WO2011030421A1 - 画像形成装置 - Google Patents
画像形成装置 Download PDFInfo
- Publication number
- WO2011030421A1 WO2011030421A1 PCT/JP2009/065809 JP2009065809W WO2011030421A1 WO 2011030421 A1 WO2011030421 A1 WO 2011030421A1 JP 2009065809 W JP2009065809 W JP 2009065809W WO 2011030421 A1 WO2011030421 A1 WO 2011030421A1
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- WIPO (PCT)
- Prior art keywords
- charging
- photosensitive drum
- image
- light
- image forming
- Prior art date
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Classifications
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/02—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices
- G03G15/0266—Arrangements for controlling the amount of charge
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/02—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/02—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices
- G03G15/0208—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices by contact, friction or induction, e.g. liquid charging apparatus
- G03G15/0216—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices by contact, friction or induction, e.g. liquid charging apparatus by bringing a charging member into contact with the member to be charged, e.g. roller, brush chargers
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/50—Machine control of apparatus for electrographic processes using a charge pattern, e.g. regulating differents parts of the machine, multimode copiers, microprocessor control
- G03G15/5004—Power supply control, e.g. power-saving mode, automatic power turn-off
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- 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
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- 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
- G03G2215/00025—Machine control, e.g. regulating different parts of the machine
- G03G2215/00071—Machine control, e.g. regulating different parts of the machine by measuring the photoconductor or its environmental characteristics
- G03G2215/00075—Machine control, e.g. regulating different parts of the machine by measuring the photoconductor or its environmental characteristics the characteristic being its speed
Definitions
- the present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, and a FAX.
- a method of charging a roller-type or blade-type charging member in contact with the photosensitive member is used to charge the photosensitive member.
- Two methods are well known for charging a photoreceptor by a contact charging method.
- the first is an “AC charging method” in which a superposed voltage of a DC voltage and an AC voltage is applied to a charging member to charge the photoconductor, and the second is to apply only a DC voltage to the charging member to charge the photoconductor.
- DC charging method Since an AC voltage is applied to the “AC charging method”, the surface of the photoreceptor can be charged relatively uniformly as compared to the “DC charging method”.
- the “AC charging method” increases the amount of discharge to the photosensitive member as compared with the “DC charging method”, so that the surface of the photosensitive member is easily scraped. Therefore, when the photoreceptor is charged by the “AC charging method”, the life of the photoreceptor is shortened compared to the case where the photoreceptor is charged by using the “DC charging method”.
- the “AC charging method” requires an AC power source. Therefore, the “AC charging method” has higher initial costs and running costs than the “DC charging method”. In other words, the “DC charging method” is more advantageous in terms of running cost and initial cost than the “AC charging method”.
- the “DC charging method” is inferior in surface potential uniformity (charging uniformity) to the photoreceptor as compared with the “AC charging method”.
- stripe-shaped charging unevenness (charging lateral stripe) in the longitudinal direction (direction perpendicular to the circumferential direction) of the electrophotographic photosensitive member due to non-uniformity of the surface potential of the photosensitive member has been a problem. This is because, in the charging gap portion (small gap) on the downstream side in the rotation direction of the photosensitive drum, peeling discharge occurs between the photosensitive member and the charging roller charged in the upstream charging gap portion in the rotation direction of the photosensitive drum. It is thought to be caused by that.
- Patent Document 1 discloses a configuration for suppressing “charging horizontal streaks” generated when the photosensitive member is charged by the “DC charging method”. Specifically, light is irradiated to the upstream charging gap portion in the photosensitive member rotating direction among the charging gap portions generated by the contact between the charging roller and the photosensitive drum (nip pre-exposure). As a result, the charging of the photosensitive member is canceled at the upstream charging gap portion, and the photosensitive member is charged at the downstream charging gap portion in the rotation direction of the photosensitive member, thereby suppressing the occurrence of charging horizontal stripes due to peeling discharge. It was.
- electrophotographic apparatuses have been required to form images on various media.
- a configuration is widely adopted in which the process speed is changed according to the type of media.
- thick paper paper having a relatively high basis weight
- plain paper paper having a basis weight of about 50 to 100 mg / m 2
- a lot of heat is required to secure the fixing property.
- a configuration is known in which the fixing speed of the fixing device is decreased to increase the heating time.
- many image forming apparatuses employ a configuration in which the process speed of the photosensitive member is decreased in the same manner as the fixing speed of the fixing device as the fixing speed of the fixing device is decreased.
- an image processing apparatus of the present invention includes a rotatable photosensitive member, a charging member that contacts the photosensitive member to charge the photosensitive member, and a power source that applies a DC voltage to the charging member. And an irradiating means for irradiating light to an upstream charging gap portion in the rotation direction of the photoconductor among the charging gap portions where the charging member charges the photoconductor, the image forming apparatus comprising: When the photoconductor rotates at the first speed, the photoconductor rotates at a second speed slower than the first speed so as to irradiate the upstream charging gap portion with the first light amount. And a control means for controlling the irradiating means so as to irradiate the upstream charging gap portion with a second light quantity larger than the first light quantity.
- FIG. 2 is a diagram for explaining a schematic configuration of an image forming apparatus according to an embodiment, a layer configuration of a photosensitive drum, and a layer configuration of a charging roller.
- 1 is a schematic configuration diagram illustrating an operation unit of an image forming apparatus according to an embodiment.
- 1 is a block diagram of an image forming apparatus according to an embodiment.
- 6 is a graph showing a relationship between a pre-nip exposure amount and a current value flowing between a charging roller and a photosensitive drum, and a relationship between a current value and a shaving amount of the photosensitive drum in the image forming apparatus according to the example.
- 6 is a flowchart for explaining the operation of the image forming apparatus according to the embodiment.
- 1 is a block diagram of an image forming apparatus according to an embodiment. 6 is a flowchart for explaining the operation of the image forming apparatus according to the embodiment. It is a figure for demonstrating the bias of the discharge accompanying the change of nip pre-exposure and a process
- FIG. 1 is a schematic diagram for explaining the overall configuration of the image forming apparatus.
- the image forming apparatus in this embodiment is an electrophotographic image forming apparatus that charges a photosensitive drum using a roller charging device.
- the laser beam printer is capable of forming an image on a maximum A3 size paper adopting a contact charging method in which a charging roller is brought into contact with a photosensitive drum and a reversal development method in which exposure is performed on an area where a toner image is to be formed. .
- the photosensitive drum 1 which is a drum-shaped photosensitive member, is a negatively chargeable organic photosensitive member (OPC) having an outer diameter of 30 mm in the present embodiment, and receives a driving force from a motor (not shown) as a driving device. Rotate.
- OPC organic photosensitive member
- the photosensitive drum 1 has a peripheral speed of 210 mm / s (hereinafter referred to as a process speed), and when an image is formed on thick paper, a peripheral speed of 105 mm / s. Is rotated in the direction of the arrow (counterclockwise). As shown in FIG.
