JP2512824B2 - 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, and the like, 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 converging an electron beam emitted from an electron gun on the fluorescent surface. For special tubes such as X-ray tubes, magnetrons, and traveling wave tubes,
The magnetic field method was 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. 4 shows an example of this, in which the end faces are magnetized in the axial direction.
A hollow cylindrical yoke 2 made of a ferromagnetic material is fixed to both end faces of a hollow cylindrical permanent magnet 1 provided with N and S magnetic poles to form a magnetic circuit.
The coil 3 is provided on the inner periphery of the coil 3 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 converging the electron beam on the central axis is expected. You can do it.

The spot diameter obtained by converging the electron beam on the central axis by the conventional focus magnet is 0.3 to 0.35 mm, but for recent high definition projectors, the spot diameter is required to be 0.25 to 0.28 mm. However, even if the spot diameter of the electron beam is reduced in the conventional focus magnet, spherical aberration is large and halation appears. In order to eliminate this drawback,
It has been proposed that at least two ring-shaped permanent magnets are connected in the same magnetic pole direction, and the magnetic flux density distribution on the Z axis of these permanent magnets is set to have a half value width and an inner diameter of the permanent magnet of 80% to 200%. (See JP-A-61-211940). This proposal is the ratio of the half-value width Bw of the magnetic flux distribution on the Z axis of the ring-shaped permanent magnet to the inner diameter L of the permanent magnet, that is, H = Bw / L
Is used as a parameter, in order to significantly increase H, it is effective to have a configuration in which at least two ring-shaped permanent magnets are separately magnetized and connected in the same magnetic pole direction, and spherical aberration In order to improve, it is preferable to set the above H to 0.8 or more.

[Problems to be Solved by the Invention]

FIG. 3 is a longitudinal sectional view of an essential part showing an example of the improved invention described above, and the same portions are designated by the same reference numerals as those in FIG. In this case, the two coils 3 are used for dynamic adjustment that changes in synchronization with vertical and horizontal scanning, respectively, but in many cases one of the coils 3 is also used for static adjustment. However, in order to perform static adjustment and dynamic adjustment with the same coil, it is necessary to pass a current in which an alternating current is superimposed on a direct current. In this case, however, the variable range of the static adjustment needs to be considered quite widely, including variations in the magnetic force of the permanent magnet 1, and the inductance of the coil 3 should be large. Since it is 15.75kHz, it has the drawback that it must be driven at a high voltage in order to perform horizontal scanning focus modulation.

In order to eliminate the above-mentioned drawbacks, the static adjustment coil and the dynamic adjustment coil are separated so that the static adjustment coil receives a DC current and the dynamic adjustment coil receives an AC current for focus correction. Since it suffices to flow it, the inductance of the dynamic adjustment coil can be reduced, and it is possible to drive at a low voltage. However, since the two adjusting coils are concentrically arranged in the same permanent magnet 1 and are electromagnetically coupled,
Due to the alternating current flowing through the dynamic adjustment coil, the static adjustment coil changes its current so as to cancel the change in the magnetic flux due to the dynamic adjustment coil, and the effect of changing the focal length of the electron beam decreases. There is a drawback in that the correction current flowing in the dynamic adjustment coil must be increased, and there is a problem in that the power consumption of the coil increases.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems existing in the above-mentioned prior art and to provide a focus magnet that can increase the half-value width of the magnetic flux density on the central axis of the permanent magnet and the coil and that consumes less power. To do.

[Means for solving the problem]

In order to achieve the above object, in the present invention, a hollow cylindrical shape is obtained by magnetizing in the axial direction, providing magnetic poles on both end faces, and fixing a hollow disk-shaped yoke made of a magnetic material to the magnetic pole faces. In a focus magnet configured by coaxially connecting three permanent magnets with opposite poles facing each other, a static adjustment coil is provided on the inner circumference of the permanent magnet in the middle part, and a coil for static adjustment is provided on the inner circumference of the permanent magnets at both ends. We adopted the technical means of providing a coil for horizontal and vertical dynamic adjustment, and concentrating the electron beam in the cathode ray tube provided coaxially with the permanent magnet and the coil.

[Work]

With the above configuration, the static adjustment coil and the dynamic adjustment coil can be separated, and only the DC current needs to flow in the static adjustment coil, and it is not necessary to set the high voltage in consideration of the AC superposition. In addition, the dynamic adjustment coil is not only separated from the static adjustment coil, but is also configured to be electromagnetically uncoupled, so that only the originally required correction current needs to flow.

