JPH10148533A - Drive circuit for angular velocity sensor, and angular velocity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a drive circuit, whose adjusting time is shortened, by connecting a variable resistance to a impedance conversion circuit, selecting a resistance value, changing the resonant frequency in Z-axis direction of a vibrating body and the resonant frequency of a weight body, and reducing the frequency difference. SOLUTION: The impedance conversion circuit 32 is connected to the variable resistance 31, and then an oscillation circuit 30 is connected to the resistance 31. The value of the variable resistance 31 is set to 0, and the resonant frequency in the Z-axis direction of a vibrating body and the resonant frequency of a weight body are measured. At this time, when the resonant frequency of the weight body is larger than the resonant frequency in the Z-axis direction, the weight body is irradiated with a laser beam so as to be trimmed, and the resonant frequency in the Z-axis direction is adjusted approximately so as to become larger that the resonant frequency of the weight body. When the resonant frequency cannot be adjusted approximately, it is removed as a defect. The value of the variable resistance 31 is made large, it is misread, and the resonant frequency is adjusted so as to become a prescribed frequency difference. When the resonant frequency of the weight body is larger than the resonant frequency in the Z-axis direction, the value of the variable resistance 31 is reduced so as to match the prescribed frequency difference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a piezoelectric vibration type angular velocity sensor and an angular velocity sensor.

[0002]

2. Description of the Related Art Angular velocity sensors capable of attitude control and position control have been developed for miniaturization and high performance for the purpose of preventing camera shake of a video camera and for use in car navigation. Although there are various types of angular velocity sensors, a piezoelectric vibration type angular velocity sensor is advantageous in terms of size and cost, and a tuning fork type, a sound piece type (quadrangular prism), a cylindrical type, a triangular prism type, and the like have been commercialized.

FIG. 1 is a structural diagram for explaining a sound piece type piezoelectric vibration angular velocity sensor. The principle of the piezoelectric vibration type angular velocity sensor is that when a rotational angular velocity (Ω0) is applied around the center axis (Z axis) of a vibrating vibrator, the original vibration direction (X axis)
On the other hand, it utilizes a mechanical phenomenon that generates a Coriolis force (Fc) proportional to the rotational angular velocity in a direction perpendicular to the axis (Y axis). The Coriolis force is detected as a voltage by the piezoelectric ceramics. The Coriolis force is generally obtained by the following equation. Fc = 2m × v × Ω0 m is mass, v is velocity, and Ω0 is angular velocity.

If the vibration frequency is the same, the displacement of the Y-axis increases as the amplitude of the X-axis increases, and the resonance-type vibration increases the amplitude of the X-axis and increases the detection efficiency of the Y-axis in order to increase the detection voltage (sensitivity). An angular velocity sensor is advantageous. The resonating type vibration angular velocity sensor is a resonance type and can increase sensitivity, but it is difficult to accurately adjust the resonance frequency without breaking the vibration posture of the driving side and the detection side, and the resonance characteristics of the driving side and the detection side Remarkable changes in characteristics due to discrepancies or deviations, and high mechanical quality factors (Q
There are also many problems such as a low response speed due to m).

There has been a demand for a sensor capable of detecting two-axis angular velocities with a single angular velocity sensor. To meet this demand, a piezoelectric element is attached to the surface of a vibrating body and the piezoelectric element is deformed by the angular velocity. Sensors have been developed that measure the amount of changing charge to detect angular velocity. FIG. 2 is an exploded perspective view of the angular velocity sensor as viewed obliquely from above. FIG. 3 is an exploded perspective view of the same angular velocity sensor viewed obliquely from below. A piezoelectric element 2 having an electrode 6 on the lower surface and a detection electrode 5 serving as four excitation electrodes on the upper surface is attached to the upper surface of the vibrating body 1. A piezoelectric element 3 having an electrode 7 on the upper surface and a feedback electrode 8 on the lower surface is attached to the lower surface of the vibrator 1.
A weight 9 is attached to the lower surface of the return electrode 8 to form an angular velocity sensor. In the angular velocity sensor unit, the bending vibration node unit 4 is fixed by a cylindrical support member 10.

