Load sensor and load detection device

Abstract

A load sensor (1) is provided with: a first electrode (20) having elastic and conductive first protrusions (21) and second protrusions (22) on the same surface; a second electrode (40) facing the first electrode (20) so as to sandwich the first protrusions (21) and the second protrusions (22); and a dielectric (30) disposed on an opposing surface (41) of the second electrode (40). The number of protrusions that contact the dielectric (30) increases as the load increases.

Description

Load sensor and load detection device

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

[0002] Conventionally, capacitive load sensors have been used in various devices, such as keyboards and game controllers, as human-machine interfaces (HMIs). For example, a load sensor may include a first electrode having a plurality of elastic conductive protrusions, a second electrode facing the first electrode across the protrusions, and a dielectric disposed on the opposing surface of the second electrode. When a load is applied to the first electrode or the second electrode, the protrusions contract in response to the load. This changes the contact area between the dielectric and the protrusions, 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.

[0003] Japanese Patent Application Laid-Open No. 2003-144994 describes this type of load sensor.

[0004] JP 2016-118545 A

[0005] In the load sensor having the above configuration, the load detection range is usually set to the range in which the protrusion can reversibly deform. However, if an object is accidentally dropped on the load sensor, a high load exceeding the yield stress may be applied to the protrusion. If such a high load causes irreversible deformation, i.e., plastic deformation, of the protrusion, the load cannot be detected properly.

[0006] In view of such problems, the present invention aims to provide a load sensor and a load detection device that can prevent plastic deformation of the protrusions even if a large load is suddenly applied to the load sensor.

[0007] A load sensor according to a first aspect of the present invention includes a first electrode having a plurality of elastic conductive protrusions on the same surface, a second electrode facing the first electrode across the plurality of protrusions, and a dielectric disposed on the facing surface of the second electrode, wherein the number of protrusions in contact with the dielectric increases as the load increases.

[0008] According to the load sensor of this aspect, the number of protrusions that come into contact with the dielectric increases as the load increases, so that even if a large load is suddenly applied to the load sensor, the stress generated in each of the multiple protrusions is alleviated. As a result, the stress generated in each protrusion is less likely to exceed the yield stress, and plastic deformation of each protrusion can be suppressed.

[0009] A load sensor according to a second aspect of the present invention includes a first electrode having a plurality of elastic conductive first protrusions, a second electrode facing the first electrode across the plurality of first protrusions, a plurality of elastic insulating second protrusions arranged on an opposing surface of the second electrode so as to protrude into a space where the first protrusions are not present, and a dielectric arranged on the opposing surface of the second electrode, wherein in a no-load state, tips of the plurality of first protrusions are in contact with the dielectric, and tips of the plurality of second protrusions are spaced from the first electrode.

[0010] According to the load sensor of this aspect, the second protrusions contact the structure on the first electrode side as the load increases, so that even if a large load is suddenly applied to the load sensor, the stress generated in each of the multiple first protrusions is alleviated. This makes it difficult for the stress generated in each first protrusion to exceed the yield stress, thereby suppressing plastic deformation of each first protrusion. Furthermore, because the second protrusions are disposed on a second electrode separate from the first electrode on which the first protrusions are disposed, it is easy to arrange the second protrusions in the gaps between the first protrusions. This eliminates the need to reduce the number of first protrusions to accommodate the second protrusions, thereby maintaining the detection sensitivity of the load sensor.

[0011] A load detection device according to a third aspect of the present invention includes a load sensor according to the first or second aspect and a control unit that detects a load based on the capacitance between the first electrode and the second electrode.

[0012] According to the load detection device of this aspect, plastic deformation of each protrusion in the load sensor is suppressed, and the control unit can continue to properly detect the load even after a large load is applied to the load sensor.

[0013] As described above, the present invention can provide a load sensor and a load detection device that can prevent plastic deformation of the protrusions even if a large load is suddenly applied to the load sensor.

[0014] 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.

[0015] FIG. 1 is an exploded perspective view schematically illustrating the configuration of a load sensor according to Embodiment 1. FIG. 2( a) is a cross-sectional view schematically illustrating the load sensor according to Embodiment 1 in an unloaded state. FIG. 2( b) is a cross-sectional view schematically illustrating the load sensor according to Embodiment 1 in a loaded state. FIG. 3( a) is a cross-sectional view schematically illustrating deformation of a protrusion according to a comparative example when a load exceeding the detection range is applied. FIG. 3( b) is a cross-sectional view schematically illustrating deformation of a protrusion according to Embodiment 1 when a load exceeding the detection range is applied. FIGS. 4( a) and 4( b) are plan views schematically illustrating deformation of a first protrusion according to a comparative example. FIGS. 5( a) and 5( b) are plan views schematically illustrating deformation of the first protrusion and the second protrusion according to Embodiment 1. FIG. 6 is a graph schematically illustrating the relationship between load and compressive stress according to a comparative example and Embodiment 1. FIG. 7( a) is a graph schematically illustrating the relationship between load and capacitance according to a comparative example and Embodiment 1 in which the second protrusions are not conductive. FIG. 7( b) is a graph schematically showing the relationship between load and capacitance according to a comparative example and embodiment 1 in which the second protrusions are conductive. FIG. 8 is a block diagram showing the configuration of a load detection device according to embodiment 1. FIG. 9( a) is a perspective view schematically showing the configuration of a first electrode according to a comparative example. FIG. 9( b) is a perspective view schematically showing the configuration of a first electrode according to configuration 1 of embodiment 1. FIG. 10( a) is a perspective view schematically showing the configuration of a first electrode according to configuration 2 of embodiment 1. FIG. 10( b) is a perspective view schematically showing the configuration of a first electrode according to configuration 3 of embodiment 1. FIG. 11( a) is a perspective view schematically showing the configuration of a first electrode according to configuration 4 of embodiment 1. FIG. 11( b) is a perspective view schematically showing the configuration of a first electrode according to configuration 5 of embodiment 1. FIGS. 12( a) and 12( b) are graphs showing simulation results for the comparative example and configurations 1 and 2 of embodiment 1. 13(a) and 13(b) are graphs showing simulation results for the comparative example and configurations 2 and 3 of embodiment 1. Figures 14(a) and 14(b) are graphs showing simulation results for the comparative example and configurations 4 and 5 of embodiment 1. Figures 15(a) and 15(b) are cross-sectional views schematically showing the configuration of a first electrode according to an example in which the shape of the protrusion is modified.16(a) and 16(b) are cross-sectional views schematically illustrating the configuration of a first electrode according to a modified example of the shape of the protrusions. FIGS. 17(a) and 17(b) are plan views schematically illustrating the configuration of a first electrode according to a modified example of the arrangement of the protrusions. FIGS. 18(a) and 18(b) are plan views schematically illustrating the configuration of a first electrode according to a modified example of the arrangement of the protrusions. FIGS. 19(a) and 19(b) are schematic views for explaining an example of a procedure for forming a first electrode according to the first embodiment. FIGS. 20(a) and 20(b) are schematic views for explaining an example of a procedure for forming a first electrode according to the first embodiment. FIGS. 21(a) and 21(b) are schematic views for explaining a procedure for forming a first electrode according to the first embodiment. FIG. 22(a) is a cross-sectional view schematically illustrating a load sensor in a no-load state according to the second embodiment. FIG. 22(b) is a cross-sectional view schematically illustrating deformation of the protrusions when a load exceeding the detection range is applied according to the second embodiment. FIG. 23(a) is a perspective view schematically illustrating a configuration of a first electrode according to a comparative example. FIG. 23(b) is a perspective view schematically illustrating a configuration of a first electrode according to a configuration 6 of the second embodiment. FIGS. 24(a) and 24(b) are graphs illustrating simulation results for the comparative example and configuration 6 of the second embodiment. FIGS. 25(a) and 25(b) are plan views schematically illustrating configurations of a first electrode according to a modified example of the protrusion arrangement. FIGS. 26(a) and 26(b) are schematic diagrams illustrating an example of a procedure for forming a first electrode according to the second embodiment. FIGS. 27(a) and 27(b) are schematic diagrams illustrating an example of a procedure for forming a first electrode according to the second embodiment. FIGS. 28(a) and 28(b) are schematic diagrams illustrating a procedure for forming a first electrode according to the second embodiment. Fig. 29(a) is a cross-sectional view schematically showing a load sensor in a no-load state according to embodiment 3. Fig. 29(b) is a cross-sectional view schematically showing deformation of a protrusion when a load exceeding the detection range is applied according to embodiment 3. Fig. 30(a) and Fig. 30(b) are cross-sectional views schematically showing the configuration of a first electrode according to an example of a modified shape of the protrusion.

[0016] However, the drawings are for illustrative purposes only and do not limit the scope of the present invention.

[0017] The present invention is applicable to an input unit for performing 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 portion for detecting an object by a robot hand, an input unit for inputting volume, air volume, light intensity, 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 amount of ink in an electronic pen, an input unit for adjusting the light intensity or color in a penlight, an input unit for adjusting the light intensity in luminous clothing, and an input unit for adjusting the volume in a musical instrument, etc.

[0018] The following embodiment is a load sensor typically provided in the above-described device. Such a load sensor is called a "capacitive pressure sensor element," a "capacitive pressure detection sensor element," a "pressure-sensitive switch element," etc. The following embodiment is one embodiment of the present invention, and the present invention is not limited to the following embodiment.

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. For convenience, each drawing is labeled with X, Y, and Z axes which are orthogonal to each other. The Z axis direction is the height direction of the load sensor 1.

[0020] First Embodiment FIG. 1 is an exploded perspective view schematically showing the configuration of a load sensor 1. As shown in FIG.

[0021] The load sensor 1 includes a substrate 10, a first electrode 20, a dielectric 30, a second electrode 40, and a substrate 50. The substrate 10, the first electrode 20, the dielectric 30, the second electrode 40, and the substrate 50 all have substantially the same square shape in plan view.

[0022] The substrates 10 and 50 are plate-like members having a predetermined thickness. The top and bottom surfaces of the substrates 10 and 50 are parallel to the XY plane. The substrate 10 is a support member for placing the first electrode 20, the dielectric 30, and the second electrode 40. The substrates 10 and 50 are made of at least one resin material selected from, for example, polyethylene terephthalate, polycarbonate, polyimide, and the like.

[0023] The first electrode 20 includes a base portion 20a, a plurality of first protrusions 21, and a plurality of second protrusions 22. The base portion 20a is a plate-shaped member, and the first protrusions 21 and the second protrusions 22 are formed to protrude upward (in the negative Z-axis direction) from the upper surface (surface on the negative Z-axis side) of the base portion 20a.

[0024] The plurality of first protrusions 21 and the plurality of second protrusions 22 are arranged in a grid pattern on the upper surface of the base portion 20a. That is, the plurality of first protrusions 21 and the plurality of second protrusions 22 are arranged alternately in the Y-axis direction and the X-axis direction on the upper surface of the base portion 20a. The pitch between the first protrusions 21 and the second protrusions 22 in the Y-axis direction is constant, and the pitch between the first protrusions 21 and the second protrusions 22 in the X-axis direction is also constant. In the example shown in FIG. 1 , a total of 36 first protrusions 21 and second protrusions 22 are formed on the upper surface of the base portion 20a, six in the X-axis direction and six in the Y-axis direction. In this embodiment, the first protrusions 21 and second protrusions 22 are arranged adjacent to each other in the X-axis direction and the Y-axis direction.

