JPH0316730B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electromagnetic focusing cathode ray tube incorporating a magnetic field generator, and more particularly to a device for adjusting the intensity of an electron beam focusing magnetic field excited by the magnetic field generator. An electromagnetic focusing cathode ray tube uses an electromagnetic lens formed by a main magnetic field approximately parallel to the electron beam traveling direction as a means for focusing the electron beam.
This magnetic field generator is generally placed outside the tube. However, electromagnetic focusing cathode ray tubes that have the above-mentioned magnetic field generating device outside the tube require a larger magnetic field generating device to supply the necessary magnetic field strength inside the tube, or a larger size to generate the magnetic field, compared to those that have the magnetic field generating device inside the tube. Requires electricity. Furthermore, a device for aligning the axes of the electron beam and the focusing magnetic field is essential. In other words, it is clear that the cost and power consumption including the magnetic field generator will increase, and the size will also increase. On the other hand, if a magnetic field generator is built-in, generally,
A permanent magnet is used as the magnetic field generator, and since this magnetic field generator can be placed near the electron beam to be focused, it is extremely compact and can generate the magnetic field necessary for focusing without using electricity. In addition, when placed inside the tube, the cathode of the electron gun, the first
Electron beam generation and controlled acceleration by the second grid etc. Since each electrode and the magnetic field generator can be assembled in advance, the axis of the focusing magnetic field can be aligned with the electron beam with sufficient accuracy. As described above, a cathode ray tube with a built-in magnetic field generator is generally more advantageous than one installed outside the tube in terms of cost, power consumption, shape, etc. An example of an electromagnetic focusing cathode ray tube with a built-in magnetic field generator is shown in FIG. In FIG. 1, a phosphor screen 4 is provided at one end of the envelope 1, and a cathode 5, a first grid 6, and a second grid 7 are sequentially arranged in a neck portion 7 at the other end. Also network part 7
A magnetic field generating device 3 for focusing an electron beam, which is made of a permanent magnet, is provided inside. A coil can be built in as this magnetic field generator, but in this case, the terminal that supplies current to the coil needs to be drawn out of the envelope 1, which makes it difficult to maintain the confidentiality of the envelope 1 and weaken its strength. In addition, since the inside of the envelope is generally high voltage (about 10 to 30 KV),
This lowers the withstand voltage reliability, and also requires consideration (protection) against high voltage in the current circuit that supplies current to the coil, making it expensive. That is, when a magnetic field generating device is built in, it is more advantageous to use a permanent magnet. The operation of the cathode ray tube shown in FIG. 1 is as follows. The electron beam 8 emitted from the cathode 4 forms a crossover point 9 at the lens formed by the cathode 4, the first grid 5, and the second grid 6, and is accelerated by the anode voltage while being accelerated by the magnetic field of the permanent magnet 3. By receiving a focusing effect, a minimum beam spot diameter is obtained on the phosphor screen 2. However, in such a cathode ray tube, there are variations in magnetization during magnetization of the permanent magnets, variations in dimensions, etc., and due to these, the focusing magnetic field varies by 5 to 6%. This variation in the focusing magnetic field causes a shift in the focal length of the electromagnetic lens, causing an increase in the beam spot diameter on the phosphor screen. Therefore, it is necessary to correct this focal length deviation to minimize the beam spot diameter on the phosphor screen. However, in a cathode ray tube with a permanent magnet built into the neck, it is not easy to adjust the focusing magnetic field. Adjusting the magnetic field by incorporating a coil is difficult due to problems such as the degree of vacuum as described above. On the other hand, installing a coil outside the tube to adjust the magnetic field eliminates the advantage of having a permanent magnet built into the neck and significantly increases costs. The purpose of the present invention is to easily adjust the above-mentioned focusing magnetic field using a magnetic material provided outside the neck portion, change the focal length of the electromagnetic lens, and obtain the smallest beam spot diameter on the phosphor screen. That is. The present invention will be explained in detail below. When a magnetic body is placed near a permanent magnet, magnetic flux concentrates inside the magnetic body, and the magnetic flux near the magnetic body and permanent magnet decreases. In other words, the situation appears as if the permanent magnet itself had been demagnetized. Further, as a matter of course, the degree of decrease in the magnetic flux near the magnetic body and the permanent magnet varies depending on the distance between the permanent magnet and the magnetic body, the material (magnetic permeability) and shape of the magnetic body, and the like. The present invention attempts to control the electron beam focusing magnetic field by utilizing the apparent demagnetizing effect of the permanent magnet caused by the above-mentioned magnetic material. This will be explained in more detail using examples. An embodiment of the present invention is shown in FIGS. 2 and 3.
Elements in the figure that are common to those in FIG. 1 are designated by the same numbers. FIG. 2 shows a magnetic field control device 1 according to the present invention.
FIG. 3 is a cross-sectional view of the magnetic field control device 17 taken along a plane B-B' perpendicular to the tube axis. In FIGS. 2 and 3, a holder 11 made of plastic or the like is placed on the outer periphery of the neck portion 7 of the band 1.
6 and screws 15, and a magnetic body 10 held in a magnetic body holder 14 made of plastic or the like is disposed on this holder 11 via bolts 12. This magnetic material 10
is arranged concentrically with respect to the neck part 7 and the cylindrical permanent magnet 3 constituting the magnetic field generator,
By rotating the head 13 of the bolt 12, the magnetic body 10 held by the magnetic body holder 14 can be moved in the direction of the arrow shown in the diagram of the neck portion, that is, in the radial direction of the neck, and can be fixed. There is. These bolts 12 are for adjustment, and if the neck is circular, it is better to use three. Also, magnetic material 1
0 and the magnetic material holder 14 may be one, but one having a cylindrical shape and divided into three equal parts as shown in FIG. 3 is more useful for the magnetic field adjustment function. Next, a cylindrical permanent magnet 3 with an outer diameter of 24.0 mm and an inner diameter of
18.0 mm, length 6.0 mm, and magnetized in the tube axis direction, the outer diameter of the magnetic body 10 is
32.0mm, thickness 1.0mm, length 5.0mm, initial permeability 2×10 ⁴
A case will be described in which a cylinder divided into three equal parts in the circumferential direction is used. Table 1 shows magnetic material 10 divided into three equal parts and bolt 1
2, each moves in the radial direction by an equal amount,
It shows the change in magnetic flux density at the center of the permanent magnet 3 on the tube axis when the distance l between the tube axis center and the magnetic body 10 is varied.

