JP3092022B2 - 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 an acceleration sensor used in an airbag system used for ensuring the safety of a car, a system for improving riding comfort on a rough road, and the like. The present invention relates to a two-axis acceleration sensor capable of detecting accelerations in two directions.

[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 (piezoelectric acceleration sensors) have a simple structure and can be used at high temperatures, so they are widely used for detecting vibration of various machines and detecting knocking of automobile engines. ing.

FIG. 7 shows a conventional piezoelectric acceleration sensor. This acceleration sensor has piezoelectric ceramic rings 20, 21 having electrodes formed on both surfaces and polarized in the thickness direction. The piezoelectric ceramic rings 20 and 21 are overlapped via a terminal plate 22 such that their polarization directions are opposite to each other. The piezoelectric ceramic rings 20 and 21 are sandwiched between a weight 23 and a base 24 also serving as a case, and fastened with a nut 25. ing.

When vibrations in the thickness direction (vertical direction in the figure) of the piezoelectric ceramic rings 20, 21 are applied to the acceleration sensor, the piezoelectric ceramic rings 20, 21
A force F expressed by F = M · α (M: mass of the weight 74, α: acceleration) acts. At this time, a voltage represented by V = K · F (K is a proportional constant) is generated between the electrodes of the piezoelectric ceramic rings 20 and 21. That is, a voltage proportional to the acceleration is generated between the electrodes of the piezoelectric ceramic rings 20 and 21. By measuring the voltage, vibration can be detected.

[0005] Normally, in an impact detection device such as an airbag system, a self-diagnosis is performed for the presence or absence of a failure in an acceleration sensor and a signal processing circuit in order to ensure high reliability. As a conventional self-diagnosis method, a method of externally applying mechanical vibration to an acceleration sensor, measuring a capacitance of piezoelectric ceramics of the acceleration sensor, and the like are known.

[0006]

However, the conventional acceleration sensor can detect only a uniaxial acceleration component. Therefore, two acceleration sensors are required to detect acceleration components in two orthogonal axes. For this reason, there is a problem that the mounting space increases with an increase in the number of components, and it is difficult to accurately provide two sensors at right angles at the time of mounting the acceleration sensor.

Further, the conventional self-diagnosis method requires a vibration generator for externally applying a mechanical vibration to the acceleration sensor, so that the system becomes large. There is a problem that even if disconnection of a signal line can be detected, deterioration of piezoelectric characteristics cannot be detected. Further, Japanese Patent Application Laid-Open No. 63-241467 discloses a method of generating pulse-like distortion in piezoelectric ceramics and detecting an output voltage thereof.
There is a problem that it can be applied only to a uniaxial acceleration sensor.

The present invention is a single sensor having a simple structure,
The so-called self-diagnosis of whether acceleration in the two-axis direction can be detected using the acceleration detection terminal without providing a special detection terminal for self-diagnosis is possible. It is an object to provide a simple acceleration sensor.

[0009]

A two-axis acceleration sensor according to the present invention comprises a piezoelectric ceramic body and a pair of piezoelectric ceramic bodies provided on outer peripheral surfaces of the piezoelectric ceramic body at positions opposed to each other via the piezoelectric ceramic body. A first output electrode and a first output electrode at a position on the outer peripheral surface of the piezoelectric ceramic body facing each other via the piezoelectric ceramic body and
And a pair of second output electrodes provided at different positions from the output electrodes, and the piezoelectric ceramic body is polarized in a direction from each output electrode to an intermediate point between the output electrode and an adjacent output electrode. It is characterized by having. One example of the two-axis acceleration sensor of the present invention is that the piezoelectric ceramic body has a portion on the outer peripheral surface of another portion of the piezoelectric ceramic body which is adjacent to the portion having the first and second output electrodes in the length direction. It has a pair of input electrodes facing each other at a predetermined interval in the circumferential direction of the piezoelectric ceramic body, and the other portion of the piezoelectric ceramic body is polarized in the length direction. .

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the acceleration sensor according to the present invention will be described with reference to FIGS. FIG. 1A shows a piezoelectric vibrator used in one embodiment of the present invention. The piezoelectric vibrator includes a piezoelectric ceramic cylinder 6 fixed on a base 62.
One. The piezoelectric ceramic cylinder 61 includes a detection unit and a driving unit. The length of the cylinder 61 is set on the outer peripheral surface of the detection unit of the piezoelectric ceramic cylinder 61 at a position where the outer peripheral surface is divided into eight equal parts as shown in FIG. Strip electrode 7 parallel to the vertical direction
1, 72, 73, 74, 75, 76, 77, and 78 are formed, and the band electrodes 71, 73, 75, 77, which are located every other of the band electrodes, are used as ground electrodes. , The common ground electrode 80 is connected to the strip electrodes 71, 73, 7
5, 77 are connected adjacent to one end and extend in the circumferential direction of the piezoelectric ceramic circumference 61.

