JPS6033023B2 - Projection image display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a projection type image display device for enlarging and projecting an image of a television or the like onto a projection screen.

There are various projection television systems for enlarging and projecting a television image onto a projection screen, each of which has advantages and disadvantages.

The concave mirror reflection type with the highest usage rate is usually the first
The screen 2 of the cathode ray tube 1 is constructed as shown in the figure.
The television image projected onto the projection screen 5 is projected onto the projection screen 5 by a spherical concave mirror 3 and an aberration correction lens 4.
projected onto the screen as a magnifying glass. In this case, the utilization rate of the light emitted from the screen 2 of the cathode ray tube 1 can be improved by increasing the angle at which the periphery of the concave mirror 3 is viewed, and the brightness on the projection screen 5 can be improved.

However, since the aberration of the concave mirror increases rapidly as it moves away from the optical axis 6, the limit of aberration correction is reached when the half angle a, viewed from the center 7 of the screen 2 of the cathode ray tube 1 to the periphery 8 of the concave mirror, becomes around 50 degrees. In reality, it is extremely difficult to increase the luminous flux utilization rate to 50% or more. SUMMARY OF THE INVENTION An object of the present invention is to provide a projection type image display device that can efficiently focus light emitted from a cathode ray tube screen onto the surface of a concave mirror, thereby increasing the efficiency of light use.

Prior to explaining the present invention, first, the concentrating means of Koto will be explained.

FIG. 2 shows the state in which light rays are emitted from the cathode ray tube screen.

Phosphor 12 excited by electrons 11 in a cathode ray tube
The angle of the light ray 13 emitted from the plane with the normal to the surface of the front glass 14 is 10=1.

It is thought that Koto has a density distribution of cos8......[1}, and Koto is 190o
It is distributed toward the front glass in a range of 90 degrees. 1 here. is the Koto density value in the normal direction. However, according to experiments conducted by the present inventors, the optical contact between the phosphor 12 and the front glass 14 in a cathode ray tube screen is generally very poor, and when the light rays 13 are incident on the front glass 14, they are refracted. All the light emitted from the phosphor 12 toward the front glass 14 is concentrated within a critical angle 8c determined by the ratio of the refractive index n of the front glass 14 to the refractive index ratio of vacuum.

Here, 8c brush C = Sin-1 (band) ---
‐‐‐‐‐■ is given.

Therefore, for example, if ratio 21, n, = 1.5, then 8 = 41.80, and if the light east departure angle can be maintained as it is, then the half angle 8 that looks around the concave mirror in Fig.
, which is the limit value of 50o.

Nevertheless, in the conventional concave mirror reflection type projection type television receiver, the boundary surface 17 is used to take out the light that has been once focused within the critical angle ac from the front glass 14 into the air. There is a drawback that the resulting refraction returns to the original Koto density distribution shown in equation [1}. The present invention reduces the amount of light emitted by the phosphor in the case where there is no optical contact between the phosphor and the glass by reducing or eliminating changes in refraction at least from the front glass of the cathode ray tube to the concave mirror. The first advantage is that the focusing effect of the light received by the front glass of the cathode ray tube can be maintained until the light rays reach the concave mirror.

The present invention will be described below with reference to the drawings and embodiments.
FIG. 3 shows an embodiment of the present invention.

As mentioned above, the light emitted from the phosphor 23 coated on the inner surface of the front glass 22 of the cathode ray tube 21 as a light emitting surface is as follows.
When it enters the front glass 22, it is refracted and concentrated within a critical angle 8c determined by the refractive index of the vacuum and the refractive index n of the front glass. The refractive index n, of the front glass 22 of a cathode ray tube has a value close to 1.5, but the refractive index of glass is generally between 1.4 and 1.7, and the refractive index n, =
1, 8c takes values in the range of 380 to 45o. A transparent optical medium 24 having a refractive index ~ equal to or close to the refractive index n of the front glass is optically brought into close contact with the outside of the front glass 22 of the cathode ray tube. A specific example of the optical medium 24 is a transparent solid such as glass or acrylic resin molded into an appropriate shape. By providing such an optical medium 24, the divergence of light at the outer boundary surface 25 of the front glass 22 is suppressed, and all the light emitted from the front glass 22 is directed to face the cathode ray tube 21 of this optical medium 24. It becomes possible to irradiate the concave reflecting mirror 27 provided on the surface at an appropriate position to constitute this projection optical system. In this way, even if there is a light loss due to the mounting portion 28 of the cathode ray tube 21, a light light utilization rate of 85 to 90% can be obtained.

