Patent Publication Number: US-2019192821-A1

Title: Actuator, actuator module, endoscope, endoscope module, and controlling method

Description:
TECHNICAL FIELD 
     The present technology relates to an actuator, an actuator module, an endoscope, an endoscope module, and a controlling method. 
     BACKGROUND ART 
     An actuator which winds a tensioned dielectric elastomer soft actuator around a spring and expand and contract or bend to be deformed by application of a voltage is suggested (refer to, for example, Patent Document 1). This actuator is characterized in generating large displacement having a small size and a light weight. 
     CITATION LIST 
     Patent Document 
     Patent Document 1: Japanese Unexamined Patent Application Publication No. 2006-520180 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, the actuator described above might cause insulation breakdown. 
     An object of the present technology is to provide an actuator, an actuator module, an endoscope, an endoscope module, and a controlling method capable of improving insulation resistance. 
     Solutions to Problems 
     In order to solve the above problem, a first technology is an actuator provided with a tubular actuator element, and a supporting body which supports an inner peripheral surface of the actuator element, in which an internal pressure of the actuator element is higher than an external pressure of the actuator element. 
     A second technology is an endoscope provided with the actuator of the first technology. 
     A third technology is an actuator module provided with an actuator including a tubular actuator element, and a supporting body which supports an inner peripheral surface of the actuator element, a control unit which controls drive of the actuator, and a pressurizing unit which pressurizes an internal space of the actuator. 
     A fourth technology is an endoscope module provided with the actuator module of the third technology. 
     A fifth technology is an actuator provided with an actuator element, and a supporting body which supports the actuator element, in which an internal pressure of the actuator element is higher than an external pressure of the actuator element. 
     A sixth technology is a controlling method provided with detecting a pressure in an internal space of an actuator, and pressurizing the internal space of the actuator on the basis of a result of the detection. 
     Effects of the Invention 
     According to the present technology, insulation resistance of the actuator may be improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a cross-sectional view illustrating a configuration of an actuator according to a first embodiment of the present technology.  FIG. 1B  is an enlarged view illustrating a part of  FIG. 1A . 
         FIG. 2A  is a side view illustrating a configuration of an actuator element.  FIG. 2B  is a cross-sectional view taken along line IIB-IIB of  FIG. 2A . 
         FIG. 3  is a cross-sectional view illustrating a variation of a supporting body. 
         FIG. 4A  is a cross-sectional view illustrating a variation of a supporting body.  FIG. 4B  is an enlarged view illustrating a part of  FIG. 4A . 
         FIG. 5A  is a cross-sectional view illustrating a variation of a supporting body.  FIG. 5B  is an enlarged view illustrating a part of  FIG. 5A . 
         FIG. 6A  is a cross-sectional view illustrating a variation of a supporting body.  FIG. 6B  is an enlarged view illustrating a part of  FIG. 6A . 
         FIG. 7A  is a cross-sectional view illustrating a variation of a supporting body.  FIG. 7B  is an enlarged view illustrating a part of  FIG. 7A . 
         FIG. 8  is a cross-sectional view illustrating a variation of a supporting body. 
         FIG. 9  is a cross-sectional view illustrating a variation of a supporting body. 
         FIGS. 10A and 10B  are flowcharts for illustrating a variation of a method of manufacturing an actuator. 
         FIG. 11  is a cross-sectional view illustrating a configuration of an endoscope module according to a second embodiment of the present technology. 
         FIG. 12  is a plan view illustrating a configuration of a tip end. 
         FIG. 13  is a flowchart for illustrating a method of controlling an internal pressure at power on. 
         FIG. 14  is a flowchart for illustrating a method of controlling an internal pressure at the time of operation. 
         FIG. 15  is a cross-sectional view illustrating a configuration of an endoscope module according to a variation of a second embodiment of the present technology. 
         FIG. 16  is a cross-sectional view illustrating a configuration of an endoscope module according to a third embodiment of the present technology. 
         FIG. 17  is a perspective view illustrating a configuration of an actuator according to a fourth embodiment of the present technology. 
         FIG. 18  is a perspective view illustrating a configuration of an actuator according to a variation of a fifth embodiment of the present technology. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     The embodiments of the present technology are described in the following order. 
     1 First Embodiment (Example of Actuator) 
     2 Second Embodiment (Example of Endoscope Module) 
     3 Third Embodiment (Example of Endoscope Module) 
     4 Fourth Embodiment (Example of Actuator) 
     5 Fifth Embodiment (Example of Actuator) 
     1 First Embodiment 
     [Summary] 
     In order to figure out a cause of occurrence of insulation breakdown, the inventors of the present invention performed finite element method (FEM) analysis regarding an actuator provided with a tubular actuator element and a coil spring (supporting body) which supports an inner peripheral surface of the actuator element. As a result, the following was found. In other words, in the actuator having the above-described configuration, the actuator element covering a side surface of the coil spring bites into a space between the coil spring and a constriction might occur on the side surface of the actuator element. When such constriction occurs, a thickness of the actuator element becomes nonuniform, and the insulation breakdown tends to occur at a portion where the thickness is small. 
     Therefore, the inventors of the present invention conducted intensive studies to suppress the constriction occurring on the side surface of the actuator element. As a result, a configuration in which an internal pressure of the actuator is made higher than an external pressure of the actuator was found. Hereinafter, the actuator having such a configuration is described. 
     [Configuration of Actuator] 
     An actuator  10  according to a first embodiment of the present technology is a so-called electrostrictive actuator, and is provided with a cylindrical actuator element  11 , a cylindrical coil spring  12  which supports an inner peripheral surface of the actuator element  11 , and sealing members  13  and  14  which close openings at both ends of the actuator element  11  as illustrated in  FIG. 1A . The actuator  10  may further be provided with a cylindrical protective layer not illustrated which covers an outer peripheral surface of the actuator element  11 . 
     The actuator  10  is suitably used in a medical instrument such as an endoscope, an industrial instrument, an electronic device, a speaker, an artificial muscle, a robot, a robot suit and the like. The actuator  10  may be continuously usable or disposable. In a case where the actuator  10  is applied to the medical instrument such as the endoscope, it is preferable that the actuator  10  is disposable from a hygienic viewpoint. 
