JP2019027977A - Capacitance detector and sensor device - Google Patents

Abstract

To provide a capacitance detector that can detect capacitance of a sensor highly linearly.SOLUTION: A capacitance detector 20 detects capacitance of a sensor element 5 which changes according to input from the outside. The capacitance detector 20 includes: a rectification part 32 for rectifying sensor output as a current signal output from the sensor element 5 by application of a carrier voltage of a predetermined frequency; a low-pass filter part 33 for removing the signal component of the frequency of a carrier voltage included in the rectification signal output from the rectification part 32; and a current voltage conversion unit 34 for converting the output of the low-pass filter 33 into a voltage signal and outputting the voltage signal as a result of detection of the capacitance.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a capacitance detection device and a sensor device.

Conventionally, a capacitance type sensor device includes a capacitance type sensor composed of a capacitance element whose capacitance changes in response to an external input, and detects the capacitance of the capacitance type sensor. Some have a capacitance detecting device for outputting.
For example, a capacitance detection device described in Patent Document 1 rectifies a voltage application element for applying a rectangular wave having a predetermined period to a capacitance type sensor, and a sensor output output from the sensor by the application of the rectangular wave. And a detection resistor for taking out the output of the rectifier as a voltage signal (see, for example, Patent Document 1).

Japanese Patent No. 5326042

  For example, when the capacitance of a sheet-like capacitive sensor that can be attached to the surface of a living body and can detect deformation of the surface of the living body is detected by the capacitance detection device, the surface of the living body can be detected with a simple configuration. In order to detect the deformation with high accuracy, it is required to detect the capacitance of the sensor representing the deformation state of the living body surface with high linearity.

FIG. 8 is a circuit diagram showing an example of a conventional electrostatic capacitance detection device. In FIG. 8, the capacitance detection device 100 extracts a capacitance-type sensor 101, a voltage element 102 that applies a rectangular wave with a predetermined period to the sensor 101, a rectifier 103, and an output of the rectifier 103 as a voltage. Detection resistor 104, a capacitive element 105 for smoothing the signal, and an amplifier 106 that amplifies and outputs the voltage across the detection resistor 104.
The capacitance detection device 100 is configured to output the voltage across the detection resistor 104 (a signal obtained by amplifying the voltage) as a detection result.

Here, since the detection resistor 104 is connected in series with the sensor 101, the voltage across the detection resistor 104 is a voltage obtained by dividing the voltage from the voltage element 102 with the sensor 101.
In the capacitance detection device 100, the larger the capacitance of the sensor 101, the larger the current flowing through the detection resistor 104, so the voltage across the detection resistor 104 increases. As a result, the voltage across the sensor 101 decreases accordingly.
That is, as the capacitance of the sensor 101 increases and the voltage across the detection resistor 104 increases, the voltage applied to the sensor 101 decreases, the current from the sensor 101 decreases, and the voltage across the detection resistor 104 decreases. Work in the direction to let you.

For this reason, if the capacitance of the sensor 101 increases, the voltage across the detection resistor 104 increases accordingly, while the voltage applied to the sensor 101 decreases and the current from the sensor 101 decreases. The increase in the voltage across the detection resistor 104 becomes smaller with respect to the increase in the electrostatic capacity.
As a result, when the capacitance of the sensor 101 is relatively small and when it is relatively large, the increment of the voltage across the detection resistor 104 with respect to the increment of the capacitance of the sensor 101 is different. The linearity at the time of detecting a capacity | capacitance will fall.

For example, if the resistance value of the detection resistor 104 is set smaller with respect to the decrease in the linearity of the detected capacitance, the voltage value across the detection resistor 104 is suppressed even if the current flowing through the detection resistor 104 increases. It is possible to detect the capacitance of the sensor 101 with higher linearity by suppressing the decrease in the applied voltage to the sensor 101.
However, this is not preferable because the voltage across the detection resistor 104 becomes small, and there is a need to provide an amplifier immediately after the detection resistor 104 or increase the amplification factor of the amplifier 105 at the subsequent stage.

  When such a conventional capacitance detection device is used in a sheet-like capacitance sensor for detecting deformation of a living body surface, the capacitance between the sensor and the output of the capacitance detection device is Because of the low linearity, it is impossible to appropriately detect the deformation of the living body surface.

  This invention is made | formed in view of such a situation, and it aims at providing the electrostatic capacitance detection apparatus which can detect the electrostatic capacitance of a sensor with high linearity.

(1) The present invention is a capacitance detection device that detects a capacitance of a capacitance type sensor whose capacitance changes in response to an input from the outside. A rectifier that rectifies a sensor output that is a current signal output from a capacitive sensor; a low-pass filter that removes a signal component of the frequency of the carrier voltage included in the rectified signal output from the rectifier; and A current-voltage conversion unit that converts the output of the low-pass filter unit into a voltage signal and outputs the result as a detection result of the capacitance.

