Deformation detection sensor

Abstract

To provide a deformation detection sensor capable of improving detecting sensitivity for deformation of a flexible base material.SOLUTION: A deformation detecting sensor includes a bendable flexible base material having a base material upper main surface and a base material lower main surface that are arranged side by side in an up-down direction, a first sensor provided on the base material upper main surface and including a first piezoelectric film, and a second sensor provided on the base material lower main surface and including a second piezoelectric film. A length of the first piezoelectric film in a left-right direction is equal to a length of a first upper electrode in a left-right direction. A length of the second piezoelectric film in the left-right direction is equal to a length of a second lower electrode in the left-right direction. The first sensor and the second sensor are provided at positions apart from an end part of the flexible base material to a direction of a bending line connecting middle points of two long sides of the flexible base material.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a deformation detection sensor for detecting deformation of a flexible substrate.

Background Art

[0002] As an invention related to a conventional deformation detection sensor, for example, a bending deformation sensor described in Patent Document 1 is known. This bending deformation sensor includes a first piezoelectric film, a second piezoelectric film, and an elastic body. The elastic body has a first main surface and a second main surface. The first piezoelectric film is provided on the first main surface. The second piezoelectric film is provided on the second main surface. Thus, when the elastic body bends, the first piezoelectric film stretches and the second piezoelectric film expands and contracts. Then, the first piezoelectric film outputs a first signal and the second piezoelectric film outputs a second signal. An arithmetic circuit (not shown) can detect the bending deformation of the elastic body based on the first signal and the second signal.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the bending deformation sensor described in Patent Document 1, there is a desire to further improve the sensitivity of detecting bending deformation.

[0005] Therefore, an object of the present invention is to provide a deformation detection sensor capable of improving the sensitivity of detecting deformation of a flexible substrate.

Means for Solving the Problems

[0006] A deformation detection sensor according to an aspect of the present invention includes: a flexible substrate having a substrate upper main surface and a substrate lower main surface arranged vertically; A first sensor is provided on the main surface of the substrate and includes a first piezoelectric film, A second sensor is provided on the lower main surface of the substrate and includes a second piezoelectric film, It is equipped with, The first piezoelectric film has a first upper main surface and a first lower main surface, The second piezoelectric film has a second upper main surface and a second lower main surface, The first sensor includes a first upper electrode provided on the first upper main surface and a first lower electrode provided on the first lower main surface. The second sensor includes a second upper electrode provided on the second upper main surface and a second lower electrode provided on the second lower main surface. When the flexible substrate is bent, the direction in which the fold line extends is defined as the front-to-back direction. The direction perpendicular to the aforementioned vertical and horizontal directions is defined as the left-right direction. The length of the first piezoelectric film in the left-right direction is equal to the length of the first upper electrode in the left-right direction. The length of the aforementioned second piezoelectric film in the left-right direction is equal to the length of the aforementioned second lower electrode in the left-right direction. The first sensor and the second sensor are provided at positions away from the end of the flexible substrate in the direction of the fold line connecting the midpoints of the two long sides of the flexible substrate, The first sensor and the second sensor bend as the flexible substrate bends so as to protrude upward or downward. It is characterized by the following: [Effects of the Invention]

[0007] The deformation detection sensor according to the present invention can improve the sensitivity of detecting deformation of a flexible substrate. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a front view of the deformation detection sensor 10. [Figure 2] Figure 2 is an exploded view of the deformation detection sensor 10. [Figure 3] Figure 3 is a front view of the deformation detection sensor 10 when the flexible substrate 12 is bent. [Figure 4] Figure 4 is a graph showing the waveforms of the first signal Sig1 and the second signal Sig2. [Figure 5] Figure 5 is a graph showing the waveform of the difference Δ. [Figure 6] Figure 6 is a front view of the deformation detection sensor 1010 according to a comparative example. [Figure 7] Figure 7 is a front view of the deformation detection sensor 10a. [Figure 8] Figure 8 is a front view of the deformation detection sensor 10a when the flexible substrate 12 is bent. [Figure 9] Figure 9 is a front view of the deformation detection sensor 10b. [Modes for carrying out the invention]

[0009] (Embodiment) [Structure of deformation detection sensor] The structure of the deformation detection sensor 10 according to an embodiment of the present invention will be described below with reference to the drawings. Figure 1 is a front view of the deformation detection sensor 10. Figure 2 is an exploded view of the deformation detection sensor 10. Figure 3 is a front view of the deformation detection sensor 10 when the flexible substrate 12 is bent.

