Research On Key Techniques Of Surface Defect Image Detection For Cold Rolled Strip

The cold rolling strip surface defect inspection technology is one of key technology, which could enhance the product market competitive strength of steel enterprise and improve the production engineering. The traditional surface defect inspection technology is being weeded out gradually, the surface defect inspection technology based on machine vision has replaced it and become the main trend of strip surface defect inspection technology. In 20 century's ends, some developed countries in European and America have designed successfully the surface defect inspection systems based on machine vision. In our country the research on this technology is limited by surface defect inspection speed, image processing speed and so on, so far no successful system has been used on-line. This situation impacts the market competitive strength of our country's cold rolling strip product partly and makes against for improving the strip product add-value.The image processing algorithm is various and complex in surface defect inspection technology based on machine vision. At the same time the image processing system has the interacting problem between flexibility and processing efficiency, which is realized by using specialized ASIC chips or general purpose MPU. The specialized ASIC chips could realize high-speed image processing reliably, but lacking flexibility and being unable to be modified once designed for certain algorithm function, also having long development cycle and complex chip-design. The general purpose MPU (such as computer, DSP and so on) could realize different image processing algorithms flexible, but limited by the processor's architecture. The parallel processor array is used in the application with high processing speed demand, which makes hugeous system, expensive price and complex maintenance. Aiming at these problems, the dynamic reconfigurable technology based on FPGA hardware platform and the image parallel processing technology based on multi-IP core are researched in this paper, which make system realize more complex function with less hardware resource, improve the system execution speed and also reduce the cost.The source and types of surface defect image noise are analyzing. Based on researching on PDE image processing model, the AMSS equation meeting contrast invariance and affine invariance condition is selected for surface defect image smoothing processing, which removing the noise information of defect image effectively. The finite difference method is used to solve AMSS equation, also the iteration step length and dimension parameter's impact on smoothing effect is analyzing. The definition format of symmetry cross entropy is improved. The iteration stop standard is brought forward based on improved symmetry cross entropy, avoiding the smoothing dimension parameter selection problem of depending on artificial observation of smoothing result and widening the application field of image smoothing method based on AMSS equation.The cold rolling strip surface defect is affected by strip material and defect forming mechanism, so transitional region exists between defect and normal strip widely. The transitional region information is helpful for the types identification of strip surface defect, so the local threshold value image segmentation method based on transitional region is brought forward. This method makes use of the transitional region information sufficiently, overcomes the problem that son image size could affect image segmentation effect in local threshold value method, enhances the accurateness and integrality of defect segmentation. Extracting the defects'gradation characteristics, veins characteristic and invariant moment characteristic based on gradation accrete matrix, the same defect characteristics are extracted using kernel PCA method, which reduces the interdependency among the same defect characteristics. Combinating defect characteristics based on information amalgamation theory and reducing the redundance among different defect characteristics in combination characteristic by using PLS to analyse combination characteristic, these make the combination characteristic describe the defect more precise and effective.The SVM classification theory is researched, the multi-class classification method based on SVM is analyzing. Combining a kind of SVM multi-class classification method with nondeterminacy theory, the defect classifier is designed and the classification experiment is done. On the situation of limited samples, the highest classification accurate ratio gets up to 95%, using different characteristics combination. The reconfigurable image parallel process system is developed, realizing surface defect image preprocessing and segmentation algorithm in the system, enhancing the mathematical operation speed of image processing algorithm. The real-time process speed of image processing system reaches to 39 frames per second.Through the theory and experiment research on surface defect inspection technology, the realization plan of reconfigurable parallel image processing system and the method of surface defect image processing and classification identification are proposed. The algorithm of defect image preprocessing and segmentation is realized in developed image processing system, reducing the complicacy of image processing system, enhancing the execution efficiency of image processing, improving the real-time ability of surface defect inspection system.