JPWO2020032255A1 - Sensor system and measuring device using it - Google Patents

Abstract

The present invention provides a sensor system capable of detecting both a stress applied gradually over a long period of time and a stress applied for a short period of time or momentarily. The sensor system of the present invention is formed on 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 another surface of the piezoelectric sheet. A piezoelectric sensor having a second electrode that is laminated and has elasticity in the surface direction of the piezoelectric sheet, a first detection unit that measures a potential generated by the piezoelectric sensor, and a first electrode and a second electrode of the piezoelectric sensor. It is characterized by including a second detection unit that detects a change in the capacitance of a capacitor configured between the electrodes and a change in the impedance between the first electrode and the second electrode of the piezoelectric sensor. ..

Description

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

The piezoelectric sheet is a material that is permanently charged inside by injecting an electric charge into an insulating polymer material. Piezoelectric sheets are expected to be applied to sensor applications by utilizing their excellent sensitivity.

Patent Document 1 describes a pair configuration in which two piezoelectric elements made of a polymer piezoelectric material and receiving an external load or force are superposed, and an electrostatic capacitance made of a dielectric polyester insulating film is connected in parallel between the electrodes. A load measuring device having a piezoelectric element, a resistor and a coil for steepening the voltage of the pair of piezoelectric elements, and a sinusoidal power source capable of resonating the voltage of the pair of piezoelectric elements is disclosed.

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 the two elements can be detected by the differential voltage output, and the magnitude of the load or force can be detected. The detection means is further provided.

Japanese Unexamined Patent Publication No. 2016-224020

However, although the load measuring device described in Patent Document 1 can detect stress applied over a long period of time (stress with a small frequency), it can sufficiently detect stress applied over a short period of time (stress with a large frequency). I can't. Further, there is a problem that the stress applied in the surface direction of the piezoelectric element (for example, the extension of the piezoelectric element in the surface direction) cannot be sufficiently detected.

For example, concrete structures such as tunnels are cracked as they deteriorate over time. Cracks in a concrete structure include cracks that are gradually formed by applying strain over time and cracks that occur when stress is applied to the concrete structure in a short time or momentarily. The former crack occurs so that the crack width gradually increases due to the stress gradually applied over a long period of time. In the latter cracks, the cracks momentarily expand toward the concrete surface or peel off.

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

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

The sensor system of the present invention
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 the piezoelectric sheet laminated on the other surface of the piezoelectric sheet. A piezoelectric sensor having a second electrode that is elastic in the plane direction,
A first detection unit that measures the potential generated by the piezoelectric sensor, and
A second detection unit that detects a change in the capacitance of the capacitor formed between the first electrode and the second electrode of the piezoelectric sensor or a change in the impedance between the first electrode and the second electrode of the piezoelectric sensor. It is characterized by having.

In addition to being able to detect the pressure applied in the thickness direction of the piezoelectric sheet and the stress applied in the surface direction of the piezoelectric sensor, the sensor system of the present invention can detect both low frequency stress and 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 caused by various movements, stress having a low frequency, and stress having a high frequency. Specifically, it can be suitably used for applications such as sticking to the skin surface of the human body (wearable applications) and inspection of concrete structures.

The sensor system of the present invention can detect stress generated in the thickness direction and the surface direction applied to the object to be measured, as well as stress having a low frequency and stress having a high frequency. Therefore, unlike the prior art, it is not necessary to prepare a sensor for detecting each stress, and the structure of the measuring device can be simplified and downsized.

It is sectional drawing which showed the piezoelectric sensor. It is a figure which showed the functional structure of a sensor system. It is a figure which showed the hardware configuration of a sensor system. It is a circuit diagram which showed the Wheatstone bridge circuit.

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

The piezoelectric sheet A1 of the piezoelectric sensor A constituting the sensor system S is a sheet capable of generating an electric charge when an external force is applied, and has elasticity in the surface direction.

The piezoelectric sheet A1 is not particularly limited, but a piezoelectric sheet obtained by imparting polarization to a synthetic resin foam sheet is preferable.

