JPH07120498A - Characteristic adjusting method for capacitance type acceleration sensor - Google Patents

Abstract

PURPOSE:To regulate dispersion of linearity within a prescribed range, and improve yield of a sensor by correcting the linearity when linearity of an output voltage characteristic to a prescribed acceleration exceeds a prescribed value. CONSTITUTION:An acceleration signal 30 generated from a centrifugal machine or the like and output voltage Vo corresponding to acceleration generated by a semiconductor capacity type acceleration sensor 1, are inputted to a control part 29. The control part 29 performs operation on linearity from the relationship between the acceleration and the output voltage, and compares a maximum value of the linearity with a prescribed value, and connects a terminal T1 to the ground when the maximum value is larger than the prescribed value. Then, a switch of the sensor 1 is turned on, and linearity of the prescribed voltage Vo can be improved by operating a linearity compensating circuit 14. Since the terminal T1 is not connected to the ground when the maximum value of the linearity is not more than the prescribed value, the switch 13 is turned off, and the compensating circuit 14 is separated, and improving the linearity is not performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an airbag system for detecting a collision of an automobile and opening an airbag to protect a passenger's body, and more particularly to a capacitance type acceleration sensor for detecting the collision of the automobile. The present invention relates to a suitable characteristic adjustment method.

[0002]

2. Description of the Related Art Conventionally, various acceleration sensors which are key sensors for airbag systems have been known.

For example, regarding the structure and characteristics of the sensor,
There is JP-A-1-152369. This sensor has a certain level of linearity in the relationship of output characteristics to acceleration. Further, the output stage has a non-linear compensation circuit (linearity compensation circuit).

[0004]

The acceleration sensor, which is the key sensor of the conventional airbag system, generally has a linearity compensation circuit in order to improve the linearity relationship of the output characteristic with respect to the acceleration. In addition, the acceleration sensor has variations in manufacturing, especially in the structure of the detection unit, and the linearity of the output characteristics with respect to acceleration also varies (some linearity is large, and some linearity is small). However, in order to improve linearity uniformly with the linearity compensation circuit,
On the contrary, the one having a small linearity has a problem that the yield of the sensor is deteriorated (increased) on the contrary and the yield of the sensor is deteriorated.

An object of the present invention is to improve the yield of the sensor by keeping the variation within a predetermined range even if the linearity of the output characteristic with respect to the acceleration varies.

[0006]

In order to achieve the above-mentioned object, the linearity of the output voltage characteristic with respect to a predetermined acceleration and the predetermined linearity of the first linearity with respect to the linearity of the output voltage characteristic with respect to a predetermined acceleration. When the linearity of the output voltage characteristic with respect to the predetermined acceleration is less than or equal to the predetermined value of the first linearity, the linearity of the output voltage characteristic with respect to the predetermined acceleration is not corrected and When the linearity of the output voltage characteristic with respect to the acceleration of exceeds the predetermined value of the first linearity,
The linearity of the output voltage characteristic with respect to a predetermined acceleration is corrected.

Further, in relation to the linearity of the capacitance characteristic with respect to a predetermined acceleration, the linearity of the capacitance characteristic with respect to a predetermined acceleration is compared with a predetermined value of the second linearity, and the predetermined acceleration is obtained. When the linearity of the capacitance characteristic with respect to the second linearity is equal to or less than the predetermined value of the second linearity, the linearity of the output voltage characteristic with respect to the predetermined acceleration is not corrected, and the straight line of the capacitance characteristic with respect to the predetermined acceleration is not corrected. When the linearity exceeds a predetermined value of the second linearity, the linearity of the output voltage characteristic with respect to a predetermined acceleration is corrected.

[0008]

In the relationship of the linearity of the output voltage characteristic with respect to the predetermined acceleration, the linearity of the output voltage characteristic with respect to the predetermined acceleration is compared with the predetermined value of the first linearity, and the output voltage characteristic with respect to the predetermined acceleration is compared. Of the first linearity is equal to or less than the predetermined value of the first linearity, the linearity of the output voltage characteristic with respect to the predetermined acceleration is not corrected, and the linearity of the output voltage characteristic with respect to the predetermined acceleration is the first linearity. When the linearity exceeds the predetermined value, the linearity of the output voltage characteristic with respect to the predetermined acceleration is corrected.

