JPH0367296B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color cathode ray tube, in which the size of a raster formed on a phosphor screen by a central and a pair of outer electron beams emitted from an in-line electron gun by a common deflection magnetic field is determined by In particular, the present invention relates to a self-convergence type in-line electron gun that can make the horizontal deflection frequency equal regardless of the horizontal deflection frequency.

FIG. 1 is a longitudinal sectional view of a conventional cathode ray tube using a so-called self-convergence type in-line electron gun that does not require dynamic convergence correction. A central electron beam B1 emitted from the in-line electron gun 1 and located in the same plane and a pair of outer electron beams B2 and B3 are deflected by a deflection device 5 disposed in a funnel-shaped portion of the evacuated glass envelope 2. Scanning is performed through a shadow mask 3 which is deflected horizontally and vertically and which is placed on the top surface of the glass envelope 2 and is placed opposite to a phosphor screen 4 on which a plurality of phosphor pixels that emit light in three colors are deposited on the inside. Form the screen. In order to make this color cathode ray tube a self-convergence type that does not require dynamic convergence correction, the horizontal deflection magnetic field of the deflection device 5 is made to have a strong capillary distortion, and the vertical deflection magnetic field is made to have a strong barrel distortion. As shown in Figure 2, these deflection magnetic fields eliminate the coma aberration of the pair of outer electron beams B2 and B3, and the phosphor screen 4
A scanning screen 6 corresponding to the top is formed. In this case, the scanning screen 7 of the central electron beam B1 is generally horizontal,
The scanning screen 6 formed by both the vertical and outer electron beams B2 and B3 is smaller. This misalignment of the scanning screens is due to comatic aberration of the deflection device 5, and in order to remove the comatic aberration and make each scanning screen consistent,
A magnetic field control element made of a magnetic material with high magnetic permeability is disposed on the bottom surface 11 of a concentrated magnetic pole 10 formed in a bottomed cylindrical shape made of a non-magnetic material and attached to the tip of the electron gun 1 to which the rear leakage magnetic field of the deflection device 5 is applied. It is set up. FIG. 3 shows an example of a magnetic field control element, in which the central electron beam transmission aperture 12 formed in the bottom surface 11 of the concentrated magnetic pole 10 is arranged opposite to each other so as to be sandwiched between the vertical axis Y-Y, which is the short axis of the fluorescent screen 4. A pair of disc-shaped magnetic enhancement elements 15 and 16
and annular magnetic shielding elements 17 and 18 arranged so as to surround both outer electron beam transmission apertures 13 and 14 formed on the horizontal axis XX, which is the long axis of the phosphor screen 4. The magnetic enhancement elements 15 and 16 increase the deflection sensitivity of the horizontal deflection magnetic field F _H of the deflection device 5 with respect to the central electron beam B1 on both outer electron beams B2 and B3.
The annular magnetic shielding elements 17 and 18 are configured to deflect the deflection device 5 with respect to both outer electron beams B2 and B3.
It has the function of lowering the deflection sensitivity of the horizontal and vertical deflection magnetic fields F _H and F _V of the center electron beam B1 compared to the center electron beam B1, and increasing the deflection sensitivity of the vertical deflection magnetic field F _V with respect to the center electron beam B1 compared to both outer electron beams. .

Therefore, the scanning screen 7 of the central electron beam B1 is expanded both horizontally and vertically by the magnetic field controllers 15, 16 and 17, 18, and conversely, the scanning screen 7 of the central electron beam B1 is enlarged in both the horizontal and vertical directions.
The scanning screen 6 of B3 is reduced, coma aberration due to the deflection magnetic field is removed, and the scanning screens 6 and 7 can be made to coincide completely.

On the other hand, recently, so-called display color cathode ray tubes, which are color cathode ray tubes with high resolution characteristics, have been used to display various types of information.This allows alphanumeric characters, symbols, kanji, charts, etc. to be displayed in high density. Ru.

To achieve high-density display, the color cathode ray tube must have high resolution and uniform focus characteristics, the video circuit must have a wide frequency band to increase the horizontal resolution of the display screen, and the vertical resolution of the display screen must be increased. This requires a large number of scanning lines.

