JPH04142428A - Piezoelectric vibration sensor - Google Patents

Abstract

PURPOSE:To precisely adjust the output by providing an auxiliary load body made of metal fine pieces and an adhesive on a basic load body made of a head material closely fixed to a measurement face to form a load body closely fixed on a film-shaped piezoelectric body. CONSTITUTION:A sensor 10 has a pedestal 11 serving as a vibration transfer body, a film-shaped piezoelectric body 13 closely fixed to the measurement face 12 of the pedestal 11 in the perpendicular direction to the detection axis G of acceleration or vibration, and a load body 14 closely fixed on it and constituted of a basic load body 15 and an auxiliary load body 16. The basic load body 15 is made of a material rarely absorbing the vibration from a measured object, e.g., relatively hard steel, brass, hard aluminum alloy. The auxiliary load body 16 is mixed with metal fine pieces serving as a load in an adhesive and stuck on the basic load body 15, and the weight of the metal fine pieces is preferably set to 0.1% or below of the weight of the basic load body 15 to precisely adjust the output of the piezoelectric body 13.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a piezoelectric vibration sensor, also called a piezoelectric acceleration sensor, using a film-like piezoelectric material, and in particular, to a piezoelectric vibration sensor that uses a film-like piezoelectric material and is also called a piezoelectric acceleration sensor. The present invention relates to a piezoelectric vibration sensor that can be used for various purposes.

[Prior Art] Piezoelectric vibration sensors can be broadly classified based on their materials: those that use an inorganic or ceramic piezoelectric material in the vibration sensing part;
Some use a polymer-based piezoelectric material in the vibration sensing section. Inorganic/ceramic materials have advantages such as good precision and a wide usable temperature range, but they have problems such as being easily destroyed by impact and difficult to miniaturize.

On the other hand, polymer-based products include those that use piezoelectric bolimate and those that use a mixture sort in which inorganic/ceramic piezoelectric powder is dispersed in a polymer, which have improved impact resistance. However, the structure is such that the periphery of the vibration sensing section, which consists of a load body acting as an inertial mass attached to the piezoelectric sheet, is fixed. Due to the low rate, there were problems such as a narrow measurable frequency band, poor crosstalk, and low net output sensitivity.

The inventors of the present invention developed a piezoelectric vibration sensor 30 shown in FIG. 3 (Japanese Patent Application No. 1-113255) to solve the above-mentioned problems of polymer-based piezoelectric materials. That is, as shown in the figure, the upper surface of a pedestal l as a vibration transmitter attached to an object to be measured (not shown) is a measurement surface 2 perpendicular to the vibration sensing axis G of the pedestal, and a polymer-based The sorted piezoelectric material 3 is closely fixed, and the load body 4 is placed and fixed directly on it, so that the sheet-like piezoelectric material 3 sandwiched between the pedestal l and the load body 4 is A load is applied point-symmetrically about the sensing axis G.

According to such a configuration, the structure is simple and can be downsized, and since the sheet-like piezoelectric body 3 is tightly held between the pedestal l and the load body 4,
The vibration to be measured is almost never absorbed or attenuated on the way, and can be reliably transmitted to the piezoelectric body 3 and given distortion to it, improving the output sensitivity. The output generated by the vibration component of the load body 4 is applied to the piezoelectric body 3 point-symmetrically with respect to the sensing axis G, so that the output generated by the vibration component is generated on both sides of the sensing axis and cancels each other out, causing a cross. It is possible to make the talk extremely small.

[Problem to be solved by the invention] In the vibration sensor in which a load body is placed and fixed directly on the sheet-like piezoelectric body, the output thereof is proportional to the weight of the load body placed on the piezoelectric body. If the weight of the load body is kept constant, there should be no individual differences in the sensor output. However, in reality, individual differences occur due to differences in the piezoelectric properties of individual piezoelectric bodies.

Conventionally, a piezoelectric pickup using such a vibration sensor measures the output via a charge amplifier, so the gain of the charge amplifier is adjusted in accordance with the sensitivity of each pickup.

However, this method requires large measuring instruments, requires a special cable from the pickup, and is therefore expensive and lacks versatility.

