CN111060250B - Device for correcting piezoelectric coefficient under dynamic force and corresponding method - Google Patents

Device for correcting piezoelectric coefficient under dynamic force and corresponding method Download PDF

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CN111060250B
CN111060250B CN201911412114.6A CN201911412114A CN111060250B CN 111060250 B CN111060250 B CN 111060250B CN 201911412114 A CN201911412114 A CN 201911412114A CN 111060250 B CN111060250 B CN 111060250B
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高硕�
陈君亮
代晏宁
石佳卉
刘勇
徐立军
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Abstract

The invention discloses a correction dynamic stateThe method decomposes the original piezoelectric signal into a plurality of eigen-mode functions by empirical mode decomposition, then performs Hilbert-Huang transform on each eigen-mode function to obtain the instantaneous frequency of each frequency component, and substitutes the instantaneous frequency into the eigen-mode functions
Figure DEST_PATH_IMAGE002
The original piezoelectric signal is corrected. The invention successfully completes the piezoelectric coefficient correction of the piezoelectric material applied to the multi-frequency component environment by introducing the Hilbert transform, has the advantages of easy realization, convenient popularization and the like according to the algorithm principle and the application method, and has pioneering property in the field of correcting the piezoelectric coefficient of the piezoelectric material. The method is suitable for the technical field of correction of piezoelectric coefficients of piezoelectric materials, and is also suitable for the technical fields of bridge detection, rail monitoring and the like.

