JPH0256619B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a resonant vibration sensor suitable for detecting elastic vibrations in a vibrating object, and particularly to a resonant vibration sensor with excellent detection sensitivity for a predetermined frequency. .

Conventional configurations and their problems Conventionally, as sensors for detecting elastic vibrations in a vibrating object, a rectangular bimorph piezoelectric vibrator with a cantilever structure in a bending vibration mode whose resonant frequency is matched to the natural frequency of the vibrating object, A peripherally supported and fixed disc-shaped bimorph piezoelectric vibrator that utilizes the plane bending mode of a disc is widely known. A rectangular or disk-shaped element has the advantage of being simple in shape, can be manufactured with high precision, and is easy to analyze and handle vibration modes.

However, in order to stabilize the resonant frequency, it is necessary to stabilize the fixing conditions of the piezoelectric vibrator, but due to stress generated by various factors such as mechanical or temperature changes, metal The part that is supported and fixed by the supporting member made of the material may shift, making it difficult to obtain stable fixing conditions. Furthermore, during the manufacturing process, variations in the predetermined resonance frequency occur due to dimensional errors or assembly errors of parts. Therefore, adjustment is required to match the predetermined resonance frequency. Therefore, in the case of a rectangular bimorph piezoelectric vibrator, the length of the vibrating portion is appropriately adjusted by cutting or other methods. Further, in the case of a disc-shaped bimorph piezoelectric vibrator, adjustment must be made by replacing the supporting member or the like. In this way, for any piezoelectric vibrator,
Adjusting the resonant frequency is complex and quite troublesome. Furthermore, the fixing conditions for the piezoelectric vibrator change depending on the tightening strength of the support member, and if the tightening strength is too strong, the element may be damaged, making the work difficult.

Purpose of the Invention The present invention aims to solve the drawbacks of conventional resonance-type vibration sensors by providing a slit in a bonded piezoelectric vibrator to stably detect elastic vibrations in a vibrating object. It is an object of the present invention to provide a vibration sensor having a structure in which a bending vibration mode vibrator having a cantilever structure having resonance at a predetermined frequency is locally formed, and a peripheral portion of the bonded piezoelectric element is supported and fixed.

DESCRIPTION OF EMBODIMENTS Examples of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a vibration sensor according to the present invention, in which FIG. 1A is a top view, FIG. 1B is a vertical sectional view, and FIG. 1C is a bottom view.

As shown in FIG. 1b, disc-shaped piezoelectric elements 1 and 2
are bonded with sufficiently thin electrodes 1a' and 2a' and electrically connected to form a bonded piezoelectric element, and a U-shaped or U-shaped slit 3 is cut in the center using a laser processing machine or the like. formed into parts. An upper surface electrode 1a is provided in a portion surrounded by the slit 3 on the surface opposite to the electrode 1a' of the piezoelectric element 1.
is provided as shown in FIG. It is being

If such a laminated piezoelectric element is supported using the portion from the periphery of the slit 3 to the outer periphery, the portion surrounded by the slit 3 functions as a so-called cantilever vibrator in a bending vibration mode. The output voltage generated by the vibration appears between the upper and lower surface electrodes 1a and 2a of the bonded piezoelectric element, and is taken out by the lead wires 4 and 4' connected thereto.

The resonance frequency Fr is approximately determined by T/l ² , where T is the plate thickness of the vibrating part and l is the length in the longitudinal direction of the part surrounded by the slit 3, so choose one or both of these values. By this, it is possible to set a predetermined frequency.

Therefore, the feature of this embodiment is that by providing a slit in the laminated piezoelectric vibrator, a bending vibration mode vibrator with a cantilever structure is locally formed. The resonant frequency of the flexural oscillator changes little with respect to changes in the oscillator, making it stable. Therefore, the resonant frequency of the flexural vibrator remains stable against changes such as displacement of the portion supported by the support member due to stress caused by mechanical or temperature changes. Furthermore, there is no need to strictly determine the attachment position of the support member, and assembly is simple. Furthermore, since the laminated piezoelectric vibrator has a bending mode vibrator with a cantilever structure locally formed, there is no convex part like a conventional cantilever vibrator, and the element can be easily handled due to careless handling. It has the characteristic of preventing damage to the Furthermore, the resonant frequency of the bending vibrator can be easily adjusted by trimming the vibrating part using a laser processing machine, which is highly productive, unlike conventional methods such as partial polishing.

FIGS. 2a and 2c are a perspective view and a cross-sectional view of the components of a vibration sensor using the vibrator of the above-described embodiment, respectively. In the figure, reference numeral 7 denotes a metallic one-sided support member for the bonded piezoelectric element, which has a threaded portion 8 for attachment to a vibrating object. 5 is the other supporting member;
The tightening member 6 is used to tighten and support and fix the periphery of the bending vibrator in the bonded piezoelectric element. Since the bottom electrode 2a of the bonded piezoelectric element is supported and fixed by the support member 7, it is also electrically connected to the support member 7, and the support member 7 is used as one terminal for taking out the output voltage of the bending vibrator. . Other terminals are taken out from the upper surface electrode 1a of the bonded piezoelectric element through lead wires 4.

FIG. 3 shows another embodiment. This is a bonded piezoelectric element made up of piezoelectric elements 1 and 2, in which two bending vibrators in a bending vibration mode are localized. Note that Figure a is a top view, Figure b is a sectional view, and Figure c is a bottom view. Since the resonant frequency is approximately determined by the shape of the slit, it is of course possible to localize two or more bending vibrators. By making the resonant frequencies of the localized bending vibrators the same or different, detection sensitivity at a predetermined frequency can be increased or correlation can be improved. Furthermore, by stabilizing the resonant frequency, a non-resonant type vibration sensor used in a frequency band sufficiently lower than the resonant frequency also becomes stable and accurate.

Effects of the Invention As is clear from the above explanation, the present invention has the following effects:
Since a bending vibration mode vibrator with a cantilever structure is locally formed in the laminated piezoelectric element, its peripheral fixing conditions are more reliably satisfied than those of conventional bimorph type vibrators. It has the characteristic that the resonant frequency of the bending vibrator is stabilized.
In addition, since multiple bending vibrators with a cantilever structure can be formed locally on the bonded piezoelectric element, it is possible to make the resonance frequencies of the multiple pieces the same or to select different resonance frequencies. It also has the feature of being able to

[Brief explanation of drawings]

FIG. 1a is a top view of essential parts of a vibration sensor according to an embodiment of the present invention, FIG. 1b is a sectional view thereof, FIG. 1c is a bottom view thereof, and FIG. 2a is an exploded perspective view showing this embodiment.
Figure b is a sectional view. FIG. 3a is a top view of essential parts of a vibration sensor according to another embodiment of the present invention, FIG. 3b is a sectional view thereof, and FIG. 3c is a bottom view thereof. 1, 2...Plate piezoelectric element, 3...Slit.

Claims (1)

[Claims] 1 A bonded piezoelectric element is constructed by bonding together two plate-shaped piezoelectric elements having polarization axes in the thickness direction, and resonance is caused at a predetermined frequency by providing a slit in the bonded piezoelectric element. A vibration sensor characterized in that a bending vibration mode vibrator having a cantilever structure is formed locally, and a peripheral portion of the bonded piezoelectric element is supported and fixed. 2. The vibration sensor according to claim 1, wherein a plurality of bending vibration mode vibrators are formed on the bonded piezoelectric element.