CN103811017A - Improved method for estimating noise power spectrum of punch press based on Welch method - Google Patents

Abstract

A kind of punching machine noise power Power estimation improved method based on Welch method, steps are as follows: initialization power composes detection device; Using punching machine blanking control signal as beginning sampling trigger signal; Punching machine is withdrawn into hydraulic hammer control signal as end sampling trigger signal; Noise sample windowing process to collecting; The sequence of average of effective noise is calculated with alternative manner Effective noise average sequence is stored, iteration count adds 1, i=i+1; It steps be repeated alternatively until iteration count i=R; Divide S sections for the sequence of average of effective noise, every segment length is M, and adjacent two sections of length of overlapped part are M/2; The Blackman window W (n) that smoothing windows are M for length is selected, pair so seeking leaf transformation in each section of L point discrete Fourier after sectionally smooth; The weighted average for asking the discrete Fourier transform square of all segmentations obtains the power Spectral Estimation value of blanking noise

Description

A kind of punch press noise power spectrum based on Welch method is estimated to improve one's methods

Technical field

The present invention relates to a kind of the Power Spectrum Estimation Method for field of noise control, specifically a kind of punch press noise power spectrum based on Welch method is estimated to improve one's methods.

Background technology

In industrial processes, concrete in the course of work of punch press, punch press clashes into material can produce a kind of stamping-out noise.This noise has: the feature of repeatability, short-time characteristic, high strength.This repeated impact noise can cause the acoustic fatigue of machinery and equipment, and long term will shorten its serviceable life, even production development accident.Strong noise very easily forms beat type infrasonic wave, effect and people's body.All there is natural frequency in each position of human body, health is 7-13HZ, and internal organ are 4-6HZ, and head is 8-12HZ, and these natural frequencys just in infrasonic wave frequency band, so pressman works in intense noise environment, often have and feel dizzy, feel sick and the sense of palpitaition.Reduce punch press noise and become the task of top priority in noise control engineering.

No matter be all to need noise to detect by traditional passive noise cancellation technology or novel active noise silencing technology, for noise control provides the prior imformation of noise.Wherein topmost information is the power spectrum information of noise.Power spectrum information can reflect the main frequency composition that noise is contained, and the size of each frequency content.Traditional passive noise cancellation technology is not very strong to the dependence of power spectrum information, the more noise information of active noise silencing Technology Need that part is novel.So the precision of the Power Spectrum Estimation Method directly affects the performance of the New Active noise cancellation technology of this class dependence noise prior imformation.

Nearly decades, existing many scholars have proposed the Power Spectrum Estimation Method of various classics and it have been conducted in-depth research, and have obtained some important achievements.In classical the Power Spectrum Estimation Method, have a kind of method be called Welch method, still this method is applied to and has repetition, in short-term, have some limitations under high intensity noise background:

1. because Welch the Power Spectrum Estimation Method is first divided into noise and has overlapping multistage, then ask the Fourier transform of noise, and the noise recording in reality is discrete time-limited, so what calculate in reality is the discrete Fourier transformation of the long noise of Discrete Finite, this value is an approximate value.In the time that short time period noise is carried out to power Spectral Estimation, very little, the error of calculation of discrete Fourier transformation can be very large for sampled data, and this error can directly affect the error of power Spectral Estimation.

2.Welch the Power Spectrum Estimation Method is applied in the serious sample frequency that relies on walkaway equipment in high strength in short-term (amplitude changes violent) noise.Only has walkaway equipment to reach sufficiently high sample frequency could effectively to record the power spectrum of this noise like.And raising equipment sample frequency is with high costs.

3.Welch the Power Spectrum Estimation Method can not be utilized this important prior imformation of repeatability of noise.It has simultaneously precision and the resolution of guaranteed output spectrum estimated performance of Overlapping Fragment method.

The stamping-out noise producing in punch press operation be exactly a class repeat, in short-term, high intensity noise, cannot effectively record the power spectrum information of stamping-out noise by Welch the Power Spectrum Estimation Method.How the repeated information of noise is used, keeping under the constant prerequisite of walkaway equipment sampling rate, raising power Spectral Estimation performance becomes the problem that punch press noise control engineering need to solve.

Summary of the invention

The present invention to overcome existing Welch the Power Spectrum Estimation Method process repeat, deficiency in short-term, when high intensity noise, propose a kind of punch press noise power spectrum based on Welch method and estimate to improve one's methods.

