JP2012163864A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus adopting a DC electrification system, which determines whether or not a nip pre-exposure is appropriately irradiated on the surface of a photoreceptor corresponding to a gap in the upstream side, and appropriately adjusts the nip pre-exposure.SOLUTION: An image forming apparatus 10 is constituted by comprising: irradiation state adjustment means 14 for adjusting a light irradiation state on a surface of a photo receptor 1 by irradiation means 8, by changing a relative position to the surface of the photoreceptor 1 of a part of the irradiation means 8, which emits light on the surface of the photoreceptor 1, the irradiation means 8 irradiating light on the surface of the photoreceptor 1 corresponding to a gap A1 in the upstream side; and control means 13 for controlling the adjustment of the irradiation state by the irradiation state adjustment means 14 using a direct current value detected by direct current detection means 12 due to the generation of electric discharge on the surface of the photoreceptor 1 irradiated by the irradiation means.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine using an electrophotographic system.

  Conventionally, in an electrophotographic image forming apparatus, as a method of charging the surface of an electrophotographic photosensitive member (photosensitive member), a high voltage is applied to a thin corona discharge wire, and the corona generated thereby is removed from the surface of the photosensitive member. A corona charging method is generally used in which charging is performed by acting on.

  In recent years, from the viewpoint of low-pressure process, low ozone generation amount, low cost, and the like, the following methods are becoming mainstream as methods for charging the surface of the photoreceptor. That is, a charging member such as a roller type or a blade type is brought close to or in contact with the surface of the photosensitive member, and a voltage is applied to the charging member, so that the discharge of the photosensitive member and the charging member causes discharge of the photosensitive member. This is a method of charging the surface (hereinafter referred to as “contact charging method”). In particular, a roller-type charging member can perform stable charging over a long period of time.

  The contact charging method includes a “DC charging method” in which only a DC voltage is applied to the charging member and an “AC charging method” in which a superimposed voltage of the DC voltage and the AC voltage is applied to the charging member.

  The AC charging method has an advantage that the surface of the photoreceptor can be uniformly charged by applying an oscillating voltage and alternately causing positive and negative discharges. However, the AC charging method increases the amount of discharge to the photosensitive member as compared with the DC charging method, so that it is easy to promote deterioration of the photosensitive member such as abrasion of the photosensitive member, and the life of the photosensitive member is likely to be shortened. In the AC charging method, an AC power source is required to superimpose an AC voltage on a DC voltage. For this reason, the AC charging method shortens the life of the photoconductor, which increases the running cost required for replacement of a process cartridge including the photoconductor, for example, and requires an AC power source to initialize the image forming apparatus. The cost may be high.

  On the other hand, the DC charging method has a smaller amount of discharge to the photoconductor than the AC charging method, so that the life of the photoconductor can be extended. For example, it is necessary to replace a process cartridge including the photoconductor. Running costs can be reduced. Further, since no AC power supply is required, the initial cost of the image forming apparatus can be suppressed.

  However, the DC charging method is inferior to the surface potential uniformity (charging uniformity) of the photoreceptor compared to the AC charging method. Therefore, in the DC charging method, for example, when forming a halftone image, a problem of image density unevenness due to non-uniformity of the surface potential of the photoconductor tends to occur.

  Further explanation will be given by taking as an example a system having a photosensitive drum that is a drum-type photosensitive member and a charging roller that is a charging member that is in contact with the photosensitive drum, and in the DC charging method, the longitudinal direction of the photosensitive drum ( The stripe-shaped image density unevenness in the direction orthogonal to the circumferential direction tends to be a problem.

  Here, the streak-like image density unevenness as described above is referred to as “charging horizontal streak”. A minute gap between the photosensitive member and the charging member is referred to as a “charging gap”. The charging gap is upstream of the moving direction of the surface (charged surface) of the photoconductor from the closest portion of the photoconductor and the charging member (the contact portion when the photoconductor and the charging member are in contact). Is called the “upstream gap”. Also, the charging gap is located downstream in the moving direction of the surface (charged surface) of the photoconductor from the closest portion between the photoconductor and the charging member (the contact portion when the photoconductor and the charging member are in contact). Is called the “downstream gap”.

  The charging horizontal streaks described above are considered to be caused by the occurrence of unstable minute discharge (such as peeling discharge) between the photosensitive drum charged in the upstream gap and the charging roller in the downstream gap. It is done. In particular, when uniform charging of the surface of the photosensitive drum is not completed in the upstream gap, it is considered that an unstable minute discharge occurs in the downstream gap and unevenness in the surface potential of the photosensitive drum occurs.

  Patent Document 1 discloses a configuration in which the surface of the photosensitive drum is uniformly charged in the downstream gap by irradiating the surface of the photosensitive drum with light in the upstream gap to neutralize the surface of the photosensitive drum. According to such a configuration, it is possible to suppress image defects due to non-uniformity of the surface potential of the photosensitive drum, such as the above-described charging stripes.

  That is, by irradiating the surface of the photosensitive drum corresponding to the upstream gap with light, the charge on the photosensitive drum is canceled in the upstream gap and the action of charging the surface of the photosensitive drum by the charging roller is biased to the downstream gap. Can be made. The irradiation of light on the surface of the photoconductor corresponding to the upstream gap in this way is called “nip pre-exposure”.

JP-A-5-341626

  However, it has been found that even when the light amount of the nip pre-exposure device that performs the nip pre-exposure is the same, the effect of suppressing the charging horizontal stripes may vary due to the nip pre-exposure.

  That is, even when the light amount of the nip pre-exposure device is the same, the nip pre-exposure does not reach the back of the upstream gap (the closest side of the photosensitive member to the charging member in the direction of movement of the photosensitive member surface). There is a case. In such a case, since the charge on the photosensitive drum cannot be completely canceled in the upstream gap, the charging roller can not fully bias the action of charging the surface of the photosensitive drum to the downstream gap, and charging horizontal streaks occur. There is.

  The upstream gap is a minute space between the photosensitive drum and the charging roller, and accuracy is required to appropriately irradiate light there. However, there has been no means for accurately determining whether or not the nip pre-exposure is effectively applied to this minute space.

  In particular, when the process cartridge including the photosensitive drum, the charging roller, or both is replaced with a new one, the nip pre-exposure is likely to deviate from a state where it is appropriately irradiated. For this reason, after the process cartridge is replaced, a problem that a charged horizontal stripe occurs on the image is likely to occur. Even when the photosensitive drum, the charging roller, or both of these can be replaced individually, the same problem is likely to occur after the replacement.

  By the way, in order to compensate for the irradiation accuracy of the nip pre-exposure, a method of irradiating light over a wide range on the photosensitive drum by extremely increasing the light amount of the nip pre-exposure device can be considered. However, according to such a method, when the nip pre-exposure is appropriately irradiated, the amount of repetition of static elimination and discharge in the upstream gap increases. Therefore, the amount of discharge between the photosensitive drum and the charging roller is excessively increased, and the outer layer of the photosensitive drum is likely to be deteriorated by discharge, and the amount that is rubbed and worn by a contact member such as a cleaner, so-called photosensitive member. There is a risk that the amount of shaving increases.

  Accordingly, an object of the present invention is to determine whether or not the nip pre-exposure is appropriately applied to the surface of the photoconductor corresponding to the upstream gap in the image forming apparatus employing the DC charging method, and appropriately It is an object of the present invention to provide an image forming apparatus that can be adjusted to the above.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to a movable photosensitive member and a charging member that charges the photosensitive member in contact with or in proximity to the photosensitive member, and the photosensitive member and the charging member in the moving direction of the photosensitive member. A gap is formed on the upstream side of the contact portion or the closest position with the member so that the distance from the photoconductor gradually decreases toward the contact portion or the closest position. A discharge is formed between the surface of the photoconductor and the surface of the photoconductor when a DC voltage is applied to form a gap on the downstream side where the distance from the photoconductor gradually increases as the distance from the contact portion or the closest position increases. A charging member for charging the photoconductor, a power source for applying a DC voltage to the charging member, an irradiating means for irradiating light on the surface of the photoconductor corresponding to the upstream gap, and the charging from the power source. DC voltage on member DC current detecting means for detecting a DC current flowing between the charging member and the photosensitive member during application, and a portion of the irradiating means that emits light toward the surface of the photosensitive member. An irradiation state adjusting means for adjusting a light irradiation state on the surface of the photoconductor by the irradiation means by changing a relative position with respect to the surface, and the discharge on the surface of the photoconductor irradiated with light by the irradiation means An image forming apparatus comprising: a control unit that controls adjustment of the irradiation state by the irradiation state adjustment unit using a direct current value detected by the DC current detection unit.

  According to the present invention, in an image forming apparatus employing a DC charging method, it is determined whether or not the nip pre-exposure is appropriately applied to the surface of the photoconductor corresponding to the upstream gap, and the adjustment is appropriately performed. can do.