- the photosensitive drum 1 has an undercoat layer 1b that suppresses light interference and improves the adhesion of the upper layer on the surface of an aluminum cylinder (conductive drum base) 1a, and generates photocharges. Three layers of a layer 1c and a charge transport layer 1d are applied in order from the bottom.
- a developing device 4, a transfer roller 5, and a cleaning device 7 are arranged by contacting a charging roller 2 as a charging member around the rotation direction (counterclockwise direction) of the photosensitive drum 1. .
- An exposure device 3 as a latent image forming unit is installed above the charging roller 2 and the developing device 4.
- a fixing device 6 is installed on the downstream side in the transfer material conveyance direction of the transfer portion d formed by the photosensitive drum 1 and the transfer roller 5.
- the charging roller 2 that charges the photosensitive drum 1 is rotatably held at both ends of the cored bar 2a by bearing members (not shown).
- the charging roller 2 is urged toward the center of the photosensitive drum 1 by a pressing pressure spring 2 e and is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force, and is driven by the rotational driving of the photosensitive drum 1.
- the photosensitive drum 1 and the charging roller 2 are in contact with each other to form a contact portion.
- the gap between the photosensitive drum 1 and the charging roller 2 increases in the rotation direction of the photosensitive member from the contact portion.
- the pressure contact portion (contact portion) between the photosensitive drum 1 and the charging roller 2 is referred to as a charging nip portion.
- the minute gap on the upstream side in the rotation direction of the photosensitive drum 1 at the press contact portion is referred to as an upstream charging gap portion A1.
- the minute gap on the downstream side in the rotation direction of the photosensitive drum 1 at the press contact portion is referred to as a downstream charging gap portion A2.
- the photosensitive drum 1 is charged in the upstream charging gap portion A1 and the downstream charging gap portion A2 with the press contact portion as the center.
- the photosensitive drum 1 is charged by discharging from the charging roller 2 to the photosensitive drum 1. Therefore, a voltage equal to or higher than a threshold voltage at which discharge starts is applied to the charging roller 2. In this embodiment, when a voltage of about ⁇ 600 V or higher is applied to the charging roller 2, the surface potential of the photosensitive member starts to rise.
- the surface potential of the photosensitive drum 1 rises while maintaining a substantially linear relationship with the applied voltage.
- this threshold voltage ( ⁇ 600 V) is referred to as a discharge start voltage (charging start voltage) Vth (V). That is, in the electrophotographic image forming process, it is necessary to apply Vd + Vth (V) to the charging roller 2 in order to charge the surface potential of the photosensitive drum 1 to Vd (V) (dark portion potential).
- the surface potential of the photosensitive drum 1 becomes Vd (V).
- the dark portion potential Vd when the photosensitive drum 1 is charged to form an image in the image forming apparatus of this embodiment is set to ⁇ 500V. Therefore, during image formation, a DC voltage of ⁇ 1100 V (hereinafter referred to as DC bias) is applied from the DC power source S1 to the charging roller 2.
- DC bias a DC voltage of ⁇ 1100 V
- the charging gap portion refers to a portion that charges the photosensitive drum by the occurrence of discharge, but it is known that the minute gap for generating discharge when a voltage is applied changes according to Paschen's law. Yes. Note that when the bias is applied to the charging roller 2 in a state where the rotation of the photosensitive drum 1 is stopped, a portion where the photosensitive drum 1 is charged corresponds to a charging gap portion.
- the longitudinal length of the charging roller 2 is 320 mm.
- the charging roller 2 has a three-layer structure in which a lower layer 2b, an intermediate layer 2c, and a surface layer 2d are laminated in this order with a cored bar (supporting member) 2a as a center.
- the lower layer 2b is a foamed sponge layer for reducing charging noise.
- the surface layer 2d functions as a protective layer for preventing current leakage even if the photosensitive drum 1 has a defect such as a pinhole.
- the core metal 2a is a stainless steel round bar having a diameter of 6 mm.
- the lower layer 2b is made of carbon-dispersed foamed EPDM having a layer thickness of 3.0 mm. Foamed EPDM having a specific gravity of 0.5 g / cm 3 and a volume resistivity of 102 to 109 ⁇ cm was used.
- the intermediate layer 2c is made of carbon-dispersed NBR rubber (volume resistance value: 102 to 105 ⁇ cm) having a layer thickness of 700 ⁇ m.
- the surface layer 2d is made of a fluororesin resin having a layer thickness of 10 ⁇ m. The resin resin used was one in which tin oxide and carbon were dispersed and the volume resistance value was 107 to 1010 ⁇ cm. Further, the surface roughness of the charging roller 2 (JIS standard 10-point average surface roughness Ra) is 1.5 ⁇ m.
- the exposure apparatus 3 is a laser beam scanner using a semiconductor laser.
- the exposure device 3 outputs a laser beam modulated in accordance with an image signal input from a host process such as an image reading device (not shown).
- the laser beam scans the surface of the charged photosensitive drum 1 at the exposure position b, and forms an electrostatic latent image corresponding to the image signal input on the photosensitive drum 1 (on the photosensitive member).
- the electrostatic latent image formed on the photosensitive drum 1 is developed by the developing device 4.
- the image forming apparatus in this embodiment uses a two-component developer and develops an electrostatic image with a magnetic brush.
- toner adheres to the exposed portion (bright portion) of the surface of the photosensitive drum 1 and the electrostatic latent image is developed.
- the configuration of the developing device 4 will be described in detail below.
- the developing device 4 includes a developing container 4a and a rotatable nonmagnetic developing sleeve 4b including a fixed magnet roller 4c in an opening of the developing container.
- the developer 4e composed of toner and carrier (magnetic particles) contained in the developing container 4a is regulated to a constant layer thickness by the regulating blade 4d, whereby a thin layer of developer is coated on the developing sleeve 4b.
- the developing sleeve 4b as a developer carrying member causes a magnetic spike to be raised by a carrier by an internal magnet and conveys the toner to the developing portion c facing the photosensitive drum 1.
- the developer 4e in the developing container 4a is a mixture of toner and a magnetic carrier, and is conveyed to the developing sleeve 4b side while being uniformly stirred by the rotation of two developer stirring members 4f (stirring screws).
- the magnetic carrier has a resistance of about 1013 ⁇ cm and a particle size of about 40 ⁇ m.
- the toner is triboelectrically charged to negative polarity by rubbing with the magnetic carrier. Further, the toner density in the developing container 4a is detected by a density sensor (not shown). Further, the toner is supplied from the toner hopper 4g to the developing container 4a so that the toner density in the developing container becomes constant based on the detection information detected by the density sensor.
- the developing sleeve 4b is provided so as to face the photosensitive drum 1 in the vicinity of the photosensitive drum 1 while keeping the closest distance to the photosensitive drum 1 in the developing section c at 300 ⁇ m.
- the developing sleeve 4b is driven to rotate in the direction opposite to the rotation direction (counterclockwise direction) of the photosensitive drum 1 in the developing unit c.
- a predetermined developing bias is applied to the developing sleeve 4b from the power source S2.
- a developing bias in which a DC voltage (Vdc) and an AC voltage (Vac) are superimposed is applied to the developing sleeve 4b.
