JP2671064B2 - 2-axis 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 a two-axis acceleration sensor, and more particularly, to an acceleration sensor in an airbag device for ensuring safety in the event of an automobile collision or a mechanism for improving the riding comfort on a bad road. The present invention relates to an acceleration sensor used for detecting size, direction, etc., and relates to a biaxial acceleration sensor capable of detecting acceleration in two directions with a single sensor.

[0002]

2. Description of the Related Art Various methods of detecting acceleration have been put to practical use. Among them, an acceleration sensor made of piezoelectric ceramics has features such as simple structure and high temperature use. Widely used for detecting knocking of

FIG. 4 shows a conventional piezoelectric acceleration sensor. In the figure, electrodes are formed on both end faces, and piezoelectric ceramic rings 12, 12 polarized in the thickness direction are overlapped via a terminal plate 9 so that the directions of polarization are opposite to each other. However, a structure is adopted in which a base 11 serving as a case together with a weight 7 is fastened by bolts 8.

In this conventional acceleration sensor, when the base 11 vibrates in the thickness direction of the piezoelectric ceramic ring 12, a force F expressed by the following formula (1) acts on the piezoelectric ceramic ring 12, and At this time, the piezoelectric ceramic ring 12
A voltage expressed by the following equation (2) is generated between the electrodes.

F = M · α (1) V = k · F (2) In the above equations (1) and (2), M is the mass of the weight, α is the acceleration,
k is a proportionality constant.

[0006]

However, the conventional acceleration sensor described above can detect only the acceleration component in the thickness direction of the piezoelectric ceramic ring 12, that is, in one direction. Therefore, for example, to obtain a two-axis acceleration sensor for detecting accelerations in two directions of the X and Y axes, it is necessary to use two acceleration sensors. In this case, the structure becomes complicated, There is also a problem that the sensor becomes large.

Further, when this acceleration sensor is mounted on an automobile or the like, it is necessary to combine the two acceleration sensors while adjusting the angle at a right angle. However, it is difficult to adjust the angle, and it is difficult to obtain a right angle with high accuracy. There is a problem such as.

It is an object of the present invention to provide a biaxial acceleration sensor which does not have the above-mentioned drawbacks of the conventional acceleration sensor and has a simple structure and is capable of detecting accelerations in two directions. .

[0009]

In the biaxial acceleration sensor of the present invention, a plurality of strip-shaped electrodes of 8 formed on the outer peripheral surface of a piezoelectric ceramic cylinder in parallel with the length direction are arranged in the circumferential direction of the outer peripheral surface. In every other as the output electrode, and the rest of the strip-shaped electrode as a common ground electrode, the adjacent electrode gap portion of the strip-shaped electrode is subjected to polarization treatment in the opposite direction to the circumferential direction, The gist is that one end of the piezoelectric ceramic cylinder is fixed to a base.

In the above structure, when the base vibrates in the plane direction perpendicular to the central axis of the piezoelectric ceramic cylinder,
By detecting the acceleration component in the direction connecting the pair of electrodes from the differential voltage of the voltage generated between the pair of electrodes facing each other with respect to the central axis of the output electrodes, the in-plane orthogonality is detected. It is possible to detect acceleration components in two directions.

[0011]

According to the above arrangement, acceleration components in two directions can be detected by one piezoelectric ceramic cylinder. As a result, it is possible to simultaneously detect accelerations in two orthogonal directions with a simple structure.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a two-axis acceleration sensor according to the present invention constituted by using eight strip electrodes will be described below. In addition, 16
It is obvious that the same effect can be obtained with the individual strip electrodes.

1 (A) and 1 (B), a biaxial acceleration sensor 1 of the present invention comprises a piezoelectric ceramic column 10 and a base 11 provided on the bottom thereof.
Eight strip electrodes are formed on the outer peripheral surface of the piezoelectric ceramic column 10 in parallel with the length (axis) direction of the piezoelectric ceramic column 10 at substantially equal intervals. Of these eight strip electrodes, every other strip electrode is a common ground electrode 9
1, 93, 95 and 97, and the other remaining strip electrodes are output electrodes 92, 94, 96 and 98. The adjacent electrode gaps of these strip electrodes are polarized in opposite directions to the circumferential direction.

FIG. 2 shows a connection state between the piezoelectric ceramic cylinder 10 and the differential amplifiers 4 and 5 in the biaxial acceleration sensor 1 of this embodiment. An output is provided to the (-) side terminal of the differential amplifier 4. The output of the electrode 92 is output to the (+) side terminal with respect to the central axis of the piezoelectric ceramic cylinder 10.
The outputs of the output electrodes 96 located so as to face each other are connected to each other.

On the other hand, at the (-) side terminal of the differential amplifier 5,
Exactly 90 ° clockwise from the output electrode 92 in the figure.
The output of the output electrode 94 provided at the shifted position is connected. The outputs of the output electrode 98 located at a position facing the center axis of the output electrode 94 are connected to the (+) side terminals, respectively.

