U.S. patent application number 10/277527 was filed with the patent office on 2003-06-05 for method and apparatus for determining properties of an electrophoretic display.
This patent application is currently assigned to E Ink Corporation. Invention is credited to Abramson, Justin, Drzaic, Paul, Gates, Holly G., Jacobson, Joseph M., O'Neil, Steven J..
Application Number | 20030102858 10/277527 |
Document ID | / |
Family ID | 26784816 |
Filed Date | 2003-06-05 |
United States Patent
Application |
20030102858 |
Kind Code |
A1 |
Jacobson, Joseph M. ; et
al. |
June 5, 2003 |
Method and apparatus for determining properties of an
electrophoretic display
Abstract
A method for sensing the state of an electrophoretic display
includes the steps of applying an electrical signal to a display
element, measuring an electrical response for the display element,
and deducing the state of the display element from the measured
electrical response. Also, the parameters of the display materials
are determined using the encapsulated electrophoretic display media
as a sensor, either alone or in conjunction with other sensors.
Inventors: |
Jacobson, Joseph M.; (Newton
Centre, MA) ; Drzaic, Paul; (Lexington, MA) ;
O'Neil, Steven J.; (Pembroke, MA) ; Gates, Holly
G.; (Somerville, MA) ; Abramson, Justin;
(Somerville, MA) |
Correspondence
Address: |
TESTA, HURWITZ & THIBEAULT, LLP
HIGH STREET TOWER
125 HIGH STREET
BOSTON
MA
02110
US
|
Assignee: |
E Ink Corporation
Cambridge
MA
|
Family ID: |
26784816 |
Appl. No.: |
10/277527 |
Filed: |
October 22, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10277527 |
Oct 22, 2002 |
|
|
|
09349808 |
Jul 8, 1999 |
|
|
|
6512354 |
|
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60092046 |
Jul 8, 1998 |
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Current U.S.
Class: |
324/537 |
Current CPC
Class: |
B41J 3/4076 20130101;
G02F 1/1685 20190101; H01L 51/005 20130101; G02B 26/026 20130101;
H01L 51/0512 20130101; H01L 51/0077 20130101; G02F 1/167 20130101;
G09G 3/344 20130101; H01L 27/28 20130101; G09G 2320/029
20130101 |
Class at
Publication: |
324/158.1 |
International
Class: |
G01R 001/00 |
Claims
What is claimed is:
1. A method for determining properties of encapsulated
electrophoretic display media, comprising the steps of: (a)
providing encapsulated electrophoretic display media comprising a
plurality of capsules dispersed in a binder phase, wherein at least
one of said plurality of capsules contains an electrophoretic
contrast media phase that includes at least one particle and a
suspending fluid; (b) providing a first electrode and a second
electrode, said first and second electrodes adjacent to said
plurality of capsules; (c) applying a first electrical signal to
said first electrode; (d) applying a second electrical signal to
said second electrode; and (e) measuring a first electrical
characteristic of said encapsulated electrophoretic display media,
said first electrical characteristic generated in response to said
applied first and second electrical signals.
2. The method of claim 1, wherein step (e) comprises measuring a
first electrical characteristic represented by a time constant.
3. The method of claim 1, wherein step (e) comprises measuring a
first electrical characteristic represented by a current.
4. The method of claim 1, wherein step (e) comprises measuring a
first electrical characteristic represented by voltage.
5. The method of claim 1, wherein step (e) comprises measuring a
first electrical characteristic represented by capacitance.
6. The method of claim 1 further comprising deducing a second
electrical characteristic of said encapsulated electrophoretic
display media based on said measured first electrical
characteristic.
7. The method of claim 6 wherein said second electrical
characteristic is resistivity of said encapsulated electrophoretic
display media.
8. The method of claim 7 further comprising measuring a first
environmental factor of said encapsulated electrophoretic display
media using an external sensor.
9. The method of claim 8 further comprising determining a second
environmental factor of said encapsulated electrophoretic display
media based on said resistivity and said measured first
environmental factor.
10. The method of claim 9 wherein one of said first and second
environmental factors is temperature and the other is humidity.
11. A method for determining properties of encapsulated
electrophoretic display media, comprising the steps of: (a)
providing encapsulated electrophoretic display media comprising a
plurality of pixels, each pixel comprising at least one capsule
dispersed in a binder phase, wherein said at least one capsule
contains an electrophoretic contrast media phase that includes at
least one particle and a suspending fluid; (b) providing a first
electrode, said first electrode common and adjacent to each of said
plurality of pixels; (c) providing at least one measurement pixel
of said plurality of pixels, said at least one measurement pixel
having a measurement electrode adjacent thereto; (d) applying a
first electrical signal to said first electrode; (e) applying a
second electrical signal to said measurement electrode; and (f)
measuring a first electrical characteristic of said at least one
measuring pixel, said first electrical characteristic generated in
response to said applied first and second electrical signals.
12. The method of claim 11, wherein step (f) comprises measuring a
first electrical characteristic represented by a time constant.
13. The method of claim 11, wherein step (f) comprises measuring a
first electrical characteristic represented by a current.
14. The method of claim 11, wherein step (f) comprises measuring a
first electrical characteristic represented by voltage.
15. The method of claim 11, wherein step (f) comprises measuring a
first electrical characteristic represented by capacitance.
16. The method of claim 11 further comprising calculating an
aggregate first electrical characteristic of said encapsulated
electrophoretic display media using measured first electrical
characteristics of each of said at least one measurement pixel.
17. The method of claim 11 further comprising deducing a second
electrical characteristic of said at least one measurement pixel
based on said measured first electrical characteristic.
18. The method of claim 17, wherein said second electrical
characteristic is resistivity of said at least one measurement
pixel.
