Voltage type angular speed sensor

Abstract

To provide a voltage type angular speed sensor with which it is possible to form a vibrator using a trigonal ilmenite-containing single crystal piezoelectric material from which a high electromechanical coupling coefficient can be expected, and to achieve both downsizing and a low resonance frequency.SOLUTION: The present invention comprises: (a) a body unit 12 including a hollow cylindrical side wall 14 having an outer peripheral surface 14t and an inner peripheral surface 14s and a bottom plate 16 having a pair of main principal surfaces 16a, 16b parallel to each other and covering one end of the side wall 14 in the direction of a center axis 44; (b) wide wall electrodes 21-28 formed on one or both of the outer peripheral surface 14t and an inner peripheral surface 14s of the side wall 14; and (c) bottom electrodes 30, 32 formed on one or both of the pair of main principal surfaces 16a, 16b of the bottom plate 16. The body unit 12 is formed using a wafer whose crystal orientation is selected so that elastic compliance is substantially constant irrespective of the bearing in the principal plane, so as to resonate in two vibration modes where drive axes 40, 42 and detection axes 41, 43 constitute the antinode or node of vibration.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a piezoelectric angular velocity sensor, and more particularly to a vibration gyroscope having a vibrator formed of a trigonal ilmenite-based single crystal piezoelectric material. [Background technology]

[0002] In recent years, research and development has been actively conducted on autonomous driving systems for vehicles and small aircraft, and inertial navigation systems are being installed, which require high-performance, low-cost angular rate sensors (vibration gyroscopes, hereafter referred to as vibration gyros). The bias stability of vibration gyros used in such applications is required to be 1° / h or less, but this has traditionally only been achieved with expensive optical fiber gyros. Therefore, there is a demand for high-performance vibration gyros using microelectromechanical systems (MEMS) technology while maintaining low cost.

[0003] A MEMS vibratory gyroscope is an inertial sensor that detects angular velocity from the amplitude of vibration excited by the Coriolis force acting on a third axis perpendicular to both axes in proportion to the rotational angular velocity around an axis perpendicular to the vibration direction of a mass vibrating in a certain axial direction. Effective means of improving performance are to improve two characteristics: the electromechanical coupling coefficient, which indicates the efficiency of mechanical-electrical conversion, and the Q value, which indicates the sharpness of the resonance peak.

[0004] Lithium niobate (LiNbO3, hereafter referred to as LN) has attracted attention as a material that has these two excellent characteristics. LN is a trigonal ilmenite-based single crystal piezoelectric material that belongs to the crystallographic point group 3m, and exhibits a high Q value of over 10,000 and a high electromechanical coupling coefficient of 30 to 70%.

[0005] On the other hand, when the shape of the vibrator is made axially symmetrical, such as a disk, annular, or hemispherical shape, it is possible to apply the Force to Rebalance method, which is robust and responsive to leakage vibration among the operating modes of the vibrating gyro, and the all-angle detection method, which is resistant to temperature changes, and high performance is expected.

[0006] However, axisymmetric vibration gyros using LN have had problems due to the anisotropy of the material properties as a single crystal material and the difficulty of processing it as a brittle material.

[0007] A vibrating gyroscope has been proposed that solves this problem by fabricating a vibrator whose dimensions are controlled with high precision by machining through appropriate selection of crystal orientation.

[0008] That is, even if the vibrating body 90 is a trigonal ilmenite-based single crystal piezoelectric material, by appropriately selecting the crystal orientation, the vibrating body 90 can be formed so as to vibrate in two vibration modes with respect to a first axis and a second axis that are parallel to a plane including the circular contour 90a of the vibrating body 90 and perpendicular to each other, as shown in Fig. 11. In the first vibration mode shown in Fig. 11(a), the contour 90a of the vibrating body 90 repeats deformations indicated by solid lines, chain lines, and dashed lines, the first axis and the second axis become vibration antinodes, and the two axial directions that equally divide the first axis and the second axis become vibration nodes. In the second vibration mode shown in Fig. 11(b), the contour 90a of the vibrating body 90 repeats deformations indicated by solid lines, chain lines, and dashed lines, the first axis and the second axis become vibration nodes, and the two axial directions that equally divide the first axis and the second axis become vibration antinodes.

