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Browse Prior Art Database

Optical Automatic Translucence Film Detector

IP.com Disclosure Number: IPCOM000087502D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 36K

Publishing Venue

IBM

Related People

Noldy, WR: AUTHOR [+2]

Abstract

The arrangement shown in the drawing provides an optical automatic translucence film detector especially useful for detecting the presence or absence of a photographic film which may be of different densities depending upon the type of film and manufacturer. Newer types of microfilm do not require black backing, and this system can read and detect this new film along with being able to detect a hole punched in the film indicating the approach of the film end.

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Optical Automatic Translucence Film Detector

The arrangement shown in the drawing provides an optical automatic translucence film detector especially useful for detecting the presence or absence of a photographic film which may be of different densities depending upon the type of film and manufacturer. Newer types of microfilm do not require black backing, and this system can read and detect this new film along with being able to detect a hole punched in the film indicating the approach of the film end.

As shown, a light source 3, which may be a light-emitting diode (LED) in the infrared range, projects light towards a phototransistor 5. The parts are mechanically arranged so that when a filmstrip 7 passes between source 3 and phototransistor 5, the amount of light reaching the phototransistor will be decreased.

Accordingly, the increase in resistance of the phototransistor 5 will cause a negative voltage shift to occur across the resistor R1. This voltage shift is coupled through voltage followers 9 and 11 to a pair of voltage discriminator circuits 13 and 15. The outputs of discriminators 13 and 15 are supplied to the set and reset inputs, respectively, of a latch circuit 17, the output of which, at terminal 19, provides an indication of the presence or absence of film.

When the negative signal shift occurs at the output of voltage follower 9, the voltage at the negative input terminal of discriminator 13 goes negative. At this time, a voltage exists across capacitor C1, which is one diode voltage drop below the original plus-valued input voltage, resulting from the presence of diode D1. The output of voltage discriminator 13 will switch to a plus value and will remain at that value until capacitor C1 discharges to the new lower level. The output from discriminator 13 will set latch 17 to its on condition, a...