U.S. patent number 3,779,166 [Application Number 05/101,681] was granted by the patent office on 1973-12-18 for electrostatic printing system and method using ions and toner particles.
This patent grant is currently assigned to Electroprint, Inc.. Invention is credited to David E. Blake, Hugh Frohbach, Gerald L. Pressman.
United States Patent |
3,779,166 |
Pressman , et al. |
December 18, 1973 |
ELECTROSTATIC PRINTING SYSTEM AND METHOD USING IONS AND TONER
PARTICLES
Abstract
A system for electrostatic printing including a corona source
and electrode for generating a substantially uniform ion stream in
the direction of a print receiving medium and a multilayered
apertured grid modulator interposed in the ion stream for
modulating the cross sectional flow density of ions in the stream
in accordance with a pattern to be reproduced. A toner supply
introduces a cloud of substantially uncharged toner marking
particles adjacent the print receiving medium whereby the modulated
ion stream selectively impinges upon and charges toner particles in
the cloud which are thereby accelerated and deposited on the print
receiving medium in accordance with the pattern to be
reproduced.
Inventors: |
Pressman; Gerald L. (Cupertino,
CA), Frohbach; Hugh (Sunnyvale, CA), Blake; David E.
(Woodside, CA) |
Assignee: |
Electroprint, Inc. (Palo Alto,
CA)
|
Family
ID: |
22285866 |
Appl.
No.: |
05/101,681 |
Filed: |
December 28, 1970 |
Current U.S.
Class: |
347/124;
430/49.1; 101/114; 430/53; 101/DIG.37; 399/290 |
Current CPC
Class: |
G03G
15/346 (20130101); B41J 2/415 (20130101); G03G
15/34 (20130101); Y10S 101/37 (20130101) |
Current International
Class: |
B41J
2/415 (20060101); B41J 2/41 (20060101); G03G
15/34 (20060101); G03G 15/00 (20060101); G03g
013/06 () |
Field of
Search: |
;101/DIG.13,426,114,1,129 ;355/3 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Burr; Edgar S.
Claims
What is claimed is:
1. Apparatus for electrostatic printing using marking particles
impacted by ions propelled along a path comprising:
means for generating a substantially uniform ion stream;
means for supporting a print receiving medium in spaced relation to
the generating means and in line with the path of the ion
stream;
particle propelling electrical field means effective at least
between the means for generating and the print receiving medium for
propelling ions of the stream along the path toward the print
receiving medium;
electrically controlled apertured means in the path between the
generating means and the print receiving means for modulating the
cross-sectional flow density of the ions in the stream along the
path in accordance with a pattern to be reproduced to convert the
ion stream into a modulated ion stream propelled toward the print
receiving means by said field means;
and means for introducing a cloud of marking particles, in which
cloud the particles carry as low a charge as possible, into the
path of the modulated ion stream between the print receiving medium
and the apertured means so that the modulated ion stream
selectively impinges upon and charges marking particles in the
cloud and the field means propels the so-charged particles to the
print receiving medium.
2. Apparatus for electrostatic printing comprising:
means for generating and directing a substantially uniform ion
stream along a path;
apertured means interposed in the ion stream for modulating the
cross-sectional flow density of ions in the stream along the path
in accordance with a pattern to be reproduced to convert the ion
stream to a modulated ion stream directed along said path away from
said modulating means;
means for supporting a print receiving medium in the path of the
modulated ion stream;
said means for directing comprising electrical field means
establishing an electrical field between the means for generating
and the supporting means;
and means for introducing a cloud of marking particles into the
path of the modulated ion stream between the print receiving medium
and the means for modulating whereby ions of the modulated ion
stream selectively impinge upon and charge marking particles in the
cloud which are thereby directed by the electrical field toward,
and deposited on, the print receiving medium in accordance with
said pattern to be reproduced, said cloud of marking particles when
so introduced being in a substantially uncharged state relative to
the charge imparted to them by the ions.
3. Apparatus for electrostatic printing as set forth in claim 2,
wherein the modulating means comprises: a line printing modulator
comprising a layer of insulating material, and layers of conductive
material coated on the sides respectively of the insulative layer,
the modulator having at least one row of apertures formed
therethrough and at least one of said conductive layers segmented
into isolated segments each including at least one aperture
opening; said segments together with portions of the insulating
layer covered thereby and the conductive layer on the side of the
insulating layer opposite said opening supporting a plurality of
separately controllable electric fields within said apertures for
modulating the stream of ions by selectively controlling the
passage of ions through the apertures, and means for applying
electric potentials to each of said segments of the segmented layer
of conductive material to establish said separately controllable
electric fields.
4. Apparatus for electrostatic printing as set forth in claim 2,
wherein the modulating means comprises a multilayered apertured
screen formed with a two-dimensional array of apertures
therethrough, the screen having at least a conductive layer and
insulative layer overlaying the conductive layer, means for
applying a potential to the conductive layer and means for
establishing an electrostatic latent image on the insulative layer
for establishing electrostatic lines of force within the apertures
across the screen for controlling passage of ions in accordance
with the electrostatic latent image.
5. A system for electrostatic printing comprising:
means for generating a directed stream of ions including an ion
source and an electrode spaced from said ion source;
means interposed in the ion stream for modulating the ion flow
comprising a multilayered apertured modulating element spaced
between said ion source and said electrode having at least a
conductive layer and an insulative layer capable of supporting
charge potentials of differing magnitude for establishing
electrostatic lines of force within the apertures of the element
for controlling passage of ions to form a modulated ion stream in
accordance with a pattern to be reproduced;
means for supporting and positioning a print receiving medium
spaced from said modulating element between said modulating element
and said electrode;
means for establishing an electrical field between said ion source
and said electrode encompassing said modulating element and the
print receiving medium;
and means for introducing a cloud of marking particles into the
path of the modulated ion stream in the space between said
modulating element and the positioned print receiving medium
whereby the modulated ion stream selectively impinges upon and
charges marking particles in the cloud which are propelled by said
electrical field and deposited on the print receiving medium in
accordance with the pattern to be reproduced; said marking
particles when so-introduced being substantially uncharged relative
to the charge imparted to them by the ions.
6. Apparatus for electrostatic printing as set forth in claim 5,
wherein said modulating means comprises a multilayered apertured
screen formed with a two-dimensional array of apertures having at
least said conductive layer and insulative layer, means for
applying a potential to said conductive layer and means for
establishing an electrostatic latent image on said insulative layer
for establishing electrostatic lines of force within said apertures
across the screen for controlling passage of ions therethrough in
accordance with the electrostatic latent image; and means for
establishing relative motion between said ion generating means and
said modulating element.
7. A system for electrostatic printing as set forth in claim 6,
wherein the multilayered apertured screen is formed in the
configuration of a hollow cylinder and wherein said ion source is
positioned within the cylinder and said electrode is outside the
cylinder.
8. A system for electrostatic printing as set forth in claim 5,
further comprising means for establishing an air pressure
differential from one side of said modulating element to the other
with the lower pressure on the side adjacent the print receiving
medium whereby a small air flow is established through the
apertures of the modulating element to prevent the marking
particles from entering the apertures of said modulating
element.
9. A system for electrostatic printing as set forth in claim 5,
further comprising means for projecting air streams along the
surfaces of said modulating element and positioned print receiving
medium to provide air boundaries around said introduced cloud.
10. Apparatus for electrostatic printing as set forth in claim 5,
wherein said modulating means comprises a line printing modulator
comprising a layer of insulating material, and layers of conductive
material coated on the sides of the insulative layer respectively,
said modulator having at least one row of apertures formed
therethrough and at least one of said conductive layers segmented
into isolated segments; and means for applying electric potentials
to each of said segments of the segmented layer of conductive
material for establishing a plurality of separately controllable
electric fields within said apertures for modulating a stream of
ions passing through the aperatures.
11. A system for electrostatic printing as set forth in claim 5,
further comprising means for imparting a lateral component of
motion relative to the modulated stream to the cloud substantially
parallel to the plane of the print receiving medium where the print
receiving medium receives charged marking particles.
