WO2020032255A1

WO2020032255A1 - Sensor system, and measuring device employing same

Info

Publication number: WO2020032255A1
Application number: PCT/JP2019/031637
Authority: WO
Inventors: 康之白坂; 信人神谷; 哲裕加藤; 裕太葛山; 高橋　良輔
Original assignee: 積水化学工業株式会社
Priority date: 2018-08-10
Filing date: 2019-08-09
Publication date: 2020-02-13
Also published as: TW202009454A; TWI821360B; JPWO2020032255A1

Abstract

The present invention provides a sensor system capable of detecting both stress applied gradually over a long period, and stress applied over a short period or instantaneously. This sensor system is characterized by being provided with: a piezoelectric sensor including a piezoelectric sheet having elasticity in a surface direction, a first electrode which is laminated onto one surface of the piezoelectric sheet and which has elasticity in the surface direction of the piezoelectric sheet, and a second electrode which is laminated onto the other surface of the piezoelectric sheet and which has elasticity in the surface direction of the piezoelectric sheet; a first detecting portion which measures an electric potential generated by the piezoelectric sensor; and a second detecting portion which detects a change in an electrostatic capacitance of a capacitor formed between the first electrode and the second electrode of the piezoelectric sensor, or a change in an impedance between the first electrode and the second electrode of the piezoelectric sensor.

Description

Sensor system and measuring device using the same

The present invention relates to a sensor system and a measuring device using the same.

The piezoelectric sheet is a material in which a permanent charge is imparted inside by injecting charges into an insulating polymer material. Piezoelectric sheets are expected to be developed for sensor applications by utilizing their excellent sensitivity.

Patent Literature 1 discloses a paired structure in which two piezoelectric elements made of a polymer piezoelectric material and subjected to an external load or force are superimposed, and a capacitance made of a dielectric polyester insulating film is connected in parallel between the electrodes. There is disclosed a load measuring device including a piezoelectric element, a resistor and a coil for increasing the voltage of the pair of piezoelectric elements, and a sine wave generation power supply capable of resonating the voltage of the pair of piezoelectric elements.

When a load or force is applied to a pair of piezoelectric elements, the load measuring device changes the frequency characteristics of the voltage of the piezoelectric elements, and the voltage between both elements can be detected by a differential voltage output, and the magnitude of the load or force is detected. And a detecting means for performing the detection.

JP 2016-22020 A

However, the load measurement device described in Patent Literature 1 can detect stress (stress having a small frequency) applied over a long time, but sufficiently detect stress (stress having a large frequency) applied in a short time. Can not. In addition, there is a problem that it is not possible to sufficiently detect stress applied to the piezoelectric element in the plane direction (for example, extension of the piezoelectric element in the plane direction).

For example, concrete structures such as tunnels are subject to cracks due to aging. Cracks in a concrete structure include cracks that are gradually formed due to strain over time, and cracks that are generated when stress is applied to a concrete structure in a short time or momentarily. The former crack is generated such that the width of the crack gradually increases due to the stress gradually applied over a long period of time. In the latter cracking, the cracks are instantaneously expanded or peeled off in the direction of the concrete surface.

応力 In order to detect the former crack, it is necessary to detect the stress gradually applied over a long time along the concrete surface. On the other hand, in order to detect the latter crack, it is necessary to detect not only stress applied in a plane direction for a short time or instantaneously, but also stress generated in a direction perpendicular to the concrete surface (thickness direction). However, the conventional technology such as the load measuring device described in Patent Document 1 has a problem that it is not possible to detect all of these stresses with one sensor, and it is necessary to arrange a plurality of sensors. ing.

The present invention can detect both the pressure in the thickness direction of the piezoelectric sheet and the stress generated in the surface direction, and can apply the stress gradually applied over a long time (stress having a small frequency) to the short time or momentarily. Provided is a sensor system capable of detecting both applied stress (stress having a large frequency).

The sensor system of the present invention comprises:
A piezoelectric sheet having elasticity in the surface direction, a first electrode laminated on one surface of the piezoelectric sheet and having elasticity in the surface direction of the piezoelectric sheet, and a first electrode laminated on the other surface of the piezoelectric sheet and A piezoelectric sensor having a second electrode having elasticity in the plane direction;
A first detection unit that measures a potential generated by the piezoelectric sensor;
A second detecting unit that detects a change in capacitance of a capacitor formed between the first electrode and the second electrode of the piezoelectric sensor or a change in impedance between the first electrode and the second electrode of the piezoelectric sensor; And characterized in that:

The sensor system of the present invention can detect both the pressure applied in the thickness direction of the piezoelectric sheet and the stress applied in the plane direction of the piezoelectric sensor, and can also detect both the low frequency stress and the high frequency stress. . Therefore, it can be suitably used for applications that require detection of stress applied in the thickness direction and the surface direction, and low-frequency stress and high-frequency stress generated by various movements. Specifically, it can be suitably used for applications (wearable applications) used by sticking to the skin surface of a human body, inspection of concrete structures, and the like.

The sensor system according to the present invention can detect stress applied to the measured object in the thickness direction and the surface direction, as well as low-frequency stress and high-frequency stress. Therefore, unlike the related art, it is not necessary to prepare sensors for detecting respective stresses, and the structure of the measuring device can be simplified and downsized.

It is sectional drawing which showed the piezoelectric sensor. FIG. 2 is a diagram illustrating a functional configuration of a sensor system. FIG. 2 is a diagram illustrating a hardware configuration of a sensor system. FIG. 2 is a circuit diagram showing a Wheatstone bridge circuit.

An example of the sensor system of the present invention will be described with reference to the drawings.
The sensor system is
A piezoelectric sheet having elasticity in the surface direction, a first electrode laminated on one surface of the piezoelectric sheet and having elasticity in the surface direction of the piezoelectric sheet, and a first electrode laminated on the other surface of the piezoelectric sheet and A piezoelectric sensor having a second electrode having elasticity in the plane direction;
A first detection unit that measures a potential generated by the piezoelectric sensor;
A second detecting unit that detects a change in capacitance of a capacitor formed between the first electrode and the second electrode of the piezoelectric sensor or a change in impedance between the first electrode and the second electrode of the piezoelectric sensor; And

圧電 The piezoelectric sheet A1 of the piezoelectric sensor A constituting the sensor system S is a sheet that can generate an electric charge when an external force is applied, and has elasticity in the plane direction.

