JP3665978B2 - Energy-confined piezoelectric vibration gyroscope - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gyroscope for detecting a rotational angular velocity, and more particularly to a piezoelectric vibration gyroscope using an energy confinement vibration mode of a piezoelectric vibrator.
[0002]
[Prior art]
A piezoelectric vibration gyroscope (hereinafter referred to as a piezoelectric vibration gyro for the sake of simplicity) is a state where a piezoelectric vibrator is excited in a certain direction, and the piezoelectric vibrator is rotated around an axis perpendicular to the excitation direction. , The Coriolis force generated in the direction perpendicular to the excitation direction and the rotation axis is detected, and the rotational angular velocity is detected, and there are various applications. Recently, for example, a car navigation system, It has come to be used for a camera shake correction mechanism of a VTR camera.
[0003]
As a piezoelectric vibration gyro, a piezoelectric vibration gyro using an energy confinement vibration mode using a piezoelectric vibrator that vibrates in an energy confinement vibration mode in which vibration energy is concentrated in the vicinity of a drive electrode is disclosed in, for example, Japanese Patent Laid-Open No. 62-162915. And Japanese Patent Laid-Open No. 5-322580.
[0004]
The piezoelectric vibration gyro using the energy confinement vibration mode is that the vibration energy is concentrated on the local part of the piezoelectric vibrator, so that the piezoelectric vibrator can be supported easily and easily, and there is no need for a free lead wire. There are advantages.
[0005]
Japanese Patent Laid-Open No. Sho 62-162915 discloses that in order to confine vibration energy locally, the vibrator is locally thickened, the portion is polarized in the thickness direction, and a drive electrode is provided on the opposed end face of the thick local area. A device in which a detection electrode is provided on a side surface is disclosed. As another example, 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.
[0006]
In Japanese Patent Laid-Open No. 5-322580, a partial area of a piezoelectric plate is polarized in the thickness direction, two sets of counter electrodes are provided on the main surface of the polarization area, and the counter directions are perpendicular, and one counter electrode is driven A piezoelectric vibration gyro using the other counter electrode as a detection electrode is disclosed.
[0007]
[Problems to be solved by the invention]
The piezoelectric vibration gyro using the energy confinement vibration mode disclosed in Japanese Patent Application Laid-Open No. 62-162915 has a manufacturing difficulty in that the thickness of the piezoelectric plate must be locally increased or the cross finger electrode must be formed. There is. In addition, since the pair of drive electrodes and the 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 direction of the drive electric field changes and accuracy is obtained. There is a drawback of not.
[0008]
The piezoelectric vibration gyro using the energy confinement vibration mode disclosed in Japanese Patent Laid-Open No. 5-322580 is simple in configuration and easy to manufacture, but 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 electrode into the piezoelectric plate is affected by the detection electrode, the drive electric field direction changes, and it is difficult to obtain an accurate detection output.
[0009]
Accordingly, an object of the present invention is to provide a piezoelectric vibration gyro using an energy confinement vibration mode that is small in size, simple in structure and manufacture, and highly accurate.
[0010]
The present invention provides a piezoelectric device using an energy confinement vibration mode in which an output electrode does not adversely affect a drive electric field by sharing an output electrode as a part of the drive electrode in a limited region of the main surface of the piezoelectric plate. An object is to provide a vibrating gyroscope.
[0011]
[Means for Solving the Problems]
The present invention provides a direction perpendicular to the first direction at one of two positions on the main surface of a portion having polarization in the thickness direction of the piezoelectric plate and spaced apart from each other by a predetermined distance in the first direction. A strip-shaped first electrode is provided on the other side, and strip-shaped second and third electrodes extending at a distance from each other in a direction substantially perpendicular to the first direction are formed at the other position, An excitation driving voltage is applied between the first electrode and the second and third electrodes, and an electromotive force corresponding to vibration caused by Coriolis force generated in the second and third electrodes is detected. A piezoelectric vibration gyroscope using an energy confinement mode of thickness shear vibration generated between the first electrode and the second and third electrodes, wherein the first, second and third electrodes Oscillation resulting in enclosed energy confinement oscillation Only on the region, is an energy-trap type piezoelectric vibrating gyroscope being characterized in that an insulating film for mass addition.
