US2219120A - Facsimile system - Google Patents

Description

Oct. 22, 1940.

F. J. SOMERS FACSIMILE SYSTEM 2 Sheets-Sheet l Filed March 2'7, 1935 ||Il T mm m m m V F mw Mn m K :R M M m v V. B m. T mm R- w m m 1 bob? c. M 5 m a 380 |..l| 1lL Oct. 22, 1940. F. J. SOMERS FACSIMILE SYSTEM Filed March 27, 1935 2 Sheets-Sheet 2 SCANNING /0.2 OSCILLATOR INVENTOR,

FRANK J. SOME/PS.

Y ATTORNEYS.

ANODE SUPPL Y Patented Oct. 22, 1940 UNITED STATES FACSIMILE SYSTEM Frank J. Somers, San

Jose, Calif, assignor, by

mesne assignments, to Farnsworth Television & Radio Corporation, Dover, Del., a corporation of Delaware Application March 27, 1935, Serial No. 13,252

9Claims.

My invention relates to a system for transmission of visual information at a distance and relates more particularly to a system designed to transmit facsimile. images.

Among the objects of my invention are: To provide a facsimile system wherein transmission is satisfactory over a circuit or channel where the signal-to-noise ratio may be as low as 3 to 1; to provide a system adapted for the transmission and reception in black and white of line drawings, handwriting, printed matter, or the like; to provide asystem adapted for the transmission of printed matter and accompanying line drawings en bloc. To provide a facsimile system having minimum inertia limitations; to provide a facsimile system wherein enlargement or reduction may be made in the size of the reproduced image from that of the original field; to pro vide a system for the transmission of news print to a distant point, utilizing the lower grades of commercial channels, either wire or radio; to provide a system of facsimile having a minimum interference factor; to provide a facsimile sys-, tem capable of operating at high speed; to provide a facsimile system utilizing desirable characteristics of a grid-controlled arc rectifier; to provide a facsimile system wherein amplitude changes during transmission have a minimum effect upon the received image; to provide a facsimile-receiving system giving a simultaneous recording and visual image; to provide a facsimile-receivlng system wherein information can be instantly made available upon reception and be preserved in recorded form thereafter; to provide a facsimile system wherein a minimum amount of time is consumed in transmission and visual reception; to provide a facsimile system utilizing the desirable characteristics of cathode ray tubes; to provide a simple and efiicient means and method of transmitting facsimile images over wire or radio channels; and to provide a preferred facsimile system utilizing at least in part certain desirable characteristics of any or all of the inventions disclosed and claimed in the following patents and application:

Patent No. Issued Philo T. Farhsworth, 1,773,980, Aug. 26-, 1930; Philo T. Farnsworth, 1,970,036, Aug. 14, 1934; Philo T. Farnsworth, 1,986,330, Jan. 1, 1 935; Philo T. Farnsworth, 2,026,374, Dec. 31, 1935; Philo T. Farnsworth, 2,037,711, Apr. 21, 1936; Farnsworth and Lubcke, 2,059,219, Nov. 3, 1936; Philo T. Farnsworth, 2,059,683, Nov. 3, 1936; Gardner and Brolly, 2,079,163, May 4, 1937; Philo T. Farnsworth, 2,099,846, Nov. 23, 1937; Robert E. Rutherford, 2,135,149, Nov. 1, 1938; Philo T. Farnsworth, 2,140,284, Dec. 13, 1938; 1

Serial No. Filed Farnsworth, 449,984, May 5, 1930; and others.

Other objects of my invention will be apparent or will be specifically pointedout in the description forming a part of this specification, but I do not limit myselfto the embodiment of the invention herein described, as various forms may be adopted within the scope of the claims.

