JPH0820478B2 - Electrostatic sensor device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrostatic sensor device for detecting a change in micro capacitance of an object to be detected.

[Conventional technology]

The electrostatic sensor device that has been used generally in the past changes the capacitance of the tank circuit of the oscillation circuit in response to the change in the capacitance of the object to be detected, and changes the oscillation frequency. However, the sensitivity is low, and for this reason, the RCA method, which has a higher sensitivity in recent years, is a method that obtains an AM modulated wave by changing the capacitor capacity of the tuning circuit that has a resonance frequency that is slightly different from the oscillation frequency of the oscillation circuit Devices are being used. As shown in FIG. 5, this RCA type electrostatic sensor device includes an oscillation circuit 1, a tuning circuit 2, and a detection electrode 3 such as a detection needle for detecting a change in electrostatic capacitance between the detected object 19. It comprises a detection circuit 4 and an amplification circuit 5. The oscillating circuit 1 and the tuning circuit 2 each include an independent resonator. For example, as shown in FIG. 3, the resonant frequency f ₀ of the tuning circuit 2 is slightly smaller than the fixed oscillation frequency f ₁ of the oscillating circuit 1. It is set to the position shifted to
The resonance frequency is deviated from f ₀ to the left and right by Δf in correspondence with the change ± ΔC of the small electrostatic capacitance detected by Δf, and the change ± ΔC of the electrostatic capacitance is ± Δ with reference to the tuning level V _0.
It is converted into a voltage change of V, and this detection signal is detected and amplified to be taken out.

[Problems to be Solved by the Invention]

However, since this type of electrostatic sensor device has too high sensitivity, when it detects a change in the small electrostatic capacitance of the detected object 19, it is sensitive to the change in the electrostatic capacitance due to the environmental change or the like. There is a drawback that. Therefore, when detecting a change in the minute electrostatic capacitance of the detected body 19, the true detection component ΔC of the electrostatic capacitance detected with respect to the movement of the detected body 19 and unnecessary component capacitance (hereinafter, unnecessary component capacitance In some cases, ΔC ′ (referred to as component capacitance) is simultaneously sent from the detection electrode 3 to the tuning circuit 2. The unnecessary component capacitance ΔC ′ is caused by various factors. For example, in the case of the VHD system of the video disk device, the fluctuation component of the electrostatic capacitance generated when the needle that functions as the detection electrode 3 is replaced and set, and the needle The change in the floating distribution capacitance between the needle and the casing that changes from the outside to the inside of the disc, the fluctuation component of the capacitance due to the variation due to the press molding of the individual disc, and the static electricity at each place on the disc surface It is caused by a change in capacity.

Further, for example, as shown in FIG. 6, a gear-shaped attachment 7 is attached to the rotary shaft 6, and the detection electrode 3 is arranged so as to face the tooth profile of the attachment 7 to detect the rotation of the rotary shaft 6. In such a case, the eccentric component of the rotary shaft 7 and the fluctuation component of the electrostatic capacitance due to the minute width irregularities such as pinholes and burrs on the tooth surface are taken in as the unnecessary component capacitance.

Such an unnecessary component capacity has a different frequency band depending on its cause. The relationship between the frequency band of the unnecessary component capacitance and the frequency band of the true detected component capacitance can be expressed as shown in FIG. 8 by plotting the frequency on the horizontal axis and the gain on the vertical axis. That is polarized across the frequency band f _W true detection Component Volume unnecessary component capacity A ₁ of the low frequency band, to the unnecessary components capacity A ₂ of the high frequency band. As the unnecessary component capacity in this low frequency band, there are vibration components close to direct current of several tens of cycles that occur when the VHD method needle is replaced and set, and changes in the stray distribution capacity due to movement of the needle, etc. In the case of detecting the rotation of the rotary shaft 6 shown in FIG. 6, a change component such as the eccentricity of the rotary shaft corresponds. As the unnecessary component capacitance in the high frequency band, for example, a variation component of the electrostatic capacitance due to a pinhole or a burr of the tooth shape of the attachment 7 detected at the time of rotation detection in FIG. 6 is applicable.

When such unnecessary component capacitance is taken in, the resonance frequency of the tuning circuit 2 changes depending on this unnecessary component capacitance, but when the unnecessary component capacitance is in the low frequency band, the tuning circuit 2
There is a problem that the potential of the tuning level fluctuates and the detection sensitivity decreases (the tuning level is set at the position with the highest sensitivity, so the sensitivity decreases when the tuning level fluctuates). Further, when the low frequency unnecessary component capacity is generated by the eccentricity of the rotating shaft, the tuning level has a low frequency frequency as shown in FIG. 7, and the tuning level corresponds to the frequency of the eccentricity of the rotating shaft 6. Then, there arises a problem of fluctuation. In this case, the tuning circuit 2 outputs a detection signal corresponding to the true detection component capacitance on the tuning level having a frequency corresponding to the eccentricity of the rotary shaft 6.

