JPH036462A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To make temp. dependence constant by constituting a piezoelectric vibrator by bonding a backing material low in the coefficient of linear expansion to one surface of a piezoelectric body having electrodes provided to both surfaces thereof. CONSTITUTION:Electrodes 2 - 4 are provided to both surfaces of a film-like piezoelectric body 1 and a backing material 5 low in the coefficient of linear expansion is bonded to one surface thereof to constitute a piezoelectric vibrator 6 which is, in turn, bonded to one surface of a printed circuit board 7 low in the coefficient of linear expansion. A signal processing electronic circuit is formed to the other surface of the board 7 and the whole of them is covered with three layers of an internal conductive layer, a heat insulating layer and an external conductive layer. By this constitution, the drift of output due to pyroelectric properties is reduced and output stable to a temp. change is obtained. At this time, the coefficient of linear expansion is selected so as to become low in the order of piezoelectric body 1 > backing material 5 >= board 7 and the backing material is bonded to one surface of the piezoelectric body 1 by an adhesive. Therefore, the participation of the backing material 5 becomes large in relation to vibration and the piezoelectric vibrator 6 made constant in a temp. gradient of sensitivity is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an acceleration sensor that detects acceleration using a piezoelectric vibrator, and is particularly sensitive to the effects of temperature changes, voltage fluctuations, electromagnetic noise, etc. , relates to a low-frequency acceleration sensor that is excellent for use in vehicles.

[Prior art]

Since acceleration is obtained by double displacement, the lower the frequency, the smaller the actual acceleration even for a large displacement.

For example, at 160 I(z), the acceleration is IG with a displacement of 10μm, and IG with a displacement of 10m at 0.16Hz.
becomes. When making low-frequency vibration measurements, the actual displacement is at most 1 m or less; for example, at 1.6 Hz, it is 0.
1G results in a displacement of l cm.

Therefore, in order to measure vibrations of 0.1 to 10Hz,
．． It must be able to measure small accelerations of 1 to 0.01G.

The inventors of the present invention applied for a low-frequency acceleration sensor in 1983-1.
It has already been proposed as No. 03602. In this acceleration sensor, a piezoelectric vibrator is sequentially coated with a conductive resin, a heat insulator, and a heat conductor, and this is mounted on an insulating base. It is made by connecting a capacitor to prevent inductive disturbances. By configuring it in this way, the piezoelectric vibrator is electromagnetically shielded by conductive resin, so it is not affected by electrical noise, and it also has excellent insulation and thermal conductivity. This not only greatly reduces temperature changes caused by external heating or cooling (the piezoelectric vibrator is electrically insulated from the object to be measured by the insulating base, so it is free from electrostatic induction and ground potential). In addition to being less susceptible to inductive disturbances such as
External high frequency noise can be bypassed,
Low-frequency.

This has the effect that low acceleration measurements can be performed with even higher precision.

[Problem to be solved by the invention]

However, in the above precedent example, in order to bypass external high-frequency noise, it is necessary to connect an external inductive failure prevention capacitor between the conductive resin and the conductive thermal conductor, which makes the structure more complicated. In addition to this, the output of the piezoelectric vibrator must be connected to a separate signal processing circuit using a cable, which prevents the structure from being made smaller and more compact, and causes external induction interference between the piezoelectric vibrator and the electronic circuit. Also, since the piezoelectric body is not held by a material with a coefficient of linear expansion smaller than this,
Another problem is that the temperature dependence of sensor sensitivity cannot be made constant.

[Summary of the invention]

In order to solve the above problems, the sensor of the present invention has electrodes on both sides of a piezoelectric body 1 as shown in the figure, and a backing material 5 with a small coefficient of linear expansion is adhered to one side of the piezoelectric body 1 to form a piezoelectric vibrator 6. The piezoelectric vibrator 6 is adhered to one side of a circuit board 7 having a small coefficient of linear expansion, and the signal processing electronic circuit 8 is formed on the other side of the circuit board 7, and the whole is covered with an internal conductive layer 10. It has a structure in which it is coated with three layers: a heat insulating layer 9 and an external conductive layer 11.