として The piezoelectric sheet A1 is not particularly limited, but is preferably a piezoelectric sheet in which a synthetic resin foam sheet is polarized.

合成 The synthetic resin constituting the synthetic resin foam sheet is not particularly limited, and examples thereof include a polyolefin resin such as a polyethylene resin and a polypropylene resin, polyvinylidene fluoride, polylactic acid, and a liquid crystal resin.

It is preferable that the synthetic resin has excellent insulating properties. As the synthetic resin, a volume resistivity (hereinafter simply referred to as a “volume resistivity”) after applying a voltage at an applied voltage of 500 V for one minute in accordance with JIS K6911 is used. ) Is preferably 1.0 × 10 ¹⁰ Ω · m or more.

The volume resistivity value of the synthetic resin is preferably 1.0 × 10 ¹² Ω · m or more, more preferably 1.0 × 10 ¹⁴ Ω · m or more, since the piezoelectric sheet A1 has more excellent piezoelectricity. .

方法 The method for imparting polarization to the synthetic resin foam sheet is not particularly limited, and examples thereof include the methods (1) to (3).

(1) A synthetic resin foam sheet is sandwiched between a pair of flat electrodes, the flat electrode in contact with the surface to be charged is connected to a high-voltage DC power supply, and the other flat electrode is grounded. A method of applying a pulsed high voltage to inject electric charge into a synthetic resin or an inorganic material to impart polarization to a synthetic resin foam sheet.
(2) Polarizing the synthetic resin or inorganic sheet by irradiating the surface of the synthetic resin foam sheet with ionizing radiation or ultraviolet rays such as electron beams and X-rays to ionize air molecules near the synthetic resin foam sheet. How to give.
(3) A needle electrically connected to a DC high-voltage power supply at a predetermined interval on the other surface of the synthetic resin foam sheet, with a grounded flat electrode superimposed on one surface of the synthetic resin foam sheet in close contact. An electrode or a wire electrode is provided. Next, a corona discharge is generated by electric field concentration at the tip of the needle electrode or near the surface of the wire electrode, ionizing air molecules, and repelling air ions generated by the polarity of the needle electrode or wire electrode to synthesize. A method for imparting polarization to a resin foam sheet.

The expansion and contraction rate of the piezoelectric sheet A1 is preferably 0.5% or more, more preferably 1% or more, more preferably 1.5% or more, and particularly preferably 1.8% or more. The expansion and contraction rate of the piezoelectric sheet A1 is preferably 30% or less, more preferably 20% or less, more preferably 10% or less, and particularly preferably 7% or less. When the expansion and contraction rate of the piezoelectric sheet A1 is 0.5% or more, stress with a small frequency can be detected with high accuracy. Further, not only stress applied in the thickness direction of the piezoelectric sheet such as compression, but also stress applied in the surface direction of the piezoelectric sheet such as elongation can be detected with high accuracy. When the expansion and contraction rate of the piezoelectric sheet A1 is 30% or less, the piezoelectric sheet A1 can maintain stable piezoelectricity over a long period of time, and can accurately detect stress having a small frequency. Note that the expansion / contraction rate (%) of the piezoelectric sheet A1 refers to a value measured in the following manner. First, a flat square test piece with a side of 5 cm is cut out from the piezoelectric sheet, and this test piece is stretched in a direction of an arbitrary edge by a force of 10 N, and the length (cm) of the test piece in the stretching direction at the time of stretching is determined. Measure. The expansion ratio (%) of the piezoelectric sheet A1 refers to a value calculated based on the following equation.
Expansion ratio (%)
= 100 × [length of test specimen in extension direction at extension (cm) -5] / 5

As shown in FIG. 1, the first electrode A2 is laminated and integrated on one surface (first surface) of the piezoelectric sheet A1, and the second electrode A3 is laminated on the other surface (second surface) of the piezoelectric sheet A1. The piezoelectric sensor A is integrally formed. Then, by measuring the potential difference between the first electrode A2 and the second electrode A3, the potential generated in the piezoelectric sheet A1 of the piezoelectric sensor can be measured. Note that one surface (first surface) of the piezoelectric sheet A1 is a surface of the piezoelectric sheet having the largest area. The other surface (second surface) of the piezoelectric sheet A1 is a surface opposite to the one surface (first surface) of the piezoelectric sheet.

伸縮 A first electrode A2 having elasticity is laminated and integrated on one surface of the piezoelectric sheet A1. The first electrode A2 only needs to have elasticity in the plane direction of the piezoelectric sheet A1. The first electrode A2 is not particularly limited, and preferably contains conductive fine particles and a binder resin having elasticity. When the first electrode A2 is made of a stretchable binder resin containing conductive fine particles, it exhibits more excellent stretchability and more accurately detects a small frequency stress applied to the piezoelectric sensor. can do. Further, not only stress applied in the thickness direction of the piezoelectric sheet such as compression but also stress applied in the surface direction of the piezoelectric sheet such as elongation can be accurately detected.

Similarly, a second electrode A3 having elasticity is laminated and integrated on the other surface of the piezoelectric sheet A1. The second electrode A3 only needs to have elasticity in the plane direction of the piezoelectric sheet A1. The second electrode A3 is not particularly limited, and preferably contains conductive fine particles and a binder resin having elasticity. When the second electrode A3 is made of an elastic binder resin containing conductive fine particles, it exhibits more excellent elasticity and more accurately detects a small frequency stress applied to the piezoelectric sensor. can do. In addition, not only stress applied in the thickness direction of the piezoelectric sheet, such as compression, but also stress applied in the surface direction of the piezoelectric sheet, such as elongation, can be accurately detected.