Improve one's methods and first utilize windowing method to intercept multistage effective noise, then ask for the sequence of average of effective noise, again the mean value of effective noise is divided into the multistage containing lap, does discrete Fourier transformation after level and smooth to each section, try to achieve noise power spectrum in conjunction with Welch method.The method has improved the estimated accuracy of discrete Fourier transformation, has indirectly improved the precision of power Spectral Estimation.The method mainly for have repetition, in short-term, the power Spectral Estimation of high intensity noise, except the stamping-out noise power spectrum that can effectively be applied to punch press is estimated, also be applicable to other have repetition, in short-term, the power Spectral Estimation of high intensity noise, as the power Spectral Estimation of the noise of ram engine, forging machine, shooting gallery.Improving conventional power spectrum estimating apparatus by the method does not need to change hardware device, only needs the computing method in update software, and cost is low.

The present invention is achieved by the following technical solutions, the present invention is on the basis of Welch the Power Spectrum Estimation Method, according to the computing method of the discrete Fourier transformation value of the improved properties noise of the stamping-out noise of punch press, improve the power Spectral Estimation precision of checkout equipment to stamping-out noise.The stamping-out noise of punch press has repeatability and short-time characteristic, so the present invention describes stamping-out noise signal with following mathematical formulae:

T ₁=ξT,(ξ≤1)

Wherein x (t) represents to contain the stamping-out noise signal that white Gaussian noise disturbs, and s (t) represents stamping-out noise, and u (t) represents that white Gaussian noise disturbs, and t represents the time, T ₁represent the effective duration of stamping-out noise one time, T represents the stamping-out cycle, and ξ represents stamping-out noise dutycycle.

The concrete steps that punch press stamping-out noise power spectrum is estimated are as follows:

(1) initialization power spectrum checkout equipment.Setting sensor sample frequency, discrete Fourier transformation parameter, truncated window function shape, truncated window function length, smoothing windows function shape, smoothing windows function length, the overlap length containing Overlapping Fragment, iterations counter i initial value, total iterations R.

(2) using punch press blanking control signal as starting sampling trigger signal.Wait for trigger pip, trigger sensor starts to gather the sample sequence of stamping-out noise x (t).

(3) punch press is regained to hydraulic hammer control signal as finishing sampling trigger signal.Wait for trigger pip, trigger sensor finishes to gather stamping-out noise sample.

(4) to the noise sample windowing process collecting.Acquiescence is selected the rectangular window that length is N, also can select to change length and the shape of window.More effective window also has Hamming window and Blackman window.The specific practice of windowing is that the noise sample to obtaining in step (3) intercepts or zero padding, and sample length is greater than the N sample sequence that intercepted length is N, and sample length is less than N in the zero padding of sample sequence end; Then sample sequence and window function sequence are done to dot product, obtain stamping-out noise sample one time

be illustrated in figure 3 the detection figure of stamping-out noise for the first time.

(5) calculate the sequence of average of effective noise with alternative manner

iteration more new formula is as follows:

$\stackrel{\‾}{\hat{x}\left(n\right)}=\left\{\begin{array}{cc}{\hat{x}}_{\left(1\right)}\left(n\right)& i=1\\ \frac{(i-1)\stackrel{\‾}{\hat{x}\left(n\right)}+{\hat{x}}_{\left(i\right)}\left(n\right)}{i}& i>1\end{array}\right.$

Wherein, i represents current iteration counter number of times.

(6) storage effective noise sequence of average, iteration count adds 1, i=i+1.

(7) repeating step (2) is to (6) until iteration count i=R.

(8) divide S section by the sequence of average of effective noise, every segment length is M, and adjacent two sections of lap length are M/2.S and M relational expression are as follows:

$S=\frac{2N-M}{M}$

(9) selecting smoothing windows is that length is the Blackman window W (n) of M, so to asking leaf transformation in the L point discrete Fourier of each section after sectionally smooth.Computing formula is as follows:

$X_{\left(j\right)}\left(k\right)=\underset{n=0}{\overset{M-1}{\mathrm{\&Sigma;}}}{\hat{x}}_{\left(j\right)}\left(n\right)W\left(n\right)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA0000457605910000021.png,HDA0000457605910000022.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;kn}/L}$

Wherein, j=1,2 ..., R, k represents frequency.

(10) ask the weighted mean value of the discrete Fourier transformation square of all segmentations, obtain the power Spectral Estimation value of stamping-out noise

formula is as follows:

$\begin{array}{c}{\hat{P}}_{\mathrm{xx}}\left(k\right)=\frac{1}{S}\underset{j=1}{\overset{\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="HDA0000457605910000011.png,HDA0000457605910000021.png"\; state="\{\{state\}\}">s</figure-callout>}}{\mathrm{\&Sigma;}}}\frac{1}{\mathrm{MU}}{\left|X_{\left(j\right)}\left(k\right)\right|}^2\\ U=\frac{1}{M}\underset{n=0}{\overset{M-1}{\mathrm{\&Sigma;}}}{W}^2\left(n\right)\end{array}$

In punch press walkaway control engineering, adopt the method that the present invention proposes can obtain enough power Spectral Estimation precision and resolution, can suppress the interference of white noise.The feature of maximum of the present invention is exactly: by windowing method and method of average calculating stamping-out noise variance Fourier transform approximate value, solve the low defect of power Spectral Estimation precision that classic method causes greatly because of discrete Fourier transformation approximate value variance, and method is simple, be easy to realize.

