Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
1999-09-17
2001-12-25
Dowling, William (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S038000, C349S008000
Reexamination Certificate
active
06332684
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection-type color image display apparatus. More particularly, the present invention relates to a single-plate projection-type color image display apparatus for producing a color display with a single LCD (“liquid crystal display”) device without using a color filter.
2. Description of the Related Art
A projection type color image display apparatus incorporating a conventional LCD device (hereinafter, referred to as a “projection type color LCD apparatus”) will be described. A projection type color LCD apparatus is expected to be further developed in the industry, because it can provide various advantages over a projection type CRT (cathode ray tube) display apparatus, e.g., it has a wide color reproduction range; it is small in size and light in weight, and thus highly portable; and it is not influenced by geomagnetism, and thus does not require a convergence adjustment. However, an LCD device used in a projection type color LCD apparatus does not normally emit light, requiring a separate light source be provided.
Display systems for such a projection type color image display apparatus include a three-plate system where three LCD devices are used for the primary colors, R (red), G (green) and B (blue) and a single-plate system where only one LCD device is used. A projection type color image display apparatus of the three-plate system includes an optical system for separating white light into R, G and B beams and three LCD devices for respectively controlling the R, G and B beams so as to form R, G and B images. The R, G and B images are optically superimposed on one another so as to produce a full-color display. In the three-plate system, the light emitted from the white light source can be efficiently used, and a color with high purity can be displayed. However, the system requires the color separating system and the color synthesizing system as described above, and the overall optical system becomes complicated, requiring a large number of components to be provided. Thus, the system is generally disadvantageous over the single-plate system in terms of the cost and the size of the apparatus.
On the other hand, a projection type color LCD apparatus of the single-plate system uses only one LCD device. In the single-plate system, the LCD device including an RGB color filter of a mosaic or stripe arrangement is projected by a projection optical system. For example, such a projection type color LCD apparatus is disclosed in Japanese Laid-Open Publication No. 59-230383. The single-plate system is suitable for a low-cost and small-size projection system as it requires only one LCD device, and the optical system is simpler than that of the three-plate system.
In the single-plate system, however, light is absorbed or reflected by the color filter, whereby only about ⅓ of the incident light can be used. Accordingly, the brightness obtained by the single-plate system with a color filter is about ⅓ of that obtained by the three-plate system using a light source having the same brightness as that used in the single-plate system.
One possible solution to the reduced brightness is to increase the brightness of the light source used. However, an increase in the light source brightness is associated with an increase in the power consumption, which is undesirable, particularly when the apparatus is used at home. When a color filter of an absorption type is used, light absorbed by the color filter is converted to heat. Therefore, the increase in the light source brightness not only increases the temperature of the LCD device, but also accelerates the discoloring of the color filter. Thus, to enhance the utility value of a projection type color image display apparatus, it is important to more effectively use the given light without undesirably increasing the brightness of the light source.
In order to solve the above-described problem associated with the single-plate projection type color image display apparatus, Japanese Laid-Open Publication No. 4-60538, for example, discloses a projection type color image display apparatus in which a plurality of dichroic mirrors are arranged in a fan-arrangement so as to improve the light efficiency.
The conventional projection type color image display apparatus improves the light efficiency by providing a plurality of dichroic mirrors
104
R,
104
G and
104
B in a fan-shaped pattern for separating the white light from a white light source
101
into R, G and B beams, as illustrated in FIG.
38
. As used herein, “R, G and B” refer to red, green and blue, respectively, and “R, G and B beams” refer to a red, green and blue light beams, respectively.
In the conventional apparatus, the light beams separated by the dichroic mirrors
104
R,
104
G and
104
B are incident upon the microlens array
105
at respectively different angles. The microlens array
105
is provided on a side of a LCD device
107
closer to the white light source
101
. After passing through the microlens array
105
, the color beams are distributed, depending on their incident angles, to different liquid crystal regions (pixel regions) of the LCD device
107
, which are driven by different signal electrodes to which different color signals are independently applied. The distributed light beams are projected while being enlarged onto a screen
110
via a field lens
108
and a projection lens
109
, which are provided on a light output side of the LCD device
107
. The conventional projection type color image display apparatus does not use an absorption-type color filter, and thus achieves an enhanced light efficiency, thereby displaying bright images.
Referring to
FIG. 39
, the LCD device
107
used in the conventional projection type color LCD apparatus includes two transparent substrates
107
a
and
107
b
and a liquid crystal layer
107
c
interposed therebetween. Although not shown in the figure, other elements such as a driving circuit (including TFTs, signal lines, etc.) and alignment films are also provided between the transparent substrates
107
a
and
107
b
. On a side of the transparent substrate
107
a
facing the liquid crystal layer
107
c
, a black matrix
111
is provided for blocking light passing through the wiring region which does not contribute to the display. A light-transmitting area of each pixel is called a “pixel aperture”. The ratio of the total area of all the pixel apertures with respect to the screen size is referred to as an aperture ratio.
The microlens array
105
is a group of microlenses
106
each having a size corresponding to three pixels of the LCD device
107
. From the incident R, G and B beams (respectively collimated), the microlens array
105
forms focused spots of the three colors on respective pixels of the corresponding colors on a side (the lower side in
FIG. 39
) of the transparent substrate
107
a
on which the black matrix
111
is provided. Then, image signals are applied to control the respective pixels on which the focused spots are formed.
In a normal LCD device which is not provided with a microlens, light incident upon the black matrix
111
cannot contribute to the display, thereby lowering the light efficiency. On the other hand, in the above-described projection type color image display apparatus provided with the microlens array
105
, light incident upon the microlenses
106
can be focused on the pixel apertures. Therefore, the amount of light which passes through the LCD device
107
is increased, thereby obtaining a brighter projection. If the size of a focused beam spot is smaller than the size of a pixel aperture, the light efficiency can be maximized. However, to realize such a condition, the following limitations exist.
The size of a focused beam spot after passing through a microlens is determined by the focal length f of the microlens and the degree of parallelization of the incident light (the spread angle of the light with respect to the principal ray). In the optical system illustrated in
FIG. 39
, the foc
Hamada Hiroshi
Nakanishi Hiroshi
Shibatani Takashi
Takahara Ikuo
Dowling William
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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