US2987037A - Xerographic printer - Google Patents

Description

June 6, 1961 w. D. BOLTON XEROGRAPI-IIC PRINTER 4 Sheets-Sheet 1 Filed Dec. 21, 1955 DRIVE L MECHANISM \13 GENEVA MECHANISM RECORD CARD CONTROLLED DATA INPUT "FIG; 1.

I N V EN TOR.

BOLTO N WALLIS D.

TONER IMAGE FIXING APPARATUS BI VARIBLE SPEED CO NTROL 82 AT TOR NEY June 6, 1961 w. D. BOLTON 2,987,037

XEROGRAPHIC PRINTER Filed Dec. 21, 1955 4 Sheets-Sheet 2 ARC CONTROLS June 6, 1961 w. D. BOLTON 2,987,037

XEROGRAPHIC PRINTER Filed Dec. 21, 1955 4 Sheets-Sheet 3 June 6, 1961 Filed Dec. 21, 1955 W. D. BOLTON XEROGRAPHIC PRINTER 4 Sheets-Sheet 4 United States Patent 2,987,037 XEROGRAPHIC PRINTER Wallis D. Bolton, Vestal, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Dec. 21, 1955, Ser. No. 554,513 4 Claims. (Cl. 118-637) This invention relates in general to electrographic printing machines and in particular to improved apparatus thereof for producing and developing latent electrostatic images.

The preferred embodiment of the invention to be described herein is adapted for use in a type of electrographic printing machine commonly referred to as a xerographic printer. As is well known to persons familiar with this phase of the graphic arts, xerography is a term applied to a printing process in which latent electrostatic images are rendered visible, i.e. developed, by a pigmented electroscopic powder, often referred to as Xerographic toner, the resulting electroscopic powder image thereafter first being transferred and then affixed to a print receiving sheet so as to afford a permanent printed copy which depicts the latent electrostatic image exactly. An apparatus employing such a printing process is shown and described in Carlson Patent No. 2,357,809 which issued on September 12, 1944, and follows the steps of electrically charging an electro-photoplate having a photoconductive insulating layer on an electrically conductive backing member, exposing the charged electrophotoplate to an optical image so as to form a latent electrostatic image thereof on the electrophotoplate, dusting the latent electrostatic image with xerographic toner in order to develop this latent image so that the configuration thereof is rendered visible, transferring the xerographic toner image onto a print receiving sheet such as paper, and finally removing any excess toner which remains on the surface of the electrophotoplate after the preceding transfer step but prior to the next electrophoto plate charging step.

Another kind of xerographic printer employing a printing process somewhat different from the aforementioned one disclosed by the Carlson patent, is shown and described in Schatfert Patent No. 2,576,047 which issued on November 20, 1951. This printing machine embodies a continuously rotating drum on which an electrically insulating image layer is secured. This permanent design image layer is electrostatically charged prior to being dusted with xerographic toner. The toner will, of course, be attracted and adhere to the charged surface area of the permanent design image layer so that when the toner supported thereby is transferred onto a print receiving sheet, the xerographic toner so transferred will define a configuration similar to the permanent design image layer. This latter type of printing where the image layer is permanently formed, is commonly referred to an xeroprinting in order to distinguish the same from other types of xerographic printing. It is to be observed that a xeroprinting machin is in essence a printing duplicator because any number of copies may be produced from a single permanent design image layer.

Before proceeding any further it would be Well to distinguish an electrophotoplate from an electroplate. The former is a member comprising a photoconductive in sulating layer on a conductive backing, whereas the electroplate is a member comprising an insulating layer, photoelectric and otherwise, on a conductive backing. Accordingly, it should be clear that the expression electroplate includes an electrophotoplate. For this reason, the term electroplate will be used throughout this specification.

The present invention is directed to-xerographicprint- 2,987,037. Patented June 6, 1961 ers generally, and has for its broad object the provision of improved apparatus thereof for bringing about improved xerographic printer operation.

As is stated in copending US. patent application, Serial No. 554,515, filed on December 21, 1955, by W. D. Bolton et al., it is Well recognized that xerography, or dryprinting as it is so often called, requires the application of pigmented powder onto the electroplate surface in order to develop the latent electrostatic images stored thereon. This has been accomplished in the past in a number of different ways, such as by the so-called cascade developer type apparatus described in the afore-mentioned Schaifert patent. The latent electrostatic image developing apparatus described in the instant application utilizes a soft fur brush for transferring xerographic toner particles from a suitable source onto the electroplate surface. In addition to transferring toner particles, the soft fur brush causes a negative triboelectric charge to be imparted to those particles actually brought into physical contact with the brush hairs. The preferred embodiment of the present invention includes a so-called segmented soft fur brush whereon toner particles are first deposited and then transferred onto the surface of a xerographic drum by a gentle wiping action of the brush in the direction of drum movement. Briefly, the so-called segmented developer brush includes a cylinder for supporting a plurality of spaced conducting segments on the outer periphery thereof, and a suitable fur brush which is secured to the outer periphery of these conducting segments in a fashion so that the brush hairs extend outwardly. As is disclosed in detail hereinafter, the transfer of toner particles onto the xerographic drum surface can be governed by applying external voltages to the developer brush. Thus, if any one or more of the segmented brush commutator segments is subjected to a positive voltage, for example, a positive charge will be applied to the brush hairs so as to prevent the transfer of 'xerographic toner fro-m the brush hairs onto the surface of the xerographic drum electroplate.

Accordingly, another object of this invention is to provide an improved latent electrostatic image developer brush.

In line with the foregoing, another object of the present invention is to provide an improved latent electrostatic image developer brush for regulating the transfer or migration of toner particles from the brush onto a charged electroplate surface.

