JPS6347110B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic focusing cathode ray tube that facilitates assembly of an electron gun and has a beam spot having a substantially perfect circular shape.

Figure 1 shows a conventional structure in which three electron guns are arranged on one horizontal plane, and an annular permanent magnet is arranged surrounding a network tube.
A pair of yokes are provided to efficiently absorb the magnetic flux of this magnet and form a magnetic lens in the opposing gap.
FIG. 2 is a cross-sectional view of the electron gun section of a magnetic electromagnetic focusing cathode ray tube outside the in-line array taken along the in-line array surface, FIG. 1,
FIG. 2 is a cross-sectional view taken along line A-A' in FIG. 2; In these figures, 1 is the valve (connection pipe), 2 is the cathode,
3 is a first grid, 4 is a second grid, 5 is a magnetic yoke, 6 is an elastic conductive strip, 7 is an internal conductive film, 8
is an annular permanent magnet, 9 is an electrode support rod, 10 is a deflection yoke, 11 is a stem pin, 12C is a center beam, 12S ₁ and 12S ₂ are side beams, 13 is a magnetic main lens, 14 is a gap electrode made of a non-magnetic material, 15 is the third grid bottom. The center beam 12C and side beams 12S ₁ and 12S ₂ emitted from the cathode 2 pass through the first grid 3 and the second grid 4, respectively, and are once focused to form a so-called crossover. a third grid bottom 15 to which an anode voltage is applied via the conductive strip 6; a magnetic yoke 5;
It is accelerated by the gap electrode 14, enters the magnetic main lens 13 through the center beam passage hole 5C, side beam passage holes 5S ₁ and 5S ₂ , and forms a crossover image on a phosphor screen (not shown). . The magnetic yokes 5 are made of a highly permeable material and efficiently absorb the magnetic flux generated by the permanent magnets 8, creating a strong focusing magnetic field along the path of the electron beam in the opposing gap between the pair of yokes 5 arranged opposite to each other. , here is the magnetic main lens 13
form. Therefore, the beams 12C, 12S ₁ ,
Make the beam spot shape of 12S ₂ a perfect circle,
Considering that the three electron beams 12C, 12S ₁ and 12S ₂ are concentrated on a shadow mask (not shown), the magnetic yoke 5 must have a cylindrical shape as shown in FIGS. 1, 2 and 3. Nakatsuta. For this reason, the yoke 5 has a problem in that it is impossible to apply the support method using the electrode support rod 9 as in the case of other electrodes, and this becomes a major cause of a decrease in electron gun assembly accuracy and an increase in cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electromagnetic focusing cathode ray tube that is free from the above-mentioned problems, has good mass productivity, and has good image quality.

In order to achieve the above object, in the present invention,
The shape of the yoke's periphery is made non-circular so that it can be supported together with other electrodes by an electrode support rod, thereby improving the accuracy of electron gun assembly and making assembly work easier.On the other hand, the non-circular shape of the yoke's periphery also reduces the shape of the beam spot. In order to correct the circular shape, the shape of the electron beam passage hole was also made non-circular, so that a substantially uniform magnetic flux distribution was obtained over the entire circumference of the beam, and the beam spot shape was made substantially circular.

4 to 6 show the electron gun section of an in-line array external magnetic type electromagnetic focusing cathode ray tube using a non-circular yoke according to the present invention, FIG. 4 is a cross-sectional view of the in-line array surface, and FIG. FIG. 6 is a sectional view taken along the line BB' in FIGS. 4 and 5. The difference between what is shown in these figures and what is shown in FIGS. 1 to 3 is that a magnetic yoke 50 having a non-circular (flat) peripheral shape is supported together with other electrodes by a long electrode support rod 90;
The electron gun assembly has become easier and assembly accuracy has been improved. However, when circular electron beam passing holes 50S ₁ , 50C, 50S ₂ as shown in FIG. 6 are used, three beams 12S ₁ , 12C, 12
In order to concentrate S ₂ on one point on the shadow mask and make the so-called static convergence (STC) zero, as shown in Figs. 4 and 5, the mounting position of the permanent magnet 8 is shown in Figs. 1 and 2. In addition, when the STC is reduced to zero, the beam spot shape becomes non-circular as shown in FIG. 7. It is clear that this is due to the change in the shape of the magnetic yoke periphery and the permanent magnet mounting position.

