JPH08201418A - Acceleration sensor mounting structure - Google Patents

Abstract

PURPOSE: To enable acceleration sensors to detect the total acceleration applied to the sensors in orthogonal three-axis directions with nearly equal sensitivity by mounting both acceleration detecting elements so that the directions of their maximum sensitivity can be inclined by a specific angle toward the z-axis from the x- and y-axes. CONSTITUTION: Each acceleration sensor A and B is mounted on a sensor mounting surface 3 by positioning and fixing the external surface of a case lid 8 constituting an insulating case 2 nd the signal electrode 4 of each bimorph element 1 is connected to each wiring pattern formed on the surface by soldering, etc., through an external electrode formed on the case 2. In other words, the directions P of the maximum sensitivity of the elements 1 incorporated in the sensors A and B are inclined upward by 20-30 deg. toward the z-axis from the y- or x-axis. An arithmetic processing means calculates the sum of the absolute values of electric signals outputted from the sensors A and B as a synthesized signal and a signal processing circuit outputs the synthesized signal to the outside after processing the signal with a comparator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mounting structure for an acceleration sensor used for shock detection.

[0002]

2. Description of the Related Art Among acceleration sensors, there is one in which a bimorph element having fixed ends is used as an acceleration detecting element. As shown in a simplified form in FIG. 4, this acceleration sensor includes a bimorph element 1 and a bimorph element 1. And an insulating case 2 for locating and accommodating the sensor, and then mounting and fixing the sensor on a sensor mounting surface 3 such as a wiring board.

The bimorph element 1 here has a rectangular flat plate shape, and two piezoelectric ceramic plates 6 each having a signal electrode 4 and an intermediate electrode 5 formed on the front and back surfaces are superposed on each other. Each of the piezoelectric ceramic plates 6 that are integrated and face-bonded via the intermediate electrode 5 is polarized along the thickness direction of the piezoelectric ceramic plate 6 in the opposite direction to that of the piezoelectric ceramic plate 6 on the other side. Has been done. The dashed arrows in the figure indicate these polarization directions. Further, at this time, each of the signal electrodes 4 is formed along the longitudinal direction of each of the piezoelectric ceramic plates 6 and is drawn out to different one end portions.

On the other hand, the insulating case 2 is composed of the bimorph element 1.
A pair of sandwiching frames 7 having a U-shape in plan view, which sandwiches only both end portions along the longitudinal direction of the two, and the bimorph element 1 and the sandwiching frames 7 arranged to face each other with the bimorph element 1 interposed therebetween.
A pair of case lids 8 for closing the open surface formed by
It consists of and. Then, each of the signal electrodes 4 of the bimorph element 1 housed in the insulating case 2 is
It is connected to an external electrode (not shown) formed on each different outer end surface of the insulating case 2.

Further, the acceleration sensor is mounted by positioning and fixing the outer surface of either the holding frame 7 or the case lid 8 constituting the insulating case 2 on the sensor mounting surface 3, and the bimorph element 1 Each of the signal electrodes 4 is connected to a wiring pattern (not shown) on the sensor mounting surface 3 after passing through an external electrode formed on the insulating case 2. These wiring patterns are connected to a signal processing circuit (not shown), and the signal processing circuit can process the electrical signal output from the acceleration sensor to detect the acceleration due to the impact. It is supposed to be done.

[0006]

By the way, the bimorph element 1 as an acceleration detecting element has a maximum value when an acceleration in a direction normal to the surface of the piezoelectric ceramic plate 6, that is, a direction along the thickness direction thereof acts. In addition, when the acceleration of 180 degrees reverse direction is applied, the maximum electric signal of opposite positive and negative values and the same absolute value is output. It is the direction in which it occurs, that is, the maximum sensitivity direction P called the main axis of the acceleration sensor. When an acceleration in a direction along the tangential direction of the surface of the piezoelectric ceramics plate 6 is applied, no electric signal is output, that is, the detection sensitivity becomes zero, while either the normal direction or the tangential direction is detected. When the acceleration along the direction acts, the detection sensitivity has a magnitude corresponding to the angle θ formed by the maximum sensitivity direction P and the acting direction of the acceleration, that is, the maximum sensitivity S × cos θ times the detection sensitivity.

Therefore, when the acceleration sensor of the conventional structure is mounted on the sensor mounting surface 3, the maximum sensitivity direction P of the bimorph element 1 is parallel or perpendicular to the sensor mounting surface 3. That is, as shown in FIG. 4, orthogonal two-dimensional coordinate axes (planar coordinate axes) are provided on the sensor mounting surface 3.
x, y are set, orthogonal three-dimensional coordinate axes (spatial coordinate axes) x, y, z with the sensor mounting surface 3 as the xy plane are set, and the insulating case 2 in which the bimorph element 1 is incorporated
When the case cover 8 is attached to the sensor mounting surface 3, the maximum sensitivity direction P of the vertically oriented bimorph element 1 is detected.
Is aligned with the y-axis on the sensor mounting surface 3, x
The acceleration in the direction along the axis and the z axis, that is, the acceleration acting along any direction in the xz plane cannot be detected.

