Electric lamp and discharge devices – Cathode ray tube – Ray generating or control
Reexamination Certificate
2001-11-19
2003-09-30
O'Shea, Sandra (Department: 2875)
Electric lamp and discharge devices
Cathode ray tube
Ray generating or control
C313S412000, C313S414000
Reexamination Certificate
active
06628061
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron gun and, more particularly, to an electron gun for a cathode ray tube (CRT) including a correction electrode having asymmetric beam through holes located between a grid having a single aperture and a shield cup.
2. Description of the Related Art
An electron gun for a color CRT generally includes a triode having cathodes, a first grid G
1
and a second grid G
2
, a third grid G
3
opposing the second grid G
2
and forming a pre-focusing lens, a fourth grid G
4
opposing the third grid G
3
and forming a main lens, and a shield cup.
When power is applied to a cathode ray tube, the electron gun emits electron beams from the cathodes. The emitted electron beams are focused and accelerated while passing through apertures in a plurality of grids. The accelerated electron beams are selectively deflected by a deflection yoke installed on a cone portion of a bulb of the CRT and excite phosphors on a screen, thereby producing a displayed image. Electron guns have various structures for correcting errors in convergence of electron beams landing on peripheral parts of the screen due to the non-uniform deflecting magnetic field of the deflection yoke.
FIG. 1
is a horizontal sectional view showing an electron gun
10
disclosed in U.S. Pat. No. 5,517,078,
FIG. 2A
shows a third grid G
3
shown in
FIG. 1
, and
FIG. 2B
shows a fourth grid G
4
shown in FIG.
1
. As shown in
FIGS. 1
,
2
A, and
2
B, the electron gun
10
includes three cathodes, KR, KG, and KB, first through fourth grids, G
1
through G
4
, sequentially arranged in the direction of a phosphor screen, and a convergence cup Cp on the fourth grid G
4
. In the third grid G
3
shown in
FIG. 2A
, three beam through holes
31
R,
31
G, and
31
B are arranged along a straight line on a surface opposing the fourth grid G
4
.
Among the beam through holes
31
R,
31
G, and
31
B of the third grid G
3
, the center beam through hole
31
G has a circular shape. However, each of the side beam through holes
31
R and
31
B has an elongated shape, elongated in a horizontal direction, that is, the X-axis direction, of the third grid G
3
. Opposite edges of each of the side beam through holes
31
R and
31
B are arcs A
1
and A
2
, respectively having radii R
1
and R
2
. The arcs A
1
and A
2
are connected to each other with straight edges L
1
and L
2
. The length of the inner arc A
1
toward the center beam through hole is greater than that of the outer arc A
2
.
The fourth grid G
4
, shown in
FIG. 2B
, includes three beam through holes
41
R,
41
G, and
41
B, arranged along a straight line on a surface opposing the third grid G
3
. The beam through holes
41
R,
41
G, and
41
B of the fourth grid, G
4
, are all circular. Among these beam through holes
41
R,
41
G, and
41
B, side beam through holes
41
R and
41
B are slightly off-center, outwardly in the arrangement direction of the three electron beams, by a distance &Dgr;S with respect to the side beam through holes
31
R and
31
B of the third grid G
3
.
In the electron gun
10
having the described configuration, side beam through holes having inner and outer arcs of different lengths are located on at least one of the surfaces of the third grid G
3
and the fourth grid G
4
that face each other. Each of the third grid G
3
and the fourth grid G
4
, forming a main lens, has three beam through holes. Thus, when forming asymmetric side beam through holes
31
R and
31
B, the effective individual aperture is reduced, thereby increasing spherical aberration. The main lens is very sensitive to alignment during assembly of the electron gun
10
. The described grid configuration cannot ensure reliability of the electron gun
10
. Also, minute adjustment of convergence is difficult.
FIG. 3
is a longitudinal sectional view of an electron gun
30
disclosed in U.S. Pat. No. 4,678,964. Referring to
FIG. 3
, the electron gun
30
includes three cathodes
31
a,
31
b,
and
31
c,
a first grid
32
, a planar second grid
33
, a third grid
34
, and a fourth grid
35
. The third grid
34
includes cup-shaped parts
34
a
and
34
b
having open ends fixedly sealed to each other. The fourth grid
35
includes three beam through holes
35
a,
35
b,
and
35
c.
Also, the fourth grid
35
further includes a cup-shaped field correction element
36
having rectangular beam through holes
36
a,
36
b,
and
36
c.
The beam through holes
36
a,
36
b,
and
36
c
of the field correction element
36
face the beam through holes
35
a,
35
b,
and
35
c.
The field correction element
36
has a flange
36
d
connecting the fourth grid
35
and a sleeve
37
.
The field correction element
36
is installed inside the fourth grid
35
and the beam through holes
36
a,
36
b,
and
36
c
are vertically or horizontally elongated. Alternatively, the field correction element
36
is part of the grids
34
and
35
, each of which has three beam through holes. Accordingly, the effective individual aperture is reduced, exhibiting a weak astigmatism correction. Because of the weakness of the correction, the improvement in distortion of beam spots at the peripheral portion of the screen is insufficient.
FIG. 4A
is a front view of an electrode
40
disclosed in Japanese Unexamined Patent Application 2000-67774,
FIG. 4B
is a plan view of
FIG. 4A
, and
FIG. 4C
is a side view of FIG.
4
A. In
FIGS. 4A
,
4
B, and
4
C, the electrode
40
is located between grids and a shield cup. The electrode
40
has three circular beam through holes
42
,
43
, and
44
arranged along a straight line on a planar portion
41
. Perpendicular portions
45
and
46
are located at opposite edges of the planar portion
41
. The electrode
40
has sloping portions
47
.
The plate-shaped electrode is installed in the rear of a main lens for horizontal focusing and vertical divergence for improving performance of a quadrupole lens. However the electrode
40
is not reliable because it has perpendicular portions. Also, it is quite difficult to overcome the distortion of beam spots caused by side beam through holes
42
and
44
.
SUMMARY OF THE INVENTION
To achieve the above object, there is provided an electron gun for a cathode ray tube including a triode having cathodes, a first grid, and a second grid; at least one third grid having a single aperture through which R, G, and B electron beams emitted from the cathodes commonly pass; a fourth grid opposing the third grid and forming a main focus lens with the third grid; a shield cup connected to the fourth grid and supplying a high voltage to the fourth grid; and a correction grid disposed between the fourth grid and the shield cup and having R, G, and B beam through holes with respective centers lying along a first line, the R and B beam through holes having respective openings that are asymmetrical about respective second lines, transverse to the first line, and passing through the centers of the R and B beam through holes, respectively.
Each of the R and B beam through holes of the correction grid may have an inner part near the center G beam through hole side that is longer than an outer part at the opposite side of the R and B beam through holes.
The R and B through holes may have edges describing trapezoidal openings.
The correction grid may have a planar surface facing the fourth grid and sloping surfaces facing the shield cup so that the correction grid has a thinnest part at the G beam through hole and becomes thicker, along the first line, toward each of opposite ends of the correction grid.
The correction grid may be a plate in which circular R, G, and B beam through holes are arranged along a straight line, and members for varying the openings of the R and B beam through holes are mounted on the plate blocking part of the R and B beam through holes, respectively.
According to another aspect of the invention, an electron gun for a cathode ray tube comprises a triode having cathodes, a first grid, and a second grid; at least one third grid through which R, G, and B ele
Bae Min-cheol
Hong Young-gon
Huh Woo-seok
Dong Dalei
Leydig , Voit & Mayer, Ltd.
O'Shea Sandra
Samsung SDI & Co., Ltd.
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