JP4309814B2 - Method for adjusting vibrator for piezoelectric vibration gyro - Google Patents

Description

  The present invention relates to a method for adjusting a vibrator for a piezoelectric vibration gyro in a manufacturing process of a piezoelectric vibration gyro for a gyroscope used mainly in a navigation system, an attitude control device for an automobile, a camera shake prevention device for a camera body type VTR, 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 mode) can be excited by applying an electrical signal, and the magnitude of mechanical vibration (detection mode) in the direction orthogonal to the drive vibration can be detected electrically. When the angular velocity about the axis parallel to the intersection line of the vibration surface of the drive mode and the vibration surface of the detection mode is given in the state where the drive mode is excited in advance, the above action of the Coriolis force causes The detection mode occurs and is detected as the output voltage. Since the detected output voltage is proportional to the magnitude and angular velocity of the drive mode, the magnitude of the angular velocity can be obtained from the magnitude of the output voltage when the magnitude of the drive mode is constant. Among vibration gyros, those that convert electrical signals and mechanical vibrations by the piezoelectric effect are called piezoelectric vibration gyros.

  A small and inexpensive piezoelectric vibration gyro is widely used as a camera shake detection sensor for digital video cameras, digital still cameras, and the like. In recent years, the demand for further miniaturization of the piezoelectric vibrating gyroscope has been increased with the progress of miniaturization of these portable digital devices and higher integration of functions. However, in order to reduce the size of the piezoelectric vibration gyro, it is necessary to consider an efficient correction means for a relative increase in variations in processing accuracy and assembly accuracy of the vibrator. These variations affect the variation in the resonance frequency difference between the driving of the vibrator and the detection mode (hereinafter referred to as Δf, and in this text, Δf = resonance frequency in the drive mode−resonance frequency in the detection mode), and Δf The variation in sensitivity affects the variation in sensitivity of the piezoelectric vibration gyro.

  In the past, variations in processing accuracy and assembly accuracy of the vibrator have been satisfied by satisfying predetermined characteristics by adjusting Δf by mechanical processing after the vibrator is assembled. As a method for adjusting such a tuning fork vibrator, for example, there is a technique disclosed in Patent Document 1. FIG. 6B shows a front view of the tuning fork vibrator. A single crystal tuning fork vibrator having the same material and the same thickness tuning fork arms 301 and 302 connected to a single crystal rectangular plate base 300 is formed, and further connected to a ceramic support substrate 311 using an adhesive. FIG. 6A shows the resonance of the ceramic support substrate length d and the tuning mode fork vibrator fx mode (corresponding to the tuning fork vibration mode of the present invention described later) and fy mode (corresponding to the out-of-plane vibration mode of the present invention described later). The frequency relationship is shown. The fx mode has good support characteristics and no vibration leakage to the support substrate. Therefore, the resonance frequency of the fx mode does not depend on the support substrate length d. However, the fy mode largely depends on the support substrate length d because torsional vibration leaks to the support substrate. As a result, the Q value of Δf and fy modes can be adjusted by adjusting the support substrate length d. As other effects, by connecting a ceramic support substrate to the base of the tuning fork vibrator, the moment can be increased with respect to the longitudinal axis of the vibrator, the toy vibration of the fy mode is suppressed, and the fy mode is suppressed. The effect of facilitating support can be expected.

  Further, as a method for adjusting a sound piece-shaped vibrator, a technique for adjusting Δf and the vibration direction by cutting the main surface on which the electrodes on the front and back of the vibrator are arranged is disclosed in Patent Document 2, for example. Yes. FIG. 7 is a perspective view showing the shape and electrode configuration of the vibrator. Piezoelectric ceramic rectangular plates 105 and 104, which are polarized in opposite directions in the thickness direction, are stacked with the intermediate electrode 103 interposed therebetween to form a bimorph type vibrator 101. On one main surface of the vibrator 101, a vibrator Drive and detection electrodes 102a and 102b divided into two in the longitudinal direction of 101 are arranged, and a reference potential electrode 106 is arranged on the other main surface. The vibrator 101 is supported by a wire 108 in the vicinity of a bending vibration node point, and the vibration gyro 100 is configured. The two main surfaces of the vibrator are cut at a position 107 to reduce the resonance frequency of the bending vibration mode substantially perpendicular to the main surface of the vibrator 101 which is the driving vibration mode and adjust the direction of vibration. be able to. This cutting process is repeated several times to adjust to an appropriate value of Δf, and at the same time the output balance is adjusted.

