JPH05172839A - Piezoelectric vibration sensor - Google Patents

Abstract

PURPOSE:To control the output voltage by forming the electrodes installed on both the surfaces of a piezoelectric film to mesh form and varying the mesh degree, and to obtain a number of piezoelectric vibration sensors which are adjusted to each equal output at one time by carrying out output adjustment before cutting a sensor part member to each chip form, reduce dispersion, suppress the variation of size and weight of a loading body, and prevent the reduction of the impact resistance. CONSTITUTION:A piezoelectric vibration sensor is equipped with a base 1 which is rigidly installed on a measured article, sensor part 2 fixed on a measurement surface vertical to the sensing axis G of the base 1, and a loading body 3 consisting of a rigid body which is fixed on the sensor part 2 and acts as inertial mass part. The sensor part 2 consists of a film shaped piezoelectric body 4 having electrodes 7 and 7 on both the surfaces of a piezoelectric film 6, and two supporting plates 5 and 5 consisting of plate shaped rigid bodies fixed on the obverse and reverse surfaces of the film shaped piezoelectric body 4. The shape of the electrode 7 is formed to a mesh form.

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, and more particularly to a piezoelectric vibration sensor which is light and compact and whose output can be easily changed.

[0002]

2. Description of the Related Art The present inventor has already proposed that, as shown in FIG.
We have applied for a piezoelectric vibration sensor that is lightweight, compact, has excellent impact resistance, and is easy to manufacture, and a method for adjusting the output of these piezoelectric vibration sensors easily (Japanese Patent Application No. 1-156019). That is, this piezoelectric vibration sensor is fixedly mounted on the object to be measured, a pedestal 1 that is rigidly attached to the object to be measured, a sensing unit 2 that is fixed to a measurement surface of the pedestal 1 that is perpendicular to the sensing axis G, and that is fixed to the sensing unit 2. A load body 3 made of a rigid body that acts as an inertial mass portion,
The sensing unit 2 includes two support plates each including a film-shaped piezoelectric body 4 having plate-shaped electrodes 8 provided on both surfaces of a piezoelectric film 6, and plate-shaped rigid bodies fixed to both front and back surfaces of the film-shaped piezoelectric body 4. 5 and the plane shape of the film-shaped piezoelectric body 4 is point-symmetrical with the sensing axis G as the center of symmetry in a plane parallel to the measurement surface, and the load body 3 The plane shape of the contacting surfaces is point-symmetrical with the sensing axis G as the center of symmetry, and when the sensing axis G is crossed in a myriad of planes passing through the sensing axis G and perpendicular to the measurement surface, the sensing axis G is the symmetry axis. It is a line symmetry.

The piezoelectric vibration sensor is manufactured as follows. First, a support plate is bonded to both front and back surfaces of a single piezoelectric film as a material, with electrodes sandwiched therebetween, to form a large-sized sensing member. Next, this member is cut into chips according to the size at the time of completion to form one sensing unit. This sensing part is bonded to the pedestal, and then the load body is bonded to complete one piezoelectric vibration sensor. The output of the piezoelectric vibration sensor is adjusted by individually increasing or decreasing the mass of the load body.

[0004]

However, in the output adjustment by increasing the amount of the load body, particularly in the output adjustment in the direction of increasing the output by increasing the mass of the load body, when the weight of the load body increases, the impact resistance decreases. There was a drawback that it would end up.
Therefore, it is unavoidable that the adjustable output has an upper limit, and in the case where there is a large difference between the regulated output and the actual output, the correction cannot be practically performed. When the output is insufficient with respect to the specified output, the main cause of the insufficient output is that the piezoelectricity of the piezoelectric film is low. Since a large number of piezoelectric vibration sensors can be formed, if the piezoelectric film used has a low piezoelectric property, it is necessary to adjust the output of all piezoelectric vibration sensors derived from this. Therefore, a method that can correct the piezoelectricity of the piezoelectric film itself before cutting the piezoelectric film into chips is desirable.

The present invention has been made in view of the above circumstances, and it is possible to increase the output and reduce the impact resistance of a large number of piezoelectric vibration sensors at one time. A piezoelectric vibration sensor whose output can be adjusted by a method.

[0006]

In the piezoelectric vibration sensor of the present invention, the electrodes provided on both sides of the piezoelectric film are mesh-shaped ones, and the means for solving the above-mentioned problems is used.

[0007]

With the mesh-shaped electrode used in the piezoelectric vibration sensor of the present invention, the ratio of the electrode area per unit area of the measurement surface of the sensing portion can be increased or decreased by changing the degree of the mesh. The output voltage can be controlled by changing the electric capacity of the. Since this electrode has a mesh shape, the ratio of the electrode area is constant between the chips even after the electrode is cut into chips. Therefore, a large number of piezoelectric vibration sensors adjusted to the same output can be obtained at one time.

[0008]

The present invention will be described in detail below. FIG. 1 shows an embodiment of the piezoelectric vibration sensor of the present invention.
(A) is a perspective view showing an external appearance, and (B) is an exploded perspective view of a sensing unit. This piezoelectric vibration sensor includes a pedestal 1 rigidly attached to an object to be measured, a sensing unit 2 fixed to a measurement surface perpendicular to the sensing axis G of the pedestal 1, and an inertial mass fixed to the sensing unit 2. It is composed of a load body 3 made of a rigid body acting as a part. The material of the pedestal 1 may be any material having sufficient rigidity such as fiber reinforced resin and metal. As the material of the load body 3, it is desirable to use a material having a relatively large specific gravity such as brass and other metals.

