The automatic printing quality detection system is a visual online detection system. The printed image is scanned online by the camera, and then sent to the memory for processing by image processing software. The result is compared with the standard data to find the difference between the two and analyze The cause of the error, and then redesign the parameters to better improve the printing quality. The emergence of this technology has greatly reduced the human intervention of printing quality control, which can greatly improve the production efficiency of printing machinery, thereby reducing the requirements for the skills of operators, and provides 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 printing quality inspection.
1. Basic principles
The on-line printing quality line detection technology is to use the CCD (Charge Coupled Device) camera to continuously take pictures of the printed matter on the printing production line, transmit each posted image to the on-site computer, and image information through image processing software. Analyze and process, find the image with quality problem, give the quality problem of the printed matter corresponding to the post image, and then feed back the information to the operator through the transmission line or directly to the printing machine for adjustment. The basic workflow is as follows:
First, in the preparation stage of printing quality inspection, a certain number of qualified products are sampled to obtain standard images (generally more than 60 samples), and then made into templates. 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 lighting conditions, and the mechanical vibration on the sampled image.
The second is the actual detection. The CCD camera on the production line is used to continuously shoot the printed products, and then the resulting image is converted into digital information and transmitted to the central processor of the printing machine. The obtained printed product image information is matched and compared with the obtained template. The result of template matching is used to judge whether there is feedback information to the central processor of the printing press or the operator of the printing press. If a fault occurs, the matching fault information is fed back to the printing press for adjustment or processing by the printing operator.
2. The manifestation of online printing quality inspection technology
The online printed product detection system can be divided into an online detection system and an offline detection system according to the carrier it is installed, and can be divided into a sampling detection system and a "100%" detection system according to the application form.
1. The difference between online detection system and offline detection system
The online detection system is installed on printing equipment such as offset presses, gravure presses, flexo presses, code printers, etc., to detect the printing quality in real time, and can be used for sheet and web printing materials. The offline inspection system is usually installed on the inspection machine or rewinding machine, which can realize the position recording and marking function of the online inspection system. At the same time, the inspection machine also has a warehouse function, according to the inspection results, automatically assign good and bad products to different Warehouse. The visual inspection part of the online inspection system and the offline inspection system are basically the same in function, and the main difference is the processing method of the defective product. When a defect is found, the online inspection system usually records the location of the defect (length: roll paper, number of sheets: single sheet), or uses a printer, labeling machine, marking machine to make marks on the edge of the paper, number Detect and record the wrong number or the number of adjacent sheets.
2. The difference between the sampling inspection system and the "100%" inspection system
The technique used by the sampling inspection system is similar to that of the 100% drum observation system. The sampling inspection system adds additional software to the drum observation system, fixes a video camera on a beam equipped with an engine, and is equipped with a flash device. The system works intermittently. The 100% cylinder observation system uses a completely different method, which is to permanently install several line scan type cameras along the entire length of the cylinder, which means that 100% print inspection is not meant as a control system, just Can detect defects within a specified area. Simply put, it means that the printing paper roll is continuously tested with a specific sensitivity for the entire width.
3. The main functions of the online printing inspection system
1. Automatically detect quality defects in the production process 2. Correct errors before waste occurs 3. Ensure that the wrong printed products are not sent to customers (quality assurance)
Whether it is installed on printing equipment, composite equipment or subsequent processing equipment, automatic detection equipment can help the printing house reduce time and save costs, while improving print quality, avoiding customer complaints and the possibility of rejecting receipts.
The current automatic inspection equipment supports all printing technologies, substrates and workflows. The inspection system can be equipped with an array camera, (such as AVT's Jupitor system), or a 100% LCCD camera (such as AVT's Apollo quality inspection equipment), or a composite camera of both (such as AVT's Argus). Meet the different needs and work processes of different customers. In the printing process, automatic detection equipment can help printers reduce waste by 50%, and the printing speed of the printing press can be increased by at least 30%, which brings considerable economic value. [next]
4. Performance Index of Online Printed Product Inspection System
The printed matter monitoring system adopts advanced image visual detection technology, collects the surface image of the printed matter through the camera, and transfers the image data to the image processing system by the special image acquisition card. Positioning and other operations, and compared with the standard template image, if found inconsistent areas and exceed the set tolerance range, output waste alarm information and rejection control signal. In most cases, it can detect missing prints, missing editions, flying ink, pasting, smudging, stains, flying insects, ink color is too light, ink color is too dark, partial or all missing characters, overprinting is not accurate, wrinkling, Common printing defects such as mechanical damage, knife wire, and stripes; for color printing detection systems, it can also detect color distortion (color difference), color unevenness, etc.
5. Application in the printing and packaging industry
The application of visual quality inspection in the printing and packaging industry can be in pre-press, during and after printing, but most applications are currently focused on post-press quality inspection. There are tens of thousands of printing companies in China, and very few of them actually use detection systems. Except for special industries such as banknote printing and ticket printing, they are mainly used in packaging printing, label printing, commercial printing, and final inspection after printing.
1. Bill printing
Bills have become an indispensable part of life, and their print quality requirements are getting higher and higher. Not only the quality of the picture is required to be accurate, but also variable information such as numbers, Chinese and English characters, barcodes, patterns and other information contained in labels and bills are extremely important. Therefore, it must be monitored in real time during the printing process. At present, China's bill printing industry is in hot water, and the introduction of automatic detection equipment has further improved the market's competitive advantage.
2. Cigarette printing
Tobacco packaging is different from the packaging of other products, and has its own characteristics. The technology and process required for the printing of cigarette packets is second only to the printing of banknotes and securities, and it is one of the most demanding packaging products at present. At present, domestic cigarette pack printing factories are paying more and more attention to automatic quality detection, and the number of companies considering the introduction of automatic monitoring systems is also increasing. This will greatly help the stability and improvement of the printing quality of enterprises.
3. Label printing
At present, China's label companies have varying levels of quality monitoring and testing, and there is a clear gap between high-end companies and small and medium-sized companies. Facing the increasingly severe situation, some companies have realized the importance of controlling costs and improving quality, and have invested in automated printed product inspection systems. In the near future, automated printed product inspection systems will dominate the development of the label printing industry.
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