     The actuator  10  includes a sealed cylindrical internal space and the coil spring  12  is provided in the internal space. The internal space is filled with gas as a fluid. The gas is at least one type of air, a rare gas, carbon dioxide and the like, for example. An internal pressure of the actuator  10  is higher than an external pressure of the actuator  10 . For this reason, it is possible to suppress occurrence of constriction as indicated by a dashed-two dotted line in  FIG. 1B  on the peripheral surface of the actuator element  11 , so that insulation resistance of the actuator  10  may be improved. In this specification, the pressure in the internal space of the actuator  10  is referred to as the internal pressure of the actuator  10 , and the pressure of the external space of the actuator element  11  is referred to as the external pressure of the actuator  10 . 
     Hereinafter, the actuator element  11 , the coil spring  12 , the sealing members  13  and  14 , and the protective layer included in the actuator  10  are sequentially described. 
     (Actuator Element) 
     The actuator element  11  has a sheet shape. The actuator element  11  may be formed into a cylindrical shape in advance, or may be wound around the coil spring  12  to have the cylindrical shape. 
     The actuator element  11  is a so-called dielectric elastomer actuator element and is provided with, as illustrated in  FIGS. 2A and 2B , a cylindrical dielectric layer  11   a , a plurality of electrodes (first electrodes)  11   b  provided on an inner peripheral surface of the dielectric layer  11   a , and a plurality of electrodes (second electrodes)  11   c  provided on an outer peripheral surface of the dielectric layer  11   a . The electrode  11   b  may be directly formed on the inner peripheral surface of the dielectric layer  11   a  or may be bonded via a bonding layer. Furthermore, the electrode  11   c  may be directly formed on the outer peripheral surface of the dielectric layer  11   a  or may be bonded via a bonding layer. Herein, an adhesive layer is defined as one type of the bonding layer. 
     (Dielectric Layer) 
     The dielectric layer lie is a sheet having a stretching property. The dielectric layer  11   a  includes, for example, an insulating elastomer as an insulating stretching material. The dielectric layer  11   a  may contain an additive as necessary. As the additive, for example, one or more types of a crosslinking agent, a plasticizer, an antioxidant, a surfactant, a viscosity adjusting agent, a reinforcing agent, a coloring agent and the like may be used. As the insulating elastomer, for example, an elastomer containing one or more types of acrylic rubber, silicone rubber, ethylene-propylene-diene terpolymer (EPDM), natural rubber (NR), butyl rubber (IIR), isoprene rubber (IR), acrylonitrile-butadiene copolymer rubber (NBR), hydrogenated-acrylonitrile-butadiene copolymer rubber (H-NBR), hydrin rubber, chloroprene rubber (CR), fluororubber, urethane rubber, and the like may be used. Pre-strain may be applied to the dielectric layer lie. 
     (Electrode) 
     The electrodes  11   b  and  11   c  are opposed to each other with the dielectric layer  11   a  interposed therebetween and extend in a height direction of the actuator element  11 . A plurality of electrodes  11   b  and a plurality of electrodes  11   c  are arranged at regular intervals in a circumferential direction of the dielectric layer  11   a .  FIGS. 2A and 2B  illustrate an example in which four electrodes  11   b  and four electrodes  11   c  are arranged at regular intervals in the circumferential direction of the dielectric layer  11   a . A wire not illustrated is connected to the electrodes  11   b  and  11   c , and voltage is applied between the electrodes  11   b  and  11   c  opposed to each other with the dielectric layer  11   a  interposed therebetween. 
     The electrodes  11   b  and  11   c  are thin films having a stretching property. Since the electrodes  11   b  and  11   c  have the stretching property, the electrodes  11   b  and  11   c  may be deformed following deformation of the dielectric layer  11   a . The electrodes  11   b  and  11   c  may be any of thin films produced by either a dry process or a wet process. The electrodes  11   b  and  11   c  include a conductive material and a binder (binding agent) as necessary. The electrodes  11   b  and  11   c  may further include an additive as necessary. 
     The conductive material may also be a conductive particle. A shape of the conductive particle may be, for example, a spherical shape, an ellipsoidal shape, a needle shape, a plate shape, a scale shape, a tubular shape, a wire shape, a bar shape (rod shape), an irregularly shape, and the like, but the shape is not especially limited thereto. Note that two or more types of particles having the above-described shape may be used in combination. 
     As the conductive material, one or more types of metal, a metal oxide, a carbon material, and a conductive polymer may be used. Here, it is defined that the metal includes semi metal. The metal includes metal such as copper, silver, gold, platinum, palladium, nickel, tin, cobalt, rhodium, iridium, steel, ruthenium, osmium, manganese, molybdenum, tungsten, niobium, tantalum, titanium, bismuth, antimony, and lead, an alloy thereof or the like, for example; however, the metal is not limited thereto. The metal oxide includes an indium tin oxide (ITO), a zinc oxide, an indium oxide, an antimony-added tin oxide, a fluorine-added tin oxide, an aluminum-added zinc oxide, a gallium-added zinc oxide, a silicon-added zinc oxide, a zinc oxide-tin oxide system, an indium oxide-tin oxide system, a zinc oxide-indium oxide-magnesium oxide system and the like, for example; however, the metal oxide is not limited thereto. 
     The carbon material includes carbon black, porous carbon, carbon fiber, fullerene, graphene, a carbon nanotube, a carbon micro coil, nanohorn and the like, for example; however, the material is not limited thereto. As the conductive polymer, for example, a conductive polymer such as a linear conjugated system, an aromatic conjugated system, a mixed conjugated system, a heterocyclic conjugated system, a hetero atom-containing conjugated system, a double stranded conjugated system, or a two-dimensional conjugated system; however, the polymer is not limited thereto. 
     As the binder, it is preferable to use at least one type of an elastomer, a gel, and oil. This is because the stretching property may be imparted to the electrodes  11   b  and  11   c . As the elastomer, for example, one or more types of silicone-based, acrylic-based, urethane-based, and styrene-based elastomers and the like may be used. As the additive, for example, one or more types of a crosslinking agent, a plasticizer, an antioxidant, a surfactant, a viscosity adjusting agent, a reinforcing agent, a coloring agent and the like may be used. 
