EP0568829B1 - Appareil de formation d'images - Google Patents

Appareil de formation d'images Download PDF

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Publication number
EP0568829B1
EP0568829B1 EP93105767A EP93105767A EP0568829B1 EP 0568829 B1 EP0568829 B1 EP 0568829B1 EP 93105767 A EP93105767 A EP 93105767A EP 93105767 A EP93105767 A EP 93105767A EP 0568829 B1 EP0568829 B1 EP 0568829B1
Authority
EP
European Patent Office
Prior art keywords
transfer
bias
sheet
transfer belt
photoconductive element
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.)
Expired - Lifetime
Application number
EP93105767A
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German (de)
English (en)
Other versions
EP0568829A2 (fr
EP0568829A3 (fr
Inventor
Yuko Harasawa
Itaru Matsuda
Satoshi Takano
Hideo Yu
Yasunori Kawaishi
Hideki Kamiyama
Toshiaki Motohashi
Mitsuru Takahashi
Takashi Bisaiji
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.)
Ricoh Co Ltd
Original Assignee
Ricoh Co Ltd
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Filing date
Publication date
Application filed by Ricoh Co Ltd filed Critical Ricoh Co Ltd
Publication of EP0568829A2 publication Critical patent/EP0568829A2/fr
Publication of EP0568829A3 publication Critical patent/EP0568829A3/fr
Application granted granted Critical
Publication of EP0568829B1 publication Critical patent/EP0568829B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime 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
    • G03G15/65—Apparatus which relate to the handling of copy material
    • G03G15/6532—Removing a copy sheet form a xerographic drum, band or plate
    • G03G15/6535—Removing a copy sheet form a xerographic drum, band or plate using electrostatic means, e.g. a separating corona
    • 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
    • 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
    • G03G15/1605—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 using at least one intermediate support
    • 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
    • G03G2215/1623—Transfer belt
    • 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
    • G03G2215/1647—Cleaning of transfer member
    • G03G2215/1661—Cleaning of transfer member of transfer belt

