Process for determining the location of edges and photoelectronic scanning device for scanning edges

摘要

A process and device for determining the location of at least one edge of a moving web within a measurement zone and in which a linear array of liquid crystal light modulators is interposed between a light source and a light receiver extending transversely to the edge along a scanning zone while a controller successively activates the light modulators to scan a transparent surface zone along the measurement zone. The point at which light is last received (because of obstruction by the edge) or the first received in a pass (because of lack of obstruction by the edge) at the receiver from the source through the scanning transparent zone is used as the measure of the location of the edge.