[0009] Fig. 12(a) is a plan view of the vibration gyroscope 111, and Fig. 12(b) is a cross-sectional view thereof. As shown in Fig. 12, the vibration gyroscope 111 has inner electrodes 121-128, 131-138 and outer electrodes 141-148, 151-158 formed on main surfaces 112s, 112t of a piezoelectric substrate 112. An electric field is applied to the piezoelectric substrate 112 using one of the inner and outer electrodes, causing it to vibrate in one of two vibration modes, and the other electrode is used to detect an electric field excited by the vibration in the other vibration mode.

[0010] In a prototype vibration gyroscope 111 in which an easily processable piezoelectric substrate 112 with a diameter of 25.8 mm was fabricated by grinding a 155° Y-cut LN wafer, it has been confirmed that the resonant frequency of the bulk wine-glass vibration mode shown in Figure 11 is approximately 95 kHz and that angular velocity can be detected (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 7223371 Summary of the Invention [Problem to be solved by the invention]

[0012] However, if the piezoelectric substrate 112 of the vibration gyroscope 111 is further miniaturized, a problem arises in that the resonance frequency becomes high.

[0013] In view of the above circumstances, the problem to be solved by the present invention is to provide a piezoelectric angular velocity sensor that can achieve both miniaturization and a low resonance frequency by forming an oscillator using a trigonal ilmenite-based single crystal piezoelectric material. [Means for solving the problem]

[0014] In order to solve the above problems, the present invention provides a piezoelectric angular velocity sensor configured as follows.

[0015] The piezoelectric angular velocity sensor includes (a) a body including a hollow cylindrical sidewall having an outer peripheral surface and an inner peripheral surface, and a bottom plate having a pair of parallel main surfaces covering one end of the sidewall in the central axis direction, (b) a plurality of sidewall electrodes spaced apart from each other on either or both of the outer peripheral surface and the inner peripheral surface of the sidewall, and (c) a bottom plate electrode formed on either or both of the pair of main surfaces of the bottom plate. One of the sidewall electrodes and the bottom plate electrode is a drive electrode for applying an electric field that vibrates the body in the directions of two drive axes parallel to the main surfaces of the bottom plate and perpendicular to each other, and the other is a detection electrode for detecting an electric field excited by the vibration of the body in the directions of two detection axes that equally divide the space between the two drive axes. The body is made of a single crystal piezoelectric material classified into the trigonal point group 3m.

[0016] In a specific embodiment, of the crystal axes X, Y, and Z of the single crystal, the Z axis is the polarization direction, and an X'Y'Z' coordinate system obtained by rotating the crystal XYZ coordinate system based on the crystal axes X, Y, and Z by an angle ψ around the Z axis in accordance with the definition of right-handed Euler angles is an X''Y''Z'' coordinate system obtained by further rotating the X'' axis by an angle θ as the wafer coordinate system of the main body. One of the two drive axes and the two detection axes is parallel to the X'' axis or the Y'' axis, and the other is parallel to one or the other of two straight lines equally dividing the space between the X'' axis and the Y'' axis, and the elastic compliance of the bottom plate of the main body in the main surface direction is approximately constant regardless of the orientation within the main surface.

[0017] In the above configuration, "the elastic compliance of the main surface of the bottom plate of the main body is substantially constant regardless of the orientation in the main surface" means that the difference in the elastic compliance of the main surface of the bottom plate of the main body due to the orientation in the main surface is substantially negligible, that is, even if there is a difference, it is within a range that allows the main body to be manufactured to function as a piezoelectric acceleration sensor. In this case, since the main body is substantially isotropic, the mechanical characteristics are substantially constant in the orientation corresponding to the operation mode, and a vibrator that drives and detects in the wine glass vibration mode can be formed.

[0018] According to the above configuration, an electric field is applied to the main body using the driving electrodes to vibrate the main body in one of the following vibration modes: a first vibration mode (hereinafter referred to as the 0° vibration mode) in which the directions of the two driving axes are the antinodes of the wine-glass vibration mode, and a second vibration mode (hereinafter referred to as the 45° vibration mode) in which the directions of the two detection axes are the nodes of the wine-glass vibration mode; and the angular velocity can be measured by using the detection electrodes to detect the electric field excited by the vibration in the other vibration mode.

