JP2868832B2 - Electron gun - Google Patents

Description

The present invention relates to an electron gun for a cathode ray tube, and more particularly to an electron gun for a color cathode ray tube which emits a plurality of beams.

(Prior Art) Generally, as shown in FIG. 5, a color cathode ray tube has an envelope composed of a panel (1) and a funnel (2) joined together, and is mounted inside the panel (1). A phosphor screen (4) comprising a three-color phosphor layer emitting blue, green, and red light on an inner surface of the panel (1), facing the shadow mask (3) having a large number of electron beam passage holes formed thereon.
Are formed, and three electron beams (7) emitted from an electron gun (6) disposed in a neck (5) of the funnel (2).
B), (7G), and (7R) are deflected by the magnetic field generated by the deflector (8) mounted outside the funnel (2),
The phosphor screen (4) is formed into a structure for displaying a color image on the phosphor screen (4) by scanning horizontally and vertically.

Among such color cathode ray tubes, in particular, the electron gun (6) is an in-line type electron gun which emits three electron beams arranged in a line composed of a center beam and a pair of side beams passing on the same horizontal plane. There is an in-line type color CRT in which three electron beams are self-concentrated as a non-uniform magnetic field in which a deflection magnetic field is a pincushion type and a vertical deflection magnetic field is a barrel type.

There are various types of electron guns that emit three electron beams in a line, and one of them is QPF (Quadr
a Potential Focus) type. This QPF
As shown in FIG. 6, the type electron gun has three cathodes (k) arranged in a line, and first to sixth grids (G1) having an integral structure sequentially arranged from the cathodes (k) in the direction of the phosphor screen. ) ~ (G6), and each grid (G1) ~
(G6) corresponding to three cathodes (k) arranged in a row
The plurality of electron beam passage holes are formed.

In this electron gun, a voltage of about 150 V is applied to the cathode (k), the first grid (G1) is grounded, the second grid (G2) is about 700 V, and the third grid (G3) is about 7.5 kV. The fourth grid (G4) is applied to the second grid (G2), and the fifth grid (G5) is applied to the third grid (G
3), and a high voltage of about 25 kV is applied to the sixth grid (G6). Thus, the cathode (k) and the first and second grids (G1) and (G2) form a triode that generates an electron beam and forms an object point with respect to a main lens described later. The fifth grids (G3) to (G5) form a sub-lens for pre-focusing the electron beam emitted from the triode, and
The sixth grids (G5) and (G6) form a main lens that finally focuses the electron beam prefocused by the sub-lens on the phosphor screen.

By the way, in order to improve the image quality of the color cathode ray tube, it is necessary to improve the focus characteristics on the phosphor screen. It is known that the aperture of the main lens is one of the factors greatly affecting the focus characteristics, and that the aperture should be as large as possible in order to obtain good focus characteristics. However, one row arrangement 3
As shown in FIG. 7A, the grid constituting the main lens of the in-line type electron gun that emits an electron beam has three electron beam passage holes (10B), (10G), and (10R) arranged in a line. However, since the outer diameter is originally large, it is difficult to accommodate the outer diameter in a neck having a limited inner diameter and increase the aperture of the main lens until the requirement for the focus characteristic is satisfied.

To solve such a problem, Japanese Patent Application Laid-Open No. 61-281439 discloses that, as shown in FIG. 7B, the outer diameter of the grid constituting the main lens is set to the maximum diameter that can be taken in the neck, and Three electron beam passage holes (10
An electron gun that corrects the asymmetry of three main lenses constituted by B), (10G), and (10R) by disposing a partition plate is shown.

However, even if various diaphragms are arranged in the main lens as shown in this publication, it is difficult to make the asymmetry of the main lens completely axially symmetric, and the arrangement of such diaphragms is difficult. It is not easy because high precision is required.

