GB2240212A

GB2240212A - Inline type electron gun for color cathode ray tube

Info

Publication number: GB2240212A
Application number: GB9001300A
Authority: GB
Inventors: In-Gyu Park
Original assignee: Samsung Electron Devices Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 1990-01-19
Filing date: 1990-01-19
Publication date: 1991-07-24
Anticipated expiration: 2010-01-19
Also published as: GB9001300D0; GB2240212B

Abstract

The multi-beam electron gun comprises a triode section consisting of a cathode K, a control grid G1, and a screen grid G2, and a plurality of electrodes G3-G6 forming a main lens, wherein at least one of a final focus electrode G5 and an anode G6 forming a major lens of the main lens consists of a first member F1, A1 with three independent beam passing holes VH5, HH6 formed in a beam passing plane, and a second member F2, A2 with a common beam passing hole HH5, HH7 formed in a beam passing plane which is spaced from the beam passing plane of the first member F1, A1. Preferably both electrode members are cup-shaped and nested together in close contact, with a bent-over burr portion 5B, 6B around the periphery of the common hole HH5, HH7 in the second member F2, A2 spacing the respective beam passing planes. Preferably also, both electrodes G5 and G6 are of this construction with the independent holes in electrode G5 being vertically elongated, Fig 3A, while those in electrode G6 are horizontally elongated, Fig. 3B (not shown). <IMAGE>

Description

INLINE TYPE ELECTRON GUN FOR COLOR CATHODE RAY TUBE The present invention relates to an electron gun for a color cathode ray tube, and particularly to an improved electron gunfora color cathode ray tube, in which the electrodes of the main lens means are improved, and consequently, the beam characteristics are improved, so that a cathode ray tube capable of producing good quality images should be realized.

An inline type electron gun is constituted such that three electron beams are caused to advance along paths on substantially the same plane, and the electrons emitted from three cathodes are focused by means of a plurality of electrodes having respectively three inline type beam passing holes, ultimately making the beams focused on the screen. A dynamic deflecting magnetic field is established between the electron gun and the screen for determining the landing positions of the beams, and this magnetic field is formed by a deflecting yoke to which horizontal and vertical deflecting signals are supplied, and which is capable of sequentially deflecting the beams onto the whole surface of the screen.

When electron beams advance toward the screen after having departed from the electron gun, and are deflected by the deflecting magnetic fields, the electron beams are distorted by non-uniform vertical and horizontal magnetic fields, and particularly the distorsions are outstanding during the periods when the beams are scanning on the peripheral portions of the screen. Due to such distorsions of the electron beams, laterally elongated beam spots may be formed on the screen.

Such a trend of the deflection aberrations is improved by the electron gun which is disclosed in U.S. Patent 4,558,253, and which, as illustrated in Figure 1, includes a cathode K, a control grid G1, a screen grid G2, and electrodes G3,G4,G5,G6. Particularly, the beam passing planes of the electrodes G5r, G6 which constitute a major lens are respectively provided with recesses 5R,6R at the centres thereof, while three beam passing holes 5H,6H having burr portions 5B,6B are provided at the bottom thereof.

Accordingly, a complex electric field is formed between the electrodes G5r, and G6, and consequently, three major lenses having large diameters and with reduced spherical aberrations are formed, while the peripheral major lenses are formed in an asymmetrical manner, thereby realizing a lowering effect for the deflection aberrations of the peripheral electron beams.

However, in the major lens formed by the electrodes G5r, G6, a focusing difference occurs between the vertical and horizontal directions, with the result that the focus characteristics are lowered, and that there is a likelihood of an increase of the spherical aberrations.

Further, the electrodes G5r, G6 are complicated in their structures, and therefore, the manufacturing process becomes fastidious. Particularly, the portions requiring a high processing precision, i.e., the beam passing holes and the rims around them,undergo plastic deformations during the performing of the press works, with the result that high stresses are concentrated on the portions where the deformations have occurred, thereby making it liable to cause the lowering of the processing precision. Further, depending on the circumstances, partial disruptions can occur, thereby bringing a failure to the manufacturing of the electrodes.