19. The method of claim 17 further comprising calculating an
aggregate second electrical characteristic of said encapsulated
electrophoretic display media using deduced second electrical
characteristics of each of said at least one measurement pixel.
20. The method of claim 17 further comprising measuring a first
environmental factor of said encapsulated electrophoretic display
media using an external sensor.
21. The method of claim 20 further comprising determining a second
environmental factor of said encapsulated electrophoretic display
media based on said resistivity and said measured first
environmental factor.
22. The method of claim 21 wherein on of said first and second
environmental factors is temperature, and the other is
humidity.
23. A method for detecting a change in an electrical characteristic
of encapsulated electrophoretic display media, comprising the steps
of: (a) providing encapsulated electrophoretic display media
comprising a plurality of pixels, each pixel comprising at least
one capsule dispersed in a binder phase, wherein said at least one
capsule contains an electrophoretic contrast media phase that
includes at least one particle and a suspending fluid; (b)
providing a first electrode, said first electrode common and
adjacent to each of said plurality of pixels; (c) providing at
least one measurement pixel of said plurality of pixels, said at
least one measurement pixel having a measurement electrode adjacent
thereto; (d) applying a first electrical signal to said first
electrode; (e) applying a second electrical signal to said
measurement electrode; (f) measuring a first electrical
characteristic of said at least one measuring pixel, thereby
obtaining a first value of said electrical characteristic; said
first electrical characteristic generated in response to said
applied first and second electrical signals; (g) repeating steps
(d)-(f), thereby obtaining a second value of said electrical
characteristic; and (h) comparing said first and second values of
said electrical characteristic thereby detecting a change
therein.
24. An apparatus for determining properties of encapsulated
electrophoretic display media, said encapsulated electrophoretic
display media comprising a plurality of capsules dispersed in a
binder phase, wherein at least one of said plurality of capsules
contains an electrophoretic contrast media phase that includes at
least one particle and a suspending fluid, and two electrodes
adjacent to said plurality of capsules; said apparatus comprising:
(a) a signal generator for applying electrical signals to said two
electrodes; and (b) a detection circuit for measuring a first
electrical characteristic of said encapsulated electrophoretic
display media generated in response to said electrical signals.
25. The apparatus of claim 24, further comprising a processor for
deducing a second electrical characteristic of said encapsulated
electrophoretic display media based on said measured first
electrical characteristic.
26. The apparatus of claim 25 wherein said second electrical
characteristic is resistivity of said encapsulated electrophoretic
display media.
27. The apparatus of claim 26 further comprising measuring a first
environmental factor of said encapsulated electrophoretic display
media using an external sensor.
28. The apparatus of claim 27 further comprising determining a
second environmental factor of said encapsulated electrophoretic
display media based on said resistivity and said measured first
environmental factor.
29. The apparatus of claim 28 wherein one of said first and second
environmental factors is temperature, and other is humidity.
30. The apparatus of claim 24 wherein said detection circuit
comprises a capacitance bridge.
31. The apparatus of claim 24 wherein said detection circuit
comprises a circuit capable of measuring time constants.
32. The apparatus of claim 24 wherein said detection circuit
comprises a circuit capable of measuring frequency.
33. The apparatus of claim 24 wherein said detection circuit
comprises a circuit capable of measuring voltage.
34. An electrophoretic display comprising encapsulated
electrophoretic display media comprising a plurality of pixels,
each pixel comprising at least one capsule dispersed in a binder
phase, wherein said at least one capsule contains an
electrophoretic contrast media phase that includes at least one
particle and a suspending fluid, and capable of determining
properties of individual pixels, said electrophoretic display
comprising: (a) a first electrode, said first electrode common and
adjacent to each of said plurality of pixels; (b) at least one
measurement pixel of said plurality of pixels, said at least one
measurement pixel having a measurement electrode adjacent thereto;
(c) a signal generator for applying electrical signals to said
first electrode and said measurement electrode; and (d) a detection
circuit for measuring a first electrical characteristic of said at
least one measurement pixel, said first electrical characteristic
generated in response to said applied electrical signals.
35. The electrophoretic display of claim 34 further comprising a
processor for deducing a second electrical characteristic of said
at least one measurement pixel based on said measured first
electrical characteristic.
36. The electrophoretic display of claim 35 wherein said second
electrical characteristic comprises resistivity of said at least
one measurement pixel.
37. The electrophoretic display of claim 36 further comprising
measuring a first environmental factor of said encapsulated
electrophoretic display media using an external sensor.
38. The electrophoretic display of claim 37 further comprising
determining a second environmental factor of said encapsulated
electrophoretic display media based on said resistivity and said
measured first environmental factor.
39. The electrophoretic display of claim 38 wherein one of said
first and second environmental factors is temperature, and the
other is humidity.
40. The electrophoretic display of claim 34 wherein said detection
circuit comprises a capacitance bridge.
41. The electrophoretic display of claim 34 wherein said detection
circuit comprises a circuit capable of measuring time
constants.
42. The electrophoretic display of claim 34 wherein said detection
circuit comprises a circuit capable of measuring frequency.
43. The electrophoretic display of claim 34 wherein said detection
circuit comprises a circuit capable of measuring voltage.
44. An input device, comprising (a) encapsulated electrophoretic
display media, said encapsulated electrophoretic display media
comprising a plurality of pixels, each pixel comprising at least
one capsule dispersed in a binder phase, wherein said at least one
capsule contains an electrophoretic contrast media phase that
includes at least one particle and a suspending fluid, each pixel
having a pixel electrode adjacent thereto; (b) a first electrode,
said first electrode common and adjacent to each of said plurality
of pixels; (c) a signal generator for applying electrical signals
to said first electrode and each of said pixel electrodes; (d) a
detection circuit for measuring a first electrical characteristic
of each of said plurality of pixels, said first electrical
characteristic generated in response to said applied electrical
signals; (e) a discriminator circuit for detecting a change in said
first electrical characteristic of at least one pixel of said
plurality of pixels; and (f) a response generator for generating a
response to said change and identifying said at least one
pixel.
