Patent GB-796579-A (GB)
Title: Automatic reading system
IPC: G06V30/192
Filed: 1957-02-27
Abstract: 796,579. Statistical apparatus. MERRITT, P. E., and STEELE, C. M. Feb. 27, 1957 [March 19, 1956], No. 6564/57. Class 106 (1). Apparatus for recognizing humanly legible symbols and presenting an electrical representation of the symbol recognized comprises means for generating an electrical wave-shape characteristic of the symbol to be identified, a correlation network for each possible symbol, means for applying the wave-shape simultaneously to all the correlation networks and means for detecting which network has the largest output signal. Principle of a correlation network.-A sensed signal having a characteristic waveform is applied to a delay line 10, Fig. 1, and tapping points are provided along the length of the delay line to sample the waveform at spaced points. These tappings are connected to potential dividers 12, 14, 16, having ratios of 0.5, 0.25 and 0.75 and connections are made from the potential dividers to three summing resistors 13, 15, 17, the output of which is applied to the grid of a cathode follower 19. The cathode follower 19 will give the highest output if the waveform corresponds to the values 0.5, 0.25 and 0.75, as shown in Fig. 2. Any other waveform will give a lesser result. Sensing.-The characters to be recognised are printed in magnetic ink and the carrier 50, Fig. 6, is passed under a magnet 51 which magnetizes the ink and under a reading head which provides an output signal having a waveform characteristic of the character read. The waveform for each character is known and a correlation circuit is designed to respond to it. The characters can alternatively be sensed by optical methods. Character recognition.-The waveform shown in Fig. 4 corresponds to the numeral 7 and the network in Fig. 5 is designed to respond to it when applied to the delay line 42. Sixteen tappings are used, each connected to a potential divider Ra1, Rb1 ... Ra16, Rb16, the resistance values of which are chosen so that the impedance at all the centre points is equal. These points can therefore be connected together to sum the voltages, those points corresponding to the positive part of the waveform being connected to the grid of a triode 32 while those corresponding to the negative part of the wave are applied to the grid of triode 38. These triodes are connected as a mixing amplifier having a common cathode load 40 and the algebraic sum of the positive and negative signals (E1-E2) appears on the plate of triode 38. As shown in Fig. 6, the tapping points of the delay line 56 are each connected to all the character recognition networks 60, 62, 64, &c., the outputs of which are passed to mixing amplifiers 70, 72, 74, &c. The signals then pass through gain control potentiometers 80, 82, 84, &c. and amplifiers 90, 92, 94, &c. to cathode followers 100, 102, 104, &c. The signals are then applied to a diode peak detector circuit 106 and to difference amplifiers 110, 112, 114, &c., the other inputs of which come from the peak detector circuit through cathode follower 116. The difference amplifiers give an output only if the signal from the cathode follower 100 &c. exceeds the signal from the diode peak detector and there is accordingly an output on one line only, the line providing the maximum signal from the mixer amplifier. The outputs from the difference amplifiers are respectively applied to gates 120, 122, 124, &c. opened by a circuit which detects when the whole of the wave shape is in the delay line. The signal from the appropriate recognition network is passed by the gate through an inverter 150, 152, 154, &c. to an output cathode follower 160, 162, 164, &c. corresponding to the character sensed. Specification 785,853 is referred to.