Load sensor

Abstract

Provided is a load sensor capable of accurately detecting a load even in a low load range. A load sensor (1) is provided with: a first base member (11); a second base member (21) disposed so as to face the first base member (11); a conductive elastic body (12) formed on a facing surface of the first base member (11); and a conductor wire (31) that is covered by a dielectric body (32) and is disposed so as to overlap the conductive elastic body (12). The thickness and the elastic modulus of the conductive elastic body (12) are adjusted such that an FC curve has an overall upward convex shape, the FC curve indicating the relationship between a load for bringing the first base member (11) and the second base member (21) close to each other and an electrostatic capacitance between the conductor wire (31) and the conductive elastic body (12).

Description

Load Sensor

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

[0002] Load sensors are widely used in fields such as industrial equipment, robots, and vehicles. In recent years, with the advancement of computer-based control technology and improvements in design, there has been progress in the development of electronic devices that make use of a variety of free-form surfaces, such as humanoid robots and automobile interior fittings. Accordingly, there is a demand for high-performance load sensors to be attached to each free-form surface.

[0003] The following Patent Document 1 describes a load sensor (pressure-sensitive element) in which a linear second conductive member coated with a dielectric is sandwiched between a first conductive member and a substrate.

[0004] International Publication No. 2018 / 096901

[0005] It is desirable for a load sensor to be able to accurately detect load even in a relatively low load range. However, in the load sensor configured as described above, the FC curve showing the relationship between load and capacitance tends to have a downward convex shape in the low load range near zero. In this case, in the low load range, the change in capacitance relative to a change in load becomes quite small, making it difficult to accurately detect the load.

[0006] In view of the above problem, an object of the present disclosure is to provide a load sensor that can accurately detect load even in a low load range.

[0007] A main aspect of the present disclosure relates to a load sensor. The load sensor according to this aspect includes a first base member, a second base member disposed opposite the first base member, a conductive elastic body formed on the opposing surface of the first base member, and a conductor wire coated with a dielectric and disposed over the conductive elastic body. The thickness and elastic modulus of the conductive elastic body are adjusted so that an FC curve showing the relationship between a load that brings the first base member and the second base member closer together and the capacitance between the conductor wire and the conductive elastic body has an upward convex shape throughout.

[0008] According to the load sensor of this aspect, since the FC curve has an upward convex shape throughout, the change in capacitance relative to the change in load can be made large in the low load range, and therefore the load can be accurately detected even in the low load range.

[0009] As described above, the load sensor of the present disclosure can provide a load sensor that can accurately detect loads even in a low load range.

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

[0011] FIG. 1A is a diagram schematically illustrating the configuration of a structure in a manufacturing process according to an embodiment. FIG. 1B is a diagram schematically illustrating the configuration of a structure in a manufacturing process according to an embodiment. FIG. 2A is a diagram schematically illustrating the configuration of a structure in a manufacturing process according to an embodiment. FIG. 2B is a diagram schematically illustrating the configuration of a second base member according to an embodiment. FIG. 3 is a perspective view schematically illustrating the configuration of a load sensor according to an embodiment. FIG. 4A is a diagram schematically illustrating a cross section of a load sensor cut along a plane parallel to the X-Z plane, near the intersection of a conductive elastic body and a wire. FIG. 4B is a diagram schematically illustrating a cross section of a load sensor cut along a plane parallel to the X-Z plane, near the intersection of a conductive elastic body and a wire. FIG. 5A is a diagram illustrating an example of an FC curve showing the relationship between load and capacitance. FIG. 5B is a diagram illustrating another example of an FC curve showing the relationship between load and capacitance. FIG. 6 is a diagram schematically illustrating the configuration of a load sensor used in a simulation to verify the influence of the thickness and elastic modulus of a conductive elastic body on the shape of the FC curve, according to an embodiment. 7A is a graph showing the results of a simulation of an FC curve when the thickness of the conductive elastic body is fixed and the elastic modulus of the conductive elastic body is changed. FIG. 7B is a graph showing the results of a simulation of an FC curve when the thickness of the conductive elastic body is fixed and the elastic modulus of the conductive elastic body is changed. FIG. 8A is a graph showing the results of a simulation of an FC curve and an inflection point when the upper limits of the thickness and elastic modulus of the conductive elastic body are combined. FIG. 8B is a graph showing the results of a simulation of an FC curve when the thickness and elastic modulus of the conductive elastic body are set such that the FC curve has an upward convex shape throughout. FIG. 9A is a graph showing the results of a simulation of an upper limit of the elastic modulus of the conductive elastic body relative to the thickness of the conductive elastic body when the FC curve has an upward convex shape throughout according to the FC curve shape criteria of the embodiment. FIG. 9B is a graph showing the range of combinations of film thickness and elastic modulus that results in the FC curve having an upward convex shape throughout, by setting a correlation curve corresponding to the relationship between the film thickness and elastic modulus of the conductive elastic body in FIG. 9A.

[0012] The load sensor according to the present disclosure is applicable to a load sensor in a management system or electronic device that performs processing in response to an applied load.

[0013] Examples of management systems include inventory management systems, driver monitoring systems, coaching management systems, security management systems, and nursing care / childcare management systems.

