Patent GB-1161027-A (GB)
Title: Improvements to optical systems for the guidance of moving bodies by multiple director beams
IPC: F41G7/26
Filed: 1967-07-12
Abstract: 1,161,027. Optical position finding means. COMPAGNIE FRANCAISE THOMSON HOUSTON-HOTCHKISS BRANDT. 12 July, 1967 [21 July, 1966], No. 32165/67. Heading H4D. Specification describes a modification of the optical navigation system described in Specification 1,160,827 wherein the transmission of an omnidirectional reference radio or light beam, is dispensed with, and the position of the mobile craft receiver with respect to a reference line is determined by comparing the interval between successive illuminations g 1 , g 2 , Fig. 11, of the craft by the direction beam, and a predetermined reference time R 1 -R 2  equal to said interval on said reference line. In addition, to reduce the number of moving parts in the beam transmitters, the rotary beam coder/modulators are replaced by fixed multi-slit apertures Fs, Fig. 4, and Fg, Fig. 5, which divide each director beam into a plurality of sub-beams, which, on scanning the mobile craft, give rise to a pulse train comprising a number of sub pulses Ns and Ng characteristic of the bearing or elevation director beam and allowing the identification thereof in decoder R23, Fig. 10. Corresponding pulses g 1 , g 2  are thus produced by the decoder R23 and fed to displacement measurement means R24. The interval g 1 -g 2  is established by a bi-stable circuit 240, triggered by the pulses g 1 , g 2  to give pulse (E1), Fig. 11. A monostable circuit 246 with controllable period is triggered by pulse g 1  (pulse g 2  being blocked by gate 245) to give an output pulse (D) with a duration normally representative of the interval To = R1-R2. A comparator 244 receives the outputs of circuits 240 and 246 and yields pulse (H1) with a duration representing the deviation of the craft from the reference line. To control circuit 246, successive first pulses g 1 , g 11  are fed to a bi-stable circuit 263 to produce a pulse Eg having a duration Tr equal to the repetition period of the scan. A threshold device 264 and integrator 265 produce a D.C. signal at one input of level comparator 266 equal to mTr. Known interval To is expressed as a fraction of Tr, whence Tr = KTo and said input signal is mKTo. The output (D) of circuit 246 of duration (To + #), where # is the error, is fed to a threshold device 260, a " times K " amplitude multiplier 261 and an integrator 262. A D.C. signal is thus produced at the second input of comparator 266 equal to mK(To + #). Comparator 266 thus produces a signal indicating T which is fed to readjust circuit 246. Alternatively reference interval To may be expressed as a multiple K of the period #r of the plurality Ng, Ns of sub-pulses. Thus a controlled pulse generator 270, Fig. 12 (not shown), may be synchronized with the subpulses, and feed its output via " times K " multiplier means 276 and integrator means 277, to control circuit 246. As another alternative, circuit 246 may be dispensed with, Fig. 13 (not shown), and the output of integrator 277 fed to one input of a level comparator 283 receiving at its other input a D.C. signal representing the interval g 1 -g 2 .