With printing speeds hitting frightening levels, the need for automatic on-line monitoring of print quality on the press has become absolute. Gone are the days when visual inspection or simple stroboscopic systems were enough to detect print defects and make the necessary adjustments. With printing webs ever going wider and printing speeds approaching the 1,000 meters per minute mark, the penalty for not detecting defects in time and correcting them forthwith is debilitating and, in the flash of an eye, large
quantities of expensive substrates would have gone through that is not deliverable to customers; what is more, being proprietary printed material, it would have to be destroyed or shredded realising a scrap value next to nothing. There is also the very real threat that some of these may defects may not be detected
at all and be sent to customers resulting in serious commercial repercussions.

In today’s competitive print market, it is imperative that manufacturers consistently deliver high print quality and defect-free material in every print run and maintain this over repeat print runs. One can, therefore, no longer depend on the human eye or subjective human judgement to ensure this. Thankfully, developments in digital technologies (photography/surveillance, high speed data transmission/processing and feedback, programmable logic control systems, data management etc.) make it possible to not
only automatically visually inspect 100 per cent of the print area but also integrate the output with immediate defect correction and use the data for archiving/MIS/standards for repeat runs and
the like.

All this can be done either with automatic closed loop systems or with manual intervention. Today, we have a number of good proven systems supplied by companies specialising in on-press visual inspection and control technologies and the progress made by the min the last few years has been quite remarkable. They now use high resolution CCD cameras that scan the entire print surface (at each print station,
if necessary), compare the images with computer stored masters (which also designate the tolerances permitted for each type of defect), raise an alarm in case of variation, trigger correction mechanisms, mark and highlight the defective portions for downstream removal and manage all the data for generating
MIS reports or for archiving. The software that ties all this together is extremely sophisticated. The process incorporates both defect detection for specified defects (lateral and longitudinal registration, spots/splashes/streaks, misprints or missing print, bleeding, hazing, doctor blade marks, speckle etc.) as well as efficient colour management.

What started off essentially as registration control using sample scanning of portions of the print surface with low to mid resolution cameras has today evolved into highly efficient and accurate 100 per cent visual inspection systems with much higher resolution than the human eye with closed loop correction mechanisms and colour management that deliver uniform and consistent results even while operating under all kinds of lighting levels. Originally, different companies specialised in different parts of the system (cameras, scanning systems, control systems, data management, software development and integration, colour management, workflow integration etc.) but, over a period of time, there has been a collaborative effort to deliver end-to-end solutions.

There have also been important mergers like the recent Quadtech take-over of Vigitek for pooling of expertise. Quite apart from the fact that these systems totally relieve manufacturers from the headaches of monitoring print quality on-press, they also provide “comfort” that this is being done automatically over 100 per cent of the print surface without human fatigue or the subjective decisions of manual inspection and that all of the data is available for correction as well as analysis. It releases one or more highly skilled printers to do other things on the press and considerably reduces operator fatigue, not to mention that non-automatic inspection can at best be only on an off-line sampling basis that can only statistically represent
the whole run and with no provision to take immediate corrective measures when any defect occurs. What is more, the system also helps a great deal during start-up and set-up waste is drastically reduced, especially when one considers the widths and speeds today’s machines run at.

There are many leading companies that have done path-breaking work on vision systems like AVT, Quadtech, Vigitek, Deco Systems, BST and Erhardt + Leimer, to name just a few. All of them
Have worked very closely with press manufacturers and converters for all kinds of printing and now even coating processes to develop and perfect their products. These systems do not come cheap but converters who have bought them have found them extremely useful and the ROI is quite attractive given the very
Narrow margins and “reliability” constraints that the print industry operates under; even one major rejection is enough to set people back and for wastage costs to wipe out any profits an individual print job could deliver. The computer controlled inspection also assures a consistent and deterministic quality level and the knowledge that automatic 100 per cent monitoring is happening all the time sets printers’ minds at ease.