On the other hand, when the unnecessary component capacitance is in the high frequency band, the unnecessary component capacitance appears as noise in the detection signal. For example, when a pinhole or a burr of a tooth type is detected in the rotation detection, this causes noise P, as shown in FIG.
It appears as P ′, and there is a problem that the S / N ratio of the detection signal becomes worse.

The present invention has been made in order to solve the above-mentioned conventional problems, and the purpose thereof is that the tuning level fluctuates under the influence of the unnecessary component capacitance and that the S / N ratio of the detection signal deteriorates. It is another object of the present invention to provide an electrostatic sensor device capable of detecting a change in minute electrostatic capacitance of an object to be detected with high sensitivity and high accuracy.

[Means for solving the problem]

The present invention is configured as follows to achieve the above object. That is, the electrostatic sensor device of the present invention has an oscillation circuit that oscillates and outputs an oscillation frequency signal, and a dielectric resonator that is independent of this oscillation circuit, and detects changes in the external capacitance detected by the detection unit. A tuning circuit that receives the frequency signal and changes its tuning point, a variable-capacitance diode that functions as one resonance element of the dielectric resonator in this tuning circuit, and an unnecessary signal in a specified frequency band included in the output signal of the tuning circuit. In addition to the variable capacitance diode, the frequency selection control circuit for correcting and controlling the displacement of the resonance frequency of the tuning circuit due to the unnecessary component capacitance taken in by the detection portion is selectively used.

[Action]

In the present invention, when the true detection component capacitance is taken into the tuning circuit together with the unnecessary component capacitance, the true detection component capacitance and the unnecessary component capacitance are converted into voltage signals from the tuning circuit and output, and a part of this output signal Is added to the frequency selection control circuit. The frequency selection control circuit has, for example, a certain frequency component with an unnecessary component capacity, and when this frequency component is clear, the selection range of the low frequency band and the high frequency band according to the frequency component is designated in advance. Cage,
When signals of frequency components in these designated bands are added, the signals are selected and added to the variable capacitance diode. Therefore, in the above case, the frequency selection control circuit presets the signal of the frequency component corresponding to the unnecessary component capacitance from among the frequency signals added from the tuning circuit side as the unnecessary signal, and applies this to the variable capacitance diode. Of. The variable capacitance diode receives an unnecessary signal applied from the frequency selection control circuit and changes the resonance frequency of the tuning circuit in a direction opposite to the direction of change due to the unnecessary component capacitance. In other words, when the change in the external capacitance includes the unnecessary component capacitance, the resonance frequency of the tuning circuit changes due to the unnecessary component capacitance, but the unnecessary signal of this unnecessary component capacitance passes through the frequency selection control circuit and becomes a variable capacitance diode. And the fluctuation of the resonance frequency due to the unnecessary component capacitance is corrected by this unnecessary signal, and the tuning level is kept constant,
And the noise component is driven.

〔Example〕

An embodiment of an electrostatic sensor device according to the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit diagram of a first embodiment of an electrostatic sensor device according to the present invention. The device of this embodiment comprises an oscillation circuit 1, a tuning circuit 2, a detection signal 3 as a detection unit, a detection circuit 4, an amplification circuit 5, a buffer circuit 14, and an AFC circuit 8. The oscillator circuit 1 uses a dielectric resonator (ceramic resonator) that oscillates at an ultrahigh frequency, in this embodiment, a fixed and constant oscillation frequency within the range of 0.5 GHz to 5 GHz. The oscillating circuit 1 oscillates the high-frequency oscillating signal and applies it to the tuning circuit 2.
The tuning circuit 2 is composed of a dielectric resonator (ceramic resonator) independent of the dielectric resonator of the oscillation circuit 1, and the tuning circuit 2 detects a change in electrostatic capacitance with the detected object 19. A detection electrode 3 including a detection needle and the like is connected.

The detection circuit 4 is connected to the tuning circuit 2 via a coupling capacitor 9, and the detection circuit 4 is an inductance element.
The detector 11, the diode 11, the capacitor 12, and the resistor 13 are included in the detector 11, and the diode 11, the capacitor 12, and the resistor 13 constitute a detector of the detector circuit 4. This detection section envelope-detects the super-high frequency output signal output from the tuning circuit 2 and converts it into a signal in the signal band of the detected object 19.

The amplification circuit 5 amplifies the signal applied from the detection circuit 4 by a factor of n, supplies it to a signal processing unit (not shown) via the buffer circuit 14, and simultaneously, AFC (Automatic Fre
quency Control) circuit 8.

