JPH036463A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To make temp. dependence constant 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 and bonding a support equal to or less than the backing material in the coefficient of linear expansion to the peripheral part of the backing material. CONSTITUTION:Electrodes 2 - 4 are provided to both surfaces of a piezoelectric body 1 and a backing material 5 low in the coefficient of linear expansion is bonded to one surface thereof and a support 34 equal to or less than the backing material 5 in the coefficient of linear expansion is bonded to the peripheral part of the backing material 5 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 and external conductive layers or the like. By this method, the drift of output due to pyroelectric properties is reduced and output stable to a temp. change is obtained. At this time, the backing material 5 is bonded to one surface of the piezoelectric body 1 by an adhesive and the participation of the backing material 5 becomes large in relation to vibration and the vibrator 6 made constant in a temp. gradient of sensitivity is obtained. The support 34 is bonded to the backing material 5 by a adhesive and the spaces of both surfaces of the vibrator 6 for the rectilinearity of output are 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 Hz and a displacement of 10 μm, the acceleration is I G , and at 0.16 Hz, the acceleration is I G for a displacement of 10 m. When making low-frequency vibration measurements, the actual displacement is at most 1 m or less; for example, at 1.6 Hz, the displacement is 0.1 m or less.
G, resulting 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 0.0 IG.

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. Not only can the body significantly reduce temperature changes caused by external heating or cooling, but the insulating base electrically isolates the piezoelectric vibrator from the object being measured, reducing electrostatic induction, ground potential, etc. In addition to being less susceptible to induction interference, an external induction interference prevention capacitor is connected between the conductive resin and the conductive heat conductor, allowing external high-frequency noise to be bypassed.

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 problem, the output of the piezoelectric vibrator must be connected to a separate signal processing electronic circuit using a cable, which prevents the structure from being made smaller and more compact, and may cause external induction interference between the piezoelectric vibrator and the electronic circuit. Furthermore, since the piezoelectric body is not supported by a material with a coefficient of linear expansion smaller than this, there is also the problem 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 provides electrodes on both sides of a piezoelectric body 1 as shown in the figure, adheres a backing material 5 with a small coefficient of linear expansion to one surface, and wires are attached to the periphery of the backing material 5. A piezoelectric vibrator 6 is constructed by adhering a support 34 with an expansion coefficient of the same or lower, and this piezoelectric vibrator 6 is attached to 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 entire 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 is simplified and there is no need to worry about installing the capacitor. There is no need to install a separate cable when connecting to 8, so the structure is compact and
It can be made compact, there is no risk of external induction interference occurring between the piezoelectric vibrator 6 and the electronic circuit 8, and since the piezoelectric body 1 is held by a material with a smaller linear expansion coefficient, the temperature dependence of the sensor sensitivity can be reduced. This will be possible to a certain extent.

[Detailed description of the invention]

The present invention will be described in detail below based on the drawings.

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 (a+, (b)) 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, polymer piezoelectric materials include PVDF-polyvinylidene resin and P (VDCN/VCA) = poly (vinylidene cyanide/vinyl acetate) copolymer resin, and polymer composite systems include PZT-zirconate titanate resin. lead·
POM is a piezoelectric body made of a composition consisting of polyacecool resin, NBR-acrylonitrile-butadiene copolymer rubber, and carbon. The durability of rubber can be improved by vulcanizing it.

It may be a piezoelectric body composed of PCT=calcium-substituted lead titanate/u-POM-urethane-modified polyacetal resin.

Electrodes are provided on both sides of the piezoelectric body by means of vapor deposition, sputtering, printing with conductive paint, etc., a backing material 5 is adhered to one surface, and a support 34 is fixed to the periphery of this backing material 5. For example, a pair of positive and negative electrodes 2.3 are provided on one surface of the piezoelectric body 1, and a neutral electrode 4 is provided on the other surface.
A piezoelectric vibrator 6 (see FIG. 3) having a structure in which a backing material 5 and a support 34 are provided thereon is effective in reducing pyroelectricity. This effect occurs when the positive and negative electrodes are 2°3
This can be further increased by making the areas of

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 (5X10-5/℃
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.

