JP6754320B2 - Capacitance detector and sensor system - Google Patents

Description

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

Conventionally, a capacitance type sensor device has detected a capacitance type sensor composed of a capacitance element whose capacitance changes according to an external input and the capacitance of this capacitance type sensor. Some are equipped with a capacitance detection device that outputs.
For example, the capacitance detection device described in Patent Document 1 has a voltage application element for applying a rectangular wave having a predetermined cycle to an electrode on one end side of a capacitance type sensor, and when the voltage is applied to the electrode on one end side. It includes a rectifier that rectifies the output signal output from the electrode on the other end side of the sensor, and a smoothing capacitor that smoothes the output signal rectified by the rectifier. This capacitance detection device detects an output signal output from the electrode on the other end side of the sensor when the rectangular wave is applied to the electrode on one end side of the sensor, and determines the amplitude of the detected output signal. Based on this, the capacitance of the sensor is determined (see, for example, Patent Document 1).

Japanese Patent No. 5326042

As described above, the output signal of the capacitance type sensor composed of the capacitive element is due to environmental noise such as electromagnetic waves emitted by surrounding electric products, in addition to the signal component based on the capacitance of the sensor. Noise components may be added.
Such environmental noise is often a relatively low frequency such as the frequency of a commercial power supply, and if such a noise component is added to the output signal, it is a factor that lowers the measurement accuracy of the capacitance of the sensor. Therefore, it needs to be removed.
In particular, when the motion of a living body such as a human body is detected by the sensor, the frequency of the signal detected according to the motion appears as a very low frequency, but it may be close to the frequency of a commercial power source, and its measurement accuracy is measured. It should be removed as much as possible to secure it.

In order to remove the noise component from the output signal of the sensor, it is conceivable to provide a low-pass filter for removing the noise after the rectifier.
By providing a low-pass filter, noise components caused by a commercial power source or the like can be removed, and static measurement accuracy can be maintained.

However, when a low-pass filter capable of removing relatively low frequency noise such as noise caused by a commercial power supply is provided, the noise component can be removed from the output signal, but only the relatively low frequency component remains as a signal component. Therefore, the change of the output signal after passing through the low-pass filter becomes excessively gentle, which may reduce the responsiveness of the output signal to the change of the capacitance of the sensor.

When the responsiveness of the output signal to a change in the capacitance of the sensor decreases, for example, when trying to dynamically measure the change in the capacitance of the sensor, the output signal follows the change in the capacitance of the sensor body. This is not possible, and there arises a problem that the accuracy of the capacitance measurement result is lowered.

In other words, the cutoff frequency of the low-pass filter provided after the rectifier to remove noise must be set lower than the frequency of the noise to be removed, and if such a low-pass filter is provided, it is static. The measurement accuracy can be maintained, but the dynamic measurement accuracy may decrease.

The present invention has been made in view of such circumstances, and is capable of removing noise added to the output signal of a sensor while suppressing a decrease in responsiveness to a change in the capacitance of the sensor. It is an object of the present invention to provide a device and a sensor system.

The present invention is a capacitance detection device that detects the capacitance of a capacitance type sensor whose capacitance changes in response to an external input, and the carrier voltage of the capacitance type sensor has a predetermined cycle. A voltage supply unit that applies a voltage signal, a conversion unit that converts a sensor output signal, which is a current signal output from the capacitance type sensor in response to the application of the carrier voltage, into a voltage signal, and a conversion unit that converts the voltage signal. A rectifying unit that rectifies the sensor output signal, a low-pass filter unit that removes the frequency component of the carrier voltage included in the sensor output signal rectified by the rectifying unit, and a connection between the conversion unit and the rectifying unit. The filter unit includes a filter unit that allows the signal output signal to pass through, and the filter unit sets the lower limit of the frequency band that allows the passage of signal components to be higher than the frequency of environmental noise around the capacitance type sensor. The cutoff frequency of the low-pass filter unit is set higher than the frequency of the environmental noise.

According to the capacitance detection device configured as described above, the lower limit of the frequency band connected between the conversion unit and the rectifying unit and allowing the passage of signal components is the environment around the capacitance type sensor. Since the filter unit is set higher than the noise frequency, for example, even if environmental noise is added to the sensor output signal, the noise can be removed by this filter unit.
Further, in the low-pass filter section after the rectifying section, it is not necessary to remove the environmental noise, and the cutoff frequency of the low-pass filter section can be set higher than the frequency of the environmental noise. As a result, the cutoff frequency of the low-pass filter section in the subsequent stage of the rectifier must be set lower than the frequency of the environmental noise in order to remove the environmental noise. This makes it possible to suppress a decrease in the responsiveness of the sensor output signal to a change in the capacitance of the capacitance type sensor.
As described above, according to the present invention, it is possible to remove noise added to the sensor output signal of the capacitance type sensor while suppressing a decrease in responsiveness to a change in capacitance of the capacitance type sensor. it can.

In the capacitance type sensor, noise such as electromagnetic waves generated by electric products operated by a commercial power source may become environmental noise and be affected by the sensor output signal.
Therefore, in the capacitance detection device, the frequency of the environmental noise may be a frequency determined based on the frequency of the commercial power supply.
In this case, even if electromagnetic waves or the like generated by electrical products or the like around the sensor become environmental noise and noise having a frequency near the frequency of the commercial power supply is added to the sensor output signal, this noise can be reduced by the filter unit.
Further, in order to remove the noise of the frequency of the commercial power supply by the low-pass filter unit as in the above-mentioned conventional example, it is necessary to set the cutoff frequency of the low-pass filter unit lower than the frequency of the commercial power supply, but in the present invention. Since the cutoff frequency of the low-pass filter unit is set higher than the frequency of the commercial power supply, it is possible to suppress a decrease in the responsiveness of the sensor output signal to a change in the capacitance of the capacitance type sensor.
As a result, it is possible to remove noise added to the sensor output signal of the capacitance type sensor while suppressing a decrease in the responsiveness of the capacitance type sensor to a change in capacitance.

Further, in the capacitance detection device, it is preferable that the low-pass filter unit is composed of a secondary or higher-order low-pass filter.
Further, it is preferable that the filter unit is composed of a second-order or higher-order high-pass filter.

