Load sensor

Abstract

This load sensor (1) comprises: a plurality of conductive elastic bodies (12) formed so as to extend in a first direction on a facing surface of a first base member (11); a plurality of conductor wires (31) extending in a second direction and arranged between the first base member (11) and a second base member (21); dielectric bodies (32) arranged between the conductive elastic bodies (12) and the conductor wires (31); and threads (40) whereby the plurality of conductor lines (31) are sewn together with the first base member (11) or the second base member (21). A plurality of sewing lines (40a) of the threads (40) are formed at a predetermined pitch in the second direction and consist of stitches arranged in the first direction. The conductor lines (31) are sewn to the target base member by the threads (40) between predetermined adjacent stitches on each of the sewing lines (40a). The threads (40) are sewn to the target base member so that ripples supporting a load do not occur in the target base member at least in a load detection range.

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) that includes a sheet-like substrate having an elastic conductive portion, a plurality of conductor wires arranged so as to cross the elastic conductive portion, a plurality of dielectrics respectively arranged between the plurality of conductor wires and the elastic conductive portion, and a thread-like member that sews the plurality of conductor wires to the substrate.

[0004] International Publication No. 2020 / 153029

[0005] In the load sensor described above, the conductor wire is sewn with thread to one of the two base members that sandwich the conductor wire. In this case, if the tension of the thread causes significant undulations in the base member, the base member will support part of the load acting on the load sensor, making it impossible to detect the load accurately.

[0006] In view of the above problem, an object of the present invention is to provide a load sensor that can accurately detect a load by appropriately suppressing undulation of a base member caused by threads.

[0007] A main aspect of the present invention 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 plurality of conductive elastic bodies formed on the opposing surface of the first base member so as to extend in a first direction, a plurality of conductor wires extending in a second direction intersecting the first direction and arranged side by side between the first base member and the second base member, a dielectric body disposed between the conductive elastic bodies and the conductor wires, and a thread for sewing the plurality of conductor wires to the first base member or the second base member. A plurality of stitch rows of the thread, each of which has stitches aligned in the first direction, are formed at a predetermined pitch in the second direction. The conductor wires are sewn to the target base member by the thread between predetermined adjacent stitches on each stitch row. The thread is sewn to the target base member so as to prevent undulations of the target base member that support the load, at least within the load detection range.

[0008] The load sensor according to this aspect prevents the base member to which the conductor wires are sewn from waviness, which would otherwise support a load, and thus allows the applied load to be detected with high accuracy.

[0009] As described above, according to the present invention, it is possible to provide a load sensor that can appropriately suppress undulation of the base member caused by threads and detect a load with high accuracy.

[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] FIGS. 1(a) and 1(b) are diagrams schematically illustrating the configuration of a structure during a manufacturing process according to the first embodiment. FIG. 2(a) is a diagram schematically illustrating the configuration of a structure during a manufacturing process according to the first embodiment. FIG. 2(b) is a perspective view schematically illustrating the configuration of a load sensor according to the first embodiment. FIG. 3 is a diagram schematically illustrating a cross section of the load sensor according to the first embodiment, when cut along a plane parallel to the X-Z plane at the position of the thread. FIGS. 4(a) and 4(b) are diagrams schematically illustrating a cross section near the intersection position of the conductive elastic body and the wire according to the first embodiment, when cut along a plane parallel to the X-Z plane at the intersection position of the conductive elastic body and the wire. FIG. 5 is a plan view schematically illustrating the internal configuration of the load sensor according to the first embodiment. FIGS. 6(a) and 6(b) are cross-sectional views schematically illustrating a state in which wavyness occurs in the second base member. FIGS. 7(a) and 7(b) are diagrams explaining the criteria for determining whether a load can be detected with high accuracy according to the first embodiment. FIGS. 8(a) and 8(b) are schematic diagrams illustrating the conditions for verifying waviness according to the first embodiment. FIG. 9 is a diagram illustrating the settings and verification results for configurations 1 to 4 used in the waviness verification according to the first embodiment. FIG. 10 is a diagram illustrating the actual plan view of configurations 1 to 4 used in the waviness verification according to the first embodiment, a cross-sectional view schematically illustrating configurations 1 to 4, and the results of the waviness state for configurations 1 to 4. FIG. 11(a) is a diagram illustrating the configuration of a structure during a manufacturing process according to the second embodiment. FIG. 11(b) is a perspective view schematically illustrating the configuration of a load sensor according to the second embodiment. FIG. 12(a) is a diagram illustrating a cross section near the intersection of a conductive elastic body and a wire according to the second embodiment, when cut along a plane parallel to the X-Z plane at the intersection. FIG. 12(b) is a cross-sectional view schematically illustrating a state in which waviness has occurred in the first base member. Fig. 13(a) is a plan view and a cross-sectional view schematically showing the vicinity of a gap between two conductive elastic bodies adjacent in the Y-axis direction according to embodiment 2. Fig. 12(b) is a plan view and a cross-sectional view schematically showing a structure when the conductive elastic bodies of Fig. 13(a) are joined by a stitching row according to embodiment 2. Fig. 14 is a diagram schematically showing a cross section near the intersection position when cutting along a plane parallel to the X-Z plane at the intersection position of the conductive elastic body and the wire according to a 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 weight distribution of 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] First Embodiment FIG. 1A is a diagram schematically illustrating the configuration of a structure 1a in a manufacturing process.

[0024] The structure 1 a includes a first base member 11 , a plurality of conductive elastic bodies 12 , and a plurality of wirings 13 .

[0025] 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.

[0026] 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.

[0027] 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.

[0028] The thickness of the first base member 11 is set to, for example, 0.02 mm or more and 1 mm or less, and the elastic modulus of the first base member 11 is set to, for example, 1 MPa or more and 3 MPa or less.

[0029] 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.

[0030] 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 make it possible to form the conductive elastic body 12 with a thickness of approximately 0.001 mm to 0.5 mm 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.

[0031] 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.

[0032] 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.

[0033] 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 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 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).

