JPS59207544A - Image tube - Google Patents

Abstract

PURPOSE:To reduce spherical aberration and effect of external electric field by the method wherein, a low voltage side electrode and a high voltage side electrode that form a focusing lens of electron gun is formed with a particular relation between the electron beam passing holes diameter and gap of said electrodes. CONSTITUTION:The focusing lens of electron gun in an image tube is formed by arranging face to face through the interval dm a low voltage side electrode 1 having the electron beam passing holes 1a-1c in the diameter D1 and a high voltage side electrode 2 having the electron beam passing holes 2a-2c in the diameter D2. At this time, sizes of D1, D2 and dm are selected to satisfy the relation of dm>=(1/D1)+0.07D1, D1>D2. Accordingly, the spherical aberration which significantly affects the focusing performance of electron beam can be reduced and simultaneously effect of external field is made to hardly occur. As a result, an electron gun comprising a large diameter focusing lens and having high electrode accuracy can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a picture tube using an electron beam, and more particularly to an electrode structure forming a focusing lens of the electron gun.

[Technical background of the invention and its problems]

Focusing performance of the electron beam is particularly important for an electron gun used in a picture tube that uses an electron beam to display an image on a fluorescent screen. There are three important factors related to the focusing performance of an electron gun: spherical aberration, focusing lens magnification, and mutual repulsion of electrons. Among these, the biggest factor that determines focusing performance is spherical aberration, and focusing performance is greatly influenced by the magnitude of spherical aberration.

For example, the focusing lens used in cathode ray tube electron guns is
As shown in the figure, a focusing electrode (1) to which 6KV to 9KV is applied and an accelerating electrode (2) to which 20KV to 30F (V is applied) are connected to the respective circular "Ako beam passing holes (3)".
They are arranged at a predetermined interval dm opposite to each other.

General [If the interval dm between the four poles constituting the above-mentioned focusing lens is too small, the electric field gradient between the focusing electrode (1) and the accelerating magnetic pole (2) becomes a dog, making it easy to cause discharge. Furthermore, if the distance dm is made too large, the shape of the focusing lens will be distorted, making it less susceptible to the influence of an external electric field. In an electron gun such as a shadow mask type color picture tube, multiple electron beams, for example, three electron beams are lined up on a horizontal axis, and these three electron beams are focused near the shadow mask.
In particular, distortion in the shape of the focusing lens has a large effect. That is 3
Since the electron beams of the book are each subjected to different forces, the three electron beams move in different directions on the screen, resulting in deterioration of color purity. Therefore, increasing the electrode spacing dm reduces spherical aberration, but this tends to cause distortion in the shape of the focusing lens, and there is a certain limit. For example, JP-A-57-103
In Japanese Patent No. 246, a proposal is made to substantially widen this electrode interval to reduce spherical aberration. That is, as shown in FIG.
c) and (2a), (2b), and (2c), respectively, and a focusing electrode (1) and an accelerating electrode (
2) are arranged facing each other. The rim (4) also has a protruding shape beyond the end faces (5a) and (5L+) of the electron beam passage hole. Therefore, the distance between the opposing end surfaces of the electron beam passage hole is sufficiently wavered to reduce spherical aberration, and the distance between the opposing rims is narrowed to prevent the influence of external electric fields.

However, an electrode having such a shape causes the following problems. First, since these electrodes are in-line three-beam electron gun electrodes rather than single-beam electron gun electrodes, the overall frame shape of the rim (4) is substantially rectangular. For this reason, the focusing lens formed by the K IJ beam (4) inevitably produces asymmetrical distortion between the center beam and the side beams, and there is a problem that aberrations are likely to occur in the side beams. Second, due to the presence of the rim (4), the focusing lens diameter, that is, the electron beam passing hole, cannot be made sufficiently large, and since a large diameter lens cannot be formed, the spherical aberration also increases accordingly. There is. Thirdly, from a manufacturing perspective, the shape is complicated, the υ forming process is complicated, the price is high, and dimensional accuracy is difficult to achieve.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to obtain a picture tube having an electron gun that reduces spherical aberration and minimizes the influence of external electric fields.

[Summary of the invention]

In the present invention, when the spacing between the low voltage applying electrode and the high voltage applying electrode forming the focusing lens is dm, and the diameter of the electron beam passing hole is Dl and D2, respectively, dm>1/'D1+0.
07D, , and D+ ) By setting D2, spherical aberration is reduced and the influence of the focusing lens due to an external electric field is compensated for.

[Embodiments of the invention]

Examples of the present invention will be described in detail below.

