US2404566A - Telephoto system - Google Patents

Description

A. G. COOLEY 2 44566 TELEPHOTO SYSTEM Filed Feb. 1, 1943 4 Sheets-Sheet l CONSTANT FREQUENCY 2 A. G. GQQLEY F IG. 1 INVENTOR.

BY mam 23, 14., A. e. COOLEY TELEPHOI'O SYSTEM 4 Sheets-Sheet 2 Filed Feb. 1, 1943 CONSTANT FREQUENCY A. G. COOLEY INVENTOR.

3 Ym4 E T w u OSL @whm mn P ma El T l F 4 Sheets-Sheet 3 FIG.

A. G. COOLEY INVENTOR allllrrlL Patentecl July 23,1946

TELEPHOTO SYSTEM Austin G. Cooley, New York,'N. Y., assignor to.

Times Telephoto Equipment Inc., New York, N. Y., a corporation of New York Application February 1, 1943, Serial No. 474,247

22 Claims. 1

The present invention relates to facsimile transmitting systems and more particularly to a secret signalling arrangement for facsimile equipment, to enable photos, maps and Printed or written messages to be transmitted with secrecy by radio, for example.

In general terms, the object of the invention is, in connection with systems and apparatus of this class, to generate facsimile signals of such character that a legible or usable copy can only be reproduced at a properly equipped receiving station; and to provide receiving apparatu adapt ed to reproduce an accurate facsimile of the original copy, said receiving apparatus being of such character that its performance cannot be matched by an unauthorized person seeking to break down the secrecy of transmission by the trial and error method, or by analyzing the transmitted signals or the record produced thereby on conventional receiving apparatus. While the most important use of the invention appears to be in connection with radio communication, it is useful in connection with any apparatus capable of transmitting facsimile signals, including wire or cable channels.

Various secret signalling systems have been devised to prevent surreptitious transcription of telegraph messages or listening in on speech communication. For example, it has been proposed in the case of speech to obtain secrecy of transmission by purposely distorting the voice currents in a predetermined manner, as by splitting the voice frequency band into sub-bands which are then re-arranged in a difierent order so that the sounds are scrambled and the At the receiving stationby so-called facsimile systems where the copy is scanned progressively from end to end, and variable signals transmitted according to the shading of elemental areas of the copy. The reason as it hardly affects the legibility of thereceivedcopy at all, although it may destroy the usefulness of the copy for purposes where a faithful reproduction is required. If a secret map is to be transmitted, it is obvious that transposition of signal components will merely darken certain areas of the received copy and lighten others without aifecting to any considerable extent the legibility of the map. Even a skewed distortion of the map will usually be entirely ineffective, since 7 the original copy ordinarily contains straight lines or lines of recognizable configuration to serve as a key to the distortion. It will be, apparent, therefore that a secret facsimile system involves difiiculties which are not encountered in secret telegraph or speech transmission systems.

In accordance with a preferred form of the invention, the picture, map or other copy to be transmitted is scanned by the transmitting device or photocell, and the recording sheet or film i marked or exposed by a synchronized recording element; however'the scanning is effected along an irregular or curvilinear path and the scanning rate is varied either continuously or at short intervals so that small adjacent parts of the entire copy are distorted in different ways in both dimensions, said parts fitting together to form a distorted copy as received on a uniform-scanning standard recorder. Since continuous lines onthe original copy or map are notonlydisplaced inposition but also broken up into dots or short fragments as received on a conventional recorder, it will be evident that the copy cannot be restored or the significant parts of the map deciphered from the recording received on a standard machine. However by employing a recorder in which-the recording lamp or; stylus is synchronized with the scanning movement of the transmitting device at the transmitting station, the copy transmitted may be-faithfully reproduced. Intransmitting certain subject matter, sufiicient secrecy may be obtained by varying 'only the scanning rate and employing linear scanning.

