For some years now, digital decorative printing has been a hot topic at industry conferences concerned with printing and coating technologies for the flooring and furniture sector. We are convinced that digital decorative printing will partially replace classic intaglio printing in the coming years, particularly considering that the volumes of individual print jobs are getting smaller and smaller.

We are also certain that because of the very high number of nozzles in single-pass printing, there is a high statistical probability that nozzles will malfunction. In our view, the additional and extremely high requirements placed on the substrate quality, mechanical precision and a number of environmental factors make permanent, automatic, optical process monitoring absolutely essential for a stable digital printing process.

For more than two years, Baumer Inspection has therefore been developing a scanner system for process monitoring in digital decorative printing. We have now completed initial test modules for the inspection system for digital single-pass decorative printing and have tested them in test installations.

For this, Baumer Inspection uses camera systems it has developed itself, which are produced within the Baumer Group. A decision in favour of this development was made since, early on, it was evident that the limitations of conventional cameras on the market restricted their ability to identify important errors in digital decorative printing.

These new camera systems are far more sensitive and also much faster than those used previously. Thanks to the fast on-board analysis with special FPGA modules, complex analysis algorithms can be processed, even at high resolutions and production speeds. As a result, it is possible to provide a modular inspection system with a resolution of < 30 µm that reliably detects a nozzle malfunction or synchronisation error.

The individual inspection modules are arranged in series on an optical rack system so that the optimum system is available for any printing width. The scanning width of the entire system depends on the number of individual modules arranged in series, whereby each module has a control width of around 175 mm. Spectrally selected, high-precision LED line lights are integrated in each of these modules, as are newly developed optical components for representation and illumination.

The ColourBrain® inspection system reliably identifies every error with the highest resolution without knowledge of the printed image. Thanks to gap-free monitoring of the printed substrate using these high-resolution, self-calibrating camera systems, a log of the produced aesthetic quality of the digital print and the stability of the inkjet printing process is continuously created.

Identified print errors are detected and evaluated with regard to their visibility to the human eye. The permanent availability and analysis of the process data in the Baumer Q-live database form the basis for continuous improvement of the digital printing process and for documentation of the quality of the printed product.

Our analysis of numerous nozzle malfunctions also shows that many of these individual nozzle malfunctions for an individual colour cannot be identified by the human eye, depending on the decor and position in which they occur. We therefore consider our automatic opticalinspection system to be an innovative and essential piece of inspection technology: a gap-free automatic visual evaluation of the digitally printed decorative image is carried out to assess the visibility of printing errors. Only errors that exceed a specific visibility threshold predefined in the quality instructions defined for the decor cause a production stop.

Based on test results so far and the results of further test installations,Baumer will further optimise the system until the end of 2015 and then, in 2016, will integrate a ColourBrain® inspection system in a production line with full production scope and production speed.