Stress sensor

Abstract

To provide a stress sensor capable of accurately detecting pressure and shearing force even when a measured object has elasticity.SOLUTION: A stress sensor capable of detecting pressure and shearing force includes: a first base material; a second base material; and a plurality of detection parts arranged between the first base material and the second base material. Each one of the detection parts comprises: a first detection part component including a first electrode arranged on one surface of the first base material, and a first pressure sensitive layer to be laminated on the first electrode; and a second detection part component including a second electrode arranged on a surface facing the first base material in the second base material so as to face the first electrode, and a second pressure sensitive layer to be laminated on the second electrode. The first base material is the base material to be fixed to a measured object when used, and the second base material is the base material to which the pressure and shearing force are applied when used. Bending rigidity of the second base material is smaller than the bending rigidity of the first base material.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 above-described stress sensor 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. For example, Patent Document 1 reports a stress sensor assuming installation of a thin stress sensor using a flexible substrate at the fingertip of a robot hand or the like.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in a conventional thin and small stress sensor, even if it is easy to attach to a robot hand or its finger formed of metal or the like to detect pressure and shear force, when attached to an elastic measurement object such as a human finger, hand, or cloth glove worn on the hand to detect pressure and shear force, it has been found that there is a problem in that it is difficult to obtain a stable detection value because the stress sensor bends as the measurement object deforms.

[0006] Therefore, an object of the present invention is to provide a stress sensor capable of accurately detecting pressure and shear force even for an object to be measured having elasticity.

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 base material, a second base material, and a plurality of detection units disposed between the first base material and the second base material. Each of the plurality of detection units includes a first detection unit structure having a first electrode provided on one surface of the first base material and a first pressure-sensitive layer laminated on the first electrode, and a second detection unit structure having a second electrode provided opposite to each of the first electrodes on the surface of the second base material facing the first base material and a second pressure-sensitive layer laminated on the second electrode. The first base material is a base material fixed to the object to be measured during use, the second base material is a base material to which pressure and shear force are input during use, and the bending rigidity of the second base material is smaller than that of the first base material.

[0008] Another aspect of the present invention is a stress sensor capable of detecting pressure and shear force, comprising a first base material, a second base material, and a plurality of detection units disposed between the first base material and the second base material. Each of the plurality of detection units includes a first detection unit structure having a first electrode provided on one surface of the first base material and a first pressure-sensitive layer laminated on the first electrode, and a second detection unit structure having a second electrode provided opposite to each of the first electrodes on the surface of the second base material facing the first base material and a second pressure-sensitive layer laminated on the second electrode. The first base material is a base material fixed to the object to be measured during use, the second base material is a base material to which pressure and shear force are input during use, and the film thickness of the second base material is smaller than that of the first base material.

Effects of the Invention

[0009] According to the present invention, it is possible to provide a stress sensor capable of accurately detecting pressure and shear force even for an object to be measured having elasticity.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0011] 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 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.

[0012] <Embodiment> FIG. 1 is a schematic diagram showing the 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 schematic diagram of the first substrate side of the stress sensor. More specifically, FIG. 2(a) is a 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 schematic diagram of the second substrate side of the stress sensor. More specifically, FIG. 3(a) is a 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).

[0013] The stress sensor 100 of the present invention is a sensor that is installed on the object to be measured on the side of the first base material 1 and detects the pressure and shear force (shearing force) applied from the side of the second base material 2. The stress sensor 100 includes a first base material 1, a second base material 2, five detection units (detection unit X1, detection unit X2, detection unit Y1, detection unit Y2, and detection unit O) arranged in a two-dimensional plane between the first base material 1 and the second base material 2, and an adhesive layer 5 that adheres 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 that includes 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 stress can be accurately detected when pressure and shear force (shearing force) are applied. Note that the pressure indicates the force component in the direction perpendicular to the sensor surface (Z-axis direction in FIG. 1), and the shear force indicates the force component in the surface direction of the base material (Z-axis and Y-axis directions in FIG. 1).