1 is a schematic cross-sectional view of a main part of an image forming apparatus according to an embodiment of the present invention. 2 is a schematic cross-sectional view illustrating a layer configuration of a photosensitive drum and a charging roller of an image forming apparatus according to an embodiment of the present invention. FIG. FIG. 6 is an operation sequence diagram of the image forming apparatus according to the embodiment of the present invention. 1 is a block diagram of a charging bias application system in an image forming apparatus according to an embodiment of the present invention. It is a schematic diagram for demonstrating the structure of the irradiation state adjustment means of the image forming apparatus which concerns on one Example of this invention. FIG. 6 is a model diagram for explaining a relationship between a nip pre-exposure position of the image forming apparatus and a charge removal effect. It is a graph showing the relationship between the light amount of the nip pre-exposure device, the DC current value flowing from the charging roller to the photosensitive drum, and the amount of abrasion of the photosensitive drum. It is a flowchart figure of execution control of the pre-charging exposure adjustment process in the image forming apparatus which concerns on one Example of this invention. It is a flowchart figure of the nip pre-exposure adjustment process in the image forming apparatus which concerns on one Example of this invention. It is a block diagram of a charging bias application system in an image forming apparatus according to another embodiment of the present invention. It is a flowchart figure of execution control of the nip pre-exposure adjustment process in the image forming apparatus which concerns on the other Example of this invention. It is a block diagram of a charging bias application system in an image forming apparatus according to still another embodiment of the present invention. FIG. 6 is a schematic diagram of a nip pre-exposure device in an image forming apparatus according to still another embodiment of the present invention. It is a flowchart figure of the nip pre-exposure adjustment process in the image forming apparatus which concerns on other Example of this invention. It is explanatory drawing for demonstrating the generation | occurrence | production mechanism of a charging horizontal stripe. It is explanatory drawing for demonstrating the generation | occurrence | production mechanism of the effect of nip pre-exposure. It is a model figure for demonstrating the relationship between the position of a nip pre-exposure apparatus, and a static elimination effect. It is a schematic diagram for demonstrating the other example of a charging member.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
1. First, the overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described. FIG. 1 is a cross-sectional view schematically showing the overall configuration of the image forming apparatus 10 of the present embodiment.

  The image forming apparatus 10 of this embodiment is an electrophotographic laser beam printer that employs a contact charging method and a reverse development method. Further, the image forming apparatus 10 of this embodiment can form and output an image on the transfer material P having a maximum size of A3.

  The image forming apparatus 10 includes a photosensitive drum 1 that is a drum-type electrophotographic photosensitive member as an image carrier. The photosensitive drum 1 is rotationally driven in the direction of the arrow R1 shown. Around the photosensitive drum 1, the following means are arranged along the rotation direction (surface movement direction). First, a charging roller (roller charger) 2 which is a roller-type contact charging member as a charging unit. Next, there is a developing device 4 as a developing unit. Next, a transfer roller 5 which is a roller-type contact transfer member as a transfer unit. Next, there is a cleaning device 7 as a cleaning means. An exposure device 3 as an exposure unit (image writing unit) is installed above the charging roller 2 and the developing device 4 in the rotational direction of the photosensitive drum 1 in the drawing. Further, a fixing device 6 as a fixing unit is installed downstream of the contact portion between the photosensitive drum 1 and the transfer roller 5 in the conveyance direction of the transfer material P. Further, the image forming apparatus 10 includes a storage portion for the transfer material P (not shown), a supply portion for supplying the transfer material P from the storage portion to the contact portion between the photosensitive drum 1 and the transfer roller 5, and after passing through the fixing device 6. A discharge portion for discharging the transfer material P to the outside of the image forming apparatus 10 is provided.

  A contact portion between the charging roller 2 and the photosensitive drum 1 is referred to as a charging nip a. The exposure position of the photosensitive drum 1 by the exposure device 3 is called an exposure unit b. A facing position between a developing sleeve 4b (described later) of the developing device 4 and the photosensitive drum 1 is referred to as a developing unit c. A contact portion between the transfer roller 5 and the photosensitive drum 1 is referred to as a transfer nip d. Further, a contact portion between a cleaning blade 7a described later of the cleaning device 7 and the photosensitive drum 1 is referred to as a cleaning portion e. The charging nip a, the exposure part b, the developing part c, the transfer nip d, and the cleaning part e are arranged in this order in the rotation direction of the photosensitive drum 1.

  In the image forming process, first, the surface (surface to be charged) of the rotating photosensitive drum 1 is uniformly charged by the charging roller 2. Thereafter, the surface of the charged photosensitive drum 1 is scanned and exposed by the exposure device 3 in accordance with the image information. Thereby, an electrostatic latent image (electrostatic image) corresponding to the image information is formed on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is developed as a toner image by developer toner by the developing device 4. The toner image formed on the photosensitive drum 1 is electrostatically transferred by the action of the transfer roller 5 onto the transfer material P separately conveyed to the transfer nip d at the transfer nip d. The transfer material P onto which the toner image has been transferred is separated from the photosensitive drum 1 and conveyed to the fixing device 6. The fixing device 6 heats and pressurizes the transfer material P to fix the toner image thereon. Thereafter, the transfer material P is discharged from the image forming apparatus 10 as a printed material (image formed material).

  In this embodiment, the photosensitive drum 1 is a negatively chargeable organic photoreceptor (OPC) having an outer diameter of 30 mm. The photosensitive drum 1 is rotationally driven in a direction indicated by an arrow R1 by a drive motor (not shown) as a drive device (drive means) at a process speed (peripheral speed) of usually 210 mm / s. As shown in FIG. 2, the photosensitive drum 1 includes an undercoat layer 1 b that suppresses interference of light and improves the adhesion of the upper layer on the surface of an aluminum cylinder (conductive drum base) 1 a, The charge generation layer 1c and the charge transport layer 1d are applied in this order from the bottom.

  As shown in FIG. 2, the charging roller 2 is rotatably held at both ends in the longitudinal direction (rotation axis direction) of the cored bar 2a by bearing members (not shown), and is attached as an urging means. The biasing member 2 is biased toward the rotation center of the photosensitive drum 1 by a pressing spring 2e. As a result, the charging roller 2 is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force. The charging roller 2 is rotated in the direction of the arrow R2 in the figure following the rotation of the photosensitive drum 1.

  The charging roller 2 is connected to a charging power source T1 as a charging voltage application unit. In the charging step, a charging voltage (charging bias) under a predetermined condition is applied from the charging power source T1 to the cored bar 2a of the charging roller 2, so that the surface of the photosensitive drum 1 has a predetermined polarity (DC charging method). In this embodiment, the negative electrode is charged to a predetermined potential. In the rotational direction of the photosensitive drum 1, on the upstream side of the charging nip a, the distance between the photosensitive drum 1 and the charging roller 2 gradually decreases toward the charging nip a. In this embodiment, the minute gap on the upstream side of the charging nip a in the rotation direction of the photosensitive drum 1 is referred to as an upstream gap A1. Further, in the rotational direction of the photosensitive drum 1, on the downstream side of the charging nip a, the distance between the photosensitive drum 1 and the charging roller 2 gradually increases as the distance from the charging nip a increases. In this embodiment, the minute gap on the downstream side of the charging nip a in the rotation direction of the photosensitive drum 1 is referred to as a downstream gap A2. The surface of the photosensitive drum 1 is charged by passing through a region (charging portion) including the upstream gap A1 and the downstream gap A2 around the charging nip a in the rotation direction of the photosensitive drum 1. In particular, in this embodiment, as will be described later, the surface of the photosensitive drum 1 is uniformly charged to a desired surface potential mainly in the downstream gap A2.

  The charging process of the surface of the photosensitive drum 1 by the charging roller 2 is performed by discharging from the charging roller 2 to the photosensitive drum 1. Therefore, in order to start the charging process on the surface of the photosensitive drum 1, it is necessary to apply a voltage higher than a certain threshold voltage to the charging roller 2. In this embodiment, if a voltage of about −600 V or more is applied to the charging roller 2, the surface potential of the photosensitive drum 1 starts to rise, and thereafter, the surface potential of the photosensitive drum 1 linearly with a slope of 1 with respect to the applied voltage. Rises. For example, in this embodiment, a voltage of −1100 V may be applied in order to obtain a surface potential of −900 V and −500 V in order to obtain a surface potential of −300 V. This threshold voltage is called a discharge start voltage (charging start voltage) Vth. That is, in order to obtain the surface potential (dark portion potential) Vd of the photosensitive drum 1 required in the image forming process, a direct current voltage (DC voltage) equal to or higher than the dark portion potential Vd, Vd + Vth, is applied to the charging roller 2. It will be necessary.

  In the present embodiment, in the charging process, the charging voltage (charging) is applied to the cored bar 2a of the charging roller 2 from the charging power source T1 in order to uniformly charge the surface of the photosensitive drum 1 to the dark portion potential Vd of −500V. As a bias), a DC voltage of −1100 V is applied.

  In this embodiment, the length of the charging roller 2 in the longitudinal direction (rotation axis direction) is 320 mm. As shown in FIG. 2, the charging roller 2 has a three-layer configuration in which a lower layer 2b, an intermediate layer 2c, and a surface layer 2d are sequentially laminated from the bottom around a core metal (support member) 2a. The lower layer 2b is a foamed sponge layer for reducing charging noise. The surface layer 2d is a protective layer provided to prevent current leakage even if there is a defect such as a pinhole on the photosensitive drum 1.

More specifically, the specification of the charging roller 2 in the present embodiment is as follows.
Metal core 2a: Stainless steel round bar lower layer 2b with a diameter of 6 mm: Foamed EPDM with carbon dispersion, specific gravity 0.5 g / cm ³ , volume resistivity 10 ² to 10 ⁹ Ωcm, layer thickness 3.0 mm
Intermediate layer 2c: carbon-dispersed NBR rubber, volume resistivity 10 ² to 10 ⁵ Ωcm, layer thickness 700 μm
Surface layer 2d: tin oxide and carbon are dispersed in a resin resin of fluorine compound, volume resistivity 10 ⁷ to 10 ¹⁰ Ωcm, surface roughness (JIS standard 10-point average surface roughness Ra) 1.5 μm, layer thickness 10 μm
In the present embodiment, a laser beam scanner using a semiconductor laser is used as the exposure device 3. The exposure device 3 outputs a laser beam L modulated in accordance with an image signal input from an image reading device (not shown) or the like. Then, the exposure device 3 performs scanning exposure (image exposure) on the uniformly charged surface of the photosensitive drum 1 with the laser beam L in the exposure unit b. As a result, the absolute value of the potential of the portion irradiated with the laser beam on the surface of the photosensitive drum 1 is lowered, and an electrostatic latent image (electrostatic image) corresponding to the image information subjected to the scanning exposure is displayed on the surface of the photosensitive drum 1. ) Is formed.