[0019] By making the main body made of piezoelectric material cylindrical with side walls and a bottom plate, the outer diameter can be made smaller than that of a conventional disk-shaped vibrator that uses a wine-glass vibration mode due to longitudinal vibration in the in-plane direction, but the wine-glass vibration mode due to bending vibration of the cylindrical surface can be used to lower the resonant frequency compared to a disk-shaped vibrator, making it possible to achieve both compact size and a low resonant frequency.

[0020] Preferably, the sidewall electrodes are the driving electrodes, and the bottom plate electrodes are the detection electrodes and are formed on both of the pair of main surfaces of the bottom plate.

[0021] In this case, the electric field excited over substantially the entire bottom plate can be detected using the bottom electrode, making it easy to increase the detection sensitivity.

[0022] In a specific embodiment, the sidewall electrodes are the driving electrodes. The bottom plate electrodes are the detection electrodes and are formed on both of the pair of main surfaces of the bottom plate. The two detection axes are parallel to the X″ axis or the Y″ axis. The two driving axes are parallel to one or the other of two straight lines equally dividing the X″ axis and the Y″ axis.

[0023] In this case, the electric field excited in substantially the entire bottom plate by the 0° vibration mode can be detected using the bottom electrode, making it easy to increase the detection sensitivity.

[0024] More preferably, the sidewall electrodes are formed at intervals in each of eight regions of the inner surface of the sidewall divided by four planes that pass through the central axis of the sidewall of the main body and are each parallel to one of the drive axis and the detection axis, and AC voltages of opposite polarity are applied to the sidewall electrodes formed in adjacent regions.

[0025] In this case, a circumferential electric field is applied to the side wall of the body, which can be driven in a 45° vibration mode.

[0026] Preferably, the device further comprises a fixing member for supporting a central portion of the bottom plate of the main body, the fixing member having electrodes electrically connected to the driving electrodes and the detection electrodes.

[0027] In this case, the electrodes of the fixed member can be used to measure the angular velocity.

[0028] In a preferred embodiment, the sidewall and the bottom of the body are made of LN.

[0029] In this case, for example, a 155° Y-cut LN wafer can be used to form the main body. Effect of the Invention

[0030] According to the present invention, a piezoelectric angular velocity sensor capable of achieving both miniaturization and a low resonance frequency can be provided by forming an oscillator using a trigonal ilmenite-based single crystal piezoelectric material that is expected to have a high electromechanical coupling coefficient. [Brief description of the drawings]

[0031] [Figure 1] Fig. 1(a) is a schematic cross-sectional view of a piezoelectric angular velocity sensor, and Fig. 1(b) is a schematic plan view of the same. (Example 1) [Diagram 2] FIG. 2 is a photograph of a piezoelectric angular velocity sensor (Example 1). [Diagram 3] FIG. 3 is a vibration analysis diagram of a piezoelectric angular velocity sensor (Example 1). [Figure 4] FIG. 4 is a schematic diagram showing the electrode arrangement. (Example 1) [Diagram 5] FIG. 5 is an equivalent circuit diagram approximating the impedance characteristics (Example 1). [Figure 6] FIG. 6 is a photograph of the measurement setup for angular velocity output. (Example 1) [Figure 7] FIG. 7 is a circuit diagram showing an outline of the control (Example 1). [Figure 8] FIG. 8 is a graph showing the results of impedance measurement. (Example 1) [Figure 9]FIG. 9 is a graph showing angular velocity output (Example 1). [Figure 10] FIG. 10 is a graph showing Allan variance. (Example 1) [Figure 11] FIG. 11 is an explanatory diagram of vibration modes. (Conventional Example 1) [Figure 12] FIG. 12 is an explanatory diagram of a vibration gyroscope (conventional example 1). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0033] Example 1 A piezoelectric angular velocity sensor 10 according to Example 1 will be described with reference to FIGS.