JP-A-8-313265 Japanese Patent No. 3285140

  However, in the technique of Patent Document 1, Δf adjustment is performed by adjusting the length of the ceramic support substrate, forming a slit, or the like, and a process for connecting the tuning fork vibrator to the ceramic support substrate is required. Yield decline is feared due to difficulty in management of the stratum.

  In the technique of Patent Document 2, cutting is performed on the main surface of the vibrator, and the direction of vibration is adjusted simultaneously with Δf. However, since the cutting is performed also on the electrode that is originally required at the time of adjustment, the excitation efficiency of the electrode is deteriorated, resulting in sensitivity variations.

  Therefore, an object of the present invention is to provide a method for adjusting a vibrator for a piezoelectric vibration gyro with high accuracy at low cost without processing the piezoelectric body or its support body.

  In order to solve the above-mentioned problems, the piezoelectric vibration gyro vibrator of the present invention employs a single crystal tuning fork vibrator in which the electrode can be constituted by only one side surface of the vibrator, and the drive, detection and reference potential electrodes are provided. A frequency adjusting electrode for adjusting Δf is formed on the other principal surface that is not arranged. Even if this frequency adjustment electrode is subjected to arbitrary trimming to adjust Δf, there is no change in the drive / detection efficiency of the vibrator, and the piezoelectric vibratory gyroscope does not deteriorate in characteristics. Provide a method of adjustment.

  In other words, the piezoelectric vibration gyro vibrator adjustment method according to the first aspect of the present invention is such that the first and second arms and the base connecting the arms are integrally formed of a piezoelectric single crystal, and the first and second arms are integrally formed. A tuning fork vibrator in which driving and detection electrodes are formed only on one main surface of the arm and the base, and a tuning fork vibration which is one of vibration modes and an out-of-plane vibration orthogonal to the tuning fork vibration In the manufacturing process of the tuning-fork type piezoelectric vibration gyro that excites and detects the frequency adjustment electrode, a frequency adjustment electrode is formed in advance on the other main surface facing the main surface, and a partial region of the frequency adjustment electrode The resonance frequency difference between the tuning fork vibration and the out-of-plane vibration is adjusted by forming a divided electrode that becomes a floating electrode by dividing the pattern by trimming.

  The piezoelectric vibration gyro vibrator adjustment method according to a second aspect of the present invention is the method according to the first aspect, wherein the charges generated on the surface of the divided electrode by the tuning fork vibration are substantially zero or the positive and negative charges cancel each other. The position of the divided electrode is such that the sum is substantially zero and the charge generated by the out-of-plane vibration and the capacitance between the frequency adjusting electrode and the divided electrode correspond to a desired frequency adjustment amount. And adjusting the shape to selectively increase the resonance frequency of the out-of-plane vibration.

  According to a third aspect of the present invention, there is provided a method for adjusting a vibrator for a piezoelectric vibration gyro according to the first aspect, wherein the charges generated on the surface of the divided electrode by the out-of-plane vibration are substantially zero or the positive and negative charges cancel each other. Thus, the position of the divided electrodes is such that the sum is substantially zero, and the electric charge generated by the tuning fork vibration and the capacitance between the frequency adjusting electrode and the divided electrode correspond to a desired frequency adjustment amount. And adjusting the shape to selectively increase the resonance frequency of the tuning fork vibration.

