Patent Publication Number: US-2022221351-A1

Title: Load sensor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/JP2020/038205 filed on Oct. 8, 2020, entitled “LOAD SENSOR”, which claims priority under 35 U.S.C. Section 119 of Japanese Patent Application No. 2019-188875 filed on Oct. 15, 2019, entitled “LOAD SENSOR AND MANUFACTURING METHOD OF LOAD SENSOR”. The disclosures of the above applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a load sensor that detects a load applied from outside, on the basis of change in capacitance. 
     2. Disclosure of Related Art 
     Load sensors are widely used in the fields of industrial apparatuses, robots, vehicles, and the like. In recent years, in accordance with advancement of control technologies by computers and improvement of design, development of electronic apparatuses that use a variety of free-form surfaces such as those in human-form robots and interior equipment of automobiles is in progress. In association therewith, it is required to mount a high performance load sensor to each free-form surface. 
     International Publication No. WO2018/096901 describes a pressure-sensitive element that includes: a pressure-sensitive part to which a pressing force is applied; and a detector that detects the pressing force. In this pressure-sensitive element, the pressure-sensitive part includes: a first electrically-conductive member; a second electrically-conductive member; and a dielectric body. The first electrically-conductive member has elasticity. The dielectric body is disposed between the first electrically-conductive member and the second electrically-conductive member, and at least partially covers a surface of the first electrically-conductive member or a surface of the second electrically-conductive member. The detector detects a pressing force on the basis of change in capacitance between the first electrically-conductive member and the second electrically-conductive member. 
     In the load sensor as described above, between during loading and during unloading, property deviation (hysteresis) occurs in the change in the capacitance. The electrically-conductive member having elasticity is a member that is provided with electrical conductivity by a filler being added to an elastic body such as rubber. When a filler is added into the rubber, the filler serves as an inhibitive factor against elastic return of the electrically-conductive member, whereby the response of elastic return is impaired. Because of this, changes in the capacitance during loading and during unloading are deviated from each other. Thus, even when the loads have the same value, the values of the capacitance become different between during loading and during unloading, thus causing deviation between the detection values of the load sensor. 
     SUMMARY OF THE INVENTION 
     A main mode of the present invention relates to a load sensor. The load sensor according to the present mode  1  includes: a base member being insulative and having elasticity; an electrode having elasticity and formed on an upper face of the base member; and a wire member being electrically conductive and disposed so as to be superposed on an upper face of the electrode, a surface of the wire member being covered by a dielectric body. Here, a ratio of a thickness of the electrode to a thickness of the base member is not less than 0.02 and not greater than 0.3. 
     According to the load sensor of the present mode, when the ratio of the thickness of the electrode to the thickness of the base member is set to be not less than 0.02 and not greater than 0.3, the thickness of the electrode can be made sufficiently smaller than the thickness of the base member. Accordingly, in deformations of the electrode and the base member during loading and during unloading, influence of the deformation of the electrode is suppressed, and influence of the deformation of the base member becomes dominant. Therefore, influence of response impairment in elastic return of the electrode can be suppressed, and as a result, changes in capacitance during loading and during unloading can be caused to substantially match each other. Therefore, deviation between the detection values of the load sensor during loading and during unloading can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  to  FIG. 1C  are each a perspective view schematically showing a configuration of each part of a load sensor according to Embodiment 1; 
         FIG. 2A  is a perspective view schematically showing a configuration of each part of the load sensor according to Embodiment 1; 
         FIG. 2B  is a perspective view schematically showing a configuration of the load sensor of which assembling has been completed, according to Embodiment 1; 
         FIG. 3A  to  FIG. 3C  are each a schematic diagram for describing screen printing according to Embodiment 1; 
         FIG. 4  is a schematic diagram for describing gravure printing according to Embodiment 1; 
         FIG. 5  is a schematic diagram for describing flexographic printing according to Embodiment 1; 
         FIG. 6  is schematic diagram for describing offset printing according to Embodiment 1; 
         FIG. 7  is a schematic diagram for describing gravure offset printing according to Embodiment 1; 
         FIG. 8  is a plan view schematically showing the load sensor when viewed in a Z-axis negative direction according to Embodiment 1; 
         FIG. 9A  and  FIG. 9B  are each a cross-sectional view schematically showing the periphery of a wire when viewed in an X-axis negative direction according to Embodiment 1; 
         FIG. 10A  is a schematic diagram obtained when the load sensor cut, at a position of a wire, along a plane parallel to an X-Z plane is viewed in a Y-axis positive direction, according to Embodiment 1; 
         FIG. 10B  is a schematic diagram obtained when a load sensor cut, at a position of a wire, along a plane parallel to an X-Z plane is viewed in the Y-axis positive direction, according to a comparative example of Embodiment 1; 
         FIG. 11  is a schematic diagram for describing a preferable size of each part of the load sensor according to Embodiment 1; 
         FIG. 12  is a perspective view schematically showing a configuration of each part of a load sensor according to Embodiment 2; 
         FIG. 13  is a perspective view schematically showing a configuration of the load sensor of which assembling has been completed, according to Embodiment 2; 
         FIG. 14A  and  FIG. 14B  are each a cross-sectional view schematically showing the periphery of a wire when viewed in the X-axis negative direction, according to Embodiment 2; 
         FIG. 15A  is a cross-sectional view schematically showing the periphery of wires when viewed in the X-axis negative direction, according to a comparative example of Embodiment 2; 
         FIG. 15B  is a cross-sectional view schematically showing the periphery of wires when viewed in the X-axis negative direction, according to Embodiment 2; 
         FIG. 16A  is a graph showing a relationship between load and capacitance according to the comparative example of Embodiment 2; 
         FIG. 16B  is a graph showing a relationship between load and capacitance according to Embodiment 2; 
         FIG. 17A  is a diagram for describing calculation of hysteresis according to Embodiment 2; 
         FIG. 17B  is a graph showing a relationship between the thickness of an electrode and hysteresis according to Embodiment 2; 
         FIG. 17C  is a graph showing a relationship between the thickness of an electrode and the volume resistivity of the electrode according to Embodiment 2; 
         FIG. 18  is a graph showing a relationship between the thickness of electrodes and hysteresis when the elastic moduli of the electrodes are different, according to Embodiment 2; 
         FIG. 19  is a perspective view schematically showing a configuration of each part of a load sensor according to Embodiment 3; and 
         FIG. 20A  and  FIG. 20B  are schematic diagrams indicating that the shape of each wire changes in accordance with stretch and contraction of a base member and electrodes according to Embodiment 3. 
     
    
    
     It should be noted that the drawings are solely for description and do not limit the scope of the present invention in any way. 
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention is applicable to a load sensor of a management system or an electronic apparatus that performs processing in accordance with an applied load. 
     Examples of the management system include a stock management system, a driver monitoring system, a coaching management system, a security management system, and a caregiving/nursing management system. 
     In the stock management system, for example, by a load sensor provided to a stock shelf, the load of a placed stock is detected, and the kinds of commodities and the number of commodities present on the stock shelf are detected. Accordingly, in a store, a factory, a warehouse, and the like, the stock can be efficiently managed, and manpower saving can be realized. In addition, by a load sensor provided in a refrigerator, the load of food in the refrigerator is detected, and the kinds of the food and the quantity and amount of the food in the refrigerator are detected. Accordingly, a menu that uses food in a refrigerator can be automatically proposed. 