[0014] 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, and electrodes and wirings for acquiring the output of the detection unit are appropriately provided on one surface of the first base material 1 and the surface of the second base material 2 on the side of the first base material 1. 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 on the side opposite to one surface (the surface facing the first base material 1).

[0015] (Detection unit) The detection units are arranged in five between the first substrate 1 and the second substrate 2, and are elements whose resistance value changes according to the applied load. Among the five detection units, the detection unit O is arranged at the geometric center of the detection region R. The detection units X1 and X2 are arranged on the first straight line (on 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 units Y1 and Y2 are point-symmetrical with respect to the geometric center of the detection region R and are arranged on the second straight line (on 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 detection unit O. The detection unit O arranged at the geometric center of the detection region R is an element for detecting pressure. Further, the detection units X1 and X2 arranged in the X-axis direction are elements for detecting the shear force in the X-axis direction, and the detection units Y1 and Y2 arranged in the Y-axis direction are elements for detecting the shear force in the Y-axis direction.

[0016] When assuming the use of attaching the stress sensor 100 to a human finger (for example, when assuming analyzing the stress acting between the finger and a tool such as a golf club or a tennis racket when swinging the tool), each detection unit is preferably arranged within a circle with a radius of 3 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 3 mm or less.

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

[0018] (Detection unit structure) Five first detection unit structures 10 are provided on one surface of the first substrate 1, and five second detection unit structures 20 are provided facing each of the first detection unit structures 10 on the surface of the second substrate 2 facing the first substrate 1. Each of the first detection unit structures 10 has a first electrode 10a and a first pressure-sensitive layer 10b laminated on the first electrode 10a. Each of the second detection unit structures 20 has a second electrode 20a and a second pressure-sensitive layer 20b laminated on the second electrode 20a.

[0019] (Electrode) The first electrode 10a is formed on one surface of the first substrate, and the second electrode 20a is provided opposite to each of the first electrodes 10a on the surface of the second substrate 2 facing the first substrate 1. The first electrode 10a and the second electrode 20a may have the same shape and area, but it is preferable that one has a relatively larger area than the other (see FIG. 1). The area of the electrode with a relatively smaller area is preferably 1 / 5 or more and 2 / 3 or less of the area of the electrode with a relatively larger area. If it is less than 1 / 5, the sensitivity of the stress sensor 100 will decrease. If it exceeds 2 / 3, it will be difficult to align the two electrodes.

[0020] The resistivity of the electrodes (the first electrode 10a and the second electrode 20a) is preferably 1.0×10 -3 Ω·cm or less. Also, the thickness of each 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. If it is less than 0.01 μm, the formed film is likely to be a discontinuous film and sufficient conductivity cannot be obtained. If it exceeds 30 μm, there is a risk of cracks occurring in the electrodes when the stress sensor 100 formed on the flexible substrate is bent.

[0021] The electrode is not limited in terms of material or formation method as long as it is 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) 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 forming a film on the entire surface of the substrate using vapor deposition methods such as vacuum evaporation method, sputtering method, etc., and patterning the film by an etching method can be used. When using a printing method, a material obtained by mixing the electrode material with a resin and making it into an ink that can be applied by each printing method can be used. In the case of the vapor deposition method, it may be formed by patterning the film formed on the entire surface of the substrate by an etching method, or it may be formed by depositing the material only at a predetermined position using a metal mask. In this embodiment, the electrode is square (Figs. 1 to 3), but it may be circular, rectangular, or the like.

[0022] (Pressure-sensitive layer) The first pressure-sensitive layer 10b is laminated on each of the first electrodes 10a, and the second pressure-sensitive layer 20b is laminated on each of the second electrodes 20a. Each pressure-sensitive layer (the first pressure-sensitive layer 10b and the second pressure-sensitive layer 20b) completely covers each electrode and is formed so as to be separated from the pressure-sensitive layer laminated on the adjacent electrode. In plan view, it is preferable that the sizes of the pressure-sensitive layers are the same.

