JPS6351032A - Cathode-ray tube - Google Patents

Abstract

PURPOSE:To obtain a high resolution property, by providing an auxiliary focus electrode between the first accelerating electrode and the second accelerating electrode, making the axial length of a cylindrical permanent magnet in the cylindrical body of the second accelerating electrode equal to or larger than its inside diameter, and making the inside diameter of a ring-formed ferromagnetic plate smaller than the inside diameter of the permanent magnet. CONSTITUTION:A cylindrical permanent magnet 7 magnetized to have the both ends in the axial direction to be N and S poles, together with the ring-formed first and second ferromagnetic plates 8 and 9 provided at the both opening end surfaces, is accomodated coaxially in a large diameter cylindrical body of the second accelerating electrode 6. The permanent magnet 7 has the axial length L equal to or larger than its inside diameter A, while the inside diameters B and C of the first and the second ferromagnetic plates 8 and 9 which consist of paramagnetic plates are made smaller than the inside diameter A of the permanent magnet 7. And the diameter D of an electron beam permeation aperture 10 provided at the bottom of an auxiliary focus electrode 5 is made 1.5 times or larger than the diameter E of an electron beam permeation aperture 11 of the first accelerating electrode 4 to restrict the influence of the electrode. Therefore, a magnetic field lens with little spherical aberration can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to cathode ray tubes used in data display devices, video projectors, etc. This relates to cathode ray tubes.

BACKGROUND ART A cathode ray tube in which a permanent magnet for electron beam focusing is provided inside the tube has a higher focusing ability than an external magnetic field focusing type cathode ray tube in which a solenoid or permanent magnet is provided outside the tube as a means for generating an electron beam focusing magnetic field. It is easy to correctly position the central axis of the magnetic field generating means on the electron gun axis, and therefore there is an advantage that no complicated mechanism or adjustment operation is required to correct the eccentricity or inclination of the focused magnetic field generating means. In addition, in external magnetic field focusing cathode ray tubes, in order to avoid raster rotation and deflection distortion due to overlap between the focusing magnetic field and the deflecting magnetic field,
Although the focusing magnetic field generating means must be provided at a sufficient distance from the deflection yoke, a cathode ray tube with a built-in permanent magnet is less likely to have such a risk, and has the advantage that the entire structure can be made compact.

In the cathode ray tube disclosed in Japanese Unexamined Patent Publication No. 55-39121, a permanent magnet is incorporated into a multiple beam type electron gun, and a magnetization plate is attached to the open end surface of this permanent magnet. , the structural non-uniformity of the magnetic field distribution can be reduced by the magnetic shunt plate.

Problems to be Solved by the Invention However, even if such a magnetic field shunt plate is of an axially symmetrical shape, the magnetic field at a position away from the central axis will be stronger than the magnetic field on the central axis. Therefore, considerable spherical aberration will occur.

Therefore, an object of the present invention is to strengthen the magnetic field on the central axis using a ferromagnetic plate such as a magnetic shunt plate and weaken the magnetic field at off-axis positions, thereby generating a uniform electron beam focusing magnetic field and achieving high resolution characteristics. The objective is to obtain a cathode ray tube having the following characteristics.

Means for Solving the Problems According to the present invention, an auxiliary focusing electrode is provided between the first accelerating electrode and the second accelerating electrode, and a cylindrical focusing electrode is provided coaxially within the cylindrical portion of the second accelerating electrode. The permanent magnet has an axial length equal to or longer than the inner diameter of the permanent magnet, and an annular ferromagnetic plate attached to both open end faces of the permanent magnet has a length longer than the inner diameter of the permanent magnet. It also has a small inner diameter.

Effect With this configuration, the magnetic flux concentration effect of the ferromagnetic plate can sandwich the difference between the magnetic field strength on the central axis and the magnetic field strength at off-axis positions, thereby reducing spherical aberration and the spread of the beam spot diameter due to it. Even if the second accelerating voltage or anode voltage deviates from the set value, the best beam focusing state can always be maintained by applying an appropriate focusing voltage to the auxiliary focusing electrode. can be obtained.

Embodiment In FIG. 1 showing an embodiment of the present invention, 1 is a neck portion of a picture tube envelope, 2 is a cathode, 3 is a control grid electrode, 4 is a plate-shaped first accelerating electrode, and 5 is a bottomed cylinder. 6 is a cylindrical second accelerating electrode; 7 is a cylindrical permanent magnet magnetized so that both axial ends thereof are N and St; Annular first and second ferromagnets 11
Together with the body plates 8 and 9, it is housed coaxially within the large-diameter cylindrical portion of the second accelerating electrode 6. The permanent magnet 7 has an axial length equal to or larger than its inner diameter A, and the inner diameters B and C of the first and second ferromagnetic bodies 8 and 9, which are composed of magnetic shunt plates, are as follows: It is made smaller than the inner diameter A of the permanent magnet 7. In addition, the diameter of the electron beam passing hole 10 provided at the bottom of the auxiliary focusing electrode 5 is set to the diameter of the electron beam passing hole 10 of the first 11-speed TL pole 4 in order to suppress the influence of the electrode.
The diameter is 1.5 times or more of the diameter E of 1. However, the auxiliary focusing electrode 5 may have a bottomless cylindrical shape.

