However, while electroanic measurement devices have proven themselves for consistency of readings and repeatability of measurements, typically ±0.1cm³/m² for process aniloxes, accuracy of measurement has been subjective.
The accuracy of measurement has been a point of contention between the different anilox manufacturers who rightfully defend their own historic (analogue) methods of measurements, which, as reported in a study in 2007, showed significant variations in measured volumes (often over 50% difference) from each manufacturer on different bands of a 12-banded test roll.
The need for accurate volumetric measurement was, therefore, demanded by printers who wanted a proven reference from which to measure their anilox inventory, and as a volumetric reference point when ordering replacement rolls from any manufacturer.
Accurate volumetric measurement
To prove accuracy two questions need to be asked. How accurate does the measurement system need to be and what reference should be used to qualify ‘accurate’?
How accurate do we need to be?
Achieving the correct densities in process colours is the most costly part of press set-up owing to the need to achieve correct colour density and is, therefore, a good starting point.
Studies have shown that process aniloxes engraved to within 0.4cm³/m² of one another will achieve a typical colour accuracy of 3DeltaE. So if inventory is within 0.4cm³/m² the printer will achieve the desired colour target faster and minimise waste. Thus a suitable target for the measurement instrument would be a repeatable accuracy of ±0.1cm³/m² for the range of process aniloxes, and of ±0.2cm³/m² for coarser screen counts.
And how do we qualify the term ‘accurate’? With electronic scanning devices it has been possible to prove volumetric accuracy that has not been possible with analogue (ink drawdown) systems.
The ability to prove accuracy has been an evolutionary process and has become a practical solution since earlier this year.
The method of proving accuracy is through simple mathematics and spheres.
If the diameter of accurately ground sphere (ball bearing) is known its X, Y and Z dimensions, its volume and surface area and any other parameters can be calculated through simple maths.
Extrapolating that data makes it possible to calibrate the electronic scanning microscopes to within ±1µm to accurately define the volume of the sphere. Once the 3D scanning microscope (AniCAM) is calibrated to the sphere, the analysis program (Anilox QC application) will correctly measure the volumes of any anilox.
Proving the theory
In February this year, working in conjunction with Swansea University’s Welsh Centre for Printing & Coating under Professor Tim Claypole (one of Europe’s most respected ‘print’ professors), Troika undertook a project to test the depth and volumetric accuracy of a sphere-calibrated AniCam against the University’s very high-end interferometer measurement system on a 12-banded anilox, engraved from 600 lpcm down to 40 lpcm. The devices used different mathematical models to calculate the volumes on the 12 different anilox engravings used for the test.The correlation of measurement between the two systems was exceptionally close.
States Dr Davide Deganello: ‘As there’s a recognised inevitable variability of volume due to surface roughness minor variations in measurement were expected. However, there’s a high degree of consistency between the two systems. The accuracy of the measurement systems is certainly well within the required measurement requirements of the industry.
Says Phil Hall, MD of Troika Systems: ‘A standard of volumetric measurement has now been scientifically proven with a practical instrument that can be used on the shop floor. Printers and anilox manufacturers can now be confident that measurements are realistic and based on credible data, from which the industry can work as a proven point of reference.’
The South African connection
Taking up the story from a local perspective is CAE’s technical director, Paul Rich, whose company represents Troika in Southern Africa. ‘We believe strongly in this equipment and the accuracy of the system,’ Paul confirms. ‘We have a similar ethos – the pursuit of accuracy, quality and repeatability with regards to screen and volumetric measurements. We also believe all serious printers should be using the system to ensure control of their anilox inventories,’ he adds.
According to Paul, this system can help printers to save money and improve print quality while reducing waste and downtime. ‘The tools are now available along with local support and training from our technical representatives,’ he maintains.
‘Printers need to take ownership of their anilox inventory management; and regular measurement ensures they can see if anilox rollers/sleeves are clean, if cleaning procedures are working efficiently, and if rollers/sleeves are fit for use,’ he continues.
Improving colour management with brand owners is just one of the key benefits he cites. ‘The beauty of the system is having one standard between multiple devices, and these devices are calibrated to a scientific standard.’
CAE is keen to demonstrate the system to printers to emphasise the ease of use and functionality, and to help them understand the quick ROI.
‘Serious printers should give us a call and let us help them purchase and implement these solutions and start saving serious money!’ are his closing words.