Description

Device for correcting piezoelectric coefficient under dynamic force and corresponding method
Technical Field
The invention belongs to the technical field of piezoelectric signal detection, and relates to a device and a corresponding method for correcting a piezoelectric coefficient under a dynamic force.
Background
In recent years, piezoelectric materials have been used more and more widely in life and work. In many application scenarios, it is necessary to measure the force applied to the piezoelectric material from the piezoelectric signal. A typical piezoelectric signal often includes many frequency components (frequency components), the frequency of the signal of different frequency components is different, and the piezoelectric coefficient d33Is a function of the frequency of the dynamic force, the dynamics at different frequenciesUnder force d33The value of (c) is different.
At present, the piezoelectric coefficient d is often measured in force measurement33This is considered a constant value, which causes an error in the force measurement.
Disclosure of Invention
The invention aims to provide a device for correcting piezoelectric coefficient under dynamic force.
The present invention further provides a method for correcting piezoelectric coefficient under dynamic force, which is implemented by introducing hilbert transform to correct piezoelectric coefficient of piezoelectric material under multi-frequency component environment.
In order to achieve the purpose, the invention adopts the following technical scheme:
a device for correcting piezoelectric coefficients under dynamic force comprises a signal acquisition unit, a charge amplification circuit, a multiplexer, an analog-to-digital converter, a microcontroller, a Bluetooth module and an upper computer;
the signal acquisition unit is connected with the input end of the multiplexer through the charge amplification circuit, the output end of the multiplexer is connected with the signal input end of the analog-to-digital converter, and the analog-to-digital converter is connected with the upper computer through the microcontroller and the Bluetooth module;
the signal acquisition unit comprises a piezoelectric material.
The method for correcting the piezoelectric coefficient under the dynamic force is realized by the device for correcting the piezoelectric coefficient under the dynamic force, and the method is carried out according to the following steps in sequence:
firstly, obtaining the original piezoelectric signal
When pressure is applied to the signal acquisition unit, the piezoelectric material generates charges and outputs the charges to the charge amplification circuit, the charge amplification circuit processes the collected charges and sends the result to the analog-to-digital converter through the multiplexer, the analog-to-digital converter converts the received analog voltage signal into a digital signal and outputs the digital signal to the microcontroller for caching, and the microcontroller sends the cached data to an upper computer through the Bluetooth module, so that the upper computer obtains an original piezoelectric signal s (t);
secondly, performing Hilbert-Huang transform to obtain the instantaneous frequency of each eigenmode function, wherein the step is performed according to the following steps in sequence,
A. decomposing the original piezoelectric signal s (t) into at least two eigenmode functions by empirical mode decomposition, wherein each eigenmode function satisfies the following conditions,
3) in a data-time curve, the difference between the number of extreme values and the number of zero-crossing points is 0 or 1;
4) at any point, the average of the envelope defined by the local maxima and by the local minima is 0;
B. hilbert transform
From the analysis signal sa(t)＝s(t)+jsh(t)＝A(t)ejθ(t)The primary piezoelectric signal s (t) is expressed as an analysis signal saThe Real part of (t), i.e. s (t) ═ Real [ a (t) ejθ(t)]，
It is further possible to analyze the signal saThe imaginary part of (t) is
Figure GDA0002845931610000021
C. Empirical AM-FM decomposition is performed to analyze the signal sa(t) is unit amplitude;
D. taking the extreme envelope curve E of the original piezoelectric signal s (t)1(t)、E2(t) for the portion where the primary electrical signal s (t) is greater than 0, using E1(t) performing normalization; for the part of the original piezoelectric signal s (t) less than 0, use E2(t) normalization, i.e.
Figure GDA0002845931610000022
Up to | E1(t)-E2(t) | tends to 0 over the full time domain;
E. the instantaneous frequency is obtained by using the exponential form of the original piezoelectric signal s (t)
According to the formula
Figure GDA0002845931610000031
Obtaining the instantaneous frequency of each eigenmode function;
thirdly, substituting the instantaneous frequency of each eigenmode functionFrequency relation curve d of piezoelectric coefficient and dynamic force33The f curve is used for correcting the original piezoelectric coefficient, so that the correction of the piezoelectric coefficient under the dynamic force is completed;
wherein the corrective formula is
Figure GDA0002845931610000032
d330The piezoelectric coefficient used before the correction is not achieved.
As a limitation, in the second step, the empirical mode decomposition process is performed according to the following sequence of steps:
