JP3002900B2 - 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 for use in an airbag used for ensuring safety in the event of a collision of an automobile and for improving riding comfort on a rough road, and more particularly to two directions orthogonal to each other with one sensor. The acceleration relates to the acceleration that can be detected.

[0002]

2. Description of the Related Art Conventionally, various types of acceleration detection have been put to practical use. Among them, acceleration sensors using piezoelectric ceramics are widely used for detecting vibration of various machines and detecting knocking of automobile engines because of their simple structure and use at high temperatures.

FIG. 5 is a side view showing an example of a conventional piezoelectric acceleration sensor. In this example, electrodes are formed on both sides, and piezoelectric ceramic rings 57, 57 'polarized in the thickness direction are superimposed via the terminal plate 56 so that the directions of polarization are opposite to each other. The structure is such that it is fastened to the base 53 serving also as a bolt with a bolt 55.

In FIG. 5, when the base 53 vibrates in the thickness direction of the piezoelectric ceramic ring, a force F approximately expressed by the following equation (1) acts on the piezoelectric ceramic ring, and the electrode F of the piezoelectric ceramic ring is placed between the electrodes. Has a voltage V expressed by equation (2).
Occurs. F = M · α (1) V = K · F (2) where M is the mass of the weight, α is the acceleration, and K is the proportionality constant. As can be seen from the above equations (1) and (2), the voltage V generated in the piezoelectric ceramic ring is proportional to the acceleration α.

[0005]

The conventional acceleration sensor shown in FIG. 5 detects only the acceleration component in the thickness direction of the piezoelectric ceramic ring, and X, Y orthogonal to each other.
In order to detect the two axes simultaneously, it is necessary to arrange the two acceleration sensors shown in FIG. 5 at a right angle. There was a drawback that it was difficult to match well.

Therefore, a technical object of the present invention is to eliminate the above-mentioned drawbacks of the conventional acceleration sensor and to provide a simple structure.
It is an object of the present invention to provide an acceleration sensor capable of detecting accelerations in two axes of X-axis and Y-axis orthogonal to each other with a plurality of sensors.

[0007]

According to the present invention, in an acceleration sensor having a piezoelectric ceramic ring having one end face fixed , a radial direction is defined between an inner peripheral surface and an outer peripheral surface of the piezoelectric ceramic ring. The piezoelectric ceramic ring is subjected to a polarization treatment, and divided electrodes are formed on one end face of the piezoelectric ceramic ring to divide the circumference into four equal parts. When the ground electrode end face of the ring is fixed to the base and the base is vibrated in a direction perpendicular to the central axis of the piezoelectric ceramic ring, acceleration is detected based on a differential voltage of voltages generated at output electrodes facing each other. A two-axis acceleration sensor characterized by being made possible is obtained.

[0008]

[Work] In the present invention, when an oscillating acceleration is applied in a direction connecting the centers of a pair of output electrodes symmetrical to each other with respect to the center axis, a slip stress acts on each output electrode portion on the piezoelectric ceramic ring. I do. At this time, since the polarization process is performed from the inner peripheral surface to the outer peripheral surface of the piezoelectric ceramics ring, a sliding stress acts on one of the pair of output electrodes in a direction opposite to the polarization direction, and the pair of output electrodes On the other side, a sliding stress acts in the same direction as the polarization direction, so that a (+) voltage is applied between the earth electrode and one output electrode of the piezoelectric ceramic ring, and between the earth electrode and the other output electrode. , A voltage having a polarity opposite to the (−) voltage is generated.

In the other pair of output electrodes, the central axis is orthogonal to the direction of the sliding stress, and the polarization direction is symmetric with respect to the central axis, so that a voltage is not applied between the other pair of output electrodes. Does not occur. Therefore, the differential output voltage between the pair of output electrodes is substantially proportional to the magnitude of the applied acceleration, and the differential output voltage between the other pair of output electrodes becomes zero.

On the other hand, in the case of acceleration in a direction intersecting with the above-described acceleration, the pair of output electrodes and the other pair of output electrodes apply a voltage corresponding to a component of a diametrical acceleration connecting each pair of output electrodes. Output. Therefore, the direction and magnitude of the acceleration can be detected from the differential output voltage.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an acceleration sensor according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing the structure of an acceleration sensor according to an embodiment of the present invention, and FIGS.
2C is a bottom view, FIG. 2B is a front view, and FIG. 2C is a plan view of a piezoelectric ceramic ring used in the acceleration sensor of FIG. In this example, the inner peripheral surface 1 of the piezoelectric ceramic ring 1
a, electrodes are formed on each of the outer peripheral surface 1b, a polarization process is performed, and after the polarization process, the electrodes are removed. The electrodes 21, 22, 23, and 24 are formed and used as output electrodes, respectively, and the entire surface electrode 25 is formed on the other end surface facing one end surface to serve as a ground electrode.
The acceleration sensor is fixed to the base 3.

