Patent GB-549984-A (GB)
Title: Methods of and apparatus for preparing facsimile master copies
IPC: H04N1/032
Filed: 1940-07-12
Abstract: 549,984. Facsimile apparatus; valve amplifying circuits; automatic volume control. CREED & CO., Ltd. July 12, 1940, No. 11633. Convention date, July 12, 1939. [Classes 40 (iii) and 40 (v)] In a facsimile apparatus for cutting a copy on a stencil by means of a stylus controlled in accordance with black and white electric signals derived from a scanned original, the recording circuit is arranged to limit the pressure exerted by the stylus to a predetermined value irrespective of the variations of the level of the incoming signals above a minimum level, and the position of the stylus is made adjustable to limit the depth of cut. In the circuit shown in Fig. 3, a photo-electric pick-up comprises a pair of cells 126, 127, one cell 126 subject to the light modulated by the original and the other cell 127 subject to constant illumination and in series with a variable resistance 128 for adjustment. The light is pulsated by a light chopper and the alternating current output from the cells is amplified by a preamplifier PA and an additional amplifier A and fed to the primary of a transformer 133. A volume control 131 is provided; and a change over switch 132 enables the transformer to be connected to a line L for reception from a distant transmitter. The secondary of the transformer 133 is connected in push-pull fashion to a pair of valves 137, the anodes of which are connected together and through a milliammeter 141, a resistance 142, and the coil 37 of the recorder to a positive potential 143. This anode circuit is shunted by a condenser 144 and is such that its current cannot exceed a predetermined limit. The mid-point of the secondary of the transformer 133 is connected to a negative bias 138 for class-C push-pull operation, but may be connected to earth and cathode by a switch 173 to increase the sensitivity when the photo-electric pick-up circuit is being adjusted to ensure the correct strength of current through the recorder coil 37. The recording apparatus shown in Figs. 1 and 2 comprises two oppositely directed permanent magnets 24, 25 and two pairs of pole pieces 26, 27 and 29, 30 clamped between two non-magnetic plates 33, 35 by bolts 36. The armature 28 extends between the pole pieces through a coil 37 in a recess in a plastic insulating member 38 secured by screws 39. The free end of the armature is fitted with a stylus 22 consisting of a U-shaped piece of wire or equivalently shaped other member, the marking point being rounded in the direction of the scanning line. The recorder 23 is attached to a block 32 mounted on an arm 98 hinged at 97 to a channel shaped base plate 96, on which is also mounted a bracket 122 supporting a solenoid 104. The plunger 112 of the solenoid is linked by a slot and roller 114 to an extension 99 of the hinged arm 98, and the extension 99 is normally held against a screw 101 on the bracket 122 by the weight of the recorder. The position of the screw is adjusted by a knob 106 and determines the distance between the stylus 22 from the copy on the drum 19. The adjustment is indicated by a pointer on a scale 108. The solenoid 104 when energized lifts the recorder away from the recording position, and when switched off allows the weight of the recorder helped by a spring 116 to return the recorder to operative position. This return is slowed down by a dash-pot formed by the inner end of the plunger 112. The spring 116 is coiled round the plunger 112 and is fully extended before the operative position is reached. The Specification as open to inspection under Sect. 91 describes the following additional features of the facsimile apparatus. Drums and driving and scanning mechanism, Fig. 1 (Cancelled).-A drum 19 comprises a portion 18 for the original sheet and a portion 21 for the copy. The original is held by spring garters 171 ; the copy adheres to the drum. The drum shaft 79 is mounted in end bearings 81, 81 on a base 10 and is driven through flexible couplings 86, 84 and reducing gearing 83 by a motor 82. Motion is transmitted by gearing 87, 88, 92, 93, 94 to a lead screw 48 for moving a photo-electric pick-up 15 and a stylus recorder 23 longitudinally along the drum while the drum rotates to produce a spiral scanning of the sheets on the drum. The pick-up 15 and the recorder 23 are guided by rollers along front and rear rails 12, 14 and provided with a half-nut adapted to be lifted into engagement with the lead screw 48 by springs. The half-nut may be depressed to disengage the nut from the lead screw by means of a longitudinal bar attached to cranks on a rock-shaft 59 mounted in bearings 62. The rockshaft has a crank 67 connected by a link 66 to the plunger 63 of a solenoid 64, which is energized to disengage the half nut from the lead screw. A coil spring 69 returns the rock-shaft when the solenoid is de-energized. Local start-stop circuits, Fig 8 (Cancelled).- Fig. 8 shows the parts in normal running condition. When it is desired to stop operation, a switch 149 is temporarily closed. This energizes relays 148, 151, closing a holding-on contact 153, and energizing coils 64 and 104. Relay 148 causes driving motor 82 to stop. Coil 64 disengages the half-nut from the lead screw, whereupon the carriage of the pick-up and recorder is returned to the left by a cord tensioned by a weight or by a spring drum. A bumper stops the carriage in its extreme left position. Coil 104 lifts recording stylus out of operative position. To start a fresh operation, a switch 156 is temporarily closed. This energizes relay 154 causing interruption of circuit through holding-on contact 153, whereupon the several parts return to the normal running condition. If the operation is not stopped by the closing of the switch 149, it is stopped by the closing of a switch 158 on the carriage of the pick-up and recorder when this carriage completes its travel to the right. The switch 158 is then closed by coming against a stop adjustably secured to the base of the apparatus. Receiving circuit for distant reception, Fig. 9 (Cancelled).-Signals received from a line L are amplified by an amplifier A and are then supplied by leads 169 to transformer 133, Fig. 3, through switch 132 to operate the recorder. To stop operation, a steady tone of predetermined frequency is sent out by the transmitting station. At the receiver, this tone is filtered by a tuner 162 and detected by a device 163, which energizes a relay 165, causing de-energization of relay 166 and energization of relay 168. This causes the solenoids 64 and 104 of the recording apparatus to be energized, whereby the recorder is put out of action and the scanning movement stopped. Operation is restarted by suppressing the aforesaid steady tone. This subject-matter does not appear in the Specification as accepted.