Cathode ray tube

Details Cathode ray tube Cathode ray tube

2003-02-07

2004-10-05

Patel, Nimeshkumar D. (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Plural beam generating or control

C313S412000, C313S413000, C313S426000, C313S427000, C313S428000, C313S417000

Reexamination Certificate

active

06800991

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to a cathode ray tube having an electron gun capable of improving a resolution of an image by preventing electron beams from striking electrodes and efficiently controlling a spot size that is susceptible to a change in current capacity.
2. Background of the Related Art
FIG. 1
is an explanatory view of a general cathode ray tube in a related art.
As depicted in
FIG. 1
, the cathode ray tube consists of a panel
1
with a fluorescent screen
13
formed on its inner surface, in which R, G, and B fluorescent substances (or phosphors) are applied to the screen, a funnel
12
fused to a rear end of the panel
10
for maintaining the inside of the tube in a vacuum state, an electron gun housed inside of a neck portion
15
of the funnel
12
for emitting electron beams, a deflection yoke
11
for deflecting the electron beams emitted from the electron gun
16
, and a shadow mask
14
with a color selecting function for the electron beams that are deflected by the deflection yoke
11
.
Normally in this kind of cathode ray tube, the electron beams emitted from the electron gun
16
are deflected by the deflection yoke
11
in the horizontal and vertical directions, and then pass through the shadow mask
14
, and eventually strike the fluorescent screen
13
.
When that happens, each fluorescent substance (i.e. R, G and B) applied to the fluorescent screen
13
is radiated or emits light, thereby creating a desired image.
FIG. 2
diagrammatically illustrates the structure of an electron gun according to a related art.
Referring to
FIG. 2
, the electron gun consists of a cathode
20
working as an electron beam generator, a first electrode (G
1
)
21
and a second electrode (G
2
)
22
whose potential difference constitutes, in combination with the cathode
20
, a pre-focus lens, a third electrode (G
3
)
23
and a fourth electrode (G
4
)
24
and a fifth electrode (G
5
)
25
that constitute a pre-main lens for converging electron beams, and a fifth electrode
25
and a sixth electrode (G
6
)
26
that constitute, in combination with the pre-main lens, a main lens for converging the electron beams onto the fluorescent screen.
Besides the above, there is one more main component of the electron gun, i.e. a shield cup
27
, which is fused to the sixth electrode
26
in order to shun off the outside electric field and magnetic field. The electrodes are then fused and fixed to a bead glass
28
.
Particularly, the fourth electrode
24
, as illustrated in
FIG. 3
, is a plate electrode having a predetermined thickness, t. Also, formed on the fourth electrode are three circular electron beam passing holes
24
b
which are spaced out by a predetermined distance from each other for passing through R, G and B electron beams.
Further, projection type bead supports
24
a
are disposed at the top and bottom sides of the fourth electrode
24
. Mainly, the bead supports
24
a
are used to make sure that the electrodes are securely fused and fixed to the bead glass
28
.
FIG.
4
(
a
) is a plan view of the second electrode
22
for the conventional electron gun, explaining the structure of the second electrode
22
, and FIG.
4
(
b
) is an enlarged cross-sectional view of a part “
22
e
” in FIG.
4
(
a
).
As depicted in the drawing, the second electrode
22
basically looks similar to the above-discussed fourth electrode
24
. That is, the second electrode
22
is a plate electrode like the fourth electrode
24
, and it has three circular electron beam passing holes
22
b
disposed at regular intervals for passing through R, G and B electron beams, and bead supports
22
a
for ensuring electrodes to be securely fused and fixed to the bead glass
28
.
As for the second electrode
22
, however, each electron beam passing hole
22
b
is surrounded by an outer concentric circle, namely, a coining part
22
b
, which serves to minimize manufacturing difficulties and deformation, and formed inside the coining part
22
d
is a rectangular shaped recess
22
c
with a constant, unified depth in the horizontal direction at an opening part of the second electrode
22
towards the third electrode
23
.
More specifically, the recess
22
c
forms a groove having a constant depth, and the electron beam passing hole
22
b
is located at the center of the groove. In fact, one can more easily fabricate the electron beam passing hole
22
b
by having the electron beam passing hole
22
b
be formed in the recess
22
c
with a relatively thinner thickness than the total thickness of the second electrode
22
.
Now turning to the operation of the electron gun with the above structure, first of all, an electron beam is formed by the first electrode
21
and the second electrode
22
, and the electron beam is primarily converged by the pre-focus lens formed by the potential difference between the second electrode
22
and the third electrode
23
, and then largely converged by the pre-main lens formed by the potential difference among the third electrode
23
, the fourth electrode
24
, and the fifth electrode
25
.
The electron beam having been primarily converged by the pre-main lens passes the main lens formed by the potential difference between the fifth electrode
25
and the sixth electrode
26
, and is again converged and accelerated, thereby forming an electron beam spot on the fluorescent screen.
The third electrode
23
and the fifth electrode
25
have the unified potential, which is, in general, between 6000V and 10000V.
In addition, the second electrode
22
and the fourth electrode
24
have the unified potential, which is, in general, between 300V and 1000V.
Each in-line type electron beam in opposition to the R, G and B fluorescent substances applied to the fluorescent screen
13
is converged to one single point so as to reproduce a desired color.
In other words, those three electron beams are respectively converged by the main lens, and combined to a focal point on the fluorescent screen
13
, forming an electron beam spot on the screen.
In connection with convergence of the spot on the screen, Japanese Patent Publication No. 53-18866 discloses a method for preventing deterioration in the convergence of spots on the screen by forming a recess
22
c
in the horizontal direction at the opening part of the second electrode
22
toward the third electrode side
23
.
FIG. 5
diagrammatically depicts the shape of an electron beam incidented upon the main lens and the shapes of electron beams exhibited on the fluorescent screen.
Referring to
FIG. 5
, the electron beam incidented upon the main lens is horizontally oblong, that is, the width (a) is longer than the length (b). It is so because the depth toward the direction of the electrode thickness of the recess
22
c
is large. In result, the electron beam is very astigmatic, and deflection aberration observed on the entire screen can be well compensated.
As such, the ratio of the length to the width, b/a, and size of the electron beam incidented on the main lens contributes to the spot size throughout the screen and further resolution of a cathode ray tube. As shown in
FIG. 6
, the ratio of the length to the width, b/a, of the electron beam incidented on the main lens is closely connected to the depth, d, of the recess formed on the second electrode
22
and the vertical width (size), W, of the recess.
There have been numbers of attempts to reduce the deflection aberration of electron beams and deterioration of beam spot in the vicinity of the screen by, for example, forming the recess
22
c
on the second electrode
22
and making the ratio of the depth, d, to the width, W, of the recess
22
c
(d/W) greater than 0.3 so as to generate severely astigmatic beams, and then adjusting the ratio of d to W of the electron beam incidented on the main lens.
However, the above attempts only gave rise to a problem that the spot size at the center of the screen was vertically elongated due to the astigmatism.
In another aspect, as more and more

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