The AFC circuit 8 comprises a frequency selection control circuit 15 and a variable capacitance diode 16, and the input side of the frequency selection control circuit 15 is connected to the output end of the amplification circuit 5 via a diode 17. The output side of the frequency selection control circuit 15 is connected to the cathode side of the variable capacitance diode 16, and the anode side of the variable capacitance diode 16 is grounded. The cathode side of the variable capacitance diode 16 is connected to the tuning circuit 2 via the coupling capacitor 18, and the variable capacitance diode 16 is connected to the tuning circuit (dielectric resonator) 2
It functions as a resonance element.

The frequency selection control circuit 15 extracts an unnecessary signal included in the signal output from the tuning circuit 2 by frequency selection. In the present embodiment, this frequency selection control circuit 15 is used.
Reference numeral 15 is composed of a filter circuit. This filter circuit may be, for example, a low-pass filter as shown in FIG. 2A, a high-pass filter as shown in FIG. 2B, or a band-pass filter as shown in FIG. The low-pass filter selectively passes unwanted signals in the low-frequency band including a DC component, and the high-pass filter selectively passes unwanted signals in the high-frequency band. Further, the bandpass filter selectively passes unwanted signals in the intermediate frequency band and adds them to the variable capacitance diode 16. In this embodiment, the unnecessary signals selected and designated by these filter circuits are limited to those in the frequency band outside the frequency band f _W of the true detected component capacitance.

The first embodiment is configured as described above, and its operation will be described below.

As shown in FIG. 3, when the oscillation frequency f ₁ of the oscillation circuit 1 is set at a position slightly deviated from the resonance frequency (tuning frequency) f ₀ of the tuning circuit 2, for example, the object to be detected 19 is detected. When is moved, a slight change in capacitance occurs between the detection electrode 3 and the detected body 19, and the resonance point (tuning point) of the tuning circuit 2 changes by Δf. Then, in the tuning circuit 2, a change component Δ of the oscillation frequency f ₁ and the resonance frequency in the tuning circuit 2
Multiplication with f is performed to obtain a so-called AM modulated signal. In this embodiment, if the oscillation frequency is an ultrahigh frequency, for example, 1 GHz, the modulation signal is centered at 1 GHz and the detected object
It becomes a very high frequency signal with a bandwidth corresponding to 19 movements.

When the unnecessary component capacitance is detected during the detection of this minute electrostatic capacitance, the resonance frequency of the tuning circuit 2 changes due to this unnecessary component capacitance, and when the unnecessary component capacitance is a component in the low frequency band, the tuning level changes. When the unnecessary component capacity is in the high frequency band, it appears as a noise component in the modulation signal (detection signal). The modulation signal containing these unnecessary signal components is added to the detection circuit 4. Detection circuit 4
Then, this ultra-high frequency signal is subjected to envelope detection to detect the detected object 19
Signal band (3 MHz signal in this embodiment). The band-converted signal is amplified n times by the amplifier circuit 5, a part of the output signal is sent to the signal processing unit (not shown) via the buffer circuit 14, and the other part of the signal is a diode. It is branched and supplied to the AFC circuit 8 through 17.

The frequency selection control circuit 15 of the AFC circuit 8 extracts the unnecessary signal based on the unnecessary component capacity from the input signal components by frequency selection. For example, when the frequency selection control circuit 15 is composed of a low pass filter, an unnecessary signal in the low frequency band is extracted, and the extracted unnecessary signal is added to the variable capacitance diode 16. Also,
When the frequency selection control circuit 15 is composed of a high pass filter, unnecessary signals in the high frequency band are extracted and added to the variable capacitance diode 16. The variable-capacitance diode 16 changes the electrostatic capacitance according to an unnecessary signal applied from the frequency selection control circuit 15 and changes the resonance frequency of the tuning circuit 2. Since the variable capacitance diode 16 is connected in the reverse bias state, the displacement direction of the resonance frequency is opposite to the displacement direction of the resonance frequency of the tuning circuit 2 due to the incorporation of the unnecessary component capacitance. That is, when the detection electrode 3 detects the unnecessary component capacitance as well as the true detection component capacitance, the capacitance of the opposite polarity to the unnecessary component capacitance is generated in the variable capacitance diode 16 to cancel the unnecessary component capacitance. . As a result, even if the tuning level is displaced due to the unnecessary component capacitance in the low frequency band, this displacement is corrected to the correct level position initially set by the reverse polarity capacitance produced by the variable capacitance diode 16 by the unnecessary signal. . Further, even when the unnecessary component capacitance in the high frequency band is detected, the capacitance change of the variable capacitance diode 16 acts in such a direction as to cancel it, and the noise components P and P ′ generated in the modulation signal are effectively removed. Of.

