Load sensor

Abstract

A load sensor (1) comprises an electrode (40), a dielectric body (50) disposed on a surface of the electrode (40), and an electroconductive elastic body (30) that is disposed facing the dielectric body (50) and is electrically conductive. A plurality of projections (31) are formed on the surface of the electroconductive elastic body (30) on the dielectric body (50) side thereof. The dielectric body (50) is reduced in thickness in the plane direction thereof from the position of initial contact thereof with the electroconductive elastic body (30).

Description

Technical Field

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

Background Art

[0002] Conventionally, as a Human Machine Interface (HMI), capacitive load sensors have been used in various devices such as keyboards and game controllers. For example, Patent Document 1 below describes a force detection device including a main board, an electrode, an insulating layer, a displacement generator, and an elastic conductive layer. In this device, the electrode is formed on the upper surface of the main board and is covered with the insulating layer. The displacement generator includes a fixed portion, a flexible portion, and an acting portion, and the acting portion is connected to the fixed portion fixed to the main board via the flexible portion. The elastic conductive layer is formed on the bottom surface of the acting portion, and a rough surface composed of a large number of uneven structures is formed on the lower surface. When the acting portion is pushed into the main board, the contact state between the upper surface of the insulating layer and the rough surface of the elastic conductive layer changes, and the capacitance based on the electrode and the elastic conductive layer changes. By electrically detecting the magnitude of the capacitance, the acting force (load) is detected.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a capacitive load sensor, it is preferable that the capacitance changes linearly in response to the load. That is, when the capacitance changes linearly in response to the load, the process for calculating the load from the magnitude of the capacitance becomes extremely simple. For this reason, in a capacitive load sensor, it is preferable that a range in which the capacitance changes linearly in response to the load can be ensured as wide as possible. However, in the configuration of Patent Document 1 described above, the range in which the capacitance based on the electrode and the elastic conductive layer changes linearly in response to the load is narrow. For this reason, with this configuration, it has been difficult to detect the load by a simple process for a wide dynamic range.

[0005] In view of such problems, an object of the present invention is to provide a load sensor capable of expanding a range in which the capacitance changes linearly in response to the load.

Means for Solving the Problems

[0006] A load sensor according to a main aspect of the present invention includes an electrode, a dielectric disposed on the surface of the electrode, and a conductive elastic body disposed to face the dielectric and having conductivity. A plurality of protrusions are formed on the surface of the conductive elastic body on the dielectric side, and the thickness of the dielectric decreases in the planar direction from the initial contact position with the conductive elastic body.

[0007] According to the load sensor according to this aspect, in the initial state where no load is applied, only some of the protrusions included in the initial contact position contact the dielectric. After that, when a load is applied, as the load increases, the protrusions contact the dielectric in order from the initial contact position, and the number of protrusions contacting the dielectric increases. Further, after the protrusion contacts the dielectric, it contracts in response to an increase in the load. As a result, the contact area between the protrusion and the dielectric increases as the load increases.

[0008] As described above, the number of protrusions in contact with the dielectric and the contact area between the protrusions and the dielectric change with the load, so that the capacitance between the electrode and the conductive elastic body changes with the load. At this time, since the thickness of the dielectric decreases in the planar direction from the initial contact position, the change in capacitance due to the thickness of the dielectric increases with the increase in load. As a result, the range in which the relationship between the load and the capacitance becomes linear can be extended to a higher load range. Therefore, according to the load sensor according to this aspect, the range in which the capacitance changes linearly according to the load can be extended.

Advantages of the Invention

[0009] As described above, according to the present invention, it is possible to provide a load sensor capable of extending the range in which the capacitance changes linearly according to the load.

[0010] The effects or significance of the present invention will become clearer from the following description of the embodiments. However, the following embodiments are merely examples for implementing the present invention, and the present invention is not limited to those described in the following embodiments at all.

Brief Description of the Drawings

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

Embodiment for Carrying Out the Invention

[0013] The present invention is applicable to an input unit for performing an input according to an applied load. Specifically, the present invention is applicable to an input unit of an electronic device such as a PC keyboard, an input unit of a game controller, a surface layer portion for a robot hand to detect an object, an input unit for inputting volume, air volume, light quantity, temperature, etc., an input unit of a wearable device such as a smart watch, an input unit of a hearable device such as a wireless earphone, an input unit of a touch panel, an input unit for adjusting the ink amount etc. in an electronic pen, an input unit for adjusting the light quantity, color, etc. in a penlight, an input unit for adjusting the light quantity etc. in a light-emitting clothing, and an input unit for adjusting the volume etc. in a musical instrument, etc.

[0014] The following embodiments are load sensors typically provided in the above-described device. Such load sensors are referred to as "capacitive pressure-sensitive sensor elements", "capacitive pressure detection sensor elements", "pressure-sensitive switch elements", etc. The following embodiments are one embodiment of the present invention, and the present invention is not limited to the following embodiments at all.

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. For convenience, X, Y, and Z axes orthogonal to each other are added to each drawing. The Z-axis direction is the height direction of the load sensor 1.

[0016] FIG. 1 is an exploded perspective view schematically showing the configuration of the load sensor 1.

