Note: Descriptions are shown in the official language in which they were submitted.
CA 02240443 1998-06-15
WO 97/33267 PCT/LTS97/09297
_ 1 - _
TWISTING BALL DISPLAYS INCORPORATING
SEGMENTED POLYCHROMAL BALLS
Inventors: Nicholas K. Sheridon, George G. Robertson,
Jock D. Mackinlay, Maureen C. Stone
The following U.S. patents are fully incorporated
herein by reference: U.S. Patent No. 4,126,854,
(Sheridon, "Twisting Ball Panel Display"); U.S. Patent
No. 4,143,103 (Sheridon, "Method of Making a Twisting
Ball Panel Display"); U.S. Patent No. 5,075,186
(Sheridon, "Image-Wise Adhesion Layers for Printing");
U.S. Patent No. 5,262,098 (Crowley et al., "Method and
Apparatus for Fabricating Bichromal Balls for a Twisting
Ball Display"); U.S. Patent No. 5,344,594 (Sheridon,
"Method for the Fabrication of Multicolored Balls for a
Twisting Ball Display"); and U.S. Patent No. 5,389,945
(Sheridon, "Writing System Including Paper-Like Digitally
Addressed Media and Addressing Device Therefor").
The invention relates to addressable, reusable,
paper-like visual displays, to gyricon or twisting-ball
displays, and to electric paper.
Electric paper is an attempt to combine the
desirable qualities of paper with those of real-time
display media in order to create something that offers
the best of both worlds. Like ordinary paper, electric
paper preferably can be written and erased, can be read
in ambient light, and can retain imposed information in
the absence of an electric field or other external
retaining force. Also like ordinary paper, electric
" paper preferably can be made in the form of a
lightweight, flexible, durable sheet that can be folded
c or rolled into tubular form about any axis and
conveniently placed into a shirt or coat pocket, and then
later retrieved, re-straightened, and read substantially
without loss of information. Yet unlike ordinary paper,
electric paper preferably can be used to display full-
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motion and other real-time imagery as well as still
images and text. Thus it is adaptable for use in a
computer system display screen or a television.
The gyricon, also called the twisting-ball
display, rotary ball display, particle display, dipolar
particle light valve, etc., offers a technology for
making a form of electric paper. Briefly, a gyricon is
an addressable display made up of a multiplicity of
optically anisotropic balls, each of which can be
selectively rotated to present a desired face to an
observer. For example, a gyricon can incorporate balls
each having two distinct hemispheres, one black and the
other white, with each hemisphere having a distinct
electrical characteristic (e. g., zeta potential with
respect to a dielectric fluid) so that the balls are
electrically as well as optically anisotropic. The
black-and-white balls are embedded in a sheet of
optically transparent material, such as an elastomer
layer, that contains a multiplicity of spheroidal
cavities and is permeated by a transparent dielectric
fluid, such as a plasticizer. The fluid-filled cavities
accomodate the balls, one ball per cavity, so as to
prevent the balls from migrating within the sheet. A
ball can be selectively rotated within its respective
fluid-filled cavity, for example by application of an
electric field, so as to present either the black or the
white hemisphere to an observer viewing the surface of
the sheet. Thus, by application of an electric field
addressable in two dimensions (as by a matrix addressing
scheme), the black and white sides of the balls can be
n
caused to appear as the image elements (e.g., pixels or
subpixels) of a displayed image.
Gyricon displays can be made that have many of
the desirable qualities of paper, such as flexibility and
stable retention of a displayed image in the absence of
power, not found in CRTs, LCDs, or other conventional
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display media. Gyricon displays can also be made that are
not paper-like, for example, in the form of rigid display
screens for flat-panel displays.
Typically, known gyricon displays are made up of
bichromal balls that are black in one hemisphere and white
in the other. Other kinds of balls are also known. For
example, U.S. Pat. No. 4,261, 653 (Goodrich) shows a
multilayer ball, although it is made at least in part from
glass and its use depends on an addressing scheme involving
1o high-frequency electric fields.
Although the gyricon represents an important step
toward the goal of electric paper, there is still a long
way to go. For example, a gyricon constructed of black-and-
white balls cannot provide a multicolor image. As another
example, a gyricon designed to operate in ambient reflected
light cannot provide a projective or transmissive display.
The invention provides advanced gyricon technology
that can provide a more full range of display capabilities
while preserving paper-like advantages. The invention will
2o be better understood with reference to the drawings and the
description that follows. In the drawings, like reference
numerals indicate like components.
In accordance with an aspect of the present invention,
there is provided a spheroidal ball comprising a plurality
of segments arrayed substantially parallel to one another,
each segment being adjacent to at least one other segment
and to no more than two other segments, adjacent segments
being adjoined to one another at substantially planar
interfaces, the plurality of segments including
3o a first segment having a first thickness and a'first
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optical modulation characteristic,
a second segment having a second thickness and a
second optical modulation characteristic, and
a third segment having a thickness different from at
least one of the first and second thicknesses and an
optical modulation characteristic different from at least
one of the first and second optical modulation
characteristics,
the ball having an anisotropy for providing an
1o electrical dipole moment, the electrical dipole moment
rendering the ball electrically responsive such that when
the ball is rotatably disposed in a nonoscillating electric
field while the electrical dipole moment of the ball is
provided, the ball tends to rotate to an orientation in
which the electrical dipole moment aligns with the field.
In accordance with another aspect of the present
invention there is provided a material comprising:
a substrate having a surface; and
a plurality of spheroidal balls disposed in the
substrate,
each spheroidal ball having a plurality of segments
adjoining one another, each segment being adjacent to at
least one other 'segment and to no more than two other
segments, the segments including
a first segment having a first optical modulation
characteristic,
a second segment having a second optical modulation
characteristic, and
a third segment having an optical modulation
3o characteristic different from at least one of the first and
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second optical modulation characteristics,
each spheroidal bell having an anisotropy for
providing an electrical dipole moment, the electrical
dipole moment rendering the ball electrically responsive
such that when the ball is rotatably disposed in a
nonoscillating electric field while the electrical dipole
moment of the ball is provided, the ball tends to rotate to
an orientation in which the electrical dipole moment aligns
with the nonoscillating electric field,
to each spheroidal ball having a plurality of observable
aspects, the aspects being observable by an observer
situated favorably to observe the surface of the substrate,
the aspects including
a first aspect associated with the first optical
modulation characteristic, the first aspect being
observable when the ball is rotationally oriented in a
first orientation with respect to the observer under the
influence of a first electric field applied in a vicinity
of the ball while the ball is disposed rotatably within the
2o substrate and the electrical dipole moment of the ball is
provided, the first applied electric field having an
electric field vector perpendicular to a planar portion of
the surface proximate to the vicinity of the ball, and
a second aspect associated with the second optical
modulation characteristic, the second aspect being
observable when the ball is rotationally oriented in a
second orientation with respect to the observer under the
influence of a second electric field applied in the
vicinity of the ball while the ball is disposed rotatably
3o within the substrate and the electrical dipole moment of
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the ball is provided, the second applied electric field
having an electric field vector including an electric field
vector component parallel to the planar portion of the
surface proximate to the vicinity of the ball.
In accordance with another aspect of the present
invention there is provided a method of fabricating
spheroidal balls, comprising the steps of:
providing a first liquid flow comprising a first
hardenable liquid flowing at a first flow rate, the first
1o hardenable liquid being associated with a first optical
modulation characteristic,
providing a second liquid flow comprising a second
hardenable liquid flowing at a second flow rate, the second
hardenable liquid being associated with a second optical
modulation characteristic;
merging the first and second liquid flows into a
combined liquid flow, the combined liquid flow comprising
the first and second liquid flows joined at a planar
interface;
2o forming a ligament from the combined liquid flow;
forming a plurality of spheroidal balls from the
ligament, each of the balls comprising a first segment due
to the first liquid flow and a second segment due to the
second liquid flow, the first and second segments being
joined at a planar interface, each of the first and second
segments having a thickness, the thickness of the first
segment being governed by the first flow rate, the
thickness of the second segment being governed by the
second flow rate, the first segment having the first
optical modulation characteristic, the second segment
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having the second optical modulation characteristic; and
hardening the balls thus formed, each hardened ball
having an anisotropy for providing an electrical dipole
moment, the electrical dipole moment rendering the hardened
ball electrically responsive such that when the hardened
ball is rotatably disposed in an electric field while the
electrical dipole moment of the ball is provided, the
hardened ball tends to rotate to an orientation in which
the electrical dipole moment aligns with the field.
s0 In accordance with another aspect of the present
invention there is provided a spheroidal ball comprising a
plurality of segments arrayed substantially parallel to one
another, each segment being adjacent to at least one other
segment and to no more than two other segments, each'
segment adjacent to exactly one other segment being an
exterior segment and each segment adjacent to exactly two
other segments being an interior segment, adjacent segments
being adjoined to one another at substantially planar
interfaces, each segment having an optical modulation
characteristic, the optical modulation characteristic of
adjacent segments being different from one another, the
plurality of segments including
a first exterior segment,
a second exterior segment, and
a transparent interior segment,
the ball having an anisotropy for providing an
electrical dipole moment, the electrical dipole moment
rendering the ball electrically responsive such that when
the ball is rotatably disposed in a nonoscillating electric
3o field while the electrical dipole moment of the ball is
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3e
provided, the ball tends to rotate to an orientation in
which the electrical dipole moment aligns with the field.
In accordance with another aspect of the present
invention there is provided a material comprising:
a substrate; and
a plurality of spheroidal balls disposed in the
substrate,
each ball comprising a plurality of component regions
including
to a first component region having a first optical
modulation characteristic, and
a second component region having a second optical
modulation characteristic,
at least one component region of each ball being
transparent, at least one component region of each ball
having a chromatic color, each ball having an anisotropy
for providing an electrical dipole moment, the electrical
dipole moment rendering the ball electrically responsive
such that when the ball is rotatably disposed in a
2o nonoscillating electric field while the electrical dipole
moment of the ball is provided, the ball tends to rotate to
an orientation in which the electrical dipole moment aligns
with the field.
In accordance with another aspect of the present
invention there is provided a spheroidal tall having a
center point and comprising three (3) segments arrayed
substantially parallel to one another, each segment being
adj acent to at least one other segment and to no more than
two other segments, each segment adjacent to exactly one
3o other segment being an exterior segment and each segment
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adjacent to exactly two other segments being an interior
segment, adjacent segments being adjoined to one another at
substantially planar interfaces, the three segments
including
a first segment, the first segment being an interior
segment including the center point, the first segment
having a first optical modulation characteristic, the first
optical modulation characteristic being such that the first
segment has a color,
to a second segment, the second segment being an exterior
segment adjacent to the first segment, the second segment
having a second optical modulation characteristic, the
second optical modulation characteristic being such that
the second segment is transparent, and
a third segment, the third segment being an exterior
segment adjacent to the first segment and situated opposite
the second segment with respect to the first segment, the
third segment having the second optical modulation
characteristic,
2o the ball having an anisotropy for providing an
electrical dipole moment, the electrical dipole moment
rendering the ball electrically responsive such that when
the ball is rotatably disposed in a nonoscillating electric
field while the electrical dipole moment of the ball is
provided, the ball tends to rotate to an orientation in
which the electrical dipole moment aligns with the field.
In accordance with another aspect of the present
invention there is provided a material comprising:
a substrate having a surface; and
3o three sets of spheroidal balls disposed in the
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substrate, including first, second, and third sets each
comprising a plurality of balls,
each ball of each set being associated with a
chromatic color observable by an observer situated
favorably to observe the substrate surface,
each ball of the first set being associated with a
first chromatic color,
each ball of the second set being associated with a
second chromatic color,
io each ball of the third set being associated with a
third chromatic color,
each ball of each set having at least two component
regions, including
a first component region having the chromatic color
with which the ball is associated, and
a second, transparent component region,
each ball of each set having an anisotropy for
providing an electrical dipole moment, the electrical
dipole moment rendering the ball electrically responsive
2o such that when the ball is rotatably disposed in a
nonoscillating electric field while the electrical dipole
moment of the ball is provided, the ball tends to rotate to
an orientation in which the electrical dipole moment aligns
with the field.
In accordance with another aspect of the present
invention there is provided a material comprising:
a substrate comprising a plurality of layers, each
layer being a nearest neighboring layer with respect to at
least one other layer of the plurality and no more than two
other layers of the plurality, the layers including.first,
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3h
second, and third layers;
a first plurality of spheroidal balls disposed in the
first layer, each ball of the first plurality having at
least two component regions including a component region
having an achromatic color and a component region having a
first chromatic color;
a second plurality of spheroidal balls disposed in the
second layer, each ball of the second plurality having at
least two component regions including a component region
io having an achromatic color and a component region having a
second chromatic color;
a third plurality of spheroidal balls being disposed
in the third layer, each ball of the third plurality having
at least two component regions including a component region
having an achromatic color and a component region having a
third chromatic color;
each ball of each of the first, second, and third
pluralities having an anisotropy for providing an
electrical dipole moment, the electrical dipole moment
2o rendering the ball electrically responsive such that when
the ball is rotatably disposed in a nonoscillating electric
field while the electrical dipole moment of the ball is
provided, the ball tends to rotate to an orientation in
which the electrical dipole moment aligns with the field.
In accordance with another aspect of the present
invention there is provided a material comprising:
a substrate; and
a plurality of spheroidal balls disposed in the
substrate, each ball having an optical anisotropy and an
3o anisotropy for providing an electrical dipole moment, the
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3i
electrical dipole moment rendering the ball electrically
responsive such that when the ball is rotatably disposed in
an electric field while the electrical dipole moment of the
ball is provided,, the ball tends to rotate to an
orientation in which the electrical dipole moment aligns
with the field, the plurality of balls including
a first set of balls comprising at least one ball,
each ball of the first set being associated with a first
threshold, and
a second set of balls comprising at least one ball,
each ball of the second set being associated with a second
threshold, the second threshold being less than the first
threshold,
the first and second thresholds being such that
for each ball of each set, a rotation of the ball is
facilitated by an application in a vicinity of the ball
while the ball is rotatably disposed in the substrate of an
electric field having a first electric field strength
exceeding the first threshold,
2o for each ball of the first set, a rotation of the ball
is not facilitated by an application in a vicinity of the
ball while the ball is rotatably disposed in the substrate
of an electric field having a second electric field
strength between the first and second thresholds, and
for each ball of the second set, a rotation of the
ball is facilitated by an application in a vicinity of the
ball while the ball is rotatably dispo$ed in the substrate
of an electric field having the second electric field
strength.
3o In accordance with another aspect of the present
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invention there is provided a method of making a product
comprising optically anisotropic spheroidal balls disposed
in a substrate, the method comprising the steps of:
providing a receiving surface comprising a material in
an adhesive state;
depositing first and second sets of spheroidal balls
on the receiving surface; each of the first and second sets
comprising at least one ball,
each ball of the first set having a first collection
of physical characteristics,
each ball of the second set having a second collection
of physical characteristics, spheroidal balls of the second
set thus being physically distinguishable from spheroidal
balls of the first set,
each ball of each set having an optical anisotropy and
an anisotropy for providing an electrical dipole moment,
the electrical dipole moment rendering the ball
electrically responsive such that when the ball is
rotatably disposed in an electric field while the
2o electrical dipole moment of the ball is provided, the ball
tends to rotate to an orientation in which the electrical
dipole moment aligns with the field,
the spheroidal balls thus deposited adhering to the
receiving surface material in the adhesive state;
depositing a material in a pourable state ~on the
receiving surface and over the spheroidal balls adhering to
the receiving surface material, thereby covering the
spheroidal balls adhering to the receiving surface material
and thus forming an uncured substrate material wherein the
balls of the first and second sets are disposed, the
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uncured substrate material comprising the receiving surface
material in the adhesive state and the material deposited
in the pourable state; and
curing at least a portion of the uncured substrate
material to a nonadhesive, nonpourable state with the
spheroidal balls of the first and second sets thus disposed
therein, so as to form a substrate in which are disposed at
least one spheroidal ball of the first set and at least one
spheroidal ball of the second set.
to In accordance with another aspect of the present
invention there is provided a spheroidal ball comprising a
plurality of segments arrayed substantially parallel to one
another, each segment being adjacent to at least one other
segment and to no more than two other segments, each
segment adjacent to exactly one other segment being an
exterior segment and each segment adjacent to exactly two
other segments being an interior segment, adjacent segments
being adjoined to one another at substantially planar
interfaces, the segments including
2o a first segment, the first segment being an interior
segment having a first optical modulation characteristic,
the first optical modulation characteristic being such that
the first segment is nontransparent,
a second segment, the second segment being an exterior
segment adjacent to the first segment, the second segment
having a second optical modulation characteristic, the
second optical modulation characteristic being such that
the second segment is transparent,
a third segment, the third segment being an interior
3o segment having a third optical modulation characteristic,
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31
the third optical modulation characteristic being such that
the third segment is nontransparent, and
a fourth segment, the fourth segment being an exterior
segment adjacent to the third segment, the fourth segment
having an optical modulation characteristic such that the
fourth segment is transparent,
the ball having an anisotropy for providing an
electrical dipole moment, the electrical dipole moment
rendering the ball electrically responsive such that when
1o the ball is rotatably disposed in a nonoscillating electric
field while the electrical dipole moment of the ball is
provided, the ball tends to rotate to an orientation in
which the electrical dipole moment alilgns with the field.
In accordance with another aspect of the present
invention there is provided a material comprising:
a substrate comprising a layer having front and rear
surfaces;
a plurality of light-modulating elements disposed in
the substrate between the front and rear surfaces of the
layer,
each element comprising at least one spheroidal ball
disposed in the substrate,
each ball of each clement comprising at least two
component regions, the component regions including
a first component region having a first optical
modulation characteristic such that the first component
region is transparent and does not have a chromatic color,
and
a second component region having a second optical
3o modulation characteristic such that the second component
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region is nontransparent and does not have a chromatic
color,
each ball of each element having an anisotropy for
providing an electrical dipole moment, the electrical
dipole moment rendering the ball electrically responsive
such that when the ball is rotatably disposed in a
nonoscillating electric field while the electrical dipole
moment of the ball is provided, the ball tends to rotate to
an orientation in which the electrical dipole moment aligns
1o with the field,
each element having at least two operational states
including
a first, transmissive state admitting a passage of
light through the element and thereby through the layer,
and
a second, nontransmissive state obstructing a passage
of light through the element and through the layer;
and
a backing joined to the rear surface of the layer, at
least a portion of the backing having a chromatic color,
the portion having the chromatic color being disposed such
that, to an observer favorably situated to observe the
front surface of the substrate layer, the chromatic color
is observable through at least one light-modulating element
when said element is in the first, transmissive state.
RriPf Description of the Drawincs
FIG. 1 illustrates a technique for fabricating
bichromal gyricon balls in the prior art;
FIGS. 2A-2B illustrate bichromal gyricon balls
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3n
obtained using unequal liquid flow rates;
FIGS. 2C-20 are close-up cross-sectional views of the
edge of a disk to which pigmented plastic liquids are
applied at unequal flow rates;
FIGS. 3A-3D illustrate a multiple-disk assembly for
fabricating multichromal gyricon balls;
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FIGS. 4A-4B show side and top views, respectively,
of a muitisegmented, highlight color gyricon ball;
FIG. 5 illustrates an example of a highlight color
gyricon display;
S FIG. 6A illustrates an enlarged cross-section of a
portion of a highlight color gyricon display;
FIG. 68 depicts an electrode assembly used to
produce an erasing field in a highlight color gyricon
display;
FIG. 6C is a close-up view of part of a rectangular
region of the electrode assembly of FIG: 6B;
FIG. 6D is an end view of the electrode assembly of
FIG. 6B;
FIG. 6E illustrates bus bar headers suitable for
producing an erasing field for a highlight color gyricon
display;
FIGS. 6F-6G illustrate an eraser for a highlight
color gyricon display;
FIG. 6H illustrates a gyricon display having
recessed erasure power electrodes, and a writing stylus
adapted for use therewith
FIG. 6I illustrates an example of a highlight color
gyricon display with built-in erasure and writing
electrodes;
23 FIG. 7A illustrates a gyricon ball suitable for
constructing an overlay trans=parency gyricon or a
gyricon-based architectural screen;
FIG. 7B illustrates the use of an overlay
transparency gyricon;
FIGS. 7C-7D show how a light-transmissive gyricon
can be used in a projection mode;
FIG. 7E illustrates an application of a gyricon in
n
an architectural screen;
FIGS. 8A-8C illustrate an electrode configuration
that provides a canted field for a gyricon;
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FIGS. 8D-8E are examples of the effects of a canted
field on a gyricon ball;
FIG. 8F illustrates an electrode configuration that
is an alternative to the canted field configuration of
FIGS. 8A-8C;
.. FIGS. 9A-9C are different views of a seven-segment
ball for a pseudo-four color gyricon;
FIG. 9D illustrates a pseudo-four color gyricon that
has a layer of backing material;
FIG. l0A illustrates a three-segment gyricon ball
made up of a colored interior segment surrounded on
either side by transparent exterior segments;
FIG. 10B illustrates an elastomer sheet for a full-
color RGB (red-green-blue) gyricon;
FIG. lOC shows a subpixel arrangement for a full-
. color RGB gyricon;
FIG. 11A illustrates an elastomer sheet for a full-
color CMY (cyan-magenta-yellow) multilayer gyricon;
FIG. 11B illustrates a pixel in the sheet of FIG.
