JP2575769Y2 - Acceleration sensor - Google Patents

Description

[Detailed description of the invention]

[0001]

The present invention relates to an acceleration sensor,
More specifically, the present invention relates to an acceleration sensor suitable for detecting relatively low-frequency acceleration, such as a sensor for an electronically controlled suspension of a vehicle.

[0002]

2. Description of the Related Art As one basic concept for detecting this kind of acceleration (including not only one-way acceleration but also braking acceleration, acceleration caused by rotation, etc.), an elastic displacement body (hereinafter, referred to as metal) made of metal or the like is used. Simply referred to as a displacement body)
A mechanism has been widely used in which a sensor body is installed in a sensor body, and when the sensor body receives acceleration, the displacement body is mechanically displaced by inertial force.

[0003] Various types of acceleration sensors have been proposed according to a method of converting a displacement proportional to the acceleration (or a strain caused by the displacement, hereinafter simply referred to as a displacement) into an electric signal as a conversion means and outputting the electric signal. Or it has been realized.

For example, a displacement body having a structure such as a cantilever support type, a center support type, or a peripheral support type is formed using an elastic plate, and a conversion element such as a strain gauge or a piezoelectric element is mounted on the displacement body. In addition, it is possible to realize an acceleration sensor that converts a displacement generated in the displacement body in accordance with the acceleration into an electric signal by the conversion unit and outputs the electric signal.

Incidentally, the following technical problems are common to such acceleration sensors.

(1) The mechanical displacement generated in the displacement body must be faithfully reproduced in accordance with the inertial force applied to the displacement body.

(2) A structure or means is provided so that the displacement is always accurately transmitted to a conversion element that converts the displacement into an electric signal.

(3) The conversion element has a capability of converting the displacement transmitted to the displacement body into an electric signal with high precision, and the converted electric signal is in a signal form easily processed by an electric circuit. thing.

However, in an acceleration sensor having a structure in which a conversion element is mounted on a displacement body as described above,
There are technical achievements in how to always solve the three issues and make them cheap and excellent in mass productivity.

[0010] Regarding the problem (1), by preventing the conversion element from being mounted on the displacement body, it is possible to convert the inertial force inherent in the displacement body, such as a constant elastic metal, into a displacement. The problem can be solved by making it possible to exert mechanical ability and detect the generated displacement in a non-contact manner. With such a configuration, the problem (2) can also be solved.

One idea for detecting the displacement generated in the displacement body in accordance with the acceleration in a non-contact manner is described in, for example, JP-A-1-197661 and JP-A-1-1976 filed earlier by the present applicant.
It is proposed in Japanese Patent Publication No. 62. According to such an acceleration sensor, an electric field generated between a displacement body provided with a fixed charge, that is, a fixed potential, and a detection electrode arranged in a non-contact manner around the displacement body generates a charge induced on the electrode. Is detected through a high resistance connected between the electrode and ground (GND). Therefore, when the displacement body is displaced by the inertial force, the acceleration sensor is configured on the principle that the distance between the displacement body and the electrode changes, and the strength of the electric field on the electrode changes to induce a new charge. can do.

FIG. 17 shows the basic structure of one such non-contact type acceleration sensor. The acceleration sensor 51 is attached to an object 52 such as an automobile frame on which the acceleration α acting as a detection target surface acts. The acceleration sensor 51 includes a displacement body 55 mounted on a substrate 53 via an insulator 54, and a fixed detection electrode 56 facing the displacement body at a distance d. 52
When the acceleration α acts on the displacement body 55, the displacement body 55 is displaced in the left-right direction by the inertia force F proportional to the acceleration α as shown by a broken line.

When a voltage is applied from a power supply V to the displacement body 55, a constant potential is maintained on the surface facing the electrode 56, and the electric field E generated by this potential has an electric field strength in inverse proportion to the distance from the electrode 56. An electric charge is induced on the electrode 56 accordingly.
On the other hand, a resistor Rg having a high resistance value is connected between the electrode 56 and the substrate 53, and the electrode 56 is connected to an output terminal 58 via an impedance converter 57 such as a field effect transistor or an operational amplifier. Reference numeral 59 denotes a shield case.

