JPH0353735B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an external magnetic type electromagnetic focusing cathode ray tube which has a good beam spot shape and good beam static convergence. Conventionally, electric field focusing electron guns have been mainly used in color cathode ray tubes and the like. The main reason for this is that it has advantages such as easy manufacture, small volumetric weight, and low cost. In recent years, there has been an increasing demand for higher resolution for color cathode ray tubes, and many types of electric field focusing electron guns have been developed to meet this demand, but their high resolution characteristics have already reached their saturation limit. has reached. On the other hand, an electromagnetic focusing electron gun is advantageous for achieving high resolution, as it can provide a lens with small spherical aberration, and it is easy to avoid spreading of the beam due to the repulsive force of electron charges. The electromagnetic focusing electron gun also has the advantage of reducing the risk of inter-electrode discharge unlike the electric field type. Against this background, as shown in Figures 1 to 3, an annular permanent magnet is attached to the outer periphery of the neck tube of the valve as a focusing magnetic field generating means, and a bottomed cylindrical magnet is installed to effectively absorb the magnetic flux generated by this magnet. A plurality of yokes made of a highly permeable magnetic material and having electron beam passage holes on the bottom surface are arranged in the neck tube so as to face each other along the electron beam path, and a magnetic main lens is installed in the gap between these opposing yokes. An in-line out-of-magnetic electromagnetic focusing cathode ray tube has been proposed. FIG. 1 is a cross-sectional view of the electron gun section of the conventional tube taken along an in-line array plane, and FIG. 2 is a cross-sectional view of the same tube taken along a plane that includes the tube axis and is orthogonal to the in-line array plane. In addition, FIG. 3 shows the A-
It is an A-line sectional view. In these figures, 1 is a valve neck tube, 2 is a cathode, 3 is a first grid, 4 is a second grid, 5 is a yoke made of a pair of high permeability magnetic materials, 6 is an elastic conductive strip, and 7 is a Internal conductive film, 8 is an annular permanent magnet, 9 is a glass electrode support rod, 10 is a deflection yoke, 11 is a stem pin, 12
C is a center beam, 12S ₁ and 12S ₂ are side beams, 13 is a magnetic main lens modeled on an optical lens, 14 is a gap electrode made of non-magnetic material, 15
is the third grid bottom. Center beam 12C and side beam 12 emitted from cathode 2
S ₁ and 12S ₂ pass through the first grid 3 and the second grid 4, respectively, and are once converged to form a so-called crossover, and then the internal conductive film 7,
The electron beam is accelerated by the third grid bottom 15 to which an anode voltage is applied via the elastic conductive strip 6, the yoke 5, the gap electrode 14, etc., and the electron beam passes through the electron beam passage hole 5.
a and enters the magnetic main lens 13, forming a crossover image on a fluorescent surface (not shown). The yoke 5 is a bottomed cylinder made of high permeability magnetic material and has a permanent magnet 8.
The magnetic flux generated by the electron beam is absorbed, and a strong focusing magnetic field is generated along the electron beam path in the gap 5g facing the bottom surfaces of the pair of yokes, thereby forming the magnetic main lens 13 here. and electron beam 12C,1
The spot shapes on the phosphor surfaces of 2S ₁ and 12S ₂ are made perfect circles, and the three beams for these three color phosphors are concentrated and intersected at one point on the shadow mask (not shown). Considering this, as shown in Figure 3,
The outer shape of the cross section perpendicular to the tube axis of the yoke 5 is circular. As a result, when assembling the electron gun, first, only the electrodes from the cathode 2 to the third grid bottom 15 are supported by the electrode support rod 9, and then the yoke on the cathode side, the gap electrode, and the yoke on the fluorescent surface side are sequentially supported. Stack it on top. I had no choice but to weld the overlapping parts. Such an assembly process requires a large number of man-hours, causes an increase in cost, and has the problem that the assembly accuracy of the product cannot be sufficiently high. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the problems of the prior art as described above, to provide an electromagnetic focusing cathode ray tube having an electron gun that can easily achieve a sufficiently high assembly accuracy, has good performance, and is low in cost. In order to achieve the above object, in the present invention,
The cross section of the yoke perpendicular to the tube axis is formed into a shape formed by an opposing circular arc and an opposing straight line, and the yoke is also supported by an electrode support rod that is common to other electrodes. We decided to use a ferrite type magnet, and as a result of our research to find the conditions under which the beam spot shape and static convergence (hereinafter abbreviated as STC) would not be adversely affected by making the outside shape of the yoke non-circular, we found that permanent magnet By setting the shape, the gap length of the yoke, and the length of the yoke in the tube axis direction within a range that satisfies a specific correlation, sufficiently good performance can be obtained. The present invention will be explained in more detail below using the drawings. 4, 5, and 6 show an electron gun section according to an embodiment of the present invention, and FIG. 4 is a cross-sectional view of an in-line array plane.
FIG. 5 is a sectional view taken along a plane including the tube axis and perpendicular to the in-line arrangement plane, and FIG. 6 is a sectional view taken along the line A-A' shown in FIGS. The major difference from the examples shown in FIGS. 1, 2, and 3 is that the yokes 51a, 51b
Also, the outer shape of the gap electrode is flat, and the gap between the flat part and the inner wall of the neck tube is used to support the yoke and the gap electrode 14a together with other electrodes by the common electrode support rod 9a. be. However, when the outer shape of the yoke is made non-circular, the 8 positions of the permanent magnets are moved in the tube axis direction so that the electron beams for the three primary colors are concentrated and converged on the shadow mask (static convergence STC) to prevent color shift. When adjusted and fixed at the optimal position,
Generally, the beam spot shape becomes distorted and significantly deviates from a circular shape. On the other hand, if the permanent magnet position is adjusted so that the beam spot shape becomes a perfect circle, the STC cannot be obtained. As shown in FIG. 7, one possible solution to this problem is to install a quadrupole magnetic field generator 16 on the outer periphery of the neck tube on the fluorescent surface side of the yoke 51a, and apply a quadrupole magnetic field to the beam to take the STC. (make it smaller). However, this method is generally undesirable because it distorts the shape of the beam spot and increases the cost. As a result of research, the present inventor has solved this problem by limiting the shape, dimensions, and arrangement of permanent magnets and yokes within specific ranges.
The problem was solved without a polar magnetic field generator. The size of the permanent magnet 8 is determined by approximately two factors. One is the usage conditions of the electromagnetic focusing cathode ray tube.
That is, the outer diameter of the network tube 1, the operating anode voltage, etc. The other condition is to efficiently generate the focusing magnetic flux from the permanent magnet, which is based on the B-H curve determined by the material of the permanent magnet, so that the operating point (permeance) has a large B・H product. The key is to select the dimensional ratio of the permanent magnet. Considering that this cathode ray tube is used in home television receivers, ferrite is currently the most suitable permanent magnet material in terms of performance and cost ratio. Therefore, the present inventor conducted research using Hitachi Metals' ferrite magnet YBM-2B. The table shows the annular magnets determined by taking the above points into consideration. For example, the specifications in the table are 14 type, 90 degree deflection, operating anode voltage.
This is for a 21kV tube. Fourth,