The sensing portion 2 is composed of a film-shaped piezoelectric body 4 having mesh-shaped electrodes 7 provided on both surfaces of a piezoelectric film 6 and a plate-shaped rigid body fixed to both front and back surfaces of the film-shaped piezoelectric body 4. The support plate 5 of FIG. Examples of the material of the piezoelectric film 6 include polyvinylidene fluoride, a copolymer of tetrafluoroethylene and trifluoroethylene, a metal titanate salt,
Various piezoelectric materials such as metal zirconate can be used. The type of metal used as the material of the mesh-shaped electrode and the method of forming the mesh are not particularly limited.

The output of the piezoelectric vibration sensor is adjusted by changing the degree of the mesh used for the electrodes when manufacturing a large member which serves as a sensing portion of the piezoelectric vibration sensor. Changing the degree of the mesh means changing the ratio of the electrode area per unit area of the measurement surface of the sensing unit, and since it is mesh-like, this ratio becomes uniform throughout the member. Therefore, if this member is cut into chips, a large number of sensing units having the same output voltage can be obtained at one time, and there is no variation in output between chips. In this method, since the mass of the load body does not change, the impact resistance does not decrease.

The electric output can be controlled by changing the electrode area as described above due to the following mechanism. That is, if the electric charge generated in the film-shaped piezoelectric body is Q and the electric capacity is C, the voltage V generated between the electrodes is represented by the formula (I).

[Equation 1] Further, assuming that the electrode area is S, the thickness of the film-shaped piezoelectric body is t, and the dielectric constant of the piezoelectric material is ε, the electric capacity is expressed by the formula (II).

[Equation 2] Therefore, the formula (III) is derived from the formulas (I) and (II).

[Equation 3] Since the thickness t of the film-shaped piezoelectric body is constant, the output voltage V can be changed by changing the electrode area S. To increase the output voltage V, the electrode area S may be reduced.

(Example) A piezoelectric vibration sensor having the shape shown in FIG. 1 was prepared. A 3 cm square mesh-shaped copper foil (electrode layer) is adhered to both sides of a 3 cm square, 100 μm thick polyvinylidene fluoride (PVDF) piezoelectric film, and a 3 cm square glass epoxy plate of 1.5 mm thickness (support) The boards) were glued together with an epoxy adhesive. 5 mm with this dicing saw
It was cut into a corner and used as a sensor chip. Each chip was fixed on a pedestal, a brass load body having a weight of 1 g was adhered onto the chip, and the load was vibrated at 80 Hz and 1 g, and the voltage output was measured. In this way, 100 piezoelectric vibration sensors were prepared, and the voltage output, its variation and impact resistance were examined. In the impact resistance test, the created piezoelectric vibration sensor was dropped and collided laterally with a pedestal from a height of 1 m on a concrete surface, and the number of piezoelectric vibration sensors damaged was examined.
The results are shown in Table 1. In Table 1, the electrode area ratio is the ratio of the area of the mesh-shaped copper foil portion to the area of the chip (25 mm ² ). The output ratio is shown as a relative value when the output obtained in the comparative example shown below is 1. The variation of the output indicates the number of the 100 generated, which are within ± 15% of the average value of the output. The impact resistance refers to the number of piezoelectric vibration sensors that were damaged in the above impact resistance test, out of the 100 piezoelectric vibration sensors that were created.

Comparative Example A piezoelectric vibration sensor having the shape shown in FIG. 2 was prepared. The same procedure as in Example was carried out except that a plate-shaped copper foil was used for the electrodes. The results are shown in Table 1.

[Table 1]

[0014]

As described above, in the piezoelectric vibration sensor of the present invention, since the electrodes provided on both sides of the film-shaped piezoelectric body are mesh-shaped, it is possible to change the degree of the mesh used for this electrode. , The output voltage can be controlled. Since this output adjustment is performed before cutting the sensing unit member into chips, it is possible to easily obtain a large number of piezoelectric vibration sensors adjusted to the same output at one time, and there is little variation. Further, in this output adjusting method, since the size and mass of the load body do not change, the impact resistance does not decrease.

[Brief description of drawings]

1A and 1B show an embodiment of a piezoelectric vibration sensor of the present invention, in which FIG. 1A is a perspective view showing an appearance and FIG. 1B is an exploded perspective view of a sensing unit.

2A and 2B show an embodiment of a conventional piezoelectric vibration sensor, FIG. 2A is a perspective view showing an external appearance, and FIG. 2B is an exploded perspective view of a sensing unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Pedestal 2 ... Sensing part 3 ... Load body 4 ... Membrane piezoelectric body 5 ... Support plate 6 ... Piezoelectric film 7 ... Mesh electrode 8 ... Plate electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takayuki Imai 1-5-1 Kiba, Koto-ku, Tokyo Inside Fujikura Electric Wire Co., Ltd.

Claims (1)

[Claims] 1. A pedestal rigidly attached to an object to be measured,
The pedestal has a sensing part fixed to a measurement surface perpendicular to the sensing axis, and a load body made of a rigid body fixed on the sensing part and acting as an inertial mass part. The sensing part is provided on both sides of the piezoelectric film. A piezoelectric vibration sensor comprising a film-shaped piezoelectric body provided with electrodes and two supporting plates made of plate-shaped rigid bodies fixed to both front and back surfaces of the film-shaped piezoelectric body, wherein the electrodes are mesh-shaped. Piezoelectric vibration sensor characterized by.