JPH09196965A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acceleration sensor of less temperature drift with which detection can be made in the range from static load to acceleration. SOLUTION: The acceleration sensor 10 includes the first and the second vibrators 12 and 14 formed into the figure 8-shaped and connection parts 16, 18 and 20. Extension parts 22a and 22b are formed so that they extend from the connection part 20 at the central part, and a weight 24 is attached to its tip. Supporting parts 26a and 26b formed at the edge part of the first and the second vibrators 12 and 14 are supported. On the same side of the first and the second vibrators 12 and 14, the first and the second piezoelectric elements 28 and 30 are formed. The first and the second piezoelectric elements 28 and 30 contain divided electrodes 36a and 36b and electrodes 42a and 42b, respectively. The electrodes 36a and 36b and the electrodes 42a and 42b are, with the central part in longitudinal direction of the first and the second vibrators 12 and 14 as a border, arranged on both sides.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor, and more particularly to an acceleration sensor used in a car navigation system or the like to measure acceleration of an automobile or the like.

[0002]

2. Description of the Related Art FIG. 9 is an illustrative view showing an example of a conventional acceleration sensor. The acceleration sensor 1 includes a substrate 2. The piezoelectric element 3 is formed on the substrate 2. One end of the substrate 2 is supported, and the weight 4 is attached to the other end. In this acceleration sensor 1, as shown by the arrow, when a force due to acceleration is applied in a direction orthogonal to the surface of the substrate 2, the substrate 2 bends. As a result, the piezoelectric element 3 also bends, and the piezoelectric element outputs a signal corresponding to the amount of bending, that is, a signal corresponding to acceleration. Further, there is also an acceleration sensor that detects a static load by applying a drive signal to the piezoelectric element to vibrate the substrate and measure the impedance change of the piezoelectric element due to bending due to the load.

[0003]

However, in these acceleration sensors, when the atmospheric temperature changes due to the difference in thermal expansion coefficient between the substrate and the piezoelectric element, the substrate may warp. When a signal due to such a warp is output, it is impossible to distinguish between a signal due to acceleration and a signal due to a change in ambient temperature, and there are many errors, so that a highly sensitive signal cannot be obtained.

Therefore, a main object of the present invention is to provide an acceleration sensor capable of detecting from static load to acceleration and having little temperature drift.

[0005]

According to the present invention, there are provided two plate-like vibrating bodies, a connecting portion for connecting both ends and a central portion of the two vibrating bodies, and a surface on the same side of the two vibrating bodies. A piezoelectric element that is formed and has two input / output parts, and a weight that is arranged at a position corresponding to the center of the vibrating body and that obtains an inertial force due to acceleration in the vibrating body, and the two vibrating bodies are opposite It is an acceleration sensor designed to be transformed into. In this acceleration sensor, the two input / output portions of the piezoelectric element can be arranged on both sides of the central portion of the vibrating body in the longitudinal direction as a boundary. Further, in this acceleration sensor, the two input / output portions of the piezoelectric element may be arranged on both sides of the central portion of the vibrating body in the width direction as a boundary. further,
The weight may be attached to an extension that extends from a connecting portion that connects the central portions of the two vibrating bodies, and in this case, the edges of the vibrating bodies at the longitudinal central portions of the two vibrating bodies are supported. Further, the weight may be attached to an extension portion extending from an edge portion of the vibrating body at a central portion in the longitudinal direction of the two vibrating bodies, and in this case, a connecting portion that connects the central portions of the two vibrating bodies is supported. . To use this acceleration sensor,
One input / output unit of each piezoelectric element is used for driving, the other input / output unit is used for detection, and the sum of output signals from the detection input / output unit is used as a feedback signal to drive to the driving input / output unit. An oscillating circuit for giving a signal is configured, and a difference between output signals from the input / output unit for detection is used as an acceleration detection signal.

By applying a drive signal to one input / output section of each piezoelectric element, the vibrating body is vibrated. When acceleration is applied to the acceleration sensor, an inertial force is applied to the vibrating body by the weight. Therefore, the two vibrating bodies bend in opposite directions, and a signal is output from the other input / output unit of the piezoelectric element according to the bending amount. Therefore, by measuring this signal, the acceleration can be detected. Thus, in order to bend the two vibrating bodies in opposite directions, the weight is an extension portion extending from the connecting portion connecting the two vibrating bodies,
Alternatively, it is attached to an extension extending from the edges of the two vibrators. In this case, a signal corresponding to the bending amount of the vibrating body, that is, a signal of opposite polarity corresponding to acceleration is output from the other input / output unit of each piezoelectric element. Therefore,
By taking the difference between these signals, a large output signal corresponding to the acceleration can be obtained.