11A;
FIG. 11C depicts a cross-section of an elastomer
sheet for a CMY multilayer gyricon;
FIG. 11D is an exploded view of a pixel in the sheet
of FIG. 11C;
FIG. 11E illustrates an exploded view of a CMY
gyricon having separate addressing hardware per layer;
FIG. 11F illustrates a CMY gyricon having a single
set of addressing hardware for all layers;
FIG. 11G is a series of views in which the position
of the addressing hardware is changed relative to the
gyricon sheet;
FIG. 11H illustrates close-packing of gyricon balls
in a CMY gyricon;
FIG. 11J (please note that there is no FIG. 11I)
illustrates a full-color CMYK (cyan-magenta-yellow-black)
multilayer gyricon;
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FIG. 12A illustrates a three-segment bistate light
valve gyricon ball for use in an ambient color RGB
display;
FIGS. 12B-12D are views of a bistate light valve
gyricon ball as used to reveal or hide an underlying
color dot;
FIG. 12E illustrates a four-segment tristate light
valve gyricon ball for use in an ambient color RGB
display;
FIG. 12F is an exploded view of an ambient color RGB
gyricon;
FIGS. 12G-12H are views of a tristate light valve
gyricon ball partiallly hiding an underlying color dot;
FIG. 12I illustrates an additional lighting mode for
use with bistate and tristate light-valve gyricons;
FIG. 12J illustrates an alternative, two-layer
embodiment of the tristate light valve gyricon;
FIG. 13 schematically depicts the 'modulation of
light in a generalized tristate light-valve color
display;
FIG. 14A is a series of views showing gyricon balls
of different sizes and thresholds in multithreshold
gyricons;
FIGS. 14B-14D are voltage response graphs for
different multithreshold gyricons;
FIG. i4E is a series of views showing successive
stages of addressing in a multilayer canted-field
gyricon;
FIG. 14F is a series of views showing color
saturations available in a multithreshold single-layer
gyricon;
FIG. 14G is a series of views showing successive
stages of addressing in a multilayer gyricon having
multithreshold color saturation control within each
layer;
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FIG. 15A illustrates a nonfusing xerographic
apparatus for gyricon ball placement;
FIG. 15B is a highly magnified view a toner-and-bead
powder mixture for use in the apparatus of FIG. 15A;
FIG. 15C illustrates a liquid elastomer being
- dispensed over a partially cured elastomer in which
gyricon balls have been placed; and
FIG. 15D illustrates a silk-screen apparatus for
gyricon ball placement.
t0 Multilayer Polychromal Gyricon Structures
The present invention uses multichromal gyricon
balls in new ways and in conjunction with other new
techniques, such as canted fields, to provide a wealth of
new possibilities for gyricon displays.
FIG. 1 illustrates a technique for fabricating
bichromal balls in the prior art, using apparatus 1.
Pigmented plastic liquids 21, 22 are applied to opposite
sides 11, 12 of a spinning disk 10, which rotates
uniformly about shaft 15. Centrifugal force causes
liquids 21, 22 to flow toward the periphery of disk 10,
where they combine at the edge to form bichromal
ligaments 30 that eventually break up as bichromal balls
40. When liquids 21, 22 flow with equal rates to the
edge of disk 20, the technique produces bichromal balls
with equal hemispheres of color.
FIGS. 2A-2B illustrate the balls obtained when the
pigmented liquid flow rates in the spinning-disk
technique of FIG. 1 are made unequal. In FIG. 2A, ball
240 has segments 241, 242 joined at planar interface
243, and in FIG. 2B, ball 260 has segments 261, 262
joined at planar interface 263. Thus in both FIGS. 2A
and 2B, the balls are made up of unequal spherical
segments of pigmented material, with a planar interface.
This planar interface is important, as will be seen
below. FIGS. 2C-2D illustrate how ligaments at the edge
of a spinning disk can produce the balls of FIGS. 2A-2B.
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_ 8 _ _
FIGS. 2C-2D show close-up cross-sectional views of the
edge of a spinning disk 210 to which pigmented plastic
liquids 221, 222 are applied at unequal rates. In FIG.
2C, black liquid 221 is applied at a lesser flow rate '
than white liquid 222. The resulting ligament 230
contains a broad white segment 231 and a narrow black
segment 232 separated by a planar interface 233. Upon
breakup, ligament 230 produces balls like the ball 240
shown in FIG. 2A. In FIG. 2D, black liquid 221 is
applied at a greater flow rate than white liquid 222.
The resulting ligament 250 contains a narrow white
segment 251 and a broad black segment 252 separated by a
planar interface 253. Upon breakup, ligament 250
produces balls like the ball 260 shown in FIG. 2B.
Again, the planar interfaces are important, as will be
seen below.
The unevenly segmented balls of FIGS. 2A-2B show
that the circular ligaments produced by the spinning
disk, and the balls that derive from these ligaments, act
as though they are made from slabs, with the widths of
the slabs depending on the feed rates of the pigmented
liquids.
A modification of the spinning-disk technique can be
used to fabricate multichr-omal balls. The modification
uses a spinning multiple-disk assembly instead of a
single spinning disk. An example is illustrated in FIG.
3A. Assembly 300 has three disks 3i0, 311, 312 that
rotate uniformly about shaft 315. The concave or "dish-
shaped" outer disks 310, 312 curve or slope toward the
flat inner disk 311 at their respective peripheries.
Other geometries are possible, and the exact geometry for
a particular embodiment can be determined, for example,
by hydrodynamic modeling, as will be appreciated by those
of skill in the art.
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The three-disk assembly of FIG. 3A_can be used to
produce multichromal balls having certain useful
properties, as will be discussed below. It will be
- appreciated, however, that other assemblies having
different numbers of disks can also be used in the
present invention, with the number and configuration of
the disks varying according to the kind of ball that is
to be produced.
If differently pigmented plastic liquids are
introduced to each side of each of the three disks 310,
311, 312 in FIG. 3A, flow patterns of pigmented liquids
at the edge of the disks can be obtained that result in
multichromal ligaments that break up to form multichromal
balls. FIG. 3B illustrates a close-up cross-sectional
view of an example of the flow of pigmented plastic
liquids at the edge of the three-disk assembly of FIG.
3A. First and second liquids 321, 322 flow over opposite
sides of disk 310, whose downward-sloping edge can be
seen in the figure. Third and fourth liquids 323, 324
flow over opposite sides of disk 311, and fifth and sixth
liquids 325, 326 flow over opposite sides of disk 312.
The combined flows give rise to ligament 330, which
breaks up into multilayer bails such as the ball 340
illustrated in FIG. 3C (side view) and FIG. 3D (top
view ) .
Ball 340 has six segments corresponding to the six
streams of plastic liquid used to make it. Segments 341
and 342 join at planar interface 343; segments 344 and
345, at planar interface 346; and segments 347 and 348,
at planar interface 349. If different pigments are used
in the various plastic liquids 321, 322, 323, 324, 325,
326, then ball 340 will be multichromal. In general, a
three-disk assembly like the one shown in FIG. 3A can
produce gyricon balls having six segments of up to six
different colors.
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More generally, a multi-disk assembly with N disks
can be used to produce gyricon balls having up to 2N
segments in arbitrary color combinations. Black, white,
or other color pigments or dyes can be used, alone or in _
combination, so that segments can be made in virtually
any desired color or shade. Segments can be made clear -
by using unpigmented, undyed plastic liquid. Different
segments can be made to have different widths by
adjusting the flow rates of the various plastic liquids
used to make the segments, with faster flow rates
corresponding to wider segments and slower rates to
narrower segments according to the techniques illustrated
previously with reference to FIGS. 2A-2D. Two or more
adjacent segments can be made the same color so that they
IS effectively merge to form a single broader segment.
By way of example, any given gyricon ball segment
can be: black; white: clear (that is, essentially
transparent and without chroma, like water or ordinary
window glass): a transparent color (e. g., transparent
red, blue, or green, as for certain additive color
applications: transparent cyan, magenta, or yellow, as
for certain subtractive color applications); an opaque
color of any hue, saturation, and luminance; any shade of
gray, whether opaque or translucent; and so forth. For
ease of reference, "achromatic colors" will be used
hereinbelow to refer to colors essentially lacking in
chroma, that is, to black, white, gray, and clear, and
"chromatic colors" will be used hereinbelow to refer to
other colors, including red, orange, yellow, green, blue,
indigo, violet, cyan, magenta, pink, brown, beige, etc.
Highlight Color Gyricon
FIGS. 4A-4B illustrate a gyricon ball 440 having
five segments 44I, 442, 443, 444, 445. FIG. 4A shows a
side view of ball 440, and FIG. 4B shows a top view. As
can be seen in FIG. 4A, central segment 443 is quite wide
in relation to the other segments, and segments 442 and
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444 are quite thin. The wide central segment 443 can be
made by using two smaller adjacent segments of identical
pigment (not shown). The thin segments 442 and 444 can
be made using low flow rates of their respective
pigmented plastic liquids.
If segments 441 and 445 are made transparent (for
example, of clear plastic liquid having an optical
refractive index closely matching the refractive indices
of the sheet material and dielectric fluid that surround
ball 440), segment 442 is made in a dark color such as
black, segment 444 is made in a contrasting color such as
red or blue, and the broad central segment 443 is made
white, a gyricon ball results that is suitable for
highlight color. A highlight color display typically
provides a black-and-white display with the addition of
one other color, such as red, blue, yellow, green, or a
"custom color" chosen for a particular application (for
example, a special color used for a company logo), that
can be applied to any selected portion or portions of the
display in order to call attention to text or other
matter there. Although highlight color is known in other
contexts, for example in certain laser printers and
copiers, highlight color in gyricon displays is new to
the present invention.
The ball of FIGS. 4A-4B can be used to construct a
highlight color gyricon display. For example, the balls
can be uniformly dispersed in a sheet of elastomer or
other substrate material permeated by dielectric fluid.
Each ball resides in its own liquid-filled cavity within
the sheet. One or more balls can be used per pixel of
display; here, for simplicity of exposition, one ball per
. pixel is assumed. The black face of the ball can be
turned toward the observer to provide a black pixel, and
the red or other highlight color face can be turned
toward the observer to provide a highlight color pixel.
The ball can be turned at 90 degrees between these two
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positions to provide a white pixel. (When the ball is
turned so as to provide a white pixel, the edges of the
black and highlight color segments can be observed along
with the white central segment; however, this does not -
significantly affect the overall white appearance of the
pixel if the black and highlight color edges are made
sufficiently thin.)
FIG. 5 illustrates an example of a highlight color
gyricon display. A portion of highlight color gyricon
display 500 is shown in enlarged cross section, with
balls 540, 550, and 560 shown in detail. Ball 540 has
five segments 541 (transparent), 542 (highlight color),
543 (white), 544 (black), 545 (transparent) and is
oriented in a direction indicated by arrow a. Ball 550
has five segments 551 (transparent), 552 (highlight
color), 553 (white), 554 (black), 555 (transparent) and
is oriented in a direction indicated by arrow b. Ball
560 has five segments 561 (transparent), 562 (highlight
color), 563 (white), 564 (black), 565 (transparent) and
is oriented in a direction indicated by arrow c. An
observer at I sees ball 540 as a highlight color pixel,
ball 550 as a black pixel, and ball 560 as a white pixel.
The balls for the highlight color gyricon display
500 are made with segments of different zeta potentials,
so that the balls can be oriented to any of the three
possible orientations by application of suitable electric
fields. For example, the transparent segment in contact
with the highlight color segment can be made to have the
highest positive zeta potential in contact with the
working fluid of the gyricon (i.e., the dielectric fluid
that permeates the optically transparent sheet of
material in which the balls are embedded), and the
transparent segment in contact with the black segment can
be made to have the highest negative zeta potential.
33 According to this scheme, in FIG. S ball 540 is made with
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transparent segment 541 having the highest positive zeta
potential of any segment of ball 540 and transparent
segment 545 having the highest negative zeta potential of
any segment of ball 540. Similarly, ball 550 is made with
transparent segment 551 having the highest positive zeta
potential-and transparent segment-555 having the highest
negative zeta potential, and ball 560 is made with
transparent segment 561 having the highest positive zeta
potential and transparent segment 565 having the highest
negative zeta potential.
Because the segments of gyricon balls are made with
different zeta potentials, the balls are electrically
anisotropic. When a suitable electric field is applied
in the vicinity of a ball, the ball will tend to rotate,
with its direction of rotation and its final orientation
being substantially determined by its electrical
anisotropy. The ball will retain its orientation even
after the applied field is removed.
Different plastic materials can have different zeta
potentials. The two transparent sections of a highlight
color gyricon ball (for example, segments 541 and 545 of
ball 540) can be made from two different plastics having
two different zeta potentials. The zeta potential
characteristics of the ball and its various segments can
thus be shaped through deliberate choice of materials, as
well as by choice of coloring agents for the
nontransparent segments.
Some illustrative examples of plastic materials
suitable for making gyricon ball segments are
polyethylene, polyester, carnuba wax, and castor wax.
(Although waxes are not polymerized hydrocarbons, they
are, strictly speaking, plastic materials.) other
materials, such as epoxy, can also be suitable. The same
or similar materials can be used for both transparent and
nontransparent ball segments, with suitable coloring
agents being added in the case of the nontransparent
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segments. For transparent segments, the materials are
preferably chosen to have retractive indices closely
matching that of the plasticizer liquid used to swell the
elastomer sheet. .
To orient an individual highlight color ball so that
the black or the highlight color faces the observer, as
for balls 550 and 540 in FIG. 5, respectively, a suitable
electric field can be applied perpendicular to the plane
of the sheet of material in which the ball is embedded.
To orient a highlight color ball so that its black and
highlight color segments are perpendicular to the
observer and its white central segment is displayed, as
for ball 560 in FIG. 5, an electric field can be applied
parallel to or in the plane of the sheet of material in
which the ball is embedded. A matrix addressing scheme
(controlled, for example, by computer or by digital
video) can be used to cause the field to be applied
selectively in the vicinity of an individual ball to be
addressed.
An electrical stylus can also be used to address the
balls, thus enabling a human user to write directly on
the gyricon. For example, the parallel field can
initially be applied to the entire sheet, orienting all
the balls so that their white central segments are
presented to the user. This effectively erases the
electric paper, giving the user a blank sheet on which to
write. Thereafter, the user can apply a stylus having a
positive potential and move it across the surface of the
sheet to reorient the balls in the vicinity of the styli.
tip so that their black faces are presented to the user.
The user can apply a stylus having a negative potential
and move it across the surface of the sheet to reorient
the balls in the vicinity of the stylus tip so that their
highlight color faces are presented to the user. The
user can erase the sheet by applying the parallel field,
so that the sheet can thereafter be reused.
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In general, a gyricon display can be made in various
sizes and shapes, and using various kinds of materials
for the gyricon balls, elastomer sheet, and plasticizer
fluid. The highlight color display of FIG. 5 is
exemplary in this regard. For instance, the highlight
color display of FIG. 5 can be made about the size of an
ordinary sheet of paper by using, for example, an 8.5 by
11 inch sheet of SYLGARD 184 elastomer material of 20
mils (thousandths of an inch) thickness with ISOPAR L
plasticizer and highlight color balls of 100 micron
diameters with center segments 50 microns thick, the top
segment of each ball being made from carnuba wax
material, the bottom from castor wax material, and the
three interior segments from castor wax colored with
i5 carbon black, titanium dioxide, and a chromatically
colored dye or pigment to provide, respectively, the
black, white, and highlight colors of the interior
segments.
Many different dyes and pigments can be suitable for
use as coloring agents to provide chromatic and
achromatic colors in gyricon balls and segments of
gyricon balls, depending on the application and on the
material or materials used in constructing the balls. By
way of example, if the balls are made from wax materials,
some dyes that can be used include BAKER CHEMICAL Cresyl
violet blue, BAKER CHEMICAL Rhodamine 6G, DUPONT
Rhodamine BI, DUPONT Spirit Blue NS, DUPONT Victoria Blue
B base, ALLIED CHEMICALS Iosol Blue, EASTMAN Acridine
orange, CALCO OIL blue N, and CALCO OIL black; and some
pigments that can be used include DUPONT 8900 titanium
dioxide, FERRO 6331 black pigment, CABOT MOGUL L carbon
black, and CABOT MONARCH 1000 carbon black.
FIGS. 6A-6G illustrate an example of an electrode
structure that can provide a parallel field suitable for
erasing a highlight color gyricon display. FIG. 6A shows
an enlarged cross-section of a portion of highlight color
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gyricon display 600. Electrode assemblies 620, 630 are
located on either side of an elastomer sheet 610 in which
balls 611 are embedded. Top electrode assembly 620,
which is closest to an observer at I, is made of an '
optically transparent conductor With a very high
resistivity. Bottom electrode assembly 630, which is on
the opposite side of sheet 610 from an observer at I,
also has a very high resistivity. Each of the top and
bottom electrode assemblies 620, 630 is divided into
rectangular regions; in particular, top electrode
assembly 620 includes regions 621 and bottom electrode
assembly 630 includes regions 631. The rectangular
regions are separated by low-resistivity bus bars; in
particular, bus bars 622 separate the regions 621 of top
electrode assembly 620 and 'bus bars 632 separate the
regions 631 of bottom electode assembly 630. Both
electrode assemblies 620, 630 can be connected to a power
supply (not shown).
Addressing electrodes for gyricons, such as
electrode assemblies 620, 630, can be made by depositing
a conductive material on a glass or plastic (e. g., MYLAR)
backing or substrate. Typically, the conductive material
is indium/tin oxide (ITO), which can be applied to glass
by sputtering. A tin oxide (NESA glass) coating can also
be used. The electrodes formed using these materials are
optically transparent, and so are well suited for ,
addressing the gyricon while minimally interfering with
the visibility thereof.
To minimize the electrical power drain caused by
passing current through electrode assemblies 620, 630, it
is preferable to use electrodes having high surface
resistivities. However, if resistivity values are too
high, switching speeds will be slow. Resistivity values
can range up to approximately 109 ohms per square (that
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is, ohms per unit of area), depending on the particular
application or environment in which display 600 is used.
Preferably, top electrode assembly 620 is made so as
- not to electrically isolate the balls 611 from an applied
S addressing field, such as the field of a writing stylus.
Since an electrode is transparent to electric fields that
change at a rate faster than the capacitive response time
of the electrode, this condition can be met by making the
regions 621 of a sufficiently high resistivity material.
For example, an elastomer layer 30 mils thick has a
capacitance of approximately 3 picofarads per square
centimeter. If sheet 6i0 is formed of such an elastomer
layer, the resistivity of top electrode assembly 620 can
be made approximately 108 ohms per square so that a user
i5 can write on display 600 with a stylus whose tip moves
across the display surface at a velocity of approximately
100 centimeters per second or greater. A DC voltage of,
for example, 80 volts can be used for this stylus.
FIG. 6B is a view from above top electrode assembly
620, showing the configuration of voltages of top
electrode assembly 620 for producing the erasing field;
the same configuration is used for bottom electrode
assembly 630. A voltage V is applied across the surface
of each of the rectangular regions 621, so that a
uniform electric field E running substantially parallel
to the surface of sheet 610 is created in the region of
sheet 610. Because the resistivity of the elastomer
sheet 610 is high, as is the resistivity of rectangular
regions 621, the power draw is low. The polarity of the
applied voltage alternates between positive and negative
from one rectangular region to the next, as shown, thus
minimizing the voltage requirement of the power supply.
The bus bars 622 are low resistivity electrodes (e. g.,
100 ohms per square) that allow uniform distribution of
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voltage across the high resistivity optically transparent
surface material of the rectangular regions 621.
