US3751156A - Electrostatic copying apparatus with means for preventing contamination of transfer material - Google Patents

Electrostatic copying apparatus with means for preventing contamination of transfer material Download PDF

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Publication number
US3751156A
US3751156A US00300376A US3751156DA US3751156A US 3751156 A US3751156 A US 3751156A US 00300376 A US00300376 A US 00300376A US 3751156D A US3751156D A US 3751156DA US 3751156 A US3751156 A US 3751156A
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Prior art keywords
transfer station
combination
cam
projection
delay
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US00300376A
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English (en)
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R Szostak
W Krueger
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Agfa Gevaert AG
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Agfa Gevaert AG
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/14—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base
    • G03G15/16—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer
    • G03G15/1665—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer by introducing the second base in the nip formed by the recording member and at least one transfer member, e.g. in combination with bias or heat
    • G03G15/167—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer by introducing the second base in the nip formed by the recording member and at least one transfer member, e.g. in combination with bias or heat at least one of the recording member or the transfer member being rotatable during the transfer

Definitions

  • ABSTRACT An electrostatic copying apparatus wherein an idler roller is movable toward and away from a rotary cylindrical xerographic surface carrying powder images for transfer onto a series of discrete sheets of transfer material.
  • a scanning device is located upstream of the transfer station for powder images to effect a delay of the movement of roller toward the xerographic surface until the leading portion of an oncoming sheet is about to reach or reaches the transfer station and to effect a delay of the movement of roller away from the xerographic surface until the trailing portion of a sheet which is in the process of receiving a powder image is about to reach or moves only slightly beyond the transfer station. This insures that the powder images cannot be transferred onto the dielectric layer of the roller and prevents a contamination of the rear sides of nextfollowing sheets.
  • the present invention relates to electrostatic copying apparatus in general, and more particularly to improvements in electrostatic copying apparatus wherein powder images formed on a moving xerographic surface are to be transferred onto a series of discrete sheets consisting of transfer material.
  • an electrostatically charged countersurface presses successive increments of a sheet against the selenium layer of the xerographic surface to insure the transfer of powder images.
  • a drawback of presently known electrostatic copying apparatus is that they are not provided with reliable means for preventing the transfer of powder images onto the countersurface.
  • the countersurface remains closely adjacent to the xerographic surface long after the trailing portion of a sheet has been advanced beyond the transfer station between the two surfaces, a powder image is likely to be transferred onto the countersurface during the interval which elapses between the movement of the trailing portion of a preceding sheet beyond and the arrival of the nextfollowing sheet at the transfer station. Any noticeable contamination of the countersurface-is highly undesirable because the latter is likely to smudge the rear side of the next-following sheet.
  • the mechanism which transports successive sheets toward the transfer station controls movements of the countersurface toward the transfer station.
  • Such operative connection between the sheet transporting mechanism and the displacing mechanism for the countersurface is satisfactory and normally prevents the transfer of powder images onto.
  • the countersurface if the transporting mechanism is capable of transporting successive sheets with a high degree of accuracy, i.e., in such a way that the width of gaps between successive sheets invariably remains within a narrow range.
  • the transporting mechanism cannot advance the sheets with such high degree of accuracy, the width of gaps between successive sheets is likely to vary tosuch an extent that portions of powder images are transferred onto the countersurface which thereupon contaminates the rear side or sides of the nextfollowing sheet or sheets.
  • the just described operative connection between the sheet transporting mechanism and the displacing mechanism for the countersurface cannot prevent a contamination of the countersurface if the apparatus is to transfer powder images onto a series of sheets having different lengths.
  • An object of the invention is to provide a novel and improved electrostatic copying apparatus wherein the countersurface which biases sheets of transfer material against the xerographic surface during transfer of powder images cannot be contaminated by toner irrespective of whether the width of gaps between successive sheets varies within a wide range and irrespective of whether or not the transporting mechanism feeds a series of sheets having identical or different lengths.
