GB1088288A - Improvements relating to facsimile systems - Google Patents

Abstract

1,088,288. Electric synchronizing. MAGNAVOX CO. Oct. 5, 1964, No. 40498/64. Heading H2L. [Also in Divisions G3 and H4] A facsimile system transmitting and receiving unit, Fig. 1, comprises transmitting transducers 64 and receiving transducers 66 mounted on a rotating turntable 28 and arranged to scan a document or piece of paper 16 disposed between a cylindrical backing member 14 and inner shoe 20, the document or piece of paper being arranged to move axially therebetween. The pick-up transducers 64 comprise a lamp 68 disposed in the hub of the turntable 28, Fig. 3, which projects via lenses 74 and mirrors 76 two scanning spots on to the surface of document 16 just above the edge 24 of the shoe 20. The light reflected from the document is focused through apertures 88 in the side of the hub via mirrors 82 on to a photo-electric cell 84. A shield 86 covers one of the apertures 88 since only one pick-up transducer is operative at a time. The resulting data signal from photoelectric cell 84 is amplified and transmitted over a telephone link. Although the document may be continuously fed through the unit during the scanning operation it is preferable that the document remains stationary during each line scan and is intermittently advanced in the intervals between the completion of one scan by one transducer and the commencement of the next scan by the other transducer. This may be accomplished by means of a feed device 102, Fig. 3, in which a switch 118 is actuated by rotation of the drive shaft 30 of the turntable so as to close and energize an electromagnet 116 during the interval when the end of a spring 112 mounted arm 104 approaches and rides into a recess 114 on the surface of a cam 108 which turns with shaft 30, the end 106 of the arm dropping into the recess during the interval between the scan periods. When the magnet is energized an iron 119 is drawn towards the magnet 116 and clamps the document therebetween and as the end 106 of arm 104 falls into recess 114 spring 112 rotates the arm and carries the document upward by the width of one scan. The reproducing transducers 66 include a pair of magnets 120 and 122, Fig. 4, with their pole faces 126 and 128 separated by a relatively narrow air gap and maintained in position by dielectric end plates 130 and 132. An armature 136 which is free to move in the air gap comprises a rectangular non-conductive fibre board 138 having a spiral conductor 140 printed on each side, the ends of which are connected to contacts 142 that project from the upper and lower sides. Two metal diaphragms 150 and 152 are secured to the end blocks 130 and 132 by means of holders 134 and 156. The diaphragms have pockets 160 and 162 to receive contacts 142 and electrical leads are attached to the diaphragms to supply an electrical current corresponding to the data signal through the contacts 142 to the conductor 140, whereby the armature 136 will tend to move and deflect diaphragms 150 and 152. A stylus 164 is provided on one of the diaphragms 152 adjacent the pocket 162 and thus is caused to move with a short stroke in response to the data signal. The stylus is arranged to extend through an elongated opening 26 in shoe 20, Fig. 1, and a tape 174, having a pressure-sensitive layer, e.g. a carbon layer, extends between the backing member 14 and the shoe 20 in alignment with the aperture 26. Turntable 28 is driven by a synchronous motor 32 via a reduction gear, a clutch and a slipping detent clutch connection, Figs. 6 and 9, not shown. The motor is controlled by a timing signal from a tuning fork and to ensure that the receiving unit is in synchronism with the transmitting unit this timing signal is transmitted from the transmitting unit to the receiving unit being detected by a low-pass filter, Fig. 5, not shown. Switching means are included in the circuit arrangement for the apparatus of Fig. 1, Fig. 5, not shown, for selecting which transducers are operable, i.e. receiving or transmitting transducers. Instead of continuously transmitting the timing signal of standard frequency, each unit may include means for providing a signal each time the turntable passes through a predetermined angular position, e.g. a pick-up such as an inductive coil or photo-cell may be disposed on the turntable to sense the passage of a reference member on the backing member 14, Fig. 7, not shown. This signal is transmitted to a receiver during the intervals between scan periods and compared with a similar signal generated at the receiver to produce an error signal indicative of any phase displacement of the turntables which is used to adjust the frequency of the oscillator of the receiver's motor causing the motor to speed up or slow down. Alternatively, a photocell (330), Fig. 8, not shown, may be used, comprising a pair of separate sensitive sections (336) and (338) that are separated from each other by an inactive dividing line (340), whereby each portion may produce an independent output signal, the transmitting unit being caused to transmit a pulse that makes the transducers 66 in the receiving unit draw a straight line that is adjacent the edge of the piece of paper outside the area where the data is reproduced. The signal for this pulse may be obtained from a line drawn in the margin of the original document. Thus each time a pick-up transducer commences to scan a sector it senses the line and transmits a pulse to cause the reproduction transducer to extend the line and as long as the receiving turntable is in synchronism with the transmitting turntable the line is straight and the signal from the two portions (336) and (338) balance. However, if the two turntables are not in synchronism the line will bend and one portion (336) or (338) will have a larger output which is fed to the motor to vary its speed.