US3847478A

US3847478A - Segmented bias roll

Info

Publication number: US3847478A
Application number: US00425417A
Authority: US
Inventors: E Young
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1973-12-17
Filing date: 1973-12-17
Publication date: 1974-11-12
Anticipated expiration: 1991-11-12
Also published as: GB1474126A; CA1051503A

Abstract

A bias roll xerographic transfer system for simultaneous single pass duplex copying is disclosed. The transfer roll is provided with multiple, discrete (segmented), conductive areas. In the transfer nip area the transfer bias potential is applied through a sliding contact to only the conductive segments which are in that area. A grounding brush contacts different conductive segments in separate image charging and cleaning areas, both spaced from the transfer nip. The surface of the transfer roll, with a toner image thereon, is independently corona charged in the image charging area. Thus, the transfer and image charging functions are independent. The image charging corona means may be switched between D.C. and A.C. outputs in response to movement of the transfer roll to effect image reversal or neutralization, respectively.

Description

[451 Nov. 12, 1974 v United States Patent [1 1 Young SEGMENTED BIAS ROLL ABSTRACT Inventor: Eugene F. Young, Henrietta, NY.

A bias roll xerographic transfer system for simulta- Assignee: Xerox Corporation, Stamford,

Conn.

Dec. 17, 1973 [22] Filed:

Appl. No.: 425,417

that area. A grounding brush contacts different conductive segments in separate image charging and cleaning areas, both spaced from the transfer nip. The surface of the transfer roll, with a toner image 66 fiw 4 31 mmm 5 W c Ur Una e "ms L l WM k UmF nH o o 555 ill thereon, is independently corona charged in the image charging area. Thus, the transfer and image charging functions are independent. The image charging corona means may be switched between DC and AC. out- [56] References Cited UNITED STATES PATENTS- puts in response to movement of the transfer roll to 1 effect image reversal orneutralization, respectively.

Primary Examiner-John M. Horan 6 Claims, 1 Drawing Figure SEGMENTED BIAS ROLL The present invention relates to an electrostatographic duplex copying system with a transfer system providing image transfer biasing independently of imaging biasing.

In a conventional transfer station in xerography, a developed image of toner particles (from the image developer material) is transferred from a photoreceptor (the imaging surface) to a cut or roll fed copy sheet (the final image support surface), either directly or after an intermediate image transfer to an intermediate surface. Such image transfers'are also required in other electrostatographic processing systems, such as electrophoretic development/In TESI systems the intermediately transferred image may be an undeveloped latent electrostatic image;

Transfer is most commonly achieved by applying electrostatic force fields in a transfer nip sufficient to overcome the forces holding the toner to its original support surface and to attract most of the toner to transfer over onto the contacting second surface. These 2,807,233, or by a D.C. biased transfer roller or belt rolling along the back of the copy sheet. Examples of bias roller transfer systems are described in allowed U.S. Pat. application Ser. No. 309,562, filed Nov. 24, 1972, by Thomas .Meagher, and in U.S. Pat. Nos. 2,807,233; 3,043,684; 3,267,840; 3,328,193; 3,598,580; 3,625,146{ 3,630,591; 3,691,993; 3,702,482; and 3,684,364.

The difficulties of successful image transfer are well known. In the pre-transfer(pre-nip) region, before the copy paper contacts the image, if the transfer fields are high the image is susceptible to premature transfer, across the air gap, leading to decreased resolution or fuzzy images. Further, if there is ionization in the prenip air gap from high fields, it may lead to strobing or other image defects, lossfof transfer efficiency, and a lower latitude of system operating parameters. Yet, in the directly adjacent nip region itself the transfer field should be large as possible (greater than approximately volts per micron) to achieve high transfer efficiency.

and stable transfer. In the next adjacent post-nip region, at the photoconductor/copy sheet separation area, if the transfer fields are too low hollow characters may be generated. On the other hand,improper ionization in the post-nip region may cause image instability or copy sheet detacking problems Variations in ambient conditions, copy paper, contaminents, etc., can all affect the necessary transfer parameters. To achieve these differenttransfer field parameters consistently, and with appropriate transitions, is dlfficult even for simplex (single side image) copies. Duplex (both sides) copying presents much greater transfer difficulties, particularly' where the two images are transferred simultanteously to the opposing sides of the copy sheet as disclosed here.

