US3914042A

US3914042A - Toner image transfer apparatus

Info

Publication number: US3914042A
Application number: US221230A
Authority: US
Inventors: Donald W Watson
Original assignee: Xerox Corp
Current assignee: Videojet Technologies Inc
Priority date: 1972-01-27
Filing date: 1972-01-27
Publication date: 1975-10-21
Anticipated expiration: 1992-10-21
Also published as: IT978467B; CA976418A; FR2169350A1; DE2301318B2; CH551031A; BE794567A; JPS5330494B2; JPS4887841A; GB1420281A; NL7301121A; DE2301318A1; BR7300578D0; FR2169350B1

Abstract

Improved toner image transfer methods and apparatus therefor are provided in accordance with the teachings of the present invention wherein a transfer member is charged using ion charging techniques and then is brought into physical contact with a portion of a toner image on a photoreceptor so that such toner image may be selectively transferred onto the transfer member. Ionization of the gap between the charged transfer member and the portion of the photoreceptor having said toner image thereon is avoided by bringing said charged transfer member into physical contact with the portion of the toner image within a time interval which is less than the time interval required by the ion charging source employed to ionize the gap between the portion of the photoreceptor and the approaching transfer member.

Description

United States Patent [:91

Watson 1 1 Oct. 21, 1975 1 TONER IMAGE TRANSFER APPARATUS Primary ExaminerRobert P. Greiner [75] Inventor: Donald W. Watson, Arlington Heights, 111. [57] ABSTRACT [73] Assignee: Xerox Corporation, Stamford, Improved toner image transfer methods and apparatus Conn. therefor are provided in accordance with the teach- Filed Jan 27 I972 ings of the present invention wherein a transfer mem- Appl. No.: 221,230

her is charged using ion charging techniques and then is brought into physical contact with a portion of a toner image on a photoreceptor so that such toner image may be selectively transferred onto the transfer member. ionization of the gap between the charged transfer member and the portion of the photoreceptor having said toner image thereon is avoided by bringing said charged transfer member into physical contact with the portion of the toner image within a time interval which is less than the time interval required by the ion charging source employed to ionize the gap between the portion of the photoreceptor an i the approaching transfer member.

13 Claims, 7 Drawing Figures Patent Oct. 21, 1975 Sheetlof4 3,914,042

Cleaning Station Fig. 28.

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US. Patent 0m. 21, 1975 Sheet 4 of4 3,914,042

TONER IMAGE TRANSFER APPARATUS This invention relates to electrophotographic transfer techniques and more particularly to improved methods and apparatus for selectively transferring developed electrostatic images present on a photoreceptor to a transfer member such as a paper sheet or web.

In conventional electrophotographic processes such as taught in U.S. Pat. No. 2,297,691, as issued to Carlson on Oct. 6, I947, or as contemplated by other electrophotographic techniques well known to those of ordinary skill in the art, a photoreceptor is charged and selectively exposed so that a latent elecctrostatic image representative of the object to be copied is formed due to the selective discharge of the surface of the photoreceptor in accordance with a light and dark pattern representative of the object to be copied. The latent electrostatic image formed is then developed or rendered viewable generally by the application of triboelectrically charged, finely divided particles known as toner, to the image area of the photoreceptor so that such charged particles are deposited in a selective pattern on the image area of the photoreceptor in accordance with the charge pattern exhibited by the latent electrostatic image formed. The developed image as thus formed may then be fixed to the surface of the photoreceptor or as is usually the case transferred to a transfer member, such as a paper sheet, and then fused so that the more expensive photoreceptor is available for subsequent recycling.

When the photoreceptor takes the form of a drum or a continuous web and the various processing stations are arranged about the periphery thereof so that the foregoing electrophotographic processes may be accomplished on a continuous basis as a point on the periphery of the photoreceptor rotates past the various charging, exposure, developing, transfer and cleaning stations in sequence; these conventional electrophotographic processes provide such a powerful, yet practical mechanism for such tasks such as document reproduction and the like that they have virtually eclipsed all other document copying techniques employed in the commercial marketplace. Therefore, it is both logical and predictable that similar electrophotographic techniques be extended to encompass the entire ambit of endeavor associated with the field of information storage and retrieval and this is particularly so whenever it is desirable that information to be selectively retrieved from storage or retrieved in bulk be provided in the form of a permanent document.

In electrophotographic printing apparatus which acts to retrieve information in bulk, such as the label printing apparatus disclosed in U.S. Ser. No. 49,208 tiled on June 22, [970, to Raymond A. Wilmes and assigned to the Xerox Corporation; a plurality of data cards in the form of address cards, microfiche or the like are loaded and processed on a continuous basis so that document information frmo each of the data cards loaded is sequentially reproduced on a paper web. Upon the completion of the run of selected data cards, the paper web may be removed from the electrophotographic printing apparatus and cut or torn along perforated portions of the web to obtain the desired label for addressing purposes or the like, from each of the data cards loaded. The electrophotographic printing apparatus disclosed in U.S. Ser. No. 49,208, supra, employs continuous electrophotographic processing techniques which are similar to those outlined above in that a photoreceptor member in the form of a drum is relied upon and charging, exposure, development, transfer and cleaning stations are disposed about the periphery thereof so that continuous processing is achieved. Thus, as each of the plurality of data cards is fed toward the exposure station, a peripheral portion of the photoreceptor, whose area is sufficient to accommodate the document information on the data card, is sensitized at a charging station formed by conventional corotron apparatus and exposed to image radiation representing the document information on the data card so that a latent electrostatic image is formed. Thereafter as the peripheral portion of the photoreceptor containing the latent electrostatic image formed rotates at a constant angular velocity toward the development station, a latent electrostatic image of the document information on the next data card is in the process of being formed on an adjacent peripheral portion of the photoreceptor member. As each peripheral portion of the photoreceptor member containing a latent electrostatic image rotates through the development station, conventional cascade development techniques are employed to cascade triboelectrically charged toner particles over the photoreceptor so that charged toner particles are deposited in a selective pattern on each peripheral image portion of the photoreceptor member in accordance with the charge pattern exhibited by the latent electrostatic image formed. Upon the completion of rotation through the development station, each peripheral image portion of the photoreceptor member rotates toward the transfer station wherein the toner image is transferred to a paper web or sheet.

At the transfer station, a transfer member which in this case takes the form of a paper web is disposed on the surface of the photoreceptor member in such manner that the transfer member will be in physical contact with the toner image formed at only a few points on the surface thereof due to the absence of a strong force of attraction between the adjacent surfaces of the uncharged paper web and the photoreceptor member while the remaining adjacent surface portions may be separated by an air gap of several microns. The transfer member is adapted for motion in the same direction as the surface of the photoreceptor member in the area of contact therebetween, and the speed of the portion of the transfer member adjacent to the surface of the photoreceptor member is equal to the surface speed of the photoreceptor member. After this initial overlying relationship is established the successive portions of the photoreceptor member having the transfer member disposed thereon are displaced with the rotation of the photoreceptor member so as to be brought into a charging relationship with a corotron present in the transfer station. The portions of the transfer member in a charging relationship with the corotron receive, in the well-known manner, ion charging current so that such surface portions are charged to a uniform potential. The charges applied to the surface of the transfer member migrate to the opposite surface thereof adjacent to the toner image on the photoreceptor and hence induce opposite charges in corresponding portions of the conductive backing of the photoreceptor member. The charge on the portions of the transfer member receiving ion charging current from the corotron thus produce a very substantial force of attraction between corresponding portions of adjacent surfaces of the transfer member and the photoreceptor member thereby bringing such portions of the transfer member into intimate contact with the portions of the toner image on the adjacent portions of the photoreceptor. When these conditions obtain the field strength between the charged portion of the transfer member and the adjacent image portion of the photoreceptor member is sufficient to cause most of the oppositely charged toner to be transferred from the photoreceptor member to the transfer member. This operation will be continued for successive portions of the transfer member on a continuous basis until the entire toner image associated with each peripheral image portion of the photoreceptor has been transferred. Thus, in the well-known manner, the toner image formed on the photoreceptor member by the developing step carried out at the development station is transferred to the paper web so that only residual toner material remains on the surface portion of the photoreceptor associated with a peripheral portion thereof which has passed through the transfer station. Upon completion of the image transfer. the toner image present on the paper web is fused to render it permanent while the peripheral portion of the photoreceptor member which has been processed through the transfer station rotates to a conventional cleaning station where the residual toner is removed so that such peripheral portion of the photoreceptor may again be employed in the formation of another latent electrostatic image when the rotation of the photoreceptor drum next brings it into an operative relation with the charging and exposure stations associated with the latent electrostatic image formation to thereby achieve continuous electrophotographic processing.

