JPH09196685A - Angular velocity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a compact and light-weight sensor of high detecting sensitivity and high detecting accuracy, by attaching a sheet-like piezoelectric element at one or both faces of a sheet-like vibrating body, forming at least an excitation electrode and a detection electrode to the piezoelectric element, setting a weight body, and supporting a node part by a supporting member. SOLUTION: A circular sheet-like piezoelectric element 22 having an electrode 26 at a lower face and four detection electrodes 25 serving also as an axcitation electrode at an upper face is attached to an upper face of a circular sheet-like vibrating body 21. At this time, plane centers of the element 22 and vibrating body 21 are agreed. A circular sheet-like piezoelectric element 23 having an electrode 27 at an upper face and a feedback electrode 28 at a lower face is attached to a lower face of the vibrating body 21 so that the plane centers of the element 23 and vibrating body 21 agree with each other. A weight body 29 is attached to a lower face of the electrode 28 so that the center of the weight body passes the plane center of the element 23. This sensor is constituted in this manner. A cylindrical supporting member 30 is fixed on a node part 24, which is secured to a substrate 32 by a wire 31. When the electrode 25 is excited, the element 22 and vibrating body 21 vibrate. Charges of the electrode 25 subsequent to the movement of the weight body 29 by a Coriolis force are detected.

Description

Detailed Description of the Invention

[0001]

The present invention relates to 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.

[0005] It has been desired that one angular velocity sensor can detect angular velocities around two axes. (Hereinafter, an angular velocity sensor capable of detecting angular velocities around two axes is referred to as a two-axis angular velocity sensor.) In response to this demand, a piezoelectric element (hereinafter, a material exhibiting a piezoelectric effect is collectively referred to as a piezoelectric element on the surface of a vibrating body) A sensor has been developed that detects the angular velocity by measuring the amount of electric charge that changes when the piezoelectric element is deformed by the angular velocity after attaching the piezoelectric element. FIG. 2 is an exploded perspective view of the angular velocity sensor as seen 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. An electrode 7 is provided on the lower surface of the vibrating body 1 and a return electrode 8 is provided on the lower surface.
The piezoelectric element 3 provided with is attached. A weight 9 is attached to the lower surface of the return electrode 8 to form a sensor unit.
The node of the bending vibration is fixed to the sensor unit by the cylindrical support member 10.

Since the electrode 6 and the vibrating body 1 are electrically connected and bonded to each other, 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 brought together. Vibrate. The detection electrodes 5 also serving as four excitation electrodes are provided inside the inner diameter of the cylindrical support member 10. As shown in the figure, the cylindrical support member 10 is fixed at two places with an L-shaped wire 11, and the other end of the wire 11 is fixed to the substrate.

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

[0008]

In the case of a resonance type angular velocity sensor, in order to increase the detection sensitivity, a method of trimming the vibration frequency of a drive (excitation) mode and a detection mode by irradiating a laser beam to a weight, for example, is used. It is good to be close by. As a premise, the mechanical quality factor (Qm) needs to be set to a relatively high value. If the mechanical quality factor (Qm) is too high, there is a problem that the response speed becomes slow. However, if the mechanical quality factor (Qm) is high to some extent, the vibration mode is stabilized and the detection sensitivity is increased. Conversely, if the mechanical quality factor (Qm) is low, the strength of resonance will be low not only in the drive mode but also in the detection mode, and it will not be possible to give sufficient deformation to the piezoelectric element. Therefore,
The generated charge obtained from the detection electrode is reduced, and the detection sensitivity is reduced. Further, when comparing the vibrating body and the piezoelectric element alone, the vibrating body has a higher mechanical quality coefficient (Qm). Therefore, the smaller the vibrating body of the piezoelectric element, the higher the mechanical quality coefficient (Qm) as the sensor section. .

