Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
2000-03-08
2002-06-04
Mahoney, Christopher (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S034000, C353S037000, C349S005000, C349S007000, C349S008000, C359S634000
Reexamination Certificate
active
06398365
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image projection display apparatus in which, from a luminance flux formed as a conglomerate of light of a plurality of wavelength bands, light of mutually different colors are separated out, each chromatic light being modulated so as to project an image onto a large screen.
2. Description of the Related Art
A projection-type image display apparatus has been developed in the past for displaying an image on a large screen, for use in outdoor displays in public places, or administrative displays, or in providing a display for high-resolution images.
Such projection-type display apparatuses can be generally classified as either transmission-type or reflection-type display apparatuses. In either case, light comprised of a conglomerate of a plurality of light wavelength bands is separated into light of mutually different wavelength bands and caused to illuminate an LCD (liquid-crystal display) panel, this incident light being modulated in pixel units according to a picture signal, so as to provide spatial modulation of the projected light.
There is a known LCD panel that makes use of three pixel electrodes corresponding to three primary colors as a unit, these being arranged in a matrix of liquid-crystal display elements in a single LCD panel, in what is known as a single-LCD projection display apparatus. A widely known single-LCD color projection display apparatus uses color-absorbing filters for the three primary colors red, green, and blue, disposed over the surface of pixel electrodes corresponding to these colors.
In an absorption-type color filter, however, although a particular wavelength is efficiently passed, light of other wavelengths is absorbed so that it is not passed. For this reason, in this type of display, there is the problem that light that passes through the color filter and reaches the pixel electrodes is reduced to ⅓ of the intensity of light (white light) that is incident to the absorption-type color filter.
A single-LCD color projection display apparatus to solve this problem was disclosed, for example, in Japanese Patent Application Laid-open Publication H4-60538.
FIG. 1
is a plan view of a color projection display apparatus of the prior art, and
FIG. 2
is a schematic representation of a liquid-crystal display device used therein.
In
FIG. 1
, white light w radiating from a light source
4
enters a collimator lens
5
, and is converted to collimated light flux by the collimator lens
5
. The collimated light flux is divided into light of three wavelength bands by a color separator
50
.
The color separator
50
is made up of an R dichroic mirror
50
R that selectively reflects only light r in the wavelength band of red light, and passes light of a different wavelength band, a G dichroic mirror
50
G that selectively reflects only light g in the wavelength band of green light, and passes light of a different wavelength band, and a B dichroic mirror
50
B that selectively reflects only light b in the wavelength band of blue light, and passes light of a different wavelength band. The dichroic mirrors
50
R,
50
G, and
50
B are disposed at mutually different angles with respect to the axis of the collimated light flux.
That is, whereas the G dichroic mirror
50
G is disposed at an angle of 45° with respect to the optical axis, the R dichroic mirror
50
R closer to the light source is disposed at an angle that is smaller than 45°, and the B dichroic mirror
50
B is disposed at an angle that is greater than 45°. By means of these orientations, the red, green, and blue light beams each exit from the color separator
50
at different angles. For example, the red light r illuminates a micro-lens array
122
at an angle of incidence of +&agr;°, the green light g illuminates a micro lens array
122
at an incidence angle of 0°, and the blue light illuminates the micro-lens array
122
at the incident angle −&agr;°.
The color projection display apparatus has a liquid-crystal display
51
. This liquid-crystal display
51
, as shown in
FIG. 2
, has a microlens array
122
on a light entering side of the liquid crystal display element
123
.
A liquid-crystal display element
123
is made up of glass substrates
125
and
129
, between which are provided a signal electrode
126
, a liquid-crystal layer
127
, and a transparent electrode
128
. The signal electrode
126
is made up of signal electrodes
126
R,
126
G, and
126
B corresponding to the colors red, green, and blue, arranged in a stripe on the glass substrate 125 m above-described and the liquid-crystal layer
127
is provided on top of the signal electrodes. The transparent electrode
128
is provided between the liquid-crystal layer
127
and the glass substrate
129
. It should be noted the alignment layer is not shown in FIG.
2
.
The micro-lens array
122
is adhered to the upper surface of the glass substrate
129
, and is formed by disposing in parallel vertical stripe lenticular lenses
122
e
each having a width that is the same as one group formed by a signal electrodes
126
R,
126
G, and
126
B and corresponding to these colors of light.
The output light from a liquid-crystal display
51
like this is condensed by a condenser lens
54
, and projected via a projection lens
52
in enlarged form as a color image on a screen
53
.
In the above-noted image projection display apparatus of the prior art, because there is a requirement for high accuracy in the assembly angles of the dichroic mirrors
50
R,
50
G, and
50
B, it is necessary to perform fine adjustment of the assembly angle at the time of assembly.
FIG. 3
illustrates a method of adjusting the assembly angles of the dichroic mirrors
50
R,
50
G,and
50
B. This drawing shows the case of adjusting the angle of incidence of the blue light b.
As shown in
FIG. 3
, of the light that enters the B dichroic mirror
50
B, only blue light b is selectively reflected, so that it enters the micro-lens array
122
at point P at an incident angle of −&agr;
1
. One method that can be envisioned of changing the angle of incidence is to rotate the B dichroic mirror
50
B by &Dgr;&thgr; about the center point O, so as to reposition it at an angle shown by
50
B′. By doing this, the angle of incidence with respect to the micro-lens array
122
is corrected from −&agr;
1
to −&agr;
2
.
With the above-noted method, however, although it is possible to correct the angle of incidence, there is an accompanying shift in the center position of incidence from point P to point P′. If this kind of shift in center incidence position occurs and there is not a margin that will allow a shift in the illuminated light flux approximately the same as the surface area of the micro-lens array
122
, there will occur a part of the light that will not enter the micro-lens array
122
, to the extent of the shift that occurs, this causing the problem of a yellow line from which blue is absent at the edge of the projection screen
53
, thereby causing a deterioration in the image quality. This occurs not just for blue light, but for red light as well.
A method that can be envisioned to prevent the occurrence of a shift in the position of incidence of light is to make the illuminated light flux diameter larger. If this is done, however, the efficiency of light usage worsens, and it is not possible to achieve a projection apparatus with high brightness.
With respect to the above problems, there is a method that is envisioned for preventing the occurrence of a shift in the center position of light incidence while adjusting the assembly angles of the dichroic mirrors
50
R,
50
G, and
50
B.
FIG. 4
shows a method of adjusting the angle of incidence of the illuminated light flux without changing the center position of incidence of the illuminated light flux.
In this method, after first translating the B dichroic mirror
50
B rearward along the axis of incidence, the mirror is rotated by an angle of &Dgr;&thgr; about the center O of the dichroic mi
Asakura Tsutou
Koyama Fujiko
Nakagaki Shintaro
Takahashi Ryusaku
Berkowitz Marvin C.
Cruz Magda
Mahoney Christopher
Nath Gary M.
Nath & Associates PLLC
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