|
(11) | EP 0 571 206 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
|
|
|
|
|||||||||||||||||||||||||||
| (54) | Cathode ray tube |
| (57) A cathode ray tube (10) has a panel (11) in which a screen (11a) is formed and a
funnel (12) attached to the panel and having an electron gun (13) housed in the neck
of the funnel (12). The curvature equation of the outer surface of the panel is expressed
as Z = A₁X² + A₂X⁴ + A₃Y² + A₄Y⁴ + A₅X²Y² + A₆X⁴Y² + A₇X²Y⁴ + A₈X⁴Y⁴, where X is the
longer axis of the panel, Y is the shorter axis of the panel, Z is the axis of the
cathode ray tube, and A₁-A₈ are constants, and when the design reference of the screen
is set as follows: assuming P satisfies an inequality - 0.1 ≦ P < 0 at a dividing point (X1,Y1), which determines the effective screen. |
[0001] The present invention relates to a cathode ray tube, and particularly to a cathode ray tube in which the curvature of the outer surface of a panel is improved so as to prevent the distortion of an image formed on a screen.
[0002] Generally, as shown in Fig.1, a cathode ray tube (CRT) is constructed to have a panel 11 on the inner surface of which a phosphor screen 11a is formed, and a funnel 12 which is attached to the panel. Funnel 12 includes a neck 12 housing an electron gun 13, and a deflection yoke 14 is installed outside the neck. A shadow mask 15 is mounted on the inner side of panel 11, while being detached from screen 11a by a predetermined distance.
[0003] In the above CRT 10, an electron beam emitted from electron gun 13 installed in neck 12a of funnel 12 is deflected by deflection yoke 14 and, as shown in Fig.2, is projected in the horizontal direction of phosphor screen 11a (which is the longer axis X-X) and in the vertical direction of the phosphor screen (which is the shorter axis Y-Y). Such two-dimensional projection forms a raster on phosphor screen 11a.
[0004] However, the outer surface of the panel of the CRT has a predetermined radius of curvature, and when a picture formed on phosphor screen 11a of the panel is viewed from the side thereof, the picture formed on the periphery of phosphor screen 11a is seen as distorted. Thus, the viewer does not experience a sense of flatness.
[0005] In order to solve the problem, the panel has been attempted to be formed flat. This, however, involves these problems: first, the structural strength of the CRT is difficult to maintain, owing to the vacuum pressure acting on its interior; secondly, when the picture formed on the phosphor screen is viewed from the side, the central portion of the picture appears concave; and thirdly, since the shadow mask is locally heated and therefore thermally expanded due to the electron beam emitted from the electron gun, the electron beam cannot precisely land on the phosphor screen, thereby creating a color blurring phenomenon.
[0006] Conventionally, in order to overcome the above problems, the diagonal curvature of the outer surface of the panel is expressed as a quadratic function. Here, the curvature according to the quadratic function has a portion in which the quadratic function has a negative value so as to accomplish flatness in the corners of the panel. However, such a panel exhibits certain problems.
[0007] First, the design of the curvature contour of the outer surface of the panel produces the problem of external-light reflection on the outer surface of the panel. Particularly, since the inflection point is placed in the corners of the panel, the peripheral light irradiated onto the outer surface of the panel is scattered.
[0008] Secondly, since the quadratic function becomes negative in the diagonal direction of the panel, the mechanical strength of the shadow mask is reduced and the shadow mask is thermally deformed more easily than the conventional one.
[0009] While, as above, investigating the relationship between the outer surface of the panel and the picture and the relationship between the outer surface of the panel and the light reflected therefrom, the inventor used the following experiment to determine the curvature of a panel and the state of a displayed picture, when the panel of CRT has an uneven curvature.
[0010] As in Fig.3, a grid 100 was installed to be detached from the outer surface of the panel which is opposite to phosphor screen 11a, by a predetermined distance (about 2m). Using a light source 110 located above grid 100, the pattern of the grid was projected onto the outer surface of the panel so as to analogically interpret the degree of deformation of a picture according to the degree of deformation of the projected shadow of grid 100.
[0011] However, in a CRT developed by Hitachi Co., Ltd of Japan. and measured using such a method, as shown in Fig.4, it is noted that the shadow of grid 100 is severely distorted on either side of the periphery while the central portion of the screen maintains the vertical and horizontal balance somewhat. Further, in the CRT developed by Toshiba Co., Ltd. of Japan, as shown in Fig.5, the shadow of the grid 100 projected onto the screen is distorted throughout the central portion and periphery of the screen.
