JPS6149783B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to means for improving the roundness of a beam spot of an electromagnetic focusing cathode ray tube.

FIG. 1 is a longitudinal sectional plan view showing an example of an electromagnetic focusing cathode ray tube developed by the inventor and which forms the basis of the present invention. This cathode ray tube has three electron guns 1,
This is a so-called in-line color cathode ray tube in which tubes 2 and 3 are arranged horizontally, and is a planar view of the tube, taken along the horizontal center plane in the tube axis direction. In the figure, 4 is a neck portion of the cathode ray tube, 5 is a cylindrical permanent magnet provided around the neck portion 4, 6,
7 is a magnetic piece with high magnetic permeability, and 8 is a fluorescent surface.

FIG. 2a is a plan view showing the neck portion 4 of the in-line color cathode ray tube shown in FIG. 1 on an enlarged scale, and FIG. A cross-sectional view is shown.

The operation of the old electromagnetic focusing cathode ray tube to which the improvements of the present invention are to be made will be described below. Electron beams 9b and 9 are emitted at a constant divergence angle from the horizontally arranged center electron gun 2 and both side electron guns 1 and 3.
a, 9c pass through the small holes 10b, 10a, 10c provided in the magnetic pieces 6 and 7, respectively, and reach the fluorescent surface 8. On the other hand, the magnetic pieces 6 and 7 absorb the magnetic velocity generated inward from the cylindrical permanent magnet 5, and it is equivalent to magnetizing the magnetic piece 6 to the S pole and the magnetic piece 7 to the N pole. Therefore, a focused magnetic field (see FIG. The electron beams passing through the small holes are each subjected to a focusing action.

However, as shown in FIG. 2b, the small holes 10a, 10b, 10c on the magnetic piece 7 are structurally asymmetrical in the X and Y directions (although there are adjacent small holes in the X direction). , there is no magnetic field in the Y direction), the strength of the magnetic field is different in the X direction, and is larger in the Y direction. When the magnetic field strength is measured for the central small hole 10b, it is found that the magnetic field strength in the Y direction is about 10% stronger than that in the X direction. Similarly, the strength of the small holes on the other sides differs in the XY directions. As a result, the electron beams 9a, 9b, 9c are
Since the focusing forces are different in the direction and the Y direction, the beam spot will not be a right circle, and if an optimal focusing spot in the X direction is created, the beam spot shape will be elongated in the Y direction.

FIG. 3 shows the shape of the beam spot when it reaches the fluorescent surface 8 after passing through the conventional magnetic pieces 6 and 7 mentioned above. Since the beam spot is rotated in the direction of the arrow, the flat direction is rotated and reflected on the fluorescent surface. Generally, when a beam spot is elongated, it is not preferable because not only the resolution in the elongated direction is significantly degraded, but also the peripheral focus is greatly affected.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electromagnetic focusing cathode ray tube which eliminates the above-mentioned drawbacks of the prior art and reduces deterioration in resolution due to elongation of the beam spot.

In order to achieve this objective, the present invention makes the hole diameter of each small hole provided in a piece of high magnetic permeability magnetic material smaller in the direction perpendicular to the arrangement direction (vertical direction) than in the arrangement direction (horizontal direction) of each small hole. ) is made larger so that the focusing magnetic field in the arrangement direction and the direction perpendicular to each small hole are equal to each other.

FIG. 4 is a diagram showing the main parts of an embodiment of the present invention.
is a longitudinal sectional plan view of the neck portion, and b is a cross-sectional view of the neck portion. Items with the same content as in Figure 2 are given the same numbers. Note that in the comparative configuration of figures a and b, the horizontal direction is the X direction and the vertical direction is the Y direction, but in the paper, they are shown rotated by 90 degrees in XY.

In the embodiment shown in FIG. 4, the difference in structure from the conventional example shown in FIG. axis, direction perpendicular to the arrangement direction (Y
The reason is that the shape is an ellipse with the long axis in the direction In this embodiment, the shape is an ellipse, but the shape is not limited to this, and the point is that the diameter of each small hole in the perpendicular direction is made larger by an appropriate amount than the diameter in the arrangement direction. By doing this, the magnetic field strength is almost the same in the elliptical small cylindrical region created by each of the elliptical small holes 11a, 11b, and 11c of the magnetic pieces 6 and 7 in the direction in which the small holes are arranged and in the direction perpendicular thereto. is obtained, and the shape of the electron beam reaching the fluorescent surface 8 becomes a perfect circle.

The principle of the present invention having such a configuration will be explained in detail based on experiments. FIG. 5a is a longitudinal cross-sectional plan view of a one-beam electromagnetic focusing cathode ray tube, and FIG. 5b is a cross-sectional view taken along the line B--B in FIG. The same parts as in FIG. 2 are given the same numbers. The small hole 10 in FIG. 5b is a perfect circle, its center is concentric with the magnetic piece 7', and its diameter is r. Also, the outer diameter of the magnetic piece 7' is r ₀
shall be. The same applies to the magnetic piece 6'.

