JP3958741B2 - Piezoelectric vibrator gyro vibrator - Google Patents

Description

  The present invention relates to a vibrator suitable for a piezoelectric vibration gyro, particularly a gyroscope used in an automobile navigation system, an attitude control device, a camera body-type VTR camera shake prevention device, and the like.

  A vibrating gyroscope is an angular velocity sensor that utilizes a dynamic phenomenon in which when an angular velocity is applied to an object having velocity, the object itself generates a Coriolis force in a direction perpendicular to the velocity direction.

  Mechanical vibration (drive vibration) can be excited by applying an electrical signal to the vibrator, and the magnitude of mechanical vibration (detection vibration) in the direction orthogonal to the drive vibration is electrically If the angular velocity about the axis parallel to the intersecting line between the drive vibration surface and the detection vibration surface is given in a state where the drive vibration is excited in advance, the above-mentioned Coriolis force acts. Detection vibration occurs and the output voltage can be detected. Since this output voltage is proportional to the magnitude and angular velocity of the driving vibration, the magnitude of the angular velocity can be obtained from the magnitude of the output voltage in a state where the magnitude of the driving vibration is constant. Among vibration gyros, a piezoelectric vibration gyro performs a conversion between an electric signal and mechanical vibration by a piezoelectric effect.

  At present, as vibrators used in piezoelectric vibratory gyros, vibrators with a piezoelectric body structure are often used because of their excellent productivity and precision. To date, further improvements in productivity and higher precision have been achieved. For this purpose, various vibrator structures have been proposed. In particular, for the purpose of small size and low cost, it is often preferable in terms of productivity that the structure of the vibrator is simpler, and there are not a few structures proposed from this viewpoint.

  In recent years, with the progress of miniaturization of piezoelectric vibration gyros, the method of mounting piezoelectric vibration gyros on the system has been changed from mounting by hand soldering to reflow solder mounting with excellent productivity. The piezoelectric vibration gyro is required to have heat resistance so that the performance and reliability of the piezoelectric vibration gyro are not impaired even if the entire piezoelectric vibration gyro is heated to a temperature of about 260 ° C. The vibration used in the piezoelectric vibration gyro The child is required to be small, inexpensive, simple in structure, and excellent in heat resistance.

  As a vibrator used for a piezoelectric vibration gyro which is small and inexpensive and has a simple structure, there is a prior document in which three electrodes for driving vibration and detection vibration are formed on one plane of a columnar piezoelectric element. FIG. 4 shows a vibrator for a piezoelectric vibration gyro characterized by a simple vibrator structure proposed in the prior art document 1. 4A is a perspective view, and FIG. 4B is a cross-sectional view.

  In FIG. 4, the vibrator 21 includes a drive electrode 23 and detection electrodes 22 and 24 on one side surface of a columnar body 25 made of piezoelectric ceramic, and is previously polarized in the arrow direction shown in the cross-sectional view of FIG. Therefore, it is possible to excite driving vibration in the in-plane direction perpendicular to the electrode forming surface and to detect the angular velocity at the center of the long axis of the columnar piezoelectric element, and to satisfy the function as a vibrator for a piezoelectric vibration gyro. . Since all the electrodes are provided on one side, productivity is remarkably superior to that provided with electrodes on a plurality of side surfaces.

  However, the Curie temperature of the piezoelectric ceramic used as the vibrator of the piezoelectric vibration gyro is about 300 ° C., and the polarization of the vibrator deteriorates when exposed to a temperature of 260 ° C. in the reflow solder mounting process. As a result, the performance of the piezoelectric vibration gyro There is a problem that reliability is lowered.