Generally, a beam spot of an electron beam emitted from an electron gun having an axisymmetric main lens and sub-lens does not cause astigmatism. That is, the horizontal and vertical diameters (spot sizes) of the beam spot with respect to the focus voltage Ec3 applied to the third grid of the electron gun shown in FIG.
Each of the curves changes as shown by the curves (12H) and (12V) in FIG. 8 (a), and the minimum values SSH and SSV in the horizontal and vertical directions coincide (SSH = SSV) and the astigmatism voltage ΔVfH−V (voltage value obtained by subtracting VfV from VfH) becomes 0, and (ΔVfH−V = Vf
H−VfV = 0) As a result, the beam spot at the focus point Fp becomes the smallest and a perfect circle. On the other hand, the diameters of the beam spot in the horizontal and vertical directions with respect to the focus voltage Ec3 of the electron beam emitted from the electron gun having the asymmetric main lens are curves (12H) and (12H), respectively.
V) the minimum value of the horizontal and vertical diameters SS as varied
Although H and SSV match, astigmatism occurs, and as a result, the value of the average diameter of the beam spot at the focus point Fp deteriorates in the vertical direction.

In other words, the main lens must correct this to complete axial symmetry, set SSH = SSV, and set ΔVfH−V = 0,
The average diameter of the beam spot is degraded, and the focus characteristics cannot be improved.

(Problems to be Solved by the Invention) As described above, in order to improve the image quality of a color cathode ray tube, it is necessary to improve the focus characteristics on the phosphor screen, and to improve the focus characteristics. For this purpose, it is known that the diameter of the main lens should be as large as possible. However, the grid constituting the main lens of the in-line type electron gun that emits three electron beams arranged in one line has three electron beam passage holes arranged in one line and its outer diameter is originally large. It is difficult to accommodate the main lens in the neck and increase the aperture of the main lens until the requirement of the focus characteristic is satisfied. Conventionally, as an electron gun that solves the problem of the focus characteristic, the outer diameter of the grid constituting the main lens is set to the maximum diameter that can be taken in the neck, and the remaining three electron beam passage holes are used. There is an electron gun that corrects the asymmetry of the main lens by disposing a diaphragm. However, even if the diaphragm is arranged in the main lens as described above, it is difficult to make the asymmetry completely axisymmetric, and the arrangement of the diaphragm is not easy because high precision is required. There is.

The present invention has been made in order to solve the above problems, and has an electron gun capable of easily correcting astigmatism of a main lens without impairing the spot size of an electron beam in order to improve focus characteristics. The purpose is to configure.

[Means for Solving the Problems] In an electron gun having at least a triode, a sub-lens and a main lens, opposed second and third grids constituting the triode and the sub-lens, respectively. When the main lens has positive astigmatism, a vertically long groove is formed on each opposing surface, and when the main lens has negative astigmatism, a horizontally long groove is formed, and at the bottom of the groove An electron beam passage hole was formed.

(Operation) As described above, when grooves are formed on the opposing surfaces of the opposing second and third grids constituting the tripolar portion and the sub lens, respectively, and when the main lens has positive astigmatism, That is, when ΔVfH−V> 0, if the groove is vertically long, the minimum value of the horizontal and vertical directions of the beam spot with respect to the focus voltage Ec3 applied to the third grid is SSH = SSV,
By setting the astigmatism voltage to ΔVfH−V <0, the positive astigmatism of the main lens can be corrected, and an electron gun having good focus characteristics can be obtained. When the main lens has negative astigmatism, that is, when ΔVfH−V <0, and the groove is horizontally long, the minimum value of the horizontal and vertical directions of the beam spot with respect to the focus voltage Ec3 is SS H = SS By setting V and the astigmatism voltage to ΔVfH−V> 0, it is possible to correct the negative astigmatism of the main lens and obtain an electron gun having good focus characteristics.

Hereinafter, the present invention will be described based on embodiments with reference to the drawings.

FIG. 1 shows an in-line type electron gun which emits three electron beams arranged in a line consisting of a center beam and a pair of side beams passing on the same horizontal plane of a color cathode ray tube as one embodiment. The electron gun is of a QPF type, and has three cathodes (K) arranged in a row in the horizontal direction, three heaters (not shown) for heating the cathodes (K) separately, and a cathode (K). And first to sixth grids (G1) to (G6) having an integral structure sequentially arranged adjacent to each other, which are integrally fixed by a pair of insulating supports (not shown).

