Load sensor

Abstract

A load sensor (10) comprises: a columnar or hemispherical first electrode (12); a holding member (14) having a substantially polygonal opening (14a) in a plan view and having the first electrode (12) fitted into the opening (14a) in the axial direction of the first electrode (12); second electrodes (16a to 16d) respectively disposed on at least two non-parallel inner side surfaces of the opening (14a); and dielectrics (15a to 15d) interposed between the first electrode (12) and the second electrodes (16a to 16d). When a load in a direction perpendicular to the axial direction is applied, at least one of the first electrode (12) and a structure (20) obtained by integrating the second electrodes (16a to 16d) with the holding member (14) is elastically deformed, and the contact areas between the first electrode (12) and the respective second electrodes (16a to 16d) with the dielectrics (15a to 15d) therebetween change.

Description

Load Sensor

[0001] The present invention relates to a load sensor that detects an externally applied load based on a change in capacitance.

[0002] 2. Description of the Related Art Load sensors for detecting an applied load have been used in various fields. For example, a load sensor that detects an applied load based on electrostatic capacitance that changes in response to the load is known.

[0003] The following Patent Document 1 describes a load sensor including a first electrode having an elastic conductive protrusion, a second electrode facing the first electrode across the protrusion in the axial direction, and a dielectric disposed on the opposing surface of the second electrode. When a load is applied in a direction that brings the first electrode and the second electrode closer together, the protrusion contracts in the axial direction in response to the load. This changes the contact area between the dielectric and the protrusion, and also reduces the distance between the dielectric and the first electrode. As a result, the capacitance between the first electrode and the second electrode changes. The load is detected from this change in capacitance.

[0004] JP 2016-118545 A

[0005] In the load sensor configured as described above, a load applied in the axial direction of the protrusion is detected by the capacitance between the first electrode and the second electrode. However, depending on the usage, it may be necessary to detect a load applied in a planar direction. For example, by detecting a load in a direction parallel to the gripping surface of the robot hand, it is possible to obtain the weight of an object gripped by the robot hand. The load sensor configured as described above can detect a load in the axial direction (vertical direction), but cannot detect a load in a planar direction.

[0006] In view of the above problem, an object of the present invention is to provide a load sensor capable of detecting a load applied in a planar direction.

[0007] A load sensor according to a main aspect of the present invention includes a columnar or hemispherical first electrode, a holding member having a substantially polygonal opening in a plan view and into which the first electrode is fitted in an axial direction of the first electrode, second electrodes respectively disposed on at least two non-parallel inner surfaces of the opening, and a dielectric interposed between the first electrode and the second electrode. When a load is applied in a direction perpendicular to the axial direction, at least one of the first electrode and a structure in which the second electrode and the holding member are integrated elastically deforms, and a contact area between the first electrode and each of the second electrodes via the dielectric changes.

[0008] In the load sensor according to this aspect, when a load is applied in a planar direction perpendicular to the axial direction of the first electrode and the first electrode and the structure move relative to each other, the contact area between the first electrode and each second electrode via the dielectric changes, and the capacitance between the first electrode and each second electrode changes. Therefore, the load in the planar direction perpendicular to the axial direction of the first electrode can be detected from the change in capacitance.

[0009] As described above, according to the present invention, it is possible to provide a load sensor capable of detecting a load applied in a planar direction.

[0010] The effects and significance of the present invention will become more apparent from the following description of the embodiments, however, the embodiments shown below are merely examples of how the present invention can be implemented, and the present invention is not limited to the embodiments described below.

[0011] FIG. 1 is an exploded perspective view showing the configuration of a load sensor according to the first embodiment. FIG. 2 is a perspective view showing a state in which structures are installed on a base member according to the first embodiment. FIG. 3 is a perspective view showing a state before a sheet member is fixed to a structure according to the first embodiment. FIG. 4 is a perspective view showing the configuration of a load sensor according to the first embodiment after assembly is completed. FIGS. 5(a) and 5(b) are cross-sectional views showing the cross-sectional structure of a load sensor according to the first embodiment. FIGS. 6(a) to 6(d) are schematic views showing the relationship between a first electrode and structures when a load is applied according to the first embodiment. FIG. 7 is a plan view showing a state in which multiple structures are installed on a base member according to a first modification of the first embodiment. FIG. 8 is a plan view showing a state in which multiple first electrodes are installed on a sheet member according to the first modification of the first embodiment. FIG. 9 is a plan view showing a state in which a sheet member is stacked on top of nine structures according to the first modification of the first embodiment. FIG. 10 is an exploded perspective view showing the configuration of a load sensor according to a second modification. FIGS. 11(a) and 11(b) are cross-sectional views showing the cross-sectional structure of a load sensor according to Modification Example 2. FIG. 12 is an exploded perspective view showing the configuration of a load sensor according to Embodiment 2. FIG. 13 is a perspective view showing a process of installing a structure on a base member on which a first electrode is installed according to Embodiment 2. FIG. 14 is a perspective view showing a process of installing a sheet member on a structure installed on a base member according to Embodiment 2. FIG. 15 is a perspective view showing the configuration of a load sensor in an assembled state according to Embodiment 2. FIGS. 16(a) and 16(b) are cross-sectional views showing the cross-sectional structure of a load sensor according to Embodiment 2. FIGS. 17(a) to 17(d) are schematic views showing the relationship between the first electrode and the structure when a load is applied according to Embodiment 2. FIG. 18 is an exploded perspective view showing the configuration of a load sensor according to Modification Example 1 of Embodiment 2. FIGS. 19(a) and 19(b) are cross-sectional views showing the cross-sectional structure of a load sensor according to Modification Example 1 of Embodiment 2. 20(a) and 20(b) are perspective views showing the configuration of a first electrode according to a modified example, and Fig. 21(a) to Fig. 21(d) are cross-sectional views showing the configuration of a first electrode and a structure according to another modified example.Fig. 22 is a plan view showing the configuration of a structure according to yet another modified example, and Fig. 23 is a plan view showing the configuration of the structure according to the modified example of Fig. 22 as viewed from the bottom surface side.

[0012] However, the drawings are for illustrative purposes only and do not limit the scope of the present invention.

[0013] The load sensor according to the present invention can be applied to a load sensor for a system or electronic device that performs processing in response to a load applied in a planar direction.

[0014] An example of such a system is a transfer system using a robot hand. In this case, a load sensor is installed on the gripping surface of the robot hand to detect the load in two dimensions parallel to the gripping surface. From this detection result, the weight, posture, etc. of the object gripped by the robot hand can be obtained.

[0015] Examples of electronic devices include game controllers, touch panels, electronic pens, etc. In electronic devices, a load sensor is provided in an input unit that receives input from a user in a planar direction.

[0016] The load sensor in the following embodiments is a capacitance type load sensor that is typically provided in the load sensors of the above-mentioned systems and electronic devices. Such load sensors are also sometimes called "capacitive pressure sensor elements," "capacitive pressure detection sensor elements," "pressure-sensitive switch elements," etc.

[0017] The load sensor in the following embodiment is connected to a detection circuit, and the load sensor and the detection circuit constitute a load detection device. The following embodiment is one embodiment of the present invention, and the present invention is not limited to the following embodiment.

[0018] First Embodiment A first embodiment of the present invention will be described below with reference to the drawings. For convenience, each drawing is labeled with X, Y, and Z axes that are orthogonal to each other. The Z-axis direction is the height direction of the load sensor 10 and the axial direction of the first electrode 12.

[0019] FIG. 1 is an exploded perspective view showing the configuration of a load sensor 10. As shown in FIG.

[0020] The load sensor 10 includes a sheet member 11, a first electrode 12, a fixing member 13, a holding member 14, dielectrics 15a to 15d, second electrodes 16a to 16d, and a base member 17.

[0021] The sheet member 11 is made of a material that is electrically insulating and elastic. The surface of the sheet member 11 (the surface on the positive side of the Z axis) preferably has high tackiness. The sheet member 11 may be made of a non-conductive rubber material or a non-conductive resin material. The sheet member 11 may be made of, for example, EPDM (ethylene propylene diene rubber). The sheet member 11 may also be made of other synthetic rubbers or natural rubber. In a plan view, the sheet member 11 is approximately square. The sheet member 11 has a constant thickness. When this thickness is large, the sheet member 11 may also be called a plate-like member.

[0022] The first electrode 12 is made of a material that is conductive and elastic. The first electrode 12 is made of a resin material with a conductive filler dispersed therein, or a rubber material with a conductive filler dispersed therein. In the first electrode 12, the conductive filler is dispersed in the elastic material. This gives the first electrode 12 conductivity and elasticity.

