MXPA96002190A

MXPA96002190A - Color picture pipe that has a discharged mask with better opening separation

Info

Publication number: MXPA96002190A
Application number: MXPA/A/1996/002190A
Authority: MX
Inventors: Frederick Simpson Theodore; George Marks Bruce
Original assignee: Thomson Consumer Electronics Inc
Priority date: 1995-06-06
Filing date: 1996-06-06
Publication date: 1998-04-01

Abstract

The present invention relates to a color image tube having a shadow mask and a dot screen, said mask being rectangular and having two long horizontal sides and two vertical short sides, said long sides being in parallel with a central major axis of said mask and such short sides in parallel with a minor central axis of said mask, said mask including a matrix of openings arranged in vertical columns and horizontal rows, the openings being in a row in different columns than in the openings in adjacent rows, the vertical passage of the openings being the vertical separation between adjacent openings within a column and the horizontal passage of the adjacent openings within a row, characterized in that said horizontal passage increases from said minor axis to the short sides of such mask, and said vertical step decreases from the center of such mask to the short sides of the mask, along said major axis, and is increased from said minor axis to the corners of such a mask, adjacent to the long sides of such a mask

Description

COLOR IMAGE PIPE THAT HAS PE SHADOW MASK WITH SEPARATION OF IMPROVED OPENING This invention relates, in general, to tubes of color images of a type having shadow masks for use with dot screens, where the openings of the shadow mask are round, almost round , elliptical or almost elliptical and are usually aligned in rows and spaced columns; and, in particular, to an improved separation between the rows and columns of said openings. Several factors can cause the incorrect registration of an electron beam with a phosphorescent element on a color image tube screen. One of these factors is the thermal expansion of a tube shading mask, when the mask is heated by electron beams from an electron tube of the tube that impinges on the mask. The shadow mask is generally attached to a peripheral structure that surrounds the mask. During the operation of the tube, the heat of the mask flows into the structure, creating a differential in temperatures between the peripheral portions and the center of the mask. Due to this differential, the center of the mask, the periphery of the mask and the structure expand at different rates. These different expansion rates result in an arc or dome formation of the shadow mask. Due to said dome formation, the electron beams passing through the mask incorrectly register the phosphorescent elements of the tube screen.

A mask dome training compensation method is taught in U.S. Patent No. 4, 136,300, issued to AM Morrell on January 23, 1979. That patent discloses the desire to increase the curvature of a mask to reduce the inadequate recording of the electron beam caused by the dome formation of the mask. The patent also teaches that, with increased curvature, the horizontal center-to-center separation between the openings of the shadow mask should be increased from the center of the mask to the ends of the horizontal axis. In the design of point-like screen type color tubes that can be used in video displays, it is desirable to use more mask curvature together with variable aperture spacing, in order to obtain the advantage of a reduced inadequate registration as well as the additional advantages of being able to use higher anode power, providing simpler fabrication, increased mask strength and reduced microphonic noise. However, there is a problem, as to how the aperture gap should be varin order to obtain a screen with uniformly straight parallel rows of phosphorescent points, in order to minimize the moire. In accordance with the present invention, a tube of improved color images includes a shadow mask and a dot screen, wherein the mask is rectangular and has two long horizontal sides and two vertical short sides. The long sides are in parallel with a larger central axis of the mask, and the short sides are in parallel with a smaller central axis of the mask. The mask includes a matrix of openings arranged in vertical columns and horizontal rows. The openings in a row are in columns different from those in the openings in the adjacent rows. The vertical separation between the openings in the same column is the vertical passage of the openings, and the horizontal separation between the openings in the same row is the horizontal passage of the openings. The improvement comprises the horizontal passage of the openings increasing from the minor axis to the short sides of the mask and decreasing from the major axis to the long sides of the mask. Also, along the major axis, the vertical passage of the mask decreases from the center to the short sides of the mask and, adjacent to the long sides of the mask, increases from the minor axis to the corners of the mask. In the drawings: Figure 1 is a partially sectioned axial side view of a tube of color images showing the present invention. Figure 2 is a front plan view of a shadow mask structure assembly of the tube of Figure 1. Figure 3 is a small section of the shadow mask of the assembly of Figure 2, used to illustrate the opening step.

Figure 4 is a small section of a dot screen of the tube of Figure 1, illustrating the point step.