According to the capacitance detection device configured as described above, since the current-voltage conversion unit converts the output of the low-pass filter unit into a voltage signal and outputs it as a capacitance detection result, the current-voltage conversion unit In the preceding stage, a signal based on the sensor output can be processed as a current signal.
For this reason, the low-pass filter unit can process a signal given from the previous stage as a current signal. Therefore, the resistance value of the resistance element included in the low-pass filter unit can be set smaller than in the case where the signal given from the previous stage is processed as a voltage signal in the low-pass filter unit.
As a result, it is possible to suppress a decrease in applied voltage to the capacitive sensor when the sensor output is output from the capacitive sensor, and to detect the capacitance of the capacitive sensor with high linearity. be able to.

(2) In the capacitance detection device, a high pass is provided between the capacitance type sensor and the rectifier, and removes a signal component having a frequency lower than the frequency of the carrier voltage included in the sensor output. It is preferable that a filter unit is further provided, and an output of the high-pass filter unit is given to the rectifying unit as the sensor output.
In this case, the sensor output, which is the signal before rectification, can be passed through a high-pass filter unit that removes a signal component having a frequency lower than the frequency of the carrier voltage, resulting from a commercial power supply that appears superimposed on the sensor output. Noise can be removed.

(3) In the capacitance detection device, the high-pass filter unit includes a capacitance element connected between the capacitance type sensor and the rectification unit, and one end of the capacitance type sensor and the capacitance sensor. It is preferable that a resistive element connected between the capacitive element is included.
In this case, the rectified signal provided from the rectifying unit can be processed as a current signal in the high-pass filter unit provided before the current-voltage converting unit. For this reason, it is possible to reduce the resistance value of the resistance element of the high-pass filter unit to such an extent that a decrease in the voltage applied to the capacitive sensor can be suppressed. Thereby, a high pass filter part can be made into a simple structure, maintaining the linearity at the time of detecting the electrostatic capacitance of an electrostatic capacitance type sensor.

(4) In the capacitance detection device, the rectifier unit is connected to the high-pass filter with a first diode connected to the high-pass filter and a forward direction opposite to the first diode. The high-pass filter section includes a third diode connected between the other end of the resistance element and the ground, and a forward direction opposite to the third diode. And a fourth diode connected between the other end of the first electrode and the ground.
When the other end of the resistance element of the high-pass filter section is grounded as it is, the capacitive element of the high-pass filter section is connected in series with the first diode and the second diode, so that the forward voltage of the first diode and the second diode Causes the high-frequency component current shunted to the capacitive element of the high-pass filter section and the low-frequency component current shunted to the resistance element to be different from the original current as the output of the high-pass filter section. May be given to the department. Thereby, there is a possibility that the linearity at the time of detecting the capacitance of the capacitance type sensor is lowered.
In this regard, in this configuration, the high-pass filter unit further includes the third diode and the fourth diode, so that the current flowing through the resistance element of the high-pass filter unit is corrected to be close to the current flowing through the capacitive element of the high-pass filter unit. can do.
As a result, it is possible to further improve the linearity when detecting the capacitance of the capacitance type sensor.

(5) In the capacitance detection device, the first diode, the second diode, the third diode, and the fourth diode may be housed in one package.
In this case, it is possible to suppress a difference in characteristics of each diode due to an environment such as temperature.

(6) Further, the sensor device according to the present invention includes a capacitance type sensor whose capacitance changes in response to an input from the outside, and a capacitance detection that detects the capacitance of the capacitance type sensor. The capacitance detection device rectifies a sensor output that is a current signal output from the capacitance sensor in response to application of a carrier voltage having a predetermined frequency. A low-pass filter that removes a signal component of the frequency of the carrier voltage included in the rectified signal output from the rectifier, and the detection result of the capacitance by converting the output of the low-pass filter into a voltage signal As a current-voltage conversion unit.

  According to the present invention, the capacitance of the sensor can be detected with high linearity.

It is a figure which shows the measurement system containing the sensor apparatus which concerns on one Embodiment. It is a partial enlarged view of a sensor apparatus. (A) is a perspective view which shows an example of a sensor element, (b) is a BB arrow directional cross-sectional view in Fig.3 (a). It is a circuit diagram which shows an example of a structure of an electrostatic capacitance detection apparatus. It is a circuit diagram which shows the structure of the electrostatic capacitance detection apparatus which concerns on a modification. (A) is a graph showing the relationship between the capacitance of the measurement target and the measured value of the voltage of the voltage signal in the example product and the comparative product, (b) in the diagram of (a), It is the graph which showed the relationship between the electrostatic capacitance of a measuring object, and inclination. It is the graph which showed the relationship between the electrostatic capacitance of a measuring object in the 1st Example goods and the 2nd Example goods, and the measured value of the voltage of a voltage signal. It is a circuit diagram which shows an example of the conventional electrostatic capacitance detection apparatus.