  • Another object of the invention is to provide an electrostatic copying apparatus with novel and improved means for preventing contamination of the countersurface by toner irregardless of thenature of mechanism which is employed to transport sheets of transfer material between the countersurface and the xerographic surface.
  • a further object of the invention is to provide novel and improved means for changing the distance between the countersurface and the xerographic surface.
  • An additional object of the invention is to provide simple, reliable, compact and relatively inexpensive means for preventing a contamination of the countersurface by the material of powder images in an electrostatic copying apparatus.
  • the invention is embodied in an electrostatic copying apparatus which comprises a driven preferably cylindrical xerographic surface arranged to transport a series of powder images toward a transfer station, a countersurface which is normally spaced apart from the xerographic surface and preferably constitutes an idler roller, means for transporting discrete sheets of transfer material along a path extending between the xerographic surface and the countersurface so that successive sheets advance toward, through and beyond the transfer station, displacing means which is actuatable to move one of the surfaces (preferably the countersurface) toward the other surface to thereby effect at the transfer stationthe transfer of a powder image from the xerographic surface onto one side of a sheet which advances through the transfer station, and control means for'preventing the transfer of powder images onto the countersurface irrespective of the width ofgaps between successive sheets and irrespective of the length of such sheets.
  • the control means comprises scanning .means'which is adjacent to the path of sheets and .is
  • time-delay means for delaying the actuation of displacing means in response to detection of the leading portion of an oncoming sheet by the scanning means until the leading portion of the oncoming sheet reaches or closely approaches the transfer station.
  • the just described time-delay means is capable of preventing a contamination of the countersurface with the material of powder images irrespective of the width of gaps between successive sheets.
  • the scanning means is preferably constructed and assembled to produce signals in response to detection of trailing portions of successive sheets which are in the process of receiving powder images at the transfer station, and the time-delay means is preferably constructed and assembled to deactivate the displacing means when the thus detected trailing portion of a sheet is immediately adjacent to or reaches or moves only slightly beyond the transfer station.
  • FIG. 1 is a fragmentary vertical sectional view of an electrostatic copying apparatus which embodies the invention
  • FIG. 2 is a sectional view as seen in the direction of arrows from the line II-II of FIG. 1;
  • FIG. 3 is a sectional view as seen in the direction of arrows from the line III-III of FIG. 2.
  • an electrostatic copying apparatus including a housing or frame 38 (FIGS. 2 and 3) supporting a shaft 1 (FIG. 1) for two carriers here shown as twoarmed levers 3, 4 (FIG. 1) which in turn support a second shaft 5 extending in parallelism with the shaft 1.
  • the shaft 5 supports a cylindrical countersurface in the form of an idler roller 9 which is freely rotatable thereon.
  • the shaft 5 is connected to the longer arms of the carriers or levers 3, 4 and the shorter arms of these levers are connected to each other by a rod 10a which is articulately connected to the reciprocable armature 10 of an electromagnet 11.
  • the armature 10 moves the levers 3,4 to the operative positions shown in FIG. 1 whereby the levers stress one or more return springs 12.
  • the armature 10 allows the spring or springs 12 to contact and to respectively return the levers 3, 4 into abutment with stationary stop pins 15, 16 mounted in the frame 38.
  • the levers 3, 4 urge the roller 9 against the underside of a sheet 19 of transfer material whereby the upper side of the sheet 19 bears against the selenium layer 13 on a drum-shaped rotary xerographic surface 14.
  • the outer side of the selenium layer 13 carries a powder image PI which is to be transferred onto the upper side of the sheet 19.
  • the transfer station where the roller 9 can engage the underside of the adjacent sheet 19 is shown at T.S.
  • the parts I, 3, 4, 5, 10, 10a, 11 together constitute a dis placing means which is actuatable on energization of the electromagnet 11 to move the roller 9 toward the selenium layer 13 on the drum 14 so that the roller 9 engages the sheet 19 at the transfer station T.S.
