JPH06100494B2 - Electret condenser type vibration sensor - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a vibration sensor for converting vibration into an electric signal.

2. Description of the Related Art Conventionally, for this type of vibration sensor, methods such as electromagnetic type and piezoelectric type have been adopted and commercialized. Here, the electromagnetic type will be described as an example.

FIG. 8 shows the configuration of a conventional electromagnetic vibration sensor.
In the figure, 11 is a magnet, 12 is a pole, 13 is a yoke, 14 is a coil, and 15 is a magnetic vibrating body. The magnetic path passes through the magnetic vibrating body 15 as shown by the broken line. When the vibrating body 15 vibrates now, the magnetic flux passing through the magnetic poles changes, and the starting force is generated in the coil 14.

In this way, even the conventional electromagnetic vibration sensor described above can convert the change of the vibrating body into an electric signal.

However, the above-mentioned conventional electromagnetic vibration sensor has a complicated structure and requires a special coil or the like with a thin wire, so that it is difficult to reduce the cost, and the disconnection of the coil or the like is also considered, which is reliable. There was a difficulty in sex. Further, since a magnetic field is used, it is easily affected by reverse activating force, eddy current, etc., so that there is a problem that it is difficult to faithfully convert changes in the vibrating body into electric signals. The present invention solves such a conventional problem, and an object of the present invention is to provide a vibration sensor which has low cost and high reliability, and which can extract an electric signal with less distortion and the like. .

Means for Solving the Problems In order to achieve the above object, the present invention provides a metal vibrating body in a cylindrical metal case having a top surface, and a metal film facing the metal vibrating body and fixed by heat fusion or the like. The fixed electrode is made into an electret, and it is held by an insulator and FE
It is configured such that it is connected to the input terminal of T and its output terminal is taken out through the printed circuit board.

Action The present invention has the following actions due to the above-mentioned configuration. That is, a capacitor is formed between the metal vibrating body and the metal fixed electrode, and the capacitance of the capacitor changes when the metal vibrating body changes due to the application of external vibration. The amount of change can be taken out as an electric signal by the built-in FET.

Embodiment FIG. 1 shows the structure of an embodiment of the present invention. In FIG. 1, 1 is a cylindrical metal case having a top surface 1a, 2
Is a donut-shaped metal spacer, 3 is a metal vibrating body, 4 is a donut-shaped gap spacer, 5 is a metal fixed electrode to which the polymer film 5a is fixed by heat fusion or an adhesive, and 6 is the metal fixed electrode. An insulator for insulating and holding 5 from the metal case 1, an input terminal 7a of 7 is connected to the metal fixed electrode 5 by spot welding, and an output terminal 7b.
Is an impedance conversion FET connected to the printed circuit board 8 by soldering 8a or the like. In these internal products, the end of the metal case 1 is fixed by a caulking portion 1b or the like.
In the above structure, the polymer film 5a is electretized by some method. Therefore, as the material for the polymer film 5a, a medium FEP film or the like of a polyester film is suitable.

The metal spacer 2 and the gap spacer 4 are for forming a capacitor by facing the metal vibrating body 3 to the metal fixed electrode 5 with a constant space therebetween, and various methods other than this embodiment can be considered. .

The printed circuit board 8 is for taking out the output of the FET 7, and does not have to be a printed circuit board separately, and a method of taking out the output terminal 7b of the FET 7 as it is or a method of taking out it through a metal terminal board or the like can be considered.

2 (a) and 2 (b) are examples showing the metal vibrating body 3. FIG. The substantial vibration part is 3a, and this part has a vibration efficiency,
Various shapes are conceivable from the resonance frequency and the like. Further, it is not limited to a metal body as long as it has conductivity.

FIG. 3 is an example of the electrical equivalent circuit diagram of FIG. 1, and also includes an example of an output extraction circuit. In the figure, R is a load resistance and Cc is a coupling capacitor. In this embodiment, the source-grounded two-wire system is used, but a source-follower three-wire system is also conceivable. Ions are present on the surface of the metal fixed electrode 5 by the electret. Co indicates a capacitor formed between the metal vibrator 3 and the metal fixed electrode 5.