[0034] The thickness of the conductive elastic body 12 is set to, for example, 1 μm or more and 30 μm or less, and the elastic modulus of the conductive elastic body 12 is set to, for example, 0.5 MPa or more and 3 MPa or less.

[0035] FIG. 1B is a diagram schematically showing the configuration of a structure 1b in the manufacturing process.

[0036] The structure 1 b includes a second base member 21 and a plurality of wires 30 .

[0037] A plurality of wires 30 are arranged on the opposing surface 21a (the surface on the positive side of the Z axis) of the second base member 21. Here, three wire groups G1 each consisting of four wires 30 are arranged on the opposing surface 21a, for a total of 12 wires 30 arranged on the opposing surface 21a. The number of wires 30 arranged on the opposing surface 21a is not limited to this.

[0038] The second base member 21 is an elastic, flat-plate-shaped member. As will be described later with reference to FIG. 2( b), 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 thickness of the second base member 21 is constant. When the thickness of the second base member 21 is small, the second base member 21 may be called a sheet member or a film member.

[0039] 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.

[0040] The wires 30 extend in the Y-axis direction (second direction) and are arranged side by side between the first base member 11 and the second base member 21 when the assembly of the load sensor 1 is complete. The wires 30 are linear and meander so as to sway slightly in the X-axis direction. 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 the wire group G1 are also arranged at predetermined intervals in the X-axis direction (first direction).

[0041] 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.

[0042] The conductor wire 31 is a conductive, linear member. The conductor wire 31 is made of, for example, a conductive metal material. Alternatively, the conductor wire 31 may be made of a glass core wire with a conductive layer formed on its surface, or a resin core wire with a conductive layer formed on its surface. For example, the conductor wire 31 may be made of a valve metal such as aluminum (Al), titanium (Ti), tantalum (Ta), niobium (Nb), zirconium (Zr), or hafnium (Hf), or tungsten (W), molybdenum (Mo), copper (Cu), nickel (Ni), silver (Ag), or gold (Au). In the first embodiment, the conductor wire 31 is made of copper. The conductor wire 31 may also be a twisted wire made of twisted wires made of a conductive metal material.

[0043] 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.

[0044] 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.

[0045] FIG. 2A is a diagram schematically showing the configuration of the structure 1c in the manufacturing process.

[0046] In the structure 1c, a wire 30 is sewn with a thread 40 to the structure 1b of FIG.

[0047] Each wire 30 is sewn to the opposing surface 21a of the second base member 21 with a thread 40. The stitching row 40a of the thread 40 extends in the X-axis direction (first direction). On the stitching row 40a, the thread 40 straddles all of the wires 30 and sews each wire 30 to the second base member 21. In FIG. 2( a), four stitching rows 40a of the thread 40 are arranged on the second base member 21. When the load sensor 1 is completed, in a plan view, the stitching rows 40a of the two inner threads 40 are located in the gap between two adjacent conductive elastic bodies 12 in the Y-axis direction, and the stitching rows 40a of the two outer threads 40 are located further outward than the two outer conductive elastic bodies 12 in the Y-axis direction. While sewn to the wires 30 by the thread 40, the wires 30 are movable in the Y-axis direction, while their movement in the X-axis direction is restricted by the thread 40. The thread 40 is made of synthetic fibers, natural fibers, or a mixture thereof.

[0048] FIG. 2B is a perspective view schematically showing the configuration of the load sensor 1. As shown in FIG.

[0049] The structure 1a in Fig. 1(a) is turned upside down and placed over the structure 1c in Fig. 2(a) from above (the positive side of the Z axis). This causes the wire 30 to come into contact with the conductive elastic body 12 formed on the first base member 11. Then, the outer periphery of the first base member 11 is connected to the second base member 21 with a thread (not shown), thereby fixing the first base member 11 to the second base member 21. In this way, the load sensor 1 is completed as shown in Fig. 2(b).

[0050] The load sensor 1 of the first embodiment 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.

[0051] Here, the load sensor 1 has a plurality of element units A1 arranged in a matrix in plan view. The load sensor 1 of FIG. 2( b) has a total of nine element units A1 arranged in the X-axis direction and the Y-axis direction. One element unit A1 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. That is, one element unit A1 includes the first base member 11, the conductive elastic body 12, the wire 30, and the second base member 21 near the intersection. When the lower surface of the load sensor 1 (the lower surface 21 b 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 11 b of the first base member 11) that constitutes the element unit A1, the electrostatic capacitance between the conductive elastic body 12 and the conductor wire 31 changes, and the load is detected based on the electrostatic capacitance.

[0052] 3 is a diagram schematically illustrating a cross section of the load sensor 1 when cut along a plane parallel to the XZ plane at the position of the thread 40. For convenience, only the second base member 21, the wire 30, and the thread 40 are illustrated in FIG.

[0053] The thread 40 is made up of an upper thread 41 arranged along the upper surface (opposing surface 21a) of the second base member 21 and a lower thread 42 arranged along the lower surface 21b of the second base member 21. The upper thread 41 and the lower thread 42 intersect with each other at the position of the needle hole 21c that passes through the second base member 21 in the Z-axis direction, and a seam 43 is formed at this intersection. The thread 40 is sewn to the second base member 21 along the X-axis direction. As a result, multiple seams 43 are lined up in the X-axis direction.

[0054] A stitch row 40a of the thread 40 is formed by a plurality of stitches 43 lined up in the X-axis direction (first direction) and the thread 40 between adjacent stitches 43. A plurality of stitch rows 40a of the thread 40 are formed on the opposing surface 21a of the second base member 21 at a predetermined pitch in the Y-axis direction (second direction). The wire 30 is sewn to the second base member 21 by the thread 40 between adjacent stitches 43 on each stitch row 40a. In order to suppress movement of the wire 30 in the X-axis direction, it is preferable that the pinhole pitch at the position of the wire 30, i.e., the distance between two stitches 43 that sandwich one wire 30, be as small as possible.