[0010] Furthermore, in this specification, directions are defined as follows: The direction in which the upper main surface S1 and lower main surface S2 of the flexible substrate 12 are aligned in an unbent state as shown in Figure 1 is defined as the vertical direction. The direction in which the fold line L (see Figures 2 and 3) extends when the flexible substrate 12 is bent is defined as the front-back direction. The direction perpendicular to the vertical direction and the front-back direction is defined as the left-right direction. Note that the definitions of directions in this specification are examples only. Therefore, the direction in actual use of the deformation detection sensor 10 does not need to match the direction in this specification. Also, the vertical direction may be reversed in Figure 1. Similarly, the left-right direction may be reversed in Figure 1. The front-back direction may be reversed in Figure 1.

[0011] The deformation detection sensor 10 detects bending of the flexible substrate 12. As shown in FIGS. 1 and 2, the deformation detection sensor 10 includes a flexible substrate 12, a first sensor 11, a second sensor 21, and an arithmetic circuit 50.

[0012] The flexible substrate 12 is a flexible sheet. The flexible substrate 12 has a substrate upper main surface S1 and a substrate lower main surface S2 arranged in the vertical direction. As shown in FIG. 2 when viewed in the vertical direction, the flexible substrate 12 has a rectangular shape having a short side extending in the front-rear direction and a long side extending in the left-right direction. As shown in FIG. 3, the flexible substrate 12 can be bent at the bending line L. The bending line L connects the midpoints of the two long sides of the flexible substrate 12. The flexible substrate 12 bends so as to protrude downward when viewed in the front-rear direction.

[0013] As shown in FIG. 1, the first sensor 11 is provided on the substrate upper main surface S1. The first sensor 11 outputs a first signal Sig1 for detecting deformation of the flexible substrate 12. The first sensor 11 includes a first piezoelectric film 14, a first upper electrode 16, and a first lower electrode 18.

[0014] The first piezoelectric film 14 is a flexible sheet. The first piezoelectric film 14 has a first upper main surface S11 and a first lower main surface S12. As shown in FIG. 2 when viewed in the vertical direction, the first piezoelectric film 14 has a rectangular shape having a short side extending in the front-rear direction and a long side extending in the left-right direction.

[0015] The first piezoelectric film 14 generates an electric charge by expanding and contracting together with the flexible substrate 12. The first piezoelectric film 14 is, for example, a film formed from a chiral polymer. A chiral polymer is, for example, polylactic acid (PLA), particularly L-type polylactic acid (PLLA). PLLA, which is made of a chiral polymer, has a helical structure in its main chain. PLLA becomes piezoelectric when it is uniaxially stretched and its molecules are oriented. The first piezoelectric film 14 has a piezoelectric constant d14. Uniaxially stretched PLLA generates a voltage when the first piezoelectric film 14 is stretched or compressed in the left-right direction. The first piezoelectric film 14 generates a positive voltage when stretched in the left-right direction. The first piezoelectric film 14 generates a negative voltage when compressed in the left-right direction. The magnitude of the voltage depends on the differential value of the deformation amount of the first piezoelectric film 14 due to stretching or compression.

[0016] As shown in Figure 2, the uniaxial stretching direction Da of the first piezoelectric film 14 forms an angle of 45 degrees with respect to both the front-to-back and left-to-right directions. This 45-degree angle includes, for example, an angle of approximately 45 degrees ± 10 degrees. The first piezoelectric film 14 may be made from a ferroelectric material that has undergone polling treatment, such as PVDF or PZT, which is polarized by ions, instead of PLLA.

