Closed-loop control for consistent quality
Electronically linking the inline camera with the controls for the ink keys in the printing units allows extensive automation in stabilising the print quality delivered by sheetfed offset presses. With the KBA QualiTronic Color Control automation module the reference density is attained much faster and maintained throughout the entire print run, cutting waste and makeready time. Colour is measured on the impression cylinder in the final printing or coating unit. On perfector presses it is possible to check print quality on both sides of the sheet by taking additional measurements directly prior to perfecting.
Inline colour measurement with QualiTronic Color Control
The densities measured inline are wet values that depend on the interaction of ink, paper and fount solution. They can change chromatically in a fraction of a second, so assessment is always relative – wet values do not comply with norms. With Instruemnt Flight®, offline reference and calibration measurements are made at the start of production and the values subsequently compared automatically with inline measurements. Unlike many other inline systems this delivers standardcompliant measurements. Reference measurements can quickly be carried out on the KBA ErgoTronic console copy table using Techkon’s handy SpectroDrive scanning device. Calibration measurements are made in the printed colour control strip. The spectral device also allows control measurements to be made on the printed sheets during production.
On-the-fly inline colour measurement and control is handled by KBA QualiTronic Color Control. The density values for each scanned sheet are passed automatically to the ink-key controls, which calculate the changes (setting values) that must be made based on the differences between the reference value (specified density value) and the actual value for each individual key in each printing unit. Functions for monitoring e.g. paper white, hickeys in the colour control strip and contamination in the control strip or ink eliminate the risk of undetected spoilage during production.
The benefits of using Instrument Flight®
Available as an option with QualiTronic Color Control, System Brunner’s Instrument Flight® not only measures the individual colours (typical solid density measurement) but also the direct threecolour overprint in mid-tones and shadows (colour balance). Ink-key controls are based on these prioritised parameters to ensure that the optical result complies with colour specifications. In a halftone image, the optical appearance depends not just on solid densities or L*a*b* values in solids but on colour balance and dot gain, and how the two are controlled. Far from remaining static relative to solid density, during the dynamic offset process dot gain is influenced by the ink, fount solution and temperature and therefore changes constantly. So printing a consistently uniform solid density is no guarantee of consistently uniform images.
This is where Instrument Flight® delivers some compelling benefits over other systems on the market: whereas QualiTronic Color Control with Instrument Flight® measures and controls colour balance and other parameters that are vital for image quality in offset, other systems take a lot of measurements but cannot subsequently carry out corrections based on these measurements. With Instrument Flight® more than 30 image-crucial parameters are measured in the colour control strip for each ink key. They are then weighted and evaluated and recommendations deduced for inline colour correction. In addition Instrument Flight® supports the user with a complete diagnostic tool that with each assessment provides detailed information on weak spots in the printing process or furnishes proof that the printing process is functioning properly.
