Патент USA US2404571код для вставки
July 23, 1946.- w. G. H. FlNCH 2,404,511 SYNCHRONI Z ING MECHANI SM Filed gan. 19,v 1944 KVH 12 RAD‘O _ FREQUENCY __ cmcun ~ 14 ’ 15 PICTURE '_' P‘CTURE SIGNAL _____ AMP ‘HER DETECTOR SYNCHRONOUS SIGNAL 36 13 s Sheets-Sheet 1 PM“ ~ L i ' svucuaonovs /16 SIGNAL AMPLIFIER FILTER ' 46 \_/\ ' \_r\ sw <<: 51 41W; \ M 102 w? 41 37 L / )1 J< . 35 7k F -- / A 24 63/ 25 e1 '\6; 6? ¢ , 721 i W MLIETORNEY July 23, 1946. -.w. G. H. FINCH , 2,404,571 SYNGHRONIZING MECHANISM Filed Jan. 19, 1944 3 sheets-snqei 2 81 / v75 77 _ - __ SYNCHRONOUS 4_ __ 76 ‘ __ 74 86 __ -v- D.C‘ . ~ ' __ MOTOR MOTOR 84 7/ jg} I441 - ATTORNEY ‘ SYNGHRONIZING ' g H_ FgNcg-g MECHANISM Filed Jan. 19, 1944 36 112 ‘ \ 3 Sheets-Sheet 5 111 \ 155 ‘i 12.5 g/A125‘ INVENTOR . m/’£ A“; ATTORNEY Patented July 23, 194-6 2,404,571 UNITED STATES PATENT OFFICE 2,404,571 SYNCHRONIZING MECHANISM William G. H. Finch, Newtown, Conn. Application January 19, 1944, Serial No. 518,837 8 Claims. (Cl. 178-695) 1 2 My invention relates in general to the ?eld of picture transmission and reception and more speci?cally to a novel continuous synchronizing chronization between transmitting and recording apparatus which utilizes a continuously trans mitted alternating current synchronizing signal, mechanism, but which does not require the excessive ampli In facsimile transmission, a signal is gener U! ?cation thereof mentioned above. In accordance ated at the transmitter which represents the light with my novel synchronizing mechanism, the shades of a single line of a picture. This signal recording apparatus is driven from any local is then ampli?ed to a suitable energy level and power supply, which may take the form of alter transmitted by wire or radio to a remote receiver. nating current mains, or a portable battery as employed in an airplane or other vehicle. As is well known in the art of facsimile, it is essential that both transmitting and receiving apparatus operate in synchronism. In the past, If a battery supply is available at the receiver then the drive mechanism may consist of an ordinary direct current shunt motor of the re quired horse power. The speed of this shunt synchronizing systems have primarily been stop start mechanical systems wherein the receiver recording mechanism was operated at a some 15 what higher speed than the transmitting mech anism. The scanning of a single line of the picture at the receiver was thus accomplished in less time than a corresponding cycle at the trans mitter, and the motor is controlled directly by comparatively simple and light apparatus which in turn is governed by a small pilot synchronous motor operated from a low level continuous synchro nizing signal ampli?er. Thus the transmitting recording mechanism was 20 apparatus has associated with it means for gen erating a continuous synchronizing signal and chronizing signal from the transmitter. This combining it with the picture signal to be trans synchronizing signal representing the start of a mitted. This multiple signal when received at new scanning cycle at the transmitter would the recording apparatus is separated electroni release the receiving mechanism to record the cally and the picture signal is passed through a following line. The mechanical disadvantages recording channel while the synchronizing signal of such a start-stop mechanism are well known is impressed upon an ampli?er having a signal in the facsimile art. output sufficient to drive the aforementioned It is possible to obtain continuous synchro small synchronous motor. nizing of transmitting and recording mechanism Immediately upon the receipt of a transmitted brought to a halt to await the receipt of a syn if both are operated from the same alternating signal, the pilot synchronous motor operates to current power supply. In this ideal instance, matched alternating current synchronous motors are utilized to provide absolute continuous syn chronization between the rotational elements at each station. Obviously, such a transmission adjust the speed of the direct current motor to that of the corresponding scanning apparatus at the transmitter. Any ?uctuation in speed of the direct current motor will thereafter be im mediately compensated for by the small pilot system would be limited to the area served by the one central power station and would be of no use whatsoever for facsimile systems operat ing between separated points such as ship-to shore or airplane-to-ground, or the like. Continuous synchronization of transmitting and recording equipment may also be obtained by the continuous generation at the transmitter of an alternating current synchronizing signal which is transmitted to the receiving station and ampli?ed thereat to a level sur?cient to drive all the required recording apparatus. With modern high speed telepicture apparatus, this particular synchronizing system becomes impractical, since the power requirements of the recording mech anism are comparatively high and require ex cessive ampli?cation of the synchronizing signal by massive, ine?icient electronic apparatus. My