[0017] The first upper electrode 16 is a ground electrode. Therefore, the first upper electrode 16 is connected to the ground potential. The first upper electrode 16 is provided on the first upper main surface S11. The first upper electrode 16 covers the entire first upper main surface S11. Therefore, the length of the first piezoelectric film 14 in the left-right direction is equal to the length of the first upper electrode 16 in the left-right direction. The length of the first piezoelectric film 14 in the front-back direction is equal to the length of the first upper electrode 16 in the front-back direction.

[0018] The first lower electrode 18 is a signal electrode. Therefore, the first signal Sig1 is output from the first lower electrode 18. The first lower electrode 18 is provided on the first lower main surface S12. The first lower electrode 18 covers the entire first lower main surface S12. Therefore, the length of the first piezoelectric film 14 in the left-right direction is equal to the length of the first lower electrode 18 in the left-right direction. The length of the first piezoelectric film 14 in the front-back direction is equal to the length of the first lower electrode 18 in the front-back direction.

[0019] The first upper electrode 16 and the first lower electrode 18 are, for example, organic electrodes such as ITO (indium tin oxide) and ZnO (zinc oxide), metal films produced by vapor deposition or plating, or printed electrode films made of silver paste.

[0020] The second sensor 21 is provided on the lower main surface S2 of the substrate. When viewed in the vertical direction, the second sensor 21 overlaps with the first sensor 11. The second sensor 21 outputs a second signal Sig2 that detects deformation of the flexible substrate 12. The second sensor 21 includes a second piezoelectric film 24, a second upper electrode 26, and a second lower electrode 28.

[0021] The second piezoelectric film 24 is a flexible sheet. The second piezoelectric film 24 has a second upper main surface S21 and a second lower main surface S22. When viewed in the vertical direction, the second piezoelectric film 24 has a rectangular shape with a short side extending in the front-to-back direction and a long side extending in the left-to-right direction. The vertical thickness D2 of the second piezoelectric film 24 is greater than the vertical thickness D1 of the first piezoelectric film 14. In this specification, the vertical thickness of the piezoelectric film is, for example, the average value of the overall vertical thickness of the piezoelectric film.

[0022] The second piezoelectric film 24 generates polarization by stretching and contracting together with the flexible substrate 12. The second piezoelectric film 24 is, for example, a film formed from a chiral polymer. A chiral polymer is, for example, polylactic acid (PLA), particularly L-type polylactic acid (PLLA). PLLA, which is made of a chiral polymer, has a helical structure in its main chain. PLLA becomes piezoelectric when it is uniaxially stretched and its molecules are oriented. The second piezoelectric film 24 has a piezoelectric constant of d14. Uniaxially stretched PLLA generates a voltage when the second piezoelectric film 24 is stretched or compressed in the left-right direction. The second piezoelectric film 24 generates a positive voltage when stretched in the left-right direction. The second piezoelectric film 24 generates a negative voltage when compressed in the left-right direction. The magnitude of the voltage depends on the differential value of the deformation amount of the second piezoelectric film 24 due to stretching or compression.

[0023] The uniaxial stretching direction Db of the second piezoelectric film 24 is parallel to the uniaxial stretching direction Da of the first piezoelectric film 14. As shown in Figure 1, the uniaxial stretching direction Db of the second piezoelectric film 24 forms a 45-degree angle with respect to both the front-to-back and left-to-right directions. This 45-degree angle includes, for example, an angle of approximately 45 degrees ± 10 degrees. Note that the second piezoelectric film 24 may be formed from a ferroelectric material that has undergone polling treatment, such as PVDF or PZT, which is polarized by ions, instead of PLLA.

[0024] The second upper electrode 26 is a signal electrode. Therefore, the second signal Sig2 is output from the second upper electrode 26. The second upper electrode 26 is provided on the second upper main surface S21. The second upper electrode 26 covers the entire second upper main surface S21. Therefore, the length of the second piezoelectric film 24 in the left-right direction is equal to the length of the second upper electrode 26 in the left-right direction. The length of the second piezoelectric film 24 in the front-back direction is equal to the length of the second upper electrode 26 in the front-back direction.