  First, according to the adjustment method of the first invention, the electrode that contributes to the drive and detection efficiency of the piezoelectric vibration gyro is not arranged on the surface on which the frequency adjustment electrode is formed, and the adjustment is performed while avoiding the conventional electrode. In contrast, it is possible to perform adjustment with a high degree of freedom. As in the conventional adjustment method, there is no defect in the vibrator electrode, and the excitation / detection efficiency of the vibrator does not change before and after the adjustment. Therefore, regardless of the amount of adjustment of Δf, the characteristic of the vibrator after the appropriate adjustment is very small, the sensitivity variation can be suppressed, and the burden on the circuit side can be reduced.

  In the adjusting method of the second invention, when forming the divided electrode by laser processing or the like, the electromechanical coupling of the divided electrode and the tuning fork vibration is made small, and the electromechanical coupling of the divided electrode and the out-of-plane vibration becomes a desired size. Trimming. As a result, the capacitance between the divided electrode and the frequency adjusting electrode does not affect the resonance frequency of the tuning fork vibration, and it is possible to selectively increase only the resonance frequency of the out-of-plane vibration. Although the capacitance ratio slightly deteriorates due to the influence of the capacitance between the divided electrode and the frequency adjusting electrode, there is essentially no problem because the force coefficient does not change.

  In the adjustment method of the third invention, when the divided electrode is formed by laser processing or the like, the electromechanical coupling between the divided electrode and the out-of-plane vibration is reduced, and the electromechanical coupling between the divided electrode and the tuning fork vibration is set to a desired size. Trimming. As a result, the capacitance between the divided electrode and the frequency adjusting electrode does not affect the resonance frequency of the out-of-plane vibration, and only the resonance frequency of the tuning fork vibration can be selectively increased.

  According to the present invention using the above solution as a whole, arbitrary trimming can be performed on the frequency adjusting electrode. The resonance frequencies of the tuning fork vibration and the out-of-plane vibration can be adjusted independently, and Δf can be adjusted in both positive and negative directions. Further, there is no substantial change in the drive / detection efficiency of the vibrator before and after adjustment, and the characteristics of the piezoelectric vibration gyro are not deteriorated. Furthermore, since the piezoelectric body itself is not processed and Δf can be adjusted by trimming only the electrodes with a laser or the like, it is possible to easily perform high-precision adjustment with less energy compared to mechanical adjustment. is there. That is, the effect of the present invention is to provide a method for adjusting a tuning fork vibrator for a piezoelectric vibration gyro with high productivity and small variations even when the vibrator is greatly reduced in size.

  Embodiments of the present invention will be described below in detail with reference to the drawings. First, the basic operation principle of the tuning fork type piezoelectric vibration gyro will be described. FIG. 1 shows a vibration mode of a vibrator for a tuning fork type piezoelectric vibration gyro according to the present invention, FIG. 1 (a) is a perspective view showing a tuning fork vibration mode, and FIG. 1 (b) is a perspective view showing an out-of-plane vibration mode. It is. An electrode coupled to the vibration mode shown in FIGS. 1A and 1B is arranged on such a tuning-fork-shaped piezoelectric body to constitute a tuning-fork-type piezoelectric vibrator that can be excited and detected. At this time, a drive signal having a frequency close to the resonance frequency of the tuning fork vibration mode is applied to the electrode to excite the tuning fork vibration mode. In this state, when an angular velocity is applied to the longitudinal axis of the vibrator, a Coriolis force proportional to the angular speed acts on the vibrator, and an out-of-plane vibration mode is generated. If an electric signal generated by this out-of-plane vibration mode is taken out from the electrode, an electric signal proportional to the angular velocity can be obtained and function as a piezoelectric vibration gyro. In this embodiment, the tuning fork vibration mode is used for the drive mode and the out-of-plane vibration mode is used for the detection mode, but these are interchanged, and the out-of-plane vibration mode is used for the drive mode and the tuning fork vibration mode is used for the detection mode. It is also possible to do.

