JP3732582B2 - Angular velocity detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an angular velocity detection device used for automobile navigation systems, attitude control, and the like, and more particularly to a vibration type angular velocity detection device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there is known a vibration type angular velocity detection device that utilizes the fact that when a vibration body is rotated, a new vibration corresponding to the rotation angular velocity is generated by the Coriolis force. In this type of angular velocity detection device, for example, a vibration angular velocity meter described in Japanese Patent Application Laid-Open No. 60-192206 detects vibration due to Coriolis force and detects excitation vibration in order to stabilize the excitation vibration. Also do.
[0003]
[Problems to be solved by the invention]
However, in the vibration type angular velocity meter described in Japanese Patent Application Laid-Open No. 60-192206, an element provided in the vibrator for detecting the excitation vibration and a vibration for detecting the Coriolis force for detecting the angular velocity are used. Since the element provided in the child is a separate body, there are the following problems. In other words, since stress due to vibration is concentrated at the root of the resonator element, it is detected that both an element for detecting excitation vibration and an element for detecting vibration due to Coriolis force are installed at the root of the resonator element. Although it is desirable in terms of efficiency, if both elements are provided at the base of the resonator element, the area given to each element becomes small, and eventually the detection efficiency cannot be increased.
[0004]
[Means for Solving the Problems]
The angular velocity detection device of the present invention has been made for such a problem. The vibrator, the excitation means for exciting the vibrator, the detection means for detecting the vibration of the vibrator, and the detection means In the angular velocity detecting device including an angular velocity calculating means for calculating a rotational angular velocity of the vibrator based on the detected vibration information, the vibrator is a tuning fork type vibrator having a pair of vibrating pieces. Each vibrating piece has an excitation electrode and a detection electrode arranged on the same cross section and on the same opposing surface , and the detecting means is connected to the detection electrode of each vibrating piece and the detection electrode of each vibrating piece. The detection electrode of each vibration piece generates a change in charge according to a change in internal stress applied to the vibration piece accompanying the vibration of the vibration piece. By synthesizing the change in the charge of the detection electrode A plurality of methods for synthesizing the change in charge generated at the detection electrode of each resonator element, which is to be converted into a desired electrical signal, so that an excitation vibration by the excitation means and a vibrator during this excitation vibration It detects the vibration based on the Coriolis force generated with the rotation of the.
[0005]
According to the present invention, since the detection of the excitation vibration and the detection of the vibration due to the Coriolis force are performed by the same vibration detection element, compared to the case where both detections are detected by separate elements, the basis of the vibration piece is limited. A sufficient area can be ensured also when arranging in the region.
[0006]
The excitation means includes an excitation electrode of each vibration piece and an excitation drive circuit connected to the excitation electrode of each vibration piece, and at least the excitation electrode on the same plane facing each other on the same cross section in each vibration piece; It is desirable that a constant potential electrode be disposed between the detection electrode. If comprised in this way, the crosstalk between the electrode for excitation and the electrode for vibration can be prevented.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a perspective view showing a vibrator used in an angular velocity detection device according to an embodiment of the present invention. FIG. 1 (a) is a view of the vibrator 1 as viewed obliquely from above, and FIG. Is rotated 90 degrees about the horizontal axis 50 from the position shown in FIG. 5A so that the back surface of the vibrator 1 can be seen. In this figure, the left-right direction is the Y axis, the left direction is the positive direction, and the orthogonal axes perpendicular to the Y axis are the X axis and the Z axis, respectively, as shown. The vibrator 1 is cut out in a tuning fork shape by a photolithography technique and an etching technique from a quartz single crystal substrate having a plane perpendicular to the Z-axis.
[0008]
Natural quartz is generally a columnar crystal, and the longitudinal central axis of the columnar crystal, that is, the <0001> crystal axis is defined as the Z axis or the optical axis, and is a line passing through the Z axis and perpendicular to each surface of the columnar crystal. Is defined as the Y axis or the machine axis. A line passing through the Z axis and orthogonal to the vertical ridge line of the columnar crystal is defined as an X axis or an electric axis.
[0009]
The single crystal substrate used in the vibrator 1 is a substrate called a Z plate, which is a single crystal substrate cut out on a plane perpendicular or substantially perpendicular to the Z axis of the crystal crystal orientation. Therefore, the Z axis of the crystal orientation coincides with the above-described Z axis indicating the arrangement direction of the vibrator 1 on the drawing. In addition, there are three sets of crystal X-axis and Y-axis that are orthogonal to each other, and one set thereof coincides with the X-axis and Y-axis indicating the arrangement direction of the vibrator 1 on the drawing. The quartz used for the vibrator 1 is an artificial quartz, but its structure is the same as that of natural quartz.
