Device and method for detecting the edge of a recording material

A device and a method detect an edge of a recording material, in particular a printing plate, in an exposer for recording printing originals. An exposer has an exposure drum for holding the printing plate, and an exposure head, which is moved axially along the exposure drum and focuses exposure beams onto the printing plate. The position of the edge of the printing plate is determined by a sensing device. To this end, a sensing finger is pivoted into a groove in the surface of the exposure drum and a signal is generated by a sensor when the sensing finger moves when it touches the edge of the recording material. The sensor used is preferably a microswitch. The axial position of the edge of the printing plate is determined by counting the cycles of the feed drive that moves the sensing device.