Stress sensor

Abstract

To provide a stress sensor with excellent accuracy in detecting pressure and shearing force.SOLUTION: A stress sensor can detect pressure and shearing force. The stress sensor includes: a first base material; a second base material; four detection parts provided between the first base material and the second base material; and an adhesive layer arranged to surround the four detection parts by adhering the first base material and the second base material. Each one of the detection parts is an element where a resistance value is changed according to an applied weight. The two of the detection parts are arranged on a first straight line so as to be point-symmetric with respect to a geometric center of a detection region of the stress sensor. The remaining two detection parts are arranged on a second straight line crossing the first straight line and to be point-symmetric with respect to the geometric center of the detection region. No detection part is provided at the geometric center of the detection region.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a stress sensor capable of detecting pressure and shear stress.

Background Art

[0002] As a stress sensor for detecting pressure or shear stress, there is known one having a structure in which a conductor layer or a resin layer is sandwiched between two opposed electrodes. This stress sensor can change the physical quantity between the electrodes by deforming the conductor layer or the resin layer by an external force, and can detect pressure or shear force based on the change in the physical quantity between the electrodes.

[0003] The stress sensor as described above has been studied for use in applications such as attaching it to a measurement object such as a finger of a robot hand or a human finger to detect the pressure or shear force applied to the measurement object (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When it is assumed that a soft object is carried by a finger, it has been found that the load applied to the carrying part of the finger becomes very small, 0.5 N or less. Therefore, when the stress sensor is attached to a finger of a robot hand or a human finger and used, it is required to be able to accurately detect pressure and shear force even in a low load range.

[0006] Therefore, an object of the present invention is to provide a stress sensor excellent in detection accuracy of pressure and shear force.

Means for Solving the Problems

[0007] One aspect of the present invention for solving the above problems is a stress sensor capable of detecting pressure and shear force, comprising a first substrate, a second substrate, four detection parts disposed between the first substrate and the second substrate, and an adhesive layer provided to bond the first substrate and the second substrate and surround the four detection parts. Each of the detection parts is an element whose resistance value changes in response to an applied load. Two of the detection parts are arranged on a first straight line so as to be point-symmetrical with respect to the geometric center of the detection region of the stress sensor, and the remaining two of the detection parts are arranged on a second straight line that is point-symmetrical with respect to the geometric center of the detection region and orthogonal to the first straight line, and no detection part is arranged at the geometric center of the detection region.

Advantages of the Invention

[0008] According to the present invention, the present invention can provide a stress sensor excellent in detection accuracy of pressure and shear force.

Brief Description of the Drawings

[0009]

Figure 1

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Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the shape and number of each component constituting the stress sensor according to the embodiment are merely examples and do not limit the present invention. Also, for the sake of simplicity of explanation, the drawings are drawn at a ratio different from the actual dimensions, but this does not impair the gist of the technology according to the present invention.

[0011] <First Embodiment> FIG. 1 is a schematic diagram showing a schematic configuration of a stress sensor according to an embodiment of the present invention. More specifically, FIG. 1(a) is a plan view of the stress sensor, and FIG. 1(b) is a cross-sectional view taken along line A-A' shown in FIG. 1(a). FIG. 2 is a partial schematic diagram of the first substrate side of the stress sensor. More specifically, FIG. 2(a) is a partial plan view of the first substrate side of the stress sensor, and FIG. 2(b) is a cross-sectional view taken along line B-B' shown in FIG. 2(a). FIG. 3 is a partial schematic diagram of the second substrate side of the stress sensor. More specifically, FIG. 3(a) is a partial plan view of the second substrate side of the stress sensor, and FIG. 3(b) is a cross-sectional view taken along line C-C' shown in FIG. 3(a).

[0012] The stress sensor 100 is a sensor capable of detecting the pressure and shear force (shearing force) applied to the base material, and includes a first base material 1, a second base material 2, four detection units (detection unit X1, detection unit X2, detection unit Y1, detection unit Y2) arranged in a two-dimensional plane between the first base material 1 and the second base material 2, and an adhesive layer 5 for adhering the first base material 1 and the second base material 2. The detection unit is an element whose resistance value changes in response to a pressure change, and the stress sensor 100 includes an output circuit such as a bridge circuit that converts the resistance value generated in each detection unit into a voltage and outputs it. In the stress sensor 100, the detection region R corresponds to the smallest circle including all the detection units, and is shown surrounded by a two-dot chain line in FIG. 1. The detection region is a region where the pressure and shear force (shearing force) can be accurately detected when applied. Note that the pressure indicates the force component in the direction perpendicular to the sensor surface (the Z-axis direction in FIG. 1), and the shear force indicates the force component in the surface direction of the base material (the Z-axis and Y-axis directions in FIG. 1).

[0013] The first base material 1 and the second base material 2 are adhered via an adhesive layer 5 provided so as to surround the detection region R. On one surface of the first base material 1, a common electrode 3, a detection electrode 4, a common wiring 3', and a signal wiring 4' are provided. Further, a buffer material 6 for applying a load to the stress sensor 100 may be provided on the surface of the second base material 2 opposite to the one surface (the surface facing the first base material 1).

[0014] (Detection unit) Four detection units are arranged between the first base material 1 and the second base material 2, and are elements whose resistance values change in response to the applied load. Among the four detection units, the detection unit X1 and the detection unit X2 are arranged on the first straight line (the X-axis in FIG. 1) so as to be point-symmetrical with respect to the geometric center of the detection region R, and the detection unit Y1 and the detection unit Y2 are point-symmetrical with respect to the geometric center of the detection region R and are arranged on a second straight line (the Y-axis in FIG. 1) orthogonal to the first straight line. That is, the detection units X1, X2, Y1, and Y2 are arranged so as to be four-fold symmetrical with respect to the geometric center of the detection region R. Note that no detection unit is arranged at the geometric center of the detection region R.

[0015] The shear force in the X-axis direction is detected by the detection units X1 and X2 arranged in the X-axis direction, and the shear force in the Y-axis direction is detected by the detection units Y1 and Y2 arranged in the Y-axis direction. Also, the pressure can be detected using all of the detection units X1, X2, Y1, and Y2.

[0016] When assuming the use of attaching the stress sensor 100 to a human finger (for example, when analyzing the stress acting between the finger and an implement such as a golf club or a tennis racket when swinging the implement), each detection unit is preferably arranged within a circle with a radius of 6 mm or less from the geometric center of the detection region R. That is, the detection region R is preferably a circle with a radius of 6 mm or less.

[0017] Each of the detection units X1, X2, Y1, and Y2 includes a first detection unit component 10 provided on one surface of the first base material 1 (the surface facing the second base material 2), and a second detection unit component 20 provided facing the first detection unit component 10 on the surface of the second base material 2 facing the first base material 1.

