JPS6126184B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention prevents a decrease in the contrast ratio of images on a cathode ray tube (hereinafter referred to as CRT) in a television projection device using a Schmidt optical system.
The objective is to obtain a projected image with a higher contrast ratio.

Conventionally, a projection CRT having a structure as shown in FIGS. 1 and 2, which includes a spherical reflecting mirror and a phosphor target surface therein, has been devised. In the figure, 1 is a bulb, 2 is a spherical reflector, 3 is a fluorescent target part,
4 is an optical system support fitting, 5 is a front sealing glass, 6 is a correction lens, 7 is a correction lens support fitting, 8 is a deflection coil, 9 is a convergence coil, 10 is a focus magnet, 11 is an electron gun, and 12 is a deflection coil. 8 indicates the center of deflection, and 13 indicates the hole in the center of the spherical reflecting mirror 2, respectively. In the figure, the phosphor target section indicated by 3 is coated with phosphor on a metal block, and has very good heat conduction, making it possible to drive the phosphor surface to the maximum and achieve high performance. This structure is very advantageous for obtaining a bright projected image.

Furthermore, as can be seen from FIG. 1, since the spherical reflector 2 is located between the phosphor target section 3 and the electron gun 11, the electron beam from the electron gun 11 is not irradiated onto the phosphor target surface. There is a hole 1 in the center of the spherical reflector 2 so as not to block the electron beam when
3 is provided. The shape of this hole 13 is generally round as shown in FIG. 3, and the size of the hole is determined between the deflection center indicated by 12 in FIG. It must be large enough to include all the lines connecting the four corners of the effective raster surface of the phosphor target section 3, and generally has a diameter approximately equal to the length of the short side of the phosphor target section 3. There is. If the diameter of the hole 13 made in the center of the spherical reflector 2 is made smaller than necessary, when the electron beam is deflected by the deflection coil 8 and a raster is drawn on the phosphor target surface, the fluorescein The effective raster on the target surface may be missing, causing inconvenience. Therefore, the diameter of the hole 13 needs to have some margin, including variations in the center of deflection due to assembly and installation errors of the deflection coil 8.

On the other hand, if the hole diameter is made larger than necessary, the effective reflection area of the spherical reflector 2 will decrease, leading to a decrease in the light utilization efficiency and a decrease in the brightness of the projected image, which is not only undesirable. Moreover, very large inconveniences will arise as will be described later.

Next, we will discuss the characteristics of the Schmitt optical system.
FIG. 4 depicts only the parts related to the optical system of the projection tube shown in FIG. 1. As can be understood from this figure, the light rays emitted from the surface of the phosphor target section 3 are reflected by the spherical reflector 2; In the positional relationship between the light ray ₂ that is directly reflected and returned near the light emitting point, the ray 1 that is reflected by the spherical reflector 2 and then returns to another position on the phosphor target surface, and the ray ₂ that is directly reflected and returns near the light emitting point, After being reflected by the reflector 2, there is a light ray ₃ which is directed onto a projection screen surface (not shown).

Of these, only ray ₃ actually contributes to the brightness of the projected screen; the other rays ₁ and ₂ only reduce the contrast ratio of the surface image drawn on the target surface, and these rays l ₁ and l ₂ It is desirable to have as few as possible.

Let us now examine in more detail the light rays l ₁ and l ₂ that are emitted from the phosphor target surface and return to the phosphor target surface.

FIG. 5 is a diagram for explaining the light ray l2 emitted from the surface of the phosphor target section 3, which returns to the light emitting point on the phosphor target surface after being reflected by the spherical reflector ₂ . be. In the figure, point C is the spherical reflector 2
indicates the center of curvature. Due to the properties of the spherical reflecting mirror 2, all light rays emitted from the center of curvature are directed to the center of curvature C.
come back to. Therefore, a line X connecting the center of curvature C and the outer circumference of the hole 13 in the center of the spherical reflector
As for the light ray emitted from the area A on the phosphor target surface surrounded by the line Y connecting the outer periphery of the effective raster surface of the phosphor target surface and the center of curvature C, there must be a spherical surface within it. There is a light ray _l2 which, after being reflected by the reflector 2, returns again to the light emitting point on the phosphor target surface. In FIG. 6, the effective raster area A on the phosphor target surface is
It shows. In the figure, 14 indicates the outer periphery of the effective raster surface. Therefore, if we want to completely remove the light rays that directly return to the light emitting point of the phosphor target section 3, the spherical reflecting mirror 2 surrounded by the two straight lines Y shown in FIG. Just remove that part. However, if the effective area of the spherical reflecting mirror 2 is reduced to that extent, the light utilization efficiency as an optical system will be extremely reduced, and the projected image brightness will also be extremely reduced, which is not desirable as a projection television apparatus.

