JPH04212243A - Electron gun for color image pickup tube - Google Patents

Abstract

PURPOSE:To increase the diameter of opening part of an electron gun effectively to thereby increase a focus characteristic. CONSTITUTION:Only electrode plates opposite to G3 and G4 electrodes are mutually moved back and arranged inside a outer circumferential electrode. With the arrangement, proper selection of shape of opening hole formed at each electrode plate, therefore, provides the similar effect as the case where the diameter of the opening hole is increased substantially to thus weaken lens converging action, leading to improvement in a focus characteristic.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron gun for a color picture tube, and more particularly to an electrode constituting a main lens.

0002

2. Description of the Related Art FIG. 1 is a sectional view of a color picture tube provided in a conventional electron gun. On the inner wall of the phase plate portion 2 of the glass envelope 1, a phosphor screen 3 is supported, in which phosphors of three colors are coated alternately in stripes. The central axes 15, 16, 17 of the cathodes 6, 7, 8 are the G1 electrode 9, the G2 electrode 10,
Coincides with the central axes of the G3 electrode 11 constituting the main lens, the apertures corresponding to the respective cathodes of the shielding cup 13, and the central axes of the inner cylinders 20, 21, 22 connected to the apertures of the G3 electrode, and has a common plane. are placed on top, approximately parallel to each other. The central aperture of the G4 electrode 12, which is the other electrode constituting the main lens, and the central axis of the inner cylinder 24 connected thereto coincide with the central axis 16, but both the outer apertures and , inner cylinder 23,2 connected to them
The central axes 18 and 19 of 5 are the respective central axes 15
, 17 and is slightly displaced outward. The inner diameter of each inner cylinder matches the diameter of the corresponding aperture. Three electron beams emitted from each cathode have central axes 15, 16, 1
7 and enters the main lens. G3 electrode 11 is G4
The G4 electrode 1 is set at a lower potential than the electrode 12 and has a higher potential.
2 is at the same potential as the shielding cup 13 and the conductive film 5 provided on the inner wall of the glass envelope 1. The opening in the center of both G3 and G4 electrodes and the inner cylinders 21 and 24 are coaxial, and since the inner cylinder cancels out the influence from the non-axisymmetric electrode outer periphery, the main lens formed in the center is axially symmetrical, and the central beam travels straight along a trajectory along the axis after being focused by the main lens. On the other hand, since the axes of the apertures on the outside of both electrodes and the inner cylinders 20, 22 and 23, 25 are shifted from each other, a non-axis-symmetric main lens is formed on the outside. Therefore, the outer beam is located in G4 of the main lens area.
In the diverging lens region formed on the electrode side, the light passes through a portion that is deviated from the lens center axis in the direction of the central beam, and is simultaneously subjected to the focusing action of the main lens and a concentrating force in the direction of the central beam. In this way, the three electron beams are transmitted to the shadow mask 4.
At the same time, the images are focused so that they overlap each other. The operation of concentrating each beam in this manner is called static convergence (hereinafter abbreviated as STC). Furthermore, each electron beam is color-selected by a shadow mask 4, and only the component that excites the phosphor of the color corresponding to each beam to emit light passes through the aperture of the shadow mask 4 and reaches the phosphor screen 3. Further, an external magnetic deflection yoke 14 is provided to scan the electron beam on the fluorescent screen.

0003

SUMMARY OF THE INVENTION Factors that greatly affect the focusing characteristics of a picture tube include the lens magnification and aberrations of the main lens, which strongly depend on the strength of the lens focusing action. In a picture tube, the distance from the main lens to the image plane is determined by determining the scanning area of the electron beam and the maximum deflection angle. Under the condition that the distance to the image plane is constant, weakening the lens focusing effect will result in a decrease in lens magnification, and in addition, to prevent an increase in deflection aberration, the beam spreading within the main lens will be reduced. Adding the condition of keeping it to a constant value will reduce the beam incidence angle to the main lens. When the beam incidence angle is αi, the minimum circle of confusion diameter δ due to the spherical aberration, which is the most dominant among the aberrations of the main lens, is expressed as δ=MCspαi3/2, and lowering the beam incidence angle reduces the spherical aberration. be able to. Here, M is the lens magnification, C
sp is a spherical aberration coefficient.

As described above, in a picture tube, weakening the lens focusing effect of the main lens reduces lens magnification and spherical aberration, and improves focus characteristics. One way to weaken this focusing effect is to enlarge the diameter of the apertures of the G3 and G4 electrodes forming the main lens and the corresponding inner cylinder. (Hereinafter, in order to simplify the explanation, when we refer to the diameter of the opening, we also include the diameter of the corresponding inner cylinder).

