JPS62122032A - Focus magnet - Google Patents

Abstract

PURPOSE:To obtain a compact and lightweight focus magnet, by fixing a yoke of a ferro magnetic material formed into a hollow body at both end surfaces of a permanent magnet consisting of a powder-sintered body with both ends made as magnetic poles and formed in a hollow cylinder, and furnishing a coil and a thermal compensating device near the permanent magnet. CONSTITUTION:At the inner surface of a permanent magnet 1 is furnished a bobbin 5, on which a coil 3 and a compensating coil 7 are accommodated, while at the outer surface of the permanent magnet 1 is furnished a ring form body 6. As the permanent magnet 1, a magnet of relatively large thermal coefficient such as a ferrite magnet can be used, because the thermal compensating measure consisting of the ring form body 6 of a thermal-sensitive magnetic material and the compensating coil 7 functions to reduce the variation of the center magnetic field (Bg) and to exercise a specific focusing function. Therefore, the strength of the magnetic field by the permanent magnet 1 can be controlled through a current flow control of the coil 3, and electron beams passing through the axial center can be focused on a given target or fluorescent screen.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus magnet for a projection type cathode ray tube used, for example, in a video projector-1 projection type television.

[Conventional technology]

Conventional devices for converging the electron beam of cathode ray tubes include:
Electrostatic types are used for special tubes such as X-ray tubes, magnetrons, and traveling wave tubes.

A magnetic field method was used. However, recently, high resolution TVs and other devices are required.

There is a transition to magnetic field methods. However, the electromagnet type, which is the magnetic field type, has the drawbacks of being large and requiring a power source, so permanent magnets are mainly used. Figure 3 shows an example of this.
A yoke 2 made of a ferromagnetic material and formed hollow is fixed to both end faces of a permanent magnet 1 formed in a hollow cylindrical shape with an S magnetic pole to form a magnetic circuit, and a A coil 3 is interposed therein. 4 is a lead wire. By forming the coil 3 as described above and energizing the coil 3 via the lead wire 4, the magnetic field produced by the permanent magnet 1 can be adjusted, and the effect of converging the electron beam on the central axis can be expected.

[Problem that the invention seeks to solve]

In the conventional focus magnet mentioned above.

In order to avoid adverse effects on the electron beam due to biased magnetism of the permanent magnets, means are taken to arrange the permanent magnets on the outside, and therefore the outer diameter of the permanent magnets becomes large. For this reason, there is a problem in that not only the external dimensions of the entire focus device become large, but also the weight becomes large, which reduces the drop resistance of the entire cathode ray tube. Also, in the case of a 3-gun system for projection-type high-definition televisions, etc.

Since the focusing devices interfere with each other, there are problems such as the overall size of the device.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the conventional devices as described above and to provide a focus magnet that is small and lightweight.

[Means for solving problems]

In order to achieve the above object, in the present invention, a hollow yoke made of a ferromagnetic material is fixed to both end faces of a permanent magnet formed into a hollow cylindrical shape made of powder sintered body and having magnetic poles on its end faces. , a coil and temperature compensation means are provided near the permanent magnet.

〔Example〕

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention.

Identical parts are designated by the same reference numerals as in FIG. As shown in the figure, a hollow yoke 2 made of a ferromagnetic material is fixed to both end faces of a permanent magnet 1 formed into a hollow cylindrical shape, as in the prior art. A bobbin 5 is placed on the inner circumference of the permanent magnet 1.
is provided to house the coil 3 and the compensation coil 7, and an annular body 6 is provided around the outer periphery of the permanent magnet l. Annular body 6
is made of a temperature-sensitive magnetic material such as Mn--Zn ferrite, and is arranged so as to partially short-circuit the magnetic field generated by the permanent magnet 1.

