GB1245534A - Improvements in or relating to location systems - Google Patents

Abstract

1,245,534. Selective signalling arrangements. MARCONI CO. Ltd. 3 Dec., 1969 [19 Feb., 1969], No. 8996/69. Heading G4H. A system for indicating the location of a vehicle comprises a base 21 carrying a set 23 of light reflecting elements placed at known locations along the vehicle route, the elements of each set being scanned in a vertical direction to obtain an identifiable sequence of light reflections, the vehicle carrying means for scanning the base and means for receiving and storing the corresponding signals. The scanner 2 projects a narrow rectangular beam of light through mask 3 and there are two receivers 6, 7 each arranged by suitable filters to receive only light of first and second frequencies. Each receiver directs the received light on to a photoelectric device 8, 10. The output of device 8 is connected to a code detector 9 and, via delay 15 and gate 14, to store 11. The detector 8 gives an output, when a heading code, e.g. 101, is detected, to open gates 12 and 14. The scanner is pivoted and oscillated by a mechanism 20 to make a vertical scan. The base 21 also carries a set 22 of reflective elements reflecting light of the second frequency, received by receiver 7. This gives rise to a train of electric pulses serving as a clock signal for store 11. The set 22 contains a mark for each mark or space position of set 23. After the first three bits (101) the set 23 on each base is different, defining a particular location along the route. The elements 22 and 23 are painted on the base, which may be a lamp-post, using special wavelength reflective paint. The light used for scanning may be outside the visible spectrum. It may be derived from a laser. A code corresponding to set 23 is stored in store 11 until a new base 21 is scanned. The signal from detector 9 resets the store and delays 15, 16 delay the entry of the new code to ensure that the resetting operation is complete. Means may be provided to prevent store 11 from being repeatedly reset and re-registering the same code when the vehicle is stationary or moving slowly past a base 21. The code stored in store 11 is transmitted back to a monitoring station when the transmitter 24 is keyed by a receiver 25 actuated by an interrogating signal from the monitoring station. The scanner illustrated may be replaced by an octagonal drum scanner.