Since the electrode 6 and the vibrating body 1 are electrically connected and adhered, when an alternating current is applied to the vibrating body 1 and the detection electrode 5 which also serves as an excitation electrode, the piezoelectric element 2 vibrates, and the vibrating body 1 is vibrated.
Also vibrate together. The detection electrodes 5 supported by the cylindrical support member 10 and also serving as four excitation electrodes are provided inside the inner diameter of the cylindrical support member 10. Cylindrical support member 10
Is fixed at two places by wire 11 as shown in the figure.
1 is fixed to the substrate at the other end.

When an angular velocity acts on the angular velocity sensor, the weight body 9 moves due to Coriolis force, so that the angular velocity sensor section is deformed and charges are generated on the detection electrodes. The direction and intensity of the angular velocity can be detected based on the amount of charges generated on the four detection electrodes 5.

FIG. 4 is a circuit diagram for driving the angular velocity sensor. The four detection electrodes 5 also serving as excitation electrodes formed on the piezoelectric element 2 affixed to the vibrating body 1 are respectively connected to the detection electrodes 5a to 5d also serving as excitation electrodes and are connected to resistors 12a to 12d.
Is connected. The resistors 12a to 12d are connected to the oscillation circuit 13. The impedance conversion circuit 14 is connected to the feedback electrode 8 formed on the piezoelectric element 3, and the impedance conversion circuit 14 is connected to the oscillation circuit 13.

An origin is set at the center of the plane including the vibrating body 1,
X axis on the same plane, Y axis orthogonal to the X axis on the same plane, X
Set the Z axis perpendicular to the axis and the Y axis. Although there are many types of vibration modes, the vibration mode used as the angular velocity sensor is such that the weight body 9 swings in the vertical direction as shown in FIGS.
The vibration mode (excitation) in the axial direction and the vibration mode (detection) in the X and Y axis directions (lateral direction) in which the weight body 9 swings in the lateral direction as shown in FIGS. 7 and 8 are used. FIG. 5 is a cross-sectional view showing a vibration mode in the Z-axis direction, and shows a state in which the vibration is caused in the Z-axis plus direction. FIG. 6 is a cross-sectional view showing a vibration mode in the Z-axis direction, and shows a state in which the vibration is caused in the Z-axis minus direction.
The vibration frequency in the vibration mode in the Z-axis direction is called the resonance frequency in the Z-axis direction. The vibration mode in the Z-axis direction is used as a drive mode. FIG. 7 is a cross-sectional view showing a vibration mode in the X and Y axis directions, and shows a state in which the vibration mode swings in the X axis plus direction. FIG. 8 is a cross-sectional view showing a vibration mode in the X and Y axis directions, and shows a state in which the vibration mode swings in the X axis minus direction.
The vibration frequency in the vibration mode in the X and Y axis directions is called the resonance frequency of the weight. The vibration mode in the X and Y axis directions is used as a detection mode. Generally, in the resonance type angular velocity sensor, the detection sensitivity increases when the vibration frequency (resonance frequency) of the drive mode and the detection mode is close. Therefore, the detection sensitivity can be increased by making the resonance frequency in the Z-axis direction close to the resonance frequency of the weight body.

When the resonance frequency in the Z-axis direction and the resonance frequency of the weight body are separated from each other and the resonance frequency in the Z-axis direction is higher than the resonance frequency of the weight body, the end face of the weight body 9 is irradiated with the laser beam. Irradiation and trimming (removal of mass) make it possible to bring the two resonance frequencies closer to each other.

[0011]

The detection sensitivity can be increased by bringing the resonance frequency in the Z-axis direction close to the resonance frequency of the weight body. As described above, for example, there is a method of trimming (removing mass) by irradiating the end face of the weight body with a laser beam. However, with this method, it is easy to roughly adjust, but fine adjustment is performed by calculating the position and amount of irradiation of the laser beam each time, and adjusting the resonance frequency to a predetermined value (frequency difference) little by little. There must be. Therefore, adjustment at a level of several Hz is extremely difficult, and it takes time to adjust the resonance frequency. The present invention is to solve such a problem.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional angular velocity sensor, and provides an inexpensive angular velocity sensor having high detection accuracy.