- the frequency of the AC voltage is 8 kHz
- the DC voltage is ⁇ 320 V
- the peak-to-peak voltage Vpp of the AC voltage is 1800 V.
- the toner image formed on the photosensitive drum 1 by the development process is transferred to the sheet in the transfer process.
- the transfer roller 5 contacts the photosensitive drum 1 with a predetermined pressing force to form a transfer portion d.
- a transfer bias positive transfer bias having a polarity opposite to the negative polarity that is the normal charging polarity of the toner; +500 V in the present embodiment
- the cleaning device 7 includes a cleaning blade 7a.
- the transfer residual toner adhering to the photosensitive drum 1 is removed by rubbing with the cleaning blade 7a.
- the symbol e represents the photosensitive drum surface contact portion of the cleaning blade 7a.
- a fixing device 6 for fixing a toner image on a sheet includes a rotatable fixing roller 6a and a pressure roller 6b.
- the fixing device 6 fixes the toner image transferred to the sheet by heating and pressing while nipping and conveying the sheet.
- the rotation speeds of the fixing roller 6a and the pressure roller 6b are controlled by a control circuit according to the material, thickness, basis weight, and the like of the sheet.
- FIG. 4 is a diagram for explaining the operation panel.
- FIG. 4A is a view for explaining the appearance of the operation panel 100.
- the operation panel 100 includes a start button 101 for causing the image forming apparatus to execute image formation based on the set information.
- the operation panel 100 includes a touch panel display 102.
- a screen as shown in FIG. 2B is displayed on the display 102.
- the user can make various settings when performing image formation by selecting a button displayed on the display 102. In this embodiment, the setting of the type of sheet on which an image is formed and the image quality priority mode will be described in detail.
- Reference numeral 103 in FIG. 2B is a button for setting the type of sheet on which an image is formed.
- the screen shown in FIG. 2C a list of sheets used for image formation is displayed.
- the user can select any of plain paper 104, thick paper 105, coated paper, and the like depending on the type of sheet used for image formation.
- the process speed is set to 210 mm / s.
- the process speed is set to 105 mm / s.
- Coated paper is a glossy sheet whose surface smoothness is improved by coating the surface of the sheet with a transparent resin.
- the process speed is set to 105 mm / s, as in the case of thick paper.
- a number 104 in FIG. 2B is a button for designating the high image quality mode. This button changes the process speed to 105 mm / s even when an image is formed on plain paper. By reducing the process speed, an electrostatic image with a higher resolution can be formed on the photosensitive drum 1 than when the process speed is high.
- the image forming apparatus After setting the paper type and mode, the image forming apparatus forms an image according to the set conditions when the start button 101 is pressed. Note that a print command may be input from a terminal such as an external PC.
- FIG. 3 is a view for explaining a nip pre-exposure device for exposing a charging gap.
- the charging roller 2 charges the photosensitive drum 1 by applying a DC voltage from the power source S1.
- the power source S4 supplies power to the nip pre-exposure device 8 according to the control of the control circuit 200.
- the nip pre-exposure device 8 irradiates light on the upstream charging gap portion in the rotation direction of the photosensitive drum 1 according to the supplied power.
- the nip pre-exposure device 8 exposes an upstream charging gap portion in the rotational direction of the photosensitive drum 1 from the nip portion of the photosensitive drum 1 and the charging roller 2, and neutralizes the image forming area in the longitudinal direction of the photosensitive drum 1.
- the nip pre-exposure device 8 is an LED (Light Emitting Diode) having a peak wavelength of 660 ( ⁇ 10) nm at room temperature (20 ° C.). It is known that the wavelength of emitted light varies depending on the temperature of the material and the applied current.
- an LED having a forward voltage drop of 1.4 V, a maximum rated output of 3 mW, a maximum operating current of 95 mA, a maximum output of 2.1 mW, and a luminous efficiency of 39 lm / W was used.
- a plurality of such LEDs are juxtaposed, and a voltage obtained by applying PWM (Pulse Width Modulation) with an LED driver to control the light amount of the nip pre-exposure device.
- the upstream charging gap portion refers to a small area where discharge is performed between the charging roller 2 and the photosensitive drum 1.
- the upstream charging gap A1 is a region 1 mm away from the nip portion between the photosensitive drum 1 and the charging roller 2 upstream in the rotation direction of the photosensitive drum 1.
- the downstream charging gap A2 is a region 1 mm away from the nip portion between the photosensitive drum 1 and the charging roller 2 on the downstream side in the rotation direction of the photosensitive drum 1.
- the control circuit 200 as a control unit includes a CPU, a RAM, and the like, and controls each unit of the image forming apparatus in accordance with an image forming signal input from an operation terminal 100 as an operation unit or an external terminal such as a PC. For example, the control circuit 200 acquires information on a sheet designated by the operation panel 100 and determines the process speed accordingly. Further, the image forming conditions of each image forming unit are controlled according to the process speed. As a specific example, the control circuit 200 can control the power supplied from the power source S4 to the pre-nip exposure apparatus 8. The nip pre-exposure device 8 can output light of 0 to 15 lx ⁇ s per unit time according to the power supplied from the power source S4 as the power supply means.
- the amount of light was measured using an illuminance meter conforming to JIS C 1609-1 (revised in 2006) general type AA.
- the illuminance meter measures the amount of light in the visible light region (420-700 nm). Therefore, for example, a photodiode may be used to detect a change in the amount of light outside the visible light region. In order to detect a change in the amount of light at a wavelength at which the charge on the surface of the photoreceptor can be removed, it is preferable to detect with a photodiode light that has passed through an optical filter that cuts the wavelength at which the sensitivity of the photoreceptor is low. .
- FIG. 8 is a schematic diagram for explaining a peeling discharge phenomenon that occurs on the photosensitive drum 1 when the upstream charging gap portion in the rotation direction of the photosensitive drum 1 is exposed with a constant light amount in order to suppress charging horizontal stripes. is there.
- FIG. 8A is a schematic diagram in which the upstream charging gap portion is exposed when the process speed is 210 mm / s.
- FIG. 8B is a schematic diagram in which, when the process speed is 105 mm / s, the upstream charging gap portion is exposed with the same light amount (7 lx ⁇ s) as when the process speed is 210 mm / s. .
- the charging roller 2 rotates in the forward direction with respect to the rotating photosensitive drum 1 to charge the photosensitive drum 1.
- the threshold value for starting discharge based on Paschen's law
- discharging is performed, so that the photosensitive drum 1 has a charging potential (Vd). Is charged.
- Vd charging potential
- the resistance of a part of the charging roller 2 is high or the part of the photosensitive drum 1 is thick, charging may not be completed uniformly in the upstream charging gap portion A1.
- a small discharge is generated in the downstream charging gap portion A2
- a charging lateral stripe is generated. Therefore, as shown in FIG.
- the photosensitive member by exposing the upstream charging gap portion A1, the photosensitive member is charged in the downstream charging gap portion to suppress the occurrence of charging lateral stripes.
