Patent Publication Number: US-2022224251-A1

Title: Electrostatic actuator having multilayer structure

Description:
TECHNICAL FIELD 
     The present invention relates to an electrostatic actuator having a multilayer structure. 
     BACKGROUND ART 
     There is a technique disclosed in a patent publication related to a dielectric elastomer actuator and a drive system thereof obtained in order to provide a dielectric elastomer actuator having an easy to use structure and a drive system thereof, and the dielectric elastomer actuator includes a drive element A having a structure in which an elastomer is sandwiched between a pair of stretchable electrodes, a drive element B having a structure in which an elastomer is sandwiched between a pair of stretchable electrodes, and a connection portion that connects the drive element A and the drive element B in series, in which when a voltage is applied between the pair of electrodes included in the drive element A and the pair of electrodes included in the drive element B, the pairs of electrodes are displaced in a direction parallel to an electric field generated between the pairs of electrodes to extend the elastomers in a direction perpendicular to the electric field, and the extension of the elastomers acts on each other via the connection portion (PTL 1). 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Patent Application Publication No. 2018-33293 A 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     The conventional electrostatic actuator has a structure in which a dielectric elastomer that is an elastic material is sandwiched between conductor layers, and has a structure in which a distance between the conductor layers is reduced by an electrostatic attraction generated by a voltage applied between the conductor layers facing each other. The dielectric elastomer also works as an insulating material between the conductor layers. Here, when a voltage is applied to the electrostatic actuator for a long time and a compressive force is applied to the dielectric elastomer by an electrostatic attraction for a long time, in a case where the dielectric elastomer is soft, the dielectric elastomer extends in the lateral direction together with the conductors, and there is a concern that molecules of a material for forming a layer of the dielectric elastomer (elastic layer) move due to a creep phenomenon, the layer collapses, and dielectric breakdown occurs. For this reason, the conventional electrostatic actuator cannot be used for a long period of time, and is difficult to put into practical use. On the other hand, in a case where a dielectric elastomer having a low elasticity is used, the contraction rate decreases and a sufficient stroke cannot be secured, which is disadvantageous. 
     An object of the present invention is to provide a stacked electrostatic actuator capable of maintaining insulation performance between conductor layers even when an elastic layer is deformed due to a creep phenomenon. Another object of the present invention is to provide a stacked electrostatic actuator capable of easily securing a sufficient stroke. 
     Solution to Problem 
     In order to solve the above-described disadvantage, a stacked electrostatic actuator according to Claim  1  includes 
     a plurality of electrode films that are stacked and bonded, 
     wherein each of the electrode films has a five-layer structure including an elastic layer, an insulating layer, a conductor layer, an insulating layer, and an elastic layer, and 
     a Young&#39;s modulus of a material for forming the elastic layers is smaller than a Young&#39;s modulus of a material for forming the insulating layers. 
     In order to solve the above-described disadvantage, a stacked electrostatic actuator according to Claim  2  includes 
     a plurality of electrode films that are stacked and bonded, 
     wherein each of the electrode films has a five-layer structure including an elastic layer, an insulating layer, a conductor layer, an insulating layer, and an elastic layer, and 
     a spring constant of a material for forming the elastic layers increases as the electrode films extend in a stacking direction. 
     The stacked electrostatic actuator according to Claim  3  is 
     the stacked electrostatic actuator according to Claim  1  or  2 , 
     wherein two adjacent ones of the electrode films are connected by adhesion, covalent bonding, or elastic body adhesive force between the elastic layers of the electrode films. 
     In order to solve the above-described disadvantage, a stacked electrostatic actuator according to Claim  4  includes 
     electrode layers each including a conductor layer and insulating layers disposed on both surfaces of the conductor layer, the electrode layers being stacked and bonded with an elastic layer interposed therebetween, 
     wherein a Young&#39;s modulus of a material for forming the elastic layer is smaller than a Young&#39;s modulus of a material for forming the insulating layers, or 
     a spring constant of a material for forming the elastic layer increases as the electrostatic actuator extends in a stacking direction. 
     The stacked electrostatic actuator according to Claim  5  is 
     the stacked electrostatic actuator according to Claim  4 , 
     wherein the elastic layer is a structure including a plurality of columns separated from each other in a surface direction of the electrode layers. 
