Load sensor

Abstract

A load sensor (1) comprises: conductive elastic bodies (12, 22); a linear conductive member disposed so as to intersect the conductive elastic bodies (12, 22); and a dielectric disposed between the conductive elastic bodies (12, 22) and the conductive member. The width of the conductive elastic bodies (12, 22) in the longitudinal direction of the conductive member changes such that the relationship between the load and the contact area between the conductive elastic bodies and the conductive member with the dielectric interposed therebetween approaches a linear relationship.

Description

Load Sensor

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

[0002] 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 pressure-sensitive element (load sensor) including a first conductive member made of a sheet-like conductive rubber, a linear second conductive member sandwiched between the first conductive member and a substrate, and a dielectric member formed to cover the second conductive member. In this configuration, as the load increases, the contact area between the first conductive member and the dielectric member increases, and thus the capacitance between the first conductive member and the second conductive member increases. By detecting the value of the capacitance between the first conductive member and the second conductive member, the load applied to the pressure-sensitive element can be detected.

[0004] International Publication No. 2018 / 096901

[0005] In the above configuration, because the second conductive member is cylindrical, the contact area between the first conductive member and the dielectric does not change linearly with increasing load, making it difficult to easily and smoothly detect the load applied to the pressure-sensitive element from the capacitance value between the first conductive member and the second conductive member.

[0006] In view of the above problem, an object of the present invention is to provide a load sensor that can easily and smoothly detect an applied load.

[0007] A load sensor according to a main aspect of the present invention includes a conductive elastic body, a linear conductive member arranged to cross the conductive elastic body, and a dielectric arranged between the conductive elastic body and the conductive member, wherein the width of the conductive elastic body in the longitudinal direction of the conductive member is changed so that the relationship between the load and the contact area between the conductive elastic body and the conductive member via the dielectric approaches linearity.

[0008] According to the load sensor of this aspect, the relationship between the load and the contact area between the conductive elastic body and the conductive member becomes closer to linear due to the change in the width of the conductive elastic body, and therefore the relationship between the load and the capacitance also becomes closer to linear. Therefore, by detecting the capacitance between the conductive elastic body and the conductive member, the applied load can be detected easily and smoothly.

[0009] As described above, according to the present invention, it is possible to provide a load sensor that can easily and smoothly detect an applied load.

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

[0011] FIG. 1( a) is a perspective view schematically illustrating a lower sheet-like member and a conductive elastic body installed on the opposing surface of the lower sheet-like member according to an embodiment. FIG. 1( b) is a perspective view schematically illustrating a state in which a conductor wire and a thread are installed on the structure of FIG. 1( a) according to an embodiment. FIG. 2( a) is a perspective view schematically illustrating an upper sheet-like member and a conductive elastic body installed on the opposing surface of the upper sheet-like member according to an embodiment. FIG. 2( b) is a perspective view schematically illustrating a state in which the structure of FIG. 2( a) is installed on the structure of FIG. 1( b) according to an embodiment. FIGS. 3( a) and 3( b) are each a schematic cross-section of a sensor unit according to an embodiment. FIG. 4 is a plan view schematically illustrating the internal configuration of a load sensor according to an embodiment. FIG. 5( a) is a cross-sectional view schematically illustrating a contact portion between a conductor wire and a conductive elastic body according to an embodiment. FIG. 5( b) is a plan view schematically illustrating a configuration near an intersection position between a conductor wire and a conductive elastic body according to a comparative example. FIG. 6( a) is a graph showing the relationship between the arc length of the contact portion and the load in a comparative example. FIG. 6( b) is a plan view schematically showing the configuration near the intersection of the conductor wire and the conductive elastic body in accordance with the embodiment. FIG. 7 is a diagram schematically showing the conditions of a simulation performed in accordance with the embodiment. FIG. 8 is a graph showing the relationship between the load and the contact area when the constant α is changed in accordance with the embodiment. FIGS. 9( a) to 9(d) are diagrams each showing the shape of a conductive elastic body in a plan view in accordance with the embodiment. FIG. 10 is a diagram schematically showing the conditions of a simulation performed in accordance with the embodiment. FIG. 11 is a graph showing the relationship between the load and the contact area when the width β is changed in accordance with the embodiment. FIGS. 12( a) to 12(d) are diagrams each showing the shape of a conductive elastic body in a plan view in accordance with the embodiment. FIG. 13 is a schematic diagram for explaining the rate of change in accordance with the embodiment. FIG. 14( a) is a graph showing the relationship between the load and the contact area when the rate of change is changed with the constant α in accordance with the embodiment. Fig. 14B is a graph showing approximate straight lines of the curves in Fig. 14A in accordance with verification of the embodiment. Fig. 15 is a schematic diagram for explaining the effect of the notch having a symmetrical shape in accordance with the embodiment.16(a) and 16(b) are plan views each showing a schematic configuration of a modified example, in the vicinity of an intersection position between a conductor wire and a conductive elastic body; 17(a) and 17(b) are plan views each showing a schematic configuration of a modified example, in the vicinity of an intersection position between a conductor wire and a conductive elastic body; 18(a) and 18(b) are plan views each showing a schematic configuration of a modified example, in the vicinity of an intersection position between a conductor wire and a conductive elastic body; and 19(a) and 19(b) are diagrams each showing a schematic cross section of a sensor unit in the modified example.

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

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

[0014] Examples of management systems include inventory management systems, driver monitoring systems, coaching management systems, security management systems, and nursing care / childcare management systems.

[0015] 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.

[0016] In a driver monitoring system, for example, a load sensor provided in the steering device monitors the load distribution of the driver on the steering device (e.g., grip force, grip position, pedal force). Also, a load sensor provided in the vehicle seat monitors the load distribution of the driver on the vehicle seat while seated (e.g., center of gravity position). This makes it possible to provide feedback on the driver's driving state (drowsiness, psychological state, etc.).

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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 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.

[0021] 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 sometimes called "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 one embodiment of the present invention, and the present invention is not limited to the following embodiments in any way.

[0022] 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.

[0023] FIG. 1A is a perspective view that schematically shows a sheet-like member 11 and a conductive elastic body 12 that is placed on an opposing surface 11a (the surface on the positive side of the Z axis) of the sheet-like member 11. FIG.

[0024] The sheet member 11 is an elastic insulating member having a flat plate shape parallel to the XY plane. The thickness of the sheet member 11 in the Z-axis direction is, for example, 0.01 mm to 2 mm.

[0025] The sheet-shaped member 11 is made of a non-conductive resin material or a non-conductive rubber material. The resin material used for the sheet-shaped member 11 is at least one resin material selected from the group consisting of, for example, 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 sheet-shaped member 11 is at least one rubber material selected from the group consisting of, for example, silicone rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, polyisobutylene, ethylene propylene rubber, chlorosulfonated polyethylene, acrylic rubber, fluororubber, epichlorohydrin rubber, urethane rubber, and natural rubber.

