JPH0158620B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron gun for a color picture tube, and more particularly to an electron gun that can improve the uniformity of focus in the center and periphery of a phosphor screen of a color picture tube. .

As shown in FIG. 1, the color picture tube 10 uses a deflection yoke 14 to deflect three electron beams 13 emitted from an electron gun 12 enclosed in a glass envelope 11 along a gun axis Z, and a shadow mask 15. By scanning the phosphor screen 16 through the phosphor screen 16, a color image is reproduced on the phosphor screen 16.

The three electron beams 13 mentioned above are generally arranged in a line on the horizontal axis The vertical deflection magnetic field is a strong barrel-shaped non-Saiichi magnetic field, and the magnetic field is a so-called self-concentration type magnetic field that converges the three electron beams 13 around the periphery of the phosphor screen 16.

When an electron beam passes through such a non-Saichi magnetic field, the electron beam is distorted by the deflection magnetic field because it has a certain finite cross-sectional area, and the electron beam spot on the phosphor screen 16 is distorted as shown in FIG. It is well known that the shape is distorted as shown in the figure. That is, in FIG. 2, the circular electron beam spot 23 ₁ at the center becomes a horizontally elongated electron beam spot 23 ₂ at the end 21 in the horizontal axis X direction.
In the diagonal section 22, there is a horizontally elongated electron beam spot 23 ₃
It consists of a vertically long halo portion 24.

As a result, the resolution around the phosphor screen 16 deteriorates, and the uniformity of focus is impaired. In particular, as the deflection angle becomes wider, such as from 100° to 110°, the uniformity of focus deteriorates significantly, which has become a serious technical problem.

To solve this problem, the cross-sectional shape of the electron beam should be made elliptical before entering the deflection magnetic field.
What is necessary is to cancel the distortion received from the deflection magnetic field. Various structures are known as such technology, for example, Japanese Patent Application Laid-open No. 54-85666,
This is disclosed in Publication No. 54-85667 and Japanese Patent Publication No. 18021/1983.

Of these, the techniques disclosed in the first two, that is, JP-A-54-85666 and JP-A-54-85667, are based on the shape of the through-hole portion of the first grid electrode of each electrode of the electron gun. is made non-rotationally symmetrical with respect to the gun axis, and the cross-sectional shape of the resulting electron beam is made into a desired shape. However, in such disclosed examples, the shape of the through-hole portion of the first grid electrode becomes complicated, and there are disadvantages such as problems in machining and relatively high costs. Furthermore, the first grid electrode of the electron gun has a large effect on the electron emission characteristics from the cathode, and has drawbacks such as deterioration of cut-off characteristics, so that it cannot necessarily be said to be an effective technique.
Furthermore, the latter technique disclosed in Japanese Patent Publication No. 18021/1980 makes the shapes of the through-holes of the first grid electrode non-rotationally symmetric among the electrodes of the electron gun, and the second grid electrode and the third An auxiliary electrode consisting of two plates arranged opposite to the grid electrode is provided, and the shape of the through hole of the auxiliary electrode is rotationally symmetrical with respect to the one closer to the second grid electrode,
A desired cross-sectional shape of the electron beam can be obtained by configuring the portion near the third grid electrode to be rotationally non-symmetrical. However, in this disclosed example, the number of electrode components increases by at least one, making the cost of the electron gun relatively high, and it is difficult to say that this is necessarily an effective means from an industrial perspective.

The present invention has been made in view of the above-mentioned drawbacks of the conventional electron gun, and uses simple means to make the cross-sectional shape of the electron beam into a desired shape, and to adjust the focus between the center and the periphery of the phosphor screen of a color picture tube. An object of the present invention is to provide an electron gun for a color picture tube that can improve the uniformity of color picture tubes.

First, the structure and operation of the electron gun for a color picture tube according to the present invention will be explained with reference to FIG.

That is, the color picture tube electron gun 30 generally includes at least a cathode 30k, a first grid electrode 31, a second grid electrode 32, and a third grid electrode 33 arranged on the gun axis Z.
and a fourth grid electrode 34. The typical voltage applied to each electrode is approximately 30k for the cathode.
150V is applied to the first grid electrode 31, approximately 5000V is applied to the second grid electrode, and approximately 25000V is applied to the fourth grid electrode 34. Thermionic electrons emitted from the cathode 30k form a crossover 35 by the cathode lens formed by the cathode 30k and the first grid electrode 31, and then diverge as an electron beam 39, and then pass through the second grid electrode 32 and the third grid electrode. The phosphor screen 16 is prefocused by a prefocus lens 36 formed by the third grid electrode 33 and the fourth grid electrode 34, and finally focused by the main lens 37 formed by the third grid electrode 33 and the fourth grid electrode 34. An electron beam spot 23 is formed on the top.