Similar continuous electrophotographic processing techniques to those outlined above are disclosed in U.S. Pat. Nos. 3,355,983 and 3,397,106 to R. E. Bogert et al. and E. D. Hewes et al., respectively, which are assigned to the Xerox Corporation. These patents are also directed to electrophotographic printing apparatus which act to retrieve information in bulk; however, here the data cards employed contain miniaturized document information which is enlarged during the reproduction process so that standard size documents are obtained from miniaturized records maintained on the data cards contemplated thereby. In all of the exemplary electrophoto printing apparatus considered above, information is retrieved in bulk and hence each latent electrostatic image formed on the photoreceptor member is developed and subsequently the resulting toner image is transferred to a paper web or sheet. This allows for optimum use of continuous electrophotographic processing techniques wherein the various processing stations are disposed about the path of rotation of the photoreceptor, as aforesaid, but in addition thereto provides for the highly efficient operation of each processing station because they too are each operated on a continuous basis. Furthermore, in each case, the transfer operation may be achieved by first bringing an uncharged transfer member into physical contact with the toner image on the photoreceptor and thereafter imposing the requisite charge level thereon to accomplish transfer whereby highly efficient corona charging techniques may be employed at the transfer station without risk that a gap between a charged transfer member and the photoreceptor, which is here essentially non-existent, will break down and place a like charge on both the toner material and the transfer member to thereby defeat the transfer mechanism by causing the toner image to be forced toward the surface of the photoreceptor due to the force of repulsion manifested between charged bodies or surfaces exhibiting like charge polarities.

ln electrophotographic printing apparatus which acts to selectively retrieve information from storage, such as the DICK STRIP printing apparatus disclosed in U.S. Pat. No. 2,859,673 to l. M. Hix et al.; data cards containing label information are loaded and a charging station, an exposure station and a development station are again disposed about the periphery of a photoreceptor in the form of a drum so that a latent electrostatic image of the document information on each data card is formed and subsequently developed on a continuous basis as the data cards are received at the exposure station. Here, however, data on each card is sensed and compared to preselected conditions as each data card is fed toward the exposure station and only toner images derived from data cards having the preselected conditions are transferred to a paper web at a transfer station which is also disposed about a peripheral portion of the photoreceptor. Thus, in this type of selective electrophotographic printing apparatus, the steps of charging, exposure and development are carried out according to conventional continuous processing techniques employed in bulk retrieval systems; however, the transfer operation to a paper web is carried out on a selective basis to achieve document production for only the document information on data cards meeting the preselected conditions.

As the selective printing apparatus disclosed in U.S. Pat. No. 2,859,673, supra, mandates that the toner images of the DICK STRIP labels be transferred to a web, since the small size of the labels associated with such toner images would render the sheet feeding apparatus needed to accomplish transfer to individual labels both impractical and highly susceptible to jamming, the transfer station employed must be capable of selectively bringing the transfer member into physical contact with the toner image on the photoreceptor and imposing the requisite charge level on the transfer member so that the transfer mechanism, as aforesaid, will operate. Furthermore, to avoid the aforementioned deleterious problems associated with transfer between the toner image and a charged transfer web being brought into physical contact therewith, it is preferable that physical contact between the transfer web and the toner image on the photoreceptor be established prior to the imposition of charge on the transfer member. In U.S. Pat. No. 2,859,673, supra, the transfer station comprises a transfer roller mounted on a pivoted bracket and located in the winding and reeling path of the transfer member in a manner such that the paper web is disposed about a major portion of the periphery of the transfer roller. The pivoted bracket is spring biased in such manner that a portion of the transfer roller having the paper web disposed thereon is normally in a physically engaging relationship with the photoreceptor so that toner image transfer may be accomplished, while a cam means is provided in association with a remote portion of the bracket and adapted, when engaged, to pivot the bracket and hence the transfer roller out of engagement with the photoreceptor. in this manner, when selective transfer is dictated by the comparison circuitry, the cam engagement is released and the web brought into physical contact with the photoreceptor while when image transfer is inappropriate, the cam is rotated into engagement whereby the transfer web is rotated away from the surface of the photoreceptor. With this configuration, the transfer web may not be continuously brought into contact with the photoreceptor prior to charging due to the uniform conductivity of the transfer roller and hence although not specifically stated. the transfer roller can only be biased to about four hundred to five hundred volts (depending upon roller and paper conductivity and paper thickness) in order to avoid the aforesaid problems of air gap ionization and attendant charge transfer between a charged transfer member and a toner image which are being brought into physical contact. The results of these limitations on the operation of the biased transfer roller at such low potential is that transfer efficiency is severely limited and the quality of the image transferred is extremely poor.

Although technically feasible, the use of transfer rollers as a means for establishing a charge on a transfer web is not preferred. This view is taken because transfer rollers as compared to corotron charging devices are notoriously inefficient devices from the stand point of imposing a substantial charge level on an insulating surface and pose a number of serious problems when employed in a toner image transfer environment. For instance, the charging characteristics of a transfer roller are symmetrical and cannot be readily controlled with respect to the transfer member while the point of entry and exit of a transfer member with respect to a charging relationship with a corotron is selectable at will. in addition, the conductivity of a transfer roller must be closely controlled for it to function properly and impose a sufficient charge level to achieve image transfer. However, with transfer rollers, the conductivity varies greatly with changing humidity conditions and aging. Corotrons, however, are not highly sensitive to aging or changing humidity factors and when utilized in a transfer environment generally will allow the transfer web feed apparatus to be highly simplified over those required for use with a transfer roller. Furthermore, while corotrons rarely require cleaning, transfer rollers tend to collect dust in a manner reminiscent of an electrostatic air cleaner and if the transfer web should break will quickly be covered with toner material removed from the photoreceptor as they act, under these conditions, directly as a transfer member. Thus, when used in a transfer environment, transfer rollers require frequent cleaning and often a separate cleaning station must be provided therefor.

Despite the many well-known advantages of corotrons from the stand point of imposing a charge on an insulating surface in general and particularly those attaching to their use within the environment of a transfer station, as aforesaid; corotrons have not, to the knowledge of the inventor, been successfully employed in transfer stations of electrophotographic printing apparatus which acts to selectively retrieve information from storage by selectively transferring toner images formed on a photoreceptor to a transfer medium in the form of a web or a transfer medium which is handled by winding and reeling techniques associated with a web even though corotrons have been widely used in the transfer stations of electrophotographic printing apparatus which acts to retrieve information in bulk. These conditions obtain because, as was brought out above, in any electrophotographic printing apparatus wherein selective information retrieval is achieved by the selective transfer of toner images from a photoreceptor to a transfer member in the form of a web or associated therewith, the transfer station must be capable of selectively bringing the transfer member into physical contact with the toner image on the photoreceptor and imposing the requisite charge level on the transfer member so that the transfer mechanism will operate. However, as is well known to those of ordinary skill in the art, if the transfer member is charged to a substantial level prior to being placed in contact with the toner image, the decreasing air gap between a charged transfer member being brought into physical contact with a toner image on a photoreceptor will generally ionize resulting in charge transfer to the toner image. This defeats the transfer mechanism which usually operates because when the transfer member and the toner image exhibit the same charge polarity they will repel each other whereby the toner image is driven into the photoreceptor and the transfer member takes on the wellknown zebra striped pattern associated with partial or complete failure of the toner image to transfer thereto. Therefore, as corotrons are highly efficient means for imposing a substantial charge level on an insulating surface but may not be practically operated at an intermittent (on-off) rate which is sufficiently fast to accommodate the rate of selective transfer operations required by the angular speed of photoreceptor drums employed in most electrophotographic printing apparatus, the use of corotron charging techniques in the transfer stations of electrophotographic printing apparatus wherein selective information retrieval is obtained by the selective transfer of toner images to a transfer medium in the form of a web or the like has heretofore been considered to be foreclosed by the inability to place the transfer member in physical contact with the toner image prior to imposing a substantial charge level thereon.

This invention proceeds from the discovery that a continuously operating corotron may be successfully employed in a transfer station in conjunction with a web-like transfer member or a transfer member which is handled by winding and reeling techniques associated with a web to obtain selective toner image transfer from a photoreceptor provided the charged transfer member is rapidly brought into initial physical contact with a portion of the toner image to be transferred. More particularly, it has been discovered that a charged transfer member which has been maintained in a charging relationship with a corotron may be brought into physical contact with a selected portion of a toner image without ionization of the gap or charge transfer to the toner image so long as such transfer member is brought into contact with a selected portion of the toner image within a time interval which is less than the time interval required by the corotron to maintain the potential on the surface of the transfer member. When these conditions are met, any charged member may be brought into physical contact with a selected portion of a toner image without exceeding the critical stressspace relationship set forth in the Paschen curve whereby all the advantages of corona' charging techniques may be appropriated for use in a transfer station environment without the risk of partial or complete failure of the transfer mechanism due to the ionization of the gap between the charged toner image and transfer member being brought into physical contact. Once initial contact is achieved between the charged transfer member and the toner image without an ionization of the gap. the transfer operation proceeds in the same manner as if the transfer member were initially brought into physical contact with a portion of the toner image and then charged since its entry point with respect to a charging relationship with the corotron may be made subsequent to its contact point with the photoreceptor.

Therefore, it is a principal object of this invention to provide improved methods and apparatus for selectively transferring toner images from a photoreceptor to a transfer member using ion charging techniques. Various other objects and advantages of the present invention will become clear from the following detailed description of an exemplary embodiment thereof and the novel features will be particularly pointed out in conjunction with the claims appended hereto.

In accordance with the teachings of the present invention, improved toner image transfer methods and apparatus therefor are provided wherein a transfer member is charged using ion charging techniques and then is brought into physical contact with a portion of a toner image on a photoreceptor so that such toner image may be transferred onto said transfer member, ionization of the gap between the charged transfer member and the portion of the photoreceptor having said toner image thereon is avoided by bringing said charged transfer member into physical contact with said portion of said toner image within a time interval which is less than the time interval required by the ion charging techniques employed to maintain the voltage level on said transfer member as said transfer member is moving toward said portion of the toner image. The invention will be more clearly understood by reference to the following detailed description of an exemplary embodiment thereof in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a conventional corona charging transfer station employed within typical electrophotographic printing apparatus which does not give rise to the problems to which the instant invention is addressed but is useful in briefly describing the process of toner image transfer within continuous process electrophotographic apparatus;

FIGS. 2A and 2B illustrate conditions which obtain when corona techniques are employed in a transfer station utilized to selectively transfer toner images to weblike transfer members;

FIG. 3 is a graph depicting the critical stress-space relationship for air gap breakdown between charged surfaces known as the Paschen curve; and

FIGS. 4A-4C illustrate an exemplary embodiment of this invention wherein the improved toner image transfer methods and apparatus therefor are illustrated in an electrophotographic environment associated with the selective transfer of toner images from the photoreceptor to a web-like transfer member.

