JPH03163370A - Electrostatic sensor apparatus - Google Patents

Abstract

PURPOSE:To achieve the stabilization of a tuning level and the removal of a noise component by feeding back the unnecessary signal corresponding to taken-in unnecessary component capacity to a variable capacity diode through a frequency selecting control circuit. CONSTITUTION:When real detected component capacity is taken in a tuning circuit 2 along with unnecessary component capacity by a detection electrode 3, both capacities are converted to voltage signals to be outputted and converted to the signals of the signal band of an object 19 to be detected by a detection circuit 4 to be outputted and a part thereof is applied to the frequency selecting control circuit 15 of an AFC circuit 8 through a diode 17. The selection range of the low frequency band and high frequency band matched with the frequency component of the unnecessary component capacity is preliminarily indicated to the circuit 15 and when the signal of the frequency component of the indicated band is applied, the signal is selected to be applied to a variable capacity diode 16. The diode 16 receives this unnecessary signal to change the resonance frequency of the circuit in the direction reverse to the change direction due to the unnecessary component capacity. Therefore, the fluctuation of the resonance frequency due to the unnecessary component capacity is corrected by the unnecessary signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrostatic sensor device that detects minute changes in capacitance of an object to be detected.

[Conventional technology]

The electrostatic sensor device that has been very commonly used changes the capacitance of the tank circuit of the oscillation circuit in response to changes in the capacitance of the detected object, thereby changing the oscillation frequency. However, the sensitivity is low, and for this reason, in recent years, the more sensitive RCA method (a method for obtaining AM modulated waves by changing the capacitance of a tuned circuit capacitor with a resonant frequency slightly shifted from the oscillation frequency of the oscillation circuit) devices have come into use. As shown in FIG. 5, this RCA type electrostatic sensor device includes an oscillation circuit l,
A tuning circuit 2, a detection electrode 3 such as a detection needle that detects a change in capacitance with the object to be detected 19, a detection circuit 4, and an amplifier circuit 5.
It consists of The oscillation circuit 1 and the tuning circuit 2 each include separate and independent resonators, for example, as shown in FIG.
The resonant frequency f of the tuned circuit 2 with respect to the fixed oscillation frequency f1 of the oscillation circuit 1. Set it to a slightly shifted position,
Change in minute capacitance detected by detection pole 3 ±Δ
The resonant frequency is shifted from f0 to the left and right by Δr corresponding to C, and the change in capacitance ±ΔC is set to the tuning level ■. This detection signal is converted into a voltage change of ±ΔV based on the reference voltage, and this detection signal is detected and amplified to be extracted.

[Problem to be solved by the invention]

However, this type of electrostatic sensor device is too sensitive, so when detecting minute changes in capacitance of the object to be detected 19, it is sensitive to changes in capacitance caused by environmental changes, etc. There is a drawback.

Therefore, when detecting a change in the minute capacitance of the detected object I9, the true detection component ΔC of the capacitance detected due to the movement of the detected object 19, etc. and the unnecessary capacitance (hereinafter referred to as (referred to as the unnecessary component capacitance) ΔC' is from the detection electrode 3 to the tuning circuit 2.
There may be cases where they are imported into the same time. The unnecessary capacitance ΔC' is caused by various factors. For example, in the case of the VHD system of a video disk device, it is caused by fluctuations in capacitance that occur when replacing and setting the needle that functions as the detection electrode 3, , changes in the floating distribution capacitance between the needle and the housing as the needle moves from the outside to the inside of the disk, the fluctuation components of the capacitance due to variations due to the breath shape of individual disks, and the fluctuation components of the capacitance at each location on the disk surface. This occurs due to changes in capacitance, etc.

For example, as shown in FIG. 6, a gear-shaped attachment 7 is attached to the rotating shaft 6, and the detection electrode 3 is arranged to face the tooth pattern of the attachment 7.
When detecting the rotation of the rotary shaft 7, an eccentric component of the rotating shaft 7 and a fluctuation component of the electrostatic capacitance due to micro-width irregularities such as holes and holes on the tooth surface are taken in as unnecessary capacitance.