45. The input device of claim 44 wherein said first electrical
characteristic is a voltage or capacitance.
46. The input device of claim 44, further comprising a processor
for deducing a second electrical characteristic of said at least
one pixel based on said measured first electrical
characteristic.
47. The input device of claim 46 wherein said second electrical
characteristic is resistivity.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of and claims
priority to U.S. Ser. No. 09/349,808 filed Jul. 8, 1999, which
claims priority to U.S. Serial No. 60/092,046 filed Jul. 8, 1998.
The contents of both applications are incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] This present invention relates to electronic displays and,
in particular, to methods and apparatus for determining properties
of electrophoretic displays.
BACKGROUND OF THE INVENTION
[0003] Electrophoretic display media, generally characterized by
the movement of particles through an applied electric field, are
highly reflective, can be made bistable, can be scaled to a large
area, and consume very little power. Encapsulated electrophoretic
displays also enable the display to be printed. These properties
allow encapsulated electrophoretic display media to be used in many
applications for which traditional electronic displays are not
suitable, such as flexible displays.
[0004] One particular application for displaying screens are input
devices, such as touch screens or keypads, or writing tablets. In
many cases, it is desirable to sense the state of the display in
order to digitize the input. For example, measuring and analyzing
certain properties of the display may enable detection of the
location of the input. A responsive event or action may then be
generated.
[0005] Also, the electrical properties of encapsulated
electrophoretic display media may vary in response to environmental
factors, such as temperature and humidity. In some circumstances,
in order to achieve a repeatable optical state in the display, it
may be desirable to compensate the drive waveform in response to
changes in electrical properties of the polymeric materials that
comprise encapsulated electrophoretic display media. Thus, it is
desirable to measure the display parameters that affect waveform
compensation scheme. Use of external display sensors, however, may
increase cost of the display and complicate the manufacturing
process. In addition, external sensors may not accurately measure
the parameters inside the display.
SUMMARY OF THE INVENTION
[0006] An encapsulated electrophoretic display can be constructed
so that the optical state of the display is stable for some length
of time. When the display has two states, which are stable in this
manner, the display is said to be bistable. If more than two states
of the display are stable, then the display can be said to be
multistable. For the purpose of this invention, the term bistable
will be used to indicate a display in which any optical state
remains fixed once the addressing voltage is removed. The
definition of a bistable state depends on the application for the
display. A slowly-decaying optical state can be effectively
bistable if the optical state is substantially unchanged over the
required viewing time. For example, in a display that is updated
every few minutes, a display image that is stable for hours or days
is effectively bistable for that application. In this invention,
the term bistable also indicates a display with an optical state
sufficiently long-lived as to be effectively bistable for the
application in mind. Alternatively, it is possible to construct
encapsulated electrophoretic displays in which the image decays
quickly once the addressing voltage to the display is removed
(i.e., the display is not bistable or multistable). As will be
described, in some applications it is advantageous to use an
encapsulated electrophoretic display that is not bistable. Whether
or not an encapsulated electrophoretic display is bistable, and its
degree of bistability, can be controlled through appropriate
chemical modification of the electrophoretic particles, the
suspending fluid, the capsule, and binder materials.
[0007] An encapsulated electrophoretic display may take many forms.
The display may comprise capsules dispersed in a binder. The
capsules may be of any size or shape. The capsules may, for
example, be spherical and may have diameters in the millimeter
range or the micron range, but is preferably from ten to a few
hundred microns. The capsules may be formed by an encapsulation
technique, as described below. Particles may be encapsulated in the
capsules. The particles may be two or more different types of
particles. The particles may be colored, luminescent,
light-absorbing or transparent, for example. The particles may
include neat pigments, dyed (laked) pigments or pigment/polymer
composites, for example. The display may further comprise a
suspending fluid in which the particles are dispersed.
[0008] The successful construction of an encapsulated
electrophoretic display requires the proper interaction of several
different types of materials and processes, such as a polymeric
binder and, optionally, a capsule membrane. These materials must be
chemically compatible with the electrophoretic particles and fluid,
as well as with each other. The capsule materials may engage in
useful surface interactions with the electrophoretic particles, or
may act as a chemical or physical boundary between the fluid and
the binder.
[0009] In some cases, the encapsulation step of the process is not
necessary, and the electrophoretic fluid may be directly dispersed
or emulsified into the binder (or a precursor to the binder
materials) and an effective "polymer-dispersed electrophoretic
display" constructed. In such displays, voids created in the binder
may be referred to as capsules or microcapsules even though no
capsule membrane is present. The binder dispersed electrophoretic
display may be of the emulsion or phase separation type.
[0010] Throughout the specification, reference will be made to
printing or printed. As used throughout the specification, printing
is intended to include all forms of printing and coating,
including: premetered coatings such as patch die coating, slot or
extrusion coating, slide or cascade coating, and curtain coating;
roll coating such as knife over roll coating, forward and reverse
roll coating; gravure coating; dip coating; spray coating; meniscus
coating; spin coating; brush coating; air knife coating; silk
screen printing processes; electrostatic printing processes;
thermal printing processes; and other similar techniques. A
"printed element" refers to an element formed using any one of the
above techniques.
[0011] The primary optical effect in a microencapsulated
electrophoretic display device is the controlled positioning of one
or more types of colloidal particles within a microcapsule. In one
embodiment, colloidal particles are suspended in a colored fluid
within the microcapsule. Application of an electrical signal will
drive the particles to one side of the microcapsule or the other.