[0017] The load sensor 1 includes substrates 10 and 20, a conductive elastic body 30, an electrode 40, and a dielectric 50.

[0018] The substrates 10 and 20 are rectangular plates with a predetermined thickness and having flexibility. The substrate 10 is a support member for installing the conductive elastic body 30, the electrode 40, and the dielectric 50. The substrates 10 and 20 are at least one resin material selected from, for example, polyethylene terephthalate, polycarbonate, polyimide, and the like. The upper and lower surfaces of the substrates 10 and 20 are parallel to the X-Y plane. The shapes and sizes of the substrates 10 and 20 in plan view are the same as each other.

[0019] The conductive elastic body 30 is an elastic member having conductivity and has a rectangular shape in plan view. The conductive elastic body 30 is composed of a resin material and a conductive filler dispersed therein, or a rubber material and a conductive filler dispersed therein. When a resin material is used for the conductive elastic body 30, the resin material is, for example, a styrene-based resin, a silicone-based resin (such as polydimethylpolysiloxane (PDMS)), an acrylic-based resin, a rotaxane-based resin, and a urethane-based resin.

[0020] When a rubber material is used for the conductive elastic body 30, the rubber material is at least one rubber material selected from, for example, silicone rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, polyisobutylene, ethylene-propylene rubber, chlorosulfonated polyethylene, acrylic rubber, fluororubber, epichlorohydrin rubber, and urethane rubber. The conductive filler used for the conductive elastic body 30 is at least one material selected from, for example, Au (gold), Ag (silver), Cu (copper), C (carbon), ZnO (zinc oxide), In2O3 (indium(III) oxide), and SnO2 (tin(IV) oxide).

[0021] On the surface (the surface on the negative side of the Z axis) of the conductive elastic body 30, a plurality of protrusions 31 protruding in the negative direction of the Z axis are arranged in a lattice pattern. That is, on the surface of the conductive elastic body 30, a plurality of protrusions 31 are arranged in the Y axis direction, and a plurality of such rows are arranged in the X axis direction. In this embodiment, the intervals between the protrusions 31 in the Y axis direction are constant, and the intervals between the protrusions 31 in the X axis direction are also constant. The thickness of the conductive elastic body 30 is constant except for the portions of the protrusions 31.

[0022] The cross-sectional area of ​​the protrusions 31 decreases as they move in the negative direction of the Z axis. Here, the protrusions 31 have a spherical shape. The shapes and sizes of the protrusions 31 are the same as each other. In the example of FIG. 1, a total of 200 protrusions 31, 10 vertically and 20 horizontally, are formed on the surface of the conductive elastic body 30. Conductors (not shown) are installed on the conductive elastic body 30 to electrically connect the conductive elastic body 30 to a device external to the load sensor 1.

[0023] The electrode 40 is made of a metal material having electrical conductivity. The material of the electrode 40 is selected from, for example, In2O3, ZnO and / or SnO2. The electrode 40 is a rectangular plate-shaped member in a plan view. 40 The size of the electrode 40 is slightly smaller than those of the substrates 10 and 20. The electrode 40 and the conductive elastic body 30 have the same shape and size in a plan view.

[0024] The dielectric 50 is made of a material having electrical insulation properties. The material of the dielectric 50 is, for example, polypropylene resin, polyethylene terephthalate, etc. TA The dielectric material 50 is selected from a group consisting of tert-butyl ether resin, polyimide resin, polyphenylene sulfide resin, Al2O3, and Ta2O5. The dielectric material 50 is formed on the surface of the electrode 40 by, for example, insert molding. The dielectric material 50 has a shape in which the thickness changes only in one direction (the Y-axis direction). Specifically, the dielectric material 50 has a cylindrical shape that is convex toward the conductive elastic body 30. The thickness of the dielectric material 50 is greatest at the middle position in the Y-axis direction and gradually decreases toward both ends in the Y-axis direction.

[0025] When assembling the load sensor 1, the conductive elastic body 30 is installed on the upper surface of the substrate 10. Further, a structure composed of the dielectric 50 and the electrode 40 is stacked on the upper surface of the conductive elastic body 30 so that the dielectric 50 faces the conductive elastic body 30. Then, the substrate 20 is placed on the electrode 40, and the periphery of the substrate 20 is installed on the substrate 10 by the installation member. Thus, the load sensor 1 is completed.

[0026] Figure 2(a) is a side view schematically showing the state of the load sensor 1 in the initial state (the state where no load is applied). Here, for the sake of convenience, the number of protrusions 31 arranged in the Y-axis direction is seven. Figures 2(b) and (c) are side views schematically showing the states of the load sensor 1 when a load is applied, respectively.

[0027] As shown in Figure 2(a), in the initial state where no load is applied, only some of the protrusions 31 included in the initial contact position P0 contact the dielectric 50. The initial contact position P0 is the position where the protrusion 31 and the dielectric 50 contact in the initial state where no load is applied. Here, since the thickness of the dielectric 50 is the largest at the intermediate position in the Y-axis direction of the dielectric 50 and the heights of all the protrusions 31 are the same, the protrusion 31 and the dielectric 50 contact only at the intermediate position in the Y-axis direction of the dielectric 50. That is, the intermediate position in the Y-axis direction of the dielectric 50 becomes the initial contact position P0.

