Patent GB-1160827-A (GB)
Title: Improvements in Angular Displacement Systems with Optical Director Beams
IPC: F41G7/26
Filed: 1967-05-19
Abstract: 1,160,827. Optical position finding. COMPAGNIE FRANCAIE THOMSON HOUSTON-HOTCHKISS BRANDT. 19 May, 1967 [1 June, 1966], No. 23486/67. Heading H4D. The Specification describes a navigation system whereby a suitably equipped mobile craft, e.g. A 4 , Fig. 4, can determine its position with respect to a desired position C by means of at least one light (i.e. including infra-red &c.) fanshaped beam o.g.h. scanning in the direction of its smaller diameter and an omni-directional transmitter at O producing a reference pulse of radio or light energy when the fan beam is in a reference position, e.g. at extreme a of its scan. The craft can thus determine its position from the interval between receiving the fan beam and the reference pulse. Two "director" fan beams o.g.h. and o.a.b. can be alternately transmitted for respectively scanning and giving positional information in bearing and elevation. The two beams can be distinguished by being of different colours or polarizations-in which latter possibility a laser light source is possible- or as is preferred, the beams may be pulsed, either at the same rate whence the beams will have different thicknesses, or at different rates whence the beams have the same thickness. In either case the receiver on board the craft will receive a different number of pulses from each beam. The light beam transmitter may comprise, Fig. 3, two orthogonal strip filament light sources 22, 32. Source 22 focused on a slit 24 defining the cross-section of the beam and on a rotating shutter having slot apertures therein whereby the beam is pulse-modulated. The pulsed beam is projected into space by a diasporameter assembly 25 which by the rotation thereof causes the beam to scan in elevation. The vertical beam o.g.h. is similarly produced and shutters 23, 33 cause the beams to be emitted and scan alternately. In the receiver, Fig. 9, the two light beams pass via optical system R 20  (made sensitive only to the lightbeams, if desired) to a detector R 21 . The detector may be cooled by device R 26  to improve the signal to noise ratio and its detection threshold controlled by means 271. The detector output is in the form of a series of pulse trains, two from one beam and then two from the other beam, which are passed via filter 272 to a selector amplifier R 22  and thence to a decoder R 23 . The decoder, by counting the pulses in each train produces pulses g 1 , g 2  at its elevation output (g) synchronously with the receptions of the elevation beam. Similar pulses S 1 , S 2  appear at bearing output (S). These pulses are fed, together with received corresponding reference signals to a processing device R 24  which produces signals representing elevation and beaming deviations of the craft which may be displayed at Is and Ig or fed to an auto pilot. The decoder, Fig. 11 (not shown), may comprise a counter giving outputs when the correct number of pulses are received, said outputs gating through pulses g 1 , g 2  &c. which are produced by differentiating the output of a monostable circuit triggered by the first pulse in a train. Since the reference signals are produced when the beams are at the beginning oa or og of their scans and the reference position is oc 1“ the way through a scan, the processing device R 24  comprises, Fig. 13 (not shown), two monostable circuits 241 and 242 triggered by the reference signal (R 14 ) and have pulse output durations of “ scan period T and ¥ scan period T. The overlapping duration is detected in comparator 243 and produces a pulse (D), Fig. 15 T T 3T (not shown), duration -, fromto -. The 2 4 4 two pulses g 1 , g 2  trigger a bi-stable circuit 240 to produce a pulse (E). Pulses (D) and (E) are compared at 244 and the difference therebetween (H) in the form of positive or negative pulse pairs gives the deviation. If the craft (e.g. a ship) is constrained to move in one plain only, the reference pulse may be omitted and the elevations beam used as the reference.