Title:
Tube for color television
United States Patent 2422937
Abstract:
This invention relates to cathode ray tubes in which the optical image appearing on the fluorescent screen is displayed in more than one color. More particularly this invention relates to a cathode ray tube for use in the reproduction of television images in color. One method commonly used...


Inventors:
Szegho, Constantin S.
Application Number:
US51270943A
Publication Date:
06/24/1947
Filing Date:
12/03/1943
Assignee:
RAULAND CORP
Primary Class:
Other Classes:
313/149, 313/476, 348/743, 348/E9.018
International Classes:
H04N9/22
View Patent Images:
US Patent References:
Foreign References:
GB508712A1939-07-05
GB328680A1930-05-05
GB395578A1933-07-20
GB318331A1929-09-05
Description:

This invention relates to cathode ray tubes in which the optical image appearing on the fluorescent screen is displayed in more than one color.

More particularly this invention relates to a cathode ray tube for use in the reproduction of television images in color.

One method commonly used at present in the art employs, in conjunction with the receiving cathode ray tube, a number of color filters, which are sequentially inserted at some point along the path between a fluorescent screen, upon which the received image appears in black and white, and the eye of the observer. These filters are commonly used in the form of color segments of a disc which is rotated, for example between the fluorescent screen and the projection screen. As well-known in color optics, it is possible synthetically to reconstruct a color image by first analyzing it into a certain number of primary elemental colors, usually two or three. The color segments just referred to are therefore chosen to correspond to the color elements into which the image is analyzed at the television transmitter.

The method just described suffers from several disadvantages. The use of color filters inevitably leads to the absorption of a certain amount of light, therefore demanding upon the fluorescent screen an image having greater brilliance than would otherwise be necessary. Likewise, as at present used in the art, the cathode ray tube employs a fluorescent screen of a translucent nature, and the image consequently must be directly projected through the body of such screen. This brings about the disadvantage that some of the light which is produced upon the inner surface of the fluorescent screen is absorbed by the fluorescent material itself, in the passage of such light through the screen. Furthermore, the need of a transparent or translucent supporting material upon which to place the screen, greatly limits the range of materials from which such support may be constructed. Since the screen and its support must dissipate a considerable amount of energy in the form of heat, it has been found that the use of material such as glass, sets a practical limit to the accelerating voltages and beam current densities which may be employed, thus in turn limiting the degree of brightness which may be imparted to the image produced upon the fluorescent screen.

In an effort to overcome certain of the disadvantages just pointed out, it has been proposed to use a screen support formed of an opaque material and to view the screen from the same side upon which the electron beam impinges.

Such type of tube will hereinafter be referred to as a front surface projection tube.

However, when a tube of this last-mentioned type is employed in connection with a rotating col6 or filter disc, as above-described, for color television purposes, certain difficulties are encountered.

The color filter disc can no longer be placed at a relatively short distance from the fluorescent screen, since the transparent window through which the light to be color filtered leaves the cathode ray tube, is situated at a relatively great distance from the screen. This leads to a considerable divergence of the light emanating from any single illuminated elemental point located upon the fluorescent screen. In fact such divergence is so great that each spot of light on the fluorescent screen spreads out so as substantially to cover the entire area of such transparent window. From this last consideration it can be seen that a color filter must have each elemental color thereof distributed over an area approximately equal to the size of the entire transparent window, bringing it about that when it is necessary for a change to occur, from one color to another, the whole surface of the filter in front of the transparent window should theoretically be changed in a time interval not greater than the time elapsing between the illumination of two adjacent points of the optical image upon the fluorescent screen. Such rapid change of a relatively large area of filter is practically impossible and, consequently, compromised solutions have been been proposed in which the time of overlap between two successive filters has been made as small as practicable. In order to bring about such reduction of overlap, an increase in the diameter of the color filter disc may be made.

