JPH06207947A - Piezoelectric vibration sensor - Google Patents

Abstract

PURPOSE:To enhance accuracy in measurement by a constitution wherein same potential difference and charge difference produced between two electrodes and an electrode on the rear offset pyroelectric effect caused by temperature variation thus restraining pyroelectric output and reducing noise. CONSTITUTION:A sensing part 2 is bonded onto the measuring plane 1a of a base 1 and the electrodes 24, 25 on the surface of a piezoelectric film 20 are bonded integrally with an electrode 26 on the rear to form a film-like piezoelectric body 21 which constitutes a sensing part 2 along with supporting plates 22, 23 bonded to the opposite sides of the piezoelectric body 21. A load 3 is bonded through the supporting plate 22 and vibration component in the direction of detecting axis 27 is measured based on the potential difference and charge difference between the surface electrode 24 and rear electrode 26 of the piezoelectric film 20 and the potential difference and charge difference between the surface electrode 25 and the rear electrode 26. When pyroelectric effect takes place due to temperature variation, identical potential difference and charge difference occur between the surface electrode 24 and the rear electrode 26 and between the surface electrode 25 and the rear electrode 26 but they are offset each other thus suppressing pyroelectric noise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric vibration sensor using a film-shaped piezoelectric body, and more particularly to a piezoelectric vibration sensor having reduced output fluctuation due to a pyroelectric effect.

[0002]

2. Description of the Related Art A vibration sensor having a simple structure, extremely small noise against vibration in a direction orthogonal to the sensing axis direction, and having a wide measurable frequency band is rigidly attached to an object to be measured. A pedestal to be mounted, a film-shaped piezoelectric body fixed to a measurement surface perpendicular to the sensing axis of the pedestal, and a load body composed of a rigid body fixed to the film-shaped piezoelectric body and acting as an inertial mass part. A characteristic sensor was devised, and a patent application was previously filed as Japanese Patent Application No. 1-113255.

However, even with this type of sensor, it is necessary to solve the following inconveniences. In the sensor having the above structure, when the temperature changes partially in the film-shaped piezoelectric body due to the temperature change, an extra electric output is generated due to the pyroelectric effect caused by the temperature distribution,
Since this becomes a noise output, it was difficult to use it in a place where the ambient temperature changes drastically. Also, since the noise output due to the pyroelectric effect is on the low frequency side as a frequency component, it can be cut by using a high-pass filter, but then there is the disadvantage that acceleration on the low frequency side cannot be measured either. It was

[0004]

Therefore, as a measure for reducing the noise output due to the pyroelectric effect, the present inventors have fixed a load body in addition to the detection film piezoelectric body to which the load body is fixed. We have previously proposed a sensor that is provided with a compensating piezoelectric body and is electrically connected so as to cancel the outputs of the film-shaped piezoelectric body and the compensating piezoelectric body. However, even in such a sensor, the detection film-like piezoelectric body and the compensating film-like piezoelectric body differ in the degree of heat transfer to the piezoelectric body due to the presence or absence of a load body, and are generated from any piezoelectric body. I was dissatisfied in terms of accuracy because the charges were not completely equal.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a piezoelectric vibration sensor capable of improving the measurement accuracy by lowering the pyroelectric output due to temperature change and the like.

[0006]

In order to solve the above-mentioned problems, the piezoelectric vibration sensor of the present invention comprises a pedestal rigidly attached to the object to be measured, and electrodes fixed to the measurement surface of this pedestal on both sides. A film-shaped piezoelectric body and a load body made of a rigid body that is fixed on the film-shaped piezoelectric body and acts as an inertial mass portion. The planar shape of the film-shaped piezoelectric body is the center of the plane of the film-shaped piezoelectric body. Of the first axis and the second axis orthogonal to each other with respect to the intersection point, the load body is line-symmetrical to the second axis, When cross-sectioned in a plane, all cross-sections are line-symmetric with respect to an axis perpendicular to the measurement surface and orthogonal to the second axis, and the first electrode and the second electrode are formed on one surface of the film-shaped piezoelectric body. Electrodes are formed, and these two electrodes are formed in line symmetry with respect to the second axis. That.

