JPS5830693B2 - electron gun - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron gun, and more particularly to a pi-potential type electron gun used in a cathode ray tube.

A focus electrode constituting a conventional pi-potential type electron gun is composed of a single component having the same inner diameter, and is disposed opposite to another electrode (high-voltage electrode) constituting the main lens.

At this time, the length of the focus electrode is determined by the inner diameter of the electrode and the length of the electrode, depending on the electrical usage conditions (focus voltage) of the electron gun.

However, when it is desired to change the electrical usage conditions of an electron gun, the inner diameter or electrode length, generally the electrode length, is changed depending on the conditions.
It is impossible to change the electrode length freely due to restrictions on the part manufacturing mold.

In addition, if it is absolutely necessary to change the electrode length,
This method has the disadvantage that a separate mold for manufacturing the part must be prepared, resulting in a very expensive part.

In order to further increase the diameter of the main lens, it is necessary to increase the inner diameters of the focus electrode and the opposing high voltage electrode.

In general, a focus electrode is made up of a single component with the same inner diameter, so increasing the inner diameter of the component increases the size of the focus electrode as a whole, resulting in some difficulty in manufacturing the component.

Therefore, the main purpose of the present invention is to provide an electron gun that can eliminate the above-mentioned drawbacks by increasing the diameter of only the necessary portion of the focus electrode, and allowing the length of the focus electrode to be freely set in response to any desired focus voltage. The goal is to provide the following.

To summarize, this invention consists of a pi-potential type electron gun 2
An electron gun in which the focus electrode is divided into a 10th cylinder electrode and a second cylindrical electrode having a larger diameter than this second cylindrical electrode, and both of the divided cylindrical electrodes of different diameters are connected so that they have the same potential. It is.

The above-mentioned object 23 and other objects and features of the present invention will become more apparent from the following detailed description with reference to the drawings.

FIG. 1 is a sectional view of one embodiment of the present invention.

As shown in the figure, a first grid electrode 1 has a cylindrical shape, and a cathode (not shown) having an electron emitting material is incorporated therein.

A cylindrical second grid electrode 2 is arranged opposite to the first grid electrode 1 .

A focus electrode 3, which is a feature of the present invention, is arranged to face the second grid electrode 2.

The focus electrode 3 is composed of a cylindrical first focus electrode 3a having different diameters and different steps, and a cylindrical second focus electrode 3b having a larger diameter than the first focus electrode 3a.

A high-voltage electrode 4 is provided with a certain gap between the second focus electrode 3b and the second focus electrode 3b.

A high voltage is applied to the high voltage electrode 4, and a main lens for focusing the electron beam is formed between the second focus electrode 3b and the high voltage electrode 4.

Note that the first focus electrode 3a and the second focus electrode 3b are electrically connected to maintain the same potential.

The twisted first grid electrode 1. Second grid electrode2. The first focus electrode 3a, the second focus electrode 3b, and the high voltage electrode 4 are arranged concentrically on the Z-axis.

Now, the diameter of the electron beam emitted from the cathode of the first grid electrode 10 is made narrower by the electric field emitted from the first grid electrode 1 and the second grid electrode 2.
The light is focused by the main lens formed by the second focus electrode 3b and the high voltage electrode 4.

The focused electron beam is then projected onto the fluorescent surface of a cathode ray tube (not shown).

The larger the inner diameter of the second focus electrode 3b and the high-voltage electrode 4 constituting the main lens, the smaller the spherical aberration, and the smaller the diameter of the electron beam projected onto the fluorescent surface.

FIG. 2 is a diagram for explaining the spherical aberration caused by this example.

In the figure, the horizontal axis represents the focal length f of the main lens, which is the paraxial focal length f near the central axis of the electron gun.

The values are shown normalized by . The vertical axis indicates a value obtained by normalizing the electron beam diameter r at the main lens surface by the inner diameter of the electrode constituting the electron lens.

In an ideal main lens without spherical aberration, the dotted line a indicates that the focal length f of the main lens does not change even if the electron beam diameter r increases.

However, a main lens without spherical aberration does not actually exist, and as shown by the curve, as the electron beam diameter in the main lens increases, the focal length becomes shorter.

In the figure, (f indicates the variation of the focal length f.

In general, it is empirically and experimentally known that the relationship between the variation Af of the focal length f and the electron beam r applied to the main lens is J f nir''.

In this way, the electron beam diameter r near the main lens surface is
Obviously, the smaller it is possible, the better.

To achieve this, either the electron beam should be made narrower before it enters the main lens surface, or the diameter of the electron beam at the main lens surface should be fixed and the inner diameter of the electrodes constituting the main lens should be increased. There are two methods, and in addition to these methods, efforts have been made to reduce spherical aberration by combining the two methods.

In the embodiment shown in FIG. 1 described above, the diameter of the electron beam at the main lens surface is fixed and the inner diameter of the electrode constituting the peeled main lens is increased.

The ratio of the electrode inner diameter to the electron beam diameter r is r/D<0.
．． When set to 25, spherical aberration can be practically ignored.

FIG. 3 is a diagram showing the relationship between focus electrode length and focus voltage.

That is, the electrical usage conditions of the electron gun, such as the focus voltage V.

It can be seen that if is given, the focus electrode length Lo is inevitably determined.

Therefore, if the length of the focus electrode shown in FIG. 1 is l, then #=L
All you have to do is arrange it so that it is OK.

That is, even if an arbitrary focus voltage is applied, the length l of the focus electrode can be determined freely.

However, as shown in Fig. 1, the limit to which the inner diameter d of the open part of the first focus electrode 3a can be inserted into the second focus electrode 3b is D/2 or less without disturbing the electric field distribution in the main lens part. is necessary.

As described above, according to the present invention, the focus electrode is composed of cylindrical electrodes made of separate members having different diameters, so that the cost of the housing electrode parts can be reduced without causing any difficulty in manufacturing the electrode parts. The aperture of the focus electrode and electrode length can be changed according to the electrical usage conditions of the electron gun without increasing the size.

[Brief explanation of drawings]

FIG. 1 is a sectional view of one embodiment of the present invention. FIG. 2 is a diagram for explaining spherical aberration for this example. FIG. 3 is a diagram showing the relationship between focus electrode length and focus voltage. In the figure, 1 is the first grid electrode, 2 is the second grid electrode, and 3 is the first grid electrode.
a is a first focus electrode, 3b is a second focus electrode, and 4 is a high voltage electrode.

Claims (1)

[Scope of Claims] 1. A pi-potential type electron gun for a cathode ray tube including a grid electrode, a focus electrode, and a high-voltage electrode, each of which is arranged on the same axis, wherein the focus electrode is a first cylindrical electrode. and a second cylindrical electrode that is made of a separate member from the first cylindrical electrode and has a larger diameter than the first cylindrical electrode, and the first cylindrical electrode has one end that is connected to the second cylindrical electrode. inserted into a second cylindrical electrode, and arranged so that the other end faces the grid electrode, the second cylindrical electrode is arranged opposite to the high voltage electrode, and the second cylindrical electrode and the first cylindrical electrode An electron gun electrically connected to the second cylindrical electrode.