However, with standards of picture transmission at present employed, it can be computed that for a picture size of approximately 4 inches x 5 inches, and a permissible color overlapping time of about 5 per cent of the duration of each color image, the diameter of such color filter disc would have to be somewhat greater than 50 inches. Therefore, it can be seen that such a solution of the problems involved would be wholly impracticable, in comparison with the color filter disc having a diameter of a little over 8 inches, which would be needed for this same picture size, were a direct projection cathode ray tube to be employed therewith.

The present invention overcomes the difficulties above-described and at the same time allows the advantages of front surface projection to be ob56 tained, without necessitating the employment of filter discs of such prohibitive size as the one Just mentioned by way of illustration.

In carrying out the present invention, the use of a color filter disc is entirely avoided. This is done by using a number of discrete fluorescent materials or phosphors, each one yielding, when excited by the electron beam, a luminous output having a color corresponding to one of the elemental colors into which the color television image has been analyzed at the transmitter.

Looked at in a different fashion, the discrete segments of the color filter disc have been replaced by corresponding segments of fluorescent materials, yielding, respectively, the desired discrete elemental colors. Furthermore, there is provided an arrangement for rotating this polychromatically fluorescing disc within the envelope of the cathode ray tube, so that the electron beam can impinge directly upon the various fluorescent materials with which one side of the disc is coated. In order to secure rotation of the disc within the body of the tube itself, there are employed devices familiar in the art for the construction of X-ray tubes having rotating anodes, for example an induction motor, the stator of which motor is located outside the tube and the rotor of which is located within the tube. The speed of rotation, which must correspond with that employed for color analysis at the transmitter, may be synchronized therewith by means familiar in the art. Likewise, the present invention contemplates the use of a disc formed of metal, which is better able to withstand relatively high accelerating voltages and beam current densities, since front surface projection may be employed with such disc. Likewise, the rotation of such fludrescent screen, causing the utilization at a given moment of only a fractional part herewith, still further facilities heat dissipation therefrom, since only a portion thereof is at one time subjected to heating.

One object of this invention is to provide a polychromatically reproducing cathode ray tube in which relatively high accelerating voltages and beam current densities may be employed, without causing undue heating of the image screen of the tube.

Another object of this invention is to provide a cathode ray tube for use as a color television receiver, in which moving color filter elements external to the tube are eliminated.

Still another purpose of this invention is to provide, in a cathode ray tube, an image screen having a number of discrete portions which are successively placed in the path of the electron beam and removed therefrom, each of these discrete portions yielding a luminous output differing from that yielded by any other portion thereof, and each portion corresponding to an elemental analytic color used in transmission.

Still another object of this invention is to provide a color television cathode ray tube receiver in which a direct projection type fluorescent screen is provided with discrete portions, each fluorescing so as to yield a different color, and in which a device is provided for moving such screen within the tube so that only a portion thereof is subjected to impact by the electron beam at any given moment.

Yet another purpose of this invention is to provide a color television cathode ray tube receiver in which the overlapping time between successive colors is greatly reduced, without the need of employing moving elements of prohibitively great size.

Another purpose of this invention is to provide a polychromatically reproducing cathode ray tube in which the successive images, having diverse color values, are each directly produced in 6 the respective colors and are directly viewed, without the interposition between the eye of the observer and the fluorescent screen of any light absorbing color filter, so that luminous efficiency of reproduction is greatly enhanced thereby. Reference is now made to the accompanying drawing where: Fig. 1 shows a color television cathode ray tube employing front surface projection and embodying this invention; Fig. 2 shows another embodiment of this invention in which a direct projection type cathode ray tube is used; Fig. 3 shows a diagrammatic plan view of the disc.

Referring now to Fig. 1, the cathode ray tube 10 is formed with a longitudinal section II and an off-set section 12. In section 12, are located devices for producing, projecting and scanningly moving an electron beam. Such devices may be of any form familiar in the art and are here schematically represented by electron gun 13, electron lens or accelerating electrode 14, and two pair of deflection coils IS and 18 respectively.

