Title: Reflective liquid crystal projector
Abstract: In a reflective liquid crystal projector, illumination light is separated into blue, green and red illumination light bundles. The three color illumination light bundles are respectively modulated through three reflective liquid crystal elements into blue, green and red color optical images. A first polarizing beam splitter prism directs the blue optical image to a first incident surface of a recombination prism, whereas a second polarizing beam splitter prism directs the red and green optical images to a second incident surface of the recombination prism. The three color optical images are recombined through the recombination prism into a full-color image, and the full-color image is projected through a projection lens onto a screen. The first and the second polarizing beam splitter prisms and the recombination prim are fixed merely at their bottom surfaces to a prism base plate.
Patent Number: 6,997,559 Issued on 02/14/2006 to Inamoto
| Inventors:
|
Inamoto; Masayuki (Saitama, JP)
|
| Assignee:
|
Fujinon Corporation (Saitama, JP)
|
| Appl. No.:
|
867733 |
| Filed:
|
June 16, 2004 |
Foreign Application Priority Data
| Aug 12, 2003[JP] | 2003-207358 |
| Current U.S. Class: |
353/20; 353/33; 353/81; 353/99; 353/119; 349/9; 359/497 |
| Current Intern'l Class: |
G03B 21/00 (20060101); G03B 21/14 (20060101); G02B 21/28 (20060101); G02B 27/28 (20060101); G02F 1/13.35 (20060101) |
| Field of Search: |
353/20,119,120,31,33,81
349/9
359/496,497,500,850,577
362/19
|
References Cited [Referenced By]
U.S. Patent Documents
| 5808795 | Sep., 1998 | Shimomura et al.
| |
| 6705731 | Mar., 2004 | Inoue.
| |
| 6749305 | Jun., 2004 | Tsao et al.
| |
| 6769779 | Aug., 2004 | Ehrne et al.
| |
| Foreign Patent Documents |
| 2001-42425 | Feb., 2001 | JP.
| |
Primary Examiner: Koval; Melissa Jan
Attorney, Agent or Firm: Arnold International, Arnold; Bruce Y.
Claims
What is claimed is:
1. A reflective liquid crystal projector comprising:
three reflective liquid crystal elements illuminated by three color illumination
light bundles of three primary colors respectively, to modulate said three color
illumination light bundles into three color optical images of three primary colors;
a rectangular recombination prism having incident surfaces for receiving said
three color optical images, a combining surface for combining said three color
optical images into a full-color optical image, and an exit surface for letting
said full-color optical image out of said recombination prism;
a projection lens for projecting said full-color optical image onto a screen;
a prism base plate to which said recombination prism is fixed at its bottom surface; and
at least two polarizing beam splitters of a rectangular prism shape, said polarizing
beam splitters being placed individually between said liquid crystal elements and
said incident surfaces of said recombination prism, for directing said three color
illumination light bundles to said liquid crystal elements and for directing said
three color optical images to said combining surface of said recombination prism,
wherein said polarizing beam splitters are fixed merely at their bottom surfaces
to said prism base plate and the top surfaces of said polarizing beam splitters
are not fixed to a support.
2. A reflective liquid crystal projector as claimed in claim 1, wherein said
polarizing beam splitters are first and second polarizing beam splitters, said
first polarizing beam splitter having an illumination light incident surface for
receiving first and second ones of said three color illumination light bundles,
an image exit surface from which first and second ones of said three color optical
images exit, and a polarizing reflection surface, wherein said polarizing reflection
surface transmits said first color illumination light bundle and reflects said
second color illumination light bundle to direct said first and said second color
illumination light bundles respectively to first and second ones of said liquid
crystal elements, and said polarizing reflection surface reflects said first color
optical image from said first liquid crystal element toward said image exit surface,
and transmits said second color optical image from said second liquid crystal element
toward said image exit surface.
3. A reflective liquid crystal projector as claimed in claim 1, wherein said
bottom surfaces of said polarizing beam splitters are fixed to said prism base
plate with an adhesive agent.
4. A reflective liquid crystal projector as claimed in claim 3, wherein said
prism base plate is provided with smooth mounting surfaces for putting said bottom
surfaces of said polarizing beam splitters thereon.
5. A reflective liquid crystal projector as claimed in claim 4, wherein said
smooth mounting surfaces are slightly recessed from a top surface of said prism
base plate, for positioning said polarizing beam splitters on said prism base plate.
6. A reflective liquid crystal projector as claimed in claim 3, wherein said
recombination prism is fixed at its bottom surface to said prism base plate with
an adhesive agent.
