JP2010156853A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device for properly controlling an exposure amount with a simple configuration to suppress the sensitivity deterioration of a photoreceptor due to excessive exposure amount or image deterioration of image deletion or the like due to excessive discharge. <P>SOLUTION: The image forming device 100 has: a current detector 202 detecting a current flowing when applying a predetermined voltage to a charger 12; an execution means 200 to enter a test mode to form a first area charged under a predetermined charging condition by the charger and exposed under a predetermined exposure condition by an image exposure device 13, and a second area charged under the predetermined charging condition by the charger and not exposed by the image exposure device, in the photoreceptor; and an adjustment means 200 adjusting a light irradiation amount by a light discharger 112 according to output of the current detector obtained when the first and second areas formed in the photoreceptor in the test mode pass a charging position. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus such as a copying machine, a printer, or a facsimile machine has an electrophotographic photosensitive member (photosensitive member) that is generally rotatable as an image carrier. Also, a charging device (charging process) that uniformly charges the photoconductor to a predetermined polarity and potential, and an exposure device (exposure process) as information writing means for forming an electrostatic latent image on the charged photoconductor Have Further, a developing device (development process) that visualizes the electrostatic latent image formed on the photoconductor with toner as a developer, and a transfer device (transfer) that transfers the toner image from the photoconductor surface to a transfer material such as paper. Step). Further, the image forming apparatus includes a cleaning device (cleaning step) that removes some residual toner on the photoconductor after the transfer step to clean the surface of the photoconductor, and a fixing device (fixing step) that fixes the toner image on the transfer material. The photoconductor is repeatedly subjected to an electrophotographic process (charging, exposure, development, transfer, cleaning) to be used for image formation.

  In an electrophotographic image forming apparatus, if a halftone image as seen in the highlight portion of an image is formed after continuously forming a clear and bright image, the following problems occur in the formed image: May occur. That is, there is a problem that an image pattern formed previously appears in an image that should originally be a uniform halftone image. Hereinafter, this development is referred to as “ghost”.

  In general, when the reversal development method is used, when forming a latent image, image information is exposed to the surface of a photosensitive member that is uniformly charged to, for example, −500 V, and the potential of the exposed portion (bright portion potential VL) is set. For example, it is about −100V. At the time of development, the toner is attached to the exposed portion due to the potential difference from the potential of the non-exposed portion (dark portion potential VD) and developed. In the subsequent transfer, the transfer material side is charged positively to transfer the toner image from the photoconductor to the transfer material. Therefore, after the transfer, the surface potential of the photoreceptor changes as a whole in the positive direction, and the potential of the exposed portion exceeds -100V and becomes, for example, -50V. If this phenomenon is repeated, the potential difference is not eliminated by the uniform negative charging of the photoconductor performed before exposure, and therefore the surface potential is shifted in the positive direction only at that portion, and a dark toner image is formed. It will be done. This is one of the causes of ghosts.

  In order to prevent such a ghost, there is an image forming apparatus provided with pre-exposure means. As pre-exposure means, it is common to use an array light source in which LEDs and the like are aligned in the direction of the rotation axis of the photosensitive member. In many cases, the pre-exposure means uses the same wavelength region as the main sensitivity wavelength region of the photoreceptor in order to completely remove charges.

  Conventionally, inorganic photoreceptors mainly composed of an inorganic photoconductive compound such as selenium, zinc oxide, cadmium sulfide have been widely used as the photoreceptor. In recent years, photoreceptors (organic photoreceptors) having a photosensitive layer containing an organic charge generating substance and a charge transporting substance have been widely used. As such a photosensitive layer, a laminate type in which a charge generation layer containing a charge generation material and a charge transport layer (hole transport layer) containing a charge transport material (hole transport material) are laminated in this order from the support side. What has a (normal layer type) layer structure is now mainstream. It is because it is excellent in productivity and durability. Examples of the charge generating material used in the organic photoreceptor include a photoreceptor having a charge transfer layer containing triallyl pyrazoline, a charge generation layer made of a derivative of perylene pigment, and a charge made of a condensate of 3-propylene and formaldehyde. A photoconductor including a moving layer is disclosed. There is also a photoreceptor using a disazo pigment or a trisazo pigment as a charge generating substance. Furthermore, the organic photoconductive compound can freely select the photosensitive wavelength region of the photoreceptor depending on the compound. For example, with regard to azo organic pigments, substances exhibiting high sensitivity in the visible region are disclosed, and some materials have sensitivity in the infrared region (for example, Patent Documents 1 and 2). Among these materials, materials having sensitivity in the red or infrared region are used in laser beam printers and LED printers that have been remarkably advanced in recent years, and the frequency of demand thereof is increasing. However, the development of today's electrophotographic technology is remarkable, and very advanced technology is required for the characteristics required of the photoreceptor. For example, process speeds are increasing year by year, and charging characteristics, higher sensitivity and durability are required.

  Conventionally, materials having sensitivity in the infrared region include copper phthalocyanine, metal-free phthalocyanine, and the like, which are insufficient for increasing sensitivity today. Oxytitanium phthalocyanine pigments (for example, Patent Documents 3 and 4), gallium phthalocyanine pigments (for example, Patent Documents 5 and 6), and chlorogallium phthalocyanine pigments (for example, Patent Documents 7 and 8) have been developed as materials that can cope with high sensitivity in recent years. And widely used.

  In the electrophotographic image forming apparatus, as described above, the surface of the electrophotographic photosensitive member is charged, and the surface of the charged electrophotographic photosensitive member is exposed to light to expose the surface of the electrophotographic photosensitive member. Form an image. Then, the electrostatic latent image is developed with toner to form a toner image on the surface of the electrophotographic photosensitive member, and the toner image is transferred from the surface of the electrophotographic photosensitive member to a transfer material such as paper. The process of charging the surface of the photographic photoreceptor and forming the next image is repeated. Here, if the residual charge on the photoconductor after transfer is transferred to the next charging process without neutralizing, the surface of the photoconductor cannot be uniformly charged due to charging, which may cause image defects.

Therefore, it is possible to avoid such a problem by performing charge removal of the residual charge remaining on the photoconductor after transfer by the pre-exposure means (for example, Patent Document 9). When performing the pre-charging exposure, it is necessary to sufficiently attenuate the charging potential, so that the exposure amount is several tens of times the image exposure amount. Thus, by providing the pre-charging exposure means, the surface potential of the photoconductor can be made uniform, and a good image can be formed.
JP-A-57-195767 Japanese Patent Laid-Open No. 61-228453 JP-A-63-366 JP-A-1-319934 JP-A-5-249716 Japanese Patent Laid-Open No. 5-263007 JP-A-5-188615 JP-A-5-194523 JP-A-5-127546

  However, for example, in an organic photoreceptor using a phthalocyanine pigment or the like as a charge generation material, a photocarrier generated due to high sensitivity tends to remain in the photosensitive layer. Therefore, in particular, in the case of a high-speed electrophotographic process, and further, when the organic photoreceptor is exposed with a light amount several tens of times that of image exposure by pre-exposure exposure, the potential of the bright portion potential on which the image is formed by image exposure. As a result, image defects such as image density reduction may occur.

  That is, in the case of a negatively charged laminated photoreceptor, it is necessary that charges are generated in the charge generation layer by exposure, and the separated hole and electron carriers do not stay in the photosensitive layer. That is, by the next exposure, holes are injected into the hole transport layer containing the hole transport material, canceling the surface potential, and electrons need to move quickly to the support. However, when an image is formed in a short cycle and the charge generation layer is exposed in a short cycle, or when the photoreceptor is strongly exposed by pre-charge exposure, the residence potential in the photosensitive layer increases. This is because the response speed at which holes are injected into the hole transporting side is not in time, or the responsiveness of electrons moving to the support side is not in time. For this reason, the hole shifts to the next image formation without completely canceling the surface potential, and this occurs as the bright portion potential increases.

  Moreover, the injection into the hole transport layer side and the movement speed of the electrons to the support are fast immediately after the start of exposure. However, by forming an image in a short cycle, the photocarrier gradually stays in the photosensitive layer, so that the rate of injection to the hole transport layer side and the movement of electrons to the support becomes slow. come. For this reason, it is known that the density fluctuations of the first several to several tens of sheets are extremely large when images are continuously formed.

  Further, it is known that the photosensitive layer is repeatedly used due to durability, and the photosensitive layer is deteriorated by repeatedly receiving light of strong pre-exposure, and the staying phenomenon of the photocarrier in the photosensitive layer is aggravated. That is, when the photoreceptor is used repeatedly due to durability, the degree of increase in the bright portion potential is further increased, and as a result, the change in image density is also increased. As described above, by irradiating the pre-exposure light amount more strongly than necessary, image defects such as density reduction due to an increase in bright portion potential are promoted.