Since the sensor output signal is output in response to the application of the carrier voltage, it may include a noise component included in the carrier voltage.
Therefore, the voltage supply unit includes a square wave generation unit that generates a square wave having a predetermined period, and a filter unit that converts the square wave into a signal wave similar to a sine wave, and converts the signal wave into the carrier. The voltage may be applied to the capacitance type sensor.
In this case, since the noise included in the carrier voltage can be reduced, the frequency component of the carrier voltage can be easily removed by the low-pass filter unit, and the noise added to the sensor output signal can be removed more effectively.

The detection device is a detection device that detects the surface state of the sample, and is an irradiation unit that irradiates the surface of the sample with blinking light that blinks at a predetermined cycle, and the blinking light is reflected on the surface of the sample. A light detection unit that detects reflected light and a processing unit that identifies the surface state of the sample based on the change in the reflected light detected by the light detection unit are provided, and the light detection unit detects the reflected light. A light receiving unit that outputs a sensor output signal that is a current signal according to the intensity of light when received, a conversion unit that converts the sensor output signal into a voltage signal, and a rectification of the sensor output signal converted into a voltage signal. The rectifying unit is connected to the low-pass filter unit that removes the frequency component of the carrier voltage contained in the sensor output signal rectified by the rectifying unit and gives it to the processing unit, and the conversion unit and the rectifying unit. The filter unit is provided with a filter unit for passing the sensor output signal, and the lower limit of the frequency band that allows the passage of the signal component is set higher than the frequency of the environmental noise around the light detection unit. The cutoff frequency of the low-pass filter unit is set higher than the frequency of the environmental noise.

Further, the sensor system according to the present invention includes 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. In the sensor system provided, the capacitance detection device includes a voltage supply unit that applies a carrier voltage of a predetermined cycle to the capacitance type sensor, and the capacitance type sensor in response to the application of the carrier voltage. A converter that converts a sensor output signal, which is a current signal output from, into a voltage signal, a rectifier that rectifies the sensor output signal that has been converted into a voltage signal, and a sensor output signal that is rectified by the rectifier. The filter unit includes a low-pass filter unit that removes a frequency component of the carrier voltage included, and a filter unit that is connected between the conversion unit and the rectifying unit and passes the sensor output signal. The lower limit of the frequency band that allows the passage of components is set higher than the frequency of the environmental noise around the capacitance type sensor, and the cutoff frequency of the low-pass filter unit is set higher than the frequency of the environmental noise. There is.

According to the sensor system having the above configuration, it is possible to remove noise added to the sensor output signal of the capacitance type sensor while suppressing a decrease in responsiveness to a change in capacitance of the capacitance type sensor.

According to the present invention, it is possible to remove noise added to the output signal of the sensor while suppressing a decrease in responsiveness to a change in the capacitance of the sensor.

It is a figure which shows the whole structure of the sensor system which concerns on 1st Embodiment. (A) is a perspective view showing an example of a sensor sheet, and (b) is a sectional view taken along line AA of FIG. 2 (a). It is a block diagram which shows an example of the structure of the capacitance detection device. It is a figure which shows the structural example of the conversion part. (A) shows an example of a carrier voltage, and (b) shows an example of an output when the sensor output signal output from the sensor sheet by applying the carrier voltage of (a) is converted by the conversion unit. It is a figure. (A) is a diagram showing an example of the sensor output signal output from the conversion unit, (b) is a diagram showing only the noise component added to the sensor output signal shown in (a), and (c) is a diagram showing only the noise component added to the sensor output signal shown in (a). It is a figure which shows the output from the filter part when the sensor output signal shown in FIG. 6A is given to the filter part. FIG. 6A is a diagram showing the output when the sensor output signal shown in FIG. 6C is applied to the rectifying unit, and FIG. 6B is a diagram showing the output when the sensor output signal shown in FIG. 6C is applied to the second low-pass filter unit. It is a figure which shows the signal wave which sometimes outputs from the 2nd low-pass filter part. It is a block diagram of the sensor system which concerns on 2nd Embodiment. (A) is a diagram showing an aspect when the LED and the light receiving portion are installed on the sample, and (b) is a diagram showing an aspect when dust is attached to the surface of the sample.

Hereinafter, preferred embodiments will be described with reference to the drawings.
[1 First Embodiment]
[1.1 Overall system configuration]
FIG. 1 is a diagram showing an overall configuration of a sensor system according to the first embodiment. In the figure, the sensor system 1 includes a sensor sheet 2 and a capacitance detecting device 3.
The sensor sheet 2 includes a dielectric layer made of an elastomer formed in a planar shape and a pair of electrode layers formed on the front and back surfaces of the dielectric layer so as to sandwich the dielectric layer, and is formed in a planar shape. It constitutes a capacitive element.
The sensor sheet 2 is formed so as to be deformable (expandable) along a direction (plane direction) parallel to the front and back surfaces of the sensor sheet 2. When the sensor sheet 2 is deformed in the surface direction, the area of the electrode layer changes following the deformation of the dielectric layer in the surface direction. Therefore, the capacitance of the sensor sheet 2 changes according to the deformation of the sensor sheet 2.
Utilizing the characteristic that the capacitance of the sensor sheet 2 changes according to the deformation of the sensor sheet 2, the sensor sheet 2 is attached to a movable part of an object to be measured, such as a joint part of a human body, and the movable part thereof. It is used to grasp the movable state of.

The sensor sheet 2 is attached to a movable portion of the object to be measured so as to be deformed according to the movement of the movable portion. When the movable portion of the sensor sheet 2 moves, the sensor sheet 2 also deforms itself, and the capacitance changes according to the deformation.
Therefore, if the movable part is moved with the sensor sheet 2 attached and the correlation between the state of the movable part and the capacitance of the sensor sheet 2 is grasped in advance, the capacitance of the sensor sheet 2 can be obtained. Based on this, the movable state of the object to be measured can be grasped.
As described above, the sensor sheet 2 is configured to output information indicating the movable state of the movable portion of the measurement object as a capacitance. That is, the sensor sheet 2 constitutes a capacitance type sensor whose capacitance changes in response to an external input such as an object to be measured.

The capacitance detection device 3 has a function of detecting the capacitance of the sensor sheet 2. The capacitance detection device 3 applies a carrier voltage of a predetermined cycle to the electrode layer on one side of the sensor sheet 2, and receives a sensor output signal output from the electrode layer on the other side of the sensor sheet 2 according to the carrier voltage. To detect.
The capacitance detection device 3 performs various signal processing on the detected sensor output signal of the sensor sheet 2 to output a detection result signal indicating a change in the detected capacitance of the sensor sheet 2.
The capacitance detection device 3 gives the detection result signal to the information processing device 4 connected to the capacitance detection device 3.