Although not shown, the holding frame 7 of the insulating case 2 is mounted on the sensor mounting surface 3 on which the orthogonal coordinate axes x and y are set, and the maximum sensitivity direction P of the bimorph element 1 is set to the sensor mounting surface 3. When the z-axis is perpendicular to the z-axis, it is impossible to detect the acceleration along any direction in the xy plane constituted by the x-axis and the y-axis. Therefore, coordinate axes x,
In order to detect all of the accelerations that will act along the y and z directions, three acceleration sensors whose maximum sensitivity direction P coincides with each of the x axis, y axis, and z axis are used. The signal must be mounted on the sensor mounting surface 3, which increases the number of accelerometers and the installation space, resulting in high cost, and also a signal for processing the electrical signals output from the three accelerometers. There is an inconvenience that the processing circuit is complicated.

By the way, in order to avoid such inconvenience, the maximum sensitivity direction of the bimorph element is tilted upward from the sensor mounting surface in advance so that the orthogonal coordinate axes x,
There has been proposed an acceleration sensor configured to detect acceleration acting along the three directions of y and z. That is, as an acceleration sensor of this type, although not shown, there is one disclosed in Japanese Patent Application Laid-Open No. 5-133974, in which the maximum sensitivity direction of an acceleration detecting element having a rectangular flat plate shape is set on the sensor mounting surface. There is shown an acceleration sensor characterized in that the acceleration sensor is installed at a tilt angle of 45 degrees (°) and the ridge line of the acceleration detecting element is further tilted at a direction of 45 degrees from the ridge line of the sensor mounting substrate. . And
When the acceleration sensor having such a configuration is adopted, the directions of the x-axis, the y-axis, and the z-axis (three directions that coincide with those shown in FIG. 2 according to the present invention: hereinafter, the same) are surely applied. It will be possible to detect the acceleration acting along.

However, three Cartesian coordinate axes x, y,
The fact that accelerations acting along z can be detected does not mean that accelerations in all directions can be detected, and it is not possible to detect accelerations that act in a plane perpendicular to the maximum sensitivity direction. It will be possible. Furthermore,
It goes without saying that the maximum sensitivity direction in the case of adopting the above configuration is 45 ° with respect to the z axis, but in this case, the x axis and the y axis and the maximum sensitivity direction are substantially 6 degrees.
Since the angle is 0 °, the detection sensitivities in the x-axis, y-axis, and z-axis directions do not become substantially equal.

The present invention was devised in view of these inconveniences, and is capable of detecting acceleration over a wide range with a small number, and for acceleration acting in either direction of the orthogonal coordinate axes. Even so, it is intended to provide a mounting structure of an acceleration sensor having substantially equal detection sensitivity.

[0012]

In order to achieve such an object, the structure for mounting an acceleration sensor according to the present invention has a rectangular coordinate axis (x, x, so that the sensor mounting surface is an xy plane).
x, on the sensor mounting surface after setting y, z)
It is provided with two acceleration sensors attached along a direction coinciding with each of the axes and the y-axis, and arithmetic processing means for calculating the sum of absolute values of electric signals output from each of these acceleration sensors. The maximum sensitivity direction of the acceleration detection element incorporated in one of the acceleration sensors is a direction inclined by 20 to 30 degrees from the y axis to the z axis, and the maximum sensitivity direction of the acceleration detection element incorporated in the other of the acceleration sensor is It is characterized in that the sensitivity direction is inclined from the x-axis toward the z-axis by 20 to 30 degrees. In addition, the acceleration detecting element in this case is a bimorph element with fixed ends, which is manufactured using piezoelectric ceramics.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partially cutaway perspective view showing the structure of the acceleration sensor itself according to this embodiment, FIG. 2 is an explanatory view showing a simplified mounting structure of the acceleration sensor, and FIG. It is a functional block diagram which shows operation | movement when a structure is employ | adopted. Since the configuration of the acceleration sensor itself is basically the same as that of the conventional example, the same parts and portions as those in FIG. 4 are denoted by the same reference numerals in FIGS. 1 and 2, and detailed description thereof is omitted here.