Bus bars 622 can be connected to one another and to
the power supply by any appropriate technique, for '
example, using wired connections along one or more edges
of sheet 610, or by printing bus bar headers on a glass
or plastic backing in a pattern such as that illustrated
in FIG. 6E, in which header 68? is held at a positive
voltage and header 688 is held at a negative voltage. The
potential difference between neighboring prongs 687a and
688a, for example, is a voltage V. Thus headers 687, 688
and their counterparts in the bottom electrode assembly
produce an alternating uniform electric field in the
plane of sheet 610 throughout an overlap region 689.
Preferably, the length and width of overlap region 689
exceed, respectively, the length and width of sheet 610.
Bus bars 622 can be, for example, evaporated gold or
aluminum electrodes, or screen-printed silver-filled
epoxy. If electrodes 620, 630 are formed of ITO
sputtered on glass, bus bars 622 can also be ITO,
sputtered onto the glass in a separate operation
involving the use of a mask. By using ITO on glass, both
the electrodes and the bus bars can be made substantially
transparent, thereby increasing the visibility of the
underlying gyricon sheet.
FIG. 6C shows a close-up view of a portion of one of
the rectangular regions 621. The particular region in
question, region 621a, is situated between two of the bus
bars 622, namely bus bars 622a and 622b. The voltage
differential between first bus bar 622a and second bus
bar 622b is V. The surface material of region 621a
provides a high-resistivity electrical connection between
low-resistivity bus bars 622a and 622b.
FIG. 6D shows an end view of electrode assemblies
620, 630 and their respective constituent regions 621,
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631. (For simplicity, elastomer sheet 610 and bus bars
622 are omitted in this view.) As can be seen, the
alternating pattern of applied positive and negative
- voltages is identical for both of the electrode
assemblies 620, 630. This ensures that the electric
field is uniformly parallel to the surface of sheet 610
within any given region of sheet.
To enable erasure, a power supply can be associated
with the highlight color gyricon display. For example,
IO in FIG. 6A, when a switch (not shown) is closed, the
erasure power supply can be connected to the top and
bottom electrode assemblies 620, 630, thereby
establishing electric fields parallel to the sheet 6I0.
The fields cause balls 611 to be oriented with their
white central segments facing an observer at I, thus
erasing the gyricon display 600. The power supply is
required only momentarily when the display is erased, so
that the actual power requirements can be quite modest
and the power supply can be made small. For example, an
electric field of about 5 volts per mil can be used to
realign the gyricon balls, so that if the resistivity of
electrodes 620, 630 is 108 ohms per square and assuming
that ball rotation completes in approximately 3
milliseconds, the energy required to erase display 600
can be, for example, 6 milliwatt seconds, which can be
readily supplied with, for example, ordinary flashlight
batteries.
The power requirement for erasure can be met, for
example, by exposing two electrodes near the edge of
' 30 display 600 and touching these electrodes to two
similarly spaced electrodes on the writing stylus (which
is assumed to have its own power supply) when erasure is
desired. This is illustrated in FIG. 6H. A stylus 695
has electrodes 696x, 696b that protrude slightly from the
end of the stylus opposite the writing tip. These
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electrodes are spaced so that they line up with similarly
spaced electrodes 697a, 697b connected to display 600.
For safety and convenience, electrodes 697x, 697b can be
disposed in a recess 698, preferably located near an edge '
or corner of the visible surface of display 600.
FIGS. 6A-6D do not depict display 600 as including
electrode assemblies that can be used for writing (as
opposed to erasing) display 600. Writing on display
600 can be accomplished by means of a stylus or other
external device. Alternatively or additionally, write
electrodes can be incorporated into display 600 together
with the erase electrodes, as illustrated in the cross-
sectional view of FIG. 6I. Display 600 has elastomer
sheet 610 with balls 611 sandwiched between top and
bottom erase electrode assemblies 620, 630, as in FIGS.
6A-6D. Additionally, an upper addressable write
electrode assembly 626 is situated above top erase
electrode assembly 620, and a lower addressable write
electrode assembly 636 is situated below bottom erase
electrode asembly 630. Write electrode assemblies 626,
636 preferably have significantly lower resistivities
than do their counterpart erase electrodes. For example,
if top and bottom erase electrode assemblies 620, 630
have resistivities of 108 ohms per square, then upper and
lower write electrode assemblies 626, 636 can have
resistivities of 102 ohms per square. Both write
electrode assemblies 626, 636 and erase electrode
assemblies 620, 630 can be made matrix-addressable, to
facilitate writing and erasure of individual pixels.
~ Erase electrode assemblies can be made external to
display 600. For example, an erase electrode can be
mounted in a special device for erasing electric paper.
Any external device that applies an electric field
substantially in the plane of elastomer sheet 610 can be
used. An example of such a device is the electric paper
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eraser shown in FIGS. 6F-6G. A user can, erase a display
such as display 600 by holding eraser 691 against the
visible surface of the display and wiping eraser 691 back
and forth across the display surface in the direction
indicated in FIG. 6F by arrows 694. Thus a user of
display 600 can erase some or all of the displayed text,
image, or other displayed matter by wiping the display
with eraser 691 in a manner analogous to that in which a
piece of conventional paper is erased with a rubber
eraser, or in which a conventional whiteboard is wiped
clean with a whiteboard eraser.
Eraser 691 is shown in cross-section in FIG. 6G. A
resistive surface 692 is subjected to a potential
difference between V1 and V2, resulting in an electric
field E in and parallel to the plane of surface 692. An
insulating housing 693 surrounds resistive surface 692,
giving the user of eraser 691 a way to hold the eraser
and also providing packaging for a power source and
circuitry (not shown) used to produce the voltages VI and
VZ at either end of surface 692. Preferably, the
electric field in resistive surface 692 penetrates into
sheet 610 to sufficient depth, and is sufficiently
parallel to the plane of sheet 610, to ensure a clean and
thorough erasure.
Overlay Transparencies
Overlay transparencies superpose printed, graphical,
or other visual information on a transparent (for
example, clear or lightly tinted) background. They can
be placed on top of an underlying opaque page such as a
map, a printed text, or a colored background. Commonly
in the prior art, overlay transparencies are made of
flexible transparent plastic sheets upon which visual
information is printed or marked. Such plastic sheets
are non-reusable and are not capable of providing real
time display.
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A gyricon display suitable for use as an overlay
transparency can be constructed. The display can be made
to have the qualities of reusability, physical
flexibility about any axis, suitability to real-time
imagery, and so forth that are characteristic of gyricon-
based electric paper; however, the display appears
transparent rather than opaque when it is blank. The
display can be used in ambient light if a diffuser, such
as a sheet of ordinary white paper, is placed behind it.
The display is similar in construction to the highlight
color display 500 of FIG. 5, except for the balls used,
as will now be described.
FIG. 7A illustrates a ball suitable for constructing
an overlay transparency gyricon display. Ball 740 is a
five-segment ball with a broad transparent central
segment 743, two thin pigmented segments 742, 744, and
two transparent outer segments 741, 745. The transparent
segments 741, 743, and 745 are chosen to have an optical
refractive index that closely matches the refractive
indices of the elastomer sheet and the dielectric fluid
that permeates the sheet, so that the ball appears
transparent when oriented with its transparent central
segment 743 facing the observer (that is, in a 90-degree
orientation comparable to the orientation of ball 560 in
FIG. 5) .
Ball 740 is made with segments of different zeta
potentials, so that it can be oriented to different
orientations by application of suitable electric fields.
In particular, segment 741 can be made with the highest
positive zeta potential of any segment in ball 740, and _
segment 745, with the highest negative zeta potential of
any segment in ball 740. w
By applying an electric field in or parallel to the
plane of the sheet in which the balls are embedded, the
balls can be oriented to present their transparent aspect
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to the observer, and thus the display can be erased. An
electrode configuration like the one described for FIGS.
6A-6G can be used to effect erasure.
The pigmentation chosen for segments 742, 744 can
depend on the intended use of the overlay transparency.
t If, for example, the overlay transparency is to be used
to highlight elements of an underlying black-and-white
textual document, the thin segment 742 can be made in an
opaque color, such as red or yellow, and the other thin
segment 744 can be made in another opaque color, such as
blue or green. As another example, if the overlay
transparency is to be used with a plain white or other
suitably colored background, such as a background of a
gray, beige, or other neutral color, the thin segment 742
can be made black and the other thin segment 744 can be
made in a highlight color.
Ball 740 can be fabricated in a manner similar to
that used to fabricate the five-segment ball 440 of FIG.
4A.
FIG. 7B illustrates schematically the use of an
overlay transparency gyricon in conjunction with an
underlying document, such as a paper document. Overlay
transparency 750 is placed over document 751 and
illuminated by light from light source 752, such as
sunlight or ambient light. The light incident on
transparency 750 is modulated, being passed through the
transparent segments of some balls and absorbed or
partially reflected by the opaque segments of other
balls, according to which segment of each ball is
- 30 presented to the observer at I. Light that passes
through transparency 750 to reach document 751 can there
be absorbed (e.g., by black text) or reflected (e.g., by
a white background). Light reflected from document 751
can then pass back through transparent portions of
transparency 750 so as to reach the observer at I.
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An overlay transparency gyricon can also be used in
a backlit mode, for example with a collimated light
source such as a projector to make a black-and-white
projected image. This is illustrated schematically in .
FIG. 7C and in a particular example (an overhead
projector 759) in FIG. 7D. In each of these figures,
light source 753 provides a bright, preferably white
light that is collimated by a condensing lens 754,
modulated by overlay transparency 755, and thereafter
projected by a projection lens 756 onto a view screen 757
so as to form an image viewable by an observer at I. If
overlay transparency 755 is made up of balls like ball
740 that have opaque background and highlight color
segments, it is not especially well-suited for backlit
use, inasmuch as the background and highlight colors,
being opaque, cannot be distinguished from one another in
the image projected on screen 757. Nevertheless, this
mode of use can be worthwhile in some instances, and is
included here for completeness of exposition. (Gyricon
devices that are capable of producing color projected
images and are thus better suited for use in projective
or other backlit modes modes include the additive and
subtractive color gyricons that are described below with
reference to FIGS. l0A-lOC and FIGS. 11A-11C,
respectively.)
Architectural Screens
Transmissive polychromal-ball gyricon technology can
be applied to make cost-effective, electrically actuated
privacy and light control screens that can be used in
architectural and interior design applications, for
example, in electronic window shades, electronic Venetian
blinds, or electronic room partition screens. A gyricon -
suitable for an architectural screen application can be
made similar in construction to the highlight color
display 500 of FIG. 5, except for the balls used. These
can be like the five-segment ball 740 illustrated in FIG.
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7A, with a broad transparent central segment 743, two
thin pigmented or dyed segments 742, 744, and two
transparent outer segments 741, 745. The bail appears
= transparent when oriented with its transparent central
segment 743 facing the observer.
- By applying an electric field in or parallel to the
plane of the sheet in which the five-segment balls are
embedded, the balls can be oriented to present their
transparent aspect to an observer, and thus the
architectural screen can be made to transmit incident
light. Similarly, an electric field perpendicular to
the sheet can be used to display the pigmented or dyed
aspects of the five-segment balls to the observer. The
perpendicular field can be made addressable, for example
IS at low resolution (for example, for each rectangular
louver or shutter element of an electronic Venetian
blind) or at high resolution (for example, for each
pixel, with one or more balls being used per pixel)
according to the particular application.
The pigmentation or dye chosen for ball segments
742, 744 can depend on the intended use of the
architectural screen. For example, light-absorbing,
light-reflecting, or light-scattering pigments can be
used, or colored pigments or dyes can be used. Moreover,
different balls in a gyricon can be differently pigmented
or dyed, and patterns are possible, so that designs,
patterns, or pictures can be imposed on the architectural .
screens. Thus gyricon architectural screens can be built
that will be almost fully transparent or that will absorb
light, reflect light, or even create changes in decor at
the touch of a button, in response to a momentary
application of low-level electrical power.
Transparent central segment 743 can be clear, but
can also be, for example, tinted, translucent, or °'smoke
glass" colored. Again, the particular choice made for
transparent central segment 743 depends on the intended
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use of the screen, and different balls in a gyricon can
use different kinds or colors of transparent segments.
An example application for the architectural screen
is in a "smart" window. The windowpane can be built to
incorporate a transmissive gyricon architectural screen,
for example by forming the windowpane of two layers of -
glass with an elastomer sheet containing five-segment
balls situated between the layers. Each glass layer is
coated with a transparent electrode coating, such as ITO,
disposed toward the elastomer sheet. The transparent
electrode coatings are used to apply voltages to the
gyricon.
FIG. 7E is a cross-sectional view of such a window.
Window 770 includes window frame 775 and windowpane ?76.
Windowpane ?76 has outer layers of glass 771a, 771b.
Layer ??la has a transparent electrode coating 772a
disposed toward the interior of windowpane 776 and layer
?7Ib has a transparent electrode coating 772b also
disposed toward the interior of windowpane 776. Between
the electrode coatings 772x, 772b is an elastomer sheet
??3 permeated with dielectric fluid and containing five-
segment balls 774. The entire windowpane is thus a
gyricon. The electrodes can be used to apply voltages
V1, V2, V3, V4 (here shown at the corners of windowpane
776, but more generally at the corners of any addressable
areal region within windowpane 7?6) that can be used to
rotate the five-segment balls to any desired orientation,
using the variable-angle or canted electric field
technique described in the next section with reference to
FIGS. 8A-8C. '
A gyricon architectural screen can be made that
provides adjustable, continuously variable light
transmission ranging from substantially complete
transmission of incident light to substantially complete
occlusion of incident light. This adjustability can be
achieved by using an electrode configuration suitable for
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causing partial rotation of the balls, so that the balls
can be oriented at any angle with respect to the surface
of the gyricon sheet.
~ Variable-Angle (Canted) Electric Fields
More generally, an electrode configuration that can
produce an electric field at any angle with respect to
the surface of the gyricon sheet, and thus provide
continuously variable ball orientation, can be used in a
wide variety of gyricon devices. For example, it can be
used with highlight color balls having transparent
central segments to build a gray-scale overlay
transparency, or with black-and-white opaque bichromal
balls to build a gray-scale ambient-light reflective
display. The same configuration can also be used to
provide both the addressing (perpendicular) and erasure
(parallel) fields in a highlight color gyricon display
and, in particular, to provide individually eraseable
pixels. (Although the electrode configuration's ability
to provide a continuous range of electric field angles
and ball rotations is not fully used in this case,
nevertheless its ability to produce both the parallel and
perpendicular fields with a single electrode structure
can be advantageous.)
FIGS. 8A-8C illustrate an electrode configuration
that provides an active matrix array so that individual
gyricon balls or groups of balls can be addressed and can
be rotated to any desired angle. The electrode
configuration can generate an electric field oriented at
an arbitrary angle to the surface of the gyricon sheet in
the vicinity of any ball or group of balls ( for example,
a group of balls forming a pixel or subpixel).
Hereinafter, this configuration sometimes will be called
a canted-field electrode configuration.
FIG. 8A shows a side view of a portion of a gyricon
800 having a canted-field electrode configuration.
Electrode assemblies 820, 830 are located on either side
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of an elastomer sheet 810 in which polychromal balls 811
are embedded. Top electrode assembly 820, which is
closest to an observer at I, is made of an optically
transparent conductor with a very high resistivity.
Bottom electrode assembly 830, which is on the opposite
side of sheet 810 from an observer at I, also has a very
high resistivity and can also be transparent, depending
on the application. Each of the top and bottom electrode
assemblies 820, 830 is divided into rectangular regions:
l0 in particular, top electrode assembly 820 includes
regions 821 and bottom electrode assembly 830 includes
regions 831. The rectangular regions are separated by
high-resistivity separators; in particular, separators
824 separate the regions 821 of top electrode assembly
820 and separators 834 separate the regions 831 of bottom
electode assembly 830. Both electrode assemblies 820, r
830 can be connected to a power supply {not shown).
Separators 824, 834 can be, for example, made of glass or
other substrate material.
2~ For some applications, it is preferable that the top
electrode assembly 820 be made so as not to electrically
isolate the polychromal balls 811 from an externally
applied addressing field, such as the field of a writing
stylus. Since an electrode is electrically transparent
to electric fields that change at a rate faster than the
capacitive response time of the electrode, this condition.
can be met by making the regions 821 of a sufficiently
high resistivity material.
Within each of the regions 821 are located
individually addressable bus bars 822, and within each of
the regions 831 are located individually addressable bus ,
bars 832. Top electrode bus bars 822 are situated
parallel to and directly above their counterpart bottom
electrode bus bars 832. The voltage at each individual
bus bar can be set using active matrix addressing
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electronics (not shown) incoporated into_ gyricon 800 or
housed separately. (For example, active matrix
addressing electronics can be pressed into contact with
sheet 810 in a manner similar to that in which active
matrix addressing electronics are pressed into contact
with a liquid crystal layer in an LCD.) Thus each of the
regions 821, 831 can be individually addressed and can
correspond, for example, to a pixel or subpixel of a
pixel-addressable display.
LO As an example, bus bars 822a and 822b are located on
either side of top electrode region 821a, and bus bars
832a and 832b are located on either side of bottom
electrode region 831x. Bus bar 822a is parallel to and
directly above bus bar 832x, and~bus bar 822b is parallel
to and directly above bus bar 832b. The voltage at bus
bar 822a is V1; at 822b, V2; at 832a, V3; and at 832b,
V4. By addressing the bus bars 822a, 822b, 832a, 832b
and setting the voltages V1, V2, V3, V4 appropriately, as
described more fully below with reference to FIG. 8C,
electric fields can be established in sheet 810 in the
vicinity of these bus bars, so that the polychromal balls
8I1 within a parallelepiped-shaped portion of sheet 810
bounded by bus bars 822x, 822b, 832a, 832b can be
addressed as an individual display element.
FIG. 8B shows a portion of top electrode assembly
820, viewed from above. Separators 824 criss-cross top
electrode assembly 820, and paired bus bars 822 flank
each of the regions 821. For example, region 821a is
delimited by separators 824a, 824b, 824c, and 824d. Bus
bars 822a, 822b are situated along either side of region
821x, within the perimeter established by separators
824x, 824b, 824c, and 824d. The structure of bottom
electrode assembly 830 (not visible in FIG. 8B) is
similar to that of top electrode assembly 820; in
particular, bottom electrode region 831a is situated
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below top electrode region 821x, and bus_bars 832a, 832b
are situated parallel to and directly below bus bars
822x, 822b, respectively.
FIG. 8C shows three examples of electric fields that
can be produced with the canted-field electrode
configuration (fringing effects are negligible and,
accordingly, are not shown). In the first example at A,
the electric field lines run parallel to the planes of
electrodes 820, 830, and thus parallel to the surface of
sheet 810 (not shown in FIG. 8C) . In the second example
at B, the electric field lines run perpendicular to the
planes of electrodes 820, 830 and thus perpendicular to
the surface of sheet 810. In the third example at C, the
electric field lines run at an angle A with respect to
the planes of electrodes 820, 830 and thus with respect
to the surface of sheet 810.
The different fields illustrated in FIG. 8C can be
generated by setting the voltages on the bus bars 822,
832 appropriately. For example, if in FIG. 8A the
voltages Vl, V2, V3, V4 at bus bars 822a, 822b, 832a,
832b, respectively are set so that V1 - V3 and V2 - V4,
then electric field lines like those at A in FIG. 8C are
generated in the vicinity of these bus bars, that is,
electric field lines running parallel to the planes of
electrodes 820, 830. If in FIG. 8A the voltages V1, V2,
V3, V4 at bus bars 822a, 822b, 832a, 832b, respectively
are set so that V1 - V2 and V3 - V4, then electric field
lines like those at B in FIG. 8C are generated in the
vicinity of these bus bars, that is, electric field lines
running perpendicular to the planes of electrodes 820,
830. If in FIG. 8A the voltages V1, V2, V3, V4 at bus -
bars 822a, 822b, 832a, 832b, respectively are set so that
VI > V3 and V2 > V4, then electric field lines like those
at C in FIG. 8C are generated in the vicinity of these
bus bars, -that is, electric field lines running at an
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angle 6 with respect to the planes of. electrodes 820,
830. The value of the angle 6 is determined by the
particular values of the voltages, and can be changed by
adjusting the voltages. Thus a continuous, 360-degree
range of electric field directions can be generated.