  • the transporting mechanism for a series of discrete sheets 19 includes two stationary guides 17, 18 which are disposed at the opposite sides of the transfer station T.S. between the xerographic surface 14 and the roller 9.
  • the remaining parts of the transporting mechanism can be constructed and may operate in a manner as disclosed in the commonly owned co-pending application Ser. No. 181,374 filed Sept. 17, 1971.
  • successive sheets can be removed from a stack and fed in the direction indicated by arrow A to advance along a substantially horizontal path toward, through and beyond the transfer station T.S.
  • the guide 17 has an aperture 17a for a scanning device 20 which can close a microswitch 21 in response to detection of the leading portion of an oncoming sheet 19.
  • the microswitch 21 controls a time-delay device 22 in the electric circuit 23, 24 of the electromagnet 11.
  • the microswitch 21 closes automatically to thereby energize the time-delay device 22 in response to detection of the leading portion of a sheet 19 by the scanning device 20, and'the microswitch 21 opens automatically when the trailing portion of a sheet 19 has been advanced beyond the scanning device 20.
  • the device 20 scans the path of sheets 19 close to or immediately upstream of the transfer station T.S.
  • the dielectric layer 9a of the roller 9 is charged by the wire 25 of a corona discharge device which further comprises a grounded housing 26.
  • the wire 25 is connected with a source 27 of high-voltage current.
  • the charging of dielectric layer 9a is made possible because the levers 3, 4 are grounded by way of the shaft 1 and conductor means 28.
  • the xerographic surface 14 is also grounded by means of an elastic contact 29. This insures the transfer of powder image PI from the selenium layer 13 onto the upper sides of successive sheets 19.
  • the xerographic surface 14 is mounted on an output element or shaft 32 which is rotated by a drive means, not shown, in a manner well known from the art.
  • the shaft 32 is journalled in the frame 38 and can drive a coaxial shaft 34 by way of a friction clutch 33.
  • the shaft 34 is journalled in the frame 38 and serves to support and rotate a diskshaped cam 35 having a peripheral cam face including a larger-diameter section35a, a smaller-diameter section 35f, and two intermediate sections 35b, 35c which provide for gradual transition between the sections 35a and 35f.
  • the clutch 33 can rotate the cam 35 in a clockwise direction (see the arrow B in FIG. 3).
  • the cam 35 constitutes an actuating means or trip for a microswitch 37 having a movable contact 36 extending into the path of movement of the cam face section 35b so that the microswitch 37 remains closed while the contact 36 engages the cam face section 35a and is allowed to open (e.g., by a suitable spring) when the cam 35 moves the section 35f along the tip of the contact 36.
  • the frame 38 further supports an electromagnet 39 having an armature including a rod 39a and an arresting element 41 provided with two stops 41a and 41b.
  • an electromagnet 39 When the electromagnet 39 is deenergized, a helical spring 40 which reacts against the frame 38 urges the armature 39a, 41 to the end position shown in FIG. 2 whereby the stop 41b extends into the path of movement of a projection 35e at one side of the cam 35.
  • the other side of the cam 35 carries a second projection 35d which can be engaged and arrested by the stop 41a when the electromagnet 39 is energized to move its armature 39a, 41 against the opposition of the spring 40.
  • the direction in which the armature 39a, 41 moves in response to energization of the electromagnet 39 is indicated by an arrow C.
  • the microswitch 21 energizes the electromagnet 39 (which forms part of the time-delay device 22 shown in FIG. 1) which moves the armature 39a, 41 in the direction indicated by arrow C so that the spring 40 stores energy and the stop 41b is disengaged from the projection 35e.
  • the shaft 32 is free to rotate the shaft 34 and the cam 35 by way of the friction clutch 33 whereby the cam 35 rotates in the direction indicated by arrow B and moves the section 35b of its cam face against the movable contact 36 of the microswitch 37.