Therefore, recent vibration sensors have come equipped with internal impedance conversion circuits that allow the output to be easily measured with a voltmeter. This sensor requires a small size to further increase its versatility, so the number of components used in the circuit is reduced, and a hybrid IC with small components is used, so a variable resistor is used to adjust the output as in the past. It is becoming difficult to use large parts such as

As mentioned above, the output of a vibration sensor is proportional to the weight of the load placed directly on the piezoelectric sheet, so the sensor output can be adjusted by adjusting the weight of the load. It was taken. Therefore, the load body that is preset in the vibration sensor is set as a basic load body whose weight is less than the reference output, and after the output is measured, the missing weight is sequentially added. Initially, several types of loads with different weights were prepared, and an appropriate load was selected from among them and placed on the load base, but this made the output correction too coarse, so it was necessary to finely correct it. It is necessary to prepare loads of many different weights, which tends to require too much cost and effort to select the appropriate load.

[Means for Solving the Problems] The piezoelectric vibration sensor of the present invention is of a type in which the weight of a load body placed directly on a sheet-like piezoelectric body is adjusted in order to adjust its output. An auxiliary load body made of metal strips and adhesive is attached to the basic load body which is set in advance to adjust the load.

Another piezoelectric vibration sensor of the present invention is such that the above-mentioned auxiliary load body is made of metal strips and adhesive and is provided in a recess formed on the top surface of the basic load body. It is something.

FIG. 1 shows a piezoelectric vibration sensor lO which is one of the embodiments of the present invention, and shows a pedestal 11 which is a base of the sensor attached to an object to be measured and which is a vibration transmitter, and a pedestal 11 which is a sensor for sensing acceleration or vibration. Measurement surface 1 of pedestal 11 perpendicular to axis G
2, and a load body 14 consisting of a basic load body 15 and an auxiliary load body 16 closely fixed to the upper surface of the membrane piezoelectric body 13.

The above-mentioned pedestal 11 is made of steel, brass, hard aluminum alloy, etc., which can transmit vibrations from the object to be measured without absorbing them. However, the shape is not limited to this, and the shape may be a plate, a column, or the like.

The measurement surface 12 on the upper surface of the pedestal 11 is a smooth plane perpendicular to the sensing axis G of the sensor in the direction of acceleration or vibration to be measured.

The film-like piezoelectric body 13 tightly fixed on the measurement surface 12 is a film-like material with a thickness of 10 to 500 μm made of a piezoelectric material. Vinylidene, polyvinylidene chloride, polyvinyl fluoride, polyvinyl chloride, nylon 11
Nylon such as and polymetaphenylene isophthalamide,
Copolymers of vinylidene fluoride with tetrafluoroethylene, trifluoroethylene, vinyl fluoride, etc.; copolymers of vinylidene cyanide with vinyl acetate, vinyl propionate, vinyl fragrant, etc.; polyvinylidene fluoride and polyfluoride. Blend polymers with vinyl chloride are known, and polymers in which powders of piezoelectric materials such as metal titanates and metal zirconate titanates are added and dispersed in polymers are used.

An electrode made of aluminum foil, copper foil, etc. for output extraction is provided on the inner surface of the film-like piezoelectric body 13, but is not shown in the drawing. This film-like piezoelectric material 13 and the pedestal 1
The close fixation with 1 is performed using, for example, a hardening type adhesive such as an epoxy adhesive.

The load body 14 tightly fixed on this film-like piezoelectric body 13 is
It functions as an inertial mass part, and for its tight fixation,
Similar to the above-mentioned fixation of the piezoelectric film 13 and the base 11 in close contact with each other, this is done using, for example, an epoxy adhesive. The load body 14 receives the vibration of the object to be measured through the pedestal 11 and the piezoelectric film 13 and is displaced, and the pedestal 11 and the load body 1
This causes distortion in the piezoelectric film 13 sandwiched between the piezoelectric film 13 and the piezoelectric film 13, and within a certain range of weight, the weight is proportional to the electrical output.