Definitions

  • the present invention relates to a copier, printer, facsimile apparatus or similar image forming apparatus of the type transferring a toner image from a photoconductive element to a transfer medium.
  • An image forming apparatus of the type described includes a transfer and separation device for transferring a toner image from a photoconductive element to a sheet or similar transfer medium and then separating the sheet from the element.
  • This kind of device has customarily been implemented by a corona transfer and separation system, i.e., a first and a second corona discharger assigned to image transfer and sheet separation, respectively.
  • the first corona discharger effects corona discharge at the rear of the sheet to transfer the toner image from the photoconductive element to the front of the sheet.
  • the second corona discharger applies corona discharge to the rear of the sheet carrying the toner image to separate it from the photoconductive element.
  • a contact type transfer and separation system is another conventional system available for the image forming apparatus.
  • a bias potential is applied to the belt from a power source to transfer the toner image from the photoconductive element to a sheet or similar medium carried on the belt.
  • the sheet with the toner image is separated from the photoconductive element by being electrostatically adhered to the belt.
  • the transfer belt is sometimes replaced with a transfer roller.
  • the contact type transfer and separation system has been proposed in various forms, as disclosed in Japanese Patent Laid-Open Publication No. 2 123385, 2 123386, and 2187380 by way of example.
  • Another conventional image forming apparatus includes a carrier for carrying a toner image transferred thereto at a transfer position and transporting it while being rotated.
  • a toner image formed on a photoconductive element is transferred to a belt at a first transfer position.
  • the belt is rotated to transport the toner image to a second transfer position, the toner image is transferred from the belt to a sheet.
  • a transfer potential is applied to the belt to transfer the toner image from the photoconductive element to the belt.
  • the contact type image transfer and sheet separation system is advantageous over the corona type system in that it reduces ozone and requires only a low power source voltage.
  • the problem with the transfer belt is that the adequate bias voltage to be applied from the power source to the belt changes due to various causes including irregularities in the resistance of the belt, varying ambient conditions, kind of sheets, and area of a toner image. This prevents the toner image from being surely transferred from the belt to the sheet.
  • the amount of charge deposited on the belt by the bias potential from the power source deviates from one required to effect desirable image transfer due to irregularities in the resistance of the belt ascribable to the production line, changes in the resistance ascribable to the varying ambient conditions, changes in the material and thickness of sheets, etc.
  • the transfer belt not only transfer the toner image from the photoconductive element to a sheet or similar transfer medium, but also separates the sheet from the element by electrostatically retaining it thereon.
  • the problem is that the separation of the sheet from the photoconductive element depends on the ambient conditions. Particularly, when the water content of the sheet increases in a hot and humid environment, it is likely that the sheet is adhered to the photoconductive element and not to the belt and cannot be separated from the element. Should the sheet be forcibly separated from the photoconductive element by a pawl or similar implementation, it would be scratched or creased to degrade the image quality.
  • a transfer potential is applied to the belt at a position upstream of the first transfer position so as to transfer the toner image from the photoconductive element to the belt.
  • an image forming apparatus which is capable of surely transferring an image to produce an attractive image and, in addition, insuring desirable separation of a transfer medium from a photoconductive element with no regard to the environment.
  • an image forming apparatus comprises a photoconductive element for forming a toner image thereon, a transfer medium movable in contact with the photoconductive element over a predetermined nip width to allow the toner image to be transferred from the photoconductive element to the transfer medium, a transfer bias applying device for applying a predetermined transfer bias to the transfer medium, and a potential gradient generating device for providing the transfer bias with a potential gradient such that an amount of transfer of the toner image from the photoconductive element to the transfer medium increases in a region upstream of a transfer region with respect to the photoconductive element and terminating at a point where the photoconductive element and transfer medium begin to contact each other.
  • an image forming apparatus comprises a photoconductive element for forming a toner image thereon, a transfer belt movable in contact with the photoconductive element over a predetermined nip width for transporting a sheet to allow the toner image to be transferred from the photoconductive element to the sheet, a transfer potential bias applying device for applying a predetermined transfer bias to the transfer belt, a potential gradient generating device for providing the transfer bias with a potential gradient such that an amount of transfer of the toner image from the photoconductive element to the sheet increases in a region upstream of a nip portion with respect to the photoconductive element and terminating at a point where the photoconductive element and transfer belt begin to contact each other, and a bias applying device for applying a bias to the potential gradient generating device after the sheet has moved a predetermined distance away from the nip portion.
  • an image forming apparatus comprises a photoconductive element for forming a toner image thereon, a transfer belt movable in contact with the photoconductive element over a predetermined nip width for transporting a sheet to allow the toner image to be transferred from the photoconductive element to the sheet, a transfer bias applying device contacting the transfer belt at a position downstream of the photoconductive element for applying a predetermined bias to the transfer belt, and a potential gradient generating device having a dielectric layer on a surface thereof and contacting the transfer belt at a position upstream of the photoconductive element for providing the transfer bias with a potential gradient such that an amount of transfer of the toner image from the photoconductive element to the sheet increases in a region upstream of the nip portion with respect to the photoconductive element and terminating at a point where the photoconductive element and transfer belt contact each other.
