U.S. patent number 3,773,417 [Application Number 05/167,007] was granted by the patent office on 1973-11-20 for method and apparatus for aperture controlled electrostatic image reproduction or constitution.
This patent grant is currently assigned to Electroprint, Inc.. Invention is credited to Thomas D. Kittredge, Gerald L. Pressman.
United States Patent |
3,773,417 |
Pressman , et al. |
November 20, 1973 |
METHOD AND APPARATUS FOR APERTURE CONTROLLED ELECTROSTATIC IMAGE
REPRODUCTION OR CONSTITUTION
Abstract
The invention basically comprises apparatus and methods relating
to the field of electrostatics, and is concerned with electrostatic
reproducing or constituting. Apertured screen means carry charge
distributions in accordance with a pattern such that particles
directed at the screen means pass therethrough under modulation
control dictated by the pattern. The invention further relates to
apparatus and methods for constituting or reproducing images
through the use of a multi-layered screen consisting of an array of
apertures. A propulsion field directs charged particles through the
screen to a receiving medium preferably spaced at a distance from
the screen. Charge distribution on the screen controls the flow of
particles through the apertures, some of which are in effect
blocked, partially blocked, unblocked, and enhanced, depending on
the local charge level. Thus, it is possible to produce patterns of
varying tone without contact with the printed or effected
substrate.
Inventors: |
Pressman; Gerald L. (San Jose,
CA), Kittredge; Thomas D. (South San Francisco, CA) |
Assignee: |
Electroprint, Inc. (Palo Alto,
CA)
|
Family
ID: |
26862768 |
Appl.
No.: |
05/167,007 |
Filed: |
July 28, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
776146 |
Nov 15, 1968 |
3647291 |
Mar 7, 1972 |
|
|
Current U.S.
Class: |
399/136; 430/68;
399/135; 430/53 |
Current CPC
Class: |
G03G
15/346 (20130101); G03G 15/051 (20130101); B41M
1/125 (20130101); G03G 2217/0025 (20130101) |
Current International
Class: |
B41M
1/12 (20060101); G03G 15/05 (20060101); G03G
15/34 (20060101); G03G 15/00 (20060101); G03g
015/00 () |
Field of
Search: |
;355/3,16,17
;96/1R,1.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Greiner; Robert P.
Parent Case Text
The present application is a divisional of U.S. Pat. No. 3,647,291,
filed Nov. 15, 1968 and issued Mar. 7, 1972, to the same inventors
and assigned to the same assignee.
Claims
What is claimed is:
1. An aperture controlled electrostatic camera comprising in
combination a housing; a removable multi-layer apertured screen
comprising at least a screen insulator layer overlying a screen
conductive layer; optical means for introducing an image to the
housing; and charging means for double charging the insulator layer
with charges varying from at least one polarity to zero in
accordance with the image to be reproduced; said charging means
comprising a transparent conductive layer and a photoconductive
layer interposed between the screen and the optical means; and
terminals whereat a source of potential is adapted to be connected
between the conductive layer of the screen and the transparent
layer.
2. The camera of claim 1 wherein the optical means comprises a
shutter and further comprising timer means for opening the shutter
while connecting the source of potential.
3. The camera of claim 2 further comprising light means within the
camera under control of the timer means and means for reversing the
potential of said source under control of the timer means whereby
the insulator layer may be charged from one polarity through zero
to reverse polarity.
4. An aperture controlled electrostatic camera comprising in
combination housing means; a removable multi-layer apertured screen
comprising at least a screen photoconductive layer overlying a
screen conductive layer; optical means for introducing an image to
the housing; and charging means for double charging the
photoconductive layer with charges varying from at least one
polarity to zero in accordance with the image to be reproduced;
said charging means comprising a transparent conductive layer and a
transparent insulative layer interposed between the screen and the
optical means; and terminals whereat a source of potential is
adapted to be connected between the transparent conductive layer
and the screen conductive layer.
5. The camera of claim 4 wherein the optical means comprises a
shutter and further comprising timer means for opening the shutter
while connecting the source of potential.
6. The camera of claim 5 further comprising light means within the
camera under control of the timer means and means for reversing the
potential of said source under control of the timer means whereby
the photoconductive layer may be charged from one polarity through
zero to reverse polarity.
7. An aperture controlled electrostatic camera comprising in
combination a housing; a multi-layer apertured screen removably
connected to the housing having a first electrically insulative
layer and a conductive layer; optical means comprising lens and
shutter means for focusing an image on the first layer of the
screen; a transparent conductor and a further insulative layer
adapted to be disposed between the screen and the optical means
with the further layer in contact with the first layer; one of said
first layer and further layer comprising a photoconductor with the
other comprising a non-light sensitive insulative layer; means for
opening and closing the shutter means; and means for charging the
first layer at least when the shutter means is open to establish an
electrostatic latent image on the first layer.
8. The camera of claim 7 wherein the means for charging the first
layer comprises a source of direct potential; and connections from
the transparent conductor and the conductive layer respectively to
opposite poles of said source.
9. The camera of claim 8 further comprising means for reversing
said connections for charging the first layer oppositely; a source
of light effective for shining light against the transparent
conductor; and timer means connected to the means for opening and
closing the shutter means, the source of light, and the reversing
means to effect precharging of the first layer by applying the
charging potential and actuating the source of light; and to effect
establishing of an electrostatic latent image on said first layer
by reversing said connections and opening the shutter means.
Description
This invention relates to aperture controlled electrostatic
reproduction processes and methods which employ a multi-layer
screen consisting of an array of apertures and comprising at least
a conductive layer and a superimposed insulative layer to enable
the deployment of opposite electrostatic charges on opposite
surfaces of the insulative layer, thus providing a double-layer of
charge which produces fringing fields within the apertures. The
screen may be precharged to produce a uniform double-layer of
charge which is then modified in accordance with an image to
produce diminished, zero, and reversed charge areas which produce
blocking, non-blocking, and enhancing fringing fields controlling
the apertures in accordance with the image to be produced.
Alternately, charged images of the required form may be established
on previously uncharged screens. The conductive screen layer is
maintained at a potential usually during charging and printing, and
a propulsion field is provided for directing charged printing
particles toward the screen. The particles will not pass or pass in
fewer numbers through apertures which lie in areas of the screen
containing charges so oriented as to produce fringing fields within
the aperture which oppose the propulsion field. Such apertures are
termed blocked or partly blocked. The particles will pass through
apertures which lie in uncharged areas of the screen or which lie
in areas of the screen which contain charges whose fringing fields
are oriented so as to assist the passage of particles through the
apertures. The latter apertures are said to contain enhancing
fields, and the charged particles pass through these apertures in
greater numbers.
This process thus uses a charge pattern which modulates the flow of
particles, such as toner, through the screen to a receiving medium,
via preferably an air gap, for subsequent fixing thereon, if
necessary.
The insulator layer of the screen may comprise a photoconductive
type which may be electrically charged. Alternatively, if the
selected insulator screen has a low dielectric strength, a thin
undercoating of a high dielectric material, not necessarily
photoconductive, is employed between the photoconductive layer and
the conductive layer. Similarly, a thin overcoating of high
resistivity material may be employed to provide a charge carrier
for photoconductors with poor surface resistivity. When employing
photoelectric materials that cannot be deposited in heavy layers,
the insulating layer may be comprised of any good insulating
material which will accept the sensitive material as a thin
deposit. Thus, a thin layer photosensitive material may be coated
over the screen comprised of an insulator and conductive layer.
Other materials which may be used as the insulator layers are
photo-emissive material, polyester films, epoxy, photoresists,
fused quartz, or combinations thereof. In addition, the conductor
backing itself may be deposited on the insulator, or a separate
insulator layer, not taking part directly in the electrostatic
process, may be used to support both the conductor and insulator
layers.
The present invention differs from the known stencil type
inventions, such as disclosed in U.S. Pat. No. 3,061,068 to C. O.
Childress, et al., issued Mar. 16, 1963 and entitled Electrostatic
Printing System, for the reason that the screen employed in this
patent must be in the form of a permanent stencil having openings
where printing is desired and through which the particles pass to
the print receiving material. However, these stencils are not
useful for producing more than one shape of image without resorting
to stencil forming processes to change the image. Such stencil
forming processes may be similar to the production of a silk-screen
image. In the present invention, the screen is instantly reusable
and there is no physical stencil required.
