U.S. patent number 3,607,256 [Application Number 04/746,177] was granted by the patent office on 1971-09-21 for fully enclosed electrophoretic-imaging system.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Morton Silverberg.
United States Patent |
3,607,256 |
Silverberg |
September 21, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
FULLY ENCLOSED ELECTROPHORETIC-IMAGING SYSTEM
Abstract
A display system which responds to a light image to form a
viewable image. The system is sealed and is filled with a fluid
carrying a dilute suspension of electrically photosensitive
particles between two conductive plates. If an image is focused
onto the space between the plates and a voltage established
therebetween, the particles in contact with the inner surface of
the conductive plates will migrate from light-struck areas of the
plates. After the fluid has been circulated for an appropriate time
after imaging, the fluid circulation is directed through a filter,
which replaces the fluid between the plates with fluid having the
undeposited particles removed. Various provisions for viewing the
images formed within the display system are described.
Inventors: |
Silverberg; Morton (Pittsford,
NY) |
Assignee: |
Xerox Corporation (Rochester,
NY)
|
Family
ID: |
26823013 |
Appl.
No.: |
04/746,177 |
Filed: |
July 19, 1968 |
Current U.S.
Class: |
430/19; 430/32;
430/33 |
Current CPC
Class: |
G03G
17/10 (20130101); G02F 1/167 (20130101); G02F
1/1675 (20190101) |
Current International
Class: |
G02F
1/01 (20060101); G02F 1/167 (20060101); G03G
17/00 (20060101); G03G 17/10 (20060101); G03g
013/00 () |
Field of
Search: |
;96/1,1.2,1.3,1.5
;117/17.5 ;204/181 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lesmes; George F.
Assistant Examiner: Wittenberg; M. B.
Claims
What is claimed is:
1. A method for producing a viewable image comprising the steps
of:
a. directing a fluid carrying a suspension of electrically
photosensitive particles between a pair of electrically conductive
plates at least one of which is transparent, a layer of said
electrically photosensitive particles depositing on the surface of
said transparent conductive plate,
b. applying a unidirectional electric field between said conductive
plates,
c. simultaneously projecting a light image upon said transparent
conductive plate the electrically photosensitive particles
contacting illuminated areas of said transparent conductive plate
migrating away from said transparent conductive plate, leaving a
visible particle image thereupon, and
d. circulating said fluid suspension through a particle filter
after imaging to substantially remove all the particles remaining
in the fluid suspension.
2. The method as defined in claim 1 further including the step of
erasing the particle image formed on said transparent conductive
plate, said erasing step comprising: illuminating said particle
image while applying an electric field between said plates of a
polarity to remove said particles from said transparent conductive
plate, and recirculating said fluid suspension between said
plates.
3. The method as defined in claim 1 wherein particle migration is
accomplished by reversing the direction of the electric field
between the plates causing the particles which were not struck by
light to migrate from said surface.
4. The method as defined in claim 1 wherein said electrically
photosensitive particles are charged before being directed between
said pair of electrically conductive plates.
5. The method as defined in claim 4 further including the steps
of:
reducing the electric field between said conductive plates to a
valve which inhibits the particles from migration during exposure,
and
increasing the electric field after image exposure to enable
particle migration.
Description
BACKGROUND OF THE INVENTION
Apparatus for reproducing images, and in particular, apparatus for
the direct reproduction of images by utilizing a light sensitive
element, a developer powder and an electric field has been known in
the past. In the aforementioned apparatus, light rays are
transmitted through an image copy and passes through a glass plate
having a conductive coating thereon. The resistance of a
photoconductive element adjacent the conductive coating becomes
reduced and charges the developer powder lying upon the illuminated
areas of the conductive coating. The electric field thereupon
attracts the charged developer powder and the particles migrate
from the conductive coating leaving a visible powder image thereon.
The developer powder particles can be suspended in a liquid medium,
as well as in air or a vacuum.
The size limitations of the prior art apparatus, the difficulty of
removing undeposited particles between the plates, the relative
complexity of the apparatus and the required viewing optics made it
advantageous to consider alternatives.
