EP1170639A1 - Appareil d'exposition blanche et dispositif de formation d'image - Google Patents

Appareil d'exposition blanche et dispositif de formation d'image Download PDF

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Publication number
EP1170639A1
EP1170639A1 EP00909643A EP00909643A EP1170639A1 EP 1170639 A1 EP1170639 A1 EP 1170639A1 EP 00909643 A EP00909643 A EP 00909643A EP 00909643 A EP00909643 A EP 00909643A EP 1170639 A1 EP1170639 A1 EP 1170639A1
Authority
EP
European Patent Office
Prior art keywords
blank
blank exposing
photosensitive object
light
state
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Withdrawn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
EP00909643A
Other languages
German (de)
English (en)
Other versions
EP1170639A4 (fr
Inventor
Hiroya Copyer Co. Ltd. HIROSE
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.)
Canon Finetech Nisca Inc
Original Assignee
Copyer Co Ltd
Canon Finetech Inc
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 Copyer Co Ltd, Canon Finetech Inc filed Critical Copyer Co Ltd
Publication of EP1170639A1 publication Critical patent/EP1170639A1/fr
Publication of EP1170639A4 publication Critical patent/EP1170639A4/fr
Withdrawn legal-status Critical Current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
    • G03G15/04—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material
    • G03G15/045—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material with means for charging or discharging distinct portions of the charge pattern on the recording material, e.g. for contrast enhancement or discharging non-image areas
    • G03G15/047—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material with means for charging or discharging distinct portions of the charge pattern on the recording material, e.g. for contrast enhancement or discharging non-image areas for discharging non-image areas
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G21/00—Arrangements not provided for by groups G03G13/00 - G03G19/00, e.g. cleaning, elimination of residual charge
    • G03G21/06—Eliminating residual charges from a reusable imaging member
    • G03G21/08—Eliminating residual charges from a reusable imaging member using optical radiation
    • 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
    • G03G2215/04—Arrangements for exposing and producing an image
    • G03G2215/0429—Changing or enhancing the image
    • G03G2215/0431—Producing a clean non-image area, i.e. avoiding show-around effects
    • G03G2215/0448—Charge-erasing means for the non-image area
    • G03G2215/0451—Light-emitting array or panel
    • G03G2215/0453—Light-emitting diodes, i.e. LED-array