As is recognized by persons familiar with this art, xerographic toner is an extremely difficult material to handle. This is due particularly to the fact that the toner particles are very fine, i.e., two to twenty microns in size, and quite tacky. Thus, to produce a successful brush developer, it is necessary to provide satisfactory means for depositing these hard-to-handle toner particles on the brush hairs evenly across the full length of the brush. The aforesaid means should include the feature whereby the amount of toner being deposited on the brush hairs can be regulated.

In keeping with the foregoing, another object of this invention is to provide an improved toner handling device.

Another object of the present invention is to provide an improved toner feeding mechanism for use with a brush developer.

Another object of this invention is to provide a piston toner feeding mechanism having yielding means for depositing a regulated rate of Xerographic toner evenly on the brush hairs of a developer brush.

As stated previously, the developer brush hairs impart a negative triboelectric charge to the toner particles that are transported from a suitable toner source to the electroplate surface. At the same time, a positive triboelectric charge is imparted to the brush hairs. This positive charge is apparently of a lesser magnitude, however, than is the positive charge on the electrophotoplate surface that defines a latent electrostatic image. 1 This appears to be so for the reason that the toner particles adhere to the charged electroplate surface rather than the brush hairs. If, however, a suitable external positive charge is applied to the brush hairs in any one of a variety of ways, toner transfer to the electrophotoplate surface may be prevented.

Accordingly, another object of this invention is to provide a selectively operable latent electrostatic image developing apparatus whereby the development of a latent electrostatic image may be readily controlled.

In line with the foregoing, another object of this invention is to provide an improved device for regulating the migration of toner particles from a toner carrier ont a charged electrophotoplate surface.

Most xerographic printers known heretofore are substantially similar to those described in the afore-mentioned Carlson and Schafiert patents in that they are for the most part copying and/or duplicating machines. That is, the latent electrostatic image of some given object is generally formed by way of an optical image thereof, which image is subsequently developed and then printed in the well-known manner. It is within the scope of the present invention to provide an original document xerographic printer which does not require optical image apparatus for producing the latent electrostatic images. Instead, this latter-mentioned xerographic printer causes symbols, characters and numerals to be formed in a lineby-line fashion directly in response to data representing signals. Briefly, latent electrostatic images of symbols, characters and numerals are formed on the surface of an electroplate by directing electrostatic field discharges, known commonly as corona currents, having configurations corresponding to these data, onto the electroplate surface. This is accomplished by employing a so-called data stencil cylinder for shaping the aforesaid field discharges selectively in accordance with incoming data representing signals. These signals might be transmitted from a calculator, for example, as well as from arecord card or tape reader.

Accordingly, another object of this invention is to provide an improved latent electrostatic image producing apparatus.

Another object of this invention is to provide. an improved mutable data xerographic printer.

Still another object of this invention is to provide an improved line-by-line xerographic printer.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of examples, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings:

FIG. 1 is a diagrammatic view of a continuously operating xerographic printer employing brush development.

FIG. 2 is a diagramamtic view'of the apparatus used to govern the forming of latent electrostatic images on the xerographic drum of the printer. 7

FIG. 3 is a somewhat diagrammatic view of optical apparatus used to form latent electrostatic images on the xerographic, drum of the printer. FIGS. 4 through 6, inclusive, are somewhat-diagrammatic views of non-optical apparatus used to form latent electrostatic images on the xerographic drum of the printer.

FIG. 7 is a diagrammatic view of a plural brush developing apparatus for a xerographic printer.

FIG. 8 is a somewhat diagrammatic view of a pressed cake toner adding mechanism.

FIG. 9 is a schematic showing of a brush. developer apparatus. a

. 4 A FIG. 10 is a cross-sectional view of a so-called "segmented" developer brush.

FIG. 11 is a somewhat diagrammatic view of the segmented developer brush assembly.

GENERAL DESCRIPTION Referring to FIG. 1 wherein the xerographic printer in which the preferred embodiment of this invention is shown, the metal cylinder 10 of xerographic drum 11 is mounted for rotation on a drive shaft 12 which is driven in a counterclockwise direction by an electric motor (not shown) within drive mechanism 13 via a conventional Geneva mechanism 14. This drum 11 has secured thereto an electroplate 16 which includes an insulating layer 17 of amorphous selenium, for example, on an electrically conductive backing member 18 of aluminum, for instance. The electroplate 16 is flexed around cylinder 10 as shown, and is attached thereto in any one of the numerous conventional ways of attaching a printing plate to a supporting cylinder. It is important, however, that in whatever manner this attachment is made, the backing member 18 be in intimate contact with the insulating layer 17 as well as in good electrical contact with the drum cylinder 10 which is connected to ground potential via shaft 12.

As successive incremental areas of the insulating layer 17 are moved in a counterclockwise direction past ionproducing charging unit 19 of the type shown and described in Carlson Patent No. 2,588,699, issued on March 11, 1952, the aforesaid layer 17 of dielectric material is electrostatically charged positive. These positively charged incremental areas are then moved past an optical image producing unit 21 (see also FIG. 3) which projects optical images of the text or matter to be copied, onto the electrically charged surface of photoconductive insulating layer 17. The apparatus by which the optical images are produced and projected onto the surface of layer 17 of electroplate 16, will be described shortly.

Consequent upon the exposure of the photo-conductive insulating layer 17 to the optical images produced by and directed from optical unit 21, latent electrostatic images thereof are produced on electroplate 16. This is for the reason that those electrically charged incremental areas of insulating layer 17 onto which light rays are directed, are discharged, whereas those areas not illuminated by light rays remain charged. Hence, afterthe positively charged electroplate 16 is exposed to the aforesaid optical images, positive latent electrostatic images thereof corresponding to the optical information projected onto the surface of xerographic drum 11, will remain.

