JPH0220162B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an oscillator that includes a resonator in a positive feedback loop.

[Prior Art] Next, a circuit diagram of a conventional oscillator using a vibrator will be described with reference to FIG. 2.

In FIG. 2, 1 is a tuning fork vibrator, 2A and 2B are piezoelectric elements, and 3 is a positive feedback amplifier.

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 elements 2A and 2B are attached to each of the sound pieces of the tuning fork vibrator so as to face each other, and the piezoelectric element 2B is used for vibration detection, and the piezoelectric element 2A is used for driving.

The positive feedback amplifier 3 applies positive feedback to the loop formed by the piezoelectric element 2A → the tuning fork vibrator 1 → the piezoelectric element 2B → the positive feedback amplifier 3 so that the mechanical vibration of the tuning fork vibrator 1 continues.

Next, a circuit diagram of another conventional oscillator using a vibrator will be explained with reference to FIG.

8A and 8B in FIG. 3 are coils, and 9A and 9B are magnets.

Although the magnets 9A and 9B are not magnetically coupled, they are attached to the vibrating portion of the tuning fork vibrator 1 so as to face each other.

The coils 8A and 8B are fixed at positions slightly apart from the tuning fork vibrator 1 so as to sandwich the magnets 9A and 9B.

Coil 8B is for vibration detection, and coil 8A is for drive.

The positive feedback amplifier 4 provides positive feedback to the loop composed of the coil 8A → magnet 9A → tuning fork vibrator 1 → magnet 9B → coil 8B → positive feedback amplifier 4 so that the mechanical vibration of the tuning fork transducer 1 continues. put on.

[Problems to be Solved by the Invention] The piezoelectric element 2B in FIG. 2 converts the mechanical amplitude of the tuning fork vibrator 1 into voltage.
The voltage conversion characteristics of B are easily affected by ambient temperature and humidity. For this reason, there is a problem in that even if only the voltage amplitude of the piezoelectric element 2B is controlled to be constant, the amplitude of the tuning fork vibrator 1 is not necessarily stabilized.

In addition, in the electromagnetically driven tuning fork oscillator circuit shown in Fig. 3,
Since the magnetic force of the magnets 9A and 9B is affected by the ambient temperature, the tuning fork vibrator 1
The problem is that the amplitude of is not necessarily stable.

In addition, there are improvements to the conventional circuits shown in Figures 2 and 3, such as in Japanese Patent Application Laid-open No. 19207-1982 and No. 149505-1983, but both of them are based on a machine using a tone fork vibrator. Since physical vibrations are converted into voltage using conversion elements such as piezoelectric elements and coils, the problem of detection sensitivity changing due to temperature, humidity, etc. remains unsolved.

The oscillators shown in FIGS. 2 and 3 are sometimes used in surface electrometers, etc.

When measuring the surface potential of the object to be measured in a non-contact manner, the surface potential of the object to be measured is converted into vibration capacitance by applying mechanical vibration to the capacitance of the measurement circuit of the object. Such a technique is also described in, for example, Japanese Patent Publication No. 58-47672.

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

In this invention, as a means for converting the mechanical vibration of a vibrator into an electrical signal, an electrode is placed in a non-contact state on the vibrating part of the vibrator, and a potential difference is created between the vibrator and the electrode. The purpose of the present invention is to provide an oscillator with stable amplitude by vibrating a capacitance with a static vibration and extracting an electric signal proportional to the amplitude of the vibrator.

[Means for Solving the Problems] In order to achieve this object, the present invention includes a vibrator 1 having a unique frequency, a piezoelectric element 2 that drives the vibrator 1, and a vibrating part of the vibrator 1. An electrode 3 that is electrostatically coupled and to which a DC voltage is applied, a positive feedback amplifier 4 that is connected between the electrode 3 and the piezoelectric element 2, a rectifier 5 that is connected to the electrode 3, and a DC output of the rectifier 5 that is and a differential amplifier 7 whose second input is the output of the reference power supply 6.
The output of the rectifier 5 is used as the power supply for the positive feedback amplifier 4, and when the output of the rectifier 5 is larger than the output of the reference power supply 6, the output of the differential amplifier 7 is reduced, and when the output of the rectifier 5 is smaller than the output of the reference power supply 6, the output of the differential amplifier 7 is Increase the output of the dynamic amplifier 7.

