JPS6321084Y2 - - Google Patents

Description

[Detailed description of the invention] The invention relates to an electron gun built into a cathode ray tube.
In particular, it concerns the structure of the second grid of the electron gun.

The image quality of a cathode ray tube is determined by the spot quality of the electron beam formed on the screen. An effective means is to reduce the divergence angle.

The thickness of the second grid in an ordinary cathode ray tube electron gun is in the range of 0.10 to 0.20 mmt.

However, in recent years, the rated focus voltage of color picture tubes, which are a type of cathode ray tube, has been increased to about 7 to 10 KV due to the demand for improved brightness and image quality.
Anode voltage is also now used at 25-30KV,
To accommodate this, the thickness of the second grid should be set to, for example, 0.4 to 1.0 times the hole diameter of the first grid (0.5 to 0.6 mmt).
It is known that the divergence angle of the electron beam can be suppressed by increasing the thickness of the second grid, but if the thickness of the second grid is made to be about three times that of the normal second grid, it is natural that the prefocus area will be reduced. The electric field formation changes, and the penetration rate from the electron beam passage hole of the second grid toward the cathode becomes weaker in inverse proportion to the plate thickness of the second grid due to the focus voltage applied to the third grid. As a result, the focusing electric field of the crossover is weakened, the divergence angle of the electron beam toward the main lens is reduced, and the spherical aberration is reduced. This has the disadvantage of increasing the spot diameter on the screen as it leads to a decrease in the spot size.

Therefore, E=V ₃ /d ₃ (V/mm) (where V ₃ is the third
A means is required to strengthen the electric field in the prefocus area, which is represented by the potential difference _d3 between the grid and the second grid (distance from the third grid to the second grid).
Since the focus voltage is usually fixed within the rated range, the gap between the electrodes will inevitably be narrowed, and the increase in the thickness of the second grid will cause various problems as well as deterioration of the thermal stability time due to the increase in heat capacity. It was hot.

In addition, the area around the electron beam passage hole of the second grid is contaminated with barium in the electron emitting material during the manufacturing process of color picture tubes, especially during the activation and aging process of the cathode during evacuation. When the gap between the grid and the third grid becomes narrow on the order of 1 mm, the field (stray) emission increases, which lowers the discharge starting electric field, so the actual gap between the second and third grids is 1.3 mm. Although it is desirable to have a design that suppresses the electric field strength to above 6 KV/mm or less, it has been extremely difficult to achieve such a design with the conventional structure due to the characteristics of the electron gun.

The present invention was devised in view of the above-mentioned problems, and the second grid has an electric field distribution equivalent to the effect of suppressing the divergence angle of the electron beam by using a thick plate, and stray emission from the second grid. The purpose of the present invention is to provide an electron gun for cathode ray tubes with improved voltage resistance.

Next, an embodiment of the electron gun of the present invention will be explained with reference to FIGS. 1 and 2.

FIG. 1 shows an electron gun with an integrated structure that emits three electron beams arranged in a row for use in a shadow mask type color picture tube.A heater 1, a cathode 2, a first grid 3, This is a bipotential electron gun formed of a second grid 4, a third grid 5, a fourth grid 6, and a convergence electrode 7, and each of the other electrodes except the cathode 2 has electron beam passage holes arranged in a row. By applying a predetermined voltage to each electrode, the thermoelectrons heated by the heater 1 are controlled, accelerated, and focused as an electron beam, and are irradiated onto a predetermined phosphor layer on a screen (not shown) through a shadow mask. It is now possible to reproduce color images.

In an electron gun having such a structure, the second grid 4 has an approximately truncated conical shape near the electron beam passage hole ₄₁ having a diameter _L1 on the side of the first grid 3, as shown in an enlarged view in FIG. D ₂ =0.8 to 1.2 between the opening diameter L ₂ of this truncated conical opening on the third grid 5 side, the protrusion length D ₂ , and the inclination angle θ ₂ of the slope 4 ₂ .
mm, L ₂ = 2D ₂ to 3D ₂ , θ = 60 to 68°, and the plate thickness D ₁ of the periphery of the electron beam passage hole 4 ₁ is set to D ₁ =
It is characterized by being set to D ₂ /7 to _{D 2} /2.

