Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2002-11-18
2004-12-28
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S403000
Reexamination Certificate
active
06836061
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
The present application claims priority under 35 U.S.C. §119 to Korean Application No. 30812/2002, filed May 31, 2002, the entire disclosure of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a shadow mask for a color cathode-ray tube and, more particularly, to a shadow mask having improved shock resistance by establishing a ratio of less than 1 between sizes of an electron beam through hole in an axial direction and in a direction vertical to the axial direction when an external shock is impressed on the cathode-ray tube, for example, during a drop intensity test. The electron beam through hole is formed by etching on the shadow mask which is included in the cathode-ray tube.
2. Description of the Background Art
Generally, a cathode-ray tube functions as a principal component in forming an image in an image display device, such as a television picture receiver or a computer monitor.
As shown in
FIG. 1
, a color cathode-ray tube is sealed by coupling a front glass, depicted as panel
10
, to a rear glass, depicted as a funnel
20
, thereby resulting in a vacuum within the color cathode-ray tube.
A fluorescent surface
40
of the color cathode-ray tube functions as a luminescent material and is located on an inner side surface of the panel
10
. An electron beam
60
, which illuminates the fluorescent surface
40
, is generated by an electron gun
130
. A shadow mask
70
sorts the electron beam
60
generated by the electron gun
130
so that the electron beam
60
can hit a predetermined part of the fluorescent surface
40
. A frame
30
fixes and supports the shadow mask
70
. A spring
80
and a stud pin
120
couples the frame
30
to the panel
10
. An inner shield
90
is coupled to a side surface of the frame
30
opposite to a side surface of the frame
30
facing the panel
10
, so that the cathode-ray tube is little affected by outer terrestrial magnetism during operation.
The electron gun
130
is mounted on an inner side surface of a neck portion
140
of the funnel
20
. A deflection yoke
50
deflects the electron beam
60
generated by the electron gun
130
to a predetermined direction. A convergence and purity magnet (CPM)
100
controls more precisely the direction of the electron beam
60
deflected by the deflection yoke
50
. Both the deflection yoke
50
and the CPM
100
are positioned on an outer side surface of the neck portion
140
.
A reinforcing band
110
is mounted on an outer circumferential portion of the color cathode-ray tube that couples the panel
10
to the funnel
20
, so that the panel
10
and the funnel
20
do not come apart as a result of atmospheric pressure on or an external disturbance to the color cathode-ray tube.
When the electron beam
60
generated by the electron gun
130
hits the fluorescent surface
40
by a positive voltage applied to the cathode-ray tube, the electron beam
60
is deflected to, for example, upper, lower, left, and right directions by the deflection yoke
50
before the electron beam
60
reaches the florescent surface
40
.
The CPM
100
may include magnets of 2, 4, or 6 poles to correct successive tracks of the electron beam
60
, so that the electron beam
60
can be more precisely directed on the predetermined fluorescent surface
40
to thereby prevent color purity defects.
The shadow mask
70
is formed in the shape of a dome, and a predetermined gap is maintained between the shadow mask
70
and the inside of the panel
10
. As shown in
FIG. 2
, the shadow mask
70
includes an effective surface portion
71
on which a plurality of electron beam through holes
74
of dot shape are formed. A peripheral portion
72
surrounds the effective surface portion
71
and does not have many electron beam through holes
74
. A mask skirt portion
73
is folded vertically from the peripheral portion
72
on the edge part of the peripheral portion
72
. The shadow mask
70
has a thickness of about 0.1~0.3 mm. As shown in
FIG. 2
, the shadow mask
70
, furthermore, has a longer length and a shorter depth.
In the conventional color cathode-ray tube, the electron beam
60
is generated by the electron gun
130
, and the electron beam
60
is deflected to the upper, lower, left, and right directions by the deflection yoke
50
before the electron beam
60
reaches the shadow mask
70
and the fluorescent surface
40
. Subsequently, the electron beam
60
passes through the shadow mask
70
, which sorts the electron beam
60
by a plurality of through holes, and hits the predetermined fluorescent surface
40
, thereby forming an image on the fluorescent surface
40
.
As shown in
FIGS. 3 and 4
, the electron beam through hole
74
includes a circular-shaped electron beam incidence hole
74
a
, formed by etching, facing the inner surface of the funnel
20
, and a circular-shaped electron beam exit hole
74
b
facing the inner surface of the panel
10
.
Also, the angle of the electron beam
60
incident on the shadow mask
70
is changed by the specific position on the shadow mask
70
at which the electron beam
60
is incident; therefore, the width of the electron beam exit hole
74
b
is gradually increased as the beam exit hole
74
b
approaches the effective surface portion
71
on the shadow mask
70
in order to prevent the electron beam
60
from being scattered.
Although the quality of the color cathode-ray tube can be affected by a number of factors, the color purity of the realized image is the most important factor. The color purity is largely affected by a distortion of the shadow mask
70
, which is mainly caused by an external shock. Dropping the color cathode-ray tube, for example, can cause a large shock to the color cathode-ray tube.
Also, when the panel
10
, which is relatively heavy compared to other components of the color cathode-ray tube, is dropped to the ground, the shadow mask
70
may suffer severe distortion.
The above distortion is actually caused by the structural characteristics of the shadow mask
70
, and this will be described in more detail as follows.
As described above, the shadow mask
70
includes the electron beam through holes
74
of predetermined shape, and the sizes of the electron beam through holes
74
gradually increase as the through holes
74
approach the peripheral parts of the shadow mask
70
in order to prevent the electron beam
60
from being scattered.
As a result, the cross sectional area and volume of the shadow mask
70
gradually decrease near the peripheral parts according to the above changes.
Consequently, in the event that the cathode-ray tube is dropped, the intensity of the shock resulting therefrom on the shadow mask
70
decreases in accordance with the decrease of the cross sectional area on the peripheral parts, and the weight also decreases in accordance with the decrease in volume.
The above structural property causes vibrations in an upper and lower direction on the shadow mask
70
, when the side of the color cathode-ray tube on which the panel
10
is formed is dropped.
That is, in the event of an external shock to the cathode-ray tube, the central part of the shadow mask
70
, which is exposed to a greater shock and has a greater weight compared to the peripheral parts, has a larger amplitude of vibration than that of the peripheral parts.
Therefore, a greater load impacts the central part of the shadow mask
70
; and, accordingly, a distortion is generated having a greater intensity on a boundary of the central part and having a weaker intensity on the peripheral part.
Actually, the shadow mask
70
inside the cathode-ray tube becomes more sensitive as the size of the cathode-ray tube increases. In the event of a shock of a similar intensity, the shadow mask of a larger cathode-ray tube is more likely to suffer permanent damage as a result of a sudden distortion.
In the conventional cathode-ray tube, a length of the electron beam exit hole
74
b
in a direction facing away from the center of the shadow ma
Guharay Karabi
LG. Philips Displays Korea Co. Ltd.
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