The load body 14 includes a basic load body 15 that is tightly fixed on the membrane piezoelectric body 13, and a basic load body 15 that is provided on the top surface of the basic load body 15 to supplement the insufficient weight of the basic load body 15 to obtain a predetermined output. Similar to the pedestal 11, this basic load body 15 is made of a material that does not absorb vibrations from the object to be measured as much as possible, such as steel, brass, hard aluminum alloy, etc., which are relatively hard metals. is used. In addition, the shape is a rectangular parallelepiped in the illustrated embodiment, but
There is no particular restriction on the three-dimensional shape, such as a prismatic, cylindrical, or truncated pyramid, but the auxiliary load body 16 can be installed on the top surface, and the surface in contact with the membrane piezoelectric material 13 can be eccentric. It is desirable that the load can be applied evenly without any strain.

In this invention, the weight of the load body 14 for obtaining a predetermined electrical output of the vibration sensor is the total weight of the basic load body 15 and the auxiliary load body 16, so the weight of the basic load body 15 is estimated to be A weight that is somewhat smaller than the total weight (
Even if there are individual differences in the output of the membrane piezoelectric body 13, the output that would be obtained when the auxiliary load body 16 is not placed will never exceed the predetermined output (weight), for example, the vibration being manufactured. It is necessary to set the weight so that most of the sensor has 90% of the predetermined output.

The auxiliary load body 16 is attached to the top surface of the basic load body 15 with an adhesive mixed with metal strips as a load.In order to precisely adjust the output of the piezoelectric body, the metal strips It is desirable that the weight of the metal strip is 0.1% or less of the weight of the basic load body 15, but all the metal strips used are not limited to less than that, and the material may be copper, iron or These alloys, etc. are used, and the size of the particles is preferably up to about 200 μm in particle size, and in the case of scales, the diameter of the flat surface is up to about 2 mm. is also not limited to these sizes. The adhesive for fixing the metal strip onto the basic load body 15 is preferably one that has good adhesion to metal, such as thermosetting, thermoplastic, rubber adhesive, or a composite adhesive of these, but it is not necessarily limited to this. It's not a thing. Further, it is desirable that the material be relatively hard after adhesion and solidification, that is, it should absorb as little vibration as possible, and it is also desirable that the amount used be as small as possible. Furthermore, the method of adhesion to the upper surface of the basic load body 15 includes whether to apply adhesive to the entire surface on which a predetermined amount of metal pieces are placed, or to apply an adhesive mixed with metal pieces. And then it is done. FIG. 1 shows the case where the auxiliary load body I6 is constructed by applying a mixture of metal strips and adhesive in three layers on the upper surface of the basic load body 15.

FIG. 2 shows a piezoelectric vibration sensor 20 which is another embodiment of the invention. In the reference numerals in the figure, the same reference numerals as those already mentioned indicate the same parts. code 11
is a pedestal that is the base of the sensor attached to the object to be measured, and a piezoelectric film 13 is tightly fixed on the measurement surface 12 in the direction perpendicular to the sensing axis G in the direction of the acceleration or vibration to be measured. . Reference numeral 24 indicates the load body 1 in FIG.
4, it is a load body that is closely fixed on the film-like piezoelectric body 13 and functions as an inertial mass section, and is composed of a basic load body 25 and an auxiliary load body 26. The basic load body 25 is a part tightly fixed to the membrane piezoelectric body 13, and has a recess 27 formed on its upper surface, and an auxiliary load body 26 is adhered and placed in the recess 27. The auxiliary load body 26 here may be the same as the auxiliary load body 16 in FIG. It can be assisted by applying a mixture of a piece and its adhesive with good flowability, or by placing the required amount of metal fragments in the recess 27 and then applying a adhesive with good flowability to cover the entire piece. Even if the load body 14 is configured, the adhesive can be solidified without flowing down from the basic load body 25.

[For the load adjustment of the action output adjustment, an auxiliary load body made of metal strips containing powder is attached to the basic load body, so it is possible to add a small amount of powder or pieces. A load body with precisely adjusted output can be easily obtained.

In addition, even if a low-viscosity adhesive mixed with metal powder or metal pieces is used as an auxiliary load, a recess will be provided above the basic load, and the auxiliary load will be applied or poured there. so that the auxiliary load body does not run off the base load body until it solidifies.