Hereinafter, preferred embodiments will be described with reference to the drawings.
[About sensor device]
FIG. 1 is a diagram illustrating a measurement system including a sensor device according to an embodiment, and FIG. 2 is a partially enlarged view of the sensor device.
The measurement system shown in FIG. 1 is a system for measuring a deformation state of a measurement target such as a biological surface, and supplies power to the sensor device 1 for detecting the deformation state of the measurement target. In addition, it includes a data processing device 2 that receives the output of the sensor device 1 and generates measurement data indicating the measurement result of the deformation state of the measurement target, and a computer 3 that manages and displays the measurement data.

The sensor device 1 is formed in a band shape as a whole, and detects the deformation state of the measurement target by being attached to the measurement target such as the surface of a living body. The sensor device 1 is connected to the data processing device 2 by a cable 4 and outputs a detection result through the cable 4. Further, the sensor device 1 is supplied with power necessary for operation from the data processing device 2 through the cable 4.
The sensor device 1 includes a sensor element 5 for detecting a deformation state of a measurement object such as a biological surface and a rigid substrate 6.

3A is a perspective view illustrating an example of the sensor element 5, and FIG. 3B is a cross-sectional view taken along line BB in FIG. 3A.
The sensor element 5 can be expanded and contracted in the plane direction, and constitutes a capacitive element formed in a strip shape.

  As shown in FIGS. 3A and 3B, the sensor element 5 includes a strip-shaped dielectric layer 7 having elasticity, a first electrode layer 8 laminated on the surface of the dielectric layer 7, and a dielectric layer 7. The second electrode layer 9 laminated on the back surface, the first wiring 10 connected to the first electrode layer 8 and exposed at one end of the sensor element 5, and the one end of the sensor element 5 connected to the second electrode layer 9 And the second wiring 11 exposed on the side. In the following description, in each layer, the upper surface in FIG. 3B is referred to as the front surface, and the lower surface in FIG.

The dielectric layer 7 is made of a dielectric material that can be stretched and deformed, and is made of, for example, an elastomer composition containing an elastomer such as urethane rubber. More specifically, examples of the elastomer include natural rubber, isoprene rubber, nitrile rubber (NBR), ethylene propylene rubber (EPDM), styrene-butadiene rubber (SBR), butadiene rubber (BR), and chloroprene rubber (CR). , Silicone rubber, fluorine rubber, acrylic rubber, hydrogenated nitrile rubber, urethane rubber and the like. These may be used alone or in combination of two or more.
The thickness of the dielectric layer 7 is set in consideration of necessary capacitance, stretchability, and detection sensitivity. More specifically, the average thickness of the dielectric layer 7 is preferably 10 to 1000 μm, and more preferably 30 to 200 μm.

The first electrode layer 8, the second electrode layer 9, the first wiring 10 and the second wiring 11 are all made of a conductive composition containing a conductive material such as a carbon nanotube. More specifically, examples of the conductive material include carbon nanotubes, graphene, carbon nanohorns, carbon fibers, conductive carbon black, graphite, metal nanowires, metal nanoparticles, and conductive polymers. These may be used alone or in combination of two or more.
As the conductive material, carbon nanotubes are preferable. This is because it is suitable for forming an electrode layer that deforms following the deformation of the dielectric layer.
In addition to the conductive material, the conductive composition may contain, for example, a binder component and various additives that function as a connecting material for the conductive material.
Examples of the additive include a dispersant for a conductive material, a crosslinking agent for a binder component, a vulcanization accelerator, a vulcanization aid, an anti-aging agent, a plasticizer, a softener, and a colorant. Can be mentioned.

A front-side protective layer 12 that covers the first electrode layer 8 is formed on the surface of the first electrode layer 8. A back side protective layer 13 that covers the second electrode layer 9 is formed on the back surface of the second electrode layer 9. Both the front side protective layer 12 and the back side protective layer 13 are made of the same elastomer composition as that of the dielectric layer 7.
The 1st electrode layer 8 and the 2nd electrode layer 9 function as an electrode by being formed with the said conductive composition.

