US3289209A

US3289209A - Electrostatic matrix printer

Info

Publication number: US3289209A
Application number: US181661A
Authority: US
Inventors: Frederick A Schwertz; Paul F King
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1962-03-22
Filing date: 1962-03-22
Publication date: 1966-11-29
Anticipated expiration: 1983-11-29
Also published as: DE1447873A1; DE1447873B2; GB1018513A

Description

Nov. 29, 1966 F sc wERTz ET AL 3,289,209

ELECTROSTATIC MATRIX PRINTER Filed March 22, 1962 4 Sheets-Sheet 1 F/G. 1 INVENTORS FREDERICK A.SCHWERTZ PAUL F. KlNG .4 T TORNEY Nov. 29, 1966 F. A. SCHWERTZ ET L 3,

ELECTROSTATIC MATRIX PRINTER 4 Sheets-Sheet 2 Filed March 22, 1962 if R v H E M q U i T dv/ PM N W "L!" E I KL VA T Du R w w E Awfi Q C T 2/? 4 N i/\x L a I A A i R m w m DJ F/G. 2A

INVENTORS FREDERICK A. SCHWERTZ PAUL F. KING ATTORNEV Nov. 29, 1966 F. A. SCHWERTZ ET AL 3,289,209

ELECTROSTATIC MATRIX PRINTER Filed March 22, 1962 4 Sheets-Sheet 5 lim 3/ 3/1" 3/ i/43 L2 ll I hli Ix I IIM \:":b. k K\ HIV i l fid/ INVENTORS FREDERICK A. SCHWERTZ PAUL F. KING A T'TOPNEY Nov. 29, 1966 scHw -rz ET AL 3,289,209

ELECTROSTATIC MATRIX PRINTER Filed March 22, 1962 4 Sheets-Sheet 4 DEVELOPMENT MECHANISM I L 57 I/ FUSER FIG. 8

INV'ENTORS F/G. 7 FREDERICK A. SCHWERTZ PAUL F. KING A T TORNEY United States Patent O 3,289,209 ELECTROSTATIC MATRIX PRINTER Frederick A. Schwertz, Pittsford, and Paul F. King,

Webster, N.Y., assignors to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed Mar. 22, 1962, Ser. No. 181,661 13 Claims. (Cl. 346--74) The present invention relates to the art of electrostatic visual recording or printing, and particularly to the selective production of complex characters, such as alphanumeric symbols, by electrostatic processes.

Electrostatic printing or visual recording may be generally characterized as involving a pair of closely spaced opposed electrodes across which an electric potential is selectively applied, sufiicient to ionize the air, gas, or other fluid therebetween. An insulating web or sheet is passed between these electrodes, and when the electrodes are energized an electrostatic charge is formed on the web or sheet in electrode configuration on the area between the energized electrodes. In this manner, as the dielectric web or sheet is passed between the electrodes, a charge pattern is formed on the dielectric material in accordance with the presence, absence, or intensity of the ionizing potential applied across the electrodes. This charge pattern, or electrostatic latent image, may then be developed into visual form by the application to the web or sheet of an electroscopic powder, which adheres in conformance with the charge pattern. The resultant developed image may, if desired, be converted into a permanent record by, for example, the application of heat, if either the dielectric web or the powder is heat softenable, or by coating the image bearing surface of the web with a fixative, or by softening the web and/ or the powder with a solvent vapor. Also, where desired, the developed image may, before being fixed, be transferred from the dielectric web to another record sheet, by such means as a further electrostatic transfer, or by a tacky adhesive material, and then fixed on the record sheet by any of the exemplary means above indicated.

The present invention contemplates using a composite matrix electrode on a first side of the printing or ionization gap. This electrode contains a number of conductive portions which may be pins, bars, etc., each conductive portion being electrically insulated from all of the others. Opposed to this electrode on the other or second side of the printing or ionization gap is a composite shaped backing electrode. This backing electrode is made up of continuous conductive members such as bars which form all of the characters to be printed. These characters are superimposed upon each other so that the vertical bar of an L would also be the vertical bar for the E and the R. Since thisbacking electrode is continuous all of its conductive portions are electrically connected together. Thus, the discontinuous electrode on the first side of the gap allows for character selection by activation of selected electrode portions, and the shaped continuous backing electrode closes up discontinuities and smoothes irregular characters by causing the ionization paths to conform to its shape.

It is accordingly an object of the present invention to provide for the electrostatic printing or visual recording of complex characters or symbols.

Another object of the present invention is to provide for the electrostatic printing or visual recording of all the elements of a complex symbol, such as an alpha-numeric character, by selective energization of desired portions of the composite electrodes.

