JPH0341400Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to an electron gun used in electron tubes including various cathode ray tubes.

BACKGROUND TECHNOLOGY AND PROBLEMS In order to obtain high resolution in a cathode ray tube, it is desirable that the beam spot on the phosphor screen not only have a small diameter but also be as perfectly round as possible. High circularity is required for the electrodes, especially the electrodes constituting the main electron lens.

Electrodes in electron guns are generally made by press-molding metal plates, but in this case, the electrodes, which require high circularity, have a relatively long cylindrical part, and this cylindrical part has notches, etc. If there is an object which does not have infinite symmetry with respect to its axis, that is, if it is asymmetric, it is difficult to obtain a high degree of circularity. In other words, such cylindrical electrodes are made from a metal plate by the so-called squeeze press molding process, but in this case, large strains remain as the long cylindrical part is squeezed out, and this is caused by the process later performed at temperatures up to 1000°C. This strain is released by annealing treatment using high temperature heating, resulting in deformation. In this case, if this electrode is asymmetrical as described above, its deformation will be even more remarkable, and its circularity will be even more remarkable.

On the other hand, in an electron gun, the desired circularity of the electrodes constituting the main electron lens is 99.7% or more. This circularity is expressed as the difference between the maximum diameter and the minimum diameter, divided by the maximum diameter, multiplied by 100. For example, for an electrode with a diameter of 20 mm,
In order to achieve a circularity of 99.7% or more, it is necessary to keep the difference between the maximum diameter and the minimum diameter to 60 μ or less, and it can be seen that this requirement is quite strict.

Purpose of the invention The present invention is intended for electrodes that require high circularity.
Even if the length of the cylindrical part is large or there is asymmetry due to the presence of notches, it is possible to reliably obtain a high degree of circularity, thereby creating a beam spot with small distortion. The purpose of the present invention is to provide an electron gun that can be obtained.

Summary of the Invention In the present invention, a cap having a high degree of circularity is fitted into the end of the cylindrical portion of the electrode which is the electrode body of an electrode that particularly requires a high degree of circularity in an electron gun. This cap is constructed by integrally molding a cylindrical portion inscribed in the electrode cylindrical portion and one end face plate having an electron beam transmission hole into a dish-like shape. Further, on the outer surface of the end plate of the cap, a cap fixing disk body having an electron beam transmission hole that matches the electron beam transmission hole bored in the end plate is superimposed and attached by spot welding. This disk body has a protrusion extending from this on its outer periphery,
A mounting piece is provided that is bent along the outer circumferential surface of the cylindrical electrode portion, and this mounting piece is attached to the outer circumferential surface of the cylindrical electrode portion using a spot weld. In this way, the circularity of the electrode cylindrical portion is forcibly corrected by the cap fitted into it, and the circularity of the electrode cylindrical portion corresponds to the circularity of the cap.

Embodiment An example in which the present invention is applied to an electron gun configuration in which aberrations are reduced will be described. In this example, a unipotential type electron gun is adopted, but first, in order to make it easier to understand, the unipotential type electron gun will be explained.

Unipotential electron guns are commonly used in color television cathode ray tubes, high-brightness cathode ray tubes for projectors, and the like because they have excellent blooming characteristics in a high current range. This unipotential electron gun includes, for example, a cathode K, a first grid (control electrode) G ₁ , a second grid (acceleration electrode) G ₂ , a third grid (first anode electrode) G ₃ , a fourth grid (focusing electrode) ) G ₄ and 5
Grids (second anode electrodes) are arranged in the order of _G5 . In this electron gun, in order to reduce the spot diameter of the electron beam incident on the phosphor screen surface, the electron lens, especially the third grid G ₃ ,
It is important to minimize the spherical aberration of the main electron lens constituted by the fourth grid _G4 and the fifth grid _G5 . To achieve this, it is sufficient to increase the aperture of each grid in the main electron lens system, but in order to increase the aperture of the grid, it is necessary to increase the inner diameter of the neck of the cathode ray tube housing the electron gun. be. However, increasing the inner diameter of the neck portion reduces the deflection sensitivity of the deflection yoke.

On the other hand, as shown in Fig. 1, the unipotential lens consists of a deceleration lens (Lens1) consisting of a third grid _G3 and a fourth grid _G4 , and an accelerating lens (Lens2) consisting of a fourth grid _G4 and a fifth grid _G5 . )
In the case where the electron lens active area can be separated from each other, the aberration system of the main electron lens system can be considered separately into the deceleration lens (Lens1) and the acceleration lens (Lens2). It is known that this aberration coefficient is small for the deceleration lens and large for the acceleration lens. Therefore, by improving the amount of aberration of the accelerating lens and making the accelerating lens a lens with a weaker lens effect, the amount of aberration of the entire unipotential lens can be improved.