[0055] The thread 40 is sewn onto the second base member 21 by, for example, a sewing machine. The sewing machine forms needle holes 21c at a predetermined pitch in the X-axis direction, and crosses the upper thread 41 and the bobbin thread 42 through the needle holes 21c to form seams 43, thereby sewing the wire 30 to the second base member 21.

[0056] In this case, the pitch of the pinholes 21c in the X-axis direction (pinhole pitch) is determined by the mechanical precision of the sewing machine and the pitch of the wires 30 in the X-axis direction. That is, based on the mechanical precision of the sewing machine, the minimum pinhole pitch that can be set is approximately 2 mm. Furthermore, because one wire 30 is sewn between two adjacent stitches 43, the maximum pinhole pitch that can be set is approximately the maximum pitch of the wires 30 in the X-axis direction. For example, if the width of the element unit A1 in the X-axis direction is approximately 24 mm and only one wire 30 is included per element unit A1 (if the wire group G1 is replaced with one wire 30), the pinhole pitch can be set to the largest possible value, and in this case the pinhole pitch is approximately 24 mm.

[0057] 3, the needle hole pitch at positions corresponding to the wire 30 is L1, and the needle hole pitch at positions not corresponding to the wire 30 is L2. As described above, the needle hole pitch L1 is set as small as possible. The needle hole pitch L2 is set, for example, so that the needle holes 21c are arranged at equal distances on the positive side of the X-axis and the negative side of the X-axis of the wire 30.

[0058] 4A and 4B are diagrams showing a schematic cross section of the conductive elastic body 12 and the wire 30 in the vicinity of the intersection when the conductive elastic body 12 and the wire 30 are cut along a plane parallel to the XZ plane at the intersection.

[0059] 4(a) shows a state where no load is applied, and FIG. 4(b) shows a state where a load is applied, in which the lower surface 21b of the second base member 21 on the negative side of the Z axis is placed on the installation surface.

[0060] As shown in Fig. 4(a), when no load is applied, the force acting between the conductive elastic body 12 and the wire 30 is almost 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. 4(b), the conductive elastic body 12 is deformed by the wire 30.

[0061] 4(b), 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.

[0062] FIG. 5 is a plan view schematically showing the internal configuration of the load sensor 1. As shown in FIG.

[0063] The wire 30 extends in the Y-axis direction and meanders in the X-axis direction, diagonally crossing the element portion A1, thereby enabling load detection over a wide range within the element portion A1 and increasing detection sensitivity.

[0064] A plurality of stitch rows 40a of the thread 40 are formed at a predetermined pitch in the Y-axis direction on the opposing surface 21a of the second base member 21. The stitch rows 40a are provided at positions that do not overlap with the conductive elastic bodies 12 in a plan view. Specifically, the stitch rows 40a are provided between two adjacent conductive elastic bodies 12, on the outer side in the positive Y-axis direction of the conductive elastic body 12 on the positive Y-axis side, and on the outer side in the negative Y-axis direction of the conductive elastic body 12 on the negative Y-axis side.

[0065] The dielectric coating 32 is removed from one end of the wire 30, exposing the conductor wire 31. The exposed conductor wire 31 is connected to a detection circuit (not shown) including a load detection circuit. This connects the three conductive elastic bodies 12 to the detection circuit. The four conductor wires 31 included in one wire group G1 are connected to each other in the load sensor 1 or the detection circuit.

[0066] The detection circuit detects the capacitance value for each element unit A1 while switching between the conductive elastic body 12 and wire group G1 to be detected. Specifically, the detection circuit applies a DC voltage via a resistor to the conductive elastic body 12 and wire group G1 that intersect in the element unit A1 to be detected, and measures the voltage value at this intersection. The voltage value at the intersection rises due to a time constant determined by the resistance and the capacitance at the intersection (the capacitance between the conductive elastic body 12 and the four conductor wires 31).

[0067] The capacitance at the intersection point has a magnitude corresponding to the load applied to the intersection point. In other words, the contact area of ​​the dielectric 32 with the conductive elastic body 12 changes depending on the load applied to the intersection point. The capacitance at the intersection point has a value corresponding to this contact area. The detection circuit measures the voltage value at the intersection point at a predetermined timing after a certain period of time has elapsed since the start of application of the DC voltage, and obtains the load of the element portion A1 corresponding to that intersection point based on the measured voltage value. In this way, the load on each element portion A1 is detected.

[0068] However, when the thread 40 is sewn to the second base member 21 as described above, the second base member 21 is pulled by the thread 40 at the position of the seam 43, causing the second base member 21 to buckle, and this buckling may cause the second base member 21 to ripple in the vertical direction.

[0069] 6(a) and 6(b) are cross-sectional views that schematically show the state in which wavy patterns are formed on the second base member 21 due to the sewing of the thread 40. Figures 6(a) and 6(b) show cross-sectional views of the load sensor 1 when cut along a plane parallel to the X-Z plane at the intersection of the conductive elastic body 12 and the wire 30. For convenience, the illustration of the thread 40 is omitted in Figures 6(a) and 6(b).

[0070] As shown in Figures 6(a) and 6(b), if the rigidity of the second base member 21 is low, the tension of the thread 40 may cause the second base member 21 to ripple. In Figure 6(b), the rigidity of the second base member 21 is lower than in Figure 6(a), resulting in greater ripples of the second base member 21. If the second base member 21 ripples significantly, the upper surface of the upwardly rippled portion may come into contact with the lower surface of the conductive elastic body 12, causing the upper end of the wire 30 to separate from the lower surface of the conductive elastic body 12. In this case, the second base member 21 in a rippled state supports the load from 0 to a predetermined value, preventing the wire 30 from contacting the conductive elastic body 12. Therefore, in the case of Figure 6(b), the detected load value remains 0 until the load reaches the predetermined value, making it impossible to accurately detect the load.

[0071] In this way, depending on conditions related to the waviness of the second base member 21, such as the rigidity of the second base member 21, the waviness of the second base member 21 may become large, which may result in a decrease in the load detection accuracy.