In comparing facsimile and telephoto transmission it will be found that facsimile is, in a number of respects, accomplished with simpler equipment. Defining the terms as herein used, telephoto transmission comprises the transmission of an original picture field and the reproduction of that field at 9. preferably distant receiving station in all its intermediate shades or half tones. On the other hand, facsimile transmission does not attempt to transmit half tones, but merely transmits the extreme contrasts of black and white. There is thus removed from the problem of facsimile the necessity "of transmitting fine variations of amplitude due to closely adjacent shades in the original picture field. I have found that whereas suitable telephoto transmission requires adequate phase correction and a signal-to-noise ratio of at least 20 to 1, satisfactory facsimile transmission can be carried on over a radio circuit or other channel in accordance with my present invention where the signal-to-noise ratio is as low as 3 to 1. Consequently, a less expensive channel can be used for facsimile and transmission can be in the form .of interrupted uniform amplitude impulses without the necessity of amplitude modulation. No substantial phase or frequency corrections are necessary, if the radio circuits and equipment are designed with ordinary care according to practices well known to the art.

For certain classes of facsimile service, as for example, the transmission of printed matter en bloc where the only detail requirement is legibility of the received image, further savings can be effected because satisfactory results can be obtained with methods of, and apparatus'for, transmission, reception and synchronization much less precise and accurate than those required either in systems for telephoto transmission or television transmission.

I have found that there are certain desirable characteristics inherent in the Farnsworth system of electronic scanning, as exemplified, de-

I describe herein a preferred embodiment of apparatus to illlustrate my invention;

In the drawings, Figure 1 is a circuit, diagrammatic and reduced to simplest terms, of a transmitter arrangement for sending over a radio channel impulses arising from scanning news print or similar subject matter.

Figure 2 is a similarly schematic diagram showing the main features of a receiving set adapted to receive images from the transmitter of Figure 1 and combining the impulses received therefrom into a visual image which may be viewed by an operator and/or recorded on a sensitized film or paper.

As to apparatus, my invention broadly comprises a facsimile system giving a continuous process of transmission from. tape or belt at the sending end, and production of corresponding automatically developed photographic tape images at the receiver; together with an instantaneous visual indication of parts of the picture or newsprint at the receiver so produced that a considerable part of the picture or several lines of newsprint remains visible for a sufllcient length of time so that the print may be read or the quality of the received picture ascertained without the necessity of waiting for development.

Referring to Figure 1 for a description of my preferred form of facsimile transmitter, the subject matter to be scanned is preferably in the form of a printed paper tape H which may comprise one, two or more columns of news print.

The paper is progressed preferably at uniform speed from a magazine not shown, by a drive wheel II. The drive wheel l2 is'preferably maintained at a uniform rate of rotation by a synchronous motor l4 which in many cases may wellfbe an alternating current synchronous motor opsuch controlled frequencies are riot available,

motor I4 may be controlled by tuning forks or similar devices as is well known in the art, and the receiver motor may be similarly controlled and synchronization maintained in any one of the customary methods. As this is no part of the instant invention, no further reference will be made to this portion of the apparatus.

While it is possible to arrange the optical system at the transmitter so that images of either translucent or opaque subjects can be focused on cathode IQ of dissector tube 20, the optical system for opaque subjects only is, for the sake of clarity in describing the system, shown in Figure l. A lamp i5 is positioned in front of the tape II and the light therefrom is directed by means of a reflector i6 onto a picture field comprising a portion of the tape l i. Light is reflected therefrom, passed to a lens I! and focused thereby on a photo-sensitive cathode is of an electronic scanning device or dessector tube 20, such as that described and claimed in the Rutherford Patent No. 2,135,149, listed above, the operation of which is fully described and claimed in the Farnsworth Patent No. 1,773,980 listed above.