  • an image forming apparatus comprises a photoconductive element for forming a toner image thereon, a transfer belt movable in contact with the photoconductive element over a predetermined nip width for transporting a sheet to allow the toner image to be transferred from the photoconductive element to the sheet, a transfer bias applying device contacting said transfer belt at a position downstream of the photoconductive element for applying a predetermined bias to the transfer belt, and a potential gradient generating device having an elastic dielectric layer on a surface thereof and contacting a rear of the transfer belt in a position upstream of the photoconductive element for providing the transfer bias with a potential gradient such that an amount of transfer of the toner image from the photoconductive element to the sheet increases in a region upstream of the nip portion with respect to said transfer belt and terminating at a point where the photoconductive element and transfer belt contact each other.
  • an image forming apparatus comprises a photoconductive element for forming a toner image thereon, a transfer medium contacting the photoconductive element over a predetermined nip width in a transfer region and undergoing a step o f transferring the toner image formed on the photoconductive element a plurality of times, a first electrode contacting the transfer medium at a position downstream of the transfer region, a second electrode contacting the transfer medium a t a position upstream of the transfer region, and a potential gradient generating device for providing the transfer bias with a potential gradient by applying a transfer bias to the first electrode or both of the first and said second electrodes, and applying, when a toner is absent on the transfer medium, a bias of the same polarity as the toner to the second electrode or applying, when the toner is present on the transfer medium, a bias of opposite polarity to the toner to the second electrode, such that an amount of transfer of the toner image from the photoconductive element to the transfer medium increases in a region upstream of a transfer
  • FIGS. 17 and 18 a brief reference will be made to a conventional image forming apparatus, particularly a contact type image transfer and sheet separation system available therewith, shown in FIGS. 17 and 18.
  • the contact type image transfer and sheet separation system is advantageous over a corona type system in that it reduces ozone and requires only a low power source voltage, as discussed earlier.
  • the problem with a transfer belt is that the adequate bias voltage to be applied from a power source to the belt changes due to various causes including irregularities in the resistance of the belt, varying ambient conditions, kind of sheets, and area of a toner image. This prevents a toner image from being desirably transferred from the belt to a sheet.
  • the amount of charge deposited on the belt by the bias potential from the power source deviates from one required to effect desirable image transfer due to irregularities in the resistance of the belt ascribable to the production line, changes in the resistance ascribable to the varying ambient conditions, changes in the material and thickness of sheets, etc. More specifically, as shown in FIG. 17, when the amount of charge required to effect desirable image transfer is deposited on a transfer belt, discharge does not occur in a pretransfer region upstream of the nip portion between a photoconductive element 37 and the belt. In this condition, a toner 39 charged to positive polarity, for example, is transferred to a sheet 38 carried on the belt in a transfer region.
  • a bias potential is applied from a power source, not shown, to the belt 38.
  • a power source not shown
  • FIG. 18 when the actual amount of charge on the belt is deviated from the expected one due to the above-stated reasons, discharge occurs in the pretransfer region. This causes a negative charge to deposit on the toner 39 and thereby charges the front and the rear of the belt to positive polarity and negative polarity, respectively.
  • the bias potential from the power source is adequate, the toner 39 is prevented from being transferred from the photoconductive element 37 to the sheet 38, resulting in the local omission of an image on the sheet.
  • the apparatus includes an image carrier in the form of a photoconductivc drum 1.
  • the drum 1 is uniformly charged by a main charger while being rotated by a drive mechanism, not shown.
  • a writing device writes image data on the charged surface of the drum 1 to form an electrostatic latent image.
  • a developing unit develops the latent image to produce a corresponding toner image.
  • a recording medium in the form of a sheet is fed from a sheet feed device to a register roller 2, brought to a stop for a moment, and then driven toward a transfer belt 3 in synchronism with the toner image formed on the drum 1.
  • At least the front of the transfer belt 3 is made of a dielectric material.
  • the transfer belt 3 is passed over a drive roller 4 and driven rollers 5-7.
  • the rollers 6 and 7 are connected to ground.
  • the roller 5 plays the role of a bias roller or bias electrode while the roller 4 remains in an electrically floating state.
  • a solenoid 9 is energized to urge a lever 10 upward.
  • the lever 10 in turn raises one side of the belt assembly, i.e., the belt 3 and rollers 4-7 until the belt 3 contacts the drum 1.
  • the drive roller 4 is driven by a motor to in turn rotate the transfer belt 3.
  • the belt 3 contacts the drive roller 4 at a position upstream of the portion where it is capable of contacting the drum 1, and contacts the bias roller 5 at a position downstream of the contact portion.
  • the belt 3 contacts the drum 1 over a predetermined nip width.
  • a power source 8 applies to the bias roller 5 a predetermined bias voltage whose polarity is opposite to the polarity of the toner deposited on the drum 1, thereby depositing a corresponding charge on the belt 3.
  • the belt 3 is made of a material having a specific volume resistivity (10 6 ⁇ cm to 1 0 12 ⁇ cm). Hence, a current flows toward the rollers 6 and 7 due to the bias voltage from the bias roller 5, resulting in the fall of voltage.
  • the toner image is transferred from the drum 1 to the sheet due to the above-mentioned bias voltage applied from the power source 8 to the belt 3.
  • the sheet is polarized by the charge applied from the power source 8 to the belt 3.
