US3766850A

US3766850A - Developing means for electrostatic printing apparatus

Info

Publication number: US3766850A
Application number: US00214111A
Authority: US
Inventors: M Silverberg
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1971-12-30
Filing date: 1971-12-30
Publication date: 1973-10-23
Anticipated expiration: 1990-10-23
Also published as: DE2252604A1; GB1415325A; JPS4874851A; FR2170630A5; SE381110B; NL7216153A; CA972551A; IT973318B

Abstract

Printing apparatus is disclosed in accordance with the teachings of the present invention wherein a plurality of applicators capable of retaining electrostatic developer particles are mounted in spaced relationship on movable support means such that said applicators sequentially contact an electrostatic latent image to deposit said electrostatic developer particles thereon. In an exemplary embodiment of the present invention the movable support means comprises an endless belt movable about a plurality of cylinder means.

Description

United. States Patent [1 1 Silverberg 1 Oct. 23, 11973 DEVELOPING MEANS FOR ELECTROSTATEC PRINTING APPARATUS [75] Inventor: Morton Silverberg, Rochester, N.Y.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

221 Filed: Dec. 30, 1971 211 Appl. No.: 214,111

[52] U.S. Cl ..101/1,101/DIG.13,117/17.5, 118/637, 346/74 ES [51] Int. Cl BOS b 5/00 [58] Field of Search 101/D1G. 13, 1; 118/637, DIG. 23; 117/175; 346/74 ES [56] References Cited UNITED STATES PATENTS 2,890,968 6/1959 Giaimo l01/D1G. 13 2,985,135 5/1961 Hickerson... 3,140,199 7/1964 York 3,251,706 5/1966 Walkup 10l/D1G. 13 3,288,605 11/1966 Macklem 118/637 X 3,357,349 12/1967 Decker et a1. 10l/D1G. 13 3,372,027 3/1968 Gundlach et 211.. 118/637 X 3,595,208 7/1971 Koizumi 118/637 Primary Examiner-Edgar S. Burr Att0meyJames J. Ralabate et a1.

[57] ABSTRACT Printing apparatus is disclosed in accordance with the teachings of the present invention wherein a plurality of applicators capable of retaining electrostatic developer particles are mounted in spaced relationship on movable support means such that said applicators sequentially contact an electrostatic latent image to deposit said electrostatic developer particles thereon. In an exemplary embodiment of the present invention the movable support means comprises an endless belt movable about a plurality of cylinder means.

5 Claims, 2 Drawing Figures DEVELOPING MEANS FOR ELECTROSTATIC PRINTING APPARATUS This invention relates to printing apparatus and in particular to apparatus for developing an electrostatic latent image. A description of similar apparatus is disclosed in co-pending application Ser. No; 214,300 filed on Dec. 30, 1971 by Howard Ring and assigned to Xerox Corporation, the assignee of the instant invention.

In the printing arts, one of the major categories of printing apparatus that has been developed may be classified as impact printers. Conventional impact printers require hammer means to strike a selected character embodied in a character matrix, which selected character is forced into-contact with a recording medium, thereby printing a character. Impact printing techniques are exemplified by slow speed, shock and vibration caused by hammer movement, and excessive wear on the mechanical components. Nevertheless impact printers are widely utilized in conventional keyboard actuated printing devices such as typewriters, teletypewriters, computer read-in and read-out devices, calculating machines, line printers, and the like.

