US2855529A

US2855529A - Color-kinescopes, etc.

Info

Publication number: US2855529A
Application number: US575022A
Authority: US
Inventors: Albert M Morrell
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1956-03-30
Filing date: 1956-03-30
Publication date: 1958-10-07
Anticipated expiration: 1975-10-07

Description

Oct. 7, 1958 A. M. MORRELL COLOR-KINESCOPES, ETC

Filed Maron so, 195e nited States Patent O COLOR-KINESCOPES, ETC.

Albert M. Morrell, East Petersburg, Pa., assigner to Radio This invention relates to improvements in S-beam tricolor kinescopes of the kind wherein the three electronbeams, in their transit to a screen-unit of the maskedtarget dot-screen variety, are subjected not only to (a) horizontal and vertical scanning forces but also to (b) dynamic convergence forces.

with the present invention, as compared with said relationship in a similar tube of the prior art;

Fig. 5 is a partly diagrammatic sectional view of a photographic lighthouse showing the apertured-mask and screen-plate of the color-kinescope of Fig. 1 set up thereon during the screen-plotting operation; and,

Fig. 6 is an enlarged plan view of the sourceof light in the lighthouse of Fig. 5.

The color kinescope shown in Fig. 1 comprises an evacuated envelope 1 having a glass neck portion 3 connected by a suitable glass-to-metal seal 5 to the small The principal object of the invention is to provide a color-tube of the subjectvariety wherein picture defects occasioned by lack of register (of the electron-spots with the phosphor dots) are minimized during normal operation (i. e., when the three beams are subjected to dynamic convergence).

Another and important object is to achieve the above mentioned principal object without any reduction in the light output of the kinescope and without complicating either its physical structure or its method of manufacture.

Stated generally, the foregoing and related objects are achieved, in accordance with the invention, by the provision of a color-kinescope of the masked-target variety wherein the phosphor-dots (on the screen) are relatively so arranged with respect to the dot-like mask-apertures that, when the three electron-beams are subjected to dynamic convergence, the spacing between the centers of the beamspots near the middle of the screen is less than the spacing between the centers of the corresponding phosphor-dots, and the spacing between the centers of the beam-spots near the edge of the screen is greater than the spacing between the centers of the phosphor-dots at the same location. The total misregister error, due to dynamic convergence, is therefore divided between the center and edge of the screen, thus reducing the magnitude of the error lat any given part of the screen by as much as 50 percent, and improving color-purity. Such balanced tolerance is achieved in accordance with the invention by: (a) making the screen-plotting exposure with a light-source located not at the position which the beams assume when they are scanning the central portion of the screen-unit (as in the prior art) but at a position which the beams assume in scanning some point (e. g. mid-way) between the center and edge of the screenunit and (b) by fixing the mask-to-screen spacing or q" at a value calculated to make the phosphor dots tangent to each other.

The invention is described in greater detail in connection with the accompanying single sheet of drawings, wherein:

Fig. 1 is a party diagrammatic longitudinal sectional view of a three-gun tri-color kinescope of the shadowmask dot-screen variety, the drawing being marked with lines indicative of the shift in the color-centers of its three dynamically converged beams as they approach their maximum angle of deection;

Fig. 2 is a fragmentary rear elevational view of the screen-unit of the color-kinescope of Fig. l;

Figs. 3 and 4 are columnar charts showing the relationship or register of beam-spots with phosphor-dots at various parts of the screen in a tube made in accordance end of a metal cone 7 which, in turn, is connected by complementary sealing anges 9 and 11 to a cylindrical metal front-end portion or cap 13. The cap 13 terminates in a spherically curved face-plate 15, the concave inner surface of which comprises the mosaic screen 17 of a bi-part screen-

unit

17, 19 of the Shadow-mask variety.

The mosaic screen 17 (see Fig. 2) comprises a multiplicity (usually 300,000 or more) of triads (i. e. groupsof-three) of red (R), blue (B) and green (G) colorphosphor dots. The phosphor-dots are here arranged in a hexagonal pattern; that is to say each dot is surrounded by six other dots, alternate ones of said other dots being of a second color-response characteristic and the interediate ones of said other dots exhibiting a third color-response characteristic. An electron-transparent, light-reflecting, metallic (e. g. aluminum) lm 17f (Fig. 1) covers the entire target surface of this dot-like mosaicscreen, and forms an electrical connection to the cap 13 of the envelope 1.

The other element or shadow mask of the bi-part screen-

unit

17, 19 comprises a suitably curved glass or metal plate 19 containing a multiplicity of apertures 19a arranged in the same systematic (hexagonal) pattern as the phosphor screen-dots; there being one mask aperture for each triad (RBG) of dots. As indicated by the single electrical connection 21 (Fig. 1) the metallized screen 17 and the mask 19 are here operated at the same potential (e. g. 20 kv.) to provide a field-free space therebetween, as is usual in color-kinescopes operating on the shadow-mask principle. The mask has an integral rim 19b and is supported about said rim on three or more pegs 23 which project radially inward from the inner surface of the cap portion 13 of the envelope. The connection between the pegs 23 and the rim 19b is such as to permit the mask to be removed from the cap during the three (later described) emulsion-coating and developing operations incident to laying down the three color-phosphors (RBG) on the glass screen-plate 15.

