Patent GB-1159403-A (GB)
Title: Facsimile System
IPC: H04N1/32
Filed: 1966-09-27
Abstract: 1,159,403. Facsimile transmission. XEROX CORP. 27 Sept., 1966 [10 Oct., 1965], No. 43077/66. Heading H4F. A facsimile transceiver adapted to operate through a telephone network comprises logic means including a plurality of resettable bistable devices in a divider configuration for generating periodic timing pulse patterns, timing means responsive to selected ones of the timing pulses for generating a plurality of repetitive timing signals in phase with the timing pulses, Figs. 6 and 7 (not shown), selectively energizable facsimile transmitter scanning means responsive to the timing means, Fig. 8 (not shown), selectively energizable facsimile receiver printer means, Fig. 12 (not shown), first control means responsive to the detected presence of a document to be transmitted for energizing the transmitter scanning means, and second control means responsive to the detected absence of an original document to be transmitted and to received video signals for energizing the receiver printer means. The first control means includes a sensing switch and reset means responsive to the actuation of the switch for operating the divider at a fixed frequency, and the second control means synchronizes the divider in accordance with received synchronizing signals. To reduce transmission time the operation of the transceiver in the transmit mode is such that in the absence of black areas or other marks which a photomultiplier, for example, is designed to detect, the document to be transmitted is rapidly scanned alternately from left to right and from right to left. Althrough no video information is transmitted in this condition, characteristic advance signals are transmitted and also directed to the transistor stepping motor to advance the document one increment at the end of each scan. If a black area is detected during a fast scan then the document is not advanced any further, a document advance signal is not transmitted, and the scanning action reverts to a slow scan. When the scanning mechanism e.g. a galvanometer, reaches the time and position at which a slow scan is about to commence, a charateristic pre-video alerting signal is transmitted and thereafter video signals corresponding to the scan are transmitted. At the end of a slow scan the document is advanced one increment, a paper advance signal is transmitted, and the galvanometer executes a rapid retrace during which video signals are not transmitted. If information is detected during the retrace, then a further slow scan is made and further paper advances or advance signals are withheld until the end of the slow scan. If no information is detected during the fast scan retrace, then the document is advanced at the end of the retrace, an advanced signal is transmitted, and further rapid scans and advances are made until other back areas are detected. Thus every elemental line of the document which contains information is scanned twice, first with a rapid scan and then with a slow scan during which video signals are transmitted. Lines bearing no information are merely scanned rapidly over. To further reduce the transmission time only every alternate elemental line of the document may be scanned. When the transceiver is in the receive mode, as controlled by the absence of a document in the scanner, and the timing circuits are in synchronism with those of the remote transmitter, the printer stepping motor exactly follows the operation of the scanner stepping motor at the remote connected transmitter. An alarm is actuated to indicate, in the absence of an original document to be transmitted, loss of synchronization or loss of incoming control signals.