12. A method of electrostatic printing comprising:
generating an ion stream;
modulating the cross-sectional flow density of ions in the stream
in accordance with a pattern to be reproduced to produce a
modulated stream of ions;
establishing an ion projection field for propelling the ions of the
ion stream for modulation and propelling the ions of a modulated
stream thus formed toward the print receiving medium;
and introducing a cloud of marking particles into the path of the
modulated ion stream whereby the modulated ion stream selectively
impinges upon and charges marking particles in the cloud which are
deposited on the print receiving medium by said projection field in
accordance with a pattern to be reproduced; said marking particles
when so-introduced being in as low a state of charge as
possible.
13. A method of electrostatic printing as set forth in claim 12
further comprising the additional steps of translating the print
receiving medium; and imparting a velocity component to the cloud
parallel to the surface of the print receiving medium receiving the
charged marking particles and in the direction of translation
thereof and substantially synchronized therewith.
14. A method for electrostatic printing comprising:
generating and propelling a stream of ions from an ion source
toward an electrode spaced from said ion source;
modulating the ion flow by interposing in the ion stream a
multilayered apertured grid having at least a conductive layer and
an insulative layer supporting charge potentials of differing
magnitude on either side of the insulative layer respectively
establishing electrostatic lines of force therebetween within the
apertures to control passage of ions therethrough and thereby to
modulate the ion stream in accordance with a pattern to be
reproduced;
propelling the modulated ion stream exiting from the grid;
supporting and positioning a print receiving medium in the space
between the grid and electrode;
introducing a cloud of marking particles into the path of the
modulated ion stream in the space between the grid and the
positioned print receiving medium whereby ions of the modulated ion
stream selectively impinge upon and charge marking particles in the
cloud, said particles so-introduced carrying substantially no
charge relative to the charge imparted to them by said ions;
and moving the so-charged particles in the direction of the print
receiving medium for deposit thereon in accordance with the pattern
to be reproduced.
15. A system for electrostatic printing as set forth in claim 14,
further comprising means for establishing an electrostatic latent
image on the insulative layer of the modulating screen in
accordance with the pattern in the form of electrostatic lines of
force in the apertures; and means for applying a potential to the
conductive layer.
16. A system for electrostatic printing comprising:
means for generating a stream of ions comprising row corona source
means and electrode means comprising an electrode spaced from said
row corona source means;
means interposed in the ion stream for modulating the ion stream
comprising a multilayered apertured screen formed with a
two-dimensional array of apertures spaced between the ion corona
source and the electrode; said screen having at least a conductive
layer and an insulative layer capable of supporting charge
potentials of differing magnitude for establishing electrostatic
lines of force within the apertures of the screen for controlling
passage of ions in accordance with a pattern to be reproduced;
means for translating said screen across the stream of ions for
modulating the stream in accordance with the pattern of
electrostatic lines of force within the apertures of the
screen;
said electrode means moving the ions in the ion stream toward the
modulating means and moving the ions exiting from the modulating
means toward the electrode in the form of a modulated ion
stream;
means for supporting and positioning a print receiving medium
between the modulating screen and the electrode in the path of the
modulated ion stream;
means for transporting said print receiving medium across the
modulated ion stream at substantially the same rate as the
modulating screen is translated across the stream of ions;
and channel means for introducing a cloud of marking particles in a
state of charge as low as possible into the path of the modulated
ion stream in the space between the modulating screen and the
positioned print receiving medium whereby the modulated ion stream
selectively impinges upon and charges marking particles in the
cloud which are deposited on the print receiving medium by the
electrode means in accordance with the pattern to be
reproduced.
17. A system for electrostatic printing as set forth in claim 16,
wherein the multilayered apertured screen is formed with the
insulative layer comprising a layer of photoconductive insulating
material adjacent the conductive layer, means for uniformly
charging the photoconductive layer, and means for optically imaging
a pattern to be reproduced onto the photoconductive layer for
selectively dissipating the uniform charging to form an
electrostatic latent image of the pattern.
18. A system for electrostatic printing as set forth in claim 16,
wherein said system has multiple copy capability, said screen
formed in the configuration of an elongate web; and a plurality of
spaced apart printing stations provided along the web; each
printing station comprising a source of ions on one side of the
web, a print receiving medium on the other side of the web, means
for translating each of said last mentioned print receiving mediums
in synchronism with the web, means for introducing marking
particles between the web and each of said last mentioned print
receiving mediums, and means for propelling ions from the last
mentioned sources toward said last mentioned print receiving
mediums selectively via the web for charging marking particles by
impact therewith whereby the so-charged marking particles are
deposited on the last mentioned print receiving mediums by the
propelling means to print multiple copies in accordance with said
pattern.
19. A system for electrostatic printing as set forth in claim 16,
further comprising means for imparting a component of motion to
said cloud in the direction of translation of the screen and
transporting of the print receiving medium, said component of
motion having substantially the same velocity as said print
receiving medium.
20. A system for electrostatic printing employing ions for charging
marking particles comprising:
a screen for modulating a flow of ions comprising a multilayered
apertured screen having at least a conductive layer and an
insulative layer capable of supporting charge potentials of
differing magnitude for establishing electrostatic lines of force
within the apertures of the screen for controlling passage of ions
in accordance with a pattern to be reproduced, said screen formed
in the configuration of a hollow cylinder;
means for electrostatically charging the screen in accordance with
said pattern;
means for generating a stream of ions, comprising a row corona
source positioned inside the cylindrical screen and electrode means
comprising an electrode spaced from said row corona source outside
the cylindrical screen;
electric field means for propelling charged particles including
ions, said field means effective between the row corona source and
the electrode;
means for rotating the cylindrical screen through said field means
thereby to modulate the ion flow in accordance with the pattern of
electrostatic lines of force within the apertures across the
screen;
means for supporting and positioning a print receiving medium
spaced from the screen between the screen and electrode;
means for transporting said print receiving medium across the path
of the modulated ion flow from the row corona source at a rate
synchronized with the rotation of the cylindrical screen;
and channel means for introducing a cloud of marking particles in
substantially uncharged state relative to the charge imparted to
them by the ions in the path of the modulated ion stream in the
space between the screen surface and the positioned print receiving
medium whereby the modulated ion stream selectively impinges upon
and charges particles in the cloud; said field means propelling the
so-charged particles to the print receiving medium in accordance
with the pattern to be reproduced.
21. A system for electrostatic printing as set forth in claim 20,
wherein the insulative layer of the modulating screen comprises a
photoconductive layer on the outer surface of the cylindrical
screen; and, wherein the means for charging the screen establishes
substantially uniform charge on the photoconductive layer and
optically images the pattern to be reproduced on the
photoconductive layer for selectively dissipating the charge and
establishing an electrostatic latent image, and further comprising
means for applying a potential to the conductive layer of said
screen.
22. A system for electrostatic printing as set forth in claim 20,
wherein said means for supporting and positioning a print receiving
medium comprises a drum.
23. An electrostatic printing head employing ions for charging
marking material particles comprising:
a multilayered apertured modulating grid element having at least a
conductive layer and an insulative layer capable of supporting
charge potentials of differing magnitude for establishing
electrostatic lines of force within the apertures of the element
for controlling passage of ions through the apertures in accordance
with a pattern to be reproduced;
means for generating and propelling a stream of ions comprising a
corona source positioned on one side of the modulating grid element
and electrode means spaced from the modulating grid element on the
other side thereof;
means for supporting and positioning a print receiving medium
spaced from the modulating element between the modulating element
and electrode means;
first channel means arranged between the modulating element and
print receiving medium adjacent the modulating element for
introducing a cloud of dry toner marking particles in substantially
uncharged state relative to the charge imparted to the particles by
the ions in the space between the modulating element and the
positioned print receiving medium whereby the modulated ion stream
passing through the modulating element selectively impinges upon
and charges toner particles in the cloud which are thereby moved by
the propelling means and deposited on the print receiving medium in
accordance with the pattern to be reproduced;
second channel means arranged between the modulating element and
print receiving medium adjacent the surface of the positioned print
receiving medium for delivering pulsed air against the print
receiving medium at the location of dry toner particles deposited
on the medium in the pattern determined by said modulating
element;
and means for initiating an air pulse in said second channel means
in order to erase a pattern of toner deposited on the paper prior
to fixing.