  FIG. 2 is a perspective view of a tuning fork vibrator as a piezoelectric vibration gyro vibrator according to an embodiment of the present invention. The dimensions of this tuning fork vibrator are a total length of 7 mm, a width of 1.12 mm, a thickness of 0.4 mm, a tuning fork arm length of 4 mm, and a tuning fork arm width of 0.35 mm. The resonance frequency of the tuning fork vibration mode and the out-of-plane vibration mode is The two arms 2 and 3 arranged in parallel and symmetrically at about 20 kHz and the piezoelectric body of the base 1 connecting them are formed. In the arm 2, the drive electrode 6 is arranged in parallel with the longitudinal direction of the arm 2, and the detection electrode 10 and the reference potential electrode 9 are arranged on the left and right sides thereof. Similarly, the drive electrode 5 and the detection electrode 7 and the reference potential electrode 8 are arranged on the left and right sides of the arm 3 in parallel with the longitudinal direction of the arm 3. Further, a uniform solid electrode is formed on the main surface (rear surface) opposite to the surfaces of these electrodes to form the frequency adjusting electrode 20. However, it is not necessary to form the frequency adjusting electrode 20 on the entire main surface. Generally, the frequency adjusting electrode 20 is formed on a wide surface so as to cover a portion where charges are concentrated, and is connected to a reference potential or ground to adjust the frequency. Do.

The piezoelectric body used here is a LiTaO ₃ piezoelectric single crystal X plate in which the longitudinal direction of the vibrator is parallel to the axis in which the Y axis of the crystal is rotated by 40 ° with respect to the X axis, or the longitudinal direction of the vibrator is crystallized. A LiNbO ₃ piezoelectric single crystal X plate whose Y axis is parallel to an axis rotated by 50 ° with respect to the X axis is used, and the piezoelectric lateral effect is large with respect to the electric field in the width direction of the vibrator. Therefore, by applying an electric field in the width direction of the vibrator, distortion can be generated in the longitudinal direction of the vibrator and the arm can be bent.

  3 is a cross-sectional view showing a state of excitation and detection of the vibration mode of the tuning fork vibrator of FIG. By applying a drive voltage between the drive electrode 6, the detection electrode 10, and the reference potential electrode 9, an electric field as shown in FIG. As a result, the left and right sides of the drive electrode 6 have opposite electric fields, and on the one hand, they extend in the length direction, and on the other hand, they contract in the length direction. Therefore, the tuning fork vibration mode can be excited by the drive electrode 6.

  Similarly, the tuning fork vibration mode can be excited with twice the efficiency by applying a voltage opposite in phase to the voltage applied to the drive electrode 6 to the drive electrode 5, the detection electrode 7 and the reference potential electrode 8. . Next, when an angular velocity is applied to the longitudinal axis of the arm, an out-of-plane vibration mode due to Coriolis force is generated as shown in FIG. In this vibration, the left and right arms vibrate in the opposite direction in the direction perpendicular to the surface of the vibrator. This vibration can be detected as a signal difference between the detection electrode 10 and the reference potential electrode 9 and between the detection electrode 7 and the reference potential electrode 8. As shown in FIG. 3, the signals of the detection electrode 7 and the detection electrode 10 generated by the out-of-plane vibration mode have the same amplitude and the same phase. In the above description, the case where the piezoelectric vibration gyro is configured using the tuning fork vibration mode as the drive mode and the out-of-plane vibration mode as the detection mode has been described, but the case where the drive mode and the detection mode are switched is also described. It can be used as well.

  FIG. 4 shows a frequency adjustment method according to an embodiment of the present invention. 4A is a schematic diagram of the charge distribution appearing on the surface of the frequency adjusting electrode in the tuning fork vibration, and FIG. 4B is a schematic diagram of the charge distribution appearing on the surface of the frequency adjusting electrode in the out-of-plane vibration. is there. As is clear from FIGS. 4 (a) and 4 (b), the charge distribution of the tuning fork vibration is divided into three regions in the width direction in each arm, and the polarity is inverted between the center and the regions at both ends. Furthermore, the polarities of the distributions are reversed between the left and right arms. The charge distribution of out-of-plane vibration is distributed along the length direction of the vibrator at the left and right ends of each arm, and the polarity is inverted between the two areas inside the vibrator and the two areas outside.

