Patent Publication Number: US-2020287478-A1

Title: Actuator

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2019-038170 filed on Mar. 4, 2019, incorporated herein by reference in its entirety 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an actuator. 
     2. Description of Related Art 
     An actuator using dielectric elastomers is known as one of conversion devices that are operated by converting an electrical energy into a mechanical energy. This actuator includes a dielectric elastomer film and a pair of electrode layers. The electrode layers are provided on respective sides of the dielectric elastomer film. When a voltage is applied between the electrode layers, the electrode layers attract each other by the Coulomb&#39;s force generated between the electrode layers. The dielectric elastomer film interposed between the electrode layers is elastically deformed so as to be compressed in a thickness direction of the film, and accordingly, elastically deformed and extend in a direction along the film surface (in a surface direction). 
     As the number of layers of dielectric elastomer film increases, a potential capacitance increases, and an output from the actuator also increases. In order to increase the number of layers of the film, a plurality of film bodies each having the dielectric elastomer film and the electrode layers are stacked as described in, for example, Japanese Unexamined Patent Application Publication No. 2011-103713 (JP 2011-103717 A). Alternatively, as described in the Japanese Unexamined Patent Application Publication No. 2018-93467 (JP 2018-93467 A), a dielectric elastomer film has an electrode layer printed on its entire surface, and two of those dielectric elastomer films are stacked on each other and rolled together. With the configurations described above, the actuator has a configuration in which the dielectric elastomer films are stacked on each other. 
     SUMMARY 
     According to the disclosure disclosed in JP 2018-93467 A, a configuration in which the plurality of layers of dielectric elastomer film are provided can be easily obtained. However, for example, when an actuator is configured to extend and be compressed in a direction of a central axis of the rolled films, a displacement amount (extension amount) is reduced as described below. That is, in the disclosure of JP 2018-93467 A, the electrode layer is provided in a planar shape in the dielectric elastomer film. With this configuration, when the film body having the dielectric elastomer film and the electrode layer is rolled, the direction in which the Coulomb&#39;s force acts is dispersed. That is, the rolled dielectric elastomer film extends in all surface directions (in all directions along the surface). This makes it difficult to obtain a desired large displacement amount with respect to the direction of the central axis of the rolled films, and thus the displacement amount becomes small. 
     In the case of the disclosures disclosed in JP 2011-103713 A and JP 2018-93467 A, the dielectric elastomer film and the electrode layer are in close contact with each other in the entire area. With this configuration, the dielectric elastomer film is hindered from being deformed by the electrode layer even if the dielectric elastomer film tries to deform in the surface direction when the voltage is applied, although the electrode layer is elastically deformable. 
     Consequently, with the actuator described above, it is difficult to obtain a large displacement amount. Therefore, the present disclosure provides an actuator that includes the dielectric elastomer film and the electrode layer and that can have a large displacement amount. 
     An actuator according to an aspect of the present disclosure includes a first film body having a first dielectric elastomer film and a first electrode layer provided on a surface of the first dielectric elastomer film; and a second film body having a second dielectric elastomer film and a second electrode layer provided on a surface of the second dielectric elastomer film. The actuator is configured such that the first film body and the second film body are stacked on each other. The electrode layer included in at least one of the first film body and the second film body includes a plurality of linear electrodes extending in a first direction and provided at intervals in a second direction that is orthogonal to the first direction. 
     According to the actuator above, when the first film body and the second film body are repeatedly stacked on each other, each of the first dielectric elastomer film and the second dielectric elastomer film is interposed between the first electrode layer and the second electrode layer. When a voltage is applied to the first electrode layer and the second electrode layer, each of the first and second dielectric elastomer films extends in a direction (surface direction) along a surface of the film. The electrode layer of the actuator according to the present disclosure has the plurality of linear electrodes extending in the first direction, and the linear electrodes are provided at intervals in the second direction. Therefore, in the electrode layer, the action of hindering extension of the dielectric elastomer film in the second direction is alleviated. Accordingly, the dielectric elastomer film is able to easily extend in the second direction, and a displacement amount (extension amount) in the second direction thus increases. With the configuration above, the actuator having a large displacement amount (extension amount) can be obtained. 
