Note: Descriptions are shown in the official language in which they were submitted.
CA 02716963 2012-07-05
PROJECTION DISPLAY
This application is a divisional of Canadian Patent Application Serial No.
2,631,144, filed on May 12, 2008 and published December 5, 2008.
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a projection display with a light-amount
control mechanism for adjusting the amount of light applied to a light valve
responsive to
a video signal.
Description of the Background Art
A projection display is apt to have difficulty in ensuring high contrast
because
dark projected images displayed are not sufficiently dark due to leakage of
light from
various optical elements in an optical system such as a guide optical system
and a
projection lens and due to stray light (unnecessary light) caused by the
optical elements. In
particular for image projection on a screen in a dark room, insufficient
darkness of dark
projected images on display gives to a viewer the impression of low contrast.
Especially in
projection displays using liquid crystal light valves, although the liquid
crystal light valves
back transmitted light in response to the polarization property of light,
complete blocking
of transmitted light is difficult and there is also a limit in counteractive
actions taken by
video signal processing so that an improvement in contrast is required.
As a measure to solve this problem, a flat light shielding plate is provided
between first and second lens arrays and is turned in response to a video
signal to control
the amount of light applied to a light valve and thereby to improve the
contrast of a
projected image on a screen or the like (for example, see W02005/026835)
In W02005/026835, in the case where the light shielding plate has at its tip a
rectangular plane in a direction vertical to the light shielding plate, if the
tip of the light
shielding plate is in the vicinity of the first lens array and in a position
of the center of the
CA 02716963 2010-09-29
2
curvature of the second lens array in the turning direction of the light
shielding plate, the
rectangular plane of the light shielding plate is imaged onto a light valve.
This
undesirably causes linear unevenness of illumination on the light valve in a
direction
perpendicular to the turning direction and the optical axis direction.
Besides, it is
difficult to provide satisfactory contrast depending on the shape of the tip
of the light
shielding plate.
SUMMARY OF THE INVENTION
An object of the invention is to provide a projection display that achieves
continuous light amount control with ease and without causing unevenness of
illumination of light applied to a light valve responsive to a video signal,
thereby allowing
constant image display with satisfactory contrast.
A projection display according to the invention includes a light valve; a
light
source generating light applied to the light valve; an integrator lens
provided on an optical
path between the light source and the light valve and making uniform an
illumination
distribution of light applied from the light source to the light valve; and a
light-amount
control mechanism provided on the optical path and including a pair of light
shielding
bodies that turn like a double door in order to adjust the amount of light
applied from the
light source to the light valve. The light shielding bodies are bent into a V
shape in a
direction so as to reduce the amount of light during their turning.
Since the light shielding bodies are bent into a V shape in a direction to
reduce
the amount of light during their turning, continuous light amount control can
be achieved
with ease and without causing unevenness of illumination of light applied to
the light
valve responsive to a video signal. This allows constant image display with
satisfactory
contrast.
CA 02716963 2010-09-29
2a
According to a broad aspect of the present invention there is provided a
projection display comprising, a light valve; a light source generating light
applied to said
light valve; an integrator lens provided on an optical path between said light
source and said
light valve and making uniform an illumination distribution of light applied
from said light
source to said light valve; and a light-amount control mechanism provided on
said optical
path and including a pair of light shielding bodies, turnable around turning
axes that are
orthogonal and symmetrical with respect to an optical axis of said optical
path in order to
adjust the amount of light applied from said light source to said light valve,
said light
shielding bodies having a cut with a curved line at their tips, said cut
including two cuts that
have different areas and are formed in said light shielding bodies to have
point symmetry
with respect to a point on an optical axis when said light shielding bodies
are closed.
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3
These and other objects, features, aspects and advantages of the invention
will
become more apparent from the following detailed description of the invention
when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram of an illumination optical system in a projection
display according to a first preferred embodiment of the invention;
Fig. 2 is a block diagram of a polarization conversion element according to
the
first preferred embodiment of the invention;
Figs. 3A and 3B show examples of the shapes of a turning mechanism
according to the first preferred embodiment of the invention;
Figs. 4A and 4B show the turning of the turning mechanism according to the
first preferred embodiment of the invention;
Fig. 5 shows the relationship between the turning angle and the relative
percentage of the amount of light in the cases where the turning mechanism is
in the
shapes of Figs. 3A and 3B according to the first preferred embodiment of the
invention;
Figs. 6A and 6B show the z-direction position of the tip of the turning
mechanism when the relative percentage of the amount of light is 20% according
to the
first preferred embodiment of the invention;
Fig. 7 shows an illumination distribution of light applied to a light valve
when
the turning mechanism in the shape of Fig. 3B provides complete light blocking
according to the first preferred embodiment of the invention;
Fig. 8 shows the relationship between the turning angle and the relative
percentage of the amount of light in the case where light shielding bodies
have no cut
according to the first preferred embodiment of the invention;
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4
Fig. 9 shows light source images in the vicinity of a second lens array
according
to the first preferred embodiment of the invention;
Fig. 10 shows an example of the shape of the turning mechanism according to
the first preferred embodiment of the invention;
Fig. 11 shows the relationship between the turning angle and the relative
percentage of the amount of light in the case where the turning mechanism is
in the shape
of Fig. 10 according to the first preferred embodiment of the invention;
Fig. 12 shows the path of light with respect to the shape of the turning
mechanism according to the first preferred embodiment of the invention;
Figs. 13A and 13B show the paths of light when the turning mechanism has a
smaller dimension than the lens arrays according to the first preferred
embodiment of the
invention;
Fig. 14 shows the paths of light when reverse ray tracing is performed from
the
center of the light valve according to the first preferred embodiment of the
invention;
Figs. 15A and 15B show the turning position of the turning mechanism when
imaged on the light valve according to the first preferred embodiment of the
invention;
Figs. 16A and 16B show the turning position of the turning mechanism when
imaged on the light valve according to the first preferred embodiment of the
invention;
Figs. 17A and 17B show illumination distributions of light applied to the
light
valve according to the first preferred embodiment of the invention;
Fig. 18 shows an illumination distribution of light applied to the light valve
according to the first preferred embodiment of the invention;
Fig. 19 shows the relative percentage of the amount of light on y axes of
Figs.
