JPH09133705A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acceleration sensor which is excellent in the detection sensitivity, dispenses with a large supporting structure or a stopper mechanism, and is difficult to break by the impact, etc. SOLUTION: An acceleration sensor 10 includes a detecting piece 12 consisting of a base plate 14 and a piezo element 18. One end of the base plate 14 is fixed to a base, etc., by a supporting member 16. A ring-shaped added mass body 28 is fitted to the other end of the base plate 14 through a spring 26. A sliding shaft 30 is inserted at a center part of the added mass body 28 so that the added mass body 28 can slide in the direction orthogonal to the surface of the base plate 14.

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, for example, an acceleration sensor having an additional mass body for increasing displacement of a detection piece due to acceleration.

[0002]

2. Description of the Related Art FIG. 6 is a perspective view showing an example of a conventional acceleration sensor. The acceleration sensor 1 includes a detection piece 2. The detection piece 2 includes a substrate 3 having a rectangular plate shape. The piezoelectric element 4 is formed on one surface of the substrate 3. One end of the substrate 3 is supported by the indicating member 5 and has a cantilever structure. further,
The additional mass body 6 is attached to the other end of the substrate 3.

In this acceleration sensor 1, when acceleration is applied in a direction orthogonal to the surface of the substrate 3, the substrate 3 bends in accordance with the magnitude of the acceleration. When the substrate 3 bends, the piezoelectric element 4 also bends, and electric charges are generated in the piezoelectric element 4 corresponding to the amount of bending. Therefore, the applied acceleration can be detected by measuring the output signal of the piezoelectric element 4.
At this time, since the additional mass body 6 is attached to the substrate 3, as compared with the acceleration sensor without the additional mass body,
The curvature of the substrate 3 when acceleration is applied can be increased. Therefore, the output signal of the piezoelectric element 4 is increased and the detection sensitivity can be improved.

[0004]

In such an acceleration sensor, it is possible to increase the detection sensitivity by attaching the additional mass body, but it is burdensome to support the substrate. Therefore, if the support portion of the substrate is reinforced, the detection sensitivity is lowered. Further, when the additional mass body is large, when an excessive impact such as a drop is applied, a large force is applied to the substrate and the substrate is deformed or damaged. In order to prevent such damage, for example, a stopper mechanism that limits the displacement of the substrate is required.

Therefore, a main object of the present invention is to provide an acceleration sensor which has good detection sensitivity, does not require a large-scale support structure, a stopper mechanism, etc., and is not easily damaged by an impact or the like.

[0006]

SUMMARY OF THE INVENTION The present invention includes a detection piece that is displaced by the application of acceleration, and an additional mass body attached to the detection piece, and the additional mass body is only in the direction of displacement of the detection piece due to acceleration. Slidable,
It is an acceleration sensor. In this acceleration sensor, the additional mass body is preferably attached to the detection piece via an elastic body.

Since the additional mass is slidable only in the direction of displacement of the detection piece due to acceleration, the additional mass does not move in any other direction. Therefore, no force is applied to the detection piece in directions other than the slidable direction by the additional mass body. That is, only when the acceleration mass is applied to the acceleration sensor and the additional mass body slides, the force by the additional mass body is applied to the detection piece. If the additional mass body is attached to the detection piece via the elastic body, the detection piece can be held in a pulled state by the restoring force of the elastic body.

[0008]

According to the present invention, when acceleration is applied to the acceleration sensor, the attached mass body slides, so that the detection piece is largely displaced. Therefore, a large output signal corresponding to the acceleration can be obtained from the detection piece, and the detection sensitivity can be improved. In addition, a force is applied to the detection piece only when acceleration is applied to the acceleration sensor and the additional mass body slides. Therefore, when acceleration is not applied, an excessive force is not applied to the detection piece, and it is not necessary to reinforce the support portion of the detection piece. Therefore, the structure of the acceleration sensor can be simplified and the detection sensitivity can be prevented from lowering. Further, since the movement of the additional mass body is limited, even if an external impact is applied, a large force is not applied to the detection piece, and the deformation or damage of the detection piece can be prevented. Therefore, it is not necessary to form a stopper mechanism or the like for limiting the displacement of the detection piece.

Further, if the additional mass body is attached to the detection piece via the elastic body, the detection piece is held in a pulled state by the restoring force of the elastic body, so that the displacement of the detection piece due to a change in ambient temperature is corrected. To be done. Therefore, it is possible to prevent erroneous detection due to changes in ambient temperature.

