JPS58239B2 - Piezoelectric vibration pickup - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric vibration detector, in particular a piezoelectric vibration detector configured so that strain force applied to a plurality of vibrators acts differentially, and an electric signal proportional to the strain force is obtained. Regarding pickup.

Piezoelectric vibration pickups are broadly classified into compression types, shear types, and bending types, each of which has the following characteristics.

(1) The compression type is a type that extracts signals by compressing and expanding a piezoelectric element, and has a simple structure and high mechanical strength.

However, when a sudden thermal change is applied to a piezoelectric element, the state of polarization of the piezoelectric element changes instantaneously, and a voltage is generated due to the pyroelectric effect.

Therefore, when the ambient temperature of the vibration pickup changes, the change is transmitted to the piezoelectric element through the case, reducing the signal/noise ratio by generating pyroelectricity, making it possible to measure low-level vibrations.
It is especially difficult to measure low frequency vibrations.

(2) The new type vibration pickup is a type that causes displacement of the piezoelectric element, and does not generate pyroelectricity.

However, in order to generate a voltage by shearing force, it is necessary to polarize the piezoelectric element parallel to the electrode plane, making the manufacturing method of the piezoelectric element extremely complicated and, as a result, expensive.

(3) The bending type is a type that gives bending to the piezoelectric element,
Due to its structure, the resonance frequency is low, making it unsuitable for measuring a wide frequency band.

Furthermore, it has low mechanical strength, so it is not used much.

Therefore, there is a need for a vibration pickup that has low noise over a wide frequency band for vibration measurement, has high mechanical strength, and is highly sensitive.

In view of such demands, the present inventor completed intensive research and completed the piezoelectric vibration pickup of the present invention.

The piezoelectric vibration pickup of the present invention includes a metal case and a fixed base fixed to the metal case, and a piezoelectric element having a polarization direction perpendicular to the fixed base on each side of the fixed base, and a weight on the outside thereof. and the weights are interconnected by a fixing member so that when the fixed base vibrates, the inertia of the weights causes one piezoelectric element to be compressed and the other piezoelectric element to expand, thereby causing the electrodes of each piezoelectric element to The electrodes of each piezoelectric element are connected so that charges of the same sign generated in the piezoelectric element are collected and taken out.

A specific example of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a preferred embodiment of the piezoelectric vibration pickup of the present invention.

Piezoelectric elements 1 and 1' made of barium titanate or lead zirconate titanate ceramics, etc., formed into a disk shape having a central hole, are polarized in the axial direction.

This polarization was obtained by placing electrodes made of metal films on parallel planes of the piezoelectric element and applying a high DC voltage between the two electrodes.

Two piezoelectric elements 1, 1' having the same shape and characteristics are located on both sides of a metal fixing base 2 having a hole in the center, and metal weights 3, 3' having a screw hole in the center are located on both sides of a metal fixing base 2 having a hole in the center.
Fixing members, ie, metal screws 4, are located on both sides of the weight and are screwed into the screw holes of the weight to mechanically fix the weight firmly.

In order to further increase the mechanical strength, each part is bonded with adhesive.

The screw 4, the piezoelectric elements 1, 1', and the fixing base 2 are electrically insulated by a tubular insulator.

Further, there is no mechanical connection between the screw 4 and the fixing base 2.

With the above structure, the weights 3, 3' can move close to free vibration.

between the fixed base 2 and the electrode surfaces of the piezoelectric elements 1, 1', between the electrode surfaces of the piezoelectric elements 1, 1' and the weights 3, 3', and the weights 3, 3'.
and the screw 4 are electrically connected to each other.

The fixing base 2 is firmly fixed to the metal case 6 with screws through an adhesive, the lead wire 7 is connected to the screw 4, and the ground side is connected to the case 6.

The polarity of the piezoelectric element 1 is positive on the weight 3 side and negative on the fixed base 2 side, and the polarity of the other piezoelectric element 1' is negative on the weight 3' side and positive on the fixed base 2 side.

Of course, the opposite polarity can also be used.

The electrical connection of this piezoelectric element is as shown in FIG.

Each piezoelectric element 1, 1' has a structure in which output is taken out from both poles on the weight 3, 3' side and the fixed base side 2.

Next, the operating principle of the piezoelectric vibration pickup of the present invention will be explained in the first place.
The figure and FIG. 2 will be explained.

