JPH02223137A - Projection type cathode-ray tube - Google Patents

Abstract

PURPOSE:To obtain stable focus characteristic against the fluctuation of the anode voltage and obtain a small beam spot diameter by combining an electrostatic focusing lens system and an electromagnetic focusing lens system, and specifying electrode voltage ratios. CONSTITUTION:An electrostatic focusing lens system 18 and an electromagnetic focusing lens system 21 are combined to form a composite lens 22. The electrostatic focusing lens system and the electromagnetic focusing lens system are adjusted to satisfy the relation 1.25Ro<Rp<0.9 for a bipotential electrostatic focusing lens and 2Ro<Rp<0.8 for a unipotential electrostatic focusing lens, where Ro is the focusing electrode voltage/anode voltage ratio for the optimum focusing on a fluorescent screen 19 only by the electrostatic focusing lens 18, and Rp is the focusing electrode voltage/anode electrode voltage ratio when the effect of the electromagnetic focusing lens system 21 is superimposed. Stable focus characteristic and a fine beam spot diameter are obtained very easily.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a projection type cathode ray tube, and more particularly to a projection type cathode ray tube for obtaining an enlarged projected image by projecting an image of the cathode ray tube onto a projection screen.

In general, a projection type cathode ray tube is placed at a required distance from the projection screen, and the reproduced image on the face plate of the cathode ray tube is projected onto the projection screen to obtain a projected image that is enlarged from the reproduced image. Widely used in projection devices.

FIG. 1 is a side view of essential parts showing an example of a video projection device using a conventional projection type cathode ray tube. In the figure, °1 is a projection type cathode ray tube, and a projection screen 2 is disposed on the central axis of the projection type cathode ray tube 1 at a certain distance apart from the face plate of the cathode ray tube 1. ing.

Further, on the front side of the face plate of the cathode ray tube 1, a projection lens system 3 is arranged on the same line as the central axis thereof,
The image reproduced on the face plate is condensed and enlarged and projected onto the projection screen 2. In the case of a color image projection apparatus, as shown in a side view of the main parts in FIG. 2, there are cathode ray tubes 4 for red images located on the central axis of the projection screen 2 and symmetrical positions with respect to the central axis of the projection screen 2. A cathode ray tube 5 for green images and a cathode ray tube 6 for blue images are provided, and these projection type cathode ray tubes 4, 5 .
Projection lens systems 7, 8.9 are arranged on the front side of the lens 6, respectively. Then, the monochromatic images reproduced on the face plates of the cathode ray tubes 4, 5.6 are condensed and expanded by the projection lens systems 7, 8.9, respectively, and projected onto the projection screen 2, so that each of the three colors is A superimposed color image is obtained by combining the images.

Here, the relationship between the screen brightness Bo of the cathode ray tube 1 and the brightness B on the projection screen 2 explained in FIG. 1 is expressed by a linear equation.

However, T: transmittance of the projection lens system 3 G: gain of the projection screen 2 f: f of the projection lens system 3 M: enlargement ratio of the reproduced image Here, as an example, T=0.8. G=10. f=2.0
．． By substituting the value of M=6 into equation (1), the brightness B on the projection screen 2 becomes 0.0IBo, and the screen brightness Bo on the cathode ray tube 1 becomes 1/1 of that on the projection screen 2.
It will drop to 00.

In addition, in the case of FIG. 2, the brightness on the projection screen 2 can be approximately three times that in the case of FIG. I couldn't escape it.

Therefore, in order to obtain a practically enlarged reproduced image in this type of image projection apparatus, the luminance output on the face plate (screen) of the cathode ray tube must be significantly increased. To this end, there is a method of improving the luminous efficiency of the phosphor screen on the inner surface of the cathode ray tube, or a method of increasing the energy of the electron beam that excites the phosphor screen. In this case, there is a limit to improving the luminous efficiency of the former phosphor screen due to restrictions on the color of the emitted light.

