U.S. patent number 3,582,954 [Application Number 04/801,647] was granted by the patent office on 1971-06-01 for printing by selective ink ejection from capillaries.
Invention is credited to Stephen F. Skala.
United States Patent |
3,582,954 |
Skala |
June 1, 1971 |
PRINTING BY SELECTIVE INK EJECTION FROM CAPILLARIES
Abstract
A capillary ink printing method and apparatus in which
capillaries are selectively filled with ink, the ink is moved to
the capillary surface, and the ink is ejected to move from the
capillary surface to a printing-receiving surface.
Inventors: |
Skala; Stephen F. (Berwyn,
IL) |
Family
ID: |
25181680 |
Appl.
No.: |
04/801,647 |
Filed: |
February 24, 1969 |
Current U.S.
Class: |
347/52; 347/55;
347/85 |
Current CPC
Class: |
B41J
2/06 (20130101); H04N 1/034 (20130101) |
Current International
Class: |
B41J
2/06 (20060101); B41J 2/04 (20060101); H04N
1/032 (20060101); H04N 1/034 (20060101); G01d
015/16 (); G01k 001/12 () |
Field of
Search: |
;346/1,75,140,74 (CR)/
;101/1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hartary; Joseph W.
Claims
What I claim is:
1. A method for graphically depositing ink dot droplets from a
plurality of capillary tubes in a capillary assembly onto an
adjoining printing surface, including the steps of
positioning a body of ink in communication with each capillary
tube,
selectively loading capillary tubes in accordance with transmitted
electric signals from an information system to urge the ink
substantially toward the surface of said capillary assembly,
imparting sufficient force to said ink at the capillary assembly
surface to overcome the surface tension in the loaded tubes to
thereby release and then deposit the droplets in a graphic pattern
on said printing surface, and
restoring capillaries in the assembly to substantially the same
state of ink content for a succeeding printing cycle.
2. A method as in claim 1 wherein an electrostatic field is
provided between said printing surface and the capillary assembly
to transfer in to induce separation of the droplets from the
capillary assembly and urge the droplets in travel to the printing
surface.
3. A method as in claim 1 wherein said capillary assembly is
accelerated in a direction away from said printing surface to
provide an inertial force, sufficient to induce separation of ink
droplets from the capillary assembly.
4. A method as in claim 3 and further including the step of
providing an electrostatic field between said printing surface and
said capillary assembly surface to facilitate transfer of ink
droplets from the capillary assembly to the printing surface.
5. A method as in claim 3, and further including the step of
impressing a negative hydrostatic pressure on said body of ink to
lower the ink levels within the loaded capillary tubes to a
substantially uniform level relative to the balance of the
capillary tubes in the capillary assembly.
6. A method as in claim 3 in which are included steps of
positioning a common body of ink for all the tubes in the assembly,
supporting said body of ink by means which are penetrable by an
electronic beam,
loading selected capillary tubes by a loading electronic beam
penetrating said supporting means and urging ink towards the
surface of said capillary assembly and the selected tubes,
affixing the capillary assembly to a transducer and impressing a
snap-back action to said transducer by an electric signal to break
the surface action of the ink in the selected capillary tubes,
and
inducing relative movement between the capillary assembly and the
printing surface so that a graphic illustration may be sequentially
established by succeeding rows of the deposited droplets.
7. A method as in claim 6 and the further step of imparting
positive potentials to the surface of the capillary assembly and
the printing surface, said printing surface potential being greater
to thereby create an electrostatic charge to facilitate transfer of
the droplets from the capillary assembly to the printing
surface.
8. An apparatus for producing rapid droplet illustrations on a
receiving surface, including
a capillary assembly, said assembly having a plurality of aligned
capillary tubes communicating with the surface of the assembly,
a body of ink communicating with said capillary assembly,
means to transmit an electric signal in accordance with information
desired to be graphically illustrated on the receiving surface,
means to load selected capillary tubes with ink from the
communicating body of ink in accordance with said transmitted
electric signals from the information system,
means to eject said ink as droplets from the capillary tubes to the
receiving surface, and
means to restore the capillaries in the assembly to substantially
the same state of ink content for a succeeding printing cycle.
