JPS6126310A - Oscillator with stable amplitude - Google Patents

Abstract

PURPOSE:To decrease the effect to be exerted on a detection sensitivity by a converting element by providing a potential difference between a vibrator and an electrode arranged to the vibrating part of the vibrator in contactless state and extracting an electric signal proportional to the amplitude of the vibrator from the electrode. CONSTITUTION:The electrode 11 is arranged to the vibrating part of a tuning fork vibrator 1 in noncontact state. A potential difference is fed to the electrode 11 and the vibrator 1, and the static capacitance between the vibrator 1 and the electrode 11 is vibrated by the mechanical vibration of the tuning folk vibrator 1. In such a case, a positive feedback amplifier 12 applies a positive feedback to a loop consisting of piezoelectric element 13 vibrator electrode 11 amplifier 12 so that the mechanical vibration of the vibrator 11 continues. Since an air capacitor comprising the vibrator and the electrode is adopted for the detection of vibration in such as way, the effect of the converting element on the detection sensitivity is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to an oscillator including a resonator in a positive feedback loop.

(b) Prior art and problems First, we will introduce a conventional circuit diagram of an oscillator using a resonator as a second example.
As shown in the figure.

In FIG. 2, 1 is a tuning fork vibrator, 2 is a piezoelectric element, 3 is a positive feedback amplifier, and 4 is a piezoelectric element.

The tuning fork vibrator 1 has a U-shaped outer shape and has a unique frequency determined by the length and shape of each sound piece.

The piezoelectric element 2 and the piezoelectric cord 4 are attached to each sound piece of the tuning fork vibrator 1 so as to face each other, and the piezoelectric cord 2 is used for vibration detection, and the piezoelectric element 4 is used for driving.

The positive feedback amplifier 3 applies positive feedback to the loop constituted by the piezoelectric cable 4 → the tuning fork transducer 1 → the piezoelectric cable 2 → the positive feedback amplifier 3 so that the mechanical vibration of the tuning fork transducer A continues.

The piezoelectric element 2 converts the mechanical amplitude of the tuning fork vibrator 1 into voltage, and the voltage conversion 1! of the piezoelectric element 2! The temperature is easily affected by the ambient temperature and humidity.

Therefore, even if only the voltage amplitude of the electric element 2 is controlled to be constant, there is a problem that the amplitude of the tuning fork vibrator 1 is not necessarily stable.

Next, FIG. 3 shows another conventional circuit diagram of an oscillator using a vibrator.

In Figure 3, 5 is a magnet, 6 is a coil, 7 is a positive feedback amplifier, 8
is a coil, and 9 is a magnet.

Although the magnet 5 and the magnet 9 are not magnetically coupled, the tuning fork vibrator 1
It is installed so that it faces the vibrating part of the

The coil 6 and the coil 8 are fixed at a position slightly apart from the tuning fork vibrator 1 so as to sandwich the magnet 5 and the magnet 9.

Coil 6 is for vibration detection, and coil 8 is for drive.

The positive feedback amplifier 7 provides positive feedback to the loop composed of the coil 8 → magnet 9 → tuning fork vibrator 1 → magnet 5 → coil 6 → positive feedback amplifier 7 so that the mechanical vibration of the tuning fork transducer 1 continues. put on.

In the electromagnetically driven tuning fork oscillator circuit shown in FIG. 3, the magnetic force of the magnet 5 is affected by the ambient temperature, so the amplitude of the tuning fork vibrator 1 is not necessarily stable, as in the case of FIG. 2. There is.

In addition, as improved versions of the conventional circuits shown in FIGS.
149505, etc., but all of them convert the mechanical vibration of the tuning fork vibrator into voltage using a conversion element such as a piezoelectric element or coil, which solves the problem of detection sensitivity changing due to temperature, humidity, etc. It has not been.

The oscillators shown in FIG. 2 and 31.lambda.I are sometimes used in surface electrometers and the like.

