CA1066042A

CA1066042A - Microfield donors with toner agitation and the methods for their manufacture

Info

Publication number: CA1066042A
Application number: CA241,041A
Authority: CA
Inventors: Ernest A.H. Weiler
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1975-02-03
Filing date: 1975-12-04
Publication date: 1979-11-13
Also published as: NL7515147A; FR2299669B1; FR2299669A1; GB1515938A

Abstract

ABSTRACT OF THE DISCLOSURE

Microfield donors used in a xerographic process in which the donor is provided with means for establishing a plurality of electrostatic microfields on the donor surface to attract and hold toner particles so they can be transported to a developing station. The polarity of the established microfields are continuously reversed to alternately repel and attract toner particles to the donor surface during their transportation in order to agitate the toner particles to prevent agglomeration of the particles from forming and to effect nullification of the microfield attracting the particles adjacent a photoconductor to form a high density image free of background deposits in uncharged area of the photoconductive surface. In one alternative embodiment, the donor is spaced from the photoconductive surface by a spacer element to thereby preclude background deposits of toner from forming in the development of an electrostatic latent image on the photoconductive surface.

Description

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I ON
Field of Invention This invelltion relates to xerography and more par-ticularly to an improved apparatus for the development oE an electrostatic imaye in which a toner layer is presented to a latent irnage for its development.

DescriPtion of Prior ~rt:
In the xerographic reproduction process, a photo-conductive surface is charged and then exposed to a light pattern of the information to be reproduced, thereby forming an electrostatic latent image on the photoconductive surface.
Toner particles, which may be finely divided, pigmented, resinous material are presented to the latent image where they arc attracted to the photoconductive surface. The toner image can be fixed and made permanent on the photocon-ductive surface or it can be transferred to another surface where it is fixed.
one known method of developing latent electro-static images is by a process called transfer development.
Transfer development broadly involves bringing a layer of toner to an imaged photoconductor where toner particles are transferred from the layer to the imaged areas.
In one transfer development technique, the layer of toner particles is applied 'ro a donor member which is capable of retaining the particles on its surface and then the donor member is brought into close proximity to the surface of the photoconductor. In the closely spaced position, particles of toner in the toner ]ayer on the donor member are attracted 1, to the photoconductor by the electrostatic charge on the I

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photoconductor so that dcvelopment takes place. In this tecllnique thc toner particles must traverse an air gap to reach the imagcd regions of the photoconductor. In two other transfer techni~ues the toner laden donor actually con-tacts the image photoreceptor and no air gap is involved.
In one such technique the toner-laden donor is rolled in non-slip relationship into and out of contact with the elcctro-static latent image to develop the image in the single rapid step. In another such technique, the toner-laden donor is skidded across the xerographic surface. Skidding the toner by as much as the width of the thinnest line will double the amount of toner available for development of a line which is perpendicular to the skid direction, and the amount of skid-ding can be increased to achieve greater density or greater area coverage.
It is to be noted, therefore, that the term "transfer development" is generic to development techniques where (1) the toner layer is out of contact with the imaged photoconductor and the toner particles must traverse an air gap to effect development (2) the toner layer is brought into rolling contact with the imaged photoconductor to effecc development, and (3) the toner layer is brought into contact with the imaged photoconductor and skidded across the imaged surface to effect development. Transfer development has also come to be known as "touchdown development".
In a typical transfer development system, a cyl.in-drical or endless donor member is rotated so that lts sur-face can be presented to the moving surface of a photoconduc-tive drum bearing an electrostatic la~ent image thereon.
Positioned about the periphery of t~le donor member are a num-lO~t;iV~
ber of processing s-ta~ions includillg a donor loading station, at W}liCh tOIle~ iS rc~aincd o~ the donor membcr surface; an ag~lomerate removal station at which toner agglomerates are removed from the toner layer retained on the surface of the donor member; a charging station at which a uniform charge is placed on the particles of the toner retain~d on the donor surface; a clean-up s~ation at which the toner layer is con-verted into one of uniform thickness and at which any toner agglomerate not removed by the agglomerate removal station are removed; a developrnent station at which the toner parti-cles are presented to the imaged photoconductor for image development; and a cleaning station at which a neutralizing charge is placed upon the residual toner particles and at which a cleaning member removes residual toner from the peripheral surface of the donor. In this manner, a more or less continuous development process is carried out.
Among the typical donor members employed in the process heretofore was a metal cylinder covered with an insulating enamel upon which was coated a metal electrode in a gravure-screen pattern. A potentia' of up to 300 volts is impressed between the electrode and cylinder while the cylinder is rotated in a vibrating tray of toner powder. In a mass of toner that appears to be electrically neutral there will be roughly equal amounts of positively and negatively charged particles. Microsized electrostatic fields for~ned between the electrode and the cylinder cause toner of one polarity to deposit on the electrode and toner of the oppo-site polarity to deposit on the squares in the electrode.
Clumps of excess toner are vacuumed off and the remaining uniformly thick toner layer is corona charged to make it all the same polarity, thus making the donor ready for use in . . .
:

d~velopi~c3 an irn~3~.
~ s discussed previously the latent image on a photoconductive sur~ace could be developed by momentarily "touching down" ~he donor mcmber to the surface. The surface of the photoconduc~r cont~ining the latent image is charged at a greater potential than the donor surface. Therefore, in charged areas of the surface, toner is attracted from the donor to the surface, in uncharged areas the toner-charge image forces ke~p the toner pa-rticles attracted to the donor, and the surface remains free of toner particles. However, it was found that several such "touchdowns" were needed to produce high density images because of a sparse migration of toner particles ~rom the donor to the photoconductive surface.
Thicker coatings of toner produced by various techniques were explored in attempts to obtain the density desired with one "touchdown", but these all seemed subject to the difficulty that where the thick coating of toner touched uncharged areas of the photoconductor surface, some surface toner particles less strongly attracted to the donor transferred to the photoconductor producing an objectionable background deposit. The obvious solution was to bring the donor only very close to the photoconductor but not into contact with it. Toner will jump across a narrow air gap to charged areas of a xerographic photoconductor surface, but not to uncharged areas. The images thus obtained were greatly improved. This latter process has been termed "spaced touchdown".
It has also been found that the quality of image development can be further enhanced if a toner particle is - . ~ . . : .