[0026] The conductive elastic bodies 12 are formed on the opposing surface 11a (the surface on the positive side of the Z axis) of the sheet-like member 11. In FIG. 1( a), three conductive elastic bodies 12 are formed on the opposing surface 11a of the sheet-like member 11. The conductive elastic bodies 12 are elastic, conductive members. Each conductive elastic body 12 has a strip-like shape that is long in the Y axis direction, and is formed side by side at a predetermined interval in the X axis direction. A cable C1 electrically connected to the conductive elastic bodies 12 is installed at the end of each conductive elastic body 12 on the negative side of the Y axis.

[0027] The conductive elastic body 12 has a plurality of notches 12a formed inward from the end on the positive side of the X-axis and the end on the negative side of the X-axis, at positions through which conductor wires 13 (described later) pass (see FIG. 1(b)).

[0028] The conductive elastic body 12 is formed on the opposing surface 11a of the sheet-like member 11 by a printing method such as screen printing, gravure printing, flexographic printing, offset printing, or gravure offset printing. These printing methods make it possible to form the conductive elastic body 12 on the opposing surface 11a of the sheet-like member 11 with a thickness of about 0.001 mm to 0.5 mm.

[0029] 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.

[0030] The resin material used for the conductive elastic body 12 is, like the resin material used for the sheet-like 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 sheet-like 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.

[0031] 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 ２The conductive material 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 poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS)), and conductive fibers such as metal-coated organic fibers and metal wires (in a fibrous state).

[0032] FIG. 1B is a perspective view that schematically shows the state in which a conductor wire 13 and a thread 14 are arranged in the structure of FIG.

[0033] The conductor wires 13 have a linear shape and extend in the X-axis direction. The conductor wires 13 are bent near the end of the sheet-like member 11 on the positive side of the X-axis. The bent conductor wires 13 (hereinafter referred to as a "pair of conductor wires 13") are composed of a conductor wire 13 extending in the X-axis direction on the positive side of the Y-axis and a conductor wire 13 extending in the X-axis direction on the negative side of the Y-axis, and these two conductor wires 13 are arranged with a predetermined gap between them. The pair of conductor wires 13 are arranged side by side in the Y-axis direction with a predetermined gap between them. In the example shown in FIG. 1(b), three pairs of conductor wires 13 are arranged. The conductor wires 13 are composed of a linear conductive member and a dielectric formed on the surface of the conductive member. The configuration of the conductor wires 13 will be described later with reference to FIGS. 3(a) and 3(b).

[0034] After a plurality of pairs of conductor wires 13 are arranged as shown in Fig. 1(b), each pair of conductor wires 13 is attached to the sheet-like member 11 by threads 14. In the example shown in Fig. 1(b), 12 threads 14 connect the pairs of conductor wires 13 to the sheet-like member 11 at positions other than the positions where the conductive elastic body 12 and the conductor wires 13 overlap. The threads 14 are made of chemical fibers, natural fibers, or a mixture of these fibers.

[0035] FIG. 2A is a perspective view that schematically shows a sheet-like member 21 and a conductive elastic body 22 that is placed on an opposing surface 21 a (the surface on the negative side of the Z axis) of the sheet-like member 21 .

[0036] The sheet-like member 21 has the same size and shape as the sheet-like member 11 in a plan view, and is made of the same material as the sheet-like member 11. The thickness of the sheet-like member 21 in the Z-axis direction is, for example, 0.01 mm to 2 mm.

[0037] The conductive elastic bodies 22 extend in the Y-axis direction and are formed side by side at predetermined intervals in the X-axis direction. The conductive elastic bodies 22 are formed on the opposing surface 21a of the sheet-like member 21 at positions facing the conductive elastic bodies 12 of the sheet-like member 11. The conductive elastic bodies 22 have the same size and shape as the conductive elastic bodies 12 in a plan view and are made of the same material as the conductive elastic bodies 12. Like the conductive elastic bodies 12, the conductive elastic bodies 22 are formed on the opposing surface 21a of the sheet-like member 21 by a predetermined printing method. A cable C2 electrically connected to the conductive elastic bodies 22 is installed at the end of each conductive elastic body 22 on the negative side of the Y-axis.

[0038] The conductive elastic body 22 also has a plurality of notches 22a formed inward from the end on the positive side of the X-axis and the end on the negative side of the X-axis. In a plan view, the notches 12a of the conductive elastic body 12 and the notches 22a of the conductive elastic body 22 have the same shape. When the load sensor 1 is assembled, the notches 12a and the notches 22a overlap at the same positions in a plan view.

[0039] FIG. 2B is a perspective view that schematically shows the state in which the structure of FIG. 2A is installed on the structure of FIG. 1B.

[0040] The structure shown in Fig. 2(a) is placed from above (the positive side of the Z axis) the structure shown in Fig. 1(b). At this time, the sheet-like member 11 and the sheet-like member 21 are placed so that the opposing surfaces 11a and 21a face each other, and the conductive elastic body 12 and the conductive elastic body 22 overlap. The four outer edges of the sheet-like member 21 are then connected to the four outer edges of the sheet-like member 11 with a silicone rubber adhesive, thread, or the like, thereby fixing the sheet-like member 11 and the sheet-like member 21 together. As a result, the conductor wire 13 is sandwiched between the conductive elastic body 12 and the conductive elastic body 22. In this way, the load sensor 1 is completed as shown in Fig. 2(b).

[0041] Here, the load sensor 1 has a plurality of sensor units A arranged in a matrix in a plan view. The load sensor 1 has a total of nine sensor units A arranged in the X-axis direction and the Y-axis direction. Each sensor unit A is positioned at an intersection between conductive elastic bodies 12, 22 arranged in the Z-axis direction and a pair of conductor wires 13. Each sensor unit A includes conductive elastic bodies 12, 22, a pair of conductor wires 13, and sheet-like members 11, 21 near the intersection. When the load sensor 1 is placed on a predetermined installation surface and a load is applied to the upper surface 21b (the surface on the positive side of the Z-axis) of the sheet-like member 21 that constitutes the sensor unit A, the electrostatic capacitance between the conductive elastic bodies 12, 22 and the conductive member in the pair of conductor wires 13 changes, and the load is detected based on the electrostatic capacitance.

[0042] 3(a) and 3(b) are diagrams schematically showing a cross section of the sensor unit A when cut along a plane parallel to the YZ plane at the center position in the X-axis direction of the sensor unit A. Fig. 3(a) shows a state where no load is applied, and Fig. 3(b) shows a state where a load is applied.

[0043] 3(a) and 3(b), the conductor wire 13 is composed of a conductive member 13a and a dielectric member 13b formed on the conductive member 13a. The conductive member 13a is a linear wire, and the dielectric member 13b covers the surface of the conductive member 13a. In FIGS. 3(a) and 3(b), the negative surface of the Z-axis of the sheet-like member 11 is placed on a mounting surface.

[0044] As shown in Fig. 3(a), when no load is applied, the force applied between the conductive elastic body 12 and the conductor wire 13 and the force applied between the conductive elastic body 22 and the conductor wire 13 are almost zero. From this state, when a load is applied downward to the upper surface 21b of the sheet-like member 21 corresponding to the sensor portion A as shown in Fig. 3(b), the conductive elastic bodies 12, 22 and the sheet-like members 11, 21 are deformed by the conductor wire 13.