[0034] Fig. 1(a) is a schematic cross-sectional view showing the basic configuration of a piezoelectric angular velocity sensor 10, and Fig. 1(b) is a schematic plan view thereof. As shown in Fig. 1, the piezoelectric angular velocity sensor 10 has a body 12 including a side wall 14 and a bottom plate 16, on which side wall electrodes 21-28, bottom plate electrodes 30, 32, and a common electrode 18 are formed.

[0035] The side wall 14 is hollow cylindrical and has an outer peripheral surface 14t and an inner peripheral surface 14s. The side wall 14 is basically symmetrical about the central axis 44, and the radial thickness is constant regardless of the circumferential position. However, depending on the need for improving characteristics, it is also possible to increase or decrease the thickness of an appropriate portion of the side wall 14, to form a through hole penetrating between the outer peripheral surface 14t and the inner peripheral surface 14s, or to form a curved upper end surface 14a.

[0036] The bottom plate 16 covers one end of the side wall 14 in the direction of the central axis 44, has a pair of main surfaces 16a, 16b perpendicular to the central axis 44 of the side wall 14 and parallel to each other, and closes the hollow hole 15 in the side wall 14. Although not shown, depending on the needs of improving characteristics, it is possible to increase or decrease the thickness of an appropriate portion of the bottom plate 16, or to form a through hole that passes between the main surfaces 16a, 16b and communicates with the hollow hole 15 in the side wall 14.

[0037] The main body 12 is formed to vibrate in two vibration modes, namely, a wine glass vibration mode. The first vibration mode is a 0° vibration mode, in which the directions of the two drive shafts 40, 42, which are parallel to the main surfaces 16a, 16b of the bottom plate 16 and perpendicular to each other, are vibration antinodes, and the directions of the two detection axes 41, 43, which equally divide the space between the two drive shafts 40, 42, are vibration nodes. The second vibration mode is a 45° vibration mode, in which the directions of the two drive shafts 40, 42 are vibration nodes, and the directions of the two detection axes 41, 43 are vibration antinodes.

[0038] The body 12 has side walls 14 and bottom plate 16 integrally formed using an optimally oriented wafer that is nearly isotropic and has mechanical properties that are substantially constant in the orientation corresponding to the operating mode so that the resonant frequencies of the 0° vibration mode and the 45° vibration mode are approximately equal.

[0039] The optimally oriented wafer for forming the main body 12 is made of a single crystal piezoelectric material classified into the trigonal point group 3m, and of the crystal axes X, Y, and Z of the single crystal, the Z axis is the polarization direction. If the crystal XYZ coordinate system based on the crystal axes X, Y, and Z is rotated by an angle ψ around the Z axis to form an X'Y'Z' coordinate system, and then further rotated by an angle θ around the X' axis to form an X''Y''Z'' coordinate system, the wafer coordinate system of the piezoelectric substrate, then the elastic compliance in the main surface direction of the wafer, i.e., the main surface direction parallel to the plane including the X'' axis and the Y'' axis, is approximately constant regardless of the orientation within the main surface.

[0040] "The elastic compliance in the main surface direction of the wafer is substantially constant regardless of the orientation in the main surface" means that the elastic compliance in the main surface direction of the wafer is constant to the extent that the difference due to the orientation in the main surface can be substantially ignored. In other words, even if there is a difference, the difference is within a range that allows the main body to be fabricated to function as a piezoelectric acceleration sensor. For example, as described in Patent Document 1, this refers to the case where the coefficient of variation CV(ψ, θ) is less than 1%.

[0041] The optimal orientation wafer for forming the main body 12 is, for example, a wafer made of LN single crystal with -4°<ψ<4° and 63°<θ<67°, and for example, a Y-cut LN wafer with a cut angle of 155° or more and 156° or less is used. Instead of the LN wafer, for example, a wafer of lithium tantalate (LT), langasite, or the like may be used.

[0042] For example, the main surface of the optimally oriented wafer is used as the lower surface 16b of the bottom plate 16 and the upper end surface 14a of the side wall 14 of the main body 12, and one main surface of the optimally oriented wafer is processed to form the inner peripheral surface 14s and the outer peripheral surface 14t of the side wall 14 of the main body 12 and the upper surface 16a of the bottom plate 16. The two drive shafts 40, 42 are parallel to the X''-axis or Y''-axis of the optimally oriented wafer.