9. An apparatus as in claim 8 wherein means form an electrostatic
field between said receiving surface and said capillary assembly to
induce separation of the droplets from the capillary assembly and
urge the droplets in travel to the printing surface.
10. An apparatus as in claim 8 wherein means accelerate said
capillary assembly in a direction away from the receiving surface
at a rate sufficient to break the surface tension of ink in the
selectively loaded capillary tubes.
11. An apparatus as in claim 10 including means to effect a
negative hydrostatic pressure in the tubes of the assembly to
thereby reduce the ink within such tubes to substantially uniform
levels prior to a succeeding cycle of preselectively loading the
tubes in the assembly in accordance with the succeeding electric
signals from the information system.
12. An apparatus as in claim 10 and further including means to
induce relative movement between the printing surface and the
capillary assembly surface so that sequential rows of droplets may
be graphically deposited on the receiving surface in accordance
with sequential electric signals to the information system in
succeeding cycles of ink droplet ejection.
13. An apparatus as in claim 10 wherein the plurality of capillary
tubes in the assembly are in communication with a common body of
ink, a thin foil supporting said common body of ink, said foil
being penetrable by a loading electron beam,
said selected capillary tubes being loaded by an electron beam
penetrating the foil and inducing movement of the ink into selected
capillary tubes towards the surface of the capillary assembly,
a potential induced on the capillary assembly surface to create an
electric field with said electron beam,
a transducer affixed to said capillary assembly, electrical means
to actuate said transducer to snap-back and eject droplets from the
selectively loaded capillary tubes,
an ink reservoir joined to said common body of ink, and said ink
reservoir including a pump assembly to effect a negative
hydrostatic pressure to reduce the ink in the capillaries to
substantially uniform levels following an ejection snap.
14. An apparatus as in claim 13 wherein said receiving surface is
paper movable relative to said capillary assembly, whereby
sequential rows of droplets are graphically formed on said moving
paper by succeeding cycles of selective loading and ejection, means
to reestablish substantially uniform levels of ink in the tubes,
and means to impress a positive potential to the surface of the
paper higher than the positive potential of the capillary assembly
surface to thereby create an electrostatic charge on the paper to
facilitate transmittal of the droplets from the selectively loaded
capillary tubes to the surface of the paper.
15. An apparatus as in claim 8 which includes a column of mercury
in a capillary well and said ink riding said mercury column, a
magnetic field, and means to form a current flow in response to
selective activation of said electron beam, said current flow in
said magnetic field resulting in predetermined pumping of the
mercury column to urge ink out of the capillary well.
16. An apparatus as in claim 8 which includes plates of a
piezoelectric material associated with each capillary, electrodes
mounted on said piezoelectric plates, and means providing an
electron beam to charge said electrodes, and to deform said plates
and thereby urge ink to protrude from the capillary prior to
droplet formation.
Description
This invention relates to a method and apparatus for producing ink
droplet illustrations on a receiving surface.
Conventional publication requires a complex system of preparation
of reproduction masters, printing facilities, and distribution
means. Despite continued improvements in the processing of
information by computer assisted preparation of text and
illustrations, intrinsic system inefficiencies remain.
Several approaches which have attracted interest overcome these
inefficiencies by transmitting information and recording this
information directly on a subscribers apparatus. Among these
approaches are the xerographic systems which convert electrical
signals to an optical image and record this image by well-known
electrostatic means. Another method produces a stream of charged
liquid ink droplets and electrostatically deflects these droplets
to form characters on a receiving surface as shown in the Winston
patent, U.S. Pat. No. 3,060,429. Of more particular interest are
the methods which print by selectively ejecting ink droplets from
capillaries, particularly from a plurality of such capillaries in
accordance with a program so that the plurality of dots deposited
on a printing surface such as paper assumes intelligible forms.
