US3043975A - Image display device - Google Patents

Description

J y 0, 1962 G. A. BURDICK 3,043,975

IMAGE DISPLAY DEVICE Filed Aug. 5, 1957 4 Sheets-Sheet 1 5m INVENTOR Y GLEN A; BURDICK ATTORNEY July 10, 1962 G. A. BURDICK IMAGE DISPLAY DEVICE 4 Sheets-Sheet 2 Filed Aug. 5, 1957 n mm Cu INVENTOR GLEN A. BURDKIK ATTORNEY July 10, 1962 G. A. BURDlCK 3,043,975

IMAGE DISPLAY DEVICE Filed Aug. 5, 1957 4 Sheets-Sheet 3 TANGENTIAL INVENTOR GLEN A. BURDICK ATTORNEY July 10, 1962 G. A. BURDICK 3,043,975

IMAGE DISPLAY DEVICE Filed Aug. 5, 195'? 4 Sheets-Sheet 4 UGHT AX\S TUBE AX\S RADIAL NVENTOR TANG'ENTIAL 4 GLEN A.'suR-mc\ F \G.7. .fl aktim ATTORNEY United States Patent IMAGE DISPLAY DEVICE I 7 Glen A. Burdick, Waterloo, N.Y., assignor, by mesne a ss'ignments, to Sylvania Electric Products Inc., Wilming'ton, Del., a corporation of. Delaware Filed Aug. 5, 1957, Ser. No. 676,331 2 Claims. (Cl. 313-92) This invention relates to image display devices and more particularly to cathode ray tubes of the type adapted to be employed in color television apparatus. 1

One of the chief problems encountered in the production of screens for image display color tubes such as those used in television apparatus involves matching of the light optics employed in the screen forming process with the electron optics existent in the finished tube. Unless ice ' between the center of the associated spot pattern and adthe discrete image display elements on the screen are positioned so that the scanning electron beam or beams will correctly register therewith, an impure or otherwise unacceptable color image will result. Some of these registration problems and their solutions, along with light optical structures and processes for forming the screen, are discussed in detail in the co-pending application, S.N. 595,144, entitled Cathode Ray Tube Structure and Process, Glen A. Burdick, which is assigned to the same assignee as the present invention. This invention is concerned in part, with that portion of the registration problem createdby dynamic convergence of the electron beams employed in the tube. It is the present practice in television art to use a continuously varying beam convergence field in conjunction with a multiple beam color tube so that the beams can be moved relative to each other in the deflection region inaccordance with the deflection angle and direction of the beam or beams at a given instant. The mask or grid utilized in the tube generally has a spacing from the screen such that the electron beams will cross one another at the mask and impinge upon the screen without overlap. This mask is constructed so that the spacing from the center of the mask to the screen is less than the spacing between these structures along their edges. However, with such a construction, the beam impinging spots for any given pattern are separated by agreater distance over certain areas of the screen than over other areas. In order to obtain a reasonable semblance of color purity in the tube, the discrete image display elements or areas are so positioned that at least a small portion of each display area will cover the associated electron beam impinging spot on the screen. The image display so produced is not uniform in appearance nor does it give good'color uniformity. Due to the critical design, manufacturing tolerances are extremely rigid and the tube operational setup requires a variety of controls and is very costly and time consuming.

Accordingly, an object of. this invention is to reduce the aforementioned disadvantages and to-provide an optirnum display area with good electron beam registration, improved color uniformity, and a uniform'appearing screen for an image display device. I

A further object is to reduce the necessity for critical control of manufacturing tolerances in the fabrication of image displays and to increase the operational set-up efliciency for such devices. I

Another object is to fabricate improved image display screens and tubes. 1

The foregoing objects are achieved in one aspect of the invention by the provision of an image display tube in which the electron beam impinging spot pattern associated with a given image display pattern is such that the average distance between the center of a given beam impingingspot and the center of the associated spot patjoining spot patterns. An exposure device and manufacturing process are providedto produce a screen having a plurality of discrete display areas, the location of each discrete area being positioned in a prescribed relationship to the impinging beam positions fora given deflection angle.

