JP2551867Y2 - Focus magnet - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus magnet which is arranged around a neck portion of a CRT such as a video projector and generates a magnetic field for focusing an electron beam.

[0002]

2. Description of the Related Art Conventionally, there are two methods of focusing an electron beam emitted from a CRT electron gun on a phosphor screen: an electric field lens system for applying an electrostatic field to the electron beam and a magnetic lens system for applying a magnetic field. There is. Further, the magnetic lens system is classified into two types, an electromagnet system and a permanent magnet system, depending on the magnetic field generation source.The electromagnet system has a large shape and requires a power supply that constantly supplies a current for electron beam focusing. At present, the permanent magnet method is predominant, and a projection lens television such as a video projector employs a magnetic lens type focus magnet using the above permanent magnet having excellent resolution.

FIG. 2 shows a conventional focus magnet shown in Japanese Patent Publication Nos. 49-4573 and 49-4574. In the figure, cylindrical permanent magnets 11 and 12 are made of sintered alnico, ferrite, samarium cobalt, or the like, which is magnetized in the axial direction and has N and S magnetic poles on its end faces. The permanent magnets 11 and 12 are arranged on the outer periphery of the CRT, not shown, away from the neck of the CRT in order to avoid adverse effects on the electron beam due to the magnetization of the magnets. A hollow disk-shaped center yoke 13 provided at an intermediate portion between the permanent magnets 11 and 12 is made of a ferromagnetic material such as soft iron. The hollow disk-shaped side yokes 14 and 15 fixed to the end faces of the permanent magnets 11 and 12 are made of a ferromagnetic material such as soft iron. A dynamic focus coil 16 provided on the inner peripheral side of the permanent magnet 11 for correcting a central magnetic field generates a correction magnetic field for converging an electron beam around a tube surface of a CRT (not shown). A parabolic current having a waveform corresponding to the deflection scanning is supplied. A static focus coil 17 for correcting a central magnetic field provided on the inner peripheral side of the permanent magnet 12 generates a correction magnetic field for converging an electron beam at a central portion of a tube surface of a CRT (not shown). A constant DC current is supplied.

When a current is applied to each of the coils 16 and 17 via a lead wire (not shown) to the focus magnet configured as described above, a magnetic field is generated, and the permanent magnets 11 and 12 are generated.
As a result, it is possible to adjust (correct) the magnetic field generated at the central portion, so that the electron beam can be uniformly focused on the entire tube surface of the CRT.

[0005]

Recently, projection-type televisions such as video projectors have attracted attention as displays for displaying high-definition television signals such as HDTV and EDTV. In this case, the horizontal scanning frequency is 33.
75KHz or 31.47KHz
The frequency becomes twice or more as compared with 5.73 KHz. On the other hand, in the above-mentioned conventional focus magnet, since the permanent magnets 11 and 12 are made of a sintered permanent magnet or a metallic permanent magnet such as ferrite or samarium cobalt, the parabolic current flowing through the dynamic focus coil 16 is reduced. When the frequency is set to 20KHz or more, the permanent magnet 1
The iron losses of 1 and 12 increase, and heat is generated to lower the efficiency.

Therefore, an object of the present invention is to provide a focus magnet which does not increase iron loss even when used at a high horizontal scanning frequency such as HDTV and EDTV, and is efficient.

[0007]

SUMMARY OF THE INVENTION Accordingly, in order to achieve the above-mentioned object, a first aspect of the present invention is to provide an axially magnetized metallic cylindrical permanent magnet and two ends of the cylindrical permanent magnet. In a focus magnet including a mounted yoke plate and a plurality of coils for correcting a central magnetic field disposed on the inner periphery of the cylindrical permanent magnet, a focus magnet is provided between the cylindrical permanent magnet and the coil for correcting a central magnetic field. Is provided with a plastic cylindrical permanent magnet which is magnetized in the axial direction.
In the second aspect of the present invention, one of the coils for correcting the central magnetic field is constituted by a litz wire.