Further, in relation to the linearity of the capacitance characteristic with respect to a predetermined acceleration, the linearity of the capacitance characteristic with respect to a predetermined acceleration is compared with a predetermined value of the second linearity to obtain the predetermined acceleration. When the linearity of the capacitance characteristic with respect to the second linearity is equal to or less than the predetermined value of the second linearity, the linearity of the output voltage characteristic with respect to the predetermined acceleration is not corrected, and the straight line of the capacitance characteristic with respect to the predetermined acceleration is not corrected. If the linearity exceeds the second linearity predetermined value, the linearity of the output voltage characteristic with respect to the predetermined acceleration is corrected. Even if there is a variation in the linearity of the output characteristic with respect to the acceleration, if the variation is small, the linearity is not corrected,
If the variation is large, the linearity is corrected so that the final variation in the linearity can be kept within a predetermined range, and the yield of the acceleration sensor can be improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram including an acceleration sensor according to the present invention.

The semiconductor capacitive acceleration sensor 1 comprises an acceleration detector 2, a capacitance detector 3, an amplifier 4, and a controller 5.

The acceleration detecting section 2 has a three-layer sandwich structure of glass, silicon and glass. In the central silicon layer 6, a movable electrode 7 having a function of a weight and a silicon cantilever 8 supporting the movable electrode 7 are integrally formed by etching silicon from both sides. The silicon cantilever 8 is composed of a single piece or plural pieces.

On the other hand, on the glass layers 9 and 10 on both sides, a pair of fixed electrodes 11 and 12 are arranged vertically so as to face the movable electrode 7. The fixed electrodes 11 and 12 are made of a metal material such as aluminum, and are formed on the glass layers 9 and 10 by vapor deposition or another appropriate method.

When the acceleration detecting section 2 is constructed as described above, the fixed electrode 1 provided on the glass layers 9 and 10 is used.
1, 12 and the movable electrode 7 are aligned and arranged in parallel with the glass layers 9 and 10 with the silicon layer 6 interposed therebetween, and each of the glass layers 9 and 10 and the silicon layer 6 are anodically bonded. Thus, with the movable electrode 7 interposed, the fixed electrode 1
1 and 12 are arranged to face each other, but an initial gap do is secured between the movable electrode 7 and each of the fixed electrodes 11 and 12.

The movable electrode 7 and the fixed electrodes 11 and 12
Are electrically connected to the capacitance detection unit 3. According to the magnitude and direction of the acceleration applied to the vehicle (not shown), when acceleration is applied in the vertical direction in the illustrated example, the movable electrode 7 moves in the direction opposite to the acceleration due to inertial force. For example, if the movable electrode 7 moves downward, the electrostatic capacitance C1 between the movable electrode 7 and the fixed electrode 11 becomes small, and the opposite movable electrode 7
The capacitance C2 between the fixed electrode 12 and the fixed electrode 12 increases.

FIG. 2 is a characteristic diagram showing the relationship of the capacitances C1, C2 and the difference ΔC between C1 and C2 with respect to the displacement of the movable electrode 7. The horizontal axis represents the displacement X of the movable electrode 7, the neutral point holding the initial gap do is set to zero, the positive displacement is the state in which the movable electrode 7 has moved to the fixed electrode 11 side, and the negative displacement is the movable electrode. 7 shows a state in which 7 has moved to the fixed electrode 12 side.

As is clear from FIG. 2, the movable electrode 7
Becomes larger toward the fixed electrode 11 side, the capacitance C1 becomes larger, and conversely, becomes closer to the fixed electrode 12 side, the capacitance C2 becomes larger.
Grows larger. Further, the difference ΔC between the electrostatic capacitances C1 and C2 is also increased in the positive and negative directions with the neutral point set to zero. That is, the displacement of the movable electrode 7, that is, the acceleration can be known by detecting any one of C1, C2, and ΔC. However, this C1, C
Both 2 and ΔC have non-linear characteristics (non-linearity).