24. A system for electrostatic printing as set forth in claim 23,
wherein the modulating grid element comprises a line printing
modulator comprising a layer of insulating material, and layers of
conductive material coated on each side of the insulative layer,
said multilayered modulator having at least one row of apertures
formed therethrough and at least one conductive layer segmented
into isolated segments for establishing a plurality of separately
controllable electric fields respectively within said apertures for
modulating the stream of ions directed toward the grid element, and
means for applying electric potentials to each of said segments of
the segmented layer of conductive material.
25. An ion flow electrostatic typewriter printing head
comprising:
a first housing having an opening for positioning adjacent a print
receiving medium;
second housing means supported within said first housing means,
said first and second housing means defining a channel for
delivering air pulses to the surface of the print receiving medium
through said opening, said second housing means also formed with an
opening in substantial alignment with the opening in said first
housing means;
third housing means positioned within said second housing means,
said second and third housing means defining a channel for
introducing a cloud of dry toner marking particles in which the
particles carry as low charge as possible in the space inside the
opening in the second housing means;
an apertured modulating grid element for controlling flow of ions
through the apertures of the modulating grid element, said element
positioned within said third housing means so that the apertures
thereof are in substantial alignment with the openings from said
first and second housing means;
and a corona discharge source within said third housing means
substantially in alignment with the apertures of said modulating
grid and the openings in said first and second housing means.
26. An electrostatic typewriter printing head for erasable
electrostatic printing on a print receiving medium using ions for
charging dry toner marking particles comprising:
means for generating ions; means for propelling charged particles
including said ions in a stream toward the print receiving
medium;
an electrically modulatable grid element interposed in the ion
stream for modulating the cross-sectional flow density of ions in
the stream in accordance with a selected typewriting pattern for
exiting a modulated stream of ions;
means for introducing a cloud of dry toner marking particles
carrying substantially no charge relative to the charge imparted to
them by the ions into the path of the modulated ion stream in the
space between the modulating grid element and the print receiving
medium whereby the modulated ion stream selectively impinges upon
and charges toner particles in the cloud; said means for propelling
charged particles propelling the so-charged toner particles to the
print receiving medium in accordance with the selected pattern to
be reproduced;
and means for delivering pulses of air to the surface of the print
receiving medium at the location of toner particles, deposited on
the print receiving medium in a pattern determined by the
modulating grid, thereby to permit dispersal of the deposited toner
pattern prior to fixing.
27. A method of erasable electrostatic printing employing ions for
charging marking particles comprising:
generating an ion stream in the direction of a print receiving
medium;
modulating the cross-sectional density flow of ions in the stream
in accordance with a pattern to be reproduced;
introducing a cloud of toner marking particles in which the
particles carry substantially no charge relative to the charge
imparted to them by the ions into the path of the modulated ion
stream adjacent the print receiving medium whereby the modulated
ion stream selectively impinges upon and charges toner particles in
the cloud; depositing the so-charged toner particles on the print
receiving medium in accordance with a pattern to be reproduced;
and blowing the so deposited pattern of toner particles off the
print receiving medium to achieve erasing.
28. A method of electrostatically controlled printing employing
ions for charging marking material for deposition on a print
receiving medium comprising the steps of:
generating the ions;
forming a stream of ions;
interposing apertured modulator means in the path of the stream to
define portions of a plurality of electrically selectable paths for
the generated ions to the print receiving medium, said modulator
means comprising at least a conductive layer overlaying an
insulative layer with the layers having coinciding apertures
defining said portions of the paths;
at least partially opening and closing said paths at the modulator
means in accordance with a pattern to be reproduced on the print
receiving medium;
introducing a cloud of marking material particles into said paths
between the modulator means and the print receiving medium, said
particles so-introduced carrying substantially no charge relative
to the charge imparted to them by said ions;
propelling the ions along said paths selectively via the modulator
means into the cloud for charging marking material impacted by the
ions and propelling the so-charged marking material directly to the
print receiving medium; and
establishing relative movement of the paths to the print receiving
medium in synchronization with the opening and closing of said
paths at the modulator means in accordance with said pattern.
29. An electrostatically controlled printing process employing ions
for charging marking material for deposition on a print receiving
medium, comprising in combination;
a source of ions for generating an ion stream;
apertured modulator means disposed in the path of the stream to
define portions of a plurality of electrically selectable paths
between the source and the print receiving medium;
said modulator means comprising at least a conductive layer
overlaying an insulative layer with the layers having coinciding
apertures to comprise said portions of the selectable paths;
means for selectively at least partially opening and closing said
paths at the modulator means in accordance with a pattern to be
reproduced on the print receiving medium;
means for introducing a cloud of marking material particles into
the space between the modulator means and the print receiving
medium, said particles so-introduced carrying substantially no
charge relative to the charge imparted to them by said ions;
means for propelling ions along said selectable paths and
selectively via the modulator means into the cloud for charging
marking material impacted and for propelling the so-charged marking
material directly to the print receiving medium; and,
means for establishing relative movement of the selectable paths to
the print receiving medium in synchronization with the opening and
closing of said paths by the means for selectively opening and
closing the paths in accordance with said pattern.
Description
This invention relates to a new and improved system for
electrostatic reproduction and in particular to an improvement in
modulated aperture non-contact electrostatic printing, useful in a
wide range of applications including document copiers, computer
printouts, silent typewriters, etc.
The system of electrostatic printing referred to herein as
modulated aperture non-contact electrostatic reproduction is
generally set forth in U.S. Pat. applications Ser. Nos. 673,499,
now U. S. Pat. No. 3,625,604 and 776,146 now U. S. Pat. No.
3,647,291 assigned to the assignee of the present case. According
to these disclosures, there is provided in a preferred embodiment a
multilayered apertured screen including at least a conductive layer
and an adjacent insulative layer on which an electrostatic latent
image is formed for modulating a flow of charged toner particles,
ions or other printing particles directed through the apertures of
the screen by an accelerating field. The minimum of two layers for
the screen construction permits establishing a double layer charge
on the opposite sides of the insulative layer for selectively
producing overlapping lines of force or "fringing" fields within
the apertures of the screen. Thus, lines of force generated by
bi-polar electrostatic fields extend within the apertures of the
screen and can be oriented to oppose the passage of charged
particles, enhance the flow of charged particles, or be neutralized
to have no effect on charged particles directed through the
apertures of the screen. Thus, the double layer charge can be
selectively established across the face of the screen to
substantially completely block the passage of charged particles
through certain apertures, enhance and accelerate the passage of
charged particles through other apertures, and control the width
and density of the particle stream through other apertures over a
continuous spectrum. A stream or flow of charged particles directed
through the screen by an overall applied accelerating field is
therefore modulated to provide a cross sectional density variation
at least substantially corresponding with the image or pattern to
be reproduced. The modulated stream of toner particles or other
charged particles passing through the apertured screen is
transferred by the overall applied electrostatic projection field
across a gap or space to the print receiving medium. The pattern
image formed by this non-contact printing arrangement is thereafter
fixed according to known techniques if dry particles are used. If
the toner particles consist of liquid aerosols the fixing step may
not be necessary. Furthermore, if the charged particle stream
consists of ions the ions impinge on the paper forming an
electrostatic latent image which is thereafter dusted and fixed. In
this latter embodiment, treated dielectric paper must be used in
order to retain the electrostatic latent image formed by the ion
stream.
