Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
2002-07-16
2004-09-07
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S444000, C313S451000, C445S046000
Reexamination Certificate
active
06787977
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an electron gun for a cathode-ray tube, and particularly relates to a technique for improving high-frequency magnetic-field-transmittance characteristics of the electron gun.
2. Related Background Art
FIG. 14
is an enlarged cross-sectional view of a neck tube portion of a projection-type monochrome cathode-ray tube.
As shown in
FIG. 14
, magnetic field modulation is applied to an electron gun provided inside the neck tube
3
from outside the neck tube
3
by velocity modulation coils
20
, to carry out the so-called velocity modulation of an electron beam so as to improve the focusing performance. This is the current advanced display technique (JP 10(1998)-74465 A). While an electron beam (not shown) is emitted from a cathode
7
and reaches a phosphor screen surface (not shown), the path of the electron beam is modulated by an alternate magnetic field generated by the velocity modulation coils
20
, convergence yokes
23
, deflection yokes
24
, and the like.
The deflection yokes
24
are attached to a cathode-ray tube funnel cone portion, and generate an alternate magnetic field to deflect the electron beam path, so as to scan the cathode-ray tube phosphor screen surface with the electron beam. The convergence yokes
23
are attached to the outside the neck tube
3
of the cathode-ray tube, and generate an alternate magnetic field to deflect an electron beam path, so as to correct raster distortions and color shifts. The velocity modulation coils
20
are attached to the outside of the neck tube
3
of the cathode-ray tube, and generate an alternate magnetic field to modulate a scanning velocity of the electron beam, so as to prevent a high-brightness portion from extending off into a low-brightness portion on the phosphor screen surface, thereby obtaining sharp images.
A frequency of the alternate magnetic field for modulating an electron beam ranges from a deflection frequency (15.75 [kHz]) to a megahertz order equal to a level of picture frequencies. Therefore, there is a drawback in that the alternate magnetic field is attenuated by metal components of the electron gun that are formed by deep-drawing or the like with a metal material such as stainless steel, with the result that a desired electron beam modulation cannot be achieved.
As shown in
FIG. 14
, a part of the alternate magnetic field
19
generated by the deflection yokes
24
passes through a second anode electrode
11
(G
5
electrode). An alternate magnetic field
22
generated by the convergence yokes
23
passes through the second anode electrode
11
. The velocity modulation coils
22
are disposed between a first anode electrode
9
(G
3
electrode) and a convergence electrode
10
(G
4
electrode), and an alternate magnetic field
21
(at a level of 4 [MHz]) generated by the velocity modulation coils
20
passes through the first anode electrode
9
and the convergence electrode
10
. When the alternate magnetic fields are applied to the electron beam via these metal electrodes, an eddy current is generated in part of the metal electrodes. Furthermore, as the frequencies of the alternate magnetic fields increase, loss of the alternate magnetic fields due to the eddy current increases. Therefore, the effect of the electron beam path modulation by the magnetic fields reduces in a high frequency range for the modulation.
A technique to solve such a problem is disclosed by JP 2000-188067 A. In the technique, an electron gun includes a G
1
electrode that houses a cathode, a G
2
electrode, a G
3
electrode, a G
4
electrode, and a G
5
electrode that are arrayed in the stated order, the G
3
electrode and the G
4
electrode together forming a main electron lens. In the electron gun, a coil-shaped part is provided in a part of the G
3
electrode so that a velocity modulation magnetic field passes therethrough, thereby reducing eddy current loss. Besides, the JP 61(1986)-29047 A discloses a technique of providing a plurality of slits on a circumferential surface portion of a cylindrical part of a bottomed cylindrical converging magnetic pole that is made of a nonmagnetic substance and that is attached to an electron-beam-emitting tip of an in-line-type electron gun, so as to prevent eddy current loss generated by a magnetic field that passes through the circumferential surface portion of the cylindrical part.
However, in the case where a technique of providing slits as taught by JP 61(1986)-29047 A is applied to an electron gun for forming an electron lens between bottomless cylindrical electrodes, the electrodes are deformed when slits are formed in cylindrical metal members. As a result, the electron lens formed between the electrodes has distortion, thereby being unable to achieve a desired effect of conversion of the electron beam having passed through the electron lens. Therefore, an electron beam spot observed on the phosphor surface has a deformed shape, thereby adversely affecting the resolution. Normally, in the case of cylindrical electrodes, when the electrode roundness thereof is lower than 99.8[%], the distortion of the electron lens apparently affects the electron beam spot. If slits are provided in the cylindrical electrode, the roundness of the electrode is impaired to 97 to 98%, thereby making the electrode unsuitable for practical application. In this case of a coil-shaped electrode taught by JP 2000-188067 A, it is not easy to form the coil so that it has a roundness of not less than 99.8[%], and in addition, a problem also arises in that the coil itself slightly hangs down due to the gravity. Therefore, it is impossible to avoid the problem of distortion of the electron beam spot shape caused by the deterioration of the roundness of the electrode.
SUMMARY OF THE INVENTION
The present invention is made to solve the foregoing problems, and it is an object of the present invention to provide a high-resolution electron gun for a cathode-ray tube with decreased resolution variation, which achieves a desired electron beam modulation effect without hindering the penetration of a modulation magnetic field from outside, and does not generate distortion of an electron lens due to distortion of an electrode, thereby obtaining an excellent beam spot shape.
An electron gun for a cathode-ray tube according to the present invention includes a plurality of cylindrical electrodes arranged so that an electron beam passes inside the electrodes, the electrodes being fixed to a support rod. In the electron gun, at least one of the electrodes is separated into at least two pieces along a plane substantially perpendicular to a central axis of the electrode, and a connecting member having a slit is provided between the pieces of the separated electrode. The pieces of the separated electrode are in electrical contact with each other via the connecting member, and are fixed to the support rod via the connecting member and support portions provided on a side of the connecting member.
The foregoing configuration reduces eddy current loss, since the modulation magnetic field passes through the slit provided in the connecting member. Furthermore, the electrode forming an electron lens at an end is configured so that the electrode is divided into at least two pieces and the connecting member with the slit is interposed between the two pieces. Therefore, it is possible to avoid a problem in that an electrode is deformed when the slit is formed in the electrode, and hence, it is possible to maintain a high roundness of an end surface of the electrode at which an electron lens is formed. Thus, by forming independently a portion of the electrode that is involved in forming an electron lens and the connecting member having the slit, and thereafter integrating the same, it is possible to prevent the distortion of the electron lens due to the deformation of an electrode forming the electron lens. According to the present invention, the roundness of an electrode forming a main electron len
Konda Masahiko
Taguchi Yuuji
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Patel Ashok
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