Machine Vision and Web Inspection
Higher resolution? Not always the solution
Roland Schupbach, regional business
development manager for Asia at Lake Image Systems, a Domino Company, and Russell Weller, head of product, digital colour at Domino Printing Sciences
L
abels are critical for branding and compliance, and even small errors can result in signifi cant losses for converters and brands. The need to detect and address defects
eff ectively is driving the popularity of machine vision and web inspection systems in digital, analogue and hybrid printing processes, with converters harnessing camera technology to check for substrate damage, monitor print quality and verify variable data and 2D codes downstream.
Inspection systems help ensure consistent print quality, enhance production effi ciency and minimise waste, providing peace of mind to converters. Setup time and supervision needed are minimal and the technology can enable unattended press operation, leaving operators free to attend to other tasks, or another press, while a job is running.
Converters new to inspection often believe adding a vision system will enable them to produce fl awless labels, but there is more to it.
Roland Schupbach, regional business development manager for Asia at Lake Image Systems, a Domino Company, and Russell Weller, head of product, digital colour at Domino Printing Sciences, explore common misconceptions about web inspection in the label industry.
A VISION INSPECTION SYSTEM WORKS LIKE ANY OTHER DIGITAL CAMERA
While a glimpse at the inspection screen may give the impression of taking a single snapshot of each label, the camera technology used as part of the inspection system works in a completely diff erent
way to a digital camera or camera phone. Web inspection systems use line scan cameras, which, comparable to scanners or photocopiers, ‘read’ each passing label in very small increments, row by row, at full production speed. The images of the rows are processed and combined into a complete label image in real time before being compared to a reference template based on the original artwork, with error alerts triggered if defects are detected. Defect monitoring typically includes print quality, registration and colour deviations, with the option of QR code verifi cation.
HIGHER CAMERA RESOLUTION EQUALS BETTER INSPECTION RESULTS
2K line scan cameras, able to detect defects as small as 0.5 to 1mm in diameter depending on the sheet or web width, have long been the go-to option for label converters, but with print quality demands and technology evolving, converters now have access to cameras running resolutions of up to 32K. Converters considering investment in these premium models need to consider the practicality of high-resolution inspection in day-to-day operation in terms of speed, tolerances and colour registration. High-resolution inspection is only possible at slower line speeds, as the high data volumes captured fi rst need to be processed by the camera sensor, followed by the monitoring application and PC, potentially limiting production output. Unlike inspection of monochrome variable data and 2D codes, where the distinction between good and bad print is clear, i.e. a code that can or cannot be
successfully read, print quality inspection works with preset tolerances for what type and size of defect is acceptable. These are set by the operator before printing, defi ning the ‘good’ standard to which all prints will be compared.
Mechanical accuracy should also be considered, as lateral movement of the substrate under the camera can aff ect inspection results, with higher resolution cameras more likely to detect false defects. Accurate web transportation from a high-quality press is key, as not all inspection applications are able to compensate.
A printing process that is incapable of maintaining reliable colour registration is unlikely to benefi t from high-resolution inspection.
CONCLUSION
There are clear misconceptions when it comes to adding inspection technology to label printing processes and converters are often surprised to discover the actual scope of what vision can and cannot achieve.
The converter’s needs and expectations should be taken into account when considering print quality inspection systems aimed at enhancing production processes.
Converters should partner with a trusted inspection technology provider for expert advice, a strong partner who will support them as they take their fi rst steps into inspection and who will work with their trusted label press supplier to optimise their printing and inspection process for successful and productive everyday operation.
36
February 2025
www.convertermag.com
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