  Further, as a factor for deteriorating the surface of the photosensitive member when charging the photosensitive member, there is a relation between the magnitude of the potential difference between the charging potential when passing through the charging means and the potential immediately before the photosensitive member passes through the charging means. Yes. That is, if the potential difference between the potential of the charging means and the potential of the photoconductor immediately before passing through the charging means (hereinafter referred to as “charging contrast”) is large, a large DC current is added from the charging means to compensate the potential difference. Will flow into the body. For this reason, deterioration of the surface of the photoreceptor due to discharge is promoted. When deterioration due to electric discharge progresses, a phenomenon called image flow occurs in an environment of high temperature and high humidity, and image defects such as image blur may occur. Further, as the deterioration due to discharge progresses, in a low-humidity environment, toner fusion (so-called filming) is promoted to the photosensitive member, and further, the increase in the amount of abrasion of the photosensitive member is promoted. This leads to image defects such as omission and deterioration of the life of the photoreceptor. Therefore, it is desirable that the charging contrast can be kept as small as possible, but the problem here is the amount of light for pre-exposure. That is, if the amount of pre-exposure is too strong, the photosensitive member is neutralized in front of the charging unit, resulting in an increase in the charge contrast immediately before passing through the charging unit. Deterioration will be promoted.

  Accordingly, an object of the present invention is to control the pre-exposure amount to an appropriate value with a simple configuration, and to suppress image deterioration such as image sensitivity deterioration due to excessive pre-exposure amount and image flow due to excessive discharge. It is an object of the present invention to provide an image forming apparatus.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the first aspect of the present invention is a photoconductor, a charger that charges the photoconductor at a charging position, an image exposure device that performs image exposure on the photoconductor charged by the charger, and the image A developing unit that develops the electrostatic image formed on the photoconductor by an exposure unit, and a photoremoval unit that transfers the developed image formed by the developing unit to a transfer target and then neutralizes the photoconductor by light irradiation. An image forming apparatus comprising: a current detector that detects a current that flows when a predetermined voltage is applied to the charger; and the image exposure device that is charged under a predetermined charging condition by the charger A first region exposed by a predetermined exposure condition and a second region charged by the charger under a predetermined charging condition and not substantially exposed by the image exposure unit. Test model to be formed Execution means for executing the light output, and the light removal according to the output of the current detector obtained when the first and second regions formed on the photoconductor pass through the charging position in the test mode. And an adjusting unit that adjusts the amount of light emitted by the electric device.

  According to a second aspect of the present invention, there is provided a photoreceptor, a charger that charges the photoreceptor at a charging position, an image exposure unit that performs image exposure on the photoreceptor charged by the charger, and the image exposure unit A developing unit that develops an electrostatic image formed on the photosensitive member, and an optical static eliminator that neutralizes the photosensitive member by light irradiation after the developed image formed by the developing unit is transferred to the transfer target. In the image forming apparatus, a potential detector for detecting a surface potential of the photoconductor, and a charging process performed under a predetermined charging condition by the charger and an exposure process performed under a predetermined exposure condition by the image exposure unit. Execution means for executing a test mode in which the first region and a second region charged by the charger under a predetermined charging condition and not substantially exposed by the image exposure unit are formed on the photoconductor; The test And adjusting means for adjusting the amount of light emitted by the light static eliminator according to the result of detection of the first and second regions formed on the photoconductor by the potential detector. An image forming apparatus.

  According to the present invention, it is possible to control the pre-exposure amount to an appropriate value with a simple configuration, and it is possible to suppress image deterioration such as image sensitivity deterioration due to excessive pre-exposure amount and image flow due to excessive discharge. it can.

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

Example 1
1. FIG. 1 shows a schematic configuration of an embodiment of an image forming apparatus according to the present invention. In the image forming apparatus 100 according to the present exemplary embodiment, four image forming units are juxtaposed along the moving direction of the end-lease belt type intermediate transfer member that is a toner support (transfer target), that is, the intermediate transfer belt 31. This is a tandem type full-color image forming apparatus.

  The image forming apparatus 100 includes an image output unit 1P. The image output unit 1P is roughly divided into four image forming units 10 (10a, 10b, 10c, 10d), a paper feeding unit 20, an intermediate transfer unit 30, a fixing unit 40, and a control unit (control processing unit) 200. . Hereinafter, each unit will be described in detail.

  In this embodiment, the four image forming units (first, second, third, and fourth image forming units) 10a, 10b, 10c, and 10d are different in the color of the image to be formed, but the configuration is substantially the same. Are identical.

  Each image forming unit 10 includes a rotatable drum-type electrophotographic photosensitive member (photosensitive drum) 11 (11a, 11b, 11c, 11d) as an image carrier. The photoconductor 11 is pivotally supported at the center thereof, and is driven to rotate at a predetermined process speed (circumferential speed) in the direction of the arrow R1 (counterclockwise) by the driving means. Opposing the outer peripheral surface of the photoconductor 11, the following means are arranged in the rotation direction. First, a roller-shaped charger as a charging unit, that is, a charging roller 12 (12a, 12b, 12c, 12d) as a charging member. Next, there are image exposure devices (laser scanner units) 13 (13a, 13b, 13c, 13d) as image exposure means (information writing means). Next, there are developing devices 14 (14a, 14b, 14c, 14d) as developing means. Next, a cleaning device 15 (15a, 15b, 15c, 15d) as a cleaning unit.

  The charging roller 12 applies a uniform charge amount to the surface of the photoconductor 11. In this embodiment, a charging voltage (charging bias) which is a direct current (DC) voltage is applied to the charging roller 12 from a charging power source as a charging voltage applying unit (bias applying unit). As a result, the surface of the photoconductor 11 is uniformly charged to a negative polarity. As the charging voltage, an oscillating voltage obtained by superimposing a DC voltage and an AC voltage can be used.

  Next, the photosensitive member 11 is exposed by a light beam such as a laser beam modulated in accordance with a recording image signal by an image exposure unit 13. As a result, an electrostatic latent image (electrostatic image) is formed on the photoreceptor 11.

  The electrostatic latent images formed on the respective photoreceptors are visualized by developing units 14a, 14b, 14c, and 14d that respectively store yellow, cyan, magenta, and black toners as developers. In this embodiment, the developing device 14 has a rotatable cylindrical developing sleeve as a developer carrier (developing member). A developing voltage (developing bias) which is a direct current (DC) voltage is applied to the developing sleeve from a developing power source as a developing voltage applying means (bias applying means). The toner is transferred to the electrostatic latent image on the photoconductor 11 by the action of an electric field formed between the development sleeve and the photoconductor 11 by this development voltage, and a toner image (development image) is formed on the photoconductor 11. Is done. As the development voltage, an oscillating voltage obtained by superimposing a DC voltage and an AC voltage can be used. In the present embodiment, the developing device 14 performs development by a reversal development method. That is, on the uniformly charged photoconductor 11, the toner charged with the same polarity as the charged polarity (negative polarity in this embodiment) of the photoconductor 11 is applied to the exposed portion (bright portion) where the charge is attenuated by exposure. Development is performed by adhering.

  The visualized visible image is transferred (primary transfer) to the intermediate transfer belt 31 at the primary transfer portion (primary transfer position) N1 (N1a, N1b, N1c, N1d).

  On the downstream side of the primary transfer portion N1 in the rotation direction of the photoconductor 11, the cleaning device 15 scrapes off the toner that is not transferred to the transfer material S and remains on the photoconductor 11, and the surface of the photoconductor 11 is removed. Clean.

  Through the above process, image formation with each toner is sequentially performed. For example, when a color image is formed, yellow, cyan, magenta, and black toner images are formed on the four photoconductors 11a, 11b, 11c, and 11d, respectively, and each toner image is sequentially intermediate transferred at each primary transfer portion N1. The image is superimposed on the belt 31 and transferred (primary transfer).

  As the photoconductor 11, it is preferable to use an amorphous silicon photoconductor capable of achieving a long life or an electron beam curable photoconductor which is cured by an electron beam instead of being cured by heat.

  As the cleaning device 15, a counter blade type device using a cleaning blade that is disposed in contact with the photoconductor 11 with its free end facing the upstream side in the surface movement direction of the photoconductor 11 is preferably used as the cleaning member. obtain. In this embodiment, the free length of the cleaning blade is 8 mm. The cleaning blade is an elastic blade made of a material mainly composed of urethane, and is brought into contact with the photoreceptor 11 with a pressing force of a linear pressure of about 35 g / cm.

  The paper feed unit 20 includes cassettes 21a and 21b and a manual feed tray 27 for storing the transfer material S, and pickup rollers 22a, 22b and 26 for feeding the transfer material S one by one from the cassette or the manual feed tray. The paper feed unit 20 has a paper feed roller pair 23 and a paper feed guide 24 for transporting the transfer material S sent from each pickup roller to the registration rollers. Further, the paper feeding unit 20 includes registration rollers 25a and 25b for sending the transfer material S to the secondary transfer portion (secondary transfer position) N2 in accordance with the image forming timing of the image forming portion.

  The intermediate transfer unit 30 includes an intermediate transfer belt 31 that is an endless belt-like intermediate transfer member. As a material for the intermediate transfer belt 31, for example, PET (polyethylene terephthalate), PVdF (polyvinylidene fluoride), or the like is preferably used. The intermediate transfer belt 31 is wound around a driving roller 32, a tension roller 33, and a driven roller 34. The driving roller 32 transmits driving to the intermediate transfer belt 31. The tension roller 33 applies an appropriate tension to the intermediate transfer belt 31 by biasing of a spring as biasing means. The driven roller 34 forms a secondary transfer portion N2 with the intermediate transfer belt 31 between the secondary transfer roller 36, which is a secondary transfer member as a secondary transfer unit. A primary transfer plane 31 </ b> A is formed between the drive roller 32 and the tension roller 33. The driving of the intermediate transfer belt 31 is transmitted by the driving roller 32, and the intermediate transfer belt 31 rotates (circulates) at a predetermined peripheral speed in the illustrated arrow R2 (clockwise).