present invention proposes continuous syn motor and result in a change of electrical or mechanical circuit constants that will restore the speed of the direct current motor to the 40 required synchronous speed. It is therefore an object of my invention to provide a facsimile transmitting and receiving system wherein the recorder is continuously gov erned to operate at the speed of the transmitter. It is another object of my invention to pro vide a continuous telepicture synchronizing sys tem utilizing a small pilot synchronous motor at the receiver. Still another object of my present invention is to provide facsimile recording apparatus which may be operated from any power source whatso ever and which is maintained in synchronism by a continuously transmitted governing signa1 gen erated at the transmitter. A further object of my invention is to provide 2,404,571 75 picture signals a translated band of higher fre quencies, the ?lters ill and it may be conven a novel, differential speed adjusting means for maintaining a direct current motor in synchro nism with a synchronous alternating current motor. A still further object of my invention is to tional high-pass and low-pass ?lters respectively. The audio-frequency picture signals are ampli ?ed by ampli?er l5 and impressed in the well provide a novel electrical circuit for controlling the speed of a direct current motor within cer known manner across an electrosensitive record tain narrow pre-determined limits. These and other object of my invention will neous facsimile recording paper of the conductive ing sheet H, which may be a sheet of instanta type. As is schematically illustrated in Figure 1, the recording sheet El is mounted upon a rotating drum 2i by a mounting bar The drum 2! is supported by suitablev bearings 23 and is driven now become apparent from the following speci ?cation taken in connection with the accom panying drawings in which: Figure 1 is a schematic representation of one modi?cation of my novel continuous synchro by a motor “24 of the required horse power. Scan ning the surface of the recording sheet I‘! is an electrically conductive stylus 25, supported on a suitable bracket 23, which in turn is driven by a conventional feed screw mechanism. nizing mechanism. Figure 2 is a fragmentary View of the diifer ential mechanism for governing the speed of a direct current motor. Figure 3 is a fragmentary view of one form of speed control means; and Figure 4 is another modi?cation of a motor The picture signal output of ampli?er i5 is impressed between the stylus 25 and the rotatable drum 25 whereby the incoming picture signal will ?ow through the recording sheet ll’ and in the speed control mechanism. well known manner produce an instantaneous re Referring now to Figure 1, there is shown a schematic representation of a facsimile system operable from radio signals received by antenna ii and coupled to the radio frequency receiving circuit E2. cording. ‘ It will become evident that the present inven tion is not particularly limited to the recording drum 2! as illustrated in Figure 1, and that any other well known facsimile recording mechanism, such as the multiple stylus arrangement, or the reciprocating arm arrangement, may be directly substituted for the particular recorder described. The facsimile signal received in circuit i2 con sists of a carrier signal modulated by audio-fre quency currents representing the variations of light along individual lines of an image. These signals are generated at the transmitter as is well known in the art by an electro-optical scanning The power source comprises a battery or other direct current supply 3!. The source of motive power for the drum 2i, as shown, is a direct cur mechanism driven from a suitable source of rent shunt motor 215, the armature terminals 32 power. of which are directly connected to the battery If an alternating source of power supply is through a switch 33. The ?eld of the direct available at the transmitter, then the transmit cur rent shunt motor 215 is also energized from the ting scanning mechanism is driven by an alter battery 5! through the ?eld rheostat 34 and nating current synchronous motor, To obtain a signal at the transmittenwhich is representa ell) through a circuit contained in the speed control apparatus 35, to be described later. tive of he speed of the synchronous motor, it is The alternating current synchronizing signal then merely necessary to modulate the carrier flowing from the signal ?lter i6 is impressed upon with this alternating current, a synchronizing signal ampli?er 36 having a If it is necessary to drive the transmittingscan power output su?icient to drive the small pilot ning mechanism from a battery or other D. C. synchronous motor 3?