     The electrodes  11   b  and  11   c  may include a composite material of the conductive polymer and a block copolymer. Specific examples of the composite material include a composite material of polyaniline and styrene-ethylene butylene-styrene (SEBS) copolymer. Furthermore, the electrodes  11   b  and  11   c  may contain a polymer gel material and an electrolyte. As a specific example of a combination of these materials, there may be a combination of a polyacrylamide gel and a LiF aqueous solution. 
     (Coil Spring) 
     The coil spring  12  is an example of a supporting body which may be curved in an arbitrary direction and elastically deformed. The coil spring  12  is a coil-shaped spring obtained by winding a linear member such as a metal wire into a cylindrical spiral shape, and a space is formed between the linear member. Therefore, the coil spring  12  supports the inner peripheral surface of the actuator element  11  discretely in the height direction of the actuator element  11 . By thus supporting the inner peripheral surface of the actuator element  11 , the actuator element  11  is easily deformed, and the actuator  10  may easily perform expanding operation and bending operation. Here, “the inner peripheral surface of the actuator element  11  is supported discretely in the height direction of the actuator element  11 ” means that the inner peripheral surface of the actuator element  11  is supported at separated positions in the height direction of the actuator element  11 . Here, intervals between the separated positions may be constant or may be changed. 
     (Sealing Member) 
     The sealing members  13  and  14  have a disk shape. The sealing members  13  and  14  include metal or a polymer material. The sealing members  13  and  14  may include an elastomer and the like and elastically deformable. The sealing members  13  and  14  may be a device (for example, an electronic device such as a camera) provided at an end of the actuator  10  or an operating unit of the actuator  10 . 
     (Protective Layer) 
     The protective layer is for protecting the electrode  11   c  and is a sheet having a stretching property. The protective layer contains a polymer resin having an insulating property. As the polymer resin, for example, vinyl chloride may be used. In the actuator  10  according to the first embodiment, the occurrence of the constriction in the actuator element  11  is suppressed, so that entry of air between the outer peripheral surface and the protective layer of the actuator element  11  may be suppressed. 
     [Operation of Actuator] 
     An example of the operation of the actuator  10  according to the first embodiment of the present technology is described below. 
     When drive voltage is applied between the electrodes  11   b  and  11   c  opposed to each other with the dielectric layer  11   a  interposed therebetween, an attractive force due to the Coulomb force is applied to both the electrodes  11   b  and  11   c . Therefore, the dielectric layer  11   a  arranged between the electrodes  11   b  and  11   c  is pressed in a thickness direction thereof to become thin and stretched. 
     On the other hand, when the drive voltage applied between the electrodes  11   b  and  11   c  opposed to each other with the dielectric layer  11   a  interposed therebetween is canceled, no attractive force due to the Coulomb force acts on the electrodes  11   b  and  11   c . Therefore, due to a restoring force of the dielectric layer  11   a , the dielectric layer  11   a  has its original thickness and contracts to return to its original size. 
     In a case where the drive voltage is applied to one set of electrodes  11   b  and  11   c  out of a plurality of sets of electrodes  11   b  and  11   c  opposed to each other with the dielectric layer  11   a  interposed therebetween, the actuator  10  bends by the stretch of the dielectric layer  11   a  arranged between the electrodes  11   b  and  11   c . When the drive voltage applied to one set of electrodes  11   b  and  11   c  is canceled, the actuator  10  returns to its original cylindrical shape. 
     [Method of Manufacturing Actuator] 
     Next, a method of manufacturing the actuator  10  is described. First, a rectangular actuator element  11  is wound around a peripheral surface of the coil spring  12  to form a tubular shape, or the coil spring  12  is inserted into the actuator element  11  formed in advance in the tubular shape. The constriction occurs on the peripheral surface of the actuator element  11  after the winding or insertion. 
     Next, one opening of the actuator element  11  is closed by fitting the sealing member  13  into one opening of the actuator element  11  and the like. Next, the other opening of the actuator element  11  is closed by fitting the sealing member  14  into the other opening of the actuator element  11  and the like. As a result, the actuator  10  having the sealed internal space is obtained. Next, a gas injection means such as a syringe is stuck into one of the sealing members  13  and  14 , gas injected into the internal space of the actuator  10  to increase the internal pressure of the actuator  10  to higher than the external pressure, and thereafter the gas injection means is pulled out. As a result, the actuator  10  illustrated in  FIG. 1A  in which the constriction on the peripheral surface of the actuator element  11  is suppressed may be obtained. 
     [Effect] 
     In the actuator  10  according to the first embodiment, since the internal pressure of the actuator  10  is higher than the external pressure of the actuator  10 , the occurrence of the constriction on the actuator element  11  may be suppressed (refer to  FIG. 1B ). This makes it possible to suppress nonuniformity of the thickness of the actuator element  11 . Therefore, the insulation resistance of the actuator  10  may be improved. 
     Furthermore, by suppressing the constriction of the actuator element  11 , the following effect is also obtained. 
     A deformation amount (bending amount) per electric field strength of the actuator  10  may be improved. 
     A side surface of the actuator  10  becomes smoother, so that the side surface of the actuator  10  is less likely to be caught by the surroundings during use. Therefore, in a case where the actuator  10  is applied to the endoscope, operability of the endoscope is improved such that the endoscope is easily inserted into a human body or the like. 
     In a case where surface treatment by spray coating and the like is applied to the side surface of the actuator element  11 , the surface treatment may be performed more uniformly. 
     Since the constriction of the actuator element  11  may be suppressed without adding a part having a weight, the above-described effect may be obtained without deteriorating bendability of the actuator  10 . 
     [Variation] 
     (Variation of Supporting Body) 
     Although the configuration of using the coil spring  12  as the supporting body is described in the first embodiment, the supporting body is not limited to the coil spring  12 , and the supporting body may be used as long as this may support the inner peripheral surface of the actuator element  11  discretely in the height direction of the actuator element  11 . An example of the supporting body other than the coil spring  12  is hereinafter described. 