[0023] When the elastic material is a resin material, examples of the resin material include styrene-based resins, silicone-based resins (such as polydimethylpolysiloxane (PDMS)), acrylic-based resins, rotaxane-based resins, and urethane-based resins. When the elastic material is a rubber material, examples of the rubber material include 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, and natural rubber. The elastic material in the first embodiment is silicone rubber.

[0024] The conductive filler contained in the first electrode 12 may be, for example, Au (gold), Ag (silver), Cu (copper), C (carbon), ZnO (zinc oxide), or In. ２ O ３(indium (III) oxide), SnO ２ (tin (IV) oxide), etc. The conductive filler in the first embodiment is C (carbon).

[0025] The first electrode 12 has a downwardly convex hemispherical shape. The first electrode 12 has a shape symmetrical about an axis (central axis) 12a. A cross section of the first electrode 12 perpendicular to the axis 12a is circular. The first electrode 12 does not have to have a strictly hemispherical shape; for example, it may have a hemispherical shape that extends axially from a strictly hemispherical shape. Furthermore, the cross section of the first electrode 12 perpendicular to the axis 12a does not have to be circular, but may have another curved shape such as an ellipse.

[0026] The fixing member 13 is a member interposed between the sheet member 11 and the holding member 14 to fix them together. The fixing member 13 can be made of adhesive or double-sided tape. In a plan view, the fixing member 13 has the same contour as the sheet member 11 and has an opening 13a in the center. When the fixing member 13 is made of adhesive, the fixing member 13 is applied to the lower surface of the sheet member 11 or the upper surface of the holding member 14. In this case, in FIG. 1 , the applied adhesive is separated for convenience and is illustrated as the fixing member 13.

[0027] The holding member 14 is a member for holding the second electrodes 16a to 16d. The holding member 14 is made of a material that is electrically insulating and rigid. The holding member 14 may be made of a hard resin material such as acrylic. In a plan view, the holding member 14 has the same contour as the sheet member 11 and has an opening 14a in its center. The opening 14a penetrates the holding member 14 from top to bottom. In a plan view, the opening 14a has a substantially square (rectangular) shape. The four inner surfaces of the opening 14a are planes parallel to the Z axis. Each inner surface of the opening 14a has four step portions 14b on which the second electrodes 16a to 16d are respectively disposed. In addition, the lower surface of the holding member 14 also has four step portions 14c on which the second electrodes 16a to 16d are respectively disposed.

[0028] The dielectrics 15a to 15d are uniformly formed on the inner surfaces (the inner surfaces of the two surfaces perpendicular to the XY plane) of the second electrodes 16a to 16d. The dielectrics 15a to 15d are made of an electrically insulating material. The dielectrics 15a to 15d are made of, for example, a resin material, a ceramic material, a metal oxide material, or the like. More specifically, the dielectrics 15a to 15d are made of polypropylene, polyethylene terephthalate, polyimide, polyphenylene sulfide, Al ２ O ３ , Ta ２ O ５ It can be configured as follows.

[0029] The second electrodes 16a-16d are made of a metal material that is rigid and conductive. Examples of such metal materials include gold (Au), silver (Ag), copper (Cu), and platinum (Pt). In the first embodiment, the second electrodes 16a-16d are made of copper. In a side view, the second electrodes 16a-16d are L-shaped. The second electrodes 16a-16d are arranged so that the long sides of the L-shape are parallel to the Z-axis. The second electrodes 16a-16d surround a square space in a plan view. The surfaces of the second electrodes 16a-16d facing the space are their inner surfaces, and the dielectrics 15a-15d are formed on these inner surfaces. The inner surfaces of the second electrodes 16a and 16b face each other, and the inner surfaces of the second electrodes 16c and 16d face each other. The angle between the inner surfaces of adjacent second electrodes is 90 degrees.

[0030] The holding member 14, the dielectrics 15a to 15d, and the second electrodes 16a to 16d constitute a structure 20. The second electrodes 16a to 16d are formed integrally with the holding member 14 by insert molding in the arrangement state shown in Figure 1. As a result, the four step portions 14b and four step portions 14c described above are formed in the holding member 14. For convenience, Figure 1 shows the components that constitute the structure 20 separately, so the four step portions 14b and four step portions 14c are formed in the holding member 14.

[0031] The dielectrics 15a to 15d may be formed in advance on the inner surfaces of the second electrodes 16a to 16d, respectively, before insert molding, or may be disposed on the inner surfaces of the second electrodes 16a to 16d by coating, etc. In the latter case, the dielectrics 15a to 15d do not necessarily have to be disposed individually on the inner surfaces of the second electrodes 16a to 16d, but may be formed uniformly around the entire periphery of the space formed by the inner surfaces of the second electrodes 16a to 16d (including the gaps between the second electrodes 16a to 16d).

[0032] The base member 17 is a plate-shaped member that is electrically insulating and rigid. For example, the base member 17 may be made of a hard resin material such as acrylic. In a plan view, the base member 17 has the same contour as the sheet member 11. The thickness of the base member 17 is constant. The structure 20 is placed on the upper surface of the base member 17.

[0033] FIG. 2 is a perspective view showing a state in which the structure 20 is installed on the base member 17. As shown in FIG.

[0034] The structure 20 is mounted on the upper surface of the base member 17, for example, with an adhesive. The ends of the second electrodes 16a to 16d are exposed from the side surfaces of the holding member 14. The internal space of the opening 14a in the holding member 14 is surrounded on all four sides by the four second electrodes 16a to 16d and the four dielectrics 15a to 15d. This makes the internal space of the opening 14a a substantially rectangular parallelepiped space. This internal space is substantially square in plan view.

[0035] Fixing member 13 is placed on the upper surface of structure 20. If fixing member 13 is double-sided tape, the lower surface of the double-sided tape is attached to the upper surface of structure 20. If fixing member 13 is adhesive, the adhesive is applied to the upper surface of structure 20. The region where fixing member 13 is placed is a region that includes the upper surface of holding member 14 and the upper surfaces of second electrodes 16a to 16d and dielectrics 15a to 15d.

[0036] That is, of the two portions of fixing member 13 extending in the Y-axis direction, the width of the portion on the positive side of the X-axis is approximately equal to the sum of the width of the portion of holding member 14 facing this portion, the thickness of second electrode 16a, and the thickness of dielectric 15a. The widths of the other portions of fixing member 13 are also approximately equal to the sum of the width of the portion of holding member 14 facing these portions, the thickness of the second electrode, and the thickness of the dielectric.

[0037] FIG. 3 is a perspective view showing the structure 20 before the sheet member 11 is fixed to the structure 20. As shown in FIG.

[0038] A first electrode 12 is installed on the underside of the sheet member 11 by a fixing means such as an adhesive. The axis 12a of the first electrode 12 coincides with the center of the sheet member 11. The underside of the sheet member 11 is placed on the upper surface of the fixing member 13, and the sheet member 11 is attached to the fixing member 13. This causes the first electrode 12 to fit into the opening 14a. In a plan view, the size of the base portion of the first electrode 12 is slightly larger than the circle inscribed in the four dielectrics 15a to 15d. Therefore, the base portion of the first electrode 12 is pressed by the dielectrics 15a to 15d, compressing it in the X-axis or Y-axis direction, while fitting into the opening 14a. In this state, the sheet member 11 is fixed to the upper surface of the structure 20 by the fixing member 13.

[0039] FIG. 4 is a perspective view showing the configuration of the load sensor 10 in a completely assembled state.

[0040] The second electrodes 16a to 16d are connected to the detection circuit via their externally exposed portions. The first electrode 12 is connected to the detection circuit via wiring (not shown). For example, during assembly as shown in FIG. 3, wiring is connected to the base of the first electrode 12. Then, the sheet member 11 is placed on the fixing member 13 so as to sandwich this wiring. The connection position of the wiring to the first electrode 12 is preferably set within a range where the first electrode 12 is not pressed against the dielectrics 15a to 15d when a load is applied.

[0041] Alternatively, a wiring pattern may be formed in advance on the underside of the sheet member 11. The wiring pattern is made of, for example, a conductive elastic material obtained by mixing a conductive filler with an elastic material such as resin or rubber. The wiring pattern is formed on the underside of the sheet member 11 by, for example, a printing method. The first electrode 12 is placed on the underside of the sheet member 11 with a conductive adhesive so as to overlap this wiring pattern. The wiring pattern extends to the edge of the sheet member 11. The end of the wiring pattern is connected to the detection circuit. This connects the first electrode 12 to the detection circuit.