In accordance 'with a further feature of the invention, the variations in scanning rate and thedisplacement of "thescanning line laterally are effectediby cams or equivalent mechanical elements. The cams are preferablyreplaceable to permit'changing the distortion pattern from time to time. 1 If the usual "rotating drums are employed 'for carrying the copy and recording sheet or film, the variationVin'scanningrate is preferablytaccomplished by altering the speed of the driving motor or the driving connection between the driving motor and thedrum,ras by changing the contact between meshing gears interposed in such connection. The speed of the motor can be accurately cdntrolledilby employing a synchronous motor connected to an alternating current source which is varied in a predetermined manner. The lateral displacement of the scanning line is preferably efiected by camming the drum or the scanning device parallel to the axis of the drum or by varying the optical system to accomplish an equivalent lateral displacement of the scanning spot (or recording spot in the case of the recorder).

In accordance With another preferred form of the invention, the driving motors of transmitter and receiver are varied in speed while being maintained in synchronism, to vary the scanning rate, by generating a variable frequency alternating current with a light chopper and photocell, for energizing the motors. For example, the light path through the chopper may include a movable slot or series of slots effective to change the rate of interruption of the light beam impinging upon the photocell. This arrangement has the advantage of mechanical simplicity. If desired, two or more variable frequency currents can be combined in a mixer to obtain a current, the frequency variations of which include the variations of the respective components. This simplifies the design and construction of the control elements required to obtain a secrecy variation pattern or code which is not repeated at frequent intervals.

Other objects and advantages of the invention will appear from the following description of the preferred embodiments of the same illustrated in the accompanying drawings, wherein Fig. 1 is a schematic diagram of the transmitting station of a facsimile system according to the invention;

Fig. 2 is a similar view of the receiving station;

Fig. 3 is a modification;

Fig. 4 is a plan view of the apparatus shown in Fig.

Fig. 5 is a further modification employing nonlinear scanning;

Fig. 6 is a modification employing a light chopper.

Several embodiments of the invention are shown in the drawings to illustrate the underlying principles involved but the invention is not limited to apparatus of the type illustrated. For example, the transmitting and receiving equipment is shown for the sake of simplicity as a con ventional type wherein the copy or recording sheet is wrapped around a rotating cylinder or drum, movable relative to the scanning element or recording device, but obviously other known or equivalent scanning arrangements may be substituted if desired.

Referring now to Figs. 1 and 2, the transmitting and receiving stations for purposes of illustration are represented as connected together by a radio channel or link. The transmitting station (Fig. 1) comprises a facsimile transmitter 10 including an amplifier II, the output of which is connected to the transmission channel. As shown the channel includes a radio transmitter l2 and a radio receiver I3 (Fig. 2) The radio receiver I3 is connected through an amplifier 4 to the facsimile receiver I5. The facsimile transmitter l0 and receiver l5, except as hereinafter described, are of conventional construction and the structural details are not shown. For example, they may be similar to those shown in my prior Patent No. 2,015,742, dated October 5, 1935, or of the wellknown type employing a recording lamp or equivalent recording device in the receiver. The scanning elements of transmitter and receiver may be maintained in synchronism by utilizing constantspeed driving motors at the respective stations, the usual system employing tuning fork control. On the other hand, the driving motors may be maintained in synchronism by transmitting ynchronizing signals as set forth in the above-mom tioned Patent No. 2,015,742 or my prior Patent No. 2,045,294, dated June 23, 1936. The phasing of the receiver may be accomplished as described in my prior Patent No. 2,275,249, dated March 3, 1942.

In the modification shown in Fi 1, the scanning rate is varied continuously or at intervals by altering the rotative speed of the drum upon which the map or copy to be transmitted is mounted, in a predetermined manner and to a predetermined extent so that the recording drum of the receiver can be similarly controlled for accurate reproduction of the copy transmitted. The variation in the scanning rate is obtained by using identical rotatable cams l8 and I9 for controlling the transmitter and receiver, respectively. In this instance, a constant-speed synchronous motor 20 is arranged, under the control of cam I3, to control the speed of the auxiliary driving motor 2| which is geared to the drum of the transmitter H3. The primary driving motor 20 may, for example, be controlled by a compensated fork such as that described in my prior Patent No. 2,174,414, dated September 26, 1939. The primary driving motor 30 at the receiver may be similarly controlled or may be maintained at con stant speed by synchronizing signals as stated above. The general arrangement at the receiver to accomplish variable-rate scanning being the same as at the transmitter, a detailed description of the transmitter will suffice.

