JP2023048627A - Image forming apparatus - Google Patents

Abstract

To perform image quality adjustment according to a difference in the potential of an exposed part of a photoreceptor.SOLUTION: An image forming apparatus develops latent images that are formed by exposing, with exposure means 21, photoreceptors on which electrification processing is uniformly performed by electrification means, transfers images obtained through the development from the photoreceptors to a transfer target material, and eliminates static electricity on the surfaces of the photoreceptors after the transfer with static elimination means. The image forming apparatus has: detection means 516a that detects an electrification current value when the electrification processing is performed; and control means 500 that controls an imaging condition based on a static elimination part electrification current value when the electrification processing is performed on the photoreceptors from which static electricity is eliminated by the static elimination means, and an exposure part electrification current value when the electrification processing is performed on the photoreceptors on which the electrification processing is performed and which are exposed by the exposure means without eliminating static electricity therefrom with the static elimination means.SELECTED DRAWING: Figure 5

Description

The present invention relates to an image forming apparatus.

Conventionally, a latent image formed by exposing a photoreceptor uniformly charged by a charging means to light with an exposing means is developed, and the image obtained by development is transferred from the photoreceptor to a transfer material. 2. Description of the Related Art There is known an image forming apparatus that removes static electricity from the surface of a photoreceptor using a static eliminating means.

In Patent Document 1, a surface potential (charging potential) of a photoreceptor after charging processing by a charging means is predicted, and a charging bias (imaging condition) applied to the charging means is controlled based on the predicted charging potential of the photoreceptor. An image forming apparatus is disclosed that adjusts image quality by In this image forming apparatus, a charging current value when charging the photoreceptor after the photoreceptor has been neutralized with light and discharge, and a charging current value when charging the photoreceptor after the photoreceptor has been neutralized with light only Based on and, the residual potential of the photoreceptor after the photoreceptor is neutralized only with light is predicted. Then, the surface potential (charging potential) of the photoreceptor after charging processing is predicted using the prediction result of the residual potential of the photoreceptor after static elimination.

However, there is still room for improvement in image quality adjustment in conventional image forming apparatuses.

In order to solve the above-mentioned problems, the present invention develops a latent image formed by exposing a photoreceptor uniformly charged by a charging means to light with an exposing means, and an image obtained by the development is transferred from the photoreceptor. An image forming apparatus that performs transfer onto a transfer material and removes static electricity from the surface of a photoreceptor after transfer by a static elimination means, comprising a detection means for detecting a charging current value during the charging process, and static elimination by the static elimination means. a static elimination unit charging current value when the charged photosensitive member is subjected to the charging process; and control means for controlling the image forming conditions based on the exposure portion charging current value at the time.

According to the present invention, image quality adjustment can be performed according to the difference in the potential of the exposed portion of the photoreceptor, so that more suitable image quality adjustment is possible.

1 is an overall configuration diagram of a full-color copier according to an embodiment; FIG. 2 is a schematic configuration diagram of an image forming unit in the copier; FIG. FIG. 2 is an explanatory diagram of a configuration example of a charging roller in the copying machine; FIG. 2 is an explanatory diagram of a configuration example of a photoreceptor in the copying machine; FIG. 2 is a block diagram showing part of an electric circuit in the copying machine; 4 is a timing chart of an operation for acquiring a static elimination unit charging current value; Schematic diagrams schematically showing charging positions, exposure positions, and neutralization positions for explanation. FIG. 10 is a diagram showing the relationship between the pre-charging potential, the post-charging potential, and the detected current of the photoreceptor during the operation of acquiring the static elimination unit charging current value; 4 is a timing chart of operations for acquiring photoreceptor characteristics; A graph plotting the detected charging current [μA] on the horizontal axis and the applied charging DC bias×α [V] on the vertical axis. 4 is a timing chart of the acquisition operation of the exposure unit charging current value;

An embodiment in which the present invention is applied to a tandem intermediate transfer type full-color copier as an image forming apparatus will be described.
FIG. 1 is an overall block diagram of a full-color copier. This full-color copier comprises an apparatus main body 100, a paper feed table 200 on which the main body is placed, a scanner 300 mounted on the copier main body, an automatic document feeder (ADF) 400 mounted on the scanner, and the like.