     Advantageous Effects of Invention 
     According to the present invention, when a voltage is applied between the electrodes, the elastic layer is deformed softly, but the conductor layer is protected by the insulating layers. Even when the elastic layer is deformed due to a creep phenomenon by long-term voltage application, insulation of the conductor layer can be maintained by the insulating layers. As a result, it is possible to use an elastic material having a high elasticity, and it is possible to achieve both sufficient stroke and reliability. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of one layer of an electrode film included in a stacked electrostatic actuator according to a first embodiment. 
         FIG. 2  is a cross-sectional view of the entire stacked electrostatic actuator having a structure in which a plurality of the electrode films illustrated in  FIG. 1  is stacked and bonded. 
         FIG. 3  is a view illustrating a state in which an external force in a direction of separating the stacked layers is applied between two end members and an interval between the electrode films is increased. 
         FIG. 4  is a view illustrating a state in which an interval between electrode films is reduced when a voltage is applied. 
         FIG. 5  is a cross-sectional view of a stacked electrostatic actuator according to a second embodiment. 
         FIG. 6  is a modification of the stacked electrostatic actuator illustrated in  FIG. 5 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     An embodiment of the present invention will be described below with reference to the drawings.  FIG. 1  is a cross-sectional view of one layer of an electrode film  10  included in a stacked electrostatic actuator  1  according to a first embodiment.  FIG. 2  is a cross-sectional view of the entire stacked electrostatic actuator  1  having a structure in which a plurality of the electrode films  10  illustrated in  FIG. 1  is stacked and bonded. 
     Configuration 
     The stacked electrostatic actuator  1  is configured by stacking and bonding a large number of the electrode films  10   a  and  10   b  sandwiched between two end members (not illustrated) ( FIG. 2 , described below). As illustrated in  FIG. 1 , each of the electrode films  10   a  and  10   b  has a five-layer structure including a first elastic layer  11   a  and  11   b , a first insulating layer  12   a  and  12   b , a conductor layer  13   a  and  13   b , a second insulating layer  14   a  and  14   b , and a second elastic layer  15   a  and  15   b . In the following description, the first insulating layer  12   a  and  12   b , the conductor layer  13   a  and  13   b , and the second insulating layer  14   a  and  14   b  may be referred to as an electrode layer  16   a  and  16   b.    
     For the first elastic layer  11 ,  11   a  and the second elastic layer  15 ,  15   a , for example, a flexible material such as a gel, an acrylic resin, or a silicone resin is used. The conductor layer  13 ,  13   a  is made of, for example, a metal film such as copper, a conductive polymer, or a film having good electrical conductivity such as a conductive carbon allotrope (or a conductive mixture mainly including carbon). On the surfaces of the conductor layer  13 ,  13   a , insulating layers (first insulating layer  12 ,  12   a  and second insulating layer  14 ,  14   a ) are formed by coating, bonding, deposition, or the like, and the conductor layer  13 ,  13   a  is sandwiched between the first insulating layer  12 ,  12   a  and the second insulating layer  14 ,  14   a  to form the electrode layer  16 ,  16   a . As a material for the first and second insulating layers  12  and  14 ;  12   a  and  14   a , for example, an insulating polymer material such as parylene (registered trademark) may be used, or a ceramic or glass material having good withstand voltage characteristics may be used. The thickness of the electrode layer  16 ,  16   a  is, for example, several micrometers. 
     Here, as a material for forming the first elastic layer  11 ,  11   a  and the second elastic layer  15 ,  15   a , a material having a Young&#39;s modulus smaller than the Young&#39;s modulus of the material for forming the first insulating layer  12 ,  12   a  and the second insulating layer  14 ,  14   a  may be used. Alternatively, as a material for forming the first elastic layer  11 ,  11   a  and the second elastic layer  15 ,  15   a , a material having characteristics of increasing the spring constant as the stacked electrostatic actuator  1  extends in the stacking direction may be used. 
     The electrode films  10   a  and  10   b  having the above-described configuration are stacked and bonded to form the stacked electrostatic actuator  1 . The stack and bonding is performed, for example, by covalent bonding or elastic body adhesive force between elastic layers. Although the structure in which the elastic layers are bonded has been described, the electrode layers each including the conductor layer and the insulating layers disposed on both surfaces of the conductor layer may be stacked and bonded with an elastic layer interposed therebetween to form the electrostatic actuator. 
