Inspection technology, in rotogravure and flexographic package printing, usually occurs at the end of the process – when a printed substrate comes off the press. In post-press converting, these errors are revealed. Then, the printer/converter prints over-runs to compensate his customer for these errors. Consequently, margins are reduced.
But today, inspection systems are available that eliminate the need for over-runs. One-hundred percent of the web-width and the entire repeat can be inspected – 100 percent of the time. However, for printers to gain a competitive advantage and reduce waste, his operators need accurate error feedback.
Web printers can perform 100 percent print inspection with systems that enable their operators to monitor and improve the quality of the entire run. Although, as printers evaluate these systems, they will want to invest in 100 percent systems that are modular; systems that have sufficient line-scanning capability; and in technology that can perform a twin-check…the twin-check of 100 percent inspection along with digital web monitoring, all in a single system.
System FunctionalityOne-hundred percent inspection systems need high-power LED (HPLED) illumination. HPLEDs emit more light than other light sources. Their efficiency is not affected by size and shape, like fluorescent light. HPLEDs have the longest life compared to other light sources. 100 percent systems typically inspect opaque printing substrates, but the best systems have the ability to supplement the illumination source and inspect transparent or reflective material.
While evaluating 100 percent inspection systems, printer/converters should consider:
Housing Module: The housing should fit into a minimum space. The housing should be completely enclosed in order to prevent contaminants from accumulating on lamps and cameras.
Masking Function: Preferred systems have masking functions. This allows the inspection of distinct areas with different sensitivities. Using masks ensures that critical areas – like logos – are finely-inspected with higher sensitivity, and that insignificant areas can be evaluated with lower sensitivity.
Line-Scan Cameras: The most-important variable in 100 percent systems is the ability to configure it with the right amount of line-scan color cameras. This alone determines its effectiveness at inspecting wider webs. Small errors must be detected, whether in a narrow web or in a wide web. Some 100 percent systems have just one (1) camera – whether that system is installed on a label press, or on a gravure packaging press. Higher-end systems can add up to four (4) high-resolution color cameras. The preferred systems add cameras based upon web-width.
System OperationSome 100 percent systems require the operator to enter multiple parameters before they can operate it. Easier-to-operate systems only require web-width and repeat-length. Entering width and repeat only requires 20 seconds. On the display monitor, the operator needs split-screen functionality, which compares the current live-image to a saved “golden master.” Inspection systems that are most user-friendly can toggle between the error image and the reference image by pressing one button. If errors are not caught in time, the system should generate a signal.
Advanced 100 percent inspection systems come standard with web-monitoring built into the system. These systems use the line-scan cameras to perform this valuable twin-check. 100 percent systems with web-monitoring also have position memory, for individual sections of the repeat. They also have automatic scan mode, to monitor the repeat in defined increments.
Error-Detection, Error-Classification, Error-HandlingUpon detection, a 100 percent system should categorize errors into two different classes: either random, non-recurring events; or errors related to the printing process. Operators need this feedback immediately. If it’s random, operators do not need to react because this error is a one-time sporadic event, like an ink-splash. But if it is related to the printing process – doctor blade streak, registration, etc. – then the operator needs feedback in order to make a fix. These process-related errors lead to waste. The best systems immediately alert operators to specific types of process-related errors. During evaluation, printers should look for:
Classification: Process-related errors should be subdivided: e.g., register errors, streaking, color errors, flaws.
Sensitivity Levels: Ability to set different levels of sensitivity for each and every error type.
Error Database: A roll-report needs to be saved on a server, for added off-line processing.
Waterfall Display: The 100 percent system must generate a graphical display of error classes – not merely a list of numbers. Operators must visualize where errors have occurred in the print format, and in which class. The ideal display format for this is a waterfall-type display, which displays on the monitor. This gives operators the most-comprehensive overview about recent errors.
Only the First, Last, and Largest Error: But operators should not be overloaded with error data. Ideally, only the three most-important errors – the first, the last, and the largest error – are displayed.
Scalable and Expandable 100 Percent Print InspectionWhen a 100 percent print inspection system is purchased, you don’t want to be forced to purchase capabilities that you may never use. If you don’t need to inspect barcodes, why buy that capability now? A 100 percent print inspection system must be modular; it must be expandable; it must be scalable. When needed, a 100 percent inspection system should offer the ability to add:
Traversable Matrix Cameras: These cameras can provide an optical zoom; some manufacturers offer up to 16-times zoom.
Special Flashes: Matrix camera flashes that can inspect cold seals, varnishes, fluorescents, embossing.
PDF Comparison: This feature saves wasted substrate, and time, by detecting inaccurate graphic layouts and/or text blocks before printing. It can immediately detect faulty press cylinders as the PDF is compared to the reference image.
Sampling Inspection: For future jobs requiring inspection of the backside of the web.
Inline Color Measurement: Web printers need to maintain consistent color throughout their run. Adding inline color measurement to the web-viewing accomplishes this. Operators can define a range of acceptable color – upper and lower limits. As the press is running, the operator is alerted if the color begins to drift into an unacceptable range. Working in the CIE-LAB color space, values of delta E, delta L, delta a/delta b, and delta C/delta H are available to aid operators in analyzing color trends – before waste is created.
Barcode Verification: This function ensures legibility of the printed barcode, according to ISO 15416 and ISO 15420 standards.
CI Flexo – Register Control: Configuring your system with this feature will achieve registration within 60 seconds. While the press is not running – and not wasting any substrate – job-specific data is entered on the touch-screen. Then, after start-up, registration marks are measured and all print units are brought into registration; within 60 seconds all print is in register.
CI Flexo – Auto Set Technology: This feature automates print impression settings. The ink-deck settings are adjusted automatically, without wasting substrate.
One-hundred percent print inspection technology enables printer/converters to print without errors and to save on waste. With a reduction in errors, there is less need to print over-runs, raising profit margins. All 100 percent inspection systems detect errors, but how these errors are handled and classified is a major separation point between alternative systems. The two essential error classifications are: (1) sporadic-print errors; (2) process-related errors. When process-related issues are managed quickly, errors dissipate and there is a dramatic reduction in waste.
The best systems are scalable and expandable. The most-important technical consideration when evaluating 100 percent systems is choosing one that can configure line-scan cameras based upon web-width. The innovative systems are expandable and scalable. These modular 100 percent print inspection systems can adapt, change, and grow – just as customers and production needs change and grow.
eltromat America Inc.