The first electrode layer 8 and the second electrode layer 9 are formed in substantially the same rectangular shape in plan view, and the dielectric layer 7 is interposed between the first electrode layer 8 and the second electrode layer 9. Yes. The dielectric layer 7 is interposed over almost the entire surface of the first electrode layer 8 and the second electrode layer 9.
Accordingly, the first electrode layer 8, the second electrode layer 9, and the dielectric layer 7 interposed between the first electrode layer 8 and the second electrode layer 9 constitute a capacitive element. That is, the sensor element 5 includes the first electrode layer 8, the second electrode layer 9, and the dielectric layer 7, thereby forming a capacitive element.

In the sensor element 5, the dielectric layer 7 can expand and contract in the surface direction. Further, when the dielectric layer 7 is deformed, the first electrode layer 8 and the second electrode layer 9, and the front side protective layer 12 and the back side protective layer 13 are also deformed following the deformation.
Therefore, when the sensor element 5 is deformed and the dielectric layer 7 is also deformed, the area of both the electrode layers 8 and 9 changes following the deformation in the surface direction of the dielectric layer 7, and the first electrode layer included in the sensor element 5 ( 8, the electrostatic capacitance of the capacitive element by the second electrode layer 9 and the dielectric layer 7 changes.
That is, the capacitance of the sensor element 5 changes in correlation with the deformation amount of the sensor element 5 (change in the area of the electrode layer). Therefore, the capacitance of the sensor element 5 indicates the deformation state of the sensor element 5.

The sensor element 5 is attached to the surface of a measurement target whose surface such as a living body surface such as a joint part of a human body is deformed by utilizing the characteristic that the capacitance changes according to the deformation of the sensor element 5. Used. Accordingly, when the surface of the measurement target is deformed, the sensor element 5 is deformed according to the deformation of the measurement target.
The sensor element 5 is configured to receive an input from the measurement target by being deformed in the same manner as the surface of the measurement target, and output information indicating a deformation state of the measurement target as a capacitance.
That is, the sensor element 5 constitutes a capacitance type sensor whose capacitance changes according to an input from the outside.

  As shown in FIG. 2, the rigid substrate 6 is connected to one end side of the sensor element 5. The rigid substrate 6 is formed in a rectangular shape by glass epoxy resin or the like, for example. The rigid substrate 6 and the sensor element 5 are connected by a non-stretchable sheet 15. The non-stretchable sheet 15 is bonded and fixed to the back surface of the sensor element 5 and is bonded and fixed to the back surface of the rigid substrate 6. Accordingly, the non-stretchable sheet 15 connects the rigid substrate 6 and the sensor element 5. In addition, the adhesion surface of the non-stretchable sheet 15 on the back surface of the sensor element 5 is a position where the first wiring 10 and the second wiring 11 are provided on the surface so that the sensor element 5 does not hinder expansion and contraction in the surface direction. It is a position corresponding to.

  A capacitance detection device 20 and an oscillation circuit 21 are mounted on the surface of the rigid substrate 6. The capacitance detection device 20 has a function of detecting the capacitance of the sensor element 5. The oscillation circuit 21 has a function of generating a carrier voltage and applying it to the sensor element 5. The electrostatic capacity detection device 20 and the oscillation circuit 21 will be described later.

  Further, a first terminal 25 for connecting the sensor element 5 to the capacitance detection device 20 and a second terminal 26 for connecting the sensor element 5 to the oscillation circuit 21 are provided on the surface of the rigid substrate 6. ing. Further, a cable terminal 27 for connecting the cable 4, the capacitance detection device 20, and the oscillation circuit 21 is provided on the surface of the rigid substrate 6.

  The first wiring 10 is connected to the first terminal 25 by a conductive adhesive layer 25a. The second wiring 11 is connected to the second terminal 26 by a conductive adhesive layer 26a. One of the first wiring 10 and the second wiring 11 is connected to the capacitance detection device 20, and the other is connected to the oscillation circuit 21. Therefore, the first wiring 10 of the sensor element 5 is connected to the capacitance detection device 20, and the second wiring 11 of the sensor element 5 is connected to the oscillation circuit 21.

The lead wire 4a extending from the cable 4 is connected to the cable terminal 27 by solder connection.
As a result, the capacitance detection device 20 and the oscillation circuit 21 are connected to the sensor element 5 and to the data processing device 2.

The capacitance detection device 20 gives the detection result of the capacitance of the sensor element 5 to the data processing device 2 through the cable 4.
Further, the capacitance detection device 20 and the oscillation circuit 21 are supplied with power necessary for operation from the data processing device 2 through the cable 4.

  As shown in FIG. 1, the capacitance detection device 20 and the oscillation circuit 21 are covered with a sealing material 29 for protecting the capacitance detection device 20 from the external environment.

