CA1216619A

CA1216619A - Cathode-ray tube having a faceplate panel with an essentially planar screen periphery

Info

Publication number: CA1216619A
Application number: CA000461552A
Authority: CA
Inventors: Albert M. Morrell; Ralph J. D'amato; Richard H. Godfrey; Frank R. Ragland, Jr.
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1983-09-06
Filing date: 1984-08-22
Publication date: 1987-01-13
Also published as: GB8422084D0; JPH0449218B2; PL148160B1; DE3432677C2; JPS6072146A; GB2147142B; CZ278548B6; HK23693A; MX157877A; KR900005543B1; DD232575A5; CZ624884A3; DE3432677A1; FR2551582B1; FR2551582A1; GB2147142A; RU2010390C1; PL249372A1; KR850002666A; IT1176642B

Abstract

Abstract of the Disclosure Improvement is provided in the appearance of a color picture type cathode-ray tube including a rectangular faceplate with an exterior surface having curvature along both the minor and major axes. The faceplate also includes a cathodoluminescent screen on an interior surface thereof. At least in the center portion of the faceplate, the curvature along the minor axis is at least 10 percent greater than the curvature along the major axis. Points on the exterior surface near the ends of the major axis, at the edges of the screen, lie in a first plane which is perpendicular to the central longitudinal axis of the tube; points on the exterior surface near the ends of the minor axis, at the edges of the screen, lie in a second plane which is spaced from and parallel to the first plane; and points on the exterior surface near the ends of the diagonals of the rectangular faceplate, at the edges of the screen, lie in a third plane which is spaced from and parallel to the first plane. The three planes are spaced from the center portion of the faceplate in the order of second plane, first plane and third plane.

Description

CATHODE-RAY TUBE HAVING A FACEPLATE PANEL, WITH
AN ESSENTIALLY PLANAR SCREEN PERIPHERY
This invention relates to cathode-ray tubes crypts) and, particularly, to the surface contours of the faceplate panels of such tubes There are two basic faceplate panel contours utilized commercially for rectangular CRT's having screen sizes greater than about a 23 cm diagonal; spherical, and cylindrical. Although flat contours are possible, the added thickness and weight of the faceplate panel required to maintain the same envelope strength are undesirable.
Furthermore, if a flat faceplate CRT is a shadow mask color picture tube, -the additional weight and complexity of an appropriate shadow mask also are undesirable.
Recently, it has been suggested that spherically-shaped CRT faceplate panels be improved by increasing the radius of curvature of the panels by a factor of 1.5 to 2. Such increase in radius of curvature reduces the curvature of the faceplate panel, thereby permitting more satisfactory off-axis viewing of a tube screen. Although such tubes having an increased radius of curvature do provide improved viewing, there is still a need for even flatter faceplates or, alternatively, for tubes that appear to be flatter.
A new faceplate panel contour concept which creates the illusion of flatness is disclosed in Canadian patent applications No. 446,486 and No. 446,487, both filed by ARC Corporation (FUR. Raglan, Jr., inventor) on January 31, 1984. The contour has curvature along both the major and minor axes of the faceplate panel, but is nonspherical.
In a preferred embodiment described in these applications, the peripheral border of the tube screen is planar. In such tubes, it is important to contour the faceplate panel diagonals so that the differing curvatures extending from the major and minor axes are properly blended. In the cited Canadian Lo