However, in the in-line electron gun shown in FIG. 1, the main lenses corresponding to each of the three colors red, green, and blue are arranged in a row on the same plane, so the diameter of the aperture is , the inner diameter of the neck portion of the glass envelope 1 housing the electron gun must be 1/3 or less. If the thickness of the electrode is taken into consideration, as well as problems in electrode processing, the limit value becomes even smaller. In order to raise this limit value, increasing the inner diameter of the neck portion increases the deflection power, and generally speaking, increasing the aperture diameter increases the eccentric distance of the aperture and worsens the convergence characteristics. A problem arises. Considering these points,
Since the opening diameter is usually made as large as possible, further enlargement is extremely difficult.

[0006] Japanese Patent Application Laid-open No. 17963/1983 discloses a method for enlarging the diameter of the aperture beyond the limit value. In this method, the overlapping part of the apertures, which is caused by making the aperture diameter larger than the eccentric distance between adjacent apertures, communicates with each other, and the communicating part is also provided with a partition plate for potential correction. is provided.

However, even with this method, there is a certain limit to the diameter of the opening. Assuming that the diameter of the outer periphery of the G3 electrode in the horizontal direction (the direction in which the three apertures passing through the electron beam are arranged) is h, and the eccentric distance of the aperture is S, the limit value L of the aperture diameter is:
L=h-2×S...(1). In reality, this limit value becomes even smaller due to problems in electrode processing. In the present invention, even when the diameter of the electron gun is restricted by the inner diameter of the neck tube, the diameter of the opening can be set to (
1) It is an object of the present invention to provide an electron gun for a color picture tube, which can effectively increase the focus characteristic even more than the value restricted by the formula (1), thereby further improving the focus characteristic.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention involves retracting only the electrode plates constituting the opposing surfaces of the G3 electrode and the G4 electrode from each other, and placing these electrode plates inside the outer peripheral electrode. It is characterized by placement. If you do this, G3
The high potential of the G4 electrode penetrates deeper into the electrode, and the low potential of the G3 electrode penetrates deeper into the G4 electrode. Furthermore, the inner cylinders 20 to 25 as in the conventional example are removed, allowing the potential to penetrate deeper. Such potential penetration has substantially the same effect as enlarging the diameter of the aperture on the opposing surface. That is, the effective diameter increases. However, the cross section of the outer peripheral electrode excluding the facing surfaces of the G3 electrode and the G4 electrode is non-circular, and the diameter in the horizontal direction is larger than the diameter in the vertical direction. Therefore, potential penetration is significant in the horizontal direction, and the effective diameter in the horizontal direction becomes larger than the effective diameter in the vertical direction. For this reason, the lens focusing effect in the horizontal direction is weaker than in the vertical direction, so astigmatism appears when focusing the electron beam. Therefore,
In the present invention, the shape of the opening formed in the counter electrode plate is non-circular, and the diameter in the horizontal direction is smaller than the diameter in the vertical direction. By suppressing the penetration of horizontal potential in this manner, the lens focusing action in the horizontal and vertical directions can be made equal, and astigmatism can be eliminated.

[0009]

[Operation] According to the present invention, by appropriately selecting the amount of retraction of the counter electrode plate and the shape of the aperture formed in the counter electrode plate, the effect is substantially the same as that of increasing the diameter of the aperture. occurs, the lens focusing effect is weakened, and the focus characteristics are improved.

Furthermore, as a secondary effect, a concentration force is generated inward in the outer electron beam, and the central axis of the G3 electrode side aperture and the central axis of the G4 electrode side aperture are aligned without deviation. Even if it is allowed, STC can be taken. This is G
This is because the potential inside the three electrodes is low near the outer periphery and high at the center where the high potential on the G4 side penetrates deeply, and an electric field is generated inward from the outer periphery.

Furthermore, the electron gun of the present invention has no communicating part in the aperture through which the electron beam passes, and also does not require a partition plate for potential correction.
This is completely different from the electrode structure shown in No. 63.

0012

Embodiments Hereinafter, embodiments of the present invention will be explained with reference to the drawings. FIG. 2 is a sectional view of a main part of an embodiment of the electron gun of the present invention, in which G3 and G4 forming a bipotential main lens are shown.
FIG. 3 is a cross-sectional view of an electrode in a horizontal direction and a vertical direction. In the figure, 111 is the outer periphery of the G3 electrode, 121 is the outer periphery of the G4 electrode, and 13 is the cup electrode. Reference numeral 112 denotes a polar plate for astigmatism correction provided inside the outer peripheral part 111 of the G3 electrode, and 122 represents a polar plate for astigmatism correction provided inside the outer peripheral part 121 of the G4 electrode. The electrode plate 112 has an aperture 114 through which the center beam passes, and apertures 113, 113' through which the outer beams pass, and the electrode plate 122 has an aperture 124 through which the center beam passes, and apertures through which the outer beams pass. 12
3,123' are provided in a row. In this example,
Opening holes 113, 113', 114, 123, 123', 1
Reference numeral 24 has an elliptical shape, and the corresponding openings on the G3 side and G4 side have the same shape and size. Outer opening 11
3,113', 123, 123' and the central opening 114,
124, the horizontal diameter of the outer aperture is made larger than the horizontal diameter of the central aperture. , equalizing the strength of the focusing action in both the horizontal and vertical directions.