In order to increase the detection accuracy, it is preferable to stabilize the vibration mode and the excitation frequency.
In particular, the elastic modulus of the vibrating body and the piezoelectric element changes in response to a temperature change (the ratio of the change in the elastic modulus to the temperature change is referred to as a temperature coefficient of the elastic modulus), and the excitation frequency tends to become unstable. In order to stabilize the temperature, the temperature coefficient of the elastic modulus of the combined vibrating body and piezoelectric element should be close to zero. Generally, the temperature coefficient of the elastic modulus of a piezoelectric element (PZT) is negative. For this reason, a constant elastic metal material such as an elinvar material is used for the vibrator, and the temperature coefficient of the elastic modulus is set to be positive by heat treatment, and the temperature coefficient of the elastic modulus obtained by combining the vibrator and the piezoelectric element is brought close to zero. I have. However, since the vibrating body and the piezoelectric element are adhered with an adhesive, even if the temperature coefficient of the elastic modulus of the vibrating body and the piezoelectric element is set, the excitation frequency is likely to be unstable due to the interposition of the adhesive. It is desirable that the area occupied by the adhesive is as small as possible.

It is desirable that the adhesive layer between the vibrating body and the piezoelectric element be uniform over the entire attachment surface of the piezoelectric element. For example, if there is a void (a portion where a space is formed without the adhesive wrapping around) in the adhesive layer, the excitation frequency becomes unstable. Further, at the time of detection, the stress distribution caused by the deformation becomes non-uniform, so that the generated charges are also non-uniform and the variations among the individual angular velocity sensors increase. For that purpose, an adhesive is applied and the entire surface of the piezoelectric element is cured while being pressed. The amount of application is such that the adhesive slightly protrudes from the piezoelectric element. However, if the adhesive hardens by sticking out from the outer periphery of the vibrating body,
Not convenient for assembly. Since the sensor unit is assembled with reference to the outer shape of the vibrating body or the piezoelectric element, the protruding adhesive cannot fix the mutual positional relationship between the respective members to a predetermined position. If the assembling accuracy is poor, the adjustment time in the process increases, which is disadvantageous in terms of performance and manufacturing cost. Further, in order to reduce the unit cost in terms of cost, it is desirable that each member has a shape that is easy to process.

[0011]

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

A plate-shaped vibrating body and a plate-shaped piezoelectric element attached to one side or both sides of the vibrating body, at least an excitation electrode and a detection electrode are formed on the piezoelectric element, and a weight body is provided. The node portion is supported by the support member. The support member preferably has a cylindrical shape. The cylindrical shape is easy to process and can be manufactured at low cost. The outer shape of the piezoelectric element is smaller than the outer shape of the vibrating body, and the piezoelectric element is attached so as not to protrude from the outer circumference of the vibrating body. Preferably, the piezoelectric element is attached inside the node portion for bending vibration. Since the vibrating body is easily bent, and the amount (area) of the adhesive interposed between the piezoelectric element and the vibrating body is reduced, the change of the excitation frequency with respect to the temperature change becomes small, and the excitation frequency is stabilized and detected. Accuracy is improved. Moreover, the adhesive does not stick out from the vibrating body, and the assembling accuracy is improved.

[0013]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail with reference to the drawings. FIG. 4 is a partial cross-sectional top view of the embodiment of the present invention. FIG. 5 is a sectional view of an embodiment of the present invention. On the upper surface of the disk-shaped vibrating body 21, an electrode 26 is provided on the lower surface and 4
A disk-shaped piezoelectric element 22 provided with a detection electrode 25 also serving as one excitation electrode is attached so that the center of the surface of the piezoelectric element 22 and the center of the surface of the vibrating body 21 coincide with each other. Vibrator 21
An electrode 27 is provided on the lower surface of the
The disk-shaped piezoelectric element 23 provided with is attached so that the center of the surface of the piezoelectric element 23 and the center of the surface of the vibrating body 21 coincide with each other. A weight 29 is provided on the lower surface of the return electrode 28.
The sensor unit is formed by pasting so that the central axis of 9 passes through the center of the surface of the piezoelectric element 23. Cylindrical support member 30
Is fixed on the node part 24 of the bending vibration of the sensor part. The cylindrical support member may support the node portion even if it is partial. As a modified example, a recess may be provided in the opening as shown in FIG. The diameters of the piezoelectric element 22 and the piezoelectric element 23 are set to be smaller than the diameter of the node portion 24. Therefore, the protruding adhesive 33 does not reach the outer peripheral portion of the vibrating body 21.

