JPH0160893B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron gun for forming an electron beam spot on the fluorescent surface of a cathode ray tube.

FIG. 1 shows an example of the electrode arrangement of a conventional electron gun, which is a structure already filed by the applicant of the present invention. At the left end of the figure, a heater 1 and a cathode 2 are connected to an insulating bead glass 4 via a cathode support 3.
is fixed inside. On the right side of the cathode 2, a first grid electrode 10, a second grid electrode 20, a third grid electrode 30, a fourth grid electrode 40, and a fifth grid electrode 50 are provided in order with a small gap between them. ing. The first grid electrode 10 and the second grid electrode 20 are formed by fixing thin plates with small holes 11 and 21 in the center to the inner surface of bead glass. 3rd grid 30
consists of a third grid bottom electrode 31, a third grid cup electrode 32, and a third grid inner electrode 33 provided in between, and the fourth grid electrode 40 is composed of fourth grid cup electrodes 41, 4.
A fifth grid electrode 50 is formed by fixing a fifth grid cup electrode 51 and a fifth grid inner electrode 52 to a shield cup 53. These three sets of electrodes 30, 4
0,50 has cylindrical parts 32a, 33a, 4 on the inside thereof.
1a to 44a, 51a, and 52a are formed, and these cylindrical portions 32a to 52a have the same inner diameter D, and are almost perfect cylinders in terms of electron optics, that is, the length of the cylindrical portion of each electrode 30, 40, and 50 is It has dimensions of 1.0D or more, and the beam spot shape is kept almost perfectly circular. The third grid electrode 30 and the fifth grid electrode 50 are maintained at the same potential.

By the way, in the conventional electron gun having such a configuration, it is necessary to make the length of the cylindrical portion of the third to fifth grid electrodes 30, 40, 50 almost completely cylindrical, and for this purpose, the fourth grid inner electrode 43, 44 and the fifth grid inner electrode 52 are essential;
Due to the electrode structure, the number of parts is large and the cost is high.

The present invention has been made in view of these circumstances, and the cylindrical portion of both the intermediate grid electrode and the grid electrode on the phosphor surface side is made smaller than the length of the cylinder, which is considered to be an almost perfect cylinder in terms of electron optics. It is an object of the present invention to provide an electron gun in which the structure of the fourth and fifth grid electrodes can be simplified without substantially impairing the roundness of the beam spot shape, and the cost can be reduced.

Embodiments of the present invention will be described below based on the drawings.
FIG. 2 shows an apparatus for obtaining basic data of the present invention, which includes a heater 1, a cathode 2, a cathode support 3, a bead glass 4, and the bottom electrodes of the first and second grid electrodes 10, 20 and the third grid electrode 30. 31 and cup electrode 32, cup electrodes 41 and 42 of fourth grid electrode 40, cup electrode 51 of fifth grid electrode 50, and shield cup 5.
3 is formed in the same manner as in FIG. The inner electrode 34 of the third grid electrode 30, the inner electrodes 45, 46 of the fourth grid electrode 40, and the inner electrode 54 of the fifth grid electrode 50 have a stepped portion 35,
47, 48, 55, and the third grid electrode 30
The length _h3 of the cylindrical portions 32a and 34a of the cylindrical portion 4 of the fourth grid electrode 40 on the third grid electrode 30 side.
1a, 45a length h ₄₁ and the fifth grid electrode 5
Each of the electrodes is formed into a special electrode so that the length h ₄₂ of the zero-side cylindrical portions 42a, 46a and the length h5 of the cylindrical portions 51a, 54a of the fifth grid electrode ₅₀ can be freely changed. Cylindrical portions 32a, 34a, 4
1a to 54a are almost coaxial and have the same inner diameter D.
has.

FIG. 3 shows the third grid electrode 30 in FIG.
The length h ₃ of the cylindrical portions 32a, 34a, the cylindrical portion 41a on the third grid electrode side of the fourth grid electrode 40,
45a length _h41 , the length _h42 of the cylindrical parts 42a and 46a on the fifth grid electrode 50 side, and the length _h5 of the cylindrical parts 51a and 54a of the fifth grid electrode 50,
The relationship between the beam spot and the aspect ratio is experimentally determined and illustrated. According to FIG. 3, it can be seen that if only _h5 is reduced, the beam spot becomes vertically elongated, and if at least one of _h41 and _h42 is reduced, the beam spot becomes horizontally elongated.

Cathode cylindrical portion 41 of fourth grid electrode 40
The beam aspect ratio is K ₄₁ when the lengths of a and 45a are h ₄₁ , and the beam aspect ratio is h 42 when the lengths of the cylindrical portions 42 a and 46 a on the fluorescent surface side of the fourth grid electrode 40 are h ₄₂ . K ₄₂ , when the length of the cylindrical portions 51a and 54a of the fifth grid cup electrode 50 is h ₅ and the beam aspect ratio is K ₅ , in order to keep the aspect ratio of the beam spot shape to be a perfect circle of 1.1 to 0.9. In this case, the value of the above-mentioned aspect ratio product K ₄₁ ×K ₄₂ ×K ₅ only needs to be 1.1 to 0.9, and in this case, the beam spot shape finally becomes a nearly perfect circle and appears on the fluorescent surface.