In recent years a new technique of printing has been developed wherein a character pattern of electrostatic charges is deposited upon a medium to form an electrostatic latent image which electrostatic latent image is developed by the deposition of developer particles thereon. This technique is embodied in the commercial process known as electrophotography wherein the aforementioned electrostatic latent image is produced byselectively dissipating a uniform layer of electro static charges by imaging modulated radiant energy thereon. Electrophotography has been utilized in document, reproducing machines such as that described in U .S. Pat. No. 3,301,126 which issued to R. F. Osborne et al. on Jan. 31, 19 67 and assigned to Xerox'Corporation, the assignee of the present invention. Electrophotography has also been utilized in photoprinting systems such as described in U.S. Pat.,'application Ser. No. 887,666 filed. on Dec. 23, 1969. 1

The" aforementioned printing technique hasfound application in electrog raphy systems wherein the electrostaticcharges are deposited on a recording medium by conductive, electrically biased electrodes or styli. Electrography systems have been utilized as high speed computer read-out devices, teletypewriter receivers, facsimile receivers, and the like.

An attendant disadvantage of prior art electrostatic printing systems such as electrophotographic photoprinting systems and conventional electrography systems is the inability ofan operator to visually perceive a character immediately, after the recording thereof. The apparatus heretofore utilized by the prior art for developing an electrostatic latent'image obstructs the field of view of an operator during the developing process such that an entire line or a plurality of lines of images must be developed before visual examination thereof is obtained. Accordingly, an operator of a keyboard actuated electrostatic printing device will not be cognizant of errors, such as typographical errors, until well after such errors are committed and the character is recorded. The delay between the recording of information and detecting same tends to limit the speed at which characters are recorded, resulting in inefficient operation of such electrostatic printing devices. This has been a critical factor in attenuating enthusiastic reception of keyboard actuated electrostatic printing devices that may be utilized as typewriters, teletypewriter transmitters, computer input terminals, and the like.

Therefore, it is an object of the present invention to provide apparatus for developing an electrostatic latent image. It is another object of the present invention to provide apparatus for recording characters on a print receiving surface wherein each character may be visually examined immediately after the recording thereof.

It is a furtherobject of this invention to provide apparatus for use in an electrostatic printing device wherein a character pattern comprised of electrostatic charges is viewed immediately after the development thereof.

Yet another object of this invention is to provide printing apparatus operable at relatively high speeds which permits immediate visual detection of a printed character.

' A still further object of the present invention is to provide apparatus for developing and viewing an electrostatic charge pattern.

, There are other objects and advantages of the invention which will become clear from the following detailed description of exemplary embodiments thereof and the novel features will be particularly pointed out in connection with the appended claims.

In accordance with this invention, apparatus for developing an electrostatic latent image is provided wherein a plurality of applicators capable of retaining electrostatic developer particles are mounted in spaced relationship on movable support means such that said applicators sequentially contact the electrostatic latent image to deposit said electrostatic developer particles thereon. An exemplary embodiment contemplates the use of an endless belt movable about a plurality of cylinder means as a movable support means.

The present invention may be utilized with anelectrophotographic device such as a document reproducing device, wherein electrostatic latent images are formed by imaging modulated radiant energy onto a charged surface. The present invention may also be utilized with electrographic devices wherein said electrostatic latent images are formed by selectively energizing electrode means disposed in the vicinity of a dielectric surface. The electrostatic printing devices with which the present invention may be utilized are adapted to be controlled by any convenient source of data such as an actuatable keyboard, an original document to be reproduced, a digital computer or the like.

The invention'will be more clearly understood by reference to the following detailed description of exemplary embodiments thereof in conjunction with the ac-' 'companying drawings in which;

FIG. 1 is a perspective view of one embodiment of the present invention; and

FIG. 2 is a perspective view of the present invention as utilized with an electrographic device.

Referring now to the drawings wherein like reference numerals are used throughout, and in particular to FIG. 1, there is, illustrated a perspective view of apparatus for developing and viewing an electrostatic latent image comprising movable support means Eli and applicators l2 l4 and 17. Movable support means 111 comprises an endless belt deployed about cylinder means t5 and 16 and movable in the direction indicated by the arrow A. Accordingly, a source of motive power, not shown, may be provided to drive cylinder means and 16. The applicators, four of which are identified by reference characters l2, l3, lid and ll'i', are mounted on the surface of endless belt ill by suitable fastening means such as cement. Each of applicators l2, l3, l4 and l7 is capable of retaining conven tional electrostatic developer particles that may be applied thereto. Such electrostatic developer particles are known as toner particles and are adapted to exhibit an electrostatic charge. The toner particles may exhibit a positive or negative charge for a purpose soon to be described. Those of ordinary skill in the art will recognize that such toner particles may consist of a pigmented resinous powder. Alternatively the toner particles may be dispersed in an insulating liquid.

