US2234919A - Facsimile synchronizing system - Google Patents

Description

March 11, 1941. H. c. RESSLER 2,234,919

FACSIMILE SYNCHRONIZING SYSTEM Filed Aug. 15, 1958 3 Sheetsheet l March 11, 1941. H,

C. RESSLER FACSIHILE SYNCHRONIZING SYSTEM Filed Aug. l5, 1938 5 Sheets-Sheet 2 Kessler March 1l, 1941. H. c. Rr-:ssLER FACSIMILE SYNCHRONIZIHG SYSTEM Filed Aug. 15, 1938 -3 Sheets-Sheet 3 |...dlllfl1 INVENTOR vzfzy: Passief Patented Mar. 11,4'1941 PATENT OFFICE FACSIMILE. SYNCHRONIZIN G SYSTEM Hugh C. Ressler, Richmond, Staten Island, N. Y., assignor to Radio Inventions, Inc., New York, N. vY., a corporation of New York Application August 15,

11 Claims.

My present invention relates to methods of and means for synchronizing facsimile recorders and the like with a desired transmitter.

One object oi my present invention is to pro- 5 vide means for generating an alternating current synchronized by impulses transmitted to a facsimile receiver and suitable for operating a synchronous motor to drive a facsimile recorder.

A particular object is to provide apparatus in the strength of the received synchronizing impulses increases.

Another particular object is to provide a synchronizin'g system which changes from a passive driven system in the presence of strong synchronizing impulses to an active self-sustaining system in the absence of synchronizing impulses.

Still another particular object is to provide means for converting rectangular impulses into damped oscillations, of applying these damped oscillations to a tuning fork for synchronization purposes and of utilizing the output of the tuning fork for driving a synchronous'direct current' to alternating current converter the output of which is utilized to drive a facsimile recorder synchronous motor.

These and other objects will be apparent from the detailed description which is given in describing the various figures of the drawings.

In the past, facsimile systems have been synchronized either by transmitting a synchronizing signal along with the picture signal or by employing very stable frequency control means at both transmitter and receiver. In the former type of system the synchronizing signals were used to control the receiving apparatus with a fixed and usually critical degree of control. Too strong a degree of control, in general, causes nonlinear distortion of the scanning lines and too i weak control permits the system to lose synchronism. Accordingly changes in signal level, especially those caused by fading in a long radio circuit have suffered from alternate distortion and loss of synchronism. In the latter type of syste-m the control apparatus is expensive and even the most elaborate systems drift over long periods of time and hence require considerable attention. The present invention overcomes these diiiiculties by employing a relatively stable system with automatic control of both stability of the local system and automatic degree oi control by received synchronizing signals.

Briefly, my present system operates in the manner described below. The transmission of faci simile signals is accomplished by cyclic scanning which the stiffness of synchronization increases as' 193s. serial No. 224,363 (ol. 17a-69.5)

of an object. A single scanning cycle for instance may last for six tenths of a second and comprise one elemental strip of a subject to be transmitted. The actual picture signal may occupy four tenthsof a second or sixty-seven percent of a. cycle. 'I'he remaining two tenths of a second or thirtythree percent of a cycle may be utilized for picture margin, synchronizing signal and the like. I prefer to use impulses for synchronizing signals oi' either rectangular shape or of a shape to con- 10 tain a maximum component of the desired synchronous frequency. i These synchronizing impulses are generated in fixed relation to portions of the transmitterA scanning cycle.

In the receiver the synchronizing impulses are impressed upon a system resonant to the desired synchronous frequency. The desired synchronous frequency may be 60 cycles suitable for driving a synchronous motor which in turn drives the receiver recording mechanism. The resonant sys- 2o tem may be a tuned electrical circuit or it may have a mechanical resonance coupled thru an electrical system as for instance in the case of a. tuning fork.

Received synchronizing'impulses are impressed 25 upon the electrical or electro-mechanical resonant system and by shock excitation produced damped trains of synchronous frequency voltage. The clamping of the damped oscillations may be decreased by using a resonant system with a higher Q, i. e. ratio of Lw to R or the eiective resistance of the system may be reduced by positive feed back or a negative resistance device in shunt.

The synchronous voltage ,produced in this way is used to operate a reed or interrupter in a direct current to alternating current converter thus producing a source of synchronous alternating current power suitable for driving a synchronous motor at the receiver recorder.

