JPH0312421B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetically focused cathode ray tube.

The magnetic focusing method, which uses a magnetic field in the tube axis direction of a cathode ray tube to focus the electron beam, provides better focus characteristics than the conventional electromagnetic focusing method, and is able to achieve better focus characteristics than the conventional electromagnetic focusing method. This has the advantage of not requiring electrodes. Therefore, there is no need to supply high voltage from the stem at the end of the neck side of the cathode ray tube, which improves the reliability of the cathode ray tube, and has the great advantage of eliminating the focus voltage supply circuit. Magnetic focusing methods include methods that use electromagnetic coils and methods that use permanent magnets, but the former has drawbacks such as focusing power, cost, and weight, and in the case of permanent magnets, it is also possible to incorporate them into the neck part. Therefore, it is better to use a permanent magnet in practice. In cathode ray tubes that have multiple electron guns, such as color picture tubes, it is necessary to divide and shape the focusing magnetic field and apply it to each electron gun.
For this purpose, the magnetic field generated by the permanent magnet is concentrated,
Requires magnetic yoke for shaping. However, there are limits to the configuration of the magnetic yoke, and it is not possible to sufficiently shape the magnetic field simply by improving the shape, plate thickness, etc. of the magnetic yoke.

FIG. 1 is a schematic diagram of a conventional magnetically focused color cathode ray tube. 1 and 2 are glass envelope panels and funnels for maintaining the interior in a vacuum;
An electron gun 5 for emitting and controlling three electron beams 4 is enclosed within the neck portion 3 of the funnel 2. Furthermore, a three-color phosphor screen 6 is coated on the inner surface of the panel 1, and a color selection shadow mask 7 is disposed near the screen 6 between the phosphor screen 6 and the electron gun 5. 8 is an omnidirectional device. FIG. 2 is an enlarged sectional view of the electron gun 5 portion of FIG. 1. A permanent magnet 10 for generating a magnetic field and a cylindrical magnetic yoke 11 corresponding to each of the three electron guns are disposed within the cathode ray tube network 3. As shown in FIG. 3, the magnetic yokes 11 for each electron gun are composed of at least two magnetic yokes 11 arranged in the tube axis direction and facing each other. The magnetic field generated by the permanent magnet 10 is concentrated on one side of the magnetic yoke 11, and the magnetic field is concentrated on one side of the magnetic yoke 11, and the magnetic field is concentrated on one side of the magnetic yoke 11, and the magnetic field is concentrated on one side of the magnetic yoke 11.
The electron beam is formed intensively on the electron beam path, and is further concentrated again on the other magnetic yoke to form a permanent magnet 1.
Return to 0. The magnetic field of the gap 12 between the magnetic yokes can be made into a nearly symmetrical magnetic field for each electron gun by adjusting its shape, gap amount, etc. using the opposing cylindrical magnetic yokes, but due to the nature of permanent magnets, it is more infinite than permanent magnets. There are always lines of magnetic force 13 that extend toward the distance.

FIG. 4 shows the magnetic field distribution in the section A-A' in FIG. 3.
That is, at the center of the central electron gun 41 of the three electron guns, there is no magnetic field within the A-A' cross section, whereas
At the center of both side electron guns 42, the magnetic field is directed outward.
Br exists. This outward magnetic field Br is perpendicular to the electron beam passing direction, and the electron beam is subjected to a unidirectional effect. Both side beams receive the deflection effect in opposite directions, and as a result, the three electron beams rotate about the central electron beam. In such a case, it is well known that the convergence characteristics of the three electron beams deteriorate, which is undesirable.

The present invention has been made in view of the above points, and it facilitates the manufacture of a magnetic yoke by minimizing the omnidirectional magnetic field components of both side beams in a permanent magnet, and minimizes the rotational effect of the three electron beams. The present invention provides a magnetically focused color cathode ray tube that achieves magnetic focusing while maintaining good convergence.

The present invention will be explained in detail below.

FIG. 5 is a perspective view of an embodiment of a permanent magnet for three-electron gun magnetic focusing according to the present invention. This permanent magnet 5
1 and 51' each have the shape of a part of a cylinder, the end face of which is arcuate, and permanent magnets 51 and 51'
The end face of the magnet is magnetized to the north or south pole, and two permanent magnets form a very uniform magnetic field inside the magnet.