In the present invention, by incorporating an external induction interference prevention capacitor into the electronic circuit 8, the structure becomes simpler and there is no need to worry about installing the capacitor. Since there is no need to separately install a cable when connecting to the piezoelectric element 1, the structure can be made small and compact, and there is no risk of external induction interference between the piezoelectric vibrator 6 and the electronic circuit 8. Since it is held by a material with a small coefficient, the temperature dependence of the sensor sensitivity can be made constant.

[Detailed description of the invention]

The present invention will be described in detail below based on FIG. 1.

FIG. 1 is a schematic sectional view showing the structure of an embodiment of the sensor of the present invention, FIG. 2 is a perspective view showing the appearance of this embodiment, and FIG. 3 is a perspective view for explaining the structure of this embodiment.

In FIG. 3 (al, fb) and FIG. 4, 1 is a piezoelectric material.

The piezoelectric material 1 has a volume resistivity of 1012 to 1 at 20°C.
It is a piezoelectric resin sheet with a thickness of 10 to 500 μM and in the range of 0.016 Ωcm.

For example, in polymeric piezoelectric materials, PVDF = polyfluorovinylidene resin and P (VDCN/VCA) -poly (vinylidene cyanide/vinyl acetate) copolymer resin, etc., and in polymer composite systems, PZT = zirconate titanate. It is a piezoelectric body made of a composition consisting of lead, POM-polyacetal resin, NBR-acrylonitrile-butadiene copolymer rubber, and carbon. The durability of rubber can be improved by vulcanizing it.

PCT-calcium-substituted lead titanate, u-POM-
A piezoelectric body made of a composition made of urethane-modified polyacetal resin may also be used.

Electrodes are provided on both sides of the piezoelectric body by means such as vapor deposition, sputtering, or printing with conductive paint, and a backing material 5 is adhered to one side of the piezoelectric body to form a piezoelectric vibrator 6. When a piezoelectric vibrator 6 (see Fig. 3) has a structure in which a pair of positive and negative electrodes 2 and 3 are provided on one surface of the 1, a neutral electrode 4 is provided on the other surface, and a backing material 5 is provided on this (see FIG. 3), pyroelectric It is effective in reducing sex. This effect is further enhanced when the areas of the positive and negative electrodes 2.3 are made equal.

In addition, a positive electrode 2 is placed on the center side of one surface of the piezoelectric body 1.

Placing the negative electrode 3 on the outside is effective in reducing electrical noise.

It goes without saying that an electrically insulating band is provided between the inner positive electrode 2 and the outer negative electrode 3.

The backing material 5 has a small coefficient of linear expansion (5 x 10-5 layers ℃
Below) Glass epoxy resin, polyimide, polyester, etc. are used.

The coefficient of linear expansion is selected to decrease in the order of piezoelectric material>backing material>substrate.

Thickness is 0.01-1.6 ml, preferably 0.03 ml
~0.5 fins are used and processed. In particular, a range of 1/3 to 10 times the thickness of the piezoelectric body is selected.

The backing material 5 is adhered to one surface of the piezoelectric body 1 using an adhesive to form a vibrator 6. According to this configuration, the backing material 5 plays a large role in vibration, so it is possible to obtain a vibrator 6 with a constant temperature gradient of sensitivity.

This piezoelectric vibrator 6 is bonded to one side of a circuit board 7 having a small coefficient of linear expansion, and a signal processing electronic circuit 8 is formed on the other side of this circuit board 7.

The circuit board 7 is made of a glass epoxy resin having a coefficient of linear expansion of 5 x 10-5/°C or less and a thickness of about 0.2 to 5 ml and having high rigidity that can withstand distortion due to the difference in coefficient of linear expansion with the housing 31. , ceramic (alumina, silicon wafer, etc.)
, metal, etc. are used.

A connection circuit is formed to connect the positive and negative electrodes 2, 3 on the piezoelectric body 1 to the electronic circuit 8 on the circuit board 7. The connection circuit is formed by connecting lead wires by wire bonding, forming a thin film by vapor deposition, sputtering, etc., thick film circuit printing, conductive coating, or the like.