The electron beam entering longitudinal section 11 of the tube impinges upon a fluorescent coating 17 carried upon one surface of a rotating disc 18. This surface of disc 18 is not coated uniformly with a single fluorescent material, but is divided into a number of segments corresponding to the number or a multiple thereof of synthetical color elements employed, and each of these segments is coated with a phosphor yielding a color corresponding to one of these syn. thetical elements used by the particular transmitter from which signals are being received and from which a given image is to be reconstituted.

As shown in Fig. 3, disc 18 may be conveniently divided into three segments colored red, green and blue.

Tube 10 is provided with another elongated off-set portion 19, housing approximately onehalf of disc 18, the portion so housed being shielded from any possible heating action due to impingement thereupon of the electron stream. Disc 18 is mounted upon a shaft 20, rotating in suitable bearings 21 and 22. Between such bearings, shaft 20 carries thereupon the rotor 23, which is actuated by the rotary electro-magnetic inductive field derived from an external stator 24, and passing through wall 25 of tube 10. Such method of driving a rotating element within an evacuated tube is well-known in the X-ray art and therefore detailed description of the motor drive is considered to be unnecessary. The speed of rotation is synchronized with the speed of color sequence at the transmitter and controlled by any suitable means, as well-known in the art. For example, with actual standards of transmission now in use, disc 18 may, for example, be divided into six color segments and the driving motor may make 1200 R. P. M., such particular values being understood to be purely illustrative.

Reference is now made to Fig. 2, where cathode ray tube 30 is formed so that one extremity thereof 31', has a diameter somewhat greater than twice that of the portion of the tube which the electron beam actually traverses. Electron gun 13 and electron lens or accelerating electrode 14, may be of any convenient types familiar in the I7 art, There is here shown by way of an illustraS5 tion, two pair of electro-static deflection plates 15' and 16', but it is to be understood that electromagnetically deflecting coils, similar to those shown in Pig. 1, may alternatively be employed.

In this form of invention, rotating disc 31 is formed of transparent material, the fluorescent coating 32 is placed upon the inner surface thereof and the light from such coating passes outwardly from the tube, by transmission through the body of the disc and the outer wall of portion 1 31' of the tube. The inner surface of disc 31 is divided into segments, each coated with a phosphor emitting a different color, as described in connection with Fig. 1.

Disc 31 is mounted upon shaft 33, held in a suitable bearing, 34, and driven by bevel gears 35 and 36, gear 36 being in turn mounted upon shaft 37, which latter is held in suitable bearings 38 and 39, and driven by an external-internal motor of the induction type which may be similar to that already described in Fig. 1, and which here bears corresponding reference numerals upon the various elements thereof.

It will be evident that the color cathode ray tube shown in Fig. 2 is of the direct projection type, instead of the front surface projection type shown in the embodiment of Fig. 1. By placing the disc normal to the plane of incidence of the electron' beam, maximum spread angle thereof is secured, this being accomplished by the use of an indirect mechanical drive of the disc.

In the case of both embodiments of this invention here shown, the fluorescent screen is constituted by several discrete segments and accordingly it is possible, if so desired, to introduce the screen into the glass envelope of the cathode ray tube in separate portions, which portions may be assembled with one another to build up the disc and screen, after such insertion has taken place. This yields the further advantage that the glass envelope, which must house a fluorescent screen support of approximately twice the diameter of the support which would be employed in the case of black and white television, can be provided with a relatively small aperture for insertion of the various elements therewithin. This necessitates the employment of. only relatively small size glass seals during the course of manufacture, thus facilitating construction of the tube.

It is likewise to be noted that the power needed for rotating the fluorescent color screens of this invention will be much less than that which would be required to drive color filter discs of the usual types, since such color filter discs would be located externally to the tube and therefore would encounter air resistance when being rotated.