When the first electrode A2 or the second electrode A3 is made of a binder resin containing conductive fine particles, if the first electrode A2 and the second electrode A3 can be provided with conductivity, the conductive fine particles are There is no particular limitation. Examples of the conductive fine particles include silver fine particles, aluminum fine particles, copper fine particles, nickel fine particles, metal fine particles such as palladium fine particles, carbon black, graphite, carbon nanotubes, carbon fibers, and carbon-based conductive fine particles such as metal-coated carbon black. Examples include conductive ceramic fine particles such as tungsten carbide, titanium nitride, zirconium nitride, and titanium carbide, and conductive potassium titanate whiskers. Among them, metal fine particles are preferable, and silver fine particles are more preferable, since they are excellent in conductivity. The conductive fine particles may be used alone or in combination of two or more. Note that the conductive fine particles included in the first electrode A2 and the conductive fine particles included in the second electrode A3 may be the same or different.

When the first electrode A2 is composed of a binder resin containing conductive fine particles, the content of the conductive fine particles in the electrode is preferably 40 to 90 parts by mass, and more preferably 60 to 90 parts by mass with respect to 100 parts by mass of the binder resin. 85 parts by mass is more preferable, and 60 to 80 parts by mass is particularly preferable. When the second electrode A3 is made of a binder resin containing conductive fine particles, the content of the conductive fine particles in the electrode is preferably 40 to 90 parts by mass, and more preferably 60 to 90 parts by mass with respect to 100 parts by mass of the binder resin. 85 parts by mass is more preferable, and 60 to 80 parts by mass is particularly preferable. When the content of the conductive fine particles contained in the first electrode A2 and the second electrode A3 is within the above range, the first electrode A2 and the second electrode A3 are maintained while maintaining the elasticity of the first electrode A2 and the second electrode A3. Conductivity can be given to the two electrodes A3.

When the first electrode A2 or the second electrode A3 is made of a binder resin, the binder resin follows the expansion and contraction of the piezoelectric sheet A1 in the plane direction, and can expand and contract without causing damage such as cracks. There is no particular limitation as long as the properties can be imparted to the first electrode A2 and the second electrode A3.

As the binder resin, for example, modified silicone, acrylic modified polymer, styrene-based thermoplastic elastomer, polyolefin-based thermoplastic elastomer, polyvinyl chloride-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer, polyester-based thermoplastic elastomer, polyamide-based Thermoplastic elastomers such as thermoplastic elastomers, polyamide-based thermoplastic elastomers, 1,2-polybutadiene-based thermoplastic elastomers, polychloroprene (CR), EPDM, polyisoprene rubber (IR), polybutadiene rubber (BR), and styrene-butadiene Rubber materials such as heavy rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), ethylene-propylene copolymer rubber, and butyl rubber are exemplified. The binder resin may be used alone, or two or more kinds may be used in combination.

The method for laminating and integrating the first electrode A2 and the second electrode A3 on the surface of the piezoelectric sheet A1 is not particularly limited, and examples thereof include the methods (1) and (2).

(1) After applying a conductive paint obtained by dispersing or dissolving conductive fine particles and a binder resin in a solvent to the surface of the piezoelectric sheet A1, by removing the solvent of the conductive paint, the first electrode A2 or A method of laminating and integrating the second electrode A3 on the surface of the piezoelectric sheet A1.
(2) After applying a conductive paint obtained by dispersing conductive fine particles in a curable resin to the surface of the piezoelectric sheet A1, the curable resin is cured by heating or ionizing radiation to form a binder resin. A method of laminating and integrating the electrode A2 or the second electrode A3 on the surface of the piezoelectric sheet A1. The ionizing radiation includes, for example, electron beams, ultraviolet rays, α rays, β rays, γ rays, and the like.

(4) In the above description, the case where the first electrode A2 and the second electrode A3 are directly laminated and integrated on the surface of the piezoelectric sheet A1 has been described, but the method of laminating and integrating is not limited to only these methods. As another method, the first electrode A2 or the second electrode A3 is supported on the surface of the stretchable synthetic resin sheet (laminated and integrated), and then the stretchable synthetic resin sheet is placed on the first electrode A2 or the second electrode A2. A method in which the surface on which the two electrodes A3 are formed faces the piezoelectric sheet A1 side, and the surface of the piezoelectric sheet A1 is laminated and integrated with a known adhesive such as a fixing agent as necessary.

(4) The stretchable synthetic resin sheet is not particularly limited as long as the stretchable synthetic resin sheet can expand and contract following the expansion and contraction in the plane direction of the piezoelectric sheet A1 without causing damage such as cracks. Examples of the synthetic resin constituting the stretchable synthetic resin sheet include styrene-based thermoplastic elastomer, polyolefin-based thermoplastic elastomer, polyvinyl chloride-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer, polyester-based thermoplastic elastomer, and polyamide-based thermoplastic elastomer. Thermoplastic elastomers such as thermoplastic elastomers, polyamide-based thermoplastic elastomers and 1,2-polybutadiene-based thermoplastic elastomers, polychloroprene (CR), EPDM, polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene copolymer Rubber materials such as rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), ethylene-propylene copolymer rubber, and butyl rubber. The synthetic resin constituting the stretchable synthetic resin sheet may be used alone, or two or more kinds may be used in combination.

The method for supporting the first electrode A2 or the second electrode A3 on the surface of the stretchable synthetic resin sheet is not particularly limited, and examples thereof include the methods (1) and (2).

(1) After applying a conductive paint obtained by dispersing or dissolving conductive fine particles and a binder resin in a solvent to the surface of a stretchable synthetic resin sheet, the solvent of the conductive paint is removed to form the first electrode. A method in which A2 or the second electrode A3 is laminated and integrated on the surface of a stretchable synthetic resin sheet.
(2) After applying a conductive paint obtained by dispersing conductive fine particles in a curable resin to the surface of a stretchable synthetic resin sheet, the curable resin is cured by heating or ionizing radiation to form a binder resin, A method of laminating and integrating the first electrode A2 or the second electrode A3 on the surface of a stretchable synthetic resin sheet.

