GB2319657A

GB2319657A - Cathode ray tubes

Info

Publication number: GB2319657A
Application number: GB9725006A
Authority: GB
Inventors: Yoshio Taka; Hisato Takamura; Shigemi Oguchi
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1996-11-26
Filing date: 1997-11-25
Publication date: 1998-05-27
Anticipated expiration: 2017-11-25
Also published as: JPH10154471A; MX9709142A; GB9725006D0; GB2319657B

Abstract

Metal foils (30a to 30d) are attached adjacent convergence plates (16R, 16G, and 16B) to which the horizontal deflection magnetic field H is applied from the horizontal coil (21) on the neck portion of a colour cathode ray tube. The metal foils (30a to 30d) form an array centred on the G electron beam with each foil being at an angle of, for example, 45 degrees with respect to the direction X. The magnetic field H applied to the R and B electron beams generates eddy current in the metal foils (30a to 30d). The magnetic field H also generates eddy current in the G convergence plate (16G), and if the force which deflects the G electron beam is weakened by the diamagnetic field, then by providing the metal foils (30a to 30d), the force which deflects R and B electron beams is adjusted to compensate. Hence mis-convergence is corrected easily. Metal rings or coatings can be used instead of foils.

Description

COLOUR PICTURE TUBE This invention relates to a colour picture tube.

Heretofore, a colour picture tube in which an in-line type electric gun having cathodes arranged in one line generates three electron beams, the respective electron beams are converged on red, blue, green, and blue (refer to R, G, and B hereinafter) fluorescent material to display a colour image has been used.

An electron gun of such colour picture tube has cathodes for emitting an electron beam respectively and a plurality of grids for controlling the quantity of electron beam to modulate and for converging so that an electron beam is converged to a smallest spot, and in the case of the electron gun is of the single-electron gun common convergence type, the electron gun is provided with a convergence plate for deflecting the path of side electron beams so that the side electron beams pass through a mask together with the center electron beam and impinge on the fluorescent material of the prescribed color.

In the horizontal fly-back interval in Fig. 6 which illustrates a horizontal deflection current, respective electron beams scanned to the right by the horizontal deflection magnetic field H generated by the horizontal coil 21 of the deflection yoke as shown in Fig. 7 is deflected to the left sharply and the horizontal deflection magnetic field H generates an eddy current in the convergence plate 16G (refer to G convergence plate hereinafter) of the G electron beam that is the center electron beam.

The horizontal deflection magnetic field H is applied approximately perpendicularly to the C convergence palate 16G, but is applied with inclination to the R convergence plate for the R electron beam and B convergence plate for the B electron beam which are both side electron beams because the horizontal deflection magnetic field H has a shape of pincushion. Hence, more eddy current is generated in the G convergence plate than in R and B convergence plates, and the force which restores the direction of the G electron beam to the left due to the diamagnetic field caused by the eddy current is weakened in comparison with the force which restores the direction of the B electron beam to the left.

The force results in asymmetric mis-convergence as shown in Fig. 9.

Even in the case that six polar ring magnets are adjusted so that the R, G, and B electron beams are coincide at the center of the raster, mis-convergence is generated at the right end and left end as shown in Fig. 10 because of sensitivity difference in adjusting.

In the case of an in-line type electron gun having no convergence plate, hood-shaped metal plates 18R and 18B are provided to the convergence cup 17 of the electron gun as shown in Fig. 11 to generates eddy current, and the horizontal deflection magnetic field applied to the metal plates 18R and 18B (X1) generates eddy current to equalize the force for restoring the direction of the R and B electron beams to the left to the force for restoring the direction of the G electron beam to the left. In this case, it takes a long time to design the shape, method for attaching, and position to be attached of the hood-shaped metal plates 18R and 18B when the electron gun is designed. Further, if the case that the convergence deviation causes a scattering, the electron gun must be redesigned again, it takes a longer time.

In view of the above-mentioned problems, the present invention provides a colour picture tube which is capable of reducing or correcting mis-convergence.

A colour picture tube in accordance with one aspect of the present invention is provided with a conductive section formed on the neck portion of the colour picture tube at the position located where a horizontal deflection magnetic field is applied to the electron gun.

The conductive section may comprise a plurality of conductive portions, the plurality of conductive portions having the centre at the position of the centre electron beam outputted from the electron gun is located with a prescribed angle with respect to the cathode arranged direction, and eddy current is generated in the conductive portions by the horizontal deflection magnetic field applied to the side electron beams outputted from the electron gun.

In an embodiment of the present invention, the conductive section is formed on the neck portion of a colour picture tube.

The conductive section is formed at the position located where a horizontal deflection magnetic field is applied to the electron gun, hence, eddy current is generated by the horizontal deflection magnetic field applied, for example, to side electron beams in the conductive section to cause diamagnetic field, and the diamagnetic field weakens the force which deflects the side electron beams.

