JP2607396B2 - 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 air bag used for ensuring safety in the event of a collision of an automobile and an acceleration sensor used for improving the riding comfort on a rough road.
The present invention relates to an acceleration sensor capable of detecting accelerations in two directions orthogonal to each other with two sensors.

[0002]

2. Description of the Related Art Conventionally, various types of acceleration detection have been put to practical use. Among them, an acceleration sensor using piezoelectric ceramics has a simple structure and can be used at a high temperature. Therefore, it is widely used for detecting vibration of various machines and detecting a knocking sensor of an automobile.

FIG. 5 is a side view showing an example of a conventional piezoelectric acceleration sensor. In the figure, electrodes are formed on both end faces facing each other, and a pair of piezoelectric ceramic rings 51 and 51 ′ polarized in a direction connecting the end faces are connected to a terminal plate 5.
Superimposed so that the direction of polarization is opposite through 2
Bolt 5 with weight 53 on base 54 which also serves as case
5 has a structure tightened. In the acceleration sensor having this structure, the case is composed of piezoelectric ceramic rings 51 and 5.
When vibrating in the thickness direction of 1 ', the piezoelectric ceramic ring 5
A force F approximately expressed by the expression (1) acts on 1, 51 ', and a voltage expressed by the expression (2) is generated between the electrodes of the piezoelectric ceramic ring. F = M × α (1) V = K × F (2) where M: mass of weight, α: acceleration, K: proportional constant. As can be seen from the above equations (1) and (2), the voltage V generated in the piezoelectric ceramic rings 51, 51 'is proportional to the acceleration α.

[0004]

The conventional acceleration sensor shown in FIG. 5 detects only the acceleration component in the thickness direction of the piezoelectric ceramic rings 51, 51 '. In order to detect the axes simultaneously, it is necessary to arrange the two acceleration sensors shown in FIG. 5 at a right angle, which is complicated and large in structure, and the accuracy of the detection axes of the two acceleration sensors is set at right angles to each other at the time of setting. There was a drawback that it was difficult to match well.

Therefore, the technical problem of the present invention is to eliminate the disadvantages of the conventional two-axis acceleration sensor described above, and to provide two sensors of X-axis and Y-axis orthogonal to each other with a single sensor having a simple structure. An object of the present invention is to provide an acceleration sensor capable of detecting the acceleration of a shaft.

[0006]

According to the present invention, in an acceleration sensor having a piezoelectric ceramic having a cylindrical outer surface and having one end fixed, the piezoelectric ceramic divides the circumference of the cylindrical outer surface into four equal parts. A pair of interdigital electrodes having finger electrodes parallel to the length direction of the piezoelectric ceramic formed at positions, and connecting the same-polarity electrodes of the interdigital electrode pairs at the time of the polarization process to connect to a ground electrode. The interdigital electrodes intersecting with the ground electrode are used as output electrodes, respectively, and the vibration in the direction orthogonal to the central axis of the piezoelectric ceramics is generated by the output electrodes facing each other via the central axis among the output electrodes. An acceleration sensor characterized by detecting acceleration based on a differential voltage generated therebetween is obtained.

[0007]

In the present invention, one of the pair of interdigital electrodes facing each other is used as the ground terminal and the other is used as the output electrode.
When vibration is applied in the diametric direction including this interdigital electrode pair of piezoelectric ceramics, one of the output electrodes outputs voltages of opposite polarities corresponding to the magnitude of the elongation strain and the other of the shrinkage strain by the piezoelectric transverse effect. . By measuring the magnitude of the differential voltage of these output voltages, the magnitude of the acceleration can be detected. By arranging four such interdigital electrode pairs at positions that divide the circumference of the piezoelectric ceramic into four equal parts,
When vibration is applied in a direction perpendicular to the central axis of the piezoelectric ceramic, the acceleration components in the diametric direction and the diametric direction perpendicular to the diametric direction are measured by two pairs of output electrode pairs of the interdigital electrodes facing each other. Therefore, the magnitude and the direction of the acceleration can be obtained.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a two-axis acceleration sensor according to the present invention. FIG. 1 is a perspective view showing the structure of the two-axis acceleration sensor of the present invention. In this example, a pair of interdigital electrodes 11. 1 having finger electrodes parallel to the circumferential direction at positions that divide the circumference of the outer peripheral surface of the piezoelectric ceramic ring 6 into four equal parts.
1 ′, 12 ・ 12 ′, 13 ・ 13 ′, and 14 ・ 14 ′ are formed, and a polarization process described later is performed using the interdigital electrodes. Electrode 1
1 ', 12', 13 ', and 14' are connected to form a common ground electrode, and each electrode 11, 1 which intersects this common ground electrode.
2, 13, and 14 are output terminals. An acceleration sensor is formed by fixing one end of the piezoelectric ceramic to the base 9.