For this reason the present invention may be embodied in various
apparatus and methods. For example, it may comprise an office copy
machine, a printing plate and/or method, a camera or photographic
arrangement, an enlarger or printing device for slides,
transparencies, negatives or positives, a typewriter, a computer or
facsimile printout arrangement, or in fact, it may be employed
wherever modulated control of charged particles is inherent or
desirable. It is broadly applicable to reproduction in black and
white or color, and is even applicable to television.
Thus, it may be appreciated that the pattern to be reproduced,
developed or handled may comprise any of shapes, distributions,
light or other radiation including electro-magnetic radiation,
configurations, surfaces, or other things. While a preferred use
may be reproduction using dry toner particles, nevertheless
aerosols, ink droplets or other chargeable particles may be
employed. For example, an electrostatic latent image may be
configurated or reproduced. Ions may be laid down in a pattern or
distribution. Other particles, such as, oliophilic or hydrophilic,
or adhesive, or chemically reactive, transparent, opaque, colorless
or color may also be employed herein. Therefore, the principles of
the invention herein set forth have very broad application. The
present invention actually electrostatically modulates the
apertures of the screen, through the provision of the enhanced
double layer charge, which is modified in accordance with the
image, be it from film, landscape or other source, to control the
flow of charged particles through the screen to the receiving
material or object.
In the composite screen structure of the present invention, the
conductive layer, at fixed potential performs two novel functions.
In the first place, it enables the insulative layer to be charged
oppositely, thereby developing the fringing fields (either blocking
or enhancing) within the apertures of the screen, which fields are
oriented in accordance with the image pattern. It also enables the
maintenance of the enhancing and blocking fields during projection
of the charged marking material, and the charges of the particles
which do not pass through the grid are rendered substantially
ineffective as the conductive layer shields the fringing fields
from the effects of those charges.
The conductor layer may also be used to establish a uniform field
between the screen and receiving material, if this is desired.
Depending on the charge level of the toner particles, the conductor
layer does not have to face the toner supply.
For these reasons, the composite screen structure is preferred, but
a less expensive screen may be comprised of only the insulator, and
it may be directly image-charged or double-charged for image
modification. In the latter case, positive and negative corona
sources may be used to spray the insulator screen from opposite
sides.
The screens may assume many different configurations, but all are
characterized by an array of apertures therethrough to permit
particle passage. The deployment, size, and shape of the apertures
may vary from mesh to parallel lines or slots. When woven material
is employed as the composite screen, the insulation is mounted on
top of the strands.
Thus, the invention may, in the preferred form, comprise a
composite screen mounted for endless movement and having at least
an insulative and a conductive layer with coinciding mesh. An
imaging station is provided which may enable positive or negative
printing. When a photoconductor is employed as the insulator of the
screen, such a material is an insulator in the dark and becomes
conductive in the light. It can be charged by ions or an electrode,
and a light image is then used to discharge those areas to be
printed. The light image is reproduced in negative form because
printing occurs where the image light impinges on the screen and
the discharge has been diminished or reduced to zero.
For positive printing without using the enhancing field, the screen
may be charged by an applied field during exposure to the light
image. Illuminated areas of the screen photoconductive layer become
conductive and, under the influence of the applied charge field,
cause a charge separation similar to the double charge previously
mentioned. After the charge separation is formed, the illumination
is removed, causing all parts of the screen photosensitive layer to
become insulative. Then, the charging field is removed and the
portions of the field which were illuminated remain charged, and
thus block the passage of the toner particles during the printing
step.
In the absence of the enhancing field, the screen could only be
modulated by blocking fields oriented in one direction, i.e., from
zero to minus or zero to plus volts. The addition of the enhancing
field enables modulated control for the full range, i.e., minus to
plus volts. Thus, it may be appreciated that the enhancing field is
always in the reverse direction of the blocking field, although
depending upon the sign of the particle to pass through the screen,
the enhancing field may block and the blocking field may enhance.
This flexibility enables either positive or negative printing at
the flip of a switch.
Normally, the enhancing field may be characterized as being in the
same direction as the propulsion field for the particles passing
through the screen to the print receiving paper or material. It may
further be characterized as deploying a reverse charge in the areas
heretofore discharged.
Of great importance is the fact that the enhancing field
electrically enlarges the aperture beyond its physical dimensions.
It may be likened to a funnel leading into the aperture from both
the entrance and exit sides so that an increased amount of toner or
marking material is caused to pass through an enhanced aperture.
This increases the printed density and fills in the dots for solid
printing with densities approaching 100 percent. Thus, the addition
of the enhancing field enables control from zero aperture opening
to a size opening effectively beyond that of the aperture.
In any event, the modulated apertures of the screen, depicting the
image area, move into or are subject to the propulsion field where
charged toner particles are projected toward the screen and pass
through the screen in accordance with the modulation to continue
across an air gap, due to the propulsion field, to a print
receiving substrate such as ordinary paper. Although the word paper
is used hereinafter, the invention is not limited to printing on
paper, or even to printing on flat surfaces. A heat fixing station
fixes the ink, where necessary, because this process may employ
powdered inks, as well as aerosol sprays, or liquid droplets. The
conductor may not face the toner source in all embodiments.
With the foregoing in mind, it is among the objects of the
invention to provide an aperture controlled electrostatic printing
process and method which enables printing through a modulated
screen onto ordinary paper, across an air gap.
Another object is the provision of aperture control from zero
opening through an effectively enlarged opening which substantially
exceeds the physical dimensions of the screen opening.
It is a further object of the invention to provide such
reproduction simulating half-tone printing with varying degrees of
gray to black printing or sequential color reproduction.
A further object of the invention is the provision of a multi-layer
screen susceptible to image modulation in both forward and reverse
directions for controlling the passage of charged toner material
therethrough.
It is a further object of the invention to provide a method wherein
a double layer charging of a screen may be employed for subsequent
modulation including reversal of the charging in selected areas to
provide blocking fields or enhancing fields in the apertures of
areas of the image being reproduced, depending on whether positive
or negative printing is being achieved.
Yet another object is the provision of selective positive or
negative printing free of holidays and with good edge effects.
Another object is the provision of apparatus and methods for
electrostatic reproducing or constituting through the use of screen
means comprising an array of apertures wherein forward and reverse
fields are established in accordance with a pattern for controlling
charged particles directed at the screen means.
A further object is the provision of arrangements for contact
charging a screen comprised of at lease an insulative layer.
Yet another object is the provision of contact charging,
incorporating enhancing fields.
A still further object of the invention is the provision of office
copy apparatus and methods incorporating electrostatic
techniques.
Another object is the provision of an electrostatic camera.
A still further object is a provision of a computer print-out
arrangement utilizing electrostatic techniques.
It is another object of the invention to provide electrostatic
typewriter arrangements.
Yet another object is a provision of electrostatic facsimile
print-out.
Further, it is an object to provide an electrostatic enlarger
and/or printing device.
A further object is the provision of printers incorporating the
electrostatic transfer of charged particles.