In order to improve the beam spot shape, the inventor first made the center beam passage hole 50C' of the non-circular yoke 50' shown in FIG. We made a number of prototype tubes with various oblateness ratios (φy/φx),
The beam spot diameter was measured. The result is
In FIG. 9, the oblateness ratio φy/φx of the beam passage hole is plotted on the horizontal axis, and the beam spot shape (Spy/Spx) is plotted on the vertical axis, which is indicated by a solid line. However, Spy is the vertical diameter of the beam spot, and Spx is the horizontal diameter. The sample is a permanent magnet with an outer diameter of 45φmm, an inner diameter of 26φmm, and a thickness of 10mm.
Magnetic field 450 Gauss, outer diameter of magnetic yoke 50' 15.4φ
mm, height 10 mm, opposing gap length 7 mm, permanent magnet 8 is
It was installed so that the STC would be zero. From Figure 9,
It can be seen that under the above measurement conditions, when the oblateness of the center beam passage hole is 0.89, the center beam spot shape becomes a perfect circle. Similarly, the results of a prototype experiment regarding the side beam spot are shown in broken lines in FIG. Also for side beams, when the vertical diameter φy of the beam passage hole is smaller than the horizontal diameter φx, Spy
A beam spot of =Spx was obtained, but the flattening ratio φy/φx in the case of this side beam is closer to 1.0 than the flattening ratio 0.89 in the same case of the center beam. In addition, in the case of side beams, even if the oblateness of the beam passage hole is set to the optimal value as described above, the beam spot shape is inevitably not perfect if the passage hole is an ordinary oval shape that is symmetrical about two orthogonal axes. I found out that it is not a circle. This is because the magnetic flux directly leaking from the permanent magnet outside the neck tube is superimposed on the focused magnetic field of the side beam. To solve this problem, as in the yoke 51 shown in FIG. 10, the side beam passage holes 51S ₁ and 51S ₂ have a long diameter in the horizontal direction, and the small diameter end extends toward the inner wall of the neck canal. By changing the shape, we were able to create an almost perfectly circular side beam spot. Note that if the dimensions of the permanent magnet are changed, the optimum conditions for the shape of the beam passage hole will also change, and similarly, if the external dimensions of the magnetic yoke are changed, the optimum conditions for the shape of the beam passage hole will also be different.
Center beam passage hole 51 as shown in FIG.
Even when using a yoke 51' having side beam passage holes 51S ₁ ' and 51S ₂ ', almost perfect circular beam spots were obtained.

As described above, according to the present invention, the electron gun can be assembled easily and with high precision, and a nearly perfect circular beam spot shape can be obtained, and the good image quality characteristic of an electromagnetic focusing tube can be maintained.

[Brief explanation of the drawing]

Figures 1 to 3 are cross-sectional views showing the electron gun section of a conventional in-line external magnetic type electromagnetic focusing cathode ray tube;
6 are cross-sectional views showing an in-line magnetic type electromagnetic focusing cathode ray tube electron gun using a yoke with a non-circular outer shape according to the present invention, and FIG. Figure 8 is a cross-sectional view of an experimental tube with improved beam spot shape, and Figure 9 is a characteristic diagram showing the relationship between beam passage hole oblateness and beam spot shape when a non-circular yoke is used. , FIG. 10, and FIG. 11 are cross-sectional views showing a yoke having a non-circular outer shape and having two different types of non-circular beam passage holes that provide a substantially perfect circular beam spot shape. 8... Permanent magnet, 12S ₁ , 12C, 12S ₂ ... Electron beam, 13... Magnetic main lens, 51... Non-circular yoke, 51C, 51S ₁ , 51S ₂ ... Non-circular beam passage hole, 90... Electrode support rod, φx... Horizontal diameter of the beam passing hole, φy...Vertical diameter of the beam passing hole, Spx...Horizontal diameter of the beam spot, Spy...Vertical diameter of the beam spot.

Claims (1)

[Scope of Claims] 1. A beam focusing magnetic field generating device is provided outside or inside the neck tube, and has an electron beam passage hole, and is disposed opposite to each other in the neck tube along the beam path passing through the hole, and the magnetic field is In an electromagnetic focusing cathode ray tube that is provided with one or more pairs of yokes made of a highly magnetically permeable material that efficiently absorb the magnetic flux generated by the generator and form a beam focusing magnetic lens in the opposing gap, The cross-sectional peripheral shape is non-circular, and the electron beam passing hole shape of the yoke is non-circular so that magnetic flux distribution is almost uniform over the entire circumference of the beam despite the yoke peripheral shape. An electromagnetic focusing cathode ray tube. 2. The electromagnetic focusing cathode ray tube according to claim 1, wherein the horizontal diameter of the three electron beam passing holes arranged on one horizontal line of the yoke is larger than the vertical diameter. 3. The electromagnetic focusing cathode ray tube according to claim 2, wherein the shape of the electron beam passing hole is different for the center beam and for the side beam. 4. The electromagnetic focusing cathode ray tube according to claim 2, wherein the side beam passage hole has an oval shape with a long diameter in the horizontal direction and a small diameter end thereof extending toward the tube wall side. 5. The electromagnetic focusing cathode ray tube according to claim 2, wherein the ratio of the vertical diameter to the horizontal diameter of the electron beam passage hole is smaller for the center beam than for the side beams.