Some exemplary duplexelectrostatographic copying systems are disclosed in the following U.S. Pat. Nos. 3,506,347 to C. F. Carlson, issued Apr. 14, 1970; 3,671,118 to J. Fantuzzo et-al., issued June 20, 1972; 3,672,765 to C. Altmann, issued June 27, 1972; 3,687,541 to G. A. Aser et al., issued Aug. 29, 1972,

2 and 3,697,171 to W.-A. Sullivan, issued Oct. 10, 1972.

The Sullivan U.S. Pat. No. 3,697,171 is of particular interest as disclosing details of the type of simultaneous duplex transfer system disclosed in the present specification embodimcnt, as well as the general requirements and theory of such a system. Accordingly, this patent is specifically made a part of this specification. This Sullivan patent, for example, teaches corona discharge polarity reversal of a first toner image (which has been intermediately transferred to the transfer roller surface) at a corona charging position spaced from the transfer nip, and subsequent simultaneous transfer to opposite sides of a copy sheet of the first toner image with a second toner image on the photoreceptor. The present invention represents an improvement over this disclosed system.

Another referenceof particular interest is U.S. Pat. No. 3,684,364, issued Aug. 15, 1972, to Fred W. Schmidlin. This patent teaches a xerographic roller electrode transfer system in which appropriate transfer potential can be provided to the roller from a transfer bias source through a plurality of fixed contacts. These contacts slidably engage moving segmented conductors mounted inside the roller, spaced around the circumference of the roller, generally similar to those disclosed herein.

U.S. Pat. No. 3,574,301, issued Apr. 13, 1971, to J. S. Bernhard discloses a segmented bias roll to enable different biases and different functions to occur at different areas of the roll'circumference. However, this bias roll is in a developer station rather than a transfer station. v

U.S. Pat. No. 3,647,292, issued Mar. 7, 1972, to D.

J. Weikel, J r., discloses a uniform transfer belt system for carrying a copy sheet through the transfer station, vacuum means for holding the sheet on the belt, and transfer field generating means, which in one embodiment includes multiplestationary transfer electrodes in a stationary segmentedplate with different (increasing) appliedpotentials acting at the back of the transfer belt.

U.S. Pat. No. 3,644,034, issued Feb. 22, 1972, to R. L. Nelson, discloses a segmented wide conductive strip transfer belt to which two different bias potentials are applied by two support rollers to those segments passing over the rollers. The conductive segments are separated by 1/16 inch insulative segments.

The transfer system of the invention may be utilized in any desired path, orientation or. configuration. It may be utilized for transferwith an imaging surface of any desired configuration, including either a cylinder or a belt. Photoconductive belt imaging surfaces in electrographic copying systems are exemplified by U.S. Pat. Nos. 3,093,039; 3,697,285; 3,707,138; 3,713,821, and

and details whereby the above-mentioned aspects of the invention are attained. Accordingly, the invention will be better understood by reference to the following description and to the drawing forming a part thereof, wherein:

The FlGURE is an axial cross-sectional view of an exemplary duplex transfer copying system in accordance with the present invention.

Referring to the FIGURE, there is shown therein an electrostatic duplex copying system as one example of the present invention. The system 10 here comprises a transfer rnember 12 in the form of a cylindrical roller. The outer or image receiving surface '14 of thetransfer member 12 resiliently engages the imaging surface 16 of a conventional photoreceptor 18 at a transfer nip 20.

In the transfer nip 20, the transfer of the two image patterns of toner particles 22 to the opposite sides of a copy sheet 24 is accomplished simultaneously. Both toner images may be conventionally xerographically formed and developed on the photoreceptor 18 imaging surface 16.

