1 Overview In recent years, the competition for domestic cigarette pack printing has become increasingly fierce. Exquisite cigarette pack products continue to emerge. The design and printing process of cigarette packs have become more and more complicated. The materials used have also become more and more sophisticated. Gravure printing, offset printing, flexo printing, silk printing, UV printing, Technologies such as UV glazing, holographic hot stamping, and laser aluminum foil have been launched in succession. Cigarette cases with a variety of printing technologies can be seen everywhere. With the complexity and diversification of the printing process, the requirements for the inspection of finished products are becoming higher and higher. After the defective products (such as flying ink, knife silk, overprinting, etc.) appear in each process, they will finally flow into the final inspection process. If all are done manually, the workload is extremely large, and it is difficult to maintain long-term and stable depending on human visual inspection , It is easy to produce fatigue and missed inspection phenomenon, and flow into the hands of tobacco factories or users, which will cause quality accidents. According to the principle of repeatability of printing, the printing defect online detection system continuously shoots the printing pattern through a high-speed camera and compares it with an intact benchmark. When the difference between the two exceeds the set range, the detection system determines the printing defect Generate, save the defect pattern and sound and light alarm, and control the labeling machine to label the defective paper. The earliest technique used for printing quality detection was the technique of comparing the grayscale of the standard image with the detected image. The technique commonly used now is based on the RGB three primary colors for comparison. In terms of actual use, the factors that affect the detection capability are as follows. 1) Problems with printed materials In addition to the common white cardboard and coated paper, there are also a large proportion of transfer paper (including gold and silver cardboard, laser paper); in addition to printing on the paper, there are post-printing processes such as plain hot stamping and holographic positioning hot stamping , Its strong reflection characteristics make it difficult to detect under ordinary lighting conditions; and the embossed pattern is also difficult to detect due to the low chromatic aberration characteristics. 2) Paper snake running problem caused by equipment fluctuation In the printing process, with the fluctuation of tension and speed, the paper will have a snake-like running phenomenon during the progress, which is expressed in different degrees of stretching in the direction of movement and different degrees of deviation in the width direction. Difficulties in collection and comparison. 3) The problem of detection accuracy The detection system of the camera-based detection system is based on the color information of the image. If the size or color difference of the defect exceeds the observation range of the camera, such defects cannot be detected theoretically, or called unreliable detection. How to make the detection accuracy and the quality standard of the enterprise Reaching agreement is the main problem faced by testing equipment manufacturers. 4) Handling problems after detection Inspection is only a means of quality management. The purpose of inspection is to guide production and prevent the occurrence of continuous waste in a timely manner; at the same time, it should also provide a basis for judgment for finished products leaving the factory. At present, most of the online detection systems at home and abroad have not proposed a better solution. 5) The problem of installation station for online testing equipment When conditions permit, online testing equipment can be installed on all production equipment such as printing machines, hot stamping machines, slitting machines, etc., but for most companies, choosing the most suitable station can reduce costs and Can improve equipment utilization. 6) The combination of inspection data and enterprise production quality management system The main content of the data management of the inspection system is how to establish the database inside the enterprise through the network to realize the data sharing, and then provide the correct basis for production management and quality control. These key issues are extremely important for printing companies to choose the type of testing equipment. This paper studies a machine vision inspection system for online defect detection of high-speed printed products. Through the unique optical system, more obvious defects are detected and marked, prompting the next process and user; and prompting the crew to deal with the continuous defects in time to avoid greater losses; through the C / S network parallel structure, the image data Perform distributed processing and centralized statistical management. 2 System description 1) System composition The online printing quality inspection system adopts multiple color line array cameras to collect large-format prints synchronously. The image data is assisted by the FPGA / DSP acquisition card. The corresponding processing unit performs image comparison, defect extraction and classification. The network is sent to the server for statistics and management, output alarm signals and defect location information, and keep in sync with the production line through the photoelectric encoder. 2) Imaging design The hardware core device of the detection system is a CCD camera, which will affect the detection method, detection capability, calculation amount and data processing method of subsequent image processing. Commonly used CCD cameras are divided into two types: area array and line array according to the imaging method. The area scan camera is to image the subject at one exposure, and then send the whole image to the image processor for processing. The disadvantage of area scan cameras is that as the perimeter of the version increases, the number of cameras required for shooting increases, making it inconvenient to use and maintain. The linear array camera only collects data for one line of the subject in each exposure. Through continuous movement of the object, the camera continuously exposes, and finally combines multiple lines of data together to form an entire image. Linear CCD cameras are widely used in surface inspection due to their small imaging system footprint and simple light source design. The linear scanning operation of the linear CCD camera is very similar to the traditional scanner. The sensor in the camera scans one line of images at a time when a moving object passes through it, and then merges all the collected lines into a complete two through an image acquisition card. Dimensional image. 