The sensor system S includes a piezoelectric sensor A, a first detection unit B for measuring a potential generated by the piezoelectric sensor A, and an electrostatic capacitance of a capacitor formed between a first electrode and a second electrode of the piezoelectric sensor A. A second detecting unit that detects a change in capacitance or a change in impedance between the first electrode and the second electrode of the piezoelectric sensor;

The sensor system S functionally includes a piezoelectric sensor A, a first detection unit B, and a second detection unit C, as shown in FIG.

As shown in FIG. 3, the sensor system S physically includes a piezoelectric sensor A, a CPU (Central Processing Unit) 11, a ROM (Read Only Memory) 12, a RAM (Random Access Memory) 13, It has an auxiliary storage device 14, a first measurement module 15, a second measurement module 16, an output module 17, and a temperature sensor 18.

(4) The piezoelectric sensor A, the ROM 12, the RAM 13, the auxiliary storage device 14, the first measuring module 15, the second measuring module 16, the output module 17, and the temperature sensor 18 are electrically connected to the CPU 11 in a communicable manner. The CPU 11, the auxiliary storage device 14, the first measurement module, the second measurement module 16, the output module 17, and the temperature sensor 18 are attached or mounted with a general-purpose wireless module, and are electrically connected to each other so as to be able to communicate with each other through wireless communication. Is also good. The wireless module is a module that performs wireless data communication with a communication terminal, and is a module that performs wireless data communication (Wi-Fi) (registered trademark), Bluetooth (registered trademark) [Bluetooth (registered trademark)], W-CDMA standard, LTE standard, This is a module for realizing a normal wireless communication system such as the LPWA (Low Power Wide Area) standard.

The auxiliary storage device 14 includes, for example, a solid state drive (SSD) and a hard disk drive (HDD). The output module 17 includes, for example, a display, a speaker, a portable terminal device, and the like.

(1) The first measurement module 15 measures a potential generated in the piezoelectric sheet A1 by applying a stress having a large frequency in the thickness direction to the piezoelectric sheet A1 of the piezoelectric sensor A. Further, the first measurement module 15 is configured to determine that the piezoelectric sheet A1 of the piezoelectric sensor A is compressed in the thickness direction for a short period of time or momentarily by being expanded in the surface direction for a short time or momentarily. Is used to measure the potential generated in the piezoelectric sheet A1. That is, the first measurement module 15 measures the potential generated in the piezoelectric sheet A1 by the high frequency stress applied to the piezoelectric sheet A1 of the piezoelectric sensor A in the thickness direction or the surface direction for a short time or instantaneously. As the first measurement module 15, a known electrometer used for measuring an electric potential can be used.

The second measurement module 16 measures the capacitance of the capacitor formed between the first electrode A2 and the second electrode A3 of the piezoelectric sensor A. The capacitance of the capacitor is measured by the second measurement module 16 to detect a change in the capacitance of the capacitor caused by the piezoelectric sensor A extending in the surface direction and the thickness of the piezoelectric sensor A decreasing. can do. Further, by measuring the capacitance of the capacitor by the second measurement module 16, a pressing force is applied to the piezoelectric sensor A in the thickness direction thereof, and the capacitance of the capacitor caused by the decrease in the thickness of the piezoelectric sensor A is generated. A change in capacitance can be detected. The second measurement module 16 can be suitably used for detecting a low frequency stress. As the second measurement module 16, a known measurement device such as an LCR meter can be used.

(4) The high frequency stress detected by the first measurement module 15 is preferably a stress having a frequency of 0.01 Hz or more. When the frequency is 0.01 Hz or more, it is easy to detect a change in potential. As a result, stress having a large frequency can be accurately detected. The stress having a large frequency is preferably a stress of 0.1 Hz or more, more preferably a stress of 1 Hz or more. Stress having a frequency lower than that of the stress detected by the first measurement module 15 can be suitably detected by the second measurement module 16.

The sensor system S operates a first measurement module 15, a second measurement module 16, an output module 17, and a temperature sensor 18 under the control of the CPU 11 by reading a predetermined program on the CPU 11 and the RAM 13. This is realized by reading and writing data in the RAM 13 and the auxiliary storage device 14.

The first detector B and the second detector C perform predetermined functions by executing a program stored in the ROM 12 or the like under the control of the CPU 11.

The first electrode A2 and the second electrode A3 of the piezoelectric sensor are electrically connected to the first measurement module 15 via a conductive wire. The second electrode A3 is used as a reference potential, and the potential of the first electrode A2 is used as the first potential. It is configured to be measurable by one measurement module 15. The potential of the second electrode A3 may be measured by the first measurement module 15 using the first electrode A2 as a reference potential.

Further, the first electrode A2 and the second electrode A3 of the piezoelectric sensor A are also electrically connected to the second measurement module 16 via a conductive wire, and are provided between the first electrode A2 and the second electrode A3. The capacitance of the formed capacitor can be measured by the second measurement module 16.

The first electrode A2 and the second electrode A3 of the piezoelectric sensor A are electrically connected to both the first measurement module 15 and the second measurement module 16, but have a potential measured by the first measurement module 15, The capacitance is measured independently from the capacitance measured by the second measurement module 16 without interference at the time of measurement.

The potential measured by the first measurement module 15 and the capacitance measured by the second measurement module 16 are constantly monitored by the CPU 11.

When the potential measured by the first measurement module 15 exceeds a predetermined threshold (potential threshold), the CPU 11 determines that a stress exceeding a predetermined magnitude has been applied to the piezoelectric sensor A, A warning signal to the effect is transmitted to the output module 17 by the CPU 11. The output module 17 notifies a manager who manages the sensor system S by displaying on a display or emitting a warning sound from a speaker. The administrator who has received the notification can take necessary actions based on the notification. Further, the potential measured by the first measurement module 15 may be stored in the auxiliary storage device 14 as needed.

The transmission of the warning signal to the output module 17 by the CPU 11 may be continued until the potential measured by the first measurement module 15 becomes equal to or less than a predetermined threshold (potential threshold), It may be stopped after a certain period of time or by an administrator.