The information processing device 4 generates information indicating the movable state of the movable part of the measurement target based on the detection result signal given from the capacitance detection device 3, and directs the information processing device 4 to the operator of the information processing device 4. Output.

[1.2 Sensor sheet configuration]
FIG. 2A is a perspective view showing an example of the sensor sheet 2, and FIG. 2B is a cross-sectional view taken along the line AA of FIG. 2A.
As shown in FIGS. 2A and 2B, the sensor sheet 2 has a sheet-shaped dielectric layer 11 and front side electrodes formed on the surface (front surface: upper side in FIG. 2) of the dielectric layer 11. The layer 12A, the back side electrode layer 12B formed on the back surface (lower side in FIG. 2) of the dielectric layer 11, the front side wiring 13A having one end connected to the front side electrode layer 12A, and one end connected to the back side electrode layer 12B. The back side wiring 13B, the front side connection terminal 14A attached to the other end of the front side wiring 13A, the back side connection terminal 14B attached to the other end of the back side wiring 13B, and the front side and the back side of the dielectric layer 11 are laminated respectively. The front side protective layer 15A and the back side protective layer 15B, and the adhesive layer 18 laminated on the back side protective layer 15B are provided.

The dielectric layer 11 is a sheet-like material made of an elastomer, and the thickness thereof is set to, for example, 10 to 1000 μm. The dielectric layer 11 is interposed between the front electrode layer 12A and the back electrode layer 12B, and has a function as a dielectric in the capacitive element.
The dielectric layer 11 is formed by using an elastomer composition containing an elastomer and other optional components, and can be reversibly deformed so that the area of the front and back surfaces thereof changes.
Examples of the elastomer include natural rubber, isoprene rubber, nitrile rubber (NBR), ethylene propylene rubber (EPDM), styrene-butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), silicone rubber, and fluorine rubber. Acrylic rubber, hydrogenated nitrile rubber, urethane rubber and the like are used, and among these, urethane rubber and silicone rubber are preferable, and urethane rubber is more preferable.

Both electrode layers 12A and 12B are made of a conductive composition containing a conductive material. Both electrode layers 12A and 12B may be composed of conductive compositions having the same composition as each other, or may be composed of conductive compositions having different compositions from each other.
The front electrode layer 12A and the back electrode layer 12B have the same plan view shape, and the front electrode layer 12A and the back electrode layer 12B face each other with the dielectric layer 11 interposed therebetween. In the sensor sheet 2, a portion of the sensor sheet 2 facing the front electrode layer 12A and the back electrode layer 12B functions as a capacitive element.
The front side electrode layer 12A and the back side electrode layer 12B do not necessarily have to face each other with the dielectric layer interposed therebetween, but at least a part thereof may face each other.

As the conductive material, for example, carbon nanotubes, graphene, carbon nanohorns, carbon fibers, conductive carbon black, graphite, metal nanowires, metal nanoparticles, conductive polymers and the like may be used alone, or two types may be used. The above may be used together. Carbon nanotubes are preferable as the conductive material. This is because it is suitable for forming an electrode layer having excellent conductivity and elasticity.
The conductive composition may contain, for example, a binder component in addition to the conductive material such as carbon nanotubes.
The binder component functions as a binder component, and by containing the binder component, the adhesion to the dielectric layer and the strength of the electrode layer itself can be improved.

The wirings 13A and 13B connecting the electrode layers 12A and 12B and the connection terminals 14A and 14B are also made of the same conductive composition as the electrode layers 12A and 12B.

The front side connection terminal 14A connected to the front side electrode layer 12A via the front side wiring 13A is, for example, a plate-shaped member formed by using a copper plate or the like, and is provided so as to be exposed to the outside to detect capacitance. A connecting line extending from the device 3 is connected.
Further, the back side connection terminal 14B connected to the back side electrode layer 12B via the back side wiring 13B is also a plate-shaped member formed by using a copper plate or the like, and is provided so as to be exposed to the outside to detect capacitance. A connecting line extending from the device 3 is connected.
The sensor sheet 2 receives the carrier voltage given from the capacitance detection device 3 by the front side connection terminal 14A, and outputs a sensor output signal corresponding to the carrier voltage from the back side connection terminal 14B.

Both protective layers 15A and 15B are provided to electrically insulate the electrode layers 12A and 12B and the like to protect them from the external environment. Further, both the protective layers 15A and 15B also have a function as a reinforcing member for enhancing the strength and durability of the sensor sheet 2 as a whole.
The materials of the protective layers 15A and 15B are not particularly limited, and can be appropriately selected according to the required characteristics. Specific examples of the materials of the protective layers 15A and 15B include an elastomer composition similar to the material of the dielectric layer 11.

The adhesive layer 18 is a layer provided for attaching the sensor sheet 2 to the object to be measured, and when attached to the surface of the movable portion of the object to be measured, the adhesive layer 18 is deformable according to the movement of the movable portion. It has enough adhesive strength to stick to.

Since the dielectric layer 11 of the sensor sheet 2 is made of an elastomer, it can be deformed (expanded and contracted) in the plane direction as described above. When the dielectric layer 11 is deformed in the plane direction, the front side electrode layer 12A and the back side electrode layer 12B, and the front side protective layer 15A and the back side protective layer 15B are deformed following the deformation.
Then, as the sensor sheet 2 is deformed, the capacitance of the detection unit changes in correlation with the amount of deformation of the dielectric layer 11. Therefore, by detecting the change in capacitance, the deformed state of the sensor sheet 2 can be grasped.

[1.3 Configuration of Capacitance Detection Device 3]
FIG. 3 is a block diagram showing an example of the configuration of the capacitance detection device 3. As shown in FIG. 3, the capacitance detection device 3 includes a voltage supply unit 20 for applying a carrier voltage to the sensor sheet 2 at a predetermined cycle.
The voltage supply unit 20 includes a rectangular wave generation unit 21 and a first low-pass filter (LPF: Low pass filter) unit 22.
The rectangular wave generation unit 21 has a function of generating a rectangular wave having a predetermined period. The square wave generation unit 21 applies a bias voltage to the generated square wave to convert it into a waveform that oscillates around 0V. The square wave generation unit 21 gives the converted square wave to the first low-pass filter unit 22.
The first low-pass filter unit 22 has a function of converting a given square wave into a signal wave similar to a sine wave by passing a signal in a frequency band lower than a predetermined cutoff frequency. That is, the square wave generated by the square wave generation unit 21 is converted into a signal wave similar to a sine wave by passing through the first low-pass filter unit 22.