[0028] After that, when a load is applied to the upper surface of the substrate 10, as shown in Figures 2(b) and (c), as the load increases, the protrusions 31 sequentially contact the dielectric 50 from the initial contact position P0, and the number of protrusions 31 contacting the dielectric 50 increases. Figure 2(c) shows a state where the load has increased compared to Figure 2(b). As shown in Figures 2(b) and (c), after the protrusion 31 contacts the dielectric 50, it contracts in response to the increase in the load. As a result, the contact area S0 between the protrusion 31 and the dielectric 50 increases as the load increases.

[0029] As described above, as the number of projections 31 in contact with the dielectric 50 and the contact area S0 between the projections 31 and the dielectric 50 change with the load, the capacitance between the electrode 40 and the conductive elastic body 30 changes with the load. This capacitance is proportional to the total contact area between the projections 31 and the dielectric 50 and inversely proportional to the thickness of the dielectric 50.

[0030] Here, since the thickness of the dielectric 50 decreases in the plane direction from the initial contact position P0, the thickness of the position of the dielectric 50 with which the new projection 31 comes into contact gradually becomes smaller as the load increases. For this reason, as the load increases, the increase in capacitance generated at the newly contacted position becomes larger. That is, the change in capacitance due to the thickness of the dielectric 50 becomes larger as the load increases. Thereby, the range in which the relationship between the load and the capacitance becomes linear can be expanded to a higher load range.

[0031] <Verification 1> The inventors verified the effects of the configuration of the above embodiment by simulation.

[0032] FIG. 3(a) is a diagram for explaining the simulation conditions of Verification 1.

[0033] In this verification, it was assumed that five projections 31 are arranged in a row in the Y-axis direction. Only one row of the projections 31 was set. The projections 31 have a semi-spherical shape, and the height H1 of the projections 31 was set to 0.06 mm. The pitch P1 of the projections 31 was set to 0.3 mm, and the length L1 of the conductive elastic body 30 in the Y-axis direction was set to 1.5 mm. The five projections 31 were evenly arranged so that the center of the central projection 31 is positioned at the intermediate position of the conductive elastic body 30 in the Y-axis direction.

[0034] The length of the electrode 40 in the Y-axis direction was also set to 1.5 mm, the same as the length L1 of the conductive elastic body 30. The dielectric 50 was set to have a cylindrical shape with a constant curvature and extend from one end to the other end of the electrode 40 in the Y-axis direction. The generatrix of the cylindrical shape is parallel to the X-axis. The dielectric 50 was arranged so that the position where the thickness of the dielectric 50 is the largest coincides with the middle position of the electrode 40 in the Y-axis direction. Therefore, in the Y-axis direction, the middle position of the conductive elastic body 30 coincides with the middle position of the electrode 40.

[0035] Under this condition, the height H2 (maximum thickness) of the dielectric 50 was changed, and the relationship between the load applied between the conductive elastic body 30 and the electrode 40 and the capacitance between the conductive elastic body 30 and the electrode 40 was obtained by simulation. In response to the change in the height H2, the curve shape (curvature) of the surface of the dielectric 50 was changed so that the dielectric 50 spreads over the entire upper surface of the electrode 40. Four types of the height H2 of the dielectric 50 were set: 0 mm, 0.01 mm, 0.03 mm, and 0.06 mm. When the height H2 is 0 mm, it corresponds to the case where the surface of the dielectric 50 is flat.

[0036] Figure 3(b) is a graph showing the simulation results of Verification 1. The vertical axis and the horizontal axis in Figure 3(b) are each normalized by a predetermined value.

[0037] From the simulation results of Fig. 3(b), when the height H2 of the dielectric 50 was set to 0.01 mm, it was confirmed that the change in capacitance with respect to the load became significantly linear and highly sensitive compared to the case where the surface of the dielectric 50 was flat. On the other hand, when the height H2 of the dielectric 50 was set to 0.03 mm, although the change in capacitance with respect to the load became linear and highly sensitive compared to the case where the surface of the dielectric 50 was flat, the sensitivity decreased compared to the case where the height H2 of the dielectric 50 was 0.01 mm. Also, when the height H2 of the dielectric 50 was 0.06 mm, the change in capacitance with respect to the load became less sensitive than when the surface of the dielectric 50 was flat. From these simulation results, it was found that there is an optimal range for the height H2 of the dielectric 50 in relation to the linearity and sensitivity of the change in capacitance with respect to the load, and that if the height H2 is made too large, the characteristics tend to deteriorate instead.

[0038] <Verification 2> Next, the inventors verified by simulation the range of the height H2 of the dielectric 50 that can effectively enhance the linearity and sensitivity of the change in capacitance with respect to the load.

[0039] Fig. 4(a) is a diagram for explaining the simulation conditions of Verification 2.

[0040] In Verification 2, the height H1 and pitch P1 of the protrusion 31 were set to 0.06 mm and 0.3 mm, respectively, in the same manner as in Verification 1 above. Also, the length L1 of the conductive elastic body 30 and the electrode 40 was set to 1.5 mm in the same manner as in Verification 1 above. Other conditions were also set in the same manner as in Verification 1 above.

