JPH10136291A - Projection display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the projection display device with a small size and a thin profile in which an excellent image display characteristic is obtained while securing a sufficient projection distance. SOLUTION: A light corresponding to a video image emitted from a projector 11 is made incident onto an area denoted by points A1, A2 of a half mirror 13 placed just before a light incidence side of a screen 12, at least part of the light is reflected thereon and goes to a full reflection mirror 14, reflected in an area denoted by points B1, B2 of the full reflection mirror 14. The light reflected in the full reflection mirror 14 is made incident on an area denoted by points C1, C2 of the half mirror 13, at least part of it is transmitted and projected onto the screen 12, then the video image is displayed on the screen 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection display device for enlarging and projecting an image on a screen.

[0002]

2. Description of the Related Art Projection display devices include liquid crystal panels and CRTs.
(Cathode ray tube) A small screen with a diagonal size of 0.5 to 14 inches is enlarged and projected on a screen by a projection lens to obtain a large screen of about 3 to 100 times the original screen. Among these projection display devices, a rear projection television projects an image on the screen from the rear side of the screen. In this rear projection television, since a small image displayed on a liquid crystal panel or the like is enlarged and projected on a screen by a projection lens, a projection distance from the projection lens to the screen of several tens to several thousand mm is required. In order to reduce the size of the rear projection television set while securing this projection distance, it has been a general method to turn the projection optical path from the projection lens to the screen at least once using a mirror. . In a conventional rear projection television, a projection optical path from a projection lens to a screen is formed using an optical system that reflects light once in the middle or an optical system that reflects light twice so that light does not overlap more than three times. I was FIGS. 3 and 4 show examples of the configuration of such a conventional rear projection television.

A rear projection television 110 shown in FIG. 3 includes a projection device 111 for emitting light corresponding to an image, a screen 112 on which the image is enlarged and projected,
There is provided a total reflection mirror 113 that reflects the light emitted from the projection device 111 once and projects it on the screen 112. The total reflection mirror 113 is disposed obliquely with respect to the screen 112 on the rear side of the screen 112,
The projection device 111 is arranged so that the emitted light is reflected by the total reflection mirror 113 and goes to the screen 112. In the rear projection television 110, light emitted from the projection device 111 is reflected by the total reflection mirror 113 and projected on the screen 112, and an image is displayed on the screen 112.

[0004] A rear projection television 120 shown in FIG. 4 has two total reflection mirrors 114 and 115 in a projection optical path between a projection device 111 and a screen 112.
Is provided. The total reflection mirror 115 is arranged obliquely behind the screen 112 with respect to the screen 112. The total reflection mirror 114 and the projection device 111 are disposed below the total reflection mirror 115, and the light emitted from the projection device 111
The light reflected by the mirror 14 is directed toward the total reflection mirror 115, and the light reflected by the total reflection mirror 115 is further reflected by the screen 11.
2 are arranged. In this rear projection television 120, the light emitted from the projection device 111 is reflected twice by the total reflection mirrors 114 and 115 and is projected on the screen 112.
Is displayed on the screen.

[0005]

In the case of the structure shown in FIG. 3, the height of the set becomes large, and in the case of the structure shown in FIG. 4, the depth of the set becomes large. Also in this case, there is a problem that the set becomes large.

[0006] In a rear projection television, reducing the size of a set can also be realized by shortening the projection distance. However, in the case of a short projection distance that is not sufficient, various distortions occur in the image displayed on the screen, and it is difficult to obtain good image display characteristics. Further, if a projection lens having a short projection distance, a large enlargement ratio, and a variety of small aberrations is to be produced, the number of components of the projection lens increases, and a huge cost is required.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a projection type which can secure a sufficient projection distance, obtain good image display characteristics, and can be reduced in size and thickness. A display device is provided.

[0008]

According to the present invention, there is provided a projection display device which emits light corresponding to an image, a screen on which the image is enlarged and projected, and a reflection device for reflecting light directed to the screen. Means for reflecting at least a part of the light emitted from the projection device toward the reflecting means, and an optical path dividing means for transmitting at least a part of the light from the reflecting means toward the screen.