The tubular glass neck 3 of the envelope 1 contains a battery of three electron-guns 25r, 2Sb and 25g each of which is allotted t-o a particular screen-color. The guns are here shown arranged delta fashion about the horizontal axis x-x of the envelope (as in Schroeder U. S. P. 2,595,548) so that their beams converge near a surface of the mask 19. The mask apertures are of a diameter (say 0.010) considerably smaller than that of the beams, hence the beam-electrons pass through said apertures in the form of electron-jets of a diameter smaller than that of the beams per se. The electron spots formed by impact of the electron-jets are, in turn smaller than the phosphor dots (which may be, Say, 0.017 in diameter).

As is now more or less standard practice the red, blue and green beams are subjected t-o dynamic convergence forces for maintaining them converged at or near the surface of the mask through-out their scanning movement. In the instant case the dynamic convergence forces are applied to the separate beams by three pairs of internal pole pieces 27 actuated by small electro-magnets 29 in the manner described in greater detail in the co- 3 pending application, Serial No. 364,041 (now U. S. P. 2,752,520), of Albert M. Morrell, for example. The copending application, Serial No. 164,444 (now U. S. P. 2,751,519) of Albert M. Friend may be referred to for other electromagnetic (and electrostatic) types of dynamic beam-convergence means.

VReferrin'g.. still to Fig; 1. Here, as in theY Schroeder patent (U. S. P; 2,595,548), the required horizontal and vertical scanning movements are applied to all three of the electron-beams from the guns 2S by a common deecting yoke 31 which will be understood to comprise two .electromagnetic coils (indicated by the double current-leads) disposed at right angles to each other on the glass neck 3. As indicated by the single vertical line A-A when the three beams ar undeected (i. e. when they are directed to the center of their target) the normal planeo`fdeection usually crosses the central axis ('x"-x) of the tube at or near the center of the yoke 31- and thecolor centers of the beams lie at the apices of a triangle in said plane, as indicated by the three points r, b, g in Fig. 1. Similarly, as will be brought out in connection with the description of Figs. 3 and 4 (wherein thefshadedrareas designate the three beams) the centers of the three beams form an electron triangle 33 on the'l screen which, ideally, coincides or registers with a "phosphor triangle 35 (i. e. a triangle formed by the center points of three phosphor dots R, B and G) near the central axis of the tube.

The continuously variable electromagnetic (or electrostatic) forces which are used to keep the several beams convergedlat or near the surface of the mask are, shown in Fig. l, appliedto the beam electrons before they reach the plane-'of-deection A-LA. As a consequence, the color-centers ofthe beams move farther away from the central axis of the tube during the scanning movement, all as indicated by the poines r', b', g. These off-axis movements of the color-centers of the three beams cause the electron-triangle 33 to grow in size as it approaches the boundaries of the raster traced on the screen by the beams scanning movements. This is illustrated in Fig. 3 where (as indicated by the legend) in a conventional tube, operated with dynamic convergence, the three (shaded) beam-spots are in register with the phosphor dots R, B, G at the center of the screen, but are de-V gruped and out of register with respect to the dotsV near theedge of the screen.

Asindicated in Fig. 4, if the beams are turned on without the application of dynamic convergence, the electron-spots and the phosphor dots in the prior art tube would be neither grouped nor degrouped (However, s will be'appreci'ated bythose skilledl in the art, such tubes cannot be operated satisfactorily without dynamic convergence because the color video-patterns become displaced from each other, especially near the edges of the screen.) e v y The present invention contemplates and its practice provide a 3bean1 tri-'color kinescope wherein the phos-A phor dots RBG are relatively so arranged with respect to the maskapertures 19a that the misregister error, resulting from the expansion and contraction of the electron-triangle, is divided between the center and edge of the screen, thus reducing the magnitude of the error at any pointron the screen by as much as 50 percent'. This is indicated in Fig. 3 wherein it will be observed that tha three beam-spots instead of being perfectly. centered on the phosphor dots at the center of the screen (as they are inV prior-art tubes) are slightly grouped and, at the edges of the screen are slightly degrouped (as contrasted with the extreme degrouping, and loss of tolerance, in the tubes of the prior art).

As previously mentioned the balanced screen-tolerance of the present invention is achieved in two steps. One o'f the steps involves a change in the spacing, with respect to Athe' central axis (xx) of the tube, of the light source (3717. 37b, 37g,Figs. 5 and 6) used in the screen-plotting operation. The other step involves fixing the mask-to-screen spacing (q, Figs. 1 and 6) at a value calculated to make the phosphor dots (RBG) tangent to each other. The two steps involved in reducing the invention to practice are best illustrated by the following example wherein the problem was to apply the invention to a conyentional twentyjonefinch color-kinescope (commercial type-'number 21AXP22).