[0042] 5(a) and 5(b) are cross-sectional views showing the cross-sectional structure of the load sensor 10. Figures 5(a) and 5(b) show cross-sectional views of the load sensor 10 cut along a plane parallel to the X-Z plane at the midpoint in the Y-axis direction. Figure 5(a) is a cross-sectional view when no load is applied, and Figure 5(b) is a cross-sectional view when a load is applied in the positive direction of the X-axis to the upper surface of the sheet member 11.

[0043] In the no-load state shown in FIG. 5A, the base portion of the first electrode 12 is in even contact with the dielectrics 15a and 15b. The contact area between the first electrode 12 and the dielectric 15a is the same as the contact area between the first electrode 12 and the dielectric 15b. Therefore, the capacitance between the first electrode 12 and the second electrode 16a is the same as the capacitance between the first electrode 12 and the second electrode 16b. Note that in the no-load state, the base portion of the first electrode 12 is in even contact with the four dielectrics 15a to 15d. Therefore, the capacitance between the first electrode 12 and the second electrode 16a, the capacitance between the first electrode 12 and the second electrode 16b, the capacitance between the first electrode 12 and the second electrode 16c, and the capacitance between the first electrode 12 and the second electrode 16d are all equal to one another.

[0044] In the load-applied state shown in FIG. 5B , the first electrode 12 moves in the X-axis direction as the sheet member 11 moves due to the load. As a result, the portion of the first electrode 12 on the positive side of the X-axis contacts the dielectric 15a over a wider area, while the portion on the negative side of the X-axis moves away from the dielectric 15b. This increases the contact area between the first electrode 12 and the dielectric 15a, thereby increasing the capacitance between the first electrode 12 and the second electrode 16a. On the other hand, the contact area between the first electrode 12 and the dielectric 15b decreases, thereby decreasing the capacitance between the first electrode 12 and the second electrode 16b. The balance of these capacitances corresponds to the magnitude of the load in the positive direction of the X-axis. Therefore, the load in the X-axis direction can be obtained from this balance.

[0045] In the state shown in Figure 5(b), the sheet member 11 is fixed to the holding member 14 in the two regions A1, so even if a load is applied in the positive direction of the X-axis, excessive movement in the positive direction of the X-axis is restricted. In contrast, if the sheet member 11 is not fixed in the two regions A1, the sheet member 11 will move significantly in the positive direction of the X-axis due to the load. Meanwhile, the movement of the first electrode 12 is restricted by the structure 20 (holding member 14, second electrode 16a, and dielectric 15a), so a large shear force is generated between the sheet member 11 and the base of the first electrode 12. This shear force may cause the first electrode 12 to peel off from the sheet member 11.

[0046] 5(b), as described above, the fixing member 13 restricts excessive movement of the sheet member 11, thereby suppressing the shear force that occurs between the sheet member 11 and the base of the first electrode 12 when a load is applied. This prevents the first electrode 12 from being torn off from the sheet member 11 due to this shear force.

[0047] 6(a) to 6(d) are diagrams schematically illustrating the relationship between the first electrode 12 and the structure 20 when a load is applied. Figures 6(a) to 6(d) show cross-sectional views of the first electrode 12 and the structure 20 cut along a plane parallel to the XY plane at a height position near the base of the first electrode 12. In these figures, the direction in which the load is applied is indicated by an outline arrow.

[0048] 6A corresponds to the state shown in FIG. 5B. In this case, the applied load can be obtained based on the balance between the capacitance between the first electrode 12 and the second electrode 16a and the capacitance between the first electrode 12 and the second electrode 16b.

[0049] 6B shows a state when a load is applied in the negative direction of the X-axis. In this state, the capacitance between the first electrode 12 and the second electrode 16a decreases compared to when no load is applied, and the capacitance between the first electrode 12 and the second electrode 16b increases compared to when no load is applied. Therefore, the applied load can be obtained based on the balance between these loads.

[0050] 6(c) shows a state when a load is applied in a direction that equally includes both the positive X-axis and negative Y-axis components. In this state, the capacitance between the first electrode 12 and the second electrode 16a and the capacitance between the first electrode 12 and the second electrode 16d increase in a similar manner compared to when no load is applied, while the capacitance between the first electrode 12 and the second electrode 16b and the capacitance between the first electrode 12 and the second electrode 16c decrease in a similar manner compared to when no load is applied. Therefore, the applied load can be obtained based on the balance between these loads.

[0051] 6(d) shows a state when a load is applied in a direction that equally includes both the negative X-axis and positive Y-axis components. In this state, the capacitance between the first electrode 12 and the second electrode 16a and the capacitance between the first electrode 12 and the second electrode 16d are similarly reduced compared to when no load is applied, while the capacitance between the first electrode 12 and the second electrode 16b and the capacitance between the first electrode 12 and the second electrode 16c are similarly increased compared to when no load is applied. Therefore, the applied load can be obtained based on the balance between these loads.

[0052] Loads in other directions can also be obtained based on the balance of the capacitance between the first electrode 12 and the second electrodes 16a to 16d. For example, if the load direction tilts toward the positive X-axis direction from the state shown in FIG. 6C, the capacitance between the first electrode 12 and the second electrode 16a becomes larger than the capacitance between the first electrode 12 and the second electrode 16d. Therefore, the direction and magnitude of the load at this time can be obtained from the balance of these capacitances. In this way, the direction of the load application can be detected based on the balance of the capacitance between the first electrode 12 and the second electrodes 16a to 16d, and the magnitude of the load in that direction can be obtained.

[0053] <Effects of First Embodiment> According to the above embodiment, the following effects are achieved.

[0054] 1 to 4, the load sensor 10 includes a hemispherical first electrode 12, a holding member 14 having a substantially polygonal (almost square) opening 14a in a plan view, the holding member 14 having the first electrode 12 fitted into the opening 14a in the axial direction of the first electrode 12, second electrodes 16a to 16d respectively disposed on two pairs of non-parallel inner surfaces of the opening 14a, and dielectrics 15a to 15d interposed between the first electrode 12 and the second electrodes 16a to 16d. When a load is applied in a direction perpendicular to the axial direction, at least one of the first electrode 12 and a structure 20 formed by integrating the second electrodes 16a to 16d and the holding member 14 (here, the first electrode 12) elastically deforms, and the contact area between the first electrode and each of the second electrodes via the dielectric changes.

[0055] 5(a), 5(b) and 6(a) to 6(d), when a load is applied in a planar direction (a direction parallel to the X-Y plane) perpendicular to the axial direction (Z-axis direction) of the first electrode 12 and the structure 20 moves relatively, the contact area between the first electrode 12 and each of the second electrodes 16a to 16d via the dielectrics 15a to 15d changes, and the capacitance between the first electrode 12 and each of the second electrodes 16a to 16d changes. Therefore, as described above, the load in the planar direction perpendicular to the axial direction of the first electrode 12 can be detected from this change in capacitance.

[0056] As described above, in the first embodiment, the first electrode 12 is made of an elastic material, and the structure 20 is made of a rigid material. That is, the first electrode 12 is made of a material that is more easily elastically deformed than the structure 20.

[0057] 5(a), (b) and 6(a) to (d), when a horizontal load is applied to the first electrode 12 via the sheet member 11, the first electrode 12 deforms, changing the contact area and causing a change in the capacitance between the first electrode 12 and the second electrodes 16a to 16d. Therefore, the horizontal load can be detected based on the balance of these capacitances.

[0058] 1 and 2, in the first embodiment, the dielectrics 15a to 15d are disposed on the second electrodes 16a to 16d. This allows the first electrode 12 to deform more smoothly than when the dielectrics are disposed on the first electrode 12. Therefore, the contact area changes smoothly when a load is applied, and horizontal loads can be stably detected.

[0059] As shown in Figures 1 to 4, the load sensor 10 is placed on the upper surface of the structure 20 and comprises an elastic sheet member 11, with a first electrode 12 protruding from the lower surface of the sheet member 11, and the lower surface of the sheet member 11 being fixed to the structure 20 at a position overlapping the upper surface of the structure 20.

[0060] 5(b), this configuration can prevent excessive movement of the sheet member 11 when a horizontal load is applied, thereby preventing a large shear force from occurring between the sheet member 11 and the base of the first electrode 12. This can prevent the first electrode 12 from being torn off from the sheet member 11 due to this shear force.

[0061] As shown in FIGS. 1 and 2, the opening 14a has a substantially rectangular (almost square) shape in plan view, and the second electrodes 16a to 16d are disposed on at least two adjacent inner surfaces of the opening 14a.