  4 (c) and 4 (d) show examples of forming divided electrodes for performing frequency adjustment in the method for adjusting a vibrator for piezoelectric vibration gyro according to the present invention based on the above charge distribution. Regions A and B in FIG. 4C are formed so that the width of the arm is divided into two. In the charge distribution of the tuning fork vibration shown in FIG. 4A, the positive and negative charges cancel each other, and the sum is almost zero. However, in the charge distribution of out-of-plane vibration in FIG. 4B, only positive or negative charge exists. Accordingly, the regions A and B in FIG. 4C are separated by laser trimming or the like, that is, trimming is performed along the separation line 42 along one side of the rectangle indicated by the broken line, and the floating electrode is separated from the central portion. By forming the divided electrode 41, the divided electrodes 41 of A and B are electrodes that have electromechanical coupling to out-of-plane vibration but do not have electromechanical coupling to tuning fork vibration. The A and B divided electrodes 41 are electrically insulated from the center frequency adjusting electrode 20 and opened to reduce the series capacity of the equivalent circuit constant of the out-of-plane vibration, and the resonance of the out-of-plane vibration. Only the frequency can be selectively increased. Further, a desired frequency adjustment amount can be obtained by adjusting the capacitances of the frequency adjusting electrode 20 and the divided electrode 41.

  Similarly, in the regions A ′ and B ′ in FIG. 4D, almost no charge is distributed in the charge distribution of out-of-plane vibration. However, in the charge distribution of tuning fork vibration, only positive or negative charge exists. Therefore, by separating the regions A ′ and B ′ of FIG. 4D by laser trimming or the like to form the divided electrodes 41, the divided electrodes 41 of A ′ and B ′ have electromechanical coupling to tuning fork vibration. However, the electrode does not have electromechanical coupling to out-of-plane vibration. By electrically isolating the A 'and B' divided electrodes 41 from the frequency adjusting electrode 20 and opening them, the series capacity of the equivalent circuit constant of the tuning fork vibration is reduced, and only the resonance frequency of the tuning fork vibration is obtained. Can be selectively increased. Further, a desired frequency adjustment amount can be obtained by adjusting the capacitances of the frequency adjusting electrode 20 and the divided electrode 41.

  The amount of frequency change when the frequency adjustment is performed by the above method is obtained by analysis by the finite element method and is shown in FIG. FIG. 5A shows the amount of change in the resonance frequency when the A and B divided electrodes are formed and when the A and B divided electrodes are formed simultaneously. The effects of the divided electrodes A and B are substantially the same, and the resonance frequency of out-of-plane vibration can be increased by about 1200 ppm. Moreover, the effect is doubled by forming A and B simultaneously. Furthermore, the amount of change in the resonance frequency of the tuning fork vibration is 20 ppm or less. Similarly, FIG. 5B shows the amount of change in the resonance frequency when the divided electrodes A ′ and B ′ are respectively formed and when the divided electrodes A ′ and B ′ are formed at the same time. The effects of the divided electrodes A ′ and B ′ are almost the same, and the resonance frequency of the tuning fork vibration can be increased by about 1400 ppm. Also, the effect is doubled by forming A 'and B' simultaneously. Furthermore, the amount of change in the resonance frequency of out-of-plane vibration is 3 ppm or less. The above-described divided electrode is an example of an adjustment method, and the frequency can be changed more greatly by forming the divided electrode limited to a portion where the charge distribution is concentrated.

