. The thickness of the layer 3 can vary over its surface, for example with thicker edges in order to reduce the accumulation of electric charges at the edge.

[0049] The charge distribution layers 4 is preferably thicker than the electrode layers 3, in order to avoid the risk of creating a concentration of charges at its own edges. In one example, the charge distribution layers have a thickness in a range between 5 and 30 μm, preferably between 10 and 15 μm. The thickness of the layer 4 can vary over its surface, for example with thicker edges in order to control the distribution of charges and reduce the accumulation of electric charges at the edge.

[0050] In all embodiments, the polymer layers 2 can be made of an elastosil film. The electrode layers 3 can be done using a liquid silicone with embedded conductive particles, for example embedded metal or fine carbon particles. The charge distribution layers 4 could comprise a silicone matrix with fine carbon particles (carbon based silicone). Carbon based silicone has the advantage of easy deposition and reliable adhesion with the polymer layers 2 and with the electrode layers 3. The diameter of the carbon particles is preferably comprised in a range between 2 and 100 nm. The density of the carbon particles is preferably comprised in a range between 0.01% and 1%. The diameter, form and/or density of carbon particles can vary through the surface of the charge distribution layer, in order to better control the charge distribution.

[0051] In all embodiments, the charge distribution layers have an electric conductivity much higher than the conductivity of the dielectric polymer layers 2, but lower than the electrode layers 3. For example, the electric resistivity of the polymer layers 2 may be in a range between 10.sup.14 and 10.sup.17 Ohm.Math.cm; the electric resistivity of the electrode layers 3 may be in a range between 1 and 10.sup.4 Ohm.Math.cm; the electric resistivity of the charge distribution layers 3 may be in a range between 10.sup.10 and 10.sup.13 Ohm.Math.cm.

[0052] In all embodiments, the resistivity of the charge distribution layer may be variable over its surface, thus allowing for a better control of the charge distribution over the surface of the electrode layers. For example, the charge distribution lay may have a variable density of conductive particles in the silicon. The resistivity of the charge distribution layer may for example decreases progressively over its surface.

[0053] In all embodiments, the permittivity of the charge distribution layer may be variable over its surface, thus allowing for a better control of the electric field created by the charges over the surface of the electrode layers. The permittivity of the charge distribution layer may be anisotropy, in order to control the direction of the electrical field.

[0054] In order to further reduce the risk of field concentration, FIG. 5 proposes another embodiment in which the surface of the charge distribution layers 4 is larger than the surface of the adjacent superimposed electrode layers 3, so that the probability of sparks between electrode layers is reduced.

[0055] FIG. 6 proposes a further embodiment in which the charge distribution layers 4 are juxtaposed adjacent to the electrode layers 3, instead of being superimposed adjacent to the electrode layers as in the previous examples. In that example, the surface of the charge distribution layers 4 may be smaller or different than the surface of the adjacent juxtaposed electrode layers 3. The lower conductivity of the charge distribution layers reduces the accumulation of charge at the edge of the electrode layers, thus decreasing the field concentration.

[0056] FIG. 7 proposes a further embodiment in which each charge distribution layer 4 surrounds the edge of an electrode layer 3, resulting again in a reduction of the accumulation of charges and of the electrical fields at the edge of the electrode layer.

[0057] FIG. 8 proposes a further embodiment in which at least one charge distribution layer 4 surrounds at least three sides of an electrode layer 3, or possibly even 4 sides. The charge spreading is further improved, resulting again in a reduction of the accumulation of charges and of the electrical fields at the edge of the electrode layer.

[0058] All embodiments can be used for creating an artificial muscle, i.e. a transducer comprising one or several such dielectric elastomer actuators for generating a force and/or displacement when a voltage is applied.

[0059] Features described in relation with different embodiments can be combined.

[0060] Conditional language used herein, such as, among others, “can,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements or states. Thus, such conditional language is not generally intended to imply that features, elements or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements or states are included or are to be performed in any particular embodiment. The terms “comprising,” “including,” “having,” and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list. Further, the term “each,” as used herein, in addition to having its ordinary meaning, can mean any subset of a set of elements to which the term “each” is applied.