Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-03-10
2001-04-24
Saras, Steven (Department: 2775)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S085000, C345S086000, C345S107000, C359S296000
Reexamination Certificate
active
06222513
ABSTRACT:
BACKGROUND
This invention relates to the use of electronic display materials for electric paper applications. The invention is designed for use with Gyricon electric paper but may also be used with electric paper based on liquid crystal, electrophoretic, and other field-effect display technologies.
Electric paper can be defined as any electronically-addressable display medium that approximates paper in form and function. Electric paper should be light-weight, thin and flexible, and it should display images indefinitely while consuming little or no power. In addition, electric paper should be re-usable. One must be able to erase images and create new ones repeatedly. Preferably, electric paper should display images using reflected light and allow a very wide-viewing angle.
One way to make electric paper possible using traditional electronic display technology is to completely remove the driving electronics from an electronic display package and use external addressing electrodes to write and erase images. This approach both reduces the per unit cost of electronic paper sheets and enables the use of cheap, flexible plastic films in place of glass plates for packaging. Multiple electronic paper sheets can then be addressed by a single set of external driving electronics, much like multiple sheets of pulp paper are printed on by a single printer.
A sheet and display system dubbed Gyricon is disclosed in various patents and articles, such as U.S. Pat. No. 4,126,854 by Sheridon titled “Twisting Ball Display.” The Gyricon display system is comprised of an elastomeric host layer a few mils thick which is heavily loaded with rotating elements, possibly spheres, tens of microns in diameter. Each bichromal rotating element has halves of contrasting colors, such as a white half and a black half. Each bichromal rotating element also possesses an electric dipole, orthogonal to the plane that divides the two colored halves. Each bichromal rotating element is contained in its own cavity filled with a dielectric liquid. Upon application of an electric field between electrodes located on opposite surfaces of the host layer, the rotating elements will rotate depending on the polarity of the field, presenting one or the other colored half to an observer.
A Gyricon sheet has many of the requisite characteristics of electric paper, namely, bistable image retention, wide viewing angle, thin and flexible packaging, and high reflectance and resolution. U.S. Pat. No. 5,389,945 issued to Sheridon on Feb. 14, 1995, and titled “Writing System Including Paper-Like Digitally Addressed Media and Addressing Device Therefor”, describes an electric paper printing system that employs independent, external addressing means to put images on the Gyricon sheets. The external addressing means is described as a one-dimensional array of electrodes connected, either directly or by wireless technology, to modulating electronics. As the one-dimensional array is scanned across the sheet, modulating electronics adjust the potential at the individual electrodes, creating electric fields between the electrodes and an equipotential surface. An image is created in the sheet according to the polarity of the electric fields. The patent recognizes that fringing fields in the vicinity of the addressing electrodes cause incomplete or excessive rotation of the imaging elements in the sheet, and it describes a method for solving this problem.
FIG. 1
shows a representation of the fringing field problem described in the '945 patent. A Gyricon sheet comprised of a plurality of bichromal rotating elements, in this case spheres, cast in a retaining medium
100
is contained between a first encapsulating layer
102
and a second encapsulating layer
104
. The sheet
100
and encapsulating layers
102
,
104
are placed in proximity to a supporting back plane
106
that is electrically grounded. An external addressing device
108
connected to a power supply
110
is depicted moving across the sheet in a direction D. Electric field lines
112
are shown in the proximity of the external addressing device
108
and bichromal spheres
126
,
132
,
138
within the electric field
112
are rotated to positions such that the planes that separate their black hemispheres
128
,
134
,
140
and white hemispheres
130
,
136
,
142
are orthogonal to the field lines
112
. Note that a bichromal sphere
120
that was previously within the electric field
112
maintains a position similar to the bichromal sphere
126
in the trailing edge of the electric field
112
. Optical properties of both of the bichromal spheres
120
,
126
are not optimal because of their over-rotated orientations. A bichromal sphere
144
not yet affected by this electric field
112
rests in a state where its optical properties are optimized because its white hemisphere
146
is positioned precisely toward an encapsulating layer
102
which is also a viewing window.
FIG. 2
shows a representation of the return-to-zero effect, a problem not heretofore described, that limits the ability to address Gyricon sheets with external addressing devices as described in the '945 patent. A Gyricon sheet comprised of a plurality of bichromal rotating elements cast in a retaining medium
200
is contained between a first encapsulating layer
202
and a second encapsulating layer
204
. The sheet
200
and encapsulating layers
202
,
204
are placed in proximity to a supporting back plane
206
that is electrically grounded. An external addressing device
208
connected to a power supply
210
is depicted moving across the sheet in a direction D. Each bichromal sphere
220
,
226
,
232
is contained in its own liquid-filled cavity
221
,
227
,
233
within the retaining medium
200
. Positive mobile ionic charge
240
and negative mobile ionic charge
242
are present in the liquid-filled cavity as well. An electric field exists directly between the external addressing device
208
and the equipotential surface
206
that causes the local bichromal sphere
226
to rotate and mobile ionic charges
240
,
242
to separate within the cavity
227
. In cavities
221
of regions trailing the path of the external addressing device and no longer under the influence of an external electric field, yet separated mobile ionic space charges create an electric field opposite to the previously applied field which imparts torque on the bichromal rotating elements
220
contained therein. This torque can dislodge the bichromal sphere
220
from its intended position, determined by the external addressing device, leaving its black half
224
and white half
222
in optically-poor position for viewing.
Another issue, heretofore undisclosed, facing electric paper printing systems is that sheets, once printed on by some external addressing device, are subject to inadvertent tribo-electric writing. In the described electric paper printing system, images are produced willfully by an external addressing device that has the ability to create electric fields. Electric charge applied inadvertently by tribo-electric exchanges during handling can equally create electric fields that cause image change. This effect poses a threat to image retention and stability. It should be emphasized that this significant problem is a threat to any electric paper technology which uses field-addressed electric paper sheets including Gyricon, liquid crystal and electrophoretic technologies.
A final issue facing the use of external addressing devices on electric paper sheets is that one-dimensional external addressing devices are limited in how quickly they can print an image on an entire sheet by the response speed of optical display elements. In Gyricon sheets, complete rotation of bichromal rotating elements is only achieved if the addressing electric field is held at least as long as the required rotation time, on the order of 100 milliseconds. For a sheet on which many rows of an image must by printed it would take many seconds or minutes to display an entire image.
Another issue facing electric paper is the difficult
Howard Matthew E.
Richley Edward A.
Sprague Robert A.
Alphonse Fritz
McBain Nola Mae
Saras Steven
Xerox Corporation
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