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repellcd rrom the donor surf<,ce when the particle comes into the reach of an elcctrostatic flux line emanating from the imagc charge on the photoconductor surface. In this case, it can home in on the field line and thus develop the latent image~ At the same time, if the proper charge relationship is established between the toner particlcs and the image and background charges on the photoconductor surface, toner should not move 1:o areas of background on the photoconductor.
For e~ample, U. S. Patent No. 3,257,223 discloses ' T'~ C/~ Ud a powder O~JU1(~ xero~raphic development apparatus in which an aerosol of toner particles are formed adjacent to a photo-conductor surface by removing the positive potential holding the particles to the donor member to create an unstable condition on the surface of the donor because of the great number of closely adjacent toner particles all having the same charge polarity. Owing to the mutual repulsion of these particles, many of the particles are rapidly forced away or "blown off" from the surface of the donor thus form-ing an aerosol in the space between the donor and the photo-conductor surface being developed. charged particles in this aerosol are picked up by the electric field set up by the charge pattern on the photoconductor, thus serving to develop or make visible the charge pattern with these toner particles.
The patentee also discloses that repulsion o~ the toner par-ticles f~ m the surface of the donor may be improved by con-necting its conductive base to a potential source opposite in polarity to that utilized during the loading step rather than merely grounding this base. In this manner the repulsive force of a field emanating from donor member is added to the force of mutual repulsion between the toner particles thereby 10~ 4~

propell:ing ~hc)lll into thc acrosol with greater velocity and uni~orrnity.
The l~rcsent invcntion cxpands and improves on this concept with application to both "in-contact" and "spaced touch~own development~ xerographic apparatus.
Developing across an air gap between the donor and the photoreceptor made it possible to produce background-free images from heavily loaded donors. The gap was maintained by spacers at the ends of the rigid cylindrical donors and photoreceptors. However, it was soon determined that the gap spacing was critical dependent upon the toner loading characteris~ics of the donor.
With the typical donor member previously described, development can be carried out by rolling the donor cylinder in near contact with a charged and exposed xerographic photo-conductive plate or drum. Spacing shims between the donor and photoreceptor, at the ends of the donor cylinder where there is not toner, maintain a space of about 0.001 to 0.002 inch between the surface of the toner and the surface of the photoconductor.
During development a bias potential is applied to the photo-conductor backing to compensate for any residual potential in background areas. If the bias potential is just equal in magnitude but opposite in polarity to the potential on the photoconductor in fully exposed areas, a good image will be produced, but some deposition of toner occurs in background areas~ Such deposition of toner can be suppressed almost completely by increasing the bias potential to about 50 volts more than the background potential of the photoconductor.
Thus, if the potential on the photoconductor in fully exposed areas is +100 volts, approximately -150 volts should be applied , . . ~ , . . . . .
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to the photoconductor b~cking. In th~ development ~tep, spacing must be precisely controlled, and the voltage relation-ships between p)lotoconductor and donor must be adjusted carefully ~o minimiæe b~c~ground deposits without de~rading fine-line detail or li~hter half-tone tints.
~ le interrelationships between the various aspects of image quality and toner-layer thickness, toner charge levels, and spacing between donor and photoconductor can bè
summarized in domain plots of the type illustrated in FIGURE 23, which applies for toner layers charged to potentials of about -200 volts. Generally acceptable images will be produced under the conditions indicated, for the central area between the two lines. As the donor-to-selenium (or photoconductor surface) spacing is reduced, background deposits will appear and become unacceptable. As the spacing is increased, image density drops and the ability of the process to reproduce fine lines and dots is reduced. Attempts to operate with toner layer thicXnesses much less than 0.001 inch produce unsatisfactory images because the donor loading is generally not sufficiently uniform for such thin layers. In general, a donor to photoconductor surface spacing of between 0.001 to 0.010 inches, depending upon toner layer thic~ness can be used with acceptable results.
A microfield donor used in a "spaced touchdown" process can therefore produce good, high density images that do not have severàl o the defects commonly associated with images produced by toner-carrier developers. Although the processing ~teps are simple, there is a need to maintain accurate ~pacings to produce uniformly good images.
SUMM~RY OF: THE INVE:NTIO,N -In accoxdance with one aspect of this invention there is provided a xerographic microfield donor member adapted to ~ - 8 -.:. ~ . -: , . . . . .
.. . ...
~. . . . .

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transport triboelectrically charged toner particles to a latent electrostatic image on the surface of a xerographic photoconductor for development of said i~age, said donor member comprising an endless electrically conductive support member including a plurality of electrically conductive elements separated by di-electric material to isolate said electrically conductive elements from each other, electrical bias means operably connected to each of said electrically conductive elements for biasing each pair of adjacent elements with an electrical potential difference to establish an electrostatic microfield therebetween to attract and hold toner particles to said support member, and means for continuously reversing the electrical bias of each pair of adjacenl elements as said donor transports said toner particles to said photoconductor for alternately repelling and attracting said tonex particles to said support member to cause ag~tation of said toner particles on said support member and when said toner particles are adjacent the surface o~ said xerographic photoconductor to effect nullification of the electrical microfield attracting the particles to said support member.
In accordance with another aspect of this invention there is provided tne method of transporting triboelectrically charged toner particles to a latent electrostatic image on the sur~ace of a xerographic photoconductor for development of said image comprising the steps of forming an electrically conductive support~member by providing a plurality of electrically con-ductive elements, separating said electrically conductive elements by disposing dielectric material between each of said conductive elements, connecting adjacent ones of said conductive elements to a source of different electrical potential so as to establish an electrical potential difference between said adjacent elements attracting toner particles to said conductive elements, "
- 8a -.. ~ . , . . ... .. -1()f~b;042 and continuously reversing the connection of adjacent ones of said conductive elements to said sources of different electrical potential while moving said electrically conductive elements towards the xerographic photoconductor.
By way of added explanation, in accordance with an embodiment of this invention, a new type of - 8b -~r~

