US2361255A - Facsimile-transmission system - Google Patents

Description

OCt. 24,

V. K. ZWORYKIN FACSIMILE-TRANSMISSION SYSTEM Original Filed July 5, 1929 l Nk n PR l HhN N Nm vVhllllllrx.l

or Vto Westinghouse lleoiric il Handhaving Company, s f mm Een Allle! 13. 1931 immuun .my s, im. serial No. :n.111

ewcd 8 Claims. (Cl. 17h-69.5)

My invention relates to facsimile-t systems. and it has particular relation to system especially adapted for thereproduction, at. la distance of moving-picture mms with, or without,

sound accompaniment.

In my copending application, Serial No. 349,956, led -March-26. 1929, and assigned to the Westinghouse Electric and Manufacturing Company, of which this application is a continuation in part, I have disclosed an improved transmission system wherein synchronism between a scanning device at `a sending station and ananalogous device, comprising a cathode-ray tube, at a receiving station is automatically maintained. Certain subject-matter here disclosed is claimed in my Patent 2,141,059'and in my application Serial No. 254,607v for Facsimile transmission systems, filed February 4, 1939.

In the said system, a plurality. of conductors are l employed vfor conveying the picture-frequen'ciesl from the sending station to the receivlngstations. As pointed out in the application referred to, `my improved film-facsimile transmission system is adaptable to radio by the mere substitution of 1 radio-channels for 'the' several wire-,conductors lshown and by the use of aplurality of carrier waves, at diderent frequencies, for accomplishingthe functions of synchronizing, scanning-control and propagation of the impulses representing picture-elements. Such use of a pluralltyof frequencies, however, is undesirable, in view of the limited number of radio-channels available, and it is, accordingly. an object of my present invention to provide a film-facsimile transmission system that shall necessitate the utilization of only a single channel for all of the functionsv enumerated above, irrespective of the transmitting medium, `whether it'be radio or wire.

Another object of my invention is to provide a film-facsimile transmission system that shall Y requirethe minimum number or carrier-channels furthe transmission of moving pictures accompanied by sounds. linother object of my invention is to provide a; film-facsimile transmission systeml wherein synchronism between the moving parts at a sendof receiving stations shall' be automatically controlled, in large measure, bythe sending station while. at the same time, permitting individual control atthe recelving'jstations if desirable.

Anotherobject of my invention is to provide a nlm-facsimile transmission system wherein the timing of the control-frequencies is determined by the travel of a iilm, or an analogous element, past a. ilxedpoint ai; the sending station. d

Another object of my invention is to provide av facsimile transmission system that shall be adaptablewwithr but minor changes, to the transv ticularityin the appended claims. 4The invenrled by a continuous, opaque beit. or similar element.

Another object of my invention is to provide, in a facsimile-transmission system of the type described. means whereby a photoelectric cell shall be more eiiiciently utilized than in previouslyknown systems. y

Still another, and more specific, ,object of my invention is to provide, in a. facsimile-transmission system, receiving devices that shall require the minimum of attention and adjustment on the part ofthe operator. 1

In' practicing my invention, I prefer, at the sending station, to cause a motion picture film,

or the like, to travel at a fixed rate of speed between an oscillating, curved mirror and a photoelectriclcell. Light froma xed source is focused by the mirror in a line point that moves from side transverselyfof the moving film and, after traversing'the said film, to bemodulated thereby, falls upon the photoelectric cell.