Therefore, based on the graph shown in FIG.
By appropriately combining the lengths h ₄₁ , h ₄₂ and h ₅ of 1a to 54a, a beam spot shape with good roundness can be obtained. For example, h ₅ = 0.23D, h ₄₁ = 0.5D, h ₄₂ =
If 0.64D, K ₅ = 1.52, K ₄₁ = 0.8, K ₄₂ = 0.82
Since the aspect ratio of the beam spot shape appearing on the fluorescent surface is 1.0, a good beam spot shape can be obtained. Further, when the cylindrical portions 41a and 45a on the cathode side of the fourth grid electrode 40 are made into almost perfect cylinders, that is, when h ₄₁ =1.0D, K ₄₁ =
1.0, so the length of the other cylinder is h ₄₂ = 0.37D,
If h ₅ =0.23D, then K ₄₂ =0.66 and K ₅ =1.52, and the product K ₄₁ ×K ₄₂ ×K ₅ is 1, so a good beam spot shape can still be obtained. Furthermore, the cylindrical portion 42 on the fluorescent surface side of the fourth grid electrode 40
a, 46a are almost perfect cylinders, that is, h ₄₂ =
If it is 1.0D, K ₄₂ = 1.0, and the other cylinder 41
The length of a, 45a, 51a, 54a is h ₄₁ =
By setting 0.37D, h ₅ = 0.23D, K ₄₁ = 0.66,
K ₅ =1.52, and the beam spot shape can be made into a perfect circle.

Cup electrodes 32, 4 generally shown in FIG.
Cylindrical parts 32a, 41a, 42 of 1, 42, 51
Since the dimensions l ₃ , l ₄₁ , l ₄₂ , and l ₅ of a and 51a cannot be set to very large values in terms of processing technology and mass productivity, conventionally the inner electrode 3 as shown in FIG.
3, 43, 44, 52 cylindrical parts 33a, 43a,
By increasing the height of 44a and 52a,
The required cylinder length was obtained. However, by utilizing the results shown in FIG.
The lengths h ₄₁ , h ₄₂ , h ₅ of ~54a do not need to be very large, and the necessary sizes can be secured only with the inner cylindrical dimensions l ₄₁ , l ₄₂ , l ₅ of the cup electrodes 41, 42, 51. This makes it possible to omit the inner electrode.

The embodiment of the invention shown in FIG. 4 is based on such a technical idea, and the two inner electrodes 43 and 44 of the fourth grid electrode 40 and the inner electrode 52 of the fifth grid electrode 50 in FIG. 1 are omitted. It shows the structure of an electron gun.

As is clear from the above description, in the electron gun of the present invention, the length of the cylindrical part of both the intermediate grid electrode and the phosphor side grid electrode is made smaller than the length of the complete cylinder, that is, the inner diameter of the cylindrical part. It is possible to eliminate the need for the fourth grid inner electrodes 43, 44 and the fifth grid inner electrode in FIG. 1 without substantially impairing the roundness of the beam spot, thereby realizing cost reduction by reducing the number of parts.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional explanatory diagram showing an outline of a conventional electron gun, FIG. 2 is a cross-sectional explanatory diagram of an apparatus for obtaining basic data of the present invention, and FIG. 3 is a third grid electrode in the apparatus of FIG. FIG. 4 is a characteristic diagram showing the relationship between the length of the cylindrical portion of the fourth grid electrode and the fifth grid electrode and the aspect ratio of the beam spot. FIG. 4 is a cross-sectional explanatory diagram showing an outline of an embodiment of the present invention. 32... Third grid cup electrode, 34... Third grid inner electrode, 41, 42... Fourth grid cup electrode, 45, 46... Fourth grid inner electrode, 51... Fifth grid cup electrode, 54... Fifth grid cup electrode.
Grid inner electrode, 32a, 34a, 41a,
42a, 45a, 46a, 51a, 54a... Cylindrical portion.

Claims (1)

[Claims] 1. In an electron gun, three sets of grid electrodes having cylindrical parts with the same inner diameter are arranged on the same axis with a gap between them, and both side electrodes of these three sets are held at the same potential. Both the electrode and the fluorescent surface side electrode are composed of only a cup electrode, and the height of the cylindrical portion of the cup electrode is less than or equal to the inner diameter dimension of the cylindrical portion, and the length of the cylindrical portion on the cathode side of the intermediate electrode is Beam aspect ratio when the length is l ₄₁
K ₄₁ , the beam aspect ratio K ₄₂ when the length of the cylindrical portion on the fluorescent surface side of the intermediate electrode is l ₄₂ , and the length of the cylindrical portion of the fluorescent surface side electrode as l ₅ An electron gun characterized in that the value of the product K ₄₁ ×K ₄₂ ×K ₅ of the beam aspect ratio K ₅ is 0.9 to 1.1.