[0072] Therefore, the inventors varied multiple parameters related to waviness of the second base member 21 to verify the actual degree of waviness, and based on the verification results, found a conditional expression including various parameters that allows for accurate detection of the load. Below, the criteria for determining whether the load can be detected accurately, the verification related to waviness, and the conditional expression will be described in order.

[0073] 7A and 7B are diagrams illustrating criteria for determining whether or not a load can be detected with high accuracy. Fig. 7A is a cross-sectional view similar to Fig. 6A and Fig. 6B. Fig. 7B is a graph schematically illustrating the relationship between load and capacitance.

[0074] Even if the second base member 21 undulates due to the thread 40, as shown in Figure 7 (a), when a load is applied, the load can be detected accurately as long as the second base member 21 does not come into contact with the conductive elastic body 12 until the outer periphery of the upper half of the wire 30 is wrapped in the conductive elastic body 12.

[0075] That is, as the load applied to the first base member 11 gradually increases, the contact area between the conductor wire 31 and the conductive elastic body 12 via the dielectric 32 changes while the outer periphery of the upper half of the wire 30 is wrapped in the conductive elastic body 12, and thereafter, even if the load increases further, the contact area does not change. As described above, the capacitance between the conductor wire 31 and the conductive elastic body 12 changes depending on the contact area. Therefore, the load can be properly detected based on the capacitance only up to the load range up to when the upper half of the wire 30 is wrapped in the conductive elastic body 12. Therefore, if the second base member 21 does not come into contact with the conductive elastic body 12 during this period, it is determined that the load can be detected accurately.

[0076] Typically, as shown in FIG. 7B, the load detection range (dynamic range) is set to a range up to a load F1 corresponding to a capacitance C1 slightly lower than the saturation value of the capacitance. That is, when the load exceeds F1 (capacitance C1), the change in capacitance relative to an increase in load is significantly small, making it difficult to accurately detect the load based on capacitance. For this reason, the load detection range (dynamic range) is set to be between 0 and F1. Therefore, if the second base member 21 does not contact the conductive elastic body 12 within this range, it is determined that the load to be detected can be properly detected.

[0077] As described above, whether or not a load can be detected accurately is determined by the method described with reference to Figures 7(a) and 7(b). Note that if the first determination criterion described with reference to Figure 7(a) is met, i.e., the second base member 21 does not contact the conductive elastic body 12 within the load range until the upper half of the wire 30 is wrapped in the conductive elastic body 12 (until the increase in contact area saturates), then the second determination criterion described with reference to Figure 7(b) is met, i.e., the second base member 21 does not contact the conductive elastic body 12 within the load detection range (dynamic range). Therefore, the first determination criterion described with reference to Figure 7(a) may be applied more broadly.

[0078] Next, the verification of waviness carried out by the inventors will be described.

[0079] 8(a) and 8(b) are schematic diagrams illustrating the conditions for verifying waviness. Fig. 8(a) is a diagram schematically illustrating a cross section near the intersection of the conductive elastic body 12 and the wire 30 when cut along a plane parallel to the X-Z plane at the intersection. Fig. 8(b) is a plan view schematically illustrating the arrangement of the wire 30 and the seams 43 (pinholes 21c).

[0080] As shown in Fig. 8(a), in the verification of waviness, similar to the first embodiment, wires 30 were arranged between the first base member 11 and the second base member 21, and the conductive elastic body 12 was arranged on the opposing surface 11a of the first base member 11. The number of wires 30 arranged was about several tens. The thickness of the second base member 21 was set to t １ It was decided.

[0081] In addition, in this verification, the diameter of the wire 30 was set to 0.6 mm. If the diameter of the wire 30 were larger than 0.6 mm, it would be difficult to meander the wire 30 in the X-axis direction as shown in Fig. 8(b), to bend the wire 30, or to connect it to the detection circuit, or to bend one wire 30 and replace it with one wire group G1. Therefore, in this verification, the diameter of the wire 30 was set to 0.6 mm, assuming a wire 30 that can be used in an actual load sensor 1.

[0082] As shown in Figure 8(b), in the verification of waviness, the wire 30 was sewn to the second base member 21 using thread 40, as in the first embodiment. At this time, needle holes 21c were provided at a predetermined pitch in the X-axis direction, and stitches 43 were formed in the needle holes 21c with an upper thread 41 and a lower thread 42 (see Figure 3), forming a stitch row 40a in which the stitches 43 and thread 40 were lined up in the X-axis direction. Of the pitches (needle hole pitches) between two adjacent needle holes 21c on the stitch row 40a, the largest needle hole pitch (longest needle hole pitch) was defined as L. In the case of Figure 3, this longest needle hole pitch L corresponds to the needle hole pitch L2. The pitch of the multiple stitch rows 40a was defined as B. １ In addition, the elastic modulus of the second base member 21 is set to E １ It was decided.

[0083] Fig. 9 shows the setting values ​​and verification results for Configurations 1 to 4 used in the verification regarding waviness. Fig. 10 shows actual plan views of Configurations 1 to 4, cross-sectional views schematically showing Configurations 1 to 4, and the results of the waviness state for Configurations 1 to 4.

[0084] As shown in FIG. 9, the inventors have determined that the thickness t １ , the elastic modulus E of the second base member 21 １ , pitch B of stitch row 40a １ Four configurations 1 to 4 were actually created in which the length L and the longest needle hole pitch L were set to predetermined values.

[0085] The material of the configurations 1 to 3 is polyurethane, and the material of the configuration 4 is PE (polyethylene) foam. １ is 0.1 mm, and the thickness t １ is 0.15 mm, and the thickness t １ is 0.2 mm, and the thickness t １ The elastic modulus E of the second base member 21 in the configurations 1 to 3 is 1.5 mm. １ is 15 MPa, and the elastic modulus E of the second base member 21 of Configuration 4 １ The pitch B of the stitch rows 40a in the configurations 1 to 4 is 0.4 MPa. １ The longest needle hole pitch L in configurations 1 to 4 is 2.6 mm.

