JP2555099B2 - Focus magnet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a focus magnet for a projection type CRT used in, for example, a video projector, a projection type high definition television, etc., and particularly a focus magnet for a high definition projector. It concerns the improvement of magnets.

[Conventional technology]

Conventionally, an electrostatic type device has been used as a device for focusing an electron beam emitted from an electron gun on a fluorescent screen, and a magnetic field type is used for special tubes such as an X-ray tube, a magnetron, and a traveling wave tube. Had been used. However, as a result of the recent demand for high-definition televisions and other high-definition televisions, there is a shift to magnetic field systems. The electromagnet method, which is one of the magnetic field methods, has a drawback that it is large and requires a power source. Therefore, the permanent magnet method is mainly used.

FIG. 3 is a cross-sectional explanatory view of a main part showing an example of an outer magnet type electromagnetic focusing cathode ray tube. In FIG. 3, the electron beam 17 emitted from the cathode 11 includes a cathode 11, a first grid 12,
It is focused by the focus system composed of the second grid 13 and forms a so-called crossover. After passing through the crossover, the electron beam 17 spreads again, and enters the magnetic main lens 16 formed by the focus magnet 15 arranged on the outer periphery of the neck 14 of the cathode ray tube, is focused again, and crosses on the fluorescent screen 18. Connect the image of the over.

FIG. 4 is a sectional view of an essential part showing an example of the focus magnet in FIG. In FIG. 4, the focus magnet is made of a ferromagnetic material and is hollow at both end surfaces of the permanent magnet 1 which is magnetized in the axial direction and provided with N and S magnetic poles on the end surfaces, and which is formed into a hollow cylindrical shape. The yoke 2 is fixed to form a magnetic circuit, and the coil 3 is provided on the inner circumference of the permanent magnet 1 via the bobbin 4. If the coil 3 is formed as described above and the coil 3 is energized via a lead wire (not shown), the central magnetic field of the permanent magnet 1 can be adjusted, and the action of focusing the electron beam on the central axis is expected. You can do it.

[Problems to be solved by the invention]

Conventionally, alnico magnets have been widely used as the permanent magnet 1 constituting the focus magnet having the above-described structure, but recently, ferrite magnets are often used for cost reduction. However, since the temperature coefficient of the ferrite magnet is about −0.2% / ° C. and the temperature characteristics are not good, there is a difference in the electron beam focusing action at low temperature and at high temperature. Further, there is a problem that the electron beam converges and deviates due to the influence of the leakage magnetic flux on the neck side.

As a means for solving the above problems, for example, there is a means for fixing magnetic shunt steel to the outer peripheral surface of a ferrite magnet,
This is not sufficient as a measure for preventing the deviation of convergence of the electron beam. Further, the use of a large amount of such expensive magnetic shunting steel has a problem that the use of the ferrite magnet is meaningless for the purpose of cost reduction and the assembly work is rather complicated.

The present invention solves the above-mentioned problems existing in the prior art,
It is an object of the present invention to provide a focus magnet that can reduce the electron beam convergence deviation and can reduce the cost.

[Means for solving problems]

In order to solve the problems existing in the above-mentioned prior art, in the present invention, a hollow disk-shaped yoke is provided on the magnetic pole surface of a hollow cylindrical ferrite magnet that is magnetized in the axial direction and magnetic poles are provided on both end surfaces. In a focus magnet, which is fixed and has a coil for central magnetic field adjustment provided on the inner circumference of the ferrite magnet, a hollow disk-shaped alignment made of a magnetic material in the yoke on the neck side and having an outer diameter larger than that of the ferrite magnet. The technical means of fixing the magnetic member and forming the leakage flux density on the neck side smaller than the leakage flux density on the electron beam side was adopted.

[Operation] With the above configuration, the electron beam on the central axis can be focused and the leakage magnetic flux on the neck side can be reduced, and as a result, the operation of preventing the convergence deviation of the electron beam can be expected.

〔Example〕

FIG. 1 is a sectional view of an essential part showing an embodiment of the present invention, and the same parts are designated by the same reference numerals as those in FIG. In FIG. 1, reference numeral 5 denotes a degaussing member, which is made of an iron plate or other ferromagnetic material into a hollow disk shape and has an outer diameter larger than that of the permanent magnet 1 so that the neck side (in FIG. Stick the magnetic pole surface on the left side. The permanent magnet 1 is a ferrite magnet, magnetized in the axial direction, and N and S magnetic poles are provided on both end faces.

