US 3702482 A
A biasable transfer member is herein disclosed suitable for use in transferring xerographic images from a photoconductor to a final support sheet. The member is adapted to electrically cooperate with the photoconductor to establish a directional force field therebetween capable of attracting toner from the photoconductor toward the member and features a structure which provides for a more efficient transfer operation while at the same time accurately matching the speed of the support sheet to the photoconductor.
Description (OCR text may contain errors)
United States Patent Dolcimascolo et al.
1451' Nov, 7, 1972  BIAS ROLL TRANSFER I  Inventors: Charles Dolclmascolo, 'Fairport;
Daniel S. Hoffman; Hugh L. Jones, both of Rochester; James E. Mercik,
Webster, all of NY.
[731 Assignee: Xerox Corporation, Stamford,
- Conn. 2
 Filed: Dec. 23, 1970  Appl. No.: 100,969
1521 11.5. C1. ..346/74 Es, 101/13,:155/3  Int. Cl.....G03g 15/04, G03g 15/08,;G03g 15/16  Field of Search..346/74 ES; lO1/DIG. 13; 355/3 I  References Cited UNITED STATES/PATENTS 3,281,857 10/1966 Kaiser ..346/74 ES 3,441,938
4/1969 Markgraf ..346/74 ES 3,285,168 11/1966 Childress ..l01/D1G. 13
3,316,555 I 4/1967 Barish ..346/74 ES. 3,534,383 10/1970 Tsukatani ..346/74 ES Primary Examiner-Howard W. Britton Attorney-James J. Ralabate, Donald F. Daley and Thomas J. Wall 1571- ABSTRACT A biasable transfer member is herein disclosed suitable for use in transferring xerographic images from a photoconductor to a final support sheet; The member is adapted to electrically cooperate with the photoconductor to establish a directional force field therebetween capable of attracting toner from the photoconductor toward the member and features a structure which provides for a more efficient transfer operation while at the same time accurately matching the speed of the support sheet to the photoconductor.
11 Claims, 3 Drawing Figures PATENTEDNUY 1 I972 $702,482
' sum 2 BF 2 FIG? as as as I 32 I 68 Mtg. I
11 Bus Ron. I
t. Thisinvention relates to xerography and, in particu- I lar, to apparatus for transferring xerographic toner 1 images from one support surface to another. In conventional xerography, atphotosensitive plate, which consists ofv a photoconductive coating placed 2 over a conductivebacking ischarged uniformly. and the charge plate then exposed to a light image of an 1 original. Under the influence of. the light image, the
charge on the plate is selectively, dissipated to record 1 the original input scene information on the plate in the 'form of a latent electrostatic image. The latent image is developed, or made visible, n by .1 applying oppositely 5 charged toner particles to the plate surface in a manner sothatthe toner particles are attracted into the imaged areas. The developed images are generally transferred from the photoconductor to a final support material, such as paper or the like, and affixed thereto to form a r permanent record of the original.
I-Ieretofor', image transfer was generally accom- -.plish ed by means of corona induction using a corona generator similar to that disclosed by Vyverberg in U.
