JPH01276546A - Focusing magnet - Google Patents

Abstract

PURPOSE:To prevent the drift of centers of two coils and the superposition of current wave-forms and precisely perform the focus correction by winding a coil feeding the correction current concentrically with a coil feeding the focus current and inside its coil. CONSTITUTION:An electron beam passing the neck 3 of a CRT is focused by the magnetic field excited by a permanent magnet 1 and the magnetic field generated by the current flowing through a coil 2, the current is adjusted so that the electron beam is converged on the fluorescent screen of the CRT. A current with a parabolic correction wave-form is fed to a correcting coil 5, the magnetic field thus generated corrects the focus on the center and periphery of the CRT fluorescent screen 6 so that the CRT fluorescent screen 6 and the focus point 8 of the electron beam 7 coincide. Mutual interference is extremely reduced, the focus on the screen can be performed with high precision.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a focus magnet, and in particular, in display devices such as television receivers and monitors, a correction current is applied to the focus magnet for improving or abolishing screen focus or for other purposes. This is related to a focus magnet for Guinamisoku focus that has an integrated coil that can flow.

[Conventional technology]

Figure 2 is a cross-sectional view of a focus magnet used, for example, in a video projector manufactured by Mitsubishi Electric. A coil, 3 a neck of a cathode ray tube (hereinafter referred to as CRT) to which a focus magnet is attached, and 4 a yoke.

FIG. 4(a) is a diagram showing a focused state of an electron beam by a conventional focus magnet, and FIG. 4(1) is a diagram showing a waveform of a focusing current flowing through the coil 2. In the figure, 6 is the CRT fluorescent surface, 7 is the focus point of the electron beam 8, 9 is the deflection center of the electron beam, and 10 is the center of the CRT fluorescent surface 6.

Next, the operation will be explained.

The electron beam passing through the neck 3 of the CRT is focused by the magnetizing magnetic field of the permanent magnet 1 and the magnetic field generated by the direct current flowing through the coil 2 (Fig. 4(b)), and is focused on the fluorescent surface 6 of the CRT. The current force is adjusted 9 times so that

[Problem to be solved by the invention]

In the conventional focusing magnet, as described above, a direct current is passed through a single focusing coil, and the resulting magnetic field focuses the electron beam of the CRT. However, in the conventional focus magnet, the position of the focus point 8 of the electron beam 7 is parabolic, as shown by the dashed line in FIG. 4(a). When applied to a CRT, the distance from the polarization center 9 of the electron beam to the fluorescent surface 6 differs depending on the position of the fluorescent surface, so the focus at the periphery of the CRT's fluorescent surface is worse than at the center. . To prevent this, it would be good to apply a magnetic field for focus correction, but if a correction current generated in a separate circuit is superimposed and a correction magnetic field is applied, an addition circuit or output circuit must be created, and If another similar focus magnet is attached behind the conventional magnet in order to apply a focus correction magnetic field, alignment adjustment will be required twice because the center points of magnetization of the two magnets are different. Furthermore, in the method of winding the coil through which the correction current flows around the same yoke 4 as the coil 2, there is a problem in that the coils function as a transformer, causing waveforms to be superimposed on each other's circuits.

This invention was made to solve the above-mentioned problems. Although one focus magnet is equipped with two coils, one for focusing and one for correction, the magnetization center of the two coils is the same and the waveform is different. The purpose of the present invention is to provide a focus magnet for dynamic focusing that is free from mutual interference.

[Means to solve the problem]

In the focus magnet according to the present invention, a coil for flowing a correction current is wound concentrically with a coil for flowing a focus current, and inside the coil.

[Effect]

In this invention, since the correction current coil is provided concentrically with the conventional coil and inside the conventional coil,
There is no misalignment between the centers of the two coils, and there is no overlap in the current waveforms.
Focus correction can be performed with high precision.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing a focus magnet according to an embodiment of the present invention. In the figure, the same symbols as in FIG. 2 indicate the same parts, and 5 is a coil for flowing a correction current.

In addition, FIG. 3 (al is a diagram showing the focused state of the electron beam by the focus magnet of the present invention, and FIG. 3 (b
1 is a diagram showing a correction current waveform to be passed through the correction current coil 5 of the present invention.

Next, the operation will be explained.

The electron beam passing through the neck 3 of the CRT is focused by the magnetizing magnetic field of the permanent magnet 1 and the magnetic field generated by passing a current through the coil 2, and the current is adjusted so as to focus on the fluorescent surface of the CRT. At this time, by passing a current with a parabolic correction waveform as shown in FIG. 3(b) through the correction coil 5, the magnetic field generated thereby is used as shown in FIG. 3(a).
), the focus of the center and periphery of the CRT fluorescent surface is corrected so that the CRT fluorescent surface 6 and the focus point 8 of the electron beam 7 coincide.

According to this embodiment, two coils, one for focusing and one for correction, are provided in one focus magnet so that their magnetization centers are the same and there is no mutual interference of waveforms, so a simple device can be used. , it is possible to focus the electron beam on the CRT fluorescent surface with high precision.

〔Effect of the invention〕

As described above, according to the present invention, the coil that flows the correction current is wound concentrically with the coil that flows the focus current, and inside this coil, so that one focus magnet can handle the basic focus current and the dynamic focus. It is possible to flow a focus current for correction such as the above, and at this time, there is extremely little misalignment of the centers of the two coils and mutual interference, so there is an effect that the focus of the screen can be made highly accurate.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a focus magnet for dynamic focusing according to an embodiment of the present invention, FIG. 2 is a sectional view of a conventional focus magnet, and FIG. 3(b) is a diagram showing the correction current waveform of the focus magnet of the present invention, FIG. 4(a) is a diagram showing the focused state of the electron beam by the conventional focus magnet, and FIG. is a diagram showing a focus current waveform of a conventional focus magnet. In the figure, 1 is a permanent magnet, 2 is a focus current coil, 3 is a neck of a CRT, 4 is a yoke, 5 is a correction current coil, and 6 is a CRT. The fluorescent surface, 7 is an electron beam, 8 is a focus point, 9 is the deflection center of the electron beam, and 10 is the center of the CRT fluorescent surface. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] (1) In a focus magnet used in a cathode ray tube that electromagnetically focuses an electron beam and is equipped with a permanent magnet and a coil through which a static focus current flows, the magnet is placed concentrically with the coil and inside the coil. A focus magnet characterized in that a correction coil is provided for flowing a dynamic focus current for focus position correction.