JP2019105604A - Electrostatic capacity type sensor - Google Patents

Abstract

To provide an electrostatic capacity type sensor capable of improving measurement precision and measurement sensitivity by making a measurement region of a sensor larger than before.SOLUTION: The present invention relates to the electrostatic capacity type sensor that comprises an electrode pair formed on a principal surface of a base material and an insulating film covering the electrode pair, and that defines, as a measurement region, an electric field region formed by applying a predetermined voltage to the electrode pair, and measures electrostatic capacity of the electrode pair by inserting a non-rigid measurement object into the measurement region and pressing it against the insulating film. The electrostatic capacity type sensor is characterized in that: the electrode pair have electrodes, paired on the principal surface of the base material, patterned to have a predetermined interval; the insulating film is formed in a shape of the patterning to cover the electrode pair on the principal surface of the base material; and the electric field generated by applying the predetermined voltage to the electrode pair is generated not only in a region, on the opposite side from the principal surface of the base material, of the insulating film covering the electrode pair, but also in a region that the insulating film covering the adjacent electrode pair faces.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a capacitive sensor, and more particularly to a capacitive sensor that measures an object to be measured.

  As shown in FIG. 1, in the case of a capacitance type sensor which is brought into contact with a measurement object and measured, the electrode pair 102 is formed on the substrate 101, and the electrode pair 102 is not brought into direct contact with the measurement object. It has a configuration in which an insulating layer 103 covering 102 is formed. In this electrostatic capacitance type sensor, the electric field portion 105 formed between the electrode pair 102 does not have the measurement object 106 as shown in FIG. 1A and the measurement object as shown in FIG. 1B. Capacitance values at the electrode pair 102 are measured in two states with the object 106 present. By measuring the capacitance value in such a state, it is possible to calculate the relative dielectric constant of the object to be measured. That is, the capacitance value at the time of the relative dielectric constant (ε = 1) of air, which is known in the absence of the measurement object, is to be measured. By measuring the capacitance value, the relative permittivity of the object to be measured can be calculated by taking the ratio or the difference between them. The physical properties and the like of the object to be measured can be known based on the relative permittivity of the object to be measured calculated in this manner.

  As an application example of such a capacitance type sensor, a skin moisture amount measuring device which measures skin moisture amount, etc. are known (patent document 1). In this skin moisture content measuring device, a sensor is formed at the tip of a tube, and this sensor portion is pressed against the skin to perform measurement. The sensor portion has the same configuration as the capacitive sensor shown in FIG. That is, the electrode pair 102 formed on the substrate which is the base material 101 is covered with the glass which is the insulating layer 103. The measurement is performed by pressing this glass portion against the skin. Other types of skin sensors of this type are known in various configurations (Patent Documents 2, 3 and 4).

Unexamined-Japanese-Patent No. 2003-169788 Japanese Patent Application Laid-Open No. 05-052798 JP 2005-052212 JP, 2014-014423, A

  In the conventional capacitance type sensor used for the skin sensor etc. mentioned above, since the insulating layer is repeatedly pressed against the object to be measured, the insulating layer is hard and durable such as glass from the viewpoint of durability. The material was used. However, since a hard and strong material has poor processability, as shown in FIG. 2, the insulating layer 103 is formed so as to uniformly cover the electrode pair 102. In this case, the portion which becomes the measurement region of the electrostatic capacitance value is only the region on the surface side of the insulating layer shown by A, and the region between the adjacent electrodes where the electric field is supposed to be formed (B The region shown) was filled with the insulating layer and did not function as a measurement region.

  The present inventors, for example, when the object is a non-rigid measurement object such as skin, if the configuration of the insulating film is devised, the sensor by causing the region conventionally covered with the insulating film to function as the measurement region. It has been found that it is possible to expand the measurement area of the above, and as a result, it is possible to dramatically improve the measurement accuracy and the measurement sensitivity, leading to the present invention.

  An object of the present invention is to provide a capacitance type sensor capable of realizing improvement in measurement accuracy and measurement sensitivity by expanding the measurement area of the sensor more than in the past.