Description
FIELD OF THE INVENTION
The present invention relates to a reflective liquid crystal projector that is
provided with three panels of reflective liquid crystal elements for three primary
colors. And more particularly, the present invention relates to a reflective liquid
crystal projector that displays a full-color image on a screen by combining three
color optical images modulated through the liquid crystal elements.
BACKGROUND ARTS
The reflective liquid crystal projector is mainly constituted of a light source,
a color separating optical element such as a dichroic mirror or a dichroic prism,
polarizing beam splitter prisms, hereinafter called briefly the PBS prisms, three
liquid crystal elements, a recombination prism, and a projection lens. White light
from the light source is separated into a blue illumination beam, a red illumination
beam and a green illumination beam. The liquid crystal elements modulate and reflect
the three color illumination beams respectively, to produce three color optical
images. The three color optical images are combined together through the recombination
prism, and the combined full-color image is projected through the projection lens
onto a screen.
In conventional liquid crystal projectors, the recombination prism is held in
a predetermined position by a prism holder, as disclosed in Japanese laid-open
Patent Application No. 2001-42425. The recombination prism is a rectangular prism,
and the prism holder is formed with mounting portions which top and bottom surfaces
of the rectangular prism adhere to. The mounting portions are provided with holes
for accepting an adhesive agent. After the top and bottom surfaces of the recombination
prism are brought into contact with the mounting portions, the adhesive agent is
poured into the holes, so that the top and bottom surfaces of the recombination
prism are fixed to the mounting portions.
In the reflective liquid crystal projector, the PBS prisms are used for separating
illumination light paths from image light paths. The PBS prism is conventionally
held by bonding top and bottom sides of the prism to respective prism holders with
the adhesive agent. Because of thermal swelling of the prism holders, which is
caused while the liquid crystal projector is being used, the PBS prism leans to
distort the image projected on the screen, deteriorating the image quality. Since
the prism holders are bonded to the top and bottom surfaces of the PBS prism, the
total size of the liquid crystal projector is enlarged by the mounting space of
the prism holders.
SUMMARY OF THE INVENTION
In view of the foregoing, a primary object of the present invention is to provide
a reflective liquid crystal projector that is compact and achieves a high quality
of the projected image.
According to the present invention, a reflective liquid crystal projector
comprises three reflective liquid crystal elements illuminated by illumination
light bundles of three primary colors respectively, to modulate the three color
illumination light bundles into optical images of three primary colors; a rectangular
recombination prism having incident surfaces for receiving the three color optical
images, a combining surface for combining the three color optical images into a
full-color optical image, and an exit surface for letting the full-color optical
image out of the recombination prism; a projection lens for projecting the full-color
optical image onto a screen; a prism base plate to which the recombination prism
is fixed at its bottom surface; and at least two polarizing beam splitters of a
rectangular prism shape, the polarizing beam splitters being placed individually
between the liquid crystal elements and the incident surfaces of the recombination
prism, for directing the three color illumination light bundles to the liquid crystal
elements and for directing the three color optical images to the combining surface
of the recombination prism, wherein the polarizing beam splitters are fixed merely
at their bottom surfaces to the prism base plate.
According to a preferred embodiment of the invention, the polarizing beam
splitters are first and second polarizing beam splitters, the first polarizing
beam splitter having an illumination light incident surface for receiving first
and second ones of the three color illumination light bundles, an image exit surface
from which first and second ones of the three color optical images exit, and a
polarizing reflection surface, wherein the polarizing reflection surface transmits
the first color illumination light bundle and reflects the second color illumination
light bundle to direct the first and the second color illumination light bundles
respectively to first and second ones of the liquid crystal elements, and the polarizing
reflection surface reflects the first color optical image from the first liquid
crystal element toward the image exit surface of the first polarizing beam splitter,
and transmits the second color optical image from the second liquid crystal element
toward the image exit surface.
As shown in FIG. 1, the polarizing beam splitters 8, 10 are fixed
merely at their bottom surfaces to the prism base plate and are not fixed to a
support at their top surfaces. Therefore, if the prism base plate swells thermally,
the polarizing beam splitters will not lean, so the image projected on the screen
will not be deteriorated. Moreover, because it is unnecessary to bond some prism
holders on the top and the bottom sides of the PBS prisms, this configuration saves
the mounting space, so the reflective liquid crystal projector of the present invention
can be made more compact.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects and advantages will be more apparent from the following
detailed description of the preferred embodiments when read in connection with
the accompanied drawings, wherein like reference numerals designate like or corresponding
parts throughout the several views, and wherein:
FIG. 1 is a schematic perspective view of a reflective liquid crystal projector
according to an embodiment of the present invention;
FIG. 2 is a schematic diagram illustrating an optical system of the reflective
liquid crystal projector of FIG. 1;
FIG. 3 is a sectional view illustrating a recombination prism and a first PBS
prism, taken along a vertical plane to a prism holding plate;
FIG. 4 is a sectional view illustrating the recombination prism and a second
PBS prism, taken along a vertical plane to the prism base plate that includes an
optical axis of a projection lens; and
FIG. 5 is a schematic perspective view of a reflective liquid crystal projector
according to a second embodiment of the invention, wherein a projection lens has
a refracted optical axis.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1, a base frame
6 consists of a prism base plate
6a
and
a lens mounting plate
6b. The prism base plate
6a holds
first and second PBS prisms
8 and
10 of a rectangular prism shape,
a recombination prism
15, and first to third polarization rotators
9,
11 and
12 thereon.
