Patent Publication Number: US-2022228938-A1

Title: Electrostatic capacity sensor

Description:
BACKGROUND 
     Technical Field 
     The present invention relates to an electrostatic capacity sensor for detecting a force. 
     Related Art 
     Conventionally, an electrostatic capacity sensor described in JP 2019-90729 A is known. The electrostatic capacity sensor is for pressure detection, and includes a flexible substrate with flexibility, a hard substrate, and the like. A first movable electrode, a second movable electrode, and a signal line connected to these movable electrodes are attached to a lower surface of the flexible substrate. 
     A fixed electrode, an insulating portion, and a metal portion are attached to an upper surface of the hard substrate. The fixed electrode is disposed so as to face the first and the second movable electrodes, and the insulating portion is provided so as to cover an outer peripheral portion of the fixed electrode. Further, the metal portion is formed in an annular shape in a plan view, and is disposed between an upper surface of the insulating portion and a lower surface of the fixed electrode in contact therewith. In the case of this electrostatic capacity sensor, when a pressure acts on an upper side of the first movable electrode in the flexible substrate, the first movable electrode moves toward the fixed electrode, and an electrostatic capacity changes, whereby the pressure is detected. 
     SUMMARY 
     By the conventional electrostatic capacity sensor described above, since the two movable electrodes and the signal line are attached to the lower surface of the flexible substrate, when the electrostatic capacity sensor is used for a long period of time in an environment where a pressure repeatedly acts on the flexible substrate, the two movable electrodes and the signal line may be peeled off from the flexible substrate, and there is a problem that durability is low. 
     The present invention has been made to solve the above problems, and an object thereof is to provide an electrostatic capacity sensor capable of improving durability. 
     In order to achieve the above object, an electrostatic capacity sensor of the present invention comprises: a substrate; a first electrode that is provided on the substrate; a flexible member that is fixed to the substrate and has dielectric properties and elasticity; and a second electrode that is provided in the flexible member so as to face the first electrode with a distance from the first electrode and is for detecting an electrostatic capacity between the second electrode and the first electrode. 
     By this electrostatic capacity sensor, the second electrode for detecting an electrostatic capacity between the second electrode and the first electrode is provided in the flexible member so as to face the first electrode with a distance from the first electrode. Therefore, when a force that moves the first electrode toward the second electrode acts on the flexible member, as a distance between the first electrode and the second electrode changes and the electrostatic capacity changes, the force can be detected. At that time, since the second electrode is provided in the flexible member, even when the electrostatic capacity sensor is used for a long time in an environment where the flexible member repeats elastic deformation, the second electrode is not peeled off from the flexible member. Accordingly, durability of the electrostatic capacity sensor can be improved as compared with the case of JP 2019-90729 A. 
     In the present invention, it is preferred to further include an electric wire that has flexibility, extends in the flexible member, and has one end connected to the second electrode. 
     By this electrostatic capacity sensor, the electric wire has flexibility, extends in the flexible member, and has one end connected to the second electrode. Therefore, even when the electrostatic capacity sensor is used for a long time in an environment where the flexible member repeats elastic deformation, the electric wire is not peeled off from the flexible member. Accordingly, durability of the electrostatic capacity sensor can be improved as compared with the case of JP 2019-90729 A. 
     In the present invention, it is preferred that a plurality of first electrodes including a pair of first electrodes be provided on the substrate with a distance from each other in a direction along a surface of the substrate, the first electrodes be connected to a wiring provided on the substrate, and each of the pair of first electrodes be disposed such that a part of a surface facing the second electrode overlaps the second electrode when viewed from a side of the second electrode. 
