JPH03214062A - Piezoelectric type acceleration sensor - Google Patents

Abstract

PURPOSE:To make adhesion between a film-shaped piezoelectric body and metal electrodes rigid and to improve shock resistance by activating the bonding surfaces of the film-shaped piezoelectric body comprising fluorocarbon resin and the metal electrodes beforehand. CONSTITUTION:A sensor part 3 is composed of a film-shaped piezoelectric body 4 and metal electrodes 5 bonded on both surfaces of the piezoelectric body. As the piezoelectric body 4, a material wherein fluorocarbon resin such as polyvinylidene fluoride is a main body is used. The surfaces of the piezoelec tric body 4 is activated. For example, there is a method by which the piezoelec tric body is submerged into fused alkali metal such as fused sodium. As the electrodes 5, a copper foil, an Al foil or the like is used. The piezoelectric body 4 and the electrodes 5 are bonded by using dielectric bonding agent such as epoxy-based bonding agent. Thus, the piezoelectric body 4 and the electrodes 5 become the rigidly bonded state. The electrodes 5 are rigidly fixed to a meas uring surface 2 of a pedestal 1 and a load body 6 with epoxy-based bonding agent or the like. Even if strong shocking force is applied from the direction perpendicular to a detecting axis G, the junction is not broken, and the sensor having the high shock resistance is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a piezoelectric acceleration sensor using a film-like piezoelectric material, which has improved impact resistance.

[Conventional technology]

The present inventors first developed a pedestal that is rigidly attached to an object to be measured, a film-like piezoelectric material fixed to a measurement surface perpendicular to the sensing axis of this pedestal, and an inertial mass fixed on this film-like piezoelectric material. We have proposed a piezoelectric acceleration sensor (hereinafter abbreviated as sensor) equipped with a load body made of a rigid body that acts as a
(Japanese Patent Application No. 1-113255, etc.)

As a method for forming electrodes for signal extraction from the film-like piezoelectric material in such sensors, metal foil such as aluminum foil or copper foil is used as an electrode, and this is bonded with a dielectric adhesive such as epoxy adhesive. There is.

Compared to forming electrodes by vapor deposition of metals such as aluminum, this electrode formation method has the advantage that the bonding strength between the membrane piezoelectric material and the electrode is greater, and it is stronger against impact forces in the direction perpendicular to the sensing axis. be.

However, depending on the use of the sensor, an impact force exceeding 1000 G may be applied, and in such cases, impact resistance may be insufficient.

Fluororesins such as polyvinylidene sulfide, polyph, vinyl chloride, etc. are mainly used as membrane piezoelectric materials, and since these fluororesins are originally inert and have poor adhesive properties, membrane piezoelectric materials and metal foil electrodes are used. This is due to not having enough tangent power or 1.

[Invention or problem to be solved]

Therefore, an object of the present invention is to provide a bonding mechanism 111 that can firmly bond a piezoelectric film to a metal electrode and has high impact resistance.

[Means for y) to solve the problem] F. The first step is to activate the surface of the film-like piezoelectric material made of citrus oil that comes into contact with the metal electrode53. 7. The activation treatment improves the adhesion of the piezoelectric film and greatly increases the contact force between the piezoelectric film and the metal electrode.7. This improves the shock resistance of the sensor.

The present invention will now be described in detail.

FIG. 1 shows an example of the sensor of the present invention, and the reference numeral 1 in the figure is a pedestal.

The pedestal 1 forms the base of the sensor and is made of a material having a certain degree of rigidity, such as metals such as steel, brass, and aluminum, glass, ceramics, fiber-reinforced plastics, hard plastics, and the like. Further, the elastic modulus of the material forming the pedestal 1 is greater than that of the film-like piezoelectric material described later, and the thickness of the pedestal 1 is desirably several times that of the film-like piezoelectric material.

Although the pedestal 1 here has a cylindrical shape, it is not limited to this, and may be a plate shape, a rectangular parallelepiped, or the like.

One surface of this pedestal 1 is a flat and smooth measurement surface 2. This measurement plane 2 needs to be a vertical plane that is exactly perpendicular to the acceleration sensing axis G of this sensor.

On the measurement surface 2 of the pedestal 1, a sensor section 3 is firmly fixed to the pedestal 1 using an epoxy adhesive or the like.