[0041] Under these conditions, the height H2 (maximum thickness) of the dielectric 50 was varied, and the relationship between the load applied between the conductive elastic body 30 and the electrode 40 and the capacitance between the conductive elastic body 30 and the electrode 40 was obtained by simulation. Similar to Verification 1 above, as the height H2 changed, the curve shape (curvature) of the surface of the dielectric 50 was changed so that the dielectric 50 spread over the entire upper surface of the electrode 40. In addition to 0.01 mm, 0.03 mm, and 0.06 mm, which were the same as those in Verification 1 above, 0.09 mm was added as the height H2 of the dielectric 50.

[0042] Figure 4(b) is a graph showing the simulation results of Verification 2. The vertical axis and the horizontal axis in Figure 4(b) are normalized with a predetermined value.

[0043] In the simulation results of Figure 4(b), the characteristics when the height H2 of the dielectric 50 was 0.09 mm were almost the same as those when the height H2 of the dielectric 50 was 0.06 mm. Also, referring to the verification results of Figure 3(b) together, it can be seen that when the height H2 of the dielectric 50 is 0.06 mm or 0.09 mm, the characteristics deteriorate compared to the case where the surface of the dielectric 50 is flat. From this, it was found that when the height H2 of the dielectric 50 is 0.06 mm or more, which is the same as the height H1 of the protrusion 31, the change in capacitance with respect to the load cannot be improved compared to the case where the surface of the dielectric 50 is flat.

[0044] Therefore, in order to effectively enhance the linearity and sensitivity of the change in capacitance with respect to the load, it is at least necessary to set the height H2 (maximum change amount of thickness) of the dielectric 50 to be smaller than the height H1 (protrusion amount) of the protrusion 31. More preferably, it can be seen from the simulation results of Figure 4(b) that the height H2 (maximum change amount of thickness) of the dielectric 50 is preferably half or less of the height H1 (protrusion amount) of the protrusion 31.

[0045] <Effect of the Embodiment> According to this embodiment, the following effects are achieved.

[0046] As shown in Fig. 2(a), in the initial state where no load is applied, only some of the protrusions 31 included in the initial contact position P0 contact the dielectric 50. Thereafter, when a load is applied, as the load increases, the protrusions 31 sequentially contact the dielectric 50 starting from the initial contact position P0, and the number of protrusions 31 contacting the dielectric 50 increases. Also, as shown in Figs. 2(b) and (c), after the protrusion 31 contacts the dielectric 50, it contracts in response to the increase in the load. As a result, the contact area S0 between the protrusion 31 and the dielectric 50 increases as the load increases.

[0047] In this way, as the number of protrusions 31 contacting the dielectric 50 and the contact area S0 between the protrusion 31 and the dielectric 50 change with the load, the capacitance between the electrode 40 and the conductive elastic body 30 changes with the load. At this time, since the thickness of the dielectric 50 decreases in the planar direction from the initial contact position P0, the change in capacitance due to the thickness of the dielectric 50 becomes larger as the load increases. As a result, the range in which the relationship between the load and the capacitance becomes linear can be expanded to a higher load range. Therefore, the range in which the capacitance changes linearly according to the load can be expanded.

[0048] As shown in Figs. 1 and 2(a), the dielectric 50 has a convex shape toward the conductive elastic body 30. Thereby, while restricting the number of protrusions 31 contacting at the initial contact position P0, the number of protrusions 31 that start to contact the dielectric 50 due to the subsequent application of a load can be efficiently increased. Therefore, the change in capacitance at the start of load application can be smoothly started.

[0049] As shown in Figs. 1 and 2(a), the surface of the dielectric 50 on the side of the conductive elastic body 30 has a curved surface shape. That is, in the present embodiment, the dielectric 50 has a shape in which the thickness changes only in the uniaxial direction, and more specifically, the dielectric 50 has a cylindrical shape. Thereby, when a load is applied, the contact area S0 between the protrusion 31 and the dielectric 50 can be smoothly changed, and the thickness of the dielectric 50 at the contact position can be smoothly changed. Therefore, the relationship between the load and the capacitance can be made closer to linear more smoothly.

[0050] As shown in FIG. 2(a), the protrusion 31 protrudes in a curved surface shape. Thereby, when a load is applied, the contact area S0 between the protrusion 31 and the dielectric 50 can be smoothly changed. Therefore, the relationship between the load and the capacitance can be made closer to linear more smoothly.

[0051] As shown in the simulation result (verification 2) of FIG. 4(b), it is preferable that the maximum change amount (height H2) of the thickness of the dielectric 50 is smaller than the protrusion amount (height H1) of the protrusion 31. Thereby, compared with the case where the surface of the dielectric 50 is flat, the change in capacitance with respect to the load can be improved to be linear and highly sensitive.

[0052] As shown in FIGS. 1 and 2(a), the plurality of protrusions 31 are arranged side by side in at least one row, and the thickness of the dielectric 50 changes in the arrangement direction of the protrusions 31. Further, as shown in FIG. 3(a), the plurality of protrusions 31 are arranged at a constant interval (pitch P1). Thereby, in response to the application of a load, the protrusions 31 can be brought into contact with the dielectric 50 in order in the arrangement direction, and the change in capacitance with respect to the load can be made closer to linear smoothly.

