MXPA96005620A - Color picture tube that has a pattern debature of best shadow mask - Google Patents

Abstract

The present invention relates to a color image tube having a shadow mask mounted thereon in a spaced relation to a display screen thereof, said mask having a rectangular periphery with two long sides and two short sides, a major axis thereof passes through the center of the mask and is parallel to the long sides, and a minor axis thereof passing through the center of the mask and parallel to the short sides, and having the mask a set of openings including longitudinally cut openings aligned in columns that are essentially parallel to the minor axis and end in one edge of the set of openings, the adjacent openings in each column being separated by tie bars in said mask, displaced the link bars of a column in a longitudinal direction, parallel to the minor axis, of the link bars in each adjacent column, and the separation being between link bar and link bar spacing bar at the location on the mask, characterized by a first set of said columns, comprising each other column, having full length end openings at least at one end thereof, and a second set of said columns, each other column comprising not in the first assembly, end openings of partial length at least at one end thereof, ending the final openings of all the columns of openings in lines of smooth curved edges, and decreasing the spacing of link bars of the columns from the center of the mask to the short sides thereof, where the spacing along each column varies from the center of the mask to the long sides of the mask.

Description

COLOR PICTURE OUE HAS A PATTERN OF OPENING. OF IMPROVED SHADOW MASK This invention relates to color picture tubes having masks with openings in the form of longitudinal cuts, wherein the openings are aligned in columns and the openings in each column are separated by link bars in the mask; and particularly to a tube wherein the mask has smoothly curved upper and lower edges in the opening portion thereof, and the screen, during operation, exhibits a reduced moire. A predominant number of color picture tubes in use today have line screens and shadow masks that include apertures in the form of a longitudinal cut. The openings are aligned in columns, and the adjacent openings in each column are separated from one another by frames or link bars in the mask. These link bars are essential in the mask, to maintain its integrity when it is formed in a dome-shaped contour in some way parallel to the outline of the inside of a tube display front plate. Link bars in a column move in the longitudinal direction of the column (vertical direction) from the link bars in the immediately adjacent columns. Because the pattern of openings and tie bars, the upper and lower edges of the aperture arrangement is somewhat toothed, some columns of openings terminate with tie bars near the edge, while other columns terminate with openings at the edge. When a display screen is formed using a mask as a photomaterial the resulting screen also has upper and lower jagged edges. Those jagged edges are aesthetically undesirable. A technique that produces screens with edges -sloses is described in U.S. Patent No. 4,300,070, issued to R.H. Godfrey et al., November 10, 1981. In that patent, the opening edge of openings is smoothed with an elaborate method of lengthening and shortening the spacings of the last two openings in each column. The method makes the geometry of the edge smooth and also equals the light output on the edges of the screen, however, the method was developed to be used with masks that have a constant link bar spacing and a straight line edge projected onto the screen. Another technique for removing jagged edges of the screen, for use with a mask having curved upper and lower edges, is described in U.S. Patent No. 4,631,440, issued to J.D. Robbins on December 23, 1986. In that patent, the upper and lower edges are smoothed by varying the vertical spacing from column to column, while keeping the number of openings per column and the spacing in each individual column constant. Changes in the spacing of openings in a mask have an effect on a phenomenon called moiré. When electron beams hit the shadow mask, the link bars block portions of the rays, causing shadows on the screen immediately behind the link bars. When the electron beams are repeatedly scanned in a direction perpendicular to the aperture columns (horizontal direction), they produce a series of bright, dark horizontal lines on the screen. These bright, dark horizontal lines interact with the shadows formed by the link bars, creating lighter and darker areas and producing an undulating pattern on the screen, called a moire pattern. This pattern worsens the visible quality of the images displayed on the screen. Therefore, when the spacing of the link bars is varied, it is very convenient to select a spacing that will minimize the moire pattern. Many techniques have been suggested to reduce the problem of moire. Most of these techniques involve rearranging the positions of the link bars in a mask, to reduce the possibility that the electron beam scanning lines hit the shadows of the link bars. Although many of these techniques have been successfully used to reduce moiré, they are often incompatible with the desire to obtain smooth and clean-looking upper and lower screen edges while simultaneously reducing moiré patterns on a tube screen. In accordance with the present invention, a color picture tube has a shadow mask mounted thereon in spaced relation to a display screen thereof. The mask has a rectangular periphery with two long sides and two short sides. A major axis passes through the center of the mask and is parallel to the long sides thereof, and a minor axis passes through the center of the mask and is parallel to the short sides thereof. The mask has a set of openings including longitudinally cut openings aligned in columns that are essentially parallel to the minor axis and terminate at the edge of the set of openings. The adjacent openings in each column are separated by link bars in the mask. The link bars in a column move in the longitudinal direction, parallel to the minor axis, from the link bars in each adjacent column. The spacing from a link bar to another link bar in a column is the spacing of the link bar in a location in the mask. The improvement comprises a first set of columns, each other column comprising, having full-length end openings at least at one end thereof, and a second set of columns, each other column not comprising the first set, having openings end of partial length at least at one end of them. The final openings of all the columns of openings end in smooth curved edge lines. The spacing of the link bars of the columns decreases from the center of the mask to the short sides of the mask, and the spacing of the link bar along each column is varied from the center of the mask to