JP2008175578A - Vibrator for piezoelectric vibrating gyroscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact, low-cost and high-performance vibrator for piezoelectric vibrating gyroscope, which is in a simple shape, has a simple electrode structure and enables a vibrator configuration to be realized in a two-axis detection. <P>SOLUTION: The vibrator for piezoelectric vibrating gyroscope using a torsional vibration mode due to a piezoelectric slip effect as a drive vibration mode comprises two first columnar arm parts 43a, 43b each being vertically connected with a second columnar arm part 42. The vibrator in a flat-plate form is made up of a piezoelectric single crystal integrally. In the piezoelectric vibrating gyroscope-use vibrator, strip detection electrodes 45a, 45b, 45c and 45d, and reference potential electrodes 46a, 46b are formed on front-back both sides of the first arm parts 43a, 43b, and strip drive electrodes 44a, 44b are formed on front-back both sides of the second arm parts 42. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a vibrator for a piezoelectric vibration gyro using an electromechanical conversion action by a piezoelectric material.

(Single axis vibratory gyro: Basic principle) A vibratory gyroscope is an angular velocity sensor that uses a mechanical phenomenon that when a rotational angular velocity is applied to an object having a velocity, a Coriolis force is generated in the direction perpendicular to the velocity direction. It is. The vibration gyro can excite mechanical vibration (hereinafter referred to as “driving mode”) by applying an electrical signal, and mechanical vibration in a direction orthogonal to the driving vibration (hereinafter, referred to as “driving mode”). A system in which the magnitude of “detection mode” can be electrically detected, and in a state where the drive mode is excited in advance, the line of intersection between the vibration surface in the drive mode and the vibration surface in the detection mode When a rotational angular velocity about a parallel axis is given, a detection mode is generated by the action of the aforementioned Coriolis force, and can be detected as an output voltage. Since the detected output voltage is proportional to the magnitude of the drive mode and the rotational angular velocity, the magnitude of the rotational angular velocity can be obtained from the magnitude of the output voltage when the magnitude of the drive mode is constant.

(Single-axis or two-axis vibration gyro: main vibration system) The vibrator for the vibration gyro uses piezoelectric materials such as piezoelectric ceramics and piezoelectric single crystals that use bending vibration due to the piezoelectric transverse effect as the drive mode and detection mode vibration mode. FIG. 10 is a perspective view showing a conventional piezoelectric vibration gyro vibrator. In FIG. 10, the vibrator 111 is composed of a square plate-like vibrating body 112 made of a constant elastic metal material such as an elimber, and a piezoelectric element 113 disposed at the center of the main surface of the vibrating body 112. A plurality of divided electrodes 116 are arranged on the surface of the piezoelectric element 113. In the vibrating body 112, four vibrating bodies 111a, 111b, 111c, and 111d are formed by four notches 121, 122, 123, and 124 from the center of each side to the center point. The vibrator 111 vibrates in an axially symmetric mode with the node axis N1 and the node axis N2 as axes, and is supported and fixed near the intersection of the node axis N1 and the node axis N2. The angular velocity is detected by using a mode that vibrates in the plane of the vibrator 111, and two angular velocities perpendicular to each other in the plane can be detected. Such a vibration gyro is disclosed in Patent Document 1.

(Single-axis vibration gyro: torsional vibration method using the piezoelectric transverse effect) Many of the vibration modes use bending vibration, but a vibrator for a piezoelectric vibration gyro that uses torsional vibration due to the piezoelectric transverse effect is disclosed in Patent Documents 2 and 3. Is disclosed.

(Uniaxial Vibrating Gyro: Vibrator Material Using Bending Vibration) Piezoelectric ceramics and piezoelectric single crystal materials are used as the material of the vibrator for the piezoelectric vibrating gyroscope. Among them, the piezoelectric single crystal material generally has a high mechanical quality factor (hereinafter referred to as Qm), a small characteristic change with respect to a temperature change, a uniform material, a high reliability, and a mass productivity of the material. In particular, it is often used as a vibrator for electronic parts such as sensors, oscillators, and surface acoustic wave filters. Further, in the future electronic component industry, lead-free electronic components are encouraged, and the materials are suitable for the environment.