[0018] (Detection unit component) Four first detection unit components 10 are provided on one surface of the first base material 1, and four second detection unit components 20 are provided facing each of the first detection unit components 10 on the surface of the second base material 2 facing the first base material 1. Each of the first detection unit components 10 has a first electrode and a first pressure-sensitive layer laminated on the first electrode. Each of the second detection unit components 20 has a second electrode and a second pressure-sensitive layer laminated on the second electrode.

[0019] (Electrode · Small electrode) Each of the first electrodes is composed of n (where n is a positive even number) first small electrodes 10a for each first detection unit structure 10, and the first small electrodes 10a are arranged at intervals in a predetermined direction on one surface of the first base material 1. Each of the second electrodes is composed of n (where n is a positive even number) second small electrodes 20a for each second detection unit structure 20, and the second small electrodes 20a are arranged on the surface of the second base material 2 facing the one surface of the first base material 1 so as to face each of the first small electrodes 10a of the opposing first detection unit structure 10. As shown in FIGS. 1 to 3, the shape of the small electrodes (the first small electrodes 10a and the second small electrodes 20a) is preferably a shape in which an annular ring is divided in the circumferential direction. By making the small electrodes have such a shape, the area of the small electrodes can be increased and the sensitivity can be enhanced. In this embodiment, as shown in FIG. 2, the number of the first small electrodes 10a is 2 (n = 2), and as shown in FIG. 3, the number of the second small electrodes 20a is 2 (n = 2).

[0020] As shown in FIG. 2, a common wiring 3' is commonly connected to one of the two first small electrodes 10a that constitute each first detection unit component 10, and signal wirings 4' are respectively connected to the other first small electrodes 10a. Further, as shown in FIG. 3, in each second detection unit component 20, a second connection wiring 8 that connects the two second small electrodes 20a is provided between the two second small electrodes 20a. Thus, in the present embodiment, the number of the first small electrodes 10a and the second small electrodes 20a in each detection unit component is 2. A common wiring 3' is connected to one of the first small electrodes 10a, a signal wiring 4' is connected to the other first small electrode 10a, and the two second small electrodes 20a are connected by a second connection wiring 8. Therefore, when a load is applied in a direction in which the first base material 1 and the second base material 2 approach each other and the opposing first small pressure-sensitive layers 10b and second small pressure-sensitive layers 20b come into contact with each other, a series current path is formed with one of the first small electrodes 10a connected to the common wiring 3' and the other first small electrode 10a connected to the signal wiring 4' as both ends and passing through the second small electrodes 20a included in the second detection unit component 20. That is, it is a path in which the current input from the first base material 1 side once flows to the second base material 2 side and then returns to the first base material 1 side again. For this reason, it is not necessary to provide a wiring for signal extraction for the second base material 2, and it is not necessary to form an input wiring and an output wiring on separate base materials (the first base material 1 and the second base material 2) like a general stress sensor.

[0021] Thus, in this embodiment, since the input wiring and the output wiring only need to be formed on the first substrate 1 side, there is no risk of electrical noise occurring between the wiring on the first substrate 1 side and the wiring on the second substrate 2 side. Therefore, it is possible to avoid a situation where the wiring structure becomes complicated to reduce noise, resulting in a structure that is disadvantageous for miniaturizing the sensor, and it is also possible to reduce defective formation of the wiring. In particular, when the stress sensor 100 is attached to an object to be measured such as a robot hand or a human finger and used for detecting the pressure and shear force applied to the object to be measured, since the sensor needs to be small, it is preferable to apply this configuration that is advantageous for miniaturization. Also, since the FPC (Flexible Printed Circuit) for connecting to the input / output device only needs to be adhered to the first substrate 1 side, the connection to the input / output device also becomes simple. Further, the manufacturing cost can be suppressed as compared with the case where the FPC is adhered to the upper and lower two substrates.

[0022] The resistivity of the small electrode is preferably 1.0×10 -3 Ω·cm or less. Also, the thickness of each small electrode is not particularly limited, but is preferably 0.01 μm or more and 30 μm or less, and more preferably 0.05 μm or more and 20 μm or less. When it is less than 0.01 μm, the formed film is likely to be a discontinuous film and sufficient conductivity cannot be obtained. Also, when it exceeds 30 μm, there is a risk of cracks occurring in the small electrode when the stress sensor 100 formed on the flexible substrate is bent. Also, the shapes and areas of the respective small electrodes facing each other up and down may be the same shape and area, but it is preferable that one has a relatively larger area than the other (see FIG. 4). The area of the small electrode with a relatively small area is preferably 1 / 5 or more and 2 / 3 or less of the area of the small electrode with a relatively large area. When it is less than 1 / 5, the sensitivity of the stress sensor 100 decreases. Also, when it exceeds 2 / 3, it becomes difficult to align the two small electrodes.

[0023] The small electrodes are not limited in terms of material or formation method as long as they are made of a conductive material suitable for the specifications of the sensor element to be used. For example, as the material, metals such as Au, Pt, Ag, Cu, Ni, Cr, Rh, Pd, Zn, Co, Ru, W, Os, Ir, Fe, Mn, Ge, Sn, Ga, In, etc., or conductive metal oxides such as ITO (indium tin oxide), ZnO (zinc oxide), SnO2 (tin oxide), etc. can be used. As the formation method, methods using printing methods such as inkjet printing method, screen printing method, offset printing method, gravure offset printing method, reverse offset printing method, etc., or methods of patterning a film formed on the entire surface of a substrate by a vapor deposition method such as vacuum evaporation method, sputtering method, etc. using an etching method can be used. When using a printing method, a mixture of the electrode material and a resin can be used after being made into ink so that it can be applied by each printing method. In the case of the vapor deposition method, it may be formed by depositing the material only at a predetermined position using a metal mask. The small electrodes may be fabricated in the same process as the common electrode 3, the common wiring 3', the detection electrode 4, and the signal wiring 4'.

[0024] In this embodiment, the small electrodes are in the shape of a ring divided in the circumferential direction (Figs. 1 to 3). However, if the small electrodes are separated from each other, they may be fan-shaped, or may be circular, rectangular, square, etc. In the case of the shape of a ring divided in the circumferential direction, by arranging the small electrodes along the circular detection region R, the area of the small electrodes in the detection region of the small electrodes can be increased. When the area of the small electrodes is increased, the pressing force can be detected over a wide range, so that even a minute change in the pressing force can be detected, and the detection accuracy of the shearing force is improved. Also, when the area of the small electrodes is increased, the area of the detection part also becomes larger, so that the load can be more uniformly dispersed to the pressure-sensitive layer, and the detection accuracy of the shearing force can be improved. Further, when the adhesive layer 5 described later is formed in an annular shape and the geometric centers of the center of the adhesive layer 5 and the detection region R are made to coincide, the distances between each small electrode and the adhesive layer 5 all become equal. In this case, the repulsive force of the adhesive layer 5 when the shearing force is applied becomes constant regardless of the direction of the shearing force, and the dependence on the application direction of the shearing force becomes small, so that the detection accuracy of the shearing force can be further improved.

