JPH044685B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electron gun for a cathode ray tube, and more particularly to an electron gun with an improved prefocus system. FIG. 1 is an explanatory diagram of the operation of a conventional electron gun for a cathode ray tube. The electrons emitted from the cathode K1 become an electron beam due to the strong focusing action of the cathode lens formed by K, the first lattice G ₁ 2, and the second lattice G ₂ 3, and first enter the crossover 6. The beam is focused to form a minimum diameter portion here. After passing through the crossover 6, the electron beam diverges, and when passing through the prefocus lens formed by G ₂ and the third grating G ₃ 4, it is focused to some extent, but still It enters the main lens formed by G ₃ and the fourth grating G ₄ 5 in a diverging state, and by the focusing action of this main lens, an image of the crossover 6 is formed on the screen, forming a so-called beam spot. Become. Therefore, the factors that determine the beam spot diameter are the crossover size, cathode lens, prefocus lens, main lens,
Each aberration, space charge effect, lens magnification, etc. must be taken into account. Various cathode lens and prefocus lens systems have been proposed in the past, such as PHILIPS TECHNICAL REVIEW Vol. 18,
1956/57, No.3pp.73-81), Figure 2 a, b, c
The one shown in figure c is written, and the one shown in figure c is
There are more electrodes than those in figures a and b, so due to the design,
It is stated that the greater the degree of freedom in use, the more flexible it is. However, although G ₂ is a joint that belongs to both the cathode lens system and the prefocus lens system, as shown in the figure,
It has a cup-shaped or plate-shaped structure, and when the applied voltage value is determined, in principle, it is possible to change the interval between G ₁ and G ₂ or between G ₂ and G ₃ .
There is no way to change the characteristics of the lens system other than changing the thickness near the hole of each grating pole. For this reason, as shown in the table below, there are restrictions on improving the characteristics of the beam spot diameter, and it is difficult to obtain good image quality.

[Table] It was difficult. For this reason, furthermore, e.g. National Technical Report (National Technical Report)
Technical Report Volume 8 No. 3, July 1960,
(pp. 256-262), a focusing lens was added near _G2 to increase the degree of freedom and improve the focusing effect.
A device as shown in FIG. 3, which can be called a modification of the one shown in FIG. 2c, has been proposed. However, even with the use of such a system, good results were not always obtained. The present invention eliminates the problems of the conventional electron gun and provides a cathode lens and prefocus lens system with a small crossover and few aberrations, which can be obtained mainly by simple modification of _G2 or its vicinity. The purpose is to provide guns. In order to achieve the above object, in the present invention,
The electrode closest to the cathode among the electrodes forming the main lens,
and one or more electrodes among the electrodes arranged between this electrode and the cathode, excluding G ₁ ,
A small-diameter cylindrical protrusion having an electrode hole, so-called a nose, was provided at the bottom of the end. In this way, not only can the number of electrodes be increased as in the electrode systems shown in Figures 2c and 3, but also _G2 , which couples between the cathode lens and the prefocus lens, or sometimes nearby. Since a nose portion is also added to _G3 , the degree of freedom is increased, making it easier to obtain the desired electric field. Moreover, with the current press technology, such nosed electrodes can be mass-produced extremely easily. Increasing the degree of freedom by providing a nose as described above means, in other words, making the cathode lens system and prefocus lens system independent, so the shape of the nose is determined by the mutual influence of both lens systems. It must be set so that it does not reach. In this type of cylindrical electrode, generally, when the electrode diameter is D and the electrode length is L, LD is a condition that the electric field at both ends of the cylinder does not affect the electric field at the other end, and the present inventor also conducted experiments. It has been confirmed that the object of the present invention can be achieved by a nose that meets the above conditions. In the example shown in FIG. 4, by making the protruding length l of the nose equal to or greater than the diameter d of the cylindrical portion, G ₂ effectively converts the G ₂ -1 portion constituting the cathode lens into
The G ₂ -2 part that makes up the prefocus lens is separated into two parts belonging to different systems, and the shape and dimensions suitable for each function can be given relatively freely, so the prefocus lens has very few aberrations. It can be used as a lens, and the condition of the beam spot can be significantly improved. In addition, from the viewpoint of a pre-focus lens system with less aberration, as shown in Fig. 4, an electrode with a nose (for example, G ₂ )
An electrode located on the phosphor screen side facing the
G ₃ ), the opening end facing the electrode having a nose is made into a cylindrical shape, and its diameter D ₃ and the electrode diameter D ₂ on the opposite opening end side of the electrode having a nose are made almost the same, and the lens passes through this lens. It is effective to make the beam paraxial. FIGS. 5 to 7 are other examples of utilizing the nose effect. FIG. 8 shows an embodiment of the present invention. 8th
In the embodiment shown in the figure, the second grating G ₂ is provided with a cylindrical nose G ₂ ′ projecting from the opening end on the third grating G ₃ side, and the third grating G ₉ is cylindrical and By providing a cylindrical nose G ₉ ′ that protrudes from the opening end on the second grating G ₂ side, and making the amount of protrusion of the cylindrical nose G ₂ ′ larger than the diameter of the cylindrical part of the nose, the cathode The lens system and the prefocus lens system are separated. This makes it easy to correct aberrations of the cathode lens system using the prefocus lens system. As explained above, according to the present invention, mainly
Just by making the extremely simple change of adding a nose to G ₂ , you can significantly improve the beam spot condition.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the operation of a conventional electron gun for cathode ray tubes, and Figures 2a and 2b are cross sections of an electron gun electrode equipped with a conventional cathode lens and prefocus lens system consisting of G ₁ , G ₂ , and G ₃ . Figure, Figure 2c, Figure 3 are
A cross-sectional view of a conventional electron gun electrode improved by adding an electrode near _G2 , Figures 4 to 7 are cross-sectional views of an electrode that utilizes the nose effect, and Figure 8 shows an embodiment of the present invention. FIG. 3 is a cross-sectional view of an electrode. 1...Cathode, 3...Second lattice, 4...Third lattice, K...Cathode, _G1 ...First lattice, _G2 ...Second
lattice, G ₃ ... third lattice, G ₄ ... fourth lattice.

Claims (1)

[Claims] 1. A cathode K, a first grating G ₁ , a second grating G ₂ , a third grating G ₃ and a fourth grating G ₄ , wherein the cathode K, the first grating G ₁ and the second grating G ₂ constitutes a cathode lens system forming a crossover 6, the second grating G ₂ and the third grating G 3 constitute a prefocus lens system, and the third grating G _{3 and the fourth grating G 3 constitute} a prefocus lens system. In a cathode ray tube electron gun in which G ₄ constitutes a main lens, the second grating G ₂ has a cylindrical nose G ₂ ′ projecting to the opening end on the third grating G ₃ side, and the third grating G ₃ is cylindrical and has a cylindrical nose G ₃ ′ that protrudes from the open end on the second lattice G ₂ side, and the protrusion amount of the cylindrical nose G ₂ ′ of the second lattice is expressed as An electron gun for a cathode ray tube, characterized in that the cathode lens system and the prefocus lens system are separated by making the diameter of the cylindrical part larger than or equal to the diameter of the cylindrical part.