  The drive roller 32 is coated with rubber (urethane or chloroprene) having a thickness of several millimeters on the surface of the metal roller to prevent slippage with the intermediate transfer belt 31. The drive roller 32 is rotationally driven by a pulse motor (not shown) as drive means. A primary transfer roller which is a primary transfer member as a primary transfer unit is provided on the inner peripheral surface side of the intermediate transfer belt 31 so as to face each of the photoreceptors 11a, 11b, 11c, and 11d with the intermediate transfer belt 31 interposed therebetween. 35 (35a, 35b, 35c, 35d) are arranged. When the primary transfer member 35 presses the intermediate transfer belt 31 toward the photosensitive drum 11, the primary transfer portion N <b> 1 is formed by the nip between the photosensitive drum 11 and the intermediate transfer belt 31. Each primary transfer roller 35 is supplied with a DC voltage having a polarity opposite to the normal charging polarity (negative polarity in this embodiment) of toner from a primary transfer power source as a primary transfer voltage application unit (bias application unit). A primary transfer voltage is applied. As a result, the toner image is transferred (primary transfer) from the photoreceptor 11 to the intermediate transfer belt 31 by the action of the electric field formed in the primary transfer portion N1.

  A secondary transfer roller 36 is disposed on the outer peripheral surface side of the intermediate transfer belt 31 so as to face the driven roller 34 with the intermediate transfer belt 31 interposed therebetween. A secondary transfer portion N2 is formed by the nip between the secondary transfer roller 36 and the intermediate transfer belt 31. The secondary transfer roller 36 is pressed with an appropriate pressure against the intermediate transfer member. The secondary transfer roller 36 is supplied with a direct current (DC) having a polarity opposite to the normal charging polarity (negative polarity in this embodiment) of the toner from a secondary transfer power source as a secondary transfer voltage applying unit (bias applying unit). A secondary transfer voltage, which is a voltage, is applied. As a result, the toner image is transferred (secondary transfer) from the intermediate transfer belt 31 to the transfer material S by the action of the electric field formed in the secondary transfer portion N2.

  Further, an intermediate transfer for cleaning the image forming surface of the intermediate transfer belt 31 located downstream of the secondary transfer portion N2 and upstream of the most upstream primary transfer portion N1a in the surface movement direction of the intermediate transfer belt 31. A belt cleaner 37 is disposed as a body cleaning means. The belt cleaner 37 may be provided with a cleaning blade or brush roller as a cleaning member, a waste toner box for storing waste toner, and the like. The belt cleaner 37 cleans the secondary transfer residual toner on the intermediate transfer belt 31.

  As described above, the toner image formed on the intermediate transfer belt 31 is collectively transferred (secondary transfer) to the transfer material S conveyed to the secondary transfer portion N2 at a predetermined timing in the secondary transfer portion N2. ) The transfer material S onto which the toner image has been transferred is then conveyed to the fixing unit 40 where the toner image is fixed and then discharged outside the apparatus.

  The fixing unit 40 includes a fixing roller 41a having a heat source such as a halogen heater inside, and a pressure roller 41b that is pressed against the fixing roller 41a. The pressure roller 41b may also be provided with a heat source. The fixing unit 40 includes a guide 43 for guiding the transfer material S to the nip portion of the roller pair, an inner discharge roller 44 and an outer discharge roller 44 for further guiding the transfer material S discharged from the roller pair to the outside of the apparatus. A paper discharge roller 45 and the like are included.

  A control unit (control processing unit) 200 as a control unit includes a control board, a motor drive board, and the like for controlling the operation of the mechanism in each unit.

  Further, the image forming apparatus 100 includes an environment sensor 50 as an environment detection unit. The environmental sensor 50 is disposed at a position where the environmental temperature and humidity around the apparatus can be accurately measured without being affected by the fixing unit 40 serving as a heat source in the apparatus. In this embodiment, the environment sensor 50 is disposed at a position separated from the fixing unit 40 with the intermediate transfer belt unit 30 interposed therebetween. Various controls of the apparatus are performed based on the environmental sensor output.

  As a characteristic of the toner, a weight average particle diameter of 5 to 8 μm is preferable for forming a good image. If the weight average particle diameter is within this range, it has sufficient resolution, can form clear and high-quality images, and has less adhesive force and cohesive force than electrostatic force, reducing various troubles. To do. The weight average particle diameter of the nonmagnetic toner particles can be measured by various methods such as a sieving method, a sedimentation method, and a photon correlation method. Here, Coulter Multisizer (trade name) manufactured by Coulter, Inc. was used as a measuring device. The measuring method is as follows. A 1% NaCl aqueous solution is prepared using special grade or first grade sodium chloride (for example, trade name: ISOTON-II manufactured by Coulter Scientific Japan Co., Ltd.). A surfactant, preferably an alkylbenzene sulfonate, is added in an amount of 0.1 to 5 mL as a dispersant in 100 to 150 mL of the electrolytic aqueous solution, and 2 to 20 mg of toner as a measurement sample is further added. The electrolytic solution in which the sample is suspended is dispersed for about 1 to 3 minutes with an ultrasonic disperser, and the volume and number of toners are measured using a 100 μm aperture to calculate the volume distribution and number distribution. Then, the weight average particle diameter of the nonmagnetic toner particles can be measured by determining the weight average particle diameter from the volume distribution (the median value of each channel is a representative value for each channel).

  Non-magnetic toner particles can be produced by a conventionally known production method. Nonmagnetic toner particles can also be produced by a pulverization method in which the constituent materials are made uniform by heating and melting, cooled and solidified, and pulverized to produce toner particles. However, since the toner particles obtained by this pulverization method are generally amorphous, it is necessary to perform mechanical, thermal, or some special treatment in order to obtain a substantially spherical shape. In order to obtain a diameter, it is necessary to classify the toner particles after the spheroidizing treatment. Therefore, it is preferable to employ a polymerization method as a preferred method for producing the non-magnetic toner particles described above.

  In the present embodiment, a polyimide belt having a thickness of 100 μm was used as the intermediate transfer belt 31. In this embodiment, a urethane sponge roller is used as the primary transfer roller 35 installed in the primary transfer portion N1. In this embodiment, the peripheral speed of the intermediate transfer belt 31 is 300 mm / sec, and the width of the transfer portion in the thrust direction (direction substantially orthogonal to the moving direction of the intermediate transfer belt) is 330 mm.

  In this embodiment, the charge retention amount of the toner on the photoconductor 11 is 30 μC / g. In this embodiment, the primary transfer voltage is applied so that a current of 40 μA flows through the core of the primary transfer roller 35 during the primary transfer. This amount of current is an appropriate current value set in an environment where the temperature / humidity is 23 ° C./60% as a normal environment. However, this amount of current is preferably changed due to fluctuations in the toner charge retention amount due to environmental fluctuations.

In this embodiment, the specific configuration of the primary transfer roller 35 is as follows. The primary transfer roller 35 has an electric resistance value of 5 × 10 ⁷ Ω when a voltage of 1 kV is applied. The primary transfer roller 35 is a urethane sponge roller having an outer diameter of 16 mm and a core metal diameter of 8 mm. In this method for producing a urethane sponge roller, a polyurethane-forming material containing a polyol component, a polyisocyanate component, a foaming agent, and optionally used conductivity-imparting agent, catalyst, foam stabilizer and the like is used. The urethane sponge roller is composed of a conductive urethane sponge layer made of the polyurethane sponge and a metal member such as a cored bar. The structure is such that a metal member obtained by plating zinc or the like on a steel material such as sulfur free-cutting steel or a part or the whole of a metal member such as aluminum or stainless steel is covered with the conductive polyurethane sponge layer. This can be produced by using a method in which a conductive polyurethane sponge is molded into a predetermined shape and then bonded. As the adhesive layer, a known material such as an adhesive made of a conductive paint or a hot melt sheet can be used.

In this embodiment, the surface of the charging roller 12 is formed of a conductive rubber having a thickness of 1 to 2 mm in which a conductive agent such as carbon black is dispersed and mixed to prevent uneven charging during image formation. The electrical resistance value is controlled to 10 ⁵ to 10 ⁷ Ωcm. The charging roller 12 makes contact with the photoconductor 11 without making a gap using the elasticity (contact charging means), and charges the photoconductor 11 with a low voltage. A contact position between the charging roller 12 and the photoconductor 11 is a charging position. Alternatively, the charging roller 12 may have the following configuration. An ABS resin containing an ion conductive polymer compound such as polyether ester amide and having a resistance value controlled to 10 ⁵ to 10 ⁷ Ωcm is coated on the surface of the conductive support by 0.5 to 1 mm by injection molding. A resistance adjustment layer is used. A protective layer made of a thermoplastic resin composition in which conductive fine particles such as tin oxide are dispersed is sequentially formed on the surface of the resistance adjusting layer. A metal shaft member is used as the conductive support for applying the charging voltage. In this shaft member, a bearing portion, a voltage application bearing portion, and a covering portion having an outer diameter of 14 mm are integrally formed. On the peripheral surface of the covering portion, a resistance adjusting layer having a volume resistance value of 10 ⁵ to 10 ⁷ Ωcm of an ABS resin which is a thermoplastic resin containing an ion conductive polymer compound such as polyether ester amide is formed by injection molding. It is coated and formed with a thickness of 0.5 to 1 mm.

