Patent GB-964570-A (GB)
Title: Mark sensing
IPC: G06K7/12
Filed: 1962-09-12
Abstract: 964, 570. Selective signalling systems. SYLVANIA ELECTRIC PRODUCTS Inc. Sept. 12, 1962 [Sept. 13, 1961], No. 34851/62. Heading G4H. [Also in Division B7] In an arrangement for identifying objects moving past a scanning station, e.g. railway vehicles moving past a detection point on a railway track, each vehicle is provided with a coded identity label, comprising a number of coloured retro-reflective stripes disposed one above another and parallel to the direction of motion of the vehicle, which is scanned vertically by a light source disposed at the detection point and means are provided, including a pair of photo-cells each made responsive to a particular colour of light, for converting the light signals reflected from the label into an indication of the vehicles identity. Each label, Figs. 3a, 3b, which comprises twelve pairs of retro-reflective stripes each coloured either blue, orange, white or black, includes an orangeblue lower pair and a blue-orange upper pair which signal "start read" and "stop read" respectively and ten intermediate pairs each of which signals a number between 0 and 9. The label is scanned vertically upwards by light from source 18 which is reflected via mirror 30 and the reflective surfaces disposed on the periphery of a rotating drum 34 and the reflected light returns via the same path and passes via an aperture in mirror 30 and a mask 48 to a dichroic mirror 35 which transmits orange light to photo-cell 36 and reflects blue light to photocell 38. The output from each cell for the various pairs of stripes is shown in Fig. 3B, times T 1  and T 2  corresponding to the times of scanning the first and second stripes respectively. The pulsed photocell signals are each amplified, Fig. 4, and applied' via a comparator 64, which rejects signals below a preset amplitude, to a gated multivibrator 66 in which each pulse of duration T 1  or T 2  is converted to a single pulse of standard duration and each pulse extending over times T 1  and T 2  is converted to two pulses of standard duration. The pulses in the blue channel are inverted and delayed before combination with the pulses in the orange channel and the combined signal is transmitted to a data processing station. At the station the channels are separated and the orange channel signals after delay and inversion appear at terminals 88 and the blue channel signals at terminal 90. The appearance of a first signal in either channel triggers a pulse generator 96a which supplies a pulse to control buffer stages 98a, 98b so that any first stripe signal present at terminal 88 may be read into stage 98a and any signal present at terminal 90 may be read into stage 98b. At the termination of the pulse from generator 96a, generator 96b is triggered to enable any second stripe signals to be read into buffer stages 98c and 98d, on termination of the pulse from generator 96b, generator 96c supplies a pulse to operate a shift driver whereby the information in stages 98a-d is transferred to the first stage of a 12 stage shift register 78. On termination of the pulse generator 96d supplies a pulse to return the buffer stages to normal. When the twelve pairs of stripes are scanned, the presence of the 'start read' code signal in the 12th stage and the ' stop read' code signal in the first stage is detected by circuits 108 and 110. The outputs supplied by these circuits and the pulse produced by generator 96d provide the three inputs required by AND gate 112 and this triggers a read out flip-flop 114. The flip-flop provides a signal which at gate 94 prevents further energization of the pulse generators 96a-d and energizes a code converter unit 118 and a clutch driver 122 of a tape punch 80. The tape punch actuates the shift driver 102 whereby the data content of the register is shifted stage by stage via a code converter in which it is converted to teletype code for the tape punch. The presence of the 'stop read' code signal in the final stage is sensed by circuit 132 which transmits a pulse to de-energize the clutch driver of the tape punch. Subsequently the flip-flop 114 is reset, the code converter de-energized and the gate 94 is switched to allow further energization of the generators 96a-d. The scanning device and the data processing station are energized when a block signal 24 indicates the presence of a train in the section and means are provided including a wheel detector arrangement and wheel counter logic circuitry for providing an indication when an unlabelled wagon passes the detection point. Reference has been directed by the Comptroller to Specification 881, 721.