Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2000-08-11
2002-11-12
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S404000, C313S407000, C313S408000
Reexamination Certificate
active
06479925
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a shadow mask support frame for a color cathode ray tube (CRT), in which a shadow mask is supported with tension.
2. Background of the Related Art
Generally, a shadow mask support frame for a color CRT supports a shadow mask that acts to selectively pass through an electron beam, so as to prevent the shadow mask from being oscillated due to external shock or sound wave. The shadow mask support frame also supports the shadow mask to maintain a predetermined distance from a fluorescent screen to land the electron beam passed through an electron beam passing hole of the shadow mask on a predetermined phosphor.
FIG. 1
is a partially exploded side view of a related art color CRT incorporating a shadow mask support frame. Referring to
FIG. 1
, the related art color CRT includes a flat panel
1
on which a dot type fluorescent screen
2
having R, C, B colors is coated, a shadow mask
4
having an electron beam passing hole
4
a that acts to selectively pass through an electron beam
3
incident upon the fluorescent screen
2
, a funnel
5
coupled to the rear of the panel
1
, a neck portion
5
a
formed at the rear of the funnel
5
, an electron gun (not shown) mounted into the neck portion
5
a
, for emitting the electron beam, a deflection yoke
6
for deflecting the electron beam surrounding an outside of the funnel
5
, a shadow mask support frame
7
for supporting the shadow mask
4
, a spring
8
mounted in the shadow mask support frame
7
, a stud pin
9
fixed into the panel
1
to be coupled to the spring
8
, for supporting the shadow mask support frame
7
, and an inner shield
10
formed at the rear of the shadow mask support frame
7
, for shielding earth-magnetic field so as not to allow the electron beam
3
to be susceptible to external earth-magnetic field when the CRT is operating.
The operation of the aforementioned color CRT will be described.
The electron beam emitted from the electron gun is horizontally/vertically deflected by magnetic field of the deflection yoke
6
and scanned on the shadow mask
4
. Then, the electron beam selectively passes through the electron beam passing hole
4
a
of the shadow mask
4
. At this time, the electron beam passing hole
4
a
of the shadow mask
4
and the fluorescent screen
2
coated on the flat panel
1
are set to geometrically match with each other. Accordingly, when the electron beam
3
passes through the electron beam passing hole
4
a
, the electron beam
3
is landed on the fluorescent screen
2
to emit light on the fluorescent screen
2
. A picture image is displayed by emitting light on the fluorescent screen
2
. The picture image can be displayed with a predetermined color purity only when the electron beam
3
is accurately landed on the fluorescent screen
2
.
However, when the electron beam
3
passes through the electron beam passing hole
4
a
of the shadow mask
4
, the shadow mask
4
emits heat so that the shadow mask
4
is thermally expanded. This is called a doming phenomenon.
Afterwards, heat of the shadow mask
4
is transferred to the as shadow mask support frame
7
so that the shadow mask support frame
7
is thermally expanded. This results in that the electron beam passing hole
4
a
of the shadow mask
4
is deviated from a preset position. Therefore, even if the electron beam
3
passes through the electron beam passing hole
4
a
, the electron beam
3
fails to be landed on the predetermined fluorescent screen
2
, thereby causing color purity on a screen any adverse effect.
Meanwhile, if outwardly provided oscillation or impact is applied to the shadow mask support frame
7
and the shadow mask
4
through the panel
1
and the stud pin
9
, a howling phenomenon of the shadow mask
4
occurs. The howling phenomenon moves the position of the electron beam passing hole
4
a
of the shadow mask
4
, thereby causing color purity any adverse effect in the same manner as the doming phenomenon.
Moreover, as a curvature radius of the shadow mask becomes flat recently, the shadow mask has a poorer rigidity than a spheric shadow mask. This seriously causes the doming phenomenon and the howling phenomenon.
To solve such a problem, as shown in
FIGS. 2
to
5
, there are provided shadow mask support frames according to first to third embodiments of the related art, in which tension is applied to the shadow mask
4
to absorb thermal expansion of the shadow mask due to the doming phenomenon and reduce oscillation due to the howling phenomenon.
Referring to
FIGS. 4
to
6
, the related art shadow mask support frame
7
includes two main frames
71
arranged in a row, and two sub frames
72
arranged in a row to be orthogonal to the main frames
71
, having both end portions fixed to respective end portions of the main frames
71
. Thus, the shadow mask support frame
7
has a square frame shape.
The aforementioned shadow mask support frame
7
is compressed in a length direction (Y direction) of the sub frame
72
by a separate compression equipment. In this state, both sides of the shadow mask
4
are fixed on the main frame
71
, and then compression load is eliminated. Thus, the main frame
71
and the sub frame
72
are restored to their original positions by elastic force. As a result, the shadow mask
4
is subject to tension in Y direction.
Since the tension applied to the shadow mask absorbs thermal expansion of the shadow mask
4
, the doming phenomenon can be avoided to some extent. However, the tension applied to the shadow mask could not completely remove the howling phenomenon due to structural characteristic of the shadow mask support frame
7
as described later.
The shadow mask support frames
7
according to the first to third embodiments of the related art have the frequency of primary unique oscillation, inertia moment values, compression load values, and weight values of the shadow mask support frame
7
, respectively, as shown in Table 1 below.
TABLE 1
first
second
third
embodiment
embodiment
embodiment
of the
of the
of the
item
related art
related art
related art
the frequency of
100%
124%
136%
primary unique
oscillation
inertia moment of main
100%
85%
120%
frame
inertia moment of sub
100%
204%
100%
frame
compression load
100%
96%
100%
required for tension
weight of shadow mask
100%
57%
114%
support frame
The frequency X of unique oscillation of the shadow mask support frame
7
is expressed by the following equation.
ω
=
K
ρ
∝
E
I
ρ
l
4
Where, &ohgr; is the frequency of unique oscillation of the support frame, K is frame rigidity, &rgr; is a density (frame mass), E is elastic coefficient, I is inertia moment, and L is a frame length.
In the above equation, the following relationship is obtained.
&ohgr;∝
I∝K
In the support frame structure having the same material, the same length, and the same elastic coefficient, if the inertia moment increases, rigidity increases with the frequency of unique frame oscillation. If the frequency of unique frame oscillation increases, the resonation range to external oscillation having a certain area or impact is reduced, thereby improving howling characteristic.
However, in the first embodiment of the related art as shown in
FIGS. 2A
to
2
C, supposing that the shadow mask support frame
7
has a characteristic value of 100%, there is a problem that compression load and weight required for tension of the shadow mask
4
increase.
Furthermore, in the second embodiment of the related art as shown in
FIGS. 3A
to
3
C, the shadow mask support frame
5
has a high inertia moment value for the sub frame
72
but a low inertia moment value for the main frame
71
. This causes twist moment to be weakened, thereby causing poor howling characteristic.
In the third embodiment of the related art disclosed in the Japanese Patent Publication No. 5-258677, as shown in
FIG. 4
, the main frame
71
has a triangle shaped hollow section and the sub frame
72
has a solid section. Sinc
Berck Kenneth A
LG Electronics Inc.
Patel Vip
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