In the system 10 a first imagewise pattern of the toner 22 is first transferred from the photoreceptor imaging surface l6 onto the image receiving surface 14 of the transfer member 12 in the transfer nip 20, inthe absence of the copy sheet 24. The first toner image is thereby temporarily retained on the image receiving surface 14 and thereby rotated around on the transfer roller 12 fora subsequent transfer to the upper surface of the'copy sheet 24, which has then been'inserted in the nip 20. A second toner image formed on the photoreceptor 18 imaging surface 16 is then transferred directly from the imaging surface 16 to the facing lower surface of the copy sheet 24. I I

It may be seen that the image receiving surface ,14 of the transfer member 12 functions as-an intermediate image supporting surface, and that twotransfers of this first image are required, the second of which occurs simultaneously with the single transfer of the second image. All image transfers are effected by electrical, transfer biases applied to the transfer member 12 to form transfer fields between the image receiving surface 14 i and the imaging surface 16 at the transfer nip 20.

For the transfer to opposite sides of the copy sheet 24 simultaneously in the transfer nip 20, the first toner im-' age, stored on theimage receiving surface 14, has its charge polarity reversed prior to retransfer tothe copy sheet 24, so thatthis first imagewill transfer in the opposite direction from thesecond image, i.e., be repelled from the image receiving surface 14 rather than attracted toward it. This polarity reversal of the first toner image is provided by a corona charging system 26 operated to provide D.C. ion emissions charging the first image at a charging. area which is substantially spaced from the transfer nip 20. The corona charging system 26 provides ion emissions opposite in polarity from the initial toner charge as the toner passes under the corona output on the image receiving'surface 14.

' Further details and descriptive material in regard to the above-described structure and function may be- 34. The conductors 34 extend axially through the transfer member 12 in a parallel, closely spaced apart relationship, closely underlying the image receiving surface A conventional transfer bias supply 36 is operatively connected to selected ones of the conductive strips 34 only adjacent the transfer nip 20 bya fixed electrical sliding contactor 38. Only one bias supply 36 and contactor 38 are shown. However, it will be appreciated that, as described in the above-cited Schmidlin U.S. Pat. No. 3,684,364, multiple contacts and bias potentials may be utilized for transfer field tailoring.

The individual conductors 34 are illustrated here for drawing clarity as scaled exaggeratedly wide in comparison to the transfer member 12 and the transfer nip 20. In an actual preferred structure the number of conductors would be much greater and a much smaller spacing would be provided therebetween. Twenty or more conductors 34 per centimeter are preferable so as to avoid any possibility of a printout of fringe field chargepatterns or other visible defects in the transferred image. It will also be appreciated that although the transfer member 12 is here illustrated as a roll cylinder it could also be in the form of an endless flexible belt.

it will be appreciated that for higher transfer fields with lower voltages applied to theconductors 34, that the roll outer layer 32 sho uld'be quitethin if it comprises a dielectric layer, for example, 0.1 millimeters. However, if the roll outer layer is relaxable (semiconductive), so that transfer charges are conducted out to the outer surface 14, then it will be appreciated that this roll outer layer may be substantially thicker. It may also be desirable to have the conductors be sufficiently flexible so as not to interfere with the desired roll duror'neter.

While the interior of the transfer roll 12 is illustrated here as hollow for clarity, it will be appreicated that it may be partially or fully filled with a suitable solid or resistive material, providin that the individual conductors 34 are not shorte together. The electrical contacts with the conductors 34 by the transfer contactor 38 and the grounding brush 39 can be at any location, such as internally circumferentially at one end of the roll as shown, or at an outside surface in a radial plane if the conductors are;brought out onto a roll end.