〔Example〕

FIG. 1 is a longitudinal sectional view of an essential part showing an embodiment of the present invention,
The same parts are designated by the same reference numerals as those in FIGS. 3 and 4. In FIG. 1, reference numerals 1a and 1b are permanent magnets, for example, an Sm-Co magnet (H-18B made by Hitachi Metals) having an outer diameter of 65 m.
It is formed into a hollow cylinder with m, inner diameter of 50 mm, and thickness of 16 mm (1a) and 8 mm (1b), and is magnetized in the axial direction to provide N and S magnetic poles on both end faces, respectively. The yoke 2 is formed of, for example, soft ferrite into a hollow disk shape having an outer diameter of 60 mm, an inner diameter of 50 mm and a thickness of 5 mm, and is fixed to the magnetic pole surfaces of the permanent magnets 1a and 1b. Permanent magnets 1b are coaxially connected to both ends of the permanent magnet 1a with opposite poles facing each other. Next, 3a and 3b are coils for static adjustment and coils for dynamic adjustment, respectively, which are provided on the inner circumferences of the permanent magnets 1a and 1b via bobbins 4. One of the two dynamic adjustment coils 3b is horizontal and the other is vertical. The coil 3a for static adjustment is, for example, 0.2 mmφ × 570 turns, and the coil 3b for dynamic adjustment is, for example, 0.5 mm.
Formed by φ × 26 turns. 5a and 5b are lead wires. The above-mentioned constituent members are integrally fixed by an adhesive and incorporated into a holder (not shown) formed of, for example, 66 nylon to form a focus magnet.

FIG. 2 is a diagram showing the relationship between the axial position of the focus magnet and the central magnetic flux density, and the permanent magnet 1a is shown as the axial position 0. As is apparent from FIG. 2, the half-value width of the central magnetic flux density is 52.4 mm in the curve a indicating the present invention, which is smaller than the half-value width 31.1 mm in the curve b indicating the conventional configuration shown in FIG. It can be seen that it has increased significantly. In the structure shown in FIG. 3, when the distance between the permanent magnets 1 and 1 is increased to increase the half-value width, the central magnetic flux density decreases near the axial position 0, and as shown by the broken line c. Although it may appear in the shape of a concave curve, in the present invention, since three permanent magnets 1a and 1b are coaxially arranged, such a decrease in the central magnetic flux density distribution of the concave curve occurs. unacceptable.

When the electron beam is focused in the cathode ray tube by the focus magnet shown in FIG. 1, the diameter of the focused spot of the electron beam can be reduced, and the correction current in the coil 3b for dynamic adjustment is reduced to the conventional one.
It was confirmed that the value can be reduced from 4 Ap-p (peak to peak value) to 3 Ap-p.

In this embodiment, an example in which the Sm-Co magnet is used as the permanent magnet has been shown, but other rare earth magnets may be used, or a permanent magnet other than the rare earth magnet may be used.
Further, the constituent material of the yoke to be fixed to the end face of the permanent magnet may be other than ferrite, and an iron plate or other magnetic material can be appropriately selected and used. Furthermore, the shape of each component that constitutes the focus magnet,
The dimensions and specifications can be appropriately selected according to the shape, dimensions and specifications of the cathode ray tube to be applied.

〔The invention's effect〕

Since the present invention has the configuration and operation as described above, it is possible to increase the half-value width of the magnetic flux density on the central axis of the permanent magnet and the coil. As a result, it is possible to increase the integral value of the magnetic flux density distribution curve and The convergent spot diameter can be reduced. Further, the static adjustment coil and the dynamic adjustment coil are independent of each other, and the interference between both coils is eliminated, so that the power consumption of the coil can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an essential part showing an embodiment of the present invention, FIG. 2 is a view showing a relation between an axial position and a central magnetic flux density, and FIGS. 3 and 4 are conventional focus magnets. FIG. 1,1a, 1b: Permanent magnet, 3,3a, 3b: Coil.

Claims (1)

(57) [Claims] 1. Three hollow cylindrical permanent magnets, each of which is magnetized in the axial direction and has magnetic poles on both end faces, and a hollow disk-shaped yoke made of a magnetic material is fixed to the magnetic pole faces. In a focus magnet constructed by coaxially connecting the poles facing each other, a coil for static adjustment is provided on the inner circumference of the permanent magnet in the middle portion, and a coil for horizontal and vertical dynamic adjustment is provided on the inner circumference of the permanent magnets at both ends. A focus magnet, characterized in that a coil is provided, and the electron beam is focused within a cathode ray tube provided coaxially with the permanent magnet and the coil.