This sensor section 3 includes a film-like piezoelectric material 4 and a film-like piezoelectric material 4.
It is composed of metal electrodes 5, 5 bonded to both surfaces of. The film-like piezoelectric material 4 used here includes polyvinylidene fluoride, polymer vinyl nitride, vinylidene 7-vinyl fluoride-tetrafluoroethylene copolymer, and a blend polymer of polyvinylidene fluoride and polyvinyritine fluoride. , piezoelectric ceramics mainly composed of fluororesin with dispersed 7 elements are used, and the thickness is 10 to 300 μm.
It is said to be about m.

The surface of such a piezoelectric film 4 is subjected to activation treatment. This activation treatment activates the surface of the film-like piezoelectric material made of fluororesin to increase its affinity with adhesives.
), and specific treatment methods include immersion in molten alkali such as molten sodium, and commercially available fluorinated citrus treatment agents containing active sodium, such as (
There are methods such as immersion in Jun-T Co., Ltd. U11 Tetrae... (trade name), and immersion in a hot strong acid, a hot strong alkali, or a halogenated solvent. It is necessary to be careful with these activation treatments because if the degree of activation becomes excessive, the membrane piezoelectric material 4 itself will deteriorate. A degree of immersion) V is preferred.

Moreover, as the metal electrode 5, copper foil, aluminum foil, etc. with a thickness of about 10 to 50 μm are used. The piezoelectric film 4 and the metal electrode 5.5 are brought into contact with each other using a dielectric adhesive such as an epoxy adhesive, a ferrite adhesive, or an acrylate adhesive.

The sensor section 3 has a disk shape as shown in FIG. 1, and is joined so that its central axis coincides with the sensing axis G of the pedestal 1.

Further, a load body 6 is firmly fixed to the sensor portion 3 using an epoxy adhesive or the like. The load body 6 is made of a rigid body that functions as an inertial mass part of the sensor, and is displaced in response to acceleration, causing strain or stress on the membrane piezoelectric body 4 of the sensor part 3, and its weight is about the middle of the sensor. Since it is related to the electrical output per acceleration, it is not particularly limited, but it is set within a range that does not cause creep in the piezoelectric film 4. Usually, it is preferable to use a material with a high specific gravity, such as a brass alloy, because the overall height of the sensor can be reduced.

Moreover, the load body 6 can be made of a composite material made of different materials in addition to being made of a homogeneous material as a whole, but in this case, each material is firmly fixed and the whole becomes a rigid body. They must be able to be regarded as such, and each must not undergo different displacements when subjected to acceleration.

This load body 6 also has a cylindrical shape and is stacked so that its central axis coincides with the sensing axis G of the pedestal l.

In such a sensor, the surface of the piezoelectric film 4 is activated to improve its adhesion, so that it is strongly bonded to the metal electrode 5.5. Further, the metal electrodes 5, 5 of the sensor section 3 are firmly fixed to the base 1 and the load body 6 using an epoxy adhesive or the like.

Therefore, all the members of this sensor are firmly fixed and integrated, and there are no weak points in their joints. Therefore, even if a strong impact force is applied from a direction perpendicular to the sensing axis G, the joint will not break, resulting in extremely high impact resistance.

In addition, in the sensor of this example, the sensor section 3 and the load body 6
The crosstalk is low because the planar shape is circular and their central axes are aligned with the sensing axis G.

Crosstalk in this invention refers to the sensing axis G of the sensor.
The ratio of the output P1 when receiving acceleration in the direction to the output P when receiving acceleration in the direction perpendicular to the sensing axis G, P, /
It is expressed as P.

There are two conditions for reducing this crosstalk, one of which is related to the planar shape of the membrane piezoelectric material 4,
The remaining one concerns the three-dimensional shape of the load body 6 and the planar shape of the surface in contact with the sensor section 3.

First, the planar shape of the piezoelectric film 4 must be point symmetric with respect to the sensing axis G as the center of symmetry in a plane parallel to the measurement surface 2. In the example shown in Figure 1, it is circular, but
Other planar shapes that satisfy the above conditions include parallelograms, squares, ellipses, regular hexagons, hexagons, and toric shapes. All of these planar shapes are point symmetrical with respect to the sensing axis G as the center of symmetry. Of course, planar shapes other than these can also be used if the above conditions are met.

Further, the planar shape of the metal electrode 5 is also preferably point symmetrical with respect to the sensing axis G as the center of symmetry, and is usually the same as the planar shape of the membrane piezoelectric material 4 in many cases.