In the above structure, the output electrodes 92 and 96
When an oscillating acceleration 20 is applied in the direction connecting the two, a stress 25 acts on the piezoelectric ceramic cylinder 10 in the same direction.

At this time, the polarization 21 is provided in the direction from the ground electrodes 91 and 93 to the output electrode 92, and the ground electrodes 95 and 9 are also provided.
7 is processed in the direction from the output electrode 96 to the output electrode 96, so that the stress 25 acts on the output electrode 92 in the same direction as the direction of the polarization 21, and the output electrode 96.
In this case, a stress 25 acts in a direction opposite to the direction of the polarization 21. As a result, the ground electrodes 91, 93, 95, 97 and the output electrode 9
2 and (+) voltage, and ground electrodes 91 and 9
The negative polarity (−) voltage is generated between 3, 95, 97 and the output electrode 96, respectively.

Since the direction of polarization 23 of the output electrode 94 and the direction of polarization 24 of the output voltage 98 are respectively orthogonal to the direction of stress 25, no voltage is generated at the output electrodes 94, 98.

Therefore, the output electrode 9 of the differential amplifier 4
The 2,94 differential output voltages are approximately proportional to the magnitude of the applied acceleration 20. On the other hand, the differential output voltage of the output electrodes 94 and 98 by the differential amplifier 5 becomes zero.

On the other hand, the applied acceleration is the acceleration 20
In the case of the direction orthogonal to, the differential amplifier 5
The differential output voltage of the output electrodes 94 and 98 due to the above is substantially proportional to the magnitude of the applied acceleration 20, while the differential output voltage of the output electrodes 92 and 96 due to the differential amplifier 4 becomes zero.

Therefore, the differential output voltages of the differential amplifiers 4 and 5 can detect acceleration components in two directions orthogonal to each other in a plane perpendicular to the central axis of the piezoelectric ceramic cylinder.

Further, when the direction of the applied acceleration is different from the opposite axial directions of the output electrodes 92 and 96 or the output electrodes 94 and 98, the two components of the acceleration in these two opposite axial directions are differential amplifiers. 4 and 5, respectively. Therefore, the direction and magnitude of the acceleration can be obtained by calculating the detection signal values in the differential amplifiers 4 and 5.

The above is an example in which the piezo-electric ceramics cylinder 10 constitutes a vibration system by itself. For example, when the frequency of the acceleration to be detected is low, as shown in FIG. The weight 7 may be fixed and loaded. By applying the weight 7, the effect of the acceleration on the piezoelectric ceramic cylinder 10 is amplified, so that the output sensitivity can be increased.

[0024]

As described above, according to the present invention, it is possible to provide a biaxial acceleration sensor having a simple structure and capable of detecting accelerations in two directions.

[Brief description of the drawings]

FIG. 1A is a perspective view showing a state in which a piezoelectric ceramic cylinder and a base used in a two-axis acceleration sensor of an embodiment are combined.
(B) is a sectional view of the piezoelectric ceramic cylinder.

FIG. 2 is an explanatory diagram showing a connection relationship between a piezoelectric ceramic cylinder and a differential amplifier in an example.

FIG. 3 is a perspective view of another example of the biaxial acceleration sensor.

FIG. 4 is a perspective view of a conventional example of an acceleration sensor.

[Explanation of symbols]

 1 2-axis acceleration sensor 4,5 Differential amplifier 7 Weight 8 Volt 9 Terminal board 10, 12 Piezoelectric ceramic cylinder 11 Base 20 Acceleration 21-24 Polarization 25 Stress 91,93,95,97 Output electrode 92,94,96,98 Common ground electrode

 ─────────────────────────────────────────────────── --Continued from the front page (56) Reference JP-A-3-273167 (JP, A) JP-A-4-188079 (JP, A) JP-A-4-213068 (JP, A) JP-A-49- 88573 (JP, A) JP 4-118515 (JP, A) JP 61-178666 (JP, A) JP 4-159429 (JP, A) JP 52-8111 (JP, B2) JP-B 54-39146 (JP, B2) JP-B 54-43905 (JP, B2) JP-A-4-506407 (JP, A))

Claims (2)

(57) [Claims] 1. A plurality of strip-shaped electrodes, each of which is a multiple of 8, formed on the outer peripheral surface of a piezoelectric ceramic cylinder in parallel with the length direction are used as output electrodes in the circumferential direction of the outer peripheral surface. The rest is used as a common ground electrode, the adjacent electrode gaps of the strip electrodes are polarized in opposite directions to the circumferential direction, and one end of the piezoelectric ceramic cylinder is fixed to the base. A two-axis acceleration sensor characterized in that 2. A difference in voltage generated between a pair of electrodes of the output electrodes facing each other with respect to the central axis when the base vibrates in a plane direction perpendicular to the central axis of the piezoelectric ceramic cylinder. 2. The biaxial acceleration sensor according to claim 1, wherein an acceleration component in a direction connecting the pair of electrodes is detected from a dynamic voltage, whereby acceleration components in two orthogonal directions in the plane can be detected. .