At least a plate-shaped vibrator, a piezoelectric element on which an excitation electrode, a detection electrode, and a return electrode are formed and attached to one or both surfaces of the vibrator, and a vibrator to which the piezoelectric element is attached In a driving circuit of an angular velocity sensor having an oscillation circuit for driving an angular velocity sensor unit composed of a support member for supporting an oscillation node unit, a feedback electrode and an oscillation circuit of the angular velocity sensor unit include a fixed resistor or a variable resistor and an impedance conversion circuit. Connect through. Also, at least,
A plate-shaped vibrator, a piezoelectric element on which an excitation electrode, a detection electrode, and a feedback electrode are formed and attached to one or both surfaces of the vibrator, and a vibration node portion of the vibrator to which the piezoelectric element is attached are supported. In the angular velocity sensor having a circuit section for driving an angular velocity sensor section constituted by a supporting member to be connected, the feedback electrode and an oscillation circuit of the circuit section are connected to each other via a fixed resistor or a variable resistor and an impedance conversion circuit. By changing the resonance frequency in the Z-axis direction and the resonance frequency of the weight body by properly selecting the resistance value, the frequency difference between the two can be reduced and the predetermined frequency difference can be adjusted. Preferably, the resistor is a variable resistor. This makes fine adjustments easier and more accurate.

[0014]

Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 9 is a top view of the first embodiment of the present invention. FIG. 10 is a front sectional view of the first embodiment of the present invention. FIG. 11 is a circuit diagram of the first embodiment of the present invention. On the upper surface of the vibrator 21, an electrode 23 is provided on the lower surface and a detection electrode 24 also serving as four excitation electrodes is provided on the upper surface, and a disk-shaped piezoelectric element 22 provided with a cross-shaped feedback electrode 25 is an epoxy-based adhesive. Is attached. Further, the piezoelectric element 22 is arranged and attached such that the center on the plane of the vibrating body 21 and the center on the plane of the piezoelectric element 22 coincide. A weight 27 is provided on the lower surface of the vibrating body 21.
Are arranged and attached such that the center on the surface of the vibrating body 21 and the central axis of the weight body 27 coincide. The weight body 27 is formed in a shape in which two cylinders having different diameters are overlapped with their central axes aligned. The end face of a small diameter cylinder is attached to the vibrating body 21. For the vibrating body 21 and the weight body 27, an elinvar material as a constant elastic material was used. The piezoelectric element 22 is made of PZT, which is a piezoelectric ceramic, and the electrodes are made of A by evaporation.
It was formed of a g-Cr alloy. The vibrating body 21 and the weight body 27 may be joined by welding or the like.

The angular velocity sensor is constituted by the vibrating body 21, the piezoelectric element 22, and the weight 27. Cylindrical support member 26
Is a bending vibration node 2 of the angular velocity sensor.
8 is adhered and fixed. As the cylindrical support member 26, an elinvar material which is a constant elastic material was used. The cylindrical support member 2
6 may be formed integrally with the vibrating body 21. The material of the member is not limited to these as long as it satisfies the function as the angular velocity sensor.

Since the electrode 23 and the vibrating body 21 are electrically connected and adhered to each other, when an alternating current is applied to the vibrating body 21 and the detection electrode 24 serving also as four excitation electrodes, the piezoelectric element 22
Is Z together with the vibrating body 21 by expanding and contracting in the radial direction.
Vibrates in the axial direction. The detection electrode 24 supported by the cylindrical support member 26 and also serving as the four excitation electrodes is provided near the inner diameter of the cylindrical support member 26.

When an angular velocity acts on the angular velocity sensor, the weight 27 moves due to the Coriolis force, so that the angular velocity sensor section is deformed and charges are generated on the detection electrodes. Four detection electrodes 2
4, the direction and intensity of the angular velocity can be detected.

