JPH1038913A - Piezoelectric oscillator - Google Patents

Abstract

(57) [Abstract] [Purpose] The object of the present invention is to manufacture a more accurate, smaller, and less expensive acceleration detector of a capacitance type. A piezoelectric vibrator comprising a weight at the center of one side of a piezoelectric element, dividing the surface of the piezoelectric element into four parts without cutting off the plane, and forming electrodes on both sides thereof; Using a piezoelectric vibrator composed of the capacitance of an electrode formed on each surface facing the electrode, the change in capacitance between the electrode of the piezoelectric vibrator and the electrode facing the electrode is converted into a frequency The object is achieved by detecting the acceleration and detecting the magnitude and direction of an arbitrary acceleration parallel to the XY plane applied to the piezoelectric vibrator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration detector using a piezoelectric oscillation element.

[0002]

2. Description of the Related Art In the prior art, as can be seen from a structure shown in a sectional view of a capacitance type acceleration detector of FIG.
Capacitance change generated by the change amount of the gap in the gap between the electrodes 10 between the two facing surfaces is directly read to detect any two horizontal accelerations (X axis, Y axis) applied to the object. doing.

[0003]

However, when detecting the change in the capacitance caused by the change in the gap in the minimum gap, it is necessary to quantitatively measure the change in the capacitance obtained therefrom. Difficult and difficult to detect accurate capacitance change. Therefore, the reliability of the detected amount of acceleration obtained by the change in capacitance is low. Further, in the direct reading method of the capacitance, it is difficult to compensate for a change in a gap in a very small gap, which is an acceleration detecting unit, due to expansion and contraction of the entire detector due to temperature, and accurate detection of acceleration is performed. Hateful.

[0004]

In recent years, electronic devices and set parts have tended to have high reliability, high accuracy, small size, light weight, and low cost. Therefore, the same is required for the electronic components used for these components. Recently, the application of so-called mechatronics, which integrates the mechanical and electronic / electrical fields, has been actively introduced into the field of private cars, which can be said to be indispensable for everyday life. Electrical sensing such as TRC, ABS and airbag systems The computer judges the information thus obtained, and as a result, the mechanical system, which is the actuator, operates, and is used as one means of ensuring safety. A pressure sensor is used as a sensor for activating the TRC or the airbag system, and can accurately measure an acceleration (G) applied during a collision from an acceleration (G) during a normal running (a range of 0.2 to 5.0 G at most). Measurement and judgment systems have been created.

In the present invention, a piezoelectric vibrator is used as a conventional capacitance type acceleration detector, and a capacitance change is replaced with a frequency change to thereby reduce a phenomenon change (a gap in a very small gap which is an acceleration detecting portion). Since it can be amplified and detected, a highly stable, highly accurate and highly reliable product can be provided. The main principle is to use a characteristic in which the frequency changes due to a change in the piezoelectric vibrator and the capacitance (load capacitance) connected in series with the piezoelectric vibrator, that is, a load capacitance characteristic as shown in FIG. In this case, similar characteristics can be obtained. The load capacitance characteristic is characterized by a change in the capacitance connected in series to the piezoelectric vibrator, and the resonance frequency varies nonlinearly.

A conventional acceleration detector employs a method of directly measuring a change in capacitance due to a change in acceleration. However, in the present invention, at least one of the electrodes constituting the piezoelectric vibrator is arranged with a small interval. And a capacitor (which is connected in series to the piezoelectric vibrator and used as a load capacitor) formed by the opposing electrodes and a plurality of diagonal lines connected to the oscillation circuit on the same substrate. The piezoelectric vibrator element is deformed according to the magnitude and direction of the change in acceleration.

As a result, a plurality of capacitance values fluctuate, and individual oscillation frequency changes are measured in accordance with the acceleration change amount and direction, and are processed by an arithmetic circuit to determine the magnitude and direction of the acceleration by the oscillation frequency. It is to detect. As can be seen from FIG. 5, the relationship between the capacitance change and the frequency change is not linear.
If L is set to be small and relatively rough, sensitivity adjustment such as increasing CL (or adding CL externally) becomes possible.