The applicators l2, l3, l4 and ll? are preferably comprised of fibrous brushes which may be made from materials such as natural fur (beaver, rabbit or the like) or other materials described in U.S. Pat. No. 3,251,706 which issued to L. E. Walkup on May 17, 1966 and assigned to Xerox Corporation. l-ience, triboelectric attraction is maintained between the applicators and the electrostatic developer particles. The applicators are mounted such that substantially equal spaces are defined between successive applicators. The particular shape of each applicator is not critical per se; however, it is desirable that the fibers included in each applicator extend in a direction parallel to the surface of endless belt l 1 such that the terminal points of the fibers define a plane substantially perpendicular to the surface of the endless belt M. It is noted that the fibers must be capable of engaging in intimate contact with an electrostatic latent image to be developed. Accordingly, applicator 12 includes fibers ll2ll extending from the surface 122 of the applicator. Similarly applicator 13 includes fibers ll3ll extending from the surface H32 of the applicator. Hence, each applicator has a working, or operating, surface that is substantially normal to the surface of endless belt ill.

The developing apparatus illustrated in FIG. 1 is adapted to be supplied with electrostatic developer particles and to deposit said particles on an electrostatic charge pattern to thereby produce a visible image. The electrostatic charge pattern may be carried by a suitable print receiving surface such as a conventional electrophotographic member or an insulating recording medium to be described in detail below.

in operation, the applicators are transported to a source of electrostatic developer particles, which source may be located for example in the vicinity of the lower portion of the endless belt ill. The electrostatic developer particles supplied by the source are retained by the fibers of each applicator in accordance with triboelectric attraction. The applicator thus loaded with electrostatic developer particles are transported to the upper portion of endless belt lll whereupon the fibers or operating surface of the applicators linearly scan the surface of a print receiving surface. When the fibers contact an electrostatic charge pattern the electrostatic developer particles retained by the applicators are removed therefrom and deposited on the charge pattern. it is understood that successive traversals of the electrostatic charge pattern by the applicators mounted on endless belt lll tend to ensure an adequately developed image. After sweeping across a line on the print receiving surface, the applicators are again transported to the source of electrostatic developer particles whereat they are resupplied with developer particles.

It is recognized that when an applicator sweeps over an electrostatic latent image the visible image developed thereby may be immediately observed along an optical path, designated by the arrow B, which passes through the space defined by two successive applicators. The optical path will be interrupted by the next successive applicator transported therepast by the endless belt llll. Accordingly, a flickering effect is introduced to the visual observation of a recorded character. Nevertheless the transport velocity of endless belt ill, the spatial separation between successive applicators and the width of each applicator may be particularly selected such that the flickering effect is not readily noticeable by an observer. Thus, if a print receiving surface is disposed in a plane above the plane of the drawings and an observer is positioned in a plane beneath the plane of the drawings each applicator traverses an entire line on the print receiving surface to develop electrostatic charge patterns deposited on said line, and the observer may view each of the characters immediately after the development thereof. it is of course recognized that the distance between the longitudinal axes of cylinder means 15 and 16 is determinative of the length of the line developed. One of ordinary skill in the art will understand that although two cylinder means l5 and 16, about which the endless belt ill is deployed are illustrated herein, any convenient number of cylinder means may be utilized such that the endless belt it assumes a corresponding geometric configuration such as triangular, rectangular or the like.