The path of the light into the dissector tube is indicated by a 1ine-of arrows 2|. The dissector tube comprises an envelope surrounding the cathode l9 and is provided with a target finger 22 having therein an aperture 23 through which electrons emitted from the cathode I! may pass to impinge upon a collecting anode 24. The finger 22 is energized at a positive potential by means of an anode battery, and the cathode is grounded to the negative end of the battery through a battery 26. Under the impact of the light in the image falling on the cathode ll electrons are emitted from the photoelectric surface thereof in proportion to the intensity of the light strikingthe various portions of the cathode and are drawn thereafter towards the finger 22, meanwhile being kept in parallel array by means of afocusing coil 21 energized by a focusing source 2! under the control of a rheostat 30. There is, therefore, formed in space an electrical image, each elementary area of which corresponds in electron intensity to the intensity of the light falling upon elementary areas of the cathode it. Thus, only a certain single elementary area of the electron image will enter the aperture 23 in the finger, providing the electron image is left undisturbed. For the complete action of the focusing coil reference may be had to Farnsworth Patent No. 1,986,330, listed above.

If, however, the electron image is scanned past the aperture, other elementary areas of the electron image will enter the anode aperture 28 and fall upon the inner anode 24. Horimntal scansion is accomplished by the use of a magnetic scanning coil 3| which is supplied with a saw tooth current from a scanning oscillator I2 either as described in the Farnsworth and Lubcke Patent No. 2,059,219, above, referred to or in other ways well known in the art. Thus, as the tape ll progresses, horizontal scanning takes place, one line following another as the tape moves along its course. The distance between lines will of course be regulated by the speed of the tape II and the frequency of the scanning oscillator. These factors are, of course, under the control of the operator and may be regulated to suit atmospheric conditions and other requirements of the service.

During scansion, electrons entering the scanning aperture 23 fall upon the collecting anode 24 to create a current which passes through the signal resistor 34 to cause a potential difference which is then applied to the grid 35 of an amplifler tube 3'6. The output of this tube is passed through an output resistor 31, the tube being energized in the usual manner by amplifier sources 39, and thence led to the grid of a thyratron or a grid-controlled are rectifier having the usual grid condenser 40A and leak 408. Such tubes are well known in the art. If supplied with an alternating anode voltage, current will start when the voltage on grid 40 becomes more positive than the critical value for breakdown, and will flow from cathode-42 to anode 43 thereof for the remainder of the cycle, or for succeeding cycles as long as the grid is so energized. I prefer to bias the grid 40 by potentiometer assembly 400.

I then energize the anode 43 of this rectifier by an oscillator 44 which may conveniently be an inductor alternator operating. for example, at two thousand cycles and two hundred and fifty volts, giving an output of one hundred watts. The output of the rectifier tube is led to a keying resistor 45 and key leads 46 taken from opposite ends of this resistor and led to the input 41 of a radio set including an oscillator, buffer, amplifier, and radio-frequency amplifier, which radiates energy into space by means of an antenna system 49. This entire radio equipment may be conventional and is shown in Figure 1 as enclosed by the dotted line 50. It should be understood that the radio set as described is not a telephone set, but is the ordinary type of radio code transmitter and it may be considered that.

the grid-controlled rectifier, passing current from the oscillator 4|, is merely keying the radio set to send out impulses of equal size and duration" but in varying groups as determined by the energization of the grid of the rectifier tube which in turn is controlled by the output of the dissector tube 20. I also prefer to utilize a portion of the output of the scanning oscillator 32 after passing through a pulse amplifier ii to energize the grid of the rectifier tube ll in order that a synchronizing signal be sent over the radio transmitter at the end of each scanning line.

Thus, I provide a facsimile system wherein a radio code transmitter sends out impulses of equal size and duration, these impulses being broken into groups of varying lengths in accordance with the impulses received from a cathode ray dissector tube having a cathode receiving light from the field to be transmitted, and also groups of elementary spot of light to which dissector 20 can respond.