  • the polarizing voltage of the sheet and the true charge of the belt 3 generate an electrostatic force.
  • the sheet is conveyed by the belt 3 while being electrostatically adhered to the belt 3.
  • the charge thereof is reduced by being released to ground via the belt 3 and rollers 6 and 7.
  • the sheet is transported toward a fixing station by the belt 3. As the sheet approaches the inlet of the fixing station, the charge thereof is reduced to in turn reduce the electrostatic force acting between the sheet and the belt 3. Consequently, the sheet is separated from the belt 3 by the roller 7 connected to ground and having a small diameter and the elasticity of the sheet. Then, the toner image carried on the sheet is fixed at the fixing station.
  • the roller 7 has a diameter ranging from 14 mm to 16 mm.
  • the solenoid 9 is deenergized to retract the lever 10 and, therefore, the belt assembly including the belt 3 and rollers 4-7. As a result, the belt 3 is brought out of contact with the drum 1. This is to protect the drum I from deterioration while the transfer of a toner image is not performed.
  • the bias roller 5 deposits a charge on the belt 3.
  • the bias voltage from the power source is applied not only to the bias roller 5 but also to the drive roller 4, the potential distribution on the belt 3 has a linear gradient in a portion T between the rollers 4 and 5.
  • the belt 3 fails to electrostatically retain a sheet thereon as the water content of the sheet is as great as 8 % to 11 % due to a hot and humid environment.
  • the bias voltage is applied only to the bias roller 5 as shown in FIG. 9, the embodiment insures the separation of the sheet from the drum 1 as shown in FIG. 3.
  • FIG. 4 shows a second embodiment of the present invention.
  • the drive roller 4 plays the role of a bias roller or bias electrode at the same time.
  • the drive roller 4 is connected to ground via a varistor, Zener diode or similar constant voltage element 13. While the bias voltage to be applied to the bias roller is open to choice, it should preferably be close to the bias voltage to be applied to the downstream bias roller 5.
  • the bias voltage from the power source 8 is applied to the downstream bias roller 5.
  • the upstream bias roller 4 is maintained at substantially the same potential as the downstream bias roller 5. This is successful in maintaining the potential at the position where the drum 1 and belt 3 contact stable and, therefore, insuring desirable toner image transfer with no regard to, for example, irregularities in the resistance of the belt 3.
  • the charge injection into the sheet in a humid environment is reduced to promote sure separation of the sheet from the drum 1.
  • this embodiment is even more stable than the first embodiment regarding the transfer of the toner image, the bias voltage to be applied from the power source 8 to the bias roller 5 can be low.
  • the drive roller 4 plays the role of a bias roller or bias electrode.
  • a power source 14 starts applying a bias voltage to the drive roller 4 at the time when the sheet enters the nip portion between the drum 1 and the belt 3 and contacts the drum 1.
  • the potential distribution of the belt 3 has a linear gradient in the portion T.
  • the third embodiment like the first embodiment, enhances the separation of the sheet from the drum 1 and transfers the toner image to the sheet stably with no regard to irregularities in the resistance of the belt 3. Consequently, the belt 3 can be produced and selected at a high yield.
  • FIG. 6 shows a fourth embodiment of the present invention which is similar to the third embodiment except for a variable power source 15 substituted for the power source 14.
  • the variable power source 15 applies a bias voltage lower than the bias voltage to the bias roller 5 to the bias roller 4 and at the same time as the voltage to the bias roller 5.
  • the power source 15 applies the same bias voltage as applied to the bias roller 5 to the bias roller 4.
  • the resulting potential distribution of the belt 3 is shown in FIG. 20.
  • the fourth embodiment maintains the bias voltage to the bias roller 4 lower than the bias voltage to the bias roller 5 until the leading edge of the sheet enters the nip portion between the drum 1 and the belt 3. This also enhances the separation of the sheet from the drum 1.
  • FIG. 7 shows a fifth embodiment of the present invention which is similar to the first embodiment except that a power source 16 applies a bias voltage to the bias rollers 4 and 5 at a timing shown in FIG. 12.
  • the power source 16 starts applying a bias voltage to the bias rollers 4 and 5 at the time when the leading edge of the sheet has moved a predetermined distance shorter than 8 8 mm away from the nip between the drum L and the belt 3.
  • the toner image is not transferred to the sheet over the predetermined distance as measured from the leading edge thereof.
  • the sheet is simply left blank over several millimeters as measured from the leading edge thereof.
  • the sheet is surely separated from the belt 3 at the inlet of the fixing station, causing the toner image to be fixed there.
  • the belt 3 has a potential gradient shown in FIG. 21.
  • FIG. 8 is representative of a sixth to an eighth embodiment corresponding to the third to fifth embodiments, respectively.
  • the distance LB between the nip portion between the drum 1 and the belt 3 and the bias roller 5 is selected to be shorter than the distance LA between the nip portion and the bias roller 4.
  • the power source 8, 15 or 16 starts applying the bias voltage to the bias roller 4 or 5 when the leading edge of the sheet has moved to a point A which is downstream of the roller 4 by the distance LB.
  • Such alternative embodiments are also successful in surely separating the sheet from the drum 1.
  • a ninth embodiment of the present invention is similar to the third embodiment of FIG. 5 except that the time for applying the bias voltage to the bias roller 4 is adjustable at the outside of the apparatus. While the third embodiment starts applying the bias voltage to the bias roller 4 from the power source 14 after the sheet has contacted the drum 1, it is likely that the sheet transport control differs from one machine to another or changes within the same machine due to the wear of a sheet transport system. When the time for applying the bias voltage to the upstream bias roller 4 is too early, a charge is apt to deposit on the belt 3 before the sheet contacts the drum 1, making the separation of the sheet from the drum 1 unstable in a humid environment.
  • the ninth embodiment allows the time for applying the bias to the bias roller 4 to be changed at the outside of the apparatus.