[0008]

According to the present invention, since the cylindrical permanent magnet is made of metal and plastic, the characteristics of a plastic magnet with small iron loss and a metal magnet with strong coercive force are exhibited, and high. This solves the problem that iron loss increases when used at a horizontal scanning frequency.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. FIG. 1 is a sectional view of a focus magnet according to the present invention. In the figure, metal cylindrical permanent magnets 1 and 2 are made of sintered alnico or ferrite or samarium cobalt, which are magnetized in the axial direction and provided with N and S magnetic poles on the end faces. A hollow disk-shaped center yoke 3 provided at an intermediate portion between the permanent magnets 1 and 2 is made of a ferromagnetic material such as soft iron. The hollow disk-shaped side yokes 4 and 5 fixed to the end faces of the permanent magnets 1 and 2 are made of a ferromagnetic material such as soft iron.
A dynamic focus coil 6 provided on the inner peripheral side of the permanent magnet 1 for correcting a central magnetic field generates a correction magnetic field for focusing an electron beam on a peripheral portion of a tube surface of a CRT (not shown). A parabolic current having a waveform corresponding to the deflection scanning is supplied. A static focus coil 7 provided on the inner peripheral side of the permanent magnet 2 for correcting the central magnetic field
It generates a correction magnetic field for converging the electron beam at the center of the tube surface of the RT, and a constant DC current is supplied from a static focus circuit (not shown).

Up to this point, there is no difference from the conventional focus magnet, but between the metal cylindrical permanent magnets 1 and 2 and the coils 6 and 7, a plastic cylindrical permanent magnet magnetized in the axial direction. Magnets 6 and 7 are provided. That is, the cylindrical permanent magnet is constituted by permanent magnets 1 and 2 made of metal and permanent magnets 8 and 9 made of plastic. The plastic cylindrical permanent magnets 6 and 7 are made of a binder made of a plastic powder such as polyamide, polyester, epoxy or the like by using a magnetic powder such as alnico and ferrite, rare earth such as samarium / cobalt, neodymium-iron-boron. After kneading by adding an additive together with a binder), the mixture is magnetized in the axial direction through an injection molding or compression molding process. However, when a ferrite magnetic powder is used, the characteristics change depending on the ambient temperature. Therefore, it is necessary to connect a temperature compensation circuit including a temperature sensor to the static focus coil 7.

Since such plastic magnets can relatively easily control the blending and magnetization of each material, it is necessary to form permanent magnets having less magnetic polarization than conventional sintered alnico or ferrite magnets. In addition, the insulating property between the magnetic powders is increased by the binder made of the plastic resin, and the iron loss is reduced. Therefore, iron loss does not increase even when used at a high frequency of 20 KHz or more. However, since the coercive force is reduced by the addition of the binder and the generation of a magnetic field is weakened, this decrease in the coercive force is caused by the metallic cylindrical permanent magnets
Is supplemented by combining with The winding of the dynamic focus coil 6 uses a litz wire to reduce the skin effect due to high frequency.

[0012]

[Effects of the Invention] As described above, the present invention is characterized by a plastic magnet having a small iron loss and a metal magnet having a strong coercive force because the cylindrical permanent magnet is made of a metal and a plastic. There is an effect that iron loss does not increase even when used at a high horizontal scanning frequency such as HDTV and EDTV.

[Brief description of the drawings]

FIG. 1 is a sectional view of a focus magnet according to the present invention.

FIG. 2 is a sectional view of a conventional focus magnet.

[Explanation of symbols]

1,2,11,12 Metallic cylindrical permanent magnet 3,13 Center yoke 4,5,14,15 Side yoke 6,16 Coil for correcting central magnetic field (dynamic focus coil) 7,17 For correcting central magnetic field Coil (static focus coil) 8,9 Plastic cylindrical permanent magnet

Claims (2)

(57) [Scope of request for utility model registration] 1. A metal-made cylindrical permanent magnet magnetized in an axial direction, a yoke plate fixed to both ends of the cylindrical permanent magnet, and a plurality of metal magnets arranged on the inner periphery of the cylindrical permanent magnet. In a focus magnet including a central magnetic field correction coil, a plastic cylindrical permanent magnet magnetized in the axial direction is provided between the cylindrical permanent magnet and the central magnetic field correction coil. And focus magnet. 2. The focus magnet according to claim 1, wherein one of the coils for correcting the central magnetic field is formed of a litz wire.