With such a configuration, when the acceleration α applied to the object 52 is 0, the apparatus is in a steady state and no voltage is generated across the resistor Rg. Next, a certain acceleration α is
Is applied, the displacement body 55 is displaced in the left-right direction by the inertial force F, so that the distance from the electrode 56 changes from d to d 'or d ". As a result, the electric field strength becomes the current E /
The charge changes from d to E / △ d 'or E / d ″, and the charge moves accordingly through the resistor Rg to flow as a current, so that the voltage across the resistor Rg fluctuates.

Therefore, by taking out this voltage fluctuation from the terminal 58 via the impedance converter 57 as the detection output Vo, the displacement of the displacement body 55 can be outputted as an electric signal. In this case, the output Vo is a value inversely proportional to the distance between the displacement body 55 and the electrode 56. Note that FIG.
With the configuration described above, the same effect can be obtained even if the positions of the displacement body 55 and the electrode 56 are exchanged as they are. That is, the displacement body 55 and the electrode 56 may be in such a relationship that a constant potential is applied to one side and a detection output is obtained on the other side. By the way, in such an acceleration sensor, the displacement body 55
Has a disadvantage that a detection output proportional to the acceleration α cannot be obtained from the displacement body 55 when the displacement occurs.

For this reason, the applicant of the present invention has proposed a non-contact type acceleration sensor having another configuration for eliminating such a disadvantage (Japanese Patent Application No. 4-24089). FIG. 18 shows the basic structure of this acceleration sensor. Reference numeral 15 denotes a plate-shaped conductive displacement body, which is provided with a plate-shaped detection electrode 16 facing the other at a distance d. The displacement body 15 and the electrode 16 are arranged so as to be parallel to the direction Z of the acceleration α and have an opposing area A. The opposing area A can be changed by displacing the displacement body 15 in the same direction Z as the acceleration α according to the acceleration α.

V is a power supply for applying a constant potential by applying a voltage to the displacement body 15, Rg is a resistor connected between the electrode 16 and the ground, and 17 is an impedance converter provided between the electrode 16 and the output terminal 18. It is. When the displacement body 15 is displaced by the acceleration α and the area A facing the electrode 16 changes, the electric field from the displacement body 15 changes and the electrode 1
6 changes, and this charge becomes the resistance R
g, the voltage at both ends changes, and the impedance converter 17 outputs this voltage change to the terminal 18 as a detection output Vo.

As a result, a voltage Vg proportional to a change in the facing area, that is, a displacement amount of the displacement body 15 can be obtained by the resistor Rg. Therefore, a detection output proportional to the acceleration can be obtained. Hereinafter, FIGS. 17 and 18
The detection method using a non-contact type acceleration sensor as shown in FIG. Here, a plurality of the displacement bodies and at least one of the electrodes arranged to face the displacement bodies can be arranged.

In any case, the potential detection type acceleration sensor is common in that a constant potential is applied to one of the displacement body and the electrode to detect the electric charge induced in the other, and the induced electric charge is applied between the electrodes. The only difference is that it changes according to a change in the distance (ie, electric field strength) or a change in the area between the electrodes (ie, electric flux). Thus, in the former, a detection output in inverse proportion to the acceleration is obtained, and in the latter, a detection output in proportion to the acceleration is obtained.

[0020]

In the conventional potential detection type acceleration sensor, the above-mentioned (3)
There is a problem that it is difficult to sufficiently solve the above problem.

That is, any of the conventional acceleration sensors is advantageous in that the displacement or strain conversion mechanism is not directly disposed on the displacement element, but has the following two problems with respect to the problem (3). .

1. Uniform acceleration (corresponding to static change of displacement body)
In the conventional acceleration sensor, in both the former (a method of reading the change in the distance between the electrodes) and the latter (a method of reading the change in the area between the electrodes), a constant potential is applied from the DC power supply V to the electrode. The charge induced above increases or decreases only with the displacement of the displacement body, and the principle is that the sensitivity is determined by the increased or decreased charge that moves per unit time through the resistance Rg, so the static change of the displacement body is detected. It is impossible to do. Further, it is difficult to detect a temporal change larger than a time constant determined by the resistance Rg and the coupling capacitance Cx between the electrodes, that is, acceleration detection in a frequency region lower than ωo = (1 / RgCx).

