JPS6134835A - Electron gun for color cathode-ray tube - Google Patents

Abstract

PURPOSE:To reduce generation of a halo due to coma abberation while obtaining good picture quality covering the whole region by inciding side beams into the main lenses slightly to the center beam. CONSTITUTION:Seen from the side of the fifth grid 6, the center distance S1 of the fourth grid 5' is made to be reduced by an excentric quantity to a center distance S0 of the aperture 4a for the side beam of the third grid 4 and of the aperture 6a for the center beam of the grid 6 while fixing the diameter D1 of the aperture 5b and the diameter D2 of the apertures 5'a and 5'c to be D2= D1-2delta. Further, the aperture 6a of the grid 6 and the aperture 4a of the grid 4 are on the same axis. Thereby, the electric field formed by the aperture 4a and the aperture 6a shows the axially symmetrical equipotential lines 15 and 16, while the electron beam 17 incides into the center of the main lens electric field formed by the electrode 6A of the grid 6 without being bent by said lens while generating no coma aberration of the side beam at the main lenses and able to suppress generation of a halo thus improving the picture quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an electron gun for a color cathode ray tube, and more particularly to an in-line type electron gun for a color cathode ray tube having a main lens portion having a multi-stage configuration.

[Background of the invention]

It is constructed in the form of a conventional color cathode ray tube electron gun, for example as shown in FIGS. 1 and 2.

That is, in these figures, three cathodes 1@.

A first grating 2. having openings corresponding to the three electron beams emitted from 1b and 1e. 2nd grid 3. Third grid 4. Fourth grid5. A fifth grating 6 and a sixth grating T are sequentially arranged at a predetermined interval toward a screen (not shown). Of these, the third grating 4 to the sixth grating 7 are main lens forming electrodes, a medium potential is applied to the third grating 4 and the fifth grating 6, and the fourth grating 5 and the sixth grating T An expanded high potential is applied to
A.

The lower electrodes 6B of the fourth grating 5 and the fifth grating 6 form a two-way potential type lens, and have the function of a front main lens. Further, the upper electrode 6A of the fifth grating B and the sixth grating 7 form a pi-potential lens, which functions as a main lens. Note that the subscript aM b l ” added to each grid code indicates the opening as an electron beam passage hole. However, the electron gun for color cathode ray tubes configured in this manner has the following problems. Namely, FIG. 2 is an enlarged view of the side beam lens section in FIG. The center of the electric field formed by the center beam is eccentric in the direction of the center beam aperture under the influence of the respective electrode apertures, as shown by equipotential lines 8 and 9. Therefore, the side beam 10 moves in the direction of the arrow 11. The center beam is deflected toward the center beam by the action in the direction indicated by 12, and enters the center beam υ from the center of the main lens electric field formed by the upper electrode 6A of the fifth grating 6 and the sixth grating 7. Therefore, As shown in FIG. 3, the side beams B and R form a halo 13.14' due to coma aberration at the center of the screen.This causes a problem in that the image quality at the periphery of the screen deteriorates.

To improve this problem, an electron gun in which the center of the side beam aperture of the lower electrode 4B of the third grating 4 is eccentrically inward than the center of the side beam aperture of the second grating 3 is disclosed, for example, in Japanese Patent Publication No. This method is disclosed in Japanese Patent Application Laid-open No. 55-10813 and Japanese Patent Application Laid-Open No. 55-109346.

However, with this configuration, since the lower electrode of the third grating with a small electrode aperture diameter is used, the asymmetry of the electric field due to the eccentricity causes unnecessary aberrations in the beam itself, which adversely affects the beam spot shape. There was the problem of overflow.

[Purpose of the invention]

Therefore, the present invention has been made in view of these circumstances, and its purpose is to eliminate coma aberration caused by the side beam being slightly biased toward the center beam entering the main lens. The present invention aims to provide an electron gun for color cathode ray tubes with improved overall focus.

[Summary of the invention]

In order to achieve such an object, the present invention provides an in-line type color cathode ray tube electron gun having a multi-stage main lens section, in which the center of the side beam aperture of the fourth grating constituting the front main lens is set to the third The upper electrode of the grid and the fifth
The lower electrode of the grating is eccentrically located L0 on the center beam side from the center of the side beam aperture.

[Embodiments of the invention]

Next, embodiments of the present invention will be described in detail using the drawings.

FIG. 4 is a cross-sectional configuration diagram of essential parts showing an example of an electron gun for a color cathode ray tube according to the present invention; FIG.

