Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
1999-06-25
2001-05-22
Patel, Ashok (Department: 2875)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S412000, C313S425000, C313S432000, C313S439000
Reexamination Certificate
active
06236153
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electron guns for a color cathode ray tube, and more particularly, to an electrode of electron guns for a color cathode ray tube which constitutes a large diameter electron lens.
2. Description of the Related Art
In general, in electron guns, since spherical aberration and focusing characteristics are largely affected by a main lens, the diameter of the main lens must be as large as possible in order to attain excellent focusing characteristics.
However, in in-line electron guns, since three electron beam-passing holes are formed, in a line, in at least two electrodes forming electron lenses, and the diameter of the neck portion of a funnel in which the electron guns are installed is restricted by the design requirements of deflection and convergence yokes, etc., it is not possible to make the diameter of the electron beam-passing holes larger than the distance between the centers of the two electron beam-passing holes.
A structure of electron guns for improving spherical aberration in a conventional main lens is disclosed in U.S. Pat. No. 4,370,592, and is shown in FIG.
1
. As shown in
FIG. 1
, burring portions
5
b
and
6
b
are formed at the inner peripheries of the exit plane
5
a
of a focusing electrode
5
and the entrance plane
6
a
of a final accelerating electrode
6
, respectively, and large diameter electron beam-passing holes (hereinafter referred to as large apertures)
5
H and
6
H having a predetermined depth are formed in the central portions of the planes. Also, small diameter electron beam-passing holes (hereinafter referred to as small apertures)
5
H′ and
6
H′ through which R, G and B electron beams independently pass, respectively, are formed in the large apertures
5
H and
6
H.
When the electron beams pass through the main lens formed by the focusing electrode
5
and the last accelerating electrode
6
, since the large apertures
5
H and
6
H are non-circular or oblong and therefore vertical and horizontal convergent components of an electron beam having passed through the central small aperture and electron beams having passed through two side small apertures are different from each other, electron beam spots on a phosphor surface one not uniform. That is, as shown in
FIG. 2
, two side beams RB and BB passing through the large aperture
5
H or
6
H of the focusing electrode
5
or the last accelerating electrode
6
are horizontally close to the burring portions
5
b
and
6
b
where a low or high voltage is distributed, and the central electron beam GB is relatively far from the burring portions
5
b
and
6
b.
Accordingly, the two side electron beams are converged to a relatively larger extent, and the central beam is converged to a smaller extent.
In addition, since the distances between the two side beams RB and BB and the burring portions
5
b
and
6
b
are different from each other depending on direction, the horizontal and vertical converging forces acting on the electron beams are different from each other. In addition, since the vertical distances between the central beam GB and the burring portions
5
b
and
6
b
are shorter than the horizontal distances between them, the central beam GB is subject to stronger vertical converging forces. Further, the central beam GB suffers diverging forces in diagonal directions of the large apertures
5
H and
6
H. Therefore, since the sections of the two side beams RB and BB having passed the main lens are generally triangular, and the section of the central beam GB has a radial shape, uniform sections of electron beams cannot be obtained.
In particular, since the diameter of the small apertures
5
H′ and
6
H′ is restricted by the diameter of the neck portion of a cathode ray tube, there is a limit in increasing the distance between the centers of the small apertures
5
H′ or
6
H′. Further, since the diameter of the neck portion tends to be reduced to reduce deflection yoke power consumption, the separation between the small apertures
5
H′ or
6
H′ become smaller and there are problems in which the spherical aberration increases and focusing characteristics are deteriorate.
A electrode structure for solving the above problems is disclosed in U.S. Pat. No. 5,414,323. As shown in
FIG. 3
, in the electrode structure, an electrode plate
16
is installed at the center of an external electrode
11
in which a large aperture is formed, a small aperture
13
of a longitudinally elongated shape is formed at the center of the electrode plate
16
, and the sides of the electrode plate are cut to have semi-elliptical shapes in order to form two side electron beam-passing holes
14
and
15
.
By making the central small aperture longitudinally elongated, the astigmatism caused by the large aperture is offset. However, in the above electrode, eight-pole astigmatism of the central electron beam-passing hole and six-pole astigmatism of the two side electron beam-passing holes are not corrected easily.
Another example of a conventional large diameter electrode is disclosed in U.S. Pat. No. 4,626,738. As shown in
FIG. 4
, the electrode includes an external electrode
21
in which a large aperture is formed, and an internal electrode
22
which is installed in the external electrode
21
and in which polygonal small apertures
22
R,
22
G and
22
B are formed. Here, the astigmatisms caused by the large aperture can be compensated for by the polygonal small apertures
22
R,
22
G and
22
B, but the polygonal small apertures
22
R,
22
G and
22
B are not easily manufactured.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide an electrode to electron guns for a color cathode ray tube in which the astigmatisms caused by the large diameter electron beam-passing hole are easily corrected enhancing the focusing characteristics.
Accordingly, to achieve the above objective, there is provided an electrode of electron guns for a color cathode ray tube including: an external rim electrode in which a large diameter electron beam-passing hole through which all three electron beams pass is formed; and first and second internal electrode pieces installed in the large diameter electron beam-passing hole to be separated from each other with a predetermined gap and forming a central small diameter electron beam-passing hole and two side small diameter electron beam-passing holes which are arranged in a line within the large diameter electron beam-passing hole, wherein the central small diameter electron beam-passing hole is formed by inner edges of the first and second internal electrode pieces between the first and second internal electrode pieces, and the inner edges have the curvature of the minor axis of an ellipse having a major axis larger than short width of the large diameter electron beam-passing hole.
In addition, the electrode further includes a flange inwardly extending from the end of the external rim electrode and defining the large diameter electron beam-passing hole.
Curved edges having the radii of curvature of the major axis of an ellipse disposed in a direction of the major axis of the large diameter electron beam-passing hole are formed at inner sides of the flange.
According to one aspect of the present invention, there is provided an electrode of electron guns for a color cathode ray tube wherein edges other than the inner edges of the first and second internal electrode pieces contact the inner surface of the external rim electrode, and the two side small diameter electron beam-passing holes are formed in the first and second internal electrode pieces, respectively.
Here, the side small diameter electron beam-passing holes are preferably circular or non-circular.
REFERENCES:
patent: 5414323 (1995-05-01), Uchida et al.
patent: 5894191 (1999-04-01), Kim
patent: 5917275 (1999-06-01), Uchida et al.
patent: 5994851 (1999-11-01), Kim
Leydig Volt & Mayer, Ltd.
Patel Ashok
Samsung Display Devices Co. Ltd.
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