- the charged photosensitive drum 1 is neutralized by the laser light L from the pre-nip exposure device 8 in the upstream charging gap A1. Therefore, the photosensitive drum 1 is charged in the downstream charging gap portion A2. As a result, it is difficult to generate a minute discharge in the downstream charging gap portion A2, and charging horizontal streaks can be suppressed.
- the image forming apparatus controls the light amount of the nip pre-exposure device to be adjusted according to the process speed.
- the control circuit 200 changes the process speed based on the sheet information set in the operation unit 100. As described above, when the upstream charging gap portion is exposed with a constant light amount regardless of the process speed, a charging horizontal stripe is generated. For this reason, the amount of light irradiated to the charging gap was changed for each process speed, and image defects caused by charged horizontal stripes generated in the printed matter output at that time were evaluated.
- Table 1 is a table summarizing evaluations for printed matter output when the exposure amount is changed when the process speed is 210 mm / s (first speed) and 105 mm / s (second speed).
- the charging horizontal streaks appear as streaks in the direction parallel to the charging roller 2 and appear remarkably when a halftone image is formed. For this reason, the printed material used was a halftone image (125 in 255 gradations) formed on the entire surface of the sheet.
- Table 1 “ ⁇ ” is shown when the output printed image is good, “ ⁇ ” when it is good, “ ⁇ ” when there is density unevenness, and “x” when there is density unevenness or unevenness in density. From Table 1, it can be seen that the slower the process speed, the more the amount of pre-nip exposure needs to be increased to suppress the charging lateral stripe.
- FIG. 4A is a graph showing the relationship between the nip pre-exposure amount and the direct current flowing between the photosensitive drum 1 and the charging roller 2.
- FIG. 4 (b) shows the photosensitivity when a full white image (0 in 255 gradations) is output to 10000 sheets (10K) of A4 size paper with a direct current flowing between the photosensitive drum 1 and the charging roller 2.
- 3 is a graph showing a relationship of a scraping amount of the drum 1. Specifically, FIG.
- FIGS. 4A and 4B show a process speed of 210 mm / s, a charging potential of ⁇ 500 V, solid white paper durability, and a DC current value measured by installing an ammeter between the photosensitive drum 1 and the ground.
- the pre-nip exposure amount when the amount of light applied to the charging gap (hereinafter referred to as the pre-nip exposure amount) is increased, the amount of abrasion of the photosensitive drum 1 is increased.
- the pre-nip exposure amount increases, the charge removal amount in the upstream charging gap portion between the photosensitive drum 1 and the charging roller 2 increases. Therefore, the amount of re-discharge for recharging the photosensitive drum 1 from the charging roller 2 increases.
- the life of the photosensitive drum 1 is deteriorated. To do. Therefore, in order to suppress the charging horizontal streak and prolong the life of the photosensitive drum 1, it is desirable to perform the nip pre-exposure with a light amount corresponding to the process speed.
- FIG. 5 is a flowchart for explaining the operation of the image forming apparatus according to this embodiment.
- the CPU in the control circuit controls the image forming apparatus so as to operate as in the flowchart shown in FIG. 5 according to a program stored in the ROM.
- image forming conditions are changed according to the type of sheet on which an image is formed. It is assumed that the user specifies the type of sheet on which an image is to be formed using the operation panel.
- the control circuit 200 as a control means is a step for acquiring the type of sheet on which an image is formed.
- the control circuit 200 acquires the sheet type set on the operation panel 100.
- Step S102 is a step for changing processing according to the type of sheet on which an image is formed. If the type of sheet on which the image acquired in S101 is formed is plain paper, the control circuit 200 executes the process of S103. If the type of sheet on which the image acquired in S101 is formed is thick paper, the control circuit 200 executes the process of S104.
- S103 is a step for setting image forming conditions when an image is formed on plain paper.
- the control circuit 200 sets a process speed for forming an image on plain paper to 210 mm / s and an exposure amount before nip to 7 lx ⁇ s (first light amount).
- S104 is a step for setting image forming conditions when an image is formed on thick paper.
- the control circuit 200 sets the process speed for forming an image on thick paper to 105 mm / s and the exposure amount before nip to 15 lx ⁇ s (second light amount).
- the control circuit 200 controls the image forming apparatus in accordance with the image forming conditions set in S103 or S104. Specifically, during image formation for forming an image on a sheet, the control circuit 200 rotationally drives the photosensitive drum 1 and the like so as to reach a set process speed. Further, the nip pre-exposure device 8 is controlled to expose with a predetermined light amount so that a predetermined charging bias is applied to the charging roller 2.
- the control circuit 200 changes the exposure amount before nip according to the process speed. That is, as described above, when the process speed is slow, the exposure amount before nip is increased. As a result, the occurrence of lateral charging streaks that occur when the photosensitive drum 1 is charged by the charging roller 2 is suppressed. That is, even if the process speed varies depending on the type of sheet on which an image is formed, the occurrence of image defects due to charged horizontal stripes can be suppressed.
- the nip pre-exposure is preferably performed when the photosensitive drum of a portion where an electrostatic latent image corresponding to an image formed on the sheet is formed on the photosensitive drum is charged.
- the amount of light applied to the upstream charging gap portion by the nip pre-exposure device 8 is changed by changing the power supplied from the power source S4 to the nip pre-exposure device 8.
- the amount of light applied to the upstream charging gap portion may be changed by changing the distance between the nip pre-exposure device and the upstream charging gap portion. That is, when the process speed is slow, the light amount irradiated to the upstream charging gap portion may be increased by bringing the nip pre-exposure device 8 closer to the upstream charging gap portion than when the process speed is fast.
- a deflecting plate that can adjust the light emitted from the pre-nip exposure device 8 to the upstream charging gap portion may be provided.
- the amount of light applied to the upstream charging gap is adjusted by a reflecting mirror as a reflecting member.
- the reflection mirror corresponds to the irradiation unit.
- a configuration is adopted in which a light source for pre-exposure for removing residual charges remaining on the photosensitive drum after transfer and a light source for pre-nip exposure are used in order to suppress the occurrence of charged horizontal stripes.
- a light source for removing residual charges on the photosensitive drum and a light source for pre-nip exposure may be provided.
- the light source for removing the residual charge on the photosensitive drum corresponds to the charge eliminating means.
- the amount of light necessary for the charging nip is smaller as the process speed is faster.
- the light from one light source is distributed to the upstream charging gap portion and the pre-exposure portion, thereby suppressing the removal of residual charges and the occurrence of charging horizontal stripes.
- a configuration for removing residual charges and suppressing charging lateral stripes will be described below.
- FIG. 6 is a diagram for explaining the configuration of an apparatus for exposing the charging gap and the pre-exposure unit.
- the power source S4 supplies a constant power to the nip pre-exposure device 8. Accordingly, the nip pre-exposure device 8 continues to output a constant light amount.
- a nip pre-exposure device 8 as a light source is provided so as to face the surface of the photosensitive drum 1, and a reflection mirror 21 as an irradiating means is disposed between the nip pre-exposure device 8 and the photosensitive drum 1.
- the position of the reflection mirror 21 as the irradiation means is finely adjusted by a motor.