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microficld donor ;s proposed or use in "touchclown develop~
ment" of clectros~atic images on a photoeonduetor surfaee.
The donor member can take a variety of forms, altho~gh all of the forms are provided with the common feature of having means to establish a plurality of electrostatic microfields on the donor surface to attract and hold toner partieles to the donor so they can be transported to the developing station and means for continuously reversing the polarity of the estab-lished mierofields to alternately repel and attraet toner partieles to th~ donor surfaee during their transportation to prevent agglomerations of the particles from forming and to effect nulliflcation of the mierofield attracting the partieles to the donor adjacent the photoconduetor so that it can readily be attracted to the latent image on the photo-eonductor to form a high density image free of baekground deposits in uncharged areas of the photoeonduetive surfaee.
In one ~orm of the invention, the donor member ean take the form of a eylindrieal drum eonstrueted from a plur-ality of lamellar segments whieh have been fused or otherwise adhered together to form the eireumferenee of the eylindrieal drum. The lamellar segments ean be punehed or etehed from sheet material whieh may be eoated on one side with a layer of dieleetrie material. The segments are then assembled in a cylindrieal pattern by fusing the dieleetrie interfaees ~o form a rigid eylinder. Onee the segments have been fused into a eylindrieal tube, further proeessing sueh as turning, grinding, lapping, coating, ete. may be used to improve the surfaee eharacteristics and radial run out of the drum.
The conduetive lamellar segments are formed with eommutator tabs and alternate segments are placed in brush _g _ - .

. -~ ~ , , ' , . : - .

106f~04Z
contack ~iith ~Jrourld or a source o~ po,itive potential. As thc drum rotates each conductive scgmcn-t will be pulsed from positive potential to grouncl and then to a positive potential.
Both positive and negativc triboelectrically charged toner particles can be picked up by the drum from a vibrating tray. ~ecau~e o~ rapid change of potential in-duced on the donor electrodes or lamellar segments, the toner will be constantly repelled and attracted from and to the electrodes alony the circum~erence o~ the drum and will be brought into a constant jumping motion along the electrostatic field lines of the donor microfields. When a toner particle comes within the reach of an electrostatic flux line emanating from the image charge on the photoconductive surface, it is repelled by the constantly alternating field induced in the donor electrodes so it can home in on the field line on the photoconductive surface and thus develop the latent image.
By constantly having the toner agitated or vibrated, the electrostatic attraction of the toner particle to the donor is nullified at some point when the donor drum is adjacent to the photoconductor surface and by thus nullifying the elec-trostatic attraction of toner to the donor, the toner may be more readily attracted by the charge induced in the photo-conductor surface, without any great increase in potential of the photoconductor surface over the electrostatic charge in-duced by the microfield of the donor, thus producing a high density image.
Furtherrnore, by inducing a constant alternating attraction and repulsion of the toner particles to the donor, a more uniform distribution of the toner particles along the surface of the donor i5 obtained. Otherwise, the toner par- -10~04;~

ticlcs tend -to agcJlonlcrate an-3 be depositcd on the surface o~ the dono~ ~Ind protru{lc well above t:hc mean thickness of the remalnincJ toner particles. If some provision is not made for cc>ntrolling the thickness of the toner layer carried by the donor, th:icker regions of the toner layer will be compacted bet~Jcen the donor surface and the surface of the photoconductive layer in the developrnent zone, also producing agglomerates. This build-up of toner in certain arcas may result in the deposit of toner on background areas on the photoconductive surface.
Owing to the constant agitation of the toner induced by the alternating field induccd in donor about its circumference, high density images are assured on the photoconductive surface.
Substantially none of the toner is adhered to the donor, but rather floats adjacent to the donor surface. As a consequence, substantially all of the toner coming into close proximity with the photoconductive surace will be attracted to the electrostatic charge on the latent image on that surface. This dispersal is uniform because of the preclusion of the agglomera~ion of toner particles in selected areas of the donor.
With the apparatus of the present invention, it is also possible to obtain a deposit of a greater number of toner particles on the donor since the toner particles con-sist of almost equal quantities of both negative and posi-tively charged particles, rather than biasing the microfield donor so it attracts only negatively charged particles, both positive and negative particles can be attracted and picked up from the toner reservoir.
In another form of the invention the donor element is a conductive cylinder connected to a reference electrical potential. A pair of conductive filaments are wound radially 10~tj04Z

about the circumel^ellce of the drum in between each other.
Each of the conductive filalllents are connected to a source of electrical pote~tial of opposite polarity so that microfields are established between each adjacent pair of filament wind-ings.
The polarity o the conductive filaments can be reversed through commutator contact to agitate the toner particles.
Alternatively, the donor element can be constructed from lamellar conductive rings fused together along dielectric interfaces to form a cylinder. The rings have radial notches cut from their inner circumference and alternate rings are assembled so that their notches are out of phase with res-pect to each other. The notches provide tabs for c~mmutator contact so that alternate rings can be connected to a source o~ electri~al potential of opposite polarity to establish microfields there~etween. As the cylinder rotates, the the polarity of each ring is continuously reversed to agitate the toner particles.
Instead of radial filaments or conductive rings, the donor member can be manufactured using a conductive cylinder having spaced a~ial wires along the cylinder surface attached to pins on opposite ends of the cylinder. The pins can be provided with brush contact so that adjacent wires are con-nected to a source of opposite potential to establish a plurality of microfields on the donor surace. The pins on opposite ends of the cylinder in contact with each axial wire are staggered in spacial relation in parallel planes so that as the cylinder rotates to transport toner particles, the polarity of each wire can be reversed for toner ayitation.

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In ccr~.;n i.nstances it may be advantageous to form ri~ ]~!s or r~ k; and valleys in thc adjacellt wires on the cy~indrical surfac( so that the toner particles will tend to migrate and be held to the cylinder in the wire valleys, rather than extend outwardly from the cylinder surface. By stagyer.ing the location of the pcaks and valleys on adjacent wires, the microEields can be established with electrostatic fl.u~ lines criss-crossing each other between the wires to create denser microfields and cause more uniform dispersal of toner parti.cles on the donor surface adjaccnt the valleys on the wires.
In a st.ill further modif.ication, a cylindrical donor member is constructed from metalized plastic or metal foil coated with a dielectric on one surface thereof which is folded or pleated in accordian-like fashion. After pl.eating, the material is compres.sed to orm a cylinder and the dielec-tric surfaces ar~ fused to rigidify the structure. ~he edges of the structure can then be bored out ancl turned down to form separate conductive segments spaced by a dielectric.
Pre-cut commutator tabs extend from the end plane of the formed cylinder so that alternate conductive segments can be connected through brush contact with a source of electrical potential of opposite polarity to establish the requisite microfields. The polarity of each segment can be continuously reversed as the cylinder rotates through contact of the end tabs with the stationary brushes to efect toner particle agitation.
With this type of construction, criss-cross fields may also be obtained by silk-scrcening or otherwise deposit-ing a staggered gridwork of conductive material on a dielec-tric foil surface and pleating, compressing, fusing and turning :
. ~ . .

