Dr. MARCUS FRANK
Head of R&D and Product Management, Large Area Coating Glass,
Bühler Leybold Optics Alzenau GmbH, DE
Marcus Frank studied physics in Erlangen, Germany and was introduced to physics of optical interference coatings while working for his PhD at the Fraunhofer Institute for Applied Optics and Precision Engineering in Jena, Germany. Subsequently he was internationally active for multiple employers in the field of large area coatings designing and developing coating products and processes for the architectural and automotive markets. Since 2018 he is responsible for product management and R&D in the Market Segment Glass at Bühler Leybold Optics Alzenau in Germany.
How to Minimize Product Setup Times in Large Area Coater Operation
“Closed-loop control” is a well-established concept for many engineering applications. This is also true in the field of architectural and automotive thin film coatings. Equipment manufacturers as well as coating companies develop and continuously refine automation solutions to decrease product setup and changeover times as well as production yield.
The closed loop control scheme is a common technical solution, and its principle is simple: Spectral data of a coating are measured. The spectra are reverse engineered by layer thickness variations based on a theoretical model. The result – actual layer thicknesses of each individual layer of the coating stack – is compared to the originally modelled layer thicknesses. From the derived thickness deviations, the optimized process parameters are calculated (e.g., power, reactive gas flow, magnet bar positions of individual processes) and fed back to the individual process compartments.
In the field of large area coatings, the required plurality of individual processes adds multidimensional complexity and challenges to this concept. This complexity and the varying conditions in a production environment typically result in a disappointing gap between measured spectra and theoretical model.
In this contribution some selected approaches are presented how to set up coating products efficiently by using the closed loop control concept. What optimization strategy should be applied? Which layers should be available for thickness tuning? What product parameters should be primarily met during the optimization? What are the key optimization targets? Measured reflectance spectra, transmission or even absorption or is it sufficient to just focus on the product color values as these are key product parameters?
All these questions will be discussed in greater detail and some specific examples will consider, what kind of measured and calculated data help to minimize product setup time when applying the closed loop control concept based on a reverse engineering approach.