Further, when the piezoelectric sensor A is extended in the surface direction to reduce the thickness of the piezoelectric sensor A, or when a stress for compressing the piezoelectric sensor A in the thickness direction is applied, the first electrode A2 and the second electrode The capacitance of the capacitor formed between A3 and A3 increases. When the capacitance measured by the second measurement module 16 exceeds a predetermined threshold (capacitance threshold), the CPU 11 determines that a stress equal to or larger than a predetermined magnitude has been applied to the piezoelectric sensor A. You. Then, the CPU 11 transmits a warning signal to that effect to the output module 17. The output module 17 notifies a manager who manages the sensor system by displaying it on a display or emitting a warning sound from a speaker. The administrator who has received the notification can take necessary actions based on the notification. If necessary, the capacitance measured by the second measurement module 16 may be stored in the auxiliary storage device 14.

The transmission of the warning signal by the CPU 11 to the output module 17 may be continuously performed until the capacitance measured by the second measurement module 16 becomes equal to or less than the capacitance threshold, or may be performed for a certain period of time. It may be stopped after a lapse or by an administrator.

Even when the thickness of the piezoelectric sensor A is gradually compressed by the stress gradually applied to the piezoelectric sensor A over a long period of time, the second detection unit C allows the first electrode A2 of the piezoelectric sensor A to be connected to the second electrode A2. It is possible to detect a change in the capacitance of the capacitor formed between the electrode A3. Therefore, by measuring the capacitance of the capacitor formed between the first electrode A2 and the second electrode A3 of the piezoelectric sensor A, the stress applied to the piezoelectric sensor A gradually applied over a long period of time, That is, it is possible to accurately detect a stress having a small frequency.

Here, the capacitance measured by the second measurement module 16 changes depending on the temperature of the measurement environment (atmosphere at the time of measurement). That is, the capacitance measured by the second measurement module 16 decreases as the temperature of the measurement environment to be measured increases. Therefore, the temperature sensor 18 constantly measures the temperature of the measurement environment, and the temperature measured by the temperature sensor 18 is transmitted to the CPU 11 as an electric signal.

The auxiliary storage device 14 stores the relationship between the temperature of the measurement environment and the capacitance threshold at the temperature of the measurement environment. Specifically, (1) a relational expression showing the relationship between the temperature of the measurement environment and the capacitance threshold at the temperature of the measurement environment, (2) the temperature of the measurement environment and the capacitance threshold at the temperature of the measurement environment Is stored.

Then, based on the temperature of the measurement environment measured by the temperature sensor 18 by the CPU 11, according to the relationship between the temperature of the measurement environment stored in the auxiliary storage device 14 and the capacitance threshold at the temperature of the measurement environment, A capacitance threshold at the temperature of the measurement environment is determined, and the above determination is made based on the capacitance threshold.

In the above description, a predetermined capacitance threshold is determined based on the temperature of the measurement environment, and the determination is performed based on the capacitance threshold. The above determination may be made by correcting the measured capacitance in the following manner and comparing the corrected capacitance with a capacitance threshold.

As described above, since the capacitance itself changes with temperature, the change in capacitance due to the temperature change in the measurement environment is corrected. The auxiliary storage device 14 has a correction temperature T _{0 as} a reference for correcting the measured capacitance, and a correction temperature of a capacitor formed between the first electrode A 2 and the second electrode A 3 of the piezoelectric sensor. The capacitance Ca at T ₀ and the temperature coefficient W (ppm / ° C.) of the capacitance are stored. The correction temperature T ₀ may be an arbitrary temperature, and is not particularly limited, but is preferably a temperature close to the average value of the temperature of the measurement environment of the sensor system.

Then, the capacitance is corrected by the CPU 11 based on the following correction formula stored in the auxiliary storage device 14.
The capacitance C after correction C = Ca + Ca × (temperature of measurement environment−T ₀ ) × W / 10 ⁶

Then, the CPU 11 may determine the capacitance by comparing the capacitance corrected as described above with the capacitance threshold.

In the above, the presence or absence of the stress applied to the piezoelectric sensor is determined based on whether or not the capacitance measured by the second measurement module 16 exceeds a predetermined threshold (capacitance threshold). However, the presence or absence of the stress applied to the piezoelectric sensor may be determined based on whether or not the change rate of the capacitance exceeds a predetermined threshold (hereinafter, referred to as “capacitance change rate threshold”). When making a judgment based on this criterion, it is necessary to determine the threshold value of the change rate of the capacitance (capacitance change rate threshold value) in consideration of the change in the capacitance itself due to the temperature change.

Specifically, the capacitance of the capacitor formed between the first electrode A2 and the second electrode A3 of the piezoelectric sensor A is constantly measured by the second measurement module 16 as described above. Further, the temperature of the measurement environment is constantly measured by the temperature sensor 18 as described above. The measured capacitance and the temperature of the measurement environment are constantly transmitted to the CPU 11 as electric signals. Then, the capacitance and the temperature of the measurement environment transmitted to the CPU 11 are paired with the measurement time (the time at which the CPU 11 receives the capacitance and the temperature of the measurement environment), and are then stored in a predetermined area of the auxiliary storage device 14. Is stored.

On the other hand, by the CPU 11, the capacitance and the temperature of the measurement environment at the time returned by the preset time from the measurement time of the capacitance and the temperature of the measurement environment transmitted from the second measurement module 16 are transmitted from the auxiliary storage device 14. Is read. Note that the capacitance transmitted from the second measurement module 16 is referred to as “current capacitance”. The temperature of the measurement environment is called “current temperature”. The measurement time of the current capacitance and the current temperature is called “current time”. The time returned from the current time by a preset time is referred to as “reference time”. The capacitance at the reference time is called “reference capacitance”. The temperature of the measurement environment at the reference time is called “reference temperature”.

(4) As described above, since the capacitance itself changes depending on the temperature, it is preferable to correct the change in the capacitance due to the temperature change in the measurement environment in the above-described manner.