[0025] In this embodiment, the cross-sectional areas of the first protrusion 21 and the second protrusion 22 decrease as they progress in the negative Z-axis direction. The tip of the first protrusion 21 has a surface 21a parallel to the X-Y plane, and the tip of the second protrusion 22 has a surface 22a parallel to the X-Y plane. The first protrusion 21 has a truncated conical shape obtained by cutting a predetermined conical shape at the surface 21a, and the second protrusion 22 has a truncated conical shape obtained by cutting a predetermined conical shape at the surface 22a. The conical shapes that form the basis of the first protrusion 21 and the second protrusion 22 are the same. Because the surface 21a is located on the negative Z-axis side of the surface 22a, the first protrusion 21 is longer in the Z-axis direction than the second protrusion 22.

[0026] The first protrusions 21 and the base portion 20a are made of the same first material and are integrally formed. The second protrusions 22 are made of a second material and are integrally formed with the base portion 20a. In FIG. 1 , the second protrusions 22 are shown by dotted lines for convenience. The first material constituting the first protrusions 21 and the base portion 20a is made of a non-conductive elastic material and a conductive filler mixed into the elastic material. In the first material, the conductive filler is dispersed within the elastic material. This provides the first protrusions 21 and the base portion 20a with both conductivity and elasticity. On the other hand, the second material constituting the second protrusions 22 is made of a non-conductive elastic material.

[0027] The elastic materials used for the first and second materials are composed of resin and rubber materials. Examples of resin materials include styrene-based resins, silicone-based resins (such as polydimethylpolysiloxane (PDMS)), acrylic resins, rotaxane-based resins, and urethane-based resins. Examples of rubber materials 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 used in this embodiment is silicone rubber.

[0028] The conductive filler used in the first material may be, for example, Au (gold), Ag (silver), Cu (copper), C (carbon), ZnO (zinc oxide), In ２ O ３ (indium(III) oxide) and SnO ２ (tin(IV) oxide). The conductive filler of this embodiment is C (carbon).

[0029] The base radius of the first protrusions 21 and the second protrusions 22 is, for example, 0.01 mm or more and 0.34 mm or less. The height of the first protrusions 21 and the second protrusions 22 is, for example, 0.05 mm or more and 0.15 mm or less. The pitch between adjacent first protrusions 21 and second protrusions 22 in the X-axis direction and the Y-axis direction is, for example, 0.215 mm or more and 0.7 mm or less.

[0030] A conductor (not shown) is provided on the base portion 20a to electrically connect the detection circuit 2a (see FIG. 8) outside the load sensor 1 to the base portion 20a.

[0031] The second electrode 40 is a plate-shaped member that faces the first electrode 20 across the first protrusion 21 and the second protrusion 22. The second electrode 40 is made of a conductive metal material. The material of the second electrode 40 is, for example, In. ２ O ３ , ZnO and SnO ２ The second electrode 40 is provided with a conductor (not shown) for electrically connecting the second electrode 40 to a detection circuit 2 a (see FIG. 8 ) external to the load sensor 1 .

[0032] The dielectric 30 is disposed on the opposing surface 41 (the surface on the positive side of the Z axis) of the second electrode 40. The opposing surface 41 is a surface parallel to the XY plane, and the surface on the negative side of the Z axis of the dielectric 30 is also a surface parallel to the XY plane. The dielectric 30 is made of a material having electrical insulation properties. Examples of materials for the dielectric 30 include polypropylene resin, polyethylene terephthalate resin, polyimide resin, polyphenylene sulfide resin, and Al. ２ O ３ and Ta ２ O ５ The dielectric 30 is formed on the opposing surface 41 of the second electrode 40 by, for example, insert molding.

[0033] When assembling the load sensor 1, the first electrode 20 is placed on the upper surface of the substrate 10, and further, a structure consisting of the dielectric 30 and the second electrode 40 is placed on the upper surface of the first electrode 20 so that the dielectric 30 faces the first electrode 20. Then, the substrate 50 is placed on top of the second electrode 40, and the periphery of the substrate 50 is attached to the substrate 10 by an attachment member. In this way, the load sensor 1 is completed.

[0034] 2(a) is a cross-sectional view schematically showing the load sensor 1 in an unloaded state (a state in which no load is applied). FIG. 2(b) is a cross-sectional view schematically showing the load sensor 1 in a loaded state (a state in which a load is applied). FIGS. 2(a) and 2(b) show a cross-section of the load sensor 1 taken along a plane parallel to the Y-Z plane passing through the centers of the first protrusions 21 and the second protrusions 22. For convenience, the number of first protrusions 21 and second protrusions 22 aligned in the Y-axis direction is five in FIGS. 2(a) and 2(b).

[0035] As shown in Fig. 2(a), in the initial state where no load is applied, only the tip surface 21a of the first protrusion 21 contacts the dielectric 30. When a load is then applied to the upper surface of the substrate 50, the first protrusion 21 contracts in response to an increase in the load, as shown in Fig. 2(b). This increases the contact area between the first protrusion 21 and the dielectric 30, and shortens the distance between the dielectric 30 and the base portion 20a.

[0036] When the contact area between the first protrusion 21 and the dielectric 30 and the distance between the dielectric 30 and the base portion 20a change with the load, the capacitance between the second electrode 40 and the first electrode 20 changes with the load. This capacitance is proportional to the total contact area between the first electrode 20 and the dielectric 30, and inversely proportional to the thickness of the dielectric 30 and the distance between the dielectric 30 and the base portion 20a. The potential reflecting this change in capacitance is measured in an external control circuit 2b (see FIG. 8), thereby detecting the load.

[0037] In a load sensor, the load detection range is usually set to the range in which the protrusion can reversibly deform. However, if an object is accidentally dropped onto the load sensor, a high load may be applied to the protrusion, causing the compressive stress in the protrusion to exceed the yield stress. If such a high load causes irreversible deformation, i.e., plastic deformation, in the protrusion, the load cannot be detected properly.

[0038] 3A, in a comparative example that is configured only with first protrusions 21 that are equal in height, when a load exceeding the detection range is applied, the compressive stress generated in the first protrusions 21 is likely to exceed the yield stress, and there is a risk of irreversible deformation (plastic deformation) of the first protrusions 21. If the first protrusions 21 are irreversibly deformed in this way, it will be impossible to properly detect the load thereafter.

[0039] In contrast to this, in this embodiment, when the magnitude of the applied load is within the detection range, the elastic modulus of the first protrusion 21, the shapes such as the height of the first protrusion 21 and the second protrusion 22, and the arrangement of the first protrusion 21 and the second protrusion 22 are set so that the tip surface 22a of the second protrusion 22 does not come into contact with the dielectric 30, as shown in Figure 2 (b).

[0040] 3(b), when the magnitude of the applied load exceeds the detection range, the second protrusions 22 come into contact with the dielectric 30, and the load applied to the load sensor 1 is also distributed to the second protrusions 22. In this way, when the number of protrusions contacting the dielectric 30 increases in response to an increase in the load, the compressive stress generated in the first protrusions 21 is alleviated, and the compressive stress generated in the first protrusions 21 becomes less likely to exceed the yield stress. As a result, even when a load equivalent to that shown in FIG. 3(a) is applied, the deformation of the first protrusions 21 remains within the range of reversible deformation, allowing subsequent load detection to be performed appropriately.

[0041] The deformation of the protrusions of the first electrode 20 in the comparative example and the first embodiment will be described in more detail with reference to FIGS. 4(a) to 5(b).

[0042] 4A and 4B are plan views of a comparative example, each showing a schematic diagram of deformation of the first protrusion 21. In Fig. 4A and 4B, for convenience, components other than the first electrode 20 are omitted, and the hatched areas indicate the portions where the first protrusion 21 and the dielectric 30 are in contact with each other.

[0043] In the comparative example, compared to the first embodiment, the second protrusions 22 are omitted, and all the protrusions are constituted by the first protrusions 21 .

[0044] 4A, in the no-load state, only the tip surface 21a of the first protrusion 21 is in contact with the dielectric 30. When a load within the detection range is applied to the load sensor of the comparative example from the no-load state, the contact area between the first protrusion 21 and the dielectric 30 becomes larger than in the no-load state, but the deformation of the first protrusion 21 remains reversible. In this case, when the load is no longer applied, the first protrusion 21 can properly return to its original shape.

[0045] 4B, when a load exceeding the detection range is applied to the load sensor of the comparative example from a no-load state, the first protrusion 21 undergoes irreversible deformation (plastic deformation), and in this case, even if the load is no longer applied, the first protrusion 21 cannot properly return to its original shape.

[0046] 5( a) and 5(b) are plan views schematically showing deformation of the first projections 21 and the second projections 22 according to embodiment 1. In Fig. 5(a) and 5(b), for convenience, configurations other than the first electrode 20 are omitted, and the hatched areas indicate the portions where the first projections 21 and the second projections 22 contact the dielectric 30.

[0047] In the first embodiment, similarly to FIG. 1, the first protrusions 21 and the second protrusions 22 are arranged alternately adjacent to each other.

[0048] As shown in Figure 5(a), in the no-load state, only the tip surface 21a of the first protrusion 21 is in contact with the dielectric 30. When a load within the detection range is applied to the load sensor 1 from the no-load state, the contact area between the first protrusion 21 and the dielectric 30 becomes larger than in the no-load state, but the deformation of the first protrusion 21 remains reversible. At this time, the second protrusion 22 is not in contact with the dielectric 30. In this case, when the load is no longer applied, the first protrusion 21 can properly return to its original shape.

[0049] 5(b), when a load exceeding the detection range is applied to the load sensor 1 from a no-load state, the second protrusions 22 come into contact with the dielectric 30. At this time, the load applied to the load sensor 1 is supported not only by the first protrusions 21 but also by the second protrusions 22, so the compressive stress generated in each first protrusion 21 tends to be less than the yield stress of the first protrusions 21, and the deformation of each first protrusion 21 tends to remain reversible. In this case, when the load is no longer applied, the first protrusions 21 can properly return to their original shape.

[0050] Furthermore, in the first embodiment, in order to prevent a load from being applied only to the first protrusions 21 regardless of where an object falls on the upper surface of the substrate 50, the plurality of first protrusions 21 and the plurality of second protrusions 22 are arranged such that at least one first protrusion 21 is sandwiched between two second protrusions 22. Specifically, as shown in Figures 5(a) and 5(b), the first protrusions 21 and the second protrusions 22 are arranged so that they are alternately adjacent to each other. In this case, the pitch between adjacent first protrusions 21 and second protrusions 22 is determined so that both the first protrusions 21 and the second protrusions 22 are included in the range in which a load is applied by a falling object.

[0051] FIG. 6 is a graph schematically showing the relationship between the load and the compressive stress according to the comparative example and the first embodiment.

[0052] In the comparative example, all of the protrusions are composed of first protrusions 21 as shown in Figures 4(a) and (b), while in embodiment 1, the first protrusions 21 and second protrusions 22 are distributed as shown in Figures 5(a) and (b). The horizontal axis represents the load applied to the upper surface of the substrate 50 of the load sensor. The vertical axis represents the value obtained by dividing the load applied to the load sensor by the contact area of ​​all the protrusions in contact with the dielectric 30. In other words, the vertical axis represents the average compressive stress generated in each protrusion in contact with the dielectric 30. In both the comparative example and embodiment 1, the first range is set as the load detection range.

