FR2579018A1 - COLOR IMAGE TUBE WITH IMPROVED SHADOW MASK - Google Patents

Abstract

COLOR IMAGE TUBE WHICH INCLUDES A SHADOW MASK MOUNTED NEAR A CATHODOLUMINESCENT LINE SCREEN, THIS SHADOW MASK COMPRISING A PLURALITY OF OPENINGS IN THE FORM OF SLOTS POSITIONED IN COLUMNS, SAID SHADOW MASK WITH BULKY PERIPHERAL , WITH TWO LONG OPPOSITE SIDES AND TWO OPPOSITE SMALL SIDES, A MAIN AXIS OF SAID MASK BEING AN AXIS PASSING THROUGH THE CENTER OF THE MASK AND THROUGH THE CENTER OF SMALL SIDES, AND A SECONDARY AXIS BEING AN AXIS PASSING THROUGH THE CENTER OF THE MASK AND THROUGH CENTER OF THE LONG SIDES, THE SAID OPENING COLUMNS EXTENDING IN THE DIRECTION OF THE SMALL AXIS AND BEING SPACED ONE OF THE OTHERS IN THE DIRECTION OF THE MAIN AXIS, THIS IMAGE TUBE IS CHARACTERIZED IN THAT THE COLUMN-COLUMN SPACING D 'OPENINGS AT, NEAR THE SMALL AXIS YY DUDIT MASQUE 24, ARE LOWER ON THE LONG SIDES OF THE MASK THAN NEAR THE MAIN AXIS XX OF THE MASK.

Description

The present invention relates to color image tubes of the type comprising

  both a shadow mask with perforations or openings in the form of windows, mounted in close proximity to a screen of cathodoluminescent lines of the tube, and it relates more particularly to improvements made to the spacing of the columns of openings at the inside such tubes, to obtain an outline

improved mask.

  Most image tubes manufactured today are of the shadow mask type with line screen slots. These tubes comprise rectangular front plates with a spherical outline on which the screens of lines of cathodoluminescent materials are deposited, and shadow masks provided with perforations in the form of slits, with a substantially spherical outline, adjacent to the screens. The slot-shaped openings of such tubes are arranged

  columns which are substantially parallel to the minor axis of the tube, or whose

  bure gradually increases from the center to the short sides of the mask.

  Several modifications to color image tubes have recently been proposed.

  According to one of these modifications, a new contour design is proposed.

  of faceplate panel that creates the illusion of flatness. Such a modification

  Tube fication is described in the patents of this holder numbers 84 02 865 and 84 02 866, both filed on February 24, 1984. The faceplate contour of the tube thus modified has a curvature both along

  main and secondary axes of the faceplate panel, but this

  bure is not spherical. The main and secondary axes are defined as the horizontal central axis and the vertical central axis respectively, when

  the tube is placed in its normal observation position. According to a pre-

  the embodiment described in these two previous patents, the peripheral border

  The risk of the tube screen is substantially planar, and it appears planar to the eye.

  In order to obtain such a planar or substantially planar peripheral border, it is necessary to give the front plate panel a curvature, along its main axis, which is greater on the sides of the panel than in the center of the latter. Such a non-spherical configuration of the faceplate panel creates a problem involving the outline of the shadow mask. When the mask elaborates has straight rectilinear sections parallel to the secondary axis,

  along its sides, the mask may have weak metallic characteristics.

  such as, in particular, undesirable bulging and / or microphonic problems. Therefore, it is preferable to give the mask a greater curvature, in these straight sections, than that suggested by the faceplate panel outline. However, such a modification of the contour of the

  mask requires other changes in the tube, including changes

  in the configuration of the mask openings or perforations.

