JPH06249871A - Piezoelectric vibration sensor - Google Patents

Abstract

(57) [Summary] [Structure] The detection section 12 in which electrodes 18a and 18b are fixed to both surfaces of the piezoelectric body 17, the circuit board 13 fixed to the surface of the detection section 12, and the surface on the opposite side are fixed. And a package 15 for accommodating the detection unit 12, the circuit board 13, and the load body 14. The package 15 has an opening on the upper surface, and the detection unit 12 and the load body 14 are internally provided. A package pedestal 22 having a recess 24 for accommodating and arranging the circuit board 13 on an upper surface thereof, and a package cap 23 placed on the package pedestal 22 with a gap between the upper surface of the circuit board 13 and the package pedestal 22. The pedestal 22 and the package cap 23 are made of a conductive material, and the gap between the circuit board 13 and the package cap 23 is filled with the foam material 16. [Effect] It is possible to provide a piezoelectric vibration sensor with improved resistance to the entry of foreign matter.

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 having improved resistance to foreign matter.

[0002]

2. Description of the Related Art Conventionally, piezoelectric type vibration sensors for measuring the vibration of an object to be measured include cantilever type, diagram type,
Various types such as a compression type and a shearing type are known, but a compression type that is highly reliable and can be downsized is often used. This compression type piezoelectric vibration sensor is composed of a laminated body in which a pedestal, a detection unit and a load body are laminated in order, and the lower surface of the pedestal is rigidly attached to the object to be measured for use. The detection unit is configured by fixing electrodes on both surfaces of the piezoelectric body. In this piezoelectric vibration sensor, when vibration occurs in the object to be measured, the vibration is transmitted to the sensor. Then, the pedestal side vibrates together with the object to be measured, but a delay occurs due to the inertial force on the load body side. Therefore, a compressive or tensile stress is generated in the piezoelectric body in proportion to the vibration acceleration, and an electric charge or voltage in proportion to the stress is generated on both sides of the piezoelectric body. Therefore, the magnitude of vibration of the object to be measured can be detected by measuring the electric output from the two electrodes arranged on both surfaces of the piezoelectric body.

The application of such a compression type vibration sensor is to detect abnormal vibration of a rotating body in a factory, to control the attitude of an automobile, etc. The sensor is always installed, in a high temperature environment, or in a metal. It is often used in a bad environment with many foreign substances such as powder.

Therefore, the applicants of the present application have already proposed a compression type vibration sensor in which the detecting portion is housed in a package to improve the environmental resistance. FIG. 3 shows an example of the compression type vibration sensor 1. The load body 3 is fixed to the surface of the detection unit 2 perpendicular to the detection axis, and the circuit board 4 is fixed to the opposite surface. . An impedance conversion circuit 5 is formed on the surface of the circuit board 4, and the impedance conversion circuit 5 and the electrode of the detection unit 2 are arranged in a connected state. Further, the package 6 includes a package pedestal 7 and a package cap 8 which are hermetically sealed by a fitting method. The package pedestal 7 has a substantially block shape, and a recess 9 for accommodating the detection unit 2 and the load body 3 is provided on the upper portion thereof.
Is provided. Further, a cable 10 for taking out the output whose impedance has been lowered is connected to the impedance conversion circuit 5 of the circuit board 4, penetrates the package cap 8, and is extended to the outside.

[0005]

However, in the piezoelectric type vibration sensor having such a structure, the package pedestal 7 is used.
And the package cap 8 are sealed by a fitting method, and the cable 10 extends through the package cap 8 to the outside. Therefore, the fitting portion between the package pedestal 7 and the package cap 8 and the outlet of the cable 10 are provided. There is a problem that foreign matter such as metal powder or water in the surrounding environment is mixed into the package 7 and reaches the circuit board 4 through the slight gap formed in the area to cause a short circuit of the impedance conversion circuit 5. there were.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a piezoelectric vibration sensor having an improved resistance to the entry of foreign matter.