[0010]
The vibrator 1 includes a vibrator base body 2 and two vibrating pieces 3 and 4 that protrude in parallel to each other in the + Y direction. The vibration pieces 3 and 4 are provided with excitation electrodes that are excitation drive elements and detection electrodes that are vibration detection elements. The electrodes 31, 32, 41, 42 on the side surfaces of the resonator elements 3 and 4, the electrodes 35, 43 on the top surface, and the electrodes 38, 46 on the back surface are excitation electrodes, respectively, and the electrodes 33, 45 on the top surface and the electrodes 36 on the back surface, Reference numerals 48 denote detection electrodes. The top electrodes 34 and 44 and the back electrodes 37 and 47 are ground electrodes (constant potential electrodes) for preventing crosstalk between the excitation electrode and the detection electrode. The excitation electrodes 32 and 42 are provided on the opposite side surfaces of the excitation electrodes 31 and 41, respectively, and are not visible in FIG. 1. However, FIG. is there. The excitation electrodes 31 and 32 are electrically connected by a strip electrode 39 at the tip of the vibrating piece 3, and the excitation electrodes 41 and 42 are electrically connected by a strip electrode 49 at the tip of the vibrating piece 4. Each electrode has a two-layer structure of chromium and gold, and is obtained by vapor-depositing these metals on the surface of the vibrator 1 and then separating them appropriately using a photolithography technique and patterning them into a desired shape. .
Bonding pads 11 to 22 are provided on the top surface of the vibrator substrate 2, and bonding pads 23 to 28 are provided on the back surface. The connection between the bonding pads 11 to 28 and each of the electrodes described above is as shown in the figure. The bonding pads 11, 12, 13, 17, 18, 19, 23, and 26 are for excitation, and the bonding pads 15, 16, and 21 are used for excitation. , 22, 25, and 28 are for detection, and the bonding pads 14, 20, 24, and 27 are for grounding.
[0011]
FIG. 2 is a block diagram showing the processing circuit of the angular velocity detection device of this embodiment and the connection between these and each electrode provided in the vibrator 1. FIG. 3 is a perspective view showing how the vibrator 1 vibrates, and FIGS. 4 and 5 are diagrams for explaining the inverse piezoelectric effect and the piezoelectric effect in excitation and vibration detection, respectively.
[0012]
The drive circuit 131 outputs a pulse wave having a predetermined repetition frequency with an amplitude corresponding to an output voltage value of an automatic gain control circuit (AGC circuit) 133 described later as an excitation drive signal from the terminals 310 and 310 ′. Electrodes 31 and 32 on the side surface of the resonator element 3 and electrodes 43 and 46 on the upper and lower surfaces of the resonator element 4 are connected to the terminal 310, and electrodes 35 and 38 on the upper and lower surfaces of the resonator element 3 are connected to the terminal 310 ′. The electrodes 41 and 42 on the side surface of the resonator element 4 are connected.
[0013]
Under such a connection, when a drive signal having a frequency that matches or is close to the natural frequency of the resonator elements 3 and 4 is output from the drive circuit 131, a vibration mode as shown in FIG. Thus, the vibrating bars 3 and 4 vibrate. That is, the vibrating bars 3 and 4 are excited in opposite phases in the X-axis direction.
[0014]
FIG. 4 illustrates the action of the inverse piezoelectric effect for exciting the resonator element in the X-axis direction. Here, the vibration piece 3 will be described as an example. FIG. 4A is a cross-sectional view of the vibrating piece 3 cut along the ZX plane, and FIG. 4B is a perspective view showing a bending operation of the vibrating piece 3. As described above, since the electrodes 31 and 32 are commonly connected to the terminal 310 and the electrodes 35 and 38 are commonly connected to the terminal 310 ′, the output signal of the terminal 310 is low level and the output signal of the terminal 310 ′. 4 is a high level, a voltage as shown in FIG. 4A, that is, a relatively negative voltage is applied to the electrodes 31 and 32, and a positive voltage is applied to the electrodes 35 and 38, respectively. This voltage is given by a drive signal, and polarity inversion is repeated at a predetermined frequency.