[0062] With this configuration, when a horizontal load is applied, the capacitance between the first electrode 12 and the second electrodes 16a to 16d can be detected in at least two directions perpendicular to each other, thereby enabling the horizontal load to be detected appropriately.

[0063] In the first embodiment, the second electrodes 16a to 16d are disposed on all the inner surfaces of the opening 14a.

[0064] With this configuration, the capacitance between the opposing second electrodes and the first electrode 12 can be obtained, and the load in the direction in which these electrodes face can be detected from the balance of these capacitances, making it possible to efficiently and accurately detect horizontal loads.

[0065] As shown in FIG. 5A, the opening 14a has a size that allows the first electrode 12 to contact the second electrodes 16a to 16d via the dielectrics 15a to 15d in the no-load state.

[0066] With this configuration, when a horizontal load is applied, the contact area changes immediately without any play, making it possible to accurately detect the horizontal load.

[0067] <Modification 1> In the first embodiment, only one detection unit (first electrode 12, structure 20) is disposed in the load sensor 10, but in modification 1, a plurality of detection units are disposed in the load sensor 10.

[0068] FIG. 7 is a plan view showing a state in which a plurality of structures 20 are placed on a base member 17 according to the first modified example.

[0069] 7, the reference symbols P1 to P4 of the four wiring patterns extending in the X-axis direction are assigned only to the three structures 20 in the upper row (negative side of the Y-axis) and are omitted for the three structures 20 in the middle and lower rows. Furthermore, the reference symbols P5 to P8 of the wiring patterns connecting the second electrodes 16a to 16d of one structure 20 to the corresponding wiring patterns P1 to P4 are assigned only to the structure 20 at the left end of the upper row and are omitted for the other structures 20.

[0070] As shown in FIG. 7 , in Modification Example 1, nine structures 20 are arranged in a matrix (3×3) on the upper surface of base member 17. Wiring patterns P1 to P8 are formed on the upper surface of base member 17 and are selectively connected to second electrodes 16a to 16d. Four wiring patterns P1 to P4 extending in the X-axis direction correspond to the three structures 20 below them. Wiring patterns P5 to P8 correspond to one structure 20. In other words, a wiring pattern P5 to P8 is assigned to each structure 20. Wiring patterns P1 to P8 are wiring patterns made of metal such as copper.

[0071] One end of each of the wiring patterns P5 to P8 is connected to the corresponding second electrodes 16a to 16d of the structure 20 by a jumper wire or the like. The other end of each of the wiring patterns P5 to P8 is selectively connected to one of the wiring patterns P1 to P4. Therefore, the second electrodes 16a to 16d of the structure 20 are connected to the wiring patterns P1 to P4 via the wiring patterns P5 to P8. Here, the second electrode 16a is connected to the wiring pattern P2, the second electrode 16b is connected to the wiring pattern P3, the second electrode 16c is connected to the wiring pattern P1, and the second electrode 16d is connected to the wiring pattern P4. This connection rule is common to all of the structures 20.

[0072] Fig. 8 is a plan view showing a state in which a plurality of first electrodes 12 are provided on a sheet member 11 according to Modification Example 1. Fig. 8 shows a plan view of the sheet member 11 as viewed from the bottom side (the negative side of the Z axis).

[0073] Three wiring patterns P11 to P13 extending in the Y-axis direction are formed on the underside of the sheet member 11. The wiring patterns P11 to P13 are made of a conductive elastic body made by mixing a conductive filler with an elastic material such as rubber or resin. The wiring patterns P11 to P13 are formed on the underside of the sheet member 11 by, for example, a printing method.

[0074] Nine first electrodes 12 are arranged on the underside of the sheet member 11 so as to overlap these wiring patterns, respectively. The nine first electrodes 12 are arranged at positions corresponding to the nine structures 20 in FIG. 9. The wiring patterns P11 to P13 are formed so as to pass through the centers of the corresponding three first electrodes 12. The nine first electrodes 12 are formed by, for example, outsert molding on the underside of the sheet member 11 having the wiring patterns P11 to P13. As a result, the nine first electrodes 12 are formed on the underside of the sheet member 11 while being electrically connected to the corresponding wiring patterns P11 to P13.

[0075] During assembly, the sheet member 11 in Fig. 8 is turned over and placed on the top surfaces of the nine structures 20 in Fig. 7. At this time, the nine first electrodes 12 formed on the bottom surface of the sheet member 11 are fitted into the openings 14a of the nine structures 20 (holding members 14) on the base member 17 side. Also, as in the first embodiment, the bottom surfaces of the sheet member 11 are fixed to the top surfaces of these structures 20 by the fixing members 13 arranged on the top surfaces of the nine structures 20.

[0076] Fig. 9 is a plan view showing a state in which the sheet member 11 is stacked on the upper surfaces of nine structures 20. For convenience, in Fig. 9, the configuration on the sheet member 11 side is shown by dashed lines, and the fixing member 13 is not shown.

[0077] The wiring patterns P1 to P4 on the base member 17 side and the wiring patterns P11 to P13 on the sheet member 11 side are each connected to a detection circuit. When detecting capacitance for structures 20 in row C1 of rows C1 to C3, the wiring patterns P1 to P4 arranged directly above these structures 20 are used. When detecting capacitance for structures 20 in column L1 of columns L1 to L3, the wiring pattern P11 is used.

[0078] For example, when detecting capacitance for the structure 20 in row C1 and column L3, the topmost wiring patterns P1 to P4 and wiring pattern P13 are used. When detecting capacitance between the first electrode 12 and the second electrode 16a for this structure 20, the detection circuit detects the capacitance between the wiring patterns P2 and P13. When detecting capacitance between the first electrode 12 and the second electrode 16b for this structure 20, the detection circuit detects the capacitance between the wiring patterns P1 and P13.

[0079] In this way, the wiring pattern used for detection is switched between the wiring patterns P1 to P4, and the capacitance between the second electrodes 16a to 16d and the first electrode 12 is detected. In this way, when detection of each capacitance for one structure 20 is completed, a similar detection process is performed for the next structure 20. In this case as well, of the three sets of wiring patterns P1 to P4 and wiring patterns P11 and P12, the vertical and horizontal wiring patterns at the intersection with the structure 20 to be detected are used for the detection process.

[0080] According to the configuration of modified example 1, a base member 17 on which a plurality of structures 20 are mounted and a sheet member 11 on which a plurality of first electrodes 12 are mounted, each of which fits into the openings 14a of the plurality of structures 20 (holding member 14), are provided, so that horizontal loads can be detected over a wider range and the distribution of horizontal loads can be further obtained.

[0081] Furthermore, as shown in FIG. 9, since a plurality of structures 20 are arranged in a matrix, the horizontal load and the distribution of the load can be detected efficiently over a wide area.

[0082] Furthermore, as described above, the lower surface of the sheet member 11 is individually fixed to the plurality of structures 20 at positions overlapping the upper surfaces of the plurality of structures 20. This prevents a large shear force from occurring between the sheet member 11 and the base of the first electrode 12 in each structure 20. This prevents each first electrode 12 from being torn off from the sheet member 11 due to the application of a horizontal load.

[0083] <Modification 2> In the above embodiment, the load sensor 10 capable of detecting a load in the horizontal direction is shown. However, in Modification 2, the load sensor 10 is configured to be able to detect a load in the vertical direction as well as the horizontal direction.

[0084] FIG. 10 is an exploded perspective view showing the configuration of the load sensor 10 according to the second modified example.

[0085] In the second modification, a third electrode 18 for detecting a load in the vertical direction is added. The third electrode 18 is installed on the upper surface of the base member 17. The third electrode 18 may be connected to a wire, for example, via a hole that passes through the base member 17 from top to bottom. A dielectric 19 is formed on the upper surface of the third electrode 18. For convenience, the dielectric 19 is shown separated from the third electrode 18 in FIG. 10. The load sensor 10 is assembled using the same steps as those shown in FIGS. 1 to 4 in the first embodiment.

[0086] 11(a) and 11(b) are cross-sectional views showing the cross-sectional structure of the load sensor 10 according to Modification Example 2. Figures 11(a) and 11(b) show cross-sectional views of the load sensor 10 cut along a plane parallel to the X-Z plane at the midpoint in the Y-axis direction. Figure 11(a) is a cross-sectional view when no load is applied, and Figure 11(b) is a cross-sectional view when a load is applied in the vertical direction (negative direction of the Z-axis) to the upper surface of the sheet member 11.