[0012]
In the piezoelectric vibrating gyroscope of the present invention, the second and third electrodes are respectively connected to first and second current detection circuits having a virtual ground function, and the first electrode is used for excitation. A driving voltage is applied, and a detection output is obtained from a differential voltage generated between the first and second current detection circuit outputs.
[0013]
A piezoelectric vibration gyroscope according to the present invention includes, as a drive and detection circuit, a differential circuit connected between outputs of the first and second current detection circuits for detecting a difference between output voltages of the current detection circuits. A self-excited driving frequency connected between the synchronous detection circuit connected to the differential circuit output, the rectifier circuit connected to the output of the synchronous detection circuit, and the outputs of the first and second current detection circuits. And an oscillation circuit for oscillating the above signal and a drive circuit connected to the output of the oscillation circuit and applying an alternating voltage of the self-excited drive frequency to the first electrode.
[0014]
As the piezoelectric plate, piezoelectric ceramics is used, and only the region between and in the vicinity of the first to third electrodes of the piezoelectric ceramics is polarized in the thickness direction.
[0015]
A piezoelectric crystal plate having a polarization axis in the thickness direction can also be used as the piezoelectric plate.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a perspective view showing a configuration of a vibrator of an energy-confined vibration gyro according to an embodiment of the present invention. As shown in FIG. 1, the piezoelectric vibrator uses a piezoelectric plate 10 made of, for example, a piezoelectric ceramic plate such as PZT or barium titanate and having a polarization axis at the center in the thickness direction. A strip-shaped first electrode 11 is provided on the main surface of the central portion of the piezoelectric plate 10. A second electrode 12 and a third electrode 13 are formed apart from each other at a position separated from the first electrode 11 by a predetermined distance in parallel with the first electrode. These electrodes 11, 12 and 13 are connected to terminal portions 14, 15 and 16 for leading out to the outside. Note that these electrodes and terminal portions are preferably made of silver paste or gold sputtering. Of course, other conductive films can be used. A lead wire may be used without providing a terminal portion for leading to the outside on the vibrator.
[0017]
An insulating film 17 is formed on the vibration region surrounded by the strip-shaped electrodes 11, 12 and 13 of the piezoelectric plate (including the electrode portion) in order to add mass to the vibration region. As the insulating film 17, an SiO2 film, an MgF2 film, frit glass, or the like is appropriate.
[0018]
Of course, a protective insulating film may be uniformly applied over the entire surface of the piezoelectric plate.
[0019]
Now, as shown in the figure, the three-dimensional coordinates are determined with the thickness direction as the Z axis, the opposing direction of the electrodes as the X axis, and the direction perpendicular to these as the Y axis.
[0020]
When a driving voltage (alternating current) is applied between the first electrode 11 and the second and third electrodes, vibration in the X direction is excited. In this state, when the piezoelectric plate 10 rotates around the Z axis, vibration due to the Coriolis force is generated in the Y direction, and an electromotive force is generated between the second and third electrodes. By detecting this electromotive force, it is possible to detect the magnitude of vibration caused by the Coriolis force, and hence the rotational angular velocity.
[0021]
Since the vibration energy is confined in the central portion of the piezoelectric plate and does not reach the periphery, it is easy to support the peripheral portion of the piezoelectric plate.
[0022]
In addition, since the vibration energy is efficiently confined by the presence of the insulating film 17 in the vibration region, energy confinement vibration with less spurious and less leakage vibration can be obtained.