Normally, in order to increase the number of scanning lines as a means of high-density display, the horizontal deflection frequency h is increased to more than 15.734 KHz of the current standard color TV system. In this case, the horizontal deflection frequency h
= 15.734 KHz, which had no problem at all, caused coma aberration in the scanning screens 6' and 7' formed by the outer and central electron beams due to the horizontal deflection magnetic field, and as shown in Figure 4, the scanning screen 7 of the central electron beam. ′, the scanning screen 6′ of both outer electron beams is slightly expanded in the horizontal direction, and the rate of expansion is different on the left and right sides of the phosphor screen 4, with the enlarged dimension d ₁ on the left side being larger than the enlarged dimension d ₂ on the right side. A larger asymmetry results. This shift in the scanning screen is a convergence error, which significantly deteriorates the quality of the image received on the phosphor screen. For example, in a 20-inch 90-degree polarization color cathode ray tube, when the horizontal deflection frequency h = 15.734KHz is doubled (h = 31.5KHz), the above-mentioned deviations d ₁ and d ₂ become d ₁ = 0.7 near the effective phosphor screen.
mm, d ₂ =0.3mm.

As the horizontal deflection frequency h increases, the scanning screen 6' formed by both outer electron beams and the central electron beam,
The cause of the horizontal shift caused by coma aberration in 7' is as follows. First of all, the concentrated magnetic pole 10
Eddy currents are generated around the outer electron beam transmission apertures 13 and 14 on both sides of the annular magnetic shielding elements 17 and 18 and around the annular magnetic shielding elements 17 and 18 due to the horizontal deflection magnetic field component that is induced in the bottom surface 11 and passes through this surface. This generates a magnetic flux that obstructs changes in the magnetic flux in the annular magnetic shielding elements 17 and 18, thereby attenuating the magnetic flux and thereby reducing the magnetic shielding effect. The loss of magnetic flux due to this eddy current is due to the conventional horizontal deflection frequency.
At h = 15.73KHz, it was completely negligible, but as the frequency increases, the loss of magnetic flux due to eddy currents becomes impossible to ignore, and as shown in Figure 4, the scanning screen 6' of both outer electron beams becomes The beam spreads in the horizontal direction with respect to the scanning screen 7'.

On the other hand, in order to perform horizontal scanning, the deflection device 5
The current waveform flowing through the horizontal deflection coil is a sawtooth wave shown in Figure 5, where the time t1 from point a to point b in the figure is the horizontal scanning time, and the time _t2 from point b to point c is the horizontal _scanning time. This is the horizontal retrace time, and _t2 is usually set to about 1/5 of _t1 . Point a or point c corresponds to the left end of horizontal scanning, and point b corresponds to the right end. That is, the left end position of the horizontal scanning screen corresponds to the end of the horizontal retrace time _t2 , the right end corresponds to the end of the horizontal retrace time _t1 , and during the horizontal retrace time _t2 , approximately 5 of the horizontal retrace time _t1 . A magnetic field is generated by the current that changes at twice the speed, and the magnetic shielding effect loss of the annular magnetic shielding elements 17 and 18 based on the eddy current loss due to the harmonic component magnetic field is larger on the left side of the phosphor screen than on the right side. , as shown in FIG. 4, the expansion width in the horizontal direction of the scanning screen 6' of both outer electron beams with respect to the scanning screen 7' of the central electron beam is that d ₁ on the left side is larger than d ₂ on the right side, and in the horizontal direction Asymmetry of comatic aberration occurs. At h = 15.734KHz used in the conventional standard color TV system (NTSC system), approximately t ₁ = 51 to 53 μsec, t ₂ =
The eddy current loss caused by this is completely negligible at 10 to 12 μsec, and therefore the above-mentioned coma aberration and its asymmetry are virtually invisible, and as h increases, t ₁ and
In order to increase the difference in t ₂ and the effective scanning time t ₁ , the retrace time t ₂ is set as small as possible, and the asymmetry of the eddy current loss becomes a non-negligible amount, causing the above-mentioned phenomenon.

The present invention has been made in consideration of the above-mentioned drawbacks, and it is possible to improve the scanning screen formed by both outer electron beams and the central electron beam in response to an increase in the horizontal deflection frequency of a self-convergence type in-line electron gun. This is to prevent misalignment due to coma aberration.

That is, the deflection magnetic field is generated in the central and both outer electron beam transmission apertures arranged in-line on the bottom surface of the bottomed cylindrical concentrated magnetic pole made of a non-magnetic metal material and attached to the tip of the electron beam exit side of the in-line electron gun. A plurality of elongated cuts are formed around the aperture in which a magnetic field control element for correcting coma aberration of a scanning screen formed by the magnetic field control element is arranged, and a plurality of elongated cuts corresponding to the cuts are formed in the magnetic field control element. be. With this configuration, the magnetic field control element disposed in the electron beam transmission hole can prevent the generation of eddy current due to the horizontal deflection frequency component of the high frequency that passes through it, thereby increasing the horizontal deflection frequency. Regardless, it is possible to eliminate asymmetric shifts due to coma aberration in the scanning screen formed by the central and both outer electron beams, making the in-line type electron gun an excellent electron gun capable of high-density display.