[0012] In such CRTs, though the picture formed on the screen of the CRT is not severely distorted when viewed from directly in front of the CRT, the picture is distorted on the periphery of the screen when viewed from the sides. In addition, the reflection of external light becomes severe such that sharp pictures cannot be viewed.
[0013] Therefore, it is an object of the present invention to provide a CRT which prevents a picture formed on the phosphor screen from being distorted according to the watching angle of a viewer.
[0014] It is another object of the present invention to provide a CRT which prevents the distortion of a picture due to the external light irradiated from the surroundings of screen so that a viewer does not feel uncomfortable when he or she watches the picture in any directions.
[0015] According to the present invention, there is provided a cathode ray tube having a panel in which a screen is formed and a funnel attached to the panel and having an electron gun housed in the neck of the funnel, wherein the curvature equation of the outer surface of the panel is expressed as Z = A₁X² + A₂X⁴ + A₃Y² + A₄Y⁴ + A₅X²Y² + A₆X⁴Y² + A₇X²Y⁴ + A₈X⁴Y⁴ where X is the longer axis of the panel, Y is the shorter axis of the panel, Z is the axis of the cathode ray tube, and A₁-A₈ are coefficients, and where the design reference of the screen is set as follows:
assuming P satisfies an inequality -0.1 ≦ P < 0 at a dividing point (X1,Y1), which determines the effective screen.
[0016] Further, there is provided a cathode ray tube having a panel wherein a grid is installed so as to be detached from the panel by a predetermined distance and a light source is installed in front of the grid, in which, with X representing the longer axis of the panel and Y representing the shorter axis of the panel, the radii of the curvatures of the X and Y axes are each less than seven times the radius of the curvature of the panel, and the radius of the curvature of the panel is equal to the effective diagonal times 1.167 while satisfying the inequalities
and
where ΔX is the degree of distortion of the shadow of the light source projected onto the panel's outer surface, with respect to its horizontal axis; ΔY is the degree of distortion of the shadow of the light source projected onto the panel's outer surface, with respect to its vertical axis; LX is the horizontal length of the panel; and LY is the vertical length of the panel.
[0017] Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:
[0020] Fig.3 is a perspective view of an apparatus for projecting the shadow of a grid onto the outer surface of the panel of a CRT.
[0021] Figs.4 and 5 are plan views showing the distortion state of a picture formed on the screen of a conventional CRT.
[0022] Figs.6-23 are plan views for showing the shadow patterns formed by projecting a grid onto the outer surface of the panel of a CRT, according to various panel curvatures.
[0023] Fig.24 is a plan view for showing the length of the longer axis of the panel versus that of the shorter axis and the degree of distortion of the shadow pattern of a grid projected onto the outer surface of the panel of a CRT according to the present invention.
[0024] As shown in Fig.1, a general cathode ray tube (CRT) is constructed to have a panel on the inner surface of which a phosphor screen is formed, and a funnel which is attached to the panel. The funnel includes a neck housing an electron gun, and a deflection yoke installed outside the neck. Here, in order to develop a panel in which a picture is not distorted and the interference of picture due to the reflection of external light is excluded, supposing the longer axis of the panel to be the X axis, the shorter axis to be the Y axis and the tube's axis to be the Z axis, the curvature equation of the outer surface of the panel is expressed as the following approximate equation by combining the elements of quadratic and biquadratic equations while considering the axis symmetry:
[0025] Using the curvature of the outer surface of panel in which the coefficients A₁-A₈ of the approximate equation are arbitrarily selected and the selected coefficients are substituted for the equation, in order to obtain the curvature of the outer surface in which the pattern of the shadow formed by projecting the grid as shown in Fig.3 is not distorted (in other words, the curvature of the outer surface of panel makes a viewer experience a sense of flatness), the reference of setting the coefficients is set as follows:
[0026] In experiments in which coefficients A₁-A₈ of equation (2) are varied, if P has a coefficient satisfying an inequality -0.1 ≦ P < 0 at a dividing point, which determines the effective screen, {(X=X1), (Y=Y1): X and Y indicate the distance from the center of the panel in the directions of the X axis and the Y axis, respectively, X1 is half the length of the X-axis effective screen, and Y1 is half the length of the Y-axis effective screen), the distortion of the shadow pattern projected on the outer surface of the panel which is opposite to the phosphor screen can be minimized. Thus, the picture formed on the phosphor screen can be prevented from being shown as distorted.