The change rate of the capacitance is always calculated by the CPU 11 based on the following equation stored in the auxiliary storage device 14 using the current capacitance and the reference capacitance corrected as described above. You.
Change rate of capacitance (%)
= 100 x [(corrected current capacitance)-(corrected reference capacitance)]
/ Corrected reference capacitance

When the CPU 11 determines that the calculated change rate of the capacitance has exceeded the capacitance change rate threshold, the CPU 11 determines that a stress equal to or larger than a predetermined magnitude has been applied to the piezoelectric sensor A. . Then, the CPU 11 transmits a warning signal to that effect to the output module 17. The output module 17 notifies an administrator who manages the sensor system by displaying it on a display or emitting a warning sound from a speaker. The administrator who has received the notification can take necessary actions based on the notification. Further, the change rate of the capacitance measured by the second measurement module 16 may be stored in the auxiliary storage device 14 as needed.

Note that the CPU 11 transmits the warning signal to the output module 17 until the potential measured by the first measurement module 15 becomes equal to or less than the potential threshold, or the capacitance measured by the second measurement module 16 or The change may be continuously performed until the change rate becomes equal to or less than the capacitance threshold value or the capacitance change rate threshold value, respectively. Alternatively, the output of the warning signal to the output module 17 by the CPU 11 may be stopped after a predetermined time has elapsed or by the administrator.

In the above description, in order to particularly detect a low frequency stress applied to the piezoelectric sensor, the capacitance of the capacitor formed by the first electrode A2 and the second electrode A3 of the piezoelectric sensor A or the rate of change of the capacitance is described. Was determined using The impedance between the first electrode A2 and the second electrode A3 of the piezoelectric sensor A may be measured by the second measurement module 16, and the determination may be made based on the measured impedance. The description of the same configuration as the above-described sensor system is omitted.

When the piezoelectric sensor A is extended in the plane direction to reduce the thickness of the piezoelectric sensor A, or when a stress for compressing the piezoelectric sensor A in the thickness direction is applied, the first electrode A2 and the second electrode A3 of the piezoelectric sensor A And the impedance between them becomes smaller. Then, when the impedance calculated based on a potential difference V ₂ described later measured by the second measurement module 16 falls below a predetermined threshold (impedance threshold), the CPU 11 causes the CPU 11 to apply a stress equal to or larger than a predetermined magnitude. Is added to the piezoelectric sensor A. Then, the CPU 11 transmits a warning signal to that effect to the output module 17. The output module 17 notifies an administrator who manages the sensor system by displaying it on a display or emitting a warning sound from a speaker. The administrator who has received the notification can take necessary actions based on the notification. Further, if necessary, the impedance measured by the second measurement module 16 may be stored in the auxiliary storage device 14.

The transmission of the warning signal by the CPU 11 to the output module 17 may be continuously performed until the impedance measured by the second measurement module 16 becomes equal to or more than the impedance threshold, or after a predetermined time elapses or when the management is performed. May be stopped by a person.

Here, the impedance of the piezoelectric sensor A changes depending on the environmental temperature to be measured. That is, the impedance of the piezoelectric sensor A increases as the environmental temperature to be measured increases. Therefore, the temperature sensor 18 constantly measures the temperature of the measurement environment, and the temperature measured by the temperature sensor 18 is transmitted to the CPU 11 as an electric signal.

The auxiliary storage device 14 stores the relationship between the temperature of the measurement environment and the impedance threshold at the temperature of the measurement environment. Specifically, (1) a relational expression showing the relationship between the temperature of the measurement environment and the impedance threshold at the temperature of the measurement environment, and (2) the relationship between the temperature of the measurement environment and the impedance threshold at the temperature of the measurement environment. The illustrated graph and the like are stored.

Then, based on the temperature of the measurement environment measured by the temperature sensor 18 by the CPU 11, the measurement environment is measured according to the relationship between the temperature of the measurement environment stored in the auxiliary storage device 14 and the impedance threshold value at the temperature of the measurement environment. Is determined, and the above determination is made based on this impedance threshold.

In the above description, a predetermined impedance threshold is determined based on the temperature of the measurement environment, and the determination is made based on the impedance threshold. A predetermined value may be determined in advance as the impedance threshold value, the calculated impedance of the piezoelectric sensor A may be corrected in the following manner, and the above-described determination may be made by comparing the corrected impedance with the impedance threshold value.

As described above, since the impedance itself changes with temperature, the change in impedance due to the temperature change in the measurement environment is corrected. The auxiliary storage device 14, the correction temperature T ₁ of which is a reference for correcting the measured impedance, and the impedance Za of the piezoelectric sensor A in the correction temperature T ₁ of, the temperature coefficient of impedance Y (ppm / ℃) is stored Have been. The correction temperature T ₁ may be any temperature, and is not particularly limited, but is preferably a temperature close to the average value of the temperature of the measurement environment of the sensor system.

Then, the impedance is corrected by the CPU 11 based on the following correction formula stored in the auxiliary storage device 14.
Impedance after correction Z = Za + Za × (Temperature of measurement environment−T ₁ ) × Y / 10 ⁶

The determination may be made by the CPU 11 comparing the impedance corrected as described above with the impedance threshold.

第 It is preferable that the second detection unit C that detects a change in impedance between the first electrode A2 and the second electrode A3 of the piezoelectric sensor has a Wheatstone bridge circuit. That is, the impedance between the first electrode A2 and the second electrode A3 of the piezoelectric sensor A is preferably calculated using a Wheatstone bridge circuit. The use of a Wheatstone bridge circuit enables more accurate detection.

Among the Wheatstone bridge circuits, a Wheatstone bridge circuit having two or more piezoelectric sensors of a measurement piezoelectric sensor and a reference piezoelectric sensor is preferable. The use of such a Wheatstone bridge circuit enables more accurate detection. In addition, since the measurement and reference piezoelectric sensors are provided, there is no need to correct impedance changes due to temperature, and detection accuracy is further improved. An example of a Wheatstone bridge circuit having two or more piezoelectric sensors, a measurement piezoelectric sensor and a reference piezoelectric sensor, includes an active dummy method.