Here, in order to increase the detection sensitivity, it is necessary to make the resonance frequency in the Z-axis direction close to the resonance frequency of the weight body to make a predetermined frequency difference. Conventionally, adjustment was performed by irradiating (trimming) a laser beam onto the end face of the weight body 27. In the present invention, the resonance frequency in the Z-axis direction and the resonance frequency of the weight are adjusted to a predetermined frequency difference by adjustment on the circuit side. Hereinafter, the circuit and the adjustment method will be described in detail.

The circuit will be described with reference to FIG. This is an embodiment in which a resistor for adjusting the resonance frequency is attached to the oscillation circuit. The four detecting electrodes 24 also serving as the excitation electrodes formed on the piezoelectric element 22 attached to the vibrating body 21 are respectively connected to the detecting electrodes 24a to 24d which also serve as the exciting electrodes.
9a to 29d are connected. The resistors 29a to 29d are connected to the oscillation circuit 30. A variable resistor 31 is connected in series to the feedback electrode 25 formed on the piezoelectric element 22. The variable resistor 31 includes an impedance conversion circuit 32
Are connected, and the impedance conversion circuit 32
Connected to 0.

By changing the variable resistance 31, the equivalent resistance on the equivalent circuit can be adjusted. Q in resonant circuit
The value is represented by Q = ω0L / R. Here, ω0 is the resonance angular frequency, L is the inductance, and R is the resistance. By changing R, Q also changes, and by changing both R and Q, the resonance angular frequency ω0 also changes. FIG. 12 is a graph showing the relationship between the resistance value connected to the feedback electrode and the resonance frequency in the Z-axis direction. FIG. 13 is a graph showing the relationship between the resistance value connected to the feedback electrode and the resonance frequency of the weight body.
It can be seen from the graph that as the resistance value increases, the resonance frequency in the Z-axis direction decreases, and the resonance frequency of the weight body hardly changes. The resonance frequency is adjusted using this property.

The adjusting method will be described. With the value of the variable resistor 31 set to 0, the resonance frequency in the Z-axis direction and the resonance frequency of the weight are measured. Here, when the resonance frequency of the weight body is higher than the resonance frequency in the Z-axis direction, trimming such as irradiation with a laser beam is performed so that the resonance frequency in the Z-axis direction becomes higher than the resonance frequency of the weight body. Make adjustments. Those that cannot be roughly adjusted are removed as defective. This is because the change in the resonance frequency of the weight body is smaller than the resonance frequency in the Z-axis direction even if the resistance value is increased, even if the resistance value is increased. When the resonance frequency in the Z-axis direction is higher than the resonance frequency of the weight body, the value of the variable resistor 31 is increased, and the measurement is adjusted so as to have a predetermined frequency difference while measuring. When the resonance frequency of the weight body becomes higher than the resonance frequency in the Z-axis direction, the value of the variable resistor 31 is reduced to match the predetermined frequency difference. Therefore, by configuring the circuit in this manner, the resonance frequency in the Z-axis direction can be very easily and accurately adjusted to the resonance frequency of the weight by adjusting the variable resistor 31 connected to the feedback electrode 25. Can be adjusted to

FIG. 14 is a top view of the second embodiment of the present invention. FIG. 15 is a front sectional view of the second embodiment of the present invention.
FIG. 16 is a circuit diagram of the second embodiment of the present invention. The second embodiment uses two piezoelectric elements. A disk-shaped piezoelectric element 42 provided with an electrode 43 on the lower surface and a detection electrode 44 also serving as four excitation electrodes on the upper surface is attached to the upper surface of the vibrating body 41 with an epoxy-based adhesive. Further, the piezoelectric element 42 is arranged and attached such that the center on the plane of the vibrating body 41 and the center on the plane of the piezoelectric element 42 coincide with each other. A disk-shaped piezoelectric element 47 having an electrode 45 on the upper surface and a feedback electrode 46 on the lower surface is attached to the lower surface of the vibrating body 41 with an epoxy adhesive. Furthermore, the piezoelectric element 47 is arranged and attached such that the center on the plane of the vibrating body 41 and the center on the plane of the piezoelectric element 47 coincide. A weight 48 is arranged and attached to the lower surface of the piezoelectric element 47 such that the center on the surface of the vibrating body 41 and the center axis of the weight 48 coincide with each other. The weight body 48 is formed in a shape in which two cylinders having different diameters are overlapped with their central axes aligned. The end face of a small diameter cylinder is attached to the piezoelectric element 47. For the vibrating body 41 and the weight body 48, an elinvar material which is a constant elastic material was used. The piezoelectric elements 42 and 47 were made of PZT, which is a piezoelectric ceramic, and the electrodes were formed of an Ag—Cr alloy by vapor deposition.