Embodiments of the present invention will be described in detail below with reference to the drawings.

6 and 7 respectively show perspective views of the concentrated magnetic pole 20 and the annular magnetic shielding element 27 (28) according to an embodiment of the present invention. A central magnetic pole 20 and a pair of outer electron beam transmitting apertures 22, 23, 24 are equally spaced on the bottom surface 21 of a concentrated magnetic pole 20 formed in the shape of a cylinder with a bottom and made of stainless steel, which is a non-magnetic material, and is attached to the tip of the electron gun. The phosphor screen 4 is perforated on the X-X axis corresponding to the long axis of the phosphor screen 4. However, four elongated cuts 25 are formed in both outer electron beam transmission apertures 23 and 24 in the XX axis direction and in a direction perpendicular thereto. Further, as shown in the figure, the annular magnetic shielding element 27 has
On one straight line of two concentric circles that form a ring,
Two elongated cuts 29A are formed starting from the edge of the outer circle in the direction of the inner circle, and further, on a diameter perpendicular to the diameter, two elongated cuts 29B are formed starting from the edge of the inner circle in the direction of the outer circle, Each cut has a width at least equal to the thickness of the element forming material so that it does not penetrate from the inside to the outside circle. On the bottom surface of the concentrated magnetic pole 20, as shown in FIG. 8, the magnetic enhancement elements 15, 16 and the annular magnetic shielding elements 27, 28 are arranged. That is, the central electron beam transmission aperture 22 is aligned with the vertical axis Y, which is the short axis of the phosphor screen 4.
A pair of disc-shaped magnetic enhancement elements 15 and 16 are arranged opposite to each other on the Y axis, and an annular magnetic field is formed so as to surround both outer electron beam transmission apertures 23 and 24 formed on the horizontal axis X-X. Shielding elements 27, 28 are provided. At this time, both outer electron beam transmission apertures 2 of the bottom surface 21 of the concentrated magnetic pole
3, 24 and the elongated cut 25 formed around the annular magnetic shielding elements 27, 28.
9A and 29B are aligned and fixed by welding. The actions of these magnetic field control elements 15, 16, 2728 on the deflection magnetic field are exactly the same as in the prior art example described above.

However, the horizontal deflection magnetic field F _H is caused by the concentrated magnetic pole 20
Even if there is a component guided to the bottom surface 21 of the
4 and around the annular magnetic shielding elements 27, 28, a plurality of elongated cuts 25, 29A, 29B are formed, so that the generation of eddy currents on the annular magnetic shielding elements 27, 28 is prevented from occurring through these holes. Ru.

Therefore, due to this eddy current, the generation of magnetic flux that obstructs magnetic flux changes in the annular magnetic shielding elements 27 and 28 becomes extremely small, and the magnetic shielding effect is particularly high when the horizontal deflection frequency is used in the current standard color TV system. Even if f _H becomes higher than 15.73KHz, it will no longer decrease regardless of the frequency. As a result, even if the horizontal deflection frequency h increases as in the conventional case, the scanning screen of both outer electron beams is enlarged relative to the scanning screen of the central electron beam, or the enlargement ratio is different from the horizontal scanning time and the horizontal retrace time. Asymmetry is no longer caused by differences in proportions.

In the above explanation, the scanning screen of the center and both outer electron beams has a magnetic field control element consisting of a combination of a pair of magnetic enhancement elements and an annular magnetic shielding element for correcting the comatic aberration of the scanning screen in the relationship shown in FIG. Although the case of use has been described, the present invention is not limited to this, and can also be applied to cases of correcting coma aberration having various patterns, or to magnetic field control elements having other shapes.

