JPH05232135A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To obtain an acceleration sensor, which can arbitrarily set the reference point and the measuring range of a sensor, and whose accuracy and reliability are improved. CONSTITUTION:An acceleration sensor generates an output voltage VO, which is proportional to acceleration G, by imparting the acceleration G on a gage part 1 for detecting the acceleration G, imparting the signal from the gage part into an electronic circuit 12 comprising a VC detector 11, a pulse modulator 8, a NOT circuit 9 and a filter 10. The difference in sizes is provided in the gap between a movable electrode 5 of the gage part 1 and facing two fixed electrodes 4 and 5 in this constitution. The gap difference is formed by using grinding, micromachining and the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor, and more particularly to an acceleration sensor mounted on an automobile or the like to control its movement.

[0002]

2. Description of the Related Art Conventionally, as a structure of a sensor, Japanese Patent Laid-Open No.
As shown in the −110383 acceleration sensor, the gap between the cantilever and the movable electrode that is displaced at the tip of the cantilever corresponding to the acceleration, and the two fixed electrodes that face each other has the same value. ..

[0003]

This gauge structure has a measurement range narrower than the theoretical value when the sensor is arranged in the direction of the earth's gravity because the gauge structure is not considered as a reference when the earth receives 1G of gravity. Become. Also, the detected acceleration range is +
No consideration was given to the case where (plus)-(minus) is set asymmetrically, for example, + 50G to -20G.

[0004]

[Means for Solving the Problems] A structure is provided in which the gap difference between a movable electrode that is displaced in accordance with the acceleration of an acceleration detecting gauge portion and two fixed electrodes facing the movable electrode has a large and small size difference. ..

[0005]

[Function] By changing the gap difference between the two fixed electrodes facing the movable electrode of the acceleration detection gauge section, the position of the acceleration detection reference point can be changed, and the acceleration range to be detected can be set arbitrarily. it can. Thereby, the optimum value of the sensitivity of the acceleration detection processing circuit can be used,
Accuracy and reliability are improved. In addition, since the gauge portion can be formed in the same process, standardization and cost reduction can be achieved.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a diagram showing a circuit configuration of an acceleration sensor. In FIG. 1, the gauge unit 1 detects an acceleration G, applies this signal to an electronic circuit 12, and processes it to produce an output V0 proportional to the acceleration G. The gauge portion 1 is formed by sandwiching the movable electrode 3 between the upper and lower glass substrates 6 and 7, and the movable portion is fixed to the glass substrates 6 and 7 by the beam 2. Fixed electrodes 4, 5 are provided above and below the movable electrode 3.
Are opposed to each other, and the fixed electrodes 4 and 5 are fixed to the upper and lower glass substrates. The fixed electrode 4 and the movable electrode 3 have a capacitance C
1, the fixed electrode 5 and the movable electrode 3 have an electrostatic capacitance C2, and this value is given to the electronic circuit 12. The electronic circuit 12 is composed of a C detector 11, a pulse modulation circuit 8, a knot circuit 9 and a filter 10,
The servo type is formed with the configuration of 8 and 9. When the acceleration G is applied to the gauge unit 1, the movable electrode 3 moves due to the inertial force based on the velocity. Therefore, the distance between both electrodes changes and the electrostatic capacitances C1 and C2 change. The VC detector 11 is
Since it operates so as to detect the difference C between C1 and C2, a voltage VC proportional to C is output. The pulse width modulator 8 is VC
A pulse voltage VE having a pulse width proportional to the value of is generated, and this pulse is applied to one of the fixed electrodes 4 and 5.
With this circuit configuration, the inertial force due to the acceleration G and the electrostatic force due to the pulse voltages VE and VF are balanced, and the pulse width of the pulse voltage VE can be extracted by the filter 10 to obtain the voltage V0 proportional to the acceleration G. .. 2 is shown in FIG.
The pulse output waveform VE of the sensor of
When the acceleration is 0, the pulse width TW of the pulse voltage VE is
When the period T is 50% and G is positive (G> 0), the pulse width increases from 50%, and when it is negative (G <0), the pulse width decreases from 50%. That is, in the configuration of FIG. 1, the pulse width TW changes according to the acceleration G, and the output voltage V0 obtained by filtering this waveform 10 has a value proportional to the acceleration G. FIG. 3 shows the circuit configuration of an open loop system that does not use a servo system, which is composed of a VC detector 11, an amplification diagram 14, and an output adjuster 13. In this capacitance type acceleration sensor, the present invention shows the structure of the gauge section 1. Acceleration detection gauge section 1
Gap d between the movable electrode 3 and the two fixed electrodes 4 and 5
By adding a dimensional difference (d1-d2 ≠ 0) to 1 and d2,
The position where the acceleration G and the electrostatic force are balanced and the position of the reference point for acceleration detection can be changed, and the acceleration measurement range to be detected can be set arbitrarily. 4 to 7
4 is an embodiment of a structure in which the gaps d1 and d2 of the present invention are provided with a dimensional difference.
Polishing), and the gap d between the movable electrode 3 and the fixed electrodes 4 and 5
1 and d2 are different in size. In FIG. 5, the gap d1 between the movable electrode 3 and the fixed electrodes 4 and 5 is changed by changing the thickness of one of the fixed electrodes 4 and 5 facing the movable electrode 3.
2 has a dimensional difference. FIG. 6 shows the fixed electrodes 4, 5 formed by silicon micromachining of the movable electrode 3.
The gaps d1 and d2 between and are added to the dimensional difference.