Parts that are the same as the second ward will be given the same subtitle. In the figure, the center of the side beam opening 5 It of the fourth grating 5' is
It is formed eccentrically to the center of the center beam aperture center by a distance δ with respect to the center of the aperture 4a for the upper electrode 4A of the third grating 4. In this case, as a specific method for decentering, the side beams of the upper electrode 4A of the third grating 4 and the lower electrode 6B of the fifth grating 6 are distance from the center beam aperture 4a to the center beam aperture 6a (hereinafter simply referred to as off-axis distance)
The off-axis distance S1 of the fourth grating 5' is set to be a value smaller than So by the eccentricity amount 1, and the aperture diameter D of the center beam aperture 5b is
I and side and room openings 5'a.

Opening diameter D of 5'c! The relationship with D! It is formed so as to satisfy the formula: =D1 2Xδ. The opening 6a of the fifth lattice 6 facing the fourth lattice 5' is a plan view seen from the fifth lattice side of the fourth lattice showing another embodiment of the third lattice. In the figure, a side beam opening 511 of the fourth grating 5'.
, 577c may be formed as an ellipse with a larger diameter on the center beam opening 5b side.

In this case as well, the fourth grid 5''
If you determine the off-axis distance S1 of

According to such a configuration, as shown in FIG. 4, the electric field formed in each of the opening 4a of the upper electrode 4A of the third lattice 4 and the opening 6a of the lower electrode 6B of the fifth lattice 6 is as follows.
As shown by equipotential lines 15 and 16, the electron beam 1T is axially symmetrical and is formed by the six upper electrodes of the fifth grating 6 and the opening of the sixth grating 7 without being bent by this lens. (It will be incident on the center of the main lens electric field)
, comatic aberration of the side beam in the main lens does not occur. Therefore, the beam shape at the center of the screen is not only the center beam G, but also the side beams R, as shown in Figure 7.
B also does not produce a halo, and the halo increases due to deflection aberration at the periphery of the screen, as shown in Figure 8 (only side beam R is shown).
This can improve the overall focus.

〔Effect of the invention〕

As explained above, according to the present invention, the side beam is prevented from being displaced toward the center beam aperture side of the main lens, and the generation of a halo due to coma aberration in the main lens can be eliminated. This has extremely excellent effects in that it is possible to reduce the occurrence of hap- when the beam is deflected to the periphery of the screen, and to obtain good image quality over the entire screen.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of the main part of an example of a conventional in-line color cathode ray tube electron gun, Fig. 2 is an enlarged cross-sectional view of the main part showing the main lens section of Fig. 4 is a sectional view of a main part showing an embodiment of an electron gun for a color cathode ray tube according to the present invention, FIG. 5 is a plan view of the fourth grating in FIG. 4, and FIG. 6 is a diagram showing three beam shapes. 7 is a plan view of the fourth grating showing another embodiment of the present invention, FIG. 7 is a diagram showing the beam shape at the center of the screen according to the present invention, and FIG. 8 is a diagram showing the beam shape over the entire screen. . 1ml 1lb, 16**s* cathode, 2@@@m first grid,
3. 2nd lattice, 4. 3rd lattice of middle cylinder, 4A... φ
- Upper electrode, 4a @ - Opening, 4B Fist... Lower electrode, 4b - Fist/Ball opening 51,511... 4th grid, 5A @ Middle/Upper electrode, 5th breath. 5'&, 5"a, 5b t 5'e, 5"ce
e @ 11 openings, 6・ψ...5th lattice, 6A...
- Upper electrode, 6a... writing/opening, 6B... lower electrode, 6b... opening, T... 6th grid, 8, 9-...
Conflict - Equipotential line, 1011...Side beam, 11,1
2...@Yu arrow direction, 13.14Φ fist/kai hello, 15
．． 16...Equipotential line, 17 -φ・electron beam. Figure 1 Figure 3 Values

Claims (1)

[Claims] It has three cathodes arranged at equal intervals in a straight line perpendicular to the tube axis direction, and is composed of a plurality of grid electrodes having electron beam passage openings arranged corresponding to the three cathodes. , an in-line type color cathode ray tube electron gun having a front main lens consisting of the third, fourth and fifth gratings of the grid electrode, and a main lens consisting of the fifth and sixth gratings of the grid electrode; The center of the side beam aperture of the fourth grating forming the front main lens is eccentric in the direction of the center beam aperture from the center of the side beam aperture of the other grating forming the front main lens. Features a color cathode ray tube electron gun.