Due to the structure of the acceleration detecting portion 2, particularly the initial gap do between the movable electrode 7 and each of the fixed electrodes 11 and 12, the mass of the movable electrode 7, and the variation of the area of the movable electrode 7, the magnitude of this non-linear characteristic (linear The size of sex varies. The initial gap do, the mass of the movable electrode 7, and the area of the movable electrode 7 have manufacturing variations.

Next, the operation of the capacitance detector 3 will be described with reference to FIG.
It will be described with reference to FIG. 3 is a detailed circuit of the capacitance detection unit 3, and FIG. 4 is a time chart showing the operation of the capacitance detection unit 3. In FIG. 4, (a) to (e) are operation waveforms showing the respective operations. These waveforms are controlled by the controller 5.

The switch 15 is normally on (φR), discharges the capacitor 16 having the capacitance Cf, and sets the output Vc of the operational amplifier 17 to VR1. The switch 15 is turned off almost in synchronization with the rising of the first rectangular wave V1 applied to the fixed electrode 11 and the falling of the second rectangular wave V2 applied to the fixed electrode 12. Then, C1 is charged and C2 is discharged. At this time, the charge Q1 moving from C1 to Cf (the charge seems to move due to the current flowing during charging / discharging) and the charge Q2 moving from C2 to Cf.
Is as follows.

[0021]

## EQU1 ## Q1 = C1 * VR1 (Equation 1)

[0022]

## EQU00002 ## Q2 = -C2 * VR1 (Expression 2) Here, VR1 is the first rectangular wave V1 and the second rectangular wave V2.
Is the amplitude value of. In addition, the electric charge Qf stored in the capacitor Cf
Becomes the sum of Q1 and Q2, so

[0023]

## EQU00003 ## Qf = Q1 + Q2 (Equation 3) Further, the voltage Vf across the capacitance Cf and the output Vc of the operational amplifier 17 are given by the following equation.

[0024]

[Equation 4]

[0025]

[Equation 5]

This voltage Vc is applied to the sample hold circuit 1
The switch 19 of No. 8 is turned on (φS) for a certain time, the capacitor 20 is charged, and the output Vc of the operational amplifier 17 is sampled to obtain the difference ΔC between the electrostatic capacitances C1 and C2.
Is detected as a voltage Vs. As a result, the acceleration acting on the acceleration detector 2 can be electrically detected. Further, the voltage Vs is input to the amplification unit 4 and adjusted to a predetermined voltage value Vo.

At this time, if the switch 13 is turned on, the linearity compensating circuit 14 operates to improve the linearity of the predetermined voltage value Vo. Further, when the switch 13 is turned off, the linearity compensation circuit 14 is disconnected, and the linearity is not improved. Here, the switch 13 is a terminal T taken out of the sensor.
It is turned on and off by controlling 1. In the case of this embodiment,
When the terminal T1 is in an open state (nothing is connected), the switch 13 is on, and when the terminal T1 is connected to the ground (earth) level, the switch 13 is off.

By adopting such a structure,
The acceleration detection unit 2 has a high acceleration (for example, ± 50 G: 1 G
= 9.8 m / s2) can be detected up to a high frequency (for example, 2 kHz). Further, since the difference between the electrostatic capacitances C1 and C2 is detected, it is possible to obtain the output voltage Vo that is proportional to the acceleration and has excellent temperature characteristics.

That is, the collision of the automobile can be detected by detecting the sudden collision acceleration caused by the collision of the automobile.

Next, the self-diagnosis operation of the semiconductor capacitive acceleration sensor 1 will be described with reference to FIGS. 1, 5 and 6. FIG. 5 shows a state in which the self-diagnosis voltage Vd is applied to the acceleration detector 2. FIG. 6 is a characteristic diagram showing the relationship between the acceleration G and the self-diagnosis voltage Vd.