0 Turning to Figure 2 for a description of the receiving equipment, impulses radiated by the transmitter of Figure 1 are received on a receiving antenna 52 and led to a radio receiver 54 of the usual type, the output from this receiver being led to the control grid of a receiving grid-controlled rectifier tube 55. The bias of this grid can be adjusted by the usual potentiometer battery assembly 56. The anode 51 of this'grid-controlled rectifier is energized by a receiving oscillator which may be, for example, an inductor alternator operating at 5,000 cycles. It is not necessary of course that the output of this receiving rectifier be as large as similar tubes used in the transmitter as here-the power necessary to operate subsequent apparatus is not nearly so great as the power required to key the radio transmitter. A vacuum tube oscillator can also beused. v

The potential drop across an output resistor in the anode circuit of the rectifier tube ills led through anoutput lead 8| first to energize the grid I! of a visual cathode ray tube 64 and also to the grid 65 of arecording cathode ray tube 66 through blocking condenser 61 and 69, respectively. The grids of both cathode ray tubes are biased by the usual potentiometer battery assemblies 10-40 attached to the grid at one end through grid resistors 1 l1 I and at the other end to filament power transformers 12-12 connected to the filaments 14-14 of the respective cathode ray tubes. Both anodes 15-15 of the respective tubes are energized from the common anode supply 16 and each of the tubes is provided with a focusing coil assembly 11, in order to provide a sharp spot for the cathode ray beam on both the visual cathode ray tube screen 18 and the recording cathode ray tube screen 80. A portion of the output energy from the receiving rectifier tube 55 is passed through a blocking condenser 8| to a pulse amplifier tube 82 and is used to control the oscillation period of a receiving scanning oscillator 84 through grid transformer 85 which also carries the windings 88 for the output of the scanning oscillator. The output is transmitted through pulse leads 81 and divided between a horizontal visual tube scanning coil 89 and a horizontal recording tube scanning coil 90. Thus, the scanning pulses, which are transmitted at the end of each scanning line, are utilized to control the oscillation of the receiving scanning oscillator so that horizontal synchronization will be exact. Automatic synchronization is thus obtained.

Positioned to receive light from the recording tube screen It is a lens train 8| forming a portion of a camera case 92 enclosing a reel 93 of film or sensitized paper 93 which is passed over a drive roll to intercept the light beam focused thereon by the lens 8|. The drive roll 84 is rotated by a synchronous motor 85 which, as explained ,8

above, may be attached to the alternating current mains so as to maintain synchronism with the transmitter or may be tuning-fork controlled as is well known in the art. The. film or paper passes from the camera into a developing case 96 '0 through developing chambers 91 and 98 thence to a dryer not shown and finally emerges in the form of an exposed developed and dried record I09. I do not wish in any way, however, to be limited to this particular form of recording device as I there are many others which will suggest themselves to those skilled in the art in order that a fixed and permanent image on a record from a source of light be created, and the particular means shown is not essential to my invention.

1 also provide for the visual cathode ray tube 64 a vertical scanning coil ill supplied with impulses from a visual tube scanning oscillator I02. I prefer to utilize a certain definite type of material for the visual tube fluorescent screen 19, preferably a screen formed from a material having a time lag. It is well known in the art that printed matter can be reproduced with a minimum of five scanning lines and I prefer to have the time lag of the monitor tube at least sufficiently long so that five scanning lines will appear on the screen at the same time so that completely formed printed matter will be visible. In case a large number of head lines or similar higher letters are to be transmitted, I prefer to have the time lag of considerable length; in fact, I have found that thirty seconds is a proper timing which will encompass most of the situations arising in newspaper copy. I, therefore, adjust the frequency of the visual tube vertical scanning oscillator I02 to have a frequency which is considerably shorter than the lag of the fluorescent screen, so that material appearing at the'top of the fluorescent screen will just fade out in time for the next traversal of the screen. Providing a thirty-second time lag is used, several lines of printing will be visible at any one time and then will gradually fade out to make way for the next few lines. With this arrangement it is possible to obtain by visual inspection of the visual tube fluorescent screen 19 the transmitted information screen on the film 93'. This permanent record, of course, will not be available except after the short interval necessary for the film or paper to make the trip through the developing and fixing tank. It will also be obvious that the visual tube can be used as a monitor for the adjustment of the circuits for proper reception, and it is also within the scope of my invention that such adjustments as made to the visual monitor will be linked with adjustments of the recording tube so that it will not be necessary to inspect the actual image on the recording tube screen.

