Patent GB-923324-A (GB)
Title: Improvements in detection of long waveshapes in automatic symbol reader
IPC: G06V10/10
Filed: 1961-05-29
Abstract: 923,324. Automatic character-reading. GENERAL ELECTRIC CO. May 29, 1961 [June 23, 1960], No. 19226/61. Class 106 (1). In an automatic character-reader of the kind disclosed in Specification 796,579, in which magnetic, specially-shaped characters 11, Fig. 1, are scanned to produce characteristic wave shape which is then sampled in a tapped delayline 16, the delay line is provided with an extra tapping L which detects wave shapes of greater than the predetermined maximum length. Spurious magnetic marks on the paper may produce a signal which combines with the wave of an adjacent character to give a wave similar to that expected from one of the characters and an erroneous recognition signal may result. To prevent this the extra tapping L is provided which responds to the presence of a long wave shape to block the recognition circuit when a speck of magnetic matter precedes the character and a corresponding signal enters the delay line 16. Tappings A, B, C detect this signal and energize the timing circuit 17, Fig. 2, which produces a gating pulse at the time the spurious signals reach the right-hand end of the delay line and the leading part of the character wave shape fills the rest of the delay line. The signals at tappings A-H produce the usual responses from the correlation circuits 18(1)-18(n) and the highest output is isolated by the differential amplifiers 20(1)-20(n) to produce a signal on a single lead 21(1) and 21(n). The output gates 22(1)-22(n) have two enabling inputs, one from the timing circuit 17 and the other from the long wave shape detector. The tapping L is connected to a potential divider 32, the tapping point of which is connected via oppositelydirected diodes to the inputs of a summing amplifier 33. The output is applied with the outputs from the correlation circuits to an Or gate 23 which passes the highest signal via an attenuator 24 to give the clipping level of the differential amplifiers 20(1)-20(n) and 34. The circuit is adjusted so that a signal of any significant amplitude (as part of a character wave shape would be) at tapping L will cause the amplifier 34 to produce an output. This is inverted at 31 and used to block the gates 22(1)-22(n). It is also applied on line 42 to And gates 36 and 39 so that the timing signal is admitted to delay circuits 37, 38 which delay the sampling pulse a space equal to the spacing between adjacent tappings so that the outputs from the correlation circuits are sampled again at this time. If the character waveform is now wholly in the delay line there will be no signal at tapping L and the gates 22(1)-22(n) will open to pass the recognition signal. If the character is not yet wholly in the delay line there will still be a signal at L and the output gates will be blocked as before. However, gate 39 is now opened by the signal on lead 42 and the timing signal is delayed again for a further sampling operation a tapping space later. Instead of causing the outputs to be re-sampled, the presence of a long wave shape signal on lead 42 may be used to reject the record being sensed.