     By this electrostatic capacity sensor, the first electrodes including the pair of first electrodes are provided on the substrate with a distance from each other in the direction along the surface of the substrate, and the first electrodes are connected to the wiring provided on the substrate, so that wiring work can be simplified as compared with a case of wiring a plurality of electric wires to the first electrodes, respectively. In addition, each of the pair of first electrodes is disposed such that at least a part of the surface facing the second electrode overlaps the second electrode when viewed from the side of the second electrode. Therefore, when a force acts on the flexible member along a direction in which the pair of first electrodes is disposed, an overlapping area of the surface facing the second electrode changes in each of the pair of first electrodes along with elastic deformation of the flexible member, and an electrostatic capacity changes. As a result, it is possible, based on this change in electrostatic capacity, to detect a force acting in a direction in which the pair of first electrodes is disposed, that is, a shearing force. 
     In the present invention, it is preferred that the first electrodes further include the other pair of first electrodes, that the other pair of first electrodes be disposed, when viewed from the side of the second electrode, along one of two straight lines orthogonal to each other and with a part of a surface of each of the other pair of first electrodes facing the second electrode, overlapping the second electrode, and that the pair of first electrodes be disposed along the other of the two straight lines when viewed from the side of the second electrode. 
     By this electrostatic capacity sensor, the first electrodes further include the other pair of first electrodes, and the other pair of first electrodes are disposed such that a part of the surface of each of the other pair of first electrodes, facing the second electrode, overlaps the second electrode when viewed from the side of the second electrode. As such, when a force acts on the flexible member along a direction in which the other pair of first electrodes is disposed, an overlapping area of the surface facing the second electrode changes in each of the other pair of first electrodes along with elastic deformation of the flexible member, and an electrostatic capacity changes. This makes it possible to detect, based on this change in electrostatic capacity, a force acting in the direction in which the other pair of first electrodes is disposed, that is, a shearing force. Further, the other pair of first electrodes is disposed along one of the two straight lines orthogonal to each other, and one pair of first electrodes is disposed along the other of the two straight lines. Therefore, this electrostatic capacity sensor can detect forces in orthogonally triaxial directions. 
     In the present invention, it is preferred that the flexible member include an electrode built-in unit that builds in the second electrode and has a gap with a surface of the substrate, and a plurality of column portions that extends between the electrode built-in unit and the substrate. 
     By this electrostatic capacity sensor, the flexible member includes the electrode built-in unit that builds in the second electrode and has a gap with the surface of the substrate, and the column portions that extend between the electrode built-in unit and the substrate. Therefore, when a force acts on the electrode built-in unit, the column portions are elastically deformed, thereby generating a state in which the second electrode and the first electrode change so that a distance therebetween in opposing directions becomes short and a state in which a positional relationship therebetween is shifted in the direction along the surface of the substrate. At this time, the state in which the positional relationship between the second electrode and the first electrode is shifted in the direction along the surface of the substrate is more likely to occur than in a case where the flexible member is solid, which can improve detection sensitivity of a shearing force. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view illustrating a configuration of an electrostatic capacity sensor and the like according to a first embodiment of the present invention; 
         FIG. 2  is a front view of an electrostatic capacity sensor; 
         FIG. 3  is a plan view illustrating a configuration of an electrostatic capacity sensor according to a second embodiment; 
         FIG. 4  is a cross-sectional view taken along a line I-I in  FIG. 3 ; and 
         FIG. 5  is a cross-sectional view taken along a line II-II in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an electrostatic capacity sensor according to a first embodiment of the present invention will be described with reference to the drawings. As illustrated in  FIG. 1 , an electrostatic capacity sensor  1  according to the present embodiment is connected to a force detection device  30  via five electric wires  16 . As will be described later, the force detection device  30  detects forces in orthogonally triaxial directions acting on the electrostatic capacity sensor  1  based on a detection result of an electrostatic capacity by the electrostatic capacity sensor  1 . 
