US2180710A - Cathode ray tube screen - Google Patents

Description

Patented Nov. 21, 1939 CATHODE RAY TUBE SCREEN Max Knoll, Bernhard Bartels, and Otto Spengler,

Berlin, Germany, assignors to Telefunken Ge- .sellschaftfiir Drahtlose Telegraphic m. b. H.,

' Berlin, Germany, a corporation of Germany Application April 19, 1937, Serial No. 1375993 2 In Germany March 19', 1936 g 1 4. Claims.

This invention relates to electric signalling, and in particular, to facsimile and television transmission systems utilizing cathode ray scanning means. i

This invention is an improvement upon the method and means. for electric signalling disclosed in my co-pending application Serial No; 106,301, filed October 19, 1936 by Fritz Schroter and Max Knoll, and entitled Transmitter systern, and now Patent Number 2,156,435.

' In certain types-of transmission, it is desirable to scan a still'picture or sign either for testing advertising or identification purposes. For example, in a television transmitting station, it is desirable at the end ,of a program to identify the station transmitting the television program.

This identification might comprise the call letters of the station and include some symbol used as a trademark or identification sign by the station. Such a symbol or picture, aswell as the call letters, may well be a half-tone picture. Instead of using the studio scanner for scanning the picturesurface for this short in accordance with the invention disclosed in the above identified application, this invention teaches the use of a special scanner which makes use of the different secondary emission properties of two or more materials. According to the' present invention, a supporting surface -for'the picture to be transmitted is madeof one' material, while the picture proper is made cfanother material and supported on the surface of the plate. A cathode ray scans the picture area and depending uponwhether the ray impinges on an elemental area of the support, orupon an elemental area of the picture proper, more or less secondary'electrons will be released in accordance with the secondary emission properties, which I characterizes the supporting surface or the elements of the picture proper. An electrode serves to capture the released secondary electrons and these electrons serve in turn to produce a voltage (Cl. ZED- 150) in which Fig.1 shows schematically a cathode ray-scanning system for use with the plate prepared in I accordance with our invention, and

Fig. 2 shows a cross-section of a half-tone plate'prepared according to our invention.

Referring now to the drawing, in Fig. 1 a cathode ray tube is shown comprisingv a glass bulb designed partially as and with the shape of a cylinder, attached to which is a frustrum of a cone. Within the cylindrical portion of the reading the description together with the claims, t

glass bulb a cathode ll andelectrode 22 are shown conventionally connected with a battery 23 to provide an'electron gun for concentrating and accelerating the electrons to provide a beam of high speedelectrons. Two pairs of deflecting plates l2 and I3 are arranged at right angles to each other for purposes of deflecting the beam of electrons generated within the electron gun so that the beamtraverses a predetermined pattern of scanning. These electrodes may, for example, be supported by the wall structure of the tube It or as is more usual, be supported'from the gun structure as is well known in the prior art. frustrum portion of the tube I ll intermediate the deflecting plates l3 and the half-tone plate I5. Connected between the plate l5 and the electrode 14 is a battery 16 in series with aresistance l1 to which are connected the terminals I8. The cathode ray beam scanning the plate I 5 causes secondary electrons to be ejected there- A metal electrode I4 'is positioned in the from due to the velocity of impact upon the plate I and these secondary electrons are collected by the electrode [4 and current flow in accordance with the electrons reflected through the resistance ll, which gives rise to signal voltage for transmitting the electro-optical effects.

Fig. 2 shows in cross sectional view, the plate 15. The plate l5may be made of metal, such as aluminum, for example, upon which the halftone image is arranged in accordance with the half-tone screening methods and further, .differs in this respect from the invention disclosed in the above identified copending application of Schroter and Knoll, in that the co-pending application provides a plate which is photo-elec-. 1 trically engraved or recessed, the recesses being filled with carbon or some other material having a different secondary emission characteristi than the supporting plate l5. 1

As will be appreciated, photo-engravingproc esses require considerable care to be taken, and are, relatively speaking, a complicated process.

. tone screening details.

