Optical print scanning device - compares reflected light with reference beam to determine print ratio

摘要

An optical device is used for the determination of the ratio of printed to non-printed surface of an object. It compares light reflected from the object with a reference beam. A discharge lamp generates a beam of radiation which is separated by a beam splitting prism into a measuring beam and a reference beam. The beams are directed by two lenses on to a chopper wheel having apertures to modulate the light beams. After collimation and reflection by a semireflecting mirror, the reference beam is directed on to a photocell. The measuring beam is directed by a scanning mirror over a rectangular test area. The diffuse reflected beam is directed by a lens and mirror to the measuring photocell.