JP2946352B2 - Acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to an acceleration sensor used for an automobile or an airbag used for ensuring safety in the event of a collision or for improving riding comfort on a rough road. The present invention relates to an acceleration sensor capable of detecting acceleration in two directions orthogonal to each other with a sensor.

(Prior Art) Conventionally, various methods have been used for detecting acceleration. 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 knocking of an automobile engine.

FIG. 4 is a cross-sectional view showing a structural example of a conventional piezoelectric acceleration sensor. In FIG. 1, electrodes are formed on both surfaces and piezoelectric ceramic rings 51, 5 polarized in the thickness direction.
1 ′ is stacked via terminal plate 52 so that the direction of polarization is reversed, and the base also serves as the base together with the disk-shaped weight 53
It has a structure in which bolts 55 are passed through and tightened.
In FIG. 4, when the case 54 vibrates in the thickness direction of the piezoelectric ceramic ring, a force F represented by the following equation (1) acts on the piezoelectric ceramic ring, and a force F is applied between the electrodes of the piezoelectric ceramic ring. The voltage represented by the equation (2) is generated.

F = M · α (1) V = K · F (2) Here, M is the mass of the weight, α is the acceleration, and K is the proportionality constant.

As can be seen from equations (1) and (2), the voltage generated in the piezoelectric ceramic ring is proportional to the acceleration.

(Problems to be Solved by the Invention) However, the conventional acceleration sensor shown in FIG. 4 detects only the acceleration component in the thickness direction of the piezoelectric ceramic ring, and has two axes of X and Y orthogonal to each other. It is necessary to arrange the two acceleration sensors shown in FIG. 4 at right angles in order to detect at the same time, the structure is complicated and large, and the squareness of the two acceleration sensors is precisely adjusted at the time of setting. There was a drawback that it was difficult.

Therefore, the technical problem of the present invention is to eliminate the above-mentioned drawbacks of the conventional two-axis acceleration sensor, and to detect acceleration in two orthogonal X- and Y-axes with a single sensor having a simple structure. It is an object of the present invention to provide an acceleration sensor.

(Means for Solving the Problems) According to the present invention, in an acceleration sensor for detecting vibration applied to a piezoelectric ceramics ring, a position formed by dividing a circumference formed by an outer peripheral surface of the piezoelectric ceramics ring into 4n equal parts. And 4n (n is an integer of 2 or more) band electrodes formed along the length direction, and the piezoelectric ceramics ring connects the band electrodes to each other along the circumference. The two terminals are polarized, and one of the two terminals is used as a ground terminal. Of the 2n band electrodes forming the other of the two terminals, with respect to the center of the circumference, By measuring a differential voltage between a pair of band electrodes located symmetrically to each other, an acceleration sensor is provided which detects a radial acceleration connecting the pair of band electrodes.

(Operation) In the present invention, the piezoelectric ceramic ring is
Polarization processing is performed at 4n equally divided positions by two terminals connected to every other provided band electrode.

Vibration applied in the diametrical direction formed by a pair of band electrodes at a symmetric position of the piezoelectric ceramic ring applies a compressive force to one of the pair of band electrodes in the direction of polarization, and the other to the other of the pair of band electrodes. Tension is applied in the polarization direction, and voltages of opposite polarities are generated between the pair of band electrodes. Since the magnitude of the differential output of these two output powers is approximately proportional to the applied acceleration, the acceleration can be measured.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIGS. 1A and 1B are a perspective view and a cross-sectional view, respectively, showing an example of a two-axis acceleration sensor according to the present invention. In this example, the strip electrodes 11, 12, 13, 14, 15, 16, 1, 1 parallel to the length direction are placed at positions that divide the circumference of the outer peripheral surface of the piezoelectric ceramic ring 10 into eight equal parts.
7, 18 are formed, and every other band electrode is electrically connected to each other to perform polarization processing as two terminals. After the polarization process, every other band electrode 11, 13, 15, 17 is electrically connected to form a common ground electrode, and the band electrodes 12, 1 sandwiched between the ground electrodes are provided.
4, 16, and 18 are output electrodes.