A lenssystem is interposed between the film and the photoelectric cell cathode.' The lens system isjso designed that, in the absence of the moving film, an image of the mirror' is focused upon the cathode of the photoelectric cell, which image does not move during the oscillation of the mirror.v

At the sending station, the light-ray from the mirror is permitted to over-shoot 'on'e edge ofthe 'semi-opaque picture-area of the film and to fall upon the photoelectric cell each time lt overshoots. The output current from the photoelectric cell, therefore. has a component correspondlng to the scanning-frequency of the light-ray, which frequency appears in the final output of the sending station. v

At each receiving station, I provide a cathoderay tube having a plurality of cathode-ray controlling devices disposed therein. One of the controlling ydevices functions to modulate the intensity of the ray in accordance with the received picture-frequencies;1 vanother of the controlling devices functions, under the control of the frequency generated' by the over-shooting ofl the scanning-ray at the sending station, to determine the speed of horizontal movement of the cathode ray, while another of the said controlling devices is periodically dce-energized, in response to an impulse sent out by the sending station each time the space between two pictures-on the film kbeing transmitted, passes before the scanning ray. The last-named.controlling-device determines the periodicity and speed of the vertical movement of thecathode ray and, automatically, adjusts the framing" of the received picture.

The novel features that I consider characteristie of my invention are .set forth with parmssion of messag, pictures' miv the like,V car'. 60 tion itself, however, both as to its organization and itsmetnod or operation. together with edditional obiets and .advantages thereof, ,will best Figure l of the drawing is a view, partly in schematic perspective, and partly diagrammatiaI of the essential elements constituting a nlm-v facsimile sending station comprising a preferred embodiment of my invention;

Fig. 2 is a diagrammatic view of the essential elements of a receiving station' comprising a preferred embodiment of my invention;

Fig. 3 is a view of a portion of a sound-andpicture nlm in its passage through the transmitting apparatus; and.v

Fig. 4 is a diagram to which reference will hereinafter be made in describing the manner in which synchronism is secured.

'I'he apparatus illustrated in Fig. l comprises a nlm-feeding sprocket l over which a motionpicture nlm 2 is drawn by a take-up sprocket 3. Other incidental apparatus, such as nlm-guiding rollers, nlm-magazines, nlm-gates, sources of motive power, belting or gearing, etc., forming no part of my invention and, further, being well known to those skilled in the art. have not been illustrated.

Light from a nxed source I is reflected, as a fine point, onto the nlm from a curved mirror l, the focus of which lies in the plane of the nlm. The mirror is supported for movement about a vertical axis parallel to the nlm and a suitable magnetic structure 6, capable of being energized from a source 1 of alternating current, having a frequency of approximately 750 cycles per second, is provided for causing the mirror to so oscillate that the reflected ray rapidly moves from side to side, transversely of the nlm, as indicated by the arrow 8. It also lies within .the scope of my invention -to anlx the mirror to a tuned reed, or to one of the tines of a tuning fork, and to excite the feed or fork from an oscillation generator of any desired type.

A photoelectric cell l is disposed behind the nlm to receive the light which is reflected there- The output circui of the photoelectric cell comprises avsource li of potential, the secondary windingofa transformer II and agresistor I1, the said output circuit being associated with the input terminals of an amplifier Il through a stopping condenser 2l and a conductor 2i.

connection 21, or it may be coupled to a power is mounted upon a rotatably supported shaft 35 having a ground connection Il.

In addition to the said disc, the shaft carries a sprocket-wheel Il having teeth which are spaced to correspond with marginal openings 38 in the nlm, the said sprocket-wheel being so disposed with respect to the path of travel of the nlm that it is caused to rotate thereby.

The number of teeth in the sprocket wheel is so correlated to the number of cam surfaces 33 that, at each instant when the space between any two picture-frames passes through the path of travel of the scanning ray, the pivoted arm 32 is raised to complete a circuit permitting potentials a't the frequency of the alternating po- I tential source 2l to be impressed across the pri-- through from the oscillating mirror. A lens il,

or a lens-system, is interposed between the nlm and the photoelectric cell, the characteristics of the lens being so chosen that, in the absence of a nlm, an image of the entire mirror is focused on the cathode i2 of the said cell. Movement of the mirror, therefore, does not cause movement of the light spot on the cathode, from side to side and, consequently, the most sensitive portion of the cathode may be continuously utilized. This relative immovabllity of the lightspot is an important feature of my invention since it prevents any modulation of the output of the photo-electric cell, by themere movement of the light ray per sefrom side to side, in addition to the modulation caused by the light and dark portions of the nlm and the overshooting" hereinbefore mentioned.

