Television – Video display – Projection device
Reexamination Certificate
2000-01-18
2003-06-03
Miller, John (Department: 2714)
Television
Video display
Projection device
C348S750000, C348S756000, C348S759000, C353S031000, C353S020000, C359S487030, C359S490020
Reexamination Certificate
active
06573950
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a projection type image display apparatus of the type which is used as a projection TV set, etc., in which white light from a light source is separated into additive primary colors, each of the primary colors is modulated with the use of a display element, and images are expanded and displayed on a screen.
Along with a diversity of video sources, projection type image display apparatuses are popular as optical projection apparatuses for a large screen as a result of its marketable properties, such as lightness in weight, low price, and compactness in size. In particular, the projection type image display apparatuses using a liquid crystal display element (hereafter, referred to as a liquid crystal panel) as a video generation source has come onto the market because of recent significant improvement of the definition and numerical aperture of a liquid crystal panel. Unlike the conventional projection type CRT, the liquid crystal panel does not emit light by itself, so it needs a light source. The projection type image display apparatus with a liquid crystal panel is composed so that a white light from its white light source is separated into additive primary colors and each of those primary colors are modulated in the liquid crystal panel, from which full-color images are displayed on the screen by expanding original images on the liquid crystal panel through a projection lens unit.
The optical system of the projection type image display apparatus that employs this liquid crystal panel is divided into two types, i.e. a three-panel type that uses three liquid crystal panels and a single-panel type that uses only one liquid crystal panel.
The three-panel type optical system has a liquid crystal panel and an optical unit (color separator) for each respective color of the primary colors (red, green, and blue) obtained by separating white light. The optical unit (color separator) propagates one of the obtained primary colors and the liquid crystal panel modulates the intensity of the colored light to form an image. Each color image is superposed with the other color images optically (color synthesizer) so as to display an image in full colors. This three-panel configuration of the optical system has advantages in that the light from the white light source can be used effectively to obtain high purity colors. In spite of this, because the optical system requires both a color separator and a color synthesizer as described above, the number of parts is increased in the optical system and, accordingly, the cost becomes higher than that of the single-panel configuration.
On the other hand, the single-panel configuration of the optical system uses only one liquid crystal panel, and it is divided into two types according to how TFT apertures are disposed in itself; delta type and stripe type. In the early single-panel configuration, a color filter was used to separate a white color into additive primary colors, but the configuration was plagued with the problem in practical use that the color filter absorbed and reflected the light, thereby the usage efficiency of the light was lowered to about ⅓ that of the three-panel configuration.
In order to solve this problem, for example, the Japanese Patent Unexamined Publication No.4-60538 has disclosed a single-panel color liquid crystal display apparatus, which, as shown in
FIG. 1
thereof, employs dichroic mirrors
4
R,
4
G, and
4
B disposed in a fan-like pattern so as to separate white color light obtained from a white color light source
1
into red, green, and blue light fluxes, thereby improving the usage efficiency of the light.
In this apparatus, each of the light fluxes R, G, and B separated by the above dichroic mirrors
4
R,
4
G, and
4
B is injected at a different angle from the others into a micro-lens array
10
disposed at the light source side of a liquid crystal display element
20
shown in
FIG. 2
in the above-referenced publication.
Each light flux passing this micro-lens array
10
is distributed and irradiated at a liquid crystal site driven by a signal electrode to which a color signal corresponding to one of those light fluxes is applied. Consequently, the usage efficiency of the light is greatly improved, thereby obtaining brighter images than the liquid crystal display element that employs an absorption type color filter.
The official gazette of Japanese Patent Laid-Open No.5-328805 has also disclosed a projection type color liquid crystal display apparatus that has improved color purity by minimizing the generation of stray lights by starting the separation of white color light into the additive primary colors at the long wavelength side so as to prevent color mixing caused by the angle dependency of the wavelength selection characteristics of each of the dichroic mirrors. According to this method, because the original light is separated into light fluxes in the order of R, G, and B, thereby shifting the characteristics of each dichroic mirror, stray lights are not generated easily and the color purity of each separated light flux is improved. Images can thus be projected at a wide range of color reproduction.
However, in the technique disclosed in the above-referenced publication where the angle &agr; is obtained when the G light flux is injected at an angle close to the normal of the liquid crystal display element, as shown in FIG.
6
(
a
) thereof, and is diffracted by a micro-lens and the angle &bgr; is obtained when each of the R and B light fluxes is injected obliquely to the normal of the liquid crystal display element, as shown in FIG.
6
(
b
) thereof, and is diffracted by a micro-lens; the angle &bgr; is larger than the angle &agr; of the light flux (G) irradiated from the liquid crystal display element. This requires a large diameter (low F value) projection lens, thus becoming a primary factor for increasing the manufacturing cost of the projection type color display apparatus.
In order to solve this problem, the Japanese Patent Unexamined Publication No. 8-114780 disclosed a method for keeping a favorable white balance with the use of a small diameter projection lens by injecting a color light emitted from the light source with the weakest spectrum at an angle close to the normal of the liquid crystal display element, thereby eliminating the eclipse at the pupil of the projection lens with the least volume color light.
Because the purity of the color light with the least light volume is improved, it is possible to obtain a wider color reproduction range and more clear images.
One of the projection lenses used for the optical system of the projection type image display apparatus described above is a retrofocus lens of the type disclosed, for example, in the Japanese Patent Unexamined Publication No.9-96759. (Because of the long flange back, it is the most suitable for the three-panel configuration of the optical system.) Because the half-angle of view of this projection lens is about 42°, the projection distance is short. If it is employed for a back-projection type image display apparatus, therefore, the arrangement will be more compact in size even when only one reflection mirror is employed.
Generally, the transmission type screen used in this case employs a two-panel configuration consisting of a lenticular sheet and a Fresnel lens sheet. In some cases, the transmission type screen is also provided with a lenticular lens on the image light injection surface of the Fresnel lens sheet so that the lenticular lens is shaped so as to be longer in the horizontal direction of the screen.
However, in the single-panel configuration described above it is difficult to obtain a predetermined purity for each color. Only with the means proposed in the Japanese Patent Unexamined Publication No. 8-114780. This is because, according to this method, each of the R, G, and B light fluxes separated by a dichroic mirror is injected at a different angle from the others into the micro-lens array
7
disposed at the light source side of the liquid crystal
Hirata Koji
Ikeda Hidehiro
Ogura Naoyuki
Yatsu Masahiko
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Miller John
Natnael Paulos
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