Cathoderay tube

Details Cathoderay tube Cathoderay tube

1999-11-12

2002-01-15

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Cathode ray tube circuits

Plural concentrating, accelerating, and/or de-accelerating...

C315S368150, C315S368160, C313S421000, C313S440000, C313S441000

Reexamination Certificate

active

06339293

ABSTRACT:

TECHNICAL FIELD
This invention relates to a cathode-ray tube, and more particularly to a cathode-ray tube incorporating an electron gun assembly which compensates for dynamic astigmatism.
BACKGROUND ART
Generally, a color cathode ray art tube has an envelope as shown on FIG.
1
. The envelope comprises a panel
1
and a funnel
2
joined to the panel
1
. A phosphorous screen
3
(target) is provided on the inner surface of the panel
1
. the screen
3
comprises striped or dot-like three-color phosphor layers for generating blue, green, and red light rays. A shadow mask
4
is provided in the funnel
2
and faces the phosphor screen
3
. The shadow mask
4
has a large number of aperatures. The funnel
2
has a neck
5
, in which an electron gun assembly
7
is provided. A deflection yoke
8
is mounted on the neck
5
. The electron gun assembly
7
emits three electron beams
6
B,
6
G, and
6
R. The yoke
8
generates a horizontal magnectic field and a vertical magnetic field. These magnetic fields deflect the electron beams
6
B,
6
G and
6
R in horizontal direction and vertical direction, respectively. The electron beams
6
B,
6
G and
6
R pass through the shadow mask
4
, scanning the phosphor screen
3
in horizontal and vertical directions. A color image is thereby displayed on the panel
1
.
A type of a color cathode-ray tube, known as a self-convergence, in-line-type color cathode-ray tube, is used widely. This cathode-ray tube comprises an in-line type gun assembly having three electron guns
7
which are arranged side by side in the same horizontal plane. The guns
7
emit a center electron beam
6
B and side electron beams
6
G and
6
R. The side beam
6
G is on one side of the center beam
6
B, and the side beam
6
R on the other side thereof. The three beams
6
B,
6
G and
6
R travel in a horizontal plane. The electron gun assembly has a main lens section, in which a low-potential grid and a high-potential grid are arranged. Each grid has three beam-guiding holes. The center beam-guiding hole of the high-potential grid is concentric to that of the low-potential grid. By contrast, the side beam-guiding holes of the high-potential grid are eccentric to those of the low-potential grid. The beams
6
B,
6
B and
6
R passing through the beam-guiding holes is converged on the center region of the phosphor screen
3
. The horizontal magnetic field generated by the yoke
8
is shaped like a pincushion, whereas the vertical magnetic field generated by the yoke
8
is shaped like a barrel. The electron beams
6
B,
6
G and
6
R deflected by the pincushion-shaped and barrel-shaped magnetic fields are converged at any region of the phosphor screen
3
.
In the self-convergence in-line-type color cathode-ray tube, an electron beam is influenced by astigmatism after passing an uneven magnetic field. For instance, the beam is distorted as shown in FIG.
2
A. The beam spot, which the beam forms on a peripheral region of the phosphor screen, is inevitably distorted as shown in FIG.
2
B. The electron beam is also affected by deflection aberration, which occurs when the electron beam is focused excessively in the vertical direction, generating a large halo
13
extending in vertical direction as shown in FIG.
2
B. The larger the cathode-ray tube, the greater the deflection aberration. The larger the angle by which the beams are deflected, the lower the image resolution at the peripheral regions of the phosphor screen.
Means for preventing the image resolution from lowering due to deflection aberration is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 61-99249, Jpn. Pat. Appln. KOKAI Publication No. 61-250934, and further, in Jpn. Pat. Appln. KOKAI Publication No. 2-72546. As shown in
FIG. 3
, the electron gun assemblies comprise first grid G
1
to fifth grid G
5
, and an electron beam generator GE, a four-pole lens QL, and a final focusing lens EL, which are arranged along the axes of electron beams. As shown in
FIGS. 4A and 4B
, the multiple lens, for example, four-pole lens QL has three electron beam guide holes
14
a,
14
b,
and
14
c
in one end of the third grid G
3
and three electron beam guide holes
15
a,
15
b
and
15
c
in that end of the fourth grid G
4
. The multiple lens, for example, four-pole lens QL and the final focusing lens EL change in synchronism with the magnetic field of the deflecting yoke. This makes it possible to prevent the electron beams from being distorted at the peripheral regions of the screen, despite of the deflection aberration of the deflecting magnetic field. Thus, the beams can form undistorted spots on any region of the screen.
If such a mean is used, however, a problem arises when the astigmatism caused by the deflecting yoke is very strong at the peripheral region of the screen, though the halo extending in a line perpendicular to the beam spot. Namely, it is not possible to eliminate the sideways expansion of the electron beam spot.
This problem with the conventional electron gun assembly will be explained with reference to FIG.
5
.
FIG. 5
illustrates the lens operation performed in the conventional electron gun assembly. In
FIG. 5
, the solid lines represent the track of an electron beam, showing how the lens focuses the beam at the center of the phosphor screen. The broken lines represent the track of the electron beam, illustrating how the lens focuses the beam at a peripheral region of the screen.
As shown in
FIG. 5
, the multiple lens, for example, four-pole lens QL
1
is provided on the cathode side of the main electron lens (EL). To direct the electron beam to the center of the screen, only the main electron lens EL indicated by the solid lines focuses the electron beam. To deflect the electron beam to the peripheral region of the screen, a deflecting lens DYL is formed by the deflecting magnetic field represented by the broken lines.
Generally, a self-convergence-type deflecting magnetic field is generated in a color cathode-ray tube. The force for focusing the beam in the horizontal direction H does not change, and the deflecting lens DYL focuses the beam in the vertical direction V only.
FIG. 5
does not show the action of the magnetic field for deflecting the beam in the horizontal direction, for the purpose of illustrating only the problem caused by the self-convergence, deflecting magnetic field.
When the deflecting lens DYL is formed, that is, when the embodiment is focused at a peripheral region of the screen, the force of the electron lens EL is decreased as shown by the broken lines in FIG.
5
. To compensate for the force of the lens EL for focusing the beam in the horizontal direction H, the multiple lens QL
1
is formed. As a result, the electron beam travels along the track shown by the broken lines and is focused at the peripheral region of the screen. The main plane of the lens for focusing the electron beam in the horizontal direction H is at position A when the electron beam is directed at the center of the screen. (The main plane is the virtual center of the lens, or a point at which the track of the emitted beam crosses that of the beam radiated onto the screen.) When the electron beam is deflected to the peripheral region of the screen, forming a multiple lens, the main plane extending in the horizontal direction H moves to position B and lies between the main electron lens EL and the multiple lens QL
1
. Further, the main plane extending in the vertical direction V moves from the position A to position C. Therefore, the main plane extending in the horizontal direction H moves back from the position A to the position B, decreasing magnification. Furthermore, the main plane extending in the vertical direction V moves forward from the position A to the position C, increasing the magnification. Consequently, a difference emerges between the magnification in the horizontal direction and the magnification in the vertical direction. The electron beam spot formed in any peripheral region of the screen inevitably expands sideways, or in the horizontal direction.
DISCLOSURE OF INVENTION
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