EP0775947A1 - Elektrophotographisches Druckgerät mit einer mittels einer Korona polarisierten Übertragungsrolle - Google Patents

Elektrophotographisches Druckgerät mit einer mittels einer Korona polarisierten Übertragungsrolle Download PDF

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Publication number
EP0775947A1
EP0775947A1 EP95830505A EP95830505A EP0775947A1 EP 0775947 A1 EP0775947 A1 EP 0775947A1 EP 95830505 A EP95830505 A EP 95830505A EP 95830505 A EP95830505 A EP 95830505A EP 0775947 A1 EP0775947 A1 EP 0775947A1
Authority
EP
European Patent Office
Prior art keywords
transfer roller
print medium
photoconductive drum
transfer
corotron
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP95830505A
Other languages
English (en)
French (fr)
Inventor
Carlo Fare
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Compuprint SpA
Original Assignee
Compuprint SpA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Compuprint SpA filed Critical Compuprint SpA
Priority to EP95830505A priority Critical patent/EP0775947A1/de
Publication of EP0775947A1 publication Critical patent/EP0775947A1/de
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • G03G15/1685—Structure, details of the transfer member, e.g. chemical composition
    • 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
    • G03G15/1675—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 with means for controlling the bias applied in the transfer nip
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G2215/00—Apparatus for electrophotographic processes
    • G03G2215/16—Transferring device, details
    • G03G2215/1604—Main transfer electrode
    • G03G2215/1614—Transfer roll