[0007]

In order to achieve such an object, the present invention has a detection part formed by fixing electrodes on both sides of a piezoelectric body, and a detection part fixed on the surface perpendicular to the detection axis. It has a circuit board, a load body fixed to the surface on the opposite side of the detection unit, and a package that accommodates the detection unit, the circuit board, and the load body, and the package has an opening on the upper surface and the detection unit inside. A package pedestal having a concave portion for accommodating a load body and the upper surface on which the circuit board is arranged, and a package cap that covers the package pedestal with a gap between the circuit board upper surface and the package pedestal. And the package cap is made of a conductive material, and the gap between the circuit board and the package cap is filled with a foam material.

[0008]

According to the piezoelectric vibration sensor of the present invention, since the gap between the circuit board and the package cap is filled with the foam material, even if foreign matter such as metal powder or water is mixed into the package. It is possible to prevent the foreign matter from reaching the circuit board and prevent a trouble such as a short circuit in the impedance conversion circuit.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a compression type vibration sensor of this embodiment. The compression type vibration sensor 11 includes a detection unit 12
A circuit board 13 fixed to a surface of the detection unit 12 perpendicular to the detection axis G; a load body 14 fixed to a surface opposite to the detection unit 12; and the detection unit 12, the circuit board 13 and a load. A package 15 for accommodating the body 14 and a foam material 16 filled in a gap in the package 1 are mainly configured.

As shown in FIG. 2, the detection unit 12 includes a piezoelectric body 17 made of an inorganic piezoelectric body, and electrodes 18a and 18b fixed to both surfaces of the piezoelectric body 17 with adhesive layers (not shown).
And support plates 19a and 19b fixed to the surfaces of these electrodes 18a and 18b. Piezoelectric 17
For example, lead zirconate titanate (PZT), lead titanate (PT), barium titanate (BAT), etc. are used, and copper foil, tin foil, etc. are used for the electrodes 18a, 18b. Examples of the adhesive used as the material of the adhesive layer include an epoxy adhesive and an acrylic resin adhesive.
A plate-shaped rigid body is used for the support plates 19a and 19b, and specific examples thereof include a glass epoxy plate.

The circuit board 13 is made of a ceramic substrate or the like, and is provided on the surface opposite to the side fixed to the detecting portion 12,
An impedance conversion circuit 20 is provided. The impedance conversion circuit 20 is connected to the two electrodes 18a and 18b of the detection unit 12. Further, a cable 21 for taking out a low-impedance output to the outside is connected to the impedance conversion circuit 20, and the cable 21 extends to the outside through a package cap 23 described later.

The load body 14 acts as an inertial mass portion, and it is desirable to use a material having a relatively large specific gravity such as brass and other metals as its material.

The package 15 is composed of two members, a package pedestal 22 and a package cap 23, which are hermetically sealed by a fitting method. A conductive material is used for both the package pedestal 22 and the package cap 23. The package pedestal 22 is made of a block made of aluminum, stainless steel, or the like, and has a recessed portion 2 which is opened on the upper surface on the upper portion thereof.
4 are provided. The detection unit 12 and the load body 14 are housed in the recess 24, and the circuit board 13 is arranged in contact with the upper surface of the package pedestal 22. The package cap 23 is the package pedestal 2
Similar to 2, the cap has a substantially bottomed tubular shape and is made of aluminum, stainless steel, or the like. The package cap 23 is covered with a space between the bottom portion of the package cap 23 and the circuit board 13, and is fitted to the package pedestal 22 at the opening edge thereof. In addition, a hole for drawing out the cable 21 connected to the circuit board 13 to the outside is opened in the bottom portion of the package cap 23.

The foam material 16 is filled in the gap between the circuit board 13 and the package cap 23. It is desirable that the foam material 16 can be filled with a gap without any gap, and that it is in a liquid or semi-liquid state before the filling, and is of a type that changes into a foam structure at room temperature or after heating after the filling.
For example, a two-pack type silicone foam that foams at room temperature is preferably used. As a method of filling the foam material 16, a silicone foam or the like immediately after mixing the two liquids is injected in a predetermined amount from the vicinity of the cable outlet of the package cap 23 with an injection device such as a syringe, and then left at room temperature for a predetermined time. The method of foaming is adopted.