Referring now to FIG. 2 there is illustrated one embodiment of the present invention which may be utilized in an electrostatic printing device, and comprises the apparatus of FlG. ll including endless belt ill and applicators 12-14 and 17, insulating recording medium Zll, electrode means 22, electrographic stylus 2d, and a source of motive power 30. The endless belt ill is understood to be a continuous structure; however to facilitate the explanation of the applicability of the present invention to an electrostatic printing device the endless belt M is diagrammatically illustrated in broken configuration. The insulating recording medium IZll may be comprised of a base paper which is electrically conduc tive and which is coated with a dielectrical plastic having a very high resistivity. Alternatively, the insulating recording medium may comprise any other dielectric sheet having a sufficiently high resistance to retain an electrostatic charge pattern. The insulating recording medium 21 is supported by electrode means 21 and guide support member 2? and is adapted to be advanced in the direction indicated by the arrow B. Electrode means 22 serves as a base electrode and supports the insulating recording medium Ell in close proximity to the electrographic stylus 2d.

Electrode means 22 includes a surface portion 221 adapted to maintain the insulating recording medium Ell in a plane parallel to the surface of electrographic stylus 2d and perpendicular to the longitudinal axes of cylinder means and 116.

The electrographic stylus Ltd may include a matrix array of parallel conductive electrodes suitably isolated electrically from each other. The matrix array of conductive electrodes may be pin electrodes supported by insulating support means 25 through which electrical S conductors maybe provided to each of'the pin electrodes for the selective energization thereof in response to electrical recording signals. The electrical signals supplied to the conductors may be generated by the actuation of a keyboard, by the receipt of facsimile signals, or by any suitable source of data signals. lnsulating support means 25 is adapted to support the electrographic stylus 24 at a suitable distance from the insulating recording medium 21 such that air ionization may occur in the air gap between the electrographic stylus 24 and the surface of the insulating recording means 21, whereby a small electrical discharge may be established between the selectively energized electrodes and the electrode means 22. Suitable distances that have heretofore been utilized are within the range three to five thousandths of an inch between the electrodes. I

To facilitate the recording of a line of characters, relative lateral displacement must exist between the insulating recording medium 21 and the electrographic stylus 24. Accordingly, insulating support means 25 may be displaced by a suitable motor, not shown, which may be a constant drive motor or a conventional stepping motor. Additional means may be provided for returning the insulating support means 25 from a rightmost position to a leftmost position after. the recording of a complete line of characters. One example of suitable drive means is described in U.S. Pat. application Ser. No. 805,694 filed on Mar.- 10, 1969, and assigned to Xerox Corporation. Alternatively, the insulating support means 25 may remain fixed, and electrode means 22 and guide support member 23 may form a conventional movable carriage adapted to transport the insulating recording medium 21 in a right to left direction, thereby enabling the electrographic stylus 24 to record successive characters thereon.

The endless belt 11 is positionedsuch that the operating surface. of each of

applicators

12, 13 and 14 and 17 mounted thereon may travel into contact with the surface of the insulating recording medium 21. Hence, the insulating recording medium may be disposed in. the plane defined by the terminal points of the fibers of the .applicatorsfThe electrographic stylus 24 is interposed between theinsulating recording medium 21 and the endless belt 11. It is understood however, thatwhen. the applicators 12-14 travel into the vicinity of the electrographic stylus 24 the fibers of each of the applicators are deformed by the insulating support means 25 to permit displacement therepast, and no interaction occurs between. the charged electrostatic developer particles retained by the applicators and the electrodes included in the electrographic stylus. A shaft 26 is suitably fastened to one of the cylinders 16 and is supplied a with a rotationaltorque by the source of motive power 30. The source of motive power3tl may comprise a conventional electric motor which may be a constant drive motor or a conventional stepping motor. Conv'en-' tionalcoupling means comprised of endless belt 2'7 deployed about

rollers

28 and 29 may be utilized to couple the motor 30 tothe shaft 26. Other mechanical coupling means such as drive speed reducing gears may be utilized if desired. It is preferable that the rotational speed of electric motor 30 be maintained at a-constant value notwithstanding the loading effects produced when an applicator travels into the vicinity of insulating support means 25.

