JP2553468B2 - Electron gun in cathode ray tube - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron gun for a cathode ray tube, and more particularly to an electron gun for a color television receiver.

2. Description of the Related Art A cathode ray tube consists of an evacuated glass container, the back of which is a substantially flat screen. The inner surface of the flat screen is coated with a cathodoluminescent material such as a fluorescent material. The cathodoluminescent material is one that emits visible light when excited by an electron beam produced by one or several electron guns. For color visible imaging, screens generally consist of triple stripes of phosphor. Each of these triple stripes is
Usually, it is provided for emitting light of each of the three primary colors of red, green and blue. In a shadow mask type color picture tube, three electron guns are provided for exciting a specific color. Furthermore, a mask provided with a large number of holes is provided in the preceding stage of the screen, and specific light emission or
The corresponding electron beam is passed to excite the emission mosaic of that particular color.

An electron gun is composed of a cathode having a surface that emits electrons when heated by a filament, and an electrode or grid generally indicated by G ₁ , G ₂ , G ₃ , and the like. The subscripts 1, 2, and 3 of the grid G indicate the position with respect to the cathode, and the larger the number, the farther from the cathode. In particular, among the above-mentioned grids, the first grid G ₁ and the grid G ₂ function to pre-focus the electron beam, and the subsequent G ₃ , G ₄ etc. are electrostatic lenses for focusing and focusing the electron beam. Is formed. The modulation of the electron beam as a function of the emission intensity of the points or dots projected on the screen is obtained by the modulation of the cathode voltage or the voltage modulation of the first grid G ₁ (Wehnelt).

Problems to be Solved by the Invention A high voltage is usually applied to the grid electrode forming the electrostatic lens. In most cases it is a few kilovolts. The present invention particularly relates to a picture tube, and in particular, the present invention is
It has at least one grid forming an electrostatic lens, which during normal operation is subjected to a high voltage of, for example, approximately 25 kilovolts, and which has a voltage of the same value for a long time even after the power supply to this picture tube is cut off. The present invention relates to a picture tube for holding a picture tube. This voltage does not disappear instantaneously for the following reason. That is, the glass container has an inner electrically conductive coating connected to the grid and an outer electrically conductive coating at ground potential. Such a glass container constitutes a large-capacity capacitor by the above two electrically conductive coatings, and retains its electric charge for a long time even after the power supply is cut off. Thus, the inner coating and the grid connected to it will carry a high voltage.

If the distance between the grid and the cathode is relatively small, the high voltage thus maintained on the grid will cause electrons to be emitted to the center of the screen if the cathode temperature is still high and one or a few Visible luminescent spots appear. Such defects are often referred to as "cathode flicker."

To avoid this deficiency, a plurality of discharge diodes have been provided in the external circuit of the picture tube. However, this solution was still expensive.

Means for Solving the Problems The present invention intends to suppress the cathode flicker phenomenon which appears after the power supply to the picture tube is cut off by an easy means.

In order to release the cathode from the effects of the high voltage remaining on the grid after the interruption of the power supply to the picture tube, the invention is characterized in that a mask means is provided between the grid and the cathode. As an example, these mask means form part of an intermediate grid. Preferably, the intermediate grid is elongate in shape and has two transverse end walls, the end wall of which the cathode side is provided has a greater wall thickness than the opposite end wall. As a variant thereof, the opening of this end wall closer to the cathode has an end or a flange, which is preferably folded back towards the interior of the elongated intermediate grid.

In another embodiment, in an intermediate grid having elongated end walls, the end wall furthest from the cathode has an opening with a diameter that is smaller than the diameter of the adjacent high voltage remaining grid opening. Especially, when the ratio of these two diameters is 0.92 or less, the best effect is obtained.

By applying the improvement according to the present invention to the intermediate grid located between the grid where the high voltage remains even after the interruption of the power supply and the cathode, it is possible to limit the high voltage influence range from the high voltage remaining grid. In particular, the high voltage influence range can be contained within the intermediate grid, the influence on the cathode can be suppressed, and the flicker phenomenon on the screen can be reduced.

