US1786812A

US1786812A - Facsimile-transmission system

Info

Publication number: US1786812A
Application number: US349956A
Authority: US
Inventors: Vladimir K Zworykin
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1929-03-26
Filing date: 1929-03-26
Publication date: 1930-12-30
Anticipated expiration: 1947-12-30
Also published as: BE368861A; USRE19314E; DE582929C; FR692302A

Description

Dec. 30, 1930. v ZWORYKIN 1,786,812

FACSIMILE TRANSMISSION SYSTEM Filed March 26, 1929 Fig. 2.

INVENTOR Vladimir/i. Zwaryhfl.

WET M/ V ATTORNEY Patented Dec. 30, 1930 UNITED STATES VLADIMIR K. ZWOBYKIN, OF SWISSVALE,

PENNSYLVANIA, ASSIGNOB TO WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA racsmrnn-rmsurssron srsrnm R S S U E 0 Application filed March 26, 1929. Serial m. 349,956.

My invention relates to facsimile-transmitting systems and it has particular relation to systems especially adapted for the reproduction, at a distance, of moving-picture films.

One of the most troublesome problems connected with television systems and with systems for transmitting pictures and the like is that of securing motional synchronism between a scanning device at the sending station and an equivalent device at the receiving station. In systems adapted for distant reproduction, at one or more points, of a moving picture film, the difiiculty of synchronization is increased by reason of the fact that the film, at the transmitting station, must be caused to pass in front of the scanning device at the same rate of speed that it traverses an ordinary moving-picture projector.

It is, accordingly, an object of my invention to provide an improved facsimile-transmission system wherein synchronism between a scanning device at a sending station and an analogous device at a receiving station is automaticall maintained.

Another 0 'ect of my invention is to provide a facsimi e-transmission system particularly adapted for the reproduction, at a distance, of moving-picture films.

In practicing my invention, I prefer, at the sending station, to cause a motion picture film to travel at a fixed rate of speed between an oscillating mirror and a photoelectric cell. Light from a fixed source is directed against themirror, and, after reflection therefrom, is focused to a fine point that moves from side to side of the moving film. Assuming that the film is moving vertically, the vertical component of the scanning motion is accordingly, provided for by the motion of the film, while the horizontal com onent is taken care of by the mirror-oscillatlons.

At the receiving station, I provide a Braun tube having a plurality of cathode-ray controlling devices mounted therein. One of the controlling devices functions in accordance with the output from the photoelectric cell at the sending station and serves to impose variations upon the amplitude of the ra another of the controlling devices causes t e ray to move horizontally to synchronism with the oscillating mirror at the sending station; while still another controlling device periodically deflects the ra vertically at a speed equal to the linear a Vance of the film at the sending station.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment, when read in connection with the accompanying drawing.

Figure 1 of the drawing is a diagrammatic view of a facsimile-transmission system comprising a preferred embodiment of my invention; and A Fig. 2 is a diagram to which reference will hereinafter be made in describing the manner in which synchronism is secured.

The apparatus illustrated in the drawings comprises a film-storage reel 1 from which a motion-picture film 2 is withdrawn by a take-up reel 3. Neither motive power for the storage reel nor various incidental ele- V ments of the device, such as a guiding tube through which the film passes, lens systems, etc., are illustrated. K

Light from a fixed source 4 is reflected upon the film from an oscillatory mirror 5 that is so arranged as to periodically cause the reflected ray to pass from side to side of the film as indicated by the arrow A. Any suitable means may be provided for causing the mirror to oscillate, such means being indicated by an inductor 6 energized from a source 7 of alternating current.

A photoelectric cell 8 is disposed immediately behind the film to receive the light which is reflected therethrough from the mirror 5. As the film travels in a downward direction, indicated by an arrow B, the ray of light reflected from the oscillatory mirror 5 I falls upon each frame of the film in a zigzag path, the longitudinal distance on the film between successive reversals of the path being a function of the speed of travel of the film and the rate of vibration of the mirror.

The light falling on the photoelectric cell is, at any instant, proportional to the transparency of the film, fluctuations in the output current from the cell, accordingly, being representative of the variations in density of the film where it is exposed to the scanmug-ray.

By choosing the oscillation frequency ofthe mirror sufficiently high, in comparison with the film-speed, the scanning can, obviously, be accomplished by as fine a pencil of light as desired and the film can thus be transmitted with great fidelity.

