Leading Edge Detection of Paper Sheets with Reflex Light Barriers

In sheet-fed printing machines for the printing industry, the leading edges of conveyed paper or film sheets must be reliably detected. In order to avoid installing reflectors that would regularly become contaminated by paper dust, a reflex light barrier with dynamic readjustment of the switching threshold is used here instead. This uses the glossy background, which is set as a reflective surface via teach-in. In this way, paper sheets and even transparent films are reliably checked for presence against the defined background when the beam is interrupted.