System for on-line measurement of color, opacity and reflectance of a

Abstract

Systems for the on-line optical measurement of properties of a translucent moving web, such as paper or plastic, as it is continually produced, colored or otherwise converted. Measured properties include color, reflectance and opacity. A backing roll has a cylindrical or approximately cylindrical surface which comprises at least one optical standard. The roll is positioned such that a circumferential portion of the roll surface contacts the back web surface where the web characteristic is to be measured, with the web curving around the circumferential portion. An optical sensing device is positioned so as to view the front web surface backed by the optical standard or standards. In several embodiments, two sets of reflectance data are collected, one with a 'white' optical standard backing and the other with a 'black' optical standard backing. The backing roll surface and the optical sensing device can be arranged such that the sensing device either alternately or simultaneously views portions of the front web surface backed by each of the optical standards. In other embodiments, the backing roll has a uniform optical standard surface.