~ It is important to note supply, it is then preferable to attach a small synchronous alternator to the scanning drive this point that the direct shunt motor 24 is motor so that an alternating current signal hav considerably larger than the pilot synchronous ing a frequency proportional to the speed of the canning apparatus is generated at all times. -;=: As in the previous example, the output of this synchronous alternator is used to modulate the carrier to provide a transmitted synchronizing motor 3? and that the energy required to drive the recording drum 25 is supplied primarily by the direct current motor 211 operating from the local direct current source 35. signal. ?er is an alternating current synchronous with the alternating current utilized to drive the trans . When wired transmission is employed, the pic ture signal and the continuous synchronizing sig nal may be directly app-lied to the lines and mod The output of the synchronizing signal ampli mitting scanning mechanism, and is impressed directly upon the armature terminals M of the pilot synchronous motor 31. ulation of a carrier and the receiving radio fre quency circuits may be dispensed with. described, the two signals are separated and the translated current restored to its original fre The direct current ?eld terminals 42 of the pilot synchronous motor 37 are energized from the local power supply 3! through the four-pole relay contacts The relay M is picture signal oper ate-d and of the latching type. That is, upon the receipt of a picture signal through picture am pli?er i5 the coil 45 of the relay M will be ener gized across the lines 48. The relay contact car rying arm ii? is normally biased as indicated sche_ quency. matically by springs 53 to the open circuit posi Again referring to Figure 1, the received signal is demodulated by the detector l3 and impressed upon the two-channel electronic circuit compris ing the picture signal ?lter l4 and the synchro nizing signal ?lter H5. If the synchronizing sig nal is, for example, an alternating current signal of approximately 60 cycles‘ per second and the 75 tion illustrated. Upon receipt of a picture signal over lines 46, the relay coil £55 will be energized and cause the movement of contact carrying arm 47 to the right as viewed in Figure 1, and accordingly close the four circuits illustrated. Eince relay at is of the latching type, any sub Since the picture currents and the synchroniz ing signal may be in the same frequency band, multiple transmission may be accomplished by 31) translating either one of these two into another frequency band by the addition of a constant fre, quency signal thereto. At the receiver, as will be " 2,404,571 sequent temporary cessation of the picture signal, 6 synchronous motor shaft ‘H between the hub of bevel gear of 12 and a pinned bushing 95. t will now become evident that with the linkv 6| positioning bevel gear 75, as illustrated in Figure 2, rotation of shafts ‘H and 14 at identical speeds but in opposite directions will cause the rotation of bevel gear 8| about shaft 82 but will nal applied to the armature terminal 41, will not result in rotation of bevel gear 9'3. cause the synchronous motor 3'1 to look into syn Bevel gear 96 is continuously engaged with chronous speed, as is well understood in the art. The speed of this synchronous motor 3i‘ is accord 10 bevel gear 9?: and hence under the last mentioned condition of identical speeds, the bevel gear 96 ingly the speed at which it is desired to operate and its attached shaft 9“! will remain stationary. the direct current shunt motor 24. And as will If the speed of the direct current shunt motor be described later, the differential speed control driving shaft ‘l4 deviates at any time from the mechanism 35 will in connection with the syn speed of the synchronous motor driving shaft ll, chronous motor 3'1 provide means for continu it is evident that bevel gear M will continue to ously adjusting the speed of the shunt motor rotate about shaft 82 but will, in addition, exert. ‘25 to maintain the desired scanning speed. a force upon the ?xed link 93 which will tend to The mechanism 35 is a mechanical coupling drive the bevel gear 94 about shaft 1 I. between the pilot synchronous motor 31 and the The angular speed of bevel gear 94 is directly direct current shunt motor 24. Since it may be dependent upon the different speed between the desirable to operate the shunt motor 24 when no D. C. motor and the synchronous motor, and the picture signal is being transmitted, it is necessary direction of rotation thereof is dependent upon to uncouple the mechanical linkage between the whether !the speed of the D. C. motor is greater motor 24 and the synchronous motor 3'5. This will not cause the contacts 43 to open. The clo sure of contacts 52 and 53 of the relay 44 will, as illustrated, energize the direct current ?eld at terminals 42 from the local D. 0, supply 3|, and in combination with the alternating current sig is accomplished by a clutch mechanism operated . by arm Bl pivoted at pin e2. The normal position'of the pivoted link ill is determined by the spring-‘53 applying tension in the direction illustrated in Figure 1. However, upon the energization of relay 45 and the closure of contacts 64 and 65 by the contact carrying arm 41, the solenoid 86 will be energized and cause counterclockwise rotation of pivoted link 6i against the normal bias of spring 63. This, as