Optics: image projectors – Reflector
Reexamination Certificate
2000-04-21
2002-07-16
Adams, Russell (Department: 2851)
Optics: image projectors
Reflector
C353S031000, C353S084000, C348S743000, C385S133000
Reexamination Certificate
active
06419365
ABSTRACT:
RELATED APPLICATIONS
Not Applicable
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
TECHNICAL FIELD
This invention relates to an image display systems, and more particularly, to an asymmetrical light integrating tunnel that improves the uniformity and brightness of images produced by color video projection displays.
BACKGROUND OF THE INVENTION
Projection systems have been used for many years to project motion pictures and still photographs onto screens for viewing. More recently, presentations using multimedia projection systems have become popular for conducting sales demonstrations, business meetings, and classroom instruction.
In a common operating mode, multimedia projection systems receive analog video signals from a personal computer (“PC”). The video signals may represent still, partial-, or full-motion display images of a type rendered by the PC. The analog video signals are typically converted in the projection system into digital video signals that control a digitally driven light valve, such as a liquid crystal display (“LCD”) or a digital micro mirror device (“DMD”).
A popular type of multimedia projection system employs a light source and optical path components upstream and downstream of the image-forming device to project the image onto a display screen. An example of a DMD-based multimedia projector is the model LP420 manufactured by In Focus Systems, Inc., of Wilsonville, Oreg., the assignee of this application.
Significant effort has been invested into developing projectors producing bright, high-quality, color images. However, the optical performance of conventional projectors is often less than satisfactory. For example, suitable projected images having suitable uniform brightness are difficult to achieve, especially when using compact portable color projectors in a well-lighted room.
Because LCD displays have significant light attenuation and triple path color light paths are heavy and bulky, portable multimedia projectors typically employ DMD displays in a single light path configuration. Producing a projected color image with this configuration typically requires employing some form of sequential color modulator, such as a color shutter, color-switchable light source, multiple light-emitting diode arrays, or a color wheel, to generate a frame sequential color image. Unfortunately, such color modulators often produce minimal light intensity and/or have significant light attenuation.
The use of color wheels in frame sequential color (“FSC”) display systems has been known for many years and was made famous (or infamous) in early attempts to develop color television sets. With technological advances, however, color wheel display implementations are still useful because of their simplicity, color purity, and inherent image convergence.
FIG. 1
shows a typical prior art FSC display system
10
in which a sensor
12
senses a timing mark
14
to detect a predetermined color index position of a motor
16
that rotates a color wheel
18
having respective red, green, and blue filter segments R, G, and B. A light source
20
projects a light beam
22
through color wheel
18
and a relay lens
24
. onto a display device
26
, such as an LCD-based light valve. A display controller (not shown) drives display device
26
with sequential red, green, and blue image data that are timed to coincide with the propagation of light beam
22
through the respective filter segments R, G, and B of color wheel
18
.
FIG. 2
, shows a prior art multimedia projector
30
capable of projecting images having increased, uniform brightness relative to the LCD-based display of
FIG. 1. A
light source
32
emits polychromatic light that propagates along an optical path
34
through projector
30
. Light source
32
generates intense light by employing a metal halide arc lamp
36
and an elliptical reflector
38
. Optical path
34
includes a condenser lens
40
, a color wheel
42
, a rectangular light integrating tunnel
44
, a relay lens
48
, a DMD
50
, and a projection lens
52
. The optical components are held together by an optical frame
54
that is enclosed within a projector housing (not shown). A display controller
56
receives color image data from a PC
58
and processes the image data into frame sequential red, green, and blue image data, sequential frames of which are conveyed to DMD
50
in proper synchronism with the angular position of color wheel
42
. A power supply
60
is electrically connected to light source
32
and display controller
56
and also powers a cooling fan
62
and a free running DC motor
64
that rotates color wheel
42
. Display controller
56
controls DMD
50
such that light propagating from relay lens
48
is selectively reflected by DMD pixel mirrors either toward projection lens
52
or toward a light-absorbing surface
66
mounted on or near optical frame
54
.
DC motor
64
rotates color wheel
42
at about 6,650 to 7,500 rpm. Color wheel
42
includes color filter segments R, G, and B that each surround about
120
degrees of color wheel
42
. Color wheel synchronization is achieved by optically detecting which color filter segment is in optical path
34
and for how long. Particular colors of light propagating through color wheel
42
are sensed by a color selective light sensor
68
to generate synchronization timing data. Light sensor
68
is positioned off optical path
34
to receive scattered light.
To increase projected image brightness uniformity, a rectangular input aperture
70
of light integrating tunnel
44
collects a majority of the light exiting color wheel
42
and homogenizes the light during propagation through tunnel
44
to a rectangular output aperture
72
. Light exiting output aperture
72
is focused by relay lens
48
onto DMD
50
. However, because DMD
50
is tilted obliquely to optical path
34
, the image of output aperture
72
on DMD
50
is Keystone distorted, causing image overfill at the far end of DMD
50
resulting in light loss, reduced brightness, and brightness nonuniformity across DMD
50
.
Conventional light integrating tunnels typically have rectangular input and output apertures and may be formed as either an air-tunnel with reflective inside surfaces or may be a solid optical material, such as glass, quartz, or plastic with polished outer surfaces. For air tunnels, the light is reflected off the reflective inside surfaces, and for solid tunnels the light is totally internally reflected off the polished outer surfaces. Because the input and output apertures are rectangular, the four tunnel walls are perpendicular at their abutting edges.
There are other previously known light integrating tunnel designs that compensate for various light path-related illumination nonuniformities. For example, U.S. Pat. No. 5,303,084 for LASER LIGHT BEAM HOMOGENIZER AND IMAGING LIDAR SYSTEM INCORPORATING SAME describes a rectangular light integrator tunnel having tapered curved recesses extending between its input and output apertures for adjusting the uniformity of the light beam exiting the integrator. In another example, U.S. Pat. No. 5,844,588 for DMD MODULATED CONTINUOUS WAVE LIGHT SOURCE FOR XEROGRAPHIC PRINTER describes a wedge-shaped light integrator tunnel for providing anamorphic illumination of a wide aspect ratio DMD. However, neither conventional integrating tunnels nor either patent addresses the above-described excess overfill problem caused by oblique illumination of a DMD.
What is needed, therefore, is a way of capturing as much of the light propagated through a color modulator as possible and uniformly imaging the light on an obliquely positioned reflective light valve without light overfill.
SUMMARY OF THE INVENTION
An object of this invention is, therefore, to provide an apparatus and a method for capturing as much of the light propagated through a color modulator as possible and uniformly imaging the light on an obliquely positioned reflective light valve without light overfill.
Another object of this invention is to provide an integrator tunnel having an input aperture shaped to o
Engle Scott
Peterson Mark
Potekev Franc
Stahl Kurt
Adams Russell
InFocus Corporation
Koval Melissa
Stoel Rives LLP
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