JP2001116764A - Acceleration meter utilizing energy confinement type piezoelectric vibration - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric type acceleration meter that is compact, has simple structure, can be manufactured easily, is accurate, and can also measure dynamic acceleration. SOLUTION: First and second electrodes in a strip shape are provided in parallel at a specific interval each other on the main surface of a part with polarization in the thickness direction of a piezoelectric plate, and a piezoelectric vibrator for generating energy confinement type vibration at the piezoelectric plate part between both electrodes by exciting the piezoelectric plate while applying a drive AC voltage for excitation between the first and second electrodes is used, thus detecting acceleration being applied in a direction that orthogonally crosses the main surface of the piezoelectric plate as an electrical signal by electrically detecting the change in the energy confinement type vibration due to the distortion of the piezoelectric plate that is generated by acceleration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an accelerometer,
In particular, it relates to an accelerometer that detects acceleration with a simple structure using a piezoelectric body.

[0002]

2. Description of the Related Art An accelerometer that converts acceleration into rotational angular acceleration and specifies it by attaching a weight or a pendulum (unbalanced weight) to an inner gimbal of a gyroscope, or by attaching an unbalanced weight instead of the inner gimbal, is an aircraft. It is used for However, such accelerometer lobes are complex and expensive.

On the other hand, as a device for detecting acceleration as an electric signal with a simple structure, a weight is combined with a piezoelectric element and the displacement of the weight due to the acceleration is measured.
2. Description of the Related Art Piezoelectric accelerometers that detect acceleration are known.

[0004]

The above-mentioned accelerometer using a piezoelectric body has a simple structure and is inexpensive, but has a drawback that only a static acceleration can be measured.

[0005] It is therefore an object of the present invention to provide an accelerometer that is compact, simple in construction and manufacture and is capable of electrically measuring dynamic acceleration with high precision.

[0006]

According to the present invention, strip-shaped first and second electrodes are provided in parallel at a predetermined distance from each other on the main surface of a portion of the piezoelectric plate having polarization in the thickness direction. A piezoelectric vibrator in which energy is trapped in a piezoelectric plate portion between the two electrodes by applying a drive AC voltage for excitation between the first and second electrodes to excite the piezoelectric plate; Detecting means for electrically detecting a change in the energy trapping type vibration due to an acceleration applied to a piezoelectric vibrator in a direction orthogonal to a main surface of the piezoelectric plate, and measuring the acceleration by using the detecting means. An accelerometer utilizing confined piezoelectric vibration is obtained.

The detecting means has a current detecting circuit connected to the second electrode and having a virtual grounding function, applies a drive voltage for excitation to the first electrode, and outputs an output of the current detecting circuit. Can be configured to obtain a detection output.

The detecting means has a synchronous detection circuit connected to the output of the current detection circuit, and a rectifier circuit connected to the output of the synchronous detection circuit. It is preferable to obtain an output corresponding to the above.

Further, an oscillation circuit connected to the output of the current detection circuit for oscillating a signal of the self-excited oscillation driving frequency, and an AC voltage of the self-excited oscillation driving frequency connected to the output of the oscillation circuit. And a driving circuit for applying a voltage to the first electrode.

A piezoelectric ceramic is used as the piezoelectric plate, and only a region between the first and second electrodes of the piezoelectric ceramic and a region in the vicinity thereof are polarized in the thickness direction.

Also, a piezoelectric crystal plate having a polarization axis in the thickness direction can be used as the piezoelectric plate.

[0012]

1 (a) and 1 (b) are a plan view showing a configuration of an energy-trapping type vibrator used in an embodiment of the present invention and a cross-sectional view showing only electrode portions, respectively. is there.

Referring to FIGS. 1A and 1B, a space (in the X-axis direction) is provided on the same plane at the center of the piezoelectric plate 10 polarized in the thickness direction (the Z-axis direction). Opposing strip-shaped electrodes D1 and D2 are formed. In addition,
T1 and T2 are terminal portions.

Here, as shown in the figure, the three-dimensional coordinates of the piezoelectric vibrator 1 in which the thickness direction of the piezoelectric plate 10 is the Z axis, the direction in which the electrodes D1 and D2 are opposed to each other is the X axis, and the direction orthogonal thereto are the Y axis. Decide.

The piezoelectric vibrator 1 uses a piezoelectric plate 10 made of, for example, a piezoelectric ceramic plate such as PZT or barium titanate and having a central portion having a polarization axis in a thickness direction.

Electrodes D1, D2 and terminals T1, T2
Is preferably composed of silver paste or gold sputter. Of course, other conductive films can be employed. The terminal for leading out to the outside may be a lead wire without being provided on the vibrator.

