Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2002-05-28
2003-12-16
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S403000, C313S404000, C313S407000, C313S408000
Reexamination Certificate
active
06664724
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a shadow mask for a color CRT (cathode ray tube), and in particular to a slot interval of a shadow mask for a color CRT (cathode ray tube).
2. Description of the Prior Art
FIG. 1
is a schematic view illustrating a general color CRT (cathode ray tube), and
FIG. 2
is a perspective view illustrating a general shadow mask.
Generally, as depicted in
FIG. 1
, in a color CRT, a panel
10
as a front glass is combined with a funnel
20
as a rear glass, and they are hermetically sealed as high vacuum.
And, the color CRT includes a fluorescent surface
40
coated to the inner surface of the panel
10
and performing a luminescent material function, an electron gun
130
discharging an electron beam
60
for radiating the fluorescent surface
40
, a shadow mask
70
for making the electron beam from the electron gun
130
land on a certain portion of the fluorescent surface
40
, a frame
30
fixing/supporting the shadow mask
70
, a spring
80
and a stud pin
120
for combining the frame assembly
30
with the panel
10
, and an inner shield
90
combined with a certain surface of the frame
30
and extended from the panel side to the funnel side in order to protect the CRT from influences of terrestrial magnetism in operation.
And, the electron gun
130
for generating the electron beam
60
is installed to the internal surface of the neck portion of the funnel
20
, a deflection yoke
50
is installed to the outer surface of the neck portion of the funnel
20
in order to deflect the electron beam
60
from the electron gun
130
in a certain direction, and a CPM (convergence & purity magnet)
100
for precisely adjusting the deflected direction of the electron beam
60
.
And, a reinforcing band
110
is installed to the outer circumference of the combining portion of the panel
10
and the funnel
20
in order to help the panel
10
and the funnel
20
stand an air pressure and external impacts.
In addition, as depicted in
FIG. 2
, the conventional shadow mask
70
includes an effective surface
74
having a plurality of circular-shaped or oval-shaped slots
72
and a skirt
76
having a certain length so as to be welded to the frame
30
.
FIG. 3
illustrates a part of the effective surface
74
of the shadow mask
70
, in order to make the electron beam
60
maintain a certain interval when it passes the slots
72
on the effective surface
74
of the shadow mask
70
and lands on the fluorescent surface
40
coated on the panel
10
, the slots
72
respectively having a certain sized hole are arranged horizontally and vertically at regular intervals.
In addition, on the shadow mask
70
, in order to maintain a strength after fabrication, each bridge
78
is formed between abutted two vertical slots
72
.
In
FIGS. 3 and 4
, a non-explained reference numeral Ph is a horizontal pitch of a screen, Pho is a horizontal pitch at the central portion of the shadow mask
70
, and Phd is a horizontal pitch at the circumference of the shadow mask
70
.
As depicted in
FIG. 4
, in a horizontal pitch Ph of the conventional color CRT screen, the slots
72
are arranged at regular intervals from the central portion toward a long axis, a short axis and a diagonal axis about X, Y axes of the shadow mask
70
or the slot interval is increased or decreased according to a certain X, Y functions or a slot column function.
And, the horizontal pitch Ph of the screen is set according to a definition of an expected screen of the color CRT. In general, the horizontal pitch Ph set as 0.095%~0.115% of the screen long side length (W) at the central portion, and a slot horizontal width (Sw) at the central portion is 27%~28% of the horizontal pitch Pho at the central portion of the mask
70
.
The shadow mask
70
passes a curved surface fabrication process, is welded to the frame
30
and fixed to the internal surface of the panel
10
so as to have a certain distance from the interior of the panel
10
in order to disperse and land the red, green, blue electron beam
60
emitted from the electron gun
130
on the screen of the panel
10
at which the fluorescent surface
40
is formed.
In the above-described shadow mask
70
, a resolution meaning a capacity for reproducing a picture is described as a product of a shadow mask definition and an electric beam definition, the definition varies depending on the shadow mask definition rather than the electron beam definition.
The shadow mask definition can be described as Equation 1.
Mask
-
MTF
max
=
cos
(
θ
2
π
P
h
μ
)
=
2
{
1
2
P
h
μ
-
(
1
P
h
+
0.5
)
}
θ
=
2
{
1
2
P
h
μ
-
(
1
P
h
+
0.5
)
}
,
μ
=
N
2
W
[
Equation
1
]
*Mask-MTF: definition of a shadow mask
Ph: horizontal pitch of a shadow mask
*m: spatial frequency
*N: the number of definition pixels
*W: screen long side length
When a definition (Mask-MTF) value of the shadow mask
70
is not less than 0.5, the horizontal pitch (Pho) applied to the central portion of the shadow mask
70
has a pertinent definition reproduction capacity. Herein, the 0.5 definition value was set on the basis of a bright ratio of a picture reproduced for a person having ordinary eyesight.
In addition, in consideration of an eyesight angle of a viewer, when a screen is divided into three equal parts, not right and left parts but the center part is important in perfect reproduction of a high definition picture.
However, in the conventional shadow mask, in particular, a shadow mask in Japan Patent 1999-007901 has a horizontal pitch of 0.088%~0.123%. As depicted in FIG.
5
and Table 1, it satisfies only low definition and intermediate definition such as a NTSC or a PAL, etc.
TABLE 1
HORIZONTAL
STANDARD
HIGH
PITCH RATIO
NTSC
PAL
DEFINITION
DEFINITION
0.095%
◯
◯
◯
&Dgr;
0.105%
◯
◯
◯
X
0.115%
◯
◯
&Dgr;
X
*◯: perfect picture reproduction *&Dgr;: imperfect picture reproduction
*X: reproduction impossible
*horizontal pitch ratio: shadow mask horizontal pitch ratio about a screen long side length
When the conventional level horizontal pitch is used for high definition picture reproduction, because it is insufficient to reproduce a high definition picture provided from a broadcast station or a picture equipment, a definition reproduction capacity is low, accordingly a viewer's sensitivity quality can not be secured.
In addition, when the horizontal pitch is reduced over than a necessity, as depicted in
FIG. 6
, a purity margin is reduced, it causes problems in color reproduction of a high definition picture.
In general, a purity margin means a possibility in which an electron beam hits a fluorescent portion abutting on a target fluorescent portion without landing on the pertinent fluorescent portion.
FIG. 6
describes it.
As depicted in
FIG. 6
, there are a screen horizontal pitch (Ph), a screen fluorescent band (a), a screen black matrix band (d) and an electron beam horizontal width (b) as main factors determining a purity margin (c).
The screen horizontal pitch (Ph) is formed on a screen by multiplying a horizontal pitch (Pho) on the central portion of the shadow mask
70
by a pitch magnifying power (&agr;) determined by a distance between a screen and a shadow mask and an interval ratio between the screen and a panel, the horizontal pitch (Pho) at the central portion of the shadow mask is considered importantly in determining a screen horizontal pitch (Ph).
And, an electron beam horizontal width (b) is obtained by multiplying a slot width (Sw) of the shadow mask
70
by an electron beam magnifying power (&bgr;).
And, the screen fluorescent band (a) and the block matrix band (d) are determined by considering a brightness, etc.
As an example of
FIG. 6
, in a color cathode ray tube including a 32 inches shadow mask having a width of 0.25 mm and a long side effective surface length of 662.4 mm, a horizontal pitch (Pho) at the central portion of the shadow ma
Fleshner & Kim LLP
Harper Holly
LG. Philips Display Korea Co., Ltd.
Patel Nimeshkumar D.
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