Reflection type projector

Details Reflection type projector Reflection type projector

2000-02-29

2001-10-09

Dowling, William (Department: 2851)

Optics: image projectors

Composite projected image

Multicolor picture

C353S081000

Reexamination Certificate

active

06299312

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflection type projector using a reflection type image forming device and, more particularly, to a reflection type projector in which three colors used for representation of a color image are overlapped so that brightness of the light projected onto a screen increases.
2. Description of the Related Art
In general, a reflection type projector is for providing an image by projecting an image generated by a reflection type image forming device onto a screen using an additional light source.
A reflection type projector for representing a color image by simultaneously projecting three colors to improve the brightness of image suggested by the present applicant is disclosed in U.S. patent application Ser. No. 09/057,585 (filed on Apr. 9, 1998, entitled “Refection Type Projector” by Soon-cheol Choi). The suggested reflection type projector, as shown in
FIG. 1
, includes a light source
110
for emitting light, reflecting mirrors
132
,
133
and
134
, first and second dichromatic mirrors
131
and
135
arranged on an optical path for transmitting or reflecting input light according to the wavelength thereof, first, second and third optical path converting devices
140
,
150
and
160
for converting a proceeding path of input light, first, second and third image forming devices
145
,
155
and
165
for forming an image from input light, a dichromatic beam splitter
170
for allowing the input light having passed the first, second and third optical path converting devices
140
,
150
and
160
to proceed in one direction, and a projection lens unit
180
for magnifying and projecting the light input from the dichromatic beam splitter
170
.
The first, second and third optical path converting devices
140
,
150
and
160
each include first through third converging lenses
141
,
151
and
161
and first through third prisms
143
,
153
and
163
. Here, to have light input at an angle greater or less than the critical angle, the first through third prisms
143
,
153
and
163
include first through third transmission/reflection surfaces
143
a,
153
a
and
163
a,
respectively, which transmit the light input from the light source
110
and total-reflect the light reflected by the first through third image forming devices
145
,
155
and
165
.
The dichromatic beam splitter
170
has three incident surfaces
171
,
172
and
173
and a single exit surface
174
. The three incident surfaces
171
,
172
and
173
face the first, second and third optical path converting devices
140
,
150
and
160
, respectively, and convert a proceeding path of input light having passed each of the first, second and third optical path converting devices
140
,
150
and
160
to proceed toward the single exit surface
174
. For this, the dichromatic beam splitter
170
has first and second mirror surfaces
176
and
177
for selectively transmitting or reflecting the input light according to the wavelength thereof. The first mirror surface
176
is coated for the transmission or reflection of the input light according to the wavelength thereof so that the input light passing the first optical path converting device
140
is reflected and the input lights passing the second and third optical path converting devices
150
and
160
are transmitted. The second mirror surface
177
is coated for the transmission or reflection of the input light according to the wavelength thereof so that the input lights passing the first and second optical path converting devices
140
and
150
are transmitted and the input light passing the third optical path converting device
160
is reflected. Thus, as the dichromatic beam splitter
170
includes the first and second mirror surfaces
176
and
177
, the lights input from three incident surfaces
171
,
172
and
173
are output through the single exit surface
174
.
The projection lens unit
180
is arranged between the dichromatic beam splitter
170
and a screen (not shown) for magnifying and projecting the light input from the dichromatic beam splitter
170
toward the screen.
The reflection type projector having the above structure, as shown in
FIG. 2
, is realized into an off-axis optical system in which an illumination optical axis A
L
and an optical axis A
P
of the projection lens unit are different from each other. Accordingly, the first through third prisms
143
,
153
and
163
and the dichromatic beam splitter
170
have such an optical arrangement as that shown in FIG.
2
.
Here, when the illumination optical axis A
L
crosses a definite line where the first and second mirror surfaces
176
and
177
cross, the efficiency of use of three colors is improved. However, in the above arrangement, as a first FLCD (ferroelectric liquid crystal display)
147
of the first image forming device
145
and a second FLCD
157
of the second image forming device are arranged too closely, installation of convergence adjustment devices
149
and
159
for adjusting convergence of the first and second FLCDs
147
and
157
becomes difficult. The reference numeral
167
denotes a third FLCD. Also, as the light input to the three incident surfaces
171
,
172
and
173
of the dichromatic beam splitter
170
after passing the first through third prisms
143
,
153
and
163
do not make an angle of 90°, the optical arrangement becomes complicated and the first through third prisms
143
,
153
and
163
occupy a large space.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide a reflection type projector having a correction prism so that the optical arrangement of the first through third prisms is simplified, the occupied space is minimized, and the installation space of the convergence adjustment device can be easily secured.
Accordingly, to achieve the above objective, there is provided a reflection type projector which comprises a light source for generating and projecting light, a first dichromatic mirror arranged on an optical path for selectively transmitting or reflecting input light according to the wavelength thereof, first, second and third image forming devices for generating an image corresponding to each color from input light, a first prism arranged on an optical path between the first dichromatic mirror and the first image forming device, and having a first transmission/reflection surface for transmitting input light transmitting the first dichromatic mirror and total-reflecting the light reflected by the first image forming device, a second dichromatic mirror for selectively transmitting or reflecting the light reflected by the first dichromatic mirror according to the wavelength thereof, a second prism arranged on an optical path between the second dichromatic mirror and the second image forming device, and having a second transmission/reflection surface for transmitting light reflected by the second dichromatic mirror and total-reflecting the light reflected by the second image forming device, a third prism arranged on an optical path between the second dichromatic mirror and the third image forming device, and having a third transmission/reflection surface for transmitting light transmitting the second dichromatic mirror and total-reflecting the light reflected by the third image forming device, a dichromatic beam splitter having first and second mirror surfaces for selectively transmitting or reflecting light according to the wavelength thereof so that the light input passing the first, second and third prisms is output in one direction, a correction prism installed on an exit surface of the dichromatic beam splitter for allowing an optical axis of the light input to the dichromatic beam splitter passing each of the first, second and third prisms to be input approximately perpendicular to each of three incident surfaces of the dichromatic beam splitter, and a projection lens unit for magnifying and projecting light input from the dichromatic beam splitter toward a screen.


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