In order to prevent the light ray from overshooting at both transparent margins of the pictures, whereby a frequency twice the scanning-frequency would appear in the output of the photoelectric cell, and to prevent a soundrecord I3, if present on one of the edges of the film, from interfering with the transmission o f the pictures, I interpose an opaque mask 'I4 between the mirror and one of thesaid edges, as indicated also in Fis. 3.

soi

mary winding of the transformer and, consequently, to induce corresponding potentials across the input circuit of the amplifier I8. In order that framing" of the picture may be expeditiously accomplished at the transmitter, in the event that the sprocket holes are not properly spaced with respect to the picture-elements, it is desirable to provide the arm 32 with supporting means (not shown) whereby it may be so ad- Justed, circumferentially of the disc ll, that the framing impulses occur earlier, or later, in the travel of the film.

In the operation of the sending station just described the nlm, in its travel from the storagereel to the take-up reel, is subjected to the oscillating scanning ray from the mirror, which ray, after its passage through the nlm, falls upon the photoelectric cell to modulate the output therefrom in accordance with the transparent and opaque portions of each picture-frame.

two frames passes through the path of the scanning-ray, the circuit including the source 28 is closed, by the movement of the pivoted arm 32, and thev output of the transmitter is, accordingly, modulated at the frequency of the said source. The manner in which the periodic modulation of the carrier-wave is utilized, at the receiving stations, will be explained, in detail, later.

Each time lthe scanning-ray overshoots, the margin of the lm that is not shielded by the mask, a momentarily larger pulse of current ap- During4 those instants when the opaque space between pears in the output circuit oi the photo-cell. these current-pulses being at the frequency' ,y u

.The carrier-wave is, therefore, also modulated at the scanning-frequency, which modulation is utilized, at the receiving stations, to control a similar scanning'operation. It should be clearly understood from the foregoing description, that theiv'requencies representative ofthe picture. the scanning-frequency impulses and the impulses introduced into the amplifier from the source 28 do not overlap, but are separated, each from the others, by definite time-intervals. The carrier1 wave, therefore, is modulated by these three frequencies which, hereinafter, will be designated always as picture, scanning and framing frequencies, respectively, without the slightest interference existing between them.

The apparatus at a receiving station comprises an energy receptor constituted by an antenna f l0, a tuning condenser 5l, an inductor 52 and a.

ground connection 53. The energy receiving circuit is coupled .to a radio-frequency amplier 5l, of any suitable type, which ampliiler is followed by a detector and audio-frequency amplifier 55. The output from the audio-frequency amplifier isimpressed upon a filter which passes the framingfrequency only, a second filter 51 which passes the scanning-frequency and upon the primary winding of a transformer 58.

The receiving apparatus further comprises a rier wave. impressed thereon by the overshooting of the scanning-ray, when impressed upon the input circuit of the oscillation generator 12, tends `f to pull it into synchronism therewith. The deflection of the cathode ray in the receiver in the The plate 51, oi' the pair of plates in the cathode-ray tube that control the deflection of the electron stream in the direction of the arrows C-D, is connected to ground, and the opposite i plate 55 is connected, by a metallic conductor 14 to the anode 15 of a thermionic rectifying device 15. the cathode 11 of which is ,connected to ground through a source of potential 18.` A plurality of adjusting condenserg lil and 8l are connected, in shunt, to the condenser constituted by the deilecting plates 55 and 51 and, therefore, in shunt to the cathode and anode of the rectifying device 16. v

The function of the rectifying device is to build up a charge upon the deilecting plates 65 and 51, and upon the condensers 5l and 0I in order that the cathode ray shall be deilected, in the direction of the arrows C-D. proportionally thereto. The deflection of the said ray in the direction `(1'D corresponds to that coordinate of the scaning operation at the transmitting station which cathode-ray tube 55 of the type having a thermionic cathode 5i, a control-electrode 62, an anode 5,3, a plurality of plates 6l and 55 for dei'lecting the electron stream in a direction indicated by the arrows A-VB, and a plurality of plates 65 and S1 for deecting the electron stream in a direction C-D at right angles to the direction A-B. The control electrode t2 of the tube is .connected to the cathode thereof through a source 68 of biasing potential andthe secondary winding of the transformer 55.