[0015]
Considering a state in which a voltage as shown in FIG. 4A is applied, an electric field as indicated by arrows 91 to 94 is applied to the inside of the resonator element 3. On the other hand, since the piezoelectric effect of quartz does not appear in the Z-axis direction, effective electric fields that affect the piezoelectric effect are arrows 95 and 96. Due to the inverse piezoelectric effect, quartz crystals expand in the Y-axis direction when an electric field is applied in the positive direction of the X axis, and contract in the Y-axis direction when an electric field is applied in the negative direction of the X axis. Therefore, in the state of FIG. 4A, the electrode 32 side of the vibrating piece 3 is contracted and the electrode 31 side is extended, so that the vibrating piece 3 is bent with the electrode 32 inside. When the polarity of the voltage applied to the electrodes 31, 32, 35, and 38 is reversed, the resonator element 3 bends with the electrode 31 inward according to the same principle. Therefore, when one end of the resonator element 3 is fixed and a drive signal having a predetermined frequency is applied from the drive circuit 131 to the electrodes 31, 32, 35, and 38, the resonator element 3 vibrates in the X direction as shown in FIG. To do.
[0016]
In the present embodiment, as already described, the side electrode of the vibrating piece 3 and the upper and lower electrodes of the vibrating piece 4 are common with respect to the excitation electrode, and the upper and lower electrodes of the vibrating piece 3 and the side electrode of the vibrating piece 4 are common. Therefore, the resonator elements 3 and 4 vibrate in the opposite directions in the X direction as shown in FIG.
[0017]
The detection circuit 132 synthesizes a change in electric charge generated in the detection electrode due to the piezoelectric effect of the quartz crystal in an appropriate combination and converts it into a desired electric signal. Changes in electric charges generated in the detection electrodes 33, 36, 45, and 48, that is, currents are input to the current detectors 324, 323, 322, and 321 and converted into voltage values. The signal synthesis is performed on the output side of the current detector, and the synthesis for generating a signal indicating the vibration in the X-axis direction by the adders 331 and 332 and the operational amplifier 325 and the Z by the adders 333 and 334 and the operational amplifier 326 are performed. There are two types of synthesis to create a signal indicating axial vibration. The signal obtained by the former synthesis is a feedback signal for stabilizing the excitation by the drive circuit 131, and the latter is an output signal for detecting the rotational angular velocity.
[0018]
Here, the piezoelectric effect accompanying the vibration in the Z-axis direction will be described with reference to FIG. As shown in FIG. 3B, when the vibrator 1 is excited in the X-axis direction in opposite phases as shown in FIG. 3A, and the vibrator 1 rotates at an angular velocity Ω around the Y-axis in this state, In addition, a Coriolis force F represented by F = 2 mV · Ω is generated in the Z direction on the resonator elements 3 and 4 of the vibrator 1. Here, m is the mass of the resonator element, and V is the vibration speed. Due to the generation of the Coriolis force F, the vibrating bars 3 and 4 are 90 degrees out of phase with respect to the vibration in the X direction and vibrate in the left and right phases in the Z direction.
[0019]
FIG. 5B is a perspective view showing a state of vibration of the vibrating piece 3 in the Z-axis direction. When the vibrating piece 3 bends in the + Z direction, the upper half of the vibrating piece 3 contracts in the Y direction and the lower half extends in the Y direction. Due to the piezoelectric effect of quartz, dielectric polarization in the X direction occurs when contracted in the Y direction, and dielectric polarization in the opposite X direction occurs when extended in the Y direction. The strength of dielectric polarization depends on the size of expansion and contraction, so that it appears strongly on the upper surface or the lower surface, and becomes weaker toward the middle portion. Accordingly, the dielectric polarization appears concentrated on the four corners of the resonator element 3, and positive or negative charges as shown in FIG. When the vibrating piece 3 swings downward, a polarity completely opposite to that described above appears based on the same principle. Since the vibration piece 4 vibrates in a phase opposite to that of the vibration piece 3, the detection electrodes 33 and 45 on the upper side of the vibration pieces 3 and 4 have opposite polarities, and the detection electrodes 36 and 48 on the back side have opposite polarities. .
[0020]
The detection circuit 132 adds the same polarity of the amount of change in the charges in the detection electrodes of the vibration pieces 3 and 4 generated in this way with the adders 333 and 334, and takes the difference with the operational amplifier 326. A signal corresponding to the vibration amplitude in the Z-axis direction of the resonator elements 3 and 4 is output from the terminal 312.
[0021]
On the other hand, due to the dielectric polarization generated by the excitation vibration in the X direction, a change in charge having the same polarity appears on the upper and lower detection electrodes, and the polarity of the charge becomes either positive or negative depending on the bending direction. In the detection circuit 132, the amount of change in the electric charge is added by the adders 331 and 332 and the same polarity is added, and a difference is obtained by the operational amplifier 325, whereby a signal corresponding to the vibration amplitude in the X-axis direction of the resonator elements 3 and 4 is obtained. Is output from the terminal 311.