When the capacitance detection device 3 of the present embodiment is configured to operate at a predetermined intermediate reference voltage by applying a predetermined bias voltage to the device as a whole, the voltage supply unit 20 has an amplitude center. A signal wave having a waveform that becomes an intermediate reference voltage is generated.

The voltage supply unit 20 applies a signal wave similar to a sine wave converted by the first low-pass filter unit 22 to the sensor sheet 2 as a carrier voltage.
The first low-pass filter unit 22 is connected to the front side connection terminal 14A (see FIG. 2) of the sensor sheet 2 via the connection line 23. Therefore, the carrier voltage is applied to the sensor sheet 2 through the connecting line 23.

The amplitude voltage V ₀ and the frequency f ₀ of the carrier voltage, which is a signal wave similar to a sine wave, are set to preset values according to the capacitance of the sensor sheet 2 and the like.
The waveform of the square wave generated by the square wave generation unit 21 and the characteristics of the first low-pass filter unit 22 are set so as to obtain a carrier voltage in which the amplitude voltage V ₀ and the frequency f ₀ are preset values. ing.

In this way, the voltage supply unit 20 generates a carrier voltage having a predetermined cycle, and applies the generated carrier voltage to the sensor sheet 2.

The back side connection terminal 14B (see FIG. 2) of the sensor sheet 2 is connected to the conversion unit 25 of the capacitance detection device 3 via the connection line 24.
The sensor sheet 2 gives a sensor output signal to the conversion unit 25 in response to the application of the carrier voltage from the voltage supply unit 20.
The conversion unit 25 has a function of converting a sensor output signal, which is a current signal output from the sensor sheet 2 in response to application of a carrier voltage, into a voltage signal.

FIG. 4 is a diagram showing a configuration example of the conversion unit 25. As shown in FIG. 4, the conversion unit 25 includes an operational amplifier 25a and a resistance element 25b. In addition to the conversion unit 25, FIG. 4 also shows the sensor sheet 2 and the voltage supply unit 20.

A sensor sheet 2 is connected to the inverting input terminal of the operational amplifier 25a. Further, the non-inverting input terminal of the operational amplifier 25a is grounded.
The resistance element 25b is connected between the output terminal and the inverting input terminal of the operational amplifier 25a, and has a function as a feedback resistor.
The operational amplifier 25a is adjusted so that the current flowing through the resistance element 25b and the current flowing through the sensor sheet 2 are equal to each other.

Here, when the carrier voltage is set to the following formula (1), the current I flowing through the sensor sheet 2 is represented by the following formula (2).
The carrier voltage _{V C = V 0 sin (2πf} 0 t) ··· (1)
Current I = j2πf ₀ CV ₀ sin (2πf ₀ t) ・ ・ ・ (2)

In the above equation (1), V ₀ is the amplitude voltage of the carrier voltage, f ₀ is the frequency of the carrier voltage, and t is the time. Further, in the above equation (2), j is an imaginary number and C is the capacitance of the sensor sheet 2.
As described above, the operational amplifier 25a is adjusted so that the current flowing through the resistance element 25b and the current flowing through the sensor sheet 2 are equal to each other. Therefore, the output voltage V _out of the operational amplifier 25a is represented by the following equation (3). To.
Output voltage V _out = j2πf ₀ CRV ₀ sin (2πf ₀ t)
... (3)

In the above equation (3), R indicates the resistance value of the resistance element 25b.
As shown in the above equation (3), the amplitude of the output voltage V _out of the operational amplifier 25a is proportional to the capacitance C of the sensor sheet 2. Therefore, the change in the capacitance C of the sensor sheet 2 can be obtained from the amplitude of the output voltage V _out of the operational amplifier 25a. Further, the capacitance C of the sensor sheet 2 can be obtained from the ratio of the amplitude voltage V ₀ of the carrier voltage and the output voltage V _out of the operational amplifier 25a.

As described above, the conversion unit 25 converts the current I as the sensor output signal output from the sensor sheet 2 into the output voltage V _out as the voltage signal. As shown in the above equations (2) and (3), the current I and the output voltage V _out as the sensor output signal have information indicating the capacitance C of the sensor sheet 2 as the amplitude.

FIG. 5A is a diagram showing an example of carrier voltage. In FIG. 5A, the vertical axis represents voltage and the horizontal axis represents time (t).
As shown in FIG. 5 (a), the carrier voltage V _C, the amplitude voltage is output as the signal waves constant at V _0. The carrier voltage V _C is generated as a signal wave approximate to a sine wave as described above.
In the present embodiment, the frequency _{f 0} of the carrier voltage is set to, for example, 5 kHz.

FIG. 5B is a diagram showing an example of the output when the sensor output signal output from the sensor sheet 2 by the application of the carrier voltage of FIG. 5A is converted by the conversion unit 25.
Note that FIG. 5B shows an example of a sensor output signal when the sensor sheet 2 is deformed and the capacitance of the sensor sheet 2 is changed over time.

As shown in FIG. 5B, the amplitude voltage of the sensor output signal converted to the output voltage V _out by the conversion unit 25 fluctuates with time because the capacitance of the sensor sheet 2 changes with time. doing.
As described above, since the amplitude of the output voltage V _out of the operational amplifier 25a is proportional to the capacitance C of the sensor sheet 2, the change in the capacitance C of the sensor sheet 2 appears in the amplitude of the output voltage V _out . ..
That is, the envelope E of the sensor output signal shown in FIG. 5B represents the change in the capacitance C of the sensor sheet 2.
Since the carrier voltage frequency is set to 5 kHz, the sensor output signal converted by the conversion unit 25 has a frequency component of 5 kHz, which is the same as the carrier voltage frequency f _0, and the capacitance of the sensor sheet 2. It contains a component that indicates a change in volume C. The frequency of the component indicating the change in the capacitance C contained in the sensor output signal can be expressed by the following equation (4).
Frequency of the component indicating the change of capacitance C contained in the sensor output signal =
f ₀ ± f _e ... (4)
In equation (4), _fe is the frequency of a component indicating a change in capacitance C in a state where it is not modulated by the carrier voltage.

As described above, the conversion unit 25 converts the sensor output signal, which is a current signal output from the sensor sheet 2, into the output voltage V _out , which is a voltage signal, in response to the application of the carrier voltage.