Further, as vibrators for vibrating gyroscopes having excellent heat resistance, there are prior literatures using LiNbO ₃ single crystal plates with a Curie temperature of about 1400 ° C. or LiTaO ₃ single crystal plates with a Curie temperature of about 870 ° C. as vibrators for vibratory gyros. is there. FIG. 5 shows a vibrator for a vibrating gyroscope excellent in heat resistance proposed in the prior document 2. FIG. 5A is a perspective view and FIG. 5B is a cross-sectional view. This vibrator 31 is composed of a single crystal plate 35 that is polarized in the thickness direction, and is provided with divided electrodes 32 and 34 on one main surface and an electrode 33 on the other main surface, so that FIG. By performing polarization in advance in the direction of the arrow shown in the cross-sectional view, it is possible to excite driving vibration in the in-plane direction perpendicular to the electrode formation surface and to detect the angular velocity at the center of the long axis of the single crystal plate. It fulfills the function as a vibrator.

If a LiNbO ₃ single crystal plate or a LiTaO ₃ single crystal plate is used, there is no polarization deterioration even when exposed to a high temperature of about 300 ° C., so that the piezoelectric vibration gyro is excellent in heat resistance. Since polarization can be reversed by using the effect, the productivity is excellent. However, the structure of the vibrator shown in FIG. 5 needs to be provided on two side surfaces, so that it is produced in comparison with the vibrator structure shown in FIG. There is a problem that it is inferior.

Therefore, the feasibility of the structure of the vibrator shown in FIG. 4 was examined below using LiNbO ₃ single crystal having excellent heat resistance.

FIG. 6 is a cross-sectional view of a columnar vibrator structure when a LiNbO ₃ single crystal Z-cut plate is used and the X-axis of the crystal is taken in the longitudinal direction of the columnar vibrator. The LiNbO ₃ single crystal has a trigonal 3m point group crystal structure and has anisotropy in the elastic constant depending on the orientation, and the existence of an electromechanical coupling coefficient k ₂₁ (efficiency of strain in the X direction due to the electric field in the Y direction). Thus, in the structure as shown in FIG. 6, the LiNbO ₃ single crystal 5 ′ can be flexibly vibrated by applying an AC voltage between the drive electrode 3 ′, the detection electrode 2 ′, and the detection electrode 4 ′. The vibrator cannot be flexibly vibrated straight and ideally, and the circuit processing of the detection signal becomes complicated. Therefore, it is difficult to realize a vibrator for a piezoelectric vibration gyro.

FIG. 7 is a cross-sectional view of a columnar vibrator structure when a LiNbO ₃ single crystal Z-cut plate is used and the X-axis of the crystal is perpendicular to the longitudinal direction of the columnar vibrator. In this case, the anisotropy of the elastic constant is left-right symmetrical in the cross section of the vibrator, and an LiNbO ₃ single crystal 5 ″ is obtained by applying an AC voltage between the drive electrode 3 ″, the detection electrode 2 ″, and the detection electrode 4 ″. Although it can be bent and vibrated straight, the LiNbO ₃ single crystal does not generate distortion due to the electric field in the X-axis direction of the crystal. Therefore, the electromechanical coupling coefficient k ′ ₂₃ rotated around the X-axis (the Y-axis after rotation) Even if a crystal having a large distortion efficiency in the Z-axis direction due to the electric field in the direction is used, bending vibration in the length direction of the columnar vibrator cannot be performed, so that there is no feasibility of a vibrator for a piezoelectric vibration gyro.

6 and FIG. 7, the case where the LiNbO ₃ single crystal is used has been described. However, the same applies to the LiTaO ₃ single crystal having the same crystal structure. As described above, the LiNbO ₃ single crystal or the LiTaO ₃ single crystal columnar body is used. It is difficult to realize a piezoelectric vibration gyro vibrator by forming electrodes only on one side.

Japanese Patent No. 3122925 Japanese Patent No. 3000891

The object of the present invention is to solve the problems described above, devise a vibrator structure that uses a columnar body of LiNbO ₃ single crystal or LiTaO ₃ single crystal, and only requires electrode formation on one side, and is small, inexpensive, and heat resistant -To provide a vibrator for a piezoelectric vibration gyro excellent in productivity.

