Liquid crystal cells – elements and systems – Particular structure – Holder – support – frame – or housing
Reexamination Certificate
2001-02-02
2003-10-14
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Holder, support, frame, or housing
C349S005000, C349S008000, C353S031000, C353S034000
Reexamination Certificate
active
06633349
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a projection type liquid crystal display unit, and more particularly to an improvement in a frame supporting a liquid crystal light bulb therewith for prevention reflection of a light therefrom.
2. Description of the Related Art
Recently, various projection type liquid crystal display units such as a liquid crystal projector have been developed. A projection type liquid crystal display unit is grouped into a light-transmission type and a light-reflection type, and further grouped into a single plate type and a three-plates type in dependence on the number of liquid crystal light bulbs to be used therein.
Hereinbelow is explained a light-transmission and single plate type liquid crystal display unit with reference to FIG.
2
.
The illustrated liquid crystal display unit is comprised of a light source
1
, a converging lens
2
, a first polarizing plate
3
a
, a liquid crystal light bulb
4
, a second polarizing plate
3
b
, a projection lens
5
, and a screen
6
.
In operation, a natural light emitted from the light source
1
passes through the converging lens
2
, and is converted into a linearly polarized light by the first polarizing plate
3
a
. The thus converted linearly polarized light enters the liquid crystal light bulb
4
, and is modulated in the liquid crystal light bulb
4
as variation in polarization in accordance with an image signal. The light leaving the liquid crystal light bulb
4
passes through the second polarizing plate
3
b
, and is projected onto the screen in an increased size by the projection lens
5
.
Hereinbelow is explained a light-transmission and three-plate type liquid crystal display unit with reference to FIG.
6
.
The illustrated liquid crystal display unit is comprised of a light source
1
, an optical system
21
for converting a light into a polarized light, two dichroic mirrors
22
, four all-reflection mirrors
23
, converging lenses
24
, first polarizing plates
25
a
, second polarizing plates
25
b
, light liquid crystal bulbs
26
, a dichroic prism
27
, a projection lens
28
, and a screen
29
.
In operation, natural lights emitted from the light source
1
are converted into linearly polarized lights having the same forwarding direction and polarizing direction, by the optical system
21
. The thus converted linearly polarized lights are separated into blue, green and red lights by an optical separation system comprised of the two dichroic mirrors
22
and the all-reflection mirrors
23
. The blue, green and red lights pass through the associated converging lenses
24
and first polarizing plates
25
a
, and then, illuminate the associated liquid crystal light bulbs
26
.
The linearly polarized lights entering the liquid crystal light bulbs
26
are modulated in the liquid crystal light bulbs
26
as variation in polarization in accordance with an image signal. The lights leaving the liquid crystal light bulbs
26
enter the associated second polarizing plates
25
b
. A portion of the lights displaying black is absorbed into the second polarizing plates
25
b
, whereas a portion of the lights displaying white passes through the second polarizing plates
25
b.
After passing through the second polarizing plates
25
b
, optical images formed on the liquid crystal light bulbs
26
are combined into a single optical image at the dichroic prism
27
. The thus produced optical image is projected onto the screen
29
in an increased size through the projection lens
28
.
Each of the liquid crystal light bulbs
26
is comprised of a liquid crystal display panel and a frame supporting the liquid crystal display panel therewith. The liquid crystal display panel is supported by the frame by being sandwiched between the frame, and is fixed to a body of the liquid crystal display unit through the frame.
In the above-mentioned projection type liquid crystal display unit, a light leaving a liquid crystal light bulb sometimes returns back to the liquid crystal light bulb because of reflection, refraction, scattering, diffraction, divergence, deviation in an optical axis and/or aberration in the parts constituting the liquid crystal display unit, before the light is projected onto a screen as an image.
If such a light once having left a liquid crystal light bulb and returned back thereto were reflected or scattered at a surface of a frame of a liquid crystal light bulb, the light would stray into an optical path having another optical data, resulting in degradation in display quality, such as reduction in contrast of a projected image, a double image or ghost, and/or local non-uniformity in brightness.
In order to avoid the above-mentioned problem, a frame of a liquid crystal light bulb is usually composed of metal to which a special coating is applied.
FIGS. 1A and 1B
illustrate cases in which a light is reflected to a frame of a liquid crystal light bulb from other parts constituting the liquid crystal display unit.
A body of a projection type liquid crystal display unit is usually coated at an inner wall thereof with black painting, and an optical part is usually coated at a surface thereof with a film which prevents light reflection.
However, as illustrated in
FIG. 1A
, a light may be reflected many time between a an all-reflection mirror
51
and a converging lens
52
, and reach a frame of a liquid crystal light bulb
53
. Then, the light is reflected at the frame and subsequently a projection lens
56
, and enters a dichroic prism
55
. Thus, the light strays into another image data.
As an alternative, as illustrated in
FIG. 1B
, a light may be wrongly reflected at a dichroic prism
55
, and resultingly, reaches a frame of a liquid crystal light bulb
53
, if lights emitted from a light source are not parallel with one another, and/or an optical axis is deviated because of non-uniformity in a gap in a liquid crystal panel.
In addition, a lamp used in a projection type liquid crystal display unit, such as a halogen lamp, a xenon lamp, a metal halide lamp or a high-pressure mercury lamp, and/or light absorption in parts having a small light-reflection rate generate heat in a body of a liquid crystal display unit, and resultingly, the body is kept at a high temperature inside. This causes convection current in the body. As a result, a light is scattered and/or reflected by dusts, and then, reaches a frame. The light is further scattered and/or reflected at the frame, resulting in that the light may enter another image data.
As mentioned above, reflection and/or scattering of a light cause degradation and non-uniformity in projected images.
As mentioned earlier, a liquid crystal light bulb in a projection type liquid crystal display unit is comprised of a liquid crystal display panel and a frame. A module structure of a liquid crystal display unit is grouped into two groups in dependence on whether positioning between a frame and a liquid crystal display panel is performed based on either a thin film transistor (TFT) substrate or an opposing substrate of the liquid crystal display panel. This is because that a thin film transistor substrate is usually arranged at a side at which a light leaves, in order to avoid the heat problem. Herein, the positioning between a frame and a liquid crystal display panel indicates positioning between a reference position defined at a frame or a body of a liquid crystal display unit and a display area or a center of a display area of a liquid crystal display panel.
FIG. 10
is an exploded perspective view of a liquid crystal light bulb.
Hereinbelow is explained how a liquid crystal display panel and a frame are positioned to each other, based on a thin film transistor substrate of the liquid crystal display panel, with reference to FIG.
10
.
First, as illustrated in FIG.
10
(
a
), a liquid crystal display panel
61
is positioned relative to a first frame
62
. A flexible printing substrate
65
is connected to the liquid crystal display panel
61
for connecting the liquid crystal display panel
61
to an external circuit (not
Chung David
Kim Robert H.
NEC Corporation
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