JPH0295263A - vibration acceleration sensor - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a vibration acceleration sensor that utilizes the electromechanical conversion characteristics of a piezoelectric material to detect vibrations of an object and acceleration caused by the vibrations of an object.

Conventional technology Conventionally, piezoelectric rapid acceleration sensors that detect elastic vibrations in vibrating objects have been divided into two types: a longitudinal effect type that uses compression and tensile force in the thickness direction of a piezoelectric element, and a shear effect type that uses shear force. is common, but it detects only specific frequency components by matching the resonance frequency to the natural frequency of the vibrating object.
Alternatively, when detecting vibration components in a predetermined frequency range and aiming to improve sensitivity at low frequencies, a transverse effect type vibrator, that is, a cantilever-dyed structure vibrator using a bending vibration mode is widely known. In the case of a vibration acceleration sensor that has a cantilever dyed structure, it is difficult to achieve the fixing condition of fixing the vibrator at one end. A bending vibrator having a dyed structure is fabricated by making a cut in a plate-shaped bonded piezoelectric element such as a disk, and the bending vibrator is integrated with the bonded plate-shaped piezoelectric element at one end, and the bending vibrator Some stabilize the fixing conditions by fixedly supporting the surrounding area.

Problems to be Solved by the Invention However, even if the vibration detection is stabilized, the signal is not stabilized against temperature changes.

Such conventional piezoelectric vibration acceleration sensors detect mechanical forces such as acceleration and at the same time generate electric charges in response to changes in ambient temperature. This is due to the pyroelectric effect of piezoelectric materials, and charge generation is given by the following equation.

dQ/d t=-dT/d t (1) where Q represents charge, T represents temperature, t represents time, and k represents a proportionality constant. That is, the generation of this charge cannot be distinguished from the charge generated by the acceleration to be detected, resulting in a large error in the detection of acceleration. Accelerometers with a structure in which two pieces of piezoelectric material are pasted together have two types of piezoelectric materials that are pasted together so that their polarization axes are opposite to each other, and a series type in which the upper and lower surfaces serve as signal extraction electrodes. In a parallel type with a signal extraction electrode and a bonded surface electrode, the generated charges can theoretically be canceled out, but in conventional acceleration sensors, the way heat is transferred to the piezoelectric material is uneven, and the acceleration Due to the asymmetrical electrodes at the signal extraction part from the bending vibration mode vibrator, which is the detection part, and the differences in the shape of the piezoelectric elements bonded together, such as thickness and length, the electric charge generated by pyroelectricity is suppressed under severe temperature conditions. An output signal appeared that could not be canceled out, making it impossible to provide a highly accurate acceleration sensor.

Furthermore, since the characteristics of the piezoelectric material itself change with respect to temperature changes, the sensitivity changes, so it is necessary to perform temperature correction using a thermistor or the like.

Claim 10 In view of the problems with conventional sensors, the present invention reduces the pyroelectric output signal caused by temperature changes,
The present invention according to claim 2 is characterized in that it provides a highly accurate vibration acceleration sensor, and the present invention provides a highly accurate vibration acceleration sensor that uses the same bonded piezoelectric element to correct sensitivity that changes due to temperature changes. With the goal.

Means for Solving the Problems The present invention as claimed in claim 1 is characterized in that two plate-shaped piezoelectric elements having polarization axes in the thickness direction and electrodes on the upper and lower surfaces are bonded together so that the polarization axes are in the same direction. A bonded piezoelectric element having a structure, a bending vibration mode vibrator formed by providing a cutout in the bonded piezoelectric element, and a lower surface of a surrounding ball of the bending vibration mode vibrator are clamped and fixed with a material having high thermal conductivity. It is composed of a fixed member, the upper and lower surface electrodes of the bonded piezoelectric element are short-circuited to form a common electrode, and the bonded surface electrode of the bonded piezoelectric element is separated between the electrode of the bending vibration mode vibrator portion and the surrounding electrode. The above-mentioned object is achieved by subtracting the signal from the surrounding electrodes of the bending vibration mode vibrator from the output signal of the bending vibration mode vibrator from the output signal of the bending vibration mode vibrator.

The present invention according to claim 2 corrects the acceleration signal from the flexural vibration mode vibrator by utilizing the capacitance change due to temperature between the bonding surface surrounding electrode and the common electrode according to claim 1, thereby achieving the above object. It is something to be achieved.

In the present invention as claimed in claim 1, the upper and lower surfaces of the periphery of the bending vibration mode vibrator are fixed by fixing members such as metals with high thermal conductivity, and heat from the surroundings passes through the fixing members and is almost absorbed by the vibrator. Because the heat is transmitted uniformly, temperature gradients depending on the location are reduced, and by attaching thin plates made of resin with poor thermal conductivity to the upper and lower surfaces of the fixing member, and molding the surrounding area with resin, the heat is transferred to the fixing member. The influence of a delay in transmission on the sensor output can be reduced.

