US2425616A - Facsimile synchronizing system - Google Patents

Description

Aug.12, 1947. H. E. HALLBORG ETAL 2,425,616 7 FACSIMILE SYNCHRONI Z ING SYSTEM Filed June 19, 1945 5 Sheets-Sheet 1 Ag. l2, 1947. H. E. HALLBORG ETAL v 2,425,616

FACSIMILE SYNCHRONIZING SYSTEM Aug; 12, 1947. H. E. HALLBORG ETAL 2,425,616

S FACSIMILE SYNCHRONIZING SYSTEM Filed June 19, 1943 3 Sheets-Sheet 3 VOL THGE C'OIVTBOL (JN/T A TTO/BNEY Patented ug. 12, 1947 OFFHCE FACSIE SYNCHRONIZING SYSTEM of Delaware Application .lune 19, 1943, Serial No. 491,537

7 Claims'.

'Ihe present invention relates to communication systems, and more particularly to systems for sending and receiving facsimile signals in secrecy. More specifically, the present invention relates to a secret communication system wherein variable speed mechanisms are provided at the transmitting and receiving stations, which mechanisms are caused to have substantially identical speed variations.

Older privacy systems have one or more of the following limitations; they require inherent change in equipment, require a wide frequency band for transmission, intermittent transmission is necessary, power is wasted in spurious signals, critical adjustments are required, the quality of the received subject made is below normal standards. Moreover, these older systems are not suitable because of multi-path effects where trans- -mission over a long radio circuit is necessary.

The secrecy system disclosed herein may be added to existing equipment substantially without change in the scanning and recording circuits or in the method of transmission normally employed. Secrecy systems in accordance with the invention are relatively simple in operation and give a high degree of privacy at a comparatively low cost for equipment and operation. A system embodying this invention may be operated normally after performing a simple switching operation at each circuit terminal. No power is wasted unnecessarily in spurious signals.

In brief, the operating speed of both an image or facsimile signal generator and an image vor facsimile signal recorder are varied in accordance with a prearranged plan or code. This may be done conveniently by a switch or cam at both the transmitting and receiving stations for varying the rotational speed of the mechanical power source at arbitrarily selected time intervals whereby unauthorized persons not knowing and having the means for changing the speed of operation of their receiver in accordance with the transmitter speed changes cannot synchronize their receiver to reproduce anything which is intelligible.

The principal object of the present invention is to provide novel methods of and apparatus for preventing the intelligible reception of facsimile signals by anyone except authorized persons.

Another object of the present invention is to provide a facsimile recorder having means for varying the degree of departure from normal synchronous operation in a predetermined manner.

A further object of the present invention is 2 to provide a novel arrangement for obtaining changes in the speed of a facsimile machine in accordance with a predetermined code.

Other and more specific objects of the invention will become apparent and suggest themselves to those skilled in the art to which the invention is directed upon reading the following specification and claims in connection with the drawings in which:

Fig. 1 is a schematic block-diagram of a facsimile transmitting station embodying the invention;

Fig. 2 is a diagrammatic showing of a receiving station in accordance with the invention;

Figs. 3 and 4 are side elevational views of details of Fig. 2;

Fig.,5 is a diagrammatic showing of a facsimile station embodying the invention in a modified form; and

Fig. 6 is a fragmentary view in side elevation of a detail of Fig. 5.

Referring to Fig. 1, there is shown a transmitting station having a facsimile scanner indicated generally by reference character I0, and comprising a copy holding drum II and a facsimile signal generating device, such as a scanning head I2. The scanning head i2 is advanced axially of the drum Il by a lead screw I4 driven from the drum shaft I6 by a gear and pinion combination i8. It will be understood that the scanner I@ may be of any known type employing either the rotating copy holding drum II, shown by way of example, or a continuous sheet or web in which the signal generatingrdevice i2 reciprocates line by line over the web. The copy holding drum l I has a message sheet I9 lsecured thereon in any suitable manner, for example, by a clamping device indicated conventionally at 2 I. Facsimile signals representing a message or picture inscribed or otherwise provided on the message sheet I9 will be generated when the copy holding drum I l is rotated with respect to the scanning head l2. The drum II and the lead screw l are driven from a motor 23 through a change speed device such as a gear box 24, and, if desired, through a combination 26, shown conventionally, or a worm and worm wheel combination as shown by Fig. 5 of the drawings. The gear box 2t provides a convenient means for changing (usually reducing) the speed of the motor 23 to the desired operating speed of the scanning drum I I. The motor 23 as will hereinafter appear is preferably an alternating current synchronous motor.

