Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2002-05-24
2004-08-24
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S407000, C445S030000
Reexamination Certificate
active
06781298
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Cathode Ray Tube (hereinafter, CRT) and particularly, to a frame of a CRT, capable of preventing tension lowering and creep phenomena caused by heat processing and howling phenomenon of the cathode ray tube.
2. Description of the Background Art
Generally, a flat screen color CRT, as shown in
FIG. 1
, is composed of a front glass which is called as a panel
10
and a rear glass which is called as a funnel
20
and they are combined to each other, being enclosed with a high-degree vacuum.
Inside the CRT, a fluorescent layer
40
which functions as a predetermined luminescent material is formed on an inner surface of the panel
10
. An electron gun
130
for scanning an electron beam for emitting the fluorescent surface
40
. A shadow mask
70
for sorting colors so that the electron beam
60
generated in the electron gun
130
can be landed to a predetermined portion of the fluorescent layer
40
. A main frame
30
and sub frame
35
fix and support the shadow mask
70
and a spring
80
combines the assembly of the above frames into the panel
10
. An inner shield
90
which is combined with a side surface of the main frame
30
in a spanned shape from the side of the panel
10
to the side of the funnel
20
, is positioned on one side surface of the main frame
30
, so that the CRT is rarely influenced by a terrestrial magnetism, in operating the CRT.
Also, the flat screen CRT is provided with a reinforcing band
110
installed in the outer circumferential portion of the panel
10
and funnel
20
, and accordingly, the flat screen CRT is constructed to have a sufficient resistance against air pressure and exterior impact.
On the other hand, the operation of the CRT shown in
FIG. 1
will be described as follows.
First, the electron beam
6
is landed to the fluorescent layer
40
formed on the inner surface of the panel
10
in the electron beam landed to a neck portion of the funnel
20
by positive voltage applied to the CRT. At this time, the electron beam
60
is deflected to the upper and lower directions and left and right directions by the deflection yoke
50
before it reaches the fluorescent layer
40
, thus to form a screen.
In addition, a magnet
100
having 2, 4 and 6 poles, for correcting the circle of the process so that the electron beam
60
can exactly land to a predetermined fluorescent material prevents degradation of color purity.
Since such CRT is composed under the condition of high-degree vacuum, a crack can be easily occurred by exterior impact. To prevent the crack, the flat screen CRT is provided with a reinforcing band formed on the circumferential surface of the skirt portion of the funnel
20
, and accordingly, the flat screen CRT is constructed to have a sufficient impact resistance by dispersing stress formed in the CRT under the condition of a high-degree vacuum.
In a tension type CRT structure as in
FIG. 1
, to apply a tension to the shadow mask
70
, a frame which supports the shadow mask
70
is compressed, a shadow mask is welded on the compressed frame and the compression added to the frame is stopped so that the tension is applied to the shadow mask
70
.
FIG. 2
is a view showing the status that the frame for supporting the shadow mask is combined with the panel.
As shown in
FIG. 2
, a shadow mask
70
to which a tension is applied, is welded to the end of the main frame
30
and the frame
30
which applies a tension to the shadow mask
70
is combined with the panel
10
, connected with a spring
80
and a stud pin
120
inside the panel
10
.
Hereinafter, the composition that the shadow mask
70
is combined with the frame
30
will be described in detail.
Conventionally, a frame before being welded is compressed with a predetermined load and welded with the shadow mask
70
. Then, a preferred curvature is embodied in the shadow mask by removing a compression load added to the frame and a tension is applied to the upper and lower directions (direction of the short-side line) at the same time. Accordingly, the natural frequency of the shadow mask is increased to prevent the howling phenomenon that a screen vibrates.
However, as the length of the screen is enlarged, the length of the short-side line (vertical direction) is increased and accordingly, the length of the short-side line (vertical direction) of the shadow mask capable of vibrating is lengthened.
Generally, since a natural frequency of a substance is inversely proportional to the length, as the length of the short-side line (vertical direction) of the shadow mask, the natural frequency of the shadow mask attached to the frame decreases.
Therefore, in the combination between the frame and shadow mask
70
, the vibration which can be occurred in the shadow mask
70
must be considered due to an additional vibration which can be occurred by the exterior circumstance or in operating the frame and shadow mask
70
.
Also, the tension applied to the upper and lower directions of the shadow mask
70
is related to the thickness of the shadow mask
70
, heights of the main frame
30
and sub frame
35
, curvature to the Z direction of the sub frame
35
and the like and the tension is also related to the ratio between the height of the whole frame and the height of the sub frame, compression load and material characteristic of the frame.
Hereinafter, among the above factors, relationship between the height of the sub frame
35
and the height of the whole frame, and the corresponding problems which is accompanied with the relationship will be described in detail.
First, in case the height of the sub frame
35
is composed smaller than that of the whole frame, that is, in case the curvature of the sub frame
35
is composed large, the suame
35
is composed large, the suth a larger compression load than in case the curvature is gentle, to apply a predetermined tension to the shadow mask
70
.
However, since the capacity of the compression motor must be increased to add a larger compression load, the cost is increased.
In addition, the tension applied to the shadow mask
70
is determined according to the degree of the compression of the sub frame
35
. The compression amount of the sub frame
35
can be known with the deflection length in the Z direction, which affects the tension applied to the shadow mask
70
as shown in FIG.
3
B.
Also, in case the height of the sub frame
35
is composed smaller than that of the whole frame, the sub frame
35
must have a sufficient yield strength that it can stand the deflection force, since a larger stress is applied to the sub frame
35
to deflect the whole frame to the Z direction in
FIG. 3
b
with the height as before.
However, since there is a limit with just the yield strength that the material itself has to have a sufficient yield strength, the material characteristic must be improved through the processing method such as additional heat processing of the frame member and the like and accordingly, the cost of the frame member itself is increased.
On the other hand, in case the height of the sub frame
35
is composed larger than that of the whole frame, that is, in case the curvature of the sub frame
35
is composed smaller, a preferred tension can be applied to the shadow mask
70
with a smaller compression load. Namely, as the curvature of the sub frame
35
is smaller, the sub frame can be compressed more easily.
However, in the composition of the sub frame having a larger height than the whole frame, the exterior portion of the sub frame
35
, a round portion where the curvature is formed and a part can be protruded to the lower side of the skirt portion
11
of the panel
10
.
In the above case, the panel
10
and the frames
30
and
35
must be moved under the condition that they are combined to each other in the manufacturing process of the CRT. In case the sub frame is protruded to the lower side of the skirt portion
11
of the panel
10
, foreign material can be inserted to the shadow mask more in moving the panel and frames and the
Hwang In-Hyuk
Kim Sung-Hun
Zheong Kyung-Jin
Fleshner & Kim LLP
Leurig Sharlene
LG Electronics Inc.
Patel Nimeshkumar D.
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