Vibrator 41, piezoelectric element 42, piezoelectric element 4
7. The angular velocity sensor unit is constituted by the weight 48. The cylindrical support member 49 is adhesively fixed on the bending vibration node 50 of the angular velocity sensor. As the cylindrical support member 49, an elinvar material which is a constant elastic material was used. The material of the member is not limited to these as long as it satisfies the function as the angular velocity sensor.

Since the electrode 43 and the vibrating body 41 are electrically connected and adhered to each other, when an alternating current is applied to the vibrating body 41 and the detection electrode 44 serving also as the four excitation electrodes, the piezoelectric element 42
Is Z together with the vibrating body 41 by expanding and contracting in the radial direction.
Vibrates in the axial direction. The detection electrode 44 supported by the cylindrical support member 49 and also serving as the four excitation electrodes is provided inside the inner diameter of the cylindrical support member 49.

When an angular velocity acts on the angular velocity sensor, the weight 48 moves due to Coriolis force, thereby deforming the angular velocity sensor and generating electric charges on the detection electrodes. Four detection electrodes 4
4, the direction and intensity of the angular velocity can be detected.

The circuit will be described with reference to FIG. The resistances 51a to 51d are connected to the detection electrodes 44a to 44d also serving as the excitation electrodes of the four excitation electrodes 44 serving as the four detection electrodes formed on the piezoelectric element 42 attached to the vibrating body 41. The resistors 51a to 51d are connected to the oscillation circuit 52. A variable resistor 53 is connected in series to a feedback electrode 46 formed on the piezoelectric element 47. An impedance conversion circuit 54 is connected to the variable resistor 53, and the impedance conversion circuit 54 is connected to the oscillation circuit 52.

The adjusting method is the same as that of the first embodiment, and will not be described. In the first embodiment and the second embodiment, an example in which a variable resistor is used as the resistor has been described. However, a fixed resistor can be used. When the frequency difference between the resonance frequency in the Z-axis direction and the resonance frequency of the weight body is known, the relationship between the resistance value, the resonance frequency in the Z-axis direction, and the resonance frequency of the weight body is determined in advance by experiments. By this (for example, FIG. 12,
13), the resistance to be used is determined from the resonance frequency and the frequency difference between the two. What is necessary is just to replace it with the variable resistor of a circuit, and to attach it. Further, the adjustment of the resonance frequency may be performed in combination with a method using a laser beam (trimming, removal of mass, etc.). In any case, the method can be manufactured at low cost by appropriately combining the methods of shortening the adjustment time depending on the type of the angular velocity sensor.

[0028]

According to the present invention, the following effects can be obtained by employing the above-described structure. (1) The resonance frequency in the Z-axis direction can be easily and accurately adjusted by adjusting the value of the resistor connected to the feedback electrode or the variable resistor. (2) Adjustment time is shortened and it can be manufactured at low cost. 3 The detection sensitivity increases.

[Brief description of the drawings]

FIG. 1 is a structural diagram for explaining a sound piece type piezoelectric vibration angular velocity sensor.

FIG. 2 is an exploded perspective view of a conventional example of an angular velocity sensor according to the present invention as viewed obliquely from above.

FIG. 3 is an exploded perspective view of a conventional example of an angular velocity sensor according to the present invention as viewed obliquely from below.

FIG. 4 is a circuit diagram of a conventional example of an angular velocity sensor according to the present invention.

FIG. 5 is a sectional view showing a vibration mode in the Z-axis direction of a conventional example of the angular velocity sensor according to the present invention.

FIG. 6 is a sectional view showing a vibration mode in the Z-axis direction of a conventional example of the angular velocity sensor according to the present invention.