Prior to circuit formation, this portion is coated with an insulator 12 in order to avoid electrical short-circuiting with the neutral electrode 4 exposed on the end face of the piezoelectric body 1. The positive and negative electrodes 2.3 of the piezoelectric vibrator 6 are connected to positive and negative electrode patterns 15 and 16 formed on one surface of the circuit board 7, respectively, by positive and negative electrode lead patterns 13 and 14, (See Figure 3), and these are also correct.

Negative electrode patterns 15 and 16 are through holes 17,
At 18, it is connected to a signal processing electronic circuit 8 formed on the other side of the circuit board 7. 24 is a circuit reference potential electrode formed integrally with the negative electrode pattern 16.

The signal processing electronic circuit 8 may be formed separately on a circuit board 7.7a as shown in the first diagram, for example. Reference numeral 19 denotes a component constituting the electronic circuit 8.

The signal processing electronic circuit 8 includes, for example, an impedance conversion section 20 .as shown in FIG. 4 . Filter section 21. It is composed of a muting section 22, an amplification section 23, and a power supply circuit 30.

Field effect transistor Q1 of impedance conversion section 20
By inserting a gate resistor R of 1 to 100 GΩ in , output drift due to pyroelectricity is reduced, and stable output can be obtained against temperature changes.

The constant of the filter section 21 is calculated from the cutoff frequency of the bypass filter determined by the lowest measured frequency.

A muting section 22 is connected after the filter section 21 to speed up the output rise immediately after power is turned on.

A circuit reference potential electrode 24 is provided on the vibrator 6 side of the circuit board 7 to protect the high impedance piezoelectric body 1 from electromagnetic noise.

Feedthrough capacitors 25, 26, and 27 are inserted into the connection lines (power supply lines, signal lines, etc.) to the outside of the sensor to protect the circuit from external high-frequency noise.

The amplifier section 23 is combined with a temperature compensation circuit 28 to obtain stable sensitivity to changes in environmental temperature, and is also provided with a gain adjustment circuit 29, thereby producing an output signal (2). The size of is adjusted.

A reverse voltage withstand element is inserted into the power supply circuit 30 to protect the circuit against abnormal reverse voltage.

In addition, a voltage drop/interruption countermeasure circuit is inserted to protect circuit operation against abnormal voltage drops or disconnections.

32 and 33 are a cable and a connector, respectively.

According to the above configuration, since the piezoelectric body 1 is held by the circuit board 7 made of a material having a coefficient of linear expansion smaller than itself, the temperature dependence of the sensor sensitivity can be made constant.

A component 19 is placed on the circuit board 7 on the side where the vibrator 6 is not fixed.
It is possible to form a hybrid electronic circuit 8 by, for example, mounting the following.

The circuit boards 7, 7a are further fixed to the housing.

When fixing, using a soft adhesive such as silicone resin or urethane resin has the advantage of being able to absorb distortion due to the difference in linear expansion coefficient between the two.

FIG. 5 is a connection diagram showing an example of the electronic circuit 30 according to the present invention, where 6 is a piezoelectric vibrator, Vc is a circuit reference potential, R is a source resistance, Vcc is a voltage terminal, R is a gate resistance, and Ql is an impedance conversion. T+ is a first time constant circuit consisting of a DC voltage blocking capacitor CI and a resistor R2, T2 is a second time constant circuit consisting of a DC voltage blocking capacitor C2 and a resistor R5; 1st. The second time constant circuits T, , T2 constitute a filter section. A1A2 is the first stage, second stage amplifier, R3
, R4, Rh, and R7 are the first stage and second stage amplifiers A1 . A2 is a gain setting resistor, and the temperature compensation circuit 28 is not shown. Q2,
Q3 is connected to the first .
Second switching field effect transistor, D+, Dz
is a diode, and Mc is a muting circuit 22.

Field effect transistor Q2 outputted from the muting circuit Me. Q3 on/off signal M.

