Patent GB-763758-A (GB)
Title: Improvements in or relating to facsimile telegraph apparatus
Inventor: MASON FREDERICK PERCIVAL
IPC: H04N1/36
Filed: 1955-01-13
Abstract: 763,758. Copying-telegraphy; synchronous movements; photo-electric pulse generators. CREED & CO., Ltd. Jan. 13, 1955, No. 1049/55. Class 40 (3). In facsimile scanning apparatus, Fig. 1, a single source of light 1 and a single photo-cell 14 are employed together for generating alternatively phasing signals and intelligence signals. The message form 15 is carried on the inside of a rotating transparent drum 4 and the internal circumference of the drum is greater than the length of the form so that a gap occurs between the ends. Located in the base of the drum is a transparent ring- shape member 7 having an internal reflecting surface 8, and the arrangement is such that during the rotation of the drum the message form prevents the reflection of light to photo-cell 14 via an aperture 12 except when the gap between the ends passes the scanning point. The photo-cell thus provides a phasing pulse once during each revolution of the drum and this pulse after amplification at 18 and frequency translation at 19 may be transmitted to the recorder 21. The transmitted pulse preferably comprises an interruption of a normally continuous carrier wave. Located between aperture 12 and photo-cell 14 is a shutter 13 which may be displaced to close aperture 12 and expose a further aperture 17 which allows light reflected from the surface of the message form to reach the photo-cell. This aperture is employed for generating intelligence signals and is brought into operation after completion of phasing. The apparatus is employed in a circuit arrangement as shown in Fig. 2 in which the upper part illustrates a transmitter incorporating scanning apparatus as described in Fig. 1, and the lower part illustrates the receiver. Operations are started by a positive D.C. calling signal which is sent from contact 26 in the transmitter over a channel 27 separate from the normal intelligence channel 20. The signal operates relay 28 which locks over contact 28a and applies power from source 30 to the recorder driven motor 31 over contact 28b. Power is simultaneously applied to the heater of triode 25 which becomes effective after a delay which is sufficient to allow motor 31 to attain synchronism with the power supply. The recording mechanism 36 rests in a datum position and the drive to it from motor 31 is through a clutch 35 which is at present disengaged. During this initial period, phasing pulses generated as described above are transmitted over channel 20 and are applied through amplifier 22 and demodulator 23 to the grid of triode 25. As soon as the cathode becomes sufficiently hot for anode current to flow, the first following phasing pulse causes relay 32 to operate and at contact 32a operate relay 33 which locks over contact 33a. Contact 33b then operates an electromagnet 34 which actuates clutch 35 and releases the recording mechanism which thus starts with the desired correspondence in phase with the transmitter. Simultaneously with this action contact 33c sends a negative D.C. " go-ahead " signal back to the transmitter over channel 27 where it operates relay 38. At contact 38a relay 38 releases an electromagnet 40 and allows a spring-loaded half-nut 41 on the scanning carriage 50 to engage lead-screw 42 which is rotated from the drum drive motor 45 via gears 43, 44. The " goahead " signal also operates shutter 13 and changes arms from the phasing aperture 12 to scanning apertures 17. Specification 680,661 is referred to.