Other objects and advantage of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of exice emplary embodiments of the invention, had in conjunction with the accompanying drawings, in which like numerals refer to like or corresponding parts, and wherein:

FIG. 1 is illustrative of a bar matrix electrode electrostatic printing system;

FIG. 1A is a cross-sectional view of the powder-cloud developer shown in FIG. 1, taken along the line 1A1A of FIG. 1;

FIG. 2 is a perspective view of one bar composite electrode embodiment, together with an illustrative sample of the lettering obtained therefrom when used with a composite continuous backing electrode;

FIG. 2A is a perspective view of another bar composite electrode embodiment, together with an illustrative sample of the lettering obtained therefrom when used with a composite continuous backing electrode;

FIG. 3 is an example of printing from an ordinary dot matrix printer;

FIG. 4 is a cross-sectional illustration of the relationship of and ionization discharge path between a bar composite electrode, a backing electrode, and a dielectric web therebetween;

FIG. 5 is a cross-sectional illustration of a modified relationship of a bar composite electrode, a backing electrode, and a dielectric bar therebetween;

FIG. 6 is a cross-sectional illustration of a modified combination of composite discharge and composite backing electrodes, illustrating the relationship and the ionization discharge path therebetween; and

FIGS. 7 and 8 illustrate a modified system for practicing the present invention.

Referring to FIG. 1, a general organization of a system for practicing the electrostatic printing is illustrated. Operation of the system and selection of alphanumeric characters to be printed are effected by the keyboard and control matrix box 10, having a power source 11, character keys 12, a spacer key 12a, and an output cable 13. Control box 10, also has a mechanical drive shaft output 21, operating through a gear linkage 22 to drive the feed rollers 23.

The character keys 12 control the alphanumeric images produced on web 15 through selective energization of desired areas of composite electrode 14, as will be subsequently described. At the same time, with each operation of a character key 12, or spacer bar 12a, the

mechanical drive mechanism

21, 22 is stepped to cause feed rollers 23 to advance the web 15 one character space in the direction indicated by the web advance arrow. Thus, in the process of printing or recording successive alphanumeric characters on web 15, this web is advanced from a supply roll 15a, through successive stages of electrostatic image charging by the composite electrode 14 and backing electrode 16, development of the electrostatic image into visual form by powder-cloud developer 17 (described in detail subsequently), fixing of the developed image by fuser 18 which may be a simple electrical heater, to the take-up roll 15b, where the permanent visual record indictated at 15c may be stored.

Although a mechanical drive 22 and a short output cable 13 are shown for illustrative purposes it should be made clear that the connection from the keyboard to the printer and its web feeder may be made via radio link, long distance telephone cable, microwave or the like.

For short to medium distances a selsyn drive might also be used for web feeding.

In order that the web 15 may obtain and retain an electrostatic latent image from the ionization discharge pattern obtained from

electrodes

14 and 16, it must be formed from an insulating material, as for example a non-conducting plastic or the like such as Mylar, or it may be a laminated web, formed by coating a paper backing with an insulating plastic or the like.

Considering more particularly the formation of the electrostatic latent image of alphanumeric characters on the web by means of the

electrodes

14 and 16, and the selective electrode area ene-rgization by control box 10, reference is had first to FIG. 2. FIG. 2 depicts one exemplary embodiment of a bar composite electrode generally denoted by the numeral 30, together with exemplary alphanumeric characters that may be composed from this composite electrode. The electrode is formed as a support or base of electrically insulating material 32, one surface of which is inlaid with a plurality of electrically conducting bars 31, to form the bar pattern or composite illustrated in FIG. 2. This composite includes all the lines necessary to compose any letter of the Roman alphabet, or any Arabic numeral. Thus, by appropriate selection of the bars 31, any alphanumeric character can be composed. Each bar 31, or each bar segment, that may be individually required in composing any of the alphanumeric characters, is electrically insulated from all other such bars or segments by the support or base material 32. It is apparent that electrical insulation between two intersecting bars or segments 31 can be effected by making both such segments discontinuous at the intersection, or by making one such bar or segment discontinuous at the intersection and providing a jumper on the back for connecting the discontinuous segments if desired, or by placing an insulating coating over the intersecting area of one bar to insulate it from the second bar which is placed over the insulating coating.