Although not illustrated in FllG. 2 it is understood that a source of electrostatic developer particles is provided to supply the applicators 12-14 and 117 with electrostatic developer particles subsequent to the deposition of such particles upon an electrostatic charge pattern. The source of electrostatic developer particles may be similar to that described in the aforementioned US. Pat. Application Serial No. 805,694 or may comprise suitable liquid dispersion apparatus well known to those of ordinary skill in the art.

The operation of the electrographic recording device illustrated in FIG. 2 incorporating the present invention will now be described. Electric motor 30 imparts a velocity to the endless belt 11 such that the endless belt is displaced in the direction indicated by the arrow A. Electrostatic developer particles are applied to each of applicators 12-14 and 17 by a source of particles not shown. The fibers included in each of the applicators serve to charge the supplied electrostatic developer particles whereby the particles are retained by triboelectric attraction to the applicators. Electrostatic developer particles will be supplied to those applicators and portions of applicators which are deficient in particles. Consequently, the consideration of non-uniform loading of an applicator, i.e., excess electrostatic developer particles supplied to an applicator, is obviated.

Electrographic stylus 24 is proximately situated with respect tothe dielectric coating of insulating recording means 21 and the conducting surface of insulating recording means 21 is an intimate contact with the surface 221 of electrode 22. The electrographic stylus 24 is selectively energized by applying data signals thereto such as by depressing a selected key of a keyboard, by supplying received facsimile signals thereto, or the like.

The selective energization of electrographic stylus 24 establishes corresponding electrical discharges between each of the selectively'energized electrodes included in the electrographic stylus 2d and electrode means 22. Accordingly, ions which are created in the air gap between the electrographic stylus 24 and the surface of insulating recording means 21 are deposited on the surface of the insulating recording means 21 in a patterncorresponding to the selectively energized electrodes. Thus an electrostatic latent image comprised of an electrostatic charge pattern is formed. The.

polarity of the electrostatic charge pattern may be positive or negative, however itshould be noted that said polarityshould be opposite to that of the electrostatic developer particles retained by the applicators 12-14 and 17. After forming an electrostatic latent image the electrographic stylus 24 supported by insulating support means 25 is displaced a suitable amount in preparation for the recording of a subsequent image. The direction of displacement may be in correspondence with or opposite to the direction of travel of the illustrated applicators.Alternatively the carriage assembly comprised of electrode means 22 and guide support means 23 may bedisplaced to prepare the insulating recording means 21 for reception of a subsequent electrostatic latent image. i