Several methods have been proposed which eject ink droplets by a
shock internal to a capillary. Reference may be made, for example,
to U.S. Pat. No. 3,211,088 issued to M. Naiman on Oct. 12, 1965. In
the Naiman patent a pressure-producing transducer, such as a
piezoelectric crystal is actuated to cause a shock wave to
propagate through a passageway having the configuration of an
exponential horn. The ink is ejected out of such passageways as
droplets and deposited on paper to form letters.
It will be understood that a row of such passageways or capillaries
can be moved across the surface of a sheet of paper while droplets
are ejected in a predetermined manner from capillaries to form
letters on the moving surface. It will be realized that a single
letter may comprise an array of deposited droplets so that the
visual perception is that of a solid block letter; and it is
further realized that such droplets may follow the line of the
letter to present a visual appearance of the letter as a result of
the closely adjoined positions of the individual droplets.
Such a means of printing has attractions but presents problems at
most of the steps or with most of the features associated with such
means. Attention is required to such steps and features,
particularly, delivering ink to the capillaries, manipulating the
ink within the capillaries for ejection, ejecting the ink, and
directing the ink to a printing surface such as paper. It is
desirable to improve these features and steps so that the system of
printing by ink droplet ejection capillaries will be made more
attractive to users.
It is accordingly a general object of this invention to provide a
novel and improved system for transmission of graphic information
and its reception and processing on a receiving surface.
Another object is to provide an improved system which can be
utilized to transmit information in an improved manner to users
such as subscribers who can receive and process such information on
conveniently accessible apparatus. In such a system, distribution
of information is immediate to the subscriber, and particular
features of the information may be selected by the subscriber.
Likewise, a large geographic area may be serviced by such a system
in which information is electronically distributed throughout a
wide geographic area, and is received by a subscribers-processing
apparatus to obtain a graphically useful form.
Another object is to provide a method and apparatus by which ink is
ejected under the control of electric signals in an improved manner
to print on ordinary pulp paper, thereby eliminating any
requirements of specially sensitized surfaces or the like.
Yet another object of this invention is to provide a method and
apparatus whereby ink droplets are ejected in an improved manner
from small-dimension capillaries whereby the normally encountered
surface forces retarding the formation and release of the small ink
droplets are overcome to obtain the desired resolution and
deposition of such droplets on paper.
Yet another object is to provide an apparatus and method in which
desirable printing speeds are obtained by providing small time
intervals between ejection cycles of the printing capillaries.
Still another object is to provide a method and apparatus whereby
improvements are obtained in capillary printing by providing means
to selectively fill and prepare predetermined capillaries to
transfer the ink from such capillaries to a printing surface.
Yet still another object is to provide an apparatus for capillary
printing wherein ink is ejected from selected capillaries in an
improved manner by utilizing a snap-back action to separate ink
droplets from such capillaries.
Other characteristics, advantages, and objects of this invention
will become apparent from the following detailed description,
including drawings wherein:
FIG. 1 is a highly diagrammatic illustration of an apparatus useful
in the practice of the method;
FIG. 2 is a diagrammatic portional perspective of an alternative
embodiment;
FIG. 3 is a diagrammatic portional perspective of still another
alternative embodiment;
FIG. 4 is a schematic circuit which operates with the embodiment
shown in FIG. 3; and
FIG. 5 is a diagrammatic portional perspective of yet another
alternative embodiment.
The present invention provides a means of forming an image from
patterns of dots on a contrasting background. Dots of constant size
may be deposited at regularly spaced coordinates. Letter characters
may be provided as a plurality of closely spaced dots separated by
areas without dots. Pictures may be provided by a plurality of dots
spaced at varying intervals. The pattern of the deposited dots are
preferably obtained from a row of aligned capillaries positioned in
depositing relationship next to a printing surface such as a sheet
of paper. Relative movement is provided between the sheet of paper
and the row of capillaries so that the graphic information is
sequentially deposited on the area of the paper. The final pattern
of the dots is a composite of the respective rows of dots, each row
being deposited sequentially.