When high power tubes are employed, the enhanced cooling effects afforded by this invention become of increasing importance. This is due, inter alia, to the fact that certain phosphors may lose, for example, as much as 80 percent of their luminosity, if the temperature of the phosphor be raised from ordinary room temperature to 3000 C.

Accordingly, a screen which would have its luminosity greatly decreased, which effect would therefore entail a loss of brilliancy of the reproduced image, if such screen were employed in the stationary manner of the prior art, may satisfactorily be used while kept in motion by means of the apparatus employed in carrying out the present invention, due to the cooling effect, previously described, secured by the use of a rotating and partly shielded fluorescent screen.

Another advantage of this invention is that color reproduction is obtained by an additive method, so that the electronic energy is more efficiently employed, by being wholly converted, at any given instant, into the desired color, instead of being spread over the entire spectrum S of white light and then only a portion of this spectrum being actually used, as is done by subtractive processes. Of course, in all such tubes the afterglow should be of very short duration.

What is claimed is: 1. In a cathode ray tube, the method of securing polychromatic reproduction with discrete phosphors exhibiting diverse colors when excited by an electron stream, which includes the steps of subjecting a first phosphor to the electron stream, removing said phosphor from the path of said stream, and placing another phosphor in said path, said discrete phosphors being selected so as to yield respective luminous outputs located in different portions of the visible spectrum. 2. Method according to claim 1, in which said discrete phosphors yield luminous outputs corresponding to the analytic color elements employed in color reproduction electro-optical devices.

3. Method according to claim 1, in which said discrete phosphors, when excited by said electron stream, are viewed from the same side upon which they are respectively struck by said electron stream.

4. Method according to claim 1, in which said discrete phosphors, when excited by said electron stream, are viewed from the opposite side from the side upon which they are respectively struck by said electron stream.

5. Method according to claim 1, in which said phosphors are moved in a circular path substantially normal to the path of said electron stream, whereby rotational movements of translation permit a given phosphor to function repeatedly, at predetermined temporal intervals.

6. Polychromatically reproducing cathode ray tube including means for producing an electron stream, a plurality of discrete phosphors, each exhibiting an electro-luminous translatory effect, the luminous output whereof is substantially located in a differing portion of the visible spectrum from the portion wherein is located the luminous output of the remaining phosphors, and means for determining a coincidental temporal and spatial relationship of said electron stream and each of said phosphors, in a predetermined sequential manner.

7. Cathode ray tube according to claim 6, in which said means for the determination of said coincidental spatial and temporal relationship ineludes means for giving to said phosphors translatory motion in a circular path, the plane of which path is substantially normal to the angle of incidence of said electron stream thereupon, in at least two dimensions.

8. Cathode ray tube for color television reproduction, including an evacuated envelope, means for producing an electron stream therewithin, a disc-like support located within said tube and segmentally coated with phosphors exhibiting discrete color output from one another, said support being shielded at any one instant for at least one-half of the coated surface thereof, with respect to said electron stream, and means for syn0chronously rotating said disc, whereby the various segments thereof are sequentially exposed to said electron stream.

9. Cathode ray tube according to claim 8, in which said disc-like support is formed of metal 76 and said evacuated envelope includes a transparent window located opposite the coated side of said support, through which window the light yielded by said phosphors is projected.

10. Cathode ray tube according to claim 8, in which said disc-like support is formed of transparent material such as glass, and said evacuated envelope includes a transparent window located on the side of said support which is not coated. through which support and which window the light yielded by said phosphors is, in turn, projected.

11. Cathode ray tube for color television reception, including an evacuated envelope, means for producing therewithin an electron stream, means for scanning with said stream, a disc, means for rotating said disc so that substantially all portions of one surface thereof pass successively across the scanning field, at least two phosphors yielding different colors and segmentally coated upon said surface of said disc, and means for utilizing the luminous output of the electron excited portion of said disc coating excited at a given instant.

CONSTANTIN S. SZEGHO.

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