The electrostatic latent image formed on insulating recording means 21 is developed to form a visible image when one of applicators 12-14 and 17 travels a into contact therewith. Itshould be understood that when an applicator sweeps over an electrostatic charge pattern the electrostatic force exerted on the electrostatic developer particles is sufficient to overcome the triboelectric attraction between the developer particles and the fibers of the applicator to thereby urge the particles into contact with the charge pattern. It may be observed that the forces exerted on the electrostatic developer particles by the impact between an applicator and the surface of the insulating recording means 21 may be sufficient to dislodge said particles from the applicator. The electrostatic developer particles however, will be attracted only to an electrostatic charge pattern. Thus, if the insulating recording means 21 sup ports a developed image, or if an electrostatic latent image is not present the dislodged electrostatic developer particles will merely cascade across the surface of the insulating recording medium 211 to be recovered by a sump located beneath the illustrated apparatus. Thus in accordance with the configuration illustrated in W0. 2 if the characters C, D" and E have been previously developed and the character F is an electrostatic charge pattern deposited on the surface of the insulating recording medium 211 by selectively energized electrographic stylus 2d, electrostatic developer particles retained by the fibers of applicator 112 will be removed therefrom to develop the image of the character F. Other electrostatic developer particles will be removed from applicator 112 in the vicinity of the developed images of characters C, D and E". However, insufficient electrostatic forces will exist between the developed images and said other removed electrostatic developer particles, and the electrostatic developer particles will fall, under the influence of the gravitational forces exerted thereon, to a sump for subsequent recovery thereof. One of ordinary skill in the art will recognize that each of the applicators 1241 5 and 17 will successively scan a line of insulating recording means 21 to deposit the electrostatic developer particles retained thereby onto the electrostatic charge patterns formed by the electrographic stylus 2d. it should be noted that electrographic stylus 2d may be aligned with either the upper half of the endless belt it or with the lower half thereof. In addition, successive portions of the fibers of each applicator will be deformed by the presence of the insulating support means 25 as-each ap plication is displaced. Thus each applicator is subjected to uniform wear. along the entire length thereof It may now be seen that an optical path may be established from an observer to a developed image through the space defined by adjacent applicators. The observer may be the operator of a keyboard adapted to be utilized with the apparatus illustrated in FIG. 2. Thus, each character may be perceived immediately after the recording thereof and it is not necessary to record a r plurality of lines of characters before observation of a first recorded line of characters is obtained. One advantage of mounting a plurality of applicators on the endless belt 111 is that improved development of electrostatic images obtains. For example if the character 13" is not adequately developed by the deposition of electrostatic developer particles thereon by the applicator 112, additional electrostatic developer particles may be deposited thereon by applicators lid and ilili until a suitably developed image is obtained. Although satisfactory development of a recorded electrostatic latent image may be realized by a multiplicity of applicators mounted on the endless belt M, it is appreciated that the flickering effect by which an observer may perceive the recorded characters may become objectionably noticeable it an inordinate amount of applicators is utilized.

After development, the electrostatic developer particles may be fixed to the insulating recording medium 211 in any of several conventional manners. For example, guide support means 23 may include a conventional heating assembly through which the insulating recording medium 21 is advanced. The heating assembly may fuse the electrostatic developer particles to the surface of the insulating recording medium 211 in the well-known manner. Flash fusing or fixing may also be used to render the developed images permanent.

It should be recognized by those of ordinary skill in the art that the electrostatic charge patterns may be deposited on the surface of the insulating recording medium 2 by conventional means other than the electrographic stylus 2d illustrated herein. For example, a linear array of energizable light emissive elements may be disposed to selectively dissipate a uniform layer of electrostatic charge deposited on the surface of the insulating recording medium 21. The insulating recording medium may comprise a conventional electrophotographic member and the linear array of light emissive elements may be selectively energized in accordance with data signals supplied thereto. in addition the light emissive elements may be positioned in a manner that does not interfere with the optical path established between an observer and a recorded character, which optical path passes through the space defined by adjacent applicators.

While the invention has been particularly shown and described with reference to exemplary embodiments thereof it will be obvious to those of ordinary skill in the art that the foregoing and various other changes and modifications in form and details may be made without departing from the spirit and scope of the in vention. It is therefore intended that the appended claims be interpreted as including all such changes and modifications.

What is claimed is:

.11. Apparatus for developing an electrostatic latent image, comprising an endless belt movable about a plurality of cylinder means, and a plurality of applicators capable of retaining electrostatic developer particles, said applicators comprising fibrous brushes each of which includes fibers extending in a direction parallel to the surface of said endless belt such that the terminal points of said fibers define a plane perpendicular to said surface of said endless belt and said plurality of applicators being mounted in spaced relationship on said endless belt suchthat said applicators successively contact said electrostatic latent image to deposit electrostatic developer particles thereon, and periodically interrupt an optical path to a developed imagewhen an applicator traverses said optical path.