If the colloidal particles are near the side of the microcapsule
nearer the viewer, the viewer will see the color of the colloid. If
the colloidal particles are nearer the opposite side of the
microcapsule from the viewer, the viewer will see the colored
fluid. The contrast between the colors of the fluid and the
colloid, based on the colloid position, provides the means for a
display device.
[0012] The position of the colloid can be controlled by application
of electrical signals to electrodes built into the display.
Additionally, it is possible to control the position of the colloid
using an externally provided voltage signal (electrostatic
writing). The display can be devised to work primarily by
application of a field to electrodes, by electrostatic writing, or
with both.
[0013] The present invention provides novel methods and apparatus
for sensing the position of the colloid, that is, for sensing the
state of electrophoretic displays electrically. The invention is
also directed to novel methods and apparatus for determining the
parameters of the display materials using the encapsulated
electrophoretic display media as a sensor, either alone or in
conjunction with other sensors.
[0014] In one aspect, the present invention relates to a method for
determining properties of encapsulated electrophoretic display
media, that includes providing encapsulated electrophoretic display
media that has a plurality of capsules dispersed in a binder phase,
wherein at least one of said plurality of capsules contains an
electrophoretic contrast media phase that includes at least one
particle and a suspending fluid. The method further includes
providing two electrodes adjacent to said plurality of capsules;
applying a first electrical signal to one of the electrodes,
applying a second electrical signal to the other electrode; and
measuring an electrical characteristic of the encapsulated
electrophoretic display media that is generated in response to the
applied first and second electrical signals.
[0015] In another aspect, the present invention relates to a method
for determining properties of encapsulated electrophoretic display
media that includes providing encapsulated electrophoretic display
media that has a plurality of pixels, each pixel includes at least
one capsule dispersed in a binder phase. The capsules contain an
electrophoretic contrast media phase that includes at least one
particle and a suspending fluid. The method further includes
providing an electrode that is common and adjacent to each pixel of
the plurality of pixels and providing at least one measurement
pixel of the plurality of pixels that has a measurement electrode
adjacent thereto. The method further includes applying a first
electrical signal to the common electrode, applying a second
electrical signal to the measurement electrode; and measuring an
electrical characteristic of the measuring pixel that is generated
in response to the applied electrical signals.
[0016] In still another aspect, the present invention relates to an
apparatus for determining properties of encapsulated
electrophoretic display media. The encapsulated electrophoretic
display media includes a plurality of capsules dispersed in a
binder phase and two electrodes adjacent to the plurality of
capsules. At least one of said plurality of capsules contains an
electrophoretic contrast media phase that includes at least one
particle and a suspending fluid. The apparatus includes a signal
generator for applying electrical signals to the two electrodes;
and a detection circuit for measuring an electrical characteristic
of the encapsulated electrophoretic display media generated in
response to the applied electrical signals.
[0017] In yet another aspect, the invention relates to an
electrophoretic display that includes encapsulated electrophoretic
display media having a plurality of pixels. Each pixel includes at
least one capsule dispersed in a binder phase. Each capsule
contains an electrophoretic contrast media phase that includes at
least one particle and a suspending fluid. The electrophoretic
display of the invention, capable of determining properties of
individual pixels, includes a first electrode that is common and
adjacent to each of the plurality of pixels and at least one
measurement pixel of the plurality of pixels, having a measurement
electrode adjacent thereto. The display also includes a signal
generator for applying electrical signals to these electrodes; and
a detection circuit for measuring a first electrical characteristic
of the measurement pixel that is generated in response to the
applied electrical signals.
[0018] In still another aspect, the invention features an input
device that includes an encapsulated electrophoretic display media
having a plurality of pixels. Each pixel includes a pixel electrode
adjacent thereto and at least one capsule dispersed in a binder
phase. Each capsule contains an electrophoretic contrast media
phase that includes at least one particle and a suspending fluid.
The input device further includes a first electrode that is common
and adjacent to each pixel of the plurality of pixels, a signal
generator for applying electrical signals to the common electrode
and each of the pixel electrodes, and a detection circuit for
measuring an electrical characteristic of each of the plurality of
pixels that is generated in response to the applied electrical
signals. The input device also includes a discriminator circuit for
detecting a change in the electrical characteristic of at least one
pixel of the plurality of pixels; and a response generator for
identifying the pixel with a change in the electrical
characteristic and generating a response to the change.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The invention is pointed out with particularity in the
appended claims. The advantages of the invention described above,
together with further advantages, may be better understood by
referring to the following description taken in conjunction with
the accompanying drawings. In the drawings, like reference
characters generally refer to the same parts throughout the
different views. Also, the drawings are not necessarily to scale,
emphasis instead generally being placed upon illustrating the
principles of the invention.
[0020] FIG. 1A is a diagrammatic side view of an electrophoretic
display element with optical particles near the sensing
electrodes.
[0021] FIG. 1B is a diagrammatic side view of an electrophoretic
display element with optical particles distant from the sensing
electrodes.
[0022] FIG. 2 is a flow chart showing the steps to be taken to
sense the state of an electrophoretic display element.
[0023] FIG. 3 shows a circuit diagram of an embodiment of the
invention
[0024] FIG. 4A shows a circuit diagram of the embodiment of FIG. 3
in a measurement mode.
[0025] FIG. 4B is a graph showing exponential change of the voltage
applied to the common electrode over the period of time in the
embodiment of FIG. 3.
[0026] FIG. 5 shows a circuit diagram of an another embodiment of
the invention
[0027] FIG. 6 shows a circuit diagram of yet another embodiment of
the invention
[0028] FIG. 7 is a diagrammatic view of an input device according
to the invention.
