JPH052173B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is a vibration sensor suitable for detecting elastic vibrations in a vibrating object, particularly a resonant type vibration sensor with excellent detection sensitivity at a predetermined frequency, and a non-resonant type vibration sensor suitable for detecting elastic vibrations in a vibrating object. The present invention relates to an acceleration sensor.

Conventional technology Conventionally, piezoelectric sensors that detect elastic vibrations in a vibrating object have been either resonant type sensors that match the resonant frequency to the natural frequency of the vibrating object and detect only a specific frequency component, or non-resonant sensors that detect vibration components in a predetermined frequency range. 2. Description of the Related Art Rectangular bonded piezoelectric vibrators, which have a cantilever structure in a bending vibration mode and have improved sensitivity, especially at low frequencies, are widely known.
In the case of a vibration sensor that has a cantilever type structure, it is difficult to achieve the fixing condition of fixing the vibrator at one end. A bending vibrator of the structure is fabricated by cutting a groove in a disk-shaped bonded piezoelectric element, and the bending vibrator is integral with the bonded piezoelectric disk at one end and fixes the peripheral portion of the disk. Some stabilize the fixing conditions by creating a supported structure. The signal of such a piezoelectric vibration sensor is outputted as a predetermined output signal through a separately prepared charge amplifier or voltage amplifier.

Problems to be Solved by the Invention In such conventional vibration sensors, the lower the frequency, the higher the output impedance of the sensor becomes, making it easier for ambient noise to enter. In addition, noise countermeasures for the circuit must be taken into consideration, making it expensive. Alternatively, when a signal processing circuit section is built into the sensor to output at low impedance and reduce the influence of noise, there is a problem that the circuit section hinders miniaturization of the sensor.

Therefore, the present invention integrates the vibration detection part and the signal processing circuit to reduce the influence of noise.
It is designed to be inexpensive and compact.

Measures to solve the problem: A flexural vibration mode vibrator is created by providing a cutout in a bonded piezoelectric element, which has a structure in which two plate-shaped piezoelectric elements having a fixed periphery and a polarization axis in the thickness direction are bonded together. In addition, an electric circuit for processing the output signal of the bending vibrator is configured on the upper surface of the bonded piezoelectric element excluding the bending vibrator section.

Function By integrating the bending vibrator part that detects vibration and the signal processing circuit, there is no need for a connecting cable between the signal of the vibration detection part and the processing circuit, and if the signal processing circuit is voltage amplification, there is no cable capacity. Therefore, uniform sensor sensitivity can be obtained. In addition, converting the high impedance output of the vibration detection section to low impedance using a signal processing circuit has the great advantage of being less susceptible to external noise and allowing cables to be connected to the outside using regular electric wires, making it cheaper and more compact. This makes it possible to mass-produce the product.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an exploded perspective view showing an embodiment of a vibration sensor according to the present invention, in which disk-shaped piezoelectric elements 1a and 1b having polarization axes in the thickness direction are bonded together. Then, a U-shaped slit (cutout) 2 is formed by laser processing or the like, and the portion surrounded by the slit 2 becomes a flexural vibration mode vibrator 3 having a cantilever structure. The bending vibrator 3 has electrodes on the upper and lower surfaces and the bonding surface,
When the piezoelectric elements 1a and 1b are bonded together so that their polarization axes directions are opposite to each other, the upper and lower surface electrodes of the bending vibrator 3 serve as output extraction electrodes. A fixing member 5 made of a conductive material such as metal and having a groove 6 in the part where the bending vibrator 3 contacts is bonded to the piezoelectric element 1 so as to be electrically connected to the lower electrode of the bending vibrator 3. and the periphery of the bending vibrator 3 is used. On the top surface of the bonded piezoelectric element except for the bending vibrator 3, there is an electrode 4 that can form an electric circuit.
The upper surface electrode of the bending vibrator 3 and the electric circuit input electrode are made common, and the fixed member 5 is used to ground the electric circuit to form a signal processing circuit such as impedance conversion. Bonded piezoelectric element 1 excluding bending vibrator 3
is necessary to stabilize the fixing condition of fixing one end of the cantilever structure, but by configuring a signal processing circuit in this part regardless of vibration detection, miniaturization can be achieved, and the signal processing The circuit can convert the output signal to low impedance, making it resistant to external noise.
No special cables are required, making it inexpensive and highly suitable for mass production.

Fig. 2 shows an example of the case assembled as a vibration sensor, in which the fixing member 5 is made of a resin-based copper clad plate such as epoxy, and the bonded piezoelectric element and signal processing circuit part 7 are made of metal or the like. It is made into a shield and then molded with polyurethane resin or the like. By using a copper clad plate as the fixing member, input and output to the signal processing circuit can be performed using the copper foil of the fixing member 5, and the groove 6 in the part where the bending vibrator hits can be easily made by etching the copper foil. This makes it easy to assemble and highly suitable for mass production.

Effects of the Invention According to the present invention, by integrating the bending vibrator of the vibration detection section and the signal processing electric circuit into the same bonded piezoelectric element, the sensor can be made smaller and more resistant to external noise. This eliminates the need for printed circuit boards, special cables, etc., making it inexpensive and highly suitable for mass production.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view of a vibration sensor according to an embodiment of the present invention, and FIG. 2 is a perspective view of the same embodiment after assembly. 1... Bonded piezoelectric element, 2... Slit,
3...Bending mode vibrator, 5...Fixing member.

Claims (1)

[Scope of Claims] 1. A bonded piezoelectric element having a structure in which two plate-shaped piezoelectric elements having polarization axes in the thickness direction are bonded together, a fixing member that fixes the periphery of the bonded piezoelectric element, and the bonded piezoelectric element. Excluding a rectangular bending vibration mode vibrator formed by providing a cutout in a piezoelectric element, electrodes provided on the upper and lower surfaces and bonding surfaces of the rectangular bending vibrator, and the rectangular bending vibrator section. A vibration sensor comprising: an electrode forming an electric circuit on the upper surface of the bonded piezoelectric element; and an electric circuit formed on the upper surface of the bonded piezoelectric element. 2. The vibration sensor according to claim 1, wherein the fixing member that fixes the periphery of the bonded piezoelectric element is made of a conductive material. 3. The vibration sensor according to claim 1, wherein the fixing member for fixing the periphery of the bonded piezoelectric element is made of a resin-based copper clad plate.