Patent GB-875525-A (GB)
Title: Improvements in data transmission and character recognition systems
IPC: G06V10/10
Filed: 1958-12-17
Abstract: 875,525. Automatic character reading. INTERNATIONAL BUSINESS MACHINES CORPORATION. Dec. 17, 1958 [Dec. 23, 1957], No. 40741/58. Class 106 (1). In a character recognition apparatus, to provide for misregistration of the character a wide strip is sensed by x sensing elements of which the character can only affect y, a set of x primary transmission channels from the x sensing elements being interconnected with (y+1) secondary transmission channels in such a way that the signals sensed from a character by a group of the x sensing elements are transferred to the secondary channels in an identifiable form. As shown in Fig. 1 the characters move in sequence under a line of sensing elements 5. These are magnetic heads, the character being printed in magnetic ink. Alternatively photo-electric cells could be used. The vertical length of the line of heads represents the character height H plus the vertical misalignment expected. The channels from all sensing heads pass to amplifiers and cross-talk eliminating circuits 7, then to circuits 9 which as described above reduce the number of channels to be considered from x to (y+1). The signals on the (y+1) channels pass through integrator amplifier and clipper circuits 11 to coding and coding storage circuits 13 which derive signals representing five types of horizontal section through a character. These signals are analysed in circuit 15 to determine what characters have been scanned. Eliminating cross-talk.-As shown in Fig. 2, the signal from the magnetic reading heads MH1, MH2, MH3, &c. are amplified in stages 21, 23. A portion of the output from each second stage 23 is fed back by a resistor, e.g. 24 to the inputs of the second stages of adjacent channels. Since the feed-back signals are of opposite phase cross-talk between adjacent channels is cancelled. Channel reduction.-The nineteen channels PC1-PC19 are connected via eight OR gates 31-38 to eight channels SC1-SC8. A character may cover seven (y) magnetic heads a further channel (y+1) being allowed to provide a blank lead to indicate the top or bottom of the character. The primary channels PC1- PC8 are connected to secondary channels SC1- SC8. Channels PC9-PC16 are also connected to channels SC1-SC8 and the remaining channels P17-P19 are connected to channels SC1- SC3. All the signals sensed are thereby applied to the secondary channels irrespective of the location of the character under the sensing heads and one of the channels SC1-SC8 will have no signal since only seven of the sensing heads are affected by the character and this blank line is used to give a reference point in the cyclic read-out to obtain the character signals in the proper order. Instead of connecting spaced sensing heads together or OR gates 31-38, groups of heads (e.g. MH1, MH9 and MH17) may be connected in series before amplification and cross-talk elimination. The signals on the secondary channels SC1-SC8 are integrated by resistor 41, Fig. 4, and capacitor 42, amplified at 43, clipped at 44, and amplified again at 45 to produce a pulse of which the duration is proportional to the width of the scanned portion of the character. This pulse is inverted at 49 and used to trigger a monostable unit 48 which produces a pulse of predetermined length, which is gated with the pulse from amplifier 45. The output from gate 51, which occurs only when the black portion of the character produces a pulse greater than a predetermined length, is inverted and stored in a trigger 54. The signal from inverter 49 is inverted at 56 and applied to a monostable trigger 57 controlling gate 58. The output from this gate indicating a white gap in a scan of greater than a predetermined length, is inverted and stored in trigger 60. The third input to gate 58 prevents a white signal occurring until a black signal has been detected and registered in a counter consisting of triggers 63, 64. This counter counts the cross-overs, i.e. the number of times the scan crosses a black area during its path across the character. The connections to gate 58 also cause white areas occurring after a second cross-over to be ignored. An input signal to trigger 63 is produced by inverter 49 each time the leading edge of a black area is detected. Five scanning indications.-The signals representing white or black areas of greater than a certain length and the cross-over count signals are combined to determine the presence of five standard indications as follows: XO (no black areas detected in a scan), XS (a single cross, over, which is short), XL (a single cross-over, which is long), 2XA (two or more cross-overs, a short white gap between the first two) and 2XB (two or more cross-overs, a long white gap between the first two). These indications are extracted by combining the outputs of triggers 54, 60, 63 and 64 in gates 69, 77, the signals being temporarily stored in latches 86-90 and read out on to five indication lines 91-95 via gates 96-100. The circuit of Fig. 4 is repeated for each of the eight secondary channels SC1-SC8 and their indication signals, XO-1, XO-2, XO-3, &c. are read out in sequence on to the lines 91-95. This is effected by a counting ring of nine stages which cycles twice in each character sensing time, the bottom of a character being determined for read-our purposes by the occurrence of an XO signal following a number of the other signals XS, XL, &c. from the other channels. Recognition circuits.-The sequences of scanning indications on the eight channels are shown for the digits 1-9 and 0 in Fig. 6. For example, numeral " 3 " has the following indications on the channels SC1 to SC8 respectively: No black (XO) single cross-over with a long black area (XL), a short white area between two cross-overs (2XA) a long black (XL), a short black (XS), a long white between two crossovers (2XB), a long black (XL) and a no black signal (XO). In Fig. 7 a chain of seven triggers is provided for each numeral, adapted to be operated in sequence by the indications XO, XS, XL, &c. occurring in the characteristic order (e.g. as set out for " 3 " above). Connections from the five indication lines 91- 95 are made to appropriate ones of the triggers 153-159 (for numeral three) so that when the sequence XO-XL-2XA-XL-XS-2XBXL-XO appears the triggers will set in turn and give a signal at terminal 151 indicating that numeral " 3 " has been recognized. Other chains are similar. The character signals are stored on ten latch circuits. Checking.-To check that one and only one character has been recognized the outputs from the latch circuits are applied to a summing amplifier and the resulting signal is passed to two threshold devices, one of which responds when more than one character signal is present and the other of which responds when no character signal is present. When more than one character or none is indicated an alarm may be given, the machine may stop or rescan the character. Where a single character signal is produced it passes to utilization equipment, e.g. a card punch, a calculator or an audio or visual output device. Specification 710,554 is referred to.