Sensing apparatus for reducing sheet detection and registration errors by using multiple light beam reflections

摘要

An apparatus for sensing the presence or an edge of a sheet, including 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; 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. The sheet sensors are useful in detecting and/or correcting sheet skew, misregistration and other potential sheet handling problems. Through the use of optic fibers, wires or other means, the light emitter(s) and light detectors that may service a network of sheet sensors positioned throughout a copying or printing machine which may be centralized and otherwise assembled in efficient modularized configurations.