the sides long of the mask. In the drawings: FIGURE 1 is a side view in axial section of a color image tube incorporated in the present invention. FIGURE 2 is a front plan view of a mask frame assembly taken in rectangle 4 of FIGURE 1. FIGURE 3 is an enlarged view of a small portion of a shadow mask of the tube of FIGURE 1. FIG. FIGURE 4 is an enlarged view of a portion of the shadow mask taken in the rectangle 4 of FIGURE 2. FIGURE 5 is an enlarged view of a portion of the shadow mask taken in the rectangle 5 of FIGURE 2. FIG. FIGURE 1 shows a rectangular color image tube 10 having a glass envelope 11 comprising a front plate panel 12 and a tubular neck 14 connected by a rectangular funnel 15. The funnel 15 has an internal conductive coating (not shown) which extends from an anode button 16 to the neck 14. The panel 12 comprises a front plate 18 and a peripheral rim or side wall 20, which is sealed to the funnel 15 by a glass frit 17. A phosphor screen of three color 22 is carried by the inner surface of the front plate 18. The screen 22 is a screen of lines, with the phosphor lines arranged in triads, each triad includes a phosphor line of each of the three colors. A multi-aperture color selection electrode or shade mask 24 is removably mounted, by conventional elements, in a separation ratio previously determined relative to the screen 22. An electron gun 26, shown schematically by dotted lines in FIG. FIGURE 1, is mounted centrally within the neck 14 to generate or direct three electron beams 28 along converging paths through the mask 24 to the screen 22. The tube of FIGURE 1 is designed to be used with a yoke of magnetic deflection, such as the yoke 30 shown in the vicinity of the junction of the funnel with the neck. When activated, the yoke subjects the three rays 28 to magnetic fields that cause the rays to scan horizontally and vertically in a rectangular trace on the screen 22. The initial plane of deflection (at zero deflection) is approximately half the yoke 30. Due to the fringed fields, the deflection zone of the tube extends axially from the yoke. 30 to the region of the gun 26. For simplicity, the actual curvatures of the paths of the deflected rays in the deflection zone are not shown in FIGURE 1. The shadow mask 24 is part of the mask frame assembly which also includes a peripheral frame 34. The mask frame assembly 32 is shown positioned within the panel of the faceplate 12 in FIGURE 1, and in the front view in FIG. FIGURE 2. The shadow mask 24 includes a portion of curved openings 25, a non-perforated edge portion 27 surrounding the opening portion 25, and a sleeve portion 29 folded back from the portion of the edge 27 and extending The mask 24 is telescoped within the frame 34 and the sleeve portion 29 is welded to the frame 34. As shown in FIGURE 2, the mask 24 has a major axis X, which passes through the center of the mask. the mask and is parallel to the long sides of it, and a minor axis Y, which passes through the center of the mask and is parallel to the short sides of it. As shown in FIGURE 3, the mask 24 includes apertures in longitudinal cut shape 36 aligned in columns that are essentially parallel to the minor axis Y. The adjacent openings 36 in each column are separated by link bars 38 in the mask, with the spacing between the centers of the adjacent link bars 38 in a column defined as the spacing: -to av at a particular location in the mask. In a preferred embodiment of. the mask 24, the spacing of the link bar is varied both in the direction of the major axis X and in the direction of the minor axis Y, in order to achieve upper and lower screen edges of clean appearance and to provide a good realization of moire on the screen. The mask 24, as shown in FIGURES 4 and 5, includes a first set of columns of openings 40, comprising each other column, with full-length end openings 42, at least at one end thereof, and one second set of opening columns 44, all other columns comprising not included in the first assembly, having end openings of partial length 46 at least at one end thereof. The final openings of all the columns of openings end in lines of smooth curved edge 48. The smooth curved edge lines 48 are obtained by gradually decreasing the spacing of the tie bars of the columns from the center of the mask towards the short sides of the mask, so that the spacing of the link bars in the mask portion shown in FIGURE 5 is less than the spacing of the link bars in the portion of the mask shown in FIGURE 4. Because the area of the most severe moire is on the short sides of the screen, the spacing of the link bars in the region of the short sides of the mask is optimized to minimize the moire in it during the operation of the tube. With the spacing of the link bars optimized in this way, an additional technique is required to reduce the moire in other portions of the screen. In mask 24, this additional technique is to vary the spacing of the link bars along each column from the center of the mask to the long sides of the mask. Generally, this variation of spacing of the link bars is a gradual decrease in the spacing of the link bars from the center to each long side of the mask. The link bars in the alternating columns are in slightly curved rows of a flat unformed mask. When the flat mask is formed in a contoured mask, these rows of link bars are essentially parallel to the scanning lines of the electron beams. The intercept of the minor axis of any link bar row is determined by the following equation: Y0 = S¡A (i) • 10p [row no.] (I), where "Y0" is the distance along the minor axis from the major axis X, "A (i)" is a coefficient that varies with the type of tube, "P" represents a power of 10, "row no." is the number of any link bar counted from the major axis X, and "i" is a number from 1 to 8. The following table lists the coefficients A (i), i in millimeters, and powers P for a tube that has a display screen - with an aspect ratio of 4/3 and a diagonal of 48 centimeters (19 inches). _i A (i) P 1 +9,975822133442 -01 2 -3.236410711583 -06 3 +6.046184314904 -07 4 -5.904474762096 -10 The vertical distance "Y" from any row of link bars to the major axis X, at any point outside the minor axis, is determined by the following equation: Y = Yo + YD » where YD = SnC (n) • 10p (Y0) j (X) k. and where "n" is a number from 1 to 72, "C (n)" is a coefficient that varies with the type of tube, "P" represents a power of 10, "X" is the distance along the major axis, and "j" and "k" are powers of Y0 and X, respectively, j and k each vary between 1 to 5. The following table lists the coefficients C (n), in millimeters, the powers P, the powers j of Y0 and the k powers of X, for a tube that has an aspect ratio of 4/3 and a diagonal display screen of 48 centimeters (19 inches). n C (n) 1 -1.889623949890 -06 1 2 2 +4.165471142317 -12 3 2 3 +2.920387672196 -16 5 2 4 +4.293817663233 -12 1 4 5 -1.910781695200 -16 3 4 6 +3.89725219733 -2-1 5 4