Next, the operation of the above embodiment will be described. In the above embodiment, when vibration is applied from the outside, the metal vibrating body 3 vibrates, and the capacitor Co causes a capacitance change ΔC corresponding to the vibration change. That is, the capacitance of the capacitor is Co '= Co ± ΔC. Therefore, the voltage change The capacitance change can be obtained as a voltage change. This voltage change is impedance converted by the FET 7 and is taken out as an electric signal.

The sensitivity Ko of the flat part of the sensor is Becomes (K = proportional coefficient, S = equivalent effective area exhibited by metal fixed electrode 5 and metal vibrating body 3, g = equivalent gap between metal fixed electrode 5 and metal vibrating body 3, Eo = surface potential of electret) and sensitivity Ko Is also influenced by the stray capacitance Cs, the gain Gv of the FET 7, and the like.

FIG. 4 shows an example of frequency characteristics of this embodiment.

As described above, according to the above-described embodiment, the metal vibrating body 3 vibrates in response to external vibration, and the capacitance between the metal vibrating body 3 and the metal fixed electrode 5 changes. This capacitance change is utilized by the charge (surface potential) of the electret. , Can be taken out as an electric signal.

FIG. 5 is a sectional view showing another embodiment of the present invention. First
The difference from the figure is that the top surface 1a of the metal case 1 has a hole 1C. Also in this case, the same operation as in FIG. 1 is performed. FIG. 6 is an example of an electrically equivalent circuit diagram in FIG.

In the case of FIG. 5, not only as a vibration sensor, but also an application to, for example, an air flow sensor can be considered.

7 (a) and 7 (b), in the case of the embodiment of FIG. 5, since the polymer film 5a is ventilated to the outside air, the electret may be deteriorated due to adhesion of water, dust, etc. This is an example. FIG. 1A shows a structure in which a thin protective film 9 for drip-proofing is attached to the outer surface (top surface 1a) of the metal case 1. If the film 9 is a conductive film, it operates as an electret condenser microphone, so that a film having a high insulating property is desirable. (B),
FIG. 3C shows a case where the thin film protective film 9a is fixed in the metal case 1 by applying a certain amount of tension to the doughnut-shaped ring 10 as shown in FIG. The thin protective film 9a is formed between the metal vibrating body 3 and the metal fixed electrode 5 in the figure (b), and between the top surface 1a of the metal case 1 and the metal vibrating body 3 in the figure (c). In the case of FIG. 7B, the ineffective capacitance is added, so that the sensitivity of the sensor deteriorates. Therefore, it is desirable to properly select the material and thickness of the film.

EFFECTS OF THE INVENTION As is apparent from the above-described embodiments of the present invention, the polymer film 5a is fixed by heat fusion or the like in the cylindrical metal case 1 having the top surface so as to face the metal vibrating body 3 at a constant interval. A metal fixed electrode 5 is provided, and this polymer film 5a is electretized and held by an insulator 6 and FE
The output terminal 7b is connected to the input terminal 7a of the T7, and the output terminal 7b is taken out through the printed board 8. A capacitor is formed between the metal vibrating body 3 and the metal fixed electrode 5, and the capacitor vibrates externally. Built-in
The FET 7 has an advantage that it can be taken out as an electric signal. Furthermore, since the configuration is simple, it has the advantages of low cost, high reliability, and the ability to extract signals with less distortion and the like.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG.
FIG. 3 is a schematic diagram showing the metal vibrating body 3 in the figure, FIG. 3 is an electrical equivalent circuit diagram in FIG. 1, FIG. 4 is a frequency characteristic diagram of this embodiment, and FIG. 5 is another embodiment of the present invention. FIG. 6 is a sectional view, FIG. 6 is an electrical equivalent circuit diagram in FIG. 5, and FIG.
FIG. 8 is a cross-sectional view showing the structure of a conventional electromagnetic vibration sensor, which is a main part cross-sectional view showing another embodiment of the figure. 1 ... metal case, 3 ... metal vibrator, 5 ... metal fixed electrode, 6 ... insulator, 7 ... FET, 8 ... printed circuit board.

Claims (1)

[Claims] 1. A metal vibrating body is provided in a cylindrical metal case having a top surface, and a metal fixed electrode having a polymer film fixed thereto by heat fusion or the like is turned into an electret and held by an insulator. An electret condenser type vibration sensor configured to be connected to the input terminal side of the FET together with its output terminal side taken out through the printed circuit board.