[0053] In the comparative example, as shown by the thick dashed line, when the load exceeds the maximum value R1 of the first range and reaches L1, the compressive stress generated in each first protrusion 21 reaches the yield stress of the first protrusion 21, and the first protrusion 21 undergoes irreversible deformation.

[0054] On the other hand, in embodiment 1, as shown by the thick solid line, when the load exceeds the maximum value R1 of the first range and reaches L21, the second protrusions 22 come into contact with the dielectric 30. Therefore, the load is distributed to the second protrusions 22, and the compressive stress generated in each first protrusion 21 increases more slowly in the subsequent load range. Then, when the load reaches L22, the compressive stress generated in each first protrusion 21 reaches the yield stress of the first protrusions 21, causing irreversible deformation of the first protrusions 21. At this time, L22 is greater than L1, and the compressive stress generated in the first protrusions 21 does not reach the yield stress of the first protrusions 21 until the load reaches L22. Therefore, in embodiment 1, the load range over which the first protrusions 21 can remain reversibly deformed is wider than in the comparative example.

[0055] FIG. 7A is a graph schematically showing the relationship between the load and the capacitance according to the comparative example and the first embodiment.

[0056] The horizontal axis represents the load applied to the upper surface of the substrate 50 of the load sensor. The vertical axis represents the capacitance between the first electrode 20 and the second electrode 40. In both the comparative example and the first embodiment, the capacitance increases as the load increases in the first range, which is the detection range. Therefore, the load can be detected based on the capacitance by the control circuit 2b (see FIG. 8) connected downstream of the load sensor.

[0057] However, in the comparative example, if a large load (for example, a load of L1 to L22) is suddenly applied and irreversible deformation occurs, the capacitance does not change appropriately in the first range thereafter, making it impossible to properly detect the load. On the other hand, in the first embodiment, irreversible deformation is unlikely to occur even when a similar large load is applied, and the capacitance continues to change appropriately in the first range thereafter, making it possible to properly detect the load.

[0058] In the first embodiment, the first protrusion 21 does not irreversibly deform until the load reaches L22. Therefore, the load detection range can be set not only to the first range but also to a second range, which has a load value greater than the first range. However, in the first embodiment shown in FIG. 1 , the second material constituting the second protrusion 22 is a non-conductive resin material, so the change in capacitance is gradual in the second range, as shown in FIG. 7A. In this case, it is difficult to obtain a change in capacitance (resolution) in response to the load in the second range, making it difficult to detect the load accurately. Therefore, when the second range is included in the detection range, the second material, like the first material of the first protrusion 21, is composed of a non-conductive resin material and a conductive filler mixed into the resin material. As a result, the second protrusion 22 is conductive, so the capacitance changes in response to the load even in the second range, as shown in FIG. 7B.

[0059] FIG. 7B is a graph schematically showing the relationship between the load and the capacitance according to the first embodiment when the secondary projections 22 are conductive.

[0060] In this case, as shown by the thick solid line, when the load applied to the load sensor 1 reaches L21, the second protrusion 22 comes into contact with the dielectric 30, causing a temporary increase in capacitance, which then gradually increases. Thus, if the second protrusion 22 is conductive, the capacitance no longer changes linearly with the load in the second range, but the capacitance increases as the load increases. Therefore, the first and second ranges can be set as detection ranges, and the control circuit 2b (see FIG. 8) can detect the load based on the capacitance.

[0061] FIG. 8 is a block diagram showing the configuration of the load detection device 2.

[0062] The load detection device 2 includes the load sensor 1, a detection circuit 2a, and a control circuit 2b.

[0063] The detection circuit 2a detects the capacitance between the first electrode 20 and the second electrode 40 based on a change in voltage when a DC voltage is applied between the first electrode 20 and the second electrode 40. The detection circuit 2a outputs a signal corresponding to the capacitance between the first electrode 20 and the second electrode 40 to the control circuit 2b. The control circuit 2b includes a processing circuit such as a CPU and a memory, and controls each component according to a predetermined program. The control circuit 2b also detects the load applied to the load sensor 1 based on the detection result of the detection circuit 2a, and transmits the load detection result to an external device (for example, a personal computer).

[0064] The control circuit 2b stores the load detection range in memory in advance. When the detected load is within the detection range, the control circuit 2b transmits the detected load to an external device as a valid load. For example, when the capacitance changes as shown in FIG. 7(a), the control circuit 2b stores the first range in memory as the detection range, and transmits the detected load to an external device when the detected load is within the first range. On the other hand, when the capacitance changes as shown in FIG. 7(b), the control circuit 2b stores the first and second ranges in memory as the detection ranges, and transmits the detected load to an external device when the detected load is within the first and second ranges.

[0065] Even when the capacitance changes as shown in Figure 7 (b), the control circuit 2b may store the first range in memory as the detection range, and transmit the detected load to an external device when the detected load is within the first range.

[0066] <Investigation of height and hardness of first and second protrusions> As shown in Figures 9(a) to 11(b), the inventors conducted simulations to verify how compressive stress and capacitance change depending on the load in various configurations in which the height and hardness of the protrusions are changed.

[0067] FIG. 9A is a perspective view schematically illustrating the configuration of a first electrode 20 according to a comparative example.

[0068] 9A shows a portion of the first electrode 20, which is repeatedly formed in the X-axis direction and the Y-axis direction. Above and below the first electrode 20, a substrate 10, a dielectric 30, a second electrode 40, and a substrate 50 are arranged, as in FIG. 1 .

[0069] In the comparative example, the second protrusions 22 are omitted compared to the configuration shown in FIG. 1 . The radius R of the bottom surface of the first protrusions 21 is 0.34 mm. The pitch P between two adjacent first protrusions 21 in the X-axis direction and the Y-axis direction is both 0.7 mm. The height H1 of the first protrusions 21 is 0.15 mm. The hardness of the first protrusions 21 is 40 degrees. The first protrusions 21 and the base portion 20a are conductive and elastic.

[0070] FIG. 9B is a perspective view schematically illustrating the configuration of the first electrode 20 according to the first configuration of the first embodiment.

[0071] In configuration 1, similar to the configuration shown in FIG. 1 , second protrusions 22 are arranged that are lower than the first protrusions 21. The radius R of the base surfaces of the first protrusions 21 and the second protrusions 22 is both 0.34 mm. The pitch P between adjacent first protrusions 21 and second protrusions 22 in the X-axis direction and the Y-axis direction is both 0.7 mm. The height H of the first protrusions 21 is 0.15 mm, and the height H2 of the second protrusions 22 is 0.05 mm. The hardness of the first protrusions 21 and the second protrusions 22 is both 40 degrees. The first protrusions 21 and the base portion 20a are conductive and elastic, and the second protrusions 22 are non-conductive and elastic.

[0072] FIG. 10A is a perspective view schematically illustrating the configuration of the first electrode 20 according to the second configuration of the first embodiment.

[0073] In the configuration 2, the height H2 of the second protrusion 22 is 0.1 mm, as compared with the configuration 1. The other configurations and sizes of the configuration 2 are similar to those of the configuration 1.

[0074] FIG. 10B is a perspective view schematically illustrating the configuration of the first electrode 20 according to the third configuration of the first embodiment.

[0075] In Configuration 3, compared to Configuration 2, one of the second protrusions 22 is replaced with a third protrusion 23 that is lower than the second protrusion 22. A surface 23a parallel to the XY plane is formed at the tip of the third protrusion 23. The height H2 of the second protrusion 22 is 0.12 mm. The height H3 of the third protrusion 23 is 0.1 mm, and the radius R of the bottom surface of the third protrusion 23 is 0.34 mm. Like the second protrusion 22, the third protrusion 23 is made of a non-conductive elastic material and is formed integrally with the base portion 20a. The other configurations and sizes of Configuration 3 are similar to those of Configuration 2.

[0076] FIG. 11A is a perspective view schematically illustrating the configuration of the first electrode 20 according to the fourth configuration of the first embodiment.

[0077] In Configuration 4, the hardness of the second projections 22 is 50 degrees, as compared to Configuration 2. Other configurations and sizes of Configuration 4 are similar to those of Configuration 2.

[0078] FIG. 11B is a perspective view schematically illustrating the configuration of the first electrode 20 according to the fifth configuration of the first embodiment.

[0079] In Configuration 5, the hardness of the second projections 22 is 30 degrees, as compared to Configuration 2. The other configurations and sizes of Configuration 5 are similar to those of Configuration 2.

[0080] 12A and 12B are graphs showing the simulation results of the comparative example and the configurations 1 and 2 of the first embodiment.

[0081] Fig. 12(a) shows the relationship between the load and the compressive stress until the primary protrusions 21 are plastically deformed. In Fig. 12(a), the horizontal axis represents the load (N) applied to the load sensor. The vertical axis, like the vertical axis in Fig. 6, represents the average compressive stress (MPa) generated in each protrusion.

[0082] In the comparative example, as shown by the dashed line, the first protrusions 21 undergo plastic deformation when the load increases to approximately 20 N. In configuration 1, as shown by the solid line, when the load increases to approximately L31 and the second protrusions 22 come into contact with the dielectric 30, the first protrusions 21 then undergo plastic deformation when the load increases to approximately 20 N, as in the comparative example. In configuration 2, as shown by the thick solid line, when the load increases to approximately L32 and the second protrusions 22 come into contact with the dielectric 30, the compressive stress then increases more gradually than in the comparative example and configuration 1, and the first protrusions 21 undergo plastic deformation when the load increases to approximately 32 N.

[0083] According to configuration 2, the load is supported by the second protrusions 22 before the first protrusions 21 are significantly compressed. Therefore, in configuration 2, compared to the comparative example, the increase in compressive stress in the first protrusions 21 is smoothly alleviated by the second protrusions 22, making the first protrusions 21 less likely to undergo plastic deformation. This increases the load capacity of the load sensor 1.

[0084] In contrast, in configuration 1, the load at which the first protrusions 21 plastically deformed was approximately the same as that in the comparative example. The reason for this is thought to be that the second protrusions 22 were too low, and therefore the load applied to the first protrusions 21 was not smoothly distributed to the second protrusions 22 within the load range after the second protrusions 22 came into contact with the dielectric 30. Therefore, it can be seen that in order to achieve sufficient load resistance, it is necessary to adjust the ratio of the height of the second protrusions 22 to the height of the first protrusions 21, etc.

[0085] 12B shows the relationship between the load and the capacitance until the primary projections 21 are plastically deformed. In FIG. 12B, the horizontal axis represents the load (N / cm ２ ) The vertical axis represents the capacitance between the first electrode 20 and the second electrode 40.

[0086] As shown in FIG. 12(b), in configuration 2, the increase in capacitance is more gradual than in the comparative example and configuration 1, and therefore the sensitivity of the load sensor 1 is slightly reduced. However, since the protrusions are less susceptible to plastic deformation, a wide range of loads can be detected.

[0087] 13A and 13B are graphs showing simulation results for the comparative example and configurations 2 and 3 of embodiment 1. Figures 13A and 13B are graphs similar to Figures 12A and 12B, respectively.

[0088] 13(a), in configuration 3, as indicated by the thick solid line, when the load increases to approximately L41 and the second projections 22 come into contact with the dielectric 30, the compressive stress thereafter changes more slowly than in configuration 2. Furthermore, even after the load increases to approximately L42 and the third projections 23 come into contact with the dielectric 30, the compressive stress changes more slowly than in configuration 2, and when the load increases to approximately 36 N, the first projections 21 undergo plastic deformation.

