JP2000047326A - Reflection type image projection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image projection device capable of miniaturizing a prism on the condition that a display light beams and non-display light beams are separated by using the prism. SOLUTION: Illumination light made incident from a light source part 10 through a prism 30 is modulated and reflected by a DMD[digital micromirror device (R)] 20 and is guided to a projection lens 40 through the prism 30. The prism 30 is provided with a first surface 31 on which the illumination light is made incident, a second surface 32 facing the DMD 20 and a third surface 33 arranged in a roof type with respect to the first surface 31. The first surface 31 and the third surface 33 are orthogonally crossed and the second surface 32 forms an angle of 45 deg. with the first surface 31 and the third surface 33. The display light beam L2 reflected from the DMD 20 is totally reflected on the first surface 31 and the third surface 33 and emitted perpendicularly from the second surface 32. The non-display light beams L31 and L32 are made incident on the third surface 33 at a smaller angle than the critical angle and transmitted through it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type image projection apparatus using a micro-specular modulation element as a modulation element.

[0002]

2. Description of the Related Art There are a transmission type and a reflection type as a modulation element of a projection apparatus. In order to increase resolution without lowering light use efficiency, it is desirable to use a reflection type modulation element. . In the case of transmissive elements, as the degree of integration increases, the ratio of the area of the non-transmissive part where the drive circuit and the like is provided to the area of the part that transmits light increases, thereby reducing the light use efficiency. This is because, in the reflection type modulation element, since the drive circuit and the like can be arranged on the back surface, the ratio of the reflection portion on the front surface can be kept high.

As a reflection-type modulation element, a micro-mirror-modulation element composed of a large number of two-dimensionally arranged micro-mirrors capable of independently switching angles, specifically a digital micro-mirror device (DMD, Texas Instruments Japan, Inc.)
(Trademark of Co., Ltd.) is known. When a DMD is used as the modulation element, the reflected light (display light) from the micro mirror at the ON position and the reflected light from the micro mirror at the OFF position
In order to make only the display light out of the (non-display light) enter the projection lens, it is necessary to separate the display light from the non-display light.

Japanese Patent Application Laid-Open No. Hei 10-82959 discloses DM
An image display device that uses D and separates display light and non-display light using a prism is disclosed. The main part of the video display device disclosed here is as shown in FIG. 3, and the illumination light L1 is incident on the first surface 2a of the second prism 2 via the first prism 1. The illumination light L1 exits from the second surface 2b of the second prism 2, enters the DMD 3, is reflected by the DMD 3, and enters the second prism 2 again. Display light L
2 is totally reflected by the first surface 2a as shown by the solid line and the second
The light is emitted from a third surface 2c perpendicular to the surface 2b, and an image is projected through a projection lens 4 onto a screen (not shown). The non-display light L3 is emitted outside from the fourth surface 2d parallel to the second surface 2b and does not enter the projection lens 4, as indicated by the broken line.

[0005]

However, in the reflection type projection device described in the above-mentioned publication, after the display light L2 and the non-display light L3 are spatially separated, the first surface 2
a, since the second prism 2 is configured to be incident on the fourth surface 2d, the first surface 2a from the DMD 3 or the fourth prism 2
There is a problem that the distance to the surface 2d is long, the size of the second prism 2 is increased, and the device cannot be made compact. Further, since the distance between the projection lens 4 and the DMD 3 is long, a long back focus is required for a short focal length, and the design restrictions of the projection lens 4 are increased.

The present invention has been made in view of the above-mentioned problems of the prior art, and aims to reduce the size of a prism while assuming a configuration in which display light and non-display light are separated by using a prism. It is an object of the present invention to provide a reflection-type image projection device capable of performing the following.