[0043] The sidewall electrodes 21-28 are formed only on the inner circumferential surface 14s of the sidewall 14. For example, the sidewall electrodes 21-28 are formed at intervals from each other in each region of the inner circumferential surface 14s of the sidewall 14 divided by a plane that is parallel to one of the two driving shafts 40, 42 and the two detection shafts 41, 43 and passes through the central axis 44. The sidewall electrodes 21-28 are formed to be aligned in the circumferential direction of the sidewall 14 at intervals from each other.

[0044] The common electrode 18 is formed continuously over the entire periphery on the outer circumferential surface 14t of the side wall 14. The common electrode 18 is usually a floating electrode.

[0045] Although not shown, the sidewall electrodes 21-28 can be formed only on the outer peripheral surface 14t of the sidewall 14, and in this case, the common electrode 18 can be formed on the inner peripheral surface 14s of the sidewall 14. Alternatively, it can be formed on both the outer peripheral surface 14t and the inner peripheral surface 14s of the sidewall 14.

[0046] The bottom plate electrodes 30, 32 are formed on each of the pair of main surfaces 16a, 16b of the bottom plate 16. Although not shown, the bottom plate electrodes 30, 32 may be formed on only one of the pair of main surfaces 16a, 16b of the bottom plate 16. A plurality of bottom plate electrodes 30 and / or 32 may be formed apart from each other.

[0047] One of the side wall electrodes 21-28 and the bottom plate electrodes 30, 32 is a drive electrode for applying an electric field so as to vibrate in one of the two vibration modes, and the other is a detection electrode for detecting the electric field excited by the other vibration mode.

[0048] When bottom plate electrodes 30, 32 are used as detection electrodes, forming bottom plate electrodes 30, 32 on each of a pair of main surfaces 16a, 16b of bottom plate 16 makes it possible to detect a larger potential difference than when bottom plate electrodes 30 or 32 are formed on only one of the pair of main surfaces 16a, 16b of bottom plate 16, thereby improving the detection sensitivity of angular velocity.

[0049] Although not shown in FIG. 1, wiring connected to sidewall electrodes 21 to 28 and / or bottom plate electrodes 30, 32 and floating electrodes may be formed at appropriate locations on main body 12.

[0050] The piezoelectric angular velocity sensor 10 supports a portion that does not move even when the main body 12 vibrates, for example, the central portion 11 of the lower surface 16b of the bottom plate 16 of the main body 12. Alternatively, it is also possible to support the central portion of the upper surface 16a of the bottom plate 16 of the main body 12.

[0051] Piezoelectric angular velocity sensor 10 may use the 0° vibration mode as a drive mode and the 45° vibration mode as a detection mode, or may use the 45° vibration mode as a drive mode and the 0° vibration mode as a detection mode. Also, sidewall electrodes 21-28 may be used as drive electrodes and bottom plate electrodes 30, 32 may be used as detection electrodes, or sidewall electrodes 21-28 may be used as detection electrodes and bottom plate electrodes 30, 32 may be used as drive electrodes.

[0052] For example, the sidewall electrodes 21-28 are used as driving electrodes, and an AC voltage is applied to vibrate them in a 45° vibration mode. At this time, voltages of opposite polarity are applied to adjacent sidewall electrodes 21-28. The bottom plate electrodes 30 and 32 are used as detection electrodes, and the angular velocity is measured by detecting the electric field excited in the 0° vibration mode of the main body 12.

[0053] When the 0° vibration mode is detected and bottom plate electrodes 30, 32 are used as detection electrodes, it is possible to improve detection sensitivity by forming only one bottom plate electrode 30, 32 on each of main surfaces 16a, 16b of bottom plate 16. In other words, there is no need to form multiple bottom plate electrodes 30, 32 lined up in the circumferential direction, as in the case where the 45° vibration mode is detected by bottom plate electrodes 30, 32.

[0054] The piezoelectric angular velocity sensor 10 has a cylindrical body 12 with a side wall 14 added to a bottom plate 16, so that the resonant frequency can be reduced even if the sensor is made compact.