2. Next, the configuration around the cleaning device 15 in the present embodiment will be further described with reference to FIG. Note that FIG. 2 shows one image forming unit 10 as a representative, but in this embodiment, all the image forming units 10 have substantially the same configuration.

  The cleaning device 15 includes a cleaning container 109, a cleaning blade 110 held in the cleaning container 109 and in contact with the surface of the photoconductor 11, and a screw 111. In this embodiment, the cleaning blade 110 is made of urethane rubber having a thickness of 3 mm.

  A pre-exposure device (pre-cleaner) is used as a pre-exposure unit (photo neutralization unit) for neutralizing the photo conductor 11 by light irradiation at a position downstream of the primary transfer position and upstream of the charging position in the rotation direction of the photo conductor 11. (Exposure device, light static eliminator) 112 is provided. In particular, in this embodiment, the pre-exposure device 112 is disposed at a position upstream of the cleaning device 15 in the rotation direction of the photoconductor 11. As a pre-exposure unit, a post-cleaner exposure device may be further arranged downstream of the cleaning device 15 in the rotation direction of the photosensitive member 11.

  In this embodiment, the pre-exposure device 112 is composed of an array light source in which LEDs as light sources are aligned in the rotation axis direction of the photoconductor 11. In the present embodiment, the pre-exposure device 112 has a peak at a light source wavelength of 400 nm to 800 nm, and the light amount on the surface of the photoconductor 11 can be controlled in the range of 0.1 Lux · sec to 50 Lux · sec. The amount of light can be adjusted by adjusting the voltage applied to the light source.

  The photosensitive member 11 is rotationally driven at a predetermined speed (circumferential speed) in the direction of the arrow R1 in the figure, and after the surface of the photoreceptor 11 is neutralized by the pre-exposure device 112, the surface is uniformly charged by the charging roller 12. When image exposure is applied to the surface of the photoconductor 11, an electrostatic latent image (electrostatic image) corresponding to the image is formed on the surface of the photoconductor 11. As described above, the electrostatic latent image is developed by the developing device 14 and visualized as a toner image.

3. Next, the photoreceptor 11 will be described in more detail with reference to FIG.

  As shown in FIG. 3, the photoreceptor used in this example is an organic layered structure in which an undercoat layer 11B, a charge generation layer 11C, a charge transport layer 11D, and a surface layer 11E are stacked in this order on a support 11A. It is a photoreceptor.

  The support 11A for the photoconductor can be used without particular limitation as long as it has conductivity and does not affect the measurement of hardness. For example, a metal or alloy such as aluminum, copper, chromium, nickel, zinc and stainless steel formed into a drum shape can be used.

  The undercoat layer 11B improves the adhesion of the photosensitive layer, improves the coatability, protects the support 11A, covers defects on the support 11A, improves charge injection from the support 11A, or electrically breaks the photosensitive layer. It is formed for protection against such as. As the material of the undercoat layer 11B, polyvinyl alcohol, poly-N-vinylimidazole, polyethylene oxide, ethyl cellulose, ethylene-acrylic acid copolymer, casein, polyamide, N-methoxymethylated 6 nylon, copolymer nylon, glue and Gelatin or the like can be used. These are dissolved in an appropriate solvent and coated on the support 11A. At that time, the thickness of the undercoat layer 11B is preferably 0.1 to 2 μm.

  Next, a photosensitive layer is formed on the undercoat layer 11B.

  In the case of forming a stacked photosensitive layer in which the charge generation layer 11C and the charge transport layer 11D are functionally separated and stacked, the charge generation layer 11C and the charge transport layer 11D are stacked in this order on the undercoat layer 11B.

  Here, as the charge generation material used for the charge generation layer 11C, selenium-tellurium, pyrylium, thiapyrylium dyes, various central metals and crystal systems, more specifically, for example, α, β, γ, ε, and X type Phthalocyanine compounds having a crystal form such as, anthanthrone pigments, dibenzpyrenequinone pigments, pyranthrone pigments, trisazo pigments, disazo pigments, monoazo pigments, indigo pigments, quinacridone pigments, asymmetric quinocyanine pigments, quinocyanine and JP-A No. 54-143645 Examples thereof include amorphous silicones described in the publication.

  In this example, the charge generation layer 11C using a phthalocyanine compound capable of increasing sensitivity to achieve high image quality was used.

  In the case of this laminated type photoconductor, the charge generation layer 11C is composed of a homogenizer, an ultrasonic dispersion, a ball mill, a vibration ball mill, a sand mill, an attritor and a roll mill together with the charge generation material 0.3 to 4 times the binder resin and solvent. And the dispersion is applied on the undercoat layer and dried, or a film comprising a single composition of the charge generating material is formed by using a vapor deposition method or the like. 11B is formed. The film thickness of the charge generation layer 11C is preferably 5 μm or less, and particularly preferably in the range of 0.1 to 2 μm.

  Examples of the binder resin include polymers and copolymers of vinyl compounds such as styrene, vinyl acetate, vinyl chloride, acrylic acid ester, methacrylic acid ester, vinylidene fluoride, trifluoroethylene, polyvinyl alcohol, polyvinyl acetal, polyvinyl Butyral, polycarbonate, polyester, polysulfone, polyphenylene oxide, polyurethane, cellulose resin, phenol resin, melamine resin, silicon resin, epoxy resin, and the like can be used.

  The surface layer 11E in the present embodiment can be formed by polymerizing or crosslinking the above-described hole transporting compound having a chain polymerizable functional group. The surface layer 11E is formed as a charge transport layer 11D on the charge generation layer 11C, or a charge transport layer 11D made of a charge transport material and a binder resin is formed on the charge generation layer 11C and then protected thereon. It is formed as a layer. In any case, a surface layer can be formed by forming a film containing a hole transporting compound, polymerizing or crosslinking the hole transporting compound, and curing the film. As a method for forming the solution into a film, for example, a coating method such as a dip coating method, a spray coating method, a curtain coating method, or a spin coating method can be used. Among them, the dip coating method is preferable from the viewpoint of efficiency / productivity. Further, vapor deposition, plasma and other known film forming methods can be applied.

  The polymerization or crosslinking can be performed using heat, visible light, light such as ultraviolet rays, and radiation. For example, the surface layer 11E is formed by applying heat or irradiating light or radiation to a film formed using the above-described hole transporting compound and, if necessary, a coating solution for the surface layer containing a polymerization initiator. It is good to form. Among these, it is more preferable to use radiation. This is because polymerization by radiation does not particularly require a polymerization initiator. This is because the surface layer 11E of a very high purity three-dimensional matrix can be produced, and a photoconductor showing good electrophotographic characteristics can be obtained. The radiation is an electron beam or γ-ray. In the case of irradiating an electron beam, it can be performed using an accelerator such as a scanning type, an electro curtain type, a broad beam type, a pulse type, and a laminar type. It is important to consider the electron beam irradiation conditions in order to obtain a photoreceptor in which the values of HU and elastic deformation rate are in a specific range and the durability against electric characteristics and mechanical deterioration is improved. For example, the acceleration voltage is preferably 250 KV or less, more preferably 150 KV or less. The irradiation dose is preferably in the range of 0.1 Mrad to 100 Mrad, and more preferably in the range of 0.5 Mrad to 20 Mrad. When the accelerating voltage exceeds the above, the electrical characteristics deteriorate. Further, when the irradiation dose is smaller than the above range, the surface layer 11E is not sufficiently cured, whereas when the irradiation dose is large, the electrical characteristics are deteriorated.

  Furthermore, in order to further harden the surface layer 11E, heat may be applied during the polymerization reaction by the electron beam. As the timing of applying heat, it is sufficient that the photoconductor is at a constant temperature while radicals are present. Therefore, heating may be performed at any stage before, during or after electron beam irradiation. The heating temperature may be adjusted so that the temperature of the photoreceptor is from room temperature to 250 ° C. More preferably, it is 50 degreeC-150 degreeC. This is because when the temperature is higher than the above range, the material of the photoreceptor is deteriorated. The time for heating depends on the temperature, but is preferably about several seconds to several tens of minutes.

  The atmosphere during irradiation and heating may be any of air, inert gas such as nitrogen and helium, and vacuum. In an inert gas or vacuum is preferable in that radical deactivation due to oxygen can be suppressed.

  The film thickness when the hole transporting compound is used as the charge transport layer 11D is preferably 1 to 50 μm, and particularly preferably 3 to 30 μm.

  When the hole transporting compound is used as a protective layer on the charge generation layer 11C / charge transport layer 11D, the charge transport layer 11D corresponding to the lower layer is formed as follows.