[0045] 3(b), when a load is applied, the conductor wire 13 is brought closer to the conductive elastic bodies 12, 22 so as to be wrapped by the conductive elastic bodies 12, 22, and the contact area between the conductor wire 13 and the conductive elastic bodies 12, 22 increases. This changes the capacitance between the conductive member 13a and the conductive elastic body 12 and the capacitance between the conductive member 13a and the conductive elastic body 22. Then, by detecting the capacitance of the pair of conductor wires 13 included in sensor unit A, the load acting on sensor unit A can be calculated.

[0046] Fig. 4 is a plan view schematically showing the internal configuration of the load sensor 1. For convenience, the thread 14 is not shown in Fig. 4.

[0047] Nine sensor units A aligned in the X-axis direction and the Y-axis direction are set in the measurement area of ​​the load sensor 1. The nine sensor units A correspond to nine positions where the conductive elastic bodies 12, 22 intersect with two adjacent conductor wires 13 (a pair of conductor wires 13). In Fig. 4, nine sensor units A11, A12, A13, A21, A22, A23, A31, A32, and A33, whose capacitance changes depending on the load, are formed at the nine positions.

[0048] In each sensor section, the pair of conductor wires 13 constitute one pole (e.g., anode) of the capacitance, and the conductive elastic bodies 12, 22 constitute the other pole (e.g., cathode) of the capacitance. That is, the conductive member 13a (see FIGS. 3(a) and 3(b)) in the pair of conductor wires 13 constitutes one electrode of the load sensor 1 (capacitive load sensor), the conductive elastic bodies 12, 22 constitute the other electrode of the load sensor 1 (capacitive load sensor), and the dielectric 13b (see FIGS. 3(a) and 3(b)) in the pair of conductor wires 13 corresponds to the dielectric that determines the capacitance in the load sensor 1 (capacitive load sensor).

[0049] When a load is applied to each sensor unit in the Z-axis direction, the pair of conductor wires 13 are wrapped in the conductive elastic bodies 12 and 22. This changes the contact area between the pair of conductor wires 13 and the conductive elastic bodies 12 and 22, and the electrostatic capacitance between the conductive member 13a of the pair of conductor wires 13 and the conductive elastic bodies 12 and 22 changes.

[0050] The ends of the pair of conductor wires 13 on the negative side of the X axis and the ends of the cables C1 and C2 on the negative side of the Y axis are connected to a detection circuit installed for the load sensor 1. The conductive members 13a in the pair of conductor wires 13 are connected to each other in the detection circuit, and the cables C1 and C2 are connected to each other in the detection circuit.

[0051] 4, the cables C1 and C2 drawn out from the three pairs of conductive elastic bodies 12 and 22 are referred to as lines L11, L12, and L13, and the conductive members 13a in the three pairs of conductor wires 13 are referred to as lines L21, L22, and L23. The positions where the conductive elastic bodies 12 and 22 connected to line L11 intersect with lines L21, L22, and L23 are sensor units A11, A12, and A13, respectively. The positions where the conductive elastic bodies 12 and 22 connected to line L12 intersect with lines L21, L22, and L23 are sensor units A21, A22, and A23, respectively. The positions where the conductive elastic bodies 12 and 22 connected to line L13 intersect with lines L21, L22, and L23 are sensor units A31, A32, and A33, respectively.

[0052] When a load is applied to sensor unit A11, the contact area between the conductive members 13a of the pair of conductor wires 13 and the conductive elastic bodies 12, 22 in sensor unit A11 increases. Therefore, the load applied to sensor unit A11 can be calculated by detecting the capacitance between line L11 and line L21. Similarly, the load applied to other sensor units can be calculated by detecting the capacitance between two lines that intersect in the other sensor units.

[0053] In this embodiment, as described above, the width of the conductive elastic bodies 12, 22 in the X-axis direction is not constant over the entire length in the Y-axis direction, but varies depending on the shapes of the notches 12a, 12b provided at the positions where the conductor wires 13 intersect. In this embodiment, by varying the width of the conductive elastic bodies 12, 22 in this way, the relationship between the contact area and the load between the conductive elastic bodies 12, 22 and the conductor wires 13 approaches a linear relationship, as will be described below.

[0054] Figure 5(a) is a cross-sectional view schematically showing the contact portion between the conductor wire 13 and the conductive elastic bodies 12, 22 when cut at the center position in the X-axis direction of the conductive elastic bodies 12, 22 by a plane parallel to the YZ plane.

[0055] 5(a), when a load is applied, the conductor wire 13 sinks into and is wrapped in the conductive elastic bodies 12, 22. At this time, the total length of the arc of the contact portion between the conductor wire 13 and the conductive elastic bodies 12, 22 when viewed in the X-axis direction is defined as x. In this case, the arc length of the upper contact portion and the arc length of the lower contact portion are each x / 2.

[0056] Fig. 5(b) is a plan view schematically illustrating the configuration near the intersection of the conductor wire 13 and the conductive elastic bodies 12, 22 when the conductive elastic bodies 12, 22 do not have the notches 12a, 22a (comparative example). That is, in the comparative example, the width of the conductive elastic bodies 12, 22 in the X-axis direction is constant at w1. In Fig. 5(b), the conductor wire 13 is indicated by a dashed line. The length of the arc at the contact portion between the conductor wire 13 and the conductive elastic bodies 12, 22 is x / 2, as in Fig. 5(a), and the total length (sum) of these arc lengths is x.

[0057] FIG. 6A is a graph (simulation results) showing the relationship between the arc length (x) of the contact portion and the load in the comparative example.

[0058] In FIG. 6(a), the horizontal axis represents the arc length x (mm) of the contact portion, and the vertical axis represents the load f(x) (N / cm ２ ) In FIG. 6(a), small fluctuations occur in the graph due to the relationship with the resolution of the simulation. The relationship between the actual load and the arc length x is defined by the graph shown by the dotted line in FIG. 6(a). As shown in FIG. 6(a), the load value can be expressed by the function f(x).

[0059] In the comparative example, since the conductive elastic bodies 12 and 22 are rectangular, the contact area S between the conductor wire 13 and the conductive elastic bodies 12 and 22 is calculated by multiplying the length x of the arc by a constant width w1. Therefore, the relationship between the load f(x) and the contact area S is not linear. In this way, when the relationship between the load f(x) and the contact area S is not linear, the relationship between the load f(x) and the capacitance detected by the sensor unit A is also not linear, making it difficult to easily and smoothly detect the load applied to the load sensor 1.

[0060] Therefore, the inventors thought that if there is a proportional relationship between the degree of increase in load f(x) and the degree of increase in contact area S at any x, then a proportional relationship (linearity) will be established between load f(x) and contact area S, and a proportional relationship (linearity) will also be established between load f(x) and the capacitance detected by sensor unit A.

[0061] That is, if the following relationship is established, a proportional relationship (linearity) can be established between the load and the contact area.