- .

iO~;t;04'~ l thc foil il~o a cyl.inder as de.~;crib-d above. Ihe end portions Or the co1~3~c~iv(~ s~reen, whcn viewed :i.n plan about the circumfc:Lcnce of the cylinder, will provide criss-crossed f:Lux linc~, about L1~e cylindcr.
In anot1~er aspect of this invention, a microfield donor is proposed for use in "spaced touchdown development"
of electrostatic images on a photoconductor surface. The donor member can take a variety of forms, although all of the forms are provided with the common feature of havi.ny an element to automati.cally regulate the spacing between the donor and photo-conductor surfaces at the developing station in the xerographic process, and means to establish a plurality of electrostatic microfields on the donor surface to attract and hold toner particles to the donor so they can be transported to the developing station. Additionally, certain ones of said donors can automatieally adjust to any unevenness in the photoconductive surface to maintain the required spacing between the donor and photoreceptor.
In one form of the invention with regard to "spaced touchdown development" the donor element is a conductive cylinder connected to a reference electrical potential. A pair of conductive filaments are wound about the circumference of the drum in between each other. Each of the conductive filaments are connected to a source of electrical potential of opposite polarity 50 that microfields are established between each adjacent pair of filament windings.
If desired, the polarity of the conductive filaments can be reversed through commutator contact to agitate the toner particles for the purposcs described herein earlier with regard to "touchdown development."

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~' , ~Of~tiO4;~

In addition to the conductive filaments windings on the donor c~l;nder, a non-conductive ~ilament of a larger diameter i5 wound about the circumference of the donor in contact with the cylinder .surface between each pair of con-ductive fi]am~nt windings establishing a microfield. The diameter oE the non-conductive filalnent is selected so as to maintain and regulate a predetermined gap between the photo-conductive sur~ace and donor cylinder. This spacing can be determined in accordance with a domain plot such as shown in FIGURE 8a.
Alternatively, a non-conductive filament of pre-determined diameter can be wound radially or in a helix configuration about the donor cylinder and seated on adjacent pairs of the conductive filament windings establishing the microfields.
In lieu of filaments, the microfield donor cylinder itself can be formed from a pair of electrically isolated conductive coil springs compressed in an axial direction with their coils in between each other and mounted between end-bells. The endbells are connected to a source of reference electrical potential such as ground, while each coil spring is connected to a source of negative and positive potential, respectively, to establish a plurality of microfields between adjacent coils. Through commutator contact, the polarity of the coils can be constantly reversed to establish alterna-ting or pulsed microfields for toner agitation as described above. A third dielectric coil spring of larger diameter is then located between the coils of each adjacent pair of coils establishing the microfields to provide the requisite spacing of the donor and photoconductive surfac~s. The ad--1~

'' ' ' " .' ',' '. ' . ',............. ., ,, ' ',, ',.

. , ' '' ', ', ' , ~ ' ' ' , 106~04A~
~).lntag~ 0~ ~li.5 COll',~rU('~i.OI- i S ~la'~ ~lle ~or.,~r cylinder, bCincJ ~lr~ l.e, call a(~just. automatical.l.y to any ~Inev~nn~ss on thc photoco~d~c~or surIacc onto ~ ic]~ ~]-,c ~p.lCC.L^ 5pri.ng con\es into contac~.
Ile~ihi]i1y of the donor drum can also be obtained by using a thin, pneumatic~l.ly pr~ssurized ru}~er drum having a cylindri.cal surface. A conductive screen pattern can be silk-~creen~d or del~osited on the drum surface and in con-junction with a conductive metal layer within tlle interior oE the dielectric rubber drum estal~lish a p].urality of elec-trostatic microEields. Spacers in tl~e form of a gridwork of 1exible protrusions molded on the rubher drum and extending outwardly from the drum surface between the elements of the conductive screen can be used to regulate and maintain ~he gap with the photoconductive surface.
Further advantages of the invention will become more apparent from the follo~ing specification and clai.ms, and rom the accompanying drawings wherein:
BRIEF DESCRIPTION OF ~-IE DR~ GS
FJGURE 1 is a sectional view of xerographic apparatus in accordance with the present invention;
FIGURE 2 is a partial isometric view of a section of a microfield donor used in the xerographic apparatus of FIGURE 1, formed in accordance with the principles of the present invention;
FIGURE ~a is a longitudinal sectional view o~ a portion o~ one embodiment o a self-spacing microfield donor construction in accordance with the present invention;
FIG~RE 3 is a fron~ vi~, partly in section, o~ a portion oE the microfield donor section illustrated in FIGURE 2;

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~06~042 FlGUR~ 3a .i.s an enlar~ed detailcd view of the micro-:field dollor scction il].ustra~ed in FIGURE 2a;
~ IGU~ 4a is a longi.tudina]. sectional view of a portion of another embodiment of a self-spacing microfield -:
donor construction in accordance with the present invention;
FIGURE 5 is a cross-sectional view taken substan-tially along the pl.anc indicated by line 5-5 of FIGURE 2;
FIGURE 5a is an enlarged transverse sectional view of a porti.on of an elllbodiment oE a flexible self-spacing microfield construction in accordance with the present invention;
FIGURE 6 is a partial, top plan view of a precut piece of metal foil used to construct another form of micro-field donor in accordance with the present invention;
FIGURE 6a is an enlarged longitudinal sectional view of the flexible, self-spacing microfield donor construc-tion of FIGURE 5a;
FIGURE 7 is a front view of the foil shown in FIGURE 6 after it has been pleated in an intermediate step of constructing a microfield donor;
FIGURE 7a is an enlarged longitudinal sectional view of a portion of still another embodi.ment of a flexible self-spacing microfield donor construction in accordance with the present invention;
FIGURE 8 is a view similar to FIGURE 7 but showing the further step of compressing the pleated foil strip;
FIGURE 8a illustrates a typical domain plot for determining the proper donor to photoreceptor gap required so as to be able to select a spacer element of predetermined size for a microfield donor construction;

., .. .. . , . . ...................... .... , .. .. . .. ~ . , ,. . : - : :
..