Each electrically insulated bar or segment 31 that may be individually required in composing any of the alphanumeric characters is coupled to an individual one of the leads 24 from cable 13, so that when a connection is made between such lead and the potential source 11, through operation of the keys in control box 10, a discharge potential is established on the particular bar segment to create a corresponding electrostatic charge pattern on the web 15. The control box 10 houses preferably an electrical switch matrix, operated by the keys 12, each key thereby constituting a compound switch operator. tween source 11 and those prescribed bars 31 which make up the letter or numeral designated by the key. For example, by depressing key 12b, contact is established between source 11 and each of those leads 24 which connect with the bar segments designated 31a in FIG. 2, delineating the character T. Similarly by depressing key 12c, the bars 31b are energized with an ionizing potential from source 11 to delineate the character V. The word Xerox in the printing example shows how the word appears when the matrix is used in conjunction with an ordinary fiat backing electrode while the words Tesi printer show how printing is improved using the shaped backing electrode technique described below in connection with FIGURE 6. The nature of the switch matrix in control box 10 is well known and understood in the art, and therefore the present description need not be rendered unnecessarily complex by a showing and description thereof. Also, as is appreciated by those skilled in the art, other well known selection matrices may be employed, such as diode and magnetic core matrices.

In FIG. 2A an alternate form of bar composite electrode is shown and designated generally by the numeral 35, along with an illustration of the alphanumeric characters obtained from this electrode. As in the case of electrode 30, the several 'bar segments 36 are insulated from each other and embedded in an insulating carrier block 37 to be selectively energized by source 11 through control box 10 and leads 24. This figure also illustrates before and after printing results similar to those of FIG. 2.

FIGURE 3 illustrates the printing obtained from an Thus, each key 12 operates to make contact bea alternate form of composite electrode, namely a dot composite electrode. This type of electrode is made up of a number of closely spaced, protruding, conductive pins embedded in an insulating base, By actuating selected pins in this pin matrix any letter, number or other arbitrary symbol may be printed. As illustrated the quality of this type of printing is rather crude with a 5 x 7 pin matrix and a flat backing electrode and as such is only suitable for rough applications such as address label printing.

FIGS. 4 and 5 are enlarged detailed cross-sectional views of the spaced bar composite electrode 14, either in the form of 30 or 35, the backing electrode 16, with the web 15 passing therebetween. In these figures the web 15 is shown as comprising a paper base 41 having a thin plastic coating 42 on one face thereof, this plastic coating being formed from a material of high dielectric properties, such as Mylar. In FIG. 4, the web 15 is shown with the paper surface 41 against the composite electrode 14, and the plastic surface facing but spaced slightly from the backing electrode 16. As illustrated by dotted lines, energization of selected

bar electrode segments

31 or 36 causes localized ionization of the air gap 43 between the energized bar electrodes and the backing electrode, resulting in an establishment of a corresponding electrostatic charge pattern on the plastic surface 42 of web 15. FIG. 5 is similar to FIG. 4, except the relation of the web 15 to the electrodes is reversed. That is, the web 15 is oriented with its paper surface 41 in contact with the backing electrode 16, and its dielectric plastic surface 42 slightly spaced from and facing the composite electrode 14. In this embodiment, as in the case of the preceding embodiment, selective energization of the

bars

31 or 36 causes corresponding localized ionization of the air gap 43, and consequent establishment of a corresponding electrostatic charge pattern on the web surface 42.

With any alphanumeric character composite pattern or matrix, one does not obtain truly conventional character configurations, but owing to limitations of bar designs, especially to discontinuities in these matrices, not all characters can be represented with true roundness where appropriate, nor can all lines be fully continuous where appropriate. To improve the configurations of the alphanumeric characters a continuous shaped backing electrode is used. In FIG. 6 there is illustrated an electrode pair utilizing a dot composite or dot matrix electrode 46 similar to that used to produce the FIGURE 3 printing and a bar matrix backing electrode 45'. In this embodiment, the bar pattern for backing electrode 45 may be of the same shape as either FIG. 2 or FIG. 3, except that the bar segments are all electrically continuous with no breaks appearing in their surfaces. Each of the pins 47 going to make up the dot composite electrode 46 are electrically insulated from each other by the base 48 of insulating material, and are separately energized by source 11 through control box 10 and leads 24. As with the bar composite electrodes of the preceding embodiments, a separate lead 24 is connected to each pin 47. By the switch matrix in control box 10, selected pins 47 are energized to delineate that alphanumeric character represented by the particular key 12 that is operated. Since the discharge takes place between the bars of the bar matrix and the corresponding selected pins of the pin matrix which form the desired character, the line structure of the bar backing electrode 45 serves to bridge the space from one energized pin to the next, and in fact, as shown by the dotted line discharge paths in FIG. 6, the charge patterns are shifted somewhat to appear on the web 15 in locations intermediate the pin and bar positions, thereby improving the appearance of the characters. A backing electrode with electrically continuous bar segments is also used opposite a bar composite electrode with electrically separated segment so as to make the lines of the printed characters smooth and continuous, by partially shifting discharge paths and the esulting charge patterns. It should also be noted that when a bar matrix and a shaped bar backing electrode are used opposite each other they may be of slightly different form. For example, the 'bar matrix electrode of FIGURE 2 might be used as the printing electrode and the electrode of FIGURE 2A (with its discontinuities closed) could be used as the backing electrode. As in the preceding embodiments the web 15 of paper backing 41 and plastic dielectric coating 42 passes between the

electrodes

45 and 46, with the paper backing in contact with one electrode, pin composite electrode 46 for example, and with the dielectric coating facing and slightly spaced from the other elect-rode, bar backing electrode 45 for example.