In the center of the main body, a tandem image forming apparatus 20 is configured by arranging four image forming units 18Y, 18C, 18M, and 18Bk of Y, C, M, and Bk side by side. Each image forming unit of the tandem image forming apparatus has photoreceptors 40Y, 40C, 40M and 40Bk on which respective color toner images of Y, C, M and Bk are formed.

An exposure device 21 is provided above the tandem image forming apparatus. The exposure device consists of four laser diode (LD) light sources prepared for each color, a set of polygon scanners composed of six-sided polygon mirrors and polygon motors, and an fθ It is composed of lenses such as lenses, long WTL, and mirrors. The laser light emitted from the LD according to the image information of each color is deflected and scanned by the polygon scanner, and is irradiated onto the photosensitive member of each color.

An endless intermediate transfer belt 10 is installed below the tandem image forming apparatus. The intermediate transfer belt can be wrapped around three support rollers 14, 15, and 16 to rotate and convey clockwise in the figure, and the support roller 14 is a drive roller that drives the intermediate transfer belt to rotate. Between the first support roller 14 and the second support roller 15, primary transfer rollers 82Y, 82C, 82M, and 82Bk are provided as primary transfer means for transferring toner images from the photoreceptors of each color to the intermediate transfer belt. It is provided so as to face each photosensitive member with the belt interposed therebetween.

Downstream of the third support roller 16, an intermediate transfer belt cleaning device 17 is provided for removing residual toner remaining on the intermediate transfer belt after image transfer. As the material of the intermediate transfer belt, resin materials such as polyvinylidene fluoride, polyimide, polycarbonate, and polyethylene terephthalate can be molded into a seamless belt and used. These materials can be used as they are, or their resistance can be adjusted with a conductive material such as carbon black. Alternatively, these resins may be used as a base layer and a surface layer may be formed by a method such as spraying or dipping to form a laminated structure.

A secondary transfer device 22 is provided below the intermediate transfer belt. The secondary transfer device comprises a secondary transfer belt 24, which is an endless belt, stretched between two rollers 23, and is pressed against a third support roller 16 via the intermediate transfer belt. The image on the belt is transferred to the transfer material. The same material as the intermediate transfer belt can be used for the secondary transfer belt.

A fixing device 25 for fixing the image on the transfer material is provided beside the secondary transfer device. The fixing device is configured by pressing a pressure roller 27 against a fixing belt 26, which is an endless belt. The secondary transfer device described above also has a sheet conveying function for conveying the transfer material after image transfer to the fixing device. Of course, a transfer roller or a transfer charger may be arranged as the secondary transfer device, and in such a case, it is necessary to separately provide this transfer material conveying function.

Below the secondary transfer device and the fixing device, in parallel with the above-described tandem image forming device, a transfer material is reversed and ejected, and the transfer material is reversed and re-used to form images on both sides of the transfer material. A sheet reversing device 28 for feeding paper is provided.

When a copy operation is performed using this full-color copier, a document is set on the document platen 30 of the ADF. Alternatively, the ADF is opened to set the document on the contact glass 32 of the scanner, and the ADF is closed to hold the document. When the start switch of the operation display unit 515 (see FIG. 5) is pressed, when the document is set on the ADF, the document is conveyed and moved onto the contact glass, and then the caner is driven, and the first traveling body 33 is driven. and the second running body 34 . On the other hand, when the document is set on the contact glass, the scanner is immediately driven to run on the first traveling member 33 and the second traveling member 34 .

Light is emitted from the light source by the first traveling body, and the reflected light from the surface of the document is further reflected to be directed to the second traveling body, reflected by the mirror of the second traveling body, and passed through the imaging lens 35 to the reading sensor 36 . to read the content of the original. After that, the image forming operation is started in the full-color mode or the black-and-white mode according to the result of the reading of the original when the mode is set by the operation unit or the automatic mode selection is set by the operation unit.

When the full color mode is selected, each photoreceptor rotates counterclockwise in FIG. Then, the surface of each photoreceptor is uniformly charged by a charging roller, which is a charging device as charging means. Then, the photoreceptor of each color is irradiated with a laser beam corresponding to an image of each color from an exposure device as an exposure means, and a latent image corresponding to image data of each color is formed. Each latent image is developed with toner of each color by the developing devices 60Y, C, M, and Bk of each color as the photosensitive member rotates. The toner images of the respective colors are sequentially transferred onto the intermediate transfer belt as the intermediate transfer belt as a transfer material is conveyed to form a full-color image on the intermediate transfer belt. After the transfer, the photoreceptor is optically neutralized by a neutralization lamp as a neutralization means, and the residual toner is removed by the cleaning means.