On the other hand, to increase the energy of the latter electron beam, the anode voltage of the cathode ray tube is increased.

Alternatively, the beam current may be increased, or both the anode voltage and beam current may be increased. However, increasing the anode potential poses problems such as withstand voltage characteristics between the electrodes of the cathode ray tube and X-ray radiation from the cathode ray tube, and there is a limit to increasing the anode voltage. therefore.

Generally, the current situation is to increase the beam current to increase the brightness output from the cathode ray tube.

However, in a projection type cathode ray tube having a conventional configuration, the converging lens system may cause various serious problems. This will be explained below.

FIG. 3 is a sectional view of a main part showing an example of a conventional projection cathode ray tube, particularly an electrostatic focusing type projection cathode ray tube. In the figure, inside the neck portion 0a of the glass bulb 10,
A cathode 12 that emits an electron beam 11. electron beam 1
an electron gun 15 consisting of a control electrode 13 that controls the amount of the electron beam 1 and an acceleration electrode 14 that accelerates the electron beam 11;
A focusing electrode 16 for focusing the electron beam 11 emitted from the electron gun 15 is housed. Further, an anode electrode 17 is disposed inside the funnel portion 10b and the neck portion 10a of the glass bulb 10, and the electrostatic focusing electrode 17 focuses the electron beam 11 using the focusing electrode 16 and the anode electrode 17. A lens system 18 is configured. Moreover, the panel part 1 of this glass bulb 10
A fluorescent screen 19 is formed on the inner surface of the 0c front side to form a projection type cathode ray tube.

In the electrostatic focusing type projection cathode ray tube configured as described above, the electron beam 11 emitted from the electron gun 15 must be focused as a minute spot on the phosphor screen 19 by the electrostatic focusing lens system 18. As described above, when the beam current is increased to improve the luminance of light emitted from the phosphor screen 19, the diameter of the electron beam 11 when passing through the electrostatic focusing lens system 18 increases accordingly. , will be greatly influenced by the spherical aberration of this electrostatic focusing lens system 18. In other words, since the influence of spherical aberration is proportional to the cube of the beam diameter, as shown in characteristic I in Fig. 4,
This has the disadvantage that the spot diameter of the beam on the phosphor screen 19 becomes significantly thicker, which significantly reduces the quality of the reproduced image formed on the phosphor screen 19.

Furthermore, FIG. 5 is a sectional view of a main part showing an example of a conventional projection type cathode ray tube, particularly an electromagnetic focusing type projection type cathode ray tube.
Since the same symbols as in FIG. 3 represent the same elements, their explanation will be omitted. In the figure, a neck portion 10a of a glass bulb 10 is shown.
An anode electrode 17 is disposed inside the funnel portion 10b, and a focusing coil 20 is disposed on the outer periphery of the glass bulb 10 corresponding to the anode electrode 17.
are arranged to constitute the electromagnetic focusing lens 21.

In the electromagnetic focusing type projection cathode ray tube configured as described above, the electron beam 11 emitted from the electron gun 15 is focused by the focusing coil 20 and is focused on the phosphor screen 19 as a minute spot. In this case as well, as described above, when the beam current is increased to improve the luminance of the phosphor screen 19, the amount of the electron beam 11 increases and the diameter of the electron beam 11 increases within the electromagnetic focusing lens system 21. However, the focusing coil 20
Since the diameter can be increased without being limited by the diameter of the neck 10a, even when the amount of electron beam 1 is increased, it is still smaller than the diameter of the electron beam 11. Since the inner diameter of the focusing coil 20 can be made sufficiently large, the influence of spherical aberration can be suppressed as much as possible. Therefore, as shown by characteristic (2) in FIG. 4, the spot diameter of the electron beam 11 on the phosphor screen 19 can be maintained at approximately the required thickness.

