CN103969326B - A kind of method of diagnosing dual-jet DC arc plasma discharge stability - Google Patents

Abstract

Diagnose a method for dual-jet DC arc plasma discharge stability, belong to hot plasma discharge stability judgment technology field. the method is characterized in that, systems soft ware synchronous acquisition obtains at the not striking voltage under in the same time and the RGB image of discharge generation, again RGB image is converted into after gray level image and obtains Luminance edge by binarization segmentation method, be origin of coordinates starting point again taking the image lower left corner, utilize 8 direction Freeman chain code coding rules, from starting point, move along clockwise direction, so that obtain by starting point coordinate and one group of directive chain code sequence the well-determined equi intensity curve that is similar to arc-plasma dimensional isothermal line, seek out isothermal girth and area with this, and the coefficient correlation of lower same thermoisopleth boundary chain code in the same time not. according to girth, area and three characteristic quantities of coefficient correlation, judge discharge plasma stability in conjunction with discharge voltage, easy to operate, safe, real-time is good.

Description

A kind of method of diagnosing dual-jet DC arc plasma discharge stability

Technical field

The present invention relates to the diagnostic method of dual-jet DC arc plasma discharge stability, belong to hot plasma stability diagnosis neckTerritory.

Background technology

Due to factors such as chemical reaction process complicated in hot plasma system, gas flow, heat transfers, cause plasma veryDifficulty is discharged sustainedly and stably; And the unstability of gas discharge can greatly affect effect, the reduction etc. of plasma material processingGas ions material processed efficiency. Therefore, from hot plasma theoretical research and practical application, steady to process gas dischargeQualitatively carry out on-line measurement for deeply understanding in hot plasma complicated electromagnetic hydroimechanics process, promoting it in materials processingThe practical application in field is very necessary.

By to hot plasma discharge voltage over time waveform analysis diagnose plasma discharge stability, beConventional analytical method at present. By analyze in discharge process arc voltage over time for research because electric arc arc root is at electricityExtremely the caused plasma pulsation of the motion on surface is highly effective, but is difficult to reflect completely due to non-electric arc arc root motionThe unstability of caused plasma jet.

Along with the development of computer digital image treatment technology, image processing techniques is incorporated into plasma stability method of discriminationIn, can make up to a certain extent the deficiency of the plasma stability analytical method based on discharge voltage completely. The bases such as Ge NanExtract and there is the plasma boundary girth of different gray values and the information of area in image chain code technology, by these two ginsengsThe quantitative analysis of number has obtained the qualitative assessment to dual-jet DC arc plasma stability. Although chain code sequence and border shapeShape is one to one, but likely there will be the girth of two borderline regions and area approximation and feelings that true form differs greatlyCondition. For example, for dual-jet DC arc plasma, the jet of its electrode below likely can be subject to the disturbance of external environmentAct on and be partial to different electrode zones, although now corresponding to the girth on a certain isothermal border and two-dimensional projection's temperature of enclosing thereofScene is long-pending differs less, but that its shape likely differs is larger.

Therefore, for describe more exactly plasma discharge image position shape on the basis of above-mentioned research work, further ask forThe coefficient correlation of image boundary of different discharging times, thereby formed in electric discharge image, have specific gray value etc.The plasma stability assessment that value line adopts girth, area and three parameters of coefficient correlation to analyze in conjunction with discharge voltageMethod, it is more accurate to make the assessment of process gas discharge applying plasma stability.

Summary of the invention

The object of the invention is to attempt to solve the deficiency of existing method for analyzing stability, make plasma stability assessment more accurateReally, spy provides a kind of method for analyzing stability combining with discharge voltage based on image processing techniques.

Technical scheme provided by the invention is: from radiation temperature measurement theory, " color " of body surface distributes to a certain extentThe temperature field of having reflected arc-plasma distributes. The present invention proposes a kind of for the Luminance edges such as visible images (isothermal limitBoundary) method of dual-jet arc-plasma being carried out to stability analysis. Utilize square-wave signal external trigger CCD camera and analog quantityCapture card gathers respectively image and the signal of telecommunication; By binary-state threshold dividing method obtain the discharging isothermal border of image; For etc.Temperature border, has defined girth, area, three characteristic quantities of coefficient correlation, and has combined with discharge voltage and carry out stability analysis.

Realizing the method that above-mentioned experimental program adopts is:

1. image and electrical signal collection

CCD camera is aimed to plasma discharge, for eliminating the saturated phenomenon of electric discharge image, before camera lens, loadNeutral colour filter. Produce electric discharge under the mode of operation of high-frequency arc strike time, arc plasma is known from experience the extremely strong electromagnetic interference of generationSignal, for avoiding Environmental Noise Influence certainty of measurement, adopts difference input mode connecting signal source. By multichannel counter/regularlySquare-wave signal external trigger CCD camera and the analog acquisition card of device card output certain frequency gather respectively image and voltage signal.