[0023] The thickness of the 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 pressure-sensitive layer is less than 1 μm, it becomes difficult to sufficiently cover the electrodes, and the upper and lower electrodes conduct without passing through the pressure-sensitive layer, resulting in a malfunction in the sensor operation. When the 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 of the pressure-sensitive layer increases, so that the detection accuracy of the pressure and the shear force decreases. Further, from the viewpoint of thinning, the first electrode 10a, the first pressure-sensitive layer 10b, the second electrode 20a, and the second pressure-sensitive layer 20b are preferably formed to have a total thickness of 260 μm or less.

[0024] 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 pressure-sensitive layer is formed of a conductive material. However, it is necessary to use a material having a higher resistivity than that of the electrodes. The resistivity of the pressure-sensitive layer is preferably 1.0×10 -1 Ω·cm or more and 1.0×10 6 Ωcm or less. 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.

[0025] Further, the stress sensor 100 can detect the input pressing force by changing the contact resistance of the contact surface between the first pressure-sensitive layer 10b and the second pressure-sensitive layer 20b due to the input pressing force. When the pressing force is input, the upper and lower 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 pressure-sensitive layer. For example, conductive carbon or conductive nanocarbon can be used. Further, unevenness on the order of several μm may be formed on the surface of each pressure-sensitive layer to make the change in the contact area remarkable and make it easier to detect the change in the resistance value. As a method of forming unevenness on the surface of the pressure-sensitive layer, for example, a method of printing and forming conductive carbon ink using screen printing can be used.

[0026] Alternatively, the pressure-sensitive layer may be formed of a material whose resistance value decreases as its thickness changes due to the applied pressing force. In this case, it is preferable to use a material having a piezoresistive effect in which the resistivity changes due to deformation. As such materials, conductive polymers such as polyethylene dioxythiophene, polyaniline, polypyrrole, and carbon paste using graphite or carbon nanotubes are preferably used. Further, it can be formed by printing methods such as inkjet printing method, screen printing method, offset printing method, or vapor deposition methods such as vacuum vapor deposition method, sputtering method, thermal chemical vapor deposition method, plasma chemical vapor deposition method. When using a vapor deposition method, it may be formed by an etching method after forming on the entire surface of the substrate, or may be formed by depositing a material only at a predetermined position using a metal mask.

[0027] Since it is preferable that the pressure-sensitive layer is less deformable than the substrate, the Young's modulus of the pressure-sensitive layer is preferably greater than that of the first substrate 1 and the second substrate 2. This is because if the pressure-sensitive layer is deformed not only in the surface shape but also in the entire thickness direction by pressure or shear force, the change in resistance value due to the deformation becomes measurement noise.

[0028] The resistivity of the 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.

[0029] (Substrate) The base materials (the first base material 1 and the second base material 2) are preferably flexible sheet-like members. For example, polyimide (PI), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), biaxially oriented polystyrene (OPS), polyethersulfone (PES), etc. can be used. Also, the base material may be formed by laminating two or more base materials. On the first base material 1, a first detection unit component 10 (a first electrode 10a, a first pressure-sensitive layer 10b) is provided. On the second base material 2, a second detection unit component 20 (a second electrode 20a, a second pressure-sensitive layer 20b) is provided. As described in FIG. 1, in this embodiment, the planar shape of the base material is a quadrilateral, but 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, etc. However, considering mass productivity, the base material before cutting is preferably a long material. Also, the materials of the first base material 1 and the second base material 2 do not have to be the same.

[0030] The first base material 1 is a base material that is fixed to the object to be measured during use, and the second base material 2 is a base material on the side where pressure and shear force are input during use. At this time, the bending rigidity of the second base material 2 is smaller than that of the first base material 1. The bending rigidity of the base material is formulated as the product of the Young's modulus and the second moment of area. Also, when the bending direction is in the film thickness direction, assuming the film thickness t and the length l, the second moment of area is defined as {(l×t 3 ) / 12}.