As mentioned above, the character of the radio signal transmitted between stations is merely that of a series of dots which are initiated as impulses having a uniform amplitude. Also, by the use of a grid-controlled keying relay as described, any ordinary continuous wave transmitter suitable for code messages can be used for transmission, the only requirement being that the power supply source have ordinarily good regula tion. In fact, neither the transmitter per se nor the actual radio receiver need be other than ordinary commercial apparatus designed for code work.

If, during transmission, there should be variation in the amplitude of the signals dueto intermediate conditions so that the signal-to-noise ratio varies, I have found that if a signal-tonoise ratio of 8 to 1 is obtained at the receiving end, satisfactory reproduction of the transmitted images will be obtained. This is due to the fact that the rectifier is capable of differentiating within a much smaller margin than 3 to 1 and I have merely selected this low value as illustrative, as the actual value will be dependent somewhat on the design of the rectifier tube. In any event, the signal-to-noise ratio which can be effectively handled by the receiver need be only a safe operating value above threshold sensitivity of the keying relay. The grid bias is adjusted so that the tube will not break down under noise impulses, but will do so under signal impulses.

The speed of transmission of material in number of words per minute which can be obtained with the apparatus as above described is ample for facsimile purposes. A speed of 20,000 words per hour333 words 'per minute-can be obtained commercially in continuous operation with the optical, photographic and mechanical devices herein described. This speed is sufficient for transmitting the facsimile of an eight page newspaper-40,000 wordsin two hours and is about eight times as fast as the telegraph printers now widely used for news service. The above figures are based upon the use of existing commercial transmitters, channels and receivers and if special equipment is substituted for these factors, a considerably greater speed can easily be obtained. a

The preferred embodiment of the apparatus, as shown and described, is designed to operate on a basis of 100 picture elements per printed character, allowing a 100 element square to include each character and the space between the lines below each character. For types and spacings of printed lines as ordinarily used in present work, there will be from 5 to 7 of a possible 10 scanning lines available for forming each letter. This amount of detail will be more than sufficient for 100 per cent legibility at the receiving end.

Under these conditions, the frequency required for a transmission speed of 333 words per minute allowing an average of 5 letters and one space for each word will be 1665 cycles per second. This of course, is the maximum frequency as the average frequency transmitted will be less because of the large percentage of dead space in the printing. The maximum frequency encountered will therefore be easily handled by the dissector and receiver tubes as they have no lag at all at any reasonable frequency and will also be easily handled by the grid-controlled rectifier tube as the frequency it is called upon to handle is much too low to be affected in any way by the deionization time of the device.

In considering the type of material to be transmitted by my preferred embodiment here shown, I have found that the maximum number of printed letters per line per unit height of letters is limited only by the optical resolving power of the transmitting and receiving tubes. The maximum ratio of length of printed line to height of individual letters will be about 60 to 1 in the apparatus described. This means, therefore, that in transmitting news print a maximum width of two columns can be transmitted at any one time. Since the process of transmission is continuous, however, there is nothing against such a procedure as it merely means that a newspaper page at the receiver will arrive in the form of four strips, one following the other. These strips can later be assembled in the form of the original paper. By refocusing the lens at the transmitter other material such as typewriting may be transmitted, no other adjustments being necessary. Line drawings of almost any size can --be transmitted either as a whole or in portions later to be assembled, the size again depending upon the resolving power required for the proper detail in the received image.