2. image pretreatment

The coloured image that CCD camera is collected converts gray level image to by linear transformation, by assign thresholds, to gray scaleImage carries out that binarization segmentation obtains and waits Luminance edge; Change threshold value and border is superposeed with specific interval, thereby having obtained descriptionThe equi intensity curve in arc-plasma two-dimensional projection temperature field. Known according to radiation temperature measurement theory, " color " of body surface pointCloth is the Temperature Distribution of judgment object roughly. Therefore, the intensity profile of electric discharge image has reflected arc-plasma to a certain extentTemperature Distribution.

3. Characteristic Extraction

For reciprocity Luminance edge (isothermal border) is quantitatively described, 8 direction Freeman chain code technologies are introduced. According to8 direction Freeman chain code coding rules are chosen definite starting point coordinate on object boundary, and chain code is in the mode of 8 neighborhoodsMove corresponding chain data code c for each moving direction along curve or boundary pixel sequence_i(c_i=0,1,2 ... 7) encode, withArbitrary given border all can be unique definite by starting point coordinate and one group of directive chain code sequence.

Based on image chain code technology, can ask for easily border girth and area corresponding to a certain gray value, girth and area are trueDetermine the physical dimension of electric arc-fluerics. And by calculating not in the same time in plasma discharge image corresponding to a certain gray valueCoefficient correlation between isopleth boundary chain code can reflect the intensity of variation of boundary shape preferably. Calculating two time-domain signalsWhen coefficient correlation, the length of two discrete signals must equate. Therefore, the nearest neighbor point in digital image processing field has been proposedMethod is carried out sample interpolation to original chain code sequence to obtain standard chain code sequence equal in length.

4. discharge stability analysis

For characterizing the pulsation situation of plasma arc-fluerics, define dimensionless groupIn order to Expressive Features amountAmplitude of variation, wherein μ_XFor a certain characteristic quantity standard deviation of a series of electric discharge images,A certain for a series of electric discharge imagesCharacteristic quantity mean value. Set the standard value of stability diagnosis according to a large amount of experimental analysis, if in a series of electric discharge image continuous threeTwo parameters of width image and discharge voltage do not meet the standard value of stability diagnosis and regard as unstable. If met, according toExperience is set the reference frame image of discharge stability, further seeks out the boundary chain code coefficient correlation of present frame and reference frame, judgementStability.

Owing to having adopted technique scheme, tool of the present invention has the following advantages:

1. this invention is incorporated into the boundary chain code algorithm in digital image processing techniques in the judgement of stability of discharge plasma.And extracted girth, area, three characteristic quantities of coefficient correlation based on boundary chain code algorithm, judge well plasma dischargingThe boundary geometrical size of body and position shape. This invention is simple and feasible, and real-time is good, and cost is lower, has practical application wellBe worth.

2. hot plasma often has very high shelf depreciation temperature, and the present invention does not need the tested plasma of actual contactBody, has ensured the security of operating personnel and device, variation that simultaneously can interference source field. Therefore, there is more applied fieldClose.

Brief description of the drawings

Below in conjunction with drawings and the embodiments, the present invention is further detailed explanation:

Fig. 1 is the master-plan schematic diagram of analysis of stability analysis system;

Fig. 2 is the Software for Design flow chart of analysis of stability analysis system.

Detailed description of the invention

Fig. 1 is the general structure of the analysis of stability analysis system designed according to the present invention. Mainly occurred by DC arc plasmaDevice, CCD camera, analog acquisition card, stability analysis software composition. Plasma generator is powered by DC current source,Working gas is argon gas, and two interelectrode distances are adjustable. Parallel placement CCD camera is aimed at plasma generator, and at cameraBefore camera lens, load three neutral colour filters. By analog acquisition card, PCI1715 carries out the collection of the signal of telecommunication, in order to reduce common modeSignal adopts difference connected mode. The resistance-capacitance network that the negative terminal of input signal source is consisted of a resistance and electric capacity and boardAIGND connects in analog, and resistance sizes is generally selected 100K Ω, and capacitance size is selected 100nF. Counted by multichannelDevice/timer card PCI1780 output square-wave signal external trigger synchronous acquisition, sample frequency is 0.5Hz, the CCD while gathering imageCamera parameter is: white balance parameter is respectively 48 and 52, focal distance f=50mm, f-number F=4.0, time for exposure Tex=1/300The image resolution ratio that s, speed ISO=200 gather is 1024 × 768, and picture format is RGB24. To dual-jet direct-current arcThe experiment condition that plasma discharge stability is studied is: angle between electrode spacing d=2.0cm, geometric electrode axisα=120 °, arc current are respectively I=50A, negative electrode and anode-side argon flow amount Qa=Qc=10.0slpm. Concrete Software for Design streamJourney as shown in Figure 2.

