Patent GB-846721-A (GB)
Title: Improvements in character sensing apparatus
IPC: G06V10/20
Filed: 1957-04-02
Abstract: 846,721. Automatic character reading. INTERNATIONAL BUSINESS MACHINES CORPORATION. April 2, 1957 [April 2, 1956], No. 10730/57. Addition to 846,722. Class 106 (1). In an apparatus for sensing characters the characters are scanned in a plurality of scans and signals are produced in each scan which, alone or with signals produced in earlier scans, are used to give signals representing different sizes of a plurality of different characteristics detected during the scanning (e.g. lengths of vertical lines, slope of upper contours and distance between top and bottom contours of character), there also being provided circuits for forming predetermined combinations of these signals and recognition circuits responsive to signals representing these combinations for providing an indication of the character sensed. The recognition circuits each consist of a series of triggers each of which is set for a predetermined time by one of the combination signals and which serves as an enabling gate to the next trigger of the series so that combination signals occurring in a predetermined sequence provide an identification output. Sensing.-The characters are sensed by a series of vertical scans from top to bottom and progressing from right to left across the character or from bottom to top and progressing from left to right. The document is illuminated by lamps 31, 32, Fig. 2, the image of the character being transmitted through lens 33 and projected on to disc 34. Seventy-five radial slits 43 in this disc co-operate at right angles with a slit 39 in a fixed block 44. As the image moves past the vertical slit the radial slits make vertical scans progressing across the width of the character. The photo-multiplier 11 therefore views elemental areas of the character and its background. The signal produced by the photomultiplier is clipped and passed through a minimum black-minimum white circuit 13, Fig. 1, and a write amplifier 14 and is supplied to a write head 40, Fig. 2, co-operating with drum 15. This information is read by heads 41 and 42 to provide respectively information relating to a present scan and to a scan which occurred three scans previously. The minimum black and minimum white circuit 13, Fig. 1, filters out signals of less than three microseconds. Larger signals are stretched to at least four microseconds. Where a white signal of less than three microseconds is produced it is filtered out and a black indication is produced signifying that a character portion has been sensed. Longer white signals produce minimum white indication of at least four microseconds. These indications are amplified and written on the magnetic drum 15 as signals of black level or white level having a duration according to the number of scans black or white areas were sensed. The read head signals are amplified in circuits 16, 17. Character components; circuit 18.-Circuit 18 receives signals from amplifier 16 and produces signals termed G0, G1, G2, G3, G4, G5, G6 and G7. The black signals obtained are studied by the circuit to determine if various lengths of black line are present. The shortest black line is a single cross over (termed X) i.e. a line of the character passing at right angles to the scanning line. This is represented by a black signal of up to ten microseconds duration. If a black signal of between ten and nineteen microseconds is produced an indication is given that a short vertical line (Vs) has been sensed. A black signal of longer duration produces an indication of a longer vertical line Vm. The signal GO indicates that no signals are produced during the scan. Signal G1 indicates that any one of these signals has been produced during a scan X, Vs or Vm. If there are two X signals in a single scan the signal G2 is produced. Signal G3 is produced if there are three signals representing either X, Vs or Vm in a single scan. Signal G4 is produced if a signal Vm or Vs is followed by an X signal in a scan or if a Vm is followed by a Vs. G5 is produced when X is followed by either Vm or Vs or when Vs is followed by Vm. G6 is produced when Vm is followed by another Vm or if Vs is followed by another Vs. G7 is produced when there is a G3 signal and in addition a Vs or Vm. All these G signals pass to sequencing circuits 21. Circuit details of block 18.