The invention will be better understood from a reading of the
following detailed description thereof when taken in conjunction
with the drawing wherein:
FIG. 1 is an arrangement to depict single charge stencil type
blocking of charged toner particles with fringe effects;
FIG. 2 is a view in section of a preferred embodiment of the screen
of the present invention;
FIG. 3 is an enlarged view of a portion of FIG. 2;
FIG. 4 depicts a computer analysis of the fringing or blocking
field in association with a single aperture of the screen;
FIG. 5 depicts a computer analysis of a combined propulsion and
fringing field for a single aperture of the screen;
FIG. 6 is a schematic illustration of the processing steps for
reproducing the light image in negative form;
FIG. 7 is a schematic illustration of the processing steps for
reproducing the light image in positive form, with and without the
enhancing field;
FIG. 8a is a view, in cross section, of a portion of a screen
showing the use of low dielectric strength photosensitive material
in conjunction with high dielectric strength insulative material
intermediate the photosensitive layer and the conductive layer;
FIG. 8b is a similar view showing the use of high resistivity
material as the charge carrier overlying photosensitive material
with poor surface resistivity;
FIG 8c is another view employing a conductive layer, a good
insulative layer and a thin layer of photosensitive material
deposited over the insulator and within the apertures;
FIG. 9 depicts a computer analysis of the electrical fields within
an aperture which is only partially charged as it has insufficient
charge for full blocking;
FIG. 10 is a schematic arrangement showing suitable apparatus for
carrying out the method with and without the enhancing field;
FIG. 11 depicts a computer analysis of the field geometry for a
combination of enhancing field and propulsion field;
FIG. 12 shows in cross section an improved arrangement for field
charging;
FIG. 13 shows the structure of FIG. 12 with the enhancing field
charge level applied prior to exposure;
FIG. 14 shows the arrangement of FIG. 13 following exposure but
prior to application of the E.sub.c field merely to represent
charge distribution;
FIG. 15 shows the final charge distribution in the field charging
arrangement with enhancing field;
FIG. 16 shows the final charge distribution for an enhancing field
of charge opposite to FIGS. 13-15;
FIG. 16a is a chart showing polarity possibilities for printing
with positive and negative particles;
FIG. 17 illustrates a continuous printer using field charging with
enhancing field charge level;
FIG. 18 shows a dielectric layer with electrostatic latent image
for transfer to the double layer screen;
FIG. 19 shows the dielectric layer in proximity to or contact with
the screen with an applied transfer source;
FIG. 20 shows the dielectric separated from the screen after
transfer of the electrostatic latent image;
FIGS. 21, 22, and 23 show the steps of FIGS. 18, 19, and 20, but
additionally include a precharge on the screen of FIG. 21 so that
after transfer of the electrostatic latent image, the screen of
FIG. 23 is charge modulated in both forward and reverse
directions;
FIG. 24 depicts a xerographic plate with electrostatic latent image
for transfer to the screen;
FIG. 25 includes the applied transfer source for proximity or
contact transfer;
FIG. 26 shows the screen with the transferred electrostatic latent
image;
FIG. 27 shows a contact charging plate applied to an insulator type
screen;
FIG. 28 shows the contact charging plate and screen separated prior
to any charging or exposure;
FIG. 29 shows the two parts together along with the charging
potential E.sub.c ;
FIG. 30 shows the polarity of the charges on the screen as a result
of exposure with the charging potential connected;
FIG. 31 shows the polarity on the screen for the opposite
potential;
FIG. 32 shows the contact charging plate prior to application to
the screen but with a precharge on the screen;
FIG. 33 shows the two parts together with a connection therebetween
to modify the precharge by exposure;
FIG. 34 shows printing using positive particles;
FIG. 35 illustrates printing using negative particles;
FIG. 36 shows the screen precharged;
FIG. 37 shows the parts together prior to application of the
charging potential;
FIG. 38 illustrates the polarity for forward and reverse fields
with positive particles used for printing;
FIG. 39 shows the polarity distribution when a negative precharge
has been used;
FIG. 40 is a chart or table for potential selection relative to
positive and negative printing employing particles of either
sign;
FIG. 41 shows a schematic arrangement incorporating contact
charging;
FIG. 42 illustrates a continuous type printer incorporating contact
charging;
In FIG. 43 there is shown components for an electrostatic camera
capable of photographing onto ordinary paper;
In FIG. 44 the components are assembled to comprise the camera;
FIG. 45 illustrates a typical developing arrangement for the
camera;
FIG. 46 shows the camera incorporating enhancing field control;
FIG. 47 is a synchronizing chart for the camera;
FIG. 48 shows a multi-copy computer print-out arrangement;
FIGS. 49 and 50 disclose alternative arrangements for the image
station of FIG. 48;
FIG. 51 depicts facsimile readout apparatus;
FIG. 52 is a schematic view of an electrostatic typewriter;
FIG. 53 shows an ion projection system using a dielectric receiving
medium;
FIGS. 53a and 53b show blocking and enhancing arrangements for the
system of FIG. 53;
FIG. 54 is an ion system incorporating toner projection for
printing or ordinary paper;
FIG. 54a and 54b show blocking and enhancing arrangements for the
system of FIG. 54;
FIG. 55 depicts an electrostatic enlarger and/or printing
arrangement incorporating a photoconductive screen;
FIG. 56 is an electrostatic enlarger and/or printing arrangement
using contact charging or field charging;
FIG. 57 is a developing station for the apparatus of FIGS. 55 or
56;
FIG. 58 discloses an electrostatic enlarger and/or printing
apparatus including developing means;
FIG. 59 shows the screen means as an insulator, per se, with a
charging arrangement;
FIG. 60 discloses an alternative arrangement for charging the
insulator of FIG. 59; and,
FIG. 61 shows detailed configurations 61a-61k for the screen
means.
In FIG. 1 there is shown an arrangement for stencil blocking
utilizing a single sign charge layer only, to show the limitations
of this approach. The substrate 15 to be printed is positioned
behind the stencil 17 which is positively charged, and the charged
ink particles or toner material 19 are similarly charged and
projected toward the substrate.
Electrostatic printing is normally achieved by the propulsion of
the charged ink particles 19 through the fixed stencil 17 by means
of an electric field. The blocked portions of the stencil 17
prevent passage of certain of the ink particles 19, thus forming
the image that is printed. This use of mechanical blocking requires
that the stencils be prepared by mechanical or photochemical means;
these are slow processes, requiring several hours for the
completion of a screen stencil.
Greater usefulness of the electrostatic printing process would be
achieved if the stencils could be substituted for and the
substitute prepared within seconds, and if the image could be
erased and the screen reused.
As is well known, the presence of a concentration of charges will
create surrounding fields such that the charges of like sign are
repelled from the charged area. It is clear that if an image is
formed of coplanar uniformly charged layers, and the sign of the
charges used to form the image is the same as the charge on the
toner particles, the toner will be repelled from the charged areas,
thus producing the blocking required to use the image as a stencil.
Since this blocking of the passage of the charged toner or
equivalent is accomplished by the field surrounding the charge
layer, these fields are called "blocking fields."
However, a one sign charge layer will not satisfy the requirements
of a blocking field since the fields of such a system extend in all
directions from the charges. Thus, toner particles will be repelled
not only from the surface of the charge layer (the desired blocking
effect) but also from the edges of the charge layer, which exist at
the image boundaries (FIG. 1). For printing to occur, particles
must pass through the uncharged areas (indicated in FIG. 1 as "AREA
TO BE PRINTED"). The lateral repulsion field existing at the edge
of the layer increases the blocking area, diffuses the edges of the
printed image, and prevents passage of ink through small gaps in
the charge layer.
The present invention overcomes the problems described above while
permitting the desired charge layer blocking in the nonprinting
areas of the image.
The screen used to carry the charges, and the disposition of
charges on the screen so as to perform the blocking action on the
toner, thus forming a printed image, are illustrated in FIG. 2. The
screen is constructed of conventional insulator material 21,
layered with a conductor 23, the holes 25, through which the ink
particles pass, extend in coincidence through both layers of the
screen.
Electrical connection is made to the conductor layer 23 of the
screen by tab 31 and lead 33 (FIG. 3) so that the potential of the
backing members can be maintained during printing and charging.
The insulator portion is charged so as to acquire a "double layer"
of charge (as indicated in FIG. 3) in which one face of the
insulator 21 contains charges of one polarity, while the other
surface contains an equal amount of charge of opposite polarity.
(The charge layer which is formed on the insulator surface, in
contact with the conductor, appears on the surface of the conductor
23, as shown in FIG. 3.) Thus, the net charge on the screen is
zero; therefore, no field exists from these charges at a distance
of more than a few screen thicknesses away from the charged double
layer. The motion of toner particles which have passes through the
screen at uncharged areas is therefore only slightly affected by
the charged areas of the screen.
Charging of the form indicated in FIG. 3, is made possible by the
presence of the conductor layer. A charge source (such as a corona
wand or radioactive strip) is used to spray ions on the surface of
the insulator; the conductor portion of the screen is maintained at
a fixed potential during this process so that any charge which
deposits on the insulator surface will attract an equal and
opposite charge to the junction between the insulator and the
conductor, thus creating the required double layer.
Blocking of ink particles in the charged areas is performed by the
fringing field which exists within the holes of the screen. The
fringing field is oriented so as to prevent charged ink particles
from passing through the hole. The field structure of such a charge
layer, as solved by computer analysis, is given in FIG. 4 in
association with one-half of an aperture. In FIG. 4, the electrical
force or field lines are depicted at 35, and the equipotential
lines at 37, their magnitude being plotted along the ordinate axis,
through the center of the hole or aperture. Thusly, it will be
apparent that the positively charged particle(s) 19 will be
deflected to one or the other sides of the aperture and collected
by the conductor 23.