Since the electrode 26 and the vibrating body 21 are electrically connected and adhered to each other, when an alternating current is applied to the detecting electrode 25 which also serves as the vibrating body and the exciting electrode, the piezoelectric element 22 vibrates and the vibrating body 21 vibrates together. To do. The cylindrical support member 30 is fixed at two places with a wire 31, and the other end of the wire is fixed to the substrate 32.

When the angular velocity acts on the angular velocity sensor, the weight 29 moves due to the Coriolis force, and the sensor portion is deformed to generate charges on the detection electrode. The direction and strength of the angular velocity can be detected by the amount of electric charge generated in the four detection electrodes 25. Although the embodiment is an example using two piezoelectric elements, the number of piezoelectric elements may be one by devising the electrode arrangement. Rather, since there are few parts where the adhesive is interposed, one piezoelectric element is more advantageous for temperature change.

The vibrating body 21 is made of an elastic material as a constant elastic material, and the piezoelectric elements 22 and 23 are made of PZT. The vibrating body 21 and the piezoelectric elements 22 and 23 are adhered to each other using an epoxy adhesive. Electrodes were formed on the flat surfaces of the piezoelectric elements 22 and 23 by vapor deposition using a thin film of an alloy such as Ag-Cr or Ni-Cr. Of course, the electrodes may be formed by using a method such as sputtering or screen printing. Weight 2
9 is SUS303, the cylindrical support member 30 is a metallic material having a spring property (for example, phosphor bronze), and the wire 31 is tungsten. The material is not limited to this as long as it satisfies a predetermined function. Further, the fixing method in assembly may be adhesion, welding, or the like.

[0017]

According to the present invention, the following effects can be obtained by employing the above-described structure. 1 By making the outer shape of the piezoelectric element smaller than the outer shape of the vibrating body, the mechanical quality factor (Qm) is increased and the detection sensitivity is increased. 2 By making the outer shape of the piezoelectric element smaller than the outer shape of the vibrating body, the excitation frequency is stabilized against temperature changes, and the detection accuracy is improved. 3 By making the outer shape of the piezoelectric element smaller than the outer shape of the vibrating body, when the piezoelectric element is attached to the vibrating body, the adhesive does not stick out of the vibrating body, and the outer shape of the vibrating body can be accurately assembled. 4. The size of the piezoelectric element can be reduced and the weight of the product itself can be reduced. 5 Piezoelectric element can be made smaller and the cost of parts can be reduced. 6 By using a cylindrical support member, parts can be easily processed,
Manufacturing cost is reduced.

[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 a conventional example of an angular velocity sensor according to the present invention as seen obliquely from above.

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

FIG. 4 is a partial cross-sectional top view of an angular velocity sensor according to an embodiment of the present invention.

FIG. 5 is a sectional view of an embodiment of an angular velocity sensor according to the present invention.

FIG. 6 is a perspective view of a modified example of the angular velocity sensor according to the present invention, which is viewed obliquely from above.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vibrating body 2 Piezoelectric element 3 Piezoelectric element 5 Detection electrode also serving as an exciting electrode 6 Electrode 7 Electrode 8 Returning electrode 9 Weight 10 Cylindrical support member 11 Wire 21 Vibrating body 22 Piezoelectric element 23 Piezoelectric element 24 Node section 25 Exciting electrode Combined detection electrode 26 electrode 27 electrode 28 feedback electrode 29 weight body 30 cylindrical support member 31 wire 32 substrate 33 adhesive

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

Claims (3)

[Claims] 1. A plate-shaped vibrating body, and a plate-shaped piezoelectric element attached to one or both surfaces of the vibrating body, wherein at least an excitation electrode and a detection electrode are formed on the piezoelectric element, and a weight body is provided. In an angular velocity sensor having a supporting member for supporting a node portion, the outer shape of the piezoelectric element is smaller than the outer shape of the vibrating body, and the piezoelectric element is attached so as not to protrude from the outer circumference of the vibrating body. An angular velocity sensor characterized by. 2. The angular velocity sensor according to claim 1, wherein the support member has a cylindrical shape. 3. The angular velocity sensor according to claim 1, wherein the plate-shaped piezoelectric element is attached inside the node portion of the bending vibration of the sensor portion.