Furthermore, the pyroelectric output due to the difference in the shape of the piezoelectric elements to be bonded can be reduced by subtracting the signal from the electrode around the bonded surface, which is the same piezoelectric element, from the sensor output signal.

In the second aspect of the present invention, since temperature correction is performed based on changes in the volume and weight of the same piezoelectric element, more accurate characteristics can be obtained.

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

The present invention as claimed in claim 1 aims to provide a highly accurate vibration acceleration sensor by reducing a pyroelectric output signal caused by a transient temperature change, and FIG. 1 shows an embodiment of the vibration acceleration sensor of the present invention. A block diagram showing an example, FIG. 2(a) is a bonded piezoelectric element, FIG. 2(b) is a perspective view showing electrodes of the bonded piezoelectric element, and FIG. FIG. 2 is an exploded perspective view showing the vibration detection unit. A "U"-shaped cutout is made by laser machining or the like into the bonded piezoelectric element 6, which has a structure in which plate-shaped piezoelectric elements 5 and 5', each having a polarization axis in the thickness direction and electrodes formed on the upper and lower surfaces, are bonded together. 8 (slit), and the part surrounded by the slit 8 is a flexural vibration mode oscillator 7 (
(hereinafter referred to as a bending vibrator). The bonded surface electrode of the bonded piezoelectric element 6 is separated into an electrode 5a of the bending vibrator 7 and a surrounding electrode 5b. Plate piezoelectric element 5.5'
In the parallel type, in which the electrodes are bonded together with their polarization axes aligned (arrows in FIG. 2), the upper and lower surface electrodes of the bending vibrator 7 are electrically connected and used as a common electrode. Become. The vibration detection unit 10 is made of a piezoelectric element bonded together with a fixing member 9 and 9' made of metal or the like having high thermal conductivity and having grooves 9a and 9b in the displaced portion of the bending vibrator 7 in order to fix the circumference of the bending vibrator 7. 6 is sandwiched and fixed by adhesive or the like. The signal output l of the bending vibrator 7 and the signal output 2 from the surrounding electrodes of the bending vibrator 7 are passed through an impedance conversion and amplification circuit 3.3', respectively, and the amplification circuit 3 is connected so that the output of the amplification circuit 3' is subtracted. .3
The output of ' is processed by the differential amplifier circuit 4 and used as a sensor output. By adopting such a structure, heat from the surroundings is transmitted through the fixed members 9 and 9', so that it is almost uniformly transmitted from the surrounding fixed parts to the bending vibrator 7, which is the acceleration detection part, and the temperature varies depending on the location. It reduces the slope.

Furthermore, the pyroelectric output caused by the difference in thickness etc. of the plate-shaped piezoelectric elements 5.5' to be bonded together is the signal output l of the bending vibrator 7.
and signal output 2 from the surrounding electrodes of the bending vibrator 7, but the signal output 2 from the surrounding electrodes, which are fixed parts and do not output acceleration signals, is subtracted from the signal output 1 of the bending vibrator 7. With this configuration, the pyroelectric output signal can be removed from the acceleration signal, and acceleration can be detected with high precision.

FIG. 4 is a longitudinal sectional view of the sensor, and FIG. 5 is an exploded perspective view of the sensor. Thin resin plates 12a and 12b with poor thermal conductivity such as printed circuit boards forming a signal processing circuit 13 consisting of an impedance conversion and amplification circuit 3.3'' and a differential amplification circuit 4 are formed on the upper and lower surfaces of the vibration detection unit) 10. Attach the
It constitutes a sensor basic unit (11), and is fixed to a housing 14 for attachment to 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 passes through the printed circuit board 12b, which has poor thermal conductivity, there is a time delay in transmission to the vibration detection unit (10f), and the signal component due to pyroelectricity is transmitted to a lower frequency. At the same time, the above (1
Since the time change in temperature expressed by the equation ) becomes smaller, 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 resin 16, the influence on the sensor signal can be roughly reduced. In this way, output signals caused by temperature changes can be reduced and acceleration can be detected with high precision.

The present invention according to claim 2 is intended to provide a highly accurate vibration acceleration sensor by correcting the sensitivity change of the sensor caused by temperature change using the same piezoelectric element, and FIG. 6 shows one embodiment of the present invention. FIG. 2 is a block diagram illustrating an example. The output signal l from the bending vibrator 7 is inputted to the voltage control amplifier (VCA) 20 through the impedance conversion and amplification circuit 3, and a common voltage control amplifier (VCA) 20 is connected to the bonded surface surrounding electrode 5b and the upper and lower surface electrodes of the bonded piezoelectric element. Electrode Garden Yo flt17
A pulse generating circuit 18 generates a pulse with a frequency corresponding to the capacitance using a DC signal from an integration/hold circuit 19 that integrates a constant signal according to the pulse period and holds the integrated value. )20 amplification factor is changed to obtain the sensor output signal. When the capacitance 17 changes with respect to temperature, the pulse period changes, so the integral value changes, and the control DC voltage to the voltage control amplifier 20 changes, so that the sensor output can be controlled with respect to the temperature.