[0031] For example, when calculating the bending rigidity of a polyimide base material with a film thickness of 25 μm, when the Young's modulus is 3.4 GPa and the base material length is 3 mm, the bending rigidity is 1.3×10 -8 (N·m 2 ). Further, when the diameter of the detection region R of the first base material 1 of the present invention is 3 mm of the sheet length, the bending rigidity of the second base material 2 is 6.0×10 -10 (N·m 2 ) or more and 1.5×10 -6 (N·m 2 ) or less, and the bending rigidity of the first base material 1 is 7.5×10 -8 (N·m 2 ) or more and 1.2×10 -5 (N·m2 ) It is particularly preferable that the following conditions are met. By satisfying these conditions, the first substrate 1 functions as a base that is difficult to deform when pressure and shear force are applied, and the pressure and shear force applied to the second substrate 2 side are easily transmitted to the detection region R without resistance. If the bending rigidity of the second substrate 2 is too large, the applied pressure and shear force will be difficult to be transmitted to the detection region R. Also, when the bending rigidity of the second substrate 2 is within the above range, if the bending rigidity of the first substrate 1 is larger than the above range, the difference in bending rigidity between the second substrate 2 and the first substrate 1 will increase, and when the second substrate 2 and the first substrate 1 are bonded together, the entire sensor will warp, making it difficult to accurately detect the value.

[0032] Also, it is preferable that the first substrate 1 has a smaller film thickness than the second substrate 2. Further, for example, when the Young's modulus of the first substrate 1 and the second substrate 2 is 2 GPa or more and 6 GPa or less, it is preferable that the film thickness of the first substrate 1 is 50 μm or more and 200 μm or less, and the film thickness of the second substrate 2 is 10 μm or more and 100 μm or less. It is even more preferable that the film thickness of the first substrate 1 is 50 μm or more and 188 μm or less, and the film thickness of the second substrate 2 is 12.5 μm or more and 75 μm or less. By satisfying these conditions, the first substrate 1 functions as a base that is difficult to deform when pressure and shear force are applied, and the pressure and shear force applied to the second substrate 2 side are easily transmitted to the detection region R without resistance. If the film thickness of the second substrate 2 is too large, the applied pressure and shear force will be difficult to be transmitted to the detection region R. Also, when the film thickness of the second substrate 2 is within the above range, if the film thickness of the first substrate 1 is larger than the above range, the difference in film thickness between the second substrate 2 and the first substrate 1 will increase, and when the second substrate 2 and the first substrate 1 are bonded together, the entire sensor will warp, making it difficult to accurately detect the value.

[0033] (Adhesive layer) Preferably, the thickness of the adhesive layer 5 is 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. When d1 / d2 is greater than 5.0, even in the no-load state, the contact between the first detection unit component 10 and the second detection unit component 20 becomes excessive, so 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 is no particular limitation on the material of the adhesive layer 5, as long as it has good adhesion to the base material. 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.

[0034] The adhesive layer 5 is preferably formed so as to surround all the detection units O, X1, X2, Y1, Y2 and has an annular shape as shown in FIG. 1. When the center of the adhesive layer 5 coincides with the geometric center of the detection region R, that is, when the detection unit O is arranged at the center of the adhesive layer 5, the distances between the detection units X1, X2, Y1, Y2 that contribute to shear detection and the adhesive layer 5 are all equal. In this case, the repulsive force of the adhesive layer 5 when a shear force is applied becomes constant regardless of the direction of the shear force, and the dependence on the application direction of the shear force becomes small, so the detection accuracy of the shear 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 the use of attaching the stress sensor 100 to a human finger (for example, when swinging tools such as a golf club or a tennis racket, or when gripping the steering wheel of a car, and assuming measuring the pressure and shear force applied from the finger to the tool or the steering wheel), the radius of the detection region R is preferably within 3 mm. In this case, the radius of the annular adhesive layer 5 can be 5 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.