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  In the first tubes of the mask type with screen slits in lines, the shadow masks were almost spherical, and the separation of the columns of adjacent openings along the main axis (horizontal separation) was kept constant over The mask. However, some more recent tubes of this type included a shadow mask with increased curvature, and they presented a variation in spacing of columns of openings as described in US Pat. No. 4,136,300. In these more recent tubes , the spacing between the axes of symmetry of the adjacent columns of openings or perforations increased from the center to the edge of the mask. This increase varied along the primary axis, generally as the square of the distance from the secondary axis. A new column-column spacing of openings is described in US patent application No. 615,589, filed March 31, 1984, and assigned to the

  present holder. In this publication, the spacing between columns of

  adjacent vertices increases, from the center to the sides of the shadow mask,

  much like the fourth power of the distance from the axis se-

  condaire of the shadow mask. This variation in column spacing can be

  expressed as a factor of the fourth power of the distance, in the-

  which the coefficient of proportionality is variable: it is more important with regard to the straight sections of the mask which are parallel but offset from the central horizontal axis, than for the straight sections located on the horizontal central axis. This variation according to the fourth power has proved suitable for the shadow mask contours of the first generation of substantially flat tubes. These first generation tubes have shadow masks which have a significantly greater curvature along the minor axis than along the main axis. However, the curvatures of the mask, for straight sections parallel to the minor axis, decrease from the minor axis towards the sides of the mask, to become relatively flat on the sides of the mask. This

  flatness is not desirable in a shadow mask, since it is

  vantage likely to cause deformations during handling and that it can cause a somewhat unpredictable bending when the tube heats up, in operation. The present invention provides improvements to the column-column spacing of openings, which make it possible to produce various curvatures in such shadow masks in order to obtain a more curvature.

  important on the sides of the mask.

  Accordingly, the subject of this invention is a color picture tube which

  includes a shadow mask mounted near a screen of cathodolumine lines-

  cent, this shadow mask comprising a plurality of slit-shaped openings positioned in columns, said shadow mask having a periphery substantially

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  rectangular, with two opposite long sides and two opposite short sides, a main axis of said mask being an axis passing through the center of the mask and through the center of the short sides, and a secondary axis being an axis passing through the

  center of the mask and through the center of the long sides, said opening columns

  tures extending in the direction of the minor axis and being spaced from each other in the direction of the main axis, this picture tube being characterized in that the column-column spacing of openings, near the minor axis of said

  mask, is weaker on the long sides of the mask than near the main axis

pal of said mask.

  Other features and advantages of this invention will emerge

  of the description given below with reference to the accompanying drawings, which in it-

  polish various embodiments, devoid of any limiting character.

  In the drawings: - Figure 1 is a plan view, partially in axial section, of a color image tube with shadow mask implementing an exemplary embodiment of this invention; - Figure 2 is a plan view of the front plate of the color image tube; - Figure 3 is a combined view illustrating the surface contours of the front plate panel along the main axis 3a-3a and along the minor axis 3b-3b, in straight sections of Figure 2;

  - Figure 4 is a plan view of the shadow mask of the image tube

  their of Figure 1; - Figure 5 is a combined view illustrating the surface contours of the shadow mask along the main axis 5a-5a, along the secondary axis 5b-5b, and along the diagonal 5c-5c, in cross sections of the Figure 4; - Figure 6 is a graph showing the spacing values

  column-column of the openings of a shadow mask of the color image tube, re-

  presented in solid lines, and the spacing of the openings in a mask

  lon the prior art, shown in broken lines;

  - Figure 7 is an enlarged view of the shadow mask, cor-

  corresponding to the part surrounded by the circle 7 in Figure 4; and,

  - Figure 8 is a graph illustrating the selection screen lines -

  born from the color image tube; - Figure 9 is a front elevational view of a shadow mask, suggested by its curvature of the front plate, showing a contour line having a constant sagittal height; and, Figure 10 is a front elevational view of a shadow mask

  improved, showing a contour line of this mask having a height sa-

constant gittal.