Claims (1)

1. A color image tube (10) having a shadow mask (24) mounted thereon in a spaced relationship with respect to a display screen (22) thereof, said mask having a rectangular periphery with two long sides and two short sides, a major axis (x) of it passes through the center of the mask and is parallel to the long sides, and a minor axis (Y) of the same that passes through the center of the mask and is parallel to the short sides, and the mask having a set of openings including openings in longitudinal cut shape (36) aligned in columns that are essentially parallel to the minor axis and end in an edge of the set of openings, the adjacent openings in each column separated by link bars (38) in said mask, the link bars of a column being displaced in a longitudinal direction, parallel to the minor axis, of the link bars in each adjacent column, and or the spacing between the link bar and the bar of the spacing of the link bar (av) at the location on the mask, characterized by a first set (40) of said columns, each other column comprising, having final openings of total length ( 42) at least at one end thereof, and a second set (44) of said columns, each other column comprising not in the first assembly, partial length end openings (46) at least at one end thereof , ending the final openings of all the columns of openings in lines of smooth curved edges (48), and decreasing the spacing of link bars (av) of the columns from the center of the mask (24) to the short sides thereof, wherein the spacing along each column varies from the center of the mask to the long sides thereof. SUMMARY A color image tube has a rectangular shadow mask mounted thereon in a separation relationship with respect to a display screen. A major axis passes through the center of the mask and parallel to the long sides thereof, and a minor axis passes through the center of the mask and parallel to the short sides thereof. The mask has a set of openings including longitudinally cut openings aligned in columns that are essentially parallel to the minor axis and terminate at one edge of the set of openings. The adjacent openings in each column are separated by link bars in the mask which are displaced longitudinally from one column to the adjacent column. The separation of link bar to link bar in a column is the spacing of link bars in a location on the mask. A first set of columns of openings, comprising each other column, has full-length end openings at least at one end thereof, and a second set of openings columns, comprises any other column that is not in the first set , has partial length end openings at least at one end thereof. The final openings of all the opening columns end in curved, smooth edge lines. The spacing of the link bars decreases from the center of the mask to / the short sides thereof and the spacing of the link bars along each column varies from the center of the mask to the long sides of the mask • k ic ic ic