CN108955866B - Piezoelectric vibration frequency sensor system based on bias flip circuit - Google Patents
Piezoelectric vibration frequency sensor system based on bias flip circuit Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H11/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by detecting changes in electric or magnetic properties
- G01H11/06—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by detecting changes in electric or magnetic properties by electric means
- G01H11/08—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by detecting changes in electric or magnetic properties by electric means using piezoelectric devices
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Abstract
A piezoelectric vibration frequency sensor system based on a bias flip circuit consists of a piezoelectric energy collector and a signal conditioning circuit; directly detecting sinusoidal vibration through a piezoelectric energy collector, and converting the vibration into corresponding output voltage; processing the output voltage through a signal conditioning circuit to obtain an output voltage signal reflecting the vibration frequency; in addition, the sensor system is relatively simple and can directly measure sinusoidal vibration frequencies.
Description
Technical Field
The invention belongs to the field of sensors, and particularly relates to a piezoelectric vibration frequency sensor system based on a bias flip circuit.
Background
The phenomenon of mechanical vibration is common in aspects of production and life, and it is desirable to control the mechanical vibration to better serve the production and life of humans. In most cases, however, mechanical vibrations are detrimental, for example, vibration phenomena can lead to mechanical failure and even to destruction of the whole production system, with serious consequences such as economic losses, casualties, environmental pollution, etc. In order to reduce the damage of mechanical vibration, ensuring the safe and reliable operation of mechanical equipment, the real-time monitoring of the mechanical vibration and the early diagnosis of mechanical faults are very important. Currently, common methods for monitoring and analyzing mechanical vibration in real time include: vibration measurement and analysis, oil sample analysis, flaw detection, noise detection, and the like, among which vibration measurement and analysis are a relatively effective method.
In recent years, various vibration sensors have appeared on the market, and can be largely classified into two types: non-contact sensor system and contact sensor system. The non-contact sensor system is mainly composed of capacitance, inductance, optical elements and the like, and achieves a certain effect to a certain extent. However, the sensor system based on capacitance and inductance has poor electromagnetic interference resistance, the sensor system based on optical elements is easily affected by factors such as rough surfaces, opaque gases, dust and the like, and the non-contact sensor system has a relatively complex structure and high cost. The touch sensor system measures the vibration of the surface of the object by using sensors such as accelerometers or probes, and is relatively simple, low in cost and good in effect compared with the non-touch sensor system.
However, existing vibration sensor systems, either contact or non-contact, suffer from the following drawbacks:
(1) Most vibration sensor systems directly measure the displacement, velocity and acceleration of vibration, but cannot directly reflect the magnitude of the vibration frequency. The existing scheme for measuring the vibration frequency is complex in system and high in cost, for example, the vibration acceleration and displacement signal frequency spectrums are measured through a frequency spectrum analyzer to measure the vibration frequency;
(2) To obtain frequency information from these common sensor systems, additional conversion or processing units must be added, resulting in a more complex, redundant system, and increased cost of use.
Disclosure of Invention
Aiming at the problems of the existing vibration sensor system, the piezoelectric vibration frequency sensor system based on the bias overturning circuit provided by the invention consists of a piezoelectric energy collector and a signal conditioning circuit; directly detecting sinusoidal vibration through a piezoelectric energy collector, and converting the vibration into corresponding output voltage; and processing the output voltage through a signal conditioning circuit to obtain an output voltage signal reflecting the vibration frequency. In addition, the sensor system is relatively simple and can directly measure sinusoidal vibration frequencies.
A piezoelectric vibration frequency sensor system based on a bias flip circuit, as shown in fig. 1, comprising: piezoelectric energy collector and signal conditioning circuit.
The piezoelectric energy collector adopts a piezoelectric cantilever beam structure, and is clamped and fixed on the vibrating table. The function signal generator generates a sine output signal, and the sine output signal is amplified by the power amplifier and then is input to the vibration table to generate corresponding sine vibration. Under the influence of input sinusoidal vibration excitation, based on the piezoelectric effect, the piezoelectric materials of the upper layer and the lower layer of the piezoelectric cantilever beam generate stretching or compression deformation due to vibration, so that sinusoidal output voltage is formed. Thus, the piezoelectric energy harvester can convert the sinusoidal vibration frequency into a corresponding sinusoidal output voltage.