[0025] (Pressure-sensitive layer and small pressure-sensitive layer) Each of the first pressure-sensitive layers is composed of first small pressure-sensitive layers 10b laminated on each of the first small electrodes 10a that constitute the corresponding first detection unit structure 10. Each of the second pressure-sensitive layers is composed of second small pressure-sensitive layers 20b laminated on each of the second small electrodes 20a that constitute the corresponding second detection unit structure 20. Each small pressure-sensitive layer (the first small pressure-sensitive layer 10b and the second small pressure-sensitive layer 20b) completely covers each small electrode and is formed so as to be separated from the small pressure-sensitive layers laminated on adjacent small electrodes. In plan view, it is preferable that the sizes of the respective small pressure-sensitive layers are the same.

[0026] The thickness of the small pressure-sensitive layer is preferably 1 μm or more and 100 μm or less, and more preferably 5 μm or more and 50 μm or less. When the small pressure-sensitive layer is less than 1 μm, it becomes difficult to sufficiently cover the small electrode, and the upper and lower small electrodes conduct without passing through the small pressure-sensitive layer, resulting in a malfunction in the sensor operation. When the small pressure-sensitive layer exceeds 100 μm, the deformation with respect to the change in the pressing force becomes dull, or the time until the pressing force is evenly transmitted to all the small pressure-sensitive layers increases, so the detection accuracy of the pressure and shear force decreases. Also, from the viewpoint of thinning, it is preferable that the first small electrode 10a and the first small pressure-sensitive layer 10b and the second small electrode 20a and the second small pressure-sensitive layer 20b are formed to have a total thickness of 260 μm or less.

[0027] Since the stress sensor 100 according to the present embodiment detects pressure and shear force based on the change in the resistance value between the opposing electrodes, the small pressure-sensitive layer is formed of a material having conductivity. However, it is necessary to use a material having a higher resistivity than the small electrode. The resistivity of the small pressure-sensitive layer is ...... -1 Ω·cm or more and 1.0×10 6 Ωcm or less is preferable. In this case, the change amount of the conduction resistance value with respect to the change in the pressing force becomes suitable, and the detection accuracy of the stress sensor 100 becomes good.

[0028] Further, the stress sensor 100 can detect the input pressing force by the change in the contact resistance of the contact surface between the first small pressure-sensitive layer 10b and the second small pressure-sensitive layer 20b due to the input pressing force. When the pressing force is input, the upper and lower small pressure-sensitive layers come into contact with each other, the unevenness on the surface is slightly deformed, and the contact area increases. Then, since the resistance value changes according to the change in the contact area, the input pressing force can be detected. In this case, it is preferable to use a material that deforms according to the pressing force for the small pressure-sensitive layer. For example, conductive carbon or conductive nanocarbon can be used.

[0029] The small pressure-sensitive layer may be formed by a known printing method such as inkjet printing, screen printing, or offset printing. Further, it may be formed entirely by using a vapor deposition method such as a vacuum evaporation method, a sputtering method, a thermal chemical vapor deposition method, or a plasma chemical vapor deposition method and then formed by an etching method. In this case, it can also be formed by depositing a material only at a predetermined position using a metal mask. Further, unevenness on the order of several μm may be formed on the surface of each small pressure-sensitive layer to make the change in the contact area prominent and facilitate the detection of the change in the resistance value. As a method for forming unevenness on the surface of the small pressure-sensitive layer, for example, a method of printing and forming conductive carbon ink using screen printing can be used.

[0030] The arithmetic mean roughness Sa of the surface of the region D1 where the first small electrode 10a exists in plan view of the first small pressure-sensitive layer 10b is preferably 0.08 μm or more and 1.5 μm or less, and more preferably 0.1 μm or more and 1.2 μm or less. Also, for the second small pressure-sensitive layer 20b, the arithmetic mean roughness Sa of the surface of the region D2 where the second small electrode 20a exists in plan view is preferably 0.08 μm or more and 1.5 μm or less, and more preferably 0.1 μm or more and 1.2 μm or less. When the arithmetic mean roughness Sa of each exceeds 1.5 μm, the pressure is not uniformly applied to the entire surface of the small electrode, and the measurement accuracy of the pressure and shear force decreases. When the arithmetic mean roughness Sa is less than 0.08 μm, the change in the contact area decreases, making it difficult to detect the change in resistance, so the measurement sensitivity and accuracy of the pressure and shear force decrease. In particular, the measurement sensitivity and accuracy of the pressure and shear force in the low load range of 0.5 N or less decrease.

[0031] The resistivity of the small pressure-sensitive layer is preferably adjusted according to the magnitude of the assumed pressing force. When the assumed pressing force is large, it is preferable to select a material with a gentle change in resistivity, and when the assumed stress is small, it is preferable to select a material with a steep change in resistivity.

[0032] (Common wiring, common electrode) The common wiring 3' is formed on the first base material 1 and connects the common electrode 3 and one of the first small electrodes 10a in each of the first detection unit components 10. The first small electrode 10a connected to the common wiring 3' is the first small electrode 10a arranged at one end in the predetermined direction among the first small electrodes 10a arranged at intervals in the predetermined direction in each first detection unit component 10. Note that the common wiring 3' and the common electrode 3 are formed only on the first base material 1 and not on the second base material 2.

[0033] (Signal wiring, detection electrode) The signal wiring 4’ is formed on the first substrate 1 and connects the detection electrode 4 and one of the first small electrodes 10a in each of the first detection unit components 10. The first small electrode 10a connected to the signal wiring 4’ is the first small electrode 10a arranged at the other end in the predetermined direction (the side opposite to the first small electrode 10a to which the common wiring 3’ is connected) among the first small electrodes 10a arranged at intervals in the predetermined direction in each of the first detection unit components 10. Note that the signal wiring 4’ and the detection electrode 4 are formed only on the first substrate 1 and not on the second substrate 2.

[0034] (Connection wiring) The second connection wiring 8 is provided to connect two adjacent second small electrodes 20a in each of the second detection unit components 20 arranged on the second substrate 2 side (FIG. 3), and four second connection wirings 8 are provided in the present embodiment.

[0035] For these electrodes and wirings (the common wiring 3’, the common electrode 3, the signal wiring 4’, the detection electrode 4, and the second connection wiring 8), a conductive material with a low resistivity can be used. For example, metals such as Au, Pt, Ag, Cu, Ni, Cr, Rh, Pd, Zn, Co, Ru, W, Os, Ir, Fe, Mn, Ge, Sn, Ga, In, or conductive metal oxides such as ITO (indium tin oxide), ZnO (zinc oxide), SnO2 (tin oxide) can be used.