If the ink particles are positive, then the double layer charges
are arranged so that the particles approach the screen's negatively
charged side; conversely, negative particles must be directed
toward the positively charged surface. The weakest fringing field
exists along the center of the hole, and the magnitude of this
field depends on both the charge magnitude (strength of the field
inside the insulator) and the thickness-to-diameter ratio (T.sub.I
/D) for the screen to aperture. Since the fringing field increases
in strength as the insulator thickness increases, it is clear that
for effective blocking, a large ratio of T.sub.I /D, as well as
high charge level is desirable. The amount of fringing field
required to block the charged particles depends on the strength of
the field used to propel the particles from the source to the
printing substrate. If the particles had no inertia, blocking would
occur if the combination of fringing field and the propulsion field
(which act in opposition) produce a net zero field or repulsive
field at any point along the centerline of the hole. However,
particle inertia effects (which increase with particle diameter)
will carry the particle through the hole unless the combined fields
within the hole exert a net repelling force.
Prototype designs have indicated that the internal field in the
insulator should be at least 8 to 10 times the propulsion field if
the T.sub.I /D ratio is 0.25. Thus, for a screen with 0.008 inch
diameter holes, an insulator thickness of 0.002 inch, and a
propulsion field of 5,000 V/in., the screen should be charged to a
potential of 100 volts.
The field structure for a blocking effect (combined propulsion and
fringing fields) is shown in FIG. 5. FIG. 5 indicates a second
major function of the conductive layer. Particles which are
blocked, deposit on the conductor portion; if the conductor were
not present, these charged particles would soon neutralize the
charge on the screen and blocking action would cease. The
conductor, when maintained at constant potential during printing,
will shield the charge on the insulator from the effects of the
accumulated ink particle charges.
In FIG. 5 the combined effects of the propulsion and fringing
fields are plotted and field force lines 35' and equipotential
lines 37', as well as, the particle paths 39 indicate how the
aperture is blocked.
To obtain printing, the charge image on the screen in one
embodiment must be the negative of the desired print; i.e.,
printing will occur where no charge exists. A number of techniques
may be used to create the charge image.
The preferred technique is the utilization of a photoconductive
material as the insulator layer of the screen. Such a material,
which is an insulator in the drak and becomes conductive in the
light, can be charged as described above (i.e., with a corona wand)
and a light image used to discharge those areas to be printed (FIG.
6). Thus, the light image would be reproduced in negative form. The
corona wand 41 is used to uniformly charge the composite screen 43.
Thereafter, the screen is illuminated from a light source 45 in
accordance with the image (not shown). Next, the toner source 47
contains particles which are charged in conventional manner and
ordinary paper serves as the print receiving medium, generally
designated at 49. The propulsion field for the particles is
represented by V.sub.I and the screen 43 has its conductive layer
maintained at V.sub.2. The blocking effect of a portion of the
screen is illustrated by the particle paths 51, some of which
penetrate the screen to deposit particles on the paper 49.
By way of example, for suitable conventional materials, the screen
may be charged by an applied field during exposure to the light
image, as in FIG. 7. The illuminated areas of the screen
photosensitive layer become conductive, and under the influence of
the applied charging field, via transparent electrode 55, acquire a
charge separation similar to that shown in FIG. 3. After the charge
separation is formed, the illumination is removed, causing all
parts of the screen photosensitive layer to become insulator. At
this point the charging field may be removed and the portions of
the screen which were illuminated would remain charged and thus
block the passage of toner particles during the printing process.
This technique produces positive reproductions of the light
image.
In FIG. 7, the enhancing field may be added simply by providing the
pre-corona spray from source 61. This is possible because screen 43
is of the double layer type capable of holding the double layer
charge. While no source of potential is shown for corona source 61,
it can be supplied by a positive or negative source, depending upon
the type charge which is desired to appear on the photo conductor
layer of screen 43.
FIGS. 12 through 16 later to be described, provide details of
charging with a positive or negative enhancing field. However, in
FIG. 7 it will be noted that the source 61 should induce charges on
the screen opposite that of source V in order that the applied
field V may overcome and reverse the enhancing field charge laydown
in the areas illuminated.
Effective field blocking of toner particles requires a combination
of high charge level and large insulator thickness. The range of
photosensitive materials which may be used for the insulator layer
can be extended by special screen configurations. If the desired
insulator material 101 (FIG. 8a) has a low dielectric strength
(thus limiting the amount of charge separation it can support) a
thin undercoating 103 of a high dielectric strength (but not
necessarily photoconductive) material can be used to separate the
photosensitive layer from high field regions near the edge of the
holes. The conductor 105 is affixed to the undercoating 103.
Similarly, a thin overcoating 107 (FIG. 8b) of high resistivity
material can be used to provide a charge carrier for
photoconductors with poor surface resistivity.
For photoelectric materials that cannot be deposited in the heavy
layers required for this purpose, the insulating layer may be
formed of any good insulating material which will accept the
sensitive material as thin deposit 109 (FIG. 8c). The entire
screen, including portions of the conductive layer, may be
coated.
It is computed that the form of the field within the hole is such
that, if a hole is only partially charged (i.e., has not developed
sufficient charge to block) the effect of the charge is to limit
the aperture of the hole (FIG. 9). Partially charged holes are
created by reduced exposure during discharge, as would occur in
gray areas of the image. Thus, gray areas reproduce with reduced
apparent aperture, forming a half-tone reproduction of a
continuous-tone source. The field lines are shown at 111 and the
equipotential lines at 113.
In FIG. 10 the composite screen is shown at 121 supported by the
four motor-driven drums 122 through 125. This screen 121 may take
the form of any of the screens of FIG. 2, FIGS. 8a, 8b, and 8c.
An image station 130 includes a light source 131, image 132, and
lens system 133, which directs the light through transparent
electrode 134 and onto the screen 121. The transparent electrode
134 may be comprised of mylar with a conductive coating or of
conductive glass. Thus, the selected charging voltage +E.sub.c or
-E.sub.c is connected by lead 136 to electrode 134 and extends to
common lead or ground 137. The conductive layer of screen 121 is
grounded by drum 123 at fixed potential to complete the charging
field and to fulfill its two functions, previously described.
The modulated image is moved to the printing station, generally
designated at 140, where a toner supply of charged particles 141 is
maintained at a toner potential E.sub.T.
A revolving brush 143 is provided to agitate the toner material,
facilitating its movement toward screen 121 under control of
propulsion field E.sub.P, and the apertures of the screen 121
control passage thereof onto the paper 145 to be printed. The
propulsion field is provided by leads 147 and 149, the former of
which extends to a roller 150 which is in contact with a continuous
backing of paper carrying belt 153. Toner is supplied in powdered
or atomized form over conduit 155 from a suitable source (not
shown).
The charged particles which pass through screen 121 are deposited
on the paper 145 in the form of a positive or negative image as
hereinfore explained and the paper passes under resistance heater
157, which fixes the image thereto, if necessary, and wedge 159
drops the printed paper into stack 161. The paper drive is taken
from motor driven drum 163 which is synchronized with conveyor
screen 121, preferably for intermittent motion to permit printing
at station 140.
A vacuum scavenger is shown as conduit 170 provided to remove the
marking particles or droplets from the conductor side of screen
140.
Propulsion field switch 148 is closed upon arrested motion of
conveyor screen 140 and paper belt 153 to cause transfer across an
air gap or in direct contact, if desired. Of course, if paper belt
153 and screen 140 are synchronized, provisions for interrupted
motion are unnecessary.
The schematic arrangements of FIG. 10 may be built using components
selected from the apparatus and control circuitry of U.S. Ser. No.
565,284 in the name of Samuel B. McFarlane, Jr., filed July 14,
1966, and entitled Method and Apparatus of Electrostatic Color
Reproduction, assigned to the same assignee as the subject
invention; with the exceptions, as depicted in FIG. 10, i.e., the
screen 140, transparent electrode 134 and the various electrical
fields herein described. Exposure and printing are preferably
carried out with the conveyor intermittently stopped although
exposure may be accomplished in line-by-line fashion on a
continuous basis and printing done as above described. Similarly,
sequential color reproduction may be achieved with the present
invention, in accordance with the apparatus disclosed herein
identified and as in the McFarlane application.
Also, the apparatus of FIG. 10 is useful as shown for positive or
negative reproductions. Moreover, if only negative reproductions
are contemplated, a conventional corona discharge source may
replace transparent electrode 134. All fields depicted are
preferably direct (D.C.) potential fields.