Continued rotation in a counterclockwise direction will cause the latent electrostatic images appearing on electroplate 16 of drum 11 to be moved into a latent electrostatic image developing chamber 22. This chamber which will be described in detail hereinafter, is one wherein xerographic toner of the general type described in'Copley Patent No. 2,659,670 which issued no November 17, 1953, is applied to the exposed surface of electroplate 16, and, of course, over the latent electrostatic images thereon. As a result, the pigmented toner particles will adhere to only the afore-mentioned image defining charged areas of electroplate 16, whereby a corresponding number of developed toner images which now visibly define their respective latent electrostatic images appear on the surface of the electroplate.

A still further counterclockwise rotation of xerographic drum 11 will cause the toner images developed on the surface of electroplate 16, to move out of developing chamber 22 and into the realm of a negative ion-producing unit 23 which is similar to afore-mentioned unit 19. The effect of this second electrostatic field produced by unit 23 is to decrease somewhat the magnitude of the image defining positive electrical charge stored in nonconducting layer 17. This is to condition the developed toner images being carried on the surface of electroplate 16 for ready transfer onto a print receiving web 24. In

'5 addition thereto, the negative electrostatic field to which the photoconductive insulating layer 17 is subjected, corrects an unfavorable condition known generally as selenium fatigue.

Further rotation of drum 11 causes the developed toner images thereon to move into a xerographic toner image transfer, or printing, station, whereat a transfer roller 26 comprising a metallic conductive portion 27 and an outer portion 28 of a very resilient material having a high electrical resistance of at least power ohms per cubic centimeter, is used to transfer the xerographic toner images from the surface of electroplate 16 onto the surface of print receiving web 24. The transfer roller 26 is similar to one shown and described in detail in copending U.S. patent application Serial No. 419,314, filed by C. I. Fitch on March 29, 1954, now US. Patent 2,807,- 233. For this reason, the same will not be described in detail herein. The print receiving web 24, which is preferably a paper strip, is advanced by conventional means (not shown) from a web supply roll 29 to a Web take-up roll 30 via the aforementioned transfer station whereat transfer roll 26 is located, and a toner image fixing station 31. The positive potential applied to transfer roller 26 causes the xerographic toner particles on the drum surface and which define the latent electrostatic images, to migrate from the surface of electroplate 16 to the opposite surface of print receiving web 24. it might be Well to mention here that web 24 is advanced at a lineal speed that corresponds to the peripheral speed of xerographic drum 11.

In order to remove any excess xerographic toner particles that might remain on the surface of electroplate 16 after the toner image transfer but prior to charging the incremental areas of the photoconductive insulating layer 17 again by ion-producing unit 19 during another machine cycle, a rotating plush cleaning roller 32 is positioned within a housing 33 for retaining the toner so removed from the surface of electroplate 16 by rolier 32. A vacuum cleaner unit (not shown) may also be utilized within the housing 33 in order to remove the xerographic toner caused to be accumulated therein. As is shown in FIG. 1, prior to subjecting the incremental areas of the photoconductive insulating layer 17 to the cleaning action of plush roller 32, the electroplate 16 is preferably subjected to another negative electrostatic field produced by corona unit 34 which is similar to afore-mentioned unit 23. A beam of light rays from a source 36 is also projected onto the surface of electroplate 16 so as to assure discharge of all of the areas of the photoconduotive insulating layer 17. The negative field produced by unit 34 tends to avoid the previously mentioned unfavorable condition selenium fatigue, and also conditions the drum surface for easy removal of the toner particles remaining on the surface of the electroplate after transfer.

The xenographic toner images transferred onto the surface of print receiving web 24 may be affixed thereto by any one of several known methods which include fixing by pressure, heat and toner chemical solvent. Pressure fixing rollers within unit 31 are employed in the preferred embodiment of this invention, and a sufiicient line contact pressure of approximately 509 pounds per lineal inch of contact is employed to cause the xerog-raphic toner supported by the surface of the web to flow into the fibers thereof. In order to assure that the web is not torn or mutilated by being pulled through the pressure fixing rollers (not shown), the rollers are connected to the main drive mechanism 13 so as to be rotated in step with movement of xerographic drum 11.

LATENT ELECTROSTATIC IMAGE FORMATION As stated previously, a latent electrostatic image of matter to be printed or copied, is created in an electrically insulating, dielectric layer by producing electrostatically charged areas thereon. This may be done in any one of several ways. For instance, the photoconductive insulating layer 17 (FIG. 1) may initially be charged positive,

for example, by an ion-producing unit 19, and thereafter while still charged may be exposed to an optical image formed by passing light rays through an opaque-transparent image defining stencil. As a result, a positively charged latent electrostatic image will be produced in photoconductive insulating layer 17 for the reasons that those electrically charged incremental areas of the photoconductive layer onto which light rays are directed, are discharged, whereas those areas not illuminated by the light rays remain charged.

Another way touched upon briefly hereinbefore in which to form latent electrostatic images on dielectric layer 17, is to direct thereon shaped electrostatic lines of force, which, in turn, act to shape an ionic current flow, so that a cross-section thereof will define the configuration of the image it is desired to store. This may be accomplished by an electrostatic stencil xerographic printer.

Optical rec0rder.-The xerographic printer shown in FIG. 1 may be employed as a record card controlled lineby-line optical data recorder by forming lines of character images on the surface of electroplate 16. The image pro ducing apparatus for such a line-by-line optical recorder, is similar to that shown and described in copending US. Patent No. 2,726,940, issued to E. Buhler on December 13, 1955. Inasmuch as the apparatus for producing the line-by-line latent electrostatic images optically is not per se a part of the present invention, the same will be described but briefly with reference to FIGS. 2 and 3. A more detailed description is available in the afore-mentioned copending Buhler patent.