     In the above aspect, the first film body and the second film body may be rolled while the first film body and the second film body are stacked on each other. With this configuration, the actuator having a cylindrical shape and having a configuration in which the first film body and the second film body are repeatedly stacked on each other can be easily fabricated. Furthermore, the first film body and the second film body may be rolled such that the first direction coincides with a direction in which the first film body and the second film body are rolled while the first film body and the second film body are stacked on each other. With this configuration, the second direction serves as an axial direction of the cylindrical shape. The actuator that is able to have a large displacement amount (extension amount) in the axial direction can be obtained. 
     In the above aspect, the electrode layer may include the plurality of linear electrodes extending in the first direction, a first connection electrode connecting a first end of one of the linear electrodes and a first end of another one of the linear electrodes that is adjacent to the one of the linear electrodes on one side, a second connection electrode connecting a second end of the one of the linear electrodes and a second end of yet another one of the linear electrodes that is adjacent to the one of the linear electrodes on the other side. With this configuration, the linear electrodes are widely disposed in a zigzag arrangement on the dielectric elastomer film. A configuration can be obtained in which the linear electrodes provided at intervals in the second direction are electrically connected in series. Therefore, an electric charge generated in the dielectric elastomer film along a longitudinal direction of the linear electrodes becomes uniform, and the Coulomb&#39;s force that is entirely uniform is generated. Therefore, the actuator can be deformed in the second direction with a uniform and impartial deformation amount. 
     According to the present disclosure, the actuator having a large displacement amount (extension amount) can be obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein: 
         FIG. 1  is a perspective view showing an embodiment of an actuator; 
         FIG. 2  is a perspective view showing the actuator in operation; 
         FIG. 3  is an illustrative view showing a state in which the actuator having a rolled shape is unrolled to be a planar state; 
         FIG. 4  is an illustrative view showing a manufacturing method of the actuator having a rolled shape; 
         FIG. 5  is a sectional view showing a part of the actuator having a cylindrical shape; 
         FIG. 6  is a view illustrating a function of the actuator; 
         FIG. 7  is a view illustrating a modification example of the actuator; 
         FIG. 8  is a view illustrating a modification example of the actuator; 
         FIG. 9  is a view illustrating a function of the actuator shown in  FIG. 8 ; 
         FIG. 10  is a perspective view showing an actuator according to another embodiment; and 
         FIG. 11  is an illustrative view showing a modification example of a first electrode layer included in a first film body. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Outline of Actuator 
       FIG. 1  is a perspective view showing an embodiment of an actuator. An actuator  7  shown in  FIG. 1  is one of conversion devices that are operated by converting an electric energy into a mechanical energy. The detailed configuration and operations of the actuator  7  are described later. The actuator  7  includes dielectric elastomer films  11 ,  21  and a pair of electrode layers  13 ,  23 . When a voltage is applied to the electrode layers  13 ,  23  with one of the electrode layers  13 ,  23  set as positive and the other set as negative, the actuator  7  is deformed as shown in  FIG. 2 . 
     The actuator  7  shown in  FIG. 1  has a cylindrical shape in which the dielectric elastomer films  11 ,  21  are rolled. The dielectric elastomer films  11 ,  21  include the electrode layers  13 ,  23 , on the surfaces of the dielectric elastomer films  11 ,  21 , respectively. When a voltage is applied to the electrode layers  13 ,  23 , the actuator  7  is elastically deformed from the initial state and extends in a direction along a central axis C 0  of the cylindrical shape of the rolled films. When application of the voltage to the electrode layers  13 ,  23  is stopped, the actuator  7  regains its initial state as shown in  FIG. 1  by an elastic restoring force. In  FIG. 2 , the deformation amount is shown larger than the actual deformation amount to make description understandable. 
     Specific Configuration of Actuator  7   
       FIG. 3  is an illustrative diagram showing a state in which the actuator  7  having a rolled shape as shown in  FIG. 1  is unrolled to be a planar state. The actuator  7  includes a first film body  10  and a second film body  20 . The actuator  7  is configured by stacking the first film body  10  and the second film body  20  on each other and rolling the stacked first film body  10  and the second film body  20 . As shown in  FIG. 4 , the actuator  7  is configured by stacking the first film body  10  and the second film body  20  on each other and rolling the stacked first film body  10  and the second film body  20  around, for example, a core  9  that has an elongated cylindrical shape. After the first film body  10  and the second film body  20  are rolled, the core  9  is taken out of the rolled film bodies. 