Now, using these magnetic pieces 6' and 7', the magnetic flux density emitted from the permanent magnet 5 is made constant, and the relationship between the hole diameter r of the small hole 10 and the focused magnetic flux density in the tube axis direction at its center is expressed. Obtained experimentally. The solid line 15 in FIG. 6 is a characteristic diagram showing the results obtained at that time.
B ₀ is the focused magnetic flux density when r/r ₀ =0.25, and B/B ₀ on the vertical axis indicates the focused magnetic flux density normalized by this B ₀ . According to the results obtained in FIG. 6, it can be seen that as the hole diameter r of the small hole 10 is increased, the focused magnetic velocity density in the tube axis direction at the center of the small hole 10 becomes smaller.

On the other hand, in FIG. 5b, the center of the small hole 10 is moved to, for example, the position of the small hole 10' for the side beam shown by the broken line, and an experiment similar to the above is carried out. The relationship between and the focused magnetic flux density 2 in the tube axis direction at the center of the small hole 10' was determined. The results obtained at that time are shown by the broken line 16 in FIG. 6, and it can be seen that there is almost no difference in the characteristics between the solid line and the broken line.

According to the results obtained in these experiments, the focusing magnetic field can be improved by increasing the diameter r of the small hole in both the center beam hole and the side beam hole in the magnetic pieces 6 and 7. It can be seen that becomes smaller. As is clear from these experimental results,
Small holes 11a, 11b, 1 as shown in FIG.
By increasing the hole diameter in the Y direction of 1c, Y
The focusing magnetic field in the direction is weakened and can be made the same as the focusing magnetic field in the X direction. Therefore, the focusing powers in the X direction and the Y direction of the electron beams passing through the magnetic pieces 6 and 7 of the present invention shown in FIG. A nearly perfect circular beam spot shape is obtained.

For example, the outer diameter of the magnetic pieces 6 and 7 is 22.4 mmφ, and the diameter of the small holes 11a, 11b, and 11c in the X direction is 5.5 mm.
If φ, the hole diameter in the Y direction is 6.7, 6.2, and 6.7, respectively.
mmφ, the magnetic flux density was equal in both the X and Y directions, and a nearly perfect circular beam spot was obtained.

7, 8, and 9 are cross-sectional views of the neck portion showing other embodiments of the present invention, and the small holes are hexagonal rectangles, 12a, 12b,
12c, or a rhombus rectangle 1 as shown in Figure 8.
3a, 13b, 13c, or rectangular shapes 14a, 14b, 14c as shown in FIG. In each of the above-mentioned embodiments, when the small hole is made into an ellipse, an almost perfect circular beam spot shape is obtained, which is ideal, but when it is made into other shapes, the roundness deteriorates somewhat. However, it is of a level that poses no problem in practical use. Further, in the present invention, the permanent magnets 5 are arranged outside the neck tube wall 4, but it is clear that the same effect can be obtained even if they are arranged inside the neck tube wall 4.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional plan view showing an example of a conventional electromagnetic focusing cathode ray tube, Fig. 2a is an enlarged explanatory view of the neck part in Fig. 1, and Fig. 2b is an enlarged cross section taken along the line A-A in Fig. 1. Figure 3 shows the shape of the beam spot when the electron beam reaches the phosphorescent surface when a conventional electromagnetic focusing cathode ray tube is used, and Figures 4a and 4b show the shape of the beam spot when the electron beam reaches the fluorescent surface when a conventional electromagnetic focusing cathode ray tube is used. 5 and 6 are diagrams explaining the principle of the present invention, and FIGS. 7, 8, and 9 are diagrams illustrating other parts of the present invention, respectively. FIG. 3 is a cross-sectional view of a neck portion showing an embodiment. 1, 2, 3: Electron gun, 4: Cathode ray tube network part,
5: Permanent magnet for electron beam focusing, 6, 7: Magnetic material piece, 9a, 9b, 9c: Electron beam {11a, 1
1b, 11c, 12a, 12b, 12c, 13
a, 13b, 13c, 14a, 14b, 14c}
Small hole.

Claims (1)

[Claims] 1. A portion of the cathode ray tube in which the focusing magnetic field is distributed, having means for generating a magnetic field within the cathode ray tube to focus a plurality of electron beams emitted from a plurality of electron guns arranged in line within the cathode ray tube. To,
Two pieces of high permeability magnetic material each having a plurality of small holes through which the electron beams pass are provided so as to be separated from each other in the tube axis direction, so that the electron beams passing through these small holes intersect approximately on the target. In the electromagnetic focusing cathode ray tube in which the focusing magnetic field is adjusted, each small hole of the magnetic material piece is formed so that the hole diameter in the direction perpendicular to the arrangement direction is larger than the hole diameter in the direction in which the small holes are arranged, A cathode ray tube characterized in that the focusing magnetic field in each small hole is made equal to the direction in which the holes are arranged and the direction perpendicular thereto.