JP3139205B2 - Acceleration sensor - Google Patents

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, the present invention relates to an acceleration sensor using a piezoelectric body.

[0002]

2. Description of the Related Art FIG. 7 is an illustrative view showing one example of a conventional acceleration sensor. The acceleration sensor 1 includes a plate 2. One end of the plate 2 is fixed, and a weight 3 is attached to the other end. Further, the piezoelectric elements 4 are formed on both surfaces of the plate 2.

When acceleration is applied in a direction perpendicular to the surface of the plate 2 of the acceleration sensor 1, as shown in FIG.
Bends. 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, the deflection of the plate body 2 can be increased even with a small acceleration, and the sensitivity of the acceleration sensor 2 can be improved.

[0004]

However, when such an acceleration sensor is mounted on an automobile or the like, the impact or vibration due to irregularities on the road is often stronger than the acceleration due to the traveling of the automobile. Therefore, the acceleration sensor having such a cantilever structure has a large influence of an impact due to unevenness of a road, which may cause a malfunction or breakage.

[0005] Therefore, a main object of the present invention is to provide an acceleration sensor capable of detecting a small acceleration with high sensitivity and having high shock resistance.

[0006]

The present invention includes a plate-shaped vibrator, a piezoelectric element formed on a surface of the vibrator, and a weight formed at a longitudinal end of the vibrator. This is an acceleration sensor in which a driving signal is applied to a piezoelectric element to cause a vibrating body to vibrate in length such that expansion and contraction are reversed on both sides of a central portion in the length direction. Further, the present invention provides a plate-shaped vibrating body, a piezoelectric element formed on a surface of the vibrating body, a frame for fixing both ends of the vibrating body, and formed at both ends in the longitudinal direction of the vibrating body. By applying a drive signal to the piezoelectric element, the vibrating body is caused to vibrate in a length such that expansion and contraction are reversed on both sides of a central portion in the length direction of the vibrating body. Is an acceleration sensor configured to support a frame portion corresponding to a central portion in the length direction of the frame.

[0007]

By applying a signal to the piezoelectric element formed on the surface of the vibrating body, the vibrating body can be vibrated in the longitudinal direction, and inertia is given to the vibrating body. In this state, if acceleration is applied so as to be orthogonal to the plane of the vibrating body, the vibrating body will bend. At this time, by attaching weights to both ends of the vibrating body, the frame bends around the support portion of the frame, and the bending of the vibrating body due to acceleration increases. Further, since both ends of the vibrating body are fixed to the frame, impact resistance is increased. Furthermore, since the vibrating body vibrates so that the expansion and contraction are opposite on both sides of the center,
Mutual displacement is absorbed, and vibration leakage to the frame is small.

[0008]

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

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

[0010]

FIG. 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 an elinvar. One side of the central portion in the longitudinal direction of the vibrating body 12
Piezoelectric elements 14a, 14b so as to face each other.
Is formed. Further, on the other side of the center in the longitudinal direction of the vibrating body 12, piezoelectric elements 16a and 16b are formed so as to face both surfaces of the vibrating body 12.

The piezoelectric element 14a includes a piezoelectric plate 18a made of, for example, piezoelectric ceramic. This piezoelectric plate 1
Electrodes 20a and 22a are formed on both surfaces of 8a. Then, one electrode 22a is bonded to the vibrating body 12. Similarly, the piezoelectric element 14b includes a piezoelectric plate 18b, and electrodes 20b and 22b are formed on both surfaces thereof. Then, one electrode 22b is bonded to the vibrating body 12. In these piezoelectric elements 14a and 14b, the piezoelectric plate 18a is polarized from the electrode 20a toward the electrode 22a, and the piezoelectric plate 18b is
0b is polarized toward the electrode 22b.

The piezoelectric elements 16a and 16b are
4a and 24b, electrodes 26a and 28a and electrodes 26b and 28b are formed on both surfaces of the piezoelectric plates 24a and 24b. Then, one electrode 2 of the piezoelectric elements 16a and 16b
8a and 28b are adhered to the vibrating body 12. In these piezoelectric elements 16a and 16b, the piezoelectric plate 24a is connected to the electrode 28a.
, And the piezoelectric plate 24b is polarized from the electrode 28b toward the electrode 26b.

Both ends of the vibrating body 12 are supported by a frame 30 as supporting means. The frame 30 is, for example, 4
The vibrating body 12 is formed in a rectangular loop shape, and the vibrating body 12 is disposed at the center thereof. Weights 3 are provided at both ends in the longitudinal direction of the vibrating body 12.
2 is attached. These weights 32 are formed, for example, opposite to both surfaces of the frame 30. Further, the frame 32 is supported by portions 34a and 34b corresponding to the center in the length direction of the vibrating body 12. That is, these support portions 34a and 34b are located at the center of the portion of the frame 30 parallel to the vibrating body 12.