     In the driver monitoring system, by a load sensor provided to a steering device, the distribution of a load (e.g., gripping force, grip position, tread force) applied on the steering device by a driver is monitored, for example. In addition, by a load sensor provided to a vehicle-mounted seat, the distribution of a load (e.g., the position of the center of gravity) applied on the vehicle-mounted seat by the driver in a seated state is monitored. Accordingly, the driving state (sleepiness, mental state, and the like) of the driver can be fed back. 
     In the coaching management system, for example, by a load sensor provided to the bottom of a shoe, the load distribution at a sole is monitored. Accordingly, correction or leading to an appropriate waking state or running state can be realized. 
     In the security management system, for example, by a load sensor provided to a floor, the load distribution is detected when a person passes, and the body weight, stride, passing speed, shoe sole pattern, and the like are detected. Accordingly, the person who has passed can be identified by checking these pieces of detection information against data. 
     In the caregiving/nursing management system, for example, by load sensors provided to bedclothes and a toilet seat, the distributions of loads applied by a human body onto the bedclothes and the toilet seat are monitored. Accordingly, at the positions of the bedclothes and the toilet seat, what action the person is going to take is estimated, whereby tumbling or falling can be prevented. 
     Examples of the electronic apparatus include a vehicle-mounted apparatus (car navigation system, audio apparatus, etc.), a household electrical appliance (electric pot, IH cooking heater, etc.), a smartphone, an electronic paper, an electronic book reader, a PC keyboard, a game controller, a smartwatch, a wireless earphone, a touch panel, an electronic pen, a penlight, lighting clothes, and a musical instrument. In an electronic apparatus, a load sensor is provided to an input part that receives an input from a user. 
     The embodiments below are of load sensors that are typically provided in a management system or an electronic apparatus as described above. Such a load sensor may be referred to as a “capacitance-type pressure-sensitive sensor element”, a “capacitive pressure detection sensor element”, a “pressure-sensitive switch element”, or the like. The embodiments below are examples of embodiments of the present invention, and the present invention is not limited to the embodiments below in any way. 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. For convenience, X-, Y-, and Z-axes orthogonal to each other are provided in the drawings. The Z-axis direction is the height direction of a load sensor  1 . 
     Embodiment 1 
     With reference to  FIG. 1A  to  FIG. 2B , a manufacturing method of the load sensor  1  of Embodiment 1 is described.  FIG. 1A  to  FIG. 2B  are each a perspective view schematically showing a configuration of each part of the load sensor  1 . 
     As shown in  FIG. 1A , a base member  11  is an insulative member having elasticity. The base member  11  has a flat plate shape parallel to an X-Y plane. 
     The base member  11  is formed from a non-electrically-conductive resin material or a non-electrically-conductive rubber material. The resin material used in the base member  11  is a resin material of at least one type selected from the group consisting of a styrene-based resin, a silicone-based resin (e.g., polydimethylpolysiloxane (PDMS)), an acrylic resin, a rotaxane-based resin, a urethane-based resin, and the like, for example. The rubber material used in the base member  11  is a rubber material of at least one type selected from the group consisting of silicone rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, polyisobutylene, ethylene-propylene rubber, chlorosulfonated polyethylene, acrylic rubber, fluororubber, epichlorohydrin rubber, urethane rubber, natural rubber, and the like, for example. 
     Subsequently, on the upper face (the face on the Z-axis positive side) of the base member  11  shown in  FIG. 1A , electrodes  12  are formed as shown in  FIG. 1B . Here, three electrodes  12  are formed on the upper face of the base member  11 . Each electrode  12  is an electrically-conductive member having elasticity. The electrodes  12  each have a band-like shape that is long in the Y-axis direction on the upper face of the base member  11 , and are formed so as to be separated from each other. Each electrode  12  is formed from a resin material and an electrically-conductive filler dispersed therein, or from a rubber material and an electrically-conductive filler dispersed therein. 
     Similar to the resin material used in the base member  11  described above, the resin material used in the electrode  12  is a resin material of at least one type selected from the group consisting of a styrene-based resin, a silicone-based resin (polydimethylpolysiloxane (e.g., PDMS)), an acrylic resin, a rotaxane-based resin, a urethane-based resin, and the like, for example. Similar to the rubber material used in the base member  11  described above, the rubber material used in the electrode  12  is a rubber material of at least one type selected from the group consisting of silicone rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, polyisobutylene, ethylene-propylene rubber, chlorosulfonated polyethylene, acrylic rubber, fluororubber, epichlorohydrin rubber, urethane rubber, natural rubber, and the like, for example. 
     The electrically-conductive filler used in the electrode  12  is a material of at least one type selected from the group consisting of: metal materials such as Au (gold), Ag (silver), Cu (copper), C (carbon), ZnO (zinc oxide), In 2 O 3  (indium oxide (III)), and SnO 2  (tin oxide (IV)); electrically-conductive macromolecule materials such as PEDOT:PSS (i.e., a complex composed of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonate (PSS)); electrically-conductive fibers such as a metal-coated organic matter fiber and a metal wire (fiber state); and the like, for example. 
     Each electrode  12  is formed by a predetermined printing method on the upper face of the base member  11 . The printing method for forming the electrode  12  will be described later with reference to  FIG. 3A  to  FIG. 7 . 
     Subsequently, wires  13  are disposed so as to be superposed on the upper faces of the three electrodes  12  shown in  FIG. 1B . Here, three wires  13  are disposed so as to be superposed on the upper faces of the three electrodes  12 . Each wire  13  is composed of an electrically-conductive wire member, and a dielectric body that covers the surface of the wire member. The three wires  13  are disposed so as to be arranged along the longitudinal direction of the electrodes  12  (the Y-axis direction). Each wire  13  is disposed, extending in the X-axis direction, so as to extend across the three electrodes  12 . The configuration of the wire  13  will be described later with reference to  FIG. 9A  and  FIG. 9B . 
     After the three wires  13  have been disposed, each wire  13  is connected to the base member  11  by connection members  14  so as to be movable in the longitudinal direction (the X-axis direction) of the wire  13 . In the example shown in  FIG. 1C, 12  connection members  14  connect the wires  13  to the base member  11  at positions other than the positions where the electrodes  12  and the wires  13  overlap each other. 
     Each connection member  14  is implemented as a thread, for example. The thread used for the connection member  14  may be a stranded thread obtained by stranding fibers, or may be a single fiber (i.e., monofilament) which is not stranded. The fiber forming the thread used for the connection member  14  may be a chemical fiber or a natural fiber, or may be a mixed fiber of a chemical fiber and a natural fiber. 
     The chemical fiber used for the connection member  14  is a synthetic fiber, a semisynthetic fiber, a regenerated fiber, an inorganic fiber, or the like. Examples of the synthetic fiber include polystyrene-based fibers, aliphatic polyamide-based fibers (e.g., nylon 6 fiber, nylon 66 fiber), aromatic polyamide-based fibers, polyvinyl alcohol-based fibers (e.g., vinylon fiber), polyvinylidene chloride-based fibers, polyvinyl chloride-based fibers, polyester-based fibers (e.g., polyester fiber, PET fiber, PBT fiber, polytrimethylen-terephthalate fiber, polyalylate fiber), polyacrylonitrile-based fibers, polyethylene-based fibers, polypropylene-based fibers, polyurethane-based fibers, phenol-based fibers, and polyfluoroethylene-based fibers. Examples of the semisynthetic fiber include cellulose-based fibers and protein-based fibers. Examples of the regenerated fiber include a rayon fiber, a cupra fiber, and a lyocell fiber. Examples of the inorganic fiber include a glass fiber, a carbon fiber, a ceramic fiber, and a metal fiber. 