An example of an impedance measuring circuit using a Wheatstone bridge circuit will be described. As shown in FIG. 4, two Wheatstone bridge circuits are formed by preparing two piezoelectric sensors A. The two piezoelectric sensors A4 and A5 are incorporated in a circuit by electrically connecting a conductive wire to each of the first electrode A2 and the second electrode A3. Then, one of the two piezoelectric sensors A4 and A5 is a piezoelectric sensor for measurement, and the other piezoelectric sensor is a piezoelectric sensor for reference. Further, fixed resistances (or reference piezoelectric sensors) R ₁ and R ₂ whose impedance values are known are incorporated between points G ₁ and G ₃ and between points G ₃ and G _4, respectively. . Since the measurement accuracy is improved, the impedance values J ₁ and R ₂ of the fixed resistors (or reference piezoelectric sensors) R ₁ and R ₂ incorporated between the points G ₁ and G ₃ and between the points G ₃ and G _4. It is preferable that each of J ₂ is approximately the same as the impedance value J ₃ of the piezoelectric sensor for measurement in a normal state (a state in which the piezoelectric sensor is not stretched). More specifically, impedance values J ₁ and J _{2 of} fixed resistors (or reference piezoelectric sensors) R ₁ and R ₂ incorporated between points G ₁ and G ₃ and between points G ₃ and G _4. It is preferable that the impedance value J ₃ of the piezoelectric sensor for measurement in a normal state (a state where the piezoelectric sensor is not stretched) satisfies the following expression.
0.8 × J ₃ ≦ J ₁ ≦ 1.2 × J ₃
0.8 × J ₃ ≦ J ₂ ≦ 1.2 × J ₃

In the following description, the piezoelectric sensor A4 constitutes a piezoelectric sensor for measurement.

Then, an AC voltage V ₁ is applied between the points G ₁ and G ₄ at predetermined time intervals (preferably, fixed time intervals), and a potential difference V ₂ between the points G ₂ and G ₃ is applied. There are measured at predetermined time intervals by the second measurement module 16, the potential difference V ₂ which is measured is sent to the CPU11 as an electric signal. Then, the impedance of the piezoelectric sensor A4 is calculated by CPU11 based on a potential difference V _2. A known electrometer or the like is used for measuring the potential difference.

And applying an alternating voltages V ₁ between the _one point and the G ₄ points G to measure the impedance of the piezoelectric sensor A. This AC voltages V _1, since the potential measured by the first measurement module 15 is causing interference, AC voltages V ₁ for measuring the impedance of the piezoelectric sensor A4 is applied at predetermined time intervals, alternating While the voltage V ₁ is being applied, the measurement of the potential in the first measurement module 15 is interrupted. Meanwhile, when the AC voltage V ₁ is not applied, the potential generated in the piezoelectric sheet A1 by the first measurement module 15 is always measured.

In the above description, the predetermined size of the piezoelectric sensor is determined based on whether or not the impedance calculated based on the potential V ₂ measured by the second measurement module 16 is lower than a predetermined threshold (impedance threshold). It was determined whether or not the above stress was applied. Whether or not a stress equal to or greater than a predetermined magnitude is applied to the piezoelectric sensor may be determined based on whether or not the rate of change of the impedance exceeds a predetermined threshold (hereinafter, referred to as “impedance change rate threshold”). . When making a judgment based on this criterion, it is necessary to determine the impedance change rate threshold value in consideration of a change in the impedance itself due to a temperature change. When the impedance is calculated using the Wheatstone bridge circuit shown in FIG. 4, it is not necessary to correct the change of the impedance itself due to the temperature change of the measurement environment in the current impedance and the reference impedance described later.

Specifically, as described above, as (preferably, at every predetermined time interval) at predetermined time intervals to CPU11 potential difference V ₂ measured by the second measurement module 16 is an electric signal is transmitted. Then, the impedance of the piezoelectric sensor A is calculated by the CPU11 on the basis of the potential difference V _2. Then, the impedance calculated by the CPU 11, on the measurement time is the pair (CPU 11 time which has received the potential difference V _2), it is stored in a predetermined area of the auxiliary storage device 14.

On the other hand, the CPU 11 reads out the impedance from the auxiliary storage device 14 at a time that is returned by a preset time from the impedance measurement time calculated based on the potential difference V ₂ transmitted from the second measurement module 16. Note that the impedance calculated based on the potential difference V ₂ transmitted from the second measurement module 16 is called “current impedance”. The measurement time of the current impedance is called “current time”. The time returned from the current time by a preset time is referred to as “reference time”. The impedance at the reference time is called “reference impedance”.

Then, the CPU 11 uses the current impedance and the reference impedance to change the rate of change of the impedance at predetermined time intervals (preferably at predetermined time intervals) based on the following equation stored in the auxiliary storage device 14. Is calculated. If the change in the impedance itself due to the temperature change of the measurement environment is not considered between the current impedance and the reference impedance, the current impedance and the reference impedance may be corrected based on the above-described correction formula. ,
Change rate of impedance (%)
= 100 x [(current impedance)-(reference impedance)]
/ (Reference impedance)

(4) When the CPU 11 determines that the calculated rate of change in impedance exceeds a predetermined threshold (impedance change rate threshold), it is determined that a stress equal to or larger than a predetermined magnitude has been applied to the piezoelectric sensor A. Then, the CPU 11 transmits a warning signal to that effect to the output module 17. The output module 17 notifies an administrator who manages the sensor system, for example, by displaying it on a display or emitting a warning sound from a speaker. The administrator who has received the notification can take necessary actions based on the notification. Further, the change rate of the impedance measured by the second measurement module 16 may be stored in the auxiliary storage device 14 as needed.

Note that the CPU 11 transmits the warning signal to the output module 17 until the potential measured by the first measurement module 15 becomes equal to or lower than the potential threshold, or the impedance measured by the second measurement module 16 or its change. It may be performed continuously until the rates become equal to or more than the impedance threshold or the impedance change rate threshold, respectively. Alternatively, the transmission of the warning signal to the output module 17 by the CPU 11 may be stopped after a predetermined time has elapsed or by the administrator.