[0053] <Modification example> The configuration of the load sensor 1 can be variously modified in addition to the configuration shown in the above embodiment.

[0054] For example, in the above embodiment, the dielectric 50 has a cylindrical shape in which the thickness changes only in the Y-axis direction. However, for example, as in Modification example 1 shown in FIG. 5(a), the dielectric 50 may have a shape in which the thickness changes not only in the Y-axis direction but also in the X-axis direction. For example, the dielectric 50 may have a spherical shape in which the thickness is maximum at the center of the electrode 40.

[0055] According to this configuration, the position with the maximum thickness becomes the initial contact position P0 between the protrusion 31 and the dielectric 50 in the initial state where no load is applied. As the load is applied, the contact position between the protrusion 31 and the dielectric 50 radially spreads from the initial contact position P0. Also according to this configuration, similar to the above-described embodiment, changes in the number of protrusions 31 in contact with the dielectric 50, changes in the contact area between the dielectric 50 and the protrusions 31, and changes in the thickness of the dielectric 50 at the contact position can improve the change in capacitance with respect to the load to be linear and highly sensitive.

[0056] In the above-described embodiment, only one cylindrical dielectric 50 is arranged on the electrode 40, but the configuration of the dielectric 50 is not limited to this. For example, the dielectric 50 may be divided into a plurality of parts, and the thickness of the dielectric 50 may change in the planar direction in each divided region. For example, as in the modification example 2 shown in FIG. 5(b), the dielectric 50 may be divided into two in the Y-axis direction, and the thickness of the dielectric 50 in each divided region A1 may change in the Y-axis direction. In the example of FIG. 5(b), the shape of the dielectric 50 in each divided region A1 is set to a cylindrical shape.

[0057] Also according to this configuration, similar to the above-described embodiment, the number of protrusions 31 in contact with the dielectric 50 and the contact area between the dielectric 50 and the protrusions 31 change as the load is applied, and the thickness of the dielectric 50 changes for each contact position. Thereby, similar to the above-described embodiment, the change in capacitance with respect to the load can be improved to be linear and highly sensitive.

[0058] Note that the number of divisions of the dielectric 50 is not limited to two, and the dielectric 50 may be divided into other numbers. Also in this case, the thickness of the dielectric 50 may be set to change in the planar direction in each divided region. The dielectric 50 may be divided not only in the Y-axis direction but also in the X-axis direction. Also, the shape of the dielectric 50 set in each divided region is not limited to a cylindrical shape, and for example, a shape in which the thickness changes in two directions as shown in FIG. 5(a) may be used.

[0059] Further, the configuration of the dielectric 50 is not limited to the configuration in which the thickness at the center in the Y-axis direction is the largest.

[0060] For example, as shown in FIG. 8(a), in the central range A1 in the Y-axis direction, the upper surface of the dielectric 50 may be a plane parallel to the X-Y plane (a plane perpendicular to the load application direction). That is, the upper surface of the dielectric 50 with which the central protrusion 31 in the Y-axis direction abuts may be a plane parallel to the X-Y plane. In this case, the range A1 can be set to a size that covers the contact area of the protrusion 31 when the central protrusion 31 is most compressed by the load. The range A1 is, for example, circular in plan view. The upper surfaces of the dielectric 50 other than the range A1 can be set to the same shape as in the above-described embodiment.

[0061] FIG. 8(b) is a graph showing the verification result obtained by simulating the relationship between the load and the capacitance for the configuration of FIG. 8(a).

[0062] In this simulation, the height H1, the pitch P1, and the length L1 were set in the same manner as in Verification 1 in the above-described embodiment. The height H2 was defined as the height from the upper surface of the electrode 40 (the lower surface of the dielectric 50) to the plane of the range A1. Here, the height H2 was set to 0.03 mm. Similar to the above Verification 1, it was assumed that five protrusions 31 are arranged in a row in the Y-axis direction, and only one row of protrusions 31 was set. The protrusion 31 had a semi-spherical shape.

[0063] Under these conditions, the relationship between the load and the capacitance was obtained by simulation for the range of the load until the capacitance in the configuration of FIG. 8(a) was substantially saturated. As a comparative example, the relationship between the load and the capacitance was obtained by simulation when the entire upper surface of the dielectric 50 was a plane parallel to the X-Y plane, similar to the above Verification 1.

[0064] From the simulation results of FIG. 8(b), even when the upper surface of the dielectric 50 is a plane parallel to the X-Y plane in the central range A1 in the Y-axis direction, the change in capacitance with respect to the load is significantly linear and highly sensitive compared to the case where the entire surface of the dielectric 50 is flat.

[0065] Also, as shown in FIG. 9(a), the ranges A2 and A3 of the upper surface of the dielectric 50 where the protrusions 31 other than the central protrusion 31 in the Y-axis direction contact may further be planes parallel to the X-Y plane. Also in this case, the ranges A2 and A3 can be set to a size that covers the contact area of the opposing protrusion 31 when the opposing protrusion 31 is most compressed by the load. The upper surface of the dielectric 50 other than the ranges A1, A2, and A3 can be set to the same shape as in the above embodiment.