Referring now to the drawings and more particularly to FIG. 1 thereof, there is shown a conventional corona charging transfer station employed within typical electrophotographic printing apparatus and although not giving rise to the problems to which the instant invention is addressed is useful in briefly describing the process of toner image transfer within continuous process electrophotographic apparatus and lending an understanding to such problems. The electrophotographic processing equipment illustrated in FIG. 1 as well as that described below has been set forth because the improved transfer methods and the apparatus therefor taught by this invention are considered to best admit of a full and complete disclosure within an environment in which they might ordinarily be expected to function; however, as will be readily appreciated by those of ordinary skill in the art, the details of the electrophotographic processing equipment, and the processes set forth form no part of the present invention per se and accordingly are disclosed for the purposes of explanation rather than limitation.

As shown in FIG. 1, the electrophotographic equipment illustrated takes the form of continuous processing electrophotographic apparatus based upon the con cepts originally disclosed in U.S. Pat. No. 2,297,69l, issued to Carlson on Oct. 6, l947, and accordingly comprises a photoreceptor 2, a charging station 4, an exposure station 6, a development station 8, a transfer station 10 and a cleaning station 12. The photoreceptor 2 as illustrated in FIG. 1 may take the conventional form of a drum or endless web adapted to rotate in the direction indicated by the arrow A. The photoreceptor 2 may take any well-known structural configuration and for the purposes of the instant disclosure has been illustrated as a simple two layer drum 2 including an insulating member 14 and a conductive member 16. As the photoreceptor 2 forms no part of the instant invention, it is here sufficient for an appropriate understand ing of this disclosure to appreciate that if the photoreceptor 2 is employed in conjunction with conventional electrophotographic techniques, the conductive member f6 may be formed of any suitable conductive material or a nonconductor overcoated with a conductive foil. Similarly, the insulating member 14 would ordinar ily be formed ofa material, such as selenium, displaying photoconductive characteristics such that the member 14 is normally insulating and exhibits excellent charge retentivity but may be rendered selectively conductive by the application of electromagnetic radiation thereto through a light and dark pattern representing an object to be copied or alternatively, reflection exposure techniques may be employed. The photoreceptor 2 is disposed in an operative relationship with each of the processing stations arranged about the periphery thereof so that upon appropriate energization of the illustrated electrophotographic equipment, the rotation of the photoreceptor 2 in the direction indicated by the arrow A, as aforesaid, will subject each point on the periphery of the insulating member 14 to the process step performed at each such station.

The charging station 4 may take the conventional form of one or more charging devices 18 which act in the well-known manner to sensitize the photoreceptor 2 by charging the surface of the insulating member 14 to a uniform potential. Although any conventional form of charging device 18 may be relied upon to impose a charge level on the surface of the photoreceptor 2, corotron devices having half-round shield configurations have been illustrated in FIG. 1 because the utilization of corotrons in typical electrophotographic equipment is usually preferred. The structure and mode of operation of corotrons such as are illustrated in FIG. 1 are well known and are described in detail in U.S. Pat. Nos. 2,836,725 and 2,879,395, to Vyverberg and Walkup, respectively. Therefore, for the purposes of the instant disclosure, it is sufficient to appreciate that the coronode 19 of the depicted corotron I8 is connected to an appropriate source of high potential V;

and the corotron l8 acts in the conventional manner to charge the surface of the photoreceptor 2 disposed thereunder to a uniform potential.

The exposure station 6 is also disposed about the periphery of the photoreceptor 2 and may take the conventional form of a projection system or the like wherein optical transmission or reflection techniques are relied upon to image a light and dark pattern representing the object to be copied onto the surface of the insulating member 14 disposed thereunder. In PK 1, a slit exposure device has been generally indicated; however, any optical system which relies upon lenses or the like may be readily employed. Additionally, although the exposure station 6 illustrated in FIG, 1, has been shown positioned in such manner that the rotating photoreceptor is initially sensitized by the charging station 4 and subsequently exposed, it will be apparent that the processing steps of charging and exposure may be carried out simultaneously by altering the position of the exposure station 6 and/or the charging station 4. Furthermore, although only the simplified processing steps of a single charging operation and a single exposure are depicted in FIG. 1, it will be obvious that additional electrophotographic processing steps such as another charging operation may be employed in the formation of the latent electrostatic image or the latent electrostatic image formed may be reversed or otherwise altered by the use of such additional processing steps as is well known to those of ordinary skill in the art. The photoreceptor 2 is next presented to the developing station indicated generally at 8 where a latent electrostatic image formed is developed.

The development station 8, as illustrated in FIG. 1, may take the form of a conventional cascade developer station which includes a hopper 24 suitable for subjecting appropriate portions of the photoreceptor to a cascade development step or the like, and a reservoir 26 for supplying developer material to the hopper 24 and receiving cascaded developer material after it has been cascaded over the photoreceptor 2. The reservoir 26 is maintained filled to an appropriate level, as indicated, with developer material in the form of conventional carrier beads and toner material and is additionally provided with conventional conveyor means, not shown, through which developer material is supplied to the hopper 24 during such times as the development station 8 is operating. The development station 8, acts in the well-known manner, to flow developer material, in the form of carrier beads having a plurality of toner particles clinging to the surface thereof, from the hopper 24 over the peripheral portions of the photoreceptor 2 in an operative relationship therewith so that toner material will be deposited on the peripheral portion of the photoreceptor in accordance with charge pattern exhibited thereby.

Upon the completion of the rotation of the periphery of the photoreceptor 2 through the development station 8, the portion of the photoreceptor 2 having a de veloped toner image thereon next proceeds to the image transfer station whereat image transfer takes place. The image transfer station 10 comprises a transfer member 28 and ion charging means 30 for imposing a predetermined charge on such transfer member 28 to thereby effect transfer of the toner image from the surface of the photoreceptor 2 to the transfer member 28. The transfer member 28 may here take the form of a sheet, web or drum formed of suitable transfer material such as paper, plastic or any of the other well-known materials conventionally employed as transfer materials, as it is here assumed that all toner images formed on the surface of the photoreceptor 2 are to be transferred in the manner characterizing the bulk informa tion retrieval systems discussed above. Alternatively, as shall become more apparent below, if the electrophotographic processing apparatus depicted in FIG. 1 is considered to be employed in a selective transfer information retrieval system, the transfer member 28 must take the form of a sheet wherein one sheet is fed for each image to be transferred so that such sheet may be placed in physical contact with a portion of the toner image to be transferred at a location which is prior to a location where charging takes place. The charging means 30 may take the form of a half-round corotron, as illustrated, which may be structured in the same manner as the charging means illustrated at the charging station 2 and described above. Alternatively, any other conventional form of charging means such as those discussed in conjunction with the charging station 2 may be employed in place of the charging means 30 illustrated in FIG. 1, it being appreciated corotron devices are preferred as they are not highly sensitive to aging or changing humidity conditions, they enable simpler transfer member handling systems to be employed, the entry point of the transfer member 28 into a region where charge is imposed may be readily controlled, and should a misfeed or break in the transfer member 28 occur, they will not be clogged with toner material deposited on the photoreceptor 2. The charging means 30 illustrated in H6. 1 is connected to a suitable source of potential V, which may take the form of a conventional d.c. supply. At this point in the description, it should be noted that the transfer member 28 and the transfer station 10 are limited to operating conditions wherein the transfer member 28 is in physical contact with the toner image prior to being charged and hence considerations relating to gap ionization between a pair of charged surfaces being brought into contact are not relevant.

Upon completion of the electrophotographic operation at the transfer station 10, the image portion of the photoreceptor 2 next passes to the cleaning station 12 where residual toner particles are removed from the surface of the photoreceptor 2 preparatory to the subsequent formation of a new latent electrostatic image on the photoreceptor 2. The cleaning station 12 may take the conventional form of rotating fur brush cleaning means, wiper means or cascade cleaning means which act in the well-known manner to remove residual toner from the surface of the photoreceptor 2.

in the operation of the electrophotographic processing apparatus illustrated in H6. 1, it will be appreciated that a latent electrostatic image of document information from each of the data records to be retrieved will initially be formed on a peripheral portion of the photoreceptor 2 by the combined action of the charging station 4 and the exposure station 6. Thus as each data record or data card is received at the exposure station 6, the rotation of the photoreceptor 2 will present succeeding, sensitized peripheral image portions of the photoreceptor 2 to the exposure station 6 so that adjacent latent electrostatic images of the document information on the data cards present are formed about the periphery of the photoreceptor 2. Each latent electrostatic image is formed, upon the energization of the electrophotographic apparatus depicted in FIG. 1, by conventional electrophotographic processes well known to those of ordinary skill in the art. Thus, when the electrophotographic apparatus illustrated in FIG. 1 is energized, the charging means 18 present at the charging station 4 will impose a charge on the portions of the photoreceptor passing therebeneath by the application of ion charging current thereto. The surface of the photoreceptor 2 will thus be charged to a uniform potential by the action of the charging means 18 which is illustrated in FIG. I as comprising a conventional corotron. Upon the completion of the charging or sensitizing operation which takes place at the charging station 4, the rotation of the photoreceptor 2 in the direction indicated by the arrow A will bring the previously charged portions of the photoreceptor 2 into an operative relationship with the exposure station 6. The exposure station 6 acts in the well-known manner to selectively expose the photoconductive portion of the photoreceptor 2, which here takes the form of the insulating member 14, to electromagnetic radiation from the document information on the data card presently at the exposure station 6. Thus, the exposure station 6 acts to image a light and dark pattern representative of the image to be formed on the charged surface of the insulating member 14 of the photoreceptor 2. Upon exposure, the photoconductive insulating member 14 is rendered selectively conductive, in the well-known manner, so that the charge levels on the light struck portions thereof are substantially reduced while charge levels on portions thereof which correspond to dark portions of the image area are maintained at the relatively high charge levels imposed at the charging station 4. Thus, in this well-known manner, latent electrostatic images are formed on the photoreceptor 2 by the combined action of the charging station 4 and the exposure station 6 for each data card received at the exposure station.