Therefore it is the object of the present invention to provide an inline type electron gun for a color cathode ray tube, in which the structure is improved such that the manufacturing should become convenient, and the focusing characteristics should be improved, thereby upgrading the resolution of the screen.

In achieving the above object the inline type electron gun fora offi*de ray tube according to the present invention comprises; a triode means consisting of a cathode, a control grid and a screen grid; and a main lens means consisting of a plurality of electrodes, characterized in that at least one of the final focus electrode and the anode forming a major lens of the main lens means consists of: a first member with three independent beam passing holes formed on the beam passing plane thereof; and a second member with a common beam passing hole formed on the beam passing plane thereof, which is disposed separated by a certain distance from the beam passing plane of said first member.

The electrode consisting of two members and for forming the major lens is very convenient to manufacture.

Particularly, because the beam passing holes are formed in vertically elongate and laterally elongate shapes, the electron beams passing through these holes become vertically elongate to form normally circular beam spots upon arrival at the screen, thereby improving the resolution of the screen to a great degree.

The above object and other advantages of the present invention will become more apparent by describing in detail by way of example a prefrrred embodiment of the present invention with reference to the attached drawings in which: Figure 1 is a schematic partly sectional view of the conventional inline type electron gun having a major lens consisting of asymmetrical electric fields; Figure 2 is a schematic partly sectional view of the preferred embodiment of the electron gun according to the present invention; Figure 3A is a perspective view of a focus electrode for forming the major lens adopted in the electron gun according to the present invention as shown in Figure 2; Figure 3B is a perspective view of an anode for forming the major lens adopted in the electron gun of the present invention as shown in Figure 2;; Figure 4A illustrates the controlling of the electron beams in the vertical direction in the electron gun of the present invention; and Figure 4B illustrates the controlling of the electron beams in the horizontal direction in the electron gun of the present invention.

Figure 2 illustrates an electron gun provided with electrodes improved according to the present invention. As in the case of the usual electron gun, this electron gun consists of a cathode K, control grid G1, a screen grid G2, and a plurality of electrodes G3,G4,G5,G6. The electrode G5 is a focusing electrode assembly on which a high potential focus voltage is applied, and this electrode assembly consists of: a prefocus electrode G5f for forming a prefocus lens in cooperation with the electrode G4; and a major focus electrode G5r for forming a major focus lens in cooperation with the electrode G6.

As shown in Figure 3A, the major focus electrode (to be called hereinafter focus electrode G5r) consists of: a cup shaped first member F1 having three vertically elongate rectangular beam passing holes VH5 therein, and provided with skirt F1S; and a cup shaped second member F2 with a single laterally elongate beam passing hole HH5 formed therein and provided with a skirt F2S. The edge of the second member around the beam passing hole HH5 is provided with a burr portion 5B in such a manner that the end of the burr portion 5B should be contacted with the beam passing plane of the first member. Meanwhile, the skirt F1S of the first member F1 and the skirt F2S of the second member F2 are made to closely contact each other.

The electrode G6 on which the highest anode voltage is applied consists of a first member Al and a second member A2 which are cup-shaped, and similar in their shapes to the first and second members F1,F2 of said electrode G5r. Here, the skirt A1S of the first member F1 and the skirt A2S of the second member A2 also closely contact each other. The beam passing plane of the first member Al is provided with three laterally elongate beam passing holes HH6 which form asymmetrical quadrupole lenses in cooperation with the three vertically elongate rectangular beam passing holes VH5. The second member A2 is provided with a burr portion 6B along the circumference of the beam passing hole HH7 in such a manner that the end of the burr portion 6B should contact with the beam passing plane of the first member Al.

The electron gun of the present invention constituted as above enables to obtain a correction effect for the deflection aberrations which are originating from the large diameter asymmetrical lens formed between the electrodes G5r,G6. Further, improved focus characteristics can be expected from the asymmetrical quadrupole lenses which are formed between the beam passing holes VH5,HH6 of the first members of the electrodes G5r,G6.

