Patent GB-785853-A (GB)
Title: Improvements in or relating to automatic reading system
IPC: G06K9/00
Filed: 1955-12-08
Abstract: 785,853. Telegraph transmitters. ELDREDGE, K. R. Dec. 8, 1955 [May 6, 1955], No. 35316/55. Class 40 (3). [Also in Group XIX] Characters written in legible characters in magnetic ink are read by first magnetizing the characters and then moving them past a reading head which generates an electric signal from each character having a wave-shape characteristic of the character, and means to identify a character from said signal wave-shape. The wave-shape of the induced signal for each character is shown in Fig. 1 and the apparatus in Fig. 2 is adapted to sample different portions of the signal and convert the amplitudes of the samples to a binary coded representation of the character, the amplitudes of the samples being compared with the maximum amplitude of the signal so as to compensate for differences of magnetization or thickness of printing ink. In Fig. 2 the magnetizing head 13 is energized by an oscillator 12 and the reading head 14 feeds an amplifier 15 which passes the signal through a full-wave rectifier 16 and a cathode follower 18 to a low-pass filter 20. The output from the filter is the modulating signal from which the carrier has been suppressed, and has the form of the envelopes shown in Fig. 1. This output is passed to a delay line of the kind which delays the entire signal, yet preserves its shape. This may be for example an artificial transmission line or a magnetic drum or closed loop of tape. The entire signal is contained in the delay line and the amplitude of the signal is detected at a number of points along the delay line. These correspond to the six sampling points on the envelopes shown in Fig. 1. Each sample point is connected through a separate one of cathode followers 24A-24F, which serve as buffers, to diodes 26A-26F and also to one input of difference amplifiers 28A-28F. The difference amplifiers are comparators which amplify the excess of input signal over a reference potential. A11 outputs from diodes 26A-26F are connected to a cathode follower 27 so that the signal applied to this cathode follower is the maximum amplitude of the signal in the delay line. The output from cathode follower 27 is connected to six potentiometers 30A-30F and the variable arms of these potentiometers provide the difference amplifiers with their reference voltage, a proportion of the maximum signal. Only a signal in excess of this reference voltage is amplified so that there are outputs only where the sample signal exceeds a predetermined fraction of the maximum. The amplified signals are applied to gates 32A-32F which are opened by a signal from the delay line as follows. When the leading edge of the signal in the delay line reaches the end an over-driven amplifier 43 passes a signal through a Schmitt trigger 46, a differentiating circuit 48, an amplifier 50 to a monostable multivibrator 52 which sends a pulse to open all the gates 32A-32F. The signal samples present in the difference amplifiers can then pass to shaping amplifiers 54A-54F which shape the signals into rectangular form. This output is passed through cathode followers to apparatus processing the information. In addition to the six signals obtained from the difference amplifiers, two more signals are derived from two of the sampling points. These points are connected to overdriven amplifiers 34, 36 which sharpen up the leading and trailing edges of the applied wave-shape. These signals are sent through two Schmitt triggers 38, 40 to gates 42, 44 opened by the delay line signal as are gates 32A-32F. Thus there are produced eight signals forming a voltage pattern unique for the wave-shape in the delay line and forming an eight digit binary code representation of the character which has passed under the reading head. In the form of Fig. 3, direct current magnetization of the characters is used, the magnetization being effected by a permanent magnet 70 as shown, or alternatively it may be arranged on the other side of the sheet from the reading head 72. The signal in the reading head is sent to an amplifier 74 and thence to an integrator 76 and a clipper 78. The output from the clipper is passed to a delay line 80 as in the previous embodiment the various points on the delay line being sampled to determine whether or not a voltage is present by opening gates 82A, 82B. Flip-flops 84A are sensitive to positive voltages and flip-flops 84B are sensitive to negative voltages so that they are tripped or not in accordance with the signal waveshape in the delay line. The voltage pattern at the outputs of all the flip-flops represents the character read.