17A, 17B, and 18 according to the first preferred embodiment of the invention;
Fig. 20 is a block diagram of an illumination optical system in a projection
CA 02716963 2010-09-29
display according to a second preferred embodiment of the invention;
Figs. 21A and 21B show the turning position of the turning mechanism when
imaged on the light valve according to the second preferred embodiment of the
invention;
Figs. 22A and 22B show the turning position of the turning mechanism when
5 imaged on the light valve according to the second preferred embodiment of
the invention;
Figs. 23A and 23B show illumination distributions of light applied to the
light
valve according to the second preferred embodiment of the invention;
Fig. 24 shows the relative percentage of the amount of light on y axes of
Figs.
23A and 23B according to the second preferred embodiment of the invention;
Figs. 25A and 25B show the shape of the tip of the turning mechanism
according to the second preferred embodiment of the invention;
Fig. 26 is a block diagram of an illumination optical system in a projection
display according to a third preferred embodiment of the invention;
Fig. 27 shows the paths of light incident on the light valve according to the
third preferred embodiment of the invention;
Figs. 28A and 28B show the paths of light passing through the second lens
array and the polarization conversion element according to the third preferred
embodiment of the invention;
Fig. 29 shows the relationship between the contrast and the angle of incidence
of light applied to the light valve according to the third preferred
embodiment of the
invention;
Fig. 30 shows an example of the shape of the turning mechanism according to
the third preferred embodiment of the invention;
Fig. 31 shows the amount of light passing through each cell in the second lens
array 4b according to the third preferred embodiment of the invention;
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Fig. 32 shows the paths of light emitted from a light source 3 according to
the
third preferred embodiment of the invention;
Fig. 33 shows an illumination distribution of light applied to the light valve
according to the third preferred embodiment of the invention;
Fig. 34 shows an example of the shape of the turning mechanism according to
the third preferred embodiment of the invention;
Fig. 35 shows the relationship between the turning angle and the relative
percentage of the amount of light in the case where the turning mechanism is
in the shape
of Fig. 30 according to the third preferred embodiment of the invention;
Fig. 36 shows an example of the shape of the turning mechanism according to
the third preferred embodiment of the invention;
Fig. 37 shows the relationship between the turning angle and the relative
percentage of the amount of light in the case where the turning mechanism is
in the shape
of Fig. 35 according to the third preferred embodiment of the invention; and
Fig. 38 shows an example of the shape of the turning mechanism according to
the third preferred embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the invention are described below with reference to
the drawings.
<First Preferred Embodiment>
Fig. 1 is a block diagram of an illumination optical system 1 in a projection
display according to a first preferred embodiment of the invention. As shown
in Fig. 1,
the illumination optical system 1 includes an integrator lens 4 between a
light source
system 3 and a light valve 2, a polarization conversion element 5, a
condensing lens 6, a
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field lens 7, and a polarizing plate 8. The projection display according to
the first
preferred embodiment of the invention further includes a projection lens (not
shown) for
projecting light emitted from the light valve 2 onto a screen. The light valve
2 is
provided on each of the optical paths of R, G, and B, and the illumination
optical system
1 shown in Fig. I is a representative example of any one of those optical
paths of R, G,
and B.
The light valve 2 according to the preferred embodiments of the invention is a
liquid crystal light valve, but in the case of using lens arrays, it may be
other display
devices such as a digital micro-mirror device (DMD) and a reflection liquid
crystal
display device.
The light source system 3 is configured to apply light to the light valve 2
and
includes a light source 3a and a reflecting mirror 3b that reflects light
emitted from the
light source 3a to irradiate the integrator lens 4. The light source 3a is in
general a
high-pressure mercury lamp, a halogen lamp, or a xenon lamp, but it may be any
other
light-emitting devices such as a light emitting diode (LED), a laser, and an
electrodeless
discharge lamp. The reflecting mirror 3b is formed in an elliptical plane or a
parabolic
plane, but it may be of any shape and any configuration and is not limited to
those
described as long as light can be concentrated on the polarization conversion
element 5.
For example, in order to make incident light on the integrator lens 4
approximately
parallel to an optical axis C, the reflecting mirror 3b should be formed in
the shape of a
parabola; or if the reflecting mirror 3b is formed in the shape of an ellipse,
a concave lens
should be provided between the light source system 3 and the integrator lens 4
(see Fig.
32).
The integrator lens 4 is provided on an optical path between the light source
system 3 and the light valve 2 and is configured to make uniform the
illumination
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distribution of light applied from the light source system 3 to the light
valve 2. The
integrator lens 4 includes a first lens array 4a and a second lens array 4b
spaced apart
from the first lens array 4a. The first lens array 4a and the second lens
array 4b each are
an array of a plurality of convex lenses. The convex lenses in the first lens
array 4a and
the convex lenses in the second lens array 4b correspond to each other and are
located to
face each other.
The polarization conversion element 5 converts light beams incident on the
polarization conversion element 5 into a single type of linearly polarized
light and emits
the linearly polarized light. It is provided with an appropriate space in the
x-axis
direction. Fig. 2 is a block diagram of the polarization conversion element 5
according
to the first preferred embodiment of the invention. As shown in Fig. 2, the
polarization
conversion element 5 includes a plurality of polarization separation films 5a
inclined (e.g.,
45 degrees) toward the direction of the optical axis C (the z direction); a
plurality of
reflection films 5b provided between the polarization separation films 5a and
inclined
(e.g., 45 degrees) toward the direction of the optical axis C (the z
direction); and A/ 2
phase-difference plates 5c provided in a plane of the polarization conversion
element 5 on
the side of the light valve 2 and in positions where light passing through the
polarization
separation films 5a are applied. Light incident on the polarization conversion
element 5
is separated into s-polarized light and p-polarized light by the polarization
separation
films 5a. The p-polarized light is transmitted through the polarization
separation films
5a, is converted into s-polarized light by the A / 2 phase-difference plates
5c, and then is
emitted from the polarization conversion element 5. On the other hand, the s-
polarized
light is reflected off the polarization separation films 5a and off the
reflection films 5b
and then is emitted from the polarization conversion element 5. Accordingly,
the
outgoing beams from the polarization conversion element 5 are almost all s-
polarized
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light.