Therefore, apart from the central part of the phosphor target section 3, the fact that light emitted from the peripheral part returns to the light emitting point is an unavoidable problem to some extent in terms of increasing the light utilization efficiency. It is clear that these rays reduce the contrast ratio of the image formed around the phosphor target.

Next, let us consider the light ray ₁ that is emitted from the phosphor target surface, is reflected by the spherical reflector 2, and then returns to a position different from the light emitting point on the target surface.
FIG. 7 is a diagram showing this situation. In the figure, point _P1 indicates a bright spot at the center of the target, and point _P1 ' indicates a bright spot at the edge of the target. The state of the light rays emitted from each of these bright spots, reflected by the spherical reflector 2, and then returned to a location other than the light emitting point on the phosphor target surface is determined by the spherical reflector 2 and the phosphor target. Part 3
Although it will vary depending on the relative position of the spherical reflector 2, the radius of curvature of the spherical reflector 2, the diameter of the hole 13 provided in the center, etc., in general, if a point light source is created at the center of the phosphor target, the phosphor target The return to the plane is as shown in FIG. 8a. In the figure, P ₁ is a point light source, and the shaded area shows the area of light emitted from P ₁ , reflected by the spherical reflector 2, and then returned to the target surface. At this time, the shape of the region where no reflected light exists in the center of the phosphor target section 3 is approximately the same size as the hole 13 made in the center of the spherical reflecting mirror 2. Also, due to the principle of ray retrograde, if a bright spot exists in the shaded area on the target surface, it will always be reflected by the spherical reflector 2.
This means that there is light that returns to point _P after being reflected by .

Next, when _point P moves on the target surface,
FIGS. 8b, c, and d show how the shadow of the hole 13 of the spherical reflecting mirror 2 moves. In the figure, P ₁ is the position of a point light source provided on the target surface, and the shaded area represents the area where the light is emitted from the point light source P ₁ , reflected by the spherical reflector 2, and returned to the target surface. There is.

The light rays that return to the phosphor target surface after being reflected by these spherical reflectors 2 clearly reduce the contrast ratio of the projected image.
Moreover, in that case, the region in which the light beam returning to the light emitting point mentioned above existed was limited to the periphery of the phosphor target section 3, whereas after being reflected, the region where the light ray returned to the light emitting point existed was The returning rays are present across the entire phosphor target surface, as seen in FIGS. 8a-d, reducing the contrast of the overall image on the phosphor target surface.

As mentioned above, when using the Schmidt optical system, there is a large factor in contrast reduction due to its fundamental configuration, and it is necessary to minimize the rise in the black level of the projected image and obtain a high-quality image with higher contrast. are these spherical reflectors 2
The amount of light that returns to the phosphor target surface after being reflected by the phosphor should be minimized as much as possible.

One way to do this is to use a spherical reflector 2.
The diameter of the hole 13 drilled in the center of the hole 13 is increased. However, as mentioned earlier, if this hole diameter is made larger than necessary, the effective reflection area of the spherical reflector 2 will decrease, which will not only cause a decrease in the light utilization efficiency and lead to a decrease in the brightness of the projected image. The following major problems arise.

As shown in FIG. 9, this is because the scanning surface of the electron beam becomes distorted, for example, when the amplitude of the deflection system becomes large or when the mounting position of the focus magnet 10 is tilted. There is a possibility that the light body will miss the target plane significantly. In such a case, as can be seen from FIG. 9, the front sealing glass 5 is directly irradiated with the electron beam. If this continues for a long time, the portion of the front sealing glass 5 that is hit by the electron beam becomes cloudy, resulting in a decrease in light transmittance and a decrease in the contrast ratio of the projected image. An even bigger problem is that there is no problem when the electron beam is irradiating the inside of the phosphor target surface, but when the front sealing glass 5 is irradiated with the electron beam, the generated X-rays come out through the front sealing glass 5 to the front. become. In order to prevent this, it is necessary to use special glass for absorbing X-rays instead of ordinary glass, which leads to a decrease in light transmittance and an increase in cost.

However, if the diameter of the hole 13 made in the spherical reflector 2 is slightly increased, the phosphor target will be returned to the phosphor target after being reflected by the spherical reflector 2, as shown in Fig. 8e to f. The amount of light rays returning to the section 3 can be reduced, which has a very large effect on improving the contrast ratio. Also, regarding the light rays that are emitted from the phosphor target wraparound part and return to the vicinity of the light emitting point, making the hole diameter slightly larger will prevent the presence of reflected rays from the center of the phosphor target as shown in Figure 6. It can be seen that since the area of the non-contrast portion becomes larger, it has a great effect on improving the contrast ratio.