[0036] The resistivity of the electrodes and wirings is preferably 1.0×10 -3 Ω·cm or less. The thickness of the electrodes and wirings is not particularly limited, but a range of 0.01 μm or more and 30 μm or less is preferable, and more preferably 0.05 μm or more and 20 μm or less. When it is less than 0.01 μm, the formed film tends to be island-shaped and sufficient conductivity cannot be obtained. Also, when it exceeds 30 μm, when the stress sensor 100 formed on the flexible substrate is bent, there is a risk of cracks occurring in the electrodes and wirings.

[0037] The method for forming the electrodes and wirings is not particularly limited. For example, printing methods such as an inkjet printing method, a screen printing method, an offset printing method, a gravure offset printing method, a reverse offset printing method, etc. can be used. When using such a printing method, a material for the electrodes can be mixed with a resin and used in the form of ink that can be applied by each printing method. Further, a film formed on the entire surface of the substrate by a vapor deposition method such as a vacuum evaporation method or a sputtering method may be formed by patterning with an etching method. In the case of the vapor deposition method, a material can be formed into a film only at a predetermined position using a metal mask. The materials and forming methods of the electrodes and wirings are not limited. For example, the common wiring 3', the common electrode 3, the signal wiring 4', and the detection electrode 4 may be formed simultaneously with the same material during the formation process of the first small electrode 10a, and the second connection wiring 8 may also be formed simultaneously with the same material during the formation process of the second small electrode 20a.

[0038] (substrate) On the first substrate 1, a first detection unit component 10 (first small electrode 10a, first small pressure-sensitive layer 10b), a common electrode 3, a detection electrode 4, a common wiring 3', and a signal wiring 4' are provided. On the second substrate 2, a second detection unit component 20 (second small electrode 20a, second small pressure-sensitive layer 20b) and a second connection wiring 8 are provided. The material of the first substrate 1 is not particularly limited as long as a detection unit, electrodes, and wirings can be formed on its surface. The material of the second substrate 2 is not particularly limited as long as a detection unit can be formed on its surface. The substrate is preferably a flexible sheet-like member. For example, plastic films such as polyester, polyethylene, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyamide, polymethyl methacrylate, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyimide, polyether ether ketone, ethylene-vinyl alcohol copolymer, and cellophane, dimethyl polysiloxane of silicone rubber, and processed papers such as clean paper, coated paper, and calendered paper can be used. Also, when considering the use of the stress sensor 100 on a living body, as the material of the substrate, polyesters made of homopolymers or copolymers such as polylactic acid, polyglycolic acid, and polycaprolactone, acrylic resins, silicones, cellulose derivatives such as cellulose acetate, cellulose propionate, and cellulose butyrate, polycarbonates, cycloolefin copolymers, styrene-butadiene-based elastomers, etc. can be used. Further, depending on the pressure to be sensed, an elastic body such as rubber may be used as a pressure buffer. When using a conductive substrate, it is desirable to coat the surface with an insulating material so as not to affect the sensor, signal lines, and electrodes. Also, not only a flexible substrate having flexibility but also a flat substrate that does not substantially bend may be used, and it can be appropriately selected according to the use of the stress sensor 100 and the like. Also, when using a plastic film as the substrate, either an unstretched substrate or a stretched substrate may be used. Considering mechanical strength and dimensional stability, it is preferable to use a stretched substrate such as a uniaxially stretched substrate and a biaxially stretched substrate, particularly a biaxially stretched substrate.

[0039] There are no particular restrictions on the thicknesses of the first substrate 1 and the second substrate 2. However, from the perspective of thinning, it is preferably thin, while on the other hand, it is necessary to have a thickness that can achieve sufficient strength as a substrate. The thickness of the substrate is preferably, for example, 6 μm or more and 200 μm or less. Further, as described in FIG. 1, in this embodiment, the planar shape of the substrate is a quadrilateral. However, the planar shape is not limited to this, and shapes such as triangles and circles can be appropriately selected according to the place where the sensor is installed. However, considering mass productivity, the substrate before cutting is preferably a long object. Also, the materials and thicknesses of the first substrate 1 and the second substrate 2 do not have to be the same.

[0040] (Adhesive layer) The thickness of the adhesive layer 5 is preferably less than the total thickness of the first detection unit component 10 and the second detection unit component 20. Specifically, the ratio d1 / d2 of the sum d1 of the heights of the first detection unit component 10 and the second detection unit component 20 to the thickness d2 of the adhesive layer 5 is preferably 1.1 to 5.0 (FIG. 1). When d1 / d2 is less than 1.1, it becomes difficult for the first detection unit component 10 and the second detection unit component 20 to come into contact, and the detection accuracy of pressure and shear force decreases. Also, when d1 / d2 is greater than 5.0, the contact between the first detection unit component 10 and the second detection unit component 20 becomes excessive even in the no-load state. Therefore, the first detection unit component 10 and the second detection unit component 20 cannot follow the pressing force, and the detection accuracy of pressure and shear force decreases. There are no particular restrictions on the material of the adhesive layer 5, as long as it has good adhesion to the substrate. For example, adhesives such as rubber-based, acrylic-based, and silicone-based are preferably used. Also, as the adhesive layer 5, a double-sided tape or the like may be used.

[0041] The subsequent layer 5 is formed so as to surround all the detection units X1, X2, Y1, and Y2, and is preferably in an annular shape as shown in FIG. 1. When the center of the adhesive layer 5 coincides with the center of the detection region R, the distances between the detection units X1, X2, Y1, and Y2 and the adhesive layer 5 are all equal. In this case, the repulsive force of the adhesive layer 5 when a shearing force is applied becomes constant regardless of the direction of the shearing force, and the dependence on the application direction of the shearing force is reduced, so the detection accuracy of the shearing force is further improved. Also, from the viewpoint of detection accuracy, the adhesive layer 5 preferably has a radius larger than that of the detection region R. For example, when assuming a use case where the stress sensor 100 is attached to a human finger (for example, when measuring the pressure and shearing force applied from the finger to tools such as a golf club or a tennis racket, or when gripping the steering wheel of a car), the radius of the detection region R is preferably within 6 mm. In this case, the radius of the annular adhesive layer 5 can be set to be 7 mm or more and 10 mm or less. Note that the adhesive layer 5 is not limited to an annular shape and may be a square annular shape.

[0042] As a method for forming the adhesive layer 5, for example, in the case of a printing method, an inkjet printing method, a screen printing method, or an offset printing method can be used. Also, it may be formed by attaching a double-sided tape processed into a desired shape to the formation position of the adhesive layer 5. The double-sided tape is preferably used when it is not desired to apply an excessive heat load to the base material or when it is desired to avoid uneven adhesion due to printing variations.

