Document sensing apparatus that detects non-specular reflected l

Details Document sensing apparatus that detects non-specular reflected l Document sensing apparatus that detects non-specular reflected l

1984-05-18

1987-01-13

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

356446, G01N 904, G06M 700, H01J 4014

Patent

active

046366334

ABSTRACT:
In a stop-and-display station in document-handling equipment wherein a document in a track is stopped and viewed through a transparent first wall, whereagainst it is supported by a non-transparent second wall, a reflective photosensor assembly is angled relative to the back wall such that a light beam from a light-emitting diode cannot be specularly reflected onto a phototransistor either from a document or from the inner surface of the transparent first wall. The phototransistor intercepts a portion of the scatter-reflected light from the document. The light from the light-emitting diode is modulated with a predetermined frequency, and the output signal from the phototransistor is filtered by a band-pass filter before threshold detection to provide indication of the presence of a document. A turn-off delay circuit prevents loss of indication of the presence of a document unless signals from the phototransistor have been absent for longer than a predetermined period. The apparatus resists false alarms of the presence of a document in consequence of extraneous light and extraneous reflections. The turn-off delay circuit prevents marks on the back face of the document inadvertently causing loss of signal indicative of document presence.

REFERENCES:
patent: 4207466 (1980-06-01), Drage et al.
patent: 4484070 (1984-11-01), Inoue
patent: 4540887 (1985-09-01), Minerd et al.

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