Such unnecessary capacity has different frequency bands depending on the cause of its occurrence. The relationship between the frequency band of this unnecessary component capacitance and the frequency band of the true detected component capacitance can be expressed as shown in FIG. 8, with frequency plotted on the horizontal axis and gain plotted on the vertical axis. That is, it is polarized into an unnecessary component capacitance A1 in a low frequency band and an unnecessary component capacitance ffl A z in a high frequency band with the frequency band f8 of the true detection capacitance interposed therebetween. The unnecessary component capacitance in this low frequency band is the VH
This applies to vibration components close to direct current of several tens of cycles that occur when replacing and setting the needle in method D, and changes in stray distributed capacitance due to movement of the needle, as well as detection of rotation of the rotating shaft 6 shown in Figure 6. In such a case, a change in the eccentricity of the rotating shaft, etc. corresponds to a certain amount. For example, as the unnecessary component capacitance in the high frequency band,
This corresponds to the fluctuation component of the capacitance caused by the tooth-shaped pinholes and bulges of the attachment 7, which are detected when the rotation is detected in the figure.

When such unnecessary component capacitance is taken in, the tuning circuit 2
The resonant frequency of changes depending on this unnecessary component capacitance, but
When the unnecessary component capacitance is in a low frequency band, there is a problem that the potential of the tuning level of the tuning circuit 2 fluctuates, and the detection sensitivity decreases (the tuning level is set at the most sensitive position, so Sensitivity decreases as the tuning level changes).

In addition, if low frequency unnecessary component capacitance is caused by the eccentricity of the rotating shaft, the tuning level will have a low frequency frequency as shown in Figure 7, and the tuning level will correspond to the frequency of the eccentricity of the rotating shaft 6. The problem arises that the amount of energy changes.

In this case, a detection signal corresponding to the true detection component capacitance is output from the tuning circuit 2 on a tuning level having a frequency corresponding to the eccentricity of the rotating shaft 6.

On the other hand, when the unnecessary component capacitance is in a high frequency band, the unnecessary component capacitance appears as noise in the detection signal. For example, in the rotation detection, if tooth-shaped pinholes or holes are detected, this causes noise P, P as shown in FIG.
', and there is a problem that the S/N ratio of the detection signal deteriorates.

The present invention has been made to solve the above-mentioned conventional problems, and its purpose is to prevent fluctuations in the tuning level and deterioration of the S/N ratio of the detection signal due to the influence of unnecessary component capacitance. However, it is an object of the present invention to provide an electrostatic sensor device capable of detecting changes in minute capacitance of an object to be detected with high sensitivity and accuracy.

[Means to solve the problem]

In order to achieve the above object, the present invention is configured as follows. That is, the electrostatic sensor device of the present invention includes an oscillation circuit that oscillates and outputs an oscillation frequency signal and a dielectric resonator that is separate and independent from the oscillation circuit, and detects changes in external capacitance detected by the detection section. A tuned circuit whose tuning point with the frequency signal changes when the frequency signal is received, a variable capacitance diode that functions as a resonant element of a dielectric resonator in this tuned circuit, and an unnecessary signal in a specified frequency band included in the output signal of the tuned circuit. The present invention is characterized by comprising a frequency selection control circuit that selects and extracts the variable capacitance diode and corrects and controls the displacement of the resonant frequency of the tuning circuit caused by the unnecessary capacitance taken in by the detection section in addition to the variable capacitance diode.

