System for detecting defects in articles using a scanning width which is less than width of portion of the article scanned

摘要

An apparatus for sensing the deflection of a beam directed at an article detects slight deflection of the beam when the beam is directed at a large angle of incidence. The large angle of incidence increases the apparatus sensitivity to detect certain characteristics within an article which cause slight deflection, and allows the use of smaller optical elements. The apparatus can detect defects such as coating voids, streaks, and caliper variations when transparent materials are coated onto transparent substrates.