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

The synthetic resin preferably has excellent insulating properties, and the synthetic resin has a volume resistivity value 1 minute after a voltage application at an applied voltage of 500 V in accordance with JIS K6911 (hereinafter, simply referred to as "volume resistivity value"). ) Is 1.0 × 10 ¹⁰ Ω · m or more, preferably a synthetic resin.

^{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, because the piezoelectric sheet A1 has more excellent piezoelectricity. ..

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 plate electrodes, the flat plate electrode that is in contact with the surface to be charged is connected to a high-pressure DC power supply, and the other flat plate electrode is grounded to direct current or the synthetic resin foam sheet. A method of applying a high pulsed voltage to inject an electric charge into a synthetic resin or an inorganic material to impart polarization to a synthetic resin foam sheet.
(2) By irradiating the surface of the synthetic resin foam sheet with ionizing radiation such as electron beams and X-rays or ultraviolet rays to ionize air molecules in the vicinity of the synthetic resin foam sheet, the synthetic resin or inorganic sheet is polarized. How to grant.
(3) A needle electrically connected to a DC high-pressure power source by superimposing a grounded flat plate electrode on one surface of the synthetic resin foam sheet in close contact with the synthetic resin foam sheet and leaving a predetermined interval on the other surface side of the synthetic resin foam sheet. A shaped electrode or a wire electrode is arranged. Next, a corona discharge is generated by concentrating an electric field near the tip of the needle-shaped electrode or the surface of the wire electrode to ionize air molecules, and the air ions generated by the polarity of the needle-shaped electrode or wire electrode are repelled and synthesized. A method of imparting polarization to a resin foam sheet.

The expansion / contraction ratio 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 / contraction ratio 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 / contraction ratio of the piezoelectric sheet A1 is 0.5% or more, stress with a small frequency can be detected with high accuracy. Further, not only the stress applied in the thickness direction of the piezoelectric sheet such as compression but also the stress applied in the surface direction of the piezoelectric sheet such as elongation can be detected with high accuracy. When the expansion / contraction ratio of the piezoelectric sheet A1 is 30% or less, the piezoelectric sheet A1 maintains stable piezoelectricity for a long period of time, and stress with a small frequency can be detected with high accuracy. The expansion / contraction rate (%) of the piezoelectric sheet A1 is a value measured as follows. First, a planar square-shaped test piece having a side of 5 cm is cut out from the piezoelectric sheet, and this test piece is stretched in the direction of an arbitrary edge with a force of 10 N to determine the length (cm) of the test piece in the stretch direction at the time of stretching. Measure. The expansion / contraction ratio (%) of the piezoelectric sheet A1 is a value calculated based on the following formula.
Expansion and contraction rate (%)
= 100 × [Length of test piece in extension direction during 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 integrated to form the piezoelectric sensor A. Then, by measuring the potential difference between the first electrode A2 and the second electrode A3, the potential generated by the piezoelectric sheet A1 of the piezoelectric sensor can be measured. The one surface (first surface) of the piezoelectric sheet A1 refers to the surface having the largest area of the piezoelectric sheet. The other surface (second surface) of the piezoelectric sheet A1 refers to the surface opposite to one surface (first surface) of the piezoelectric sheet.

The first electrode A2 having elasticity is laminated and integrated on one surface of the piezoelectric sheet A1. The first electrode A2 may have elasticity in the surface direction of the piezoelectric sheet A1. The first electrode A2 is not particularly limited, and preferably contains conductive fine particles and a binding resin having elasticity. When the first electrode A2 is made of an elastic binder resin containing conductive fine particles, it exhibits better elasticity and more accurately detects low-frequency stress applied to the piezoelectric sensor. can do. Further, not only the stress applied in the thickness direction of the piezoelectric sheet such as compression but also the stress applied in the surface direction of the piezoelectric sheet such as elongation can be detected with high accuracy.

Similarly, the elastic second electrode A3 is laminated and integrated on the other surface of the piezoelectric sheet A1. The second electrode A3 may have elasticity in the surface direction of the piezoelectric sheet A1. The second electrode A3 is not particularly limited, and preferably contains conductive fine particles and a binding resin having elasticity. When the second electrode A3 is made of an elastic binding resin containing conductive fine particles, it exhibits better elasticity and more accurately detects low-frequency stress applied to the piezoelectric sensor. can do. Further, not only the stress applied in the thickness direction of the piezoelectric sheet such as compression but also the stress applied in the surface direction of the piezoelectric sheet such as elongation can be detected with high accuracy.