[0023]
FIG. 2 is a block diagram showing a circuit configuration connected to the piezoelectric vibrator 1 of FIG. Referring to FIG. 2, current detection circuits 18 and 19 are connected to the second and third electrodes 12 and 13 of the piezoelectric vibrator 1, respectively. A differential circuit 22 is connected to the output side of the current detection circuits 18 and 19, and a detection output of the piezoelectric vibration gyro is obtained via the synchronous detection circuit 23 and the rectification circuit 24. On the other hand, the current detection circuits 18 and 19 are connected to an oscillation circuit 25 for satisfying the self-excited oscillation condition, and are connected to the first electrode 11 via a drive circuit 26 for applying X-direction vibration. An oscillation circuit is configured. By this self-excited oscillation circuit, an AC voltage having a frequency substantially equal to the resonance frequency of the thickness shear vibration of the piezoelectric vibrator is applied to the electrode 11.
[0024]
FIG. 3 is a diagram illustrating a configuration example of the current detection circuits 18 and 19 of FIG. 2 and has a function of virtually grounding the second and third electrodes 12 and 13. 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 a current flows into the inverting terminal, it is converted into a voltage by the resistor R. That is, an output of Vout = −iR is obtained. In other words, this current detection circuit is a circuit that has an input impedance that is substantially zero and that can obtain an output voltage proportional to the input current.
[0025]
This current detection circuit is used for the current detection circuits 18 and 19 in FIG. At that time, the inverting input terminal (−) is connected to the second and third electrodes 12 and 13. As a result, the drive voltage is applied between the first electrode 11 and the second and third electrodes 12 and 13, and the electromotive force between the second and third electrodes 12 and 13 is detected by current detection. It can be detected as a potential difference between the outputs of the circuits 18 and 19.
[0026]
Next, the driving principle of the piezoelectric vibrator in the above-described embodiment of the present invention will be specifically described with reference to the drawings.
[0027]
FIGS. 4A and 4B are a plan view and a cross-sectional view showing only the electrode part, respectively, showing the basic structure of the energy confinement type vibrator shown in FIGS. Referring to FIGS. 4A and 4B, slit-like surfaces facing each other with a gap in the X-axis direction on the same surface of the central portion of the piezoelectric plate 10 polarized in the thickness direction (Z-axis direction). Electrodes D1 and D2 are formed. T1 and T2 are terminal portions. When a voltage is applied between the terminals T1 and T2, an electric field in a direction substantially parallel to the plane of the plate (X direction) is applied to the region (interelectrode region) of the piezoelectric plate 10 between the opposing electrodes D1 and D2. Therefore, strain in the X direction occurs in the inter-electrode region due to the interaction with the polarization in the thickness direction (Z-axis direction) orthogonal to the electric field. When the dimensions of the electrodes D1 and D2 are designed in accordance with the characteristics of the piezoelectric plate 10 and the applied voltage is an AC voltage having a frequency that matches the resonance frequency of the interelectrode region, thickness shear vibration can be excited in the interelectrode region. . The vibration is trapped without being attenuated and propagated around the area between the electrodes. That is, an energy confinement oscillator can be configured. Further, since this vibration is a thickness shear vibration caused by an electric field parallel to the surface of the piezoelectric plate, it is called a parallel electric field excitation type thickness shear vibration. The thickness shear vibration is vibration in which the direction of displacement of the piezoelectric plate is parallel to the plate surface and the wave propagation direction is in the thickness direction of the plate. In order to illustrate the state of this vibration, FIG. 5 shows a displacement distribution in the thickness direction (Z-axis direction) when resonating at a half wavelength.