  • FIG. 13 shows circuitry for implementing the ninth embodiment.
  • a main control section 17 has a CPU (Central Processing Unit 18, a ROM (Read Only Memory) 19, a RAM (Random Access Memory) 20, an input circuit 21, a load driver 22, and a system control interface (I/F) 23.
  • a system controller 24, a high tension power source 25 and an operating section (SP mode) 26 are connected to the main control section 17.
  • a serviceman manipulates the operating section 26 to condition the apparatus for a serviceman program (SP) mode and again manipulates it to enter an adjusting value associated with the application of the bias voltage to the bias roller 4.
  • SP serviceman program
  • the ROM 19 stores a program according to which the CPU 18 operates. As a signal indicative of the SP mode is entered on the operating section 26 and applied to the CPU 18 via the input circuit 21, the CPU 18 sets up the SP mode. When the adjusting value associated with the application of the bias voltage is entered on the operating section 26, it is written to the RAM 20 which is backed up by a battery. The CPU 18 adjusts the time for applying the bias voltage to the bias roller 4 from the power source 14 via the load driver 22 on the basis of the adjusting value stored in the RAM 20. If desired, in the fourth to eighth embodiments, the time for applying the the bias to the upstream bias roller 4 may also be adjusted at the outside of the apparatus to insure both of sure image transfer and sure sheet separation.
  • a main control section 26 has a CPU 27, a ROM 28, a RAM 29, an input section 30, a load driver 31, and a system control I/F 32.
  • a system controller 33, a high tension power source 34 and a humidity sensor 35 are connected to the main control section 26.
  • the humidity sensor senses humidity around sheets stacked in the sheet feed device.
  • the CPU 27 determines whether or not the sensed humidity is higher than a predetermined humidity, e.g., 70 % in terms of relative humidity.
  • the CPU 27 retards the time for applying the bias voltage to the bias roller 4 from the power source 14 via the load driver 31, i.e., causes the power source 14 to start applying the bias voltage to the roller 4 after the sheet has contacted the drum 1.
  • the CPU 27 causes the power source 14 to start applying the bias voltage to the bias roller 4 at the same time as the power source 8 applies the bias voltage to the bias roller 5 via the load driver 31.
  • the bias rollers 4 and 5 inject charges into the sheet.
  • the toner image is stably transferred to the sheet at the rear of the leading end portion of the belt 3. So long as the humidity is lower than 70 %, the separation of the sheet from the drum I is satisfactory. Since the bias rollers 4 and 5 sequentially deposit a charge on the sheet, the toner image is stably transferred from the leading edge toward the trailing edge of the sheet at all times.
  • the above-stated advantages of the tenth embodiment are also achievable with an absolute humidity sensor in place of the relative humidity sensor.
  • the humidity sensor may be used in combination with a temperature sensor to control the time for applying the bias voltage from the power source 14 to the bias roller 4.
  • the humidity sensor scheme of the tenth embodiment is also applicable to the fourth to eighth embodiments, if desired.
  • FIG. 15 shows an eleventh embodiment which is similar to the fifth embodiment except that the bias roller 4 is provided with a surface layer 4a made of a dielectric material.
  • the surface layer 4a has a specific volume resistivity of, for example, 10 6 ⁇ cm to 10 12 ⁇ cm and a thickness of 0.2 mm to 3 mm.
  • the rollers 5 and 7 contacting the belt 3 at positions downstream of the drum 1 are made of metal.
  • the power source 16 applies a voltage to the bias rollers 4 and 5, the rollers 4 and 5 sequentially deposit a voltage on the belt 3 to maintain the potential at the portion where the belt 3 contacts the drum 1 stable, thereby insuring desirable transfer of the toner image.
  • the bias roller 5 deposits a charge on the belt 3 more efficiently than the bias roller 4, the charge injection from the upstream bias roller 4 into the sheet sparingly occurs in a humid environment. This promotes sure separation of the sheet from the drum 1 in such a humid environment.
  • the potential distribution of the belt 3 has a linear gradient in the portion T between the portions where the rollers 4 and 5 contact the belt 3.
  • FIG. 16 shows a twelfth embodiment of the present invention.
  • this embodiment is similar to the eleventh embodiment except that a bias roller 36 is held in contact with the rear of the belt 3 at the position where the belt 3 contacts the drum 1, and in that the power source 16 applies a voltage to a bias roller 36 as well as to the roller 5.
  • the bias roller 36 has a surface layer made of an elastic dielectric material.
  • the surface layer of the roller 36 is made of a material having a specific volume resistivity of 10 6 ⁇ cm to 10 12 ⁇ cm and a hardness less than 50° in terms of modulus hardness.and provided with a thickness of greater than I mm.
  • the potential of the belt 3 linearly changes in the portion T between the portions where the rollers 4 and 5 contact the belt 3.
  • the rollers 36 and 5 each efficiently deposits a charge on the belt 3 even when the transfer voltage in the position where the belt 3 contacts the drum 1 is low.
  • High transfer voltages are apt to cause an image to be locally omitted when transferred to a sheet.
  • the surface layer of the bias roller 36 has a medium resistance, there can be eliminated the damage to the bias roller 36 and belt 3 due to the leakage of the charge and, therefore, the resulting defective image transfer.
  • the charge deposition on the belt 3 by the bias rollers 36 and 5 does not occur at the upstream side with respect to the transfer station, no charges are injected into the sheet in a humid environment before the image transfer, insuring positive sheet separation.
  • the transfer belt 3 may be replaced with a transfer roller, if desired.
  • the transfer roller is as effective as the belt 3 regarding the stable sheet separation and, in addition, frees the sheets from the trace of a separator, creases and jams.
  • the present invention provides an image forming apparatus having various unprecedented advantages, as enumerated below.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electrostatic Charge, Transfer And Separation In Electrography (AREA)
  • Control Or Security For Electrophotography (AREA)
  • Color Electrophotography (AREA)
  • Fax Reproducing Arrangements (AREA)
  • Decoration By Transfer Pictures (AREA)
  • Combination Of More Than One Step In Electrophotography (AREA)