     As illustrated in  FIGS. 1 and 2 , the electrostatic capacity sensor  1  according to the present embodiment includes a printed circuit board  10 , four first electrodes  11   a  to  11   d,  a second electrode  12 , an electric wire  13 , an electrode support  14 , and the like. 
     Note that, in the following description, for convenience, a left side of  FIG. 1  is referred to as “left”, a right side of  FIG. 1  is referred to as “right”, a lower side of  FIG. 1  is referred to as “front”, an upper side of  FIG. 1  is referred to as “rear”, a front side of  FIG. 1  is referred to as “upper”, and a back side of  FIG. 1  is referred to as “lower”. 
     The printed circuit board (hereinafter referred to as “substrate”)  10  is of a rigid board type having a rectangular shape in a plan view, and has a printed wiring (not illustrated) formed on a surface thereof. The substrate  10  may be formed of a flexible substrate. 
     The four first electrodes  11   a  to  11   d  are disposed, in a plan view, such that a straight line connecting centers of a pair of front and rear first electrodes  11   a  and  11   b  is orthogonal to a straight line connecting centers of a pair of left and right first electrodes  11   c  and  11   d,  and such that a distance between the centers of the front and the rear first electrodes  11   a  and  11   b  and a distance between the centers of the left and the right first electrodes  11   c  and  11   d  are identical. In the present embodiment, one of the pair of front and rear first electrodes  11   a  and  11   b  and the pair of left and right first electrodes  11   c  and  11   d  corresponds to one pair of first electrodes, and the other corresponds to the other pair of first electrodes. 
     In addition, as illustrated in  FIG. 2 , the four first electrodes  11   a  to  11   d  are in a plate shape and thinner than the substrate  10 , are provided flush on an upper surface of the substrate  10 , and are connected to the force detection device  30  via the printed wiring of the substrate  10  and the five electric wires  16 . 
     Further, the four first electrodes  11   a  to  11   d  are formed into equal-size squares in a plan view, and disposed such that four sides are each parallel to each other. In the following description, each of the four first electrodes  11   a  to  11   d  is appropriately referred to as “each first electrode  11 ”. 
     On the other hand, the electrode support  14  is made of translucent silicon rubber with dielectric properties and elasticity (or flexibility), and is fixed to the upper surface of the substrate  10 . The electrode support  14  includes a main body  14   a  and an electric wire protection portion  14   b,  and the main body  14   a  has a solid rectangular parallelepiped shape. The electric wire protection portion  14   b  is formed in a columnar shape having a rectangular cross-section, extends leftward from the main body  14   a,  and then bends at a right angle to extend to the substrate  10 . In the present embodiment, the electrode support  14  corresponds to a flexible member. 
     The second electrode  12  is of a plate-shaped flexible electrode type with flexibility, and is formed in a square shape in a plan view. The second electrode  12  is, in a plan view, disposed such that each of the four sides is parallel to each of the four sides of each first electrode  11 , and such that a half of a surface of each first electrode  11  overlaps the second electrode  12 . The second electrode  12  is built in the main body  14   a,  held in a posture parallel to the substrate  10  and entirely in close contact with the main body  14   a.    
     Furthermore, the electric wire  13  is of a flexible electric wire type with flexibility, extends leftward from the second electrode  12  inside the main body  14   a  and the electric wire protection portion  14   b  of the electrode support  14 , then bends downward at a right angle to extend inside the electric wire protection portion  14   b,  and has a distal end portion thereof connected to a terminal  15 . This terminal  15  is connected to the printed wiring of the substrate  10 , so that the second electrode  12  is connected to the force detection device  30  via the electric wire  13 , the terminal  15 , the printed wiring, and the electric wire  16 . 
     On the other hand, the force detection device  30  combines a microcomputer and an electric circuit. In the force detection device  30 , by applying a voltage between each first electrode  11  and the second electrode  12 , an electrostatic capacity between each first electrode  11  and the second electrode  12  is detected. 