On the other hand, the size and weight of the piezoelectric vibrator can be reduced by using an etching technique for processing the piezoelectric vibrator, and the cost can be reduced because a plurality of piezoelectric vibrators can be processed simultaneously in a single manufacturing process. In addition, the stability of the acceleration detector can be measured by using a temperature compensation circuit cultivated in a piezoelectric oscillator, in addition to using a piezoelectric vibrator whose temperature characteristics are originally stable compared to the conventional capacitance type. Since the management can be easily controlled, a stable frequency can be obtained over the entire operating temperature range in response to changes in the ambient temperature, so that stable acceleration can be detected.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In each drawing, the same reference numeral indicates the same object. FIG. 1 shows a perspective view of the piezoelectric oscillation element of the present invention. As an example, a piezoelectric vibrator 1 manufactured by etching is used, a slit portion 9 is formed by punching a part of the same plane of the piezoelectric vibrator 1 and divided into four parts. A piezoelectric oscillator having a shape sandwiching a flat surface from both sides (FIG. 3) is formed by, for example, a container 5 and a container 6 made of a glass material. The joining (sandwiching) of the piezoelectric vibrator 1 to the container 5 and the container 6 is performed by four legs 7 protruding from the end of the piezoelectric vibrator 1.

The four legs 7 protruding from one end of the piezoelectric vibrator 1
The piezoelectric vibrator 1 has a structure in which the piezoelectric vibrator 1 is freely bent by a weight 8 provided at the center of one surface of the piezoelectric vibrator 1. FIG.
Although the four legs 7 of the piezoelectric vibrator 1 shown in FIG. 4 are overhanged from the piezoelectric vibrator 1, there is no structural restriction such as disposing the legs 7 at the center of the piezoelectric vibrator 1, and the container The material to be used may be ceramic other than glass. The X direction and the Y direction described later are described in FIG. The weight 8 does not come into contact with the container 6 in any state.

As shown in the plan view of the piezoelectric vibrator 1 shown in FIG. 2, the piezoelectric vibrator 1 used in the present invention comprises one piezoelectric element plate.
There are electrodes 2 on both sides of each divided part,
A weight 8 is formed in the center of the back surface of the piezoelectric vibrator 1, and four piezoelectric vibrators 1 are independently formed in the same piezoelectric element plate by division by a slit portion 9.

Each of the four piezoelectric vibrators 1 is 1A,
1B, 1C, and 1D. The drawing (electrode) from the electrode 2 and the counter electrode 3 is omitted in the figure. The thickness of the piezoelectric vibrator 1 is 30 μm, the distance between the electrode 2 and the counter electrode 3 is 3 to 5 μm, and the thickness of the electrode 2 and the counter electrode 3 is about 1500 Å.

The piezoelectric vibrator 1 (1A, 1B, 1C, 1D)
The counter electrode 3 is disposed in the container 5 covering the piezoelectric vibrator 1 so as to face the piezoelectric vibrator 1. The electrode 2 of the piezoelectric vibrator 1
To the piezoelectric vibrator 1A, the piezoelectric vibrator 1B, the piezoelectric vibrator 1C,
The electrodes 2A, 2B, and 2 correspond to the piezoelectric vibrator 1D, respectively.
In the case of C and 2D, the counter electrodes 3 when the piezoelectric vibrator 1 is covered with the container 5 are 3A, 3B, 3C and 3D, respectively.

Although the wiring of the electrodes from the electrode 2 and the counter electrode 3 of the piezoelectric vibrator 1 is not shown, the capacitance generated between the electrode 2 of the piezoelectric vibrator 1 and the counter electrode 3 of the container 5 is represented by
When a circuit is configured by a circuit example for detecting acceleration using the piezoelectric oscillation element of the present invention shown in FIG.
The respective frequencies change from the amount of change in the capacitance between the electrode 2 and the counter electrode 3 of the container 5, and by comparing the frequency values with an arithmetic circuit, the magnitude and direction of an arbitrary acceleration parallel to the XY plane can be determined. It is to detect.