(Uniaxial vibration gyro: characteristics of single crystal material) However, many piezoelectric single crystal materials have anisotropy in physical properties, and the magnitude of the piezoelectric effect changes by rotating the crystal direction. This rotation angle in the crystal direction is called crystal orientation, and there is a crystal orientation effective for the piezoelectric transverse effect for bending vibration and torsional vibration.

As an index of the magnitude of the piezoelectric effect, there is a coupling coefficient kij which is the efficiency of converting electrical energy into mechanical energy, and is calculated from the piezoelectric constant, elastic constant, and dielectric constant of the piezoelectric material. The higher the coupling coefficient kij is, the more efficient the drive vibration and the detection vibration, and the higher-performance piezoelectric vibration gyro vibrator can be manufactured. The coupling coefficient kij is a third-order tensor, the subscript i indicates the voltage application direction, and numbers 1 to 3 are assigned. The subscript j indicates the direction of the piezoelectric effect, and numbers 1 to 6 are assigned. The subscripts i, j assigned to the subscripts i, j are the X-axis direction, Y-axis direction, Z-axis direction, 4, 5, and 6 arbitrarily set for the vibrator, respectively, around the X-axis and Y-axis, The direction of rotation about the Z axis is shown. For example, the Y-axis direction of the size of the transverse piezoelectric effect when a voltage is applied to the X-axis direction is k _12. The size of the piezoelectric shear effect around the Z axis when the voltage applied to the X-axis direction is k _16. The coupling coefficient used in the piezoelectric lateral effect is k ₁₂ , k ₁₃ , k ₂₁ , k ₂₃ , k ₃₁ , and k ₃₂ which are piezoelectric effects in the direction perpendicular to the voltage application direction. Therefore, when a piezoelectric vibration gyro vibrator is formed of a piezoelectric single crystal material, it is important at which angle the crystal orientation is set with respect to the vibrator structure.

(Vibration Gyro: Development in Two Axes in Gyro Industry in Recent Years) In recent years, vibration gyros have been rapidly reduced in size and price as with other electronic components. In addition, for example, an anti-shake device or the like generally requires detection of a biaxial rotational angular velocity, and therefore, in most cases, two products that can detect a uniaxial rotational angular velocity are used. Under such circumstances, as one approach to reducing the size and cost of a vibrating gyroscope, studies have been made to enable detection of a biaxial rotational angular velocity within one product. In such a configuration, it is possible to share common parts such as a circuit and an external input / output terminal as compared with the case where a single-axis product is produced separately, thereby achieving a reduction in size and price. In addition, studies on mounting on mobile devices such as mobile phones have begun, and more shock resistance and higher stability are required than ever.

Japanese Patent No. 3206551 Japanese Patent No. 2521493 JP 2000-310534 A

  As described above, in order to reduce the size and cost, it is not only possible to detect the biaxial rotational angular velocity within one product, but also high-efficiency piezoelectric vibration must be used.

FIG. 11 is a graph of crystal orientation and coupling coefficient during typical Z-axis rotation of quartz. Coupling coefficient when the crystal orientation 0 ° is k ₁₂ is the coupling coefficient k ₁₃ in the direction perpendicular to it is a maximum k ₁₂ is 0 at any azimuth. Therefore, it is difficult to excite bending vibrations in two vertical directions as shown in the perspective view of FIG. Even if the crystal orientation is rotated, the maximum efficiency cannot be obtained with any coupling coefficient, and the piezoelectric transverse effect with high efficiency cannot be obtained.

On the other hand, Patent Document 3 discloses a technique that enables bending vibration in two directions. In Patent Document 3, quartz is used as a piezoelectric single crystal material, and a second branch portion that excites detection vibration at an inclination of 60 ° is connected to a branch portion that excites drive vibration, and electrodes are provided on the front and back surfaces. utilizing the components of k ₁₂ by forming. However, when the crystal orientation is 60 °, even if the coupling coefficient is maximized, it has an inclination of 60 ° with respect to the vibration direction, so it is difficult to obtain a high-performance piezoelectric vibratory gyro vibrator with loss of energy.

  In general, when a piezoelectric single crystal material is used, there is a problem that miniaturization, low cost, and high performance become difficult because of such structural limitations of crystal orientation, electrodes, and shape.

