JPH0682131B2 - Vibration acceleration sensor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibration acceleration sensor that utilizes the electromechanical conversion characteristics of a piezoelectric material to detect the vibration of an object and the acceleration caused thereby.

2. Description of the Related Art Conventionally, as a piezoelectric vibration acceleration sensor for detecting elastic vibration in a vibrating object, a vertical effect type using compression and tensile force of the piezoelectric element in the thickness direction and a send effect type using shear force are generally used. However, if the resonance frequency is matched to the natural frequency of the vibrating object and only the specific frequency component is detected, or if the vibration component in the predetermined frequency region is detected and the sensitivity is improved at low frequencies, the lateral effect type, That is, a cantilever type vibrator using a bending vibration mode is widely known. In the case of a vibration acceleration sensor having a cantilever type structure, it is difficult to realize the fixed condition that one end of the vibrator is fixed, but the cantilever which is the vibration detecting portion as disclosed in Japanese Patent Laid-Open No. 59-70923. A bending oscillator having a die structure is made by making a cut in a plate-shaped laminated piezoelectric element such as a disk, and the bending oscillator is integrated with the laminated plate-shaped piezoelectric element at one end of the bending oscillator. In some cases, the fixed conditions are stabilized by fixing and supporting.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In such a conventional piezoelectric vibration acceleration sensor, a mechanical force such as acceleration is detected and, at the same time, an electric charge is generated in response to a change in ambient temperature. Due to the pyroelectric effect of the piezoelectric material, charge generation is given by the following equation.

dQ / dt = k · dT / dt (1) where Q is charge, T is temperature, t is time, and k is a proportional constant. That is, it is impossible to distinguish the generation of this charge from the charge generated by the acceleration to be detected,
It causes a large error in the detection of acceleration. Accelerometers with two piezoelectric materials attached are laminated so that the polarization axis directions are opposite to each other, and the serial type has upper and lower surfaces as signal extraction electrodes, and the polarization axis directions are aligned to establish continuity between the upper and lower electrodes. In the parallel type in which the signal extraction electrode is used together with the bonding surface electrode, the generated charges can theoretically cancel each other out, but in the conventional acceleration sensor, the heat transfer to the piezoelectric material is non-uniform, and the acceleration is detected. Due to the asymmetric electrodes such as the signal extraction part from the bending vibration mode oscillator, which is a part, the charge generated by pyroelectricity could not be canceled out under severe temperature conditions and an output signal appeared, so it was not possible to supply a highly accurate acceleration sensor. .

Therefore, an object of the present invention is to provide a highly accurate vibration acceleration sensor by reducing an output signal generated by a temperature change.

Means for Solving the Problems According to the present invention of claim 1, a vibration detecting unit having a bending oscillator formed in a plate-shaped laminated piezoelectric element, and poor heat conduction attached to the upper and lower surfaces of the vibration detecting unit. A sensor basic unit consisting of a thin plate made of resin or the like and a signal processing circuit formed on the thin plate is fixed to a housing for mounting on a vibration detection object, and the periphery of the sensor basic unit is molded with resin having poor heat conduction. The above structure achieves the above object.

According to the present invention of claim 1, in the vibration detecting unit in which the upper and lower peripheral surfaces of the plate-shaped bonded piezoelectric element having the bending vibration mode vibrator are fixed by the fixing member such as metal, heat from the surrounding passes through the fixing member. Almost evenly transmitted to the flexural vibration mode oscillator through the bonded piezoelectric element, the temperature gradient depending on the location is reduced.Furthermore, thin plates made of resin with poor heat conduction are attached to the upper and lower surfaces of the vibration detection unit to surround it. Since the resin is molded with resin, it is possible to reduce the influence on the sensor output due to delay in heat transfer to the vibration detection unit.

Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sensor sectional view showing an embodiment of a vibration acceleration sensor of the present invention, FIG. 2 is an exploded perspective view thereof, and FIG.
It is an exploded perspective view showing a vibration detection unit of the sensor. As shown in FIG. 3, a bonded piezoelectric element 1 having a structure in which plate-shaped piezoelectric elements 1a and 1b having polarization axes in the thickness direction and having symmetrical electrodes formed on the upper and lower surfaces are bonded together.
In addition, a U-shaped cutout 10 by laser processing etc.
The (slit) is formed, and the portion surrounded by the slit 10 becomes a bending vibration mode oscillator 11 having a cantilever structure. In the case of a serial type in which the plate-shaped piezoelectric elements 1a and 1b are bonded so that the polarization axis directions thereof are opposite to each other, the upper and lower electrodes of the flexural vibration mode oscillator 11 serve as output extraction electrodes. Plate-shaped piezoelectric element 1a,
In the case of the parallel type in which the polarization axis directions of 1b are aligned and pasted,
The upper and lower electrodes of the flexural vibration mode oscillator 11 are electrically connected, and serve as an output extracting electrode together with the bonding surface electrode. The vibration detection unit 3 includes a bonded piezoelectric element 1 formed with a bending oscillator 11 and is made of metal or the like having a high thermal conductivity so as to fix the periphery of the bending oscillator 11, and has a groove 12a at a displacement portion of the bending oscillator 11. It is sandwiched between fixing members 2a and 2b having 12b and fixed by adhesion or the like. By adopting such a structure, heat from the surroundings is transferred through the fixing member, so that it is almost evenly transferred from the surrounding fixed part to the flexural vibrator 11 which is the acceleration detecting part, and the temperature gradient depending on the place is reduced. ing. Furthermore, on the upper and lower surfaces of the vibration detection unit 3,
The sensor basic unit 6 is configured by attaching the resin thin plates 4a and 4b having poor heat conduction such as a printed circuit board which constitutes the signal processing circuit 5 such as the impedance conversion circuit and the filter amplifier circuit to the vibration detection object made of metal or the like. It is fixed to the mounting case 8. The heat change from the vibration detection object is transmitted through the housing 8, but the printed circuit board having poor heat conduction.
Since it passes through 4b to the vibration detection unit 3, there is a time delay, the signal component due to pyroelectric becomes a lower frequency, and the time change amount of the temperature shown in the equation (1) becomes smaller, so the signal is attenuated, The influence on the sensor signal can be reduced. By molding the space between the sensor cover 9 and the sensor basic unit 6 with the resin mold 7, the influence on the sensor signal can be further reduced. In this way, the output signal generated by the temperature change can be reduced and the acceleration can be detected with high accuracy.

FIG. 4 is a perspective view of a bonded piezoelectric element portion showing another embodiment of the vibration acceleration sensor according to the present invention. By using the bonded piezoelectric element 1 having a structure in which the plate-shaped piezoelectric elements 1a and 1b are bonded to each other with a metal thin plate 13 of Kovar or 42% Ni-Fe having the same or similar thermal expansion coefficient sandwiched therebetween, Can be made stronger against the impact of.

By setting the depth of the grooves 12a, 12b provided in the fixing members 2a, 2b to the amount of displacement of the bending oscillator 11 at the time of allowable acceleration, the bending oscillator cannot be displaced with respect to an input exceeding the allowable acceleration. 11 will be protected and can be made strong against impact such as dropping.

EFFECTS OF THE INVENTION According to the present invention, a thin plate made of resin or the like having poor heat conduction is attached to the upper and lower surfaces of the vibration detection unit, and the periphery is molded with resin, so that heat transfer to the vibration detection unit is delayed. The influence on the sensor output can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing a vibration acceleration sensor according to an embodiment of the present invention, FIG. 2 is an exploded perspective view thereof, FIG. 3 is an exploded perspective view showing a vibration detection unit of the vibration acceleration sensor, and FIG. It is a perspective view showing other examples of the vibration acceleration sensor. 1 ... Bonded piezoelectric elements, 1a, 1b ... Plate-shaped piezoelectric elements, 2a, 2
b ... fixing member, 3 ... vibration detection unit, 4a, 4b ... printed circuit board, 5 ... signal processing circuit, 6 ... sensor basic unit,
7 ... Resin mold, 8 ... Housing, 11 ... Bending vibration mode oscillator, 13 ... Metal thin plate.

Claims (4)

[Claims] 1. A vibration detecting unit having a plate-shaped piezoelectric bending oscillator having a polarization axis in the thickness direction and electrodes on the upper and lower surfaces, and a heat conduction unit mounted on the upper and lower surfaces of the vibration detecting unit. A sensor basic unit equipped with a thin plate made of resin or the like and a signal processing circuit formed on the thin plate is fixed to a housing for mounting on a vibration detection object, and heat conduction around the sensor basic unit is poor. Vibration acceleration sensor molded with resin. 2. A vibration detecting unit, wherein a bending vibration mode vibrator is formed by bonding two piezoelectric bending vibrators, and a cutout is provided in the bonded piezoelectric bending vibrator, and the bending vibration mode vibrator. 2. The vibration acceleration sensor according to claim 1, further comprising a fixing member that clamps and fixes the periphery of the material with a material having a large thermal conductivity. 3. A flexural vibration mode oscillator having a structure in which two plate-shaped piezoelectric elements having a polarization axis in the thickness direction are bonded together by sandwiching a metal thin plate having an expansion coefficient equal to or near the piezoelectric element. The vibration acceleration sensor according to claim 2. 4. A groove having a depth equivalent to the displacement amount of the bending vibration mode oscillator generated at the maximum permissible acceleration is formed in the bending vibration mode oscillator displacement portion of the fixing member that clamps and fixes the periphery of the bending vibration mode oscillator. The vibration acceleration sensor according to claim 2, wherein the vibration acceleration sensor is provided.