  In this embodiment, the developing device 4 employs a two-component magnetic brush developing system that uses a two-component developer containing non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as a developer. In the present embodiment, the developing device 4 develops the electrostatic latent image by the reversal development method. That is, the toner charged to the same polarity as the charged polarity of the photosensitive drum 1 is applied to the exposed portion (bright portion) of the surface of the photosensitive drum 1 where the absolute value of the potential has been lowered by being exposed after being uniformly charged. By attaching, the electrostatic latent image on the photosensitive drum 1 is developed.

  The developing device 4 includes a developing container 4a that contains a two-component developer 4e. A developing sleeve 4b as a developer carrying member is rotatably provided in the developing container 4a so that a part of the developing container 4a is exposed to the outside from an opening provided at a position facing the photosensitive drum 1 of the developing container 4a. . The developing sleeve 4b is made of a nonmagnetic material. The developing sleeve 4b is disposed to face the photosensitive drum 1 so that the closest distance to the photosensitive drum 1 is maintained at 300 μm. The developing sleeve 4b is in the direction indicated by the arrow R4 in the drawing so that the moving direction of the surface of the developing portion c, which is the facing portion between the developing sleeve 4b and the photosensitive drum 1, is opposite to the moving direction of the surface of the photosensitive drum 1. Is driven to rotate. The developing sleeve 4b accommodates therein a magnet roller 4c as magnetic field generating means, and this magnet roller 4c is fixedly disposed so as not to rotate with respect to the developing container 4a. A regulating blade 4d is provided as a regulating member that faces the developing sleeve 4a and regulates the amount of the two-component developer 4e carried on the developing sleeve 4b. Further, in the developing container 4a, two stirring screws 4f and 4f as developer stirring members are arranged. The two-component developer 4e, which is a mixture of toner and carrier in the developing container 4a, is circulated and conveyed in the developing container 4a while being stirred by the rotation of the stirring screws 4f and 4f.

  The two-component developer 4e in the developing container 4a conveyed to the developing sleeve 4b by the stirring screws 4f and 4f is carried on the developing sleeve 4 by the action of the magnet roller 4c, and has a predetermined thickness by the action of the regulating blade 4d. It is coated in a thin layer. Thereafter, the two-component developer 4e coated on the developing sleeve 4 is conveyed to the developing unit c facing the photosensitive drum 1. In the developing part c, the two-component developer 4e on the developing sleeve 4b rises by the action of the magnet roller 4c to form a magnetic brush. The developing sleeve 4b rotates so that the magnetic brush is brought close to or in contact with the surface of the photosensitive drum 1 (in this embodiment). In the developing unit c, toner is transferred from the magnetic brush to the photosensitive drum 1 according to the electrostatic latent image on the photosensitive drum 1 by the action of an electric field formed by a developing voltage described later, and the toner is transferred onto the photosensitive drum 1. An image is formed. Thereafter, the two-component developer 4e forming the magnetic brush that has passed through the developing section c is returned to the developing container 4a by the rotation of the developing sleeve 4b.

  A developing power source T2 as a developing voltage applying unit is connected to the developing sleeve 4b. In the developing process, a predetermined developing voltage (developing bias) is applied to the developing sleeve 4b from the developing power source T2. In the present embodiment, the developing voltage is an oscillating voltage obtained by superimposing a DC voltage (Vdc) and an AC voltage (Vac). More specifically, in this embodiment, it is an oscillating voltage obtained by superimposing a DC voltage of −320 V and an AC voltage having a frequency of 8 kHz and a peak-to-peak voltage of 1800 Vpp.

In this embodiment, the resistance of the carrier is about 10 ¹³ Ωcm and the particle size of the carrier is 40 μm. Further, the toner is triboelectrically charged to a negative polarity by rubbing with the carrier. Further, the toner concentration of the developer in the developing container 4a (the amount of toner contained in the two-component developer) is detected by a density sensor (not shown). Based on this detection information, an appropriate amount of toner is appropriately supplied from the toner hopper 4g to the developing container 4a, and the toner concentration of the developer in the developing container 4a is adjusted to be constant.

  The transfer roller 5 is pressed against the photosensitive drum 1 with a predetermined pressing force. The transfer roller 5 is connected to a transfer power source T3 as a transfer voltage application unit. In the transfer process, a predetermined transfer voltage (transfer bias) is applied to the transfer roller 5 from the transfer power source T3. In this embodiment, a DC voltage of +500 V having a polarity (positive polarity in this embodiment) opposite to the normal charging polarity of the toner (negative polarity in this embodiment) is applied as the transfer voltage. By the action of the electric field formed by this transfer voltage, the toner image on the photosensitive drum 1 is transferred to a transfer material P such as paper at a transfer nip d that is a contact portion between the photosensitive drum 1 and the transfer roller 5.

  The fixing device 6 includes a fixing roller 6a as a fixing member provided with a heating unit, and a pressure roller 6b as a pressure member pressed against the fixing roller 6b. The fixing roller 6a and the pressure roller 6b Is driven to rotate. The fixing device 6 heats and applies the toner image transferred to the surface of the transfer material P while nipping and transporting the transfer material P at the contact portion (fixing nip) between the fixing roller 6a and the pressure roller 6b. Press. As a result, the toner image on the transfer material P is fixed on the transfer material P. In this embodiment, the rotation speeds of the fixing roller 6a and the pressure roller 6b are variably controlled according to the material, thickness, and basis weight of the transfer material P.

  The cleaning device 7 includes a cleaning blade 7a as a cleaning member and a cleaning container 7b. The surface of the rotating photosensitive drum 1 is rubbed by the cleaning blade 7a in a cleaning portion e which is a contact portion between the cleaning blade 7a and the photosensitive drum 1. As a result, the toner (transfer residual toner) remaining on the surface of the photosensitive drum 1 after the transfer of the toner image to the transfer material P is removed from the surface of the photosensitive drum 1 and collected in the cleaning container 7b. Thus, the surface of the photosensitive drum 1 is cleaned and repeatedly used for image formation.

  In the present embodiment, the photosensitive drum 1 and the charging roller 2 as a process unit that acts on the photosensitive drum 1 are integrally formed into a cartridge by a frame (not shown), and the main body (device) of the image forming apparatus 10. The process cartridge is detachable from the main body. The process cartridge is not limited to the embodiment. The process cartridge is a cartridge in which a photosensitive member and at least one of a charging unit, a developing unit, and a cleaning unit serving as a processing unit that acts on the photosensitive unit are integrated into a cartridge and can be attached to and detached from the apparatus main body. is there.

  FIG. 3 is an operation sequence diagram of the image forming apparatus 10 according to the present exemplary embodiment.

a. Initial rotation operation (front multiple rotation process)
The initial rotation operation period is a start operation period (start operation period, warming period) when the image forming apparatus 10 is started. In the initial rotation operation period, when the power switch of the image forming apparatus 10 is turned on, the photosensitive drum 1 starts to rotate and various process devices such as raising the temperature of the fixing device 6 to a predetermined temperature. The predetermined preparatory operation is executed.

b. Print preparation rotation operation (pre-rotation process)
The print preparation rotation operation period is a preparation rotation operation period from when a print signal (image formation start instruction) is input to when the printing process is actually executed. When a print signal is input during the initial rotation operation, a print preparation rotation operation is executed following the initial rotation operation. When no print signal is input during the initial rotation operation, the drive of the main motor is temporarily stopped after the initial rotation operation is completed, the rotation drive of the photosensitive drum 1 is stopped, and the image forming apparatus 10 receives the print signal. Until it is kept in the standby (standby) state. When a print signal is input, a print preparation rotation operation is executed.

  In the present embodiment, a nip pre-exposure adjustment process is performed in the print preparation rotation operation period in order to appropriately perform the nip pre-exposure during the printing process. This nip pre-exposure adjustment step will be described in detail later.

c. Printing process (image forming process, image forming process)
When the predetermined printing preparation rotation operation is completed, the photosensitive drum 1 is continuously driven to rotate, and the printing process is started. In the printing process, a toner image is formed on the rotating photosensitive drum 1, the toner image on the photosensitive drum 1 is transferred to the transfer material P, and the toner image on the transfer material P is fixed to the transfer material P. Thus, the image formed product is output (printed out) from the image forming apparatus 10.

  In the continuous printing (continuous printing) mode, the above-described printing process is repeated for a predetermined set number of prints.

d. Inter-Paper Step Inter-Paper Step refers to the interval between the trailing edge of one transfer material P passing the transfer nip d and the leading edge of the next transfer material P reaching the transfer nip d in the continuous printing mode. This is a period during which the transfer material P is not present in the transfer nip d.

e. Post-rotation operation In the post-rotation operation period, after the printing process for the last transfer material P is completed, the main motor is continuously driven for a while to continue the rotational drive of the photosensitive drum 1, and a predetermined organizing (preparation) operation It is a period to execute.

f. Standby When the predetermined post-rotation operation is completed, the drive of the main motor is stopped, the rotation of the photosensitive drum 1 is stopped, and the image forming apparatus 10 is kept in the standby state until the next print signal is input. In the case of printing only one sheet, after the printing is completed, the image forming apparatus 10 enters a standby state through a post-rotation operation. When a print signal is input in the standby state, a print preparation rotation operation is executed.