  In this situation, an object of the present invention is to provide a vibrator for a piezoelectric vibration gyro that has a simple shape, an electrode structure, and a vibrator structure with two-axis detection, and that is small, low in price, and high in performance. is there.

  In order to solve the above-described problems, according to claim 1 of the present invention, a torsional vibration mode based on a piezoelectric sliding effect is configured as a vibrator for a piezoelectric vibration gyro that uses at least one of a drive vibration mode and a detection vibration mode. It is possible to excite torsional vibration due to the piezoelectric sliding effect exhibiting a high coupling coefficient and solve the problem.

In addition, as for the sliding effect due to piezoelectricity, for example, in a flat plate model of crystal or piezoelectric ceramic, there are a “piezoelectric surface slip” and a “piezoelectric thickness slip”, but in this application, these are collectively referred to as piezoelectric. This is called a slip effect. Further, the piezoelectric constant slippage _effect, there is a _{d 14, d 15, d 16} , d 24, d 25, d 26, d 34, d 35, d 36.

  In addition, in order to constitute a bi-directional vibration mode, it has two or more columnar first arm portions that are connected perpendicularly to the columnar second arm portion, and is integrally formed of a piezoelectric single crystal material. A piezoelectric vibrator for a piezoelectric vibration gyro that is formed on the surface of the first arm and the second arm portion, a belt-like drive electrode for electric signal input, a belt-like detection electrode for vibration detection, and a reference potential The structure to which the electrode for this was given is desirable.

  Further, in order to stabilize the vibration in the two-direction vibration mode, the vibrator for a plate-like piezoelectric vibration gyro having two or more first arm portions connected perpendicularly to the second arm portion, The first and second vibration modes that vibrate in the plane of the vibrator and the third vibration mode whose vibration direction is orthogonal to the first and second vibration modes can be excited and detected. Is desirable.

  In order to make the drive vibration mode and the detection vibration mode highly efficient, at least one vibration mode of the drive vibration mode and the detection vibration mode includes a piezoelectric thickness in the thickness direction of the second arm portion or in the main surface direction. Torsional vibration related to a plane perpendicular to the longitudinal direction of the second arm portion due to the slip effect is used, and in the other vibration modes, the torsional vibration is applied in the thickness direction of the first arm portion or in the main surface direction. A configuration using bending vibration related to the first arm portion by a piezoelectric lateral effect in a direction perpendicular to the rotation center axis of vibration is desirable.

  Further, in order to improve the assembly property of the vibrator and to detect the biaxial angular velocity, the frame body, a support part having both ends supported by the frame body, and one or more formed to intersect the support part The first arm portion, two or more first arm portions connected to the second arm portion, and a load mass portion supported by the first arm portion. In the mode, the second vibration mode, and the third vibration mode, it is desirable that the frame body be a vibration node.

Further, in order to obtain a piezoelectric lateral effect and a piezoelectric thickness sliding effect with a large coupling coefficient, the piezoelectric single crystal material is LiNbO ₃ , and the thickness directions of the first arm portion and the second arm portion are the piezoelectric directions. It is desirable that the X axis is the crystal orientation of the single crystal, and the direction parallel to the longitudinal direction of the second arm portion is the Y axis of 140 ° ± 15 ° rotation of the crystal orientation of the piezoelectric single crystal.

Similarly, in order to obtain a piezoelectric lateral effect and a piezoelectric thickness slip effect with a large coupling coefficient, the piezoelectric single crystal material is LiTaO ₃ , and the thickness directions of the first arm portion and the second arm portion are Desirably, the X-axis of the crystal orientation of the piezoelectric single crystal is parallel to the longitudinal direction of the second arm portion, and the Y-axis is rotated by 140 ° ± 15 ° of the crystal orientation of the piezoelectric single crystal. .

  As described above, by applying the present invention, a simple shape, an electrode structure, and a configuration with two-axis detection are possible, and a small-sized, low-cost, high-performance vibrator for a piezoelectric vibration gyro can be obtained.

  Embodiments of the present invention will be described with reference to the drawings using an example of a vibrator for a piezoelectric vibration gyro according to the present invention.