s1, connecting all local maximum values of the original voltage signals S (t) by three sample lines, and calculating the average value m of all local maximum values1(t)；
S2, comparing the original piezoelectric signal S (t) with the average value m1(t) making a difference, and calculating by the formula h10(t)＝s(t)-m1(t)；
S3, if h10(t) does not satisfy condition 1) or 2), then h will be10(t) repeating the steps in place of the original piezoelectric signal s (t)
S1-S2, the calculation formula is h11(t)＝h10(t)-m10(t)；
S4, and so on, if the calculation result h1(k-1)(t) does not satisfy condition 1) or 2), then h will be1(k-1)(t) repeating the steps S1-S2 instead of the original piezoelectric signal S (t), wherein the calculation formula is h1k(t)＝h1(k-1)(t)-m1(k-1)(t)；
Until the calculation result satisfies the conditions 1) and 2), the first eigenmode function IMF is obtained1；
Wherein m is1(k-1)(t) is h1(k-1)(t) the average value of the envelope lines, k is more than or equal to 1;
s5, Slave S1(t) starting with S1-S4, wherein S1(t)＝s(t)-IMF1；
S6, finally decomposing the original piezoelectric signal S (t) into IMFiAnd error term rk(t) sum, i.e.
Figure GDA0002845931610000033
Wherein, IMFiRepresents the ith eigenmode function, i ≧ 2.
Due to the adoption of the technical scheme, compared with the prior art, the invention has the technical progress that:
(1) the invention successfully completes the piezoelectric coefficient correction of the piezoelectric material applied to the multi-frequency component environment by introducing the Hilbert transform, has the advantages of easy realization, convenient popularization and the like according to the algorithm principle and the application method, and has pioneering property in the field of correcting the piezoelectric coefficient of the piezoelectric material;
(2) the method provided by the invention can be used for correcting the data of the piezoelectric gait sensor to obtain more accurate gait signals, and has important significance for the researches such as clinical disease diagnosis, postoperative effect evaluation, rehabilitation degree evaluation and the like;
(3) the invention also provides a new method for separating different frequency components from the original piezoelectric signal to determine the source of the specific frequency component, and is also suitable for the technical fields of bridge detection, rail monitoring and the like.
The method is suitable for the technical field of correction of the piezoelectric coefficient of the piezoelectric material.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention.
In the drawings:
FIG. 1 is a schematic block diagram of embodiment 1 of the present invention;
FIG. 2 is a flowchart of example 2 of the present invention;
FIG. 3 is a diagram of original signals of embodiment 2 of the present invention;
FIG. 4 is an exemplary signal diagram in step three of embodiment 2 of the present invention;
FIGS. 5-6 are schematic diagrams of eigenmode function extraction according to embodiment 2 of the present invention;
IMF in FIG. 71-IMF4Corresponding to the first to fourth eigenmode function diagrams of embodiment 2 of the present invention, respectively;
FIG. 8 is an instantaneous frequency chart of the first to fourth eigenmode functions according to embodiment 2 of the present invention;
FIG. 9 shows an embodiment 2 of the present invention for the eigenmode function IMF1Schematic illustration of normalization;
FIG. 10 is an IMF of embodiment 2 of the present invention1A graph of the normalized results;
FIG. 11 is a diagram showing the effects of embodiment 2 of the present invention before and after correction of an original piezoelectric signal;
FIG. 12 is a graph showing the dependence of the piezoelectric coefficient on the frequency of the dynamic force according to the present invention.
Detailed Description
Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for purposes of illustration and explanation only and are not intended to limit the present invention.
Embodiment 1 a device for correcting piezoelectric coefficient under dynamic force
As shown in fig. 1, the present embodiment includes a signal acquisition unit, a charge amplification circuit, a multiplexer, an analog-to-digital converter, a microcontroller, a bluetooth module, and an upper computer. The signal acquisition unit is connected with the input end of the multiplexer through the charge amplification circuit, the output end of the multiplexer is connected with the signal input end of the analog-to-digital converter, and the analog-to-digital converter is connected with the upper computer through the microcontroller and the Bluetooth module and uploads data to the upper computer for subsequent processing. Wherein, the signal acquisition unit comprises a piezoelectric material.
Embodiment 2 method for correcting piezoelectric coefficient under dynamic force
This embodiment is implemented by embodiment 1, and as shown in fig. 2, the following steps are performed in this order:
firstly, acquiring an original piezoelectric signal;
secondly, performing Hilbert-Huang transformation on the original piezoelectric signal;
and thirdly, correcting the original piezoelectric coefficient, and further correcting the original piezoelectric signal.