     The natural fiber used for the connection member  14  is a vegetable fiber, an animal fiber, or the like. Examples of the vegetable fiber include cotton and hemp (e.g., flax, ramie). Examples of the animal fiber include hair (e.g., wool, angora, cashmere, mohair), silk, and feathers (e.g., down, feather). 
     Preferably, the thread used for the connection member  14  is a stretchable thread such as a thread for knitting. The stretchable thread is available as a commercial product such as EIFFEL (Kanagawa Co., Ltd.) or SOLOTEX (TEIJIN FRONTIER Co., Ltd.), for example. 
     Subsequently, as shown in  FIG. 2A , cables  21   a  are respectively drawn from end portions on the Y-axis negative side of the three electrodes  12  shown in  FIG. 1C , and the three cables  21   a  are connected to a connector  21 . In addition, end portions on the X-axis negative side of the wires  13  shown in  FIG. 1C  are connected to a connector  22  as shown in  FIG. 2A . In this manner, the three cables  21   a  are connected to the connector  21 , and the three wires  13  are connected to the connector  22 , whereby the capacitance according to combinations of the three electrodes  12  and the wire members in the three wires  13  can be detected. 
     Subsequently, from above the three wires  13  shown in  FIG. 2A , a base member  15  is set as shown in  FIG. 2B . The base member  15  is an insulative member. The base member  15  is a resin material of at least one type selected from the group consisting of polyethylene terephthalate, polycarbonate, polyimide, and the like, for example. The base member  15  has a flat plate shape parallel to the X-Y plane, and the size of the base member  15  in the X-Y plane is similar to that of the base member  11 . The vertexes at the four corners of the base member  15  are connected to the vertexes at the four corners of the base member  11  by a silicone rubber-based adhesive, a thread, or the like, whereby the base member  15  is fixed to the base member  11 . Accordingly, the load sensor  1  is completed as shown in  FIG. 2B . 
     Next, five printing methods that can be used when the electrodes  12  are to be formed on the upper face of the base member  11  are described one by one. The printing methods for forming the electrodes  12  on the upper face of the base member  11  are not limited to the five printing methods below, and may be a printing method that can form the electrodes  12  on the upper face of the base member  11  such that the electrodes  12  have a thickness similar to that according to the five printing methods below. 
       FIG. 3A  to  FIG. 3C  are schematic diagrams for describing screen printing. The screen printing is a kind of hole printing in which printing is performed by passing an ink through holes. 
     As shown in  FIG. 3A , in the screen printing, a screen printing plate  111  and a squeegee  112  are used. In the screen printing plate  111 , holes  111   a  extending in the Y-axis direction are formed in accordance with the shapes of the electrodes  12  to be formed on the upper face of the base member  11 . An ink  100  to be applied during the screen printing is an ink composed of the same material as that of the electrodes  12 . 
     When screen printing is performed, as shown in  FIG. 3A , the screen printing plate  111  is brought close to the upper face of the base member  11  in a state where the ink  100  is applied to the upper face of the screen printing plate  111 . As shown in  FIG. 3B , when the screen printing plate  111  has been placed on the upper face of the base member  11 , the squeegee  112  is moved in the X-axis direction. Accordingly, the ink  100  enters the holes  111   a  and the ink  100  is transferred to the upper face, of the base member  11 , that corresponds to the portions of the holes  111   a . The thickness of the ink  100  (the electrode  12 ) formed on the upper face of the base member  11  is determined by the depth (the width in the Z-axis direction) of each hole  111   a . Then, as shown in  FIG. 3C , the screen printing plate  111  is released from the base member  11 . Then, formation of the electrodes  12  onto the base member  11  ends. 
       FIG. 4  is a schematic diagram for describing gravure printing. Gravure printing is a kind of intaglio printing in which an ink having entered a recess is transferred. 
     As shown in  FIG. 4 , in gravure printing, a container  121 , a plate cylinder  122 , and an impression cylinder  123  are used. The container  121  stores the ink  100 . The plate cylinder  122  has formed therein recesses  122   a  extending in the Y-axis direction in accordance with the shapes of the electrodes  12  to be formed on the face on the Z-axis positive side of the base member  11 . 
     When gravure printing is performed, the plate cylinder  122  and the impression cylinder  123  are rotated, and the base member  11  is passed between the plate cylinder  122  and the impression cylinder  123 . Accordingly, the ink  100  in the container  121  enters the recesses  122   a  of the plate cylinder  122 , and the ink  100  in each recess  122   a  is transferred to the face on the Z-axis positive side of the base member  11 , as a result of the impression cylinder  123  pressing the base member  11  in the Z-axis positive direction. The thickness of the ink  100  (the electrode  12 ) formed on the face on the Z-axis positive side of the base member  11  is determined by the depth of each recess  122   a  of the plate cylinder  122 . Then, formation of the electrodes  12  onto the base member  11  ends. 
       FIG. 5  is a schematic diagram for describing flexographic printing. Flexographic printing is a kind of letterpress printing in which an ink attached to protrusions is transferred. 
     As shown in  FIG. 5 , in flexographic printing, a doctor chamber  131 , an anilox roll  132 , a plate  133 , and a center drum  134  are used. The doctor chamber  131  stores the ink  100 . The plate  133  has formed therein protrusions  133   a  extending in the Y-axis direction in accordance with the shapes of the electrodes  12  to be formed on the face on the Z-axis positive side of the base member  11 . 
     When flexographic printing is performed, the anilox roll  132  and the plate  133  are rotated, and the ink  100  in the doctor chamber  131  is applied to the protrusions  133   a  of the plate  133 . The base member  11  is disposed on the center drum  134 , and due to rotation of the center drum  134 , the base member  11  is transported between the plate  133  and the center drum  134 . Accordingly, the ink  100  on the protrusions  133   a  is transferred onto the face on the Z-axis positive side of the base member  11 . The thickness of the ink  100  (the electrode  12 ) formed on the face on the Z-axis positive side of the base member  11  is determined by the distance at which each protrusion  133   a  of the plate  133  and the base member  11  come closest to each other. Then, formation of the electrodes  12  onto the base member  11  ends. 
       FIG. 6  is a schematic diagram for describing offset printing. 
     As shown in  FIG. 6 , in offset printing, an ink roller  141 , a water roller  142 , a container  143 , a plate cylinder  144 , a blanket  145 , and an impression cylinder  146  are used. The container  143  stores dampening water  101 . 
     When offset printing is performed, the ink roller  141  is rotated, whereby the ink  100  is applied to the plate cylinder  144 . In addition, the water roller  142  is rotated, whereby the dampening water  101  in the container  143  is applied to the plate cylinder  144 . At this time, the ink  100  is applied to the plate cylinder  144  such that the ink  100  on the plate cylinder  144  corresponds to the width (the length in the X-axis direction) of each electrode  12  to be formed on the base member  11 . Due to rotation of the plate cylinder  144  and the blanket  145 , out of the dampening water  101  and the ink  100  on the plate cylinder  144 , the ink  100  is moved onto the blanket  145 . Then, the blanket  145  and the impression cylinder  146  are rotated, and the base member  11  is passed between the blanket  145  and the impression cylinder  146 . Accordingly, the ink  100  on the blanket  145  is transferred to the upper face of the base member  11 . The thickness of the ink  100  (the electrode  12 ) formed on the upper face of the base member  11  is determined by the distance between the blanket  145  and the impression cylinder  146 . Then, formation of the electrodes  12  onto the base member  11  ends. 