[0025] The second lower electrode 28 is a ground electrode. Therefore, the second lower electrode 28 is connected to the ground potential. The second lower electrode 28 is provided on the second lower main surface S22. The second lower electrode 28 covers the entire second lower main surface S22. Therefore, the length of the second piezoelectric film 24 in the left-right direction is equal to the length of the second lower electrode 28 in the left-right direction. The length of the second piezoelectric film 24 in the front-back direction is equal to the length of the second lower electrode 28 in the front-back direction.

[0026] The second upper electrode 26 and the second lower electrode 28 are, for example, organic electrodes such as ITO (indium tin oxide) and ZnO (zinc oxide), metal films produced by vapor deposition or plating, or printed electrode films made of silver paste.

[0027] The calculation circuit 50 is an IC (Integrated Circuit). The calculation circuit 50 calculates the difference Δ between the electrical parameters of the first signal Sig1 output from the first lower electrode 18 and the electrical parameters of the second signal Sig2 output from the second upper electrode 26. The electrical parameter is electric potential. However, the electrical parameter may be a value other than electric potential. A value other than electric potential is, for example, the amount of charge or the current value. The calculation circuit 50 also calculates the amount of bending of the flexible substrate 12 based on the difference Δ. The following explanation will be given with reference to the drawings. Figure 4 is a graph showing the waveforms of the first signal Sig1 and the second signal Sig2. Figure 5 is a graph showing the waveform of the difference Δ. The vertical axis in Figures 4 and 5 is electric potential. The horizontal axis in Figures 4 and 5 is time.

[0028] As shown in Figure 3, the first sensor 11 and the second sensor 21 bend when the flexible substrate 12 bends so that it protrudes upward or downward. In this embodiment, the first sensor 11 and the second sensor 21 bend when the flexible substrate 12 bends so that it protrudes downward. That is, the flexible substrate 12 bends so that the upper main surface S1 of the substrate is located inside the lower main surface S2 of the substrate. At this time, the first piezoelectric film 14 is compressed. Therefore, the first signal Sig1 has a negative potential with respect to the reference potential (hereinafter simply referred to as a negative potential). The second piezoelectric film 24 is stretched. Therefore, the second signal Sig2 has a positive potential with respect to the reference potential (hereinafter simply referred to as a positive potential). However, the waveforms of the first signal Sig1 and the second signal Sig2 are symmetric with respect to the reference potential. Therefore, the calculation circuit 50 subtracts the first signal Sig1 from the second signal Sig2 to calculate the difference Δ shown in Figure 5. As a result, the calculation circuit 50 can obtain a difference Δ greater than the potential of the first signal Sig1 and the potential of the second signal Sig2. Based on this difference Δ, the calculation circuit 50 calculates the amount of bending of the flexible substrate 12.

[0029] [effect] The deformation detection sensor 10 can improve the sensitivity of detecting deformation of the flexible substrate 12. The deformation detection sensor 1010 according to the comparative example will be explained below. Figure 6 is a front view of the deformation detection sensor 1010 according to the comparative example. The deformation detection sensor 1010 according to the comparative example differs from the deformation detection sensor 10 in that the vertical thickness of the second piezoelectric film 1024 is equal to the vertical thickness of the first piezoelectric film 1014.

[0030] When the flexible substrates 12 and 1012 are bent, surfaces appear in the flexible substrates 12 and 1012 where neither stretching nor compression occurs. These surfaces are called neutral surfaces C1 and C1001. As shown in Figure 6, the neutral surface C1001 is located midway between the upper main surface of the first upper electrode 1016 and the second lower electrode 1028. Since the vertical thickness of the second piezoelectric film 1024 is equal to the vertical thickness of the first piezoelectric film 1014, the neutral surface C1001 is located midway in the vertical direction of the flexible substrate 1012. In this case, the magnitude of the potential V1002 generated by the stretching of the second piezoelectric film 1024 is substantially equal to the magnitude of the potential V1001 generated by the compression of the first piezoelectric film 1014.