Although I have shown the controlling plates 64, 65. 66 and i1 as being disposed within the tube, it should be distinctly understood vthat the said plates may be supported exteriorly thereof and that deilecting coils may be substituted for the plates 64 and 55 without departing from the spirit of my invention. y

The potential gradient between the control electrode of the cathode-ray tube and the cathode thereof comprises two components. an unidirectional biasing-potential from the source B5 and an alternating potential, representative fof the picture-modulation of the incoming signal from the transformer 58. Since the magnitude of the electron stream between the cathode and the anode is a function of the potential between the control electrode and the cathode, and since the brilliance of the fluorescence of the screen at the end of the tube is at very instant a function of the magnitude of the electron stream, or

cathode ray, passing through the anode. the said` brilliance is always proportional to the picture modulation.

'The deilecting plate 85 is connected to ground, and the opposite deflecting plate 54 is connected. by a conductor 1l, to the anode 1i, of a therm'ionicv device 12, so disposed and connected as to normally generate oscillations at the scanning frequency.y v

The input circuit of the thermionic device comprises a resistor Il which is included in the output circuit of the scanning-frequency filter 51'. The scanning-frequency modulation -of the caris introduced by the motion of the film longitudinally thereof. The size of the adjusting condensers lll and 5I and the potential of the source 15 are so chosen thatv the charge upon the deflectingplates in the Braun tube will build from zero to the desired maximum during the time rev quired for the lm at the transmitter to travel a densers 80 and 8| are charged at straight linear charge as shown in Fig. 4.

Accordingly, if at the instant the light from I the oscillating mirror starts to traverse ina given picture frame, the charge upon the deecting plates 56 and 61 is zero, or substantially zero, the successive portions of the path traced by the scanning ray on a single picture-frame of the lm will be represented by successive shifts of the electron stream in the Braun tube .in the direction of the arrows CD.

In order, therefore, that the defiecting plates 66 and 51 shall be completely discharged at the beginning of the scanning operationv of each individual picture-frame at the transmitter, means are providedvwhereby their charge is controlled by theframing-frequency impulses sent out by the transmitting station each time the framingv pose I have advantageously employed a grid-glow,v

tube Sii, having a plurality of cold electrodes namely, an anode 9|, a cathode 92 and a grid 93, and being of the ty-pe disclosed and claimed in the copending application of Dewey D. Knowles, Serial No. 149,290, filed November 19, 1926, and assigned to the Westinghouse Electric and Manu' facturing Company. 'I'he grid-glow tube has the property of changing from a non-conductive to a conductive state, depending upon the potential applied to the grid thereof, with substantially inappreciable time-lag.

The input circuit of the grid-glow tube comprises a resistor I and a source 95 of potential for biasing, the device, normally. to the nonconductive state. The resistor is included in series with a condenser I8, in the output circuit of the framing-frequency filter 56.

Each incoming impulse at the framing-frequency impressed across the condenser, overcomes the bias from the source Ol. causes the grid-glow tube to assume the conductive state and to, accordingly, deprive the defiecting plates I8, and 61 of the charge they have acquired during the scanning of a single picture-frame at -the transmitter.

The periodic charge and discharge of the deflecting plates is illustrated graphically in Fig. 4, wherein distances on the Y axis represent potentials existing across the said plates, and disf tances across the X axis are representative of the time.

