CN103969326A - Method for diagnosing discharging stability of double-jet-flow direct current arc plasma - Google Patents

Abstract

The invention provides a method for diagnosing the discharging stability of a double-jet-flow direct current arc plasma, and belongs to the technical field of the judgment of the discharging stability of thermal plasmas. The method is characterized in that system software synchronously acquires an RGB image generated by striking voltage and discharging at different times, then the RGB image is transformed into a gray image to be processed by a binaryzation segmentation method to obtain a gray level boundary, then the left lower corner of the image is used as a starting point of a coordinate origin, eight-direction Freeman chain code encoding rules are adopted to start to move from the starting point clockwise to obtain a gray-isotherm line which is similar to a two-dimensional gray-isotherm line of the arc plasma and is uniquely determined by starting point coordinates and a group of chain code sequence with the direction, so as to find out the perimeter and the area of the isotherm line as well as correlation coefficients of boundary chain codes of the same isotherm line at different times. Based on the three characteristic quantities of the perimeter, the area and the correlation coefficients as well as combined with discharging voltage, the discharging stability of the plasma can be judged, the operation is convenient, the safety is high and the real-time performance 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 diagnostic field.

Background technology

Due to factors such as chemical reaction process complicated in hot plasma system, gas flow, heat transfers, cause plasma to be difficult to electric discharge sustainedly and stably; And the instability of gas discharge can greatly affect effect, the reduction plasma material treatment effeciency of plasma material processing.Therefore, from hot plasma theoretical research and practical application, to the stability of process gas discharge carry out on-line measurement for deeply understanding in hot plasma complicated electromagnetic hydroimechanics process, to promote its practical application in material processing field very necessary.

By to hot plasma sparking voltage over time waveform analysis diagnose plasma discharge stability, be current conventional analytical approach.By analyze in discharge process arc voltage over time for research because electric arc arc root is highly effective in the caused plasma pulsation of motion of electrode surface, but be difficult to reflect completely due to the move instability of caused plasma jet of non-electric arc arc root.

Along with the development of computer digital image treatment technology, image processing techniques is incorporated in plasma stability method of discrimination, can make up to a certain extent the deficiency of the plasma stability analytical approach based on sparking voltage completely.Ge Nan etc. extract and have the plasma boundary girth of different gray-scale values and the information of area based on image chain code technology, by the quantitative test of these two parameters has been obtained to the qualitative assessment to dual-jet DC arc plasma stability.Although chain code sequence and boundary shape are one to one, likely there will be the girth of two borderline regions and area approximation and situation that true form differs greatly.For example, for dual-jet DC arc plasma, the jet of its electrode below likely can be subject to the perturbation action of external environment and be partial to different electrode zones, although now differ less corresponding to the girth on a certain isothermal border and the two-dimensional projection's temperature field area enclosing thereof, it is larger that its shape likely differs.

Therefore, for describe more exactly plasma discharge image position shape on the basis of above-mentioned research work, further ask for the related coefficient of the image boundary of different discharging times, thereby formed the plasma stability appraisal procedure that the isoline to having specific gray value in electric discharge image adopts girth, area and three parameters of related coefficient to analyze in conjunction with sparking voltage, 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 accurate, spy provides a kind of method for analyzing stability combining with sparking voltage based on image processing techniques.

Technical scheme provided by the invention is: from radiation temperature measurement theory, " color " of body surface distributes and reflected that to a certain extent the temperature field of arc-plasma distributes.The present invention proposes a kind of method of dual-jet arc-plasma being carried out to stability analysis for the Luminance edges such as visible images (isothermal border).Utilize square-wave signal external trigger CCD camera and analog acquisition card to gather respectively image and electric signal; By binary-state threshold dividing method obtain the discharging isothermal border of image; For isothermal border, define girth, area, three characteristic quantities of related coefficient, and combined with sparking 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, loaded neutral 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 signal of generation, for avoiding Environmental Noise Influence measuring accuracy, adopts difference input mode connecting signal source.Square-wave signal external trigger CCD camera and analog acquisition card by hyperchannel counter/timer card output certain frequency gather respectively image and voltage signal.

