Patent GB-640446-A (GB)
Title: Improvements in or relating to electrical facsimile signalling systems and electro-mechanical synchronizing arrangements therefor
IPC: H04N1/00
Filed: 1944-07-13
Abstract: 640,446. Copying-telegraphy; electric synchronous movements. SKILLING, W. H. July 13, 1944, No. 13388. [A Specification was laid open to inspection under Sect. 91 of the Acts, June 16, 1947.] [Class 40 (iii)] In an electrical facsimile signalling system in which the transmitting and receiving apparatus comprise a tape which is traversed laterally by a reciprocating transmitting or receiving arm respectively and which is stepped forward at the end of each stroke of the arm, the transmitting means associated with the arm and tape and which operates to produce the picture or like signals is also utilized at the end of the arm strokes, and separately from its operation during the intervening portion of the stroke or strokes, to produce a signal to maintain in synchronism the stepping movement of the tape at the receiver. The signals or characters on a tape 26 are scanned by a beam from a lightsource 24 provided with a small aperture 27 and mounted in a frame 23 on a scanning bar 25 moved transversely of the tape by a slide member 19, connecting rod 18 and crank connected to a wheel 16 on a driving-shaft 14. The tape is supported between guide members 35, 36 on a frame 31 provided with an elongated aperture 47 above a photo-electric cell 39 and vertically below the path of the aperture 27. At the end of each line the tape 26 is advanced by a roller 34 on the shaft of a toothed wheel 33 engaged by spaced teeth 29, 30 on a wheel 28 on the main shaft 14 driven by the motor 11. The tape 26 is held against the feed roller 34 by an upper roller 37. The interruption of the incidence of the beam on the photo-electric cell produces signal impulses which are rectified, amplified and fed to a relay 40 having an armature which in one position transmits an impulse to the .line. The stroke of the frame 23 is arranged to be greater than the length of the aperture 47 so that an impulse is transmitted at the end of each scanned line. Receiver. The received impulses are applied to a magnet 79 controlling an arm 80 mounted in a support 81 and engaging a short arm 73 carrying a stylus 74 and mounted in a frame 71 which is moved across the recording tape 75 by a connecting-rod 70 and crank 64 driven by a shaft 53. The tape is stepped forward at the end of each line by a roller 62 on a shaft 61 having a toothed wheel 60 engaged by diametrically opposed projections on a wheel 59 on the shaft 53. As shown, an inking ribbon 72 carried on a spool 67 is fed underneath the stylus 74, but this arrangement may be replaced by a self-inking style. The shaft 53 is connected through a clutch 54 to a spring-pressed gearwheel 52 driven from the main shaft of the motor 48. A disc 56 adjustably mounted on the shaft 53 has a tooth 57, Fig. 5, which engages with a projection 58 carried by the armature 55 of an electromagnet 55a when the latter is energized by the impulse transmitted at the end of every line. The magnet 55a will be energized intermittently by the dark positions of the subject transmitted but these operations will be without effect on the toothed disc 56. The receiver motor 48 is arranged to operate at a rate slightly faster than that of the transmitter and the shaft 53 will normally be arrested at the end of each line. Circuit arrangements. The relay 40 may be in the anode circuit of a valve whose grid is directly controlled by the output of the photoelectric cell, Fig. 8 (not shown), or as shown in Fig. 9, alternating current from a source 89a is fed via a condenser 94 to a rectifier 92 and a circuit extends through the rectifier, the winding of the relay 40, anode 97 and cathode 99 of the photo-electric cell 98 and in parallel through the anode cathode circuit of an amplifying valve 100. The grid G of the valve 100 has an adjustable bias from a tapping point 102 and is additionally controlled in accordance with the incidence of light on the photo-electric cell 98 by a connection to its cathode 99.