[0089] According to configuration 3, the load is supported by the third protrusions 23 together with the second protrusions 22, making the first protrusions 21 even less susceptible to plastic deformation than in configuration 2. This increases the load capacity of the load sensor 1 compared to configuration 2. In configuration 3, the height of the lower third protrusions 23 is 0.1 mm, and it is believed that the third protrusions 23, together with the second protrusions 22, contribute to alleviating the compressive stress in the first protrusions 21.

[0090] As shown in FIG. 13(b), in configuration 3, as indicated by the thick solid line, the increase in capacitance is more gradual than in configuration 2, so the sensitivity of the load sensor 1 is slightly reduced. However, since the protrusions are less susceptible to plastic deformation, a wide range of loads can be detected.

[0091] 14(a) and 14(b) are graphs showing the simulation results of the comparative example and configurations 4 and 5 of embodiment 1. Figures 14(a) and 14(b) are graphs similar to Figures 12(a) and 12(b), respectively.

[0092] 14A, in configuration 4, as indicated by the thick solid line, when the load increases to approximately L51 and the second protrusions 22 come into contact with the dielectric 30, the compressive stress then increases more gradually than in the comparative example, and when the load increases to approximately 34 N, the first protrusions 21 undergo plastic deformation. According to configuration 4, the hardness of the second protrusions 22 is higher than that of the first protrusions 21, so the load is more reliably supported by the second protrusions 22. Therefore, the load resistance of the load sensor 1 can be increased compared to configuration 2 described above, in which the hardness of the first protrusions 21 and the hardness of the second protrusions 22 are equal.

[0093] On the other hand, in configuration 5, as shown by the dashed dotted line, after the load increases to approximately L51 and the second protrusions 22 come into contact with the dielectric 30, when the load increases to approximately 14 N, the second protrusions 22 undergo plastic deformation earlier than the first protrusions 21. For configuration 5 in Figure 14(a), a graph is shown up to the time when the second protrusions 22 undergo plastic deformation.

[0094] In this case, when the load is released after the secondary protrusions 22 have undergone plastic deformation, the secondary protrusions 22 enter a state of plastic deformation in which they have shrunk slightly. Therefore, when a load is subsequently applied, the compressive stress changes in a manner similar to that of Configuration 1 in which the secondary protrusions 22 are low as shown in Figure 12(a). Therefore, in this case, as with Configuration 1, it is considered that the range of loads required for the primary protrusions 21 to undergo plastic deformation is similar to that of the comparative example.

[0095] Thus, according to configuration 5, the hardness of the second protrusions 22 is lower than the hardness of the first protrusions 21, so the second protrusions 22 undergo plastic deformation faster than the first protrusions 21, resulting in a lower load capacity as in configuration 1. Therefore, it can be said that the hardness of the second protrusions 22 is preferably higher than the hardness of the first protrusions 21.

[0096] As shown in Figure 14 (b), in configuration 4, as shown by the thick solid line, the increase in capacitance is more gradual than in the comparative example and configuration 5, so the sensitivity of the load sensor 1 is slightly reduced, but since the protrusions are less likely to undergo plastic deformation, a wide range of loads can be detected.

[0097] Furthermore, it was found that, according to configuration 4, the load capacity of the load sensor 1 can be set high by increasing the hardness of the second protrusions 22. Therefore, in configuration 1 shown in Fig. 12(a), by making the hardness of the second protrusions 22 higher than the hardness of the first protrusions 21, a high load capacity can be expected even when the height of the second protrusions 22 is low as in configuration 1.

[0098] <Effects of First Embodiment> According to the first embodiment, the following effects are achieved.

[0099] As shown in Fig. 1, the first electrode 20 has elastic, conductive first protrusions 21 and second protrusions 22 (multiple protrusions) on the same surface. The second electrode 40 faces the first electrode 20 with the first protrusions 21 and second protrusions 22 (multiple protrusions) sandwiched between them. The dielectric 30 is disposed on the opposing surface 41 of the second electrode 40. As shown in Figs. 5(a) and 5(b), the number of first protrusions 21 and second protrusions 22 (protrusions) that come into contact with the dielectric 30 increases as the load increases.

[0100] According to this configuration, the number of protrusions that come into contact with the dielectric 30 increases as the load increases, and therefore, the stress generated in each of the multiple protrusions is alleviated even if a large load is suddenly applied to the load sensor 1. This makes it difficult for the stress generated in each protrusion to exceed the yield stress, and it is possible to suppress the occurrence of plastic deformation in each protrusion.

[0101] 1, the multiple protrusions of the first electrode 20 include multiple first protrusions 21 and multiple second protrusions 22. As shown in Fig. 2(a) , in a no-load state, the surfaces 21a (tips) of the multiple first protrusions 21 are in contact with the dielectric 30, and the surfaces 22a (tips) of the multiple second protrusions 22 are spaced apart from the dielectric 30.

[0102] 5(b), with an increase in load, a transition occurs from a state in which the plurality of first projections 21 are in contact with the dielectric 30 to a state in which the plurality of second projections 22 are also in contact with the dielectric 30. This makes it possible to increase the number of projections in contact with the dielectric 30 in response to an increase in load.

[0103] 2A, the dielectric 30 is formed on the planar opposing surface 41 of the second electrode 40. The plurality of first protrusions 21 and the plurality of second protrusions 22 protrude from the upper surface (the same reference plane) of the base portion 20a on the first electrode 20. The height of the plurality of second protrusions 22 is lower than the height of the plurality of first protrusions 21.

[0104] According to this configuration, the number of protrusions that come into contact with the dielectric 30 can be increased in accordance with an increase in the load with a simple configuration.

[0105] As shown in FIG. 1, a plurality of first protrusions 21 and a plurality of second protrusions 22 are arranged such that at least one first protrusion 21 is sandwiched between two second protrusions 22 .

[0106] According to this configuration, since the second protrusions 22 are present on both sides of at least one first protrusion 21, when the dielectric 30 comes into contact with the second protrusions 22 due to an increase in load, the second electrode 40 and the dielectric 30 can be supported in a well-balanced manner by the first protrusions 21 and the second protrusions 22. This makes it possible to prevent an unbalanced load from occurring and improve the accuracy of load detection.

[0107] Furthermore, as shown in FIG. 1, when the first protrusions 21 and the second protrusions 22 are arranged alternately on the first electrode 20, the load applied to the load sensor 1 can be supported by the first protrusions 21 and the second protrusions 22 in an even more balanced manner.

[0108] 11A, the hardness of the secondary projections 22 is higher than the hardness of the primary projections 21. In other words, the modulus of elasticity of the secondary projections 22 is higher than the modulus of elasticity of the primary projections 21.

[0109] According to this configuration, as shown in FIG. 14( a ), the load is more reliably supported by the second protrusions 22 , and therefore the load resistance of the load sensor 1 can be increased.

[0110] 2A, the cross-sectional areas of the first protrusions 21 and the second protrusions 22 become smaller toward the surfaces 21a and 22a (tips). The contact area between the dielectric 30 and the first protrusions 21 in the no-load state is smaller than the contact area between the dielectric 30 and the second protrusions 22 when the dielectric 30 starts to come into contact with the second protrusions 22.

[0111] According to this configuration, the first protrusions 21, which come into contact with the dielectric 30 first, begin to contact the dielectric 30 over a small area, so the change in contact area in response to an increase in load becomes larger, resulting in a faster increase in capacitance. This increases the sensitivity of the load sensor 1 when a load begins to be applied. Furthermore, the second protrusions 22, which come into contact with the dielectric 30 later, begin to contact the dielectric 30 over a larger area, so that even if a large load is suddenly applied, the second protrusions 22 can absorb the applied load and prevent plastic deformation of the protrusions.

[0112] A surface 21a (first plane) is formed at the tip of each of the plurality of first protrusions 21, and a surface 22a (second plane) is formed at the tip of each of the plurality of second protrusions 22, and the area of ​​surface 21a (first plane) is smaller than the area of ​​surface 22a (second plane).

[0113] According to this configuration, when the application of the load starts, the contact area between the dielectric 30 and the first protrusion 21 increases gradually, which further improves the linearity of the sensitivity characteristics.

[0114] As shown in FIG. 5B, when a load (load L1 in FIG. 6) smaller than the range of loads that generates a yield stress in the primary projections 21 is applied, the secondary projections 22 come into contact with the dielectric 30.

[0115] According to this configuration, yield stress is less likely to occur in the primary projections 21, and plastic deformation of the primary projections 21 can be appropriately suppressed.

[0116] In configuration 3 shown in Figure 10 (b), the multiple protrusions of the first electrode 20 further include multiple third protrusions 23, and in the no-load state, the surfaces 23a (tips) of the multiple third protrusions 23 are further away from the dielectric 30 than the surfaces 22a (tips) of the multiple second protrusions 22.

[0117] According to this configuration, an increase in load causes a transition from a state in which the plurality of first projections 21 and second projections 22 are in contact with the dielectric 30 to a state in which the plurality of third projections 23 are also in contact with the dielectric 30. As a result, as shown in the graph of Fig. 13(a), it is possible to increase the number of projections in contact with the dielectric 30 in response to an increase in load, and it is possible to further suppress the occurrence of plastic deformation in each projection.

[0118] As shown in FIG. 2A, the cross-sectional area of ​​the first projections 21 and the second projections 22 (plural projections) decreases toward the surfaces 21a and 22a (tips).

[0119] According to this configuration, the contact area between the first protrusion 21 and the dielectric 30 increases as the load increases, thereby improving the linearity of the sensitivity characteristics.

[0120] As shown in FIG. 8, the load detection device 2 includes a control circuit 2 b (control unit) that detects the load based on the electrostatic capacitance between the first electrode 20 and the second electrode 40 .

[0121] With this configuration, plastic deformation of each protrusion in the load sensor 1 is suppressed, so that the control circuit 2b can continue to detect the load properly even after a large load is suddenly applied to the load sensor 1.

[0122] As shown in FIG. 7B, the control circuit 2b (controller) detects the load based on the capacitance, for example, in a first range below a second range in which the sensitivity characteristic of the load sensor 1 decreases.

[0123] According to this configuration, the load is detected in a range (first range) with high sensitivity characteristics, so that the reliability of the load detected by the load detection device 2 can be improved.

[0124] <Examples of changes to the shape of the protrusions> In the no-load state, the configuration in which the tip of the first protrusion 21 contacts the dielectric 30 and the tip of the second protrusion 22 is separated from the dielectric 30 is not limited to the configuration of embodiment 1 shown in FIG. 2(a), and may be, for example, the configurations shown in FIGS. 15(a) to 16(b).

[0125] 15( a), the height (length in the Z-axis direction) of the first protrusions 21 and the height (length in the Z-axis direction) of the second protrusions 22 are equal to each other, compared to the first embodiment. Furthermore, the position of the second protrusions 22 on the first electrode 20 (the position of the second protrusions 22 on the base portion 20 a) is farther away from the dielectric 30 than the position of the first protrusions 21 on the first electrode 20 (the position of the second protrusions 22 on the base portion 20 a). That is, the distance d2 between the lower surface of the dielectric 30 and the position of the second protrusions 22 is longer than the distance d1 between the lower surface of the dielectric 30 and the position of the first protrusions 21. This allows the number of protrusions in contact with the dielectric 30 to be increased as the load increases, similar to the first embodiment.