As shown in FIG. 6, M2 is output at the same time immediately after the power is turned on, but the timing of stopping is such that M stops first, and then f&Mz stops for a certain period of time.

Immediately after the power is turned on, the muting signals M, , M2 set to a higher voltage than the reference potential Vc are applied to the muting circuit Mc.
When applied to the diodes D, , D2, the field effect transistors Q2, . Q3 becomes the gate-source voltage VGS-〇■ due to diode leakage current and turns on. For a certain period of time 1. ．． After 12, when the muting signals M, , M2 become lower than the reference potential Vc to below the field effect transistor pinch-off voltage, the field effect 1 to transistor Q + ,
Q2 each turns off. Here, the ON setting time tI+t2 of the field effect 1 helangistor Q2Q3 is 1. <12.

When the power is turned on in such a configuration, the impedance conversion field effect transistor Q1 and the amplifier A1
．． Power supply voltage Vcc is applied to A2. At the same time, the muting circuit Mc is activated and the resistance R of the first time constant circuit TI is
A switching field effect transistor Q2 connected in parallel with 1. It is turned on and then turned off.

Further, the switching field effect transistor Q3 connected in parallel to the resistor R5 of the second time constant circuit T2 is also turned on for a set time t2 by the muting signal M2 via the diode D2, and then turned off. .

This operation causes the first time constant circuit T to have a period R2# of t5.
0Ω, and the DC blocking capacitor C1 is quickly charged to a predetermined voltage. 1. After the period, the first time constant circuit T1 transmits the impedance-converted sensor detection signal output Vs to the first stage amplifier A using a regular time constant.

Similarly, in the second time constant circuit T2, the period t2 is 5#0Ω.
Therefore, the DC blocking capacitor C2 is quickly charged against the DC offset voltage fluctuation of the first stage amplifier A1 with respect to the reference potential Vc. After the period t2, the second time constant circuit T2 transmits the sensor detection signal output (1) amplified by the first stage amplifier A1 to the second stage amplifier A2 at a regular time constant.

As a result of the above operation, the sensor amplifier output signal V. becomes the reference potential Vc for a period t2 after the power is turned on, and then becomes a stable sensor detection signal amplified output signal, making it possible to shorten the settling time delay of the input response.

For example, when the low cutoff frequency is set to about 0.1 Hz, the sensor amplifier of the present invention requires about 6 seconds to stabilize its output.

Piezoelectric vibrator6. and the circuit board 7, 7a has an internal conductive layer 10
．． It is housed in a housing 31 consisting of a heat insulating layer 9 and an external conductive layer 11. 32 is a cable connected to each feedthrough capacitor 25 to 227, and 33 is a connector connected to the cable 32.

In order to protect the vibrator 6 and the electronic circuit 8 from electromagnetic noise, the whole is surrounded by an internal conductive layer 10, and the conductive layer 10 is connected to the signal ground of the electronic circuit 8.

The internal conductive layer 10 is formed of a conductive resin mixed with carbon and/or carbon fiber, resin plating, conductive coating, or the like.

Furthermore, by mixing ferrite, high frequencies can also be shielded.

In order to prevent output zero drift from occurring due to the pyroelectric effect of the piezoelectric body 1, the entire body is surrounded by a heat insulating layer 9. The heat insulating layer 9 is formed of a pleated resin molded body, a foamed resin body, or the like.

Further, in order to eliminate the influence of external high frequency noise, an external conductive layer 11 connected to the ground terminals of the feedthrough capacitors 25 to 27 is formed of metal or the like and is grounded to the object to be measured.

To specifically illustrate the present invention, a polymer composite system having the following composition was used as the piezoelectric body 1.

PZT 82.3% by weight POM 15.8% by weight NBR 1.75% by weight Carbon 0.13% by weight This piezoelectric body 1 was formed into a disk shape with a thickness of 100 μm and a diameter of 191 mm.