       FIG. 7  is a schematic diagram for describing gravure offset printing. 
     As shown in  FIG. 7 , in gravure offset printing, an ink roll  151 , an ink dish  152 , a doctor  153 , a gravure plate cylinder  154 , a blanket cylinder  155 , and an impression cylinder  156  are used. The ink dish  152  stores the ink  100 . The gravure plate cylinder  154  has formed therein recesses  154   a  extending in the Y-axis direction in accordance with the shapes of the electrodes  12  to be formed on the upper face of the base member  11 . 
     When gravure offset printing is performed, the ink roll  151  is rotated, whereby the ink  100  in the ink dish  152  is applied to the gravure plate cylinder  154 . The ink  100  applied to the gravure plate cylinder  154  is caused to be held in each recess  154   a  of the gravure plate cylinder  154  by the doctor  153 . The gravure plate cylinder  154  and the blanket cylinder  155  are rotated, whereby the ink  100  in each recess  154   a  is moved onto the blanket cylinder  155 . Then, the blanket cylinder  155  and the impression cylinder  156  are rotated, and the base member  11  is passed between the blanket cylinder  155  and the impression cylinder  156 . Accordingly, the ink  100  on the blanket cylinder  155  is transferred to the upper face of the base member  11 . The thickness of the ink  100  (the electrode  12 ) formed on the upper face of the base member  11  is determined by the depth of each recess  154   a  and the distance between the blanket cylinder  155  and the impression cylinder  156 . Then, formation of the electrodes  12  onto the base member  11  ends. 
     As described above, according to each printing method, each electrode  12  can be formed so as to have a thickness of about 0.001 mm to 0.5 mm, on the upper face of the base member  11 . 
       FIG. 8  is a plan view schematically showing the load sensor  1  when viewed in the Z-axis negative direction. For convenience, the base member  15  is not shown in  FIG. 8 . 
     As shown in  FIG. 8 , at positions at which the three electrodes  12  and the three wires  13  cross each other, regions A11, A12, A13, A21, A22, A23, A31, A32, A33 for detecting loads are set. When a load is applied in the Z-axis direction to each region, the electrode  12  warps so as to wrap the wire  13 . Accordingly, the contact area between the electrode  12  and the wire  13  changes, and the capacitance between the electrode  12  and the wire  13  changes. 
     As shown in  FIG. 8 , the cables  21   a  drawn from the three electrodes  12  are referred to lines L11, L12, L13, and the wire members  13   a  in the three wires  13  are referred to as lines L21, L22, L23. The positions at which the line L21 crosses the lines L11, L12, L13 are defined as regions A11, A12, A13, respectively, the positions at which the line L22 crosses the lines L11, L12, L13 are defined as regions A21, A22, A23, respectively, and the positions at which the line L23 crosses the lines L11, L12, L13 are defined as regions A31, A32, A33, respectively. 
     When a load is applied to the region A11, the contact area between the electrode  12  and the wire  13  increases in the region A11. Therefore, when the capacitance between the line L11 and the line L21 is detected, the load applied to the region A11 can be calculated. Similarly, in another region as well, when the capacitance between the two lines crossing each other in the other region is detected, the load applied to the other region can be calculated. 
     For example, when one of the three cables  21   a  is selectively connected to the ground, and the voltage between this cable  21   a  and one of the three wires  13  is detected, the capacitance in the region in which the cable  21   a  and the wire  13  cross each other can be detected. On the basis of this capacitance, the load applied to the region can be calculated. 
       FIG. 9A  and  FIG. 9B  are each a cross-sectional view schematically showing the periphery of a wire  13  when viewed in the X-axis negative direction.  FIG. 9A  shows a state where no load is applied, and  FIG. 9B  shows a state where loads are applied. 
     As shown in  FIG. 9A , the wire  13  is composed of an electrically-conductive wire member  13   a  and a dielectric body  13   b  covering the wire member  13   a . The wire member  13   a  is implemented as, for example: a metal body; a glass body and an electrically-conductive layer formed on the surface thereof; a resin body and an electrically-conductive layer formed on the surface thereof; or the like. When a glass body is used, an electrically-conductive filler may be dispersed in the glass body. When a resin body is used, an electrically-conductive filler may be dispersed in the resin body. 
     The metal body used for the wire member  13   a  is a metal of at least one type selected from the group consisting of Au (gold), Ag (silver), Cu (copper), a Ni—Cr alloy (nichrome), C (carbon), ZnO (zinc oxide), In 2 O 3  (indium oxide (III)), SnO 2  (tin oxide (IV)), and the like, for example. The glass body used for the wire member  13   a  is not limited in particular, and may be any glass body that has a network-like structure of silicon oxide, and is a glass material of at least one type selected from the group consisting of quartz glass, soda-lime glass, borosilicate glass, lead glass, and the like, for example. The resin body used for the wire member  13   a  is a resin material of at least one type selected from the group consisting of a styrene-based resin, a silicone-based resin (e.g., PDMS), an acrylic resin, a rotaxane-based resin, a urethane-based resin, and the like. 
     The electrically-conductive layer of the glass body and the resin body may be formed, for example, by vapor deposition of a metal of at least one type selected from the group consisting of metals similar to the metals that can form the metal body, or may be formed by application of an electrically-conductive ink. The electrically-conductive filler of the glass body and the resin body is a metal of at least one type selected from the group consisting of metals similar to the metals that can form the metal body. 
     The dielectric body  13   b  has an electric insulation property, and is formed from a resin material, a ceramic material, a metal oxide material, or the like, for example. The dielectric body  13   b  may be a resin material of at least one type selected from the group consisting of a polypropylene resin, a polyester resin (e.g., polyethylene terephthalate resin), a polyimide resin, a polyphenylene sulfide resin, a polyvinyl formal resin, a polyurethane resin, a polyamide imide resin, a polyamide resin, and the like, or may be a metal oxide material of at least one type selected from the group consisting of Al 2 O 3 , Ta 2 O 5 , and the like. 
     When no load is applied to the region shown in  FIG. 9A , the force applied between the electrode  12  and the wire  13 , and the force applied between the wire  13  and the base member  15  are substantially zero. From this state, when a load is applied in the upward direction to the lower face of the base member  11  and a load is applied in the downward direction to the upper face of the base member  15  as shown in  FIG. 9B , the electrode  12  and the base member  11  which have elasticity are deformed by the wire  13 , as shown in  FIG. 9B . It should be noted that, when the lower face of the base member  11  or the upper face of the base member  15  is placed on a stationary object and a load is applied only to the other base member as well, a load will be similarly received from the stationary object side due to reaction. 
     As shown in  FIG. 9B , when the loads are applied, the wire  13  is brought close to the electrode  12  and the base member  11  so as to be wrapped by the electrode  12  and the base member  11 , and the contact area between the wire  13  and the electrode  12  increases. Accordingly, the capacitance between the wire member  13   a  in the wire  13  and the electrode  12  changes, and as described with reference to  FIG. 8 , the capacitance between two lines corresponding to this region is detected, and the load applied to this region is calculated. 