It will be appreciated that application of a canted
field to a gyricon ball can cause the ball to rotate, for
example, through an angle of less than 180 degrees. In
FIG. 8D, exemplary gyricon ball 891 in substrate 890 has
its maximum positive zeta potential at a first end 892
and its maximum negative zeta potential at a second end
893. Thus ball 891 has a dipole moment, here represented
by a vector p. In a gyricon of the prior art, dipole
moment vector p would, in the absence of an applied
electric field, preferably be oriented either parallel or
antiparallel to a vector N defining a normal to a surface
895 of the substrate 890 in which ball 891 was disposed.
Application of an electric field to bail 891 would cause
ball 891 to rotate, if at all, through a 180-degree
angle, so that upon deactivation of the field, dipole
moment vector p would once again be either parallel or
antiparallel to surface normal vector N. Canted fields
can likewise accomplish this 180-degree rotation, but
they can also do more. According to the invention,
application of a canted field oriented neither parallel
nor antiparallel to the surface normal vector N causes
the ball to rotate through an angle of less than 180
degrees so as to align with the canted field, and to
remain there after the field is turned off until such
time as another, differently oriented electric field is
applied. For example, as shown in FIG. 8D, application
of a canted field having electric field vector E at a
time to will cause ball 891 to align with the field by
rotating through an angle a.: removal of the field at a
later time tl as shown in FIG. 8E leaves the ball's dipole
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moment vector p at the angle oc to surface normal vector
N. To summarize, whereas in the prior art, in which the
application of an electric field served to rotate the
dipole moment vector of a gyricon ball either through an
angle of 180 degrees, or not at all, according to the
invention, the application of a canted electric field can -
serve to rotate the dipole moment vector of the ball
through any desired angle.
An alternative approach to the canted-field
electrode configuration is illustrated in the exploded
view of FIG. 8F. A gyricon 850 has elastomer sheet 853
with gyricon balls 861. Sheet 853 is surrounded by two
high-resistivity erase electrodes 852, 854 that can
generate electric fields in or parallel to the plane of
sheet 853, in a manner similar to that previously
described with reference to FIGS. 6A-6D. A low-
resistance ground-plane electrode 851 is disposed on the
opposite side of erase electrode 854 from sheet 853. A
matrix addressing electrode assembly 855 is disposed on
the opposite side of erase electrode 852 from sheet 853.
Thin dielectric separator layers 856a, 856b separate,
respectively, erase electrode 852 from ground plane 851
and erase electrode 854 from addressing electrode
assembly 855. The layers 856x, 856b can be, for
example, a deposited polymer or a plastic sheet.
Surrounding the electrode configuration are two substrate
layers 870x, 870b. At least one face of gyricon 850 is
optically transparent. For example, if an observer at I
is to view gyricon 850, then substrate layer 870b,
addressing electrode assembly 855, dielectric separator
856b, and erase electrode 854 preferably should all be
transparent. For some applications, such as the "smart"
window application previously described with reference to
FIG. 7E and other architectural screen applications, all
components outside gyricon sheet 853 (that is, the
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electrodes 851, 852, 854, 855, both dielectric separators
856a, 856b, and both substrate layers 870a, 870b) can
advantageously be made transparent.
The voltages V1, V2, V3, V4 provided by the erase
electrodes 852, 854 should be set such that V1=V3 and
V2=V4 for an in-plane erasure field, which when applied
to balls 861 causes balls 861 to align with their
electrical dipole moments in the plane of sheet 853.
Alternatively, if other values of V1, V2, V3, and V4 are
chosen, a canted field is produced by which balls 861 can
be oriented with their dipole moments at an arbitrary
angle to the plane of sheet 853.
The electrode configuration of FIG. 8F provides only
a limited canted-field capability. This is because the
erase electrodes 852, 854 do not provide pixels or other
addressable image elements, but instead act on all the
balls 861 together. Addressing electrode assembly 855,
which does have addressable elements, in conjunction with
ground plane 851 can only produce electric fields that
are perpendicular to the plane of sheet 853, and cannot
produce canted fields. Thus the electrode configuration
of FIG. 8F is not readily adaptable to a display in
which, for example, it is desired to have different
canted field angles on a per-pixel or per-subpixel basis.
Even so, the configuration can be useful in certain
circumstances, as for example in a low-cose, low-
resolution application in which it is desired to have a
first subset of balls 861 of the gyricon to be oriented
with their electrical dipole moments pointed upwards with
respect to the the plane of sheet 853, a second subset
oriented with their dipole moments pointed downwards with
respect to the plane of sheet 853, and a third subset
oriented with their dipole moments at a selected cant
angle with respect to the plane of sheet 853, the
selected angle being the same for all balls of the third
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_ g4 _ _ .
subset. The configuration is also useful in conjunction
with certain multithreshold gyricons, as will be
discussed below with reference to FIGS. 14A-14G.
Pseudo-Four Color Gyricon
A gyricon with a canted-field electrode
configuration can be used to provide a display having
four colors plus white (or another suitable background
color). A multichromal ball suitable for such a display
can be made with seven segments including a transparent
io central segment, transparent first and second exterior
segments, and four colored interior segments, two on each
side of the central segment. The ball and display will
now be described with reference to FIGS. 9A-9D.
FIG. 9A shows a side view of a seven-segment
IS polychromal ball 940. The broad central segment 944 and
the endmost segments 941, 947 are transparent (for
example, clear). Each of the four thinner segments 942,
943, 945, 946 can be a different color; for example,
segment 942 can be red, segment 943 can be green, segment
20 945 can be yellow or black, and segment 946 can be blue.
Many other color combinations are also possible. For
example, combinations of achromatic and chromatic colors
can be used; two segments can be made the same color (for
instance, both segments 943 and 945 can be green, or both
25 segments 942 and 946 can be red); and so forth_ The
fabrication techniques described above can be used to
make ball 940; in particular, the broad central segment
944 can be composed of two thinner transparent segments
of like material that effectively merge to form the broad
30 central segment. .
Ball 940 is made with segments of different zeta
potentials, so that it can be oriented to different
orientations by application of suitable electric fields.
In particular, segment 941 can be made with the highest
35 positive zeta potential of any segment in ball 940, and
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segment 945, with the highest negative zeta potential of
any segment in ball 940.
If ball 940 is rotated so that segment 946 faces an
observer, the observer sees the color of segment 946, for
example, blue. This is illustrated in FIG. 9B.
Similarly, if ball 940 is rotated so that segment 942
faces the observer, the observer sees the color of
segment 942, for example, red. If ball 940 is rotated to
an orientation between these two extremes, for example,
by using the canted-field electrode configuration to
generate an angled electric field as was described with
reference to FIG. 8C, the observer sees a combination of
two colors. These will be either the colors of segments
942 and 945 (for example, red and yellow) or, as shown in
FIG. 9C, the colors of segments 943 and 946 (for example,
green and blue).
Finally, white can be obtained by using a white
background below the ball, and turning the ball to the
90-degree position so that the broad central segment 944
faces the observer. The background can be provided, for
example, by adhesively attaching an opaque white backing
to the elastomer sheet on the side away from the
observer. An example is shown in FIG. 9D, which
illustrates a side view of a portion of a gyricon 900
that includes elastomer layer 910, seven-segment balls
91I, and a layer of backing material 9I2 attached to
elastomer layer 910. Alternatively, the backing can be
omitted or can be made of a transparent material, so that
the gyricon sheet can be used as an overlay transparency,
for example, to be overlaid on a textual document or
other opaque or reflective background.
With this arrangement, the resulting display
provides good color saturation for the colors of segments
942 and 946, and lesser color saturation of the colors of
segments 943 and 945. Thus it can display parts of the
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color gamut that are unobtainable with a two-color
display.
Full-Color (RGB) Additive Color Gyricon
A gyricon with a canted-field electrode
configuration can be used to provide a full-color, red
green-blue (RGB) additive color image. FIG. 10A
illustrates a three-segment gyricon ball suitable for
such a display. Ball 1040 has two broad transparent (for
example, clear) outer segments 1041, 1043 and a thin
central segment 1042. For an RGB display, central
segment 1042 is pigmented or dyed red, blue, or green.
Ball 1040 is made with segments of different zeta
potentials, so that it can be oriented to different
orientations by application of suitable electric fields.
IS In particular, segment 1041 can be made with the highest
positive zeta potential of any of the three segments in
ball 1040, and segment 1043, with the highest negative
zeta potential of any of the three segments.
To make a full-color RGB display, a gyricon sheet
can be formed of balls like ball 1040. For a pixel
addressable RGB display, each pixel can include a red
subpixel, a green subpixel, and a blue subpixel, with
each subpixel containing one or more balls of its
respective color. Preferably, a subpixel contains a
large number of balls (for example, nine or more) located
near to one another. A canted-field electrode
configuration is provided such that each pixel or
subpixel can be individually addressed and the ball or
balls within that pixel or subpixel can be oriented at
any angle with respect to the sheet's surface. -
FIG. 10B illustrates a side view of a portion of an
elastomer sheet 1010 from an RGB gyricon. Sheet 1010 '
contains balls such as balls 1040, 1050, and 1060, each
of which has two broad transparent outer segments and a
thin, colored central segment. Ball 1040 is oriented in
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a direction indicated by arrow a, with its thin central
segment 1042 seen edge-on by an observer at z. In this
orientation, which can be achieved by applying an
electric field parallel to the surface of sheet 1010 in
the vicinity of ball 1040, ball 1040 appears
substantially transparent to an observer at I. Ball
1050, which has transparent outer segments 1051, 1053 and
central segment 1052, is oriented in a direction
indicated by arrow b. In this orientation, which can be
IO achieved by applying an electric field perpendicular to
the surface of sheet 1010 in the vicinity of ball 1050,
central segment 1052 is seen face-on so that ball 1050
appears as a fully saturated color to an observer at I.
Ball 1060, which has transparent outer segments 1061,
IS 1063 and central segment 1062, is oriented in a direction
indicated by arrow c. In this orientation, which can be
achieved by applying an electric field at an angle
intermediate between parallel and perpendicular to the
surface of sheet 1010 in the vicinity of ball 1060,
20 central segment 1062 is seen at an angle, so that ball
1060 appears as a partially saturated color to an
observer at I.
If, for example, central segments 1042, 1052, and
1062 are colored red, green, and blue, respectively, then
25 the pardon of sheet 1010 indicated as 1010a in FIG. IOB
can serve as a pixel having one ball of each color; each
of balls 1040, 1050, 1060 provides a subpixel of this
pixel. (In practice, as indicated above, an RGB gyricon
is likely to have many balls per subpixel. Nevertheless,
30 the one-ball-per-subpixel arrangement illustrated here is
also possible, and provides an easily understood example
for purposes of exposition and discussion.)
The colored central segments of the balls used in an
RGB gyricon, such as balls 1040, 1050, 1060, can be
35 either light-reflective (i.e., of opaque colors) or
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light-transmissive (i.e., of transparent colors). If the
central segments are light-reflective, the RGB gyricon
provides a reflective display that can be viewed in
ambient light. For example, an RGB gyricon having a
S transparent elastomer layer and balls with light-
reflective central segments can be used as an overlay -
transparency, in a manner similar to that previously
described for transparency 750 in FIG. 7B above. If the
central segments are light-transmissive and if other
components are suitably transparent, the gyricon provides
a transmissive display that can be viewed by being
backlit or used in conjunction with a projector, such as
an overhead projector, or by being placed on a sheet of
ordinary white paper or other diffuser.
For example, an RGB gyricon having a transparent
elastomer layer and balls with light-transmissive central
segments can be used in a projector in a manner similar
to that previously described for transparency 755 in
FIGS. 7C-7D above. However, whereas the projected image
produced with the highlight color gyricon previously
described was a black-and-white image, here the image
projected on screen 757 appears in full color. This is
because the central color segments of the balls of the
gyricon are transmissive rather than opaque.
As another example, an RGB gyricon having a
transparent elastomer layer and balls with light-
transmissive central segments can be used in a manner
similar to that previously described for transparency 750
in FIG. 7B above. However, whereas the black and
highlight color segments of the balls in the highlight -
color gyricon previously described absorbed or reflected
incident light, here the color segments of the balls
within the RGB gyricon act as color filters. White light
passing through the color segments of the balls can be
reflected by an underlying white sheet of paper (such as
document 751) and then pass back through the gyricon to
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the observer at I, where it will appear red, green, or
blue as the case may be. Again, this is because the
central color segments of the balls of the gyricon are
- transmissive rather than opaque.
As yet another example, in some cases it is useful
- to provide a display that is readable either by
transmitted light or by ambient light. This can be done
for an RGB gyricon having a transparent elastomer layer
and balls with light-transmissive central segments, again
by using an overlay arrangement in a manner similar to
that previously described for transparency ?50 in FIG. 7B
above, but with the underlying document ?51 being
replaced by a special surface that appears white in
reflected light, yet is reasonably transmissive to
i5 backlight. A suitable material for such a surface is so-
called opal glass (available from the EDMUND SCIENTIFIC
CO.; said to be "similar to ground glass but one surface
is flashed with a milky white 'opal' covering to diffuse
light evenly," Edmund Scientific Co. Catalog #14N1,
p. 47). With this arrangement, the display appears white
both by reflected ambient light and by transmitted
backlight (e.g., projected light as in FIG. 7D} with the
balls oriented with their center segments perpendicular
to the plane of the gyricon, so as to reveal the opal
glass to the observer. When the balls are oriented with
their center segments parallel to the plane of the
gyricon, the display takes on the colors of the colored
center segments, both by reflected and by transmitted
light.
The transmissive RGB gyricon does not, by itself,
provide a black color. Thus in the previous two examples
in which the transmissive RGB gyricon is used with a
sheet of white paper or with opal glass, the available
color gamut ranges from fully saturated colors to white,
but does not include black. However, if underlying
document ?51 is a black and white document, such as an
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ordinary page of black printed text on white paper, then
the black of this document can be perceived through the
transparency 750. Thus an application for which the RGB
gyricon transparency can be well-suited is as an -
"electric highlighter" overlay for black and white
documents, the electric paper analog of a highlighting -
marker pen. For this application, RGB color capability
is but one possibility, and other colors in addition to
or instead of red, green, and blue can be used for the
t0 center segments of the balls that make up the gyricon.
For example, an electric highlighter gyricon can be made
from three-segment gyricon balls that have center
segments of a transparent yellow or pink color, similar
to the colors of conventional highlighting pens. (If the
IS electric highlighter is to be used to provide a single
highlight color only, then all the balls in the gyricon
can have the same center segment color and the ball-
placement techniques described below are thus not needed
for the gyricon's fabrication.)
20 To control the red, green, and blue colors of an RGB
gyricon independently of one another, it is necessary to
be able to rotate balls of one color without affecting
balls of the other two colors. This can be achieved, for
example, by localizing balls of one color together in
25 subpixels, as illustrated in FIG. IOC. A top view of an
enlarged portion of elastomer sheet 1010 is shown. Pixel
1070 includes red subpixel 1071, green subpixel 1072,.
blue subpixel 1073. Each subpixel contains gyricon balls
1074, 1075, 1076 of its respective color only; for
30 example, all the gyricon balls 10?4 in red subpixel 1071 ,
are red. The arrangement of the subpixels within each
pixel can vary in different embodiments; for example, as -
shown in FIG. lOC, the subpixels can be arranged as the
vertices of an equilateral triangle.
35 Techniques for placement of gyricon balls at
specified positions within an elastomer sheet will be
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described below with reference to FIGS._I5A-15D. These
techniques can be used, in particular, to position red,
green, and blue gyricon balls in any desired pattern of
_ subpixels.
Multilayer Subtractive Color Gyricon
- A gyricon with a canted-field electrode
configuration can also be used to provide a full-color,
cyan-magenta-yellow (CMY) subtractive color image. In
subtractive color imaging, unwanted color components are
filtered out of incident light, typically by means of
transparent color filters or dyes. Here, the gyricon
balls, and more particularly their center segments, act
as color filters.
A three-segment ball like the ball 1040 illustrated
in FIG. l0A can be used for a subtractive color CMY
gyricon, with central segment 1042 being pigmented or
dyed a light-transmissive cyan, magenta, or yellow. The
gyricon sheet contains three layers, situated one above
the other. One layer contains cyan balls (that is, balls
whose central segments are cyan); one contains magenta
balls; and one contains yellow balls. Within a given
layer, a group of one or more balls can serve to provide
a component color for color subtraction. Preferably, a
large number of balls (for example, nine or more) located
near one another are used for each component color in
each pixel. A pixel is made up of a column of three
color regions situated above one another, one region from
each of the three layers.
FIG. 11A illustrates a side view of a portion of an
elastomer sheet 1110 from a CMY gyricon. Sheet 1110 has
three layers 1116, 1117, 1118. Balls in layer 1116,
including balls 1140a, 1140b, and 1140c, have central
segments of a first color, such as yellow; for example,
ball 1I40a has yellow central segment 1142a. Balls in
layer 1117, including balls 1150x, 1150b, and 1150c, have
central segments of a second color, such as magenta; for
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example, ball 1150a has magenta central. segment I152a.
Balls in layer 2118, including balls 1160x, I160b, and
1160e, have central segments of a third color, such as
cyan; for example, ball II60a has cyan central segment
1I62a. Each of the balls 1140x, 1140b, 1140c, 1150x,
1150b, 1150c, 1160x, 1160b, and 116Oc can be made
individually addressable. The orientation directions of
these balls are indicated by arrows a, b, c, d, e, f, g,
h, and j, respectively.
A pixel is formed by a combination of one or more
color regions that can be seen in superposition by an
observer at I. Thus, for example, the balls I140a,
1350x, and 1160a in the rectangular columnar portion of
sheet 1110 denoted as 1110a together can form a pixel.
Similarly, the balls 1I40b, 1150b, and 1160b in the
rectangular columnar portion of sheet 1110 denoted as
lllOb together can form another pixel, and the balls
I140c, 1150c, and 1I60e in the rectangular columnar
portion of sheet 1210 denoted as 1110e together can form
still another pixel. (In practice, as indicated above, a
CMY gyricon is likely to have many balls far each
component color in each pixel. Nevertheless, the one-
ball-per-color arrangement illustrated here is also
possible, and provides an easily understood example for
purposes of exposition and discussion.y
The balls I140a, 1150x, and 1160a all are oriented
with their central segments 1142x, II52a, I162a facing
an observer at I, so that full color saturation obtains
for the cyan, magenta, and yellow components. ,
Accordingly, the pixel at 1110a appears black. The balls
1140c, I150c, and 1160c all are oriented with their
central segments edge-on with respect to an observer at
I, so that all these balls look substantially
transparent. Accordingly, the pixel at 1110e appears
substantially transparent. Ball 1140b is oriented with
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its central segment facing an observer at I; ball 1150b,
with its central segment at a first angle with respect to
an observer at I; and ball 1160b, with its central
- segment at a second angle with respect to an observer at
I. Accordingly, the yellow component of the pixel at
1110b appears fully saturated, the magenta component less
saturated, and the cyan component still less saturated.
FIG. 11B shows a view from above the pixel at 1110b.
The central segment of ball I140b appears as a circle A.
i0 The central segment of ball 1150b appears as a first
ellipse B superposed on the circle A. The central
segment of ball 1160b appears as a second, narrower
ellipse C superposed on the first ellipse 8. Thus in the
narrow ellipse C, ail three color components (yellow,
i5 magenta, cyan) are superposed.
A CMY gyricon can be fabricated either from three
separate elastomer sheets (one for each color of balls)
laid down on top of one another, or from a single sheet
in which successive layers of different colored balls are
20 laid down. In either case, each component color region
in each pixel is preferably made up of a large number of
balls, and therefore the balls of one sheet or layer need
not be aligned with those of any other sheet or layer.
This is illustrated in the cross-sectional view of FIG.
25 11C, which shows a portion of an elastomer sheet 1170 for
a CMY gyricon. Sheet il?0 has a layer 1171 of cyan balls
11?4 (that is, balls 11?4 have cyan center segments), a
layer I1?2 of magenta balls il?5, and a layer 1173 of
yellow balls 11?6. A pixel 11?? visible to an observer
30 at I includes a column-shaped portion of sheet 1170.
FIG. 11D shows an exploded view of pixel 117? separated
from the remainder of sheet 1i?0. (If a CMY gyricon is
constructed so that each pixel contains only one ball of
each color, as shown in FIGS. 11A-11B, balls in the
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different layers preferably should be aligned so as to
facilitate proper color subtraction.)
Preferably each of the three layers of a CMY gyricon
can be addressed separately from the other two layers. .
