JPH1123286A - Piezoelectric vibrating gyro - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a piezoelectric vibrating gyro which is supported easily, which is manufactured simply, which is thin and which can be driven and detected with high efficiency by a method wherein lithium niobate (LiNbO3 ) is used as a piezoelectric single-crystal vibrator and an angle of rotation around the X-axis is set within a specific range. SOLUTION: In a piezoelectric substrate 1, one pair of opposite electrodes 13, 14 are arranged on the main face of a rotating Y-plate composed of LiNbO3 . The direction 15 of an electric field is parallel to the X-axis, and a so-called parallel electric- field exciting operating is performed. When the effective electromechanical coupling coefficient of the parallel electric-field exciting operation with reference to an angle of rotation θ is computed in the case of the parallel electric-field exciting operation, the electromechanical coupling coefficient of a thickness longitudinal vibration and that of a thickness slide vibration having a displacement in the Z-axis direction becomes 0 at all cutting angles, and only a thickness slide vibration 16 having a displacement in the X-axis direction can be excited strongly. Then, on the basis of the dependence on the rotation of the effective electromechanical coupling coefficient of the thickness slide vibration 16 having the displacement in the X-axis direction, the angle of rotation θaround the X-axis of LiNbO3 is set at 150 to 175 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezoelectric vibratory gyroscope (hereinafter, referred to as the piezoelectric vibrating gyro) applying relates, in particular LiNbO _3, LiTaO piezoelectric crystal plate trigonal such _3, the vertical electric field and an electric field parallel The present invention relates to a piezoelectric gyro configured to excite two orthogonal thickness shear vibrations and to use the same.

[0002]

2. Description of the Related Art Piezoelectric vibrating gyroscopes are used as angular velocity sensors in various fields such as image stabilization of VTR images, attitude control systems, car navigation systems, etc., and their applications are increasing due to improved performance, lower prices, miniaturization, etc. Is spreading more and more. The piezoelectric vibrating gyroscope is an angle sensor that drives one vibration mode of two orthogonal vibration modes and utilizes that the other vibration mode is excited by Coriolis force when a rotational angular velocity is applied. When configuring such a piezoelectric vibrating gyroscope, it is preferable that the vibrator can electrically drive and detect two orthogonal vibration modes independently, and that their resonance frequencies are close to each other.

FIG. 10A shows a conventional piezoelectric vibrating gyroscope 2.
It is a perspective view showing an example of 0, and a coordinate axis (x, y, z) is selected as shown in the figure. The narrow prism 21 is a vibrating body processed from a constant elastic material (alloy). The dimensions in the x-axis and y-axis directions are substantially equal, and the dimension in the z-axis direction is sufficiently larger than the dimensions in the x-axis and y-axis directions. Set longer. Piezoelectric elements 22 and 23 made of piezoelectric ceramics or the like are bonded and fixed to an approximate center of the x- and y-planes of the narrow prism 21 with an adhesive or the like. FIG. 10B is a plan view of the piezoelectric vibrating gyroscope 20 viewed from the z-axis direction, and FIG. 10C shows a schematic vibration mode of the bending vibration fx mode in the x-axis direction and the bending vibration fy mode in the y-axis direction. ing. When an AC voltage is applied to the piezoelectric element 22 while being supported and grounded at the vibration nodes of the narrow prism 21, the displacement speed dx in the X-axis direction is increased.
The bending vibration fx mode that resonates at / dt is excited. Under this condition, the support for supporting the piezoelectric gyro 20 is z
When rotated around the axis at an angular velocity Ω ₀ , a Coriolis force is generated, and a bending vibration fy mode having substantially the same frequency is excited in the y-axis direction to vibrate at a displacement velocity dy / dt. Here, since the displacement speed dy / dt in the y-axis direction is proportional to the angular speed Ω ₀ , the angular speed Ω is determined by measuring the displacement speed dy / dt.
₀ can be obtained. Further, the angle can be measured by electrically integrating the angular velocity Ω ₀ .