Figure 5 is a right upper quadrant of the shadow mask of Figure 2, showing the curvatures of several rows and columns of openings in the mask and presenting horizontal and vertical passages for a particular embodiment of the mask. Figure 6 is a right upper quadrant of the shadow mask embodiment of Figure 5, showing the horizontal steps between the openings within the rows at four locations. Figure 7 is a top right quadrant of the shadow mask embodiment of Figure 5, showing the vertical steps between the openings within the columns in four locations. Figure 8 is a top right quadrant of the observation screen of the tube of Figure 1, associated with the shadow mask of Figure 5, showing the center-to-center horizontal separation between the centers of phosphorescent point triads at four locations. Figure 9 is an upper right quadrant of the observation screen of the tube of Figure 1, associated with the shadow mask of Figure 5, showing the vertical center-to-center separation between the centers of phosphorescent point triads at four locations . Figure 1 shows a rectangular color image tube 10, having a glass envelope 1 1, comprising a rectangular 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) extending from an anode button 16 to the neck 14. The panel 12 comprises an observation front plate 18, and a peripheral bracket or side wall 20, which is sealed to the funnel 15, by means of a glass frit 17. A three-color phosphorescent screen 22 is located on the inner surface of the faceplate 18. The screen 22 is a dot screen, with phosphorescent dots arranged in triads, each triad including a phosphorescent point of each of the three colors . A multi-aperture color selection electrode or shadow mask 24 is removably mounted, by conventional means, in predetermined spaced relation to the screen 22. An electron gun 26, shown schematically by dashed lines in the Figure 1, is centrally mounted within the neck 14, for generating and directing three electron beams 28 along converging paths through mask 24 to the screen 22. The tube of Figure 1 is designed to be used with a yoke of external magnetic deflection, such as the yoke 30 shown in the vicinity of the funnel-to-neck junction. When the yoke 30 is activated, it subjects the three beams 28 to magnetic fields which cause the beams to scan horizontally and vertically in a rectangular frame on the screen 22. The initial plane of deviation (in zero deviation) is approximately half of the yoke 30 Due to the marginal fields, the deflection zone of the tube extends axially from the yoke 30 to the region of the canyon 26. For simplicity, the actual curvatures of the trajectories of the deviated beams in the deviation zone are not shown in the Figure 1. The shadow mask 24 is part of a mask structure assembly 32 that also includes a peripheral structure 34. The mask structure assembly 32 is shown positioned within the face plate panel 12 in Figure 1. The mask of shadows 24 includes a curved portion with opening 25, a perforated edge portion 27, surrounding the apertured portion 25, and a skirt portion 29 folded back from the edge portion 27 and extending away from the shade 22. The mask 24 is embedded within (or alternatively over) the structure 34, and the skirt portion 29, is welded to the structure 34. The shadow mask 24, shown in plan view in Figure 2, has a rectangular periphery with two long sides and two short sides. The mask 24 has a major axis X, which passes through the center of the mask and is parallel to the long sides, and a minor axis Y, which passes through the center of the mask and is parallel to the short sides. The mask 24 includes a matrix of round openings 36, arranged in vertical columns 38, and horizontal rows 40, spaced as shown in detail in Figure 3. The columns 38 are approximately parallel to the minor axis Y, and the rows 40 are approximately parallel to the major axis X.

