Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
2001-04-24
2003-06-24
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S439000, C313S409000
Reexamination Certificate
active
06583548
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to an in-line type electron gun in a color cathode ray tube, which can improve a focusing characteristic.
2. Background of the Related Art
In general, electrodes in the in-line type electron guns are positioned at intervals to each other vertical to electron beam paths for controlling the electron beams to reach to a screen in a required form, which will be described in detail, with reference to
FIG. 1
illustrating a section of a related art cathode ray tube.
Referring to
FIG. 1
, the in-line type electron gun is provided with three cathodes
10
independent from one another, a first electrode
11
which is a common electrode for the three cathodes, and a second electrode
12
, a third electrode
13
, a fourth electrode
14
, a fifth electrode
15
, and a sixth electrode
16
, each spaced a distance away from each other. Moreover, there is a shield cup
17
above the sixth electrode
16
, and there is a B.S.C (Bulb Space Connector)
18
attached to the shield cup for electrical connection of the electron gun to the tube and fastening the electron gun to a neck portion
3
of the tube. Accordingly, the electron beams
4
are emitted from heaters (not shown) each built-in the respective cathodes
10
, controlled by the first electrode
11
which is a control electrode, accelerated by the second electrode
12
which is an accelerating electrode, pre-focused/accelerated by a pre-focus lens formed by the second electrode
12
, the third electrode
13
, the fourth electrode
14
, and the fifth electrode
15
, and mainly focused/accelerated by the fifth electrode
15
which is called as a focus electrode and the sixth electrode
16
which is called as an anode, both form a main lens. Then, the electron beams
4
pass through a shadow mask
1
which selects colors, and collide on a fluorescent surface
2
, to make the fluorescent surface luminescent. Eventually, the electron beams
4
from the electron gun can form a picture by means of a deflection yoke, which deflects the electron beams to the entire screen.
FIG. 2
illustrates a perspective view of one example of a related art main lens forming electrode, and
FIG. 3
illustrates a front view of an electrostatic field controlling electrode in the related art main lens forming electrode.
Referring to
FIG. 2
, the main lens forming electrode is provided with the focus electrode
15
and the anode
16
, each with a rim part
15
a
and
16
a
in a form of a running track common for the three electron beams at positions to face each other, and the electrostatic field controlling electrode
25
and
26
as shown in
FIG. 3
at a position inside of the focus electrode
15
or the anode
16
. The electrostatic field controlling electrode
25
or
26
is a plate having three circular pass through holes
25
a
and
26
a
, for enlarging a main lens diameter.
The foregoing main lens forming electrode has the following problems.
Before explaining the problems, factors that give influences to a spot diameter on a picture will be explained. In general, as electron gun design criteria that influences the spot diameter on the picture, there are lens magnitudes, space charge repelling powers, and a main lens spherical aberration. The influence of the lens magnitude to the spot diameter Dx that can be utilized as the design criteria for the electron gun is little and has a slight effect too, because basic voltage conditions, focal distances, a length of the electron gun, and the like are fixed. As the space charge repelling power enlarges the spot diameter Dst owing to repellence and collision between the electrons, and it is favorable to design an angle of the electron beam divergence (called as a divergence angel) great for reducing the enlargement of the spot diameter Dst caused by the space charge repelling power. Opposite to this, the spherical aberration of the main lens, a characteristic representing an enlargement of the spot diameter Dic caused by a difference of focal distances of electrons passed through a radical axis and passed through a protaxis, forms the smaller spot diameter on the screen as the divergence angle is the smaller. In general, the spot diameter Dt on the screen can be expressed by using the following three parameters.
D
t
=
(
D
x
+
D
st
)
2
+
D
ic
2
Particularly, as the best method for reducing the spherical aberration together with a reduction of the space charge repelling force, the main lens with a larger diameter is provided. However, the greater rim parts
15
a
and
16
a
and the greater depth of the electrostatic field controlling electrode
25
and
26
from the rim parts
15
a
and
16
a
to the electrostatic field controlling electrode
25
and
26
for providing a greater diametered main lens causes the following deterioration of the electron beam spot. As shown in
FIG. 3
, the electrostatic field controlling electrode
25
or
26
has pass through holes
25
a
and
26
b
for passing the three electron beams of R, G, B beams, wherein the center beam, the G beam, passes thorough the center beam pass through hole
25
b
, and the outer beams, R and B beams, pass through the outer beam pass through holes
25
a
, each a distance away from the center beam pass through hole
25
b
in opposite directions. That is,
FIG. 4
illustrates forms of spots according to one exemplary related art main lens forming electrode.
Referring to
FIG. 4
, each of the spots formed by the outer electron beams has a form similar to an isosceles triangle, with an apex ‘A’ thereof at which two equal sides ‘B’ thereof meet together positioned at an outer side (an opposite side of the center beam side) and halos along the two equal sides thereof, that deteriorate the outer beam spots, because the rim part
15
a
of the focus electrode
15
weakens the focusing power at upper and lower portions of an inside portion of the outer beam (a center beam side) and enhances the focusing power at upper and lower portions of an outside (opposite sides of the center beam) of the outer beam. This may be explained extensively as follows. Alike a rubber ball with full of air, that bulges at the other side if one side is pressed, if the focusing power at the outside of the electron beam is enhanced, the focusing power of the inside of the electron beam is weakened, to show spot forms similar to the isosceles triangles on the screen. Moreover, there are fine halos formed along the two equal sides ‘B’. Though the anode
16
can correct the spots of the outer beams slightly as the anode
16
acts opposite to the action of the focus electrode
15
, since the main lens enhances the focusing power by the focus electrode more than acceleration by the anode, a spot form by the focusing power only is exhibited at the end.
FIG. 5
illustrates a perspective view of another example of a related art main lens forming electrode,
FIG. 6A
illustrates a front view of an electrostatic field controlling electrode in a focus electrode of a related art main lens forming electrode, and
FIG. 6B
illustrates a front view of an electrostatic field controlling electrode in an anode of a related art main lens forming electrode.
Referring to
FIG. 5
, another example of the related art main lens forming electrode
15
is provided with a focus electrode
15
, an anode
16
, rim parts
15
a
and
16
a
of track forms at opposite sides of the focus electrode
15
and the anode
16
respectively for three electron beams in common, and electrostatic field controlling electrodes
35
and
36
insides of the focus electrode
15
and the anode
16
at distances away from the rim parts as shown in
FIGS. 6A and 6B
, respectively. As shown in
FIG. 6A
, the electrostatic field controlling electrode
35
in the focus electrode
15
has a form of plate with three vertically elongated pass through holes
35
a
and
35
b
, for enlarging a diameter of the main lens. As shown in
FIG. 6B
, the electrostatic field controlling electrode
36
in the anode
16
has a
Cho Sung Ho
Kim Dong Young
Kim Ok Tae
Lee Soo Keun
Leurig Sharlene
LG Electronics Inc.
Patel Ashok
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