In the illustrated embodiment, the capillaries are selectively
loaded by an injected electron beam so that ink from a reservoir or
the like is moved into the selected capillaries. Such an electron
beam selects the particular capillaries which will be loaded by
moving through the reservoir at a point in registry with the
particular capillary. The ejection means includes accelerating
movement of the row of capillaries by inducing a snap-back action
of the row of capillary tubes. The ink droplets which are ejected
are directed in an improved manner by providing an electrostatic
field between the paper and the capillary assembly. The ejection
means, therefore, preferably include the combination of the
snap-back capillary assembly and the electrostatic field to thereby
effectively overcome any surface binding forces which would
otherwise prevent successful ejection and subsequent
deposition.
Referring now to the drawing, a source of graphic information is
indicated by S. Its input may be in analogue or symbolic form. An
analogue input includes a surface having characters and
illustrations in substantially the form to be printed. The image on
this surface is converted by a video scanning device into an
electrical signal of varying amplitude proportional to the light
reflectance along the line scanned. This electrical signal, having
characteristics well known in television technology, controls a
pulse generator. At the beginning of the scanning sweep is a
synchronization pulse. The subsequent pulses conveying graphic
information are generated in proportion to the amplitude of the
electrical signal and further are entrained to occur at definite
intervals, if at all. The entrainment assures proper alignment with
the capillaries after reception.
The input to S may also be symbolic as, for example, a punched tape
having codes for characters, type size, and font. A computer may
process the coded information together with stored character
parameters and added illustrations, and then store the resultant
composition. The stored composition may be read out to control a
pulse generator which will produce pulses having the
characteristics described previously.
Regardless of the form of the input, the output of S is a
pulse-modulated electromagnetic wave represented by pulse
modulation envelope 1. Such signal is received, detected and
amplified by a receiver 2. The output from the receiver 2 is
coupled to a control grid 3 of a vacuum tube 4, so that an electron
beam 5 may be turned on and off. A high-voltage power supply 6a is
connected to an accelerating and focusing electrode 6 to impart
energy to the electron beam 5.
A beam sweep output indicated at 7 is generated by unit 7a, and
such beam sweep is coupled to deflection plates 8. The deflection
plates cause the beam to be properly aligned with respect to the
individual capillaries, one of which is indicated at 9, in the
capillary assembly. The electron beam has sufficient energy to
penetrate a thin metal foil 10. The beam 5 then penetrates a layer
or body of ink 12. Some of the electrons, after dissipating their
energy, stop and remain in the ink associated with the capillary.
The ink is a good insulator so that the charge remains for at least
several milliseconds.
The capillaries selected by the action of the electron beam now
contain charged ink. An electric field, constant in time, exists
between the ground foil 10 and the upper surface 13 of the
capillary assembly. A positive potential from a power source 14
connected to the conducting surface layer 13 establishes a voltage
gradient in the capillary assembly. The charge internal to the ink
is forced upward by the electric field drawing the ink to the end
of the capillary. The surface tension of the ink tends to prevent
further flow. At this point of the printing cycle, certain
capillaries corresponding to the sequence of pulses in the received
signal, are filled with ink.
A voltage indicated at 15 is applied by an ink ejection drive
circuit 16 to electrodes 17, 17a which are bonded to a
piezoelectric transducer 18. The transducer contracts rapidly and a
longitudinal wave travels through an impedance-matching ejection
pulse coupler 19, and snaps the capillary assembly downward so that
the inertial force on the protruding ink overcomes the surface
forces and separates it from the capillary.
The following description relates to the illustrated embodiment of
FIG. 1, but reference may be made to the Winston patent previously
cited for further details.