When measuring the surface potential of the object to be measured without contact,
By applying mechanical vibration to the capacitance between the measured object and the measurement circuit, the surface potential of the measured object is converted into vibration capacitance. Regarding such technology, for example,
It is also described in Publication No. 672, etc.

Surface electrometers that use a vibrator have a problem in that measurement errors occur if the vibration amplitude of the vibrator is not constant.

(C) Purpose of the Invention This invention provides a means for converting the mechanical vibration of a vibrator into an electrical signal by disposing an electrode in a non-contact state on the vibrating part of the vibrator, and creating a potential difference between the vibrator and the electrode. It is an object of the present invention to provide an oscillator with stable amplitude by vibrating the capacitance with the mechanical vibration of the vibrator and preventing extracting an electric signal proportional to the amplitude of the vibrator.

(d) Examples of the invention First, a circuit diagram of an embodiment according to the present invention is shown in FIG.

In FIG. 1, 11 is an electrode, 12 is a positive feedback amplifier, and 13 is a piezoelectric element.

The electrode 11 is placed in a non-contact manner on the vibrating part of the tuning fork vibrator 1.

A potential difference is applied between the tuning fork vibrator 1 and the electrode 11, and the mechanical part vibration of the tuning fork vibrator 1 causes the capacitance between the tuning fork vibrator 1 and the electrode 11 to vibrate.

The piezoelectric element 13 is for driving, and the coil 8 and magnet 9 shown in FIG. 3 may be used instead of the piezoelectric element 13 as a vibration driver.

The positive feedback amplifier 12 applies positive feedback to the loop formed by the piezoelectric cable 13 → the tuning fork vibrator 1 → the electrode 11 → the positive feedback amplifier 12 so that the mechanical vibration of the tuning fork vibrator 1 continues.

In Fig. 1, the facing area of the tuning fork vibrator 1 and the electrode 11 is A(c
m2), and the opposing distance between the tuning fork vibrator 1 and the electrode 11 is L(c
m), then the capacitance C between the tuning fork vibrator 1 and the electrode 11 is
o is expressed by the following formula.

Co=A/11.3L (pF)・・・・・・・・・
(1) Since the bias voltage -V is applied to the electrode 11 via the resistor 14, a potential difference of 1.5 mm is applied between the tuning fork vibrator 1 and the electrode 11.

Therefore, an electrostatic charge Q expressed by the following equation (2) is accumulated in the capacitance Co.

Q”CoX(-V)・・・・・・・・・・・・・・・
(2) When a voltage is applied to the piezoelectric element 13, the tuning fork vibrator 1 undergoes mechanical displacement and vibrates at a specific period.

If the amplitude of the tuning fork vibrator 1 is ΔL, a voltage ΔV proportional to the amplitude ΔL is induced in the electrode 11 as shown in equation (3).

△V=11.3QX△L/A・・・・・・・・・・・・
(3) The circuit shown in FIG. 1 maintains oscillation by amplifying the voltage ΔV with the positive feedback amplifier 12 and applying it to the piezoelectric element 13.

Although the electrode 11 is placed inside the tuning fork vibrator 1 in FIG. 1, the electrode 11 may be placed outside the tuning fork vibrator 1. If the electrode 11 is placed outside the tuning fork vibrator 1, the vibration direction of the tuning fork vibrator 1 will be opposite to that shown in Fig. 1, so the phase should be adjusted so that the output of the positive feedback amplifier 1'2 becomes positive feedback. Be careful when matching.

Next, a circuit diagram of another embodiment according to the present invention is shown in FIG.

15 in FIG. 4 is a cantilever rod vibrator, and the cantilever rod vibrator 15
One end is fixed and the other end is free.

The electrode 11 is placed in a non-contact manner on the free end of the cantilever rod vibrator 15, and a bias voltage -■ is applied through the resistor 14 in the same manner as in FIG.

As the vibration driver, the coil 8 and magnet 9 shown in FIG. 3 may be used instead of the piezoelectric element 13 shown in FIG. 4.

As shown in Figures 1 and 4, this invention detects the vibration of a vibrator by using the vibration capacity of an air capacitor formed between the vibrator and an electrode placed in the vibrating part of the vibrator. It is something.