Embodiment An embodiment according to the present invention will be described below with reference to the drawings.

The present embodiment relates to an electron gun in a shadow mask type color television receiver, and more particularly to an in-line arrangement for emitting three electron beams, that is, a (triple) electron gun arranged on a common plane. is there.

FIG. 1 is a sectional view showing a schematic configuration of an embodiment of the present invention.

Such an electron gun has three cathodes K each having a radiation surface 10 perpendicular to the picture tube axis 11 and heated by a filament (not shown), and an electrode or grid.
It includes one assembly consisting of G ₁ , G ₂ , G ₃ , G ₄ , G ₅ , G ₆ . The first two grids in this assembly
G ₁ and G ₂ have a function of pre-focusing the electron beam, and the rear grids G ₃ , G ₄ , G ₅ , and G ₆ constitute electrostatic lenses that focus and concentrate the electron beam.

The cathode K in FIG. 1 is arranged on the picture tube shaft 11,
The other cathodes are arranged in the same plane symmetrically parallel to each other with the axis 11 interposed therebetween.

The grids G ₁ , G ₂ and G ₄ are planar bodies, and each grid has three circular holes drilled around the corresponding cathode axes, and the electron beams emitted from the corresponding cathodes are I am passing it. On the other hand, each of the grids G ₃ , G ₅ , and G ₆ , which are substantially cylindrical or parallelepiped-shaped, has an end wall, and each end wall has three circular holes formed around the corresponding cathode axis. Have

As described above, FIG. 1 is a cross-sectional view taken along the axis of the picture tube, and shows a cross section of only the central cathode, the grid corresponding thereto and the holes on the grid among the three cathodes.

The electrodes or grids G ₃ , G ₅ are connected to terminal 3 which is energized on average about 8 kilovolts. On the other hand, the electrode or grid G _4, G ₆ is connected to a terminal 3 connected to a high voltage source of approximately 25 kilovolts. The assembly consisting of the grids G ₃ , G ₄ and G ₅ constitutes a unipotential type electrostatic lens, a so-called Heinzel type lens, while the grids G ₅ and G ₆ form an electrostatic lens called a bipotential type lens. I am configuring.

Each of these grids is metal and is made of metal foil having a certain thickness. Therefore, the elongated portion 12 of the grid G ₅ has the same thickness as the both end walls 13 and 14. For example, in order to facilitate the manufacture of the electron gun, the holes in the grid G ₄ , as well as the holes in the end wall 15 located furthest from the cathode K in the grid G ₃ ,
All G _5, the end wall of the hole of the G ₆ is the same diameter. On the other hand, like the holes in the end wall 16 of the grid G ₃ facing the cathode K,
The holes of the grids G ₁ , G ₂ all have a smaller diameter.

Like the grid G ₅ , the grid G ₃ has a substantially cylindrical shape or a parallelepiped shape, and the wall 17 and the end walls 15 and 16 of the cylindrical portion have the same thickness. In one embodiment of the invention, a plate or insert 18 is welded to the inner surface of end wall 16 having the same thickness as end wall 15. The plate 18
3 is a plan view and FIG. 4 is a sectional view. The plate 18 has the same diameter as the three holes on the end wall 16 and is also provided with three holes at corresponding positions. For example, the plate 18 is welded onto the inner surface of the end wall 16 by its four square weld points.

This welding is carried out before connecting the two cup-shaped members 22, 23 forming the two parts of the grid G ₃ to each other.

The portion formed by the end wall 16 and the plate 18 is, for example, approximately three times the thickness of the end wall 15. In other words, the plate 18 is about twice the thickness of the end wall of the grid G _3.

Here, for example, if the power supply to the picture tube is interrupted,
Terminal 4 holds a voltage of about 25 kilovolts, while the other grid voltages drop almost instantaneously to a zero value (ground potential) as the total potential.