-Present data is passed to a single-shot multivibrator 500, Figs. 22a, 22b which generates a two-microsecond pulse from the leading edge of the black data signal for application to triggers 503, 504. These triggers are connected to provide output pulses of ten and nineteen microseconds respectively upon receipt of the input pulse. Present data is also passed via an inverter 505 to a multivibrator 506 which generates a two-microsecond pulse from the trailing edge of the black signal. The outputs from trigger 503 and from multivibrator 506 are gated by gate 507 and an output indicates that black signal is less than ten microseconds long. This is represented by X. The signal from multivibrator 506 is also gated in gate 508 with the output from trigger 504 and the inverted output from trigger 503. An output from gate 508 indicates that the black signal is longer than ten but less than nineteen microseconds and produces a Vs signal. By similar connections a gate 509 produces a Vm signal where appropriate. These gates are connected to the inputs of an Or gate 513 the output from which indicates that one of signals X, Vs or Vm has been produced. This output is inverted (516) and fed to a ring of triggers 517, 519, 520 and 521 connected so that successive signals from inverter 516 turn the triggers on in turn. If no signals are supplied from inverter 516 trigger 517 supplies an output to gate 522 which also receives an end of scan signal ES from sync generator 22 (Fig. 1). The output from gate 522 gives a GO signal indicating an absence of components X, Vs and Vm. This is expressed by #GO = X + Vs + Vm. If one signal passed from Or gate 513 trigger 519 is on and gate 524 accordingly passes an end of scan pulse to give G1 indication representing that either X, Vs or Vm is present. If two signals are passed from Or gate 513, trigger 520 is set and gate 526 passes a G2 signal if there is also a signal from Or gate 546 through inverter 547 indicating that no G4, G5 or G6 signals have been found. In actual fact one of these signals will be given if one of the two signals to Or gate 513 is Vs or Vm so that a G2 indication is restricted to the case where an X signal is followed by another X signal. Where three signals pass the Or gate 513 trigger 521 is set and gate 528 passes a G3 indication. To determine whether G4, G5, G6 and G7 components exist, an inverter 530 receives the X signal from gate 507 and turns on trigger 531 and, if trigger 532 has previously been turned on, it turns it off. A Vs signal from gate 508 is passed to inverters 533, 534. The former is connected in common with inverter 539, receiving the Vm signal from gate 509, to the left side of trigger 531 to turn it off if previously turned on, and to the right side of trigger 532 to turn it on. This double signal Vs + Vm is also used to turn trigger 536 on. A Vs signal from inverter 534 is used to turn trigger 535 off if already on, to turn triggers 537 and 538 on and trigger 538 off if already on. The first Vs turns trigger 538 on and the second turns it off again. A Vm signal from gate 509 passes to inverters 539 and 540. The output from 540 turns trigger 537 off, if already on, and turns trigger 535 on. It is also connected to turn trigger 541 on when it first occurs and to turn it off on the second occurrence in the same scan. All triggers are reset after each scan by a delayed end of scan pulse Esr. Trigger 535 produces a signal if a Vm has been followed by a Vs. Trigger 531 gives a signal if an X has been followed by a Vs or Vm. Trigger 537 gives a signal if a Vs is followed by a Vm. Trigger 538 will give a signal if a Vs is followed by another Vs. Trigger 541 gives an output if a Vm is followed by another Vm. Trigger 532 will give an output if a Vs or Vm is followed by an X. The outputs from all these triggers are applied in combinations to gates 548, 551, 553 and 555 to set up conditions for producing the G4, G5, G6 and G7 signals previously referred to. Circuit 19.-Present scan signals from amplifier 16, Fig. 1, and previous scan signals from amplifier 17 are passed to circuit 19 which produces signals termed H0, H1, H2, H3 and H4 or K0, K1, K2, K3 and K4. The H signals relate to scans which pass from top to bottom of the character progressing from right to left. By making a different plug connection the circuit is adapted to produce the K signals which relate to sensing by scanning from bottom to top moving from left to right. The circuit 19 is concerned with the configuration of the upper contour of a character which is detected by measuring the difference between the altitude of the first cross-over for the present scan and for the previous scan. This is done by comparing the beginnings of the first cross-over signals in the present and previous scans. If the difference is less than three microseconds a signal HO is produced. If the beginning of the first crossover on the present scan is followed by that of the previous scan with a time lag of between three and more microseconds, a signal H1 is produced. Where the time lag is more than nine microseconds a signal H3 is produced. H1 and H3 both indicate a positive slope. Negative slopes of similar values give rise to H2 and H4 signals. For K signals, since it is still necessary to look at the upper contour and since the scanning is in the opposite direction, the circuit compares indications of the ends of the last cross-overs of the two scans to produce signals as before. The circuits are described in detail in the Specification with reference to characters which are upright when scanned (giving H components) or upside down (giving K component