JP2607395B2 - 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 surfaces facing each other, and a pair of piezoelectric ceramic rings 51, 51 'polarized in the thickness direction connecting these end surfaces are polarized in opposite directions via a terminal plate 52. In this way, the weights 53 and the bases 54 are also fastened together with the weights 53 by bolts 55 on a base 54 also serving as a case. In the acceleration sensor having this structure, the case is made of a piezoelectric ceramic ring 5.
When vibrating in the thickness direction of the piezoelectric ceramics 51, 51 ', a force F substantially expressed by the formula (1) acts on the piezoelectric ceramics rings 51, 51', and the formula (2) is applied between the electrodes of the piezoelectric ceramics rings. A voltage represented by 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 ring. In order to simultaneously detect two axes of X and Y, the conventional acceleration sensor shown in FIG. Is disadvantageous in that it is necessary to arrange the two acceleration sensors shown in FIG. 5 at right angles, which is structurally complicated and large, and that it is difficult to precisely match the detection axes of the two acceleration sensors at right angles to each other during setting. was there.

Accordingly, the technical problem of the present invention is to eliminate the above-mentioned disadvantages of the conventional two-axis acceleration sensor, 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 acceleration.

[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 circumferential direction formed at positions, wherein a polarization process is performed using the interdigital electrode pairs, and the polarization process of the interdigital electrode pairs is performed. At the same time, the same polarity electrodes are connected to each other to form a ground electrode, and the interdigital electrodes intersecting with the ground electrode are each used as an output electrode, and the vibration in the direction perpendicular to the center axis of the piezoelectric ceramic is applied to the output electrode. In the acceleration sensor, an acceleration is detected based on a differential voltage generated between output electrodes facing each other via the central axis.

[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 to the piezoelectric ceramic in the diameter direction including this interdigital electrode pair, one of the output electrodes outputs voltages of opposite polarities corresponding to the magnitude of the extension strain and the other of the contraction strain by the piezoelectric longitudinal effect. I do. 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 vibration is applied to the diametric direction and Since the components of the acceleration in the diametric direction perpendicular to are measured by two pairs of output electrode pairs among the interdigital electrodes facing each other, the magnitude and 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 an example 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 ring 6 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 same direction from the output electrodes 12 and 14 to the ground electrodes 12 'and 14', respectively, as indicated by broken arrows 17 and 18, respectively. 12 part and output electrode 14
Are opposite to each other as shown by arrows 15 and 16, the output electrode 12 and the output electrode 1
In FIG. 4, a voltage of the opposite polarity shown by solid arrows 19 and 20 is generated by the piezoelectric longitudinal effect. In addition, since the center axis of each electrode section is orthogonal to the direction of the oscillating acceleration and the polarization direction is symmetrical with respect to the center axis of the electrode section, the output electrodes 11 and 13 have the same output. The voltage is canceled and does not occur.

Therefore, two of the output electrodes 12 and 14
The differential output of the two output voltages V will be substantially proportional to the magnitude of the applied acceleration α. Similarly, output voltage 1
When an oscillating acceleration is applied in a direction connecting 1 to the center of the output voltage 13, a voltage of opposite polarity is generated in the output voltage 11 and the output voltage 13 by a piezoelectric longitudinal effect, and a differential voltage of these two output voltages is added. It is almost proportional to the magnitude of the applied acceleration.

In FIG. 2, when the direction of the applied acceleration is different from the direction of the opposing axis of the output electrode, components of the output electrode which are orthogonal to each other in the direction of the opposing axis are detected. That is,
By processing the two detection signals, the direction and magnitude of the applied acceleration can also be obtained.

Further, in the two-axis acceleration sensor according to the embodiment of the present invention, the vibration in the direction perpendicular to the detection axis, that is, the vibration in the center axis direction of the piezoelectric ceramic ring 6 in FIG. Since the polarities of the voltages generated at the output electrodes facing each other are the same for both axes, they are hardly output as their 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, as shown in FIG. The weight 8 may be applied to one end of the piezoelectric ceramic ring 6 and the other end may be fixed to the base 9.

[0015]

As described above, according to the present invention, a two-axis acceleration sensor having a simple structure using a single piezoelectric ceramics ring and requiring no angle adjustment at the time of setting can be obtained. Great effect.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a two-axis acceleration sensor of 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 structure of the two-axis acceleration sensor of the present invention.

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

[Explanation of symbols]

6 Piezoelectric ceramic ring 9 Base 11.11 ', 12.12', 13.13 ', 14.1
4 ′ interdigital electrode pair 51 · 51 ′ piezoelectric ceramics ring 52 terminal board 53 weight 54 base 55 volt

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 is formed in a position in the circumferential direction formed at a position dividing the circumference of the cylindrical outer surface into four equal parts. An interdigital electrode pair having parallel finger electrodes is provided, and a polarization process is performed using the interdigital electrode pair. The same polarity electrodes of the interdigital electrode pair during the polarization process are connected to each other. An interdigital electrode intersecting with the earth electrode is used as an output electrode, and vibrations in a direction perpendicular to the center axis of the piezoelectric ceramic are opposed to each other via the center axis among the output electrodes. An acceleration sensor for detecting acceleration based on a differential voltage generated between output electrodes.