     As shown in  FIG. 3 , the first film body  10  includes a first dielectric elastomer film  11  and a first electrode layer  13  provided on a surface  12  of the first dielectric elastomer film  11 . The second film body  20  includes the second dielectric elastomer film  21  and the second electrode layer  23  provided on the surface  22  of the second dielectric elastomer film  21 . The first dielectric elastomer film  11  is a different member (dielectric film) from the second dielectric elastomer film  21 . The first electrode layer  13  is a different electrode (member) from the second electrode layer  23 . The first electrode layer  13  and the second electrode layer  23  are electrodes having electrically different (positive and negative) signs. 
     As shown in  FIG. 3 , the first dielectric elastomer film  11  includes a plurality of linear electrodes  14 , and first connection electrodes  15  and second connection electrodes  16  on the surface  12  of the first dielectric elastomer film  11 . The first connection electrode  15  and the second connection electrode  16  connect between the ends of the linear electrodes  14  that are adjacent to each other. Each of the linear electrodes  14  extends linearly along a first direction X. The linear electrodes  14  are provided at intervals in a second direction Y. The first direction X is orthogonal to the second direction Y. The reference numeral for one of the linear electrodes  14  is denoted as “ 14 - 1 ” in the first film body  10  shown in  FIG. 3 . The reference numeral for another one of the linear electrodes  14  that is adjacent to the linear electrode  14 - 1  on one side in the second direction Y is denoted as “ 14 - 2 ”. The reference numeral for yet another one of the linear electrodes  14  that is adjacent to the linear electrode  14 - 1  on the other side in the second direction Y is denoted as “ 14 - 3 ”. The first connection electrode  15  connects a first end  14 - 1   a  of the linear electrode  14 - 1  in the first direction X and a first end  14 - 2   a  of the linear electrode  14 - 2  in the first direction X. The second connection electrode  16  connects a second end  14 - 1   b  of the linear electrode  14 - 1  in the first direction X and a second end  14 - 3   b  of the linear electrode  14 - 3  in the first direction X. 
     A configuration is thus obtained in which electrodes (wiring pattern) are disposed in a zigzag arrangement consisting of the linear electrodes  14 , the first connection electrodes  15 , and the second connection electrodes  16 . The first electrode layer  13  consists of the linear electrodes  14 , the first connection electrodes  15 , and the second connection electrodes  16 . The linear electrodes  14 , the first connection electrodes  15 , and the second connection electrodes  16  are provided on the surface  12  of the dielectric elastomer film  11  by printing or coating. That is, the electrode layer  13  is fixed to the dielectric elastomer film  11 . 
     The second electrode layer  23  of the second film body  20  has the same configuration as that of the first electrode layer  13 . That is, the second dielectric elastomer film  21  includes a plurality of linear electrodes  24 , and first connection electrodes  25  and second connection electrodes  26  on the surface  22  of the second dielectric elastomer film  21 . The first connection electrode  25  and the second connection electrode  26  connect the respective ends of the linear electrodes  24  that are adjacent to each other. Each of the linear electrodes  24  extends linearly along the first direction X. The linear electrodes  24  are provided at intervals in the second direction Y. The reference numeral for one of the linear electrodes  24  is denoted as “ 24 - 1 ” in the second film body  20  shown in  FIG. 3 . The reference numeral for another one of the linear electrodes  24  that is adjacent to the linear electrode  24 - 1  on the one side in the second direction Y is denoted as “ 24 - 2 ”. The reference numeral for yet another one of the linear electrodes  24  that is adjacent to the linear electrode  24 - 1  on the other side in the second direction Y is denoted as “ 24 - 3 ”. The first connection electrode  25  connects a first end  24 - 1   a  of the linear electrode  24 - 1  in the first direction X and a first end  24 - 2   a  of the linear electrode  24 - 2  in the first direction X. The second connection electrode  26  connects a second end  24 - 1   b  of the linear electrode  24 - 1  in the first direction X and a second end  24 - 3   b  of the linear electrode  24 - 3  in the first direction X. 