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 imparted with conductivity, the conductive fine particles will be present. There is no particular limitation. Examples of the conductive fine particles include metal fine particles such as silver fine particles, aluminum fine particles, copper fine particles, nickel fine particles, and palladium fine particles, and carbon-based conductive fine particles such as carbon black, graphite, carbon nanotubes, carbon fibers, and metal-coated carbon black. Examples thereof include ceramic-based conductive 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, because they are excellent in conductivity. The conductive fine particles may be used alone or in combination of two or more. The conductive fine particles contained in the first electrode A2 and the conductive fine particles contained 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, 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 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, 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 first electrode A2 and the first electrode A2 and the first electrode A2 and the second electrode A2 and the first electrode A2 and the first electrode A2 while maintaining the elasticity of the first electrode A2 and the second electrode A3 are maintained. Conductivity can be imparted 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 surface direction and expands and contracts without causing damage such as cracks. It suffices if the property can be imparted to the first electrode A2 and the second electrode A3, and is not particularly limited.

Examples of the binder resin include 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, and polyamide-based resin. Thermoplastic elastomer, polyamide-based thermoplastic elastomer, thermoplastic elastomer such as 1,2-polybutadiene-based thermoplastic elastomer, polychloroprene (CR), EPDM, polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene Examples thereof include rubber materials such as heavy rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), ethylene-propylene copolymer rubber, and butyl rubber. The binder resin may be used alone or in combination of two or more.

The method of 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) The first electrode A2 or the first electrode A2 or by removing the solvent of the conductive paint after applying the conductive paint obtained by dispersing or dissolving the conductive fine particles and the binder resin in the solvent to the surface of the piezoelectric sheet A1. A method of laminating and integrating the second electrode A3 on the surface of the piezoelectric sheet A1.
(2) A conductive coating material in which conductive fine particles are dispersed in a curable resin is applied to the surface of the piezoelectric sheet A1, and then 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. Examples of ionizing radiation include electron beams, ultraviolet rays, α rays, β rays, and γ rays.

In the above, 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 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 attached to the first electrode A2 or the first electrode A2 or the first electrode. Examples thereof include a method in which the formation surface of the two electrodes A3 is directed toward the piezoelectric sheet A1 side and laminated and integrated on the surface of the piezoelectric sheet A1 using a known adhesive such as a fixing agent, if necessary.

The stretchable synthetic resin sheet is not particularly limited as long as it can expand and contract according to the expansion and contraction of the piezoelectric sheet A1 in the surface direction 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 thermal. Thermoplastic elastomers such as plastic elastomers, polyamide-based thermoplastic elastomers, 1,2-polybutadiene-based thermoplastic elastomers, polychloroprene (CR), EPDM, polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene copolymers Examples thereof include 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 in combination of two or more.

The method of 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) The first electrode is formed by applying a conductive paint obtained by dispersing or dissolving conductive fine particles and a binder resin in a solvent on the surface of a stretchable synthetic resin sheet, and then removing the solvent of the conductive paint. A method of laminating and integrating A2 or the second electrode A3 on the surface of an elastic synthetic resin sheet.
(2) A conductive coating material in which conductive fine particles are dispersed in a curable resin is applied to the surface of a stretchable synthetic resin sheet, and then the curable resin is cured by heating or ionizing radiation to obtain a binder resin. A method of laminating and integrating the first electrode A2 or the second electrode A3 on the surface of an elastic synthetic resin sheet.

In the sensor system S, the capacitance of the capacitor formed between the piezoelectric sensor A, the first detection unit B for measuring the potential generated by the piezoelectric sensor A, and the first and second electrodes of the piezoelectric sensor A is electrostatic. A second detection unit C for detecting a change in capacitance or a change in impedance between the first electrode and the second electrode of the piezoelectric sensor is provided.

Functionally, as shown in FIG. 2, the sensor system S includes a piezoelectric sensor A, a first detection unit B, and a second detection unit C.