[0126] In the example shown in FIG. 15( b), compared to the first embodiment, the tips of the first protrusions 21 and the second protrusions 22 are located at the same position in the height direction (Z-axis direction). Specifically, the height (length in the Z-axis direction) of the first protrusions 21 and the height (length in the Z-axis direction) of the second protrusions 22 are equal to each other. Furthermore, the portion of the dielectric 30 located above the second protrusions 22 is located higher (in the negative Z-axis direction) than the portion of the dielectric 30 located above the first protrusions 21. In this case, too, the distance d2 between the bottom surface of the dielectric 30 and the position of the second protrusions 22 is longer than the distance d1 between the bottom surface of the dielectric 30 and the position of the first protrusions 21. As a result, similar to the first embodiment, the number of protrusions contacting the dielectric 30 can be increased as the load increases.

[0127] 16(a), compared to the first embodiment, the first protrusions 21 and the second protrusions 22 are similar in shape, and the first protrusions 21 are larger than the second protrusions 22. In this case, the area of ​​the surface 21a at the tip of the first protrusion 21 is larger than the area of ​​the surface 22a at the tip of the second protrusion 22. From the viewpoint of gradually increasing the contact area between the dielectric 30 and the first protrusions 21 and improving the linearity of the sensitivity characteristics when the application of a load is started, it is preferable that the area of ​​the surface 21a be smaller than the area of ​​the surface 22a, as in the first embodiment.

[0128] 16(b), compared to the first embodiment, the first protrusion 21 and the second protrusion 22 have a shape obtained by cutting the upper end of a hemispherical shape of the same shape and size along a plane parallel to the X-Y plane. In this case as well, in a no-load state, the tip surface 21a of the first protrusion 21 contacts the dielectric 30, and the tip surface 22a of the second protrusion 22 is spaced apart from the dielectric 30. When the first protrusion 21 and the second protrusion 22 have a hemispherical shape, the contact area between the first protrusion 21 and the second protrusion 22 and the dielectric 30 increases smoothly as the load increases. This improves the linearity of the sensitivity characteristics.

[0129] The first protrusions 21 and the second protrusions 22 may be conical, pyramidal, or truncated pyramidal. If the second protrusions 22 are non-conductive, the second protrusions 22 may be columnar in shape with a constant cross-sectional area toward the apex.

[0130] <Modification of Protrusion Arrangement> The arrangement of the first protrusions 21 and the second protrusions 22 on the first electrode 20 is not limited to the arrangement in embodiment 1 shown in Fig. 1, and may be arranged such that two second protrusions 22 sandwich at least one first protrusion 21, as shown in Fig. 17(a) to Fig. 18(b), for example. In each figure, the second protrusions 22 are shown by dotted lines for convenience.

[0131] In the example shown in Figure 17(a), rows of first protrusions 21 aligned in the X-axis direction and rows of second protrusions 22 aligned in the X-axis direction are alternately arranged in the Y-axis direction. In this case, even if a large load is suddenly applied to the load sensor 1, plastic deformation of each protrusion can be suppressed. Note that, when the first protrusions 21 and the second protrusions 22 are arranged in rows as shown in Figure 17(a), it is preferable to arrange the rows of second protrusions 22 at the outer edge portion of the first electrode 20. This makes it easier for the second protrusions 22 to support a load applied near the outer edge of the first electrode 20.

[0132] 17(a), in the example shown in Fig. 17(b), multiple rows of first protrusions 21 are arranged between rows of second protrusions 22. In this case, since more first protrusions 21 are arranged than in the configuration of Fig. 17(a), it is less likely that the second protrusions 22 will support the load, but it is possible to increase the sensitivity of the load sensor 1. Note that, like the first protrusions 21, multiple rows of second protrusions 22 may also be arranged adjacent to each other.

[0133] 18(a), the first protrusions 21 and the second protrusions 22 are arranged concentrically with respect to the center of the first electrode 20. In this case, a large load applied to the center of the load sensor 1 is more likely to be supported evenly by the second protrusions 22, thereby suppressing plastic deformation of each protrusion.

[0134] 18(b), the second protrusions 22 are arranged radially from the center of the first electrode 20. In this case, too, a large load applied to the center of the load sensor 1 is more likely to be supported evenly by the second protrusions 22, thereby suppressing plastic deformation of each protrusion.

[0135] 19(a) to 21(b) are schematic diagrams for explaining an example of a procedure for forming the first electrode 20. Figures 19(a) to 21(b) show cross sections of each part cut along a plane perpendicular to the XY plane.

[0136] 19( a), the first electrode 20 is formed using a material injection unit 110, a material induction unit 120, a mask plate 130, and a protrusion formation unit 140. The protrusion formation unit 140 has a plurality of recesses 141, 142 formed therein corresponding to the positions of the first protrusions 21 and the second protrusions 22. The mask plate 130 has holes 131 formed therein that penetrate vertically at positions corresponding to the positions of the second protrusions 22.

[0137] 19( b), the mask plate 130 is fitted into the protrusion forming section 140, and the material injection section 110 and the material guiding section 120 are placed on the upper surface of the mask plate 130. In this state, the second material 152 that will become the source of the second protrusions 22 is injected from the material injection section 110. The second material 152 passes through the flow path 121 of the material guiding section 120 and the holes 131 of the mask plate 130, and fills the recesses 142.

[0138] 20(a), the material injection section 110, the material induction section 120 and the mask plate 130 are separated from the protrusion forming section 140. In this way, the second protrusions 22 are formed.

[0139] As shown in FIG. 20( b ), a material guiding section 160 is installed at the lower end of the material injection section 110 in place of the material guiding section 120 .

[0140] 21( a), the material injection unit 110 and the material induction unit 160 are installed on the upper surface of the protrusion forming unit 140. In this state, a first material 151, which will be the source of the first protrusions 21 and the base portion 20a, is injected from the material injection unit 110. The first material 151 flows through a flow path 161 of the material induction unit 160 and fills the recess 141 and the position corresponding to the base portion 20a.

[0141] 21B, the material injection section 110 and the material induction section 160 are separated from the protrusion formation section 140, and the first electrode 20 is extracted from within the protrusion formation section 140. In this way, the first electrode 20 is completed.

[0142] The procedure for forming the first electrode 20 is not limited to the examples shown in FIGS. 19(a) to 21(b), and other procedures may also be used.

[0143] 19(a) to 21(b) are formation procedures when the first material 151 of the first projections 21 and the second material 152 of the second projections 22 are different materials. In contrast, when the first material 151 and the second material 152 are the same material, it is not necessary to form the first projections 21 and the second projections 22 separately, and therefore the first projections 21 and the second projections 22 may be formed simultaneously by filling all of the recesses 141, 142 with one material.

[0144] <Embodiment 2> In embodiment 1, the second protrusions 22 are formed on the upper surface (surface on the negative side of the Z axis) of the base portion 20a of the first electrode 20. In contrast, in embodiment 2, the second protrusions 22 are formed on the base portion 20a so as to penetrate the base portion 20a in the Z axis direction. In plan view, the arrangement positions of the first protrusions 21 and the second protrusions 22 are the same as in embodiment 1.

[0145] FIG. 22A is a cross-sectional view schematically illustrating the load sensor 1 in a no-load state (a state in which no load is applied) according to the second embodiment.

[0146] In embodiment 2, compared to embodiment 1 shown in Figure 2 (a), the second protrusion 22 penetrates the base portion 20a in the Z-axis direction and protrudes toward the second electrode 40 (in the negative Z-axis direction), and the lower surface (the surface on the positive Z-axis side) of the second protrusion 22 and the lower surface (the surface on the positive Z-axis side) of the base portion 20a are included in the same plane.

[0147] In this case as well, in the initial state where no load is applied, only the surface 21 a at the tip of the first protrusion 21 contacts the dielectric 30. Then, when the capacitance between the second electrode 40 and the first electrode 20 changes in accordance with the load, the load is detected based on the potential that reflects this change in capacitance.

[0148] FIG. 22B is a cross-sectional view schematically illustrating deformation of the protrusion when a load exceeding the detection range is applied according to the second embodiment.

[0149] Also in the second embodiment, when the magnitude of the applied load exceeds the detection range, the second protrusion 22 comes into contact with the dielectric 30, and the load applied to the load sensor 1 is also distributed to the second protrusion 22. As a result, even if a load exceeding the detection range is applied, the deformation of the first protrusion 21 is suppressed to within the range of reversible deformation.

[0150] 22(a) and 22(b), in the second embodiment, the second protrusions 22 penetrate the base portion 20a, and therefore the lower surfaces of the second protrusions 22 are supported by the upper surface of the substrate 10. This prevents the second protrusions 22 from sinking into the base portion 20a, as occurs when the second protrusions 22 are formed on the upper surface of the base portion 20a, and makes it easier for the second protrusions 22 to support the load. This further prevents the first protrusions 21 from plastically deforming.

[0151] <Study on Height and Hardness of Primary and Secondary Protrusions> The inventors also performed a simulation similar to that of the first embodiment for the configuration of the second embodiment.

[0152] The inventors set up two comparative examples in this simulation. One comparative example has the same configuration as FIG. 9( a), and two first protrusions 21 are formed on the first electrode 20 in a predetermined range. The other comparative example has four first protrusions 21 formed on the first electrode 20 in a predetermined range, as shown in FIG. 23( a). The configuration and size of the comparative example in FIG. 23( a) are the same as those of the comparative example shown in FIG. 9( a), except for the number of first protrusions 21.

[0153] FIG. 23B is a perspective view schematically illustrating the configuration of the first electrode 20 according to the sixth configuration of the second embodiment.

[0154] In configuration 6, as shown in FIG. 22( a), the second protrusion 22 penetrates the base portion 20a and protrudes in the negative direction of the Z axis, and the lower surface of the second protrusion 22 and the lower surface of the base portion 20a are included in the same plane. In addition, the hardness of the second protrusion 22 is 80 degrees. The configuration and size of configuration 6 are similar to those of configuration 4 shown in FIG. 11( a), except for the position of the lower surface of the base portion 20a and the hardness of the second protrusion 22.

[0155] 24(a) and 24(b) are graphs showing simulation results for the comparative example shown in FIG. 9(a), the comparative example shown in FIG. 23(a), and the configuration 6 of the second embodiment shown in FIG. 23(b).

[0156] 24(a), in the comparative example shown in Fig. 9(a) (two first protrusions 21), the first protrusions 21 underwent plastic deformation when the load increased to approximately 20 N, as indicated by the dashed line, and in the comparative example shown in Fig. 23(a) (four first protrusions 21), the first protrusions 21 underwent plastic deformation when the load increased to approximately 39 N, as indicated by the dashed-dotted line. In the comparative example with four first protrusions 21, the load applied to the load sensor 1 is distributed to each of the first protrusions 21 compared to the comparative example with two first protrusions 21, and therefore it is thought that the load that causes plastic deformation becomes larger.

[0157] In contrast, in configuration 6, as shown by the thick solid line, when the load rises to around L61 and the second protrusion 22 comes into contact with the dielectric 30, the compressive stress then rises more gradually compared to the comparative examples with two and four first protrusions 21, and when the load rises to around 62 N, the first protrusions 21 undergo plastic deformation.