[0004]

However, in the above-mentioned piezoelectric vibrating gyroscope, a bending vibrator is used. However, the bending vibrator depends on the state of the assembly such as bonding of the piezoelectric element, support, and taking out of a lead wire. There has been a problem that gyro characteristics tend to vary and deteriorate, and trimming for improving sensitivity is indispensable. Further, since the element requires a predetermined length in the axial direction of the rotational angular velocity to be measured, there is a problem that there is a limit in reducing the height. Recently, three or four electrodes are arranged only on one surface of a piezoelectric ceramic plate polarized in the thickness direction, and two orthogonal thickness shear vibrations are driven by electric fields parallel to each other (perpendicular to each other). There has been reported an energy confinement type vibrating gyroscope using a parallel electric field excitation method for detection. In this vibrating gyroscope, the drive side and the detection side are excited and detected by an electric field orthogonal to each other, so it is difficult to increase the capacitance of the electrodes. There is a problem that it is difficult to do. In addition, since ceramic is used, there is a problem if the Q of resonance does not become too high. The present invention has been made in order to solve the above problems, and provides a thin piezoelectric vibrating gyroscope that does not require bonding of a piezoelectric element, is easy to support, and easy to manufacture, and has a high resonance Q. It is another object of the present invention to provide a piezoelectric vibrating gyroscope using vertical electric field excitation and parallel electric field excitation that can be driven and detected with high efficiency without causing any difficulty in the arrangement of the electrodes.

[0005]

In order to achieve the above object, a piezoelectric vibrating gyroscope using a thickness shear vibration of a piezoelectric single crystal according to the present invention is characterized in that the crystal coordinate system (X, Y, Z) a coordinate system (X, Y ′, X ′, Y ′) obtained by rotating the coordinate system around its X axis in a range of 0 to 180 degrees from a trigonal piezoelectric single crystal having spontaneous polarization in the Z-axis direction.
Z ′) In a plate-shaped piezoelectric single crystal vibrator cut out so that the main surface is substantially parallel to the X axis and the Z ′ axis, two orthogonal directions of the Z ′ axis direction displacement and the X axis direction displacement A piezoelectric vibrating gyroscope for detecting angular velocity of rotation characterized by utilizing thickness shear vibration. The invention according to claim 2 is characterized in that electrodes are attached to both main surfaces of the piezoelectric vibrator on the flat plate, and one of the electrodes is two or three parallel to the Z ′ axis.
A transducer which is divided into two, and drives and detects the thickness-shear vibration of Z ′ direction displacement by a voltage applied between the electrodes on both surfaces, and generates an electric field in the X-axis direction by the voltage applied between the divided electrodes. Drives the thickness-shear vibration of displacement in the X-axis direction,
The piezoelectric vibrating gyroscope according to claim 1, wherein the gyroscope detects the vibration. According to a third aspect of the present invention, the thickness shear vibration of the Z′-axis displacement and the X-axis displacement is adjusted by finely adjusting the cutting direction of the piezoelectric single crystal vibrator and adjusting the thickness and shape of the electrodes on both main surfaces. 3. The piezoelectric vibrating gyroscope according to claim 1, wherein the resonance frequencies are adjusted to be close to each other. The invention according to claim 4 is characterized in that the energy of the two thickness shear vibrations of the displacement orthogonal to each other is confined in the vicinity of the electrode by using the additional mass effect and the piezoelectric reaction effect of the electrode. 3. The piezoelectric vibrating gyroscope according to 3. According to a fifth aspect of the present invention, in the piezoelectric single crystal vibrator, the crystal is lithium niobate (LiNbO ₃ ), and the rotation angle θ about the X axis is 150 to 175 degrees. Claim 1
A piezoelectric vibrating gyroscope according to any one of claims 4 to 5. Claim 6
The invention described in claim 1, wherein in the piezoelectric single crystal resonator, the crystal is lithium tantalate (LiTaO ₃ ), and the rotation angle θ about the X axis is 150 to 175 degrees. A piezoelectric vibrating gyroscope according to any one of claims 4 to 5.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. The present invention relates to a piezoelectric vibratory gyroscope using two orthogonal vibration modes of thickness shear vibration of a piezoelectric substrate. FIG. 1A is a perspective view showing a configuration of an embodiment of a piezoelectric gyro using the thickness shear vibration of a piezoelectric single crystal according to the present invention, and is substantially the upper surface of a rotating Y plate of a piezoelectric substrate 1, for example, LiNbO _3. in the center,
The electrodes 2, 3, and 4 are arranged close to each other along the X-axis direction of the coordinate axes shown in FIG. 1, and the electrode 5 is attached to the lower surface of the substrate 1 so as to face the electrodes 2, 3 and 4. Lead electrodes extend from the electrodes 2, 3, and 4 toward the ends of the piezoelectric substrate 1, respectively, and the end electrode pads are Pick-up1, GND, and Pick.
-Up2. Further, the lead electrode extends from the electrode 5 toward the end of the piezoelectric substrate 1, and the end electrode pad is set to Drive.