According to the fluctuating range canonical reference value of a large amount of experimental data setting voltage, girth, area and coefficient correlation as following table instituteShow.

Based on boundary chain code algorithm, can obtain girth and two characteristic quantities of area of electric arc-fluerics.

If the lower left corner, border pixel is the origin of coordinates, mobile formation along clockwise direction according to pixels put on border. As chain data code c_iDuring for even number, corresponding boundary length is 1; And work as c_iDuring for odd number, corresponding boundary length isObtain thus corresponding toThe border girth (L) of a certain gray value is:

$L=N_e+\sqrt{2}{N}_0$

In formula, N_eAnd N₀Be respectively the number of walking even number step in 8 direction boundary chain codes and walking odd number step.

For a certain equi intensity curve, be (x if establish the coordinate of its initial pixel₀,y₀), corresponding chain code sequence is c₀c₁……c_N-1, the area (S) that this equi intensity curve encloses can be calculated by following formula:

$S=\underset{i=0}{\overset{N-1}{\Σ}}{c}_{ix}(y_i+c_{iy}/2)$

In formula, N is chain code length (number of pixels), y_iChain data code c_iThe y coordinate figure of starting point, c_ix，c_iy∈ 1,0 ,-1} tableShow i chain data code c_iAlong the changing value of x coordinate and y coordinate.

Discharge plasma is carried out to stability analysis every the electric discharge image of 2s and corresponding arc voltage as example in t=0～10s.Picking and placeing respectively electrical image gray value is the limits of 190 and 10 corresponding isopleth borders as plasma arc district and fluericsBoundary. The characteristic quantity of obtaining is as follows:

According to upper table data, the fluctuating range that can obtain voltage is 0.055, and the fluctuating range of arc region girth and area is respectively0.048 and 0.076, the fluctuating range of fluerics girth and area is respectively 0.087 and 0.088. Process and fluctuating range standard valueCompare, can tentatively judge that discharge plasma electric arc-fluerics is stable. Suppose electric discharge initial time (t₀=0s) electric discharge etc.Gas ions is stable state, the plasma arc-jet boundary while further seeking out t=2,4,6,8,10s and t=0sTime coefficient correlation. Because the length requirement that requires two row chain code sequences equates, original chain code sequence is adopted to nearest neighbor interpolationSample interpolation method.

If the original chain code sequence that note length is N is c_i, i ∈ 0,1,2 ..., N-1}, the standard chain code sequence that corresponding length is MFor c '_i′, i' ∈ 0,1,2 ..., M-1}, so, can obtain following relation according to nearest neighbor interpolation:

$c_{i^{\′}}^{\′}=c_{k_I}$

$k_1=i^{\′}\·\frac{N}{M},i^{\′}=0,1,2,...,M-1$

In calculating, need the k in above formula_IThe method that employing rounds up is taken as integer. Original chain code is changed into mark equal in lengthAfter accurate chain code, carry out solving of coefficient correlation, computing formula is as follows:

$\mathrm{\ρ}(A,B)=\frac{Cov(A,B)}{\sqrt{Cov(A,A)}\sqrt{Cov(B,B)}}$

In formula, E (A)=ω and E (B)=υ are respectively the desired value between A, B two row boundary standard chain code sequences, and Cov (A, B) is A, BThe covariance of two column signals. ρ (A, B) is value between [1,1]. The absolute value of ρ (A, B) is larger, characterizes the degree of correlation of A and BHigher.

Result of calculation is as shown in the table:

From upper table data, in the time of t=4s, arc region coefficient correlation is 0.1729, a little less than the standard ginseng of coefficient correlationThe value of examining 0.2, can judge the arc region discharge instability in this moment. Other moment is in stable discharging state.

Claims (1)

1. a method of diagnosing dual-jet DC arc plasma discharge stability, is characterized in that, is at a dual-jetIn DC arc plasma discharge stability analytical system, realize according to following steps successively, hereinafter to be referred as system:

Step (1), the system described in constructing, comprising: IPC610 industrial computer platform, square wave generation module, CCD camera,Analog acquisition card and stability analysis software, hereinafter to be referred as systems soft ware;

Wherein, IPC610 industrial computer platform, controls described square wave generation module, the square-wave voltage of output setpoint frequency;

Square wave generation module, is multichannel counter/timer card PCI1780, adopts to described CCD camera and analog quantityThe square-wave voltage of the described setpoint frequency of the synchronous output of truck;

Analog acquisition card, adopts PCI1715 board, adopts difference connected mode, after being triggered to tested plasmaVoltage gathers;

CCD camera, is a MV-VD078SC industrial camera that adopts M5018-MP industrial lens, time for exposure, white balanceCan, by software control, support external trigger type collection with yield value, be called for short CCD camera, for gathering visible images data;

