AUTOMATIC INSPECTION OF PHOTOGRAPHIC MATERIALS

An infra-red laser scanning instrument has been developed for the automatic inspection of unexposed photographic strip products (film and paper) for visible defects. The system has been developed jointly by Sira and Kodak and one unit has been in constant use in an on-line application for over 2 years. The laser scanning head is designed to inspect web with a width of up to 1500 mm at line speeds up to at least 100 m/min. Scratches of width down to 50 μm running along the strip, and certain other defects such as digs down to 300 μm in diameter, can be detected. The basic optical principle is to scan an infra-red laser beam with a mirror drum scanner sequentially across the inspected surface, from which the specularly reflected light is collected by a large cylindrical mirror and directed at a photomultiplier detector. When defects in the surface are scanned the photomultiplier signal is temporarily increased or decreased, and it is these features which are extracted by the electronic signal processing units. The output from the instrument can be displayed on an oscilloscope in the form of a ’ videoprint ’ (which is a picture of the web surface showing only defects); a permanent ’ videoprint ’ can be recorded on a photographic hard-copy instrument. © 1978 Taylor & Francis Group, LLC.