A reflective liquid crystal element
20 for modulating blue illumination
light is disposed in opposition to a side surface of the first PBS prism
8,
and the first PBS prism
8 separates the light path of the blue optical image
that is modulated through the liquid crystal element
20, from the light
path of the blue illumination light.
A reflective liquid crystal element
22 for modulating red illumination
light
and a reflective liquid crystal element
24 for modulating green illumination
light are disposed in opposition to first and second side surfaces of the second
PBS prism
10. The second PBS prism
10 separates the light path of
the red optical image that is modulated through the liquid crystal element
22,
from the light path of the red illumination light, and also separates the light
path of the green optical image that is modulated through the liquid crystal element
24, from the light path of the green illumination light.
Light from a not-shown light source, e.g. a super-high voltage mercury lamp,
includes blue, green and red light bundles, and falls on a color separation mirror
40. The color separation mirror
40 separates the light from the light
source into the blue, red and green illumination light bundles. The blue illumination
light bundle from the color separation mirror
40 falls on the first PBS
prism
8, whereas the red and green illumination light bundles fall on the
second PBS prism
10. A not-shown integrator for equalizing light intensity
and a condenser lens
42 for condensing light bundles from the integrator
are disposed between the light source and the color separation mirror
40
in this order from the light source side.
As shown in FIG. 2, the recombination prism
15 is a rectangular prism,
wherein two of the four side surfaces are incident surfaces
15c and
15d for the optical images modulated through the liquid crystal elements
20,
22 and
24. Another side surface is an exit surface
15b
from which a combined optical image exits.
The lens mounting portion
6b of the base frame
6 is formed
vertically to the prism base plate
6a, and a lens barrel
17
holding a projection lens
30 is screwed to the lens mounting portion
6b.
Concretely, a rear end of the lens barrel
17 is fitted in an opening
of the lens mounting portion
6b, and a rectangular flange
17a
of the lens barrel
17 is screwed at its four corners to the lens mounting
portion
6b.
The prism base plate
6a is provided with a smooth mounting surface
6c for the recombination prism
15 and a smooth mounting surface
6d for the second PBS prism
10. A bottom surface
15a
of the recombination prism
15 and the bottom surface
10a of
the second PBS prism
10 are fixed to the mounting surfaces
6c
and
6d with the adhesive agent. As being held in this manner,
the second PBS prism
10 would not lean but just move in a parallel direction
on the plate surface if the prism base plate
6a thermally swells.
It is to be noted that the mounting surfaces
6c and
6d
are slightly recessed from a top surface of the prism base plate
6a,
in order to confine the positions of the recombination prism
15 and the
second PBS prism
10.
The exit surface
15b of the recombination prism
15 and the
second incident surface
15d are perpendicular to an optical axis
of the projection lens
30. An image exit surface
10b of the
second PBS prism
10, which is opposite to the second incident surface
15d,
is also perpendicular to the optical axis of the projection lens
30. The
third polarization rotator
12 is mounted through a base member on the prism
base plate
6a, in between the second PBS prism
10 and the
recombination prism
15. The third polarization rotator
12 changes
the polarization of the red optical image from S-type polarization to P-type polarization
that is rotated by 90 degrees from S-type polarization.
As shown in FIG. 3, the first PBS prism
8 has an image exit surface
8b
that faces the first incident surface
15c of the recombination
prism
15. A bottom surface
8a of the first PBS prism
8
is fixed to a smooth mounting surface
6e of the prism base plate
6a with the adhesive agent. As being held merely at its bottom surface
8a, the first PBS prism
8 would not lean if the prism base
plate
6a thermally swells. Also the mounting surface
6e
is slightly recessed from the top surface of the prism base plate
6a,
thereby positioning the first PBS prism
8 on the prism base plate
6a.