  • This microswitch also forms part of the time-delay device 22 and is closed with a delay which is necessary for the cam 35 to cover the angle shown in FIG. 3.
  • the closing of microswitch 37 coincides with or immediately precedes the arrival of the leading portion of a fresh sheet 19 at the transfer station T.S. of FIG. 1.
  • the microswitch 37 energizes the electromagnet 11 so that the armature pivots the levers 3, 4 and the roller 9 to the position shown in FIG.
  • the energized electromagnet 39 of the time-delay device 22 maintains the stop 41a in the path of movement of projection 35d on the cam 35 so that the cam 35 is arrested by the armature 39a, 41 after it completes an angular movement through about one-half of a revolution.
  • the projection 35d engages the stop 41a before the cam face section 35a moves beyond the contact 36 of the microswitch 37 so that the electromagnet 11 remains energized and maintains the roller 9 in the operative position of FIG. 1 as' shaft 34 and the cam 35 by way of the friction clutch 33. Because the projection 35d is free to bypass the stop 41a.
  • the movable contact 36 allows the microswitch 37 to open and to deenergize the electromagnet 11 with a delay which is required by the cam 35 to cover the distance a 2 shown in FIG. 3. This delay generally corresponds to the interval which is required to advance the trailing portion of a sheet 19 from the opening 17a to the transfer station T.S.
  • the deenergized electromagnet 11 then allows the spring or springs 12 to return the roller 9 to the inoperative position in which the levers 3, 4 respectively abut against the stationary stops 15, 16.
  • the roller 9 moves its dielectric layer 9a away from the selenium layer 13 on the xerographic surface 14 preferably not later than when the trailing portion of a sheet 19 moves through the transfer station T.S. to thus prevent the transfer of toner onto the outer side of the layer 9a. Such transfer could result in smudging of the underside of the next-following sheet or sheets 19.
  • the cam 35 is automatically arrested in the starting position of FIG. 3 as soon as the projection 35:: returns into engagement with the stop 41! of the armature 39a, 41.
  • the apparatus is then ready for the next copying operation which can begin as soon as the leading portion of the next-following sheet 19 reaches the scanning device 20. It will be noted that the duration of energization of the electromagnet 11 is not dependent on the width of gaps between successive sheets 19 in the path defined by the guides l7, 18 but only on the length of such sheets.
  • a relatively long sheet 19 can be followed by a relatively short sheet, and the width of gaps between successive sheets may vary within any practical range without running the risk that the exposed surface of the dielectric layer 9a would be contaminated with toner due to bodily contact with the selenium layer 13 on the xerographic surface 14.
  • the spring or springs 12 of FIG. 1 can be omitted if the longer arms of the levers 3, 4 (with the shaft 5 and roller 9 thereon) are heavy enough to return into abutment with the stops 15, 16 by gravity as soon as the electromagnet 11 is deenergized.
  • the purpose of the spring or springs 12 (and/or the tendency of the roller 9 to move away from the transfer station T.S. by gravity) is to insure that the layer 9a remains spaced apart from the xerographic surface in the event of a power failure.
  • the scanning device 20, the microswitch 21 and the time-delay device 22 together constitute a control unit which actuates the displacing means 1, 3, 4, 5, 10, 10a, 11 with a predetermined delay following the engagement of scanning device 20 by the leading portion of an oncoming sheet 19 and which deactivates the displacing means with a predetermined delay following movement of the trailing portion of a sheet 19 beyond the scanning device 20.
  • time-delay device 22 (including the cam 35, microswitch 37 and electromagnet 39) constitutes but one of a variety of mechanical and/or electrical time-delay means which can be utilizedin the copying apparatus of the present invention to insure that the roller 9 is held in its operative position (as shown in FIG. 1) only when a sheet 19 advances through the transfer station T.S.