[0055] Next, the prototype piezoelectric angular velocity sensor 10 will be described with reference to FIGS.

[0056] Figure 2 is a photograph of the prototype piezoelectric angular velocity sensor 10. As shown in Figure 2, the piezoelectric angular velocity sensor 10 has a side wall 14 with an outer diameter of 9.5 mm, an inner diameter of 8.5 mm, a radial thickness of 0.5 mm, a body 12 with a height of 3 mm, and a bottom plate 16 with a thickness of 0.5 mm.

[0057] FIG. 3 is a vibration analysis diagram of the piezoelectric angular velocity sensor 10. As shown in FIG. 3, a first axis and a second axis that are mutually orthogonal are taken within the plane of a 155° Y-cut LN wafer, and the polarization axis is orthogonal to the first axis. FIG. 3(a) shows the 0° vibration mode in which the first axis and the second axis directions are antinodes. FIG. 3(b) shows the 45° vibration mode in which the first axis and the second axis directions are nodes. The 45° vibration mode was driven, and the 0° vibration mode was detected.

[0058] FIG. 4 is a schematic diagram showing the electrode arrangement. As shown in FIG. 4, in consideration of efficiently detecting vibrations in each mode, the 45° vibration mode drives eight sidewall electrodes 20 formed in each of eight regions dividing the inner surface of the sidewall 14 by applying a voltage between adjacent electrodes, and measures the displacement from the current and performs feedback control. At this time, voltages of opposite polarity are applied to adjacent sidewall electrodes 20. In the 0° vibration mode, the displacement is detected from the current flowing between the bottom plate electrodes 30, 32 on both main surfaces 16a, 16b of the bottom plate 16. The electrodes 29, 34 formed on the outer peripheral surface 14t of the sidewall 14 and the lower surface 16b of the bottom plate 16 are floating electrodes and are not used for driving or detection.

[0059] The main body 12 was fabricated by ultrasonic core drilling and ultrasonic milling. First, a gold thin film is deposited on both sides of a 3 mm thick 155° Y-cut LN wafer using a chromium thin film as an adhesive layer, and alignment marks and electrodes 32, 34 on the lower surface 16b of the bottom plate 16 are formed. Then, the wafer is cut into a square shape by dicing, and roughly ground into a cylindrical shape by single core processing and milling. Next, the inner peripheral surface 14s and the outer peripheral surface 14t of the side wall 14 are finished by ultrasonic double core processing, and the upper surface 16a of the bottom plate 16 is finished by ultrasonic milling. Then, chromium and gold are deposited on the upper surface 16a of the bottom plate 16 and the inner peripheral surface 14s and the outer peripheral surface 14t of the side wall 14, and an electrochemical resist is applied. Oblique exposure from three directions is used to pattern electrodes on the inner peripheral surface 14s and the outer peripheral surface 14t of the side wall 14 and the upper surface 16a of the bottom plate 16, and gold and chromium are wet etched to form the electrodes 20, 29, 30, and 34. Finally, the resist is removed, and the cylindrical main body 12 is cut off from the square frame by grinding from the back side.

[0060] (Mounting method) The manufactured vibrator is fixed at the center of the lower surface 16b of the bottom plate 16 of the main body 12 to the tip of a cylinder with a diameter of 0.3 mm and a height of 50 μm, which is placed at the center of a SUS plate (not shown), using silver paste, which is a conductive adhesive. A gold thin film is deposited on the surface of the SUS plate, and through this thin film, an electrode 32 for detecting the 0° vibration mode on the lower surface 16a of the bottom plate 16 of the vibrator is electrically connected to an electrode of a donut-shaped relay board prepared on the SUS plate so as to surround the vibrator. The other electrodes 20 and 30 on the upper surface side of the vibrator are electrically connected by wire bonding from the center of the upper surface 16a of the bottom plate 16 to each electrode of the relay board (not shown). The SUS plate is bonded onto a vibrator package (not shown), and each electrode on the relay board and the electrode of the vibrator package are connected by a nichrome wire, so that it can be mounted on a printed circuit board. The SUS plate is a fixing member that supports the center portion 11 of the bottom plate 16 of the main body 12.