On the other hand, one of the paper feed table paper feed rollers 42 is selectively rotated, and the transfer material is sent out from one of the paper feed cassettes 44 provided in multiple stages on the paper feed table 43 . Next, the sheet is separated one by one by the separation roller 45 and put into the paper feed path 46, transported by the transport roller 47, guided to the paper feed path 48 in the main body, and stopped by hitting the registration roller 49. - 特許庁Alternatively, the paper feed roller 50 is rotated to send out the transfer material on the manual feed tray 51, and the separation roller 52 separates the transfer material sheet by sheet into the manual feed path 53, and similarly hits the registration roller to stop. Then, the registration rollers are rotated in time with the full-color image on the intermediate transfer belt, the transfer material is fed between the intermediate transfer belt and the secondary transfer device, and the secondary transfer device transfers the toner onto the transfer material. Transfer the image.

The transfer material onto which the toner image has been transferred is conveyed by the secondary transfer device and sent to the fixing device, where heat and pressure are applied by the fixing device to fix the transfer material on the transfer material. It is ejected by rollers 56 and stacked on an ejection tray 57 . Alternatively, the sheet is switched by the switching claw to enter the sheet reversing device 28, where it is reversed and re-fed to the transfer position, and after an image is recorded on the back side, the sheet is discharged onto the discharge tray by the discharge rollers. Thereafter, when image formation of two or more sheets is instructed, the image forming process described above is repeated.

After the formation of a predetermined number of images is completed, post-image formation processing is performed, and then the rotation of the photoreceptor is stopped. In post-imaging processing, the photoreceptor is rotated more than once with the charging bias and transfer bias turned off. Prevent the body from deteriorating.

When the black-and-white mode is selected, the support roller 15 moves downward to separate the intermediate transfer belt from the photoreceptors Y, C, and M. Only the Bk photoreceptor rotates counterclockwise in FIG. 1, the surface of the Bk photoreceptor is uniformly charged by the charging roller, a laser beam corresponding to the Bk image is irradiated, and a latent image is formed. It is developed with Bk toner to form a toner image. This toner image is transferred onto the intermediate transfer belt. At this time, the photoreceptors for the three colors other than Bk and the developing device are stopped to prevent unnecessary consumption of the photoreceptors and developers.

On the other hand, a transfer material is fed from a paper feed cassette and conveyed by registration rollers at a timing that coincides with the toner image formed on the intermediate transfer belt. The transfer material onto which the toner image has been transferred is fixed by a fixing device in the same manner as in the case of a full-color image, and is processed through a paper discharge system according to the designated mode. Thereafter, when image formation of two or more sheets is instructed, the image forming process described above is repeated.

FIG. 2 shows the configuration of the image forming unit. An opening is provided around the photoreceptor 40, which is an image carrier, for passing exposure light 76 from an exposure device as an exposure means. A charging roller 70, which is a charging member as charging means for uniformly charging the photoreceptor, a developing device 60 for developing an electrostatic latent image formed on the photoreceptor, and a charge-removing device for discharging the surface of the photoreceptor after the toner image has been transferred. A charge removing lamp 72 as charge removing means, a brush roller 73 and a cleaning blade 75 for cleaning transfer residual toner are arranged.

A solid lubricant 78 is in contact with the brush roller 74 arranged downstream thereof, and the coating blade 80 applies the lubricant scraped off by the brush roller to the photosensitive member. Examples of solid lubricants that can be used include fatty acid metal salts such as zinc stearate and zinc palmitate, natural waxes such as carnauba wax, and fluorine-based resins such as polytetrafluoroethylene. . Other materials can also be mixed as needed. A solid lubricant can be produced by melting and solidifying lubricant particles or by compression molding.

Toner scraped from the photosensitive member by a brush roller or a cleaning blade made of polyurethane rubber is collected by a toner conveying coil 79 and conveyed to a waste toner storage section.