As described above, the compression type vibration sensor 11 in this embodiment has the circuit board 13 and the package cap 23.
Since the foamed material 16 is filled in the gap between the package 15 and the inside of the package 15, even if a small gap such as near the cable outlet or near the fitting portion between the package pedestal 22 and the package cap 23, metal powder is filled inside the package 15. (Al powder, Cu powder)
Even if foreign matter such as water or water is mixed in, it is possible to prevent the foreign matter from reaching the circuit board 13. Therefore, it is possible to prevent a trouble that the foreign matter causes a short circuit of the impedance conversion circuit 20.

Hereinafter, concrete examples will be shown to clarify the effects of the present invention. (Examples 1, 2, 3) As a piezoelectric body, a 5 cm square, 0.5
Using a PZT piezoelectric plate with a thickness of mm, a copper foil of the same size with a thickness of 30 μm is adhered to both sides of the PZT piezoelectric plate with epoxy adhesive, and a glass epoxy plate of 5 mm square and 1 mm thick is further adhered to the both faces with an epoxy adhesive. It was adhered and used as a detection part. This detection part is adhered to the central part of the surface of a ceramic substrate of 15 mm square and 0.8 mm thickness, and the impedance conversion circuit formed on the opposite surface of the ceramic substrate and the electrode (copper foil) are connected. Then, a brass piece having a weight of 1 g was adhered on the detecting portion. On the other hand, the diameter is 8 mm in the center of the upper surface.
φ, diameter 23 mmφ having a recess with a depth of 8 mm,
A 11 mm high stainless steel block was prepared as a package pedestal. A circuit board was adhered to the upper surface of the package pedestal in a state where the detection unit was accommodated in the recess of the package pedestal. After connecting the cable to the impedance conversion circuit of the circuit board, the package cap was covered, and the package pedestal and the package cap were fitted and sealed to obtain a compression type vibration sensor. From the vicinity of the cable outlet of the package cap, a silicon foam immediately after mixing the two liquids was injected with a syringe, followed by foaming at room temperature to fill the gap inside the package.

(Comparative Examples 1, 2, 3) A compression type vibration sensor was obtained in the same manner as in Example except that the foam was not injected.

(Evaluation of resistance to contamination by foreign matter) The circumference of the sensor of Example 1 and Comparative Example 1 was filled with Cu powder, and in that state, vibration of 500 Hz and 10 g was applied, and the time until the sensor failed was measured. did. The sensors of Example 2 and Comparative Example 2 were filled with Al powder in the surroundings, and the sensors of Example 3 and Comparative Example 3 were filled with water in the surroundings, and the same measurement was performed. The results are shown in Table 1.

[0019]

[Table 1]

From Table 1, it is clear that the sensor of the embodiment in which the gap in the package is filled with the foam material has a significantly improved resistance to foreign matter.

[0021]

As described above, according to the compression type vibration sensor of the present invention, since the foam material is filled in the gap between the circuit board and the package cap, even if the inside of the package contains metal powder or water. Even if foreign matter such as
This foreign substance can be prevented from reaching the circuit board, and troubles such as a short circuit in the impedance conversion circuit can be prevented.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a compression type vibration sensor of the present invention.

FIG. 2 is a perspective view showing a detection unit in the compression type vibration sensor.

FIG. 3 is a cross-sectional view showing an example of a conventional compression type vibration sensor.

[Explanation of symbols]

 11 Compression Type Vibration Sensor 12 Detecting Part 13 Circuit Board 14 Load Body 15 Package 16 Foam Material 17 Piezoelectric Materials 18a, 18b Electrode 22 Package Pedestal 23 Package Cap 24 Recess

Claims (1)

[Claims] 1. A detection part having electrodes fixed to both sides of a piezoelectric body, a circuit board fixed to a surface of the detection part perpendicular to a detection axis, and a load fixed to a surface opposite to the detection part. A package for accommodating the detection unit, the circuit board, and the load body, the package having a concave portion for opening the detection unit and the load body therein, and the package for accommodating the detection unit and the load body. A package pedestal on which a substrate is arranged, and a package cap that covers the package pedestal with a gap between the package pedestal and the package cap, and the circuit board and the package cap. A piezoelectric vibration sensor, characterized in that a gap between and is filled with a foam material.