In order to improve the contrast ratio more efficiently, as shown in FIGS. 10a and 10b, instead of a round hole in the center of the spherical reflector 2, a hole 13' having the same shape as the phosphor target part 3 is installed. (See US Pat. No. 2,960,615).

At this time, Figure 11 shows how the light rays emitted from one point on the phosphor target surface are reflected by the spherical reflector 2 and then return to other parts of the phosphor target surface. I'll keep it. Again, P ₁ indicates the position of the point light source. In this case, the size of the hole made in the spherical reflector 2 is I'm looking for it to be almost the same size as it is and to cast a shadow on the target surface.

As is clear from a comparison between FIG. 8 and FIG. 11, making the hole 13' of the spherical reflector 2 almost the same shape as the phosphor target section 3 is extremely effective against reflected light. It turns out that it is effective for

One of the problems in this case is that if the hole is made in the same shape as the phosphor target section 3, the amplitude of the deflection circuit becomes large, the center of deflection shifts, or the focus magnet If the mounting position of the electron beam 10 is inclined, there is a possibility that the electron beam will miss the phosphor target portion 3 significantly and hit the front sealing glass 5. If this happens, problems such as fogging of the front sealing glass 5 or X-rays will occur. Another problem is that it is very difficult to cut out the central part of the spherical reflecting mirror 2 into a rectangular shape, which leads to an increase in cost.

The present invention aims to solve these difficulties, and examples thereof will be described below.

In the present invention, even if the amplitude of the deflection system changes, the center of deflection shifts, or the mounting position of the focus magnet is tilted, the electron beam will not protrude significantly from the target surface of the phosphor.
It also attempts to more effectively remove the reflected light component that is reflected by the spherical reflector and returns onto the phosphor target surface, causing a reduction in image contrast ratio. Figure 12 shows the first implementation. An example is shown.

In this embodiment, the hole 13 provided in the center of the spherical reflecting mirror 2 is minimized to the necessary minimum, and is round in consideration of ease of manufacture. Then, the surrounding part of the hole 13 is painted in the same size as the fluorescent target part 3 or in a similar shape with black or a color complementary to the color emitted from the target surface to form a light absorbing part. form 15. This arrangement minimizes the amount of electron beams that extend beyond the phosphor target surface and impinge on the front sealing glass, while still allowing the spherical reflector 2 to be removed as shown in the aforementioned U.S. Pat. No. 2,960,615. It is possible to obtain the same effect of improving the contrast ratio as when a hole portion of approximately the same size as the fluorescent target portion 3 is provided in the center portion.

Here, in the example shown in U.S. Patent No. 2,960,615 and FIG. 12, if we compare it with a simple round hole and look at what kind of difference there is in the light utilization efficiency as an optical system, first of all, Looking at the light rays emitted from the center of the phosphor target, in Fig. 12, the light absorption part 1
Conventionally, all of the light rays reflected within the area 5 return onto the target surface, so installing such a light absorbing section 15 reduces the image brightness at the center of the projection screen surface. Not at all.
However, although there is a slight decrease in the light utilization efficiency at locations other than the central portion of the phosphor target surface (particularly at the edges of the target surface), this is not a problem as it does not appear as a difference in power.

Moreover, if we look strictly at the leakage of the electron beam from the phosphor target surface, the hole 13 of the spherical reflector 2
As long as the beam is round and the target is rectangular, it is impossible to completely eliminate beam leakage, and there is still a possibility that the beam will leak from the top and bottom of the target. By minimizing the diameter of the hole 13 made in the center of the hole 2, leakage of the electron beam can be minimized. Furthermore, if it is desired to completely eliminate this electron beam leakage, a structure as shown in FIG. 13 may be used. That is, although manufacturing difficulties remain, instead of a round hole in the center of the spherical reflecting mirror 2, a hole 13' similar in shape to the minimum required phosphor target portion 3 is made. A light absorbing portion 15 is provided around this hole 13' as in FIG. 12.
With such a structure, it is possible to eliminate the electron beam leaking from the target surface, and it is also possible to obtain a projected image with a good contrast ratio.

Another embodiment according to the present invention is shown in FIG. In the figure, 16 indicates a light absorber 16 treated to be black or a color complementary to the emitted color, and this light absorber 16 is attached to a hole provided in the center of the spherical reflecting mirror 2. A cylindrical portion 17 is integrally formed therein. FIG. 15 shows the above light absorber 16.
This shows the state when the is attached to the spherical reflector 2. It is clear that the same effect as shown in FIG. 12 can be obtained with such a structure.