[Table] However, in Table 1, the center magnetic flux density when l = 15.0 mm is
It is shown relatively as 100%. According to Table 1, by moving the distance l from 15.0 mm to 23.0 mm, the magnetic flux density can be changed from 100% to 112%. This magnetic flux density change is approximately 12%
However, this amount of change can be further increased by changing the distance l or the like. As mentioned above, due to variations in the amount of magnetization of the permanent magnets, the electromagnetic lens focal length deviates from the optimum value (design value), causing an increase in the beam spot diameter on the phosphor screen, but using the magnetic field control device according to the present invention By doing this, the magnetic flux density can be adjusted so that the electromagnetic lens focal length always matches the optimum value, and the best beam spot can always be obtained. In other words, if the magnetic field strength is insufficient compared to the optimum value due to variations in magnetization, the distance l between the magnetic body and the tube axis is increased relative to the set value, and if the magnetic field strength is excessive, the distance l is increased.
All you have to do is decrease it. It goes without saying that the magnetic field control device of the present invention is also effective when it is necessary to finely adjust the focal length due to variations in the dimensions of the permanent magnets, variations in the positions of the permanent magnets, etc. In FIGS. 2 and 3, the magnetic body 10 has a cylindrical shape and is divided into multiple parts, but this is not necessarily necessary. That is, the quantity, shape, arrangement, movable distance, movable direction, etc. of the magnetic bodies 10 may cause changes that substantially deteriorate the beam focusing state, such as impairing the symmetry of the magnetic flux distribution excited by the permanent magnet 3. You can freely choose as long as it does not cause any problems. As described above, according to the present invention, it is possible to prevent an increase in the beam spot diameter, or in other words, a deterioration in resolution, due to manufacturing variations in electromagnetic focusing cathode ray tubes with built-in magnetic field generators. is big.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view showing an example of an electromagnetic focusing cathode ray tube incorporating a conventional magnetic field generating device, and Fig. 2 shows an example of an electromagnetic focusing cathode ray tube magnetic field control device of the present invention attached to the neck portion of the cathode ray tube. A schematic cross-sectional view showing one embodiment, FIG. 3 is a sectional view taken along line BB' in FIG. 2. DESCRIPTION OF SYMBOLS 1... Envelope, 2... Fluorescent screen, 3... Permanent magnet, 4... Cathode, 5... First grid, 6...
...Second grid, 7...Network part, 8...Electron beam, 9...Crossover point, 10...Magnetic material,
DESCRIPTION OF SYMBOLS 11... Holder, 12... Bolt, 13... Bolt head, 14... Magnetic material holder, 15... Screw, 16... Band, 17... Magnetic field control device.

Claims (1)

[Scope of Claims] 1. In an electromagnetic focusing cathode ray tube in which a magnetic field generating device including at least a permanent magnet for focusing an electron beam is built into the neck portion, a neck tube shaft is provided outside the neck corresponding to the magnetic field generating device. 1. An electromagnetic focusing cathode ray tube characterized in that at least one magnetic body is arranged that can be moved and fixed in a radial direction. 2. The electromagnetic focusing cathode ray tube according to claim 1, wherein the magnetic body has a cylindrical shape and is divided into three equal parts.