Definitions

  • the present invention relates to a blank exposing device for removing unnecessary electric charge on a photosensitive object, to be used in such an image forming apparatus as a copying machine, a printer, a facsimile or the like for forming image information on a recording medium by means of an electrophotographic method.
  • An image forming apparatus of an electrophotographic method for forming an image on a recording medium using a developer (toner) is widely used as an output apparatus of a computer or a workstation.
  • Such an image forming apparatus makes the surface of a photosensitive object charged uniformly with electricity prior to exposing the photosensitive object to an image light.
  • the photosensitive object turns at a fixed speed.
  • the size of an image area on the photosensitive object is smaller than the size of a charged area of the photosensitive object, electric charge remains on a non-image area on the photosensitive object. And this remaining electric charge has toner adhered to it and brings a result that a more quantity of toner than a necessary quantity is consumed.
  • an image forming apparatus is ordinarily provided with a blank exposing device on the periphery of its photosensitive object to remove unnecessary electric charge on the photosensitive object.
  • This blank exposing device is composed of a light emitting diode array (blank exposing lamp) in which a number of light emitting diodes are arranged.
  • a light emitting diode array (blank exposing lamp) in which a number of light emitting diodes are arranged.
  • FIG. 10 is a diagram for explaining this black stripe and shows a timing chart when forming an image on a sheet of recording paper.
  • the same figure (a) shows change in electric potential of the surface of a photosensitive object
  • the same figure (b) shows change in voltage applied to a blank exposing lamp
  • the same figure (c) shows change in quantity of light of the blank exposing lamp.
  • the same figure (d) shows a real image on the recording paper.
  • the respective timing charts of Figures 10(a), 10(b) and 10(c) are drawn correspondingly to the positions on the recording paper of Figure 10(d).
  • the example of Figure 10 forms a solid white image, a solid black image, a halftone image, a solid white image, a halftone image, a solid white image, a solid black image and a solid white image in order from the front end side of the recording paper.
  • the photosensitive object turns at a fixed speed.
  • the blank exposing lamp is turned on to a non-image area on the photosensitive object and is turned off to an image area, as shown in Figures 10(b) and 10(c).
  • the image area is irradiated with a light carrying image information and thereby the distribution of electric potential as shown in Figure 10(a), namely, an electrostatic latent image is formed.
  • this electrostatic latent image is developed and a toner image is fixed on a recording paper and thereby a recording paper shown in Figure 10(d) is obtained. Seeing this recording paper, it is found that a black stripe appears on the boundary between a blank space of the front end side of the recording paper and a solid white image adjacent to it.
  • the present invention has been performed under such a technical background, and aims at providing a blank exposing device and an image forming apparatus being capable of preventing a black stripe from appearing on the front end portion of a recording paper.
  • a blank exposing device is characterized by comprising a blank exposing lamp for removing electric charge on the surface of a photosensitive object and forming a non-image area on said photosensitive object by exposing said surface of the photosensitive object to light, a light quantity adjusting means for adjusting the quantity of light of said blank exposing lamp, and a control means for controlling said light quantity adjusting means so that the quantity of light of said blank exposing lamp gradually changes when changing over said blank exposing lamp from the on state to the off state.
  • a blank exposing device is characterized by comprising a blank exposing lamp for removing electric charge on the surface of a photosensitive object and forming a non-image area on said photosensitive object by exposing said surface of the photosensitive object to light, a constant-voltage power supply circuit for applying a constant voltage to said blank exposing lamp, a switching means for performing an on-off operation of a voltage to be applied to said blank exposing lamp, and a control means for controlling said switching means so that the quantity of light of said blank exposing lamp gradually changes when changing over said blank exposing lamp from the on state to the off state.
  • the present invention is characterized by an image forming apparatus for forming image information on a recording medium by means of an electrophotographic method, said image forming apparatus comprising a developing device for developing an electrostatic latent image formed on a photosensitive object on the basis of said image information with a mono-component developer, a blank exposing device which has a blank exposing lamp for removing electric charge on the surface of the photosensitive object and forming a non-image area on said photosensitive object by exposing the surface of said photosensitive object to light before performing the development by means of said developing device and a light quantity adjusting means for adjusting the quantity of light of said blank exposing lamp, and a control means for controlling said light quantity adjusting means so that the quantity of light of said blank exposing lamp gradually changes when changing over said blank exposing lamp from the on state to the off state.
  • the present invention is characterized by an image forming apparatus for forming image information on a recording medium by means of an electrophotographic method, said image forming apparatus comprising a developing device for developing an electrostatic latent image formed on a photosensitive object on the basis of said image.
  • a blank exposing device which has a blank exposing lamp for removing electric charge on the surface of the photosensitive object and forming a non-image area on said photosensitive object by exposing the surface of said photosensitive object to light before performing the development by means of said developing device, has a constant-voltage power supply circuit for applying a constant voltage to said blank exposing lamp and has a switching means for performing an on-off operation of a voltage to be applied to said blank exposing lamp, and a control means for controlling said switching means so that the quantity of light of said blank exposing lamp gradually changes when changing over said blank exposing lamp from the on state to the off state.
  • Figure 1 is a schematic composition diagram of a main part of an image forming apparatus being an embodiment of the present invention
  • Figure 2 is a schematic composition diagram of a main charger and a blank exposing device of the image forming apparatus
  • Figure 3 is a schematic perspective view of the main charger of the image forming apparatus
  • Figure 4 is a schematic perspective view of the blank exposing device of the image forming apparatus
  • Figure 5 is a schematic circuit diagram for explaining control of turning on/off light emitting diodes in the blank exposing device.
  • an image forming apparatus of this embodiment is provided with a photosensitive object 10, a main charger 20, a blank exposing device 30, a developing device 40, a transfer charger 50, a separation charger 60, a fixing device 70, a cleaning device 80, a pre-exposure device 90 and a control portion (see Figure 5).