-2- RCA 80184 application No. 446,486, this blending is accomplished by permitting at least one sign change of the second derivative of the diagonal contour in the center-to-corner direction.
The present invention provides an improvement in a cathode-ray tube including a rectangular faceplate which has an exterior surface having curvature along both the minor and major axes. The faceplate also includes a cathodoluminescent screen on an interior surface thereof.
At least in the center portion of the faceplate, the curvature along the minor axis is at least 10 percent greater than the curvature along the major axis. In the improvement, points on the exterior surface near the ends of the major axis, at the edges of the screen, lie in a first plane which is perpendicular to the central longitudinal axis of the tube; points on the exterior surface near the ends of the minor axis, at the edges of the screen, lie in a second plane which is spaced from and parallel to the first plane; and points on the exterior surface near the ends of the diagonals of the rectangular faceplate, at the edges of the screen, lie in a third plane which is spaced from and parallel to the first plane. The three planes are spaced from the center portion of the faceplate in the order of second plane, first plane and third plane.
The present invention provides a faceplate panel contour which appears flatter than the previously-suggested longer radius tubes and which does not require the use of much thicker glass to maintain tube strength.
In the drawings:
FIGURE 1 is a plan view, partially in axial section, of a shadow mask color picture tube incorporating one embodiment of the present invention.
FIGURE 2 is a front view of the faceplate panel of the tube of FIGURE 1, taken at line 2-2 of FIGURE l.

-3- RCA 80,184 FIGURES 3, 4 and 5 are cross-sections of the faceplate panel of FIGURE 2, taken at lines 3-3, 4-4 and 5-5, respectively, of FIGURE 2.
FIGURE 6 is a composite diagram of the major axis, minor axis and diagonal contours of the faceplate panel of the tube of FIGURE 1.
FIGURE 7 is a composite diagram of the contours of the faceplate panel, taken at lines 3-3, A-A, B-B and C-C of FIGURE 2.
FIGURE 8 is a diagram of a quadrant of the inventive faceplate panel showing radii and functions of curvature.
FIGURE 9 is a diagram of major axis, minor axis and diagonal contours of the inventive faceplate panel compared to a standard radius spherical panel.
FIGURE 10 is a diagram of major axis, minor axis and diagonal contours of the inventive faceplate panel compared to a 1.5-times-standard radius spherical panel.
FIGURE 11 is a diagram of major axis, minor axis and diagonal contours of the inventive faceplate panel compared to a 2-times-standard radius spherical panel.
FIGURE 12 is a diagram of major axis, minor axis and diagonal contours of the inventive faceplate panel compared to a nonspherical planar edge panel.
FIGURE 1 shows a rectangular cathode-ray tube (CRT), in the form of a color picture tube 10 having a glass envelope if, comprising a rectangular faceplate panel 12 and a tubular neck 14 connected by a funnel 16.
The panel comprises a viewing faceplate 18 and a peripheral flange or sidewall 20, which is sealed to the funnel 16 by a glass fruit 17. A rectangular three-color cathodoluminescent phosphor screen 22 is carried by the inner surface of the faceplate 18. The screen is preferably a line screen, with the phosphor lines extending substantially parallel to the minor axis Y-Y of the tube (normal to the plane of FIGURE 1).
Alternatively, the screen may be a dot screen. A

-4- RCA 80,184 multi-apertured color selection electrode or shadow mask 24 it removably mounted within the faceplate panel 12 in predetermined spaced relation to the screen 22~ An incline electron gun I shown schematically by dotted lines in FIGURE 1, is centrally mounted within the neck 14 to generate and direct three electron beams 28 along coplanar convergent paths through the mask 24 to the screen 22.
Alternatively, the electron gun may hove a triangular or delta configuration.
The tube lo of FIGURE 1 is designed to be used with an external magnetic deflection yoke, such as the yoke 30 schematically shown surrounding the neck 14 and funnel 16 in the neighborhood of their junction, for subjecting the three beams 28 to vertical and horizontal magnetic flux, to scan the beams horizontally in the direction of the major axis (X-X) and vertically in the direction of the minor axis (Y-Y), respectively, in a rectangular raster over the screen 22.
FIGURE 2 shows the front of the faceplate panel 12. The periphery of the panel 12 forms a rectangle with slightly curved sides. The border of the screen 22 is shown with dashed lines. This screen border is rectangular, with straight sides and square corners.
The specific panel cross-sections along the minor axis (YO-YO, the major axis (X-X) and the diagonal are shown in FIGURES 3, 4 and 5, respectively. The exterior surface of the faceplate panel 12 is curved along both the major and minor axes, with the curvature along the minor axis being greater than the curvature along the major axis at least in the center portion of the faceplate panel 12. For example, at the center of the faceplate, the ratio of the radius of curvature of the exterior surface contour along the major axis to the radius of curvature along the minor axis is greater than 1.1 (or greater than 10% difference). The "sagittal height" of a point on the panel contour is measured, from a plane (P) which is perpendicular to the longitudinal axis Z-Z of the tube and tangent to the center of the panel 12, to another I