Claims (11)

  1. Dispositif de formation d'image, comportant :
    un élément photoconducteur (1) pour former dessus une image de toner,
    une courroie de transfert (3) mobile en contact avec ledit élément photoconducteur (1) sur une partie de contact prédéterminée pour transporter une feuille afin de permettre à l'image de toner d'être transférée dudit élément photoconducteur à ladite feuille,
    des premiers moyens d'application de polarisation de potentiel de transfert (5, 8) pour appliquer une première polarisation de transfert prédéterminée à ladite courroie de transfert en aval de la partie de contact en venant au contact de la courroie de transfert,
    des seconds moyens d'application de polarisation de potentiel de transfert (4, 13 ; 4, 14 ; 4, 15 ; 4, 16) qui sont en amont de la partie de contact et viennent au contact de la courroie de transfert, et
       caractérisé en ce que
       lesdits moyens d'application de polarisation de transfert restent dans un état électriquement flottant, et
       en ce que la première polarisation de transfert prédéterminée commence à être appliquée lorsque le bord avant de la feuille s'approche de la partie de contact.
  2. Dispositif de formation d'image, comportant :
    un élément photoconducteur (1) pour former dessus une image de toner,
    une courroie de transfert (3) mobile en contact avec ledit élément photoconducteur (1) sur une partie de contact prédéterminée pour transporter une feuille afin de permettre à l'image de toner d'être transférée dudit élément photoconducteur à ladite feuille,
    des premiers moyens d'application de polarisation de potentiel de transfert (5, 8) pour appliquer une première polarisation de transfert prédéterminée à ladite courroie de transfert en aval de la partie de contact en venant au contact de la courroie de transfert,
    des seconds moyens d'application de polarisation de potentiel de transfert (4, 13 ; 4, 14 ; 4, 15 ; 4, 16) pour appliquer une seconde polarisation de transfert à ladite courroie de transfert en amont de la partie de contact en venant au contact de la courroie de transfert, et
       caractérisé en ce que
       les seconds moyens d'application sont connectés à la masse via une varistance ou une diode Zener ou un élément de tension constante similaire (13) ce qui a pour résultat un potentiel proche de la première polarisation de transfert prédéterminée.
  3. Dispositif de formation d'image, comportant :
    un élément photoconducteur (1) pour former dessus une image de toner,
    une courroie de transfert (3) mobile en contact avec ledit élément photoconducteur (1) sur une partie de contact prédéterminée pour transporter une feuille afin de permettre à l'image de toner d'être transférée dudit élément photoconducteur à ladite feuille,
    des premiers moyens d'application de polarisation de potentiel de transfert (5, 8) pour appliquer une première polarisation de transfert prédéterminée à ladite courroie de transport en aval de la partie de contact en venant au contact de la courroie de transfert,
    des seconds moyens d'application de polarisation de potentiel de transfert (4, 13 ; 4, 14 ; 4, 15 ; 4, 16) pour appliquer une seconde polarisation de transfert à ladite courroie de transfert en amont de la partie de contact en venant au contact de la courroie de transfert, et
       caractérisé en ce que
       la seconde polarisation de transfert commence à être appliquée lorsque la feuille entre dans la partie de contact de sorte que la distribution de potentiel de la courroie (3) a un gradient linéaire, dans la partie de contact, qui augmente dans la direction amont.
  4. Dispositif selon la revendication 3, dans lequel le temps d'application de la seconde polarisation de transfert est variable.
  5. Dispositif selon la revendication 3, comportant de plus :
    des moyens de détection d'humidité pour détecter de l'humidité, et
    des moyens de commande sensibles à une sortie desdits moyens de détection d'humidité pour ajuster le temps d'application de la seconde polarisation de transfert lorsqu'une humidité est supérieure à une valeur prédéterminée ou pour ne pas ajuster ledit temps lorsque l'humidité est inférieure à ladite valeur prédéterminée.
  6. Dispositif de formation d'image, comportant :
    un élément photoconducteur (1) pour former dessus une image de toner,
    une courroie de transfert (3) mobile en contact avec ledit élément photoconducteur (1) sur une partie de contact prédéterminée pour transporter une feuille afin de permettre à l'image de toner d'être transférée dudit élément photoconducteur à ladite feuille,
    des premiers moyens d'application de polarisation de potentiel de transfert (5, 8) pour appliquer une polarisation de transfert à ladite courroie de transport en aval de la partie de contact en venant au contact de la courroie de transfert,
    des seconds moyens d'application de polarisation de potentiel de transfert (4, 13 ; 4, 14 ; 4, 15 ; 4, 16) pour appliquer une polarisation de transfert à ladite courroie de transfert en amont de la partie de contact venant en contact de la courroie de transfert, et
       caractérisé en ce que
       la même polarisation de transfert commence à être appliquée aux premiers et seconds moyens de polarisation d'application de polarisation de potentiel de transfert lorsque le bord avant de la feuille entre dans la partie de contact ou à l'instant où le bord avant de la feuille s'est déplacé d'une distance prédéterminée inférieure à 8 mm par rapport à la partie de contact.
  7. Dispositif de formation d'image, comportant :
    un élément photoconducteur (1) pour former dessus une image de toner,