[0061] (Frequency characteristics) Figure 5 shows an equivalent circuit that approximates the impedance characteristics near the resonance point of the vibrator. An impedance analyzer (4294A, Keysight) was used for the measurements. The amplitude of the AC voltage applied during measurements in both vibration modes was 500 mV. From the measured impedance spectrum, the values ​​of each element of the equivalent circuit were calculated by fitting, and the electromechanical coupling coefficient k and Q value for each vibration mode were calculated using the following equations (1) and (2).

number

[0062] (Angular velocity output) Figure 6 is a photograph of the measurement setup for the angular velocity output. As shown in Figure 6, the transducer package was soldered to a printed circuit board (PCB) and fixed to a rate table (RT-02-120-S11U, COSMATE) via an aluminum jig. Two sets of inverting amplifier circuits for driving (amplification factor of 1) and inverting amplifier circuits for detection (amplification factor of approximately 4.5) were placed on the PCB for each vibration mode and connected to the respective electrodes. These input / output signals and the power supply for the operational amplifier are connected to a digital lock-in amplifier and a constant-voltage power supply, respectively, via slip rings. The lock-in amplifier and rate table are controlled by a PC, and data is recorded.

[0063] The control system for the vibration gyro was constructed by synchronizing two digital lock-in amplifiers (MF-LI, Zurich Instruments). Figure 7 is a circuit diagram showing an overview of the control. As shown in Figure 7, the driving side applies an AC voltage to drive the 45° vibration mode, and the displacement signal is input to the lock-in amplifier, where oscillation is performed by a phase locked loop (PLL) and constant amplitude control is performed by automatic gain control (AGC). The PLL controls so that the phase difference Φ0 between the displacement signal and the driving signal is constant, and the AGC controls so that the amplitude of the displacement signal is constant. The detection side synchronously detected the displacement signal in the 0° vibration mode using the driving signal from the driving side as a reference signal. The displacement signal contains a component proportional to the angular velocity excited by the Coriolis force and a leakage vibration component with a phase shift of 90°, and the phase difference Φ between the displacement signal and the reference signal is constant. 45 was adjusted so that the angular velocity signal excited by the Coriolis force could be output at its maximum. Specifically, the output signal was observed by synchronous detection while applying a constant amplitude angular velocity modulated by a sine wave of 0.1 Hz to the sensor, and the phase difference Φ 45 We searched for a phase difference and conducted an experiment to measure the angular rate output.

[0064] The experimental results are as follows:

[0065] (Frequency characteristics) Fig. 8 is a graph showing the impedance measurement results for each vibration mode. The equivalent circuit element values, resonant frequency, electromechanical coupling coefficient, and Q value for each vibration mode obtained from the measurement results in Fig. 8 are shown in Table 1 below. [Table 1] As can be seen from Table 1, the resonant frequency is reduced to approximately 35 kHz. Compared with a conventional disk-shaped vibrator (diameter 25.8 mm, resonant frequency approximately 95 kHz), the prototype cylindrical vibrator has a diameter that is approximately 40% smaller, while lowering the resonant frequency to approximately 1 / 3.

[0066] (Angular velocity output) Figure 9 is a graph showing the angular velocity output when an angular velocity of 120° / sec is applied alternately in the clockwise and counterclockwise directions. As shown in Figure 9, the output according to the applied angular velocity was confirmed, and it was confirmed that the prototype vibrator functions as an angular velocity sensor. The sensitivity was 0.57μV / ° / sec.

[0067] After that, the angular velocity output was measured for 600 seconds in a stationary state with a sampling interval of 0.6 msec, and the Allan variance was calculated. Figure 10 is a graph showing the Allan variance. As shown in Figure 10, the bias stability was 0.51° / sec=1.8×10 3 To improve the bias stability, it is necessary not only to improve the Q value and coupling coefficient, but also to optimize the PID parameters of the feedback control and to consider output methods such as the Force to Rebalance method and the full angle detection method.