  • the photosensitive object 10 turns at a predetermined circumferential speed (process speed) in the clockwise direction as shown by an arrow A.
  • the main charger 20, which charges uniformly the surface of the photosensitive object 10 with electricity by means of corona discharge, comprises a wire 21 which is made from tungsten in general, a shield 22, a grid 23 and a power supply 24, as shown in Figures 2 and 3. A high voltage is applied to the wire 21 by the power supply 24.
  • the grid 23 has a number of openings 23a formed by applying an etching process to a plate member of about 0.1 mm in thickness, as shown in Figure 3. By this, it is possible to make the photosensitive object 10 uniformly charged with electricity.
  • the blank exposing device 30 removes electric charge on the surface of the photosensitive object 10 corresponding to a non-image area and prevents unnecessary developer (toner) from adhering to the photosensitive object 10.
  • An original lighting lamp not illustrated irradiates an original with a scanning light and reads image information of the original. And an irradiation light L carrying the image information is led through an unshown optical system to the photosensitive object 10, and thereby an electrostatic latent image is formed on the photosensitive object 10.
  • the developing device 40 supplies toner onto the photosensitive object 10 by rotation of a sleeve 41 in the direction of an arrow B. Due to this, an electrostatic latent image formed on the photosensitive object 10 is visualized.
  • this embodiment uses a mono-component toner as its toner.
  • a transfer paper being a recording medium is fed by a pair of resist rollers 121 and 122 along the direction of an arrow C in such timing that the front end of an image on the photosensitive object 10 and the front end of the transfer paper coincide with each other. And the toner on the surface of the photosensitive object 10 is transferred onto the transfer paper by the transfer charger 50.
  • the separation charger 60 removes electric charge from the reverse face of the transfer paper having a toner image transferred onto it, and separates the transfer paper static-electrically from the photosensitive object 10.
  • the static-electrically separated transfer paper is carried in the direction of an arrow D and is fed to the fixing device 70.
  • the fixing device 70 fixes the toner image on the transfer paper by means of the heat and pressure of a pair of fixing rollers 71 and 72. Due to this, the toner image is semipermanently recorded. After this, the transfer paper is discharged from the image forming apparatus main body to the outside.
  • untransferred toner slightly remaining on the photosensitive object 10 is recovered from the photosensitive object 10 by the cleaning device 80. And the residual electric potential being traces of an electrostatic latent image on the photosensitive object 10 is eliminated by the pre-exposure device 90. And the control portion 110 supervises control of each portion of the image forming apparatus.
  • the blank exposing device 30 performs the following two main roles. That is to say, these are a role of removing electric charge on a non-image area on the photosensitive object 10 corresponding to blank spaces at the front end and the rear end of a recording paper by irradiating the whole area in the axial direction of the photosensitive object 10, and a role of removing electric charge on a non-image area on the photosensitive object 10 corresponding to, for example, the peripheral area of the recording paper by irradiating a partial area in the axial direction of the photosensitive object 10.
  • such a blank exposing device 30 has a light emitting diode array (blank exposing lamp) formed by arranging a number of light emitting diodes 31, a substrate 32 mounted with the light emitting diode array, a housing 33, a partition wall 34, a constant-voltage power supply circuit 35 for applying a constant voltage to the respective light emitting diodes 31 and a switching element 36 of a transistor or the like for performing an on-off operation of a voltage to be applied to the respective light emitting diodes 31.
  • a light emitting diode array bladenk exposing lamp
  • the housing 33 is provided with a partition wall 34 for regulating the width of exposure in order to make it possible to perform exposure so as to clearly define the boundary between an image area and a non-image area, namely, between a charged area and a non-charged area along the axial direction of the photosensitive object 10.
  • This partition wall 34 has a number of openings 34a formed in it. The formation of the openings 34a regulates the width of exposure of the individual light emitting diodes 31 onto the surface of the photosensitive object 10. By turning on predetermined light emitting diodes 31, electric charge on the surface of the photosensitive object 10 within the width of exposure of them is removed. The timing of turning on/off each light emitting diode 31 is controlled by the control portion 110.
  • control portion 110 controls the switching element 36 so that the quantity of light of each light emitting diode 31 gradually changes when changing over each light emitting diode 31 from the on state to the off state.
  • control portion 110 sends an on/off signal to the switching element 36, changes a voltage outputted from the constant-voltage power supply circuit 35 into a pulse voltage and applies it to the light emitting diodes 31.
  • the control of turning on/off the blank exposing lamp by means of such a pulse voltage is described in detail later.
  • Figure 6 shows the development characteristics of the image forming apparatus.
  • the ordinate represents the density of an image
  • the abscissa represents the electric potential of the surface of a photosensitive object 10 (hereinafter, referred to as a photosensitive object potential also).
  • the density of an image is represented by a Macbeth reflection density.
  • a development method using a mono-component toner is adopted and a photosensitive object potential when an ordinary image is formed is between 150 V and 700 V.
  • the photosensitive object potential is set so as to be about 700 V.
  • the photosensitive object potential is set so as to be about 400 V, and in case of forming a solid white image being a white ground portion, the photosensitive object potential is set so as to be about 150 V.
  • a phenomenon that toner is slightly put on a white ground portion of a recording paper namely, what is called a fogging phenomenon occurs.
  • This is a phenomenon caused by a fact that a photosensitive object potential is within the range of regular fog from 150 V to 300 V.
  • the photosensitive object potential being lower than 150 V comes into the range of reversal fog.
  • the toner of reverse polarity existing in the developing device 40 namely, what is called the reversal toner is developed and the toner results in being adhered to an area on the photosensitive object 10 to be a non-image area in image information.
  • FIG. 7(a) is a diagram for explaining change in electric potential of an area on a photosensitive object 10 corresponding to the front end portion of a recording paper
  • Figure 7(b) is a diagram for explaining change in electric potential of an area on the photosensitive object 10 corresponding to the rear end portion of a recording paper.
  • the ordinate represents electric potential of the surface of the photosensitive object 10 (a photosensitive object potential) and the abscissa represents time (or position along the direction of rotation of the photosensitive object 10).
  • the photosensitive object potential is an electric potential obtained after exposure by an irradiation light L.