Physically, as shown in FIG. 3, the sensor system S includes a piezoelectric sensor A, a CPU (Central Processing Unit) 11, a ROM (Read Only Memory) 12, a RAM (Random Access Memory) 13, and the same. 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.

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

Examples of the auxiliary storage device 14 include SSD (Solid State Drive) and HDD (Hard Disk Drive). Examples of the output module 17 include a display, a speaker, a mobile terminal device, and the like.

The first measurement module 15 measures the 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, in the first measurement module 15, the piezoelectric sheet A1 of the piezoelectric sensor A is stretched in the plane direction for a short time or momentarily, so that the piezoelectric sheet A1 is compressed in the thickness direction for a short time or momentarily. Measure the potential generated on the piezoelectric sheet A1. That is, the first measurement module 15 measures the potential generated in the piezoelectric sheet A1 due to 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 momentarily. As the first measurement module 15, a known electrometer used for measuring the 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. By measuring the capacitance of the capacitor with the second measurement module 16, the piezoelectric sensor A is extended in the plane direction thereof, and the change in the capacitance of the capacitor caused by the decrease in the thickness of the piezoelectric sensor A is detected. can do. Further, by measuring the capacitance of the capacitor with 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 generated by reducing the thickness of the piezoelectric sensor A. Changes in capacitance can be detected. The second measurement module 16 can be suitably used for detecting stress having a low frequency. As the second measurement module 16, a known measuring device such as an LCR meter can be used.

The stress having a large frequency 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 higher, it is easy to detect the change in potential. As a result, stress with a large frequency can be detected with high accuracy. The stress having a large frequency is more preferably 0.1 Hz or higher, and further preferably 1 Hz or higher. A stress having a frequency smaller than the stress detected by the first measurement module 15 can be suitably detected by the second measurement module 16.

The sensor system S operates the first measurement module 15, the second measurement module 16, the output module 17, and the temperature sensor 18 under the control of the CPU 11 by loading 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 detection unit B and the second detection unit C exert a predetermined function 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. 1 It is configured to be measurable by the measurement module 15. The potential of the second electrode A3 may be measured by the first measurement module 15 with 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 between the first electrode A2 and the second electrode A3. The capacitance of the configured capacitor is configured to be measurable 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 the potential measured by the first measurement module 15 and the potential measured by the first measurement module 15 It is measured independently of the capacitance measured by the second measurement module 16 without interfering with the capacitance 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.

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

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

Further, when the piezoelectric sensor A is extended in the plane direction to reduce the thickness of the piezoelectric sensor A, or when a stress is applied to compress the piezoelectric sensor A in the thickness direction, the first electrode A2 and the second electrode of the piezoelectric sensor A2 and the second electrode are applied. 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 value (capacitance threshold value), it is determined by the CPU 11 that a stress of a predetermined magnitude or more has been applied to the piezoelectric sensor A. NS. Then, the CPU 11 transmits a warning signal to that effect to the output module 17. The output module 17 notifies the administrator who manages the sensor system by displaying it on the display or emitting a warning sound from the speaker. The administrator who receives the notification can take necessary measures based on the notification. Further, if necessary, the capacitance measured by the second measurement module 16 may be stored in the auxiliary storage device 14.

The warning signal may be continuously transmitted by the CPU 11 to the output module 17 until the capacitance measured by the second measurement module 16 becomes equal to or less than the capacitance threshold value, or may be continuously performed for a certain period of time. It may be stopped after the lapse of time or by the 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 first electrodes A2 and the second of the piezoelectric sensor A are subjected to the second detection unit C. The change in the capacitance of the capacitor formed between the electrode A3 and the electrode A3 can be detected. 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 over a long period of time, That is, stress with a small frequency can be detected with high accuracy.

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 becomes smaller as the temperature of the measurement environment to be measured becomes higher. 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 value 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. A graph showing the relationship with is stored.

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

In the above, a predetermined capacitance threshold value is determined based on the temperature of the measurement environment, and the judgment is made based on this capacitance threshold value. , The measured capacitance may be corrected as follows, and the above determination may be made by comparing the corrected capacitance with the capacitance threshold value.