With the foregoing in mind, it will be appreciated that the
invention is preferably characterized by an insulating screen of
sufficient thickness compared to hole diameter to produce a
repulsive field within the holes when a double layer charge is
modified in accordance with the image. The conductive layer,
directly or indirectly connected to the insulator layer, provides
charging of the insulator in this double form. The conductor layer,
when maintained at a constant potential during printing, limits the
discharging effect of the ink or toner particles by shielding the
insulator screen and absorbing the charges of the particles. The
propulsion field of sufficient magnitude propels the particles to
the substrate or conductor, but has insufficient force to cause the
particles to pass through charged areas of the screen. The holes
which have less than sufficient charge to completely block the
printing material act as holes of reduced aperture thereby
permitting the reproduction of continuous tone gray scale, as in
half-tone printing. Also, the use of multiple layer configurations
has been described to protect photo-sensitive layers from excessive
fields, as is the case when insulator layers are used to form the
base for thin film photosensitive materials to obtain the charge
separation distance.
Alternately, if charge neutralization is not a problem, the
conductor layer may be used to establish a uniform field between
the screen and receiving surface for accurate reproduction of the
charge image, in which case the conductor layer faces the receiving
surface.
By way of example, screens having from 80 to 1,000 lines per inch
are effective for good reproduction. A screen with 200 lines per
inch will reproduce as faithfully as present-day office machines
and exhibits the characteristic that the edges of the reproduction
are clearly and strongly outlined with little or no holidays,
thereby enhancing the resolution available from this system.
It is, of course, desired that a maximum charge be carried by the
insulator of the multi-layer grid so that good and strong control
can be had at the individual apertures. It is for this reason that
several modifications of the screen are present to encompass the
conventional materials available today. The T.sub.I /D ratio is
just as important as total charge in determining the blocking
effectiveness. This ratio, of course, is limited by construction
difficulties.
When using photosensitive materials in connection with the
apparatus of FIG. 10, a light-tight box, indicated by the dotted
line 200, is employed with suitable ingress and egress openings
being provided.
It has also been determined that highly viscous mediums are
desirable for the supply of toner material, and one example is a
suspension in fluoride gas. The preferred gap for marking material
transfer between screen and paper is of the order of one-sixteenth
to one-fourth inch, but it should be noted that contact printing
may also be achieved with the process of this invention. Toner
particles of the order of 4 to 8 microns have been found to be
operative within the teaching of this invention to provide the good
edge effects which are readily achieved. Even smaller sizes are of
course preferred. Contact printing on any medium can be achieved if
the conductor layer faces the printed surface--otherwise only
insulators may be printed in contact.
In FIG. 10, the insulator or dielectric material 165 enables
improved performance in the field charging method, but requires at
least light contact with the screen 121. This dielectric material
may be selected from any number of suitable transparent
dielectrics, such as mylar, epoxy, polystyrene, quartz and many
others.
The enhancing field can readily be included in the arrangement of
FIG. 10 through the provision of corona source 161, adapted to be
connected over switch 163 to either the negative or positive
enhancing voltage E.sub.E. The appropriate charge level may be
sprayed onto screen 121 from source 161 and by way of example, the
magnitude of the enhancing field charge level may be of the order
of 350-750 volts.
It is through the provision of source 161 that densities
approaching 100 percent are provided for solid printed areas. This
is readily understood from FIG. 11 where a particle path 199
illustrates the oversized entrance and exit openings produced
electrically as a result of the enhancing field. Also, the
provision of source 161 enables ready negative or positive printing
with the arrangement of FIG. 10 as will be explained in the
description of FIGS. 13-16.
First, however, FIG. 12 shows the improved field charging apparatus
without the enhancing field. A transparent support 203 of glass or
even pliable material is provided for thin conductor 205 and the
insulator or dielectric 207, the latter corresponding to dielectric
165 of FIG. 10. The screen shown in detail in FIG. 12 includes the
photoconductor layer 209 and the conductor layer 211.
FIGS. 13 through 16 show the structure used in the improved field
contacting method and illustrate the application of both a positive
and a negative enhancing field.
In FIG. 13, the enhancing field is shown as the positive charges
213, uniformly covering the photoconductor 209. Screen 211 is
grounded or held at a given potential level and the positive
charges 213 provide the double layer charging of photoconductor
209, when in the dark, due to its resistance.
FIG. 14 shows the image elements (203,205,207) in contact with the
photoconductor 209 of the screen. Additional provision is made for
connecting the applied field E.sub.C to the conductor layer 205 of
the image elements and to the conductor layer 211 of the screen.
The structure of FIG. 14 is shown after light e.g. from an image
(not shown) has been shined on the right hand side, as legended,
but prior to application of the voltage E.sub.C. Normally, for
optimum charge transfer, contact would be established and then the
image would be applied at the same time that the voltage E.sub.C is
applied. The image would be turned off and the voltage maintained
until the image elements are separated from the screen. However, in
FIG. 14, it may be noted that the light simply reduces the
resistance of the photoconductor 209 such that the charges in the
light exposed area leak away.
In FIG. 15, the effects of the applied voltage E.sub.C are seen as
a reversed field in the light or print areas. The voltage E.sub.C
should be as high as possible without breaking down the
photoconductor and of course be commensurate with other materials
and their thicknesses. Preferably, this voltage will be about twice
that of the enhancing field, in order that it may eliminate the
enhancing field and apply a reverse charge to the areas where the
enhancing field was eliminated. Thus, in FIG. 15, the force lines
of the blocking, fringing or enhancing fields of the apertures are
depicted. The positive printing material 219 is shown being
deflected to the conductor 211 because the hole directly above is
electrically blocked. However, particle 221 is permitted and aided
to pass through the electrically unblocked and reversed aperture
directly thereabove to print on the material (not shown) which
would normally be adjacent to the propulsion field (E.sub.P)
backing member 217. Thus, for positive marking material, the
enhancing field actually becomes the blocking field and the applied
field becomes the enhancing field.
The opposite situation prevails in FIG. 15, wherein the negative
charge level 223 was laid down as the enhancing field and it was
reversed by the applied field to the right of the printing area.
Thus, it may be seen that the enhancing field enables passage of
marking material 221, and of course actually assists or aids this
material in its projection toward the material to be printed. It is
this aiding or assisting due to the field force lines which funnels
the printing material through the enhanced openings to provide the
excellent printing densities achieved. The particle 219 cannot pass
through the now blocked right hand apertures due to charges created
by the applied field E.sub.C.
Since the enhancing field can be either positive or negative and
since the applied and propulsion fields may be reversed, positive
or negative printing can be obtained using either positively or
negatively charged printing material. Thus, in FIG. 15 positive
printing would be obtained if E.sub.P were reversed and negatively
charged printing material used, the enhancing and applied fields
remaining, as shown.
Other methods of charge image transfer may be employed with or
without the enhancing field. For example, the insulation or
dielectric layer 207 may be used per se, to carry a charge in
accordance with the image. One such charge pattern would be an
electrostatic latent image. Without the enhancing field, the
electrostatic latent image charge would simply be transferred to an
insulator in the position of element 209. To incorporate the
enhancing field, the insulator 209 could be precharged with the
enhancing field level and the electrostatic latent image would then
overcome and reverse the precharge in the image areas to operate in
the same manner as depicted in FIGS. 15 and 16.
A continuous type printer is shown in FIG. 17 and it could simply
replace the left hand end of the apparatus of FIG. 10. The
light-tight box 200' houses the screen 121' carried on rollers 124'
and 125'. However, additional rollers 127 and 129 are provided to
cause the screen 121' to snugly fit against the transparent
insulator or dielectric 165' overlaying transparent conductor 205',
in turn supported by transparent support 203'. The applied voltage
field E.sub.C is connected to a brush or slider contact 229 for
transparent conductor 211 of screen 121'.
Conventional optics are shown at 225 simply to provide line by line
scanning of a positive or negative to be reproduced. The scanning
is of course synchronized with the movement of the screen 121'.
Switch 163' permits corona source 161' to supply a positive or
negative enhancing field, as explained previously.
In FIG. 16a there is shown a polarity chart to indicate the proper
polarity for the voltage E.sub.C and voltage E.sub.E for printing
with positive particles and for printing with negative particles,
it being understood that these voltages are switched together in
accordance with this chart. The chart is applicable to the device
of FIG. 10, the arrangements of FIGS. 13 through 16, and the
apparatus of FIG. 17, it being apparent that in FIG. 13 the charge
213 corresponds to voltage E.sub.C. Thus, referring to the chart,
when both voltages E.sub.C and E.sub.E are positive, negative
printing is produced when using positive particles and positive
printing is produced when using negative particles. When the
polarity of voltages E.sub.C and E.sub.E is negative, then positive
printing is produced by using positive particles and negative
printing is produced by using negative particles.
