The Research Of Real-time Measuring Method About Subpixel Level Edge Warp Of The Ceramic Tile

1. Proposition of the subjectThe ceramic tiles,as a kind of important building material, obtain thewidespread application in the modern life. Because construction industry'sdevelopment add the competition and The ceramic product enter the internationalmarket, each factory set a stricter request to the ceramic product quality. Theproduct quality examination is an important link in the ceramic tile productionprocess, which directly affects the product quality. Speaking of the ceramic tileproduction process, at present, our country ceramic tile product quality examinationgraduation is completed artificially. Many research have indicated, the human isn'tcompetent long time for the work which is monotonous and unceasingly duplicated.this has brought the multitudinous question for the quality examination graduation,and limited the quality examination graduation precision and the improvement ofstability. As the picture measuring technique has many advantages, such as thenon-contact, the high velocity, the big dynamic range, the rich information content,the relatively inexpensive cost and so on, simultaneously through the investigationand study as well as according to the ceramic tile factory request, this paperproposes the research of real-time measuring method about subpixel level edgewarp of the ceramic tile. In the computer vision measure field, orientation accuracyabout measured object's image edge and line light strip center or the edge precisionoften directly affects the entire measure precision, therefore, the research of lightstrip center and the edge accuracy orientation, as well as the precise real-timeexamination algorithm has the practical significance very much. It can be appliedto many product measure which request accuracy cooperation widely.2. Difficult point of the subjectThe task of paper is realizing the ceramic tile warp degree and the sizeaccuracy measure, according to the factory request as well as the reference countrystandard request, the paper request that we can finish the on-line real-timemeasurement to the ceramic tiles within 500mm×500mm. the warp degree isgenerally in 1mm, The general measuring technique uses the sensor measuringtechnique, the sensor measurement can only sampling a sigal point once. this paper usesthe image measuring technique to be allowed to sampling many point, but simultaneouslylost the depth information, the measuring accuracy request can achieve 0.1mm, theprecision request was relatively higher.. Research difficulty focus mainly on twoaspects of precision and real time process, usually this is two mutuallycontradictory aspects, if you want to reach the high measuring accuracy, pictureprocessing algorithm will be quite complex, this makes the real time process isvery difficult to obtain the guarantee. In my paper research. accuracy and algorithmcomplexity can balance as far as possible in the promise of measure accuracyrequired.The majority picture processing technology is executed in pixel level,because this article requests the precision is higher, the pixel level measurementcannot satisfied the request . this article proposed the subpixel level measuringtechnique. As the practical image has a lot of noise, how therefore reduces theinfluence of the noise to reach the high accuracy subpixel localization is animportant question in this topic, also is one of difficulties. In order to carries on thereal-time processing to the picture, this article proposed a real-time pictureprocessing system based on the FPGA+DSP hardware. How subpixel localizationalgorithm realize on the hardware is another difficulty in this paper.3. Overall design of the measuring systemThis article has constructed the whole plan which the ceramic tile measuresincluding how to place a CCD, how to choose a photosource and the illuminationway, how to sample the image data and how to process the image data and so on. Inthe warp measure of ceramic tile, we has designed a measurement systemcomposed of one single CCD and multi-photosources , which has covered theentire ceramic tile well by placing four lines photosources around the ceramic tile.At the same time, we has selected the dark-ground illumination way through theanalysis, this caused an obvious difference between the available image and thebackground, and makes the image easy to process. In the image processing plan,we selected the special-purpose hardware to process, and real time characterimproved greatly.4. The research of the measurng principle of warp degreeThe measure of warp used the principle of the triangle mensuration , in theinitiative visual system based on the triangle mensuration principle, structure lightwhich was shoot the surface of a measured object cause a distortion. This kind ofdistortion has reflected three dimensional information of the measured surface. Inthe article we has analyzed relations between the warp of the ceramic tile andbending of the light strip specifically, and know they are in line proportionalrelationship.5. The research of the subpixel algorithmThis paper introduced the all kinds of common subpixel algorithm simply,we proposed a method which use ideal light strip to evaluate the algorithm in viewof the present kinds of subpixel algorithm allocation accuracy and the anti-noiseability indefinite question, we analyzed influence factor of each kind of commonsubpixel algorithm. In the ideal light strip, the subpixel center or edge position ofeach row of light strip was confirmed by gray of points composed of the row. Thelight strip middle line is determined by the smallest gray change,that is a gray level.It include the whole possible position of subpixel point in the same light structure,it is used to detect the algorithm's adaption degree to all kinds of states of somelight strip.We have made some improvement to the subpixel algorithm based on thealgorithm's influence factor of precision and anti-noise performance by analyzingthe practical image. And we obtained the good effect. At the same time wedesigned an experiment in order to compare the repetition measuring accuracy ofimproved algorithms, and we drew a conclusion that improved gradient gravitymethod, namely multi-windows gradient gravity method is better in the repetitionmeasuring as well as the anti-noise aspect.6. Real-time image processing systemThe real-time image sampling and process system this paper proposed wascomposed of SK-802 CCD, SAA7111 chip, FPGA chip of 1K50 andTMS320VC5416. The A/D conversion part of the system was finished by theSAA7111 video input processor. The control part and partial algorithm wereimplemented in the FPGA, DSP chip was used to finish the computation of the sizeand the warp degree, and give the output result. Using FPGA and DSP to realizevideo signal collection and processing will enhance the system capability, and atthe same time it has advantages of adaptability and flexibility, and easy to designand debug.7. Measurement result experimental studyWe have taken some experimental research under our measure system,finished the demarcation of the measure system, and has given the experimentalresult of size measure and warp meaure, and has analyzed this system measuringaccuracy as well as influence factor, and proposed the future improvement project.