[0062] dS / dx ∝ f'(x)... (1)

[0063] Here, the change in the contact area S on the left side of equation (1) corresponds to the width in the X-axis direction of the conductive elastic bodies 12, 22. Therefore, if the variable x is expanded in the longitudinal direction of the conductive elastic bodies 12, 22 and the width of the conductive elastic bodies 12, 22 is represented by W(x), a proportional relationship (linearity) can be established between the load f(x) and the contact area S when the following relational equation (2) is established:

[0064] W(x)=α・f'(x)...(2)

[0065] 6(b), by providing notches 12a, 22a in the conductive elastic bodies 12, 22, respectively, and setting the conductive elastic bodies 12, 22 so that the width W(x) varies with the arc length x based on the above formula (2), it is possible to establish a proportional relationship (linearity) between the load f(x) and the contact area S. In this case, the width w2 of the notches 12a, 22a in the Y-axis direction is set to a range in which the conductor wire 13 contacts the conductive elastic bodies 12, 22 when the maximum load of the detection range is applied. The width w2 is set to, for example, ½ the perimeter length of the cross section of the conductor wire 13.

[0066] The constant α required for the proportional relationship (linearity) between the load and the contact area can vary depending on the diameter of the conductor wire 13, the elastic force of the conductive elastic bodies 12 and 22, the width w1 of the conductive elastic bodies 12 and 22, etc.

[0067] Next, the inventors verified the relationship between the magnitude of the constant α and the linearity between the load f(x) and the contact area S through simulation.

[0068] FIG. 7 is a diagram showing the simulation conditions.

[0069] As shown in Figure 7, the inventors assumed a single sensor unit A similar to the configuration shown in Figures 3(a) and (b) for the simulation configuration. The lower surface of the sheet-like member 11 was placed on the upper surface of the base 101. A pusher 102 was placed on the upper surface 21b of the sheet-like member 21. The thickness d1 of the sheet-like members 11 and 21 was 1 mm. The thickness d2 of the conductive elastic bodies 12 and 22 was 0.03 mm. The outer diameter d3 of the conductor wire 13 was 0.3 mm. The center-to-center distance d4 of the two conductor wires 13 was 5 mm. The elastic modulus of the sheet-like members 11 and 21 was 3 MPa. The elastic modulus of the conductive elastic bodies 12 and 22 was 3 MPa.

[0070] FIG. 8 is a graph showing the relationship between the load and the contact area when the constant α is changed.

[0071] In the graph of FIG. 8, the horizontal axis represents the load (N / cm ２The vertical axis shows the contact area normalized by the contact area value at the maximum load (6.464). The contact area here is the sum of the areas where one conductor wire 13 contacts the conductive elastic bodies 12 and 22.

[0072] As shown in Fig. 8, when the conductive elastic bodies 12, 22 have a constant width, i.e., when the conductive elastic bodies 12, 22 are not provided with notches 12a, 22a as in the comparative example shown in Fig. 5(b), the relationship between the load and the contact area is a curve with the greatest curvature. Also, the smaller the constant α, the more linear the relationship between the load and the contact area. When the constant α is 0.6, the graph is approximated to a straight line, where the horizontal axis is x and the vertical axis is y, and the equation of the approximated line is y = 0.1528x + 0.1187. In this case, the coefficient of determination R ２ The value of is 0.95.

[0073] From these verification results, it can be seen that the smaller the constant α, the more linear the relationship between the load and the contact area. Therefore, in order to make the relationship between the load and the contact area more linear, it is preferable to set the constant α as small as possible. However, on the other hand, the smaller the constant α, the smaller the contact area between the conductor wire 13 and the conductive elastic bodies 12, 22 when the same load is applied.

[0074] 9A to 9D are diagrams showing the shapes of the conductive elastic bodies 12 and 22 in plan view.

[0075] 9(a) to 9(d), the horizontal axis represents the distance (mm) when the center position of the conductor wire 13 in the Y-axis direction is set to 0, and the vertical axis represents the distance (mm) when the center position of the conductive elastic bodies 12 and 22 in the X-axis direction (width direction) is set to 0. Figures 9(a) to 9(d) show the shapes of the conductive elastic bodies 12 and 22 when the constant α is 0.10, 0.20, 0.60, and 1.00, respectively.

[0076] 9(a) to 9(d), as the constant α decreases, the width of the notches 12a, 22a in the horizontal direction (Y-axis direction) increases, and the width of the conductive elastic bodies 12, 22 in the vertical direction (X-axis direction) decreases. Therefore, as the constant α decreases, the change in capacitance in response to a change in load decreases, and the sensitivity of load detection decreases. Furthermore, as the constant α decreases, the width of the conductive elastic bodies 12, 22 in the X-axis direction decreases, and the resistance value of the conductive elastic bodies 12, 22 increases.

[0077] In this way, when the constant α is reduced, there is a trade-off between improving the linearity of the relationship between the load and the contact area, and reducing the load detection sensitivity and increasing the resistance value of the conductive elastic bodies 12 and 22. Therefore, it is preferable to set the constant α while taking such a trade-off into consideration.

[0078] In the simulation results shown in FIG. 8, when the constant α is 0.6, the coefficient of determination R ２ The constant α is preferably set in the range of greater than 0 and equal to or less than 0.6, taking into consideration the above trade-off relationship.

[0079] In the above verification, it was assumed that the width of the conductive elastic bodies 12, 22 in the X-axis direction at the position where the conductor wire 13 is arranged is 0, as shown in Fig. 6(b) . However, when the conductive elastic bodies 12, 22 are formed by a printing method, the width of the conductive elastic bodies 12, 22 cannot be set to 0 and must be set to at least 1 µm or more.

[0080] Therefore, the inventors conducted a simulation to verify the relationship between the load and the contact area when the width of the conductive elastic bodies 12 and 22 at the position where the conductor wire 13 is arranged is changed.

[0081] FIG. 10 is a diagram showing the conditions of this simulation.

[0082] As shown in FIG. 10 , the width of the conductive elastic bodies 12 and 22 in the X-axis direction at the intersection of the conductor wire 13 and the conductive elastic bodies 12 and 22 was defined as β. The midpoint of the width β coincided with the midpoint of the width w1. A straight line portion 31 parallel to the Y-axis direction was set at the position of the width β. Curved lines 32 were set from both ends of the width w2 at a slope of constant α until they reached the straight line portion 31. The notches 12a and 22a were formed by one straight line portion 31 and the curved lines 32 on both sides of it. The notches 12a and 22a were symmetrical in the direction perpendicular to the longitudinal direction of the conductor wire 13 (the Y-axis direction) and in the longitudinal direction of the conductor wire 13 (the X-axis direction). The axis of symmetry of the notches 12a and 22a in the Y-axis direction was set at the midpoint of the conductor wire 13 in the Y-axis direction.

[0083] In the simulation, the value of the constant α was fixed at 0.6, and the width β was varied to verify how the relationship between the load and the contact area changed depending on the width β.

[0084] FIG. 11 is a graph showing the relationship between the load and the contact area when the width β is changed.

[0085] In the graph of FIG. 11, the horizontal axis also represents the load (N / cm ２ ) and the vertical axis shows the value of the contact area normalized by the value of the contact area at the maximum load value (6.464).

[0086] As shown in Fig. 11, when the conductive elastic bodies 12, 22 have a constant width, i.e., when the conductive elastic bodies 12, 22 are not provided with notches 12a, 22a as in the comparative example shown in Fig. 5(b), the relationship between the load and the contact area is a curve with the greatest curvature. Also, as the width β becomes smaller, the relationship between the load and the contact area becomes more linear. When the graph when the width β is 0.5 is approximated to a straight line, the equation of the approximated line is y = 0.1415x + 0.1538, where the horizontal axis is x and the vertical axis is y. In this case, the coefficient of determination R ２ The value is 0.9711.