The light-amount control system 9 (light-amount control mechanism) is
provided on the optical path and includes a turning mechanism 9a which
includes a pair
of light shielding bodies that turn like a double door in order to adjust the
amount of light
applied from the light source system 3 to the light valve 2. The light-amount
control
system 9 includes the turning mechanism 9a provided between the first lens
array 4a and
the second lens array 4b; a signal detector 9b detecting a video signal fed to
the light
valve 2 and calculating, based on the result of detection, the relative
percentage of the
amount of light applied to the light valve 2; and a turning controller 9c
controlling the
turning of the turning mechanism 9a based on the relative percentage of the
amount of
light calculated by the signal detector 9b. As shown in Fig. 3B, the turning
mechanism
9a includes light shielding bodies 9T and 9B that are bent into a V shape in a
direction to
reduce the amount of light (to block the light). The light shielding bodies 9T
and 9B
have at their tips cuts 9g that regulate passage of light. The cuts 9g may be
of any shape
such as a concave curve, a parabola, a semi-ellipse, and a triangle.
Next, description is given on improvement in contrast. When a video signal
represents 100% of the relative percentage of the amount of light, control is
performed
based on 100% of the relative percentage of the amount of light with no light
blocking by
the turning mechanism 9a. For example when a video signal represents 20% of
the
relative percentage of the amount of light, the turning mechanism 9a blocks
the light until
the relative percentage of the amount of light becomes 20%, so that
approximately a
five-fold fine adjustment of the video signal is possible. By lowering the
relative
percentage of the amount of light by light blocking using the turning
mechanism 9a,
darker black can be obtained as compared with the case where a video signal
represents
0% of the relative percentage of the amount of light in which case no light
blocking is
CA 02716963 2010-09-29
provided. In other words, since the transmittance of the light valve 2 is
approximately
constant, reducing the amount of light applied to the light valve 2 using the
turning
mechanism 9a makes it possible to darken a projected image on a screen,
thereby
achieving improvement in contrast.
5 Fig. 4A shows a 15-degree turning of the light shielding bodies 9T and 9B of
Fig. 3A, and Fig. 4B shows a 15-degree turning of the light shielding bodies
9T and 9B of
Fig. 3B. Referring to the amounts of travel of the tips of the light shielding
bodies 9T
and 9B in the z direction, as shown in Figs. 4A and 4B, the amount of travel
Zb in Fig.
4B is smaller than the amount of travel Za in Fig. 4A (Za > Zb), from which it
can be
10 found that the amount of travel of the light shielding bodies 9T and 9B in
the y direction
per turning angle is greater in Fig. 4B. Accordingly, the light shielding
bodies 9T and
9B in the shape as shown in Fig. 4B can provide illumination with 100% of the
relative
percentage of the amount of light at a smaller turning angle.
Fig. 5 shows the relationship between the turning angle and the relative
percentage of the amount of light in the cases where the turning mechanism 9a
is in the
shapes of Figs. 3A and 3B. The angles yT and yB in Fig. 3B shall be 20 degrees
and
the turning mechanism 9a in both Figs. 3A and 3B turns two degrees at a time.
The
turning angle of 0 degree refers to the condition that the light shielding
bodies 9T and 9B
are in completely closed positions, i.e., the light shielding bodies 9T and 9B
are in the
positions indicated by 41a in Fig. 4A and 41b in Fig. 4B, respectively. The
curve 50
shows the simulation result for the turning mechanism 9a in the shape of Fig.
3A, and the
curve 51 shows the simulation result for the turning mechanism 9a in the shape
of Fig. 3B.
As shown in Fig. 5, the curve 51 starts to rise earlier than the curve 50 with
a low relative
percentage of the amount of light and reaches 100% of the relative percentage
of the
amount of light at the turning angle of approximately 75 degrees. Because of
its
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narrower operating angle range, the shape of Fig. 3B allows highly responsive
control as
compared with the shape of Fig. 3A. It can also be seen from the curves 50 and
51 that,
except where the relative percentage of the amount of light is low, the rate
of change in
the relative percentage of the amount of light with respect to the turning
angle is
approximately the same. From this, as will be described later with Fig. 14, in
the case of
a low relative percentage of the amount of light, unevenness of illumination
can be
reduced by bending the end portions of the light shielding bodies 9T and 9B
into a V
shape in the direction of the radius of turning. It can also be seen from Fig.
5 that the
light shielding bodies 9T and 9B each having the two cuts 9g at the tip as
shown in Figs.
3A and 3B allow continuous light amount control. While, in this preferred
embodiment
of the invention, the angles yT and yB are set to 20 degrees, they may be of
any
degree, and the same effect can be achieved without satisfying yT = yB . The
relationship between the turning angle of the turning mechanism 9a and the
relative
percentage of the amount of light on the light valve 2, shown in the preferred
embodiment
of the invention, is for the case where input is a signal representing 100% of
the relative
percentage of the amount of light, so that only the property of the turning
mechanism 9a
is represented.