     Then, based on these four electrostatic capacities, a force (load) acting downward, a shearing force acting in a left-right direction, and a shearing force acting in a front-rear direction on the electrostatic capacity sensor  1  are calculated by an arithmetic expression (not illustrated). In brief, the electrostatic capacity sensor  1  according to the present embodiment has a function as a triaxial force sensor. 
     As described above, by the electrostatic capacity sensor  1  according to the first embodiment, the second electrode  12  is provided in the electrode support  14  so as to face each first electrode  11  with a distance from each first electrode  11 . Thus, when a downward force (load) acts on the electrode support  14 , a distance between each first electrode  11  and the second electrode  12  changes, and as an electrostatic capacity changes, the force can be detected. At this time, since the second electrode  12  is built in the electrode support  14 , a short circuit between each first electrode  11  and the second electrode  12  can be avoided, and even when the electrostatic capacity sensor  1  is used for a long time under an environment where the electrode support  14  repeats elastic deformation, the second electrode  12  is not peeled off from the electrode support  14 . Accordingly, as compared with the case of JP 2019-90729 A, durability of the electrostatic capacity sensor  1  can be improved. 
     In addition, since the four first electrodes  11   a  to  11   d  are connected to the printed wiring provided on the substrate  10 , wiring work can be simplified as compared with a case where four electric wires are respectively wired to the four first electrodes  11   a  to  11   d.  Further, the four first electrodes  11   a  to  11   d  are, in a plan view, disposed such that the straight line connecting the centers of the pair of front and rear first electrodes  11   a  and  11   b  is orthogonal to the straight line connecting the centers of the pair of left and right first electrodes  11   c  and  11   d,  and such that a half of the surface of each first electrode  11  overlaps the second electrode  12 . 
     Thus, when a force in orthogonally biaxial directions along the surface of the substrate  10 , that is, a shearing force acts on the electrode support  14 , as the electrode support  14  is elastically deformed, an overlapping area of surfaces facing each other between each first electrode  11  and the second electrode  12  changes, and an electrostatic capacity changes. This makes it possible to detect the shearing force in the orthogonally biaxial directions based on these changes in electrostatic capacity. As described above, the electrostatic capacity sensor  1  can be used to detect forces in orthogonally triaxial directions. 
     In the first embodiment, the entire second electrode  12  is built in the electrode support  14 , but alternatively, a part of the second electrode  12  may be exposed outward from the electrode support  14 . In this case, it is only necessary that the second electrode  12  be not short-circuited with the first electrode  11  when the electrode support  14  is elastically deformed. 
     In addition, in the electrostatic capacity sensor  1  according to the first embodiment, a shield may be provided on an upper side of the second electrode  12  in the electrode support  14 , and a third electrode for detecting approach of an object may be further provided on an upper side of the shield. With such a configuration, in addition to a function as a triaxial force sensor, a function as a proximity sensor can be secured. 
     Further, the first embodiment is an example in which the electrode support  14  made of silicon rubber is used as a flexible member, but the flexible member of the present invention is not limited thereto, and any member may be used as long as it has dielectric properties and elasticity. For example, as a flexible member, a dielectric such as a conductive resin such as a thiophene-based conductive polymer or PSS, PVC gel, polyvinylidene fluoride (PVDF), polydimethylsiloxane (PDMS), a silicon-based resin, an urethane-based resin, or an epoxy-based resin, or a composite material of any combination thereof may be used. 
     The first embodiment is also an example in which the rectangular parallelepiped electrode support  14  is used as a flexible member, but alternatively, flexible members having various shapes such as an oval shape, a cylindrical shape, and a hemispherical shape may be used. 
     On the other hand, the first embodiment is an example in which a square shape in a plan view is used for the four first electrodes  11   a  to  11   d,  but alternatively, a rectangular shape other than a square shape in a plan view may be used for the four first electrodes  11   a  to  11   d,  and any shape may be used as long as it has symmetry in a plan view. 
