Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2002-04-23
2003-09-16
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S407000, C313S403000
Reexamination Certificate
active
06621201
ABSTRACT:
CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from my application FLAT MASK AND METHOD FOR ASSEMBLING THEREOF, AND TENSION MASK ASSEMBLY MADE IN ACCORDANCE WITH THIS METHOD filed with the Korean Industrial Property Office on May 8, 2001 and there duly assigned Ser. No.0024972/2001.
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a flat mask for a cathode ray tube, an assembling method for assembling the flat mask, and a tension mask assembly manufactured by using the method.
2. Related Art
In general, a color cathode ray tube (CRT) for television and computer displays is a device for displaying images by guiding electrons emitted from an electron gun to strike and illuminate particular phosphor areas on an inner surface of the cathode ray tube. The cathode ray tube employs three electron beams, one for each of the primary color components (red, blue and green) of the color video signal, and employs a screen made up of an array of phosphor elements in the three primary colors. A shadow mask is interposed between the electron gun and the screen to permit each electron beam to strike only phosphor elements associated with the particular electron beam.
The shadow mask is usually contoured to be somewhat parallel to the inner surface of the cathode ray tube faceplate, and to be bowed outwardly for a path of the electron beams deflected by a deflection yoke.
Some electrons do not pass through the apertures of the shadow mask. Instead of passing through the apertures, these electrons hit the shadow mask, thereby heating the shadow mask locally. This localized heating causes a transient localized expansion of the mask known as “doming phenomenon”. This doming can cause mislanding of the electron beams, which degrades the color purity of the display.
Therefore, shadow masks that are fixed on their frame with a predetermined tension, called a tension mask, have been developed to overcome the above-noted drawbacks and to meet the current trend of making displays large and flat.
Exemplars of efforts in the art include U.S. Pat. No. 4,942,332 for TIED SLIT MASK FOR COLOR CATHODE RAY TUBES issued to Adler et al. on Jul. 17, 1990, U.S. Pat. No. 3,638,063 for GRID STRUCTURE FOR COLOR PICTURE TUBES issued to Tachikawa et al. on Jan. 25, 1972, and Japanese Patent. No. P2000-133161 for COLOR CATHODERAY TUBE with publication date May 17, 2000 and listing inventors Minami Go, Kashihara Shiro, and Oshima Shigenari.
Tachikawa '063 describes a tension mask using an aperture grill. In Tachikawa '063, a plurality of parallel strips is stretched on a pair of opposed supporting members of a mask frame under predetermined tension. In this structure, when the shadow mask is heated by irradiation of electron beams during operation of the color cathode ray tube, the restoring force of the prestressed frame compensates elongation of the strips due to thermal expansion of that portion. Therefore, it is possible to avoid doming. However, in Tachikawa '063, the strips of the tension mask are fabricated from a thin steel of about 0.1 millimeters (mm) in thickness and are stretched between a pair of supports without being connected to each other, and therefore they vibrate independently due to even a slight impact, which causes the tension mask to resonate. This phenomenon is referred to as howling.
Adler '332 describes a slot-type tension mask to prevent the above-described problems. The slot-type tension mask for a color cathode ray tube comprises a series of parallel strips being disposed at a predetermined pitch and pattern, the strips being loosely coupled by widely spaced real bridges under tension. The strips are connected by real bridges, which are arranged so that the slots form a brick wall-like pattern. In addition, all strips terminate at the top and bottom in end members, which are welded to supporting members of the mask frame. Many slots are formed to pass electron beams emitted from an electron gun. In the tension mask of Adler '332, the strips are connected by real bridges, thereby reducing howling somewhat. However, since the strength of the supporting ends located at edges of the tension mask is greater than that of the apertured portion, the stress is concentrated on the supporting ends so that the portions near the edges of the apertured portion are liable to vibrate.
The Japanese Patent No. P2000-133161 describes a tension mask to solve the above-described problems. In this structure, the tension mask comprises an apertured portion with a plurality of small slots and supporting ends located at edges of the apertured portion, which are fixed on the supporting members of the mask frame with a predetermined tension. A width of short supporting ends becomes wider from a center portion to each corner portion. Before applying tension to the flat mask, if the width of the center portion and the corner portion thereof are assumed to be “a” and “b”, respectively, the values are satisfied by the inequality 2≦b/a≦6. With regard to the flat mask, one side of the short supporting ends is half-etched and then the stress concentrated thereon is decreased, thereby increasing the tension acting on portions near the edges of the apertured portion when tension is applied. As to a tension mask assembly manufactured from the flat mask, the tension acting on portions near the edges of the apertured portion can be the same as that of the central apertured portion by making the width of the each corner portion of the short supporting ends greater than that of central portion thereof by a predetermined ratio, and by half-etching one side of the short supporting ends.
In the Japanese Patent No. P2000-133161, there is a limitation that the width of the corner portions of the short supporting ends should be twice more than that of the central portion thereof to prevent tension acting on portions near the edges of the apertured portion from being less than that of the central apertured portion. In addition, according to Japanese Patent No. P2000-133161, before applying tension, the apertured portion of the mask is formed to have a rectangular shape. As a result, since the mask is expanded longitudinally while being compressed transversely when the shadow mask is applied under tension, slots at portions near the edges of the apertured portion are displaced.
Therefore, the Japanese Patent No. P2000-133161 does not solve all problems, because apertured portions of the tension mask do not maintain a rectangular shape. In addition, since one side of the short supporting ends is half-etched, the mask is liable to bend toward half-etched portions after being held under tension.
While these recent efforts provide advantages, I note that they fail to adequately provide an efficiently and conveniently improved flat mask for cathode ray tube, and assembling method thereof.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a flat mask of which an apertured portion has satisfactory thermal expansion, uniform stress distribution and linearity, and the width of curved short supporting ends is formed to be the same in the longitudinal direction. The present invention also provides the flat mask, which is manufactured to prevent deformation caused by heat treatment after being held under tension.
Another object of this invention is to provide a method of assembling the flat mask with a mask frame, and a tension mask assembly assembled by using the above method.
In accomplishing these and other objects, according to a first aspect of the present invention, there is provided a flat mask comprising an apertured portion including a plurality of slots formed for passing electron beams and being separated at a predetermined interval, and a plurality of pin-cushion type or barrel type strips. The flat mask also comprises supporting ends including short supporting ends and long supporting ends facing edges of the apertured portion.
The width of the short
Jeon Sang-Ho
Kim Dong-Hwan
Koh Hyang-Jin
Lee Jun-Jong
Rhee Jong-Han
Bushnell , Esq. Robert E.
Patel Vip
Perry Anthony
SamSung SDI Co., Ltd.
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