A conventional radio transmitter 28, comprising the conventional oscillator and modulator,

3 radiates signals from an antenna 23 which signals contain the intelligence derived from scanning the message sheet i9. It will be understood, however, that any communication channel such as a wire line, for example, may be substituted for the radio link 29.

The novel means of this invention for insuring secrecy and now to be described are independent of the conventional facsimile station equipment just described. A standard frequency source 3l, which serves as a reference frequency for vthe transmitter, is of any suitable type and .produces a substantially constant tone frequency of the order of 600 cycles per second, for example, It will be understood, however, that any desired tone frequency may vbe employed, although the frequency of 600 cycles is herein 'selected and asu sumed as the standard since it is a multiple of the usual power supply frequency of 60 cycles for which readily available equipment is manufactured. The output of the standard frequency source 3l is applied to two frequency dividers and frequency generators 33 and 34, which serve in the illustrative example of Fig. 1 not only lto produce a sub-multiple of the output frequency of the Astandard source 3| but to change the 'frequency of the sub-multiple in la predetermined manner. For example, the device 33 may .produce a frequency of 60 cycles plus another frequency f. The device 34 may produce a frequency of 60 cycles minus the same frequency f. Thisfrequency f is selected to be within the range of stable operating frequencies of the motor 23 and may, for example, be 1 per cent yof the selected submultiple of the frequency of the source 3l. Practically any speed change may .be utilized up to the limit of synchronous response'by the motor. The output of the generator and dividers 33 and 34 will then be 6l and 59 cycles respectively. The generator and divider devices 33 and 34 are connected to switching devices A3'1 and 538 respectively vwhich are controlled by a device ywhich may be a code generator 3'9 and preferably is of the nonrepeating type; that is to say, .the group of code pulses produced by the code generator 39 are not repeated in normal operation during a transmission or a series of transmissions from the radio transmitter 2,8. 'I'he code generator"39 vpreferably provides cut-.off bias for the switching devices 31 and 38, and its operation is timed Afrom 4the standard `frequency source 3i through a frequency generator and divider lll over a connection 42. It Ywill -be understood that the code generator 39 may be connected directly tothe standard source 3|,.'if desired, rather than to the frequency generator and divider llc as shown. The code generator-39-maybe a counter controlled or a cam controlledelectronic device, or itmay comprise a rotary cam and switch such as is shown by Way of example in Fig. 3 of the drawings. The switching ' devices 31 and 33 may -be yrepeaters orvampliers biased to cut-on over Vconnections 44 and 46 from the code generator39 or electromagnetic relays held in an inoperative condition at times by the code generator. The latter cuts off switching device 31 when switching device v38 is operative and vice versa. The'outputterminals-of the switching devices 31 and 38 are connected by way-of conductors 0.1 toa pair .of terminal studs 49 on adouble throw switch-5l. The Yswitch arms of this switch are connectedby way of an amplier-SZ-tothe scanner drive motor 23.

q `If desired, the switch 5ly maybe provided with additional switch arms and studs in any well known manner to cut out the code controlled frquency changing equipment, shown at the top of Fig. 1. When the switch arms of the switch 5I are in their left hand position in contact with studs 54 to connect the motor and amplifier 52 directly to the rated motor frequency source, namely, standard source '3i and divider 40, ordinary operation is obtained so that intelligible copy may be received by ordinary receivers within the transmitting range of transmitter 28. It will be understood by those skilled in the art that the source `3| may be a commercial `power source where .the transmitter and receivers can be connected to the same commercial power network to insure synchronism. Also, dividers 33, B, and 4] may be a single unit if desired.

A description of the operation of the equipment shown by Fig. l in conjunction with a similarly equipped receiving station will be described in detail following a description of Fig. 2 which shows, by way of example, a receiving station equipped ywith apparatus necessary for the intelligible reception of signals transmitted b y a transmitter embodying the invention, such, Vfor example, as that shown by Fig.Y l of the drawings.

Referring to Fig. 2, reference character '56 indicates a recording scanner which is or may be similar to the transmitting scanner lil of Fig, 1, the principal difference being that a copying head v51 is substituted for the scanning head l2 of Fig. 1, Radio signals are intercepted by an antenna 59 connected to a radio receiver 6I. A signal amplier and detector combination 62 serves to amplify picture signals which are suppliedto the copying head 51 in known manner. A synchronous motor 64, which may be similar to the motor 23 of Fig. 1 drives the recorder 56 through a gear and pinion combination 66, shown conventionally, and the Vgear box 61. If desired, a worm and worm wheel combination, as shown on Fig. 5 of the drawings, may be substituted Yforthe gear and pinion S6.