Returning to FIG. 3, the conversion unit 25 gives the sensor output signal converted into the output voltage V _out , which is a voltage signal, to the filter unit 26 connected to the subsequent stage of the conversion unit 25.

The filter unit 26 is composed of a high-pass filter (High pass filter). The filter unit 26 has a function of passing a sensor output signal by allowing the passage of a signal component in a frequency band higher than a preset cutoff frequency. Further, the filter unit 26 has a function of limiting and removing the passage of noise components existing in a frequency band lower than the cutoff frequency. The filter unit 26 of the present embodiment is configured by using a third-order high-pass filter using an operational amplifier.

FIG. 6A is a diagram showing an example of a sensor output signal output from the conversion unit 25.
In the sensor output signal shown in FIG. 6A, for example, the center of amplitude gently fluctuates along the time axis direction as compared with the sensor output signal shown in FIG. 5B. That is, low-frequency noise having a frequency lower than the frequency of the sensor output signal is added to the sensor output signal shown in FIG. 6A.
High-frequency noise is also added to the sensor output signal shown in FIG. 6A.
That is, a sensor output signal to which a noise component is added is given to the filter unit 26.

FIG. 6B is a diagram showing only the noise component added to the sensor output signal shown in FIG. 6A.
In FIG. 6B, the low frequency noise includes environmental noise generated due to the environment around the sensor sheet 2 as a main component.
The environmental noise of the present embodiment is, for example, noise generated by the influence of electromagnetic waves generated by an electric product installed around the sensor sheet 2 or a DC power source of the own system. Environmental noise caused by surrounding electric appliances, DC power supply, etc. is added to the sensor output signal via the sensor sheet 2 and the like.
The noise generated by such electric products includes the frequency component of a commercial power source. Further, the noise generated by the converter or the like provided in the DC power supply includes a noise component due to ripple generated when rectifying the AC obtained from the commercial power supply and a noise component due to switching. Such noise generated when rectifying alternating current contains a frequency component twice the frequency of a commercial power supply. Therefore, the frequency of environmental noise is 50 to 120 Hz.

In FIG. 6 (b), the high frequency noise is reflected in a spike, being applied to the sensor output signal as a higher frequency of noise than the frequency f ₀ of the carrier voltage. Such high-frequency noise is added to the sensor output signal by being generated due to each component of the capacitance detection device 3 or being mixed from the outside.

Here, the cutoff frequency f _C1 of the filter unit 26 is set higher than the frequency of environmental noise of 50 to 120 Hz and lower than the frequency f _{0 of the} carrier voltage. More particularly, from the frequency f ₀ of the carrier voltage, a frequency of the frequency to be acquired as the component obtained by subtracting showing the change of the electrostatic capacitance C of the sensor sheet 2 When f _g, cutoff frequency f _C1 of the filter 26, It is set to be lower than the frequency f _g. More specifically, the cutoff frequency f _C1 of the filter unit 26 is set to 3 kHz.
Therefore, when the sensor output signal to which the noise is added is given from the conversion unit 25 to the filter unit 26, the filter unit 26 allows the sensor output signal existing in the frequency band around the frequency f _{0 of the} carrier voltage to pass through. However, low-frequency noise containing environmental noise having a frequency of 50 to 120 Hz as a main component is blocked from passing.
Therefore, low frequency noise is removed from the sensor output signal after passing through the filter unit 26.

FIG. 6C is a diagram showing an output from the filter unit 26 when the sensor output signal shown in FIG. 6A is applied to the filter unit 26.
In the sensor output signal shown in FIG. 6C, the amplitude voltage fluctuates with time in a state where the center of the amplitude is substantially constant near 0 V, and low-frequency noise is removed.
On the other hand, high frequency noise, which is a frequency higher than the cutoff frequency of the filter unit 26, is not removed and remains added to the sensor output signal.

Returning to FIG. 3, when the sensor output signal to which noise is added is given from the conversion unit 25, the filter unit 26 transfers the sensor output signal after removing the low frequency noise to the filter unit 26 as described above. It is given to the rectifying unit 27 connected to the subsequent stage.

The rectifier unit 27 is composed of a half-wave rectifier circuit using an operational amplifier, and half-wave rectifies the sensor output signal given from the filter unit 26.
Further, a second low-pass filter unit 28 is connected to the subsequent stage of the rectifying unit 27.
The second low-pass filter unit 28 passes a signal in a frequency band lower than the preset cutoff frequency to pass a component indicating capacitance, which is a component included in the sensor output signal after half-wave rectification. Tolerate. Further, the second low-pass filter unit 28 has a function of removing the frequency component of the carrier voltage and the high frequency noise. The second low-pass filter unit 28 of the present embodiment is configured by using a third-order low-pass filter using an operational amplifier.

FIG. 7A is a diagram showing an output when the sensor output signal shown in FIG. 6C is applied to the rectifying unit 27. As shown in FIG. 7A, the rectifying unit 27 half-wave rectifies and outputs the sensor output signal given from the filter unit 26.
The above-mentioned high-frequency noise is added to the half-wave rectified sensor output signal shown in FIG. 7A.
Therefore, the rectifying unit 27 gives the second low-pass filter unit 28 a half-wave rectified sensor output signal to which high-frequency noise is added.

The cutoff frequency f _C2 of the second low-pass filter unit 28 is set lower than the frequency f ₀ of the high frequency noise and the carrier voltage. That is, the cutoff frequency f _C2 of the second low-pass filter unit 28 is set to a value that can remove the frequency component of the carrier voltage and the high frequency noise while leaving the component indicating the capacitance.
Therefore, when a half-wave rectified sensor output signal to which high-frequency noise is added is given to the second low-pass filter unit 28, the second low-pass filter unit 28 allows the component indicating the capacitance to pass through. It blocks the passage of high-frequency noise and the frequency component of the carrier voltage that causes ripples to the component that indicates capacitance when remaining.
As a result, high-frequency noise and frequency components of the carrier voltage are removed from the signal wave after passing through the second low-pass filter unit 28.

The half-wave rectified sensor output signal shown in FIG. 7A has low-frequency noise removed by the filter unit 26. Therefore, the second low-pass filter unit 28 does not need to consider limiting the passage of this low-frequency noise. Therefore, the cutoff frequency f _C2 of the second low-pass filter unit 28 of the present embodiment is set higher than the frequency of low frequency noise (environmental noise) of 50 to 120 Hz.