That is, considering the difference in voltage applied between the second grid 4 and the third grid 5 and the space gap, the protrusion length D ₂ is set in the range of 0.8 to 1.2 mm,
Adjustment of the aperture diameter _L2 on the third grid 5 side prevents a drop in the object point potential, while providing an inclined surface ₄₂ provides a focusing effect in the electron beam passage area of the second grid 4. Crossover (object point) diameter between protrusion length D ₂ and opening diameter L ₂ = K ₁ · Sinθ／D ₂ · L ₂ sin α (scattering angle) = K ₂ D ₂・L ₂ However, K ₁ and K ₂ are constants and have a contradictory relationship, so this example uses this D ₂
As a result of finding the optimal shape by electric field calculation within the range of L 2 = L ₂ = the range in which the drop in penetration voltage can be maintained at about 10 to 15% even if the divergence angle is reduced by 30% compared to the conventional one.
2D ₂ ~ 3D ₂ , θ = 60 ~ 68° Also, the plate thickness D ₁ of the second grid, especially around the electron beam passage hole, is set to D ₂ /7 ~
When D ₂ /2 is selected, it is particularly effective in suppressing the beam divergence angle, and the halo size around the screen of a convergence-free color picture tube can be reduced to about 1/2 compared to conventional ones. Ta. In this case, the beam focusing electric field can be strengthened by increasing the inclination angle θ.
It is susceptible to aberrations due to concentric errors in the tube axis direction during the manufacturing process and assembly of the electron gun, and the beam focusing effect becomes weak below 60 degrees.

In the above embodiment, the second plate is cut from a relatively thick plate.
However, as mentioned above, increasing the thickness will increase the heat capacity and lead to undesirable results, so as shown in Figure 3, a second grid is made from a relatively thin plate and a hole is placed around the periphery of the electron beam passage hole. By providing cylindrical protrusions 4a in the three-grid direction, it may be formed to equivalently have a thickness of _D1 . By making the second grid thinner in this way, thermal stability can also be obtained with respect to the white balance of the three colors red, green, and blue, as in a color picture tube.

Next, this embodiment was actually assembled into a cathode ray tube, and the cathode 2
50V to 1st grid 3, 0V to 2nd grid 4
When 600V is applied to the third grid 5, 5000V is applied to the third grid 5, and 22000V is applied to the fourth grid 6, the half potential distribution 21 from the gun axis Z on the plane including the gun axis Z and the vertical axis Y perpendicular to the plane of the paper and the electron beam. The trajectory is shown in Figure 4.
In this figure, the scale on the horizontal axis Z indicates the distance from the two surfaces of the cathode, and the vertical axis R is symmetrical about the Z axis, so it is indicated as a radius.

As can be seen from this figure, thermionic electrons emitted from the cathode 2 pass through the second grid 4 as an electron beam 22 while forming a so-called crossover between the first grid 3 and the second grid 4. but,
It can be seen that the equipotential lines are formed so as to direct the electron beam 22 in an equiaxial direction, that is, to have a focusing effect, as shown in the figure.

That is, it can be seen that the electron gun of this example has a small electron beam divergence angle, small spherical aberration, small deflection aberration, and has few halos and high image quality.

In the above embodiment, the electron gun for color picture tubes is arranged in a single line and has an integrated structure. However, the present invention is not limited to this, and can be applied to single electron guns, separate type electron guns, etc. Of course, it can also be used in other electron guns.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing one embodiment of the present invention;
The figure is an enlarged sectional view of the main part of the second grid in Fig. 1, Fig. 3 is an enlarged sectional view of the main part of the second grid of this embodiment formed of a thin member, and Fig. 4 is FIG. 2 is an explanatory diagram showing an electron beam trajectory and potential distribution. 2...Cathode, 3...First grid, 4...Second
Grid, 5... Third grid, 21... Potential distribution, 22... Electron beam trajectory.

Claims (1)

[Claims for Utility Model Registration] (1) A first grid and a second grid installed in a cathode ray tube and provided with a cathode and an electron beam passage hole;
In the electron gun, a third grid and other electrode groups are arranged at predetermined intervals to control, accelerate, and focus thermionic electrons emitted from the cathode as an electron beam. The vicinity of the electron beam passage hole of the second grid is formed to protrude toward the first grid side in a substantially truncated conical shape, and the diameter L ₂ of the opening of the conical cap shape on the third grid side is protruded. Between the length D ₂ and the slope angle θ ₂ , D ₂ = 0.8 to 1.2 mm, L ₂ =
An electron gun characterized in that 2.D ₂ to 3.D ₂ , θ ₂ =60 to 68°. (2) A utility model characterized in that the plate thickness D ₁ of the peripheral edge of the electron beam passage hole of the second grid opposite to the first grid is set to D ₁ =D ₂ /7 to _{D 2} /2. An electron gun according to registered claim 1. (3) The plate thickness D ₁ of the periphery of the electron beam passage hole of the second grid opposite to the first grid can be made equivalent by providing a cylindrical protrusion on the periphery of the electron beam passage hole in the direction of the third grid. An electron gun according to claim 2 of the utility model registration, characterized in that the electron gun is formed as follows.