US2467950A - Facsimile receiving system - Google Patents

Description

April, 19,1949. THOMPSON 2,467,950

FACS IMILE RECEIVING SYSTEM Filed Sept. 21, 1943 T/PANSM/Z'TEE PECE/ VEE m '26 nun mm.

- INVENTOR. 100/5 /1- THOMPSON flw www- ATTO/PNE'YS Patented Apr. 19, 1949 FACSIMILE RECEIVING SYSTEM Louis A. Thompson, Rocky River, Ohio, assignor to NEA Service, Inc., Cleveland, Ohio, a corporation of Delaware Application September 21, 1943, Serial No. 503,233

3 Claims. 1

This invention relates to methods and apparatus for the transmission of facsimiles or pictures, and more particularly relates to an improved facsimile receiver.

( In the transmission of pictures by wire or radio, where high fidelity and good reproduction is desired, it has become common practice to provide a transmitter which picks up the picture by scanning the picture. The scanner may comprise a light source which throws a small beam of light on the picture and the light reflected from the picture is picked up by a light sensitive element and converted into electric current which varies in intensity in proportion to the amount of light reflected. The picture, which is usually a positive print, may be wrapped around a cylinder which is revolved at a predetermined speed while the scanning mechanism traverses the cylinder longitudinally to provide a continuous helical scanning line. Apparatus of this character is shown and described in my Patent No. 2,284,027 of May 26, 1942. The output from the light sensitive cell, which may be a photo electric tube or a photo voltaic cell, is ordinarily used to modulate an alternating current carrier which may be of 1800 cycle frequency. In these prior devices the exposure of the light sensitive material in the receiver was usually such that the received picture was a negative. Although some attempts have been made to provide a positive at the receiver these attempts have not been as successful as could be desired. Furthermore, in the prior devices the received pictures, especially when it was a positive, were often lacking in the detail desired for high fidelity pictures. By my present invention I have provided an improved method of scanning or exposure in the receiver wherein high fidelity pictures can be made and wherein the receiver can be set to make either positives or negatives by a simple manipulation of the controls.

' It is therefore an object of my invention to provide an improved method of transmitting pictures or facsimiles.

' Another object of my invention is to provide an improved scanner for facsimile receivers.

Another object of my invention is to provide an improved facsimile receiver where the picture received is a positive.

Another object of my invention is to provide a facsimile receiver wherein the receiver may be adjusted to provide either a positive or a negative picture.

, Another object of my invention is to provide a 2 facsimile receiver which is capable of producing pictures with high fidelity.

These and still other objects of my invention will become more apparent from the following description of an embodiment thereof which description is illustrated by the accompanying drawings and forms a part of this specification.

In the drawings:

Fig. 1 is a schematic View of a picture transmission system;

Fig. 2 is a diagrammatic view of the exposure unit for the receiver;

Fig. 3 is a view illustrating the picture signal as it comes from the amplifier of Fig. 2;

Fig. 4 is a view illustrating the signal as it is applied to the galvanometer unit; and

Fig. 5 is an enlarged diagram illustrating one method of adjusting the system to provide either positives or negatives.

Referring now to the drawings throughout which like parts have been designated by like reference characters:

As best shown in Fig. 1 the system contemplates a transmitter connected by a transmission line, which may be a telephone line or a radio communication channel, to a receiver.

In this description I have contemplated the same as being used with a telephone line for simplicity of discussion, however, it is equally usable in connection with pictures sent by radio, and it will be obvious to those versed in the art that in the case of radio transmission certain other components could be used in conjunction therewith depending upon the particular type of communication channel used.

The picture in this case is picked up by scanning a positive picture (or it could be a negative) which may be transmitted by means of the line i. This signal may be an alternating current which is modulated in amplitude by the variations in pictures being scanned and the resultant wave could be similar to that shown in Fig. 3 which illustrates a portion of a 1800 cycle carrier modulated by the picture. If frequency modulation was used it would obviously take a different form which is well known. In either event, the picture signal is picked up by the receiver where it is converted to the form shown in Fig. 3 and amplified in the amplifier shown in Fig. 2 which amplifier may be of any conventional distortionless type.

The output of the amplifier is connected to the primary 2 of a push pull transformer 3. The secondary 4 of the transformer is of the center tapped type and the outer leads 5 are connected to a rectifier 6 where the signal is rectified, but

The mirror H is preferably pivoted about its center point and the rectified picture signal moves the mirror which is returned to its normal position by a spring means not shown and which is well known.

A light source is illustrated at l2 which shines on a lens l3 that directs the rays in a parallel manner toward a mask M which has an aperture l5.

This provides a beam of light l6, which may be square but is not necessarily square, upon the mirror H. The mirror is so disposed that the beam [6 reflected therefrom is directed through an image forming mask 30 and toward a shutter mask l'l disposed in line with the lens l8 and the receiving drum 19. With no signal on the galvanometer the mirror shines the light through apertures 3| in the image forming mask and 20 in the shutter mask I1 and the lens [8 focuses the light to a point 2| on the cylinder H3. The cylinder l9 carries a light sensitive material such as photographic paper or film. When I state that the mirror focuses the light beam to a point at 2| I mean that it is an image which in this instance may be that of the aperture 3| in the mask 30. This is more clearly described in the aforementioned patent.

