JPH0316731B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electromagnetic focusing cathode ray tube having a magnetic field generating device built into the tube, and particularly to correction of variations in the focusing state thereof. In an electromagnetic focusing cathode ray tube, an electromagnetic focusing lens is formed by a main magnetic field (focusing magnetic field) substantially parallel to the tube axis (electron beam traveling direction) as an electron beam focusing means. The device that generates the above-mentioned focusing magnetic field is generally equipped with an electromagnetic coil attached to the outer periphery of the neck of a cathode ray tube, but a device that generates a magnetic field by combining a permanent magnet or a magnetic yoke made of a permanent magnet and a magnetic material in the neck is used. A device with a built-in device has also been proposed. However, those in which the above-mentioned magnetic field generating device is externally packaged in the neck portion and those in which it is incorporated have the following drawbacks. In other words, in the case where the electromagnetic coil is attached to the external neck part, there is a limit to the inner diameter of the electromagnetic coil, that is, the outer diameter of the neck, so a large amount of electric power is required to obtain the necessary focused magnetic field, and there is no suitable current source. is necessary. Furthermore, in order to prevent coma aberration, it is necessary to precisely align the axes of the electron beam and the focused magnetic field, and a position adjustment device for the electromagnetic coil is required. These are undesirable because they lead to increased power consumption and to larger and more sophisticated cathode ray tubes and the equipment necessary to operate them. On the other hand, if a permanent magnet or a combination with a magnetic yoke is built-in, the permanent magnet can be placed very close to the electron beam, so a small and lightweight magnet can provide enough magnetic field to focus the electron beam. Available. Furthermore, the cathode that generates and controls the electron beam, the permanent magnet part that forms the electron gun prefocus part such as the first and second grids, and the main focusing lens part are as follows:
It can be assembled in advance with high accuracy. Therefore, there is no need for a device for adjusting the position of the magnetic field generating device, which was necessary when the electromagnetic coil was externally packaged. Having a built-in permanent magnet has the above-mentioned advantages, but on the other hand, since the magnetic field generator is inside the tube, there are problems with the electron beam focusing state due to various manufacturing variations in the permanent magnet's dimensions, amount of magnetization, assembly accuracy, etc. It has the disadvantage that it is difficult to compensate for variations and deterioration.
When using an auxiliary focusing electromagnetic coil outside the tube,
This creates problems with the positioning and power of the auxiliary focusing coil itself, which negates the advantage of having a built-in permanent magnet. It is also possible to incorporate the auxiliary focusing coil, but it is necessary to draw out the terminal outside the tube in order to supply power to the auxiliary focusing coil. This is the vacuum maintenance of the cathode ray tube, the strength of the envelope, and the 10KV~ applied to the cathode ray tube.
This causes reliability problems with high voltage of 30KV. In view of the above points, the present invention provides a simple device for controlling the electron beam focusing magnetic field excited by a permanent magnet built into the tube from outside the tube, and incorporates a small, lightweight, inexpensive magnetic field generator with good resolution. The purpose of the present invention is to provide an electromagnetic focusing cathode ray tube. The present invention will be explained in detail below. When a magnetic body is placed near a permanent magnet, magnetic flux is concentrated inside the magnetic body, and the magnetic flux near the magnetic body and permanent magnet is reduced. In other words, the phenomenon appears as if the permanent magnet itself had been demagnetized. Naturally, the above apparent demagnetization effect depends on the distance between the permanent magnet and the magnetic material,
It varies depending on the magnetic material (magnetic permeability), shape, etc. The present invention attempts to control the electron beam focusing magnetic field by utilizing the apparent demagnetizing effect of the permanent magnet caused by this magnetic material. Figure 1 shows an electromagnetic focusing cathode ray tube with a built-in magnetic field generator. In FIG. 1, numeral 1 is a glass envelope for maintaining the interior at a high vacuum, and 2 is a phosphor screen, the interior of which is coated with phosphor 3. 14 is an internal conductive film that keeps the inside of the tube at the same potential as the inside of the phosphor screen 2. Reference numeral 4 denotes a network part, inside which are provided a heater 6, a cathode 7, a first grid 8 for controlling and accelerating the electron beam emitted from the cathode 7, a second grid 9, and an anode 1.
0, an electromagnetic focusing type electron gun 5 formed of a permanent magnet supporter 11 and a cylindrical permanent magnet 12 as main components is enclosed. The anode 10 and the permanent magnet supporter 11 are maintained at the same potential as the inner surface of the phosphor screen via a contact spring 15. The electron beam emitted from the cathode 7 is controlled by the first and second grids 8 and 9, once forms a crossover near the first grid 8, and is then accelerated by the second grid 9 and the anode 10, forming a permanent cylindrical beam. An image of the crossover is focused on the phosphor screen 2 by an electromagnetic focusing lens formed by a focusing magnetic field excited by the magnet 12. Here, the cylindrical permanent magnet 12 is magnetized in the direction of the tube axis, and the amount of magnetization, that is, the magnetic field strength on the tube axis, depends on the inner diameter, outer shape, and length of the cylindrical permanent magnet 12, as well as the phosphor screen 2 and the cross section. It is selected so that the electron beam spot size on the phosphor screen 2 is minimized depending on the distance to the over point, the potential inside the tube, etc. However, as mentioned above, manufacturing variations in the amount of magnetization, dimensions of the cylindrical permanent magnet 12, distance from the phosphor screen 2, etc. are unavoidable, and the electron beam spot size on the phosphor screen 2 may deviate from the optimal state. This reduces the quality of the screen on the fluorescent screen. Reference numeral 13 denotes an electron beam auxiliary focusing device for controlling the focusing magnetic field of the electron beam from outside the tube, which is applied to the present invention, and is shown enlarged in FIG. Parts common to those in FIG. 1 are indicated by the same numbers. In FIG. 2, the auxiliary focusing device 20 has a fastening tool 2 at one end thereof for externally fixing it to the neck 4.
7, a plastic holder 26 movable on this holder in the tube axis direction and
Two plastic magnetic body holders 2 holding cylindrical magnetic bodies 22 and 23 on the exterior surface of 6
8, and a screw 24 which is attached to the protrusion 25 of the magnetic holder 28 and rotates to move the two magnetic holders 28 by equal amounts in opposite directions. Moreover, the cylindrical magnetic bodies 22 and 23 are made of exactly the same material,
The dimensions are better. The auxiliary focusing device is arranged so that when the distance l between the cylindrical magnetic bodies 23 and 22 is zero, the boundary surface thereof coincides with the line AA' of the center of the cylindrical permanent magnet. The cylindrical permanent magnet 12 has an inner diameter of 15.5φmm and an outer diameter of
21.3φmm, length 5.4mm, and cylindrical magnetic body 2
2 and 23 have an inner diameter of 29.2φmm, an outer diameter of 31.2φmm, and a length of
When using a cylindrical permanent magnet with a diameter of 6.0 mm and an initial permeability of 2 × 10 ⁴ , the distance l between cylindrical magnetic bodies and the cylindrical permanent magnet 1
Table 1 shows the relationship between the relative changes in the focused magnetic field strength at the center points of 2.