[0007]

SUMMARY OF THE INVENTION A reflection type image projection apparatus according to the present invention comprises a two-dimensional light source which emits illumination light and a plurality of two-dimensional mirrors which can be independently angle-switched between an on position and an off position. A micro-mirror modulator that is arranged and configured to modulate and reflect illumination light from a light source according to an image, and a first surface that is arranged between the light source and the micro-mirror modulator and receives illumination light. It has a second surface facing the specular modulation element and a third surface that forms a roof-type arrangement together with the first surface, and is located at the ON position among the reflected light reflected by the minute specular modulation element and incident from the second surface. The light reflected from the micromirror is arranged so as to satisfy the condition of total reflection on the first and third surfaces, and the light reflected from the micromirror in the off position is arranged so as not to satisfy the condition of total reflection on the third surface. The prism and the first and third surfaces are totally reflected from the second surface Characterized in that it comprises a projection lens for projecting the reflected light out on the screen.

According to the above arrangement, the display light, which is the reflected light from the micromirror at the on position of the micromirror modulator, is totally reflected in the order of the first surface and the third surface, enters the projection lens, and turns off. Non-display light, which is light reflected from a micromirror at the position, directly or totally reflected on the first surface, and then enters the third surface, but none of them satisfies the condition for total reflection on the third surface. Therefore, the light passes through the third surface. Therefore, before the display light and the non-display light are spatially separated, the first surface and the third surface
Even if the surfaces are arranged, they can be separated using the total reflection condition of the third surface.

In order to ensure the separation between the display light and the non-display light, and in view of the ease of manufacture, the first surface and the third surface should be orthogonal to each other, that is, the prism should be a right-angle prism. desirable. Further, in this case, the second surface can be formed so as to be substantially orthogonal to the optical axis of the projection lens, and to make an angle of 45 degrees with the first surface and the third surface. In order to shift the projection range on the screen, a shift mechanism for moving the projection lens in a direction orthogonal to the optical axis may be provided. In this case, it is desirable that the projection lens be telecentric with respect to the micro-specular modulation element.

Further, the reflection type image projecting apparatus of the present invention comprises:
A light source that emits illumination light, and a large number of two-dimensionally arranged micromirrors that can independently switch the angle between the on position and the off position are configured. The illumination light from the light source is modulated and reflected according to the image. A first surface on which illumination light is incident, and a second surface opposed to the small mirror surface modulation device, and the light reflected by the small mirror surface modulation device is disposed between the light source and the small mirror surface modulation device. Of the reflected light incident from the second surface, the reflected light from the micromirror at the ON position is arranged so as to be totally reflected by the first surface, and the reflected light totally reflected by the first surface is screened. A projection lens for projecting upward and a shift mechanism for moving the projection lens in a direction perpendicular to the optical axis thereof are provided.

According to the above arrangement, the projection range can be shifted by shifting the projection lens by the shift mechanism. Further, the direction of incidence of the illumination light and the direction of emission of the display light to the projection lens can be appropriately set by using the prism, so that the interference of the shift of the projection lens with the optical path of the illumination light can be prevented.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a reflection type image projection apparatus according to the present invention will be described below. FIG. 1 is a schematic diagram illustrating an optical system of the reflection type image projection apparatus according to the embodiment.

As shown in FIG. 1, the optical system of the reflection type image projection apparatus according to the embodiment includes a light source section 10 for emitting illumination light.
A DMD 20 that is a micro-mirror surface modulation element that modulates and reflects illumination light from the light source unit 10 according to an image, and a first surface 31 that is disposed between the light source unit 10 and the DMD 20 and receives illumination light. The second surface 32 facing the DMD 20, the first
A prism having a third surface forming a roof-type arrangement together with the surface; and a projection lens for projecting light reflected by the DMD and emitted from the second surface of the prism onto a screen (not shown). ing.

The light source unit 10 includes a high-intensity lamp 11 such as a xenon lamp, a halogen lamp, a metal halide lamp, and an ultra-high pressure mercury lamp, and a reflector that directs the non-directional light from the high-intensity lamp 11 to the prism 30 as substantially parallel light. And a beam expander 13 for converting the diameter of the parallel light.