The output current from the photo-cell, after the requisite amplification, is utilized to modulate a carrier-wave, in any well known manner, for either radio transmission to the distant receivers, or transmission thereto over metallic conductors. In order to simplify the drawing, the miscellaneous apparatus, incident to the amplification of the photo-cell current, the generation and modulation of the carrier-wave, the coupling devices for impressing the carrier current on the transmitting medium, etc., have been illustrated merely as a rectangular cabinet 9.

One of the output terminals of the transmitting apparatus 9 is connected to a distantly situated receiver 10 by a conductor 11 and the other terminal has a connection 12 to ground.

The receiver 10, preferably, comprises a pluralityofhigh-frequencyamplifyingstages, a demodulator, and an audio-frequency amplifying stage if the picture transmission is accomplished through the modulation of a carrier-wave. The particular type of receiver, however, constitutes specifically no part of the present invention, it being merely necessary to provide receiving apparatus of conventional type that will give an output proportional to such characteristic of the received signal that represents the varying translucence of the transmitted film. The amplitude of the output must be suflicient to control the magnitude of an electron stream in a Braun tube 13 and, consequently, the brilliancy of the fluorescence where the cathode stream therein strikes a screen at the end of the tube.

The Braun tube is preferably of the type having a thermionic cathode 14, a control element 15, an anode 16, a plurality of

plates

17 and 18 for deflecting the electron stream in a direction indicated by the arrows A-B, and a plurality of plates 19 and 20 for defleeting the electron stream in a direction C-D at right angles to the direction A.B

The control electrode 15 of the Braun tube is connected to the cathode thereof through a source 21 of biasing potential and the secondiry winding 22 of a transformer. The primary winding included in the output circuit of the receiver 23 of the transformer is 10. The potential radient between the control electrode and t e cathode comprises two com onents, a direct-current biasing potential rom the source 21, and an alternatin potential representative of the picture-m ulation of the incoming signal. Since the magnitude of the electron stream between the cathode 14 and the anode 16 is a function of the potential between the control-electrode and the cathode and, since the fluorescence of the screen at the end of the tube is a function of the magnitude of the electron stream or cathode ray, passing through the anode, the brilliance of the said fluorescence is, at any instant, proportional to the picture-modulation.

The deflecting plate 18 is connected to ground, and the opposite deflecting plate 17 is connected, by a conductor 24, to one of the terminals of the alternating-current source 7 that causes the mirror to oscillate. terminal of the alternating-current source is connected to ground through the actuating winding 6 of the oscillatory mirror.

The plate 20 of the pair of plates in the Braun tube that control the deflection of the' electron stream in the direction of the arrows CD is connected to ground, and the opposite plate 19 is connected, by a metallic conductor 25, to a fixed contact member 26 that is normally disconnected from a movable grounded contact 27.

As the film travels from the storage reel to the take-up reel, it is driven by a toothed wheel 28, the projections 29 of which engage a series of marginal perforations 30 in the film. The toothed wheel is connected, through a shaft 31, to a disc 32 that is provided with a plurality of peripheral projections 33. The free end of the contact member.

27 normally rides upon the periphery of the disc 32, except at such times as the projections 33 engage it. The diameter of the disc and the number of projections thereon are so chosen that one of the projections raises the movable contact member 27 to engage the contact member 26 at each instant during the travel of the film that the scanning ray is about to leave the upper edge of one of the picture frames.

The plates 19 and 20, in the Braun tube, are connected across a condenser 35 having a Vernier condenser 36 disposed in'shunt thereto. The condenser 35 is so disposed as to be charged from a source 37 of constant current, a rectitfying device 38, operating at or near saturation, preferably being utilized for placing the charge on the said condenser.

In theopcration of the system as described, the film, in its travel between the store e and take-up reels, is exposed to a beam 0 light from the oscillating mirror that moves from side to side across it at a frequency corresponding to that of the alternating-current source. At the same time, since one terminal traverse the moving of the alternating-current source is connected to groiind throu h the actuating winding of the mirror, an the other terminal is connected to ground through the capacity existing between the pair of deflecting

lates

17 and 18 nearest the anode in the raun tube, the electron stream in the said Braun tube oscillates from side to side in the direction of the arrows A--B at the same frequency that the ray of light is being caused to One coordinate of the scanning operation, at the receiver, is, accordingly, provided by the direct connection between the alternatingcurrent source that actuates the mirror and the first pair of deflecting plates.

It is necessary, however, to provide the coordinate of the scannin operation corresponding to the longitudinal motion of the film at the transmitting end. This coordinate is provided by the gradual building up, from the rectifying device, of a charge upon the condenser connected across the pair of deflecting plates 19 and 20. The size of the condenser and the potential of the source are so chosen that the charge upon the condenser plates will build from zero 'to the desired maximum during the time required for the film at the transmitter to travel a distance corresponding to the distance between the centers of the spaces bounding a single picture-frame of the film.