One way to accomplish this is to provide a separate
addressing electrode for each gyricon layer, as -
illustrated in the exploded view of FIG. 11E. Gyricon
1180 has a layer 1181 of cyan balls, a layer 1182 of
magenta balls, and a layer 1183 of yellow balls. On
IO either side of each layer is disposed a transparent
addressing electrode in the form of a pixel array, so
that a different canted field can be applied at each
pixel position in each layer. Electrodes 1184x, 1184b
are disposed on either side of cyan layer 1181.
i5 Electrodes 1185a, 1185b are disposed on either side of
magenta layer 1182. Electrodes 1186x, 1186b are disposed
on either side of yellow layer 1183. Electrodes of
successive layers are shielded from one another by
transparent conductors 1187a, 1187b, 1187c disposed
20 between the electrodes of one layer and the next.
A CMY gyricon having a separate electrode per layer,
as shown in FIG. 11E, can be cumbersome and expensive to
produce. Also, the many layers of electrodes and
conductive shielding can cut down on the amount of light
25 that passes through the gyricon, so that the gyricon
image is less bright than it would otherwise be. Thus it
can be preferable in some circumstances to address all
layers of a CMY gyricon with a single electrode assembly.
For example, in FIG. I1F, sheet 1188 of gyricon 113? is a
30 three-layer elastomer sheet, similar in construction to
sheet 11?0 of FIG. 11C. Electrodes 1189a, 1189b are
disposed on either side of sheet 1188. It is desired to -
use the electrodes 1189a,1189b to cause rotations of
balls of any or all of the three layers of sheet 1188.
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A single set of electrodes (as depicted in FIG. 11F)
suffices to control an entire CMY gyricon if balls in
different layers of the gyricon have different rotational
thresholds. For example, in FIG. 11A, if balls in the
top layer 1116 will begin to rotate only upon
~ application of a strong electric field E1, balls in the
middle layer 1127 upon application of an intermediate
electric field E2, and balls in the bottom layer 1118
upon application of a weak electric field E3, then a
single set of electrodes can be used to address balls of
all three colors in a pixel { for example, to address all
of balls 1140a, 1150a, 1160a of the pixel at 1110a). As
another example, if in FIG. 11C, balls in top layer II71
will begin to rotate only upon application of a strong
i5 electric field E1, balls in the middle layer 1172 upon
application of an intermediate electric field E2, and
balls in the bottom layer 11?3 upon application of a weak
electric field E3, then a single set of electrodes can be
used to address all three color components of pixel 11??.
In both examples, application of the strong electric
field E1 will cause balls in all three layers to rotate.
Application of the intermediate field E2 will cause only
those balls in the middle and bottom layers to rotate.
Application of the weak field E3 causes only those in the
bottom layer to rotate. Thus the bails in all three
layers can be rotated as desired by successive
application of strong, intermediate, and weak addressing
fields. This multipass, multithreshold addressing
technique is further described below with reference to
. 30 FIGS. 14A-14G.
A pixel-addressable subtractive color gyricon
- display can be constructed without any need for precision
alignment of the addressing electrodes with respect to
the gyricon sheet. Instead, pixels will be formed
wherever the electrodes happen to be. This is an
advantage of the subtractive color gyricon over the
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additive color gyricon previously described with
reference to FIGS. l0A-IOC. In the RGB gyricon subpixel
arrangement as shown in FIG. lOC, for example, each of
the subpixels 1071, 1072, 1073 must be aligned properly
3 with the subpixel array elements of the addressing
electrodes to ensure that an applied electric field
causes one and only one subpixel of the appropriate color
to be addressed. A misalignment between the array
elements of the addressing electrode and the array
elements of the gyricon sheet can cause portions of
multiple subpixels of the sheet to be addressed by a
single array element of the electrode, and can cause
color errors, such as substitution of red subpixels for
green and blue for red, in the produced image. With the
subtractive color gyricon of FIGS. 11A-11D, addressed
with a single electrode assembly as in FIG. 11F, none of
these problems can arise. Instead, the addressing
electrodes 1189a, 1189b need only be aligned to each
other, and can be placed anywhere with respect to the
gyricon sheet 1188. If a multiple-electrode assembly is
used as in FIG. 11E, the electrodes for the different
layers must be aligned with one another, but again, there
is no need to align the layers of elastomer to the
electrodes, or to align the layers to each other. For
example, it is unnecessary to align cyan layer 1181 with
its electrodes 1184x, 1184b, or to align cyan layer 1181
with magenta layer 1182 or yellow layer 1183.
The series of views in FIG. 11G further illustrates
these ideas. In the first view of FIG. 11G, pixel array
addressing electrodes 1191a, 1191b are placed on either ,
side of a rectangular multilayer gyricon sheet 1190,
oriented parallel to the boundaries of the rectangle of -
sheet 1190. Pixels, such as pixel 1192, are formed in
rectangular columnar regions of sheet 1190. The
locations of pixel 1192 and other pixels with respect to
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the boundaries of rectangular sheet. 1190 is not
predefined. Rather, the placement of electrodes 1191x,
1191b with respect to sheet 1190 defines where the pixels
will be. If the electrodes are placed differently with
respect to the sheet, the pixels will end up somewhere
' else in the sheet. For example, the second view of FIG.
I1G shows what happens if the addressing electrodes
1191x, 1191b are removed from contact with sheet 1190 and
thereafter are replaced such that they are now oriented
at an angle ~ to the boundaries of the rectangle of sheet
1190. The pixel array is now skewed with respect to the
boundaries of the rectangle. For example, the
counterpart to pixel 1192 of the first view of FIG. 11G
is pixel 1192 in the second view of FIG. IIG.
In contrast with the additive color gyricon, there
are no subpixels of different colors in the subtractive
color gyricon. Rather, the entire field of each pixel is
filled with all the component colors, superposed on one
another. This can improve the richness and accuracy of
the resulting color image over what is obtainable with
additive color techniques.
To ensure the highest levels of color saturation and
overall image quality in a subtractive color gyricon,
each component color layer of each pixel can present a
complete ball fill to the observer. For example, within
each color layer, there can be two or more layers of
balls, stacked one on another as illustrated in FIG. I1H.
Gyricon sheet 1133 includes layers 1134, 1135, 1136 that
contain three-segment balls having cyan, magenta, and
yellow center segments respectively. The balls in layer
1134 are themselves arranged in three close-packed layers
' 1134x, 1134b, 1i34c. The balls in layer 1135 are
arranged in three close-packed layers 1135a, 1135b,
1135c. The balls in layer 1136 are arranged in three
close-packed layers 1136x, 1136b, 1136c. Thus little or
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no light can pass through gyricon sheet II33 without
being color filtered when the balls are suitably rotated.
To minimize light scattering and to obtain the highest
light efficiencies, it is preferable for the balls to
have the same refractive indicies as the elastomer and
the dielectric fluid permeating the elastomer.
The colors of the cyan, magenta, and yellow center
segments of the balls used in the CMY subtractive color
gyricon are typically transparent colors rather than
opaque colors. Thus the CMY gyricon can be used with a
backlighting source, such as a projector, or with a
reflective backing (e. g., a sheet of ordinary white paper
or other diffuser) in ambient light. Typically, bright
incident light is preferable, inasmuch as the gyricon
t5 acts to filter out incident light in order to produce the
colors of the image. Examples of use are comparable to
those previously described with reference to FIGS. 7B,
7C, and 7D above as adapted for the RGB gyricon with
balls having transparent central segments. The use of
the CMY gyricon as in FIGS. 7C-7D provides a full-color
projected image on screen 757. The use of the CMY
gyricon as in FIG. 7B provides an image in which light
filtered by the transparent color segments of the balls
can be reflected from an underlying surface (e. g.,
document 751) back through the gyricon and thence to the
observer at I: note that, unlike the RGB gyricon, light
can be effectively absorbed within the CMY gyricon if it
is filtered through all three component colors.
A subtractive color gyricon need not be limited to
cyan, magenta, and yellow component colors. Other
colors can be substituted and additional layers carrying
additional colors can be added. In particular, a full _
four-color CMYK (cyan-magenta-yellow-black) gyricon can
be constructed by adding a fourth layer to the CMY
gyricon. The CMYK gyricon provides a color capability
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analogous to the CMYK color scheme typically used in
four-color printing.
FIG. 11J illustrates a CMYK subtractive color
gyricon. Gyricon 1195 has layers 1196, 1197, 1198, and
1199 which contribute, respectively, cyan, magenta,
yellow, and black component colors to the image. The
gyricon balls used in layers 1196, 1197, 1198 are as
described previously for layers 1116, 1117, 1118 in
gyricon sheet 1110 of FIG. 11A. The balls used in the
black layer 1199 are also three-segment balls, similar in
construction to the balls used in the other layers.
However, the center segments are opaque black rather than
transparent chromatic colors as in the other layers. As
for the CMY gyricon, the CMYK gyricon can be used with
backlighting, such as a projector, or with a reflective
backing. Examples of use are comparable to those
previously described with reference to FIGS. 7B, 7C, and
7D above, as adapted for the CMY gyricon; note with
reference to FIG. 7B that the black segments of the balls
in layer 1199 can fully absorb incident light.
A subtractive color gyricon can also have fewer than
three component colors. For example, a two-layer
gyricon based on three-segment gyricon balls with
transparent exterior segments can be made that includes a
first layer of balls with black center segments (as in
the CMYK display) and a second layer of balls with center
segments of a transparent color. Such a gyricon would be '
useful for providing a display of black plus a highlight
color over a white background or in a backlit mode.
. 30 Another possibility is a two-layer gyricon that has a
first layer of a first transparent color and a second
layer of its complementary (also transparent) color. For
example, the first layer can be blue and the second one
yellow. This gyricon can produce each of its component
colors plus black, which is produced by the subtraction
of two complementary colors. Controlled by a canted-
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field electrode, the gyricon thus provides variable
saturations of the component colors plus variable gray
scale.
Additive Color Gyricon using Bi-state or Tri-state >;iqht
Valves
A gyricon in which the balls themselves have no -
chromatically colored segments can be used to provide a
full-color, red-green-blue fRGB) display. Two approaches
to such a display will be described. In both approaches,
the balls in the gyricon sheet act as light valves, in
that they can be used to reveal or obscure color dots to
or from an observer. Using a canted-field electrode
configuration as previously described, balls can be
rotated through a continuous range of angles, thus
allowing a continuous range of color saturation. Each of
the dots can be red, green, or blue, and can be formed
using, for example, an active light source, a backlit
colored filter or transparency, or a reflective colored
backing attached to the gyricon sheet and illuminated by
ambient light. Thus the gyricon can be adapted for use
in a backlit or projective mode or in ambient light.
The two approaches differ in the kind of gyricon
balls used. In the first approach, a layer of three-
segment balls that can act as bistate (two-state) light
valves is used to reveal or obscure the color dots . The
balls can be, for example, bails similar in construction
to those used in the RGB and CMY gyricons discussed
above, but with opaque (e. g., white or black) central
segments instead of transparent chromatically colored
central segments. In the second approach, a layer of
four-segment ball that can act as tristate (three-state)
light valves is used to reveal or obscure the color dots.
The balls, which will be described, have black, white,
and transparent (e.g., clear) segments. In an
alternative embodiment of the second approach, two layers
of three-segment balls are used in place of the four-
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51 _ _
segment ball, one layer in which the balls have black
center segments and the other in which the balls have
white center segments.
The terminology "bistate" and "tristate" light
valves is not meant to imply that these light valves are
- restricted to only two states or three states as the case
may be. Rather, the light valves have two or three basic
states (eigenstates) and a range of intermediate states
obtainable with the canted field electrode configuration.
Thus, as will be discussed momentarily, the bistate light
valve has two basic states: fully open, with the center
segment oriented perpendicular to the surface of the
gyricon sheet and the color dot maximally revealed; and
fully closed, with the center segment oriented parallel
to the surface and the color dot maximally obscured.
Intermediate states, in which the light valve is partly
open or partly closed are also attainable. Similarly,
the tristate light valve has three basic states: fully
open, with the center segment oriented perpendicular to
the surface of the gyricon sheet and the color dot
maximally revealed; fully closed/black, with a black
center segment facing the surface and oriented parallel
to the surface, and the color dot maximally obscured; and
fully closed/white, with a white center segment facing
the surface and oriented parallel to the surface, and the
color dot once again maximally obscured.
Turning now to the first approach, a three-segment
ball such as that illustrated in FIG. 12A is used. Ball
1235 has two transparent (for example, clear) end
segments 1236, 1238 and a central opaque segment 1237.
Ball 1235 is made with segments of different zeta
potentials, so that it can be oriented to different
orientations by application of suitable electric fields.
In particular, segment 1236 can be made with the highest
positive zeta potential of any of the three segments in
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ball 1235, and segment 1238, with the highest negative
zeta potential of any of the three segments.
Ball 1235 can act as a bistate light valve, as is
depicted schematically in the examples of FIGS. 12B-12D.
In each of these examples, a color dot 1239 is situated
below ball 1235 and an observer at I is situated above
ball 1235 and opposite to color dot 1239. A canted-
field electrode is used to orient ball 1235. In FIG.
I2B, ball 1235 is oriented in the direction shown by
arrow a, with its opaque central segment parallel to the
plane of dot 1239, so that opaque central segment 1237
completely obscures dot 1239 from the view of the
observer at I. As shown, dot 1239 appears black to the
observer at I. In FIG. 12C, ball 1235 is oriented in the
direction shown by arrow b, so that opaque central
segment 1237 is transverse to the plane of dot 1239. As
shown, substantially all (more precisely, all but a thin
band) of dot 1239 is seen by the observer at I. In FIG.
12D, ball 1235 is oriented in the direction shown by
arrow c, so that opaque central segment 1237 is at an
angle intermediate betwen parallel and perpendicular to
the plane of dot 1239. (The canted-field electrode
permits any intermediate angle to be obtained.) Opaque
central segment 1237 partially obscures dot 1239 from the
view of the observer at I.
A full-color RGB display can be built with balls.
like ball 1235, for example by placing a gyricon sheet
formed of such balls in front of a background
transparency or backing material patterned with
transparent red, green, and blue color filters (for a
backlit display) , or in front of a background surface or -
backing material patterned with reflective red, green,
and blue dots (for an ambient light display). Each pixel
of the display includes a red, a green, and a blue dot,
with each of these color dots corresponding to a
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subpixel. Each color dot is associated with its own
independently addressable ball or, preferably, set of
many balls that act as the light valve for that dot. Thus
the color saturation of a subpixel can be controlled by
adjusting the angle of the ball or balls over the dot to
reveal or obscure more or less of the color dot. If many
balls are used per subpixel, color saturation can also be
controlled without canted fields by turning a greater or
lesser number of the balls parallel or transverse to the
plane of the color dots, using multithreshold techniques
as described below with reference to FIGS. 14A-14G. The
arrangement of the subpixels within each pixel can vary
in different embodiments; for example, the subpixels can
be arranged as the vertices of an equilateral triangle.
Examples of use of the bistate light-valve RGB
gyricon in backlit and projective modes are comparable to
those previously described with reference to FIGS. ?B,
7C, and 7D. Used in projective mode as in FIGS. 7C-7D,
the gyricon provides a full-color RGB projected image on
screen 757. Used in overlay mode as in FIG. 7B, the
gyricon provides a transparent full-color overlay for the
underlying document 751. In overlay mode, light incident
on bistate light-valve gyricon 750 can be absorbed by, or
reflected from, the center segments of the balls when the
balls are oriented with their center segments parallel to
the plane of the gyricon. When the balls are oriented
with their center segments transverse to the plane of the
gyricon, light is transmitted through the transparent
segments of the balls, filtered by the transparent color
filters, and reflected from white portions of the
underlying document 751 back through the transparent
color filters and the transparent ball segments of
gyricon 750 to the observer at I.
An example of use of the bistate light-valve RGB
gyricon as a self-contained (rather than overlay) ambient
light display is also comparable to FIG. 7B, except that
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the patterned backing material of the gyricon itself
takes the place of underlying document 751. Ambient
light incident on the gyricon can be reflected by or
absorbed by the opaque center segments of the balls, or
can pass through the transparent segments of the balls to
be reflected by the color dots of the patterned backing
material and back through the gyricon sheet to the
observer at I.
The first, bistate light-valve approach is well
suited for a backlit display. It can be less suitable
for a self-contained ambient light display because of
light loss due to scattering, which can lead to a dim and
desaturated or "washed-out" display appearance. For
example, if the opaque center segments of the balls are
black, then "white" is achieved by turning all three
subpixels on at once. This "white" can appear gray as
compared to the white offered by traditional reflective
media, such as ordinary paper.
The second, tristate light-valve approach addresses
this concern. The tristate light valves have black,
white, and transparent states, with the underlying color
dot being visible through the transparent portions of the
gyricon balls. The availability of both white and black
in conjunction with red, green, and blue provides an
~5 enhanced color gamut over the first, bistate light-valve
approach, and makes the second approach particularly
well-suited for use in ambient light displays.
FIG. 12E illustrates a four-segment gyricon ball
suitable for an ambient light RGB display according to
the second approach. Ball 1240 has two broad transparent
(for example, clear) outer segments 1241, 1244 and two
thin central segments 1242, 1243. Segment 1242 is
pigmented white and segment 1243 is pigmented black.
Ball 1240 is made with segments of different zeta
potentials, so that it can be oriented to different
orientations by application of suitable electric fields.
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In particular, segment 1241 can be made with the most
positive zeta potential of any of the four segments in
ball 1240, and segment 1244, with the most negative zeta
potential of any of the four segments.
To make an ambient color display, a gyricon sheet
formed of balls like ball 1240 can be placed over a
reflective backing of red, green, and blue color dots. A
canted-field electrode configuration is provided such
that each ball can be individually addressed and oriented
at any angle with respect to the sheet's surface. Each
ball can provide a subpixel of a pixel-addressable
display in which each pixel includes a ball located above
a red dot, a ball located above a green dot, and a ball
located above a blue dot, similarly to the first
approach. However, because the ball has both black and
white central segments, it can do more than just reveal
or obscure the underlying dot. Rather, as the ball
rotates through 180 degrees, the light from a subpixel
will adjust as follows: black, dark color, saturated
color, light color, white . For example, with a red dot,
an observer will see a range of colors as follows:
black, dark red, red, light red, white. (Preferably, as
with the bistate light-valve approach, many balls are
used per subpixel, in particular to obviate the need to
align individual balls with individual subpixels during
manufacture of the gyricon. Nevertheless, the one-ball-
per-subpixel arrangement described here is also possible,
and provides-an easily understood example for purposes of
exposition and discussion.)
Accordingly, the second approach can increase the
brightness of the display, especially in the part of the
color space between fully saturated color and white. The
entire color cube of color space can be generated.
Moreover, a light-colored primary color (for example,
light red) can be generated with a single subpixel.
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FIG. 12F illustrates an exploded view of a portion
of an ambient color display gyricon 1200 in the second
approach. Elastomer sheet 1210 is affixed to a backing
1290 that has red, green, and blue dots (dots 1291, 1292, .
and 1293, respectively). Embedded in sheet 1210 are
four-segment balls including balls 1240, 1250, 1260, '
which can act as tristate light valves to reveal the dots
of backing 1290 or to obscure the dots of backing 1290
using either their respective black or white center
l0 segments. Thus, for example, ball 1240, whose
orientation direction is indicated by arrow a, presents a
substantially transparent aspect to an observer at I,
thus revealing a fully saturated red dot 1291. Ball
1250, whose orientation direction is indicated by arrow
IS b, presents a white face to an observer at I and
completely occludes the view of underlying green dot
1292. Ball 1260, whose orientation. direction is
indicated by arrow e, is oriented at an angle to the
surface of sheet 2210 and thus presents a portion of a
20 black face to an observer at I, while revealing a portion
of the blue dot 1293 below.
The view from the standpoint of an observer at I of
the subpixel formed by ball 1240 in combination with red
dot 1291 is schematically depicted for two different
25 orientations of ball 1240 in the examples of FIGS. 12G
and 12H. In both figures, red dot 1291 appears as a
circle A. In FIG. 12G, the thin black segment 1243 of
ball 1240 is seen as an ellipse B superposed on circle A.
Thus the subpixel has black and red color components,
30 and so appears dark red. In FIG. 12H, the thin white
segment 1242 of ball 1240 is seen as an ellipse B
superposed on circle A. Thus the subpixel has white and
red color components, and so appears light red.
Examples of use of the tristate light-valve RGB
35 gyricon in_backlit and projective modes are comparable to
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- 57 _ _
those previously described with reference to FTGS. 7B,
7C, and 7D. Used in projective mode as in FIGS. 7C-7D,
the gyricon provides a full-color RGB projected image on
screen ?57. It should be noted, however, that because
the black and white center segments are opaque, they are
- not distinguishable from one another in the projected
image. Thus the tristate light-valve gyricon has no color
gamut advantage over the bistate light-valve when used in
projective mode. The color gamut advantage obtains when
the gyricon is used in overlay or self-contained ambient
light modes as in FIG. 7B, the description of FIG. 7B
here being modified as previously described for the
bistate light-valve gyricon.