[0014] In an inventory management system, for example, a load sensor installed on a stock shelf detects the weight of the stock piled up, and detects the type and number of products on the stock shelf. This allows for efficient inventory management and labor savings in stores, factories, warehouses, etc. Furthermore, a load sensor installed inside a refrigerator detects the weight of food in the refrigerator, and detects the type, number, and amount of food in the refrigerator. This allows for automatic menu suggestions using the food in the refrigerator.

[0015] In a driver monitoring system, for example, a load sensor provided in the steering device of a moving body such as an automobile monitors the load distribution (e.g., grip force, grip position, and pedal force) of the driver relative to the steering device. Also, a load sensor provided in the vehicle seat monitors the load distribution (e.g., center of gravity position) of the driver relative to the vehicle seat while seated. This allows feedback of the driver's driving state (drowsiness, psychological state, etc.).

[0016] In a coaching management system, for example, load sensors installed in the bottom of shoes monitor the load distribution on the soles of the feet, which can correct or guide the wearer to an appropriate walking or running state.

[0017] In a security management system, for example, load sensors installed on the floor detect the load distribution as a person passes through, and detect the person's weight, stride length, passing speed, shoe sole pattern, etc. By comparing this detected information with data, it becomes possible to identify the person who has passed through.

[0018] In a caregiving / childcare management system, for example, load sensors installed on bedding and toilet seats monitor the distribution of load on the human body relative to the bedding and toilet seat. This makes it possible to estimate what actions the person is about to take in relation to the position of the bedding and toilet seat and prevent falls.

[0019] Examples of electronic devices include in-vehicle devices (car navigation systems, audio equipment, etc.), home appliances (electric kettles, induction cooking heaters, etc.), smartphones, electronic paper, electronic book readers, PC (personal computer) keyboards, game controllers, smart watches, wireless earphones, touch panels, electronic pens, penlights, luminous clothing, musical instruments, etc. In electronic devices, a load sensor is provided in an input unit that receives input from a user.

[0020] The load sensor in the following embodiments is a capacitance-type load sensor that is typically provided in the load sensors of the management systems and electronic devices described above. Such load sensors are also sometimes referred to as "capacitive pressure-sensitive sensor elements," "capacitive pressure detection sensor elements," "pressure-sensitive switch elements," etc. The load sensors in the following embodiments are connected to a detection circuit, and the load sensor and the detection circuit constitute a load detection device. The following embodiments are examples of the present disclosure, and the present disclosure is not limited to the following embodiments in any way.

[0021] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. For convenience, X, Y, and Z axes, which are orthogonal to each other, are indicated in some drawings. The Z axis direction is the height direction of the load sensor 1.

[0022] FIG. 1A is a diagram schematically illustrating the configuration of a structure 1a in a manufacturing process according to an embodiment.

[0023] The structure 1 a includes a first base member 11 , a plurality of conductive elastic bodies 12 , and a plurality of wirings 13 .

[0024] A plurality of conductive elastic bodies 12 are provided on the opposing surface 11a (the surface on the negative side of the Z axis) of the first base member 11. Wiring 13 is connected to each of the plurality of conductive elastic bodies 12. Here, three conductive elastic bodies 12 are formed on the opposing surface 11a. The number of conductive elastic bodies 12 provided on the opposing surface 11a is not limited to this.

[0025] The first base member 11 is an elastic, flat-plate-like member. The first base member 11 has a rectangular shape in a plan view. The thickness of the first base member 11 is constant. When the thickness of the first base member 11 is small, the first base member 11 is sometimes called a sheet member or a film member.

[0026] The first base member 11 is insulating and is made of, for example, a non-conductive resin material or a non-conductive rubber material. The resin material used for the first base member 11 is, for example, at least one resin material selected from the group consisting of styrene-based resins, silicone-based resins (e.g., polydimethylpolysiloxane (PDMS)), acrylic-based resins, rotaxane-based resins, and urethane-based resins. The rubber material used for the first base member 11 is, for example, at least one rubber material selected from the group consisting of silicone rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, polyisobutylene, ethylene propylene rubber, chlorosulfonated polyethylene, acrylic rubber, fluororubber, epichlorohydrin rubber, urethane rubber, and natural rubber.

[0027] The thickness of the first base member 11 is set to, for example, 0.02 mm or more and 1 mm or less. The elastic modulus of the first base member 11 is set to, for example, 1 MPa or more and 3 MPa or less. The hardness (rubber A hardness) of the first base member 11 is set to, for example, 10 degrees or more and 70 degrees or less.

[0028] The conductive elastic bodies 12 are formed on the opposing surface 11a of the first base member 11 so as to extend in a first direction (X-axis direction). The conductive elastic bodies 12 are elastic, conductive members. Each conductive elastic body 12 has a strip-like shape that is long in the first direction (X-axis direction) and is arranged so as to extend in the first direction (X-axis direction). That is, the long sides of the conductive elastic bodies 12 are parallel to the X-axis. The three conductive elastic bodies 12 have the same width, length, and thickness. A predetermined gap is provided between adjacent conductive elastic bodies 12. One end of the wiring 13 is connected to the conductive elastic bodies 12, and the other end of the wiring 13 is connected to the detection circuit.

[0029] The conductive elastic body 12 is formed on the opposing surface 11a of the first base member 11 by a printing method such as screen printing, gravure printing, flexographic printing, offset printing, or gravure offset printing. These printing methods allow the conductive elastic body 12 to be formed with a predetermined thickness on the opposing surface 11a of the first base member 11. However, the method for forming the conductive elastic body 12 is not limited to the printing method.

