Talking about the Status Quo of Online Print Quality Inspection Technology
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The automatic print quality inspection system is a visual online detection system. The print image is scanned online by the camera and then sent to the memory for processing by the image processing software. The results are compared with the standard data to find out the difference between the two and analyze the difference. The cause of the error is generated, and the parameters are redesigned to better improve the printing quality. The emergence of this technology has greatly reduced the human intervention of print quality control, which can greatly improve the production efficiency of printing machinery, thereby reducing the requirements on the operator's skills, and providing a feasible way to truly realize the automation and intelligence of printing machinery. The implementation plan has broad development and application prospects. The following is a detailed introduction to online print quality inspection.
First, the basic principle
The online print quality line detection technology uses a CCD (Charge Coupled Device) camera to continuously take photos of printed matter on a printing production line, and transmits each captured image to a field computer through image processing software. Perform analysis and processing to find the image with quality problems, give the quality problem of the printed matter corresponding to the image, and then feed the information back to the operator through the transmission line or directly feedback to the printing machine for adjustment. The basic workflow is as follows:
First, in the preparation stage of the quality inspection of the printed matter, a certain number of qualified products are sampled to obtain a standard image (the sampling is generally greater than 60 sheets), and then formed into a template. The sampling process should pay attention to the influence of the scanning resolution, the spatial resolution of the image, the correction of the spatial coordinates of the image, the hue of the color image, the CCD speed, the illumination conditions, and the mechanical vibration on the sampled image.
Followed by the actual detection, through the CCD camera on the production line to continuously shoot the printed product, and then convert the obtained image into digital information to the central processor of the printing machine, and compare the obtained printed image information with the obtained template, according to The result of the template matching is used to determine whether feedback information is transmitted to the central processing unit or the printing machine operator of the printing machine. If a failure occurs, the matching failure information is fed back to the printing machine for adjustment or by the printing operator.
Second, online printing quality inspection technical expressions
The online printing inspection system can be divided into an online detection system and an offline detection system according to the installed carrier, and can be divided into a sampling detection system and a "100%" detection system according to the application form.
1. Differences between online detection systems and offline detection systems
The on-line inspection system is installed on printing equipment such as offset printing machines, gravure printing machines, flexo printing machines, and printing machines. It can detect printing quality in real time and can be used for sheet and web printing materials. The off-line inspection system is usually installed on the inspection machine or the rewinder, which can realize the position recording and marking function of the online inspection system. At the same time, the inspection machine also has the function of dividing the position, and automatically assigns good and bad products to different according to the detection result. In the warehouse. The visual detection part of the online detection system and the offline detection system are basically the same in function, and the most important difference lies in the processing method of the defective product. When a defect is found, the on-line inspection system usually records the location of the defect (length: web, number of sheets: sheet), or uses a printer, labeler, marking machine to mark the paper, number Detect the error number or the number of the adjacent sheet.
2. Differences between sampling and detection systems and "100%" detection systems
The technique used in the sampling inspection system is similar to that of the 100% roller observation system. The sampling inspection system adds additional software to the drum viewing system, attaching a video camera to an engine-mounted beam and equipped with a flash device that works intermittently. The 100% roller viewing system uses a completely different approach, which is to permanently install several line scan type cameras across the length of the drum, which means that 100% print inspection is not meant as a control system, only Can detect defects within a specified area. Simply stated, it is meant that the roll of printing paper is continuously detected with a specific sensitivity to the entire width.
Third, the main function of the online print detection system
1. Automatically detect the quality in the production process瑕疵
2. Correct the error before it is wasted
3. Ensure that the wrong printed product is not sent to the customer (quality assurance)
Whether installed on printing equipment, composite equipment or subsequent processing equipment, automatic inspection equipment can help printers reduce time and cost, improve print quality, avoid customer complaints and reject the possibility of receiving goods.
Current automated inspection equipment supports all printing technologies, substrates and workflows. The detection system can be configured with an array camera (such as AVT's Jupitor system), a 100% LCCD camera (such as AVT's Apollo quality inspection device), or a composite camera (such as AVT's Argus). Meet the different needs and workflows of different customers. In the printing process, automatic inspection equipment can help printers reduce waste by 50%, and the printing speed of the printing press can be increased by at least 30%, and the economic value is considerable.
Fourth, online print inspection system performance indicators
The printed product monitoring system adopts advanced image visual inspection technology, collects the surface image of the printed matter through the camera, and transmits the image data to the image processing system by the dedicated image acquisition card. The image processing system preprocesses, color segments and matches each image. Positioning and other operations are compared with the standard template image. If an inconsistent area is found and the set tolerance range is exceeded, the scrap alarm information and the reject control signal are output. In most cases, it is possible to detect missing marks, missing plates, flying ink, paste, smudges, stains, flying insects, too light ink, too dark ink, partial or full missing characters, inaccurate overprinting, wrinkles, Common printing defects such as mechanical damage, wire, and stripes; for color printing detection systems, color distortion (color difference) and color unevenness can also be detected.
V. Application in the printing and packaging industry
Visual quality inspection can be applied in the printing and packaging industry before, during and after printing, but most applications today focus on post-print quality inspections. There are tens of thousands of printing companies in China, and there are very few real-use detection systems. In addition to special industries such as printing money and tickets, they mainly focus on packaging printing, label printing, commercial printing and post-press rewinding.
1, bill printing
Bills become an indispensable part of life, and their printing quality requirements are getting higher and higher. Not only the picture quality is required to be accurate, but also the variable information such as numbers, Chinese and English characters, barcodes and patterns contained in labels and bills is extremely important. Therefore, it must be monitored in real time during the printing process. At present, China's bill printing industry is in the midst of a hot spring, and the introduction of automatic testing equipment has further enhanced the market competitive advantage.
2, cigarette package printing
Tobacco packaging differs from other products in packaging. It has its own characteristics. The technology and technology required for cigarette printing is second only to the printing of banknotes and securities. It is one of the most demanding packaging products. At present, domestic cigarette pack printing factories are paying more and more attention to automatic quality inspection. The number of companies considering the introduction of automatic monitoring systems is also increasing, which will greatly help the stability and improvement of printing quality of enterprises.
3, label printing
At present, the level of quality monitoring and testing in China's labeling enterprises is uneven. There is a clear gap between high-end enterprises and small and medium-sized enterprises. With the rising prices of domestic raw materials, the severe economic situation, and the high labor and operating costs, printing enterprises The situation is becoming more and more serious. Some enterprises are aware of the importance of controlling costs and improving quality. They have turned to automated printing inspection systems. In the near future, automated printing inspection systems will dominate the development of the label printing industry.