According to the present invention, on one side of the columnar body having a plurality of side surfaces of a piezoelectric body in the longitudinal direction and the piezoelectric vibrating gyro vibrator parallel to three primary bending vibration mode of forming the strip-shaped electrodes of the columnar body The columnar body is made of a piezoelectric single crystal polarized so that the polarization direction is opposed to a plane perpendicular to the plane on which the strip electrode is formed and parallel to the longitudinal direction. A vibrator is obtained. Further, according to the present invention, in the piezoelectric vibration gyro vibrator, the piezoelectric vibration gyro vibrator is characterized in that the piezoelectric single crystal is made of a LiNbO ₃ single crystal or a LiTaO ₃ single crystal.

According to the columnar vibrator for a piezoelectric vibration gyro according to the present invention, there is no performance deterioration even when the gyro body is exposed to high temperature during solder reflow mounting using a LiNbO ₃ single crystal or a LiTaO ₃ single crystal. Since the vibrator can be configured by forming electrodes only on the side surfaces, the input / output wiring during electrode formation and assembly is easy, productivity is improved, and the vibration for piezoelectric vibration gyro that is compact, inexpensive, and has excellent heat resistance There is an effect that can get a child.

  Hereinafter, embodiments of the vibrator for a piezoelectric vibration gyro according to the present invention will be described in detail with reference to the following examples.

A commercially available LiNbO ₃ single crystal plate with a thickness of 1 mm and polarization in the thickness direction is heat-treated near the Curie temperature, and the polarization axis is reversed from the + C plane side in the plate thickness direction by a mechanism considered to be due to the pyroelectric effect. Then, using the phenomenon that the reversal stops at approximately the center of the plate thickness, polarization was performed so that the polarization directions were opposite. Incidentally, even the polarization axis is not perpendicular to the thickness of the single crystal plate, since the polarization reversal phenomenon occurs, in the case of using a bending vibration mode electromechanical coupling factor k _'23 has the largest cut angle 140 ° rotation Y plate Is preferably used.

1A and 1B are diagrams showing a piezoelectric vibration gyro vibrator according to an embodiment of the present invention. FIG. 1A is a perspective view, and FIG. 1B is a cross-sectional view orthogonal to the length direction. A piezoelectric vibration gyro vibrator 1 shown in FIG. 1 is a columnar body having a square cross section of 1 mm × 1 mm × 15 mm of a LiNbO ₃ single crystal body 5 cut out from the polarization-reversed LiNbO ₃ single crystal plate. A drive electrode 3 for exciting drive vibration and detection electrodes 2 and 4 for detecting detection vibration were formed on two cut-out surfaces. In addition, the columnar body is polarized in advance so that the polarization direction is opposed to the longitudinal direction surface perpendicular to the electrode formation surface, which is indicated by a dotted line in FIG. The arrows in FIG. 1 indicate the direction of polarization when using a 140 ° rotated Y-plate.

  Here, when an AC drive voltage of 2 V at a resonance frequency of 27 kHz of the primary bending vibration mode of the columnar body is applied to the drive electrode 3 and the detection electrodes 2 and 4, the drive electrode 3, the vicinity of the detection electrode 2, and the drive electrode 3 In the vicinity of the detection electrode 4, expansion and contraction in the same phase occurs, and the columnar body in the vicinity immediately below the electrode expands and contracts. Therefore, the entire columnar body can excite primary bending vibration in the length direction. A model of the primary bending vibration mode of the columnar body is shown in FIG.

  Similarly, when an AC voltage is applied to the detection electrode 2 and the drive electrode 3, expansion and contraction of opposite phases occurs in the vicinity of the drive electrode 3 and the detection electrode 2 and in the vicinity of the drive electrode 3 and the detection electrode 4. The vibration when applied to the electrode 3 and the detection electrodes 2 and 4 bends in a direction perpendicular to the vibration. The vibrator configuration of this embodiment can excite and detect vibrations in two orthogonal directions, thereby realizing a vibrator for a piezoelectric vibration gyro.