  Suitable charge transport materials, for example, poly-N-vinylcarbazole, polystyryl anthracene, and other heterocyclic compounds and condensed polycyclic aromatic polymer compounds, pyrazoline, imidazole, oxazole, triazole, carbazole and other heterocyclic compounds, Low molecular weight compounds such as triarylalkane derivatives such as phenylmethane, triarylamine derivatives such as triphenylamine, phenylenediamine derivatives, N-phenylcarbazole derivatives, stilbene derivatives, hydrazone derivatives, etc. The same resin as described in the generation layer can be applied) and dispersed / dissolved in a solvent, and the solution is applied onto the charge generation layer 11C and dried using the above-described known method. In this case, the ratio of the charge transport material to the binder resin is preferably 20 to 100, more preferably 30 to 100, when the total weight of both is 100. If the amount of the charge transporting material is less than that, the charge transporting ability is lowered, and problems such as a decrease in sensitivity and an increase in residual potential occur. The thickness of the charge transport layer 11D in the multilayer photoconductor on which the protective layer is formed is preferably 1 to 50 μm, more preferably 3 to 30 μm. Further, the thickness of the surface layer 11E at this time is preferably 0.5 to 10 μm, more preferably 1 to 7 μm. In this embodiment, a photosensitive member having a film thickness of 18 μm is used for the charge transport layer 11D and 5 μm for the surface layer 11E.

4). Pre-exposure optimization control (a) Principle In the present embodiment, the image forming apparatus 100 causes a direct current to flow from the charging roller 12 to the photosensitive member 11 when the photosensitive member 11 and the charging roller 12 pass through a charging position facing each other. It has a current detector (detection circuit) 202 (FIG. 11) as charging current detection means for detecting current. Then, the current detector 202 detects a charging direct current when the dark portion potential VD region where the latent image is not formed on the photoconductor 11 and the bright portion potential VL region where the latent image is formed pass through the charging roller 12. . Based on the detected value, the exposure amount (light irradiation amount) irradiated by the pre-exposure device 112 during image formation is controlled. In particular, in this embodiment, the pre-exposure device 112 uses the pre-exposure device 112 to detect the charging current in the dark portion potential VD region where the latent image is not formed and the bright portion potential VL region where the latent image is formed. 11 is performed by changing the amount of pre-exposure irradiated to at least two stages. Then, a desired pre-exposure amount is controlled by detecting a difference in DC current amount between the dark portion potential VD region and the light portion potential VL region.

  In other words, in this embodiment, the image forming apparatus 100 includes a current detector 202 that detects a current that flows when a predetermined voltage is applied to the charger 12. The image forming apparatus 100 also includes execution means for executing a test mode in which the next first area and second area are formed on the photoconductor 11. That is, the first area is an area that is charged by the charger 12 under a predetermined charging condition and exposed by the image exposure unit 13 under a predetermined exposure condition. The second region is a region that is charged by the charger 12 under a predetermined charging condition and is not substantially exposed by the image exposure unit 13. In this embodiment, the control unit (control processing unit) 200 has the function of the execution means. Further, the image forming apparatus 100 uses the photostatic discharger 112 according to the output of the current detector 202 obtained when the first and second regions formed on the photoconductor 11 pass through the charging position in the test mode. And adjusting means for adjusting the light irradiation amount. In this embodiment, the control unit (control processing unit) 200 has the function of the adjusting means. In particular, in the present embodiment, the execution means is configured to form a plurality of first and second regions of the photosensitive member 11 by performing a charge removal process with a light discharger 112 under a plurality of predetermined charge removal conditions. .

  With such a configuration, it is possible to calculate and set the pre-exposure amount necessary to eliminate the ghost in real time according to the environment and the deterioration state of the photoconductor 11. Therefore, it is possible to prevent the photoconductor 11 from being irradiated with an excessive pre-exposure amount. Accordingly, it is possible to suppress an image defect such as an increase in the bright portion potential that occurs as a negative effect of the pre-exposure, or an image flow or filming due to a discharge deterioration of the photoconductor 11, and a decrease in the life of the photoconductor 11. Can be prevented. Further, in this embodiment, since the charging roller 12 is used as means for detecting information corresponding to the potential of the photoconductor 11, the information can be detected without providing any special means. This will be described in more detail below.

(B) Overall Sequence Next, referring to the control flow of FIG. 4, the timing chart of FIG. 5, and a schematic diagram showing the potential transition of the light portion potential VL region and the dark portion potential VD region of the photoconductor 11 of FIG. 6. The pre-exposure optimization control (potential prediction control), which is a test mode in this embodiment, will be described.

  In the following description, the operation in one image forming unit 10 will be described as a representative, but in the present embodiment, the same operation is performed in all the image forming units 10. Typically, the pre-exposure optimization control is executed at substantially the same timing in all the image forming units 10, but may be executed at different timings.

  In the present embodiment, the control and information processing of each part of the image forming apparatus 100 in the pre-exposure optimization control is a control processing unit (control unit) 200 as a control unit that comprehensively controls the operation of the image forming apparatus. Do.

  The image forming apparatus 100 according to the present exemplary embodiment includes a counter (counter memory) 203 (FIG. 11) that counts the number of output sheets (number of image forming sheets) as a usage amount detecting unit of the image forming apparatus 100 in the apparatus main body. As shown in FIG. 4, even during the image forming operation, the potential prediction control is performed once for each predetermined number of output sheets based on the count result of the number of output sheets by the counter 203. This control interval can be changed according to the environment in which the apparatus main body is placed and the total number of output sheets of the image forming apparatus 100. Usually, it is desirable to perform control once for about 500 to 5000 output sheets. In this embodiment, the control is set to perform control once per 1000 sheets regardless of the total output number of the image forming apparatus 100.

  Referring to FIGS. 4 and 5, first, when it is determined by the counter 203 within the apparatus main body that the number of output sheets has reached 1000, STEP 1 is controlled. At this time, the bias applied to the charging roller 12, the developing device 14, the primary transfer roller 35, the image exposure device 3 and the pre-exposure device 112 are once turned off, and the image formation is interrupted once.

  Next, in STEP 1, after the photosensitive member 11 is charged under a predetermined charging condition, the light amount of the pre-exposure device 112 is set to the first light amount. Then, by controlling the amount of light of the image exposure device 3, the light portion potential VL region (first region) exposed on the photoconductor 11 under predetermined exposure conditions and the image exposure device 3 are not subjected to substantial exposure processing. A dark portion potential VD region (second region) is formed.

  In the control of STEP 1, the amount of image exposure is switched in order to create a bright portion potential and a dark portion potential region. Here, for example, in the flowchart of FIG. 7 to be described later, it is described that the image exposure is turned off when the dark portion potential is created. Of course, the exposure amount that greatly affects the potential on the photoconductor 11. Instead, the image exposure may be performed if the exposure is weak. It is important in the present invention to create a bright portion potential region and a dark portion potential region as potentials on the photoconductor 11.

  The potential difference between the potential of the charging roller 12 (the value of the DC component of the applied voltage) and the potential of the surface of the photoconductor 11 immediately before reaching the charging roller 12 for each of the bright portion potential VL region and the dark portion potential VD region. That is, the charging contrast is calculated. As will be described in detail later, the charging contrast in each of the bright portion potential VL region and the dark portion potential VD region is detected by using a current detector 202 as a charging current detecting unit, and is photosensitive when passing through the charging roller 12. This corresponds to the potential of the body 11. Then, a potential difference ΔV (D−L) that is a potential difference (corresponding to a difference in charging contrast) between the bright portion potential VL region and the dark portion potential VD region is calculated.

  Next, in STEP 1, the light amount of the pre-exposure device 112 is changed to the second light amount, and the light amount of the image exposure device 3 is controlled in the same manner as described above to control the light portion potential VL region and the photosensitive member 11. A dark portion potential VD region is formed. In the same manner as described above, the potential difference ΔV (D−L) between the bright portion potential VL region and the dark portion potential VD region is calculated.

  Subsequently, the process proceeds to the control of STEP 2, from each pre-exposure amount in the control of STEP 1 and the potential difference ΔV (D−L) between the bright part potential VL region and the dark part potential VD region calculated for each pre-exposure amount. Then, a relational expression P between the pre-exposure amount L and the potential difference ΔV (D−L) is calculated. Then, from this relational expression P, a pre-exposure amount L ′ that gives a predetermined potential difference ΔV ′ (D−L) is calculated, and the pre-exposure amount at the time of image formation is calculated as the newly calculated pre-exposure amount L. Set to '.

  The pre-exposure amount is not limited to two steps of the first light amount and the second light amount. Increasing the sampling points in three steps and four steps means that the pre-exposure amount L and the potential difference ΔV (D− This is an effective means for improving the accuracy of the relational expression with L). Control can also be performed using the result of detecting the potential without performing pre-exposure and the result of detecting the potential by performing pre-exposure with one or a plurality of pre-exposure amounts.

  More specifically, as shown in FIG. 6, the surface potential of the photoconductor 11 after the charging process by the charging roller 12 includes a bright portion potential VL_int region that is a portion subjected to subsequent image exposure, and an image exposure. It is divided into two regions, a dark portion potential VD_int region, which is a portion that has not received light.

  Here, since the pre-exposure amount optimization control of this embodiment is intended only to eliminate the ghost potential, it is preferable to set the bright portion potential to a state in which there is a maximum potential difference from the dark portion potential. That is, it is desirable that the bright part potential VL_int area is an area formed with the maximum image exposure amount used at the time of image formation under the environment. Typically, it is preferable to perform so-called solid black latent image formation by performing so-called maximum overall exposure.

