JPS58657B2 - Ink Yokusen Kansouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cathode ray tube device comprising a cathode ray tube having a bipotential electrostatic focusing electron gun and a dynamic electromagnetic focusing coil. This is an attempt to simplify the .

Conventionally, in cathode ray tubes that require a resolution of 100 μm or less in spot diameter, such as fiber tubes, flying spot cathode ray tubes, display cathode ray tubes, etc., electromagnetic focusing and electromagnetic deflection as shown in Figure 1 has been widely used. Ta.

This is excellent in terms of aberrations because the diameter of the electron lens 12 formed by the electromagnetic focusing coil 11 is large, and the object point formed near the cathode of the electron gun 13, that is, the crossover 14, is faithfully displayed on the screen 15 according to its magnification. By forming an image as an image, that is, a beam spot 16.

In addition, in a cathode ray tube, the deflection coil 17 scans the screen with a beam to create a raster, creating a one-dimensional or two-dimensional screen, but normally the screen is flat or has a curvature close to a flat surface. Therefore, as shown in FIG. 1, the distance to the scanning plane changes depending on the deflection angle, resulting in beam defocus.

Therefore, a so-called dynamic focusing lens must be used as a focusing lens, which adjusts its strength depending on the degree of deflection.

This can be easily achieved by winding a dynamic coil into the air gap of the static focusing coil and passing a functional waveform current through it.

However, such an electromagnetic focusing method has major drawbacks as described below.

One of them is that the central magnetic effect of the electromagnetic focusing coil must be precisely aligned with the electron beam emitted from the cathode section.

This requires a coil position fine adjustment device, which requires mechanical adjustment of the vertical, horizontal, and tilt angles with respect to the tube axis, which is cumbersome to operate, requires a large device, and is expensive. Become something.

The reason why the above electron beam must pass through the center of the electromagnetic focusing coil will be explained in detail later.

In addition, for example, in the case of a cathode ray tube with a 36.5φ net and an anode voltage of 15 KV, the chamber magnetic focusing coil requires a magnetomotive force of about 500 AT or more for focusing, and the focusing coil itself has a large structure and weight due to the heat generated. Put it away.

Next, a cathode ray tube employing a bipotential type electrostatic focusing electron gun will be explained with reference to FIG.

In FIG. 3, the third grid 31 and the fourth grid 32 (
A potential difference is created between the electron beam and the anode (anode), and the electron beam is focused by the action of the electrostatic electron lens 33 created by this potential difference.

Compared to the electromagnetic focusing method described above, this method does not require a focusing coil, and the exterior parts of the cathode ray tube are simplified.

Furthermore, the size of the electron beam can be comparable to that of the electromagnetic focusing method.

However, this method also has serious drawbacks as described below.

As mentioned above, the focusing lens requires dynamic focusing whose intensity is adjusted depending on the position of the scanning plane.

By the way, the focusing electrode of a bipotential type electrostatic focusing electron gun, the third grid 31 in FIG.
If the anode voltage is 15 KV, the third grid voltage reaches 4000 to 5000 V, although it varies slightly depending on the structure.

The dynamic focusing voltage also varies depending on the structure of the cathode ray tube, but at the periphery of the screen the voltage of the focusing electrode is 400 to 800 V higher than at the center, and as the functional waveform of this voltage moves from the center of the screen to the periphery. This must be added in addition to the basic voltage of 4,000 to 5,000 V, making the actual device extremely complicated.

Furthermore, in the first-mentioned high-resolution cathode ray tube, in order to increase the resolution, the third grid 31 in FIG. It is designed to guide only the portion of the beam to the converging lens.

For this reason, a current higher than the anode current flows into the third grid, resulting in the third grid becoming an electrode with low impedance.

Due to the above-mentioned two reasons, the use of bipotential electrostatic focusing cathode ray tubes is severely restricted, and at present the electromagnetic focusing method is still the mainstream, even though it is difficult to handle.

In view of the advantages and disadvantages described above, the present invention provides a cathode ray tube device comprising a cathode ray tube having a bipotential electrostatic focusing electron gun and an electromagnetic focusing coil 41 exclusively for dynamic focusing, as shown in FIG. It has the following excellent features:

That is, the dynamic focusing coil 41 does not need to be precisely positioned, and does not require the above-mentioned coil position fine adjustment device.

In addition, the overall length can be significantly shortened compared to conventional electromagnetic focusing types to obtain the same spot size.

Before explaining the reasons in detail below, the reason why the electromagnetic focusing coil must be precisely adjusted in the conventional electromagnetic focusing cathode ray tube will be explained first.

