JPH06249873A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To obtain an acceleration sensor which can detect even the fine acceleration with high sensitivity and possesses the large shock resistance. CONSTITUTION:An acceleration sensor 10 includes a plate-shaped vibrating body 12. A weight 14 is installed at the center part of the vibrating body 12. On both the sides of the weight 14, piezoelectric elements 16a and 16b and piezoelectric elements 18a and 18b are formed so as to be opposed to both surfaces of the vibrating body 12. The piezoelectric plates 20a and 20b of the piezoelectric elements 16a and 16b are polarized toward the inside from the outside, and the piezoelectric plates 26a and 26b of the piezoelectric elements 18a and 18b are polarized toward the outside from the inside. Both the edges of the vibrating body 12 are supported by a supporting frame 32. Each driving signal having the same phase is applied to the piezoelectric elements 16a, 16b, 18a, and 18b, which are vibrated in the lengthwise direction of the vibrating body 12. At this time, the vibrating body 12 vibrates so that extension and contraction become reverse, on both the sides of the weight 14. Then, each output voltage of the piezoelectric elements 16a and 16b is measured through a differential circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor,
In particular, for example, it relates to an acceleration sensor using a piezoelectric body.

[0002]

2. Description of the Related Art FIG. 3 is an illustrative view showing an example of a conventional acceleration sensor. The acceleration sensor 1 includes a plate body 2. One end of the plate body 2 is fixed, and the weight 3 is attached to the other end. Further, piezoelectric elements 4 are formed on both sides of the plate body 2.

When acceleration is applied in a direction orthogonal to the surface of the plate body 2 of the acceleration sensor 1, as shown in FIG.
Deflection occurs in the. As a result, a voltage corresponding to the bending is generated in the piezoelectric element 4. By measuring this voltage, the acceleration can be detected. By attaching the weight 3, it is possible to increase the flexure of the plate 2 even with a small acceleration, and improve the sensitivity of the acceleration sensor 2.

[0004]

However, when such an acceleration sensor is mounted on an automobile or the like, the impact or vibration due to the unevenness of the road is often stronger than the acceleration due to the traveling of the automobile. Therefore, the acceleration sensor having such a cantilever structure is greatly affected by the impact due to the unevenness of the road, which may lead to malfunction or damage.

Therefore, a main object of the present invention is to provide an acceleration sensor which can detect even a small acceleration with high sensitivity and has a high impact resistance.

[0006]

According to the present invention, there is provided a plate-shaped vibrating body, and piezoelectric elements formed so as to face each other on both sides of the vibrating body.
The vibrating body includes a weight formed in the central portion of the vibrating body and supporting means for supporting both ends of the vibrating body. It is an acceleration sensor that vibrates for a length such that extension and contraction are opposite to each other.

[0007]

Since the piezoelectric element is formed on both sides of the vibrating body, the vibrating body can be vibrated in the longitudinal direction, and inertia is given to the vibrating body and the weight. In this state, when acceleration is applied so as to be orthogonal to the surface of the vibrating body, the vibrating body is bent. By attaching the weight to the central portion of the vibrating body, the flexure of the vibrating body due to acceleration increases. Further, since both ends of the vibrating body are supported, impact resistance is increased. Further, since the vibrations vibrate so that the expansion and the contraction are opposite to each other on both sides of the central portion of the vibrating body, the mutual displacement is absorbed and the vibration leakage to the supporting means is small.

[0008]

According to the present invention, even if a minute acceleration is applied, the vibrating body is largely bent. Therefore, the voltage generated in the piezoelectric element increases, and the detection sensitivity can be increased. Further, since this acceleration sensor has a double-supported beam structure, it has a high impact resistance, and even if it is mounted on an automobile or the like, it will not be damaged by the impact due to the unevenness of the road. Further, since there is little leakage of vibration of the vibrating body, stable vibration can be obtained and the characteristics can be stabilized.