FIGS. 18 through 26 illustrate arrangements for establishing charge
patterns directly on the screen means with and without enhancing
fields, and using either a dielectric or insulative layer, as well
as a photoconductor layer.
In FIG. 18, an electrostatic latent image is shown in the form of
the negative charges carried by a dielectric or insulator layer 253
backed by a conductive layer 251. It is desired to charge the
screen comprising the insulator layer 255 and the conductor layer
257 to the charge pattern corresponding to the electrostatic latent
image.
In FIG. 19, the charge-carrying elements are brought together with
the screen either in proximity or contact such that the
electrostatic latent image is transferred to double-charge the
insulator layer 255 of the screen by closure of 261 to apply
voltage from transfer source E.sub.T shown in 259.
In FIG. 20, the elements are shown apart with insulator layer 255
of the screen being charged in accordance with the electrostatic
latent image.
In FIGS. 21 through 23, the same type charging is carried out
except that a precharge has been applied to the insulator layer 255
of the screen to take advantage of the enhancing field approach
previously described. From FIG. 23, it will be seen that the
transfer charges of the electrostatic latent image overcome and
reverse the precharge in the areas of the electrostatic latent
image, whereas the precharge remains undisturbed in the other
areas.
In FIGS. 24 through 26, a conventional xerographic plate is shown
comprising photoconductive layer 263 and conductive backing layer
251. The electrostatic latent image is transferred in FIG. 25 by
application of transfer source E.sub.T to produce the charged
screen of FIG. 26. It will be appreciated, of course, that the
enhancing field approach is equally applicable to the xerographic
plate, from a review of the description of FIGS. 21 through 23.
FIG. 27 shows the apparatus and its arrangement for putting
electrostatic charge images on the insulator coated screen by
contact charging. The contact charging plate consists of a
transparent support 303 which carries a transparent conductive
coating 305 and a photoconductive coating 307. During the charging
operation, this contact charging plate is placed in direct contact
with the screen which consists of an insulator layer 309 and a
conductive backing 311. A charging voltage 315 is applied between
the transparent conductive coating 305 of the contact charging
plate and conductive backing 311 of the screen.
FIG. 28 shows the contact charging plate and the screen just prior
to contact. At this point, the screen insulator layer 309 is
uncharged.
In FIG. 29 the contact charging plate is placed in direct contact
with the insulator layer of the screen and the charging voltage
E.sub.C (shown at 315) is applied between the conductive coating
305 of the charging plate and conductive backing 311 of the screen.
A light image is then projected through the transparent support 303
and transparent conductor 305, exposing the photoconductive layer
which becomes conductive in those areas struck by light. This
permits charge to accumulate at the interface between the
conductive layer 309 of the screen and the surface of the charging
plate. These charges accumulate only in those areas illuminated by
the image in amounts proportional to the intensity of the
illumination. The contact charging plate is then removed from the
surface of the screen and the accumulated charges remain as shown
in FIG. 30.
The polarity of charge shown in FIG. 30 will produce blocking
fields for negative particles 321 which will not pass through the
highly illuminated areas but particles 319 will pass through the
dark areas of the image, thus producing direct positive printing.
Alternatively, as shown in FIG. 31, positive particles 319 may be
blocked by reversing the charge potential E.sub.C, thereby applying
positive charges on the surface of the screen in the illuminated
areas. Positive particles 321 pass through the unilluminated areas
to print.
In FIG. 32, the screen is shown as being precharged with charge
levels indicated 313. The contact charging plate is then placed in
contact with the screen as shown in FIG. 33. The light image is
projected through the transparent support 303 and transparent
conductor plate 305. During this exposure, the conductive backing
305 of the contact charging plate is connected by means of
connection or short 310 to the conductive backing 311 of the
screen. The illuminated portions of the image falling on the
photoconductor 307 cause discharge of the previously charged areas
of the screen in the illuminated areas. The photoconductive plate
is then removed from the surface of the screen and the charges
which remain on the screen correspond to the dark areas of the
original image.
In FIG. 34 there is shown how these charges block particles 319 of
positive sign. But the particles 221 will pass through the holes
corresponding to the illuminated areas of the image, thus producing
a negative print. Propulsion field E.sub.P encompasses the screen
and usually the print receiving medium would be disposed in the
space between the screen and boundary plate 317.
In FIG. 35, it is shown that with a reversed polarity of the
precharged 313, i.e., negative charge 323 negative particles may
also be used in the same manner.
In FIG. 36, the screen is again shown with the precharge 313 prior
to contact with the contact charging plate.
In FIG. 37, the contact charging plate is placed in contact with
the insulator layer 309 of the screen and a light image is
projected through the transparent portions of the contact plate to
photoconductor 307. A charging potential E.sub.C is applied between
the conductive coating 305 of the charging plate and conductive
backing 311 of the screen. In those areas of light image which
illuminate the photoconductor, the charging voltage E.sub.C
reverses the applied precharge by causing an accumulation of
charges in the interface between the photoconductive layer and
insulator layer. The contact charging plate is then removed from
the surface of the screen, allowing both the original precharge
(which remains in the unilluminated portions of the image) and the
accumulated charge which appears in the illuminated portion of the
image, to remain on the surface of the screen.
Thus, looking at FIG. 38, there is shown the polarity of charges
which will produce negative printing with positive particles.
Particles 321 will pass in the illuminated areas and their passage
is enhanced by the forward fields in this region. By the same
token, particles such as 319 will pass through the screen because
of the reverse fields which provide even further control over the
concept using fields from only zero to plus or zero to minus.
In FIG. 39 the polarity of the precharge 323 is shown reversed as
well as the polarity of the charging potential E.sub.C. Therefore,
for positive particles, such as 321, positive printing is permitted
because they pass through areas corresponding to the dark portions
of the image.
There has been found that in employing the contact charging plate,
some pressure between the screen and the contact plate is
desirable. Also by way of example, the precharge potential may be
of the order 100 to 300 volts and the charging potential E.sub.C in
the order of 700 to 1,000 volts which produces on the screen
surface resulting potential upward from 100 to 300 volts of
opposite polarity of that of the precharged potentials. It is not
necessary that maximum forward and the maximum reverse fields be of
equivalent magnitude. In partially illuminated areas, fields will
vary in intensity between maximum forward and maximum reverse
levels. The advantages of contact charging are that the charging
image is produced on an insulated surface which can be of very high
quality, and which is generally easier to apply to screens than
photoconductive coatings, and which also can support the charge
image for long periods of time extending into many hours; and it is
compatible with both image charging as well as modification of
precharge; and the ability of selection of potential polarity to
produce either direct positive or negative reproduction of the
image as demonstrated in FIG. 40.
In FIG. 40, method A refers to direct image charging without
precharge. Method B refers to the use of precharge only with a
direct connection between charging plate and screen during
exposure, thus producing modification of precharge. Method C refers
to the combination of both a precharge and a charging voltage to
provide enhancing field capability. In FIG. 40 E.sub.E refers to
the polarity the charging potentials while E.sub.C refers to the
polarity of the precharge on the screen. From the table, it may be
seen that whether either positive or negative printing may be
achieved depending on the polarity selected for E.sub.E and
E.sub.C.
In apparatus of FIG. 41, contact charging is applied to the
equipment in FIG. 10 and, therefore, only the distinctions will be
described. First, an insulator coated screen is used instead of a
photoconductive screen. Dielectric 165 is replaced by
photoconductor 165'". Also the polarity of charging potential
E.sub.C is reversed with respect to the precharge potential
E.sub.E. Polarity E.sub.P is selected according to the sign of the
charged particles used for printing. Similarly, FIG. 42 shows the
equipment of FIG. 17 incorporating contact charging. The changes
are that dielectric 165' is replaced by photoconductor 165'" and
polarity of charging potential E.sub.C is reversed with respect to
the precharge E.sub.E and the screen is an insulator coated
screen.
In FIGS. 43 through 47 there are shown the incorporation of the
screen in a camera modification for the reproduction of illuminated
scenes. The camera 401 comprises a light-tight box with
conventional lens 403 to form an image of the scene to be
photographed through shutter 405, onto contact charging plate 407.
However, prior to exposure or operation of shutter 405 the screen
409 is brought into contact with the contact plate 407 which plate
may comprise the elements heretofore described, such as the
photoconductor 406 and transparent electrode 408. The clamps 415
are provided for snugly fitting the screen 409 against
photoconductor 406. The combination removable screen 409 and
contact charging plate 407 along with charging potential E.sub.C
permit charging of the screen 409 upon exposure, thus producing a
charge image on the screen surface corresponding to the image
thereby photographed.