The control state of the electron beams realized through the electrodes G5r,G6 in the vertical direction is as shown in Figure 4A. That is, when the electron beams pass through the first member F1 of the electrode G5r, the electron beams receive weak focusing forces in the vertical direction, while, when they pass through the first member Al of the electrode G6, they receive strong diverging forces in the vertical direction.

The control state of the electron beams in the horizontal direction is as shown in figure 4B. That is, when the electron beams pass through the first member F1 of the electrode G5r, they receive strong focusing forces in the horizontal direction, while, when they pass through the first member Al of the electrode G6, they receive weak diverging forces in the horizontal direction.

Thus the electron beams are controlled in different ways in the vertical and horizontal directions, in such a manner that the electron beams are vertically elongated during the passing through the major lends, so that they should form substantially normal circular beam spots upon landing on the screen owing to the influence of the deflection aberrations caused by the deflecting magnetic fields.

As described above, the electron gun according to the present invention is provided with major lens-forming electrodes which are divided respectively into the first and second members which are simple and convenient to manufacture, and therefore, the control errors for the electron beams originating from the manufacturing (processing) errors can be reduced to a great degree.

That is, the first members Fl,A1 and the second members F2,A2 of the respective electrodes are shaped like a cup, and the skirts of them closely contact each other, with the result that the relative positional errors between the beam passing holes VH5,HH6 of the first members F1,A1 and the beam passing holes HH5,HH7 of the second members F2,A2 are minimized. Further, the gaps between the pairs of the beam passing holes are decided by the height of the burr portions 5B,6B, and therefore, the widths of the spaces between the beam passing holes can be adjusted.

The electron gun of the present invention constituted as described above is easy to manufacture and high in its assembling precision, as well as making it possible to expect an upgrading of the focus characteristics of the electron beams through the major lens consisting of a large diameter lens and a quadrupole lens. Therefore, the result is brought that the product defect rate is lowered, and the quality of the cathode ray tube is improved.

Claims

1. An inline type electron gun for a cathode ray tube comprising: a triode means consisting of a cathode, a control grid, and a screen grid; and a main lens means consisting of a plurality of electrodes, characterized in that at least one of a final focus electrode and an anode forming a major lens of said main lens means consists of: a first member with three independent beam passing holes formed through the beam passing plane thereof; and a second member with a common beam passing hole formed on the beam passing plane thereof, which is disposed separated by a certain distance from the beam passing plane of said first member.

2. An inline type electron gun for a cathode ray tube as claimed in claim 1, wherein a burr portion is formed along the edge of said second member and around said common beam passing hole, in such a manner that said burr portion has a certain height, is directed toward the beam passing plane of said first member.

3. An inline type electron gun for a cathode ray tube as claimed in claim 2, wherein said burr extends into contact with said first member.

4. An inline type electron gun for a cathode ray tube asclaSedin claim1 2 or 3wherein the edges of the beam passing planes of said first and second members are respectively provided with a skirt, in such a manner that said skirts of said first and second members closely contact each other.

An An inline type electron gun for a cathode ray tube as claimed in claim 1, 2, 3 or 4, wherein the focus electrode forming a major lens of said main lens means consists of: a first member with three independent vertically elongate beam passing holes formed on the beam passing plane thereof; and a second member with a laterally elongate common beam passing hole formed on the beam passing plane thereof, which is separated by a certain distance from the beam passing plane of said first member; and the anode forming said major lens in cooperation with said focus electrode consists of: a first member with three independent laterally elongate beam passing holes formed on the beam passing plane thereof; and a second member with a single laterally elongate common beam passing hole formed on the beam passing plane thereof, which is separated by a certain distance from the beam passing plane of said first member.

6. An inline type electron gun for cathode ray tube, substantially as hereinbefore described with reference to Figures 2 to 4B of the accompanying drawings.