In one approach for establishing the double layer charge or
bi-polar electrostatic latent image across the screen, a
substantially uniform charged distribution is initially established
across both sides of the insulative layer with opposite charges on
the respective sides to provide fringing fields within the
apertures. These fringing fields are oriented to produce blocking
fields to block or partially block particles of a predetermined
charge sign. By use of photosensitive insulating materials the
charge distribution and therefore the blocking fields are
dissipated according to a light pattern projected on the screen.
The fringing fields also may be oriented to include enhancing
fields which are established by additional techniques. The screen
must generally be charged initially with blocking fields which
block the passage of charged toner particles through the screen
however. The blocking fields are thereafter selectively neutralized
according to the light pattern or reversed to enhancing fields
according to additional procedures, and the resulting modulation of
the flow of toner particles through the screen results in certain
embodiments in negative printing. In order to achieve positive
printing special contact charging techniques for charging the
screen and other special expedients for non-contact or field
charging are used.
Modulated aperture electrostatic printing systems permitting direct
positive printing without the necessity for contact charging the
screen modulator or other special expedients are described in other
patent applications assigned to the present assignee. In the U.S.
Pat. application Ser. No. 85,070, now U.S. Pat. No. 3,694,200
entitled Electrostatic Modulator for Controlling Flow of Charged
Particles, filed on Oct. 29, 1970, there is described an apertured
screen having substantially the entire surfaces formed of a
dielectric material with the dielectric preferably thicker on one
face of the screen than on the other. The screen is charged with
like charges over substantially its entire surfaces to develop
fringing fields in the apertures and is preferably charged to a
higher level on the thicker side so that the screen initially
carried a higher potential on one side providing a uniform charge
inequality or potential difference through the screen apertures.
The charge inequality or potential difference is oriented to
provide enhancing fields within the apertures of the screen to
enhance the flow of charged particles passing through the screen
from the direction of the side of higher charge density. The charge
distributed across the side of the screen having a higher charge
density is selectively dissipated in accordance with a pattern to
be reproduced thereby establishing a bi-polar electrostatic latent
image as a modification of the fringing fields for density control
of a flow of charged particles directed through the screen. Full
modulation control of the particle flow including blocking fields,
enhancing fields, and a spectrum of fringing fields over a range in
between, is therefore possible with a single selective charge
dissipation. This arrangement also permits direct positive printing
when the charge is selectively dissipated by optical light image
addressing. For optical addressing the insulating material on the
thicker side is a photoconductive insulating material. Thus, the
passage of charged particles is enhanced or unimpeded in the dark
areas while the passage of charged toner particles is blocked or
impeded in the light areas. A different modulated aperture
non-contact printing screen and system permitting direct positive
printing is also set forth in the U.S. Pat. application Ser. No.
197,877, entitled Method and Apparatus for Forming A Positive
Electrostatic Printing, filed on Nov. 11, 1971.
Another approach to modulated aperture non-contact electrostatic
printing is set forth in U.S. Pat. application Ser. No. 864,022,
now U.S. Pat. No. 3,713,734 entitled Electrostatic Line Printer,
filed on Oct. 6, 1969 and assigned to the assignee of the present
case, now U. S. Pat. No. 3,689,935. This arrangement is
particularly applicable in electronically addressed electrostatic
printing and computer printout. The Electrostatic Line Printer
incorporates in one embodiment, a multilayered particle modulator
comprising a layer of insulating material, a continuous layer of
conducting material on one side of the insulating layer, and a
segmented layer of conducting material on the other side of the
insulating layer. Both conductive layers can be segmented however.
At least one row of apertures is formed through the multilayered
particle modulator. Each segment of the segmented layer of
conductive material is formed adjacent or around at least one
aperture and is insulatively isolated from every other segment of
the segmented conductive layer. More than one aperture may be
formed through each segment. Selected potentials are applied to
each of the segments of the segmented conductive layer while a
fixed potential is applied to the continuous conductive layer.
Charged layers are thereby established on either side of the
insulating layer permitting fringing fields to be established
within the modulator apertures oriented to block or enhance a flow
of charged particles directed through the screen or to control the
flow over a continuous range in between. The bi-polar fringing
fields established within the apertures are separately controllable
according to the electric potentials applied to the insulatively
isolated segments along the row of apertures. An overall applied
field projects charged particles through the row of apertures of
the particle modulator and the density of the particle stream is
modulated according to the pattern of potentials applied to the
segments of the segmented conductive layer. A modulated stream of
charged particles impinge upon a print receiving medium interposed
in the modulated particle stream and translated relative to the
particle modulator to provide line by line or line scan
printing.
In each of the above arrangements for modulated aperture
non-contact electrostatic printing the two-dimensional screen or
line grid modulator can be used to modulate a flow of charged toner
particles or ions. When the screen or line grid modulator is used
to control a flow of toner particles either dry or liquid, a toner
cloud is produced from a toner source on the side of the modulator
opposite the print receiving medium and an overall applied
accelerating field generates a stream of toner particles toward the
print receiving medium which is modulated by the interposed screen
or line grid. This arrangement enables direct deposition of toner
particles on any surface, regular or irregular, dielectric or
conductive. However, a percentage of the toner particles charged by
the toner source on the other side of the screen or line grid do
not pass through the apertures but land on solid portions of the
screen or line grid, or on walls of the toner supply ducts.
The use of ions in the particle flow, instead of toner marking
material itself, avoids any problem of toner buildup and further
permits the use of lower potentials for gating the particle stream.
However, the use of an ion stream generated from a corona source
for establishing an electrostatic latent image on the print
receiving medium requires the use of high dielectric paper or
treated paper in order to permit retention of sufficient charge
magnitude in the electrostatic latent image.
It is therefore an object of the present invention to provide a
modulated aperture electrostatic printing system incorporating the
advantages of both modulated toner particle flow and modulated ion
stream flow non-contact printing while suffering the disadvantages
of neither. In order to accomplish this result the present
invention generally contemplates the method of generating an ion
stream in the direction of a print receiving medium, modulating the
cross sectional flow density of ions in the stream in accordance
with a pattern to be reproduced, and introducing a cloud of
substantially uncharged toner marking particles adjacent the print
receiving medium whereby the modulated ion stream selectively
impinges upon and charges toner particles in the cloud which are
thereby deposited on the print receiving medium in accordance with
a pattern to be reproduced.
Thus, the invention generally contemplates providing in one
embodiment a corona source and spaced electrode for generating a
substantially uniform ion stream, and a support for positioning a
print receiving medium in the path of the ion stream. A
multilayered apertured two-dimensional screen or line grid
modulator is interposed in the ion stream between the source and
print receiving medium for modulating the cross sectional flow
density of ions in the stream in accordance with a pattern to be
reproduced. Finally, a toner source is provided and arranged for
introducing a cloud of substantially uncharged toner marking
particles adjacent the print receiving medium whereby the modulated
ion stream selectively impinges upon and charges toner particles in
the cloud. The selectively charged toner particles adjacent the
print receiving medium are thereafter accelerated and deposited on
the medium in accordance with the pattern to be reproduced.
A feature and advantage of this system is that charged toner
particles need not be ducted or transported through channels in the
machinery or through the screen or line grid modulator thereby
avoiding toner loss and toner contamination while at the same time
permitting direct toner deposition printing on the print receiving
medium so that electrostatic printing can take place on any
surface.
Another feature and advantage of this arrangement is that the ion
stream alone passes through the screen or line grid modulator
permitting the use of lower gating potentials, high frequency gate
switching, and high velocity particle transport for high speed
printing.
In a preferred form of the invention, modulation of the ion flow is
accomplished using a multilayered apertured element spaced between
the ion source and the accelerating electrode having at least a
conductive layer and an insulative layer capable of supporting
charged potentials of differing magnitude on different layers of
the element for establishing the electrostatic lines of force
within the apertures of the element for controlling passage of ions
in accordance with a pattern to be reproduced. Thus, the preferred
embodiments generally include all of the two-dimensional screen and
one-dimensional line grid modulators described in the patent
applications referred to above and assigned to the assignee of the
present case.