will be illustrated later, will cause the mechanical l coupling between the synchronous motor 3'! and shunt motor 24 to maintain the desired synchro or less than that of the synchronous motor. correspondingly, the rotation of shaft 91 and the direction thereof is directly a measure of the non-synchronous condition of the D. C. motor and the direction of this deviation. As is evident from Figure 2, the angular movement of bevel gear fit will be considerably greater than that of engaged bevel gear 234 and hence, is an extremely sensitive detector of this aforementioned non synchronous condition. y In accordance with my invention, I propose to utilize the rotation of shaft 9? to maintain a facsimile recorder at the speed of a correspond ing unit at the transmitter. The speed of the shunt motor 24, as is well Referring now to Figure 2, there is illustrated one possible mechanical structure of the synchro 40 known in the art, is determined by the magnitude of its shunt ?eld current which in turn is deter nizing linkage between the pilot motor 31 and mined by the variable resistor 34, and additional the shunt motor 24. electrical means in the differential mechanism 35. As illustrated, the synchronous motor 3? drives The means of accomplishing the speed control of shaft ‘H to which is secured bevel gear 72. rI‘lhe direct current shunt motor 26 is illustrated in 45 attachment is accomplished, as illustrated by pin Figure 3. 13 passing through the hub of gear 12 and The variable resistor I0! is connected in series through shaft 1 l. with the shunt ?eld circuit at the terminals we, The direct current shunt motor 24 drives shaft as illustrated, and hence the complete shunt ?eld 14 to which bevel gear ‘i5 is slidably but non circuit comprises resistors 34 and lill, and the rotatably keyed. Thus, keyways milled in shaft ?eld itself. 74 and bevel gear 15 engage a key 16 which is The bevel gear 96 and the attached shaft 91, secured to the shaft 14. The keyway in bevel which is preferably of an insulating material, gear 15 is somewhat larger than the key 16 and control the magnitude of the resistance ml in nous condition. hence the bevel gear 15 may move to the right or to the left as viewed in Figure 2. The movement of bevel gear 15, is determined by the movement of coupling link 6i illustrated in Figures 1 and 2. The link 6| slidably engages the hub of the bevel gear 15 in a cylindrical de pression T! wherea't friction has been reduced to a minimum by proper polishing. The position of bevel gear '15 as illustrated in serted into» the shunt ?eld circuit. Thus, con ductive arm M23 is rigidly attached to shaft 91 by means of a pin “34, and completes the circuit from the rheostat it! through the lines Hi2. When the D. C. motor begins to run below the synchronous speed, arm I23 will tend to rotate in the direction of the arrow S, as illustrated in Fig ure 3. Such rotation will increase the resistance in the shunt ?eld circuit, thereby decreasing the Figure 2, corresponds to the energization of sole current and causing an immediate increase in noid 66 shown in Figure 1. Upon de-energization 65 the armature speed thereof. of this solenoid 6B, the spring 63 will act to move bevel gear 75 to the right, as viewed in Figure 2, It is important to note that it is desirable to have the resistor it! of such magnitude that ex and cause the disengagement of the gear ‘(5 with tremely small rotation of the arm Hi3 will cause a another bevel gear 81. The bevel gear BI is ro considerable variation of resistance in the shunt tatably positioned upon a shaft 82 by bushings 70 ?eld circuit, thus resulting in an immediate tend ency to restore the speed. Conversely, any tend 83 and 84 pinned to the shaft by pins 85 and 86. ency of the direct current motor to run at above The shaft 82 is rotatably positioned by ?xed the synchronous speed of the motor 31 will cause bushings SI and 92 upon a link 93 which is an the arm N13 to rotate in the direction F, as illus integral extension of a large bevel gear 94. The bevel gear 94 is rotatably positioned upon the 76 trated. in Figure 3, and result in an increase. of. 2,404,671 7 8 ?eld current which ‘will tend to restore the speed to that which corresponds to no rotation of the bevel gear 96. It is therefore evident that by utilization of an extremely small synchronous motor governed by signals transmitted from the scanning apparatus at the transmitting station, I have been able to immediately result in an increase in ?eld current which correspondingly causes a decrease in the speed of the motor 24. This decrease in speed will through the diiferential mechanism illus trated in Figure 2, immediately re-act to cause the rotation of bevel gear 96 in the direction marked S in Figure 4. Continued rotation in this synchronize a comparatively large direct current motor thereby and insure proper operation of the recording apparatus 2|. The power requirement of the synchronous mo direction will ?rst cause contacts II 4 to disen gage from the contact bridge II3. However, this 10 tor 37 is extremely small, and as may be seen from Figure 