1()6~()4~
.
F~GUI~L 9 is a front view in elevation, partly in section of tl~c oil strip of Fl~UI~ 8 after it has becn fused and cut into a donor cyl.inder.
FlGlJRE 10 is a partial isometric view of a section of the microfield donor cylinder formed in accordance with the steps illustrated in FIGUR~S 6 to 9;
FIGUR~ 11 is a view similar to FIGURE 6, but showing a conductive grid sil]c-scrcened onto a dielectric foil which is used to construct still another microfield donor in ; :
accordance with the steps illustr~ted in FIGURES 6 to 9;
FIGURE 12 is a partial sectional view through the cylinder formed with the foil illustrated in FIGURE 11;
FIGURE 13 is a perspective view of still another microfield donor in accordance with the present invention;
FIGURE 14 is a partial perspective view of the donor illustrated in FIGURE 13 as seen from its opposite end;
FIGU~E 15 is a view similar to FIGURE 14 but using a rippled wire electrode to form cri~s-cro~sed micro~ields on the donor;
FIGURE 16 is a partial, enlarged top plan view of the donor element illustrated in FIGURE 15;
FIGURE 17 is an exploded isometric view of still another microfi.eld donor in accordance with the present ..
invention;
FIGURE 18 is a front view in elevation of one of the lamellar ring elements used i.n the construction of the donor shown in FIGU~E 17;
FIGURE 19 is a front view in elevation of the sub-sequent conductive lamellar ring used in the donor construc-tion shown in FIGUXE 17;

:: , ' ' ' : ` ;, ' ' : , 106~4;~

FIGURF. ~0 is an isometric view of yet another microficld donor in accordance with the present invention;
FIGURE 21 is a partial isometric view of the donor i.llust rated in FIGUR~ 20 as seen from its opposite end; and E~IGURE 22 is a front view in elevation of the donor of FIGURE 20.

El'~ILED DESCRIPTION OF PR13FERRE~D l~MBODI~ ITS
The present invention relates to a transfer deve-lopment xerographic apparatus in which toner particles are applied to an electrostatic latent image on a photoconductive surface to develop an image. Although the apparatus is des-cribed herein as part of a xerographic copier, it can be utilized in conjunction with any reproduction system wherein a latent image is to be developed by applying toner thereto.
Referring now to the drawings in detail wherein like numerals indicate like elements throughout the several views, and more particuIarly to FIGURE 1, there is shown a xerographic reproduction apparatus utilizing the concept of the present invention. In this apparatus a xerographic plate in the form of a cylindrical drum 10 passes through stations A-E in the direction shown by the arrow. The drum has a suitable photosensitive surface, such as one including selenium overlying a layer of conductive material, on which a latent electrostatic image can be formed. The various stations about the periphery of the drum which carry out the reproduction process are: charging station A, exposing sta-tion B, developing station C, transfer station D, and clean-ing station E. Stations A, B, D and E represent conventional means for carrying out their respective functions. Apart , ~
- - ` . ~' , :' ' . ' 10~;~04'~
~rom t~eir ar,socia-tion wi-th the novel arrangement to be cleicribe~ wi~ xesi~ect -to station ~ they form no part of the prcsent invelltion.
~ t station ~, a suitclble charging means 12, e.g., a corotron, places a uniform electrostatic charge on the photoconductivc mater:ial. As the drum rotates, a light pat-tern, via a suitable exposiny apparatus 14, e.g., a projector, is exposed onto the charged surface of drum 10. The latent image thereby formed on the surface of the drum is developed or made visible by the application of a ~inely divided pig-mented, resinous powder called toner, at developing station C, which is described in greater detail below. ~fter the drum is developed at station C, it passes through transfer station D comprising a copy sheet 16, corona charging device 18 and fusing device 20. Following transfer and fixing of the deve-loped image to the copy sheet, the drum rotates through cleaning station E, comprising cleaning device 22, e.g., a rotating brush, at which residu,al toner is removed.
At developing station C, the apparatus includes a donor member 24 (more particularly described below) rota-tably mounted adjacent a toner reservoir 26, containing a supply of toner particles 28~ The donor member 24 is posi-tioned so that a portion of its periphery comes into contact with toner particles 28. 'rhe donor member is also located so as to provide a small gap between the surface of drum 10 and the outer surface of a toner layer carried by donor roll 24. As toner particles are presented to the electrostatic imaged regions of drum 10, the particles traverse this small gap thereby developing the latent image.
Located between toner reservoir 26 and the develop-... . ~ - . : -, 106~i0~

ment ~onc is a c:harging means 30, such as a corona charging device, which is adapted to place a uniform charge on the toncr par~icles of a polarity opposite to thc polarity of the latent illlaye on the photoconductive drum lO.
The construction of microfield donor 24, which carries the toner particles 28 to developing station C, comprises the subj~ct of the instant invention. One form of a particular donor structure which is suitable to carry out the concepts of the invention i5 illustrated in FIGURES 2 to 5, inclusive.
As illustrated in FIGURE 2, microfield donor 24a is constructed from a plurality of lamellae 32. Lamellae 32 are punched or etched from conductive sheet material and sand-wiched between layers of dielectric material 34 which preselec-ted electrical properties. Lamellae 32 may be coated on one side with a similar dielectric material and the lamellar seg-ments may be fi~ed together by fusion of the dielectric interfaces of dielectric segments 34 and the dielectric coat-ing on conductive lamellae 32 in a cylindrical pattern as shown clearly in FIGURE 2. The rigid cylinder 24a so formed may be further processed such as by turning, grinding, lap-ping, etc.
The conductive lamellar segments 32 are formed with a radial extension 36 adjacent their front end. Radial exten-sion 36 is provided with a pair of commutator tabs 38, 40 forming a conductive edge 46 and a pair of commutator tabs 42, 44 forming a conductive edge 48.
Each lamellar segment 32 of microfield donor 24a is oriented so that an electrical potential may be established between any two adjacent segments by alternately electrifying .