[0087] From these verification results, it can be seen that the smaller the width β, the more linear the relationship between the load and the contact area. Therefore, in order to make the relationship between the load and the contact area more linear, it is preferable to set the width β as small as possible. However, on the other hand, the smaller the width β, the smaller the contact area between the conductor wire 13 and the conductive elastic bodies 12, 22 when the same load is applied.

[0088] 12(a) to 12(d) are diagrams showing the shapes in plan view of the conductive elastic bodies 12 and 22. Figures 12(a) to 12(d) show the shapes of the conductive elastic bodies 12 and 22 when the width β is 0, 0.1 × w1, 0.5 × w1, and 0.8 × w1, respectively.

[0089] As shown in Figures 12(a) to 12(d), the smaller the width β, the narrower the width of the conductive elastic bodies 12, 22 in the vertical direction (X-axis direction). This reduces the change in capacitance in response to a change in load, reducing the sensitivity of load detection. Furthermore, the smaller the width β, the narrower the width of the conductive elastic bodies 12, 22 in the X-axis direction, resulting in a higher resistance value of the conductive elastic bodies 12, 22. Furthermore, as the width β decreases, the range in which the width in the vertical direction (X-axis direction) is constant narrows, making it difficult to position the conductor wire 13 within this range. Furthermore, as mentioned above, there are limitations to reducing the width β due to the printing method.

[0090] In this way, when the width β is reduced, there is a trade-off between improving the linearity of the relationship between the load and the contact area and reducing the load detection sensitivity and increasing the resistance value of the conductive elastic bodies 12 and 22. Therefore, it is preferable to set the width β while taking such a trade-off into consideration.

[0091] In the simulation results shown in FIG. 11, when the width β is 0.5×w1, the coefficient of determination R ２ Therefore, taking the above trade-off into consideration, the width β should be set to a value greater than 1 μm and less than or equal to 0.5 times the width w1 of the conductive elastic bodies 12 and 22.

[0092] Next, the inventors investigated the preferable rate of change in the area of ​​the conductive elastic bodies 12, 22 due to the notches 12a, 22a when the value of the width β was fixed at 0 and the constant α was changed.

[0093] Here, the rate of change is defined as the ratio of the total area of ​​the notches 12a, 22a included in the rectangular region R0 defined in the conductive elastic body 12, 22 by the width w1 and the width w2, as shown in FIG. 13, to the total area of ​​this region R0.

[0094] Fig. 14(a) is a graph showing the relationship between the load and the contact area when the rate of change is changed in accordance with the change in the constant α, and Fig. 14(b) is a graph showing the approximation lines of the curves in Fig. 14(a).

[0095] In the graphs of FIGS. 14(a) and 14(b), the horizontal axis represents the load (N / cm ２ ), and the vertical axis represents the contact area (mm ２ ) is shown.

[0096] The change rate of 0% indicates the case where the width of the conductive elastic bodies 12 and 22 is constant at w1, i.e., the case where the notches 12a and 22a are not provided as in the comparative example shown in Figure 5(b). The coefficient of determination R for change rates of 0%, 15%, 20%, 30%, 51%, and 72% ２ were 0.9145, 0.9383, 0.95, 0.97, 0.9962, and 0.9999, respectively.

[0097] As shown in Figures 14(a) and 14(b), the relationship between the load and the contact area approaches a straight line as the rate of change increases, and the coefficient of determination R ２ approaches 1. However, as explained with reference to Figures 9(a) to (d), if the area occupied by the notches 12a, 22a increases and the rate of change increases, this will result in a decrease in the load detection sensitivity and an increase in the resistance value of the conductive elastic bodies 12, 22. Therefore, it is preferable to set the rate of change while taking into consideration this trade-off relationship.

[0098] According to the simulation results shown in FIGS. 14(a) and 14(b), when the rate of change is 20%, the coefficient of determination R ２The change rate is preferably set to a range of 20% or more, taking into consideration the above trade-off relationship.

[0099] Next, the effect of the notches 12a and 22a having symmetrical shapes will be described.

[0100] FIG. 15 is an exemplary view showing the configuration of the notches 12a and 22a in this embodiment, similar to FIG.

[0101] 15 , the initial contact region R1 is the region where the conductor wire 13 and the conductive elastic bodies 12, 22 come into contact with each other in a no-load state. In other words, the initial contact region R1 is a linear region that passes through the center of the conductor wire 13 in the Y-axis direction and extends in the X-axis direction. The center O1 is the center of the initial contact region R1. In other words, the center O1 is the center of the intersection of the conductor wire 13 and the conductive elastic bodies 12, 22.

[0102] In this embodiment, notches 12a, 22a are formed on both sides of the initial contact region R1 so that the width in the X-axis direction of the conductive elastic bodies 12, 22 changes. This allows the contact area to change efficiently in response to the load, making it easier to make the relationship between the load and the contact area closer to linear.

[0103] In this embodiment, the notches 12a and 22a are arranged symmetrically in the Y-axis direction with respect to the initial contact region R1. As a result, even if the center of gravity of the load is displaced in the positive or negative Y-axis direction from the center O1 in FIG. 15 , the contact area between the conductor wire 13 and the conductive elastic bodies 12 and 22 remains substantially the same. This reduces the variation in the detected load when an unbalanced load occurs in the Y-axis direction. Additionally, because the notches 12a and 22a are arranged symmetrically in the X-axis direction with respect to the initial contact region R1, the contact area between the conductor wire 13 and the conductive elastic bodies 12 and 22 remains substantially the same even when an unbalanced load occurs in the X-axis direction. This reduces the variation in the detected load when an unbalanced load occurs in the X-axis direction.

[0104] In this manner, in the present embodiment, the notches 12 a and 22 a are provided symmetrically in the Y-axis direction and the X-axis direction with respect to the initial contact region R1, so that even if an unbalanced load occurs in the Y-axis direction and the X-axis direction with respect to the center O1, the variation in the detected load can be suppressed. In the present embodiment, the notches 12 a and 22 a have a symmetrical shape with respect to the center O1, so that the variation in the load detection caused by an unbalanced load in a direction parallel to the X-Y plane can be suppressed.

[0105] <Effects of the embodiment> According to the embodiment, the following effects are achieved.

[0106] The widths of the conductive elastic bodies 12, 22 in the longitudinal direction of the conductive member 13a are changed so that the relationship between the load and the contact area between the conductive elastic bodies 12, 22 and the conductive member 13a via the dielectric 13b approaches a linear relationship. With this configuration, as described with reference to Figure 8, the change in the widths of the conductive elastic bodies 12, 22 makes the relationship between the load and the contact area between the conductive elastic bodies 12, 22 and the conductive member 13a approach a linear relationship, and therefore the relationship between the load and the capacitance also approaches a linear relationship. Therefore, by detecting the capacitance between the conductive elastic bodies 12, 22 and the conductive member 13a, the applied load can be detected easily and smoothly.