When pressure is applied to the signal acquisition unit, the piezoelectric material generates charges and outputs the charges to the charge amplifier, the charge amplifier processes the collected charges and sends the result to the analog-to-digital converter through the multiplexer, the analog-to-digital converter converts the received analog voltage signal into a digital signal and outputs the digital signal to the microcontroller for caching, and the microcontroller sends cached data to an upper computer through the Bluetooth module, so that the upper computer obtains an original piezoelectric signal s (t) as shown in fig. 3.
Step two, comprising the following processes: a. decomposing the original piezoelectric signal into a plurality of eigen-mode functions through empirical mode decomposition; b. performing Hilbert transform on each eigenmode function; c. and decomposing each eigenmode function by using empirical amplitude modulation-frequency modulation, taking out the frequency modulation part of each eigenmode function, and further obtaining the instantaneous frequency of each frequency component.
In the second step, in order to avoid the situation that the instantaneous frequency is negative and the like, which is not meaningful physically, before hilbert transformation is performed, empirical mode decomposition needs to be performed on the original piezoelectric signal s (t), and the original piezoelectric signal is decomposed into a plurality of eigenmode functions, wherein each eigenmode function should satisfy the following two conditions, 1) in a data-time curve, the difference between the number of extreme values and the number of zero-crossing points is 0 or 1; 2) at any point, the average of the envelope defined by the local maxima and by the local minima is 0.
The empirical mode decomposition process is illustrated by taking the signals shown in fig. 4 as an example:
s1, as shown in FIG. 5, connecting the original voltage signals S (t) with three sample lines, and calculating the average value m of all local maximum values1(t)；
S2, comparing the original piezoelectric signal S (t) with the average value m1(t) making a difference, and calculating by the formula h10(t)＝s(t)-m1(t), the results are shown in FIG. 6,
s3, if h10(t) does not satisfy condition 1) or 2), then h will be10(t) repeating the steps S1-S2 instead of the original piezoelectric signal S (t), wherein the calculation formula is h11(t)＝h10(t)-m10(t)；
S4, and so onIf the result h is calculated1(k-1)(t) does not satisfy condition 1) or 2), then h will be1(k-1)(t) repeating the steps S1-S2 instead of the original piezoelectric signal S (t), wherein the calculation formula is h1k(t)＝h1(k-1)(t)-m1(k-1)(t)；
Until the calculation result satisfies the conditions 1) and 2), the first eigenmode function IMF is obtained1；
Wherein m is1(k-1)(t) is h1(k-1)(t) the average value of the envelope lines, k is more than or equal to 1;
s5, Slave S1(t) starting with S1-S4, wherein S1(t)＝s(t)-IMF1；
S6, finally decomposing the original piezoelectric signal S (t) into IMFiAnd error term rk(t) sum, i.e.
Figure GDA0002845931610000061
Wherein, IMFiRepresents the ith eigenmode function, i ≧ 2.
For example, i.gtoreq.4 is shown in FIG. 7 as a graph of the first to fourth eigenmode functions, and shown in FIG. 8 as a graph of the instantaneous frequencies of the first to fourth eigenmode functions.
The hilbert transform in step b is performed according to the following method: from the analysis signal sa(t)＝s(t)+jsh(t)＝A(t)ejθ(t)The primary piezoelectric signal s (t) is expressed as an analysis signal saThe Real part of (t), i.e. s (t) ═ Real [ a (t) ejθ(t)](ii) a It is further possible to analyze the signal saThe imaginary part of (t) is
Figure GDA0002845931610000062
(convolution).
According to Berdesy-Seisan's theorem, the amplitude-modulated part of the signal affects the accuracy of the instantaneous frequency, in order to compare A (t) with ejθ(t)By separating amplitude modulation from frequency modulation (AM-FM) of the signal, we need to perform empirical AM-FM decomposition to analyze the signal saA (t) of (t) is unit amplitude. The empirical amplitude modulation-frequency modulation decomposition is carried out according to the following steps:
c. taking the example shown in FIG. 9, the extreme envelope E of the original piezoelectric signal s (t) is taken1(t)、E2(t) for signal greater than 0, using E1(t) performing normalization; for the part with signal less than 0, use E2(t) normalization, i.e.
Figure GDA0002845931610000071
Up to | E1(t)-E2(t) | goes to 0 over the full time domain, with the results shown in FIG. 10.
Then, the instantaneous frequency of each frequency component is obtained by using the exponential form of the original piezoelectric signal s (t), and the specific process is as follows: according to the formula
Figure GDA0002845931610000072
The instantaneous frequency of each eigenmode function is obtained.
All the instantaneous frequencies of the eigenmode functions are substituted into the frequency relation curve d of the piezoelectric coefficient and the dynamic force as shown in FIG. 1233The f curve is used for correcting the original piezoelectric signal, so that the correction of the piezoelectric coefficient under the dynamic force is completed; wherein the corrective formula is
Figure GDA0002845931610000073
d330The piezoelectric coefficient used before the correction is not achieved.
And finally, the corrected piezoelectric coefficient is adopted to finish the correction of the original piezoelectric signal. As shown in fig. 11, the signal is compared before and after correction.

