Patent GB-845106-A (GB)
Title: Improvements in or relating to symbol recognition system
IPC: G06V10/24
Filed: 1956-07-13
Abstract: 845,106. Photo-electric character reading apparatus. LABORATORY FOR ELECTRONICS Inc. July 13, 1956 [July 21, 1955], No. 21824/56. Class 40(3). [Also in Group XIX] In a character recognition apparatus, e.g. for reading numbers on a bank cheque and controlling printing, sorting or tabulating devices, the character is scanned photo-electrically in a series of lines as indicated at 1-12 in Fig. 7 and the resulting long and short "black" pulses counted to establish in each line scan: (1) the total number of pulses both long and short, and (2) the number of long pulses (e.g. for scan 3 the totals are respectively 2 and 0, whilst for scan 8 they are 1 and 1). The results of the line scans are then compared according to a programme (see below) and the results inserted in a special shift-register store (see below) which is advanced only at each entry. At the completion of the scan of a character a pattern of activated stages exists throughout the store, the pattern being different for each character, and is interpreted to produce a potential on the appropriate one of a group of terminals. The interpretation is effected by means of a matrix interrogation circuit, Fig. 9 (not shown), in which groups of rectifiers are connected to the various possible pattern of stages in the store and control the terminals via gate stages. According to one programme, an entry is made in the store only when the result of adjacent scans are different, provision being made to enter the first two scans irrespective of identity so as to allow for possible inaccuracies in the first scan which may not wholly coincide with the character. The store is arranged as illustrated in Fig. 6 in a group of five columns, each of seven stages, and entry is made in the various columns as shown in accordance with a code number indicating the results of the two counts. The first digit of the code number indicates to the total number of pulses and the second digit indicates the number of long pulses. The shift control, which is applied only when an entry is made, influences all stages simultaneously so that the pattern as it is built up travels as a whole, down the store. The result of this programme for the number 3 scanned as shown in Fig. 7 is set out scan-by-scan in Fig. 8. The shift control is applied during blank scans 9-12, no entry being made however and the emergence of the code for the first scan at the bottom of a column (column 1 for the example considered) serves to indicate that the stored pattern is ready for interpretation and causes the matrix interrogation circuit to be brought into operation. Fig. 6 shows the store with the pattern for number 3 at the moment of interrogation. The code for the first scan is not used in the interpretation since it may contain inaccuracies and merely serves as explained above to bring about the interrogation. The programme ensures that the second scan is always entered. The process of counting pulses renders the apparatus insensitive to the vertical height and position of the characters, and process according to the programme of making a store entry only when adjacent scans differ renders the apparatus insensitive to character width and speed of travel relative to the scanning station. According to an alternative programme, there must be two identical scans before an entry is made in the store, subsequent adjacent identical scans not causing an entry. In the case of number 3 scanned as in Fig. 7, scan 3 would be entered (because it is the same as 2), not scans 4 and 5 (because they are the same as 3), and scan 7 (because it is the same as 6). This programme results in less store entries and thus reduces the number of stages required, inherently rejects the first (possibly inaccurate) scan, and by virtue of the integrative effect over two scans is stated to render the apparatus insensitive to the effects of dust particles &c. Fig. 5 (not shown) illustrates, in block diagram form only, an apparatus set up to operate according to the first programme described above. The counting is effected by binary counters, two being provided for each count which operate alternately with one retaining the count of the preceding line to permit comparison. The comparison, coding and various switching operations are effected by conventional rectifier-type gating and buffer stages. The shift-register store comprises a chain of binary stages, preferably saturable magnetic-core elements. The scanning station Fig. 3 (not shown), comprises a vertical line of photo-electric cells under which the medium bearing the characters is traversed, the cells being brought into operation cyclically in rapid succession so as to produce the effect of a line scan. The cells respond only to infra-red so as to avoid the effects of ambient lighting.