[Circuit configuration of capacitance detection device]
FIG. 4 is a circuit diagram showing an example of the configuration of the capacitance detection device 20.
In FIG. 4, an oscillation circuit 21 is connected to one end (second wiring 11) of the sensor element 5. In addition, a capacitance detection device 20 is connected to the other end (first wiring 10) of the sensor element 5.
The oscillation circuit 21 has a function of generating a rectangular wave having a predetermined frequency and applying the generated rectangular wave to the sensor element 5 as a carrier voltage. In the present embodiment, the oscillation circuit 21 oscillates a rectangular wave having a frequency of 5 kHz.

When the carrier voltage generated by the oscillation circuit 21 is applied, the sensor element 5 constituting the capacitive element outputs a sensor output that is a current signal corresponding to the capacitance of the sensor element 5 by the application of the carrier voltage. .
The sensor output output from the sensor element 5 by the application of the carrier voltage includes a signal component having a frequency of the carrier voltage, and the amplitude thereof indicates the capacitance of the sensor element 5. That is, the envelope of the sensor output indicates a change in the capacitance of the sensor element 5.
As described above, the sensor output is output as a signal obtained by modulating the signal component indicating the capacitance of the sensor element 5 with the signal having the frequency of the carrier voltage.
The sensor output of the sensor element 5 is given to the capacitance detection device 20.

The capacitance detection device 20 includes a high-pass filter unit 31, a rectification unit 32, a low-pass filter unit 33, and a current-voltage conversion unit 34.
The high-pass filter unit 31 is provided between the sensor element 5 and the rectifying unit 32, and a sensor output from the sensor element 5 is given.
The high-pass filter unit 31 includes a capacitive element 31a, a resistive element 31b, a capacitive element 31c, and a resistive element 31d, and constitutes a secondary high-pass filter.

  The high pass filter unit 31 further includes a third diode 41 and a fourth diode 42 between the resistance element 31b and the resistance element 31d and the ground. The third diode 41 and the fourth diode 42 will be described later.

The high-pass filter unit 31 is set so that the cutoff frequency is lower than the frequency of the carrier voltage so that a signal component having a frequency lower than the frequency of the carrier voltage included in the sensor output can be removed. The cutoff frequency of the high-pass filter unit 31 is set to a frequency that is at least higher than the frequency of the commercial power supply.
In this case, by providing the sensor output before rectification to the high-pass filter unit 31, it is possible to pass the noise, and noise caused by a commercial power supply or the like that may appear superimposed on the sensor output can be removed.
Therefore, the output of the high-pass filter unit 31 includes a sensor output from which noise caused by a commercial power source or the like is removed.

In addition, since the high-pass filter unit 31 of this embodiment is configured as a so-called passive filter that does not include an operational amplifier, even if a signal that rises instantaneously or falls instantaneously is given, it is not saturated. A given signal can be passed.
For this reason, a carrier voltage can be made into a rectangular wave. In this case, the sensor output from the sensor element 5 is a rectangular wave, but the high-pass filter unit 31 can pass the sensor output without being saturated.
In addition, since the carrier voltage can be a rectangular wave, the number of components can be reduced and the cost can be reduced by making the oscillation circuit 21 simple.
In addition, although the case where the high-pass filter part 31 of this embodiment was comprised with the capacitive element and the resistive element was illustrated, it may be comprised with an inductive element (inductor) and a resistive element, and is comprised with a capacitive element and an inductive element. May be. Moreover, you may comprise with a capacitive element, an induction element, and a resistive element.

The rectifying unit 32 includes a first diode 32a whose cathode side is connected to the high-pass filter unit 31, and a second diode 32b whose anode side is connected to the high-pass filter unit 31, and constitutes a half-end rectifier circuit.
The output of the high-pass filter unit 31 is given to the rectifying unit 32 as a sensor output.
The rectification unit 32 rectifies the output of the high-pass filter unit 31 and provides the rectified rectified signal to the subsequent low-pass filter unit 33.

The low-pass filter unit 33 is provided between the rectification unit 32 and the current-voltage conversion unit 34, and receives a rectification signal from the rectification unit 32 that is a current signal.
The low-pass filter unit 33 includes a resistive element 33a, a capacitive element 33b, a resistive element 33c, and a capacitive element 33d, and constitutes a secondary low-pass filter.

The low-pass filter unit 33 is set to a cutoff frequency that allows passage of a signal component indicating the capacitance of the sensor element 5 and can remove a signal component having a frequency of the carrier voltage.
As a result, the low-pass filter unit 33 passes the signal component indicating the capacitance of the sensor element 5 and removes the signal component having the frequency of the carrier voltage from the rectified signal output from the rectifying unit 32.
Therefore, the output of the low-pass filter unit 33 from which the signal component of the carrier voltage frequency has been removed includes a signal component indicating the capacitance of the sensor element 5.
The output of the low-pass filter unit 33 is given to the current-voltage conversion unit 34.