In a preferred form of my present system a o tuning fork is coupled to a thermionic vacuum tube amplifier in such a way that energy is fed back from the output of the amplifier to the input thru the mechanical impedance o! the tuning fork. The feed-back circuit is proportioned and 5 coupled in such a way that it is regenerative and may be made to increase the Q oi.' the tuning fork or generate sustained oscillations by varying the amplifier gain as by varying the amplier tube bias. When synchronizing impulses are fed chronizing impulses serve to synchronize the frequency of oscillation. The strongest synchronization takes place just below the point of self-oscillation. By rectifying either the amplifier output or the received impulses and' using 'the filtered rectier output to control the ampliiier gain, the system may be made to change from a passive system generating damped oscillations or tightly controlled synchronous oscillations to an active system generating steady unsynchronized oscillations depending on the amplitude of synchronizing impulses present in the input. In this way the system operates asa tightly synchronized driven system in the presence of strong synchronizing impulses, as a weakly synchronized self-oscillating system in the presence of weak synchronizing impulses and as a stable non-synchronized selfoscillator in the absence of synchronizing impulses. This mode of operation is particularly valuable in connection with long radio circuits where fading may destroy the synchronizing impulses for short periods of time, but since the system then becomes self-sustaining only small drifts will take placebei'ore theY signal returns. This system thus has the advantage that the degree of control of synchronizing signals depends on their amplitude whereby the system is not critical in adjustment and does not lose lsynchronism on momentary loss of signal.

The synchronizing signal sent out from the transmitter may be a group of waves of the desired frequency which, except for a transient term, are essentially sine waves. In the receiver this synchronizing signal may be fed to the regenerated tuning fork. The tuning fork when made less sensitive to external signals is, of course, more stable. Thesynchronizing signal, consisting of several cycles of the desired frequency, acts to correct the tuning fork frequency a slight amount during each cycle of synchronizing signal. Since these are several cycles of correcting signal, the fork frequency may be made very stable, minimizing disturbing effects of stray signals and yet maintaining good average synchronism.

lAnother mode of operation is to transmit on a radio carrier or over a line substantially rectanguiar impulses which may be modulations of subcai'rier signal for synchronization purposes. In

the receiver these impulses are rectified producing unidirectional rectangular impulses or corresponding groups of sub-carrier signals which are impressed on an. electrical circuit tuned to the desired synchronous frequency. The im'- pulses by shock excitation generate damped wave trains of synchronous frequency voltage which may be used to synchronize the tuning fork as described above for groups of sine wave synchronizing.

In the drawings: v

Fig. 1 shows a circuit diagram of the present synchronizing system.

Fig. 2 shows a modification of the present synchronizing system. l

Fig. 3 shows various signal waves useful in explaining the operation of thel synchronlm'ng system.

Fig, 4 shows `further explanatory waves.

Fig. 1 shows a circuit of one form of the presentA synchronizing system. A cascade two stage amplier employing thermionic vacuum tubes I and 2 is connected with its input across a tuned electro-magnet I0 and its output across a second tuned electro-magnet I2. Electro-magnets I0 and I2 are coupled by coupling each magnetically to a tine of the tuning fork 9. The amplitude of oscillation or the amount of regeneration thus produced is'controlled by rectier 3. The generated signal controls a direct current to alternating current converter by means of amplier tube 4. The alternating current output of the converter is used to operate the synchronous motor 66 which turns the mechanism of the facsimile receiving scanner 68. The facsimile receiver 5 supplies picture signals to the scanner 68 and synchronizing signals to the tuning fork through the use of electromagnet 8.

The operation of the system of Fig. l will now be traced in detail. While 'the system may be operated from a wire line signal, a radio system will be described. Radio signals modulated with facsimile picture signals and synchronizing signais are picked up on antenna 'I and amplied land detected by the facsimile receiver 5. Picture signals from the receiver are applied to receiving scanner 68 over leads 86 and 8'I and synchronizing signals are applied to tuning fork 9 by means of electro-magnet 8.