When two input / output portions are formed in each piezoelectric element, the input / output portions can be arranged on both sides of the central portion in the longitudinal direction of the vibrating body as a boundary.
In addition, these input / output sections may be arranged on both sides of the center of the vibrating body in the width direction. Further, in order to vibrate the vibrating body of the acceleration sensor, it is possible to configure an oscillating circuit which gives a drive signal to the driving input / output unit by using the sum of the output signals of the detecting input / output unit as a feedback signal.

When the ambient temperature changes, the vibrating body bends due to the difference in thermal expansion coefficient between the piezoelectric element and the vibrating body. At this time, since the piezoelectric element is formed on the same side of the two vibrating bodies, the bending directions are the same. Therefore, a signal of the same polarity is output from the piezoelectric element, and it can be distinguished from a signal due to acceleration.

[0009]

According to the present invention, since the vibrating body is vibrated, it is possible to output a signal from the piezoelectric element even when a static load is applied. Therefore, it is possible to detect from static load to acceleration by this acceleration sensor.
In addition, while signals of opposite polarities are output due to acceleration, signals of the same polarity are output due to changes in ambient temperature. Therefore, if the difference between the output signals from the input / output portions for detection of the respective piezoelectric elements is calculated, a large signal is output due to acceleration, and the signal due to the change in ambient temperature is canceled. Therefore, temperature drift can be suppressed, and a highly sensitive acceleration sensor with few errors can be obtained.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments of the present invention with reference to the accompanying drawings.

[0011]

1 is a perspective view showing an example of an acceleration sensor of the present invention, FIG. 2 is a sectional view taken along line II-II of FIG. 1, and FIG. 3 is a line III-III of FIG. FIG. The acceleration sensor 10 includes a rectangular plate-shaped first vibrating body 12 and a second vibrating body 14. First
The vibrating body 12 and the second vibrating body 14 are connected by the connecting portions 16 and 18 at both ends thereof. Furthermore, the first
The vibrating body 12 and the second vibrating body 14 are connected by the connecting portion 20 at the central portion in the longitudinal direction. Therefore, the first vibrating body 12, the second vibrating body 14, and the connecting portions 16, 18, and 20 form an 8-shaped substrate.

Two extending portions 22a and 22b are formed so as to extend from both edges of the central connecting portion 20. The tips of these extension portions 22a and 22b are aligned, and a weight 24 is attached to the tips. In addition, in the central portions of the first vibrating body 12 and the second vibrating body 14 in the longitudinal direction, the supporting portion 2 is provided at the edge portions of these vibrating bodies 12 and 14.
6a and 26b are formed. And these support parts 2
6a and 26b are supported. These first and second vibrating bodies 12, 14, connecting portions 16, 18, 20, extension portion 2
In order to form the 2a, 22b and the supporting portions 26a, 26b, a rectangular plate-shaped metal plate having a convex portion to be the supporting portions 26a, 26b is prepared, and a reverse U-shaped cut is formed in the metal plate. The metal plate may be formed and bent along the notch with the connecting portion 20 as a reference to form the extension portions 22a and 22b.

A first piezoelectric element 28 is formed on one surface of the first vibrating body 12. Further, the second piezoelectric element 30 is formed on one surface of the second vibrating body 14. First
The piezoelectric element 28 includes a piezoelectric layer 32 formed of, for example, piezoelectric ceramic. An electrode 34 is formed on the entire surface of one surface of the piezoelectric element 32. Further, the piezoelectric layer 32
On the other surface of the two divided electrodes 36a, 36b
Is formed. Then, the one electrode 34 is bonded to the first vibrating body 12. At this time, the divided electrodes 36
The a and 36b are arranged on both sides of the central portion of the first vibrating body 12 in the longitudinal direction as a boundary. These electrodes 36
a and 36b are used as signal input / output units.

Similarly, the second vibrating body 14 includes a piezoelectric layer 38, and an electrode 40 is formed on the entire surface on one surface thereof. Further, on the other surface of the piezoelectric layer 38, two divided
Two electrodes 42a and 42b are formed. These electrodes 4
2a and 42b are arranged on both sides of the central portion of the second vibrating body 14 in the longitudinal direction as a boundary. These electrodes 42
a and 42b are used as signal input / output units. Then, the electrode 36a of the first piezoelectric element 28 and the electrode 42a of the second piezoelectric element 30 are used for driving to vibrate these vibrating bodies 12, 14. In addition, the electrode 36 b of the first piezoelectric element 28 and the electrode 4 of the second piezoelectric element 30
2b is used for detection to obtain a signal corresponding to acceleration.