Figs. 6A and 6B show the positions of the tips of the light shielding bodies
9T
and 9B in the z direction when the relative percentage of the amount of light
is 20% in
Fig. 5. As shown in Fig. 6A, the turning angle in the case of the shape of
Fig. 3A is
approximately 24 degrees, i.e., al 24, while the turning angle in the case of
the shape
of Fig. 3B is approximately 34 degrees, i.e., a2 34. The angle a3 in Fig. 6B
is
equal to yT and shall be 20 degrees. Let dl be the length of the light
shielding bodies
9T and 9B of Fig. 6A; d2 be the length of the light shielding bodies 9T and 9B
of Fig. 6B
from the turning axis to their bend; and d3 be the length of the light
shielding bodies 9T
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and 9B of Fig. 6B from their bends to tips. Based on the conditions described
above, the
positions of the tips of the light shielding bodies 9T and 9B in the shape of
Fig. 3B in the
z direction can be calculated.
From Figs. 6A and 6B, the amounts of travel Zc and Zd of the light shielding
bodies 9T and 9B in the z direction can be expressed by the following
equations (1) and
(2), respectively.
Zc = dl x sin(al)
d1x0.41 (1)
Zd = d2 x sin(a2) + d3 x sin(a2 - a3) (2)
;zz d2 x 0.56 + d3 x 0.24
From Fig. 4B, dl can be expressed by the following equation (3).
dl = d2 x cos(a3) + d3
%t; d2x0.94+d3
(3)
Thus, Zc can be expressed by the following equation (4), so that the condition
Zc > Zd can be satisfied by equation (5).
Zc d2 x 0.39 + d3 x 0.41 ...(4)
1 > d2/d3 ...(5)
Accordingly, by making the length d2 shorter than the length d3, the shape of
Fig. 3B can reduce unevenness of illumination as compared with the shape of
Fig. 3A.
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Since the distance of travel of the tips of the light shielding bodies 9T and
9B is not the
only cause of unevenness of illumination, the condition of equation (5) should
preferably
be satisfied but it is not a necessity.
Fig. 7 shows the illumination distribution of light applied to the light valve
2 when
the shape of Fig. 3B provides complete light blocking. In the case of complete
light
blocking, unevenness of illumination does not occur because light incident on
the second
lens array 4b is uniformly superimposed and applied onto the generally whole
(area 7a) and
around both x-direction end portions (areas 7b) of the light valve 2. The area
7a shows the
illumination distribution of light applied from cells to the light valve 2
(area 30 in Fig. 3B)
when the opening of the cells in the second lens array 4b is approximately
full open, and the
areas 7b show the illumination distribution of light applied from cells to the
light valve 2
(areas 31 in Fig. 3B) when the opening of the cells in the second lens array
4b is
approximately half opened.
Fig. 8 shows the relationship between the turning angle and the relative
percentage
of the amount of light in the case where the light shielding bodies 9T and 9B
with no bend
have no cut. Simulation is conducted for every two degrees of the turning
angle. It can be
seen from the curve 80 that the rate of change in the relative percentage of
the amount of
light with respect to the turning angle is not continuous, and that the curve
has four flat parts
(8a, 8b, 8c, and 8d).
Fig. 9 shows light source images in the vicinity of the second lens array 4b.
Fig. 9
shows the images with 256 levels of gray scale. In Fig. 9, reference
characters 91 to 94
designate a dark part between the light source images in the +y direction. The
four flat parts
8a, 8b, 8c, and 8d in Fig. 8 correspond to the four dark parts 91 , 92, 93 ,
and 94 between the
light source images in Fig. 9, which confirms that the dark parts between the
light source
images are the result of influence of the flat parts in Fig. 8. Thus, in order
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to provide a continuous change in the amount of light, it is necessary to
simultaneously
block light in both dark and light parts between the light source images.
Since the light
shielding bodies 9T and 9B with the cuts as shown in Figs. 3A and 3B allow a
continuous
change in the amount of light as shown in Fig. 5, simultaneous light blocking
in both dark
and light parts between the light source images is made possible by forming
cuts in the
light shielding bodies 9T and 9B.
Fig. 10 shows an example of the shape of the light shielding bodies 9T and 9B,
in which the light shielding bodies 9T and 9B each have a single cut 9g to
have symmetry
with respect to the optical axis C. When such a shape provides complete light
blocking,
an approximately uniform illumination distribution of light is given on the
light valve 2.
Fig. 11 shows the relationship between the turning angle and the relative
percentage of the amount of light in the case where the light shielding bodies
9T and 9B
are in the shape of Fig. 10. In Fig. 10, the angles yT and yB of the light
shielding
bodies 9T and 9B shall be 20 degrees. The curve 110 shows the simulation
result for the
turning mechanism 9a in the shape of Fig. 10. The curve 80 shows the
simulation result
shown in Fig. 8 for the turning mechanism 9a with no cut, for comparison of
the effect
between the presence and absence of the cuts 9g. For ease of comparison, the
curve 80
is shifted to overlap with the curve 110. It can be seen from Fig. 11 that
even the light
shielding bodies 9T and 9B with only one cut 9g can provide more continuous
light
amount control than the light shielding bodies 9T and 9B with no cut. In other
words,
forming at least one cut 9g in the light shielding bodies 9T and 9B is
effective at
achieving continuous light amount control. However, it can be seen from the
curve 51
in Fig. 5 and the curve 110 in Fig. 11 that the light shielding plates 9T and
9B with two
cuts produce a smoother change in the amount of light than those with only one
cut.
From this, it is more preferable to provide a plurality of cuts for smoother
light amount
CA 02716963 2010-09-29
control.
Fig. 12 shows the paths of light when the light shielding bodies 9T and 9B
turn
toward the first lens array 4a at the time of light blocking, and especially
shows the paths
of light passing through the lens cell that is farthest in the +y direction in
the first lens
5 array 4a. Although only the light shielding body 9T is described here, the
same applies
to the light shielding body 9B. Reference character 120a designates the path
of light
passing through the +y side of the center of the lens cell; reference
character 120b
designates the path of light passing through the center of the lens cell; and
reference
character 120c designates the path of light passing through the -y side of the
center of the
10 lens cell. As shown in Fig. 12, when the light shielding body 9T is bent at
a small angle
or bent in a position that is far from the turning axis, unnecessary light
reflected off the
light shielding body 9T passes through the second lens array 4b and, after
multipath
reflection inside a housing (not shown) of the illumination optical system 1,
it may appear
on a screen. From this, the light shielding bodies 9T and 9B turning toward
the second
15 lens array 4b at the time of light blocking are more preferable than the
light shielding
bodies 9T and 9B that open and close in the direction as shown in Fig. 12.