The signal conditioning circuit consists of a bias overturning circuit, a pulse shaper and a low-pass filter, and can be used for processing the sine output voltage of the piezoelectric energy collector and outputting a voltage signal related to the vibration frequency.
The bias flip circuit is shown in phantom in fig. 2. The bias flip circuit is formed by an inductorAnd MOS switch, the circuit shown in the unshaded part of figure 2 is an equivalent circuit model of the piezoelectric energy collecting device. Voltage->For MOS switch control voltage, when the switch is closed, the inductor is +.>And capacitance->Constitute high frequency->Resonant tank, at the same time the->The resonant tank begins to oscillate; through->The switch is switched off and the capacitor is switched off in each oscillation period>The voltage on is>Turned into->The method comprises the steps of carrying out a first treatment on the surface of the Once the output current of the piezoelectric energy harvester is +.>The zero crossing or sign change, the bias flip circuit will work, so its output voltage +.>And current->Is in phase. In summary, the bias flip circuit can be used for tracking the zero point of the output current of the piezoelectric energy collector and turning the polarity of the output voltage of the piezoelectric energy collector so as to realize vibration frequency tracking and obtain the output voltage of the bias flip circuit at the same time>。
The pulse shaper, as shown in fig. 3, is connected with the bias flip circuit and mainly comprises:the differential circuit, the voltage comparator and the monostable trigger are connected in sequence. Said->The differentiating circuit biases the flip-flop voltage signal +.>Conversion to periodic spike signal +.>The specific values of capacitance and resistance in the differentiating circuit are determined by the vibration frequency and +.>Time constant->And (5) determining. />Time constant->And vibration period->The following relationship should be satisfied: />Thus, at the rising and falling edges of the bias flip-flop signal, the output voltage of the differentiating circuit +.>Higher pulse peaks occur, thereby facilitating the processing of the later stage voltage comparator; the voltage comparator is connected with->The differentiating circuit is connected by comparing the spikes +.>And a DC reference voltage>Can be sharp pulse->Conversion into rectangular pulses>The pulse width of the rectangular pulse changes along with the vibration frequency, and in order to obtain a better conversion effect, the direct current reference voltage is +.>Should be less than 50mV; the monostable trigger is connected with the voltage comparator and positioned at the tail end of the pulse shaper and can change the rectangular pulse with the pulse width +.>Converted into rectangular pulses with fixed pulse widthWith the monostable flip-flop, a periodic rectangular pulse with a constant pulse width and a constant high level can be obtained. In summary, the output voltage of the bias flip circuit can be +_ by the pulse shaper>Conversion to rectangular pulses of fixed pulse width and high level。
The low-pass filter, as shown in FIG. 4, is located at the end of the signal modulation circuit and is formed by a first orderThe low-pass filter and the second-order Sallen-Key low-pass filter. A low pass filter may be used to filter out rectangular pulses of fixed pulse width and high levelTo extract the DC component +.>Thereby obtaining a specific value of the vibration frequency +.>。
Theoretically, the process of acquiring the sinusoidal vibration frequency is as follows:
the specific mathematical expression of the periodic rectangular pulse with the fixed pulse width and the high level is as follows:
wherein,representing pulse width +.>Indicates period, & lt + & gt>Is the output voltage high level. Function->The fourier series form of (a) can be expressed as:
from the above, it can be seen that the DC component and pulse width of the periodic rectangular pulse with fixed pulse width and high levelPeriod->Output voltage high level->Related to the following. During vibration, if +_ can be ensured>And->The direct current component is unchanged only with period +.>In this connection, the frequency of vibration can thus be determined from the direct current component.
The specific form of the third-order Sallen-Key low-pass filter transfer function is as follows:
wherein,is the cut-off frequency of the first order RC filter, < >>Is the cut-off frequency of the second order Sallen-Key filter,is the attenuation coefficient. />A value of 0.707 to obtain a maximum passband frequency response; />And->The value of (2) may be +.>So as to obtain better filtering effect.