     A configuration is thus obtained in which the electrodes (wiring pattern) are disposed in a zigzag arrangement consisting of the linear electrodes  24 , the first connection electrodes  25 , and the second connection electrodes  26 . The second electrode layer  23  consists of the linear electrodes  24 , the first connection electrodes  25 , and the second connection electrodes  26 . The linear electrodes  24 , the first connection electrodes  25 , and the second connection electrodes  26  are provided on the surface  22  of the second dielectric elastomer film  21  by printing or coating. That is, the electrode layer  23  is fixed to the second dielectric elastomer film  21 . 
     Each of the first dielectric elastomer film  11  and the second dielectric elastomer film  21  consists of a rectangular sheet. The first and second dielectric elastomer films  11 ,  21  are made of rubber, such as silicon rubber, acrylic rubber, urethane rubber, and nitrile rubber (NBR). Each of the first electrode layer  13  and the second electrode layer  23  is made of an elastic material having conductivity. For example, the electrode layers  13 ,  23  are made of conductive silicon rubber and conductive gel. A conductive material (conductive filler), such as carbon black, is added to the elastic material such that the electrode layers  13 ,  23  have conductivity. 
     As described above (see  FIGS. 1 and 4 ), the first film body  10  and the second film body  20  are stacked on each other and rolled in a stacked state such that the first film body  10  and the second film body  20  are alternately arranged and the actuator  7  has a cylindrical shape.  FIG. 5  is a sectional view showing a part of the actuator  7  having a cylindrical shape.  FIG. 5  shows a part of a section including the central axis C 0  (see  FIG. 1 ) of the actuator  7  having a cylindrical shape. The right side in  FIG. 5  is closer to the central axis C 0 , and referred to as a radially inner side. The left side in  FIG. 5  is a side opposite to the central axis C 0 , and referred to as a radially outer side. 
     The first film body  10  is stacked on the second film body  20  on the radially outer side (on the right side in  FIG. 5 ) such that the first electrode layer  13  is positioned along a surface (the surface  12 ) of the first dielectric elastomer film  11  on the radially outer side, and the second electrode layer  23  is positioned along a surface of the first dielectric elastomer film  11  on the radially inner side. That is, the first dielectric elastomer film  11  is interposed between the first electrode layer  13  and the second electrode layer  23 . The second film body  20  is stacked on the first film body  10  on the radially outer side such that the second electrode layer  23  is positioned along a surface (the surface  22 ) of the second dielectric elastomer film  21  on the radially outer side, and the first electrode layer  13  is positioned along a surface of the second dielectric elastomer film  21  on the radially inner side. That is, the second dielectric elastomer film  21  is interposed between the first electrode layer  13  and the second electrode layer  23 . 
     As described above (see  FIGS. 3 and 4 ), the first linear electrodes  14  are provided at intervals in the second direction Y. Therefore, in  FIG. 5 , a gap (space) g 1  is provided between the first linear electrodes  14  that are adjacent to each other in the second direction Y. The gap g 1  is continuous in a circumferential direction (in the first direction X). Similarly, the second linear electrodes  24  are provided at intervals in the second direction Y. Therefore, a gap (space) g 2  is provided between the second linear electrodes  24  that are adjacent to each other in the second direction Y. The gap g 2  is continuous in the circumferential direction (in the first direction X). 
     A voltage is applied to the first electrode layer  13  and the second electrode layer  23 . Application of the voltage will be described with reference to  FIG. 3  that shows a state in which the actuator  7  is unrolled. The voltage is applied to the first electrode layer  13  and the second electrode layer  23  with an end  27  of the linear electrode  14  that is a part of the first electrode layer  13  and an end  28  of the linear electrode  24  that is a part of the second electrode layer  23  serve as terminals. For example, the end  27  of the first electrode layer  13  serves as a positive terminal, and the end  28  of the second electrode layer  23  serves as a negative terminal. 