Accompanying drawing explanation

Fig. 1 is the program flow diagram that adopts the inventive method.

Fig. 2 is the detection figure in ten cycles of stamping-out noise in the embodiment of the present invention.

Fig. 3 is the detection figure of stamping-out noise for the first time in the embodiment of the present invention.

Fig. 4 is the power spectrum comparison diagram of not improving one's methods and improving one's methods in the embodiment of the present invention and obtaining.

Embodiment

Below in conjunction with drawings and Examples, technical scheme of the present invention is further described.

As shown in Figure 1, power spectrum checkout equipment is initialization apparatus parameter first, then wait for punch press blanking control signal, trigger sensor acquisition noise sample sequence, in the time that punch press withdrawal hydraulic hammer control signal is sent, trigger sensor stops acquisition noise sample, has so just completed stamping-out noise and intercept and add the step of rectangular window.It is exactly to select rectangular window that windowing program is left intact, and also can select non-rectangle window according to the feature of noise, further improves algorithm performance.Here power spectrum checkout equipment has used the method for iteration to calculate the sequence of average of effective noise, does not need to store repeatedly stamping-out noise, saves memory headroom.Afterwards by the sequence of average segmentation of effective noise, adjacent two sections of signals that overlap, more each segmentation is done smoothly, ask discrete Fourier transformation, finally the discrete Fourier transformation of each segmentation is asked to weighted mean, obtain the power Spectral Estimation value of stamping-out noise.

As shown in Figure 2, stamping-out noise periods is 1 second, and a stamping-out noise duration is 0.1 second, and signal to noise ratio (S/N ratio) is 10dB.As embodiment, stamping-out noise power spectrum of the present invention estimates that flow process is as follows:

(1) initialization power spectrum checkout equipment.Setting sensor sample frequency is 40KHz, and it is 4096 that discrete Fourier transformation is counted, and truncated window function is selected the rectangular window that length is 4000, smoothing windows is selected the rectangular window that length is 2000, overlap length is 1000, and iterations counter i is 1, and total iterations is 10.

(2) using punch press blanking control signal as starting sampling trigger signal.Wait for trigger pip, trigger sensor starts to gather stamping-out noise sample sequence.

(3) punch press is regained to hydraulic hammer control signal as finishing sampling trigger signal.Wait for trigger pip, trigger sensor finishes to gather stamping-out noise sample.

(4) to the noise sample windowing process collecting.Acquiescence is selected the rectangular window that length is 4000, also can select to change length and the shape of window.More effective window also has Hamming window and Blackman window.The specific practice of windowing is that the noise sample to obtaining in step (3) intercepts or zero padding, and sample length is greater than the sample sequence that 4000 intercepted lengths are 4000, and sample length is less than 4000 in the zero padding of sample sequence end.Then sample sequence and window function sequence are done to dot product, obtain stamping-out noise sample one time

be illustrated in figure 3 the detection figure of stamping-out noise for the first time.

(5) calculate the sequence of average of effective noise with alternative manner

iteration more new formula is as follows:

$\stackrel{\&OverBar;}{\hat{x}\left(n\right)}=\left\{\begin{array}{cc}{\hat{x}}_{\left(1\right)}\left(n\right)& i=1\\ \frac{(i-1)\stackrel{\&OverBar;}{\hat{x}\left(n\right)}+{\hat{x}}_{\left(i\right)}\left(n\right)}{i}& i>1\end{array}\right.$

Wherein, i represents current iteration counter number of times.

(6) storage effective noise sequence of average, iteration count adds 1, i=i+1.

(7) repeating step (2) is to (6) until iteration count i=10.

(8) divide 6 sections by the sequence of average of effective noise, every segment length is 2000, and adjacent two sections of lap length are 1000.

(9) selecting smoothing windows is that length is 2000 Blackman window W (n), so to ask the discrete Fourier transformation of each section after sectionally smooth with FFT.Computing formula is as follows:

$X_{\left(j\right)}\left(k\right)=\underset{n=0}{\overset{M-1}{\mathrm{\&Sigma;}}}{\hat{x}}_{\left(j\right)}\left(n\right)W\left(n\right)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA0000457605910000021.png,HDA0000457605910000022.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;kn}/L}$

Wherein, j=1,2 ..., 10, k represents frequency.

