Colour picture tube

BACKGROUND OF THE INVENTION The present invention relates to an electron gun color tube for generating and directing a plurality of electron beams along a canoplanar path to a screen, comprising a main electron beam focusing lens comprising two separate focusing electrodes, each having an aperture portion equal to the number of electron beams , and each electrode is also provided with a circumferential sleeve, the sleeves of the two electrodes facing each other.

The in-line electron gun is designed to generate preferably three electron beams in a common plane and to direct these electron beams along the convergent paths in that plane to a point or small region of convergence near the screen. In one type of inline electron gun as described in U.S. Pat. No. 3,973,879, the main electrostatic focusing lenses for focusing electron beams are formed between two electrodes, the first and second accelerating and focusing electrodes being called. These electrodes comprise two cup-like members, wherein the bottoms of these members are opposed. Three openings are provided in each bottom to allow the passage of three electron beams and to create three separate main focusing lenses, one for each electron beam. In a preferred embodiment, the overall diameter of the electron gun is such that the gun fits into a 29 mm wide neck of the screen. Due to this dimensional requirement, the three focusing lenses are located very close to each other, resulting in severe constraints on the focusing lens design. It is known in the art that the larger the diameter of the focusing lens, the less will be the spherical aberration limiting the focusing quality.

In addition to the focusing lens diameter, the spacing between the electrode surfaces of the focusing lenses is also important, since a larger pitch will provide a finer voltage gradient in the lens, which also reduces spherical aberration. Unfortunately, an electrode spacing greater than a certain distance, typically about 1.27 mm, is not acceptable because the beam is bent by electrostatic charges formed on the glass of the throat of the screen whose fields penetrate the space between the electrodes, causing the convergence to break. electron beams. Therefore, there is a need for further development of the main focusing lens electrode design, which provides improved focusing lenses with reduced spherical aberration.

These disadvantages of the prior art are largely eliminated with the color screen of the invention, where the essence of the invention is that portions of the first and second focusing electrodes are located in a recess recessed backward from the cuff.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described with reference to the accompanying drawings, in which: Figure 1 is a partially axial sectional view of a color television screen with a shielding mask according to the invention; Figure 2 is a partial axial sectional view of the electron gun shown in dashed line in Figure 1; Fig. 4 is a sectional view of the electron gun of Fig. 2 taken along line 4-4 of Fig. 3; 5 and 6 are axial cross-sectional views from above or from the side of the prior art focusing electrode electron focusing lens electrodes showing the equipotential field lines of the electrostatic focusing lens, the view of Fig. 6 being taken along line 6-6 of Fig. 5; Figures 7 and 8 are axial cross-sectional views, viewed from above or from the side, of the electron focusing lens electrodes of the electron gun of Figs. 2 8 is a view of line 8-8 of FIG. 7, and FIG. 9 is a view of the electrode G4 of the electron gun, and FIG. 2 is taken along line 9-9 of FIG. 2.

Giant. 1 is a view of a rectangular color screen having a glass envelope 10 comprising a rectangular faceplate 12 and a cylindrical neck 14 joined by a rectangular funnel 16. The panel includes a display faceplate 18 and a side wall 20 that is fused to the funnel 16. Mosaic tricolor phosphor screen 22 is mounted on the inner face of the faceplate 18. The screen is preferably line-wise with phosphor lines extending perpendicular to the high-frequency sweep of the screen raster lines, i.e. perpendicular to the plane of Figure 1. The improved electron gun 26 in line, shown schematically in dashed lines in FIG. 1 is mounted centrally in the throat 14 to form and direct three electron beams 28 along coplanar 'convergent' paths through the mask 24 to the screen 22. '

The screen of FIG. 1 is designed for use with an external megapixel deflection yoke 20 schematically shown in a position surrounding the neck 14 and funnel 16 adjacent their joint. Upon excitation, the yoke 30 acts on three electron beams · 28 by a vertical and horizontal matpletic flow, which causes the electron beams to be horizontally or in a rectangular pattern along the screen 22. The initial deflection plane, i.e. the plane where the deflection is still zero, is represented by the line PP in FIG.

Due to the dispersion fields, the deflection region of the screen extends axially, from the yoke 30 to the area of ​​the electron gun 26. For simplicity, the actual curvature of the deflected electron beam paths in the deflection is not shown in FIG. 1.

The electron gun 26 is shown in FIGS. 2 and 4. The electron gun comprises two glass support rods 3.2 on which different electrodes are attached. These electrodes include three equally spaced coplants! the cathodes 34, one for each electron beam, the electrode 36 of the control ball G1, the electrode 38 of the shielding ball G2, the first and the focusing electrode 40G3, and the second acceleration and focusing electrode.42 G 4. distributed along the glass rods 32 in the listed order. All electrodes downstream of the cathodes are provided with three holes in a row to allow the passage of three coplanar electron beams. formed by four hermetic elements 44. The open ends of the first and second cup-like elements 44 and 46 are adjacent to each other, and the open ends of the third and fourth cup-like elements 48. 50 are also attached to each other. The closed end of the third cup element 48 is adjacent to the closed end of the second cup element 46. Although the first focusing electrode 40G3 is shown as a four piece construction, it may be made of a Ubo free piece, including a single element of the same length. The second focusing electrode 42G4 is also cup-shaped but has an open end closed by a plate 52 with holes.

