Patent GB-1480474-A (GB)
Title: Guidance systems
IPC: G01S1/44
Filed: 1974-07-02
Abstract: 1480474 Guidance systems SOC DE FABRICATION D'INSTRUMENTS DE MESURE 2 July 1974 [3 July 1973 21 Jan 1974] 29391/74 Heading H4D  In a guidance system a pencil beam of radiation is oscillated in a plane on either side of a mean position according to a predetermined oscillation programme, and the beam energy is modulated as a function of the angular position of the beam with respect to the mean position, the modulator comprising a rotating member having opaque and transparent regions which intersect the beam. As described, the beam from a laser 1, Fig. 1, passes through a polarizer 17, and is deflected by a mirror 2 which is oscillated about an axis 18 by a mechanism 3,4 receiving control signals from a programmer 5. In an alternative arrangement the beam is oscillated by means of a diasporameter, comprising two contra-rotating prisms (Fig. 7, not shown). The beam, which is oscillating in a plane perpendicular to the axis 18, then passes through a disc 6, which is parallel to said axis, and which is revolved at constant speed by a motor 7. The disc 6 comprises concentric circular paths 20, each comprising alternate lighttransmitting and light-obscuring portions which impose a modulation upon the beam which is dependent upon its angular deflection from a mean position. After passing through the modulation disc 6, the beam is widened in a plane containing the axis 18 by an annular anamorphoser 11. Said anamorphoser may be straight if the angular movement of the beam is small, or it may be arranged to oscillate with the mirror 2, when its width may be reduced. As applied to the guidance of a boat, in a narrow central region the modulation frequency indicates "on course", and in one or more regions on each side, the modulation frequencies indicate that the boat is to the left or to the right of the course line. On the boat are a diode or photomultiplier, modulation frequency filters, and visual or sound indicators. A pair of photodetectors 11, 11<SP>1</SP>, Fig. 5, may be spaced across the boat. The detector 11 has filters 12 for the modulation frequencies a, b corresponding to angular displacement to one side of the "on course" area, with associated indicators 13, whilst the detector 11<SP>1</SP> has filters 12<SP>1</SP> for the modulation frequencies d, e corresponding to angular displacement to the other side of the "on course" area, with associated indicators 13<SP>1</SP>. Each detector also has a filter for the "on course" modulation frequency c, and in order to obtain an accurate indication of the course line the amplitudes of the outputs of these are compared in a comparator 26 having an associated indicator 27. The vessel may be provided with an integrating ship's log 28 giving the distance from the transmitter. This enables the angular deviations corresponding to the signals from the comparator 26 to be converted into linear deviation signals, which can be utilized to control a mechanical device 30 for adjusting the spacing between the detectors 11, 11<SP>1</SP>. In other embodiments, the modulator is a rotating drum 45, Fig. 8, inside which is the oscillating beam producing means 47, said beam being swept along one generatrix 46 of said drum. Two paths 48, 49 are provided, the respective blocking-out regions 50, 51 of which may correspond to respective modulation frequencies which are either multiples of each other (Fig. 9, not shown) or are relatively prime (Fig. 10, not shown). In the central ("on course") region they may overlap (Fig. 11, not shown), and in another arrangement they are separated by a zig-zag line, as shown in Fig. 12. The receiving apparatus has two channels, one for each modulation frequency, with respective indicators, both of which are operated when "on course" (Fig. 15, not shown). An additional wall may be provided on the modulating drum to provide superimposed low-frequency Morse code signals A (dot-dash) and N (dash-dot) on respective sides of the course line (Figs. 13, 14, not shown). These may be separated out at the receiving apparatus and be applied to an audio indicator (Fig. 16, not shown). A receiving apparatus for specific use with a transmitter having a modulating drum of the kind shown in Fig. 12 is also described (Fig. 17, not shown).