JPH0634653A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To obtain a capacitance type acceleration sensor being excellent in durability and bringing forth few errors in measurement. CONSTITUTION:A recession 7 of a prescribed depth is provided in a base 1 formed of an insulative plate-shaped member and a fixed electrode 4 is fixed at a prescribed position of this recession 7. A detecting part 3d corresponding to the fixed electrode 4 and formed of a flat plate member and a movable electrode 3 which connects this detecting part 3d with an outer peripheral part 3b on the outside through a plurality of support parts 3c and supports the detecting part 3d displaceably in the vertical direction to the fixed electrode 3 are fixed to the base 1 so that the detecting part 3d faces the fixed electrode 4 with a prescribed gap between them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an acceleration sensor that detects acceleration as a change in capacitance.

[0002]

2. Description of the Related Art In recent years, an air bag device, an active suspension and the like are mounted on a vehicle and the like, and an acceleration sensor for detecting acceleration is used for controlling these devices. Capacitance type sensors as shown in FIGS. 3 to 5 are known as the acceleration sensor, and the base end 23b of the movable electrode 23 formed of a plate-like member is fixed to the convex portion 21a of the substrate 21 to be predetermined. The free end 23a having the area of 5 is projected above the recess 27 formed in the center of the substrate 21.

A fixed electrode 24 is provided in a recess 27 facing the free end 23a of the movable electrode 23, and a predetermined gap is provided between the fixed electrode 24 and the movable electrode 23.
When acceleration in the direction of the arrow in the figure is applied to this acceleration sensor,
The free end 23a as the inertial mass bends in the direction opposite to the acceleration to change the gap with the fixed electrode 27, and the acceleration can be known by measuring the increase / decrease value of the electrostatic capacitance generated in this gap.

[0004]

However, in the above-mentioned conventional acceleration sensor, the movable electrode 23 is used during acceleration or deceleration.
Since the free end 23a inclines about the base end 23b as a fulcrum, the distance between the movable electrode 23 and the fixed electrode 24 is not parallel as shown in FIG. Although not shown, a tilt may also occur in the width direction of the free end 23a, and the tilt may cause the capacitance to vary, resulting in a measurement error.

When an excessive acceleration is applied, the movable electrode 2
In some cases, the free end 23a of No. 3 bends and collides with the fixed electrode 24, causing the free end 23a to be deformed, causing the preset capacitance to be deviated and failing to obtain accurate acceleration.

Therefore, it is an object of the present invention to provide an acceleration sensor which is excellent in durability and has a small measurement error.

[0007]

According to the present invention, a concave portion having a predetermined depth is provided on a substrate formed of an insulating plate-like member, and a fixed electrode is fixed to a predetermined position of the concave portion.
The detection unit formed of a flat plate member corresponding to the fixed electrode and the detection unit and the outer peripheral portion are connected via a plurality of support units to support the detection unit in a freely displaceable manner in the vertical direction of the fixed electrode. The movable electrode is fixed to the substrate so that the detection unit faces the fixed electrode with a predetermined gap.

[0008]

Therefore, when acceleration is applied, the detecting portion of the movable electrode bends within the range allowed by the support portion, and the gap between the movable electrode and the fixed electrode changes, so that the capacitance also changes and the acceleration can be detected. Since the detection part is supported at multiple points on the outer peripheral edge by the support part, it maintains parallel to the fixed electrode and is displaced only in the vertical direction, reducing fluctuations in capacitance due to tilting of the detection part and making measurement accuracy. Further, since the displacement amount of the detecting portion of the movable electrode is regulated by the supporting portion, the movable electrode does not collide with the fixed electrode even if it receives an excessive acceleration.

[0009]

1 and 2 show an embodiment of the present invention.

As shown in FIGS. 1 and 2, reference numeral 1 is a plate-shaped substrate made of an insulating material, and a circular recess 7 having a predetermined depth is provided in the center of the side surface of the substrate 1. 2 is substrate 1
The substrate is a substrate that is fastened to the inside to hermetically protect the inside.
It has the same shape as.

Flat end faces 8 are formed around the recesses 7 of the substrates 1 and 2, respectively, and the end faces 8 are in contact with each other, and the substrates 1 and 2 are joined by a fastening means (not shown).

A fixed electrode 4 having a predetermined area is fixed to the center of the recess 7 of the substrate 1. The fixed electrode 4 is formed of a circular plate member.

Reference numeral 3 denotes a movable electrode integrally formed of a circular plate member, and a detection portion 3d formed in a circular shape having a predetermined area is provided in the central portion of the movable electrode 3 facing the fixed electrode 4. An outer peripheral portion 3b fixed to the end surface 8 is provided on the outer periphery.
Between the outer peripheral portion 3b and the detecting portion 3d, there are two on the same circumference.
A plurality of annular grooves 3a formed by punching a predetermined circular arc (substantially semicircle) are provided at predetermined locations at predetermined radiuses.

The movable electrode 3 sandwiched in the circumferential direction at the ends of the annular grooves 3a serves as a support portion 3c, and the annular groove 3 is formed in the radial direction.
When the arcuate movable electrode 3 surrounded by a is used as the connecting portion 3e, the supporting portion 3c has a predetermined width and prevents the outer peripheral end of the detecting portion 3d and the connecting portion 3e from being displaced in the twisting direction. While being arranged at every 180 degrees on the circumference, these supporting portions 3
c is displaced from the outer circumference of the movable electrode 3 toward the detecting portion 3d by 90 degrees each time the annular groove 3a is crossed.

