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FLEXO Magazine : April 2011
Technologies & Techniques There are several options in strobe and lighting technology, as well. Depending on the application, inspection systems can use special varnish strobes, UV strobes, LED strobes and xenon in a wide range of combinations. These are especially effective for use with clear and opaque films and metal- ized substrates. At the same time, electronic shutters are now 1,000 times faster and totally eliminate “false positives” created by overhead fluorescent lights or sunlight coming through skylights in the plant ceiling. Finally, web backer technology has improved. Although they are often overlooked, special web backers for clear and opaque film substrates comprise a critical element in effective defect detection. Today ’s systems use sandwich-style web backers with special coatings that minimize reflectance while optimizing image contrast. Line Scan Camera Technology High-resolution color line scan cameras for print inspection applications have evolved at a moderate pace, with improve- ments in speed, pixel size and price. When modular array architecture became available, it was the tipping point that made inspection with line scan cameras possible for wide web applications. For example, the wide web flexo 100-percent inspection system by BST Pro Mark uses an array of 2,300 -pixel cameras with dedicated dual-core microprocessors, allowing it to inspect webs of 81 inches at 1,800 feet per minute, and it finds defects as small as 0.18mm2. Folded optical beam camera design minimizes what would otherwise be huge space requirements for the camera, and allows the system to be used with clear, opaque or reflective substrates. Although there are many light- ing schemes in use with line scan cameras, non water-cooled LED lighting is evolving as the stan- dard for line scan print inspection. LED lighting can be readily con- trolled to optimize image quality on multiple substrates; it has a clean reflectance profile, requires little maintenance and has an extremely long life. Mathematics and Software Recent years have seen the evolution of mathematics and software, as well. The effective- ness of defect detection and 100-percent inspection has greatly improved as software research and development specialists have engineered the algorithms used to identify print defects. Image processing has become more sophisticated. In addition to defect detection, color monitoring and barcode verification, today ’s wide web systems take control of the press and automatically set register and impression of the anilox and plate cylinders. This is done in minutes using only hundreds of feet of mate- rial. The savings in time and material alone will generally pay for the entire system in a few months, which is why few new wide web presses are installed today without it. Modern software allows the master job PDF file from the prepress department to be linked to the press. Once there is print on the web, the actual print is compared against the master PDF file. This will identify any incorrect plates on the press and detect if dropout occurred during platemaking. Different interfaces offer varying degrees of operator ease of use. Leading systems tend to be operator-friendly and incorporate “ wizards” to simplify job setup. Interfaces now allow users to define acceptable defect sizes and tolerances in quantifiable terms. For example, operators can set the sys- tem’s parameters to identify streaks of 0.05 mm or larger. Finally, because converters rely on these systems to ensure quality and minimize start-up time, they require around-the-clock remote service support. Remote services via Internet connection allow manufacturers to troubleshoot, and often they can correct problems in hours rather than days at a fraction of the cost and with far less disruption of the converter’s operations. Some flexo presses are extremely consistent from repeat to repeat, and some are not. Today ’s 100-percent inspection systems will identify process variations from one repeat to an- other as defects. Be sure the system you buy has the capabil- Photo 1. Press with multiple systems. 20 FLeXO aPril 2011 www.flexography.org