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

[0010]

1A is a plan view showing an embodiment of the present invention, and FIG. 1B is a sectional view thereof. The acceleration sensor 10 includes a plate-shaped vibrating body 12. The vibrating body 12 is formed of a constant elastic metal material such as elinvar. A weight 14 is attached to the center of the vibrating body 12. Piezoelectric elements 16a and 16b are formed on both sides of the vibrating body 12 on one side of the weight 14 so as to face each other. Also,
On the other side of the weight 14, piezoelectric elements 18a and 18b are formed on both surfaces of the vibrating body 12 so as to face each other.

The piezoelectric element 16a includes a piezoelectric plate 20a made of, for example, a piezoelectric ceramic. This piezoelectric plate 2
Electrodes 22a and 24a are formed on both surfaces of 0a. Then, one electrode 24a is bonded to the vibrating body 12. Similarly, the piezoelectric element 16b includes a piezoelectric plate 20b, and electrodes 22b and 24b are formed on both surfaces thereof. Then, one electrode 24b is bonded to the vibrating body 12. In these piezoelectric elements 16a and 16b, the piezoelectric plate 20a is polarized from the electrode 22a toward the electrode 24a, and the piezoelectric plate 20b is connected to the electrode 2a.
It is polarized from 2b towards the electrode 24b.

The piezoelectric elements 18a and 18b are the piezoelectric plate 2
Electrodes 28a and 30a and electrodes 28b and 30b are formed on both surfaces of the piezoelectric plates 26a and 26b, including 6a and 26b. Then, one electrode 3 of the piezoelectric elements 18a and 18b
0a and 30b are bonded to the vibrating body 12. In these piezoelectric elements 18a and 18b, the piezoelectric plate 26a has an electrode 30a.
To the electrode 28a, the piezoelectric plate 26b is polarized from the electrode 30b to the electrode 28b.

Both ends of the vibrating body 12 are supported by a supporting frame 32 as a supporting means. The support frame 32 is formed in, for example, a quadrangular loop shape, and the vibrating body 12 is arranged in the center thereof. Note that the vibrating body 12 may be supported by a method other than the support frame as long as it can support both ends of the vibrating body 12.

To use this acceleration sensor 10, an oscillation circuit is connected to the piezoelectric elements 16a and 16b and the piezoelectric elements 18a and 18b. At this time, the piezoelectric elements 16a, 1
Drive signals of the same phase are applied to 6b and the piezoelectric elements 18a and 18b. Since the piezoelectric elements 16a and 16b are formed to face each other and the piezoelectric elements 18a and 18b are also formed to face each other, the vibrating body 12 vibrates in the longitudinal direction. Further, since the piezoelectric elements 16a and 16b and the piezoelectric elements 18a and 18b are polarized in opposite directions, they are displaced in opposite directions by the drive signals of the same phase. Therefore, as shown by the solid arrow in FIG.
When one side of the vibrating body 12 extends around 4, the other side contracts. Further, as indicated by the one-dot chain line arrow in FIG. 1A, when one side of the vibrating body 12 contracts, the other side thereof expands. In this way, the vibrating body 12 vibrates in its length direction. Therefore, the displacement of both sides of the vibrating body 12 is absorbed, and both ends of the vibrating body 12 are not displaced,
There is little vibration leakage of the vibrating body 12 to the support frame 32. Therefore, stable vibration can be obtained.