Here, in order to help understand the operation of the piezoelectric vibrating gyroscope according to the present invention, the vibration modes excited by the vertical electric field excitation and the parallel electric field excitation will be described a little. FIG. 2A shows a pair of electrodes 9 and 10 opposing each other above and below the main surface of a piezoelectric substrate 1, for example, a rotating Y plate of LiNbO _3.
Is a perspective view in which is arranged. When the coordinate axes are selected as shown in the figure, the direction 11 of the electric field is perpendicular to the main surface of the piezoelectric substrate 1, which is a so-called vertical electric field excitation. By this vertical electric field excitation, a thickness longitudinal vibration, a thickness shear vibration having a displacement in the X-axis direction, and a thickness shear vibration 12 having a displacement in the Z′-axis direction are excited. For the rotating Y plate of LiNbO _3, the rotation angle (DEGRE
For the dependence of the effective electromechanical coupling coefficient (COUPLING FACTOR k _eff ) of the vertical electric field excitation on ES θ), see Warne
It has been known that the values are calculated by r et al. and exhibit the characteristics as shown in FIG. The solid line is the thickness longitudinal vibration (EXTENSIO
NAL) and the dotted line indicate the thickness shear vibration 12 (SHEAR) having displacement in the Z ′ axis direction. 163 degree rotation Y
The plate has a large effective electromechanical coupling coefficient of the thickness shear vibration 12 having a displacement in the Z′-axis direction due to the vertical electric field excitation of 0.62, and an effective electric force of the thickness longitudinal vibration and the thickness shear vibration of the X-axis direction displacement. Since the mechanical coupling coefficient becomes 0, only the thickness shear vibration 12 having a displacement in the Z′-axis direction can be strongly excited.

Next, as shown in FIG. 2B, it is a perspective view showing a case where a pair of opposed electrodes 13 and 14 are arranged on the main surface of a piezoelectric substrate 1, for example, a rotating Y plate of LiNbO ₃ .
When the coordinate axes are selected as shown in the figure, the direction 15 of the electric field is parallel to the X-axis, which is a so-called parallel electric field excitation. Calculating the effective electromechanical coupling coefficient (COUPLING FACTORk _eff ) of the parallel electric field excitation with respect to the rotation angle (DEGREES θ) in the case of the parallel electric field excitation, the thickness longitudinal vibration and the thickness shear vibration with displacement in the Z 'axis direction Is zero at all cutting angles, and the thickness shear vibration 16
It can be seen that only (SHEAR) can be vigorously excited. FIG.
(B) shows the rotation angle dependence of the effective electromechanical coupling coefficient k _eff of the thickness shear vibration 16 having a displacement in the X-axis direction. It can be seen that the effective electromechanical coupling coefficient of the thickness shear vibration 16 having a displacement in the X-axis direction is as large as 0.56 in the 163-degree rotated Y plate of LiNbO ₃ .