The distance L separating the cathode K from the grid G ₄ is relatively small, for example about 1 cm. The influence of the voltage of the grid G ₄ connected to the terminal 4 of the above-mentioned electron of about 25 kilovolts is remarkable in the vicinity of the cathode K and induces the formation of an undesired electron beam on the axis of the electron gun. That is, an interference flicker is induced in the center of the screen. The reason for this is that in the case of the prior art in which the plate 18 is not provided, as shown in FIG. 2a, an equipotential of about 3.5 V to 5 V which constitutes the limit of the influence region of the voltage induced by the grid G ₄ is formed. This is because the surface 25 appears near the grid G _{2 and} a considerable amount of electrons reach the central area of the screen. On the other hand, according to the present invention in which the plate 18 is provided, as shown in FIG. 2b, the influence limit of the voltage induced in the grid G ₄ corresponding to the equipotential surface 25 (equipotential surface) 2
5'is clearly separated from the cathode K. As a result, a considerable number of electrons that reach the central area of the screen can be reduced, so that visible interference flicker does not actually occur in the central portion of the screen.

Experiments were carried out with and without the improvement according to the invention.

In the case of the prior art without the improvement according to the invention, the end wall 16
The interference flicker occurred when the voltage of the electrode G ₄ reached 12 kilovolts under the condition that the thickness was 0.25 mm, and the nominal supply voltage to the filament of the cathode K was 6.3 volts. on the other hand,
With the improvement according to the invention, the thickness of the end wall 16 of the grid G ₃ facing the cathode K side is 0.75 mm, the supply voltage to the filament of the cathode is 9 V and at least 32 kV is applied to the grid G _4. Interference flicker occurred only when. The thickness of the front end wall 16 of the grid G ₃ when the improvement of the present invention is added is about 3 times the thickness of the rear end wall 15.
In order to sufficiently reduce the flicker, it is possible to obtain the thickness of the front end wall 16 that is about twice the thickness of the rear end wall 15.

A modification of the above embodiment is shown in FIG. FIG. 5 shows a cross section of only the grid G _{3 according} to the present invention. In Figure 5, the grid G ₃ consists of two parts, the first
This part is constituted only by the front end wall 30 having a thickness larger than the thickness of the other part 31 of the grid G ₃ . On the other hand, the second portion 31 is composed of an elongated portion and another end wall.
The first portion 30 and the second portion 31 are connected to each other by welding or the like.

FIG. 6 shows a sectional view of a grid G ₃ which is a second embodiment of the present invention. In this embodiment, 'but has the same thickness as other portions of the grid G _3, the end wall 16' front end wall 16 of the grid G ₃ holes of covered by the flange or edge 32 There is. The advantage of this embodiment is that known electron guns need only be easily modified.

As a modification of the embodiment shown in FIG. 1, the end wall 16 corresponding to the diameters of the three holes 19, 20, 21 of the plate 18 respectively.
It is to be larger than the diameter of the upper hole. However, in this case, the thickness of the plate 18 is preferably made larger than that when the holes of the end wall 16 and the plate 18 have the same diameter. In other words, the thickness of the plate 18 is preferably increased in proportion to the diameter of the hole drilled on the plate 18.

FIG. 7 is a cross-sectional view of a grid structure according to the third embodiment of the present invention. As shown in FIG. 7, the grid G ₃
The diameter d ₃ of the holes of the end wall 15 of the hole and the grid of the grid G ₄
It is smaller than the diameter d ₄ of the hole in the front end wall on the cathode K side of G ₅ . In other words, the ratio d ₃ / d ₄ is smaller than 1. In this way, by making the ratio d ₃ / d ₄ smaller than 1, it is possible to reduce the interference flicker after the power supply is interrupted.

In FIG. 7, the equipotential surface L ₂ corresponding to the equipotential surface 25 in FIG. 2a or the equipotential surface 25 ′ in FIG. 2b intersects the axis Z at the point B. Effectively, this point is inside the grid G ₃ .
Thus, the effect of high voltage on the grid G ₄ can be reduced by making the diameter d ₃ smaller than in the case of FIG. 2a. For example, when the d ₃ / d ₄ ratio was set to 0.6875, good results were obtained combining the quality of the cathode ray image in image formation with the reduction of interference flicker after interruption of power supply.