  The current-voltage conversion unit 34 converts the output of the low-pass filter unit 33 including a signal component indicating the capacitance of the sensor element 5 into a voltage signal. The current-voltage conversion unit 34 outputs the converted voltage signal as a detection result of the capacitance of the sensor element 5.

The current-voltage conversion unit 34 includes an operational amplifier 34a, a feedback resistor 34b, and a capacitive element 34c. The operational amplifier 34a converts the current flowing through the feedback resistor 34b into a voltage, thereby converting the output of the low-pass filter 33, which is a current signal, into a voltage signal.
The capacitive element 34 c functions as a low-pass filter for removing noise superimposed on the output of the low-pass filter unit 33.
Note that the current-voltage conversion unit 34 is connected so that the output of the low-pass filter unit 33 can be given to the inverting input terminal. This is because the rectification unit 32 is configured to rectify the output of the high-pass filter unit 31 to the minus side and invert the signal on the minus side.

The voltage signal output by the current-voltage conversion unit 34 as the capacitance of the sensor element 5 is given to the data processing device 2 via the cable 4 as the output of the sensor device 1.
The data processing device 2 to which the voltage signal output by the current-voltage conversion unit 34 is given generates measurement data indicating the measurement result of the deformation state of the measurement target based on the voltage signal. The data processing device 2 stores a table in which information indicating the deformation state of the sensor element 5 and a voltage signal value indicating the detection result of the capacitance of the sensor element 5 are associated with each other. When the voltage signal is given from the sensor device 1, the data processing device 2 refers to the table and acquires information indicating the deformation state of the sensor element 5 according to the voltage signal. The data processing device 2 gives information indicating the acquired deformation state of the sensor element 5 to the computer 3 as measurement data.
The computer 3 to which the measurement data is given displays the measurement data for the user or stores and manages it.

According to the electrostatic capacitance detection device 20 configured as described above, the output of the low-pass filter unit 33 is converted into a voltage signal and output as a detection result of the electrostatic capacitance. In, a signal based on the sensor output can be processed as a current signal.
For this reason, in the low-pass filter part 33, the rectification signal which is a signal given from the preceding stage can be processed as a current signal. Therefore, the resistance values of the resistance elements 33a and 33c included in the low-pass filter unit 33 can be set smaller than in the case where the signal provided from the previous stage is processed as a voltage signal in the low-pass filter unit 33.
As a result, it is possible to suppress a decrease in the voltage applied to the sensor element 5 when the sensor output is output from the sensor element 5, and to detect the capacitance of the sensor element 5 with high linearity.

  In the present embodiment, the high-pass filter unit 31 includes capacitive elements 31a and 31c connected between the sensor element 5 and the rectifying unit 32, and one end connected between the sensor element 5 and the capacitive element 31a. The resistor element 31b is configured to include a resistor element 31d having one end connected between the capacitor element 31a and the capacitor element 31c.

Therefore, the resistance values of the resistance elements 31b and 31d of the high-pass filter section 31 can be reduced to such an extent that a decrease in the voltage applied to the sensor element 5 can be suppressed, similarly to the resistance elements 33a and 33c of the low-pass filter section 33.
Thereby, it can be set as the simple structure of comprising the high pass filter part 31 by a capacitive element and a resistive element, maintaining the linearity at the time of detecting the electrostatic capacitance of the sensor element 5. FIG.

  Further, when the other ends of the resistance elements 31b and 31d of the high-pass filter section 31 are grounded as they are, the capacitive elements 31a and 31c of the high-pass filter section 31 are connected in series to the first diode 32a and the second diode 32b. Therefore, a high-frequency component current that is shunted to the capacitive elements 31a and 31c of the high-pass filter unit 31 by a forward voltage of the first diode 32a and the second diode 32b, and a low-frequency component current that is shunted to the resistance elements 31b and 31d May be different, and a current different from the original current as the output of the high-pass filter unit 31 may be applied to the rectifier unit 32. Thereby, there exists a possibility that the linearity at the time of detecting the electrostatic capacitance of the sensor element 5 may fall.

In this regard, the high-pass filter unit 31 of the present embodiment includes a third diode 41 connected between the resistance elements 31b and 31d and the ground, and a forward direction opposite to the third diode 41 so that the resistance element 31b. , 31d and a fourth diode 42 connected to the ground.
The third diode 41 has an anode connected to the other ends of the resistance elements 31b and 31d, and a cathode connected to the ground. The fourth diode 42 has a cathode connected to the other ends of the resistance elements 31b and 31d and an anode connected to the ground.