FIG. 6a shows a cross-sectional view of the arc-shaped permanent magnet 61, and the angle θ is the angle at which the permanent magnet 61 is viewed from the central electron gun 62. FIG. 6b shows the relative intensity distribution of the radial magnetic field component (Br) at the positions of the electron guns 63 on both sides. In this embodiment, the distance between the center and side electron guns was 6.0 mm, the inner diameter of the permanent magnet was about 20 mm, and the outer diameter of the permanent magnet was about 24 mm. In the figure, the relative value of Br and Bz at the center of the permanent magnet is shown using the angle of view θ of the permanent magnet as a parameter.
When θ = 18°, this corresponds to the case where the permanent magnet exists only near the Y-axis in Figure 6a, and Br increases from the center of the permanent magnet toward the Z-axis and reaches its maximum value near the end face of the permanent magnet. It shows that it gradually decreases after that. On the other hand, when θ = 180°, it corresponds to a cylindrical permanent magnet, and in this case, compared to the case when θ = 18°, the Br at the end of the permanent magnet has opposite characteristics, and the polarity changes at a distance. It shows that it has reversed and become very small. Also, in the case of θ=108°, the distribution is similar to that of θ=18°, but the intensity is about 1/3. θ=
Even when comparing 180° and θ=144°, the strength is about 1/3.
That is, by optimally setting the viewing angle θ of the permanent magnet, the Br component that causes beam deflection can be made extremely small. The angle of view θ of the permanent magnet in this example is preferably 100° to 150°.

As described above, by using a magnetic field shaping yoke on a permanent magnet having a predetermined angle of view θ, it is possible to apply a focusing magnetic field with the deflection magnetic field Br as small as possible to each of the three electron guns. A magnetically focused cathode ray tube having good focus characteristics can be obtained without deteriorating the convergence characteristics of the tube.

FIGS. 7 to 9 show other embodiments of the present invention. In FIG. 7, two permanent magnets 70 are arranged above and below the horizontal array line of three electron guns, and the distance between the permanent magnets and the electron guns above and below the central electron gun 71 is larger than the distance between the permanent magnets and the electron guns above and below the central electron gun 71. The permanent magnet-electron gun distance is kept small. That is, the permanent magnet cross section is inclined, and the upper and lower sides of the side electron guns are brought closer to the electron beam path. In this way, place the permanent magnet in the specified position,
By arranging them at an angle, the same effect as in the case of the arc-shaped permanent magnet described above can be obtained. Further, FIGS. 8 and 9 show still other embodiments of the present invention,
Figure 8 shows the permanent magnets 7 above and below the electron guns on both sides.
9 is one in which a plurality of permanent magnets 70 are arranged. In the case of FIGS. 8 and 9 as well, the radial direction magnetic field components on both side electron guns can be reduced as much as possible as in FIGS. 5 to 7.

As described above, according to the present invention, by using a permanent magnet and a magnetic yoke in combination, it is possible to provide a well-symmetrical focusing magnetic field to each of the three electron guns, and to have good focus characteristics without causing deterioration of convergence characteristics. Magnetically focused cathode rays can be obtained.

[Brief explanation of drawings]

Fig. 1 is a schematic cross-sectional view showing a conventional magnetically focused cathode ray tube, Fig. 2 is a schematic cross-sectional view of the electron gun portion of Fig. 1, and Fig. 3 is a schematic cross-sectional view to explain the operation of Fig. 2. 4 is a schematic sectional view taken along line A-A' in FIG. 3, FIG. 5 is a schematic perspective view showing an embodiment of the present invention, FIG. 6a is a schematic sectional view of FIG. 5, Figure 6b
5 is a schematic characteristic diagram showing the magnetic field distribution, and FIGS. 7 to 9 are schematic sectional views showing other embodiments of the present invention. 51,61,70...Permanent magnet, 62,71...
...Central electron gun, 63,72...Side electron gun.

Claims (1)

[Scope of Claims] 1. A glass envelope, three electron guns sealed in a neck portion at one end of the envelope and arranged in-line and having control means for emitting electron beams, and the envelope. It is a cathode ray tube mainly composed of a phosphor screen coated on the inner surface of the other end and a shadow mask disposed near the phosphor screen, and a permanent magnet for generating a magnetic field in the tube axis direction as a focusing means for the electron beam. In a magnetically focused cathode ray tube equipped with a magnet and a magnetic yoke for shaping the magnetic field, the magnetic yoke is arranged corresponding to each of the three electron guns, and the permanent magnet is arranged so as to correspond to the horizontal array line of the three electron guns. arranged one above the other,
In addition, the viewing angle θ from the center of the central electron gun to the outermost end of the permanent magnet is 100°≦θ≦150°, and the radial component of the magnetic field generated by the permanent magnet is substantially zero on the central electron gun. A magnetically focused cathode ray tube characterized by having the side electron gun as small as possible. 2. The radial component of the magnetic field generated by the permanent magnet has opposite polarity in the vicinity of the end face of the permanent magnet and in the distance on both side electron guns, and is as small as possible. Magnetic focusing cathode ray tube. 3 The permanent magnets are arranged above and below the horizontal array line of the 3 electron guns, and as they move away from the top and bottom of the central electron gun, they approach the electron guns on both sides, or the amount of magnetization increases, or the permanent magnets 2. The magnetically focused cathode ray tube according to claim 1, wherein the thickness of the magnetically focused cathode ray tube increases. 4. Claim 1, wherein each of the permanent magnets has a substantially arc-shaped cross section above and below the horizontal array line of the three electron guns, and has a longitudinal direction along the tube axis. The magnetically focused cathode ray tube described above.