Accordingly,if, at the instant the light from the oscillating mirror starts to traverse any given picture frame, the charge upon the defleeting plates 19 and 20 is zero or substantially zero, the successive portions of the path traced by the scanning light on the film will be represented by successive shifts of the electron stream in the Braun tube in the direction of the arrows 0-1), the rate of shift being determined by the rate at which the condenser charges and being made equivalent to the film-speed.

In order, therefore, that the condenser shall be in the discharged state at the beginning of the scanning operation of each picture frame, the peripheral projections iipon the disc are so chosen and spaced that the contact 26 is connected to ground, by reason of the engagement therewith of the contact member 27, at each instant when the light ray ffom the oscillating mirror strikes a point midway between successive frames of the moving film.

The periodic charge and discharge of the condenser is illustrated graphically in Fig. 2, wherein distances on the Y-axis represent potentials existing across the pair of deflecting plates 19 and 20, and distances along the X-axis are representative of time. From an inspection of Fig. 2, it will be noted that the potential across the condenser is indicated as rising gradually from zero to its maximum in a period of 1/20th of a second and then dropping quickly to zero. The charging period chosen corresponds to a film speed of substantially 20 pictures per second, which speed is ample for. the satisfactory transmission of pictures.

If it is desired to transmit a combined picture-and-sound film, the film speed may be increased and the condenser may be reduced in capacity, proportionally, in order that it shall acquire its charge in a shorter space of time.

Although not illustrated in the-drawing, in certain instances, it has been found necessary to interpose loading coils in the conductors extending between the transmitting and the receiving station in order that the distributed capacity of the lines shall not prevent proper synchronization of the electron-stream travel in the receiving tube with the rate of oscillation of the scanning mirror and the film speed at the transmitting end.

It is quite feasible to dispense with all metallic conductors between the transmitting and the receiving stat-ions and to utilizeseparate carrier frequencies for conveying both the timing impulses and the picture impulses, or these impulses may be conveyed as separate modulations over the same carrier wave. Various methods for substitu' ing radio transmission for metallic conductors are well known to those skilled in the art to which my invention pertains and I have, accordingly, not illustrated any specific apparatus for adapting my invention to radio.

Itwill accordingly be apparent that I have provided a novel method of securing synchronism between a scanning operation at the transmitting end of a television or facsimile-transmission system and the scanning operation at the receiving end. The rate of shift of the cathode ray may be very accurately correlated to the film-speed and, since the beginning of the scanning operation for each picture frame at the receiver is posi tively controlled by the movement of the film at the transmitter, the received picture is remarkably free from the usual annoying tendency to move out of frame.

Although I have chosen a specific embodiment of my invention for purposes of illustration and description, many 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:

1. In a television system, means for causing a local scanning operation in s nchronism with a distant scanning operation and ing a local scanning operation in syn chronism with a distant scanning operation and means for introducing a periodic 1nodification of said local scanning operation in accordance with a movement of an object subjected to said distant scanning operation.

3. In'a television system, means for causing a local scanning operation in synchronism with a distant scanning operation and means for causing a periodic repetition of said local scanning operation in accordance with a movement of an object subjected to said distant scannin operation.

4. In a television system, means for causing a local scanning operation in one dimension-in synchronism with a distant scanning operation and means for causing periodic repetition ofcsaid local scanning operation in accordance with a movement of an object subjected to said distant scanning operation, whereby two dimensional scanning is locally obtained.

5. In a television sys'em, electromagnetic means for causing a local scanning operation in synchronism with a distant scanning operation and electrostatic means for causing repetitions of said local scanning operation in accordance with a movement of an object subjected to said distant scanning operation.

6. In a television system, electromagnetic means for causing a local scanning operation in syhchronism witha distant scanning operation, electrostatic means for causing repetitions of said local scanning operations and means whereby the influence of said electrostatic means on said scanning operation is controlled-in accordance with a movement of an object subjected to said distant scanning operation.

7. In a television system, receiving apparatus including a ray-receptive screen, means for generating a ray, means for causing said ray to traverse said screen in one dimension in accordance with a distant scanning operation and means for causing said my to repeatedly traverse said screen in accordance with a movement of an object subjected to said distant scanning o eration.

In testimony whereof, have hereunto subscribed my name this 19th day of March,

VLADIMIR K. ZWORYKIN.