     As illustrated in  FIG. 3 , the actuator  10  may be provided with a connected body  21  including a plurality of supporting units  21   a  and a plurality of joint mechanisms  21   b  in place of the coil spring  12 . The plurality of supporting units  21   a  supports the inner peripheral surface of the actuator element  11  discretely in the height direction of the actuator element  11 . The joint mechanism  21   b  has, for example, a spherical shape and connects adjacent supporting units  21   a  so as to be rotatable in an arbitrary direction. Note that the joint mechanism  21   b  may be a part of the supporting unit  21   a.    
     As illustrated in  FIGS. 4A and 4B , the actuator  10  may be provided with a connected body  22  including a plurality of disk-shaped supporting units  22   a  and a plurality of ball joint mechanisms  22   b  in place of the coil spring  12 . The plurality of ball joint mechanisms  22   b  connects adjacent supporting units  22   a  so as to be rotatable in an arbitrary direction. The plurality of supporting units  22   a  is provided so as to be spaced apart from each other by a predetermined distance and supports the inner peripheral surface of the actuator element  11  discretely in the height direction of the actuator element  11 . A shaft portion  22   c  is perpendicularly erected at the center of one surface of the supporting unit  22   a , and a spherical portion (so-called ball stud)  22   d  is provided at a tip end thereof. On the other hand, a shaft portion  22   e  is perpendicularly erected at the center of the other surface of the supporting unit  22   a , and a socket  22   f  which is in spherical contact with the spherical portion  22   d  is provided at a tip end thereof. The socket  22   f  is in spherical contact with the spherical portion  22   d  to support the spherical portion  22   d  so as to be rotatable in an arbitrary direction. The spherical portion  22   d  and the socket  22   f  form the ball joint mechanism  22   b . The openings at both ends of the actuator element  11  are closed by the supporting units  22   a.    
     As illustrated in  FIGS. 5A and 5B , the actuator  10  may be provided with a connected body  23  including a plurality of disk-shaped supporting units  23   a  and a plurality of joint mechanisms  23   b  imitating a joint structure of a human body in place of the coil spring  12 . The plurality of joint mechanisms  23   b  connects adjacent supporting units  23   a  so as to be rotatable in an arbitrary direction. The plurality of supporting units  23   a  is provided so as to be spaced apart from each other by a predetermined distance and supports the inner peripheral surface of the actuator element  11  discretely in the height direction of the actuator element  11 . A shaft portion  23   c  is perpendicularly erected at the center of one surface of the supporting unit  23   a , and a spherical portion (so-called ball stud)  23   d  is provided at a tip end thereof. On the other hand, a shaft portion  23   e  is also perpendicularly erected at the center of the other surface of the supporting unit  23   a , and a spherical portion (so-called ball stud)  23   f  is provided at a tip end thereof. The spherical portions  23   d  and  23   f  abut each other so as to be rotatable in an arbitrary direction. By adopting a configuration in which the spherical portions  23   d  and  23   f  abut in this manner, friction during rotation may be reduced. Furthermore, the abutted spherical portions  23   d  and  23   f  are covered with a membrane  23   g . By covering the spherical portions  23   d  and  23   f  with the membrane  23   g  in this manner, it is possible to suppress displacement between the abutted spherical portions  23   d  and  23   f . An inner side of the membrane  23   g  may be filled with liquid, a gel and the like. The spherical portions  23   d  and  23   f  and the membrane  23   g  form the joint mechanism  23   b . The openings at both ends of the actuator element  11  are closed by the supporting units  23   a.    
     As illustrated in  FIGS. 6A and 6B , the actuator  10  may be provided with a connected body  24  including a plurality of disk-shaped supporting units  24   a  and a plurality of joint mechanisms  24   b  imitating a joint structure of insects in place of the coil spring  12 . The joint mechanism  24   b  connects adjacent supporting units  24   a  so as to be rotatable in an arbitrary direction. The plurality of supporting units  24   a  is provided so as to be spaced apart from each other by a predetermined distance and supports the inner peripheral surface of the actuator element  11  discretely in the height direction of the actuator element  11 . A shaft portion  24   c  is perpendicularly erected at the center of one surface of the supporting unit  24   a , and a shaft portion  24   d  is perpendicularly erected also at the center of the other surface of the supporting unit  24   a . Tip ends of the shaft portions  24   c  and  24   d  are separated by a predetermined distance, and the tip ends of the shaft portions  24   c  and  24   d  are connected by an elastic body  24   e . Therefore, the shaft portions  24   c  and  24   d  are rotatable in an arbitrary direction. The elastic body  24   e  is of a material of low rigidity (material of high flexibility) such as an elastomer, a cushion material, or a spring. The shaft portions  24   c  and  24   d  and the elastic body  24   e  form the joint mechanism  24   b . The openings at both ends of the actuator element  11  are closed by the supporting units  24   a.    
     As illustrated in  FIGS. 7A and 7B , the actuator  10  may be provided with a connected body  25  including a plurality of disk-shaped supporting units  25   a  and a plurality of joint mechanisms  25   b  imitating a joint structure of a human body in place of the coil spring  12 . The plurality of joint mechanisms  25   b  connects adjacent supporting units  25   a  so as to be rotatable in an arbitrary direction. The plurality of supporting units  25   a  is provided so as to be spaced apart from each other by a predetermined distance and supports the inner peripheral surface of the actuator element  11  discretely in the height direction of the actuator element  11 . Between the adjacent supporting units  25   a , a bar-shaped shaft portion  25   c  having a spherical portion  25   d  at one end and a spherical portion  25   e  at the other end is provided. The shaft portion  25   c  is a magnet in which a side on the spherical portion  25   d  is a north pole and a side of the spherical portion  25   e  is a south pole. The spherical portion  25   d  is located at the center of one surface of the supporting unit  25   a  and the spherical portion  25   e  is located at the center of the other surface of the supporting unit  25   a . The spherical portions  25   e  and  25   d  having different polarities attract each other across the supporting unit  25   a . Therefore, the shaft portion  25   c  adjacent across the supporting unit  25   a  may rotate in an arbitrary direction. The spherical portions  25   e  and  25   d  may be covered with a membrane  25   f , but unlike the joint mechanism  23   b  illustrated in  FIG. 5 , in the joint mechanism  25   b , the spherical portions  25   e  and  25   d  attract by a magnetic force, so that it is not required that the spherical portions  25   e  are  25   d  are covered with the membrane  25   f . The openings at both ends of the actuator element  11  are closed by the supporting units  25   a.    