FIG. 7 shows the cantilever 2 which supports the movable electrode 3 and which is made different by silicon micromachining so that the gaps d1 and d2 between the fixed electrode 4 and 5 are made different.

The gap difference d1−d2 is | d1−d2 | = 0 from the value of capacitance change and the sensitivity of the electronic circuit section.
It is set so as to be between 4 μm and 4 μm. The embodiment of FIGS. 4 to 7 is a diagram in the case where the movable electrode 3 is installed so as to face the fixed electrode upper 4 and lower 5 so as to receive the gravity of the earth, and the upper gap d1 and the lower gap d2 are arranged. Relationship with
Although d2 ≧ d1 holds, the same holds true for the opposite case of d2 ≦ d1.

According to the present invention, the movable electrode 3 and the fixed electrode 4,
By giving a dimensional difference to the gap difference of 5, the optimum value of the sensitivity of the acceleration detection processing circuit can be used, and the acceleration measurement range can be set arbitrarily, so that accuracy and reliability are improved. Moreover, since the gauge part can be created in the same process, standardization and cost reduction can be achieved.

[0010]

As described above, according to the present invention, the size of the gap between the movable electrode and the fixed electrode is made different from each other to form the gauge portion, so that the precision and reliability of the miniaturized acceleration sensor is improved. Has the effect of providing.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram in the case where the acceleration sensor according to an embodiment of the present invention is configured by a servo system.

FIG. 2 is an operation waveform diagram.

FIG. 3 is a circuit configuration diagram in the case of being configured by an open loop system.

FIG. 4 is a cross-sectional view when the dimensional difference of the gap between the movable electrode and the fixed electrode is changed, and is a view showing a case where the thickness of the glass substrate is changed.

FIG. 5 is a diagram showing a case where the thickness of the fixed electrode is changed similarly.

FIG. 6 is a diagram showing a case where the thickness of the fixed electrode is changed similarly.

FIG. 7 is a diagram showing a case where the thickness of the cantilever is changed similarly.

[Explanation of symbols]

1 ... Gauge part, 2 ... Cantilever, 3 ... Movable electrode, 4 ...
Fixed electrode, 5 ... Fixed electrode (lower side), 6 ... Glass substrate (upper), 7 ... Glass substrate (lower), 8 ... Pulse modulation circuit,
9 ... Knot circuit, 10 ... Filter, 11 ... VC detector,
12 ... Electronic circuit, 13 ... Output regulator, 14 ... Amplifier.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiji Hanzawa 2477 Kashima Yatsu, Takaba, Katsuta-shi, Ibaraki Prefecture 3 Hitachi Automotive Engineering Co., Ltd. (72) Hirokazu Fujita 2520 Takata, Katsuta-shi, Ibaraki Stocks Company Hitachi, Ltd. Automotive Equipment Division

Claims (4)

[Claims] 1. A gauge, which is an acceleration detecting element having at least one or more cantilevers and a movable electrode displacing in response to acceleration at its tip, and two fixed electrodes facing the movable electrode, and a gauge thereof. As an electric signal processing, in an acceleration sensor having an acceleration detection processing circuit composed of an integrated circuit (IC) or the like, a gap between two fixed electrodes facing the movable electrode of the gauge part is made different in size. And the acceleration sensor. 2. The acceleration sensor according to claim 1, wherein the range for detecting acceleration is changed by changing the gap difference between the fixed electrode facing the movable electrode and the fixed electrode. 3. The gap according to claim 1, wherein the fixed electrode facing the movable electrode has a gap of d1 and d2, and a reference 0G (G =
In the condition of 9.8 m / s ² ), the gap difference (| d1-d2
|) Is an acceleration sensor characterized in that d = 0 to 4 μm. 4. The gap according to claim 1, wherein when the gauge is installed so that the fixed electrode is vertically opposed to the movable electrode so as to receive the gravity of the earth, an upper gap d1 and a lower gap d2 are provided. An acceleration sensor characterized in that the relationship with is d2 ≧ d1.