JPH08271266A - Electrode structure of angular velocity sensor - Google Patents

Abstract

PURPOSE: To enhance the detection sensitivity of a small sensor which can detect an angular velocity in two axes by a constitution wherein two each of detection electrodes are formed in the positive direction and the negative direction in two orthogonal axes of a piezoelectric element and the detection electrodes as a pair are arranged in different positions in which positive and negative stresses are generated by the piezoelectric element when an angular velocity acts. CONSTITUTION: A total of eight detection electrodes 5a to 5h are formed at the inside of a cylindrical support member 10 and in a concentric cicle shape by leaving a circular part in the center in such a way that two each are installed in the positive direction and the negative direction in the X- and Y-axses which are at right angles in the center on the face of a piezoelectric element 2. A feedback electrode 4 is formed at the outside and in the circular part of the member 10. A weight body 9 is pasted in order to detect the action of Coriolis' force with good sensitivity. When an angular velocity acts around the Y-axis, Coriolis' force acts in the X-axis direction, and the center of gravity of the weight body 9 is moved in the X-axis direction. Since one end of the weight body 9 is fixed to a sensor part, an angular moment is applied to a fixation part, and the sensor part is deformed. In the sensor part which is fixed by the member 10, a strain is generated at the inside from the inside diameter of the member 10, and it is hardly generated at the outside.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode structure of a piezoelectric vibration type angular velocity sensor.

[0002]

2. Description of the Related Art An angular velocity sensor capable of attitude control and position control has been developed to have a smaller size and higher performance for the purpose of preventing camera shake of a video camera and being used for car navigation. Although there are various angular velocity sensors, the piezoelectric vibration type angular velocity sensor is advantageous in terms of size and cost, and tuning fork type, tuning piece type (square column), columnar type, 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 the rotation angular velocity (ω0) is applied around the center axis (Z axis) of the vibrating vibrator, the original vibration direction (X axis)
On the other hand, it utilizes a mechanical phenomenon in which a Coriolis force (Fc) proportional to the rotational angular velocity is generated in the direction perpendicular to the axis (Y axis), and vibration is applied to the X axis by using a driving piezoelectric ceramic, and detection provided on the Y axis. The piezoelectric ceramics for use detects Coriolis force as a voltage. 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 larger the X-axis amplitude is, the larger the Y-axis displacement is, and the higher the detection voltage (sensitivity) is, the larger the X-axis amplitude is and the higher the Y-axis detection efficiency is, the resonance type vibration. An angular velocity sensor is advantageous. The speech piece type vibration angular velocity sensor is a resonance type and can have high sensitivity, but it is difficult to accurately adjust the resonance frequency without disturbing the vibration posture of the drive side and the detection side, and the resonance characteristics of the drive side and the detection side. Characteristic change and high mechanical quality factor (Q
Due to m), there are many problems such as slow response speed. Moreover, the angular velocity can be detected in only one direction, and there is a problem in terms of usability.

[Problems to be Solved by the Invention]

A so-called uniaxial angular velocity sensor must be used in combination to detect angular velocities in a plurality of axial directions. If there are two axes, then two, and if there are three axes, then three. It was inconvenient for use in portable products that are becoming lighter, thinner and smaller. The present invention relates to an electrode structure of a piezoelectric vibration type angular velocity sensor capable of detecting biaxial angular velocity with a single angular velocity sensor, and an object thereof is to reduce the size and improve the detection sensitivity.

[Means for Solving the Problems]

A plate-shaped vibrating body, a plate-shaped piezoelectric element is attached to the surface of the vibrating body, and two detection electrodes in total are formed in two positive and negative directions of two axes perpendicular to the center of the piezoelectric element. A return electrode is formed around the eight detection electrodes. The vibrating body is vibrated by the vibration of the piezoelectric element, and the strain of the vibrating body due to the Coriolis force generated by the angular velocity is used as the strain of the piezoelectric element, and the magnitude of the angular velocity is detected by the amount of electric charges generated by the strain.

A plate-shaped vibrating body having a circular inner side having a slit formed therein, and a plate-shaped piezoelectric element is attached to the surface of the vibrating body, and the vibrating body is directly or through the plate-shaped piezoelectric element. In an electrode structure of an angular velocity sensor for detecting an angular velocity by providing a weight body, two detection electrodes are formed in each of two positive and negative directions of two axes orthogonal to the center of the piezoelectric element, and a total of eight detection electrodes are arranged. The place is a position where the positive and negative stresses generated in the piezoelectric element when the angular velocity acts are different. Moreover, the circuit is simplified by reversing the polarization direction of the piezoelectric element at each electrode and connecting the electrodes on the piezoelectric element.

According to the present invention, a plate-shaped vibrating body having a circular shape and a slit formed inside is supported, and a plate-shaped piezoelectric element is attached to the surface of the vibrating body. The present invention was completed by analyzing that the stress generated between the center of the vibrating body and the supporting portion is reversed in the angular velocity sensor that detects the angular velocity by providing the weight body through the element. I arrived.