3) Lighting design The requirements for the lighting system of the printed matter camera are: ①sufficient brightness; ② prevent glare from entering the camera; ③ no stroboscopic; ④ uniform wavelength distribution of the light source; ⑤ large irradiation area. According to the above requirements, there are two kinds of light sources that can be selected, white LED light source and three primary color fluorescent light source. Compared with incandescent tungsten filament bulbs and fluorescent lamps, white LED light sources have the advantages of small size, low calorific value, low power consumption, long life, etc., but there are problems of high maintenance costs; rare earth trichromatic straight tube fluorescent lamps are an efficient, The new energy-saving light source has good color rendering and is a veritable daylight type light source. It has been widely used in TV camera lighting. Although its life span is less than that of LED light sources, it is inexpensive and easy to maintain. This system uses this type of light source. The design of the light source structure uses 4 fluorescent lamps to enter the roller surface at high and low angles respectively. The low-angle light highlights the surface contour of the printed product and the high-angle light compensates the overall brightness. In order to prevent specular reflection light from entering the lens, diffuse transmission surface filtering is used for high-angle light. 4) Processor structure In printing production, the size of the printed product is larger than 650mm, and the printing accuracy is very high (0.1mm / pixel). Single camera and single processor cannot complete the processing of huge data volume (more than 100MBbyte / s), so multiple cameras are used. Structure, simultaneous and parallel processing of different areas, the processing results are transmitted to the server through high-speed Ethernet for data management and statistics. The key problem to be solved by the system is the synchronization problem. There are two types of synchronization problems, one is the synchronization of collection and processing, and the other is the synchronization of defective data transmission. The synchronization of acquisition and processing is realized by the pulse encoder, and each processor is simultaneously triggered by the pulse encoded signal. The synchronization of the uploading of defect data of printed products on the same layout is guaranteed by the fixed timing generated by the pulse encoder. [next] 3 System characteristics 1) Detection technology for bronzing and holographic trademarks Through the unique laser holographic lighting technology, it can achieve accurate extraction of bronzing and holographic trademark features, and can simultaneously detect printing defects, as shown in Figure 3. 2) Image precise positioning technology Independently developed a signal positioning processing technology called ONE, which can automatically track the serpentine series of printed paper. This technology is the basis for the stable operation of the detection system. 3) Sub-regional detection technology Different detection accuracy can be set for different areas, and the detection of a certain area can also be shielded. 4) Automatic adjustment technology for detection accuracy According to the fluctuation state of the printing press, the detection accuracy can be automatically adjusted to achieve the optimal detection effect. 5) Forecast technology of defect trend Arbitrarily set the defect alarm threshold and labeling machine action threshold, predict the trend of defects, and identify major defects in time. 6) High-speed image processing technology Adopt self-developed multi-thread processing algorithm, work stably for a long time at the printing speed of 300m / min. 7) Management technology of historical data Can print, statistics, display, and query historical defect data; the storage time can reach any number of years as needed. 8) Multi-screen display technology In addition to the control cabinet, an optional display is installed at the key station to display the operation interface and defect data and real-time images respectively, which is convenient for the operator to check the quality status and system operation status at any time. 9) Friendly man-machine interface After the operator sets the parameters, it can automatically detect the startup, shutdown, roll change and equipment fluctuation status. No manual intervention is required from the beginning to the end of printing. Different alarms can be set for different defects to remind the operator to pay attention. 4 Use effect In this study, two color linear array CCD cameras with a horizontal resolution of 4K and a vertical resolution of 15K were used to detect the 820mm wide printed layout. Parallel processing and distributed control were performed through Gigabit Ethernet, and the client / server method Conduct centralized data query and management. 1) Algorithm efficiency In this system, the image processing part is all written with MMX / SSE optimized instruction set, which realizes parallel processing of single instruction and multiple data. When the speed of the production line is maximum (300m / min), the cycle of the detection system to collect a complete version of the image is 211ms, the processing time (128ms) is sufficient to meet the real-time requirements, and the maximum can meet the printing speed of 500m / min. 2) Detection accuracy The detection accuracy of this system depends on the detection resolution and detection level. CCD is a discrete sampling device. According to the Nyquist sampling theorem, the smallest defect size can be detected at more than twice the detection resolution; for example, the above camera is used to observe the 410mm format, and the printing speed is 200m / min. The rate is 0.1mm, the longitudinal resolution is 0.22mm, and the smallest defect that can be detected stably is 0.2mm × 0.44mm; Detection level is an important function of this system. Because the detection requirements of each position of the printed matter are different, for example, the barcode area is the strictest, and the adhesive area or the cutting area is the loosest, it is unrealistic to use the same level for all areas, which will cause many unnecessary alarms. Therefore, the setting of the regional level actually adopts different thresholds for different regions. These thresholds are set in advance according to the requirements of quality management before the system detection starts. 3) Types of defects detected Figure 4 demonstrates four typical printing defects and defect detection legends, the actual pictures are all color pictures. Among the printing defects, flying ink accounts for more than 80%, and the most continuous defects are wire defects. Such defects are small in size and have slight traces, which are sometimes difficult to detect with the naked eye. In this example, the Pixel analysis detected a 0.25mm wide wire. 5 Summary Print quality online inspection technology and system has been monopolized by Europe, America and Japan. This system uses the industry's most advanced hardware equipment (including cameras, capture cards and processors), software with independent intellectual property rights (registration number: 2008SR12259) and invention patents (200410061396.7 and 200410061395.2), which can effectively print products on high-speed printing production lines. Detection and alarm of printing defects such as knife wire, flying ink, ink cross, leaking, dirty version, roll change, ink dot, overprint deviation, etc., and installed and used in Dali Mideng Printing Co., Ltd., stable and reliable operation. In addition, the online detection technology for printing defects is not omnipotent, and there are technical bottlenecks. For example, the resolution of the vertical pixels is much greater than the detection accuracy of the overprint system. Therefore, this system is not sensitive to overprint running of less than 0.2mm. Better detection effect. In addition, it is insensitive to low-contrast color aberration, and a color difference meter needs to be used for color spot check. Slip Sheet,Slip Sheet For Shipping,Slip Sheet For Transport,Slip Sheet For Pallet DONGGUAN YEE HUP TRADING CO,.LTD , https://www.dgyeehupack.com
A New On-line Detection System for Defects in Cigarette Label Printing