An additional lighting mode will now be described
with reference to FIG. 12I. This mode is particularly
interesting for use with the tristate light-valve
gyricon, although it can also be used with the bistate
light-valve gyricon. Display 1280 includes a gyricon
1285 that is made up of a transparent elastomer layer
128? of four-segment tristate light-valve balls
(including balls 1287a, 1287b, 128?c) attached to a
transparent backing material 1286 patterned with
transparent color filters (including red subpixel filter
1286a, green subpixel filter 1286b, and blue subpixel
filter 1286x). Gyricon 1285 is illuminated
simultaneously from the front (that is, from the side
closest to the observer at I) by ambient light
originating at light source 2281, and from behind by a
uniform diffuse white light, here provided by an
- 30 electrically powered light source 1282 in conjunction
with a diffuser 1283, both of which can be built into
display housing 1284 as shown. Such built-in
backlighting is appropriate, for example, if display 1280
is to be used as a display for a laptop computer or the
like .
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In operation of display 1280, backlight source 1282
serves to make the colors observable by the observer at I
bright and vivid. For example, balls 1287a are oriented
so that light from source 1282 is transmitted through
3 diffuser 1283 and thence through red color filter 1286a
can pass through the transparent segments of balls 1287a.
The observer at I sees a red subpixel. A small amount of
ambient light from source 1281 is transmitted through
layer 1287 and red color filter 1286a and reflected by
diffuser 1283 back through filter 1286a and layer 1287 to
the observer at I; but the backlighting provides the most
significant light source for the subpixel.
Ambient light from light source 1281 serves to
illuminate the white center segments of balls in layer
1287, so that they are visible to the observer at I when
the balls are oriented with the white center segments
disposed toward the front of gyricon 1280. For example,
balls 1287b are oriented so as to hide green color filter
1286b from the observer at I. The white center segments
of balls i287b are visible in ambient light to the
observer at I, who sees a white subpixel. Backlighting
from source 1282 is blocked by the opaque center
segments.
Ambient light from light source 1281 is absorbed by
~5 the black center segments of balls in layer 1287. For
example, balls 1287c are oriented so as to hide blue
color filter 1286c from the observer at I. The black
center segments of balls 1287c absorb ambient light. The
observer at I sees a black subpixel. Again, backlighting _
from source 1282 is blocked by the opaque center
segments. -
FIG. 12J illustrates an alternative embodiment of
the tristate light valve gyricon. Here, two layers of
three-segment balls are used. Elastomer sheet 1270 has
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layers 1270a and 12?Ob, each layer containing bistate
light valve balls (similar in construction to ball 1235
of FIG. 12A). The balls in layer I270a have white center
segments. The balls in layer 1270b have black center
segments. Backing material 1279 provides the color dots
that are revealed or obscured by the balls so as to
provide colors visible to an observer at I.
The two layers of balls cooperate to provide a
tristate light valve, as shown: In region 1271 of sheet
1270, balls 12?la in upper layer 1270a and balls 1271b in
lower layer 1270b are rotated so that their center
segments are transverse to the plane of backing material
1279, thereby revealing the underlying dot I271c to the
observer at I. In region 1272 of sheet 1270, balls
1272a in upper layer 1270a are rotated so that their
white center segments are transverse to the plane of
backing material 12?9, and balls 1271b in lower layer
1270b are rotated so that their black center segments are
parallel to the plane of backing material 1279, obscuring
the underlying dot 1272c and presenting a black
appearance to the observer at I. In region 1273 of sheet
1270, balls 1273a in upper layer 1270a are rotated so
that their white center segments are parallel to the
plane of backing material 1279, obscuring the underlying
dot 1273c and presenting a white appearance to the
observer at I.
Balls in the two layers 1270x, 1270b can be
separately addressed by using multithreshold, multipass
addressing as per FIGS. 14A-14G below. If many balls are
used per subpixel, there is no need to align the upper
and lower layers with one another during manufacture.
The bistate and tristate light valve approaches both
offer certain advantages over the RGB gyricon described
previously with reference to FIGS. l0A-IOC. Notably,
there is no need to place different kinds of balls in
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different places within the elastomer sheet. Instead,
the same balls are used throughout the gyricon, and the
RGB subpixel regions of a reflective backing material,
for example, can be printed on the material using
conventional printing or color xerographic techniques.
Furthermore, if many balls are used per subpixel, the -
elastomer sheet need not be precisely aligned with the
backing material during manufacture. (However, it is
necessary to align the subpixels of the backing material
with the subpixels of the addressing electrodes.)
It will be appreciated that the bistate and tristate
light valve approaches can be used with color displays
other than RGB displays. For example, dots of additional
colors can be added. As another example, a highlight
i5 color display can be made using a backing material of a
single uniform highlight color, such as red or yellow, in
place of the dot-patterned backing material previously
described. Such a display, used for example with a
canted-field electrode, can provide a full range of the
highlight color, varying from white through light color
to fully saturated color to dark color to black, and,
like the CMY gyricon described earlier, does not require
precise alignment between the gyricon sheet and the
addressing electrode assembly. Instead, the pixels of
this highlight color display are defined by the relative
placement of the gyricon sheet and the electrodes, in a
manner similar to that previously described with
reference to FIG. 11G above. Still further, for use in
ambient light, the center segments of the balls (for
example) need not be black or white. For example,, a
highlight color overlay transparency for use with a white -
background (e.g., ordinary white paper) can be made by
providing a transparent elastomer and tristate balls
having black and highlight color center segments (e. g.,
black and red segments). Many other variations will be
apparent to persons skilled in the art.
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The operational principles of the tristate light
valve RGB display can be generalized beyond the
embodiments described here. Notably, it is not necessary
. that the tristate light valves be gyricon-based. As
other tristate light valves and devices or technologies
suitable for producing such valves are developed, they
can be adapted for use in color displays in which color
sources, such as RGB or other chromatic color sources,
are revealed or obscured by tristate light valves
i0 according to the principles that have been described
above. This is illustrated schematically for a single
pixel in FIG. 13. A light source 1300 provides a colored
light, such as a chromatically colored light, for the
pixel. A selector 1305 selects between black and white
mixture colors, and a mixture control 1307 selects the
proportions in which the colored light from light source
1300 and the mixture color (black or white) selected with
selector 1305 are to be mixed. The colored light is
mixed with the selected black or white mixture color in a
color mixer 1310, and the resulting color mixture is
provided to output 1315.
Multithreshold and Multipass Addressing Techniques
The CMY and CMYK subtractive color gyricons and the
two-layer tristate valve gyricon described above require
separate addressability for different balls in different
layers. It can be advantageous to provide this separate
addressability without using a separate addressing
electrode for each layer. More generally, there are
various circumstances in which it can be beneficial to
use a single electrode to address separately different
groups of different kinds of balls within a gyricon
sheet. For example, one way to achieve variable color
saturation in an RGB gyricon based on three-segment balls
(as in FIGS. 10A-lOC) or a CMY gyricon (as in FIGS. 11A-
11C) without using canted fields is to provide a
multiplicity of balls associated with each color in each
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subpixel. This multithreshold technique for controlling
color presence will be described more fully below with
reference to FIG. 14F.
Selective rotation of different kinds of gyricon
balls disposed in the same vicinity within the elastomer
sheet of the gyricon can be accomplished if each kind of -
ball has a distinct rotation threshold, that is, a
minimum electric field strength to which it will respond.
For example, in the two-layer arrangement of FIG. 12J,
suppose that the balls in layer 12?Oa will begin to
rotate only upon application of an electric potential
gradient of at least 90 volts per 30 mils of elastomer
thickness, and that the balls gyricon in layer 12?Ob
will begin to rotate only upon application of an electric
potential gradient of at least 80 volts per 30 mils of
elastomer thickness. Then if the total thickness of
sheet 12?0 is 30 mils (that is, 15 mils per layer), an
80-volt electric potential difference applied across
sheet 12?0 will cause balls in layer I2?0b to rotate but
will not affect balls in layer 12?Oa. A 90-volt
potential difference across sheet 12?0 will cause balls
in both layers I2?0a and 12?Ob to rotate. For example,
. the balls in region 12?1 can be oriented as shown, with
their center segments oriented transversely to the plane
of backing material 12?9, by a single application of a
90-volt potential difference across both layers of sheet
12?0 in region 12?1. The balls in region 12?3 can be
oriented as shown, with their center segments oriented
parallel to the plane of backing material 22?9, by a
single application of a 90-volt potential difference in
the plane of sheet 12?0 in region 12?3. The balls in
region 12?2 can be oriented as shown, with the center '
segments of balls 12?2a in layer 12?Oa oriented
transversely to the plane of backing material 12?9 and
the center segments of balls 12?2b in layer 12?Ob
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oriented parallel to the plane of backing material 1279,
by an application of a 90-volt potential difference
across sheet 1270 in region 1272 (which turns the balls
to the same orientation as the balls in region 1271)
followed by an application of an 80-volt potential
difference in the plane of sheet 1270 in region 1272
(which turns balls 1272b in layer 1270b so that their
center segments are parallel to the plane of backing
material 1279 but leaves balls I272a in layer I270a
l0 unaffected) .
Thus it can be seen that for two different kinds of
balls, at most two different electric field applications,
or "passes, " suffice to orient the balls as desired. In
general, if there are N distinct sets of balls to be
addressed, at most N passes are required.
FIGS. 14A-14G illustrate various principles and
applications of multithreshold, multipass gyricon
addressing. FIG. 14A shows one way that different
thresholds can be achieved: namely, by varying the size
of the balls. Two examples are shown. In example (a)
spherical balls in a first layer 1401 of a three-layer
gyricon sheet 1400 have a first radius Rl, spherical
balls in a second layer 1402 have a second radius R2, and
spherical balls in a third layer 1403 have a third radius
R3. In example (b) a single layer gyricon sheet 1405
includes balls 1405a, 1405b, and 1405c, having first
radius Rl, second radius R2, and third radius Rg
respectively. In both examples (a) and (b), RI > R2 > R3.
Other things being equal, the amount of torque that must
be applied to a ball of radius R1 in order to cause the
ball of radius R1 to rotate from a standing start will
tend to be greater than the amount of torque that must be
applied to a ball of radius R~ in order to cause the ball
of radius R2 to rotate from a standing start. Similarly,
other things being equal, the amount of torque that must
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be applied to a ball of radius R2 in order to cause the
ball of radius R2 to rotate from a standing start will
tend to be greater than the amount of torque that must be
applied to a ball of radius R3 in order to cause the ball
of radius R3 to rotate from a standing start.
A simple calculation illustrates why. Assuming that
the balls are of constant mass density and the electrical
dipole moment of each ball arises from a separation of
positive and negative surface charges in segments at
opposite ends of the ball, it follows that balls in layer
1401 have greater mass, greater moment of inertia and
greater dipole moment than balls in layer 1402, and balls
in layer 1402 have greater mass, moment of inertia, and
dipole moment than balls in layer 1403. However, it can
be shown that the moment of inertia grows faster with
increasing radius than does the dipole moment. This
suggests that the greater the radius of the ball, the
stronger the electric field that must be applied to cause
rotation.
Other parameters, such as the dipole moment, can be
varied to affect rotation threshold. In general, a wide
variety of parameters, both of the balls themselves and
of the cavities in the elastomer in which the balls
rotate, can affect the rotational thresholds of the
balls. (It is more precise to speak of "the rotational
threshold of a particular ball in a particular cavity
filled with a particular dielectric fluid in a particular
elastomer," the overall threshold being a result of a
complex interaction between the ball and its environment.
Nevertheless, it is convenient to speak of "the threshold
of the ball" as though the rotational threshold were .
associated with the ball alone. That practice is adopted
here, it being understood that other factors come into
play as well.)
Some of the factors that can affect the strength of
the electric field that must be applied to cause rotation
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of a given ball include: the ball's electrical
characteristics, such as the electrical dipole moment of
the ball and monopole moment, if any, due to the zeta
potentials of the ball segments which arise when the ball
is disposed in dielectric fluid within the substrate; the
ball's mechanical characteristics, especially those
affecting moment of inertia, such as mass, distribution
of mass within the ball, shape of the ball (including
deviation of the ball from a purely spherical shape to
l0 an ellipsoidal or other shape), size, and radius or mean
radius, as well as characteristics affecting the ball's
interaction with its spherical cavity, such as the ball's
coefficient of friction and surface roughness; the
structure of the ball, including the sizes and shapes of
any component segments or other regions within the ball
and the disposition of these component segments or other
regions relative to one another; and the materials that
make up the ball and its segments or regions, including
any materials) used in the manufacture of any component
regions) within the ball and any material used to coat
all or part of the surface of the ball. Additional
factors that can affect the strength of the electric
field that must be applied to cause rotation of a given
ball include: the characteristics of the cavity in which
the ball is situated, such as deviation from purely
spherical shape (including use of piezoelectric fields to
affect this, as disclosed in U.S. Patent No. 4,126,854,
incorporated hereinabove by reference, at col. 5, lines
16-29) and surface roughness or other factors affecting
coefficient of friction of the ball against the cavity
- wall: the material and mechanical characteristics of the
elastomer, including the stickiness of the elastomer
material; and the characteristics of the plasticizer
fluid permeating the elastomer and filling the cavity,
including viscosity and dielectric properties. The
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- 66 -
foregoing lists of factors are illustrative and by no
means exhaustive.
It should also be noted that other things being
equal, a thicker elastomer layer requires a higher -
applied voltage perpendicular to the layer surface in
order to cause rotation of balls of a given threshold.
Similarly, for in-plane fields, the larger the width of
the substrate region (e.g., the pixel or subpixel) to
which the field is applied, the greater must be the
voltage applied between one side of the pixel and the
other. These observations follow from the definition of
the electric field as the gradient of the electric
potential; for a uniform electric field this reduces to E
-- V/d, where V is the applied voltage and d is the
distance over which the voltage is applied.
The graph of FIG. 14B illustrates the behavior in
response to an applied voltage of an ideal gyricon in
which the gyricon balls are of three different rotation
thresholds. The graph plots the number of balls that
rotate in response to application of a given electric
field (ordinate) versus the voltage that must be applied
to a given thickness of elastomer sheeting in order to
produce that field (abscissa). For applied voltages
below threshold potential ~3, no balls rotate. For
applied voltages greater than or equal to threshold
potential cog and less than threshold potential ~2, balls
having the third (lowest) threshold rotate, while other
balls are unaffected. For applied voltages greater than
or equal to threshold potential ~2 and less than
threshold potential ~1, balls having the third or second _
(intermediate) threshold rotate, while balls having a
first (highest) threshold are unaffected. For applied
voltages above threshold potential ~1, all the balls
rotate.
In a practical gyricon, the ideal graph of FIG. 14B
is modified somewhat because of statistical variations
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among the balls. Typically, a given population of balls
having approximately equal physical characteristics will
have a range of thresholds clustered around a mean value,
due to minor variations in size, shape, electrical
characteristics and so forth from one ball to another.
Thus the response graph is not likely to be the series of
step functions of FIG. 14B. Instead, for a gyricon having
three populations of balls, each population having a
different average rotation threshold, the graph will be
as shown in FIG. 14C. As the voltage is increased from
zero, no balls rotate until a minimum threshold potential
~3 is reached, at which point balls of the third (lowest-
threshold) population begin to rotate. As the voltage is
further increased over the range between ~3 and ~3 + D3,
an increasing number of balls of the third population
rotate until, after the voltage exceeds ~3 + O3, all of
-11 - _t YL- 1L_ ~-7 ~ ~-7 . L 1 1 ~Y~L
thG ba115 O= LL1C Lillru pOpL11dt1UL1 will rVLCtt.C 1i1 reSEJOIlse
to the applied voltage. If the voltage is further
increased to a second minimum threshold potential
balls of the second (intermediate-threshold) population
begin to rotate, along with all the balls in the third
population. As the voltage is further increased over the
range between ~2 and c~2 + D2, an increasing number of
balls of the second population rotate until, after the
voltage exceeds ~2 + ~2, all of the balls of the third
and second populations will rotate in response to the
applied voltage. Further increasing the voltage beyond a
third minimum threshold potential ~1 causes some balls of
the first (highes-threshold) population to rotate along
- 30, with all the balls in the third and second populations.
Finally, as the voltage is further increased over the
range between ~1 and ~1 + O1, an increasing number of
balls of the second population rotate until, after the
voltage exceeds ~1 + O1, all of the balls of all three
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- 6s _ _
populations will rotate in response ,to the applied
voltage.
When a sharp threshold response is desired (for
example, when passive-matrix rather than active-matrix -
addressing electronics are to be used), the values of D3,
02, and D1 in FIG. 14C should preferably be made as small
as possible. This can be done, for example, by
tightening manufacturing tolerances for the balls so as
to reduce the variance of any physical characteristics of
t0 the balls strongly affecting rotation threshold (e. g.,
radius). In any case, the values of Og, d2, and D1
should be sufficiently small that the ranges of voltages
used for addressing different sets of balls do not
overlap. That is, if individual sets of balls are to be
separately addressed, the inequalities ~3 + D3 < ~2 and
+ 0~ < cal must be strictly satisfied.
Alternatively, it can be advantageous. in some cases
to make the values 03, 02, and D1 larger rather than
smaller. This is shown in FIG. 14D. The behavior of the
balls in response to increasing applied voltage is
similar to that described with reference to FIG. 14C.
However, because a3, 02, and O1 are larger relative to
their respective minimum thresholds ~3, ~2, and cal than
was the case in FIG. 14C, the slope of the graph in the
threshold regions is more gentle. If muitithresholding
is being used to control color saturation, as will be
described with reference to FIG. 14F below, this means
that the rate at which each color saturates with
increasing applied voltage is more gradual with the wider
O values of FIG. 14D than would be the case with the
narrower ~ values of FIG. 14C. Thus finer control over
color saturation is possible. Once again, the
inequalities ~3 + 03 < ~2 and ~2 + D2 < ~1 must be
strictly satisfied, and preferably the gaps y32 and Y21
between successive O ranges should be substantial. For
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example, if the overall elastomer sheeting thickness is
30 mils (that is, 10 mils per layer for a three-layer CMY
gyricon), some possible minimum threshold values are ~
' 80 volts, ~2 - 90 volts, and ~1 = 100 volts, with 03 = 02
- O1 - 5 volts . Consequently the gaps y32 and y21 are 5
volts.
A gyricon in which the gyricon balls have multiple
rotation thresholds can be addressed with multiple-pass
addressing. The series of views in FIG. 14E depicts
successive stages in addressing one pixel of a three-
layer CMY gyricon in which all the balls within any given
layer have a common, ideally sharp threshold (i.e., 03 -
d~ =O1 =0 ) . The views of the series are all side views
of a single-pixel region in gyricon sheet 1410. For a
thickness T of elastomer, balls in layer 1413 have a
lowest threshold potential fig, balls in layer 1412 have
an intermediate threshold potential ~2, and balls in
layer 1411 have a highest threshold potential ~1. Each
layer is to be addressed with a canted field, generated
on a per-pixel basis by a canted-field electrode that can
provide voltages V1, V2, V3, V4 at the periphery of the
rectangular columnar region of sheet 1410 that makes up
the pixel, as shown. The single-pixel region of sheet
1410 is assumed to have thickness T and width W.
In the first view of FIG. 14E, corresponding to the
first addressing pass, the voltages are set such that V1
V3~ ~. V2 - V4, and (V3 - V2)/W > ~1/T. The resulting
electric field E1 has a magnitude (V3 - V2)/W greater
_ than the threshold electric field magnitude sl - ~1/T
required to cause rotations of balls in layer 1411. The
field E1 is oriented in the direction of arrow a.
Application of the field E1 causes the balls of all three
layers 1411, 1412, 1413 to align their respective dipole
moments with the applied field. The dipole moment of
each ball, which arises from the zeta potential
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_ ~~ _ _
difference between the end segments of the ball in the
presence of the dielectric fluid permeating sheet 1410
(as indicated in the first view of FIG. 14E by + and -
signs in the end segments) is perpendicular to the plane
of the center segment of the ball. Thus the center
segments of the balls of all three layers are caused to '
be oriented parallel to the direction of arrows a° (that
is, perpendicular to the planar surfaces 1419a, 1419b of
gyricon sheet 1410).