[0158] According to configuration 6, the load is supported by the second protrusions 22 before the first protrusions 21 are significantly compressed. Therefore, in configuration 6, compared to the comparative examples with two and four first protrusions 21, it is thought that the increase in compressive stress in the first protrusions 21 is smoothly alleviated by the second protrusions 22, making the first protrusions 21 less susceptible to plastic deformation. In this way, even when the second protrusions 22 are formed to penetrate the base portion 20a, the load capacity of the load sensor 1 can be increased.

[0159] As shown in Figure 24 (b), in configuration 6, as shown by the thick solid line, the increase in capacitance is more gradual than in the comparative examples with two and four first protrusions 21, so the sensitivity of the load sensor 1 is slightly reduced, but since the protrusions are less likely to undergo plastic deformation, a wide range of loads can be detected.

[0160] <Effects of Second Embodiment> According to the second embodiment, the following effects are achieved.

[0161] 22(a) and 22(b), the first protrusion 21 protrudes from the elastic base portion 20a toward the second electrode 40, and the second protrusion 22 penetrates the base portion 20a and protrudes toward the second electrode 40. The lower surface of the second protrusion 22 and the lower surface of the base portion 20a are included in the same plane.

[0162] According to this configuration, the second protrusions 22 are not supported by the elastic base portion 20a, so when the dielectric 30 on the second electrode 40 side comes into contact with the second protrusions 22 as the load increases, the load can be efficiently received by the second protrusions 22. This makes it possible to more reliably suppress plastic deformation of the first protrusions 21 due to an overload, and to increase the load resistance of the load sensor 1.

[0163] In the configuration of embodiment 1, the thickness of the region of the base portion 20a where the second protrusions 22 are arranged may be smaller than the thickness of other regions of the base portion 20a (regions where neither the first protrusions 21 nor the second protrusions 22 are arranged). That is, the second protrusions 22 protruding toward the second electrode 40 may be formed in recesses formed on the upper surface of the base portion 20a. This makes it less likely that the second protrusions 22 will sink into the base portion 20a when a load is applied to them, making it easier for the second protrusions 22 to support the load. Therefore, compared to the configuration of embodiment 1, plastic deformation of the first protrusions 21 due to an overload can be more reliably suppressed, and the load capacity of the load sensor 1 can be increased.

[0164] <Example of modified protrusion arrangement> In embodiments 1 and 2, the size and arrangement of the first protrusions 21 and second protrusions 22 on the first electrode 20 are not limited to the example shown in FIG. 1 and may be set, for example, as shown in FIGS. 25(a) and 25(b).

[0165] In the example shown in Figures 25(a) and (b), the second protrusions 22 are smaller than the first protrusions 21 in a plan view, and each second protrusion 22 is arranged so as to be surrounded by a plurality of first protrusions 21.

[0166] More specifically, in the cross-sectional area when the first protrusions 21 and the second protrusions 22 are cut along a plane including the upper surface of the base portion 20a, the second protrusions 22 are smaller than the first protrusions 21. Furthermore, each second protrusion 22 is surrounded by a plurality of first protrusions 21 so that the cut surfaces are close to each other.

[0167] In the examples shown in Figures 25(a) and (b), the multiple first protrusions 21 are arranged at positions with n-fold rotational symmetry around one second protrusion 22. In the example shown in Figure 25(a), the multiple first protrusions 21 are arranged at positions with 3-fold rotational symmetry. That is, three first protrusions 21 are arranged at 120° intervals in the circumferential direction with respect to one second protrusion 22. In the example shown in Figure 25(b), the multiple first protrusions 21 are arranged at positions with 4-fold rotational symmetry. That is, four first protrusions 21 are arranged at 90° intervals in the circumferential direction with respect to one second protrusion 22. In Figure 25(b), when the multiple first protrusions 21 are arranged close to each other in a matrix, one second protrusion 22 is arranged so as to fit within an area surrounded by four adjacent first protrusions 21.

[0168] In this way, when the second protrusions 22 are smaller than the first protrusions 21 in a plan view and each second protrusion 22 is surrounded by a plurality of first protrusions 21, in a load sensor 1 having a certain detection area, the second protrusions 22 can be efficiently arranged between the plurality of first protrusions 21 while suppressing a reduction in the number of first protrusions 21 due to the arrangement of the second protrusions 22. This allows the load applied to the load sensor 1 to be efficiently distributed to the first protrusions 21 and the second protrusions 22 while maintaining the detection sensitivity of the load sensor 1 due to the plurality of first protrusions 21, and suppresses plastic deformation of the first protrusions 21 due to an overload.

[0169] Note that if the second protrusions 22 are smaller than the first protrusions 21 in a plan view, the load support force of the second protrusions 22 will also be smaller, and therefore it is preferable to increase the hardness of the second protrusions 22. However, if the second protrusions 22 are conductive and the second range shown in FIG. 7( b) is included in the detection range, increasing the hardness of the second protrusions 22 will reduce the detection sensitivity in the second range. For this reason, it is preferable to set the hardness and size in a plan view of the second protrusions 22 so that the support force and sensitivity of the second protrusions 22 exceed desired values ​​in the second range shown in FIG. 7( b).

[0170] Furthermore, when the multiple first protrusions 21 are arranged at positions that are n-fold rotationally symmetric around one second protrusion 22, it is possible to increase the installation area of ​​the multiple first protrusions 21 and the multiple second protrusions 22 with respect to a certain detection surface of the load sensor 1, and as a result, it is possible to efficiently arrange the multiple first protrusions 21 and the multiple second protrusions 22. Furthermore, since the multiple second protrusions 22 are regularly arranged around the first protrusion 21, it is possible for the multiple second protrusions 22 to uniformly support the detection surface of the load sensor 1.

[0171] From the viewpoint of increasing the detection sensitivity by arranging more first protrusions 21 on a certain detection surface of the load sensor 1, it is preferable that the area of ​​the second protrusions 22 (the area of ​​the cross section when the second protrusions 22 are cut on a plane including the upper surface of the base portion 20a) is smaller than the area of ​​the first protrusions 21 (the area of ​​the cross section when the first protrusions 21 are cut on a plane including the upper surface of the base portion 20a). For example, the area of ​​the second protrusions 22 is set to ½ or less of the area of ​​the first protrusions 21, and more preferably ⅓ or less of the area of ​​the first protrusions 21.

[0172] Furthermore, by arranging two adjacent first protrusions 21 close enough that their deformation when a load is applied is not hindered, and by arranging a second protrusion 22 with an area small enough that it does not hinder the deformation of the first protrusions 21 in a gap formed by the multiple first protrusions 21, the area of ​​the second protrusions 22 can be set to the smallest possible size.

[0173] 26(a) to 28(b) are schematic diagrams for explaining an example of a procedure for forming the first electrode 20 according to embodiment 2. Figures 26(a) to 28(b) show cross sections of each part cut along a plane perpendicular to the XY plane.

[0174] 26( a), compared to FIG. 19( a), a mask plate 170 is further used to form the first electrode 20. A hole 171 penetrating vertically is formed in the mask plate 170 at a position corresponding to the arrangement position of the second protrusion 22. The hole 171 is formed to match the shape of the end of the second protrusion 22 on the negative side of the Z axis.

[0175] 26(b), the mask plates 130 and 170 are fitted into the protrusion forming section 140, and the material injection section 110 and the material guide section 120 are placed on the upper surface of the mask plate 130. In this state, the second material 152 that will become the source of the second protrusions 22 is injected from the material injection section 110. The second material 152 fills the recesses 142 and the holes 171.

[0176] As shown in Fig. 27(a), material injection section 110, material guiding section 120, and mask plate 130 are separated from mask plate 170 and protrusion forming section 140. Thereafter, mask plate 170 is separated from protrusion forming section 140, thereby forming second protrusions 22, as shown in Fig. 27(b). Then, material guiding section 160 is installed at the lower end of material injection section 110 in place of material guiding section 120.

[0177] 28( a), the material injection unit 110 and the material induction unit 160 are installed on the upper surface of the protrusion forming unit 140. In this state, a first material 151, which will be the source of the first protrusions 21 and the base portion 20a, is injected from the material injection unit 110. The first material 151 flows through a flow path 161 of the material induction unit 160 and fills the recess 141 and the position corresponding to the base portion 20a.

[0178] 28(b), the material injection section 110 and the material guide section 160 are separated from the protrusion formation section 140, and the first electrode 20 is extracted from within the protrusion formation section 140. In this way, the first electrode 20 is completed.

[0179] The procedure for forming the first electrode 20 in the second embodiment is not limited to the examples shown in FIGS. 26(a) to 28(b), and other procedures may also be used.

[0180] Third Embodiment In the second embodiment, the second protrusions 22 are formed on the first electrode 20. In contrast, in the third embodiment, the second protrusions 61 are formed on the second electrode 40. In a plan view, the arrangement positions of the first protrusions 21 and the second protrusions 61 are the same as those in the first embodiment.

[0181] FIG. 29A is a cross-sectional view schematically illustrating the load sensor 1 in a no-load state (a state in which no load is applied) according to the third embodiment.

[0182] In the third embodiment, compared to the first embodiment shown in FIG. 2( a), only the first protrusions 21 are formed on the first electrode 20, and a plurality of second protrusions 61 are formed on the opposing surface (the surface on the positive side of the Z axis) of the second electrode 40. A surface 61a parallel to the X-Y plane is formed at the tip of the second protrusion 61. The second protrusions 61 are made of a non-conductive elastic material. In the third embodiment, a support portion 70 having a higher elastic modulus than the base portion 20a is provided in a region of the base portion 20a opposing the tip of the second protrusion 61. The support portion 70 is made of, for example, an insulating material.

[0183] In this case as well, in the initial state where no load is applied, only the surface 21 a at the tip of the first protrusion 21 contacts the dielectric 30. Then, when the capacitance between the second electrode 40 and the first electrode 20 changes in accordance with the load, the load is detected based on the potential that reflects this change in capacitance.

[0184] FIG. 29B is a cross-sectional view schematically illustrating deformation of the protrusion when a load exceeding the detection range is applied according to the third embodiment.

[0185] In the third embodiment, when the magnitude of the applied load exceeds the detection range, the second protrusion 61 comes into contact with the support portion 70, and the load applied to the load sensor 1 is also distributed to the second protrusion 61. As a result, even if a load exceeding the detection range is applied, the deformation of the first protrusion 21 is suppressed to within the range of reversible deformation.

[0186] 29( a) and 29(b), in the third embodiment, as a load is applied, the tip of the second protrusion 61 abuts against the support portion 70, which has a higher elastic modulus than the base portion 20a. When the second protrusion 61 abuts against the support portion 70 as the load increases, the tip of the second protrusion 61 is less likely to sink more than necessary into the base portion 20a, and the load is stably supported by the second protrusion 61. Therefore, plastic deformation of the first protrusion 21 can be further suppressed.

[0187] <Effects of Third Embodiment> According to the third embodiment, the following effects are achieved.

[0188] 29( a) and 29(b), the first electrode 20 has a plurality of elastic, conductive first protrusions 21. The second electrode 40 faces the first electrode 20 across the plurality of first protrusions 21. The plurality of second protrusions 61 are arranged on the opposing surface of the second electrode 40 so as to protrude into a space where the first protrusions 21 are not present, and have elasticity and insulation properties. The dielectric 30 is arranged on the opposing surface 41 of the second electrode 40. In a no-load state, the tips of the plurality of first protrusions 21 contact the dielectric 30, and the tips of the plurality of second protrusions 61 are spaced apart from the first electrode 20.

