Electric lamp and discharge devices – Cathode ray tube – Ray generating or control
Reexamination Certificate
1999-12-21
2004-02-24
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Ray generating or control
C313S427000, C313S453000
Reexamination Certificate
active
06696780
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an electron gun for a cathode ray tube. More specifically, this invention relates to a technique to improve high frequency magnetic field transmission property of an electron gun.
BACKGROUND OF THE INVENTION
FIG. 5
shows a structure of a conventional electron gun for a projection-type monochrome cathode ray tube disclosed in Unexamined Published Japanese Patent Application (Tokkai-Hei) 10-74465. In
FIG. 5
,
14
denotes a neck tube having an electron gun disposed inside the tube. The electron gun is formed by sequentially arranging a cup-shaped G
1
electrode (control electrode)
5
housing a cathode
6
, a cup-shaped G
2
electrode (acceleration electrode)
7
, a tubular G
3
electrode (pre-anodic electrode)
8
, a G
4
electrode (focusing electrode)
9
, and a G
5
electrode (anodic electrode)
10
enveloping the top end part of the G
4
electrode
9
. A main electron lens is formed between the G
3
electrode
8
and the G
4
electrode
9
. Another electron lens is formed inside the G
5
electrode
10
at a position between the G
4
electrode
9
and the G
5
electrode
10
. Outside of the neck tube
14
, a velocity modulation coil
18
, a convergence yoke
15
, and a deflection yoke
16
are disposed.
As shown in
FIG. 5
, the state-of-the-art for improving focusing performance is subjecting the electron gun disposed inside the neck tube
14
to magnetic field modulation caused by the velocity modulation coil
18
from outside of the neck tube
14
in order to carry out velocity modulation of an electron beam. Namely, a track of an electron beam outgoing from a cathode
6
is modulated by an alternating magnetic field generated by the deflection yoke
16
, the convergence yoke
15
, the velocity modulation coil
18
and the like, before the electron beam reaches a phosphorous screen surface. The deflection yoke
16
, which is attached to a funnel cone portion of the cathode ray tube, generates an alternating magnetic field
17
to deflect an electron beam track, so that the electron beam scans the phosphorous screen surface of the cathode ray tube. The convergence yoke
15
, attached to the outside of the neck tube
14
of the cathode ray tube, corrects raster distortion and color displacement by generating an alternating magnetic field
20
to modulate the electron beam track. The velocity modulation coil
18
is attached to the outside of the neck tube
14
of the cathode ray tube and generates alternating magnetic field
19
to modulate the scanning speed of the electron beam in order to prevent a high-intensity part on the phosphorous screen from extending to a low-intensity part and to sharpen images.
The frequency of an alternating magnetic field for modulating an electron beam reaches a mega-Hertz order equivalent to a frequency for images. Therefore, when an electron gun includes metal portions formed by deep-drawing metal materials such as stainless steel, the alternating magnetic field is damped and a desired electrode beam modulation cannot be obtained.
As shown in
FIG. 5
, most of the alternating magnetic field
20
generated by the convergence yoke
15
passes the G
5
electrode
10
. The deflection yoke
16
is attached to the funnel cone portion. A portion of the alternating magnetic field
17
generated by the deflection yoke
16
passes the G
5
electrode
10
. The velocity modulation coil
18
is disposed between the G
3
electrode
8
and the G
4
electrode
9
. Most of the alternating magnetic field
19
generated by the velocity modulation coil
18
passes the G
3
electrode
8
and the G
4
electrode
9
.
When an alternating magnetic field is applied through these metal electrodes, eddy current is generated at the metal electrode. The eddy current loss is increased as the frequency of the alternating magnetic field becomes high. Thus, modulation effect of the electron beam track due to the magnetic field in the high frequency modulation band is reduced. For example, eddy current is generated at the G
5
electrode
10
due to the alternating magnetic field
20
generated by the convergence yoke
15
. This decreases the electron beam track modulation effect provided by the convergence yoke
15
.
Furthermore, this eddy current loss can heat the electrodes and break the neck tube. If the source of the alternating magnetic field and the metal electrodes of the electron gun are positioned fully apart in order to prevent the loss of the alternating magnetic field or the electrode heat, the electron beam focusing lens is arranged inevitably separated from the phosphorous screen surface. As a result, the electron beam magnification becomes high and the resolution is lowered. Especially for image display apparatuses having high deflection frequencies and wide signal bands such as high definition television, the loss in the alternating magnetic field is increased. This increased loss causes problems in use.
Tokkai-Hei 8-115684 discloses the improvement of transmission property of the magnetic field by dividing the deep-drawn metal portions into several sections and providing clearances between the respective sections. However, this method causes problems such as deterioration in assembly accuracy or increased cost. Moreover, in order to maintain the mechanical strength, the divided sections cannot be made too small and thus, the magnetic field transmission property cannot be improved remarkably.
SUMMARY OF THE INVENTION
It is an object of one or more embodiments of this invention to solve these problems and provide a cathode ray tube having an electron gun that can provide a desired electron beam modulation effect without interrupting transmission of the modulation magnetic field from the exterior of the vacuum portion.
An electron gun in accordance with an embodiment of the present invention includes a tubular electrode for an electron beam to pass through the inside and at least one part of the tubular portion of the electrode is formed into a coiled portion. Accordingly, a modulation magnetic field passes through the clearances between parts of the coiled portion and thus, eddy current loss can be decreased.
Preferably in one or more embodiments of the electron gun, at least one part of the pre-anodic electrode (G
3
electrode) is formed into a coiled portion, so that an equipotential space can be formed inside the pre-anodic electrode.
Preferably, in one or more embodiments, the coiled portion is composed of a nonmetal material, so that the transmission effect of the modulation magnetic field is further improved.
In an embodiment the electron gun, the coiled portion may be a coiled wire.
Preferably, in one or more embodiments, the coiled portion is formed so that clearances between the parts adjacent to each other in the axial direction are not more than 2.5 mm. Accordingly, influences from the outer electric field can be reduced. Furthermore, the coiled portion may be formed so that the parts adjacent in the axial direction are contacted with each other. Accordingly, the strength of the electrode members can be improved while maintaining the effect of transmission of the modulation magnetic field.
A manufacturing method in accordance with an embodiment of the present invention is applied to provide an electron gun having a tubular electrode for passing an electron beam inside the electrode, in which at least one part of the tubular portion of the electrode is formed into a coiled portion. In the method, a coiled portion is formed by cutting spirally a tubular electrode member and then stretching the electrode member in the axial direction. According to the method, the coiled portion can easily be manufactured.
A cathode ray tube device in accordance with an embodiment of the present invention includes a cathode ray tube having an electron gun inside the neck portion, and a velocity modulation coil outside the cathode ray tube. At least one part of a pre-anodic electrode of the electron gun is formed into a coiled portion, and the velocity modulation coil is provided around the coiled portion of the pre-ano
Hoshi Toshiharu
Konda Masahiko
Ohmae Hideharu
Patel Vip
Rosenthal & Osha LLP
Williams Joseph
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