FIG. 3 is a block diagram showing a circuit configuration of the piezoelectric vibration gyro according to the present embodiment. The function as a gyro will be described below. The detection electrodes 2 and 4 are connected to the inverting terminals of the operational amplifiers 6 and 7, respectively. The operational amplifiers 6 and 7 apply negative feedback by the resistors 8 and 9, and the non-inverting terminal is grounded to the reference potential. Constitute. The potentials of the detection electrodes 2 and 4 are fixed to the reference potential by the virtual ground function of the operational amplifiers 6 and 7. When an alternating voltage in the vicinity of the resonance frequency of the bending vibration mode is applied between the drive electrode 3 and the detection electrodes 2 and 4, the expansion and contraction of the same phase occurs in the vicinity of the drive electrode 3 -detection electrode 2 and the drive electrode 3 -detection electrode 4 in the vicinity under the electrode Is caused by the effect of k ′ ₂₃ and bending vibration (driving vibration) becomes possible. At the same time, currents of the same phase are detected from the detection electrodes 2 and 4. When the piezoelectric vibration gyro vibrator is rotated around the major axis in this state, the bending driving vibration and the bending vibration (detection vibration) in the orthogonal direction are excited by the Coriolis force.

  The output current obtained from the detection electrodes 2 and 4 is converted into a voltage by the operational amplifiers 6 and 7, and the output voltage component obtained by the drive vibration can be separated by the adding circuit, and the output voltage component obtained by the detection vibration is differential. Since the circuit can be separated and extracted, the output terminals of the operational amplifiers 6 and 7 are connected to the adder circuit 10 and the differential circuit 12, respectively. The output terminal of the adder circuit 10 is fed back to the drive electrode 3 after passing through the oscillation circuit 11. As a result, the vibrator 1 can stably oscillate by itself. Further, the output of the differential circuit 12 is rectified by the low-pass filter 14 after passing through the synchronous detection circuit 13 detected at the timing of the output signal of the adder circuit 10, thereby obtaining a DC voltage proportional to the angular velocity. . That is, the piezoelectric vibration gyro vibrator according to the present invention can function as a gyro by being connected to a simple circuit as described above.

The figure which shows the vibrator | oscillator for piezoelectric vibration gyroscopes in the Example of this invention. 1A is a perspective view, and FIG. 1B is a cross-sectional view orthogonal to the length direction. The figure which shows the model of the primary bending vibration mode of a columnar body. The block diagram which shows the circuit connection example of the piezoelectric vibration gyro in an Example. The figure which shows the vibrator | oscillator for piezoelectric vibration gyro proposed in the prior art reference 1. 4A is a perspective view, and FIG. 4B is a cross-sectional view. The figure which shows the vibrator | oscillator for piezoelectric vibration gyro proposed by the prior art reference 2. FIG. 5A is a perspective view, and FIG. 5B is a cross-sectional view. Sectional drawing of the vibrator | oscillator for demonstrating the conventional problem. Sectional drawing of the vibrator | oscillator for demonstrating the conventional problem.

Explanation of symbols

1 vibrator 2, 2 ', 2 ", 4, 4', 4" detection electrode 3, 3 ', 3 "drive electrode 5, 5', 5" LiNbO ₃ single crystal or LiTaO ₃ single crystal 6, 7 Operational amplifiers 8 and 9 Resistance 10 Addition circuit 11 Oscillation circuit 12 Differential circuit 13 Detection circuit 14 Low-pass filter 21 Vibrator 22 and 24 Detection electrode
23 Drive electrode 25 Columnar body 31 made of piezoelectric ceramics Vibrator 32, 34 Divided electrode 33 Electrode 35 Single crystal plate

Claims (2)

On one side of the columnar body having a plurality of side surfaces of piezoelectric bodies, a longitudinal direction and the piezoelectric vibrating gyro vibrator parallel to three primary bending vibration mode of forming the strip-shaped electrodes of the columnar body, the columnar body Is made of a piezoelectric single crystal polarized so that the polarization direction is opposed to a plane perpendicular to the plane on which the strip electrode is formed and parallel to the longitudinal direction. 2. The vibrator for piezoelectric vibration gyro according to claim 1, wherein the piezoelectric single crystal is made of a LiNbO ₃ single crystal or a LiTaO ₃ single crystal.

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