  • the blank exposing lamp is changed over from the on state to the off state on an area on the photosensitive object 10 corresponding to the front end portion of a recording paper.
  • a portion irradiated with light from the blank exposing lamp becomes a blank space portion, and a portion not irradiated becomes an image area.
  • the photosensitive object potential is sharply changed at the boundary between the blank space portion and the image area adjacent to it, and at this time a transient falling and rising phenomenon occurs and potential edges E 1 and E 2 are formed.
  • the photosensitive object 10 further turns, its image area is irradiated with an irradiation light L carrying image information.
  • this irradiation light L contains image information being a solid white image.
  • the photosensitive object potential V SL of a blank space portion is about 50 V and the photosensitive object potential V L of a solid white image area is about 150 V.
  • the photosensitive object potential at the blank space side is decreased by the potential edge E 1 from V SL (about 50 V) to about 0 V near the boundary between the blank space portion and the solid white image area, and on the other hand the photosensitive object potential at the solid white image area side is increased by the potential edge E 2 from V L (about 150 V) to about 200 V.
  • a portion in which the potential edge E 1 is formed has an electric potential at which a reversal fogging phenomenon appears conspicuously.
  • Figure 8(a) is a diagram showing an ideal change in photosensitive object potential
  • Figure 8(b) is a diagram showing an ideal change in quantity of light of the blank exposing lamp
  • Figure 8(c) is a diagram for explaining a pulse voltage to be applied to the blank exposing lamp
  • Figure 8(d) is a diagram showing a concrete example of a pulse voltage to be applied to the blank exposing lamp.
  • the blank exposing device 30 using light emitting diodes 31 can easily obtain a necessary quantity of light and moreover adopts an inexpensive constant-voltage power supply circuit 35. Therefore, it is easily thought to gradually change the quantity of light of the blank exposing lamp by providing with a constant-current circuit in place of the constant-voltage power supply circuit 35, or by providing with a light adjusting device separately.
  • these methods bring a result of high cost.
  • the blank exposing device 30 of this embodiment is provided with the switching element 36 for performing an on-off operation of a voltage to be applied to the blank exposing lamp, and the control portion 110 controls the switching element 36 to generate a pulse voltage of one or plural pulses as shown in Figure 8(c) and apply the pulse voltage to the blank exposing lamp when changing over the blank exposing lamp from the on state to the off state. Due to this, the quantity of light of the blank exposing lamp substantially falls gradually as shown in Figure 8(b) and therefore the photosensitive object potential also changes gradually as shown in Figure 8(a), and thus it is possible to suppress formation of a sharp potential edge.
  • An image forming apparatus of this embodiment actually applies a pulse voltage shown in Figure 8(d) to the blank exposing lamp.
  • This pulse voltage is such an irregular pulse voltage that it starts at the on state, is kept in the off state for 6 milliseconds, in the on state for 4 milliseconds, in the off state for 4 milliseconds, in the on state for 2 milliseconds and then comes completely into the off state.
  • the inventors have set such a pulse condition, aiming at reducing the quantity of light of the blank exposing lamp by 10 to 90 % in 80 to 100 milliseconds when changing over the blank exposing lamp from the on state to the off state.
  • the quantity of light of a conventional blank exposing lamp has been reduced by 10 to 90 % in 20 or less milliseconds.
  • a pulse voltage having pulse intervals T 1 , T 2 and T 3 being made shorter in stages can be used.
  • a pulse voltage having a fixed duty factor "t 1 /(t 1 + t 2 )" can be used.
  • time t 1 of the off state and time t 2 of the on state are different from each other (t 2 ⁇ t 1 ). If the longer time t 1 of the off state and the shorter time t 2 of the on state are set taking a delay time required for turning on the blank exposing lamp into account, it is possible to more properly control the change in quantity of light of the blank exposing lamp. And the duty factor may be changed in stages.
  • a pulse voltage shown in Figure 9(c) is more increased in number of pulses than the pulse voltage shown in Figure 9(a).
  • An image forming apparatus of this embodiment is provided with a switching element for performing an on-off operation of a constant-voltage power supply circuit and makes a control portion control the switching element to generate a pulse voltage of one or plural pulses and apply the pulse voltage to the blank exposing lamp when changing over the blank exposing lamp from the on state to the off state, and thereby can make the quantity of light of the blank exposing lamp fall gradually. Thanks to this, since the photosensitive object potential also gradually changes, it is possible to suppress formation of a sharp potential edge and suppress occurrence of a black stripe at the front end portion of a recording paper.
  • this image forming apparatus uses a constant-voltage power supply circuit as it is without using an expensive constant-current power supply circuit, it has also a merit that it is not so high in cost and is comparatively simple in control.
  • the present invention is not limited to the above-mentioned embodiment but can be modified variously within the scope of its gist.
  • a constant-current power supply circuit may be used in place of the constant-voltage power supply circuit.
  • a light adjusting device may change the quantity of light of the blank exposing lamp.
  • a blank exposing device of the present invention is provided with a switching means for performing an on-off operation of a constant-voltage power supply circuit and makes a control means control the switching means to generate, for example, a pulse voltage of one or plural pulses and apply the pulse voltage to the blank exposing lamp when changing over the blank exposing lamp from the on state to the off state, and thereby can make the quantity of light of the blank exposing lamp fall gradually. Due to this, since the photosensitive object potential also gradually changes, it is possible to suppress formation of a sharp potential edge and suppress occurrence of a black stripe at the front end portion of a recording paper. Therefore, a blank exposing device according to the present invention can be used in an image forming apparatus for forming image information on a recording medium by means of an electrophotographic method.
  • an image forming apparatus of the present invention can suppress occurrence of a black stripe at the front end portion of a recording paper in the same way by being provided with the above-mentioned blank exposing device, the image forming apparatus can be used in a copying machine, a printer, a facsimile and the like for forming image information on a recording medium by means of an electrophotographic method.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Exposure Or Original Feeding In Electrophotography (AREA)
  • Control Or Security For Electrophotography (AREA)
  • Fax Reproducing Arrangements (AREA)
EP00909643A 1999-03-15 2000-03-15 Appareil d'exposition blanche et dispositif de formation d'image Withdrawn EP1170639A4 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
JP06924099A JP3374906B2 (ja) 1999-03-15 1999-03-15 ブランク露光装置及び画像形成装置
JP6924099 1999-03-15
PCT/JP2000/001566 WO2000055693A1 (fr) 1999-03-15 2000-03-15 Appareil d'exposition blanche et dispositif de formation d'image