S P-at. No. 2,836,725: In corona induced transfer, the
- final support sheet isplaced in direct contact with the toner image while the. image is supported on the y. photoconductive surface. The back of the sheet, that is, the side away from theimage, is sprayed with a corona discharge having apolarity opposite to that carried by the toner particlecausing the toner to be electrostatically transferred to thesheet. v y The Vyverberggenerator, as attested to" by its wide commercial acceptance, has proven to be an extremely reliable device for transferring a single toner image to a final support sheet. The term single toner image as herein used, is employed in the broad sense to define an image that is created by means of a single exposure and developing step and the image may include many separate and distinct pieces of information. However corona induced transfer doesnotlend itself readily for use in systems where a multiplicity of toner images must be sequentially tran'sferredto a single support sheet as exemplified by many xerOgraphiccoIOr and Biased roll transfer has been tried with some limited success as a means of controlling the forces'actin'g on the toner during transfer. This type of transfer was first disclosed by Fitch in U. S. Pat. No. 2,807,233 and involved the use of a metalroll coated with a resilient coating having a resistivity of about/ to 10 cm. Because of the resistivity of the coating, the amount of bias that can be applied to the roll is limited to relatively low operating values because, at the higher ranges,
the air in and about the transfer zone begins to break down, i.e. ionizes, causing the image to be degradated during transfer. Shelffo in U. S. Pat. No. 3,520,604,
suggests that the resilient coating have a resistivity of between l0l0 ohms cm. Here, in order to give the roll the needed resiliency required in most practical applications, the coating must be relatively thick. A thick coating of high resistivity acts to build up I a surface charge on the roll resulting in air breakdown in the transfer region and eventually copy degradation.
, It is therefore an object of this invention to improve -'apparatus for electrically transferring a toner image from a photoconductivesurface-to a final support sheet. I a;
further object of this invention i's 'to provide a device to better match the speed ofthe support sheet to that of the photoconductivesurface on which is supported to toned image to be transferred.
efficiently transferred from a photoconductive surface to a singlesheet of final support material. I
- These and other objects of the present invention are I attained by means of a biased transfer member being capable of electrically cooperating with a conductive support surface to attract charge toner particles from the support surface towardsthe member, the member having a conductive substrate for supporting a biased "potential thereon, an intermediate blanket placed in contact with the substrate having an electrical resistivity capable of readily transmitting the bias potential on the-substrate to the outer periphery of the blanket and a relatively thin outer coating placed over the blanket having an electrical resistivity to minimize ionization of the atmosphere when thetransferred member is placed in electrical cooperation with the image support surface and provides a good toner release property enabling the device to be cleaned of said toner.
' Fora better understandingas well as other objects and further features thereof, reference is had tothe following detailed description of the invention to be read in connection wherein; I 'FIG. 1 isa schematic view in partial section illustrating an automatic xerographic reproducing apparatus embodying the present invention; 7 I I FIG. 2 is a perspective view inpartial section showing the construction of .a transfer roll embodyingythe teachingsof the present invention that is suitable for with the accompanying drawings,
' use in the apparatus illustrated inFIG. l; j
' FIG. 3 isv a partial sectional view showinga paper gripping mechanism associated with the transfer roll illustrated in FIG. 2 with the paper gripper extended in a paper stripping position. I
Although the apparatus of the present invention has application in any number of xerographic devices in which a plurality of images are to be applied to a single sheetof support material, it will nevertheless be dis closed, for explanatory reasons, with reference to an automatic machine having a duplex capability and it should be clear that this particular machine environment is in no way intended to limit the present invention. Referring now specifically to FIG. 1, the apparatus of the present invention is shown embodied in a drum type automatic xerographic reproducing dicated by means of a motor (not shown). The drum basically comprises an outer surface 13 of a photoconductive insulating material such as vitreous selenium or the like that is placed upon a grounded conductive substrate 14'. 1
. A uniform electrostatic charge is placed on the photoconductive surface by means of a conventional corona charging device similar to that disclosed by Vyverberg in the above noted U. S. patent. The uniformly charged surface is then moved past an exposure means, generally referenced 17, capable of exposing the charged surface to a flowing light image of the original input scene information to be reproduced thus forming a latent electrostatic image on the photoconductor. The optical system herein utilized is similar to that disclosed in U. S. ,Pat. No. 2,940,358 and is of the type wherein the original input scene information to be reproduced is stored as minified data upon a film input 18. A' movable mirror system 19 is positioned in the optical light path and is arranged to redirect theflowing light image of the original onto the bottom portion of the drum surface. The mirror system comprises a plane mirror surface 20 and a roof mirror 21 which, in operation, are alternately interposed into the light path of the optical system so that each successive image presented to the drum surface is optically reversed. In operation, the optical means exposes the photoconductive drum to a first input wherein a right reading latent image is formulated thereon. Following the formation of the first right reading latent image, the image is moved past a conventional xerographic developing device 25 wherein the latent image is brought in contact with oppositely charged toner particles and the particles are attracted'into the imaged areas thus making the image visible. I After development, the now visible first right reading image is transported on the drum to' a transfer station I 26 where the image is temporarily transferred .to and stored in image configuration upon the surface of an intermediate biased transfer roll 30. The transfer roll is arranged to extend transversely across the photoconductive drum surface and to move in intimate contact therewith as shown in FIG. 1. In practice, the. roll, which is initially placed ata relatively high bias potential, is arranged to coact electrically. with the grounded photoconductive drum to establish an electrostatic force field. in and about'the contact region. The force field is of sufficient strength to attract the charged toner particles moving through. this region from the photoconductive surface towards the transfer member.