- the reflection mirror 21 reflects the laser beam L output from the nip pre-exposure device 8 to guide the laser beam L1 to the upstream charging gap portion.
- the laser beam L2 that is not reflected by the reflection mirror 21 is applied to the photosensitive drum 1.
- the laser beam L2 reflected by the reflecting mirror 21 neutralizes the image forming area in the longitudinal direction of the photosensitive drum 1.
- the power source S4 supplies power so that the nip pre-exposure device 8 emits light at 20 lx ⁇ s.
- the position of the reflecting mirror 21 is adjusted by the motor 20, and when the reflecting mirror 21 is at the position (i), the laser beam L1 is 7 lx ⁇ s (first light amount), and the laser beam L2 is 13 lx ⁇ s. (Third light quantity).
- the laser light L1 is 15 lx ⁇ s (second light amount), and the laser light L2 is 5 lx ⁇ s (fourth light amount).
- a pre-exposure device as a removing means for removing residual charges may be provided separately from the inter-nip exposure device.
- the control circuit as the control unit controls the pre-exposure device to remove residual charges on the photosensitive drum at 13 lx ⁇ s (third light amount).
- the control circuit controls the pre-exposure device to remove the residual charge on the photosensitive drum at 5 lx ⁇ s (fourth light amount) when the process speed is 105 mm / s.
- the photosensitive drum 1 is irradiated with the laser beam L2 for neutralizing residual charges.
- the control circuit 200 includes a CPU, a RAM, and the like, and controls each unit of the image forming apparatus in accordance with an image forming signal input from an operation terminal 100 as an operation unit or an external terminal such as a PC.
- the motor 20 can move the reflecting mirror 21 to the position (i) or (ii) according to the input from the control circuit 200.
- FIG. 7 is a flowchart for explaining the operation of the image forming apparatus according to the present embodiment. In this embodiment, an example in which image forming conditions are changed according to the type of sheet on which an image is formed will be described.
- step S201 the control circuit 200 as a control unit is a step for acquiring the type of sheet on which an image is formed.
- the control circuit 200 acquires the sheet type set on the operation panel 100.
- Step S202 is a step for changing processing according to the type of sheet on which an image is formed. If the type of sheet forming the image acquired in S201 is plain paper, the control circuit 200 executes the process of S203. If the type of sheet on which the image acquired in S201 is formed is thick paper, the control circuit 200 executes the process of S204.
- S203 is a step for setting image forming conditions when an image is formed on plain paper. The control circuit 200 sets the process speed for forming an image on plain paper to 210 mm / s and the position of the reflection mirror 21 to be (i).
- S204 is a step for setting image forming conditions when an image is formed on thick paper.
- the control circuit 200 sets the process speed for forming an image on thick paper to 105 mm / s and the position of the reflection mirror 21 to (ii).
- the control circuit 200 controls the image forming apparatus in accordance with the image forming conditions set in S203 or S204. Specifically, the control circuit 200 rotationally drives the photosensitive drum 1 and the like so as to achieve a set process speed. Further, the motor 20 is controlled so that the reflection mirror 21 is in a predetermined position so that a predetermined charging bias is applied to the charging roller 2.
- the control circuit 200 changes the position of the reflecting mirror 21 according to the process speed.
- the process speed is slow, the nip pre-exposure amount is large and the pre-exposure amount is small.
- the control circuit 200 changes the position of the reflecting mirror 21 according to the process speed.
- the process speed is slow, the nip pre-exposure amount is large and the pre-exposure amount is small.
- a semi-transparent transmittance variable element (a mirror whose reflectance and transmittance can be changed by applying a voltage) may be used as a reflecting member capable of adjusting the amount of light reflected and transmitted. If a semi-transparent transmittance variable element is used instead of the reflecting mirror 21, the reflecting mirror 21 does not need to be moved. Therefore, it is possible to expose the upstream charging gap portion with higher accuracy than when the mirror is moved by the motor. Further, in the first and second embodiments, the case where the types of sheets on which an image is formed is two types of plain paper and cardboard has been described as an example.
- the image forming apparatus forms an image at a predetermined process speed according to the type of sheet.
- LEDs are used for the nip pre-exposure device and the pre-exposure device, but other exposure devices such as a light irradiation device comprising a fuse lamp may be used. Further, exposure may be performed from the inside of the transparent photoreceptor to the upstream charging gap portion.
- the charging roller 2 as a flexible contact charging member has been described as an example.
- a conductive charging belt may be used as the charging member, or a conductive rubber blade that contacts the photoconductor at the edge portion to charge the photoconductor.
- the charging roller 2 as the charging member and the photosensitive drum 1 as the photosensitive member are in contact with each other, but a minute gap may be formed. In such a configuration, the distance between the photosensitive drum 1 and the charging roller 2 decreases toward the closest position between the charging roller 2 and the photosensitive drum 1 with respect to the rotation direction of the photosensitive drum 1.
- the rotatable drum-shaped photosensitive drum 1 is used.
- a movable belt-shaped photosensitive belt may be used as the photosensitive member.
- the upstream and downstream in the rotation direction of the photosensitive drum 1 correspond to the upstream and downstream in the movement direction of the photosensitive belt, respectively.
- the photosensitive member longitudinal image region in the upstream charging gap portion of the photosensitive drum 1 and the charging roller 2 is exposed. Good.
- an apparatus for forming an image on a small-sized sheet and a large-sized sheet when the image is continuously formed on small-sized paper, unevenness in the scraping amount in the longitudinal direction of the photosensitive drum 1 occurs. Can be suppressed.
- the present invention can be similarly applied to an image forming apparatus having a so-called cleaner-less configuration in which cleaning is performed simultaneously with development using a developing device.
