US 3582954 A
Description (OCR text may contain errors)
United States Patent Stephen F. Skills 3839 South Wenonah, Berwyn, 111. 60402 801,647
Feb. 24, 1969 June 1, 197 1 lnventor Appl. No. Filed Patented PRINTING BY SELECTIVE INK EJECTION FROM CAPILLARIES 16 Claims, 5 Drawing Figs.
US. Cl 346/1, 346/140, 101/1 nn. Cl ..g;01d 15/1 G06k 1/12 Field of Search 346/1, 75,
 References Cited UNITED STATES PATENTS 2,512,743 6/1950 Hansell 346/75 3,341,859 9/1967 Adams 346/140 3,452,360 6/1969 Williamson 346/ 140 3,480,962 1 1/1969 Weigl et al 346/1 Primary Examiner-Joseph W. Hartary Attorney-Dominik, Knechtel & Godula 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.
PATENTED JUN 1 l97| SHEET 2 [1F 3 4 m F x x r.) NJ 5 b m & 6 W 7 I, 0 6 w 1 5 m m nw 8 5 m 8 M 6 m 0 6 E 3 m F 07 6 INVENTOR STEPHEN E SKALA ATTYS.
PATENTEDIJUNV Han SHEET 3 BF 3 umm M Wm KIL H INVENTOI? STEPHEN E SKALA $2M; MA
A TTYS PRENTENG BY SELECTEVE HNK EMECTHON FROM CAPTLLARHES 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 sur- .face 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 as sociated 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 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;
H0. 2 is a diagrammatic portional perspective of an alternative embodiment;
FlG. 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 ob tained 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.
ln 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 furtherare 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 ID. 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 impedancematching ejection pulse coupler l9, 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 l0 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. lnk 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 sufiicient 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 usedfor 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. I. 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 56. Walls 56, 56a define a capillary 58 therebetween. A wall 56 of one capillary assembly is spaced from an adjoining wall 561) 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 lo-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. Thelowered 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 theelectrostatic 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.
What I claim is:
l. 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 receivin surface, means to oad 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.
Q. 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.