Here, each strip-shaped electrode is used for polarization processing of the piezoelectric ceramic cylinder 61. The polarization process is performed by applying a high DC voltage between the common ground electrode 80 and the other strip electrodes 72, 74, 76, 78. The direction of the polarization obtained in the detection unit in this manner is shown in FIG.
(A) is indicated by a dotted arrow.

Further, strip electrodes 72 and 7 facing each other are provided.
6. The strip electrodes 74 and 78 form a pair, one pair being used as an output electrode for the X-axis and the other pair being used as an output electrode for the Y-axis.

Next, the operation of the acceleration sensor of this embodiment will be described with reference to FIG. Here, the direction connecting the strip electrodes 72 and 76 is defined as the X-axis direction, and the direction connecting the strip electrodes 74 and 78 is defined as the Y-axis direction. Accordingly, the strip electrodes 72 and 76 are used for the X axis, and the strip electrodes 74 and 78 are used for the Y axis, and are connected to the inputs of the differential amplifier 83 and the differential amplifier 84, respectively.

When an oscillating acceleration in the X-axis direction is applied to the acceleration sensor as shown by a solid arrow in FIG.
A compressive force and a tensile force are generated alternately at the electrodes 72 and 76 of the piezoelectric ceramic cylinder 61. The directions of polarization viewed from the electrodes 72 and 76 of the piezoelectric ceramic cylinder 61 are the same, and the directions of the forces generated at the electrodes 72 and 76 are opposite (if one is compressed, the other is pulled). If one is pulled, the other is compressed), the voltages generated at the electrodes 72 and 76 have opposite polarities. Therefore, when the output voltages of the electrodes 72 and 76 are input to the differential amplifier 83 and acceleration is applied in the X-axis direction, an output proportional to the acceleration in the X-axis direction is obtained. Similarly, when acceleration is applied in the Y-axis direction, an output proportional to the acceleration in the Y-axis direction is obtained from the output electrodes 74 and 78 via the differential amplifiers 83 and 84.

When an acceleration other than the X-axis direction or the Y-axis direction is applied, the X-axis direction component and the Y-axis direction component are obtained.
By processing the signal output from No. 4, the magnitude of the acceleration can be obtained. In the acceleration sensor according to the present embodiment, the acceleration in the Z-axis direction (the axial direction of the piezoelectric ceramic cylinder: the front and back directions in FIG. 3) is determined by the electrodes 72, 74,
Since a voltage of the same polarity is generated in each of 76 and 78, it cannot be detected.

Next, the self-diagnosis function of the acceleration sensor according to the present embodiment will be described. As shown in FIG. 1B, a predetermined distance is provided on the outer peripheral surface of the driving portion of the piezoelectric ceramic cylinder 61 at a predetermined distance from the strip-shaped electrode 80 in the longitudinal direction thereof, and in the circumferential direction of the piezoelectric ceramic cylinder 61. The strip electrodes 81 and 82 are formed at intervals of. The strip electrodes 81 and 82 are used as drive electrodes. Here, the drive electrodes 81 and 82 are used for polarization processing of the piezoelectric ceramic cylinder 61 before being used as drive electrodes. The polarization process is performed by the drive electrodes 81 and 82 and the earth electrode 8.
This is carried out by applying a DC high voltage between zero. The direction of the polarization obtained in the driving unit in this manner is indicated by a dotted arrow in FIG. Next, as shown in FIG. 5A, a driving AC power source is connected to the electrodes 81 and 82, and an AC voltage is applied. Then, the left half and the right half of the piezoelectric ceramic cylinder 61 expand and contract alternately. As a result, the piezoelectric ceramic cylinder 61 performs a bending motion in the direction of the arrow (left-right direction) shown in FIG. At this time, if the frequency of the input AC voltage is made equal to the resonance frequency of the two-axis acceleration sensor shown in FIG. 1, the amplitude of the vibration (bending motion) becomes maximum, and the self-diagnosis detection sensitivity becomes the best.