[0043] (Buffer material) The buffer material 6 is a member for inputting the load applied to the stress sensor 100, and is provided via an adhesive or the like on the surface of the second base material 2 opposite to one surface (the surface facing the first base material 1). By providing the buffer material 6, the position of the detection region R becomes easier to understand, and it also becomes easier to apply force stably and dispersedly to all the electrodes. In plan view, the center of the buffer material 6 coincides with the geometric center of the detection region R, and the buffer material 6 is provided so as to include all the detection portions X1, X2, Y1, and Y2. The buffer material 6 can be, for example, circular. When the buffer material 6 is circular and the adhesive layer 5 is annular, it is particularly preferable that the outer periphery of the buffer material 6 coincides with the outer periphery of the detection region R, or is outside the detection region R and inside the inner periphery of the adhesive layer 5. Note that the shape of the buffer material 6 may be other than circular.

[0044] For the buffer material 6, rubber materials such as silicone rubber and butadiene rubber, and resin materials such as epoxy resin and urethane resin can be used. Also, it is not necessarily required to have elasticity. In that case, metals such as aluminum and stainless steel with an insulating treatment on the surface, glass, etc. can be used. Further, it may be formed of a plurality of layers. The buffer material 6 is appropriately selected according to the pressure region to be detected. Note that the buffer material 6 may be omitted.

[0045] (Detection principle) Next, the detection of pressure and shear force in the stress sensor 100 according to the present embodiment will be described.

[0046] First, the method for detecting pressure will be described. FIG. 4 is a partial cross-sectional view of the stress sensor during pressure measurement, and FIG. 5 is an enlarged cross-sectional view around the detection portion during pressure measurement. Note that in FIGS. 4 and 5, the buffer material 6 is omitted for convenience, and the case where the first small electrode 10a is larger than the second small electrode 20a in plan view is shown. Further, FIG. 5 shows the case where irregularities are formed on the surface of the small pressure-sensitive layer.

[0047] First, the method for detecting pressure will be described. The pressure can be obtained from the average of the pressures applied to the four detection units X1, X2, Y1, and Y2. The detection units X1, X2, Y1, and Y2 of the stress sensor 100 each have a pair of first small electrodes 10a and second small electrodes 20a connected via a first small pressure-sensitive layer 10b and a second small pressure-sensitive layer 20b. When there is no load in the pressure direction, the contact area between the upper and lower small pressure-sensitive layers is small, or the upper and lower small pressure-sensitive layers do not contact each other, so the electrical resistance value between the first small electrode 10a of the first detection unit structure 10 and the second small electrode 20a of the second detection unit structure 20 is large (see Fig. 5(a)). By applying the pressure F1, the uneven shape formed on the surfaces of the upper and lower small pressure-sensitive layers is slightly deformed, and the contact area increases (see Fig. 5(b)). When the contact area increases, the number of conduction paths between the first small electrode 10a and the second small electrode 20a increases, so the electrical resistance value decreases. Therefore, based on the electrical resistance values of the first small electrode 10a on the first base material 1 and the second small electrode 20a on the second base material 2, the pressure can be detected for each of the detection units X1, X2, Y1, and Y2. Then, the average of these is calculated as the pressure applied to the stress sensor 100.

[0048] Next, the method for detecting shear force will be described. Here, the detection of the shear force in the X-axis direction will be described. Fig. 6 is a cross-sectional view of the stress sensor during shear force measurement. Note that the buffer material 6 is omitted in Fig. 6.

[0049] First, as shown in Fig. 6(a), when a pressure F1 that does not include a component in the shear direction is applied to the detection region R of the stress sensor 100, the forces applied to any of the small electrodes are equal, and the pressures detected by the detection units X1 and X2 are both equal.

[0050] Next, when a shearing force F2 is applied in the right direction of the paper surface without changing the magnitude of the force in the downward direction of the paper surface from the state of FIG. 6(a), the pressure applied to the small electrodes of the detection unit X2 increases due to the change in the balance of the load, and the pressure applied to the small electrodes of the detection unit X1 decreases. Therefore, in the state shown in FIG. 6(b), compared with the state shown in FIG. 6(a), the pressure detected by the detection unit X1 decreases, and the pressure detected by the detection unit X2 increases. The shearing force can be detected from the pressure difference between the detection units X1 and X2. Similarly, when a force is input in the Y direction, the shearing force can also be detected from the pressure difference between the detection units Y1 and Y2.

[0051] As described above, the stress sensor 100 according to the present embodiment utilizes the increase or decrease in the force (the component in the Z-axis direction) applied to the electrodes of each detection unit when a load is applied to detect the direction and magnitude of the input shearing force. By previously obtaining the relationship between the pressure and the shearing force and the resistance value between the upper and lower small electrodes paired with each other as a calibration curve, the measured resistance value can be converted into the pressure and the shearing force hereafter.

[0052] (Effect) FIG. 11 is a schematic view of the first substrate side of the stress sensor according to the reference example, and FIG. 12 is a schematic view of the second substrate side of the stress sensor according to the reference example. As shown in FIGS. 11 and 12, in the stress sensor according to the reference example, a detection unit (detection unit O) is also arranged at the geometric center of the detection region R. In contrast, in the stress sensor 100 according to the present embodiment, no detection unit is arranged at the geometric center of the detection region R. In the reference example, the detection unit O (which may be referred to as the central detection unit hereinafter) is an element for pressure detection. However, as described above, in the present embodiment, since the detection units X1, X2, Y1, and Y2 for shear detection can also be used to detect pressure, it is not necessary to provide the detection unit O at the geometric center of the detection region R as in the reference example. Therefore, the stress sensor 100 of the present invention can reduce the number of detection units and wirings compared with the stress sensor of the reference example, and the area of each small electrode can be increased. When the area of the small electrode increases, the load applied to the small electrode is dispersed, so it becomes easier to detect minute changes, and the measurement sensitivity of pressure and shear force is improved. Also, since it is easier for the pressure to be dispersed, a rapid change in the resistance value is less likely to occur, so the measurement accuracy of pressure and shear force is improved.

[0053] In addition, since the stress sensor 100 of the present embodiment has no central detection unit, the tilting load applied to the central detection unit in the stress sensor according to the reference example is applied to the detection unit for shear detection in the stress sensor 100 of the present invention. As a result, it becomes easier to detect changes in the shear force, particularly improving the measurement sensitivity in the low load range and the detection accuracy in the low load range.

[0054] In the present embodiment, the number of detection units is four. However, as long as no detection unit is arranged at the geometric center of the detection region R, it is not limited to this, and it may be appropriately selected according to the application. Also, the detection units do not necessarily have to be provided at equal intervals. However, arranging them to be rotationally symmetric four times with respect to the geometric center of the detection region R as in the present embodiment can make the thickness of the entire sensor uniform and improve the stability of the measurement.