On the other hand, the hole of the end wall 15 of the grid G ₃ are as in Figure 1, and has a cylindrical flange directed inwardly of the grid G ₃ is cylindrical. This flange is obtained during the production of the grid G ₃ by extrusion. This flange has an effect of reducing the limit of the d ₃ / d ₄ ratio necessary for carrying out the present invention. As one example thereof, the present invention effect can be obtained that are comparable to the case of the above d ₃ / d ₄ ratio 0.6875 be d ₃ / d ₄ ratio 0.844.

As described above, the present invention realizes a given effect by limiting the influence of the high level equipotential surface in the electron beam format region. The same effect can be obtained as a technical method other than the above, particularly by enlarging the size of the hole of the grid following the high-voltage electrode (or grid).

The present invention can also be applied to the case where the grid G ₄ is thick, for example, a cylindrical shape. If the filament vicinity is the same, the problems and solutions of the present invention are the same.

[Brief description of drawings]

FIG. 1 is a sectional view of an electron gun according to a first embodiment of the present invention, FIG. 2a is a sectional view showing a defect of an electron gun according to the prior art, and FIG. 2b is a first embodiment shown in FIG. FIG. 3 is a cross-sectional view of an electron gun showing the effect of the example, FIG. 3 is a plan view of one component member in the electron gun of the first embodiment shown in FIG. 1, and FIG. 4 is a first embodiment shown in FIG. FIG. 5 is a sectional view of a partly modified constituent member of the electron gun of the first embodiment shown in FIG. 1, and FIG. 6 is a second embodiment of the present invention. FIG. 7 is a sectional view of one component member of the electron gun, and FIG. 7 is a sectional view of the electron gun of the third embodiment of the present invention. (Main reference number) K ...... _{cathode, G 1, G 2, G} 3, G 4, G 5, G 6 ...... grid, 13, 14, 15, 16 ...... end walls, 18 ...... plate, 19 , 20, 21 …… Hole, 32 …… Flange

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) The inventor Gierard Pourdon France 69200 Vueniceuriyu Rozier Sarangro 3 (56) References JP-A-48-82770 (JP, A) Actual exploitation S54-50954 (JP, U) Special features Public Sho 42-5895 (JP, B1) Actual Public Sho 35-6319 (JP, Y1) Actual Public Sho 46-7869 (JP, Y1)

Claims (19)