FIG. 7 is a cross-sectional view showing a vibration mode in the X and Y axis directions of a conventional example of the angular velocity sensor according to the present invention.

FIG. 8 is a cross-sectional view showing a vibration mode in the X and Y axis directions of a conventional example of the angular velocity sensor according to the present invention.

FIG. 9 is a top view of the angular velocity sensor according to the first embodiment of the present invention.

FIG. 10 is a front sectional view of the first embodiment of the angular velocity sensor according to the present invention.

FIG. 11 is a circuit diagram of a first embodiment of an angular velocity sensor according to the present invention.

FIG. 12 is a graph showing a relationship between a resistance value connected to a feedback electrode of the angular velocity sensor according to the present invention and a resonance frequency in the Z-axis direction.

FIG. 13 is a graph showing the relationship between the resistance value connected to the feedback electrode of the angular velocity sensor according to the present invention and the resonance frequency in the X and Y axis directions.

FIG. 14 is a top view of a second embodiment of the angular velocity sensor according to the present invention.

FIG. 15 is a front sectional view of an angular velocity sensor according to a second embodiment of the present invention.

FIG. 16 is a circuit diagram of a second embodiment of the angular velocity sensor according to the present invention.

[Description of Signs] 1 Vibration body 2 Piezoelectric element 3 Piezoelectric element 4 Node unit 5 Detection electrode also serving as excitation electrode 5a Detection electrode also serving as excitation electrode 5b Detection electrode also serving as excitation electrode 5c Detection electrode also serving as excitation electrode 5d Also serving as excitation electrode Detection electrode 6 Electrode 7 Electrode 8 Return electrode 9 Weight body 10 Cylindrical support member 11 Wire 12a Resistance 12b Resistance 12c Resistance 12d Resistance 13 Oscillation circuit 14 Impedance conversion circuit 21 Vibrator 22 Piezoelectric element 23 Electrode 24 Detection electrode serving also as excitation electrode 24a Detection electrode also serving as excitation electrode 24b Detection electrode also serving as excitation electrode 24c Detection electrode also serving as excitation electrode 24d Detection electrode also serving as excitation electrode 25 Return electrode 26 Cylindrical support member 27 Weight body 28 Node 29a Resistance 29b Resistance 29c Resistance 29d Resistance 30 Oscillation circuit 31 Variable resistance 32 Impedance conversion circuit 41 Vibrator 42 Piezoelectric element 43 Electrode 44 Detection electrode 44a also serving as excitation electrode 44a Detection electrode also serving as excitation electrode 44b Detection electrode also serving as excitation electrode 44c Detection electrode also serving as excitation electrode 44d Detection electrode also serving as excitation electrode 45 Electrode 46 Return electrode 47 Piezoelectric element 48 Weight body 49 Cylindrical support member 50 Node part 51 Resistance 51a Resistance 51b Resistance 51c Resistance 51d Resistance 52 Oscillation circuit 53 Variable resistance 54 Impedance conversion circuit

Claims (2)

[Claims] At least a plate-shaped vibrator, a piezoelectric element having an excitation electrode, a detection electrode, and a return electrode formed thereon and attached to one or both surfaces of the oscillator, and a vibration attached to the piezoelectric element In a driving circuit for an angular velocity sensor having an oscillation circuit for driving an angular velocity sensor unit composed of a support member for supporting a vibration node part of a body, a feedback electrode and an oscillation circuit of the angular velocity sensor unit are provided with a fixed resistor or a variable resistor and an impedance. A driving circuit for an angular velocity sensor, wherein the driving circuit is connected via a conversion circuit. 2. A piezoelectric element having at least a plate-shaped vibrator, an excitation electrode, a detection electrode, and a return electrode formed thereon and affixed to one or both surfaces of the vibrator, and a vibration affixed to the piezoelectric element An angular velocity sensor having a circuit unit for driving an angular velocity sensor unit composed of a support member for supporting a vibration node unit of a body, wherein the feedback electrode and an oscillation circuit of the circuit unit include a fixed resistor or a variable resistor and an impedance conversion circuit. The angular velocity sensor is connected via a.