[0055] In the above description, the case where the number of the first small electrodes 10a and the second small electrodes 20a in each detection component is 2 (n = 2) has been described. However, if n is an even number, as shown in FIGS. 7 and 8, it may be 4 (n = 4), 6 (n = 6), etc. In FIGS. 7 and 8, for the sake of convenience, the shape of each small electrode is shown as a rectangle, and the state where each small electrode is arranged in a straight line is shown.

[0056] (Case where n = 4) FIG. 7 is a diagram for explaining the connection of small electrodes and wirings in the case where n = 4. As shown in FIG. 7(a), in the first detection unit component 10 on the first base material 1 side, a common wiring 3' is connected to the first small electrode 10a arranged at one end in the alignment direction, a signal wiring 4' is connected to the first small electrode 10a arranged at the other end, and further, one first connection wiring 7 for connecting two adjacent first small electrodes 10a among the first small electrodes 10a excluding both ends is provided. In the second detection unit component 20 on the second base material 2 side, two second connection wirings 8 for connecting two adjacent second small electrodes 20a are provided.

[0057] (Case where n = 6) FIG. 8 is a diagram for explaining the connection of small electrodes and wirings in the case where n = 6. As shown in FIG. 8(a), in the first detection unit component 10 on the first base material 1 side, a common wiring 3' is connected to the first small electrode 10a arranged at one end in the alignment direction, a common wiring 3' is connected to the first small electrode 10a arranged at the other end, and further, two first connection wirings 7 for connecting two adjacent first small electrodes 10a among the first small electrodes 10a excluding both ends are provided. In the second detection unit component 20 on the second base material 2 side, three second connection wirings 8 for connecting two adjacent second small electrodes 20a are provided.

[0058] That is, in one first detection unit component 10, when the number of first small electrodes 10a arranged at intervals in a predetermined direction on one surface of the first base material 1 is n (where n is a positive even number), the common wiring 3' is connected to the first small electrode 10a arranged at one end in the predetermined direction, the signal wiring 4' is connected to the first small electrode 10a arranged at the other end in the predetermined direction, and (n / 2 - 1) first connection wirings 7 connect two adjacent first small electrodes 10a among the first small electrodes 10a other than the first small electrodes 10a arranged at both ends in the predetermined direction. In the second base material 2, n / 2 second connection wirings 8 connect two adjacent second small electrodes 20a. Therefore, when the opposing first small pressure-sensitive layers 10b and second small pressure-sensitive layers 20b come into contact with each other, a series current path is formed via the first small electrode 10a connected to the common wiring 3', the first small electrode 10a connected to the signal wiring 4', the remaining first small electrodes 10a included in the first detection unit component 10, and the second small electrodes 20a included in the second detection unit component 20. Therefore, similar to the case of n = 2, even when n is 4 or more (where n is a positive even number), the current input from the first base material 1 side once flows to the second base material 2 side and then returns to the first base material 1 side again. Thus, for the second base material 2, since there is no need to provide input / output wiring, the stress sensor 100 can have a simple wiring structure. Therefore, the stress sensor 100 according to the present embodiment is also easy to miniaturize and can be easily connected to an input / output device.

[0059] As described above, when the number of first small electrodes 10a (second small electrodes 20a) is 4 or more (n = 4), the first connection wiring 7 is provided between the first small electrodes 10a, and the first connection wiring 7 can be formed of the same material and by the same method as the second connection wiring 8.

[0060] Instead of connecting the second small electrode 20a with the second connection wiring 8, one second small electrode 20a may be provided so as to overlap with a pair (n pieces) of adjacent first small electrodes 10a (FIG. 9). That is, it may be n / 2 second small electrodes 20a for n first small electrodes 10a. In this case, compared with the configuration of the second small electrode 20a shown in FIG. 3, the area of the second small electrode 20a increases by the amount that the second connection wiring 8 disappears. In the stress sensor 100 configured as shown in FIG. 1, a slight misalignment between the first small electrode 10a and the second small electrode 20a caused by bonding the first base material 1 and the second base material 2, and a slight difference in the size of the electrodes when forming the first small electrode 10a and the second small electrode 20a can be reduced, enabling more accurate stress measurement.

[0061] Further, in the present embodiment, in each detection unit, small electrodes having a shape obtained by dividing an annular shape in the circumferential direction are arranged in the circumferential direction, but as shown in FIG. 10, they may be arranged in the radial direction.

[0062] Also, the bridge circuit included in the stress sensor 100 outputs a combined resistance value between a first small electrode 10a to which a common wiring 3' is connected and a first small electrode 10a to which a signal wiring 4' is connected in a pair of first detection unit components 10 and second detection unit components 20.

Example

[0063] (Example 1) Stress sensors 100 each having four detection units shown in FIG. 1 were fabricated. Specifically, a 50-μm polyimide film (Toray DuPont: Kapton 100H) was used as the first base material 1, and the first small electrode 10a having a shape obtained by dividing the annular shape shown in FIG. 2(a) in the circumferential direction was formed by screen printing using conductive silver ink. All of the first small electrodes 10a had an area of 0.28 mm 2 and were formed in two side-by-side arrangements in the circumferential direction. At the same time as the first small electrode 10a, a common electrode 3 and a detection electrode 4 having a width of 250 μm and a length of 5 mm, and a common wiring 3' and a signal wiring 4' having a width of 100 μm were fabricated. The thickness of the electrodes and the wiring was 10 μm.

[0064] Next, on each of the first small electrodes 10a, a first small pressure-sensitive layer 10b was formed with a thickness of 10 μm by screen printing using a conductive carbon ink having a viscosity of 10,000 mPa·s (CP).

[0065] Next, an annular double-sided tape with an inner diameter of 7 mm and a width of 1 mm was adhered around the detection region R of the first substrate 1 to form an adhesive layer 5. The thickness of the adhesive layer 5 was set to 30 μm.

[0066] Next, a 50-μm polyimide film (Toray DuPont: Kapton 100H) was used as the second substrate 2, and second small electrodes 20a having a shape in which the annulus shown in Fig. 3(a) was divided in the circumferential direction were formed by screen printing using a conductive silver ink. Each of the second small electrodes 20a had an area of 0.28 mm 2 and two were formed side by side in the circumferential direction. The second small electrodes 20a were connected by a second connection wiring 8 having a length of 100 μm and a width of 100 μm. The thicknesses of the second small electrodes 20a and the second connection wiring 8 were 10 μm.

[0067] Next, on each of the second small electrodes 20a, a second small pressure-sensitive layer 20b was formed with a thickness of 10 μm by screen printing using a conductive carbon ink having a viscosity of 10,000 mPa·s (CP).

[0068] Next, the first substrate 1 and the second substrate 2 were bonded together via the adhesive layer 5.