Referring to FIG. 3, a constantly rotating drum 41 is provided with rows and columns of transparent characters 42 (see also FIG. 2) on an opaque background 43. To facilitate illustration, the background is shown to be light and the characters are dark, but it will be understood that the characters are transparent. An individual column of characters 42 spaced around the periphery of drum 41, is associated with each of eighty possible print positions, one for each column of the well-known eighty column IBM record card. A plurality of are units 44 each comprising a plurality of electrodes 20, 30 and 40, are mounted inside drum 41 and are so aligned that there is one are unit behind each column of characters 42. The electrodes 30 and 49 are arcing electrodes and electrode 20 is a triggering electrode that is used to alter the breakdown characteristic of the gap between electrodes 30 and 40 to initiate arcing. Opaque barriers (not shown) are interposed between adjacent are units and serve the dual purpose of preventing any possible tendency of the discharge of one are to cause the discharge of an adjacent arc, and of preventthe illumination produced by one are from falling upon a character 42 associated with an adjacent arc unit. Reference may be had to the copending F. Demer et al. US. Patent No. 2,714,841, filed on August 9, 1955, for a detailed disclosure of the are unit.

Adjacent the drum 41 and in alignment with each arc unit 44 corresponding to each column of characters 42, are individual focusing lenses 46. A plurality of so-called zoning slots 47 are arranged in five columns on one end of drum 41, which slots cooperate with five light sources (not shown) that are mounted inside drum 41 and with five photocells 48. It is to be observed that a given char actor 42 and a corresponding Zoning slot 47 pass respective arc unit 44 and phototubes 48 at the same time. The preceding elements: cooperate to emit timed pulses which are adapted by suitable circuits represented by block 57 to cooperate with other timed pulses derived from the sensing of the afore-mentioned record cards 45, so as to effect a selective triggering of the individual are units 44 as select characters 42 pass between their arc units and respective focusing lenses 46. As a result, a character shaped light beam will be passed through a lens 46. A photoemissive material plate 49 is arranged to be exposed to the light emitted from an arc unit, shaped by the character stencil and passed througha corresponding lens 46. Hence, upon exposure to light, the plate 49 will emit'a cloud of electrons whose cross-sectional configuration is similar to that of the shaped light beam passing through its lens 46. These electrons are attracted toward a high potential plate 51 connected to battery 55. A web 52 made of dielectric material is interposed between photoemissive plate 49 and high potential plate 51 so that as the electrons emitted from plate 49 are attracted toward the high potential plate 51, they are deposited on web 52 as a latent electrostatic image of the corresponding optical image. The web 52 of dielectric material is thereafter passed through a toner image developing chamber 58 whereat the latent electrostatic images are developed, and prior to being permanent aflixed to the web by electrically heating units 53. a

In summation, a latent electrostatic image of a character 42 on the periphery of drum 41 is caused to be formed when corresponding data representing pulses from photocells 48 and record card reading station 54 operate circuits represented by block 56 which, in turn, elfect the operation of associated arc control circuits 57 in order to fire select are units 44. That is, assuming that record card sensing brush 37 for reading the second card column, detects punched holes indicative of the letter A, this information will be storcd in circuits 56. Thereafter, when phototubes 48 detect zoning slots 47 which are also indicative of the letter A (it will be recalled that at this time the corresponding. characters 42, i.e., the letters A, are aligned with their respective arc units 44), the coincidence of information from phototubes 48 and the second record card column will cause a triggering signal to be directed from circuits 57 via line 38 to electrode of the arc imit 44 associated with the second record card column. The ensuing arc will cause a latent image of a letter A to be formed on dielectric web 52 at a position aligned with the arc unit 44 that was fired. Other latent images may be formed in a similar fashion, and then may be developed and fixed as afore-desoribed.

Non-optical recorder.A non-optical, line-by-line xerographic printer does not require the ion-producing unit 19 (FIG. 1) for reasons to become clear shortly. A stencil cylinder 61 (see also FIG. 4) and associated apparatus would replace previously described cylinder 41 and its associated apparatus (FIG. 3), and would be continuously rotated by drive mechanism 13 (FIG. 1) so that the stencil cylinder would complete a single revolution for each aforementioned line-by-line movement of xerographic drum 11. The xerographic drum is also driven by drive mechanism 13, but via a conventional Geneva mechanism 14. It is by way of the Geneva mechanism 14 that the continuous rotational movement of the stencil cylinder is correlated to the step-by-step movement of xerographic drum 11. Referring to FIG. 4, stencil cylinder 61 is a somewhat thin-walled conductor supported at each end by two hubs (not shown) which may be rotated about a stationary hollow shaft 62 through which wires are passed. The preferred embodiment of this invention includes a stencil cylinder having eighty columns of circircumferentially disposed characters 63 (see also FIG. 4), one for each column of the well-known IBM record card, which eighty columns of characters are identical and are similarly disposed to provide rows of identical characters extending lengthwise on the periphery of the drum. The characters might be comprised of a plurality of holes as depicted by stencils 63a (FIG. 6) or a plurality of prearranged slits as depicted by stencils 63b.