3 (a), 3 (b) and 3 (c) are explanatory views of the operation principle of the acceleration sensor shown in FIG. 1, (a) is a plan view,
(B) is a sectional view, and (c) is a configuration diagram of a detection circuit. 3A and 3B, when an oscillating acceleration 11 is applied in a direction connecting the centers of the output electrodes 22 and 24, the portion of the output electrode 22 and the output electrode 2
A sliding stress as shown by an arrow 12 acts on the portion 4. At this time, since the polarization processing is performed in the direction from the inner peripheral surface to the outer peripheral surface of the piezoelectric ceramic ring 1, that is, in the direction indicated by the dashed arrow 13, the polarization direction 13
A sliding stress 12 acts in a direction opposite to that of the output electrode 22.
In this case, a sliding stress 12 acts in the same direction as the polarization 83 direction.
5 and the output electrode 22, and a voltage of the opposite polarity of the (−) voltage is generated between the ground electrode 25 and the output electrode 24. The central axes of the output electrode 21 and the output electrode 23 are orthogonal to the slip stress direction 12 and
3 is symmetric with respect to this central axis, so that the output electrode 21
No voltage is generated between the output electrode 23 and the output electrode 23.

Therefore, as shown in FIG. 3 (c), the differential output voltage between the output electrode 21 and the output electrode 23 by the differential amplifier 9 detected at the terminal 14 becomes 0, and the output detected at the terminal 15 becomes zero. The differential output voltage between electrode 22 and output electrode 24 will be approximately proportional to the magnitude of the applied acceleration.
Similarly, when an oscillating acceleration is applied in a direction connecting the centers of the output electrodes 21 and 23, the output electrodes 21 and 23
And the differential output of these two output voltages is approximately proportional to the magnitude of the applied acceleration.

In FIG. 3, when the direction of the applied acceleration is different from the direction of the opposing axis of the output electrode, the components of the opposing axis of the output electrode that are orthogonal to each other 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 acceleration sensor according to the embodiment of the present invention, for the vibration in the direction perpendicular to the detection axis, that is, the vibration in the direction of the center axis of the piezoelectric ceramic ring in FIG. Since the polarities of the voltages generated at the 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 the piezoelectric ceramic ring alone. 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 4 may be applied to one end of the piezoelectric ceramic ring 1 and the other end may be fixed to the base 3. Further, in the acceleration sensor according to the embodiment of the present invention, the voltage is generated by the sliding stress of the piezoelectric ceramic, and the effect of the pyro effect is small since the direction of the polarization is parallel to the surface of the electrode.

[0016]

As described above, according to the present invention, it is possible to obtain an acceleration sensor having a simple structure using a single piezoelectric ceramic ring and not requiring an angle adjustment at the time of setting. Great effect.

[Brief description of the drawings]

FIG. 1 is a perspective view of an acceleration sensor according to an embodiment of the present invention.

2 (a), (b) and (c) are structural views of a piezoelectric ceramic ring used for the acceleration sensor of FIG. 1, (a) is a bottom view, (b) is a front view, and (c) is It is a top view.

FIGS. 3A, 3B and 3C are explanatory views of the operation principle of the two-axis acceleration sensor according to the embodiment of the present invention, wherein FIG. 3A is a plan view, FIG. (c) is a configuration diagram of the detection circuit.

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]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric ceramic ring 21, 22, 23, 24 Split electrode 25 Earth electrode, 3 Base 4 Weight 5 volts 53 Base 54 Weight 55 Volt 56 Terminal plate 57, 57 'Piezoelectric ceramic ring

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-56275 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01P 15/09 G01P 15/00

Claims (1)

(57) [Claims] 1. An acceleration sensor having a piezoelectric ceramic ring having one end face fixed thereto, wherein a radial polarization process is performed between an inner peripheral surface and an outer peripheral surface of the piezoelectric ceramic ring, and the piezoelectric ceramic circular ring is provided. On one end face of the ring, divided electrodes are formed to divide the circumference into four equal parts, each is used as an output electrode, and the other end face is formed with a full-surface electrode to serve as a ground electrode. An acceleration sensor characterized in that when the fixed end is vibrated in a direction perpendicular to the center axis of the piezoelectric ceramic ring, acceleration can be detected based on a differential voltage of voltages generated at output electrodes facing each other.