In this embodiment, the photoreceptor cleaned after transfer is cleaned, but the photoreceptor cleaned after transfer may be cleaned.

FIG. 3 shows the configuration of the charging roller 70 that can be used in this embodiment. The charging roller 70 is composed of a metal core 101 which is a conductive support, a resin layer 102 and a gap holding member 103 . A metal such as stainless steel is used for the metal core. If the metal core is too thin, the influence of bending when the resin layer 102 is cut or when the photosensitive member 40 is pressed cannot be ignored, making it difficult to obtain the required gap accuracy. Also, if the core metal 101 is too thick, the charge roller 70 may become large or heavy.

The resin layer of the charging roller 70 is preferably made of a material having a volume resistivity of 1×10 ⁴ to 1×10 ⁹ [Ωcm]. If the resistance is too low, charging bias leakage is likely to occur when the photoreceptor 40 has a defect such as a pinhole. A desired volume resistivity can be obtained by blending a conductive material into the base resin. As the base resin, resins such as polyethylene, polypropylene, polymethyl methacrylate, polystyrene, acrylonitrile-butadiene-styrene copolymer, and polycarbonate can be used. These base resins have good moldability and can be easily molded.

The conductive material is preferably an ionically conductive material such as a polymeric compound having a quaternary ammonium base. Examples of polyolefins with quaternary ammonium groups include polyethylene, polypropylene, polybutene, polyisoprene, ethylene-ethyl acrylate copolymers, ethylene-methyl acrylate copolymers, ethylene-vinyl acetate copolymers, ethylene- Polyolefins such as propylene copolymer and ethylene-hexene copolymer. In the present embodiment, polyolefin having a quaternary ammonium base was exemplified, but polymer compounds other than polyolefin having a quaternary ammonium base may be used.

The ion-conductive material is uniformly blended with the base resin by using a means such as a twin-screw kneader or a kneader. By injection molding or extrusion molding the compounded material onto a core bar, it can be easily molded into a roller shape. The amount of the ion conductive material and the base resin to be mixed is desirably 30 to 80 parts by weight of the ion conductive material per 100 parts by weight of the base resin. The thickness of the resin layer of the charging roller 70 is desirably 0.5 to 3 [mm]. If the resin layer is too thin, molding is difficult and there is also a problem in terms of strength. If the resin layer is too thick, the charging roller 70 becomes large and the actual resistance of the resin layer increases, resulting in a decrease in charging efficiency.

After the resin layer 102 is molded, the gap holding members 103 which have been molded in advance are fixed to the metal core 101 by press-fitting, bonding, or both. After the resin layer 102 and the gap maintaining member 103 are integrated in this manner, processing such as cutting and grinding is performed to adjust the outer diameter of the charging roller 70 , thereby adjusting the phase of deflection between the resin layer 102 and the gap maintaining member 103 . can be aligned, and variations in the charging gap can be reduced.

As the material of the gap holding member 103, resins such as polyethylene, polypropylene, polymethyl methacrylate, polystyrene, acrylonitrile-butadiene-styrene copolymer, and polycarbonate can be used like the base material of the resin layer . However, since the gap holding member 103 is brought into contact with the photosensitive layer, it is desirable to use a grade having a hardness lower than that of the resin layer 102 in order to prevent the photosensitive layer from being damaged. In addition, resin materials with excellent slidability and less damage to the photosensitive layer include polyacetal, ethylene-ethyl acrylate copolymer, polyvinylidene fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene-hexafluoro. Resins such as propylene copolymers can also be used.

In addition, a surface layer to which toner or the like hardly adheres can be formed on the resin layer 102 and the gap holding member 103 with a thickness of about several tens [μm] by coating or the like. A gap is formed between the resin layer of the charging roller and the photoreceptor by applying the gap holding member to the outside of the image area of the photoreceptor. In the charging roller, a gear attached to the end of the core metal meshes with a gear formed on the photoreceptor flange. When the photoreceptor is rotated by the photoreceptor driving motor, the charging roller also rotates in the rotation direction. Since the resin layer and the photosensitive member do not come into contact with each other, the photosensitive layer in the image area is not damaged even when a hard resin material and an organic photosensitive member are used as the charging roller. Also, if the gap is too large, abnormal discharge occurs and uniform charging cannot be achieved. When using such a charging roller having a gap between the photosensitive member and the charging roller, it is desirable to superimpose an AC voltage on a DC voltage as a charging bias.