The shaft 22 of the primary driving motor 20 is provided at its upper end with a worm adapted to drive a worm gear 23 on the shaft 24 of an alternating-current generator 25. The output terminals of the generator 25 are connected to the terminals of the motor 2| which, being a syn chronous motor, will follow the speed variations of the shaft 24 of said generator. The rotative speed of the generator shaft 24 is varied in the following manner to vary the scanning speed of the transmitter: The vertical shaft 22 of the motor 2|] is supported or positioned by the cam l8 so that as the cam is rotated, the motor together with its shaft 22 are raised and lowered in accordance with the changing contour of the cam. This oscillatory vertical movement of the shaft increases and decreases the rotative speed of the shaft 24, the worm on the shaft 22 acting as a rack engaging the gear 23 so far as this endwise movement of the shaft is concerned. Since the speed variations of the shaft 24 are directly reflected by the motor 2 I, it will be seen that the rotation of the transmitter drum and consequently the scanning rate is varied precisel in accordance with the contour of the cam l8. If desired, the shaft 24 can be geared to the drum, and the generator 25 and motor 2| omitted. The arrangement shown however permits the conversion of standard equipment for secret transmission by merely connecting an auxiliary control unit to the motor such as 2| arranged to drive the drum of the facsimile transmitter or receiver.

The cam I3 is rotated at constant speed through drive shaft 26 and friction clutch 21. The shaft 26 may be geared to the motor 20 or to a separate constant-speed motor, the speed of which like that of motor 20 is maintained as fixed and invariable as possible. The rotative speed of the cam may vary with different designs of equipment but is preferably about 1 6 to ;to of the rotative speed of the motor shaft 22. 'For example, it is desirable to revolve the facsimile drum at least five or six times for each revolution of the cam 18 or IE1, and preferably many more than that. In addition, it is preferred to choose or cut the cam so that the rotative speed of the drum is varied as much as 30% (above and below normal) within the time required for the drum to make a, fraction of a revolution; also preferably but not necessarily the cam should be designed to cause appreciable changes in the scanning rate at frequent intervals, 1. e., after the drum makes only a few revolutions.

The cam l9, being identical with the cam l8 and driven at the same rate, is operative to vary the scanning speed on the facsimile drum 'ofthe receiver l5 in precisely the same manner as the cam l8 varies the scanning rate of the transmitter. The cams are preferably replaceable, 'to enable the secrecy characteristics of the equipment to be changed when desired, and are constructed so as to be capable of being oriented properly with respect to the latches 28 and 38 whereby simultaneous operation of the latch mechanisms at transmitter and receiver as hereinafter described starts the rotation of each cam at the same moment and in phase with' the other cam.

In transmitting a map, picture or message-with the apparatus shown in Figs. 1 and 2, the following procedure may be followed, it being understood that certain of the steps enumerated below may be omitted or modified under certainconditions: First the copy should be prepared or altered in such a manner as to eliminate border lines or other areas which would provide a s'tarting point or key for deciphering the scrambling of the picture elements employed for rendering the transmission secret. If the overlapping ends of the copy form a horizontal stripe similar to a border or the clamp for the sheet on the drum presents the appearance of such a horizontal stripe or border, these areas on the drum should be covered by a paper strip or other mask bearing irregular lines or marking, preferably similar in weight or tone to the body of the map or picture. In other words, when the map or copy is mounted on the drum ready for transmission, the entire circumference of the portion of the'drum which is scanned by the transmitting photocell should present a generally uniform appearance and not be outlined by prominent horizontal borders or any other regularly recurring. pattern which is parallel to the axis of the scanning drum so that, as received on a standard machine by one who is attempting to copy the transmission surreptitiously, a reference line would be provided from which the secrecy distortion plan could be determined. In addition, where the copy consists of typed letters or numbers or of lines, as in a map, it is helpful to intersperse random markings between the characters or lines on the copy since this can be done in such a way that the legibility of the received copy is not materially aifected. These random markings should be of about the same weight or density as the original characters or lines.

