Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2002-02-20
2004-11-02
Williams, Joseph (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S408000
Reexamination Certificate
active
06812627
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a mask assembly for a cathode ray tube having real bridges and dummy bridges, and more particularly to a mask assembly for a cathode ray tube in which real bridges are formed in bad view portions for improved clarity.
2. Related Art
In general, a cathode ray tube employed in a monitor of a computer and a television set is a display which forms images by exciting red (R), green (G), and blue (B) phosphors by landing three electron beams, which are emitted from an electron gun, onto the phosphors of a screen via electron beam apertures of a shadow mask.
A screen surface of a color cathode ray tube, which forms images as described above, is designed with a predetermined curvature considering deflection tracks of the electron beams which are deflected by a deflection yoke. The shadow mask is designed with a curvature corresponding to a curvature of an inner surface of the screen surface.
The shadow mask is thermally expanded by electron beams which cannot pass through the electron beam passing apertures. As a result of the thermal expansion, the shadow mask is expanded toward a panel, a doming phenomenon occurs due to a change of the landing positions of the electron beams, and phosphors of unintended colors are excited, causing the purity of color to be degraded.
In order to remove the above-described disadvantages, and to comply with the increased demand for larger and flatter display screens, U.S. Pat. No. 3,683,063 entitled “GRID STRUCTURE FOR COLOR PICTURE TUBES”, and issued on Jan. 25, 1972 to Tachikawa et al., discloses a tension mask that is fixed to a mask frame under tension. The tension mask disclosed in Tachikawa '063 is an aperture grill type tension mask. In the tension mask of Tachikawa '063, a plurality of strips are separated from one another by a predetermined interval and supported by the mask frame under tension applied in one direction. In the shadow mask of Tachikawa '063, the thermal expansion generated during the operation of the cathode ray tube is absorbed by the applied tension in order to prevent the doming phenomenon. The strips, formed of thin steel with a thickness of 0.1 millimeters (mm), are not connected to proximate strips, but are supported by the mask frame at both end parts only so that the strips become vibrating even at a small impact, inducing the vibration of images. The mask of Tachikawa '063 has a disadvantage in that a weight of the mask frame must be increased in order to maintain the structural strength, since the tension applied to the strips is proportional to the thickness of the mask.
In order to remove the above-described disadvantages, a different tension mask is disclosed in U.S. Pat. No. 4,942,332 entitled “TIED SLIT MASK FOR COLOR CATHODE RAY TUBES”, and issued on Jul. 17, 1990 to Adler et al. The tension mask of Adler '332 has a valid screen part that includes a plurality of strips which are separated by a predetermined interval from one another, and a plurality of slots formed by real bridges which connect the strips to one another, wherein a long side part of the mask is fixed to supporting members. The slots formed by the real bridges have a length of approximately 5.0 millimeters or more. The Adler '332 mask has a disadvantage in that black lines are clearly generated on the screen due to the shadows of the real bridges, even though the howling phenomenon generated by the vibration of the mask due to the external impact may be reduced by the real bridges.
In order to remove the above-described disadvantages, another tension mask is disclosed in U.S. Pat. No. 4,926,089 entitled “TIED SLIT FOIL SHADOW MASK WITH FALSE TIES”, and issued on May 15, 1990 to Moore. In Moore '089, there is disclosed a tension mask in which the generation of the black lines is restrained by a plurality of dummy bridges provided on slots defined by the real bridges. The dummy bridges are formed in almost equal areas with the real bridges for generating similar black lines as generated by the real bridges, thereby preventing the black lines of the real bridges from being shown to viewers. The above tension mask is generally manufactured by photolithography. That is, a thin plate forming a mask is deposited with a photosensitive film at both surfaces, and the photosensitive films and the thin plate are etched in a predetermined pattern.
While the above-described efforts provide advantages related to cathode ray tubes, they do have some disadvantages as explained above, and they fail to adequately provide an efficient and convenient mask assembly for a cathode ray tube.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a mask assembly which does not have the above-described disadvantages.
It is a further object of the present invention to provide a cathode ray tube with an improved visibility. It is another object of the present invention to provide an improved cathode ray tube that displays clearer images.
The present invention is derived to resolve the above problems, and has an object of providing a cathode ray tube with improved visibility.
In order to achieve the above and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a mask assembly for a cathode ray tube includes a tension mask having a valid screen part for transmitting electron beams, and extending in either a longitudinal or a transverse direction, and a mask frame for reinforcing the structural strength while maintaining the extended state of the tension mask, wherein the valid screen part includes slots, dummy slots and strip parts, the slots are provided in a predetermined area including the center of the valid screen part, and the dummy slots are provided in an area outside the slot area.
It is preferable that the predetermined area be formed symmetrically with respect to a horizontal central line H—H and a vertical central line V—V, which respectively pass through a center point of the valid screen part.
More specifically, the predetermined area is formed in the shape of a rectangle including the center point of the valid screen part, or concave in the middle section of the vertical central line V—V including the center point of the valid screen part, or convex in the middle section of a vertical central line V—V including the center point of the valid screen part, or the predetermined area may be formed in the vertical parts except the central part of the valid screen part.
If it is assumed that a whole horizontal length and a whole vertical length of the valid screen part are respectively x′ and y′ in plane coordinates, in which horizontal and vertical directions from a left lower peak of the valid screen part are defined respectively by an axis x and an axis y, and the predetermined area is formed of an inner space which is defined by straight or curve lines connecting six points P
1
-P
6
in sequence, wherein in the six points, P
1
(x,y)={(x′/4~x′/3),0}, P
2
(x,y)={(2x′/3~3x′/4),0}, P
3
(x,y)={(2x′/3~3x′/4),y′/2}, P
4
(x,y)={(2x′/3~3x′/4),y′}, P
5
(x,y)={(x′/4~x′/3),y′}, and P
6
(x,y)={(x′/4~x′/3),y′/2}.
The rectangular area is formed of an inner space which is defined by straight or curved lines connecting six points P
1
-P
6
in sequence, wherein in the six points, P
1
(x,y)=(x′/4,0), P
2
(x,y)=(3x′/4,y′/4,0), P
3
(x,y)=(3x′/4,y′/2), P
4
(x,y)=(3x′/4,y′), P
5
(x,y)=(x′/4,y′), and P
6
(x,y)=(x′/4,y′/2).
The concave area is formed of an inner space which is defined by straight or curved lines connecting six points P
1
~P
6
in sequence, wherein in the six points, P
1
(x,y)=(x′/4,0), P
2
(x,y)=(3x′/4,0), P
3
(x,y)=(2x′/3,y&pri
Chun Sang-Ho
Ko Hyang-Jin
Lee Jong-Han
Lee Jun-Jong
Bushnell , Esq. Robert E.
Samsung SDI & Co., Ltd.
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