[0030] The conductive elastic body 12 is made of a resin material with a conductive filler dispersed therein, or a rubber material with a conductive filler dispersed therein.

[0031] The resin material used for the conductive elastic body 12 is, like the resin material used for the first base member 11 described above, at least one resin material selected from the group consisting of styrene-based resins, silicone-based resins (polydimethylpolysiloxane (e.g., PDMS)), acrylic-based resins, rotaxane-based resins, and urethane-based resins. The rubber material used for the conductive elastic body 12 is, like the rubber material used for the first base member 11 described above, at least one rubber material selected from the group consisting of silicone rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, polyisobutylene, ethylene propylene rubber, chlorosulfonated polyethylene, acrylic rubber, fluororubber, epichlorohydrin rubber, urethane rubber, and natural rubber.

[0032] The conductive filler used in the conductive elastic body 12 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 The filler is at least one material selected from the group consisting of metal materials such as tin (IV) oxide, conductive polymer materials such as PEDOT:PSS (i.e., a composite of poly3,4-ethylenedioxythiophene (PEDOT) and polystyrene sulfonic acid (PSS)), and conductive fibers such as metal-coated organic fibers and metal wires (in a fibrous state). In this embodiment, C (carbon) is used as the filler.

[0033] The thickness of the conductive elastic body 12 is set to, for example, 1 μm or more and 15 μm or less, and the elastic modulus of the conductive elastic body 12 is set to, for example, 0.5 MPa or more and 160 MPa or less.

[0034] FIG. 1B is a diagram schematically illustrating the configuration of a structure 1b in a manufacturing process according to the embodiment.

[0035] The structure 1 b includes a first base member 11 and a plurality of wires 30 .

[0036] A plurality of wires 30 extending in the Y-axis direction (second direction) are arranged on the opposing surface 11a of the first base member 11 so as to overlap the three conductive elastic bodies 12. Here, three wire groups G1 each consisting of four wires 30 are arranged on the opposing surface 11a, for a total of 12 wires 30. The number of wires 30 arranged on the opposing surface 11a is not limited to this.

[0037] When the assembly of the load sensor 1 is complete, the wires 30 are arranged side by side between the first base member 11 and a second base member 21 (described later). A wire group G1 consisting of four wires 30 is arranged at predetermined intervals in the X-axis direction (first direction). The four wires 30 in each wire group G1 are also arranged at predetermined intervals in the X-axis direction (first direction).

[0038] The wire 30 is composed of a conductor wire 31 and a dielectric 32 formed on the conductor wire 31. The dielectric 32 is formed on the outer periphery of the conductor wire 31 and covers the surface of the conductor wire 31. The end of the conductor wire 31 on the negative side of the Y axis is not covered by the dielectric 32, and this end is connected to the detection circuit.

[0039] The conductor wire 31 is a linear member having electrical conductivity. The conductor wire 31 is made of, for example, a conductive metal material. Alternatively, the conductor wire 31 may be made of a core wire made of glass and a conductive layer formed on the surface thereof, or may be made of a core wire made of resin and a conductive layer formed on the surface thereof.

[0040] For example, the conductor wire 31 may be made of at least one metal selected from valve metals such as aluminum (Al), titanium (Ti), tantalum (Ta), niobium (Nb), zirconium (Zr), and hafnium (Hf), or at least one metal selected from tungsten (W), molybdenum (Mo), copper (Cu), nickel (Ni), silver (Ag), and gold (Au). For example, the conductor wire 31 may be made of copper. The conductor wire 31 may also be a twisted wire made of twisted wires made of a conductive metal material.

[0041] The dielectric 32 has electrical insulating properties and is made of, for example, a resin material, a ceramic material, a metal oxide material, etc. The dielectric 32 may be at least one resin material selected from the group consisting of polypropylene resin, polyester resin (for example, polyethylene terephthalate resin), polyimide resin, polyphenylene sulfide resin, polyvinyl formal resin, polyurethane resin, polyamideimide resin, polyamide resin, etc., and may be Al. ２ O ３ and Ta ２ O ５ and the like.

[0042] The diameter of the conductor wire 31 may be, for example, 0.01 mm or more and 1.5 mm or less, or 0.05 mm or more and 0.8 mm or less. Such a configuration of the conductor wire 31 is preferable from the viewpoint of the strength and resistance of the conductor wire 31. The thickness of the dielectric 32 is preferably 5 nm or more and 100 μm or less, and can be appropriately selected depending on the design of the sensor sensitivity, etc.

[0043] FIG. 2A is a diagram schematically illustrating the configuration of a structure 1c in a manufacturing process according to an embodiment.

[0044] 1B and a plurality of threads 41. A plurality of wires 30 are loosely sewn to the opposing surface 11a of the first base member 11 by the plurality of threads 41. Each wire 30 is sewn to the opposing surface 11a of the first base member 11 at both ends and at the positions of the gaps between adjacent conductive elastic bodies 12. The threads 41 are made of chemical fibers, natural fibers, or a mixture thereof.

[0045] FIG. 2B is a diagram schematically illustrating the configuration of the second base member 21 according to the embodiment.