With the above configuration, the magnetic flux leakage on the neck side is reduced by the degaussing member 5.
Since it is absorbed or demagnetized by the demagnetization field, it is possible to reduce the demagnetizing field that cannot contribute to the focusing of the electron beam described later.

FIG. 2 is a sectional view of an essential part showing another embodiment of the present invention, and the same parts are designated by the same reference numerals as those in FIGS. 1 and 4. In the present embodiment, two permanent magnets 1 are used, different poles are opposed to each other, and they are fixed coaxially via a yoke 2, and a bobbin 4 is provided on the inner circumference of each permanent magnet 1, 1. The coil 3 is interposed.

With the above configuration, the half width on the magnetic field curve is increased,
Except that the convergent spot diameter of the electron beam can be reduced, the same effect as that of the above-mentioned embodiment can be expected.

FIG. 5 is a diagram showing the relationship between the magnetic flux density of the central magnetic field of the focus magnet and the position in the axial direction, and the values correspond to those of the configuration shown in FIG. Magnetic field curve in Fig. 5
A and B show the structure of this embodiment and the conventional structure, respectively. The dimensions of each constituent member in this case are as follows.

Permanent magnet 1 outer diameter 62mm, inner diameter 42mm (Hitachi Metals YBM-2B) thickness 10.5mm 2 pieces yoke 2 outer diameter 57mm, inner diameter 32mm (SPCD) thickness 1.6mm 4 pieces degaussing member 5 outer diameter 70mm, inner diameter 42mm (SPCD) 1.6 mm thick 1 piece As is clear from FIG. 5, the maximum value of the central magnetic field is slightly reduced by providing the magnetic shunting member 5 as shown in FIG. 2, but the neck side ( The leakage magnetic flux density on the left side in FIG. 5 is significantly reduced. Then, the maximum value A ₁ of the demagnetizing field due to this leakage magnetic flux is reduced to about 75% of that of B ₁ .
On the other hand, on the electron beam side (right side in FIG. 5),
The maximum values of demagnetizing field A ₂ and B ₂ remain almost the same.
The maximum axial positions of the magnetic field curves A and B are almost the same. That is, in the present invention, the leakage flux density on the neck side is made smaller than the leakage flux density on the electron beam side.

Video projector real machine (40in) with the above focus magnets having three electron beams for red, green and blue
It was mounted on the neck of a cathode ray tube and its performance was evaluated in an environment of -10 to 60 ° C. The maximum and average values of the raster rotation angle θ (rad) were 0.0098 and 0.0056, respectively. It was confirmed that the values were reduced from 0.0103 and 0.0064, respectively, in the conventional structure in which the degaussing member 5 in FIG. It was also found that the amount of axis deviation around 40 inches (calculated based on the above raster rotation angle) was about 1.75 mm, which is an improvement over 2.0 mm in the conventional structure.
It was confirmed that the convergent spot diameters of the electron beams were equivalent to each other, although the magnetic field curve was asymmetric as shown in FIG.

EFFECTS OF THE INVENTION Since the present invention has the configuration and operation as described above, the deviation of the convergence of the electron beam can be made extremely small, which can prevent the color deviation, and the structure cost can be reduced because the structure is simple. There is an effect that it can be reduced.

[Brief description of drawings]

1 and 2 are cross-sectional views of a main part showing an embodiment of the present invention, FIG. 3 is a cross-sectional view of a main part showing an example of an outer magnet type electromagnetic focusing cathode ray tube, and FIG. FIG. 5 is a cross-sectional view of an essential part showing an example of a focus magnet, and FIG. 5 is a view showing the relationship between the magnetic flux density of the central magnetic field of the focus magnet and the axial position. 1: Permanent magnet, 2: Yoke, 5: Degaussing member.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumihiko Takahashi 5200 Sankejiri, Kumagaya-shi, Saitama, Kumagaya Plant, Hitachi Metals, Ltd. (56) Reference JP 58-48343 (JP, A) (JP, U) Actual development Sho 57-201751 (JP, U)

Claims (1)

(57) [Claims] 1. A hollow disk-shaped yoke is fixed to the magnetic pole surface of a hollow cylindrical ferrite magnet which is magnetized in the axial direction and magnetic poles are provided on both end surfaces, and a central magnetic field is adjusted on the inner circumference of the ferrite magnet. In the focus magnet having the coil of No. 2, a hollow disk-shaped degaussing member made of a magnetic material and having an outer diameter larger than that of the ferrite magnet is fixed to the yoke on the neck side, and the leakage magnetic flux density on the neck side is reduced. A focus magnet characterized by being formed to have a smaller leakage magnetic flux density on the electron beam side.