[0027] Therefore, with the P values obtained from experiments in which the coefficients of equation (2) are varied, the present invention will be described in more detail below.
[0028] Figs.6-24 illustrate the results of simulations of the shadow patterns formed by projecting the grid net onto the panel, the curvature of which is obtained by varying the coefficients of equation (1).
Experiment 1
[0029] In designing a panel of a 29" (73.7cm) CRT, given the distance from the center of the panel in the X-axis direction to be 270.4 and the distance from the center of the panel in the Y-axis direction to be 202.8, the P values are obtained as shown in the following TABLE 1 by substituting constants for equation (2).
<TABLE 1>
| Coefficients | P values obtained by substituting coefficients A₁-A₈ for equation (2) | |
| 29'' CRT (73.7cm) | A₁=2.275831 E-10 | 0.0 |
| A₂=-9.165778 E-11 | ||
| A₃=2.36601 E-04 | ||
| A₄=-1.053829 E-10 | ||
| A₅=0.0 | ||
| A₆=1.67825 E-16 | ||
| A₇=2.058604 E-16 | ||
| A₈=0.0 | ||
| A₁=2.275831 E-10 | -0.025 | |
| A₂=-9.165778 E-11 | ||
| A₃=2.36601 E-04 | ||
| A₄=-1.053829 E-10 | ||
| A₅=-2.13787 E-10 | ||
| A₆=1.67825 E-16 | ||
| A₇=2.058604 E-16 | ||
| A₈=-2.38673 E-22 | ||
| A₁=2.275831 E-10 | -0.1 | |
| A₂=-9.165778 E-11 | ||
| A₃=2.36601 E-04 | ||
| A₄=-1.053829 E-10 | ||
| A₅=-8.56969 E-10 | ||
| A₆=1.67825 E-16 | ||
| A₇=2.058604 E-16 | ||
| A₈=0.0 |
[0030] In TABLE 1, when the P value is 0.0, the shadow projected onto the outer surface of the panel becomes barrel-shaped as shown in Fig.6.
[0031] When the P value is -0.025, the distortion of the shadow projected onto the outer surface of the panel is completely removed as shown in Fig.7, so that the picture formed on the phosphor screen of the panel is not distorted when the television screen is viewed from any direction.
[0032] When the P value is -0.1, the pattern of the grid projected on the outer surface of the panel is slightly distorted in the pincushion shape on the periphery of the panel as shown in Fig.8, so that the picture formed on the phosphor screen is distorted on the periphery of the panel.
[0033] As noted in Experiment 1, when the P value is greater than -0.1, the pattern of the grid projected on the panel is not distorted.
Experiment 2
[0034] In designing a panel of a 29" (73.7cm) CRT, given X1 and Y1 (the dividing points for determining the effective screen) to be 270.4 and 202.8, respectively, the P values are obtained as shown in the following TABLE 2 by substituting the coefficients therein for equation (2).
[0035] In TABLE 2, when the P value is -3.80303 E-2, the pattern of the shadow projected on the outer surface of the panel has an undistorted lattice shape as shown in Fig.9. In this panel, the distortion of the picture formed on the phosphor screen and the interference of the picture due to the external light reflection are not created.
[0036] When the P value is -0.110355, the pattern of the grid projected onto the outer surface of the panel is distorted in the pincushion shape as shown in Fig.10. In this panel, the picture formed on the phosphor screen is distorted on the periphery of the panel and interference of the picture due to external light appears slightly on the periphery of the panel.
[0037] When the P value is -0.182854, the pattern of the shadow projected onto the outer surface of the panel becomes the pincushion shape throughout the outer surface while excluding the central portion of the panel as shown in Fig. 11. Accordingly, the picture formed on the phosphor screen appears distorted throughout the outer surface while excluding the central portion.
[0038] When the P value is 7.41864 E-02, the shadow projected onto the outer surface of the panel is severely distorted in the barrel shape on the periphery of the outer surface of the panel as shown in Fig.12. Accordingly, a picture formed on the phosphor screen would be seen as distorted on the periphery.
[0039] When the P value is 0.0, the shadow of the grid projected onto the outer surface of the panel is distorted in the barrel shape on the periphery of the outer surface of the panel as shown in Fig.l3, so that the periphery of the picture formed on the phosphor screen would be distorted.
[0040] As noted in Experiment 2, when the coefficients are set so that the P values are -3.80303 E-02 which is greater than -0.1, panel curvatures with which the pattern of the shadow projected onto the outer surface of the panel is not distorted, can be obtained. Also, the picture formed on the phosphor screen of the panel would not be distorted and the external light irradiated from the outside of the panel would not interfere in the picture.