For a better understanding of the-invention, reference is made to the following description, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a plan view of a typical cathode ray tube adapted for the reproduction of color images;

FIG. 2 illustrates the manner in which the electron beams are dynamically converged in the-tube;

FIG. 3 shows a portion of an image-display structure illustrating one embodiment ofthe invention;

1 FIG. '4 illustrates the spatial relationship between beam impinging spot patterns formed in accordancexwith one aspect of the invention; I

FIG. 5 shows a portion of acathode ray tube screen; FIG. 6 illustrates the optical system employed in the screen forming process; I

FIG. 7 is an enlarged view of a portion of the discrete image display configurations showing the beam impinging spots located thereon; and

, FIG. 8 illustrates the relationship between the image display areas and the electron beam impinging positions; Referring to the drawings, FIG. 1 shows a typical plural beam shadow mask type cathode ray tube. Disposed within envelope 11 are three electron emitters 12 positioned approximately apart to provide three electron beams 13 which may be deflected by coils 15 over the raster area and converged at mask 17 to impingeiupon screen 19. The screen comprises a large number of triads, each triad consisting of, discrete areas or elements of red, green and blue color fluorescing materials which are positioned at the intercepting pointsof', the appropriate one of the electron beams 13 employed in the tube. Although a tri-gun shadow mask tube is shown in FIG. *1, it will be apparent that the invention described herein is also applicable to other plural beam types of image reproduction devices.

In order to have the electron beams 13 converge at the apertures in grid 17 over the entire screen, dynamic convergence magnets 21 are conventionally employed. Two of the three beams used in a shadow mask cathode ray tube are shown in FIG. 2 to illustrate the dynamic convergence efiect-s. The static convergence beam paths pass through points a and b in the defle'ctionregion and pro lceed toward mask 17 and screen :19 at an angle. to the tube axis to converge at point g: When the beams 13 are deflected to some-angle alpha (ix) withoutthe aid'of dynamic convergence fields supplied by-coils 21, the beams appear to originate fromp'oints a" and b and intersect at point c. This situation is highly unsatisfactory. In prac@ tice, the coils 21 provide'rna-gnetic' fields which move the beams 13 radially outward in thedefiection region to cause beams 13 to appear to come fromzpoints' e and f to provide the desired convergence at point gf within an aperture in mask 17. The points e and f designate positions which-are approximately onthe locus of motion of the apparent center of deflection for each beam 13 as more fully described in the above mentioned Burdick application; Q

It has been the practice to use a mask' 17 which has a spacing d lat the center/of the mask between the mask and screen 19 which is less than the spacing d; at the edge of the mask. This construction, in conjunction with dynamic convergence,'may produce an electron beam and fluorescent dot registration of the type shown in FIG. 2'

' displaced from the screen. The electron beams 13' may be separated by a considerable distance at the edges of the screen, as shown, or they may be separated or pulled together at other pre sele'cted positions by moving the entire mask toward'or away from the screen in a manner well understood inthe art. In any event, a tube having this'type of structure produces a-beam pattern which has given areas wherein the beams are undesirably separated or pulled together.- This situation causes the beams to impinge upon the fluorescent dots very close to their borders at those locations on the screen where the beams. are adversely affected to the greatest extent. i In order'to improve the beam landing position pattern uniformity over the screen and the spacing between the beamimpinging positions in a given triad, it has been found that the mask curvature shouldbe such that the spacing's FIGJ3, along the tube axis or central portion,

should be greater than the spacing s at the edges or peripheral portions of the grid 17. This grid or mask structure takesinto account the non-linearity of the fields provided by yoke coils 21, the amount of beam displacementneeded in the tube for dynamic convergence, and

the geometric configurations and spatial relationships of the gun electrodes 12, screen 19, etc. Since the grid or mask 17 and screen 19 are generally curvilinear in form,

- the screen. To illustrate this pattern, FIG. 4 shows two adjoining average triads spaced from one another in a tangential direction The individual average beam pog of the type shown in FIG. 3 l

less than the radial dimension, it is used as a basis for the beam spot and phosphor dot patterns. The phosphor dot triad pattern should fit into the smallest beam triad pattern so that there will not be an overlap of phosphor dots on the screen.

FIG. 5 illustrates the derivation of the average beam spots centers, R, B, G, R, B, and G" shown in FIG. 4. Three locations on screen 19 are indicated at 3 oclock, 7 oclock and 11 oclock for a deflection angle of 33 degrees. The sum of 12 numbers of B-O distances, i.e.