  The printing process of c is the time of image formation, and the initial rotation operation of a, the printing preparation rotation operation of b, the paper gap process of d, and the post-rotation operation of e are non-image formation.

2. In this embodiment, a DC charging method is adopted as a charging method for the photosensitive drum 1. In the DC charging method, as described above, image defects such as charging horizontal stripes are likely to occur.

  Here, a mechanism for generating the charging lateral stripe will be further described. FIG. 15 is a schematic diagram for explaining a mechanism in which a charging horizontal stripe is generated.

  The photosensitive drum 1 and the charging roller 2 rotate so that the moving directions of the respective surfaces at the contact portion are the same direction. In the upstream gap A1, when the potential difference between the photosensitive drum 1 and the charging roller 2 exceeds the discharge start threshold based on the Paschen's rule, a discharge is performed between the photosensitive drum 1 and the charging roller 2, and the discharge is performed on the photosensitive drum 1. The surface of the photosensitive drum 1 is charged to the charging potential Vd by the charge. As shown in FIG. 15A, if the discharge is uniformly performed in the upstream gap A1, the image defect such as the charging horizontal stripe as described above does not occur. However, even if the electrical resistance of a part of the charging roller 2 is increased or the film thickness of the photosensitive drum 1 is increased, uniform charging of the surface of the photosensitive drum 1 may not be completed in the upstream gap A1. In this case, as shown in FIG. 15B, unstable minute discharge occurs in the downstream gap A2, unevenness occurs in the surface potential of the photosensitive drum 1 at that portion, and the above-described charging horizontal streak occurs. To do.

  This charged horizontal stripe can be suppressed by performing the pre-nip exposure as described above. FIG. 16 is a schematic diagram for explaining a mechanism for suppressing charging lateral stripes when nip pre-exposure is performed in which light is applied to the surface of the photosensitive drum 1 corresponding to the upstream gap A1.

  As shown in FIG. 16A, the charge once placed on the photosensitive drum 1 in the upstream gap A1 is canceled by the nip pre-exposure I, and as shown in FIG. The surface charging action is biased toward the downstream gap A2. This makes it difficult for unstable micro-discharge due to the downstream gap A2, which is the cause of the occurrence of charging horizontal streaks, to suppress the charging horizontal streaks.

3. Nip Pre-exposure Device The image forming apparatus 100 of the present embodiment includes a nip pre-exposure device 8 as an irradiation unit that performs nip pre-exposure in order to suppress charging horizontal stripes. The nip pre-exposure device 8 irradiates at least an image forming area on the surface of the photosensitive drum 1 corresponding to the upstream gap A1 in the longitudinal direction (rotational axis direction) of the photosensitive drum 1 to neutralize the portion. Is provided.

  In this embodiment, the maximum sheet passing width is A3 size, and the maximum width of the image forming area in the longitudinal direction of the photosensitive drum 1 is 297 mm. Therefore, in this embodiment, the nip pre-exposure device 8 is provided so as to irradiate light to a 297 mm region in the longitudinal direction of the photosensitive drum 1 on the surface of the photosensitive drum 1 corresponding to the upstream gap A1.

  In this example, as the nip pre-exposure device 8, an LED lamp having a peak wavelength of 660 nm as a light source and capable of adjusting the light amount to 5 to 15 (lx · s) was used. The illuminance of the nip pre-exposure device 8 can be adjusted by changing the bias applied from the nip pre-exposure power source T4 as power supply means for supplying power to the nip pre-exposure device 8.

  The upstream gap A <b> 1 is a slight region where discharge is performed between the charging roller 2 and the photosensitive drum 1. In this embodiment, the upstream gap A1 is a region from the end of the charging nip a upstream of the photosensitive drum 1 in the rotation direction to a position 1 mm away from the upstream in the same direction. Similarly, the downstream gap A <b> 2 is a slight region where discharge is performed between the charging roller 2 and the photosensitive drum 1. In the present embodiment, the downstream gap A2 is an area from the downstream end of the charging nip a in the rotation direction of the photosensitive drum 1 to a position 1 mm away from the downstream in the same direction.

4). FIG. 4 is a block circuit diagram for explaining a schematic control mode of the image forming apparatus 10 according to the present embodiment. The image forming apparatus 10 includes a charging power source T <b> 1 that is a voltage applying unit for the charging roller 2. The charging power source T1 has a direct current (DC) power source 11. By applying a DC voltage from the charging power source T1 to the charging roller 2 via the cored bar 2a, the peripheral surface of the rotating photosensitive drum 1 is charged to a predetermined potential. In addition, the image forming apparatus 10 includes a direct current detection circuit 12 as a direct current detection unit that measures a direct current value flowing through the charging roller 2 via the photosensitive drum 1. Information on the DC current value measured by the DC current detection circuit 12 is input from the DC voltage detection circuit 12 to the control circuit 13 as a control means. In this embodiment, the image forming apparatus 10 detects that the process cartridge has been replaced with a new one as a replacement detection unit for detecting that at least one of the photosensitive drum 1 and the charging roller 2 has been replaced. A new article detecting means 16 is provided. The new article detection means 16 is composed of, for example, a recognition means on the apparatus main body side and an instruction means on the process cartridge side, such as a push switch or a photo interrupter, and detects exchange based on the presence or absence of interaction between them. Is mentioned. Alternatively, the new article detection unit 16 includes a memory as a storage unit provided on the process cartridge side and a reading unit (or reading / writing unit) on the apparatus main body side, and stores specific information in the memory. There are those that detect exchanges based on the presence or absence and changes. In this embodiment, the new article detection means 16 is configured to include the memory and the reading means. When the process cartridge is mounted on the apparatus main body, the control circuit 13 can read the information stored in the memory on the process cartridge side by the reading means on the apparatus main body side, and determines whether or not the process cartridge is new. Judgment can be made.

  The control circuit 13 includes a CPU that is an arithmetic control unit, a ROM and a RAM that are storage units, and comprehensively controls each unit of the image forming apparatus 10. In particular, in the context of this embodiment, the control circuit 13 determines whether or not to perform a nip pre-exposure adjustment process, which will be described in detail later, during the pre-rotation process. In addition, the control circuit 13 controls the driving of the power sources T1, T3, and T4 in the nip pre-exposure adjustment step, and controls the irradiation state adjustment means for the nip pre-exposure based on the measurement result by the DC current detection circuit 12.

5). Variation in Effect of Nip Pre-exposure Next, with reference to FIG. 17, a phenomenon in which the effect on the charging lateral stripe is reduced even when the light amount (light emission amount) of the nip pre-exposure device 8 is the same will be described.

  FIG. 17A shows a state in which the pre-nip exposure is appropriately applied and the generation of the charging lateral stripe is effectively suppressed. In this case, the charge on the photosensitive drum 1 is neutralized by the pre-nip exposure I in the upstream gap A1 and the surface of the photosensitive drum 1 is charged by the charging roller 2 can be biased toward the downstream gap A2. . For this reason, it is possible to suppress the occurrence of charging horizontal streaks caused by unstable minute discharge in the downstream gap A2.

  On the other hand, in FIG. 17B, the light amount of the nip pre-exposure device 8 is the same as that in FIG. 17A, but the nip pre-exposure I is in the back of the upstream gap A1 (the rotation of the photosensitive drum 1). In this direction, the charging nip a side) is not reached. In this case, the charge on the photosensitive drum 1 cannot be canceled by the pre-nip exposure I in the upstream gap A1, and the charging roller 2 does not completely bias the action of charging the surface of the photosensitive drum 1 to the downstream gap A2. A few streaks occur.

  That is, when images are compared in a plurality of image forming apparatuses 10 having substantially the same configuration in which the light amount of the nip pre-exposure device 8 is the same, there may be variations in the effect of suppressing the charging horizontal stripe due to the nip pre-exposure. I found out.

  Table 1 shows the charge laterality generated when the light quantity of the nip pre-exposure device 8 is changed to 5 to 15 (lx · s) in the three image forming apparatuses A, B, and C configured according to the present embodiment. Indicates the level of streaks.

  The charging horizontal streak is printed on the halftone image (for example, a 128-level image of 256 gradations formed in the entire image forming area) on the printing direction (transfer material P conveyance direction, photosensitive drum 1 surface movement direction). This is a defective image in which a streak-like image perpendicular to the image is generated. The evaluation criteria for the level of the charged horizontal stripe are as follows. “◎” indicates that the obtained image is very good, “◯” indicates good, “Δ” indicates that the halftone image has slightly uneven density, and “×” indicates that the halftone image has uneven density and roughness.

  From Table 1, the image forming apparatus A has a charge horizontal stripe level of ◎ by setting the light quantity to 7 (lx · s), whereas the image forming apparatus B has a light quantity of 13 (lx · s) and an image. In the forming apparatus C, unless the light quantity was set to 15 (lx · s), the level of the charging lateral stripe did not become ◎.

  FIG. 6 shows the irradiation state of the nip pre-exposure I and the charge removal on the surface of the photosensitive drum 1 when the light amount of the nip pre-exposure device 8 is 9 (lx · s) in the three image forming apparatuses A, B, and C. The model of the relationship with an effect is shown typically.