Experiment 3
[0041] In designing a panel of a 29" (73.7cm) CRT, given X1 and Y1 (the dividing points for determining the effective screen) to be 270.4 and 202.8, respectively, the P values are obtained as shown in the following TABLE 3 by substituting the constants therein for equation (2).
[0042] In TABLE 3, when the P value is 2.23943 E-2, the pattern of the shadow projected on the outer surface of the panel has an undistorted lattice shape as shown in Fig.14.
[0043] When the P value is -6.28764 E-02, the pattern of the grid projected onto the outer surface of the panel is distorted in the pincushion shape as shown in Fig.15.
[0044] When the P value is -0.122161, the pattern of shadow projected onto the outer surface of the panel becomes the pincushion shape throughout the outer surface excluding the central portion of the panel as shown in Fig.16.
[0045] When the P value is 0.0, the shadow projected onto the outer surface of the panel is distorted in the barrel shape on the periphery of the outer surface of the panel as shown in Fig.17.
[0046] When the P value is 0.1221609, the shadow of the grid projected on the outer surface of the panel is severely distorted in the barrel shape on the periphery of the outer surface of the panel while excluding the central portion of the panel, as shown in Fig.18.
[0047] As noted in Experiment 3, when the coefficients are set so that the P value is -2.23943 E-02 which is greater than -0.1, panel curvatures with which the pattern of the shadow projected onto the outer surface of the panel is not distorted, can be obtained. Also, the picture formed on the phosphor screen of the panel would not be distorted, and a viewer can experience a sense of flatness when watching the picture formed on the screen of the panel with respect to the outer surface of the panel. When the P value is greater than 0, the pattern of the shadow projected onto the outer surface of the panel is severely distorted so that the viewer does not experience a sense of flatness.
Experiment 4
[0048] In designing a panel of a 20" (50.8cm) CRT, given X1 and Y1 (the dividing points for determining the effective screen) to be 200 and 150, respectively, the P values are obtained as shown in the following TABLE 4 by substituting the constants therein for equation (2).
[0049] In TABLE 4, when the P value is -3.09353 E-02, the pattern of the shadow projected on the outer surface of the panel has an undistorted lattice shape as shown in Fig.19.
[0050] When the P value is -0.104158, the pattern of the grid projected onto the outer surface of the panel is distorted in the pincushion shape on the periphery of the panel, as shown in Fig.20.
[0051] When the P value is -0.155457, the pattern of the shadow projected onto the outer surface of the panel becomes the pincushion shape throughout the outer surface while excluding the central portion of the panel, as shown in Fig.21.
[0052] When the P value is 0.0, the shadow projected onto the outer surface of the panel is distorted in the barrel shape on the periphery of the outer surface of the panel as shown in Fig.22.
[0053] When the P value is 0.1041579, the shadow of the grid projected on the outer surface of the panel is severely distorted in the barrel shape on the periphery of the outer surface of the panel while excluding the central portion of the panel, as shown in Fig.23.
[0054] As noted in Experiment 4, when the coefficients are set so that the P values are -3.09353 E-02 which is greater than -0.1, the pattern of the shadow projected onto the outer surface of the panel is not distorted. Thus, the picture formed on the phosphor screen of the panel would not be distorted and the external light does not interfere in the picture.
[0055] As indicated in the experiments, when the coefficients satisfying P values greater than or equal to -0.1 and smaller than 0.0 are set, the shadow of the grid projected onto the outer surface of the panel is not distorted so that, as a result, the picture formed on the screen of the panel is prevented from being distorted. Even if the outer surface of the panel is formed as curved, a viewer can experience a sense of flatness.
[0056] Through the experiments the inventor found that, when the length ratio of the longer axis to the shorter axis of the panel and the distortion amount of the shadow pattern formed by projecting grid 100 (as shown in Fig.3) onto the outer surface of the panel in which, given the radius R of the curvature of a panel to be the length of the effective diagonal times 1.167, the radii of the curvatures of the X and Y axes are each less than seven times the radius R, were within a predetermined range, the picture formed on the phosphor screen was not distorted even if the outer surface of the panel is formed as curved and the external light did not interfere in the picture. More specifically, as shown in Fig.24, supposing the longer axis of the panel (its length in the direction of the X axis) as LX, the shorter axis of the panel (its length in the direction of the Y axis) as LY, and the maximum degree of distortion in the vertical direction with respect to the Y axis of the shadow formed on the outer surface of the panel and that with respect to the X axis as ΔX and ΔY, respectively, when the quotients of ΔX divided by LY and ΔY divided by LX are each within the range of -0.01 and 0.01, the picture formed on the phosphor screen is not seen as being distorted from any direction.