[Effect]

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 each converted into a voltage signal and output from the tuning circuit, and this output signal is A portion is added to the frequency selection control circuit. For example, if the frequency selection control circuit has a certain frequency component with an unnecessary component capacity, and this frequency component is clear, a selection range of a low frequency band and a high frequency band that matches the frequency component is set in advance. It is specified,
When signals of frequency components in these designated bands are added, that signal is selected and applied to the variable capacitance diode. Therefore, in the above case, the frequency selection control circuit presets as an unnecessary signal a frequency component signal corresponding to the unnecessary capacitance from among the frequency signals applied from the tuning circuit side, and applies this to the variable capacitance diode. Add it. The variable capacitance diode receives an unnecessary signal applied from the frequency selection control circuit and changes the resonant frequency of the tuning circuit in a direction opposite to the direction of change due to the unnecessary component capacitance. In other words, when changes in external capacitance include unnecessary component capacitance, the resonant frequency of the tuning circuit changes due to this unnecessary capacitance, but the unnecessary signal of this unnecessary component capacitance passes through the frequency selection control circuit and changes to the variable capacitor. This unnecessary signal is fed back to the diode, and the fluctuation in the resonant frequency due to the unnecessary capacitance is corrected, and the tuning level is kept constant.
Moreover, noise components are removed.

〔Example〕

Hereinafter, implementation of the electrostatic sensor device according to the present invention will be explained based on 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 includes an oscillation circuit 1, a tuning circuit 2, a detection electrode 3 as a detection section, a detection circuit 4, an amplifier circuit 5, a buffer circuit 14, and an AFC circuit 8. The oscillation circuit 1 uses a dielectric resonator (ceramic resonator) that oscillates at a fixed and constant oscillation frequency within the range of ultra-high frequency, in the present embodiment, 0.5 Gz to 5 GHz. This oscillation circuit 1 oscillates the high frequency oscillation signal and applies it to the tuning circuit 2. This tuning circuit 2 is a dielectric resonator (ceramic resonator) that is separate and independent from the dielectric resonator of the oscillation circuit 1.
A detection electrode 3 consisting of a detection needle or the like for detecting a change in capacitance with the detected object 19 is connected to this tuning circuit 2.

The detection circuit 4 is connected to the tuning circuit 2 via a coupling capacitor 9, and this detection circuit 4 is connected to an inductance element 1.
0, diode 11, capacitor 12, and resistor 1
3, the diode 11,
The capacitor 12 and the resistor 13 constitute a detection section of the detection circuit 4. This detection section performs envelope detection of the ultra-high frequency output signal outputted from the tuning circuit 2 and converts it into a signal in the signal band of the detected object 19.

The amplifier circuit 5 amplifies the signal applied from the detection circuit 4 by n times, supplies it to a signal processing section (not shown) via the buffer circuit 14, and simultaneously amplifies the signal applied from the detection circuit 4
tomatic Frequency Control
) Add to circuit 8.

This AFC circuit 8 consists of a frequency selection control circuit 15 and a variable capacitance diode 16.
The input side of the amplifier circuit 5 is connected to the output end of the amplifier circuit 5 via a diode 17. In addition, the frequency selection control circuit 1
The output side of the variable capacitance diode 16 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 a coupling capacitor 18, and the variable capacitance diode 16 functions as one resonant element of the tuning circuit (dielectric resonator) 2.

The frequency selection control circuit 15 extracts unnecessary signals contained in the signal output from the tuning circuit 2 by frequency selection, but in this embodiment, the frequency selection control circuit 15 is configured by a filter circuit. There is. This filter circuit includes, for example, a low-pass filter as shown in FIG. 2(a), a high-pass filter as shown in FIG. 2(b), or a band-pass filter as shown in FIG. 2(C). The low-pass filter selectively passes unnecessary signals in a low frequency band including DC components, and the high-pass filter selectively passes unnecessary signals in a high frequency band. In addition, the bandpass filter selectively passes unnecessary signals in the intermediate frequency band and is connected to the variable capacitance diode 16.
It is added to. In this embodiment, the unnecessary signals selected and designated by these filter circuits are limited to those in a frequency band outside the frequency band f of the true detection capacity.