- Photosensitive drum photoconductor
- Charging roller Charging means, contact charging means
- Exposure device latent image forming means
- Exposure device latent image forming means
- Developing device Developing means
- Fixing device fixing means
- Nip pre-exposure device irradiation means
- S1 DC power source S4 power source
- Operation panel operation unit
- Control circuit control means
- Control means 21
- Reflection mirror reflection member, irradiation means, removal means
- Motor rotation mirror moving means
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Abstract
Description
図1は画像形成装置の全体構成を説明するための概略図である。図1の(a)に示すように、本実施例における画像形成装置はローラ帯電装置を用いて感光体ドラムを帯電させる電子写真方式の画像形成装置である。詳しくは、感光体ドラムに帯電ローラを接触させる接触帯電方式及びトナー像を形成したい領域に露光を行う反転現像方式を採用した最大A3サイズの紙に画像を形成することができるレーザビームプリンタである。ドラム形状の感光体である感光ドラム1は、本実施の形態では外径30mmの負帯電性の有機感光体(OPC)であり、駆動装置としてのモータ(不図示)からの駆動力を受けて回転する。ここで、普通紙に画像を形成する際には、感光ドラム1は210mm/sの周速度(以下、プロセススピードと呼ぶ)で、厚紙に画像を形成する際には、105mm/sの周速度で矢印方向(反時計方向)に回転駆動される。図1の(b)に示すように、感光ドラム1はアルミニウム製シリンダ(導電性ドラム基体)1aの表面に、光の干渉を抑え上層の接着性を向上させる下引き層1bと、光電荷発生層1cと、電荷輸送層1dの3層を下から順に塗布して構成されている。画像形成装置は、感光ドラム1の回転方向(反時計方向)に沿ってその周囲に帯電部材としての帯電ローラ2を接触させて、現像装置4、転写ローラ5、クリーニング装置7が配置されている。また、帯電ローラ2と現像装置4間の上方には潜像形成手段としての露光装置3が設置されている。感光ドラム1と転写ローラ5によって形成される転写部dの転写材搬送方向の下流側には、定着装置6が設置されている。以下に画像形成装置工程に沿って各構成について詳しく説明する。
感光ドラム1を帯電する帯電ローラ2は芯金2aの両端部をそれぞれ軸受け部材(不図示)により回転自在に保持されている。なお、帯電ローラ2は押し圧ばね2eによって感光ドラム1の中心方向に付勢して感光ドラム1の表面に対して所定の押圧力をもって圧接されており、感光ドラム1の回転駆動に従動して回転する。感光ドラム1と帯電ローラ2は接触して接触部を形成する。接触部から感光体の回転方向に、感光ドラム1と帯電ローラ2との間のギャップは広がっていく。ここで、感光ドラム1と帯電ローラ2との圧接部(接触部)を帯電ニップ部と呼ぶ。なお、圧接部の感光ドラム1の回転方向における上流側の微小空隙を上流側帯電ギャップ部A1と呼ぶ。同様に、圧接部の感光ドラム1の回転方向における下流側の微小空隙を下流側帯電ギャップ部A2と呼ぶ。感光ドラム1は圧接部を中心として上流側帯電ギャップ部A1及び下流側帯電ギャップ部A2において帯電される。感光ドラム1の帯電は、帯電ローラ2から感光ドラム1への放電によって行われる。そのため、放電が開始する閾値電圧以上の電圧を帯電ローラ2に印加する。本実施例において、帯電ローラ2に約-600V以上の電圧を印加すると感光体の表面電位が上昇を始める。約-600V以降、印加した電圧に対して略線形関係を保ちながら感光ドラム1の表面電位は上昇する。なお、本実施例の画像形成装置において、帯電ローラ2に-900Vを印加すると、感光ドラム1の表面は-300Vとなる。また、帯電ローラ2に-1100Vを印加すると、感光ドラム1の表面は-500Vとなる。以後、この閾値電圧(-600V)を放電開始電圧(帯電開始電圧)Vth(V)と呼ぶ。つまり、電子写真方式の画像形成プロセスにおいて、感光ドラム1の表面の電位をVd(V)(暗部電位)に帯電させるためには、帯電ローラ2にVd+Vth(V)を印加する必要がある。つまり、電源S1によってVd+Vth(V)の電圧が帯電ローラ2の芯金2aに印加されることによって、感光ドラム1の表面の電位がVd(V)となる。本実施例の画像形成装置の画像形成するために感光ドラム1を帯電したときの暗部電位Vdは-500Vとなるようにした。そのため、画像形成中は直流電源S1から帯電ローラ2に-1100Vの直流電圧(以下、DCバイアスと呼ぶ)が印加される。ここで、帯電ローラが感光ドラム1を放電によって帯電させる帯電ギャップ部の感光体ドラム方向の幅は帯電ローラに印加する電圧によって変わる。つまり、帯電ギャップ部とは、放電が発生することによって感光ドラムを帯電させる部分を指すのだが、電圧を印加したときに放電が発生するための微小空隙はパッシェン則に従って変化することが知られている。なお、感光ドラム1の回転を停止させた状態で帯電ローラ2に対してバイアスを印加させた時に、感光ドラム1が帯電している箇所が帯電ギャップ部に相当する。
帯電された感光ドラム1に潜像像を形成する潜像形成手段としての露光装置3について説明する。本実施例において、露光装置3は半導体レーザを用いたレーザビームスキャナである。露光装置3は不図示の画像読み取り装置等のホスト処理から入力される画像信号に対応して変調されたレーザ光を出力する。レーザ光は帯電された感光ドラム1の表面を露光位置bにおいて走査され、感光ドラム1上(感光体上)に入力された画像信号に応じた静電潜像を形成する。
続いて、現像工程について説明する。感光ドラム1上に形成された静電潜像は現像装置4によって現像される。本実施例における画像形成装置は2成分現像剤を用い、磁気ブラシによって静電像を現像する。本実施例では反転現像方式を採用した画像形成装置であるため、感光ドラム1表面の露光部分(明部)にトナーが付着して静電潜像が現像される。以下に現像装置4の構成について詳しく説明する。現像装置4は現像容器4aと現像容器の開口部に固定マグネットローラ4cを内包した回転自在な非磁性の現像スリーブ4bを備えている。現像容器4aに収容されたトナーとキャリア(磁性粒子)からなる現像剤4eを規制ブレード4dで一定の層厚に規制されることによって、現像スリーブ4b上に現像剤の薄層がコーティングされる。現像剤担持体としての現像スリーブ4bは内部のマグネットによってキャリアによって磁気穂を立たせてトナーを感光ドラム1と対向する現像部cへ搬送する。現像容器4a内の現像剤4eはトナーと磁性のキャリアとの混合物であり、2つの現像剤攪拌部材4f(攪拌スクリュー)の回転によって均一に攪拌されながら現像スリーブ4b側に搬送される。本実施の形態における磁性キャリアの抵抗は約1013Ωcm、粒径は約40μmである。トナーは磁性キャリアとの摺擦により負極性に摩擦帯電される。また、現像容器4a内のトナー濃度は、濃度センサ(不図示)によって検知される。また、トナーは濃度センサによって検知された検知情報に基づいて、現像容器内のトナー濃度を一定になるように、トナーホッパー4gから現像容器4aに補給される。現像スリーブ4bは現像部cにおいて感光ドラム1との最近接距離を300μmに保持して感光ドラム1に近接して対向するように設けられる。また、現像スリーブ4bは現像部cにおいて感光ドラム1の回転方向(反時計方向)とは逆方向に回転駆動される。また、現像スリーブ4bは、電源S2から、所定の現像バイアスが印加される。本実施例において、現像スリーブ4bには直流電圧(Vdc)と交流電圧(Vac)とを重畳した現像バイアスが印加される。具体的には、交流電圧の周波数は8kHz、直流電圧は-320V、交流電圧のピーク間電圧Vppは1800Vである。
