JPH0677026B2 - 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 vibration of an object and acceleration caused thereby.

2. Description of the Related Art Conventionally, as a piezoelectric vibration acceleration sensor that detects elastic vibration in a vibrating object, a vertical effect type that uses compression and tensile force in the thickness direction of a piezoelectric element and a Sendan effect type that uses Sendan recording Generally, only the specific frequency component is detected by matching the resonance frequency with the natural frequency of the vibrating object.
Alternatively, when a vibration component in a predetermined frequency region is detected and sensitivity is improved at a low frequency, a lateral effect type vibrator, that is, a cantilever type structure 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 as shown in JP-A-59-70923,
A cantilever type bending oscillator, which is the vibration detection part, is made by making a notch in a plate-bonded piezoelectric element such as a disk, and the bending vibrator is integrated with the bonded plate-shaped piezoelectric element at one end. In some cases, the fixing condition is stabilized by instructing the periphery of the bending oscillator to be fixed.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, even if the vibration detection is stabilized, the signal is not stabilized against the temperature change.

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. An acceleration sensor having a structure in which two piezoelectric materials are bonded together is bonded in such a manner that the polarization axis directions are opposite to each other, and the serial type in which the upper and lower surfaces serve as signal extraction electrodes, and the polarization axis directions are aligned, and conduction between the upper and lower surface electrodes is established. In the parallel type in which the electrodes are taken out along with the bonding and bonding surface electrodes, the generated charges can theoretically cancel each other out, but in the conventional acceleration sensor, the heat transfer to the piezoelectric material is uneven and the acceleration detection is not possible. Due to the asymmetrical electrodes due to the signal extraction part from the bending vibration mode oscillator which is a part, and the difference in shape such as thickness and length of the piezoelectric element to be bonded, the charge generated by pyroelectricity is canceled out under severe temperature conditions An output signal appeared without being able to provide a high-precision acceleration sensor.

Further, since the characteristics of the piezoelectric material itself change in response to temperature changes, the sensitivity also changes, so it was necessary to perform temperature correction using a thermistor or the like.

In view of the problems of the conventional sensor, the present invention of claim 1 reduces the pyroelectric output signal caused by a temperature change,
An object is to provide a highly accurate vibration acceleration sensor.

An object of the present invention of claim 2 is to provide a highly accurate vibration acceleration sensor in which the same bonded piezoelectric element is used to correct the sensitivity that changes due to temperature changes.

Means for Solving the Problems According to the present invention of claim 1, two plate-shaped piezoelectric elements each having a polarization axis in the thickness direction and electrodes on the upper and lower surfaces are bonded so that the polarization axis directions are the same. A bonded piezoelectric element having a structure, a bending vibration mode oscillator formed by providing a cutout in the bonded piezoelectric element, and an upper and lower peripheral surface of the bending vibration mode vibrator are sandwiched and fixed by a material having a large thermal conductivity. The bonding piezoelectric element is composed of a fixing member, and the upper and lower electrodes of the bonded piezoelectric element are short-circuited to form a common electrode, and the bonding surface electrode of the bonded piezoelectric element is separated by the electrode of the bending vibration mode oscillator part and the surrounding electrode. To achieve the above object by subtracting the signals of the peripheral electrodes of the bending vibration mode oscillator from the output signal of the bending vibration mode oscillator. It

According to a second aspect of the present invention, the acceleration signal from the bending vibration mode oscillator is corrected by utilizing the capacitance change due to the temperature between the bonding surface peripheral electrode and the common electrode according to the first aspect. To achieve.

In the present invention of claim 1, the upper and lower peripheral surfaces of the flexural vibration mode oscillator are fixed by a fixing member such as a metal having a large thermal conductivity, and heat from the surroundings passes through the fixing member and is substantially applied to the oscillator. Since the temperature is gradually transferred evenly, the temperature gradient depending on the location is reduced. Furthermore, since the thin plates made of resin with poor heat conductivity are attached to the upper and lower surfaces of the fixing member, and the periphery is molded with resin, heat transfer to the fixing member Therefore, the influence on the sensor output can be reduced. Furthermore, the pyroelectric output due to the difference in shape of the piezoelectric elements to be bonded together can be reduced by subtracting the signal from the bonding surface peripheral electrode, which is the same piezoelectric element, from the sensor output signal.

According to the second aspect of the present invention, since temperature correction is performed based on the capacitance change of the same piezoelectric element, more accurate characteristics can be obtained.

