Patent GB-729101-A (GB)
Title: Receiver for facsimile telegraphy
IPC: H04N1/16
Filed: 1953-05-04
Abstract: 729,101. Facsimile receivers ; electric synchronous movements. HELL, R. May 4, 1953 [May 2, 1952], No. 12374/53. Class 40 (3). A receiver for facsimile telegraphy with lineby-line recording on a recording sheet, comprises a recording spiral having a number of turns and having its axis parallel to the direction'of the line combined with an element which is moved in the direction of the line and co-operates with only one turn of the recording spiral for each received recording impulse. A synchronous motor 1 drives through a clutch 2 a cylinder 3 carrying a multi-turn spiral knife-edge 4 inked by roller 5. Recording paper 6 is fed by rollers 11 over guide plate 8, paper table 10 and guide plate 9. A brake 14 ensures that the paper passes tautly over slot 22 in table 10. The feed rollers 11 are driven through gears 15, 16 by the motor 1 and at the same time guide wheels 17, 18 are driven through the gear 16. An endless band 19 travels round wheels 17, 18 and carries lugs 20 which comprise a short knife-edge guided in slot 22 along a scanning line. The gear 16 is so chosen that the lug 20 always lies opposite a turn of the recording spiral 4. A pressure bar 23 which extends the full width of the paper bears against lug 20 from the rear and when an image impulse is received the moving-iron system 24 is actuated to cause the knife-edge of lug 20 to press the paper 6 against the spiral knife-edge 4. Owing to the relatively small pitch of the spiral, the inked element impressed on the paper is substantially square (Fig. 3, not shown). The lug 20 is of resilient U-shaped form such that undue force is not transmitted either to the band 19 or paper 6 and the tension of the latter is sufficient to effect return of the lug 20 after an impulse. Synchronism with the transmitter is attained by control of clutch 2 by an electromagnet 30. Terminals 29 are connected in the circuit of a receiver amplifier valve that passes current when there is no signal and contacts 31 are arranged to be closed when a lug 20 is in position at the start of a line. Thus, the magnet 30 is energized to allow the motor 1 to run freely and lug 20 to remain stationary until a phase signal is received, when the receiver valve is blocked and current in magnet 30 ceases, clutch 2 is engaged and contacts 31 open as soon as the lug 20 commences a scan. Further phase signals are received at each line commencement. The'motor 1 may be started by a relay responsive to a special starting signal of two seconds' duration, but not to the shorter recording impulses. Stopping may be effected by a thermo-contact heated by a ten-second stop signal. Instead of a band 19, a chain may be used, and Fig. 4 (not shown) illustrates a construction of lug formed by two leaf springs screwed together at one end for use with a chain drive. Instead of only one lug 20 on the band or chain, a number may be provided such that each lug is followed by another after completion of a line scan, in order to scan the next line. By providing two or more lugs at different levels anumber of lines maybe scanned simultaneously, the lugs having separate pressure bars operated over separate channels, e.g. different audiofrequency modulations on a high-frequency carrier. A multi-thread spiral may be employed with individual lugs (which scan successively or simultaneously) allocated to the different threads of the spiral and these threads may be inked with different colours to obtain a multi-colour recording.