As shown in FIG. 1, each of the acceleration sensors according to the present embodiment comprises a bimorph element 1 of fixed both ends which functions as an acceleration detecting element, and an insulating case 2 which houses the bimorph element 1. These acceleration sensors are to be mounted on the sensor mounting surface 3 such as a wiring board. At this time, the bimorph element 1 is positioned and housed in the insulating case 2 after the maximum sensitivity direction P is tilted with respect to the sensor mounting surface 3, and the maximum sensitivity direction P is in the sensor mounting surface 3. The inclination angle θ from is set to be 20 ° or more and 30 ° or less, for example, 25 ° in an upward direction.

That is, the bimorph element 1 here is
A pair of piezoelectric ceramic plates 6 each having a rectangular flat plate shape and having a signal electrode 4 and an intermediate electrode 5 formed on the front and back surfaces are face-to-face joined together, and this is adjusted to the inclination angle θ.
It has been cut off with °. Each of the piezoelectric ceramic plates 6 bonded via the intermediate electrode 5 is polarized in the direction opposite to the other side along the thickness direction of the piezoelectric ceramic plate 6, and each of the signal electrodes 4 is provided in each piezoelectric ceramic plate. It is the same as the conventional example in that it is pulled out to different one end portions along the longitudinal direction of 6. In addition, the insulating case 2 at this time is configured by using the sandwiching frame 7 and the case lid 8 similar to the conventional example, and the signal electrodes 4 of the bimorph element 1 are formed on different outer end surfaces of the insulating case 2. And an external electrode (not shown).

Furthermore, as shown in FIGS. 2 and 3, the mounting structure of the acceleration sensor according to the present embodiment is arranged along the directions corresponding to the orthogonal coordinate axes x and y on the same sensor mounting surface 3. Two accelerometers A attached,
B and the absolute value of the electrical signals V _A and V _B output from each of these acceleration sensors A and B (│V _A │ + │V
_B |) to calculate the processing means 10 and the signal processing circuit 1
1 and. Note that the configuration of the arithmetic processing means 10 itself that executes the above-described arithmetic processing is well known, so a detailed description thereof will be omitted here.

Each of the acceleration sensors A and B is mounted on the sensor mounting surface 3 by positioning and fixing the outer surface of the case lid 8 which constitutes the insulating case 2, and the signals of the bimorph element 1 are attached. Each of the electrodes 4 passes through an external electrode (not shown) formed on the insulating case 2 and is connected to each of wiring patterns (not shown) formed on the sensor mounting surface 3 by soldering or the like. There is. That is, the maximum sensitivity direction P of the bimorph element 1 incorporated in the acceleration sensor A at this time is an upward direction inclined by 25 ° from the y axis to the z axis, and the maximum sensitivity direction P of the bimorph element 1 in the acceleration sensor B is set. P is upwardly tilted by 25 ° from the x-axis toward the z-axis.

The operation of the acceleration sensors A and B according to this embodiment will be described below with reference to FIGS. In the following description, the maximum sensitivity of the acceleration sensors A and B is S (mV / G: G is gravitational acceleration).

First, consider a case where an acceleration of 1 G acts from the positive direction of the Cartesian coordinate axis x on the mounting structure composed of two acceleration sensors A and B arranged according to the positional relationship shown in FIG. The detection sensitivity of the acceleration sensor A mounted along the direction coinciding with the axis is cos 9 of the maximum sensitivity S.
It will be expressed as 0 ° times, and the detection sensitivity of the acceleration sensor B mounted along the direction coinciding with the x-axis will be expressed as cos 25 ° times the maximum sensitivity S. Therefore, the electrical signal V _A output from the acceleration sensor A at this time is S × cos 90 ° × 1 (mV), and the electrical signal V _B output from the acceleration sensor _B is S × cos 25 ° × 1 (m).
V), the sum of absolute values of the electric signals V _A and V _B output from the acceleration sensors A and B (│V _A │ + │V _B │). , │S × cos 90 ° │ + │S × cos 25 ° │ = S × 0.91
(MV) will be calculated as the composite signal V _AB .

Then, the combined signal V _AB calculated according to such a procedure is output to the signal processing circuit 11, and in this signal processing circuit 11, a preset S ₀ is used as a threshold value. Then, the comparator process is performed. That is, in the signal processing circuit 11,
If V _AB > S ₀ , the comparator signal V _S = 1 and V _AB
If <S ₀ , the comparator processing is performed such that the comparator signal V _S = 0, and then the comparator signal V _S is output to the outside. Note that the above description is for the case where an acceleration of 1 G acts from the positive direction of the orthogonal coordinate axis x, but the same applies to the case where an acceleration of 1 G acts from the positive direction of the orthogonal coordinate axis y, and S × as the composite signal V _AB. 0.
91 (mV) will be calculated.