A standard frequency source suppliesa substantially constant frequency alternating current voltage to a frequency divider 1i, the output of which is a sub-multiple of the frequency ,produced or `generated by the standard frequency source 69. The frequency of the standard source may conveniently be 600 cycles per second vwith the frequency divider having a ratio of l0 to 1 so that the output of the latter to an amplifier v'i2 is 60 cycles, a frequency which is suitable for ope erating a synchronous motor 1,4. This motor-.may be of the small .synchronous clock .drive type which Vis readilyeobtainable commercially. Tione wheel rotors 16 and 1v1 of a pair of induction generators are .carried by a shaft 18 which is driven from the motor 154 through aspeed reducing gear box 13. The speed at which the shaft 18 is to-be driven depends upon the frequency of the fout-put .of the induction generators 16 `and -11 assuming a given number of teeth on their rotors. The output frequency of these generators `preferably is such that their output may be amplified in an amplier 8| andapplied to the terminals ofthe synchronousmotor 64. For example, if --the mo-tor 14 is a 60 cycle two pole clockmotor, the speed reducing gear'should have gear ratio ofGOto rr1 so that with-59 teeth on the rotor' kand the 6l teeth on the rotor 11,*these two inductor genera,- tors will provide output Vvoltages at 59 vand .6l Vcycles respectively which is l lpercent above and 1 per cent below the frequency of the output of the divider 1l.

The stators of the inductor generators are 5 similar, and generator 16 is shown more in detail by Fig. 4 of the drawings. It is seen to comprise a permanently magnetized yoke 83, and the two polar tips 84 are separated by a distance equal to several times the pitch of the teeth on the rotor. A winding 86 surrounds a portion of the magnetic circuit, for example one of the pole tips, and one of its terminals is connected by way of a conductor 88 to a contact 89 of a. cam operated switch 9| in the manner shown diagrammatically on Fig. 2 ofthe drawings and more in detail by Fig. 3. The remaining terminal is connected to a conductor 93 which connects with one stud 94 of a double pole double throw switch 96. The corresponding stud ofthe switch 96 is connected to the tongue 91 of the switch 9| by way of a conductor 99. The winding |02 of the generator 11 is connected by a conductor |03 to contact |04 of the switch 9|. The remaining terminal of the winding |02 is connected to the conductor 93. With the switch 96 in its right hand position, as shown, the receiver will operate in conjunction with a'transmitter such as the one shown in Fig. l to give a legible record.

The cam |01 which operates the cam switch 9| is provided with notches |08 cut in accordance with a predetermined code to match the code of the similar device employed at the transmitter, for example, the device 39 of Fig. 1.

In operation of the system so far described, the transmitting station, which may be provided with a code Wheel arrangement as shown in Figs. 2 and 3 of the drawings or with a code generator 39, as pointed out above, is placed in operation, with a message sheet I9 bearing subject matter for transmission secured on'the drum of scanner I0. The code generator 39 is arranged to operate in accordance with an irregularly occurring code or, if a cam switch type of code device is employed, the cam is selected so as to have irregularly occurring indentations or, conversely, irregularly occurring teeth. The latter arrangement necessitates merely a reversal of the cam switch contacts. generators are employed, the selective code may be further complicated to prevent its solution by an unauthorized party by increasing the number of the tones generated by adding a cam code wheel and cam operated switch per pair of added frequencies. The code generator at the receiver, which may comprise the cam |01 and the cam operated switch 9|, operates to connect either the inductor generator 86 or the inductor generator |02 in circuit at the same time as the switching device 31 or the switching device 38 at the transmitter is in circuit. The speed of operation of the transmitter scanner I will then correspond at any instant to the speed of operation of the recording scanner 56, and a legible copy of the transmitted subject matter will be recorded.

The apparatus at the transmitting station may be employed to transmit in a normal manner to any receiving station by placing the switch in its left-hand position. Likewise, the receiver of Fig. 2 may be employed to receive signals from; any transmitter station by placing the switch 96 in its left-hand position.

Fig. 5 of the drawings discloses a modification.