The cascade amplifier, including thermionic vacuum tubes I and 2, is used to regenerate tuning fork 9 and may be operated to cause selfsustaining oscillations. Tube I includes heater 22, cathode I'I, controlgrid I8, screen grid I9, suppressor grid 20 and plate 2I. A plate battery 43 is shown energizing electrodes of tubes I and 2- although other well known means may be used. Heater voltage supply for heaters 22, 36, 52, 89 and is not shown, but will be understood to be any well known means. Plate 2| is energized from battery 43 through the decoupling resistor 88, interstage coupling transformer 30 and plate current meter 33. Screen I9 is energized from the voltage supply 43 through the decoupling resistor 88 and the screen dropping and decoupling |resistor 28. Cathode I'I receives a bias from the voltage drop across resistor 25 due to the cathode current plus the current through resistors 23 and 24. The plate voltage is by-passed by condenser 2l and the screen voltage is Icy-passed by condenser 26. The voltage across electro-magnet I0 tuned by condenser II is applied to grid I8. Coupling transformer 29 is connected with its primary connected to plate 2| and its secondary connected to grid 38 of tube 2. The secondary 3| is tuned to the synchronizing frequency by condenser 32. Heater 36 of tube 2 energizes cathode 3l. Cathode 3l receives a bias due .to cathode current flowing thru resistor 35 connected to common ground 6 and by-passed by condenser 34. Plate 39 of tube 2 is energized from voltage source A33 Ithrough primaryv 4I) of output transformer 4I. Output transformer 4I receives signal voltage from plate 39 and feeds rectier 3 from its secondary 42. Secondary 42 is shunted by resistor 44. Rectifier 3 comprises cathodes 4l and 48 energized by heaters 89 and 98 and anodes 46 and 45. Lead 9| applies a bias to cathodes 41 and 48 from" the drop across resistors 24 and 25. Signal voltage across secondary 42 is applied between anodes 45 and 46 and cathodes 41 and 48. Rectifled voltage is developed by the charges produced in condenser 50 leaking oft' through resistor 49.'

The anode end of resistor 49 which is connected between anodes 45 and 46 and ground 6 will become negative with respect fto ground due to rectied cur-rents owing in it and this negative voltage is applied to gri-d IB through filter resistor I0 and the winding of electro-magnet I0. Condenser 'II cooperates with resistor 10 to smooth the rectied voltage applied to grid I8. The sigthe gain of the amplifier.

nal voltage across secondary I2 is also applied .to electromguet I2 tuned by condenser I3 through control resistors I5 and I5. Inaddltion, the signal across secondary 42 is applied to grid 53 of amplifier l. Amplifier 4 `includes heater 52, energizing cathode 5I, control grid 53 and plate 54. Cathode 5I is connected to ground'9 through bias resistor- 55 which in -.turn is by-pas'sed by condenser 59. Plate 54 is energized from a plate voltage source 51 which is shown as a battery, but not limited to such. The plate current of tube l is caused lto flow through the interruptor electro- 'magnet 58 and hence causes reed 59 to vibrate in .response-to signals applied .to grid 53. The mid-point of winding 55 of the auto-,transformer 64 ls connected to one side of a source of direct current power by means of lead 93. 'Ihe other side of rthe source of direct current power is connected alternately to opposite sides `of winding 95 .through reed 59 and Ithe alternating contacts SII and i I Thus an alternating current is caused to ilow in winding 65 in step with the signal voltage applied to .grid 53 since electro-magnet 59 operates the reed 59 at this frequency. if no direct current were permitted Ito iiow through electromagnet 5l the alternating frequen-cy would be doubled. A The synchronous motor 66 is supplied with alternating current voltage from transformer` 64 :through taps 92 and 93. "Ihesynchronous motor -95 is mechanically coupled to drive receiving scanner 69.

In operation, tuning fork 9 is set in vibration by pressing starting button I4, causing a surge of current to flow through the winding of electromagnet I2. This surge of current magnetizes magnet I2 attracting one tine of fork 9. The motion of this tine induces a motion in the other tine and hence a voltage in the winding of electro-magnet Ill. 'I'his voltage is amplified -by tubes Il and 2 and reapplied to fork 9 through electro-magnet I2 Fork 9 acts as a mechanical filter and with sufficient gain in the amplifier and proper polarity of electro-magnets I0 and I2 self-sustaining oscillations will be set up at a frequency very close to the natural frequency of the fork-9. Tuning electro-magnets I0 and I2 by means oi' condensers II and I3 to the frequency of the fork assists the production of oscillations. After the system has started t0 oscillate, button Il is vreleased and a partial control of oscillation amplitude may be affected by adjustment of control resistance IE in series with fixed control resistance I5. well known methods may be employedl for initially setting the amplifier gain as for instance by varying the turns ratio of transformer 29-30--3L With the system oscillating an alternating current, voltage will be fed to rectifier 3. The rectified direct current produced by rectifier 3 is applied to grid I8 and here reduces This reduction in amplifier gain tends to reduce the amplitude of oscillation and a stable automatically controlled oscillation amplitude results.