The movable electrode 7 and the fixed electrode 1 of the acceleration detector 2
When a certain self-diagnosis voltage Vd1 is applied between the two electrodes, the movable electrode 7 moves due to electrostatic force. This is the acceleration detection unit 2
It becomes equal to the state in which the acceleration G1 is applied. Needless to say, if the self-diagnosis voltage Vd1 is applied between the movable electrode 7 and the fixed electrode 11, if the above-mentioned acceleration G1 is a positive acceleration, it becomes equal to the state in which the negative acceleration −G1 is applied.

That is, the self-diagnosis voltage Vd is alternately applied between the movable electrode 7 and the fixed electrode 12 and between the movable electrode 7 and the fixed electrode 11, and the output voltage Vo of the semiconductor capacitive acceleration sensor 1 is monitored to determine whether it is positive or negative. It is possible to perform self-diagnosis for acceleration.

On the other hand, the semiconductor capacitive acceleration sensor 1 is switched between the normal acceleration detection detection mode and the self-diagnosis mode by a control signal S1 as shown in FIG. For example, when the control signal S1 is at a low level, the switch SW1 is turned on and the self-diagnosis voltage Vd is alternately applied between the movable electrode 7 and the fixed electrodes 11 and 12 (self-diagnosis voltage Vd
Is the amplitude value of the low-frequency rectangular wave signal to which the movable electrode 7 responds sufficiently, and the self-diagnosis mode is set. When the control signal S1 is at a high level, the switch SW1 is turned off and a relatively high frequency rectangular wave signal is applied to the fixed electrodes 11 and 12 to set a mode for detecting normal acceleration detection.

From these operations, it is possible to obtain the equivalent acceleration application state by forcibly displacing the movable electrode by the electrostatic force without directly applying the acceleration to the acceleration detecting section 2. Therefore, the relationship between the equivalent acceleration and the output characteristic of the sensor is obtained.

Further, the semiconductor capacitive acceleration sensor 1 is
It is provided with a power supply Vcc, an output voltage Vo, a circuit ground GND, and a control signal S1.

Next, the control unit 29 of the present invention will be described with reference to FIG.

The control unit 29 is a computer (hereinafter abbreviated as CPU) 21, an RO in which a program is stored.
M (Read Only Memoly) 22, RA for storing data etc.
An M (Randam Access Memoly) 23, a digital input / output circuit 24, an A / D conversion circuit 25, an address / data bus line 26 and other appropriate circuits (not shown).

The CPU 21, ROM 22, RAM 23, digital input / output circuit 24, A / D conversion circuit 25, and address / data bus line 26 are generally integrated in a single-chip microcomputer MCU (Microcomputer Unit). A personal computer may be used instead of these.

The acceleration signal 30 and the output voltage Vo generated by a centrifuge, an adder, etc. (not shown) are A / D conversion circuit 2
Input to 5. The semiconductor capacitive acceleration sensor 1 is mounted on a centrifuge, a centering machine, or the like, and an output voltage Vo corresponding to acceleration is applied.
To occur. Then, the control unit 29 calculates the linearity and the like.

Next, a flow chart of arithmetic processing and the like which is an embodiment of the present invention will be described. The acceleration G and the output voltage Vo of the semiconductor capacitive acceleration sensor 1 are input and stored in the RAM 31. The linearity is calculated from the relationship between the acceleration and the output voltage, and the maximum linearity value Er is calculated 32. The maximum linearity value Er is compared 33 with a predetermined value. Maximum linearity Er
If is larger than a predetermined value, the terminal T1 is connected to the ground to correct the linearity 34.

Further, a similar result can be obtained by utilizing the relationship between the voltage Vs corresponding to the difference ΔC between the electrostatic capacitances C1 and C2 and the acceleration.

[0042]

According to the present invention, even if the structure of the acceleration sensor, especially the structure of the detecting portion is varied in manufacturing, and the linearity of the output characteristic with respect to the acceleration is varied, the linearity is small if the variation is small. If the variation is large without performing the correction, the linearity is corrected so that the final variation in the linearity can be kept within a predetermined range, and the yield of the acceleration sensor can be improved. .

[Brief description of drawings]

FIG. 1 is an overall configuration diagram including an acceleration sensor of the present invention.