[0022]
The AGC circuit 133 inputs a feedback signal from the terminal 311 and outputs a control signal to the drive circuit 131 so that the value becomes a target value. The feedback signal output from the terminal 311 indicates a value corresponding to the vibration amplitude of the vibration pieces 3 and 4, that is, the vibration speed v, and the excitation amplitude becomes smaller if this value becomes larger than a preset target value. On the other hand, the drive circuit 131 is controlled so that the excitation amplitude increases as it decreases.
[0023]
The offset correction circuit 134 is a circuit that corrects an offset component when the rotational angular velocity Ω is zero with respect to the signal output from the output terminal 312 of the detection circuit 132, and the correction is a feedback signal extracted from the AGC circuit 133. It is done based on the change of. As a result, the offset output when the rotational angular velocity Ω is zero is stabilized to eliminate the factor that degrades the sensor performance such as temperature drift, and the angular velocity detecting device with high detection accuracy is obtained.
[0024]
The synchronous detection circuit 135 synchronously detects the offset-corrected detection output signal using the signal that is 90 degrees out of phase by the phase shifter 136 as a reference signal, and converts the detection signal into a DC signal. Circuit. The output signal of the synchronous detection circuit 135 is given to an angular velocity calculation circuit (not shown). The angular velocity calculation circuit is centered on an axis parallel to the Y axis of the vibrator 1 based on the above-described formula of F = 2 mV · Ω. A rotational angular velocity is calculated.
[0025]
Next, the overall operation of the angular velocity detection device configured as described above will be described. When the resonator elements 3 and 4 are excited in the X-axis direction as shown in FIG. 3A by the drive circuit 131 and the vibrator 1 rotates at an angular velocity Ω around an axis parallel to the Y-axis, the amplitude is proportional to the angular velocity Ω. The vibration in the Z-axis direction is generated as shown in FIG. This vibration amplitude appears as a change in charge on the detection electrodes 34, 36, 45, and 48, is detected by the detection circuit 132, is offset corrected by the offset correction circuit 134, is converted into a DC signal by the synchronous detection circuit 135, and is subjected to angular velocity calculation. The circuit calculates Ω. On the other hand, during this operation, a change in charge corresponding to the excitation amplitude also appears on the detection electrodes 34, 36, 45, and 48, similarly to a change in charge corresponding to vibration in the Z-axis direction. This is processed by the detection circuit 132 and fed back to the drive circuit 131 via the AGC circuit 133. With this feedback, the excitation amplitude operates stably. As described above, the detection circuit 132 performs two kinds of signal synthesis, and is provided on the one side of the lower surface of the vibrating piece 3 and the charge of the electrode 33 provided on the one side of the upper surface of the vibrating piece 3. Adding the charge of the electrode 36 is a synthesis method for detecting the excitation vibration, and acquiring a difference between the charges is a synthesis method for detecting the vibration based on the Coriolis force.
[0026]
During these operations, the ground electrodes 34, 37, 44, and 47 are grounded via the bonding pads 14 and 20, so that crosstalk does not occur between the detection electrode and the excitation electrode. Yes. The electrodes 34, 37, 44, and 47 may be connected to a constant potential such as a power supply potential or an intermediate potential.
[0027]
FIG. 6 shows a second embodiment of the present invention. The difference from the first embodiment is only the number of electrodes provided on the resonator element. That is, the excitation electrodes 32 and 41 and the ground electrodes 34, 37, 44, and 47 of the first embodiment are omitted, and the other electrodes are the same as those of the first embodiment and the wiring is the same. Although the operation principle is the same as that of the first embodiment, there is an advantage that electrode formation is easy because patterning of the electrodes inside the resonator elements 3 and 4 is not necessary.
[0028]
FIG. 7 shows a third embodiment of the present invention. The second embodiment is that the positions of the detection electrodes 33, 36, 45, and 48 of the second embodiment shown in FIG. Is different. As described above, the influence of polarization accompanying the vibration in the Z-axis direction is collected at the corner of the resonator element. Therefore, the detection electrode may be provided on the side surface as in this embodiment as long as it is in the vicinity of the corner. .
[0029]
FIG. 8 shows a fourth embodiment of the present invention, in which the side electrodes 31, 32, 41, 42 of the first embodiment are divided into two, respectively, so that the electrodes 31a, 31b, 32a, 32b, 41a, 41b, 42a and 42b, and the inner electrodes 32a, 32b, 41a and 41b are used for detection. If comprised in this way, since an excitation electric field can be made symmetrical up and down, the vibration leakage of the detection direction by excitation is few. Further, by acquiring the detection voltage by combining the two electrodes on the upper surface and the side surface, it is possible to efficiently detect the charge generated in the corner portion by applying the angular velocity. Therefore, leakage in the detection direction accompanying excitation can be reduced, offset voltage generation can be suppressed, and improvement in detection sensitivity and S / N can be expected.