Note that this optical medium 24 may be composed of a combination of a plurality of optical media depending on the processing/assembly of the component parts or the optical characteristic design.

In addition, since the light 29 reflected by the concave mirror 27 is refracted when it is emitted into the air from the optical medium 24, by selecting the shape of the emitting surface 30 to be an appropriate curved surface, it is possible to It is possible to achieve exactly the same effect as the aberration correction lens (see 4 in FIG. 1) in a projection television receiver.

The shape of this curved surface 30 is in the form of an i-refunction of r, where the axis of the optical system is the z-axis, the direction perpendicular to it is the r-axis, and the center of curvature 31 when the concave mirror is a spherical surface is taken as the origin 0. It is something that is expressed.

The values of an and m in formula '3' are determined for any combination of the position of the phosphor-coated surface and the position of the projection screen by the ray tracing method, just as in the design of conventional aberration correction lenses. be able to. However, it is preferable that the sleeves be ○ for general ceremonies. FIG. 4 shows another embodiment of the invention.

In this case, the effect of increasing the luminous flux utilization rate stopped in the case shown in FIG. By installing the slanted plane mirror 38, the irradiation direction of the light beam can be changed, the installation space for components around the cathode ray tube such as the deflection bracket 39 can be expanded, and the optical medium 33 can be installed.
The volume occupied by is reduced. The above explanation is based on the case where there is almost no optical contact between the phosphor and the front glass, but according to the inventors' experiments, if a special method is used when applying the phosphor to the glass surface,
It is possible to increase the optical contact between the two, and in this case, the light east utilization rate can be further improved.

This is because, as shown in FIG. Among them, the light ray 43 with a divergence angle greater than the critical angle is the front glass 41.
It is completely reflected at the interface 44 and is not taken out of the front glass 41.

On the other hand, as shown in FIG.
6, no rays with a divergence angle greater than the critical angle are incident on the front glass 46, so all of the incident light is taken out of the front glass 46. . Therefore, when the same light emitters 42 and 45 are excited and emit light under the same conditions, the light density distribution after passing through the front glasses 41 and 46 is the same, and there appears to be no difference in the amount of light depending on the presence or absence of optical contact. . However, if the optical medium 24 as described above is interposed between the front glass 41 and the concave reflecting mirror, more light can be extracted by the amount of light ray 43 that was completely reflected in the front glass 41. It is. The ratio of the amount of light emitted from the light emitting body that increases due to optical contact is expressed by the relationship between equations 1 and 2, and is proportional to the refractive index of the front glass in contact.

This means that if the light exit surface of the front glass is formed so that complete reflection does not occur, the optical efficiency will be twice as high as the refractive index when there is optical contact compared to when there is no optical contact. means. In the present invention, if the phosphor and the front glass of the cathode ray tube are brought into optical contact, a light utilization rate twice as high as the refractive index nl of the front glass can be obtained compared to the conventional system. For example, if n,=1.5, the brightness on the projection screen can be increased by 2.25 times.
As explained above, in the projection type image display device of the present invention, the light emitted from the light emitting surface passes through the interior of the optical medium with a refractive index greater than 1 and is reflected by the reflecting mirror. The Shuto effect can be maintained until it reaches the reflector.

Furthermore, in the present invention, a concave reflecting mirror facing the front glass is provided on the convex end surface of the optical medium, and the light exit surface of the optical soot body is made into a lens curved surface for aberration correction. Not only can it be used as a base for a mirror, but it also has the advantage of not requiring an independent aberration correction lens, allowing the device to be configured compactly.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the configuration of a conventional projection image display device, and FIG. 2 is a diagram showing the state of light rays emitted from a light emitting surface.
FIG. 3 is a diagram showing the configuration of one embodiment of the projection type image display device of the present invention, FIG. 4 is a diagram showing the configuration of another embodiment of the present invention, and FIGS. FIG. 3 is a diagram illustrating the difference in light output due to optical contact with glass. 21, 34... Braun tube, 22... Front glass, 23, 42, 45... Phosphor, 24, 33
, 41, 46... Front glass, 27, 36...
...Reflector, 38...Flat mirror. Figure 5 Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. A transparent solid optical medium having a refractive index greater than 1 is brought into close contact with the outer surface of a front glass of a cathode ray tube, and a convex end surface of the optical medium is provided with a concave reflecting mirror facing the front glass, and the optical medium 1. A projection type image display device, characterized in that the light exit surface itself is a curved lens surface for correcting aberrations.