Patent GB-1208040-A (GB)
Title: Facsimile system
Inventor: AMASS PETER
IPC: H04N1/32
Filed: 1968-06-12
Abstract: 1,208,040. Facsimile system. MINNESOTA MINING & MFG. CO. 12 June, 1968 [13 June, 1967; 23 June, 1967; 13 Oct., 1967], No. 27946/68. Heading H4F. A system for recording facsimile data from a local or remote source and for reproducing it locally or at a remote destination comprises a record carrier, such as a tape, on which the data is recorded simultaneously with a frequency reference signal, the record carrier being driven by a motor which is controlled during recording by a fixed D.C. signal and during data reproduction by a D.C. signal derived from a control circuit. This control circuit compares the frequency reference signal from the recording with a constant frequency reference signal to sense any phase error between them and produces the D.C. correction signal according to this error. For efficient use of the transmission circuits image signals are recorded as and when required on the record carrier and later transmitted at high speed without a break over the transmission circuits where they are recorded and later reproduced as and when required. There are four modes of operation. In the initial transmitrecord mode in station A a facsimile picture is scanned in synchronism with a local power frequency and a corresponding signal produced by transmitter A1 and recorded on a tape A5 by a transducer A4 concurrently with a reference signal inscribed by a transducer A8 in a second track on the tape, the reference signal being derived from the power supply 210 by a network A11. The tape is advanced by a motor operated under constant speed without feedback control. The reference signal represents the phase and frequency fluctuations which the process has been subjected to. During the transmit-reproduce mode the signals are read from the tape A5, a crystal oscillator source A25 acting as frequency standard for the tape control. This standard is fed to a phase detector A30 and compared with the reference signal from the tape via transducer A8, when the phase detector provides a D.C. output signal dependent on all errors which occurred during previous operations which is fed to the motor control. The motor runs at a faster speed than is required and is controlled by braking in accordance with signals from this motor control unit A22. The tape speed is thus controlled to a constant phase between reference signals from unit A25 and the reproduced line reference. The data signal is then transmitted via line C to receive station B. The signals from station A are received by a signal receiver B33 and passed to the record circuit B2 which converts the signal to a form capable of operating a transducer B4 inscribing a tape B5. A reference track is also inscribed on the tape by a transducer B8 from a signal derived from a crystal reference unit B25 via stage B10 which adjusts the signal to a level suitable for recording. The tape drive unit B21 is controlled by brake unit B22 to which a constant D.C. signal is applied. Although the tape may undergo fluctuations the data signals are accompanied by a reference signal so that a phase relationship is established between the two. Following this receive-record mode is the receive-reproduce mode wherein the data is reproduced. The facsimile receiver B34 produces an image from the signals fed from the tape B5 via transducer B4 and reproduce circuit B6. To control the tape speed the motor control unit B22 receives a D.C. signal from the phase detector B30, this detector sensing the phase relationship between a signal phased to the local power frequency from line reference circuit B11 and the reference signal from the tape via transducer B8 and producing a D.C. control signal accordingly to ensure that the tape is driven always at the correct speed. An equivalent embodiment, Fig. 6 (not shown), is described for an F.M. system.