JP3690449B2 - Piezoelectric vibrator for piezoelectric vibration gyro - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric vibrator for a vibration gyro that uses ultrasonic vibration belonging to a gyroscope mainly used in an automobile navigation system, a camera shake correction mechanism of a camera-integrated VTR camera, and the like. The present invention relates to a piezoelectric vibrator for a piezoelectric vibration gyro using a confinement vibration mode.
[0002]
[Prior art]
Conventionally, this type of piezoelectric vibratory gyroscope (herein simply referred to as a piezoelectric vibratory gyroscope) has an axis in a direction perpendicular to the vibration direction of the piezoelectric vibrator while the piezoelectric vibrator is excited in a certain direction. When rotating around, the rotational angular velocity is detected by detecting the Coriolis force generated in the excitation direction and the direction perpendicular to the rotation axis.
[0003]
As such a piezoelectric vibration gyro, recently, as a vibration mode of a piezoelectric vibrator, a piezoelectric vibration gyro using an energy confinement vibration mode in which vibration energy is concentrated near the drive electrode (hereinafter referred to as an energy confinement type piezoelectric vibration gyro). Has been developed). In this energy confinement type piezoelectric vibration gyro, the vibration energy is concentrated on the local part of the piezoelectric vibrator, so that the support structure of the piezoelectric vibrator can be simplified and made easy, and there is no need for a free lead wire. In addition to its advantages, it has excellent vibration resistance and impact resistance.
[0004]
For example, in the energy confinement type piezoelectric vibration gyro disclosed in Japanese Patent Application Laid-Open No. Sho 62-162915, in order to confine the vibration energy of the piezoelectric vibrator locally, the thickness of the piezoelectric vibrator is locally increased, The eye portion is polarized in the thickness direction, and a drive electrode is provided on one surface of the opposed end surface of the thick local portion, and a detection electrode is provided on the other surface. As another example, there is a configuration in which a drive electrode and a detection electrode are provided on one surface of a piezoelectric plate and a cross finger electrode is provided as a detection electrode between the drive electrodes.
[0005]
[Problems to be solved by the invention]
In the case of the piezoelectric vibrator for the existing energy confinement type piezoelectric vibration gyro described above, it is necessary to locally increase the thickness of the piezoelectric plate or to form a cross finger electrode. It has become difficult.
[0006]
In addition, when the piezoelectric plate has a configuration in which a pair of drive electrodes and a pair of detection electrodes are provided in the vicinity of each other, the drive electric field applied from the drive electrodes into the piezoelectric plate is affected by the detection electrodes, and the drive electric field direction changes. In addition, there is a disadvantage that high accuracy cannot be obtained.
[0007]
The present invention has been made to solve such problems, and its technical problem is that it is small in size, simple in structure and manufacture, has a high concentration of energy confinement vibrations, and has excellent gyro characteristics. An object of the present invention is to provide a piezoelectric vibrator for a confinement vibration type piezoelectric vibration gyro.
[0008]
[Means for Solving the Problems]
According to the present invention, a plurality of electrodes including driving and detection electrodes extending from the outside toward the vicinity of the central portion are formed on at least one main surface of the piezoelectric plate having a polarization axis component in the thickness direction, In the piezoelectric vibrator for vibrating gyroscope using the parallel electric field excitation type energy confinement thickness shear vibration, the piezoelectric plate is obtained as a piezoelectric vibrator for piezoelectric vibrating gyroscope having an elliptical shape including a circular shape or a substantially circular shape with six or more polygons. It is done.
[0009]
According to the present invention, in the piezoelectric vibrator for a piezoelectric vibration gyro, the parallel electric field excitation type energy confinement thickness shear vibration surrounded by the local portions of the plurality of electrodes in the vicinity of the central portion of the main surface of the piezoelectric plate is generated. A piezoelectric vibrator for a piezoelectric vibration gyro in which only the vibration region is polarized into an elliptical shape including a circular shape or a substantially circular shape having a polygonal shape of six or more corners is obtained.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the piezoelectric vibrator for piezoelectric vibration gyro of the present invention will be described in detail with reference to the drawings.
[0011]
FIG. 1 shows a basic configuration of a piezoelectric vibrator 1 for a piezoelectric vibration gyro according to an embodiment of the present invention. FIG. 1 (a) relates to a plan view thereof, and FIG. It is related with the side view from.
[0012]
This piezoelectric vibrator 1 uses parallel electric field excitation type energy confinement thickness-shear vibration described later. From one outer surface of a circular piezoelectric plate 10 having a polarization axis component in the thickness direction to the vicinity of the center portion. A plurality (three in this case) of electrodes 11, 12, and 13 including driving and detection extending in the direction are formed.