According to another aspect of the invention, there is provided a colour picture tube, capable of correcting mis-convergence by way of a method that a conductive portion is formed on the neck of the colour picture tube, the conductive portion is located at the position where a horizontal deflection magnetic field is applied to an electric gun to generate an eddy current in the conductive portion caused by the horizontal deflection magnetic field, and the diamagnetic field due to the eddy current is utilized to correct mis-convergence.

For a better understanding of the present invention, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a view for illustrating the structure of a colour picture tube in accordance with an illustrative embodiment of the present invention; Figure 2 is a view for illustrating the case in which metal foils are used as the conductive section in the tube of Figure 1; Figure 3 is a schematic cross-sectional view along the line I-I' in Figure 2; Figure 4 is a view for illustrating the raster after correction of mis-convergence; Figure 5 is a view for illustrating the case in which metal rings are used as the conductive sections in the tube of Figure 1; Figure 6 is a view for illustrating the horizontal deflection current; Figure 7 is a view for illustrating the eddy current generated by the horizontal deflection magnetic field; Figure 8 is a view for illustrating the horizontal deflection magnetic field; Figure 9 is a view for illustrating the raster before adjustment; Figure 10 is a view for illustrating the raster after six polar ring magnet is adjusted; Figure 11 is a view for illustrating the mis-convergence using hood-shaped metal plates.

Figure 1 is the structure of a colour picture tube embodying an illustrative example of the present invention. The colour picture tube is provided with an in-line type electron gum 15, and a deflection yoke 20 for generating horizontal deflection magnetic field and vertical deflection magnetic field for deflecting electron beams outputted from the electron gun 15 is attached. The area on which the deflection yoke 20 is attached is shown in Figure 2.

In Figure 2, the position of the deflection yoke 20 in the front-rear direction of the colour picture tube 10 (Z direction) is determined depending on the beam landing characteristics.

Usually a yoke is located near electron beam output section of the electron gun 15, for example, in the case that the electron gun 15 is a single-electron gun common convergence type electron gun, the deflection yoke 20 is located near the convergence plates 16R, 16G, and 16B for adjusting convergence of electron beams.

In accordance with an illustrative embodiment of the invention, metal foils 30a to 30d which serve as conductive sections beams are restored to the left end of the screen, the R, G, and B electron beams are thereby restored to the same position, and the positions of the R, G, and B electron beams are becomes identical as shown in Fig. 4, mis-convergence is thus corrected.

If scattering of convergence deviation happens to occur, magnitude of eddy current can be adjusted by changing size or position of the metal foils 30a to 30d to be attached on the neck portion 11 of the color picture tube 10, and by changing angle with respect to the cathode arranged direction X, therefore mis-convergence is easy corrected.

As describedherein'oefore, mis-convergence is corrected by means of inexpensive method in which conductive sections are formed at the position of the electron gum to which the horizontal deflection magnetic field H is applied on the neck portion 11 of the color picture tube 10. As required, the scattering of convergence deviation is easily corrected by changing size and position of the conductive sections.

Material used for the conductive section is by no means limited to metal foil, for example, rod-like metal rings 40a to 40d may be attached on the neck portion 11 as conductive section as shown in Fig. 5. Alternatively, the conductive section may be formed by depositing metal on the neck portion 11 by way of evaporation. The number and position of the conductive sections in the embodiment is exemplary and by no means limited to the case shown above. The present invention is by no means limited to the single-electron gun common convergence type electron gum, for example, the same effect is obtained for a three electron gun separated type electron gun and a three electron gun combined type electron gun.

In embodiments of the present invent ion, by forming conductive sections on the neck portion of a colour picture tube and forming these conductive sections at the position located where the horizontal deflection magnetic field is applied to the electron gun, eddy current is generated in the conductive sections due to the horizontal deflection magnetic field to generate diamagnetic field, and the diamagnetic field weakens the force which deflects the electron beam. Hence, if the force which deflects the main electron beam and the force which deflects side electron beams are not equal and causes mis-convergence, the force which deflects the electron beam can be adjusted by adjusting the conductive sections, the mis-convergence is thus corrected easily and inexpensively. If convergence deviation happens to scatter, mis-convergence is corrected easily by adjusting the position of the conductive sections.

Claims

1. A colour picture tube having a built-in in-line type electron gun (15), wherein a conductive section is formed on the neck portion (11) of said colour picture tube (10) at the position where a horizontal deflection magnetic field is applied to said electron gun (15).

2. A colour picture tube as claimed in claim 1, wherein said conductive section comprises a plurality of conductive portions, said plurality of conductive portions having the centre at the position of the centre electron beam outputted from said electron gun (15) are located with a prescribed angle with respect to the cathode arranged direction, and eddy current is generated in said plurality of conductive portions by said horizontal defection magnetic field applied to side electron beams outputted from said electron gun (15).

3. A colour picture tube as claimed in claim 2, wherein there are four conductive portions, and said four conductive portions are located with an angle of approximately 45 degrees with respect to the cathode arranged direction and with an angular interval of approximately 90 degrees each other.

4. A colour picture tube substantially as hereinbefore described with reference to Figures 1 together with Figures 2 and 3, or Figure 5 of the accompanying drawings.