[0068] <Summary> As described above, the piezoelectric angular velocity sensor 10 is capable of achieving both compact size and a low resonant frequency by forming the cylindrical body 12 using an optimally oriented wafer of trigonal ilmenite-based single crystal piezoelectric material, which is expected to have a high electromechanical coupling coefficient.

[0069] The present invention is not limited to the above-described embodiment, but can be implemented with various modifications.

[0070] For example, the inner and outer diameters of sidewall 14, the thicknesses of sidewall 14 and bottom plate 16, the dimensions, shapes, numbers, arrangements, wiring, etc. of sidewall electrodes 21-28, common electrode 18, and bottom plate electrodes 30, 32 can be appropriately selected. [Explanation of symbols]

[0071] 10 Piezoelectric angular rate sensor 12 Main unit (transducer) 14 Side wall 14s Inner surface 14t outer surface 16 Bottom plate 16a Main surface (top surface) 16b Main surface (bottom surface) 20, 21 to 28 Side wall electrodes (driving electrodes or detection electrodes) 30, 32 Bottom plate electrode (detection electrode or driving electrode) 40 Drive shaft 41 Detection axis 42 Drive shaft 43 Detection axis 44 Center axis

Claims

1. a main body including a hollow cylindrical side wall having an outer peripheral surface and an inner peripheral surface, and a bottom plate having a pair of main surfaces parallel to each other and covering one end of the side wall in a central axis direction; a plurality of sidewall electrodes formed at intervals on either or both of the outer circumferential surface and the inner circumferential surface of the sidewall; a bottom plate electrode formed on one or both of the pair of main surfaces of the bottom plate; Equipped with one of the side wall electrode and the bottom plate electrode is a drive electrode for applying an electric field that vibrates the body in the directions of two drive axes that are parallel to the main surface of the bottom plate and perpendicular to each other, and the other is a detection electrode for detecting an electric field excited by the vibration of the body in the directions of two detection axes that equally divide the space between the two drive axes; The main body is a piezoelectric angular velocity sensor made of a single crystal piezoelectric material classified into the trigonal crystal point group 3m.

2. Among the crystal axes X, Y, and Z of the single crystal, the Z axis is the polarization direction, The crystal XYZ coordinate system based on the crystal axes X, Y, and Z is rotated around the Z axis by an angle ψ according to the definition of right-handed Euler angles, and the X'Y'Z' coordinate system is further rotated around the X' axis by an angle θ to obtain the X''Y''Z'' coordinate system, which is the wafer coordinate system of the main body. one of the two drive axes and the two detection axes is parallel to the X″ axis or the Y″ axis, and the other is parallel to one or the other of two straight lines equally dividing the X″ axis and the Y″ axis; 2. The piezoelectric angular velocity sensor according to claim 1, wherein the elastic compliance of the bottom plate of the main body in the direction of the main surface is substantially constant regardless of the direction in the main surface.

3. the side wall electrode is the driving electrode, 2. The piezoelectric angular velocity sensor according to claim 1, wherein the bottom plate electrodes are the detection electrodes and are formed on both of the pair of main surfaces of the bottom plate.

4. the side wall electrode is the driving electrode, the bottom plate electrodes are the detection electrodes and are formed on both of the pair of main surfaces of the bottom plate, the two detection axes being parallel to the X″ axis or the Y″ axis, 3. The piezoelectric angular velocity sensor according to claim 2, wherein the two drive axes are parallel to one or the other of two straight lines equally dividing the X'' axis and the Y'' axis.

5. the side wall electrodes are formed at intervals from one another in eight regions of the inner circumferential surface of the side wall divided by four planes that pass through a central axis of the side wall of the main body and are parallel to one of the drive axis and the detection axis, 4. The piezoelectric angular velocity sensor according to claim 3, wherein AC voltages of opposite polarities are applied to the sidewall electrodes formed in the adjacent regions.

6. A fixing member for supporting a central portion of the bottom plate of the main body is further provided, 6. The piezoelectric angular velocity sensor according to claim 1, wherein the fixing member has electrodes electrically connected to the driving electrodes and the detecting electrodes.

7. 7. The piezoelectric angular velocity sensor according to claim 6, wherein the sidewalls and the bottom of the body are made of lithium niobate.

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