From an inspection of Fig. 4, it will lbe noted that the potential across theplates is indicated as rising gradually from zero to its maximum in a period of one-twentieth of a second, and then dropping quickly to zero to again repeat. The charging period indicated corresponds to a fllm speed of substantially pictures per second, which speed is satisfactory for the transmission of sim-facsimiies with the iuusion or motion. Ir it is desired to transmit a combined picture and sound film, thefilm speed may be increased and the condensers Bl and 8i may be reduced in capacity proportionally in order that they shall so acquire their charge in a shorter space of time.

The scanning frequency has been indicated as 750k cycles per second, and the framing-frequency as 1200 cycles .per second. These frequencies are not at all fixed, however, it being only necessary that the frequency of scanning be sumciently different from the framing frequency that they may be separated easily at the receiver. Although the framing of the received picture in the direction C--D is automatically accomplished through the medium of the controlled oscillation generator 12, it is feasible to superimpose a certain measure of manual control at the receiving end. One way in which this may be accomplished is by momentarily altering the capacity of the condenser 8l, which influences the rate at which the deflecting plates Si and t1 receive their charge from the rectifying device. .A certain measure-of control may also be had by varying the resistor 9i connected across the input terminals of the grid glow tube. by manipulating a variable condenser i0!! connected in shunt to the transformer which impresses the framing-frequency across the rectifier, or by a1- tering the potential supplied by the source 'Il systems wherein a visual image of a moving object, such as a person. is produced at a distant point. In such case, the object may be scanned, in one direction, by a ray of light from a rapidly oscillating mirror, the said ray, in its passage from the mirror to the object. being reflected from the surface of a slowly rotating. polygonal mirror to cause it to move slowly in a direction at right angles to the first-mentioned direction. Means, equivalent to the cam-disc Il and the arm 82, may be associated with the polygonal mirror to send the framing (impulses whenever the ray reaches the end of its slow travel, thus introducing the component of the scanning operation provided for by the movement of the film in the system hereinbefore described. The scanning frequency may be developed, in the output of a photoeiectric cell in the modified system, by disposing either a bright surface or a dull surface at one side of the object, on which the scanning ray falls when it overahoots.

My improved facsimile transmission system is mainly advantageous in that it permits the utilization of a single carrier wave for the propagation of the picture frequencies and all of the necessary synchronizing frequencies as well.

Another important advantage of my improved system lies in the disposition of the lens system.

between the film and the photoelectric cell. whereby the image of the mirror does not move, at the point where it falls upon the cell, even though the point of light focused by the mirror is moving transversely of the film. The movement of the ray per se, accordingly, vacross the space normally occupied by the film, does not cause any modulation of the photo-cell output and the generation of interfering harmonic frequencies is thus prevented.

Although I have chosen a Aspecific embodiment of my invention for purposes of illustration and description, modifications thereof will be apparent to those skilled in the art. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art or by the spirit of the appended claims.

I claim as my invention:

l. In a facsimile transmission system, means for continuously subjecting an object to a scanning-ray, means energized by said ray for generating a synchronizing frequency and means controlled, by said object for generating an additional synchronizing frequency.

2. In a facsimile-transmission system, means for moving an object, means for subjecting said object to the action of' a scanning-ray, means for generating a carrier-current land for modulating it in accordance with the scanning ray as modified by said object, and means whereby said object and said ray cooperate to generate a synchronizing' frequency for modulating said carrier-current, and additional means ,controlled by the movement of said obiect for periodically modulating said carrier-current.

3. The apparatus covered inv claim l in combination with receiving means comprising a scanning device responsive to both of the said synchronizing frequencies.Y

4. The apparatus covered in claim 2 in combination with receiving means comprising a scanning device responsive to the synchronizing frequency and to the said periodical modulation of the carrier current.

5. In combination, a tube of the cathode ray type having means in proximity thereto for deflecting said cathode ray, a storage condenser comprising a. grid controlled gaseous discharge tube, a charging and storage circuit associated therewith, and means responsive to signaling impulses above a predetermined amplitude only for 5 initiating a gas discharge and permitting said storage circuit to relieve itself.

VLADIMIR K. ZWORYUN.

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