  The image forming apparatus A shown in FIG. 6A is a model in which the charging lateral stripe is well suppressed. In this case, the nip pre-exposure I is irradiated to the depth of the upstream gap A1, and almost all charges on the photosensitive drum 1 are discharged by the upstream gap A1. Therefore, the action of charging the surface of the photosensitive drum 1 by the charging roller 2 can be sufficiently biased to the downstream gap A2.

  The image forming apparatus B in FIG. 6B is a model in which the pre-nip exposure I is irradiated from the photosensitive drum 1 slightly from the charging roller 2 in the upstream gap A1. In this case, the nip pre-exposure I is not irradiated to the depth of the upstream gap A1, and the charges on the photosensitive drum 1 are not completely discharged by the upstream gap A1. For this reason, the action of charging the surface of the photosensitive drum 1 by the charging roller 2 cannot be sufficiently biased to the downstream gap A2, and charging horizontal stripes are likely to occur.

  The image forming apparatus C in FIG. 6C is a model in which the nip pre-exposure I is irradiated from the charging roller 2 slightly from the photosensitive drum 1 in the upstream gap A1. Also in this case, the nip pre-exposure I is not irradiated to the depth of the upstream gap A1, and the charge on the photosensitive drum 1 is not completely discharged by the upstream gap A1. For this reason, the action of charging the surface of the photosensitive drum 1 by the charging roller 2 cannot be sufficiently biased to the downstream gap A2, and charging horizontal stripes are likely to occur.

  As described above, in order to suppress the charging horizontal stripe, it is important to irradiate the nip pre-exposure I to the depth of the upstream gap A1, and the positioning accuracy of the nip pre-exposure device 8 is required.

  Here, even when the position of the nip pre-exposure device 8 is deviated, the light amount of the nip pre-exposure device 8 is increased so that the charging lateral streaks can be suppressed, and the surface of the photosensitive drum 1 on the upstream side gap A1 is wider. A method of irradiating the nip pre-exposure I with a nip is considered.

  However, in such a method, there is a possibility that the amount of discharge between the photosensitive drum 1 and the charging roller 2 increases excessively and the amount of abrasion of the photosensitive drum 1 increases.

  FIG. 7 shows the relationship between the light amount of the nip pre-exposure device 8 and the DC current value flowing from the charging roller 2 to the photosensitive drum 1, and the light amount of the nip pre-exposure device 8 per 10K (10000 sheets). 3 is a graph showing a relationship with a shaving amount of the photosensitive drum 1; The data shown in FIG. 7 shows that the process speed is 210 mm / s, the charged potential (dark portion potential) Vd of the photosensitive drum 1 is −500 V, and the image density is solid white (256) in the image forming apparatus to be tested configured according to this embodiment. It was obtained by setting to 0 level of gradation. The DC current value was measured by installing an ammeter between the photosensitive drum 1 and the ground. The data of 0 light quantity was measured with the nip pre-exposure device 8 turned off.

  From FIG. 7, it can be seen that when the light amount of the nip pre-exposure device 8 is increased, the amount of abrasion of the photosensitive drum 1 is increased accordingly. Further, when the light amount of the nip pre-exposure device 8 is increased, the DC current value flowing from the charging roller 2 to the photosensitive drum 1 is also increased. The DC current value is increased in this way because, when the light amount of the nip pre-exposure device 8 is increased, the charge removal amount on the photosensitive drum 1 in the upstream gap A1 or the surface area of the photosensitive drum 1 to be discharged is increased. This is because the amount of re-discharge increases accordingly. As the amount of discharge increases in this way, the amount of abrasion of the photosensitive drum 1 also increases.

  That is, when the light amount of the nip pre-exposure device 8 is increased so that the charging lateral stripe can be suppressed even when the position of the nip pre-exposure device 8 is shifted as described above, the nip pre-exposure I is appropriately irradiated. Therefore, the amount of abrasion of the photosensitive drum 1 increases more than necessary. Therefore, the life of the photosensitive drum 1 is shortened.

  Accordingly, one of the objects of the present embodiment is to determine whether or not the nip pre-exposure is appropriately applied to the surface of the photoreceptor corresponding to the upstream gap in the image forming apparatus adopting the DC charging method. To adjust it appropriately. In this embodiment, the image forming apparatus adopting the DC charging method also suppresses streak-like image unevenness caused by the charging process of the photosensitive member, which is likely to occur particularly after the replacement of the photosensitive member or the charging member. Is one of the purposes.

6). In this embodiment, as shown in FIG. 4, the irradiation state of the pre-nip exposure I applied to the image forming apparatus 10 from the pre-nip exposure apparatus 8 to the surface of the photosensitive drum 1 corresponding to the upstream gap A1. Irradiation state adjusting means 14 for adjusting the above is provided. The irradiation state adjusting means 14 can adjust the angle and position of irradiating the surface of the photosensitive drum 1 corresponding to the upstream gap A1 with the nip pre-exposure I as the irradiation state. In other words, the irradiation state adjusting means 14 changes the relative position of at least a portion that emits light toward the surface of the photosensitive drum 1 corresponding to the upstream gap A1 in the nip pre-exposure device 8 with respect to the surface of the photosensitive drum 1. Can be adjusted.

  In this embodiment, as an example, the irradiation state adjusting unit 14 rotates the nip pre-exposure device 8 around a rotation axis along the longitudinal direction (substantially parallel to the longitudinal direction of the photosensitive drum 1). Then, the irradiation direction of the nip pre-exposure I is changed around the rotation axis along a plane substantially orthogonal to the longitudinal direction of the photosensitive drum 1. Thereby, the charge removal amount (exposure amount) on the photosensitive drum 1 in the upstream gap A1 or the surface area (exposure position, exposure range) of the photosensitive drum 1 to be discharged can be changed. Specifically, the irradiation state adjusting means 14 moves the pre-nip exposure device 8 in the clockwise direction around the rotation axis along a plane substantially orthogonal to the longitudinal direction of the photosensitive drum 1 ((i) in the drawing). ) Or counterclockwise (ii). When rotated in the direction (i) in the figure, the irradiation direction of the nip pre-exposure I can be changed from that of the photosensitive drum 1 in the upstream gap A1. Also, when the nip pre-exposure I is irradiated in the direction (ii) in the figure, the irradiation direction of the nip pre-exposure I can be changed from the charging roller 2 in the upstream gap A2. The operation of the irradiation state adjusting means 14 is controlled by the control circuit 13.

  In this embodiment, as shown in FIG. 5, the irradiation state adjusting means 14 includes a drive receiving gear 14a fixed to the rotation shaft of the nip pre-exposure device 8, a drive gear 14b meshing with the drive receiving gear 14a, and a drive And a motor M that is a driving source for transmitting a driving force to the gear 14b. Then, by controlling the rotation of the motor M, the drive receiving gear 14a is rotated via the drive gear 14b, whereby the nip exposure device 8 is rotated around the rotation axis. The drive receiving gear 14a is coupled to the rotating shaft of the nip pre-exposure device 8, and the tip of the nip pre-exposure device 8 is rotated as described above every time the drive receiving gear 14a rotates by one of its teeth. Rotate 2 ° around the axis. The tip of the nip pre-exposure device 8 is a portion where light is finally emitted toward the upstream gap A1 in the nip pre-exposure device 8.

  Here, the light amount of the nip pre-exposure device 8 is set to 7 (lx · s), and the angle of the nip pre-exposure device 8 when the charged horizontal stripe completely disappears is set to 0 °. The light amount 7 (lx · s) is the minimum light amount of the nip pre-exposure device 8 at which the charged horizontal stripe disappears completely. The nip pre-exposure device 8 can be rotated from the photosensitive drum 1 ((i) in the drawing) or from the charging roller 2 ((i) in the drawing) with the 0 ° position as a reference.

  Table 2 shows the level of the charged horizontal stripe when the angle of the nip pre-exposure device 8 is changed by the irradiation state adjusting means 14 in the image forming apparatus to be tested configured according to the present embodiment, and measured by the DC current detection circuit 12. The relationship with the measured direct current value is shown. The angle of the nip pre-exposure device 8 is + when it is rotated from the photosensitive drum 1 ((i) in the figure) with respect to the position of 0 °, and from the charging roller 2 ((ii) in the figure). The angle when rotated is shown as-The angle of the nip pre-exposure device 8 was changed by 2 °, and the method of evaluating the level of the charged horizontal stripe was the same as described above.

  From Table 2, it can be seen that when the light amount of the nip pre-exposure device 8 is the same, the level of the charging lateral stripe is very good when the direct current value measured by the direct current detection circuit 12 shows the maximum value. . This is because the nip pre-exposure I is irradiated to the depth of the upstream gap A1, and the area of the photosensitive drum 1 irradiated by the upstream gap A1 is widened, so that the area where static elimination and re-discharge are performed is widened. This indicates that the DC current value increases. That is, as the direct current value increases, the irradiation with the pre-nip exposure I in the upstream gap A1 is appropriately performed. Therefore, it can be determined from this direct current value whether or not the irradiation state of the nip pre-exposure I is appropriate.

  Next, the execution control of the pre-nip exposure adjustment process and the operation control of the pre-nip exposure adjustment process in this embodiment will be described with reference to FIGS.

  FIG. 8 shows a flowchart of the execution control of the nip pre-exposure adjustment process in this embodiment. In this embodiment, when at least one of the photosensitive drum 1 and the charging roller 2 is newly installed on the main body (apparatus main body) of the image forming apparatus 10, the nip pre-exposure adjustment step is executed. In other words, in this embodiment, the control unit 13 causes the irradiation state adjustment unit 14 to adjust the irradiation state when it is determined that at least one of the photoreceptor 1 or the charging member 2 is new. In this embodiment, as described above, the photosensitive drum 1 and the charging roller 2 are integrally configured as a process cartridge. In the present embodiment, as described above, the nip pre-exposure adjustment process is executed in the pre-rotation process. Therefore, in this embodiment, when the process cartridge is replaced, the nip pre-exposure adjustment step is executed in the pre-rotation step.