In order to further eliminate toner contamination in the printing
machinery the invention contemplates establishing an air pressure
differential from one side of the modulating element to the other
with the low pressure on the side adjacent the print receiving
medium whereby a small air flow is established through the
apertures of the modulating element to prevent the toner particles
from entering the apertures. According to another aspect of the
invention, air streams can be injected along the surfaces of the
modulating element and positioned print receiving medium in order
to provide air boundaries around the introduced toner cloud.
In the preferred forms, whether using the two-dimensional screen or
the one-dimensional line grid modulator, the invention contemplates
line by line or line scan printing to provide optimum control over
the uniformity of toner distribution. A feature and advantage of
this approach is that toner cloud uniformity is necessary only
along one major dimension namely the printing line. This result,
when printing with the two-dimensional screen, is accomplished as
follows.
A row corona source and spaced accelerating electrode generate a
substantially uniform stream of ions having a line or linear cross
sectional configuration. A multilayered apertured screen formed
with a two-dimensional array of apertures for modulating the ion
flow is interposed in the space between the row corona source and
the accelerating electrode. The multilayered apertured screen is
formed with at least a conductive layer and an insulative layer as
heretofore described capable of supporting charge potentials of
different magnitude on different layers of the screen for
establishing electrostatic lines of force within the apertures of
the screen for controlling passage of ions. Means are provided for
translating the screen across the linear cross-section stream of
ions for variably modulating the line stream in accordance with the
pattern of electrostatic lines of force within the apertures across
the screen. At the same time a print receiving medium is supported
and positioned between the modulating screen and the accelerating
electrode in the path of the linear ion stream and the print
receiving medium is transported across the line cross-section of
the ion stream at a rate synchronized with the modulating screen.
It is, of course, the relative motion of the ion stream to the
modulator and print receiver which is useful, and thus, the latter
two may be fixed and the ion stream translated. Finally a channel
is provided for introducing a cloud of substantially uncharged
toner marking particles into the path of the linear cross-section
ion stream in the space between the translating modulating screen
and the translating print receiving medium whereby the modulated
linear cross-section ion stream selectively impinges upon and
charges toner particles in the cloud which are accelerated and
deposited on the print receiving medium in accordance with the
pattern to be reproduced. Preferably, a velocity component is
imparted to the toner cloud substantially equal to and in the
direction of motion of the modulating screen and print receiving
medium.
The system also incorporates elements for establishing an
electrostatic latent image on the insulative layer of the
two-dimensional modulating screen and for applying a potential to
the conductive layer of the screen. In one example optical
addressing is utilized to establish the electrostatic latent image
and the insulative layer comprises a layer of photoconductive
insulating material. The photoconductive layer is first uniformly
charged and the pattern to be reproduced is optically imaged onto
the photoconductive layer for selectively dissipating the charge to
form an electrostatic latent image. A potential is applied to the
conductive layer to provide the bi-polar electrostatic latent image
of fringing fields within the apertures. The screen can be formed
in the configuration of an elongate web transported along a
plurality of printing stations for multiple copy electrostatic
printing.
According to one embodiment of this aspect of the invention the
screen is formed in the configuration of a hollow cylinder and a
row corona source is positioned inside the cylindrical screen with
the accelerating electrode spaced from the row corona source
outside the cylindrical screen. The cylindrical screen is rotated
relative to the row corona source and the accelerating electrode to
variably modulate the line cross-section ion flow in accordance
with the pattern of electrostatic lines of force within the
apertures across the screen. A printing receiving medium is spaced
from the cylindrical screen between the cylindrical screen
modulator and accelerating electrodes and is transported across the
path of the line cross-section ion flow at a rate synchronized with
the rotation of the cylinder. As in the previous embodiment a
channel is provided for introducing a cloud of substantially
uncharged toner marking particles in the path of the linear ion
stream and the space between the cylindrical screen surface and the
print receiving medium. The cylindrical screen may also be
optically addressed for establishing the double layer charge
electrostatic latent image.
The invention is also applied in a novel method for erasure in
electrostatic printing with dry toner particles comprising
depositing a pattern of dry toner particles on a print receiving
medium and selectively blowing the deposited dry toner particles
off the print receiving medium prior to fixing. Thus, an
electrostatic printing head with erasing capability is provided
with a first channel arranged between the modulating element and
print receiving medium for introducing a cloud of substantially
uncharged dry toner marking particles in the space between the
modulating element and a positioned print receiving medium. A
modulated ion stream passing through the modulating elements
selectively impinges upon and charges toner particles in the cloud
which are accelerated and deposited upon the print receiving medium
in accordance with the pattern to be reproduced. The printing head,
however, is also provided with a second channel arranged adjacent
the surface of the positioned print receiving medium for delivering
pulses of air against the print receiving medium at the location of
dry toner particles desposited on the medium in order to disperse a
pattern of toner particles deposited on the paper prior to
fixing.
The invention thus generally contemplates the method of
electrostatic printing comprising generating an ion stream in the
direction of a print receiving medium, modulating the cross
sectional density flow of ions in the stream in accordance with a
pattern to be reproduced, and introducing a cloud of substantially
uncharged toner marking particles adjacent the print receiving
medium whereby the modulated ion stream selectively impinges upon
and charges toner particles in the cloud which are deposited on the
print receiving medium in accordance with a pattern to be
reproduced. In the event dry toner marking particles are used, the
invention also contemplates the additional step of selectively
blowing the so deposited toner particles off the print receiving
medium for erasure.
The invention also contemplates a novel character sequential
printing method using the electrostatic printing head according to
which the printing head is returned to its original position after
the character has been printed by a small deflection of the paper
carrier and return, a small deflection of the printing head and
return, or electrostatic deflection of the stream of charged
particles.
Other objects, features and advantages of the present invention
will become apparent in the following specification and
accompanying drawings.
FIG. 1 is a fragmentary plan view and FIG. 1A a fragmentary side
cross-sectional view of a multilayered apertured screen for
modulating the flow of charged particles.
FIG. 2 is a detailed cross-sectional view of one aperture of the
screen showing a portion of the double layer charge electrostatic
latent image supported by the screen.
FIG. 3 is a fragmentary side cross-sectional view of another
multilayered screen.
FIG. 4 is a sequence of diagrammatic views showing the steps in
modulated aperture electrostatic printing.
FIG. 5 is a fragmentary plan view and FIG. 5A a fragmentary side
cross-sectional view of a line or bar modulating element for
modulated aperture electrostatic line printing.
FIG. 6 is a diagrammatic view of a system for modulated aperture
electrostatic line printing.
FIG. 7 is a fragmentary side cross-sectional view of a system for
modulated aperture electrostatic printing in which a flow of
charged toner particles is modulated.
FIG. 8 is a fragmentary side cross-sectional view of a system for
modulated aperture electrostatic printing according to the present
invention in which a flow of ions is modulated to impinge on an
introduced cloud of toner marking particles.
FIG. 8A is a fragmentary perspective view of the system of FIG.
8.
FIGS. 9, 10 and 11 are fragmentary side cross-sectional views of
variations of the modulated aperture electrostatic printing system
illustrated in FIG. 8.
FIG. 12 is a diagrammatic side cross-sectional view of a system for
modulated aperture electrostatic printing according to the present
invention utilizing a two-dimensional modulated aperture
screen.
FIG. 13 is a diagrammatic view of another system for modulated
aperture electrostatic printing in which the screen is formed in
the configuration of a drum or cylinder.
FIG. 14 is a diagrammatic side view of a system with multiple
printing stations of the type shown in FIG. 13.
FIG. 15 is a fragmentary diagrammatic view of a system for
optically addressing the cylindrical screen to establish the double
layer charge electrostatic latent image.
FIG. 16 is a diagrammatic side cross-sectional view of an
electrostatic printing head with erasing capability.
In order to more fully understand the invention, a general
description of modulated aperture electrostatic printing as
heretofore developed is first presented with reference to FIGS.