SUMMARY OF THE INVENTION
The present invention provides a system utilizing sealed particle
migration systems to produce temporary image buffers. A temporary
image buffer is defined as a system which responds to a light image
by forming a viewable image. The viewable image is capable of being
stored indefinitely if desired and being erased on demand, thereby
being suitable for reuse. The image buffers of the present
invention have possible uses as viewing screens for microimage
viewers, display panels and as intermediates for electronic graphic
communications systems, display projection systems and imaging
systems. The circulation system used in conjunction with the
temporary image buffer serves to provide clear fluid during the
viewing process and for imparting a sideways component of force to
the particles migrating from an illuminated area.
It is an object of the present invention to provide a novel method
for forming a viewable image.
It is another object of the present invention to provide a novel
method of imaging wherein selective or imagewise exposure of a
particle migration system produces a viewable image of the type
enabling either indefinite storage or erasure.
It is a further object of the invention to provide a novel sealed
particle migration method which utilizes a fluid circulation
system, the fluid circulation system providing clear fluid during
the viewing process and providing a sideways component of force to
the particles migrating from an illuminated area.
It is still a further object of the present invention to provide
novel techniques for viewing the images formed within a
particle-migration-imaging cell.
For a more complete understanding of the invention, the above
listed objects and other aspects of the invention will be further
explained in the following detailed description in conjunction with
the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a is a diagram of the display and circulation systems of the
present invention.
FIG. 1b illustrates a portion of the circulation system operative
during the viewing process.
FIGS. 2 and 3 illustrate a portion of the display panel cell after
imaging has occurred and produced by different embodiment of the
invention.
FIGS. 4a and 4b illustrate a portion of the display panel before
and after imaging, respectively, and produced by another embodiment
of the invention .
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1a, there is shown a diagram of the system of
the present invention.
NESA plates 10 and 12, marketed by the Pittsburgh Plate Glass
Company and comprising a transparent conducting tin-oxide coating
overlaying a glass substrate, are shown slightly separated from one
another. Fluid 16, flowing in the direction of the arrow, flows
between plates 10 and 12. The plates 10 and 12 and the portion of
the fluid 16 therebetween are completely sealed, forming an
enclosed plate assembly. Fluid 16 carries a dilute suspension of
particles. The fluid may be air, although an appropriate high
breakdown voltage liquid is preferable. The fluid within the plates
10 and 12 is delivered to pump 20 via tube 18. The output of pump
20 initially is passed through open valve 22 and returned to the
enclosed plate assembly. A source of voltage 26 is shown connected
between plates 10 and 12 and produces an electric field
therebetween. Structures 26 and 28 serve to align and support the
enclosed assembly.
In one embodiment the system operation will be considered when the
particles in suspension are electrically photosensitive and in
addition are dark and bipolar, such as selenium or phthalocyanine.
Examples of additional photosensitive particles which may be
utilized in the present invention are disclosed in U.S. Pat. No.
3,383,993 issued May 21, 1968. A light image is focused into the
space between plates 10 and 12 by transmitting light rays through,
or reflective from, any optically visible subject 14 such as a
film, picture, text, drawing or surface area placed adjacent the
outer surface of plate 10. Voltage source 26 establishes an
electric field between the conducting layers of plates 10 and 12
simultaneously with the projection of the light image and valve 22
is then opened to permit the particle-carrying liquid 27 to
circulate through the system. As illustrated schematically in the
figure, with the valve open, the fluid flow is through the valve
22. The particles, due to either their bipolar characteristics or
their initial charge, will deposit on the inner surfaces of plates
10 and 12. Due to the properties of the optical visible subject 14,
only certain portions of the inner surfaces will be irradiated by
light. Since the particles in this embodiment are electrically
photosensitive, the particles adjacent to the irradiated portions
of the inner plates will have their resistance reduced due to their
electrically photosensitive characteristic. The particles, such as
selenium particles, assume the charge of the surface with which
they are in contact and the electric field between the plates
causes the charged selenium particles to be repelled and migrate to
the dark inner surfaces of plates 10 and 12. In the inner surface
dark areas the particles adhere thereto due to their being charged
in a polarity opposite to that of the charged plates or to their
bipolar characteristic.
