JPH01144547A - Focus magnet - Google Patents

Abstract

PURPOSE:To improve the performance by setting the half-value width of the magnetic flux density distribution on the Z axis of permanent magnets to the specific ratio with respect to the inner diameter of the permanent magnets in a focus magnet connected with two ring-shaped permanent magnets. CONSTITUTION:Two permanent magnets 1 are coaxially connected and fixed via a yoke 2 with opposite poles faced to each other. A coil 3 wound on a bobbin 4 is inserted into the inner periphery of each magnet 1. The half-value width of the magnetic flux density distribution on the axis of the permanent magnets is set to 40-80% of the inner diameter of the magnet 1. When this value is below 40%, the magnetic flux density is small, when it is above 80%, the eccentric magnetization factor is too large. The good performance is obtained within the range of 40-80%.

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 in, for example, a video projector-1 projection type high-definition television, etc., and particularly relates to a focus magnet for a high-definition projector. The present invention relates to an improvement of the focus magnet.

[Conventional technology]

Conventionally, an electrostatic type device has been used to focus the electron beam emitted from an electron gun onto a fluorescent surface.
Magnetic field methods were used for special tubes such as X-ray tubes, magnetrons, and traveling wave tubes.

However, as a result of the recent demand for high-resolution devices such as high-definition televisions, there is a shift toward magnetic field methods.

The electromagnet type, which is one type of magnetic field type, has the drawbacks of being large and requiring a power source, and therefore permanent magnets are mainly used.

Figure 2 shows an example of this. A permanent magnet 1 is magnetized in the axial direction and has N and S magnetic poles on the end face, and is formed into a hollow cylindrical shape.
Consists of two ferromagnetic materials on both end faces.

A magnetic circuit is formed by fixing a hollow coke 2, and a coil 3 is interposed on the inner circumference of the permanent magnet 1 via a bobbin 4. Form as above,
If 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 effect of converging the electron beam on the central axis can be expected.

The spot diameter of the converged electron beam on the central axis by the conventional focus magnet is 0.3 to 0.350 m, but for recent high-definition projectors, the spot diameter is 0.25 to 0.28 m. is required. However, in conventional focusing magnets, even if an attempt is made to narrow down the spot diameter of the electron beam, one spherical aberration is large and halation occurs. In order to eliminate this drawback, at least two ring-shaped permanent magnets are connected in the same magnetic pole direction, and the half-value width of the magnetic flux density distribution on the Z axis of these permanent magnets is set to 80% to 200% of the inner diameter of the permanent magnet. It has been proposed that the content of
(see publication). This proposal uses the ratio of the half width Bw of the magnetic flux distribution on the Z axis of a ring-shaped permanent magnet to the inner diameter of the permanent magnet, that is, the value of H = B w / L, as a parameter, and significantly increases H. In order to achieve this, it is effective to have a configuration in which at least two ring-shaped permanent magnets are magnetized separately and connected in the same magnetic pole direction, and in order to improve spherical aberration, the above H should be set to 0.8. The content above is what is preferable.

[Problem that the invention seeks to solve]

The performance required of the focus magnet for the above-mentioned high-definition projector is extremely high in terms of magnetic flux density on the Z-axis, half-width of magnetic flux density, axis misalignment, ellipticity, polarization, etc. . Here, the magnetic polarization is 1. For example, a virtual cylindrical surface (diameter 20
m) is the variation in the magnetic flux density at the maximum and minimum points of the axial magnetic flux density on the axial direction, and may be specified as 3% or less. In a focus magnet that is required to have such performance, if the value of H is set to a large value as described above, there is a problem in that the magnetic polarization increases, making it impossible to focus the electron beam well.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a focus magnet that has a small polarization and high electron beam focusing performance while ensuring the magnetic flux density and half-width on the Z-axis.

[Means for solving problems]

In order to solve the above-mentioned problems of the prior art, the present invention provides at least two magnetic poles, which are magnetized in the axial direction and provided with magnetic poles on both end faces, and a hollow disk-shaped yoke is fixed to the magnetic pole faces. A hollow cylindrical permanent magnet.

In a focus magnet formed by coaxially connecting different poles facing each other, the half width of the magnetic flux density distribution on two axes of the permanent magnet is set to 40 to 80% of the inner diameter of the permanent magnet. This technical method was adopted.

〔Example〕

FIG. 1 is a cross-sectional view of essential parts showing an embodiment of the present invention, and the same parts are designated by the same reference numerals as in FIG. and are coaxially coupled and fixed via the yoke 2. Note that a coil 3 is interposed on the inner circumference of the permanent magnet 1.1 via a bobbin 4. Next, permanent magnet 1 is a ferrite magnet (YB manufactured by Hitachi Metals)
The table shows the results of measuring the magnetic flux density Bz on the Z axis and the magnetic polarization δ by changing the half width Bw of the magnetic flux density and the inner diameter variously.

As is clear from the table, in No. 1, the magnetic flux density Bz on the Z axis is insufficient and cannot satisfy the electron beam focusing function required for a focus magnet, while in No. 7, the above magnetic flux density BzO value is sufficient. However, the value of magnetic polarization δ is too large.

It does not satisfy the performance of 3% or less required for focus magnets for high-definition projectors. On the other hand, in Sō 2 to 6, the value of the magnetic flux density Bz on the Z axis is sufficiently large, and the value of the magnetic polarization δ is small, as well as having a satisfactory electron beam focusing function, so that the above-mentioned required function is achieved. It is recognized that the following are satisfied.

In this embodiment, an example is described in which a ferrite magnet is used as a permanent magnet, but a cast magnet such as an alnico magnet may also be used. Further, as the constituent material of the yoke to be fixed to the end face of the permanent magnet, an iron plate or other magnetic material is appropriately selected and used.

〔Effect of the invention〕

Since the present invention has the configuration and operation as described above, it is possible to sufficiently increase the magnetic flux density and half-width on the Z-axis, which contribute to the focusing performance of the electron beam, and also to sufficiently increase the magnetic flux density and half-width, which are required for high-definition projectors. This has the effect that the magnetic polarization can be significantly reduced, and the performance of the focus magnet can be greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part showing an embodiment of the present invention, and FIG. 2 is a sectional view of a main part showing an example of a conventional focus magnet. l: permanent magnet, 2: yoke.

Claims (2)

[Claims] (1) At least two hollow cylindrical permanent magnets are magnetized in the axial direction and have magnetic poles on both end faces, and a hollow disc-shaped yoke is fixed to the magnetic pole faces, with different poles facing each other. A focus magnet connected coaxially, characterized in that the half width of the magnetic flux density distribution on the Z axis of the permanent magnet is 40 to 80% of the inner diameter of the permanent magnet. (2) The focus magnet according to claim 1, wherein the permanent magnet is a ferrite magnet.