[0086] Fig. 10 shows actual plan views of the thus-created structures 1 to 4, photographed from the positive side of the Z axis. As shown in the actual plan view of Fig. 10, large waviness occurred in structure 1, small waviness occurred in structure 2, and almost no waviness occurred in structure 3 and 4. Fig. 10 also shows cross-sectional views of the waviness state of structure 1 to 4 at this time, as well as the waviness state itself.

[0087] Furthermore, in configurations 1 to 4, the inventor placed the lower surface 21b of the second base member 21 on a mounting surface, applied a load from the upper surface 11b of the first base member 11, and confirmed whether the second base member 21 contacted the conductive elastic body 12 within the load range until the upper half of the wire 30 was wrapped in the conductive elastic body 12 (until the increase in contact area reached saturation), based on the first judgment criterion shown in Figure 7(a). As described above, if the second base member 21 does not contact the conductive elastic body 12 within this range, it is determined that the load can be detected accurately. As a result, it was determined that configuration 1 could not detect the load accurately, while configurations 2 to 4 could detect the load accurately. Furthermore, configuration 2 had a wavy state near the limit of satisfying the first judgment criterion.

[0088] Here, the inventors considered that Euler's buckling load formula could be used to quantitatively evaluate the waviness of the second base member 21 .

[0089] That is, in FIG. 8(b), tension (a force in the contraction direction) of the thread 40 is applied between adjacent stitches 43 (pinholes 21c) on the stitching row 40a, and this tension causes buckling in the region between the stitches 43. Therefore, by assuming this region as a pillar, the waviness of this region due to buckling can be found from Euler's buckling load formula. In this case, the region with the largest pitch between adjacent stitches 43 (pinholes 21c) buckles the most. Therefore, in order to perform an evaluation based on the above criteria, it is sufficient to find the state of waviness due to buckling from Euler's buckling load formula for the region with the largest pitch between adjacent stitches 43 (pinholes 21c). The region assumed to be a pillar has one side equal to this maximum pitch (L in FIG. 8(b)) and the other side equal to the pitch of the adjacent stitching row 40a (B in FIG. 8(b)). １ ) is a rectangular region of the second base member 21 having the other side, and the thickness of this region is the thickness of the second base member 21.

[0090] In Euler's buckling load formula, if the terminal modulus is C, the elastic modulus of the column material is E, the moment of inertia of the column material is I, and the length of the column is L, the buckling load P is expressed by the following formula (1).

[0091]

[0092] When the lengths of two sides of a rectangular cross section are b and t, and the length in the direction in which bending occurs is t, the second moment of area is expressed by the following equation (2).

[0093]

[0094] From the above formulas (1) and (2), the buckling load P is expressed by the following formula (3).

[0095]

[0096] When the parameters of the formula (3) are replaced with the parameters of the verification regarding waviness described with reference to FIGS. 8(a) and 8(b), the formula (3) becomes the following formula (4).

[0097]

[0098] Dividing both sides of the above equation (4) by the terminal coefficient C gives the following equation (5).

[0099]

[0100] The inventors considered that by calculating the buckling load P / terminal coefficient C in the above formula (5) for the above configurations 1 to 4, it would be possible to quantitatively evaluate the waviness (buckling state) of the configurations 1 to 4.

[0101] The calculation results of the buckling load P / end modulus C are shown in Figure 9. The values ​​of the buckling load P / end modulus C were 0.022 N for configuration 1, 0.074 N for configuration 2, 0.175 N for configuration 3, and 1.971 N for configuration 4.

[0102] As mentioned above, of Configurations 1 to 4, only Configurations 2 to 4 were able to detect the load with high accuracy, and therefore it is estimated that the load can be properly detected if the value of buckling load P / end modulus C is equal to or greater than 0.074 N, which is the value for Configuration 2, which was near the limit of the above-mentioned criteria. Here, by multiplying the right-hand side of the above equation (5) by 1 / 0.074 (=13.5), the value of (buckling load P / end modulus C) × 13.5 for Configuration 2 can be normalized to 1.0. The value obtained by multiplying the right-hand side of the above equation (5) by 13.5 is the same as setting the end modulus C to 13.5 in the above equation (4).

[0103] In this way, in relation to the diameter of the wire 30 to be installed, the terminal coefficient C should be set near the maximum value of the reciprocal of the above-mentioned buckling load P / terminal coefficient C when the second base member 21 (target base member) does not support the load, at least within the load detection range.

[0104] Therefore, when the terminal coefficient C is set to 13.5, it can be estimated that by satisfying the following relational expression (6), waviness of the second base member 21 is suppressed and the load can be detected with high accuracy.

[0105]

[0106] The value of the right-hand side of the above formula (6) (the value of the seam buckling strength) when the terminal coefficient C is set to 13.5 is as shown in Figure 9. The seam buckling strength values ​​were 0.3 for configuration 1, 1.0 for configuration 2, 2.4 for configuration 3, and 26.7 for configuration 4. In the case of configuration 1, the above formula (6) was not satisfied, and this result coincides with the results actually confirmed in the verification regarding waviness. In addition, in the cases of configurations 2 to 4, the above formula (6) was satisfied, and this result coincides with the results actually confirmed in the verification regarding waviness. Therefore, the above formula (6) can be used as a conditional formula for suppressing waviness of the second base member 21 so as to enable proper load detection.

[0107] <Effects of First Embodiment> According to the first embodiment, the following effects are achieved.

[0108] The thread 40 is sewn to the second base member 21 (target base member) to which the plurality of conductor wires 31 are sewn so that undulations that support the load do not occur in the second base member 21 (target base member) at least within the load detection range (see FIG. 7 ). This prevents undulations that support the load from occurring in the second base member 21. In other words, undulations that occur when the second base member 21 (target base member) comes into contact with the first base member 11 and the conductive elastic body 12 on the opposing first base member 11 (other base member) side are prevented. This allows the applied load to be detected with high accuracy.