Claims (2)

1. A method for correcting the piezoelectric coefficient under the dynamic force is realized by adopting a device for correcting the piezoelectric coefficient under the dynamic force, wherein the device for correcting the piezoelectric coefficient under the dynamic force comprises a signal acquisition unit, a charge amplification circuit, a multiplexer, an analog-to-digital converter, a microcontroller, a Bluetooth module and an upper computer;
the signal acquisition unit is connected with the input end of the multiplexer through the charge amplification circuit, the output end of the multiplexer is connected with the signal input end of the analog-to-digital converter, and the analog-to-digital converter is connected with the upper computer through the microcontroller and the Bluetooth module;
the signal acquisition unit comprises a piezoelectric material;
the method for correcting the piezoelectric coefficient under the dynamic force is characterized by comprising the following steps:
firstly, obtaining the original piezoelectric signal
When pressure is applied to the signal acquisition unit, the piezoelectric material generates charges and outputs the charges to the charge amplification circuit, the charge amplification circuit processes the collected charges and sends the result to the analog-to-digital converter through the multiplexer, the analog-to-digital converter converts the received analog voltage signal into a digital signal and outputs the digital signal to the microcontroller for caching, and the microcontroller sends the cached data to an upper computer through the Bluetooth module, so that the upper computer obtains an original piezoelectric signal s (t);
secondly, performing Hilbert-Huang transform to obtain the instantaneous frequency of each eigenmode function, wherein the step is performed according to the following steps in sequence,
A. decomposing the original piezoelectric signal s (t) into at least two eigenmode functions by empirical mode decomposition
Wherein each eigenmode function satisfies the following condition,
1) in a data-time curve, the difference between the number of extreme values and the number of zero-crossing points is 0 or 1;
2) at any point, the average of the envelope defined by the local maxima and by the local minima is 0;
B. hilbert transform
From the analysis signal sa(t)＝s(t)+jsh(t)＝A(t)ejθ(t)The primary piezoelectric signal s (t) is expressed as an analysis signal saThe Real part of (t), i.e. s (t) ═ Real [ a (t) ejθ(t)]，
It is further possible to analyze the signal saThe imaginary part of (t) is
Figure FDA0002845931600000021
C. Empirical AM-FM decomposition is performed to analyze the signal saA (t) of (t) is unit amplitude；
D. Taking the extreme envelope curve E of the original piezoelectric signal s (t)1(t)、E2(t) for the portion where the primary electrical signal s (t) is greater than 0, using E1(t) performing normalization; for the part of the original piezoelectric signal s (t) less than 0, use E2(t) normalization, i.e.
Figure FDA0002845931600000022
Up to | E1(t)-E2(t) | tends to 0 over the full time domain;
E. the instantaneous frequency is obtained by using the exponential form of the original piezoelectric signal s (t)
According to the formula
Figure FDA0002845931600000023
Obtaining the instantaneous frequency of each eigenmode function;
thirdly, substituting the instantaneous frequency of each eigenmode function into a frequency relation curve d of the piezoelectric coefficient and the dynamic force33The f curve is used for correcting the original piezoelectric coefficient, so that the correction of the piezoelectric coefficient under the dynamic force is completed;
wherein the corrective formula is
Figure FDA0002845931600000024
d330The piezoelectric coefficient used before the correction is not achieved.
2. The method for correcting piezoelectric coefficient under dynamic force according to claim 1, wherein in the second step, the empirical mode decomposition is performed according to the following sequence of steps:
s1, connecting all local maximum values of the original voltage signals S (t) by three sample lines, and calculating the average value m of all local maximum values1(t)；
S2, comparing the original piezoelectric signal S (t) with the average value m1(t) making a difference, and calculating by the formula h10(t)＝s(t)-m1(t)；
S3, if h10(t) does not satisfy condition 1) or 2), then h will be10(t) replacing the original piezoelectric signal s (t), andrepeating the steps S1-S2, wherein the calculation formula is h11(t)＝h10(t)-m10(t)；
S4, and so on, if the calculation result h1(k-1)(t) does not satisfy condition 1) or 2), then h will be1(k-1)(t) repeating the steps S1-S2 instead of the original piezoelectric signal S (t), wherein the calculation formula is h1k(t)＝h1(k-1)(t)-m1(k-1)(t)；
Until the calculation result satisfies the conditions 1) and 2), the first eigenmode function IMF is obtained1；
Wherein m is1(k-1)(t) is h1(k-1)(t) the average value of the envelope lines, k is more than or equal to 1;
s5, Slave S1(t) starting with S1-S4, wherein S1(t)＝s(t)-IMF1；
S6, finally decomposing the original piezoelectric signal S (t) into IMFiAnd error term rk(t) sum, i.e.
Figure FDA0002845931600000031
Wherein, IMFiRepresents the ith eigenmode function, i ≧ 2.
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Publication number Priority date Publication date Assignee Title
US5444641A (en) * 1993-09-24 1995-08-22 Rockwell International Corporation Admittance-parameter estimator for a piezoelectric resonator in an oscillator circuit
JP2005233789A (en) * 2004-02-19 2005-09-02 Nsk Ltd Abnormality diagnosis method of rotary machine, abnormality diagnosis apparatus, and abnormality diagnosis system
CN101000293A (en) * 2007-01-18 2007-07-18 南京航空航天大学 Investigating method for impact position of aircraft laminated structure and its investigating device
CN104535229A (en) * 2014-12-04 2015-04-22 广东省自动化研究所 Pressure detection device and method based on piezoresistive and piezoelectric flexible sensor combination
CN107569226A (en) * 2017-09-27 2018-01-12 广州中科新知科技有限公司 HRV method and application is obtained based on piezoelectric sensing

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5444641A (en) * 1993-09-24 1995-08-22 Rockwell International Corporation Admittance-parameter estimator for a piezoelectric resonator in an oscillator circuit
JP2005233789A (en) * 2004-02-19 2005-09-02 Nsk Ltd Abnormality diagnosis method of rotary machine, abnormality diagnosis apparatus, and abnormality diagnosis system
CN101000293A (en) * 2007-01-18 2007-07-18 南京航空航天大学 Investigating method for impact position of aircraft laminated structure and its investigating device
CN104535229A (en) * 2014-12-04 2015-04-22 广东省自动化研究所 Pressure detection device and method based on piezoresistive and piezoelectric flexible sensor combination
CN107569226A (en) * 2017-09-27 2018-01-12 广州中科新知科技有限公司 HRV method and application is obtained based on piezoelectric sensing

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