The first polarization rotator
9 is mounted through a base member on the
prism base plate
6a, in between the first PBS prism
8 and
the recombination prism
15. The first polarization rotator
9 changes
the blue optical image from P-type polarization to S-type polarization.
Now the operation of the reflective liquid crystal projector of the present embodiment
will be described with reference to FIG. 2.
The light from the not-shown light source, which includes three primary color
light bundles, is equalized in intensity through the not-shown integrator and is
condensed through the condenser lens
42, before falling on the color separation
mirror
40. The color separation mirror
40 transmits the blue illumination
light bundle and reflects the red and green illumination light bundles. After being
transmitted through the color separation mirror
40, the blue illumination
light bundle falls on an illumination light incident surface
8c of
the first PBS prism
8.
When falling on the illumination light incident surface
8c, the
blue illumination light bundle is of S-type polarization, and is reflected from
a polarizing reflection surface
8d of the first PBS prism
8
toward the liquid crystal element
20. The liquid crystal element
20
modulates the blue illumination light bundle into the blue optical image and also
changes the blue optical image from S-type polarization to P-type polarization.
Thus, the blue optical image is transmitted through the polarizing reflection surface
8d, and exits from the image exit surface
8b of the
first PBS prism
8 toward the first polarization rotator
9. The blue
optical image is changed again from P-type polarization to S-type polarization
through the first polarization rotator
9, and falls on the first incident
surface
15c of the recombination prism
15.
The red and green illumination light bundles, after reflected from the color
separation mirror
40, fall on the second polarization rotator
11.
Through the second polarization rotator
11, only the red illumination light
bundle is changed from S-type polarization to P-type polarization. Then the red
illumination light bundle of P-type polarization and the green illumination light
bundle of S-type polarization are directed to an illumination light incident surface
10c of the second PBS prism
10 that faces the second polarization
rotator
11. The red illumination light bundle is passed through a polarizing
reflection surface
10d of the second PBS prism
10, and falls
on the liquid crystal element
22, whereas the green illumination light bundle
is reflected from the polarizing reflection surface
10d, and falls
on the liquid crystal element
24.
The liquid crystal element
22 modulates the red illumination light bundle
into the red optical image, and changes its polarity from P-type polarization to
S-type polarization. Thus, the red optical image is reflected from the polarizing
reflection surface
10d, to exit from the image exit surface
10b
of the second PBS prism
10. The liquid crystal element
24 modulates
the green illumination light bundle into the green optical image, and changes the
green optical image from S-type polarization to P-type polarization. Thus, the
green optical image is transmitted through the polarizing reflection surface
10d,
and exits from the image exit surface
10b of the second PBS prism
10.
The red and green optical images from the image exit surface
10b travel
through the third polarization rotator
12, and fall on the second incident
surface
15d of the recombination prism
15. Also, the third
polarization rotator
12 changes the polarity of the red optical image from
S-type polarization to P-type polarization.
The blue optical image entering through the first incident surface
15c
is reflected from a combining surface
15e of the recombination
prism
15, while the red and green optical images entering through the second
incident surface
15d are transmitted through the combining surface
15e. Thus the three color optical images exit from the exit surface
15b of the recombination prism
15 toward the projection lens
30. The projection lens
30 projects the three color optical images
onto the screen, so a full-color image is displayed on the screen.
In the above embodiment, the optical axis of the projection lens group extends
along a straight-linear line. But the present invention is applicable to a projector
which is provided with a front lens group
45 whose optical axis is refracted,
as shown in FIG. 5. In this liquid crystal projector, a first rear lens group
50
and a second rear lens group
52 are mounted to a mounting frame
55
that is formed vertically to a prism base plate
6a, and the front
lens group
45 and the rear lens groups
50 and
52 constitute
a projection lens.
Although the above embodiment uses two PBS prisms, it is possible to use
three PBS prisms. In that case, a cross dichroic prism is used as a recombination
prism, wherein three of the four side surfaces are incident surfaces. Image exit
surfaces of the three PBS prisms are disposed in opposition to the three incident
surfaces of the recombination prism respectively. The present invention is preferably
applicable to such a liquid crystal projector, in order to prevent deterioration
of the image projected on the screen.
In the above embodiment, the blue illumination light bundle is first separated
through the color separation mirror, and then the red and green illumination light
bundles are separated. However, the sequence of color separation is not limited
to the above embodiment. For example, the red illumination light bundle or the
green illumination light bundle may be separated first.
Although the PBS prisms and the recombination prism are directly fixed to
the prism base plate according to the above embodiment, it is possible to fix them
to a prism base plate through respective base members that are screwed to the prism
base plate.
Thus, the present invention is not to be limited by the above embodiments,
but various modifications will be possible within the scope and sprit of the appended claims.
*