Fig. 13A shows the paths of light when the light shielding bodies 9T and 9B
are
smaller in x- and y-direction dimensions than the first lens array 4a and the
second lens
array 4b. Fig. 13B shows a comparison of the x- and y-direction dimensions
between
the light shielding bodies 9T and 9B and the second lens array 4b, from which
it can be
seen that the light shielding bodies 9T and 9B have smaller x- and y-direction
dimensions
than the second lens array 4b. Although only the light shielding body 9T is
described
here, the same applies to the light shielding body 9B. Reference character
130a
designates the path of light passing through the center of the lens cell that
is the fifth one
in the +y direction from the optical axis C in the first lens array 4a; and
reference
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character 130b designates the path of light passing through the +x side of the
center of the
lens cell that is the second one in the +y direction and the third one in the
+x direction
from the optical axis C in the first lens array 4a. It can be seen from Fig.
13A that light
passing through those cells which are on the +y side of the turning axes of
the light
shielding bodies 9T and 9B in the first lens array 4a passes through the +y
side without
entering the light shielding bodies 9T and 9B. Thus, in order to control the
amount of
light emitted from the first lens array 4a using the light shielding bodies 9T
and 9B, the
light shielding bodies 9T and 9B should preferably have larger x- and y-
direction
dimensions than the first lens array 4a and the second lens array 4b. In the
case where
the second lens array 4b is larger in dimension than the first lens array 4a,
although it is
preferable that the light shielding bodies 9T and 9B should have larger x- and
y-direction
dimensions than the second lens array 4b, it is also possible to block
unnecessary light
passing through the second lens array 4b by providing a light shielding plate
between the
second lens array 4b and the polarization conversion element 5. From this, it
can be said
that the light shielding bodies 9T and 9B are not necessarily larger in x- and
y-direction
dimensions than the first lens array 4a and the second lens array 4b.
Fig. 14 shows the paths of light calculated by reverse ray tracing from the
center of the light valve 2. Reference character 140 designates the paths of
light; and
reference character 141 designates the area where the paths of light indicated
by 140 are
concentrated. Since it can be seen from Fig. 14 that an image in the vicinity
of the first
lens array 4a is formed on the light valve 2, the light valve 2 and the
neighborhood of the
light incident surface of the first lens array 4a are in conjugation. Thus,
when the tips of
the light shielding bodies 9T and 9B are in the vicinity of the area 141, the
tips of the
light shielding bodies 9T and 9B are imaged onto the light valve 2, which
undesirably
causes linear unevenness of illumination in the x direction in the vicinity of
the center on
CA 02716963 2010-09-29
17
the light valve 2. Therefore, it is preferable that the tips of the light
shielding bodies 9T
and 9B are brought close to the second lens array 4b, i.e., the turning axes
are in the
vicinity of the second lens array 4b.
Focusing on the tips of the light shielding bodies 9T and 9B, since the light
shielding bodies 9T and 9B bent into a V shape in a direction to reduce the
amount of
light (to block the light) are imaged with a narrower width in the y direction
than the light
shielding bodies 9T and 9B with no bend (cf. dyl in Fig. 15B and dy2 in Fig.
16B), they
can reduce unevenness of illumination on the light valve 2. Therefore, it can
be said that
unevenness of illumination on the light valve 2 can be reduced by bending the
light
shielding bodies 9T and 9B into a V shape in a direction to reduce the amount
of light (to
block the light).
Figs. 15A and 15B and Figs. 16A and 16B show the turning positions of the
light shielding bodies 9T and 9B in the shapes of Figs. 3A and 3B when the
tips of the
light shielding bodies 9T and 9B are imaged on the light valve 2. The
condition that an
image is formed on the light valve 2 is that the tips of the light shielding
bodies 9T and
9B are in the vicinity of the first lens array 4a and in positions that are
equivalent to the
centers of the curvatures of the lens cells that are the second ones in the +y
and -y
directions from the optical axis C in the second lens array 4b. Reference
characters 150,
151, 160, and 161 designate the axis passing through the center of the
curvature of the
lens cell that is the second one in the + y or -y direction from the optical
axis C in the
second lens array 4b; and reference characters 152 and 162 designate the tip
of the light
shielding body 9T.
Now we describe the reason why the tips of the light shielding bodies 9T and
9B should be in the positions equivalent to the centers of the curvatures of
the lens cells
that are the second ones in the +y and -y directions from the optical axis C
in the second
CA 02716963 2010-09-29
18
lens array 4b. First of all, in positions that are equivalent to the centers
of the curvatures
of the lens cells that are the first ones in the +y and -y directions from the
optical axis C
in the second lens array 4b, it is difficult to check unevenness of
illumination on the light
valve 2 due to low illumination. In positions that are equivalent to the
centers of the
curvatures of the lens cells that are the third ones in the +y and -y
directions from the
optical axis in the second lens array 4b, light with illumination uniformity
is
superimposed on the light valve 2 from the lens cells that are the first ones
in the +y and
-y directions from the optical axis C and from the lens cells that are the
second ones in
the +y and -y directions from the optical axis C, which relatively reduces
unevenness of
illumination on the light valve 2 and thus makes it difficult to check
unevenness of
illumination caused by the lens cells that are the third ones in the +y and -y
directions
from the optical axis C. Accordingly, as a condition that allows the easy
checking of
imaging of the tips of the light shielding bodies 9T and 9B on the light valve
2, the tips of
the light shielding bodies 9T and 9B should be in the positions equivalent to
the centers
of the curvatures of the lens cells that are the second ones in the +y and -y
directions
from the optical axis C in the second lens array 4b.
