Patent GB-750422-A (GB)
Title: A method of, and apparatus for, electronically interpreting a pattern code
IPC: B07C3/14
Filed: 1953-07-03
Abstract: 750,422. Photo-electric code-scanning devices. POSTMASTER GENERAL. July 3, 1953 [April 29, 1953], No. 18586/53. Class 40 (3). [Also in Group XIX] Articles are classified or sorted by placing on them a pattern code which includes synchronization marks and-classifying marks, scanning the marks by means of an electronic sensing device and utilizing the pulses produced in the sensing device by the synchronization marks to isolate and identify the pulses produced in the sensing device by the classification marks. As shown (Figs. 1 and 2) a number or letter may be represented by combinations of marks 1 in one of rows R1 to R5 and columns C1 to C5. The synchronization marks S1, S2 referred to above are wider than the classification mark to facilitate identification. The code is scanned by traversing the pattern in the direction of the rows R, each row being examined by one of photo-cells 2-6. Initially cells 2 and 6 receive pulses from the synchronizing marks S1, S2. These pulses which are wider than those produced by the classification mark 1 are selected by pulse selectors 7 (to be described) and applied to a gate 9 which operates a known sorting system. This system is thus only operated if the pattern is correctly aligned. The pulses produced in cell 2 are also applied to a further sync. pulse selector 10 which allows only the large sync. pulses to pass to a delay line 11 along which tapping points 12-17 are provided. This pulse appears at the tapping points preparing a column of gates 18 which are connected to each point at the same instant as a column of the pattern corresponding to that gate being scanned. If one of cells 2 to 6 detects a mark in one of rows R1 to R5 a pulse is fed to the corresponding row of gates 18 fed by the cell and the gate energized both by this cell and the tapping on the delay line corresponding to the column being scanned is opened to produce a pulse which represents the position of the classification mark. At the end of the pattern marks S3, S6 and S7 produce pulses at the same time as the pulse in the delay line reaches tap 17. The coincidence of these pulses checked by a gate circuit 19 provides a speed check. In a modification (Fig. 3, not shown), the scanning is made independent of the speed of traverse of the pattern by means of marks provided above the columns. The synchronizing marks prepare in turn a counting chain consisting of a number of cold cathode tubes (see below). Each time another such mark is detected by a photoelectric cell provided for this purpose, the previous tube in the ring.is.blocked and the one corresponding to the column is unblocked, thus preparing the corresponding column of gates 18 (Fig. 2). Each time a tube is unblocked it prepares the next one in the ring. In Figs. 5 and 6 is shown a system wherein a card moving in the direction of the rows is scanned by means of a flying spot beam produced, for example, by means of a cathode-ray tube 29a, which beam traverses in the direction of the columns and is detected by a photo-cell 30. Alternatively, the card may be stationary, means being provided for scanning the columns of the card successively by moving the beam of the cathode-ray tube in steps. The cards are provided with narrow synchronization marks S18-835 provided along the top of the columns and at the bottom leading and trailing edge. Initially the flying spot scanner traverses synchronizing marks S18, S19. The narrow pulses produced in the cell are separated by a selector 37 and feed a second selector 39 which combines them to produce a pulse of sufficient amplitude to open a gate circuit 38 which is maintained open throughout the scanning of the code. The synchronizing pulses S20 to S34 detected by cell 30 are selected' by selector 37 and pass through the gate 38, electronic switch 40, and a pulse widening circuit 41 to a high frequency delay line 42. The pulses appear at tappings 43-48 along this line at the instant that the scanning spot is traversing the corresponding row of the card. In practice each column is traversed five times by the scanning spot and five pulses are produced at the tapping corresponding to the row in which a mark appears. The pulses appearing at the tapping points 43-48 are applied to gating circuits 31-36 so that when pulses corresponding to the rows are applied to the gates a succession of five pulses are applied to a low-pass filter 49-54 which supplies one large pulse to one of a row of gating circuits 18 as shown in Fig. 2. The pulses appearing at the output of gate 38 are applied through a low-pass filter 55 which produces one long pulse from a series of short ones through a delay line 56 which delays the pulse by three-quarters of the period between synchronization marks and are used to produce two short pulses in a pulse generator 57. Only the leading positive pulse is used and this pulse is applied to the first of a row of cold cathode counters, or multivibrators M1 to M5<SP>1</SP> for counting. The pulse obtained from pulse combining circuit 39 (see above) is applied to a starter 58 which prepares the multivibrator M1 for striking due to delay line 56, the multivibrator M1 triggers at the instant scanning of the first column of the card commences. An output voltage produced from each multivibrator is used to prepare a column of gates 18 (see Fig. 2). The next synchronizing pulse (S20) detected by cell 30 cuts off multivibrator M1 and opens M2 already prepared by the multivibrator M1, thus preparing another column of gates 18. The last multivibrator in the line M5<SP>1</SP> is operated by synchronizing mark S24 and resets starter 58. This last pulse is also used through tapping 48 on delay line 42 to open gate 36 so that synchronizing mark S16 is able after differentiation in unit 59 to operate a starter 60 for the next row of multivibration M6 to M10<SP>1</SP>. No synchronizing mark is necessary at the beginning of a new, column since the last multivibrator in one column may prepare the first one in the next. The Specification gives circuit diagrams of certain of the components used. In the arrangement of Fig. 7, the wide synchronizing pulse is selected by applying it to a delay 63, the delay of which is such that the reflected pulse is additive at the input to the line to the original wide pulse. The combined higher amplitude produced is sufficient to trigger a blocked triode 67. In the arrangement of Fig. 10 is shown a circuit for selecting the narrow pulse used in Fig. 6. The start of a narrow pulse applied to triode 81 sets up oscillation in circuit 86, 87. The termination of the pulse increases the oscillations thus triggering a valve 90. The pulse width is so related to oscillation frequency that a wide pulse damps out the oscillation. A gating circuit of conventional type and cold cathode ring counting circuit are also described.