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 according to the present invention, and FIG. 2 is a sectional view thereof. The acceleration sensor 10 includes a detection piece 12. The detection piece 12 is
For example, a rectangular plate-shaped substrate 14 is included. Support members 16 are formed on both sides of one end of the substrate 14. The support member 16 includes four legs 16a.
a is fixed to the side portion of the substrate 14 at a distance. Further, the support member 16 includes a plate-shaped portion 16b formed by bending the leg portion 16a. The acceleration sensor 10 is housed in, for example, a case, and the plate-shaped portion 16b is fixed to a base or the like.

A piezoelectric element 18 is formed on the main surface of the substrate 14. The piezoelectric element 18 includes a piezoelectric layer 20 formed of, for example, piezoelectric ceramic, and electrodes 22 and 24 are formed on both surfaces of the piezoelectric layer 20. Then, one electrode 24 is bonded to the substrate 14.

Further, an attached mass body 28 is attached to the other end of the substrate 14 via an elastic body such as a spring 26. The additional mass body 28 is formed, for example, in a ring shape. At the center of the additional mass body 28, the sliding shaft 3
0 is inserted. The sliding shaft 30 is arranged in a direction orthogonal to the main surface of the substrate 14, and both ends thereof are fixed to a base or the like. Therefore, the additional mass 28
Can slide only in the direction along the sliding shaft 30.

In this acceleration sensor 10, when acceleration is applied in a direction orthogonal to the main surface of the substrate 14, the substrate 14 bends. Along with that, the piezoelectric element 18 also bends, and electric charges are generated in the piezoelectric element 18 according to the amount of bending. Therefore, the acceleration applied to the acceleration sensor 10 can be detected by measuring the output signal of the piezoelectric element 18. At this time, the additional mass 28
Slides along the slide shaft 30. As the additional mass 28 slides, the end of the substrate 14 is pulled. Therefore, the amount of bending of the substrate 14 is larger than that when the additional mass body 28 is not provided. Therefore, a large signal can be obtained from the piezoelectric element 18, and the detection sensitivity can be improved. The sliding shaft 30 may be concentric with the curved arc of the substrate 14.

In this acceleration sensor 10, the additional mass body 2
Since the sliding shaft 30 is inserted through the slide shaft 8, the mass of the additional mass body 28 is not added to the substrate 14 when no acceleration is applied. Therefore, it is not necessary to reinforce the fixing member 16 portion as compared with an acceleration sensor having no additional mass body. Further, even if an impact is applied from the outside in the longitudinal direction of the substrate 14, the additional mass body 28 is supported by the sliding shaft 30, so that the additional mass body 28 does not move. Therefore, the impact of the impact on the substrate 14 is small, and the acceleration sensor 10 can be prevented from being damaged. Therefore, unlike the conventional acceleration sensor, it is not necessary to form a stopper mechanism or the like for limiting the displacement of the substrate 14 in order to prevent damage.

When the ambient temperature changes, the substrate 1
4 and the piezoelectric element 18 cause a difference in thermal expansion coefficient between the substrate 14 and
Warp may occur. In such a case, the piezoelectric element 18 also warps, which causes a signal to be output.
Such a signal is indistinguishable from a signal due to acceleration and causes a false detection. However, in this acceleration sensor 10, since the base plate 14 and the additional mass body 28 are connected by the spring 26, the base plate 14 is
It is held in a pulled state by 6. Therefore, the warp of the substrate 14 due to the temperature change is corrected by the spring 26, and the output signal due to the temperature change can be reduced. Therefore, erroneous detection due to temperature change can be prevented.

The additional mass body 28 may be in the shape of a rectangular block as shown in FIG. On both sides of the additional mass body 28, for example, the ball bearing 3
2 is attached. The additional mass body 28 is held inside a rail 34 having a U-shaped cross section. For example, a V-shaped groove 36 is formed on the two inner surfaces of the rail 34 that face each other. The ball bearing 32 is fitted in the groove 36, so that the additional mass body 28 can slide inside the rail 34. The groove 36 may be concentric with the curved arc of the substrate 14.

Further, as shown in FIG. 4, a leaf spring 38 having a curved portion is formed on the opposite side surface of the rectangular mass-shaped additional mass body 28.
May be held at. In the example shown in FIG. 4, four leaf springs 3
8 hold the four ends of the mass 28. Therefore, the additional mass body 28 can be slid only in the thickness direction without being displaced in the width direction of the leaf spring 38. At this time, since the curved portion is formed in the leaf spring 38, the expansion and contraction of the leaf spring 38 accompanying the movement of the additional mass body 28 is absorbed. It should be noted that the leaf springs 38 may be formed on the opposing end surfaces of the additional mass body 28 one by one.