[0066] FIG. 9(b) is a graph showing the verification results obtained by simulating the relationship between the load and the capacitance for the configuration of FIG. 9(a).

[0067] The simulation conditions other than the height H2 were set in the same manner as in the case of FIG. 8(b). The height H2 was defined as the height from the upper surface of the electrode 40 (the lower surface of the dielectric 50) to each plane of the ranges A1, A2, and A3. Here, the height H2 to the plane of the range A1 was set to 0.03 mm, the height H2 to the plane of the range A2 was set to 0.02 mm, and the height H2 to the plane of the range A3 was set to 0.01 mm.

[0068] Under this condition, for the range of the load until the capacitance substantially saturates in the configuration of FIG. 9(a), the relationship between the load and the capacitance was obtained by simulation. Similarly to the above, the relationship between the load and the capacitance was also obtained by simulation for the comparative example.

[0069] From the simulation results of FIG. 9(b), it was confirmed that also in the ranges A2 and A3 together with the range A1, when the upper surface of the dielectric 50 is a plane parallel to the X-Y plane, the change in capacitance with respect to the load is linear and highly sensitive compared to the case where the entire surface of the dielectric 50 is flat.

[0070] Further, as shown in FIG. 10(a), the upper surface of the dielectric 50 may be configured in a concave shape in which the thicknesses at both ends in the Y-axis direction are the largest and the thickness at the intermediate position in the Y-axis direction is the smallest. In this case, the upper surface of the dielectric 50 may be formed on a cylindrical surface whose generatrix is parallel to the X-axis.

[0071] FIG. 10(b) is a graph showing the verification results obtained by simulating the relationship between the load and the capacitance for the configuration of FIG. 10(a).

[0072] The simulation conditions other than the height H2 were set in the same manner as in the case of FIG. 8(b). The height H2 was defined based on the upper surface of the electrode 40 (the lower surface of the dielectric 50). The height H2 from the upper surface of the dielectric 50 at both ends in the Y-axis direction was set to 0.03 mm, and the height H2 to the upper surface at the center in the Y-axis direction of the dielectric 50 was set to 0.0009 mm.

[0073] Under these conditions, for the range of the load until the capacitance substantially saturates in the configuration of FIG. 10(a), the relationship between the load and the capacitance was obtained by simulation. Similarly to the above, for the comparative example, the relationship between the load and the capacitance was also obtained by simulation. From the simulation results in FIG. 10(b), even when the upper surface of the dielectric 50 is formed in a concave shape in which the thicknesses at both ends in the Y-axis direction are the largest and the thickness at the intermediate position in the Y-axis direction is the smallest, the change in capacitance with respect to the load is significantly linear and highly sensitive compared to the case where the entire surface of the dielectric 50 is flat.

[0074] Further, as shown in FIG. 11(a), the range A1 of the upper surface of the dielectric 50 with which the central protrusion 31 in the Y-axis direction abuts may be a plane parallel to the X-Y plane. Also in this case, the range A1 can be set to a size that covers the contact area of the protrusion 31 when the opposing protrusion 31 is most compressed by the load. The upper surface of the dielectric 50 other than the range A1 can be set to a cylindrical surface similar to that in FIG. 10(a).

[0075] FIG. 11(b) is a graph showing the verification results obtained by simulating the relationship between the load and the capacitance for the configuration of FIG. 11(a).

[0076] The simulation conditions other than the height H2 were set in the same manner as in the case of FIG. 8(b). The height H2 was defined with reference to the upper surface of the electrode 40 (the lower surface of the dielectric 50). The height H2 up to the upper surfaces at both ends of the dielectric 50 in the Y-axis direction was set to 0.03 mm, and the height H2 up to the upper surface of the range A1 was set to 0.0009 mm.

[0077] Under these conditions, the relationship between the load and the capacitance was obtained by simulation for the range of the load until the capacitance in the configuration of FIG. 11(a) was substantially saturated. Similarly, for the comparative example, the relationship between the load and the capacitance was also obtained by simulation.

[0078] From the simulation results of FIG. 11(b), it was confirmed that even when the upper surface of the dielectric 50 is flat at the center in the Y-axis direction, the change in capacitance with respect to the load becomes significantly linear and highly sensitive compared to the case where the entire surface of the dielectric 50 is flat.

[0079] Also, as shown in FIG. 12(a), the ranges A2 and A3 of the upper surface of the dielectric 50 where the protrusions 31 other than the central protrusion 31 in the Y-axis direction contact may also be planes parallel to the X-Y plane. Also in this case, the ranges A2 and A3 can be set to a size that covers the contact area of the opposing protrusions 31 when the opposing protrusions 31 are most compressed by the load. The upper surface of the dielectric 50 other than the ranges A1, A2, and A3 can be set to a cylindrical surface similar to that of FIG. 10(a).

[0080] FIG. 12(b) is a graph showing the verification results obtained by simulating the relationship between the load and the capacitance for the configuration of FIG. 12(a).

