Recorded image detection system for updatable microfilm

Abstract

The present invention is used in photo-recording machines, such as microfiche recorders, which receive a document and record an image of the document on a photo-recording medium such as photoplastic film. The invention inhibits double exposures on frames of the film by use of distinctive indicator marks recorded on the film at preselected locations called indicator mark fields. The presence or absence of an indicator mark in such an indicator mark field signifies, respectively, that its corresponding frame is or is not available for recording a document image. In an improved recorder, prior to a proposed recording, a detector scans the indicator mark field corresponding to the frame selected for recording. If the detector detects an indicator mark, the recorder is inihibited from recording the document in the selected frame. A projection light source forms the image of the indicator mark field and projects it along an optical path in which a sensor of the detector is interposed. Where the indicator mark includes lighter and darker portions, the sensor responds to the intensity variations and may be mounted on motive means and swept thereby across the optical path transversely. The sensor output is automatically evaluated by means which may include or cooperate with a logic circuit responding to an evaluation signal and preventing recording despite a operator-entered record instruction. If no indicator mark is dectected, document recording proceeds in the selected frame, and an indicator mark is simultaneously recorded in the corresponding indicator mark field.