Patent GB-913785-A (GB)
Title: Graphic character recognition
IPC: G06V30/144
Filed: 1960-10-27
Abstract: 913,785. Automatic character reading. BURROUGHS CORPORATION. Oct. 27, 1960 [Nov. 2, 1959], No. 36982/60. Class 106 (1). In apparatus for recognizing magnetic characters of the types in which a characteristic waveform is derived by the sensing head, this waveform being applied to a tapped delay line to obtain sample signals which pass to correlation circuits, one for each character, the correct time for making a comparison between the outputs of the correlation circuits is determined by developing a peaked voltage waveform from the outputs of all the correlation circuits, producing a sample interval pulse straddling the largest peak and producing timing signals within the sample pulse at the occurrence of each ascending peak up to and including the largest, ignoring peaks smaller than preceding peaks. The character is magnetized by a bias head 10, Fig. 1, and passed under a read head 12 to derive a waveform representing the character as shown in Fig. 3. The signal at 14 is amplified and applied to a filter which eliminates high-frequency spurious signals and after further amplification in an amplifier 15 which produces positive and negative waveforms is applied to a dual polarity delay line 18. At any instant the waveform in the delay line is sampled by a series of pairs of taps 0-7. For each possible character there is a correlation network which consists of a series of parallel-connected resistors one connected to each tapping the conductances of which are proportional to the amplitude of the signal at the tapping at the instant an ideal waveform for that character is properly positioned in the delay line. One correlation circuit for the character waveform in the delay line produces at the instant the waveform is properly positioned a signal higher than that produced by any other correlation circuit. To determine which circuit produces the highest signal the outputs of all the correlation circuits 20, Fig. 2, are applied through a mixer or OR gate 28 to an amplifier adapted to amplify the highest amplitude signal and feed back to the correlation circuit outputs a signal equal to about 90% of the highest output. No correlation circuit except the correct one should have an output exceeding 90% of the highest signal so that the effect of the feed-back signal is that only one of the leads is positive. Individual gates 40 determine which lead has the positive signal and a signal on the corresponding lead passes to a diode encoder producing a binary scale representation of the digit recognized. This representation is stored in four flip-flops 46, 47, &c. If a second correlation circuit produces a signal within 90% of the highest, a second gate 40 will deliver an output and at least one of the storage flip-flops will receive inputs on both " 1 " and " 0 " input terminals. This condition sets a reject flip-flop 48 which through circuit 50 prevents the generation of the coarse timing signal so that the recognition is ignored. Coarse timing circuit.-Connected to tappings of the delay-line adjacent the end tap " 0 " are a number of resistors comprising a network 52 Fig. 6. As the characteristic waveform reaches the end of the delay line the leading part of the signal A, Fig. 7, produces at the output of the network a waveform as shown at B. The use of several taps averaged by the resistor network prevents spurious signals superimposed on the character signals giving a false timing indication. The beginning of the coarse timing interval is determined by point 68 where the curve B crosses the zero line. The signal B is passed to a circuit 72 which consists of two transistors connected as emitter followers with a D.C. bias so that the output, signal C, Fig. 7, is raised by the D.C. level of 1.5 v. In circuit 104 a transistor threshold device conducts when the wave C goes negative to produce signal D, Fig. 7, a function of cross-over points 68, 69. This signal is applied through a capacitor in which it is changed as shown at E, Fig. 7, to a transistor gate which provides a pulse F, for application to a delay multivibrator 120 having a time of 40 Ásecs. This is the coarse timing interval designated SI (sample interval). The trailing edge of the signal SI is used in shaper 150 to develop a signal J for application to a phantastron which has a time of 215 Ásecs. and applies a signal to gate 108 to prevent the circuit producing another sample interval signal for a period approximately equal to the time between characters. Fine timing circuit.-Within the coarse sample interval the fine timing circuit takes the highest peak in the output of the mixer 28. The characteristic waveform passing through the delay line produces response peaks in the several correlation circuits. Within the sample interval these, when added in mixer 28, may appear as in graph B, Fig. 10, the response from the correct correlation circuit giving the highest peak 306. The fine timing circuit is required to produce a read-out pulse for the comparison gates 40 at the instant of peak 306, the highest peak. This is achieved by storing incoming peaks in a condenser, as shown at C, Fig. 10, and amplifying the difference between this and the input wave B. The resulting signal D, Fig. 10, represents the times during which the wave B is greater than the stored level C. The peaks B are also differentiated in a transformer and signals E and F produced. Signals F and D are gated with the coarse sample interval signal and a signal G is produced representing the ascending peaks 304 and 306 of wave B. In the recognition circuit this signal is used to read out the signals in gates 40. The first peak 304 and the corresponding pulse in signal C relates to an incorrect correlation circuit and the incorrect digit is temporarily stored in flip-flops 46, 47 &c. The next and last pulse signal G, relating to the highest peak 306 and therefor the correct correlation circuit, causes the correct digit to be stored. No further recognition signals are read out so that at the end of the sample interval the correct digit is available in the store. Strong and weak signals.-When the output signals of the correlation circuits are too weak or too strong means are provided to cause circuit 50 to prevent a read-out taking place. Specifications 888,718 and 913,786 are referred to.