     As illustrated in  FIG. 8 , the actuator  10  may also be provided with a supporting body  26  including a plurality of spherical bodies  26   a  accommodated in the tubular actuator element  11  in place of the coil spring  12 . The plurality of spherical bodies  26   a  is accommodated in the actuator element  11  such that the spherical bodies  26   a  adjacent to each other in the height direction of the actuator element  11  come into contact with each other. As a result, the inner peripheral surface of the actuator element  11  is supported discretely in the height direction of the actuator element  11  by the plurality of spherical bodies  26   a , and the actuator  10  is rotatable in an arbitrary direction. 
     The actuator  10  may be provided with a supporting body including a polymer resin capable of supporting the inner peripheral surface of the actuator element  11  discretely in the height direction of the actuator element  11  in place of the coil spring  12 . As a specific example of the polymer resin, for example, there may be an insulating elastomer similar to that of the dielectric layer  11   a.    
     As illustrated in  FIG. 9 , a supporting body  27  including a polymer resin may include a plurality of supporting units  27   a  and a plurality of shaft portions  27   b . The supporting unit  27   a  and the shaft portion  27   b  are integrally molded of the polymer resin. The supporting unit  27   a  has a disk shape and supports the inner peripheral surface of the actuator element  11  by an outer peripheral portion thereof. The shaft portion  27   b  connects the supporting units  27   a  adjacent to each other in the height direction of the actuator element  11 . The sealing members  13  and  14  and the supporting body  27  may be integrally molded of the polymer resin. 
     (Variation of Method of Manufacturing Actuator) 
     The actuator  10  may also be manufactured in the following manner. First, as illustrated in  FIG. 10A , the actuator  10  is assembled in a state in which the coil spring  12  is stretched. At that time, a volume of the internal space of the actuator  10  is larger than the volume of the internal space of the actuator  10  finally obtained, and the constriction occurs on the side surface of the actuator element  11 . Next, as illustrated in  FIG. 10B , the stretch of the coil spring  12  is released to reduce the volume of the internal space of the actuator  10 , thereby increasing the internal pressure of the actuator  10 . As a result, an intended actuator  10  in which the constriction on the peripheral surface of the actuator element  11  is suppressed is obtained. 
     Note that it is also possible to increase the internal pressure of the actuator  10  by reducing the volume of the internal space of the actuator  10  by pressurizing one or both ends of the actuator  10  to decrease a height of the actuator  10  after assembling the actuator  10  in a state in which the coil spring  12  is not stretched. 
     (Other Variations) 
     The actuator element  11  may also include stacked sheets of dielectric elastomer actuator elements. In this case, a plurality of dielectric elastomer actuator elements formed in advance into a cylindrical shape may be concentrically stacked around the coil spring  12 , or a single dielectric elastomer actuator element having a band shape may be wound around the coil spring  12  to stacked. As described in the first embodiment, the occurrence of the constriction on the peripheral surface of the actuator element  11  is suppressed, so that it is possible to suppress entry of air between the stacked dielectric elastomer actuator elements in a case where the dielectric elastomer actuator elements are stacked. 
     The actuator  10  may also be provided with first and second electrodes provided on entire or substantially entire both surfaces of the dielectric layer  11   a  in place of the electrodes  11   a  and  11   b.    
     In the first embodiment, the configuration in which the actuator element  11  and the coil spring  12  have the cylindrical shape is described as an example; however, the actuator element  11  and the coil spring  12  may have a rectangular tubular shape such as a square tubular shape. 
     The internal space of the actuator  10  may be filled with liquid or a solid in place of gas. Here, the liquid is, for example, water, saline solution, or the like. Furthermore, the solid is, for example, a sol, a gel, or the like. 
     2 Second Embodiment 
     [Configuration of Endoscope Module] 
     As illustrated in  FIG. 11 , an endoscope module according to a second embodiment of the present technology is provided with an endoscope  30 , a control unit  41 , a bending drive circuit  42 , an internal pressure detection circuit  43 , a pressurizing unit  44 , and a depressurizing unit  45 . The control unit  41  is connected to a power supply  46 . Note that, in the second embodiment, a portion similar to that in the first embodiment is assigned with the same reference sign and the description thereof is omitted. 
     The endoscope  30  is provided with an operating unit  31 , a supporting unit  32 , an actuator  33  being a bending unit, a tip end  34 , and a pressure-sensitive sensor  35 . The actuator  33 , the pressure-sensitive sensor  35 , the control unit  41 , the bending drive circuit  42 , the internal pressure detection circuit  43 , the pressurizing unit  44 , and the depressurizing unit  45  form an actuator module. The pressure-sensitive sensor  35  and the internal pressure detection circuit  43  form a detecting unit which detects a pressure in an internal space of the actuator  33 . 
     The operating unit  31  is provided with a button, a knob, and the like for operating the endoscope. The supporting unit  32  is provided between the operating unit  31  and the actuator  33  to support the actuator  33 . The supporting unit  32  has rigidity and is provided with a vent hole therein which connects the pressurizing unit  44  and the actuator  33 . 
     The actuator  33  is provided with an actuator element  11  and a coil spring  12 , and the internal space of the actuator  33  is sealed. One opening of the actuator element  11  is closed by the tip end  34  and an opening at the other end is closed by the supporting unit  32 . As illustrated in  FIG. 12 , an illumination lens  34   a  and an objective lens  34   b  are provided on a tip end surface of the tip end  34 . A portion of the illumination lens  34   a  and the objective lens  34   b  on the surface of the tip end  34  is of, for example, stainless steel or the like. The illumination lens  34   a  and the objective lens  34   b  are, for example, glass lenses. An illumination device is provided inside the illumination lens  34   a , and an imaging element such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) is provided inside the objective lens  34   b . The imaging element is connected to a display device not illustrated via an image processing unit not illustrated. 