[Table] As shown in Table 1, if l = 5 m/m is taken as the central value, then by rotating the screw 24, l will be 5 ± 5 m/m.
By changing the electron beam focusing magnetic field strength, it is possible to change the electron beam focusing magnetic field strength by about ±5%. Furthermore, it is clear that the amount of change in this focusing magnetic field can be further adjusted and expanded depending on the movable range of l, the material and dimensions of the magnetic body, etc. Since the focal length of an electromagnetic lens is proportional to the square of the magnetic flux density, the above ±5% change in magnetic flux density means that the focal length can be adjusted by ±10%. Therefore, even if we consider magnetization technology with a magnetization accuracy of about ±1 to 4%, permanent magnet manufacturing, mounting accuracy, etc., the electron beam spot size on the phosphor screen will increase or deteriorate due to manufacturing variations such as these. can be reduced and prevented. Even if only one cylindrical magnetic body is used in the electromagnetic focusing cathode ray tube of the present invention, by varying the positional relationship along the tube axis direction with the cylindrical permanent magnet 12,
Similarly, the magnetic flux density at the center of the cylindrical permanent magnet 12 can vary;
Since the entire magnetic field distribution excited by 2 moves in the direction in which the magnetic body moves, in other words, the position of the electromagnetic lens moves, and it is better to use two or more magnetic bodies to cancel out the effects caused by changes in magnetic flux density. preferable. Furthermore, although the magnetic body in the above embodiment was cylindrical,
Each of the cylindrical magnetic bodies 22 or 23 may be an aggregate of a plurality of cylindrical magnetic bodies, or may be divided into multiple parts in the circumferential direction to the extent that the symmetry of the electron beam focusing magnetic field is not impaired. . Further, it goes without saying that the effects of the present invention will not change even if a combination of a permanent magnet and a magnetic yoke is built into the neck portion. As described above, according to the present invention, it is possible to provide an electromagnetic focusing cathode ray tube having a magnetic field generating device that is small, inexpensive, and consumes little power.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of an electromagnetic focusing cathode ray tube, FIG. 2a is an enlarged schematic sectional view of an auxiliary focusing device showing an embodiment of the present invention, and FIG. It is a schematic sectional view. 12... Cylindrical permanent magnet, 13, 20... Auxiliary focusing device, 22, 23... Cylindrical magnetic body, 24...
...Screw, 25...Protrusion, 26, 28...Holder, 27...Tightening tool.

Claims (1)

[Scope of Claims] 1. A magnetic field generating device for electron beam focusing including at least a permanent magnet is built into the tube neck portion, and the magnetic field generating device is interlocked with the outside of the magnetic field generating device and outside the neck in mutually opposite directions along the tube axis direction. An electromagnetic focusing cathode ray tube characterized by being equipped with at least two magnetic cylinders. 2. The electromagnetic focusing cathode ray tube according to claim 1, wherein each of the two magnetic cylinders is made of a magnetic material or an aggregate thereof that is multi-divided in the tube axis direction or circumferential direction.