In the state where the piezoelectric ceramic cylinder 61 is bent and vibrated as described above, when no external acceleration is applied, the acceleration components in the X-axis direction and the Y-axis direction have the same magnitude. Therefore, the amplitudes of the output voltages output from the differential amplifiers 83 and 84 should be equal.
Therefore, when there is a difference between the amplitudes of the output voltages from the differential amplifier 83 and the differential amplifier 84, it can be determined that the function of the acceleration sensor is abnormal. As described above, if a drive voltage for self-diagnosis is applied to the drive unit in a state where no acceleration is externally applied to the acceleration sensor, abnormalities such as disconnection and deterioration of piezoelectric characteristics can be detected.

As shown in FIG. 3, when a weight 63 is provided at one end of the piezoelectric ceramic column 61 and the other end is fixed to the base 62, the sensitivity of the acceleration sensor is improved. .

The same operation as described above can be achieved by using a pipe-shaped piezoelectric ceramic body instead of the piezoelectric ceramic cylinder.

Further, even when the direction connecting the pair of output electrodes 72 and 76 is not orthogonal to the direction connecting the pair of output electrodes 74 and 78, the piezoelectric ceramic cylinder 61 is externally provided.
Is obtained in proportion to the acceleration applied (excluding the Z-axis direction).

[0021]

According to the present invention, a pair of electrodes provided at positions facing each other via a piezoelectric ceramic body are connected to a first output terminal, and the piezoelectric ceramic body is formed on the outer peripheral surface of the piezoelectric ceramic body. By using a pair of electrodes provided at positions opposite to each other and at a position different from the first output electrode as a second output electrode, and using the first and second output electrodes as detection electrodes In addition, a two-axis acceleration sensor that does not require angle adjustment at the time of installation and does not require a large space for installation is obtained. Also, a predetermined distance in the circumferential direction of the piezoelectric ceramic body is provided on an outer peripheral surface of another portion of the piezoelectric ceramic body that is adjacent to the portion having the first and second output electrodes in the length direction. A pair of input electrodes facing each other is formed, and the input electrodes are used as drive electrodes,
By applying an AC voltage to the drive electrode to vibrate the piezoelectric ceramic body and detecting an output voltage corresponding to the vibration from the detection electrode, an abnormality of the acceleration sensor can be detected. Therefore, it is possible to detect an abnormality of the acceleration sensor without providing a special self-diagnosis detection terminal.

[Brief description of the drawings]

FIG. 1 shows one embodiment of the present invention, wherein (a) is a perspective view,
(B) is a partial development view.

FIGS. 2A and 2B show polarization directions of a piezoelectric ceramic cylinder used in the two-axis acceleration sensor of FIG. 1, wherein FIG. 2A is a cross-sectional view of a detection unit and FIG. 2B is a perspective view of a driving unit.

FIG. 3 is a diagram for explaining the operation of the two-axis acceleration sensor of FIG. 1;

FIG. 4 is a perspective view showing another embodiment of the present invention.

5A and 5B are views for explaining a self-diagnosis operation of the two-axis acceleration sensor in FIG. 1, wherein FIG. 5A is an overall perspective view, FIG. 5B is a driving section, and FIG. FIG.

FIG. 6 is a perspective view of a conventional acceleration sensor.

FIG. 7 is a side view of a conventional acceleration sensor.

[Explanation of symbols]

 20, 21 Piezoelectric ceramic ring 22 Terminal plate 23 Weight 24 Base 25 Nut 61 Piezoelectric ceramic cylinder 62 Base 63 Weight 71 to 78 Strip electrode 80 Common ground electrode 81, 82 Drive electrode 83, 84 Differential amplifier

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-268240 (JP, A) JP-A-63-241467 (JP, A) JP-A-1-102372 (JP, A) JP-A-3-302 273167 (JP, A) Japanese Utility Model Showa 60-56275 (JP, U) Japanese Utility Model Showa 50-62581 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01P 15/09

Claims (2)

(57) [Claims] A piezoelectric ceramic body, a pair of first output electrodes provided on the outer peripheral surface of the piezoelectric ceramic body at positions opposed to each other via the piezoelectric ceramic body, and A pair of second output electrodes provided on the outer peripheral surface at positions opposite to each other via the piezoelectric ceramic body and at a position different from the first output electrode, wherein the piezoelectric ceramic body has
A two-axis acceleration sensor, wherein each of the output electrodes is polarized in a direction toward an intermediate point between the output electrode and an adjacent output electrode. 2. The two-axis acceleration sensor according to claim 1, wherein
A predetermined interval is provided in the circumferential direction of the piezoelectric ceramic body on the outer peripheral surface of another portion of the piezoelectric ceramic body that is adjacent to the portion having the first and second output electrodes in the length direction. A two-axis acceleration sensor having a pair of input electrodes facing each other and wherein the other portion of the piezoelectric ceramic body is polarized in a length direction.