Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
1999-11-08
2003-12-16
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S408000
Reexamination Certificate
active
06664723
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a shadow mask in a color cathode ray tube, and more particularly, to a shadow mask in the color cathode ray tube, having a curvature structure with a reinforced center portion for implementing a flat image.
2. Background of the Related Art
In general, the cathode ray tubes are mainly used in image displays, such as TV receivers, or computer monitors.
FIG. 1
illustrates a side view of a related art color cathode ray tube with a partial cut away view.
Referring to
FIG. 1
, the related art color cathode ray tube is provided with a fluorescent film
2
inside of a panel
1
having red, green and blue fluorescent material coated thereon, a funnel
3
welded to rear of the panel
1
, and an electron gun
4
provided in a neck portion
3
a
of the funnel. There is the shadow mask
6
fixed to a frame
7
close to the fluorescent film
2
for selecting colors form the electron beams
5
emitted from the electron gun
4
. The frame
7
is fixed to a sidewall of the panel
1
hung therefrom by means of a holding spring
8
fixed to the frame
7
and inserted in a stud pin
9
fixed to the sidewall. There is an inner shield
10
on one side on one side of the frame
7
fixed by a holding spring
1
for protecting the electron beams
5
moving toward the fluorescent film
2
from an external geomagnetic field. There are
2
,
4
, or
6
pole magnet
13
on an outer circumference of the neck portion
3
a
for adjusting a path of travel of the electron beams so that the electron beams
5
can hit onto a desired fluorescent material exactly, and there is a reinforcement band
12
wounded around on an outer circumference of the cathode ray tube for preventing damage from an external impact when the cathode ray tube is in operation. In the foregoing basic structure of the cathode ray tube, the shadow mask
6
is formed to have a designed radius of curvature and assembled with the panel with a fixed space between the panel
1
and the shadow mask
6
, to form a panel assembly. The shadow mask
6
facilitates the three electron beams emitted from the electron gun
4
to hit on the fluorescent material inside of the panel
1
through the shadow mask
6
exactly, for reproducing an image.
FIG. 2
illustrates a cross section of a panel assembly, referring to which the curvature and layout of the shadow mask
6
will be explained in detail.
In general, the radius of curvature of the shadow mask
6
is designed such that a relation of 0.70<Rm/Rp is established with reference to a diagonal axis where Rp is an inside surface radius of curvature of the panel
1
, and Rm is a radius of curvature of the shadow mask
6
. Accordingly, provided that the inside surface radius of curvature Rp of the panel
1
is given, the radius of curvature Rm of the shadow mask
6
is primarily dependent on the inside surface radius of curvature Rp of the panel
1
. Along with the primary dependence on the inside surface radius of curvature of the panel, the shadow mask
6
is designed taking a G/R (grouping rate) which fixes a color purity of the image into consideration, which G/R, an array of the electron beams (distance) can be expressed with the following equation with reference to FIGS.
3
A~
3
C.
Beam
Grouping
Rate
(
G
/
R
)
=
3
×
S
×
Q
Ph
×
L
=
B
A
×
1.5
Where, S: a deflection yoke component
Q: a distance from a slot in the shadow mask to an inside surface of the panel
Ph: a center distance between slots in shadow mask(or a pitch of the slot=A)
L: a distance from an electron beam deflection center of a deflection yoke to an inside surface of the panel
B: a center distance to each of centers of R(red) and B(blue) beams from the center of G(green) beam
A: a pitch of the slot(Ph)
The beam grouping rate(G/R) in general color cathode ray tube is set such that the electron beams hit a desired fluorescent dot exactly all over the effective surface of the shadow mask to improve a color purity, i.e., set to G/R=1.000(Just). That is, if the inside surface radius of curvature Rp of the panel
1
is fixed, the deflection yoke, i.e., a deflection yoke component ‘S’ is fixed, and an electron beam incident angle for each position is set according to the fixed deflection yoke component ‘S’. And, as illustrated in
FIG. 3C
showing a relative array of the three beams passing through the slits in the shadow mask
6
, a critical horizontal pitch ‘Ph’ represented as ‘A’ is fixed to meet a screen resolution requirement for a given video signal, and once the panel
1
, the funnel
3
and the deflection yoke are fixed, a distance ‘L’ from a deflection center of the deflection yoke to the inside surface of the panel
1
is fixed. Therefore, if changes in the curvature and the radius of curvature Rm of the shadow mask
6
is required, as ‘L’ and ‘S’ are constants, the slop pitch Ph should be changed. According to the equation, in order to make the radius of the curvature Rm of the shadow mask
6
smaller under a state the array of electron beam is fixed, the pitch Ph of the slot
6
a
should be designed greater, but, in order to make the radius of curvature Rm of the shadow mask
6
is greater, the pitch Ph of the slot
6
a
should be designed smaller. For example, as shown in
FIG. 4
a
, when the radius of curvature of the shadow mask
6
is made smaller, the slot horizontal pitch Ph is set so that the slot horizontal pitch Ph has a relation of Ph
0
<Ph
1
<Ph
2
- - - Ph
n
starting from a center to a periphery of the shadow mask
6
. As shown in
FIG. 4B
, if the horizontal slot pitch Ph is set greater, due to a limitation of effective surface of the shadow mask
6
, the vertical pitch is changed appropriately to have a relation of Ph
00
>Ph
0n
, Ph
n/20
≈Ph
n/2n
, and Ph
n0
>Ph
nn
. In conclusion, as discussed, since the beam grouping rate (G/R) is influenced from the inside surface radius of curvature of the panel
1
basically, the curvature of the shadow mask
6
is varied under a condition of fixed G/R, i.e., G/R=1.00, taking color purity characteristics into consideration. Accordingly, the curvature and the radius of curvature Rm of a conventional shadow mask
6
is dependent on the inside surface curvature of the panel
1
under the condition of the basic design criteria(0.70<Rm/Rp) and a fixed G/R(=1.00).
Recently, as the inside surface curvature at a center of the panel
1
has become greater for implementing a flat image, as shown in
FIG. 5
, the inside radius of curvature Rp of the panel becomes smaller as it goes from the center of the inside surface of the panel
1
towards ends of long axis (X-axis), short axis (Y-axis) and diagonal axis (D-axis). That is, the center portion of the panel
1
becomes flatter.
long axis radius of curvature Rpx: Rpx
1
>Rpx
2
>Rpx
3
>Rpx
4
> - - -
short axis radius of curvature Rpy: Rpy
1
>Rpy
2
>Rpy
3
>Rpy
4
> - - -
diagonal axis radius of curvature Rpd: Rpd
1
>Rpd
2
>Rpd
3
>Rpd
4
> - - -
Accordingly, as discussed, because the curvature and the radius of curvature Rm of the shadow mask
6
is dependent on an inside curvature structure of the panel, a shadow mask having a great radius of curvature at a center thereof is designed. In such a[s] shadow mask
6
, for example, when the center radius of curvature is greater than 3,300 mm, the shadow mask
6
becomes weak, and is susceptible to deformation by an external physical force in handling the shadow mask
6
in a fabrication process, or deterioration of howling characteristics by an impact or a speaker sound during operation of the cathode ray tube.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a shadow mask in a color cathode ray 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 shadow mask in a color cathode ray tube, which provides an ap
Ha Gwang Heon
Park Yoon San
Guharay Karabi
Patel Nimeshkumar D.
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