  That is, according to the present invention, arbitrary trimming can be performed on the frequency adjusting electrode. The resonance frequencies of the tuning fork vibration and the out-of-plane vibration can be adjusted independently, and Δf can be adjusted in both positive and negative directions. Further, there is no substantial change in the drive / detection efficiency of the vibrator before and after adjustment, and the characteristics of the piezoelectric vibration gyro are not deteriorated. Furthermore, since Δf can be adjusted only by cutting out only the electrode with a laser or the like, it is possible to easily perform highly accurate adjustment with less energy than mechanical adjustment. Therefore, according to the present invention, it is possible to provide a method for adjusting a vibrator for a piezoelectric vibration gyro with high productivity and small variation even when the vibrator is greatly reduced in size.

FIG. 1A is a perspective view illustrating a tuning fork vibration mode, and FIG. 1B is a perspective view illustrating an out-of-plane vibration mode. 1 is a perspective view of a tuning fork vibrator according to an embodiment of the present invention. FIG. 3A shows a state of excitation and detection of a vibration mode of a tuning fork vibrator according to an embodiment of the present invention. FIG. 3A is a cross-sectional view related to the tuning fork vibration mode, and FIG. Sectional drawing. FIG. 4A shows a method for adjusting a resonance frequency according to the present invention, FIG. 4A is a schematic diagram of a charge distribution appearing on the surface of the frequency adjusting electrode in tuning fork vibration, and FIG. 4B is a frequency adjusting electrode in out-of-plane vibration. FIG. 4C is a schematic diagram showing a charge distribution appearing on the surface, FIG. 4C is a diagram showing an example of forming a first divided electrode, and FIG. 4D is a diagram showing an example of forming a second divided electrode. FIG. 5A shows a frequency change amount according to the present invention, FIG. 5A is a diagram in the case of A and B divided electrodes, and FIG. 5B is a diagram in the case of A ′ and B ′ divided electrodes. FIG. 6A is a graph showing resonance frequency characteristics with respect to the length of a support substrate, and FIG. 6B is a front view of the vibrator. The perspective view of the vibrator | oscillator of a prior art example.

Explanation of symbols

1 Base 2, 3 Arm 5, 6 Drive electrode 7, 10 Detecting electrode 8, 9 Reference potential electrode 20 Frequency adjusting electrode 41 Split electrode 42 Separation line

Claims (3)

  A base connecting the first and second arms and the arm is integrally formed of a piezoelectric single crystal, and only one main surface of the first and second arms and the base is used for driving and detection. A tuning fork-type vibratory gyroscope comprising a tuning-fork vibrator having an electrode and exciting and detecting one tuning-fork vibration in vibration mode and out-of-plane vibration orthogonal to the tuning-fork vibration; A frequency adjusting electrode is formed in advance on the other opposing main surface, and the tuning fork is formed by dividing a partial region of the frequency adjusting electrode by trimming to form a divided electrode that becomes a floating electrode. A method for adjusting a vibrator for a piezoelectric vibration gyro, wherein a difference in resonance frequency between vibration and the out-of-plane vibration is adjusted.   2. The method for adjusting a vibrator for a piezoelectric vibration gyro according to claim 1, wherein charges generated on the surface of the divided electrode due to the tuning fork vibration are substantially zero, or the sum is substantially zero by canceling out positive and negative charges. And adjusting the position and shape of the divided electrodes so that the charge generated by the out-of-plane vibration and the capacitance between the frequency adjusting electrode and the divided electrode correspond to a desired frequency adjustment amount. And adjusting the resonance frequency of the out-of-plane vibration selectively to adjust the piezoelectric vibration gyro vibrator.   2. The method of adjusting a vibrator for a piezoelectric vibration gyro according to claim 1, wherein the charges generated on the surface of the divided electrode by the out-of-plane vibration are substantially zero, or the sum is substantially zero by canceling the positive and negative charges. And the position and shape of the divided electrode are adjusted so that the electric charge generated by the tuning fork vibration and the capacitance between the frequency adjusting electrode and the divided electrode correspond to a desired frequency adjustment amount. Then, the adjustment method for selectively increasing the resonance frequency of the tuning fork vibration is performed.

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