2, is only that required to overcome friction of the gears, and the rheostat mechanism. The synchronous motor 37 does not to any extent contribute directly to the driving force required by the rotatable drum and scanning mechanism 2|. Another modi?cation of my novel speed con disengagement of contact II4 which accordingly results in an open circuit between contacts H4 and H5 will not cause the de-energization of contact relay coil I34, since this relay, when ?rst energized, caused the engagement of armature I23 with contact I25, which through wires I35 and I 36 serves to supply an alternate path for en ergization of the coil I34. Accordingly, the short-circuiting of resistor I I 6 which tends to slow down the shunt motor 24 will continue even though I I4 has been disengaged by trol mechanism is illustrated in Figure 4, and uti~ lizes the differential gear mechanism illustrated the arm H3. in Figure 2. Thus, di?erences in speed between As the shunt motor continues to run below the the D. C. motor and the synchronous motor re speed of the synchronous motor, the arm I I I will sults in rotation of bevel gear Q6 and attached continue to rotate in the direction F of Figure 4 shaft 91, the direction being dependent upon the 25 until the contact bridge II3 leaves the contact relative speeds thereof. IIE, under which circumstances both paths As illustrated in Figure 4, a link III of insulat through which relay coil I34 could be energized ing material is attached at one end to shaft 97 are open. This will immediately cause springs I24 by means of a pin H2, and carries at the oppo and I25 to open circuit contacts H7, H8 and I26 site end thereof a conducting contact bridge H3. 30 resulting in the re-insertion of resistor II6 into The length of contact bridge H3 is suf?cient to the ?eld current circuit of the shunt motor 24. interconnect contacts I I4 and I I 5 which are ?xed Accordingly, as previously mentioned, this will to the frame of the facsimile apparatus. As illus— again, due to the predetermined value of resistor trated in Figure 4, the circuit between contacts I I 6, result in an increase of speed in the motor 24. I I4 and I I5 is not completed by the bridge I I3. 35 Consequently, it may be seen that the electro For this modi?cation, a ?xed resistor lid is mechanical circuit illustrated in Figure 4, will connected in series with the variable resistor 34 serve to maintain the shunt motor 24 in a non and the shunt ?eld of motor 24 at the terminals synchronous condition by maintaining the speed I62, as is illustrated in Figure 1. Contacts Ill either above or below the synchronous speed of and H8 disposed at the ends of resistor II? are 40 motor 3?. However, it is important to note that engageable by the armature I2I of a relay I22. the angle of rotation of arm I II is comparatively The armature I2I and an additional contactor great for even extremely small differences in I23 of the relay I22 are normally biased by the speed between the pilot motor 31 and the shunt spring I24 and I25 respectively, into position motor 24. Evidently, therefore, the departure wherein they are normally disengaged from the from synchronous speed can be made to be ex contacts II‘I, II8 and I26. tremely small by the continuous and rapid open Energization of the relay I22 will cause the ing and closing of the contact arm I2I of the re displacement of armatures IZI and I23 against lay I22. That is to say, that the shunt motor 24 the normal spring bias illustrated, and cause the when operated by the control mechanism illus engagement of the armatures with their respec- 1. trated in Figure 4, will be continuously hunting, tive contacts. With the contact bridge I I3 in the that is, fluctuating about the synchronous speed position illustrated in Figure 4, the resistor III} of the motor 37, and Will on the average run at is part of the shunt ?eld circuit. This resistor I I6 has been adjusted in connection with the var synchronous speed. iable resistor 34 so as to provide a speed of the I D. C. motor 24 which is above that of the syn— chronous motor 3i when in circuit and a speed lower than that of motor 3? when shorted out of the circuit. The maximum departure from synchronous speed as determined by the angular displacement of contacts H4, and H5, will be so small as to make the effect upon a straight line in a picture ure 2, such a condition of relative speed will cause transmitted indiscernable. Summarizing, therefore, the circuits of Figure 3 and Figure 4 when utilized with the mechanical linkage between the synchronous motor and the the rotation of bevel gear 96 and hence, of link I I I in the direction marked F in Figure 4. The continued rotation of the link III and its shunt motor illustrated in Figure 2, comprise a governor of the speed of motor 24. However, it is evident that the governor thus formed is at all As previously described in connection with Fig associated contact bridge I I3 will ultimately cause the closure of contacts I I4 and I I5. Closure co times responsive to changes in synchronous speed which may be encountered at the