[0087] 11(a), the lower surface of the first electrode 12 is in contact with the dielectric 19 of the third electrode 18. The contact state of the first electrode 12 with the surrounding dielectrics 15a to 15d is the same as in the case of FIG.

[0088] 11(b), when a vertical load is applied, the lower surface of the first electrode 12 is pressed against the dielectric 19 of the third electrode 18, causing the first electrode 12 to deform. This increases the contact area between the first electrode 12 and the dielectric 19, and increases the capacitance between the first electrode 12 and the third electrode 18. The vertical load is detected from this increase in capacitance. The horizontal load is detected in the same manner as in the first embodiment.

[0089] According to the configuration of Modification Example 2, when a load in the vertical direction (a load in a direction parallel to the axial direction of the first electrode 12) is applied, as described above, at least one of the first electrode 12 and the third electrode 18 (here, the first electrode 12) elastically deforms, increasing the contact area between the first electrode 12 and the third electrode 18 via the dielectric 19, and changing the capacitance between the first electrode 12 and the third electrode 18. Therefore, the load in the vertical direction can be detected from this change in capacitance.

[0090] Furthermore, if the vertical load affects the detection of the horizontal load, the detected value of the horizontal load can be corrected using the detected value of the vertical load, or conversely, the detected value of the vertical load can be corrected using the detected value of the horizontal load.

[0091] In the configuration of the above-described modified example 1, each structure 20 may also have the configuration of modified example 2. This makes it possible to detect the distribution of load in the vertical direction as well as the distribution of load in the horizontal direction.

[0092] Second Embodiment In the first embodiment, the first electrode 12 has elasticity and the structure 20 has rigidity. In contrast, in the second embodiment, the first electrode 35 has rigidity and the structure 40 has elasticity.

[0093] FIG. 12 is an exploded perspective view showing the configuration of the load sensor 30 according to the second embodiment.

[0094] The load sensor 30 according to the second embodiment includes a sheet member 31, second electrodes 32a to 32d, a holding member 33, a fixing member 34, a first electrode 35, a dielectric 36, and a base member 37. The second electrodes 32a to 32d and the holding member 33 constitute a structure 40.

[0095] The configurations of sheet member 31, fixing member 34, and base member 37 are similar to those of sheet member 11, fixing member 13, and base member 17 in the above-described first embodiment. Unlike the first embodiment, fixing member 34 is interposed between structure 40 and base member 37, and fixes the lower surface of structure 40 to the upper surface of base member 37. Fixing member 34 has an opening 34a in the center and has the same shape as holding member 33 in a plan view.

[0096] The second electrodes 32a to 32d are made of a conductive and elastic material. Similar to the first electrode 12 of embodiment 1, the second electrodes 32a to 32d are made by mixing a filler with a rubber material or a resin material. The rubber material, resin material, and filler may be the same as the rubber material, resin material, and filler of the first electrode 12 of embodiment 1.

[0097] Unlike the holding member 14 of the first embodiment, the holding member 33 is made of an elastic material. The holding member 33 may be made of a non-conductive rubber material or a non-conductive resin material. The holding member 33 has a substantially square outline in a plan view and has an opening 33a that penetrates vertically. The opening 33a has a substantially square outline in a plan view and is located in the center of the holding member 33. The four inner surfaces of the opening 33a are flat surfaces parallel to the Z axis.

[0098] The first electrode 35 has an upwardly convex hemispherical shape. The shape of the first electrode 35 may be the same as that of the first electrode 12 in embodiment 1, or may be modified as shown in embodiment 1. The material of the first electrode 35 may be the same as that of the second electrodes 16a to 16d in embodiment 1. The dielectric 36 is formed on the entire spherical surface of the first electrode 35 except for the lower surface. The material of the dielectric 36 may be the same as that of the dielectrics 15a to 15d in embodiment 1.

[0099] The second electrodes 32a to 32d are disposed on the four inner surfaces of the opening 33a, respectively. For example, the second electrodes 32a to 32d may be formed on the four inner surfaces of the opening 33a, respectively, by a printing method. Alternatively, the second electrodes 32a to 32d may be attached to the four inner surfaces of the opening 33a, respectively. The second electrodes 32a to 32d and the holding member 33 may be integrally formed by insert molding. In this manner, the structure 40 is formed by disposing the second electrodes 32a to 32d on the holding member 33.

[0100] The first electrode 35 on which the dielectric 36 is formed is attached at its lower surface to the upper surface of the base member 37 with an adhesive, and is thus installed on the base member 37. The axis 35a of the first electrode 35 coincides with the center of the upper surface of the base member 37.

[0101] A wiring pattern for connecting the first electrode 35 to an external detection circuit may be formed on the upper surface of the base member 37. In this case, the lower surface of the first electrode 35 is fixed to the upper surface of the base member 37 with a conductive adhesive so as to overlap this wiring pattern. Alternatively, a hole penetrating the base member 37 from top to bottom may be formed, and wiring may be connected to the lower surface of the first electrode 35 through this hole. In this case, a recess may be formed in the lower surface of the first electrode 35 at a position corresponding to the hole in the base member 37. One end of the wiring is connected to this recess with solder. The wiring is then passed through the hole in the base member 37. In this state, the lower surface of the first electrode 35 is fixed to the upper surface of the base member 37 with an adhesive.

[0102] FIG. 13 is a perspective view showing a process of placing the structure 40 on the base member 37 on which the first electrode 35 is placed.

[0103] One end of each of four wires (not shown) may be connected to the lower ends of the second electrodes 32a to 32d by soldering. These wires are preferably connected to the second electrodes 32a to 32d near the corners of the opening 33a.

[0104] The fixing member 34 is placed on the upper surface of the base member 37 in an area where the structure 40 overlaps. As in the first embodiment, double-sided tape or adhesive can be used as the fixing member 34. Thereafter, the structure 40 is placed on the fixing member 34 and fixed to the base member 37. At this time, the wiring, one end of which is connected to the second electrodes 32a to 32d, is sandwiched between the holding member 33 and the base member 37 and drawn out to the outside. The drawn out wiring is connected to a detection circuit for detecting the load.

[0105] Fig. 14 is a perspective view showing the process of installing the sheet member 31 on the structure 40 installed on the base member 37. Fig. 15 is a perspective view showing the configuration of the load sensor 30 in a fully assembled state.

[0106] 14, the sheet member 31 is fixed with adhesive to the upper surface of the structure 40. This completes the assembly of the load sensor 30 as shown in FIG.

[0107] 16(a) and 16(b) are cross-sectional views showing the cross-sectional structure of the load sensor 30. Figures 16(a) and 16(b) show cross-sectional views of the load sensor 30 cut along a plane parallel to the X-Z plane at the midpoint in the Y-axis direction. Figure 16(a) is a cross-sectional view when no load is applied, and Figure 16(b) is a cross-sectional view when a load is applied to the upper surface of the sheet member 11 in the positive direction of the X-axis.

[0108] In the no-load state shown in FIG. 16( a), the base portion of the dielectric 36 formed on the first electrode 35 is in even contact with the second electrodes 32a and 32b. The contact area between the second electrode 32a and the dielectric 36 is the same as the contact area between the second electrode 32b and the dielectric 36. Therefore, the capacitance between the first electrode 35 and the second electrode 32a is the same as the capacitance between the first electrode 35 and the second electrode 32b. Note that in the no-load state, the base portion of the dielectric 36 is in even contact with the four second electrodes 32a to 32d. Therefore, the capacitance between the first electrode 35 and the second electrode 32a, the capacitance between the first electrode 35 and the second electrode 32b, the capacitance between the first electrode 35 and the second electrode 32c, and the capacitance between the first electrode 35 and the second electrode 32d are all equal to one another.

[0109] In the load-applied state shown in FIG. 16( b), the structure 40 (second electrodes 32a, 32b, and holding member 33) deforms as shown in FIG. 16( b) as the sheet member 11 moves due to the applied load. As a result, the second electrode 32b on the negative side of the X-axis contacts the dielectric 36 over a wider area than the second electrode 32a on the positive side of the X-axis. This increases the contact area between the second electrode 32b and the dielectric 36, thereby increasing the capacitance between the first electrode 35 and the second electrode 32b. On the other hand, the contact area between the second electrode 32a and the dielectric 36 decreases, thereby decreasing the capacitance between the first electrode 35 and the second electrode 32a. The balance of these capacitances corresponds to the magnitude of the load in the positive direction of the X-axis. Therefore, the load in the X-axis direction can be obtained from this capacitance balance.