  In Figure 1, there is shown a rectangular color image tube 10, which comprises a glass envelope 11, comprising a front plate panel 12 and a tubular neck 14, these two elements being connected by a frustoconical part 16 in the form of funnel. The panel includes a front plate

  observation or display 18, and a lateral wall or peripheral flange

  risk 20 which is sealed on the frusto-conical part 16 by a glass frit 17. A rectangular screen of three-color cathodoluminescent phosphors 22 is supported by the internal surface of the front plate 18. The screen is a screen of lines, the lines of phosphors extending substantially parallel to the minor axis YY of the tube (perpendicular to the plane of Figure 1). The contours of the phosphor lines will be specified below. A shadow mask, or color selection electrode, provided with perforations according to the invention 24, is removably mounted in the front plate panel 12, according to a

  predetermined spacing relation to screen 22. An electric cannon

  tronic line 26, illustrated schematically by a rectangular contour in broken lines in Figure 1, is mounted in the center in the neck 14, so as to generate and direct three electron beams 28 along convergent paths, initially coplanar, through of mask 24

to screen 22.

  The tube 10 of Figure 1 is designed and constructed to be used

  read with an external magnetic deflection collar, such as the collar 30

  shown schematically in the drawing, surrounding the neck 14 and the section

  conical 16 in the vicinity of the junction of these two elements, in order to subject the three beams 28 to vertical and horizontal magnetic fluxes, so as to ensure horizontal scanning of the beams in the direction of the main axis (XX), and a vertical scanning in the direction of the minor axis or secondary axis (YY), respectively, according to a rectangular grid on

screen 22.

  Figure 2 shows the front of the front plate panel.

  tale 12. The periphery of the panel 12 constitutes a rectangle, with slightly curved sides. The border of the screen 22 is represented, in FIG. 2,

  by broken lines. This screen border is rectangular.

  In Figure 3, we can see a comparison between the related contours

  tifs of the outer surface of the front plate panel along the minor axis Y-Y and along the main axis X-X. The outer surface of the faceplate panel 12 is curved both along the main axis and along the minor axis, the curvature along the minor axis being greater than the curvature along the main axis, in the central part of the panel 12. For example, in the center of the front plate, the ratio: radius of curvature of the contour of the external surface along the main axis / radius of curvature

  along the minor axis, is greater than 1.1 (i.e. larger than a diff-

  10% ference). However, the curvature, along the main axis, is more

  small in the central part of the front plate, and it increases sharply-

  close to the edges of the faceplate. In this example of realization

  tion, the curvature along the main axis, near the edges of the fron-

  tale, is larger than the general curvature along the minor axis. Thanks to this design, the central part of the front plate becomes flatter, while the points of the external surface of the front plate, on the edges of the screen, are located substantially in a plane P and define a

  substantially rectangular peripheral contour line. The curvature of over-

  face along the diagonal is chosen so as to "smooth" the transition

  between the different curvatures along the minor axis and the major axis. Preferably

  rence, the curvature along the minor axis is about 4/3 greater than the cur-

  along the long axis, in the central part of the front plate. However

  However, the curvature along the minor axis can also be similar to the curvature.

  bure along the major axis, in the central part, this curvature increasing

  near the edges of the faceplate.

  Using the different curvatures along the main axis and

  secondary, the dots, on the outer surface of the panel, directly op-

  placed at the edges of the screen 22, are located substantially in the same plane P. These points located substantially in the same plane, when viewed from the front of the panel 12 (as in Figure 2), form a contour line, on the outer surface of the panel, which constitutes substantially a rectangle superimposed on the edges of the screen 22. Consequently, when a tube is introduced into a television receiver, it is possible to use, around the tube, a mask with a uniform width border. The edge of such a mask, which comes into contact with the tube along the rectangular contour line, is also located in the plane P. Since the peripheral border of an image on the screen of the tube appears flat, it produces the illusion of a flat image, although the faceplate panel is curved outward at a time

  along the main and secondary axes.