transmitter, particularly if the transmitter as previously de scribed is operated by a battery which in turn serves to generate an alternating current signal of the contacts II4 and H5 will, through wires I3I and I32 and the battery supply I33, cause the energization of the coil I34 of relay I22 which in turn will cause the displacement of armatures I2I 70 for synchronizing signal transmission. and I23 against their normal spring bias. If, as previously mentioned, between picture The engagement of contacts I I ‘I and M8 by the transmission it is desirable to operate the direct armature I 2] will short-circuit the resistor IIS current motor 24, the latching relay 44 may be and hence reduce the total resistance in the shunt released to the open circuit position illustrated ?eld circuit of the motor 24. This reduction will ' in Figure 1. This will immediately de-energlze 2,404,571 10 the solenoid 66 and cause the rotation of link 6i under the in?uence of spring 63 as illustrated in Figures 1 and 2. This will cause slidably posi tioned bevel gear 15 to move to the right and result in disengagement thereof from bevel gear 8|. Accordingly, the mechanical linkage through the synchronizing mechanism as illustrated in Figure 2, will not be complete between the shafts ‘II and 74. mitter, a di?erential coupling gear between said direct current motor and said synchronous‘ motor having an element responsive to speed differ ences between said motors, said speed responsive element being continuously operative to adjust the ?eld of said direct current motor to maintain said direct current motor at tho speed'of said synchronous motor. ' 4. In a picture transmission system, a trans mitter for generating signals in, accordance with the lights and shades of ‘a picture, means for The synchronous control mechanism described generating a continuous alternating current sig in the above paragraph obviously may be ex nal of a frequency representative of the speed of tended to the speed control of various other said transmitter, means for transmitting said types of motors. Thus, the shaft 91 controlled by rotation of the bevel gear 96 may be used to 15 signals, a receiver for receiving said signals, means for impressing said picture signals upon actuate mechanism to control the speed of var a picture recording mechanism, means for driv ious other forms of motive power including the ing said recording mechanism, comprising a mo~ Well known alternating current speed control motors. ' tor, means for impressing said alternating cur Accordingly, I do not wish the scope of the present invention to be limited to the particular modi?cations described above, but to be bound rent signal upon a synchronous pilot motor, said driving motor and said synchronous motor being by the appended claims. means to cause said recording motor to fluctuate mechanically coupled, said coupling comprising signal upon a synchronous pilot motor, said driv ing motor and said synchronous motor being me in speed, said ?uctuations being rapid and con tinuous and within narrow predetermined limits above and below the speed of said synchronous motor. 5. In a picture transmission system, a transmit ter for generating signals in accordance with the lights and shades of a picture, means for gen erating a continuous alternating current signal of a frequency representative of the speed of said transmitter, means for transmitting said signals, a receiver for receiving said signals, means for impressing said picture signals upon a picture re cording mechanism, means for driving said re cording mechanism, comprising a motor, means chanically coupled, said coupling comprising for impressing said alternating current signal I claim: 1. In a picture transmission system, a trans- = mitter for generating signals in accordance with the lights and shades of a picture, means for generating a continuous alternating current sig nal of a frequency representative of the speed of said transmitter, means for transmitting said signals, a receiver for receiving said signals, means for impressing said picture signals upon a picture recording mechanism, means for driving said recording mechanism, comprising a' motor, means for impressing said alternating current - upon a synchronous pilot motor, said driving mo ence between said motors to adjust the speed of in tor and said synchronous motor being mechan ically coupled, said coupling comprising means said drive motor to the speed of said synchronous to cause the speed of said recording motor to ?rst motor. rise above the speed of said synchronous motor 2. In a picture transmission system, a trans and operative when said recording motor has mitter for generating signals in accordance with reached a predetermined upper speed limit to the lights and shades of a picture, means for gen cause said speed to fall below the speed of said erating a continuous alternating current signal synchronous motor, whereby the average speed of a frequency representative of the speed of said is equal to the speed of the synchronous motor. transmitter, means for transmitting said signals, 