現像工程によって感光ドラム1に形成されたトナー像は転写工程においてシートに転写される。転写ローラ5は感光ドラム1に所定の押圧力をもって当接して転写部dを形成する。また、転写ローラ5には電源S3から転写バイアス(トナーの正規帯電極性である負極性とは逆極性である正極性の転写バイアス;本実施の形態では+500V)が印加される。これによって、感光ドラム1表面のトナー像は転写部dに搬送されるシートに転写される。感光ドラム1からシートに転写されなかったトナーはクリーニング装置7によって清掃される。本実施例においてクリーニング装置7はクリーニングブレード7aを備える。感光体ドラム1に付着している転写残トナーはクリーニングブレード7aにより摺擦されることによって除去される。なお、図1の(a)中の符番eはクリーニングブレード7aの感光体ドラム面当接部を表す。
続いて、転写部dにおいてシートに転写されたトナー像を定着する定着工程について説明する。シートにトナー像を定着する定着装置6は回転自在な定着ローラ6aと加圧ローラ6b備える。定着ローラ6aと加圧ローラ6bによって形成される定着ニップ部において、定着装置6はシートを狭持搬送しながらシートに転写されたトナー像を加熱加圧して定着する。本実施例において、シートの材質、厚さ、坪量等に応じて、定着ローラ6aと加圧ローラ6bの回転速度は制御回路によって制御される。具体的には、厚紙(坪量101~200g/m2)に画像を定着する際には、プロセススピードが105mm/sになるように回転する。また、普通紙(坪量50~100g/m2)に画像を定着する際には、プロセススピードが210mm/sになるように回転する。
続いて、画像形成装置における操作パネル部について説明する。図4は操作パネルを説明するための図である。図4の(a)は操作パネル100の外観を説明するための図である。操作パネル100は設定された情報に基づき画像形成を画像形成装置に実行させるためのスタートボタン101を備える。また、操作パネル100はタッチパネル式のディスプレイ102を備える。ディスプレイ102には図2の(b)に示すような画面が表示される。ユーザはディスプレイ102に表示されたボタンを選択することによって、画像形成を行う際の各種設定を行うことができる。本実施例ではとりわけ、画像を形成するシートの種類の設定及び画質優先モードについて詳しく説明する。図2の(b)の符番103は画像を形成するシートの種類を設定するためのボタンである。符番103が選択されると、図2の(c)の画面がディスプレイ102に表示される。図2の(c)には画像形成に用いられるシートの一覧が表示される。画像形成に用いられるシートの種類に応じて、ユーザは普通紙104、厚紙105、コート紙等のいずれかを選択することができる。前述の通り、普通紙104が選択された場合、プロセススピードは210mm/sに設定される。また、厚紙105が選択された場合、プロセススピードは105mm/sに設定される。コート紙とは、シートの表面に透明の樹脂によってコーティングすることによって表面の平滑度を向上させた光沢のあるシートである。コート紙に画像を形成する際も、厚紙と同様、プロセススピードは105mm/sに設定される。なお、シートの種類の設定はユーザが設定する場合に限るものではなく、センサ等を用いてシートの種類を判別してもよい。図2の(b)の符番104は高画質モードを指定するためのボタンである。このボタンは普通紙に画像を形成する場合においても、プロセススピードを105mm/sに変更する。プロセススピードが遅くなることによって、プロセススピードが速い場合よりも高解像度の静電像を感光ドラム1上に形成することができる。
以下に、帯電横スジを抑制するために光を照射する照射手段としてのニップ前露光装置について説明する。図3は帯電ギャップを露光するニップ前露光装置を説明するための図である。帯電ローラ2は電源S1によって直流電圧を印加されることによって、感光ドラム1を帯電する。また、電源S4は制御回路200の制御に従いニップ前露光装置8に電力を供給する。ニップ前露光装置8は供給された電力に応じて、感光ドラム1の回転方向の上流側帯電ギャップ部に光を照射する。詳しくは、ニップ前露光装置8は感光ドラム1と帯電ローラ2のニップ部から感光ドラム1の回転方向の上流側帯電ギャップ部に対して露光し、感光ドラム1の長手方向に画像形成領域を除電する。本実施例においてニップ前露光装置8は室温(20℃)においてピーク波長が660(±10)nmのLED(Light Emitting Diode)を使用した。なお、放出される光の波長は材料の温度及び印加電流に依存して変動することが知られている。本実施例において順方向降下電圧が1.4V、最大定格出力が3 mW、最大動作電流が95 mA、最大出力が2.1 mW、発光効率が39lm/WであるLEDを用いた。このようなLEDを複数個して並置し、これらをLEDドライバでPWM(Pulse Width Modulation)された電圧を印加することによって、ニップ前露光装置の光量を制御した。なお、上流側帯電ギャップ部は、帯電ローラ2と感光ドラム1との間において放電が行われるわずかな領域を指す。本実施例においては、上流側帯電ギャップA1は感光ドラム1と帯電ローラ2のニップ部から感光ドラム1の回転方向上流側に1mm離れた領域であった。同様に、下流側帯電ギャップA2は感光ドラム1と帯電ローラ2のニップ部から感光ドラム1の回転方向下流側に1mm離れた領域であった。
以下に、プロセススピードに依らず、ニップ前露光の光量を一定にした場合について説明する。図8は帯電横スジを抑制するために、一定の光量で感光ドラム1の回転方向の上流側帯電ギャップ部に露光した時の感光ドラム1に発生する剥離放電現象を説明するための模式図である。図8の(a)はプロセススピードが210mm/sの場合において、上流側帯電ギャップ部に露光した模式図である。また、図8の(b)はプロセススピードが105mm/sの場合において、プロセススピードが210mm/sの場合と同一の光量(7lx・s)で、上流側帯電ギャップ部に露光した模式図である。
制御回路200は操作部100において設定されたシートの情報等に基づきプロセススピードを変更する。前述のように、プロセススピードに関わらず上流側帯電ギャップ部に一定の光量で露光すると帯電横スジが発生する。そのため、プロセススピード毎に帯電ギャップに光を照射する光量を変化させ、その時に出力される印刷物に生じる帯電横スジに起因する画像不良について評価を行った。
以下に、ニップ前露光量と感光ドラム1の削れ量について説明する。図4の(a)はニップ前露光量と感光ドラム1と帯電ローラ2の間に流れる直流電流の関係を示すグラフである。また、図4の(b)は感光ドラム1と帯電ローラ2の間に流れる直流電流とA4サイズの用紙10000枚(10K)に全面ベタ白画像(255階調における0)を出力した際の感光ドラム1の削れ量の関係を示すグラフである。具体的には、図4はプロセススピードを210mm/s、帯電電位-500V、ベタ白通紙耐久、DC電流値は感光ドラム1とアースの間に電流計を設置して測定したものである。図4の(a)および(b)からも判るように、帯電ギャップに照射する光量(以下、ニップ前露光量と呼ぶ)を大きくすると感光ドラム1の削れ量が大きくなる。これはニップ前露光量が大きくなると、感光ドラム1と帯電ローラ2との上流帯電ギャップ部における除電量が多くなる。そのため、帯電ローラ2から感光ドラム1を再帯電するための再放電量が増えるためである。そのため、遅いプロセススピード(105mm/s)において感光ドラム1の帯電横スジを抑制するために要する光量(15lx・s)を速いプロセススピード(210mm/s)において照射すると、感光ドラム1の寿命が悪化する。そのため、帯電横スジを抑制して感光ドラム1の寿命を長持ちさせるためには、プロセススピードに応じた光量でニップ前露光を行うことが望ましい。