[0081] The simulation conditions other than the height H2 were set in the same manner as in the case of FIG. 8(b). The height H2 was defined as the height from the upper surface of the electrode 40 (the lower surface of the dielectric 50) to each plane of the ranges A1, A2, and A3. Here, the height H2 to the plane of the range A1 was set to 0.0009 mm, the height H2 to the plane of the range A2 was set to 0.01 mm, and the height H2 to the plane of the range A3 was set to 0.02 mm. The height H3 to the upper surface of the dielectric 50 at both ends in the Y-axis direction was set to 0.03 mm.

[0082] Under this condition, for the range of the load until the capacitance substantially saturates in the configuration of FIG. 12(a), the relationship between the load and the capacitance was obtained by simulation. Similarly to the above, for the comparative example, the relationship between the load and the capacitance was also obtained by simulation.

[0083] From the simulation results of FIG. 12(b), it was confirmed that even when the upper surface of the dielectric 50 is flat at the center in the Y-axis direction, the change in capacitance with respect to the load becomes linear and highly sensitive compared to the case where the entire surface of the dielectric 50 is flat.

[0084] Also, as shown in FIG. 13(a), a protrusion 51 is formed on the upper surface of the dielectric 50 facing the protrusion 31, and by changing the height of this protrusion 51, the thickness of the dielectric 50 may decrease in the plane direction from the initial contact position between the dielectric 50 and the conductive elastic body 30. PO The protrusion 51 is, for example, hemispherical. In this case, the protrusion 51 may not be formed at the facing position of a predetermined protrusion 31. In FIG. 13(a), the protrusion 51 is not formed at the facing position of the central protrusion 31 in the Y-axis direction.

[0085] FIG. 13(b) is a graph showing the verification results obtained by simulating the relationship between the load and the capacitance for the configuration of FIG. 13(a).

[0086] The simulation conditions other than the height H2 were set in the same manner as in the case of FIG. 8(b). The height H2 was defined based on the upper surface of the electrode 40 (the lower surface of the dielectric 50). The height H2 up to the apex of the protrusions 51 at both ends in the Y-axis direction was set to 0.03 mm, and the height H2 up to the apex of the inner protrusions 51 was set to 0.02 mm. The height H2 up to the upper surface of the dielectric 50 at the position facing the central protrusion 31 was set to 0.01 mm.

[0087] Under these conditions, regarding the range of the load until the capacitance substantially saturates in the configuration of FIG. 13(a), the relationship between the load and the capacitance was obtained by simulation. Similarly to the above, for the comparative example, the relationship between the load and the capacitance was also obtained by simulation.

[0088] From the simulation results of FIG. 13(b), it was confirmed that even when the height of the protrusions 51 was made different, the change in capacitance with respect to the load became linear and highly sensitive compared to the case where the entire surface of the dielectric 50 was flat.

[0089] When comparing the simulation results of FIG. 8(b) and the simulation results of FIG. 9(b), the simulation results of FIG. 8(b) had a wider range of load until the capacitance saturated, that is, a wider dynamic range. This is presumably because when the protrusion 31 is pressed against a plane parallel to the X-Y plane, the protrusion 31 deforms more efficiently in the Z-axis direction. From this, it can be said that in order to ensure a wider dynamic range, it is preferable that the upper surface of the dielectric 50 at the position facing the protrusion 31 is not a plane perpendicular to the load application direction.

[0090] Moreover, when comparing the simulation results in Fig. 8(b) with those in Fig. 10(b), it was found that the simulation results in Fig. 8(b) had a significantly wider range of load, that is, a wider dynamic range, until the capacitance saturated. This is because in the structure of Fig. 10(a), as the load increases, the upper surfaces of the dielectrics 50 at both ends in the Y-axis direction come into contact with the lower surfaces other than the protrusions 31 of the conductive elastic body 30. From this, it can be said that in order to ensure a wider dynamic range, it is preferable that the upper surface of the dielectric 50 has a shape where the center in the Y-axis direction is high and both ends in the Y-axis direction are low.

[0091] In addition, in the modification examples shown in Figs. 8(a) to 13(b), the five protrusions 31 were arranged in a row in the Y-axis direction. Similar to the above-described embodiment, a plurality of such rows may be further arranged in the X-axis direction, and accordingly, the electrodes 40 and the dielectrics 50 may be expanded in the X-axis direction. Also, the configurations of the above-described modification examples 1 to 4 may be applied to the modification examples shown in Figs. 8(a) to 13(b).

[0092] Alternatively, the dielectric 50 may have a configuration where the thickness is the largest at one end in the Y-axis direction and gradually decreases toward the other end in the Y-axis direction.

[0093] Also, the surface of the dielectric 50 is not limited to a curved surface and may be a plane inclined at a predetermined angle with respect to the plane on the dielectric 50 side of the electrode 40.

[0094] In the above-described embodiment, the plurality of protrusions 31 are arranged on the surface of the conductive elastic body 30 so as to be arranged at regular intervals in the X-axis direction and the Y-axis direction. However, the arrangement method of the plurality of protrusions 31 is not limited to this. For example, as in Modification Example 3 shown in Figs. 6(a) and 6(b), the row of protrusions 31 at the center in the Y-axis direction may be omitted from the form in which the plurality of protrusions 31 are arranged at regular intervals in the X-axis direction and the Y-axis direction. In this case, as shown in Fig. 6(b), the positions of the rows on both sides of the omitted row become the initial contact positions P0.

