JPH0926321A - Electrode structure for angular velocity sensor - Google Patents

Abstract

PURPOSE: To obtain an electrode structure which can be miniaturized and whose sensitivity can be increased by pasting a sheetlike piezoelectric element on the surface of a sheetlike vibrating body, forming one each, i.e., total of four detection electrodes in the positive direction, and forming the negative direction on two axes which are at right angles in the center of the element and feedback electrodes around the respective electrodes. CONSTITUTION: A plurality of grooves or recessed parts 11 are formed in the central part of a sheetlike vibrating body 1 so as to be easily deformed. One each, i.e., total of four detection electrodes 5 are formed on the rear surface of a sheetlike piezoelectric element 2 inside a support member 10 in the positive direction and the negative direction on X-axis and Y-axis which crass at right angles in the center of the rear surface, and a circular part is left in the center so as to be a concentric circle shape. Feedback electrodes 4 are formed inside the member 10 and in the circular part in the center. An electrode is formed on the surface of the element 2, and an electrode 7 and an exciting electrode 8 are formed respectively on the rear surface and the surface of the piezoelectric element 2. Since the electrodes 4 are formed in the central part of the element 2 and outside the member 10 in this manner, a vibration becomes stable. Since the electrodes 5 are formed inside the member 10, an angular velocity can be detected with good efficiency by the small electrodes 5.

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 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 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 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
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 four detection electrodes in total are formed in positive and negative directions of two axes orthogonal to each other at the center of the piezoelectric element. A return electrode is formed around the four 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.

In order to stably vibrate the piezoelectric element, an excitation electrode and a return electrode are required. Further, a detection electrode is required to detect the angular velocity. Then, the three electrodes must be efficiently arranged according to the purpose. The excitation electrode may supply energy for vibrating the vibrating body together with the piezoelectric element, and may have a certain size. Since the detection electrode must detect a small amount of charge generated in the piezoelectric element, it is desirable to form the detection electrode as large as possible at the position where the charge is generated by the Coriolis force. Since the return electrode is for stabilizing the vibration and is not directly related to the detection of the angular velocity, it suffices to secure the necessary size as the return electrode in a place other than the detection electrode forming portion, but it is preferable to have it in the center. Better to be.

According to the present invention, in the electrode structure of the angular velocity sensor, the sensor portion composed of the plate-shaped vibrating body and the plate-shaped piezoelectric element is fixed by the cylindrical supporting member, and the weight body is provided on the lower surface of the sensor portion. , A total of four detection electrodes, one in each of the positive and negative directions of two axes orthogonal to each other at the center of the piezoelectric element, are formed concentrically inside the cylindrical support member, leaving a circular portion in the center, and outside the cylindrical support member. A return electrode was formed on the central circular portion. The present invention has been completed by analyzing that the electric charges generated in the piezoelectric element due to the angular velocity are concentrated inside the cylindrical support member.

【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. Four detection electrodes 5 and return electrodes 4 are formed on the lower surface of the plate-shaped piezoelectric element 2. A total of four detection electrodes 5, one in each of the positive and negative directions of two axes (X, Y) perpendicular to the center of the surface of the piezoelectric element, are concentric inside the cylindrical support member 10 and leave a circular portion in the center. Then, the return electrode 4 was formed on the outer side of the cylindrical support member 10 and on the central circular portion. 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.
Is formed. The return electrode 4 is formed on the inner circular portion of the detection electrode 5, and the weight body 9 is further attached. The weight body 9 is for detecting the action of the Coriolis force with high sensitivity.

FIG. 4 shows an example of the excitation circuit of the angular velocity sensor according to the present invention. FIG. 5 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. The angular velocity sensor is connected to the excitation circuit (feedback circuit) shown in FIG. The feedback electrode 4 is connected to the amplifier 12.
The output of the amplifier 12 is input to the phase correction circuit 13, and the output of the phase correction circuit 13 is connected to the excitation electrode 8. The signal obtained at the feedback electrode 4 is amplified by the amplifier 12 and becomes a rectangular wave whose phase is inverted by 180 degrees. The phase of the rectangular wave is delayed by 90 degrees in the phase correction circuit 13. Further, the phase is delayed by 90 degrees by the piezoelectric element of the angular velocity sensor, and the signal is taken out from the feedback electrode 4.