     When the voltage is applied to the first electrode layer  13  and the second electrode layer  23 , the electrode layers  13 ,  23  attract each other by the Coulomb&#39;s force generated between the electrode layers  13 ,  23 . The first dielectric elastomer film  11  interposed between the electrode layers  13 ,  23 , as shown in  FIG. 5 , is elastically deformed to be compressed in a film thickness direction, that is, in a radial direction. Similarly, the second dielectric elastomer film  21  interposed between the electrode layers  13 ,  23  is elastically deformed to be compressed in the film thickness direction, that is, in the radial direction. Accordingly, the entire actuator  7  becomes thin (smaller in the radial direction) as shown in  FIG. 2 . 
     On the other hand, when the voltage is applied, each of the first and the second dielectric elastomer films  11 ,  21  extends in a direction along the surfaces of the films (in the surface direction), as shown in  FIG. 5 . Each of the dielectric elastomer films  11 ,  21  extends in a direction orthogonal to the paper surface in  FIG. 5 , in other words, in the circumferential direction about the central axis C, and also extends in a direction parallel to the central axis C that is along a vertical direction in  FIG. 5 . The direction parallel to the central axis C is coincident with the second direction Y. The linear electrodes  14 ,  24  are elongated along the circumferential direction about the central axis C. Therefore, extension of the first and second dielectric elastomer films  11 ,  21  in the circumferential direction is partially hindered by the linear electrodes  14 ,  24 . On the other hand, the linear electrodes  14 ,  24  are provided at intervals in the direction parallel to the central axis C (the second direction Y). Therefore, extension of the first and the second dielectric elastomer films  11 ,  21  in the direction parallel to the central axis C is not hindered by the linear electrodes  14 ,  24 . Therefore, the actuator  7  extends to a greater extent in the direction parallel to the central axis C, in other words, in the second direction Y. 
     As described above, the actuator  7  of the present disclosure is configured such that the first film body  10  and the second film body  20  are stacked on each other. The first film body  10  includes the first dielectric elastomer film  11  and the first electrode layer  13  provided on the surface  12  of the first dielectric elastomer film  11 . The second film body  20  includes the second dielectric elastomer film  21  and the second electrode layer  23  provided on the surface  22  of the second dielectric elastomer film  21 . As shown in  FIG. 3 , the first electrode layer  13  includes the plurality of linear electrodes  14  extending in the first direction X and provided at intervals in the second direction Y. The second electrode layer  23  includes the plurality of linear electrodes  24  extending in the first direction X and provided at intervals in the second direction Y. 
     In the actuator  7 , as shown in  FIG. 5 , the first film body  10  and the second film body  20  are stacked on each other, and each of the first dielectric elastomer film  11  and the second dielectric elastomer film  21  is interposed between the first electrode layer  13  and the second electrode layer  23 . When the voltage is applied to the first electrode layer  13  and the second electrode layer  23 , the electrode layers  13 ,  23  attract each other by the Coulomb&#39;s force generated between the electrode layers  13 ,  23 . Then, the first dielectric elastomer film  11  interposed between the electrode layers  13 ,  23  and the second dielectric elastomer film  21  interposed between the electrode layers  13 ,  23  are each elastically deformed such that the first dielectric elastomer film  11  and the second dielectric elastomer film  21  are compressed in the film thickness direction. This extends each of the first dielectric elastomer film  11  and the second dielectric elastomer film  21  in the direction along the surfaces of the films (in the surface direction). 
     In the first film body  10 , the first electrode layer  13  is provided (fixed) on the surface  12  of the first dielectric elastomer film  11 . With this configuration, the first dielectric elastomer film  11  is hindered from being deformed by the first electrode layer  13  even if the first dielectric elastomer film  11  tries to extend in the surface direction, although the first electrode layer  13  is elastically deformable. However, the first electrode layer  13  included in the actuator  7  of the present disclosure has the plurality of linear electrodes  14  extending in the first direction X, and the linear electrodes  14  are provided at intervals in the second direction Y as described above. Accordingly, the action of the first electrode layer  13  to hinder the extension of the first dielectric elastomer film  11  in the second direction Y is alleviated. Therefore, the first dielectric elastomer film  11  has a large displacement amount (extension amount) in the second direction Y. 