[0046] The second base member 21 is an elastic, flat-plate-shaped member. As will be described later with reference to FIG. 3 , the second base member 21 is disposed opposite the first base member 11. The second base member 21 has the same shape as the first base member 11 in a plan view. The second base member 21 has a constant thickness. When the second base member 21 has a small thickness, it may be called a sheet member or a film member.

[0047] The second base member 21 has insulating properties and is made of, for example, a non-conductive resin material or a non-conductive rubber material. The second base member 21 is made of, for example, a material that can be used for the first base member 11. More specifically, the second base member 21 is made of silicone rubber, ethylene propylene diene rubber, urethane rubber, fluororubber, nitrile rubber, acrylic rubber, or ethylene propylene rubber.

[0048] FIG. 3 is a perspective view schematically showing the configuration of the load sensor 1 according to the embodiment.

[0049] The structure 1c of Fig. 2A is turned upside down and placed on the opposing surface 21a of the second base member 21 of Fig. 2B. Then, the outer periphery of the first base member 11 is connected to the second base member 21 with a thread (not shown), and the first base member 11 is fixed to the second base member 21. In this way, the load sensor 1 shown in Fig. 3 is completed.

[0050] The load sensor 1 is used with the first base member 11 facing upward (positive side of the Z axis) and the second base member 21 facing downward (negative side of the Z axis). In this case, the upper surface 11b of the first base member 11 is the surface to which the load is applied, and the lower surface 21b of the second base member 21 is placed on the installation surface. A push plate may be further placed on the upper surface 11b of the first base member 11, and a padding plate may be further placed on the lower surface 21b of the second base member 21.

[0051] The load sensor 1 has a plurality of element units A0 arranged in a matrix in plan view. The load sensor 1 in Fig. 3 has a total of nine element units A0 arranged in the X-axis direction and the Y-axis direction. One element unit A0 corresponds to a region including an intersection between the conductive elastic body 12 and the wire group G1 arranged below the conductive elastic body 12. In other words, one element unit A0 includes the first base member 11, the conductive elastic body 12, the wire 30, and the second base member 21 near the intersection.

[0052] When the lower surface of the load sensor 1 (the lower surface 21b of the second base member 21) is placed on a predetermined installation surface and a load is applied to the upper surface of the load sensor 1 (the upper surface 11b of the first base member 11), the capacitance between the conductive elastic body 12 and the conductor wire 31 changes in the element part A0 to which the load is applied, and the load is detected based on this capacitance.

[0053] 4A and 4B are diagrams illustrating a cross section of the load sensor 1 according to the embodiment, taken along a plane parallel to the XZ plane, near the intersection of the conductive elastic body 12 and the wire 30.

[0054] 4A shows a state where no load is applied, and FIG. 4B shows a state where a load is applied. In FIG. 4A and FIG. 4B, the lower surface 21b of the second base member 21 on the negative side of the Z axis is placed on the installation surface.

[0055] As shown in Fig. 4A, when no load is applied, the force acting between the conductive elastic body 12 and the wire 30 is substantially zero. From this state, when a load is applied downward to the upper surface 11b of the first base member 11 as shown in Fig. 4B, the conductive elastic body 12 is deformed by the wire 30.

[0056] 4B , when a load is applied, the wire 30 is brought closer to the conductive elastic body 12 so as to be wrapped in the conductive elastic body 12, and the contact area between the wire 30 and the conductive elastic body 12 increases. This causes a change in the capacitance between the conductor wire 31 and the conductive elastic body 12. The potential reflecting this change in capacitance is then measured in the detection circuit, and the load is calculated.

[0057] 5A and 5B are diagrams showing examples of an FC curve indicating the relationship between load and capacitance. It is desirable for the load sensor 1 configured as described above to be able to accurately detect load even in a relatively low load range. However, with the load sensor 1 configured as described above, the FC curve indicating the relationship between load and capacitance tends to have a downward convex shape in the low load range A1 near zero, as shown in FIG. 5A . In this case, the change in capacitance relative to a change in load becomes significantly small in the low load range A1. That is, the change width B1 of capacitance in the low load range A1 is significantly small. With such an FC curve, the load detection sensitivity is significantly low in the low load range A1, making it difficult to accurately detect load.

[0058] 5B, if the FC curve showing the relationship between load and capacitance has an upwardly convex shape throughout, the capacitance change width B1 in the low load range A1 becomes large. Therefore, with such an FC curve, the load detection sensitivity can be increased in the low load range A1, and the load can be detected accurately.

[0059] Therefore, the inventors have conducted extensive research into the conditions for forming an FC curve with an upward convex shape, and have found that the thickness and elastic modulus of the conductive elastic body 12 have a significant effect on the shape of the FC curve.

[0060] FIG. 6 is a diagram schematically showing the configuration of a load sensor used in a simulation to verify the influence of the thickness and elastic modulus of the conductive elastic body 12 on the shape of the FC curve.

[0061] In the verification, a push plate 51 and a support plate 52 were installed on the upper and lower surfaces of the load sensor 1 configured as described above. The wire 30 was a solid wire rather than a twisted wire. The simulation conditions were set as follows:

[0062] Thickness D1 of push plate 51: 3 mm Thickness D2 of first base member 11: 0.5 mm Thickness D4 of second base member 21: 0.2 mm Thickness D5 of floor plate 52: 3 mm Diameter of wire 30 (single wire): 0.3 mm Size of element section A0: 25 mm x 25 mm square Pitch of wire 30: 5.75 mm Elastic modulus of push plate 51: 200,000 MPa Elastic modulus of floor plate 52: 200,000 MPa Elastic modulus of wire 30: 110,000 MPa Elastic modulus of first base member 11: 1.5 MPa Elastic modulus of second base member 21: 25 MPa Under these conditions, the thickness D3 and elastic modulus of the conductive elastic body 12 were changed to obtain an FC curve for one wire 30. The load of the FC curve was calculated as the load per unit area.