Now, if synchronizing signal voltage of the same frequency a's lthe fork frequency, or of nearly the same frequency is-applied to fork 9 by means of electro-magnet 8, the fork frequency may be locked in step with the synchronizing signal frequency. With large synchronizing signal voltage applied to electromagnet 9. the system may be adjusted so that it will not oscillate in a self-sustaining manner at the same amplifier gain or net bias on grid I3. In this condition synchronization is very tight Other and exact. If now the synchronizing signal is removed due to fading of the radio signal, the amplitude of oscillation of the fork will start to die out. As it dies out the rectifier 3 receives a smaller and smaller signal voltage andA produces a decreasing bias on grid I8. A point is finally reached at which the gain of the amplifier is increased until self-sustaining oscillations are again produced andthe system continues at the natural frequency of fork 9. If fading periods are short, the system will drift but little until synchronizing signals are again produced and the system returns to its initial tightly synchronized condition.

'I'he operation is much the same if synchronizing signals are sent for short intervals interspaced with the facsimile signal, as for instance, at the end of each line. When the synchronizing signal is received, the frequency is corrected and, during the picture signal interval, the fork carries the system along.

The synchronous voltage producedin the fork amplifier controls the direct current to alternating current converter as described above, and

-runs the synchronous motor 66, and hence scanner 68, in step with the received synchroniz# ing signal.

The level of received synchronizing signalat which the self-sustaining condition of the fork oscillation system takes place may be predetermined by adjustment of control resistor I6 or by adjustment of the amplier gain.

One form of composite picture signal and synchronizing signal wave suitable for operating the system as described is shown in Fig. 4. A complete scanning cycle is represented by synchronizing signal K plus picture signal I where I represents one line of the picture being transmitted. The number of cycles in the synchronizing signal K may be determined by practical considerations. 'Ihe larger the number of cycles the more stable may be the fork and still by a small correction on each cycle reach exact synchronism at each synchronizing interval. If the synchronous frequency is 60 cycles and the synchronizing interval is two tenths of a second, twelve cycles of synchronizing frequency may be transmitted during each interval. The effective-- receives, amplies and demodulates the facsimile modulated carrier signals and if necessary separates synchronizing and picture signals. It will be understood that as in the case of Fig. l

receiver 5 may be replaced by suitable apparatus for operation from a wire line. In Fig. 2 the synchronous motor 66 and receiving scanner 68 of Fig. 1 are represented by synchronous motor and receiving scanner block 85. Similarly the various components of the converter system are represented by block 84 and the tuningfork amplifier and rectifier control system by block 33. The tuning fork 9 and its associated electromagnets 8, IU and I3 are repeated for purposes of explanation in Fig. 2. The circuit of Fig. 2 is especially adapted to operate from a rectangular or other impulse type of synchronizing signal as shown at a in Fig. 3, These synchronizing Plate voltage for amplier 12 may be supplied l5 by battery 82 or its equivalent. The damped oscillations applied to grid 14 are amplified and applied to fork magnet 8 by placing it in series with plate 13. With a bias, as battery 82, in series with magnet 8, its operation on tuning fork 9 is at fundamental frequency While without such bias its control will be exerted at twice fundamental frequency. Thus, magnet 8 receives damped oscillations of synchronous frequency voltage instead of the type of signal shown in Fig. 4, but the remainder of the system is op.- erated and synchronizes in a manner similar to the system'described in connection with Fig. l.

In both Figs. l and 2 the synchronizing signals are shown. applied to fork 9 by means of a tertiary magnet 8. This method of synchronous signal application causes the fork to act as a lter selecting the desired synchronous frequency components and eliminating the picture signal.

Fig. 3 shows at e a synchronous impulse a space b picture signal c and second space d. At f is shown the modulated carrier resulting from modulation by signals of lin'e e. At g is shown the received and rectified carrier voltages which should be a reproduction of line e. On line h 4.0 is shown the damped oscillations resulting from the synchronizing impulse a as described in connection with Fig. 2. While no sub-carrier waves have been shown, it will be understood that the picture signal and synchronizingsignals shown 45 may be impressed on a suitable sub-carrier before transmission and that this sub-carrier, usually a high audio frequency, may be retained to any desired point in the receiver.

It is not intended to limit the invention to the 50 particular embodiment shown but only to those embodiments falling within the spirit and scope of the invention as -set forth in the appended claims.