As shown in the load capacitance characteristic diagram of FIG. 5, a characteristic in which the oscillation frequency is changed by the change of the capacitance connected in series to the piezoelectric vibrator 1 is applied. When a capacitor is connected to the power supply, the frequency decreases as the capacity increases, and the characteristic is not linear.

FIG. 4 is a conceptual diagram showing how acceleration is detected using the piezoelectric vibrator 1 of the present invention. FIG.
When the acceleration is generated from left to right on the paper as shown in FIG. 3, the piezoelectric vibrator 1 has the shape of a “C” due to the inertia of the weight 8. Therefore, although the capacitances CA, CB, CC, and CD change, C
Since A and CC change in the same direction, and CB and CD change in the opposite direction, the oscillation frequency difference due to the change in the capacitance of CA and CC becomes zero, and only the oscillation frequency due to the change in the capacitance of CB and CD is detected as ΔF. You.

Similarly, when an acceleration occurs perpendicular to the plane of the paper, the capacitances CA, CB, CC, and CD also change.
Since DB and CD change in the same direction, and CA and CC change in the opposite direction, the oscillation frequency due to the change in CB and CD becomes zero, and only the difference in the oscillation frequency due to the change in the capacitance of CA and CC is detected as ΔF. As described above, by further processing the difference between the oscillation frequencies in the X direction and the Y direction by the arithmetic circuit, it is possible to detect the direction and magnitude of the acceleration in any direction parallel to the XY plane.

In this embodiment, the electrodes 2 of the piezoelectric vibrator 1 are used.
Although the counter electrode 3 opposing to the above is described in the configuration of the container 5, the counter electrode 3 may be configured in the container 6, or the counter electrode 3 may be configured in both the container 5 and the container 6. Absent.

[0019]

By applying the piezoelectric oscillation element according to the present invention as an acceleration detector, it is possible to detect acceleration at a small size, with high accuracy and at low cost. Also, by detecting the amount of frequency change of the piezoelectric vibrator as the change in acceleration,
For a change in the operating environment temperature, high-performance detection can be obtained by employing a temperature compensation circuit of the piezoelectric vibrator. As described above, by providing a small, inexpensive, and high-quality acceleration detector, acceleration can be easily and accurately detected.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an entire piezoelectric oscillation element of the present invention.

FIG. 2 is a plan view of a piezoelectric vibrator of the piezoelectric oscillation element according to the present invention.

FIG. 3 is a side view showing the structure of the piezoelectric oscillation element of the present invention.

FIG. 4 is a conceptual diagram showing how acceleration is detected using the piezoelectric oscillation element of the present invention.

FIG. 5 is a load capacitance characteristic diagram showing a frequency change with a general capacitance change.

FIG. 6 is an example of a circuit for detecting acceleration by the piezoelectric oscillation element of the present invention.

FIG. 7 is a cross-sectional view of a conventional capacitance type acceleration detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric vibrator 2 electrode 3 Counter electrode 4 Piezoelectric oscillator 8 Weight

Claims (2)

[Claims] 1. A piezoelectric oscillation element having a structure in which a capacitance is provided between an electrode of a piezoelectric vibrator and an opposing electrode provided on a surface facing the electrode, wherein the electrode of the piezoelectric vibrator and the piezoelectric vibrator are provided. A frequency change is detected by a change in capacitance generated between the electrode and a counter electrode provided on at least one surface facing the electrode. 2. A piezoelectric oscillation element having a structure in which a capacitance is provided between a piezoelectric vibrator having electrodes on both surfaces of the same piezoelectric element plate and a counter electrode provided on a surface of the piezoelectric vibrator facing the electrode, A piezoelectric vibrator having a weight integral with the piezoelectric plate at the center of one surface of the piezoelectric plate, and having electrodes on both surfaces obtained by dividing the plane of the piezoelectric plate into four parts, and opposing the electrodes of the piezoelectric vibrator. A piezoelectric oscillation element for detecting acceleration by an amount of frequency change due to a change in capacitance with respect to at least one opposing electrode formed on each of the opposing surfaces.