It will therefore be seen that when no signal is on the galvanometer, which corresponds to black on the picture being transmitted, the full exposure is provided for the paper or film on the drum It. When a signal is put through the galvanometer like that shown in Fig. 4 the mirror H is rotated and the beam I6 is swung as illus trated at I6 so that it passes out of the aperture 20.

It will therefore be seen that when the transmitter scans white, a signal of high amplitude is produced as indicated at of Fig. 3, and that this when converted to the type of signal shown in Fig. 4 at 25' causes the beam I6 to swing out of the aperture 20 to the point indicated at I6", thence during this period no light passes through the apertures and no exposure of the material on the drum I9 is effected and therefore white on the transmitter produces white on the receiver.

It should also be noted at this point that the positive and negative halves of the wave Fig. 3 are utilized and that this provides a continuous scanning line at the receiver affording greater fidelity.

If the signal is intermediate white and black the amplitude is less, as shown at 26 on Fig. 3, this provides a signal 25' in Fig. 4 and since it is lower in amplitude and since the movements of the mirror is a function of the amplitude of the signal the beam will not be swung completely out of the aperture and therefore partial exposure occurs.

It will therefore be seen that the picture being produced on the drum of the receiver is an exact facsimile of the original and not a negative as in ordinary practice.

It will also be seen that the full signal wave iii is utilized and that because of the complete utilization of the signal the negative half of the signal provides picture exposure as well as the positive half to provide continuous scanning or exposure with the resultant high fidelity. Because the portions of the high amplitude signal approaching the zero potential line are of such short duration as compared to the high portions of the signal which are of much longer duration, little or no exposure occurs due to the time lag of the emulsion and the exposure efiect is an average of the peaks of the waves which average varies sufificiently to provide a properly exposed and high fidelity picture.

This device may also be adjusted to provide a negative picture should it be so desired. This can be accomplished in several ways one of which is shown in Fig. 5. Here the mask I1 is merely moved as shown in dotted lines to a position such that the beam l6 instead of swinging out of the aperture 20 swings into the aperture 20.

This change could also be effected by moving the galvanometer so that during the no signal periods the light would shine to one side of the aperture 20 and then swing into the aperture when a signal was applied.

Having thus described my invention I am aware that numerous and extensive departures may be made therefrom without departing from the spirit or scope of the invention.

I claim:

1. In a system for transmitting pictures, a receiver therefor comprising means to receive the picture signal, a full wave rectifier for converting the signal to a pulsating direct current signal, a galvanometer connected directly to said rectifier and controlled by the signal, a light source positioned to direct a beam of light onto the galvanometer mirror, a mask for intercepting the reflected beam of light from the gal -zanometer positioned to allow full passage of the beam during minimum signals and to intercept the passage of the beam during maximum signals.

2.. In a system for transmitting pictures to pro- I videa positive of the original at the receiver including a. receiver therefore comprising means to receive the picture signal, a full wave rectifier connected to the receiver for converting the signal to a pulsating direct current signal, a galvanometer connected directly to the rectifier and controlled by the signal, a source of light and means for directing a beam of light from the source onto the galvanometer mirror, said galvanometer positioned to reflect said beam toward a. light sensitive material, a mask positioned to intercept the reflected beam of light from the galvanometer during maximum swing of the mirror and allow full passage of the beam during minimum swing of the mirror;

3. In a system for transmitting pictures, a receiver therefor including means to amplify an. alterating picture signal, a full wave rectifier for converting the. alternating signal to a. pulsating: direct current signal, a galvanometer connected to, the. rectifier and having a mirror which. is moved by the signal in. the. galvanometer, alight source, means for forming. av beam. of light from said source and to. direct the beam onto the. gal.- vanometer mirror, said mirror reflecting said light toward a light sensitive material, a mask interposed betweerrthe mirror and the light sensitive material and positioned to allow full passage of the beam during minimum signal and to intercept the beam when it is moved by the min-- rorupon. an increase in signal, and said mask 6 being movable to an alternate position to selec- Number Name Date tively position the mask to allow full passage of 1,938,990 Woodward Dec. 12, 1933 light during maximum signal and intercept light 2,041,822 Dowd May 26', 1936 during minimum signals. 2,152,348 Finch Mar. 28, 1939 LOUIS A. THOMPSON. 5 2,284,027 Thompson May 26, 1942 2,294,643 Wurzburg Sept. 1, 1942 REFERENCES CITED 2,301,375 Cox Nov. 10, 1942 2 311 159 Dimmiek Feb. 16 1943 The following references are of record in the me of this patent: 10 2,315,362 Wise Mar. 30, 1943 UNITED STATES PATENTS FOREIGN PATENTS Numb Name Date Number Country Date 1,854,159 Robinson ADI. 1 2 708,514 France July 24, 1931 1,935,417 Robinson NOV. 14, 1933

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