Secured to stationary hollow shaft 62 within cylinder 61 is a single corona discharge unit 64 including a corona wire 66 which runs the length of cylinder 61. As a result, when electrical power is applied to wire 66, a corona field discharge is directed through a channeled opening 67 in unit 64, which extends the full length of cylinder 61, towards the inner surface of stencil cylinder 61. Normally, this corona field discharge is .prevented from passing throughthe stencil characters in stencil cylinder 61 for the reason that all eighty pairs of control electrodes 68 (see also FIG. 5) associated with each' columnar position of stencil drum 61, are normally biased electrically to a potential of approximately -800 volts. 1 Connecting wires for each of these control electrodes are shown in FIG. 5, and are run within hollow shaft 62. Thus, since the conductive backing member 18 (see also FIG. 1) is at ground potential, as mentioned previously, and inasmuch as the corona field discharge from unit 64 (FIG. 3) is a positive one, the field discharge will normally be divided into approximately separate paths which include the eighty pairs of highly negative control electrodes 68 (FIG. 5). It should be pointed out that electrostatic field barrier plates (not shown) are used to divide opening 67 into eighty separated openings corresponding to the number of characters on stencil cylinder 61. This is to prevent a lateral deflection of the corona discharge field from one character position to another position. At a time that a select character stencil 63 is aligned with the channeled opening 67 in unit 64, a positive potential in the order of approximately +800 volts is caused to be applied to the pair of corresponding character position control electrodes 68. This action causes the positive corona field discharge to pass through the opening 67 defined by the afore-mentioned electrostatic barrier plates and the oppositely placed columnar control electrodes 68 each of which is raised to +800 volts, through the character stencil 63 aligned therewith, and onto the previously uncharged surface of the dielectric layer 17 (FIG. 1) on electroplate 16. The afore-mentioned barrier plates '(not shown) will restrict such a field to a region opposite the select character stencil. During a complete revolution of cylinder 61, a line of characters as depicted by latent electrostatic images thereof may be formed before the xerographic drum 11 is advanced one line position. This non-optical xerographic recorder might be a record card controlled machine governed in a manner similar to the way in which the optical recorder (FIGS. 2 and 3) is governed. That is, consequent upon the coincidence of record card indicia and zoning slot data generated as a result of the position of the stencil cylinder 61 (FIG. 5) relative opening 67, a suitable negative voltage generator would be triggered ofi and a positive voltage generator trigged on. There would be one such positive voltage generator as well "as one such negative voltage generator for each character position, i.e., for each pair of control electrodes 68. Connections from these generators to the control electrodes would be completed via the wires within hollow shaft 62. As stated previously, it is within the concept of this invention to provide such a nonoptical line-by-line printer which would transcribe data directed from a calculator. Thus, consequent upon the coincidence of calculator output data signals and zoning slot data generated as a result of the position of the stencil cylinder 61 relative opening 67, a suitable positive voltage would be applied to a pair of control electrodes 68.

ELECTROSCOPIC TONER In xerographic printers, latent electrostatic images are developed by applying an electroscopic or xerographic toner to the surface of the insulating material whereon said latent images appear. The constituent make-up and characteristic properties of this toner that make the same suitable for developing such latent electrostatic images, are described in Copley Patent No. 2,659,670 which issued on November 17, 1953. One of the most important properties of xerographic toner resides in its property to become charged triboelectrically. Thus, the constituent toner and carrier parts of an electroscopic or xerographic developer, such as is described in Walkup et al. Patent No. 2,638,416 which issued on May 12, 1953, are selected in accordance with their triboclcctric properties so that when brought into mutual contact, one

the other material part, e.g., the toner, is charged negative if the first material part is above it in the triboelectric series. The carrier particles may be of a size in the order of 30 to 60 mesh, so that these particles will flow easily over the electroplate by gravity. As brought out in the afore-mentioned Schaifert patent, satisfactory latent electrostatic image development is obtainable by cascading xerographic developer comprised of carrier and electroscopic toner over the surface of the electroplate whereon the latent images are formed. However, experimental and field use to date has very decidedly shown that the comparatively large and hard granular carrier particles have a deleterious efifect on the surface of the insulating layer 17 (FIG. 1) of the electroplate 16 due to abrasion. This is particularly the case when delicate amorphous selenium is used as the insulating layer.

BRUSH DEVELOPMENT Introduction-4t has already been brought out that xerographic developer includes comparatively large and hard granular carrier particles as well as fine electroscopic toner particles. It has also been brought out that physical contact between the carrier particles and the toner particles causes a triboelectric charge of one po larity to be imparted to the toner and of the other polarity to the carrier particles. The toner charge is such as to be electrically opposite to the charge which defines the latent electrostatic images appearing on the insulating layer of the electroplate. In brush development to be described herein, a soft fur brush is used in place of the coarse granular carrier particles necessary for cascade development, to impart the necessary triboelectric charge to the toner particles. It is by the somewhat vigorous agitation of the soft fur brush hairs relative the xerographic toner particles that the triboelectric charge is imparted to the toner particles. It might be well to mention here that the brush hairs per se also have a triboelectric charge imparted thereto but of the opposite polarity to the afore-mentioned carrier particles. As is to be expected, the brush is also used to convey toner particles from a suitable source of toner supply to the surface of the insulating layer of the electroplate whereon the latent electrostatic images are formed.

GeneraL-Referring to FIG. 9, the principle of brush development as it is now understood in its simplest form may be explained quite easily. A brush 71 of either beaver or red fox skin, for example, is secured to a rotatable drum or cylinder 72 which, in turn, is so arranged that the non-conducting brush hairs 73 move through a mass of xerographic toner 74 in a source reservoir 76, and also in physical contact with the surface of a dielectric layer of an electroplate 77. The physical contact, and resulting agitation, between the brush hairs 73 and the toner particles 74 causes a triboelectric charge to be imparted to the toner particles so acted upon. The use of a fur skin such as the beaver or the red fox referred to hereinabove, as well as use of xerographic toner such as described previously, causes a negative triboelectric charge to be imparted to the toner particles and a positive triboelectric charge to be imparted to the brush hairs. Thus, as incremental areas of the insulating layer of electroplate 77 having positively charged latent electrostatic images thereon, are subjected to the negatively charged toner particles 74, the charged particles are caused to adhere to the positively charged surface areas of electroplate 77. As a result, the said latent electrostatic images are rendered visible and are caused to be developed. It should be evident that the use of a soft fur brush in place of the granular carrier particles eliminates the deleterious abrasive action of the carrier particles, particularly as they tumble over the delicate surface layer of an electroplate such as amorphous selenium.