[0013]
Further, in this piezoelectric vibrator 1, the local portions of the electrodes 11, 12, 13 near the central portion of the main surface of the circular piezoelectric plate 10 (that is, the terminal portions 11 a, 12 a, 13a), only the vibration region E for generating the parallel electric field excitation type energy confinement thickness shear vibration is polarized in a circular shape.
[0014]
More specifically, the circular piezoelectric plate 10 is made of, for example, a piezoelectric ceramic plate such as PZT or barium titanate, and as shown by a broken line in FIG. It has a polarization axis component in the direction. In the central portion of one main surface of the piezoelectric plate 10, the strip-shaped three electrodes 11, 12, and 13 are symmetrical with respect to the vertical bisector at each vertex of the equilateral triangle. These electrodes are connected to terminal portions 11a, 12a, and 13a for leading to the outside.
[0015]
Here, the electrodes 11, 12, 13 and the terminal portions 11a, 12a, 13a provided on the piezoelectric plate 10 are suitable to be formed by depositing, for example, a Ni—Cu—Ag multilayer film by vapor deposition or sputtering. Besides this, it is also possible to form by printing silver paste or the like. Further, the terminal portions 11a, 12a, and 13a for leading to the outside are not provided on the piezoelectric vibrator 1 (on the surface of the piezoelectric plate 10), but instead, lead wires may be connected.
[0016]
That is, in the case of this piezoelectric vibrator 1, only a substantially circular region surrounded by the three electrodes 11, 12, 13 in the piezoelectric plate 10 is polarized in the thickness direction of the piezoelectric plate 10 as a vibration region E. Thus, when only the substantially circular vibration region E surrounded by the electrodes 11, 12, 13 is polarized, the piezoelectric characteristics of the polarized vibration region E and the non-polarized region change, so that the energy confinement state (Concentration) is improved.
[0017]
FIG. 2 is a block diagram showing a configuration of an electric circuit when the piezoelectric vibrator 1 shown in FIG. 1 is applied to a piezoelectric vibration gyro. In this electric circuit, current detection circuits 18 and 19 are connected to the electrodes 12 and 13 of the piezoelectric vibrator 1, respectively, and a differential circuit 22 is connected to the output side of these current detection circuits 18 and 19. A sensor output is obtained through a synchronous detection circuit 23 connected to the circuit 22 and a rectifier circuit 24 connected to the synchronous detection circuit 23.
[0018]
On the other hand, each of the current detection circuits 18 and 19 is connected to an oscillation circuit 25 for satisfying the self-excited oscillation condition, and the oscillation circuit 25 and the electrode 11 are connected to the drive circuit 26 for vibration in the X-axis direction. An excitation oscillation circuit is configured. By this self-excited oscillation circuit, an AC drive voltage having a frequency substantially equal to the resonance frequency of the thickness shear vibration of the piezoelectric vibrator 1 is applied to the electrode 11.
[0019]
FIG. 3 is a circuit diagram illustrating a detailed configuration of the current detection circuits 18 and 19. Here, the non-inverting input terminal on the positive side of the operational amplifier 27 is grounded to the reference voltage, and a resistor R is connected between the output terminal of the operational amplifier 27 and the inverting input terminal on the negative side, so that The virtual ground function of the amplifier 27 ensures that the inverting input terminal is always kept at the reference potential.
[0020]
When the input current i flows into the inverting input terminal, it is converted into a voltage by the resistor R. Therefore, the operational amplifier 27 can obtain V _OUT = −i · R as the output voltage V _OUT proportional to the input current i. it can. Therefore, the output voltage V _OUT of the current detection circuits 18 and 19 is obtained as −i · R.
[0021]
In the piezoelectric vibration gyro having such a piezoelectric vibrator 1 and an electric circuit, when a driving AC voltage is applied between the electrode 11 and the electrodes 12 and 13, vibration in the X direction is excited, and in this state, the piezoelectric plate 10 When rotating around the Z axis, vibration due to Coriolis force is generated in the Y direction, and an electromotive force is generated between the electrodes 12 and 13. Therefore, by detecting this electromotive force, the rotational angular velocity can be detected from the magnitude of vibration caused by the Coriolis force.
