Optics: image projectors – Lens support – Lens position adjustable
Reissue Patent
2001-02-01
2003-04-22
Dowling, William (Department: 2851)
Optics: image projectors
Lens support
Lens position adjustable
C353S119000, C353S038000, C353S020000, C353S031000, C353S037000, C349S009000
Reissue Patent
active
RE038084
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a projection-type display apparatus that modulates an output light beam from a light source in response to a video signal using a modulating device such as a liquid-crystal light valve or the like and enlarges and projects the modulated light beam through a projection lens onto a screen. More particularly, the present invention relates to a projection-type display apparatus that illuminates an image forming area of the modulating device such as a liquid-crystal light valve.
2. Description of Related Art
Japanese Unexamined Patent Publication 3-111806 discloses a projection-type display apparatus that forms a modulated light beam in response to a video signal using a liquid-crystal light valve and enlarges and projects the modulated light beam onto a screen. As shown in
FIG. 13
, the projection-type display apparatus includes an integrator optical system
923
having two lens plates
921
and
922
, for uniformly illuminating the image forming area of a liquid-crystal valve
925
, as a modulating device, with light from a light source.
The single light beam emitted from a light source lamp unit
8
is split into a plurality of intermediate light beams by lenses
921
a constituting the first lens plate
921
, and is superimposed on the liquid-crystal light valve
925
through lenses
922
a constituting the second lens plate
922
.
In this projection-type display apparatus, the brightness of an image projected onto the screen will drop or the projected image suffers an outlining shadow if the image forming area of the liquid-crystal light valve
925
is not accurately illuminated. To cope with this problem, as shown in
FIG. 14
, a certain margin M is assured around the image forming area A of the liquid-crystal light valve
925
in view of the positioning accuracies of the liquid-crystal light valve
925
and the lens plates
921
,
922
constituting the integrator optical system
923
, the positional errors in the focal points of the lenses
921
a,
922
a of the lens plates and the positioning accuracies of the remaining optical systems disposed along the optical axis.
More particularly, the image forming area A is sized to be distinctly smaller than an illumination area B by the output light from the light source. Even if the illumination area B is offset vertically upward or downward, or horizontally leftward or rightward depending on the overall positioning accuracy of the above components, the image forming area A is designed to be kept within the illumination area B. This avoids the outlining shadow around the projected image and drop in brightness of the projected image. To cope with a large quantity of positional error of the components, the margin M is simply widened.
To increase the brightness of a projected image, the efficiency in the utilization of the light that illuminates the liquid-crystal light valve
925
needs to be increased. If the margin M is enlarged to accommodate errors of the components, the efficiency in the utilization of light drops, thereby dimming the projected image. Thus, the width of the margin formed around the image forming area of the liquid-crystal light valve is preferably narrow. A narrow margin in turn offsets the illumination area from the image forming area of the liquid-crystal light valve, possibly presenting a shadow outlining the projected image.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a projection-type display apparatus that offers an increased image brightness without any shadow around a projected image while presenting a narrow margin around the image forming area of a liquid-crystal light valve.
A first projection-type display apparatus of the present invention may include a light source, a modulating device for modulating a light beam emitted by the light source and a projection device for enlarging and projecting the modulated light beam from the modulating device onto a projection area. An optical element may be disposed in an optical path between the light source. The modulating device may split the light beam emitted from the light source into a plurality of intermediate light beams. A superimposing device may also be provided for superimposing each of the slit intermediate light beams from the optical element on an image forming area of the modulating device. The mounting position of the superimposing device may be adjustable.
This may increase the efficiency in the utilization of illumination light that illuminates the modulating device, thereby brightening a projected image. Even when the margin around the image forming area of the modulating device is narrowed, the illumination area relative to the modulating device is fine-adjusted so that the image forming area is kept within the illumination area and the projected image is free from the outlining shadow attributed to any offset between the image forming area and the illumination area.
After components of the optical systems are mounted, the image forming area of the modulating device is illuminated by the optical element and the superimposing device. When the illumination area is offset from the image forming area of the modulating device, the superimposing device is fine-adjusted so that the image forming area of the modulating device is fully included within the illumination area. Taking into consideration the offset between the illumination area and the image forming area, attributed to the positioning error of the optical components, the margin formed around the outline of the image forming area of the modulating device is narrowed.
Since the mounting position of the superimposing device, which is an optical component chiefly determining the illumination area of the modulating device, may be fine-adjusted, the position of the illumination area of the modulating device is easily and efficiently adjusted. The adjustment of the position of the illumination area is thus performed taking into consideration the overall mounting error of optical components (optical elements) in front of the superimposing device (upstream of the superimposing device in the optical path).
Since the plurality of split intermediate light beams are finally superimposed on a single illumination area through the superimposing device and are then delivered, a constant-brightness polarized light beam with no illuminance variations is obtained as an illumination light even when an incident light beam has a large light intensity distribution in its cross section. A constant-brightness polarized light beam with no illuminance variations may be obtained as an illumination light when the incident light beam has a uniform light intensity, when the intermediate light beam cannot be separated into a p-polarized light and an s-polarized light beam because of spectral characteristics, or when the light intensity and spectral characteristics change in the course of aligning the polarization directions of both polarized light beams.
The projection-type display apparatus may present a particularly bright projected image that is uniform and bright on an entire display area or projection area.
A reflection device for bending an optical path may be disposed in the optical path extending from the light source to the modulating device. If an error is introduced in the mounting angle of the reflection device, the illumination area may be offset from the image forming area of the modulating device. The mounting angle of the reflection device is such that it is preferably adjustable relative to its incident optical axis.
The projection-type display apparatus may be applied to a projection-type display apparatus for projecting a color image. More particularly, it may be applied to a projection-type display apparatus including a color separating optical system for separating an output light from the superimposing device into color light beams, a plurality of modulating devices for modulating the color light beams separated by the color separating optical system, and a color synthesizing optical sy
Haba Shinji
Hashizume Toshiaki
Iechika Hisashi
Ogawa Yasunori
Yajima Akitaka
Oliff & Berridg,e PLC
Seiko Epson Corporation
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