The first to fourth grids (G1) among the above grids
To (G4) are plate-shaped electrodes, and three electron beam passage holes are formed on the plate surface corresponding to the three cathodes (K) arranged in a line. The fifth and sixth grids (G5) and (G6) are composed of cylindrical electrodes,
On the fourth grid (G4) side of the fifth grid (G5),
Similarly, three electron beam passage holes are formed. On the sixth grid (G6) side of the fifth grid (G5), a large opening common to the three electron beams emitted from the three cathodes (K) is provided. Formed at both ends of the sixth grid (G6)
Similarly, a large opening common to the three electron beams is formed. The cathode (K) and the first and second grids (G1) and (G2) form a triode that generates an electron beam and forms an object point with respect to the main lens. According to G3) to (G5), the sub-lens for pre-focusing the electron beam emitted from the triode is further pre-focused by the sub-lens by the fifth and sixth grids (G5) and (G6). The main lens that finally focuses the electron beam on the phosphor screen is formed.

Further, in the electron gun of this example, a partition plate (20) for correcting the asymmetry of the main lens is disposed inside the opposed portions of the fifth and sixth grids (G5) and (G6). In order to correct the asymmetry of the main lens that cannot be completely corrected by (20), opposing second and third grids (G2) and (G
3) Vertical or horizontal grooves (21a) and (21b) are formed on each facing surface according to the positive or negative of the astigmatism of the beam spot based on the asymmetry of the main lens, and the grooves (21a),
Electron beam passage holes (22a) and (22b) are formed at the bottom of (21b). The triode shown in FIG.
In this case, vertically elongated grooves (21a) and (21b) are formed on the opposing surfaces of the third grids (G2) and (G3).

By the way, the second and third grids (G2), (G
The formation of the grooves (21a) and (21b) in 3) was determined based on the following experimental results.

That is, when the main lens has positive astigmatism based on its asymmetry, the horizontal and vertical diameters of the beam spot with respect to the focus voltage Ec3 applied to the third grid (G3) are as shown in FIG. Changes as shown by the curves (12H) and (12V) to generate a positive astigmatism voltage satisfying ΔVfH−V> 0, and the minimum values of the horizontal and vertical diameters of the beam spot coincide with each other. = SSV.

On the other hand, when a vertically elongated groove (21a) is formed around the electron beam passage hole on the third grid (G3) side of the second grid (G2), the horizontal and vertical diameters of the beam spot with respect to the focus voltage Ec3 become the same ( Curves (12H) and (12H) shown in b)
V), a negative astigmatism voltage of ΔVfH−V <0 is generated, and the minimum value of the vertical diameter of the beam spot is smaller than the minimum value of the horizontal diameter, and SSH> SSV. Become.
When a vertically long groove (21b) is formed around the electron beam passage hole on the second grid (G2) side of the third grid (G3), the horizontal and vertical diameters of the beam spot with respect to the focus voltage Ec3 become the same ( Curves (12H) and (12H) shown in c)
V), a negative astigmatism voltage ΔVfH−V <0 is generated, and the minimum value of the horizontal diameter of the beam spot is smaller than the minimum value of the vertical diameter, and SSH <SSV. Become.

Therefore, a vertically elongated groove (21) is formed around the electron beam passage hole on each of the opposing surfaces of the second and third grids (G2) and (G3).
When a) and (21b) are formed, the horizontal and vertical diameters of the beam spot with respect to the focus voltage Ec3 change as shown by the curves (12H) and (12V) shown in FIG.
Due to the synergistic effect of a) and (21b), a negative astigmatism voltage satisfying ΔVfH−V <0 is generated, and the horizontal and vertical positions of the beam spot are adjusted.
The minimum values of the vertical diameters match, and SSH = SSV.

Therefore, the second and third grids (G2),
Electron beam passage holes (22a), (22b) on each facing surface of (G3)
The width and length of the vertically elongated grooves (21a) and (21b) formed around are restricted to positive astigmatism (ΔVfH−V> 0)
When combined with the main lens having, as shown in FIG.
Astigmatism can be eliminated (ΔVfH−V = 0), and the minimum value of the beam spot in the horizontal and vertical directions with respect to the focus voltage Ec3 can be matched (SSH = SSV).

