Patent GB-985399-A (GB)
Title: Character recognition apparatus
IPC: G06V30/196
Filed: 1963-11-21
Abstract: 985, 399. Automatic character reading. NATIONAL CASH REGISTER CO. Nov. 21, 1963 [Dec. 17, 1962], No. 46014/63. Heading G4R. In a character reading apparatus the character is subjected to a series of shaped scans, one for each possible character, a matching scan serving to identify the character. In the form of Fig. 5 the character is scanned by a flying spot from C.R.T. 201, reflected light being received in photo-cell 206. The signals generated pass via amplifier 207 to gates 208, 209, the former being open at the start of the cycle and the latter during the ten shaped scans. Preliminary scans of the character are made to position the shaped scans correctly. For this purpose the character is scanned by a horizontal raster from the top and from the bottom and by vertical rasters from each side. In each case the deflection voltage at the time the second consecutive character-cutting scan occurs is stored on a capacitor and correction voltages are derived by potential dividing to position the following scans. The second black scan is taken in case a spurious mark gives a false first black signal. The shaped scans are shown in Fig. 2. These and the registration scans are performed by the C.R.T. under the control of signals recorded on a magnetic tape in block 205. The signals e S  from the photo-cell 206 may be as indicated in Fig. 4. For each shaped scan there is also recorded corresponding expected black and white signals. These are shown at e b  and e w  Fig. 4B and C. The photo-cell signals are applied to the smoothing and comparator circuit Fig. 3. This consists of two integrators 131, 132 consisting of diodes, resistors and capacitors. The input diodes are oppositely poled so that the circuit receives ten white signals (-5 volts) and the other the black signals (+5 volts). The stored signals e b  and e w  are applied to ten circuits through diodes 131 e , 132 e  so that the black signal eb disables the white circuit 132 and the white signal e W  disables ten black circuit 131. If the signal e s  substantially agrees with signals e b  and e w  the charges on the capacitors do not charge significantly. Short period spurious signals such as 133,137 are ignored by the smoothing effect of the capacitor and shunt resistors. In the case of a mis-match Fig. 4D, the capacitors 131c, 132c charge above a certain threshold and a signal er is produced which indicates a mis-match. During each of the ten scans, a corresponding gate 40-49 Fig. 1 is opened and the reject signal e r  is passed to set the corresponding flip-flop 10-19. At the end of the recognition cycle a counter pulse K S  opens all the read-out gates 50-59, producing an output on the line corresponding to the flip-flop not set. If in the initial scan it was found that proper registration was impossible an "attempt counter" is set to its highest count giving a signal J5. This then opens gate 60 so that at the end of the first recognition attempt a signal X is produced signifying that recognition is impossible. Normally after a first attempt, four more attempts at recognition are made, each with the shaped scans in a slightly different position. After the fifth attempt the counter produces signal J5 and the "X" signal is given as before. A reject signal is also given if more than one recognition signal is produced. For this purpose the outputs are Or-gated in ten groups of nine 10-18, 11-19 &c. and each output is Andgated with the remaining output 19, 10 &c. Any output signifies a double recognition. In the form of Fig. 13 the flying spot is replaced by an optical dissecting device 303 which makes a series of vertical scans through the character and reads corresponding signals into a matrix flip-flop store 325. Clock pulses on a magnetic drum 302 are applied to counter 320 to obtain ten row and column distribution signals. A registration circuit 350 interrupts the entry of the character into the store when it has arrived at the correct horizontal position and generates up and down shift pulses to obtain the correct vertical position. These positions are found by the "centre of black" method, black signals above and below a certain line being summed by summing resistors and the pattern moved until an approximate balance is obtained. The same principle is used in horizontal registration, balancing the black areas about a vertical centre line. The circuit 375 reads out a succession of points on the matrix as indicated in Fig. 15 for character "2". A different succession is read out for each possible character and the outputs are compared with stored references as before. If a cycle produces no recognition, the pattern is shifted slightly in the store and a second attempt is made. This is repeated four times as before.