As it is being assumed that document information from each data card presented to the exposure station 6 is to be retrieved, the development station 8 may be considered to be continuously energized. Therefore, as each of the latent electrostatic images previously formed enter the environment of the development station 8, developer material is cascaded over each image in a continuous manner until the rotation of the photoreceptor causes that peripheral image area to again leave the peripheral area occupied by the developing station 8. The developer material delivered to the surface of the photoreceptor 2 from the hopper 24 will flow over the surface of the photoreceptor 2 in the form of carrier beads having a plurality of toner particles clinging to the surface thereof due to the electrostatic force of attraction exhibited therebetween. As the developer material is applied to the surface of the photoreceptor 2, the carrier-to-toner bond of the cascading developer material will be overcome by the charged portions of the latent electrostatic image on the photoreceptor 2 in proportion to their magnitude, causing such toner particles to selectively adhere to the area occupied by the latent electrostatic image in accordance with the charge variations displayed thereby. In this manner, as is well known to those of ordinary skill in the art, upon the completion of the rotation of each peripheral image area through the development station 8, toner material is deposited on each image area of the photoreceptor 2 in accordance with the charge configuration of the latent electrostatic image formed so that a toner image thereof is established.

When each image area of the photoreceptor 2, as now represented by a developed toner image arrives at the transfer station 10, it will come into physical contact with the transfer member 28, which is disposed on the surface of the photoreceptor 2 and moving in the direction indicated by the arrow B at the same speed as an adjacent point on the periphery of the photoreceptor 2 in contact therewith. The physical contact established at this juncture between the transfer member 28 and corresponding points on the photoreceptor 2 is such that the transfer member 28 will be in physical contact with the toner image formed at only a few points on the surface thereof due to the absence of a strong force of attraction between the adjacent surfaces of the transfer member 28 and the photoreceptor 2 while the remaining adjacent surface portions therebetween may be separated by an air gap of several microns. When the successive portions of the photoreceptor 2 having the transfer member 28 disposed thereon are displaced so as to be in a charging relationship with the corotron 30, portions of the transfer member 28 in a charging relationship therewith will receive ion charging current along the width thereof so that such surface portions are charged to a uniform potential. The charges applied to the surface of transfer member 28 will migrate in the well-known manner to the opposite surface thereof adjacent to the toner image and hence will induce opposite charges in corresponding portions of the conductive backing 16 of the photoreceptor 2. The charge on the portions of the transfer member 28 receiving ion charging current from the corotron 30 will produce a very substantial force of attraction between corresponding portions of the adjacent surfaces of the transfer member 28 and the photoreceptor 2 thereby bringing such portions of the transfer member 28 into intimate contact with the portions of the toner image on the adjacent portions of the photoreceptor 2. When these conditions obtain, the field strength between the charged portion of the transfer member 28 and the adjacent portion of the photoreceptor 2 will be sufficient to cause most of the oppositely charged toner to be transferred from the photoreceptor 2 to the transfer member 28. This operation will be continued for successive portions of the transfer member 28 on a continuous basis until the entire toner image rotating through the transfer station 10 has been transferred to the transfer member 28 and under the conditions here assumed will be repeated for each succeeding toner image until the bulk retrieval operation is completed. Thus, in the well-known manner, each toner image formed on the photoreceptor 2 by the developing step carried out at the development station 8 is transferred to the transfer member 28 so that only residual toner material from the step of development remains on the surface of the photoreceptor 2.

The rotating image portions of the photoreceptor 2 are next brought into an operative relationship with the cleaning station 12 so that residual toner material may be removed from the image portion of the photoreceptor 2 prior to reuse. The cleaning station 12 may be entirely conventional, as aforesaid, so that if nontacky toner material was relied upon. the image portion of the photoreceptor 2 may be wiped by a conventional rotating fur brush or cotton wiping means may be employed. Alternatively, the cleaning station 12 may employ cascade cleaning techniques wherein granular material, which acts similarly to the carrier beads in a two component developer material, is cascaded over the image portion of the photoreceptor in the well-known manner and residual toner particles are attracted from the surface of the photoreceptor 2 by triboelectric attraction without danger of marring or scratching the surface of the photoreceptor. Upon the completion of the cleaning step, each peripheral image location on the photoreceptor 2 may be again utilized to form additional toner images of the document information being supplied to the exposure station 6 whereupon the steps of the formation of succeeding latent electrostatic images, development, transfer and cleaning may again be repeated.

[f the succeeding image transfer operations disclosed in conjunction with HQ. 1 are reviewed, it will be appreciated that the continuously moving transfer member 28 always had an uncharged portion thereof in physical contact with the photoreceptor surface throughout the course of the bulk information retrieval operation discussed. These uncharged portions of transfer member 28 were subsequently charged by the corotron 30 to affect toner image transfer; however, at no time was the transfer member 28 first charged to a substantial level and thereafter brought into physical contact with the toner image on the photoreceptor. These conditions here obtain because in the bulk retrieval operation assumed, each toner image formed is transferred and hence the continuously moving transfer member may be maintained in a contacting relationship with the photoreceptor 2 at a point prior to that at which a charge is imposed so long as the speed of the transfer member 28 at the points of contact is equal to the rotational speed of adjacent points on the photoreceptor. A similar relationship could be achieved in a selective transfer operation provided a sheet-like transfer member is employed and the toner images to be transferred are sufficiently large so that practical sheet feed apparatus could be designed to feed an individuai sheet at the proper speed and time to serve as an independent transfer member for each selected image. However, where the toner images to be selectively transferred are small, representing label'information or the like, and are closely spaced about peripheral portions of the photoreceptor 2; jam-free sheet feed apparatus to supply an individual transfer member for each toner image to be transferred is not practically available. Under these conditions, a web-iike transfer member which may be stopped and then quickly brought to speed by conventional winding and reeling techniques is the only practical solution. Therefore, if a transfer station employing a corotron such as that shown in FIG. 1 is desired, such transfer station must be operated by maintaining the corotron energized, and selectively starting and stopping the web in relation to the presence or absence of a toner image to be transferred and selectively bringing an appropriate portion of the web which is moving at the same speed as the toner image to be transferred into physical contact with an appropriate portion of the toner image to be transferred. FIGS. 2A and 2B illustrate pertinent conditions which obtain when a transfer station utilizing a corotron and a web-like transfer member are operated in the foregoing manner and are employed to provide what is considered to be the most probable explanation for the failure of the prior art to successfully operate ion charging transfer stations in this manner as well as what is thought to be the most probable explanation for the success of the instant invention.

FIGS. 2A and 2B illustrate conditions which obtain when corona charging techniques are employed in a transfer station utilized to selectively transfer toner images to a web. In FIGS. 2A and 28 only a photoreceptor and a transfer station 33 employing a corotron 34 have been illustrated because only conditions which obtain in a selective transfer operation are here of interest; however, it will be appreciated that these elec trophotographic components may be present within continuous electrophotographic processing apparatus of the type described in conjunction with FIG. 1 and that a latent electrostatic image which may be subsequently developed into a toner image is formed for the document information on each data card or the like presented to the exposure station and subsequently presented to the transfer station 33 due to the rotation of the photoreceptor 32. For more details anent selective printing apparatus wherein selective toner image transfer to a web is employed, reference may be had to application Serial No. 221,229 filed on equal date herewith in the names of Hutner et al. The photoreceptor 32 and the corotron 34 illustrated in FIGS. 2A and 28 may be considered to take the same form and perform the same functions as the photoreceptor 2 and the corotron described in conjunction with FIG. 1 however, the partially shown transfer web 35 is disposed about a turn-around roller 36. The winding and reeling apparatus for driving the transfer web or strip 35 has been indicated in FIGS. 2A and 28 by the arrows C-C', it being appreciated, as will become apparent below, that any conventional winding and reeling apparatus capable of selectively stopping and starting the transfer web 35 could be employed so long as once the motion of the transfer web is started, it is quickly brought to speed. Specific details of suitable winding and reeling apparatus for the transfer web 28 may be had by reference to application Ser. No. 221,229 supra. Additionally in FIGS. 2A and 2B the corotron 34 should be considered to be operating on a continuous basis wherever the depicted electrophotographic processing apparatus is energized, the peripheral image portion 37 of the photoreceptor 32 should be considered to represent an image which is not to be transferred while peripheral image portion 38 should be viewed as representing a toner image to be transferred.

When, as illustrated in FlG. 2A, the peripheral image portion 37 of the photoreceptor 32, which is not to be transferred, is present at the transfer station 33, the transfer web 35 must be displaced from the surface of the photoreceptor 32 and preferably stopped. The displacement of the transfer web 35 is required so that erroneous transfer and toner fouling of the transfer member will not result while stopping of the transfer member during periods when no transfer is to occur is preferred to avoid the presence of long intervals on the transfer member where no images are present and the waste and inconvenience associated therewith. Under the static conditions illustrated in FIG. 2A, the corotron 34 will charge the transfer web 35, across the portion of the width thereof disposed under the coronode wire and along an effective length of about I in. for the single corotron configuration shown, to a uniform potential associated with the potential applied to the coronode by potential source V Thus, if it is assumed for the purposes of explanation that the coronode is maintained at a potential of 7 KV by the d.c. potential source V,. the corotron 34 will charge the portion of the transfer web 35 disposed thereunder to a potential of approximately 2 KV and this will occur substantially independent of the spacing between the coronode and the transfer web 35 so long as reasonable spacing relationships are maintained between the coronode, the transfer web 35 and the photoreceptor 32 whose interior layer, illustrated in FIG. 1, acts as a ground plane. This occurs in corona charging configurations because even though the ion current delivered to a surface being charged will vary in accordance with the potential on that surface as viewed by the coronode, the potential to which an insulating surface is charged for a given set of corotron parameters under steady state conditions tends to remain constant. Thus, when the transfer web 35 is stopped and disposed in a removed position from the surface of the photoreceptor by a distance which may here be assumed to be approximately /5 in., the surface of the transfer web disposed under the corotron 34 will be charged, under the exemplary conditions specified herein, to a uniform potential of approximately 2 KV.