[0107] When the magnitude of the load at the contact portion between the conductive elastic bodies 12, 22 and the conductive member 13a via the dielectric 13b is expressed as a function f(x), where x is the circumferential length of the conductive member 13a, as shown in the above equation (2), the width W(x) of the conductive elastic bodies 12, 22 at the contact portion is adjusted to be proportional to f'(x), which is a differential function of the function f(x). This configuration allows the relationship between the contact area between the conductive elastic bodies 12, 22 and the conductive member 13a and the load to become more linear. Therefore, by detecting the capacitance between the conductive elastic bodies 12, 22 and the conductive member 13a, the applied load can be detected with greater accuracy.

[0108] The contact area when the maximum load of the detection range is applied is reduced by 20% or more compared to when the width of the conductive elastic bodies 12, 22 in the X-axis direction is constant. As described with reference to Figures 14(a) and 14(b), in order to make the relationship between the contact area and the load between the conductive elastic bodies 12, 22 and the conductive member 13a more linear, it is necessary to change the width of the conductive elastic bodies 12, 22 so that the contact area when the maximum load of the detection range is applied is reduced by 20% or more compared to when the width is constant. Therefore, by changing the width of the conductive elastic bodies 12, 22 in this way so that the contact area when the maximum load of the detection range is applied is reduced by 20% or more compared to when the width is constant, the relationship between the contact area and the load can be made more linear, and the applied load can be detected more accurately.

[0109] The widths of the conductive elastic bodies 12, 22, which have a constant width in the X-axis direction, are changed by omitting a portion of the conductive elastic bodies 12, 22. Specifically, a notch 12a is provided at the end in the width direction (X-axis direction) of the conductive elastic body 12, which has a constant width, and a notch 22a is provided at the end in the width direction (X-axis direction) of the conductive elastic body 22, which has a constant width, thereby changing the widths of the conductive elastic bodies 12, 22. This makes it possible to easily change the width of the conductive elastic bodies 12, 22 in the longitudinal direction of the conductive member 13a to a desired state.

[0110] 15, the notches 12a and 22a provide a shape change on both sides of the initial contact region R1 to change the width of the conductive elastic bodies 12 and 22 in the X-axis direction. This allows the contact area to be changed efficiently in response to the load, making it easier to make the relationship between the load and the contact area linear. This allows the applied load to be detected more accurately.

[0111] 15, the shape changes required to change the width of the conductive elastic bodies 12 and 22 in the X-axis direction are symmetrical with respect to the initial contact region R1 in the direction perpendicular to the longitudinal direction of the conductive member 13a (the Y-axis direction). This ensures that the contact area between the conductor wire 13 and the conductive elastic bodies 12 and 22 remains substantially the same even if the center of gravity of the load is displaced from the center O1 in the positive or negative Y-axis direction. This reduces variations in the detected load when an unbalanced load occurs in the Y-axis direction.

[0112] 15, the shape changes required to change the width of the conductive elastic bodies 12 and 22 in the X-axis direction are symmetrical in the longitudinal direction (X-axis direction) of the conductive member 13a with respect to the center O1 of the initial contact region R1. This ensures that the contact area between the conductor wire 13 and the conductive elastic bodies 12 and 22 remains substantially constant even if the center of gravity of the load is displaced from the center O1 in the positive or negative X-axis direction. This reduces variations in the detected load when an unbalanced load occurs in the X-axis direction.

[0113] <Examples of Modifications to the Shape of the Conductive Elastic Body> In the above embodiment, as shown in Figure 15, notches 12a, 22a are provided at the ends of the conductive elastic bodies 12, 22 in the X-axis direction as a shape for changing the width of the conductive elastic bodies 12, 22 in the X-axis direction. However, the shape for changing the width of the conductive elastic bodies 12, 22 in the X-axis direction is not limited to the above and may be, for example, the shapes shown in Figures 16(a) to 18(b). With the configurations such as those shown in Figures 16(a) to 18(b), the width of the conductive elastic bodies 12, 22 in the longitudinal direction of the conductive member 13a can be easily changed to a desired state.

[0114] 16(a), notches 12a, 22a are provided only at the ends of the conductive elastic bodies 12, 22 on the positive side of the X axis. Linear portions 31 extending in the Y axis direction are formed at the ends of the notches 12a, 22a on the negative side of the X axis, and curved portions 32 are formed on the positive and negative sides of the Y axis of the linear portion 31. The width of the conductive elastic bodies 12, 22 in the X axis direction corresponding to the linear portion 31 is the constant width β described above. The width of the conductive elastic bodies 12, 22 in the X axis direction corresponding to the curved portion 32 is adjusted to change based on the function W(x) of the above equation (1).

[0115] In this case, as in the above embodiment, by appropriately setting the constant α and the width β, the relationship between the contact area between the conductive elastic body 12, 22 and the conductive member 13a and the load can be made closer to linear, and the relationship between the load and the capacitance can also be made closer to linear.

[0116] 16(a), the shapes of the conductive elastic bodies 12 and 22 near the center O1 are symmetrical in the Y-axis direction. Therefore, even if the center of gravity of the load is displaced from the center O1 in the positive or negative Y-axis direction, the contact area between the conductor wire 13 and the conductive elastic bodies 12 and 22 remains substantially the same. This makes it possible to suppress variations in the detected load when an unbalanced load occurs in the Y-axis direction.

[0117] In the modified example shown in FIG. 16( b), an opening 12b is provided near the center O1 of the conductive elastic body 12 in the width direction (X-axis direction) and penetrates the conductive elastic body 12. An opening 22b is provided near the center O1 of the conductive elastic body 22 in the width direction (X-axis direction). The openings 12b and 22b are located at the same position and have the same shape in a plan view. Linear portions 31 extending in the Y-axis direction are formed at the ends of the openings 12b and 22b on the positive and negative sides of the X-axis, and curved portions 32 are formed on the positive and negative sides of the Y-axis of the linear portions 31. The width of the conductive elastic bodies 12 and 22 corresponding to the linear portions 31 is a constant value L31. The value of L31×2 is the constant width β described above. The width of the conductive elastic bodies 12 and 22 corresponding to the positive and negative sides of the X-axis of the curved portions 32 is L32. The value of L32×2 is the above-described W(x).

[0118] In this case, as in the above embodiment, by appropriately setting the constant α and the width β, the relationship between the contact area between the conductive elastic body 12, 22 and the conductive member 13a and the load can be made closer to linear, and the relationship between the load and the capacitance can also be made closer to linear.

[0119] 16(b), the shapes of the conductive elastic bodies 12, 22 near the center O1 are symmetrical in the X-axis direction and the Y-axis direction with respect to the center O1, so that even if an unbalanced load occurs in the X-axis direction and the Y-axis direction with respect to the center O1, the variation in the detection load can be suppressed. Also, because the shapes of the conductive elastic bodies 12, 22 near the center O1 are symmetrical with respect to the center O1, the variation in the detection load can be suppressed even if an unbalanced load occurs in a direction parallel to the X-Y plane.