[0029] FIG. 8 is a flow chart of the operation of the input device
according to the embodiment of FIG. 7
DETAILED DESCRIPTION OF THE INVENTION
[0030] An electronic ink is an optoelectronically active material
which comprises at least two phases: an electrophoretic contrast
media phase and a coating/binding phase. The electrophoretic phase
comprises, in some embodiments, a single species of electrophoretic
particles dispersed in a clear or dyed medium, or more than one
species of electrophoretic particles having distinct physical and
electrical characteristics dispersed in a clear or dyed medium. In
some embodiments the electrophoretic phase is encapsulated, that
is, there is a capsule wall phase between the two phases. The
coating/binding phase includes, in one embodiment, a polymer matrix
that surrounds the electrophoretic phase. In this embodiment, the
polymer in the polymeric binder is capable of being dried,
crosslinked, or otherwise cured as in traditional inks, and
therefore a printing process can be used to deposit the electronic
ink onto a substrate. An electronic ink is capable of being printed
by several different processes, depending on the mechanical
properties of the specific ink employed. For example, the fragility
or viscosity of a particular ink may result in a different process
selection. A very viscous ink would not be well-suited to
deposition by an inkjet printing process, while a fragile ink might
not be used in a knife over roll coating process.
[0031] The optical quality of an electronic ink is quite distinct
from other electronic display materials. The most notable
difference is that the electronic ink provides a high degree of
both reflectance and contrast because it is pigment based (as are
ordinary printing inks). The light scattered from the electronic
ink comes from a very thin layer of pigment close to the top of the
viewing surface. In this respect it resembles an ordinary, printed
image. Also, electronic ink is easily viewed from a wide range of
viewing angles in the same manner as a printed page, and such ink
approximates a Lambertian contrast curve more closely than any
other electronic display material. Since electronic ink can be
printed, it can be included on the same surface with any other
printed material, including traditional inks. Electronic ink can be
made optically stable in all display configurations, that is, the
ink can be set to a persistent optical state. Fabrication of a
display by printing an electronic ink is particularly useful in low
power applications because of this stability.
[0032] Electronic ink displays are novel in that they can be
addressed by DC voltages and draw very little current. As such, the
conductive leads and electrodes used to deliver the voltage to
electronic ink displays can be of relatively high resistivity. The
ability to use resistive conductors substantially widens the number
and type of materials that can be used as conductors in electronic
ink displays. In particular, the use of costly vacuum-sputtered
indium tin oxide (ITO) conductors, a standard material in liquid
crystal devices, is not required. Aside from cost savings, the
replacement of ITO with other materials can provide benefits in
appearance, processing capabilities (printed conductors),
flexibility, and durability. Additionally, the printed electrodes
are in contact only with a solid binder, not with a fluid layer
(like liquid crystals). This means that some conductive materials,
which would otherwise dissolve or be degraded by contact with
liquid crystals, can be used in an electronic ink application.
These include opaque metallic inks for the rear electrode (e.g.,
silver and graphite inks), as well as conductive transparent inks
for either substrate. These conductive coatings include
semiconducting colloids, examples of which are indium tin oxide and
antimony-doped tin oxide. Organic conductors (polymeric conductors
and molecular organic conductors) also may be used. Polymers
include, but are not limited to, polyaniline and derivatives,
polythiophene and derivatives, poly3,4-ethylenedioxythiophene
(PEDOT) and derivatives, polypyrrole and derivatives, and
polyphenylenevinylene (PPV) and derivatives. Organic molecular
conductors include, but are not limited to, derivatives of
naphthalene, phthalocyanine, and pentacene. Polymer layers can be
made thinner and more transparent than with traditional displays
because conductivity requirements are not as stringent.
[0033] As an example, there is a class of materials called
electroconductive powders which are also useful as coatable
transparent conductors in electronic ink displays. One example is
Zelec ECP electroconductive powders from DuPont Chemical Co. of
Wilmington, Del.
[0034] Referring now to FIGS. 1A and 1B, a highly diagrammatic view
of an electrophoretic display element is shown. An electronic ink
typically comprises many such elements in a binder phase. In brief
overview, capsule 40 is provided and contains electrophoretic
particles 50 suspended in a dispersing fluid 55. Dispersing fluid
55 may be clear or dyed. The particles 50 typically possess optical
properties of interest, such as color, luminescence, or
reflectance. In some embodiments, multiple species of particles 50
may be provided in the same capsule. Electrodes 10, 20, 30 are used
to translate the particles 50 within the capsule 40, thus changing
the appearance of the capsule 40 to a viewer 5. Electrodes 10, 20
may be used to apply a field 60 to the capsule 40 in order to sense
its state.
[0035] The position of the particles 50 within the capsule 40 may
be electrically determined by applying an electrical signal to
electrodes 10, 20 and measuring the electrical properties of the
capsule 40 in response to the applied electrical signal.
[0036] In greater detail, the steps to be taken in sensing the
state of an electrophoretic display are shown in FIG. 2. A display
element to be measured is provided (step 202). In some embodiments,
the display element is already attached to measurement device,
i.e., the display includes circuitry for sensing the state of
individual display elements. In other embodiments, the state of a
display is measured by a separate device or devices.
[0037] An electrical signal is applied to the provided display
element (step 204). Typically this is done via electrodes 10, 20,
30 adjacent the element. These can be the same electrodes used to
translate the electrophoretic particles within the capsule or they
can be a separate set of electrodes adjacent the capsule. The
electrical signal applied to the capsule may be either an
alternating-current (AC) field, a direct-current (DC) field, or
some combination of the two.
[0038] Whether the signal applied to the capsule is AC, DC, or
hybrid AC/DC, the signal is typically selected to minimize
disturbance of the particles within the capsule. For example, an AC
signal may be selected having a frequency less than 100 KHz,
preferably less than 70 KHz, most preferably less than 10 KHz. In
certain preferred embodiments, the selected AC signal has a
frequency greater than 1Hz. Further, voltages of such signals are
selected to be less than I volt, preferably less than 500
millivolts, and most preferably less than 100 millivolts. In some
preferred embodiments, the applied signal has an amplitude greater
than 1 millivolt.