The lines of magnetic force generated in the cylindrical permanent magnet 7 when the first and second ferromagnetic plates 8.9 are not attached are as shown by the broken line arrows in FIG. As shown in the figure, it is minimum on the central axis. On the other hand, when first and second ferromagnetic plates 8.9 having a higher magnetic permeability are attached to the permanent magnet 7, lines of magnetic force are generated as shown by broken line arrows in FIG. The magnetic field strength distribution is the fifth
As shown in the figure, a magnetic field lens with little spherical aberration is generated.

The degree of the spherical aberration is largely influenced by the axial length of the permanent magnet 7. That is, the magnetic field strength at the center of the axis is 13o, the magnetic field strength at the off-axis distance r1 is Br+, and the non-uniformity of the magnetic field is <Br+-Bo)/BoX100 (%)
Then, a characteristic as shown by curve a in FIG. 6 was obtained. However, the inner diameter A of the permanent magnet used here is 20 mm.
, the inner diameter of each of the first and second ferromagnetic plates 8, 9 is 81
111+ (=0.4A), each plate thickness is 0.5mm (=0
．． 025A), the off-axis distance r1 is 2 m+a (=
A/2 position 2096). Moreover, the curved line shows the same characteristics when the first and second ferromagnetic plates 8.9 are not used.

As can be seen from this, the larger the L,/'A value of the permanent magnet is, the smaller the non-uniformity of the magnetic field is.In the song H$ a, if the LZA value is 1 or less, the non-uniformity of the magnetic field 11 is reduced by 1%.
It can be kept below.

In FIG. 7, the non-uniformity 11 of the magnetic field is compared between the internal magnet type and the external magnet type.

The former is shown by curve a, and the latter is a song! It is indicated by fAb r c. Generally, the axial length of a permanent magnet enclosed in a cathode ray tube having a diameter of approximately 291 NFFL at the neck portion of the envelope is approximately 15 m, and the inner diameter is 30 ilI11-40 m. The characteristic curve when the inner diameter is 30n+m and the characteristic curve C when the inner diameter is <40mm are shown below.
As can be seen from the figure, the non-uniformity of the magnetic field in the magnet-sheathed type is 0.9 to 1,596. On the other hand, in the cathode ray tube according to the present invention, by setting the axial length A of the permanent magnet to 20 mm or more, the non-uniformity of the magnetic field can be suppressed to 1 to 6 or less, which is equivalent to or higher than that of the external type. The occurrence of spherical aberration can be suppressed.

Effects of the Invention Since the present invention is configured as described above, the distribution of the magnetic field for electron beam focusing can be flattened, and the axial length of the permanent magnet can be relatively increased, so a permanent magnet with a small diameter can be used. However, it is hardly affected by spherical aberration, and in combination with the auxiliary electrostatic lens action provided by the auxiliary focusing electrode, it is possible to generate a beam spot with a small diameter. In addition, since the ferromagnetic 11-piece plate cuts the tail of the axial distribution of the deflection magnetic field, there is very little risk that the deflection magnetic field will overlap the focusing magnetic field, thus further reducing the constraints on the axial length of the permanent magnet. Therefore, a cathode ray tube with high resolution characteristics can be obtained at a low cost.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the main part of a cathode ray tube embodying the present invention, Fig. 2 is a cross-sectional view for explaining the lines of magnetic force generated in a permanent magnet without a ferromagnetic plate attached, and Fig. 3 is The magnetic field strength distribution diagram in the same state, Figure 4 is a cross-sectional view to explain the magnetic lines of force generated when the ferromagnetic plate is attached, Figure 5 is the magnetic field strength distribution diagram in the same state, Figure 6 and FIG. 7 is a characteristic diagram mainly showing the relationship between the axial length of the permanent magnet and the non-uniformity 11 of the magnetic field. 4...First accelerating electrode, 5...Auxiliary focusing electrode, 6...Second accelerating electrode, 7...Permanent magnet, 8,9... ...Ferromagnetic plate. Agent's name Patent attorney Toshio Nakao 18 years old 2riJ itpbJt=! Buddha t~-ノ

Claims (1)

[Claims] An auxiliary focusing electrode is provided between the first accelerating electrode and the second accelerating electrode, and a cylindrical permanent magnet provided coaxially within the cylindrical part of the second accelerating electrode has an inner diameter equal to or larger than the inner diameter of the permanent magnet. The cathode ray has an axial length of , and an annular ferromagnetic plate attached on both open end faces of the permanent magnet has an inner diameter smaller than the inner diameter of the permanent magnet. tube.