[0022]
In the embodiment described above, the piezoelectric plate 10 is circular, but the shape of the piezoelectric plate 10 may be, for example, an ellipse or a polygon having six or more corners. Therefore, if an elliptical shape including a circular shape or a polygon having six or more corners is expressed as a substantially circular shape, when the shape of the circular piezoelectric plate 10 is another substantially circular shape, only the vibration region is limited to another substantially circular shape (elliptical shape). The shape or a polygonal shape of 6 or more corners).
[0023]
FIG. 4 shows a basic configuration of a piezoelectric vibrator 1 ′ having a simplified structure for explaining the parallel electric field excitation type energy confinement thickness shear vibration employed in the piezoelectric vibrator 1 shown in FIG. The figure (a) relates to the plan view, and the figure (b) relates to the side view in the one direction.
[0024]
In this piezoelectric vibrator 1 ′, a rectangular (rectangular) piezoelectric plate 10 ′ is used. The piezoelectric plate 10 ′ is polarized in the thickness direction (Z-axis direction), and strip-like electrodes D 1 and D 2 that are opposed to each other with a predetermined interval in the X-axis direction are formed on the same surface of the central portion. ing. Here, when a voltage is applied between the respective terminal portions T1 and T2 of the opposing electrodes D1 and D2, the local region (interelectrode region) of the piezoelectric plate 10 ′ between the electrodes D1 and D2 is substantially plate-shaped. Since an electric field in the direction parallel to (X-axis direction) is applied, distortion in the X direction occurs in the interelectrode region due to the interaction with the polarization in the thickness direction (Z-axis direction) orthogonal to the electric field. become.
[0025]
Therefore, if the dimensions of the electrodes D1 and D2 are appropriately designed in accordance with the characteristics of the piezoelectric plate 10 ', the thickness shear vibration can be excited in the distorted portion. The vibration is damped around the interelectrode region and confined without propagating, and as a result, an energy confined oscillator can be formed. This thickness shear vibration is a vibration in which the displacement direction is parallel to the plate surface and the wave propagation direction is in the plate thickness direction, but here it is caused by an electric field parallel to the plate surface of the piezoelectric plate 10 ′. It can be regarded as mold thickness sliding vibration.
[0026]
FIG. 5 shows the displacement distribution of the thickness shear vibration of the piezoelectric plate 10 ′. In general, in the case of a piezoelectric plate, the displacement distribution of thickness shear vibration attenuates exponentially as it goes from the excitation portion toward the end surface. However, if the piezoelectric plate is finite, the displacement does not become zero at the end surface. For this reason, various side vibrations are generated by leakage.
[0027]
FIG. 7 shows the distribution of electric lines of force in the piezoelectric plate in order to explain the occurrence of the secondary vibration. Here, when the polarization direction of the piezoelectric plate is indicated by the direction of the white arrow, the electric field due to the distribution of the electric field lines indicated by the arrow direction between the electrodes is not completely parallel to the plate surface, but the thickness direction (polarization direction). ) Component, which causes contour vibration (secondary vibration).
[0028]
In the case of the rectangular piezoelectric plate 10 ′, side vibrations are not canceled out, so that many spurious appear in the impedance characteristics. However, in the case of the circular piezoelectric plate 10, the secondary vibration is canceled out, so that the displacement distribution of the thickness-shear vibration is approximated to infinity, that is, a vibrator having no influence of leakage can be formed.
[0029]
6A and 6B show comparison of impedance characteristics of thickness-shear vibration of piezoelectric plates having different shapes. FIG. 6A shows a rectangular piezoelectric plate 10 ′, and FIG. 6B shows a substantially circular shape (16). Square-shaped piezoelectric plate. Here, with respect to the absolute value (kΩ) of the impedance Z with respect to the frequency f (kHz), in the case of the rectangular piezoelectric plate 10 ′, the secondary vibrations appear considerably large in addition to the main vibrations, but are substantially circular (16 In the case of a (rectangular) piezoelectric plate, it is shown that only the secondary vibration is suppressed leaving the main vibration.
[0030]
FIG. 8 shows a comparison of impedance characteristics of thickness-shear vibration when electrodes are provided on both surfaces of differently shaped piezoelectric plates. FIG. 8A shows a rectangular piezoelectric plate, and FIG. ) Relates to a circular piezoelectric plate. However, here, when measuring the impedance characteristics, as shown in FIG. 9, electrodes are provided on the upper and lower surfaces of the piezoelectric plate, lead terminals are connected, and measurement is performed between the electrodes.