Vin which the facsimile scanner |I2 is driven by an induction motor I I4. This apparatus may beused either at a transmitting or receiving station. The motor ||4 drives the copy holding drum IIB of the scanner |I2 through gearing ||1 and a worm and worm-wheel combination |I8. The: gearing ||1 also drives a shaft I 2| on which If a cam switch and inductor4 are vmounted the rotors/of inductor generators |22, |23, |24. The shaft |2| also has secured thereto a cam disc |26 which operates a cam controlled switch |21. The proper time phase of switching between the inductor generators |23 and |24 is controlled by the switch |21. A cam operated switch |29 is controlled by a code disc |3| having code teeth cut thereon. This code disc |3| is mounted on a shaft |28 and correspends in function to the cam |01 of Figs. 2 and 3 of the drawings and is driven at reduced speed relative to disc |26 by gearing |30.

The motor I|4 obtains driving power from a suitable alternating current source which may be a standard -volt, (iO-cycle yservice outlet connected at terminal points |33. The driving speed of the motor ||4 is varied in accordance with the code provided on the code disc |3| by means of a phase detector |36 and a voltage control unit |31. These pieces of apparatus are disclosed and claimed in a copending application of Hallborg et al., Serial No. 491,538, filed June 19, 1943. So much of the description appearing in this copending application as is necessary to an understanding of the present invention lwill be repeated herein for the sake of completeness of the disclosure. Briefly, the device |36 beats the output of the generators |22 to |24 with the output of the standard frequency source |39 to produce a phase shift in the beat Wave. This phase shift produces a proportional change in resistance in the motor ycircuitI resulting in a proportional change in motor speed.

The standard frequency source |39 provides a regulated frequency output which is fed to the phase detector |36 over a connection |4| and inductor generators |22 to |24 are also connected to the phase detector |36 over a connection |42 under control of a polar relay |44, the operating coils of which are connected to the contacts of the cam operated switch |29. A suitable source of operating potential |46 in series with the cam operated switch |21 provides for energization of the relay coils. A manually operable switch |41 interposed in one leg of the connection |42 provides for operating the system as a privacy system or in the normal manner in conjunction with any type of transmitting or receiving station. The tongue |48 of the polar relay, when in its right-hand position (and with switch |41 in the privacy position, as shown), connects the inductor generator |24 to the phase detector |36. This inductor generator |24 is provided with a number of teeth such that it would generate a frequency higher than the frequency of the frequency standard |39 if the shaft |2| were permitted to run at normal speed. .With the tongue |48 of polar relay |44 in its left-hand position, and the manual switch |41 in the -position shown,

the inductor generator |23 is connected to the phase detector |36. The inductor generator |23 is provided with a number of teeth such that it would generate a frequency lower than the normal operating frequency of the motor ||4 if the shaft |2| were permitted to run at normal speed.

The inductor generator |22 is provided with a number of teeth such that it will generate a frequency equal to the normal operating frequency of the motor |I4 when it is operating at normal speed. Therefore, with the switch |41 in its right-hand position, the motor II4 will operate at a constant speed under -control of the output of the standard frequency source |39.

In operation of the apparatus described, the switch |29 will operate to place either of .the in- -ductor generators |23 or V4Min connection with fthe-phasepetector |36 so as-to supply voltage thereto. -Assumingv-that the `code disc 13| .has rnovedth'e switch L29 into the position shown Y-t-lfie tong-ue 448 of the polar lrelay will, when switch t2?! closes, :connect-the .-i'nductorz generator |24 to fthe phase detector device |35.. yl2.b.e.mo mentary increase in frequency will :result-in 'instantaneous 'decrease .in the ,motorspeed gto .the -point lat which-the vindulotor. generator |24 generates precisely .standar/d frequencyloy .reasonr of a decrease in the supply .voltage .applied'to I.the motor I-I4 `througnthe .voltage control unit 431. viii/Then `the cam .code disc causes theswitch vk|23 to `move .to its right-hand position, -the tongue .lfof the polar relay .will `connect 'the inductor generator |23 tothe phase detector 1.36. An in- .,s'tantaneous 4increase in the .speed .of the motor 'Ille wiIlJ-be produced and vmaintained.until the :codedisc '|3l again .operatesthe Aswitch '129. The .tongue .1152. o'fthe relay Mil-short circuits aresistor ,|53 whichis 'in series with the motor '|14 and assists in obtaining -the Avery rapidirrcrease in speed.