[0028]
The vibrator shown in FIGS. 1 and 2 utilizes the above basic structure. That is, the 1st electrode 11 is D1 electrode, and the 2nd electrode 12 and the 3rd electrode 13 which oppose this are D2 electrodes. The D2 electrode is divided into two to constitute a detection electrode, constitutes a second electrode 12 and a third electrode 13, and is connected to current detection circuits 18 and 19 each having a virtual ground function. Thereby, since the second electrode 12 and the third electrode 13 are virtually maintained at the reference potential, they can be regarded as ground terminals in terms of potential. Therefore, when a driving voltage for excitation having a frequency substantially equal to the resonance frequency of the thickness shear vibration mode of the piezoelectric plate is applied to the first electrode 11, the first, second, In addition, the middle point of the straight line connecting the center of the first electrode 11 and the centers of the second and third electrodes 12 and 13 is connected to a region (interelectrode region) surrounded by the third electrodes 11, 12 and 13. Thickness shear vibration in the energy confinement vibration mode in the direction of the straight line (X direction) occurs.
[0029]
In this state, when the piezoelectric plate 10 is rotated about an axis orthogonal to the principal surface, the direction of the thickness shear vibration that is excited (Y direction) is caused by the action of the Coriolis force. Thickness sliding vibration occurs. The thickness shear vibration generated by this Coriolis force changes the impedance between the first electrode 11 and the second electrode 12 and between the first electrode 11 and the third electrode 13, and as a result. As a result, the current value flowing into the current detection circuits 18 and 19 changes. As described above, the second electrode 12 and the third electrode 13 are arranged symmetrically with respect to the excited thickness-shear vibration direction (X direction). The currents that change due to the vibration caused by the flowing Coriolis force are equal in amplitude and different in phase by 180 degrees. Accordingly, the output voltages of the current detection circuits 18 and 19 are also voltages that are 180 degrees out of phase with each other, the difference between these output voltages is detected as a differential voltage by the differential circuit 22, and this voltage is determined by the synchronous detection circuit 23. Is detected at the same timing and rectified by the rectifier circuit 24, a DC output voltage proportional to the applied rotational angular velocity can be obtained as a detection output.
[0030]
On the other hand, the current detection circuits 18 and 19 are connected to the electrode 11 through an oscillation circuit 25 and a drive circuit 26 for satisfying the self-excited oscillation condition, and constitute a self-excited oscillation loop. As a result, the resonance frequency of the vibrator is automatically adjusted and the vibrator can be driven efficiently, so that a highly sensitive gyro can be obtained.
[0031]
FIG. 6 shows another circuit configuration, in which the first electrode 11 is grounded, and a voltage dividing circuit composed of a series circuit of resistors R1 and R2 is connected between the second and third electrodes. The oscillation drive circuit 27 is controlled by the voltage. This oscillation drive circuit is grounded, and thereby a drive voltage is applied between the first electrode 11 and the second and third electrodes. The oscillation drive circuit 27 includes the oscillation circuit 25 and the drive circuit 26 shown in FIG. Both ends of the voltage dividing circuit are connected to the differential circuit 22. The differential circuit 22, the detection circuit 23, and the rectifier circuit 24 are the same as those in FIG.
[0032]
Here, the phrase “having polarization in the thickness direction” of the piezoelectric plate used in the present invention is not limited to being polarized only in the thickness direction, but also includes one having a polarization component in the thickness direction. Of course, since the larger polarization component in the thickness direction is better, the one polarized only in the thickness direction is most advantageous.
[0033]
When a piezoelectric ceramic is used as the piezoelectric plate 10, polarization processing is required as is well known, but the polarization region may extend over the entire piezoelectric plate, or may be limited to only a region confining vibration. .
[0034]
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, a Z-cut plate is most preferable, but a rotating Y-cut plate can also be used.
[0035]
【The invention's effect】
According to the present invention, driving is performed using only a pair of slit-like electrodes arranged in parallel on the main surface of the piezoelectric plate, and one of the pair of electrodes is divided into two to be detected as detection electrodes. Therefore, the drive electric field is not adversely affected by the presence of the detection electrode, and the vibration in the Y direction can be detected while maintaining the electric field for exciting the vibration in the X direction, thereby obtaining a highly accurate and highly sensitive vibration gyro. Can do. In addition, since energy-confined vibration is used, a gyro that is easy to support and highly reliable can be obtained. Furthermore, since the insulating film for mass addition is provided only in the vibration region, it is easy to concentrate the vibration only in the vibration region where the mass is increased, and it is possible to realize an energy-confined resonator with less spurious and less leakage vibration. Therefore, an accurate piezoelectric vibration gyro with little influence of characteristic change and disturbance due to fixing of the support or the like can be obtained.