Here, the angle 38 at which the electron beam 39 passes through the prefocus lens 36 and looks into the main lens 37 is called the divergence angle, and is a major factor determining the cross-sectional shape of the electron beam 39. That is, if the prefocus lens 36 is made stronger, the divergence angle 38 becomes smaller, and therefore the electron beam 39 that occupies the main lens 37 becomes smaller.
Since the proportion of the electron beam is reduced, the aberration component received from the main lens 37 is reduced, and a good electron beam spot can be obtained.

The electron gun for a color picture tube of the present invention is designed to control the divergence angle in the horizontal axis X direction and the vertical axis Y direction of the color picture tube by devising the prefocus lens 36 described above. That is, an electron beam spot 23 at the periphery of the phosphor screen as shown in FIG.
This is because the shape _{No. 3} is underfocused (insufficient focusing) in the horizontal axis X direction and overfocused (overfocused) in the vertical axis Y direction. Therefore, to correct this phenomenon, the horizontal axis
Relative overfocus in direction, vertical axis Y
In the direction, it may be relatively under-focused.

In order to satisfy this requirement, the divergence angle in the horizontal axis X direction may be made relatively smaller than the divergence angle in the vertical axis Y direction. For this purpose, the prefocus lens that acts in the vertical axis Y direction should be relatively strong, and the prefocus lens that acts in the horizontal axis X direction should be relatively weak.

Next, one embodiment of the electron gun of the present invention will be described with reference to FIGS. 4 and 5.

That is, the electron gun 40 includes a cathode 40k, a first grid electrode 41, and a second grid electrode 4 arranged along the gun axis Z.
2. Consisting of a third grid electrode 43 and a fourth grid electrode (not shown), the through hole 4 at the bottom of the third grid electrode 43
4, that is, the through-hole portion 44 facing the second grid electrode 42
A rectangular cylindrical semi-transparent hole 46 as a first basic shape bored from a position close to the second grid electrode 42 toward the inside of the third grid electrode 43; It is composed of a cylindrical semi-transparent hole 45 as a second basic shape that is bored on the fourth grid electrode side in communication with the semi-transparent hole 46 . The rectangular cylindrical semi-transparent hole 46 and the cylindrical semi-transparent hole 45
The center of is on the gun axis. Further, the long axis 47 of the semi-transparent hole 46 on the rectangular tube is in the same direction as the horizontal axis X of the color picture tube. Note that the cylindrical semi-transparent hole portion 45 is located at a position away from the second grid electrode 42, that is, inside the third grid electrode 43.

By providing such a through hole 44 in the third grid electrode 43, the function of the prefocus lens formed between the second grid electrode 42 and the third grid electrode 43 is relatively strong in the vertical axis Y direction. It becomes relatively weak in the horizontal axis X direction, and a desired divergence angle can be obtained. That is, as shown in FIG. 6, the spots on the phosphor screen 16 of the color picture tube incorporating the electron gun of this embodiment are a slightly vertically long spot 531 at the center of the screen 16, and a slightly horizontally long spot ₅₃₁ at the periphery. The spot 532 becomes a spot ₅₃₂ , and the spot ₅₃₃ has a substantially perfect circular shape in the middle. Therefore, the electron beam spot 5 in the center of the phosphor screen 16
Since the _3.1 shape is a little taller than the conventional one, the resolution in the vertical axis Y direction will be slightly degraded, but the shape of the beam spot at the periphery has been greatly improved, so the entire surface of the phosphor screen can be covered. The uniformity of focus is greatly improved.

Next, to explain a specific example of this embodiment, in FIGS. 4 and 5, the long axis 47 of the rectangular cylindrical semi-transparent hole 46 is 3.0 mm, and the short axis 48 perpendicular to this long axis is 3.0 mm. 1.5
mm, the depth 49 in the tube axis Z direction is 0.7 mm, the cylindrical semi-transparent hole 45 has a diameter of 1.5 mmφ and shares the central axis with the rectangular cylindrical semi-transparent hole 46, and the depth 50 is 0.3 mm. By setting the total thickness of the bottom portion ₄₃₁ of the third grid 43 to 1.0 mm, it was possible to obtain a spot of extremely high quality.

Next, another embodiment of the electron gun of the present invention will be described with reference to FIG.