FIG. 2 shows an electron gun with low aberrations proposed in Japanese Patent Application No. 155881/1983 based on the fact that the aberration coefficients of the above-mentioned main electron lens system can be considered separately for the deceleration lens and the acceleration lens. This electron gun has a cathode K, a first grid G ₁ , a second grid G ₂ , a third grid G ₃ , a fourth grid G ₄ and a fifth grid G ₅
are arranged in sequence, the anode voltage V _A is applied to the third grid _G3 and the fifth grid _G5 , and the fourth grid
In an electron gun in which a focus voltage V _F is applied to G ₄ and a unipotential main electron lens system is formed by the third grid G ₃ to the fifth grid G ₅ , the front stage of the main electron lens system is The electron lens aperture D ₁ of the deceleration lens (Lens1) (i.e. the aperture of each opposing end of the third grid G ₃ and the fourth grid G ₄ )
is selected to be smaller than the electron lens aperture shape D ₂ (i.e., the aperture of each opposing end of the fourth grid G ₄ and the fifth grid G ₅ ) of the subsequent accelerating lens (Lens 2) (D ₄ <D ₁ ), and The length l (l ₁ + l ₂ ) of the fourth grid _G4 is selected to be a length that allows the electron lens action areas of the front and rear lenses (Lens1) and (Lens2) to be separated, and the aberration coefficient of the main electron lens system is reduced. This is what I did. Conventionally, each of the first grid _G1 to the fifth grid _G5 is generally supported by a common insulating support rod (so-called beading glass). Therefore, when an electron gun supported by an insulating support rod is housed in the neck portion, there is a limit to the diameter of the grid, taking into account the insulating support rod. For example, the inner diameter is 29mm
When housed in the neck of the grid, the effective inner diameter of the grid was approximately 14 mm at most. The electron gun shown in FIG. 2 was designed to reduce the aberration coefficient by reducing the mouth shape D ₁ of the deceleration lens (Lens 1) in such a situation.

In view of the above points, the electron gun to which the present invention is applied is
Furthermore, it adopts a configuration that reduces spherical aberration.

The electron gun according to the present invention will be explained below.

Figure 3 shows a basic example of a unipotential type electron gun, with a cathode K, a first grid G ₁ ~
The fifth grid _G5 is arranged in sequence, and the third grid
G ₃ and the fifth grid G ₅ with high voltage e.g. anode voltage
V _A is given, and the fourth grid G ₄ is given a focus voltage V _F that is sufficiently lower than this, so that the third grid G ₃ to the fifth grid G ₅ constitute a unipotential main electron lens system. It consists of

In this case as well, the third grid _G3 and the fourth
Grid _G4 constitutes a deceleration type front-stage electron lens (Lens1), and fourth grid _G4 and fifth
Grid _G5 constitutes the accelerating type rear-stage electron lens (Lens2), but the front-stage electron lens (Lens1) and the rear-stage electron lens (Lens2) are
The length l of the fourth grid _G4 is set so that the electron action areas are separated from each other, and the electron lens aperture of the front-stage electron lens (Lens1) is made smaller than the electron lens aperture of the rear-stage electron lens (Lens2). At the same time, the aperture of the fifth grid _G5 is selected to be larger than the aperture of the fourth grid _G4 in the subsequent electronic lens (Lens2). That is, the fourth grid
The diameter D ₂ on the fifth grid side of the fourth grid G ₄ is made larger than the diameter D ₁ on the third grid G ₃ side of G ₄ , and the diameter D ₃ of the fifth grid G ₅ is further made larger (D ₁ < D ₂
< _D3 ). In addition, the fourth grid _G4 is arranged so that the front-stage electron lens (Lens1) and the rear-stage electron lens (Lens2) are separated from each other in their electron lens action areas.
The length l (l ₁ +l ₂ ) is selected to be at least 1.5 times the diameter of the third grid G ₃ , that is, the diameter D ₁ of the small diameter portion of the fourth grid G ₄ , that is, l≧1.5D ₁ . With this configuration, the amount of aberration of the accelerating type rear-stage electron lens (Lens2) is improved, and the amount of aberration of the entire main electron lens system is further improved.