FIG. 3 shows that in the embodiment shown in FIG. 2, the horizontal diameter h of the outer peripheral portions 111 and 121 is 20.0 mm, the vertical diameter v of the outer peripheral portions 111 and 121 is 9.4 mm, and the vertical diameter of the central openings 114 and 124. a1 = outer opening 113, 113', 123,
123' vertical diameter a2 = 8.4 mm, retraction amount d1 of the electrode plate 112 = retraction amount d2 of the electrode plate 122 = 1.5 mm, eccentric distance S = 6.6 mm, the central opening 114,1
The ratio of the focus distance in both the horizontal and vertical directions to the horizontal diameter b1 of No. 24 was determined by computer simulation.

[0014] Here, the horizontal or vertical focus distance means that an electron beam that is emitted from one point on the central axis at a certain emission angle and passes through the horizontal or vertical axis of symmetry of the central aperture is focused by the main lens. The distance from the G3 electrode to the G4 electrode side end face is measured from the G3 electrode to the point where the G4 electrode crosses the central axis again. The distance from the same end face to the fluorescent screen is 3.40 mm, the emission angle is set to a constant value, the emission points whose horizontal and vertical focus distances match this value of 340 mm are determined, and these emission points are The electron beam is emitted from the middle with the same emission angle. FIG. 3 shows the ratio of the focus distances in both the horizontal and vertical directions at this time. As can be seen from the figure, if the horizontal diameter of the central aperture is set to b1 to 5.5 mm, the vertical and horizontal focus distances will match, and the strength of the focusing action in both directions will be equal, so astigmatism can be eliminated. I can do it.

[0015] Also, at this time, the lens focusing effect is 1 mm.
It has the same strength as a cylindrical bipotential lens with a diameter of 8 mm, which are placed together at an interval of . This is h=20
．． 0 mm and S=6.6 mm, this value is larger than the limit value of 6.8 mm for the electrode opening, which is restricted by equation (1).

FIG. 4 shows the outer openings 113, 113', 123 when the above dimensions are used in the embodiment shown in FIG.
, 123' and the horizontal spot movement distance of the outer electron beam on the phosphor screen were determined by computer simulation. 7 kV was applied to the G3 electrode, and 25 kV was applied to the G4 electrode, and the distance from the end of the G3 electrode on the G4 electrode side to the phosphor screen was 340 mm. The outer electron beam and the center electron beam are separated by 6.6 mm in the horizontal direction, so the spot movement distance required to obtain STC is 6.6 mm, but in reality, the color purity can be adjusted freely. In order to preserve the degree of strength, it is often designed to be around 6.1 mm. In order to secure this moving distance, the value of b2 is 5.8 mm.

FIG. 5 is a sectional view of a main part of another embodiment of the electron gun of the present invention, showing a vertical cross section of the G3 electrode. The openings 41, 41', and 42 provided in the electrode plate 112 have a shape in which the end points of two circular arcs are connected by two parallel straight lines. Although the spot shape on the phosphor screen is worse than one with an elliptical aperture, it has the advantage that it can be easily and precisely machined because the aperture consists of circular arcs and straight lines. Also in this embodiment, the horizontal diameter of the opening is smaller than the vertical diameter.

FIGS. 6 and 7 are sectional views of main parts of still another embodiment of the electron gun of the present invention, and show the G3 electrode and G4 electrode, respectively.
FIG. 3 is a diagram showing a vertical cross section of an electrode. central opening 52
, 62 have vertical symmetry axes, but the outer openings 51, 5
1', 61, 61' do not have a vertical axis of symmetry. The outer openings 51, 51', 52, and 52' have the same major axis,
It is a combination of two ellipses with different minor axes, and G
In the outer openings 51 and 51' of the three electrodes, the short axis of the ellipse combined on the outside is smaller than the short axis of the ellipse combined on the inside. If the outer aperture of the G3 electrode is shaped like this, the aperture will become 1
The force that focuses the electron beam toward the center is stronger than in the case of two ellipses, so even if the horizontal diameter is made smaller,
You can take STC.