When the rotation of the photoreceptor 32 causes the peripheral image portion 37 to leave the region of the transfer station 33 and bring the toner image 38, which is to be transferred, into a transfer relationship therewith, the transfer web 35 must be brought to the same speed as the velocity ofa point on the toner image to be transferred and placed in physical contact with the surface of the photoreceptor 32 as shown in FIG. 2B. This may be readily achieved by energizing the winding and reeling apparatus associated with the transfer web drive and by displacing the turn-around roller 36 or any other appropriate guide means associated with the transfer web drive in an upward direction so that point or are contact is established between the transfer web 35 and the surface of the photoreceptor 32. This action might be expected to achieve transfer of the toner image 38 from the surface of the photoreceptor 32 to the transfer web 35; however, what generally occurs is a partial or complete failure of the transfer mechanism resulting in the well-known zebra striping of the image on the transfer web 35.

An analysis of this situation has indicated that when a charged, insulating transfer surface, such as represented by the transfer web 35 in FIGS. 2A and 2B, is brought toward the photoreceptor 32 in the presence of a charging corotron, the air gap between the approaching transfer member and the photoreceptor surface will ionize resulting in charge transfer between the charged transfer member 35 and the toner image 38. This results in the toner image acquiring the same charge polarity as the approaching transfer member and hence the toner image is repelled by the approaching transfer member rather than being attracted thereto as in cases where the transfer member is initially disposed on the surface ofthe photoreceptor and is subsequently charged. These conditions thereby cause the toner image to be driven into the photoreceptor and defeats the transfer mechanism which normally operates. This invention however, as stated in the introduc tory portions of this specification is based upon the discovery that a charged transfer member may be brought into physical contact with a toner image on a photoreceptor in the presence of a continuously operating corotron to accomplish successful image transfer so long as the approach and contact with the photoreceptor is achieved rapidly with respect to the charging rate.

A detailed investigation of the reasons underlying air gap ionization under conditions such as disclosed above was undertaken in an effort to ascertain the operative factors enabling the inventive transfer principles contained herein. The conclusions reached during this investigation are briefly set forth below in an effort to provide what is considered to be the most probable explanation for the ionization of the air gap which defeats toner image transfer under the conditions described above as well as what is thought to be the most probable explanation of the operative factors enabling the instant invention. In setting forth these conclusions, periodic reference will be made to FIG. 3 which is a graph depicting the critical stress-space relationship for air gap breakdown between charged surfaces known as the Paschen curve. In the graph set forth in FIG. 3, the air gap in microns t) is plotted along the abscissa while the electric field in the air gap in volts per micron (V/p.) is plotted along the ordinate. As will be apparent to those of ordinary skill in the art, the Paschen curve indicates the values of electric field in the air gap which will cause air gaps of various dimensions to ionize. Hence to successfully bring a charged transfer member into physical contact with a toner image on a photoreceptor 32 without the ionization of the air gap, which defeats the transfer mechanism as aforesaid, the entire approach and ultimate physical contact of the transfer member 35 must operate beneath the Paschen curve. The Paschen curve plotted in FIG. 3 may be considered to define typical critical stress conditions when conventional photoreceptor and transfer member materials are employed.

For the static conditions associated with the transfer web 35 depicted in FIG. 2A, it will be recalled that it was assumed that the transfer web 35 was displaced by a distance of 56 in. from its point or are of contact with the surface of the photoreceptor 32, i.e., the condition illustrated in FIG. 2B, and that the coronode of corotron 34 was maintained at a potential of 7KV by the d.c. potential source V, whereupon the effective portion of the transfer web 35 in a charging relationship with the corotron 34 was charged to a uniform poten tial of approximately 2 KV. This establishes a field of approximately 5% v/p. in the one-eighth inch (h in.) air gap. Reference to the Paschen curve depicted in FIG. 3 will indicate that for large air gaps, i.e., those exceeding 50 p. the Paschen curve is asymptotic to a value of approximately 8 v/p. and rises slowly to a value of approximately 40 v/p, for an air gap of 10 p. before breaking sharply upward to become asymptotic to a vertical axis drawn through the zero (0) air gap value of the abscissa which indicates, incidentally, why placing an uncharged transfer member in physical contact with a photoreceptor and thereafter charging the transfer member will not result in a breakdown. Therefore as the A v/p. field established for the static conditions illustrated in FIG. 2A is at least a full order of magnitude below the critical stress value of approximately 8 V/p. indicated by the Paschen curve for large air gaps; the static conditions assumed to be present on the photoreceptor 32 when the same is displaced by a distance of b in from the portion of the surface of the photoreceptor 32 to be contacted during transfer are clearly below the critical stress values indicated by the Paschen curve and hence such static conditions will not result in an ionization of the $6 in air gap.

Focusing now on the transfer member, it will be appreciated by those of ordinary skill in the art that the charge in coulombs on the transfer web 35 is given by the expression Q CV, m where C represents the capacitance between the transfer web 35 and the photoreceptor 32 in farads and V represents the voltage in volts on the transfer web 35 with respect to the ground plane of the photoreceptor 32. In terms of unit area, the expression Q CV becomes where s equals the permittivity of free space and of the air.

If it was practically feasible to turn off the corotron 34 when the transfer web 32 is to be brought from its displaced position in FIG. 2A to the selective transfer position shown in FIG. 2B, The equation 0' 0V plainly indicates that no ionization of the air gap could occur to defeat the transfer mechanism because as most transfer members are fairly good insulators, cr would remain constant so that the linear increase in capacitance with the linear decrease in the distance between the photoreceptor and the approaching transfer member, as given by the expression where 0 represents the capacitance, A is the area of the charged plates as represented by adjacent surface portions of the photoreceptor and transfer members and d represents the distance between the photoreceptor and the approaching transfer member, would only result in a linear decrease in the voltage V. Therefore, as under these conditions awould remain constant, the electric field in the air gap, as yielded by expression 3, would remain constant. Thus, as the initial conditions established in the air gap were well below the critical stress for ionization delineated by the Paschen curve, no ionization would occur because while the Paschen curve increases, as aforesaid, in terms of critical stress for decreasing air gaps, the electric field would remain constant since the potential of the transfer member would merely be sliding down the potential gradient established under the static conditions depicted in FIG. 2A.

The corotron 34, however, may not be practically operated in such manner that it is turned off whenever a selective transfer is to occur and hence it must remain energized while the transfer web 35 is being brought into selective physical contact with the photoreceptor 32. Therefore, since the corotron 34, as aforesaid, seeks to maintain a uniform potential in the effective portion of the transfer web 35 disposed in a charging relationship therewith regardless of its displacement therefrom, whenever selective transfer is to occur the corotron 34 will attempt to maintain the potential on the portion of the transfer member 35 approaching the photoreceptor 32 constant. Thus, if the conditions imposed by the continuously operating corotron 34 are considered in light of the expression (2) 0' 6V, it will be appreciated that as the corotron 34 seeks to hold V constant and c linearly increases with the decreasing size of the air gap as the transfer web 35 approaches the photoreceptor 32, the charge density 0' will tend to increase in a linear manner as the transfer member 35 approaches the photoreceptor. This tencency of the charge density 0' to linearly increase with the approach of the transfer member 35 to the photoreceptor 32 will result in a directly porportional increase in the electric field E. in the air gap as yielded by equation (3), i.e., E 0/6,; and clearly places the transfer operation above the critical stress limitations imposed by the Paschen curve because this curve exhibits only a very slowly rising characteristic for the interval of the approach of the transfer member defined between large air gaps and those of 10 1 Thus, it will be apparent that in previous attempts to provide selective transfer operations to a selectively engaged web which was continuously exposed to an energized ion charging device, the failure to obtain proper transfer which generally occurred resulted from an overwhelming of the critical stress limitations of the air gap as the transfer member approached the toner image to be transferred due to the action of the ion charging device.

in considering the manner in which the corotron 34 seeks to maintain the potential on the transfer member 35 constant despite its approach to the photoreceptor 32, equation (2) should be first transposed to yield the expression which renders it apparent that if the voltage V is to be maintained constant the charge density aon the portion of the transfer member 35 approaching the photoreceptor must be increased to compensate for the linear increase in the per unit area capacitance c with the decrease in the air gap as the transfer member is brought toward the photoreceptor 32. Therefore, as the first derivative of the charge density with respect to time (do'ldr) is equal to the ion current (i) delivered by the corotron, it will be apparent that the charge density a which the corotron is capable of establishing is yielded by the equation a Kit (6) where K is a constant, i is the instantaneous ion current per unit area being delivered to the surface of transfer member 35 and t is the time interval during which such current is delivered. Because the current delivered to a surface being charged by a corotron, as aforesaid, is a function of the voltage on that surface as seen by the coronode, an appropriate expression for i under conditions where the transfer member 35 is being displaced toward the photoreceptor 32 would take the form of an exceedingly complex dynamic equation. However, it may be readily observed that the ion current delivered by the corotron 34 to a surface at some finite positive potential could never exceed the bare plate current density of the corotron, i.e., the current delivered per unit area to a ground plane or a surface which is maintained at zero potential, which is generally set at approximately one-half a microamp per square centimeter (A pamplcm Thus, by assuming maximum delivered current density delivered by the corotron 34 through the entire dynamic interval defined by when the transfer web 35 first starts moving toward the photoreceptor 32 from its static condition illustrated in FIG. 2A until it arrives in physical contact with the toner image 38 to be transferred, as shown in FIG. 2B, the corotrons maximum ability to vary the charge density ois considered with the assurance that this substantially exceeds actual delivered current conditions which could occur as transfer member 35 approaches the photoreceptor because at no time does the voltage on the transfer member go to zero.