In this projection type display device, the light emitted from the projection device enters the optical path dividing means and is at least partially reflected toward the reflecting means. This light is reflected by the reflecting means, re-enters the optical path splitting means, and at least partially transmits to the screen.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing a configuration of a rear projection television as a projection display device according to a first embodiment of the present invention.
The rear projection television 10 includes a projection device 11 that emits light corresponding to an image, a screen 12 on which the image is enlarged and projected, and an optical path dividing unit disposed at a position immediately before the light incident side on the screen 12. And a total reflection mirror 14 as reflection means disposed obliquely with respect to the screen 12 behind the half mirror 13. Projection device 11, half mirror 13, and total reflection mirror 14
Means that the light emitted from the projection device 11 is
Are reflected at least partially toward the total reflection mirror 14, and the light reflected by the total reflection mirror 14 is further disposed toward the half mirror 13. Further, the projection device 11, the half mirror 13, and the total reflection mirror 14
Is such that the incident angles α1 and α2 when the light from the projection device 11 enters the half mirror 13 are larger than the incident angles β1 and β2 when the light from the total reflection mirror 14 enters the half mirror 13. Are located in Here, α1 is the incident angle at the upper end A1 of the range where the light from the projection device 11 enters the half mirror 13, and α2 is the incident angle at the lower end A2 of the range where the light from the projection device 11 enters the half mirror 13. Β1 is the incident angle at the upper end C1 of the range where the light from the total reflection mirror 14 is incident on the half mirror 13, and β2 is the incident angle at the lower end C2 of the range where the light from the total reflection mirror 14 is incident on the half mirror 13. is there.

The projection device 11 includes an image output device using a lamp, a liquid crystal panel, a CRT, and the like, and a projection lens for enlarging and projecting light corresponding to an image emitted from the image output device. .

Next, the operation of the rear projection television 10 according to the present embodiment will be described. The light emitted from the projection device 11
To the area A2, at least a part of the light is reflected and travels toward the total reflection mirror 14, and B1 to B2 of the total reflection mirror 14
2 are reflected. The light reflected by the total reflection mirror 14 is incident on the areas C1 and C2 of the half mirror 13,
At least a part of the light is transmitted, projected on the screen 12, and an image is displayed on the screen 12.

As described above, according to the rear projection television 10 according to the present embodiment, the half mirror 1
3 is inserted in the optical path from the total reflection mirror 14 to the screen 12, so that an optical system that reflects light twice as in the conventional rear projection television 120 as shown in FIG. The conventional rear projection television 120 shown in FIG.
As compared with the case, the size of the set can be reduced while securing a sufficient projection distance. In addition, since the rear projection television 10 according to the present embodiment employs an optical system that reflects light twice, a sufficient projection is achieved even in comparison with the conventional rear projection television 110 shown in FIG. The set can be reduced in size while securing the distance.
Therefore, according to the rear projection television 10 according to the present embodiment, a sufficient projection distance can be ensured, good image display characteristics can be obtained, and miniaturization and thinning can be achieved.

In this embodiment, the half mirror 1
3, light is incident twice, but the incident angles α1 to α2 when the light from the projection device 11 is incident on the half mirror 13.
Is relatively large (eg, about 45-60 °), while
The angles of incidence β1 and β2 when the light from the total reflection mirror 14 enters the half mirror 13 are quite small (close to normal incidence). In general, as the incident angle increases, the reflectance increases and the transmittance decreases. As the incident angle decreases, the reflectance decreases and the transmittance increases. Therefore, according to the rear projection television 10 according to the present embodiment, when the light from the projection device 11 is incident on the half mirror 13, the reflectance is large, and the light from the total reflection mirror 14 is reflected on the half mirror 13. At the time of incidence, the transmittance becomes large, so that reflection and transmission at the half mirror 13 can be performed efficiently, and light from the projection device 11 side is
3, the amount of light that passes through and reaches the screen 12 can be reduced, and good image display characteristics can be obtained.

In general, when the incident angle is increased to some extent, S-polarized light (polarized light whose electric field oscillates in a direction perpendicular to the plane of incidence) becomes P-polarized (polarized light whose electric field oscillates in a direction parallel to the plane of incidence). In this embodiment, when the projection device 11 emits polarized light, if the light incident on the half mirror 13 from the projection device 11 side is S-polarized light, The reflectance of the light incident on the half mirror 13 from the side 11 can be increased, the light use efficiency can be improved, and the amount of light transmitted from the projector 11 through the half mirror 13 and reaching the screen 12 Can be made smaller, and better image display characteristics can be obtained.