[0035] 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. Alternatively, it may be formed by attaching a double-sided tape processed into a desired shape to the formation position of the adhesive layer 5. 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, the double-sided tape is preferably used.

[0036] (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 stably disperse and apply force to all the electrodes. In a 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 encompass all the detection portions O, 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, and the buffer material 6 may be omitted.

[0037] Since it is preferable that the buffer material 6 is more easily deformed than the base material, it is preferable to use a resin material having a smaller Young's modulus than the first base material 1 and the second base material 2 for the buffer material 6, and for example, rubber materials such as silicone rubber and butadiene rubber can be used. The material of the buffer material 6 is appropriately selected according to the pressure region to be detected. Note that the buffer material 6 may be omitted.

[0038] (Detection principle) Next, the detection of pressure and shear force in the stress sensor 100 according to the present embodiment will be described.

[0039] First, the method for detecting pressure will be described. FIG. 4 is a cross-sectional view of the stress sensor during pressure measurement, and FIG. 5 is an enlarged cross-sectional view around the detection unit during pressure measurement. Note that in FIGS. 4 and 5, the buffer material 6 is omitted for convenience. Further, in FIG. 5, a case where irregularities are formed on the surface of the pressure-sensitive layer is shown.

[0040] First, the method for detecting pressure will be described. The pressure can be obtained from the output of the detection unit O disposed at the geometric center of the detection region R. In the detection unit O of the stress sensor 100, a pair of first electrodes 10a and second electrodes 20a are connected via a first pressure-sensitive layer 10b and a second pressure-sensitive layer 20b. When there is no load in the pressure direction, the contact area between the upper and lower pressure-sensitive layers is small, or the upper and lower pressure-sensitive layers do not contact each other, so the electrical resistance value between the first electrode 10a of the first detection unit structure 10 and the second electrode 20a of the second detection unit structure 20 is large (see FIG. 5(a)). By applying the pressure F1, the irregular shape formed on the surface of the upper and lower 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 electrode 10a and the second electrode 20a increases, so the electrical resistance value decreases. Therefore, the pressure can be detected by the detection unit O based on the electrical resistance value between the first electrode 10a on the first base material 1 and the second electrode 20a on the second base material 2.

[0041] 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 in FIG. 6, the buffer material 6 is omitted.

[0042] 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 electrodes are equal, and the pressures detected by the detection units X1 and X2 are all equal.

[0043] 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 electrodes of the detection unit X2 increases due to the change in the balance of the load, and the pressure applied to the 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. When a shearing force is input in the Y direction, the shearing force can be detected from the pressure difference between the detection unit Y1 and the detection unit Y2 in the same manner as the detection of the shearing force in the X-axis direction.

[0044] 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 each pair of upper and lower electrodes as a calibration curve, the measured resistance value can be converted into the pressure and the shearing force hereafter.

[0045] In the present embodiment, the number of detection units is five. However, if the number of detection units is two, it is possible to detect the change in the pressure and the shearing stress in either the X-axis direction or the Y-axis direction. Also, if the number of detection units is three or more, it is possible to detect the change in the pressure and the shearing forces in the X-axis direction and the Y-axis direction. Therefore, the number and arrangement of the detection units can be appropriately selected according to the application.

Example

[0046] (Example 1) The stress sensor 100 shown in FIG. 1 was fabricated. Specifically, a square first electrode 10a with a size of 500 μm × 500 μm was formed on the first substrate 1 by screen printing using conductive silver ink. The material, film thickness, Young's modulus, and bending rigidity of the used first substrate 1 are described in Table 1. Note that the bending rigidities of the first substrate 1 and the second substrate 2 were calculated from the product of Young's modulus and the second moment of area. The second moment of area was calculated by the formula {(l × t 3 ) / 12}, where the sheet length l was set to 3 mm, which is the diameter of the detection region R, and t is the film thickness value of the substrate.