A droplet of ink 20, which has acquired an electric charge, is
attracted electrostatically to a sheet of paper 21, moving over a
guide roll 22. The electric field is the result of a potential
difference between the positively charged surface of the capillary
assembly and the guide roll which has a positive charge produced by
power supply 23, which in turn is at a higher positive potential
than power supply 14. The ejection of a row of ink droplets
completes the printing cycle. A negative hydrostatic pressure is
applied to the ink layer or body within channel 24 by a pump
assembly and ink reservoir 25 to withdraw ink from all the
capillaries. The ink level falls until surface tension stabilizes
the ink at the bottom of the capillaries. The hydrostatic pressure
on the ink is released to a less negative magnitude. The ink
pressure in the channel 24 and capillary 9 is indicated graphically
at 26 during such cycle. The cycle described above is repeated
producing another row of dots on the moving paper, and continuing
sequentially until a graphic illustration is obtained such as
illustrated letter "E" at 27.
The following disclosure of use and operation includes
representative operational ranges for a better understanding of the
invention.
A resolution of 140 dots per inch corresponds to conventional
gravure quality. This represents an information density of about
7,000,000 bits for a typical newspaper page. A typical page has
about 3,000 words plus illustrations and drawings. With a printing
time of 1 minute per page, the bandwidth of the transmitted signal
is about 10.sup.5 Hz for monochrome. The printing cycle rate is
about 50 rows of dots per second or 20 milliseconds per cycle.
Accordingly, the capillary dimensions are about 0.003 inch in
diameter on about 0.004-inch centers.
The behavior of fluids in small capillaries is determined to a
large extent by their surface energy. In the printing cycle, the
ink emerges from the capillary under the force of an electrostatic
field. As it begins to protrude, an opposing force of surface
tension develops and increases to a maximum when a hemispherical
surface develops. Surface tension thus provides a stable range in
which forces bringing the ink outward are balanced by the opposing
inward force of surface tension. A similar balance of forces occurs
when the ink is withdrawn to the bottom of the capillaries to
return them to the same state.
An important feature of the invention is the selective loading or
filling of particular capillary tubes so that the subsequent
ejection step is facilitated. The droplets are ejected from such
preselected tubes by the step of accelerating movement of the
capillary assembly in a direction away from the proximate printing
surface. As an added step, an electrostatic field is created
between the printing surface and the surface of the capillary
assembly. This electrostatic field tends to prevent loss of
resolution of the droplets as they travel from the capillary tubes
to the printing surface.
The selection and loading step has been described in association
with the use of an electron beam which can be directed to
particular capillaries. Such a beam may sweep the capillaries, with
electrons acting at selected capillaries to fill them. The
actuation of the electron beam may be controlled by the information
system. With the illustrated loading electron beam, a layer of ink
in the channel has been shown as being common to the plurality of
capillaries in the capillary assembly. This ink layer is supported
by a thin foil of a low atomic number metal such as beryllium. This
type of foil also serves to minimize undesired scattering of the
electron beam as it passes therethrough and also constitutes an
electrode with an associated potential. The potential participates
in directing the electron beam to the capillaries and also
participates in forcing charged ink through selected
capillaries.
Substantially uniform loading of the selected or predetermined
capillary tubes is required in order to obtain ejected dots of
substantially uniform size and density on the printing surface.
This desirable feature is obtained by the substantially uniform
filling of the capillaries and the later step of effecting a
negative hydrostatic pressure so that the ink level in the
capillary tubes is lowered to a substantially uniform level. A
loading or energizing of the individual, preselected capillary tube
urges the ink substantially to the surface of each tube so that the
later acceleration or snap-back step can break the surface tension
to release the droplets which travel to the paper or the like.
An alternative embodiment particularly useful for computer printout
or message printing is shown in FIG. 2. It includes a plurality of
generally aligned rows, two of which are indicated by reference to
capillaries 28 and 30, shown in section. An electron beam 32 moves
through foil 34 and a body of ink 36 to selectively load a
capillary or a plurality of capillaries. Ink droplets such as 38
are ejected by a snap-back action of the assembly 40, as by
energizing a piezoelectric material 42, as described heretobefore.