    une courroie de transfert (3) mobile en contact avec ledit élément photoconducteur (1) sur une partie de contact prédéterminée pour transporter une feuille afin de permettre à l'image de toner d'être transférée dudit élément photoconducteur à ladite feuille,
    des premiers moyens d'application de polarisation de potentiel de transfert (5, 8) pour appliquer une première polarisation de transfert prédéterminée à ladite courroie de transport en aval de la partie de contact en venant au contact de la courroie de transfert,
    des seconds moyens d'application de polarisation de potentiel de transfert (4, 13 ; 4, 14 ; 4, 15 ; 4, 16) pour appliquer une seconde polarisation de transfert à ladite courroie de transfert en amont de la partie de contact en venant au contact de la courroie de transfert, et
       caractérisé en ce que
       la seconde polarisation de transfert commence à être appliquée aux seconds moyens d'application de polarisation après avoir transporté le bord de la feuille depuis les seconds moyens d'application de polarisation de potentiel de transfert vers la partie de contact sur une distance dépassant la distance existant entre les premiers moyens d'application de polarisation et ledit élément photoconducteur, ladite distance étant plus courte que la distance existant entre les seconds moyens d'application de polarisation de potentiel de transfert et la partie de contact.
  8. Dispositif de formation d'image, comportant :
    un élément photoconducteur (1) pour former dessus une image de toner,
    une courroie de transfert (3) mobile en contact avec ledit élément photoconducteur (1) sur une partie de contact prédéterminée pour transporter une feuille afin de permettre à l'image de toner d'être transférée dudit élément photoconducteur à ladite feuille,
    des premiers moyens d'application de polarisation de potentiel de transfert (5, 8) pour appliquer une polarisation de transfert à ladite courroie de transport en aval de la partie de contact en venant au contact de la courroie de transfert,
    des seconds moyens d'application de polarisation de potentiel de transfert (4, 13 ; 4, 14 ; 4, 15 ; 4, 16) pour appliquer une polarisation de transfert à ladite courroie de transfert en amont de la partie de contact en venant au contact de la courroie de transfert, et
       caractérisé en ce que
       la même polarisation de transfert commence à être appliquée aux moyens d'application de polarisation après avoir transporté le bord avant de la feuille depuis les seconds moyens d'application de polarisation de potentiel de transfert vers la partie de contact sur une distance dépassant la distance existant entre lesdits premiers moyens d'application de polarisation et ledit élément photoconducteur, ladite distance étant plus courte que la distance existant entre les seconds moyens d'application de polarisation de potentiel de transfert et la partie de contact.
  9. Dispositif selon la revendication 7 ou 8, comportant de plus :
    des moyens de détection d'humidité pour détecter une humidité, et
    des moyens de commande sensibles à une sortie desdits moyens de détection d'humidité pour ajuster le temps d'application de la seconde polarisation de transfert lorsqu'une humidité est supérieure à une valeur prédéterminée ou pour ne pas ajuster ledit temps lorsque l'humidité est inférieure à ladite valeur prédéterminée.
  10. Dispositif de formation d'image, comportant :
    un élément photoconducteur (1) pour former dessus une image de toner,
    une courroie de transfert (3) mobile en contact avec ledit élément photoconducteur (1) sur une partie de contact prédéterminée pour transporter une feuille afin de permettre à l'image de toner d'être transférée dudit élément photoconducteur à ladite feuille,
    des premiers moyens d'application de polarisation de potentiel de transfert (5, 8) pour appliquer une première polarisation de transfert prédéterminée à ladite courroie de transport en aval de la partie de contact en venant au contact de la courroie de transfert,
    des seconds moyens d'application de polarisation de potentiel de transfert (4, 13 ; 4, 14 ; 4, 15 ; 4, 16) pour appliquer une seconde polarisation de transfert DC à ladite courroie de transfert en amont de la partie de contact en venant au contact de la courroie de transfert, et
       caractérisé en ce que
       les seconds moyens d'application de polarisation de potentiel de transfert sont munis d'une couche surfacique (4a) constituée d'un matériau diélectrique ayant une résistivité volumique spécifique de 106 à 1012 Ω/cm.
  11. Dispositif de formation d'image, comportant :
    un élément photoconducteur (1) pour former dessus une image de toner,
    une courroie de transfert (3) mobile en contact avec ledit élément photoconducteur (1) sur une partie de contact prédéterminée pour transporter une feuille afin de permettre à l'image de toner d'être transférée dudit élément photoconducteur à ladite feuille,
    des premiers moyens d'application de polarisation de potentiel de transfert (5, 8) pour appliquer une première polarisation de transfert prédéterminée à ladite courroie de transfert en aval de la partie de contact en venant au contact de la courroie de transfert,
    des seconds moyens d'application de polarisation de potentiel de transfert (36) pour appliquer une seconde polarisation de transfert à ladite courroie de transfert au niveau de la partie de contact en venant au contact de la courroie de transfert, et
       caractérisé en ce que
       les seconds moyens d'application de polarisation de potentiel de transfert (36) ont une surface constituée d'un matériau diélectrique élastique ayant une résistivité volumique spécifique de 106 à 1012 Ω cm.
EP93105767A 1992-04-09 1993-04-07 Appareil de formation d'images Expired - Lifetime EP0568829B1 (fr)