Next, the communication path should beset up, the facsimile transmitter and receiver-started up and the receiving drum brought into phase with the transmitting drum in the usualmanner. The transmittin and receiving units are then adjusted to start progressive scanning of the drums relative to the pick-up andrecording devices, as by coupling each drum to'its lead screw, as usual in commencing transmissioirf At this point, the transmitter photocell should be 'so positioned as to scan the surface of the drum or a portion of the copy containing no lines or picture (a blank edge at the front side of the copy). After several revolutions of the transmitting drum, to give the receiving operator suificient time to adjust the receiver, the manual switch 4| associated with the transmitter is momentarily depressed. This opens the circuit between the transmitter amplifier H and the-radio transmitter l2 through the lower normally closed contacts of the switch 4|, and momentarily connects the tone generator 42 to the keying unit 43 which is connected to the radio transmitter l2 by conductor 44. -The tone generator 42 and keying unit 43' thus transmit a tone signal to the receiving station 'which'is operative tov release the-cam l9 forrotation in a manner to be explained below. At the same time, an impulse is applied through the circuit 45 from the'keying' unit 43 to the release magnet 29 associated withthe latch. 28,- to thereby release the cam 18 for rotation in synchronism'with the cam l9. -As shown, the,latch;28- is provided with a spring detent or equivalent means whereby when once released the cam 18 continues to rotate freely until the latch 28 is manually restored to the latching position. At the receiving station, the fstart signal or tone is detected by the tuned rectifier 4B and impressed through'the circuit 49 upon the latch release magnet 39, to thereby release the latch 38-and start the rotation-of the cam-l9 at the same instant the cam l8 starts to rotate. During the transmission period the cams l8 and l9 rotate in synchronism, since they are driven by' motors having the same rotative speed as explained above, and cause identical variations in the scanning rate at the transmitter Ill and receiver l5.. As-shown, the motors 30 and 3|,7and generator 35, at the receiving station correspond to the motors 20 and 2 I, and generator 25, at the transmitting station and perform the same functions. Thus while the map, picture or message transmitted would be so distorted as to be undecipherable as received on a standard receiver with uniform scanning rate, the receiver IE will reproduce an accurate copy or facsimile thereof.

It should be particularly noted that since facsimile transmission ordinarily involves scanning the copy vwith a feed or advancement of the drum, of only about A of an inch, perrevolution, relatively small areas or-dots ar scanned repeatedly during consecutive revolutions of the drum. It will thus be evident that a comparatively slow variation in'scanning rate is ineffective in producing undecipherable distortion of the copy unless the rotative speed of the drum is very slow, and that the maximum variation must cause the drum tobe advanced or retarded by aconsiderable amount, saya quarter or a third of its circumference. The construction embodying the invention is particularly advantageous because .the maximum variation in scanning rate obtainable is large and can be effected very rapidly, and therefore secret transmission with this system can be accomplished in the same time as required for the transmission of pictures or messages in -of three cams 5!, 52 and 53. The cams 5|, 52 and 5.3, are driven by. theconstant-speed motor: 54

;through"g'earing,55; 56, and 51, preferably zof-difdriving motor 20 of Fig. 1.

ferent ratios in order that the resultant motion produced by the separate cams is not repeated during each revolution. The cam plate 58, which is controlled by the cams, supports the end of the motor shaft 59 of motor 60 so that the height to which the motor is raised is controlled jointly by the several cams 52 and 53. As shown, the motor 60 is supported for vertical movement in the vertical guides 6| so as to vary the spe d of the driven shaft 64 in a similar manner to the In this instance the facsimile drum 65 is shown as mounted on shaft 64 but it may be driven by a separat motor as shown in Fig. 1.

