Ellerhold uses Global Graphics screening

The German company Ellerhold, which makes printing systems for billboard advertising, has used screening software from Global Graphics to solve a banding problem caused by variations between printheads. 

This image shows the effects of banding on the left, and then with the Global Graphics’ ScreenPro software having removed the banding on the right.

Ellerhold manufactures and operates 6 MLM_2600_NG double side 2.5 m wide scanning head web systems for printing 200 x 252 dpi billboard displays. The company was experiencing quality issues on its large-format posters, known in Germany as Mega-Lights. The printheads showed variation in printed density both between the heads and across each head, which produced clearly visible bands within some types of printed output.

Frank Ellerhold, founder of Ellerhold AG, explains: “Certain jobs were worse than others. We knew the problem lay in the fact that the printheads were not balanced. We had seen Global Graphics Software’s Martin Bailey introduce ScreenPro at The Inkjet Conference in Düsseldorf and believed this new technology might be the answer to this problem.”

To counter this Global Graphics’ Technical Services team recommended its PrintFlat software, which is part of its ScreenPro technology. In ScreenPro every nozzle can be addressed separately on any head/electronics to achieve very fine granularity. PrintFlat adjusts the density within ScreenPro to produce uniform density across a print bar. The process can be automated for closed-loop correction, and unlike correction by adjustment of voltages, there is no effect on jetting stability or head lifetime, nor ink pressure and timing/drop speed variation. The team also used a variant of Global Graphics’ Advanced Inkjet Screens (AIS), available with ScreenPro and with the Harlequin RIP which they adapted specially for scanning-head systems and which proved very effective.

The Technical Services team carried out tests, analyzed the scanned prints and created a PrintFlat calibration workflow for the MLM_2600_NG designed to compensate for the non-uniformity in output across the print bar. Ellerhold is now using Global Graphics’ online inkjet press calibration service, printflat.com, to upload the scans and automatically receive the correct calibrations. This service is available to registered users who upload their PrintFlat scans and receive the calibrations they need to run their inkjet press at optimum quality.

Dr Danny Hall, Global Graphics Software’s chief screening scientist, who developed the Advanced Inkjet Screens, commented: “The project brought many unique challenges. As it was a multi-pass process we needed to efficiently capture repeating density variations across the entire print area in an unbiased way. The project confirms that PrintFlat is a significant enabling technology, allowing the uniformity typical of analogue printing to be achieved routinely on a wide range of digital presses.”

ScreenPro can be used in any print workflow, including Adobe, Caldera, Esko, EFI and Sofha, with any combination of inks, substrates, printheads and electronics.

You can find further details at GlobalGraphics.com.

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