Machine Vision & Web Inspection What’s next for the print inspection industry?


BY JIM DOERR, TRUCOLOR VISION SYSTEMS, AND CONOR O’NEILL, ONEBOXVISION


I


nspection systems have been used in the printing and converting industry for decades now. We see new generations


come and go. As early as the 1940’s we saw the rotating mirrors optimised on roll-to-roll presses. That was soon followed by the use of high frequency strobes, and then passive sampling based viewing systems and active sampling based viewing systems. Finally, within the past decade full web width, 100 per cent inspection solutions came along.


PROGRESS OVER THE YEARS: - Rotating mirror viewers used from the 1930’s through to the 1990’s; - Stroboscopic viewers from the 1970’s to today; - Camera-based video viewers in the 1980’s; - AOI Sampling became the buzz in the 1990’s; - AOI 100 per cent print inspection in colour took off in the 2000’s; - Cloud-based networks using scanners.


So why do printers require Automated Optical


Inspection (AOI) and what is the return on investment? The print inspection industry has constantly targeted the packaging segment. Packaging is the ideal entry point because of three distinct characteristics: - Client quality standards are extremely high.


The vast bulk of printed packaging is used in the FMCG industries, where consumers associate packaging quality with product quality. The industry is also mainly in the hands of large, commercially aware companies that can impose stringent quality standards on all their suppliers.


- The raw materials used in the packaging


industry, such as plastics or coated cardboard, are significantly more expensive than the paper used in publication printing. This means that packaging printers are more acutely sensitive to wastage rates. - Designs are often intricate and usually small.


Packaging also frequently carries product information printed in small point sizes and bar codes. Manual inspection is unsuited (more-or- less useless with bar codes) to such material. Printing is a material-intensive and relatively


low-margin industry. Printers are under continuous and increasing pressure to increase productivity and improve output quality while at the same time reducing production costs. Even a small reduction in waste levels can have a significant impact on the printer’s profitability. Current solutions initially targeted customers in three distinct niches within the carton printing and packaging sector: Flexible packaging for the food industry, for example confectionery wraps; folding cartons, for example tobacco cartons; and pharmaceutical packaging on foils, for example printed foil for contact lens blisters. Purchasing drivers include marketing


requirements - for contract tenders; maintenance of existing printing contracts – minimising defects in shipped products; and the benefits of early detection of defective print in reducing waste.


ADVANTAGES OF AOI IN PRINTING The benefits that printers derive from AOI are far from unique to their industry. Nonetheless they constitute a compelling argument and are worth recapitulating in some detail. The printing process is subject to a number of


faults. The most common faults are: - Mis-registration, where one colour impression


is misaligned against others; - Colour variations, where ink quality or


operational conditions such as temperature or 20 February 2017


humidity changes the colours from those desired; - Defects, where physical incidents in the


printing process, such as ink shortage or excess at critical points, lead typically to streaks or blank patches. Intrusive dust particles are a common cause of defects.


Operator attention is inconsistent


even under ideal conditions. Human inspection is subject to a range of further disadvantages


Prior to AOI, printers had only very weak tools


available to inspect print jobs while they were in process. Strobe, rotating mirrors and video monitors can all give an image of print output. Ultimately, however, they all depend on operator attention, speed and competence. Operator attention is inconsistent even under


ideal conditions. It is essentially reactive, declining once the print job has started and only rising once output quality has fallen below acceptable level and requires rectification. Attention starts to decline again once the fault has been rectified. Human inspection is subject to a range of further disadvantages, such as: - Inconsistent attention span - a problem


compounded by the print industry’s traditional bias towards male workers; - Judgement as to what is acceptable; - Workplace distractions; - Insuficient sensitivity for process control; - Varying skill level from operator to operator; - Imprecision - the human eye is inevitably


relatively insensitive in gauging variations. Current commercial and operational trends


within the printing industry all magnify the ill effects of these disadvantages on printing companies. Most are related to time or speed or to the relatively weak commercial position of the printer, vis-à-vis his client.


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