Fig. 5 shows a construction in which the scanning rate on the transmitting drum 10 is controlled by the cam H and motor 12 substantially as shown in Fig. 1. lhe receiving drum is similarly controlled. In this modification non-linear scanning is produced by lateral movement of the photocell or scanning device 73 which varies durn ing each rotation of the drum. The threaded shaft 14 serves as the usual lead screw for the photocell, being rotated by a constant-speed motor 15 Which also rotates the cam 1| through the gear ll. The lead screw 14 is also oscillated axially by the cam 79 and fork member 80. The cam 19 is also driven by motor 15 through the gear 82. As shown the cams II and 19 are removably secured to their respective shafts by the thumb screws 85 and 86. In order to assist in orienting these cams at the commencement of transmission, the cams may also be provided with marks or pointers as indicated 88 to show the angular position of the cam at the start. The photocell i3 is shown as connected to amplifier 90 which in turn is connected to suitable limiting, and modulating and transmission equipment. Similar apparatus at the receiving station to that shown in Fig. 5 enables the accurate reproduction of the picture or map by producing corresponding relative movement between the recording lamp and the recording sheet or film.

Fig. 6 illustrates an arrangement employing a primary chopper 9| and a plurality of shutter disks 92 and 93 in order to obtain variable modulation of a plurality of light beams impinging upon the photocells 94. In accordance with the invention the output currents from a plurality of such cells are amplified and combined in a mixer whereby the variable frequency current in the output circuit 96 is the sum of the currents generated by the cells 94. By electrically combining the frequencies in this manner the mechanical construction may be simplified.

As shown for purposes of explanation, a motor 91 is arranged to rotate the chopper wheel 9| directly mounted upon the motor shaft and also rotate the shutter discs 82 and 93 through gearing 98.

No claim is made herein specifically to th embodiment of the invention comprising a light chopper or a generator including a mixer or equivalent means for combining two or more variable frequencies, these and related features being claimed in my copending application, Ser. No. 590,369, filed April 26, 1945.

I claim:

1. A facsimile transmitter comprising a rotatable drum for supporting the picture or copy to be transmitted, means to rotate said drum and means to scan the copy along a non-linear path.

2. In a facsimile system embodying a motor unit, a rotatable drum controlled by said motor, means for varying the rotative speed of the drum 8 including a rotatable worm and cooperating worm gear driven by said motor, and means for oscillating the worm axially to vary the relative speeds of said Worm and worm gear.

3. A facsimile machine of the character described comprising a constant-speed driving motor, a rotatable drum and means interposed between said motor and said drum whereby a nonuniform rotative speed is imparted to the drum, varying at intervals above and below the average rotative speed, said means including a mechanical gear drive system embodying a rotatable worm gear, a rotatable and axially movable worm engaging said worm gear and means to oscillate said worm axially to thereby vary the relative speeds of the worm and worm gear.

4. A facsimile machine for secret transmission of copy by non-uniform scanning comprising a rotatable drive shaft and means including a mechanical gear drive system for imparting non-uniform rotative speed to said drive shaft, said drive system embodying a rotatable worm gear and a rotatable and axially movable worm engaging said worm gear.

5. A facsimile machine for secret transmission of copy by non-uniform scanning comprising a rotatable drive shaft and means including a mechanical gear drive system for imparting nonuniform rotative speed to said drive shaft, said drive system embodying a rotatable worm gear, a rotatable and axially movable Worm engaging said worm gear, a motor for rotating said Worm, and cam means for oscillating said worm axially to vary the relative speeds of said worm and worm gear while maintaining thedrive relation therebetween.

6. In a facsimile machine operating on a scanning-distortion principle for secrecy, in combination, a rotatable copy or recording-sheet supporting drum, a variable-speed driving member operatively associated with said drum and cam means for imparting predetermined variations in speed to said driving member.

'7. In a facsimile machine operating on a scanning-distortion principle for secrecy, in combination, a copy or recording-sheet supporting element, scanning means operatively associated therewith, and drive means for moving said supporting element, said drive means including a motor connected to said element, and cam means for obtaining an irregular but predetermined relative movement of said element and scanning means.