After the fluid suspension has been circulated for an appropriate
time, valve 22 is closed and the fluid circulation must now pass
through filter 24 as illustrated schematically in FIG. 1b.
Particles which may have remained in the fluid 27 after imaging and
have not been deposited on the inner surfaces of the plates will be
removed by filter 24 and be replaced with clear fluid 29. Following
imaging, pump 20 is stopped and the voltage potential 26 between
the plates removed. The resulting particle pattern is that shown in
FIG. 2 wherein the particles remaining on the inner surfaces of
plates 10 and 12 correspond to the dark images on the subject 14
and wherein the areas devoid of particles deposited on the inner
surfaces correspond to the light areas of subject 14. The rear
illumination system 30 is then turned on and the exposed areas will
show up as bright areas when viewed through the front surface of
plate 10. Thus this embodiment will produce positive images.
Erasure is accomplished by reapplying the voltage source 26 while
maintaining the rear illumination on, opening valve 22 and turning
on pump 20. The combination of the electrostatic field produced by
voltage source 26 and the illumination flooding produced by rear
illumination system 30 causes the particles on the inner surfaces
of plates 10 and 12 to become redistributed and ready for
reimaging. The particles initially filtered by filter 24 are also
redistributed in the fluid. The rear illumination system 30 can now
be turned off and the image buffer is ready to accept a new input.
In order to facilitate the removal and redistribution of the
deposited particles, it may also be necessary to apply a low
frequency, large amplitude voltage source to the plates and/or
ultrasonic energy to the fluid between the plates. If necessary, a
mechanical scraper system can be utilized.
The circulation system comprising pump 20, valve 22, and filter 24
serves two functions. The first one is to provide clear fluid
during the viewing process if the particles are not completely
deposited and, secondly, provide a sidewise component of force to
the particles migrating from an illuminated area.
The enclosed assembly can be imagewise exposed and viewed from the
same side or imagewise exposed from one side and viewed from the
other side. In the first situation, if the assembly is shielded
from ambient illumination during the exposure step, the preceding
details are sufficient. If however, the assembly is exposed from
one side and viewed from the other, the ambient illumination must
be prevented from reaching the particles during the exposure step.
This can be achieved by working in a dark room, covering the front
face of plate 10 during image exposure or selecting particles which
respond (become conductive) upon exposure to a given portion of the
illumination spectrum such as ultraviolet and placing a filter in
front of the front surface of plate 10 which only passes this
portion of the spectrum.
The display portion of the imaging system can be arranged so that
it may be removed from the circulation system and the supporting
structures 26 and 28, enabling the image to be stored or viewed by
an appropriate projection device.
Surface reflections from the plate may be reduced for example, by
etching the front surface of plate 10 and making the plate 10 thin
to minimize possible image blurring effects.
In another embodiment of the invention, the particles in suspension
are light in color, electrically photosensitive and nonpolar, such
as zinc oxide. Examples of additional photosensitive particles
which may be utilized in the present embodiment are also disclosed
in the aforementioned U.S. Pat. No. 3,383,993. Since the particles
are nonpolar they would not normally be attracted to either of the
inner surfaces of plates 10 or 12. The particles can be charged
prior to image exposure by providing a section in the flow path in
which the particles are illuminated and then brought into contact
with charging electrodes or possibly by flooding the plate with
light prior to the exposure. This precharging process is not
limited to use with light particles but is also applicable to dark
particles such as selenium.
When the white particles are used in the system such as described
previously, the rear illumination system is not used for viewing.
The interior recesses of the system are preferably light-absorbing
and the areas on the plate which have been struck by light appear
dark. Thus, this system is a negative process. The requirements for
control of the ambient illumination are the same as before and the
same solutions are applicable. An additional feature might be to
coat the rear surface of plate 12 with a dark coating which
transmits a portion of the spectrum used for image exposure. An
opaque coating can be used for a front exposure system. This
eliminates the need for a light absorbing cavity behind plate
10.
In another embodiment of the invention, the input image will be
entered over a period of time, as from a cathode ray tube display
for example, as opposed to a slide transparency. For this
embodiment nonpolar particles are preferred. The initial operation
consists of charging all the particles entering the space between
the plates while maintaining a potential difference between them.