The receiving surface for the droplets is shown as paper 44 moving
between rollers 46, 46a to provide a surface of sufficient area to
span the capillaries in the plurality of rows disposed from ink
ejection surface 48. An electrostatic field is again created to
attract the ink droplets.
With the foregoing embodiment, a line of letters may be printed in
one cycle. Character codes from a computer or message transmitter,
such as S in FIG. 1, are converted to an analog form capable of
controlling the electron beam 32 through the control grid 3, such
as shown in FIG. 1. The electron beam 32 is positioned by two sets
of mutually perpendicular deflection plates, such as 8 in FIG. 1.
The beam pattern traces a character at a time by combination of ON
or OFF actuations and a conventional x-y scan. An alternate beam
pattern generator would utilize the method of the charactron
tube.
A device of the embodiment shown in FIG. 2 may also be used for
color printing, in which four rows are provided, one for each
primary color and one for black. Each row is then provided with a
separate ink feed channel, such as 24 in FIG. 1. The capillary rows
are actuated with a delay of one cycle so that the deposited color
droplets are in register.
The diagrammatic illustration of FIG. 3 shows another embodiment
for selectively filling the capillaries. The capillary assembly 50
is flanked by a permanent magnet 52 one pole of which is shown, and
an opposite pole is similarly placed on the other side, but not
shown. The assembly includes a steel coupler 53 and a ferrite block
54. Walls 56, 56a define a capillary 58 therebetween. A wall 56 of
one capillary assembly is spaced from an adjoining wall 56b of
another capillary assembly which is only partially illustrated. An
electric circuit includes the walls 56, 56a; electrodes 60 and 62;
a photoconductor 65 having a phosphor layer; and electron beam 66;
and a column of mercury 68 within the capillary. The electrodes 60,
62 are connected to a power source 69 which provides a current flow
of either polarity. The electron beam may be directed to selected
capillaries, and to the phosphors thereof. The phosphor emits light
when energized by the electron beam, and such light causes the
photoconductor to lower its resistance and allow current flow
through power source or supply 69, electrodes 60, 62,
photoconductor with phosphor layer 65, capillary walls 56, 56a and
the column of mercury 68.
An ink reservoir 70 feeds ink channel 71 which is common to all the
capillaries in the assembly and communicates therewith so that the
ink may fill the capillaries. The ink and capillary walls are such
that the ink adheres to the walls, but not to the outer surfaces.
The capillaries therefore are filled by capillary action, but the
ink does not spill over the outside surface during the ink ejection
step. The capillary may, for example, be made of porous metal and
the upper surfaces may be made of a substantially nonwetting
material such as silver against water. A mercury channel 72
commonly communicates with all the capillaries in the assembly so
as to permit a column of mercury to form in each capillary.
At the beginning of the cycle, a body of ink 74 is on top of the
mercury column. The persistence of the phosphor and the response of
the photoconductor are selected so that the time constant is
somewhat less than the period of the printing cycle. The flow of
the current in the magnetic field causes the mercury to rise in the
capillary and thereby shut off the ink channel 71. The body of
mercury does not enter the ink channel 71 because of the high
surface tension of the mercury. The column of mercury rises until
the mercury reaches a constriction formed by opposed projections 76
and 76a in the capillary walls. Surface tension prevents any
further rise. The ink now protrudes as indicated by phantom line
78, and may be ejected following snap-back action of the capillary
assembly 50.
Following ink ejection, the electron beam sweeps across the
phosphors of the photoconductors, and the polarity of the power
source is reversed. Current flow in the magnetic field now drives
the mercury column down and past the ink channel 71, to thereby
allow the capillary 58 to refill with ink over the top of the
mercury column. A schematic circuit is shown in the view of FIG. 4.
The voltage cycle is graphically indicated in the representation of
the power supply 69. By way of exemplary illustration, the dynamic
function of aqueous ink and mercury is satisfactory at a 16
-millisecond period and an 0.10-inch ink amplitude.