  In order to solve the above problems, the invention described in one embodiment includes an electrode pair formed on the main surface of a substrate and an insulating film covering the electrode pair, and a predetermined voltage is applied to the electrode pair. An electrostatic capacitance type sensor which measures an electrostatic capacitance in the electrode pair by inserting a non-rigid measurement object into the measurement area with the electric field area formed by applying as a measurement area and pressing the object against the insulating film The electrode pair is patterned such that the electrodes forming the pair have a predetermined distance on the main surface of the substrate, and the insulating film has the shape of the patterning so as to cover the electrode pair on the main surface of the substrate The electric field formed by applying a predetermined voltage to the electrode pair is not only the region opposite to the main surface of the base of the insulating film covering the electrode pair, but also the adjacent electrodes. The area where the insulating film covering the pair is opposite A capacitive sensor, characterized in that also formed.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining the structure of the conventional electrostatic capacitance type sensor, (a) is each not showing a measuring object, (b) has each shown the time of a measuring object. It is a figure explaining the measurement field in the conventional capacitance type sensor. It is a figure which shows the structural example of the sensor apparatus incorporating the electrostatic capacitance type sensor of this embodiment. FIG. 1 is a perspective view showing a schematic configuration of an example of a capacitance type sensor 10 of the present embodiment. It is V-V 'sectional drawing of FIG. It is a figure explaining the measurement field in the electric capacity type sensor of this embodiment. It is a figure which shows an example of the state of the measurement area | region in the case of comprising as a skin sensor. It is a figure which shows an example of the state of the measurement area | region in the case of comprising as a touch sensor. It is a figure which shows an example of the state of the measurement area | region in the case of comprising as a liquid volume monitoring sensor. It is a figure which shows the measurement result of detection response amount (DELTA) C in each of the electrostatic capacitance type sensor of an Example, and the conventional electrostatic capacitance type sensor which is a comparative example.

  Hereinafter, embodiments of the present invention will be described in detail.

  The capacitive sensor according to the present embodiment includes an electrode pair formed on the main surface of a substrate and an insulating film covering the electrode pair, and an electric field formed by applying a predetermined voltage to the electrode pair. It is an electrostatic capacitance type sensor which inserts a non-rigid measurement object into the measurement area by pressing the area as the measurement area and presses it against the insulating film to measure the capacitance of the electrode pair. In this capacitance type sensor, the electrode pair is patterned so that the pair of electrodes on the main surface of the base has a predetermined distance, and the insulating film covers the electrode pair on the main surface of the base The electric field formed along the shape of the patterning and formed by applying a predetermined voltage to the electrode pair is not only a region on the opposite side to the main surface of the base of the insulating film covering the electrode pair. The insulating film covering the adjacent electrode pair is also formed in the opposing region.

  With this configuration, the electric field formed by applying a predetermined voltage to the electrode pair is not only the region on the opposite side of the main surface of the insulating film covering the electrode pair but also the insulating film covering the adjacent electrode pair Since the non-rigid measurement object is pressed against the insulating film, the non-rigid measurement object is also disposed in this region, and the measurement region is expanded. Sensor responsiveness can be improved.

  FIG. 3 is a diagram showing an example of a schematic configuration of a sensor device incorporating the capacitance type sensor of the present embodiment. As shown in FIG. 3, the sensor device 1 includes a capacitive sensor 10 provided with an electrode pair, and a high frequency power source for applying an alternating voltage with a predetermined frequency at a predetermined frequency to the capacitive sensor 10. 20, and a measuring unit 30 such as an LCR meter that measures a capacitance value in the capacitance type sensor 10, and a relative permittivity and a dielectric constant of the object to be measured based on the capacitance value measured by the measuring unit 30. And a calculation unit 40 that calculates physical properties and the like based on the rate. When only the capacitance value of the object to be measured is measured in the sensor device 1, the calculating unit 40 may not be provided.

  The sensor device 1 incorporating the capacitance type sensor 10 of the present embodiment performs measurement by pressing the capacitance type sensor 10 against a measurement target in a state where a predetermined voltage is applied in the high frequency power supply 20. The object to be measured can be a non-rigid material, that is, a flexible material. The flexible material is a material that causes some deformation when the capacitive sensor 10 is pressed. The physical properties and the like of the measurement object can be calculated by measuring the capacitance value before placing the measurement object and the capacitance value when pressed.

  FIG. 4 is a perspective view showing a schematic configuration of an example of the capacitance type sensor 10 of the present embodiment, and FIG. 5 is a V-V cross-sectional view of FIG. 4. Here, the configuration of the capacitance type sensor 10 of the present embodiment will be described in more detail. As shown in FIG. 5, in the capacitive sensor 10, an electrode pair 12 (hereinafter referred to as a first electrode 12a and a second electrode) formed of a first electrode 12a and a second electrode 12b on a substrate 11 When it does not distinguish with 12b mutually, insulating film 13a, 13b which covers the 1st electrode 12a and the 2nd electrode 12b which form "electrode 12" or "electrode pair 12", and this electrode pair 12 respectively And is configured.

  The base 11 is a base of the capacitance type sensor 10, and a thin film made of an insulating material such as polyethylene terephthalate, polyethylene naphthalate, or polyimide can be used.

  The electrodes 12a and 12b are an electrode pair that forms an electric field when a voltage is applied by the high frequency power supply 20, and the formed electric field portion is used as a measurement area, and the capacitance value with and without the measurement object is It is measured by the measuring unit 30. The electrode pair 12a, 12b is made of, for example, a conductive material such as copper, silver, gold, aluminum, nickel, tin, carbon, etc., and various methods such as printing such as screen printing, vapor deposition or sputtering are used. Can be formed into a predetermined pattern. In this example, as shown in FIG. 4, the electrode pairs 12 a and 12 b are formed in a comb-teeth-like pattern by being separated by a predetermined distance. The pattern shape of the electrode pair 12a, 12b is not limited to the comb shape, but is a circular comb shape, a space filling curve, etc., and an isotropic shape while increasing the opposing surface area of the electrode pair 12a, 12b as much as possible. It can be formed.

  Further, when the electrode pairs 12a and 12b are arranged at high density, the electric field region is concentrated near the electrodes, so the electric field is extremely strong near the electrodes and extremely weak electric fields are formed far away. It is considered to be higher. On the other hand, when arranged at low density, the electric field region is widely distributed around the electrode, so it is considered that an electric field which is not strong near and not weak at distant places is formed as compared with high density arrangement. Therefore, high density (narrow pitch) is not always preferable, and the preferred electric field area, ie, detection area, varies depending on the sensor application.

  The insulating films 13a and 13b insulate the electrode pair 12a and 12b from the object to be measured, and protect the surface of the electrode pair 12a and 12b. If the insulating film is too thick, the distance between the electrode pair and the object to be measured is large, and the object to be measured may not enter the electric field region formed by the electrode pair. preferable. The insulating films 13a and 13b are, for example, a thermoplastic resin, a thermosetting resin, a two-component curable resin, and an ultraviolet curable resin so as not to conduct with the electrode pairs 12a and 12b when pressed against the measurement object. And insulating resin materials including silicon rubber, oxide paste, nitride paste, glass powder paste, etc., and printing methods such as screen printing, or dispensing methods, spray methods, and spin coating methods. The electrode pair 12a, 12b can be formed to cover the base 11 by using various methods. That is, the insulating films 13a and 13b are formed so as to cover the electrode pairs 12a and 12b, and to make the region on the base 11 without the electrode pairs 12a and 12b concave in cross section. Therefore, the pattern shape of the insulating films 13a and 13b covers the pattern shape of the electrode pair 12a and 12b.

  Since the pattern shape of the insulating films 13a and 13b covers the pattern shape of the electrode pairs 12a and 12b, a region of a cross-sectional concave shape without the electrode pairs 12a and 12b is formed on the substrate 11, An electric field is also formed in the region filled with the insulating film. Furthermore, when the non-rigid measurement object is pressed against the insulating films 13a and 13b, as shown in FIG. 6, the measurement object 106 can be deformed and intrude also into the cross-sectional concave portion. That is, the electric field area 105 affecting the capacitance value to be measured is expanded, and the expanded electric field area 105 is also filled with the measurement object 106, so the electric field area 105 including the measurement object 106 is expanded. It becomes. Therefore, it can be said that the measurement area is expanded, and the measurement accuracy and the measurement sensitivity are dramatically improved.

  The measurement in the sensor device 1 incorporating the capacitance type sensor 10 of the present embodiment will be described. First, in a state in which there is no object to be measured in the measurement area of the capacitive sensor 10, an AC voltage of a predetermined frequency and a predetermined amplitude is applied to the capacitive sensor 10 by the high frequency power supply 20 to measure The capacitance value of the electrode pair of the capacitive sensor 10 is measured by 30. The capacitance value measured at this time is the capacitance value (Ca) of the relative dielectric constant of the air (εa). Next, in a state where the object to be measured is pressed against the insulating films 13a and 13b of the capacitive sensor 10, an alternating current voltage of a predetermined amplitude and a predetermined frequency is applied to the capacitive sensor 10 by the high frequency power supply 20. The voltage is applied and the capacitance value of the electrode pair of the capacitance type sensor 10 is measured by the measurement unit 30. The electrostatic capacitance value measured at this time is the electrostatic capacitance value (Cx) with respect to the relative dielectric constant (referred to as εx) of the object to be measured.

  When these capacitance values Ca and Cx are measured, the calculation unit 40 calculates the difference (ΔC = Cx−Ca) or the ratio (ΔC = Cx−Ca) of the capacitance value Cx of the measurement object to the capacitance value Ca of air. By taking δ = (Cx / Ca), it is possible to calculate physical properties and the like of the object to be measured.

  In the sensor device of the present embodiment, the calculation method in the calculation unit 40 varies depending on the measurement object. For example, when the sensor device 1 is configured as a skin sensor that measures the moisture content of the skin, the moisture content of the skin can be known based on the calculated skin moisture ratio x.

  In the case of calculating the physical property x of the object to be measured by the method of calculating the difference or the ratio between the capacitance value of air and the object to be measured, such as the capacitance type sensor of this embodiment, Although it is influenced by the conditions such as the environmental humidity and the hardness of the object to be measured, the effect of the expansion of the measurement area is larger, and the influence of these conditions can be almost ignored.

  The sensor device of the present embodiment can be configured as a touch sensor, a monitoring sensor of the liquid volume in the pack, or the like, in addition to the skin sensor that measures the amount of skin moisture. The process in the calculation unit 40 will be described with respect to an example in which the sensor device of the present embodiment is configured as a specific sensor.

(Skin sensor)
FIG. 7 is a view showing an example of the state of the measurement area when the sensor device of the present embodiment is configured as a skin sensor. As shown in FIG. 7, in the case of the skin sensor, the measurement object 106 is the skin T1. In the case of the skin sensor, there is no object to be measured in the measurement area of the sensor device, that is, the capacitance value Ca (= ε _a × S / d) when air is present in the measurement area, and the sufficiently dried skin Capacitance value C ₁ (= ε ₁ × S / d) when present in the measurement region, and capacitance value C ₂ (= ε ₂ × S / d when the sufficiently wet skin is present in the measurement region It is necessary to measure in advance. Here, S corresponds to the electrode area constituting the capacitance, and d corresponds to the distance between the electrodes.

  When the sensor device is a skin sensor, there are two calculation methods in the calculation unit 40.

As the first method, the moisture content of the skin can be calculated by determining the ratio δ of the capacitance value Cx of the skin T1 to the capacitance value Ca of air. In this case, the capacitance value Cx when the skin of unknown water content is present in the measurement area as the measurement object is the capacitance value of air Ca and when the sufficiently dried skin is present in the measurement area Using capacitance value C ₁ and capacitance value C ₂ when sufficiently moist skin exists in the measurement area,
Cx / Ca = is given by _{{(C 2 -C 1) /} Ca} x + C 1 / Ca ··· ( Equation 1). Here, x indicates a skin moisture percentage which is a measure of skin moisture, and x = 0 indicates that the skin is sufficiently dry and x = 1 indicates that the skin is sufficiently moist.

  Therefore, the moisture content x of the skin can be calculated by measuring the capacitance value Cx of the measurement object and substituting it into the above (formula 1), that is, the skin moisture amount can be calculated.

As another method, the moisture amount of the skin can be calculated by obtaining the difference ΔC of the capacitance value Cx of the skin T1 with respect to the capacitance value Ca of air. In this case, the capacitance value Cx when the skin of unknown water content is present in the measurement area as the measurement object is the capacitance value of air Ca and when the sufficiently dried skin is present in the measurement area Using capacitance value C ₁ and capacitance value C ₂ when sufficiently moist skin exists in the measurement area,
_{Cx-Ca = (C 2 -C} 1) is given by x + C ₁ -Ca ··· (Equation 2).

  Therefore, the moisture content x of the skin can be calculated by measuring the capacitance value Cx of the measurement object and substituting it in the above (formula 2), that is, the skin moisture amount can be calculated.

(Touch sensor)
FIG. 8 is a view showing an example of the state of the measurement region when the sensor device of the present embodiment is configured as a touch sensor. In the case of a touch sensor, the normal measurement object 106 is a hand, but as shown in FIG. 8, the measurement object 106 may be a hand T2 wearing a glove T3.

  In the case of a touch sensor, the capacitance value in the case where the hand T2 wearing the glove T3 enters the detection area of the capacitance type sensor 10 (detection state) is determined in advance, and the electrostatic capacitance measured in the detection state A touch is detected depending on whether or not the capacitance value is exceeded with the capacitance value as a threshold value.

  When configured as a touch sensor, measure the capacitance value when air is present in the measurement area before making it into the detection state, and calibrate the sensor (correct the threshold value) to determine the touch detection accuracy. It can be improved.

  When the capacitive sensor 10 of the present embodiment is used as a touch sensor, the touch detection sensitivity in the state where the glove T3 is worn is increased. For example, since the glove is an insulating material, in the conventional flat insulating layer configuration, the thickness of the glove T3 interferes with the amount of penetration of the hand T2 which is a conductor into the detection area, so that the touch is reduced. In the configuration of the capacitance type sensor 10 according to this embodiment, that is, the configuration of the insulating layer having a concave cross section, the glove T3 is pressed into the concave cross section and detection is performed. Possible or strong signal.

(Liquid volume monitoring sensor)
FIG. 9 is a view showing an example of the state of the measurement area when the sensor device of the present embodiment is configured as a liquid volume monitoring sensor. As shown in FIG. 9, in the case of a liquid volume monitoring sensor, the measurement object 106 is a pack T4 which is a container of liquid and a liquid T5 in the pack. In the case of a liquid volume monitoring sensor, there is no measurement object in the measurement area of the sensor device, that is, the capacitance value Ca (= ε _a × S / d) when air is present in the measurement area, and an empty pack ( the capacitance value C ₁ when empty) is present in the measurement region and _{(= ε 1 × S / d} ), the capacitance value C ₂ when the pack flooded condition exists in the measurement area (= epsilon It is necessary to measure ₂ × S / d in advance. Here, S corresponds to the electrode area constituting the capacitance, and d corresponds to the distance between the electrodes.

  When the sensor device is a liquid volume monitoring sensor, the calculation unit 40 has two calculation methods.

As the first method, the amount of liquid in the pack, ie, the water level in the pack, is obtained by determining the ratio δ of the combined capacitance value Cx of the pack T4 and the liquid T5 to the capacitance value Ca of air. Can be calculated. In this case, the capacitance value Cx in the case where a pack with an unknown water level exists in the measurement area as the measurement object is the capacitance value Ca of air and the capacitance value C _{1 in the} empty state. Using the capacitance value C ₂ when the liquid is full,
Cx / Ca = is given by _{{(C 2 -C 1) /} Ca} x + C 1 / Ca ··· ( Equation 3). Here, x indicates a water level ratio in the pack, and x = 0 indicates an empty state, and x = 1 indicates a liquid level in a full liquid state.

  Therefore, the water level rate x in the pack can be calculated by measuring the capacitance value Cx of the object to be measured and substituting it in the above (Equation 3), that is, calculating the liquid volume of the pack it can.

As another method, the water level of the pack, that is, the liquid volume can be calculated by determining the difference ΔC of the combined capacitance value Cx of the pack T4 and the liquid T5 with respect to the capacitance value Ca of air. . In this case, the electrostatic capacitance value Cx when the pack of unknown water level present in the measuring region of the measuring object, and the capacitance value Ca of air, the capacitance value C ₁ of the pack of empty, Using the capacitance value C ₂ of the pack in the full liquid state,
Cx-Ca = (C2-C1) x + C1-Ca (Equation 4).

  Therefore, the water level ratio x in the pack can be obtained by measuring the capacitance value Cx of the object to be measured and substituting it in the above (Equation 4), that is, the liquid volume of the pack can be calculated. .

  In this embodiment, in order to illustrate the effect of the capacitive sensor described in the above embodiment, the detection response amount ΔC (the capacitance value Cx of the object to be measured is compared with the capacitive sensor of the conventional configuration. Of air and the capacitance value Ca of the air) were measured. In the present embodiment, the measurement object is skin.

  The capacitance type sensor 10 used in this embodiment has a configuration as shown in FIG. 4 and FIG. 5, and the electrode pairs 12a and 12b in the capacitance type sensor 10 have Line / Space = 200 μm / 200 μm, comb teeth The conductive paste is formed so that the number of the electrodes is 12 pairs (3 pairs in FIGS. 4 and 5) and the electrode length is 8.6 mm. The insulating films 13a and 13b in the capacitance type sensor 10 are formed of an ultraviolet curable resin having an insulating property so that Line / Space = 240 μm / 160 μm.

  As a comparative example, the same as the above-described capacitance type sensor 10 except that the conventional configuration, that is, the insulating film is uniformly applied to the electrode pair forming surface of the base so that the cross section concave portion is not formed on the base The amount of detection response ΔC was measured using a capacitive sensor having a configuration.

  The measurement conditions were such that an alternating current voltage with a measurement frequency of 10 kHz and an applied voltage amplitude of 1 V was applied to the capacitance type sensor, and measurement was performed three times by using a Keysight LCR meter E4980AL.

  FIG. 10 is a diagram showing measurement results of the detection response amount ΔC in each of the capacitance type sensor of the embodiment and the conventional capacitance type sensor as a comparative example. As apparent from FIG. 10, it is understood that the detection response amount ΔC in the case of using the capacitance type sensor of the present embodiment is about 10 times that of the comparative example. That is, it can be said that the measurement sensitivity is dramatically improved.

  As described above, according to the capacitance type sensor of the present embodiment, the measurement area of the sensor can be expanded more than that of the conventional capacitance type sensor, and as a result, the measurement accuracy and the measurement sensitivity are dramatically improved. Can be realized.

Reference Signs List 1 sensor device 10 capacitance type sensor 11 base 12a, 12b electrode 13a, 13b insulating film 20 high frequency power source 30 measurement unit 40 calculation unit 101 base 102 electrode pair 103 insulating layer 105 electric field portion 106 object to be measured

Claims (4)

A non-rigid measurement target having an electric field region formed by applying a predetermined voltage to an electrode pair formed on the main surface of a substrate and an insulating film covering the electrode pair. A capacitance type sensor that inserts an object into the measurement area and presses it against the insulating film to measure the capacitance of the electrode pair,
The electrode pair is patterned so that the pair of electrodes on the main surface of the base has a predetermined distance, and the insulating film is formed along the shape of the patterning to cover the electrode pair on the main surface of the base And
The electric field formed by applying a predetermined voltage to the electrode pair is not only the region on the opposite side of the main surface of the base of the insulating film covering the electrode pair but also the insulating film covering the adjacent electrode pair A capacitive sensor characterized in that it is also formed in opposing regions.   The capacitance type sensor according to claim 1, wherein the insulating film is formed of an easily processable insulating material. A capacitive sensor according to claim 1 or 2;
A high frequency power supply for applying an alternating voltage to an electrode pair of the capacitive sensor;
What is claimed is: 1. A sensor device comprising: a measuring unit that measures a capacitance of an electrode pair of the capacitive sensor to which the alternating voltage is applied.   The sensor device according to claim 3, wherein the amount of moisture on the skin is detected based on the measured capacitance value.

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