Referring now to the corpna charging system 26, this comprises an alternating c rrent power supply 40, a direct current power supply,- 42, and a switch 44 alternately connecting one of tpese two

power supplies

40 or 42 to a conventional corotron 46 which is spaced over the image receiving surface 14 man image charging area substantially spaced from the transfer nip 20. A grounding brush 39 makes. an electrical grounding connection with all of the donductors 34 underlying the image receiving surface 14 in this same charging area,

i I When the switch 26 conhectsthe conventional D.C.

corotron supply 42 to the corotron46, the previously described image polarity/reversal is provided by ion emission from the corotron 46 onto the image receiving surface 14, including the toner 22 thereon. When the switch 26 is alternately switched to connect trie corotron 46 to the conventional A.C. supply 40, an alternating polarity ion emission output is provided therefrom for charge neutralization of the underlying surface 14, including the toner 22. It will be appreciated, of course, that two separate alternately activated corotrons could be utilized instead, if desired, rather than switching only the input to a single corotron as disclosed here. The actuation of the switch 44 is preferably automatic, in coordination with the movement of the transfer member 12. That is, during the initial rotation of the transfer member 12 in which the first toner image is being placed on the surface 14 for subsequent retransfer, the DC. supply 42 will be connected for polarity reversal of this image. Then after this first toner image begins to retransfer to the copy sheet 24, the switch 44 is preferably switched automatically in response to the further rotation of the transfer member 12 (or other system components) to electrically neutralize the remaining (untransferred) toner particles on the image receiving surface 14 so that they may be removed at a cleaning station.

Cleaning of the A.C. neutralized toner particles from the image receiving surface 14 of the transfer member 12 may be accomplished by any conventional toner cleaning means, such as a blade, web, or brush system. A conventional xerographic cleaning brush 50 is illustrated here in rotational sweeping cleaning engagement with the surface 14 opposite from the transfer nip 20. This cleaning brush 50 is pivotally mounted here on a lever arm connected to a solenoid 52, for periodically pivotally lifting the cleaning brush 50 away from the surface 14. This brush 50 disengagement allows the first toner image transferred to pass this cleaning station without being disturbed prior to its retransfer. It will be noted that the grounding brush 39 preferably extends into this cleaning area for grounding the conductors 34 in this region. Thisprevents any charges from being maintained on the conductors 34 adjacent the cleaning brush'50 which might resist removal of toner by the cleaning brush.

The grounding brush 39, together with the discrete conductors 34, provides complete electrical isolation of the toner charging or discharging, the toner'cleaning, and the toner transfer functions in this system 10. As noted, the grounding brush or contactor 39 grounds all of the conductors 34 adjacent both the charging system 26 and the cleaning brush 50. This electrically grounds any charges which would otherwise be retained on the conductors 34 from the transfer bias supply 36. lt also provides, in effect, one (grounded) plate of a capacitor formed between the charges on the surface 14 and the conductors 34 in the charging area. This considerably increases the charge density which may be applied by the charging system 26, as well as stabilizing the voltage reference level so as to avoid any random charge effects on the subsequent transfer. More complete A.C. charge neutralization may also be provided for the same reasons. Further, with this system no transfer bias charges or transfer fields can be present in the charging area. Such transfer charges could otherwise resist the reversal charging output of the charging system 26, since the polarity of the DC. supply 42 (and the connected corotron 46 output) is the same as that of the applied transfer bias, The transfer field level may be set independently by adjustment of the bias supply 36, and the output of the corotron 46 may be set independently by adjustment ofits D.C. supply 42, without any possible mutual interference due to conduction through, or charge transfer with, the transfer member 12.

The electrostatographic duplex copying system disclosed herein is presently considered to be preferred; however, it is contemplated that further variations and modifications within the purview of those skilled in the art can be made herein. The following claims are intended to cover all such variations and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In an electrostatographic duplex copying system, wherein one image is transferred from an imaging surface to a transfer member and then is subsequently retransferred to a final support surface at a transfer nip, and wherein another image is transferred from an imaging surface to said same final support surface by said same transfer member:

wherein said transfer member has an image receiving surface and a multiplicity of electrically discrete conductive strips underlying said image receiving surface;

transfer bias means for applying an electrical transfer bias to selected ones of said conductive strips only adjacent said transfer nip for said image transfer to said final support surface; and

selectively operable image charging means for selectively applying an electrical charge to said image receiving surface of said transfer member, at a charging area of said surface substantially spaced away from said transfer nip, independently of said transfer bias means; wherein said image charging means includes A.C. and DC corona charging means and switching means for switching between said A.C. and.D.C. corona charging means in coordination with movement of said transfer member; where said D.C. corona charging means is for po- 1 larity reversal of said one image and said A.C. corona charging means is for charge neutralizing.