2. High Detection Accuracy and High S / N In order to achieve this subject even in the conventional acceleration sensor, mass is added to the tip of the displacement element to increase the inertial force even for the same acceleration, and to increase the active point of the displacement. In order to increase the displacement by devising, or to provide a shield window between the displacement body and the counter electrode to prevent disturbance due to unnecessary electric flux, and furthermore, the purpose of the electric flux condition does not change due to the displacement of the displacement body It has been considered to process a displacement body or an electrode as a columnar or spherical charged body so as to obtain a radial electric flux.

However, when circuit processing is performed to further reduce the influence of power supply line noise, electromagnetic noise, and the like, for example, signals unnecessary after impedance conversion are unnecessary (ie, other than the frequency band of the acceleration to be detected). It is effective to provide a filter that cuts the band. However, although a wider detection target band is advantageous for an acceleration sensor, the filter band is also widened accordingly, which is disadvantageous in terms of noise.

The present invention has been made in view of the above-described problems, and has as its object to provide an acceleration sensor that solves the above-mentioned problems.

[0026]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a displacement body which produces a displacement in accordance with an acceleration, a conductor which is opposed to the displacement body in a non-contact state, and the displacement body and the conductor. An acceleration sensor comprising a power supply for applying a constant potential to one of the sides of the body, wherein the power supply comprises an alternating potential, and when a change occurs in the displacement body, the power source is induced from the displacement body or the conductor. It is characterized by outputting a detection signal based on the displacement of the electric charge.

[0027]

According to the configuration of the present invention, an alternating potential is used as a power supply for applying a constant potential, so that acceleration can be detected in a low frequency band including uniform acceleration.

According to the configuration of the present invention described in claim 2,
By arranging at least one of the displacement body and the conductor, the same operation as the first aspect can be performed.

According to the configuration of the present invention described in claim 3,
By connecting a bandpass filter having a center frequency substantially coincident with the frequency of the alternating power supply to the output side of the detection signal, the same operation as the first aspect can be performed.

According to the configuration of the present invention, there is provided a demodulation means for demodulating a modulated wave obtained by modulating a signal based on an alternating potential with a carrier based on a signal based on the displacement of the displacement body. The same operation as the first aspect can be performed.

According to the fifth aspect of the present invention, the same operation as that of the first aspect can be performed by using the cantilever-type displacement body.

According to the configuration of the present invention described in claim 6, the same operation as in claim 1 can be performed by integrally forming the cantilever support type displacement body with the silicon crystal body.

According to the configuration of the present invention described in claim 7, the same operation as in claim 1 can be performed by enclosing both the operable displacement body and the conductor in the shield case.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the acceleration sensor 1 according to the present invention, in which 5 is a displacement body, 6 is an acceleration detecting electrode disposed opposite to the displacement body 5, and Rg is the electrode 6 and the ground (GND). ), A resistor having a high resistance value, Tr is a field effect transistor (FET) operating as an impedance converter 7, Vcc is a power supply for Tr, R is a resistor connected between the source of Tr and GND, and Vc is This is an alternating potential for giving a constant potential to the displacement body 5. The alternating potential Vc is composed of a sine wave, a rectangular wave, a triangular wave, etc. having a specific frequency ω1.

FIG. 2 is a block diagram showing a configuration for operating the acceleration sensor 1 of FIG. 1. An output terminal 8 drawn from the drain of Tr as an impedance converter 7 has a center substantially coincident with the frequency ω1. A band-pass filter 3 having a frequency is connected to a detection / amplification unit 5 for obtaining a detection output from this output. The detection operation may be performed using the alternating potential Vc. In actually assembling the device, these components may be formed on the same substrate as the resistor Rg or the like constituting the acceleration sensor 1 or may be formed separately from the sensor unit as a separate circuit.

Next, regarding the operation of the present embodiment, the first type acceleration sensor (a method for reading a change in interelectrode distance) and the second type acceleration sensor (a method for reading a change in opposing electrode area) in the potential detection method will be described. Each case will be described.