Previously, it had been necessary to use alphanumeric character cylinders rotating at very high speeds and complex pulsing circuitry to get good character quality along with high speed in electrostatic printing since stationary matrix electrodes produced discontinuous jagged looking characters.

With reference to FIGS. 7 and 8, there is presented a system for transducing the electrical output of control box 10 of FIG. 1 into a visual record. The system shown in FIGS. 7 and 8 is basically similar to that shown in FIG. 1, but some of the components are varied and in some respects are shown in greater detail. The thin electrically insulating web drawn from supply roll 15a may be a plastic film, such as polyethylene terephthalate (Mylar), polystyrene, cellulose acetate, ethyl celluose, or like sheet material of good insulating properties, and preferably of the order of one or two mils thick; or it may be of paper coated on the working surface with one of these plastics, or with a wax; or in some instances thoroughlydry paper or cellophane can be used. As the web 15 is drawn from its supply roll, it first passes through a preliminary charging device 51, where the web is brought to a uniform state of electrostatic charge. From the preliminary charger, the web is then passed between the composite electrode 14 adjacent one surface of the web, and the ground plate or backing electrode 16 adjacent the opposite surface, where an electrostatic charge pattern depicting the desired alphanumeric characters is adduced on the web. The web then enters a development mechanism 56, where the electrostatic charge pattern on the web is rendered visible by the selective application of a finely divided material, such as electroscopic powder, or a liquid ink, or like material. As the web emerges from the developer, the intelligence carried thereon is visually intelligible. Where a permanent record of the intelligence is desired, the web is then passed to fuser 57, where the powder is permanently fused to the web, or the ink is dried. As is apparent, if only a transistory presentation of the intelligence is desired, the fuser may be omitted, and instead of a fresh web supply roll, the web may be in the form of an endless belt, with means interposed between the developer 56 and the preliminary charger 51, on the return side, to clean the intelligence off the web.

The purpose of preliminary charger 51 is to establish over the web a uniform electrostatic charge preparatory to receiving the intelligence charge pattern. Charger 51 comprises a housing within which is located an electrode 52 coated with a radioactive source of ionizing particles, such as a polonium layer, which faces one surface of the web. The opposite surface of the web 15 is contacted by a ground plate 54, while voltage source as tapped by a potentiometer 55 is connected to the electrode 52.. The potentiometer 55 is center-tapped to ground, and the battery of voltage source 53 is preferably one hundred to several hundred volts. By varying the potentiometer setting, one can thus establish a field of either polarity and of adjustable intensity between electrode 52 and web 15.

The alpha or other ionizing particles emitted by the radioactive layer on electrode 52 produces ionization of the air in the chamber 51 into negative and positive ions, and these ions migrate in opposite directions, depending on their polarity, under the influence of the electrostatic field existing between electrode 52 and plate 54. As ions of one polarity deposit their charge on Web 15, the field becomes altered by the charge on the web until a state of equilibrium is reached, in which the potential of the web surface is equal to the potential applied to electrode 28 by the potentiometer. Whether a small positive potential or negative potential is applied to the Web, as controlled by the setting of the potentiometer tap, depends on factors subsequently considered. In some instances the electrode 28 may be held at ground potential, in which case the device merely serves to remove incidentally acquired electrostatic charges from the web in preparation for receiving the electrostatic intelligence charge pattern. Instead of a radioactive source of ionizing particles, the electrostatic charges may be supplied by corona emission as disclosed, for example, in U.S. 2,588,699 to C. F. Carlson.

With the web 15 thus prepared, it passes between composite electrode 14 and ground or backing electrode or plate 16. The backing plate 16 is preferably a fiat plate coextensive with the working surface of electrode 14. The web is preferably held in contact with the base or backing plate 16, but spaced by a very small gap, of the order of 2-3 mils, from the composite electrode 14. Under these conditions, and using a potential difference of about 750 volts between backing plate 16 and electrode 14, a silent or field discharge occurs between the energized electrode 14 and the surface of the web, establishing a controllable and localized electrostatic charge on the web opposite the energized areas of discharge electrode 14. The polarity of electrostatic charge on the web is, of course, determined by the polarity of the discharge electrode.