[0109] 8(a) to 10, satisfying the above formula (6) appropriately suppresses waving of the second base member 21. This prevents the second base member 21 from supporting a portion of the load applied to the load sensor 1, enabling accurate detection of the load.

[0110] 5, the stitching row 40a is provided at a position where it does not overlap the conductive elastic body 12 in a plan view. In this way, the stitching row 40a does not overlap the conductive elastic body 12, so that the influence of the stitching row 40a on load detection can be suppressed. Therefore, the load can be detected with high accuracy.

[0111] In this way, when the stitch rows 40a are provided at positions that do not overlap with the conductive elastic body 12 in a plan view, the pitch B of the plurality of stitch rows 40a １ is preferably 3 mm or more and 26 mm or less.

[0112] That is, based on printing accuracy, there is a possibility that the conductive elastic body 12 may be displaced by about 1 mm in the positive and negative directions of the Y axis, so the interval between the needle holes 21c (the distance between the boundaries of the needle holes 21c) needs to be 2 mm or more. Therefore, if the diameter of the needle of the sewing machine is about 1 mm, the pitch B of the stitching row 40a is １ is preferably 3 mm or more. Furthermore, when the pitch of the element portions A1 in the Y-axis direction increases, each element portion A1 becomes larger. In this case, the resolution of load detection decreases as the area of ​​the element portion A1 increases, making it difficult to determine the shape and load distribution of an object placed on the load sensor 1. In contrast, when the pitch B １ When the pitch B is set to 26 mm or less, it can also be used when the pitch of the element portion A1 is 1 inch (25.4 mm), and the shape and load distribution of the object can be detected in units of approximately 1 inch. １ Even when is set within the above range, by setting each value so that the above formula (6) is satisfied, it is possible to appropriately suppress undulation of the second base member 21 and to accurately detect the load.

[0113] As explained with reference to Figure 3, the minimum settable needle hole pitch (the pitch of the needle holes 21c in the X-axis direction) is approximately 2 mm, and the maximum settable needle hole pitch is approximately 24 mm. Therefore, among the needle hole pitches of the thread 40 on the stitching row 40a, the maximum needle hole pitch (longest needle hole pitch L) is preferably 2 mm or more and 24 mm or less. Even when the longest needle hole pitch L is set within the above range, by setting each value so that the above formula (6) is satisfied, it is possible to appropriately suppress undulation of the second base member 21 and accurately detect the load.

[0114] The elastic modulus of the first base member 11 is preferably 1 MPa or more and 3 MPa or less. An elastic modulus of 1 MPa or more and 3 MPa or less corresponds to a hardness of approximately A50°. When the elastic modulus of the first base member 11 is set in this manner, a good balance is maintained between parameters related to the load detection characteristics, such as the elastic deformation (detection sensitivity) of the first base member 11 when a load is applied and the recovery of the first base member 11 due to rebound resilience when the load is released. This allows for stable load detection.

[0115] The thickness of the first base member 11 is preferably 0.02 mm or more and 1 mm or less. When a load is applied, the wire 30 sinks into the first base member 11, compressing the first base member 11. This compression can reduce the thickness of the first base member 11 by up to the diameter of the wire 30. Therefore, if the thickness of the first base member 11 is smaller than the diameter of the wire 30, excessive distortion occurs at the compressed position, potentially damaging the first base member 11. Therefore, the thickness of the first base member 11 is preferably equal to or greater than the diameter of the wire 30. The minimum diameter of the wire 30 (conductor wire 31) according to the JIS standard is 0.02 mm. Therefore, it is preferable that the thickness of the first base member 11 be set to 0.02 mm or more. On the other hand, the thicker the first base member 11, the higher the material cost of the first base member 11. Therefore, from the perspective of reducing material costs, it is preferable that the thickness of the first base member 11 be set to 1 mm or less.

[0116] The elastic modulus of the conductive elastic body 12 is preferably smaller than that of the first base member 11 and is between 0.5 MPa and 3 MPa, inclusive, so that when a load is applied, the conductive elastic body 12 elastically deforms well, and the contact area between the wire 30 and the conductive elastic body 12 changes smoothly.

[0117] The dielectric 32 is disposed so as to cover the surface of the conductor wire 31. According to this configuration, the dielectric 32 can be disposed between the conductive elastic body 12 and the conductor wire 31 simply by covering the surface of the conductor wire 31 with the dielectric 32.

[0118] In the first embodiment, the wire 30 is sewn to the second base member 21 on which the conductive elastic body 12 is not disposed. In contrast, in the second embodiment, the wire 30 is sewn to the first base member 11 on which the conductive elastic body 12 is disposed.

[0119] Hereinafter, in the second embodiment, components that are given the same reference numerals as those in the first embodiment are configured in the same manner as in the first embodiment unless otherwise specified.

[0120] FIG. 11A is a diagram schematically illustrating the configuration of a structure 1d in a manufacturing process according to the second embodiment.

[0121] In the structure 1d, a wire 30 is sewn with a thread 40 to the structure 1a of FIG.

[0122] Each wire 30 is sewn to the opposing surface 11a of the first base member 11 with a thread 40. Similar to the first embodiment, the stitching row 40a of the thread 40 extends in the X-axis direction (first direction). On the stitching row 40a, the thread 40 straddles all of the wires 30 and sews each wire 30 to the first base member 11. In FIG. 11( a), four stitching rows 40a of the thread 40 are arranged on the first base member 11. When the load sensor 1 is completed, the stitching rows 40a of the second embodiment are arranged in a position that does not overlap with the conductive elastic body 12 in a plan view, similar to the first embodiment.

[0123] FIG. 11B is a perspective view schematically illustrating the configuration of the load sensor 1 according to the second embodiment.

[0124] The structure 1d of Fig. 11(a) is placed upside down on top (the Z-axis positive side) of the second base member 21, which is the same as that of the first embodiment shown in Fig. 1(b). Then, the outer periphery of the first base member 11 is connected to the second base member 21 with a thread (not shown), thereby fixing the first base member 11 to the second base member 21. In this way, the load sensor 1 is completed as shown in Fig. 12(b).

