Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1985-08-28
1987-04-21
LaRoche, Eugene R.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250214RC, G06K 710
Patent
active
046599398
ABSTRACT:
An optical scanning system including an amplifier which automatically adjusts the background reference level. A photodetector, which is preferably a photocell, detects light reflected from or transmitted through objects such as code markings on forms and produces an output signal representative of the intensity of the detected light. This signal is coupled to the differential input of an amplifier through two circuits. One circuit rapidly couples the signal to one of the inputs and the second circuit couples an integral of the signal to the second input to automatically establish a background reference level. The amplifier may include means for adjusting the amplifier sensitivity and a small amount of positive feedback to increase the amplifier hysteresis so that once an object is detected, the amplifier output is unafffected by small changes in the input signal. This embodiment is useful in applications such as proximity detection. In one embodiment of the invention the light source used is an incandescent light having a broad spectrum output which is powered at an audiofrequency greater than 60 hertz chosen with respect to the thermal time constant of the light and the response time of the photodetector so that variations in light output at the operating frequency do not affect the amplifier output. In another embodiment a visible display of the amplifier output is provided so that service technicians may easily adjust the amplifier sensitivity.
REFERENCES:
patent: 4445031 (1984-04-01), Kamoshida
LaRoche Eugene R.
Pascal Robert J.
Pitchenik David E.
Pitney Bowes Inc.
Scolnick Melvin J.
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