After exposure, the screen is removed from the back of camera 401
and placed in a toning device (FIG. 45) which provides the desired
development.
In FIG 45, it is desired to project toner from toner source 410
(which may be by a conventional toner source) to ordinary paper or
other print-receiving material shown at 412 through the charged
screen 409. Thus, a propulsion field E.sub.P is shown between a
boundary conductive plate 413 and ground. It should be pointed out
that the source of voltage for E.sub.P, while shown as a battery,
would normally comprise an adjustable source such as a
potentiometer or in certain applications it may comprise sources of
alternating voltages. But in any event, throughout the various
embodiment of this invention, it would be understood that all
sources may be variable for better control of the quality of
printing. This, of course, is true of the potential E.sub.S applied
to the screen 409. By adjusting these potentials and by controlling
the length of time of projection of toner particles, some quality
control of tonal variations may be had.
It should be noted that field charging may be applied to this
camera by replacing the photoconductor 406 with a dielectric
transparent insulator and using a photoconductor coating on screen
409. However, the arrangements shown using an insulator layer on
screen 409 is preferred because the charge image on the screen is
not light sensitive and development may be delayed for several
hours. But either type screen will provide many copies. However,
processing need not be so rapidly accomplished when using the
insulative screen.
FIGS. 46 and 47 illustrate an arrangement for incorporating the
enhancing field level into the camera by permitting reversal of the
charging potential E.sub.C and by synchronizing internal lights 420
and the shutter opening with E.sub..sub.C by way of a conventional
timer 421. The light flooding produced by internal lamps 420 during
application of (for example) positive E.sub.C produces the uniform
precharge needed for the enhancing field. The exposure during the
negative cycle of E.sub.C as shown in FIG. 47 modifies (diminishes
and even reverses) the precharge in the illuminated areas of the
image, producing the required charge distribution for the enhancing
and blocking field actions. In FIG. 47 the preferred timing
sequence is shown as first applying E.sub.C, then turning on lamps
420 for the period corresponding to the time interval 430, then
reversing E.sub.C, and then opening the shutter for the time
interval 431.
In FIG. 48 there is shown computer print-out apparatus capable of
providing single or multiple copies simultaneously. The conveyor
preferrably comprises the double layer screen 501 arrangement in
endless fashion. A corona source 503 is shown as the apparatus for
producing precharge from potential level E.sub.E. The computer
readout is made available to image station 505 for modulating the
screen 501 either with or without the precharge. Printing is
accomplished at one or more of a desired number of printing
stations herein shown as four stations. An endless source of paper
507 or other receiving material is shown opposite a toner source
508 at each station. The screen 501, toner source 508, and
receiving paper 507 may operate in a continuous high-speed manner
to affect rapid print-out. A vacuum system comprising main exhaust
conduit 510 and upright conduits such as 511 are provided to clean
toner from the conductive side of the screen. One suitable image
station is shown in FIG. 49 as comprising cathode ray display tube
512 with optics 514 for imaging the computer output information
onto screen 501. For field charging or xerographic charging of
screen 501, the outer layer would comprise a photoconductor whereas
for contact charging the outer layer of screen 501 would be an
insulator other than a photoconductor.
In FIG. 50, there is shown an alternative arrangement for image
station 505. This comprises a direct writing cathode ray tube 520
charge modulating screen 501 using the insulative layer thereof.
Thus, it may be seen that essentially simultaneous multiple copies
of the computer output may be printed on ordinary paper.
In FIG. 51 a facsimile readout system is depicted wherein the
charge pattern is laid down by charging stylus 601; thus, in this
case, the pattern to be reproduced is in the form of the electrical
signals received throughout the facsimile transmission line and the
charging varies in intensity in proportion to the electrical
signals received at stylus 601. While the stylus could be shown
traversing a flat screen, the embodiment is illustrated using a
drum 603. However, the drum is comprised of the screen mounted for
rotation such that the stylus may completely scan the drum 603 to
produce the charge image. In this case, the outer surface of drum
603 would be the insulative layer 605 of the screen.
Print-out is affected by bringing the paper 607 to be printed, as
by conveyor 608, opposite the toner source 610. The toner particles
pass through the charged screen 603 to paper 607, and where
necessary fixing may be accomplished at station 615.
In FIG. 52, there is shown an embodiment of the invention
comprising an electrostatic typewriter which may be of the silent
operating type, if desired. In the preferred embodiment an
insulator coated screen 701 is shown in the form of a cylindrical
drum 703 mounted for rotation. A character wheel 705, which
alternatively might comprise a ball or other array, includes the
characters, such as 707, with the purpose being to write the charge
image of the characters on the screen 701 by bringing the selected
characters 707 into slight contact with the screen 701 or into
proximity therewith.
The keyboard 709 may comprise more or less standard typewriter keys
711, and depression of a selected key 711 merely brings the
corresponding character on wheel or ball 705 into printing
position, shown as 713, to write on screen 701.
At first the screen is uniformly precharged by means of corona
source 729 in conjunction with potential E.sub.E. This precharge
provides a uniform overall blocking field on the screen. A charging
pulse E.sub.C is applied through timer 731 between the selected
character of wheel 705 and the conductive backing of screen 701
through slider or roller 715, producing a charge image in the shape
of the character on the surface of screen 701. When a page of
typing is completed, paper 723, which may be ordinary office
stationery, is carried by conveyor 721 into proximity with the
screen to the paper. The image is then fixed at station 727.
Multiple copies can then be produced of this page without retyping.
Additional paper is brought up and the printing cycle or rotation
of the drum is repeated.
An alternate arrangement for the print wheel is one in which the
print wheel is a continuously rotating member and selection of a
character on the keyboard merely selects the appropriate time
interval for the pulse E.sub.C, such that the pulse occurs only at
the time the selected character is facing the screen.
The print wheel may have an erase position which consists merely of
a flat raised surface slightly larger than the largest character
printed. When local erasure is desired, the drum and wheel are
indexed to the desired character position and the erase element of
the character wheel is placed in slight contact with the screen.
Then a pulse of reversed charging voltage (-E.sub.C) is applied
which removes the existing charge image at that character location.
A new character may then be entered in that location if
desired.
A selector may be included on the keyboard which permits the
selection of varying degrees of intensity of the typing by
essentially varying E.sub.C which controls the intensity of the
charge placed onto the drum by the character. Thus, it would be
possible to obtain boldface and lightface typing from the same
machine without changing the typewheel.
In FIG. 53 there is shown a first conveyor 811 of the double layer
type. It comprises an insulative, or photoconductive, screen layer
813 and a conductive screen layer 815.
A detailed showing of a portion of the conveyor is shown in FIG.
53a, wherein it is seen that the corona source of Corotron 817
projects negative ions onto the insulative layer 813, which ions
cause the double charge to appear across the insulator 813. The
source E.sub.1 is a direct current source of conventional nature,
and the proximity of the discharge wire of the corona source to the
conveyor 811 determines the preferred potential, which may be in
the range of 3,000 to 5,000 volts or higher.
FIG. 53 illustrates the application of the principles hereof to ion
projection as well as the combined use of different types of
charged particles.
The charged conveyor moves to the scanner station wherein a
conventional scanner 819 is provided to project image light via
lens 821 onto the conveyor 811. This may be done in line-by-line
fashion or image-by-image fashion, particularly for intermittent
movement. The charge on the conveyor 811 is not dissipated until
the light shines on the photoconductor 813 to lower its resistance,
the unit being within light-tight housing 825 provided with an
access for the original of the image 827 to be reproduced in known
fashion. Where the light impinges, however, the charge is
dissipated, as is also represented in FIG. 53a by the bracket
bearing the legend "Light."
The conveyor 811 is then moved past further Corotron or corona
source 831 which sprays negative ions, generated by source E.sub.2,
toward the now exposed (image) areas. As can be seen in FIG. 53,
the ions, such as 835, move through the exposed apertures, such as
827, but the ions 839 in the regions of the unexposed apertures 841
are blocked due to the fringing field in these unexposed apertures;
therefore, the second conveyor 851, which may be identical to
conveyor 811, receives a double layer charge in the regions of
light exposure.