[0189] According to this configuration, the second protrusions 61 come into contact with the support portion 70 on the first electrode 20 side as the load increases, so that even if a large load is suddenly applied to the load sensor 1, the stress generated in each of the multiple first protrusions 21 is alleviated. This makes it difficult for the stress generated in each first protrusion 21 to exceed the yield stress, and it is possible to suppress plastic deformation of each first protrusion 21. Furthermore, because the second protrusions 61 are disposed on a second electrode 40 separate from the first electrode 20 on which the first protrusions 21 are disposed, it is easy to dispose the second protrusions 61 in the gaps between the first protrusions 21. This eliminates the need to reduce the number of first protrusions 21 in order to dispose the second protrusions 61, and therefore the detection sensitivity of the load sensor 1 can be maintained.

[0190] The first projection 21 protrudes from the elastic base portion 20a, and a support portion 70 having a higher elastic modulus than the base portion 20a is disposed in an area facing the tip of the second projection 61.

[0191] Because the support portion 70 is harder than the base portion 20a, when the second protrusion 61 comes into contact with the support portion 70 in response to an increase in load, the second protrusion 61 can efficiently receive the load. This makes it possible to more reliably suppress plastic deformation of the first protrusion 21 due to an overload, and to increase the load resistance of the load sensor 1.

[0192] 29( a) and 29(b), the second protrusion 61 is formed on the lower surface (surface on the positive side of the Z axis) of the second electrode 40, but the second protrusion 61 may penetrate the second electrode 40, and the upper surface (surface on the negative side of the Z axis) of the second protrusion 61 and the upper surface (surface on the negative side of the Z axis) of the second electrode 40 may be included in the same plane. Also, the upper surface of the second protrusion 22 may be positioned between the upper and lower surfaces of the second electrode 40. That is, the second protrusion 61 may be formed in a recess formed in the lower surface of the second electrode 40, protruding toward the first electrode 20.

[0193] Furthermore, the support portion 70 is not limited to being made of an insulating material, and may be made of a conductive material.

[0194] <Modification of the Shape of the Protrusion> The configuration of the protrusion provided on the second electrode 40 side is not limited to the configuration of embodiment 3 shown in FIG. 29( a), and may be, for example, the configuration shown in FIGS. 30( a) and 30(b).

[0195] 30(a), unlike the third embodiment, a plurality of third protrusions 62 having a height lower than that of the second protrusions 61 are formed on the opposing surface (the surface on the positive side of the Z axis) of the second electrode 40. A surface 62a parallel to the X-Y plane is formed at the tip of the third protrusions 62. Like the second protrusions 61, the third protrusions 62 are made of a non-conductive elastic material. In a plan view, the second protrusions 61 and the third protrusions 62 are, for example, arranged alternately adjacent to each other on the opposing surface of the second electrode 40. A support portion 70 is also arranged in a region of the base portion 20a opposing the tips of the third protrusions 62.

[0196] In this case as well, in the initial state where no load is applied, only the surface 21 a at the tip of the first protrusion 21 contacts the dielectric 30. Then, as the load increases, the state where only the first protrusion 21 contacts the dielectric 30 transitions to a state where the second protrusion 61 also contacts the support portion 70, and then to a state where the third protrusion 62 also contacts the support portion 70. As a result, similar to the configuration 3 shown in FIG. 10( b), the number of protrusions contacting the first electrode 20 side and the second electrode 40 side can be increased as the load increases, and plastic deformation of each protrusion can be further suppressed.

[0197] 30(b), the support portion 70 is omitted compared to the third embodiment. In this case, as the load increases, the tip of the second protrusion 61 tends to sink into the base portion 20a, and the supporting force of the second protrusion 61 decreases slightly. Therefore, in order to more stably support the load with the second protrusion 61, it is preferable to arrange the support portion 70 at the contact position of the second protrusion 61, as in the third embodiment.

[0198] <Other Modifications> The configurations of the load sensor 1 and the load detection device 2 can be modified in various ways other than those described in the above embodiment.

[0199] In the above-described first and second embodiments, surfaces 21a, 22a are formed at the tips of the first protrusion 21 and the second protrusion 22, but the tips of the first protrusion 21 and the second protrusion 22 may be pointed. Similarly, in the configuration 3 shown in Fig. 10(b), the tip of the third protrusion 23 may be pointed. In the third embodiment and the modified examples shown in Figs. 30(a) and (b), the tip of the second protrusion 61 may be pointed, and in the modified example shown in Fig. 30(a), the tip of the third protrusion 62 may be pointed.

[0200] In the above-described first and second embodiments, the first protrusions 21 may be configured separately from the base portion 20a, similar to the second protrusions 22 in the above-described first and second embodiments, and in the above-described first embodiment, the second protrusions 22 may be formed integrally with the base portion 20a, similar to the first protrusions 21 in the above-described first embodiment. Also, in the first embodiment, the first electrode 20 may be configured by overlapping and integrating the first protrusions 21 and the second protrusions 22 with a metal electrode.

[0201] In the above-described first and second embodiments, the first electrode 20 includes a plurality of first protrusions 21 and a plurality of second protrusions 22, but the first electrode 20 may include only one first protrusion 21 and the first electrode 20 may include only one second protrusion 22. In the above-described third embodiment, the first electrode 20 includes a plurality of first protrusions 21 and the second electrode 40 includes a plurality of second protrusions 61, but the first electrode 20 may include only one first protrusion 21 and the second electrode 40 may include only one second protrusion 61.

[0202] In the above-described first and second embodiments, the number of first protrusions 21 and the number of second protrusions 22 do not have to be the same. In order to suppress plastic deformation of the first protrusions 21, it is preferable that the number of second protrusions 22 is greater than the number of first protrusions 21. In the above-described third embodiment, the number of first protrusions 21 and the number of second protrusions 61 do not have to be the same. In order to suppress plastic deformation of the first protrusions 21, it is preferable that the number of second protrusions 61 is greater than the number of first protrusions 21.

[0203] In the above embodiment, the first protrusion 21 and the second protrusion 22, 61 may have a ridge shape that is long in the X-axis direction or the Y-axis direction. In this case, the ridge shape may be a prismatic shape or a semi-cylindrical shape.

[0204] In the above embodiment, the first protrusion 21 and the second protrusions 22, 61 are arranged on the upper surface of the base portion 20a so as to be aligned at a constant pitch in the X-axis direction and the Y-axis direction, but the pitch of the first protrusion 21 and the second protrusions 22, 61 does not necessarily have to be constant.

[0205] In the above embodiment, the elastic material forming the first protrusion 21 and the second protrusions 22, 61 may be a material other than silicone rubber. The elastic material forming the first protrusion 21 and the elastic material forming the second protrusions 22, 61 may be different materials.

[0206] When three types of protrusions are formed, as in configuration 3 shown in Fig. 10(b) and the modified example shown in Fig. 30(a), the hardness of the three types of protrusions may be different from one another. For example, the hardness of the first protrusions 21 and the second protrusions 22, 61 may be set to 40 degrees, and the hardness of the third protrusions 23, 62 may be set to 50 degrees. In this way, if the hardness of the lower protrusions is set higher than the hardness of the higher protrusions, it can be expected that the effect of suppressing plastic deformation of the protrusions will be further improved.

[0207] As in Figures 15(a) and (b), in embodiment 2, the height of the first protrusion 21 and the height of the second protrusion 22 may be set to be equal to each other by deforming the shapes of the base portion 20a and the second electrode 40, and in embodiment 3, the height of the first protrusion 21 and the height of the second protrusion 61 may be set to be equal to each other by deforming the shapes of the base portion 20a and the second electrode 40.

[0208] 16(a), in the second embodiment, the first protrusion 21 and the second protrusion 22 may have similar shapes, and the first protrusion 21 may be larger than the second protrusion 22, and in the third embodiment, the first protrusion 21 and the second protrusion 61 may have similar shapes, and the first protrusion 21 may be larger than the second protrusion 61. As in Fig. 16(b), in the second embodiment, the shapes of the first protrusion 21 and the second protrusion 22 may be set based on a hemispherical shape, and in the third embodiment, the shapes of the first protrusion 21 and the second protrusion 61 may be set based on a hemispherical shape.

[0209] Also in the second and third embodiments, the first protrusions 21 and the second protrusions 22, 61 may have a conical, pyramidal or truncated pyramidal shape. When the second protrusions 22, 61 are non-conductive, the second protrusions 22, 61 may have a columnar shape with a constant cross-sectional area toward the top.

[0210] In the modified examples of the protrusion arrangement shown in FIGS. 25(a) and 25(b), the value of n, which indicates the number of rotational symmetries, is not limited to 3 or 4 as described above, but may be 5 or more.

[0211] As in Figures 17(a) to 18(b), in embodiment 2, the planar arrangement of the first protrusion 21 and the second protrusion 22 may be set, and in embodiment 3, the planar arrangement of the first protrusion 21 and the second protrusion 61 may be set.

[0212] A load sensor system may be configured by arranging a plurality of the load sensors of the above embodiment in a planar direction. In this case, when a load is applied across the upper surfaces of the substrates 50 of the plurality of load sensors 1, the control circuit 2b (see FIG. 8) adds up the loads calculated by the plurality of load sensors 1, and detects the load applied to the upper surfaces of the plurality of load sensors 1.

[0213] 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.

[0214] <Supplementary Notes> The above description of the embodiments discloses the following techniques.

[0215] (Technology 1) A load sensor comprising: a first electrode having a plurality of elastic conductive protrusions on the same surface; a second electrode facing the first electrode across the plurality of protrusions; and a dielectric disposed on the opposing surface of the second electrode; wherein the number of protrusions contacting the dielectric increases as the load increases.

[0216] According to this technology, the number of protrusions that come into contact with the dielectric increases as the load increases, so even if a large load is suddenly applied to the load sensor, the stress generated in each of the multiple protrusions is alleviated. This makes it difficult for the stress generated in each protrusion to exceed the yield stress, and it is possible to suppress the occurrence of plastic deformation in each protrusion.

[0217] (Technology 2) The load sensor according to Technology 1, wherein the plurality of protrusions include a plurality of first protrusions and a plurality of second protrusions, and in a no-load state, tips of the plurality of first protrusions are in contact with the dielectric, and tips of the plurality of second protrusions are spaced apart from the dielectric.

[0218] According to this technology, an increase in load causes a transition from a state in which the multiple first projections are in contact with the dielectric to a state in which the multiple second projections are also in contact with the dielectric, thereby making it possible to increase the number of projections in contact with the dielectric as the load increases.

[0219] (Technology 3) In the load sensor described in Technology 2, the dielectric is formed on the planar opposing surface, the multiple first protrusions and the multiple second protrusions protrude from the same reference plane on the first electrode, and the height of the multiple second protrusions is lower than the height of the multiple first protrusions.

[0220] According to this technique, with a simple configuration, the number of protrusions that come into contact with the dielectric can be increased in response to an increase in load.

[0221] (Technology 4) The load sensor according to Technology 2 or 3, wherein the plurality of first protrusions and the plurality of second protrusions are arranged such that two of the second protrusions sandwich at least one of the first protrusions.

