Optics: image projectors – Temperature control – Liquid coolant
Reexamination Certificate
2000-07-26
2001-10-09
Lester, Evelyn A (Department: 2873)
Optics: image projectors
Temperature control
Liquid coolant
C349S005000, C349S096000, C349S138000, C349S122000, C349S161000, C348S749000, C348S766000, C348S751000
Reexamination Certificate
active
06299313
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection display apparatus such as a projection television apparatus and a projection lens device suitable for use therein, and in particular, relates to those in which an original image displayed upon a liquid crystal panel is expansively projected so that the apparatus as a whole can be made in compactness, with a little distortion in picture, as well as being suitable for improvement of brightness, focus and contrast thereof.
2. Description of Related Art
Accompany with diversity of image sources, projection display apparatuses have been widely spread on market because of the commercial values in light weight, low price and compactness thereof. Among of those, following with a remarkable improvement in definition and vignetting factor in a liquid crystal panel, a set of a projection type image display device, in which the liquid crystal panel is used as an original image source to be projected, begins to be brought on market in recent years. This projection type image display apparatus is so constructed that the original image displayed on the liquid crystal panel is enlarged by a projection lens on a screen with full colors.
As an optical system for the projection type image display apparatus, there are already known two types, in one of which, as is disclosed in
FIG. 19
of Japanese Patent Laying-Open No. Hei 9-96759 (1997), three (3) pieces of the liquid crystal panels are used (three-plate type), and in the other of which, as is disclosed in
FIG. 1
of Japanese Patent Laying-Open No. Hei 4-60538 (1992), a single (1) piece of the liquid crystal panel is used (singular-plate type). However, in those days, in view of being small in the number of parts and of cost reduction thereof, the optical system of the singular-plate type has been extensively developed.
Construction in the optical system of this singular plate type (using a single piece of the liquid crystal panel) will be explained by referring to
FIGS. 22 and 23
. As is shown in
FIG. 22
, a light beam emitting from a white light source
28
of a metal halide lamp (other than that, a xenon lamp or a halogen lamp can be used) is reflected by a reflection mirror
29
so as to be effectively irradiated upon a condenser lens
27
, then obtaining a white light beam being almost in parallel by a collimator lens
26
.
In a front of the collimator lens
26
are positioned three kinds of dichroic mirrors
23
,
24
and
25
. Each of those dichroic mirrors
23
,
24
and
25
has a characteristic of selectively reflecting a light of wavelength of green, red or blue, respectively, while penetrating others therethrough. R, G and B indicate the lights of red color, green color and blue color, which are separated by those dichroic mirrors
23
,
24
and
25
, respectively. In this conventional art, it is so constructed that the blue color light beam and the green color light beam enter into the liquid crystal panel
22
diagonally as a standard of the red color light beam.
On the liquid crystal panel
22
, there are provided pixels corresponding to the three primary colors, i.e., red, green and blue, and each pixel is so set that it can obtain a light transmittance corresponding to the level of luminance signal in a picture signal, respectively. Therefore, the lights of the red, green and blue are modulated meeting with the picture signal level so as to obtain a desired picture on the liquid crystal. This picture which is displayed on the liquid crystal
22
is enlarged and projected on the screen
20
by the projection lens device
21
.
In order to take the picture light emitted from the liquid crystal
22
into the projection lens device
21
effectively, there was proposed an optical system in which a convex lens showing condensing function is provided between the liquid crystal panel
22
and the projection lens device
21
(not shown in FIGS.
22
and
23
).
The white light source
28
generates heat by itself and the liquid crystal panel (including a polarization plate thereof) is heated due to absorption of the incident light thereon, therefore they come to be reasons of causing damages thereon, respectively. Then, for reducing the increase of the temperature of them, a cooling fan (not shown in the figure) is provided to compulsively cool them, so that they can be used within a predetermined range of the temperature.
FIG. 23
shows an another example of the optical system of the conventional singular-plate type (using a single liquid crystal panel). In this, the same reference numerals are attached to the same elements in the optical system shown in
FIG. 22. A
light beam emitting from the white light source
28
of the metal halide lamp (other than that, the xenon lamp or the halogen lamp can be used) is reflected by the reflection mirror
29
so as to be effectively irradiated upon the condenser lens
27
, then obtaining the white light beam being almost in parallel by the collimator lens
32
. Then, by means of a polarization beam splitter
31
(hereinafter, it is abbreviated with “PBS”), a S-polarization light and a P-polarization light are combined to each other. Thereafter, the white light which is converged by the condenser lens
30
is converted into a light which is almost in parallel through the collimator lens
26
to be entered into the three kinds of dichroic mirrors
23
,
24
and
25
in a front thereof. Those dichroic mirrors
23
,
24
and
25
, the liquid crystal panel
22
, the projection lens device
21
and the screen
20
have the same functions as in the conventional example shown in
FIG. 22
, therefore, the detailed explanations of those are omitted here.
On a while, the compulsive cooling of the white light source
28
and the liquid crystal panel (including the polarization plate thereof) is also same to that shown in
FIG. 22
, therefore, the detailed explanation of it is omitted here.
For realizing an image display device of a projection type being compact in size and of a rear type with using the optical system shown in
FIG. 22
or
23
, it is essential to shorten the projection distance (i.e., the distance from the projection lens device to the screen), and a wide-angle projection lens device is necessitated.
At this moment, if an ordinal wide-angle projection lens device is used, a ratio of light amount at a peripheral portion decreases down because of a characteristic in distribution of light by the liquid crystal panel. The reason of this will be given in detail. In the optical system of the singular-plate type (using only one piece of the liquid crystal panel), as shown in
FIG. 22
or
23
, since the dichroic mirrors
23
,
24
and
25
, which are positioned between the liquid crystal panel
22
and the white light source
28
, vary the respective spectrum transmittance and reflectance thereof depending on the incident angles, therefore, the light beam from the white light source
28
comes to be almost in parallel to be radiated upon the liquid crystal panel
22
. Also there was already known an apparatus, in which a micro-lens is provided on a light incident surface of the liquid crystal panel
22
for a purpose of increasing the vignetting factor thereof (hereinafter, an explanation will be given on the liquid crystal panel on which the such micro-lens is provided).
A principle light beam of luminous or light flux incident upon the projection lens device
21
from respective object points on the liquid crystal panel
22
comes to be almost in parallel to an optical axis of the projection lens device due to the reason mentioned in the above, and an expansion angle of it is proportional to an aperture number of the micro-lens. If an ordinal projection lens device of wide-angle is used in such the optical system, the light flux which is incident upon the projection lens device
21
from the periphery of the liquid crystal panel is extremely reduced down, thereby the peripheral portion of the enlarged picture projected upon the screen
20
. Furthermore, for the projection lens device which is
Hirata Koji
Mori Shigeru
Ogura Naoyuki
Otsuka Yasuo
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Lester Evelyn A
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