In the present embodiment, the high-pass filter unit 31 further includes a third diode 41 and a fourth diode 42, so that the current flowing through the resistance elements 31b and 31d of the high-pass filter unit 31 can be converted into the capacitive elements 31a and 31c of the high-pass filter unit 31. It can correct | amend so that it may approximate the electric current which flows into.
As a result, the linearity when the electrostatic capacitance detection device 20 detects the electrostatic capacitance of the sensor element 5 can be further improved.

[Others]
The present invention is not limited to the above embodiment.
For example, the first diode 32a, the second diode 32b, the third diode 41, and the fourth diode 42 may be accommodated in one package.
In this case, it is possible to suppress a difference in characteristics of each diode due to an environment such as temperature. As a result, the linearity when the electrostatic capacitance detection device 20 detects the electrostatic capacitance of the sensor element 5 can be further improved.

  In the above embodiment, the case where the high-pass filter unit 31 includes the third diode 41 and the fourth diode 42 is illustrated. However, when the influence of the forward voltage of the third diode 41 and the fourth diode 42 is not large. May be configured such that the other ends of the resistance elements 31b and 31d are directly grounded and the third diode 41 and the fourth diode 42 are not provided.

Moreover, in the said embodiment, although the case where the high-pass filter part 31 was provided between the sensor element 5 and the rectification | straightening part 32 was illustrated, as shown in FIG. 5, when the noise of a commercial power source does not become a problem, for example In addition, the sensor element 5 and the rectifying unit 32 may be connected so that the sensor output of the sensor element 5 is supplied to the rectifying unit 32, and the high-pass filter unit 31 may not be provided.
In this case, there is no noise removal function by the high-pass filter, but there is an advantage that the configuration of the capacitance detection device 20 can be made compact.
In this configuration, when it is necessary to remove noise from the commercial power source, noise caused by the commercial power source or the like can be eliminated by setting the cutoff frequency of the low-pass filter unit 33 to a frequency lower than the frequency of the commercial power source. . Further, unnecessary frequency data can be deleted by the computer 3 managing the measurement data.

[About verification test]
Next, the result of verifying the linearity when detecting the capacitance in the capacitance detection device 20 will be described.

In this verification test, the above-described capacitance detection device 20 shown in FIG. 4 was used as an example product, and the capacitance detection device 100 shown in FIG. 8 was used as a comparative example product.
The test method is to prepare a plurality of capacitive elements with different capacitances, and measure the voltage of the voltage signal output from the example product and the comparative product when each of these multiple capacitive elements is connected. The linearity of the voltage signal with respect to the capacitance of was evaluated.
The example product and the comparative product were set so as to output approximately the same power signal with respect to the capacitance to be measured.

FIG. 6A is a graph showing the relationship between the capacitance of the measurement target and the measured value of the voltage of the voltage signal in the example product and the comparative example product. In FIG. 6A, the horizontal axis indicates the capacitance to be measured, and the vertical axis indicates the voltage of the voltage signal. In FIG. 6A, a diagram L1 shows the measurement result of the example product, and a diagram L2 shows the measurement result of the comparative product.
As shown in FIG. 6A, in the example product, the relationship between the capacitance to be measured and the voltage signal appears almost linearly. On the other hand, it can be seen that the comparative product is slightly curved upward in the drawing.

FIG. 6B is a graph showing the relationship between the capacitance to be measured and the inclination in the diagram of FIG. In FIG. 6B, the horizontal axis indicates the capacitance to be measured, and the vertical axis indicates the slope corresponding to the electrostatic capacitance of the diagram of FIG. 6A and the average value of the slope of the diagram. The value divided by. In other words, a value obtained by dividing the differential value corresponding to the capacitance in the diagram of FIG. 6A by the average value of the differential value is shown. That is, the vertical axis shows a normalized change in the slope of the diagram of FIG. In FIG. 6B, a diagram L3 shows the measurement result of the example product, and a diagram L4 shows the measurement result of the comparative product.
As shown in FIG. 6B, in the example product, the value of the inclination with respect to the capacitance of the measurement object changes in the range of 0.95 to 1.05, whereas in the comparative product, The value of the inclination with respect to the capacitance of the measurement object changes in the range of 0.90 to 1.10, and it can be seen that the degree of change in inclination is smaller in the example product than in the comparative product.

From these results, it can be confirmed that the example product has better linearity in detecting the capacitance than the comparative example product.
From the above, according to the capacitance detection device according to the example product, it was confirmed that the capacitance of the capacitance type sensor can be detected with high linearity.

  Next, the result of verifying the effects of the third diode 41 and the fourth diode 42 provided in the high-pass filter unit 31 will be described.