[0110] 16(b), the structure 40 including the holding member 33 and the second electrodes 32a to 32d is fixed to the base member 17 in the two regions A1, so that even if a load in the X-axis direction is applied, excessive movement in the X-axis direction is restricted. Therefore, as in the first embodiment, the shear force between the first electrode 35 and the base member 37 is suppressed, and it is possible to prevent the first electrode 35 from being torn off from the base member 37.

[0111] 17(a) to 17(d) are diagrams schematically showing the relationship between the first electrode 35 and the structure 40 when a load is applied. Figures 17(a) to 17(d) show cross-sectional views of the first electrode 35 and the structure 40 cut along a plane parallel to the XY plane at a height position near the base of the first electrode 35. In these figures, the direction in which the load is applied is indicated by an outline arrow.

[0112] 17A shows a state when a load is applied in the negative direction of the X-axis. In this state, the capacitance between the first electrode 35 and the second electrode 32b decreases compared to when no load is applied, and the capacitance between the first electrode 35 and the second electrode 32a increases compared to when no load is applied. Therefore, the applied load can be obtained based on the balance between these loads.

[0113] Fig. 17(b) corresponds to the state of Fig. 16(b) described above. In this case, the applied load can be obtained based on the balance between the capacitance between the first electrode 35 and the second electrode 32a and the capacitance between the first electrode 35 and the second electrode 32b.

[0114] 17(c) shows a state when a load is applied in a direction that equally includes both the negative X-axis and positive Y-axis components. In this state, the capacitance between the first electrode 35 and the second electrode 32b and the capacitance between the first electrode 35 and the second electrode 32c are similarly reduced compared to when no load is applied, while the capacitance between the first electrode 35 and the second electrode 32a and the capacitance between the first electrode 35 and the second electrode 32d are similarly increased compared to when no load is applied. Therefore, the applied load can be obtained based on the balance between these loads.

[0115] 17(d) shows a state when a load is applied in a direction that equally includes both the positive X-axis and negative Y-axis components. In this state, the capacitance between the first electrode 35 and the second electrode 32b and the capacitance between the first electrode 35 and the second electrode 32c increase in a similar manner compared to when no load is applied, while the capacitance between the first electrode 35 and the second electrode 32a and the capacitance between the first electrode 35 and the second electrode 32d decrease in a similar manner compared to when no load is applied. Therefore, the applied load can be obtained based on the balance between these loads.

[0116] Loads in other directions can also be obtained based on the balance of the capacitance between the first electrode 35 and the second electrodes 32a to 32d. For example, if the load direction tilts toward the positive X-axis direction from the state shown in FIG. 17(d), the capacitance between the first electrode 35 and the second electrode 32b becomes larger than the capacitance between the first electrode 35 and the second electrode 32c. Therefore, the direction and magnitude of the load at this time can be obtained from the balance of these capacitances. In this way, the direction of the load application can be detected based on the balance of the capacitance between the first electrode 35 and the second electrodes 32a to 32d, and the magnitude of the load in that direction can be obtained.

[0117] Effect of Second Embodiment As in the first embodiment, the configuration of the second embodiment also makes it possible to detect a load in a plane direction perpendicular to the axial direction of the first electrode 35 .

[0118] As described above, in the second embodiment, the first electrode 35 is made of a rigid material, and the structure 40 is made of an elastic material. That is, the structure 40 is made of a material that is more easily elastically deformed than the first electrode.

[0119] 16(a), 16(b) and 17(a) to 17(d), when a horizontal load is applied to the upper surface of sheet member 31, structure 40 deforms, changing the contact area and causing a change in the capacitance between first electrode 35 and second electrodes 32a to 32d. Therefore, the horizontal load can be detected based on the balance of these capacitances.

[0120] 12 to 14 and 16(a) and (b), the dielectric 36 is disposed on the first electrode 35. This allows the structure 40 to deform more smoothly than when the dielectric is disposed on the second electrodes 32a to 32d. As a result, the contact area changes smoothly when a load is applied, and horizontal loads can be detected stably.

[0121] As shown in Figures 12 to 14, the load sensor 30 has a base member 37 from whose upper surface the first electrode 35 protrudes, and the lower surface of the structure 20 is fixed to the base member 37 at a position overlapping the upper surface of the base member 37.

[0122] 16(b), this configuration can prevent excessive movement of the sheet member 31 and the structure 40 when a horizontal load is applied, thereby preventing a large shear force from occurring between the base member 37 and the base of the first electrode 35. This prevents the first electrode 35 from being torn off from the base member 37 due to this shear force.

[0123] In the configuration of the second embodiment, a plurality of structures 40 may be arranged, as in the first modified example. In this case, the base member 17 in Fig. 7 is replaced with a sheet member 31, and a wiring pattern made of a conductive elastic material is arranged on the sheet member 31. Furthermore, the sheet member 11 in Fig. 8 is replaced with a base member 37, and a wiring pattern made of copper or the like is arranged on the base member 37. With this configuration, the same effects as those of the first modified example can be achieved.

[0124] <Modification 1> FIG. 18 is an exploded perspective view showing the configuration of a load sensor 30 according to Modification 1 of the second embodiment.

[0125] In the first modified example, a third electrode 38 for detecting a vertical load is added. The third electrode 38 is installed on the underside of the sheet member 31. The third electrode 38 is conductive and elastic. The third electrode 38 may be made of the same material as the second electrodes 32a to 32d. The third electrode 38 may be connected, for example, to a wiring pattern (conductive elastic body) formed on the underside of the sheet member 31. The wiring pattern is formed, for example, by a printing method, so as to extend to the edge of the sheet member 31. Wiring is connected to the end of the wiring pattern, and this wiring is connected to an external detection circuit. The load sensor 10 is assembled using the same processes as those shown in FIGS. 12 to 15 in the second embodiment.

[0126] 19(a) and 19(b) are cross-sectional views showing the cross-sectional structure of a load sensor 10 according to Modification 1 of Embodiment 2. Figures 19(a) and 19(b) show cross-sectional views of the load sensor 10 cut along a plane parallel to the X-Z plane at a midpoint in the Y-axis direction. Figure 19(a) is a cross-sectional view when no load is applied, and Figure 19(b) is a cross-sectional view when a load is applied in the vertical direction (negative direction of the Z-axis) to the upper surface of the sheet member 11.

[0127] 19(a), the upper surface of the dielectric 36 is in contact with the lower surface of the third electrode 38. The contact state of the dielectric 36 with the surrounding second electrodes 32a to 32d is the same as in the case of FIG.

[0128] 19(b), when a vertical load is applied, the lower surface of the third electrode 38 is pressed against the dielectric 36 of the first electrode 35, compressing the sheet member 11 and the third electrode 38. This increases the contact area between the third electrode 38 and the dielectric 36, and increases the capacitance between the first electrode 35 and the third electrode 38. The vertical load is detected from this increase in capacitance. The horizontal load is detected in the same manner as in the second embodiment.

[0129] According to the configuration of Modification Example 1, when a load in the vertical direction (a load in a direction parallel to the axial direction of the first electrode 35) is applied, as described above, at least one of the first electrode 35 and the third electrode 38 (here, the third electrode 38) elastically deforms, increasing the contact area between the first electrode 35 and the third electrode 38 via the dielectric 36, and changing the capacitance between the first electrode 35 and the third electrode 38. Therefore, the load in the vertical direction can be detected from this change in capacitance.

[0130] Note that even when the configuration of Modification 1 of Embodiment 1 is provided to the configuration of Embodiment 2, a third electrode 38 may be added to each structure 40 and each first electrode 35. This makes it possible to detect the distribution of load in the vertical direction as well as the distribution of load in the horizontal direction.

[0131] <Other Modifications> The embodiments according to the present invention are not limited to the above-described first and second embodiments and their modifications, and various modifications are possible.

[0132] For example, in the first embodiment, the first electrode 12 has a hemispherical shape, but the first electrode 12 may have a columnar shape. For example, as shown in Fig. 20(a), the first electrode 12 may have a cylindrical shape, or as shown in Fig. 20(b), the first electrode 12 may have a truncated cone shape. The first electrode 12 may have another columnar shape, such as a polygonal column. Similarly, the first electrode 35 in the second embodiment may have a columnar shape.

[0133] Furthermore, in the first embodiment, the second electrodes 16a to 16d are arranged on all of the inner surfaces of the opening 14a, but as shown in Figure 21(a), the second electrodes 16a, 16d and the dielectrics 15a, 15d may be arranged on only one pair of adjacent inner surfaces. In this configuration, the load in the X-axis direction can be detected by the capacitance between the first electrode 12 and the second electrode 16a, and the load in the Y-axis direction can be detected by the capacitance between the first electrode 12 and the second electrode 16d. In the second embodiment as well, the second electrodes may be arranged on only one pair of adjacent inner surfaces of the opening 33a.