Since the resin layer 102 and the gap holding member are made of a resin material, the charging roller can be easily processed and manufactured with high precision. A cleaning roller 77 for cleaning the roller surface is in contact with the charging roller. This cleaning roller is a roller with melamine foam mounted on a metal core. It abuts against the charging roller under its own weight and rotates with the rotation of the charging roller, removing dirt such as toner adhering to the surface of the charging roller. to remove The cleaning roller may be kept in contact with the charging roller all the time, but a cleaning roller contact/separation mechanism is provided so that the cleaning roller is normally kept apart and periodically brought into contact with the charging roller as necessary to intermittently charge. It can also be configured to clean the roller surface. The above-described charging roller 70 includes the gap holding member 103 to bring the surface of the photoreceptor 40 and the resin layer 102 of the charging roller 70 close to each other.

Each developing device has the same structure, and they are two-component developing devices that differ only in the color of the toner used. Each developing device contains a two-component developer consisting of toner and carrier. It is

The developing device comprises a developing roller 61 facing the photosensitive member, screws 62 and 63 for conveying and stirring the developer, a toner density sensor 64, and the like. The developer roller consists of an outer rotatable sleeve and an inner fixed magnet. A necessary amount of toner is replenished from the toner replenishing device according to the output of the toner density sensor.

The toner is mainly composed of a binder resin, a colorant, and a charge control agent, and if necessary, other additives are added. Specific examples of binder resins that can be used include polystyrene, styrene-acrylic acid ester copolymers, polyester resins, and the like. As the coloring materials (eg, yellow, magenta, cyan and black) used in the toner, those known for toner can be used. An appropriate amount of the coloring material is 0.1 to 15 parts by weight with respect to 100 parts by weight of the binder resin.

Specific examples of the charge control agent include nigrosine dyes, chromium-containing complexes, quaternary ammonium salts, and the like, which are used according to the polarity of the toner particles. The amount of the charge control agent is 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

Advantageously, the toner particles have been added with a fluidity-imparting agent. Fluidity imparting agents include fine particles of metal oxides such as silica, titania, and alumina, and those fine particles surface-treated with silane coupling agents, titanate coupling agents, etc., polystyrene, polymethyl methacrylate, and polyvinylidene fluoride. Polymer microparticles such as, for example, are used. The particle size of these fluidity imparting agents is in the range of 0.01 to 3 [μm]. The amount of these fluidity imparting agents to be added is preferably in the range of 0.1 to 7.0 parts by weight with respect to 100 parts by weight of the toner particles.

Generally, the carrier consists of the core material itself, or a core material with a coating layer provided thereon. The core material of the resin-coated carrier that can be used in this embodiment is ferrite or magnetite. The particle size of this core substance is suitably about 20 to 60 [μm].

Materials used for forming the carrier coating layer include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinyl ether substituted with fluorine atoms, and vinyl ketone substituted with fluorine atoms. As a method for forming the coating layer, the surface of the carrier core particles may be coated with a resin by means of a spraying method, a dipping method, or the like, as in the conventional method.

FIG. 4 shows the structure of the photoreceptor 40 that can be used in this embodiment. An example of the photoreceptor 40 used in this embodiment is a laminated organic photoreceptor composed of a charge generation layer 203 and a charge transport layer 204 which are photosensitive layers formed on a conductive support 201 . The conductive support 201 is made of a material exhibiting conductivity with a volume resistivity of 1×10 ¹⁰ [Ωcm] or less, for example, a tubular member made of aluminum, an aluminum alloy, nickel, stainless steel, or the like, which is surface-treated by cutting, polishing, or the like. Become. The charge generation layer 203 is a layer containing a charge generation material as a main component.

Inorganic or organic materials are used for the charge generation material, and typical examples include monoazo pigments, disazo pigments, trisazo pigments, perylene pigments, perinone pigments, quinacridone pigments, quinone condensed polycyclic compounds, squalic Acid-based dyes, phthalocyanine-based pigments, naphthalocyanine-based pigments, azulenium salt-based dyes, selenium, selenium-tellurium alloys, selenium-arsenic alloys, amorphous silicon, and the like. These charge-generating materials may be used alone or in combination of two or more.