Applications Claiming Priority (9)

Application Number Priority Date Filing Date Title
JP8891692 1992-04-09
JP8891692 1992-04-09
JP88916/92 1992-04-09
JP90701/92 1992-04-10
JP9070192 1992-04-10
JP9070192 1992-04-10
JP10159/93 1993-01-25
JP1015993 1993-01-25
JP01015993A JP3271811B2 (ja) 1992-04-09 1993-01-25 画像形成装置

Publications (3)

Publication Number Publication Date
EP0568829A2 EP0568829A2 (fr) 1993-11-10
EP0568829A3 EP0568829A3 (fr) 1995-05-10
EP0568829B1 true EP0568829B1 (fr) 2001-08-16

Family

ID=27278864

Family Applications (1)

Application Number Title Priority Date Filing Date
EP93105767A Expired - Lifetime EP0568829B1 (fr) 1992-04-09 1993-04-07 Appareil de formation d'images

Country Status (5)

Country Link
EP (1) EP0568829B1 (fr)
JP (1) JP3271811B2 (fr)
KR (1) KR0145748B1 (fr)
DE (1) DE69330579T2 (fr)
ES (1) ES2161701T3 (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3488328B2 (ja) * 1996-02-02 2004-01-19 株式会社リコー 転写ベルト装置
JP3306310B2 (ja) * 1996-08-29 2002-07-24 シャープ株式会社 画像形成装置
JP2004109706A (ja) 2002-09-19 2004-04-08 Ricoh Co Ltd ベルト駆動装置・転写駆動システム・画像形成装置
JP2006047707A (ja) * 2004-08-05 2006-02-16 Ricoh Co Ltd 画像形成方法及び画像形成装置
JP5564993B2 (ja) * 2010-03-01 2014-08-06 株式会社リコー 画像形成装置

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58111960A (ja) * 1981-12-25 1983-07-04 Ricoh Co Ltd 転写紙分離装置
JPH0623900B2 (ja) * 1986-03-03 1994-03-30 ヤマウチ株式会社 画像形成装置において使用される転写ベルト
JPH02110586A (ja) * 1988-10-20 1990-04-23 Canon Inc 画像形成装置
US5172173A (en) * 1988-09-01 1992-12-15 Canon Kabushiki Kaisha Image forming device and transfer belt having contact-type electricity feeding means
EP0368617B1 (fr) * 1988-11-08 1994-02-02 Canon Kabushiki Kaisha Appareil de formation d'images avec des moyens de contrôle de l'attraction électrostatique de matière de transfert
JPH03186876A (ja) * 1989-12-16 1991-08-14 Canon Inc 画像形成装置

Also Published As

Publication number Publication date
DE69330579T2 (de) 2002-06-27
KR0145748B1 (ko) 1998-09-15
ES2161701T3 (es) 2001-12-16
JPH06167896A (ja) 1994-06-14
EP0568829A2 (fr) 1993-11-10
KR930022160A (ko) 1993-11-23
DE69330579D1 (de) 2001-09-20
EP0568829A3 (fr) 1995-05-10
JP3271811B2 (ja) 2002-04-08

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