The web 15 now carrying a character image in electrostatic charge form, passes into the developer 56, shown in detail in FIG. 8. This device comprises a pair of

rollers

60 and 65. Roller 60 includes a central bearing shaft 64 carrying a pair of axially spaced disks 62 over which the web edge peripheries pass. Flanges 61 confine the web in place on disks 62. The web and disks 62 thus form a hopper in which a supply of electroscopic powder 53 is contained. It is preferable, although not necessary, that the powder 63 be charged by triboelectric or other means to carry an electrostatic charge opposite from that established on the web by the discharge electrode 14. The powder adheres in the areas charged by electrode 14, to produce a visible presentation of the characters carried by the web. As the powder 63 is tumbled over the web 15, if the initial preliminary charging of the web at 51 is of a polarity opposite from that at the electrode 14, then this background charge on the web is of the same polarity as the charged powder, and assists in repelling the developer powder from this background area. After being developed, the web passes from roller 60 up over roller 65', and down into fuser 57. In fuser 57 the web passes about roller 58 where it is heated to a temperature su fficient to fuse the developer to dry the ink thereon, thus forming a permanent visual and directly readable record of' the characters transduced at electrode 18. The web may then pass between suitable drive rolls such as 80. Controlled by a suitable step drive related to key operation of a control box, such as 10 in FIG. 1.

The described method of rendering the pattern of electrostatic charges visible, i.e., developing the image, is known as loop development. This system is disclosed in U.S. 2,761,416 to C. F. Carlson. The method of development is not critical in the instant invention and other methods for contacting electrostatically charged marking particles with the electrostatic latent image may be used. Thus, a spray of electrostatically charged liquid droplets on dry powder particles, as disclosed in U.S. 2,784,109 to L. E. Walkup may be used or magnetic brush development described in U.S. 2,791,949 to Simons and Saul are all operable. A powder cloud development apparatus particularly suited for use as element 17 of FIG. 1 is the device known as a slot development apparatus more particularly described in US. Patent 2,815,734 to C. F. Carlson. As can be seen in FIG. 1A the device includes a chamber running the width of image member 15 and formed by walls 5, the chamber being divided into an entrance chamber 3 and an exit chamber 4 by conductive electrode 6 which is positioned under aperture 9 in walls 5 directly opposite in close spaced relationship to Web 15. The distance between web 15 and electrode 6 is no more than about Ai-inch and desirably is no more than about 4 -inch. At these spacings electrode 6 draws the lines of force of the electrostatic image externally above the surface of member 15. Electr-ostatically charged marking particles as from a powder cloud generator enter chamber 3 through entrance means 7 and are channelled by walls to flow around electrode 6 into chamber 4 and thence through exit means 8 to a collecting box, or other disposal means. While passing through space 9, the particles are attracted to the electrostatic image and deposit thereon to render an accurate, visible reproduction thereof all as more fully and completely described in the said application of C. F. Carlson. The choice of the particular developing process or apparatus would be dependent on the combination and design limitations imposed in assembling the machine for a particular operation.

Similarly, the means of permanently afiixing the powder image to the backing material is not critical in the instant invention. Thus, if no permanent image is desired, after examination of the web, the loosely adhering powder image may be wiped off as by swabbing with cotton and the web reused. If a permanent record is desired, the powder particles may be rendered adherent to the backing material by heating, as previously disclosed herein, by contacting the powder-bearing sheet with the vapors of a solvent for the marking particles or for a resin coating on the image receiving web member as disclosed for example in US. 2,776,907 to C. F. Carlson. Where liquid droplets are used, the absorption of .the liquid into the capillaries of the backing member or an evaporation of the liquid would serve to affix the image to the image receiving sheet. Other means of afiixing the powder image, as by the use of pressure, by spraying with a fixative liquid, etc., also may be used if desired.

A number of interrelated factors determine the quality of reproduction obtainable in the instant device. One of these elements is the gap spacing, that is, the distance between the recording Web member and the discharge electrode. The electrode may be designed so that the discharge surfaces are flush with the outer surface of its housing. This permits rigidity of construction for fine electrodes and accurate spacing of the gap without affecting the efiiciency of electrostatic transfer. In general, it has been found that the electrostatic potential required for charge to transfer across an air gap is dependent on the width of. the gap for any given electrostatic system. This potential reaches a minimum in the neighborhood of a particular spacing which is gene-rally in the range of 10 to 30 microns. For shorter gaps the voltage required for charge transfer increases asymptomatically so that at spacings of about 2 microns charge transfer becomes virtual-ly impossible in any practicable system. As the air gap increases, the potential required for charge transfer also increases but at a more gradual rate than when the gap is decreased in width from this minimum value. However, increasing gap width results in spreading and loss of resolution of the electrostatic image transferred to the transfer member. In general, spacings of from about 5 to 150 microns may be used with a particular preferred range of gap width being from about microns to about 100 microns. Shorter spacings place additional and unnecessary strain on the mechanical design of the system to assure the reliability of gap spacing and increase the voltage required for reliable electrostatic transfer. The practical limit on the upper side for the gap spacing is largely determined by the image quality desired. The spacings given herein are practical limitations for obtaining good quality reproduction.