FIG. 2 is an explanatory diagram of the operation principle of the acceleration sensor of the present invention. In FIG. 2, when an oscillating acceleration is applied in the direction connecting the centers of the output electrodes 12 and 16 (the direction indicated by the white arrow 79), the portion of the output electrode 12 and the output electrode When the compressive force and the tensile force alternately act on the portion 16, the compressive force acts on the output electrode 12, and the tensile force acts on the output electrode 16, the common ground electrode of the output electrodes 12 and 16 The direction of the polarization with respect to the output electrode is the direction indicated by the dashed arrow 20 from the output electrode to the ground electrode, and the direction of the force acting on the portion of the output electrode 12 and the portion of the output electrode 16 is indicated by the solid lines 21 and 22 As described above, the polarities are opposite to each other, so that voltages of opposite polarities are generated at the output electrodes 12 and 16. Therefore, the differential output of these two output voltages will be approximately proportional to the magnitude of the applied acceleration. Similarly, when an oscillating acceleration is applied in the direction connecting the centers of the output electrodes 14 and 18, voltages of opposite polarities are generated at the output electrodes 14 and 18, and the differential output 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 that 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 be obtained.

On the other hand, in the two-axis acceleration sensor according to the embodiment of the present invention, with respect to the vibration in the direction orthogonal 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 output electrodes are the same, they are hardly output as differential outputs.

FIG. 3 is a perspective view showing another example of the vibration sensor according to the embodiment of the present invention.

The above description has been made on the case where the vibration system is composed of a single piezoelectric ceramic ring. However, if the frequency of the acceleration to be detected is low and the output voltage sensitivity should be as large as possible, as shown in FIG. A structure in which a disc-shaped weight 31 is loaded on one end of the ceramic ring 10 and the other end is fixed to the base 32 may be adopted. In the embodiment of the present invention, the band electrode is provided at a position that divides the circumference of the outer peripheral surface of the piezoelectric ceramic ring into eight equal parts.
It is needless to say that the same effect can be obtained even if it is provided at a position where it is equally divided by n.

(Effects of the Invention) 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 requiring no angle adjustment at the time of setting, and is very effective in practice. Is big.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a) and 1 (b) are a perspective view and a sectional view showing an example of an acceleration sensor according to the present invention, and FIG. 2 is an explanation of the structure and operation principle of the acceleration sensor of FIG. FIG. 3 is a sectional view showing another example of the acceleration sensor of the present invention, and FIG. 4 is a front view showing an example of the structure of a conventional piezoelectric acceleration sensor. In the figure, 10 ... Piezoelectric ceramic rings, 11, 12, 13, 14, 15, 16,
17, 18 ... strip electrode, 31 ... weight, 32 ... base, 51, 5
1 ': Piezoelectric ceramic ring, 52: Terminal plate, 53: Weight, 54: Base, 55: Bolt.

Claims (1)

(57) [Claims] 1. An acceleration sensor for detecting vibration applied to a piezoelectric ceramic ring, the acceleration sensor being formed along a length direction at a position dividing a circumference formed by an outer peripheral surface of the piezoelectric ceramic ring into 4n equal parts. The piezoelectric ceramic ring is provided with 4n (n is an integer of 2 or more) band electrodes, and the piezoelectric ceramics ring is subjected to polarization processing as two terminals connecting the band electrodes to every other one along the circumference. , One of the two terminals is used as a ground terminal, and among 2n band electrodes forming the other terminal of the two terminals, between a pair of band electrodes symmetrically positioned with respect to the center of the circumference. An acceleration sensor for detecting a diametrical acceleration connecting the pair of band electrodes by measuring a differential voltage of the acceleration sensor.