(Embodiment 1) FIG. 1 is a perspective view showing a piezoelectric vibration gyro vibrator 41 according to Embodiment 1 of the present invention. A second arm portion 42 is formed in the same plane of a single piezoelectric single crystal plate made of a LiNbO ₃ piezoelectric single crystal, and the two first portions connected to the second arm portion 42 so as to be T-shaped. The arm portions 43a and 43b were formed by pattern processing such as blast processing and dry etching processing using a photolithography technique. In the present embodiment, the shape is bilaterally symmetric with respect to the center line of the second arm portion 42. Further, the end surface 47 of the second arm portion 42 is a fixed surface.

  The arrangement of the coordinate axes is such that the axis parallel to the longitudinal direction of the second arm portion 42 is the Y axis, the axis parallel to the longitudinal direction of the first arm portions 43a and 43b is the Z axis, and the direction perpendicular to the YZ plane is The X axis was used. The electrodes are formed with belt-like drive electrodes 44a and 44b for torsional vibration using the piezoelectric sliding effect on the surface of the second arm portion 42, and the piezoelectric lateral effect is formed on the surfaces of the first arm portions 43a and 43b. Detection electrodes 45a, 45b, 45c, 45d for bending vibration and reference potential electrodes 46a, 46b were formed in a strip shape. 2A is a cross-sectional view of the second arm portion 42, and FIG. 2B is a cross-sectional view of the first arm portion 43a. Thus, an electrode similar to the surface was formed on the back surface of the flat plate. The electrode was formed of a gold electrode with chromium as a base.

The coupling coefficients required in the above configuration are k ₂₁ , k ₂₃ , and k ₁₆ . FIG. 3 is a graph of the crystal orientation around the X axis of LiNbO ₃ and the coupling coefficients k ₂₁ , k ₂₃ , and k ₁₆ .

Since the coupling coefficients k ₂₁ , k ₂₃ , and k ₁₆ are high in the vicinity of 140 °, the crystal orientation is arranged so that the Y direction of the element (piezoelectric vibratory gyro vibrator 41) coincides with ± 140 ° Y of the crystal orientation. Therefore, by using the coupling coefficients k ₂₁ , k ₂₃ , and k ₁₆ , the piezoelectric vibration gyro vibrations are formed by the electrodes of only the front and back surfaces of the second arm part 42 and the first arm parts 43 a and 43 b of the piezoelectric vibration gyro vibrator. Child can be configured.

  Here, the operation principle of the piezoelectric vibration gyro configured as described above will be described. By applying alternating voltages having opposite phases to the drive electrodes 44a and 44b, the torsional vibration is excited as a drive vibration mode (X mode) by the piezoelectric thickness sliding effect.

  FIG. 4 is a perspective view showing the behavior of the second arm portion 42 and the first arm portions 43a and 43b in the X mode. The first arm portions 43a and 43b vibrate in opposite phases in a direction parallel to the X-axis direction. Thus, torsional vibration 48 is generated in the second arm portion 42.

  FIG. 5 is a perspective view of the Y mode in which the first arm portions 43a and 43b vibrate in opposite phases with respect to the Y-axis direction.

  For example, when an angular velocity is applied around the Y axis in the state where the X mode that is driving vibration is excited, the Y mode is generated due to the influence of the Coriolis force acting on the two first arm portions. At this time, if the vibration speed of the X mode is constant, the magnitude of the generated Y mode amplitude is proportional to the applied angular velocity, and functions as an angular velocity sensor if these vibrations are extracted electrically.

Even if LiTaO ₃ is applied as the piezoelectric single crystal material in addition to LiNbO _3, a useful vibrator for a piezoelectric vibration gyro can be configured according to the present invention. Further, even if the crystal orientation allows a rotation range of ± 15 ° with respect to the 140 ° rotation Y axis, a sufficiently high efficiency can be obtained practically.

(Embodiment 2)
FIG. 6 shows the first arm portions 91a, 91b, and the like, in addition to the piezoelectric vibration gyro vibrator according to the first embodiment, a similar T-shaped vibrator with the end face 47 (FIG. 1) as a symmetry plane is connected. It is a top view of the vibrator for piezoelectric vibration gyroscope which connected load mass parts 92a, 92b, 92c, and 92d to the tip of 91c and 91d.