  When the bright portion potential VL_int region and the dark portion potential VD_int region both pass through the primary transfer portion, a bias having a polarity opposite to that applied at the charging portion (charging position) by the charging roller 12 is applied. Therefore, the potential difference between the bright part potential and the dark part potential becomes small. However, at this time, the potential difference between the bright part potential and the dark part potential is not lost unless the transfer potential of the primary transfer part is considerably increased. In the setting of the transfer potential that is normally used, in general, some potential difference remains. This causes image defects such as ghosts. Therefore, in this embodiment, the pre-exposure device 112 is installed to further reduce the potential difference between the bright part potential and the dark part potential.

  Generally, the amount of pre-exposure is often set so that the potential difference between the bright portion potential and the dark portion potential remaining after transfer is completely eliminated by pre-exposure. That is, the potential when the bright portion potential passes through the pre-exposure portion (pre-exposure position) by the pre-exposure device 112 is VL_last, and the potential when the dark portion potential passes through the pre-exposure portion is VD_last. At this time, the potential difference ΔV (D−L) between VD_last and VL_last is often set to 0V. Typically, the pre-exposure amount is often set to about 10 times the image exposure light amount, and is generally about 30 to 50 Lux · sec, although it varies depending on the process speed.

  However, according to the study of the present inventor, in order to make an image defect such as a ghost almost unrecognizable visually, it is possible to use a potential difference ΔV (D−D) between VD_last and VL_last for a copying machine used in a general office. It is sufficient if L) is about 10V. Further, in order to make it possible for the user to vary the degree of suppression of image defects such as ghosts, it is possible to change the setting of the pre-exposure device 112 by changing the target of this potential difference ΔV (DL). . That is, the present embodiment provides control that allows the pre-exposure amount of the pre-exposure device 112 to be appropriately set according to the target if a target having a potential difference ΔV (D−L) is set.

(C) STEP 1 Control Next, STEP 1 control in the pre-exposure amount optimization control of the present embodiment will be described in more detail.

  A predetermined voltage is applied to the charging roller 12 and the primary transfer roller 35 in a state in which the surface of the photoconductor 11 is irradiated with a predetermined first light amount of pre-exposure from the pre-exposure device 112. Then, two types of regions are created: a bright portion potential VL_int region where image exposure is performed by the image exposure unit 3 and a dark portion potential VD_int region where image exposure is not performed.

  A charging DC current in each region of the bright portion potential VL_int region and the dark portion potential VD_int region is detected by a current detector 202 as a charging current detection means. The current detector 202 detects a current flowing from the charging roller 12 to the photoconductor 11 when the charging power supply 201 outputs a voltage to the charging roller 12. Thereby, the potential VL_last of the surface of the photoconductor 11 immediately before the bright portion potential VL_int region passes through the pre-exposed portion and enters the charging portion is calculated. This also calculates the potential VD_last of the surface of the photoconductor 11 immediately before the dark portion potential VD_int region passes through the pre-exposed portion and enters the charging portion.

  Then, a potential difference ΔV (D−L) between the surface potential VL_last of the photoconductor 11 immediately before the bright portion potential enters the charging portion and the surface potential VD_last of the photoconductor 11 immediately before the dark portion potential enters the charging portion is calculated. To do.

  Subsequently, the light amount of the pre-exposure device 112 is switched to a predetermined second light amount, and the potential difference ΔV (D−L) is calculated in the same manner as described above.

  Here, the relationship between the bright part potential VL_last and the dark part potential VD_last and the charging direct current will be described. More specifically, this relationship is the difference between the potential of the surface of the photoconductor 11 immediately before the two regions enter the charging portion and the potential of the charging roller 12 (the value of the DC component of the applied voltage), that is, charging. Corresponds to the relationship of charging direct current to contrast.

  The relationship of the charging direct current with respect to the charging contrast is almost unambiguously determined by the environment, the deterioration of the surface of the photosensitive member 11, the deterioration of the charging means, and the like. In this embodiment, the relationship is as shown in FIG. Further, it is known that the relationship of the charging direct current with respect to the charging contrast changes only by the change in the film thickness of the surface layer of the photoreceptor 11. As described above, in the present embodiment, a material that is hardly scraped is used as the surface layer of the photoconductor 11. Therefore, in this embodiment, the relationship between the charging DC current and the charging contrast is uniquely determined as shown in FIG. 12, and this relationship is used to determine the potential of the surface of the photoconductor 11 from the detected value of the charging DC current. Is calculated. In the present embodiment, the relational expression representing the relationship of FIG. 12 is stored in a storage unit (storage unit) included in the control processing unit 200 of the apparatus main body. Thereby, the control processing unit 200 can calculate the potential of the surface of the photoconductor 11, more specifically, the charging contrast, according to the output of the current detector 202.

  Note that, when the photoconductor 11 having a variable thickness is used as the surface layer of the photoconductor 11, the relationship of the charging DC current to the charging contrast may vary depending on the film thickness state of the photoconductor 11. In this case, it is preferable to set a relational expression of the charging direct current with respect to the charging contrast in accordance with each film thickness state of the photoconductor 11. Such a relational expression can be stored in a storage unit included in the apparatus main body, and using this improves the accuracy of detection of the potential of the surface of the photoconductor 11.

  The control of STEP 1 will be described in more detail later with reference to a specific example.

(D) STEP2 Control Next, the STEP2 control in the pre-exposure optimization control of this embodiment will be described in more detail.

  From the potential difference ΔV (DL) between the potential VL_last and the potential VD_last for the two types of pre-exposure amounts calculated in STEP 1, the light amount L and the potential difference ΔV (DL) of the pre-exposure device 112 as shown in FIG. The relational expression P is calculated.

  Subsequently, the light amount L ′ of the pre-exposure device 112 at which the potential difference ΔV (D−L) becomes a desired value is calculated from the relational expression P, and the setting of the pre-exposure amount at the time of image formation is calculated. Change to light quantity L ′.

  The control of STEP 2 will be described in more detail later with reference to a specific example.

(E) Specific Example of STEP 1 Control Next, with reference to FIG. 7 and FIG. 10, the control of STEP 1 will be described in more detail with an example.

  The control processing unit 200 of the apparatus main body detects the number of output sheets by the counter 203, and interrupts image formation as a preparatory step so as to enter the control of STEP1 when it is the timing of pre-exposure amount optimization control. Specifically, the charging DC voltage is turned off, the image exposure is turned off, the pre-exposure is turned off, the development DC voltage is turned off, and the transfer DC voltage is turned off.

  In addition, as a preparatory stage, in order to erase the previous image formation history from the photoconductor 11, the image formation is stopped after at least one pre-exposure of the photoconductor 11 is irradiated with the image exposure turned off. It is preferable to enter the process. Depending on the image forming conditions, this step may be omitted.

  Next, in a state where the pre-exposure amount is 10 Lux · sec, a transfer DC voltage of +300 V is applied, and a charging DC voltage of −700 V is applied. As a result, a dark portion potential VD region where no image exposure is performed is formed on the photoconductor 11, and the surface of the photoconductor 11 charged to −700 V reaches the primary transfer portion. Thereafter, the potential of the photoconductor 11 in the dark portion potential VD region becomes about −100 to −500 V after passing through the primary transfer portion. Here, the pre-exposure setting and the charging potential and transfer potential setting may be freely set according to the environment in which the apparatus main body is placed, the process speed of the apparatus main body, and the like. In this example, the voltage became −300 V after passing through the primary transfer portion.

  Next, the region where the potential of the photoreceptor 11 after passing through the primary transfer portion is −300 V is neutralized by pre-exposure and becomes approximately −50 to −200 V. In this example, the voltage became −100 V after passing through the pre-exposure part.

  Next, in the region where the potential of the photoconductor 11 after passing through the pre-exposure portion is −100 V, the amount of direct current flowing through the charging portion and flowing through the charging roller 12 at that time is determined as charging current detecting means (charging current amount). Measurement is performed by a current detector 202 as a measurement means. At this time, the control processing unit 200 calculates the potential VD_last after the dark portion potential VD region passes through the pre-exposure portion, using the relationship shown in FIG. That is, in this embodiment, even if there is no potential sensor or the like, it is calculated from the charged direct current amount that the potential of the photoconductor 11 after passing through the pre-exposure portion is −100V.

  Next, while the settings of the transfer DC voltage and the charging DC voltage are kept as they are, this time image exposure is performed to form a light portion potential VL region that is image-exposed on the photoconductor 11, and the light portion potential VL region is Passes through the primary transfer section. Thereafter, in this region, after passing through the pre-exposure section, the potential VL_last is calculated from the amount of direct current flowing through the charging section 12 and flowing through the charging roller 12 at that time. In this example, the potential of the bright portion potential VL region of the photoconductor 11 immediately after the image exposure is −200 V, the potential of the photoconductor 11 after this region passes through the primary transfer portion is −100 V, and further this region. The potential of the photoconductor 11 after passing through the pre-exposed portion was −50V.

  Next, in the control processing unit 200, when the pre-exposure amount is 10 Lux · sec, the potential VD_last after the dark portion potential VD region has passed the pre-exposure portion and the bright portion potential VL region after having passed the pre-exposure portion A potential difference ΔV (D−L) of the potential VL_last is calculated. This calculation result is stored as a calculated value A. Here, the calculated value A was 50V.

  Subsequently, the potential after the dark portion potential VD region has passed through the pre-exposed portion in the same manner as in the case where the exposure amount is 10 Lux · sec with the pre-exposure amount setting changed to 30 Lux · sec. VD_last is calculated. By strengthening the pre-exposure, in this example, the potential VD_last of the photoconductor 11 after passing through the pre-exposure part became −50V.