[0069] Next, a buffer material 6 was adhered to the second substrate 2 with an adhesive to obtain a stress sensor 100. At this time, the diameter of the buffer material 6 was 6 mm and the thickness was 1 mm.

[0070] (Example 2) A stress sensor 100 was fabricated in the same manner as in Example 1, except that the first small pressure-sensitive layer 10b and the second small pressure-sensitive layer 20b were each formed by screen printing using a conductive carbon ink having a viscosity of 5,000 mPa·s (CP).

[0071] (Example 3) A stress sensor 100 was fabricated in the same manner as in Example 1, except that the first small pressure-sensitive layer 10b and the second small pressure-sensitive layer 20b were formed by screen printing using conductive carbon ink with a viscosity of 22000 mPa·s (CP), respectively.

[0072] (Example 4) A stress sensor 100 was fabricated in the same manner as in Example 1, except that the first small pressure-sensitive layer 10b and the second small pressure-sensitive layer 20b were formed by screen printing using conductive carbon ink with a viscosity of 4000 mPa·s (CP), respectively.

[0073] (Example 5) A stress sensor 100 was fabricated in the same manner as in Example 1, except that the first small pressure-sensitive layer 10b and the second small pressure-sensitive layer 20b were formed by screen printing using conductive carbon ink with a viscosity of 25000 mPa·s (CP), respectively.

[0074] (Comparative Example 1) A stress sensor was fabricated in the same manner as in Example 1, except that the number of detection units was five, that is, a central detection unit (detection unit O) was formed as shown in FIGS. 11 and 12. At this time, the area of each small electrode was 0.22 mm 2 was.

[0075] (Measurement of arithmetic mean roughness) For the stress sensors according to Examples 1 to 5 and Comparative Example 1, the arithmetic mean roughness Sa of the surface of the first small pressure-sensitive layer 10b in the region D1 where the first small electrode 10a is present in plan view and the arithmetic mean roughness Sa of the surface of the second small pressure-sensitive layer 20b in the region D2 where the second small electrode 20a is present in plan view were measured. Specifically, for each of the eight first small pressure-sensitive layers 10b, an arbitrary location (however, within the region D1) was measured at one location (that is, measured eight times). Then, the average value of the surface roughness of each of the first small pressure-sensitive layers 10b was determined as the arithmetic mean roughness Sa of the surface of the first small pressure-sensitive layer 10b in the region D1. Also, for each of the eight second small pressure-sensitive layers 20b, an arbitrary location (however, within the region D2) was measured at one location (that is, measured eight times). Then, the average value of the surface roughness of each of the second small pressure-sensitive layers 20b was determined as the arithmetic mean roughness Sa of the surface of the second small pressure-sensitive layer 20b in the region D2. The measurement conditions and calculation conditions for the arithmetic mean roughness Sa are shown below. The measurement results are shown in Table 1. For Comparative Example 1, the first small pressure-sensitive layer 10b and the second small pressure-sensitive layer 20b of the detection unit O were excluded from the measurement targets. [Measurement Conditions for Arithmetic Mean Roughness Sa] · Measuring instrument: Zygo white interference measuring instrument NexView NX2 · Measurement magnification: Objective lens ×50 (NA0.55), Zoom ×1 (Field of view (FOV): 173.188 μm) · Horizontal resolution (pixel pitch): 0.173 μm [Calculation Conditions for Arithmetic Mean Roughness Sa (ISO025178)] · Software used: Zygo MX · F operator (shape removal): Removal of the overall average plane (only tilt correction) · S filter (low-pass filter): None · L filter (high-pass filter): Spline filter Cutoff 80 μm

[0076] <Pressure Detection Accuracy Evaluation> For the stress sensors according to Examples 1 to 5 and Comparative Example 1, the pressure detection accuracy was evaluated for each of the low load range (0.1 N to 0.5 N) and the standard load range (0.5 N to 5.0 N).

[0077] (Evaluation of Pressure Detection Accuracy in Low Load Range) The stress sensor was fixed on the measurement stage of a load application device (load cell: Aiko Engineering MODEL-3005 (50 N)). The measurement terminals were applied to the stress sensor, and while increasing only the vertical load from 0.1 N to 0.5 N in 0.1 N increments without applying shear, the output value of the pressure of the stress sensor was acquired, and the applied load value was compared with the output value of the stress sensor. The output value of the pressure of the stress sensor is the average value of the values output by the detection units X1, X2, Y1, and Y2. (Evaluation of Pressure Detection Accuracy in Standard Load Range) Similar to the evaluation of the pressure detection accuracy in the low load range, while increasing only the vertical load from 0.5 N to 5.0 N in 0.1 N increments, the output value of the pressure of the stress sensor was acquired, and the applied load value was compared with the output value of the stress sensor.

[0078] The detection accuracy of the pressure of the stress sensor was evaluated according to the following criteria. ◎: The maximum value of the difference between the applied pressure value and the pressure value output from the sensor is within ±5%. 〇: The maximum value of the difference between the applied pressure value and the pressure value output from the sensor is within ±10%. ×: The maximum value of the difference between the applied pressure value and the pressure value output from the sensor exceeds the range of ±10%.

[0079] (Evaluation of Shear Force Detection Accuracy) Regarding the stress sensors according to Examples 1 to 5 and Comparative Example 1, the detection accuracy of the shear force was evaluated for each of the low load range (pressure of 0.5 N) and the standard load range (pressure of 3.0 N).

[0080] (Evaluation of Shear Force Detection Accuracy in Low Load Range) A stress sensor was fixed on the measurement stage of a load application device (load cell: Aiko Engineering MODEL - 3005 (50N)). With a vertical load of 0.5N applied to the stress sensor, while increasing each shear load in the X - axis direction and the Y - axis direction from 0N to 0.1N in increments of 0.02N, the output value of the shear force of the stress sensor was acquired, and the applied shear load value was compared with the output value of the obtained shear force. Also, while decreasing each shear load in the X - axis direction and the Y - axis direction from 0N to - 0.1N in increments of 0.02N, the output value of the shear force of the stress sensor was acquired, and the applied shear load value was compared with the output value of the obtained shear force. (Evaluation of Shear Force Detection Accuracy in the Standard Load Range) Similar to the evaluation of shear force detection accuracy in the low - load range, with a vertical load of 3.0N applied to the stress sensor, while increasing each shear load in the X - axis direction and the Y - axis direction from 0N to 0.3N in increments of 0.05N, the output value of the shear force of the stress sensor was acquired, and the applied shear load value was compared with the output value of the obtained shear force. Also, while decreasing each shear load in the X - axis direction and the Y - axis direction from 0N to - 0.3N in increments of 0.05N, the output value of the shear force of the stress sensor was acquired, and the applied shear load value was compared with the output value of the obtained shear force.