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

The present invention according to claim 1 is intended to supply a highly accurate vibration acceleration sensor by reducing a pyroelectric output signal generated by a transient temperature change. FIG. 1 shows an embodiment of the vibration acceleration sensor of the present invention. 2A is a perspective view showing the electrodes of the laminated piezoelectric element, FIG. 2B is a perspective view showing the electrodes of the laminated piezoelectric element, and FIG. 3 is a vibration in which the periphery of the flexural vibration mode oscillator is fixed. It is an exploded perspective view showing a detection unit. A laminated piezoelectric element 6 having a structure in which plate-shaped piezoelectric elements 5 and 5 ′ having electrodes on the upper and lower surfaces thereof, which have a polarization axis in the thickness direction, are bonded to each other by a laser process or the like to have a “U” shape. A cutout 8 (slit) is formed, and a portion surrounded by the slit 8 becomes a bending vibration mode oscillator 7 (hereinafter referred to as a bending oscillator) having a cantilever structure. Laminated piezoelectric element 6
The bonding surface electrode of is separated into the electrode 5a of the bending oscillator 7 and the peripheral electrode 5b. In the parallel type in which the polarization axis directions (arrows in FIG. 2) of the plate-shaped piezoelectric elements 5 and 5'are aligned and bonded, the upper and lower electrodes of the bending oscillator 7 are made to be a common electrode, and the bonding surface electrode 5a , 5b serve as electrodes for taking out the output. The vibration detection unit 10 is made of metal or the like having a high thermal conductivity for fixing the periphery of the bending vibrator 7, and is bonded by fixing members 9 and 9'having grooves 9a and 9b at the displacement portion of the bending vibrator 7 and bonded together. 6 is sandwiched and fixed by adhesion or the like. The signal output 1 of the bending oscillator 7 and the signal output 2 from the surrounding electrodes of the bending oscillator 7 are respectively passed through the impedance conversion and amplification circuits 3 and 3 ', and the amplification circuit 3 is subtracted so that the output of the amplification circuit 3'is subtracted. The output of 3'is processed by the differential amplifier circuit 4 to be a sensor output. By adopting such a structure, heat from the surroundings is fixed by the fixing member 9,
Since it is transmitted through 9 ', it is transmitted almost uniformly from the fixed portion in the surroundings to the bending oscillator 7 which is the acceleration detecting portion,
The temperature gradient depending on the place is reduced. Further, the pyroelectric output caused by the difference in the thickness of the plate-shaped piezoelectric elements 5 and 5 ′ to be bonded is the signal output 1 of the bending oscillator 7 and the bending oscillator 7.
If the signal output 2 from the peripheral electrode that is a fixed part and does not output the acceleration signal is subtracted from the signal output 1 of the bending oscillator 7, the acceleration signal is output. The pyroelectric output signal can be removed from the signal, and the acceleration can be detected with high accuracy.

FIG. 4 is a vertical sectional view of the sensor, and FIG. 5 is an exploded perspective view of the sensor. On the upper and lower surfaces of the vibration detection unit 10, resin thin plates 12a, 12b having poor heat conduction such as a printed circuit board forming an impedance conversion and amplification circuit 3, 3 ', and a signal processing circuit 13 composed of a differential amplification circuit 4 are formed. Attachment, constituting a sensor basic unit 11 and fixed to an attachment housing 14 for a vibration detection object made of metal or the like. The heat change from the vibration detection object is transmitted through the housing 14, but since it is transmitted through the printed board 12b having poor heat conduction to the vibration detection unit 10, there is a time delay and the signal component due to pyroelectric becomes a lower frequency. At the same time, the temperature change shown in the equation (1) is reduced by the time change, so that the signal is attenuated and the influence on the sensor signal can be reduced. By molding the space between the sensor cover 15 and the sensor basic unit 11 with the resin mold 16, 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.

The present invention according to claim 2 intends to supply a highly accurate vibration acceleration sensor by correcting the sensitivity change of the sensor caused by the temperature change by using the same piezoelectric element, and FIG. 6 shows one embodiment of the present invention. It is a block diagram which shows an example. The output signal 1 from the bending oscillator 7 is input to the voltage controlled amplifier (VCA) 20 through the impedance conversion and amplification circuit 3, and the bonding surface peripheral electrode 5b and the bonding piezoelectric element upper and lower surface electrodes are short-circuited in common. A pulse having a frequency corresponding to the capacitance is generated by the pulse generation circuit 18 using the capacitance 17 between the electrodes, a constant signal is integrated by the pulse period, and a DC signal from the integration / hold circuit 19 that holds the integrated value is used. The amplification factor of the voltage controlled amplifier (VCA) 20 is changed and used as the sensor output signal. When the capacitance 17 changes with temperature, the pulse period changes, the integrated value changes, and the control DC voltage to the voltage controlled amplifier 20 changes, so the sensor output can be controlled with respect to temperature. Since the capacitance 17 is composed of the same bonded piezoelectric element as the bending oscillator 7 and is a partial value, it shows an accurate temperature change and can perform highly accurate temperature correction.