[Example] (Example 1) As the basic load body, one having a structure having a concave portion on the upper surface as shown in FIG. 2 was used, and the load was set to 90% of the target output. Then, in order to obtain the target output, copper powder with a particle size of 100 μm or less is placed in the recess as an auxiliary load, and a two-component heating type naturally hardening epoxy adhesive is applied on top of it. has been corrected.

(Example 2) The basic load is the same as in Example 1, and as an auxiliary load for output correction, a mixture of copper powder with a particle size of 100 μM or less mixed in the same adhesive as in Example 1 was applied to the top surface of the basic load. It was injected or applied into the recesses to correct the output.

(Comparative Example 1) As the basic load body, one without a concave portion on the upper surface was used, and the load was such that 90% of the target output could be obtained. Then, in order to obtain the target output, an auxiliary load body was bonded to the top surface of the basic load body using the same adhesive as above using copper foil with a thickness of 30 μm and aluminum foil with a thickness of 30 μM. Corrected.

(Comparative Example 2) A load body with a load such that the target output could be obtained from the beginning was used, and no output correction was performed.

Fifty sensors were created for each side, and the output was first measured without output correction, and then, except for Comparative Example 2, output correction was performed. Table 1 shows the frequency distribution of the output before the output correction, and Table 2 shows the frequency distribution of the output after the output correction. However, the target output is set to 1.

Table 1 Frequency distribution of output before output correction Table 2 Frequency distribution of output after output correction For those in which the basic load body was created at a load of 90% of the target output, the difference in piezoelectricity of the membrane piezoelectric material Based on this, there are variations in output as shown in Table 1. However, as a result of the output correction, as shown in Table 2, the target output is ±2.
In Comparative Example 1, only 1 case (82%) of 50 cases of poisoning was corrected to within 5%, whereas in both Examples 1 and 2, up to 8 cases (96%) of 50 cases of poisoning were corrected. Precise corrections have been made to fall within that range.

[Effects of the Invention] According to the piezoelectric vibration sensor of the present invention, since the auxiliary load body for output correction is constructed by bonding a metal strip onto the basic load body, it is possible to make minute adjustments. ,
Therefore, variations in the output of the sensor product due to differences in piezoelectricity of the piezoelectric film can be precisely adjusted by the auxiliary load, and products with accurate and uniform sensor output can be manufactured in many cases.

In addition, according to another vibration sensor of the present invention, even if an adhesive with high fluidity is used as the adhesive for the auxiliary load body before it is solidified, a recess is not formed on the top surface of the basic load body. As a result, there is no fear that the adhesive will run down the outside of the basic load body, and the workability of applying or building up the auxiliary load body can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing one embodiment of a piezoelectric vibration sensor of the present invention, FIG. 2 is a partially cutaway perspective view of an auxiliary load body showing another embodiment of the invention, and FIG. is a perspective view of a conventional piezoelectric vibration sensor of this type. DESCRIPTION OF SYMBOLS 1; Pedestal, 2: Measurement surface, 3; Film piezoelectric body, 4; Load body, 10; Piezoelectric vibration sensor of the present invention, 11; Pedestal, 12
: measurement surface, 13. Membrane piezoelectric material, 14. Load body, 15; Basic load body, 16. Auxiliary load body, 20; Another piezoelectric vibration sensor of the present invention, 24; Load body, 25; Basic load body, 26: Auxiliary load body, 27; Recessed portion. 30: Conventional piezoelectric vibration sensor; G: Sensing axis.

Claims (2)

[Claims] (1) A piezoelectric vibration sensor consisting of a pedestal that is attached to the object to be measured, a piezoelectric film that is tightly fixed to the measurement surface perpendicular to the sensing axis of the pedestal, and a load body that is tightly fixed on top of the piezoelectric film. A piezoelectric vibration sensor characterized in that the load body is configured by providing a basic load body made of a hard material closely fixed to the measurement surface and an auxiliary load body made of metal strips and adhesive. . (2) The load body is a basic load body that is closely fixed to the measurement surface and has a load fixing recess formed on its upper surface, and an auxiliary load body made of metal strips and adhesive is provided in the load fixing recess. The piezoelectric vibration sensor according to claim 1, characterized in that the piezoelectric vibration sensor is constructed by: