Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2000-05-31
2002-05-14
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S407000
Reexamination Certificate
active
06388369
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a mask support assembly of a color CRT(Cathode Ray Tube), and more particularly to a tension aperture grill mask which is placed at the inside surface of a screen of a flat CRT and serves to discriminate colors and a tension mask assembly of the flat CRT which supports the aperture grill mask in the state where a predetermined tension is maintained.
2. Description of the Related Art
Generally, the front panel for picture display in a flat CRT is formed to be flat, the electron beam emitted from an electron gun strikes a phosphor screen formed at the inside of a screen in a predetermined pattern with executing a uniform motion, and thus the phosphor is radiated so as to embody the pictures.
A tension aperture grill mask of thin film (hereinafter, referred to as a tension mask) which maintains a predetermined distance from the phosphor screen is combined at the inner surface of the panel of the flat CRT in the state where a predetermined tension is maintained by an additional support assembly, so as to discriminate the colors of the emitted electron beam.
The flat CRT of such construction prevents the image distortion which occurs depending on the angle at which a viewer watches a television by making the curvature of the screen be flat as compared with a general CRT, and it is possible to maximize the effective visual angle to the visual angle of 180° right and left.
It also has an advantage that it can prevent the external light from being reflected to the eyes of a viewer by minimizing the reflection of the screen due to the external light and thus diminish the eye strain even if the viewer watches the television for a long time.
A description will be made on a flat CRT to which a general tension mask is applied with reference to
FIGS. 1
to
3
.
The outer appearance of the flat CRT is formed by a panel
2
at an inner surface of which a phosphor screen
1
is formed and a funnel
3
which is joined at the rear of the panel
2
by a frit glass.
An electron gun
5
for emitting three electron beams
6
of R, G and B is disposed in a neck portion
4
of the funnel
3
, and a deflection yoke
7
is placed at one side of the neck portion
4
so as to radiate the electron beams
6
emitted from the electron gun
5
to the screen.
A tension mask
7
having an aperture grill
11
for discriminating the colors of the emitted electron beams is placed at the inner surface of the panel
2
, and the tension mask
7
is supported by a support assembly
8
which is disposed with maintaining a predetermined distance from the inner surface of the panel
2
. The support assembly
8
is fixed against a stud pin
9
formed at the inner surface of the panel
2
by a support spring
10
.
As shown in
FIG. 2
, the tension mask
7
is made of a thin metal plate (about 0.1~0.2 mm), and has a vertical (or horizontal ) slot-shaped aperture grill
11
through which the electron beams pass. The edges arranged at both sides of the aperture grill
11
are stretched by the tension applied from the support assembly
8
and are welded to both rails
12
of the support assembly
8
.
The support assembly
8
is composed of a rail
12
which has two long sides in a horizontal direction and an L-shaped section, and a support bar
13
which has two short sides in a vertical direction and is welded to both ends of the rail
12
so as to support the rail
12
.
The support bar
13
serves to expand the rail
12
to the outside direction against the vertical direction together with the function of supporting the rail
12
, and also serves to stretch and tension the tension mask
7
welded at the rail
12
when the rail
12
is expanded to the outside direction.
A plurality of damper wires
14
which cross the effective surface of the tension mask
7
in a direction which intersects the aperture grill
11
ate fixed at the support bar
13
by a wire bracket
15
in the state where the tension is applied to both ends thereof, and the damper wire
14
offsets the vibration of the tension mask
7
due to an external sound wave generated from a speaker.
The process for manufacturing the tension mask assembly comprised of the tension mask
7
and support assembly
8
of such construction will be discussed hereinafter.
As shown in
FIG. 3
, the tension mask
7
is welded and fixed to the rail
12
after the rail
12
is deformed by &dgr;1 by the force F applied to both ends of the rail
12
of the support assembly
8
. Thereafter, if the force F is removed, the rail
12
is deformed to the point where a restoring force maintains balance with a resistance of the tension mask
7
, i.e., by &dgr;3 to an outside direction. Consequentially, the rail
12
is deformed by &dgr;2 as compared with an original state and this state is maintained.
The deformation amounts by the position of the rail
12
generated in this process are shown in
FIGS. 4 and 5
. The CRT of 76 cm (diagonal line of the screen) is taken as an example for these deformation amounts.
As shown in
FIG. 5
, the deformation amount (&dgr;2) of the rail
12
maintains balance with the force of the tension mask
7
in the state where the rail
12
is deformed by 12.7 mm from the central portion and by 2.1 mm from the end portion. That is, the central portion has greater deformation amount than the peripheral portion by 6 times and the deformation amount becomes decreased from the central portion to the peripheral portion. The reason why such a phenomenon occurs is that the peripheral portion of the rail
12
is directly welded to the support bar
13
to apply the expansion force to the rail
12
, while the central portion of the rail
12
is deformed by the expansion force applied from the support bar
13
and the resistance of the tension mask
7
.
FIGS. 6 and 7
show the tension and the deformation amount applied to the tension mask
7
by the expansion force of the rail
12
.
FIG. 6
shows the tension by the position applied to the tension mask
7
in the state where the tension mask
7
maintains balance with the rail
12
. This shows that the tension is increased from the central portion to the peripheral portion and is remarkably increased at the end of the peripheral portion where the support bar
13
is placed.
FIG. 7
shows the deformation amount of the tension mask
7
by the tension as described above. As is apparent from the figure, the tension mask
7
is deformed in proportional to the tension and the deformation amount at the peripheral portion is comparatively great.
When the deformation amount (about 0.15%) at a yield point of the material for a general tension mask
7
is set as a basis, the central portion of the tension mask
7
is below the yield point, i.e., in the elastic deformation state, and the peripheral portion exceeds the yield point and is maintained in the plastic deformation state.
The combining structure of the tension mask
7
and support assembly
8
as described above is processed by several heat treatments (about 400~450° C.) in a high temperature furnace in the process of manufacturing the CRT. As the rail
12
and the support bar
13
are thermally expanded in this process, the expansion force is increased in a vertical direction of the rail
12
and thereby the tension applied to the tension mask
7
is increased. The peripheral portion of the tension mask
7
which is maintained in the plastic deformation state is applied with the increased tension. Thereby, the break of the aperture grill
11
or the permanent plastic deformation may occur and this causes the drooping of the peripheral grill when the peripheral portion returns to a normal temperature after the heat treatments.
If there occurs the drooping of the grill as described above, there is generated a difference between the inherent vibration frequencies by the portion due to the difference of the tension between the central portion arid the peripheral portion of the tension mask
7
. Therefore, if the tension mask
7
resonates by the sound wave or shock provided from an
Day Michael H.
Fleshner & Kim LLP
LG Electronics Inc.
Williams Joseph
LandOfFree
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