JPH0132453B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application 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. be.

Conventional configuration and its problems Conventionally, a rectangular bimorph piezoelectric vibrator with a cantilevered structure in a bending vibration mode, whose resonance frequency is matched to the natural frequency of the vibrating object, has been used as a sensor for detecting elastic vibrations in a vibrating object. Are known.
However, it has had the disadvantage that the supporting portion may shift due to stress generated mechanically or due to temperature changes, etc., making it impossible to obtain a stable resonant frequency. Therefore, the bonded piezoelectric vibrator pieces are melted and cut using a laser processing machine or the like to obtain a bending vibrator that resonates at a predetermined frequency, and by supporting and fixing the periphery of the bending vibrator, a stable resonance frequency can be obtained. A resonant vibration sensor was obtained. However, when performing laser processing, it is known that at the starting point of processing, a hole larger than the laser beam diameter is created due to disturbance of the laser auxiliary gas due to non-penetration, and when processing ends, the laser beam must be shut off. It is known that the time delay of the shutter can also cause large holes. Figure 1 shows such a conventional bending vibrator, in which two disk-shaped piezoelectric elements having polarization axes in the thickness direction are bonded together.
This figure shows the processing results when a bending vibration mode vibrator is localized by laser processing and the start and end of processing are located in the vibrating part. Figure a is a top view, figure b is a longitudinal sectional view, figure c is a bottom view,
The disk-shaped piezoelectric elements 1 and 2 are bonded to form a bonded piezoelectric vibrator, which is sufficiently thin so that the electrodes 1a' and 2a' of the disk-shaped piezoelectric elements 1 and 2 are electrically connected. The vibrator is cut through (the partially cut portion 3 will be referred to as a slit hereinafter) using a laser processing machine as shown in the arrow, and the upper surface electrode 1a is the portion surrounded by the slit 3 and the output voltage extraction portion, and the bottom surface electrode 2a is This structure consists of a partial electrode extending from the part surrounded by the slit 3 to the peripheral edge. If the area from the vicinity of the slit 3 to the outer periphery of the bonded piezoelectric vibrator is the supported portion, the portion surrounded by the slit 3 functions as a so-called cantilever type vibrator in a bending vibration mode. However, since the vibrating part of the bending vibrator has the start and end points of laser processing, a hole larger than the width of the slit is formed, and the length of the vibrating part changes, causing a change in the resonant frequency. In addition, since processing starts from an unpierced state at the starting point, the molten material is not sufficiently blown away due to disturbances in the auxiliary gas flow of the laser processing machine, resulting in a considerable amount of conductive molten material adhering to the cut surface. , the insulation resistance between the vibrating part electrodes is lowered. Furthermore, since thermal strain is greater at the start and end portions of machining than at other portions, there is a drawback that if these are located in the vibrating portion, long life and reliability will be lacking.

Purpose of the Invention The present invention aims to solve such drawbacks, and by separating the start and end parts of laser processing from the vibrating part of the bending vibrator, the present invention designs and manufactures a vibration sensor that resonates at a predetermined frequency. The purpose of this invention is to provide a vibration sensor that is easy to operate, has a long life, and has high reliability.

Structure of the Invention The present invention involves forming a slit in a piezoelectric vibrator in which two plate-shaped piezoelectric elements having polarization axes in the thickness direction are bonded together, and cutting a penetrating portion of the piezoelectric vibrator by melt cutting using laser processing or the like. The part surrounded by is a bending vibration mode vibrator, and the starting end and the end of the penetrating part cutting are separated from the bending vibration mode vibrator part.

DESCRIPTION OF EMBODIMENTS FIG. 2 shows a case where a bending vibration mode vibrator is machined into a bonded piezoelectric vibrator according to the present invention, and the machining start and end parts are separated from the vibrating part.
Figure a is a top view, figure b is a longitudinal sectional view, and figure c is a bottom view. Machining was started right next to the vibrating part of the bending vibration mode vibrator, and after cutting the slit 3 as shown by the arrow, the machining was completed right next to the vibrating part. Since the part surrounded by the slit 3 becomes the vibration part of the bending vibration mode vibrator, the resonance frequency Fr is determined by the vibration part length l and the vibration part thickness, Fr∝T/l ₂
Therefore, the length of the vibrating section can be made constant regardless of the size of the hole at the start and end portions of slit processing, and the resonance frequency can be easily adjusted to a predetermined frequency. Further, by using only the vibrating portion and the output extraction portion as the electrodes 1a and 2a, it is possible to prevent a decrease in insulation resistance between the electrodes caused by molten matter adhering to the cut surfaces at the start and end portions of machining. Furthermore, although the thermal strain is large at the start and end portions of machining, it is not located in the vibrating section, so it has high reliability.

In addition, multiple bending vibration mode vibrators can be processed into the same bonded piezoelectric vibrator, so by making the individual bending vibration mode vibrators the same or different, detection sensitivity at a predetermined frequency can be increased or correlation can be improved. It will be excellent.

Effects of the Invention As is clear from the above description, according to the present invention, the length of the vibration section of the flexural vibration mode vibrator can be made constant, so the resonance frequency can be easily matched to a predetermined frequency, and the insulation resistance between the electrodes can be reduced. It has the characteristics of preventing this and achieving high reliability. Furthermore, since a plurality of bending vibration mode vibrators can be localized in the same bonded piezoelectric vibrator, it is possible to select a plurality of elements having the same resonance frequency or mutually different resonance frequencies.

[Brief explanation of drawings]

Figure 1 shows a conventional example in which a bending vibration mode vibrator is localized by laser processing in a bonded piezoelectric vibrator, in which a is a top view, b is a longitudinal cross-sectional view,
c is a bottom view, FIG. 2 is a diagram showing one embodiment of the present invention, when the processing start and end parts of the bending vibration mode vibrator are separated from the vibrating part, a is a top view, and b is a vertical cross-sectional view. , c is a bottom view. 1, 2... Disc-shaped piezoelectric element, 3... Slit cut through, 1a, 2a... Electrode.

Claims (1)

[Claims] 1. A flexural vibration mode vibrator that resonates at a predetermined frequency is localized by forming a slit in a piezoelectric vibrator made by bonding two plate-like piezoelectric elements having polarization axes in the thickness direction. A vibration sensor characterized in that a starting end and a terminal end of the slit for forming the bending vibration mode vibrator are separated from a vibrating part. 2. The vibration sensor according to claim 1, wherein the opposing electrodes of the bending vibration mode vibrator are provided only in the vibrating part and the output voltage extraction part. 3. The vibration sensor according to claim 1 or 2, characterized in that a plurality of the bending vibration mode vibrators are localized in the bonded piezoelectric vibrator.