FIG. 2 is an explanatory diagram showing a configuration of a rear projection television as a projection display according to a second embodiment of the present invention. The rear projection television 20 according to the present embodiment is different from the rear projection television 10 according to the first embodiment in that the light passes through the front surface of the total reflection mirror 14 twice so as to reciprocate the S-polarized component by P. The configuration is such that a phase difference plate (λ / 4 plate) 21 for changing to a polarization component is provided. Also,
The projection device 11 emits light so that light incident on the half mirror 13 from the projection device 11 side becomes S-polarized light.

In the rear projection television 20 according to the present embodiment, the light emitted from the projection device 11 is incident on the areas A1 and A2 of the half mirror 13, and at least a part thereof is reflected to the total reflection mirror 14 The light passes through the phase difference plate 21 and becomes circularly polarized light on the way. This light is reflected by the areas B1 and B2 of the total reflection mirror 14, passes through the phase difference plate 21 again, and becomes P-polarized light. This light is incident on the areas C1 and C2 of the half mirror 13, is transmitted at least partially, is projected on the screen 12, and an image is displayed on the screen 12.

As described above, in the rear projection television 20 according to the present embodiment, light incident on the half mirror 13 from the projection device 11 side is S-polarized light, and light incident on the half mirror 13 from the total reflection mirror 14 side. P-polarized light is used. In general, the S-polarized light has a higher reflectance than the P-polarized light, and the P-polarized light has a higher transmittance than the S-polarized light. Therefore, according to the rear projection television 20 according to the present embodiment, In addition to increasing the reflectance of the light incident on the half mirror 13 from the side, the transmittance of the light incident on the half mirror 13 from the total reflection mirror 14 side can be increased, the light use efficiency can be improved, and the projection apparatus can be used. The amount of light from the side 11 passing through the half mirror 13 and reaching the screen 12 can be reduced, and good image display characteristics can be obtained.

In this embodiment, if a polarization beam splitter that reflects S-polarized light and transmits P-polarized light is used in place of the half mirror 13, the light use efficiency can be further improved and the projection can be performed. Light that passes through the polarizing beam splitter from the device 11 and reaches the screen 12 can be eliminated, and better image display characteristics can be obtained.

The rear projection television 20 having the configuration shown in FIG. 2 is also effective when the light emitted from the projection device 11 is not polarized light. That is, the light emitted from the projection device 11 side is the half mirror 1
In the case of reflection at 3, the S-polarized component has a higher reflectance than the P-polarized component, so that the reflected light has more S-polarized components than the P-polarized component. When this reflected light passes through the phase difference plate 21 and is reflected by the total reflection mirror 14 and again passes through the phase difference plate 21 and enters the half mirror 13, S
The P-polarized light component is larger than the polarized light component, and the transmittance is increased.

Other configurations, operations, and effects of the present embodiment are the same as those of the first embodiment.

The present invention is not limited to the above embodiments. For example, in each of the above embodiments, the half mirror 1
Although 3 is disposed at a position immediately before the light incident side on the screen 12, the optical path dividing means such as the half mirror 13 can be disposed at an arbitrary position in the projection optical path from the projection lens of the projection device 11 to the screen 12. is there. As described above, by providing the same optical path turning optical system as the half mirror 13 and the total reflection mirror 14 at an arbitrary position in the projection optical path from the projection lens of the projection device 11 to the screen 12, the projection distance is not changed. The size of the set can be reduced.

Further, according to the present invention, at least the reflecting means (total reflection mirror 14) and the optical path dividing means (half mirror 13)
And a configuration in which an additional mirror is provided as necessary to make the number of reflections three or more times.

[0024]

As described above, according to the projection display device of any one of the first to seventh aspects, the light emitted from the projection device enters the optical path dividing means and is at least partially reflected. The light is reflected toward the means, and this light is reflected by the reflecting means, again incident on the optical path dividing means, and at least a part of the light is transmitted to the screen. It is possible to obtain an image display characteristic, and it is possible to achieve a reduction in size and thickness.