In addition, if the cylindrical part 17, which is the attachment part to the light absorber 16 and the spherical reflector 2, is made of metal, if this metal part is connected to the anode voltage, the light from the electron gun can be removed. When the electron beam hits the inside of the hole 13 of the spherical reflecting mirror 2, it is also possible to prevent that part from being charged and causing image distortion.

If such a structure is not used, it is necessary to make the inside of the hole 13 conductive in some way, and it is necessary to connect it together with the rear surface of the spherical reflecting mirror 2 to an anode voltage. Of course, even if a structure as shown in FIG. 14 is used, the rear surface of the spherical reflector 2 must be made conductive and connected to the anode voltage, but the inside of the hole 13 must be made conductive and connected to the anode voltage. The trouble of making it conductive can be omitted.

Further, FIG. 16 shows another embodiment of the light absorber 16. This embodiment also aims to omit the effort of painting the mirror surface of the spherical reflecting mirror 2.
In this case as well, the same effect of improving the contrast ratio can be obtained. Here, 17' indicates a mounting bracket.

In still another embodiment, a light absorber is used as the first
A structure as shown in FIG. 7 may also be used. That is, in the center of the light absorber 16, there is not a round hole but a rectangular hole similar to the fluorescent target part, and the minimum necessary rectangular hole is made, and the light absorber mounting bracket 17' is made in the hole of the spherical reflector 2. Make the shape so that it can be installed even if the shape is a round hole. By doing this, even if a relatively simple round hole is made in the center of the spherical reflector 2, if a light absorber as shown in Fig. 17 is attached, the electron beam will be directed from above the target surface. A high-contrast, high-quality projected image can be obtained without leakage.

As is clear from the above embodiments, according to the present invention, projection with a high contrast ratio is achieved by providing a light absorbing portion having the same shape or similar shape to the fluorescent target around the hole provided in the spherical reflecting mirror. Images can be obtained, which is extremely useful in practice.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the configuration of the main parts of a conventional television projection device, FIG. 2 is a cross-sectional view taken along line AA' in FIG. 1, and FIG. 3 is a view showing the spherical reflector 2 in FIG. 1. , Figure 4 is an enlarged sectional view of the optical system in Figure 1, and Figure 5 is an enlarged sectional view of the optical system in Figure 1.
9 to 9 are diagrams for explaining the problems of the present invention,
10 and 11 are diagrams showing other conventional examples of spherical reflecting mirrors, FIG. 12 is a front view and sectional view showing essential parts of a television projection device according to an embodiment of the present invention, and FIGS. FIG. 17 is a diagram showing other embodiments of the present invention. DESCRIPTION OF SYMBOLS 1... Bulb, 2... Spherical reflecting mirror, 3... Fluorescent target portion, 4... Optical system support fitting, 5...
Front sealing glass, 6... Correction lens, 7... Correction lens support fitting, 8... Deflection coil, 9... Convergence coil, 10... Focus magnet, 11... Electron gun, 12... Deflection center, 13 ，
13'... Hole made in the spherical reflecting mirror, 15... Light absorbing part, 16... Light absorber.

Claims (1)

[Scope of Claims] 1. A cathode ray tube includes a spherical reflecting mirror and a phosphor target facing opposite to the spherical reflecting mirror, and an electron beam from an electron gun is directed to the center of the spherical reflecting mirror. A cathode ray tube for projection, which is configured with a hole for irradiating a light target surface, is provided with a hole having the same shape as the phosphor target around the hole on the side facing the phosphor target. A television projection device characterized by being provided with a light absorbing section having a similar shape or a light absorbing section having a similar shape. 2. Paint the circumference of the hole provided in the center of the spherical reflector as a light absorption part in the same shape as the fluorescent target or in a similar shape, with black or a color complementary to the emitted color. A television projection apparatus according to claim 1, characterized in that: 3. As a light absorbing part, a light absorbing body having the same shape or similar shape as the phosphor target whose surface is treated with black or a color complementary to the emitted color is provided, and the central part of the light absorbing body is is provided with a hole approximately the same size as the hole provided in the center of the spherical reflector, and a cylindrical portion for fixing the light absorber to the hole provided in the center of the spherical reflector. The television projection device according to claim 1, further comprising an arm portion. 4. As a light absorbing part, a light absorbing body whose surface is treated with black or a color complementary to the luminescent color and having the same shape or similar shape as the phosphor target is provided, and the light absorbing body is A hole having a similar shape to the target surface of the phosphor is provided in the center, and a cylindrical portion or an arm for fixing the light absorber is provided in the hole provided in the center of the spherical reflecting mirror. A television projection device according to claim 1, characterized in that: 5. Claim 3, characterized in that the light absorber and the light absorbing part consisting of the cylindrical part are metal objects.
The television projection device according to item 1 or 4.