device for reducing blattnachweis and blattausrichtfehlern

摘要

The appts for sensing the presence or an edge of a sheet, includes a light emitter, a set of reflectors and at least one light detecting member. A light beam is reflected between the emitter and detector in a repeating wave form so as to intersect a sheet path, and interruption of the light beam indicates the presence of a sheet. False indications of the presence, absence or true edge of the sheet such as may be caused by sheet holes or edge irregularities are avoided by the multiple passes of a beam of light across the path of the sheet. A continuous cleaning action of the sensor may be provided by the movement of the sheet over the light emitters, light detectors and/or reflectors.