The vibration of the object to be measured is transmitted to the case 6 and the fixed base 2, and then to the weights 3, 3.
At a frequency sufficiently lower than the resonance frequency determined by the mass of the fixed base 2, the screw 4, and the mass of the fixed base 2, the piezoelectric elements 1 and 1' are compressed and expanded by the inertia of the weights 3 and 3' due to the strain force proportional to the vibration acceleration of the fixed base 2. Repeat the exercise.

When one piezoelectric element 1 is compressed, the other piezoelectric element 1' is expanded.

At this time, a positive charge is induced in the female electrodes of the piezoelectric elements 1 and 1' relative to the fixed base 2 side.

Conversely, when the piezoelectric element 1 expands, the other piezoelectric element 1' is compressed.

At this time, negative charges are induced in the weights 3 and 3' side electrodes with respect to the fixed base 2 (the polarization directions 8 are opposite to each other with respect to the fixed base 2).

). As a result, an electric charge proportional to the vibration acceleration of the fixed base 2 is induced between the fixed base 2 and the weights 3, 3'.

This induced voltage is taken out through the lead wire.

In the present invention, the piezoelectric element can be disk-shaped, square plate-shaped, or cylindrical.

FIG. 3 shows a vibration pickup using a cylindrical piezoelectric element as another embodiment of the present invention.

These cylindrical piezoelectric elements 1'', 1''' are provided with electrodes on the inner diameter surface and the outer diameter surface, and the polarization axis is made perpendicular to the electrode surface.

The other structures are the same as in FIG. 1.

In the vibration pickup of this embodiment, if the electrical connections are made in the same way as shown in Fig. 2, when a strain force is applied to the parallel planes of the piezoelectric element, a strain force determined by Poisson's ratio is applied between the electrodes. As a result, a charge is generated between the electrodes, and the above objective is achieved.

It is also possible to provide two or more piezoelectric elements on each side of the fixing base.

FIG. 4 shows a piezoelectric vibration pickup of the present invention in which two piezoelectric elements are provided on each side of a fixed base.

Piezoelectric elements 9, 10, 9', 10' having electrodes arranged in parallel planes are mounted between the fixed base 2 and the weights 3, 3'.

The piezoelectric elements 9 and 10 and 9' and 10' are polarized in opposite directions.

These piezoelectric elements are electrically connected as shown in FIGS. 4 and 5.

In FIG. 4, the fixing base, the piezoelectric element, and the weight are connected, but it is of course possible to fix them using fixing members, that is, screws, as in FIG. 1.

Just like in the case of two piezoelectric elements, when one piezoelectric element group is compressed, the other piezoelectric element group operates so as to be expanded.

The vibration pickup of the present invention has the following features compared to conventional vibration pickups.

(a) With conventional compression-type pickups, it is difficult to measure low-level vibrations and low frequencies due to the presence of the pyroelectric effect.

However, in the piezoelectric vibration pickup according to the present invention, the polarization direction of the piezoelectric element (piezoelectric element group) is opposite to that of the fixed base, and thermal changes act on each piezoelectric element in the same direction. Pyroelectricity with different signs is generated at the side electrode and the female side electrode, respectively.

Therefore, by making the characteristics of each piezoelectric element the same, it is possible to cancel out the pyroelectricity (with opposite signs) generated in each electrode.

As described above, the vibration pickup structure of the present invention allows the pyroelectric effect to be extremely reduced, improves the signal-to-noise ratio, and is advantageous for low-level, low-frequency vibrations.

(b) The compression-type vibration pickup, which has a structure that does not generate pyroelectricity, is not suitable for measuring large accelerations as described above, and the piezoelectric element is expensive, but the compression-type vibration pickup according to the present invention has high strength. It is possible to measure large accelerations.

Moreover, since the piezoelectric element is easier to produce than the conventional type, it is inexpensive.

(c) The piezoelectric vibration pickup of the present invention has high sensitivity because when one piezoelectric element is compressed, the other piezoelectric element expands and vibrates almost freely.

Both weights are interconnected by screws, so that when one piezoelectric element(s) is compressed, the other piezoelectric element(s) simultaneously expands to an extent that corresponds exactly to said compression amount, thus The same amount of charge is induced in the female electrode of the piezoelectric element(s), significantly increasing the reliability of the device.

In particular, the resonance sharpness is large at the resonance frequency.

Further, stable resonance is obtained without being affected by physical loads external to the case 6, and low-level vibrations can be measured at the resonance point.