Next, a circuit diagram of an oscillator with stable amplitude according to the present invention will be explained with reference to FIG.

In FIG. 1, 2 is a piezoelectric element, 3 is an electrode, 5 is a rectifier, 6 is a reference power source, and 7 is a differential amplifier.

The electrode 3 is electrostatically coupled to the vibrating part of the vibrator 1,
DC voltage is supplied from the power supply -V.

A positive feedback amplifier 4 is connected between the electrode 3 and the piezoelectric element 2, and a rectifier 5 is connected to the electrode 3.

Differential amplifier 6 is connected between the DC output of rectifier 5 and the power supply of positive feedback amplifier 4 .

[Operation] The detection signal of the electrode 3 is proportional to the amplitude of the tuning fork vibrator 1. Therefore, if the output level of the positive feedback amplifier 4 can be controlled so that the amplitude of this detection signal is constant, the amplitude of the tuning fork vibrator 1 can be kept constant. FIG. 1 is intended to achieve this purpose.

In FIG. 1, the detection signal of the electrode 3 is applied to the input of the positive feedback amplifier 4, and a part of the signal is sent to the rectifier 5.
The signal is then rectified by the voltage and applied to one input of the differential amplifier 7.

The voltage of the reference power supply 6 is applied to the other input of the differential amplifier 7, and the differential amplifier 7 amplifies the difference between these two input voltages. When the output of the rectifier 5 is higher than the voltage of the reference power supply 6, the differential amplifier 7
The output of the differential amplifier 7 is set so that the output of the differential amplifier 7 becomes small, and in the opposite case, the output of the differential amplifier 7 becomes large.

As the positive feedback amplifier 4, an amplifier whose output level increases or decreases depending on changes in the supplied power supply voltage is used.

In FIG. 1, the output of the differential amplifier 7 is supplied as the power supply voltage of the positive feedback amplifier 4. Therefore, as the detection signal of the electrode 3 increases, the output of the differential amplifier 7 decreases, and therefore the output level of the positive feedback amplifier 4 decreases.

Conversely, when the detection signal of the electrode 3 becomes smaller, the output of the differential amplifier 7 becomes larger, so the positive feedback amplifier 4
The output level of the electrode becomes large, and the detection signal of the electrode 3 becomes constant.

That is, the positive feedback amplifier 4 applies negative feedback to the positive feedback loop for continuing vibration, so that the amplitude of the tuning fork vibrator 1 becomes constant.

[Effects of the Invention] According to the present invention, an air capacitor consisting of a vibrator and an electrode is used for vibration detection in an oscillator that includes a vibrator in a positive feedback loop, so that the influence of the conversion element on detection sensitivity is reduced. This results in an oscillator with less noise.

Therefore, if the oscillator according to the present invention is used in a surface electrometer, a surface electrometer with less measurement error can be provided.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an oscillator with stable amplitude according to the present invention, and FIGS. 2 and 3 are circuit diagrams of a conventional oscillator using a vibrator. 1... Tuning fork vibrator, 2... Piezoelectric element, 3... Electrode, 4... Positive feedback amplifier, 5... Rectifier, 6...
Reference power supply, 7...differential amplifier.

Claims (1)

[Claims] 1. A vibrator 1 having a unique frequency; a piezoelectric element 2 that drives the vibrator 1; an electrode 3 that is electrostatically coupled to the vibrating part of the vibrator 1 and to which a DC voltage is applied; a positive feedback amplifier 4 connected between the electrode 3 and the piezoelectric element 2; a rectifier 5 connected to the electrode 3; the DC output of the rectifier 5 is used as the first input, and the output of the reference power source 6 is used as the second input. and a differential amplifier 7, the output of the differential amplifier 7 is used as a power source for the positive feedback amplifier 4, and when the output of the rectifier 5 is larger than the output of the reference power source 6, the output of the differential amplifier 7 is reduced, and the output of the rectifier 7 is 5
An oscillator with stable amplitude, characterized in that when the output of the differential amplifier 7 is smaller than the output of the reference power supply 6, the output of the differential amplifier 7 is increased.