Figs. 17A shows the simulation result of the illumination distribution on the
light valve 2 when the light shielding bodies 9T and 9B have not such a cut 9g
as shown
in Fig. 3A and are in the condition of Figs. 15A and 15B; and Fig. 17B shows
the
simulation result of the illumination distribution on the light valve 2 when
the light
shielding bodies 9T and 9B have no such a cut 9g as shown in Fig. 3B and are
in the
condition of Figs. 16A and 16B. In Figs. 17A and 17B, reference characters
170a and
170b designate the area with low illumination; and reference characters 171a
and 171b
designate the y axis passing through the center of the light valve 2. The
comparison of
the areas 170a and 170b shows that the area 170b has higher illumination
uniformity than
CA 02716963 2010-09-29
19
the area 170a. This is because there is the inequality relation dyl > dy2
between the
width dyl of Fig. 15B and the width dy2 of Fig. 16B. Accordingly, unevenness
of
illumination on the light valve 2 can be reduced by bending the light
shielding bodies 9T
and 9B into a V shape in a direction to reduce the amount of light (to block
the light).
From this, it can be said that, without satisfying the aforementioned
condition of equation
(5), the light shielding bodies 9T and 9B with bends can reduce unevenness of
illumination.
Fig. 18 shows the simulation result of the illumination distribution on the
light
valve 2 when the light shielding bodies 9T and 9B are in the shape of Fig. 3B
and in the
condition of Figs. 16A and 16B. As shown in Fig. 18, there is little area with
low
illumination in the x direction from the center of the light valve 2.
Reference character
180 designates the area with low illumination in y direction extending from
the center of
the light valve 2; and reference character 181 designates the y axis passing
through the
center of the light valve 2. Although there is only some slight unevenness of
illumination in the area 180 because of the cuts 9g in the light shielding
bodies 9T and 9B
forming the light gathering places in the second lens array 4b, this is not a
problem
because the whole illumination distribution of the light valve 2 is
approximately uniform.
Accordingly, superimposition of the tips imaged on the light valve 2 can be
reduced by
bending the light shielding bodies 9T and 9B into a V shape in a direction to
reduce the
amount of light (to block the light); by forming at least one cut at the tips
of the light
shielding bodies 9T and 9B; and further by reducing flat parts of those tips
other than the
cuts. This results in a considerable reduction of unevenness of illumination.
Fig. 19 shows the relative percentage of the amount of light in the y
direction
on the y axes 171a, 171b, and 181 shown in Figs. 17A and 17B and Fig. 18,
respectively.
The horizontal axis corresponds to the vertical axis on the light valve 2
shown in Fig. 18.
CA 02716963 2010-09-29
In Fig, 19, reference character 190 designates the relative percentage of the
amount of
light on the y axis 171 a; reference character 191 designates the relative
percentage of the
amount of light on the y axis 171b; and reference character 192 designates the
relative
percentage of the amount of light on the y axis 181. Referring to Fig. 19,
comparison of
5 the values of the relative percentage of the amount of light at 0.50Y, which
is the
y-direction center of the light valve 2, yields the inequality 190<191<192 and
shows that
unevenness of illumination decreases in the order of 190, 191, and 192. This
indicates
that unevenness of illumination can be reduced by forming the light shielding
bodies 9T
and 9B with V-shaped bends in a direction to reduce the amount of light (to
block the
10 light) and with cuts at the tips.
While this preferred embodiment has described the case where yT = a2 = a3
in Fig. 6B when the light shielding bodies 9T and 9B are in the position 41 b
shown in Fig.
4B, the width dy2 in Fig. 16B can further be reduced in the case where a3 > a2
= yT, in
which case unevenness of illumination can further be reduced than in the case
of the
15 shape of Fig. 4B. Further, while the light shielding bodies 9T and 9B each
have only
one bend, they may have two bends if the width dy2 in Fig. 16B can further be
reduced.
By so doing, unevenness of illumination can further be reduced. While the
light
shielding bodies 9T and 9B in Fig. 3B are bent in the vicinity of the lens
cell that is the
second one in the y direction from the optical axis C as a center in the
second lens array
20 4b, they may be bent in any position.
From the above description, it is clear that continuous light amount control
without causing unevenness of illumination on the light valve 2 can be
achieved by
forming the light shielding bodies 9T and 9B in the turning mechanism 9a with
a
V-shaped bend in a direction to reduce the amount of light (to block the
light) and with at
least one cut at their tips.
CA 02716963 2010-09-29
21
<Second Preferred Embodiment>
Fig. 20 is a block diagram of an illumination optical system lb in a
projection
display according to a second preferred embodiment of the invention. The
second
preferred embodiment of the invention is characterized in that the light
shielding bodies
9T and 9B in the turning mechanism 9a have a sharp edged tip. The other parts
of the
configuration and the operation are identical to those described in the first
preferred
embodiment and thus not described here.
Figs. 21A and 21B are the same drawings as Figs. 15A and 15B; and Figs. 22A
and 22B are similar to Figs. 15A and 15B in the positions of the light
shielding bodies 9T
and 9B. Reference characters 210, 211, 220, and 221 designate the axis passing
through
the center of the curvature of a lens cell that is the second one in the +y or
-y direction
from the optical axis C in the second lens array 4b. As shown in Figs. 22A and
22B, the
light shielding bodies 9T and 9B on the optical axis C side of the axis 220
have a sharp
edged tip. By so doing, the widths of the tips are reduced by dy. The width t
of the
light shielding bodies 9T and 9B is in general approximately 0.5 mm in
consideration of
the intensity of the light shielding bodies 9T and 9B with respect to the
turning of the
turning mechanism 9a. Reference characters 212 and 222 designate the tip of
the light
shielding body 9T.