Therefore, as in the above conventional example, the cutoff frequency of the low-pass filter in the subsequent stage of the rectifier is set lower than the frequency of the commercial power supply to limit the passage of the noise in order to remove the noise of the frequency of the commercial power supply which is a predetermined frequency. In this embodiment, the cutoff frequency f _C2 of the second low-pass filter unit 28 can be set higher than in the case. As a result, it is possible to suppress a decrease in the responsiveness of the sensor output signal to a change in the capacitance C of the sensor sheet 2.

FIG. 7B is a diagram showing a signal wave output from the second low-pass filter unit 28 when the sensor output signal shown in FIG. 7A is applied to the second low-pass filter unit 28.
In FIG. 7B, FIG. F shows a signal wave output from the second low-pass filter unit 28.
FIG. F shows the envelope of the sensor output signal of FIG. 7 (a) by removing the frequency components of the high frequency noise and the carrier voltage from the sensor output signal of FIG. 7 (a).
As described above, the sensor output signal represents a change in the capacitance C of the sensor sheet 2 depending on its amplitude. Therefore, the diagram F in FIG. 7B shows the change in the capacitance C of the sensor sheet 2.

Returning to FIG. 3, the second low-pass filter unit 28 represents a change in the capacitance C of the sensor sheet 2 shown in FIG. 7 (b) when a half-wave rectified sensor output signal is given from the rectifier unit 27. The signal wave is given as a detection result signal to the output unit 29 connected to the subsequent stage of the second low-pass filter unit 28.

The output unit 29 performs signal processing such as amplification and gain adjustment on the detection result signal given from the second low-pass filter unit 28, and supplies the signal-processed detection result signal to the information processing device 4.

The information processing device 4 is composed of, for example, a computer or the like, and processes a given detection result signal to obtain the value of the capacitance C of the sensor sheet 2 or to obtain the value of the capacitance C of the sensor sheet 2 or to obtain the value of the capacitance C of the measurement target. Generates information indicating the movable state and generates result information regarding the detection result.
The information processing device 4 outputs the generated result information to the operator of the information processing device 4.

In the present embodiment, the case where the second low-pass filter unit 28 gives the detection result signal to the output unit 29 is shown, but the detection result signal is transmitted between the second low-pass filter unit 28 and the output unit 29. An amplifier for amplifying and an incomplete differentiating circuit may be provided.
In this case, the amplifier can detect minute changes by amplifying the detection result signal. The inexact differential circuit also operates to match the voltage offset to the level of the amplified detection result signal.

[1.4 Effect]
The capacitance detection device 3 of the present embodiment is output from the voltage supply unit 20 that applies a carrier voltage of a predetermined cycle to the sensor sheet 2 that is a capacitance type sensor, and the sensor sheet 2 in response to the application of the carrier voltage. It is included in the conversion unit 25 that converts the sensor output signal, which is a current signal, into a voltage signal, the rectifying unit 27 that rectifies the sensor output signal converted into a voltage signal, and the sensor output signal rectified by the rectifying unit 27. The filter unit 26 includes a second low-pass filter unit 28 that removes the frequency component of the carrier voltage, and a filter unit 26 that is connected between the conversion unit 25 and the rectifying unit 27 and passes the sensor output signal. The cutoff frequency f _C1, which is the lower limit of the frequency band that allows the passage of signal components, is set higher than the frequency of the commercial power supply, which is the frequency of the environmental noise around the sensor sheet 2, and the cutoff frequency of the second low-pass filter unit 28. f _C2 is set higher than the frequency of the commercial power supply.

According to the capacitance detection device 3 configured as described above, the filter unit 26 is connected between the conversion unit 25 and the rectifier unit 27 and the cutoff frequency f _C1 is set higher than the frequency of the commercial power supply. Therefore, even if noise of the frequency of the commercial power supply is added to the sensor output signal, the noise can be removed by the filter unit 26.
Further, in the second low-pass filter unit 28 after the rectifying unit 27, the noise of the frequency of the commercial power supply is removed by the filter unit 26, so that it is not necessary to remove the noise of the frequency of the commercial power supply. Therefore, the cutoff frequency f _C2 of the second low-pass filter unit 28 can be set higher than the frequency of the commercial power supply. As a result, the cutoff frequency f _C2 of the second low-pass filter unit 28 can be set higher than that of the conventional example. Therefore, it is possible to suppress a decrease in the responsiveness of the sensor output signal to a change in the capacitance C of the sensor sheet 2.
Further, the second low-pass filter unit 28 can remove high-frequency noise and frequency components of the carrier voltage.
As described above, according to the capacitance detection device 3 of the present embodiment, it is included in the sensor output signal of the sensor sheet 2 while suppressing a decrease in the responsiveness of the sensor sheet 2 to a change in the capacitance C. Environmental noise caused by commercial power sources and the like can be removed. In addition to this, high frequency noise can also be removed.

[2 Second Embodiment]
FIG. 8 is a block diagram of the sensor system according to the second embodiment. In the figure, the sensor system 40 of the present embodiment includes an irradiation device 41 that irradiates the surface of the sample 50 with light, and a photodetector 42. An information processing device is connected to the subsequent stage of the photodetector 42. The information processing device receives the detection result signal output by the photodetector 42, and generates result information regarding the surface state such as the presence / absence of a change in the surface 50a of the sample 50 and the presence / absence of dust adhesion.

The irradiation device 41 includes an LED (Light Emitting Diode) 45, which is a light source that irradiates the surface of the sample 50, and a lighting control unit 46 that controls the LED 45.
The LED 45 is provided so that the surface of the sample 50 can be irradiated with light. The lighting control unit 46 controls the LED 45 so that the surface of the sample 50 is irradiated with blinking light that blinks at a predetermined cycle.

The light detection device 42 is a device that detects the reflected light reflected by the light emitted by the irradiation device 41 on the surface of the sample 50, and includes a light receiving unit 47, a conversion unit 25, a filter unit 26, and a light receiving unit 47 that receives the reflected light. It includes a rectifying unit 27, a second low-pass filter unit 28, and an output unit 29.
The light receiving unit 47 is composed of a PD (Photodiode), and outputs a sensor output signal which is a current signal corresponding to the light receiving intensity of the received reflected light. The light receiving unit 47 is connected to the conversion unit 25 in the subsequent stage, and gives the sensor output signal to the conversion unit 25.