1-7. In FIGS. 1 and 1A is illustrated a multilayered apertured
screen suitable for use in the present invention. The screen 10
generally comprises a conductive layer 11 and an insulative layer
12 with rows of holes 13 formed therethrough. As shown in more
detail in FIG. 2, the construction of the screen is such that a
layer of charges can be supported on either side of the insulative
layer 12. Thus, a potential can be applied to the conductive layer
11 in order to supply charges 14 of a particular sign such as, for
example, positive, along the side of the insulative layer 12
adjacent the conductive layer 11. A second layer of charges 15 can
be established along the outer side of the insulative layer of 12
or for example opposite or negative charge around the apertures 13
of the screen. The double layer charge establishes lines of force
within the apertures 13 of the screen which can be oriented to
either block or enhance a flow of charged particles directed
through the apertures or to control the density of particles
passing through the apertures over a continuous range in between.
The pattern of electrostatic lines of force established within the
apertures 13 and the screen is also referred to herein as a
bi-polar electrostatic latent image.
The pattern of charges 15 on the outside of the insulative layer
can be established by a variety of contact charging techniques or
by optical addressing as set forth in the patent applications
referred to above. By way of example the insulative layer 12 can be
formed of a photoconductive insulating material. As shown in FIG.
4, the double layer screen 10 is first sprayed from a corona source
20, the photoconductive insulative layer facing the corona source,
and the conductive layer maintained at some fixed potential such as
ground so that a bi-polar electrostatic latent image is formed
across the insulative layer of the screen. The screen 10 is then
exposed to light from a source 21 in a pattern in accordance with
an image to be reproduced thereby selectively to dissipate the
charge on the photoconductive insulative layer. This step of course
occurs in a dark environment. Finally, the screen 10 is positioned
adjacent a print receiving medium carried on an accelerating
electrode 22 with a toner source 23 positioned on the opposite side
of the screen. A potential derived from source 24 establishes an
accelerating field between the toner supply 23 and the accelerating
electrode 22 so that a stream of charged toner particles is
directed through the apertures of the screen 10. At the same time,
a selected potential from source 25 is applied to the conductive
layer of the screen to maintain the electrostatic field between the
screen and source and between the screen and accelerating
electrode. With blocking fields initially established across the
screen, toner is permitted to pass through those apertures from
which the charge on the insulative layer is dissipated by light
exposure in the previous step, while the unexposed apertures
continue to block the passage of charged toner particles forming a
deposit of toner particles on the print receiving medium at
electrode 22 in accordance with the pattern to be reproduced.
A variety of other modulating screen configurations are described
in the patent applications referred to above. By way of example in
FIG. 3 there is shown a three-layered apertured screen comprising a
conductive layer 26 and a photoconductive insulating layer 27
separated by a high dielectric insulating material 28. A bi-polar
or double layer charged electrostatic latent image is established
across the insulative layers of this screen according to a variety
of charging techniques set forth in the patent applications
referred to above.
Another type of modulating element for modulated aperture
electrostatic line printing is set forth in FIGS. 5 and 5A. The
modulating element 30 consists of an elongate length or bar of
insulating material 31 having formed along one side a continuous
layer of conducting material 32 and having formed along the
opposite side a segmented conductive layer 33 consisting of
individual insulatively isolated segments 33A, 33B, 33C, etc. The
so formed elongate bar is formed with a row of apertures
therethrough, each aperture surrounded by a conductive segment 33A,
33B, 33C etc. An electrical lead is provided to the continuous
conductive layer 32 for applying a uniform potential across one
face of the insulative layer 31 and around one side of each
aperture. A plurality of electrical leads are provided one for each
of the conductive segments 33A, 33B, 33C, etc., so that a different
potential can be applied to each of the segments for building up
differing selective charge layers around the other side of each of
the apertures 35 in accordance with a pattern to be reproduced. The
double layer charge along each side of the insulative layer 31
permits development of electrostatic lines of force or fringing
fields within the apertures for controlling the flow of a linear
cross-sectional stream of ions directed through the modulating
element. A system for electrostatic line printing using the line or
bar modulator of FIGS. 5 and 5A is shown in the diagrammatic view
of FIG. 6. A toner supply 40 and an accelerating electrode 41 are
spaced apart and interconnected with a potential source for
charging and accelerating toner particles from the toner source 40
in the direction of the electrode 41. The outlet from the toner
source is shaped to provide an elongate or linear cross-sectional
stream of toner particles. The modulating element 30 is positioned
in the path of the toner flow with a biasing potential applied to
the conductive layer 32 via electrical lead 41 and with selected
electrical potentials applied to the segmented elements to the
segmented layer 33 via the bank of electrical leads 42 which may be
addressed for example by appropriate logic circuitry to provide a
changing pattern of charges across the segmented layer in
accordance with a pattern to be reproduced. The flow of toner
particles directed through the apertures of the modulating element
is appropriately shaped or modulated in accordance with the pattern
to be reproduced and accelerated toward the back electrode 41. A
print receiving medium 43 is transported across the modulated toner
stream in a space between the modulating element 30 and electrode
41 and the speed of transport of the paper or other print receiving
medium 43 is synchronized with the frequency or rate of change of
potentials applied to the segmented portions of the segmented layer
33. As an alternative to the continuous line printing described
above, other modes of modulated aperture electrostatic line
printing are set forth in the patent application Ser. No. 864,022
now U.S. Pat. No. 3,689,935 referred to above.
Representative screens and systems for modulated aperture
electrostatic printing have been described in the foregoing
discussion. Other examples of modulated aperture printing screens
and systems are set forth in detail in the patent applications
referred to above. One example of a printing operation of these
systems is shown in FIG. 7 with reference to a line modulator of
the type shown in FIGS. 5 and 5A. As illustrated in FIG. 7, a
corona source 45, particle modulator 54, print receiving medium 47,
and accelerating electrode 48 are provided in sequence. The
accelerating electrode 48 can itself form the support for the print
receiving medium 47. The corona source 45 generates a stream of
charged particles 50 which are accelerated toward the back
electrode 48 by a suitable potential difference applied between the
corona source 45 and electrode 48. Toner marking particles 51 are
delivered by a source 52 into the vicinity of the corona emissions
and acquire charges. The charged toner particles 53 are thereafter
accelerated toward the electrode 48 through the apertures of the
line modulator 46. As heretofore described, the modulating element
46 consists of an insulative layer 54 with conductive layers 55 and
56 formed on either side thereof, at least one of which is
segmented into insulatively isolated segments surrounding the
apertures formed in a row along the modulating element. One or more
rows of apertures can be used as set forth in U.S. Pat. application
Ser. No. 864,022 referred to above. Potentials applied to the
conductive layers over electrical lines 57 and 58 one of which
comprises a bank of electrical leads to the segments of the
segmented layer selectively develop lines of force within the
apertures in accordance with a pattern to be reproduced selectively
modulating the flow of toner particles so that the particles come
to rest on the print receiving medium 47 in accordance with the
pattern to be reproduced.
Alternatively, as described in the above referenced patent
application, the ion stream itself can be modulated by the
modulating element so that the modulated stream of ions impinges
upon the print receiving medium 47 in accordance with the pattern
to be reproduced. In this arrangement high dielectric paper, for
example, is used for the print receiving medium 47 in order to
retain the electrostatic latent image deposited by the ions. The
paper is thereafter dusted and fixed in accordance with known
techniques of electrostatic printing.