Applicants, therefore, have done away with the necessity of using a photographically etched plate by providing a plate upon which the picture proper is disposed upon the supporting metal plate. In general, the process consists in coating the smooth surface of the plate with a photo-chemical substance. By photo-chemical substance is meant a substance Whose chemical and physical properties undergo changes when exposed to light. And for this purpose, applicants may utilize a coating of chrome gelatin, which comprises gelatin in which has been included potassium bi-chromate. Such a gelatin is soft and pliable, but upon exposure to light, the area of the chrome gelatin so exposed, hardens. Thereafter, if the layer is Washed in water, the unexposed portions are washed away, leaving in relief the portions of the film which have been exposed to light which are insoluble. The changed chrome gelatin remaining upon the layer has secondary emission properties which are not greatly different from carbon, and consequently, differs appreciably from the secondary emission properties of the metallic plate supporting the film of chrome gelatin. Thus, to prepare the plate, it is merely necessary to flow the chrome gelatin upon the polished surface of the plate in the dark, exposing the plate to the picture of which representation is desired, by projecting the picture upon the plate and through a halftone screen where the picture is different from a black and white picture, to provide the half- Thereafter, the plate is rinsed in water and the unexposed portions of the gelatin layer are washed away, leaving the raised portions I9 upon the plate I5. The plate I5 is then dried and may then be sealed in the tube for generating the signals above described.

Alternatively, a solution of bitumin of judea dissolved in oil or lavender may be flowed across the plate to provide the photo-chemical variable layer. The action of light makes the bitumin insoluble so that after exposing the picture through a half-tonescreen upon the layer of bitumin on the metal plate, the plate maybe developed in oil of lavender, which removes the unexposed bitumin. The plate is then dried and may be used, as indicated above, for the chrome gelatin plate above described.

It will be appreciated, of course that the metal plate may be of some other metal other than aluminum, such as copper or nickel or tantalum, or any other metal whose secondary emission properties are different than the properties of the picture elements in relief upon the plate.

It will thus be appreciated that applicants new plate provides a simpler plate for use in a cathode ray scanner and that the combination of applicants plate and the cathode ray scanner described above results in an improved method of transmitting the electro-optical representations.

Having described our invention, what We claim is:

1. A cathode ray tube comprising an envelope, means for producing a focused beam of electrons within the envelope, means for deflecting the produced focused beam of electrons in two mutually perpendicular directions, a planar electrode of predetermined specific secondary electron emissivity, isolated minute particles of a material having a specific secondary electron emissivity different from that of the electrode positioned on the electrode and forming a halftone picture, the area .of said particles corresponding to the density of the elemental areas of the half-tone picture, said electrode being positioned to be impacted by the deflected beam of electrons, and means to collect secondary electrons emitted from the particles. and the electrode under the impact of the deflected focused beam, said beam producing means, said secondary electron collecting means and said electrode being within said envelope.

2. In combination, means for producing a focused beam of electrons, a target electrode of predetermined specific secondary electron emissivity, a plurality of elemental particles of a material having a difierent specific secondary electron emissivity than that of the electrode, said particles being positioned on the target electrode to form elemental areas of a-half-tone picture, the area of said particles corresponding to the density of the elemental areas of the half-tone picture, means for deflecting the focused beam to scan substantially the entire area of the target and all of the plurality of particles to cause secondary electrons to be emitted from the target and plurality of particlesand means to collect the emitted secondary electrons, beam producing means, said secondary electron collecting said means and said electrode being Within said envelope.

3. A cathode ray tube. comprising an envelope, means for producing a focused beam of electrons within the envelope, means for deflecting the produced focused beam of electrons in two mutually perpendicular directions, a planar metallic electrode of predetermined specific secondary electron emissivity, isolated minute particles of a material having a specific secondary electron emissivity diiferent from that of the electrode positioned on the electrode and forming a halfondary electrons emitted from the particles and I the electrode under the impact of the deflected focused beam, said beam producing means, said electrode means and said metallic electrode being positioned within said envelope.

4. An electronic device comprising an envelope, an electron gun for producing a beam of focused electrons positioned within the envelope, a metallic target electrode of predetermined specific secondary electron emissivity positioned within the envelope in register with the electron gun, a halftone picture formed of isolated particles of materialhaving a specific secondary electron emissivity different from that of the target electrode positioned upon the target electrode, the areas of said particles corresponding to the density of the elemental areas of the half-tone picture, means within the envelope intermediate the gun and said target electrode for scanning said target electrode and the half-tone picture thereon by the focused beam of electrons, and electrode means .within the envelope intermediate the target and the scanning means for collecting secondary electrons emitted from the half-tone picture and the target electrode under the impact of the scanning focused beam of electrons.

' MAX KNOLL.

BERNHARD BARTELS. OTTO SPENGLER.

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