     The tip end  34  and the operating unit  31  are connected to each other by a cable arranged in the internal space of the actuator  33 , and an operation signal is supplied from the operating unit  31  to the tip end  34  via this cable. Furthermore, the tip end  34  and the image processing unit are connected by a cable arranged in the internal space of the actuator  33 , and a video signal is supplied from the tip end  34  to the image processing unit via this cable. However, the operating unit  31  may wirelessly supply the operation signal to the tip end  34 , or the tip end  34  may wirelessly supply the video signal to the image processing unit. 
     The pressure-sensitive sensor  35  is arranged in a portion to close the opening on one end of the actuator element  11  out of the tip end  34 . However, an arrangement position of the pressure-sensitive sensor  35  is not limited to there as long as this is a position where the sensor may detect the internal pressure of the actuator  33 . The pressure-sensitive sensor  35  outputs an electric signal corresponding to the internal pressure of the actuator  33  to the internal pressure detection circuit  43 . As the pressure-sensitive sensor  35 , for example, a diaphragm gauge or the like may be used. 
     The internal pressure detection circuit  43  detects the internal pressure of the actuator  33  on the basis of the electric signal supplied from the pressure-sensitive sensor  35  and supplies the same to the control unit  41 . The pressurizing unit  44  is a pump, a regulator or the like, and supplies gas to the internal space of the actuator  33  under the control of the control unit  41  to pressurize the internal space of the actuator  33 . The gas is at least one type of air, a rare gas, carbon dioxide and the like, for example. The depressurizing unit  45  is a solenoid valve such as a diaphragm valve and discharges the gas in the internal space of the actuator  33  to decrease the pressure in the internal space of the actuator  33  under the control of the control unit  41 . 
     The control unit  41  controls the bending drive circuit  42  and the pressurizing unit  44  on the basis of the control signal supplied from the operating unit  31 . On the basis of the internal pressure supplied from the internal pressure detection circuit  43 , the control unit  41  feedback-controls the pressurizing unit  44  and the depressurizing unit  45  such that the internal pressure of the actuator  33  becomes a prescribed pressure. Here, the prescribed pressure is a pressure at which occurrence of constriction of the actuator  33  is suppressed. Note that, when the internal pressure of the actuator  33  is too high, there is a possibility that swelling might occur in the actuator element  11 , so that an upper limit value of the internal pressure of the actuator  33  is preferably a pressure at which the swelling of the actuator element  11  does not occur. The bending drive circuit  42  drives the actuator  33  to bend on the basis of the control signal supplied from the control unit  41 . 
     [Method of Controlling Internal Pressure at Power On] 
     Next, with reference to  FIG. 13 , a method of controlling the internal pressure at power on described. First, when the power supply  46  is put on at step S 11 , the control unit  41  drives the pressurizing unit  44  at step S 12  to pressurize the actuator  33 , thereby increasing the internal pressure of the actuator  33 . Next, at step S 13 , the internal pressure detection circuit  43  detects the internal pressure of the actuator  33  on the basis of the electric signal supplied from the pressure-sensitive sensor  35 , and supplies a detection result to the control unit  41 . 
     Next, at step S 14 , the control unit  41  determines whether or not the internal pressure of the actuator  33  reaches the prescribed pressure on the basis of the internal pressure supplied from the internal pressure detection circuit  43 . In a case where it is determined at step S 14  that the internal pressure of the actuator  33  reaches the prescribed pressure, the control unit  41  stops the pressurizing unit  44  at step S 15 , and at step S 16 , the control unit  41  is put into a stand-by state for operation on the endoscope  30 . On the other hand, in a case where it is determined at step S 14  that the internal pressure of the actuator  33  does not reach the prescribed pressure, the control unit  41  returns the process to step S 12 . 
     [Method of Controlling Internal Pressure at Operation Time] 
     Next, with reference to  FIG. 14 , a method of controlling the internal pressure at the time of operation is described. First, when the operation of the endoscope  30  is started at step S 21 , the internal pressure detection circuit  43  detects the internal pressure of the actuator  33  on the basis of the electric signal supplied from the pressure-sensitive sensor  35  at step S 22 , and supplies a detection result to the control unit  41 . Next, at step S 23 , the control unit  41  determines whether or not the internal pressure of the actuator  33  is lower than the prescribed pressure on the basis of the internal pressure supplied from the internal pressure detection circuit  43 . 
     In a case where it is determined at step S 23  that the internal pressure of the actuator  33  is lower than the prescribed pressure, at step S 24 , the control unit  41  drives the pressurizing unit  44  to pressurize the interior of the actuator  33 , thereby increasing the internal pressure of the actuator  33 . Next, at step S 25  the internal pressure detection circuit  43  detects the internal pressure of the actuator  33  on the basis of the electric signal supplied from the pressure-sensitive sensor  35 , and supplies a detection result to the control unit  41 . 
     Next, at step S 26 , the control unit  41  determines whether or not the internal pressure of the actuator  33  reaches the prescribed pressure on the basis of the internal pressure supplied from the internal pressure detection circuit  43 . In a case where it is determined at step S 26  that the internal pressure of the actuator  33  reaches the prescribed pressure, at step S 27 , the control unit  41  stops the pressurizing unit  44  and returns the procedure to step S 22 . On the other hand, in a case where it is determined at step S 26  that the internal pressure of the actuator  33  does not reach the prescribed pressure, the control unit  41  returns the process to step S 24 . 
     In a case where it is determined at step S 23  that the internal pressure of the actuator  33  is not lower than the prescribed pressure, at step S 28 , the control unit  41  determines whether or not the internal pressure of the actuator  33  is higher than the prescribed pressure on the basis of the internal pressure supplied from the internal pressure detection circuit  43 . In a case where it is determined at step S 28  that the internal pressure of the actuator  33  is higher than the prescribed pressure, at step S 29 , the control unit  41  drives the depressurizing unit  45  to depressurize the interior of the actuator  33 , thereby decreasing the internal pressure of the actuator  33 . On the other hand, in a case where it is determined at step S 28  that the internal pressure of the actuator  33  is not higher than the prescribed pressure, the control unit  41  returns the procedure to step S 22 . 
