Electric lamp and discharge devices – Cathode ray tube – Beam deflecting means
Reexamination Certificate
2000-08-28
2002-04-30
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Beam deflecting means
C313S431000, C335S299000
Reexamination Certificate
active
06380667
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color cathoderay tube apparatus such as a TV Braun tube or a monitor Braun tube, and more particularly to a color cathoderay tube apparatus in which no degradation occurs in focusing or distortion characteristics even where an electron beam trajectory correction means with a high degree of magnetic field distribution displacement is provided in realizing a flat screen by incorporation of a press-formed shadow mask.
In general, a color cathode-ray tube apparatus has a vacuum envelope comprising a panel with a substantially rectangular display section, a funnel formed to be continuous with the panel, and a cylindrical neck formed to be continuous with a small-diameter end portion of the funnel. A deflection yoke is mounted on a region extending from a funnel-side portion of the neck to a small-diameter portion of the funnel. An inner face of the panel is provided with a phosphor screen having dot-like or striped three-color phosphor layers which emit blue, green and red. A shadow mask is disposed to be opposed to the phosphor screen, at a distance from the phosphor screen. That surface of the shadow mask, which is opposed to the phosphor screen, has a great number of electron beam passage holes arranged with a predetermined pitch. The shadow mask has a so-called color selection function for guiding electron beams to the associated phosphor layers of the phosphor screen. The neck includes an electron gun apparatus for emitting three electron beams. The electron beams emitted from the electron gun apparatus are deflected horizontally and vertically by horizontal and vertical deflection magnetic fields produced by the deflection yoke, and the electron beams are directed to the phosphor screen through the shadow mask. The electron beams horizontally and vertically scan the phosphor screen and thus this screen displays a color image.
This kind of modern color cathode-ray tube apparatus is, in general, of an in-line type wherein three in-line electron beams comprising a center beam and a pair of side beams, which travel in the same plane, are emitted from the electron gun apparatus. In addition, most of practically used color cathode-ray tube apparatuses are of a self-convergence type wherein the horizontal deflection magnetic field produced by the deflection yoke has a pincushion shape and the vertical deflection magnetic field has a barrel shape, and the three in-line electron beams are deflected by the horizontal and vertical deflection magnetic fields, whereby the three electron beams can be converged over the entire screen without using a special convergence correction means.
Recently, there is a strong demand for flatness of the screen in this type of color cathode-ray tube apparatus. If the panel is flattened in order to realize the flatness of the screen, it is necessary to flatten the shadow mask, too. As a result, the following problem will arise.
In general, in the color cathode-ray tube apparatus, the three electron beams are converged at the center of the phosphor screen, mainly by a purity convergence magnet attached to the neck-side portion of the deflection yoke. The three electron beams pass through the electron beam passage holes in the shadow mask at predetermined angles, respectively, and land on the associated phosphor layers. In order to obtain a proper landing tolerance for the phosphor layers, it is required to properly set the distance between the inner face of the panel and the shadow mask.
Assume that, as shown in
FIG. 1
, a distance in a tube axis direction between a purity convergence magnet
1
and a shadow mask
2
is L (the distance L at the center of the phosphor screen is Lo), a distance in the tube axis direction between the shadow mask
2
and the inner face of a panel
3
is q (the distance q at the center of the phosphor screen is qO), a distance between a center beam
4
G and each of paired side beams
4
R,
4
B in a direction of arrangement of the three electron beams is Sg (the distance Sg at the position of the purity convergence magnet is Sg
0
), a distance between the center beam
4
G and the side beam
4
B,
4
R is &sgr;, and a pitch of the landing position of the center beam
4
G on the inner face of the panel
3
in the direction of arrangement of three electron beams is Ph (the pitch Ph at the center of the phosphor screen is Ph
0
). Since
q=L×&sgr;/Sg
&sgr;=Ph/3
the following equation (1) is established:
q=L×Ph/(3×g) (1)
Normally, the distance L and distance Sg are substantially constant over the entire area of the phosphor screen, and the pitch Ph, too, is basically constant. Accordingly, if the panel is flattened, it is necessary to flatten the shadow mask, too.
However, the shadow mask, in general, is manufactured by forming a flat, thin-plate-like shadow mask material, in which electron beam passage holes have been formed by photoetching, so as to have a predetermined curved surface. Using a forming apparatus as shown in
FIG. 2
, the shadow mask is formed to have a predetermined shape. Specifically, in the forming apparatus shown in
FIG. 2
, a non-hole portion
7
surrounding a region
6
with electron beam passage holes is clamped and fixed between a die
8
and a blank holder
9
. The region
6
with electron beam passage holes is extended and formed in a predetermined shape by a punch
10
and a knockout
11
. If the shadow mask is flattened and the amount of extension is reduced, plastic deformation cannot adequately be effected. The predetermined curved surface cannot be obtained due to degradation in workability. In addition, the strength of the formed shadow mask deteriorates and the shadow mask tends to be easily deformed.
FIGS. 3 and 4
show techniques for solving the above problems. In the techniques, trajectory correction means
14
and
15
for correcting the trajectories of the side beams
4
R and
4
B are provided between a cathode K of the electron gun apparatus, which emits three in-line electron beams
4
R,
4
G and
4
B, and a phosphor screen
13
. The trajectory correction means
14
and
15
exert force to the pair of side beams
4
R and
4
B, thereby to correct and turn the trajectories of the side beams
14
and
15
toward the center beam
4
G. This force is made different between a central area and a peripheral area of the phosphor screen
13
. More specifically, this force is varied in the following manner. That is, an imaginary distance Sg between the center beam
4
G and the side beam
4
R,
4
B in the direction of arrangement of the three electron beams at the central area and peripheral area of the phosphor screen
13
is determined such that the distance Sg toward the peripheral portion of the phosphor screen
13
may be smaller than the distance Sg toward the center of the phosphor screen
13
.
In the structure shown in
FIG. 3
, forces FrO and FfO produced by the two trajectory correction means
14
and
15
are set at zero at the center of the phosphor screen
13
. In the peripheral region of the phosphor screen
13
, the side beam
4
B,
4
R is over-converged by the force Fr
1
produced by the neck-side trajectory correction means
14
and the side beam
4
B,
4
R is under-converged by the force Ff
1
produced by the phosphor-screen-side trajectory correction means
15
. Thereby, the imaginary distance Sg at the cathode K decreases from a distance Sgc
0
to a distance Sgc
1
from the center toward the periphery of the phosphor screen
13
. Thus, the distance q in the tube axis direction between the inner face of the panel
3
and the shadow mask
2
at the peripheral region of the phosphor screen
13
is increased by a degree given below, relative to a distance q
0
in the tube axis direction between the inner face of the panel
3
and the shadow mask
2
at the central region of the phosphor screen
13
:
&Dgr;q=q−q
0
Assume, in this case, that a distance in the tube axis direction between the phosphor screen-side trajectory correction means
15
and the phosphor screen
Ibuki Hiroaki
Sano Yuuichi
Yokota Masahiro
Kabushiki Kaisha Toshiba
Patel Ashok
Pillsbury & Winthrop LLP
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