[0031] On the other hand, as shown in Figure 1, the neutral plane C1 is located midway between the upper main surface of the first upper electrode 16 and the lower main surface of the second lower electrode 28. However, since the vertical thickness D2 of the second piezoelectric film 1024 is greater than the vertical thickness D1 of the first piezoelectric film 1014, the neutral plane C1 is located below the midpoint in the vertical direction of the flexible substrate 12. In this case, the amount of compression of the first piezoelectric film 14 is greater than the amount of compression of the first piezoelectric film 1014. As a result, the magnitude of the potential V1 generated by the compression of the first piezoelectric film 14 is greater than the magnitude of the potential V1001 generated by the compression of the first piezoelectric film 1014.

[0032] Here, the region of the second piezoelectric film 24 from the second upper main surface S21 to the thickness D1 is called region A1. The region of the second piezoelectric film 24 excluding region A1 is called region A2. As described above, the neutral surface C1 is located below the midpoint in the vertical direction of the flexible substrate 12. In this case, the amount of stretching of region A1 is smaller than the amount of stretching of the second piezoelectric film 1024. As a result, the magnitude of the potential VA1 generated by the stretching of region A1 is smaller than the magnitude of the potential V1002 generated by the stretching of the second piezoelectric film 1024. That is, the increase in the magnitude of the potential V1 generated by the compression of the first piezoelectric film 14 is canceled out by the decrease in the magnitude of the potential VA1 generated by the stretching of region A1.

[0033] However, when the flexible substrate 12 is bent, region A2 stretches. As a result, region A2 generates a potential of magnitude VA2. Therefore, the deformation detection sensor 10 can obtain a difference Δ that is larger by magnitude VA2 than the difference Δ obtained by the deformation detection sensor 1010. Consequently, the deformation detection sensor 10 can improve the sensitivity of detecting the deformation of the flexible substrate 12.

[0034] The deformation detection sensor 10 can improve the sensitivity of detecting deformation of the flexible substrate 12 for the following reasons. More specifically, the first signal Sig1 has a negative potential. The second signal Sig2 has a positive potential. However, the waveforms of the first signal Sig1 and the second signal Sig2 are symmetric with respect to a reference potential. Therefore, the calculation circuit 50 subtracts the potential of the first signal Sig1 from the potential of the second signal Sig2 to calculate the difference Δ shown in Figure 5. As a result, the calculation circuit 50 can obtain a larger difference Δ between the potentials of the first signal Sig1 and the second signal Sig2. Based on this large difference Δ, the calculation circuit 50 can calculate the amount of deformation of the flexible substrate 12. As a result, the deformation detection sensor 10 can improve the sensitivity of detecting deformation of the flexible substrate 12.

[0035] The deformation detection sensor 10 reduces the computational load on the calculation circuit 50. More specifically, the calculation circuit 50 subtracts the potential of the first signal Sig1 from the potential of the second signal Sig2 to calculate the difference Δ shown in Figure 5. In this process, the reference potential of the first signal Sig1 is subtracted from the reference potential of the second signal Sig2. As a result, the reference potential in the difference Δ becomes 0V.

[0036] Here, the reference potential is a value that changes moment by moment. If the calculation circuit 50 calculates the reference potential each time in accordance with this fluctuation, the calculation time will increase. Therefore, there is a method to calculate the reference potential from the first signal Sig1 and the second signal Sig2 acquired over a certain period of time in the past. However, this method has the following problems.

[0037] The calculated reference potential is an estimated value for the first signal Sig1 and the second signal Sig2, which are acquired after the calculation. • The discrepancy between the estimated reference potential and the actual reference potential causes a discrepancy in the calculation result of the deformation amount of the flexible substrate 12.