(1) Operation of Static Displacement (under Constant Acceleration) FIG. 3 shows that the constant acceleration acts on the sensor of the first type, and the distance y between the electrodes is changed from y = d (acceleration 0) to y = d + △. The horizontal axis represents time elapse when the d is constant (a) and when the same acceleration acts in the opposite direction and y = d− △ d is constant (b).

FIG. 4 shows a case in which a constant acceleration acts on the second type sensor and the inter-electrode facing area S is constant from S = A (acceleration 0) to S = A + △ A (a). And (b) where the same acceleration acts in the opposite direction and S = A−ΔA is constant, the horizontal axis represents time passage.

Here, in the method of applying a constant potential from the power supply V (static potential as shown in FIG. 5) as in the configuration as shown in FIGS. 17 and 18, the temporal displacement as shown in FIGS. No detection output is obtained for the displacement of the displacement body not accompanied by.

In the present invention, by using a signal having a specific frequency ω1 and a constant amplitude V1 as the alternating potential Vc, a detection output can be obtained even for a static displacement as shown in FIGS.

Assuming that a sine wave of Vc = V + V1sin ω1t (V is a bias potential and may be 0) is used as the alternating potential Vc as shown in FIG. 6, as shown in FIG. For such a static displacement, a detection voltage Vg as shown in FIGS. 7A and 7B is obtained. Similarly, for FIGS. 4A and 4B, FIGS.
A detection voltage Vg is obtained as shown in FIG.
Is a constant).

(2) Dynamic Displacement Operation Here, as an example, a case where a vibration acceleration having an angular frequency p acts on the sensor will be described. With respect to such vibration acceleration, in the first type sensor, the inter-electrode distance y changes as y = d + △ dsinpt as shown in FIG. Similarly, in the second type sensor, the inter-electrode facing area S changes as shown in FIG. Here, Vc = V + V
When the acceleration is 0, the detection voltage generated by 1 sinω1t on the detection electrode is α (V1 / V1 /
d) sinω1t, which is βV in the sensor of the second type.
1Asinω1t (α and β are constants). This signal amplitude changes in inverse proportion to the distance changed by the acceleration or in proportion to the facing area.

That is, the detection signal when the acceleration is 0 undergoes amplitude modulation due to a change in the distance between the electrodes or the facing area. In other words, the signal is considered to be a carrier, and this carrier is modulated as shown in FIG. 11 (a) by the acceleration of the first type sensor and acts as ((a) in FIG. 12) by the second type sensor. It is modulated and detected as in a).

Further, the frequency of the carrier wave, that is, ω
In order to extract the frequency component 1, the signal of FIG. 11A and the signal of FIG. 12A are passed through a band-pass filter 3 of a fixed band having a center frequency substantially coincident with the frequency ω1. Can obtain a modulated wave whose envelope corresponds to the acceleration (displacement of the displacement body), such as the signal of FIG. 11 (b) and the signal of FIG. 12 (b).

Accordingly, by detecting and amplifying the modulated wave by the detection / amplification unit 5, the modulated wave is shown in FIGS.
The control signal required for the acceleration detection system as shown in FIG. 4 can be obtained.

(3) Acceleration detection band As is clear from the explanations such as (1) and (2), according to the present invention, it is impossible to detect with the conventional potential detection method, and in the low frequency band including the uniform acceleration. Can be detected. However, the detection upper limit frequency is limited by the natural resonance frequency ω1 of the displacement body. This is because the area where the displacement of the displacement body is proportional to the acceleration regardless of the frequency is limited to the non-resonant area of the displacement body.

Therefore, the alternating potential ω1 which is also a carrier is ω
n (mechanical resonance frequency of the displacement body), it is necessary to prevent modulation at the acceleration of the resonance frequency. At the same time, by setting it sufficiently higher than the detection band required for the sensor, the accuracy after demodulation is set. It is necessary to design to increase.

FIGS. 15 and 16 are characteristic diagrams showing the relationship between acceleration and output in the sensors of the first system and the second system.

(4) High S / N According to the present invention, not only the acceleration can be detected from the DC (constant acceleration) level as described above, but also the frequency ω1 of the alternating potential, which is also the frequency of the carrier wave, can be obtained. If the detection sensitivity is set appropriately, it is not necessary to maintain high sensitivity in other frequency bands, so that a noise component can be easily removed using a band-pass filter or the like. Therefore, a high S / N ratio can be achieved.