     Here, in a case of an electrode obtained by dispersing an electrically-conductive filler in an elastic material, it is known that the electrically-conductive filler serves as an inhibitive factor against elastic return of the electrode, whereby response of the elastic return is impaired. When such an electrode is used and a load is provided and removed, property deviation (hysteresis) occurs in change in capacitance, and thus, changes in capacitance during loading and during unloading are deviated from each other. 
     Therefore, the inventors have conducted various studies, and found that when the thickness of each electrode  12  formed on the upper face of the base member  11  is reduced by using the printing methods as described with reference to  FIG. 3A  to  FIG. 7 , the property deviation of the electrode  12  can be suppressed. As described above, when the electrode  12  is formed to be thin by a predetermined printing method on the upper face of the base member  11 , the structure composed of the electrode  12  and the base member  11  has a sufficient elastic force while the capacitance between the electrode  12  and the wire member  13   a  is allowed to change in accordance with the load, as shown in  FIG. 9B . Therefore, during unloading, the state in  FIG. 9B  quickly returns to the state in  FIG. 9A . That is, in elastic deformations of the electrode  12  and the base member  11 , influence of the elastic deformation of the base member  11  becomes dominant, and influence of the filler contained in the electrode  12  is significantly suppressed. Accordingly, change in capacitance during unloading can be made close to change in capacitance during loading. 
       FIG. 10A  is a schematic diagram obtained when the load sensor  1  cut, at the position of wire  13 , along a plane parallel to the X-Z plane is viewed in the Y-axis positive direction. 
     As described with reference to  FIG. 1C , the connection members  14  connect the wires  13  to the base member  11  on the X-axis positive side and the X-axis negative side of each electrode  12 . Here, as described above, the electrode  12  on the upper face of the base member  11  is an electrode formed, by a printing method, so as to be very thin such that the thickness thereof is 10 μm to 150 μm. Accordingly, as shown in  FIG. 10A , an interval D1 between the wire  13  and the base member  11  is also very small. Therefore, even when the wire  13  and the base member  11  are brought close to each other due to fastening of the connection members  14 , the warps in the Z-axis direction of the wire  13  and the base member  11  can be suppressed to the distance D1 or less. 
     Meanwhile, when electrodes  12  created in advance are set on the upper face of the base member  11  with an adhesive or the like, the thickness of each electrode  12  on the upper face of the base member  11  is increased to be about 0.5 mm to 1 mm, as shown in  FIG. 10B . Thus, when the thickness of the electrode  12  is large, an interval D2 between the wire  13  and the base member  11  becomes greater than the interval D1 shown in  FIG. 10A . In this case, when the wire  13  and the base member  11  are brought close to each other due to fastening of the connection members  14 , the warps in the Z-axis direction of the wire  13  and the base member  11  are increased to be about the distance D2. This may causes decrease of load detection accuracy. In contrast to this, in Embodiment 1, since the interval between the wire  13  and the base member  11  is small as described above, unintended deformation of the base member  11  and the wire  13  is suppressed. Therefore, load detection accuracy can be ensured to be high. 
     Next, a preferable size of each part of the load sensor  1  is described with reference to  FIG. 11 . 
     As shown in  FIG. 11 , the thickness (the height in the Z-axis direction) of each electrode  12  is defined as d1, the thickness (the height in the Z-axis direction) of the base member  11  is defined as d2, the width (the length in the X-axis direction) of each electrode  12  is defined as d21, the interval between electrodes  12  (the distance in the X-axis direction between two electrodes  12 ) is defined as d22, the elastic modulus of each electrode  12  is defined as E1, the electrical conductivity of each electrode  12  is defined as σ, and the elastic modulus of the base member  11  is defined as E2. 
     According to the studies by the inventors, the following can be assumed. That is, when the elastic modulus E1 of the electrode  12  is set to be 0.1 MPa to 10 MPa, the electrical conductivity σ of the electrode  12  is set to be not greater than 100 Ω·cm, the elastic modulus E2 of the base member  11  is set to be 0.01 MPa to 10 MPa, the thickness d1 of the electrode  12  is set to be 0.001 mm to 0.5 mm, the thickness d2 of the base member  11  is set to be 0.01 mm to 2 mm, the width d21 of the electrode  12  is set to be 2 mm to 50 mm, and the interval d22 of the electrode  12  is set to be 1 mm to 5 mm, change in capacitance during unloading can be made close to change in capacitance during loading, as described with reference to  FIG. 9A  and  FIG. 9B , and warps of the wire  13  and the base member  11  at the time of fastening of the connection members  14  can be suppressed, as described with reference to  FIG. 10A  and  FIG. 10B . 
     Effects of Embodiment 1 
     According to Embodiment 1, the following effects are exhibited. 
     When the thickness of the base member  11  and the thickness of the electrode are set as described above, the thickness of the electrode  12  can be made sufficiently smaller than the thickness of the base member  11 . Accordingly, in deformations of the electrode  12  and the base member  11  during loading and during unloading, influence of the deformation of the electrode  12  is suppressed, and influence of the deformation of the base member  11  becomes dominant. Therefore, influence of response impairment in elastic return of the electrode  12  can be suppressed, and as a result, changes in capacitance during loading and during unloading can be caused to substantially match each other. Therefore, deviation between the detection values of the load sensor  1  during loading and during unloading can be suppressed. 
     As described with reference to  FIG. 10A , the interval D1 between the wire  13  and the base member  11  is a very small value in accordance with the thickness of the electrode  12 . Therefore, deformations of the wire  13  and the base member  11  due to fastening of the connection members  14  can be suppressed. Accordingly, load detection accuracy can be enhanced. 
     Each electrode  12  is an electrode formed on the upper face of the base member  11  by a predetermined printing method as shown in  FIG. 3A  to  FIG. 7 , i.e., screen printing, gravure printing, flexographic printing, offset printing, or gravure offset printing. Thus, by using the printing method, it is possible to smoothly and accurately form, on the upper face of the base member  11 , the electrode  12  that has a thickness sufficiently smaller than the thickness of the base member  11 . 
     A plurality of electrodes  12  are formed so as to be separate from each other on the upper face of the base member  11 . Therefore, the load detection range of the load sensor  1  can be divided into a plurality of ranges. 
     Each electrode  12  has a band-like shape that is long in one direction (the Y-axis direction), and a wire  13  (the wire member  13   a ) is disposed so as to extend across the plurality of electrodes  12 . Therefore, at the crossing positions (in  FIG. 8 , the regions A11, A12, A13, A21, A22, A23, A31, A32, A33) at which the wire members  13   a  extend across the plurality of electrodes  12 , loads can be detected. 
     In addition, a plurality of wires  13  (the wire members  13   a ) are disposed along the longitudinal direction (the Y-axis direction) of the electrodes  12 . Therefore, as shown in  FIG. 8 , the crossing positions at which the plurality of electrodes  12  and the plurality of wire members  13   a  cross each other can be arranged in a matrix shape. Thus, detection positions can be finely set. 
     Each wire  13  (the wire member  13   a ) is connected to the base member  11  by connection members  14  so as to be movable in the longitudinal direction (the X-axis direction). In a case where the wire  13  is fixed to the base member  11  by an adhesive or the like, when the base member  11  and the electrodes  12  stretch and contract, a situation in which the dielectric body  13   b  covering the wire member  13   a  is detached because of the adhesive may occur. In contrast to this, in Embodiment 1, the wire  13  (the wire member  13   a ) is connected to the base member  11  so as to be movable in the longitudinal direction (the X-axis direction) by connection members  14  each implemented as a thread or the like. Therefore, even if the base member  11  and the electrodes  12  stretch and contract, the positional relationship between the wire  13  (the wire member  13   a ) and the connection members  14  changes, and thus, breakage of the dielectric body  13   b  can be inhibited. Therefore, decrease of the load detection accuracy due to breakage of the dielectric body  13   b  can be inhibited. 