Definitions

  • the present invention concerns electrophotographic printing apparatus with a transfer roller electrically polarised by a corona effect discharge or "corotron".
  • the transfer of the electrically charged toner from the photoconductive drum to the print medium occurs with the help of an electrostatic discharger or corotron facing the contact generatrix of the face of the print medium opposite the face in contact with the photosensitive drum and the toner.
  • This face is electrically charged by the corotron with a charge opposite to that of the toner which is therefore attracted to the print medium.
  • the process is very effective and widely used but has the disadvantage that because the transfer takes place between moving surfaces, even if they are accurately synchronized, there is relative microscopic slippage between the print medium and the photoconductive drum which degrades the print quality.
  • a further disadvantage lies in the fact that the regions of the photosensitive drum devoid of toner are also electrically charged with an opposite charge to that of the print medium, such that a not insignificant force of attraction arises between the photosensitive drum and the print medium which, although it locally reduces the microscopic slippage, tends however to wrap the print medium onto the drum and impede its correct conveyance towards a toner fixing station, with possible jamming of the apparatus.
  • electrophotographic printing apparatus has been proposed and is available on the market in which the corotron is replaced by a resilient transfer roller, pressed against the photosensitive drum along a generatrix thereof to form a nip through which the print medium passes.
  • the print medium is subjected to elastoplastic forces which encourage it to separate from the photosensitive drum.
  • the surface of the transfer roller can be conductive and connected to an appropriate voltage source and, beneath the conductive surface, there is a resilient, insulating layer which ensures the necessary elasticity of the roller.
  • the transfer roller is made with a conductive cylindrical core and an outer resilient layer having suitable resistivity.
  • the core is connected to a voltage supply, such that a charging current flows from the conductive core through the resilient layer to the surface of the print medium.
  • the circuit is closed by means of the capacitances, in series, formed by the print medium, of the photosensitive layer of the photoconductive drum, and the conductive core of the photoconductive drum, which is usually earthed.
  • This critical operative condition is obtained either by calibrating the force with which the transfer roller presses against the photoconductive drum, or by making the transfer roller from material having adequate electrical conductivity which is consistent with the mechanical situation so as to allow the desired quantity of electrical charge to be deposited onto the print medium, that is onto the paper.
  • the electrophotographic printing apparatus which is the subject of the present invention, comprising a transfer roller with a conductive core and an external resilient, resistive cylindrical layer, in which the external surface of the transfer roller is polarised and electrically charged by an electrostatic discharger or corotron, the surface electrical charge partially discharging in a controlled way and in an inverse sense with respect to that usually adopted, through the series of resistors constituted by the resilient resistive layer of the transfer roller and an adjustment element having variable resistance.
  • the residual charge is transferred in a controlled manner to the print medium along the nip between the transfer roller and the photoconductive drum.
  • the charge transferred is easily controlled and regulated as a function of specific requirements and the possible different modes of operation of the electrophotographic printing apparatus.
  • an electrophotographic printing apparatus includes a photoconductive drum made from a conductive core 1 and an external photoconductive layer 2, rotated by a motor 3 and controlled by a control unit 4 which causes the drum to move at predetermined peripheral velocity in the direction of rotation indicated by the arrow 5.
  • the print medium is moved forward to a fixing station 14 at a controlled speed which is equal to the peripheral velocity of the photoconductive drum.
  • the transfer device includes a transfer roller 15 in pressure contact with the photoconductive drum along a generatrix, forming a nip through which the print medium 13 passes.
  • the transfer roller is rotated by the motor 3 with a peripheral velocity coordinated (equal to or slightly greater than) with the peripheral velocity of the photoconductive drum.
  • the transfer roller 15 is made from a resilient external layer 16 having a high resistivity of the order of 10 8 ⁇ .cm or more and a conductive core 17, rotatably supported by supports 18 electrically insulated from ground.
  • the conductive core 17 is earthed via a variable resistor 19 or equivalent means, for example a field-effect MOS device.
  • the transfer device also includes a corotron 20 supplied by a source 21 of positive voltage +V of an appropriate value, for example +5/10KV, facing a generatrix of the transfer roller 15 in order to charge the surface with a predetermined electric charge.
  • a corotron 20 supplied by a source 21 of positive voltage +V of an appropriate value, for example +5/10KV, facing a generatrix of the transfer roller 15 in order to charge the surface with a predetermined electric charge.
  • the angular velocity of rotation of the transfer roller multiplied by the angle of rotation necessary to carry the electrical charge along the generatrix into contact with the print medium defines the delay with which the electrical charge is transferred.
  • the different conductivity of the transfer roller which can arise from the productive processes or from the use of different materials can be compensated within a broad range, by releasing the transfer device from the design and production criticality of known devices.
  • the charge applied to the print medium to be regulated within a broad range as a function of variations in the print process parameters such as the thickness and humidity of the print medium.
  • a thickness detector 22 which, by utilising known electrical capacitive techniques, is also able to detect the humidity of the print medium and, by means of a regulatory unit 23, to send an adjustment command to the variable resistor 19.
  • Figure 2 schematically represents a known transfer roller formed from an internal conductive core 24 and an external resilient, resistive layer 25 pressed against a generatrix of a photoconductive drum 26, with an interposed print medium 27.
  • a voltage generator 28 applies a suitable voltage V to the core 24 of the transfer roller.
  • the conductive core of the photosensitive drum 26 is earthed.
  • the resistor 29 represents the resistance of a limited cylindrical arc 31 of the resistive layer 25, and the capacitor 30 represents the capacity formed by a limited cylindrical arc 32 of the conductive core of the photosensitive drum and of the juxtaposed external surface of the cylindrical arc 31 separated from a dielectric constituted by the print medium 27 and the photoconductive layer of the drum 26.
  • the capacitor 30 is charged during the short and finite transit period of juxtaposition with the arc 31 to a voltage which depends on the time constant RC of the circuit and which varies with R.
  • the variability of the charge can to some extent be limited by making the resistive layer from low resistivity materials, which is difficult to achieve.
  • Figure 4 shows schematically the structure of the transfer device according to the present invention and Figure 5 shows the equivalent electrical circuit.
  • a corotron 33 applies a specific charge Qs to every surface element 34 of the transfer roller 36 which, to a first approximation, depends only on the voltage V applied to the corotron 33 by a voltage generator 35 and on the exposure time ⁇ t of the surface element to the discharge from the corotron (it is therefore inversely proportional to the peripheral velocity of the transfer roller).
  • the charge Qs gradually discharges, with an exponential law, through the series connected resistance 37 of the resistive, resilient layer and the variable resistance 38 which earths the transfer roller core.
  • Figure 6 is a qualitative timing diagram of the value of the specific charge Qs.
  • the initial value Qs1 depends as mentioned on the corotron voltage supply, the peripheral velocity of the transfer roller and, to a certain extent, also the resistivity of the resilient layer and the value of the variable resistance.
  • the specific charge Qs falls exponentially over time as defined by the time constant of the discharge circuit ( Figure 5) and shown by the line 41.
  • variable resistance 38 By decreasing the value of the variable resistance 38 the time constant diminishes, as does the initial specific charge and the specific charge decreases according to the line 43.
  • variable resistance 38 can be easily calibrated in such a way that, at the transfer station, the specific charge has an optimal value Qs0 to cause the transfer of toner.
  • the speed of the print process is doubled, it causes a substantial reduction, virtually a halving, of the initial specific charge of the transfer roller.
  • electrographic printing apparatus It is therefore very easy to make electrographic printing apparatus able to operate at different speeds, for example at low speed to give high print resolution and at high speed, for example double, to give greater throughput, although with inferior resolution.
  • Figure 7 schematically represents apparatus of this type.
  • control unit 50 receives from a bistable control button 51 or from a system processor 52 such as a PC, a signal which selects the operating mode, high or low speed and, in dependence on this signal, controls the speed of rotation of the motor 53 which drives the moving parts of the apparatus (photoconductive drum 54, transfer roller 55, fixing station 56).
  • a bistable control button 51 or from a system processor 52 such as a PC, a signal which selects the operating mode, high or low speed and, in dependence on this signal, controls the speed of rotation of the motor 53 which drives the moving parts of the apparatus (photoconductive drum 54, transfer roller 55, fixing station 56).
  • variable resistor preferably made from an electronic device such as a metal-oxide-semiconductor field-effect transistor (MOSFET) 57 across a control circuit 58.
  • MOSFET metal-oxide-semiconductor field-effect transistor
  • the MOSFET constitutes a controlled variable resistor which earths the conductive core of the transfer roller.
  • electrophotographic printing apparatus of the type commonly known as a "laser printer”
  • electrophotographic printing apparatus meaning any printing apparatus which uses electrophotographic techniques for forming a latent image on a photoconductive element and its transfer to a print medium, such as diode array printers or photocopiers.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electrostatic Charge, Transfer And Separation In Electrography (AREA)
EP95830505A 1995-12-07 1995-12-07 Elektrophotographisches Druckgerät mit einer mittels einer Korona polarisierten Übertragungsrolle Withdrawn EP0775947A1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP95830505A EP0775947A1 (de) 1995-12-07 1995-12-07 Elektrophotographisches Druckgerät mit einer mittels einer Korona polarisierten Übertragungsrolle