Reference to the Paschen curve shown in FIG. 3 will render it manifest that for large air gaps critical stress in the air gap may not exceed 8 Vin; thereafter, the characteristic of the Paschen curve slowly raises to a value of approximately 40 V/u, occurring at a 10 in. air gap, where the characteristic then breaks sharply upward becoming asymptotic to a vertical axis drawn through the zero abscissa position. The characteristic of the curve thereby indicates that if the transfer member 35 is moved through the lOp. air gap position without an ionization of the gap, no ionization will occur. If it is now recalled that the electric field in the air gap for the static condition illustrated in FIG. 2A was approximately h V/u); it will be seen that for air gap ionization to occur, the corotron must increase the field by approximately (39 h V/n) before the photoreceptor 35 is brought into physical contact with the toner image 38 on the surface of the photoreceptor 32. Recalling from equation (3) that IT I; I.

where e, equals 8.85Xl", it will be appreciated that this would require the corotron 34 to increase the charge density a on the surface of the transfer member 35 by a value of approximately 3.6Xl0" coulomb/m However, even if the corotron were delivering current to the transfer member at the maximum base plate density of h amp/cm, equation (6) indicates that this would take at least 72 ms. This indicates that the transfer web 35 when maintained in the static condition illustrated in FIG. 2A may be placed selectively in physical contact with the toner image 38 on the photoreceptor 32 in the manner indicated in FIG. 28 without the air gap therebetween ionizing to defeat the transfer mechanism so long as physical contact is established in a shorter time interval than it takes the corotron 34 to deliver sufficient current to the transfer web 35 to maintain the voltage thereon constant. Furthermore, once the transfer web is within the critical I0 p. air gap range defined by the Paschen curve, the rapid diminishing of the air gap between the electrostatically attractive transfer member 35 and photoreceptor 32 will insure that no ionization of the air gap may occur due to the same factors which operate in normal toner transfer operations wherein the transfer member is first placed in physical contact with the toner image and subsequently charged. Accordingly, the discovery that a transfer station operating under the conditions illus trated in FIGS. 2A and 2B may successfully achieve high quality image transfer so long as the charged transfer member is rapidly brought into initial physical contact with the toner image is considered to be scientifically grounded upon the theory of beating the current delivering capabilities of the corotron under dynamic conditions.

As will be apparent to those of ordinary skill in the art, the present invention gives rise to the ability to successfully achieve selective transfer by bringing a charged web-like transfer member or a transfer member which is handled by winding and reeling techniques associated with a web or strip into selective contact with a toner image while all the advantages of corotron charging and utilization are retained. Thus, by employing the novel transfer methods set forth herein, typical structure presently employed only in bulk electrophotographic information retrieval apparatus may be adapted for use in selective electrophotographic information retrieval systems. An exemplary embodiment of apparatus for carrying out the inventive transfer methods contemplated herein is set forth in conjunction with FIGS. 4A-4C.

FIGS. 4A-4C illustrate an exemplary embodiment of this invention wherein the improved toner image transfer methods and apparatus therefor are illustrated in an electrophotographic environment associated with the selective transfer of toner images from the photoreceptor to a web-like transfer member. More particularly, FIG. 4A is a pictorial view of a turn-around roller assembly which is so configured that a web-like transfer member employed therewith is highly responsive to vertical displacement of such turn-around roller assembly whereby the web-like transfer member may be selectively engaged and disengaged with a peripheral portion of a photoreceptor by the selective displacement of such turn-around roller assembly. FIGS. 4B and 4C illustrate the turn-around roller assembly of FIG. 4A together with a web-like transfer member disposed thereon and means for selectively displacing such turnaround roller assembly, FIG. 4B depicting conditions wherein the web-like transfer member is disengaged from a selected portion of a photoreceptor while FIG. 4C shows conditions which obtain when the web-like transfer member is engaged with a selected portion of a photoreceptor at which toner image transfer is to occur. As shown in FIG. 4A, the exemplary embodiment of the turn-around roller assembly in accordance with the teachings of the present invention comprises a pair of parallel extending T shaped support members 40, a pair of anchor members 41, a support shaft 42, a web or strip turn-around roller 43, stripper bar means 44 and a base member 45. The pair of parallel extending T shaped support members 40 are horizontally disposed as indicated and have corresponding first end portions thereof coupled to respective ones of the pair of anchor members 41 in a manner to permit pivotable movement about a fixed axis 46. The fixed axis 46 about which the pair of parallel extending T shaped support members may rotate is generally disposed within electrophotographic printing apparatus in a manner so as to be parallel to the axis of rotation of the photoreceptor employed. The pair of anchor members 41 are fixedly mounted to the housing, not shown, of the electrophotographic printing apparatus in which the illustrated assembly is employed. The support shaft 42 is mounted for rotation in each of the pair of parallel extending T shaped support members 40 in a manner so as to extend between the central portions thereof along an axis which is preferably parallel to fixed axis 46 and hence the axis of rotation of the photoreceptor employed within the electrophotographic printing apparatus. The web or strip turn-around roller 43 is concentrically mounted upon the support shaft 42 and is freely rotatable thereabout. The web or strip turnaround roller 43, as shall become apparent below, is adapted to have a web or strip like transfer member disposed thereabout in a similar manner to the turnaround roller 36 described in conjunction with FIGS. 2A and 2B and although both the support shaft 42 and web or strip turn-around roller 43 have both been indicated as mounted for rotation, either of these members may be fixedly mounted, as will be apparent to those of ordinary skill in the art, so long as the web or strip turnaround roller 32 is freely rotatable. The stripper bar means 44 may take the form of a conventional knife edge or vacuum bar stripper and is mounted between the opposite ends of the horizontal portions of the pair of parallel extending T shaped support members 40 and acts, as shall become apparent below, to strip portions of the transfer web or strip which are engaged with the photoreceptor therefrom when the transfer web or strip is to be disengaged from the photoreceptor. The base member 45 is fixedly mounted across the ends of the vertical extending portions of the pair of parallel extending T shaped support members 40 and provides a rigid platform from which the displacement of the turnaround roller assembly as a whole may be achieved. The base member 45 has been illustrated in FIG. 4A as including an upwardly extending flange portion 47 which is disposed at an acute angle with the longitudinal axis of the base member 45. The flange portion 47 of the base member 45 is here provided, as shall be seen below, as a convenient means for mating the turnaround roller assembly with a portion of the means for displacing such assembly, however, so long as the base member 45 is sufficiently rigid, it may take any configuration which is suitable for connection to means for selectively displacing the turnaround roller assembly in a vertical direction.

FIGS. 48 and 4C illustrate the turn-around roller assembly of FIG. 4A together with a web-like transfer member 48 disposed thereon and means 49 for selectively displacing such turn-around roller assembly. Additionally in FIGS. 48 and 4C a drum-like photoreceptor 50 having images 51A and 51B thereon has been illustrated for the purpose of facilitating an explanation of the exemplary embodiment of the invention depicted in FIGS. 4A-4C. The drum-like photoreceptor 50, as shown in FIGS. 48 and 4C, may take the same form as that described in conjunction with FIG. 1 and although a photoreceptor in the form of a drum has been illustrated, it will be appreciated by those of ordinary skill in the art, that photoreceptors taking other well-known configurations such as an endless web may be alternatively employed. Furthermore, as was the case with respect to FIGS. 2A and 2B, in FIGS. 4B and 4C only the transfer station including the continuously operating corotron 34, described in conjunction with FIGS. 2A and 2B, of the selective electrophotographic printing apparatus has here been shown as it is only this portion of the electrophotographic environment which is here ofinterest. Similarly, the web-like transfer member 48 comprises conventional material such as paper, plastic or similarly insulating material in the form of a web or strip and is disposed, as shown in FIGS. 48 and 4C, about the turn-around roller 43 and arranged to pass beneath the stripper bar means 44. The winding and reeling apparatus for the web-like transfer member 48, as indicated generally at D-D' in FIGS. 48 and 4C, may take any conventional form so long as such winding and reeling apparatus is capable of selectively starting and stopping the motion of the web-like transfer member 48 in the direction indicated by the arrow C and once such motion is started, to quickly bring the speed of the web up to that of an adjacent point on the toner image to be transferred. Additionally, it is preferable that the winding and reeling apparatus employed continuously maintain the web-like transfer member 48 taut so that the positive displacement action of the turn-around roller assembly will be enhanced. Although, any appropriate winding and reeling apparatus for the web-like transfer member 48 may be employed, preferred winding and reeling apparatus for transfer members in the form of a strip is disclosed in application Ser. No. 221,229, supra. Of the images 51A and 51B indicated in FIGS. 43 and 4C as present on the photoreceptor 50, image 51A should be considered to be an image on the photoreceptor for which no transfer is desired while image 513 should be considered to take the form ofa toner image which is desired to be selectively transferred to the transfer web 48.