  • roller 9 The movement of roller 9 to the position of FIG. 1 as soon as the leading portion of a sheet 9 reaches the transfer station T.S. is desirable to insure that the front portion of the powder image PI is invariably transferred onto such sheet. By the same token, it is desirable to insure that the roller 9 moves away from the station T.S. only when the station T.S. receives the trailing portion of a sheet and not later than when the trailing portion has advanced only slightly beyond the transfer station. Such mode of operation insures the transfer of entire powder images provided that the image is not longer than a sheet 19.
  • the configuration of the face on the cam 35 is preferably selected in such a way that a short-lasting contact between the layers 9a and 13 might take place at the transfer station T.S. before the leading portion of a sheet reaches the transfer station and after the trailing portion of a sheet has been moved beyond the transfer station.
  • said displacing means comprising carrier means supporting said countersurface and being movable between first and second positions in which said countersurface is respectively remote from and is located at said transfer station, and electromagnet means energizable with a delay determined by said time-delay means to, move said carrier means to said second position.
  • said carrier means comprises lever means pivotable between said first and second positions.
  • control means further comprises electric switch means arranged to be closed by said scanning means in response to detection of the leading portion of an oncoming sheet, said time-delay means comprising drive means having a rotary output element, rotary cam means, friction clutch means interposed between said output element and said cam means, and electromagnet means energizable in response to closing of said switch means to thereby permit said clutch means to rotate said cam means through a predetermined distance including a first portion which said cam means covers while maintaining said displacing means in deactivated condition and a second portion which said cam means covers while causing said displacing means to maintain said one surface in contact with a sheet at said transfer station.
  • said cam means comprises a first projection, an angularly offset second projection and a cam face
  • said electromagnet means having an armature including first stop means located in the path of movement of said first projection in deenergized condition of said electromagnet means and second stop means located in the path of movement of said second projection in the energized condition of said electromagnet means
  • said displacing means comprising second electromagnet means energizable to move said one surface toward said other surface and said time-delay means further comprising normally open second electric switch means adjacent to said cam face, said cam face being arranged to close said second switch means and to thereby energize said second electromagnet means with a predetermined delay following disengagement of said first stop means from said first projection and before said second projection engages said second stop means.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electrostatic Charge, Transfer And Separation In Electrography (AREA)
  • Paper Feeding For Electrophotography (AREA)
US00300376A 1971-10-21 1972-10-24 Electrostatic copying apparatus with means for preventing contamination of transfer material Expired - Lifetime US3751156A (en)

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DE19712152500 DE2152500A1 (de) 1971-10-21 1971-10-21 Vorrichtung zur uebertragung von pulverfoermigen tonerbildern

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Cited By (34)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3848204A (en) * 1973-09-21 1974-11-12 Xerox Corp Pressure adjustable electrophotographic printing machine transfer apparatus