When a voltage is applied between the terminal portions T1 and T2, a region (inter-electrode region) of the piezoelectric plate 10 between the opposing electrodes D1 and D2 has a direction substantially parallel to the plate surface (X direction). Since an electric field is applied, an interaction between the electric field and polarization in a thickness direction (Z-axis direction) orthogonal to the electric field causes a strain in the inter-electrode region in the X direction. Electrode D1,
If the dimension of D2 is designed according to the characteristics of the piezoelectric plate 10 and the applied voltage is an AC voltage having a frequency matching the resonance frequency of the inter-electrode region, thickness shear vibration can be excited in the inter-electrode region. The vibration is attenuated and does not propagate around the inter-electrode region, but is confined within that region. That is, an energy trapping oscillator can be configured.

Since the energy of the vibration is confined in the region between the electrodes in the central portion of the piezoelectric plate 10 and does not reach the periphery, it is easy to support the peripheral portion of the piezoelectric plate 10.

Since this vibration is a thickness shear vibration generated by an electric field parallel to the surface of the piezoelectric plate 10, it is called a parallel electric field excitation type thickness shear vibration. Note that the thickness shear vibration means that the direction of displacement of the piezoelectric plate 10 is parallel to the plate surface,
The direction of wave propagation is vibration in the thickness direction of the plate.

To illustrate the state of the vibration, FIG. 2 shows a displacement distribution in the thickness direction (Z-axis direction) when resonating at a half wavelength.

In this state, when the piezoelectric plate 10 rotates around the Z axis, a vibration due to the Coriolis force occurs in the Y axis direction,
Thus, an electromotive force is generated between the first and second electrodes. By detecting this electromotive force, it is possible to detect the magnitude of the vibration due to the Coriolis force, and thus the rotational angular velocity. This is the principle of a gyroscope using an energy trap type piezoelectric vibrator.

When an acceleration α is applied to the piezoelectric vibrator 1 in the Z-axis direction in the vibrating state, that is, in a direction perpendicular to the main surface of the piezoelectric plate 10, the piezoelectric vibrating plate responds to the magnitude of the acceleration. Under the strain, the parallel electric field excitation type thickness shear vibration changes. That is, the displacement distribution in the Z-axis direction in FIG. 2 changes. As a result, both electrodes D1
And the impedance between D2 and D2 changes. Therefore, the acceleration α can be detected by electrically measuring the change in the impedance.

When the acceleration α applied to the piezoelectric plate 10 changes continuously with time, the distortion changes accordingly, and the impedance also changes continuously. Therefore, by electrically measuring the change in impedance,
The dynamic acceleration can be detected as an electric signal.

FIG. 3 is a block diagram showing a circuit configuration connected to the piezoelectric vibrator 1 having the configuration shown in FIG. FIG.
Referring to FIG. 2, the second electrode D2 of the piezoelectric vibrator 1 includes:
The current detection circuit 18 is connected. Current detection circuit 18
The synchronous detection circuit 23 is connected to the output side of the rectifier circuit 24, and the rectifier circuit 24 is connected to the output side.

On the other hand, the output of the current detection circuit 18 is
It is connected to an oscillation circuit 25 for generating a self-excited vibration driving frequency satisfying the self-excited oscillation condition, and is connected to a first electrode D1 via a drive circuit 26 for applying X-axis direction vibration to the piezoelectric vibrator 1. And constitutes a self-excited vibration drive loop. The self-excited vibration drive loop automatically tracks a frequency substantially equal to the resonance frequency of the thickness-shear vibration of the piezoelectric vibrator 1, and an AC voltage of that frequency is applied to the electrode D1. Thus, since the piezoelectric vibrator 1 can be efficiently driven, a highly sensitive accelerometer can be obtained.

FIG. 4 is a diagram showing an example of the configuration of the current detection circuit 18 in FIG. 3, and has a function of virtually grounding the second electrode D2. In this circuit, the non-inverting input terminal (+) of the operational amplifier 31 is grounded to the reference voltage, and the resistor R is connected from the output terminal of the operational amplifier 31 to the inverting input terminal. The inverting input terminal (-) is always kept at the ground reference potential by the virtual ground function of the operational amplifier. When the current i flows into the inversion terminal, the current i is converted into the voltage Vout by the resistor R. That is, Vout = −i
An output R is obtained. Thus, this current detection circuit
Functionally, the input impedance is almost zero, and the output voltage is proportional to the input current.

This current detecting circuit is the current detecting circuit 1 shown in FIG.
8, the inverting input terminal (-) is connected to the second electrode D2. As a result, the drive voltage is applied between the first electrode D1 and the second electrode D2.