+B3-O3 B r- -oq B11011' by n is approximately equal to one-third the tangential distance between the centers of adjoining triads, e.g. dimension O7O7I.' This relationship exists for all R, B and G beam spots located on each deflection radius over the entire screen to provideanimproved beam spot pattern;

It has been found that for a 22 inch 70 degree deflection shadow mask color tube, a spacing s equal to .530 inch varying to an edge spacing of 5 of .491 inch provides the pattern illustrated in FIG. 5. Such a spacing may be achieved by forming the mask 17 with'a radius of curvature substantially equal to the 26 inch radius used for the screen surface. Generally, the center of the mask radius is positioned farther from the screen than the cen-" ter of the screen radius so that even if the mask and screen have the same or a slightly smaller or larger radius, the peripheral portions of the mask will becloser'to,

; while also providing a maximum border offluorescent sitions in an'average triad at a given deflection angle rela- 'tive to the center ofthe triad,'and the relationship between adjoiuing average triads may be expressed in terms ofv distances measured from the triad centers 0 and 0'.

This beam spot pattern is such that for any given triad joining triad. In' FIG. 4, the letters R, B and G have R-0 and G-O distances in triad T in additionto the The tangential distance between beam spot triads is used to define the relative triadpositions since it is a less constant dimension over jthe*'screen than the radial 'dimension and since it-may-be expressed in terms of a simple relationship. 1 FIGS. 1, 2 .and 3 illustrate the material around each beam impinging position or spot when the spot patternis of the type shown in FIG. 5. Although the above mentioned Burdick application explains in detail the method of forming a fluorescent-screen by a photo-printing process, it will be discussed here briefly. In this process, a light hardenable photo-sensitive material such as polyvinyl alcohol sensitized with ammonium dichromate and an appropriate fluorescent material such as the 'red phosphor, zinc phosphate, are deposited on the glass panel 25. Discrete areas of this coating are then exposed to light rays radiated from a point source light transmitter 27 through the lens 29 and through apertures in a'negative or grid 17. The areas 23 of the sensitized-coating which are exposed to light become hardened and adhere to the glass envelope While the unexposed portions are removed by a developing fluid such as deionized water. The above process is then repeated using the blue and green phosphors, with proper oif-setting of the transmitterand lens with each exposure manner in which the electron beams are converged at an aperture in mask 17 to cross one another and impinge upon screen 19 to form a triad of beam spots; The rela-' tive positions of adjoining triads are therefore dependent, in part, upon the relative positions of-the-apertures in mask 17. It is wellfknown that the mask "is stretchednon-uniformly in a tangential direction during fabrication, with the distance between adjoining mask apertures ,decreasing pro'gressively toward the mask periphery.

operation to provide the complete image display screen. Zinc ortho-silicate'is one example-of an acceptable green phosphormaterial while zinc sulfide is at present consid ered to be a satisfactory blue phosphor;

FIG. shows an optica-lsystem associated with one beam position ofa multiple beam tube which is capable of positioning the discrete screen elements 23 at the loca tion where the beams 13 will land by substantially supere imposing in space the locusrof motion of apparent light ray origin upon the locus of motion of apparent center of deflection of the electron beam. This relationship is accomplished by cit-setting light source 27 from the tube "axis a distance p and elf-setting lens 29 a distance 'r and an angle beta 13) fromthe axis of the transmitter. With this arrangement, "the locus 32 of apparent light ray origin utilized in thescreen forming process is located in. space at substantially the same position relative to the screen and mask as is the locus 33 of the electron beam apparent center of deflection in the operating tube. Although the light rays 26 originated from the tip of transmitter 27,

they appearto come from apoint on locus 33, when viewedfrom' the screen, since they are refracted by the plano-concave symmetrical lens 29. The amount of offset and tilt of lens 29 are inter-related in such a manner that an increase in oflset will allow a reduction in tilt and vice versa to achieve similar results. In addition, although a symmetrical planoconcave lens is shown, other types of lens elements could be employed in conjunction with the correct positioning of transmitter 27 and the lens 29 relative to one another and to the mask 17 and the axis of the tube to achieve the desired results. For instance, an asymmetrical and/ or an aspherical lens could be used in this system with little or no tilt, if desired. It has been found that for a 22 inch shadow mask tube of the type described above, the application of a 90 millimeter diameter plano-concave lens 29 with a center thickness of .45 centimeter and a radius of curvature equal to 23.55 centimeters spaced from transmitter 27 a distance of 1.875 inches, offset a distance r of .265 inch and tilted an angle beta (,8) of 3 degrees will produce the improved phosphor dot pattern for this tube.