This is done without any illumination on the panel. Thus all the
particles should deposit on one of the inner surfaces of plates 10
and 12. However, the polarity is preferably arranged so that the
particles deposit on the inner surface of the front plate 10.
Following this initial step, two exposure/development sequences are
significant. In the first, the potential difference between plates
10 and 12 is reduced to a lower value. This lower potential
difference is chosen so that during the image exposure, the
particles do not transfer although the attraction (repulsion)
forces developed in the exposed areas will be in this direction.
After the assembly has been imagewise exposed, the potential
difference is raised and the light-struck particles will be
transferred to the inner surface of plate 12.
If the transfer time between inner surfaces is slower than the
elemental exposure time either due to a slow transfer process (due
to substantial separation between the electrodes, high suspension
fluid viscosity, etc.) or the elemental exposure time is brief the
voltage potential does not need to be lowered. The constraint of
lower voltage during exposure resulted from wishing to avoid the
possibility of the particles reaching the opposite surface while
they are still illuminated, charging to the potential of this
electrode and returning to the front plate. It should be noted that
since it is unlikely that all the particles returning to the
original plate would return to the empty areas, then under some
circumstances this blurring condition would be acceptable. In
addition, if the elemental illumination lasts long enough (relative
to transit times) the particles would redistribute themselves on
both inner surfaces in the areas which are not illuminated.
An alternate exposure and development step involves using the
reduced voltage during exposure but the particle transfer is
accomplished by reversing the potential between the electrodes and
causing the particles which were not struck by light to transfer to
the other plate.
In either of the above sequences, the particle distribution is as
shown in FIG. 3. The potential difference between the tow plates is
reduced to zero to avoid image disturbance by the viewing
illumination. The image can be viewed by either rear illumination
using dark particles or with front illumination using reflective
particles. When large solid areas are transferred to the inner
surface of plate 12, they tend to interfere with the viewing
process. A possible method of overcoming this interference includes
a frosted light-scattering surface on the inner surface of plate 10
and using dark particles or a dark suspension fluid (which in the
case of rear-imaging is transparent to the imaging spectrum) for a
reflective particle system.
Another embodiment of the image buffer of the present invention is
shown in FIG. 4. The circulation system described with reference to
FIG. 1 is equally applicable to the image buffer embodiment as
shown in FIG. 4. A thin glass sheet 32, transparent to visible
light but opaque to ultraviolet light, has a transparent conductive
layer 34, initially negatively charged, deposited thereon. A
transparent photoconductor 36 which is sensitive to ultraviolet
light is deposited upon layer 34. Spaced between layer 36 and a
conductive transparent layer 40, initially positively charged, is a
dilute liquid developer which contains dark, positively charged
particles 38, not necessarily electrically photosensitive. A
preferred arrangement for rear surface imaging would have the dark
particles 38 transparent to ultraviolet light.
The initial condition in which particles 38 are deposited on
photoconductive surface 36 is shown in FIG. 4(a). If the potential
difference between the two layers 34 and 40 is now reversed and the
photoconductor 36 image exposed, particles 38 will be selectively
removed from the surface of photoconductor 36 and transported to
the surface of layer 40 in the light-struck area as shown in FIG.
4b. The resulting image can be viewed by rear illumination
utilizing light sources 44 as discussed with reference to the
viewing procedure of FIG. 1.
Erasure is accomplished by flooding the rear surface of plate 42
with ultraviolet illumination to which photoconductor 36 is
sensitive and applying an alternately potential between conductive
layers 34 and 40. This will redistribute the particles. The
illumination can then be turned off and a polarity established
between the conductive layers 34 and 40 that causes the charged
particles to deposit on the photoconductor as initially
established.
It should be noted that the image formed after particle migration
has occurred in the embodiments set forth hereinabove may be
recorded.
While the invention has been described with reference to its
preferred embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents
substituted for elements thereof without departing from the true
spirit and scope of the invention. In addition, many modifications
may be made to adapt a particular situation or material to the
teachings of the invention without departing from its essential
teachings.
* * * * *