As described above, the low pass filter can extract the dc componentBy direct current component->Calculate vibration frequency +.>The method of (2) is as follows:
a piezoelectric vibration frequency sensor based on a bias flip circuit can directly measure sinusoidal vibration frequency, and the system is relatively simple, low in cost and has accurate measurement results in a wider frequency range.
Drawings
FIG. 1 is a schematic diagram of a piezoelectric vibration frequency sensor system based on a bias flip circuit of the present invention;
FIG. 2 is a schematic diagram of the bias flip circuit of the present invention;
FIG. 3 is a schematic diagram of the pulse shaper of the present invention;
FIG. 4 is a schematic diagram of the low pass filter of the present invention;
FIG. 5 is a schematic diagram of the experimental set-up;
FIG. 6 is a measured waveform of a vibration frequency sensor system according to the present invention at 300 Hz;
FIG. 7 is a filter output voltageTheoretical, simulation and actual measurement results.
Detailed Description
The experimental apparatus of the specific embodiment is shown in fig. 5, and includes: the system comprises a digital oscilloscope, a function signal generator, a signal conditioning circuit, a power amplifier, a piezoelectric energy collector, a vibrating table, a driving power supply and the like. Wherein the piezoelectric energy collector is fixed on the vibrating table through a clamp.
The minimum value of the vibration frequency in the specific embodiment is 200Hz, and the cutoff frequencyAnd->The value of (2) is 10Hz.
In this embodiment, the corresponding DC component is used when the vibration frequency is 300HzThe theoretical value of (2) is 750mV, the experimental waveform of the vibration frequency sensor system is shown in FIG. 6, the DC component +.>Is 752.47mV, very close to the theoretical value.
In addition, when the vibration frequency is increased from 200Hz to 500Hz, the vibration frequency and the voltageThe relationship is shown in fig. 7. As can be seen from fig. 7: the theoretical result is proportional to the vibration frequency; the simulation result is also proportional to the vibration frequency and is very close to a theoretical curve; in addition, the measured results are very close to the theoretical and simulation results.
Claims (1)
1. A piezoelectric vibration frequency sensor system based on a bias flip circuit, characterized in that: comprising the following steps: a piezoelectric energy collector and a signal conditioning circuit; the signal conditioning circuit consists of a bias overturning circuit, a pulse shaper and a low-pass filter, and can be used for processing the sine output voltage of the piezoelectric energy collector and outputting a voltage signal related to the vibration frequency; the bias flip circuit is formed by an inductorAnd MOS switch for tracking piezoelectric energyThe quantity collector outputs a current zero point and turns over the polarity of the output voltage of the piezoelectric energy collector so as to realize vibration frequency tracking, and meanwhile, the output voltage of the bias turning circuit is obtained>The method comprises the steps of carrying out a first treatment on the surface of the The pulse shaper is connected with the bias flip circuit and mainly comprises: />The differential circuit, the voltage comparator and the monostable trigger are connected in sequence; the output voltage of the bias flip-flop can be +.>Rectangular pulse converted into fixed pulse width and high level +.>The method comprises the steps of carrying out a first treatment on the surface of the Said->The differentiating circuit biases the flip-flop voltage signal +.>Conversion to periodic spike signal +.>The specific values of capacitance and resistance in the differentiating circuit are determined by the vibration frequency and +.>Time constant->Determining; />Time constant->And vibration period->The following relationship should be satisfied: />The method comprises the steps of carrying out a first treatment on the surface of the The voltage comparator is connected with->The differentiating circuit is connected; the low-pass filter is positioned at the tail end of the signal modulation circuit and consists of first order +.>The filter and the second-order Sallen-Key low-pass filter are formed, and the low-pass filter can be used for filtering rectangular pulses with fixed pulse width and high level>To extract the DC component +.>Thereby obtaining a specific value of the vibration frequency +.>。
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| US9344014B2 (en) * | 2012-09-05 | 2016-05-17 | Texas Instruments Incorporated | Piezoelectric device |
| US10056849B2 (en) * | 2015-01-09 | 2018-08-21 | Analog Devices Global | Piezoelectric energy harvesting system with frequency mismatch tolerance |
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