The application of brush development in a xerographic printer is shown in FIG. 1. A continuously rotating brush 71, the conventional drive for which is not shown} is moved in a clockwise direction at a greater speed than is the drum 11 so that the brush hairs 73 effect a gentle wiping action relative to the insulating layer surface of electroplate 16 in the direction of drum movement. For example, the peripheral speed of the drum 11 can be 700 inches per minute, whereas the speed of the brush hair ends can be 1700 inches per minute. These brush hairs 73 initially pick up, or have deposited thereon, toner particles 74 from the orifice end of a piston-type toner feeding mechanism 81. Then, during the course of clockwise movement of brush 71, the toner particles so deposited contact the fur brush hairs 73, whereby a negative triboelectric charge is imparted to these particles. Brush agitator rods 86 (see also FIG. 10), or the like, are normally used in order to effect a better and more intimate contact between the individual toner particles and the brush hairs. Finally, as the negatively charged toner particles are transferred from brush 71 onto the surface of electroplate 16, there is of course adherence to the charged surface thereof due to an attraction between the positively charged latent electrostatic images and the negatively charged toner particles.

TONER FEEDING DESCRIPTION Piston feeding device.--Those persons familiar with this art are aware that xerographic toner is an extremely difficult material to work with, because among other things, it is so extremely fine and tacky. In a cascade type developer of the afore-mentioned type disclosed in afore-cited Schaffert patent, it is necessary to add a batch of toner to the developer from time to time. On the other hand, by employing a toner feeding device such as is shown and described in copending U.S. patent application, Serial No. 496,833, filed on March 25, 1955, by H. Dunn, now US. Patent 2,779,306 the toner may be added continuously and the amount of toner in the de veloper may be kept at a proper level. However, such a toner feeding device does not appear to be adaptable for use with a brush developer apparatus. For one thing, the brush is comparatively long and requires toner to be added along its full length. For another thing, the toner added this way exceeds the amount actually required.

t should be pointed out that the problem is not solved simply by causing a developer brush to move through a batch of toner. The principal reason is that before very long the brush will form channels or scooped out areas in the batch of toner which will remain as such unless there is some additional toner agitating action.

Xerographic toner can be supplied to the fur brush hairs 73 very admirably via the aforementioned piston feed mechanism 81 (FIG. 1). This may be done at a rate which may be varied either manually or automatically. That is, a variable speed control apparatus 82 which is driven by motor 84, may be manually governed in order to change the rate of advancement of piston 83 and therefore the amount of toner being deposited on the brush hairs from the toner tube or chamber via its discharge orifice. On the other hand, if a suitable photoelectric apparatus is used to detect the density of the developed toner image on the surface of the xerographic drum 11, this photoelectric apparatus might be used to govern a variable speed control apparatus for controlling the rate of movement of piston 83. In either case, the piston shaft 75 which is loosely connected to piston 83, is connected for rotation to a screw 85, which, in turn, is meshed to a drive gear that is secured to a shaft projecting from the variable speed control apparatus 82. It is within the concept of the present invention to employ a suitable slip clutch of any conventional design between the piston 83 and its drive mechanism, e.g., within the speed control apparatus 82, so that the said piston will be yieldingly urged toward the discharge orifice end of the toner container body, which orifice is 1 1 substantially the length of the brush 71. Thus, should for some reason the brush hairs not remove as much toner as is being fed by the piston feed mechanism, there would be a sufficient back force caused by the compression of the toner to prevent any further advancement of the piston 83 while the aforementioned clutch slipped.

Toner adding device.-Referring to FIG. 8, a pressed cake of toner 105 is positioned within a piston feeding device 106 comprising a piston 107 for pushing the toner cake through its body container or chamber 108, a piston driving member 109, and a drive shaft 110. This shaft 110 is supported by a bushing 111 in frame member 112, and is secured to a pulley 113 which is operated by a suitable drive means (not shown). Furthermore, the shaft 110 is engaged with piston driving member 109 at threaded bushing 114. Thus, as pulley 113 and shaft 110 rotate slowly, piston 107 is pushed to the left by slowly advancing member 109.

Glass fiber brush 115 is rotated via the belt and pulley arrangement 116, and is used as a toner abrasive. This brush is also caused to walk relative a stationary rack 117 which is in mesh with gear 11.8 while the said gear is caused to rotate by the belt and pulley arrangement 119. It should be clear now that gear 118 is secured to shaft 120, whereas belt and pulley 116 are loosely supported by the shaft.

The toner cake 105 is one which can be molded at a pressure of approximately 5000 pounds per square inch. lIf the toner adding device is to be used with a brush developer apparatus, this toner cake should be as long as the brush. .Thus, as the rotating glass fibers 115 move along the exposed end of the toner cake, toner particles thereof are deagglomerated and caused to fall into a suitable container such as reservoir 76 of FIG. 9 or be deposited onto the brush hairs. The arrangement for moving the toner abrasive brush 115 relative the length of the cake of toner includes a drive pulley (not shown) for supporting pulley 119. This drive pulley is secured to a shaft (not shown) that has a clutch (not shown) at each end for connecting the said shaft to eachof a pair of drive motors (not shown) operating in opposite directions. This arrangement also includes a pair of microswitches, one at each end of the rack 117 for governing the operation of an associated clutch. Thus, when the gear 118 has been moved to one end of rack 117, a microswitch is operated to cause the engaged clutch to disengage and the disengaged clutch to engage. As a result, the gear 118 is rotated in the opposite direction, and the brush 115 is caused to move back relative the long end of pressed toner cake 105. When the gear 118 has been moved all of the way back, another microswitch is operated, to thereby reverse the rotation of gear 118 once again.