  Referring to FIG. 8, when a print signal is input (S101), control circuit 13 determines whether or not the process cartridge is new by new article detection means 16 (S102). If the control circuit 13 determines that the process cartridge is new in S102, the control circuit 13 executes the nip pre-exposure adjustment process during the pre-rotation process (S103), and executes the image forming process after the pre-rotation process is completed. (S104). On the other hand, if the control circuit 13 determines in S102 that the process cartridge is not new, the control circuit 13 executes a pre-rotation process in which the nip pre-exposure adjustment process is not performed (S105), and the image forming process is performed after the pre-rotation process is completed. Is executed (S104).

  FIG. 9 shows a flowchart of the nip pre-exposure adjustment process in this embodiment. In the present embodiment, roughly, while measuring the direct current value Ia by the current detection circuit 12, the angle of the nip pre-exposure device 8 is changed by the irradiation state adjusting means 14, and the absolute value of the direct current value Ia is maximized. Find the angle that will be.

  Referring to FIG. 9, when the nip pre-exposure adjustment step is started, first, the control circuit 13 sets the position of the nip pre-exposure device 8 to the initial position (S201). The initial position is not limited, but can be the maximum value or the minimum value of the range in which the angle of the nip pre-exposure device 8 is changed in the pre-nip exposure process. For example, in this embodiment, the position is changed in a range of ± 12 ° with respect to the 0 ° position, which is an appropriate position of the nip pre-exposure device 8 according to the device design. In this case, the initial position is a position of + 12 ° or −12 °.

  Next, the control circuit 13 turns on a predetermined charging bias, transfer bias, and nip pre-exposure, respectively (S202). In this embodiment, in the nip pre-exposure adjustment process, in order to set the surface potential of the photosensitive drum 1 after the charging process (before reaching the transfer nip) to −500 V, which is the same as that during normal image formation, a charging bias of −1100 V is used. Was applied. In the nip pre-exposure adjustment step, the transfer bias was + 500V. In the nip pre-exposure adjustment step, the light amount of the nip pre-exposure device 8 is 7 (lx · s). Next, the control circuit 13 detects the direct current value Ia by the current detection circuit 12 (S203). Next, the control circuit 13 determines whether or not the measurement of the DC current value Ia by the current detection circuit 12 has been completed for all the variable positions within the angle change range of the nip pre-exposure device 8 (S204). If it is determined in S204 that the measurement has not been completed for all the variable positions, the control circuit 13 sends a signal to the irradiation state adjusting means 14 to change the angle of the nip pre-exposure device 8 (S205). In this embodiment, the angle of the nip pre-exposure device 8 is changed by 2 °. Thereafter, the control circuit 13 changes the angle of the nip pre-exposure device 8 and measures the DC current value Ia by the current detection circuit 12 until it is determined in S204 that the measurement of the DC voltage value Ia has been completed for all the variable positions. repeat.

  Note that the DC voltage values Ia measured corresponding to the respective angles of the nip pre-exposure device 8 are respectively associated with the angles of the nip pre-exposure device 8 and stored in the storage means provided in the control circuit 13. The direct current values Ia corresponding to the respective angles of the nip pre-exposure device 8 are obtained during the occurrence of discharge on the surface of the photosensitive drum 1 irradiated with light from the nip pre-exposure device 8 after the angle change. taking measurement.

  Next, when the control circuit 13 determines in S204 that the measurement has been completed for all the variable positions, the angle of the nip pre-exposure device 8 when the absolute value of the measured DC current value Ia is the maximum value is determined. Determine (S206). At this time, the control circuit 13 changes the angle of the nip pre-exposure device 8 to the determined angle by the irradiation state adjusting unit 14 as necessary. In this embodiment, when the absolute value of the direct current value Ia is the maximum value, the direct current value is −60 μA. When there are a plurality of angles of the nip pre-exposure device 8 in which the absolute value of the direct current value Ia has the maximum value, any one of the angles may be selected.

  Thereafter, the control circuit 13 completes the pre-rotation process including the nip pre-exposure adjustment process, and proceeds to an image forming operation (S104 in FIG. 8).

  In this embodiment, the angle of the nip pre-exposure device 8 at which the measured DC voltage value Ia becomes the maximum value is searched for, but the present invention is not limited to this mode. For example, the maximum absolute value of the direct current value Ia, which is measured when the angle of the nip pre-exposure device 8 is appropriate according to the device design, can be set in advance as a reference value. In the nip pre-exposure adjustment step, the angle of the nip pre-exposure device 8 is changed while measuring the direct current value Ia. Then, the measured DC voltage value Ia is compared with the reference value, and the measured DC current value Ia is the same value as the reference value or before the nip when the value is within a predetermined range with respect to the reference value. The angle of the exposure device 8 is searched.

  As described above, in this embodiment, the image forming apparatus 10 applies the DC voltage to the movable photosensitive member 1, the charging member 2 that contacts the photosensitive member 1 and charges the photosensitive member 1, and the charging member 2. And a power source T1. The charging member 2 has a gap in which the distance between the photosensitive member 1 and the photosensitive member 1 gradually decreases toward the contact portion a on the upstream side of the contact portion a between the photosensitive member 1 and the charging member 2 in the moving direction of the photosensitive member 1. A1 is formed. In addition, the charging member 2 forms a gap A2 in which the distance between the charging member 2 and the photosensitive member 1 gradually increases as the distance from the charging portion 2 decreases away from the contact portion a. The charging member 2 charges the photosensitive member 1 by a discharge generated between the charging member 2 and the surface of the photosensitive member 1 when a DC voltage is applied. In addition, the image forming apparatus 10 includes an irradiation unit 8 that irradiates light on the surface of the photosensitive member 1 corresponding to the upstream gap A1, and the charging member 2 when a DC voltage is applied to the charging member 2 from the power source T1. And a direct current detection means 12 for detecting a direct current flowing between the photosensitive member 1 and the photosensitive member 1. In addition, the image forming apparatus 10 changes the relative position of the portion of the irradiating unit 8 that emits light toward the surface of the photosensitive member 1 with respect to the surface of the photosensitive member 1, and applies the irradiation unit 8 to the surface of the photosensitive member 1. It has the irradiation state adjustment means 14 which adjusts the irradiation state of light. Further, the image forming apparatus 10 uses the direct current value detected by the direct current detection means 12 when a discharge occurs on the surface of the photoreceptor 1 irradiated with light by the irradiation means 8, and the irradiation state adjustment means 14 performs irradiation. Control means 13 for controlling state adjustment is provided. In the present embodiment, the control unit 13 controls the adjustment of the irradiation state by the irradiation state adjustment unit 14 so that the detected direct current value becomes the maximum value.

  As described above, in this embodiment, the irradiation state of the nip pre-exposure I with respect to the upstream gap A1 is adjusted so that the absolute value of the DC current value Ia flowing between the photosensitive drum 1 and the charging roller 2 shows the maximum value. Thereby, for example, even when the irradiation state of the nip pre-exposure I such as replacement of the photosensitive drum 1 or the charging roller 2 is easily deviated from an appropriate state, the irradiation state of the nip pre-exposure I is adjusted to an appropriate state. can do. Therefore, even when the DC charging method, which is more advantageous than the AC charging method, is adopted, it is possible to prevent the occurrence of charging horizontal streaks due to, for example, replacement of the photosensitive drum or the charging roller 2 and the like. Images can be maintained.

Example 2
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Accordingly, elements having the same functions or configurations as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In Example 1, when at least one of the photosensitive drum 1 and the charging roller 2 was newly installed in the main body (apparatus main body) of the image forming apparatus 10, the nip pre-exposure adjustment process was executed.

  In addition to the initial state after the installation of the photosensitive drum 1 and the charging roller 2 as in the first embodiment, for example, during use of the image forming apparatus 10, vibration due to the photosensitive drum 1, the charging roller 2, or other driving members is generated. By continuing, the irradiation state of the nip pre-exposure I may change. For example, the irradiation state of the nip pre-exposure I may change because the position of the nip pre-exposure device 8 is gradually shifted due to the vibration.

  Therefore, in this embodiment, the pre-nip exposure adjustment process is executed at a predetermined timing other than the initial state after the installation of the photosensitive drum 1 and the charging roller 2 as in the first embodiment. In addition to executing the pre-nip exposure adjustment process in the initial state after the installation of the photosensitive drum 1 and the charging roller 2 as in the first embodiment, the pre-nip exposure adjustment process is executed at a predetermined timing in this embodiment. can do.

  FIG. 10 is a block circuit diagram for explaining a schematic control mode of the image forming apparatus 10 according to the present embodiment. The control mode in the present embodiment is the same as that in the first embodiment shown in FIG. 4, but in this embodiment, the image forming apparatus 10 includes a rotation number detection means 17 of the photosensitive drum 1 as an apparatus usage amount detection means. Is provided. The rotational speed of the photosensitive drum 1 is measured by the rotational speed detection means 17, and the measurement result is input to the control circuit 13 and stored in the storage means provided in the control circuit 13.

  FIG. 11 shows a flowchart of the execution control of the nip pre-exposure adjustment process in this embodiment. In this embodiment, as in the first embodiment, the photosensitive drum 1 and the charging roller 2 are integrally configured as a process cartridge.