Fig. 23A shows the simulation result of the illumination distribution on the
light valve 2 when the light shielding bodies 9T and 9B have no such a cut 9g
as shown
in Fig. 3A and are in the condition of Figs. 21A and 21B; and Fig. 23B shows
the
simulation result of the illumination distribution on the light valve 2 when
the light
shielding bodies 9T and 9B have no such a cut 9g as shown in Fig. 3A and are
in the
condition of Figs. 22A and 22B. It is assumed that t = 0.55 mm. In Figs. 23A
and 23B,
reference characters 230 and 230b designate the area with low illumination;
and reference
CA 02716963 2010-09-29
22
characters 23la and 231b designate the y axis passing through the center of
the light
valve 2. Comparison of the areas 230a and 230b shows that unevenness of
illumination
in the area 230b is considerably improved. Accordingly, as shown in Figs. 22A
and 22B,
unevenness of illumination can considerably be reduced by sharply edging the
tips of the
light shielding bodies 9T and 9B on the optical axis C side of the axes
passing through
the centers of the curvatures of the lens cells that are the second ones in
the +y and -y
directions from the optical axis C in the second lens array 4b.
Fig. 24 shows the relative percentage of the amount of light in the y
direction
on the y axes 231a and 231b shown in Figs. 23A and 23B, respectively. In Fig.
24,
reference character 240 designates the relative percentage of the amount of
light on the y
axis 231 a; and reference character 241 designates the relative percentage of
the amount of
light on the y axis 231 b. Referring to Fig. 24, comparison of the values of
the relative
percentage of the amount of light at 0.50Y, which is the y-direction center of
the light
valve 2, shows that the relative percentage indicated by 241 is higher than
the relative
percentage indicated by 240, i.e., unevenness of illumination is considerably
reduced.
This indicates that unevenness of illumination can considerably be reduced by
sharply
edging the tips of the light shielding bodies 9T and 9B on the optical axis C
side of the
axes passing through the centers of the curvatures of the lens cells that are
the second
ones in the +y and -y directions from the optical axis C in the second lens
array 4b.
Figs. 25A and 25B shows the shape of the tips of the light shielding bodies 9T
and 9B. Reference characters 250 and 251 designate the axis passing through
the center
of the curvature of a lens cell that are the second one in the +y or -y
direction from the
optical axis C in the second lens array 4b. It can be seen from Figs. 25A and
25B that
the angles at the tips of the light shielding bodies 9T and 9B should
preferably be smaller
than Q .
CA 02716963 2010-09-29
23
From the above description, it is clear that continuous light amount control
without causing unevenness of illumination on the light valve 2 can be
achieved by
forming at least one cut at the tips of the light shielding bodies 9T and 9B
and further by
sharply edging the tips of the light shielding bodies 9T and 9B.
<Third Preferred Embodiment>
Fig. 26 is a block diagram of an illumination optical system lc in a
projection
display according to a third preferred embodiment of the invention. The third
preferred
embodiment of the invention is characterized in that the light shielding
bodies 9T and 9B
with small opening areas at their tips can achieve sufficiently high contrast
without
causing unevenness of illumination on the light valve 2. The other parts of
the
configuration and the operation are identical to those described in the first
preferred
embodiment and thus not described here.
Light 270 emitted from the second lens array 4b is incident on the light valve
2
at a great incident angle. At this time, since the contrast decreases with
increasing
incident angle of light on the light valve 2 due to the property of light
valves (see Fig. 29),
the light shielding bodies 9T and 9B should preferably be configured to block
light
incident at great incident angles on the light valve 2, i.e., to block
incident light in the x
direction.
Fig. 28A shows an example of the xy plane of the second lens array 4b and the
polarization conversion element 5, in which the right hand part (a) shows a
front view and
the left hand part (b) shows a side view. Fig. 28B shows a detailed
representation of Fig.
2. Also, Fig. 28B shows the paths of light incident on the second lens array
4b. The
dotted line part shows the polarization conversion element 5, and the hatched
parts show
the A/2 phase-difference plates 5c. In general, polarization conversion is
performed
with efficiency by concentrating light only in the areas of the 2 / 2 phase-
difference
CA 02716963 2010-09-29
24
plates 5c. Thus, light beams 270, 271, 272, 273, 274, and 275 are
polarization-converted light beams. Referring to Fig. 28B, out of linearly p-
and
s-polarized incident light, p-polarized light incident on the polarization
conversion
element 5 is converted into s-polarized light by the 2 / 2 phase-difference
plates 5c and
is thus emitted from the x-direction position of the polarization conversion
element 5 that
is equivalent to the position of incidence; however, it is emitted to the
position that is a
distance dx (the distance between 275a and 275b) away from the optical axis C
as
compared with s-polarized light. Therefore, blocking the incident light on the
x-direction side of the optical axis C becomes essential to the improvement in
contrast.
That is, the light beams 270 and 275 have an influence on the contrast. In
other words,
the application of light beams to positions that are close to the optical axis
C in the x
direction is the condition for improvement in contrast.
Fig. 30 shows the shapes of the light shielding bodies 9T and 9B. The light
shielding bodies 9T and 9B have two cuts 9g and 9h with different areas at
their tips.
The cuts 9g have a smaller opening area than the cuts 9h. The cuts 9g and 9h
are formed
in the light shielding bodies 9T and 9B to have point symmetry with respect to
a point on
the optical axis C when the light shielding bodies 9T and 9B are closed.
Fig. 31 numerically shows the amount of light passing through each cell in the
second lens array 4b, which amount is calculated by simulation. The shapes of
the light
shielding bodies 9T and 9B as shown in Fig. 30 can reduce a difference in
contrast in the
x direction. Fig. 31 representatively shows the upper right quadrant of the
second lens
array 4b since the second lens array 4b shows a symmetry both between upper
and lower
halves and between right and left halves.
Fig. 32 shows the simulation result for the case where light emitted from the
light source 3a is reflected off the reflecting mirror 3b. The reflecting
mirror 3b shall be
CA 02716963 2010-09-29
in the shape of an ellipse, and light emitted from the light source system 3
shall be made
parallel by a concave lens 310. In general, there is a valve of the light
source in the
vicinity of the optical axis C, and reference character 311 designates an
opening of such a
valve.