Referring now more specifically to FIG. 2, there is shown a cut-away view of the transfer roll 30 clearly illustrating the internal construction thereof. The roll is basically formed upon a rigid hollow cylinder 31 that is fabricated of a conductive metal, such as aluminum or the like, capable of readily responding to a biasing potential placed thereon. Overthe core is placed a rela tively thick intermediate blanket 32 of elastomeric material having a hardness of between 15-25 durometers. The intermediate blanket is preferably formed of a polyurethane rubber approximately 0.25 in thickness having sufficient resiliency to allow the roll to deform when brought into moving contact with the photoconductive drum surface to provide an extended contact region in which the toner particles can be transferredbetween the contacting bodies. The intermediate blanket should be capable of responding rapidly to the biasing potential to electrically impart the charge potential on the core to the outer extremities of the roll surface. The blanket therefore should have a resistivity of blanket is placed a relatively outer coating 33 which is also formed of an elastomeric material being approximately 0.0025 in thickness and having a hardness in the 65-75 D durometer range. However, in
"order to minimize ionization of the atmospherein and "aboutthe contact region, it is 'preferredthat the outer coating have a resistivityof about 3.2 X 10 ohms cm or, alternatively, in a range between 10 and 10" ohm cm. It is further preferred that the outer coating of the roll should be formulated of a material capable of providing a'relatively smooth surface exhibiting relatively good mechanical release properties'in respect to the toner materials employed. A polyurethane material manufactured by the duPont Company under the tradename Adiprene has been found .to possess the heretofore mentioned desired properties and shows extremely good release characteristics in respect to most commercially availabletoners. v
.The transfer roll member is closed atboth ends by means of a pair of dielectric end caps 35, 36 which serveto electrically isolate the transfer roll member from the supporting machine frame. Segmented shafts 37 are secured in both end caps and are mounted in coaxial alignment with the cylindrical core 31. The shafts, in turn, are joumaled for rotation in the machine frame in bearing means provided (not shown) so that the outer surface of the roll continually moves'through the transfer zone in contact with the photoconductive surface 13. A pulley 38, operatively connected to the machines main drive system, is secured to one end of the shaft and causes the transfer roll to be rotated in with the moving shown in FIG. 1, a commutating brush 41, which is electrically connected to a suitable source of DC power 42 via electrical connector 43, is arranged to ride in contact with theouter surface of the commutator ring and provides a moving contact by which theconductive core is electrically connected to the biasing source. The transfer force field associated with the electrically isolated roll is dependent upon the establishment of a voltage contrast between the roll and the photoconductor. The strength of the field is proportional to the initial charge placed on the roll and inversely proportional to the distance between the two coacting bodies. Initially, the roll is biased to about 3,500 volts DC, the polarity of which is, of course, opposite to that of the charged toner particles, whereby the first image delivered into the transfer zone is transferred, in image configuration, from the photoconductor to the surface of the-transfer roll.