  Figure 4 is a front view of the shadow mask 24. The lines in-

  terrpmpus 32 represent the border of the perforated part of the mask. The con-

  surface turns, along the main axis XX, along the secondary axis YY, and along the diagonal of the mask 24, are represented by the curves 5a, 5b and 5c, respectively, in Figure 5. The mask 24 has a curvature, along its main axis, which is different from that along its

  secondary axis. The curvature along the main axis has a slight cur-

  bure near the center of the mask, and greater curvature on the sides of the

  mask. The outline of such a shadow mask can generally be obtained by

  1C writing the curvature along the main axis XX in the form of a circle of large radius on about the central part of the main axis, and a circle of smaller radius. On the remaining part of the main axis . However, more specifically, the sagittal height, along the main axis, varies substantially as the fourth power of the distance from the minor Y-Y axis. The sagittal height is the distance from an imaginary plane tangent to the center of the

  mask surface. The curvature parallel to the minor axis Y-Y is such that it

  sure an easy adaptation of the curvature of the main axis to the periphery of the mask required, and that it can include a variation of curvature when used along the major axis. Such a mask contour has certain improved thermal expansion properties, due to the increase in

  the curvature near the ends of the main axis. Obtaining pro-

  improved thermal expansion properties from an increase in

  bure is described in US Patent No. 4,136,300 cited above.

  FIG. 6 is a graph which illustrates the value of the column-column spacing of the openings or perforations, AH, inside a quadrant of the shadow mask 24, represented by curves in solid lines and designated

  by the reference H, and in a quadrant of a shadow mask produced according to the de-

  Application for US Patent No. 615,589, filed March 31, 1984 and assigned to the pre-

  titular path, represented by curves in broken lines and designated by the reference F. The vertical axis (ordinates) represents the distance from the main axis, and the horizontal axis (abscisses) represents the column-column spacing mask openings, which, as shown in Figure 7, is measured from the central axis of a column to the central axis of the adjacent column. Each curve is numbered so as to identify the space from the minor axis it represents. For example, each curve marked 200

  identifies the space between the 200th and 201st columns of openings.

  In a shadow mask according to the prior art, illustrated by the dashed curves, the column-column spacing of the openings is uniform along and near the minor axis, as indicated by the rectilinear curves

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  "F" -1 and "F" -150. We can observe a slight curvature on the line "F" 200, this

  which indicates that the column-column spacing, for space 200, increases slightly

  steadily with the distance from the main axis. Curves "F" 300 and "F" -306 show considerable curvature, which indicates a substantial increase in column-column spacing, as the distance increases.

tance from the main axis.

  Column-to-column spacing of openings of the improved shadow mask

  24 differs considerably from that of the shadow mask according to the prior art.

  higher, near the minor axis. As can be seen in Figure 6, the column-column spacing of openings AH, near the minor axis, decreases when the distance from the minor axis increases, as illustrated by the curves "H" -1, "H "-50 and

  "H" -100. Near the 150th space, the column-column spacing of openings com-

  starts by increasing slightly, at the same time as increasing the distance from

  of the main axis, as shown by the slight curvature of the curve "H" 150.

  This curving of the curves, representing the column-column spacing of

  vertures, increases with the distance from the minor axis, as shown by the curves "H" -200 and "H" -300, but it decreases slightly on the sides of the mask,

  as we can see by comparing the curve "H" -305 to the curve "H" -300.

  The column-column spacing of openings along the main axis increases approximately as a function of the fourth power of the distance from the minor axis. In the particular examination illustrated in Figure 6, this variation of the main axis (expressed in thousandths of an inch, i.e. 0.025 mm), is substantially: AH = 30 + 0.00185 x However, apart from the main axis, the variation in column-column spacing is more complex, and it varies significantly like the equation:

2 4

  AH = a + bx + cx in which: a, b, and c are functions different from the square of the distance

  from the main axis, and x is the distance from the minor axis.