     Embodiment 2 
     In Embodiment 1, the base member  15  is superposed from above on the structure shown in  FIG. 2A , whereby the load sensor  1  is formed. However, in Embodiment 2, the structure shown in  FIG. 1B  is superposed on the structure shown in  FIG. 2A , whereby a load sensor  1  is formed. 
     With reference to  FIG. 12  and  FIG. 13 , a manufacturing method of the load sensor  1  of Embodiment 2 is described.  FIG. 12  and  FIG. 13  are each a perspective view schematically showing a configuration of each part of the load sensor  1 . 
     As shown in  FIG. 12 , in Embodiment 2, a structure  1   a  similar to that in  FIG. 2A  is produced by a procedure similar to that in Embodiment 1. Then, separately from the structure  1   a , a structure similar to that in  FIG. 1B  is produced by a procedure similar to that in Embodiment 1. In a state where this structure is reversed in the up-down direction, three cables  21   a  and a connector  21  are connected to three electrodes  12 , whereby a structure  1   b  is produced. 
     Subsequently, the structure  1   b  is set from above the structure  1   a , and the four corners of the upper face of the base member  11  on the lower side and the four corners of the lower face of the base member  11  on the upper side are fixed to each other by an adhesive, a thread, or the like. Then, as shown in  FIG. 13 , the load sensor  1  of Embodiment 2 is completed. In Embodiment 2 as well, nine regions for load detection are set as in  FIG. 8 . 
       FIG. 14A  and  FIG. 14B  are each a cross-sectional view schematically showing the periphery of a wire  13  when viewed in the X-axis negative direction.  FIG. 14A  shows a state where no load is applied, and  FIG. 14B  shows a state where loads are applied. 
     When no load is applied to the region shown in  FIG. 14A , the force applied between the upper electrode  12  and the wire  13  and the force applied between the lower electrode  12  and the wire  13  are substantially zero. From this state, as shown in  FIG. 14B , when a load is applied in the downward direction to the upper face of the upper base member  11 , and a load is applied in the upward direction to the lower face of the lower base member  11 , the electrodes  12  and the base member  11  which have elasticity are deformed by the wire  13  as shown in  FIG. 14B . 
     As shown in  FIG. 14B , when the loads are applied, the wire  13  is brought close to the upper electrode  12  and the upper base member  11  so as to be wrapped by the upper electrode  12  and the upper base member  11 . Similarly, the wire  13  is brought close to the lower electrode  12  and the lower base member  11  so as to be wrapped by the lower electrode  12  and the lower base member  11 . Accordingly, the capacitance between the wire member  13   a  and the upper electrode  12 , and the capacitance between the wire member  13   a  and the lower electrode  12  change. Then, on the basis of the sum of the two capacitances, a load applied to the corresponding region among the nine regions shown in  FIG. 8  is calculated. 
     &lt;Verification Experiment 1&gt; 
     With respect to the load sensor  1  of Embodiment 2 and a load sensor  200  of a comparative example, the inventors actually confirmed the relationship between capacitance and load through a verification experiment. 
     With reference to  FIG. 15A  and  FIG. 15B , the size of each part of the load sensor  1  used in the verification experiment is described.  FIG. 15A  and  FIG. 15B  are each a cross-sectional view schematically showing the periphery of wires  13  when viewed in the X-axis negative direction.  FIG. 15A  shows the load sensor  200  of the comparative example, and  FIG. 15B  shows the load sensor  1  that is substantially the same as that of Embodiment 2. In each of the configurations in  FIG. 15A  and  FIG. 15B , base members  11  and electrodes  12  are positioned on the upper side and on the lower side, respectively, with two wires  13  extending in the X-axis direction therebetween. 
     As shown in  FIG. 15A , in the case of the load sensor  200  of the comparative example, a thickness d11 of the lower electrode  12  was set to be 1 mm, and a thickness d12 of the upper electrode  12  was set to be 0.5 mm. Here, these two electrodes  12  were created in advance, and were set on the respective base members  11  with an adhesive or the like. The thickness d2 of each of the upper and lower base members  11  was set to be 0.5 mm. As shown in  FIG. 15B , in the case of the load sensor  1  of Embodiment 2, the thickness d11 of the lower electrode  12  and the thickness d12 of the upper electrode  12  were each set to be 10 μm to 150 μm by a printing method as described above. The thickness d2 of each of the upper and lower base members  11  was set to be 0.5 mm, as in the case of the comparative example. That is, the ratio of the thickness of the electrode  12  to the thickness of the base member  11  was set to be not less than 0.02 and not greater than 0.3. 
     In each of the cases of  FIG. 15A  and  FIG. 15B , the upper and lower electrodes  12  were connected to the ground (GND), and the wire members  13   a  of the two wires  13  were connected to each other. The two kinds of load sensors set as in  FIG. 15A  and  FIG. 15B  were each set on a fixation base, a load was applied within 1 cm 2  at the upper face of the upper base member  11 , and the capacitance between the electrode  12  and each wire member  13   a  was measured. 
       FIG. 16A  is a graph showing a relationship between load and capacitance of the case of the comparative example. As shown in  FIG. 16A , in the comparative example, with respect to during loading and during unloading, curves different from each other were generated. Therefore, in the comparative example, even when the same load is applied, the capacitances are different between during loading and during unloading. Thus, the values of the load calculated on the basis of the capacitances become different from each other. 
     Meanwhile,  FIG. 16B  is a graph showing a relationship between load and capacitance in the case of Embodiment 2. As shown in  FIG. 16B , in Embodiment 2, with respect to during loading and during unloading, curves that are substantially the same with each other were generated. Therefore, in Embodiment 2, when the same load is applied, the capacitances become substantially the same with each other between during loading and during unloading. Therefore, the values of the load calculated on the basis of the capacitances also become substantially the same with each other. 
     Thus, the following has been found. That is, when the thickness of each electrode  12  is set to be not less than 10 μm and not greater than 150 μm on the basis of a printing method described above, and the thickness of the base member  11  is set to be 0.5 mm, in other words, when the ratio of the thickness of the electrode  12  to the thickness of the base member  11  is set to be not less than 0.02 and not greater than 0.3, property deviation (hysteresis) that occurs in change in capacitance is suppressed, and changes in capacitance during loading and during unloading match each other. 
     When the thickness of the base member  11  is not less than 0.5 mm, in deformations of the electrode  12  and the base member  11  during loading and during unloading, influence of the deformation of the electrode  12  is still further suppressed and influence of the deformation of the base member  11  becomes dominant. Therefore, it is assumed that, when the thickness of the base member  11  is set to be not less than 0.5 mm, in other words, when the ratio of the thickness of the electrode  12  to the thickness of the base member  11  is set to be smaller than a range of 0.02 to 0.3, property deviation that occurs in change in capacitance is still further suppressed. 