22, when comparing the two types of electrostatic focusing type and electromagnetic focusing type mentioned above in Fig. 4, we find that the electrostatic focusing type (characteristic I) and the electromagnetic focusing type (characteristic ■) have different beam currents. There is a significant difference in the spot diameter of the electron beam 11 compared to the conventional one, and as is clear from this figure, it is clear that an electromagnetic focusing type is most suitable as a projection cathode ray tube that operates with a large current.

Normally, in a projection video device, the brightness of the image to be reproduced on the face plate of the panel section changes from moment to moment, and the beam current also changes accordingly. It is extremely difficult to make such high voltages completely constant, and as shown in the example shown in Figure 6, it is inevitable that the anode voltage will fluctuate by about 10% as the beam current fluctuates. . Therefore, in the electrostatic focusing type cathode ray tube shown in FIG. 3 as described above, the anode electrode 17 and the focusing electrode 16
Since the voltage applied to the anode electrodes is supplied from the same high-voltage power supply via the bleeder circuit, if the voltage of the anode electrode 17 changes by a certain value, the voltage of the focusing electrode 16 will also change proportionally. The electrode voltage ratio is always kept constant. Therefore, even if the anode electrode voltage changes due to changes in the beam current, the focusing electrode voltage also changes accordingly, so the focus state of the electrostatic focusing type cathode ray tube does not change at all based on the principle of an electrostatic focusing lens. On the other hand, in the case of the electromagnetic focusing type cathode ray tube shown in FIG. Therefore, if the beam amount changes and the voltage of the anode electrode 17 fluctuates, a significant defocus state will occur, resulting in a disadvantage that the image reproduced on the face plate of the panel portion 10c will be significantly degraded.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a projection cathode ray tube that has stable focus characteristics against fluctuations in anode voltage and has a small beam spot diameter. It's about doing.

A projection type cathode ray tube according to the present invention for achieving the above object is a combination of an electrostatic focusing lens system and an electromagnetic focusing lens system. The projection type cathode ray tube according to the present invention will be explained in detail below with reference to the drawings.

FIG. 7 is a sectional view of a main part showing an embodiment of a projection type cathode ray tube according to the present invention, and since the same symbols as in FIGS. 3 and 5 represent the same elements, a description thereof will be omitted.

In the figure, on the outer periphery of an electrostatic focusing lens system 18 (rR not shown) consisting of a focusing electrode 16 and an anode electrode 17 formed on the neck portion 10a of the glass bulb 10,
A projection cathode ray tube is constructed by disposing a focusing coil 20 and forming a composite lens 22 that combines an electrostatic focusing lens system 18 (not shown) and an electromagnetic focusing lens system 21 (not shown) using this focusing coil 20. This is what I did.

In the projection type cathode ray tube configured in this way.

First, no current is supplied to the focusing coil 20 and the electromagnetic focusing lens system 21 (not shown) is not operated, that is, the projection type cathode ray tube is operated only by pure electrostatic focusing operation, and the electron beam 11 is emitted from the electron gun 15. When the beam 11 is emitted and a voltage is applied to the focusing electrode 16 and the anode electrode 17 so that the voltage ratio of the focusing electrode voltage to the anode electrode voltage is RO=0.2, the beam 11 becomes the minimum spot on the phosphor screen 19. In a measurement example of a cathode ray tube according to the present invention designed in a similar manner, the spot diameter of the electron beam 11 on the phosphor screen 19 is approximately 1.5 (arbitrary unit) as shown at point a in FIG. Then, the ratio of the focusing electrode voltage to the anode electrode voltage, that is, RP, is 0.
If the electron beam 11 is successively varied within the range of 2 or more and less than 1.0, the electron beam 11 cannot be focused on the fluorescent screen 19 in the best condition only by the focusing effect of the electrostatic focusing lens system 18 (not shown), so the focusing A predetermined current is provided to the coil 20, and an electromagnetic focusing lens system 21 (not shown) is formed by the coil 20.
By activating the focusing effect and adjusting to obtain the best focus state, the spot diameter on the phosphor screen 19 is gradually reduced to within the range of approximately 1°5 to 0.95 (arbitrary unit) as shown in FIG. To the zeroth order, which can be made smaller, the voltage ratio R
When P is further increased to 1.0, the focusing electrode 16 and the anode electrode 17 have the same potential, so the electrostatic focusing lens system 1
8 completely disappears, and there is only the focusing effect of the electromagnetic focusing lens system 21 by the focusing coil 20, that is, the pure electromagnetic focusing effect, and as shown at point b in FIG. 8, the spot diameter is 1.0 (in arbitrary units). ).