According to the projection type display device of the third aspect, the projection device, the reflection means and the optical path splitting means are provided so that the light from the projection apparatus enters the optical path splitting means at an incident angle of:
Since the light from the reflecting means is arranged so as to be larger than the incident angle when the light is incident on the light path dividing means, in addition to the effect of the projection type display device according to claim 1, the light from the projection device is transmitted to the light path dividing means. The reflectance at the time of incidence is large, and the transmittance at the time when the light from the reflection unit enters the optical path division unit can be increased, and the reflection and transmission at the optical path division unit can be performed efficiently, It is possible to reduce the amount of light from the projection device side that passes through the optical path dividing means and reaches the screen, thereby achieving an effect that good image display characteristics can be obtained.

According to the projection display device of the fourth aspect, the projection device emits light so that the light incident on the optical path dividing means from the projection device side becomes S-polarized light. In addition to the effects of the projection display device according to claim 3,
It is possible to increase the reflectance of light incident on the light path dividing means from the projection device side, and to improve the light use efficiency, and to reduce the amount of light transmitted from the projection device side through the light path dividing means and reaching the screen. This has the effect of making it possible to reduce the size and to obtain better image display characteristics.

According to the projection display device of the fifth aspect, a phase difference plate that changes an S-polarized component into a P-polarized component by passing light twice back and forth between an optical path dividing unit and a reflecting unit. Is provided, in addition to the effect of the projection type display device according to the third aspect, it is possible to increase the transmittance when the light from the reflecting means enters the optical path dividing means, and to increase the light use efficiency. This produces the effect.

According to the projection type display device of the present invention, the phase difference plate changes the S-polarized light component to the P-polarized light component between the optical path dividing means and the reflecting means by passing light twice back and forth. And the projection device emits light so that the light incident on the optical path splitting means from the projection device side becomes S-polarized light, so that in addition to the effect of the projection display device according to claim 1, It is possible to increase the reflectance when the light from the projection device enters the optical path dividing unit, and to increase the transmittance when the light from the reflecting unit enters the optical path dividing unit. The transmission can be performed efficiently, and the amount of light from the projection device side that passes through the optical path splitting means and reaches the screen can be reduced, so that good image display characteristics can be obtained.

According to the projection type display device of the present invention, the optical path splitting means is a polarization beam splitter which reflects S-polarized light and transmits P-polarized light. In addition to the effect, the light use efficiency can be further improved, and the light that passes through the polarizing beam splitter from the projection device and reaches the screen can be eliminated, so that better image display characteristics can be obtained. To play.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a rear projection television as a projection display device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a rear projection television as a projection display device according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an example of a configuration of a conventional rear projection television.

FIG. 4 is an explanatory diagram showing another example of the configuration of a conventional rear projection television.

[Explanation of symbols]

10 rear projection television, 11 projection device, 12 screen, 13 half mirror, 14
Total reflection mirror

Claims (7)

[Claims] 1. A projection device for emitting light corresponding to an image, a screen on which the image is enlarged and projected, a reflection unit for reflecting light directed to the screen, and at least one of light emitted from the projection device. An optical path splitting means for reflecting a part of the light toward the reflecting means and transmitting at least a part of the light from the reflecting means toward the screen. 2. The projection display apparatus according to claim 1, wherein said optical path dividing means is arranged at a position immediately before the light incident side on said screen. 3. The projection device, the reflection device, and the optical path splitting device, wherein the light from the projection device is incident on the optical path splitting device at an angle of incidence, and the light from the reflection device is output from the light path splitting device. The projection type display device according to claim 1, wherein the projection type display device is arranged so as to be larger than an incident angle when the light is incident on the display. 4. The projection type display device according to claim 3, wherein said projection device emits light so that light incident on said optical path dividing means from said projection device side becomes S-polarized light. 5. A phase difference plate provided between the optical path splitting means and the reflecting means, wherein the phase difference plate changes an S-polarized component into a P-polarized component by passing light twice back and forth. The projection display device according to claim 3. 6. A phase difference plate provided between the optical path splitting means and the reflecting means for changing an S-polarized light component into a P-polarized light component by passing light twice back and forth, and the projection device is further provided with: 2. The projection display device according to claim 1, wherein the light is emitted so that light incident on the optical path dividing means from the projection device side becomes S-polarized light. 7. The optical path dividing means reflects S-polarized light and
The projection display device according to claim 6, wherein the projection display device is a polarization beam splitter that transmits polarized light.