Color cathode ray tube

Details Color cathode ray tube Color cathode ray tube

2001-01-09

2002-06-25

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Plural beam generating or control

C313S412000

Reexamination Certificate

active

06411026

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color cathode ray tube equipped with an in-line electron gun so constituted as to emit three electron beams in one horizontal line toward a fluorescent screen.
2. Description of the Prior Art
In a cathode ray tube equipped with at least an electron gun comprising a cathode and a plurality of grid electrodes, a deflection device, and a fluorescent screen, the following arts have been known to obtain a preferable reproduced image extending from the central portion to the periphery of the fluorescent screen: one for providing an astigmatic lens in a region of an electrode constituting a focusing lens (main lens), and the other for forming an electron beam passing hole of the main lens constituting electrode of an in-line electron gun into a slot and making the sizes of central and side electron beam passing holes different (Japanese Pat. Laid-Open No. 64368/1976).
This type of color cathode ray tube, as shown in
FIG. 1
, is equipped with at least a vacuum vessel comprising a panel
61
, a funnel
62
, and a neck
63
which are made of an insulator such as glass, an electron gun
64
, a shadow mask
65
, and a fluorescent screen
66
contained in the vacuum vessel, and reproduces an image by impinging electron beams emitted from an electron gun
64
onto the fluorescent screen
66
.
FIG. 2
is a sectional view of an essential portion of a main lens, schematically illustrating the structure of a conventional in-line electron gun used for the above cathode ray tube.
In
FIG. 2
, reference numerals
08
,
09
and
010
are cathodes,
011
is a first grid electrode,
012
is a second grid electrode,
013
is a third grid electrode which is one of the electrodes constituting a main lens,
014
is a fourth grid electrode which is the other electrode constituting the main lens,
015
,
016
, and
017
are inner cylinders connected to the opening portions of the third grid electrode
013
on the fourth grid electrode
014
side, and
018
,
019
, and
020
are inner cylinders connected to the opening portions of the fourth grid electrode
014
on the third grid electrode
013
side. Numerals
021
,
022
, and
023
are central axes of electron beams, respectively and the central axis
022
of the center electron beam is aligned with the axis of the electron gun (tube axis). These central axes
021
,
022
, and
023
are aligned with the openings corresponding to the cathodes
08
,
09
, and
010
of the first, second, and third grid electrodes
011
,
012
, and
013
, and with the central axes of the inner cylinders
015
,
016
, and
017
connected with the opening portions of the third grid electrode
013
, and they are arranged on the same plane almost in parallel.
The central axes of the central opening portion of the fourth grid electrode
014
and the inner cylinder
019
connected to the central opening portion are aligned with the central axes
022
. However, the central axes of the opening portions on the both sides and the inner cylinders
018
and
020
connected to the opening portions are not aligned with their corresponding central axes of the third grid electrodes, but they are slightly shifted outwards.
Symbol S in
FIG. 2
represents the interval between central axes
021
,
022
and
023
of the electron beams, L represents the distance between the central axes
021
and
023
of the outer electron beams and the inner wall of the neck, and D represents the inside diameter of the inner cylinder connected to the opening portion of the G3 electrode
013
.
The in-line electron gun having the above constitution operates as shown below.
Thermionic electrons emitted from three cathodes
08
,
09
, and
010
heated by a heater are attracted toward the first grid electrode
011
by a positive voltage applied to the second grid electrode
012
, and three electron beams are formed. Then, these three electron beams pass through the openings of the first grid electrode
011
and then through the opening of the second grid electrode
012
. The beams are accelerated by positive voltages applied to the third grid electrode
013
and the fourth grid electrode
014
, and enters the main lens.
In this case, a low voltage of approximately 5 to 10 kV is applied to the third grid electrode
013
constituting the main lens; a high voltage of approximately 20 to 35 kV to be applied to the fluorescent screen is applied to the fourth grid electrode
014
through a conductive film coated on the inner wall of the funnel
62
. Therefore, a electrostatic field is formed between the third grid electrode
013
and fourth grid electrode
014
by the difference in voltage between the third grid electrode
013
to which the low voltage is applied and the fourth grid electrode
014
to which the high voltage is applied. Therefore, the paths of three electron beams in the main lens are bent by the electrostatic field. As a result, three electron beams are focused on the fluorescent screen.
Moreover, because the central axes of the opposing openings of cylinders for side beams of the third grid electrode
013
and fourth grid electrode
014
are not aligned with each other, the main lens for the side beams is not symmetric about the central axis. Therefore, the side electron beams are so deflected inward that they are converged in accordance with the center electron beam on the fluorescent screen. Thereby, three electron beams are converged on the fluorescent screen, images of three colors of R, G, and B generated by three electron beams are correctly registered, and a color image is displayed.
SUMMARY OF THE INVENTION
In an in-line electron gun constituted as described above, three electron beams do not satisfy the convergence conditions due to slight variations of the electron gun component accuracy and assembling accuracy. Therefore, it is necessary to make adjustment for convergence of electron beams.
In this convergence adjustment, as the beam spacing S between the electron beams decreases, deviation of the electron beams from the convergence conditions decreases and the adjustment gets easier. From past experiment results, it has been known that it is preferable to set the S value to less than approximately 5 mm.
In conventional focusing electrode structures, however, the opening diameter of the focusing electrode is restricted to a value smaller than the beam spacing S between the adjacent electron beams entering the lens. Therefore, a limit is put on the opening diameter for setting the beam spacing S between electron beams to be less than 5 mm.
The effective aperture of the focusing lens of each electron beam is determined by this opening diameter. Therefore, a problem arises that the spherical aberration of a lens increases and the electron beam spot diameter increases as the opening diameter decreases.
To solve the above problem, a structure is known which is disclosed in Japanese Pat. Laid-Open No. 103752/1983. This structure makes it possible to decrease the spherical aberration while the beam spacing S is maintained at less than 5 mm.
The structure of the electron gun disclosed in the above publication will be schematically described below, referring to FIGS.
3
(
a
) and
3
(
b
). FIG.
3
(
a
) is a longitudinal sectional view of the essential portion, illustrating the main lens of an in-line electron gun and FIG.
3
(
b
) is a transverse sectional view of the essential portion of FIG.
3
(
a
), taken along the line A—A′ of FIG.
3
(
a
).
In FIGS.
3
(
a
) and
3
(
b
), reference numeral
13
is a third cylindrical grid electrode whose opening cross section is almost elliptic,
14
is a fourth cylindrical grid electrode whose opening cross section is also almost elliptic,
13
-
1
is a flat electrode provided in a third grid electrode
1
,
14
-
1
is a flat electrode provided in a fourth grid electrode
2
,
13
R,
13
G, and
13
B are electron beam passing holes (openings) of the flat electrode
13
-
1
,
14
R,
14
G, and
14
B are electron beam passing holes (openings) of the flat electrode
14
-

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