     The second film body  20  also has the function to alleviate the action of hindering the extension in the second direction Y as described above. That is, the second electrode layer  23  has the plurality of linear electrodes  24  extending in the first direction X, and the linear electrodes  24  are provided at intervals in the second direction Y as described above. Therefore, the second dielectric elastomer film  21  has a large displacement amount (extension amount) in the second direction. Consequently, the actuator  7  having a large displacement amount (extension amount) can be obtained. 
     Here, in general, as the number of layers of the dielectric elastomer film increases, the potential capacitance increases, and the output of the actuator increases. In the present disclosure, to increase the number of layers, the first film body  10  and the second film body  20  are rolled while the first film body  10  and the second film body  20  are stacked on each ether. With this configuration, the actuator  7  having a cylindrical shape and having a configuration in which the first film body  10  and the second film body  20  are repeatedly stacked on each other can be easily fabricated. In particular, as shown in  FIG. 4 , the first film body  10  and the second film body  20  are rolled in the stacked state such that the direction in which the first film body  10  and the second film body  20  are rolled coincides with the first direction X. The second direction Y thus coincides with an axial direction along the central axis C 0 . Accordingly, the actuator  7  can have a large displacement amount (extent amount) in the axial direction as the output from the actuator  7 . 
     As described above, the first electrode layer  13  includes the plurality of linear electrodes  14  extending in the first direction, the first connection electrode  15  connecting the first ends of the linear electrode  14 - 1  and the linear electrode  14 - 2  that are adjacent to each other in the second direction Y, and the second connection electrode  16  connecting the second ends of the linear electrode  14 - 1  and the linear electrode  14 - 3  that are adjacent to each other in the second direction Y. Similar to the first electrode layer  13 , the second electrode layer  23  includes the plurality of linear electrodes  24  extending in the first direction, the first connection electrode  25  connecting the first ends of the linear electrodes  24 - 1  and the linear electrode  24 - 2  that are adjacent to each other in the second direction Y, and the second connection electrode  26  connecting the second ends of the linear electrode  24 - 1  and the linear electrode  24 - 3  that are adjacent to each other in the second direction Y. 
     Therefore, as shown in  FIG. 3 , in the first dielectric elastomer film  11 , the linear electrodes  14  are widely disposed in a zigzag arrangement. Then, a configuration is obtained in which the linear electrodes  14  provided at intervals in the second direction Y are electrically connected in series. Accordingly, an electric charge generated in the first dielectric elastomer film  11  along a longitudinal direction of the linear electrode  14  is uniform. Similar to the first dielectric elastomer film  11 , the linear electrodes  24  are widely disposed in a zigzag arrangement in the second dielectric elastomer film  21 . A configuration is obtained in which the linear electrodes  24  provided at intervals in the second direction Y are electrically connected in series. Accordingly, an electric charge generated in the first dielectric elastomer film  11  along a longitudinal direction of the linear electrode  24  is uniform. From the above, the Coulomb&#39;s force that is entirely uniform is generated in each of the first film body  10  and the second film body  20 . Therefore, the actuator  7  can be deformed in the second direction Y with a uniform and impartial deformation amount. 
       FIG. 6  is a diagram that describes a function of the actuator  7  including the configuration described above. Support surfaces  31 ,  32  are provided on respective axial sides of the actuator  7  having the configuration in which the film bodies are rolled. The support surfaces  31 ,  32  are the surfaces of a first member and a second member, respectively, between which the actuator  7  is interposed. When the voltage is applied to the electrode layers  13 ,  23 , the actuator  7  extends in the axial direction. Accordingly, the first member (the support surface  31 ) and the second member (the support surface  32 ) become relatively distant away from each other in the axial direction. When application of the voltage is stopped, the extended actuator  7  is compressed in the axial direction by the elastic restoring force and regains its initial state. 
     As shown in  FIG. 7 , a plurality of the actuators  7  may be interposed between the support surfaces  31 ,  32 . The central axes C 0  of the respective actuators  7  are parallel to each other. With this configuration, the actuators  7  having a large thrust force can be obtained. 