[0134] However, in order to more efficiently detect a change in capacitance due to a load, it is preferable that the second electrodes 16a to 16d are disposed on all of the inner surfaces of the opening 14a, as in the first embodiment.

[0135] 21(b), the cross section of the first electrode 12 when cut along a plane parallel to the XY plane may be polygonal. In this case, the first electrode 12 has a polygonal pyramid or truncated polygonal pyramid shape. The cross section of the first electrode 12 may also be polygonal other than octagonal. In the second embodiment, the cross section of the first electrode 35 may also be polygonal.

[0136] 21(c), the opening 14a of the holding member 14 may be substantially triangular in plan view. In this case, too, the three inner surfaces of the opening 14a are planes parallel to the Z axis. The second electrodes 16a-16c and the dielectrics 15a-15c are respectively arranged on these inner surfaces. In this case, too, the electrodes and the dielectrics may be arranged on only one pair of adjacent inner surfaces. In the second embodiment, the opening 33a of the holding member 33 may also be substantially triangular in plan view, and second electrodes may be arranged on at least two adjacent inner surfaces of the opening 33a.

[0137] The shape of the opening 14a in plan view is not limited to a rectangle or a triangle, and may be another polygon. For example, as shown in FIG. 21(d), the shape of the opening 14a in plan view may be substantially pentagonal. In this case, too, the three inner surfaces of the opening 14a are planes parallel to the Z axis. Second electrodes 16a-16e and dielectrics 15a-15e are respectively arranged on these inner surfaces. In this case, too, electrodes and dielectrics may be arranged on only one pair of adjacent inner surfaces, or electrodes and dielectrics may be arranged on two pairs of adjacent inner surfaces. In the second embodiment, the opening 33a of the holding member 33 in plan view may also be a polygon other than a triangle or a rectangle, and second electrodes may be arranged on at least two adjacent inner surfaces of the opening 33a.

[0138] Furthermore, in the first modification of the first embodiment, each structure 20 has its own holding member 14 , but a common holding member 14 may be used for a plurality of structures 20 .

[0139] 22 and 23 are plan views showing the configuration of the structure 20 in this case. Fig. 22 is a plan view of the structure 20 as seen from above, and Fig. 23 is a plan view of the structure 20 as seen from below.

[0140] In this configuration, the holding member 14′ has the same contour as the sheet member 11 in a plan view. The thickness of the holding member 14′ is the same as that of the holding member 14 in embodiment 1. As in embodiment 1, the holding member 14′ is made of a non-conductive and rigid material.

[0141] As shown in Figure 22, nine openings 14a are formed in the holding member 14', penetrating vertically. The shape of the openings 14a is the same as in the first embodiment. The nine openings 14a are arranged in a matrix in the holding member 14'. As in the first embodiment, second electrodes 16a to 16d are arranged by insert molding on the four inner surfaces of each opening 14a. Dielectrics 15a to 15d are arranged on the inner surfaces of the second electrodes 16a to 16d.

[0142] The configurations of the second electrodes 16a to 16d and the dielectrics 15a to 15d are the same as those in embodiment 1. The portion of the holding member 14′ near the opening 14a, the second electrodes 16a to 16d, and the dielectrics 15a to 15d form a structure 20. Nine structures 20 are arranged in a matrix.

[0143] As shown in Fig. 23, wiring patterns P1 to P8 are formed on the underside of the holding member 14'. The layout of the wiring patterns P1 to P8 is the same as that in Fig. 7. The wiring patterns P5 to P8 are connected by solder or the like to second electrodes 16a to 16d exposed from the underside of the holding member 14', respectively. The connection relationship between the second electrodes 16a to 16d and the wiring patterns P5 to P8 is the same as that in Fig. 7.

[0144] 8 is placed on the upper surface of the holding member 14' via the fixing members 13. At this time, the nine first electrodes 12 arranged on the lower surface of the sheet member 11 are fitted into the nine openings 14a of the holding member 14'. The fixing members 13 may be arranged over the entire range of the upper surface of the holding member 14', or may be arranged individually around the nine openings 14a.

[0145] A base member 17 is installed on the underside of the holding member 14'. The outline of the base member 17 in a plan view is the same as that of the holding member 14. Unlike the case of FIG. 7, the base member 17 does not have a wiring pattern. Here, because the holding member 14 has mechanical strength, the base member 17 may be a sheet-like member. If there is no need to cover the underside of the holding member 14, the base member 17 may be omitted.

[0146] This configuration also achieves the same effects as Modification 1 of Embodiment 1. Furthermore, this configuration simplifies the configuration because a common holding member 14' is used for the nine structures 20. Furthermore, this configuration facilitates electrical connection between the second electrodes 16a-16d of each structure 20 and the wiring patterns P5-P8 because the wiring patterns P1-P8 are formed on the underside of the holding member 14'.

[0147] Furthermore, in the first embodiment, the fixing member 13 is arranged so as to cover almost the entire area of ​​the upper surface of the structure 20, but the fixing member 13 may be arranged in a partial area of ​​the upper surface of the structure 20 as long as it is possible to prevent the sheet member 11 from moving from the upper surface of the structure 20 due to a load in the planar direction. This point is also the same for the fixing member 34 in the second embodiment.

[0148] Furthermore, in the above-described embodiment 1, the second electrodes 16a to 16d are arranged so as to cover the entire area of ​​the step portion 14b of the holding member 14, but the second electrodes 16a to 16d only need to be arranged in a range where the first electrode 12 can come into contact with them via the dielectrics 15a to 15d at least within the load detection range.

[0149] Furthermore, in the above-described first embodiment, when a load is applied in a direction perpendicular to the axial direction (Z-axis direction) of the first electrode 12, the first electrode 12 elastically deforms, and in the above-described second embodiment, a load in this direction elastically deforms the structure 40. However, this is not limiting, and in the configuration of the above-described first embodiment, when a load is applied in a direction perpendicular to the axial direction of the first electrode 12, both the first electrode 12 and the structure 20 may elastically deform, and the contact area between the first electrode 12 and the second electrodes 16a to 16d via the dielectrics 15a to 15d may change.

[0150] In this case, if the first electrode 12 and the structure 20 have approximately the same elastic modulus, the structure 20 will deform as the first electrode 12 moves due to the load, making it difficult for the contact area to change in response to the load. Therefore, even when both the first electrode 12 and the structure 20 elastically deform in response to the load, a certain degree of difference in elastic modulus between them is necessary. In this case, for example, it is preferable to set the elastic modulus of the structure 20 to about 10 times the elastic modulus of the first electrode 12. This allows the contact area between the first electrode 12 and the second electrodes 16a-16d, via the dielectrics 15a-15d, to change significantly due to the load, making it possible to accurately calculate the magnitude and direction of the load based on the change in capacitance.

[0151] Similarly, in the configuration of the second embodiment, when a load is applied in a direction perpendicular to the axial direction of the first electrode 12, both the first electrode 35 and the structure 40 may elastically deform, changing the contact area between the first electrode 35 and the second electrodes 32a to 32d via the dielectric 36. In this case, too, the elastic modulus of the first electrode 35 may be set to about 10 times the elastic modulus of the structure 40, as described above.

[0152] Furthermore, in the second modification of the first embodiment, both the first electrode 12 and the third electrode 18 may be deformed by a vertical load (a load parallel to the axial direction of the first electrode 12). In this case, as in the above, the elastic modulus of the third electrode 18 may be set to be relatively higher (for example, about 10 times) than the elastic modulus of the first electrode 12.

[0153] Furthermore, in the first modification of the second embodiment, both the first electrode 35 and the third electrode 38 may be deformed by a load in the vertical direction (a load in a direction parallel to the axial direction of the first electrode 35). In this case, as in the above, the elastic modulus of the first electrode 35 may be set to be relatively higher (for example, about 10 times) than the elastic modulus of the third electrode 38.

[0154] In addition, the embodiments of the present invention can be modified in various ways as appropriate within the scope of the technical ideas set forth in the claims.

[0155] <Supplementary Notes> The above description of the embodiments discloses the following techniques.

[0156] (Technology 1) A load sensor comprising: a columnar or hemispherical first electrode; a holding member having a substantially polygonal opening in a plan view, with the first electrode fitted into the opening in the axial direction of the first electrode; second electrodes respectively disposed on at least two non-parallel inner surfaces of the opening; and a dielectric interposed between the first electrode and the second electrode, wherein when a load is applied in a direction perpendicular to the axial direction, at least one of the first electrode and a structure in which the second electrode and the holding member are integrated elastically deforms, and a contact area between the first electrode and each of the second electrodes via the dielectric changes.