As described above, the sensor system can detect both stress (stress having a small frequency) applied gradually over a long period of time and stress (stress having a large frequency) applied for a short time or instantaneously. It is possible to detect two types of stress in the object to be detected. In addition, not only stress applied in the thickness direction of the piezoelectric sheet such as compression but also stress applied in the surface direction of the piezoelectric sheet such as elongation can be detected.

In the above description, the piezoelectric sensor A, the ROM 12, the RAM 13, the auxiliary storage device 14, the first measuring module 15, the second measuring module 16, the output module 17, the temperature sensor 18, and the CPU 11 are electrically connected so as to be able to communicate with each other by wire or wirelessly. The connected sensor system has been described. A server device having a CPU 11, a ROM 12, and a RAM 13 and a database server device as an auxiliary storage device 14 are prepared. Then, the database server device is electrically connected to the server device in a communicable manner, and the server device is connected to the piezoelectric sensor A, the first measurement module 15, the second measurement module 16, the output module 17, and the like via a network such as the Internet. The sensor system may be configured to be communicably connected to the temperature sensor 18.

In the sensor system via the network, the measurement result measured by the first measurement module 15, the second measurement module 16 and the temperature sensor 18 is transmitted to the server device via the network, and the measurement result or the measurement is measured by the CPU 11. A predetermined value is calculated based on the result. In the following, the measurement result or a value calculated based on the measurement result is referred to as a “comparison value”.

(4) When the CPU 11 determines that the comparison value exceeds or falls below the predetermined various thresholds, a warning signal is transmitted to the output module 17 via the network. The output module 17 notifies an administrator who manages the sensor system, for example, by displaying it on a display or emitting a warning sound from a speaker. The notified administrator can take necessary measures based on the warning signal. Other operations of the sensor system via the network are the same as those of the above-described sensor system, and a description thereof will be omitted.

Further, since the charge generated by the pressure or elongation gradually applied to the piezoelectric sensor A over a long period of time leaks, when measuring the pressure or elongation gradually applied to the piezoelectric sensor A over a long period of time, (2) It is preferable to detect by capacitance or impedance measured by the measurement module.

(4) Examples of the object to be detected by the sensor system include a human body, a robot, an unmanned aerial vehicle, a concrete structure, a bridge, and a transportation device (for example, a vehicle).

The sensor system can be suitably used for applications in which the piezoelectric sensor A is attached to or attached to the skin of a human body, so-called wearable applications, and biological signals such as pulse waves and respiratory signals and movements of the skin surface. Can be accurately detected.

The sensor system may constitute a measuring device itself, or may be used as a sensor unit of a conventionally known measuring device or a part thereof.

The sensor system can accurately detect contact with another object and movement of a movable part of the machine by attaching the piezoelectric sensor A to a surface of a machine such as a robot or an unmanned aerial vehicle.

(4) The sensor system can detect cracks generated in the concrete structure by attaching the piezoelectric sensor A to the surface of a concrete structure such as a tunnel.

Specifically, concrete structures such as tunnels crack with the aging. The cracks in the concrete structure include a crack that is gradually formed by the strain applied over time and a crack that is generated by applying the stress to the concrete structure for a short time or momentarily.

For the former crack, it is necessary to detect the movement along the concrete surface. Since the former cracks are caused by temporal distortion, they gradually occur and proceed with almost no vibration.

On the other hand, the latter cracks are caused by stress applied to concrete structures. Therefore, when the latter crack is formed, the concrete structure vibrates due to the crack.

According to the above sensor system, the former crack can be detected by detecting a change in the capacitance or impedance of a capacitor formed between the first electrode A2 and the second electrode A3 of the piezoelectric sensor A. . Further, according to the above sensor system, the latter crack can be detected by detecting the vibration generated when the latter crack is formed as a stress having a large frequency.

The sensor system can detect both the pressure in the thickness direction of the piezoelectric sheet and the stress generated in the surface direction. In addition, the sensor system can detect both stresses applied gradually over a long period of time (stresses of low frequency) and stresses applied shortly or momentarily (stresses of high frequency). The sensor system is applied to various detected objects such as a human body, a robot, an unmanned aerial vehicle, a concrete structure, a bridge, and a transportation device (for example, a vehicle), and detects various stresses applied to the detected objects, Can be detected.

(Cross-reference of related applications)
This application claims priority based on Japanese Patent Application No. 2018-151257 filed on August 10, 2018, the disclosure of which is incorporated herein by reference in its entirety.

A Piezoelectric sensor
A1 Piezoelectric sheet
A2 1st electrode
A3 2nd electrode
A4 Piezoelectric sensor
A5 Piezoelectric sensor B First detector C Second detector S Sensor system

Claims

A piezoelectric sheet having elasticity in the surface direction, a first electrode laminated on one surface of the piezoelectric sheet and having elasticity in the surface direction of the piezoelectric sheet, and a first electrode laminated on the other surface of the piezoelectric sheet and A piezoelectric sensor having a second electrode having elasticity in the plane direction;
A first detection unit that measures a potential generated by the piezoelectric sensor;
A second detecting unit that detects a change in capacitance of a capacitor formed between the first electrode and the second electrode of the piezoelectric sensor or a change in impedance between the first electrode and the second electrode of the piezoelectric sensor; A sensor system comprising:
2. The sensor system according to claim 1, wherein the second detection unit that detects a change in impedance between the first electrode and the second electrode of the piezoelectric sensor includes a Wheatstone bridge circuit. 3.
A second detection unit that detects a change in impedance between the first electrode and the second electrode of the piezoelectric sensor includes a Wheatstone bridge circuit having two or more piezoelectric sensors, a piezoelectric sensor for measurement and a piezoelectric sensor for reference. The sensor system according to claim 1, further comprising:
4. The sensor system according to claim 1, wherein the change in the capacitance or the change in the impedance is calculated as a change rate of the capacitance or a change rate of the impedance, respectively.
(5) A measuring device comprising the sensor system according to any one of (1) to (4).