FIG. 6 is a curve diagram comparing the spherical aberration coefficients of this electron gun and a conventional general electron gun. In the figure, the vertical axis represents the quantity g ₃ related to the spherical aberration coefficient (this is shown in the aberration coefficient relational expression below), and the horizontal axis represents the focal length fPH on the object point (crossover point) side. . The curve is the third one shown in Figure 4.
Grid G ₃ , 4th grid G ₄ and 5th grid
This is the case of a general unipotential type electron gun in which the diameters of _G5 are the same and the length l of the fourth grid _G4 is 21.0 mm. The curve shows the aperture D ₂ of the rear electron lens (Lens2) shown in Figure 5 (the apertures on the fifth grid side of the fifth grid _G5 and the fourth grid _G4 are equal in diameter) to Select the aperture of the lens (Lens1) to be larger than D ₁ , D ₁ = 13.8mm,
This is a case where D ₂ =16.4 mm, l = 28.1 mm, and l ₂ =10 mm. Curves _A , _B , and _C are the unipotential electron gun shown in Figure 3, respectively, and l = 28.1 mm.
33.1mm and 38.1mm (however, D ₁ =
13.8mm, D ₂ = 16.4mm, D ₃ = 22.0mm, l ₂ = 10mm constant).

Incidentally, the relational expression of the aberration coefficients is shown with reference to FIG. Aberration amount (beam spot radius at imaging plane 1)
Δr is the spherical aberration coefficient C _S , the lens magnification M,
If the half angle of the maximum divergence angle from the beam crossover point (object point) is α ₀ , then Δr＝MC _S α ₀ ³ C _S = C _S0 + C _S1 /M+C _S2 /M ₄ +C _S3 /M ₄ +C _S4 / given by M ₄ . And g ₃ given in Figure 6 refers to the amount shown below.

g ₃ C _S0 /f ₂ Δr〓(Lα ₀ ³ )·g ₃ However, f ₂ is the focal length on the image side, and L is the distance from the object point to the imaging plane.

As is clear from Fig. 6 above, the electron gun shown in Fig. 3 shows an even better aberration coefficient than the conventional electron gun shown in Fig. 5, with an improvement in the aberration coefficient of about 15% to 20%. has been done. In addition, in the electron gun shown in FIG. 3, the fourth grid _G4 is replaced by the fifth grid _G5.
It has also been confirmed through experiments that the amount of aberration hardly changes even if the two lenses are placed inside each other and overlapped.

Next, the specific structure of the present invention will be explained with reference to FIGS. 8 and 9. In this case as well, the cathode K and the first grid G ₁ to the fifth grid G ₅ are sequentially arranged on the same axis, and in particular, the fifth grid G ₅ having the diameter D ₃ and the third grid G having the diameter D _{1 3}
The fourth grid _G4 is disposed within the cylindrical portion 2 of the fifth grid _G5 . At the cathode side end of the cylindrical portion 2 of the fifth grid _G5 , an end plate 3 is provided which is perpendicular to the axis, and at the center of the end plate ₃ there is a diameter that is the same as the diameter _D1 of the third grid G3. A through hole 4 having a diameter is provided. In addition, a pair of notches or windows 5 are formed on the side of the cylindrical portion 2 having the end plate 3 with an angular spacing of, for example, 180°. And especially in this invention,
The cylindrical portion 2 of the fifth grid _G5 is shown in its cross-sectional view in FIG. 10 and as an exploded perspective view in FIG. Cap 6 forcibly correcting the roundness of
Insert.

This cap 6 has a cylindrical portion 6a having an outer diameter that is press-fitted into the cylindrical portion 2 and is inscribed within the cylindrical portion 2, and an end face plate 6 having an electron beam transmission hole 6b in the center thereof.
c and are integrally molded into a plate shape by press molding. Further, a mounting disc body 7 is joined to the outer surface of the end plate 6c by spot welding in a state where it is superimposed on the outer surface of the end plate 6c. This disc body 7 has an outer diameter corresponding to the end face plate 6c of the cap 6, and has a similar beam transmission hole 7 in its center that coincides with the beam transmission hole 6b of the cap 6.
b is drilled. Moreover, three mounting pieces 7a are extended from the periphery of the disc body 7 and integrally therewith, for example, at positions having a special angle interval from each other. It is bent in the axial direction along the circumferential surface of the portion 2. Then, with each mounting piece 7a in contact with the outer surface of the cylindrical part 2 of the electrode body, both are spot-welded,
This fixes the disc body 7 to the cylindrical part 2,
The cap 6 attached to the disk body 7 is fixed to the cylindrical portion 2 of the electrode body so as not to move in the axial direction or in the rotational direction.