With the above configuration, even if a magnet with a relatively large temperature coefficient, such as a ferrite magnet, is used as the permanent magnet 1, the effect of the temperature compensation means constituted by the annular body 6 made of a temperature-sensitive magnetic material and the compensation coil 7 , central magnetic field (
Bg) changes can be reduced, and a predetermined focusing effect can be achieved. That is, by controlling the current flowing through the coil 3, the strength of the magnetic field generated by the permanent magnet 1 can be adjusted, and the electron beam passing through the axis can be focused on a predetermined target or phosphor screen. For example, without using temperature compensation means, a ferrite magnet with a temperature coefficient of -0.2%/℃ can be heated between -10'' and +60℃.
When used in the temperature range.

The change in Bg is as high as 14%, but by using Mn-Zn thermal ferrite, the change in Bg can be reduced to 1.5%.
I was able to fit it in below.

Next, FIG. 2 is a longitudinal sectional view showing another embodiment of the present invention, and the same parts are designated by the same reference numerals as in FIGS. 1 and 3. The temperature compensation means of the permanent magnet 1, which is a ferrite magnet, in this embodiment is an annular bobbin 5 made of a temperature-sensitive magnetic material. That is, for example, as described above < M n −Z
A bobbin 5 is formed of a temperature-sensitive magnetic material such as n-type ferrite, houses a coil 3, and is provided around the outer periphery of the permanent magnet 1. The convergence effect of the electron beam passing through the axis is the same as in the previous embodiment. This structure allows
We were able to keep the change in Bg to 1% or less.

In this embodiment, an example is shown in which the coil 3 and the compensation coil 7 are arranged on the inner periphery of the permanent magnet l, and the annular body 6 made of a temperature-sensitive magnetic material is arranged on the outer periphery of the permanent magnet. Either the inner or outer circumference of the permanent magnet 1 may be used. Note that the upper limit of the operating temperature range of focus magnets is set at around 60'C, so the temperature-sensitive magnetic material mentioned above is suitable for temperatures ranging from 45°C to 85°C.
It is desirable to have a characteristic such that the saturation magnetic flux density (Bs) becomes approximately 0 at a temperature of .

〔Effect of the invention〕

Since the focus magnet of the present invention has the structure and function as described above, it can achieve the following effects.

(1) Since the inner diameter of a permanent magnet is inversely proportional to the strength of the magnetic field, the magnetic field becomes stronger as the inner diameter becomes smaller, allowing the permanent magnet to be made thinner.

(2) Since the permanent magnet is smaller, the weight is about 1/3 compared to the conventional type, so the drop resistance of the cathode ray tube can be greatly improved.

(3) By reducing the diameter of the permanent magnet, it is possible not only to reduce the external dimensions of the focus magnet, but also to reduce the distance between the cathode ray tubes in a 3-gun system.
The entire device can be downsized.

[Brief explanation of drawings]

FIGS. 1 and 2 are longitudinal cross-sectional views showing embodiments of the present invention, and FIG. 3 is a vertical cross-sectional view showing a focus magnet of a conventional structure. 1: Permanent magnet, 2: Yoke, 3: Coil, 7: Compensation coil.

Claims (6)

[Claims] (1) A hollow cylindrical permanent magnet made of powdered sintered material with magnetic poles provided on the end face has a hollow yoke made of ferromagnetic material fixed to both end faces, and a coil and temperature A focus magnet characterized by having a compensation means (2) The focus magnet according to claim 1, wherein the permanent magnet is a ferrite magnet. (3) The focus magnet according to claim 1 or 2, wherein the temperature-sensitive magnetic material is a temperature-sensitive ferrite. (4) The focus magnet according to claim 3, which is a temperature-sensitive ferrite such that Bs≈0 at 45° to 85°C. (5) The focus magnet according to any one of claims 1 to 4, wherein the temperature compensation means is a bobbin made of a temperature-sensitive magnetic material, and the bobbin is provided on the outer periphery of the permanent magnet and accommodates a coil. (6) The focus magnet according to any one of claims 1 to 4, wherein the temperature compensation means is an annular body made of a temperature-sensitive magnetic material and a compensation coil.