Publications (2)

Publication Number Publication Date
EP1170639A1 true EP1170639A1 (fr) 2002-01-09
EP1170639A4 EP1170639A4 (fr) 2007-12-12

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EP00909643A Withdrawn EP1170639A4 (fr) 1999-03-15 2000-03-15 Appareil d'exposition blanche et dispositif de formation d'image

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EP (1) EP1170639A4 (fr)
JP (1) JP3374906B2 (fr)
WO (1) WO2000055693A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP7395956B2 (ja) * 2019-10-25 2023-12-12 株式会社リコー 画像形成装置、画像形成方法及びプログラム

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS55121452A (en) * 1979-03-12 1980-09-18 Olympus Optical Co Ltd Electrophotographic apparatus
JPS5857870U (ja) * 1981-10-15 1983-04-19 株式会社リコー 感光体の非画像領域電位消去装置
JPS59171969A (ja) * 1983-03-18 1984-09-28 Fuji Photo Film Co Ltd 電子写真装置
JPS6157977A (ja) * 1984-08-29 1986-03-25 Canon Inc 像形成装置
JPS63125962A (ja) * 1986-11-14 1988-05-30 Mita Ind Co Ltd 複写機
JPH01177584A (ja) * 1988-01-06 1989-07-13 Sanyo Electric Co Ltd 静電記録装置の画像形成方法
JPH07152294A (ja) * 1993-11-30 1995-06-16 Mita Ind Co Ltd 画像形成装置における前帯電・除電方法
JP3372879B2 (ja) 1998-11-24 2003-02-04 キヤノン株式会社 画像形成装置

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Publication number Publication date
EP1170639A4 (fr) 2007-12-12
WO2000055693A1 (fr) 2000-09-21
JP3374906B2 (ja) 2003-02-10
JP2000267403A (ja) 2000-09-29

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