[Table] As shown in Figure 5, the deflection yoke 1 is placed near the permanent magnet 8.
0 exists, it is necessary to prevent the leakage magnetic field of the permanent magnet from interfering with the deflection magnetic field. For this purpose, it is conceivable to lengthen the neck tube 1 and widen the distance between the permanent magnet and the deflection yoke, but there is a limit as this increases the depth of the receiver. Therefore, the values of t and φ _p may have to be made smaller than the values shown in Table 1. Also, the gap length lg between the yokes 51a and 51b
Of course, this greatly influences the determination of the permeance, but if lg is made too small, the lens becomes small and strong, resulting in increased spherical aberration, and if lg is made too large, it becomes impossible to obtain STC. The allowable range of lg is 0.3t≦lg≦1.0t for the magnet thickness t, but experiments were mainly conducted with lg=0.5t. The shape and dimensions of the permanent magnet are almost determined by the above factors, and the applicable ranges for the cathode ray tubes shown in Figures 4 to 6 are: 1.7≦φ _p /φ _i ≦2.3, 0.35≦t/φ _i ≦ It has been revealed from computer simulation and experimental results that it is 0.65. FIG. 8 shows the ratio of the length h u of the yoke 51a on the fluorescent surface side in the tube axis direction and the length h _b of the yoke 51b on the cathode side according to the present invention for permanent magnets with various specifications shown in Table ₁ . h _b /h _u and the amount of static convergence, that is, the center beam 12C on the fluorescent surface.
indicates the distance of the side beam 12S ₁ , and is positive when the side beam 12S ₁ is located above the center beam 12C in the y direction. The numbers for the curves correspond to the magnet specification numbers shown in Table 1. Note that, as described above, the distance between the permanent magnet 8 and the deflection yoke 10 is not large. Since the high magnetic permeability magnetic yoke is originally located near the permanent magnet, the distance between the yoke, especially the yoke 51a on the fluorescent surface side, and the deflection yoke 10 is not large. Therefore, the length h _u of the yoke 51a in the tube axis direction
is limited in order to prevent the yoke 51a from shielding the electron beam from the magnetic field of the deflection yoke 10. In general, in order to utilize as much of the magnetic flux generated by the permanent magnet as possible for the focusing magnetic field, it is better for h _u to be large, but for the reasons mentioned above, it cannot actually be made very large. Now, as can be seen from Figure 8, there is a value of h _b /h _u that makes the beam spot shape a perfect circle and the STC amount zero for permanent magnets of various sizes, and that value is depends on the shape and size of. For example, h _b /h _u =2.1 for the shape, h _b /h _u =1.13 for the shape, and h _b /h _u =1.45 or 1.52 for the shape. Based on these results, FIG. 9 shows the outer diameter φ _p and inner diameter φ _i of the permanent magnet 8 that will make the STC amount zero,
It shows the relationship between the lengths h _b and h _u of the yoke. The horizontal axis shows h _b /h _u and the vertical axis shows φ _p /φ _i , and the relationship between the two is t / φ _i (t is The thickness of the permanent magnet is used as a parameter. In other words, by using the magnet 8 and the magnetic yokes 51a and 51b whose shape and size correspond to the points on the curve shown in FIG. 9, an electromagnetic focusing cathode ray tube with a perfect circular beam spot and zero STC amount can be obtained can get. The shaded area in FIG. 9 is the allowable range of h _b / _hu determined from the size and shape of the permanent magnet that can be used in the present invention described above. As described above, according to the present invention, it is possible to obtain an inexpensive electromagnetic focusing cathode ray tube that has a perfect circular beam spot shape, good static convergence, and can be easily assembled with high precision.