As described above, since the capacitance itself changes depending on the temperature, the change in the capacitance due to the temperature change in the measurement environment is corrected. _{The auxiliary storage device 14 has a correction temperature T 0,} which is a reference for correcting the measured capacitance, and a correction temperature of a capacitor formed between the first electrode A2 and the second electrode A3 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 temperatures in the measurement environment of the sensor system.

Then, the CPU 11 corrects the capacitance based on the following correction formula stored in the auxiliary storage device 14.
Corrected capacitance C = Ca + Ca × (Temperature of measurement environment −T ₀ ) × W / 10 ⁶

Then, the CPU 11 may compare the capacitance corrected as described above with the capacitance threshold value for determination.

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

Specifically, as described above, 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. Further, as for the temperature of the measurement environment, as described above, the temperature of the measurement environment is constantly measured by the temperature sensor 18. 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 when the CPU 11 receives the capacitance and the temperature of the measurement environment), and then a predetermined area of the auxiliary storage device 14. Is remembered in.

On the other hand, the CPU 11 sets the capacitance and the temperature of the measurement environment from the auxiliary storage device 14 at a time returned by a preset time from the measurement time of the capacitance and the temperature of the measurement environment transmitted from the second measurement module 16. Read out. The capacitance transmitted from the second measurement module 16 is referred to as "current capacitance". The temperature of the measurement environment is called the "current temperature". The measurement time of the current capacitance and the current temperature is called the "current time". The time returned from the current time by a preset time is called "reference time". The capacitance at the reference time is called "reference capacitance". The temperature of the measurement environment at the reference time is called the "reference temperature".

As described above, since the capacitance itself changes with temperature, it is preferable to correct the change in capacitance due to the temperature change in the measurement environment as described above.

Then, the CPU 11 constantly calculates the rate of change of the capacitance based on the following formula stored in the auxiliary storage device 14 using the current capacitance and the reference capacitance corrected as described above. NS.
Change rate of capacitance (%)
= 100 × [(Current capacitance after correction)-(Reference capacitance after correction)]
/ Reference capacitance after correction

When the CPU 11 determines that the calculated capacitance change rate exceeds the capacitance change rate threshold value, the CPU 11 determines that a stress of a predetermined magnitude or more 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 the administrator who manages the sensor system by displaying it on the display or emitting a warning sound from the speaker. The administrator who receives the notification can take necessary measures based on the notification. Further, if necessary, the rate of change in capacitance measured by the second measurement module 16 may be stored in the auxiliary storage device 14.

The warning signal is transmitted by the CPU 11 to the output module 17 until the potential measured by the first measurement module 15 becomes equal to or lower than the potential threshold value, or the capacitance measured by the second measurement module 16. It may be continued until the rate of change 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 certain period of time or by the administrator.

In the above, in order to particularly detect the low frequency stress applied to the piezoelectric sensor, the capacitance or the rate of change of the capacitance of the capacitor composed of the first electrode A2 and the second electrode A3 of the piezoelectric sensor A is detected. Was used for judgment. 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 determined based on the measured impedance. The description of the same configuration as the sensor system described above will be omitted.

When the piezoelectric sensor A is stretched in the plane direction to reduce the thickness of the piezoelectric sensor A, or when a stress is applied to compress the piezoelectric sensor A in the thickness direction, the first electrode A2 and the second electrode A3 of the piezoelectric sensor A are applied. The impedance between and is small. _{Therefore, when the impedance calculated based on the potential difference V 2} measured by the second measurement module 16, which will be described later, falls below a predetermined threshold value (impedance threshold value), the stress of the predetermined magnitude or more is determined by the CPU 11. Is determined to have joined 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 the administrator who manages the sensor system by displaying it on the display or emitting a warning sound from the speaker. The administrator who receives the notification can take necessary measures 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 warning signal may be continuously transmitted by the CPU 11 to the output module 17 until the impedance measured by the second measurement module 16 becomes equal to or higher than the impedance threshold value, or after a certain period of time has elapsed or is managed. May be stopped by a person.

Here, the impedance of the piezoelectric sensor A changes depending on the ambient temperature to be measured. That is, the impedance of the piezoelectric sensor A increases as the measured environmental temperature 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 value 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 graphs shown are stored.