FIG. 7 is a block diagram showing another embodiment of the vibration acceleration sensor of the present invention according to claim 2. The output signal 1 from the bending oscillator 7 is an impedance conversion and amplification circuit 3
Through a voltage controlled amplifier (VCA) 20 through the common electrode between the bonding surface peripheral electrode 5b and the upper and lower electrodes of the bonding piezoelectric element, and a constant pulse from the pulse generator 22. The DC voltage from the integration / hold circuit 21 that performs integration at a cycle and holds the integration result is used as the control voltage of the voltage control amplifier circuit 20. Since the integrated value changes due to the change in the capacitance 17, the sensor output can be controlled, and highly accurate temperature correction can be performed.

EFFECTS OF THE INVENTION According to the present invention, in the vibration detection unit, the heat from the surroundings is transferred to the vibrator almost uniformly through the fixing member, so that the temperature gradient depending on the place is reduced. Since a thin plate made of resin or the like having poor heat conduction is attached to and the periphery 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. The pyroelectric output due to the shape error of the bonded piezoelectric element can be reduced by subtracting the signal from the bonding surface peripheral electrode having the same variation from the sensor output signal.

According to the second aspect of the present invention, since temperature correction is performed based on the capacitance change of the same piezoelectric element, more accurate characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the vibration acceleration sensor of the invention of claim 1, FIG. 2 (a) is a bonding piezoelectric element of the same embodiment, and FIG. 2 (b) is a bonding of the same embodiment. FIG. 3 is a perspective view showing the electrodes of the piezoelectric element, FIG. 3 is an exploded perspective view showing the vibration detection unit of the same embodiment, FIG. 4 is a longitudinal sectional view of the sensor of the same embodiment, and FIG. Exploded perspective view,
FIG. 6 is a block diagram showing an embodiment of the present invention according to claim 2, and FIG. 7 is a block diagram showing another embodiment of the present invention according to claim 2. 1 ... Bending vibrator output, 2 ... Signal output from surrounding electrodes of bending vibrator, 3,3 '... impedance conversion and amplification circuit, 4 ... differential amplifier, 5,5' ... plate piezoelectric Element, 5a, 5b ... Electrode, 6 ... Laminated piezoelectric element, 7 ...
… Bending vibration mode oscillator, 10 …… Vibration detection unit, 11
…… Sensor basic unit, 13 …… Signal processing circuit, 17 ……
Capacitance around the bending oscillator, 18, 21 ...... Pulse generation circuit, 19, 21 …… Integration / hold circuit, 20 …… Voltage control amplifier.

Claims (2)

[Claims] 1. A bonded piezoelectric element having a structure in which two plate-shaped piezoelectric elements having a polarization axis in the thickness direction and having electrodes on the upper and lower surfaces are bonded so that the polarization axis directions are the same.
A bending vibration mode oscillator formed by cutting out the laminated piezoelectric element, and a fixing member for sandwiching and fixing the upper and lower peripheral surfaces of the bending vibration mode oscillator with a material having a large thermal conductivity. The upper and lower electrodes of the laminated piezoelectric element are short-circuited to form a common electrode, and the laminated surface electrode of the laminated piezoelectric element is separated by the electrode of the bending vibration mode oscillator portion and the surrounding electrode to serve as signal extraction electrodes, respectively. A vibration acceleration sensor, wherein a signal of a peripheral electrode of the bending vibration mode vibrator is subtracted from an output signal of the bending vibration mode vibrator. 2. A bonded piezoelectric element having a structure in which two plate-shaped piezoelectric elements having a polarization axis in the thickness direction and having electrodes on the upper and lower surfaces are bonded so that the polarization axis directions are the same.
A bending vibration mode oscillator formed by cutting out the laminated piezoelectric element, and a fixing member for sandwiching and fixing the upper and lower peripheral surfaces of the bending vibration mode oscillator with a material having a large thermal conductivity. The upper and lower electrodes of the laminated piezoelectric element are short-circuited to form a common electrode, and the laminated surface electrode of the laminated piezoelectric element is separated by the electrode of the bending vibration mode oscillator portion and the peripheral electrode, and the periphery of the laminated surface A vibration acceleration sensor, wherein an acceleration signal from the flexural vibration mode oscillator is corrected by using a capacitance value between an electrode and the common electrode.