Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2000-12-11
2003-06-17
Patidar, Jay (Department: 2862)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S402000
Reexamination Certificate
active
06580205
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a frame assembly of a shadow mask in a flat Braun tube, and, more particularly, to a frame assembly of a shadow mask in a flat Braun tube, in which a stress on a shadow mask is reduced for minimizing creep during an elevated temperature process, and a low tension on the shadow mask is corrected effectively during operation of a flat Braun tube after the elevated temperature process, for preventing deterioration of a color purity caused by deterioration of howling and doming.
2. Background of the Related Art
FIG. 1
illustrates a side view with a partial cut away view of a related art flat Braun tube. Referring to
FIG. 1
, the related art flat Braun tube is provided with a flat panel
1
having three colors of red, green, and blue fluorescent film
4
of a dot type, a shadow mask
3
having a plurality of electron beam pass through holes
3
c
for selective pass of the incident electron beams, a funnel
2
welded to rear of the panel
1
, a neck part
2
a
formed in a rear portion of the funnel
2
, electron beams(not shown) fitted inside of the neck part
2
a
for emitting electron beams, a deflection yoke
5
around an outer circumference of the funnel
2
for deflecting the electron beams
6
, a shadow mask frame assembly
7
for supporting the shadow mask
3
, springs
8
fitted to a supporting frame, stud pins
10
coupled with the spring
8
fixed to an inside of the panel
1
for holding the shadow mask frame assembly
7
, and an inner shield
9
in rear of the supporting frame
5
for shielding the electron beams
3
from an external geomagnetism in operation of the cathode ray tube for preventing the electron beams from being influenced by the geomagnetism.
Upon putting the flat Braun tube into operation, the electron beams
6
emitted from the electron gun is deflected in a horizontal, or vertical direction by a magnetism of the deflection yoke
5
, directed onto the shadow mask
3
, pass through the electron beam pass through hole
3
c
in the shadow mask
3
selectively, land on the fluorescent film
4
, to form a picture.
FIG. 2
illustrates a perspective view of a shadow mask frame assembly in a related art Braun tube, and
FIG. 3
illustrates a shadow mask showing a state of tension applied to the shadow mask, schematically.
Referring to
FIGS. 2 and 3
, the shadow mask frame assembly
7
in a related art Braun tube is provided with two main frames
7
a
for applying a tension P
1
to the shadow mask
3
having fixed opposite ends, two sub-frames
7
b
perpendicular to the main frame
7
a
connected to one ends of the main frames
7
a,
and a thermal compensating plate
11
attached under the sub-frames
7
b
. The shadow mask
3
has an effective surface
3
a
having the electron beam pass through holes
3
c
formed therein, and an edge part
3
b
having no electron beam pass through holes
3
c
formed therein for reinforcing a rigidity of the effective surface
3
a.
The shadow mask frame assembly
7
is designed to have a high rigidity in a structure basis. If a preset tension P
1
is provided to the shadow mask
3
by the shadow mask frame assembly
7
having such a high rigidity, a natural frequency of the shadow mask
3
becomes higher, thereby permitting to prevent howling, in which the shadow mask
3
vibrates during operation of the cathode ray tube.
In the meantime, the shadow mask
3
having the preset tension applied thereto by the shadow mask frame assembly
7
is subjected to an elevated temperature process(at approx. 470°). Due to this elevated temperature process, there is a permanent deformation occurred at the shadow mask
3
caused by creep. In the creep, if a constant load is applied to the material for a prolonged time period under a certain temperature, a strain increases as time passes by while the stress on the material is reduced. Therefore, the permanent deformation of the shadow mask caused by the creep becomes the greater as the stress on the shadow mask becomes the greater in the elevated temperature process. At the end, the creep reduces the tension on the shadow mask
3
provided by the frame
7
after the elevated temperature process in comparison to the same before the elevated temperature process, which leads to a poor howling characteristics of the shadow mask
3
during operation of the cathode ray tube, causing a poor color purity by a beam landing error of the electron beams
6
. Therefore, in order to reduce the stress relaxation following deformation of the shadow mask
3
caused by the creep during the elevated temperature process, the thermal compensating plate
11
is fitted under the sub-frame
7
b
.
FIG. 4
illustrates shadow mask assemblies for showing stresses to the shadow masks from the thermal compensating plate
11
under a room temperature and the elevated temperature, schematically. Referring to
FIG. 4
, the thermal compensating plate
11
is formed of a material having a thermal expansion coefficient greater than the sub-frames
7
b,
so that the thermal compensating plate
11
makes the sub-frames
7
b
to deform in a “U” form when the thermal compensating plate
11
is heated in the elevated temperature process. This deformation reduces the tension P
1
to the shadow mask
3
, to reduce the stress on the shadow mask
3
, allowing to reduce the stress &sgr; on the shadow mask
3
in the elevated temperature process in comparison to the stress a on the shadow mask
3
in the room temperature, which reduces an influence of the creep and deformation caused by the creep. According to this, the tension to the shadow mask
3
can be maintained a state the most close to the tension before the elevated temperature process is carried out even after the elevated temperature process is carried out. At the end, the creep of the shadow mask
3
can be reduced by the thermal compensating plate
11
, to reduce the stress relaxation caused by the shadow mask
3
after the elevated temperature process is carried out.
However, though the bimetallic action of the thermal compensating plate
11
in the related art can reduce the influence of creep in the elevated temperature process by deforming the sub-frames
7
b,
there is a problem in that the sub-frames
7
b
are deformed in the “U” form even when the flat Braun tube is in operation as the shadow mask
3
is heated by the electron beam
6
, and the heat is transferred to the thermal compensating plate
11
. As shown in
FIG. 5
, this deformation causes a problem of poor color purity of the picture, which deteriorates a reliability of the product, by a beam landing error of the electron beams
6
as the doming in which the shadow mask
3
moves toward the panel is occurred, and the weak tension to the shadow mask
3
deteriorates the howling characteristics.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a frame assembly of a shadow mask in a flat Braun tube that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a frame assembly of a shadow mask in a flat Braun tube, which can reduce a stress on the shadow mask during an elevated temperature process for minimizing an influence from creep, and compensate for tension reduction of the shadow mask effectively when the flat Braun tube is in operation after the elevated temperature process for minimizing doming, and improve howling characteristics.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the frame assembly of a shadow
Birch & Stewart Kolasch & Birch, LLP
LG Electronics Inc.
Patidar Jay
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