However, conveyor 851 has been precharged with a uniform potential
level for enhancing provided by corona discharge source 850. This
is represented in FIG. 53b wherein the insulator 853 (which need
not be photoconductive) is sprayed with negative ions and the
conductive screen layer 855 permits the double layer to be
produced. Thus, in FIG. 53b the negative ions, such as 857, will
pass through apertures, such as 859, in the uncharged regions and
through partially blocked or enhanced regions and the ions, such as
861, are blocked in the regions containing blocking fields, such as
aperture 863. It may be seen that a particle may be either ions or
powdered marking material, as will be apparent from the description
of FIG. 54.
The negative ion source 865, which is at a d.c. potential E.sub.3,
may correspond to the negative ion sources 817 and 831.
Alternatively, the sources 831 and 865 may comprise banks of
Corotrons at potentials up to 8,000 volts d.c. for spraying entire
images at once. Corona source 850 removes any image charge that may
have existed on belt 851.
The negative ions, such as 857, passing through the regions
(apertures 859) produce a charge pattern on print-receiving
material 867 carried by an ordinary conveyor 869. The
print-receiving material 867 preferably has a thin insulative
coating in order that the charge pattern will not dissipate. The
paper 867 is then conveyed under a conventional powdering source
871, which includes the charged marking material 873, charged by
revolving brush 875 connected to the positive source E.sub.4.
Thereafter, the printing material 873 adhering to the charged
pattern on paper 867 is fixed by heat source 877 and then removed
from the light-tight housing 875 by wedge 879.
The conveyors 811, 851, and 869 may be at potentials other than
ground to aid in propelling the ions across the air gaps or the
powder to the substrate.
In FIG. 54 the ion principle is employed with powder projection
across an air gap to reproduce on ordinary paper. The first
conveyor 901 is charged by ion projection from Corotron 903,
powered by source E.sub.1 '. The scanner 905 exposes conveyor 901
within the light-tight housing 907. Scanner 905 may have a door or
slot 909 through which the original to be reproduced is
inserted.
In FIG. 54a, the charged and exposed conveyor 901 is shown in
detail as comprising photoconductor 911 and conductive backing 913.
Where the photoconductor 911 is exposed is indicated by the legend
"Light." Here the fringing fields have been eliminated, as at
aperture 915. In the dark regions (indicated by aperture 917),
however, the blocking fields remain.
Thus, when the conveyor reaches Corotron or ion source 919, powered
by d.c. source E.sub.2 ', the negative ions emitted, such as 921
(FIG. 54a), can only pass through the exposed apertures, indicated
at 915, and pass through partially blocked apertures, in fewer
numbers.
In the manner hereinbefore explained, the second conveyor 925
(which has been precharged to an enhancing field level by corona
926) is sprayed with negative ions across the air gap wherein the
ions can only pass proportionately with the light regions of the
original image. Thus, conveyor 925 becomes an electrostatic
modulated control with both enhancing and blocking fields in
varying degrees for the powder or marking material source 931. The
powder is charged negatively by source E.sub.5 and a particular
powder particle 933 is shown passing through aperture 935
corresponding to the dark region of the original image, which
aperture has been unblocked anc contains an enhancing field.
Aperture 937 is blocked in the light region and so prevents powder
passage to the ordinary paper 939 carried by ordinary conveyor 941.
Heat fixing means 943 is depicted, and the conveyor exits from
housing 907 with the image reproduced thereon. Insulator screens
may be incorporated in conveyors 901 and 811 through the use of
field charging or contact charging as described herein.
Again the fundamental principles of this invention can be employed
to make a photographic projection printer (often called an
enlarger) incorporating either the modifications of a precharge or
the direct image charging approach, as well as incorporating or not
the enhancing field and using either the contact charging plate,
field charging arrangement, or xerographic charging. A projection
printing apparatus 1001 (FIG. 55) such as normally used for
photographic purposes is also used in this invention, with the
exception that the silver halide photographic materials and
chemicals are not required. The image may be projected onto a
precharged photoconductive coated screen 1003 (FIG. 55) thus
producing a charge image by selective discharging of the
illuminated portions of the screen, or an insulative screen 1003'
(FIG. 56) may be used in conjunction with the contact charging
arrangement or the photoconductor screen may be used in conjunction
with the field charging arrangement. The enhancing field may be
incorporated in the latter two systems simply by applying a uniform
precharge E.sub.E to the screen prior to placing in contact with
the contact charging or field charging plate 1005 (FIG. 56). After
the charge image is produced on the screen by one of the above
methods, the screen is removed to a development apparatus (FIG. 57)
which projects toner from supply 1010 through the screen onto the
print receiving medium 1012 in accordance with the image formed on
the screen where hinged supporting electrode is down. Alternately,
the development apparatus may be a part of a single unit device
(FIG. 58) such that removal of the screen to a separate development
apparatus is not required. This device may also provide for placing
a contact charging or field charging plate 1005' (if used) against
screen 1003. After the charge image has been created on the screen,
the receiving medium 1012 and propulsion field producing electrode
1015' are brought into position over the screen; the toner supply
1010 is then activated to produce the print. Many prints may be
made from one exposure and a degree of control of print density and
contrast is possible during the development stage. As discussed
earlier, the direct positive or negative reproduction can be
accomplished.
In FIG. 59, it is shown how an insulator screen 1101, per se may
also be charged with the double layer charge through the use of
double corona sources 1102 and 1103. Corona source 1102 charges one
side of the screen with negative charges, corona source 1103
produces substantially equal and opposite charges on the opposite
side of the screen. These charges may then be modified to produce
the required charge image.
FIG. 60 shows another approach for producing the double-layer
charge in the form of an image onto screen 1101, which is
insulator, per se. The screen 1101 is sandwiched between conductor
backing sheet 1111 and a contact charging plate consisting of
transparent support 1105, transparent conductor 1107, and
photoconductor coating 1109. The light image is projected onto the
photoconductor layer through the transparent support and conductor
as in the manner of contact charging previously described. During
exposure, a charging potential E.sub.C is supplied between the
conductive backing plate 1111 and the conductive transparent
coating 1107. Thus, substantially equal and opposite charges in the
form of a light image are deposited onto the insulator screen
1101.
Other approaches for charging the insulator per se screen include
writing on the screen surface by means of a conductor stylus or
through the use of another multilayer aperture control screen
containing a charge image, as in the case of the ion projection
system previously described.
It should be noted that the screens described herein are not
limited to any given shape, size, or distribution of apertures and
may even contain apertures of varying size and/or shape and/or
distribution even in a random fashion as shown as FIG. 61. In
screen 1201 (FIG. 61a), apertures 1203 are distributed in a random
fashion and may have randomly distributed size and irregular shape
as well. Alternately, the screen 1205 (FIG. 61b) may consist of the
uniform array of circular apertures 1207 in essentially a square or
90.degree. pattern. Alternately, the apertures 1211 as shown in
screen 1209 (FIG. 61c) may be circular, arrayed in a uniform
pattern of a triangular or 60.degree. distribution. Alternately, as
in screen 1213 (FIG. 61d), the apertures 1215 may be square and
arrayed in a square or 90 degree pattern, or as in screen 1217
(FIG. 61e) the apertures may consist of triangular holes 1219
arrayed in a triangular pattern, or as in screen 1221 (FIG. 61f),
the apertures may consist of hexagonal holes 1223 arranged in a
hexagonal pattern, or as shown in screen 1225, (FIG. 61g), the
apertures may consist of extended slots 1227 arranged in parallel
fashion. It is also possible as indicated in screen 1229 (FIG. 61h)
that the screen be composed of a distribution of wires which may be
woven into a mesh as indicated in FIG. 61i in which wires 1231 and
1233 are interwoven to provide a woven wire screen; or as in FIG.
61j, the wires arranged in substantially parallel fashion to
provide a grid; and as shown in FIG. 61k, the coatings 1235
required for these wires to provide the multilayer screen are
disposed on one side of the wire.
Various combinations and modifications of the apparatus herein
disclosed may be made following the principles of the invention.
For example, the screens may be stacked or comprise repetitive
layers to increase the fields. Charge patterns may be directly
transferred from one screen to another. The ion printer may
comprise a positive or negative printer using only a single belt or
screen if contact or field charging is employed. In FIG. 53, for
example, precharge source E.sub.1 may apply a negative precharge.
Then scanner 819 could operate through a field charging plate to
modify and reverse the fields in the light impinged areas. If
source E.sub.2 provided positive particles, printing could be
achieved in positive manner on paper disposed oppositely of source
E.sub.2 relative to conveyor 813. Negative particles would produce
negative printing.
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