FIG. 5 is a block diagram of a circuit for detecting the angular velocity from the generated charges. It is a circuit block diagram for detecting the Coriolis force proportional to the rotational angular velocity in the X-axis direction and the Y-axis direction, but since the same signal processing is performed for both the X-axis and the Y-axis, the case where the Coriolis force is generated in the X-axis direction will be described as an example. (When the rotational angular velocity acts around the Y axis). Each of the detection electrodes 5 is connected to the impedance conversion circuit 18, and the output of the impedance conversion circuit 18 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 four detection electrodes 5 are polarized in the same direction, the output signals have the same phase. 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, since the opposite detection voltages due to the Coriolis force have the same phase, the output voltages 19 and 20 have a difference in voltage output. Differential amplifier circuit 14
When subtracted by, 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 15 and passed through the filter 16 to obtain an output signal. 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 FIG.
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, particularly when the groove or the recess 11 is formed in the center of the vibrating body as employed in this embodiment. However, the portion where one end surface of the weight body 9 is fixed is hardly distorted. Therefore, it is preferable that the detection electrode is formed inside the inner diameter of the cylindrical support member and excluding the central portion where the weight body is fixed.

On the other hand, since the feedback electrode 4 forms a self-exciting circuit in cooperation with the exciting electrode 8, it is necessary to collect charges at a certain level in order to stabilize the vibration. Piezoelectric element 2 due to vibration
The portion where the strain is large is the central portion of the piezoelectric element 2, and it is efficient to form a part of the return electrode in this portion.

In the present embodiment in which the weight body is provided, since the Coriolis force generates less electric charge in the vicinity of the weight body and the vibration of the sensor unit generates more electric charge in the vicinity of the weight body, the electrodes are arranged. By taking into consideration, it is possible to obtain an efficient angular velocity sensor with high detection sensitivity.

[0017]

According to the present invention, the following effects can be obtained by employing the above-described structure. 1. Since the feedback electrode is provided at the center of the piezoelectric element and outside the cylindrical support member, stable vibration can be obtained. 2 Since the detection electrode is provided inside the cylindrical support member, the angular velocity can be detected efficiently even with a small detection electrode. 3 Stable oscillation causes less drift.

[Brief description of drawings]

FIG. 1 is a structural diagram for explaining a resonator element type piezoelectric vibration angular velocity sensor.

FIG. 2 is an exploded perspective view of an angular velocity sensor according to the present invention when viewed 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] Excitation circuit

FIG. 5 Angular velocity detection circuit

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vibrating body 2 Piezoelectric element 3 Piezoelectric element 4 Feedback electrode 5 Detection electrode 6 Electrode 7 Electrode 8 Excitation electrode 9 Weight body 10 Cylindrical support member 11 Groove 12 Amplification circuit 13 Phase correction circuit 14 Differential amplification circuit 15 Synchronous detection circuit 16 Filter 17 DC amplification circuit 18 Impedance conversion circuit 19 Output voltage 20 Output voltage

 ─────────────────────────────────────────────────── ─── 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 (2)

[Claims] 1. A plate-shaped vibrating body, a plate-shaped piezoelectric element is attached to the surface of the vibrating body, and a total of four detection electrodes are formed in positive and negative directions of two axes orthogonal to the center of the piezoelectric element. An electrode structure of an angular velocity sensor, characterized in that feedback electrodes are formed around four detection electrodes. 2. An electrode structure of an angular velocity sensor, wherein a sensor portion composed of a plate-shaped vibrating body and a plate-shaped piezoelectric element is fixed by a cylindrical supporting member, and a weight body is provided on the lower surface of the sensor portion. A total of four detection electrodes, one each in the positive and negative directions of two axes orthogonal to each other at the center of the element, are formed concentrically inside the cylindrical support member, leaving a circular portion in the center. An electrode structure of an angular velocity sensor, characterized in that a return electrode is formed on a central circular portion.