It should be noted that, .while the resolving power of both transmitter and receiver tubes are limited by their effective apertures and therefore control the minimum size of received elements, the optical systems associated with the transmitter and receiver are both adjustable and separately so. This means that no initial preparation of material to be transmitted need be made. In explanation of this feature of my invention, I would like to point out that in the usual type of facsimile transmitter, the actual field scanned by the transmitter is almost invariably made especially for the purpose in respect to its dimensions. In other words, drum type telephoto and fascimile apparatus such as is well known in the art require. that the material to be transmitted be reduced or enlarged and transferred as a special print of standard dimensions which can be mounted upon the transmitting drum. The received facsimile is limited to the dimensions of a drum and it is almost the invariable custom to have the transmitting and receiving drums of the same exact size, The print which is to be transmitted and the print which is received are, therefore, both identical in size and it is quite often the case that the time factor involved in preparing the material to be transmitted in the form of a special print either reduced or enlarged is often important in transmitting spot news.

My invention, however, obviates any special the limits of the apparatus, the image desired on the receiving end, the optical system comprising the image tape ll, lens I! and cathode l9 in the transmitter may be adjusted so that the image thrown upon the cathode IQ of the transmitter may'be of the proper size irrespective of the size of the material itself, as long as the material is of high contrast and plenty of light is always available. A similar adjustment can be made' between the screen 80 of the receiving tube 88, the lens 9| and the film or paper 93, 'thus providing a material advantage in my system, which is not present in the devices of the priorart.

It should be noted that, while the transmitted signals are interrupted sequences, they are rectified at the receiver and supplied as maximum and the frequency can be made sufilciently high to cause overlap.

It is of course obvious that my invention is not to be limited to the use of a radio-frequency carrier in space or over wire lines, and that the transmission may .be accomplished without departing from the spirit of my invention over wire lines or similar channels utilizing direct-current transmission currents modulated in accordance with the output of the grid-controlled arc rectifier M.

I claim:

1. In combination, a transmitter, a grid-controlled arc rectifier connected to key said transmitter, said rectifier being energized by an alternating source, an electron image dissector, a picture field within said dissector, means within said dissector for creating an electron image of said picture field, means for moving said picture field uniformly along one dimension, means to move said electron image in another direction to produce 'line-by-line scansion thereby creating a train of picture impulses, and means for applying said impulses to the grid of said rectifier to control the output thereof.

2. The combination as in claim 1 wherein the picture field is moved vertically and is scanned horizontally.

3. The combination as set forth in claim 1,

- impulses, a cathode ray tube containing a screen having a relatively long time his. a cathode ray tube containing a screen having a relatively short time lag, means for simultaneously modulating the beam of both tubes in accordance with said impulses, means for moving the beam of the first tube in two dimensions to produce a visual picture thereon, means-for moving the beam of the second tube in one dimension only, and means for applying the light from the screen of the second tube to a light-sensitive surface moving in a direction to produce a residual picture thereon.

6. The combination as set forth in claim 5 with means for moving said light-sensitive surface in synchronism with the picture field originating said impulses. g

7. The combination as set forth in claim 5 with means for limiting received impulsa to a constant amplitude.

8. A facsimile system comprising means at a sending station for scanning printed matter line for line with at least five scanning lines per line of printed matter, a receiving station, and a cathode ray type of image reconstructing device at said receiving station having an image viewing screen with a time lag enabling at least five scanning lines to be viewed simultaneously.

9. In combination, a transmitter, a'grid-controlled arc rectifier connected to key said transmitter, said rectifier being energized by an alternating source, a picture field, means for scanning-said field to produce a train of picture impulses and means for applying said impulses to the grid of said rectifier to control the output thereof, said scanning means comprising an electron .Image dissector, an optical system adapted to project an image of said picture field into said electron image dissector for producing an electron image within said electron image dissector, means for uniformly moving said picture field in one direction, and means for moving said electron image in a direction transverse to said firstnamed direction.

J. SOMERS.

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