Further, the cap fixing disc body 7 is provided with support legs 7c that support a container (not shown) of, for example, getter material, which is folded up integrally with the disc body 7.
Further, on this fixing disk body 7, for example, three conductive springs 7d are spot-welded at equal angular intervals, and these are applied to the inner circumferential surface of, for example, the neck portion of the cathode ray tube body shown in FIGS. 8 and 9. The high voltage is supplied to the fifth grid _G5 and the _third grid G3 connected thereto via the spring 7d by elastically contacting an internal conductive film (not shown) to which a high voltage is applied. The position of the electron gun is maintained within the cathode ray tube tube, that is, the position is maintained coaxially.

It should be noted that welding of the fixing disc body 7 and the cap 6, and further fixing, that is, welding, of the disc body 7 to which the cap 6 is fixed to the electrode cylindrical part 2 is performed by welding the fixing disc body 7, the cap 6, and the cylinder. This is done after each part 2 has been annealed by high-temperature heating.

In the cap 6, the axial length or width of the cylindrical portion 6a is sufficiently smaller than that of the cylindrical portion 2, so that molding can be performed with high degree of circularity. Since the length of the cylindrical portion 6a in the axial direction is small, the metal plate used to form the cap 6 has a relatively thick thickness of, for example, 0.5 mm.
It is possible to press a thick stainless steel metal plate and form it into a highly circular shape. Meanwhile the electrode body of grid G ₅ ,
That is, the cylindrical part 2 is formed by pressing a stainless steel plate with a thickness of 4 mm, for example, and a fourth grid G ₄ is formed inside the cylindrical part 2 _.
Since it is necessary to integrate the third grid at the end plate 3 at the end of the cylindrical part 2 on the cathode side, the axial length of the cylindrical part 2 is quite large. Moreover, since this has a window 5 bored therein and does not have infinite symmetry with respect to its axis, that is, it has an asymmetric shape, when it is squeezed and press-molded, A lot of distortion occurs, which makes the cylindrical part 2 less circular after the annealing process.
However, as described above, a highly circular cap 6 is fitted into one end of this cylindrical body, and the outer circumferential surface of the cylindrical portion 6a of this cap 6 is inscribed in the inner circumferential surface of the electrode cylindrical portion 2. Therefore, the cylindrical portion 2 is corrected along the outer circumferential shape of the cap 6, and a high degree of circularity is achieved in accordance with the circularity of the cap 6.

In addition, this fifth grid _G5 may be the third grid in some cases.
It can also be molded integrally with Grits G ₃ , but
As described above, the end plate 3 is provided, and the flange portion 8 is provided at the end of the third grid _G3 facing the fifth grid _G5 , and this and the end plate 3 are aligned and welded. Therefore, it can be made into an integral structure.

Further, the fourth grid _G4 consists of a small diameter part having a diameter _D1 and a large diameter part having a diameter _D2 , and the window part 5 of the cylindrical part ₂ of the fifth grid G5 is bored in the large diameter part. The small diameter part is located at the end side where the window part 5 is located.
It is arranged so that it faces the A front-stage electron lens system (Lens1) is formed by the small diameter part of the fourth grid _G4 and the third grid _G3 , and the large diameter part of the fourth grid _G4 and the cylindrical part ₂ of the fifth grid G5. The latter stage electron lens system (Lens2) is formed by this.

In this state, the first grid _G1 to the fourth grid _G4 are fixed to the common beading glass 9 via the support pins 10, and are mechanically connected to each other. In this case pin 10 of the fourth grid G ₄
The connection to the beading glass via is made through the window 5 of the cylindrical part 2.

In addition, here is the fourth grid G ₄ and the fifth grid
The distance L from the inner surface of the end plate 6c of the cap 6 to the end of the fourth grid _G4 is selected to be L/D ₃ ≧0.57 so that no electron lens is formed between the end plate 6c of the cap ₆ and the end plate 6c of the cap 6. It was confirmed that it is desirable to do so.

The electron gun configured in this manner has an internal conductive film (not shown) to which a high voltage is applied within the neck portion 11 of the cathode ray tube body, the spring 7d of which extends into the neck portion 11 as described above. ), and the electron gun is placed concentrically with the neck of the tube. Here, the diameter D ₃ of the fifth grid G ₅ can be selected so that D ₄ >D ₃ >0.65D ₄ , where D ₄ is the inner diameter of the neck portion 11.

