Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
1998-07-16
2001-02-27
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S431000, C313S440000
Reexamination Certificate
active
06194824
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a color cathode ray tube apparatus for a television or a computer display monitor, and more particularly to a color cathode ray tube apparatus that is configured to obtain a high resolution over the whole phosphor screen.
BACKGROUND OF THE INVENTION
In a self-convergence type color cathode ray tube comprising an in-line type electron gun for aligning three electron beams and a deflection yoke for generating a horizontal deflection magnetic field distorted in a pincushion shape and a vertical deflection magnetic field distorted in a barrel shape, the distortion of the deflection magnetic fields for self-convergence causes a quadrupole astigmatism of the electron beams.
As a technology for correcting the astigmatism, Japanese Patent Application (Tokkai Sho) No. 61-99249 describes correcting the cross-sectional shape of the electron beams by producing a nonaxisymmetric lens between a first focusing electrode and a second focusing electrode according to the deflection degree.
FIG. 7
shows the electron gun of a color cathode ray tube apparatus according to this prior art. Vertically long electron beam openings
18
are provided on the face of a first focusing electrode
14
at the side facing a second focusing electrode
15
. Horizontally long electron beam openings
19
are provided on the face of the second focusing electrode
15
at the side facing the first focusing electrode
14
. A constant focusing voltage Vfoc is applied to the first focusing electrode
14
. A dynamic focusing voltage that gradually increases from the focusing voltage Vfoc with the increase of the deflection amount is applied to the second focusing electrode
15
. This technology can obtain a dynamic focusing action in response to a change in the electron beam focusing amount caused by a difference in the distance between the electrode gun and the phosphor screen when the electron beams are deflected and an action for correcting the astigmatism of the electron beams caused by the deflection magnetic field simultaneously.
However, the above prior art can only correct the same amount of astigmatism of the three electron beams simultaneously.
The actual astigmatism amounts of the right and left electron beams are different from each other. Furthermore, the difference in the astigmatism amount is opposite depending on the deflection derection.
FIG. 8
shows the size of forces acting on three electron beams emitted from an in-line type electron gun in the deflection magnetic field generated by a self-convergence type deflection yoke. As can be seen from
FIG. 8
, a force that distorts the cross-sectional shape of the electron beams to be horizontally long acts most strongly on the right electron beam (R beam) when the electron beams are deflected to the right side of the screen. The larger the deflection degree is, the stronger the force is. On the other hand, the force that distorts the cross-sectional shape of the electron beams to be horizontally long acts most strongly on the left electron beam (B beam) when the electron beams are deflected to the left side of the screen.
The difference in the astigmatism amount among the electron beams is significant especially in a color cathode ray tube having a large deflection angle and a short total length and a color cathode ray tube having a substantially flat phosphor screen, and prevents implementing a high resolution over the whole phosphor screen.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a color cathode ray tube apparatus that can implement a high resolution over the whole phosphor screen of a color cathode ray tube having a large deflection angle and a short total length or a color cathode ray tube having a substantially flat phosphor screen.
In order to accomplish the above object, the present invention provides a color cathode ray tube apparatus comprising a color cathode ray tube comprising an in-line type electron gun for emitting three electron beams and a self-convergence type deflection yoke, wherein the electron gun comprises a correction system for correcting a difference in astigmatism amount among the three electron beams emitted from the electron gun. According to the color cathode ray tube apparatus of the present invention, the difference in astigmatism amount among the electron beams can be corrected. Thus, a high resolution can be obtained over the whole phosphor screen of a color cathode ray tube having a large deflection angle and a short total length or a color cathode ray tube having a substantially flat phosphor screen.
It is preferable that the correction system causes a correction magnetic field to act on at least one outer electron beam of the three electron beams by using a deflection magnetic field generated by the deflection yoke or a magnetic field whose strength varies in synchronization with the deflection magnetic field, thereby changing the cross-sectional shape of the at least one outer electron beam. According to this preferable example, the difference in astigmatism amount among the electron beams can be eliminated by the correction magnetic field having a strength corresponding to the astigmatism amount by using the deflection magnetic field or the magnetic field in synchronism with the deflection magnetic field.
It is preferable that the correction system comprises magnetic pieces comprising a principal face portion for absorbing an external magnetic field, an arm for guiding the external magnetic field absorbed by the principal face portion near the electron beam, and a correction magnetic field generating face provided at the tip of the arm and facing the electron beam, the magnetic pieces being positioned so that the correction magnetic field generating faces sandwich at least one outer electron beam of the three electron beams. According to this preferable example, the correction system can be located easily and reliably, and the correction magnetic field acts on the electron beam efficiently.
It is preferable that the in-line type electron gun further comprises a second correction system for correcting the astigmatism of the three electron beams simultaneously. According to this preferable example, the astigmatism of the three electron beams can be corrected most preferably.
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Day Michael H.
Matsushita Electronics Corporation
Merchant & Gould P.C
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