Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2001-10-09
2003-02-04
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C313S414000
Reexamination Certificate
active
06515438
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron gun in a color CRT (Cathode Ray Tube), in which a distance between a central electron beam and an outer electron beam is made greater on a deflection center plane for improving a resolution.
2. Background of the Related Art
FIG. 1
illustrates a horizontal longitudinal section of a related art cathode ray tube.
Referring to
FIG. 1
, the related art cathode ray tube is provided with a panel
1
and a funnel
2
of a front part and a rear part of the cathode ray tube, a neck part
2
a
at an end of the funnel
2
, an electron gun
3
in the neck part
2
a
for emitting R, G, B electron beams
3
a,
a deflection yoke
4
on an outer circumference of the funnel
2
for deflection of the electron beams in an upper, lower, left, of right direction, a color purity magnet
5
in front of the deflection yoke
4
for fining tuning a path of the electron beams
3
a,
a shadow mask
6
fitted between the electron gun
3
and the panel
1
for selective pass of the deflected electron beams
3
a,
and a fluorescent surface
7
of R, G, B fluorescent materials on an inside surface of the panel
1
.
FIG. 2
illustrates a partial longitudinal section of an electron gun built in a neck part of a color CRT in FIG.
1
.
Referring to
FIG. 2
, the electron gun
3
is provided with cathodes
8
, a control electrode
9
, an acceleration electrode
10
, first and second pre-focusing electrodes
11
a
and
11
b,
a focusing electrode
12
and an anode
13
, in an order thereof, so that a preset voltage is applied to each of the electrodes.
Upon putting the cathode ray tube into operation, electron beams
3
a
are emitted from the cathodes
8
, controlled, accelerated, and pre-focused by the control electrode
9
, the acceleration electrode
10
, and the first and second pre-focusing electrodes
11
(
11
a
and
11
b
), and subjected to main focusing by a main focusing electro-static lens formed between the focusing electrode
12
and the anode
13
of a potential difference. Then, the electron beams
3
a
are deflected in an upper, lower, left, or right direction by the deflection yoke
4
, pass through a shadow mask
6
selectively, and land on a fluorescent surface, to form a picture on the panel
1
. A color purity of the picture formed thus may be adjusted more precisely as worker adjusts the color purity magnet
5
to change a path of the electron beams.
In the meantime, it is known that a picture quality becomes the better as a spot size of the landed electron beams
3
a
is made the smaller. The spot size of the electron beams
3
a
is proportional to a diameter of the main focusing electrostatic lens, and the size of the main focusing electrostatic lens is proportional to sizes of electron beam pass through holes
12
a
and
13
a
formed in parts opposite to the focusing electrode
12
and the anode
13
.
FIG. 3
illustrates a perspective view of the focusing electrode and the anode of the electron gun in FIG.
2
.
Referring to
FIG. 3
, in order to form a large diametered main focusing electrostatic lens, there are horizontally elongated track type rims
12
b
and
13
b
each forming single electron pass through hole
12
a
or
13
a
for passing the three electron beams
3
a
in parts opposite to the focusing electrode
12
and the anode
13
respectively, and electrostatic field controlling bodies
14
and
15
each provided at a point moved a distance back from the rim
12
b
or
13
b,
respectively.
The horizontally elongated track type rim
12
b
or
13
b
has a small height and a great width, permitting an electric field to penetrate shallow in a vertical direction and deep in a horizontal direction, forming a large equipotential surface curvature in the vertical direction, and a small equipotential surface curvature in the horizontal direction. According to this, a single horizontally elongated main focusing electrostatic lens focuses the electron beams
3
a
strongly in the vertical direction, and weakly in the horizontal direction.
However, the electrostatic field controlling bodies
14
and
15
suppress a horizontal field penetration, resulting to form the curvature of horizontal equipotential surface larger. Consequently, a horizontal focusing power of the main focusing electrostatic lens becomes stronger, making the horizontal and vertical focusing powers of the main focusing electrostatic lens the same.
FIGS. 4A-4D
illustrate various examples of electrostatic field controlling bodies fitted to the focusing electrode and the accelerating electrode in FIG.
3
.
FIG. 4A
illustrates a front view of an LB (large aperture with blade) type electrostatic field controlling body disclosed in U.S. Pat. No. 5,512,797 by the inventor. The LB type electrostatic field controlling body
14
or
15
is provided with a rectangular electron beam pass through hole
14
G or
15
G at a center, and vertical blades
14
a
and
15
a
at both sides thereof. The blades
14
a
and
15
a
make a section modulus greater, to reinforce the electrostatic field controlling bodies
14
and
15
against deformation. However, the blades
14
a
and
15
a
interfere horizontal penetration of an electric field, resulting to form a greater horizontal curvature of the main focusing electrostatic lens, that focuses the electron beams
3
a
excessively in the horizontal direction.
FIG. 4B
illustrates a front view of an EA (elliptical aperture) type electrostatic field controlling body developed by Hitachi. The EA type electrostatic field controlling body
14
or
15
is a plate having a vertically elongated elliptical central electron beam pass through hole
14
G or
15
G, and vertically elongated semi-elliptical outer electron beam pass through holes
14
R and
14
B, or
15
R and
15
B. Since the electrostatic field controlling body is not provided with the blades
14
a
and
15
a
as shown in
FIG. 4A
, the horizontal penetration of the electric field in not interfered, to reduce the horizontal curvature of the main focusing electrostatic lens, that permits to form a large sized main focusing electrostatic lens having vertical and horizontal direction harmonized. However, since the electrostatic field controlling body is not provided with the blades
14
a
and
15
a,
the electrostatic field controlling body has a smaller section modulus, and is liable to deform.
FIG. 4C
illustrates a front view of an AEA (Advanced Elliptical Aperture) type electrostatic controlling body disclosed in U.S. Pat. No. 5,146,133 by Hitachi. The AEA type electrostatic controlling body
14
is a plate having three, in line, vertically elongated elliptical electron beam pass through holes
14
R,
14
G, and
14
B, fitted inside of the focusing electrode
12
. It is known that the AEA type electrostatic controlling body
14
prevents unbalance between the outer electron beams R, and B and the central electron beam G when the electrostatic controlling body
14
is placed away from the rim
12
b,
i.e., near to the second pre-focusing electrode for making a size of the main focusing electrostatic lens greater.
FIG. 4D
illustrates a front view of an XL (Extended Large Aperture) type electrostatic controlling body developed by RCA. The XL type electrostatic controlling body
14
or
15
is a plate having the circular three in-line electron beam pass through holes
14
R,
14
G, and
14
B, or
15
R,
15
G, and
15
B. It is known that it is difficult to form spot sizes of the central electron beam G and the outer electron beam R, or B are the same.
In the meantime,
FIG. 5
illustrates an exemplary process in which the electron beams are deflected at the deflection center plane, pass through a shadow mask, and land on the fluorescent surface, schematically. In this instance, the shorter the distance ‘Q’ between the fluorescent surface
7
and the shadow mask
6
, the less the mis-landing of the electron beams
3
a
(R, G, and B) on the fluorescent surface
7
caused by deformation of the shadow mask
6
coming from thermal expansion or vibration. Th
Lee Wilson
Wong Don
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