The minimum potential required to obtain charge transfer across an air gap will be slightly greater than the breakdown potential of air for the air gap used. In general, the determining factor is the relationship of the capacitance of the transfer member compared to the capacitance of the discharge electrode to ground. Representative values required to initiate charge transfer are within the range of 600 to 1,000 volts. In order to simplify the design of the electrode energizing circuitry, a bias may be applied to the air gap by placing a constant DC. potential between the backing electrode 16 and the composite electrode 14, which voltage is close to but insuflicient in magnitude to initiate charge transfer. The use of a bias has the disadvantage of sweeping ions from the gap so that when the pulse is applied it must be of greater magnitude than simple addition to the bias potential would indicate if reliability of discharge is to be assured for short pulses.

Only the voltage over that required to initiate breakdown is transferred across the gap. Thus, if the air breakdown potential is -800 volts and a potential of 1,000 volts is applied to the gap, only about 200 volts is transferred.

A second factor affecting discharge is the width of the pulse applied to the discharge electrode. Increasing the magnitude of the applied voltage improves reliability. However, care must be taken not to transfer excessive charge to the transfer member as Lichtenberg figures appear in the developed image with positive polarity image. Lichtenbe'rg figures are due to the inability of the surface of the transfer member to sustain the lateral potential gradient. Breakdown, therefore, occurs on the recording surface and the charge spreads laterally. On development, this spreading of charge manifests itself in image deformities referred to as Lichtenberg figures, or treeing. For discharge potentials of 10 microseconds or longer duration, breakdown occurs fairly reliably. Down to about 5 microseconds, there is a decrease in reliability but the system still operates satisfactorily. As the time duration of the application of a discharge potential decreases below this value, reliability drastically falls off. The electrostatic discharge itself takes at least about 0.01 microsecond and this sets a definite lower limit on duration of potential application. It has been observed that negative voltages permit the use of significantly higher voltages Without treeing than if positive voltages are used, however excessively high negative voltages result in excessive image spreading.

It is advisable to use discharge voltages of far greater magnitude than is required to transfer the minimum charge sufficient to give powder images of adequate density. Thus, depending on the development system used, a potential of 50 volts or less will give a readable image. However, in practical operation of the system, excellent results are obtained using a bias on an micron air gap of -1,000 volts with discharge voltage pulses of ---500 volts. For short pulses (2 microseconds or less) a pulse voltage of -1,000 has been used without objectionable deterioration in image quality.

Reliability of discharge on application of the discharge voltage can be further improved by increasing humidity in the air gap or increasing the number of ions in the air gap. The breakdown of the air gap by a short duration discharge voltage is, of course, dependent on the statistical fluctuations of the quantity of charge carriers in the gap. Increasing the ambient ionization therefore increases the reliability of breakdown on the application of the short duration discharge voltage. One method of doing this is to irradiate the gap with ultraviolet light.

The output impedance of the circuit employed to pro- 9 vide the discharge voltage to the air gap is of particular importance; the lower the output impedance the greater the .reliability of image formation in the situation where electric fields of moderate strength are applied to the gap. For example, in the very simplest situation where the air gap is connected in series with a switch, a resistor, and a battery, image formation can be throttled through the use of a high impedance resistor. In general, the resistance should not be greater than about 100,000 ohms and it is preferred to have it as low as possible. The discharge electrode may be connected directly to 3+ in the output circuit wherein B+ acts as a partial bias on the air gap. If a blocking condenser is used in the discharge circuit, it must not be so small as to present an impedance high enough to throttle the discharge. Thus, for 2,000 volts on an 80 micron gap, the condenser in series with the electrode should be at least 40 micromicrofarads and preferably is 100. The use of a blocking condenser may also be helpful in preventing treeing. Where a bias is used, at least part of the bias potential should be applied to the backing electrode 16. It has been found that discharge is facilitated if neither the discharge nor backing electrode is grounded. An alternative method of biasing the gap is to apply a uniform electrostatic charge to the insulating web as shown in FIG. 7.