【Example】

FIG. 2 is an exploded perspective view of the angular velocity sensor according to the present invention seen from the upper side. FIG. 3 is an exploded perspective view seen from the lower surface side.

A plurality of grooves or recesses 11 are formed in the central portion of the plate-shaped vibrating body 1 so that the vibrating body 1 can be easily deformed. Eight detection electrodes 5a are provided on the lower surface of the plate-shaped piezoelectric element 2.
~ 5h and the return electrode 4 are formed. Two in total in the positive and negative directions of the two axes (X, Y) orthogonal to each other on the center of the surface of the piezoelectric element
Two detection electrodes 5a to 5h are formed concentrically inside the cylindrical support member 10 and leaving a circular portion in the center, and the return electrode 4 is formed outside the cylindrical support member 10 and in the central circular portion.
Was formed. Further, a weight body 9 is attached. The weight body 9 is for detecting the action of the Coriolis force with high sensitivity. An electrode 6 is formed on the upper surface of the plate-shaped piezoelectric element 2.
An electrode 7 is formed on the lower surface of the plate-shaped piezoelectric element 3, and an excitation electrode 8 is formed on the upper surface.

FIG. 4 is a diagram showing a stress generation distribution of the angular velocity sensor which is the basis of the present invention. FIG. 5 is a schematic view showing the electrode structure of the present invention and the polarization direction of the piezoelectric element. FIG. 6 is a block diagram of a circuit for detecting an angular velocity as a voltage signal by the angular velocity sensor according to the present invention. FIG. 7 is a front view of another embodiment of the electrode structure of the angular velocity sensor of the present invention.

FIG. 4 shows a stress distribution generated in the piezoelectric element when an angular velocity acts on the angular velocity sensor of the present invention. The vertical axis represents stress, and the horizontal axis represents the dimension from the center to the outer periphery of the piezoelectric element. A diameter of 0.15 at the center of the piezoelectric element with radius R
It is a stress distribution when an R weight body is provided and is supported by a cylindrical support member having a diameter of 1.2R. As can be seen from the figure, 0.
The stress is reversed near 4R. Almost no stress is generated on the outer side of the support portion and the central portion of the weight body.

FIG. 5 is a diagram showing the shape of electrodes formed on the piezoelectric element and the direction of polarization from the results analyzed in FIG. 4, a front view and a sectional view. The detection electrodes are provided on both sides of the boundary A where the stress is reversed inside the support portion. Eight detection electrodes 15a to 15 in total
In h, the electrode portions paired with each other across the boundary A in the positive and negative directions of the X axis and the Y axis have the polarization of the piezoelectric element reversed, and are connected by thin electrodes. Since the pair of electrodes are connected on the piezoelectric element, the angular velocity detection circuit described later can be simplified. For the sake of convenience of explanation, "+" is given to the electrode portion, and when + stress is generated in the piezoelectric element, + charge is generated,
The minus sign on the electrode portion indicates that a plus charge is generated when a minus stress is generated on the piezoelectric element. When the boundary A and the supporting portion have an electrode structure matching FIG. 5, a + charge is generated at the + electrode part, and a + charge is also generated at the − electrode part. Therefore, by connecting them to each other, a large + charge is generated. Occurrence occurs and the detection efficiency of angular velocity increases.

FIG. 7 is a front view of another embodiment of the electrode structure of the angular velocity sensor of the present invention. It is the electrode structure shown in FIG. The arrangement of the detection electrodes is the same as that of the above-described embodiment, but the polarization directions of the piezoelectric elements are the same on both sides of the boundary A, and the pair of detection electrodes are not connected.

FIG. 6 is a configuration diagram of a circuit for detecting the angular velocity from the electric charge generated from the electrode structure and the polarization direction of FIG. X
It is a circuit block diagram for detecting the Coriolis force proportional to the rotational angular velocities in the axial direction and the Y-axis direction, but the same signal processing is performed for both the X-axis and the Y-axis. (When rotational angular velocity acts around the Y-axis). The detection electrodes 5b and 5c are connected to the impedance conversion circuit 18, and the detection electrodes 5a and 5d are connected to the impedance conversion circuit 18 '.
The output of 8'is connected to the differential amplifier circuit 14.

A drive signal is applied through the amplifier circuit 12 and the phase correction circuit 13 to excite the sensor section. Since the eight detection electrodes 5a to 5h are polarized in the same direction, 5a and 5d, 5b and 5c are arranged so that the output signals have the same phase.
Are connected. When rotation is applied in this state, electric charges generated by the Coriolis force proportional to the rotational angular velocity are superimposed on the drive signal as a voltage. At this time, the detection voltages that are opposed to each other due to the Coriolis force have the same phase, so that a difference occurs in the voltage output. When subtracted by the differential amplifier circuit 14, the drive signals are canceled and only the voltage generated by the Coriolis force can be taken out. The voltage generated by this Coriolis force is half-wave rectified by the synchronous detection circuit 19, and the filter 1
After passing through 6, the output signal is obtained. This output voltage is smoothed by the DC amplification circuit 17, and an output voltage proportional to the rotational angular velocity is obtained.