In this conventionaLtub'e it. was found that the degrouping erro-r (i: e.'y the" displacement, due to dynamic convergence, ofy the center of `eachbeam-spot with respect to its phosphor dot, in a direction rdilly' outward from the centerv of a given trio) w's of the order of y=0.003 to 0.004. This error corresponds to the movement (AS) of each beam, in its plane-of-deflection, of the order of 0.100". This fact was determined in agreement with thefo'rm'ula P v q (l) where P=the distance from the plane-of-deection to the mask (Figl) and q=the mask-to-screen spacing.

The position (S) of the light source, used in laying down the phosphor dots; was selected in agreement with the formula:

sf=s+^s 2) where S was' the distance the light source was displaced from the central axis (x-x) of the original (21AXP22) tube. i

To obtain tangent phosphor-dots onthe screen the mask-to-screen spacing (q) was changed in accordance with the formula Eig@ (3) where: L=the distance from the screen to the pl-ane-ofdeection and a='the center-to-center spacing of the apertures in the mask.

In this particular application of the invention to a (21) color-tube wherein s=0.276" andq=0.550 the new value of S, i; e. S=`0.327-', and new value q=0.471.

When the modifications of the S and q values were m-ade, as above described, the actual screeningroperation was carried out in the usual way, in a 1ighthouse, as shownin Fig. 5. l

In Fig. 5 the screen-assembly is shown at that stage o its manufacture whereatthe inner or target surface of the screen-plate 15 Yhas been provided with a coating 39 comprising a photographic emulsion for recording the mosaic pattern impressed thereon by reason of the presence of the apertured mask 19 in the path of the light rays from a quartz rod or other point source of light 37. Assumingthat the' point 37, in the plane-of-deflection A-A, is the one to be traversed by the red beam of the finished kinescope then the emulsion coating 39 on the inner surface of the glass plate 15 should contain a red phosphor such, for example, as manganese activated zinc phosphate. Since, as previously mentioned, the apertured mask 19 isrernovably supported on the inner surface of the cap 13 by three or more pins 23, it may be removed from the assembly during the three emulsioncoating and developing operations Yincident to laying down the three (red, blue and green) color-phosphors. When the tube cap 13 is restored to its indicated axial position on the pedestal 41 ofthe lighthouse, for the blue and green exposures, the lightsource 37 must be moved from its position during the previous exposure to bring it to the position (37b) of the blue and (37g) green guns, respectively.

When the screen-plotting operation is complete the cap 13 is sealed tothe. open end of the cone 7 (Fig. i) in the usual way, that is torsay, with the'vmcsaic patterns Feb of the mask-apertures and phosphor dots centered on the central axis (x-x) of the tube.

What is claimed is:

1. In a multiple-beam color-kinescope wherein the multiple electron-beams are subjected to dynamic convergence in scanning a screen-unit of the kind comprising a mask containing a pattern of equally spaced dot-like apertures through which electrons, derived from said beams, pass in the form of electron-jets, of a diameter smaller than that of said beams, in their transit along substantially straight paths to pre-selected, tangent, dot-like, color-phosphor, screen-areas arranged in a pattern which is systematically related to said first mentioned pattern; the improvement which comprises: a `systematic relationship of the spacing and arrangement of said dot-like patterns wherein the distance between the centers of those screen-areas which lie yadjacent to the central region of said screen-pattern is greater than the distance between the centers of the straight jet-paths which terminate thereon.

2. In a multiple-beam color-kinescope wherein the multiple electron-beams are subjected to dynamic convergence in scanning a screen unit of the kind comprising a mask containing a pattern of equally spaced dot-like apertures through which electrons, derived from said beams, pass in the form of electron-jets, of a diameter smaller than that p of said beams, in their transit along substantially straight paths to pre-selected, tangent, dot-like, color-phosphor, screen-areas arranged in a pattern which is systematically related to said rst mentioned pattern, the improvement which comprises: a systematic relationship of the spacing and arrangement of said dot-like patterns wherein the distance between the centers of those screen-areas which lie adjacent to the central region of said screen-pattern is greater than the distance between the centers of the straight jet-paths which terminate thereon, and the distance between the centers of those screen-areas which lie in a region surrounding said central region of said screen pattern is less than the distance between the centers of the straight jet-path which terminate on said last-mentioned screeneareas.

3. The invention as set forth in claim 2 and wherein said last mentioned region of said screen-pattern comprises a marginal edge portion of said screen-pattern.

4. The invention as set forth in claim 3 and wherein the variation in the distance between the centers of said screen-areas and the centers of said straight jet-paths is substantially uniform as measured outwardly from the the center of said screen-pattern to the marginal edges thereof.

References Cited in the le of this patent UNITED STATES PATENTS 2,568,448 Hansen Sept. 18, 1951 2,659,026 Epstein A Nov. 10, 1953 2,690,518 Fyler Sept. 28, 1954 2,755,402 Morrell July 17, 1956