To use this acceleration sensor 10, for example, as shown in FIG. 2, the piezoelectric elements 14a and 14b and the piezoelectric elements 16a and 16b are connected to resistors 36a, 36b and 3 respectively.
The oscillation circuit 38 is connected via 6c and 36d. At this time, the piezoelectric elements 14a and 14b and the piezoelectric elements 16a and 16
A drive signal having the same phase is applied to b. Piezoelectric element 14
The vibrating body 12 vibrates in the length direction because the piezoelectric elements 16a and 16b are also formed to face each other. Further, since the piezoelectric elements 14a and 14b and the piezoelectric elements 16a and 16b are polarized in opposite directions, the piezoelectric elements 14a and 14b are displaced in opposite directions by a drive signal having the same phase. Therefore, as shown by a solid arrow in FIG.
When one side of the vibrating body 12 extends, the other side contracts.
1A, when one side of the vibrating body 12 contracts, the other side elongates. 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,
Since both ends of the vibrating body 12 are not displaced, vibration leakage of the vibrating body 12 to the frame 30 is small. Therefore, stable vibration can be obtained.

When the vibrating body 12 vibrates, inertia is given to the vibrating body 12. In this state, when acceleration is applied so as to be orthogonal to the surface of the vibrating body 12, the vibrating body 12 bends as shown in FIGS. 3A and 3B. When the vibrating body 12 bends, the mass of the weight 32 attached to both ends in the longitudinal direction of the vibrating body 12 causes the frame 3
0 is deformed around the support portions 34a and 34b. Thereby, the bending of the vibrating body 12 due to the acceleration increases.
Due to this bending, the vibration of the vibrating body 12 is hindered, and the resonance characteristics change. By measuring the change in the resonance characteristics, the acceleration can be detected.

In order to measure the acceleration, for example, the voltage generated in the piezoelectric elements 14a and 14b and the piezoelectric elements 16a and 16b due to the bending of the vibrating body 12 is measured. For this purpose, for example, as shown in FIG.
14b is connected to the differential circuit 40, and the piezoelectric elements 16a, 1
6b is connected to the differential circuit 42. However, it is not necessary to use two differential circuits, and it is sufficient that one of the differential circuits 40 and 42 is connected. Then, for example, by connecting the opposing piezoelectric elements 14a and 14b to the differential circuit 40, the drive signal is canceled, and only the output signal corresponding to the acceleration is measured. In addition, since the piezoelectric elements 14 a and 14 b are polarized from the outside to the inside, voltages having phases opposite to each other are generated with respect to the bending of the vibrating body 12. Therefore, these piezoelectric elements 14a, 1
By obtaining the difference between the output voltages 4b, a large output can be obtained from the differential circuit 40, and the sensitivity can be improved.
In addition, the weight 32 can increase the distortion of the vibrating body 12 due to the acceleration, and can further improve the sensitivity.

As described above, in this acceleration sensor 10,
The deflection of the vibrating body 12 with respect to the acceleration is increased by the mass of the weight 32, so that the responsiveness is good and the sensitivity is high. Further, since both ends of the vibrating body 12 are supported by the frame 30, it is possible to obtain the acceleration sensor 10 which has high shock resistance and is hardly damaged. Therefore, for example, even if the acceleration sensor 10 is mounted on an automobile or the like, the acceleration sensor 10 is not damaged by an impact due to unevenness of a road or the like, and acceleration with the advance 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 14
Although the example in which the output voltages a and b are input to the differential circuit 40 has been described,
The difference between the output voltages a and 16b may be measured. Alternatively, the difference between the output voltages of the piezoelectric elements 14a and 16a formed on the same side or the difference between the output voltages of the piezoelectric elements 14b and 16b may be measured. Further, four piezoelectric elements 14a, 14b,
The acceleration can also be detected by connecting 16a and 16b to a bridge circuit or the like.

Although the polarization directions of the piezoelectric elements 14a and 14b and the polarization directions of the piezoelectric elements 16a and 16b are reversed, these piezoelectric elements may be polarized in the same direction. In this case, the piezoelectric elements 14a and 14b and the piezoelectric elements 16a and 16b
, Drive signals having phases opposite to each other are input. Even in this case, the same vibration as in the above-described embodiment can be obtained. When such a driving method is adopted, the voltage generated in the piezoelectric elements 14a and 16a on the same side and the piezoelectric element 14a
The voltages generated at b and 16b have the same phase. Therefore, when measuring the output signal of the piezoelectric element 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.