According to the present invention, a novel system and method for
modulated aperture electrostatic printing using screens of the type
set forth above is provided. The basic system and method are
depicted in FIGS. 8 and 8A in contrast to the arrangement of FIG. 7
with corresponding elements numbered accordingly. Thus, according
to the embodiment of the present invention illustrated in FIG. 8
there is provided a corona source 45 modulating element 46 print
receiving medium 47 and accelerating electrode 48 in sequence as
described with reference to FIG. 7. Corona source 45 generates a
stream of ions 50 which are accelerating toward the back electrode
38 through the apertures of modulating element 46. In the example
of FIG. 8A, a linear corona source in the form of a wire is shown,
but a row of point source or other corona source arrangement may be
used. In contrast to the previously developed modulated aperture
printing systems and methods described above, and in the patent
applications referred to, the toner particles 51 are introduced by
a source 60 into the space between the modulated element 46 and
positioned print receiving medium 47. The toner particles 51 are
neutral and form a cloud in the interspace between the modulating
element 46 and print receiving medium 47. The ion stream passing
through the apertures of the modulating element 46 and modulated
according to the array of fields established within the apertures,
impinges on the cloud of uncharged toner particles selectively
charging the particles in accordance with the pattern to be
reproduced so that the charged particles are accelerated by the
electrode 48 to deposit on the print receiving medium 47 in
accordance with the pattern to be reproduced. This novel
arrangement and method incorporates the advantages of both the
toner modulating and ion modulating systems described in the patent
applications referred to above. Thus, because only the ion stream
is modulated by the modulating element 46 lower potentials can be
used on electrical leads 57 and 58 with higher switching
frequencies. Because of the higher transit speed of the ions
printing can be conducted at higher speeds. Toner loss at the
screen or modulated element is avoided as are any cleaning
problems. After the ions pass through the apertures of the
modulating element they intercept and charge the toner particles
which are then propelled by the accelerating electrostatic field
toward the electrode to deposit on the print receiving medium 47.
Thus, printing with the toner particles is accomplished directly,
rather than first creating an electrostatic latent image on the
print receiving medium. Printing can therefore take place on any
surface without the necessity of treated or high dielectric paper.
Furthermore, because the injected toner particles 51 either in
solid or aerosol form are neutral, there is little tendency for
toner to drift and deposit on the printing medium or other
apparatus prior to charging by the ion stream. The toner particles
become charged toner particles 53 generally only upon impingement
of or close proximity to the ion stream 50.
A feature and advantage of this arrangement is that either liquid
aerosol or solid particles can be used with equal facility. When
the toner stream itself is modulated with the modulating element or
screen, the use of solid particles causes a percentage of particles
to deposit on the screen or modulating element thereby making
cleaning steps desirable in the printing process. Therefore, when
the toner stream itself is modulated liquid aerosols have been used
to more easily facilitate removal of aerosol particles deposited on
the printing screen or modulating element. Liquid droplets
coalescing on the face of the bar or screen modulator would be
drawn off at the low edge by means of a wick. In the configuration
of the present invention as shown in FIGS. 8 and 8A, however, toner
is not deposited on the bar or screen modulator and is kept out of
the apertures. Therefore dry toner can be used with equal facility
and fused by heat after printing is completed with the fuser
located beyond the printing station.
In order to further prevent any drift of toner particles toward the
print receiving medium prior to charging and to further prevent any
drift of toner particles toward the modulating element or screen,
protective "air boundaries" can be injected over the surface of the
modulating element and paper as shown in FIG. 9. As shown in that
example, the toner source 62 positioned for delivering toner in the
space between the modulating element 63 and print receiving medium
64 is shaped to define air passageways or channels 65 and 66 along
the surface of the modulating element 63 and print receiving medium
64 respectively. Air under slightly higher pressure is delivered
via channel 65 and 66 to effectively contain the neutral toner
particles within air boundaries until they become charged by
impingement from the ion stream and are accelerated toward
electrode 67.
Another approach for preventing drift of uncharged toner particles
into the apertures of the modulating element is illustrated in FIG.
10. According to this arrangement a slight pressure differential is
established on either side of the modulating element with the
slightly higher pressure on the corona side. As a result, a very
small air flow 70 is established through the apertures of the
modulating element 71 thereby preventing the toner cloud from
entering the apertures.
By means of the expedients illustrated in FIGS. 9 and 10, a
directional velocity parallel to the plane of the printing surface
can be imparted to the tomer cloud in a lateral direction between
the print receiving medium and modulating element. The velocity
component imparted to the toner cloud can be correlated with the
speed of transport of the print receiving medium in order to
prevent any distortion in the reproduced pattern.
Another arrangement for delivering and picking up toner and
imparting a controlled lateral velocity component to the toner
cloud is shown in FIG. 11. In that arrangement the toner source 75
tapers to a narrow delivery outlet while a toner pick up channel 76
is positioned across from the toner source on the other side of the
apertures of the screen or modulating element. The pick up channel
76 is provided with an inlet having a larger diameter than the
outlet from the toner source 75. By means of differential pressures
established within the channels 75 and 76, the toner can be
delivered with a controlled lateral component of motion
synchronized with the velocity of transport of the print receiving
medium 77.
In one example of the electrostatic line printing embodiment of the
present invention described above, charged toner particles were
accelerated to a velocity of 15 centimeters per second through a
line modulating element having a thickness of 0.25 millimeters. The
resulting transit time of 1.6 milliseconds theoretically permits a
highest addressing frequency or switching frequency of the
potentials applied to the conductive layers of approximately 300
cycles per second. A practical addressing frequency of
approximately 100 cycles per second was achieved. The switching
rate for controlling ions is greater by a factor of more than one
hundred.
Embodiments of the present invention for modulated aperture
electrostatic printing using a screen formed with a two-dimensional
array of apertures spaced between an ion source and accelerating
electrode are illustrated in FIGS. 12 through 15. As shown
diagrammatically in FIG. 12, the multilayered apertured screen 80
is interposed between a corona source 81, and accelerating
electrode 82 having positioned across its surface a print receiving
medium 83. The screen 80 is formed with a two-dimensional array of
apertures and at least a conductive layer and an insulative layer
capable of supporting charge potentials of differing magnitude on
different layers of the screen for establishing electrostatic lines
of force within the apertures of the screen for controlling passage
of ions in accordance with a pattern to be reproduced as heretofore
described. Uncharged toner particles 84 in the form of an aerosol
or solid toner cloud is introduced into the space between the
screen 80 and the print receiving medium 83. A stream of ions
originating from corona source 81 in the direction of accelerating
electrode 82 intercepts the cloud of neutral toner particles and
the particles become charged and are transported in the direction
of the accelerating field. Because the ion flow is modulated as it
passes through the apparatus of screen 80 as heretofore described,
the toner cloud is selectively charged and the charged particles
are attracted to the printing surface 83 by the accelerating
electrostatic field in accordance with the pattern to be
reproduced. Because the printing takes place over a two-dimensional
area, however, problems are encountered in the embodiment
illustrated in FIG. 12 in uniformly distributing a cloud of toner
particles 84 throughout the space over the surface area to be
printed. Non-uniform printing density may result.
In order to overcome this difficulty the invention is embodied in a
form so that printing occurs at any instance only over a linear
cross-section of the printing surface area even though a
two-dimensional screen is utilized. This is accomplished according
to one example as shown in FIG. 13. In this arrangement, the
printing or toning occurs along a narrow slit defined by baffles 90
while the screen 92 and print receiving medium 93 are transported
synchronously across the slit. The paper or other printing surface
93 is transported across the slit by means of a drum support 94,
which also serves as the accelerating electrode, and appropriate
rollers 95. A stream of ions generated by corona source 96 is
accelerated in the direction of the drum passing through the
apertures of screen 92. Uncharged toner is delivered to the space
over the slit defined by baffles 90 in the path of the modulated
ion stream through a channel defined by the baffle walls 90 and
walls 91 so that the line cross-section ion stream passing through
the apertures of screen 92 impinge upon the neutral cloud
selectively charging particles in the cloud which are accelerated
toward the drum 94 to deposit on the print receiving medium 93 in
accordance with the pattern to be reproduced. The linear
cross-section stream of ions originating from row corona source 96
is variably modulated as the screen 92 is transported across the
ion stream path. The toner cloud is therefore variably charged and
comes to rest on the printing surface 93 in a continuously changing
pattern as the paper or other printing surface is transported
across the path of charged particles. Continuous line printing can
therefore be achieved.
In a preferred embodiment the cloud of toner particles 98 is
delivered through the channels defined by walls 90 and 91 with a
lateral component of motion in the direction of transport of the
screen and printing surface. By this expedient, distortion at the
printing surface due to differential velocity between the printing
particles and printing surface is avoided. Thus, the velocity
component imparted to the cloud in the direction of transport is
synchronized with the velocity of transport of the screen and paper
or other printing surface.