[0047] Next, a square first pressure-sensitive layer 10b with a size of 600 μm × 600 μm was formed on each first electrode 10a by screen printing using conductive carbon ink, with a thickness of 10 μm.

[0048] Next, a square second electrode 20a with a size of 500 μm × 500 μm was formed on the second substrate 2 by screen printing using conductive silver ink. The material, film thickness, Young's modulus, and bending rigidity of the used second substrate 2 are described in Table 1.

[0049] Next, a square second pressure-sensitive layer 20b with a size of 600 μm × 600 μm was formed on each second electrode 20a by screen printing using conductive carbon ink, with a thickness of 10 μm.

[0050] Next, an annular double-sided tape with an inner diameter of 7 mm and a width of 1 mm was attached around the detection region R of the first substrate 1 to form the adhesive layer 5. The thickness of the adhesive layer 5 was set to 30 μm.

[0051] Next, the first substrate 1 and the second substrate 2 were bonded together via the adhesive layer 5 to obtain the stress sensor 100.

[0052] (Examples 2 to 13, Comparative Examples 1 to 3) The stress sensor 100 was fabricated in the same manner as in Example 1, except that the materials, film thicknesses, Young's moduli, and bending rigidities of the first substrate 1 and the second substrate 2 were as described in Table 1.

[0053] <Pressure Detection Accuracy Evaluation> For the stress sensors according to Examples 1 to 12 and Comparative Examples 1 to 3, the pressure detection accuracy was evaluated when the object to be measured was a silicone rubber sheet (thickness: 3 mm, Young's modulus: 0.7 MPa) and when it was the belly of a human finger (Young's modulus: 0.01 MPa). The Young's modulus of the belly of a human finger was referred to the description of soft tissues in the following non-patent literature. Non-patent literature: K. Nohara et al., “Contact mechanics of a finger pad with individual variation, Proc. of the 2009 JSME Conference on Robotics and Mechatronics, 2009

[0054] The stress sensor was fixed on the measurement metal stage of a load applying device (load cell: Aiko Engineering MODEL-3005 (50 N)). The measurement terminal was applied to the stress sensor, and only a vertical load of 1 N was applied without applying shear, and the output value of the pressure of the stress sensor was obtained.

[0055] Next, a silicone rubber sheet was placed on the measurement stage, and the stress sensor was fixed on the silicone rubber sheet. The measurement terminal was applied to the stress sensor, and a vertical load of 1 N was applied without applying shear, and the output value of the pressure of the stress sensor was acquired. The output values when the object to be measured was the metal stage and the silicone rubber sheet were compared, and the difference (detection error) between the output value measured with the stress sensor fixed to the metal stage and the output value measured with the stress sensor fixed to the silicone rubber was determined.

[0056] Next, the stress sensor was fixed at the center of the belly of a human finger, and the finger was fixed on the measurement stage. The measurement terminal was applied to the stress sensor, and a vertical load of 1 N was applied without applying shear, and the output value of the pressure of the stress sensor 100 was acquired. The output values when the object to be measured was the metal stage and the human finger were compared, and the difference (detection error) between the output value measured with the stress sensor fixed to the metal stage and the output value measured with the stress sensor fixed to the belly of the finger was determined.

[0057] When the object to be measured is silicone rubber and when it is a human finger, the detection accuracy of pressure was evaluated based on the following criteria. ◎: Detection error is within ±5%. 〇: Detection error is within ±10%. △: Detection error is within ±15%. ×: Detection error exceeds ±15%.

[0058] <Shearing force detection accuracy evaluation> Regarding the stress sensors according to Examples 1 to 12 and Comparative Examples 1 to 3, the detection accuracy of the shearing force was evaluated when the object to be measured was a silicone rubber sheet (thickness: 3 mm, Young's modulus: 0.7 MPa) and when it was the belly of a human finger (Young's modulus: 0.01 MPa), respectively.

[0059] The stress sensor was fixed on the measurement metal stage of a load applying device (load cell: Aiko Engineering MODEL-3005 (50 N)). With the measurement terminal applied to the stress sensor and a 1 N vertical load applied, while increasing the shearing load in the X-axis direction and the Y-axis direction from 0 N to 0.3 N in increments of 0.05 N, the output value of the shearing force was acquired. Also, while decreasing the shearing load in the X-axis direction and the Y-axis direction from 0 N to -0.3 N in increments of 0.05 N, the output value of the shearing force was acquired.

[0060] Next, a silicone rubber sheet was placed on the measurement stage, and the stress sensor was fixed on the silicone rubber sheet. With the measurement terminal applied to the stress sensor, the shearing force was applied in the same way as when measuring the shearing force of the metal stage, and the output value of the shearing force was acquired. The output values when the object to be measured was the metal stage and when it was the silicone rubber sheet were compared, and the difference (detection error) between the output value measured with the stress sensor fixed to the metal stage and the output value measured with the stress sensor fixed to the silicone rubber was determined.

[0061] Next, the stress sensor was fixed to the center of the fingertip of a person, and the finger was fixed on the measurement stage. The measurement terminal was applied to the stress sensor, and a shear force was applied in the same manner as when measuring the shear force of the metal stage, and the output value of the shear force was obtained. The output values when the object to be measured was a metal stage and when it was a person's finger were compared, and the difference (detection error) between the output value measured by fixing the stress sensor to the metal stage and the output value measured by fixing the stress sensor to the fingertip was determined.

[0062] When the object to be measured was silicone rubber and when it was a person's finger, the detection accuracy of the shear force was evaluated based on the following criteria. ◎: Detection error is within ±5%. 〇: Detection error is within ±10%. △: Detection error is within ±15%. ×: Detection error exceeds ±15%.

[0063] The evaluation results of the stress sensors according to Examples 1 to 13 and Comparative Examples 1 to 3 are described together in Table 1.

[0064]

Table 1

[0065] In the stress sensors according to Examples 1 to 13, the bending rigidity of the second base material 2 was smaller than the bending rigidity of the first base material 1, and the film thickness of the second base material 2 was smaller than the film thickness of the first base material 1. Therefore, even when the stress sensor was fixed to the silicone rubber and the fingertip for measurement, the detection errors of the pressure and the shear force were within ±15%, and it was confirmed that excellent detection accuracy was shown for both the pressure and the shear force even when the object to be measured was an elastic body such as silicone rubber or a finger.

[0066] Particularly, in the stress sensors according to Examples 1 to 12, the Young's modulus of the first base material 1 and the second base material 2 was 2 GPa or more and 6 GPa or less, and the film thickness of the first base material 1 was 50 μm or more and 200 μm or less, and the film thickness of the second base material 2 was 10 μm or more and 100 μm or less. Therefore, the first base material 1 functioned as a base that was difficult to deform when pressure and shear force were applied, and the pressure and shear force applied to the second base material 2 side were easily transmitted to the detection region R without resistance. Therefore, it was confirmed that the detection error of the pressure and shear force was within ±10%, indicating more excellent detection accuracy. On the other hand, in Example 13, the film thickness of the first base material 1 exceeded 200 μm, and the film thickness of the second base material 2 was less than 10 μm, and the film thickness difference (bending rigidity difference) between the first base material 1 and the second base material 2 was large. Therefore, when the two base materials were bonded with the adhesive layer 5, warping occurred in the entire sensor, and the detection accuracy decreased compared to Examples 1 to 12.