(57) [Claims] 1. An electron gun for a color television picture tube having an electrostatic lens having an electrode in which a high voltage remains even after power supply is cut off, in a cathode of a high voltage remaining after power supply to the electrode is interrupted. In order to reduce the influence on the electron gun, the distance between the equipotential surface and the cathode, which limits the region where the voltage induced by the high voltage remaining in the electrode affects the Of the intermediate high voltage electrode of the electron gun disposed between the high voltage electrode and the cathode of the mask. Means, wherein the intermediate electrode has two end walls, is formed in an elongated shape along the central axis of the electron gun, and the end wall facing the cathode is larger than the end wall on the opposite side. Characterized by being thick An electron gun that. 2. The electron gun according to claim 1, wherein a ratio of thicknesses of both end walls of the intermediate electrode is at least 2. 3. The intermediate electrode includes a main portion and an end wall having the same thickness, and the end wall facing the cathode is provided with a plate having a corresponding shape. The electron gun according to claim 1. 4. The electron gun according to claim 3, wherein the plate is welded to the end wall. 5. The electron gun according to claim 3, wherein the plate is provided on an inner surface of the end wall. 6. The intermediate electrode comprises a first part composed of the thickest end wall and a second part composed of an axially elongated part and an opposite end wall. The electron gun according to claim 1. 7. The electrode on which the high voltage remains has a circular hole, the diameter of the circular hole being the same as the diameter of the corresponding hole in the end wall of the intermediate electrode opposite the cathode. Any one of claims 1 to 6 characterized in that
The electron gun according to the item. 8. A bipotential type lens and a Heitzel type lens are provided, and the intermediate electrode and the high-voltage residual electrode constitute a Heinzel type lens. Item 7. The electron gun according to any one of items 7. 9. An electron gun for a color television picture tube having an electrostatic lens provided with an electrode in which a high voltage remains even after power supply is cut off, in a cathode of a remaining high voltage after power supply to the electrode is interrupted. In order to reduce the influence on the electron gun, the distance between the equipotential surface and the cathode, which limits the region where the voltage induced by the high voltage remaining in the electrode affects the Of the mask for forming a part of an intermediate electrode arranged between the high voltage electrode and the cathode of the electron gun, the means having a value such that the residual high voltage of the electron gun has a small influence on the cathode. Means, the intermediate electrode has two end walls, is formed in an elongated shape along a central axis of the electron gun, and has a flanged hole in the end wall facing the cathode of the intermediate electrode. Provided Electron gun, characterized in that is. 10. The electron gun according to claim 9, wherein the flange is folded back toward the inside of the intermediate electrode. 11. The electrode on which the high voltage remains has a circular hole, the diameter of the circular hole being the same as the diameter of the corresponding hole in the end wall of the intermediate electrode opposite the cathode. The electron gun according to claim 9 or 10, characterized in that. 12. A bipotential type lens and a Heitzel type lens are provided, and the intermediate electrode and the high voltage residual electrode constitute a Heinzel type lens. Item 11. The electron gun according to any one of items 11. 13. An electron gun for a color television picture tube having an electrostatic lens provided with an electrode in which a high voltage remains even after power supply is cut off, in a cathode of a residual high voltage after interruption of power supply to the electrode. In order to reduce the influence on the electron gun, the distance between the equipotential surface and the cathode, which limits the region where the voltage induced by the high voltage remaining in the electrode affects the Of the mask for forming a part of an intermediate electrode arranged between the high voltage electrode and the cathode of the electron gun, the means having a value such that the residual high voltage of the electron gun has a small influence on the cathode. Means, the intermediate electrode has two end walls, has an elongated shape along the central axis of the electron gun, and has a diameter d of a hole provided in the end wall on the electrode side where the high voltage remains. ₃ and the high electrostatic Electron gun There, characterized in that the ratio d ₃ / d ₄ between the diameter d ₄ of the holes provided in the electrode remaining is less than 1. 14. The electron gun according to claim 13, wherein the diameter ratio d ₃ / d ₄ is 0.6875. 15. The electron according to claim 13, wherein the hole in the end wall of the intermediate electrode on the high voltage electrode side is surrounded by a flange facing the inside of the intermediate electrode. gun. 16. The electron gun according to claim 15, wherein the diameter ratio d ₃ / d ₄ is 0.844. 17. A bipotential type lens and a Heitzel type lens are provided, and the intermediate electrode and the high voltage residual electrode constitute a Heinzel type lens. The electron gun according to any one of 16 items. 18. An electron gun having an electrostatic lens having an electrode in which a high voltage remains even after the power supply is cut off, and the influence of the remaining high voltage after the power supply to the electrode is reduced on the cathode. Therefore, the electron gun determines the distance between the equipotential surface and the cathode, which limits the region affected by the voltage induced by the high voltage remaining in the electrode, as the residual high voltage after interruption of the power supply to the electrode. It is provided with a means for reducing the influence on the cathode, which means
A mask means forming a part of an intermediate electrode arranged between the high voltage electrode and the cathode of the electron gun, the intermediate electrode having two end walls, A cathode ray tube, which is formed in an elongated shape along the side wall, and is provided with an electron gun whose end wall on the side facing the cathode is thicker than the end wall on the opposite side. 19. An electron gun having an electrostatic lens having an electrode in which a high voltage remains even after the power supply is cut off, and the influence of the remaining high voltage after the power supply to the electrode on the cathode is reduced. Therefore, the electron gun determines the distance between the equipotential surface and the cathode, which limits the region affected by the voltage induced by the high voltage remaining in the electrode, as the residual high voltage after interruption of the power supply to the electrode. It is provided with a means for reducing the influence on the cathode, which means
A mask means forming a part of an intermediate electrode arranged between the high voltage electrode and the cathode of the electron gun, the intermediate electrode having two end walls, A color television receiver, characterized in that it comprises a cathode ray tube having an elongate shape, the end wall facing the cathode including an electron gun thicker than the end wall facing the cathode.