A positive electrode 2 with a diameter of 13.5φ and an inner diameter of 14 are placed on one surface of the piezoelectric body 1.
A negative electrode 3 having an outer diameter of 19φ was provided on the other side, and a neutral electrode 4 was provided on the entire surface by printing conductive paint.

A glass epoxy resin backing material 5 with a thickness of 200 μm and a diameter of 19φ is bonded to an adhesive layer with a thickness of 10 μm using an epoxy adhesive.
A vibrator 6 was formed by adhering to the neutral electrode 4 of the piezoelectric body 1 in the following manner.

The vibrator 6 was bonded using an epoxy adhesive to an alumina substrate having a thickness of 0.8 mm and a size of 23 square meters on which a hybrid electronic circuit 8 was mounted.

The hybridized electronic circuit 8 was provided with a connection circuit, a signal processing circuit, and a power supply circuit.

The above-mentioned substrate is formed into a housing 3 consisting of three layers: a conductive resin layer IO, an insulating heat-insulating resin layer 9, and a metal layer 11.
1 and completed the sensor of the present invention.

〔effect〕

As can be understood from the above description, according to the present invention, electrodes are provided on both sides of the piezoelectric body 1, and a backing material 5 with a small coefficient of linear expansion is adhered to one side of the piezoelectric body 1 to form a piezoelectric vibrator 6. The vibrator 6 is bonded to one side of a circuit board 7 with a small coefficient of linear expansion,
A signal processing electronic circuit 8 is formed on the other side of the circuit board 7, and the whole is covered with an internal conductive layer 10. Since it is coated with three layers, the heat insulating layer 9 and the external conductive layer 11, output drift due to pyroelectricity can be reduced, and the output V is stable against temperature changes.

can be obtained. In addition, since the piezoelectric vibrator 6 is held by the circuit board vi7, which has a smaller wire film 56 than the piezoelectric body 1, the temperature dependence of the sensor sensitivity can be made constant, and the circuit board 7 can be connected to the inner conductive layer 1d. .

By using a soft adhesive when fixing the three layers of the heat insulating layer 9 and the external conductive layer 11, it is possible to absorb distortion due to the difference in linear expansion coefficient between the circuit board 7 and the three layers. Furthermore, since the piezoelectric vibrator 6 and the circuit board 7 are entirely covered with an internal conductive layer 10 connected to the signal ground of the electronic circuit 8, they are not only protected from electromagnetic noise but also protected from feedthrough capacitors 25 to 25. By connecting the external conductive layer 11 to the ground terminal 27, the influence of external high frequency noise can be removed.

Further, by incorporating the external induction interference prevention capacitor into the electronic circuit 8, the structure becomes simpler, and there is no need to worry about installing the capacitor, and the electronic circuit 8 can be made smaller and more compact.

In particular, since the backing material 5 plays a large role in vibration, it is possible to obtain a piezoelectric vibrator 6 with a constant temperature gradient of sensitivity.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the sensor of the present invention, and FIG.
FIG. 5 is a connection diagram showing an example of the configuration of the signal processing electronic circuit in this embodiment, FIG. 5 is a connection diagram showing an example of the electronic circuit in the present invention, and FIG. 6 is an explanatory diagram of its operation. 1... Piezoelectric body, 2, 3... Positive and negative electrodes, 4... Neutral electrode, 5... Backing material, 6
... Piezoelectric vibrator, 77a ... Circuit board, 8 ... Signal processing electronic circuit, 9 ... Heat insulation layer, 10 , 11 ...・Inner and outer conductive layers. 7 8 468

Claims (1)

[Claims] Electrodes are provided on both sides of the piezoelectric body 1, and a backing material 5 with a small coefficient of linear expansion is adhered to one side of the piezoelectric body 1 to form a piezoelectric vibrator 6. This piezoelectric vibrator 6 is attached to one side of a circuit board 7 with a low coefficient of linear expansion. An acceleration sensor is formed by adhering the circuit board 7 to form a signal processing electronic circuit 8 on the other side of the circuit board 7, and covering the entire body with three layers: an inner conductive layer 10, a heat insulating layer 9, and an outer conductive layer 11.