[0039] An internal or external signal source may be used to
generate the electrical signal. For example, a preselected signal
can be stored digitally in ROM or PROM that is electrically coupled
to a digital-to-analog convertor and a driver that drives the
signal to the electrodes. Alternatively, the display may be
provided with an input jack, such as a BNA or similar jack, that
allows a signal to be driven to the electrodes from an external
signal generator.
[0040] If the electrical characteristic of particles 50 and
dispersing fluid 55 differ, then the applied electrical signal will
evoke a different electrical response from the display element
depending on whether the particles 50 intersect the field 60 of the
electrical signal applied to the electrodes or not.
[0041] The electrical response of the display element is measured
(step 206). The electrical response measured can be capacitave,
resistive, or some combination of two such as an RC time constant.
The measurement circuit used can be a voltmeter, ammeter, ohmmeter,
capacitance bridge, or some other circuit capable of measuring the
desired electrical characteristic, such as a circuit capable of
measuring frequency, time constant, or charge.
[0042] The state of the display element is deduced from the
measured electrical response (step 208). For example, if the
particles 50 have a much higher impedance than the dispersing fluid
55, then a voltage applied to the capsule 40 will be more
attenuated if the particles 50 are nearer the electrodes than if
they are not. In its simplest form, the circuit which performs this
function (the "discriminator circuit") is a comparator. A measured
electrical characteristic is compared to a predetermined threshold
to determine if the particles 50 are near the electrodes or not. In
another embodiment, AC current is passed through the display
element at a particular frequency to determine a frequency response
for the element.
[0043] The discriminator circuit may be analog or digital. In one
embodiment, the discriminator circuit includes a processor that
analyzes the measured electrical response of the display element.
In a further embodiment, both the discriminator circuit and the
signal generator are controlled by a processor.
EXAMPLE 1
[0044] A microencapsulated electrophoretic display comprising
rutile titania dispersed in a low dielectric constant hydrocarbon
fluid was provided. Two electrodes were positioned adjacent each
other on the same substrate, adjacent also to a microcapsule, and
on the back side of the display from the viewer. An AC electrical
signal was placed across the electrodes, and the current passed
between the electrodes measured. The frequency of the AC signal was
set so that the capacitive characteristics of the microcapsules
were measured. Typically, electrical frequencies in the range of 10
Hz to 10 KHz are useful in this regard. The dielectric constant
near the electrodes depended on whether the colloid was on the same
side of the microcapsule as the electrodes, or on the opposite
sides. It is advantageous to have the spacing of the electrodes
small compared to the microcapsule diameter. A high dielectric
constant indicated that the colloidal particles were near the
electrodes, and the display is dark. A low dielectric constant
indicated that the colloidal particles were away from the
electrodes and at the front of the microcapsule, and that the
display is light. Low amplitude voltages were used to make the
measurement. Preferably, the applied voltage is less than the
operating voltage of the display. Typically, AC voltages in the
range of 1 mV to 1 V, and particularly in the range of 10 mV to 100
mV, are useful.
EXAMPLE 2
[0045] A microencapsulated electrophoretic display was constructed
with sensing electrodes on opposing sides of the display. These
electrodes could be separate structures, or could be the same
electrodes used to address the display. The colloidal dispersion
was constructed so that the colloid contains a net negative charge.
A negative charge is placed on the front electrode, sufficient to
address some or all of the pixel. If the colloid is near the front
of the microcapsule, the colloid will be repelled from the front
surface and attracted to the back. The movement of the colloid
gives a characteristic current signal, which rises, peaks, and then
diminishes as the colloid transits the cell. This peak has a
characteristic time constant and amplitude, depending on the
display characteristics. For example, in a display which requires
90 V to address and a cell gap of 100 microns, the colloid transits
in the range of 100 ms to 2 seconds, depending on the
formulation.
[0046] Alternatively, if the colloid was already near the back,
then application of this voltage will cause no change in the
colloid position, and the electrical signal will be indicative of
only background ions transiting the cell.
[0047] In this case, the discriminator circuit looks for the
presence of absence of a peak with a constant in this range. If the
colloid transits the cell, then the particles were near the front.
If no peak is seen, the colloid was already near the back.
[0048] Alternatively, the detection circuit can be constructed to
measure the total charged or current passed by the cell. The charge
or current will be higher if the colloidal particles transit the
cell, and be lower if they do not transit the cell.
EXAMPLE 3
[0049] The case of example 2, except the electrodes were adjacent
as single side of the display, and spaced close together relative
to the microcapsule size. Application of a voltage in the range of
1 V to 100 V causes some of the colloid to move from one electrode
to the other if the colloid is near the surface of microcapsule
adjacent the electrodes. If the colloid is on the other side of the
microcapsule, no such transit will be seen. The discriminator
circuit looks for the presence or absence of a current representing
the colloidal particles, and thus determine if the colloid is on
the face nearer or further from the electrodes. This method has the
advantage of not disturbing the relative position of the colloid in
the front or back of the display.
[0050] While the examples described here are listed using
encapsulated electrophoretic displays, there are other
particle-based display media which should also work as well,
including encapsulated suspended particles and rotating ball
displays.
[0051] In another embodiment, the invention is directed to methods
and apparatus for determining the parameters of the display
materials using the encapsulated electrophoretic display media as a
sensor, either alone or in conjunction with other sensors.
[0052] Encapsulated electrophoretic display media is generally
composed of polymeric materials, whose electrical properties, such
as resistivity and capacitance, vary in response to environmental
factors, such as temperature and humidity. In order to achieve a
repeatable optical state in the display, it may be desirable to
compensate the drive waveform in response to changes in electrical
properties of the polymeric materials that comprise encapsulated
electrophoretic display media. By enabling a waveform compensation
scheme or increasing its effectiveness, the display quality and
period of operation could be enhanced.