  In the X mode of the second embodiment, as shown in FIG. 7, the second arm portions 93a, 93b perform torsional vibration, and the first arm portions 91a, 91b, 91c, 91d are the second arm portions 93a, 93b. Rotate around the axis. As a result, the load mass portions 92a and 92d and the load mass portions 92b and 92c vibrate out of plane with opposite phases.

  Further, in the Y mode, as shown in FIG. 8, the first arm portions 91a and 91d and the other first arm portions 91b and 91c are in the in-plane direction in opposite phases with respect to the Y-axis direction. Vibrate.

  In addition, as shown in FIG. 9, as the Z mode, the first arm portions 91a and 91c and the other first arm portions 91b and 91d are connected to the load mass portions 92a and 92c and the other load mass portions 92b and 92d. As a result, they vibrate in the in-plane direction with phases opposite to each other in the Z-axis direction.

  Accordingly, if the Y-mode in-plane vibration and the Z-mode in-plane vibration are separated and output based on the respective phase relationships, two axes can be detected by one piezoelectric vibration gyro vibrator. Further, as shown in FIG. 6, the vicinity of the node point of the torsional vibration of the second arm portions 93a and 93b is connected to the outer edge portion (frame body) 95 by beam portions (support portions) 94a and 94b.

  Thus, since the vibrations of the arms connected to the load masses adjacent to each other are in opposite phases, the vibration energy is confined inside, and the vibration in the driving mode is difficult to be transmitted to the frame. Therefore, stable support characteristics can be obtained without impeding vibration in the drive mode. And a sensor output is stabilized and an output drift is also reduced. Further, since the entire circumference of the outer edge portion 95 can be supported, even if an impact is applied to the piezoelectric vibration gyro vibrator, the force can be dispersed and a structure having high impact resistance can be obtained. In addition, since the outer edge portion 95 can be supported and fixed, mounting is easy and productivity is increased.

  In the manufacturing process, even when a plurality of the vibrating gyro elements are simultaneously formed on the piezoelectric single crystal wafer and the outer edge portions 95 are joined to each other, the characteristics can be easily inspected. Therefore, it is possible to perform vibration characteristic inspection, frequency adjustment, and balance adjustment without cutting out the vibration gyro elements one by one, which can be easily inspected and adjusted, and the yield of subsequent processes can be improved.

As described above, by combining a piezoelectric single crystal LiNbO ₃ rotation 140 ° plate with a structure in which torsional vibration and bending vibration are applied to the vibration mode, high performance, small size, and low cost are realized with a simple structure and high mass productivity. A vibrator for a piezoelectric vibration gyro can be obtained.

  By the way, in said embodiment, although the case where the number of the 1st arm parts was 2 or 4 was demonstrated, the number of the 1st arm parts is 3 or 5 or more, and in order to balance vibration, Alternatively, an appropriate number can be selected according to the purpose, for example, to increase sensitivity.

  In the above embodiment, the case of using the piezoelectric sliding effect by “piezoelectric thickness sliding” has been described, but it is obvious that the piezoelectric sliding effect by “piezoelectric surface sliding” may be used.

1 is a perspective view of a first embodiment of a vibrator for a piezoelectric vibration gyro according to the present invention. FIG. 2A is a cross-sectional view of a second arm portion, and FIG. 2B is a cross-sectional view of a first arm portion according to the first embodiment of a vibrator for a piezoelectric vibration gyro according to the present invention. A graph of crystal orientation around the X axis of LiNbO ₃ and coupling coefficients k ₂₁ , k ₂₃ , and k ₁₆ . The perspective view which shows the vibration direction of the X mode in Embodiment 1 of the vibrator | oscillator for piezoelectric vibration gyroscopes of this invention. FIG. 3 is an external perspective view showing the Y-mode vibration direction in the first embodiment of the vibrator for piezoelectric vibration gyro according to the present invention. The top view in Embodiment 2 of the vibrator | oscillator for piezoelectric vibration gyroscopes of this invention. FIG. 7A is a perspective view, FIG. 7B is a top view, and FIG. 7C is a side view, illustrating an X-mode vibration direction in the second embodiment of the vibrator for piezoelectric vibration gyro according to the present invention. Figure. FIG. 8A is a perspective view, FIG. 8B is a top view, and FIG. 8C is a side view, illustrating a Y-mode vibration direction in the second embodiment of the vibrator for piezoelectric vibration gyro according to the present invention. Figure. FIG. 9A is a perspective view, FIG. 9B is a top view, and FIG. 9C is a side view, illustrating a Z-mode vibration direction in the second embodiment of the vibrator for piezoelectric vibration gyro according to the present invention. . FIG. 6 is a perspective view of a vibrator for a piezoelectric vibration gyro for explaining a conventional technique. The graph of the relationship between the crystal azimuth angle of a quartz crystal and a coupling coefficient for demonstrating the conventional problem. FIG. 6 is a perspective view of a piezoelectric vibration gyro vibrator for explaining a conventional problem.