LATENT IMAGE DEVELOPING CONTROL The brush 71 (FIG. 1) is shown to be secured to a rotatable cylinder which has an electrically conductive cylinder 65 attached thereto for supporting brush 71 within an electrically conductive shell 88 whose inner surface is always in physical contact with brush hairs 73 of brush 71. By applying a positive potential to this electrically conductive cylinder 65 or shell 88, e.g., +3000 volts, being careful, of course, to electrically isolate the electrified parts from ground, the transfer of toner particles from the brush hairs 73 onto the latent electrostatic image bearing surface of electroplate 16 is prevented. The action that takes place to preclude toner transfer is not too clear, although it is believed that the applied high positive potential imparts a positive charge to the brush hairs which therefore have a greater attraction for the triboelectrically charged negative toner particles than do the positively charged latent electrostatic images appearing on the surface of the xerographic drum. Whatever the explanation may be, it is a known fact that toner transfer suppression, and therefore print selection, maybe eflected 12 simply by closing switch '89 so that either shell 88 or conductive cylinder is subjected to the necessary positive voltage.

As has just been disclosed, the application of a positive charge or potential onto the hairs of an image developing brush via an electrode, such as shell 88 or the brush mounting shell 65 for example, will aifect the latent electrostatic image developing operation. Whereas a potential of approximately +3000 volts may be applied to shell 88 so as to electrify or charge the brush hairs 73, the developing brush shown in FIGS. 10 and 11 may be electrified or charged at various select points thereof via commutator segments 93. As is shown in FIG. 10, the conducting commutator segments 93 are each embedded in a'suitable insulating member or notched cylinder 94 which, in turn, is secured for movement to rotatable member 95. Furthermore, the commutator segments 93 are in direct contact with the under side of non-conducting pelt 96 which, in fact, is the backing layer for the non-conducting brush hairs 73. Of course, the pelt 96 need not be a continuous piece but instead a plurality of separated brushes can be used, one for each conducting segment. The application of a voltage to select ones of the plurality of commutator segments. 93 may be used to govern the latent electrostatic image developing operation of the brush developer. For example, a high positive potential might be applied to each of the moving segments brought into alignment with the radial lines 97 and 98 so as to prevent the escapement of xerographic toner in the form of a toner cloud at the end points 97a and 98a of contact between the brush hairs and the electroplate surface. On the other hand, the application of a suitable negative voltage to a commutator segment 93 lying between the radial lines 97 and 98, would cause an increase in the density of the developed toner image. It might be pointed out here that there might also be an increase in the density of the image background. Notwithstanding this latter point, however, it is significant that there would appear an increase in image density with the application of a negative voltage to the commutator segment between the afore-mentioned radial lines. Once again, it is not too clear just what the physical action is that takes place to cause the aforedescribed results actually realized. One explanation for this behavior, however, might be that the triboelectric action between the xerographic toner particles and the brush hairs, such as those found in theskins of beaver or red fox for example, produces negatively charged toner particles and positively charged brush hairs. When these brush hairs are subjected to an outside positive voltage, the negatively charged toner particles are simply attracted much more tothe brush hairs than to the latent electrostatic images so as to prevent the migration of the negatively charged toner particles to the charged image defining areas on thesurface of the electroplate. This is probably for the reason that with the application of an external positive potential to the brush, the brush hairs are charged to a higher positive value than are the latent electrostatic image areas. On the other hand, the application of a negative potential to the brush hairs repels the negatively charged toner particles so that more toner particles are caused to be attracted to and/or driven towards, the positively charged image areas of the electroplate. In fact, the slightly positive residual potential of approximately 50 volts which nearly always appears toremain in the background areas of the latent electrostatic images on the electroplate, attracts more of these negatively charged toner particles when the brush is subjected to a negative voltage. There appear to be many possible uses for a segmented toner brush, and many more are certain to be realized and understood as the chemical and physical properties of natural and synthetic fur brushes as well as electroscopic toners, are understood. H

The distributor for the segmented brush, is shown in FIG. 11, Each of the conductive segments 93 is con nectedv to a respective wiping electrode 93a. A stationary 13 disc having wiping electrodes 93b protruding therefrom, is freely arranged over the brush shaft 131. Any one or more of the electrodes 93b may be connected to a suitable voltage supply, whereby a voltage will be applied to each conducting segment 93 as it passes a given point.

Brush stippling-As is disclosed and claimed in the afore-mentioned copending Bolton et al. patent application, improved toner images have been realized by stippling the rotating developing brush relative to the surface of the electroplate whereon the latent electrostatic images are formed. The stippling action is performed by moving brush 71 (FIG. 1) towards and away from the electroplate 16 so that the hairs 73 thereof are caused to produce a patting or powdering action relative the electroplate surface. It has been found that good results are obtainable by moving the brush 71 from one limit whereat the brush hair ends are barely in contact with the electroplate surface to another limit whereat the brush has been moved radially towards the xerographic drum along a line defined by the brush and xerographic drum centers, a dis tance of approximately This is not to be taken as a limitation but rather as an example. It will be clear to those persons having ordinary skill in the art that other arrangements and/or parameters might be employed to produce a satisfactory stippling action.

