Only a small variation of the coating thickness in a range of a nanometer can create an inhomogeneity visible to the human eye. This control task is especially difficult as this uniformity must be controlled on the full glass surface, in different viewing angles and on the complete production lot to avoid any claims and improve the process. The new “Color Channel” technology by ISRA is able to provide all that.
Inspection systems based on this technology are equipped with state-of-the-art special RGB line scan cameras in combination with long life, full visible spectrum LED technology and sophisticated algorithm-based software. “Color Channel” offers complete color variation monitoring in ΔE as well as the calculation of color differences in ΔC, Δa*, Δb*, etc. The use of a full spectrum LED illumination is an essential factor for the inspection effectiveness. The signal given by the LED over the full visible spectrum is mirrored and measured on the glass surface in reflection. That way, RGB line scan cameras can give a full colored picture of the coated glass. RGB-measured values are then computed in L*a*b* color space to calculate the color variation sensation. This procedure allows for a 100 percent surface color homogeneity monitoring with a ΔE repeatability equivalent to spectrometers but now on the full surface.
Furthermore the systems enable the optical inspection of the color angle shift by using the patented multi-view technology, and in addition for a complete homogeneity control of the fully coated surface by using the so called Large Area Inspection (L.A.I.), a special supersampling method.
The advantages in short: no additional cameras or illumination setups are needed. A complete, in-process surface angle shift control is given, by using narrow and wide view angles. As well the homogeneity control is not influenced by small defects and allows even for the reliable detection of low contrast defects.
Systems for surface color monitoring allow for the automated in-process identification of the slightest color deviations. Defects are reliably identified on the complete surface, recorded and then visualized. The line operator is able to analyze defect trends and adjust production parameters accordingly. Other methods such as spectrometer measurements are not able to match the precision, efficiency and speed provided by “Color Channel” technology.