以下に、プロセススピードに応じてニップ前露光量を変化させる画像形成装置の動作についてフローチャートを用いて説明する。図5は本実施例に係る画像形成装置の動作を説明するためのフローチャートである。制御回路内部のCPUはROMに保存されているプログラムに従い画像形成装置を図5に記載のフローチャートのように動作するように制御する。本実施例においては画像を形成するシートの種類に応じて画像形成条件を変更する例について説明する。なお、ユーザが操作パネルによって画像を形成するシートの種類を指定しているものとする。
本実施例において、感光ドラム上の残留電荷の除去と帯電横スジを抑制するために、一定の光量で発光するニップ前露光装置とモータによって位置を微調整される反射ミラーとを用いた。図6は帯電ギャップと前露光部に露光する装置の構成を説明するための図である。本実施例において、電源S4は一定の電力をニップ前露光装置8に供給する。これにより、ニップ前露光装置8は一定の光量を出力しつづける。光源としてのニップ前露光装置8は感光ドラム1の表面に対向するように設けられ、ニップ前露光装置8と感光ドラム1との間には照射手段としての反射ミラー21が配置されている。
以下に、プロセススピードに応じて上流側帯電ギャップ部に照射される光量と感光ドラム上の残留電荷を除去するために前露光される光量とを調整する画像形成装置の動作についてフローチャートを用いて説明する。図7は本実施例に係る画像形成装置の動作を説明するためのフローチャートである。本実施例においては画像を形成するシートの種類に応じて画像形成条件を変更する例について説明する。
本実施例において、反射ミラー21の位置を調整することによって、残留電荷の除電と帯電横スジの発生を抑制した。しかしながら、光の反射量と透過量を調整できる反射部材としての半透鏡性透過率可変素子(電圧を印加することによって反射率と透過率が変わるミラー)を用いてもよい。反射ミラー21の変わりに半透鏡性透過率可変素子を用いれば、反射ミラー21を移動させなくともよい。そのため、モータによってミラーを移動させるよりも高い精度で上流側帯電ギャップ部に露光することができる。また、実施例1及び実施例2において、画像を形成するシートの種類が普通紙、厚紙の2種類である場合を例に挙げて説明した。しかしながら、他の紙種(コート紙、薄紙)や、他のメディア(OHT)等においてもプロセススピードが変化する限りにおいて同様の問題が発生することは言うまでも無い。なお、画像形成装置はシートの種類に応じて予め決められたプロセススピードで画像を形成する。また上記実施例では、ニップ前露光装置、前露光装置にLEDを採用したが、ヒューズランプからなる光照射装置などの他の露光装置を用いてもよい。また、透明の感光体の内部から上流側帯電ギャップ部に露光を行っても良い。実施例1及び2において、可撓性の接触帯電部材としての帯電ローラ2を例に挙げて説明した。しかし、上流側帯電ギャップ部の距離が減少、下流側帯電ギャップ部の距離が増加する限り、帯電部材と感光体との間の距離が線形的に増加しても、非線形的に増加しても同様な効果が期待できる。例えば、帯電部材として導電性の帯電ベルト、エッジ部で感光体に当接して感光体を帯電させる導電性のゴムブレード等を用いてもよい。なお、本実施例において、帯電部材としての帯電ローラ2と感光体としての感光ドラム1は接触していたが、微小のギャップを形成させても良い。このような構成においては、感光ドラム1と帯電ローラ2との距離は感光ドラム1の回転方向に対して帯電ローラ2と感光ドラム1の最近接位置に向かって減少する。さらに、本実施例においては、回転可能なドラム形状の感光ドラム1を用いたが、感光体として移動可能なベルト状の感光ベルトを用いてもよい。このとき、感光ドラム1の回転方向上流及び下流と感光ベルトの移動方向上流及び下流はそれぞれ対応するものとする。
2 帯電ローラ(帯電手段、接触帯電手段)
3 露光装置(潜像形成手段)
4 現像装置(現像手段)
6 定着装置(定着手段)
8 ニップ前露光装置(照射手段)
S1 DC電源
S4 電源
100 操作パネル(操作部)
200 制御回路(制御手段)
21 反射ミラー(反射部材、照射手段、除去手段)
20 モータ(反射ミラー移動手段)
Claims (2)
- 回転可能な感光体と、前記感光体と接触して前記感光体を帯電する帯電部材と、前記帯電部材に直流電圧を印加する電源と、前記帯電部材が前記感光体を帯電する帯電ギャップ部のうち、前記感光体の回転方向における上流側の帯電ギャップ部に光を照射する照射手段と、を有する画像形成装置であって、
前記感光体が第1の速度で回転するときは、前記上流側の帯電ギャップ部を第1の光量で照射するように、前記感光体が前記第1の速度よりも遅い第2の速度で回転するときは、前記上流側の帯電ギャップ部を前記第1の光量よりも多い第2の光量で照射するように、前記照射手段を制御する制御手段と、
を有することを特徴とする画像形成装置。 - 前記帯電部材によって帯電された前記感光体に潜像を形成する潜像形成手段と、前記感光体上に形成された潜像をトナーによって現像する現像装置と、前記感光体上に現像されたトナー像を被転写部材に転写する転写部材とを備え、トナー像が前記被転写部材に転写されてから前記上流側のギャップ部に移動する間の前記感光体の表面に光を照射して電荷を除去する除去手段とを有し、
前記制御手段は前記除去手段を、前記感光体が第1の速度で回転するときは、前記感光体の表面に第3の光量で照射するように、前記感光体が前記第1の速度よりも遅い第2の速度で回転するときは、前記感光体の表面に前記第3の光量よりも少ない第4の光量で照射するように制御することを特徴とする請求項1に記載の画像形成装置。
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JP2011530676A JP4927235B2 (ja) | 2009-09-10 | 2009-09-10 | 画像形成装置 |
KR1020117021356A KR101235706B1 (ko) | 2009-09-10 | 2009-09-10 | 화상 형성 장치 |
EP09849201.0A EP2477075A4 (en) | 2009-09-10 | 2009-09-10 | IMAGE FORMING DEVICE |
CN200980158144.7A CN102356358B (zh) | 2009-09-10 | 2009-09-10 | 图像形成装置 |
PCT/JP2009/065809 WO2011030421A1 (ja) | 2009-09-10 | 2009-09-10 | 画像形成装置 |
US12/875,595 US8412064B2 (en) | 2009-09-10 | 2010-09-03 | Image forming apparatus to control photosensitive member irradiation |
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JP2013088761A (ja) * | 2011-10-21 | 2013-05-13 | Oki Data Corp | 画像形成装置 |
JP2018004917A (ja) * | 2016-06-30 | 2018-01-11 | キヤノン株式会社 | 画像形成装置 |
JP2019028234A (ja) * | 2017-07-28 | 2019-02-21 | 株式会社リコー | 除電装置、除電方法、及び画像形成装置 |
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KR101235706B1 (ko) | 2013-02-21 |
JPWO2011030421A1 (ja) | 2013-02-04 |
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US8412064B2 (en) | 2013-04-02 |
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