JPS6348732A - Cathode-ray tube - Google Patents

Abstract

PURPOSE:To obtain a high-resolution CRT by making the axial length of a cylindrical permanent magnet coaxially provided in a cylindrical electrode of an electron gun equal to or larger than its inner diameter and making the inner diameters of annular ferromagnetic plates provided on both opening ends of this permanent magnet smaller than the inner diameter of the permanent magnet. CONSTITUTION:A cylindrical permanent magnet 6 has N,S poles on both ends in the axial direction and are stored axially in the cylindrical section of an accelerating electrode 5 together with annular ferromagnetic plates 7, 8 provided on both opening ends. The axial length L of the permanent magnet 6 is made equal to or larger than its inner diameter A, and the inner diameters B, C of the magnetic plates 7, 8 are made smaller than the inner diameter of the permanent magnet 6. According to this constitution, the electron beam focusing magnetic field distribution is made flat, the axial length of the permanent magnet 6 can be made relatively large, and a small- diameter beam spot with little spherical aberration can be obtained with the small- diameter permanent magnet. In addition, the ferromagnetic plates cut the bottom of the axial distribution of the deflecting magnetic field, the restriction of the axial length of the permanent magnet can be reduced, and a CRT with the high-resolution characteristic can be obtained.

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 has the advantage of being able to have a compact overall structure since there is less of such a risk.

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 on the open end surface of this permanent magnet.
In this case, 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 shunt plate is axially symmetrical, the magnetic field at a position away from the central axis is 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, a cylindrical permanent magnet provided coaxially within a cylindrical electrode constituting an electron gun has an axial length equal to or greater than the inner diameter of the cylindrical permanent magnet. An annular ferromagnetic plate attached to both open end faces of the permanent magnet has an inner diameter smaller than the inner diameter of the permanent magnet.

Function: With this configuration, the difference between the magnetic field strength on the central axis and the magnetic field strength at the off-axis position can be reduced by the magnetic flux concentration effect of the ferromagnetic plate, and the spherical aberration and the spread of the beam spot diameter due to it can be reduced. Therefore, a cathode ray tube with high resolution characteristics can be obtained.

Embodiment In FIG. 1 showing an embodiment of the present invention, 1 is the neck of the picture tube envelope, 2 is the cathode, 3 is the control grid electrode, and 4 is the first
Accelerating electrode, 5 is a cylindrical second accelerating electrode, 6 is a cylindrical permanent magnet magnetized so that both ends in the axial direction are N and S poles, and a circle attached to both opening end faces 2. It is housed coaxially within the large-diameter cylindrical portion of the second accelerating electrode 5 together with the annular first and second ferromagnetic plates 7.8. The permanent magnet 6 is
First and second ferromagnetic plates having an axial length equal to or larger than the inner diameter A and consisting of magnetic shunt plates 7.
The inner diameters B and C of the permanent magnets 8 are smaller than the inner diameter A of the permanent magnet 6.

The lines of magnetic force generated in the cylindrical permanent magnet 6 when the first and second ferromagnetic plates 7.8 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 the first and second ferromagnetic plates 7.8 with higher magnetic permeability are attached to the permanent magnet 6, lines of magnetic force are generated as shown by the broken line arrows in FIG. Since the magnetic field strength distribution becomes as shown in FIG. 5, a magnetic field lens with little spherical aberration is generated.

The degree of the spherical aberration is greatly influenced by the axial length of the permanent magnet 6. That is, assuming that the magnetic field strength at the center of the axis is Brl, and the magnetic field strength at the BOS off-axis distance r1 is (Brl-Bo)/BoX100 (%), the characteristic is as shown by curve a in Figure 6. was gotten. However, the inner diameter A of the permanent magnet used here is 20M1, and the inner diameter of each of the first and second ferromagnetic plates 7.8 is 8mm (~0.4mm).
A), each plate thickness is Q, 5mm (~0.025A), i
The axial distance r1 was 2+nm (=20% position of A/2). Moreover, the curved line is the first and second ferromagnetic plate 7.
．． This shows the same characteristics when 8 is not used.

As can be seen from this, the larger the L/A value of the permanent magnet, the smaller the non-uniformity of the magnetic field, and in curve a, L
If the /A value is 1 or less, the non-uniformity of the magnetic field can be suppressed to 1% or less.

In FIG. 7, the non-uniformity 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 by curve b g C. Generally, the diameter at the neck of the envelope is approximately 2
The axial length of the permanent magnet enclosed in a 9 mm cathode ray tube is about 15 mm, and the inner diameter is 30 mm to 40 mm. As can be seen from the characteristic curve ab and characteristic curve C when the inner diameter is 30 mm and the same (40 order), the non-uniformity of the magnetic field in the magnet exterior type is as follows:
It becomes 0.9-1.5%. In contrast, in the cathode ray tube according to the present invention, by setting the axial length A of the permanent magnet to a value of 20 or more, the non-uniformity of the magnetic field can be suppressed to 196 or less, and the spherical surface is equal to or greater than that of the exterior type. It is possible to suppress the occurrence of aberrations.

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 that a permanent magnet with a small diameter can be used. It is possible to generate a beam spot with a small diameter that is almost unaffected by spherical aberration. In addition, since the ferromagnetic 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.
Therefore, restrictions on the axial length of the permanent magnet can be further reduced, and a cathode ray tube with high resolution characteristics can be obtained at a low cost.

[Brief explanation of the drawing]

Fig. 1: A sectional view of the main parts of a cathode ray tube in which the present invention is implemented; Figure 3 is a magnetic field strength distribution diagram in the same state, Figure 4 is a cross-sectional view for explaining the magnetic lines of force that occur when the 11 ferromagnetic plate is attached, and Figure 5 is a magnetic field strength distribution diagram in the same state. 6 and 7 are characteristic diagrams mainly showing the relationship between the axial length of the permanent magnet and the non-uniformity of the magnetic field. 5...Second accelerating electrode, 6...Permanent magnet, 7.8...Ferromagnetic plate. Name of agent: Patent attorney Toshio Nakao and 1 other person $1 Fig. 5 Rod 2 toyon mei 6 Permanent magnet grass 2 times + YI $6 times (Soko) Procedural amendment December 12, 1985 Patented in 1986 Application No. 190766 2 Name of the invention Cathode ray tube 3 Relationship to the case of the person making the amendment Patent Applicant Address 1006 Kadoma, Kadoma City, Osaka Prefecture Name (584)
Matsushita Electronics Co., Ltd. Representative Fujimoto
4th husband, Toshihito 571 address 1006 Oaza Kadoma, Kadoma City, Osaka [Contact phone number (Tokyo) 437-1121 Tokyo Legal Affairs Branch] 5 Subject of amendment 6 Contents of amendment (1) Line 2 of page 6 of the specification “If it is less than 1”
If it is 1 or more, it will be corrected to "If it is 1 or more." (2) In the same book, page 6, line 17, ``more than that'' has been corrected to ``more than that.''

Claims (1)

[Claims] A cylindrical permanent magnet coaxially provided within the cylindrical electrode constituting the electron gun has an axial length equal to or greater than the inner diameter of the cylindrical permanent magnet, and is attached on both open end surfaces of the permanent magnet. 1. A cathode ray tube characterized in that an annular ferromagnetic plate has an inner diameter smaller than the inner diameter of the permanent magnet.