-5- RCA 80,184 plane (e.g., Pi, Pi or Pi) which is parallel to the plane P. The sagittal heights, Sol, SHY and SHY, for points on the exterior surface of the faceplate 18 near the ends of the minor axis, major axis and diagonal, at the edges of the screen 22 r are indicated in FIGURES 3, 4 and 5, respectively. The three sagittal heights shown follow the relationship: Sol < SHY < SHY.
FIGURE 6 shows the major axis, minor axis and diagonal exterior panel surface contours superposed on each other. Each contour ends at the edge of the screen.
The major axis contour ends at a first plane Pi which is perpendicular to the longitudinal axis Z-Z of the tube.
The minor axis contour ends at a second plane Pi which is spaced from and parallel to the first plane Pi. The diagonal contour ends at a third plane Pi which is spaced from and parallel to the first plane Pi. The three planes are spaced from the center portion of the faceplate in the order of second plane Pi, first plane Pi and third plane Pi. Points on the exterior surface near the ends of the major axis, at the edges of the screen, lie in the first plane Pi. Points on the exterior surface near the ends of the minor axis, at the edges of the screen, lie in the second plane Pi. Points on the exterior surface near the ends of the diagonals, at the edges of the screen, lie in the third plane Pi. The ratio of the spacing measured along the central longitudinal axis of the tube between the second plane Pi and the plane P tangent to the center of the faceplate, to the spacing between the third plane Pi and the plane P, is greater than the minor axis of the screen, squared, divided by the diagonal dimension of the screen, squared, and less than one. In a tube having a screen with a 4:3 aspect ratio, the lower limit of this spacing ratio is about 9/25. In another tube having a screen with a 5:3 aspect ratio, the lower limit of the spacing ratio is about 9/3~. Other minor factors also enter into the exact calculations of faceplate contours so that the stated ratios can only be considered to be approximate. Similarly, the ratio of the spacing between

-6- RCA 80,184 the first plane Pi and the plane P, to the spacing between the third plane Pi and the plane P, is greater than the major axis dimension of the screen, squared, divided by the diagonal dimension of the screen, squared, and less than one. In a tube having a 4:3 aspect ratio, the lower limit of this spacing ratio is about 16/25. In a tube with a 5:3 aspect ratio, the lower limit of the major axis spacing ratio is 25/34. In each case, the upper limit of one is excluded from the included range, since a ratio of one would indicate a planar edge faceplate.
Alternatively, the spacing between the second plane Pi and the third plane Pi is substantially equal to the minor axis dimension of the screen, squared, divided by the diagonal dimension of the screen, squared, times the spacing between the third plane Pi and the plane P.
FIGURE 7 shows the exterior surface contours parallel to the minor axis Y-Y taken at lines 3-3 (the minor axis), A-A, B-B and C-C of FIGURE 2. Each contour is circular, with the radius of curvature of each cross-section increasing with increasing distance from the minor axis.
The exterior surface for one embodiment of the faceplate is described by a fourth-ordered, even-functional, bivariant polynomial which provides a quadrant-symmetric, smoothed-surface description to a basic surface developed as shown in FIGURE 8. The surface curvature along the minor axis is circular, with a radius of curvature Row The surface curvature at the sides of the faceplate, parallel to the minor axis and at the edge of the screen, also is circular, but with a radius of curvature Rev The surface curvature at sections parallel to the minor axis that are in between the minor axis and the sides of the screen are circular, with a radius of curvature Rip The radius of curvature Rip is a function of distance along the major axis from the minor axis and meets the relationship: Row < Rip Rev The surface curvature at the top and bottom of the faceplate, parallel to the major axis and at the edge of the screen, is Jo