  Referring to FIG. 11, when a print signal is input (S301), control circuit 13 determines whether the number of rotations of photosensitive drum 1 has reached a predetermined number of rotations after the previous nip pre-exposure adjustment step. Is determined (S301). In this embodiment, the predetermined rotational speed is 10,000. If the control circuit 13 determines that the predetermined number of rotations has been reached in S301, the control circuit 13 executes the nip pre-exposure adjustment process during the pre-rotation process (S303), and performs the image forming process after the pre-rotation process is completed. This is executed (S304). On the other hand, if the control circuit 13 determines in S302 that the predetermined rotational speed has not been reached, the control circuit 13 executes a pre-rotation process in which the nip pre-exposure adjustment process is not performed (S305), and the image is output after the pre-rotation process is completed. A formation process is performed (S304).

  In this embodiment, the operation of the nip pre-exposure adjustment process itself is the same as that of Embodiment 1 described with reference to FIG.

  As described above, in the present embodiment, the upstream gap A1 is set so that the absolute value of the DC current value Ia flowing between the photosensitive drum 1 and the charging roller 2 at the predetermined timing is the maximum value using the apparatus usage amount as an index. The irradiation state of the nip pre-exposure I is adjusted. Thereby, the irradiation state of the nip pre-exposure I can be maintained in an appropriate state over a long period of time. Therefore, even when the DC charging method, which is advantageous in terms of cost as compared with the AC charging method, is adopted, it is possible to prevent the occurrence of charging horizontal stripes over a long period of time and maintain a good image.

Example 3
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Accordingly, elements having the same functions or configurations as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In Examples 1 and 2, the irradiation state adjusting unit 14 rotated the nip pre-exposure device 8 around a rotation axis along the longitudinal direction (substantially parallel to the longitudinal direction of the photosensitive drum 1). Then, the irradiation direction of the nip pre-exposure I was changed around the rotation axis along a plane substantially orthogonal to the longitudinal direction of the photosensitive drum 1.

  On the other hand, in this embodiment, the irradiation state adjusting unit 14 moves the nip pre-exposure device 8 along a plane substantially parallel to the longitudinal direction of the photosensitive drum 1. In this embodiment, the nip pre-exposure device 8 can be rotated or slid along the plane. In the present embodiment, in particular, the plane is substantially parallel to the longitudinal direction of the photosensitive drum 1 and is along a direction intersecting with the light direction from the pre-nip exposure device 8 toward the upstream gap A1. Thereby, the charge removal amount (exposure amount) on the photosensitive drum 1 in the upstream gap A1 or the surface area (exposure position, exposure range) of the photosensitive drum 1 to be discharged can be changed.

  Here, in this embodiment, one end side in the longitudinal direction of the photosensitive drum 1 is referred to as a front side, and the other end side is referred to as a back side.

  In this embodiment, when the longitudinal direction of the nip pre-exposure device 8 is substantially parallel to the longitudinal direction of the upstream gap A1 (substantially parallel to the longitudinal direction of the photosensitive drum 1), the above-described neutralization in the longitudinal direction is possible. This is an appropriate position at which the charge in the region can be removed almost uniformly to prevent charging lateral stripes. When the longitudinal direction of the upstream gap A1 and the nip pre-exposure device 8 deviates from parallel, the nip pre-exposure I from the photosensitive drum 1 or the charging roller 2 at the front end or the rear end of the nip pre-exposure device 8 occurs. Irradiation is biased to. For this reason, it is difficult to irradiate the pre-nip exposure I to the back of the upstream gap A1 at the front end or back end of the nip pre-exposure device 8, and the charge on the photosensitive drum 1 is neutralized by the upstream gap A1. Accordingly, the charged horizontal stripes are likely to occur.

  FIG. 12 is a block circuit diagram for explaining a schematic control mode of the image forming apparatus 10 according to the present embodiment. The control mode in the present embodiment is the same as that in the first embodiment shown in FIG. 4, but the configuration of the irradiation state adjusting means 14 is different from that in the first embodiment.

  As shown in FIG. 12, in this embodiment, the irradiation state adjusting means 14 includes a front side actuator 14F that moves the front side end of the nip pre-exposure device 8 and a back side end of the nip pre-exposure device 8. A rear actuator 14R to be moved. More specifically, in this embodiment, the front side actuator 14F and the back side actuator 14R respectively set the positions of the front side end and the back side end in the longitudinal direction of the nip pre-exposure device 8 with respect to the photosensitive drum 1. To move vertically up and down. Thereby, in this embodiment, the nip pre-exposure device 8 is rotated (oscillated) along the plane substantially parallel to the longitudinal direction of the photosensitive drum 1. As described above, the nip pre-exposure device 8 can be slid along the plane. The operation of the front side actuator 14F and the back side actuator 14R is controlled by the control circuit 13.

  Further, as shown in FIG. 13, in this embodiment, as the nip pre-exposure device 8, an LED lamp capable of emitting light in a plurality of divided areas in the longitudinal direction (substantially parallel to the longitudinal direction of the photosensitive drum 1) is used. did. In particular, in this embodiment, the nip pre-exposure device 8 can emit light for each of the regions divided into three in the longitudinal direction. These three regions are referred to as a first region 8F, a second region 8C, and a third region 8R, respectively, from the front side to the back side. During image formation, the nip pre-exposure device 8 lights all of the first, second, and third regions 8F, 8C, and 8R.

  Next, execution control of the nip pre-exposure adjustment process and operation control of the nip pre-exposure adjustment process in the present embodiment will be described.

  In the present embodiment, the execution control of the nip pre-exposure adjustment process is the same as that of the first embodiment described with reference to FIG. In other words, in this embodiment, when at least one of the photosensitive drum 1 and the charging roller 2 is newly installed on the main body (apparatus main body) of the image forming apparatus 10, the nip pre-exposure adjustment process is executed. . As in the second embodiment, the nip pre-exposure adjustment process may be executed at a predetermined timing.

  FIG. 14 shows a flowchart of the nip pre-exposure adjustment process in the present embodiment.

  Referring to FIG. 14, when the pre-nip exposure adjustment process is started, first, the control circuit 13 sets the position of the pre-nip exposure device 8 to the initial position (S401). The initial position is not limited, but can be the maximum value or the minimum value of the range in which the angle of the nip pre-exposure device 8 is changed in the pre-nip exposure process. For example, in this embodiment, it is assumed that the front actuator 14F is lowered to the lowest position and the back actuator 14R is raised to the highest position.

  Next, the control circuit 13 turns on only the first region 8F among the three light emitting regions of the predetermined charging bias, transfer bias, and nip pre-exposure device 8 (S402). In this embodiment, in the nip pre-exposure adjustment process, in order to set the surface potential of the photosensitive drum 1 after the charging process (before reaching the transfer nip) to −500 V, which is the same as that during normal image formation, a charging bias of −1100 V is used. Was applied. In the nip pre-exposure step, the transfer bias was + 500V. In the nip pre-exposure adjustment step, the light amount of the nip pre-exposure device 8 is 7 (lx · s). Then, the control circuit 13 detects the direct current value If by the current detection circuit 12 (S403). Next, the control circuit 13 switches the light emission area of the nip pre-exposure device 8 in the state where the charging bias and the transfer bias are turned on with the same bias value setting as described above, and the second area 8C among the three light emission areas. Is turned on with the same light emission amount setting as above (S404). Then, the control circuit 13 detects the direct current value Ic by the current detection circuit 12 (S405). Next, the control circuit 13 switches the light emitting area of the nip pre-exposure device 8 with the charging bias and transfer bias set to ON with the same bias value setting as described above, and the third area 8R among the three light emitting areas. Is turned on with the same light emission amount setting as above (S406). Then, the control circuit 13 detects the direct current value Ir by the current detection circuit 12 (S407).

  The DC voltage values If, Ic, Ir measured corresponding to the respective light emitting areas of the nip pre-exposure device 8 are stored in the storage means provided in the control circuit 13, respectively. The direct current values If, Ic, Ir corresponding to the respective light emitting areas are measured while the surface of the photosensitive drum 1 irradiated with light from the respective light emitting areas is discharged.

  Next, the control circuit 13 determines whether or not the standard deviation σ of the measured DC current values If, Ic, Ir is within a predetermined value of 1.6 (S408). As a result of intensive studies by the present inventors, in the image forming apparatus 10 of the present embodiment, when the standard deviation σ is within 1.6, the upstream gap A1 and the position in the longitudinal direction of the nip pre-exposure device 8 are the same. This is because the accuracy has been found to be good. However, the value of the standard deviation can be appropriately set depending on the configuration of each image forming apparatus. For example, if If = −59 μA, Ic = −60 μA, Ir = −58 μA, the average value is −59 μA, and the deviation is 0 in the first region 8F, 1 in the second region 8C, and −1 in the third region 8R. The sum of the squares of the deviations is 2. The variance σ2 = 2/3, and σ≈0.8. In this case, it can be determined that there is little difference in position (displacement from parallel) in the longitudinal direction between the upstream gap A1 and the nip pre-exposure device 8.

  Next, if the control circuit 13 determines in S408 that the standard deviation σ is within 1.6, the control circuit 13 determines the position of the nip pre-exposure device 8 as that position (S409). Thereafter, the control circuit 13 ends the pre-rotation process including the nip pre-exposure adjustment process, and proceeds to the image forming operation (S104 in FIG. 8).