The charge-generating layer 203 is formed by dispersing a charge-generating material together with an appropriate binder resin using a solvent such as tetrahydrofuran, cyclohexanone, dioxane, 2-butanone, and dichloroethane using a ball mill, an attritor, a sand mill, or the like, and applying the dispersion. can be formed by
Application of the charge generation layer can be performed by a dip coating method, a spray coating method, a bead coating method, or the like.

Binder resins that are appropriately used include resins such as polyamide, polyurethane, polyester, epoxy, polyketone, polycarbonate, silicone, acrylic, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, polyacryl, and polyamide. The appropriate amount of the binder resin is 0 to 2 parts by weight based on 1 part of the charge generating material.

The film thickness of the charge generation layer 203 is usually 0.01 to 5 [μm], preferably 0.1 to 2 [μm]. The charge transport layer can be formed by dissolving or dispersing a charge transport material and a binder resin in a suitable solvent, coating and drying the solution. Moreover, a plasticizer, a leveling agent, etc. can also be added if necessary.

Among charge transport materials, low-molecular-weight charge transport materials include electron transport materials and hole transport materials. Examples of electron transport materials include chloranil, bromoanyl, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2, 4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 2,6,8-trinitro-4H-indeno[1,2-b]thiophene-4one, 1,3,7-tri Examples include electron-accepting substances such as nitrodibenzothiophene-5,5-dioxide.

These electron transport materials may be used alone or as a mixture of two or more. Examples of hole transport materials include oxazole derivatives, oxadiazole derivatives, imidazole derivatives, triphenylamine derivatives, 9-(p-diethylaminostyrylanthracene), 1,1-bis-(4-dibenzylaminophenyl)propane. , styrylanthracene, styrylpyrazoline, phenylhydrazones, α-phenylstilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, benzofuran derivatives, benzimidazole derivatives, and thiophene derivatives. These hole transport materials may be used alone or as a mixture of two or more.

Binder resins used in the charge transport layer together with the charge transport material include polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride- Vinyl acetate copolymer, polyvinyl acetate, polyvinylidene chloride, polyarylate, phenoxy, polycarbonate, cellulose acetate, ethyl cellulose, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, acrylic, silicone, epoxy, melamine, urethane, phenol, alkyd, etc. Thermoplastic or thermosetting resins may be mentioned.

Examples of solvents include tetrahydrofuran, dioxane, toluene, 2-butanone, monochlorobenzene, dichloroethane, methylene chloride and the like.

The thickness of the charge transport layer 204 may be appropriately selected within the range of 10 to 40 [μm] according to desired photoreceptor characteristics.

In the photoreceptor 40 of this embodiment, an undercoat layer 202 can be formed between the conductive support 201 and the photoreceptor layer. The undercoat layer 202 is generally composed of a resin as a main component, and these resins are highly resistant to dissolution in general organic solvents, considering that the photosensitive layer is coated thereon using a solvent. is desirable. Such resins include water-soluble resins such as polyvinyl alcohol, casein and sodium polyacrylate; alcohol-soluble resins such as copolymerized nylon and methoxymethylated nylon; A curable resin that forms a network structure and the like are included.

In addition, fine powder of metal oxide such as titanium oxide, silica, alumina, zirconium oxide, tin oxide, and indium oxide may be added to the undercoat layer 202 in order to prevent moiré and reduce residual potential. The undercoat layer 202 can be formed using an appropriate solvent and coating method, as in the photosensitive layer described above. Furthermore, as the undercoat layer 202, it is also useful to use a metal oxide layer formed by, for example, a sol-gel method using a silane coupling agent, a titanium coupling agent, a chromium coupling agent, or the like. In addition, the undercoat layer 202 may be made of anodized Al ₂ O ₃ , organic materials such as polyparaxylylene (parylene), SiO, SnO ₂ , TiO ₂ , ITO, CeO ₂ and the like. An inorganic material formed by a vacuum thin film forming method is also effective. The appropriate thickness of the undercoat layer 202 is 0 to 5 [μm].