[0063] FIG. 7A is a graph showing the simulation results of the FC curve when the elastic modulus of the conductive elastic body 12 is changed while the thickness D3 of the conductive elastic body 12 is fixed.

[0064] In this simulation, the thickness D3 of the conductive elastic body 12 was fixed at 10 μm, and the elastic modulus of the conductive elastic body 12 was set to 20 MPa, 40 MPa, 60 MPa, 80 MPa, and 320 MPa.

[0065] The verification results in Figure 7A show that the elastic modulus of the conductive elastic body 12 has a significant effect on the FC curve. It was also confirmed that the downward convex shape of the FC curve gradually reduces as the elastic modulus of the conductive elastic body 12 decreases. When the thickness D3 of the conductive elastic body 12 is set to 10 µm, the FC curve can be adjusted to an upward convex shape throughout by setting the thickness D3 of the conductive elastic body 12 to 20 MPa. This confirms that the FC curve can be adjusted to an upward convex shape throughout by adjusting the combination of the thickness D3 and elastic modulus of the conductive elastic body 12.

[0066] FIG. 7B is a graph showing the simulation results of the FC curve when the thickness D3 of the conductive elastic body 12 is changed while the elastic modulus of the conductive elastic body 12 is fixed.

[0067] In this simulation, the elastic modulus of the conductive elastic body 12 was fixed at 80 MPa, and the thickness D3 of the conductive elastic body 12 was set to 6.3 μm, 10 μm, and 15.9 μm.

[0068] 7B, it was found that the thickness D3 of the conductive elastic body 12 has a significant effect on the FC curve. It was also confirmed that the downward convex shape of the FC curve gradually becomes less convex as the thickness D3 of the conductive elastic body 12 decreases.

[0069] Furthermore, it was confirmed that the load at the inflection point of the FC curve indicated by the arrow in Fig. 7B (i.e., the boundary position where the FC curve transitions from a downward convex shape to an upward convex shape) decreases as the thickness D3 decreases. This can also be confirmed from the verification results in Fig. 7A, that the load at the inflection point indicated by the arrow decreases as the elastic modulus of the conductive elastic body 12 decreases.

[0070] Therefore, the inflection point load obtained when the upper limit values ​​of the thickness and elastic modulus are combined within the range of thickness and elastic modulus of the conductive elastic body 12 that can be assumed when constructing the load sensor 1 is the largest among the inflection point loads obtained by combining these ranges. In other words, if inflection points occur on the FC curve for other combinations of thickness and elastic modulus of the conductive elastic body 12, all of these inflection points will be smaller than the maximum inflection point load obtained by combining the above upper limit values.

[0071] Here, the upper limit of the thickness of the conductive elastic body 12 is set in relation to constraints imposed by the manufacturing method for forming the conductive elastic body 12. Furthermore, the upper limit of the elastic modulus of the conductive elastic body 12 is set from the viewpoint of whether the conductive elastic body 12 satisfies the basic structural deformation function of the load sensor 1, such as deforming along the wire 30. In view of these constraints and viewpoints, the thickness of the conductive elastic body 12 may be set to 15 μm or less, and the elastic modulus of the conductive elastic body 12 may be set to 160 MPa or less.

[0072] FIG. 8A is a diagram showing the simulation results of the FC curve and the inflection point P0 when the upper limit values ​​of the thickness and elastic modulus of the conductive elastic body 12 are combined.

[0073] As described above, when the thickness of the conductive elastic body 12 is 15 μm, which is the upper limit, and the elastic modulus of the conductive elastic body 12 is 160 MPa, which is the upper limit, the FC curve and inflection point P0 in FIG. 8A are obtained. In this case, the load at the inflection point P0, i.e., the maximum inflection point load, is 0.28 N / cm ２ The FC curve in Fig. 8A includes a portion that is below the line connecting the inflection point P0 and the origin in the vertical axis direction (the direction of capacitance).

[0074] As described above, when the FC curve has an inflection point at a combination of thickness and elastic modulus other than these upper limits, the load at each of these inflection points is the maximum inflection point load of 0.28 N / cm ２ Therefore, in these FC curves, the value of 0.28 N / cm ２ If a straight line is set connecting the origin and the points corresponding to the points 1 and 2, each of these FC curves will include a portion below this straight line.

[0075] Therefore, whether the FC curve includes a portion below this straight line can be used to determine whether the FC curve includes a portion with a downward convex shape. As shown in FIG. 8A, taking into account factors such as error, the ２ Slightly larger than 0.30 N / cm ２The straight line L0 connecting the origin and the point on the FC curve corresponding to the load (above) may be set as the straight line used for the above determination. This makes it possible to more accurately determine whether the FC curve includes a downwardly convex portion.

[0076] FIG. 8B is a diagram showing the simulation results of the FC curve when the thickness and elastic modulus of the conductive elastic body 12 are such that the FC curve has an upward convex shape over the entire surface.