As described above, according to the present embodiment, even when the unnecessary component capacitance is detected by the detection electrode 3, the tuning level does not change, and the noise component generated due to the unnecessary component capacitance is removed. It becomes possible to detect a small electrostatic capacitance of about 1 × 10 ⁻⁵ PF under high sensitivity with an excellent S / N ratio.

FIG. 4 shows a second embodiment of the electrostatic sensor device according to the present invention. This second embodiment is based on the tuning circuit 2
A plurality of circuits each including a detection electrode 3, a detection circuit 4, an amplification circuit 5, and a variable capacitance diode 16 are arranged in parallel, and one common oscillation circuit 1 is connected via a distribution resistor 20 and a coupling capacitor. It is connected to the series tuning circuit 2. And
The input side of the frequency selection control circuit 15 is connected to the output side of the amplification circuit 5 of each series via a resistor, and the output end of the frequency selection control circuit 15 is connected to the variable capacitance diode 16 of each series. Has been added. The electrostatic sensor device according to the second embodiment is a device of a type that parallel-processes a detection signal of a minute electrostatic capacitance detected from the detection electrodes 3 of each series.

In the second embodiment, when the detection electrode 3 of each series detects the unnecessary component capacitance, the unnecessary signal is added to the frequency selection control circuit 15 to obtain the frequency band specified by the frequency selection control circuit 15. Since an unnecessary signal is added to the variable capacitance diode 16 of the corresponding series and the fluctuation of the resonance frequency of the tuning circuit 2 is corrected as in the first embodiment, the tuning level is stabilized and the noise component is removed. is there.

The present invention is not limited to the above-mentioned embodiments, but can take various modes. For example,
In the above embodiment, the resonator of the oscillation circuit 1 is composed of a dielectric resonator, but it may be composed of a strip line.

〔The invention's effect〕

According to the present invention, when detecting an extremely small capacitance, when an unnecessary component capacitance is fetched together with a detection component capacitance to be obtained, an unnecessary signal corresponding to this unnecessary component capacitance is sent to the variable capacitance diode side via a frequency selection control circuit. Since it is configured to be fed back to correct the change in the resonance frequency of the tuning circuit due to the unnecessary signal, it is possible to stabilize the tuning level and remove the noise component.
It is possible to detect highly sensitive minute electrostatic capacitance with high N ratio.

Further, since the method of performing the resonance frequency correction control by feeding back the unnecessary signal, the device configuration becomes extremely simple, and it is possible to greatly reduce the size of the device and reduce the cost of the device.

[Brief description of drawings]

1 is a circuit diagram showing a first embodiment of an electrostatic sensor device according to the present invention, FIG. 2 is a circuit diagram of various filter circuits showing a concrete example of a frequency selection control circuit in the same embodiment, and FIG. Is an explanatory view showing the detection operation of the minute electrostatic capacitance of the same embodiment, FIG. 4 is a circuit diagram showing a second embodiment of the electrostatic sensor device according to the present invention, and FIG. 5 is a general RCA system. FIG. 6 is a block diagram showing an electrostatic sensor device, FIG. 6 is an explanatory diagram showing an example of detection of a rotary shaft using the electrostatic sensor device, and FIG. 7 is a case where the rotary shaft has an eccentricity when the rotation is detected in FIG. FIG. 8 is an explanatory diagram showing the relationship between the tuning level and the detection signal, and FIG. 8 is an explanatory diagram showing the relationship between the frequency band of the detected component capacitance and the frequency band of the unnecessary component capacitance taken in by the detection electrode of the electrostatic sensor device. . 1 ... Oscillation circuit, 2 ... Tuning circuit, 3 ... Detection electrode, 4
...... Detection circuit, 5 …… Amplification circuit, 6 …… Rotation axis, 7 ……
Attachment, 8 ... AFC circuit, 9 ... Coupling capacitor, 10 ... Inductance element, 11 ... Diode, 12
...... Capacitor, 13 ...... Resistor, 14 ...... Buffer circuit,
15 …… Frequency selection control circuit, 16 …… Variable capacitance diode, 17 …… Diode, 18 …… Coupling capacitor, 19 ……
Detected object, 20 …… Distribution resistor.

Claims (1)

[Claims] 1. An oscillating circuit for oscillating and outputting an oscillating frequency signal, and a dielectric resonator which is independent of the oscillating circuit and has a frequency signal in response to a change in external capacitance detected by a detecting section. A tuning circuit whose tuning point changes, a variable-capacitance diode that functions as one resonance element of a dielectric resonator in the tuning circuit, and an unnecessary signal in a specified frequency band included in the output signal of the tuning circuit are selectively extracted to An electrostatic sensor device having a variable-capacitance diode and a frequency selection control circuit for correcting and controlling the displacement of the resonance frequency of the tuning circuit caused by the unnecessary component capacitance taken in by the detection unit.