TIMING SYSTEM FOR OPTICALLY SCANNED DOCUMENTS

摘要

A system for use in document readers of the type in which manually-entered responses in predetermined data response areas on a document are optically scanned or read electronically as the document is conveyed at high speed. The data response areas are arranged in regularly spaced rows, and the timing of the scanning of each data row is usually controlled solely by preprinted regularly-spaced indicator marks along an edge of each document. The system of the invention measures the time interval between the initial indicator marks by counting timed pulses at a predetermined rate and these pulses are then used as a reference to control scanning of the data rows in the event that the timing indicator marks fail to produce the necessary signals to control the scanning of the data rows. The system also provides for continuous synchronizing of the timed pulses with those produced directly from the indicator marks.