US3851966A (en) * 1972-12-11 1974-12-03 Xerox Corp Reproduction apparatus
US3877416A (en) * 1973-04-23 1975-04-15 Xerox Corp Humidity corrected transfer apparatus
US3900591A (en) * 1973-06-08 1975-08-19 Minnesota Mining & Mfg Developed image transfer
US3901186A (en) * 1973-07-02 1975-08-26 Xerox Corp Transfer roller assembly
US3955530A (en) * 1973-06-28 1976-05-11 Canon Kabushiki Kaisha Transfer-fixing device
US3963340A (en) * 1975-04-18 1976-06-15 Xerox Corporation Imaging apparatus for typewriter employing electrostatic printing process
US3977779A (en) * 1973-12-21 1976-08-31 Xerox Corporation Electrostatographic transfer with air
US3990393A (en) * 1975-04-18 1976-11-09 Xerox Corporation Apparatus for depositing magnetic material on an image bearing member
US3993021A (en) * 1973-06-08 1976-11-23 Minnesota Mining And Manufacturing Company Transfer device
US4046472A (en) * 1975-04-18 1977-09-06 Xerox Corporation Electrostatic imaging apparatus
US4087169A (en) * 1975-11-14 1978-05-02 Xerox Corporation Transfer roller system
US4101212A (en) * 1976-01-19 1978-07-18 Konishiroku Photo Industry Co., Ltd. Image transfer complementary apparatus for electrophotographic copying machine
US4103995A (en) * 1975-04-18 1978-08-01 Xerox Corporation Imaging apparatus
US4165171A (en) * 1974-04-08 1979-08-21 Oce-Van Der Grinten N.V. Electrographic apparatus and process
US4218691A (en) * 1977-08-30 1980-08-19 Ricoh Company, Ltd. Recording apparatus with improved counter electrode
US4257700A (en) * 1978-04-18 1981-03-24 Olympus Optical Co., Ltd. Electrophotographic apparatus
US4268157A (en) * 1975-06-20 1981-05-19 Ricoh Company, Ltd. Toner image transfer method and apparatus for electrostatic photography
US4302093A (en) * 1979-10-17 1981-11-24 Savin Corporation Combined transfer and registration system for electrophotographic copier
US4431301A (en) * 1980-03-12 1984-02-14 Tokyo Shibaura Denki Kabushiki Kaisha Electrostatic copying apparatus with means for preventing contamination of reverse side of copying medium
US4516847A (en) * 1981-12-04 1985-05-14 Delphax Systems Electrostatic printing apparatus and method
US4660964A (en) * 1985-07-12 1987-04-28 Fuji Photo Film Co., Ltd. Image recording apparatus
US4839697A (en) * 1987-06-01 1989-06-13 Minolta Camera Kabushiki Kaisha Image forming apparatus
US4907032A (en) * 1987-07-31 1990-03-06 Minolta Camera Kabushiki Kaisha Monocomponent developing device
US4998143A (en) * 1988-09-20 1991-03-05 Hitachi, Ltd. Electrophotographic image transfer member, electrophotographic image transfer device and electrophotographic recording apparatus
US5168313A (en) * 1988-04-28 1992-12-01 Kabushiki Kaisha Toshiba Toner image transfer method and device for electrophotographic printing apparatus
US5220387A (en) * 1990-11-14 1993-06-15 Mita Industrial Co., Ltd. Transfer unit of an image forming apparatus
US5233394A (en) * 1991-05-29 1993-08-03 Mita Industrial Co., Ltd. Transfer device for use in an image forming apparatus
US5302203A (en) * 1990-07-10 1994-04-12 Johannes Zimmer Apparatus for pressing webs usually in contact with a flowable substance
US5491543A (en) * 1993-04-21 1996-02-13 Sanyo Electric Co., Ltd. Transfer roller controlled to position the paper in registration with the toner image
US6347196B1 (en) * 1998-11-27 2002-02-12 Fuji Xerox Co., Ltd. Image sticking reducing method and apparatus
US20080226321A1 (en) * 2007-03-13 2008-09-18 Akitomo Kuwabara Image forming apparatus and tandem image forming apparatus
US20090010667A1 (en) * 2007-07-05 2009-01-08 Hiroyuki Mabuchi Transfer apparatus, transfer method, and image forming apparatus
US20110069990A1 (en) * 2009-09-18 2011-03-24 Fuji Xerox Co., Ltd. Transfer device and image forming apparatus

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JPS54137347A (en) * 1978-04-18 1979-10-25 Olympus Optical Co Ltd Zerographic apparatus