106~04Z
or goundi.lly any one of the two adjacent segments through thci.r commutator tah pairs 3~, ~0 and ~2, 44 (~orming cdge 4~) which arc placc(] in sliding contact with statianary brushes 50 and 52, respectively, as the donor 24a rotates about the axis of shaft 54. ~ll of the brushes 50 are con-nected to ground 56 through a slip ring 58 on shaft 54, while all of the brushes 52 are connected to a source of positive potential 58 through a slip ring 60 on shaft 54.
As microfi.eld donor 24a rotates in the direction of the arrow shown in FI~URE 2, each lamellar s~gment 32 on the microfield donor 24a is alternately and rapidly pulsed between ground and a posi.tive potential and then from a positive potential back to ground through sliding contact with brushes 50 and 52. Thus, charged toner 28, which was initially picked up from vibrating reservoir 26 and subjected to a charge of the same polarity by corona charging device 30, is alternately repelled and attracted :
between adjacent lamellar segment.s 32, which act as elec-trodes. In this manner the toner particles 28 are brought into a constant jumping motion along the electrost~tic field lines between the lamellar segments or electrodes 32 as the donor 24a transports them to the development station C.
When a toner particle 28 is repelled from the sur-face of the microfield donor 24a and comes within the reach o an electrostatic flux line emanating from the image charge on the photoconductive surface of drum lO adjacent station C
it can home in on the field line more readi.ly and thus develop the latent image. A~ the same time, toner should not move to the areas of background on the photoconductive drum lO.
Basically the toner is agitated or vibrated on the 106~042 microield donor ~a so tl~at thc toner particles may be at-tracted to the im~e area on the photoconductor more readily by nullifyinc3 -the electrostatic attraction o~ the toner par-ticles 28 to the donor cylinder 2~a. By nullifying the electrostatic attraction at station C the charge on a latent image will be more readily able to pull the toner particles to the image. Further, by enabling the toner to be brought into a constant jumping motion along the donor surface sub-stantially all toner on the surface is attracted to the photoconductive surface of drum 10 enabling a high density image to be developed.
Because o~ the conditions difficult to control, some of the toner particles 28 would normally tend to agglo-merate on a conventional donor surface. These agglomerations would be deposited on the surface of the photoconductive drum 10 causing back~round development. In addition, if some provision is not made for controlling the thickness of the toner layer carried by the donor, thicker regions of the toner layer will be compacted between the donor and the surface of the photoconductor in the development zone adjasent station C
also causing background development.
With the microfield donor 2~a of the present in-vention, however, such agglomeration is substantially eli-minated. By constantly agitating the toner particles 28 by reversing the established microfields, buildups of toner particles on the donor is substantially elirninated as the particles tend to be uniformly dispersed about the cylindri-cal surface.
Also the quantity of toner particles removed from reservoir 28 can be increased. S~nce the re~servoir 26 will : , . :. - - - -; , , . :

04~
contain toner particles which are charyed positively and neg~tiv~ly in ~ubstan-tially ~qual amounts, by constantly re-versing the nlicroEi~lds on the ~onor surface, both types of particles will be initially attractcd to the donor surface.
Also the quantity of toner particles removed from reservoir 28 can be increased. Since the reservoir 26 will contain toner particles which are charged positively and negativcly in substantially equal amounts, by constantly re-versing the rnicrofields on the donor surface, both types of particles will be initially attracted to the donor surface.
It shoùld be understood that alternatc lamellar segments or electrodes 32 in lieu of being connected alter-nately to ground and positive potentials, could be connected to positive and negative potentials, respectively. In this instance the proximity of donor 24a to the toner reservoir 26 or photoconductive drum 10 establishes the necessary ground reference potential. This configuration will not only result in the attraction of a greater amount of electrosta-tically charged toner particles from reservoir 26, but wi~l aid in impelling the particles across the gap at station C i;
by increasing the repelling force on e.g. negative charged particles, rather than merely nullifying the electrostatic attraction to the microfield donor 24a.
Other types of drums or microfield donors could unction with the same alternating or pulse field concept.
For example, a cylindrical donor member 24b as shown in FIGUl~ 10, can be formed as illustrated in FIGUR~S
6 to 9 from metallized plastic or metal foil 70 coated with a dielectric 72 on one surface thereof. The foil 70 is folded or pleated alon~ lines 74 in accordian-like fashion, -2~-, .

:1 0~4Z

as shown in FI~UI~ 7. After pleating, the material is com-pxes~cd as shown in FIGUR~ 8 into a cylindrical configuration and thc adjaccnt dielectric surface 72 arc fused toyether to rigidify the str~lcturc. The edges o~ the structure can then be cut to form separate conductive segments 74 spaced by a d.ielectric 76 as illustrated in FIGURES 9 and lO.
Pre-cut comrnutator tabs 80 and 82 extend from the end plane of the donor cylinder 24b. When donor cylinder 24b is assembled as shown in FIGURES 9 and lO, tabs 82 form a top row and tabs 80 ~orm a bottom row. Each conductive segment 74 has one of each of tabs 80, 82. Stationary brushes 84 and 86 are positioned to contact tabs 82 and 80, respectively, on adjacent segments 74 spaced by dielectric 76, so that alternate conductive segments 74 can be connected to a source of electrical potential of opposite polarity to establish the requisite microfields between alternate con-ductive segments 74. The polarity of each segment 74 can be continuously reversed as the cyli.nder rotates through alter~
nate contact of the end tabs 80, 82 on each segment 74 with the stationary brushes to effect toner particle agitation.
~ lith this type of donor construction, criss-cross fields may also be obtained by silk-screening or otherwise depositing staggered gridworXs 90 and 92 of conductive mate-rial on a dielectric foil surface 70' as shown in FIGURE ll and pleating, compressing, fusing and turning the foil into a cylinder 24c as described above. The end portions of the conductive screen, when viewed in plan about the circumfer-ence of the cylinder as shown in FIGURE 12, will provide criss-crosses flux lines between screen grid elements 94 and 96 about the cylinder 24c. The commutator tab arrange-04;~