The vibration of the vibrating body 12 gives inertia to the vibrating body 12 and the weight 14. In this state, when acceleration is applied so as to be orthogonal to the surface of the vibrating body 12, the vibrating body 12 is bent as shown in FIG. Due to this bending, a voltage is generated in the piezoelectric elements 16a and 16b and the piezoelectric elements 18a and 18b. Therefore, the acceleration can be detected by measuring these voltages. At this time, for example, the opposing piezoelectric elements 16
By connecting a and 16b to the differential circuit, the drive signal is canceled and only the output signal corresponding to the acceleration is measured. Further, since the piezoelectric elements 16a and 16b are polarized from the outer side to the inner side, respectively, the vibrating body 12
A voltage having an opposite phase is generated with respect to the deflection. Therefore, if the difference between the output voltages of the piezoelectric elements 16a and 16b is calculated, a large output can be obtained from the differential circuit and the sensitivity can be improved. Further, the weight 14 can increase the distortion of the vibrating body 12 due to the acceleration, and the sensitivity can be further improved by adjusting the weight 14 according to the detection range of the acceleration.

As described above, in the acceleration sensor 10,
Since the weight 14 is vibrated, it has good responsiveness and high sensitivity. Further, since the vibrating body 12 has the double-supported beam structure, it is possible to obtain the acceleration sensor 10 that has high impact resistance and is not easily damaged. Therefore, for example, even if the acceleration sensor 10 is mounted on an automobile or the like, it is not damaged by the impact due to the unevenness of the road, and the acceleration due to the traveling of the automobile can be detected with high sensitivity. Further, the vibrating body 12 can be manufactured by press punching or etching, and can be easily manufactured at low cost.

In the above embodiment, the piezoelectric element 16
Although the output voltages of a and 16b are input to the differential circuit, of course, the difference between the output voltages of the piezoelectric elements 18a and 18b may be measured. In addition, the piezoelectric elements 16a and 18 formed on the same side
The difference in the output voltage of a or the difference in the output voltage of the piezoelectric elements 16b and 18b may be measured. Furthermore, four piezoelectric elements 1
The acceleration can be detected by connecting 6a, 16b, 18a, 18b to a bridge circuit or the like.

Although the polarization directions of the piezoelectric elements 16a and 16b are opposite to the polarization directions of the piezoelectric elements 18a and 18b, these piezoelectric elements may be polarized in the same direction. In this case, the piezoelectric elements 16a and 16b and the piezoelectric elements 18a and 18b
Drive signals having mutually opposite phases are input to. Even in this case, it is possible to obtain the same vibration as that of the above-described embodiment. When such a driving method is adopted, the voltage generated in the piezoelectric elements 16a, 18a on the same side and the piezoelectric element 16
The voltages generated in b and 18b have the same phase. Therefore, when measuring the output signals of the piezoelectric elements on the same side, a large output can be obtained by using the summing circuit. At this time, since the drive signals input to these piezoelectric elements have opposite phases, they can be canceled by the summing circuit.

Furthermore, four piezoelectric elements are not necessarily required, and for example, two opposing piezoelectric elements 16a, 16b are provided.
Only one may be formed. In this way, the vibrating body 12
If the piezoelectric elements facing each other are formed, the above-mentioned vibration can be excited.

[Brief description of drawings]

FIG. 1A is a plan view showing an embodiment of the present invention, and FIG. 1B is a sectional view thereof.

FIG. 2 is an illustrative view showing a state of a vibrating body when acceleration is applied to the acceleration sensor shown in FIG.

FIG. 3 is an illustrative view showing one example of a conventional acceleration sensor.

FIG. 4 is an illustrative view showing a state when acceleration is applied to the conventional acceleration sensor shown in FIG.

[Explanation of symbols]

 10 Acceleration Sensor 12 Vibration Body 14 Weight 16a Piezoelectric Element 16b Piezoelectric Element 18a Piezoelectric Element 18b Piezoelectric Element 32 Support Frame

Claims (1)

[Claims] 1. A plate-shaped vibrating body, a piezoelectric element formed on both sides of the vibrating body, a weight formed in a central portion of the vibrating body, and a support for supporting both ends of the vibrating body. Means for applying a drive signal to the piezoelectric element so as to cause the vibrating body to vibrate for a length such that expansion and contraction are opposite on both sides of the central portion in the longitudinal direction, Sensor.