The first embodiment is configured as explained above,
The operation will be explained below.

As shown in FIG. 3, in a state where the oscillation frequency f of the oscillation circuit l is set at a position slightly shifted from the resonant frequency (tuned frequency) fo of the tuning circuit 2, for example, when the detected object l9 When it moves, a slight change in capacitance occurs between the detection electrode 3 and the detected object 19, and the resonance point (tuning point) of the tuning circuit 2 changes by Δr. Then, in the tuning circuit 2, the oscillation frequency f is multiplied by the variation Δf of the resonance frequency in the tuning circuit 2, and a so-called AM modulation signal is obtained. In this embodiment, if the oscillation frequency is a very high frequency, for example IG}{z, the modulation signal is IG}{z
It becomes an ultra-high frequency signal with a bandwidth corresponding to the movement of the object 19 to be detected.

When detecting this minute capacitance, if an unnecessary capacitance is detected, the resonance frequency of the tuning circuit 2 changes due to the unnecessary component capacitance, and if the unnecessary component capacitance is in the low frequency band, the tuning level In addition, if the unnecessary component capacitance is in a high frequency band, it appears as noise in the modulation signal (detection signal). The modulated signal containing some of these unnecessary signals is applied to the detection circuit 4. The detection circuit 4 performs envelope detection on this ultra-high frequency signal to detect the detected object 19.
(3 MHz signal in this embodiment). This 11? The range-converted signal is amplified by n times by the amplifier circuit 5, and a part of the output signal is sent to the buffer circuit 1.
4 to a signal processing section (not shown), and some other signals are branched and supplied to the AFC circuit 8 through a diode 17.

The frequency selection control circuit 15 of the AFC circuit 8 extracts unnecessary signals based on the capacitance from among the input signal components by frequency selection. For example, when the frequency selection control circuit I5 is configured with a low-pass filter, an unnecessary signal in a low frequency band is extracted, and the extracted unnecessary signal is applied to the variable capacitance diode I6.

Furthermore, when the frequency selection control circuit 15 is configured with a high-pass filter, unnecessary signals in the high frequency band are extracted and added to the variable capacitance diode l6. The variable capacitance diode 16 changes its capacitance by an unnecessary signal applied from the frequency selection control circuit 15,
The resonant frequency of the tuned circuit 2 is changed.

Since the variable capacitance diode I6 is connected in a reverse biased state, the direction of displacement of this resonant frequency is opposite to the direction of displacement of the resonant frequency of the tuned circuit 2 due to the introduction of unnecessary capacitance. In other words, when the detection electrode 3 detects an unnecessary partial capacitance together with the true detection component capacitance, a capacitance with a polarity opposite to the unnecessary partial capacitance is generated in the variable capacitance diode l6, thereby reducing the unnecessary partial capacitance. It cancels it out. As a result, even if the tuning level is displaced due to unnecessary capacitance in the low frequency band, this displacement is corrected to the correct level position initially set by the reverse polarity capacitance created by the variable capacitance diode l6 due to the unnecessary signal. Ru. Furthermore, even if unnecessary component capacitance in a high frequency band is detected, this will be canceled due to the change in capacitance of the variable capacitance diode 16, and the noise P and P' generated in the modulation signal will not be effectively removed. It is possible.

In this way, according to this embodiment, even when unnecessary component capacitance is detected by the detection electrode 3, there is no change in the tuning level, and the noise component generated due to this unnecessary component capacitance can be removed. This makes it possible to detect minute capacitances on the order of IXIO-'PF with high sensitivity and excellent S/N ratio.