[0007]

Since the piezoelectric vibration sensor of the present invention has the above-mentioned structure, the vibration component in the axial direction is formed on one surface of the film-shaped piezoelectric body with the first axis as the detection axis. Difference between the potential difference and charge difference between the first electrode and the electrode formed on the other surface, and the potential difference and charge difference between the second electrode formed on the one surface and the electrode on the other side. It is measured based on, and is not output for vibration in the direction perpendicular to the measurement surface. Then, when the pyroelectric effect due to the temperature change occurs, between the first electrode and the electrodes on the other surface,
The same potential difference and electric charge difference are generated between the electrode of and the electrode on the other surface. Since these cancel each other out, the potential output and the charge output become 0, and pyroelectric noise due to temperature change is not detected.

[0008]

The present invention will be described in detail below. 1 and 2 show an embodiment of the piezoelectric vibration sensor of the present invention. FIG. 1 is a perspective view, and FIG. 2 is a plan view of a film-shaped piezoelectric body. This piezoelectric vibration sensor includes a pedestal 1 rigidly attached to an object to be measured, a sensing section 2 fixed to a measurement surface 1a of the pedestal 1, and a rigid body fixed on the sensing section 2 and acting as an inertial weight section. And a load body 3 consisting of

The pedestal 1 forms the base of the sensor and is rigidly attached to the object to be measured, and is made of a material having sufficient rigidity, such as steel, brass or aluminum. The pedestal 1 in this example is formed in a rectangular parallelepiped shape, but the shape of the pedestal 1 is not limited to this, and may be a plate shape, a cylindrical shape, or the like. The surface (upper surface) of the pedestal 1 is formed to be flat and smooth and serves as a measurement surface 1a. Pedestal 1
The sensing unit 2 is mounted on the measuring surface 1a of the pedestal 1 through the adhesive layer.
It is firmly fixed to the unit. In addition, the fixing of the sensing unit 2 and the pedestal 1 is performed using a curable adhesive such as an epoxy adhesive.

The sensing section 2 has a film-shaped piezoelectric body 21 in which two electrodes 24 and 25 are bonded on one surface of the piezoelectric film 20, and an electrode 26 is integrally bonded to the other surface of the piezoelectric film 20, and both surfaces of the film-shaped piezoelectric body 21. Two support plates 2 made of a plate-shaped rigid body fixed to the
2 and 23. Here, the piezoelectric film 20 and the electrodes 24, 25, 26 are fixed to each other, and the piezoelectric film 20 or the electrodes 24, 25, 26 and the support plate 22,
A curable adhesive such as an epoxy-based adhesive is used for fixing to 23.

The material of the piezoelectric film 20 is not particularly limited as long as it is made of a piezoelectric material. For example, it can be formed using polyvinylidene fluoride, a copolymer of tetrafluoroethylene and trifluoroethylene, a metal salt of titanate, a metal salt of zirconate, or the like. Further, in the present embodiment, the piezoelectric film 20 has a rectangular planar shape. Here, in the piezoelectric vibration sensor of the present invention, the planar shape of the film-shaped piezoelectric body 21, that is, the shape of the piezoelectric film 20 is not limited to the rectangular shape. The planar shape of the film-shaped piezoelectric body 21 is such that two axes orthogonal to each other with the center of the plane as an intersection point are a first axis 27 and a second axis 28.
Are formed so as to be line-symmetric with respect to the second axis 28.

The surface (upper surface) of the piezoelectric film 20 is made of aluminum foil or the like for extracting electric output, and has a square-shaped first electrode 24 and a second electrode having an area about half the surface of the piezoelectric film 20. 25 is fixed.
A third electrode 26 covering the back surface (bottom surface) of the piezoelectric film 20 is fixed to the back surface (bottom surface). The first electrode 24 and the second electrode 25 are fixed to each other with a space of about several mm (preferably 3 mm or less and as small as possible) therebetween. Here, in the piezoelectric vibration sensor of the present invention, the first electrode 24 and the second electrode 2 are
The shape of 5 is not limited to the square shape, and these 2
The two electrodes are formed in line symmetry with respect to the second axis 28. That is, the two electrodes on the surface of the piezoelectric film 20 are formed symmetrically in terms of position and shape with respect to the second axis 28, and their areas are equal.