Further, four piezoelectric elements are not necessarily required. For example, two piezoelectric elements 14a and 14b
Only one may be formed. Thus, the vibrating body 12
If the opposing piezoelectric elements are formed on both sides, the above-described vibration can be excited.

As shown in FIG. 4, in addition to the driving piezoelectric elements 14a, 14b, 16a and 16b, detection piezoelectric elements 44a, 44b, 44c and 44d may be formed. In the embodiment shown in FIG. 4, the detecting piezoelectric elements 44a to 44a-4
4 d is formed on the frame 30 side of the vibrating body 12. The acceleration applied to the acceleration sensor 10 can be detected by measuring the voltage generated in the detecting piezoelectric elements 44a to 44d due to the deflection of the vibrating body 12 due to the acceleration.

Further, as shown in FIG. 5, driving piezoelectric elements 14a and 16a may be formed on one side of the vibrating body 12, and a detecting piezoelectric element 46 may be formed on the other side of the vibrating body 12. . In this case, the detecting piezoelectric element 46 is formed so as to be line-symmetric with respect to the center in the longitudinal direction of the vibrating body 12. In the acceleration sensor 10, the oscillation circuit 38 is connected to the two driving piezoelectric elements 14a and 16a, and the vibration body 12 is vibrated. When the vibrating body 12 of the acceleration sensor 10 is not bent, the opposite expansion and contraction occurs on both sides of the center of the detecting piezoelectric element 46, so that the voltage generated in the detecting piezoelectric element 46 is canceled. Further, when the vibration body 12 bends due to the application of acceleration,
There is a difference in the way of bending on both sides of the center of the detecting piezoelectric element 46, and a voltage that is not canceled out is output. Therefore, acceleration can be detected by measuring the output voltage of the detecting piezoelectric element 46.

In each of the embodiments described above, the vibrator and the frame made of a metal material or the like are used, but these may be made of a piezoelectric ceramic. In this case, an electrode is formed on the vibrating body instead of the piezoelectric element of each of the above embodiments.
By providing a drive signal to these electrodes, the vibrating body can be vibrated in the length direction. The acceleration can be detected by measuring the output signal from the electrode.

Further, the vibrating body 12 does not necessarily need to be fixed to the frame, but may be a cantilever as shown in FIG. In this case, the weight 32 is attached to one end of the vibrating body 12 in the length direction. Also in such an acceleration sensor 10, the vibrating body 12 bends due to the acceleration, and an output corresponding to the warp can be obtained.

[Brief description of the 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 a circuit diagram for using the acceleration sensor shown in FIG.

FIG. 3A is a plan view illustrating a state of the acceleration sensor when acceleration is applied to the acceleration sensor illustrated in FIG. 1;
(B) is an illustrative sectional view thereof.

FIG. 4 is an illustrative sectional view showing another embodiment of the present invention.

FIG. 5 is an illustrative sectional view showing still another embodiment of the present invention.

FIG. 6 is an illustrative sectional view showing another embodiment of the present invention.

FIG. 7 is an illustrative view showing one example of a conventional acceleration sensor.

8 is an illustrative view showing a state when acceleration is applied to the conventional acceleration sensor shown in FIG. 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Acceleration sensor 12 Vibration body 14a, 14b Piezoelectric element 16a, 16b Piezoelectric element 30 Frame 32 Weight 34a, 34b Supporting part 44a, 44b, 44c, 44d Detection piezoelectric element 46 Detection piezoelectric element

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-51-71175 (JP, A) JP-A-53-131078 (JP, A) JP-A-2-24867 (JP, A) JP-A-1 302166 (JP, A) JP-A 2-101277 (JP, U) JP-A-59-27466 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01P 15/09 G01P 15 / 10 H03H 9/24

Claims (2)

(57) [Claims] A piezoelectric element formed on a surface of the vibrating body; and a weight formed at a longitudinal end of the vibrating body, wherein a driving signal is supplied to the piezoelectric element. An acceleration sensor in which the vibrating body is vibrated by applying voltage so that the vibrating body expands and contracts in opposite directions on both sides of a central portion in the longitudinal direction. 2. A plate-shaped vibrating body, a piezoelectric element formed on a surface of the vibrating body, a frame for fixing both ends of the vibrating body, and formed on both ends in a longitudinal direction of the vibrating body. By applying a drive signal to the piezoelectric element, the vibrating body is oscillated in length such that expansion and contraction are opposite on both sides of a central portion in the length direction thereof, An acceleration sensor configured to support the frame portion corresponding to a central portion in the length direction of the vibrator.