2. image pre-service

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

3. Characteristic Extraction

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

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

4. discharge stability analysis

For characterizing the pulsation situation of plasma arc-fluerics, define dimensionless group in order to the amplitude of variation of Expressive Features amount, wherein μ _xfor a certain characteristic quantity standard deviation of a series of electric discharge images, for a certain characteristic quantity mean value of a series of electric discharge images.Set the standard value of stability diagnosis according to a large amount of experimental analysis, if the standard value that in a series of electric discharge image, two parameters of continuous three width images and sparking voltage do not meet stability diagnosis is regarded as unstable.If met, rule of thumb set the reference frame image of discharge stability, further seek out the boundary chain code related coefficient of present frame and reference frame, judge stability.

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 related coefficient based on boundary chain code algorithm, judge well boundary geometrical size and the position shape of discharge plasma.This invention is simple and feasible, and real-time is good, and cost is lower, has actual application value well.

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

Brief description of the drawings

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

Fig. 1 is the overall design schematic diagram of analysis of stability analysis system;

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

Embodiment

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

As shown in the table according to the fluctuating range canonical reference value of a large amount of experimental data setting voltage, girth, area and related coefficient.

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 true origin, 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 is obtain thus corresponding to the border girth (L) of a certain gray-scale value be:

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

In formula, N _eand N ₀be 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 pixel ₀, y ₀), corresponding chain code sequence is c ₀c ₁c _n-1, the area (S) that this equi intensity curve encloses can be calculated by following formula:

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

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} represents i chain data code c to ∈ _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-scale value is the borders of 190 and 10 corresponding isoline borders as plasma arc district and fluerics.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 respectively 0.048 and 0.076, and the fluctuating range of fluerics girth and area is respectively 0.087 and 0.088.Through comparing with fluctuating range standard value, can tentatively judge that discharge plasma electric arc-fluerics is stable.The discharge plasma of supposing electric discharge initial time (t0=0s) is steady state (SS), the related coefficient when plasma arc-jet boundary while further seeking out t=2,4,6,8,10s and t=0s.Because the length requirement that requires two row chain code sequences equates, original chain code sequence is adopted to nearest neighbor interpolation sample interpolation method.

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

$c_i^{\′}=c_{k_I}$

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

In calculating, need the k in above formula _ithe method that employing rounds up is taken as integer.After original chain code is changed into standard chain code equal in length, carry out solving of related coefficient, computing formula is as follows:

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

In formula, E (A)=ω and E (B)=υ are respectively the expectation value between A, B two row boundary standard chain code sequences, and Cov (A, B) is the covariance of A, B two column signals.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.

Result of calculation is as shown in the table:

From upper table data, in the time of t=4s, arc region related coefficient is 0.1729, a little less than the canonical reference value 0.2 of related coefficient, 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, in a dual-jet DC arc plasma discharge stability analytic system, realizes 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 system software;

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

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

Analog acquisition card, adopts PCI1715 board, adopts difference connected mode, after being triggered, tested plasma electrically is compressed into row collection;

CCD camera, is a MV-VD078SC industrial camera that adopts M5018-MP industrial lens, and time shutter, white balance and yield value can, by software control, be supported external trigger type collection, are called for short CCD camera, for gathering visible images data;

System software adopts two-wire journey mode, main thread initializes CCD camera, and the visible images data that described CCD camera is read in are carried out image processing; 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 initialization: set the camera parameter including time shutter, white balance and gain;

Step (2.2), analog acquisition card initialization: gather 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 images data, described analog acquisition card gathers discharge voltage data;

Step (2.4), the successively girth of calculating plasma sparking voltage arc region under striking voltage in the same time not according to the following steps:

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), sets girth, according to iEEE Proceedings-Vision, Image and Signal Processing, 1997,144 (3): in 145-149, G.R.Wilson is at Proporties of contour codes[J]in the method mentioned, set gray threshold (in zero to one scope), described gray level image data are carried out to binarization segmentation obtains and wait Luminance edge;

Step (2.4.3), taking described Luminance edge lower left corner pixel as zero point, adopts pattern recognition, 1999,32 (2), 235-251 page, " the A new chain code " of Ernesto Bribiesca8 direction chain code coding rules described in one literary composition, described boundary chain code is started along moving by the direction that waits gray-scale value clockwise from described starting point, obtain the border perimeter L corresponding to described starting point gray-scale value, unique definite with starting point coordinate and one group of directive chain code sequence, thus an Isothermal Line Distribution that reflects plasma two-dimensional projection temperature field obtained: wherein, N _eand N ₀be 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 isothermal area corresponding to perimeter L described in step (2.4.3), presses iAPR workshop on machine vision applications, YANG LuRen in 1994,272-276 page, Albregten Frise, lonnestad Tor etc. " Method to estimate areas and perimeters of blob-like objects: a comparision[J] "the described method of one literary composition is set: the coordinate of described starting point is (x ₀, y ₀), corresponding to described starting point (x ₀, y ₀) the chain data code on border be c ₀c ₁c _n-1, the area S following formula that this equi intensity curve encloses calculates; N is the number of chain data code: wherein: 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}, represents i chain data code c to ∈ _ialong the changing value of x coordinate and y coordinate;

Step (2.6), obtains not the voltage fluctuation amplitude ▽ of inferior plasma discharge in the same time _Φand in electric discharge image corresponding to the fluctuating range ▽ of the perimeter L of the equi intensity curve of a certain gray-scale value and the area S that encloses _l, ▽ _s;

Step (2.7), be calculated as follows not in inferior plasma discharge image in the same time corresponding to the correlation coefficient ρ (A between the chain code on two row equi intensity curve borders of a certain gray-scale value, B), 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 sequence of lower same gray-scale value unified boundary chain code sequence for standard in length in the same time by following formula:

If the long original link sequence for N is c _i, i ∈ 0,1,2 ..., and N-1}, the standard chain code sequence that corresponding length is M is c ' _i', i' ∈ 0,1,2 ..., and M-1}, by China's Space science and technology, 2005,3: 14-18 page, the described method of paper " digital picture optimal interpolation method research [J] " literary composition of You Yuhu, Zhou Xiaokuan, obtains: i'=0,1,2 ..., M-1, makes obtained boundary standard chain code sequence approach as much as possible described original boundaries chain code, wherein k _ifor being greater than zero limited integer;

Step (2.7.2), under being calculated as follows not in the same time in plasma discharge image the correlation coefficient ρ (A between the boundary chain code sequence on the equi intensity curve of same gray-scale value, B), wherein A, B are two row boundary standard chain code sequences under in the same time not:

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

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

Step (2.8) is judged the stability of dual-jet DC arc plasma electric discharge:

Step (2.8.1) is according to the result of many experiments, the fluctuating range canonical reference value ▽ ' of setting voltage, girth, area and related coefficient _Φ, ▽ ' _l, ▽ ' _sand ρ ';

Step (2.8.2) is by the ▽ obtaining in step (2.6) _Φ, ▽ _l, ▽ _sfluctuating range canonical reference value ▽ ' with step (2.8.1) setting _Φ, ▽ ' _l, ▽ ' _s; If ▽ _Φ< ▽ ' _Φ, ▽ _l< ▽ ' _l, ▽ _s< ▽ ' _sagain by the correlation coefficient ρ (A obtaining in step (2.7.2), B) canonical correlation coefficient and in step (2.8.1) compares, if ρ is (A, B)>=ρ ', dual-jet DC arc plasma discharge stability is described so, otherwise discharge instability.