Subsequent to the formation of the first right reading image upon the drum, a second area on the photoconductive surface thereof is again uniformly charged by I means of the charging corotron 15. This second ps static image, roof mirror 21 is interposed into the optical light path of the system'replacing mirror 20. This wrong-readinglatent electrostatic image is then transported on the moving drum surface to the development station -23'and the second'image is made visible in a manner similarto that herein described in reference to the first right reading image. I
The time sequence 'of charging, exposing and- 1 developing the two oppositely .reading images on the drumsurfac e is controlled in predetermined timed rela- 82, preferably paper, are forwarded from a supply bin 'tionf by means of ,the machine-control logic circuitry ;(not shown). Of course, the particular selection of the 6 ln operation, sheets of individual support material orthelikeintoa sheet'receiving station 83 (FIG. 1) by means of a feed roll assembly27. At this time, tabs 84, (FIG. 3) on the lifting arm are elevated slightly above the roll surface and the leading edge of the sheet is driven into alignment against stop face 85.v Once aligned,the tabelement is caused to move downwardly thus locking the sheet against recess surface 87 on the roll. When in the sheet locking position, the entire gripping mechanism is sufficientlyretractedbelow the "roll surface to allow the roll to'move freely through the times sequence of operation may be dependent 'on many factors, such as the location ofsthe various processing stations around the drum surface, thelength and velocity of the image storage member relative to .sthezsiz e of the drum surface, and-the like. Eorconvenienceof illustration, however, the circumference of the transfer .roll -isherein deemed to be one'half that of the ,photoconductive drum. Byrotating the two-members"at-ithe'lsame PQfiPheral speed, the first image,
which has been transferred-to the transfer -roll,'--is trans- .ported'around -the circularpath of travel transcribed by the drum and will arrive atthe transfer station at ap-.
proximately the same time as the second developed image carried on the photoreceptor. Accordingly, the --leading edges of the two images lying respectively on the storage drum and the xerographic drum surface,
confront each other atapproximately the same mor'nent-in-ztime.
contactor transfer zone. v v
, With'the support sheet 82 secured to the roll surface over the first image the first image is recirculated once again through the transferor contact region in synchronization with thesecond image carried on the lphotoconductive drum. The introduction of an added dielectric, such asapaper sheet, into the contact region I usually: requires that thetransfer bias be reduced'in from the photoconductor to the outside surface of the Prior to bringing the two toner images together within the contact region, a sheet of "final" support material, such as paper or the like, is secured to the transfer roll member in a manner wherein the sheet overlies the first image supported' ther'eon. "A sheet sheet. I
After transfer, the support sheet is moved onthe roll surface to a region of low voltage contrast wherein there-is positioned a corona generator 55 similar to that described in the previously noted Vyverberg patent. A
region of low .voltage contrast is a regionwherein the gripping-device is providedwithin the roll to properly align and secure individual sheetsof material to theroll surface. Basically, two sheet aligning and gripping assemblies 60 (516.3.) are supported'in spaced parallel alignment within the roll-to act ,upon the two leading edge corners of a support sheet that is broughtinto operative communication therewith. Each assembly is made up of two components, alever arm component bias roll surface does not electrically communicate with another voltage source. it should be understood, that the term -voltage sourcej as herein used is broad enough to' include a .groundedjbody or the like. The
corona generator is dapted o' apply corona to the top and a lifting component 64 .tha't are supported upon a common base plate 65 by means of a mounting bracket 66. The base plate is rigidly affixed to the interior walls of the roll and is arranged to move in unison with the roll member. I
Mounting bracket 66 also serves to rotatably support a control shaft 67 which runs longitudinally across the interior of the roll and eittends through the end cap 36 (FIG. 2). Each of the lever, arm components are rotatably secured to bracket 66 by means of a pin 68 and the arms arranged to rotate freely in openings '69 I provided in the roll surface. Lifting elements '64 are secured to the control shaft 67 and move in accordance therewith. A 'cam face 70 is machined on the lifting ele .ment and is forced to ride in contact with the bottom surface of the lever arm by means of a spring 71 so that the lifting arm is raised and lowered in response to the movement of the control, shaft. The portion of the control shaft that extends beyond end cap 36 is provided with a cam followed 78 arranged to ride in contact with 1 impart a predetermined motion- Ea profile surface 79 to to thelever arm.
