| With the rapid development of photoelectric technology and information processing technology,machine vision detection has been widely used in the online defect detection of industry,instead of manual detection,improve the controllability of product quality.Machine vision detection system is mainly composed of information acquisition system,lighting system and data image processing system,among which the performance of lighting system plays a vital role in the accuracy of information acquisition.At present,the lighting sources used for surface defect detection of machine vision in the market are mainly coaxial or symmetrical lighting.However,the surface defect detection of some products has the problem of illumination anisotropy,and only off-axis lighting can highlight the defect information.In industry,the main hardware for on-line detection of surface defects with large or long area of leather is composed of linear array acquisition system and linear light source.However,there is still a lack of research on off-axis light source in the market.Based on the theory of single LED lighting,the theoretical model of LED full free-form surface array off-axis lighting is deduced,the relationship between LED deflection Angle and its spatial position is found out,and a light source of full free-form surface array off-axis lighting with narrow linewidness is designed and manufactured,which is applied to the orthogonal on-line detection system of surface defects in machine vision.The specific content is as follows:Firstly,the theoretical model of LED full free-form surface array off-axis lighting and the relationship between LED deflection Angle and its spatial position are constructed.According to the theoretical model of coaxial illumination of a single LED and the theory of non-imaging optics,the analytical formula of illumination distribution of multiple LEDs in space freely distributed on the target surface is obtained.In order to solve the problems of curvature mutation and overlapping among LEDs in the optimization process,the constraints of LED spacing distribution and deflection Angle were set up.The relationship between the deflection Angle of LED and its spatial position is deduced,so that the spatial position of LED can be optimized only by optimizing the two-dimensional deflection Angle.Then,through the optimization calculation and optical simulation,the LED free-form surface array off-axis lighting source is designed.Based on the theoretical model and optimization objective function established,the simulated annealing algorithm was used to calculate the optimization with different optimization parameters,and the optimal solution of multiple LED arrays in space was obtained.Then,the optimal solution was imported into the lighting design software for simulation lighting analysis.The results show that the optimal design of coaxial and off-axis lighting surface arrays can be achieved by optimizing the two-dimensional deflection Angle of LED.The arrays present full free-form surface morphology,which can effectively converge the light energy outside the light source.With high optimization degree of freedom,the illumination uniformity of the target surface(μ)and the light energy utilization ratio(η)are significantly improved.Different optimization parameters have a certain influence on μ and η.Compared with the optimization of two-dimensional LED irradiation Angle and single Angle or single spacing,η is increased by 29.8%and 15.0%,and,μ is increased by 19.6%and 6.3%,respectively.Finally,a narrow-linewidth LED full free-form surface array off-axis light source was fabricated and applied to leather inspection.The effects of the change of the width of the target surface on the average illumination(?),μ and η of the center of the target surface under the condition of constant length of the target surface are studied.The results show that when the width of the target surface decreases from 55mm to 20mm,(?) and,μ increase continuously,butη slightly decrease slowly.As the width continues to decrease,(?) and μ are basically unchanged,while the η decreases rapidly.According to this,a line light source with a line width of 20mm on the target surface was designed and made.The designed and measured values of μreached more than 91%.The method is applied to the orthogonal on-line detection system of machine vision,and linear CCD camera and linear light source are used for image acquisition,which reduces the difficulty of image processing.The experimental results show that the orthogonal machine vision system based on this off-axis light source can not only detect the normal defects on the leather surface,but also effectively detect the anisotropic defects.The blind spot detection of leather surface defects is realized... |
PDF Full Text Request