[0077] As shown in FIG. 8B, for this FC curve, 0.30 N / cm ２ When a straight line L0 is set connecting the origin and a point on the FC curve corresponding to the load, the FC curve does not include any portion below this straight line L0. Therefore, depending on whether the FC curve includes any portion below the straight line L0, it can be determined whether the FC curve includes any portion that is downwardly convex, i.e., whether the FC curve is upwardly convex throughout.

[0078] Fig. 9A is a graph showing the results of a simulation in which the maximum value of the elastic modulus of the conductive elastic body 12 with respect to the thickness of the conductive elastic body 12 when the FC curve has an upward convex shape overall according to the above-mentioned FC curve shape judgment criteria. Fig. 9B is a diagram showing the range of combinations of film thickness and elastic modulus for making the FC curve have an upward convex shape overall, by setting a correlation curve according to the relationship between the film thickness and elastic modulus of the conductive elastic body in Fig. 9A.

[0079] For convenience, the simulation in FIG. 9A also included thicknesses greater than the upper limit of the thickness (15 μm) and elastic modulus greater than the upper limit of the elastic modulus (160 MPa). As shown in FIG. 9A , the plot of the simulation results can be arranged along a predetermined correlation curve. Therefore, as shown in FIG. 9B , by setting the thickness and elastic modulus of the conductive elastic body 12 in the hatched range where the elastic modulus is smaller than the correlation curve L1, the FC curve can be set to an upwardly convex shape throughout. By setting the thickness and elastic modulus of the conductive elastic body 12 in this manner, the load detection sensitivity can be improved even in a low load range, allowing for accurate load detection.

[0080] Although the elastic modulus of the conductive elastic body 12 is dominated by the elastic modulus of the resin material or rubber material described above, it may also be affected by the elastic modulus of the filler mixed therein. Specifically, the elastic modulus of the resin material or rubber material mixed with the filler is higher than the elastic modulus of the resin material or rubber material itself. Therefore, when adjusting the elastic modulus of the conductive elastic body 12 so that the FC curve has an upward convex shape throughout as described above, the elastic modulus can be adjusted taking into account the state of the filler mixed into the resin material or rubber material.

[0081] Generally, when an elastic body contains a material with high electrical conductivity, the elastic modulus becomes high. Therefore, by using carbon, which has low electrical conductivity and low elastic modulus compared to silver etc., as a filler, the elastic modulus of the conductive elastic body 12 can be smoothly adjusted to an elastic modulus that makes the FC curve upwardly convex over the entire surface.

[0082] <Effects of the embodiment> According to the embodiment, the following effects are achieved.

[0083] As explained with reference to Figures 6 to 9B, in the load sensor 1, the thickness and elastic modulus of the conductive elastic body 12 are adjusted so that the FC curve showing the relationship between the load that brings the first base member 11 and the second base member 21 closer to each other and the capacitance between the conductor wire 31 and the conductive elastic body 12 has an upward convex shape throughout.

[0084] With this configuration, the FC curve has an upward convex shape throughout, so that the change in capacitance relative to the change in load can be made large in the low load range A1, as shown in Fig. 5B, and therefore the load can be accurately detected even in the low load range.

[0085] As described with reference to FIGS. 8A and 8B, the load sensor 1 has a resistance of 0 to 0.3 N / cm ２ In the following load range, the load is 0.3 N / cm ２ The thickness and elastic modulus of the conductive elastic body 12 are adjusted so that the FC curve does not fall below a straight line L0 that connects the origin and a point on the FC curve at this time.

[0086] As shown in FIG. 8A, when the upper limits (15 μm, 160 MPa) of the thickness and elastic modulus of the conductive elastic body 12 are combined, the inflection point P0 of the FC curve (the boundary position where the shape transitions from a downward convex shape to an upward convex shape) is at a load of 0.28 N / cm ２ 7A and 7B, it is clear that the thickness of the conductive elastic body 12 and the modulus of elasticity of the conductive elastic body 12 are different from each other in other combinations. ２ Therefore, the inflection point of the FC curve occurs at a position where the load is lower than 0.28 N / cm ２ Slightly higher than 0.3 N / cm ２ If the FC curve does not fall below the line L0 connecting the origin and a point on the FC curve at this time, the FC curve will have an upward convex shape over its entirety. Therefore, by adjusting the thickness and elastic modulus of the conductive elastic body 12 so that the FC curve does not fall below this line L0, as in the above configuration, the FC curve can be set to have an upward convex shape over its entirety, and the load can be accurately detected even in the low load range.

[0087] As described above, the elastic modulus of the conductive elastic body 12 is preferably set to 160 MPa or less.

[0088] This allows the conductive elastic body 12 to have the basic structural deformation function of the load sensor 1 , such as deformation along the conductor wire 31 .

[0089] As described above, it is preferable that the thickness of the conductive elastic body 12 be set to 15 μm or less.

[0090] This allows the conductive elastic body 12 to be properly formed on the opposing surface 11a of the first base member 11 by a printing method.

[0091] As described above, the hardness of the first base member 11 is preferably set to be equal to or greater than 10 degrees and equal to or less than 70 degrees.

[0092] By setting the hardness (rubber A hardness) of the first base member 11 within the above range, the posture of the first base member 11 is properly maintained when no load is applied, and when a load is applied to each element part A0, the load can be smoothly transmitted to the corresponding element part A0 due to elastic deformation of the first base member 11.