FIG. 4 shows a second embodiment of the electrostatic sensor device according to the present invention. This second embodiment includes a tuning circuit 2,
A plurality of circuits each consisting of a detection electrode 3, a detection circuit 4, an amplifier circuit 5, and a variable capacitance diode 16 are arranged in parallel, and each series is connected from one common oscillation circuit 1 through a distribution resistor 20 and a coupling capacitor. Connected to tuning circuit 2. and,
The input side of the frequency selection control circuit 15 is connected to the output side of the amplifier circuit 5 of each series via a resistor, and the output terminal of the frequency selection control circuit 15 is connected to the variable capacitance diode 16 of each corresponding series. has been added. The electrostatic sensor device of this second embodiment is a type of device that processes in parallel the detection signals of minute voltages detected from the detection electrodes 3 of each series.

In this second embodiment, when the detection electrodes 3 of each series detect unnecessary capacitance, the unnecessary signals are respectively applied to the frequency selection control circuit 15, and the frequency band designated by the frequency selection control circuit 15 is The unnecessary signal is added to the variable capacitance diode l6 of the corresponding series, and the variation in the resonant frequency of the tuning circuit 2 is corrected in the same manner as in the first embodiment, thereby stabilizing the tuning level and removing noise components. It will be destroyed.

Note that the present invention is not limited to the above embodiments,
Various implementation modes are possible.

For example, in the embodiment described above, the resonator of the oscillation circuit 1 is a dielectric resonator, but it may also be a strinoplane.

〔Effect of the invention〕

In the present invention, when detecting minute capacitance, if an unnecessary capacitance is captured together with the desired detected capacitance, an unnecessary signal corresponding to the unnecessary capacitance is transmitted to the variable capacitor via a frequency selection control circuit. Feedback to the diode side,
Since it is designed to compensate for changes in the resonant frequency of the tuning circuit caused by unnecessary signals, it is possible to stabilize the tuning level and remove noise components, resulting in a reduction in S/N.
It becomes possible to detect minute capacitance with high sensitivity and high ratio.

Furthermore, since the system employs a system in which unnecessary signals are fed back to perform correction control for two resonance frequencies, the device structure is extremely simple, and it is possible to significantly reduce the size of the device and the cost of the device.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of the electrostatic sensor device according to the present invention, FIG. 2 is a circuit diagram of various filter circuits showing specific examples of the frequency selection control circuit in the same embodiment, and FIG. is an explanatory diagram showing the micro-capacitance detection operation of the same embodiment, FIG. 4 is a circuit diagram showing the second embodiment of the electrostatic sensor device according to the present invention, and FIG. 5 is a general diagram of the RCA method. A block diagram showing an electrostatic sensor device, FIG. 6 is an explanatory diagram showing an example of detecting a rotating shaft using the electrostatic sensor device, and FIG. 7 shows a case where the rotating shaft has eccentricity when detecting rotation as shown in FIG. 6. FIG. 8 is an explanatory diagram showing the relationship between the tuning level of the electrostatic sensor device and the detection signal. FIG. . DESCRIPTION OF SYMBOLS 1... Oscillation circuit, 2... Tuning circuit, 3... Detection electrode, 4... Detection circuit, 5... Amplification circuit, 6... Rotating shaft, 7... Attachment, 8...・・AFC circuit,
9... Coupling capacitor, 10... Inductance element, 1l... Diode, 12... Capacitor, 1
3...Resistor, 14...Buffer circuit, 15...
Frequency selection control circuit, l6... variable capacitance diode,
17...Diode, l8...Coupling capacitor, 1
9... Object to be detected, 20... Distribution resistor.

Claims (1)

[Claims] It has an oscillation circuit that oscillates and outputs an oscillation frequency signal and a dielectric resonator separate from this oscillation circuit, and the tuning point with the frequency signal changes in response to changes in the external capacitance detected by the detection section. A tuned circuit, a variable capacitance diode that functions as a resonant element of a dielectric resonator in this tuned circuit, and an unnecessary signal in a specified frequency band included in the output signal of the tuned circuit is selectively extracted and added to the variable capacitance diode. An electrostatic sensor device comprising: a frequency selection control circuit that corrects and controls displacement of a resonance frequency of a tuned circuit caused by unnecessary component capacitance taken in by a detection section.