On the contrary, in the G4 electrode, 61, 61 in FIG.
If the outer aperture is constructed by combining two ellipses in which the minor axis of the inner ellipse is smaller than the minor axis of the outer ellipse as shown in ', the force for concentrating the electron beam toward the center becomes stronger.

[0020] In this way, by making the outer aperture asymmetrical with respect to the vertical direction, the concentration of the electron beam increases and the STC
becomes easier to remove. Also, if your concentration is too strong,
If the aperture shown in FIG. 7 is used on the G4 electrode side and the aperture shown in FIG. 7 is used on the G3 electrode side, the concentration force can be weakened.

FIG. 8 is a sectional view of a main part of still another embodiment of the present invention, and is an embodiment in which the electrode plates 112 and 122 are not retracted but are arranged on the same plane as the facing surface of the electrode outer enclosure. Oval openings 113, 113', 114, 123, 123'
, 124 to correct astigmatism.

In this embodiment, since the electrode plate is not retracted, the counter electrode potential does not penetrate as deeply into the electrode as in the embodiments shown in FIGS. 2, 5, 6, and 7. However, since the inner cylinder as in the conventional example is removed, the counter electrode potential penetrates deeper than in the conventional electrode structure shown in Figure 1, so the same effect as increasing the aperture diameter can be obtained to some extent. The focus characteristics are improved.

The embodiment shown in FIG. 8 has the advantage that the outer circumferential portion of the electrode and the electrode plate can be simultaneously molded by press working, making it easy to manufacture.

[0024]

Effects of the Invention According to the present invention, a cylinder with the maximum diameter that is possible when the main lenses corresponding to the three colors of red, green, and blue are arranged in parallel on the same horizontal plane while the outer shape of the electron gun is restricted. Since it is possible to construct a main lens with a weaker focusing effect than when the electrodes are butted together, this has the effect of significantly improving the focusing characteristics of the color cathode ray tube.

Furthermore, the G3 electrode and the G3 electrode constituting the main lens
STC can be achieved by appropriately selecting the amount of retraction of the electrode plate and the shape of the hole formed in the electrode plate without deviating the central axis of the outer hole formed in the four electrodes. During assembly, jigs with the same diameter and coaxiality can be used for the G3 electrode and the G4 electrode, and assembly accuracy can be improved.

The present invention is of course applicable not only to the bipotential type main lens exemplified in the above explanation, but also to a unipotential type or other main lens. Further, in the above explanation, an example was described in which the present invention was applied to both of a pair of electrodes that constitute the main lens.
A similar effect can be obtained even if it is applied to only one of the electrodes.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically showing a conventional in-line color picture tube.

FIG. 2 is a sectional view of essential parts of an embodiment of the electron gun of the present invention.

FIG. 3 is a diagram showing an example of the relationship between the horizontal and vertical focus distances of the central main lens of the electron gun of the present invention and the short diameter of the aperture.

FIG. 4 is a diagram showing an example of the relationship between the short diameter of the aperture of the outer main lens and the horizontal spot movement distance on the phosphor screen.

FIG. 5 is a sectional view of a main part of another embodiment of the electron gun of the present invention.

FIG. 6 is a sectional view of a main part of another embodiment of the electron gun of the present invention.

FIG. 7 is a sectional view of a main part of another embodiment of the electron gun of the present invention.

FIG. 8 is a sectional view of a main part of another embodiment of the electron gun of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Glass envelope, 2... Face plate, 3... Fluorescent screen, 4... Shadow mask, 5... Conductive film, 6, 7, 8... Cathode, 9... G1 electrode, 10... G2 electrode, 11... G3 electrode, 1
2... G4 electrode, 13... Shielding cup, 14... External magnetic deflection yoke, 121... G3 side astigmatism correction polar plate, 122...
G4 side astigmatism correction polar plate, 113, 114, 123,
124, 41, 42, 51, 52, 61, 62...Apertures for beam passage.

Claims (2)

[Claims] 1. An electron beam generating means for generating three electron beams toward a phosphor screen, and a main lens for focusing the three electron beams on the phosphor screen, provided at a distance from each other; two outer circumferential electrodes surrounding the three electron beams, and three openings arranged in one direction, arranged at opposing ends of the outer circumferential electrodes, through which the three electron beams pass. In a color picture tube electron gun having two electrode plates, at least one of the two electrode plates is retracted and disposed inside the outer peripheral electrode, and the retracted electrode plate An electron gun for a color picture tube, characterized in that the diameter of the central opening in the one direction among the openings is smaller than the diameter in the vertical direction. 2. The diameter of the outer opening in the one direction is larger than the diameter of the central opening in the one direction. electron gun for color picture tubes.