That is, if the main lens has positive astigmatism based on its asymmetry, the second and third grids (G2),
Vertical grooves (21a) and (21b) consisting of elongated steps extending in the vertical direction are formed on each of the facing surfaces of (G3), and round electron beam passage holes (22a) and (22b) are formed at the bottoms of the grooves. Is formed, it is possible to effectively correct the positive astigmatism of the main lens and improve the focus characteristics.

When the main lens has negative astigmatism, the second lens has a positive astigmatism, as is clear from the description of the case where the main lens has positive astigmatism.
And the third grids (G2) and (G3) are formed with a horizontally long groove on each of the opposing surfaces, and a perfect circular electron beam passage hole at the bottom of the groove to form a negative astigmatism of the main lens. It is possible to effectively correct aberrations and improve focus characteristics.

[Effects of the Invention] In an electron gun having at least a triode portion, a sub lens, and a main lens, a main lens is provided on each facing surface of opposing second and third grids constituting the triode portion and the sub lens, respectively. When the main lens has a negative astigmatism (ΔVfH−V> 0), a vertically long groove is formed when the main lens has a negative astigmatism (ΔVfH−V> 0).
When an electron beam passage hole is formed at the bottom of the groove, when the main lens has a positive astigmatism, the horizontal position of the beam spot with respect to the focus voltage Ec3 applied to the third grid is determined.
The minimum value of the vertical diameter is SSH = SSV and the astigmatism voltage is ΔVfH
When −V <0, the positive astigmatism of the main lens is corrected. When the main lens has negative astigmatism, the horizontal and vertical directions of the beam spot with respect to the focus voltage Ec3 applied to the third grid are set. Assuming that the minimum value of the diameter is SSH = SSV and the astigmatism voltage is ΔVfH−V> 0, the negative astigmatism (ΔVfH−V <0) of the main lens is corrected to form an electron gun with good focus characteristics. can do.

[Brief description of the drawings]

FIGS. 1 to 4 are explanatory views of an embodiment of the present invention. FIG. 1 is a view showing a configuration of a QPF type electron gun of an in-line type color cathode ray tube which is an embodiment of the present invention, and FIGS. (B) is a plan view and a side view showing the first to third grids in cross section, respectively. FIGS. 3 (a) to (d) are second and third grids respectively for the main lens having positive astigmatism. FIG. 4 is a view for explaining an effect when a vertically elongated groove is formed on each opposing surface of the grid. FIG. 4 shows a main lens having positive astigmatism and formed on each opposing surface of the second and third grids. FIG. 5 is a diagram showing a change in the horizontal and vertical diameters of a beam spot with respect to a focus voltage when a vertically elongated groove is combined, FIG. 5 is a diagram showing a configuration of a color CRT, and FIG. FIG. 7 shows the structure of a QPF type electron gun. 8 (a) and 8 (b) show the structure of the grid constituting the main lens of the electron gun and the structure of the improved grid in which the diaphragm is arranged, respectively. FIGS. 8 (a) and 8 (b) show the structure of the main lens, respectively. Changes in the horizontal and vertical diameters of the beam spot with respect to the focus voltage of an electron gun without astigmatism and changes in the horizontal and vertical diameters of the beam spot with respect to the focus voltage of an electron gun whose main lens has astigmatism. FIG. 20 Separators, 21a, 21b Vertical grooves 22a, 22b Electron beam passage holes K Cathode, G1 First grid G2 Second grid G3 Third grid G4 Fourth Grid G5: Fifth grid G6: Sixth grid

Claims (1)

(57) [Claims] A triode for generating at least an electron beam;
A sub-lens for pre-focusing the electron beam from the triode portion and a main lens for finally converging the electron beam pre-focused by the sub-lens are constituted by a plurality of grids formed with electron beam passage holes. When the main lens has a positive astigmatism, a vertically long groove is formed on each of the opposing surfaces of the opposing second and third grids constituting the triode portion and the sub-lens, respectively. And
An electron gun, wherein when the main lens has negative astigmatism, a horizontally long groove is formed, and the electron beam passage hole is formed at the bottom of the groove.