The thickness is 0.01-1.6 fins, preferably 0.03-0
．． Five cranes are used. In particular, 1/3 of the piezoelectric thickness
A range of 10 times is selected.

The backing material 5 is adhered to one surface of the piezoelectric body 1 using an adhesive. By doing this, the contribution of the backing material 5 to vibration increases, so the vibrator 6 has a constant temperature gradient of sensitivity.
can be obtained.

The support 34 is made of glass epoxy resin or ceramic whose coefficient of linear expansion is similar to or smaller than that of the backing material 5.

Metal etc. are used.

The shape is dish-shaped with a depression or hole in the center,
A ring shape etc. is suitable.

Regarding the hole diameter, the outer diameter of the inner positive electrode 2 of the piezoelectric body 1 is A,
Assuming that the outer diameter of the outer negative electrode 3 is B, the inner diameter of the support body 34 is C1, and the outer dimension is D, each relationship is defined by the following equation.

A/2≦C<B≦D Preferably A≦C≦(B-A)*3/4+A<B≦D The support body 34 is adhered to the backing material 5 using an adhesive, and the vibrator 6 is configured. be done.

In order to obtain linearity of the output with respect to the excitation force, continuous spaces are formed on both sides of the vibrator 6.

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 5×10-5/'C or less and a thickness of approximately 0.2 to 5 mm, and having high rigidity that can withstand distortion due to the difference in coefficient of linear expansion with the housing 31. , ceramics (alumina, silicon wafers, etc.), metals, etc. are used.

A connecting 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, through positive and negative electrode lead patterns 13 and 14 ( (See Figure 3)
, further these positive.

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 the circuit boards 7 and 7a, for example, as shown in the first diagram. 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.

A field effect transistor Q of the 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.

0. A muting section 22 is connected after the filter section 21 to speed up the output rise immediately after the 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 that of the piezoelectric body 1, 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, R4 is a source resistance, Vcc is a voltage terminal, R is a gate resistance, and Ql is a Field effect 1 for impedance conversion - transistor, T1 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 R9, The first of these.
The second time constant circuits T, , T2 constitute a filter section. A
1. A2 is the first stage, second stage amplifier, R3, R4, Rh,
R7ba1 2 Resistors for setting the gains of the first-stage and second-stage amplifiers A+ and Az, respectively, which constitute the gain adjustment circuit 29, and the temperature compensation circuit 28 is not shown. Qz and Qs are each resistance Rz
, Rs connected in parallel. Second switching field effect transistors D, D2 are diodes, and Mc is a muting circuit 22.

Field effect transistor Q2 outputted from muting circuit Mc. Q, 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 M2 stops after 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 the voltage is applied to the diode DI+D2, the field effect transistors Q Z and Q 3 become gate-to-source voltage V(,s-〇■) due to the diode leakage current, and are turned on.After a certain period of time 1...12, the muting signal M,
, M2 becomes lower than the reference potential Vc below the field effect transistor pinch-off voltage, the field effect transistor Q, ,
Q2 is turned off. Here, the ON setting time tl+t2 of the field effect transistor Q2Q3 is 1. <12.

When the power is turned on in such a configuration, the impedance conversion field effect transistor Q1 and the amplifier A
A power supply voltage Vcc is applied to I and A2. at the same time,
When the muting circuit Mc is activated, the switching field effect transistor Q2 connected in parallel to the resistor R2 of the first time constant circuit TI is turned on for a set time t1 by the muting signal M via the diode D, and then turned off. It will be done.

Furthermore, 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.

With this operation, the first time constant circuit T, has a t1 period length 2#
0Ω, and the DC blocking capacitor C8 is quickly charged to a predetermined voltage. After the t1 period, the 341 time constant circuit T 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 6#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 using a regular time constant.

As a result of the above operation, the sensor amplifier output signal Vo 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 seven-tring 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 27, 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 zero output drift from occurring due to the pyroelectric effect of the piezoelectric body 1, the entire piezoelectric body 1 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, the following five piezoelectric bodies 1 are used. 6 A polymer composite system with the composition was used.

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 1!1 ln.

