Patent GB-1169912-A (GB)
Title: Facsimile System
Inventor: GERHARD ALLEN ROBERT
IPC: H04N1/36
Filed: 1966-09-27
Abstract: 1,169,912. Electric synchronizing; control of stepping motors. XEROX CORP. 27 Sept., 1966 [1 Oct., 1965], No. 43078/66. Headings H2J and H2L. [Also in Division G3] A system for synchronizing incoming signals having a predetermined pulse repetition frequency with locally generated signals, comprises a controllable frequency oscillator, timing means responsive to said oscillator for generating a pattern of repetitive signals including timing signals having a pulse repetition frequency substantially equal to said predetermined pulse repetition frequency, first control means responsive to the detection of a grossly out-of-synchronous condition for increasing the frequency of said oscillator to a first higher frequency, second control means responsive to the detection of a slightly out-of-synchronous condition for increasing the frequency of said oscillator to a second higher frequency, said second higher frequency being higher than said predetermined frequency but lower than said first higher frequency, and means responsive to the detection of a substantially synchronized condition terminating the action of the first and/or said second control means. The system is applied to facsimile transceivers adapted to operate through a direct dialling telephone network, telephone 135 being used to dial the corresponding telephone at another location, after which handset 137 is placed in box 127. A document is inserted in one of the scanners 126 which sends a control signal to circuit 140 is adapting the transceiver to the transmit mode. Scanner 126 also sends video signals to transmitter 138 which combines them with the control signals and introduces them into the handset for transmission over the telephone line. At the same time circuit 139 exchanges signals with printer 142 and processes circuit 140. At the other transceiver, a signal is picked up from the handset and is detected by receiver 141 which causes circuit 140 to put the transceiver into the receive mode and to control circuit 139 to bring printer 142 into synchronism with scanner 126. A supervisory circuit 143 sounds an alarm when a transmission is completed or interrupted. The printing mechanism comprises a drum geared to a two-pole synchronous motor and attached to a pair of camoperated switches, a pen carriage carrying a marking tip which is urged into contact with the drum by an electromagnet. The pen is driven by forward and reverse stepping motors, Fig. 3 (not shown). The scanning mechanism has a pair of rolls driven by a stepping motor for feeding paper through the scanner. A mirror galvanometer samples light reflected from the paper and passes it to a photomultiplier. Fig. 4 (not shown). The timing circuits comprise an oscillator 201 providing a train of pulses to a divider chain 203 of flip-flops I-VII, the output of stage VI being the signal A which drives the drum motor, the associated cam-switches generating signals M, #M, and S. The counter 203 is connected to gates 205-209, 215-223, and inverters 210-214, 226-233 to provide the various timing signals C-N. The telephone box has a loud-speaker sealed to the microphone of the handset and connected to an oscillator followed by an audio-amplifier, and a two-level input signal is applied to the oscillator for introducing facsimile signals into the telephone circuit. An inductive coil is placed under the earphone to pick up incoming signals. In the absence of black areas which the photomultiplier is adapted to detect, a document is scanned rapidly and no video information is transmitted but advance signals are directed to the transmitter stepping motor. If a black area is detected during a fast scan, the document is not advanced and the scanning action reverts to a slow mode, an alerting signal is sent and thereafter video signals are transmitted. At the end of a slow scan, the document is advanced one increment, a paper advance signal is transmitted, and the scanner executes a rapid retrace during which video signals are not transmitted. If information is detected during the retrace, a further slow scan is made and paper advance is withheld, but, if no information is detected, rapid scans and advances are continued. Faster transmission may be afforded optionally by skipping alternate scan lines. Recording drum 122 is driven by motor 150 operated by signal A, pen carriage 154 being driven by stepping motors 160, 161, in accordance with the D signals are by pulses from NOR gate 609. The video signal is applied to marking tip 156 and the pen-engage signal to the appropriate coil. Cams 162, 163 provide signals S, M, M to control the timing circuits, and limit switches 612, 613, regulate the reversal of the stepping motors 160, 161. Relay K5 operates alarm signal 624. The facsimile transceiver transmits a series of B signals prior to the transmission of control or video signals so that synchronization is established. If the receiver is initially far out of synchronism, a pulse from multivibrator 719 is applied to diodes 204 to reset all stages of counter 203 to zero, whereby drum 122 is accelerated and synchronism is approached. If a coincidence is detected between the incoming B signal and the Q signal, then L signals are enabled to re-set the counter which cycles at an average rate only slightly above normal. This permits the receiver to advance slowly the small amount required to achieve full synchronization. When substantial synchronization is achieved, the printer control circuit responds to incoming signals. The oscillator 201 and divider 203 may be replaced by a variable frequency oscillator. In the receiving mode, flip-flop 705 gates either of two control voltages to the oscillator to cause it to speed up. Achievement of approximate synchronization re-sets flip-flop 716 and passes signals through gates 721, 723, 725, 726, to a phasesensitive detector which compares them with an internal B signal and produces a phase lock correction for application to the oscillator.