The means 49 for selectively displacing the turnaround roller assembly, as shown in FIGS. 48 and 4C, comprises a conventional solenoid whose plunger core or armature 52 is connected to the base member 45 of the turn-around roller assembly through a tab-like support member 53 to which the armature 52 is pinned. A limit means 54 in the form of a concentrically mounted abutment member is provided on the armature 52 to limit the downward displacement of armature 52 when the solenoid is energized to thereby displace base member 45 and hence the turn-around roller assembly in the downward direction due to the pivotal movement of the turn-around roller assembly about the fixed axis 46. Additionally, a shaft 55 having adjustable stops thereon is mounted through an aperture in the upwardly extending flange portion 47 of the base member 45 of the turn-around roller assembly. A spring means 56 is mounted on shaft 55 to maintain a constant upward bias on the flange portion 47 and hence the base member 45 while the shaft 55 is fixedly mounted in support block 57.

In the operation of the instant exemplary embodiment of this invention, whenever, as shown in FIG. 43, no transfer is to take place such as when image 51A is present at the transfer station illustrated, the solenoid is energized by externally supplied signals such as are disclosed for instance in US. application Ser. No. 22l,229, supra. When the solenoid is energized it will pull in its armature 52 in the well known manner causing base member 45 to be displaced in the downward direction until the limit means 54 abuts the solenoid housing as indicated in FIG. 4B. This causes the entire turn-around roller assembly shown in FIG. 4A to rotate in the clockwise direction about the fixed axis 46 whereby the upwardly extending flange portion 47 of the base member 45 is caused to slip down the shaft 55 placing spring means 56 in compression. In this condition, as shown in FIG. 4B, the surface of the web-like transfer member 48 opposite the peripheral portion of the surface of the photoreceptor 50 at which transfer is to occur is displaced from such surface by a distance of approximately 16 in.. From the standpoint of moving the web-like transfer member 48 from the surface of the photoreceptor 50 which occurs when the solenoid is energized, it should be noted that as the stripper bar means 44 is a greater distance away from the fixed axis of rotation 46 than is support shaft 42, the stripper bar means 44 will be displaced a greater distance than the turn-around roller 43. This allows the knife edge of the stripper bar means 44 to engage the surface of the weblike transfer member 48 from a disengaged position at approximately the same time that the turn-around roller 43 begins to exert a downward force on the web-like transfer member 48. Therefore, since the web-like transfer member 48 is maintained taut by the winding and reeling apparatus associated therewith, as aforesaid, the portion of the web-like transfer member 48 will be rotated away from its contacting position with the photoreceptor 50 in a manner which may be likened to the rotational characteristics of a rigid sheet due to the two point engagement provided by the knife edge of the stripper bar means 44 and the lower surface portions of the turn-around roller 43. More particularly, when the solenoid is initially engaged, the end portions of the section of the transfer member 48 intermediate the stripper bar means 44 and the lower surface portions of the turn-around roller 43 will be rapidly displaced in a downward direction while the portion of the transfer member in contact with the photoreceptor 50 will be maintained in momentary contact therewith due to the electrostatic tacking force therebetween giving this section of the transfer member 48 a momentary tented appearance. As the downward force on the end portions of the taut transfer member 48 begins to build due to the increasing downward displacement of stripper bar means 44 and the turnaround roller 43, the tacking force between the photoreceptor 50 and the contacting section of the transfer member 48 will be rapidly overcome causing the contact section of the transfer member 48 to snap down from its contacting relationship with the photoreceptor 50 and into a linear relationship with the end portions of the transfer member 48 associated with the stripper bar means 44 and the turn-around roller 43. This is highly advantageous because it ensures that the transfer member 48 is removed from a transfer relationship with the photoreceptor 50in such a rapid manner that the entire removal operation occurs above the Paschen curve whereby the localized discharge between the transfer member 48 and the photoreceptor 50, which attends the linear increase in the voltage on the transfer member 48 with an increase in displacement, is continuous and results in an ion current charge spray which actually enhances the toner particle to transfer member bond. If the displacement ofthe transfer member 43 from the photoreceptor 50 was not accomplished in this rapid manner, the highly localized discharge therebetween would be intermittently operating above the Paschen curve, then being quenched and falling below the Paschen curve and then building to avalanche where it again goes above the Paschen curve. This, however, is to be avoided, as disruptive sparking often attends avalanche discharge and causes deleterious results both with respect to damage to the photoreceptor and to the toner image transferred be- 5 cause rather than enhancing the toner particle to paper bond, such disruptive discharge tends to explode localized portions of the toner image resulting in semicircular spots or fish scales where the toner is dislodged from the transferred toner image. Thus, the turnaround roller assembly provides rapid positive displacement for the moving web-like transfer web 48 to overcome the electrostatic tacking force between it and the photoreceptor and remove it from its transfer condition where it is in physical engagement with the surface of the photoreceptor at the peripheral transfer portion thereof. When the web-like transfer member 48 reaches the position illustrated in FIG. 48, where it is in a fully disengaged condition, the motion of the web-like transfer member 48 in the direction indicated by the arrow C is stopped or alternatively, the motion of the web-like transfer member 48 may be stopped at a time subsequent to the energizing of the solenoid after a selected length of the transfer member has been displaced to properly complete a border area on the transfer member for the image transferred. The corotron 34, however, remains in its energized condition as it does whenever the selective electrophotographic apparatus in which it is operating is in an energized condition. When a toner image to be transferred such as 518 approaches the transfer station, a signal for starting the motion of the web-like transfer member 48 is supplied to the winding and reeling apparatus therefor and after a time interval (for instance 10 ms), which is sufficient for the web-like transfer member 48 to come to speed has elapsed, a signal to deenergize the solenoid is provided. Circuitry for accomplishing each of these functions is described in U.S. application Ser. No. 22l,229, supra. When the solenoid is deenergized, the armature 52 releases whereby the upwardly extending flange portion 47 of base member is driven to its full upward position on shaft 55 due to the action of spring means 56. This action occurs rapidly and in actual apparatus which has been built and tested in accordance with the instant embodiment of this invention has resulted in full displacement of the flange portion 47 to its extreme upward position on shaft 55 within an interval of about 30 ms which is well below the time interval of approximately 72 ms, as aforesaid, which is required by the corotron 34 to cause an ionization of the gap between the transfer member 48 and the surface of the photoreceptor 50 for the A in. gap considered and employed in this embodiment. When the flange portion 47 of the base member 45 is driven to its full upward position on shaft due to the action of spring means 56, the entire turn-around roller assembly depicted in FIG. 4A will pivot in the counterclockwise direction about the fixed axis of rotation 46. This limited rotation will disengage the knife edge of the stripper bar 44 from the web-like transfer member 48 due to the larger displacement thereof and will cause the turn-around roller 43 to displace the web-like transfer member 48 in an upward direction so that it is brought into physical contact with the toner image SIB to be transferred on the photoreceptor 50 in the manner indicated in H6. 4C. As the web-like transfer member 48 is maintained taut, selective engagement of the web-like transfer member is accomplished in the same interval as is required by the spring means 56 to displace the flange portion 47 of the base member 45. Therefore, as selective physical contact of the web-like transfer member 48 with the toner image 518 is established before the continuously operating corotron can cause the air gap to ionize and the web-like transfer member 48 is moving at the same speed as the adjacent points on the toner image to be transferred; the transfer of the toner image 518 is properly initiated and may continue as in normal transfer operations until the transfer of the toner image 518 has been completed. Should the toner image 518 be followed by another adjacent toner image to be transferred, the web-like transfer member 48 will be maintained in a contacting relationship with the photoreceptor 50 while if the succeeding image is not to be transferred the solenoid 49 will again be energized to reestablish the conditions depicted in FIG. 4B and described above.

in FIG. 4C, the physical contact between the weblike transfer member 48 and the photoreceptor 50 has been illustrated as occurring along an arc of contact. This relationship is achieved by making the stroke displacement of flange portion 47 on shaft 55 longer than the vertical displacement to which the contacting portion of the web-like transfer member is capable due to the location of the photoreceptor. Thus, initial contact between the web-like transfer member 48 and the toner image is established at some instant before the flange portion 47 is fully displaced and is considered advantageous because the critical initial contact between the web-like transfer member 48 and the toner image is established in a somewhat shorter interval than the full time of displacement of flange portion 47 along shaft 55. Furthermore, transfer time is enhanced as the initial portion of the transfer cycle takes place along the area associated with the are rather than the line which would be associated with point contact while an initial arc of contact also serves to help compensate for any flutter in the web. However, although the initial contact between the web-like transfer member 48 and the toner image 518 is illustrated as occurring along an arc in FIG. 4C, it will be appreciated by those of ordinary skill in the art, that initial contact may also be established at a point of tangency without violating the tenets of the present invention. in addition, although the exemplary embodiment of the selective transfer apparatus depicted in FIGS. 4A-4C is capable of establishing initial contact between a web-like transfer member 48 and the toner image 515 in a much shorter time than is required by the corotron 34 to cause ionization of the air gap, apparatus achieving this relationship within a longer time interval may be employed with equal facility so long as such longer interval is reasonably shorter than the time required for the corotron 34 to cause ionization of the air gap between the photoreceptor and the transfer member under the initial conditions established. Thus it is seen that the exemplary embodiment of the selective transfer apparatus depicted in FIGS. 4A-4C allows a continuously operating corotron to be employed at a transfer station wherein toner images are selectively transferred to a web; however, as initial contact between the transfer web and the toner image is established before such continuously operating corotron can achieve air gap ionization, the transfer mechanism will not be defeated by charge transfer between the charged transfer web and the toner image.