     &lt;Verification Experiment 2&gt; 
     Further, through an experiment, the inventors examined the hysteresis property of the load sensor  1  in a case where the thickness of the electrode  12  was changed in the configuration of Embodiment 2 shown in  FIG. 15B . In this experiment, other than the thickness of the electrode  12  being changed, the same condition as the condition applied to Embodiment 2 in the above verification experiment 1 was set. In the configuration in  FIG. 15B , in a state where the thickness d11 of the lower electrode  12  and the thickness d12 of the upper electrode  12  were maintained to be equal with each other, the thickness d11, d12 was changed. The thickness d2 of the base member  11  was fixed to 0.5 mm. Under this condition, the inventors confirmed the thickness of the electrode  12  that allows appropriate load detection, and the ratio of the thickness of the electrode  12  to the thickness of the base member  11 . 
     In the experiment, hysteresis was obtained by the calculation method shown in  FIG. 17A . 
     In  FIG. 17A , C1 is a capacitance that corresponds to a predetermined load F during loading, and C2 is a capacitance that corresponds to the predetermined load F during unloading. ΔC is the difference between C1 and C2. Hysteresis (%) is calculated as a value of ΔC/C2 at the time when the value of ΔC/C2 becomes greatest in accordance with variation of the load F. 
     In the verification experiment 1 above, the hysteresis in the comparative example in  FIG. 16A  was 12%, and the hysteresis in Embodiment 2 in  FIG. 16B  was less than 0.2%. Thus, according to the configuration of Embodiment 2, the hysteresis can be considerably reduced when compared with that in the comparative example. 
       FIG. 17B  is a graph showing a result of the experiment on hysteresis property. The horizontal axis represents the thickness of the electrode  12 . At the horizontal axis, the ratio of the thickness of the electrode  12  to the thickness (0.5 mm) of the base member  11  is indicated by an arrow in association with the thickness of the electrode  12 . The vertical axis represents hysteresis (%). 
     According to the studies of the inventors, in both of during loading and during unloading, an allowable range of hysteresis that allows appropriate load detection is preferably not greater than 5%, and more preferably not greater than 2%. Therefore, from the experimental result in  FIG. 17B , the thickness of the electrode  12  is preferably not greater than 250 μm, and further preferably not greater than 150 μm. Similarly, from this experimental result, the ratio of the thickness of the electrode  12  to the thickness of the base member  11  is preferably not greater than 0.5, and further preferably not greater than 0.3. 
     Further, the inventors examined the relationship between the thickness of the electrode  12  and the volume resistivity of the electrode  12  under a similar condition. 
     The electrode  12  is formed from a resin material or a rubber material, and an electrically-conductive filler having a size of about several μm dispersed therein. Therefore, when the thickness of the electrode  12  is as small as about the size of the filler, the electrically-conductive filler becomes difficult to be distributed in a three-dimensional manner in the electrode  12 , and as a result, the density in a plan view of the electrically-conductive filler in the electrode  12  rapidly decreases. Therefore, when the thickness of the electrode  12  is as small as about the size of the filler, the electrical conductivity of the electrode  12  significantly decreases, the volume resistivity of the electrode  12  rapidly increases, and the resistance value of the electrode  12  greatly increases. In addition, when the electrically-conductive filler becomes difficult to be distributed in a three-dimensional manner in association with decrease in the thickness of the electrode  12 , variation in the volume resistivity of each electrode  12  becomes large when compared with a case where the electrically-conductive filler is appropriately distributed in a three-dimensional manner. Therefore, when the thickness of the electrode  12  is as small as about the size of the filler, variation in the volume resistivity of each electrode  12  becomes large. 
     As described above, when the thickness of the electrode  12  is as small as about the size of the filler, the resistance value of the electrode  12  becomes significantly large, and the variation in the resistance value of each electrode  12  becomes large. Therefore, the accuracy of measurement of the capacitance between the wire  13  and the electrode  12  performed by a measurement circuit in a later stage decreases, and a load according to the capacitance cannot be appropriately calculated. This was clarified by the inventors through a verification experiment shown below. 
       FIG. 17C  is a graph showing a verification result of the relationship between the thickness of the electrode  12  and the volume resistivity of the electrode  12 . Similar to  FIG. 17B , the horizontal axis represents the thickness of the electrode  12 . Similar to  FIG. 17B , at the horizontal axis, the ratio of the thickness of the electrode  12  to the thickness of the base member  11  is indicated by an arrow in association with the thickness of the electrode  12 . The vertical axis represents the volume resistivity of the electrode  12 . 
     As shown in  FIG. 17C , it is seen that, when the thickness of the electrode  12  decreases, it becomes difficult for the electrically-conductive fillers to conduct electricity with each other, and thus, the volume resistivity increases. In particular, around the point where the thickness of the electrode  12  becomes slightly smaller than 10 μm, which is close to the size of the filler, the volume resistivity rapidly increases. Further, in accordance with the thickness of the electrode  12  becoming smaller than 10 μm, the degree of increase in the volume resistivity increases. Therefore, in a range where the thickness of the electrode  12  is smaller than 10 μm, the load cannot be appropriately detected due to the above-described factor. Therefore, from the verification result in  FIG. 17C , the thickness of the electrode  12  is preferably not less than 10 μm, and the ratio of the thickness of the electrode  12  to the thickness of the base member  11  is preferably not less than 0.02. 
     Further, with respect to a case of the electrodes  12  having different elastic moduli as well, the inventors conducted an experiment similar to that in  FIG. 17B  and  FIG. 17C  to examine the conditions of the ratio and thickness of the electrode  12  for performing appropriate load detection. 
       FIG. 18  is a graph showing a relationship between the thickness of the electrodes  12  and the hysteresis in this experiment. The graph in  FIG. 18  is a graph similar to that in  FIG. 17B . The black plots indicate a case where an electrode  12  having an elastic modulus of not less than 10 5  Pa and not greater than 10 9  Pa (setting  1 ) was used. The white plots indicate a case where an electrode  12  having an elastic modulus of less than 10 5  (setting  2 ) was used. The electrode  12  based on setting  1  is the same as the electrode  12  used in the experiment in  FIG. 17B  and  FIG. 17C . Therefore, the black plots are the same as the plots in  FIG. 17B  and  FIG. 17C . 
     In the case of setting  1 , the condition for causing the hysteresis to be in an allowable range (not greater than 5% or not greater than 2%) and for causing the volume resistivity of the electrode  12  to be in an allowable range (not greater than 75 Ω·cm) is the same as the condition described with reference to  FIG. 17B  and  FIG. 17C . Therefore, a more preferable ratio of the thickness of the electrode  12  to the thickness of the base member  11  in the case of setting  1  is not less than 0.02 and not greater than 0.3. 
     Meanwhile, in the case of setting  2  as well, an allowable range of the hysteresis that allows appropriate load detection is preferably not greater than 5%, and more preferably not greater than 2%. Therefore, on the basis of the graph in  FIG. 18 , the thickness of the electrode  12  is preferably not greater than 100 μm, and further preferably, not greater than 50 μm. Therefore, the ratio of the thickness of the electrode  12  to the thickness of the base member  11  is preferably not greater than 0.2, and further preferably not greater than 0.1. In the case of setting  2 , the relationship between the thickness and the volume resistivity of the electrode  12  is substantially the same as that in  FIG. 17C . Therefore, in the case of setting  2 , similar to the case in  FIG. 17C , the thickness of the electrode  12  is preferably not less than 10 μm, and the ratio of the thickness of the electrode  12  is preferably not less than 0.02. Therefore, a more preferable ratio of the thickness of the electrode  12  to the thickness of the base member  11  in the case of setting  2  is not less than 0.02 and not greater than 0.1. 