8. In a facsimile machine operating on a scanning-distortion principle for secrecy, in combination, a copy or recording-sheet supportin element, scanning means operatively associated therewith, said element and scanning means being relatively movable, rotary synchronous motor means to effect such relative movement and means to generate an alternating-current of a frequency varying at intervals to drive said motor means at a variable speed, the magnitude of such speed variations being suflicient to render a copy received at constant scanning rate illegible or useless.

9. In a facsimile system for secret communication, in combination, a transmitter provided with a rotatable drum for supporting thecopy or picture to be transmitted, a motor for driving said drum, scanning means associated with said drum, cam means for imparting predetermined variations to the relative movement between said drum and said scanning means to distort the signal output as compared to linear, uniformrate scanning, and a receiver connected to be operated by the signal output of said transmitter, said receiver embodying cam means similar to that of the transmitter for correcting for the distortion of the signal output of the transmitter.

10. In a facsimile system for secret communication, in combination, a transmitter provided with a rotatable drum for supporting the copy or picture to be transmitted, a driving motor for rotating said drum, scanning means associated with said drum, a variable-frequency generator connected to said motor to impart predetermined variations to the rotative speed of the drum to distort the signal output as compared to uniformrate scanning, and a receiver connected to be operated by the signal output of said transmitter and provided with means for correcting for the distortion of the signal output of the transmitter.

11. In a facsimile receiver for a system of the character described employing signals generated by scanning the copy at a non-uniform rate, in combination, recording mechanism, a driving motor therefor and a variable-frequency generator connected to said motor and arranged to operate the same at variable speed to correct the signal distortion.

12. In a facsimile receiver for a system of the character described employing signals generated by scanning the copy at a non-uniform rate, in combination, recording mechanism, a driving motor therefor and cam means for controlling the recording mechanism to correct the signal distortion.

13. In a facsimile receiver for a system of the character described employing signals generated by scanning the copy along a non-linear path, in combination, recording mechanism including a rotatable drum for carrying the recording sheet, a driving motor for the drum and means for oscillating the drum axially to an extent corresponding to the non-linear scanning of the transmitted picture or copy.

14. A facsimile machine operating on a scanning-distortion principle for secrecy comprising supporting means for the copy or recording sheet, relatively movable scanning means associated therewith, a variable-speed motor connected to one of said means and cam-controlled means including said motor for correcting the signal distortion to enable substantially distortion-less reproduction.

15. In a facsimile transmitter for secret transmission of pictures and the like, in combination, relatively movable supporting and scanning means for the copy to be transmitted whereby successive elemental areas of the copy are translated into electrical signals, a variable-speed motor, cam mechanism and means including said motor and cam mechanism for varying the rate of scanning to effect predetermined distortion of the signals.

16. In a facsimile transmitter for secret transmission of pictures and the like, in combination,

the drum and scanning means parallel to the axis of the drum, a cam arranged to oscillate said lead screw in an axial direction to effect non-linear scanning, and means including a constant-speed motor for driving said lead screw and drum.

18. In a facsimile machine of the character described, in combination, scanning means, a plurality of cams of varying contour, means for rotating said cams and means for controlling the scanning means in accordance with the resultant cam motion.

19. A scanning arrangement for a facsimile system comprising, in combination, a rotaryelement, a synchronous motor for driving said rotary element, and a variable-frequency generator for driving said motor.

20. A scanning arrangement for a facsimile system comprising, in combination, a rotary drum, a scanning element, said drum and scanning element being mounted for relative movement axially of the drum, a rotary synchronous motor for producing said relative movement, and a variable-frequency generator for driving said motor.

21. A scanning arrangement for a facsimile system comprising, in combination, a rotary drum, a synchronous motor for rotating said drum, a scanning element, said drum and scanning element being mounted for relative movement axially of said drum, a rotary synchronous motor for producing said relative movement, and a variable-frequency generator for operating both of said motors.

22. A scanning arrangement for a facsimile system comprising, in combination, a rotary V the axis of said drum, and means for simultaneously causing relative oscillation betweensaid drum and said seaming element in a direction parallel with the axis of said drum.

AUSTIN G. COOLEY.

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