Since the capacitance 17 is the value of the part composed of the same bonded piezoelectric element as the bending vibrator 7, it shows accurate temperature changes,
Highly accurate temperature correction can be performed.

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 l from the bending vibrator 7 is passed through impedance conversion and amplifier #1.
3 to the voltage control amplifier (VCA) 20, and the voltage from the pulse generator 22 is inputted to the voltage control amplifier (VCA) 20 through a common electrode (fl17) which short-circuits the bonded surface surrounding electrode 5b and the upper and lower surface electrodes of the bonded piezoelectric element. The DC voltage from the integration/hold circuit 21 that performs integration at a constant pulse period and holds the integration result is used as the M control voltage of the voltage control amplifier circuit 20. Since the integral value changes due to a change in the capacity fft17, 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, heat from the surroundings is almost uniformly transmitted to the vibrator through the fixed member, so temperature gradients depending on the location are reduced. Since a thin plate made of resin or the like having poor thermal conductivity is attached to the sensor and the surrounding area is molded with resin, it is possible to reduce the effect that a delay in heat transfer to the vibration detection unit has on the sensor output. The pyroelectric output due to the shape error of the bonded piezoelectric element can be reduced by subtracting the signals from the electrodes around the bonded surface having the same variation from the sensor output signal.

In 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 explanation of the drawing]

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 bonded piezoelectric element of the same embodiment, and FIG. 2(b) is a bonded piezoelectric element of the same embodiment. 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. 5 is a diagram of the sensor of the same embodiment. Exploded perspective view,
FIG. 6 is a block diagram showing one embodiment of the invention according to claim 2, and FIG. 7 is a block diagram showing another embodiment of the invention according to claim 2. l...Bending vibrator output, 2... Signal output from surrounding electrodes of the bending vibrator, 3.3'... Impedance conversion and amplification circuit, 4... Differential amplifier, 5.5'.・・・
Plate piezoelectric element, 5a, 5b...electrode, 6...bonded piezoelectric element, 7...bending vibration mode vibrator, IO・
...Vibration detection unit, 11...Sensor basic unit, 13...Signal processing circuit, ]7...Capacitance around bending vibrator, 18.21...Pulse generation circuit, 19.
21... Integration/hold circuit, 20... Voltage control amplifier. Name of agent: Patent attorney Shigetaka Awano No. 1] Fig.] Flexural oscillator ratio No. 8 Nda music 1 shaku ) Fig. Fig. Fig. 22 Pulse starting times

Claims (2)

[Claims] (1) A bonded piezoelectric element having a structure in which two plate-shaped piezoelectric elements having polarization axes in the thickness direction and electrodes on the upper and lower surfaces are bonded together so that the polarization axes are in the same direction, and the bonding The bonded piezoelectric element includes a bending vibration mode vibrator formed by providing a cutout in a piezoelectric element, and a fixing member that clamps and fixes the upper and lower surfaces of the periphery of the bending vibration mode vibrator with a material having high thermal conductivity. The upper and lower surface electrodes of the bonded piezoelectric element are short-circuited to form a common electrode, and the bonded surface electrode of the bonded piezoelectric element is separated by the electrode of the bending vibration mode vibrator portion and the surrounding electrode to serve as signal extraction electrodes. A vibration acceleration sensor characterized in that a signal of a surrounding electrode of the bending mode vibrator is subtracted from an output signal of the mode vibrator. (2) A bonded piezoelectric element having a structure in which two plate-shaped piezoelectric elements having polarization axes in the thickness direction and electrodes on the upper and lower surfaces are bonded together so that the polarization axes are in the same direction, and the bonding The bonded piezoelectric element includes a bending vibration mode vibrator formed by providing a cutout in a piezoelectric element, and a fixing member that clamps and fixes the upper and lower surfaces of the periphery of the bending vibration mode vibrator with a material having high thermal conductivity. The upper and lower surface electrodes of the bonded piezoelectric element are short-circuited to form a common electrode, and the bonded surface electrode of the bonded piezoelectric element is separated by the electrode of the bending vibration mode vibrator portion and the surrounding electrode, and the bonded surface surrounding electrode and the A vibration acceleration sensor characterized in that an acceleration signal from the bending vibration mode vibrator is corrected by using a capacitance value between common electrodes.