     Further, the first embodiment is an example in which a square shape in a plan view is used for the second electrode  12 , but alternatively, a rectangular shape other than a square shape in a plan view may be used for the second electrode  12 , and any shape may be used as long as it has symmetry in a plan view. 
     Furthermore, the first embodiment is an example in which the electrostatic capacity sensor  1  includes the pair of front and rear first electrodes  11   a  and  11   b  and the pair of left and right first electrodes  11   c  and  11   d,  but alternatively, the electrostatic capacity sensor  1  may include one of the pair of front and rear first electrodes  11   a  and  11   b  and the pair of left and right first electrodes  11   c  and  11   d,  or may include one first electrode  11 . 
     On the other hand, the first embodiment is an example in which the electric wire  13  extends in the main body  14   a  of the electrode support  14 , but alternatively, the electric wire  13  may extend outside the main body  14   a  of the electrode support  14 . 
     Hereinafter, an electrostatic capacity sensor  1 A according to a second embodiment of the present invention will be described with reference to  FIGS. 3 to 5 . The electrostatic capacity sensor  1 A according to the present embodiment is different from the electrostatic capacity sensor  1  according to the first embodiment in that an electrode support  20  is provided instead of the electrode support  14 , and thus the electrode support  20  will be mainly described below. 
     Configurations identical to ones according to the first embodiment are denoted by identical reference signs, and descriptions thereof will be omitted. In  FIG. 3 , the force detection device  30  and the like illustrated in  FIG. 1  are omitted. 
     The electrostatic capacity sensor  1 A according to the present embodiment includes the electrode support  20  illustrated in  FIGS. 3 to 5 , and the electrode support  20  is, similarly to the electrode support  14  according to the first embodiment, made of translucent silicon rubber. The electrode support  20  has a hollow shape (see  FIG. 4 ), and includes an electrode built-in unit  21 , 10 first column portions  22 , 11 second column portions  23 , and the like. In the present embodiment, the electrode support  20  corresponds to a flexible member. 
     The electrode built-in unit  21  is formed in a thin plate shape having a rectangular shape in a plan view, is provided in parallel to the substrate  10 , and is thicker than the second electrode  12  in a vertical direction. The second electrode  12  is located in a central portion of the electrode built-in unit  21  in a plan view, and is built in the electrode built-in unit  21  in a posture parallel to the substrate  10  and in a state of not being exposed to the outside. 
     As illustrated in  FIGS. 3 and 5 , the 10 first column portions  22  each and the 11 second column portions  23  each are disposed alternately in the left-right direction and the front-rear direction at an equal distance. Each of the first column portions  22  has a rectangular cross-sectional shape in a plan view (see  FIG. 5 ), and a size thereof is set to be identical to one of the first electrode  11  in a plan view. Each of the first column portions  22  integrally extends downward from the electrode built-in unit  21 , and a distal end portion thereof is fixed to the substrate  10 . 
     As illustrated in  FIG. 3 , when the electrode support  20  is viewed in a plan view, the four first column portions  22  are disposed in a cross shape at positions equidistant from a center of the electrode support  20 . Of these four first column portions  22 , two first column portions  22  and  22  on inner sides are provided at positions corresponding to the left and the right first electrodes  11   c  and  11   d,  and are fixed to the first electrode  11  in a state where distal end portions thereof cover surfaces of the left and the right first electrodes  11   c  and  11   d  (see  FIG. 4 ). 
     In addition, the remaining two first column portions  22  and  22  are provided at positions corresponding to the two first electrodes  11   a  and  11   b  disposed in the front-rear direction through a center of the substrate  10 , and are fixed to the first electrode  11  in a state where distal end portions thereof cover surfaces of the two first electrodes  11   a  and  11   b.    
     Further, the electric wire  13  extends leftward from the second electrode  12  through the electrode built-in unit  21 , then bends downward, and extends to the substrate  10  through the first column portion  22  at a left end. 