     Next, at step S 30 , the internal pressure detection circuit  43  detects the internal pressure of the actuator  33  on the basis of the electric signal supplied from the pressure-sensitive sensor  35 , and supplies a detection result to the control unit  41 . Next, at step S 31 , the control unit  41  determines whether or not the internal pressure of the actuator  33  reaches the prescribed pressure on the basis of the internal pressure supplied from the internal pressure detection circuit  43 . In a case where it is determined at step S 31  that the internal pressure of the actuator  33  reaches the prescribed pressure, at step S 32 , the control unit  41  stops the depressurizing unit  45  and returns the procedure to step S 22 . On the other hand, in a case where it is determined at step S 31  that the internal pressure of the actuator  33  does not reach the prescribed pressure, the control unit  41  returns the process to step S 29 . 
     [Effect] 
     Since the endoscope module according to the second embodiment is provided with the pressurizing unit  44  for increasing the internal pressure of the actuator  33 , the internal pressure of the actuator  33  may be made higher than the external pressure of the actuator  33 . Therefore, an effect similar to that of the first embodiment may be obtained. 
     Furthermore, since the pressurizing unit  44  for increasing the internal pressure of the actuator  33  and the depressurizing unit  45  for decreasing the internal pressure of the actuator  33  are provided, the internal pressure of the actuator  33  may be adjusted to the prescribed pressure at the time of the operation of the endoscope module. 
     [Variation] 
     As illustrated in  FIG. 15 , the endoscope module may also be provided with a heating unit  47  in place of the pressurizing unit  44 . As the heating unit  47 , for example, an infrared heater or the like may be used. The control unit  41   a  controls the heating unit  47  to heat the internal space of the actuator  33  to expand the gas, thereby increasing the internal pressure of the actuator  33 . 
     The endoscope module may also be provided with both the pressurizing unit  44  and the heating unit  47 . In this case, both the pressurizing unit  44  and the heating unit  47  may be operated at the same time, or the pressurizing unit  44  and the heating unit  47  may be selectively operated by mode switching. 
     The endoscope module is not required to be provided with the depressurizing unit  45 . In this case, the control unit  41  executes only the operation of increasing the internal pressure of the actuator  33  in a flowchart illustrated in  FIG. 14 . 
     Pressure detecting operations at steps S 22 , S 25 , and S 30  illustrated in  FIG. 14  may be repeatedly performed at predetermined time intervals when the endoscope module is operated. 
     3 Third Embodiment 
     [Configuration of Endoscope Module] 
     As illustrated in  FIG. 16 , an endoscope module according to a third embodiment of the present technology is provided with an endoscope  30 , a control unit  41   b , a bending drive circuit  42 , a bending angle detection circuit  48 , an internal pressure detection circuit  43   b , a pressurizing unit  44 , and a depressurizing unit  45 . The control unit  41   b  is connected to a power supply  46 . Note that, in the third embodiment, a portion similar to that in the second embodiment is assigned with the same reference sign and the description thereof is omitted. 
     Electrodes  11   b  and  11   c  (refer to  FIGS. 2A and 2B ) provided on an inner peripheral surface and an outer peripheral surface, respectively, of a dielectric layer  11   a  included in an actuator element  11  are deformed by bending or a change in internal pressure of the actuator  33 . The internal pressure detection circuit  43   b  detects the internal pressure of the actuator  33  from a change in electrostatic capacitance (change in distance) between the electrodes  11   b  and  11   c  opposed to each other with the dielectric layer  11   a  interposed therebetween and supplies a detection result to the control unit  41   b . The bending angle detection circuit  48  detects a bending angle of the actuator  33  from a change in electric resistance caused by the deformation of the electrodes  11   b  and  11   c  and supplies a detection result to the control unit  41   b . On the basis of the internal pressure supplied from the internal pressure detection circuit  43   b  and the bending angle supplied from the bending angle detection circuit  48 , the control unit  41   b  feedback-controls the pressurizing unit  44  and the depressurizing unit  45  such that the internal pressure of the actuator  33  becomes a prescribed pressure. 
     [Effect] 
     The endoscope module according to the third embodiment feedback-controls the pressurizing unit  44  and the depressurizing unit  45  such that the internal pressure of the actuator  33  becomes the prescribed pressure on the basis of the internal pressure and the bending angle of the actuator  33 . Therefore, it is possible to appropriately control the internal pressure of the actuator  33  when operating the actuator  33  as compared with the endoscope module according to the second embodiment. 
     [Variation] 
     The endoscope module may be provided with a heating unit  47  in place of the pressurizing unit  44  or may be provided with the heating unit  47  together with the pressurizing unit  44 . Furthermore, the endoscope module is not required to be provided with the depressurizing unit  45 . 
     4 Fourth Embodiment 
     [Configuration of Actuator] 
     An actuator  50  according to a fourth embodiment of the present technology is a speaker having a sealed structure and is provided with a cylindrical actuator element  51  and a supporting body  52  which supports both ends of the actuator element  11  as illustrated in  FIG. 17 . An internal pressure of the actuator  50  is higher than an external pressure of the actuator  50 . 
     The cylindrical actuator element  51  is provided with a cylindrical dielectric layer, a first electrode provided on an inner peripheral surface of the dielectric layer, and a second electrode provided on an outer peripheral surface of the dielectric layer. The first and second electrodes may be provided on the inner peripheral surface and the outer peripheral surface, respectively, of the dielectric layer in a predetermined pattern or provided on entire or substantially entire inner peripheral surface and outer peripheral surface, respectively, of the dielectric layer. The supporting body  52  is provided with a shaft portion  52   a  and disk-shaped supporting units  52   b  and  52   c  provided at both ends of the shaft portion  52   a.    
     [Effect] 
     In the actuator  50  according to the fourth embodiment, since the internal pressure of the actuator  50  is higher than the external pressure of the actuator  50 , an effect similar to that of the actuator  10  according to the first embodiment may be obtained. 
     [Variation] 
     The actuator element  11  may have a rectangular tubular shape such as a square tubular shape and the supporting units  52   b  and  52   c  may have a polygonal shape such as a square shape. 