Next, the planar shape of the surface of the load body 6 in contact with the sensor section 3 must be exactly perpendicular to the sensing axis G, and the planar shape of the bottom surface must be line symmetrical with the sensing axis G as the center of symmetry. be. Therefore, as a shape that satisfies this condition, a shape similar to the planar shape of the film-like piezoelectric body 4 described above can be adopted. however,
In the combination of the membrane piezoelectric body 4 and the load body 6, the planar shape of the bottom surface of the load body 6 and the plane shape of the membrane piezoelectric body 4 do not necessarily have to be the same.
The planar shape of the load body 6 may be a square, and the bottom surface of the load body 6 may have a circular planar shape, as long as the sensing axes G are the same, as will be described later.

At the same time, when the load body 6 is cross-sectioned through countless planes passing through the sensing axis G and perpendicular to the bottom surface, it is necessary that all the cross sections have line symmetry with the sensing axis G as the axis of symmetry. Examples of devices that satisfy this condition of line symmetry are those shown in FIGS. 2 to 8. The one shown in Figure 2 is plate-shaped, the one in Figure 3 is columnar, the one in Figure 4 is cone-shaped, the one in Figure 5 is a sphere cut out on a plane, and the one in Figure 6 is an ellipsoid. The one cut out on a plane, the one in Figure 7 has an empty space 111 inside the columnar shape.
1, the one shown in Fig. 8 is a combination of a column and a plate. In these figures, the symbol S indicates the bottom surface, and G is the axis of symmetry that coincides with the sensing axis. Also, the load body 6 that satisfies this line symmetry condition has its center of gravity on the sensing axis G. It will be located in

Under these conditions, the load body 6 having symmetry has its axis of symmetry aligned with the center of symmetry of the sensor section 3. In other words, the center of symmetry of the sensor section 3 and the symmetry of the load body 6 are aligned on the sensing axis G. It must be placed in alignment with the axis and secured.

A load body 6 and a membrane piezoelectric body 4 that satisfy the following conditions
Crosstalk can be reduced by combining silk with .

- Generally, when acceleration is applied to a sensor in a direction other than the direction of its sensing axis, it is divided into at least two components in the direction perpendicular to the sensing axis and a component in the direction of the sensing axis, according to the law of vector decomposition. It will be done. r in the noj direction perpendicular to this sensing axis
The component acts on the center of gravity of the load body 6, and a bending moment centered on the center of gravity acts on the load body 6. For this reason,
A compressive force acts on a portion of the piezoelectric film 4, and an attraction Ij acts on the remaining portion.
The R force will act. The film-like piezoelectric material 4 generates an electric charge of anti-λ, 1 sign due to If-contraction force and tensile force, or if this electric charge (distributed equally) is canceled by 1j, no output is output. 9. If a compressive force and a tensile force that are equal to each other act on the membrane piezoelectric body 1 in the sheet piezoelectric body 1, the output from the membrane piezoelectric body 4 will be zero, and the output from the piezoelectric body 4 will be zero, and Acceleration in the direction of is no longer detected.

each of the yo-pa C1 membrane-like piezoelectric body 4 and the load body 6)
If the f′/ shape has the symmetry described in 1-1, even if acceleration in a direction other than the direction of the sensing axis G is applied, compressive force and tensile force of equal magnitude will act on the piezoelectric film 4. As a result, there is no output from the piezoelectric film 4, and crosstalk becomes extremely small.

Further, this sensor has a high measurable frequency limit and a wide measurable frequency band.

The northern limit of measurable frequencies for this type of sensor is determined by the sensor's resonant frequency. The resonant frequency of this sensor is determined by the elastic modulus of what exists between the pedestal l and the front heavy body 6, that is, the membrane piezoelectric body 4, the metal electrodes 5, 5, and the adhesive layer bonding these together. Since it is proportional to the value divided by the mass of 6, the resonant frequency is 2 times higher than the conventional vibrating membrane type sensor, and is on the order of kilohelp.

However, it should be noted that as the elastic modulus of the bone cement layer decreases, the resonance frequency also decreases.

Therefore, for the adhesive used to fix the sensor part 3 itself and the pedestal 1 and load body 6, the composite equivalent elastic modulus of the adhesive layer and the metal electrode 5 is EA, and the sum of these thicknesses is tA. The elastic modulus of the film-like piezoelectric material 4 is Iε1, and the thickness is 1. Then, it is necessary to satisfy the relationship expressed by the following formula.