In the second view of FIG. 14E, corresponding to the
second addressing pass, the voltages are set such that V3
> V1, V1 - V4, V4 > V2, and ~1/T > (V3 - V2)/Y > ~2/T,
where Y - (T2 + yJ2) 1/2. The resulting electric field E2
has a magnitude of (V3 - V2)/Y, which is greater than the
threshold electric field magnitude sz - ~2/T required to
cause rotations of balls in layer 1412. The field E2 is
oriented in the direction of arrow b. Application of the
field E2 causes the balls of layers 1412 and 1413 to
align their respective dipole moments with the applied
field and has no effect on balls of layer 1411. The
center segments of the balls of layers 1412 and 1413 are
caused to be oriented parallel to the direction of arrows
b' (that is, at an acute angle with respect to the planar
surfaces 1419a,1419b of gyricon sheet 1410).
In the third view of FIG. 14E, corresponding to the
third addressing pass, the voltages are set such that V1~
V2, V3 ~ V4, and ~2 > V3 - V2 > ~3. The resulting
electric field E3 has a magnitude of (V3 - V2)/T and is
oriented in the direction of arrow c. Application of the
field E3 causes the balls of layer 1413 to align their
respective dipole moments with the applied field, which -
in turn causes the center segments of the balls of layer
1413 to become oriented parallel to the direction of
arrows c' (that is, parallel to the planar surfaces
1419a,1419b of gyricon sheet 1410). The balls in layers
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1411 and 1412 are not affected, because the applied
voltage gradient is below their respective thresholds
~1/T and ~2/T.
' Multiple-pass addressing can also be used to address
selectively balls of different rotation thresholds within
- a single layer of a single-layer or multilayer gyricon.
An application of this technique is for controlling the
color saturation of a chromatic color in an image
element, the gray scale level for black in an image
element, or, in general, the degree to which a color or
other optical modulation characteristic is observably
present in an image element, without the need for canted
fields. For example, one way to achieve variable color
saturation in an RGB gyricon based on three-segment balls
(as in FIGS. l0A-lOC) without using canted fields is to
provide a multiplicity of balls associated with each
__, ,
color in each subpixei . To gez a fully saturated color,
all of the balls in the subpixel are turned with their
center segments parallel to the surface of the elastomer
sheet. To get a minimally saturated color, all of the
balls in the subpixel are turned with their center
segments perpendicular to the surface of the elastomer
sheet. To get an intermediate color saturation, a subset
of the balls in the subpixel are turned with their center
segments parallel to the surface of the elastomer sheet,
while the remaining balls of the subpixel are turned with
their center segments perpendicular to the sheet surface.
In other words, the more balls that are turned so that
their center segments are parallel to the plane of the
3o gyricon sheet, the more saturated the resulting color of
the subpixel appears. The same principle can be used to
control color saturation without the use of canted fields
in other color gyricons, such as CMY(K) or bistate or
tristate light-valve gyricons. It can also be used to
provide gray-scale capability in, for example, gyricons
based on black-and-white bichromal balls of the prior
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art. The darkness of the gray of a pixel depends on the
percentage of balls in that pixel which have their white
and black hemispheres facing toward the observable
surface of the gyricon sheet.
The series of views in FIG. 14F depicts several
different degrees of color saturation obtainable in a
single-layer gyricon having three different sets of balls
disposed within the single layer, each set of balls
having a different rotation threshold, all three sets
being associated with the same observable color. Each of
the gyricon balls is a three-segment ball with
transparent end segments and a colored center segment.
For example, if the colored center segments are red, the
balls could be disposed in a single red subpixel of the
IS RGB gyricon previously described with reference to FIGS.
l0A-lOC.
The views in FIG. 14F are all side views of a region
constituting one addressable image element (e. g.,
subpixel) in gyricon sheet 1420. For clarity of
exposition, a single ball of each threshold is shown,
although in practice, preferably a large number of balls
of each threshold are dispersed uniformly {e. g.,
randomly) throughout each pixel. For a thickness T of
elastomer, ball 1423 has a lowest threshold potential ~3
ball 1422 has an intermediate threshold potential ~2, and
ball 1421 has a highest threshold potential ~1. Once
again, as in FIG. 14E, the layer thickness is T and the
image element width is W, and ideally sharp thresholds
are assumed (i.e., ~3= 02 =dl =0).
In the first view of FIG. 14F, balls 1421, 1422, and -
1423 all are oriented with their center segments parallel
to the plane of gyricon sheet 1420. An observer at I '
sees a maximally saturated color. This orientation of
the balls is obtainable by applying an electric field
perpendicular to the plane of gyricon with a field
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strength E > ~1/T, or in other words, a voltage
difference V across sheet 1420 such that V > ~1.
In the second view of FIG. 14F, ball 1421 is
oriented with its center segment perpendicular to the
plane of gyricon sheet 1420, and balls 1422 and 1423 are
oriented with their center segments parallel to the plane
of gyricon sheet 1420. An observer at I sees a
moderately saturated color. This orientation of the
balls is obtainable by applying, in a first pass, an
electric field in the plane of gyricon with a field
strength E1 > ~1/T (in other words, a voltage difference
V such that V/W > ~1/T), and thereafter applying, in a
second pass, an electric field perpendicular to the plane
of the gyricon with a field strength E2 such that ~1/T >
E2 > ~2/T (in other words, a voltage difference V across
sheet 1420 such that ~r1 > V > ~2). The first pass
orients all three balls 1421, 1422, and 1423 with their
center segments perpendicular to the plane of sheet 1420.
The second pass reorients balls 1422 and 1423 so that
their center segments become parallel to the plane of
gyricon sheet 1420. The second pass has no effect on the
orientation of ball 1421, because the applied field is
less than the rotation threshold for ball 1421.
In the third view of FIG. 14F, balls 1421 and 1422
are oriented with their center segments perpendicular to
the plane of gyricon sheet 1420, and ball 1423 is
oriented with its center segment parallel to the plane of
gyricon sheet 1420. An observer at I sees a lightly
- saturated color. This orientation of the balls is
obtainable by applying, in a first pass, an electric
field in the plane of gyricon with a field strength E1 >
~1/T (in other words, a voltage difference V such that
V/W > ~1/T), and thereafter applying, in a second pass,
an electric field perpendicular to the plane of the
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gyricon with a field strength E2 such that ~2/T > E2 >
c~3/T (in other words, a voltage difference V across sheet
1420 such that c~2 > V > ~3). The first pass orients all
three balls 1421, 1422, and 1423 with their center '
segments perpendicular to the plane of sheet 1420. The
second pass reorients ball 1423 so that its center
segment becomes parallel to the plane of gyricon sheet
1420. The second pass has no effect on the orientation
of balls 1421 and 1422, because the applied field is less
than the rotation threshold for these balls.
In the fourth and final view of FIG. 14F, balls
1421, 1422, and 1423 all are oriented with their center
segments perpendicular to the plane of gyricon sheet
1420. An observer at I sees a minimally saturated color.
This orientation of the balls is obtainable by applying
an electric field in the plane of gyricon with a field
strength E > ~1/T, or in other words, a voltage
difference V such that V/W > ~1/T.
From these examples, it can be seen that in order to
provide variable color saturation with gyricon sheet
1420, a series of one or more electric fields can be
applied. Each applied field of the series has its
electric field vector oriented in one of two directions:
either in the plane of sheet 1420, or else perpendicular
to the plane of sheet 1420. Color saturation is
controlled by controlling the proportion of balls
oriented such that their colored center segments are
parallel to the plane of sheet 1420 and thus observable
to the observer at I. Each ball is in one of two
dispositions: either "fully on," that is, oriented so as
to make its maximal possible contribution to the
observable color, or else "fully off," that is, oriented
so as to make its minimal contribution to the observable
color. In contrast with the canted-field technique
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described earlier, intermediate orientations are not
used.
In general, a gyricon image element in which there
are N different sets of gyricon balls, each set having a
distinct threshold Vin, with each ball capable of being in
- one of two orientations, can provide up to 2N different
combinations of ball orientations if N addressing passes
are used (that is, if each set is addressed
individually). For example, if a red subpixel of the RGB
gyricon previously described with reference to FIGS. l0A-
lOC has in it five sets of red-center-segment balls, each
set having a distinct rotation threshold, and each ball
in the subpixel can be oriented with its center segment
either parallel to the observable surface ("fully on") or
perpendicular to the observable surface ("fully off"),
then up to (2)5 - 32 different levels of red color
saturation can be provided for the subpixel.
Unfortunately, it is not always practical to provide
access to all 2N available combinations of ball
orientations. Thus, in this example, accessing of all 32
saturation levels of the red subpixel requires that each
of the five sets of balls be separately addressed, which
in turn requires five-pass addressing. In general, to
access any arbitrary one of the 2N available combinations
of ball orientations, N-pass addressing is required,
which can be prohibitively time-consuming for even modest
values of N. -
An alternative approach to controlling variable
color saturation in a multithreshold gyricon image
element provides N+1 levels of available saturation and
requires at most two addressing passes per population of
_ balls. This approach works as follows: A cutoff value
is selected, typically a value between two adjacent
thresholds ~i and ~i+1- The cutoff value serves to
divide the N sets of balls of the population into two
larger groups. All balls having rotation thresholds
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greater than the cutoff value are in a .first group, and
all balls having thresholds less than or equal to the
cutoff value are in a second group. The two groups can
be addressed in two passes: a first pass in which all
balls in both the first and second groups are reset to a
default orientation (for example, the "fully off" -
orientation), followed by a second pass in which balls in
the second group only are oriented in a non-default
orientation (for example, the "fully on" orientation) by
application of an electric field having a strength equal
to the chosen cutoff value.
An example of this alternative approach is seen in
the foregoing description of the second and third views
of FIG. 14F, in which it was explained how two addressing
passes can be used to obtain the ball orientations shown.
Expressed as a voltage to be applied across the elastomer
thickness T, the cutoff value ~c for the second view of
FIG. 14F is chosen such that ~l > ~c > ~2 , and for the
third view of FIG. 14F, such that ~2 > ~c > ~3~
Further, it will be appreciated that if the cutoff
value c~C is chosen such that ~c > ~1 (for example, if ~c =
t~), the alternative approach can be used to obtain the
ball orientations shown in the first view of FIG. 14F.
Similarly, if the cutoff value is chosen such that ~g >
~c ( for example, if ~c - 0 ) , the approach can be used to
obtain the ball orientations shown in the fourth and
final view of FIG. 14F. In each of these cases, two-pass
addressing is somewhat redundant, inasmuch as single-pass
addressing would suffice. That is, for the first view c,::
FIG. 14F, the results of the first addressing pass arm "
completely undone by the second pass, and for the fourt~:
view of FIG. 14F, the results of the first pass require
no further correction by the second pass. Accordingly,
in such cases it can be worthwhile to omit redundant
addressing steps, in order to reduce addressing time.
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The alternative, cutoff-value . approach to
multithreshold, multipass addressing is often to be
preferred over the more general but more time-consuming
r N-pass approach described previously for color presence
control applications. In particular, the two-pass
- approach works especially well for controlling color
presence when N is large. The number of available
gradations of control is N+l, and the number of
addressing passes is never more than two. Thus fine
control over color saturation, gray scale, and the like
are facilitated.
Moreover, the cutoff-value addressing approach can
obviate the need for very sharp thresholds. A nonzero
value of D defines a range of thresholds for a given
population of balls; choosing a cutoff value ~c in this
range divides the population in two. For example,
referring once again to FIG. 14D, each ball in the first
population has a rotation threshold somewhere between ~1
and ~1 + O1. A color saturation (for example) associated
with the third population of balls can be controlled by
resetting all the balls of the third population to a
default orientation with an applied voltage exceeding ~1
+ D1 in a first pass, and thereafter orienting a subset
of the balls to a new, non-default orientation with an
applied voltage at a cutoff value ~c such that ~1 < ~c <
~l + ~1 in a second pass. This can be repeated for the
balls in the second and third populations, reducing the
applied voltage appropriately each time, until the
desired saturations are established for each color. From
this example, it can be appreciated that the threshold
width 0 for each population can affect the degree of
precision with which color saturation can be controlled.
Assuming that the precision with which ~c can be chosen
is limited, then as 0 is reduced towards zero, there will
be effectively fewer available cutoff values within each
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population and thus fewer gradations of color saturation
control for the color associated with that population.
Thus the cutoff-value multithreshold addressing approach
turns a wide threshold width ~ to best advantage; sharp
thresholds are not especially desirable in this approach.
For the three populations of balls in FIG. 14D, at -
most six addressing passes are required for the cutoff-
value multithreshold addressing approach. In general,
for K populations of bails, at most 2K addressing passes
are required for this approach.
The series of views of FIG. 14G illustrates an
example of the cutoff-value addressing approach as
applied to a three-layer gyricon having three populations
of three-segment balls, one population per layer. For
example, the gyricon can be a CMY gyricon. Each layer's
ball population has a different associated minimum
threshold ~ and a nonzero threshold width 0. In
particular, it is assumed for purposes of this example
that each layer's population of balls consists of several
subpopulations, each subpopulation having a distinct
(sharp) threshold in the range from ~ to ~+ ~. The views
of the series are all side views of a single-pixel region
in gyricon sheet 1450 having thickness T (that is, each
layer in sheet 1450 has thickness T/3y and width W.
2S For a thickness T of elastomer, balls in layer 1453
have a lowest minimum threshold potential ~g and a
nonzero threshold width D3; balls in layer 1452 have an
intermediate threshold potential ~2 arid a nonzero
threshold width O2; and balls in layer 1451 have a
highest threshold potential ~1 and a nonzero threshold
width D1. Each layer is to be addressed with an electric
field that can be oriented either parallel or
perpendicular to the plane of sheet 1450.
The population of balls in layer 1453 includes balls
1453x, 1453b, 1453e, 1453d, and 1453e, which have
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individual rotation thresholds ~3a, ~3b~ ~3c~ ~3d~ and
~3e~ respectively, such that (~3+D,3) > ~3a > ~3b > ~3c >
~3d > ~3e > ~3~ The population of balls in layer 1452
includes balls 1452a, 1452b, I452c, 1452d, and 1452e,
which have individual rotation thresholds ~Za~ ~2b~ ~2c~
~2d, and ~2e, respectively, such that (~2+A~) > ~za > ~2b
> ~2c > ~2d > ~2e > ~2- The population of bails in layer
1451 includes balls 1451a, 1451b, 1451c, 1451d, and
1451e, which have individual rotation thresholds Vila,
IO ~lb~ ~lc~ ~ld~ and ale. respectively, such that (~1+O1) >
Vila > alb > plc > old > ale > ~1~
In the first view of FIG. 14G, corresponding to the
first addressing pass, an electric field El~) is applied
in the plane of sheet 1450. The field is of sufficient
i5 strength to rotate all the balls in all three layers;
that is, the applied voltage Vl~~ is such that (VI~~/W) >
(~1+ Ol)/T. All Of balls 1451a, 1451b,~ I451c, 1451d,
1451e, 1452a, 1452b, 1452c, 1452d, I452e, 1453a, 1453b,
1453c, 1453d, and 1453e are rotated so that their dipole
20 moments align with the applied field, which causes their
center segments to be oriented perpendicularly to the
plane of sheet 1450. In other words, all the balls are
reset to their "fully off" orientations.
In the second view of FIG. 14G, corresponding to the
25 second addressing pass, an electric field E11 is applied
perpendicular to the plane of sheet 1450. The field is
of sufficient strength to rotate some of the balls in
layer 1451 and all of the balls in layers 1452 and 1453;
- that is, the applied voltage V11 across the thickness T
30 of sheet 1450 is such that (~l+O1) > V11 > ~1. More
particularly in this example, the applied voltage V11 is
chosen such that balls 1451c, 1451d, and i451e are
affected by the applied voltage while balls 1451a and
1451b are not. Thus alb > V11 > plc . (Put another way,
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Vl,l defines the cutoff value ~c for the first population
of balls.) In response to the applied field E11. balls
1451c, 1451d, and 1451e, along with all of balls 1452x,
1452b, 1452c, 1452d, 1452e, 1453x, 1453b, 1453c, 1453d,
and 1453e, are rotated so that their dipole moments align
with the applied field, which causes their center -
segments to be oriented parallel to the plane of sheet
1450. That is, all these balls 1451c, 1451d, 1451e,
1452a, 1452b, 1452c, 1452d, 1452e, 1453a, 1453b, 1453c,
1453d, and 1453e are oriented in their "fully on°'
orientations at the end of the second pass. Balls 1451a
and 145Ib remain in their reset, "fully off"
orientations.
In the third view of FIG. 14G, corresponding to the
I5 third addressing pass, an electric field E2(( is applied
in the plane of sheet 1450. The field is of sufficient
strength to rotate all of the balls in layers 1452 and
1453 while leaving all of the balls in layer 1451
unaffected; that is, the applied voltage V2(( is such that
(~I/T) > (V2((/W) > (~2+02) /T. Balls 1452x, 1452b, 1452c,
1452d, 1452e, 1453x, 1453b, 1453c, 1453d, and 1453e are
rotated so that their dipole moments align with the
applied field, which causes their center segments to be
oriented perpendicularly to the plane of sheet 1450. In
other words, all the balls in layers 1452 and 1453 are
again reset to their "fully off°' orientations, while
balls in layer 1451 remain as they were.
In the fourth view of FIG. 14G, corresponding to the
fourth addressing pass, an electric field E21 is applied
perpendicular to the plane of sheet 1450. The field is
of sufficient strength to rotate some of the balls in
layer 1452 and all of the balls in layer 1453, without
affecting any balls in layer 1451; that is, the applied
voltage V21 across the thickness T of sheet 1450 is such
that (~2+02) > V21 > ~2. More particularly in this
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example, the applied voltage V21 is chosen such that
balls 1452b, 1452c, 1452d, and 1452e are affected by the
applied voltage while ball 1452a is not. Thus ~2a > V21
> ~2b. (put another way, V21 defines the cutoff value ~C
for the second population of balls.) In response to the
' applied field E21. balls 1452b, 1452c, 1452d, and 1452e,
along with all of balls 1453a, 1453b, 1453c, 1453d, and
1453e, are rotated so that their dipole moments align
with the applied field, which causes their center
to segments to be oriented parallel to the plane of sheet
1450. That is, all these balls 1452b, 1452c, 1452d,
1452e, 1453a, 1453b, 1453c, 1453d, and 1453e are oriented
in their "fully on" orientations at the end of the fourth
pass. Ball 1452a remains in its reset, "fully off"
orientation.
In the fifth view of FIG. 14G, corresponding to the
fifth addressing pass, an electric field E3~~ is applied
in the plane of sheet 1450. The field is of sufficient
strength to rotate all of the balls in layer 1453 while
leaving all of the balls in layer 1451 and 1452
unaffected; that is, the applied voltage V3j~ is such that
(~2/T) > (V3~~/W) > ~g+~3)/T. Balls 1453a, 1453b, 1453c,
1453d, and 1453a are rotated so that their dipole moments
align with the applied field, which causes their center
segments to be oriented perpendicularly to the plane of
sheet 1450. In other words, all the balls in layer 1453
are yet again reset to their "fully off" orientations,
while balls in layers 1451 and 1452 remain as they were.
In the sixth and final view of FIG. 14G,
corresponding to the sixth addressing pass, an electric
field E31 is applied perpendicular to the plane of sheet
1450. The field is of sufficient strength to rotate some
of the balls in layer 1453, without affecting any balls
in layers 1451 and 1452; that is, the applied voltage V31
across the thickness T of sheet 1450 is such that (~3+03)
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> V31 > ~3. More particularly in this example, the
applied voltage V31 is chosen such that ball 1453e is
affected by the applied voltage while balls 1453x, 1453b,
1453c, and 1453d are not. Thus ~3d > V31 > ~3e . (Put -
another way, V31 defines the cutoff value ~c for the
third population of balls.) In response to the applied -
field E31, ball 1453e is rotated so that its dipole
moment aligns with the applied field, which causes its
center segment to be oriented parallel to the plane of
sheet 1450. None of the other balls is affected.
This completes the addressing sequence of FIG. 14G.
After the sixth pass is complete, an observer at I sees a
pixel in which the color provided by the center segments
of the balls in layer 1451 is moderately saturated, the
color provided by the center segments of the balls in
layer 1452 is heavily saturated, and the color provided
by the center segments of the balls in layer 1453 is very
lightly saturated. Again, it is worth noting that
although the balls are illustrated in FIG. 14G as having
five discrete thresholds and neatly arranged in order of
decreasing rotation threshold, this is done only for
purposes of clarifying the exposition. In practice, each
population of balls will have a large number of
thresholds, which will be statistically distributed over
the interval between ~1 and (~1+01) for layer 1451, over
the interval between ~2 and (~2+02) for layer 1452, and
over the interval between ~3 and (fig+03); and balls of
these different thresholds will be spatially distributed
throughout their respective layers.