The DMD 20 is a device configured by arranging a large number of two-dimensionally arranged micromirrors capable of independently switching the angle between an on position and an off position. Plane (hereinafter referred to as a macroscopic incident end face)
When the light is made incident at an incident angle of 20 degrees, the reflected light (display light) from the micro mirror at the ON position is reflected perpendicularly to the macroscopic incident end face. The reflected light (non-display light) from the micro mirror at the off position is reflected with a predetermined angle difference from the display light.

The prism 30 has a first surface 31 and a third surface 33.
Are orthogonal, and the second surface 32 is a right-angle prism formed such that the second surface 32 forms an angle of 45 degrees with the first surface 31 and the third surface 33. Further, the second surface 32 is arranged to be orthogonal to the optical axis Ax of the projection lens 40. Light source unit 1
0 is the illumination light L incident from the first surface 31 of the prism 30
The position is determined so that 1 is incident on the macroscopic incident end face of the DMD 20 at an incident angle of 20 degrees.

According to such an arrangement, the display light L2 indicated by a solid line in the reflected light reflected by the DMD 20 is:
The light enters the prism 30 perpendicularly to the second surface 32,
The incident angle with respect to the surface 31 is 45 degrees. Prism 30
If the refractive index is 1.5, for example, the critical angle is about 42 degrees, so that the display light L2 incident at 45 degrees satisfies the condition of total reflection, and 100% is reflected on the third surface 33 side. Display light L
Since the angle of incidence of 2 on the third surface is also 45 degrees, the display light L2 is totally reflected again on the third surface 33 and exits perpendicularly from the second surface 32.

On the other hand, non-display light indicated by a broken line is applied to the first surface 31 and the third surface 3 with the ridge of the prism 30 interposed therebetween.
And 3. The non-display light L31 that has entered the first surface is totally reflected by the first surface 31 and enters the third surface 33. At this time, the incident angle becomes smaller than the critical angle, and the third surface 33
Through. The non-display light L32 directly incident on the third surface 33 without being reflected by the first surface 31 is incident on the third surface 33 at an angle smaller than the critical angle, and transmits through the third surface 33. First
Since the surface 31 is orthogonal to the third surface 33, if the incident angle of the non-display light L31 on the third surface 33 is θ, the incident angle of the other non-display light L32 on the third surface 33 is −θ. , The absolute values are equal.

Therefore, by using the prism 30, the incident angle of the display light on the third surface 33 can be made larger than the critical angle, and the incident angle of the non-display light on the third surface 33 can be made smaller than the critical angle. The display light and the non-display light can be separated by utilizing the total reflection of the prism by the difference in the angles. For this reason, the display light and the non-display light do not need to be spatially separated at the position where they enter the third surface 33, and the prism can be made smaller than before, and the optical path from the DMD 20 to the projection lens 40 can be reduced. The length can be shortened.

The projection lens 40 is movable in a direction orthogonal to the optical axis Ax by a shift mechanism 50 provided adjacently. As the shift mechanism 50, a known mechanism including, for example, a feed screw and a motor can be used. By shifting the projection lens 40 in a direction perpendicular to the optical axis, the range of the image projected on the screen can be moved in parallel. Therefore,
Even when the position of the screen is fixed and the projection device cannot be arranged in front of the screen, an image can be projected on the screen by arbitrarily shifting the projection range. The projection lens 40 allows the DMD 20
So that the reflected light (display light L2) does not deviate from the pupil.
It is configured to be telecentric with respect to the MD 20.
By using the prism 30, the direction of incidence of the illumination light L1 on the DMD 20 and the display light L2 on the projection lens 40 can be reduced.
Can be completely separated from the emission direction of the light, and interference of the illumination light with the incident optical path due to the shift of the projection lens can be prevented.