Explanation of symbols

41 Piezoelectric vibratory gyro vibrators 42, 93a, 93b Second arm parts 43a, 43b, 91a, 91b, 91c, 91d First arm parts 44a, 44b Drive electrodes 45a, 45b, 45c, 45d Detection electrodes 46a, 46b Reference potential electrode 47 End face 48 Torsional vibration 92a, 92b, 92c, 92d Load mass portion 94a, 94b Beam portion 95 Outer edge portion 111 Vibrators 111a, 111b, 111c, 111d, 112 Vibrating body 113 Piezoelectric element 116 Electrodes 121, 122, 123 , 124 Notch N1, N2 Node axis

Claims (7)

  A vibrator for a piezoelectric vibration gyro, wherein a torsional vibration mode based on a piezoelectric sliding effect is used for at least one of a drive vibration mode and a detection vibration mode.   Two or more columnar first arm portions connected perpendicularly to the columnar second arm portion are formed integrally with a piezoelectric single crystal in a flat plate shape, and the first arm portion and the The vibrator for a piezoelectric vibration gyro according to claim 1, wherein a band-shaped drive electrode for electric signal input and a band-shaped detection electrode for vibration detection are formed on the surface of the second arm portion.   It has two or more columnar first arm portions that are vertically connected to the columnar second arm portion, and is formed integrally with a piezoelectric single crystal in a flat plate shape, and vibrates in the plane of the flat plate. The first and second vibration modes and the third vibration mode whose vibration direction is orthogonal to the first and second vibration modes are used for the drive vibration mode and the detection vibration mode. 3. A vibrator for a piezoelectric vibration gyro according to claim 1 or 2.   In at least one of the drive vibration mode and the detection vibration mode, the longitudinal direction of the second arm portion generated by the piezoelectric thickness slip effect in the thickness direction of the second arm portion or in the main surface direction is used. The piezoelectric transverse effect in the direction perpendicular to the rotational center axis of the torsional vibration is used in the thickness direction or the principal plane direction of the first arm portion in other vibration modes. 4. The piezoelectric vibration gyro vibrator according to claim 2, wherein bending vibration of the first arm portion is used.   A frame, a support part having both ends supported by the frame, one or more second arm parts formed to intersect the support part, and two or more connected to the second arm part The first arm portion and a load mass portion supported by the first arm portion, and the frame body is a vibration node for both the drive vibration mode and the detection mode. 5. The piezoelectric vibration gyro vibrator according to claim 3, wherein the piezoelectric vibration gyro vibrator is provided. The piezoelectric single crystal is LiNbO ₃ , the thickness direction of the first arm portion and the second arm portion is the X axis of the crystal orientation of the piezoelectric single crystal, and the longitudinal direction of the second arm portion 6. The vibrator for a piezoelectric vibration gyro according to claim 2, wherein the direction parallel to the piezoelectric axis is a Y axis of 140 ° ± 15 ° rotation of the crystal orientation of the piezoelectric single crystal. The piezoelectric single crystal is LiTaO ₃ , the thickness direction of the first arm portion and the second arm portion is the X axis of the crystal orientation of the piezoelectric single crystal, and the longitudinal direction of the second arm portion 6. The vibrator for a piezoelectric vibration gyro according to claim 2, wherein the direction parallel to the piezoelectric axis is a Y axis of 140 ° ± 15 ° rotation of the crystal orientation of the piezoelectric single crystal.

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