Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
1999-12-28
2002-12-10
Dowling, William (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S102000
Reexamination Certificate
active
06491398
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a video projector. In particular, the invention relates to a video projector using a reflection type optical modulation element.
2. Description of the Prior Art
Video projectors for projecting an image in accordance with a received video signal are known.
Among those video projectors is one using a transmission type optical modulation element such as an LCD (Liquid Crystal Display) panel or the like and one using a reflection type optical modulation element such as a DMD (Digital Micromirror Device: a trademark of Texas Instruments, Incorporated) or the like.
Conventional video projectors using a reflection type optical modulation element will be described here with reference to the drawings.
FIG. 6
is a side view showing the structure of a video projector as a first conventional example.
FIG. 7
is a sectional plan view taken along a line VI—VI in FIG.
6
.
In the video projector shown in
FIGS. 6 and 7
, light emitted from an optical source
101
is reflected by a reflecting mirror
102
and thereby condensed onto a rod-shaped optical integrator
103
. The light is reflected plural times in the rod-shaped optical integrator
103
and then output therefrom in a state that its illumination intensity distribution is uniformized.
The light exiting from the rod-shaped optical integrator
103
sequentially passes through relay lenses
104
a
-
104
c
reflected by a reflecting mirror
105
, passes through a relay lens
104
d,
and then reflected by the bonding surface of wedge-shaped prisms
106
a
and
106
b
that configure a reflecting prism
106
.
The light reflected by the reflecting prism
106
is separated by color prisms
107
R,
107
G, and
107
B into red light, green light, and blue light, respectively, which enter DMDs (Digital Micromirror Device: atrademark of Texas Instruments, Incorporated)
109
R,
109
G, and
109
B, respectively.
The DMDs
109
R,
109
G, and
109
B are supplied with video signals corresponding to red, green, and blue components, respectively. The reflectance values of the incident light beams are controlled on a pixel-by-pixel basis in accordance with those video signals.
Light beams reflected by the DMDs
109
R,
109
G, and
109
B enter color prisms
107
R,
107
G, and
107
B, respectively, whereby the red light, green light, and the blue light are combined into full-colored image light. The full-colored image light passes through the reflecting prism
106
straightly and is then enlarged by a projecting lens
110
.
The light enlarged by the projecting lens
110
is projected onto a screen
111
as a projected image.
Japanese Patent Laid-Open No. Hei 9-96867 (Laid-Open in Japan on Apr. 8, 1997) discloses a video projector. The technique disclosed in this publication will be described below as a second conventional example.
FIG. 8
is a side view showing the structure of a video projector as a second conventional example.
FIG. 9
is a plan view of the video projector of FIG.
8
.
The video projector shown in
FIGS. 8 and 9
has an optical radiating system
212
, a tri-colored optical separating system
214
, DMDs
216
R,
216
G, and
216
B, and a projecting lens system
218
.
The optical radiating system
212
is composed of an optical source
220
, a condenser lens
222
, a mirror
224
, and a prism
226
. White-colored light emitted from the optical source
220
is condensed by the condenser lens
222
, reflected by the mirror
224
, again reflected by the prism
226
, and then enters the tri-colored optical separating system
214
.
The white-colored light entering the tri-colored optical separating system
214
is separated by prisms
228
R,
228
G, and
228
B into red light, green light, and blue light, respectively, which enter the DMDs
216
R,
216
G, and
216
B that are disposed behind the respective prisms
228
R,
228
G, and
228
B.
Light beams reflected by the respective DMDs
216
R,
216
G, and
216
B are combined by the prisms
228
R,
228
G, and
228
B and then projected onto a front screen (not shown) by lenses
234
and
236
of the projecting lens system
218
.
However, the video projectors as the two conventional examples have the following problems.
In the first conventional example, first, since it is difficult to make the diameter of a light beam sufficiently small at the pupil position
110
p of the projecting lens
110
, it is impossible to cause all of light beams emitted from the optical source
101
to pass to the pupil position
110
p of the projecting lens
110
without undue loss of light, resulting in a problem that a high-brightness, high-contrast projected image cannot be obtained.
Second, if to solve the first problem it is attempted to make the diameter of a light beam sufficiently small at the pupil position
110
p of the projecting lens
110
by using the relay lenses
104
a
-
104
d
, many relay lenses
104
a
-
104
d
need to be combined in a complex manner, resulting in a problem that the transmittance of the relay lenses
104
a
-
104
d
decreases and hence a high-brightness, high-contrast projected image cannot be obtained. Moreover, this complicated structure of the relay lenses
104
a
-
104
d
increases their volumes; thus the video projector cannot be miniaturized.
The above problems also occur in the video projector as the second conventional example in completely the same manners.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to provide a video projector using a reflection type optical modulation element whose lens system is simple in configuration and which can produce a high-brightness, high-contrast projected image.
According to a first aspect of the invention, there is provided a video projector having an optical source for radiatinglight; a reflecting mirror for reflecting the light radiated by the optical source as a reflected light beam goes along a particular optical axis; a converting optical system for converting a profile of the reflected light beam from the reflecting mirror; a plurality of color prisms for wavelength-separating the converted-light from the converting optical system into a plurality of colored light beams; a plurality of reflection type optical modulation elements for selectively reflecting each of the colored light beams from the color prisms on a pixel—pixel basis in accordance with each of received video signals, respectively; a projecting lens for projecting light obtained through wavelength-combining, by the color prisms, of light beams reflected by each of the reflection type optical modulation elements; and a plurality of condenser lenses disposed between the color prisms and the reflection type optical modulation elements, respectively.
According to a second aspect of the invention, in the video projector according to the first aspect, further having a relay lens disposed between the converting optical system and the color prisms.
In the video projector according to the first and second aspects of the invention, the condenser lenses corresponding to the respective colors are disposed immediately before the reflection type optical modulation elements corresponding to the respective colors. Therefore, the diameter of a light beam at the pupil position of the projecting lens can sufficiently be decreased, and hence all of a light beam emitted from the optical source can be used effectively without undue loss of light. Further, since the number of lenses configuring the lens system disposed between the optical source and the reflection type optical modulation elements can be reduced; the light transmittance can be kept high. As a result, the brightness and the contrast of a projected image on the screen can be increased.
Further, since the diameters of the condenser lenses can greatly be decreased, the video projector can be miniaturized.
According to a third aspect of the invention, in the video projector according to the second aspect, wherein the converting optical system has a rod-shaped optical integrator.
According to a fourth aspect of the invention, in t
Matsumoto Takayuki
Shouji Eisaku
Takeuchi Katsuyuki
Dowling William
NEC Viewtechnology Ltd.
Young & Thompson
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