[0030]
In the first to fourth embodiments described above, a quartz single crystal Z plate is used as the vibrator, but the present invention is not limited to this. For example, a so-called Y plate of lithium tantalate (LiTaO ₃ ) may be used instead of the quartz Z plate. In FIG. 9, a lithium tantalate Y plate as a vibrator is cut into a tuning fork by machining such as a wire saw, and two vibrating pieces 403 and 404 are projected in the + Z direction. FIG. 10 is a diagram showing an electrode arrangement and a processing circuit for the vibrator 401 composed of this lithium tantalate. When the outer four electrodes 411, 413, 420, and 423 are connected to the output terminals 310 and 310 ′ of the driving circuit 131 as shown in the figure and a driving signal is given, the vibrating bars 403 and 404 are as shown in FIG. Excited in opposite directions in the X-axis direction. The detection circuit 132 ′ differs from the detection circuit 132 of the first to third embodiments in the connection of the adder. By connecting in this way, an output signal is output from the terminal 312 and a feedback signal is output from the terminal 311. can do.
[0031]
【The invention's effect】
As described above, according to the angular velocity detection device of the present invention, the detection of the excitation vibration for stabilizing the excitation and the detection of the vibration by the Coriolis force in the direction orthogonal thereto are performed by the same vibration detection element. A sufficient area can be secured as compared with the case where both detections are detected by separate elements. It is the root of the stress concentration when the vibrating piece is vibrated. According to the present invention, since the vibration detection element can be arranged with a sufficient area even in a limited area called the root of the vibration piece, it is high both in terms of the position of the vibration detection element and in terms of area. Detection efficiency can be ensured.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a vibrator used in an angular velocity detection device according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a processing circuit of the angular velocity detection device according to the embodiment.
FIG. 3 is a perspective view showing a vibration mode of the vibrator of this embodiment.
FIG. 4 is a view for explaining an inverse piezoelectric effect at the time of excitation of this embodiment.
FIG. 5 is a view for explaining a piezoelectric effect when detecting vibration according to the embodiment;
FIG. 6 is a block diagram showing a second embodiment of the present invention.
FIG. 7 is a block diagram showing a third embodiment of the present invention.
FIG. 8 is a block diagram showing a fourth embodiment of the present invention.
FIG. 9 is a perspective view showing a lithium tantalate vibrator used in a fifth embodiment of the present invention.
FIG. 10 is a block diagram showing the processing circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,401 ... Vibrator, 2 ... Vibrator base | substrate, 3, 4, 403, 404 ... Vibrating piece 31-39, 31a, 31b, 32a, 32b, 41-49, 41a, 41b, 42a, 42b, 410 413, 420 to 423 ... electrodes, 131 ... drive circuit, 132, 132 '... detection circuit, 133 ... AGC circuit, 134 ... offset circuit, 135 ... synchronous detection circuit, 136 ... phase shifter.

Claims (2)

Vibrator, exciting means for exciting the vibrator, detecting means for detecting vibration of the vibrator, and angular velocity calculating means for calculating the rotational angular velocity of the vibrator based on vibration information detected by the detecting means In an angular velocity detection device comprising:
The vibrator is a tuning-fork type vibrator having a pair of vibrating pieces, and an excitation electrode and a detection electrode are arranged on the same cross section and on the same surface facing each vibrating piece of the pair of vibrating pieces , respectively. ,
The detection means includes a detection electrode of each vibration piece and a detection circuit connected to the detection electrode of each vibration piece,
The detection electrode of each vibration piece generates a change in charge according to a change in internal stress applied to the vibration piece with vibration of the vibration piece,
The detection circuit synthesizes the change in charge of the detection electrode of each vibrating piece and converts it into a desired electrical signal, and combines the change in charge generated at the detection electrode of each vibration piece. By providing a plurality of types of the above-described method, it is possible to detect excitation vibration by the excitation means and vibration based on Coriolis force generated as the vibrator rotates during the excitation vibration. Angular velocity detector. The excitation means includes an excitation electrode of each vibration piece and an excitation drive circuit connected to the excitation electrode of each vibration piece, and the vibration pieces are at least on the same cross section and opposed to each other on the same surface. The angular velocity detection device according to claim 1, wherein a constant potential electrode is disposed between the excitation electrode and the detection electrode.

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