m(n~ i~ idcn~ical to tha~ on cyl.ind~r 24b as the condue-tive ~ri.~l~ 90, ~2 cl~-e ext::erldcd onto Ihe dielcctric tabs 80' and 82'.
~ n another ~orm of the invention, the donor member can be manuf~cturecl uciincJ a conductive eyli.nder 24d as shown in FIGU~ES 13 and 14 having an axial wire 100, with two spacecl strands of its conductive surfaces exposed and extending along the eylinder surEace. Wire 100 is looped around a conductive pin 102 and 104 extending outwardly from opposite ends 106 and 108, respective].y, of the eylinder 24d.
An adjaeent axial wi.re 16 is eonneeted to a pin 102 on cyllnder encl 108 and a pin 104 on eylinder end 106. Accordingly, as eylinder 24d rotates, pin 102 on eylinder end 106 ean eon-taet a stationary brush 112 whieh will eonneet both strands of axial wire 100 to a souree of eleetrie pot~ntial of one polarity. At the same time, the strands of adjaeent axial wire 116 are eonneeted to a source of eleetrieal potential of opposite polarity throuyh eontaet of lower pin 102 on eylinder end 108 with a stationary brush 114~ Adjaeent strands of wires 100 and 116 are therefore eonneeted to a souree of opposite potential to establish a mierofield on the donor surfaee between these strands. A series of brushes 112 and 114 arranged at opposite ends of eylinder 24d in eontaet with pins 102 assure that adjaeent strands of the looped axial wires are of different polarity as the eylinder 24d rotates to transport toner par-tieles and the polarity of eaeh wire strand ean be reversed eonti.nuously for toner agitation if eaeh of the series of brushes 112 and 114 are eonneetecl alternatively to sourees of eleetrieal potential having opposite polarity.

-: - .. .. . .

~0~;04'~

:Ln cc~rtain instanccs it may be advantageous to I~onn ri~?L>lcs or l~ca]~s 120 and valleys 122 in thc adjacent axial stran(ls on a cylindrical surface 24e so t:hat the toner part;.clcs wi.ll tend to migrate and be held to the cylinder in the wire vallcys 122, rather than extend out~ardly from the cylindcr surace. sy staggering the location o:E the peaks 120 and valleys 122 on adjacent strands o:E the axial wires, the microfields can bc established with electrostatlc flux llncs crlss--crossing each other between the strands to creatc denser microfield.s and cause more uniform di.spersa].
oE toner particles on the donor surface 24e adjacent the valleys 122.
Alternatively, a donor element 24f can be construc-ted from lamellar conductive rings 124, 126 coated with a dielectric on one surface and fused together through the in-termediary of a dielectric ring 128 to fonn the cyl.inder 24f as shown in FIGUI~E 17. The rings have radial notches 130 cut from their inner circumference. Z~lternate rings 124, 126 are assembled so that their notches 130 are out O:e phase with respect to each other, as shown in FIGURl~S 18 and 19.
The notches 130 provide tabs 132 for contact with stationary brushes 134 and 136 connected to sources oX electrical po-tential of opposite polarity. Brushes 134 and 136 extend the length of cylinder 24f, so that alternate rings can be connected to a source of electrical potential of opposite polarity to establish microfields therebetween. As the cy-li.nder 24f rotates, the polarity of each alternate ring is continuou.sly reversed to agitate the toner particles.
Instead of conductive rings/ in another form of the invention the donor element can be a conducti.ve cylinder ., '" . .:' 10~ 4~ `

24y as shown in FlGUI~ 2() to 22 Wlli.CIl iS subjected to a refercnce ~le~tric~l potcrltial. ~ p~lir of conductive fila-ments 1~0, 142 ~re wo~lnd ra~i~lly about the circumference o~ the drum in ~etween each other. Each of the conductive filamen~s 140, 142 are connected to a source of clectrical potential of opposite polarity through commutator contact so that microfields are established hetween cach adjacent pair of filament windings.
As shown in FIGURF. 20, one end of exposèd filament 140 is connected to a pin 144 extending outwardly from the plane of cylindcr end 146. Onc end of exposed filament 142 is connected to a pin 148 which also extends ou~wardly from the plane of cylinder end 146. I'he opposite ends of fila-ments 140 and 142 are connected to pins 150 and 152, res-pectively, extending outwardly from the plane of cylinder end 154.
Pin 148 connected to filament 142 is initially in contact with a stationary brush 156 and pin lS() connec~cd to filament 140 is initially in contact with a stationary brush 158. Brushes 156 and 158 are connected to sources of electric potential of opposite polarity to establish micro-fields between the adjacent windings of filaments 140 and 142. As cylinder 24g rotates, pin 144 connected to filament 140 will contact stationary brush 160, while pin 152 connec-ted to filament 142 will simultaneously contact stationary brush 162, reversing the polarity of the filaments 140 and 142 to cause toner agitation. When brushes 160 and 162 are operative, brushes 156 ancl 158 are inoperative and conversely, when brushes 156 and 158 are operativc, brushes 16g and 162 are inoperative. Brushes 160 and 158 are connec-ted to sources ,, : . .
.~ , . . . ... . .

04'~

o~ ele~:tr:ical l)otential of the samc polarity, while brushes ~ nd 1.~ C ~imilarl~ situatcd. ~ series of stati~nary brushr.s a; cl:i.;c~.osed are uscd in order to continuously re-vcrse or pulse the established microfields.
Anotl~er form of particular donor structure which is suitable to c~rry-out the concepts of the invention .is il].ustrated i.n FIG~RIS 2a and 3a.
Donor element 24 compri.ses a metalli.c cylindrical drum 24h. Drum 24h is biased to a ground reference potential by its close proximity to toner reservoir 28 and/or the adjacent photoreceptor drum 10. A pair of conductive filaments 32 and 34 are wound about the circumfcrence of drum 24h in between each other. Each of the conductive filaments 31 and 33 are connected to a source of electrical potential of opposite polarity (not shown) so that electrostatic micro-fields are establishecl between each adjacent pair of filament windings such as indicated at 35. If desired, the polarity of the conductive filaments 31 and 33 can be periodically reverscd through commutati.ve contact to agitate the toner particles to preclude the formation of agglomerates on the surface of the donor drum 24h and to effect nulli.fication of the electrostatic attraction of the triboelectrically charged toner particles to the surface of drum 24h as the particles approach the developing station C.
In addition to the conductive filament windings 31, 33 on the donor cyJ.inder 24h, a non-conductive filament 37 of a larger diameter is wound about the circumference of the donor drum 24h in contact with the drum surface between each pair of conductive filament windings 35 establishing a microfield, as clearly illustrated in FIGURE 3a. The diameter .-;04;~