For example, in the magnetic field control elements 37 and 38 shown in FIG. 9, cuts 39A and 39B are formed to match the long and narrow cuts 25 formed in the bottom opening of the concentrated magnetic pole 20 in which the magnetic field control elements 37 and 38 are arranged. The function of this element is effective in correcting the coma aberration shown in FIG. That is, by adjusting the size of the annular portions 39C of the magnetic field control elements 37 and 38, the horizontal scanning screen of both outer electron beams is reduced to match that of both outer electron beams, and the center electron beam transmits on the X-X axis. The protrusion 39D facing toward the aperture 22 serves to increase the sensitivity of the center electron beam to the vertical deflection magnetic field, thereby enlarging the vertical scanning field to match that of both outer electron beams. In this case as well, the generation of eddy currents is prevented by the bottom surface of the concentrated magnetic pole and the notches made in the magnetic field control element, and the dependence of the operation of the magnetic field control element on the horizontal deflection frequency is eliminated.

Furthermore, if the present invention is applied not to the above-mentioned raster scanning method in which the scanning speed is constant during the effective scanning period in line sequential order, but to a random scanning method in which the scanning speed is indeterminate, coma aberration will not occur in this case as well. ,
Its effectiveness becomes even more obvious.

Alternatively, according to the present invention, there is no need to optimize the magnetic field control element disposed on the bottom surface of the concentrated magnetic pole for each horizontal deflection frequency used, and it is possible to use the same magnetic field control element for all frequencies. Can be shared.

As described above, according to the present invention, among the central and both outer electron beam transmission apertures arranged in-line and drilled on the bottom surface of the concentrated magnetic pole attached to the tip of the self-convergence type in-line electron gun, A plurality of elongated cuts are formed around the opening in which a magnetic field control element for correcting coma aberration of a scanning screen formed by a deflection magnetic field is disposed, and a plurality of elongated cuts are formed in the magnetic field control element to match the cuts. By forming the cut, it is possible to eliminate the dependence of the effect of the magnetic field control element disposed here on the horizontal deflection frequency and the difference in the effect due to the difference between the horizontal scanning time and the horizontal retrace time. As a result, regardless of the increase in the horizontal deflection frequency, it is possible to eliminate asymmetric shifts based on coma in the scanning screen formed by the central and both outer electron beams, and the in-line electron gun has extremely excellent characteristics that enable high-density display. It can be used as an electron gun, and its practical value is extremely high.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view of a color cathode ray tube using a conventional self-convergence type in-line electron gun, and Figure 2 shows the central and outer electron guns on the phosphor screen of this color cathode ray tube. A diagram showing a scanning screen formed by an electron beam, FIG. 3 shows a magnetic field control element for correcting coma aberration of the scanning screen,
A diagram showing its effect on horizontal and vertical deflection magnetic fields,
Figure 4 is a diagram explaining the shift in the scanning screen formed by the electron beams from the central and both outer electron guns that appear on the phosphor screen when the horizontal deflection frequency increases, and Figure 5 is the waveform of the current flowing through the horizontal deflection coil. , FIGS. 6 to 8 are perspective views of a concentrated magnetic pole and annular magnetic shielding element according to an embodiment of the present invention, and a plan view showing a state in which a magnetic field control element is arranged on the bottom surface of the concentrated magnetic pole, and FIG. 9 is a perspective view of a concentrated magnetic pole according to an embodiment of the present invention. FIG. 6 is a plan view showing a pair of magnetic field control elements disposed on the bottom surface of a concentrated magnetic pole according to another embodiment of the present invention. 1... In-line electron gun, 2... Glass envelope, 4... Fluorescent screen, 5... Deflection device, 6, 6'...
...Scanning screen formed by both outer electron beams, 7,
7'... Scanning screen formed by the central electron beam, 1
0,20...Concentrated magnetic pole, 12,22...Central electron beam transmission aperture on the bottom of the concentrated magnetic pole, 13,14,2
3, 24...Both outer electron beam transmission apertures on the bottom surface of the concentrated magnetic pole, 15, 16...Magnetic enhancement element, 17, 1
8, 27, 28...Annular magnetic shielding element, 37, 3
8...Magnetic field control element, 25, 29A, 29B, 3
9A, 39B...Elongated cut, _t1 : Horizontal travel time, _t2 : Horizontal retrace time.

Claims (1)

[Claims] 1. Center and both outer electron beam transmission apertures arranged in-line on the bottom surface of a bottomed cylindrical concentrated magnetic pole made of a non-magnetic metal material attached to the tip of the electron beam exit side of an in-line electron gun for color cathode ray tubes. A plurality of elongated cuts are formed around the aperture in which a magnetic field control element for correcting coma aberration of a scanning screen formed by a deflection magnetic field is disposed, and a plurality of elongated cuts are formed in the magnetic field control element in accordance with the above-mentioned cuts. An in-line electron gun characterized by having a long and narrow notch formed therein.