[0081] The detection accuracy of the shear force of the stress sensor was evaluated according to the following criteria. ◎: The maximum value of the difference between the applied shear load value and the shear force value output from the sensor is within ±5%. ○: The maximum value of the difference between the applied shear load value and the shear force value output from the sensor is within ±10%. ×: The maximum value of the difference between the applied shear load value and the shear force value output from the sensor exceeds the range of ±10%.

[0082] <Comprehensive Evaluation> Based on the evaluation results of pressure and shear force detection accuracy, a comprehensive evaluation was conducted. The evaluation criteria are as follows. ◎: The evaluations of both pressure detection accuracy and shear force detection accuracy are ◎. ○: Either the evaluation of pressure detection accuracy or shear force detection accuracy is ○, and neither the evaluation of pressure detection accuracy nor shear force detection accuracy is ×. ×: Either the evaluation of pressure detection accuracy or shear force detection accuracy is ×.

[0083] The number of detection parts and evaluation results of the stress sensors according to Examples 1 to 5 and Comparative Example 1 are shown together in Table 1.

[0084]

Table 1

[0085] In the stress sensors 100 according to Examples 1 to 5, it was confirmed that excellent detection accuracy was shown regardless of whether the applied pressure and shear force were in the low load range of 0.5 N or less or the standard load range of 0.5 N or more. In particular, for the stress sensors 100 according to Examples 1 to 3, since the arithmetic mean roughness Sa of the surface in the region D1 or D2 of the small pressure-sensitive layer was 0.1 μm or more and 1.2 μm or less, particularly excellent detection accuracy was shown.

[0086] In the stress sensor 100 according to Example 4, the arithmetic mean roughness of the surface in the region D1 or D2 of the small pressure-sensitive layer was less than 0.1 μm. Therefore, the change in the contact area was reduced during load application, making it difficult to detect the change in resistance, resulting in a decrease in the measurement sensitivity and accuracy of pressure and shear force, and the detection accuracy was inferior to that of Examples 1 to 3.

[0087] In the stress sensor 100 according to Example 5, the arithmetic mean roughness of the surface in the region D1 or D2 of the small pressure-sensitive layer was greater than 1.2 μm. Therefore, it became difficult for the applied pressure to be uniformly applied to the surface of the small electrode, resulting in a decrease in measurement accuracy, and the detection accuracy was inferior to that of Examples 1 to 3.

[0088] Regarding the stress sensor according to Comparative Example 1, unlike Examples 1 to 5, in the low load range of 0.5 N or less, the detection errors of pressure and shear force exceeded 10%, and the accuracy was poor. This is because the detection part O was formed, so the area of each electrode became smaller than that in the examples.

Industrial Applicability

[0089] The present invention can be applied to a stress sensor capable of detecting pressure and shear force.

Explanation of Signs

[0090] 1: First substrate 2: Second substrate 3: Common electrode 3': Common wiring 4: Detection electrode 4': Signal wiring 5: Adhesive layer 6: Buffer material 7: First connection wiring 8: Second connection wiring 10: First detection part component 10a: First small electrode 10b: First small pressure-sensitive layer 20: Second detection part component 20a: Second small electrode 20b: Second small pressure-sensitive layer 100: Stress sensor D1: Region where the first small electrode exists in plan view D2: Region where the second small electrode exists in plan view R: Detection region X1: Detection part X2: Detection part Y1: Detection part Y2: Detection part O: Detection part

Claims

1. A stress sensor capable of detecting pressure and shear force, comprising: a first substrate; a second substrate; four detection units disposed between the first substrate and the second substrate; an adhesive layer provided to bond the first substrate and the second substrate and surround the four detection units; each of the detection units is an element whose resistance value changes according to an applied load; two of the detection units are arranged on a first straight line so as to be point-symmetrical with respect to the geometric center of the detection region of the stress sensor; the remaining two of the detection units are arranged on a second straight line that is point-symmetrical with respect to the geometric center of the detection region and orthogonal to the first straight line; A stress sensor in which no detection unit is arranged at the geometric center of the detection region.

2. Each of the detection units includes: a first detection unit structure having a first electrode provided on one surface of the first substrate and a first pressure-sensitive layer laminated on the first electrode; a second detection unit structure having a second electrode provided on the surface of the second substrate facing the first substrate so as to face each of the first electrodes, and a second pressure-sensitive layer laminated on the second electrode; each of the first electrodes is composed of n (where n is a positive even number) first small electrodes arranged at intervals in a predetermined direction on the one surface of the first substrate; each of the first pressure-sensitive layers is composed of first small pressure-sensitive layers laminated on each of the first small electrodes constituting the corresponding first detection unit structure; each of the second electrodes is composed of n second small electrodes arranged on the surface of the second substrate facing the first substrate so as to face each of the first small electrodes; each of the second pressure-sensitive layers is composed of second small pressure-sensitive layers laminated on each of the second small electrodes constituting the corresponding second detection unit structure; the first substrate further includes: a common wiring connected to the first small electrode disposed at one end in the predetermined direction; a signal wiring connected to the first small electrode disposed at the other end in the predetermined direction; (n / 2 - 1) first connection wirings for connecting two adjacent first small electrodes among the first small electrodes other than the first small electrodes disposed at both ends in the predetermined direction; the second substrate further includes: n / 2 second connection wirings for connecting two adjacent second small electrodes. When a load is applied in a direction in which the first base material and the second base material approach each other, in a pair of opposing first detection unit components and second detection unit components, the opposing first small pressure-sensitive layers and second small pressure-sensitive layers come into contact with each other, and a series current path via the second small electrode is formed with both ends being the first small electrode to which the common wiring is connected and the first small electrode to which the signal wiring is connected. The stress sensor according to claim 1, wherein both the common electrode connected to the common wiring and the detection electrode connected to the signal wiring are provided on the one surface of the first base material.

3. The stress sensor according to claim 2, wherein the arithmetic mean roughness of the surface of the region where the first small electrode exists in the first small pressure-sensitive layer in plan view and the arithmetic mean roughness of the surface of the region where the second small electrode exists in the second small pressure-sensitive layer in plan view are 0.08 μm or more and 1.5 μm or less.

4. The stress sensor according to claim 2, wherein each of the first electrode and the second electrode has a shape in which an annular ring is divided in the circumferential direction.

5. The stress sensor according to claim 1, wherein the adhesive layer is annular.

6. The stress sensor according to claim 1, wherein the geometric center of the adhesive layer coincides with the geometric center of the detection region.

7. The stress sensor according to claim 1, wherein a cushioning material is provided on the surface of the second base material opposite to the first base material so as to include the detection region in plan view.

8. The stress sensor according to claim 2, comprising a bridge circuit that outputs a combined resistance value between the first small electrode to which the common wiring is connected and the first small electrode to which the signal wiring is connected in a pair of opposing first detection unit components and second detection unit components.

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