B) The piezoelectric vibration pickup of the present invention can be made symmetrical with respect to the fixed base, and the same characteristics can be obtained even if it is turned upside down (the conventional type is asymmetrical).

As described above, the piezoelectric vibration pickup of the present invention has a completely new structure and features compared to conventional piezoelectric vibration pickups, and provides a transducer with high sensitivity and low noise that suppresses vibration over a wide frequency range. It is something to do.

Various modifications can be made without departing from the spirit of the invention.

For example, as a method of fixing the piezoelectric element, weight, and fixing base, in addition to fixing with screws and adhesives, there are also methods of using the screw hole of the weight as a simple hole and tightening it with nuts from above and below, and fixing the weight and screw part by caulking, screws, and welding. There are methods etc.

Further, it is also possible to use one weight and attach it to the screw part so that the one weight applies strain force to two or more piezoelectric elements.

Furthermore, if the configuration is such that the strain force caused by the weights acts differentially on the piezoelectric element, it is possible to provide two or more weights.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of the present invention, and FIG.
Figure 3 showing the polarization direction and electrical connection of the piezoelectric element in Figure 3.
The figure is a partial cross-sectional view showing another embodiment of the present invention using an annular piezoelectric element, FIG. 4 is a partial cross-sectional view showing still another embodiment of the present invention using four piezoelectric elements, and FIG. 5 is a diagram showing the polarization direction and electrical connection of the piezoelectric element in FIG. 4. FIG. 1.1', 1", 1"', 9,9', 10,10'...piezoelectric element, 2...fixing base, 3,3'...weight, 4...screw, 5...insulation, 6...case, 7...Lead wire, 8...Arrow indicating polarization direction.

Claims (1)

[Claims] 1. A piezoelectric element including a metal case and a fixed base fixed to the metal case, and a piezoelectric element having a polarization direction perpendicular to the fixed base on each side of the fixed base, and a weight fixed to the outside thereof. The weights are interconnected by a fixing member, so that when the fixing base vibrates, one piezoelectric element is compressed by the inertia of the weights and the other piezoelectric element is expanded, thereby causing each piezoelectric element to expand. A piezoelectric vibration pickup in which the electrodes of the piezoelectric elements are connected so that charges of the same sign generated on the electrodes of the elements are collected and taken out. 2. The piezoelectric vibration pickup according to claim 1, wherein the fixing member passes through holes provided in the piezoelectric element and the fixing base. 3. In the piezoelectric vibration pickup according to claim 2, the polarization direction of each of the piezoelectric elements is opposite to the fixed base, and the pole of the piezoelectric element on the weight side is polarized through the weight. The piezoelectric element is electrically connected to the fixing member, and a pole of the piezoelectric element on the fixing base side is connected to the metal case via the fixing base, and conductive wires are connected to the fixing member and the metal case, respectively. A piezoelectric vibration pickup characterized by: 4. The piezoelectric vibrating pick amplifier according to any one of claims 1 to 3, wherein the piezoelectric element has a disk shape, a square plate shape, or a cylindrical shape. vibration pickup. 5% Permissible In the piezoelectric vibration pickup according to claim 4, the cylindrical piezoelectric element has electrodes on an inner diameter surface and an outer diameter surface, and the polarization axis is perpendicular to the electrode surface. Features a piezoelectric vibration pickup. 6. Contains a metal case and a fixed base fixed to the metal case, two or more piezoelectric elements having a polarization direction perpendicular to the fixed base on each side of the fixed base, and a weight fixed to the outside thereof, The weights are interconnected by a fixing member, so that when the fixing base vibrates, the piezoelectric element group on one side is compressed due to the inertia of the weight, and the piezoelectric element group on the other side is expanded; A piezoelectric vibration pickup in which the piezoelectric elements on the same side are connected so that their polarization directions are electrically parallel. 7. The piezoelectric vibration pickup according to claim 6, wherein the fixing member passes through holes provided in the piezoelectric element and the fixing base. 8% Permissible The piezoelectric vibration pickup according to claim 6, wherein the piezoelectric element has a disk shape, a square plate shape, or a cylindrical shape. 9. The piezoelectric vibration pickup according to claim 8, wherein the cylindrical piezoelectric element has electrodes on an inner diameter surface and an outer diameter surface, and the polarization axis is perpendicular to the electrode surface. A piezoelectric vibration pickup.