[0125] The load sensor 1 of the second embodiment is also 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 a load is applied, and the lower surface 21b of the second base member 21 is placed on the installation surface. Also in the second embodiment, when the conductive elastic body 12 and the wire 30 are cut at the intersection of the conductive elastic body 12 and the wire 30 along a plane parallel to the X-Z plane, the cross section near the intersection will be in the state shown in FIG. 12(a), as in the first embodiment.

[0126] Furthermore, in the second embodiment, the plurality of wires 30 are sewn to the first base member 11 with thread 40. Therefore, as shown in FIG. 12( b), the first base member 11 may undulate due to the tension of the thread 40. In this case, if the undulating portion of the first base member 11 (target base member) comes into contact with the second base member 21 directly or via the conductive elastic body 12 when a load is applied, the first base member 11 will support the load. Therefore, in the second embodiment, it is sufficient that the plurality of wires 30 are sewn to the first base member 11 with thread 40 so that the first base member 11 does not come into contact with the second base member 21 at least within the load detection range.

[0127] Here, the inventors considered that conditional expression (6) shown in embodiment 1 for suppressing waving of the second base member 21 to which the wire 30 is sewn can also be applied to embodiment 2. That is, similar to conditional expression (6) in embodiment 1, they considered that a conditional expression for suppressing waving of the first base member 11 to which the wire 30 is sewn can also be derived in embodiment 2. However, in the case of embodiment 2, the conductive elastic body 12 is formed on the opposing surface 11 a of the first base member 11 to which the wire 30 is sewn, and therefore conditional expression (6) needs to be modified in consideration of the influence of the conductive elastic body 12.

[0128] FIG. 13A is a plan view and a cross-sectional view schematically showing the vicinity of a gap between two conductive elastic bodies 12 adjacent to each other in the Y-axis direction.

[0129] 13A shows the distance from the center of one conductive elastic body 12 in the Y-axis direction to the center of another conductive elastic body 12 adjacent to the one conductive elastic body 12 in the Y-axis direction. １ The pitch of the stitching row 40a of the thread 40 (the width of the structure in the Y-axis direction of FIG. 13(a)) is B １ The thickness of the conductive elastic body 12 is t ２ and the width of the conductive elastic body 12 in the Y-axis direction is B ２ Let's say.

[0130] In Fig. 13(a), the conductive elastic bodies 12 are arranged symmetrically in the Y-axis direction with the stitching row 40a in between, but for convenience, when the conductive elastic bodies 12 shown in Fig. 13(a) are joined at the stitching row 40a, the structure of Fig. 13(a) becomes the state shown in Fig. 13(b). As a result, the moment of inertia of the structure shown in Fig. 13(a) becomes equal to the moment of inertia of the structure shown in Fig. 13(b).

[0131] Therefore, the geometric moment of inertia I of the structure shown in Figure 13(a) can be calculated by the following equation (7) with reference to Figure 13(b). In Figure 13(b), the y-axis is an axis extending in the positive direction of the Y-axis, and the z-axis is an axis extending in the negative direction of the Z-axis. The origin of the y-axis and the origin of the z-axis are the center of the first base member 11 included in the structure of Figure 13(b).

[0132]

[0133] By modifying the above equation (7), the following equation (8) is derived.

[0134]

[0135] Next, the right side of the above formula (8) is substituted into the second moment of area I of the above formula (1) shown in the first embodiment. At this time, the coefficient B of the above formula (8) １ The term is a term related to the first base member 11, and is the coefficient B ２ The term is a term related to the conductive elastic body 12. Therefore, in the above formula (8), the term related to the first base member 11 includes the elastic modulus E of the first base member 11. １ and the term relating to the conductive elastic body 12 is multiplied by the elastic modulus E of the conductive elastic body 12. ２ This leads to the following equation (9):

[0136]

[0137] Here, in the above formula (9), the thickness t of the conductive elastic body 12 ２ When the thickness t is set to 0, the above formula (9) must be the same as the formula (4) shown in the first embodiment. ２ In the above equation (9) when is set to 0, the buckling load P on the left side is the same as the buckling load P on the left side of equation (4) shown in embodiment 1, so the terminal coefficient C in the above equation (9) is the same value (13.5) as the terminal coefficient C obtained in embodiment 1.

[0138] Therefore, when the terminal coefficient is set to 13.5 as in the case of the first embodiment, by satisfying the following relational expression (10), waviness of the first base member 11 is suppressed and the load can be detected with high accuracy.

[0139]

[0140] Effect of Second Embodiment In the second embodiment, too, the thread 40 is sewn to the first base member 11 (target base member) to which the plurality of conductor wires 31 are sewn so that undulations that support the load do not occur in the first base member 11 (target base member) at least within the load detection range (see FIG. 7 ). This prevents undulations that support the load from occurring in the first base member 11. In other words, undulations that occur when the first base member 11 and the conductive elastic body 12 on the first base member 11 (target base member) side come into contact with the opposing second base member 21 (the other base member) are prevented. This allows the applied load to be detected with high accuracy.

[0141] By satisfying the above formula (10), undulation of the first base member 11 is appropriately suppressed, which prevents the first base member 11 from supporting a portion of the load applied to the load sensor 1, thereby enabling accurate detection of the load.

[0142] <Modification> In the above-described first and second embodiments, the conductive elastic body is disposed on either the first base member 11 or the second base member 21, 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-described second embodiment, by satisfying the above-described formula (10), it is possible to appropriately suppress rippling of the target base member to which the wire 30 is sewn.

[0143] In the above-described first and second embodiments, 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 configured from 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.