     As shown in  FIG. 2 , the actuator  7  extends in the axial direction and is compressed in the radial direction. Therefore, as shown in  FIG. 8 , the actuator  7  having the configuration in which the film bodies are rolled may be flattened. That is, the actuator  7  shown in  FIG. 8  has a flattened shape in which a dimension B 2  in a second radial direction that is orthogonal to a first radial direction is larger than a dimension B 131  in the first radial direction. 
     With this configuration, as shown in  FIG. 9 , the support surfaces  31 ,  32  are provided on the respective sides of, in the first radial direction, the actuator  7  having the configuration in which the film bodies are rolled as shown in  FIG. 8 . The actuator  7  is compressed in the first radial direction when the voltage is applied to the electrode layers  13 ,  23 . Consequently, the first member (the support surface  31 ) and the second member (the support surface  32 ) relatively approach with each other in the axial direction. When application of the voltage is stopped, the compressed actuator  7  extends by the elastic restoring force and regains its initial state. This widens a gap between the first member (the support surface  31 ) and the second member (the support surface  32 ). The support surfaces  31 ,  32  may be provided on the respective sides of the actuator  7  in the second radial direction, which is a different configuration from that shown in  FIG. 9 . 
       FIG. 10  is a perspective view showing another embodiment of the actuator  7 .  FIG. 10  shows an exploded view of a part of the actuator  7  (the first film body  10 ). The actuator  7  shown in  FIG. 10  includes the first film body  10  and the second film body  20 . This configuration is the same as those of the embodiments described above. The actuators  7  in the above embodiments (see  FIG. 1 , for example) are configured by rolling the film bodies. In contrast, the actuator  7  shown in  FIG. 10  includes a plurality of the first film bodies  10 , each of which has a sheet shape, and a plurality of the second film bodies  20 , each of which has a sheet shape. In the actuator  7 , the first film bodies  10  and the second film bodies  20  are alternately stacked on each other. The first direction X in the first film body  10  is the same direction as the first direction X in the second film body  20 . 
     The first electrode layer  13  included in the first film body  10  includes the plurality of linear electrodes  14  extending in the first direction X and provided at intervals in the second direction Y. The second electrode layer  23  included in the second film body  20  includes the plurality of linear electrodes  24  extending in the first direction X and provided at intervals in the second direction Y. The configuration of each portion in each of the first film body  10  and the second film body  20  is the same as the configuration of each portion described in the above embodiments as shown in, for example,  FIG. 3 . Therefore, the description thereof will be omitted. 
       FIG. 11  is an illustrative view showing a modification example of the first electrode layer  13  included in the first film body  10 . In each of the above embodiments, as shown in  FIG. 3  for example, the first electrode layer  13  has a configuration in which the electrodes are disposed in a zigzag arrangement. On the other hand, the first electrode layer  13  shown in  FIG. 11  includes the plurality of the linear electrodes  14  extending in the first direction X and provided at intervals in the second direction Y, and connection electrodes  17  connecting ends  14   a  of the linear electrodes  14  in the longitudinal direction. The first electrode layer  13  has a configuration in which the electrodes are disposed in a pectinate arrangement consisting of the linear electrodes  14  and the connection electrodes  17 . With this configuration, even if wire disconnection occurs in one of the linear electrodes  14 , the function of the actuator  7  is not impaired. Although not shown, the second film body  20  also has the same configuration (pectinate arrangement of electrodes) as that of the first film body  10  shown in  FIG. 11 . 
     In each of the above embodiments, both the first electrode layer  13  of the first film body  10  and the second electrode layer  23  of the second film body  20  include the plurality of linear electrodes ( 14 ,  24 ) extending in the first direction X and provided at intervals in the second direction Y. However, the electrode layer having the configuration including the linear electrodes described above may be an electrode layer included in at least one of the first film body  10  and the second film body  20 . That is, in one of the film bodies, the electrode layer may be provided in a planar shape on the entire dielectric elastomer film. 
     As described above, the actuator  7  of the present disclosure can have a large displacement amount (extension amount). 
     The embodiments disclosed herein are illustrative but not restrictive in all respects. The scope of the disclosure is not limited to the embodiments described above, and includes any and all modifications within the scope equivalent to the configuration described in the claims.