FIGS. 2 and 3 (a), 3 (b) and 3 (c) are explanatory views of the operation principle of the two-axis acceleration sensor of the present invention. FIG. 2 is a plan view, FIG. 3 (a) is a perspective view, FIG. 3 (b) is the same as FIG.
FIG. 3 (c) is the right side of FIG.
The left side (c) of (a) and the cross finger electrode portion are shown. In FIG. 2, a direction (diameter direction) connecting the centers of the output electrode 12 and the output electrode 14 facing each other via the central axis.
When vibratory acceleration is applied to the piezoelectric ceramic ring 6
, A compressive force and a tensile force alternately act on the output electrode 12 and the output electrode 14.

For example, when a compressive force acts on the output electrode 12 and a tensile force acts on the output electrode 14, as shown in FIGS. 3 (a), 3 (b) and 3 (c), The direction of polarization of the output electrodes 12 and 14 with respect to the common ground electrode is the direction from the output electrodes 12 and 14 toward the ground electrodes 12 'and 14', respectively, as indicated by the dashed arrows. Since the directions of the forces acting on the portion and the portion of the output electrode 14 are opposite as shown by arrows 15 and 16, a voltage of the opposite polarity shown by a solid arrow is applied to the output electrode 12 and the output electrode 14. This is caused by the lateral piezoelectric effect.

On the other hand, the output electrodes 11 and 13
Since the central axis of each electrode section is orthogonal to the direction of the oscillating acceleration and the polarization direction is symmetric with respect to the central axis of the electrode section, the output voltage is canceled and does not occur. Therefore, the differential output of the two output voltages generated at the output electrode 12 and the output electrode 14 is substantially proportional to the magnitude of the applied acceleration.

Similarly, output voltage 11 and output voltage 13
When an oscillating acceleration is applied in a direction connecting the centers of the two, a voltage having a polarity opposite to that of the output voltage 11 and the output voltage 13 is generated by a piezoelectric transverse effect, and the differential voltage between these two output voltages is the magnitude of the applied acceleration. This is almost proportional to the above (see the above-described equations (1) and (2)).

On the other hand, in FIG. 2, when the direction of the applied acceleration is different from the direction of the opposite axis of the output electrode, that is, the direction of the diameter passing through each electrode, the component of the orthogonal direction of the output electrode that is orthogonal to each other is detected. That is, by processing the two detection signals, the direction and magnitude of the applied acceleration can be obtained.

Further, in the acceleration sensor according to the embodiment of the present invention, with respect to the vibration in the direction perpendicular to the detection axis, that is, the vibration in the center axis direction of the piezoelectric ceramic ring in FIG. Since the polarities of the voltages generated at the opposing output electrodes are the same, they are hardly output as differential outputs.

The above description has been made on the case where the vibration system is constituted by a single piezoelectric ceramic ring. However, when the frequency of the acceleration to be detected is low and the output voltage sensitivity is to be increased as much as possible, FIG. As described above, the weight 8 may be loaded on one end of the piezoelectric ceramic ring 6 and the other end may be fixed to the base 9.

[0016]

As described above, according to the present invention,
With a simple structure using a single piezoelectric ceramic, a two-axis acceleration sensor that does not require angle adjustment at the time of setting is obtained, and is very effective in practice.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a two-axis acceleration sensor according to the present invention.

FIG. 2 is an explanatory diagram of the operation principle of the two-axis acceleration sensor of the present invention.

FIGS. 3 (a), (b) and (c) are explanatory diagrams of the operation principle of the two-axis acceleration sensor of the present invention.

FIG. 4 is a perspective view showing another example of the two-axis acceleration sensor of the present invention.

FIG. 5 is a side view showing a structural example of a conventional piezoelectric acceleration sensor.

[Explanation of symbols]

 6 Piezoelectric ceramics ring 8 Weight 9 Base 11 ・ 11 ′, 12 ・ 12 ′ Cross finger electrode pair 13 ・ 13 ′, 14.14 ′ Cross finger electrode pair 51, 51 ′ Piezoelectric ceramics ring 52 Terminal plate 53 Weight 54 Base 55 bolt

Continuation of the front page (56) References JP-A-3-273167 (JP, A) JP-A-4-315999 (JP, A) JP-A-4-213068 (JP, A) JP-B-52-8111 (JP) , B2) JP-B-54-39146 (JP, B2) JP-B-54-43905 (JP, B2) JP-B-4-506407 (JP, A)

Claims (1)

(57) [Claims] 1. An acceleration sensor having a piezoelectric ceramic having a cylindrical outer surface and having one end fixed, wherein the piezoelectric ceramic has a length equal to the length of the piezoelectric ceramic formed at a position dividing the circumference of the cylindrical outer surface into four equal parts. A pair of interdigital electrodes having finger electrodes parallel to the direction, wherein a polarization process is performed using the interdigital electrode pairs, and the same-polarity electrodes of the interdigital electrode pairs during the polarization process are connected to each other. do it,
An interdigital electrode intersecting with the ground electrode is used as an output electrode, and vibrations in a direction perpendicular to the central axis of the piezoelectric ceramics are opposed to each other via the central axis among the output electrodes. An acceleration sensor for detecting acceleration based on a differential voltage generated between output electrodes.