(EA/tA)/(EP/tp)≧0.1
The key to this equation is the condition under which the force exerted on the load body 6 due to acceleration is well transmitted to the membrane piezoelectric material 4 without being absorbed or relaxed by the cement layer and the metal electrode 5. If the value of Equation 1 becomes less than O1, the absorption relaxation by the adhesive layer cannot be ignored, and the resonant frequency decreases as described above, narrowing the frequency band that can be measured.

In addition, if the type of adhesive is different and the modulus of elasticity is also different, find the ratio between the modulus of elasticity and the thickness of each adhesive layer, add this up, and substitute it into the -L formula1. ], the bone cement here should be a hardening type such as epoxy type, fluoride type, /anoacrylate type, etc., and should be selected with a high elastic modulus, and comb type etc. Adhesive type is inappropriate.

Below)゛, [One example is shown.

(Example 1) A polyvinylidene fluoride film with a thickness of 100 μm was prepared as a membrane piezoelectric material, and it was immersed in an activation treatment agent "Tetra Etch 1" for 10 seconds at room temperature, and then washed with water. After drying, , metal electrodes of body foil with a thickness of 30 ttm were attached to both sides with epoxy adhesive, and this was made into a 1CI
It was cut into a square with 11 sides to form a sensor section. This sensor part is attached to an aluminum plate-shaped pedestal with a thickness of 51III using epoxy adhesive, and a rectangular parallelepiped load body made of uniform material and having a lee angle bottom is attached to 1- of this sensor part using epoxy adhesive as well. A sensor was created by attaching the bone with adhesive so that its central axis coincided with the central axis of the sensor part.

(Example 2) A sensor was produced in the same manner as in Example 1, except that only one side of the piezoelectric film was brought into contact with "Tetra Etch" for 10 seconds at room temperature.

(Comparative Example 1) A sensor was produced in the same manner as in Example 1 without subjecting the film-like piezoelectric material to any treatment.

Comparative Example 2) A sensor was produced in the same manner as in Example 1, except that the piezoelectric film was immersed in 1-tetraetch for 2 seconds at room temperature.

(Comparative Example 3) A sensor was produced in the same manner as in Example 1, except that the piezoelectric film was immersed in Tetra Etch J for 1 minute at room temperature.

The basic output of the valley sensor and the impact resistance of the sensors obtained in these examples and comparative examples were evaluated.

The basic output of the sensor was detected as a voltage output by connecting an impedance conversion circuit. In addition, regarding impact resistance,
An impact acceleration of 5,000 G was applied in the direction perpendicular to the sensing axis, and evaluation was performed based on the number of impacts applied until the sensor part was destroyed.

The results are shown in Table 1.

From the results in Table 1, it can be seen that with the sensor of this invention, there is almost no change in the sensor output, but the impact resistance is thicker (improved). In Comparative Example 3), the impact resistance deteriorated and the sensor output also decreased. This seems to be because the drug penetrates into the interior of the piezoelectric membrane and deteriorates the piezoelectric membrane itself.

〔Effect of the invention〕

As explained above, the piezoelectric acceleration sensor of the present invention is one in which the surface of the film-like piezoelectric material made of fluororesin is activated to increase its adhesion to metal electrodes, so it can withstand large impact forces. The adhesion between the film-like piezoelectric material and the metal electrode will not be destroyed even if the film-like piezoelectric material is acted upon (and the impact resistance will be extremely excellent).

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view showing an example of the sensor of the invention, and FIGS. 2 to 8 are sectional views showing examples of the three-dimensional shape of a load body suitable for the sensor of the invention. 1...Pedestal, 2...Measurement surface, 3...Sensor section, 4...Membrane piezoelectric body, 5...Metal electrode , 6... Load body.

Claims (1)

[Claims] A load consisting of a pedestal that is rigidly attached to the object to be measured, a piezoelectric film that is fixed to the measurement surface perpendicular to the sensing axis of the pedestal, and a rigid body that is fixed to the piezoelectric film and acts as an inertial mass. In a piezoelectric acceleration sensor, the piezoelectric film is made of a fluororesin, and the metal electrode is bonded to at least one side of the piezoelectric film using a dielectric adhesive. A piezoelectric acceleration sensor whose surface is activated.