Patent GB-549775-A (GB)
Title: Improvements in or relating to facsimile telegraph equipment
IPC: H04N1/06
Filed: 1941-05-23
Abstract: 549,775. Facsimile telegraphy. FINCH, W. G. H. May 23, 1941, Nos. 6636 and 6637. Convention dates, July 5, 1940 and July 12, 1940. [Class 40 (iii)] In a fascimile receiver comprising an electrically conducting drum around which the recording stylus is rotated, the stylus is held in a carriage carried by a rotatable mount in such a manner that for synchronization, the stylus carriage alone is arrested while the mount continues its movement. Specification 549,776 is referred to in this respect. The apparatus shown can be used as a receiver or as a transmitter. It is driven by a motor 36, Figs. 2 and 5, geared by a pinion 61 to a wheel 58 free on a shaft 65. For receiving, the wheel 58 is clutched to a wheel 73 on one side fast with the shaft 65 ; and for recording, the wheel 58 is clutched to a wheel 72 on the other side free on the shaft 65. These clutching operations are performed by a handle 55, Figs. 1 and 12, through a cam 81 and a fork 86 slidable on a shaft 87. When the apparatus is set for receiving, motion is transmitted by wheel 73 to wheel 101, and by shaft 65 and pinion 165 to wheel 175. Wheel 101 is fast with lead screw 46 with which engages a segmental nut forming part of a lever 125 pivoted on the end 114 of the drum 226, so that the drum is moved longitudinally, its rotation being prevented by longitudinal guiding rods 111, 112. The guiding rods 111, 112 pass through bushings in the end 114 of the drum, and the other end 113 of the drum is provided with a bushing for the lead screw 46. Wheel 175 is attached to annular members 191, 192 and rides round a supporting ring 176 around the drum. The members 191, 192 form a T-shaped annular groove in which is fitted a small carriage 202, Fig. 7, tightened in the groove by a backing spring 222. A lever 206 is pivoted to this carriage and the recording stylus 33 is adjustably clamped in a slot in this lever by a screw 213. A spring 214 is provided to hold the stylus in on and off positions. The rotation of the wheel 175 during the receiving operation causes the carriage and its stylus to move round the drum while the drum is being bodily moved longitudinally Thus a spiral scanning action is obtained. For synchronization, the carriage is temporarily stopped at each revolution of the receiving drum which is driven slightly faster than the transmitting drum. This stoppage is produced by a lever 231 against the end of which the carriage comes to bear. The lever is pivoted at 232 and its other end is bent and forms the armature of an electromagnet 237 which receives the synchronizing pulses sent by the transmitter. When such a pulse arrives, the carriage is released and the stylus resumes its movement round the drum. The separation of the synchronizing pulses from the image signals is performed by a changeover switch 255, 261, 264 operated through a sliding rod 252, Fig. 12, by a notch 251 a cam 103 rotating with the lead screw 46. When the apparatus is set for transmission, motion is transmitted by wheel T2 through idler pinion 301 to wheel 104 free on lead screw 46 which now remains stationary. The longitudinal guiding rods 111, 112 are attached to the wheel 104 at one end and to a cam disc 54 at the other end. The rotation of the wheel 104 therefore causes the rotation of the drum 226, while a nut formed on lever 125 causes the drum to move longitudinally. The surface of the drum is therefore scanned spirally by a beam of light projected on it from a lamp 311 by a lens system 34 provided with adjustments clamped by a screw 321. The light reflected by the drum is received by a photo-electric cell 35. This photo-electric system may be as described in Specification 547,154. The synchronizing pulses at each revolution of the drum are produced by the closing of switch 145, 146, Fig. 15, operated through a rod 144 by a notch 143 in the cam disc 54. To prevent rotation of the rods 111, 112 around the lead screw 46 during reception, the notch 143, Fig. 15, of the cam disc 54 to which the rods are attached is formed with a radial shoulder 161 which is stopped by the sliding rod 144. The other end of the notch is inclined to operate the rod 144 when rotation is in the opposite direction when the apparatus is transmitting. To prevent rotation of the lead screw 46 during transmission, the notch 251, Fig. 12, of the cam 103 is similarly formed with a radial shoulder which is stopped by the sliding rod 252. In a modification, Figs. 16 - 20 (not shown), the clutching change required for receiving and recording is performed by two ratchetlike pawls controlled by two levers selectively actuated by cams on a spindle provided with a handle. The levers also control catches for preventing undesired rotations instead of the radial shoulders on the cams.