[0053] The correction of the drive waveform for humidity using the
resistivity measurement is essentially empirical. Many encapsulated
electrophoretic media, because they use hydrophilic wall materials
such as gelatin, are sensitive to ambient humidity, depending on
how well the medium is sealed. Also, as with most other materials,
the resistivity of the encapsulated electrophoretic medium varies
with its temperature. In a well-sealed medium, the water content of
the display material is essentially unaffected by ambient humidity
and the temperature dependence predominates. In one embodiment, the
temperature is measured by a thermocouple or similar device
embedded in the medium because measuring the internal temperature
of the display is relatively simple using readily available
industry-standard components, while the resistivity measurement is
used to adjust the drive waveform for humidity, because measuring
the humidity inside a display directly is complicated.
[0054] Referring to FIG. 3, an encapsulated electrophoretic display
300 includes an encapsulated electrophoretic display media 310
having two electrodes, a common electrode 320 and a backplane
electrode 330. In one embodiment, the resistivity of the
encapsulated electrophoretic display media 310 is determined using
the common electrode 320 of the electrophoretic display 300 as a
sensor. In this embodiment, the resistivity is averaged over the
entire area of the encapsulated electrophoretic display media
310.
[0055] Referring to FIG. 3, the common electrode 320 is connected
to a detection circuit and a capacitor 340 having a known
capacitance C. In the embodiment shown in FIG. 3, the detection
circuit is a high-impedance voltage measurement circuit 350. Other
circuits for detecting other electrical properties, such as a
capacitance bridge or circuits capable of measuring time constants,
frequency, or electrical charge can also be used.
[0056] Referring still to FIG. 3, the common electrode 320 and the
encapsulated electrophoretic display media 310 are driven to a
voltage V1 by a signal generator 305. The electrical signal applied
to the encapsulated electrophoretic display media 310 through the
common electrode 320 may be either an alternating-current (AC)
field, a direct-current (DC) field, or some combination of the two.
Then, the common electrode 320 is disconnected from the signal
generator by a switch 312 and is connected to an auxiliary circuit,
for example, an analog switch 315. Then, the encapsulated
electrophoretic display media 310 and the back electrode 330 are
driven to a voltage V2. The potential difference (V2-V1) is
measured by the high-impedance voltage measurement circuit 350.
[0057] Referring to FIGS. 3 and 4A-4B, before the voltage V2 was
applied, the capacitor 340 had a voltage V1. In the measurement
mode, after the encapsulated electrophoretic display media 310 and
the back electrode 330 are driven to the voltage V2, the voltage
waveform V that appears at the common electrode 320 over a period
of time would follow an exponential 410 with time constant RC,
where R is the equivalent resistivity of all microcapsules of the
encapsulated electrophoretic display media 310, and C is a known
capacitance of the capacitor 340. The corresponding formula that
reflects a relationship between V and V2-V1 as a function of time t
is:
V=(V2-V1)(1-e.sup.(-t/RC)) (1)
[0058] where t is the lapsed time that the circuit voltage is
changing, and e is the base of natural logarithms, which is a
constant that equals about 2.7183. Thus, the equivalent resistivity
R of the encapsulated electrophoretic display media 310 may be
deduced using formula (1).
[0059] Referring to FIG. 5, in another embodiment, the common
electrode 320 is connected to a detection circuit and a resistor
345 having a known resistance R2. In one embodiment, the detection
circuit is a high-impedance voltage measurement circuit 350. In
this embodiment, in the measurement mode, the common electrode 320
is driven to the voltage V1 through the resistor 345, while the
encapsulated electrophoretic display media 310 and the back
electrode 330 are driven to the voltage V2. The formula that
reflects a relationship between the voltage waveform V that appears
at the common electrode 320 and the equivalent resistivity of all
microcapsules of the encapsulated electrophoretic display media 310
is:
V=(V2-V1)*R2/(R+R2) (2)
[0060] Thus, the equivalent resistivity R of the encapsulated
electrophoretic display media 310 may be deduced using formula (2).
The amount of time necessary to take the measurement in this
embodiment of the invention is relatively short, e.g. on the order
of milliseconds, which could minimize the effect of undesirable
transient voltages applied to the encapsulated electrophoretic
display media 310.
[0061] Referring to FIG. 6, in another embodiment, the resistivity
of the encapsulated electrophoretic display media 310 is determined
using one or more of individual encapsulated electrophoretic
display media elements 312 as sensors. In this embodiment, the
resistivity of different parts of the electrophoretic display media
310 can be measured. Also, the resistivity of the entire
electrophoretic display media 310 may be approximated by
calculating an average between the measurements taken from
individual encapsulated electrophoretic display media elements 312.
In one version of this embodiment, each sensor 312 is one of the
active electrophoretic display pixels, which-is connected to the
measurement circuit 350 when the electrophoretic display 300 is not
in an update state. Alternatively, in another version of this
embodiment, designated individual encapsulated electrophoretic
display media elements that lie outside the active pixel area could
be used for the resistivity measurement, if transient currents or
the size of an active pixel make use of the active pixel as a
sensor undesirable.
[0062] Referring still to FIG. 6, the sensing individual
encapsulated electrophoretic display media element 312 is connected
to a detection circuit and a capacitor 340 having a known
capacitance C. In one embodiment, the detection circuit is a
high-impedance voltage measurement circuit 350. Other circuits for
detecting other electrical properties, such as a capacitance bridge
or circuits capable of measuring time constants, frequency, or
electrical charge can also be used.