     Operation 
       FIG. 3  is a view illustrating a state in which an external force in a direction of separating the stacked layers is applied between two end members (not illustrated) and the interval between the electrode films  10   a  and  10   b  is increased, and  FIG. 4  is a view illustrating a state in which a voltage is applied and the interval between the electrode films  10   a  and  10   b  is reduced. 
     When receiving an external force in a direction of separating the electrode films  10 , the elastic layers  15   a  and  11   b  between the first electrode film  10   a  and the second electrode film  10   b  extend in the stacking direction, and at the same time, are recessed in the inward direction between the electrode films in a direction perpendicular to the stacking direction ( FIG. 3 ). When a voltage is applied between the conductor layers  13   a  and  13   b  of the first and second electrode films  10   a  and  10   b , the first and second electrode films  10   a  and  10   b  attract each other, and the elastic layers  15   a  and  11   b  contract in the stacking direction, and at the same time, bulge outward between the electrode films  10   a  and  10   b  in a direction perpendicular to the stacking direction ( FIG. 4 ). 
     When a voltage is applied, the elastic layers  15   a  and  11   b  are deformed, but the conductor layers  13   a  and  13   b  are protected by the insulating layers  14   a  and  12   b . Therefore, even if creep occurs in the elastic layers  15   a  and  11   b  due to long-time voltage application, dielectric breakdown does not occur due to the existence of the insulating layers  14   a  and  12   b  between the conductor layers  13   a  and  13   b  and the elastic layers  15   a  and  11   b , and the insulation performance of the conductor layers  13   a  and  13   b  is secured. As a result, it is possible to use a soft material for the elastic layers  15   a  and  11   b , and it is possible to achieve both securing of a sufficient stroke as an electrostatic actuator and reliability on insulation performance. 
     Second Embodiment 
       FIG. 5  is a cross-sectional view of a stacked electrostatic actuator  101  according to a second embodiment.  FIG. 6  is a modification of the stacked electrostatic actuator  101  illustrated in  FIG. 5 . The same or similar elements as those of the stacked electrostatic actuator  1  according to the first embodiment are denoted by the same or similar reference signs, and the description thereof will not be repeated. As illustrated in  FIG. 5 , the stacked electrostatic actuator  101  is formed by stacking and bonding electrode layers  116 , each of which includes a conductor layer  113  and insulating layers  112  and  114  disposed on respective surfaces of the conductor layer  113 , with an elastic layer  115  interposed therebetween. The elastic layer  115  has a plurality of columns  121   a  and  121   b  separated from each other in the surface direction of the electrode layer  116  with gaps  120   a  and  120   b  therein. 
     In the stacked electrostatic actuator  1  according to the first embodiment, the deformation amount in the vicinity of the outer peripheral surface of the elastic layer bulging outward becomes large, and a large stress is generated in the elastic layers  11  and  15 , particularly in the connection portion between the elastic layers  11  and  15  and the insulating layers  12  and  14 , in the vicinity of the outer peripheral surface of the stacked electrostatic actuator  1  (see  FIG. 4 ). On the other hand, by dividing the elastic layer  115  into columns as illustrated in  FIG. 5 , the columns  121   a  and  121   b  are deformed independently, so that the amount of deformation of the columns  121   a  and  121   b  is reduced, and the stress generated in the elastic layer  115  can be reduced. As a result, it is possible to achieve both securing of a sufficient stroke as a stacked electrostatic actuator and reliability on insulation performance. In addition, since all the columns  121   a  and  121   b  support each other against pulling, the strength is increased. The columns  121  may be connected at their ends ( FIG. 6( a ) ), or may be individually and independently connected to the insulating layers  114   a  and  112   b  ( FIG. 6( b ) ). In addition, the number, cross-sectional shape, and position of the columns are appropriately set considering the size of the surface of the electrode layer, the magnitude of the force applied to the stacked electrostatic actuator, required response performance, and the like. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Stacked electrostatic actuator 
               10 ,  10   a ,  10   b  Electrode film 
               11 ,  11   a ,  11   b  First elastic layer 
               12 ,  12   a .  12   b  First insulating layer 
               13 ,  13   a ,  13   b  Conductor layer 
               14 ,  14   a  Second insulating layer 
               15 ,  15   a  Second elastic layer 
               16 ,  16   a  Electrode layer 
               101  Stacked electrostatic actuator 
               113  Conductor layer 
               115  Elastic layer 
               116  Electrode portion 
               120   a ,  120   b  Gap 
               121   a ,  121   b  Column