[0222] According to this technology, since the second protrusions are present on both sides of at least one first protrusion, when the dielectric comes into contact with the second protrusions due to an increase in load, the second electrode and the dielectric can be supported in a balanced manner by the first protrusions and the second protrusions, thereby suppressing the occurrence of an unbalanced load and improving the load detection accuracy.

[0223] (Technology 5) The load sensor according to any one of Technologies 2 to 4, wherein the second protrusion has a higher elastic modulus than the first protrusion.

[0224] According to this technique, the load is more reliably supported by the second protrusion, thereby increasing the load resistance of the load sensor.

[0225] (Technology 6) A load sensor according to any one of technologies 2 to 5, characterized in that the cross-sectional areas of the plurality of first protrusions and the plurality of second protrusions become smaller toward the tips, and the contact area between the dielectric and the first protrusions when no load is applied is smaller than the contact area between the dielectric and the second protrusions when the dielectric begins to contact the second protrusions.

[0226] According to this technology, the first protrusions, which come into contact with the dielectric first, begin contacting the dielectric over a small area, resulting in a larger change in contact area in response to an increase in load, and a faster increase in capacitance. This increases the sensitivity of the load sensor when a load begins to be applied. Furthermore, the second protrusions, which come into contact with the dielectric later, begin contacting the dielectric over a larger area, and therefore can absorb the applied load even when a large load is suddenly applied, thereby preventing the protrusions from undergoing plastic deformation.

[0227] (Technology 7) The load sensor according to Technology 6, characterized in that a first plane is formed at the tip of each of the plurality of first protrusions, a second plane is formed at the tip of each of the plurality of second protrusions, and the area of ​​the first plane is smaller than the area of ​​the second plane.

[0228] According to this technique, when the application of the load starts, the contact area between the dielectric and the primary projections increases gradually, which can further improve the linearity of the sensitivity characteristics.

[0229] (Technology 8) The load sensor according to any one of Technologies 2 to 7, wherein the second protrusion comes into contact with the dielectric when a load smaller than a range of loads that generates a yield stress in the first protrusion is applied.

[0230] According to this technique, yield stress is less likely to occur in the primary projections, and plastic deformation of the primary projections can be appropriately suppressed.

[0231] (Technology 9) The load sensor according to any one of technologies 2 to 8, wherein the plurality of protrusions further include a plurality of third protrusions, and in a no-load state, the tips of the plurality of third protrusions are further away from the dielectric than the tips of the plurality of second protrusions.

[0232] According to this technology, an increase in load causes a transition from a state in which the multiple first and second projections are in contact with the dielectric to a state in which the multiple third projections are also in contact with the dielectric, thereby making it possible to increase the number of projections in contact with the dielectric as the load increases, and further suppressing the occurrence of plastic deformation in each projection.

[0233] (Technology 10) A load sensor according to any one of technologies 1 to 9, characterized in that: the dielectric is formed on the planar opposing surface; the plurality of protrusions protrude from the same reference surface on the first electrode; a plurality of rows each including a plurality of the protrusions are arranged; and the height of the protrusions in each row is selectively set to any one of a plurality of heights.

[0234] According to this technique, the first electrode can be easily formed even when the size of the protrusion is small.

[0235] (Technology 11) The load sensor according to any one of Technologies 1 to 10, wherein the plurality of protrusions have cross-sectional areas that decrease toward their tips.

[0236] According to this technology, the contact area between the protrusion and the dielectric increases as the load increases, thereby improving the linearity of the sensitivity characteristics.

[0237] (Technology 12) In the load sensor described in Technology 5, the first protrusion protrudes from an elastic base portion toward the second electrode, the second protrusion protrudes through the base portion toward the second electrode, and a lower surface of the second protrusion and a lower surface of the base portion are included in the same plane.

[0238] According to this technology, since the second protrusions are not supported by the elastic base portion, when the dielectric on the second electrode side comes into contact with the second protrusions as the load increases, the second protrusions can efficiently absorb the load. This makes it possible to more reliably suppress plastic deformation of the first protrusions due to excessive loads, and to increase the load capacity of the load sensor.

[0239] (Technology 13) The load sensor according to any one of technologies 2 to 9 and 12, wherein, in a plan view, the second protrusions are smaller than the first protrusions, and each of the second protrusions is surrounded by a plurality of the first protrusions.

[0240] According to this technology, in a load sensor having a certain detection area, the second protrusions can be efficiently arranged among a plurality of first protrusions while suppressing a decrease in the number of first protrusions due to the arrangement of the second protrusions. As a result, the load applied to the load sensor can be efficiently distributed to the first and second protrusions while suppressing a decrease in load detection sensitivity, and plastic deformation of the first protrusions can be suppressed.

[0241] (Technology 14) In the load sensor described in Technology 13, the plurality of first protrusions arranged around the one second protrusion are arranged at positions rotationally symmetrical with respect to the one second protrusion.

[0242] This technology allows the installation area of ​​the multiple first protrusions and multiple second protrusions to be increased relative to a given detection surface of the load sensor, resulting in efficient arrangement of the multiple first protrusions and multiple second protrusions. Furthermore, since the multiple second protrusions are regularly arranged around the first protrusions, the detection surface of the load sensor can be uniformly supported by the multiple second protrusions.

[0243] (Technology 15) A load sensor comprising: a first electrode having a plurality of elastic, conductive first protrusions; a second electrode facing the first electrode across the plurality of first protrusions; a plurality of elastic, insulating second protrusions arranged on the opposing surface of the second electrode so as to protrude into a space where the first protrusions are not present; and a dielectric arranged on the opposing surface of the second electrode; wherein, in a no-load state, tips of the plurality of first protrusions are in contact with the dielectric and tips of the plurality of second protrusions are spaced apart from the first electrode.

[0244] According to this technology, the second protrusions contact the first electrode as the load increases, so that even if a large load is suddenly applied to the load sensor, the stress generated in each of the multiple first protrusions is alleviated. This makes it difficult for the stress generated in each first protrusion to exceed the yield stress, thereby suppressing plastic deformation of each first protrusion. Furthermore, because the second protrusions are disposed on a second electrode separate from the first electrode on which the first protrusions are disposed, it is easy to arrange the second protrusions in the gaps between the first protrusions. This eliminates the need to reduce the number of first protrusions in order to accommodate the second protrusions, thereby maintaining the detection sensitivity of the load sensor.

[0245] (Technology 16) The load sensor according to Technology 15, wherein the first protrusion protrudes from an elastic base portion, and a support portion having a higher elastic modulus than the base portion is disposed in an area facing the tip of the second protrusion.

[0246] According to this technology, because the support portion is harder than the base portion, when the second electrode comes into contact with the support portion in response to an increase in load, the second protrusion can efficiently absorb the load. This makes it possible to more reliably suppress plastic deformation of the first protrusion due to an excessive load, thereby increasing the load capacity of the load sensor.

[0247] (Technology 17) A load detection device comprising: the load sensor according to any one of technologies 1 to 16; and a control unit that detects a load based on the electrostatic capacitance between the first electrode and the second electrode.

[0248] This technology prevents plastic deformation of each protrusion in the load sensor, allowing the control unit to continue to properly detect the load even after a large load is suddenly applied to the load sensor.

[0249] REFERENCE SIGNS LIST 1 Load sensor 2 Load detection device 2b Control circuit (controller) 20 First electrode 20a Base portion 21 First protrusion (protrusion) 21a Surface (tip, first plane) 22 Second protrusion (protrusion) 22a Surface (tip, second plane) 23 Third protrusion (protrusion) 23a Surface (tip) 30 Dielectric 40 Second electrode 41 Opposing surface 61 Second protrusion 62 Third protrusion (second protrusion) 70 Support portion

Claims

1. A load sensor comprising: a first electrode having a number of elastic, conductive protrusions on the same surface; a second electrode facing the first electrode across the protrusions; and a dielectric arranged on the opposing surface of the second electrode, wherein the number of protrusions in contact with the dielectric increases as the load increases.

2. A load sensor as described in claim 1, wherein the plurality of protrusions include a plurality of first protrusions and a plurality of second protrusions, and in a no-load state, the tips of the plurality of first protrusions are in contact with the dielectric material, and the tips of the plurality of second protrusions are spaced apart from the dielectric material.

3. A load sensor as described in claim 2, characterized in that the dielectric is formed on the planar opposing surface, the multiple first protrusions and the multiple second protrusions protrude from the same reference plane on the first electrode, and the height of the multiple second protrusions is lower than the height of the multiple first protrusions.

4. A load sensor as claimed in claim 2, characterized in that the plurality of first protrusions and the plurality of second protrusions are arranged such that two of the second protrusions sandwich at least one of the first protrusions.

5. A load sensor according to claim 2, characterized in that the elastic modulus of said second projection is higher than the elastic modulus of said first projection.

6. A load sensor as described in claim 2, wherein the cross-sectional area of ​​the multiple first protrusions and the multiple second protrusions decreases toward the tip, and the contact area between the dielectric and the first protrusions when no load is applied is smaller than the contact area between the dielectric and the second protrusions when the dielectric begins to contact the second protrusions.

7. A load sensor as claimed in claim 6, characterized in that a first plane is formed at the tips of the plurality of first protrusions, a second plane is formed at the tips of the plurality of second protrusions, and the area of ​​the first plane is smaller than the area of ​​the second plane.

8. A load sensor according to claim 2, characterized in that the second projection comes into contact with the dielectric material when a load smaller than the range of loads that produces a yield stress in the first projection is applied.

9. A load sensor as described in claim 2, wherein the plurality of protrusions further include a plurality of third protrusions, and in a no-load state, the tips of the plurality of third protrusions are further away from the dielectric than the tips of the plurality of second protrusions.

10. A load sensor as described in claim 1, characterized in that: the dielectric is formed on the planar opposing surface; the multiple protrusions protrude from the same reference surface on the first electrode; a plurality of rows each including a plurality of the protrusions are arranged; and the height of the protrusions in each row is selectively set to any one of a plurality of heights.

11. The load sensor according to claim 1, wherein the cross-sectional area of ​​the plurality of protrusions decreases toward the tip.

12. A load sensor as described in claim 5, characterized in that the first protrusion protrudes from an elastic base portion toward the second electrode, the second protrusion protrudes through the base portion toward the second electrode, and the lower surface of the second protrusion and the lower surface of the base portion are included in the same plane.

13. A load sensor according to claim 2, characterized in that, in a plan view, the second protrusions are smaller than the first protrusions, and each of the second protrusions is surrounded by a plurality of the first protrusions.

14. A load sensor as described in claim 13, characterized in that the multiple first protrusions arranged around the one second protrusion are arranged in rotationally symmetric positions with the one second protrusion as the center.

15. A load sensor comprising: a first electrode having a plurality of elastic conductive first protrusions; a second electrode facing the first electrode across the plurality of first protrusions; a plurality of elastic insulating second protrusions arranged on the opposing surface of the second electrode so as to protrude into a space where the first protrusions are not present; and a dielectric arranged on the opposing surface of the second electrode, wherein in a no-load state, tips of the plurality of first protrusions are in contact with the dielectric and tips of the plurality of second protrusions are spaced from the first electrode.

16. A load sensor as claimed in claim 15, characterized in that the first projection protrudes from an elastic base portion, and a support portion having a higher elasticity than the base portion is disposed in an area facing the tip of the second projection.

17. A load detection device comprising: a load sensor according to any one of claims 1 to 16; and a control unit that detects a load based on the electrostatic capacitance between the first electrode and the second electrode.