[0157] According to this technology, when a load is applied in a planar direction perpendicular to the axial direction of the first electrode and the first electrode and the structure move relative to each other, the contact area between the first electrode and each second electrode via the dielectric changes, and the capacitance between the first electrode and each second electrode changes. Therefore, the load in the planar direction perpendicular to the axial direction of the first electrode can be detected from this change in capacitance.

[0158] (Technology 2) The load sensor according to Technology 1, wherein the first electrode is made of a material that is more easily elastically deformed than the structure.

[0159] According to this technology, when a horizontal load is applied to the first electrode, the first electrode deforms, changing the contact area and the capacitance between the first electrode and the second electrode, and therefore the horizontal load can be detected based on the balance of these capacitances.

[0160] (Technology 3) The load sensor according to claim 2, wherein the dielectric is disposed on the second electrode.

[0161] This technology allows the first electrode to deform more smoothly than when a dielectric is placed on the first electrode, which allows the contact area to change smoothly when a load is applied, making it possible to stably detect horizontal loads.

[0162] (Technology 4) The load sensor according to Technology 2 or 3, further comprising an elastic sheet member placed on an upper surface of the structure, the first electrode protruding from a lower surface of the sheet member, and the lower surface of the sheet member fixed to the structure at a position overlapping the upper surface of the structure.

[0163] This technology can prevent excessive movement of the sheet member when a horizontal load is applied, which would otherwise cause a large shear force to be generated between the sheet member and the base of the first electrode, thereby preventing the first electrode from being torn off from the sheet member due to this shear force.

[0164] (Technology 5) The load sensor according to Technology 1, wherein the structure is made of a member that is more easily elastically deformed than the first electrode.

[0165] According to this technology, when a horizontal load is applied to the structure, the structure deforms, changing the contact area and the capacitance between the first electrode and the second electrode, and therefore the horizontal load can be detected based on the balance of these capacitances.

[0166] (Technology 6) The load sensor according to Technology 5, wherein the dielectric is disposed on the first electrode.

[0167] This technology allows the structure to deform more smoothly than when the dielectric is placed on the second electrode, which allows the contact area to change smoothly when a load is applied, making it possible to stably detect horizontal loads.

[0168] (Technology 7) The load sensor according to Technology 5 or 6, further comprising a base member on which the structure is placed and from which the first electrode protrudes on an upper surface, and the lower surface of the structure is fixed to the base member at a position overlapping with the upper surface of the base member.

[0169] This technique can prevent excessive movement of the structure when a horizontal load is applied, which would otherwise cause a large shear force between the base member and the base of the first electrode, thereby preventing the first electrode from being torn off from the base member due to this shear force.

[0170] (Technology 8) A load sensor according to any one of technologies 1 to 7, characterized in that the opening has a substantially rectangular shape in a plan view, and the second electrodes are arranged on at least two adjacent inner surfaces of the opening.

[0171] According to this technique, when a horizontal load is applied, the capacitance between the first electrode and the second electrode can be detected in at least two directions perpendicular to each other, thereby enabling the horizontal load to be detected appropriately.

[0172] (Technology 9) The load sensor according to Technology 8, wherein the second electrodes are disposed on all inner surfaces of the opening.

[0173] This technology allows the capacitance between the opposing second electrodes and the first electrode to be obtained, and the balance of these capacitances can be used to detect the load in the direction in which these electrodes face each other, making it possible to efficiently and accurately detect horizontal loads.

[0174] (Technology 10) A load sensor according to any one of technologies 1 to 9, wherein the first electrode has a cross-sectional area that decreases toward the tip, and further comprises a third electrode that contacts the tip of the first electrode via another dielectric, and when a load is applied in a direction parallel to the axial direction, at least one of the first electrode and the third electrode elastically deforms, changing the contact area between the first electrode and the third electrode via the other dielectric.

[0175] According to this technology, when a vertical load (a load parallel to the axial direction of the first electrode) is applied to the load sensor, the contact area between the first electrode and the third electrode increases, causing a change in the capacitance between the first electrode and the third electrode. Therefore, the vertical load can be detected from this change in capacitance.

[0176] (Technology 11) The load sensor according to any one of technologies 1 to 10, wherein the opening has a size such that the first electrode contacts the second electrode via the dielectric in a no-load state.

[0177] According to this technology, when a horizontal load is applied, the contact area changes immediately without any play, making it possible to accurately detect the horizontal load.

[0178] (Technology 12) The load sensor according to any one of technologies 1 to 11, characterized in that it comprises: a base member on which a plurality of structures are arranged; and a sheet member on which a plurality of the first electrodes are arranged, the first electrodes fitting into the recesses of the plurality of structures, respectively.

[0179] This technology makes it possible to detect horizontal loads over a wider range and to obtain the distribution of horizontal loads.

[0180] (Technology 13) The load sensor according to Technology 12, wherein the plurality of structures are arranged in a matrix.

[0181] This technology makes it possible to efficiently detect horizontal loads and their distribution over a wide area.

[0182] (Technology 14) The load sensor according to Technology 12 or 13, wherein the lower surface of the sheet member is fixed to the plurality of structures at a position where the lower surface overlaps the upper surfaces of the plurality of structures.

[0183] This technique suppresses the generation of large shear forces between the sheet member and the base of the first electrode in each structure, thereby preventing each first electrode from being torn off from the sheet member when a horizontal load is applied.

[0184] 10, 30 Load sensor 11, 31 Sheet member 12, 35 First electrode 13, 34 Fixing member 14, 33 Holding member 14a, 33a Opening 15a to 15d, 19, 36 Dielectric 16a to 16d, 32a to 32d Second electrode 17, 37 Base member 18, 38 Third electrode 20, 40 Structure

Claims

1. A load sensor comprising: a columnar or hemispherical first electrode; a retaining member having an opening that is substantially polygonal in a planar view, with the first electrode being fitted into the opening in the axial direction of the first electrode; second electrodes respectively disposed on at least two non-parallel inner surfaces of the opening; and a dielectric interposed between the first electrode and the second electrode, wherein when a load is applied in a direction perpendicular to the axial direction, at least one of the first electrode and a structure formed by integrating the second electrode and the retaining member elastically deforms, causing a change in the contact area between the first electrode and each of the second electrodes via the dielectric.

2. A load sensor according to claim 1, characterized in that the first electrode is made of a material that is more easily elastically deformed than the structure.

3. A load sensor according to claim 2, characterized in that the dielectric is disposed on the second electrode.

4. A load sensor as described in claim 2, comprising an elastic sheet member placed on an upper surface of the structure, the first electrode protruding from a lower surface of the sheet member, and the lower surface of the sheet member fixed to the structure at a position overlapping with the upper surface of the structure.

5. A load sensor according to claim 1, characterized in that the structure is made of a material that is more easily elastically deformed than the first electrode.

6. The load sensor according to claim 5, wherein the dielectric is disposed on the first electrode.

7. A load sensor as claimed in claim 5, further comprising a base member on which the structure is placed and from which the first electrode protrudes, and the lower surface of the structure is fixed to the base member at a position overlapping with the upper surface of the base member.

8. A load sensor as claimed in any one of claims 1 to 7, characterized in that the opening has a substantially rectangular shape in a plan view, and the second electrodes are disposed on at least two adjacent inner surfaces of the opening.

9. The load sensor according to claim 8, wherein the second electrodes are disposed on all inner surfaces of the opening.

10. A load sensor as claimed in any one of claims 1 to 7, characterized in that the first electrode has a cross-sectional area that decreases towards its tip, and further comprises a third electrode that contacts the tip of the first electrode via another dielectric, and when a load is applied in a direction parallel to the axial direction, at least one of the first electrode and the third electrode elastically deforms, changing the contact area between the first electrode and the third electrode via the other dielectric.

11. A load sensor according to any one of claims 1 to 7, characterized in that the opening has a size such that, in a no-load state, the first electrode contacts the second electrode via the dielectric.

12. A load sensor as claimed in any one of claims 1 to 7, comprising: a base member on which a plurality of structures are arranged; and a sheet member on which a plurality of the first electrodes are arranged, the first electrodes fitting into the recesses of the plurality of structures, respectively.

13. The load sensor according to claim 12, wherein the plurality of structures are arranged in a matrix.

14. A load sensor according to claim 12, wherein the lower surface of the sheet member is fixed to the plurality of structures at a position where it overlaps with the upper surfaces of the plurality of structures.

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