Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
2000-11-03
2002-10-01
Perkey, W. B. (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S084000, C353S081000, C353S099000
Reexamination Certificate
active
06457830
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflection-type projector, and more particularly, to a reflection-type projector having an improved light separation structure in order to reduce the effect of light reflected from a window surface of an image forming means, such as a micromirror device.
2. Description of the Related Art
In general, in a reflection-type projector employing a micro-mirror device, a plurality of micro-mirrors provided to correspond to pixels of a screen are independently operated, and the paths of rays reflected from the movable mirrors are differentiated by the movable mirrors, so that an image can be formed.
Referring to
FIG. 1
, a reflection-type projector employing a conventional micromirror device includes a light source
10
emitting light rays, a color wheel
20
for embodying a color image, a glass rod
30
for generating uniform rays, a lens element
40
for converging incident rays, a light path changing means
50
for changing the paths of light rays, a micromirror device
60
for forming an image, and a projection lens unit
70
for projecting incident rays onto a screen to form a magnified image on the screen.
The light path changing means
50
is provided with a beam separation prism
51
which changes the paths of rays by transmitting the incident rays entering the beam separation prism
51
at angles smaller than a critical angle and by reflecting the incident rays entering the beam separation prism
51
at angles greater than a critical angle. A compensating prism
55
is further provided to compensate for deviations of the paths of the separated beams.
The beam separation prism
51
has an incident surface
51
a
through which the rays emitted from the light source
10
enter, a critical surface
51
b
slanted with respect to the incident surface
51
a,
and an entrance-exit surface
51
c
facing the micro-mirror device
60
and transmitting incident rays reflected from the critical surface
51
b
and rays reflected from the micro-mirror device
60
. The critical surface
51
b
reflects the incident rays entering the beam separation prism
51
via the incident surface
51
a
at angles greater than the critical angle toward the entrance-exit surface
51
c,
and transmits the incident rays from the micro-mirror device
60
at angles smaller than the critical angle. The compensating prism
55
is disposed so that one of its surfaces faces the critical surface
51
b
of the beam separation prism
51
and compensates for the deviations of the paths of the rays traveling toward the projection lens unit
70
.
As shown in
FIGS. 2 and 3
, the micro-mirror device
60
comprises a plurality of movable mirrors
62
installed on a substrate
61
to correspond to respective pixels, a plurality of posts
63
each for supporting the respective movable mirrors
62
so that the movable mirrors
62
can pivot, and a window
65
for protecting the movable mirrors
62
. Each movable mirror
62
is driven to rotate by electrostatic attraction forces between the movable mirror
62
and electrodes provided on the substrate
61
.
Therefore, the angles of the reflection surfaces of the movable mirrors
62
are individually selected according to whether the electrodes corresponding to the respective pixels are driven or not, that is, depending on whether the electrodes are in an on-state or in an off-state. Therefore, an image is formed by causing only necessary rays reflected from mirrors
62
in the on-state to be directed to the projection lens unit
70
, and by causing unnecessary rays reflected from mirrors
62
in the off-state to travel away from the projection lens unit
70
so as not to be used.
In the micro-mirror device
60
, the incident rays are reflected from the surface of the window
65
as well as the movable mirrors
62
. The rays reflected from the surface of the window
65
are called surface-reflected rays.
Reviewing
FIG. 1
, a reflection-type projector employing a conventional micro-mirror device is configured so that both the necessary reflected rays and the surface-reflected rays reflected from the micro-mirror device
60
travel after passing through the critical surface
51
b,
and a portion of the surface-reflected rays are directed to a screen together with the necessary rays after passing through the projection lens unit
70
. Therefore, the reflection-type projector employing a conventional micro-mirror device is problematic, in that the contrast of an image formed on the screen deteriorates noticeably.
SUMMARY OF THE INVENTION
To solve the above problem, it is an objective of the present invention to provide a reflection-type projector that has an improved light separation structure, so that surface-reflected rays reflected from the surface of a window of an image forming means may not be directed to a screen.
Accordingly, to achieve the above objective, there is provided a reflection-type projector including a light source for generating and emitting light; an optical path changer for changing the traveling path of an incident beam; an image former that is provided to correspond to respective pixels for reflecting incident rays to form necessary reflected rays and unnecessary reflected rays having reflection paths different from each other according to the driven states of the image former and which has a window for enclosing the image former; and a projection lens unit for magnifying incident rays and projecting the rays, wherein the optical path changer is a beam separation prism having: a first critical surface that is slanted so that incident rays from the light source pass through the first critical surface, and the necessary reflected rays and surface-reflected rays reflected from the window are reflected by the first critical surface; an entrance-exit surface that faces the image former and one surface of the projection lens unit and through which rays enter or exit; and a second critical surface slanted with respect to the optical axis of necessary reflected rays reflected from the first critical surface in order to transmit unnecessary reflected rays and surfacereflected rays reflected from the first critical surface, and in order to reflect necessary reflected rays reflected from the first critical surface to the projection lens unit
REFERENCES:
patent: 5309188 (1994-05-01), Brustyn
patent: 5552922 (1996-09-01), Magarill
patent: 5865520 (1999-02-01), Kavanagh et al.
patent: 6179424 (2001-01-01), Sawamura
patent: 2 311 447 (1997-09-01), None
patent: 2 324 166 (1998-10-01), None
patent: 96/31953 (1996-10-01), None
C.B. Shung et al. “Area-Efficient Architectures for the Viterbi Algorithm” vol. 3; Dec. 1990; pp. 1787-1793.
Perkey W. B.
Samsung Electronics Co,. Ltd.
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