Liquid crystal cells – elements and systems – Particular structure – Interconnection of plural cells in series
Reexamination Certificate
2002-12-04
2004-04-06
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Interconnection of plural cells in series
C349S113000, C349S007000
Reexamination Certificate
active
06717636
ABSTRACT:
This application is a U.S. National Phase Application under 35 USC 371 of International Application PCT/JP02/02010 filed Mar. 5, 2002.
TECHNICAL FIELD
The present invention relates to image display apparatus in which high-resolution images are displayed by using a pixel shifting unit for shifting pixels by means of optical wobbling operation.
BACKGROUND OF THE INVENTION
Among image display apparatus using a liquid crystal display device or the like, an image display apparatus has been disclosed for example in Japanese patent applications laid open No.6-324320 and No.7-7704 in which resolution of the liquid crystal display device is improved by effecting a pixel shifting operation called wobbling where the optical axis of light from the liquid crystal display device is wobbled in predetermined directions.
A description will now be given with respect to the general construction of an image display apparatus in which resolution is improved by such optical wobbling operation. As shown in
FIG. 1
, a back light
102
for emitting white light is placed on the back side of a color liquid crystal display device
101
, and a wobbling device (a pixel shifting unit)
103
for wobbling in predetermined directions the optical axis of light from the color liquid crystal device
101
is placed on the front side of the color liquid crystal display device
101
. Here, odd field images and even field images of input video signal are displayed on the color liquid crystal display device
101
at the same pixels thereof through an image display control circuit
104
. In accordance with their display timing, the optical axis of light from the color liquid crystal display device
101
is wobbled in predetermined directions by the wobbling device
103
.
The wobbling device
103
includes a polarization changing liquid crystal plate
105
and a birefringence plate
106
which is placed on the front side thereof. Here, ON/OFF of voltage across the polarization changing liquid crystal plate
105
is controlled by a wobbling liquid crystal drive circuit
107
based on synchronizing signal of the video signal to be displayed on the color liquid crystal display device
101
. The light from the color liquid crystal display device
101
is thereby transmitted without changing its polarization when the voltage is ON, while, when the voltage is OFF, the light from the color liquid crystal display device
101
is transmitted with changing its polarization through 90 degrees, effecting the wobbling operation by changing the location to be emitted from the birefringence plate
106
in accordance with such direction of polarization. It should be noted that, since the color liquid crystal display device
101
retains the image of the preceding field until rewriting of the image of the next field, one of the electrodes of the polarization changing liquid crystal plate
105
is divided into parts each with a plurality of lines such as 5 lines. The other electrode is used as a common electrode and application of voltage is controlled by selecting the one of the electrodes in accordance with the timing of line scan of the color liquid crystal display device
101
.
The following operation is performed when alternately displaying odd field images and even field images on the color liquid crystal display device
101
. In particular, a case is supposed here as shown in
FIG. 2A
that the horizontal pixel pitch is Px and the vertical pixel pitch is Py of a pixel group in delta array of the color liquid crystal display device
101
. An oblique wobbling operation of 0.75 Px in the horizontal direction and 0.5 Py in the vertical direction, for example, is performed by the above described wobbling device
103
so that the pixel array of the color liquid crystal display device
101
is located at the position as indicated by the broken lines in
FIG. 2B
when an odd field image is to be displayed, while the pixel array is located at the position indicated by solid lines when an even field is to be displayed. Specifically, if for example Px is 18 &mgr;m and Py is 47.5 &mgr;m, the wobbling operation is effected so as to achieve an oblique distance of about 27.3 &mgr;m, shifted by 13.5 &mgr;m horizontally and 23.75 &mgr;m vertically.
For this reason, a crystallographic axis
106
a
of the birefringence plate
106
is set as shown in
FIG. 3
in a direction inclined with respect to the XY coordinate of on the color liquid crystal display device surface and Z direction which is normal thereto. Here, when the direction of polarization of incidence agrees with the direction of polarization of light from the color liquid crystal display device, the light from the color liquid crystal display device is transmitted as extraordinary rays so as to shift the pixels. When the direction of polarization of incidence is rotated through 90 degrees with respect to the direction of polarization of light from the color liquid crystal display device, it is transmitted intact as ordinary rays without shifting the pixels.
In this manner, as shown in
FIG. 4
, when the image of an odd field is to be displayed on the color liquid crystal display device
101
, voltage application to the region of the polarization changing liquid crystal plate
105
corresponding to the horizontal lines to be rewritten is turned ON, so as to transmit the light from such lines intact without rotating the direction of polarization through 90 degrees. The light is emitted by the birefringence plate
106
as extraordinary rays to shift the pixels. On the other hand, when the image of an even field is to be displayed, voltage application to the region of the polarization changing liquid crystal plate
105
corresponding to the horizontal lines to be rewritten is turned OFF, so as to transmit the light from the lines as rotated in the direction of polarization through 90 degrees, causing the birefringence plate
106
to emit the light intact as ordinary rays without shifting the pixels.
In addition, an image display apparatus is known to be provided with two units of such one-dimensional two-point pixel shifting unit each having a polarization changing liquid crystal plate and birefringence plate so as to achieve a high resolution of two-dimensional four-point pixel shift. These are combined to form a laminate where one of the units is rotated through 90 degrees about the axis of incident light with respect to the other, thereby performing four times of pixel shift in the vertical and horizontal directions within one frame or one field.
On the other hand, Digital Micromirror Device [abbreviated as: DMD (trademark)], referred to as variable form mirror device for example used in the image display apparatus disclosed in Japanese patent application laid open No.8-190072, is known in addition to the above liquid crystal display device (LCD) as a display device in the image display apparatus. Such DMD has an array of several hundred or several thousand small inclined mirrors each representing one pixel. To achieve an inclination, each mirror is attached to one or more hinges placed on a supporting column, and a control circuit thereunder is disposed with an interval from others. An electrostatic force is then imparted by the control circuit, to thereby selectively incline each mirror. When it is applied to a display, image data is loaded to DMD and, in accordance with the data, light is selectively reflected or not reflected from each mirror to the image plane.
Further, in addition to polarization beam splitter (PBS), half-mirror (HM), etc., one as disclosed in Japanese patent application laid open No.9-189809 is known as a control device of optical beam. Specifically, in that publication, a disclosure is made with respect to a color image display apparatus using Holographic Optical Element (abbreviated as: HOE) where an incident light is diffracted/separated into the respective components such as R, G, B so as to obtain convergence at a desired portion by the diffraction/spectroscopic function of a transmitting type hologram.
In high-resolution image display apparatus usi
Dudek James A.
Frishauf Holtz Goodman & Chick P.C.
Olympus Optical Co,. Ltd.
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