Referring to FIG. 7 it can be seen that the discrete image display phosphor areas or dots 23 are so positioned by the optical system shown in FIG. 6, when it has the ideal combination of tilt and off-set, that the discrete areas are substantially tangent in a tangential direction to provide maximum coverage of the panel in addition to substantially increasing the uniformity of brightness and quality of the reproduced image while providing color pattern uniformity with a minimum amount of color impurity. The relationship between the beam impinging spots or positions 13 and the discrete phosphor dots 23 on the screen is clearly shown in FIGS. 7 and 8. For any given deflection angle, i.e. for those positions on the screen located at a given radius from the axis of the screen, the centers as of the areas 23 are positioned substantially coincident with the location of the average centers y of the impinging beam spots 13. The beam positions shown by solid lines in FIG. 8 indicate one location on the screen, e.g. a 36 degree deflection angle at 3 oclock. Disposed exactly opposite (in dotted lines) to the positions shown by the solid lines would be the location of the beam spots 13 at a 36 degree deflection angle and at 6 oclock. Therefore, it can be seen that the centers x of discrete phosphor areas 23 are substantially coincident with the average centers y of the spots 13 at all locations on a given screen radius or for a given deflection angle. Such an arrangement provides improved registration over the entire screen and minimizes the possibility of color impurity in the reproduced image.

Referring particularly to FIG. 7, the pattern of fluorescent dots 23 is shown to consist of red, green and blue fluorescing dot triads which are substantially contiguous in a tangential direction and are separated from one another in the radial direction for reasons explained more fully in conjunction with FIGS. 4 and 5. That is, if a line is drawn from the center of the screen radially outward, the successive triads which the line intercepts will be separated from one another by increasing amounts with increasing deflection angle whereas the adjacent triads lying along a line tangent to the radial line will be substantially contiguous to one another. This type of phosphor pattern achieves maximum coverage of face plate 25 without overlap.

It is apparent from the foregoing description that a mask configuration has been illustrated in FIG. 3 to provide a more symmetrical and uniform beam impinging spot pattern as illustrated in FIGS. 4 and 5. In addition, a process and exposure device such as that shown in FIG. 6 is adapted to form a phosphor dot pattern (FIGS. 7 and 8) which registers with the beam spot pattern to provide a highly satisfactory image display.

Although several embodiments of the invention have been shown anddescribed, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. A cathode ray tube of the type adapted to employ a plurality of dynamically converged electron beams directed to'be deflected over and impinge upon an image display screen, said screen comprising a curvilinear support having discrete light emitting areas arranged thereon to form a plurality of patterns located in radial and tangential relationships with one another, said patterns being spaced from one another radially outwardly from the center of said curved support and disposed substantially tangent with one another in a tangential direction extending normal to the radial direction, said patterns varying in spacing from each other in said radial direction to locate each discrete area substantially coincident with the average location of the center of the impinging beam at each deflection angle.

2. A cathode ray tube of the type adapted to employ a plurality of dynamically converged electron beams directed to be deflected over and impinge upon an image display screen, said screen comprising a curvilinear support having discrete light emitting areas arranged thereon to form a plurality of triad patterns located in radial and tangential relationships with one another, said triad patterns being spaced from one another radially outwardly from the center of said curved support and disposed substantially tangent with one another in a tangential direction extending normal to the radial direction, the radial spacing between triad patterns increasing with increased radial distance from the center of said screen, said triad patterns being formed to locate each discrete area substantially coincident with the average location of the center of the impinging beam at each deflection angle.

References Cited in the file of this patent UNITED STATES PATENTS 2,416,056 Kallmann Feb. 18, 1947 2,745,978 Van Ormer May 15, 1956 2,795,719 Morrell June 11, 1957 2,795,720 Epstein June 11, 1957 2,801,355 Nunan July 30, 1957 2,817,276 Epstein Dec. 24, 1957 2,823,254 Heuer Feb. 11, 1958 2,855,529 Morrell Oct. 7, 1958 2,885,935 Epstein May 12, 1959 OTHER REFERENCES RCA Publication, Recent Improvements in the 21AXP22 Color Kinescope, by R. B. J-anes, L. B. Headrick, and J. Evans, printed June 6.

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