Next, means for suppressing an angle error due to the wavelength of the illumination light will be described with reference to FIG. When the prism 30 is used alone as in the example of FIG. 1, if the wavelength of the illumination light shifts, the angle of incidence of the illumination light on the DMD 20 changes due to the dispersion of the prism 30. When the change in the angle is large, the angle of the reflected light shifts and the projection direction changes. Therefore, in the example of FIG. 2, an auxiliary prism is arranged in front of the prism 30 so as to offset the influence of the wavelength fluctuation. In the following description, the prism 3
In order to distinguish 0 from the auxiliary prism, it is called a main prism.

In the example of FIG. 2A, the first prism 30
The auxiliary prism 60 is spaced from the surface 31 by a predetermined gap S.
Is arranged. The auxiliary prism 60 is a main prism 3
It has the same dispersion and refractive index as 0, and has an apex angle α of 45 degrees, which is set equal to the opposite apex angle of the main prism 30. Therefore, the incident-side end face 60a of the auxiliary prism 60,
The light source unit (not shown) is arranged in parallel with the second surface 32 of the main prism 30 so that the illumination light L1 is incident on the end surface 60a of the auxiliary prism 60 at an incident angle of 20 degrees to the DMD 20. According to the configuration of FIG. 2A, it is possible to prevent an angle shift depending on the wavelength of the illumination light L1. In order to maintain the condition of total reflection of the reflected light from the DMD 20,
The auxiliary prism 60 is arranged with a predetermined gap S without being in close contact with the prism 30.

FIG. 2B shows a modification of FIG. 2A. In this example, the macroscopic outer shape is a parallel plane, but an auxiliary prism 61 having a small step having a sawtooth cross section such as a Fresnel lens on one end surface is provided on the first surface 31 of the main prism 30. They are arranged with a predetermined gap S. The optical function of the auxiliary prism 61 is the same as that of the auxiliary prism 60 in FIG. Therefore, the light source unit is provided with illumination light L
2 are arranged so as to be incident from the same direction as in FIG.

In the example of FIG. 2C, the first prism 30
The auxiliary prism 62 is arranged on the surface 31 with a predetermined gap S therebetween, and the apex angle is smaller than the opposite apex angle (45 degrees) of the main prism 30. The main angle of the auxiliary prism 62 is set mainly for setting the incident direction of the illumination light L 1, and the incident direction of the illumination light L 1
Is set to be perpendicular to the second surface 32. Therefore, the angle error due to the dispersion of the main prism 30 cannot be completely suppressed as in the examples of FIGS. 2A and 2B, but after achieving the main purpose of setting the incident direction of the illumination light L1, A slight angle error correction effect can be exhibited.

In the embodiment shown in FIGS. 1 and 2, a right-angle prism is used as the prism 30, and the display light L2 from the DMD 20 is totally reflected twice and guided to the projection lens 40. In order to avoid interference with the illumination light path at the time of shifting, it is not always necessary to use two reflecting surfaces. For example, a configuration is used in which the display light from the DMD 20 is totally reflected by the first surface and the non-display light is spatially separated so that the non-display light is not totally reflected by the first surface, using the same prism as the conventional one shown in FIG. And a shift mechanism for the projection lens can be provided.

[0026]

As described above, according to the first aspect, the incident angle of the display light on the third surface of the prism is larger than the critical angle, and the incident angle of the non-display light is smaller than the critical angle. With this arrangement, display light and non-display light can be separated using the total reflection condition of the third surface. Therefore, the display light and the non-display light do not have to be spatially separated at the position where the light enters the third surface, and the prism can be made smaller and the device can be made more compact than before. Further, by shortening the optical path length from the micro-specular modulation element to the projection lens, it is possible to reduce restrictions on the design of the projection lens and to facilitate the design.

