Patent GB-932414-A (GB)
Title: Character recognition system
IPC: G06V30/10
Filed: 1962-05-16
Abstract: 932,414. Automatic character reading. NATIONAL CASH REGISTER CO. May 16, 1962 [July 6, 1961], No. 18886/62. Class 106 (1). In apparatus for reading characters stylized as shown in Fig. 11 to lie in certain ones of five columns in the upper and lower parts, the characters being scanned across in a plurality of spaced sweeps by two scanning holes 22b, 22c and the signals derived in a scan being stored, there is an auxiliary scanning hole 22d, spaced from the others so that the first scan in which the auxiliary hole misses the character completely is the scan in which the main holes are properly registered with the character in a vertical direction, the store being cleared at the beginning of each scan, and there being means for reading out the stored signals from the scan in which the auxiliary hole first misses the character. The apparatus is shown in Fig. 3. Lines of characters, Fig. 2, are printed across a tape 12 driven on reels by a synchronous motor 13. A lens 28 projects an image of the line of characters on to the scanning device which consists of a drum 20 having a number of groups of four diamond-shaped scanning holes 22a- 22d. Light guides take the light transmitted through the holes to form photo-cells 30a-30d. As the tape moves the photo-cells sense the character in a series of horizontal scans. In blocks 32 the photo-cell signals are clipped to eliminate noise, differentiated to generate a positive and negative pulse and applied to a circuit which gives a square pulse at the negative-going zero transition. This coincides with the middle of the sensed character stroke and is independent of the strength and thickness of the stroke. The scanning holes are large enough to ignore small specks on the paper so that a noise-free, accurate constant-amplitude pulse is obtained for each stroke crossed. The signals from all four photo-cells are applied via Or gate 72, Fig. 10A, to indicate the detection of the reference mark 46, Fig. 2, at the beginning of each line of characters. This signal allows pulses from a generator G1 to pass to a counter 80, which counts up to sixteen (p0-p15, Fig. 11) and then resets. The counter is restarted at the beginning of each character by the pulse from any of the photocells indicating that a character stroke has been detected. The counter therefore restarts at the first black of each character and its sixteen distributed outputs are energized accurately at the positions shown in Fig. 11 at P0-P15. The counter outputs are used to gate the signals derived from the two main scans 22b and 22c units ten flip-flops F1-F10. Resetting is by the zero count signal Po. Circuit 110 which re-codes the ten inputs to give an equivalent on five leads, is enabled at the end of the properly registered scan by a signal indicating that the bottom scan D has missed the character. The five bits representing the character stroke sensed in that scan are then entered into buffer flipflops M1-M5 and from there gated into the corresponding column of five cores in a storage matrix. During the scanning of a line of characters the eight columns of cores are selected in turn by character counter 105, advanced by the P1 signal from counter 80. The stored signals for each character are entered as soon as the signal comes indicating proper registry for that character. Once a group of five bits has been entered into a column a feedback circuit through gates 172-180 prevents any subsequent character being entered into that column. The circuit 110 also has gating means to test the combination of bits applied to it to determine whether or not it is a valid combination. If it is a signal on lead Vc advances " correct character counter " 210. If not an error signal appears on lead Ve. These are counted in counter 230. A count of eight correct characters is required to allow a line of characters to be read out of the core matrix. If there are less than eight or if an error signal is produced a rescan takes place. The first scanning operation stops as soon as the scan 22b misses the lower end of the indicator mark, the tape motor 13 being switched off to stop the tape, if necessary, while the sensed data is processed as described. If a rescan is necessary the motor 13 is reversed and scanning takes place during reverse movement of the tape in a manner similar to that described above. The lines of scan on the reverse traverse are unlikely to coincide exactly with the first scans because of the inherent mechanical sloppiness in the apparatus so that if the original scan was in error because of a gap in the character the re-scan may miss the gap and generate a valid character signal. If not, the process is repeated until eight rescans have taken place. If the counter 230 then records eight error characters, a signal E8 is applied to a marker 18, Fig. 3, to put a mark on the defective line of characters to indicate that it could not be properly read. The tape then moves on to present the next line of characters to the scanner. The first character of a line is a letter " M," " B " or " F " which defines the way the subsequent characters are to be read out. A gating circuit 275 recognizes the presence of any of these letters and applies a signal on a corresponding lead to an input of the counter 105. The arrangement is such that, during read-out of the core matrix to external equipment, the order of energization of the eight outputs of counter 105 is determined by the initial letter. The order may be reversed for one control letter, even ordered characters only may be read out for another letter and odd ordered characters for the last letter. Specification 909,942 is referred to.