On the other hand, resonance (Resonance) and anti-resonance frequency (Anti-resonance) in vertical electric field excitation (PERPENDICULAR) are described.
FIG. 4 shows the rotation angle dependence of the resonance frequency (Resonance) for the parallel electric field excitation (LATERAL) and the parallel electric field excitation (LATERAL). The resonance frequency of the actual vertical electric field excitation energy confinement oscillation is the resonance frequency (solid line) in FIG.
(Dash-dotted line). In the Y-plate rotated at 163 degrees, the resonance frequency (dotted line) of the parallel electric field excitation is located in the middle, and the resonance frequencies of the two orthogonal energy confinement thickness shear vibrations can be almost matched.

In consideration of the above, the energy trap type piezoelectric vibrating gyroscope is made of, for example, LiNbO ₃ .
It can be said that a 63-degree rotated Y plate is suitable. The operation mode of FIG. 1A will be described in detail based on the above consideration. FIG. 5A is a detailed plan view of FIG. 1A, in which the widths of the electrodes 2, 3, and 4 in the X-axis direction are respectively set to a.
2, a1 and a2, and the depth in the Z′-axis direction is w.
The gap between the electrodes 2, 3, and 4 is represented by g. As shown in FIG. 5A, the GND of the electrode 3 is provided between the Pick-up 1 of the electrode 2 and the Pick-up 2 of the electrode 4. FIG. 5B is a detailed plan view of the lower surface of FIG.
The width of the electrode 5 (X-axis direction) is set to b, the depth (Z'-axis direction) is set to w, and a terminal Drive is provided. Drive of the energy trap type piezoelectric vibrating gyroscope is Drive-GN
Detection is performed by applying a voltage between D and taking out the output between Pick-up1 and Pick-up2.

Various experiments were conducted to make two orthogonal resonance frequencies close to each other, that is, the resonance frequency due to the vertical electric field and the resonance frequency due to the parallel electric field. The prototype piezoelectric vibrating gyroscope is LiNbO ₃ 163 having a thickness of 2 mm as a piezoelectric substrate.
Chrome-gold (Cr-A)
u) was used. The resonance frequency of two orthogonal thickness shear vibrations when the electrode shape of the piezoelectric vibrating gyroscope was changed was obtained from admittance measurement. The admittance of the vertical electric field excitation is Pick-up1 and Pick-u
p2 was short-circuited to GND, and measured between Drive and GND. The admittance characteristic of the parallel electric field excitation is Dri
short between ve and GND, Pick-up1 and Pic
It measured between k-up2. GN in the center of the upper surface of the piezoelectric substrate
FIGS. 6A, 6B, and 6C show resonance frequencies when the width a1 of the D electrode, the width b of the lower drive electrode, and the depth w of the upper electrode are changed, respectively. FIG. 6A shows that the smaller the width a1 of the GND electrode is, and FIG.
It can be seen that the larger the width b of the live electrode, the closer the two resonance frequencies, that is, the resonance frequency of the vertical electric field excitation and the resonance frequency of the parallel electric field excitation. FIG. 6C shows that the difference between the two resonance frequencies hardly changes with the depth w. These results show that the resonance frequencies of the vertical electric field excitation and the parallel electric field excitation can be brought close to each other.

Based on the above results, a = 12 mm, a
1 = 3 mm, a2 = 4.3 mm, b = 12 mm, w = 1
A prototype of a 0 mm piezoelectric vibrating gyroscope was manufactured. FIG. 7 shows a state in which the piezoelectric vibrating gyroscope is excited by a vertical electric field (Perpendicula).
r) shows a resonance frequency and a frequency (Frequency) -admittance (S) characteristic during parallel electric field excitation (Lateral). FIG. 7A shows the characteristics when no sound absorbing material is attached to the periphery of the piezoelectric vibrating gyroscope, and FIG. 7B shows the characteristics when the sound absorbing material is added. When the sound absorbing material is added, the Q of the main resonance of the thickness shear vibration does not change much, but the spurious response is small. Therefore, it is considered that the vibration energy of the main resonance is confined near the center electrode. Also, it can be seen that the resonance frequencies of the vertical electric field excitation and the parallel electric field excitation are almost the same. FIG.
In (b), in the characteristics of the vertical electric field excitation, a relatively large resonance appears on the high frequency side in addition to the main vibration of the thickness shear vibration. This seems to be the first nonharmonic higher order mode. This mode does not significantly affect the piezoelectric vibrating gyro characteristic because the frequency is relatively far away.