Although the improved methods and apparatus for selectively transferring developed electrostatic images taught by the present invention have been disclosed in conjunction with a detailed exemplary embodiment thereof, it will be appreciated that many modifications and alterations in the techniques set forth are available and hence contemplated by the instant invention. For instance, although the selective displacement of a weblike transfer member has been accomplished herein by providing a positive responding turn-around roller assembly which promptly responds to the release of a solenoid, any rapidly acting bistable displacement means could be employed in place of the spring biased solenoid arrangement and a suitably responding web positioning arrangement could be provided at any appropriate location in the winding and reeling apparatus associated with the web-like transfer member so long as appropriate displacement of the web is achieved. Furthermore, this invention has been disclosed in association with selective printing apparatus wherein toner images of generally small dimension are transferred to a web or strip because it is this type of relationship wherein the problem of air gap ionization due to the presence of a continuously operating corotron could not be practically avoided by the prior art. However, the principles taught by this invention are fully applicable to toner images of any dimension and to any transfer process employing any convenient form of transfer member such as a sheet, web, strip or drum wherein it is desired to charge such transfer member in the presence of a continuously operating ion charging device and thereafter bring such transfer member into physical contact with a toner image to be transferred be- 3 cause, with the concepts taught by the present invention, the problem of ionization of the air gap can be avoided regardless of the form of transfer member employed, the size of the toner image to be transferred or the feeding apparatus associated therewith. In addition,

40 although the present invention has been disclosed in terms of the transfer of complete toner images, the concepts taught herein may be employed with equal facility for the transfer of selected portions of toner images or the rearrangement of the format thereof on the transfer member. Further, as will be apparent to those of ordinary skill in the art, the improved transfer methods and apparatus taught herein are independent of the specific electrophotographic process employed in the formation of an image to be transferred.

While the invention has been described in connection with a single exemplary embodiment thereof, it will be understood that many modifications will be readily apparent to those of ordinary skill in the art; and that this application is intended to cover any adaptations or variations thereof. Therefore, it is manifestly intended that this invention be only limited by the claims and the equivalents thereof.

What is claimed is:

1. [n electrophotographic apparatus including a pho toreceptor, means for forming electrostatic images on said photoreceptor and means for providing each electrostatic image formed at a transfer station where selective transfer of said electrostatic images to transfer member means may occur, the improvement in said electrophotographic apparatus comprising:

ion charging means disposed at a location opposite to said transfer station;

means for feeding transfer member means intermediate said photoreceptor and said ion charging means; and

means for selectively placing said transfer member means in a transfer relationship with said photoreceptor within a time interval which is less than that required by said ion charging means, when energized, to cause ionization of a gap between said photoreceptor and said transfer member means being placed in a transfer relationship therewith,

2. The improved electrophotographic apparatus according to claim I wherein said means for placing said transfer member means in a transfer relationship with said photoreceptor includes means for selectively displacing said transfer member means from said transfer relationship with said photoreceptor to a position intermediate said photoreceptor and said ion charging means.

3. The improved electrophotographic apparatus according to claim 2 wherein said means for selectively placing said transfer means in a transfer relationship with said photoreceptor comprises transfer member feeder assembly means having first and second positions, said transfer member feeder assembly means when in one of said first and second positions being arranged to place transfer member means from said means for feeding transfer member means in a transfer relationship with said photoreceptor and being arranged when in another of said first and second positions to place transfer member means from said means for feeding transfer member means in said position intermediate said photoreceptor and said ion charging means 4. The improved electrophotographic apparatus according to claim 3 additionally comprising means for selectively displacing said feeder assembly means from said first position to said second position and conversely for selectively displacing said feeder assembly means from said second position to said first position, said means for selectively displacing said feeder assembly means accomplishing the displacement of said feeder assembly means from said another of said first and second positions to said one of said first and second positions within a time interval which is less than that required by said ion charging means, when energized, to cause ionization of a gap between said photoreceptor and said transfer member means being placed in a transfer relationship therewith.

5. The improved electrophotographic apparatus according to claim 2 wherein said ion charging means is fixedly positioned at said location opposite to said transfer station.

6. The improved electrophotographic apparatus according to claim 3 wherein said ion charging means comprises corotron means.

7. The improved electrophotographic apparatus according to claim 6 wherein said means for selectively placing said transfer means in a transfer relationship with said photoreceptor comprises transfer member feeder assembly means having first and second positions, said transfer member feeder assembly means when in one of said first and second positions being arranged to place transfer member means from said means for feeding transfer member means in a transfer relationship with said photoreceptor and being arranged when in another of said first and second positions to place transfer member means from said means for feeding transfer member means in said position intermediate said photoreceptor and said ion charging means.

8. The improved electrophotographic apparatus according to claim 7 additionally comprising means for selectively displacing said feeder assembly means from said first position to said second position and conversely for selectively displacing said feeder assembly means from said second position to said first position, said means for selectively displacing said feeder assembly means accomplishing the displacement of said feeder assembly means from said another of said first and second positions to said one of said first and second positions within a time interval which is less than that required by said ion charging means, when energized, to cause ionization of a gap between said photoreceptor and said transfer member means being placed in a transfer relationship therewith.

9. The improved electrophotographic apparatus according to claim 8 wherein said feeder assembly means includes a base member from which said feeder assembly means is displaceable to said first and second position and wherein said means for selectively displacing said feeder assembly means comprises solenoid means having an armature and means for biasing said feeder assembly means in said one of said first and second positions, said armature of said solenoid means and said means for biasing said feeder assembly means being mechanically coupled to said base member from which said feeder assembly means is displaceable, said armature of said solenoid means being operative when said solenoid means is in a first state to overcome said means for biasing and place said feeder assembly means in said another of said first and second positions and said means for biasing being operative when said solenoid means is in a second state to place said feeder assembly means in said one of said first and second positions within a time interval which is less than that required by said ion charging means, when energized, to cause ionization of a gap between said photoreceptor and said transfer means being placed in a transfer relationship therewith.

10. The improved electrophotographic apparatus according to claim 9 wherein said feeder assembly means includes a rotatable guide means, said rotatable guide means and said base member being fixedly positioned with respect to each other and pivotable about an axis which is parallel to a surface of said photoreceptor at said transfer station, said means for selectively displacing said feeder assembly means acting to pivot said base member and said rotatable guide means about said axis to displace said feeder assembly means to said first and second positions.

11. The improved electrophotographic apparatus according to claim 10 wherein said feeder assembly means includes stripper bar means fixedly positioned with respect to said base member and said rotatable guide means and pivotable about said axis therewith, said rotatable guide means being positioned intermediate said axis and said stripper bar means and further positioned to receive transfer member means from said means for feeding transfer member means and to guide said transfer member means with respect to said transfer station in accordance with the first and second positions of said feeder assembly means. said stripper bar means thereby being displaced a greater distance than said rotatable guide means when said feeder assembly means is displaced between said first and second positions and being positioned to engage said transfer member means when said feeder assembly means is selectively displaced from said one of said first and second positions to said another of said first and second positions.

12. The improved eleetrophotographic apparatus according to claim 11 wherein said means for biasing said feeder assembly means in said one of said first and second positions includes means for defining the location of said feeder assembly means when said feeder assembly means is in said one of said first and second posimeans.

Claims

1. In electrophotographic apparatus including a photoreceptor, means for forming electrostatic images on said photoreceptor and means for providing each electrostatic image formed at a transfer station where selective transfer of said electrostatic images to transfer member means may occur, the improvement in said electrophotographic apparatus comprising: ion charging means disposed at a location opposite to said transfer station; means for feeding transfer member means intermediate said photoreceptor and said ion charging means; and means for selectively placing said transfer member means in a transfer relationship with said photoreceptor within a time interval which is less than that required by said ion charging means, when energized, to cause ionization of a gap between said photoreceptor and said transfer member means being placed in a transfer relationship therewith.

2. The improved electrophotographic apparatus according to claim 1 wherein said means for placing said transfer member means in a transfer relationship with said photoreceptor includes means for selectively displacing said transfer member means from said transfer relationship with said photoreceptor to a position intermediate said photoreceptor and said ion charging means.

3. The improved electrophotographic apparatus according to claim 2 wherein said means for selectively placing said transfer means in a transfer relationship with said photoreceptor comprises transfer member feeder assembly means having first and second positions, said transfer member feeder assembly means when in one of said first and second positions being arranged to place transfer member means from said means for feeding transfer member means in a transfer relationship with said photoreceptor and being arranged when in another of said first and second positions to place transfer member means from said means for feeding transfer member means in said position intermediate said photoreceptor and said ion charging means.

4. The improved electrophotographic apparatus according to claim 3 additionally comprising means for selectively displacing said feeder assembly means from said first position to said second position and conversely for selectively displacing said feeder assembly means from said second position to said first position, said means for selectively displacing said feeder assembly means accomplishing the displacement of said feeder assembly means from said another of said first and second positions to said one of said first and second positions within a time interval which is less than that required by said ion charging means, when energized, to cause ionization of a gap between said photoreceptor and said transfer member means being placed in a transfer relationship therewith.

11. The improved electrophotographic apparatus according to claim 10 wherein said feeder assembly means includes stripper bar means fixedly positioned with respect to said base member and said rotatable guide means and pivotable about said axis therewith, said rotatable guide means being positioned intermediate said axis and said stripper bar means and further positioned to receive transfer member means from said means for feeding transfer member means and to guide said transfer member means with respect to said transfer station in accordance with the first and second positions of said feeder assembly means, said stripper bar means thereby being displaced a greater distance than said rotatable guide means when said feeder assembly means is displaced between said first and second positions and being positioned to engage said transfer member means when said feeder assEmbly means is selectively displaced from said one of said first and second positions to said another of said first and second positions.

12. The improved electrophotographic apparatus according to claim 11 wherein said means for biasing said feeder assembly means in said one of said first and second positions includes means for defining the location of said feeder assembly means when said feeder assembly means is in said one of said first and second positions, said means for defining said location being set so that when said feeder assembly means is selectively displaced to said one of said first and second positions said transfer member means is placed in a transfer relationship with said photoreceptor along an arc.

13. The improved electrophotographic apparatus according to claim 12 wherein said transfer member means is in the form of a web-like member and said rotatable guide means comprises turn-around roller means.