That is, the through-hole portion 64 at the bottom of the third grating electrode 63 facing the second grating electrode 62 is constituted by two rectangular cylindrical semi-through holes 65 and 66, and is located closest to the second grating electrode 62. A first rectangular cylindrical semi-transparent hole 66 that is a first basic shape located in the area and a second rectangular shape that is a second basic shape that is continuous with the first rectangular cylindrical semi-transparent hole 66. The respective long axes 67 and 68 of the semi-transparent hole portion 65 are provided so as to be in the same direction as the horizontal axis X direction and the vertical axis Y direction. Also in this embodiment, the uniformity of the focus between the center and the periphery of the phosphor screen is greatly improved, as in the previous embodiment.

The first basic shape and the second basic shape are mainly concerned with the shape of the opening, and therefore are not limited to a cylindrical shape. It goes without saying that the opening may be formed to transition from the opening in the second basic shape to the opening in the second basic shape.

As described above, in the electron gun of the present invention, the through hole formed at the bottom of the third grid electrode has the first basic shape in which the opening at the closest position facing the second grid electrode has the first basic shape. It is characterized in that the semi-transparent hole part and the second semi-permeable hole part connected thereto and having a second basic shape are bored as one body so as to form different shapes. In the case of an electron gun disclosed in Publication No. 55-18021, in which the circular hole and the rectangular hole are formed in separate members and then fixed together by welding, the accuracy of assembling the two members is high. It goes without saying that it is possible to align with much higher precision than those that still have the problem of , and is mechanically superior as well.

Note that the aspect ratio of the spot shape of the electron beam on the phosphor screen of the color picture tube is determined by the long axis 47 of the opening of the rectangular cylindrical semi-transparent hole 46 shown in FIGS. 4 and 5 and the long axis shown in FIG. It depends on the dimensions of the shafts 67, 68. That is, when the deflection angle is large, for example 110 degrees, and the distortion of the spot shape of the electron beam in the peripheral area is large, the spot shape of the electron beam can be easily corrected by increasing the dimensions of the long axes 47, 67, and 68. is possible.

In the embodiment described above, at least the opening of the rotationally asymmetric semi-transparent hole is made into a rectangular shape, but the shape is not limited to this, and any other shape having a major axis and a minor axis may be used. The example described a bipotential electron gun, but other types of electron guns,
For example, it goes without saying that the same effect can be obtained by applying the present invention to the opening of the third grid electrode of an electron gun of a type called a unipotential type electron gun or a composite type electron gun.

As described above, by devising the shape of at least the opening of the through-hole at the bottom of the third grid electrode, the electron gun of the present invention is simple and accurate, and has no adverse effect on the electron emission characteristics of the cathode. It is possible to significantly improve the focus uniformity between the center and the periphery of the phosphor screen of the picture tube without giving any problems.

[Brief explanation of drawings]

FIG. 1 is a simplified cross-sectional view of a color picture tube, FIG. 2 is an explanatory diagram showing a beam spot on a phosphor screen by a conventional electron gun for a color picture tube, and FIG. 3 is a configuration of an electron gun for a color picture tube according to the present invention. 4 and 5 are views showing essential parts of an embodiment of the electron gun for color picture tube of the present invention, FIG. 4 is a sectional view, FIG. 5 is a perspective view, FIG. 6 is an explanatory view showing the beam spot on the phosphor screen by the electron gun of FIGS. 4 and 5, and FIG. 7 is a perspective view showing the main part of another embodiment of the electron gun for a color picture tube according to the present invention. It is a diagram. 32, 42, 62...second grid electrode, 33, 4
3, 63...Third grid electrode, 44, 64...Through hole part,
45, 65...Second semi-transparent hole portion having the second basic shape, 46,66...First hole portion having the first basic shape
semi-transparent hole.

Claims (1)

[Claims] 1. In a color picture tube electron gun that is configured of at least a cathode, a first grid electrode, a second grid electrode, a third grid electrode, and a fourth grid electrode and that emits a plurality of electron beams, the second grid electrode of the third grid electrode A plurality of through-holes through which the plurality of electron beams pass are formed in a bottom portion facing the grid electrode, and at least one of the plurality of through-holes extends from a position close to the second grid electrode to the third grid. A first opening facing inwardly of the electrode having at least the first basic shape;
a second semi-transparent hole communicating with the first semi-hole to form the transparent hole and having at least an opening having a second basic shape; The basic shape of the color picture tube is approximately rectangular or elliptical with its long axis along the horizontal axis of the color picture tube;
An electron gun for a color picture tube, wherein the second basic shape is circular or approximately rectangular or elliptical having a long axis along the vertical axis of the color picture tube.