[0093] As described above, the conductive elastic body 12 is made by mixing a conductive filler into an elastic material.

[0094] According to this configuration, the conductive elastic body 12 can be easily and smoothly formed on the opposing surface 11a of the first base member 11 by a printing method.

[0095] In this case, the filler is preferably carbon.

[0096] As described above, carbon has a lower conductivity and a lower elastic modulus than silver and the like, so by using carbon as a filler, it is possible to smoothly adjust the elastic modulus of the conductive elastic body 12 to an elastic modulus that makes the FC curve have an upward convex shape over the entire surface. In addition, because carbon is inexpensive, it is possible to suppress an increase in the cost of the load sensor 1.

[0097] As shown in Figures 1A and 1B, a plurality of conductive elastic bodies 12 are formed in a row on the opposing surface 11a of the first base member 11, and the conductor wire 31 is arranged so as to overlap the plurality of conductive elastic bodies 12.

[0098] This configuration makes it possible to widen the area in which the load can be detected.

[0099] As shown in FIGS. 1A, 1B and 3, a plurality of conductor wires 31 are overlapped on the conductive elastic body 12 to form one element portion A0 for detecting a load.

[0100] This configuration can improve the load detection sensitivity of the element portion A0.

[0101] As shown in FIG. 3, a plurality of element portions A0 are arranged in a matrix.

[0102] According to this configuration, the element portions A0 are arranged in a matrix, so that the area in which the load can be detected can be further expanded.

[0103] <Modification> In the above embodiment, the conductive elastic body 12 is disposed on the first base member 11, but the conductive elastic body may be disposed on both the first base member 11 and the second base member 21. In this case, as in the above embodiment, the thickness and elastic modulus of each conductive elastic body may be adjusted so that the FC curve has an upward convex shape throughout.

[0104] In the above embodiment, the dielectric 32 is disposed so as to cover the entire circumference of the conductor wire 31, but the dielectric 32 may be disposed so as to cover at least the area of ​​the surface of the conductor wire 31 where the contact area changes depending on the load. Furthermore, the dielectric 32 is made of one type of material in the thickness direction, but may have a structure in which two or more types of materials are laminated in the thickness direction.

[0105] In addition, in the above embodiment, the cross-sectional shape of the conductor wire 31 is circular, but the cross-sectional shape of the conductor wire 31 is not limited to circular and may be other shapes such as elliptical or pseudo-circular. In this case, too, the thickness and elastic modulus of each conductive elastic body may be adjusted so that the FC curve has an upward convex shape throughout.

[0106] In addition, in the above embodiment, three wire groups G1 corresponding to one element portion A0 are arranged, and one wire group G1 includes four wires 30, but the number of wire groups G1 and wires 30 is not limited to this. For example, one, two, or four or more wire groups G1 may be arranged, and one wire group G1 may include one to three, or five or more wires 30.

[0107] In addition, although three conductive elastic bodies 12 are arranged in the above embodiment, the number of conductive elastic bodies 12 arranged in the load sensor 1 is not limited to this. For example, one, two, four or more conductive elastic bodies 12 may be arranged.

[0108] In the above embodiment, the method of disposing the conductive elastic body 12 on the opposing surface 11a of the first base member 11 is not necessarily limited to printing, but may be other methods such as bonding foil.

[0109] In the above embodiment, the first direction and the second direction are perpendicular to each other, but this is not limiting, and the angle between the first direction and the second direction may be an angle other than 90°. In other words, the wire 30 may cross the conductive elastic body 12 obliquely.

[0110] In the above embodiment, the width of the conductive elastic body 12 does not necessarily have to be constant. For example, the width of the conductive elastic body 12 may be narrower in the range between the element portions A0 in the first direction.

[0111] The FC curve, whose upward convex shape is adjusted by the thickness and elastic modulus of the conductive elastic body 12, does not have to be strictly upward convex over the entire curve, and may include a small portion below the line L0 due to errors, slight distortion or fluctuation in characteristics when a load is applied from no load, etc. In other words, the adjusted FC curve only needs to be substantially upward convex over the entire curve, and the configurations described in the claims can be understood in this way.

[0112] 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.

[0113] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0114] (Technology 1) A load sensor comprising: a first base member; a second base member arranged opposite the first base member; a conductive elastic body formed on the opposing surface of the first base member; and a conductor wire coated with a dielectric and arranged overlapping the conductive elastic body, wherein the thickness and elastic modulus of the conductive elastic body are adjusted so that an FC curve showing the relationship between a load that brings the first base member and the second base member closer together and the electrostatic capacitance between the conductor wire and the conductive elastic body has an upward convex shape throughout.

[0115] According to this technique, since the FC curve has an upward convex shape over the entire surface, the change in capacitance relative to the change in load can be made large in the low load range, and therefore the load can be accurately detected even in the low load range.

[0116] (Technology 2) In the load sensor according to Technology 1, ２ In the following load range, the load is 0.3 N / cm ２ a thickness and a modulus of elasticity of the conductive elastic body are adjusted so that the FC curve does not fall below a straight line connecting a point on the FC curve and the origin at time t.