The parallel and perpendicular addressing fields
used in FIGS. 14F and 14G can be generated separately for
each pixel or other image element, using an electrode
configuration that is similar in appearance to the
canted-field electrode configuration previously described
with reference to FIG. 8A. However, only parallel and
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perpendicular fields are needed, so the voltages V1, V2,
V3, and V4 can be constrained such that either V1=V2 and
V3 - V4, or else V1 --V3 and V2 - V4. Thus the voltage
control circuitry can be simplified as compared with the
control circuitry necessary to provide a fully general
canted-field capability.
Alternatively, the parallel and perpendicular fields
can be generated with the less complex and less expensive
electrode configuration depicted in FIG. 8F, in which the
in-plane "erase" field is applied to the entire gyricon
sheet at once, and only the perpendicular field is
separately addressable for each image element. This
configuration works well with the cutoff-value approach
to multithreshold, multipass addressing as exemplified in
FIG. 14G, because if the default orientation is "fully
off" then the first addressing pass for each population
of balls in every pixel is always a bulk erasure. The
second pass, which turns some of the balls to "fully on,"
can vary in applied voltage from pixel to pixel. The
electrode configuration of FIG. 8F is not sufficient for
more general N-pass approach in which all 2N possible
combinations of ball orientations are to be made
accessible.
It should be noted in conjunction with the
multithreshold approaches for color presence control that
if the different rotation thresholds for the balls of
each color in a gyricon are achieved by using balls of
different sizes, the choice of which balls should be
larger and which balls should be smaller can depend on
the number of steps of presence resolution required for
each color. For example, suppose that in a multilayer
CMYK gyricon, balls in the cyan layer have a first mean
radius, balls in the magenta layer have a second mean
radius, balls in the yellow layer have a third mean
radius, and balls in the black layer have a fourth mean
radius. It is advantageous in this case for the balls
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having the largest radius to be in the yellow layer, and
the balls having the smallest radius to'be in the black
layer, because typically the human eye resolves more
gradations of gray-scale than gradations of color
saturation, and resolves gradations of yellow less well
than gradations of other colors. If multithresholding is _
used, the number of available gradations for a given
color in a given pixel depends on the number of
separately addressable balls of that color in the pixel;
the more balls of a given color, the finer the control
that can be had over the presence of that color in the
final color mix. Thus, since the least precise control
is required for yellow and the most precise control is
required for black, there can be relatively fewer yellow
balls per pixel as compared with the number of cyan or
magenta balls per pixel, and relatively more black balls
per pixel as compared with the number of cyan or magenta
balls per pixel.
The multithreshold, multipass techniques illustrated
in FIGS. 14F-14G and the canted-field techniques
described earlier with reference to FIGS. 8A-8C provide
two distinct sets of approaches to controlling the degree
of presence (e. g., color saturation, gray-scale level,
etc.) of any given color in any single image element of a
gyricon. Briefly summarized, these two sets of
approaches can be contrasted as follows:
~ The canted-field approaches work by varying the
angle of each ball with respect to the gyricon's
observable surface, and thus the degree to which
each ball contributes to the observable color. Each
ball can be rotated by the canted field to any angle '
of a continuous range of angles. All balls in a
given region are rotated at once. Addressing takes
place in a single operation.
~ The multithreshold, multipass approaches work
by varying the proportion of balls rotated, and thus
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the number of balls available to contribute to the
observable color. Each ball can be rotated to one
of two positions, either "fully on" (maximum
contribution to the observable color) or "fully off"
(minimum contribution to the observable color);
unlike the canted-field approach, there are no
intermediate positions. Not all balls in a given
region need be rotated at once. Addressing takes
place in series of passes; for example, all balls
can be reset to the "fully off" orientation in a
first pass, and then a subset of balls can be
oriented in the "fully on" orientation in a second
pass.
As previously mentioned with reference to FIG. 14E,
multithreshold and canted field techniques can be used
together in a single gyricon, with multithresholding
being used to select particular groups (e.g., layers) of
balls and canted fields being used to control color
presence within each selected group.
Fabrication Techniques for Strategic Placement of
Different Balls in a Gyricon Sheet
The RGB gyricon of FIGS. 10A-lOC is constructed from
three different kinds of balls, namely, balls with red
center segments, balls with green center segments, and
balls with blue center segments. These three different
kinds of balls are placed in different subpixel regions
in the gyricon sheet. A red subpixel contains balls with
red center segments only, and does not contain balls of
the other two kinds. Similarly, a green subpixel
contains balls with green center segments only, and a
' blue subpixel contains balls with blue center segments
only. To build this gyricon, then, requires a
manufacturing technique for placing the different kinds
of balls in their respective different locations in the
elastomer sheet, so that the desired geometric pattern of
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red, green, and blue subpixels (e. g., the pattern of FIG.
IOC) is obtained.
There are other occasions when it is desirable to
create a display from assembled patches of distinctly
colored gyricon balls. As an example, in the case of an
automobile display, the speedometer might be displayed
using bichromal red and white balls: the odometer, a
region of green and white bichromal balls; the fuel
gauge, black and white bichromal balls: and the
IO tachometer fluorescent blue and white bichromal balls.
Yet another example would be in a decoratively patterned
gyricon-based architectural screen, made according to the
principles previously described with reference to FIGS.
7A and 7E. For example, a pattern of different bails
IS having different kinds of transparent center segments
(e. g., some clear, others "smoke-glass" colored, still
others tinted pink or another chromatic color), might be
desired.
In general, there can be various circumstances in
20 which it is necessary or advantageous to place different
kinds of gyricon balls at different preferred chosen
locations in the elastomer layer during the manufacturing
process. By "different kinds" is meant any physical
distinctions between balls of one set and balls of
25 another set, including different optical properties (of
which color is only one example) and distributions of
optical properties among regions within the balls: any
and all of the aforementioned electrical, mechanical,
structural, and material properties, such as size, shape,
30 electrical monopole and dipole moments, and so forth,
that were previously mentioned as being among the '
properties that can affect ball rotation thresholds; and,
in general, any other physical characteristics that can '
be used to differentiate between different balls, such
35 as, for example, ferromagnetic properties in gyricon
balls that have such properties (see U.S. Patent No.
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4,126,854, incorporated hereinabove by reference, at col.
6, lines 16-30, for an example of this).
Various techniques can be used to obtain patterned
or other strategic ball placement during manufacture of
the gyricon elastomer sheet. One such technique is a
nonfusing xerographic technique in which the desired
pattern of gyricon balls of different kinds is
xerographically "printed" on a partially cured elastomer
using "toners" that comprises the gyricon balls
l0 themselves. In this manner, different kinds of gyricon
balls can be placed at any desired locations on the
partially cured sheet. Once the balls are placed as
desired, additional elastomer material in uncured liquid
form is poured over them so that the resulting elastomer
sheet has the gyricon balls disposed inside it rather
than on top of it.
The xerographic technique is informed by the
observation that the spheroidal gyricon balls are, in
certain ways, very much like the toner particles used in
conventional xerography. In particular, they are
dielectric and easily triboelectrically charged, like
toner particles, and typically they are about the same
size as toner particles. This means that the gyricon
balls can be placed in a xerographic development system,
in place of ordinary toner, and if the development system
is subsequently placed in a xerographic engine the
latter can produce images made from the balls.
A common form of xerographic development system
works by mixing toner particles with steel or ferrite
(magnetic) beads in a sump. In the process of mixing the
' toner particles with the steel or ferrite beads, the
toner particles develop a triboelectric charge. A
fraction of this mixture of toner particles and beads is
brushed against the surface of a photoconductor drum that
has an imagewise distribution of charges of the opposite
polarity on its surface. This can be obtained by
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uniformly charging the surface of the photoconductor drum
with ions from a corona discharge apparatus and
subsequently imagewise discharging the photoconductor by
exposing it to light from an image, as is well understood
in the xerographic arts. The toner particles adhere to
areas of the photoconductor drum that have a high density
(voltage) of charge of the opposite polarity. This
creates an imagewise toner image.
In conventional xerography, the toner image formed
on the photoconductor drum is subsequently transferred to
paper, usually by placing a sheet of paper in contact
with the photoconductor drum and placing another corona
discharge apparatus on the opposite side of the paper,
attracting the toner to the paper surface. Thereafter,
the toner is fused (melted) into the paper. Here, of
course, it is preferred not to melt the gyricon balls,
and the preferred receiving surface is not paper but
rather the elastomer sheet of the gyricon itself.
Accordingly, a nonfusing xerographic process is used.
(Other nonfusing xerographic processes are known; see,
for example, U.S. Patent No. 5,075,186, incorporated
hereinabove by reference). Toner made from gyricon balls
is imaged onto a photoconductor drum and is transferred
from the photoconductor onto an adhesive receiving
medium, which can conveniently be made of elastomer
material in a sticky, partially cured state.
An example of a nonfusing xerographic color printer
1500 suitable for gyricon ball placement is shown in
FIG. 15A. For purposes of discussion of FIG. 15A it
will be assumed that three sets of gyricon balls, one
red, one green, and one blue (e.g., three-segment balls
with red, green, and blue center segments, respectively)
are to be placed in the gyricon sheet, it being
understood that any two or more sets can be placed with
this technique.
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A photoconductor drum 1505 is exposed to a first
laser light image, which imagewise discharges drum 1505.
Laser light for the image is produced by scanning laser
1502 in conjunction with mirror 1503 and lens 1504, in a
S manner like that used in known laser printing and digital
xerographic techniques. As drum 1505 rotates counter-
clockwise (in the direction of arrow a), red development
housing 1510, which contains a mixture of ferrite beads
and toner made from the red balls, is moved (as indicated
by arrows d) into near contact with drum 1505. The
mixture of magnetic beads and toner brushes the surface
of the photoconductor drum 1505. A magnetic field (not
shown) holds onto the magnetic beads. A bias voltage
between development housing 1510 and drum 1505 allows
the toner (here, the red bails) to stick to the surface
of drum 1505 only in those areas of the photoconductor
drum where the charge has previously been removed by
exposure to the first laser light image. In this manner
an imagewise layer of red balls is built up on the
surface of the photoconductor drum. This image 1526 is
next transferred to a storage drum 1525 by creating a
high electrical field between the surface of
photoconductor drum 1505 and the surface of storage drum
1525. Storage drum 1525 rotates (as indicated by arrow
b) in the opposite direction to drum 1505. The image
1526, formed of the red bails, is shown stored on storage
s~___ ~ rn~
uruum.a'~ .
Next, the photoconductor drum 1505 is again
uniformly charged by means of a corona discharge
apparatus and this time it is discharged by a second
laser light image, again produced with laser 1502. This
time, green development housing 1511, which contains a
mixture of ferrite beads and toner made from the green
balls, is engaged, and it imagewise deposits green balls
on the surface of photoconductor drum 1505 in the same
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_ 90 _ _
manner as was done previously for the red ball image
1526. The green ball image 1527, here seen while still
present on drum 2505, is transferred to storage drum 1525
in such a way that it exactly superimposes on the red -
ball image 1526 that is already there.
In like manner, a third image (not shown) made from '
toner from blue development housing 1512 can be produced
on photoconductor drum 1505 and transferred to storage
drum 1525, exactly superimposed on the previously
superimposed red and green ball images 1526, 1527.
When all three (or more) colored images have been
accumulated on the surface of storage drum 1525, the
images are transferred to a receiving surface 1530. In a
conventional xerographic printer, the receiving surface
IS is normally paper, and the next step thereafter is heat
fusing of the toner image to paper. Here, the receiving
surface is an adhesive surface that will position the
balls for inclusion in the elastomer layer of the
gyricon, and there is no fusing step.
It has been found that a thin layer of partially
cured SYLGARD 184 elastomer, a preferred elastomer
material for making gyricon sheets, is very sticky. If
receiving surface 1530 is a surface of partially cured
elastomer, and this surface is moved (arrows c) in the
same direction as the surface of storage drum 1525, at
the same surface speed, and is allowed to come very close
to the surface of storage drum 1525, a significant
fraction of the colored ball image stored on storage drum
1525 will transfer to receiving surface 1530. (The
surface of storage drum 1525 can advantageously be coated '
with a non-stick substance, such as TEFLON, so that it
can actually be placed in direct contact with the sticky
elastomer of receiving surface 1530. ) If a strong
electrical field is placed across these two surfaces, an
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_ gl _ _
even larger fraction of the colored ball image will
transfer.
Pouring uncured elastomer onto the surface of the
_ transferred colored ball image, removing the trapped air
(for example, by the application of a vacuum or the use
_ of a centrifuge), and curing the elastomer will result in
encapsulation of the colored ball image. Thus the
superposition of colored ball images that has been formed
on storage drum 1525 becomes the pattern of balls in the
elastomer sheet of the gyricon. After plasticization by
application of a dielectric plasticizer fluid to swell
the elastomer sheet, rendering the balls free to rotate
therein, the gyricon will be ready for use.
FIG. 15B is a highly magnified view of a powder
mixture of toner and beads for use in the development
housings 1510, 1511, 1512 of the xerographic apparatus of
FIG. 15A. Powder 1515 includes a large number of gyricon
balls 1516 mixed together with a large number of beads
1517 made from ferrite or other magnetic substance.
Beads 1517 serve to impart triboelectric charge to balls
1516, in a manner similar to that in which in which
ferrite beads serve to impart triboelectric charge to
particles of a dry ink or other marking substance in
conventional xerographic toner. Typically, the number of
ZS beads 1517 will be approximately equal to the number of
balls 1516, and the beads 1517 are also spheroidal but
about an order of magnitude larger in size than balls
1516. However, it will be understood that different
kinds of gyricon balls, different bead materials and
. 30 sizes, and different proportions of balls to beads in the
mixture can be used, as appropriate for the particular
- application.
FIG. 15C illustrates the step of pouring the uncured
elastomer onto the transferred colored ball image. A
35 section 1542 of partially cured elastomer from receiving
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surface 1530, onto which the colored ball image has been
transferred from storage drum 1525, has been removed to a
holding platform 1538 and placed between retaining walls
1539x, I539b as shown. Balls 1545 are the gyricon balls .
that make up the transferred colored ball image. Uncured
elastomer 1541, which is a liquid, is dispensed from '
vessel 1540 onto the partially cured elastomer section
1542 and over bails 1545, in such a manner as to cover
balls 1545 while not moving them from their respective
positions in the elastomer. Thus the colored ball image
formed of balls 1545 remains undisturbed as the
additional uncured elastomer 1541 is poured over it.
Retaining walls 1539x, I539b hold the dispensed uncured
elastomer in place during the curing process.
The xerographic ball placement technique is useful
for fabricating any gyricon that includes two or more
distinct kinds of balls that are not uniformly
distributed throughout the entirety of the elastomer
material. Another technique for obtaining low cost,
imagewise colored ball distributions takes advantage of
the fact that the gyricon balls are highly spherical and,
in the absence of electrostatic charges on their
surfaces, exhibit excellent flow characteristics. Thus a
kind of "silk screening" is possible.
The silk screen ball placement technique is
illustrated in FIG. 15D. Balls 15?5 are dispensed from
dispenser 1570 onto a screen 1580 that is disposed above
a sticky layer 1590 of partially cured elastomer. Screen
1580 has holes that define the desired image or pattern
in which balls 15?5 are to be placed in the gyricon '
sheet. The holes are large enough for balls to I5?5 to
pass through, yet small enough to give the desired
resolution of ball placement. Balls 15?5 are placed on
screen 1580 and, with appropriate vibration supplied by
agitator 1581, pass through the holes of screen 1580 in
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an imagewise manner. Upon impacting the surface of the
partially cured elastomer layer 1590, balls 1575 are
stuck to the surface.
The foregoing process can be repeated, using
different screens for different kinds of balls, until the
desired pattern of different balls is placed on the
elastomer surface. For example, a first silk screen can
be used to place red balls in elastomer layer 1590, and
thereafter a second silk screen can be used to place
green balls in elastomer layer 1590. An additional
screening step is used for each additional color.
Finally, when ail the balls are in place, uncured
elastomer can be poured over the surface, in a manner
similar to that which was shown in FIG. 15C, so as to
cover over the placed balls. Next, trapped air is
removed from the elastomer, which is then ready to be
cured and plasticized.
Conclusion
The foregoing specific embodiments represent just
some of the possibilities for practicing the present
invention. Many others are possible within the spirit of
the invention. For example:
~ A gyricon used in a full-color display or full
coior electric paper application need not be
restricted to conventional RGB or CMY/CMYK color
schemes. To improve the color gamut, additional
colors can be incorporated. Moreover, as indicated
above with regard to the highlight color
application, a special custom color can be provided,
for example to ensure accurate rendering of a
company logo.
~ The electrical anisotropy of a gyricon ball
need not be based on zeta potential. It is
sufficient that there is an electrical dipole moment
associated with the ball, the dipole moment being
aligned with respect to the ball in such a way as to
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facilitate a useful rotation of the ball in the
presence of an applied external electric field.
(Typically, the dipole moment is oriented along an
axis of symmetry of the ball.) Further, it should
be noted that a gyricon ball can have an electrical
monopole moment in addition to its electrical dipole
moment, as for example when the dipole moment arises
from a separation of two positive charges of
different magnitudes, the resulting charge
distribution being equivalent to a positive
electrical monopole superposed with a electrical
dipole.
Although the gyricon balls that have been
described above are rotationally responsive to DC
addressing voltages, these bails can also respond to
certain AC addressing voltages. In particular,
multisegmented zeta-potential-based gyricon balls
are suitable for use in raster-scanned addressable
displays operating at video frame rates. Moreover,
it will be appreciated that certain aspects of the
present invention are adaptable even to gyricons in
which the balls are rotationally responsive only to
non-DC voltages (e. g., RF voltages).
The optical anisotropy of a gyricon bail need
not be based on color. Other optical properties can
vary as different aspects of the gyricon ball are
presented to an observer, including (but not limited
to) polarization, birefringence, phase retardation,
light scattering, and light reflection. In general,
the gyricon balls can be used to modulate light in a
wide variety of ways.
The incident light that encounters a gyricon
need not be restricted to visible light. Given
suitable materials for the gyricon balls, the
incident "light" can be, for example, infrared light
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or ultraviolet light, and such light can be
modulated by the gyricon.
On several occasions the foregoing description
refers to a planar gyricon sheet and to electric
fields that are parallel to the sheet, in the plane
_ of the sheet, perpendicular to the sheet, at a
specified angle to the sheet, and so forth.
However, persons of skill in the art will appreciate
that a gyricon sheet made of a flexible material
can be temporarily or permanently deformed (for
example, flexed, folded, or rolled) so as not to be
strictly planar overall. In such cases, electric
field angles can be measured, for example, with
respect to the sheet in a locally planar
neighborhood that includes the gyricon ball or balls
of interest. Also, it will further be apprecated
that in practice the electric fields can vary
somewhat from the parallel, perpendicular, and other
angles described, for example, due to manufacturing
tolerances or slight imperfections of particular
gyricon sheets and electrode assemblies.
The gyricon's paper-like advantages of
flexibility, light weight, and so forth make it
particularly useful for electric paper applications.
However, as noted earlier, the gyricon can also be
used in rigid or fixed flat-panel displays, such as
for computer screens, automobile dashboards, display
signs, etc. Moreover, as seen above with regard to
electric Venetian blinds and windowshades, a gyricon
need not be used as an information display medium.
' The light-modulating capabilities provided by the
gyricon of the present invention can find many other
' applications.
The canted-field and multithreshold techniques
described hereinabove lend themselves to further
applications. One possibility is to use canted-
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field electrodes in conjunction with an elastomer
sheet containing black-and-white gyricon balls of
the prior art. The canted fields can rotate the
balls to any desired angle, that is, any desired
mixture of black and white, thereby making the
gyricon capable of gray-scale imaging. Another
possibility is to write on RGB multithreshold
electric paper with a voltage source, such as a
powered stylus, that provides three distinct
voltages or voltage ranges. This allows the user to
write on electric paper in three different colors.
~ Full-color gyricons have been described
hereinabove that provide color saturation control,
for example by way of canted fields and
is mu3~tithresholding techniques. However, a full-color
pixel-addressable gyricon that provides only two
saturations of each color per pixel, namely, fully
saturated or minimally saturated, and does not
provide variable color saturation control, can
nevertheless be useful. In particular, a CMY
display can be built that is suitable for halftone
color applications.