2. Apparatus for printing characters on a print receiving surface, comprising:

means for forming characters comprised of electrostatic charge patterns on said print receiving surface;

an endless belt having a surface movable in a plane applicator means having a surface thereof substantially normal to said endless belt surface for successively contacting said print receiving surface to deface of said endless belt, said plurality of applicators being mounted in spaced relationship on said endless belt such that said applicators successively posit electrostatic developer particles'on said electrostatic charge patterns and for periodically interrupting an optical path to a printed character.

3. Apparatus for printing characters on a print receiving surface, comprising:

means for forming characters comprised of electrostatic charge patterns on said print receiving sur- 10 face;

an endless belt having a surface movable in a plane normal to said print receiving surface and deployed about a plurality of cylinder means, said cylinder means having their respective longitudinal axes disposed in perpendicular relationship with respect to said print receiving surface; and

a plurality of applicators capable of retaining electrostatic developer particles, said applicators comprising fibrous brushes each of which includes fibers contact said print receiving surface to deposit electrostatic developer particles on said electrostatic charge patterns and periodically interrupt an optical path to a printed character.

4. The apparatus of claim 3 wherein said at least two longitudinal axes are spaced apart a distance corresponding to the lateral dimension of said print receiving surface.

5. The apparatus of claim 4 wherein said means for forming characters comprised of electrostatic charge patterns comprises stylus means interposed between said endless belt and said print receiving surface and adapted for relative lateral displacement with respect to said print receiving surface; said stylus means being responsive to the selective energization thereof to deposit an electrostatic charge pattern on said print reextending in a direction parallel to the s rfa e of ceiving surface in accordance with said selective enersaid endless belt such that the terminal points of gization. said fibers define a plane perpendicular to said sur-

Claims

1. Apparatus for developing an electrostatic latent image, comprisinG an endless belt movable about a plurality of cylinder means, and a plurality of applicators capable of retaining electrostatic developer particles, said applicators comprising fibrous brushes each of which includes fibers extending in a direction parallel to the surface of said endless belt such that the terminal points of said fibers define a plane perpendicular to said surface of said endless belt and said plurality of applicators being mounted in spaced relationship on said endless belt such that said applicators successively contact said electrostatic latent image to deposit electrostatic developer particles thereon, and periodically interrupt an optical path to a developed image when an applicator traverses said optical path.

2. Apparatus for printing characters on a print receiving surface, comprising: means for forming characters comprised of electrostatic charge patterns on said print receiving surface; an endless belt having a surface movable in a plane normal to said print receiving surface and deployed about a plurality of cylinder means, said cylinder means having their respective longitudinal axes disposed in perpendicular relationship with respect to said print receiving surface; and a plurality of applicator means capable of retaining electrostatic developer particles and mounted in spaced relationship on said endless belt, each said applicator means having a surface thereof substantially normal to said endless belt surface for successively contacting said print receiving surface to deposit electrostatic developer particles on said electrostatic charge patterns and for periodically interrupting an optical path to a printed character.

3. Apparatus for printing characters on a print receiving surface, comprising: means for forming characters comprised of electrostatic charge patterns on said print receiving surface; an endless belt having a surface movable in a plane normal to said print receiving surface and deployed about a plurality of cylinder means, said cylinder means having their respective longitudinal axes disposed in perpendicular relationship with respect to said print receiving surface; and a plurality of applicators capable of retaining electrostatic developer particles, said applicators comprising fibrous brushes each of which includes fibers extending in a direction parallel to the surface of said endless belt such that the terminal points of said fibers define a plane perpendicular to said surface of said endless belt, said plurality of applicators being mounted in spaced relationship on said endless belt such that said applicators successively contact said print receiving surface to deposit electrostatic developer particles on said electrostatic charge patterns and periodically interrupt an optical path to a printed character.

5. The apparatus of claim 4 wherein said means for forming characters comprised of electrostatic charge patterns comprises stylus means interposed between said endless belt and said print receiving surface and adapted for relative lateral displacement with respect to said print receiving surface; said stylus means being responsive to the selective energization thereof to deposit an electrostatic charge pattern on said print receiving surface in accordance with said selective energization.