Therefore, as is clear from the data in FIG. 8, the spot diameter of the electron beam 11 on the phosphor screen 19 changes from pure electrostatic focusing to pure electromagnetic focusing. Improved and smaller than time. In other words, data was obtained in which the focus characteristics were improved and the best condition was obtained especially when the voltage ratio RP was around 0.8.

Next, FIG. 9 shows the change in the spot diameter of the electron beam 11 on the phosphor screen 19 when the voltage of the anode electrode changes. When the current of the focusing coil 20 is fixed at the value when the fluctuation of the anode electrode voltage is zero for each voltage ratio (RP) above, and only the anode electrode voltage and the focusing electrode voltage are varied by ±10%, using as a parameter. It shows the change in beam spot diameter as a ratio.

Here, characteristic I is the voltage ratio (RP) in the case of pure electrostatic focusing.
=0.2. Characteristic ■ has RP = 0.4, characteristic ■ has RP = 0
．． 6. For characteristic (2), RP=0.8, and for characteristic (2), RP=1.0 in the case of pure electromagnetic focusing. Therefore, as can be seen from FIG. 9, the spot of the electron beam 11 changes with respect to the voltage fluctuation of the anode electrode 19 when the focusing electrode voltage/anode electrode voltage ratio (RP) ranges from 0.2 to 1.0. In other words, it was confirmed that the condition worsened as one went from pure electrostatic focusing to pure electromagnetic focusing.

Therefore, from the experimental results shown in FIGS. 8 and 9, it is possible to make the focal spot diameter on the phosphor screen 19 sufficiently small by setting the focusing electrode voltage/anode electrode voltage ratio RP to 0°4 to 0.6. In addition, changes in the diameter of the electron beam spot on the phosphor screen 19 due to fluctuations in the anode voltage can be suppressed within a permissible range, and stable focusing characteristics can be obtained. Also, here the above voltage ratio (
Regarding the setting of the operating conditions for RP), the voltage ratio (RP) is selected appropriately depending on whether the absolute value of the beam spot diameter is important or the fluctuation of the electron beam spot diameter due to fluctuations in the anode electrode voltage is important. can do. Here, the 10th figure obtained from FIGS. 8 and 9
The characteristic curve (■) in the figure shows the spot diameter of the electron beam 11 on the phosphor screen 19 when a predetermined 7-node voltage is applied, and the characteristic curve (■) shows the spot diameter of the electron beam 11 on the phosphor screen 19 when a predetermined 7-node voltage is applied. In the same figure, which shows the maximum value of the spot diameter when it fluctuates by 10% from the value, RP = 0
．． In the case of 25, both the minimum spot diameter and the spot diameter when the anode voltage fluctuates by 10% are improved by approximately 10% compared to the case of RP = 0.2 without the lens action by the focusing coil 20, and the spot diameter is not affected by anode voltage fluctuations, and therefore, in applications where fluctuations in beam spot diameter due to fluctuations in anode voltage caused by changes in beam current are undesirable, the anode voltage and focusing electrode should be adjusted so that RP is approximately 0.25. In the case of the cathode ray tube in the zero measurement example in which it is effective to set the voltage, when the focusing electrode voltage/anode electrode voltage ratio RO during pure electrostatic operation is set to 0.2 as described above, the electrons on the phosphor screen 19 Since the beam 11 is designed so that the spot diameter is minimized, RP under the above conditions is RP.
= corresponds to 1.25RO. As the ratio RP is further increased, both the spot diameter when a given anode voltage is applied and the spot diameter when the anode voltage is varied by 10% decrease, but the difference between the two tends to increase. However, the amount of change in beam current For applications where the beam current is small or where the beam current changes infrequently, applications that require a minute spot, applications where fluctuations in the beam spot diameter are not a big problem, the voltage ratio RP should be set to 0 or 8, where the spot diameter is minimal. It is effective to set it to a value close to RP, and this voltage ratio generally exists in the range of approximately RP=0.8 to 0.9. Therefore, it is essential to select the above voltage ratio RP within the range of 1°25RO < RP < 0.9 so that the spot diameter when a predetermined anode voltage is applied and the spot diameter when the anode voltage is varied satisfy the intended use. In the explanation of 0 or more which achieves the gist of the invention, the case where RO=0.2 was explained as an example.