It has been found that a rate of 1200 stipples per minute is very effective for good image development. This, for all practical purposes and within presently known engineering limits, appears to be independent of the xerographic drum rotational speed. However, once again, the foregoing is not to be taken as a limitation in view of the fact that acceptable results are obtainable when the stippling action occurs at a rate other than 1200 per minute. It is believed that brush stippling is as effective as it is because the uniformity of toner particle charge depends on the effectiveness of agitation between the brush hairs and the toner. During the course of the stippling action, the brush becomes fully extended in the direction of oscillation so as to afford a violent motion which is believed necessary to realize the desired toner charge. The toned brush, i.e., the toner applying brush, is rotated slightly faster in the direction of movement of the xerographic drum 11 than is the peripheral surface speed of the xerographic drum. Thus, the freshly toned brush hairs 73 are presented in a wiping motion in the direction of drum movement to every portio'n of the surface whereon the latent electrostatic images are to be found. Since the stippling action is in a direction substantially normal to the xerographic drum surface, the brush hairs bend randomly upon contact with the surface. The over-all effect is to produce a combined patting-wiping action relative the electroplate surface. -As a point of interest in this general field, an extremely rapid developer brush rotation without a stippling action, produces a dense cloud of toner particles. By operating the rapidly rotating brush in grazing contact with the surface of the electroplate, the resulting developed toner image closely resembles one form by powder clo'ud development.

Plural brush developing-As is brought out in copending patent application Serial No. 554,514, filed on December 21, 1955, by T. Hider, it has been found that at higher printing speeds improved printed copy such as appears on the surface of web 24, for example, may be had by employing a plurality of developing brushes. Various brush arrangements may be used depending upon the physical design limitations of the printer as well as the requirements for the printed copy desired. Referring to FIG. 7, the first toned brush 99 is employed to develop the latent electrostatic images on the surface of electroplate 101 in the manner described hereinbefore. The second toned brush 102 is similarly used, and may be spaced apart from the first brush approximately 6 to 8 inches, for example. A developed toner image is produced by the gentle patting-wiping action of the first brush 99 relative the surface of electroplate 101. The

99 and 102 for example, along with a sci-called toner background removing brush 103. This latter-mentioned brush is one which is similar and is operated similarly in all respects to the brushes 99 and 102 except for the fact that the hairs of brush 103 are not moved through a toner source in order to add more toner to the surface of electroplate 101. Instead, brush 103 is caused to run dry" as it were, and to contact only the surface of electroplate 101 whereon there is a toner image already. There is, however, a potential of approximately +600 volts to +1000 volts applied to the hairs of brush 103. As a result, it has been found that such use of a brush 103 permits the removal of nearly all, and for practical purposes, all of the background toner without noticeably altering the toner density of the developed images, thereby producing a clear, clean background printed record.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. A brush developing device for use to develop latent electrostatic images stored in a dielectric member, comprising an electrically insulating member; a plurality of spaced conducting segments positioned on and supported by said member; a latent electrostatic image developing fur brush comprising a non-conductive layer and fibers extending therefrom, said non-conductive layer being secured to and in electrical contact with said conducting segments; means for moving said insulating member so as to move said developing brush relative to the surface of said dielectric member; a source of DC. potential; and distributor means associated with said moving means for connecting said source of potential to difierent select ones of said conducting segments.

2. A brush developer device for use in the latent electrostatic image developing station of an electrographic printer to deposit electroscopic to'ner onto the surface of the printing member whereon the latent electrostatic images are stored, comprising an electrically insulating cylinder; a plurality of spaced conducting segments positioned on and connected to said cylinder; a latent image developing fur brush comprising a non-conducting layer and fibers extending therefrom, said non-conduoting layer being attached to and in electrical contact with the outer peripheral surfaces of said conducting segments; a source of potential; and distributor means for connecting said source of potential to select ones of said conducting segments.

3. For use in a xerographic printer including a xerographic drum having an insulating layer supported by a conductive plate backing therefor, the combination of an electrically insulating cylinder; a plurality of spaced conducting segments positioned on and connected to said cylinder; a latent electrostatic image developing fur brush comprising a non-conducting layer and fibers extending therefrom, said non-conducting layer being secured to and in electrical contact with the outer peripheral surfaces defined by said segments; a source of DO voltage; electrical circuit means for connecting one side of said D.C. source to the said conductive plate of said xerographic drum; and distributor means for connecting the other side of said D.C. source to select ones of said conducting segments.

15 4. For use in a xerographic printer having a rotating Xerographic drum for storing positive latent electrostatic .images, said drum including an insulating layer supported by a conductive plate backing therefor, the combination of a notched electrically insulating cylinder; a plu- 6 rality of spaced conducting segments connected to said cylinder and positioned within the notches thereof; a

a latent electrostatic image developing fur brush comprising a non-conducting layer and fibers extending therefrom, said non-conducting layer being secured to and,

in electrical contact with the outer peripheral surfaces of said conducting segments; a source of DC. voltage; electrical circuit means for connecting the negative side of said D.C. source to said conductive plate; a distributor member connected to the positive side of said D.C.

UNITED STATES PATENTS Lowe Feb. 12, 1867 Vaughan July '10, 1883 Saunders et al. 2.; June 5, 1906 Pino 1-; ;Aug.'6, 1929 Carlson Sept. 12, 1944 Dulken et a1. Feb. 6, 1945 Thomas Oct. 15, 1946 Thomas Apr. 17, 1951 Ewing et a1. June 15, 1954 Mayo et al. .July 27, 1954 Buhler Dec. 13, 1955 Young etal. Jan. 31, 1956 Carlson Sept. 4, 1956 Gundlach Jan. 15, 1957 Grieg Oct. 29, 1957 Hayford Apr. 7, 1959 Vyverberg May 12, 1959 FOREIGN PATENTS Great Britain, 1899

Images