[0038] In contrast, the deformation detection sensor 10 has a fixed reference potential of 0V. Therefore, the calculation circuit 50 does not need to calculate the reference potential. As a result, the computational load on the calculation circuit 50 is reduced.

[0039] According to the deformation detection sensor 10, the second sensor 21 overlaps with the first sensor 11 when viewed in the vertical direction. This allows for miniaturization of the deformation detection sensor 10.

[0040] In the deformation detection sensor 10, when the flexible substrate 12 is bent, the polarity of the potential of the first signal Sig1 and the polarity of the potential of the second signal Sig2 are different. Therefore, for example, if the polarity of the potential of the first signal Sig1 and the polarity of the potential of the second signal Sig2 are the same, the calculation circuit 50 can determine that the deformation detection sensor 10 is malfunctioning or that the flexible substrate 12 is undergoing unintended deformation.

[0041] In the deformation detection sensor 10, the first upper electrode 16 and the second lower electrode 28 are connected to ground potential. As a result, the first piezoelectric film 14 is shielded by the first upper electrode 16, and the second piezoelectric film 24 is shielded by the second lower electrode 28. Consequently, the first sensor 11 and the second sensor 21 become less susceptible to noise.

[0042] In the deformation detection sensor 10, the length of the first piezoelectric film 14 in the left-right direction is equal to the length of the first upper electrode 16 in the left-right direction. This ensures that the first piezoelectric film 14 is more reliably shielded by the first upper electrode 16. Similarly, the length of the second piezoelectric film 24 in the left-right direction is equal to the length of the second lower electrode 28 in the left-right direction. This ensures that the second piezoelectric film 24 is more reliably shielded by the second lower electrode 28. As a result, the first sensor 11 and the second sensor 21 become less susceptible to noise.

[0043] (First variation) The deformation detection sensor 10a according to the first modified example will be described below with reference to the drawings. Figure 7 is a front view of the deformation detection sensor 10a. Figure 8 is a front view of the deformation detection sensor 10a when the flexible substrate 12 is bent.

[0044] The deformation detection sensor 10a differs from the deformation detection sensor 10 in the positions of the first sensor 11 and the second sensor 21. More specifically, the second sensor 21 does not overlap with the first sensor 11 when viewed in the vertical direction. However, the first piezoelectric film 14 is compressed when the flexible substrate 12 is bent. The second piezoelectric film 24 is stretched when the flexible substrate 12 is bent. The other structures of the deformation detection sensor 10a are the same as those of the deformation detection sensor 10, so their description is omitted. The deformation detection sensor 10a can perform the same functions and effects as the deformation detection sensor 10.

[0045] (Second variation) The deformation detection sensor 10b according to the second modified example will be described below with reference to the drawings. Figure 9 is a front view of the deformation detection sensor 10b.

[0046] The deformation detection sensor 10b differs from the deformation detection sensor 10a in that it further comprises a third sensor 31 and a fourth sensor 41. The third sensor 31 is provided on the upper main surface S1 of the substrate. The third sensor 31 includes a third piezoelectric film 34 that generates polarization by expanding and contracting together with the flexible substrate 12. However, the structure of the third sensor 31 is the same as that of the first sensor 11, so its description is omitted. The fourth sensor 41 is provided on the lower main surface S2 of the substrate. The fourth sensor 41 includes a fourth piezoelectric film 44 that generates polarization by expanding and contracting together with the flexible substrate 12. However, the structure of the fourth sensor 41 is the same as that of the second sensor 21, so its description is omitted. Also, the fourth sensor 41 does not overlap with the third sensor 31 when viewed in the vertical direction. The other structures of the deformation detection sensor 10b are the same as those of the deformation detection sensor 10a, so their description is omitted. The deformation detection sensor 10b can achieve the same effects as the deformation detection sensor 10a. Furthermore, since the deformation detection sensor 10b is equipped with a third sensor 31 and a fourth sensor 41, it can detect the amount of deformation at multiple locations on the flexible substrate 12.

