Patent GB-1451086-A (GB)
Title: Facsimile receiver
IPC: H04N1/23
Filed: 1973-12-07
Abstract: 1451086 Facsimile receivers GRAPHIC SCIENCES Inc 7 Dec 1973 [7 Dec 1972] 56927/73 Heading H4F In a facsimile receiver of the kind in which a copy sheet is fed to a flat writing table across which a single stylus is traversed in a straight line motion, the information to be reproduced, which is received in the form of an analogue electric signal, is converted to digital form temporarily stored and then converted to analogue form and supplied to the stylus when it is in the correct position to commence recording. Referring to Figs. 1, 2, 5, 7 and 9 the stylus 16, mounted on a sprocket driven belt 18, effects linear scans of the copy sheet 20 as the latter, which is drawn from roll 30 by a feed roller 62, passes over a flat writing table 68. In the writing position the stylus makes contact with the edges 206a, 206b of a commutator bar 206 (Fig. 7) to which the signals are supplied, the correct writing positions being signalled by a photocell 208 responsive to light from a source 210 on the passage of an aperture 212 in the belt 18. Fig. 12, shows the circuit arrangement for processing the received analogue signal waveforms operative in such circuit being shown in Fig. 13. As shown, the received analogue waveform comprises a continuous (video) part 380 and a synchronising part 382. The video part 380 is supplied to input 300a and the synch. part 382 is supplied to line 322b. (The latter determines which of two clock pulse rates is to be employed, i.e. the pulse determines whether or not divider 326 is employed). In response to these inputs the analogue signal is converted to a four-bit digital signal in a counter 302 the outputs of which are loaded, under the control of a timing circuit 350, into respective A-shift Registers 320a, 322a, 324a, and 326a during the first half of waveform 380 as shown by waveform 384 and into respective B-shift Registers 320b, 322b, 324b and 326b during the second half of waveform 380 as shown by waveform 390. During the first half of the "Load-B" cycle the contents of the A registers are recycled, (waveform 396,) by means of an output 352 from the timing circuit supplied to AND gate 344 and recycling clock pulses (to preserve the contents) and immediately after this the A-registers are unloaded (waveform 392) and the contents passed to D/A converter 360 via AND gate 346 and OR gate 348 during the second half of the Load B cycle. The B registers are now unloaded, waveform 394, recycling being unnecessary since there is no delay between loading and unloading and the contents passed to D/A converter via AND gates 356 and OR gate 348. The unloaded signals applied to the sets of gates 346 and 356 are synchronised with the stylus position signals derived from the photodetector 208 (Fig. 7) and the output of the converter is supplied to the stylus commutator 206 via an amplifier. In the operation of the apparatus a wiper 182 (Fig. 2) presses the copy sheet 20 against the writing table 68 at a position just below the point of contact of stylus 16 and in addition to causing the sheet to bend against the guide 58A (by creating frictional forces on sheet 20) and thus ensure smooth continuous paper feed, it also serves to guide the efflux generated by the (pyrographic) stylus into a filter 180 to prevent clogging of the paper feed by carbon particles. The filter has an exhaust fan 184 which draws air over the stylus via an inlet section 180a. When the recording has been completed the copy sheet is advanced until the end of the recording is "beyond" the writing table and when a predetermined length has been advanced a solenoid 270 (Fig. 10) is actuated and releases a spring urged cutter blade 250 which is then driven along shafts 224, 232 (See also Fig. 11) so that it passes between the writing table 68 and the bridge portion 70 which abuts the table 68 and is retained by springs 260, 262. The cutter blade which thus severs the copy sheet remains at the other side of the assembly until the sheet has been removed after which it is returned to the position shown in Fig. 10 by a chain 246 driven by motor 249. To remove the copy sheet a motor 288 (Fig. 11) drives a pair of extractor wheels 76 (only one shown) having a flat portion 76a such that during one revolution the circular portion presses the sheet against a pair of springs 82 (only one shown) which project through guide plate 72 and removes most of the sheet towards tray 92. At this time, a cam 280 driven by the motor (via shaft 282) and carrying a gear 284 driving gear 286 (having one half the number of teeth of gear 284) on wheel 76, has completed 180 degrees and a bail 290 now moved downwardly (by a pin and link mechanism 300, 296, 294) as the cam rotates in a clockwise direction draws the remainder of the sheet out from the guides 71, 72 (See also Fig. 2) on to tray 92. The latter then pushes a bar 98 downwardly against spring 102 and the trailing edge of the sheet falls into the tray 92. Because, during the first 180 degrees rotation, the motor is only required to supply enough torque to overcome the frictional forces between the sheet and the guide plates 71, 72, whereas, during the next 180 degrees rotation the torque must be sufficient to overcome the tension of springs 102 and 295, a cam follower roller 316 operates via lever 312 to store energy in a spring 310 during the first 180 degrees rotation which energy is returned via the cam during the second 180 degrees rotation. Thus a small motor only is required for the constant torque requirement.