Design Of Flexographic Printing Dot Detection System Based On FPGA

In the printing industry,flexographic printing has the unique advantages of environmental protection and has achieved rapid development at home and abroad.At the same time,people have increasingly demanded the printing quality of flexographic printing.As the basic unit constituting a printed image,the dots reproduce the tone and color of the image through its area and spatial frequency changes,which directly determines the printing quality.Therefore,the detection of flexographic printing dots plays an important role in printing quality control.With the development of flexographic printing towards automation and digitalization,the traditional method of dot detection cannot meet the needs of modern printing production.This thesis studies the problem of flexographic printing dot detection,and aims to design a system that can accurately perform flexographic printing dot detection.After analysis and comparison of research status at home and abroad,this thesis uses the digital image method based on image processing in the method of dot detection.Based on the principle of digital image method to detect dot and the functional requirements of the system,this paper designs the overall scheme,and constructs a printing dot detection system with FPGA as the core processing device,camera as the image acquisition device and LCD display as the result display device.In terms of dot detection algorithms,this thesis addresses the difficult point of dot image segmentation in a dot detection system,analyzes and studies different segmentation methods,and then uses the OTSU method in threshold segmentation to segment dot images.For the problem that the OSTU method fails to effectively segment the stuck dot images,the sliding window is used to improve the OTSU method.After the dot image segmentation is completed,a dot area ratio detection algorithm based on the connected domains in the dot image and a dot shape analysis algorithm based on the dot aspect ratio,dot circularity,and other parameters are designed.Finally,experiments are performed on the algorithm with tools such as MATLAB and Open CV,and the effectiveness of the algorithm is verified.At the system construction level,this thesis divides the system into two parts,hardware development and software development,based on the design principles and methods of the FPGA system and the actual situation of the Xilinx's ZYNQ series FPGAs.In the hardware development part,according to the characteristics of the hardware description language,combined with the characteristics of programmable logic circuits,using high-level synthesis technology and reasonable use of FPGA internal resources,the camera image acquisition IP cores,dot image segmentation IP core and images Encoding IP core,etc.In the software development part,the relevant drivers were written.The compiler tools provided by Xilinx were used to customize the Linux system.The applications needed for the design were transplanted.Finally,a dot detection program based on the dot area ratio detection algorithm and the dot shape analysis algorithm is constructed.This thesis then conducts module simulation and system debugging.The results show that the system designed in this paper can detect flexographic printing dots well.