FIG. 2a shows the structure of a conventional electromagnetic focusing lens, in which an electron beam 21 emitted from an electron gun enters a focusing magnetic field 22 at a small divergence angle θ.

If the magnetic flux density of the magnetic field is B, then the Lorentz force F acting on an electron with velocity V is F=-eV×B・・・・・・・・・・・・・・・・・・
・・・・・・Since it is given by (1), the equation of motion is m(d2γ)/(dt2)=−eV×B・・・・・・
(2) where e: Charge of electron m: Mass of electron γ: Position vector representing the beam traveling direction.

Now, using three-dimensional orthogonal coordinates (x, y, z) and assuming that the components of the magnetic flux density in the x, y, and z directions are Bx, By, and Bz, respectively, the equation of motion is expressed as follows.

Fx=-e(VyBz-VzBy)・・・・・・・・・
(3) Fy=-e(VzBx-VxBz)...
...(4) Fz=-e(VxBy-VyBx)...
(5) However, z is the direction of the tube axis.

In FIG. 2a, the direction of the magnetic field B generated by the electromagnetic focusing coil is oriented substantially in the tube axis direction on the B plane at the center of the magnetic field, and in the radial direction on the A planes and 0 planes before and after it.

Suppose now that the electromagnetic focusing coil is fully adjusted and the electron beam passes through the center of the magnetic field, and then the A plane, B plane, and 0
The movement of the electron beam on the surface is shown in Figure 2, c and d, respectively.

Since the radial direction component is strong on the A plane, if Bz≒O, then Fx≒eVzBy・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・(6) Fy≒−eVzBx・・・・・・
・・・・・・・・・・・・・・・・・・(7) Fz≒0
・・・・・・・・・・・・・・・・・・(8) (Assuming that the divergence angle θ of the electron beam is very small and almost parallel to the tube axis, Vx≒Vy≒0) , the force acts in the azimuthal direction, so the electrons begin a spiral motion around the tube axis.

When the magnetic field reaches the center B plane, the tube axis direction component of the magnetic field becomes dominant, ≒Bx≒By≒O, and Fx≒−eVyBz
・・・・・・・・・・・・・・・・・・・・・・・・
・・・(9) Fy≒eVxBz・・・・・・・・・・・・
・・・・・・・・・・・・・・・(10) Fz≒0・・
・・・・・・・・・・・・・・・・・・・・・・・・
(11), the electrons are drawn in the direction of the tube axis by the action of the velocity components Vx and Vy in the azimuthal direction, producing a focusing effect.

As it progresses further and reaches the 0 plane, the radial direction component of B becomes strong again, and equations (6), (7), and (8) hold true.

However, since the direction of the magnetic field in the radial direction is opposite to that of the A plane, a force is generated that stops the rotation of the electrons in the azimuthal direction.

Thus, the electron beam travels straight from the electron gun to plane A;
It receives a focusing effect while rotating around the tube axis on 8 planes, stops rotating at 0 plane, moves straight toward the rear axis, intersects the tube axis, and focuses an image, or beam spot there. Image.

Next, if the movement of the electron beam on planes A, 8, and 0 is shown from the screen side as shown in Figure 2e, the electron beam 23
It can be seen that after a certain rotation from 24 on the A plane to 25 on the C plane, they are on the same axis and are subjected to a focusing effect.

The angle of rotation δ(z) at this time is v: acceleration voltage of the electron beam, but in the figure, an appropriate value is used for convenience of explanation.

The case where the electron beam passes through the center of the magnetic field has been described in detail above, but if the electron beam is incident off the center of the magnetic field, there will be a movement acting on the periphery of the electron beam, as shown in Figure 2 f, which shows the movement of the electron beam. Due to the different radial magnetic field strengths,
The helical motion of the electron beam 26 in the A-plane 27 differs depending on the surrounding parts.

As a result, the focusing effect on the 8 planes becomes non-uniform, and the effect on the 0 plane 28 also becomes non-uniform.

Therefore, when the electron beam travels straight from the 0 plane toward the rear axis, it is not coaxial with the beam 27 on the A plane, and its shape becomes an ellipse with aberrations, which significantly deteriorates the beam spot.

For the above reasons, it is clear that in conventional electromagnetic focusing, the center of the electron beam and the center of the magnetic field must be precisely aligned.

In contrast, in the cathode ray tube device of the present invention, as shown in FIG. This is done electromagnetically at step 53.

Therefore, the magnetic field 5 generated by the dynamic focusing coil 53
4 may be weaker than 115 compared to conventional electromagnetic focusing.