of tl-e no~ condllcLivc filamcrlt 37 is selected so as to main-t<-lirl arl~ r(-~Julat~ d ~)r~cletc~rnl:i.n~(l g.lp l.~etw(e~ th~ photocon-duc~ive surface of drllm 10 arld the donor cylindcr 24h. Th.is spac.incj c,ln be detel-Mi.lled in accordance with a domain plot such as shQ~n in ~I~UR~: ga.
~ lternativc1y, as i]lustrated in FIGURE 4a, a non-conductive filament 39 of predetermined diamèter can be wound radially or in a helix confiyurat;.on about a similar donor cylinder 24i and seated on adjacen-t pairs 35i of the eorlductive filament windings 31i, 33j establishi.ng the mi.ero-fields.
In lieu of filaments, a mieroield donor cylinder sueh as indieated at 24j in FIGURE 6a ean be formed from a pair of electrically isolated eonduetive eoil spr.i.ngs eom-pressed in an axial direetion wlth their eoils 41 and 43 in between eaeh other and mounted between endbells 45. The eoils 41 and 43 of the eompressed springs ean be eoated with a dieleetrie 47 along their faeing surfaees to eleetrieally isolate them from eaeh other.
The endbells 45 are eonneeted to a souree of elee-trieal referenee potential sueh as ground and eaeh eoil spring 41, 43 is eonneeted to a souree of positive and nega-tive potential, respeetively, to establish a plurality of miero-fields, between adjaeent eoils. Through eommutator eontaet, the polarity of the eoils ean be eonstant~y reversed to establish alternating or pulsed mierofields for toner agitation.
A third eoil spring of dieleetrie material and of a larger diameter has its eoils 49 loeated between the eoils of eaeh adjacent pai.r of eoils 41, 43 esta~lishing the miero-fields to provide for appropriate spaeing of the donor 241 ~0~04'~

Erol~ til(- p~otc)~ (e~tor d~um l.O at tlle clevc1.opment station C.
T~e a(lv;lnl age c,r sucl~ a collstrucli.o3l is tll;lt tlle donor cy-~ d(:r 241, I.)~in-J flexi.l~le, can adjuct automatically to any unev~-mncs-~ in the p~oto~onductive surfac~ of photorec~ptor 10 wlli.ch the spacer coils 48 con~act at station C.
Fle~ibility oE the donor drum can also be attained by using a thi.n pneumatically pressured ruhber drum 2~;
as shown in FIGURES 5a and 6a, which has a cylindrical surface.
A conductlve screen pattern 51. can be siJ.k-screen~(l or depo-sited on the drum surface and in conjunction with a conductive metal layer 53 within the interior of the dlelectric rubber drum 24j establish plurality of electrostatic microfields.
Spacers in the form of a gridwork of fleY.ible protrusi.ons 55 molded on the rubber drum 24j and extending outwardly from the drwn surface between the conduct.ive elements of screen 51 can be used to regulate and maintain the gap of drum 24] with the photoreceptor drum 10 at development st~tion C.
With the spacing elements as described above, each of the mierofield donors 24h - 24k can be used in a "spaced touehdown" xerographic process and will produee good high density images. Because of the maintenanee and regulation of the gap between the donor and the photoreeeptor at the developing station C, unaeceptable background deposi.ts will be eliminated~

., .. .~ , ," ~ ~ ,, ,

Claims

WHAT IS CLAIMED IS:

1. A xerographic microfield donor member adapted to transport triboelectrically charged toner particles to a latent electrostatic image on the surface of a xerographic photoconductor for development of said image said donor member comprising an endless electrically conductive support member including a plurality of electrically conductive elements separated by dielectric material. to isolate said electrically conductive elements from each other electrical bias means operably connected to each of said electrically conductive elements for biasing each pair of adjacent elements with an electrical potential dif-ference to establish an electrostatic microfield therebetween to attract and hold toner particles to said support member and means for continuously reversing the electrical bias of each pair of adjacent elements as said donor trans-ports said toner particles to said photoconductor for alter-nately repelling and attracting said toner particles to said support member to cause agitation of said toner particles on said support member and when said toner particles are ad-jacent the surface of said xerographic photoconductor to ef-fect nullification of the electrical microfield attracting the particles to said support member.

2. A xerographic microfield donor member in accordance with Claim 1 wherein each pair of adjacent electrically conductive elements is alternately biased between a reference potential and a positive potential.

3. A xerographic microfield donor member in accordance with Claim 1 wherein each pair of adjacent electrically conductive elements is alternately biased between a negative potential and a positive potential.

4. A xerographic microfield donor member in accordance with Claim 1 wherein said means for continu-ously reversing the electrical bias of each pair of ad-jacent conductive elements includes an electrical commutator system between said electrical bias means and each of said adjacent con-ductive elements.

5. A xerographic microfield donor member in accordance with Claim 4 wherein each of said electrical conductive elements include commutator tabs and said electrical commutator system includes stationary brushes electrically connected to different electrical potentials alternately contacting the commutator tabs on each of said electrically con-ductive elements.

6. A xerographic microfield donor member in accordance with Claim 1 wherein said electrically conductive elements are lamellar segments fused together along dielectric inter-faces.

7. A xerographic microfield donor member in accordance with Claim 1 wherein said electrically conductive elements are formed from conductive foil fused together along dielec-tric interfaces.

8. A xerographic microfield donor member in accordance with Claim 1 wherein said electrically conductive elements are formed from a dielectric foil fused together which has a gridwork of conductive strips printed thereon.

9. A xerographic microfield donor member in accordance with Claim 1 wherein said electrically conductive elements are con-ductive filaments.

10. A xerographic microfield donor member in accordance with Claim 9 wherein said endless conductive support member is a cylindrical drum, and said conductive filaments extend axially along the circumference of said drum.

11. A xerographic microfield donor member in accordance with Claim 9 wherein said endless conductive support number is a cylindrical drum, and said conductive filaments include two conductive filaments wound radially about said drum in between each other.

12. A xerographic microfield donor member in accordance with Claim 9 wherein said conductive filaments include peaks and valleys.

13. A xerographic microfield donor member in accordance with Claim 1 wherein said conductive elements include electrically conductive rings fused together along dielectric inter-faces.

14. The method of transporting triboelectrically charged toner particles to a latent electrostatic image on the surface of a xerographic photoconductor for development of said image comprising the steps of forming an electrically conductive support member by providing a plurality of electrically conductive elements, separating said electrically conductive elements by disposing dielectric material between each of said conductive elements, connecting adjacent ones of said conductive elements to a source of different electrical potential so as to establish an electrical potential difference between said adjacent elements attracting toner particles to said conductive elements, and continuously reversing the connection of adjacent ones of said conductive elements to said sources of different electrical potential while moving said electrically conduc-tive elements towards the xerographic photoconductor.