Furthermore, when an acceleration of 1 G acts on the mounting structure of FIG. 2 from the positive direction of the orthogonal coordinate axis z, the following operation is performed. That is, the detection sensitivities of the acceleration sensors A and B in the directions coinciding with the z-axis are cos65 of the maximum sensitivity S because the inclination angle θ of the acceleration sensors A and B with respect to the sensor mounting surface 3 is 25 °.
It will be expressed as a multiple of °, that is, (90 ° -25 °). Therefore, the electric signals V _A and V _B output from the acceleration sensors A and B at this time are both S × cos 6
It is expressed as 5 ° × 1 (mV), and in the arithmetic processing means 10, | S × co which is the sum of absolute values of the electric signals V _A and V _B output from the acceleration sensors A and B.
s65 ° │ + │S × cos65 ° │ = S × 0.85 (mV)
_Will be calculated as the combined signal V _AB .

That is, when the mounting structure of the acceleration sensor according to the present embodiment is adopted, substantially the same detection sensitivity is obtained in any of the orthogonal coordinate axes x, y, z. Further, in the mounting structure according to the present embodiment, the direction in which the sensitivity is not detected exists only along the direction orthogonal to the maximum sensitivity direction P of each of the acceleration sensors A and B, and the acceleration over a wide range is detected. There is also an advantage that it can be done.

By the way, in the present embodiment, the combined signal V _AB when the acceleration along the x-axis and the y-axis acts is S ×.
It becomes 0.91 (mV), and the combined signal V _AB when the acceleration along the z axis acts is S × 0.85 (mV). However, such a difference occurs between the acceleration sensors A and B. This is because the inclination angle θ with respect to each sensor mounting surface 3 is set to 25 ° for manufacturing convenience. That is, in the calculation, the inclination angle θ is set to 26.565 ... °, so that the detection sensitivities which are completely matched can be obtained in any of the x-axis, y-axis, and z-axis directions. .

By the way, the inventors of the present invention have studied, and as a result, they have been incorporated into two acceleration sensors A and B, respectively, which are arranged along the direction on the sensor mounting surface 3 which coincides with the orthogonal coordinate axes x and y. Maximum sensitivity direction P of bimorph element 1
When the inclination angle θ of the sensor mounting surface 3 from 0 ° to 90 ° is changed, the sum of absolute values of the electric signals V _A and V _B output from the acceleration sensors A and B (│V _A │ + │V
It has been confirmed that _B | shows the changes shown in Table 1.

[0026]

[Table 1]

Further, according to Table 1, the maximum sensitivity direction P of the bimorph element 1 constituting each of the acceleration sensors A and B is inclined from the sensor mounting surface 3 within a range of 20 ° to 30 °. Only in this case, by calculating the sum of the absolute values of the electric signals V _A and V _B output from the acceleration sensors A and B, it becomes clear that the detection sensitivities in the directions of the three axes orthogonal to each other become substantially equal. Has become.

[0028]

As described above, according to the mounting structure of the acceleration sensor of the present invention, the accelerations acting in any of the three axial directions orthogonal to each other can be detected by the two acceleration sensors. Sensitivity can be detected, and acceleration can be detected over a wide range. As a result, not only the mounting structure is simplified, but also the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing the configuration of an acceleration sensor itself according to the present embodiment.

FIG. 2 is an explanatory view showing a simplified mounting structure of the acceleration sensor according to the present embodiment.

FIG. 3 is a functional block diagram showing an operation when the mounting structure of the present embodiment is adopted.

FIG. 4 is a partially cutaway perspective view showing a configuration of an acceleration sensor according to a conventional example.

[Explanation of symbols]

 1 bimorph element (acceleration detecting element) 3 sensor mounting surface 10 arithmetic processing means A acceleration sensor B acceleration sensor P maximum sensitivity direction x Cartesian coordinate axis y Cartesian coordinate axis θ Tilt angle

Claims (2)

[Claims] 1. The Cartesian coordinate axes (x, y, z) are set so that the sensor mounting surface (3) is an xy plane, and they coincide with the x axis and the y axis on the sensor mounting surface (3). Two acceleration sensors (A,
And B), the sum of the absolute values of these acceleration sensors (A, B) respectively output from the electrical signal _{(V A, V B) (} │V A │ +
│V _B │), the maximum sensitivity direction (P) of the acceleration detection element (1) incorporated in one of the acceleration sensors (A, B) is from the y-axis. The maximum sensitivity direction (P) of the acceleration detecting element (1) which is inclined by 20 to 30 degrees toward the z axis and is incorporated in the other of the acceleration sensors (A, B) is changed from the x axis to the z axis. A mounting structure for an acceleration sensor, wherein the mounting structure is an inclination of 20 to 30 degrees. 2. The mounting structure for an acceleration sensor according to claim 1, wherein the acceleration detecting element (1) is a bimorph element having fixed ends and made of piezoelectric ceramics.