A positive electrode 2 with a diameter of 13.5ψ and an inner diameter of 14 are placed on one surface of the piezoelectric body 1.
A negative electrode 3 with an outer diameter of 19φ is placed on the other side, and a neutral electrode 4 is placed on the entire surface on the other side.
was provided 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 thickness of 10 μm using an epoxy adhesive.
It was bonded to the neutral electrode 4 of the piezoelectric body 1 in the following manner.

A glass epoxy resin ring 34 having a thickness of 1.2N and an outer diameter of 19.5φ and an inner diameter of 15.5φ was adhered to the backing material 5 surface of the adhesive body using an epoxy adhesive to form a vibrator 6.

The vibrator 6 was bonded using an epoxy adhesive to a 0.81 mm thick, 23 mm square alumina substrate 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 10, an insulating heat-insulating resin layer 9, and a metal layer 11.
[Effects] As understood from the above explanation, according to the present invention, electrodes are provided on both sides of the piezoelectric body 1, and a backing with a small coefficient of linear expansion is provided on one side. A piezoelectric vibrator 6 is constructed by gluing the material 5 and adhering a support 34 having a linear expansion coefficient of the same or lower to the circumference of the backing material 5,
This piezoelectric vibrator 6 is adhered to one side of a circuit board 7 having a small coefficient of linear expansion, and a signal processing electronic circuit 8 is attached to the other side of this circuit board 7.
, and the entire 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 an output Vo that is stable against temperature changes can be obtained. Furthermore, since the piezoelectric vibrator 6 is held by the circuit board 7 which has a coefficient of linear expansion smaller than that of the piezoelectric body 1, the dependence of the sensor sensitivity on the temperature 78 can be made constant, and the circuit board 7 can be connected to the internal conductive layer 10. The circuit board 7 is fixed to the three layers of the heat insulating layer 9 and the external conductive layer 11 by using a soft adhesive.
It can absorb the strain caused by the difference in linear expansion coefficient between 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 high frequency electromagnetic waves can be removed. Furthermore, by incorporating the external induction interference prevention capacitor into the electronic circuit 8, the structure becomes simpler and more compact.

In particular, since the backing material 5 and the support body 34 are greatly involved in vibration, it is possible to obtain a piezoelectric vibrator 6 with a constant temperature gradient of sensitivity.

[Brief explanation of the drawing]

Fig. 1 is a schematic sectional view showing the configuration of one embodiment of the sensor of the present invention, Fig. 2 is a perspective view showing the external appearance of this embodiment, and Fig. 4 shows two configuration examples of the signal processing electronic circuit in this embodiment. FIG. 5 is a connection diagram showing an example of the electronic circuit according to the present invention, and FIG. 6 is an explanatory diagram of its operation. ■...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, 34・
...Support. 9 0

Claims (3)

[Claims] (1) Electrodes are provided on both sides of the piezoelectric body 1, a backing material 5 with a small coefficient of linear expansion is adhered to one surface of the electrode, and a support material 34 with a coefficient of linear expansion equal to or lower than the other is adhered to the periphery of this backing material 5. Piezoelectric vibrator 6
The piezoelectric vibrator 6 is bonded 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. An acceleration sensor coated with three layers: layer 9 and outer conductive layer 11. (2) In the piezoelectric vibrator 6, a pair of positive and negative electrodes 2 and 3 are provided on one surface of the piezoelectric body 1, a neutral electrode 4 is provided on the other surface, a backing material 5 is adhered to the neutral electrode 4, and the backing material 2. The acceleration sensor according to claim 1, further comprising a support member 34 adhered to the circumferential portion of the acceleration sensor 5. (3) The signal processing electronic circuit 8 applies the output of the piezoelectric vibrator 6 to
Impedance conversion section 20, filter section 21, amplifier section 2
3 are connected in this order, and the muting section 22 is connected between the filter section 21 and the amplification section 23, and a power supply circuit 30 for operating these sections is provided, and the output of the amplification section 23, the input of the power supply circuit 30, and the signal 3. The acceleration sensor according to claim 1, wherein feedthrough capacitors (26, 25, 27) are connected to the ground, respectively.