[Brief explanation of drawings]

1 to 3 are diagrams showing an electron gun section of a conventional electromagnetic focusing cathode ray tube, FIGS. 4 to 6 are diagrams showing an electron gun section according to an embodiment of the present invention, and FIG. Figure 8 shows the relationship between the ratio of the lengths of a pair of high permeability magnetic yokes in the tube axis direction and the amount of static convergence, and Figure 9 shows the above-mentioned diagram for setting the STC amount to zero. FIG. 7 is a diagram showing the relationship between the length ratio of a pair of yokes and the inner/outer diameter ratio of a permanent magnet, using the ratio of the magnet's thickness to inner diameter as a parameter. 8... Annular permanent magnet, 9a... Electrode support rod that also supports the magnetic yoke, 13... Magnetic main lens, 5
1a...Magnetic yoke on the fluorescent surface side with a flat cross-sectional shape, 51b...Magnetic yoke on the cathode side with a flat cross-sectional shape, _φi ...Inner diameter of the annular permanent magnet 8, _φp ...Magnet 8 outer diameter, t...Thickness of magnet, lg
...Magnetic yoke opposing gap length, h _u ...Length of the magnetic yoke 51a in the tube axis direction, h _b ...Magnetic yoke 5
1b length.

Claims (1)

[Claims] 1 An annular ferrite permanent magnet is attached to the outer circumference of the neck tube of the valve, and at least one pair of yokes made of a high permeability magnetic material that effectively absorbs the magnetic flux generated by this magnet are placed facing each other in the tube axis direction. In an electromagnetic focusing cathode ray tube that is disposed inside the tube and has a magnetic main lens formed between opposing yokes, a cross section of the yokes perpendicular to the tube axis is formed by opposing circular arcs and opposing straight lines. The shape is
The shape of a ferrite permanent magnet with outer diameter φ _p , inner diameter φ _i and thickness t is 1.7≦φ _p /φ _i ≦2.3, 0.35≦t/φ _i ≦0.65
Furthermore, the length between the corresponding yokes is 1g, and 0.3t.
≦1g≦1.0t, length of yoke on fluorescent surface side in tube axis direction
An electromagnetic focusing cathode ray tube characterized in that, where h _u is the length of the yoke on the cathode side in the tube axis direction, h _b is 0.15h _u ≦h _b ≦2.04h _u .