Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
2000-03-10
2002-11-12
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S432000, C313S449000, C315S015000
Reexamination Certificate
active
06479926
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a cathode ray tube, particularly, to a cathode ray tube provided with an electron gun performing a dynamic astigmatic compensation.
BACKGROUND ART
In general, a color cathode ray tube comprises an envelope consisting of a panel P
1
and a funnel P
2
integrally fused to the panel P
1
, as shown in
FIG. 1. A
phosphor screen P
3
(target) consisting of three phosphor layers emitting blue, green and red light rays, respectively, which are in the shape of stripes or dots, is formed on the inner surface of the panel P
1
. Also, a shadow mask P
4
having a large number of apertures formed therethrough is mounted inside the phosphor screen P
3
in a manner to face the phosphor screen P
3
. On the other hand, an electron gun P
7
emitting three electron beams P
6
B, P
6
G, and P
6
R is arranged within a neck P
5
of the funnel P
2
. The electron beams P
6
B, P
6
G, and P
6
R emitted from the electron gun P
7
are deflected by horizontal and vertical deflection magnetic fields generated from a deflection yoke P
8
mounted on the outside of the funnel P
2
. As a result, the phosphor screen P
3
is scanned horizontally and vertically by these electron beams P
6
B, P
6
G, and P
6
R passing through the shadow mask P
4
to strike the phosphor screen P
4
, thereby displaying a color picture image.
An in-line type color cathode ray tube of a self-convergence system is widely put to a practical use as a color cathode ray tube of the construction outlined above. In the in-line type color cathode ray tube, the electron gun P
7
consists of an in-line type electron gun emitting the three electron beams P
6
B, P
6
G, and P
6
R aligned to form a row, i.e., a center beam P
6
G running on a single horizontal plane and a pair of side beams P
6
B and P
6
R running on both sides of the center beam P
6
G. The positions of the side beam holes in grids on the low voltage side and high voltage side of the main lens portion of the electron gun are deviated from each other to permit the three electron beams to be converged in the center of the screen. Also, the horizontal deflection magnetic field generated from the deflection yoke P
8
is made to be of a pin cushion type, and a vertical deflection magnetic field generated from the deflection yoke P
8
is made to be of a barrel type. By these particular constructions, the three electron beams P
6
B, P
6
G, P
6
R arranged to form a single row are self-converged on the entire region of the screen to provide the in-line type color cathode ray tube of a self-convergence system.
In the in-line type color cathode ray tube of the self-convergence system, the electron beam passing through a non-uniform magnetic field generally receives astigmatism and, thus, strains
11
H and
11
V are imparted to the electron beam as shown in FIG.
2
A. As a result, the beam spot
12
of the electron beam in a periphery of the phosphor screen is distorted as shown in FIG.
2
B. The deflecting distortion received by the electron beam, which is generated because the electron beam is put in an excessively focused state in the vertical direction, gives rise to a large halo (blurring)
13
in the vertical direction, as shown in FIG.
2
B. The deflecting distortion received by the electron beam is increased with increase in the size of the tube and with increase in the deflecting angle so as to markedly deteriorate the resolution at the periphery of the phosphor screen.
Means for overcoming the deterioration of the resolution caused by the deflecting distortion is disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 61-99249 and Japanese Patent Disclosure No. 2-72546. The electron gun disclosed in each of these prior arts is basically constructed as shown in FIG.
3
. As shown in the drawing, the electron gun comprises first grid G
1
to fifth grid G
5
. Also, an electron beam-generating section GE, a quadrupole lens QL, and a final focusing lens EL are formed in the order mentioned in the running direction of the electron beam. The quadrupole lens QL for each electron gun is formed by forming symmetrical electron beam holes
14
a
,
14
b
,
14
c
and
15
a
,
15
b
,
15
c
through the mutually facing surfaces of the adjacent electrode G
3
and G
4
, as shown in
FIGS. 4A and 4B
, respectively. By allowing these quadrupole lens QL and the final focusing lens EL to be changed in synchronism with the change in the magnetic field generated from the deflection yoke, the electron beam deflected toward the periphery of the screen can be prevented from receiving the deflecting distortion of the deflecting magnetic field and, thus, from being markedly distorted. As a result, satisfactory beam spots can be obtained over the entire region of the screen.
The correcting means disclosed in the prior arts certainly makes it possible to eliminate the halo portion in the vertical direction of the electron beam spot. However, since a strong deflecting distortion is generated by the deflection yoke in the periphery of the screen, it is impossible to correct the phenomenon of the lateral deformation of the electron beam spot.
The problem inherent in the conventional electron gun will now be described with reference to
FIG. 5
showing the lens operation of the conventional electron gun. Solid lines in
FIG. 5
denote the orbit and lens function of the electron beam where the electron beam is focused on the center of the screen. Also, broken lines in
FIG. 5
denote the orbit and lens function of the electron beam where the electron beam is focused in a periphery of the screen. In the conventional electron gun, a quadrupole lens QL is arranged on the side of the cathode of the main electron lens EL, as shown in FIG.
5
. Where the electron beam is directed toward the center of the screen, the electron beam is focused on the screen by only the function of the main electron lens EL denoted by the solid line. On the other hand, if the electron beam is deflected toward a periphery of the screen, a deflecting lens DYL is generated by the deflecting magnetic field as denoted by the broken line in FIG.
5
.
In general, a self-convergence type deflection magnetic field is utilized in a color cathode ray tube. Therefore, the focusing force is not changed in the horizontal direction (H), and a focusing lens as a deflection lens DYL is generated in only the vertical direction (V).
Incidentally,
FIG. 5
is intended to point out the problem inherent in the self-convergence type deflecting magnetic field and, thus, the lens function of the deflecting magnetic field in the horizontal direction, i.e., within a horizontal plane, is not shown in the drawing.
When the deflecting lens DYL is generated, that is, when the electron beam is deflected toward a periphery of the screen, the electron lens EL is weakened as denoted by the broken line, and the quadrupole lens QL
1
is generated to compensate for the focusing function in the horizontal direction (H), as denoted by the broken line. Also, the electron beam is allowed to run through the orbit denoted by the broken line so as to be focused on a periphery of the screen. When the electron beam is directed to the center of the screen, the principle plane of the lens for focusing the electron beam in the horizontal direction (H), i.e., within a horizontal plane (imaginary center of the lens, i.e., cross point between the orbit of the electron beam emitted from the electron gun and the orbit of the electron beam incident on the phosphor screen) is on a principle plane PPA. When the electron beam is deflected toward a periphery of the screen to generate a quadrupole lens, the principle plane in the horizontal direction (H) is moved to a principle plane PPB interposed between the main electron lens EL and the quadrupole lens QL
1
. Also, the position of the principle plane in the vertical direction (V) is moved from the principle plane PPA to the principle plane PPC. It follows that the position of the principle plane in the horizontal direction is moved backward from the principle plane PPA to the principle plane PPB
Awano Takashi
Kimiya Junichi
Clove Thelma Sheree
Patel Nimeshkumar D.
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