Patent GB-661708-A (GB)
Title: Improvement in combined facsimile transmitting and receiving equipment
IPC: H04N1/23
Filed: 1949-04-29
Abstract: 661,708. Facsimile telegraphy. STANDARD TELEPHONES & CABLES, Ltd., and POLLARD, L. G. April 29, 1949 [May 29, 1948], No. 11464/49. Class 40 (iii). A two-way facsimile telegraph system utilizes at each station a combined transmitter receiver which is so constructed that, when either instrument is taken into use as a transmitter, the other is seized as a receiver and both instruments are locked until a predetermined length of tape has been scanned after which the drive circuits are opened and the instruments freed. The same tape is used for transmitting and receiving and is of the kind described in Specification 494,224, which for transmitting purposes has its conductivity varied by pencil writing and for recording purposes produces a change of colour when an electric current passes through it. The same scanning stylus (or four styli as shown) is used for transmitting a written message and recording a received message. Each transmitter-receiver comprises a housing 11, Fig. 1, latched to a base-plate 10, the housing when applied closing a mains switch. The tape 16 passes from a roll 35 over a horizontal support 29, Figs. 2, 7, and through a scanning device 41 to a feed roller 44 driven through gearing including a chain 64, Fig. 3, by a motor 72. A stripper 56 engaging a groove in the feed roller 44 passes the tape out through an aperture 57. Motor 72 also drives a disc 76 carrying a spring arm 78 which after one revolution of the disc opens a switch 81. The scanning device comprises four rotary styli 102, Fig. 7, driven by a synchronous motor 85, Fig. 3, having a phaseadjusting pin-and-slot mounting 88, Fig. 7. In the scanning device the tape is bent to arcuate form by a cylindrical block 95 and a co-operating plate 109 removably held in position by a carrier 114 hinged to the supporting plate 32. When an instrument is seized for transmitting, a hinged flap 15 is opened exposing a section of tape 16 in which a message is then inscribed. The raising of the flap operates switches 128 by means of an arm 125, Fig. 2, causing busy lamps 13 to be lit and locking magnets 143 to be actuated at both stations, the magnets operating bolts 137 to prevent the raising of flap 15 at the receiving station and to lock the flap at the transmitting station as soon as it is closed. The closing of the flap, through the change-over of switches 128 causes motors 72, 85 at both stations to start. At the transmitting station, the inscribed section of tape is drawn through the scanner 41 and the styli output modulates a transmitting carrier. At the receiving station, a blank portion of the tap is drawn through the scanner and the received signals after amplification are fed to the styli which record the message. After a time sufficient for the whole of the inscribed message to be transmitted and the recorded message to be projected through aperture 57, the switches 81 are operated to open the circuits of the driving motors and the locking magnets 143. Complete circuits including electromagnetic relays for controlling the sequence of operations described above are illustrated in Figs. 8 and 9 (not shown).