side of'the support sheet'of a polarity to cause the first image, tha't'is, the image in contact with the roll surface-to be transferred from the roll to the bottom side of the support sheet. Alternately, the bias potential on the roll can be removed prior to the corona induced transferstep. 1
With the two toner images thus electrostatically adhering t0 Opp site sides of the support sheet, the sheet is once again moved on the roll surface into the sheet receiving station 83. Here, the lever arm 63 of the gripping mechanism is moved to a fully extended position, as shown in FIG. 3, causing the .sheet to be elevated 'well above the roll surface. As the-roll continues to move in the direction indicatedpthe elevated sheet is carried over a stripping bar 89 which guides the sheet into a fuser assembly 90.v The sheet is advanced through the fuserassembly by means of a transport 91 and the images are permanently fixed to both sides of the support 'sheet. The now duplexed copies are taken from the fuser and stored in a collecting tray 83.
' Finally, the rotating photoconductive surface as it moves out of transfer station is brought into operative communication with a fibrous brush member 50 that is moving at'a speed sufficient to dislodge any residual toner remaining on the drum surface after the transfer operation. The residual toner is collected and removed from "the machine environment by means of conventional apparatus'known and used in the art.
changes as may come within the scope of the following claims. a I
What is claimed is: v t 1. A transfer member forv electrically cooperating with a conductive support surface to electrically attract charge particles from the support surface towards the member including, I I I va conductive substrate for supporting a uniform bias I potential thereon,
an intermediate resilient blanket placed in contact with said substrate having an electrical resistivity such that the blanket is capable of transmitting said bias potential on said substrate to the outer periphery of said blanket, and I an outer coating placed over saidblanket having an electrical resistivity to minimize ionization of the surrounding atmosphere when said transfer member is placed in electrical cooperation with said support surface.
2. The transfer member of claim 1 wherein said intermediate blanket is formed of an elastomeric material having a resistivity of between and 10 ohms cm.
3. The transfer member of claim 2 wherein said outer coating is formedvof an elastomeric material having a resistivity of between 10 and 10 ohms cm.
4. The transfer member of claim 3 wherein said sub strate is formed of a conductive metal in the shape of an endless belt.
5. A transfer roll for electrically cooperating with a photoconductive plate when brought into contact therewith to attract charged toner particles from the plate toward the roll including a rigid cylindrical core or electrically conductive material,
.rneans.to connect said core to a biasing source whereby a uniform biasing potential is placed upon said core,
a resilient intermediate blanket placed over said I core, in contact therewith, having an electrical re- I sistivity such that the blanket is capable of trans- Imittingsaid bias potential from said conductive core to the outer periphery of said blanket,
an outer resilient coating placed over said blanket having a resistivity to minimize ionization of the surrounding atmosphere in and about the zone of contact between the transfer roll and the photoconductive plate. I
6. The transfer roll of claim 5 wherein said intermediate blanket is formed of a polyurethane material having a resistivity of between 10 and 10 ohms cm.
7. The transfer roll of claim 6 wherein said outer coating is formed of a, polyurethane material having a resistivity of between l0 and 10 ohms cm.
8. The transfer roll of claim 7 further including dielectric end caps for rotatably supporting and electrically isolating said transfer roll.
9. The apparatus-of claim 8 further including sheet gripping means to secure a sheet of final support material to the outer surface of said transfer roll.
10. The apparatus of claim 7 wherein said intermediate blanket has a hardness of between 15 and 25 durometers, Shore A.
1. The apparatus of claim 10 wherein said outer coating has a hardness of between 65 and durometers, Shore D. I