The present invention will be described in detail with reference to FIGS. When an angular velocity acts around the Y axis, Coriolis force acts in the X axis direction and the center of gravity of the weight body 9 moves in the X axis direction. Since one end of the weight body 9 is fixed to the sensor portion, a rotational moment is applied to the fixed portion by the weight body 9, and the sensor portion is deformed. The sensor portion fixed by the cylindrical support member 10 is distorted inside the inner diameter of the cylindrical support member 10 and is hardly generated outside. It can be said that the characteristics are determined by the strain inside the inner diameter of the cylindrical support member 10, especially when the groove or the recess 11 is formed in the center of the vibrating body as employed in this embodiment. However, the central portion where one end surface of the weight body 9 is fixed is hardly distorted. Further, the positive / negative of the stress is inverted in the vicinity of 0.4 R from the center of the piezoelectric element. Therefore, the detection electrode is inside the inner diameter of the cylindrical support member,
Moreover, it is preferable to form it except for the central portion where the weight body is fixed, but if the portions where the stress is reversed are used as the same electrode, the generated charges will be canceled.

Therefore, in the portion where the stress is reversed, the polarization direction is changed so that the same charge is generated, or the connection is made.
It is advisable to effectively utilize the electric charge generated by connecting the electrode parts that generate the same electric charge without changing the polarization direction for angular velocity detection.

The manufacturing in which the polarization directions are aligned requires only one polarization process, but the sensor is easy to manufacture, but the connection between the electrode and the circuit becomes complicated, and the polarization is reversed to connect the electrode on the piezoelectric element. Has an advantage that the detection circuit can be simplified although the polarization process is performed twice.

[0020]

EFFECTS OF THE INVENTION The present invention having the above-mentioned structure has the following effects. (1) Since the detection electrodes are provided in accordance with the stress generation distribution, the angular velocity detection sensitivity is improved. Since the two pairs of detection electrodes were connected on the piezoelectric element with the polarization directions reversed, a reliable connection can be obtained.
This made it possible to reduce the connections between the circuit and the electrodes and increase the reliability.

[Brief description of 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 an angular velocity sensor according to the present invention seen obliquely from above.

FIG. 3 is an exploded perspective view of an angular velocity sensor according to the present invention seen obliquely from below.

FIG. 4 is a stress generation distribution map.

FIG. 5 is a plan view and a cross-sectional view showing the electrode structure of the present invention and the polarization direction of the piezoelectric element.

FIG. 6 is a block diagram of an angular velocity detection circuit.

FIG. 7 is a plan view and a cross-sectional view showing the electrode structure of the present invention and the polarization direction of the piezoelectric element.

[Explanation of symbols]

 1 Vibrating body 2 Piezoelectric element 3 Piezoelectric element 4 Return electrode 5a-5h Detection electrode 6 Electrode 7 Electrode 8 Excitation electrode 9 Weight body 10 Cylindrical support member 11 Groove 12 Amplifier 13 Phase correction circuit 14 Differential amplification circuit 15a-15h Detection Electrode 16 Filter 17 DC amplification circuit 18 Impedance conversion circuit 18 'Impedance conversion circuit 19 Synchronous detection circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomio Namiki 4107, Miyota, Miyota-cho, Kitasaku-gun, Kitano, Nagano 5 Miyota Co., Ltd. (72) Riyasu Shigeta 4107, 5107 Miyota, Kitadaku-cho, Kitasaku-gun, Nagano Prefecture In Miyota Co., Ltd. (72) Minor Hatakeyama Minoru Hatakeyama 4107, Miyota, Miyota-cho, Kitasaku-gun, Nagano 5 In Miyota Co., Ltd. (72) Inventor Kazuhiro Okada 4-73, Sugaya, Ageo City, Saitama Prefecture

Claims (3)

[Claims] 1. A plate-shaped vibrating body having slits formed inside a circular shape for supporting in a circular shape, and a plate-shaped piezoelectric element is attached to a surface of the vibrating body, and the vibrating body is provided with the plate-shaped piezoelectric element directly or on the plate-shaped piezoelectric element. In the electrode structure of the angular velocity sensor for detecting the angular velocity by providing the weight body through the two, two detection electrodes are formed in each of two positive and negative directions of two axes orthogonal to the center of the piezoelectric element, and two detection electrodes are formed. The electrode structure of the angular velocity sensor is characterized in that the position of is set to a position where the positive and negative stresses generated in the piezoelectric element when the angular velocity acts is different. 2. The electrode structure of the angular velocity sensor according to claim 1, wherein the polarization directions of the piezoelectric elements of the two electrode portions are reversed. 3. The electrode structure of the angular velocity sensor according to claim 2, wherein two electrodes are connected.