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US2807233A (en) * 1954-03-29 1957-09-24 Ibm Electrophotographic printing machine
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Cited By (37)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3851966A (en) * 1972-12-11 1974-12-03 Xerox Corp Reproduction apparatus
US3877416A (en) * 1973-04-23 1975-04-15 Xerox Corp Humidity corrected transfer apparatus
US3993021A (en) * 1973-06-08 1976-11-23 Minnesota Mining And Manufacturing Company Transfer device
US3900591A (en) * 1973-06-08 1975-08-19 Minnesota Mining & Mfg Developed image transfer
US3955530A (en) * 1973-06-28 1976-05-11 Canon Kabushiki Kaisha Transfer-fixing device
US3901186A (en) * 1973-07-02 1975-08-26 Xerox Corp Transfer roller assembly
US3848204A (en) * 1973-09-21 1974-11-12 Xerox Corp Pressure adjustable electrophotographic printing machine transfer apparatus
US3977779A (en) * 1973-12-21 1976-08-31 Xerox Corporation Electrostatographic transfer with air
US4165171A (en) * 1974-04-08 1979-08-21 Oce-Van Der Grinten N.V. Electrographic apparatus and process
US3990393A (en) * 1975-04-18 1976-11-09 Xerox Corporation Apparatus for depositing magnetic material on an image bearing member
US4046472A (en) * 1975-04-18 1977-09-06 Xerox Corporation Electrostatic imaging apparatus
US4103995A (en) * 1975-04-18 1978-08-01 Xerox Corporation Imaging apparatus
US3963340A (en) * 1975-04-18 1976-06-15 Xerox Corporation Imaging apparatus for typewriter employing electrostatic printing process
US4268157A (en) * 1975-06-20 1981-05-19 Ricoh Company, Ltd. Toner image transfer method and apparatus for electrostatic photography
US4087169A (en) * 1975-11-14 1978-05-02 Xerox Corporation Transfer roller system
US4101212A (en) * 1976-01-19 1978-07-18 Konishiroku Photo Industry Co., Ltd. Image transfer complementary apparatus for electrophotographic copying machine
US4218691A (en) * 1977-08-30 1980-08-19 Ricoh Company, Ltd. Recording apparatus with improved counter electrode
US4257700A (en) * 1978-04-18 1981-03-24 Olympus Optical Co., Ltd. Electrophotographic apparatus
US4302093A (en) * 1979-10-17 1981-11-24 Savin Corporation Combined transfer and registration system for electrophotographic copier
US4431301A (en) * 1980-03-12 1984-02-14 Tokyo Shibaura Denki Kabushiki Kaisha Electrostatic copying apparatus with means for preventing contamination of reverse side of copying medium
US4516847A (en) * 1981-12-04 1985-05-14 Delphax Systems Electrostatic printing apparatus and method
US4660964A (en) * 1985-07-12 1987-04-28 Fuji Photo Film Co., Ltd. Image recording apparatus
US4839697A (en) * 1987-06-01 1989-06-13 Minolta Camera Kabushiki Kaisha Image forming apparatus
US4907032A (en) * 1987-07-31 1990-03-06 Minolta Camera Kabushiki Kaisha Monocomponent developing device
US5168313A (en) * 1988-04-28 1992-12-01 Kabushiki Kaisha Toshiba Toner image transfer method and device for electrophotographic printing apparatus
US4998143A (en) * 1988-09-20 1991-03-05 Hitachi, Ltd. Electrophotographic image transfer member, electrophotographic image transfer device and electrophotographic recording apparatus
US5302203A (en) * 1990-07-10 1994-04-12 Johannes Zimmer Apparatus for pressing webs usually in contact with a flowable substance
US5220387A (en) * 1990-11-14 1993-06-15 Mita Industrial Co., Ltd. Transfer unit of an image forming apparatus
US5233394A (en) * 1991-05-29 1993-08-03 Mita Industrial Co., Ltd. Transfer device for use in an image forming apparatus
US5491543A (en) * 1993-04-21 1996-02-13 Sanyo Electric Co., Ltd. Transfer roller controlled to position the paper in registration with the toner image
US6347196B1 (en) * 1998-11-27 2002-02-12 Fuji Xerox Co., Ltd. Image sticking reducing method and apparatus
US20080226321A1 (en) * 2007-03-13 2008-09-18 Akitomo Kuwabara Image forming apparatus and tandem image forming apparatus
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