Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-04-11
2004-05-18
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C359S296000
Reexamination Certificate
active
06738039
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophoretic display method and device in which charged migratory particles are migrated for display of an image.
2. Description of the Related Art
Recently, with rapid development of information equipment, the amount of data included in various kinds of information has increased more and more, and output of the information has been made in various forms. Generally, information is outputted in two primary ways, i.e., display-screen representation using a CRT or a liquid crystal, and hard-copy representation on paper using a printer or the like. In the display-screen representation, increasing needs exist for a display device that has low power consumption and is thin. Above all, a liquid crystal display has been actively developed and commercialized as a display device adaptable for such needs.
However, a current liquid crystal display has problems, which are not yet overcome to a satisfactory level, in that characters displayed on a screen become hard to perceive depending on the angle of viewing the screen and the presence of reflected light, and a burden is imposed on a viewer's visual organ due to, e.g., flickering and low luminance of a light source. Also, the display-screen representation using a CRT can provide the contrast and luminance at a satisfactory high level as compared with the case of using a liquid crystal display, but it accompanies flickering, etc. and hence also cannot be regarded as having a sufficient display quality as compared with the hard-copy representation described below. Additionally, the display-screen representation using a CRT entails a large and heavy body, and is therefore very poor in portability.
Meanwhile, at the beginning of the electronization era, it was thought that the hard-copy representation would no longer be required with the progress of electronization of information. In practice, however, a great deal of information is still outputted in the form of hard copies. The reasons are as follows. When information is displayed using a display unit, there occurs not only the above-mentioned problems with regard to display quality, but also another problem that a resolution achieved by the display-screen representation is generally about 120 dpi at maximum, which is fairly lower than that in the case of printing out information on paper (usually not lower than 300 dpi). Accordingly, the display-screen representation imposes a greater burden on a viewer's visual organ than the hard-copy representation. As a result, although information can be confirmed on a display screen, the information is often outputted in the form of hard copies. Another major reason why the hard-copy representation is utilized in spite of a capability of displaying information on a display screen, is that, unlike the display-screen representation, hard copies of information can be arranged side by side in large number without being restricted by a display size defining a display area, and they can be rearranged or checked in order with no need of complicated device operations. Furthermore, the hard-copy representation requires no energy for holding information in a represented state, and has superior portability enabling information to be read or checked in any place and at any time unless the amount of information is extremely large.
Thus, the hard-copy representation has various merits over the display-screen representation so long as moving images or frequent rewriting is not needed, but it is disadvantageous in consuming a great deal of paper. In recent years, therefore, a rewritable recording medium (i.e., a recording medium that enables an image to be displayed in many recording and erasing cycles with high viewability, but does not require energy for holding the image in a displayed state) has been actively developed. Such a third rewritable display system taking over superior characteristics of hard copies is herein called a paper-like display.
Requirements of the paper-like display are, for example, that it is rewritable, requires no or a sufficiently small amount of energy for holding an image in a displayed state (memory character), has superior portability, and has a high display quality. At present, one example of a display system, which can be regarded as the paper-like display, is a reversible display medium employing an organic low-molecular and high-molecular resin matrix and being able to record or erase an image by a thermal printer head (e.g., see Japanese Patent Laid-Open Nos. 55-154198 and 57-82086). Such a matrix is employed in display portions of some prepaid cards, but still has problems that the contrast is not so high and the number of times at which an image can be recorded and erased repeatedly is relatively small, i.e., on the order of 150 to 500.
As another display system capable of being utilized as the paper-like display, there is known an electrophoretic display device (U.S. Pat. No. 3,612,758) invented by Harold D. Lees, et al. Also, Japanese Patent Laid-Open No. 9-185087 discloses an electrophoretic display device. Such a display device comprises a disperse system wherein charged migratory particles are dispersed in a dielectric liquid, and a pair of electrodes is arranged in an opposing relation with the disperse system situated between the electrodes. By applying a voltage to the disperse system through the electrodes, charged migratory particles are attracted under electrostatic forces to the side of the electrode having a polarity opposite to that of charges of the migratory particles themselves based on the electrophoresis of charged particles. Display of information is performed by coloring the migratory particles and utilizing a difference between the color of the migratory particles and the color of the dyed dielectric liquid. More specifically, when the migratory particles are attracted onto the surface of a first electrode that is closer to the viewer and is light transparent, the color of the migratory particles is observed. On the contrary, when the migratory particles are attracted onto the surface of a second electrode that is farther away from the viewer, the color of the dielectric liquid, which is dyed so as to have different optical characteristics from those of the migratory particles, is observed.
In the above-described electrophoretic display device, however, a dye and a coloring material in the form of ions, for example, must be mixed in the dielectric liquid, and the presence of such a coloring material tends to act as an unstable factor in the electrophoretic operation because of giving rise to a new transfer of charges. This tendency may deteriorate the performance, useful life and stability of the display device.
To overcome the above problem, Japanese Patent Laid-Open Nos. 49-5598 and 11-202804 propose a display device wherein a pair of electrodes, i.e., first and second driving electrodes, are arranged on the same substrate and migratory particles are migrated horizontally as viewed from the viewer. By applying voltages to the first and second driving electrodes, the migratory particles in a transparent dielectric liquid are horizontally migrated parallel to the substrate surface between the first and second driving electrodes based on the electrophoresis of charged particles, whereby an image is displayed.
In such an electrophoretic display device of the horizontally migrating type, the dielectric liquid is transparent and the first and second driving electrodes have different colors as viewed from the viewer side such that the color of one electrode coincides with the color of the migratory particles. Assuming, for example, that the color of the first driving electrode is black, the color of the second driving electrode is white, and the color of the migratory particles is black. The second driving electrode is exposed to provide a white view when the migratory particles are distributed over the first driving electrode, and the black color of the migratory particles is viewed when the migratory part
Hjerpe Richard
Nguyen Frances
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