Figure 3 shows the electrodes constituting the focusing lens of the electron gun applied to the present invention, in which the focusing electrode (1) and the accelerating bridge (2) to which a relatively higher voltage is applied than the focusing electrode are spaced apart. d
They are placed facing each other with a distance of m. Opposing surfaces of both electrodes have respective electron beam passage holes (la).

(Ib), (Ic) and (2a), (2b),
(2c), and does not have a folded-back portion at the peripheral edge of the electron beam passage hole as shown in FIG. 2, and all the passage holes are provided independently. This slanted shape is advantageous against the influence of external electric fields and mutual interference from adjacent passage holes. In the electrode configuration forming such a focusing lens, spherical aberration due to the electrode spacing dm will be discussed. As the electrode spacing dm giving the critical spherical aberration when the electron beam passage aperture diameter D1 was changed, the characteristics shown in FIG. 4 were obtained. This characteristic curve can be expressed by extrapolation as dm = 1/Dr + 0.07 D+. That is, dm-? If l/D1+0.07D, the spherical aberration can be further reduced. Here 1
If /DI is a dog, dm can be made a dog to reduce the influence of the external electric field. Also, the more Dl is a dog, the more dm
If it is a dog, the spherical aberration will be small. However, if the electrode spacing dm is increased only by increasing the electrode spacing dm, the effect of the external electric field becomes more susceptible, so it is necessary to further reduce the spherical aberration and compensate for the influence of the external electric field by using other means. To this end, it is possible to strengthen the focusing lens and further reduce spherical aberration by setting the diameters D1 and D2 of the electron beam passage holes of the focusing electrode (1) and the accelerating electrode (2) to >D2. Figure 5 shows the diameter of the electron beam passage hole of the focusing electrode (1).
is kept constant at 4.9 nm, and the electron beam passing hole diameter D2 of the accelerating electrode (2) is changed (D).

-D2) is a characteristic diagram for determining the spherical aberration coefficient.

The electrode spacing dm was constant at 21 m. As is clear from Fig. 5, when Dl ''t > 0.6, the spherical aberration is reduced to about 1/2, and the influence of the external electric field can be compensated for.The electrode configuration shown in Fig. 3 The shape is very simple and a large diameter focusing lens can be formed.
The structure shown in Japanese Patent No. 23635 can be assembled very easily and with high precision.

In the above embodiments, an electrode configuration without a folded portion at the periphery of the electron beam passage hole has been described, but even an electrode configuration as shown in FIG. 6 has the same effect. In this case, the diameter of the focusing lens is almost determined by the focusing electrode (1), and since the rim of the outer frame does not protrude, the diameter of the electron beam passing hole is determined by the second diameter.
It can be made larger than the one shown in the figure, and it is easier to achieve electrode accuracy.

Furthermore, it goes without saying that the present invention can be applied not only to an in-line array electron gun but also to a delta array electron gun or a single-gauge gun.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a picture tube having a large-diameter focusing lens with small spherical aberration and capable of compensating for the influence of an external electric field, and having an electron gun with high electrode precision.

[Brief explanation of drawings]

FIGS. 1 and 2 are schematic diagrams of main parts showing electrodes constituting a focusing lens, FIG. 3 is a schematic diagram of main parts showing electrodes constituting a focusing lens applied to the present invention, and FIG. A characteristic diagram showing the relationship between the electron beam passing aperture and the electrode spacing regarding spherical aberration, FIG. 5 is a characteristic diagram showing the relationship between the electron beam passing aperture difference between the focusing electrode and the accelerating electrode, and spherical aberration, and FIG. FIG. 7 is an electrode configuration diagram of a main part showing another example. (1)・Focusing electrode (2)・Accelerating electrode (Ia
), (lb), (lc), (2a), (2b), (2c
), (3) - Electron beam passage hole representative Patent attorney Kensuke Chika (and 1 other person) Figure 1 Figure 2-dd Figure 4 Figure 5 (D, -02) Houki Figure 6

Claims (1)

[Scope of Claims] 1) A picture tube comprising an electron gun comprising a plurality of electrodes that generates an electron beam toward a fluorescent screen of the picture tube and accelerates and focuses the electron beam, the electron gun having a both have opposing electrodes for forming a focusing lens by being supplied with a low voltage and a high voltage, and the electron beam passing hole diameter of the low voltage side electrode and the high voltage side electrode is determined;
When the facing distance is dm, drz+ > n, 10o,
07 A video tube characterized by being a DJ, and a fishing > D. 2) The picture tube according to claim 1, characterized in that the DI and the length -D are >0.6 m.