2. The electrostatographic system of claim 1 further including grounding ,meansfor grounding a selected number of said conductive strips which are adjacent said corona charging means.

3. In an electrostatographic duplex copying system, wherein one image is transferred from an imaging surface to a transfer member and then is subsequently retransferred to a final support surface at a transfer nip,

and wherein another image is transferred from an imaging surface to said same final support surface by said same transfer member:

selectively operable imaging charging means for selectively applying an electrical charge to said image receiving surface of said transfer member, at a charging area of said surface substantially spaced away from said transfer nip, independently of said transfer bias means; wherein said image charging 7 means comprises a single corona charging apparatus and AC. and DC corona power supplies and switch means for selectively connecting said corona power supplies for selecting between image polarity reversal and charge neutralizing in coordination with movement of said transfer member. 4. In an electrostatographic duplex copying system, wherein one image is transferred from an imaging surface to a transfer member and then is subsequently retransferred to a final support surface at a transfer nip, and wherein another image is transferred from an imaging surface to said same final support surface by said same transfer member:

wherein said transfer member has an image receiving surface and a multiplicity of electrically discrete conductive strips underlying said image receiving surface; transfer bias means for applying an electrical transfer bias to selected ones of said conductive strips only adjacent said transfer nip for said image transfer to said final support surface; and selectively operable image charging, means for selectively applying an electrical charge to said image receiving surface of said transfer member, at a charging area of said surface substantially spaced away from said transfer nip, independently of said transfer bias means; further including grounding means for grounding a selected member of said conductive strips which are adjacent said image charging means. I 5. In an electrostatographic duplex copying system, wherein one image is transferred from an imaging surface to a transfer member. and then is subsequently retransferred to a final support surface at a transfer nip, and wherein another image is transferred from an imaging surface to said same final support surface by said same transfer member:

transfer bias means for applying an electrical transfer bias to selected ones of said conductive strips only tively applying an electrical charge to said image receiving surface of said transfer member, at a charging area of said surface substantially spaced away from said transfer nip,.independently of said transfer bias. means; wherein said images comprise charged toner particles, and further including cleaning means substantially spaced away from said transfer nip forcleaning said image receiving surface and grounding means for grounding conductive strips which are adjacent said cleaning means and adjacent said image charging means.

6. In an electrostatographic duplex copying system,

wherein one image is transferred from an imaging surface to a transfer member and then is subsequently retransferred to a final support surface at a transfer nip, and wherein another image is transferred from-an imaging surface to said same final support surface by said same transfer member:

wherein said transfer member has an image receiving surface and a multiplicity of electrically discrete conductive strips underlying said image receiving surface; transfer bias means for applying-an electrical transfer bias to .selected ones of said conductive strips only adjacent said transfer nip for said image transfer to said final support surface; and r selectively operable image charging means for selectively applying an electrical charge to said image receiving surface of said transfer member, at a charging area of said surface substantially spaced away from said transfer nip, independently of said transfer bias means; wherein said image charging means includes A.C. and DC. corona charging means and switching means forswitching between said A.C. and DC. corona charging means in coordination with movementrof said transfer member, where said D.C. corona charging means is for polarity reversal of said one image and said A.C. co-

rona charging means is for charge neutralizing,

Claims

1. In an electrostatographic duplex copying system, wherein one image is transferred from an imaging surface to a transfer member and then is subsequently retransferred to a final support surface at a transfer nip, and wherein another image is transferred from an imaging surface to said same final support surface by said same transfer member: wherein said transfer member has an image receiving surface and a multiplicity of electrically discrete conductive strips underlying said image receiving surface; transfer bias means for applying an electrical transfer bias to selected ones of said conductive strips only adjacent said transfer nip for said image transfer to said final support surface; anD selectively operable image charging means for selectively applying an electrical charge to said image receiving surface of said transfer member, at a charging area of said surface substantially spaced away from said transfer nip, independently of said transfer bias means; wherein said image charging means includes A.C. and D.C. corona charging means and switching means for switching between said A.C. and D.C. corona charging means in coordination with movement of said transfer member; where said D.C. corona charging means is for polarity reversal of said one image and said A.C. corona charging means is for charge neutralizing.