(10) ask the weighted mean value of the discrete Fourier transformation of all segmentations, obtain the power Spectral Estimation value of stamping-out noise formula is as follows:

$\begin{array}{c}{\hat{P}}_{\mathrm{xx}}\left(k\right)=\frac{1}{S}\underset{j=1}{\overset{\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="HDA0000457605910000011.png,HDA0000457605910000021.png"\; state="\{\{state\}\}">s</figure-callout>}}{\mathrm{\&Sigma;}}}\frac{1}{\mathrm{MU}}{\left|X_{\left(j\right)}\left(k\right)\right|}^2\\ U=\frac{1}{M}\underset{n=0}{\overset{M-1}{\mathrm{\&Sigma;}}}{W}^2\left(n\right)\end{array}$

Result is presented in Fig. 4, and wherein solid line is not improve the power Spectral Estimation result of algorithm to stamping-out noise, and dotted line is the power Spectral Estimation result of improvement algorithm of the present invention to stamping-out noise.The crest of dotted line is obvious, can measure by a dotted line and in noise, contain 9 main frequency component: 130Hz, 290Hz, 400Hz, 500Hz, 611Hz, 772Hz, 810Hz, 881Hz, 1000Hz.

Claims (1)

1. the punch press noise power spectrum based on Welch method is estimated to improve one's methods, and step is as follows:

(1) initialization power spectrum checkout equipment; Setting sensor sample frequency, discrete Fourier transformation parameter, truncated window function shape, truncated window function length, smoothing windows function shape, smoothing windows function length, the overlap length containing Overlapping Fragment, iterations counter i initial value, total iterations R;

(2) using punch press blanking control signal as starting sampling trigger signal; Wait for trigger pip, trigger sensor starts to gather the sample sequence of stamping-out noise x (t);

(3) punch press is regained to hydraulic hammer control signal as finishing sampling trigger signal; Wait for trigger pip, trigger sensor finishes to gather stamping-out noise sample;

(4) to the noise sample windowing process collecting; Acquiescence is selected the rectangular window that length is N, also can select to change length and the shape of window; More effective window also has Hamming window and Blackman window; The specific practice of windowing is that the noise sample to obtaining in step (3) intercepts or zero padding, and sample length is greater than the N sample sequence that intercepted length is N, and sample length is less than N in the zero padding of sample sequence end; Then sample sequence and window function sequence are done to dot product, obtain stamping-out noise sample one time

(5) calculate the sequence of average of effective noise with alternative manner

iteration more new formula is as follows:

$\stackrel{\&OverBar;}{\hat{x}\left(n\right)}=\left\{\begin{array}{cc}{\hat{x}}_{\left(1\right)}\left(n\right)& i=1\\ \frac{(i-1)\stackrel{\&OverBar;}{\hat{x}\left(n\right)}+{\hat{x}}_{\left(i\right)}\left(n\right)}{i}& i>1\end{array}\right.$

Wherein, i represents current iteration counter number of times;

(6) storage effective noise sequence of average, iteration count adds 1, i=i+1;

(7) repeating step (2) is to (6) until iteration count i=R;

(8) divide S section by the sequence of average of effective noise, every segment length is M, and adjacent two sections of lap length are M/2; S and M relational expression are as follows:

$S=\frac{2N-M}{M}$

(9) selecting smoothing windows is that length is the Blackman window W (n) of M, so to asking leaf transformation in the L point discrete Fourier of each section after sectionally smooth; Computing formula is as follows:

$X_{\left(j\right)}\left(k\right)=\underset{n=0}{\overset{M-1}{\mathrm{\&Sigma;}}}{\hat{x}}_{\left(j\right)}\left(n\right)W\left(n\right)e^{-j2\mathrm{\&pi;kn}/L}$

Wherein, j=1,2 ..., R, k represents frequency;

(10) ask the weighted mean value of the discrete Fourier transformation square of all segmentations, obtain the power Spectral Estimation value of stamping-out noise

formula is as follows:

$\begin{array}{c}{\hat{P}}_{\mathrm{xx}}\left(k\right)=\frac{1}{S}\underset{j=1}{\overset{s}{\mathrm{\&Sigma;}}}\frac{1}{\mathrm{MU}}{\left|X_{\left(j\right)}\left(k\right)\right|}^2\\ U=\frac{1}{M}\underset{n=0}{\overset{M-1}{\mathrm{\&Sigma;}}}{W}^2\left(n\right)\end{array}$

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