[0036]
In addition, it is not necessary to form piezoelectric plates with locally different thicknesses or to form complicated electrode structures. As a vibrator, a pair of parallel electrodes (one of which is divided into two) in a predetermined area of a piezoelectric plate of arbitrary shape. However, it is only necessary to form an insulating film in the vibration region by coating or the like, so that the structure and manufacture are simple.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a configuration of a piezoelectric vibrator according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a circuit configuration of a gyro using a piezoelectric vibrator.
3 is a circuit diagram showing an example of a current detection circuit used in the circuit of FIG. 2. FIG.
4A and 4B are diagrams showing a basic structure of a vibrator employed in the piezoelectric vibrator of FIGS. 1 and 2, wherein FIG. 4A is a plan view, and FIG. 4B is a side view excluding electrode terminal portions.
5 is a diagram showing a displacement distribution in the thickness direction in the thickness shear vibration of the vibrator having the basic structure shown in FIG. 4;
FIG. 6 is a block diagram showing another circuit configuration of a gyro using a piezoelectric vibrator.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Piezoelectric vibrator 10 Piezoelectric plate 11 1st electrode 12 2nd electrode 13 3rd electrodes 14, 15, 16 Terminal part 17 Insulating film 18 Current detection circuit 19 Current detection circuit 22 Differential circuit 23 Synchronous detection circuit 24 Rectification Circuit 25 Oscillation circuit 26 Drive circuit 27 Oscillation drive circuit 31 Operational amplifier

Claims (5)

One of two positions on the main surface of the portion having polarization in the thickness direction of the piezoelectric plate and spaced apart from each other in the first direction by a strip shape in a direction perpendicular to the first direction. A first electrode is provided, and strip-like second and third electrodes extending at a distance from each other in a direction substantially perpendicular to the first direction are formed at the other position, and the first electrode and An excitation drive voltage is applied between the second and third electrodes, and an electromotive force corresponding to vibration caused by Coriolis force generated in the second and third electrodes is detected, and the first A piezoelectric vibration gyroscope using an energy confinement vibration mode of thickness shear vibration generated between an electrode and the second and third electrodes, wherein the energy is surrounded by the first, second and third electrodes On the vibration region where confinement vibration occurs Mini, energy trapping-type piezoelectric vibrating gyroscope being characterized in that an insulating film for mass addition. 2. The piezoelectric vibration gyroscope according to claim 1, wherein the second and third electrodes are connected to first and second current detection circuits each having a virtual ground function, and the first electrode is used for excitation. A piezoelectric vibration gyroscope configured to apply a drive voltage and obtain a detection output from a difference voltage generated between the outputs of the first and second current detection circuits. 3. The piezoelectric vibration gyroscope according to claim 2, wherein the differential circuit is connected between outputs of the first and second current detection circuits for detecting a difference between output voltages of the two current detection circuits, and the differential circuit. A synchronous detection circuit connected to the output, a rectifier circuit connected to the output of the synchronous detection circuit, and an output of the self-excited drive frequency connected between the outputs of the first and second current detection circuits. And a drive circuit connected to an output of the oscillation circuit and applying an alternating voltage of the self-excited drive frequency to the first electrode. 4. The piezoelectric vibrating gyroscope according to claim 1, wherein a piezoelectric ceramic is used as the piezoelectric plate, and only a region between and near the first to third electrodes of the piezoelectric ceramic is arranged in a thickness direction. A piezoelectric vibrating gyroscope characterized by polarization. 4. The piezoelectric vibration gyroscope according to claim 1, wherein a piezoelectric crystal plate having a polarization axis in a thickness direction is used as the piezoelectric plate.

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