The apparatus described in connection jwith Fig. '5 'is operated in the manner 'already described .in connection .with Figs. l fand 2 'of the drawings. For example, atth'e transmitter 'station amessage sheet "bearing ja'ccpy fortransmission will be 'placed V'on' the drum ""HB Aand a code disc |3I will be selected "and mounted Aon "At the receiver `station a lsuitable -type ormessage blank will be placed'onfthe drum -|f|l6 4and a codeidisc 3| ji'denticalwith ythat'at thetransmittenwill Abe used. `Phasing 'orfrarning Vof the copy may 'be accomplishedin accordance "with well known methods.

Solely by way of "example-a vtypicalesystem operated-in`accordancewiththeinventionemployed `a motor |14 with-anormal speed of 1760 R. P.M.

A gear ratio of '30u (ffl to l) 'was-provided `in 'the .reducing gear, where in '.Was the number rof iteeth in .the .reference 'frequency tone .wheel |122, `f1 'was vthe :standard reference frequency, and 7i-.l and 'n+1 :the number of teeth for producing drum-speeds above .andbelow normalrbymeansof in'ductor generatorsY |23 and |24. The driving irationfthezworm y, and .worm wheel combination I IB .was l to-. 30. The-'driving gear ratio. forthe wormfishaft'wasf45 tof44. .The gear .ratio Ibetween .the motor |-4 .and tnefsbaft |.2| Ain the speciiic example now-ilbeingydescribed has .already been given.

AHavingnow described our invention, what we Vclaim .as :new .and desire yto nhave protected by Letters .Patentxisz 1. Inan electrical icommunicationsystem comprising a movable .intelligence :transferring-mem- .ber ,and power drive vmeans for saidmovable lating device,` analternati-ng kcurrent power source having -an .output :of a .predetermined frequency, asecond alternating .current vpower source haV.- .ing .a ftrequency .dinering `from the frequency of .said rstnamedsourca .and code operated means V@to ,connectsaid .power drive means with eitherof .said .power sources.

'.3.. .A secrecy .system comprising a signal 'translating Adevice,power drive means for said translating `device, astable Yfrequency alternating .currentpower source, .an .alternating current ,power source ,having .ia .frequency higher than the fre- .quencynf .said .stable `frequency source, .an alternating .current :power source .having a frequency lower :than the .frequency of said stable frequency .power source, .code-.operated means tot connect said power drivemeans with eithenofsadsecond cr third ,named :power sources, and means associated .with .said .stable frequency :alternating current powersource for controlling ,said code :.operatedrlneans.

4.ln an electrical communication system com- .prising a movableintelligence transferringmernber and power.1drive means Vfor said mm/able member, Ameans cooperating Y with said member 'to igenerate .intelligence signals, -ia frequency controll'ed electrical power supply for said power `drive means, means toproduce aseparate alterable frequency, means to compare said vseparate frequency with the frequency of said supply,

Ameans* to `.produce a change in Lspeedof said vpower drive,means inaccordance with said com'- Kparison, and .code controlled means for control- .ling .said frequency varying means andthereby contrllingfsaid intelligence transferring member lsc .that communication by the intellgencesignals .means,. means1for,providing `a supplementalpower supply-.havinge Characteristic different from a v.like characteristic of vthe ,power supply .for said r,powerldrive means, means to compare s aid charv acteristics.means toproduce a change in the speedof said .powerdrive means as aresult of .said comparison, ,and code controlled means for controlling said .supplemental ,power .supply so that secrecy .of communication by the intelligence Signals i-s maintained '.`6.1In-an electrica1 communication vsystem comprisinga.movable'intelligence transferring memloer and power drive-.means for.said mov able .member-means cooperating with said member to guency, .meansito ,compare ,saidscpaljate ifre- V .quency .withtheirequency ofsaid Supply,.1neans to, pro.duce a change. in speed orsaidpower `drive means in accordance with said:comparison,' and code.:controlledv means for .controlling v`said .frequency .varying .means .and .thereby controlling said intelligence -transferring 4member ,so..that

...communication by .the intelligence signals at a .plurality of differentsp eeds. is .obtainedsat-predegenerating .intelligence signa-ls, electrical .means tor drivingsaid. scanner, .a v,frequency regulated alternatingcurrent power` supply for said scanner drive means; means to vary the frequency of said alternating current power supply to produce a change in speed of the scanner drive means, and a code operated switch for controlling said frequency varying means in accordance with a prearranged code.

HENRY E. HALLBORG.

GILBERT R. CLARK.

REFERENCES CITED The following references are of record in the le of this patent:

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