  On the other hand, when the control circuit 13 determines in S408 that the standard deviation σ is larger than 1.6, the control circuit 13 adjusts the position of the nip pre-exposure device 8 by the front side actuator 14F and the back side actuator 14R of the irradiation state adjusting means 14. (S410). This is because it can be determined that the difference between the positions of the upstream gap A1 and the nip pre-exposure device 8 in the longitudinal direction is large (remarkably out of parallel). At this time, in this embodiment, the front side actuator 14F is moved upward by a predetermined movement amount, and the back side actuator 14R is moved downward by a predetermined movement amount. Thereafter, the change of the position of the nip pre-exposure device 8 and the measurement of the DC current values If, Ic, Ir by the current detection circuit 12 are repeated until the standard deviation σ is within 1.6 in S408.

  As described above, in this embodiment, the irradiating unit 8 can irradiate the surface of the photosensitive member 1 with light in every region divided into a plurality of directions in a direction substantially orthogonal to the moving direction of the photosensitive member 1. Then, the control means 13 causes the standard deviation of each DC current value detected by the DC current detection means 12 to fall within a predetermined range when a discharge occurs on the surface of the photoreceptor 1 irradiated with light for each divided area. The adjustment of the irradiation state by the irradiation state adjusting means 14 is controlled so as to be a value.

  As described above, in this embodiment, the displacement of the position in the longitudinal direction of the nip pre-exposure device 8 can be adjusted, and the irradiation state of the nip pre-exposure I can be adjusted to an appropriate state.

Other Embodiments Although the present invention has been described based on the specific embodiments, the present invention is not limited to the above-described embodiments.

  For example, in the first and second embodiments, the positional deviation (angular deviation) of the nip pre-exposure device 8 in the rotational direction along a plane substantially orthogonal to the longitudinal direction of the photosensitive drum 1 is adjusted. In the third embodiment, the upstream gap The positional deviation in the longitudinal direction of the nip pre-exposure device 8 (deviation from parallel) was adjusted. In addition, the first and second embodiments may be combined with the third embodiment to adjust the positional deviation in both directions so that the exposure state of the pre-nip exposure I can be adjusted more appropriately. In the third embodiment, the irradiation state adjusting means 14 is a plane that is substantially parallel to the longitudinal direction of the photosensitive drum 1 and that intersects the direction of light from the pre-nip exposure device 8 toward the upstream gap A1. The nip pre-exposure device 8 was moved along Alternatively or in addition, the irradiation state adjusting means 14 is substantially parallel to the longitudinal direction of the photosensitive drum 1 and in a direction substantially parallel to the direction of light from the pre-nip exposure device 8 toward the upstream gap A1. The nip pre-exposure device 8 may be moved along the flat plane.

  In the first and second embodiments, the angle of the nip pre-exposure apparatus itself is adjusted. However, using a reflector such as a mirror, the irradiation angle of the nip pre-exposure to the surface of the photosensitive drum corresponding to the upstream gap is adjusted. May be. For example, a mirror capable of adjusting the angle by the irradiation state adjusting means is installed in the process cartridge, and an LED lamp is installed outside the process cartridge. And it is set as the structure which reflects the light from an LED lamp with a mirror, and irradiates an upstream gap. According to such a configuration, it is not necessary to replace the LED lamp when replacing the process cartridge, which is advantageous in reducing the running cost.

  In the second embodiment, the predetermined timing for executing the nip pre-exposure adjustment step is set by using the rotational speed of the photosensitive drum as an index. However, the present invention is not limited to this. In addition to the photosensitive drum, a predetermined nip pre-exposure adjustment step is performed using as an index any parameter that correlates with the amount of use of the apparatus, such as the number of images formed, the number of rotations of the charging roller, and the time for applying the charging bias to the charging roller Timing can be set. That is, the control unit 13 can cause the irradiation state adjustment unit 14 to perform adjustment of the irradiation state when it is determined that a predetermined period has elapsed since the irradiation state adjustment unit 14 performed the adjustment of the irradiation state last time. It is also possible to allow the user or service person to arbitrarily execute the pre-nip exposure adjustment process when a charged horizontal stripe occurs on the image.

  In the above-described embodiments, LED lamps are used for the nip pre-exposure device and the pre-exposure device. However, the present invention is not limited to this, and other exposure devices such as a light irradiation device including a fuse lamp may be used. Good. Further, the photosensitive member may be transparent, and a nip pre-exposure device may be disposed inside the photosensitive member to expose the upstream gap from the inside of the photosensitive member.

  In the above-described embodiments, the charging roller as a flexible contact charging member has been described as an example. However, the distance between the photosensitive member in the upstream gap and the charging member gradually decreases as the distance from the contact portion in the moving direction of the photosensitive member decreases, and gradually decreases as the distance in the downstream charging gap moves away from the contact portion in the same direction. The present invention can be similarly applied as long as it increases. If this is the case, whether the distance between the charging member and the photosensitive member decreases linearly (or increases) or decreases nonlinearly (or increases), the same as in the above-described embodiment. The effect can be expected. For example, a conductive charging belt 21 (see FIG. 18A) as a charging member, a conductive rubber blade 22 (see FIG. 18B) that contacts the photosensitive member at the edge portion to charge the photosensitive member, and the like. It may be used.

  In the above-described embodiment, the charging roller as the charging member and the photosensitive drum as the photosensitive member are in contact with each other, but a minute gap may be formed to be close to each other. In such a configuration, the distance between the photosensitive member and the charging member gradually decreases toward the closest position (closest portion) between the charging member and the photosensitive member in the moving direction of the photosensitive member, and the closest position It gradually increases as you move away from.

  In the above-described embodiments, a rotatable drum-shaped photosensitive member is used. However, a movable belt-shaped photosensitive belt may be used as the photosensitive member. At this time, the upstream and downstream in the rotation direction of the photosensitive drum correspond to the upstream and downstream in the movement direction of the photosensitive belt, respectively.

  Further, in the above-described embodiment, in order to suppress the charging horizontal stripe appearing on the image, the image forming area in the longitudinal direction of the photosensitive drum is exposed by the nip pre-exposure device in the upstream charging gap. However, the entire area in the longitudinal direction of the photosensitive drum may be exposed. As a result, in an apparatus for forming an image on a small-size transfer material and a large-size transfer material, when the image is continuously formed on the small-size transfer material, the amount of shaving in the longitudinal direction of the photosensitive drum is uneven. This can be suppressed. For example, when an image is formed on a small-size transfer material and a large-size transfer material, the range is shorter when an image is formed on a small-size transfer material than when an image is formed on a large-size transfer material. If the photoconductor is irradiated with nip pre-exposure, charging horizontal stripes can be suppressed. However, when a small-size image is formed over a long period of time, the shaving amount of the photoconductor may be uneven between the portion irradiated with the pre-nip exposure and the portion not irradiated in the longitudinal direction of the photoconductor. In such a case, it is better to irradiate the entire area in the longitudinal direction of the photoconductor with nip pre-exposure.

  The present invention can also exhibit the same effect in a charging control circuit in an image forming apparatus having a so-called cleaner-less configuration in which cleaning is performed simultaneously with development using a developing device.

1 Photosensitive drum (photoconductor)
2 Charging roller (charging member)
8 Nip pre-exposure device (irradiation means)
12 DC current detection circuit 13 Control circuit (control means)
14 Irradiation state adjustment means

Claims (5)

A movable photoreceptor,
A charging member that charges the photoconductor in contact with or in proximity to the photoconductor, the contact between the photoconductor and the charging member in the moving direction of the photoconductor or upstream of the closest position A gap in which the distance between the photosensitive member and the photosensitive member is gradually narrowed toward the contact portion or the closest position, and the photosensitivity is increased as the distance from the contact portion or the closest position decreases toward the downstream side of the contact portion or the closest position. A charging member that forms a gap that gradually increases the distance to the body, and charges the photoconductor by a discharge generated between the surface of the photoconductor by applying a DC voltage;
A power source for applying a DC voltage to the charging member;
Irradiating means for irradiating light on the surface of the photoconductor corresponding to the upstream gap;
DC current detecting means for detecting a DC current flowing between the charging member and the photosensitive member when a DC voltage is applied to the charging member from the power source;
An irradiation state in which the irradiation unit adjusts the light irradiation state on the surface of the photoconductor by changing the relative position of the portion of the irradiation unit that emits light toward the surface of the photoconductor to the surface of the photoconductor Adjusting means;
The adjustment of the irradiation state by the irradiation state adjusting unit is controlled using a direct current value detected by the direct current detecting unit due to the occurrence of the discharge on the surface of the photosensitive member irradiated with light by the irradiation unit. Control means;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the control unit controls the adjustment of the irradiation state by the irradiation state adjustment unit so that the detected direct current value becomes a maximum value.   3. The control unit according to claim 1, wherein the control unit causes the irradiation state adjustment unit to adjust the irradiation state when it is determined that at least one of the photosensitive member or the charging member is new. 4. The image forming apparatus described.   The control unit causes the irradiation state adjustment unit to perform the adjustment of the irradiation state when it is determined that a predetermined period has elapsed since the previous adjustment of the irradiation state by the irradiation state adjustment unit was performed. The image forming apparatus according to claim 1.   The irradiating means can irradiate light on the surface of the photoconductor for each of the areas divided in a direction substantially orthogonal to the moving direction of the photoconductor, and the control means can emit light for each of the divided areas. The irradiation state adjusting means so that the standard deviation of each DC current value detected by the DC current detecting means becomes a value within a predetermined range when the discharge is generated on the surface of the photosensitive member irradiated with light. The image forming apparatus according to any one of claims 1 to 4, wherein the adjustment of the irradiation state by the control is controlled.

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