In the acceleration sensor 10, as shown in FIG. 4, the output signals of the detection electrodes 36b and 42b are combined and input to the oscillation circuit 44. The oscillation circuit 44 includes an AC amplification circuit 46 and a phase correction circuit 48. Then, the output signals from the electrodes 36b and 42b are input to the AC amplification circuit 46, the amplified signal is phase-corrected by the phase correction circuit 48, and is input to the electrodes 36a and 42a as a drive signal.

The electrode 36b of the first piezoelectric element 28 and the electrode 42b of the second piezoelectric element 30 are connected to the two input terminals of the differential amplifier circuit 50, respectively. The differential amplifier circuit 50 is connected to the synchronous detection circuit 52. In the synchronous detection circuit 52, the output signal of the differential amplifier circuit 50 is detected in synchronization with the signal of the phase correction circuit 48 of the oscillation circuit 44.
The synchronous detection circuit 52 is connected to the smoothing circuit 54, and the smoothing circuit 54 is further connected to the DC amplification circuit 56.

In this acceleration sensor 10, the oscillation circuit 44
The electrode 36a of the first piezoelectric element 28 and the second
A drive signal is applied to the electrode 42a of the piezoelectric element 30 of FIG.
As a result, the two piezoelectric elements 28 and 30 are synchronously displaced, and the first vibrating body 12 and the second vibrating body 14 vibrate in the lengthwise direction. Due to the vibrations of the first and second vibrating bodies 12 and 14, the electrodes 36b and 42b forming portions also vibrate, and the same signals are output from these electrodes 36b and 42b. This signal is combined and fed back to the oscillation circuit 44. Further, these signals are canceled by the differential amplifier circuit 50, and no signal is output from the differential amplifier circuit 50. Therefore, the output signal of the DC amplification circuit 56 is also 0, and it can be seen that acceleration is not applied.

In this state, when a force due to acceleration is applied from the first vibrating body 12 side toward the second vibrating body 14 side as shown by the arrow in FIG. 5, the weight 24 causes the first vibrating body to move. A force is applied to 12 and the second vibrating body 14. Thereby, the first vibrating body 12 and the second vibrating body 14 are
Bend in opposite directions. A signal is output from the first piezoelectric element 28 and the second piezoelectric element 30 by this bending, but since the bending states of the electrode 36b forming portion and the electrode 42b forming portion are opposite, these electrodes 36b,
A signal of opposite polarity is output from 42b. Therefore, a large output signal can be obtained from the differential amplifier circuit 50.

The output signal of the differential amplifier circuit 50 is detected in the synchronous detection circuit 52 in synchronization with the signal of the phase correction circuit 48 of the oscillation circuit 44. The synchronous detection circuit 52 detects both the positive part and the negative part of the output signal of the differential amplifier circuit 50, or both of the positive and negative phase-inverted waves. The detected signal is smoothed by the smoothing circuit 54 and further amplified by the DC amplification circuit 56. The output signal of the DC amplifier circuit 56 is the first and second vibrating bodies 12, 1
It is a signal corresponding to the bending amount of 4, that is, the acceleration. Therefore, the applied acceleration can be detected by measuring this output signal. When acceleration is applied in the opposite direction, the first and second vibrating bodies 12, 1
Since the bending direction of 4 is opposite, the polarity of the signal detected by the synchronous detection circuit 52 changes, and the polarity of the output signal of the DC amplification circuit 56 also changes. Therefore, the direction of acceleration can be known from the polarity of the output signal of the DC amplification circuit 56.

In this acceleration sensor 10, since the first vibrating body 12 and the second vibrating body 14 are vibrated, signals are always output from the first piezoelectric element 28 and the second piezoelectric element 30. Therefore, a signal corresponding to static weighting can be output. Therefore, the acceleration sensor 10 can detect from static load to acceleration.

Further, the first and second piezoelectric elements 28, 3
Since 0 is formed on the same side surface of the first and second vibrating bodies 12 and 14, when the atmospheric temperature changes, the vibrating bodies 12 and 14 bend in the same direction due to the difference in thermal expansion coefficient. . Therefore, due to such curvature, the electrode 36
The signals output from b and 42b are the same and are canceled by the differential amplifier circuit 50. Therefore, it is possible to obtain an acceleration sensor which is less affected by the change in the ambient temperature, has a small error, and has good sensitivity.

In the circuit shown in FIG. 4, the electrodes 36a,
Although the drive signal is given to 42a and the output signals from the electrodes 36b and 42b are used for acceleration detection, these relationships may be reversed. Further, a drive signal may be given to the electrodes 36a and 42b, and the output signals from the electrodes 36b and 42a may be used for acceleration detection. Also, as shown in FIG.
The electrodes 36a and 36b of the first piezoelectric element 28 may be arranged on both sides of the first vibrating body 12 with the central portion in the width direction as a boundary. Similarly, the electrode 42 of the second piezoelectric element 30
The a and 42b may be arranged on both sides of the center of the second vibrating body 14 in the width direction as a boundary. In this case, for example, a drive signal is given to the two outer electrodes 36a and 42b, and an output signal from the two inner electrodes 36b and 42a is used for acceleration detection.

Further, as shown in FIG. 7, the first and second
The extension portions 58a and 58b may be formed so as to extend from the edge portions of the vibrating bodies 12 and 14 at the longitudinal center portions of the vibrating bodies 12 and 14. Then, the weight 24 is attached between the extension portions 58a and 58b. In this case, the support portion 60 is formed so as to extend from the connecting portion 20 in the central portion. The support portion 60 may be a single plate as shown in FIG. 7, instead of being formed by cutting a metal plate and bending it.
Even in such a structure, similarly to the above-described acceleration sensor, by applying acceleration, the first and second vibrating bodies 1
2, 2 and 14 can be bent in opposite directions.

Further, as shown in FIG. 8, bent portions 62 may be formed at the ends of the first and second vibrating bodies 12, 14 and the ends of the connecting portions 16, 18. Such a bent portion 62 acts as a reinforcing material for preventing the end portions of the first and second vibrating bodies 12 and 14 from being deformed. Therefore, only the bending due to the acceleration can be generated in the first and second vibrating bodies 12 and 14, and a highly accurate acceleration sensor can be obtained.

Further, in the above acceleration sensor, the two input / output portions are formed by dividing the electrodes of the respective piezoelectric elements, but two piezoelectric elements may be used as the input / output portions. In this case, two piezoelectric elements are formed on the first vibrating body 12, and two piezoelectric elements are formed on the second vibrating body 14.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of an acceleration sensor of the present invention.

FIG. 2 is a sectional view taken along line II-II in FIG.

FIG. 3 is a sectional view taken along line III-III in FIG. 1;

FIG. 4 is a block diagram showing a circuit for using the acceleration sensor shown in FIG.

FIG. 5 is a perspective view showing a state of the acceleration sensor when acceleration is applied.

FIG. 6 is a perspective view showing another example of the acceleration sensor of the present invention.

FIG. 7 is a perspective view showing still another example of the acceleration sensor of the present invention.

FIG. 8 is a perspective view showing another example of the acceleration sensor of the present invention.

FIG. 9 is an illustrative view showing one example of a conventional acceleration sensor.

[Explanation of reference numerals] 10 acceleration sensor 12 first vibrating body 14 second vibrating body 16,18 connecting part 20 connecting part 22a, 22b extension part 24 weights 26a, 26b supporting part 28 first piezoelectric element 30 second Piezoelectric element 44 Oscillation circuit 46 AC amplification circuit 48 Phase correction circuit 50 Differential amplification circuit 52 Synchronous detection circuit 54 Smoothing circuit 56 DC amplification circuit 58a, 58b Extension part 60 Support part 62 Bent part

Claims (6)

[Claims] 1. A plate-shaped vibrating body, a connecting part for connecting both ends and a central part of the two vibrating bodies, and two input / output parts formed on the same side surface of the two vibrating bodies. And a piezoelectric element having a weight for obtaining an inertial force due to acceleration, the piezoelectric element being arranged at a position corresponding to a central portion of the vibrating body, and the two vibrating bodies being deformed in opposite directions by the acceleration. Acceleration sensor 2. The acceleration sensor according to claim 1, wherein the two input / output portions of the piezoelectric element are arranged on both sides of a central portion in the longitudinal direction of the vibrating body as boundaries. 3. The acceleration sensor according to claim 1, wherein the two input / output portions of the piezoelectric element are arranged on both sides of a center portion in the width direction of the vibrating body as boundaries. 4. The weight is attached to an extension portion extending from the connecting portion connecting the central portions of the two vibrating bodies,
The acceleration sensor according to claim 1, wherein an edge portion of the vibrating body at a central portion in the longitudinal direction of the two vibrating bodies is supported. 5. The weight is attached to an extension portion extending from an edge portion of the vibrating body at a central portion in the longitudinal direction of the two vibrating bodies, and the connecting portion that connects the central portions of the two vibrating bodies is supported. The acceleration sensor according to any one of claims 1 to 3, which is performed. 6. One of the input / output portions of each of the piezoelectric elements is used for driving, the other input / output portion is used for detection, and the sum of output signals from the input / output portions for detection is used as a feedback signal for the drive. 6. An oscillating circuit for supplying a drive signal to an input / output unit for use in a vehicle, and a difference between output signals from the input / output unit for detection is used as an acceleration detection signal. Acceleration sensor.