On the other hand, the first and second electrodes D1 and D1
A change in the impedance between the two can be detected as a change in the output voltage of the current detection circuit 18. That is,
When the impedance between the first and second electrodes D1 and D2 changes, the current i flowing into the current detection circuit 18 changes. Therefore, the output voltage Vout of the current detection circuit 18
Changes.

The output voltage of the current detection circuit 18 is synchronously detected at a predetermined timing by the synchronous detection circuit 23 and rectified by the rectification circuit 24, thereby obtaining a DC output voltage proportional to the applied acceleration α as a detection output. I can do it.

Here, the expression that the piezoelectric plate used in the present invention has polarization in the thickness direction is not limited to one having polarization only in the thickness direction, but also includes one having a polarization component in the thickness direction. Shall be considered. Of course, the larger the polarization component in the thickness direction is, the better the polarization component is in the thickness direction.

When a piezoelectric ceramic is used as the piezoelectric plate 10, a polarization process is required as is well known. However, the polarization region may be over the entire piezoelectric plate, or is limited to only the region that confine the vibration. May be.

As the piezoelectric plate 10, a piezoelectric crystal plate (for example, quartz, LiNbO3, LiTO3, etc.) can be used. In that case, in order to have a polarization axis in the thickness direction, Z
Although a cut plate is most preferred, a rotational Y-cut plate can also be used.

[0033]

According to the present invention, the energy trapping type vibration is excited by using a pair of slit-shaped electrodes arranged in parallel on the main surface of the piezoelectric plate, and the acceleration applied to the main surface of the piezoelectric plate at right angles. Accelerometer that can measure not only static acceleration but also dynamic acceleration because the acceleration can be detected by electrically extracting changes in energy-trapped vibration based on distortion generated by the piezoelectric diaphragm. Can be provided.

Further, since the energy-trapping vibration is used, the support is easy and a highly reliable accelerometer can be obtained.

Further, it is not necessary to locally change the thickness of the piezoelectric plate or to form a complicated electrode structure. As a vibrator, it is only necessary to form a pair of parallel electrodes in a predetermined region of an arbitrary-shaped piezoelectric plate. Therefore, the structure and manufacturing are simple.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams showing a structure of a piezoelectric vibrator according to an embodiment of the present invention, wherein FIG. 1A is a plan view and FIG. 1B is a side view excluding a terminal portion of an electrode.

FIG. 2 is a diagram showing a displacement distribution in a thickness direction in thickness shear vibration of the vibrator of FIG. 1;

FIG. 3 is a block diagram showing a circuit configuration of an accelerometer using the piezoelectric vibrator of FIG.

FIG. 4 is a circuit diagram showing an example of a current detection circuit used in the circuit of FIG.

[Explanation of symbols]

 Reference Signs List 1 piezoelectric vibrator 10 piezoelectric plate D1 first electrode D2 second electrode T1, T2 terminal 18 current detection circuit 23 synchronous detection circuit 24 rectifier circuit 25 oscillation circuit 26 drive circuit 31 operational amplifier

Claims (4)

[Claims] 1. A strip-shaped first and second electrode is provided in parallel on a main surface of a portion of a piezoelectric plate having a polarization in a thickness direction at a predetermined interval from each other, and a gap between the first and second electrodes is provided. A piezoelectric vibrator in which energy is trapped in a piezoelectric plate portion between both electrodes by applying a drive AC voltage for excitation to the piezoelectric plate to excite the piezoelectric plate; and a main surface of the piezoelectric plate on the piezoelectric vibrator. Detecting means for electrically detecting a change in the energy-trapping type vibration due to acceleration applied in a direction perpendicular to the direction, and measuring the acceleration by using the detecting means. 2. The accelerometer utilizing energy trapping type piezoelectric vibration according to claim 1, wherein said detecting means has a current detecting circuit connected to said second electrode and having a virtual grounding function. An accelerometer utilizing energy-trapped piezoelectric vibration, wherein a drive voltage for excitation is applied to one of the electrodes and a detection output is obtained from an output of the current detection circuit. 3. An accelerometer using energy trapping type piezoelectric vibration according to claim 2, wherein said detection means is connected to a synchronous detection circuit connected to an output of said current detection circuit, and to an output of said synchronous detection circuit. An accelerometer using energy confinement type piezoelectric vibration, characterized by having an output corresponding to the acceleration as an output of the rectifier circuit. 4. An accelerometer using energy trapping type piezoelectric vibration according to claim 3, wherein the oscillation circuit is connected to an output of the current detection circuit and oscillates a signal of a frequency for driving self-excited vibration, and the oscillation circuit. And a drive circuit connected to the output of the first electrode and applying an AC voltage having the self-excited vibration drive frequency to the first electrode.