[0031]
From FIGS. 8A and 8B, regarding the absolute value of the impedance Z with respect to the frequency f, in the case of a rectangular piezoelectric plate, spurious is riding on the contour vibration in the contour vibration region E1 on the low frequency side. In the case of the piezoelectric plate, it is clear that the vibration is simple, and it is understood that the spurious is caused by the contour vibration factor in the thickness direction component of the electric field shown in FIG. 8A and 8B, the thickness vibration in the thickness vibration region E2 is not stable in the case of a rectangular piezoelectric plate, but appears stably in the case of a circular piezoelectric plate. I understand.
[0032]
Incidentally, when a piezoelectric vibration gyro is configured, it is required to equalize the vibration characteristics in two directions orthogonal to each other in the plane of the piezoelectric plate, so that the shape of the polarization region should be at least one axis symmetrical. Desirably, a circular shape as shown in FIG. 1 is most suitable as the shape of the piezoelectric plate.
[0033]
【The invention's effect】
As described above, according to the piezoelectric vibrator for piezoelectric vibration gyro of the present invention, the shape of the piezoelectric plate is substantially circular, and only the region surrounded by the local portion of the electrode near the center is polarized into a substantially circular shape. Therefore, the concentration of the energy confining vibration can be increased, there is no side vibration such as contour vibration due to vibration leakage, and high accuracy with excellent symmetry in which a single vibration is excited. As a result, it is possible to obtain an energy confinement vibration type piezoelectric vibration gyro which is small in size, simple in structure and manufacture, and has excellent gyro characteristics in which variations in output when stationary are extremely suppressed.
[Brief description of the drawings]
1A and 1B show a basic configuration of a piezoelectric vibrator for a piezoelectric vibration gyro according to an embodiment of the present invention, where FIG. 1A is a plan view and FIG. 1B is a side view from one direction; Is.
FIG. 2 is a block diagram showing a configuration of an electric circuit when the piezoelectric vibrator for a piezoelectric vibration gyro shown in FIG. 1 is applied to the piezoelectric vibration gyro.
3 is a circuit diagram illustrating a detailed configuration of a current detection circuit used in the electrical circuit shown in FIG. 2;
FIG. 4 shows a basic configuration of a piezoelectric vibrator having a simplified structure for explaining parallel electric field excitation type energy confinement thickness shear vibration adopted in the piezoelectric vibrator for a piezoelectric vibration gyro shown in FIG. (A) relates to the plan view, and (b) relates to the side view in the one direction.
5 shows the displacement distribution of thickness shear vibration of the piezoelectric plate shown in FIG.
6A and 6B show a comparison of impedance characteristics of thickness-shear vibration of piezoelectric plates having different shapes; FIG. 6A shows a rectangular piezoelectric plate, and FIG. 6B shows a substantially circular (hexagonal) piezoelectric plate. This relates to the plate 10.
FIG. 7 shows the distribution of lines of electric force in the piezoelectric plate in order to explain the occurrence of secondary vibration.
FIGS. 8A and 8B show a comparison of impedance characteristics of thickness-shear vibration when electrodes are provided on both surfaces of differently shaped piezoelectric plates. FIG. 8A shows a rectangular piezoelectric plate, and FIG. 8B shows a circular shape. The present invention relates to a piezoelectric plate.
FIG. 9 is a side view showing a state in which electrodes are provided on the upper and lower surfaces of a piezoelectric plate and lead terminals are connected when the impedance characteristics of FIGS. 8A and 8B are measured.
[Explanation of symbols]
1, 1 'Piezoelectric vibrator 10, 10' Piezoelectric plates 11, 12, 13 Electrodes 11a, 12a, 13a Terminal portions 18, 19 Current detection circuit 22 Differential circuit 23 Synchronous detection circuit 24 Rectifier circuit 25 Oscillation circuit 26 Drive circuit 27 Operational amplifier E Vibration area

Claims (2)

A plurality of electrodes including driving and detection electrodes extending from the outside toward the vicinity of the central portion are formed on at least one main surface of the piezoelectric plate having a polarization axis component in the thickness direction, and parallel electric field excitation type energy confinement A piezoelectric vibrator for a vibrating gyroscope using thickness shear vibration, wherein the piezoelectric plate is an elliptical shape including a circular shape or a substantially circular shape having six or more polygons. 2. The piezoelectric vibrator for a piezoelectric vibration gyro according to claim 1, wherein the parallel electric field excitation type energy confinement thickness shear vibration surrounded by local portions of the plurality of electrodes in the vicinity of the central portion of the main surface of the piezoelectric plate is generated. A piezoelectric vibrator for a piezoelectric vibration gyro, wherein only a vibration region for polarization is polarized into an elliptical shape including a circular shape or a substantially circular shape having a polygonal shape of six or more corners.

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