Systems soft ware adopts two-wire journey mode, main thread initializes CCD camera, and the visible ray figure that described CCD camera is read inCarry out image processing as data; From thread according to the collection of difference connected mode and preserve the voltage data of described analog acquisition card;Master and slave two threads are specified operation in 4 CPU on described IPC610 industrial computer platform respectively;

Step (2), 4 CPU on described IPC610 industrial computer platform carry out respectively discharge stability judgement according to the following steps;

Step (2.1), CCD camera initializes: set the camera parameter including time for exposure, white balance and gain;

Step (2.2), analog acquisition card initialization: adopt difference connected mode, to reduce common-mode signal;

Step (2.3), after described CCD camera and analog acquisition card are triggered, described CCD collected by camera visible imagesData, described analog acquisition card gathers discharge voltage data;

Step (2.4), successively calculating plasma discharge voltage arc region under the striking voltage in the same time not according to the following stepsGirth:

Step (2.4.1), the plasma rgb image data that described CCD camera is read in is converted into gray level image data;

Step (2.4.2), set gray threshold, to described gray level image data carry out that binarization segmentation obtains wait Luminance edge,

Step (2.4.3), taking the described Luminance edge lower left corner pixel that waits as zero point, is compiled according to 8 direction Freeman chain codesCode rule, chain code, obtains corresponding to described starting point ash by moving along boundary pixel direction clockwise in the mode of 8 neighborhoodsThe border perimeter L of degree value, described Luminance edge such as grade is unique definite with starting point coordinate and one group of directive chain code sequence,Thereby obtain the Isothermal Line Distribution in a reflection plasma two-dimensional projection temperature field:Wherein, N_eWithN₀Be respectively the number of walking even number step in 8 direction boundary chain codes and walking odd number step;

Step (2.5), next asks for the area S that described in step (2.4.3), thermoisopleth corresponding to perimeter L encloses, area SCalculate with following formula;Wherein: N is chain code length, y_iChain data code c_iThe y coordinate of starting pointValue, c_ix∈{1,0,-1}，c_iy{ 1,0 ,-1}, represents respectively i chain data code c to ∈_iAlong the changing value of x coordinate and y coordinate;

Step (2.6), obtains not the voltage pulsation amplitude of inferior plasma discharge in the same timeAnd in electric discharge image corresponding to certainThe fluctuating range of the perimeter L that waits Luminance edge of one gray value and the area S enclosing

Step (2.7), calculates not in the same time the two row equi intensity curve limits corresponding to a certain gray value in inferior plasma discharge imageCorrelation coefficient ρ (A, B) between the chain code on boundary, to express the changes shape of boundary shape with the moment:

Step (2.7.1), in plasma discharge image, makes not the equi intensity curve boundary chain code order of lower same gray value in the same timeBe listed in the unified boundary chain code sequence for standard in length:

If the long original chain code sequence for N is c_i, i ∈ 0,1,2 ..., and N-1}, the standard chain code sequence that corresponding length is M isc′_i', i' ∈ 0,1,2 ..., M-1}, according to nearest neighbor point interpolation method, obtains:k_I＝i'·N/M，i'＝0,1,2,...,M-1，Make obtained boundary standard chain code sequence approach as much as possible described original chain code sequence, wherein k_IFor be greater than zero limited wholeNumber;

Step (2.7.2), be calculated as follows not in the same time under in plasma discharge image the waiting on Luminance edge of same gray valueBoundary chain code sequence between correlation coefficient ρ (A, B), wherein A, B are two row boundary standard chain code sequences under in the same time not:

$\mathrm{\ρ}(A,B)=\frac{Cov(A,B)}{\sqrt{Cov(A,A)}\·\sqrt{Cov(B,B)}}$

E (A)=ω and E (B)=υ are respectively the desired value of the setting between A, B two row boundary standard chain code sequences, Cov (A, B) be A,The covariance of B two column signals, is defined as: Cov (A, B)=E[(A-ω) (B-υ)], ρ (A, B) is value between [1,1],The absolute value of ρ (A, B) is larger, and the degree of correlation that characterizes A and B is higher,

Step (2.8), judge the stability that dual-jet DC arc plasma discharges:

Step (2.8.1), according to the result of many experiments, the fluctuating range canonical reference value of setting voltage, girth and area andCoefficient correlationCanonical reference value ρ ';

Step (2.8.2), by what obtain in step (2.6)Fluctuating range standard with step (2.8.1) settingReference valueCompare accordingly by subscript respectively; IfAgain by step (2.7.2)In coefficient correlation canonical reference value in the correlation coefficient ρ (A, B) and the step (2.8.1) that obtain compare, if ρ (A, B) >=ρ ',Dual-jet DC arc plasma discharge stability is described so, otherwise discharge instability.