[0063] The common electrode 320 and the encapsulated
electrophoretic display media 310 are driven to a voltage V3 by a
signal generator 305. The electrical signal applied to the
encapsulated electrophoretic display media 310 through the common
electrode 320 may be either an alternating-current (AC) field, a
direct-current (DC) field, or some combination of the two. Then,
the sensor 312 is driven to a voltage V4. The potential difference
(V4-V3) at the sensor 312 is measured by the high-impedance voltage
measurement circuit 350. As discussed above with respect to the
embodiment of FIG. 3, the formula that reflects a relationship
between the sensor voltage and V4-V3 as a function of time t is
V=(V4-V3)(1-e.sup.(-t/RC)) (3)
[0064] where t is the lapsed time that the circuit voltage is
changing, and e is the base of natural logarithms, which is a
constant that equals about 2.7183. Thus, the resistivity R of the
sensor element 312 may be deduced using formula (3).
[0065] Referring to FIG. 7, in another embodiment, the sensing
element 312 is connected to a detection circuit and a resistor 345
having a known resistance R2. In one embodiment, the detection
circuit is a high-impedance voltage measurement circuit 350. In
this embodiment, in the measurement mode, the sensing element 312
is driven to the voltage V4 through the resistor 345, while the
encapsulated electrophoretic display media 310 and the common
electrode 320 are driven to the voltage V3. As discussed above, the
formula that reflects a relationship between the voltage waveform V
that appears at the sensing element 312 and its resistivity is:
V=(V4-V3)R2/(R+R2) (4)
[0066] Thus, the resistivity R of each sensing element 312 of the
encapsulated electrophoretic display media 310 may be deduced using
formula (4).
[0067] After the resistivity of the encapsulated electrophoretic
display media has been measured, its ambient humidity can then be
deduced based on the resisitivity value. As mentioned above, many
encapsulated electrophoretic media, because they use hydrophilic
wall materials such as gelatin, are sensitive to ambient humidity,
depending on how well the medium is sealed. The correlation between
the resistivity of the display and the ambient humidity therein is
essentially empirical.
[0068] Other environmental factors of the encapsulated
electrophoretic display media, such as, for example, an ambient
temperature, can be determined based on the resistivity value as
well. Because the internal temperature of the display usually
tracks the external temperature rather rapidly, with a lag time of
a few minutes, in one embodiment of the invention, the ambient
temperature is measured using an external sensor 395, as shown in
FIG. 3. In another embodiment, the internal temperature is measured
using a thermocouple embedded in a display. Other environmental
factors of the encapsulated electrophoretic display media, can be
determined using an external sensors as well.
[0069] Referring to FIG. 8, in one embodiment, the encapsulated
electrophoretic display 300, whose parameters can be determined
using the encapsulated electrophoretic display media itself as a
sensor is used as part of an input device 900, for example, a
touch-screen display or a keypad. The input device 900 includes an
encapsulated electrophoretic display media 310 and a common
electrode 320. The common electrode 320 is formed from a conductive
material capable of elastic deformation, such as indium tin oxide.
Conductive polymers, such as polythiophene or polyaniline, can also
be used. The encapsulated electrophoretic display media 310
includes a plurality of pixels 905, each of which includes at least
one individual encapsulated electrophoretic display media element
312. Each pixel has a pixel electrode 910 adjacent thereto.
[0070] Referring still to FIG. 8, the input device 900 also
includes a signal generator 920 for applying electrical signals to
the common electrode 320 and each of pixel electrodes 910. The
electrical signal applied to the encapsulated electrophoretic
display media 310 by the common electrode 320 and each of pixel
electrodes 910 may be either an alternating-current (AC) field, a
direct-current (DC) field, or some combination of the two. A
detection circuit 930, such as one described above in connection
with the embodiments illustrated in FIG. 6, is provided for
periodically measuring an electrical characteristic of each of said
plurality of pixels, generated in response to the applied
electrical signal.
[0071] Referring still to FIG. 8, the input device 900 also
includes a discriminator circuit 940 for detecting a change in the
electrical characteristic of at least one pixel of the plurality of
pixels. In its simplest form, the circuit which performs this
function (the "discriminator circuit") is a comparator. A measured
electrical characteristic is compared to a previously measured
value of this characteristic to detect a variation. The input
device 900 also includes a response generator 950 in electrical
communication with the discriminator circuit that is capable of
identifying the pixel, whose electrical characteristic has changed
since the previous measurement, and generating a response to this
change. The discriminator circuit may be analog or digital. In one
embodiment, the discriminator circuit includes a processor that
analyzes the measured electrical response of the display element.
In a further embodiment, the detection circuit, discriminator
circuit, the response generator, and the signal generator are
controlled by a processor.
[0072] Referring to FIG. 9, in operation, the detection circuit 930
periodically measures the electrical properties of each of the
pixels of encapsulated electrophoretic display media 310. When a
user depresses a part of the common electrode 320 of the
encapsulated electrophoretic display 300 (STEP 1020), certain
electrical properties of the encapsulated electrophoretic display
media 310 in the area adjacent to the depression in the common
electrode 320, such as, for example, voltage, resistivity, or
capacitance, change (STEP 1030). The detection circuit 930 takes
new measurements of the electrical properties (STEP 1040). The
discriminating circuit 940 compares the new measurements with
previously obtained measurements and detects a change in electrical
properties of the pixels adjacent to the depression in the common
electrode 320 (STEP 1050). The response generator 950 identifies
one or more pixels whose electrical properties have changed and
generates a response (STEP 1060). For example, the response
generator may generate an output signal to be used by devices
receiving input from the input device 900.
[0073] While the invention has been particularly shown and
described with reference to specific preferred embodiments, it
should be understood by those skilled in the art that various
changes in form and detail may be made therein without departing
from the spirit and scope of the invention as defined by the
appended claims.
* * * * *