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

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

As described above, since the impedance itself changes depending on the 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 Has been done. The correction temperature T ₁ may be an arbitrary temperature and is not particularly limited, but is preferably a temperature close to the average value of the temperatures in 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 impedance may be determined by comparing the impedance corrected as described above with the impedance threshold value by the CPU 11.

The second detection unit C for detecting the change in impedance between the first electrode A2 and the second electrode A3 of the piezoelectric sensor preferably 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. By using the Wheatstone bridge circuit, it can be detected more accurately.

Among the Wheatstone bridge circuits, a Wheatstone bridge circuit having two or more piezoelectric sensors, a piezoelectric sensor for measurement and a piezoelectric sensor for reference, is preferable. By using such a Wheatstone bridge circuit, it is possible to detect with higher accuracy. Further, since the piezoelectric sensors for measurement and reference are provided, there is no need to correct the impedance change due to temperature, and the detection accuracy is further improved. Examples of the Wheatstone bridge circuit having two or more piezoelectric sensors, a piezoelectric sensor for measurement and a piezoelectric sensor for reference, include an active dummy method.

An example of an impedance measurement circuit using a Wheatstone bridge circuit will be described. As shown in FIG. 4, two piezoelectric sensors A are prepared to form a Wheatstone bridge circuit. The two piezoelectric sensors A4 and A5 are incorporated in the 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 serves as a piezoelectric sensor for measurement, and the other piezoelectric sensor serves as a reference piezoelectric sensor. Furthermore, fixed resistors R ₁ and R ₂ with known impedance values are incorporated _{between G 1} and G ₃ points and between G ₃ and G _{4, respectively.} .. Since the measurement accuracy is improved, the impedance values J ₁ and _{the impedance values J 1 and R 2} of the fixed resistors (or reference piezoelectric sensors) R ₁ and R _{2 incorporated between the G 1} point and the G ₃ point and between the G ₃ point and the G _{4 point.} It _{is preferable that each of J 2} is about the same as _{the impedance value J 3} of the piezoelectric sensor for measurement in the normal state (in the unextended state). Specifically, the impedance values J ₁ and J _{2 of the} fixed resistors (or reference piezoelectric sensors) R ₁ and R _{2 built between the G 1} point and the G ₃ point and between the G ₃ point and the G _{4 point. It is preferable that the impedance value J 3} of the piezoelectric sensor for measurement in the normal state (unextended state) satisfies the following equation.
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 G 1} point and the G ₄ point at predetermined time intervals (preferably at regular time intervals), and the potential difference V _{2 between the G 2} points and the G _{3 points is applied.} Is measured by the second measurement module 16 at predetermined time intervals, and the measured potential difference V ₂ is transmitted to the CPU 11 as an electric signal. Then, the impedance of the piezoelectric sensor A4 is calculated by the CPU 11 based on the potential difference V _2. A known electrometer or the like is used for measuring the potential difference.

An AC voltage V ₁ is applied _{between the G 1} point and the G ₄ point in order to measure the impedance of the piezoelectric sensor A. Since the AC voltage V ₁ and the potential measured by the first measurement module 15 interfere with _{each other, the AC voltage V 1} for measuring the impedance of the piezoelectric sensor A4 is applied at predetermined time intervals and is AC. While the voltage V ₁ is applied, the potential measurement in the first measurement module 15 is interrupted. On the other hand, when the AC voltage V ₁ is not applied, the potential generated in the piezoelectric sheet A1 is always measured by the first measurement module 15.

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

Specifically, as described above, the potential difference V ₂ measured by the second measurement module 16 is transmitted to the CPU 11 as an electric signal at predetermined time intervals (preferably at regular time intervals). Then, the impedance of the piezoelectric sensor A is calculated by the CPU 11 based on the potential difference V _2. Then, the impedance calculated by the CPU 11 is _{paired with the measurement time (the time when the CPU 11 receives the potential difference V 2} ) and is stored in a predetermined area of the auxiliary storage device 14.

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

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

When the CPU 11 determines that the calculated impedance change rate exceeds a predetermined threshold value (impedance change rate threshold value), it is determined that a stress of a predetermined magnitude or more 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 the administrator who manages the sensor system by displaying it on the display or emitting a warning sound from the speaker. The administrator who receives the notification can take necessary measures based on the notification. Further, if necessary, the rate of change in impedance measured by the second measurement module 16 may be stored in the auxiliary storage device 14.

