Optics: image projectors – Reflector – Plural
Reexamination Certificate
2002-10-09
2004-03-02
Dowling, William C. (Department: 2851)
Optics: image projectors
Reflector
Plural
C353S122000, C348S771000, C359S254000
Reexamination Certificate
active
06698902
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection type image displaying apparatus in which light reflected by a reflection type optical spatial modulator element, such as a digital mirror device (DMD™, simply called DMD hereinafter) chip, is projected onto a screen to display am image included in the light.
2. Description of Related Art
A projection type image displaying apparatus is generally called a digital light processor (DLP) and denotes a projector using a DMD chip. In the DMD chip, a large number of micro-mirrors respectively having a size of 16 &mgr;m square are disposed in a two-dimensional matrix shape at pitches (or intervals) of 17 &mgr;m. Each micro-mirror of the DMD chip is inclined by an angle of +10 degrees so as to be set to an on-state and is inclined by an angle of −10 degrees so as to be set to an off-state. In this case, a flux of light reflected by the micro-mirror in the on-state propagates in an on-direction, and a flux of light reflected by the micro-mirror in the off-state propagates in an off-direction. Therefore, a flux of light reflected on the micro-mirror is switched from the on-direction (or the off-direction) to the off-direction (or the on-direction).
In this case, the position relation between the DMD chip and a projection lens is set so as to make a flux of light reflected by each micro-mirror in the on-state pass through an entrance pupil of the projection lens, and each flux of light passing through the entrance pupil of the projection lens reaches a pixel of a screen. Also, the position relation between the DMD chip and a projection lens is set so as to make a flux of light reflected by each micro-mirror in the off-state pass out of the entrance pupil of the projection lens, and no light reaches the screen. Therefore, a flux of light reflected by each micro-mirror in the on-state brightens the corresponding pixel of the screen, and a flux of light reflected by each micro-mirror in the off-state does not brighten the corresponding pixel of the screen. When fluxes of light are incident on the micro-mirrors of the DMD chip respectively, fluxes of outgoing light reflected by the micro-mirrors in the on-state have image information. The fluxes of outgoing light having the image information pass through the projection lens and are projected onto the screen. Therefore, an image is displayed on the screen according to the image information.
FIG. 9
is a view showing the configuration of a conventional image displaying apparatus.
FIG. 10A
shows the position relation between a total internal reflection (TIR) prism and a DMD chip shown in FIG.
9
.
FIG. 10B
shows fluxes of light incident on micro-mirrors of a DMD chip shown in FIG.
9
.
In
FIG. 9
,
110
indicates a high pressure mercury lamp (or a lighting source system) for generating light and radiating parallel light.
120
indicates a plurality of condenser lenses (or the lighting source system) for converging the parallel light radiated from the high pressure mercury lamp
110
onto a focal point.
130
indicates a rod integrator (or the lighting source system) for receiving the converged light output from the condenser lenses
120
and outputting a plurality of fluxes of light having a uniform intensity distribution.
140
indicates a relay lens system for relaying the fluxes of light output from the rod integrator
130
. A diaphragm
141
having an aperture is placed in the relay lens system
140
. The fluxes of light output from the rod integrator
130
are deformed in the diaphragm
141
.
160
indicates a DMD chip.
150
indicates a total internal reflection (TIR) prism (or a total reflection prism) for totally reflecting the fluxes of light received from the relay lens system
140
so as to send the fluxes of light to the DMD chip
160
and transmitting the fluxes of light reflected by the DMD chip
160
.
170
indicates a projection lens (or a projecting optical system) for projecting the fluxes of light, which are reflected by the DMD chip
160
and transmitted through the TIR prism
150
, onto a screen. Here, the screen of the conventional image displaying apparatus is omitted in FIG.
9
.
Also, in
FIG. 10A
,
151
indicates a surface (hereinafter, called an opposite-to-DMD surface) of the TIR prism
150
. The opposite-to-DMD surface
151
is opposite to the DMD chip
160
.
161
indicates a glass cover plate of the DMD chip
160
.
162
indicates each of a large number of micro-mirrors of the DMD chip
160
.
163
indicates a substrate of the DMD chip
160
. The substrate
163
of the DMD chip
160
is placed so as to be parallel to the opposite-to-DMD surface
151
of the TIR prism
150
. Also, the glass cover plate
161
is placed so as to be parallel to a flat surface of the substrate
163
.
Next, an operation of the conventional image displaying apparatus will be described below.
Parallel light is emitted from the high pressure mercury lamp
110
and is converged onto a focal point of the condenser lens
120
. An incident end face of the rod integrator
130
is placed at the focal point of the condenser lens
120
. Therefore, converged light output from the condenser lens
120
is incident on the rod integrator
130
. In the rod integrator
130
, a plurality of fluxes of light are produced from the converged light, intensities of the fluxes of light are equalized, and the fluxes of light having an almost uniform intensity distribution are output from an outgoing end face of the rod integrator
130
.
Thereafter, the fluxes of light output from the rod integrator
130
pass through the relay lens system
140
having the diaphragm
141
and are incident on the TIR prism
150
. The fluxes of light incident on the TIR prism
150
are totally reflected on a face of the TIR prism
150
and pass through the opposite-to-DMD surface
151
and the glass cover plate
161
in that order, and the fluxes of light are incident on the DMD chip
160
. In the DMD chip
160
, each flux of incident light is reflected on the corresponding micro-mirror
162
set to either the on-state or the off-state and propagates in the on-direction or off-direction as a flux of outgoing light. A plurality of fluxes of outgoing light reflected on the micro-mirrors
162
of the on-state and propagating in the on-direction are returned from the DMD chip
160
to the TIR prism
150
, pass through the projection lens
170
and are projected onto a screen (not shown). Therefore, an image is displayed on the screen.
Because the conventional image displaying apparatus has the above-described configuration, a portion of the light totally reflected on a face of the TIR prism
150
is reflected on the opposite-to-DMD surface
151
placed at a boundary surface between the TIR prism
150
and the air, and the portion of the light undesirably passes through the projection lens
170
. Also, another portion of the light totally reflected on a face of the TIR prism
150
is reflected on a boundary surface between the glass cover plate
161
and the air, and the portion of the light undesirably passes through the projection lens
170
. Therefore, the portions of the light are projected on the screen, and a problem has arisen that a contrast of the image displayed on the screen deteriorates due to the portions of the light.
This problem will be described in detail with reference to FIG.
10
A and FIG.
10
B.
In cases where rays of light other than light reflected on the micro-mirrors
162
of the on-state pass through the entrance pupil of the projection lens
170
, a contrast between white and black in the image displayed on the screen deteriorates due to the rays of light. The rays of light other than light reflected on the micro-mirrors
162
of the on-state are derived from light reflected on a top surface of the glass cover plate
161
, light reflected on a bottom surface of the glass cover plate
161
and light reflected on the opposite-to-DMD surface
151
of the TIR prism
150
.
As shown in
FIG. 10A
, C
1
denotes rays of specular reflection light. The rays
Kawano Hiroyuki
Nishimae Jun-ichi
Okamoto Tatsuki
Satou Yukio
Sono Atsuhiro
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