[0117] When the upper limits of the thickness and modulus of elasticity of the conductive elastic body are combined, the inflection point of the FC curve (the boundary position where the shape transitions from a downward convex shape to an upward convex shape) is at a load of 0.28 N / cm ２ Therefore, for other combinations of thickness and modulus, ２ Therefore, the inflection point of the FC curve occurs at a position where the load is lower than 0.28 N / cm ２ Slightly higher than 0.3 N / cm ２ If the FC curve does not fall below the line connecting the origin and the point on the FC curve at time , then the FC curve will have an upward convex shape over its entirety. Therefore, according to this technology, by adjusting the thickness and elastic modulus of the conductive elastic body so that the FC curve does not fall below this line, it is possible to set the FC curve to have an upward convex shape over its entirety, and to accurately detect loads even in the low load range.

[0118] (Technology 3) The load sensor according to Technology 1 or 2, wherein the elastic modulus of the conductive elastic body is set to 160 MPa or less.

[0119] According to this technology, the conductive elastic body can be provided with a basic structural deformation function of a load sensor, such as deformation along the conductor wire.

[0120] (Technology 4) The load sensor according to any one of Technologies 1 to 3, wherein the conductive elastic body has a thickness set to 15 μm or less.

[0121] According to this technique, the conductive elastic body can be properly formed on the opposing surface of the first base member by a printing method.

[0122] (Technology 5) The load sensor according to any one of Technologies 1 to 4, wherein the hardness of the first base member is set to be equal to or greater than 10 degrees and equal to or less than 70 degrees.

[0123] According to this technology, by setting the hardness (rubber A hardness) of the first base member within the above range, the posture of the first base member can be properly maintained when no load is applied, and when a load is applied to each element portion, the load can be smoothly transmitted to the corresponding element portion due to elastic deformation of the first base member.

[0124] (Technology 6) The load sensor according to any one of Technologies 1 to 5, wherein the conductive elastic body is formed by mixing a conductive filler into an elastic material.

[0125] According to this technique, the conductive elastic body can be easily and smoothly formed on the opposing surface of the first base member by a printing method.

[0126] (Technology 7) The load sensor according to Technology 6, wherein the filler is carbon.

[0127] Generally, when an elastic body contains a material with high conductivity, the elastic modulus becomes high. Therefore, according to this technology, by using carbon, which has low conductivity and low elastic modulus compared to silver and the like, as a filler, the elastic modulus of the conductive elastic body can be smoothly adjusted to an elastic modulus that makes the FC curve upwardly convex throughout. In addition, because carbon is inexpensive, it is possible to suppress increases in the cost of the load sensor.

[0128] (Technology 8) The load sensor according to any one of Technologies 1 to 7, wherein a plurality of the conductive elastic bodies are formed side by side on the opposing surface of the first base member, and the conductor wire is arranged so as to overlap the plurality of conductive elastic bodies.

[0129] This technology can widen the area in which the load can be detected.

[0130] (Technology 9) The load sensor according to Technology 8, wherein a plurality of the conductor wires are overlapped on the conductive elastic body to form one element unit for detecting a load.

[0131] This technique can improve the load detection sensitivity of the element section.

[0132] (Technology 10) The load sensor according to Technology 9, wherein the plurality of element portions are arranged in a matrix.

[0133] According to this technology, the element portions are arranged in a matrix, so that the area in which the load can be detected can be further expanded.

[0134] The load sensor of the present disclosure can be applied to management systems and electronic devices that perform processing in response to an applied load, and can accurately detect loads even in a low load range. Thus, the load sensor of the present disclosure is industrially useful.

[0135] REFERENCE SIGNS LIST 1 load sensor 11 first base member 11a, 21a opposing surface 12 conductive elastic body 21 second base member 31 conductor wire 32 dielectric

Claims

1. A load sensor comprising a first base member, a second base member disposed opposite to the first base member, a conductive elastic body formed on the opposing surface of the first base member, and a conductor wire coated with a dielectric and disposed overlapping the conductive elastic body, wherein the thickness and elastic modulus of the conductive elastic body are adjusted such that an FC curve showing the relationship between the load for bringing the first base member and the second base member closer and the capacitance between the conductor wire and the conductive elastic body is convex upward throughout.

2. In the load sensor according to claim 1, in the load range of 0 or more and 0.3 N / cm ２ or less, the thickness and elastic modulus of the conductive elastic body are adjusted so that the straight line connecting the point on the FC curve and the origin when the load is 0.3 N / cm ２ does not fall below the FC curve. Load sensor.

3. The load sensor according to claim 1, wherein the elastic modulus of the conductive elastic body is set to 160 MPa or less.

4. The load sensor according to claim 1, wherein the thickness of the conductive elastic body is set to 15 µm or less.

5. The load sensor according to claim 1, wherein the hardness of the first base member is set to 10 degrees or more and 70 degrees or less.

6. The load sensor according to claim 1, wherein the conductive elastic body is configured by mixing a conductive filler into an elastic material.

7. The load sensor according to claim 6, wherein the filler is carbon.

8. The load sensor according to claim 1, wherein a plurality of the conductive elastic bodies are formed side by side on the opposing surface of the first base member, and the conductor wire is disposed so as to overlap the plurality of conductive elastic bodies.

9. The load sensor according to claim 8, wherein a plurality of the conductor wires are overlapped on the conductive elastic body to form one element portion for detecting a load.

10. The load sensor according to claim 9, wherein a plurality of the element portions are arranged side by side in a matrix.

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