  Next, in a state where the pre-exposure amount is 30 Lux · sec, the potential VL_last after the bright portion potential VL region has passed through the pre-exposure portion is calculated by the same method as in the case where the exposure amount is 10 Lux · sec. Also in this case, by increasing the pre-exposure, in this example, the potential VL_last of the photoconductor 11 after passing through the pre-exposure section becomes −45V.

  Next, in the control processing unit 200, when the pre-exposure amount is 30 Lux · sec, the potential VD_last after the dark portion potential VD region has passed the pre-exposure portion and the bright portion potential VL region after having passed the pre-exposure portion A potential difference ΔV (D−L) of the potential VL_last is calculated. This calculation result is stored as a calculated value B. Here, the calculated value B was 5V.

(F) Specific Example of STEP 2 Control Next, with reference to FIGS. 8 and 10, the control of STEP 2 will be described in more detail with an example.

  The control processing unit 200 calculates the relational expression P from the calculated values A and B of the potential difference ΔV (D−L) calculated in STEP 1 and the light amount setting L of the pre-exposure device 112 at that time.

In this example, the relational expression P calculated by the control processing unit 200 is as follows.
y = −2x + 65... P ′ formula (where x is the light amount setting value L and y is the potential difference ΔV (D−L)).

  Next, the charging DC voltage and the transfer DC voltage are turned off, and the pre-exposure is turned off, and the process proceeds to image formation. At this time, a pre-exposure amount L ′ at the time of image formation to be newly set is calculated according to the formula P ′.

  In this embodiment, since the image forming apparatus 100 is a general office machine, if the potential difference ΔV (D−L) between the potential VD_last and the potential VL_last is 10 V or less, image defects such as ghosts may not be a problem. Absent. Therefore, in this embodiment, the target of the potential difference ΔV (D−L) is set to 10V.

  Here, as a condition for causing an image defect such as a ghost, the potential difference ΔV (DL) calculated as described above, that is, the dark portion potential VD region and the bright portion potential VL region after passing through the pre-exposed portion. It is important to make the potential difference between the two as small as possible. Then, as shown in FIG. 9, it is possible to control the potential difference ΔV (D−L) to be small by increasing the pre-exposure amount. If the pre-exposure amount is extremely increased, as shown in FIG. 9, the potential difference ΔV (D−L) can be made substantially 0V. For this reason, conventionally, the pre-exposure amount is set to be as large as possible so that ghosts can be satisfactorily suppressed under various circumstances.

  However, there is no point in irradiating pre-exposure more than necessary and keeping the potential difference ΔV (D−L) smaller than necessary. As described above, the potential difference ΔV (D−L) of about 10 V or less is sufficient in an environment normally used in an office. Preferably, it may be controlled to about 4 to 10V. Further, if desired, for example, when an image with a noticeable ghost is frequently output, the potential difference ΔV (DL) may be set to 4 V or less. According to the method of the present embodiment, it is possible to freely change the target of the potential difference ΔV (D−L) as desired, and it is possible to suppress the necessary pre-exposure amount under various circumstances. It becomes possible.

  Therefore, the control processing unit 200 calculates x by substituting 10 for y in the expression P ′. Thus, in this example, x = 27.5, and it is calculated that the pre-exposure amount L ′ to be set at the time of image formation is 27.5 Lux · sec. In the present embodiment, until the next pre-exposure amount optimization control is performed, the pre-exposure amount condition at the time of image formation is changed to the pre-exposure amount newly calculated here.

  As described above, according to the present exemplary embodiment, the image forming apparatus 100 includes the detection unit 202 that detects information corresponding to the potential of the surface of the photoconductor 11 immediately before reaching the charging position. The image forming apparatus 100 also includes a control unit 200 that controls the exposure amount of the pre-exposure unit 112 during image formation based on the detection result of the following information by the detection unit 202. That is, the first information is information corresponding to the surface potential of the photoconductor 11 immediately after reaching the charging position without being exposed by the image exposure unit 3 after being charged by the charging unit 12. Secondly, the information corresponds to the potential of the surface of the photoconductor 11 immediately after being charged by the charging unit 12 and then exposed to the image exposure unit 3 and reaching the charging position again. In particular, in the present embodiment, image formation is performed based on the result of detecting the first and second information in a state where the pre-exposure unit 112 irradiates the photoconductor 11 with at least two different exposure amounts. The exposure amount of the pre-exposure means 112 at the time is controlled.

  As described above, by setting the pre-exposure amount according to the present embodiment, it is possible to avoid excessive pre-exposure irradiation and suppress deterioration of the photoconductor 11. In this embodiment, the configuration is simpler because it is not necessary to use a potential sensor or the like. That is, according to the present embodiment, the optimum pre-exposure amount can be set with a simple configuration, and the bright portion potential of the photoconductor 11 is increased due to the excessive pre-exposure amount, image flow and filming. Image defects due to occurrence can be suppressed. As a result, it is possible to maintain an output with more stable image quality.

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.

  As shown in FIGS. 13, 14, and 17, in this embodiment, a potential sensor (potential detector) 120 as a potential detection unit (charging potential measurement unit) is disposed around the photoconductor 11.

  That is, in Example 1, the potential VD_last and the potential VL_last after passing through the pre-exposure portion were calculated from the result of measuring the charging direct current when the target region on the photoconductor 11 passes through the charging portion. On the other hand, in this embodiment, the surface potential of the photoconductor 11 can be directly measured. Therefore, the control of STEP 1 is simpler than that of the first embodiment.

  That is, in this embodiment, the image forming apparatus 100 includes a potential detector 120 that detects the surface potential of the photoconductor 11. Further, the image forming apparatus 100 includes an execution unit that executes a test mode in which the first region and the second region similar to those in the first embodiment are formed on the photosensitive member 11. In this embodiment, the image forming apparatus 100 further uses the light neutralizer 112 in accordance with the result of detection of the first and second regions formed on the photoconductor 11 by the potential detector 120 in the test mode. An adjusting means for adjusting the light irradiation amount is provided. In this embodiment, the control unit (control processing unit) 200 has the function of the adjusting means. In particular, in the present embodiment, the execution means is configured to form a plurality of first and second regions of the photosensitive member 11 by performing a charge removal process with a light discharger 112 under a plurality of predetermined charge removal conditions. .

  When the potential sensor 120 is disposed at a location as shown in FIG. 13, that is, downstream of the cleaning device 15 and upstream of the charging roller 12 in the rotation direction of the photoconductor 11, the photoconductor 11 after passing through the pre-exposure section is arranged. The potential matches the value of the potential detected by the direct potential sensor 120.

  However, when the potential sensor 120 is arranged at a location as shown in FIG. 14, that is, downstream of the charging roller 12 in the rotation direction of the photosensitive member 11, the potential of the photosensitive member 11 after passing through the pre-exposure portion is directly The potential value detected by the potential sensor 120 may not match. That is, in this case, if it passes through the charging portion again and returns to the dark portion potential VD state again, it becomes impossible to accurately know the potential of the photoconductor 11 after passing through the pre-exposure portion. Accordingly, in this case, as shown in FIG. 16, the application of the charging voltage is temporarily stopped immediately before the potential of the photosensitive member 11 is measured by the potential sensor 120, and the photosensitive member 11 after passing through the pre-exposure portion is measured. Control is performed so that the potential reaches the detection unit by the potential sensor 120 as it is. The detection of the potential of the photoconductor 11 by the potential sensor 120 is performed while the application of the charging voltage is temporarily stopped.

  In this embodiment, a charging roller 12 which is a member (contact charging member) in contact with the photoconductor 11 is used as a charging unit. However, when the potential of the photoconductor 11 is directly measured by the potential sensor 120 as in this embodiment, a non-contact charging unit such as a corona charger or a non-contact charging roller may be used.

  In this embodiment, the image forming apparatus 100 directly detects the potential on the photoconductor 11 immediately before passing through the charging position where the photoconductor 11 and the charging roller 12 face each other. A sensor 120 is included. The potential of the photosensitive member 11 immediately before the dark portion potential VD region where the latent image is not formed on the photosensitive member 11 and the bright portion potential VL region where the latent image is formed passes through the charging roller 12 is directly measured by the potential sensor 120. Detect. Based on the detected value, the exposure amount irradiated by the pre-exposure device 112 during image formation is controlled. In particular, in this embodiment, the operation of detecting the potential of the photosensitive member 11 in the dark portion potential VD region where the latent image is not formed on the photosensitive member 11 and the bright portion potential VL region where the latent image is formed is performed by the pre-exposure device 112. The pre-exposure amount applied to the photosensitive member 11 is changed in at least two stages. Then, a desired pre-exposure amount is controlled by detecting a difference in potential of the photoconductor 11 in each of the dark portion potential VD region and the light portion potential VL region.

  With this configuration, as in the first embodiment, it is possible to calculate and set the pre-exposure amount necessary to eliminate the ghost in real time according to the environment and the deterioration state of the photoconductor 11. Therefore, it is possible to prevent the photoconductor 11 from being irradiated with an excessive pre-exposure amount. Accordingly, it is possible to suppress an image defect such as an increase in the bright portion potential that occurs as a negative effect of the pre-exposure, or an image flow or filming due to a discharge deterioration of the photoconductor 11, and a decrease in the life of the photoconductor 11. Can be prevented.