2. The electrostatographic system of claim 1 further including grounding means for grounding a selected number of said conductive strips which are adjacent said corona charging means.

3. In an electrostatographic duplex copying system, wherein one image is transferred from an imaging surface to a transfer member and then is subsequently retransferred to a final support surface at a transfer nip, and wherein another image is transferred from an imaging surface to said same final support surface by said same transfer member: wherein said transfer member has an image receiving surface and a multiplicity of electrically discrete conductive strips underlying said image receiving surface; transfer bias means for applying an electrical transfer bias to selected ones of said conductive strips only adjacent said transfer nip for said image transfer to said final support surface; and selectively operable imaging charging means for selectively applying an electrical charge to said image receiving surface of said transfer member, at a charging area of said surface substantially spaced away from said transfer nip, independently of said transfer bias means; wherein said image charging means comprises a single corona charging apparatus and A.C. and D.C. corona power supplies and switch means for selectively connecting said corona power supplies for selecting between image polarity reversal and charge neutralizing in coordination with movement of said transfer member.

4. In an electrostatographic duplex copying system, wherein one image is transferred from an imaging surface to a transfer member and then is subsequently retransferred to a final support surface at a transfer nip, and wherein another image is transferred from an imaging surface to said same final support surface by said same transfer member: wherein said transfer member has an image receiving surface and a multiplicity of electrically discrete conductive strips underlying said image receiving surface; transfer bias means for applying an electrical transfer bias to selected ones of said conductive strips only adjacent said transfer nip for said image transfer to said final support surface; and selectively operable image charging means for selectively applying an electrical charge to said image receiving surface of said transfer member, at a charging area of said surface substantially spaced away from said transfer nip, independently of said transfer bias means; further including grounding means for grounding a selected member of said conductive strips which are adjacent said image charging means.

5. In an electrostatographic duplex copying system, wherein one image is transferred from an imaging surface to a transfer member and then is subsequently retransferred to a final support surface at a transfer nip, and wherein another image is transferred from an imaging surface to said same final support surface by said same transfer member: wherein said transfer member has an image receiving surface and a multiplicity of electrically discrete conductive strips underlying said image receiving surface; transfer bias means for applying an electrical transfer bias to selected ones of said conductive strips only adjacent said transfer nip for said image transfer to said final support surface; and selectively operable image charging meanS for selectively applying an electrical charge to said image receiving surface of said transfer member, at a charging area of said surface substantially spaced away from said transfer nip, independently of said transfer bias means; wherein said images comprise charged toner particles, and further including cleaning means substantially spaced away from said transfer nip for cleaning said image receiving surface and grounding means for grounding conductive strips which are adjacent said cleaning means and adjacent said image charging means.

6. In an electrostatographic duplex copying system, wherein one image is transferred from an imaging surface to a transfer member and then is subsequently retransferred to a final support surface at a transfer nip, and wherein another image is transferred from an imaging surface to said same final support surface by said same transfer member: wherein said transfer member has an image receiving surface and a multiplicity of electrically discrete conductive strips underlying said image receiving surface; transfer bias means for applying an electrical transfer bias to selected ones of said conductive strips only adjacent said transfer nip for said image transfer to said final support surface; and selectively operable image charging means for selectively applying an electrical charge to said image receiving surface of said transfer member, at a charging area of said surface substantially spaced away from said transfer nip, independently of said transfer bias means; wherein said image charging means includes A.C. and D.C. corona charging means and switching means for switching between said A.C. and D.C. corona charging means in coordination with movement of said transfer member, where said D.C. corona charging means is for polarity reversal of said one image and said A.C. corona charging means is for charge neutralizing, wherein said one image comprises charged toner particles; and further including cleaning means substantially spaced away from said transfer nip for cleaning said image receiving surface and grounding means for grounding conductive strips which are adjacent said cleaning means and also for grounding conductive strips which are adjacent said corona charging means.