     On the other hand, each of the 11 second column portions  23  has a cross section in an “x” shape in a plan view, integrally extends downward from the electrode built-in unit  21 , and is provided such that a distal end portion thereof has a predetermined distance from the surface of the substrate  10 . With the above configuration, when a downward load (force) acts on the electrode support  20  and some of the second column portions  23  abut on the substrate  10  as the electrode built-in unit  21  bends toward the substrate  10 , the load is supported by these second column portions  23 . That suppresses a degree of elastic deformation of the electrode support  20  thereafter. In other words, excessive elastic deformation of the electrode support  20  can be avoided. 
     As described above, the electrostatic capacity sensor  1 A according to the second embodiment can detect forces in orthogonally triaxial directions, similarly to the electrostatic capacity sensor  1  according to the first embodiment. Furthermore, even when the electrostatic capacity sensor  1 A is used for a long time under an environment where the electrode support  20  repeats elastic deformation, the second electrode  12  is not peeled off from the electrode support  20 , and thus durability of the electrostatic capacity sensor  1 A can be improved as compared with the case of JP 2019-90729 A. 
     In addition, since the electrode support  20  has the electrode built-in unit  21  and the 10 first column portions  22  extending between the electrode built-in unit  21  and the substrate  10 , when a force acts on the electrode built-in unit  21 , the 10 first column portions  22  are elastically deformed, so that a positional relationship between the second electrode  12  and the each first electrode  11  is easily shifted in a direction along the surface of the substrate  10 , and this state is more likely to be generated than the electrode support  14  according to the first embodiment. Thus, this electrostatic capacity sensor  1 A can improve detection sensitivity of a shearing force as compared with the electrostatic capacity sensor  1  according to the first embodiment. 
     Although the second embodiment is an example in which the electrode support  20  is used as a flexible member, the flexible member of the present invention is not limited thereto, and any member may be used as long as it has dielectric properties and elasticity. As the electrode support  20 , one that has the first column portion  22  having a cross-sectional shape other than a square shape (for example, a circular or a regular polygonal cross-sectional shape) may be used. 
     Furthermore, the number of the first column portions  22  of the electrode support  20  is not limited to 10, and any number may be used as long as it is plural. The number of the second column portions  23  of the electrode support  20  is not limited to 11, any number may be used as long as it is equal to or greater than one, and the second column portions  23  may be omitted. Further, the second column portion  23  is not limited to one having a cross section of the “x” shape in a plan view, and one having a polygonal or a circular cross section in a plan view may be used. 
     On the other hand, in the second embodiment, the second electrode  12  is entirely built in the electrode built-in unit  21  of the electrode support  20 , but alternatively, a part of the second electrode  12  may be exposed outward from the electrode built-in unit  21 . In this case, it is only necessary that the second electrode  12  be not short-circuited with the first electrode  11  when the electrode support  20  is elastically deformed. 
     In addition, the second embodiment is an example in which the electrode support  20  made of silicon rubber is used as a flexible member, but the flexible member of the present invention is not limited thereto, and any member may be used as long as it has dielectric properties and elasticity. For example, as a flexible member, a dielectric such as a conductive resin such as a thiophene-based conductive polymer or PSS, PVC gel, polyvinylidene fluoride (PVDF), polydimethylsiloxane (PDMS), a silicon-based resin, an urethane-based resin, or an epoxy-based resin, or a composite material of any combination thereof may be used. 
     Furthermore, the second embodiment is an example in which the electrostatic capacity sensor  1 A includes the pair of front and rear first electrodes  11   a  and  11   b  and the pair of left and right first electrodes  11   c  and  11   d,  but alternatively, the electrostatic capacity sensor  1 A may include one of the pair of front and rear first electrodes  11   a  and  11   b  and the pair of left and right first electrodes  11   c  and  11   d,  or may include one first electrode  11 . 
     REFERENCE SIGNS LIST 
       1  electrostatic capacity sensor
 
 10  printed circuit board (substrate)
 
 11   a  first electrode
 
 11   b  first electrode
 
 11   c  first electrode
 
 11   d  first electrode
 
 12  second electrode
 
 13  electric wire
 
 14  electrode support (flexible member)
 
 1 A electrostatic capacity sensor
 
 20  electrode support (flexible member)
 
 21  electrode built-in unit
 
 22  first column portion (a plurality of column portions)