The openings in a row are in columns different from those in the openings in the adjacent rows. The vertical separation between the adjacent openings in the same column is defined as the vertical passage av of the openings, and the horizontal separation between the adjacent openings in the same row is defined as the horizontal passage ah of the openings. The screen 22 includes a pattern of phosphorescent dots 42 arranged in vertical columns 44 and horizontal rows 46, separated as shown in Figure 4. The columns 44 are approximately parallel to the minor axis Y, and the rows 46 are approximately parallel to the major axis X. The vertical separation between adjacent points in the same column is defined as the vertical step D of the points, and the horizontal separation between points in the same row that emit light of the same color is defined as the horizontal step Dh of the points. The opening step at any location in a mask can be determined by calculating either vertical or horizontal separation between two adjacent openings in the location. This calculation can be performed using the following equations (1) and (3) for the vertical position Yn of an opening in row n and for the horizontal position Xm of an opening in column m, of the mask, respectively. Yn = Y? P + + A2Y0 n V + A3Y0n + A4Y0n X * + A5Y0p V + A6Yon 6 x4 (1) where x is the horizontal distance of the opening from the minor axis, along row n; wherein A1 t A, A3, A4, A5 and A6 are coefficients that are related to the relative curvatures of the faceplate panel and the shadow mask; and where Y0n is the intercept of the minor axis of opening row number n, which is determined by the equation, Yon = Ci n + C2n2 + C3n3 + C4n4, (2) where Ci, C2, C3 and C4 are coefficients that are related to the relative curvatures of the faceplate panel and the shadow mask, and n is a row number for a particular aperture row. Xm = X? M + B? X0my2 + B2X? M V + B3X0m V + B4X0m y4 + B5X0m V + B6Xop, y6 (3) where y is the vertical distance of the opening from the major axis, along the column m; where Bi, B2, B3, B, B5 and Be are coefficients that are related to the relative curvatures of the faceplate panel and the "shadow mask; and where X0m is the intercept of the major axis of opening column number m, which is determined by the equation, Xom = Di m + D2m2 + D3m3 + D4m4 + D5m5, (4) where Di, D2, D3, D and D5 are coefficients that are related to the relative curvatures of the faceplate panel and the shadow mask, and m is a column number for a particular aperture column. The vertical step av (76-74) between rows 74 and 76 is determined by solving the vertical position equation Y "twice, once for n = 74 and once for n = 76. Note that row 75 does not contain a opening that is in the same column as that of the openings in rows 74 and 76. Then the vertical step av (76-74) is equal to Y76 - Y7 - Similarly, the horizontal step ah (80-78) between columns 78 and 80 are determined by solving the horizontal position equation Xm twice, once for m = 78 and once for m = 80. Then the vertical step ah (80-78) is equal to Y8o - Y78- In a particular mode the coefficients for the previous equations are the following, with all dimensions in millimeters (mm). These coefficients were selected to ensure that the vertical step Dv of the screen points remains constant over the entire screen. C? = 0.461 X 10 ° C2 = 0.765 X 10'6 C3 = 0.632 X 10"7 C4 = -0.765 X 10 10 A, = -0.382 X 10" 6 A2 = 0.244 X 10"1 1 A3 = 0.284 X 10 '15 A4 = 0.321 X 10"1 1 A5 = -0.174 X 10" 15 A6 = 0.525 X 10 20 D, = 7.844 X 10 D2 = 7.818 X 10 D3 = 3.858 X 10 -7 D4 = 9.233 X 10 -10 D5 = 9.557 X 10 -13 B? = -1.703 X 10 '6 B2 = 2.394 X 10 -12 B3 = 2.412 X 10 -16 B4 = 5.072 X 10"11 B5 = -2.453 X 10 '15 B6 = 3.059 X 10 -16 Figure 5 shows the horizontal and vertical steps, ah and av, respectively, in selected locations of a upper right quadrant of a mask, which were calculated using the specific coefficients above in the previous equations.The step variations between the center, sides and corner of the mask 24 of Figure 5 are shown in Figures 6 and 7. Figure 6 shows that the horizontal step of the mask ah increases from the minor axis Y to the short sides of the mask, and decreases from the major axis X to the sides long of the mask. Figure 7 shows that the vertical passage of the mask av increases from the major axis X to the long sides of the mask; but, along the major axis X, it decreases from the center to the short sides of the most expensive and, adjacent to the long sides, increases from the minor axis Y to the corners of the mask. The increment in the vertical passage av from the major axis X to the long sides of the mask generally occurs when the sides of the screen are tilted outward. By using the mask specified above, a screen having the horizontal and vertical steps Dh and Dv, shown in Figures 8 and 9, respectively, can be obtained. Although the horizontal step of the screen Dh increases from the minor axis Y to the short sides of the screen, and decreases from the major axis X to the long sides of the screen, there is no variation in the vertical step of the screen Dv in the whole screen. Because the vertical step of the screen is constant on the screen, the moiré is minimized.

Claims

1. A color image tube having a shadow mask and a dot screen, said mask being rectangular and having two long horizontal sides and two vertical short sides, said long sides being in parallel with a central major axis of said mask and such short sides in parallel with a minor central axis of said mask, said mask including a matrix of openings arranged in vertical columns and horizontal rows, the openings being in a row in different columns than in which the openings are in adjacent rows, the vertical passage of the openings being the vertical separation between adjacent openings within a column and the horizontal passage of the openings being the horizontal separation between adjacent openings within a row; characterized in that said horizontal step is increased from said minor axis to the short sides of said mask and decreases from said major axis to the long sides of said mask, and said vertical passage decreases from the center of such mask to the short sides of the mask. mask, at the edge of said major axis, and is increased from said minor axis to the corners of such chew, adjacent to the long sides of such mask. The tube as defined in claim 1, wherein said screen includes vertical columns and horizontal rows of phosphorescent dots, the vertical point passage at said corner being the vertical distance between two adjacent points within the same column; characterized by the vertical dot pitch being essentially the same over the entire screen. The tube as defined in claim 1, wherein said screen has sides that slope outwardly; characterized in that said vertical passage increases from said major axis to the long sides of said mask.