Finally, handling of the transfer or web member almost necessarily produces random electrostatic charges thereon due to a variety of causes such as triboelectrification, etc. Unless steps are taken to nullify these random charges, they will be developed to give spurious results interfering with the legibility of the desired information. Accordingly, it is desirable to provide suitable means for eliminating these charges. This can be done by a variety of means known to those skilled in the art, such as providing an AC. controlled corona discharge just prior to the passage of the transfer member or web through the charge transfer station between the

electrodes

14 and 16 shown in FIGS. 1 and 7.

While the invention has been discussed herein in terms of controlled electrostatic discharge across an air gap, it is understood that any type of gas may be used which is not corrosive under the conditions of use. Thus, nitrogen, argon, carbon dioxide, etc.,' may be use-d in the gap.

Although for the purpose of illustration the present embodiments of the invention have been shown and described with relation to a single discharge or composite electrode operating to produce a single line of characters, it is apparent that the web or the electrode may be shiftably mounted to produce plural successive lines of characters. Also, an array of a plurality of composite electrodes may be employed with appropriate commutating of the inputs thereto to enable production of plural successive lines of characters. Also, the present invention is not limited to keyboard operation as above described. The input to the system may be an electrical transmission, a magnetic or punched tape, or other medium or means, with the characters to be printed appropriately coded in the transmission or on the tape. This coded intelligence medium would then be designed to cooperate with a control matrix or the like to appropriately energize the composite electrode to translate and reproduce the coded characters in visual intelligible form.

Although it is presently thought that production of alphanumeric characters represents the most desirable field for the opeartion of the present invention, it is understood that it is not contemplated that this invention should be limited to such designations. For it will be apparent to those skilled in the art that various matrix or composite electrodes can be developed and the present invention applied to the production of all types of complex character designations.

From the foregoing illustrative specific embodiments, it will be appreciated that by the present invention there is provided a system for recording or printing complex characters, such as alphanumeric symbols. It is understood that the foregoing specific examples of the system are presented merely by way of example to facilitate a complete understanding of the present invention. Since various equivalents and modifications of the instant embodiments will be apparent to those skilled in the art, such as are within the spirit and scope of the appended claims are considered to be embraced by the present invention.

What is claimed is:

1. An electrostatic printing system comprising at least two spaced electrodes defining a gap therebetween, a recording member positioned in said gap and spaced from at least one of said electrodes, a first electrode on one side of said gap having a surface configuration comprising a plurality of electrically continuous bars arranged in a pattern adapted to compose any one of a plurality of complex symbols, a second electrode on the opposite side of said gap being a composite electrode having upon its discharge surface a plurality of electrically conducting members insulated from each other and arranged in a pattern adapted to compose any one of a plurality of complex symbols similar to the symbols composable by said first electrode, means for individually coupling each of said mutually insulated conducting members of said second electrode with a voltage source of suflicient magnitude to initiate an ionizing discharge across said gap, and control means cooperating with said coupling means to simultaneously couple selected ones of said mutually insulated conducting members of said second electrode to said potential source so as to initate discharge across said gap between said selected conducting members of said second electrode and corresponding portions of said electrically continuous electrode of said first electrode whereby a high resolution charge pattern representing all the components of at least one selected complex character are simultaneously formed on said recording member in a continuous and developable pleasing appearance.

2. A system according to claim 1 in which the recording member is in the form of a dielectric web and further including means to move said recording web through said electrode gap and means to develop said charge pattern by the deposition thereon of charged finely divided electroscopic material.

3. A system for electrostatic printing as set forth in claim 1 wherein said control means effects simultaneous potential application to pre-prugrammed groups of mutually insulated conductive members in said second electrode.

4. A system for electrostatic printing according to claim 2 further including means following said developing means in the path of recording Web advance for converting said visible pattern into permanent form on said recording web.

5. A system for electrostatic printing according to claim 1 in which said mutually insulated electrically conductive members in said second electrode are in the form of pins.

6. A system for electrostatic printing according to claim 1 in which said mutually insulated electrically conductive members of said second electrode have a surface in the plane of said electrode face.

7. An electrostaic printing electrode system comprising a pair of closely spaced electrode surfaces adapted to produce a gas ionizing discharge therebetween upon the application of a suitable voltage thereacross, one of said electrode surfaces having an electrically conductive matrix of electrically continuous bars arranged in a pattern adapted to compose a plurality of complex symbols, and the other of said electrode surfaces being a dot matrix of electrically conducting pins electrically insulated from each other and arranged in a pattern adapted to compose a plurality of complex symbols corresponding to the symbols composable from said first electrode surface.