The paper or other print receiving medium can be either sheet-fed
or web-fed. For simultaneous copies on web-fed paper, a system such
as that shown in FIG. 14 is provided. In this arrangement multiple
printing stations 100, 101 and 102 of the type shown in FIG. 13
produce essentially simultaneous identical copies of the same
charge image formed across the two-dimensional multilayered
apertured screen 103, except that the continuous line printing
occurs simultaneously across different linear cross-sectional
portions of the screen 103. The amount of ion current used from the
sources 104, 105 and 106 is adjusted to a level so that the screen
charge pattern is not discharged and therefore so that three or
more images can be printed from the same double layer charge
bi-polar electrostatic latent image formed on the two-dimensional
screen 103. The embodiment of FIG. 14 is particularly suited to
computer output applications where web-fed paper is often used.
Another embodiment for the two-dimensional modulated aperture
screen system is shown in FIG. 15 in which the screen 110 is formed
in the configuration of a drum 111. In this configuration the back
electrode 112 which also serves as the carrying element for the
paper or other print receiving medium 13 is either flat as
illustrated in FIG. 15 or curved as shown in FIG. 13. As in each of
the previous embodiments, the substantially neutral toner cloud may
consist either of solid or liquid toner particles introduced into
the channel defined by baffles 114 and walls 115. The toner is
again transported across the slit defined by the two sections of
the channel to be exposed to the linear cross-section ion stream
originating from the corona source 116 positioned inside the drum
111. The ion stream is modulated as it passes through the apertures
of the screen 110, which forms the surface of drum 111. The toner
cloud is selectively charged and accelerated toward the electrode
112 so that toner particles deposit on the print receiving medium
113 in the pattern to be reproduced as the paper or other medium
113 is transported across the path of the charged particles.
Continuous line printing is thereby achieved as the ion stream is
variably modulated by the rotating drum. Again, a velocity
component is preferably imparted to the toner cloud in the
direction of transport, synchronized with the velocity of the
transport of the drum surface and printing surface so that printing
distortions resulting from differential velocities are avoided.
Problems of printing "smear" are also eliminated by "narrow slit"
printing. In this embodiment the width of the toner aperture slit
formed by the two sides of the toner delivery channel formed by
baffles 114 and walls 115 has an effective width electrostatically
as wide as a row of screen apertures formed in the two-dimensional
screen. Because the narrow slit is reduced in width to that of one
aperture, the relative velocity of paper and screen and toner
during printing is not critical in obtaining high resolutions. This
permits mechanical simplicity to the design of the machine.
However, the best performance is obtained when the screen velocity,
toner cloud velocity, and paper or other printing medium velocity
are all nearly equal. The quantity of toner in the form of liquid
aerosol or solid particles in the space between the screen and
print receiving medium will then determine the density of the print
for a given toner material, and the most uniform toning is then
achieved.
In the embodiment of FIG. 15, the double layer charge bi-polar
electrostatic latent image is established across the screen by
optical addressing in the manner heretofore described. In this
example, the screen is initially charged uniformly over the surface
of a photoconductive insulative layer by means of corona source
120. The charge on the photoconductive insulating layer is
thereafter selectively dissipated through the conductive layer
which may be, for example, grounded. This is accomplished by
imaging, by means of a lens system 121, the light pattern to be
reproduced, onto the surface of the photoconductive insulating
layer while the conductive layer is for example grounded. A uniform
potential is thereafter applied to the conductive layer so that
selective fringing fields are established within the apertures of
the screen for modulating the ion stream.
A feature and advantage of the modulated aperture electrostatic
non-contact printing system contemplated by the present invention
is that non-contact printing with dry toner particles is greatly
facilitated as heretofore described. Thus, the invention enables an
electrostatic printing head with erasure capability for application
in, for example, typewriters and consoles. According to this
aspect, the invention generally contemplates the electrostatic
printing method of forming a pattern of dry toner particles on a
print receiving medium in accordance with a pattern to be
reproduced and selectively blowing the dry toner particles off the
print receiving medium prior to fixing.
A representative printing head for accomplishing this function is
shown in FIG. 16. The printing head incorporates a modulating
element 130 for modulated aperture electrostatic line printing of
the type illustrated in FIG. 5 and 6. Thus, the modulating element
130 includes a central insulative layer with conductive layers
coated on either side thereof at least one of which consists of
segments insulatively isolated and surrounding apertures of a row
of apertures formed across the modulating element for line
printing. The conductive segments are electrically addressed for
modulating a stream of ions in accordance with the letters or other
symbols to be reproduced by the printing head. The ion stream
originates from corona source 131 in the direction of a back
accelerating electrode 132. A print receiving medium 133 is
positioned in the path of ions originating from corona source 131
and passing through the apertures of screen 130. A first channel
134 is provided defined by walls 135 and 136 for delivering or
introducing a cloud of substantially uncharged dry toner marking
particles in the space between the modulating element 130 and a
positioned print receiving medium 133 and adjacent the modulating
element 130. The modulated ion stream passing through the apertures
of the modulating element selectively impinge upon and charge toner
particles in the cloud which are accelerated and deposited on the
print receiving medium 133 in accordance with the pattern to be
reproduced. A second channel 137 defined by walls 135 and 138 is
arranged between the modulating element and print receiving medium
adjacent the surface of the print receiving medium 133 for
delivering pulses of air against the print receiving medium at the
location of dry toner particles deposited on the medium in the
pattern determined by the modulating element 130. Air pulses are
initiated in channel 137 in order to erase a pattern of toner
particles erroneously deposited on the paper and prior to
fixing.
From another point of view, the novel electrostatic typewriter
printing head consists of a first housing 138 having an opening for
positioning adjacent a print receiving medium 133. A second housing
135 is supported within the first housing 138 so that the first and
second housings 138 and 135 define a channel for delivering air
pulses to the surface of the print receiving medium through the
opening. The second housing is also formed with an opening in
alignment with the opening in the first housing. A third housing
136 is positioned within the second housing 135, the second and
third housing 135 and 136 defining a channel 134 for introducing a
cloud of substantially uncharged dry toner marking particles in the
space adjacent the opening in the second housing. An apertured
modulated grid element 130 for controlling the flow of ions through
the apertures of the modulating grid element is constructed with
the housing 136 so that the apertures are in substantial alignment
with the openings with the first and second housings. Finally, a
corona discharge source 130 is positioned within the third housing
136 for delivering a stream of ions in alignment with the apertures
of the modulating element 130 and the openings within the first and
second housings 138 and 135.
In a typewriter or console environment, the printing head is
adapted for printing individual symbols each in a continuous line
printing mode and thereafter permitting erasure of any symbol
erroneously deposited in the form of dry toner particles on the
print receiving medium, by blowing off and dispersing the deposited
toner particles via the toner conduit 134. The desired symbol can
then be retoned or redeposited on the printing surface in the same
location.
This invention contemplates a variety of methods for this type of
character sequential printing suitable for use in a continuous
writing printer such as typewriter or console. This type of
operation is particularly important when the printer is hand or
keyboard addressed and where it is important for the operator to
observe the printing as it is entered. To perform this function,
where one character at a time is being printed, the writing head,
as described with reference to FIG. 16, scans the distance of one
character height, and during this scan forms the addressed
character in the appropriately indexed position. After the
character has been printed the position of the writing head is
returned to the original position, shifted one lateral position for
printing the next character. Or, the writing head is returned to
the original position for erasure as heretofore described. The
scanning action of this character sequential mode can be achieved
in either of several ways. According to one method a small
deflection of the paper carriage and return is used. According to a
second method a small deflection of the printing head and return is
used. And according to a third method, electrostatic deflection of
the writing toner particles charged by the ion stream accomplishes
this scanning action. Indexing and character forming and control
operations are performed electronically with the use of shift
registers.
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