-7- RCA 80,184 circular, with a radius of curvature RQ. The surface curvature along the major axis is a somewhat more complex function Ho of distance from the minor axis. Basically, this major axis curvature is circular near the center of the faceplate, with a radius of curvature R, but increases in curvature near the sides of the faceplate. Such increase near the sides of the faceplate can be considered a perturbation on the basic radius of curvature R.
The following table gives dimensions for one tube having a 69-cm (27-inch) diagonal viewing screen constructed as disclosed herein.
TABLE
SHY -------------------------------- ---- 18 mm SHY -----I ------------------------- 22 mm SHY ------------------------------------- 26 mm Row ------------------------------------ 1150 mm Rye -----------I---------- 5126 mm Rip I -------------- >1150 mm and < 5126 mm RQ ------------------------------------ 4574 mm Ho ------------------ Pertubated R of 1673 mm.
The interior screen surface of the faceplate is defined by adding suitable wedging to the glass for strengthening purposes, as is known in the art, and reformulating the contour in bivariant polynomial form.
FIGURES 9 to 12 illustrate the major axis, minor axis and diagonal surface contours of a faceplate constructed in accordance with the present invention, as shown in dashed lines, compared to four prior faceplate contours, as shown in solid lines. All the tubes have a 69-cm (27-inch) viewing screen diagonal dimension.
A standard radius, lo, spherical faceplate contour is shown in FIGURE 9. An example of a standard radius, for a tube having diagonal dimension of about 635 mm, is about 1034 mm. Since the lo faceplate is spherical, the major axis and minor axis contours lie on the diagonal contour. The sagittal height, measured between parallel planes passing the ends of the diagonal and the center surface of the 'faceplate, for the lo

-8- RCA 8C,184 faceplate is 52 mm. The sagittal height difference between the ends of the major and minor axes is about 15 mm, and the sagittal height difference between the ends of the major axis and the ends of the diagonals is about 19 mm.
Although the sagittal height at the end of the diagonal of the inventive ("novel") faceplate contour (26 mm) is one half that of the standard lo faceplate (52 mm), it should be noted that the curvature of the novel faceplate contour along the minor axis is very similar to the curvature of the lo faceplate. Such curvature along the minor axis of the novel faceplate provides the strength needed, without greatly increasing glass thickness, to withstand atmospheric pressure when a tube is evacuated. In the following two spherical faceplates having longer radii of curvature, needed strength is obtained by using relatively thicker glass, resulting in heavier tubes.
FIGURE I shows a spherical faceplate contour 29 having reduced curvature, with a radius of curvature 1.5 times that of the standard lo faceplate of FIGURE 9, e.g.
about 1500 mm. The sagittal height for the 1.5R faceplate is about 39 mm. The sagittal height difference between the ends of the major and minor axes is about 11 mm, and the sagittal height difference between the ends of the major axis and the ends of the diagonals is about 15 mm.
FIGURE 11 shows a spherical faceplate contour having even less curvature, with a radius of curvature 2 times that of the standard lo faceplate of FIGURE 9, e.g.
about 2000 mm. The sagittal height for the OR faceplate is 26 mm, the same as that of the novel faceplate contour.
The sagittal height difference between the ends of the major and minor axes is 8 mm, and the sagittal height difference between the ends of the major axis and the ends of the diagonals is about 9 mm.
Although spherical faceplates having even longer radii of curvature than the OR faceplate are theoretically possible, the additional weight required in the faceplate