     The actuator  50  in the fourth embodiment, the pressure-sensitive sensor  35 , the control unit  41 , the internal pressure detection circuit  43 , the pressurizing unit  44 , and the depressurizing unit  45  in the second embodiment may form the actuator module. In this case, the actuator module may be provided with a heating unit  47  in place of the pressurizing unit  44 , or may be provided with the heating unit  47  together with the pressurizing unit  44 . Furthermore, the actuator module is not required to be provided with the depressurizing unit  45 . 
     5 Fifth Embodiment 
     [Configuration of Actuator] 
     An actuator  60  according to a fifth embodiment of the present technology is a speaker having a sealed structure and is provided with a rectangular actuator element  61  and a supporting body  62  which supports a peripheral edge of the actuator element  61  as illustrated in  FIG. 18 . An internal pressure of the actuator  60  is higher than an external pressure of the actuator  60 . 
     The rectangular actuator element  61  is provided with a rectangular dielectric layer, a first electrode provided on one surface of the dielectric layer, and a second electrode provided on the other surface of the dielectric layer. The first and second electrodes may be provided on both surfaces of the dielectric layer in a predetermined pattern or may be provided on entire or substantially entire both surfaces of the dielectric layer. The supporting body  62  supports the actuator element  61  in a convexly curved state. 
     [Effect] 
     In the actuator  60  according to the fifth embodiment, since the internal pressure of the actuator  60  is higher than the external pressure of the actuator  60 , an effect similar to that of the actuator  10  according to the first embodiment may be obtained. 
     [Variation] 
     The actuator  60  may form the actuator module in a manner similar to that of the variation of the fourth embodiment. 
     Although the embodiments of the present technology are heretofore described specifically, the present technology is not limited to the above-described embodiments, and various modifications based on the technical idea of the present technology may be made. 
     For example, the configuration, the method, the step, the shape, the material, the numerical value and the like described in the above-described embodiments are merely examples, and the configuration, the method, the step, the shape, the material, the numerical value and the like different from those may also be used as necessary. 
     Furthermore, the configuration, the method, the step, the shape, the material, the numerical value and the like of the above-described embodiments may be combined with each other without departing from the gist of the present technology. 
     Furthermore, the present technology may also adopt the following configurations. 
     (1) 
     An actuator provided with: 
     a tubular actuator element; and 
     a supporting body which supports an inner peripheral surface of the actuator element, 
     in which an internal pressure of the actuator element is higher than an external pressure of the actuator element. 
     (2) 
     The actuator according to (1), 
     in which the supporting body supports the inner peripheral surface of the actuator element discretely in a height direction of the actuator element. 
     (3) 
     The actuator according to (1) or (2), 
     in which the supporting body is a coil spring, a connected body obtained by connecting a plurality of supporting units by a joint mechanism, or a plurality of spherical bodies. 
     (4) 
     The actuator according to any one of (1) to (3), further provided with: gas or liquid filling an internal space of the actuator element. 
     (5) 
     The actuator according to any one of (1) to (4), 
     in which the actuator element is a dielectric elastomer actuator element. 
     (6) 
     The actuator according to (5), 
     in which the dielectric elastomer actuator element is stacked. 
     (7) 
     The actuator according to (5) or (6), 
     in which the actuator element is provided with a tubular dielectric layer, a first electrode provided on an inner peripheral surface of the dielectric layer, and a second electrode provided on an outer peripheral surface of the dielectric layer. 
     (8) 
     The actuator according to (5) or (6), 
     in which the actuator element is provided with a tubular dielectric layer, a plurality of first electrodes provided on an inner peripheral surface of the dielectric layer, and a plurality of second electrodes provided on an outer peripheral surface of the dielectric layer, and 
     the first and second electrodes are opposed to each other with the dielectric layer interposed therebetween and extend in a height direction of the actuator element. 
     (9) 
     An endoscope provided with: 
     the actuator according to any one of (1) to (8). 
     (10) 
     An actuator module provided with: 
     an actuator including a tubular actuator element, and a supporting body which supports an inner peripheral surface of the actuator element; 
     a control unit which controls drive of the actuator; and 
     a pressurizing unit which pressurizes an internal space of the actuator. 
     (11) 
     The actuator module according to (10), further provided with: 
     a detecting unit which detects a pressure in the internal space, 
     in which the control unit controls the pressurizing unit according to a detection result of the detecting unit. 
     (12) 
     The actuator module according to (11), further provided with: 
     a depressurizing unit which depressurizes the internal space, 
     in which the control unit controls the depressurizing unit according to a detection result of the detecting unit. 
     (13) 
     The actuator module according to any one of (10) to (12), 
     in which the pressurizing unit pressurizes the internal space of the actuator by supplying gas or liquid to the internal space. 
     (14) 
     An endoscope module provided with: 
     the actuator module according to any one of (10) to (13). 
     (15) 
     An actuator provided with: 
     an actuator element; and 
     a supporting body which supports the actuator element, 
     in which an internal pressure of the actuator element is higher than an external pressure of the actuator element. 
     (16) 
     The actuator according to (15), 
     in which the actuator element has a tubular shape, and 
     the supporting body supports both ends of the actuator element. 
     (17) 
     The actuator according to (15) or (16), 
     in which the supporting body supports a peripheral edge of the actuator element. 
     (18) 
     A controlling method provided with: 
     detecting a pressure in an internal space of an actuator; and 
     pressurizing or depressurizing the internal space of the actuator on the basis of a result of the detection. 
     REFERENCE SIGNS LIST 
     
         
           10 ,  33 ,  50 ,  60  Actuator 
           11 ,  51 ,  61  Actuator element  11   
           12  Coil spring (supporting body) 
           13 ,  14  Sealing member 
           21 ,  22 ,  23 ,  24 ,  25  Connected body (supporting body) 
           26 ,  27 ,  52 ,  62  Supporting body 
           26   a  Spherical body 
           35  Pressure-sensitive sensor 
           41 ,  41   a ,  41   b  Control unit 
           42  Bending drive circuit 
           43  Internal pressure detection circuit 
           44  Pressurizing unit 
           45  Depressurizing unit