8. An electrostatic printing electrode array as set forth in claim 7 and further including means for individually connecting eachof said pins in an electrical circuit with a discharge voltage source and said first electrode surface, and control means cooperating with the last mentioned means foreffecting simultaneous energization of a pluf rality of selected ones of said pins to induce an ionizing discharge between said energized pins and closely corresponding areas of said bar matrix surface.

9. Apparatus for the formation of shaped latent electrostatic images on a recording medium comprising at least one electrode on either side of said recording medium one of said electrodes being spaced slightly from said recording medium, said electrodes on both sides of said recording medium having opposing faces made up of conductive and non-conductive portions arranged so that two or more conductive portions of an electrode may be selected to compose any one or more of a plurality of characters, the conductive portions of the electrode on a first side of said web being electrically continuous bars arranged in a pattern adapted to compose any one of a plurality of complex symbols, the conductive portions of the electrode on the other side of said web being electrically separated, and means to apply a voltage across said electrically continuous electrode and selected conductive portions of said electrically discontinuous electrode, said voltage being of sufiicient magnitude to initiate an ionizing discharge across the gap between said electrodes.

10. Apparatus according to claim 9 including control means to apply said discharge initiating voltage simultaneously to pre-programmed groups of the conductive portions of said electrically discontinuous electrode.

11.. Apparatus according to claim 9 further including means to move said recording medium through the gap defined by said opposing electrodes.

12. Apparatus according to claim 11 further including means to develop the latent electrostatic images deposited on said recording medium by said electrodes comprising means to deposit charged finely divided electroscopic marking material on said recording media.

13. Apparatus according to claim 12 further including means to permanently fix said developed images on said recording media.

References Cited by the Examiner UNITED STATES PATENTS 2,951,121 8/1960 Conrad 17830 2,997,361 8/1961 Christopherson et al. 178-30 3,012,839 12/1961 Epstein et a1. 178-30 3,066,298 11/1962 McNaney 346-74 BERNARD KONICK, Primary Examiner.

IRVING SRAGOW, Examiner.

M. K. KIRK, J. BREIMAYER, Assistant Examiners.

Claims

1. AN ELECTROSTATIC PRINTING SYSTEM COMPRISING AT LEAST TWO SPACED ELECTRODES DEFINING A GAP THEREBETWEEN, A RECORDING MEMBER POSITIONED IN SAID GAP AND SPACED FROM AT LEAST ONE OF SAID ELECTRODES, A FIRST ELECTRODE ON ONE SIDE OF SAID GAP HAVING A SURFACE CONFIGURATION COMPRISING A PLURALITY OF ELECTRICALLY CONTINUOUS BARS ARRANGED IN A PATTERN ADAPTED TO COMPOSE ANY ONE OF A PLURALITY OF COMPLEX SYMBOLS, A SECOND ELECTRODE ON THE OPPOSITE SIDE OF SAID GAP BEING A COMPOSITE ELECTRODE HAVING UPON ITS DISCHARGE SURFACE A PLURALITY OF ELECTRICALLY CONDUCTING MEMBERS INSULATED FROM EACH OTHER AND ARRANGED IN A PATTERN ADAPTED TO COMPOSE ANY ONE OF A PLURALITY OF COMPLEX SYMBOLS SIMILAR TO THE SYMBOLS COMPOSABLE BY SAID FIRST ELECTRODE, MEANS FOR INDIVIDUALLY COUPLING EACH OF SAID MUTUALLY INSULATED CONDUCTING MEMBERS OF SAID SECOND ELECTRODE WITH A VOLTAGE SOURCE OF SUFFICIENT MAGNITUDE TO INITIATE AN IONIZING DISCHARGE ACROSS SAID GAP, AND CONTROL MEANS COOPERATING WITH SAID COUPLING MEANS TO SIMULTANEOUSLY COUPLE SELECTED ONES OF SAID MUTUALLY INSULATED CONDUCTING MEMBERS OF SAID SECOND ELECTRODE TO SAID POTENTIAL SOURCE SO AS TO INITATE DISCHARGE ACROSS SAID GAP BETWEEN SAID SELECTED CONDUCTING MEMBERS OF SAID SECOND ELECTRODE AND CORRESPONDING PORTIONS OF SAID ELECTRICALLY CONTINUOUS ELECTRODE OF SAID FIRST ELECTRODE WHEREBY A HIGH RESOLUTION CHARGE PATTERN REPRESENTING ALL THE COMPONENTS OF AT LEAST ONE SELECTED COMPLEX CHARACTER ARE SIMULTANEOUSLY FORMED ON SAID RECORDING MEMBER IN A CONTINUOUS AND DEVELOPABLE PLEASING APPEARANCE.