[0120] In the modified example shown in FIG. 17( a), notches 12a and 22a are provided at the ends of the conductive elastic bodies 12 and 22 on the negative side of the X axis. Openings 12b and 22b and openings 12c and 22c are also provided side by side in the X axis direction. The notches 12a and openings 12b and 12c are provided in the conductive elastic body 12, while the notches 22a and openings 22b and 22c are provided in the conductive elastic body 22. The lengths of the notches 12a and 22a and openings 12b, 22b, 12c, and 22c in the Y axis direction are all w2. Within the range of width w2, the widths of the conductive elastic bodies 12 and 22 in the X axis direction are L41, L42, and L43. The value of L41 + L42 + L43 is the above-mentioned W(x).

[0121] In this case, as in the above embodiment, by appropriately setting the constant α and the width β, the relationship between the contact area between the conductive elastic body 12, 22 and the conductive member 13a and the load can be made closer to linear, and the relationship between the load and the capacitance can also be made closer to linear.

[0122] In the modified example of Figure 17(a), the shapes of the conductive elastic bodies 12 and 22 near the center O1 are symmetrical in the Y-axis direction with respect to the center O1, so even if an unbalanced load occurs in the Y-axis direction with respect to the center O1, the variation in the detection load can be suppressed.

[0123] In the modified example shown in FIG. 17( b), openings 12d and 22d are provided at the ends of the conductive elastic bodies 12 and 22 on the positive and negative sides of the X axis. The opening 12d is a recess having a bottom that is one step lower in the negative Z axis direction from the surface of the conductive elastic body 12 on the positive Z axis (the surface that contacts the conductor wire 13). The opening 22d is a recess having a bottom that is one step lower in the positive Z axis direction from the surface of the conductive elastic body 22 on the negative Z axis (the surface that contacts the conductor wire 13). The bottoms of the openings 12d and 22d do not contact the conductor wire 13. The length of each of the openings 12d and 22d in the Y axis direction is w2. Within the range of width w2, the width of the conductive elastic bodies 12 and 22 in the X axis direction is W(x) as described above.

[0124] In this case, as in the above embodiment, by appropriately setting the constant α and the width β, the relationship between the contact area between the conductive elastic body 12, 22 and the conductive member 13a and the load can be made closer to linear, and the relationship between the load and the capacitance can also be made closer to linear.

[0125] 17(b), the shapes of the conductive elastic bodies 12, 22 near the center O1 are symmetrical in the X-axis direction and the Y-axis direction with respect to the center O1, so that even if an unbalanced load occurs in the X-axis direction and the Y-axis direction with respect to the center O1, the variation in the detection load can be suppressed. Also, because the shapes of the conductive elastic bodies 12, 22 near the center O1 are symmetrical with respect to the center O1, the variation in the detection load can be suppressed even if an unbalanced load occurs in a direction parallel to the X-Y plane.

[0126] In the modified example shown in Figure 18(a), notches 12a, 22a are provided at the ends of the conductive elastic bodies 12, 22 on the positive and negative sides of the X-axis. The notches 12a, 22a on the positive side of the X-axis are positioned offset to the positive side of the Y-axis within the range of width w2, while the notches 12a, 22a on the negative side of the X-axis are positioned offset to the negative side of the Y-axis within the range of width w2. The notches 12a and 22a have shapes that are point-symmetric with respect to the center O1. Within the range of width w2, the width of the conductive elastic bodies 12, 22 in the X-axis direction is W(x) as described above.

[0127] In this case, as in the above embodiment, by appropriately setting the constant α and the width β, the relationship between the contact area between the conductive elastic body 12, 22 and the conductive member 13a and the load can be made closer to linear, and the relationship between the load and the capacitance can also be made closer to linear.

[0128] In the modified example of Figure 18(a), the shapes of the conductive elastic bodies 12 and 22 near the center O1 are symmetrical with respect to the center O1, so even if an unbalanced load occurs in a direction parallel to the XY plane, the variation in the detected load can be suppressed.

[0129] In the modified example shown in Figure 18(b), the conductor wire 13 is positioned at a position rotated about center O1 in the X-Y plane from the position where it intersects perpendicularly with the conductive elastic bodies 12, 22. That is, the conductor wire 13 and the conductive elastic bodies 12, 22 intersect at an angle other than 90° in plan view. Accordingly, the notches 12a, 22a of the conductive elastic bodies 12, 22 are also formed at similarly rotated positions in the X-Y plane. In the longitudinal direction of the conductor wire 13, the distance between two opposing straight portions 31 is the constant width β described above, and the distance between two opposing curved portions 32 in the longitudinal direction of the conductor wire 13 is W(x) described above.

[0130] In this case, as in the above embodiment, by appropriately setting the constant α and the width β, the relationship between the contact area between the conductive elastic body 12, 22 and the conductive member 13a and the load can be made closer to linear, and the relationship between the load and the capacitance can also be made closer to linear.

[0131] In the modified example of Figure 18 (b), the shapes of the conductive elastic bodies 12 and 22 near the center O1 are symmetrical with respect to the center O1, so even if an unbalanced load occurs in a direction parallel to the XY plane, the variation in the detected load can be suppressed.

[0132] <Other Modifications> The configuration of the load sensor 1 can be modified in various ways in addition to the configurations shown in the above embodiment and the above modifications.

[0133] For example, in the above embodiment, the notch 12a provided in the conductive elastic body 12 and the notch 22a provided in the conductive elastic body 22 have the same shape and are arranged to overlap in a plan view. However, this is not limited to this, and the notch 12a and the notch 22a may be arranged to be the same shape but offset from each other, or may have different shapes, or only one of the notches 12a, 22a may be provided. In the above modified example, the notch and opening of the conductive elastic body 12 and the notch and opening of the conductive elastic body 22 may be arranged to be the same shape but offset from each other, or may have different shapes, or only one of the notches and openings of the conductive elastic body 12, 22 may be provided.

[0134] In this way, even when the shape and arrangement of the notches and openings are changed, as in the above embodiment and modified examples, the widths of the conductive elastic bodies 12 and 22 are set so that the relationship between the load and the contact area between the conductive member 13a via the dielectric 13b and the conductive elastic bodies 12 and 22 approaches a linear relationship. This makes it possible to easily and smoothly detect the applied load by detecting the electrostatic capacitance between the conductive elastic bodies 12 and 22 and the conductive member 13a.

[0135] In the above embodiment, one set of notches (notches 12a, 22a) is provided in the conductive elastic bodies 12, 22, but this is not limiting, and two or more sets of notches may be provided side by side in the Y-axis direction.

[0136] 16(b), one set of through-holes (openings 12b, 22b) is provided in the conductive elastic bodies 12, 22, but this is not limiting and two or more sets of through-holes may be provided. In this case, the two or more sets of through-holes may be aligned in the X-axis direction or in the Y-axis direction.

[0137] 17(b), one set of concave openings (openings 12d, 22d) is provided in the conductive elastic bodies 12, 22, but the concave openings may be provided inside the conductive elastic bodies 12, 22. Also, two or more sets of concave openings may be provided in the conductive elastic bodies 12, 22. In this case, the two or more sets of concave openings may be aligned in the X-axis direction or in the Y-axis direction.