I claim:

1. In a facsimile synchronizing system, the combination of,means for receiving synchronizing signals, a regenerated tuning fork, means for automatically varying the degree of regeneration as a function of the amplitude of said synchron- 60 izing signals.

2. In a facsimile synchronizing system, the combination of, means for receiving synchronizing signals, a regenerative tuning fork circuit, means for automatically increasing said regeneration to the point of self-oscillation in response to synchronizing signals below a predetermined level.

3. In a facsimile synchronizing system, the combination of, means for receiving synchronizing signals, a regenerative self-oscillatory tuning fork,and means for automatically decreasing the regeneration below the point of self-oscillation in the presence of received synchronizing signals of greater than a predetermined amplitude.

4. In a synchronizing system, the combination Cathode 15 may receive a bias thru of, synchronizing signal receiving means, low decrement vibratory means, electricalmeans for automatically varying the decrement of said vibratory means as a function of the amplitude of received synchronizing signals, and means for controlling the frequency of vibration of said vibratory means in accordance with synchronizing signals having amplitudes greater than a means coupling said output with said fork, elec- I tro-magnetic means coupling said receiver with said fork, and electro-magnetic means coupling said amplifier output with said reed whereby the speed of operation of said receiving scanner is determined by signals traversing said receiver.

6. In a facsimile receiving system, means for maintaining synchronism with a desired transmitter comprising, in combination, a facsimile receiver, a tuning fork composed of magnetic material, a direct current to alternating current inverter including a magnetic reed for determining the frequency of said alternating current, a receiving scanner, a synchronous motor driven by said alternating current for driving s'aid receiving scanner, an amplifier including input and output circuits, electromagnetic means coupling-'said input and output with said fork, electromagnetic meanscoupling saidreceiver with said fork, electromagnetic means coupling said amplifier output with said reed whereby the speed of operation of said receiving scanner is determined by signals traversing said receiver, and means for rendering said tuning fork and amplifier a self-sustaining oscillatory system for all received signals belowa predetermined level.

7. In a facsimile receiving system, means for maintaining synchronism with a desired transmitter comprising, in combination, a. facsimile receiver, a tuning fork composed of magnetic material, a direct current to alternating current inverter. including a magnetic'reed for determining the frequency of said alternating current, a receiving scanner, a synchronous motor driven by said alternating current for driving said receiving sca-nner, an amplifier including input and output circuits, electromagnetic means coupling said input with said fork, electromagnetic means coupling said output with said fork, electro-magneticmeans coupling said receiver with said fork, electro-magnetic means coupling said amplifier output with said reed whereby the speed of operation of said receiving scanner is determined by signals traversing said receiver, and meansV interposed between said receiver and said third electromagnetic means for converting at least a portion of said Vreceived signals into damped oscillations.

8. In -a. motor driven facsimile receiving system, a system for synchronizing said motor with received synchronizing signals including in combination, an oscillatory device, a controllable regenerative circuit coupled to said oscillatory device capable of generating sustained oscillasesamoA vice for operating` said motor.

9. In a motor driven facsimile recording system', a system for operating said motorin synchronism .with a predetermined synchronizing signal including in combination, an oscillatory device, a controllable regenerative circuit coupled to said oscillatory device for generating sustained oscillations at substantially the natural frequency of the oscillatory device at regenerative levels above a predetermined value, a .regeneration control circuit connected to a source of synchronizing signals for decreasing saldregeneration below said critical =value for ampliltudes of synchronizing signal greater than a predetermined value, an alternating current generator foroperating said motor. and cir' cuits for controlling the frequency of said yalternating current from'the frequency of said oscillatory device. f

10. The method lof operating a tuning fork in a regenerative circuit in the presence or absence of synchronizing signals for controlling the speed ofa motor which includes synchronizing said fork strongly in the presence of substantial ainplitudes of synchronizing signal, of automatically increasing the regeneration atleast to the point 'of self-oscillation with said fork in the absence of substantial amplitudes of synchronizing sighal, and of operating 'said motor in synchronisrn with said tuningtork. t

v1l. I'he method of operating a synchronizingsystem including an alternating current synchronous motor.; a direct current to alternating current converter. and a regenerated tuning fork system which includes. applying synchronizing signals to said tuning fork system, utilizing said synchronizing signals to control the average regeneration in said tuning forl system, utilizing signals derived from said tuning fork to control the frequency of alternating current generated by said direct current to alternating current converter. and operating saidsynchronous vmotor from alternating current derived

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