According to the second aspect of the present invention, the first surface and the third surface are orthogonal to each other, so that the non-display light reflected on the first surface and then incident on the third surface passes through the first surface. Without this, the incident angle of the non-display light incident on the third surface with respect to the third surface can be made the same, and the total reflection condition can be studied simultaneously. If a right-angle prism is used, the prism itself is easier to manufacture than prisms of other angles. In particular, when the second surface of the prism forms an angle of 45 degrees with respect to the first surface and the third surface, positioning of the prism and the projection lens and positioning of the prism and the DMD are easy.

If the projection lens is made shiftable as in claims 4 and 5, the projected image can be moved in parallel without distorting, and the positional relationship between the projection device and the screen is changed. The projection range can be adjusted to fit the screen without any need. In this case, by using a lens that is telecentric to the micro-specular modulation element as the projection lens, it is possible to prevent the reflected light (display light) from deviating from the pupil.

When the auxiliary prism is disposed on the first surface of the prism as in claim 6, when the apex angle of the auxiliary prism is substantially equal to the apex angle of the main prism, the auxiliary prism is arranged as follows.
It is possible to correct the angle shift due to the wavelength variation of the illumination light. Also, by appropriately setting the apex angle of the auxiliary prism, the incident direction of the illumination light can be arbitrarily defined.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an optical system of a reflection type image projection apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing a modified example of the prism of the apparatus of FIG.

FIG. 3 is an explanatory view showing a main part of an optical system of a conventional reflection type image projection apparatus.

[Explanation of symbols]

 Reference Signs List 10 light source unit 20 DMD 30 prism (main prism) 31 first surface 32 second surface 33 third surface 40 projection lens 50 shift mechanism 60 auxiliary prism

Claims (6)

[Claims] 1. A light source that emits illumination light, and a large number of two-dimensionally arranged micromirrors capable of independently switching the angle between an on position and an off position are configured to two-dimensionally arrange the illumination light from the light source into an image. A micro-specular modulation element that modulates and reflects the light, a first surface that is disposed between the light source and the micro-specular modulation device, and that receives the illumination light, a second surface that faces the micro-specular modulation device, The reflected light from the micromirror in the ON position has a third surface that forms a roof-type arrangement together with the first surface, and among the reflected light reflected by the micromirror modulator and incident from the second surface, A prism that satisfies the condition of total reflection with respect to the first surface and the third surface, and is arranged so that reflected light from the micromirror in the off position does not satisfy the condition of total reflection with respect to the third surface; Emitted from the second surface after being totally reflected by the first and third surfaces A projection lens for projecting reflected light onto a screen. 2. The reflection type image projection device according to claim 1, wherein the first surface and the third surface are orthogonal to each other. 3. The apparatus according to claim 2, wherein the second surface is substantially orthogonal to the optical axis of the projection lens, and forms an angle of 45 degrees with the first surface and the third surface. Reflective image projector. 4. A projection lens according to claim 1, wherein said projection lens is telecentric with respect to said micro-specular modulation element, and a shift mechanism is provided for moving said projection lens in a direction perpendicular to its optical axis. The reflective image projector according to any one of 1 to 3. 5. A light source that emits illumination light and a plurality of two-dimensionally arranged micromirrors capable of independently switching an angle between an on position and an off position are configured to two-dimensionally arrange the illumination light from the light source into an image. A micro-mirror modulation element that modulates and reflects the light in accordance with the first surface and the second surface that is disposed between the light source and the micro-mirror modulation device and that receives the illumination light and faces the micro-mirror modulation device. A prism arranged so that, among the reflected light reflected by the micromirror modulator and incident from the second surface, the reflected light from the micromirror at the ON position is totally reflected by the first surface; A reflection type image projection, comprising: a projection lens for projecting reflected light totally reflected on the first surface onto a screen; and a shift mechanism for moving the projection lens in a direction perpendicular to the optical axis. apparatus. 6. The reflection type image projection apparatus according to claim 1, wherein an auxiliary prism is arranged at a predetermined gap from the first surface of the prism.