Since the connecting portion 3e connecting these supporting portions 3c is restrained from the adjacent connecting portion 3e in the radial direction by the through hole 3a, it is possible to make a minute displacement in the vertical direction of the surface of the movable electrode 3 and to detect it. The portion 3d is 2 at the outer peripheral end in the diametrical direction.
The points are supported by the supporting portion 3c and the outer peripheral portion 3 is supported by the connecting portion 3e.
The fixed electrode 4 facing b is supported so as to be displaceable in the vertical direction.

The movable electrode 3 has the outer peripheral portion 3b formed in the concave portion 7 of the substrate 1.
Fixed to the end face 8 on the concentric circle of the detection part 3d of the movable electrode 3
A predetermined gap is provided between the fixed electrode 4 and the fixed electrode 4.

Pins 5 that penetrate the through holes 30 and 31 of the movable electrode 3 and that engage with the substrate 2 and fix it at a predetermined position are provided at opposing positions on the end face 8 of the substrate 1.

2 is provided on the end surface of the substrate 1 which is not provided with the recess 7.
The terminals 6 of the book project and are electrically connected to the movable electrode 3 and the fixed electrode 4, respectively, while these terminals 6 are connected to a measuring circuit (not shown).

With the above construction, the operation will be described below.

This acceleration sensor is installed in a direction in which the movable electrode 3 is orthogonal to the axial direction of the acceleration to be measured.

In a constant speed or a stopped state where no acceleration is applied, the gap between the detecting portion 3d and the fixed electrode 4 is maintained at a preset value, and the electrostatic capacitance detected in this state indicates a state of zero acceleration.

When acceleration is applied, the detection portion 3d having a predetermined area, that is, a predetermined inertia, is slightly displaced by the inertial mass in the direction toward or away from the fixed electrode 4 to change the gap. Due to this change in the gap, the detection unit 3 of the movable electrode 3
The electrostatic capacitance between d and the fixed electrode 4 changes, and the acceleration is obtained from the increase / decrease value of the electrostatic capacitance by a measuring circuit (not shown).
When the detecting unit 3d is displaced, the supporting unit 3c and the connecting unit 3e are deflected by the acceleration to change the gap between the detecting unit 3d and the fixed electrode 4. The detecting unit 3d is a supporting unit 3c having a predetermined width at two positions on both ends. Since it is supported and is displaced in the vertical direction, it can be displaced in the vertical direction while maintaining a parallel state while preventing tilting and twisting with respect to the fixed electrode 4 which faces it, and only changes in electrostatic capacitance depending on acceleration. Obtainable.

Further, since the displacement of the detecting portion 3d is a minute displacement due to the bending generated in the supporting portion 3c and the connecting portion 3e due to the acceleration, even if an excessive acceleration is applied, the supporting portion 3d.
It is possible to configure an acceleration sensor that has a high durability against impact such as a drop without the c and the connecting portion 3e restricting the excessive displacement of the detecting portion 3d and colliding with the fixed electrode 4.

In the above embodiment, the movable electrode 3 is provided with the annular groove 3a in the single plate-like member to form the outer peripheral portion 3b, the support portion 3c, the detecting portion 3d and the connecting portion 3e. Each part of 3 may be constituted by a separate member if necessary.

Further, although the annular groove 3a is formed into an arc and the detecting portion 3d is formed into a circular shape in the above embodiment, the shape is not limited to these shapes, and although not shown, the detecting portion 3d is formed in a rectangular shape. The rectangular outer peripheral portion 3b may be connected by a plurality of supporting portions 3c formed of wire members. In this case, the annular groove 3a corresponds to the detecting portion 3d, the outer peripheral portion 3b and the supporting portion 3c. It becomes the enclosed space, and other functions and effects are the same as those in the above-mentioned embodiment.

[0026]

As described above, according to the present invention, a plurality of positions of the detecting portion of the movable electrode are supported by the supporting portion, and the detecting portion is displaced only in the vertical direction while always maintaining the parallel with the fixed electrode. The accuracy of measurement can be improved by reducing the fluctuation of the capacitance due to the inclination of the movable electrode, and the amount of displacement of the detection part of the movable electrode is regulated by the support part. It is possible to provide a highly durable acceleration sensor which does not collide with.

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment of the present invention.

FIG. 2 is a view on arrow AA of FIG.

FIG. 3 is a front view showing a conventional example.

FIG. 4 is a side view of FIG.

FIG. 5 is an enlarged view showing the movable electrode in a state where acceleration is applied.

[Explanation of symbols]

 1 substrate 3 movable electrode 3a annular groove 3b outer peripheral portion 3c support portion 3d detecting portion 4 fixed electrode 7 concave portion

Claims (1)

[Claims] 1. A substrate formed of an insulating plate-like member is provided with a recess having a predetermined depth, and a fixed electrode is fixed to a predetermined position of this recess, while a flat plate member corresponding to the fixed electrode is used. The detection unit fixes the formed detection unit and a movable electrode that connects the detection unit and the outer peripheral portion through a plurality of support units to support the detection unit so that the detection unit is freely displaced in the vertical direction of the fixed electrode. An acceleration sensor, which is fixed to a substrate so as to face an electrode with a predetermined gap.