Mask in color cathode ray tube

Details Mask in color cathode ray tube Mask in color cathode ray tube

2001-10-18

2004-10-19

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Shadow mask, support or shield

C313S402000

Reexamination Certificate

active

06806632

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a shadow mask in a cathode ray tube, and more particularly, to a shadow mask in a color cathode ray tube having an open type bridge no electron beam passes therethrough.
2. Background of the Related Art
As well known, the color cathode ray tube, one of electronic tubes, is a display used the most widely in many fields, starting from TV receivers and computer monitors to oscilloscopes and radar observation, and the like. The color cathode ray tube is called three color cathode ray tube, because a principle in which red, green, and blue colors are added together to reproduce a variety of colors. That is, three color fluorescent materials and three cathodes are used, and electron beams of electrons emitted from the cathodes are made to land on a screen having the three fluorescent materials coated thereon, for displaying a picture on the screen.
An exemplary related art color cathode ray tube having the shadow mask shown in
FIGS. 1-3
employed therein will be explained.
FIG. 1
illustrates a related art color cathode ray tube having a tension shadow mask schematically,
FIG. 2
illustrates a plan view of a shadow mask, and
FIG. 3
illustrates a section across a line B—B showing slots and an open type bridge of a shadow mask.
Referring to
FIG. 1
, the color cathode ray tube is provided with a substantially rectangular panel
1
, a funnel
4
of a funnel shape fitted to the panel
2
, an in-line type electron gun
10
having a cylindrical neck
6
fitted continuous to a small diametered end of the funnel
4
to form an outer appearance thereof, for emitting the electron beams
8
. A bonding force of the panel
2
and the funnel
4
is enhanced by a reinforcing band
12
, a fluorescent screen
13
having the three color fluorescent materials of emitting red, green, and blue lights respectively is provided on an inside surface of the panel
2
, and the shadow mask
20
supported on a frame
16
fitted to the panel
2
through springs
14
is provided with a gap from the fluorescent screen
13
. There is a deflection yoke
18
on an outer circumference of the funnel
4
in the vicinity of the neck
6
, for producing a pin-cushion type horizontal magnetic field, and a barrel type vertical magnetic field, to deflect the electron beams
8
to all of the surface of the fluorescent screen
13
, and an inner shield
19
fixed to the frame
16
for shielding the electron beams
8
from external geomagnetism enclosed under a high vacuum. Particularly, as shown in
FIG. 2
, the shadow mask
20
welded to the frame
16
on the inside surface of the panel
2
has a plurality of slots
22
, forming openings, formed at fixed intervals in horizontal and vertical directions, and a bridge
24
between adjacent vertical slots
22
.
Under this state, the electron beams
8
from the electron gun
10
is deflected at a large angle by the vertical and horizontal deflection magnetic field, and the deflected electron beams
8
are converged onto the plurality of slots
22
in the shadow mask
20
. When the electron beams
13
, color selected as the electron beams
13
pass through the slots
22
, land onto the fluorescent screen
13
, the three color fluorescent materials emit lights, to reproduce a color picture on the panel
2
.
FIG. 3
illustrates a partial section of the shadow mask
20
showing the slots
22
and the open type bridges
24
. The open type bridge
24
is formed by removing a portion of the bridge to make the bridge discontinuous.
As can be known from the section, the slot
22
for passing the electron beams has a tapered form inclusive of an inlet
222
for receiving the electron beams
8
from the electron gun
10
, and an outlet
224
for letting the electron beams
8
to leave for the fluorescent screen
13
, which is formed to have a greater area than the inlet
222
, wherein a difference STi of horizontal distances of an inlet edge
222
a
and an outlet edge
224
a
of the slot
22
, near to a vertical center line ‘l’ of the shadow mask
20
, is smaller than a difference STo of horizontal distances the inlet edge
222
b
and the outlet edge
224
b
of the slot
22
, far from the vertical center line ‘l’ of the shadow mask
20
. The same is applicable to the open type bridge
24
wherein a difference ‘Ti’ of horizontal distances of an inlet edge
242
a
and an outlet edge
244
a
of the open type bridge
24
, near to a vertical center line ‘l’ of the shadow mask
20
, is also smaller than a difference To of horizontal distances the inlet edge
242
b
and the outlet edge
244
b
of the open type bridge
24
, far from the vertical center line ‘l’ of the shadow mask
20
. Sections of the slot
22
or the open type bridge
24
are formed to prevent distortion of the electron beams. For prevention of distortion of the electron beams, it is required to design the To and the STo shown in
FIG. 4
to meet the following.
Referring to
FIG. 4
, with regard to the shadow mask
20
with a curvature, when it is assumed that ‘t’ denotes a thickness of the shadow mask
20
, ‘&agr;’ denotes a deflection angle of the electron beams incident to the shadow mask
20
, and ‘&bgr;’ denotes an angle of a normal vector to a surface to an axis of the cathode ray tube, To or STo can be expressed as follows;
To
(or
STo
)=
t
×tan(&thgr;), &thgr;=&agr;−&bgr;,
A minimum value of STo or To that causes no distortion of the electron beams passing through the slot
22
or the open type bridge
24
of the shadow mask
20
can be calculated by above equation. Recently, of quality characteristics of the cathode ray tube, enhancement of the luminance values highly. For enhancing the luminance, it is required to lengthen the slot
22
for adjusting a transmissivity of the electron beams.
However, though the shadow mask with short slots and many number of bridges causes no problem with respect to vision as no shadows of the bridges are seen on the screen, the shadow mask with long slots and small number of bridges deteriorates a picture quality as shadows of the bridges are seen on the screen in forms of lines.
Only one horizontal slot may be provided removing the bridges entirely for eliminating such shadows of the bridges, when strength of the shadow mask is too weak to handle the shadow mask, and susceptible to vibration caused by external impact.
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 can enhance luminance while open type bridges having an advantage over doming are maintained, and quality deterioration caused by bridge shadows in view coming from lengthened slots with a reduced number of bridges can be overcome.
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 shadow mask in a color cathode ray tube includes a plurality of slots for passing electron beams, and an open type bridge having a portion removed therefrom and dividing into slots in a vertical direction, wherein a difference ‘Ti’ of horizontal distances of an electron beam inlet edge and an electron beam outlet edge of the open type bridge formed near to a vertical center line ‘l’ of the shadow mask is equal to, or greater than a difference ‘To’ of horizontal distances of an electron beam inlet edge and an electron beam outlet edge of the open type bridge formed far from a v

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