[0058] The relationship between the outer surface of the panel and the above inequalities will be described below in detail.
[0059] When ΔY/LX and AX/LY are each smaller than -0.01, the shadow of the grid which is formed in the directions of the X axis and the Y axis of the outer surface of the panel, is severely distorted, outward from the center of the outer surface. This indicates that the surface of the panel is convex so that the picture is severely distorted on the periphery and the external light incident on the surface of the panel is dispersed thereon.
[0060] When ΔY/LX and ΔX/LY are each greater than 0.01, the shadow of the grid is severely distorted from the periphery of the outer surface to the center thereof. This indicates that the surface of the panel is concave so that the picture is severely distorted on the periphery and the external light incident on the surface of the panel is dispersed thereon.
[0061] As described above, in the CRT of the present invention the outer surface of the panel has a curvature in which the shadow pattern formed by projecting the latticed-shape grid is not distorted, so that, when a picture formed on the phosphor screen of the panel is viewed from any direction, the picture formed thereon is not distorted and the external light does not interfere in the picture.
1. A cathode ray tube (10) having a panel (11) in which a screen (11a) is formed and
a funnel (12) attached to the panel (11) and having an electron gun (13) housed in
the neck of the funnel (12), wherein the curvature equation of the outer surface of
the panel is expressed as Z = A₁X² + A₂X⁴ + A₃Y² + A₄Y⁴ + A₅X²Y² + A₆X⁴Y² + A₇X²Y⁴
+ A₈X⁴Y⁴ where X is the longer axis of the panel, Y is the shorter axis of the panel,
Z is the axis of the cathode ray tube, and A₁-A₈ are coefficients, and wherein the
design reference of the screen is set as follows:
assuming P satisfies an inequality -0.1 ≦ P < 0 at a dividing point (X1 ,Y1), which determines the effective screen.
assuming P satisfies an inequality -0.1 ≦ P < 0 at a dividing point (X1 ,Y1), which determines the effective screen.
2. A cathode ray tube having a panel (11) wherein a grid (100) is installed so as to
be detached from the panel (11) by a predetermined distance and a light source (110)
is installed in front of the grid (100), in which, with X representing the longer
axis of the panel (11) and Y representing the shorter axis of the panel (11), the
radii of the curvatures of the X and Y axes are each less than seven times the radius
of the curvature of the panel (11), and the radius of the curvature of the panel (11)
is equal to the effective diagonal times 1.167 while satisfying the inequalities
and
where ΔX is the degree of distortion of the shadow of the light source (110) projected onto the panel's outer surface, with respect to its horizontal axis; ΔY is the degree of distortion of the shadow of the light source (110) projected onto the panel's outer surface, with respect to its vertical axis; LX is the horizontal length of the panel (11); and LY is the vertical length of the panel (11).
and
where ΔX is the degree of distortion of the shadow of the light source (110) projected onto the panel's outer surface, with respect to its horizontal axis; ΔY is the degree of distortion of the shadow of the light source (110) projected onto the panel's outer surface, with respect to its vertical axis; LX is the horizontal length of the panel (11); and LY is the vertical length of the panel (11).
3. A cathode ray tube having a panel (11) wherein the radii of the curvatures of the
longer axis of the panel, X, and the shorter axis of the panel, Y, are each less than
seven times the radius of the curvature of the panel, and the radius of the curvature
of the panel is equal to the effective diagonal times 1.167 while satisfying the inequalities
and
where ΔX is the degree of distortion of the shadow of a grid (100) projected onto the panel's outer surface by a light source (110), with respect to its horizontal axis; ΔY is the degree of distortion of the shadow of the grid (100) projected onto the panel's outer surface, with respect to its vertical axis; LX is the horizontal length of the panel (11); and LY is the vertical length of the panel (11).
and
where ΔX is the degree of distortion of the shadow of a grid (100) projected onto the panel's outer surface by a light source (110), with respect to its horizontal axis; ΔY is the degree of distortion of the shadow of the grid (100) projected onto the panel's outer surface, with respect to its vertical axis; LX is the horizontal length of the panel (11); and LY is the vertical length of the panel (11).