32 n MACHINE VISION April 2026 www.drivesncontrols.com Non-contact vision system inspects R2R thin-film production at high speeds Researchers at TU Wien University in Austria have developed an inline system that delivers real-time optical thickness measurements of functional coatings on moving foils, eliminating the sampling delays and blind spots that have long plagued R2R (roll-toroll) quality assurance. The ellipsometer – a non-contact optical instrument that measures the thickness and optical constants (refractive index, dielectric function) of thin films and surfaces – has been purpose-built for R2R production applications. R2R systems lay down functional coatings onto flexible substrates at speeds of more than 100m/min, to produce items such as lithium-ion battery electrodes and flexible displays. At these speeds, a single process excursion – such as a viscosity shift, temperature drift or misalignment – can propagate undetected across an entire roll. What's been missing so far has been a metrology platform that is capable of measuring coating uniformity, thickness consistency, and surface defects simultaneously – non-destructively, and in real time across the full width of the substrate. This gap is precisely what the Austrian system is designed to close. Conventional ellipsometry is confined to laboratories because foils that are several metres wide require collimated illumination across enormous apertures. TU Wien’s answer is to replace conventional refractive optics with large-aperture Fresnel lenses, thus cutting costs and footprints, while preserving the precise angle-of-incidence control that ellipsometry demands. The result is the first imaging-ellipsometer to be deployed on an active R2R production line. The researchers have demonstrated the technology on a 300mm-wide foil. The system is centred on an Allied Vision EXO250ZU3 polarised camera. A userselectable LED provides illumination across the camera’s 350–1100nm spectral window. Light passes through a single fixed linear polariser at an angle of 45 degrees, allowing the camera to resolve all four reflected intensity channels in one exposure. Two streamlined calculation methods translate polarisation ratios into spatially resolved thickness maps with low latency, frame-byframe, at line speeds. The camera is based on a Sony sensor with 3.45μm pixels in a 2448 × 2048 array, and an operating rate of 75 frames/s. A nanowire polariser above the pixel array captures all four polarisation states (0°, 45°, 90° and 135°) simultaneously. Industrial validation The system was tested on Pedot conductive polymer layers on a PET foil (used to produce transparent electrodes) and on battery electrolyte coatings on a copper foil. In both cases, it delivered thickness maps at production speeds. The results revealed deviations in coating uniformity, edge anomalies, and surface defects that would be invisible to conventional optical inspection techniques. This could help to boost yields and reject any defects early in a process. Vibrating foils, backside reflections and substrate birefringence have historically made reliable inline ellipsometry almost impossible. The new system addresses all of these issues by allowing measurements directly on a roll, thus suppressing vibration and redirecting backside reflections away from the detector. The LED’s 20–60nm spectral bandwidth ensures front- and back-surface reflections are mutually incoherent, eliminating interference. The system is said to scale linearly with foil width, positioning it for wide-web battery, display and flexible electronics manufacturing. The measurable thickness spans values from nanometers (for highly absorbing layers) to microns (for transparent layers), and can adapt to different process chemistries on a single hardware platform. The TU Wien researchers are now planning to target in-line and in-time thickness measurements, as well as R2R lines with foil widths of up to 2m. Because the ellipsometer uses simple components and works without moving parts on a fixed wavelength with a fixed illumination angle, it promises cost-effective and easy installation on production lines. n Austrian researchers have developed a vision system that measures the thickness of thin coatings on rolls of substrate as they whizz past at production speeds of up to 100 metres per minute. The system monitors the whole width of the roll, and can spot problems before they become serious. Thin-film cameras installed on a Coateme Click&Coat R2R substrate processing system (Photo: TU Wien)
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