FIG. 2 shows electrostatic capacitances C1 and C2 with respect to displacement of a movable electrode 7.
FIG. 6 is a characteristic diagram showing the relationship between the difference ΔC between C1 and C2.

FIG. 3 is a detailed circuit of a capacitance detection unit 3.

FIG. 4 is a time chart showing the operation of the capacitance detection unit 3.

FIG. 5 is a diagram showing a state in which a self-diagnosis voltage Vd is applied to the acceleration detection unit 2.

FIG. 6 is a characteristic diagram showing a relationship between acceleration G and self-diagnosis voltage Vd.

[Explanation of symbols]

1 ... Semiconductor capacitance type acceleration sensor, 2 ... Acceleration detecting section, 3
... Capacitance detection section, 4 ... Amplification section, 5 ... Control section, 7 ... Movable electrode, 8 ... Silicon cantilever, 11, 12 ... Fixed electrode, 13 ... Switch, 14 ... Linearity compensation circuit, 21 ... C
PU, 22 ... ROM, 23 ... RAM, 24 ... Digital input / output circuit, 25 ... A / D conversion circuit, 29 ... Control unit, T1 ... Terminal, Vcc ... Power supply, Vo ... Output voltage, Vd
... Self-diagnosis voltage, S1 ... Control signal, 31, 32, 33,
34 ... Flow chart.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Terumi Nakazawa Inventor Terumi Nakazawa 2520 Takaba, Takata, Ibaraki Prefecture Hitachi Automotive Systems Division (72) Inventor Tetsuo Matsukura 2520 Takata, Katsuta, Ibaraki Hitachi, Ltd. Mfg. Co., Ltd. Automotive Equipment Division (72) Inventor Yasuhiro Asano 2477 Kashima Yatsu Kashima, Katsuta City, Ibaraki Pref. 3 Hitachi Automotive Engineering Co., Ltd.

Claims (4)

[Claims] 1. A movable electrode, the position of which is displaced in response to an acceleration, and one or more fixed electrodes which are arranged so as to face the movable electrode. The displacement of the position is regarded as a change in electrostatic capacitance, In the characteristic adjustment method of the capacitance type acceleration sensor that detects the acceleration from the change of the electrostatic capacitance, the linearity of the output voltage characteristic with respect to the predetermined acceleration is compared with the linearity of the output voltage characteristic with respect to the predetermined acceleration. If the linearity of the output voltage characteristic with respect to the predetermined acceleration is less than or equal to the predetermined value of the first linearity,
When the linearity of the output voltage characteristic with respect to the predetermined acceleration exceeds the predetermined value of the first linearity without correcting the linearity of the output voltage characteristic with respect to the predetermined acceleration, the output voltage characteristic with respect to the predetermined acceleration is obtained. The method for adjusting the characteristics of the electrostatic capacitance type acceleration sensor is characterized in that the linearity correction is performed. 2. A movable electrode, the position of which is displaced in response to acceleration, and one or more fixed electrodes arranged facing the movable electrode, wherein the displacement of the position is regarded as a change in electrostatic capacitance, In the characteristic adjustment method of the capacitance type acceleration sensor that detects the acceleration from the change of the capacitance, the linearity of the capacitance characteristic with respect to the predetermined acceleration is defined as the linearity of the capacitance characteristic with respect to the predetermined acceleration. , A second linearity predetermined value is compared, and the linearity of the capacitance characteristic with respect to the predetermined acceleration is equal to or less than the second linearity predetermined value,
When the linearity of the capacitance characteristic with respect to the predetermined acceleration exceeds the predetermined value of the second linearity without correcting the linearity of the output voltage characteristic with respect to the predetermined acceleration, the output voltage with respect to the predetermined acceleration is A characteristic adjustment method for a capacitance type acceleration sensor, characterized in that the linearity of the characteristic is corrected. 3. The characteristic adjustment of a capacitance type acceleration sensor, wherein, of the predetermined accelerations according to claim 1 or 2, the acceleration is a rate of increase or decrease of speed per unit time. Method. 4. The capacitance acceleration sensor according to claim 1 or 2, wherein the acceleration is an equivalent acceleration by forcibly displacing the movable electrode. Characteristic adjustment method.