  Next, with reference to FIG. 15, the control of STEP1 in the pre-exposure amount optimization control of the present embodiment will be described in more detail.

  The control processing unit 200 of the apparatus main body detects the number of output sheets by the counter 203, and interrupts image formation as a preparatory step so as to enter the control of STEP1 when it is the timing of pre-exposure amount optimization control. Specifically, the charging DC voltage is turned off, the image exposure is turned off, the pre-exposure is turned off, the development DC voltage is turned off, and the transfer DC voltage is turned off.

  In addition, as a preparatory stage, in order to erase the previous image formation history from the photoconductor 11, the image formation is stopped after at least one pre-exposure of the photoconductor 11 is irradiated with the image exposure turned off. It is preferable to enter the process. Depending on the image forming conditions, this step may be omitted.

  Next, in a state where the pre-exposure amount is 10 Lux · sec, a transfer DC voltage of +300 V is applied, and a charging DC voltage of −700 V is applied. As a result, a dark portion potential VD region where no image exposure is performed is formed on the photoconductor 11, and the surface of the photoconductor 11 charged to −700 V reaches the primary transfer portion. Thereafter, the potential of the photoconductor 11 in the dark portion potential VD region becomes about −100 to −500 V after passing through the primary transfer portion. Here, the pre-exposure setting and the charging potential and transfer potential setting may be freely set according to the environment in which the apparatus main body is placed, the process speed of the apparatus main body, and the like. In this example, the voltage became −300 V after passing through the primary transfer portion.

  Next, the region where the potential of the photoreceptor 11 after passing through the primary transfer portion is −300 V is neutralized by pre-exposure and becomes approximately −50 to −200 V. In this example, the voltage became −100 V after passing through the pre-exposure part.

  Next, the region where the potential of the photoconductor 11 after passing through the pre-exposure unit reaches −100V reaches the detection unit of the potential sensor 120, and the potential VD_last (−100V in this example) of this region is directly It is measured by the potential sensor 120.

  Next, while the settings of the transfer DC voltage and the charging DC voltage are kept as they are, this time image exposure is performed to form a light portion potential VL region that is image-exposed on the photoconductor 11, and the light portion potential VL region is Passes through the primary transfer section. Thereafter, this region passes through the pre-exposure unit and then reaches the detection unit of the potential sensor 120, and the potential VL_last is directly measured by the potential sensor 120. In this example, the potential of the bright portion potential VL region of the photoconductor 11 immediately after the image exposure is −200 V, the potential of the photoconductor 11 after this region passes through the primary transfer portion is −100 V, and further this region. The potential of the photoconductor 11 after passing through the pre-exposed portion was −50V.

  Next, in the control processing unit 200, when the pre-exposure amount is 10 Lux · sec, the potential VD_last after the dark portion potential VD region has passed the pre-exposure portion and the bright portion potential VL region after having passed the pre-exposure portion A potential difference ΔV (D−L) of the potential VL_last is calculated. This calculation result is stored as a calculated value A. Here, the calculated value A was 50V.

  Subsequently, the potential after the dark portion potential VD region has passed through the pre-exposed portion in the same manner as in the case where the exposure amount is 10 Lux · sec with the pre-exposure amount setting changed to 30 Lux · sec. VD_last is calculated. By strengthening the pre-exposure, in this example, the potential VD_last of the photoconductor 11 after passing through the pre-exposure part became −50V.

  Next, in a state where the pre-exposure amount is 30 Lux · sec, the potential VL_last after the bright portion potential VL region has passed through the pre-exposure portion is calculated by the same method as in the case where the exposure amount is 10 Lux · sec. Also in this case, by increasing the pre-exposure, in this example, the potential VL_last of the photoconductor 11 after passing through the pre-exposure section becomes −45V.

  Next, in the control processing unit 200, when the pre-exposure amount is 30 Lux · sec, the potential VD_last after the dark portion potential VD region has passed the pre-exposure portion and the bright portion potential VL region after having passed the pre-exposure portion A potential difference ΔV (D−L) of the potential VL_last is calculated. This calculation result is stored as a calculated value B. Here, the calculated value B was 5V.

  Next, STEP2 control will be described. STEP2 control is substantially the same as STEP2 control in the first embodiment.

  That is, the control processing unit 200 calculates the relational expression P from the calculated values A and B of the potential difference ΔV (D−L) calculated by the control of STEP 1 and the light amount setting L of the pre-exposure device 112 at that time. .

In this example, the relational expression P calculated by the control processing unit 200 is as follows.
y = −2x + 65... P ′ formula (where x is the light amount setting value L and y is the potential difference ΔV (D−L)).

  Also in this embodiment, according to the above method, the target of the potential difference ΔV (D−L) can be freely changed as desired, and the necessary minimum pre-exposure is possible even under various circumstances. It becomes possible to reduce the amount.

  In this embodiment, the image forming apparatus 100 is a general office machine. However, here, assuming that the ghost is more severely suppressed, the potential VD_last after the dark portion potential VD region passes through the pre-exposure portion and the potential VL_last after the bright portion potential VL region passes through the pre-exposure portion. The potential difference ΔV (D−L) was set to 5V.

  Therefore, the control processing unit 200 calculates x by substituting 5 for y in the expression P ′. Thereby, in this example, x = 30, and it is calculated that the pre-exposure amount L ′ to be set at the time of image formation is 30 Lux · sec. In the present embodiment, until the next pre-exposure amount optimization control is performed, the pre-exposure amount condition at the time of image formation is changed to the pre-exposure amount newly calculated here.

  As described above, by setting the pre-exposure amount according to the present embodiment, it is possible to avoid excessive pre-exposure irradiation and suppress deterioration of the photoconductor 11. Further, in this embodiment, by using the potential sensor 120, the potential of the photoconductor 11 can be directly measured, so that the control process is simpler.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic cross-sectional view illustrating a configuration around a photoconductor of an image forming unit in an embodiment of the image forming apparatus according to the present invention. It is a schematic diagram for demonstrating the layer structure of a photoreceptor. It is a flowchart figure of the control according to this invention. It is a timing chart figure of the control according to this invention. It is a schematic diagram which shows transition of the electric potential of the bright part electric potential VL area | region and the dark part electric potential VD area | region. It is a flowchart figure of the control according to this invention. It is a flowchart figure of the control according to this invention. It is a schematic diagram of the relational expression calculated during control according to the present invention. It is a schematic diagram which shows an example of transition of a photoreceptor potential. 1 is a schematic control block diagram in an embodiment of an image forming apparatus according to the present invention. It is the schematic diagram which showed the relationship between charging direct current and (DELTA) V (DL). FIG. 6 is a schematic cross-sectional view showing a configuration around a photoreceptor of an image forming unit in another embodiment of the image forming apparatus according to the present invention. FIG. 6 is a schematic cross-sectional view showing a configuration around a photoreceptor of an image forming unit in another embodiment of the image forming apparatus according to the present invention. It is a flowchart figure of the control according to this invention. It is a timing chart figure of the control according to this invention. It is a general | schematic control block diagram in the other Example of the image forming apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Photoconductor 12 Charging roller 112 Pre-exposure device 200 Control processing part 201 Charging power supply 202 Charging current detection means

Claims (4)

Formed on the photoconductor by the photoconductor, a charger for charging the photoconductor at a charging position, an image exposure device for performing image exposure on the photoconductor charged by the charger, and the image exposure device In an image forming apparatus, comprising: a developing unit that develops an electrostatic image; and a light static eliminator that neutralizes the photosensitive member by light irradiation after the developed image formed by the developing unit is transferred to a transfer target.
A current detector for detecting a current flowing when a predetermined voltage is applied to the charger;
A first region that is charged by the charger under a predetermined charging condition and exposed by the image exposure device under a predetermined exposure condition; and charged by the charger under a predetermined charging condition; and Execution means for executing a test mode in which a second region that is not substantially exposed by the image exposure device is formed on the photoconductor;
In the test mode, the amount of light irradiated by the light static eliminator is adjusted according to the output of the current detector obtained when the first and second regions formed on the photoconductor pass through the charging position. Adjusting means;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the execution unit forms a plurality of first and second regions of the photoconductor by performing a charge removal process under a plurality of predetermined charge removal conditions by the light discharger. apparatus. Formed on the photoconductor by the photoconductor, a charger for charging the photoconductor at a charging position, an image exposure device for performing image exposure on the photoconductor charged by the charger, and the image exposure device In an image forming apparatus, comprising: a developing unit that develops an electrostatic image; and a light static eliminator that neutralizes the photosensitive member by light irradiation after the developed image formed by the developing unit is transferred to a transfer target.
A potential detector for detecting the surface potential of the photoreceptor;
A first region that is charged by the charger under a predetermined charging condition and exposed by the image exposure device under a predetermined exposure condition; and charged by the charger under a predetermined charging condition; and Execution means for executing a test mode in which a second region that is not substantially exposed by the image exposure device is formed on the photoconductor;
Adjusting means for adjusting the amount of light irradiated by the light neutralizer according to the result of detection of the first and second regions formed on the photoconductor in the test mode by the potential detector;
An image forming apparatus comprising:   The image forming apparatus according to claim 3, wherein the execution unit forms a plurality of first and second regions of the photoconductor by performing a charge removal process under a plurality of predetermined charge removal conditions by the light discharger. apparatus.

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