Such a piezoelectric film 20 and electrode 2
On the surface of the film-shaped piezoelectric body 21 composed of 4, 25, 26,
A rectangular parallelepiped load body 3 made of a rigid body that functions as an inertial mass portion is integrally fixed via a support plate 22.
The load body 3 is displaced in response to vibration and causes strain or stress in the film-shaped piezoelectric body 21, and its weight is not particularly limited because it is related to the sensitivity of the sensor, but it does not cause creep in the film-shaped piezoelectric body 21. Ranged. The fixing of the load body 3 and the support plate 22 (sensing unit 2) is the same as the fixing of the pedestal 1 and the sensing unit 2. Here, in the piezoelectric vibration sensor of the present invention, the shape of the load body 3 is not limited to the rectangular parallelepiped shape. When the load body 3 is sectioned in a myriad of planes parallel to the first axis 27 and orthogonal to the measurement surface 1a, the load body 3 is perpendicular to the measurement surface 1a and orthogonal to the second axis 28 for all sections. It is formed symmetrically with respect to the axis. That is, the load body 3 is formed so as to be plane-symmetric with respect to a plane that passes through the second axis 28 and is orthogonal to the measurement surface 1a.

FIG. 3 is a circuit diagram of the sensor having the above structure. As shown in FIG. 3A, the first electrode 24 and the second electrode 25 formed on the surface of the piezoelectric film 20.
Are each configured to extract an electrical output. In the piezoelectric type vibration sensor having such a configuration, the vibration component in the direction of the detection axis is the first electrode 24 on the front surface of the piezoelectric film and the third electrode 2 on the back surface thereof, with the first shaft 27 as the detection axis.
It is measured based on the difference between the potential difference and the charge difference generated between 6 and the potential difference and the charge difference generated between the second electrode 25 and the third electrode 26. Then, when the pyroelectric effect due to the temperature change occurs, as shown in FIG. 3B, between the first electrode 24 and the third electrode 26, and between the second electrode 25 and the third electrode 26.
The same potential difference and charge difference are generated between the electrodes 26, and these cancel each other out, so that the potential output and the charge output become zero. Therefore, pyroelectric noise due to temperature change is not detected. Further, with respect to the vibration in the direction perpendicular to the measurement surface 1a, the same as in FIG. 3 (b) is not output. As described above, according to the present invention, it is possible to obtain a piezoelectric vibration sensor in which not only pyroelectric noise does not occur but also directivity is extremely high.

Example 1 A piezoelectric vibration sensor as shown in FIGS. 1 and 2 was manufactured as a prototype. Height 5 mm, width 1 cm, thickness 10
After attaching electrodes made of copper foil with a thickness of 30 μm to both sides of a 0 μm polyvinylidene fluoride (PVDF) piezoelectric film with an epoxy adhesive, cut the electrodes on the surface side with a dicer and attach the electrodes as shown in FIG. Split. At this time, the areas of the two electrodes obtained by division were made equal. 5mm long, 1cm wide,
A glass epoxy support plate having a thickness of 1 mm was adhered. further,
5 mm long, 1 cm wide, 2 mm thick on the epoxy support plate on the front side
A brass load element was adhered, and the epoxy support plate on the back side was adhered to an aluminum pedestal having a length of 2 cm, a width of 2 cm, and a thickness of 5 mm to obtain a piezoelectric vibration sensor.

(Example 2) In Example 1, PVDF
Lead zirconate titanate (PZT) instead of piezoelectric film
A piezoelectric vibration sensor was manufactured in the same manner except that the piezoelectric film was used.

(Comparative Example 1) The same as Example 1 except that when the electrode on the surface of the piezoelectric film was divided into two, the area ratio of the two electrodes obtained by the division was set to 1: 2. A piezoelectric vibration sensor was prototyped.

Comparative Example 2 The same as Example 1 except that when the electrode on the surface of the piezoelectric film was divided into two, the area ratio of the two electrodes obtained by division was set to 1: 3. A piezoelectric vibration sensor was prototyped.

(Comparative Example 3) The same as Example 2 except that when the electrode on the surface of the piezoelectric film was divided into two, the area ratio of the two electrodes obtained by division was set to 1: 2. A piezoelectric vibration sensor was prototyped.

(Comparative Example 4) The same as Example 2 except that when the electrodes on the surface of the piezoelectric film were divided into two, the area ratio of the two electrodes obtained by the division was set to 1: 3. A piezoelectric vibration sensor was prototyped.

(Comparative Example 5) A piezoelectric vibration sensor was manufactured in the same manner as in Example 1 except that the electrodes on the surface side of the piezoelectric film were not divided.