[0067] Furthermore, in the stress sensors according to Examples 1 to 9, the conditions that the film thickness of the first base material 1 was 50 μm or more and 188 μm or less, and the film thickness of the second base material 2 was 12.5 μm or more and 75 μm or less were satisfied. Therefore, the detection accuracy was higher compared to Examples 10 to 13 that did not satisfy the said conditions. In Example 10, since the film thickness of the second base material 2 was slightly thick at 100 μm, the pressure and shear force applied from the second base material 2 side were difficult to be transmitted to the detection part, and the accuracy decreased compared to Examples 1 to 9. In Example 11, since the film thickness difference (bending rigidity difference) between the first base material 1 and the second base material 2 was set to be slightly large, when the two base materials were bonded with the adhesive layer 5, slight warping occurred in the entire sensor, and the accuracy decreased compared to Examples 1 to 9. In Example 12, although the film thickness of the first base material 1 was the same as that in Example 1, it was originally slightly thin at 50 μm, and furthermore, a material with a smaller Young's modulus than that in Example 1 was used, so the bending rigidity was also low. Therefore, it was difficult for the first base material 1 to function as a base when pressure and shear force were applied, and the accuracy decreased compared to Examples 1 to 9.

[0068] In the stress sensors according to Comparative Examples 1 to 3, in each case, the bending rigidity of the second base material 2 was greater than the bending rigidity of the first base material 1, and the film thickness of the second base material 2 was greater than the film thickness of the first base material 1. Therefore, the first base material 1 did not function as a base that was difficult to deform when pressure and shear force were applied, and furthermore, the pressure and shear force applied to the second base material 2 side were less likely to be transmitted to the detection region R, resulting in a large detection error and a decrease in detection accuracy.

Industrial Applicability

[0069] The present invention can be applied to a stress sensor that detects the pressure and shear force of an object to be measured having elasticity, such as a human finger, hand, or cloth glove worn on the hand.

Explanation of Signs

[0070] 1: First base material 2: Second base material 10: First detection unit component 10a: First electrode 10b: First pressure-sensitive layer 20: Second detection unit component 20a: Second electrode 20b: Second pressure-sensitive layer 100: Stress sensor F1: Pressure F2: Shear force O: Detection unit X1: Detection unit X2: Detection unit Y1: Detection unit Y2: Detection unit R: Detection region

Claims

1. A stress sensor capable of detecting pressure and shear force, comprising: a first substrate; a second substrate; a plurality of detection units disposed between the first substrate and the second substrate, each of the plurality of detection units comprising: 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 opposite to each of the first electrodes on the surface of the second substrate facing the first substrate and a second pressure-sensitive layer laminated on the second electrode; wherein the first substrate is a substrate fixed to an object to be measured during use, and the second substrate is a substrate to which the pressure and the shear force are input during use; a stress sensor in which the bending rigidity of the second substrate is smaller than that of the first substrate.

2. A stress sensor capable of detecting pressure and shear force, comprising: a first substrate; a second substrate; a plurality of detection units disposed between the first substrate and the second substrate, each of the plurality of detection units comprising: 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 opposite to each of the first electrodes on the surface of the second substrate facing the first substrate and a second pressure-sensitive layer laminated on the second electrode; wherein the first substrate is a substrate fixed to an object to be measured during use, and the second substrate is a substrate to which the pressure and the shear force are input during use; a stress sensor in which the film thickness of the second substrate is smaller than that of the first substrate.

3. The Young's modulus of the first substrate and the second substrate is 2 GPa or more and 6 GPa or less; The stress sensor according to claim 2, wherein the film thickness of the first substrate is 50 μm or more and 200 μm or less, and the film thickness of the second substrate is 10 μm or more and 100 μm or less.

4. The stress sensor according to claim 3, wherein the film thickness of the first substrate is 50 μm or more and 188 μm or less, and the film thickness of the second substrate is 12.5 μm or more and 75 μm or less.

5. The stress sensor according to claim 1, wherein the Young's modulus of the object to be measured is smaller than that of the first substrate.

6. The stress sensor according to claim 1, wherein the object to be measured is a human finger or hand.

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