6. In a picture transmission system, a trans a receiver for receiving said signals, means for impressing said picture signals upon a picture 50 mitter for generating signals in accordance with the lights and shades of a picture, means for recording mechanism, means for driving said re generating a continuous alternating current sig cording mechanism, comprising a motor, means nal of a frequency representative of the speed of for impressing said alternating current signal said transmitter, means for transmitting said sig upon a synchronous pilot motor, said driving mo nals, a receiver for receiving said signals, means tor and said synchronous motor being mechani for impressing said picture signals upon a picture cally coupled, through a differential mechanism recording mechanism, means for dI'iVll’lg said re having an element responsive to the di?erence cording mechanism comprising a direct current in speed between said motors, said element being motor, means for impressing said alternating cur continuously operative to maintain the speed of rent signal upon a synchronous pilot motor said driving motor at the speed of said syn whereby said synchronous motor is continuously chronous motor. operative at the speed of said transmitter, a, dif 3. In a picture transmission system, a trans ferential coupling gear between said direct cur mitter for generating signals in accordance with rent motor and said synchronous motor having the lights and shades of a picture, means for an element responsive to speed differences be generating a continuous alternating current sig~ tween said motors, said element being operative nal of a frequency representative of the speed of continuously to insert or remove resistance from said transmitter, means for transmitting said the ?eld circuit of said direct current motor signals, a receiver for receiving said signals, whereby the speed of said direct current motor means for impressing said picture signals upon is caused to rise above and fall below the speed a picture recording mechanism, means for driv of said synchronous motor. ing said recording mechanism comprising a direct '7. In a picture transmission system, a trans current motor, means for impressing said alter mitter for generating signals in accordance with nating current signal upon a synchronous pilot the lights and shades of a picture, means for motor whereby said synchronous motor is con generating a continuous alternating current sig tinuously operative at the speed of said trans comprising means operative upon a speed differ A 2,404,571 11 nal of a frequency representative of the speed of said transmitter, means for transmitting said sig nals, a receiver for receiving said signals, means for impressing said picture signals upon a picture recording mechanism, means for driving said re cording mechanism comprising a direct current 12 of a frequency representative of the speed of said transmitter, means for transmitting said signals, a receiver for receiving said signals, means for impressing said picture signals upon a picture recording mechanism, means for driving said re cording mechanism comprising a direct current motor, means for impressing said alternating cur motor, means for impressing said alternating cur rent signal upon a synchronous pilot motor rent signal upon a synchronous pilot motor whereby said synchronous motor is continuously whereby said synchronous motor is continuously operative at the speed of said transmitter, a dif operative at the speed of said transmitter, a dif ferential coupling gear between said direct cur ferential coupling gear between said direct cur rent motor and said synchronous motor having rent motor and said synchronous motor having an element responsive to speed differences be an element responsive to speed differences be tween said motors, said element cooperating with‘ tween said motors, said element cooperating with an electrical time delay circuit to insert resistance 15 an electrical time delay circuit to insert resistance into the field circuit of said direct current motor into the ?eld circuit of said direct current motor until the speed of said direct current motor rises until the speed of said direct current motor rises to a predetermined speed above the speed of said to a predetermined speed above the speed of said synchronous motor and then to remove resistance synchronous motor and then to remove resistance from the ?eld circuit of said recording motor un from the ?eld circuit of said recording motor un til the speed of said recording motor falls to a til the speed of said recording motor falls to predetermined speed below the speed of said a predetermined speed below the speed of said synchronous motor. synchronous motor, said resistance variations be 8. In a picture transmission system, a trans ing continuous and rapid whereby the average mitter for generating signals in accordance with 25 speed of said recording motor is equal to the the lights and shades of a picture, means for gen speed of said synchronous motor. erating a continuous alternating current signal WILLIAM G. H. F'INCH.