As a result, as shown in Fig. 6, even if the center of the beam 61 and the center of the magnetic field are shifted from each other on the A plane and the strength of the magnetic field applied to the periphery of the beam is different, Bz shown in equation (12) is small. Therefore, there is little rotation, and the beam 62, which has been slightly focused on the 8 plane, does not become an ellipse, but maintains a roughly circular shape, and the deviation from the tube axis is extremely small, and the beam 62 on the C plane
It will be like 3.

In the electrostatic focusing electron gun, the beam is focused and moves straight toward the rear axis, intersects with the axis, and forms an image, or beam spot, there.

In this combination of electrostatic and electromagnetic focusing, the electrostatic focusing lens is adjusted to provide a spot of best focus at the periphery of the screen.

At this time, since the distance from the center of the lens from the center of the screen is shorter than that at the periphery of the screen, the spot is not sufficiently focused and becomes a defocused spot.

To correct this, a dynamic focusing coil generates a focusing magnetic field to achieve the best focus at the center of the screen.

In other words, the dynamic focusing coil does not perform a lens action when the beam scans the periphery of the screen, but gradually strengthens the lens action as the beam approaches the center of the screen, so that the focusing action is maximized at the center of the screen.

The waveform of the current flowing through the focusing coil during this time is approximately a parabolic waveform, and if it is asymmetrical between the left and right sides of the screen, it may be corrected.

Alternatively, the electrostatic focusing lens may be slightly weakened so that the peripheral area of the screen is out of the best focus, and a slight DC component may be added to the dynamic focusing coil to achieve the best focus.

Furthermore, when a dynamic electromagnetic focusing coil is used together with a pi-potential type electrostatic focusing electron gun, there is an advantage that the overall length can be significantly shortened compared to the electromagnetic focusing type.

The beam spot size β1 on both sides of the electromagnetic focusing cathode ray tube shown in Fig. 1 is expressed as: α: Size of the object point P1: Distance from the object point to the focusing coil Q1: Distance from the focusing coil to the screen It will be done.

On the other hand, the beam spot size P2 on the screen of the pi-potential electrostatic focusing cathode ray tube shown in Fig. 3 is α: Size of the object point P2: Distance from the object point to the focusing lens Q2: Focusing Distance from the lens to the screen V3: Voltage of the third grid V4: Voltage of the fourth grid (anode).

Normally, V3/V4=about 1/3, which becomes.

As is clear from the above equations (13) and (14), the lens magnification is smaller when using a bipotential type electrostatically focused electron gun than when using an electromagnetically focused electron gun, so the overall length can be shortened and high resolution can be achieved. It can be seen that it is possible to

Since the cathode ray tube used in the present invention employs such a pi-potential type electrostatic focusing electron gun, it is obvious that the overall length can be shortened.

Note that at the periphery of the screen, the spot is generally distorted into an elliptical shape due to oblique incidence of the beam on the screen and aberrations due to the deflection yoke magnetic field.

To correct this, as shown in FIG. 7, a well-known 8-pole magnetic field generating coil, such as an astigma correction coil 71, should be placed between the deflection yoke 72 and the dynamic focusing coil 73, or just before the dynamic focusing coil. By distorting the beam shape in advance using the magnetic field, it is possible to obtain the best spot at both the center and the periphery of the screen.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a cathode ray tube that uses electromagnetic focusing and electromagnetic deflection, Figure 2a is a magnetic field distribution diagram of the electromagnetic focusing coil,
Figures b, c, and d are explanatory diagrams showing the state in which the focusing magnetic field exerts a force on the electron beam, Figure 2 elf is an explanatory diagram showing the state in which the electron beam moves due to this force, and Figure 3 is an explanatory diagram showing the state in which the electron beam is moved by this force. Figure 3 is the conventional pi potential type. FIG. 4 is a schematic diagram of a cathode ray tube that employs an electrostatic focusing electron gun, and FIG. FIG. 6 is an enlarged view of the main part, and FIG. 6 is an explanatory diagram showing the state in which the electron beam is moved by the dynamic focusing magnetic field. FIG. 7 is a schematic diagram of the cathode ray tube according to the present invention provided with an astigma correction coil. 11.22... Electromagnetic focusing coil, its focusing magnetic field, 23.26... Electron beam, 33,52...
... Electrostatic focusing lens, 41.53 ... Dynamic focusing coil, 61 ... Electron beam, 7
1...Astigma correction coil.

Claims (1)

[Claims] 1. A dynamic electromagnetic focusing coil is used in a cathode ray tube having a bipotential type electrostatic focusing lens, and the focus of the peripheral area of the screen is adjusted almost to the best using the electrostatic focusing lens, and the electron beam is scanned by the electromagnetic focusing coil. A cathode ray tube device characterized by flowing a required current in synchronization with the current to optimally adjust the focus of the entire screen.