Therefore, compared to conventional oscillators such as those shown in FIGS. 2 and 3, the influence of temperature and humidity is reduced, allowing accurate and stable vibration detection.

Next, a circuit diagram of another embodiment according to the present invention is shown in FIG.

In FIG. 5, 16 is a positive feedback amplifier, 17 is a rectifier, 18 is a reference power supply, and 19 is a DC amplifier.

In FIG. 5, a positive feedback amplifier 16 is used in place of the positive feedback amplifier 12 in FIG. 1, and a rectifier 17, a reference power supply 18 and a DC amplifier 19 are used to control the output of the positive feedback amplifier 16.

The detection signal of the electrode 11 is proportional to the amplitude of the tuning fork vibrator 1.

Therefore, if the output level of the positive feedback amplifier 16 can be controlled so that the amplitude of the detection signal is constant, the amplitude of the tuning fork vibrator 1 can be kept constant. FIG. 5 is a circuit diagram for such purpose.

In FIG. 5, the detection signal of the electrode 11 is applied to the input of the positive feedback amplifier 16, and a part of it is rectified by the rectifier 17 and applied to one input of the DC amplifier 19. The voltage of the reference power supply 18 is applied to the other input of the DC amplifier 19, and the DC amplifier 19 amplifies the difference between these two input voltages. Then, the output of the DC amplifier 19 is set so that when the output of the rectifier 17 is higher than the voltage of the reference power supply 18, the output of the DC amplifier 19 becomes smaller, and in the opposite case, the output horn of the DC amplifier 19 becomes larger. do.

As the positive feedback amplifier 16, an amplifier whose output level increases or decreases depending on changes in the supplied power supply voltage is used.

In FIG. 5, the output of the DC amplifier 19 is transferred to the positive feedback amplifier 16.
It is supplied as the power supply voltage. Therefore, electrode 1
When the detection signal of 1 becomes large, the output of the DC amplifier 19 becomes small, and therefore the output level of the positive feedback amplifier 16 becomes small. On the other hand, when the detection signal of the electrode 11 becomes smaller, the output of the DC amplifier 19 becomes larger, so the output level of the positive feedback amplifier 16 increases, and the detection signal of the electrode 11 becomes constant. That is, the positive feedback amplifier 16 applies negative feedback to the positive feedback loop for continuing vibration so that the amplitude of the tuning fork vibrator 1 becomes constant.

(e) Effects of the Invention According to the present invention, an air capacitor composed of a vibrator and an electrode is used for vibration detection in an oscillator that includes a vibrator in the positive feedback loop, so that the detection sensitivity by the conversion element is improved. This results in an oscillator with less influence on the oscillator.

Therefore, if the oscillator according to the present invention is used in a surface electrometer, it is possible to obtain ε, which provides a surface electrometer with less measurement error.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment according to the present invention, FIGS.
The figure is a conventional circuit diagram, and FIGS. 4 and 5 are circuit diagrams of other embodiments according to the present invention. 1...Tune fork vibrator, 2...Piezoelectric element, 3...
...Positive feedback amplifier, 4...Piezoelectric element, 5...
... Magnet, 6 ... Coil, 7 ... Positive feedback amplifier, 8 ... Coil, 9 ... Magnet,
11... Electrode, 12... Positive feedback amplifier, 1
3... Piezoelectric element, 14... Resistor, 15
...Cantilever bar vibrator, 16...Positive feedback amplifier, 17...Rectifier, 18;...Reference power supply, 19...DC amplifier . Agent Patent Attorney Kin Omata Figure 2

Claims (1)

[Claims] 1. A vibrator having a unique frequency, a vibration driver for driving the vibrator, an electrode electrostatically coupled to a vibrating portion of the vibrator, and the electrode and the vibration driver and a positive feedback amplifier connected between the oscillator and the oscillator, the oscillator having a stable amplitude, characterized in that the mechanical vibration of the oscillator is extracted as a change in capacitance between the oscillator and the electrode.