Comparative Example 6 A piezoelectric vibration sensor was produced in the same manner as in Example 2 except that the electrodes on the surface side of the piezoelectric film were not divided.

(Test Example) The piezoelectric vibration sensors obtained in the above Examples and Comparative Examples were connected to an impedance conversion circuit, and the main axis sensitivity and the other axis sensitivity were measured by a usual method to obtain the ratio. In addition, from the piezoelectric vibration sensor 10
From the position away from cm, blow warm air of 60 ℃ to the sensor,
The generated pyroelectric output peak value was measured. The results are summarized in Table 1 below.

[0024]

[Table 1]

From the results shown in Table 1, in Comparative Examples 5 and 6 in which the electrodes were not divided, the other axis / spindle sensitivity ratio was small and good, but the pyroelectric output due to temperature change was extremely large. On the other hand, in Examples 1 and 2, a small other axis / spindle sensitivity ratio comparable to the case where the electrodes were not divided was obtained, and the pyroelectric output due to the temperature change was small, which was good. Further, in Comparative Examples 1 to 4 in which the two electrodes on the surface of the piezoelectric film are not line-symmetric with respect to the second axis, the pyroelectric effect due to temperature change is large, and the other axis / main axis sensitivity ratio is also large. there were.

The piezoelectric vibration sensor as in the above embodiment is
The electrode can be formed by dividing the electrode on the surface of the piezoelectric film into two parts, and since it does not require any other difficult steps, it can be easily manufactured and can be manufactured with high accuracy.

[0027]

As described above, the piezoelectric vibration sensor of the present invention includes a pedestal rigidly attached to the object to be measured, and a film-shaped piezoelectric body fixed to the measurement surface of the pedestal and provided with electrodes on both sides. A load body made of a rigid body fixed on the film-shaped piezoelectric body and acting as an inertial mass portion, wherein the planar shape of the film-shaped piezoelectric body is orthogonal to the center of the plane of the film-shaped piezoelectric body as an intersection point; Of the first axis and the second axis, the load body is line-symmetric with respect to the second axis, and the load body is cross-sectioned in a myriad of planes parallel to the first axis and orthogonal to the measurement surface, All cross sections are line-symmetric with respect to an axis perpendicular to the measurement surface and orthogonal to the second axis, and the first electrode and the second electrode are formed on one surface of the film-shaped piezoelectric body. The two electrodes are formed in line symmetry with respect to the second axis.

Therefore, the vibration component in this direction can be detected with high sensitivity using the first axis as the detection axis, and the pyroelectric output due to temperature changes can be made extremely low, and the measurement accuracy can be greatly improved. . Further, the terminals can be formed only on the electrodes on the upper surface side of the film-shaped piezoelectric body, which is advantageous in manufacturing as compared with the case where the terminals are formed on the upper and lower surfaces of the film-shaped piezoelectric body.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a piezoelectric vibration sensor of the present invention.

FIG. 2 is a plan view showing a film-shaped piezoelectric body in an embodiment of the piezoelectric vibration sensor of the present invention.

FIG. 3 is a circuit diagram of an embodiment of the piezoelectric vibration sensor of the present invention.

[Explanation of symbols]

1 ... Pedestal, 1a ... Measuring surface, 2 ... Sensor, 3 ... Load body, 2
DESCRIPTION OF SYMBOLS 1 ... Membrane piezoelectric material, 24 ... 1st electrode, 25 ... 2nd electrode, 26 ... 3rd electrode, 27 ... 1st axis | shaft, 28 ... 2nd axis

Claims (1)

[Claims] 1. A pedestal rigidly attached to an object to be measured,
The membranous piezoelectric body includes a film-shaped piezoelectric body fixed to the measurement surface of the pedestal and having electrodes on both sides, and a load body made of a rigid body fixed to the membranous piezoelectric body and acting as an inertial mass portion. Has a plane symmetry with respect to a second axis of the first axis and the second axis which are orthogonal to each other with the center of the plane of the film-shaped piezoelectric body as an intersection, and When cross-sectioned in a myriad of planes parallel to the first axis and orthogonal to the measurement plane,
All cross sections are line-symmetric with respect to an axis perpendicular to the measurement surface and orthogonal to the second axis, and the first electrode and the second electrode are formed on one surface of the film-shaped piezoelectric body. Two
A piezoelectric vibration sensor, wherein one electrode is formed line-symmetrically with respect to the second axis.