In this verification test, the above-described capacitance detection device 20 shown in FIG. 4 is used as the first embodiment product, and the above-described capacitance detection device 20 shown in FIG. Except for the third diode 41 and the fourth diode 42, the other end of the resistance elements 31b and 31d was directly grounded.
The test method is the same as described above, and a plurality of capacitive elements having different electrostatic capacities are prepared, and the voltage of the voltage signal output from the example product and the comparative example product when each of the plurality of capacitive elements is connected is measured. Thus, the linearity of the voltage signal with respect to the capacitance of the measurement object was evaluated.

  FIG. 7 is a graph showing the relationship between the capacitance of the measurement target and the measured value of the voltage of the voltage signal in the first embodiment product and the second embodiment product. In FIG. 7, the horizontal axis indicates the capacitance to be measured, and the vertical axis indicates the voltage of the voltage signal. In FIG. 7, a line L5 shows the measurement results of the first embodiment product, and a line L6 shows the measurement results of the second embodiment product.

  As shown in FIG. 7, in the first embodiment product in which the third diode 41 and the fourth diode 42 are provided in the high-pass filter unit 31, the relationship between the capacitance to be measured and the voltage signal is substantially linear. Appears. On the other hand, it can be seen that the second embodiment product is slightly curved downward in the drawing.

From this result, the degree of change in inclination is smaller in the first embodiment product than in the second embodiment product, and the first embodiment product detects the capacitance more than the second embodiment product. It can be confirmed that the linearity of is good.
From the above, it was found that providing the third diode 41 and the fourth diode 42 in the high-pass filter portion 31 can further improve the linearity when detecting the capacitance of the sensor element 5.

DESCRIPTION OF SYMBOLS 1 Sensor apparatus 2 Data processing apparatus 3 Computer 4 Cable 4a Lead wire 5 Sensor element 6 Rigid board 7 Dielectric layer 8 1st electrode layer 9 2nd electrode layer 10 1st wiring 11 2nd wiring 12 Front side protective layer 13 Back side protective layer 15 Non-stretchable sheet 20 Capacitance detection device 21 Oscillation circuit 25 First terminal 25a Conductive adhesive layer 26 Second terminal 26a Conductive adhesive layer 27 Terminal for cable 29 Sealing material 31 High-pass filter portion 31a Capacitance element 31b Resistance Element 31c Capacitor 31d Resistor 32 Rectifier 32a First diode 32b Second diode 33 Low pass filter 33a Resistor 33b Capacitor 33c Resistor 33d Capacitor 34 Current-voltage converter 34a Operational amplifier 34b Feedback resistor 34c Capacitor 41 Third Diode 42 4th Diode

Claims (6)

A capacitance detection device that detects a capacitance of a capacitance type sensor whose capacitance changes in response to an external input,
A rectifier that rectifies a sensor output that is a current signal output from the capacitive sensor by applying a carrier voltage of a predetermined frequency;
A low-pass filter that removes a signal component of the frequency of the carrier voltage included in the rectified signal output by the rectifier;
And a current-voltage conversion unit that converts the output of the low-pass filter unit into a voltage signal and outputs the voltage signal as a detection result of the capacitance. A high-pass filter unit that is provided between the capacitance type sensor and the rectifying unit and removes a signal component having a frequency lower than the frequency of the carrier voltage included in the sensor output;
The capacitance detection device according to claim 1, wherein an output of the high-pass filter unit is given to the rectifying unit as the sensor output. The high-pass filter unit includes a capacitive element connected between the capacitive sensor and the rectifying unit, a resistive element having one end connected between the capacitive sensor and the capacitive element, The electrostatic capacitance detection apparatus of Claim 2 containing. The rectifying unit includes: a first diode connected to the high-pass filter; and a second diode connected to the high-pass filter with a forward direction opposite to the first diode.
The high-pass filter unit is
A third diode connected between the other end of the resistive element and ground;
The capacitance detection device according to claim 3, further comprising a fourth diode having a forward direction opposite to the third diode and connected between the other end of the resistance element and the ground. The capacitance detection device according to claim 4, wherein the first diode, the second diode, the third diode, and the fourth diode are accommodated in one package. A sensor device comprising: a capacitance type sensor whose capacitance changes in response to an external input; and a capacitance detection device that detects the capacitance of the capacitance type sensor,
The capacitance detection device is:
A rectifying unit that rectifies a sensor output that is a current signal output from the capacitive sensor in response to application of a carrier voltage of a predetermined frequency;
A low-pass filter that removes a signal component of the frequency of the carrier voltage included in the rectified signal output by the rectifier;
A sensor device comprising: a current-voltage conversion unit that converts an output of the low-pass filter unit into a voltage signal and outputs the voltage signal as a detection result of the capacitance.

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