The warning signal is transmitted by the CPU 11 to the output module 17 until the potential measured by the first measurement module 15 becomes equal to or lower than the potential threshold value, or the impedance measured by the second measurement module 16 or its change. It may be continued until the rate becomes equal to or higher than the impedance threshold value or the impedance change rate threshold value, respectively. Alternatively, the transmission of the warning signal to the output module 17 by the CPU 11 may be stopped after a certain period of time or by the administrator.

As described above, the sensor system can detect both stress that is gradually applied over a long period of time (stress with a low frequency) and stress that is applied for a short time or momentarily (stress with a high frequency). Two types of stress in the object to be detected can be detected. Further, not only the stress applied in the thickness direction of the piezoelectric sheet such as compression but also the stress applied in the surface direction of the piezoelectric sheet such as elongation can be detected.

In the above, the piezoelectric sensor A, ROM 12, RAM 13, auxiliary storage device 14, first measurement module 15, second measurement module 16, output module 17, temperature sensor 18, and CPU 11 can be electrically communicated 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 so as to be able to communicate with the server device, 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 by being communicatively connected to the temperature sensor 18.

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

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

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

Examples of objects 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 the skin of the human body or attached to the human body, so-called wearable applications, and biological signals such as pulse waves and respiratory signals and movement of the skin surface. Can be detected with high accuracy.

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

Further, the sensor system can accurately detect contact with other objects and movement of moving parts of the machine by attaching the piezoelectric sensor A to a machine such as a robot or an unmanned aerial vehicle on the surface.

Further, the sensor system can detect cracks generated in the concrete structure by attaching the piezoelectric sensor A to the surface of the concrete structure such as a tunnel.

Specifically, concrete structures such as tunnels are cracked as they deteriorate over time. Cracks in a concrete structure include cracks that are gradually formed by applying strain over time and cracks that occur when stress is applied to the concrete structure in a short time or momentarily.

For the former crack, it is necessary to detect the movement along the concrete surface. Since the former crack is caused by distortion over time, it gradually occurs and progresses with almost no vibration.

On the other hand, the latter cracks are caused by stress applied to the concrete structure. 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 the 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 at the time of forming the latter crack as a stress having a high frequency.

The sensor system can detect both the pressure in the thickness direction and the stress generated in the surface direction of the piezoelectric sheet. In addition, the sensor system can detect both stresses that are applied gradually over a long period of time (stresses with a low frequency) and stresses that are applied for a short period of time or momentarily (stresses with a high frequency). The sensor system is applied to various objects to be detected such as human bodies, robots, unmanned aerial vehicles, concrete structures, bridges, and transportation equipment (for example, vehicles), and various stresses applied to the objects to be detected and the objects to be detected. Various movements can be detected.

(Cross-reference of related applications)
This application claims priority under Japanese Patent Application No. 2018-151257 filed on August 10, 2018, and the disclosure of this application 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 1st detector C 2nd detector S sensor system

Claims (5)

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 the piezoelectric sheet laminated on the other surface of the piezoelectric sheet. A piezoelectric sensor having a second electrode that is elastic in the plane direction,
A first detection unit that measures the potential generated by the piezoelectric sensor, and
A second detection unit that detects a change in the capacitance of a capacitor formed between the first electrode and the second electrode of the piezoelectric sensor or a change in the impedance between the first electrode and the second electrode of the piezoelectric sensor. A sensor system characterized by being equipped with. The sensor system according to claim 1, wherein 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. A second detector that detects a change in impedance between the first and second electrodes of a piezoelectric sensor is a Wheatstone bridge circuit that has two or more piezoelectric sensors, a piezoelectric sensor for measurement and a piezoelectric sensor for reference. The sensor system according to claim 1 or 2, wherein the sensor system has. The sensor system according to any one of claims 1 to 3, wherein the change in capacitance or change in impedance is calculated as the rate of change in capacitance or the rate of change in impedance, respectively. A measuring device comprising the sensor system according to any one of claims 1 to 4.

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