FIG. 8 is an example of a circuit block diagram using a piezoelectric vibrating gyroscope according to the present invention. This measurement circuit
Oscillation circuit for driving and current-voltage conversion circuit for detection (Current detection Ci
rcuit), differential amplifier (Differential Amplifier),
It is composed of an AC-DC converter (AC-DC Converter). A DC voltage proportional to the angular velocity when the piezoelectric vibrating gyroscope is rotated appears at the output of the AC-DC converter. This measurement circuit was placed in a grounded aluminum case together with a piezoelectric vibrating gyroscope and rotated by an electromagnetic motor. Figure 9 shows the angular velocity of the vibrating gyroscope (Angular Velocity)
5 shows the characteristics of the output voltage (Output Voltage) with respect to. A piezoelectric vibrating gyro device was obtained in which the output voltage was substantially proportional to the angular velocity although the measured values varied.

FIG. 1B shows another embodiment according to the present invention, in which electrodes 6 and 7 are arranged substantially in the center of the main surface of the piezoelectric substrate 1 along the X-axis direction and the lower surface of the substrate 1 is provided. The electrode 8 is adhered to the electrodes 6 and 7. Lead electrodes extend from the electrodes 6 and 7 toward the ends of the piezoelectric substrate 1, and the end electrode pads are connected to Pick-up 1 and Pic-up.
Let k-up2. Further, a lead electrode is extended from the electrode 8 toward the end of the piezoelectric substrate 1, and the end electrode pad is set to Drive. In the configuration shown in FIG.
Drive is performed by applying a voltage between Pick-up1 and Pick-up2 (more precisely, a voltage is applied between Drive and the ground potential point), and detection is performed by Pick-up.
1 and Pick-up2, the output is taken out differentially. The function of the piezoelectric vibrating gyroscope was confirmed also in the configuration of this modified example.

In the above description, LiNbO ₃ was used for the piezoelectric substrate. However, the present invention is not limited to this.
It goes without saying that the present invention can be applied to piezoelectric materials such as O ₃ , ceramic, and quartz. In the above description, rotation about the X axis (rotating Y plate), that is, one-axis rotation has been described, but rotation is not limited to one-axis rotation, and two orthogonal sliding vibrations can be used by two-axis rotation or the like. Should be fine. Further, although an example of chromium-gold (Cr-Au) has been described as an electrode material, it is needless to say that other metals may be used.

[0016]

According to the present invention, as described above, LiNb
Since the energy confinement type vibration gyro is configured by using the O ₃ rotation Y plate as the piezoelectric substrate, it is easier to support and does not require trimming compared to the conventional vibration gyro using bending vibration.
Excellent effects such as thin shape and easy manufacturing. Furthermore,
Since the piezoelectric single crystal is used for the substrate, the Q of resonance is high, and vertical electric field excitation is used for driving and detection, and parallel electric field excitation is used for the other. In addition, an excellent effect of being able to be driven and detected with high efficiency is exhibited.

[Brief description of the drawings]

FIG. 1A is a perspective view showing an embodiment of a piezoelectric vibrating gyroscope using thickness-shear vibration of a piezoelectric single crystal according to the present invention, and FIG. 1B is another embodiment.

2A and 2B are diagrams illustrating the present invention, wherein FIG. 2A shows the electric field direction and the vibration direction of a vertical electric field excitation, and FIG. 2B shows the electric field direction and the vibration direction of a parallel electric field excitation.

FIG. 3A is a diagram showing a relationship between a rotation angle and a electromechanical coupling coefficient of a LiNbO ₃ rotating Y plate during vertical electric field excitation,
(B) is a diagram showing the relationship between the rotation angle and the electromechanical coupling coefficient during parallel electric field excitation.