A bi potential lens (bi potential lens) consisting of a focusing electrode 16 and an anode electrode 17
) generally show the same tendency and the above conditions can be applied.

In the above embodiment, the case where the electrostatic focusing lens system and the electromagnetic focusing lens system are aligned on the neck portion 10a has been described, but the present invention is not limited to this, and the present invention is not limited to this. As shown in FIG. 12, which is a cross-sectional view of the main part, the same effect as described above can be obtained even when the focusing coil 2o is placed at position A or B on the neck portion 10a, for example, as the focusing coil 20a or 20b. .

Further, in the above embodiment, a pi potential lens (bi potential lens) consisting of a focusing electrode 16 and an anode electrode 17 is used.
However, as shown in the cross-sectional view of the main part in FIG. 13, a unipotential lens (uni potential 1ens) in which a focusing electrode 23 is provided between an anode electrode 17 or any other electrostatic focusing lens may be used. It is clear that effects similar to those described above can be obtained in a cathode ray tube using this system. In addition, a focusing coil 2o is used as an electromagnetic focusing lens system.
Although the present invention is not limited to this, it goes without saying that the same effects as described above can be obtained even when an electromagnetic focusing lens system using a permanent magnet is used. Here, when using a unipotential lens, its characteristic curve is
In the same figure, the characteristic curve ■ is shown in Figure 1.

The spot diameter of the electron beam 11 on the phosphor screen 19 when a predetermined anode voltage is applied is shown by the characteristic curve ■, while the current flowing through the focusing coil 20 is fixed at a value adjusted so that the spot becomes the minimum spot when a predetermined anode voltage is applied. , the cathode ray tube in the zero measurement example showing the maximum value of the spot diameter when the anode voltage fluctuates by 10% from the predetermined value corresponds to the example in Figure 13, and the focusing electrode during pure electrostatic operation When the voltage/anode electrode voltage ratio RO is set to 0.002, a beam designed so that the spot diameter of the electron beam 11 on the phosphor screen 19 is focused to the minimum is used. Focusing electrode voltage/anode electrode voltage ratio RO=0 during pure electrostatic operation without incorporating the lens action by the focusing coil 20
．． The focusing electrode voltage/anode electrode voltage ratio RP for the spot diameter when a predetermined 7-node voltage is applied and the spot diameter when the anode voltage fluctuates by 10% from the predetermined value in the case of 0. When the value exceeds 004, the spot diameter under both of the above conditions is improved by 10% or more, and the focusing electrode voltage/anode electrode voltage ratio RP = 0.6 to 0.8.
The above spot diameter has an extreme value in the vicinity. However, the difference between the spot diameter when a predetermined anode voltage is applied and the spot diameter when the anode voltage fluctuates by 10% from the predetermined value increases as the voltage ratio RP increases. In applying the gist of the present invention, as described in the section that takes a cathode ray tube using a pi-potential lens as an example, the voltage ratio RP is set to 2RO<RP<0.8 (RO
is the focusing electrode voltage/anode electrode voltage ratio during pure electrostatic operation)
If the selection is made within a range that satisfies the above, the gist of the present invention can be effectively utilized.