The conversion unit 25, the filter unit 26, the rectifying unit 27, the second low-pass filter unit 28, and the output unit 29 have the same configuration as that of the first embodiment.
Therefore, each part converts the sensor output signal, which is a current signal corresponding to the received intensity of the reflected light, into a voltage signal, detects a change in the received intensity of the reflected light from the sensor output signal converted into the voltage signal, and receives the received intensity. A signal wave representing the change in is given as a detection result signal to the information processing device connected to the subsequent stage of the output unit 29.

FIG. 9A is a diagram showing an aspect when the LED 45 and the light receiving unit 47 are installed on the sample 50. In FIG. 9A, the alternate long and short dash line indicates a light ray.
In FIG. 9A, the LED 45 is installed so that the irradiation angle of the blinking light is almost parallel to the surface 50a of the sample 50. Further, the light receiving unit 47 is arranged directly above the irradiation range in which the blinking light from the LED 45 on the surface 50a of the sample 50 is irradiated.

Since the blinking light is emitted at an angle close to parallel to the surface 50a, the reflected light reflected by the blinking light on the surface 50a is also reflected at an angle close to parallel to the surface 50a.
Therefore, for example, as shown in FIG. 9A, if there is nothing on the surface 50a, the reflected light is not directly irradiated to the light receiving portion 47.
Therefore, in this case, the light receiving intensity of the reflected light received by the light receiving unit 47 appears low.

FIG. 9B is a diagram showing an aspect when dust is attached to the surface 50a of the sample 50.
In FIG. 9B, when the dust 55 is present on the surface 50a, the blinking light is irradiated to the dust, so that scattered light is generated.
This scattered light, unlike the reflected light, is scattered around. Therefore, the light receiving unit 47 receives the scattered light with a light receiving intensity higher than that of the reflected light.
That is, when there is no dust on the surface 50a, the light receiving intensity detected by the photodetector 42 is relatively low, and when dust is present on the surface 50a, the light receiving intensity detected by the photodetector 42 is relatively high. Become.
The sensor system 40 of the present embodiment detects a surface state such as the presence / absence of a change in the surface 50a of the sample 50 and the presence / absence of dust adhesion due to such a difference in light receiving intensity.

Here, for example, as shown in FIG. 9B, when the surface state is detected by the sensor system 40 under the illumination environment of the fluorescent lamp 60, the light receiving unit 47 of the light detection device 42 is the fluorescent lamp 60. It receives direct light and reflected light.
As a result, noise due to receiving light from the illumination may be added to the sensor output signal output by the light receiving unit 47 in addition to the information indicating the surface state of the surface 50a.
Such noise caused by the light from the illumination is environmental noise caused by the environment around the sensor.

Some fluorescent lamps repeatedly blink at the frequency of a commercial power source (50 to 60 Hz). In such a case, the frequency of environmental noise added to the sensor output signal output by the light receiving unit 47 is 50 to 60 Hz. Become.

On the other hand, also in the present embodiment, since the filter unit 26 which is connected between the conversion unit 25 and the rectifying unit 27 and whose cutoff frequency f _C1 is set higher than the frequency of the commercial power supply is provided, the sensor is provided. Even if noise of the frequency of a commercial power source is added to the output signal as environmental noise, the noise can be removed by the filter unit 26.

[Other]
The present invention is not limited to the above embodiments.
For example, in the sensor system of the first embodiment, the case where the sensor sheet 2 is attached to a movable portion of an object to be measured such as a joint portion of a human body and the movable state of the movable portion is measured is illustrated. The frequency of the environmental noise in this case is 50 to 120 Hz.

On the other hand, the measurement target of the sensor system is not limited to those that are relatively gently displaced, such as the movement of joints of the human body. Depending on the measurement target, unnecessary noise may be given due to the measurement target itself in addition to the displacement due to the operation of the measurement target itself. In such a case, the environmental noise is not limited to the frequency determined based on the frequency of the commercial power source as shown in the first embodiment.

For example, when the sensor system measures the expansion and contraction deformation operation of the gut when hitting a ball by a tennis racket, the gut itself may be displaced due to vibration or the like in addition to the expansion and contraction deformation operation of the entire gut as a racket surface. is there. The frequency of vibration of such a gut itself is about 5 kHz.
Such displacements other than the expansion / contraction deformation operation of the entire gut have little relation to the expansion / contraction deformation operation of the entire gut, and appear as noise in the sensor output signal.

Therefore, as described above, when measuring the expansion / contraction deformation operation of the gut of the tennis racket by the sensor system, the frequency of the environmental noise is set to less than 5 kHz, and the filter unit 26 and the second low-pass filter unit 28 accordingly. Set the cutoff frequency.
This makes it possible to remove environmental noise when measuring the expansion and contraction deformation motion of the gut of the tennis racket.

Further, in the first embodiment, the case where the frequency of the carrier voltage is set to 5 kHz is illustrated, but the frequency of the carrier voltage may be set to a frequency higher than the frequency of the noise to be removed by the filter unit 26. For example, it can be set to 10 times or more the frequency of the noise to be removed by the filter unit 26.

Further, in the first embodiment, the case where the sensor sheet 2 which is a capacitive element formed in a planar shape and expands and contracts in the plane direction is used as a capacitance type sensor is illustrated, but for example, the electrode on the movable side It is also used for a capacitance type sensor that has a fixed side electrode and is configured to change the capacitance between both electrodes by moving the movable side electrode by external input such as acceleration. be able to.

Further, in the first embodiment, a signal wave similar to a sine wave is used as a carrier voltage, but it may not be approximated to a sine wave and may be used as a square wave as a carrier voltage. However, when the rectangular wave is used as the carrier voltage, the output of the sensor sheet 2 becomes larger than necessary, and an excessive current may flow through the conversion unit 25. Therefore, the carrier voltage is preferably a sine wave or a signal wave similar to a sine wave.
Since the sensor output signal is output in response to the application of the carrier voltage, it may include a noise component included in the carrier voltage.
Therefore, in the first embodiment, the voltage supply unit 20 is a square wave generation unit 21 that generates a square wave having a predetermined period, and a filter unit that converts the square wave into a signal wave that is close to a sine wave. A low-pass filter unit 22 is provided, and the signal wave is applied to the sensor sheet 2 as a carrier voltage.
As a result, noise included in the carrier voltage can be reduced, so that the frequency component of the carrier voltage can be easily removed by the second low-pass filter unit 28. Therefore, the noise included in the sensor output signal can be removed more effectively.