FIG. 4 is a diagram showing resonance and anti-resonance frequencies when the vibration gyro according to the present invention is excited by a vertical electric field and resonance frequencies when excited by a parallel electric field;

FIGS. 5A and 5B are diagrams showing electrode dimensions of the piezoelectric vibrating gyroscope according to the present invention.

FIGS. 6A and 6B are diagrams showing a change in resonance frequency of the vertical electric field and the parallel electric field excitation when the electrode dimensions of the piezoelectric vibrating gyroscope according to the present invention are changed, wherein FIG. 6A shows the width of the electrode 3, and FIG. The width of the electrode, (c), is a frequency variation when the depth is changed.

FIG. 7 shows admittance characteristics of the piezoelectric vibrating gyro vibrator according to the present invention when a vertical electric field and a parallel electric field are excited, in which (a) a sound absorbing material is not attached to a peripheral portion and (b) is attached.

FIG. 8 is an example of a circuit block diagram using the piezoelectric vibrating gyroscope according to the present invention.

FIG. 9 is a relationship diagram between an angular velocity and an output voltage of the piezoelectric vibrating gyroscope according to the present invention.

10A and 10B show an example of a conventional piezoelectric gyro, in which FIG. 10A is a perspective view, FIG. 10B is a plan view seen from the z-axis direction, and FIG. 10C shows a vibration mode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Piezoelectric substrate 2, 3, 4, 5, 6, 7, 8 ... Electrode 9, 10, 13, 14 ... Electrode 11, 15 ... Electric field direction 12, 16 ... Vibration direction pick-up1, pick-up2: output terminals a, a1, a2, b: electrode width W: electrode depth g: electrode gap

Claims (6)

[Claims] 1. A trigonal piezoelectric single crystal having a spontaneous polarization in a Z-axis direction of a crystal coordinate system (X, Y, Z), wherein said coordinate system is moved from 0 to 180 degrees around its X axis. In the flat plate-shaped piezoelectric single crystal vibrator cut out so that the main surface is substantially parallel to the X axis and the Z ′ axis of the coordinate system (X, Y ′, Z ′) rotated by the Z ′ axis, A piezoelectric vibrating gyroscope for detecting a rotational angular velocity, wherein two thickness shear vibrations orthogonal to each other, i.e., a direction displacement and an X-axis direction displacement, are used. 2. A vibrator in which electrodes are attached to both main surfaces of the piezoelectric vibrator on the flat plate, and one of the electrodes is divided into two or three parallel to the Z ′ axis. Drives and detects the thickness-shear vibration of the displacement in the Z ′ direction by the voltage applied to, and drives and detects the thickness-shear vibration of the displacement in the X-axis direction by generating an electric field in the X-axis direction by the voltage applied between the divided electrodes. The piezoelectric vibrating gyroscope according to claim 1, wherein: 3. A fine adjustment of a cutting direction of the piezoelectric single crystal oscillator and an adjustment of a thickness and a shape of an electrode on both main surfaces,
3. The piezoelectric vibratory gyroscope according to claim 1, wherein the resonance frequencies of the thickness shear vibrations of the Z 'axis displacement and the X axis displacement are adjusted to be close to each other. 4. The method according to claim 1, wherein the energy of the two thickness shear vibrations having the displacements orthogonal to each other is confined in the vicinity of the electrode by utilizing an additional mass effect and a piezoelectric reaction effect of the electrode. Piezoelectric vibration gyro. 5. The piezoelectric single crystal resonator according to claim 1, wherein the crystal is lithium niobate (LiNbO ₃ ), and the rotation angle θ about the X axis is 150 to 175 degrees. The piezoelectric vibrating gyroscope according to claim 4. 6. The piezoelectric single crystal resonator according to claim 1, wherein the crystal is lithium tantalate (LiTaO ₃ ), and the rotation angle θ about the X axis is 150 to 175 degrees. The piezoelectric vibrating gyroscope according to claim 4.