When using these additional mass bodies 28, the additional mass body 28 is attached to the substrate 14 so that the slidable direction of the additional mass body 28 and the direction of the acceleration to be measured coincide with each other. Further, the substrate 14 and the additional mass body 28 are coupled via an elastic body such as a spring. As a result, it is possible to obtain an acceleration sensor having good sensitivity and being less affected by changes in ambient temperature and impact.

In the acceleration sensor 10 described above, the acceleration is detected by the electromotive force of one piezoelectric element 18,
As shown in FIG. 5, an acceleration sensor 10 using a plurality of piezoelectric elements may be used. In this acceleration sensor 10, the piezoelectric elements 40a, 40b, 40c, 4 are provided on both surfaces of the substrate 14.
0d is formed. Here, the piezoelectric elements 40a, 40
c is arranged to face the substrate 14, and the piezoelectric elements 40b and 40d are also arranged to face the substrate 14. The piezoelectric elements 40a and 40c and the piezoelectric elements 40b and 40d are polarized in opposite directions. That is, when the piezoelectric elements 40a and 40c are polarized from the outside toward the substrate 14 side, the piezoelectric elements 40b and 40d are polarized from the substrate 14 side toward the outside.

In this acceleration sensor 10, the piezoelectric element 40
By applying the same drive signal to a to 40d, the piezoelectric elements 40a and 40c and the piezoelectric elements 40b and 40d are displaced in opposite directions. That is, when the piezoelectric elements 40a and 40c expand, the piezoelectric elements 40b and 40d contract. On the contrary, the piezoelectric element 4
When 0a and 40c contract, the piezoelectric elements 40b and 40d expand. Therefore, the substrate 14 performs stretching vibration in opposite directions on both sides of the central portion of the substrate 14 as shown by the arrow in FIG. Therefore, with the total length of the substrate 14 unchanged,
The substrate 14 vibrates in the longitudinal direction.

In the acceleration sensor 10, for example, the output signals of the opposing piezoelectric elements 40b and 40d are input to the differential circuit. When acceleration is not applied to the acceleration sensor 10, the output signals of the piezoelectric elements 40b and 40d are the same, and the output signal of the differential circuit is 0. Acceleration sensor 10
When acceleration is applied to the substrate 14 and the substrate 14 bends, a difference occurs between the output signals of the piezoelectric elements 40b and 40d, and the difference is output from the differential circuit. Therefore, the acceleration applied to the acceleration sensor 10 can be detected by measuring the output signal of the differential circuit. The piezoelectric element 40b,
As the difference between the output signals of 40d, for example, the frequency difference between the signals is measured. Moreover, the impedance difference or the capacitance difference between the piezoelectric elements 40b and 40d caused by the bending of the substrate 12 may be measured. Furthermore, instead of the piezoelectric element for detection, a resistance element or a dielectric element may be used to measure impedance changes such as resistance, capacitance and inductance due to the bending of the substrate 14.

The acceleration sensor 10 as described above also has
By attaching the additional mass body 28 as described above, the curvature of the substrate 14 can be increased, and a highly sensitive acceleration sensor can be obtained. Further, since the additional mass body 28 can slide only in the direction in which acceleration is applied, it is not necessary to reinforce the supporting portion of the substrate 14 and is less likely to be damaged by an external impact. Further, in this acceleration sensor 10, since the acceleration detection direction is set to one direction, it is possible to detect only the acceleration in a certain direction with high sensitivity without being affected by the acceleration in the other directions.

[Brief description of the drawings]

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

FIG. 2 is a sectional view of the acceleration sensor shown in FIG.

FIG. 3 is a perspective view showing another example of the additional mass body used in the acceleration sensor of the present invention.

FIG. 4 is a perspective view showing still another example of the additional mass body used in the acceleration sensor of the present invention.

FIG. 5 is an illustrative view showing another example of the acceleration sensor of the present invention.

FIG. 6 is a perspective view showing an example of a conventional acceleration sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Acceleration sensor 12 Detection piece 14 Substrate 16 Support member 18 Piezoelectric element 26 Spring 28 Attached mass body 30 Sliding shaft 32 Ball bearing 34 Rail 36 Leaf spring 40a-40d Piezoelectric element

Claims (2)

[Claims] 1. A detection piece that is displaced by applying acceleration, and an additional mass body attached to the detection piece, wherein the additional mass body is slidable only in the direction of displacement of the detection piece due to acceleration. Accelerometer. 2. The acceleration sensor according to claim 1, wherein the additional mass body is attached to the detection piece via an elastic body.