According to the electron gun having such a configuration, the fifth grid _G5 is the third grid _G3 or the fourth grid G5.
Beading glass 1 mechanically integrated with G ₄
0, the substantial diameter _D3 of this fifth grid _G5 can be made large enough to approach the inner diameter _D4 of the neck portion 11. Therefore, in the subsequent electronic lens system (Lens2), the aperture D ₃ of the fifth grid G ₅ is
The diameter D ₂ of the fourth grid G ₄ can be made larger without changing the inner diameter D ₄ of the neck portion 11.
Furthermore, by increasing the substantial aperture of the main electron lens system, the spherical aberration can be reduced.

FIG. 12 shows the electron gun according to the present invention described above and the fourth
FIG. 2 is a curve diagram showing the relationship between the amount of current (mA) and the average diameter (mm) of the beam spot on the phosphor screen with respect to the conventional unipotential electron gun shown in the figure. In the figure, the curve is that of the conventional electron gun, and the curve is that of the electron gun of the present invention. As is clear from FIG. 12, it can be seen that the beam spot has been significantly improved over the entire current range. It is also possible to create an electron gun in which the subsequent electron lens (Lens 2) is an electric field extension type lens and the inner diameter of the final electrode is increased, and in this case as well, spherical aberration can be further reduced.

As described above, according to the proposed configuration, the spherical aberration of the electron gun is even smaller than that of an electron gun whose electron lens aperture is selected to be smaller than the electron lens aperture of the preceding stage electron lens system in which the electron lens action area is separated. This is suitable for application to cathode ray tubes and the like.

Effects of the Invention As described above, the configuration of the present invention can configure a main electron lens, such as the one described above, which has an asymmetrical cylindrical portion and has a relatively long axial length, and which requires high circularity. In the fifth grid _G5 ,
By inserting a cap with high circularity into the end, the circularity of the cylindrical part 2 of the electrode body is forcibly corrected or corrected. Accordingly, an electron beam spot with less distortion can be formed, and the resolution of the cathode ray tube can be improved.

In addition, in the present invention, the cap 6 for correcting the roundness is not directly welded to the cylindrical part 2, but instead a fixing disc body 7 is provided, and the cap 6 is connected to the cylindrical part 2 through the mounting piece 7a. Another feature is that the cap is fixed, so that when the cap 6 is welded directly to the cylindrical part 2, the force during welding causes the cylindrical part 6a of the cap 6 to be welded. Inconveniences such as causing deformation and inhibiting high roundness can be avoided.

In the above example, the present invention is applied to an electron gun having a configuration in which the fourth grid _G4 is arranged within the fifth grid _G5 , but it can be applied to other types of electron guns that require high circularity. It is obvious that the present invention can be applied to an electron gun having an electrode in which it is difficult to obtain an electrode body with high circularity to produce a similar effect.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the main electron lens system of an electron gun used to explain the present invention, FIG. 2 is a cross-sectional view showing an example of a conventional unipotential electron gun, and FIG.
The figure is a cross-sectional view showing the basic structure of an electron gun according to the present invention, FIGS. 4 and 5 are cross-sectional views of main parts of a conventional electron gun, and FIG. 6 is an example of an electron gun according to the present invention and a conventional electron gun. A curve diagram relating to the spherical aberration coefficient and focal length in an electron gun, FIG. 7 is an explanatory diagram for determining the relational expression of the aberration coefficient, and FIGS. 8 and 9 are side views showing an embodiment of the electron gun according to the present invention. and its cross-sectional view,
Fig. 10 is a cross-sectional view of the main part, Fig. 11 is an exploded perspective view thereof, and Fig. 12 is a curve showing the relationship between current amount and beam spot diameter of an example of an electron gun according to the present invention and a conventional electron gun. It is a diagram. K is the cathode, G ₁ to G ₅ are the first to fifth grids,
2 is a cylindrical portion of the electrode body, 6 is a cap, and 7 is a fixing disk.

Claims (1)

[Scope of utility model registration request] A cap having a high degree of circularity is fitted into the end of the electrode cylindrical portion which requires a high degree of circularity, and the cap includes a cylindrical portion inscribed in the electrode cylindrical portion and one end face plate having an electron beam transmission hole. is integrally molded into a dish shape as a whole, and a disc body having an electron beam transmission hole that matches the electron beam transmission hole is attached to the outer surface of the end plate of the cap, and the disc body has: A mounting piece is provided on the outer periphery of the electrode cylindrical part and is extended and bent along the outer circumferential surface of the electrode cylindrical part. An electron gun with high circularity that corresponds to circularity.