  The screen 22 of the tube 10 is formed by a known photographic method, which uses the shadow mask 24 as a photographic model. As mentioned

  above, there is a problem when using a li

  born during an exposure stage of the photographic process. This problem re-

  side in a misalignment of the image of the linear light source with

  the axes of symmetry of the phosphor lines. This misalignment, also-

  referred to as "warping error", widens the distribution of intensity

  luminous sity used for the printing of phosphor lines, which results in an increase in the sensitivity of the line width of the

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  phosphor on light exposure, making it more difficult to control

  the line width. In the prior art, compensation for this er-

  warping was obtained by various means, among which one can

  cite an area exposure technique performed by synchronizing a toggle-

  ment of the linear light source with sequential exposure of the different areas of the screen, as described for example in the American patent

  No. 3,888,673, and the technique of bending the perforation columns

  tions and lines of phosphors, as described in US Pat. No. 3,889,145. In tube 10 according to this invention, this problem of warping is resolved by varying the column-column spacing of openings in the form of '' a function of both the distance from the minor axis and

  the distance from the major axis. The resulting configuration of beamlines

  nophores has curved lines in a region of the screen where the warping error is greatest, and straight lines on the sides of

  the screen, where the warping error in the tube is minimal. Such a confi-

  guration is visible in Figure 8, in which the solid lines 40 to 45 represent

  have selected spaced phosphor lines, and the broken lines

  pus 46 represent straight lines parallel to the minor axis. As one can see,

  the curvature of the phosphor lines increases with increasing distance

  tance from the secondary axis, to a maximum curvature in line 42 to the vicinity of line 43, and it then decreases to the line

end 45, which is straight.

  An advantage of the spacing of the columns of openings according to the invention lies in that its use makes it possible to obtain a greater curvature of the shadow mask, in straight sections close to the sides of the mask which are parallel to the minor axis. , that it would be possible without this use. The outline of the faceplate panel, having a substantially planar edge, suggests a mask outline as shown by line 50 in Figure 9. This line 50 represents a contour line on a mask 52 of equal sagittal height. As can be seen, the line 50 is substantially rectilinear on the right and left sides of the mask. This linearity poses serious problems of training and manipulation. For example, a light touch made by touching

  the mask can cause it to bend inward, when handling

  normal pulation. Therefore, it is preferable to design the mask by giving it a greater curvature on the sides of the mask to prevent this drawback. The use of the spacing of the opening columns according to the invention makes it possible to obtain an improved mask contour, such as that represented by line 54, in FIG. 10. This line 54 represents a contour line on a mask 56 of equal sagittal height. In this case, we can see that the line 54 is substantially curved on the left and right sides of the mask, which gives it a greater curvature parallel to the axis

  secondary, and therefore higher resistance.

  It remains to be understood that this invention is not limited to the embodiments described and shown, but that it encompasses all of them.

variants.

Claims (4)

  1 - Color image tube which includes a shadow mask mounted nearby   a screen of cathodoluminescent lines, this shadow mask comprising a plurality   reality of slots-shaped openings positioned in columns, said shadow mask having a substantially rectangular periphery, with two opposite long sides and two opposite short sides, a main axis of said mask being an axis passing through the center of the mask and through the center of the short sides, and a secondary axis being an axis passing through the center of the mask and through the center of the long sides, said columns of openings extending in the direction of the   minor axis and being spaced from each other in the direction of the main axis   cipal, this image tube being characterized in that the column-column spacing of openings (AH), near the minor axis (Y-Y) of said mask (24), is smaller   on the long sides of the mask only near the main axis (X-X) of said mask.   2 - Color image tube according to claim 1, characterized in that the column-column spacing of openings (AH) is greater near the corners   of said mask (24) only near the main axis (X-X).   3 - Color image tube according to claim 1, characterized in that the column-column spacing of openings (AH), along straight sections   parallel to the main axis (X-X), but offset from the main axis, varies   just like the equation: A = a + bx + cx4   where: A is the column-column spacing, a, b and c are functions   different from the square of the distance from the main axis, and x   is the distance from the secondary axis (Y-Y).   4 - Image tube according to one of claims 1 or 3, characterized in   that the column-column spacing of openings (AH), along the main axis,   increases substantially as a function of the fourth power of the dis-   tance from the secondary axis (Y-Y).