As described above, according to the present invention, the alternating potential is used as a power source for applying a constant potential to one of the displacement body and the conductor arranged opposite to the displacement body. It is possible to detect low-frequency acceleration including possible equal acceleration, and also to solve the problems of high detection accuracy and high S / N.

Incidentally, the acceleration sensor of the equipotential detection type is
It is clear from the principle that the sensitivity depends on the magnitude of the electric field between the electrodes, and the dielectric constant between the electrodes varies with humidity because it is the dielectric constant of air. For this reason, the sensor housing is designed to prevent the ingress of humidity,
It is important to adopt a structure that completely seals against the outside air. Further, if a silicon single crystal body having excellent mechanical properties as an elastic displacement body is processed as a displacement body by a processing means such as etching and the peripheral circuit is formed directly on the crystal body, miniaturization is advantageous.

[0053]

As described above, according to the present invention, the alternating potential is used as a power source for applying a constant potential to one of the displacement body and the electrode disposed opposite to the displacement body. Low frequency acceleration can be detected, and high detection accuracy and high S / N can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the acceleration sensor of the present invention.

FIG. 2 is a block diagram showing a configuration for operating the sensor of the embodiment.

FIG. 3 is a diagram showing characteristics obtained when the present invention is applied to a first type sensor of a potential detection type.

FIG. 4 is a diagram showing characteristics obtained when the present invention is applied to a sensor of a second type of a potential detection type.

FIG. 5 is a characteristic diagram of a supply potential used in a conventional potential detection method.

FIG. 6 is a characteristic diagram obtained when an alternating potential is used as a power supply.

FIG. 7 is a characteristic diagram of a detection signal obtained corresponding to FIG.

8 is a characteristic diagram of a detection signal obtained corresponding to FIG.

FIG. 9 is a characteristic diagram obtained when the present invention is applied to the first type sensor.

FIG. 10 is a characteristic diagram obtained when the present invention is applied to a second type sensor.

FIG. 11 is a characteristic diagram of a modulated signal obtained corresponding to FIG. 9;

12 is a characteristic diagram of a modulated signal obtained corresponding to FIG.

13 is a characteristic diagram of a detection signal obtained corresponding to FIG.

14 is a characteristic diagram of a detection signal obtained corresponding to FIG.

FIG. 15 is a characteristic diagram showing a relationship between acceleration and output in the first type sensor.

FIG. 16 is a characteristic diagram showing a relationship between acceleration and output in the second type sensor.

FIG. 17 is a configuration diagram illustrating a sensor of a first type of a potential detection type.

FIG. 18 is a configuration diagram illustrating a sensor of a second type of the potential detection type.

[Explanation of symbols]

 Reference Signs List 3 band pass filter 4 detection / amplification unit 5 displacement body 6 detection electrode 7 impedance converter Vc alternating potential

Claims (7)

(57) [Scope of request for utility model registration] A displacement body that produces a displacement according to acceleration;
An acceleration sensor comprising a conductor facing the displacement body in a non-contact state, and a power supply for applying a constant potential to one of the displacement body and the conductor, wherein the power supply comprises an alternating potential; When a change occurs in the acceleration sensor, the acceleration sensor outputs a detection signal based on the displacement of the electric charge induced either from the displacement body or the conductor. 2. The acceleration sensor according to claim 1, wherein a plurality of at least one of the displacement body and the conductor are arranged. 3. The acceleration sensor according to claim 1, wherein a band-pass filter having a center frequency substantially coincident with the frequency of the alternating potential is connected to a detection signal output side. 4. A signal based on the alternating potential is a carrier wave,
The acceleration sensor according to any one of claims 1 to 3, further comprising demodulation means for demodulating a modulated wave obtained by modulating the carrier with a signal based on the displacement of the displacement body. 5. The acceleration sensor according to claim 1, wherein the displacement body is of a cantilever type. 6. The acceleration sensor according to claim 1, wherein the cantilever-supporting displacement body is formed integrally with a silicon single crystal body. 7. The displacement body according to claim 1, wherein the displacement body is configured to be able to function as an electrode, and the displacement body and a conductor disposed opposite to the displacement body are both sealed in a shield case. Acceleration sensor.