Patent GB-549776-A (GB)
Title: Improvements in or relating to facsimile telegraph receivers
IPC: H04N1/00
Filed: 1941-05-27
Abstract: 549,776. Facsimile telegraph receivers; synchronizing. FINCH, W. G. H. May 27, 1941, Nos. 6782 and 6783. Convention dates, May 10, 1940 and Aug. 16, 1940. [Class 40 (iii)] A facsimile telegraph receiver is so arranged that the synchronizing signal received between each successive line causes the temporary stoppage of a small member of light weight carrying the recording stylus or a mirror of an optical recorder, while the main moving parts of the apparatus continue their normal movement. In the form shown in Figs. 1, 2 and 3, three stylus assemblies 52 are attached to an endless chain 51 stretched between a driving sprocket 53 and an idle sprocket 54, so that the styli are operative for successive lines along a sheet of paper 55 over a platen 207. The paper comes from a reel 200, and passes over a roller 206 and around the platen 207 to a driving roller 1'62 with a pressure roller 208, and from thence to a take up reel 238. The driving chain sprocket 53 and the driving paper roller 162 are driven in correct speed relationship by a motor 56 through a gear box 60 and a shaft 83. The sprocket 53 is keyed to a hollow shaft concentric with the shaft 83 and adapted to be clutched thereto by a clutch 95. A pinion 120 also keyed to the hollow shaft is in mesh with a pinion 121 on a shaft 122 connected by worm gearing 125 to another shaft 137 itself connected by worm gearing 160, 161 to the shaft of the paper driving roller 162. The clutch 95 is intended to be operated automatically by an electromagnet 610 at the beginning of a message transmission to ensure starting in correct phase. Thereafter the clutch remains for the duration of the message ; or the message signals are temporarily suspended at intervals of say ten minutes to reoperate the clutch to rephase the receiver if it is liable to lose phase beyond the control of the line synchronization device described below. Line synchronizing device.-Each stylus 425, Fig. 9, is mounted on a small carrier 420 slidably fitted to a support 403 attached to the chain 51 and guided along a rail 117 by a grooved member 430 in conjunction with a spring urged conical member 431 and an adjusting set screw 436. The stylus carrier 420 is gripped on the support 403 by a spring urged clamping member 407, so that the stylus carrier follows the movement of the support 403 with the chain 51 except when forcibly arrested. For this purpose, a double-armed lever 468, Fig. 5, is pivoted at 469, so that one arm of the lever projects in the path of the stylus carrier 420 and the other arm is engaged by a hook 481 on the armature 462 of an electromagnet 71. At the beginning of each line, the stylus carrier 420 is arrested by the lever 468 and slides on its support 403 until the synchronizing signal is received by the magnet 71, whereupon armature 462 releases lever 468 and the stylus carrier proceeds on its line recording operation correctly positioned. During the return of the stylus carrier on the outward inoperative stretch of the chain 51, a gear segment 451 on the support 403 is rocked by a fixed projection 700, Figs. 1 and 2, and, acting on a rack 450 on the stylus carrier returns the carrier to a normal position in readiness for the next control by the lever 468 and magnet 71. If the lack of synchronization to be corrected should exceed a certain value, the delay in the operation of the magnet 71 might cause the stylus carrier 420 to be ejected out of its support 403. To prevent this, a second double-armed lever 471 is provided on the same pivot 469 with one arm projecting in the path of the support 403 and the other arm co-operating with a pin 486 on the armature 462. If the magnet has not operated before the support 403 reaches the lever 471, this lever in being deflected by the further travel of the support, deflects the armature and thereby releases the lever 468. A fixed pin 472 limits the downward movement of the lower arm of the lever 471 ; and a pin 470 on this lever similarly limits the movement of the lever 468. In a modification, the chain 51 is replaced by a pair of parallel belts on which the stylus carriers slide. In this arrangement, the stylus carriers can never come off their support, the second lever 471 of Fig. 5 is not required, and the stylus carriers themselves can be adjusted along the belts for initial correction of phasing. In other modifications, a single stylus carrier is slidably mounted on a carrier attached to the end of a lever which is oscillated to scan successive lines on a paper against a concave cylindrical platen. In a receiver utilizing a beam of light from an optical device 760, Fig. 15, traversed along a rotating drum 750, the optical system is made to include a narrow mirror 766 extending alongside the drum to reflect the light beam from the device 760 to the drum 750 ; and at the beginning of each operative rotation of the drum, the mirror 766 is made to move in synchronism with the drum to keep the light spot on the same point on the drum until the line synchronizing signal arrives. Various parts of the apparatus are similar to those described in Specification 523,157.