[0144] Furthermore, in the first and second embodiments, the dielectric 32 is disposed on the surface of the conductor wire 31. However, the dielectric 32 that determines the capacitance between the conductor wire 31 and the conductive elastic body 12 may be disposed between the conductor wire 31 and the conductive elastic body 12. For example, the dielectric 32 may be disposed on the surface of the conductive elastic body 12. Specifically, in the configurations of the first and second embodiments, the dielectric 32 may be formed on the surface of the conductive elastic body 12, as shown in FIG. 14. In this case, the dielectric 32 is made of an elastically deformable material so that the contact area with the conductor wire 31 changes in response to a load. For example, the dielectric 32 is made of a material having a modulus of elasticity similar to that of the conductive elastic body 12.

[0145] 14, even when the dielectric 32 is disposed on the surface of the conductive elastic body 12, if the base member to which the wire 30 is sewn is the second base member 21, the above formula (6) is satisfied, and waving of the second base member 21 can be appropriately suppressed, as in the first embodiment. On the other hand, if the base member to which the wire 30 is sewn is the first base member 11, the first base member 11, the conductive elastic body 12, and the dielectric 32 are involved in the waving of the first base member 11. In this case, if the thickness of the dielectric 31 is set to t ３ , the elastic modulus of the dielectric 31 is E ３ Then, the buckling load P can be expressed by the following equation (11).

[0146]

[0147] In this case, too, when the terminal coefficient is set to 13.5 as in the first embodiment, by satisfying the following relational expression (12), waviness of the first base member 11 is suppressed and the load can be detected with high accuracy.

[0148]

[0149] Furthermore, in the first and second embodiments, 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 thread 40 is sewn to the target base member to which the wire 30 is sewn so that the base member (target base member) to which the wire 30 is sewn does not undulate to support the load, at least within the load detection range. This allows the applied load to be detected with high accuracy.

[0150] Furthermore, in the above-mentioned embodiments 1 and 2, the wire 30 extends in the Y-axis direction (second direction) while meandering in the X-axis direction (first direction), but this is not limited thereto and the wire 30 may extend linearly in the Y-axis direction (second direction).

[0151] Furthermore, in the above-described first and second embodiments, three wire groups G1 corresponding to one element portion A1 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.

[0152] Furthermore, although three conductive elastic bodies 12 are arranged in the first and second embodiments, 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.

[0153] In the above-mentioned first and second embodiments, 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 gluing foil.

[0154] In the first and second embodiments, the first and second directions are perpendicular to each other, but the angle between the first and second directions may be an angle other than 90°. That is, the first and second directions may intersect at an angle.

[0155] In the first and second embodiments, 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 A1 in the first direction. Furthermore, a conductor having a lower resistance than the conductive elastic body 12 may be formed along the first direction between the first base member 11 and the conductive elastic body 12. In this case, the conductor may be elastic. For example, similar to the conductive elastic body 12, the conductor may be formed by dispersing a conductive filler (e.g., silver) in a resin material or a rubber material. In this configuration, the conductive elastic body 12 and the conductor constitute the "conductive elastic body" described in the claims. In this case, the conductive elastic body 12 may be omitted in the range between the element portions A1 in the first direction, and only the conductor may remain in this range.

[0156] 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.

[0157] REFERENCE SIGNS LIST 1 load sensor 11 first base member 11a opposing surface 12 conductive elastic body 21 second base member 31 conductor wire 32 dielectric material 40 thread 40a stitch row 43 stitch

Claims

a plurality of conductive elastic bodies formed on the opposing surface of the first base member so as to extend in a first direction; a plurality of conductor wires extending in a second direction intersecting the first direction and arranged side by side between the first base member and the second base member; a dielectric body arranged between the conductive elastic bodies and the conductor wires; and a thread for sewing the plurality of conductor wires to the first base member or the second base member, wherein a plurality of stitch rows of the thread, each with stitches aligned in the first direction, are formed at a predetermined pitch in the second direction, the conductor wires are sewn to the target base member by the thread between predetermined adjacent stitches on each stitch row, and the thread is sewn to the target base member so as to prevent undulations that support a load from occurring in the target base member at least within the load detection range.

2. The load sensor according to claim 1, wherein the plurality of conductor wires are sewn to the second base member, and the thickness of the second base member is set to t １ , the elastic modulus of the second base member is E １ , the pitch of the plurality of stitch rows is B １ , the longest needle hole pitch of the thread on the stitch row is L, and the terminal coefficient C is 13.5, １ , the elastic modulus E １ , the pitch B １ The load sensor is characterized in that the longest pinhole pitch L satisfies the following relational expression:

3. The load sensor according to claim 1, wherein the plurality of conductor wires are sewn to the first base member, and the thickness of the first base member is set to t １ , the elastic modulus of the first base member is E １ , the thickness of the conductive elastic body is t ２ , the elastic modulus of the conductive elastic body is E ２ , the pitch of the plurality of stitch rows is B １ , the width of the conductive elastic body in the second direction is B ２ , the longest needle hole pitch of the thread on the stitch row is L, and the terminal coefficient C is 13.5, １ , t ２ , the elastic modulus E １ , E ２ , the pitch B １ , the width B ２ The load sensor is characterized in that the longest pinhole pitch L satisfies the following relational expression:

4. A load sensor according to any one of claims 1 to 3, characterized in that the stitching row is provided at a position that does not overlap the conductive elastic body in a plan view.

5. The load sensor according to any one of claims 1 to 4, wherein the pitch B of the plurality of stitch rows １ is 3 mm or more and 26 mm or less.

6. A load sensor according to any one of claims 1 to 5, characterized in that the longest needle hole pitch L of the thread is 2 mm or more and 24 mm or less.

7. A load sensor according to any one of claims 1 to 6, wherein the modulus of elasticity of the first base member is 1 MPa or more and 3 MPa or less.

8. A load sensor according to any one of claims 1 to 7, wherein the thickness of the first base member is 0.02 mm or more and 1 mm or less.

9. A load sensor according to any one of claims 1 to 8, characterized in that the second base member is made of silicone rubber, ethylene propylene diene rubber, urethane rubber, fluororubber, nitrile rubber, acrylic rubber or ethylene propylene rubber.

10. A load sensor according to any one of claims 1 to 9, wherein the dielectric is disposed so as to cover the surface of the conductor wire.

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