[0095] With this configuration as well, similar to the above-described embodiment, it is possible to improve the change in capacitance with respect to the load so as to be linear and highly sensitive. Also, since the change in the contact area between the protrusion 31 and the dielectric 50 before and after the start of load application is suppressed as compared with the above-described embodiment, it is possible to suppress the rise of the capacitance immediately after the start of load application from becoming significantly steep. As a result, the rise of the capacitance immediately after the start of load application can be made closer to a more linear state.

[0096] Also, as in the modification example 4 shown in FIG. 7(a), in the protrusions 31 arranged in the odd-numbered columns L11 and the protrusions 31 arranged in the even-numbered columns L12, the positions of the protrusions 31 may be shifted by a half pitch in the Y-axis direction. Alternatively, the protrusions 31 may be arranged radially from the center of the conductive elastic body 30.

[0097] Also, in the above-described embodiment, the protrusion 31 has a hemispherical shape, but the shape of the protrusion 31 is not limited to this. For example, the shape of the protrusion 31 may be a shape in which the top of the hemispherical surface is cut away by a plane parallel to the X-Y plane. Alternatively, the shape of the protrusion 31 may be a cone or a pyramid, or a shape in which the top of the cone or pyramid is cut away by a plane parallel to the X-Y plane. The protrusion 31 preferably has a shape in which the cross-sectional area decreases toward the tip.

[0098] Alternatively, the protrusion 31 may be a ridge that is long in the X-axis direction. For example, as in the modification example 5 shown in FIG. 7(b), the protrusion 31 may be a ridge having a semi-cylindrical shape. Also in this case, the same effects as those of the above-described embodiment can be obtained.

[0099] Also, the shapes and heights of the protrusions 31 may be different from each other, and the pitch of the protrusions 31 may not be constant. For example, the height and pitch of the protrusions 31 may be adjusted so that the change in capacitance with respect to the load becomes closer to linearity. Similarly, the change in the thickness of the dielectric 50 may be adjusted so that the change in capacitance with respect to the load becomes closer to linearity.

[0100] Also, in the above embodiment, one conductive elastic body 30 is arranged for one electrode 40. However, the present invention is not limited to this, and two or more conductive elastic bodies 30 may be arranged side by side in the X-Y plane with a predetermined interval therebetween for one electrode 40. In this case, an external device detects changes in capacitance based on a plurality of conductive elastic bodies 30 respectively, and adds the obtained plurality of capacitances to detect a change in the overall capacitance. Then, the external device detects the load applied to the load sensor 1 based on the change in the overall capacitance.

[0101] In addition, the embodiments of the present invention can be appropriately modified in various ways within the scope of the technical idea shown in the claims.

Explanation of Reference Numerals

[0102] 1 Load sensor 30 Conductive elastic body 31 Protrusion 40 Electrode 50 Dielectric A1 Division region P0 Initial contact position

Claims

1. An electrode, a dielectric disposed on the surface of the electrode, and a conductive elastic body disposed opposite to the dielectric and having conductivity, wherein a plurality of protrusions are formed on the surface of the conductive elastic body on the dielectric side, the dielectric has a thickness that decreases in the planar direction from an initial contact position with the conductive elastic body, characterizing a load sensor.

2. In the load sensor according to Claim 1, the dielectric has a convex shape toward the conductive elastic body, characterizing a load sensor.

3. In the load sensor according to Claim 1, the dielectric has a concave shape in a direction away from the conductive elastic body, characterizing a load sensor.

4. In the load sensor according to any one of Claims 1 to 3, the surface of the dielectric on the conductive elastic body side has a curved surface shape, characterizing a load sensor.

5. In the load sensor according to any one of Claims 1 to 4, the dielectric has a shape in which the thickness changes only in one axial direction, characterizing a load sensor.

6. In the load sensor according to Claim 5, the dielectric has a cylindrical shape, characterizing a load sensor.

7. In the load sensor according to any one of Claims 1 to 3, a plane perpendicular to the load application direction is formed at a position on the surface of the dielectric on the conductive elastic body side and facing the protrusion, characterizing a load sensor.

8. In the load sensor according to any one of Claims 1 to 7, the dielectric is divided into a plurality of parts, and in each divided region, the thickness of the dielectric changes in the planar direction, characterizing a load sensor.

9. In the load sensor according to any one of Claims 1 to 8, the protrusion protrudes in a curved surface shape, characterizing a load sensor.

10. In the load sensor according to any one of Claims 1 to 9, the maximum change amount of the thickness of the dielectric is smaller than the protruding amount of the protrusion, characterizing a load sensor.

11. In the load sensor according to any one of Claims 1 to 10, the plurality of protrusions are arranged side by side in at least one row, and the thickness of the dielectric changes in the arrangement direction of the protrusions, characterizing a load sensor.

12. In the load sensor according to Claim 11, the plurality of protrusions are arranged at regular intervals, characterizing a load sensor.

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