The opposed closed ends of the first focusing electrode 40'G 3 and the second focusing electrodes 42G 4 are provided with large recesses 54 and 56, respectively. holes £ 8. 60 and 62 from that portion of the closed end of the second focusing electrode 42G4 that is provided with three apertures 64, 66 and 68. The remaining closed ends of the first focusing electrode 40G3 and the second focusing electrode 42G4 form dummies 70 and 72, respectively, that extend circumferentially along recesses 54 and 66. 70 and 72 are those portions of the two electrodes 40 and 42 that are closest to each other.

Figures 5 and 6 show cross-sections of two electrodes 74 and 76 forming a main focusing lens of a prior art electron gun of a unified type, viewed from above or from the side. The electrode 74 is G 3 and the electrode 76 is G 4. The electrode 74 is cup-shaped and has three separate holes 84, 86 and 8 in its bottom. During the operation of the screen, a 25 kV polennial of 7 kV is applied to the 74 G 3 electrode and a 76 G 4 electrode is applied. As a result of these potentials, an electrostatic field is formed near the apertures 78, 80 and 82 of the electrode G 3 and the apertures 36 and 88 of the electrode 76 G 4. The shape of the ecripotential lines of this electrostatic field determines the prior art electron gun main focusing lens. Some of these equivalents of lines 90 are shown in FIGS. 5 and 6. A comparison of these equivalents of lines 90 at the top, i.e. the curvature of the outer lines 90 as seen from above in FIG. 5 6 is much less than the curvature of the outer lines 90 when viewed from the side in FIG. 6. - Because of these differences in curvature called astigraatisnium, the electron beam 92 through the center holes 80 and 86 will be focused vertically. more, see FIG. 6 than horizontally, see FIG. 5. However, as seen in FIG. 5 the two outer electron beams encounter greater curvature of the electrostatic lines than the central electron beam and will therefore be horizontally focused. slightly more than the central electron beam, which will * mt result in a slightly lesser astlgmatism of the peripheral electron beams.

As better illustrated in Figures 7 and 8, the improved electron gun 26 of Figure 2 provides a main focusing lens with substantially reduced spherical aberration compared to that described with the prior art electron gun of Figures 5 and 6. The reduction in spherical aberration is due to an increase in the size of the main focusing lens. This increase in size is the result of recessed open electrodes. In the prior art electron gun of FIG. 5 and 6, the strongest equipotential lines of the electrostatic field are concentrated at each opposing pair of openings. In the electron gun 26 of FIG. 2, however, the most intense β1c line extends continuously from the space between the cuffs 70 and 22, so that the leading portion of the main focusing lens appears to be the only large lens extending over all. three electron beam paths. The remaining portion of the main focusing lens is formed by weaker equipotential lines with holes in the electrodes. Some of the equipotential lines 94 of the main focusing field of the improved electron gun 26 are shown from above or from the side in Figures 7 and 8, respectively.

As can be seen, the vertical curvature of the equipolent lines shown in FIG. 8 is more similar to the horizontal curvature shown in FIG. 7 than similar views of the prior art electron gun. Due to this similarity of curvature, the electron beam running along one of the electron beam paths will be focused evenly! both vertically and horizontally. Therefore, the αitigsαtiss type described in connection with the prior art electron gun shown in Figs. 5 and 6 is strongly ommzen.

In a preferred embodiment, the number of electron beams is three and the depths F of the recesses 54 and 56 are approximately a quarter of the pitch C between the two straight sides of the recesses. to just touch the equipotential line in the range of 4% of the electrode voltage that would exist if the aperture portion of the electrode was not there. In the embodiment shown, this 4% line is approximately semicircular. The spacing of the first and second focusing electrodes 40 and 42 b in mm and be sufficiently mmad to avoid throat charging by deflected elegance beams.

For the static two outer electron beams to the central electron beam, the width E of the recess 56 in the second focusing electrode 42G 4 is slightly larger than the width D of the recess 54 in the first focusing electrode 40G 3, see Figure 3. The focusing electrode 42 G 4 is the same as that described with respect to the offset holes in U.S. Pat. No. 3,772,554.

Some typical dimensions of the electron gun 26 of FIG. 2 are given in the following table

Table

The outside diameter of the screen throat

Inner diameter of the neck of the screen

Pitch between the first and second focusing electrodes 40. G 3 and 42 G 4

Center-to-center pitch of openings in front focusing electrode 40 G 3 (A in Fig. 3) mm mm

1.27 mm

6,6 mm

Continuation table

Inner diameter of holes 58, 60 and 62 in first focusing electrode 40 G 3 (B in Fig. 3) Pitch between two straight sides of recesses in first and second focusing electrodes 40 and 42 (C in Fig. 4)

Width of recesses in first focusing electrode 40 G 3 (D in Fig. 3) Width of recesses in second focusing electrode 42 G 4 (E in Fig. 3)

Recess depth in first and second focusing electrodes 40 and 42 (F in Fig. 3)

5,44 mm

6,99 mm

20.19 mm

20.8 mm

1.6> mm

In various other embodiments of the electron gun of the in-line system, the depth of the recesses in the first and second focusing electrodes 40 and 42 may vary between 1.3 mm and 2.8 mm.