-9- RCA 80,184 glass and the additional complexity in shadow mask design provide serious drawbacks to their commercialization .
However, the present invention provides a novel faceplate and tube that circumvent these drawbacks while providing the viewing advantages of flatter faceplate tubes. The periphery of the novel faceplate 18 at the edges of the screen varies only I mm from a plane passing through the ends of the major axis contour for a 69 cm diagonal tube.
Because this variation is minor, the edges of the screen appear essentially flat to an observer. Such flatness at the edges of the screen creates an illusion that the screen is flat, even though there is curvature in the faceplate. As indicated by the sagittal height differences noted for the lo, 1.5R and OR spherical faceplate embodiments, such illusion of flatness is not possible for these spherical embodiments.
FIGURE 12 shows the major axis, minor axis and diagonal faceplate contours for a planar edge faceplate, such as discussed above in the introductory paragraphs.
Such contours do provide a truly planar screen periphery;
however, in general, if the diagonal contour of this planar edge faceplate is formed with a substantial inflection, some surface distortion may be observed. The present invention permits the formation of a smooth faceplate surface with no objectionable surface distortion.
Although the preferred embodiment for a 69 cm diagonal tube is described with a sagittal height difference between the first plane Pi and second plane Pi of 4 mm, and a difference between the first plane Pi and the third plane Pi also of 4 mm, the scope of the present invention also includes other sagittal height differences, as indicated by the previously cited limits on spacing ratios. Furthermore, the present invention is not limited to any particular type of cathode-ray tube screen or electron gun.

Claims

-10-

1. A cathode-ray tube including a rectangular faceplate with an exterior surface having curvature along both its minor and major axes and said faceplate having a cathodoluminescent screen on an interior surface thereof, and wherein, at least in a center portion of the faceplate, the curvature along the minor axis is at least 10 percent greater than the curvature along the major axis; comprising:
points on said exterior surface near the ends of said major axis, at the edges of said screen, lying in a first plane which is perpendicular to a central longitudinal axis of said tube;
points on said exterior surface near the ends of said minor axis, at the edges of said screen, lying in a second plane which is spaced from and parallel to said first plane; and points on said exterior surface near the ends of the diagonals of said rectangular faceplate, at the edges of said screen, lying in a third plane which is spaced from and parallel to said first plane;
said first, second and third planes being spaced from a fourth plane, which is parallel to said first, second and third planes and is tangent to the center portion of said faceplate, in the order of said second plane, said first plane and said third plane.

2. The tube as defined in Claim 1, wherein the ratio of the spacing between said second and fourth planes, measured along said central longitudinal axis of said tube, to the spacing between said third and fourth planes, is greater than the minor axis dimension of said screen, squared, divided by the diagonal dimension of said screen, squared, and less than one.

3. The tube as defined in Claim 2 and having a 4:3 aspect ratio, wherein said minor axis dimension of said screen, squared, divided by said diagonal dimension of said screen, squared, is greater than 9/25 and less than one.

4. The tube as defined in Claim 2 and having a 5:3 aspect ratio, wherein said minor axis dimension of said screen, squared, divided by said diagonal dimension of said screen, squared, is greater than 9/34 and less than one.

5. The tube as defined in Claim 1, wherein the ratio of the spacing between said first and fourth planes, measured along said central longitudinal axis of said tube, to the spacing between said third and fourth planes, is greater than the major axis dimension of said screen, squared, divided by the diagonal dimension of said screen, squared, and less than one.

6. The tube as defined in Claim 5 and having a 4:3 aspect ratio, wherein said major axis dimension of said screen, squared, divided by said diagonal dimension of said screen, squared, is greater than 16/25 and less than one.

7. The tube as defined in Claim 5 and having a 5:3 aspect ratio, wherein said major axis dimension of said screen, squared, divided by said diagonal dimension of said screen, squared, is greater than 25/34 and less than one.