     The elastic modulus of the electrode  12  used in the load sensor  1  is normally included in a range of not less than 10 5  Pa and not greater than 10 9  Pa (setting  1 ). Therefore, it is preferable that the ratio of the thickness of the electrode  12  to the thickness of the base member  11  is set to be not less than 0.02 and not greater than 0.3, as described above. On the other hand, when the elastic modulus of the electrode  12  used in the load sensor  1  is included in a range of less than 10 5  (setting  2 ), the ratio of the thickness of the electrode  12  to the thickness of the base member  11  may be set to be not less than 0.02 and not greater than 0.1, as described above. 
     Effects of Embodiment 2 
     According to Embodiment 2, the following effects are exhibited in addition to effects similar to those in Embodiment 1. 
     As shown in the verification experiment in  FIG. 16B ,  FIG. 17B , and  FIG. 17C , when the ratio of the thickness of the electrode  12  to the thickness of the base member  11  is set to be not less than 0.02 and not greater than 0.3, the thickness of the electrode  12  can be made sufficiently smaller than the thickness of the base member  11 . Accordingly, in deformations of the electrode  12  and the base member  11  during loading and during unloading, influence of the deformation of the electrode  12  is suppressed, and influence of the deformation of the base member  11  becomes dominant. Therefore, influence of response impairment in elastic return of the electrode  12  can be suppressed, and as a result, changes in capacitance during loading and during unloading can be caused to substantially match each other. Thus, hysteresis can be suppressed. Accordingly, deviation between the detection values of the load sensor  1  during loading and during unloading can be suppressed. 
     As shown in  FIG. 12 , the structure  1   b  has a configuration similar to that of the structure  1   a , and the structure  1   b  is disposed on the upper side of the structure  1   a  such that each electrode  12  of the structure  1   b  is superposed on each wire  13  (the wire member  13   a ). Then, a load is calculated on the basis of the sum of the capacitance between the wire member  13   a  and the lower electrode  12 , and the capacitance between the wire member  13   a  and the upper electrode  12 . Accordingly, the capacitance is enhanced when compared with that in Embodiment 1, and thus, sensitivity of the load sensor  1  can be enhanced. Therefore, the load detection accuracy of the load sensor  1  can be enhanced. In addition, since the upper and lower sides of the wire member  13   a  are shielded by the electrodes  12 , respectively, noise occurring in the wire member  13   a  can be suppressed. 
     It is sufficient that, in each of the two structures  1   a ,  1   b , each electrode  12  is an electrode formed by a printing method as described above. The thickness, width, length, and elastic modulus of the electrode  12  and the thickness, elastic modulus, and the like of the base member  11  may be different between the two structures. 
     Embodiment 3 
     In Embodiment 2, each wire  13  is disposed so as to linearly extend in the X-axis direction. However, in Embodiment 3, each wire  13  has a shape in which the wire  13  is cyclically bent in the X-Y plane. 
       FIG. 19  is a perspective view schematically showing a configuration of each part of a load sensor  1  according to Embodiment 3. 
     Each wire  13  of Embodiment 3 is cyclically bent in advance when compared with that of Embodiment 2. Each wire  13  cyclically bent in this manner is disposed on the upper side of each electrode  12 , and is connected to the base member  11  by connection members  14 , as in Embodiments 1, 2, whereby a structure  1   a  is completed. Then, a structure  1   b  similar to that of Embodiment 2 is set from above the structure  1   a , whereby the load sensor  1  is completed. 
     Each wire  13  of Embodiment 3 is configured to be similar to that of Embodiments 1, 2 above, or may be implemented as a stranded wire obtained by stranding a plurality of insulation-coated conductor wires. In addition, each wire  13  of Embodiments 1, 2 above may be implemented as a stranded wire obtained by stranding a plurality of insulation-coated conductor wires. 
       FIG. 20A  and  FIG. 20B  are schematic diagrams indicating that the shape of each wire  13  changes in accordance with stretch and contraction of the base member  11  and the electrodes  12 .  FIG. 20A  and  FIG. 20B  are each a plan view schematically showing the configuration of the load sensor  1  when viewed in the Z-axis negative direction. For convenience, the structure  1   b  of the load sensor  1  is not shown. 
     As shown in  FIG. 20A , in a normal state, each wire  13  is cyclically bent, as in  FIG. 19 . From this state, when the base member  11  and the electrodes  12  stretch and contract, the wires  13  enter a state of being linearly extended as shown in  FIG. 20B , for example. At this time, since the connection members  14  are each implemented as a thread, the positions at which the connection members  14  fasten the wires  13  vary in accordance with stretch and contraction of the base member  11  and the electrodes  12 . 
     Effects of Embodiment 3 
     According to Embodiment 3, the following effects are exhibited in addition to effects similar to those in Embodiments 1, 2. 
     As shown in  FIG. 19  and  FIG. 20A , each wire  13  (the wire member  13   a ) is cyclically bent. Therefore, even if the base member  11  and the electrodes  12  stretch and contract, since the bent state of the wire member  13   a  changes, breakage of the wire member  13   a  can be avoided. In addition, when compared with a case where the wire member  13   a  is linearly disposed, the density of the wire member  13   a  per unit area is increased. Thus, the detection sensitivity of the load sensor  1  can be enhanced, and the detection range of the load sensor  1  can be enlarged. 
     Each wire  13  (the wire member  13   a ) is connected to the base member  11  by connection members  14  so as to be movable in the longitudinal direction (the X-axis direction). Accordingly, as shown in  FIG. 20A  and  FIG. 20B , even if the base member  11  and the electrodes  12  stretch and contract, since the positional relationship between the wire  13  (the wire member  13   a ) and the connection members  14  changes, breakage of the dielectric body  13   b  can be inhibited. 
     &lt;Modification&gt; 
     Various modifications of the configuration of the load sensor  1  can be made in addition to the configurations shown in Embodiments 1 to 3 above. 
     For example, in Embodiments 1 to 3 above, three electrodes  12  are formed on a surface of the base member  11 . However, one electrode  12  may be formed on the entire surface of the base member  11 . In addition, although three wires  13  (the wire members  13   a ) are disposed with respect to three electrodes  12 , the numbers of electrodes  12  and wires  13  are not limited thereto. For example, a plurality of wires  13  (the wire members  13   a ) extending in the X-axis direction may be disposed so as to be arranged in the Y-axis direction with respect to one electrode  12  extending in the Y-axis direction. Alternatively, the load sensor  1  may be provided with one electrode  12  and one wire  13  only. 
     In Embodiment 1 above, the base member  15  is set from above the structure shown in  FIG. 2A . However, the base member  15  is not necessarily required, and the structure shown in  FIG. 2A , as is, may be used as the load sensor  1 . 
     In Embodiments 1 to 3 above, each electrode  12  is formed by using a predetermined printing method. However, the method for forming the electrode  12  is not limited thereto. As long as the electrode  12  that has a thickness sufficiently smaller than that of the base member  11  can be formed, another method may be used in formation of the electrode  12 . For example, by injection molding, an electrode  12  having a thickness similar to that obtained by using a printing method described above, may be formed on the base member  11 . When the thickness of the base member  11  is large, a sheet-shaped electrode  12  separately formed may be affixed to the base member  11 . 
     In addition to the above, various modifications can be made as appropriate to the embodiments of the present invention without departing from the scope of the technical idea defined by the claims.