5 Since the opening 311 is in such a shape as shown in Fig. 311, the cell that
is in
the fourth column VI and the fifth row HI (V 1 H 1) of the second lens array
4b shown in
Fig. 31 receives only a small amount of light emitted from the light source
system 3.
When the light shielding bodies 9T and 9B in the shape of Fig. 30 provide
complete light
blocking, the cuts 9g irradiate both end portions of the light valve 2 in the
x direction, and
10 the cuts 9h irradiate a central portion of the light valve 2. Therefore, a
uniform
illumination distribution can be obtained by equalizing and superimposing the
relative
amounts of light applied to the both end portions in the x direction and the
central portion
of the light valve 2. For example when the cuts 9g and 9h are of the same
shape, as
shown in Fig. 33, unevenness of illumination occurs due to low illumination in
the central
15 portion of the light valve 2. From this, the cuts 9h need to have a larger
opening area
than the cuts 9g. Referring to Fig. 33, light emitted from the cuts 9g
irradiate an area
32b on the light valve 2, and light emitted from the cuts 9h irradiate an area
32a on the
light valve 2.
Fig. 34 shows the shapes of the light shielding bodies 9T and 9B that are
20 determined in consideration of contrast. A cut 9i is formed in the cell (V
I H1) to form a
right-angled triangular opening, so that a uniform illumination distribution
is provided on
the light valve 2. However, Fig. 31 shows that only a small amount of light
passes
through the cell (V 1 H 1). Thus in the case where a 100 percent video signal
is displayed
on the screen, the contrast of an image projected on the screen is
unsatisfactory due to a
25 small amount of light.
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26
From the above, generally, in order to prevent the occurrence of unevenness of
illumination on the light valve 2, approximately eight cells are necessary as
an opening.
However, by consideration of the shape and the relative percentage of the
amount of light
incident on the opening, illumination uniformity on the light valve 2 can be
achieved with
approximately four cells. Specifically, the vertex of each of the cuts 9h with
a larger
opening area in the x direction is made to be equivalent to the x-direction
center of the
cell (in the fourth column V 1 and the fifth row H 1) that is closest to the
optical axis C,
and the vertex of each of the cuts 9g with a smaller opening area is made to
be equivalent
to a junction between the cell (in the fourth column VI and the fifth row HI)
that is
closest to the optical axis C and the adjacent cell (in the fifth column V2
and the fifth row
H1) on the opposite side of the optical axis C. By so doing, improvement in
contrast
can be achieved with approximately four cells, without causing unevenness of
illumination on the light valve 2.
Fig. 35 shows the relationship between the turning angle and the relative
percentage of the amount of light in the case where the light shielding bodies
9T and 9B
are in the shape of Fig. 30. The curve 331 shows the simulation result for the
turning
mechanism 9a with the shape of Fig. 30; and the curve 330 shows the simulation
result of
Fig. 8 for the turning mechanism 9a with no cut. For ease of comparison, the
curve 330
is shifted to overlap with the curve 331. It can be seen from Fig. 35 that the
light
shielding bodies 9T and 9B in the shape as shown in Fig. 30 allows almost
continuous
light amount control on the light valve 2 with respect to the turning angle.
Accordingly,
it can be said that the light shielding bodies 9T and 9B with the tips as
shown in Fig. 30
can achieve continuous light amount control without causing unevenness of
illumination
on the light valve 2, thereby improving the contrast.
While this preferred embodiment illustrates an example of the cuts in the
shape
CA 02716963 2010-09-29
27
of an ellipse, the same effect can be achieved with cuts in the shape of a
triangle as long
as the same consideration as described in this preferred embodiment is given
on the
opening area and the positions of the vertices.
Fig. 36 shows the shapes of the light shielding bodies 9T and 9B. The light
shielding bodies 9T and 9B have triangular cuts formed at their tips. The
shape of Fig.
36 allows fine light amount control when the relative percentage of the amount
of light is
30% or smaller. Providing the cuts 9g on both sides of the second lens array
in the x
direction allows fine control of a portion with a low relative percentage of
the amount of
light. Although only a small number of cells in the second lens array 4b are
used for
complete light blocking, the triangular shape as shown in Fig. 36 provides a
uniform
illumination distribution on the light valve 2 by superimposition of
irradiated areas,
thereby preventing the occurrence of unevenness of illumination.
Fig. 37 shows the relationship between the turning angle and the relative
percentage of the amount of light in the case where the light shielding bodies
9T and 9B
are in the shape of Fig. 36. The curve 351 shows the simulation result for the
turning
mechanism 9a in the shape of Fig. 36, and the curve 350 shows the simulation
result for
the turning mechanism in the shape shown in Fig. 38. For ease of comparison,
the curve
350 is shifted to overlap with the curve 351. It canbe seen from Fig. 37 that,
in the case
of the light shielding bodies 9T and 9B of the shape of Fig. 36, the curve has
a gentle
inclination around the range between 10% and 30%. The reason of such a gentle
curve
is that, in the case of a small turning angle of the turning mechanism 9a,
light blocking in
the lens cell in the fourth column V1 and the fifth row HI shown in Fig. 31
reduces the
rate of change of illumination. In the range with a low relative percentage of
the amount
of light, namely between 10% and 30%, the sensitivity of human eyes to the
change in the
relative percentage of the amount of light is especially high, so that fine
light amount
CA 02716963 2010-09-29
28
control using the turning mechanism 9a becomes important. The shape as shown
in Fig.
36 allows fine light amount control when the relative percentage of the amount
of light is
30% or smaller.
From the above description, the light shielding bodies 9T and 9B with the
shape
as shown in Fig. 36 allow fine light amount control with a low relative
percentage of the
amount of light.
While the invention has been shown and described in detail, the foregoing
description is in all aspects illustrative and not restrictive. It is
therefore understood that
numerous modifications and variations can be devised without departing from
the scope
of the invention.