[0138] Furthermore, in the above-described embodiment and modified example, a structure (notch or opening) for changing the width of the conductive elastic bodies 12 and 22 in the X-axis direction is provided on both the positive and negative Y-axis sides of the initial contact region R1 (see FIG. 15 ). However, such a structure may be provided only on either the positive or negative Y-axis side of the initial contact region R1. However, with this structure, variations in the detected load are likely to occur when a load is applied at a position symmetrical in the Y-axis direction with respect to the initial contact region R1. Therefore, in order to suppress variations in the detected load, it is preferable to provide a structure (notch or opening) for changing the width of the conductive elastic bodies 12 and 22 in the X-axis direction on both the positive and negative Y-axis sides of the initial contact region R1, as in the above-described embodiment and modified example.

[0139] In the above embodiment, the pair of conductor lines 13 are connected at their ends on the positive side of the X-axis, but they may be separated at their ends on the positive side of the X-axis. That is, separate conductor lines 13 may be arranged side by side in the Y-axis direction. In this case, the two conductor lines 13 passing through one sensor unit A are connected to each other in subsequent wiring or circuitry.

[0140] In the above embodiment, the load sensor 1 includes three pairs of conductor wires 13, but may include one or more pairs of conductor wires 13. For example, the load sensor 1 may include only one pair of conductor wires 13. Furthermore, the sensor unit A of the load sensor 1 includes two conductor wires 13 aligned in the Y-axis direction, but may include one or more conductor wires 13. For example, the sensor unit A may include only one conductor wire 13. When the sensor unit A of the load sensor 1 includes three or more conductor wires 13 aligned in the Y-axis direction, these conductor wires 13 may be connected at their ends in the X-axis direction, or may be connected to each other in subsequent wiring or circuits.

[0141] In the above embodiment, the load sensor 1 includes three pairs of conductive elastic bodies 12, 22 that face each other vertically, but it is sufficient to include at least one pair of conductive elastic bodies 12, 22. For example, the load sensor 1 may include only one pair of conductive elastic bodies 12, 22.

[0142] In the above embodiment, the cross-sectional shape of the conductive member 13a is circular, but the cross-sectional shape of the conductive member 13a is not limited to circular and may be other shapes such as elliptical or pseudo-circular. Furthermore, the conductive member 13a may be formed of a twisted wire in which multiple conductive members are twisted together. In these cases, as in the above embodiment and modified example, the width of the conductive elastic bodies 12 and 22 is set so that the relationship between the contact area between the conductive member 13a and the conductive elastic bodies 12 and 22 via the dielectric 13b and the load approaches a linear relationship.

[0143] In the above embodiment, the sensor unit A includes a pair of conductive elastic bodies 12 and 22 that face each other vertically, but it may include only one of the conductive elastic bodies 12 and 22. In other words, only one of the conductive elastic bodies 12 and 22 may be disposed.

[0144] 19(a) is a schematic diagram illustrating a modified example in which only the conductive elastic body 12 of the conductive elastic bodies 12, 22 is disposed. In this case, when a load is applied to the upper surface 21b of the upper sheet-like member 21, the conductor wire 13 is enveloped by the conductive elastic body 12, and the contact area between the conductive member 13a and the conductive elastic body 12 changes via the dielectric 13b. In this case, as in the above embodiment and modified example, the width of the conductive elastic body 12 is set so that the relationship between the load and the contact area between the conductive member 13a and the conductive elastic body 12 via the dielectric 13b approaches a linear relationship. Note that in this case, the variable x used in the above equations (1) and (2) is the length of the arc of the contact portion between the conductor wire 13 and the conductive elastic body 12 when viewed in the X-axis direction.

[0145] In the above embodiment, the dielectric 13b is disposed so as to cover the conductive member 13a, but instead, the dielectric may be disposed on the opposing surfaces of the conductive elastic bodies 12, 22.

[0146] FIG. 19( b) is a schematic diagram illustrating a modified example in which the dielectrics 41 and 42 are disposed on the opposing surfaces of the conductive elastic bodies 12 and 22, respectively. In this case, when a load is applied to the sensor unit A, the conductive member 13 a moves relatively toward the conductive elastic bodies 12 and 22, changing the contact area between the conductive member 13 a and the dielectrics 41 and 42. This changes the capacitance between the conductive elastic bodies 12 and 22 and the conductive member 13 a, allowing the load to be detected at each sensor unit A. In this case, as in the above embodiment and modified example, the widths of the conductive elastic bodies 12 and 22 are set so that the relationship between the load and the contact area between the conductive member 13 a and the conductive elastic bodies 12 and 22 via the dielectrics 41 and 42 approaches a linear relationship. In this case, the variable x used in the above equations (1) and (2) is the total length of the arc of the contact portion between the conductive member 13 a and the dielectrics 41 and 42 when viewed in the X-axis direction.

[0147] 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.

[0148] 1 Load sensor 12, 22 Conductive elastic body 12a, 22a Notch 12b, 22b Opening 12c, 22c Opening 12d, 22d Opening 13a Conductive member 13b Dielectric 41, 42 Dielectric C1 Center R1 Initial contact area

Claims

1. A load sensor comprising: a conductive elastic body; a linear conductive member arranged so as to intersect with said conductive elastic body; and a dielectric arranged between said conductive elastic body and said conductive member, wherein the width of said conductive elastic body in the longitudinal direction of said conductive member is changed so that the relationship between the load and the contact area between said conductive elastic body and said conductive member via said dielectric approaches a linear relationship.

2. A load sensor as claimed in claim 1, characterized in that, when the magnitude of the load at the contact portion between the conductive elastic body and the conductive member via the dielectric is expressed as a function f(x) when the circumferential length of the conductive member is x, the width of the conductive elastic body at the contact portion is adjusted to be proportional to f'(x), which is a differential function of the function f(x).

3. A load sensor according to claim 1 or 2, wherein the contact area when the maximum load of the detection range is applied is reduced by 20% or more compared to when the width is constant.

4. A load sensor according to any one of claims 1 to 3, wherein the width is changed by omitting a part of the conductive elastic body, which has a constant width.

5. A load sensor according to claim 4, wherein the width is changed by providing a notch at an end in the width direction of the conductive elastic body, which has a constant width.

6. A load sensor according to claim 4 or 5, wherein the width is changed by providing an opening inside the conductive elastic body in the width direction, the width of which is constant.

7. A load sensor according to any one of claims 1 to 6, characterized in that a shape change for changing the width is provided on both sides of an initial contact area where the conductive elastic body and the conductive member come into contact via the dielectric in a no-load state.

8. A load sensor according to claim 7, wherein the shape change is provided symmetrically with respect to the initial contact area in a direction perpendicular to the longitudinal direction of the conductive member.

9. A load sensor according to claim 7 or 8, characterized in that the shape change is provided symmetrically in the longitudinal direction of the conductive member with respect to the center of the initial contact area.

10. A load sensor according to any one of claims 1 to 9, characterized in that the dielectric material is formed on the outer periphery of the conductive member.

11. A load sensor according to any one of claims 1 to 10, characterized in that the conductive elastic body has a shape that is long in one direction, and a plurality of the conductive members are arranged in a line in the longitudinal direction of the conductive elastic body.

12. A load sensor according to any one of claims 1 to 11, characterized in that a plurality of the conductive elastic bodies are arranged along the conductive member.