Further, in each of the above embodiments, the case where the high-pass filter is used for the filter unit 26 is shown, but a band-pass filter can be used instead of the high-pass filter. In this case, the cutoff frequency on the low frequency side, which is the lower limit of the frequency band that allows the passage of signal components, is set higher than the frequency of environmental noise.

Further, in each of the above embodiments, the case where a third-order high-pass filter is used for the filter unit 26 is shown, but for example, a first-order or second-order high-pass filter other than the third-order may be used.
Since the filter characteristics of a second-order or higher-order high-pass filter are steeper than those of a first-order high-pass filter, it is easier to set so that only signals in the required frequency band pass through. Become.
Further, similarly to the filter unit 26, the case where a third-order low-pass filter is used for the second low-pass filter unit 28 is shown in the above embodiment, but a first-order or second-order low-pass filter other than the third-order may be used. Good. Since the filter characteristics of a low-pass filter of second order or higher are steeper than those of a high-pass filter of first order, it is easier to set so as to pass only signals in the required frequency band in this case as well. It becomes.

Further, in each of the above embodiments, the case where the rectifying unit 27 performs odd rectification is shown, but the rectifying unit 27 may be configured to perform full-wave rectification. In this case, the value indicating the amplitude of the rectified sensor output signal output by the rectifying unit 27 is twice that in the case of odd rectification. Therefore, the component indicating the capacitance included in the sensor output signal increases, and then the frequency component of the carrier voltage can be easily removed by the second low-pass filter unit 28.

1 Sensor system 2 Sensor sheet 3 Capacitance detection device 4 Information processing device 11 Dielectric layer 12A Front side electrode layer 12B Back side electrode layer 13A Front side wiring 13B Back side wiring 14A Front side connection terminal 14B Back side connection terminal 15A Front side protection layer 15B Back side protection layer 18 Adhesive layer 20 Voltage supply unit 21 Rectangular wave generator 22 1st low-pass filter unit 23 Connection line 24 Connection line 25 Conversion unit 25a Operate 25b Resistance element 26 Filter unit 27 Rectification unit 28 2nd low-pass filter unit 29 Output unit 40 Sensor system 41 Irradiation device 42 Light detection device 46 Lighting control unit 47 Light receiving unit 50 Sample 50a Surface 55 Dust 60 Fluorescent lamp

Claims (6)

It is a capacitance detection device that detects the capacitance of a capacitance type sensor whose capacitance changes in response to external input.
A voltage supply unit that applies a carrier voltage of a predetermined cycle to the capacitance type sensor, and
A conversion unit that converts a sensor output signal, which is a current signal output from the capacitance type sensor, into a voltage signal in response to the application of the carrier voltage.
A rectifying unit that rectifies the sensor output signal converted into a voltage signal,
A low-pass filter unit that removes the frequency component of the carrier voltage included in the sensor output signal rectified by the rectifying unit, and a low-pass filter unit.
A filter unit connected between the conversion unit and the rectifying unit and passing the sensor output signal is provided.
In the filter unit, the lower limit of the frequency band that allows the passage of signal components is set higher than the frequency of the environmental noise around the capacitance type sensor.
The cutoff frequency of the low-pass filter unit is set higher than the frequency of the environmental noise.
The conversion unit converts the sensor output signal into a voltage signal in proportion to the capacitance of the capacitance type sensor .
The capacitance type sensor is attached to a movable part of an object to be measured, and the capacitance type sensor is deformed according to the operation of the movable part, and the capacitance changes according to the deformation. A capacitance detection device that outputs information indicating the operating state of moving parts of an object as a change in capacitance. The capacitance detection device according to claim 1, wherein the frequency of the environmental noise is a frequency determined based on the frequency of a commercial power source. The capacitance detection device according to claim 1 or 2, wherein the low-pass filter unit is composed of a secondary or higher-order low-pass filter. The capacitance detection device according to any one of claims 1 to 3 , wherein the filter unit is composed of a second-order or higher-order high-pass filter. It is a capacitance detection device that detects the capacitance of a capacitance type sensor whose capacitance changes in response to external input.
A voltage supply unit that applies a carrier voltage of a predetermined cycle to the capacitance type sensor, and
A conversion unit that converts a sensor output signal, which is a current signal output from the capacitance type sensor, into a voltage signal in response to the application of the carrier voltage.
A rectifying unit that rectifies the sensor output signal converted into a voltage signal,
A low-pass filter unit that removes the frequency component of the carrier voltage included in the sensor output signal rectified by the rectifying unit, and a low-pass filter unit.
A filter unit connected between the conversion unit and the rectifying unit and passing the sensor output signal is provided.
In the filter unit, the lower limit of the frequency band that allows the passage of signal components is set higher than the frequency of the environmental noise around the capacitance type sensor.
The cutoff frequency of the low-pass filter unit is set higher than the frequency of the environmental noise.
The conversion unit converts the sensor output signal into a voltage signal in proportion to the capacitance of the capacitance type sensor.
The voltage supply unit
A square wave generator that generates a square wave with a predetermined period,
A filter unit that converts the rectangular wave into a signal wave similar to a sine wave is provided.
It applied to the capacitive sensor of the signal wave as the carrier voltage <br/> electrostatic capacitance detection device. A sensor system including 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 voltage supply unit that applies a carrier voltage of a predetermined cycle to the capacitance type sensor, and
A conversion unit that converts a sensor output signal, which is a current signal output from the capacitance type sensor, into a voltage signal in response to the application of the carrier voltage.
A rectifying unit that rectifies the sensor output signal converted into a voltage signal,
A low-pass filter unit that removes the frequency component of the carrier voltage included in the sensor output signal rectified by the rectifying unit, and a low-pass filter unit.
A filter unit connected between the conversion unit and the rectifying unit and passing the sensor output signal is provided.
In the filter unit, the lower limit of the frequency band that allows the passage of signal components is set higher than the frequency of the environmental noise around the capacitance type sensor.
The cutoff frequency of the low-pass filter unit is set higher than the frequency of the environmental noise.
The conversion unit converts the sensor output signal into a voltage signal in proportion to the capacitance of the capacitance type sensor .
The capacitance type sensor is attached to a movable part of an object to be measured, and the capacitance type sensor is deformed according to the operation of the movable part, and the capacitance changes according to the deformation. A sensor system that outputs information indicating the operating state of moving parts of an object as a change in capacitance .

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