In some embodiments, the ink may be pumped out of the capillary to
a sufficient degree so that the surface tension of the protrusion
may be broken to form a droplet and allow it to travel to a
receiving surface, even without developing the inertial force by
the snap-back action. This could be attained by a combination of
sufficient protrusion and a static charge on the receiving surface,
for example.
It is apparent that a conductive ink may be used rather than a
mercury and ink combination. Other equivalent methods may also be
used for controlling and driving the mercury column. For example,
an integrated circuit may be used having sequencing and gating
properties as a substitute for the electron beam. Another example
may provide driving all the capillaries in the assembly until the
ink is pumped to form protrusions, thereafter latching the mercury
columns, and releasing capillaries with the electron beam which are
not intended to perform printing steps. Other equivalent means will
occur to practitioners.
Another embodiment of this invention utilizes dimensional changes
of piezoelectric materials to force ink through a capillary. Each
capillary is actuated by a piezoelectric plate which, when
electrically charged, expands into an ink-filled chamber or
passageway. The function and structure of this embodiment may be
better understood with reference to FIG. 5. The capillary assembly
includes a plurality of cells each having a capillary 80, a
piezoelectric plate 82, which is attached to cell walls 83 by
compliant strips 84 and rigid strips 85. The plate has metal film
electrodes 86 on each of its opposite major sides, and such film
electrodes have flap portions 86a and 86b which are shown
positioned on the outer edge 82a of the plate 82. The cells are
enclosed in a vacuum tube assembly similar to that shown in FIG. 1
and are exposed to an electron beam 81. An ink channel 88 is common
to the plurality of cells and communicates with passageways 89. A
valving means includes a body of mercury 87, in a mercury duct or
reservoir 90, which is located below an ink duct or reservoir 91.
The mercury is raised or lowered by conducting an electric current
across a magnetic field in a manner similar to that previously
described.
The printing cycle begins with ink positioned in the capillary 80.
The plate electrode 86 is uncharged, and the ink channel 88 is
sealed off by the mercury 87. The electron beam is swept and
modulated to charge selected capillaries for printing. The electron
beam establishes a potential between the opposite electrodes of the
plate. The plate 82 expands into the ink in chamber or passageway
89. The compliant strips 84 then deform along with the plate 82.
Ink flows through the selected capillaries and protrudes from the
openings thereof. The ink protruding from selected capillaries is
then ejected by means such as those previously described.
The next step in the practice of the invention restores all the
capillaries to the same state, and requires discharge of the
electrodes 86 with consequent relaxation of the plate 82 and
lowering of the mercury body 87. The lowered mercury body operates
as an opening valve to allow the ink to pass through the ink
channel 88, passageway 89, and then to the capillaries. Discharge
of the electrodes is effected by constructing them of a low work
function metal which will emit electrons photoelectrically, such as
cesium silver bismuth. The electrodes are then illuminated by means
such as a light source, and the ejected electrons travel from the
negative to a grounded electrode such as 86b. As the electrodes are
discharged, the plate resumes its initial size. While the
electrodes are being discharged, the mercury valve remains open and
ink flows into the capillary by capillary action. After the
capillaries are filled, the mercury is actuated to rise until it
encounters outlet 92 in the ink channel and inlet 94 in the duct.
The mercury now operates as a closing valve. The printing cycle is
completed and the printer is ready to repeat the process.
In the foregoing embodiment, the ink is preferably ejected from the
capillaries by a snap-back action of the capillary assembly. It
will be understood that the ink may also be ejected
electrostatically following protrusion from the capillary opening.
The dynamics of the interaction of the ink protrusion with the
electrostatic field and droplet formation, under such conditions,
may be better understood by reference to the Winston patent,
previously cited.
The invention may now be practiced in the various ways which will
occur to practitioners, and it should be understood that all such
practice will comprise a part of the present invention so long as
it comes within the terms of the following claims as given further
meaning by the language of the preceding disclosure.
* * * * *