As explained above, according to the projection cathode ray tube according to the present invention, stable focus characteristics and a small beam spot diameter can be obtained extremely easily, so that the luminance of light emitted on the phosphor screen and the image quality are greatly improved. It has excellent effects such as being able to significantly improve quality, performance, etc.

[Brief explanation of the drawing]

Figures 1 and 2 are side views of essential parts showing an example of an image projection device using a projection cathode ray tube, and Figure 3 is a sectional view of essential parts showing an example of a conventional e-electronic focusing type projection cathode ray tube. , Figure 4 is a characteristic diagram showing the spot diameter ratio to beam current, and Figure 5 is a characteristic diagram showing the spot diameter ratio to beam current.
The figure is a sectional view of essential parts showing an example of a conventional electromagnetic focusing type projection cathode ray tube, FIG. 6 is a variation characteristic diagram of anode voltage with respect to beam current, and FIG. 7 is an embodiment of a projection cathode ray tube according to the present invention. Figure 8 is a sectional view of the main parts showing the voltage ratio (RP).
FIG. 9 is a characteristic diagram showing the spot diameter ratio with respect to the fluctuation rate of the anode voltage,
Fig. 10 is a characteristic curve showing the spot diameter ratio to voltage ratio (RP) of a pi-potential lens, Fig. 11 is a characteristic curve showing the spot diameter ratio to voltage ratio (RP) of a unipotential lens, and Fig. 12 is a characteristic curve showing the spot diameter ratio to the voltage ratio (RP) of a unipotential lens. FIG. 13 is a sectional view of a main part showing still another embodiment of a projection cathode ray tube according to the present invention. l... Projection type cathode ray tube, 2... Projection screen, 3
...Projection lens system, 4,5.6...Cathode ray tube, ? ,
8.9... Projection lens system, 10... Glass bulb,
10a...Neck part, 10b...Funnel part, 1
0c...Panel section. 11...electron beam, 12...cathode, 13...
・Control electrode, 14... Accelerating electrode, 15... Electron gun,
16... Focusing electrode, 17... Anode electrode, ・Phosphor screen, 21・ Combined lens, 18... Electrostatic focusing lens system, 19... 20.20a,
20b... Focusing coil... Electromagnetic focusing lens system, 22... Multiple 23... Focusing electrode. Fig. 1 Fig. 2 Fig. 4 Heem current (AA) Fig. 3 Fig. 5 Fig. 6 Fig. 6 Heem current (mm) Fig. 8 Symptom potential p) Fig. 11 Focused potential voltage Anode voltage S z& ratio (RPl Fig. 9 Focused electrocuring condensation anode 马; ~ Voltage baboon +RP1 Fig. 12 Fig. 13

Claims (1)

[Claims] 1. A glass bulb consisting of a panel part, a funnel part and a neck part, a fluorescent screen formed on the inner surface of the panel part, and an anode electrode formed on the inner surface of the funnel part,
an electron gun housed within the neck portion and emitting an electron beam onto the phosphor screen; an electrostatic focusing lens system comprising a focusing electrode disposed within the neck portion and a portion of the anode electrode; and an outer periphery of the neck portion. and an electromagnetic focusing lens system disposed in the electrostatic focusing lens system, the focusing electrode voltage/anode electrode voltage ratio for focusing the electron beam onto the phosphor screen to the best focus only by the electrostatic focusing lens system is R_O; If the focusing electrode voltage/anode electrode voltage ratio when the effect of the electromagnetic focusing lens system is superimposed is R_P, then 1.25R_O<R_P for the bipotential electrostatic focusing lens.
<0.9, 2R_ for unipotential electrostatic focusing lens
A projection type cathode ray characterized in that the electron beam is focused on the phosphor screen by adjusting the electrostatic focusing lens system and the electromagnetic focusing lens system so as to satisfy the relationship O<R_P<0.8. tube.