[0047] (Other embodiments) The deformation detection sensor according to the present invention is not limited to deformation detection sensors 10, 10a, and 10b, but can be modified within the scope of its gist. Furthermore, the structures of deformation detection sensors 10, 10a, and 10b may be combined in any way.

[0048] The first piezoelectric film 14, the second piezoelectric film 24, the third piezoelectric film 34, and the fourth piezoelectric film 44 may be films other than those formed from chiral polymers.

[0049] Note that the uniaxial stretching direction Db of the second piezoelectric film 24 does not have to be parallel to the uniaxial stretching direction Da of the first piezoelectric film 14. The uniaxial stretching direction Db of the second piezoelectric film 24 may be perpendicular to the uniaxial stretching direction Da of the first piezoelectric film 14. In this case, the polarity of the potential of the second signal Sig2 will be the same as the polarity of the potential of the first signal Sig1. Therefore, the calculation circuit 50 adds the potential of the first signal Sig1 and the potential of the second signal Sig2.

[0050] The first lower electrode 18 and the second upper electrode 26 may be connected to ground potential.

[0051] Note that the length of the first piezoelectric film 14 in the left-right direction does not have to be equal to the length of the first upper electrode 16 in the left-right direction. The length of the second piezoelectric film 24 in the left-right direction does not have to be equal to the length of the second lower electrode 28 in the left-right direction. [Explanation of symbols]

[0052] 10, 10a, 10b: Deformation detection sensor 11: First sensor 12: Flexible base material 14: First piezoelectric film 16: 1st upper electrode 18: 1st lower electrode 21: Second sensor 24: Second piezoelectric film 26: 2nd upper electrode 28:Second lower electrode 31: Third sensor 34: Third piezoelectric film 41: Fourth sensor 44: Fourth piezoelectric film 50: Arithmetic circuit A1,A2:Area C1: Neutral plane L: Fold line S1: Main surface on base material S11: 1st upper main surface S12: 1st lower main surface S2: Bottom main surface of base material S21: 2nd upper main surface S22: 2nd lower main surface Sig1: First signal Sig2: 2nd signal

Claims

1. A flexible substrate having an upper main surface and a lower main surface aligned in the vertical direction, A first sensor is provided on the main surface of the substrate and includes a first piezoelectric film, A second sensor is provided on the lower main surface of the substrate and includes a second piezoelectric film, A third sensor is provided on the main surface of the substrate and includes a third piezoelectric film, A fourth sensor is provided on the lower main surface of the substrate and includes a fourth piezoelectric film, Calculation circuit and, It is equipped with, The first piezoelectric film has a first upper main surface and a first lower main surface, The second piezoelectric film has a second upper main surface and a second lower main surface, The first sensor includes a first upper electrode provided on the first upper main surface and a first lower electrode provided on the first lower main surface. The second sensor includes a second upper electrode provided on the second upper main surface and a second lower electrode provided on the second lower main surface. The first upper electrode and the second lower electrode are connected to the ground potential. When the flexible substrate is bent, the direction in which the fold line extends is defined as the front-to-back direction. The direction perpendicular to the aforementioned vertical and horizontal directions is defined as the left-right direction. The length of the first piezoelectric film in the left-right direction is equal to the length of the first upper electrode in the left-right direction. The length of the second piezoelectric film in the left-right direction is equal to the length of the second lower electrode in the left-right direction. The first sensor and the second sensor are provided at positions that are spaced in the left-right direction from the left-right ends of the flexible substrate, The flexible substrate bends so as to protrude upward or downward, causing the first sensor, the second sensor, the third sensor and the fourth sensor to bend. The calculation circuit calculates the difference between the potential of the first signal output from the first lower electrode and the potential of the second signal output from the second upper electrode. The reference potentials of the first signal and the second signal are values ​​that change moment by moment. Deformation detection sensor.

2. Viewed in the vertical direction, the second sensor overlaps with the first sensor. The deformation detection sensor according to claim 1.

3. The first piezoelectric film and the second piezoelectric film have a piezoelectric constant of d14. A deformation detection sensor according to claim 1 or claim 2.

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