Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Patent
1975-11-14
1980-08-26
Moore, David K.
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
250209, 250571, 250567, 3401463AG, G01V 500
Patent
active
042197368
ABSTRACT:
An answer document or form, on which the user darkens certain discrete response areas with a graphite or lead pencil to denote his selected choices or data entries, has a bias bar printed across one end with the same color ink used in printing the remainder of the document. When the document is read by the optical scanner, the light passing through the translucent paper also passes through the printed bias bar. Analog voltage signals are obtained from each of the photocells in the optical scanner and these signals are capacitively stored, then converted to digital values. The digital values are averaged and the individual digital values for each photocell are compared with the computed average to check for bad cells. If a poor photocell response persists for a predetermined number of answer documents, the entire scanning operation is stopped. Concomitantly, a predetermined value is added to the average response value derived from the bias bar so as to provide a light mark threshold with which the various response values obtained from the discrete response areas in each row are compared. Only the photocell values for those response areas having an opacity darker than the light mark threshold, that is those passing the comparison test, are further processed and scored. The need for individually calibrating the various photocells for various types of document paper and ink marks is obviated when utilizing my system.
REFERENCES:
patent: 3159815 (1964-12-01), Groce
patent: 3619569 (1971-11-01), Hoehn et al.
patent: 3654434 (1972-04-01), Forman et al.
patent: 3683193 (1972-08-01), Weimer
patent: 3818189 (1974-06-01), Stone et al.
patent: 3820068 (1974-06-01), McMillin
patent: 3918049 (1975-11-01), Snyder et al.
Moore David K.
National Computer Systems, Inc.
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