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP95830505A EP0775947A1 (de) 1995-12-07 1995-12-07 Elektrophotographisches Druckgerät mit einer mittels einer Korona polarisierten Übertragungsrolle

Publications (1)

Publication Number Publication Date
EP0775947A1 true EP0775947A1 (de) 1997-05-28

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EP95830505A Withdrawn EP0775947A1 (de) 1995-12-07 1995-12-07 Elektrophotographisches Druckgerät mit einer mittels einer Korona polarisierten Übertragungsrolle

Country Status (1)

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EP (1) EP0775947A1 (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6160969A (en) * 1997-08-18 2000-12-12 Ricoh Company, Ltd. Image forming apparatus with a voltage applying unit for image transfer

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3866573A (en) * 1971-10-21 1975-02-18 Agfa Gevaert Ag Electrostatic copying apparatus
US4110031A (en) * 1975-09-30 1978-08-29 Ricoh Company, Ltd. Electrostatic copying apparatus
WO1992014194A1 (en) * 1991-01-31 1992-08-20 Compaq Computer Corporation Electrostatic roller transfer of toned images from a photoconductor member to a sheet substrate
EP0660197A2 (de) * 1993-12-20 1995-06-28 Konica Corporation Bilderzeugungsgerät mit einer Vorrichtung zur Messung des Widerstandes eines Übertragungsblattes
US5455664A (en) * 1992-05-27 1995-10-03 Oki Electric Industry Co., Ltd. Electrophotographic printer for transferring images on different sized print medium and transferring method of the same

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3866573A (en) * 1971-10-21 1975-02-18 Agfa Gevaert Ag Electrostatic copying apparatus
US4110031A (en) * 1975-09-30 1978-08-29 Ricoh Company, Ltd. Electrostatic copying apparatus
WO1992014194A1 (en) * 1991-01-31 1992-08-20 Compaq Computer Corporation Electrostatic roller transfer of toned images from a photoconductor member to a sheet substrate
US5455664A (en) * 1992-05-27 1995-10-03 Oki Electric Industry Co., Ltd. Electrophotographic printer for transferring images on different sized print medium and transferring method of the same
EP0660197A2 (de) * 1993-12-20 1995-06-28 Konica Corporation Bilderzeugungsgerät mit einer Vorrichtung zur Messung des Widerstandes eines Übertragungsblattes

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6160969A (en) * 1997-08-18 2000-12-12 Ricoh Company, Ltd. Image forming apparatus with a voltage applying unit for image transfer

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