In the photoreceptor 40 of the present embodiment, a protective layer 205 can be formed on the photosensitive layer as shown in FIG. 4B for the purpose of protecting the photosensitive layer and improving durability. The protective layer 205 has a structure in which metal oxide fine particles such as alumina, silica, titanium oxide, tin oxide, zirconium oxide, and indium oxide are added to the binder resin for the purpose of improving abrasion resistance. Binder resins include styrene-acrylonitrile copolymer, styrene-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, olefin-vinyl monomer copolymer, chlorinated polyether, allyl, phenol, polyacetal, polyamide, polyamide Imide, polyacrylate, polyarylsulfone, polybutylene, polybutylene terephthalate, polycarbonate, polyethersulfone, polyethylene, polyethylene terephthalate, polyimide, acrylic, polymethylpentene, polypropylene, polyphenylene oxide, polysulfone, polyurethane, polyvinyl chloride, polyvinylidene chloride , epoxy and the like.

The amount of metal oxide fine particles added to the protective layer 205 is usually 5 to 30% by weight. If the amount of the metal oxide fine particles is less than 5%, abrasion is large and the effect of improving the abrasion resistance is small, resulting in poor durability. is not negligible. As a method for forming the protective layer 205, a normal coating method such as a spray method is employed. The thickness of the protective layer 205 is appropriately about 1 to 10 [μm], preferably about 3 to 8 [μm]. If the film thickness of the protective layer 205 is too thin, the durability will be poor, and if the film thickness of the protective layer 205 is too thick, not only will the productivity during the production of the photoreceptor decrease, but also the residual potential will increase over time. end up A suitable particle size of the metal oxide particles added to the protective layer 205 is 0.1 to 0.8 [μm]. If the particle size of the metal oxide fine particles is too large, the surface of the protective layer becomes uneven, resulting in poor cleanability, and the exposure light is likely to be scattered by the protective layer, resulting in low resolution and poor image quality. If the particle size of the metal oxide fine particles is too small, the wear resistance will be poor.

Furthermore, a dispersing aid can be added to the protective layer 205 in order to improve the dispersibility of the metal oxide fine particles in the base resin. As the dispersing aid to be added, those used in paints and the like can be appropriately used. %. Further, by adding a charge transport material to the protective layer 205, charge transfer in the protective layer can be promoted. As the charge transport material added to the protective layer, the same material as the charge transport layer can be used.

FIG. 5 is a block diagram showing part of the electric circuit of the full-color copier according to the embodiment. In the figure, a main control unit 500 governs drive control of each device of the full-color copying machine, and includes a CPU (Central Processing Unit), a RAM (Random Access Memory) as data storage means, and a ROM (Read Memory) as data storage means. Only Memory), etc. Based on the programs stored in the ROM, it controls the driving of various devices and executes predetermined arithmetic processing.

A process motor 510 , a development bias power supply 511 , a transfer bias power supply 512 , a registration clutch 513 and the like are connected to the main control unit 500 . An operation display unit 515, a charging power source 516 for applying a voltage to the charging roller 70, a power source 517 for the charge removing lamp 72, an optical writing control unit 518, an image information receiving unit 519, and the like are also connected.

The image information receiving section 519 receives image information sent from the scanner 300 and sends it to the main control section 500 and the optical writing control section 518 . The optical writing control unit 518 optically scans the surface of the photoreceptor 40 by controlling the driving of the exposure device 21 based on the image information sent from the image information receiving unit 519 .

A process motor 510 is a motor that serves as a drive source for the photoreceptor 40, the developing device 60, various rollers, and the like. The rotational driving force of the process motor 510 is transmitted to the registration rollers 49 via the registration clutch 513 . The main control unit 500 turns on the registration clutch 513 at a predetermined timing to connect the rotational driving force of the process motor 510 to the registration rollers 49 .

The developing bias power supply 511 supplies the developing roller 61 with the same polarity as the toner, the absolute value of which is greater than the absolute value of the exposure portion potential (latent image potential) VL, and the background portion potential (charging potential) VD of the photosensitive member 40 . A developing bias smaller than is applied. For example, a developing bias of -550 [V] is applied under the condition that the surface potential of the photosensitive member is VD=-600 [V] and the exposed portion potential VL is -30 [V]. The main control unit 500 sends an output command signal to the developing bias power supply 511 to cause the developing bias power supply 11 to output the developing bias at a predetermined timing.

Further, the main control unit 500 causes the transfer bias power supply 512 to output the transfer bias by sending an output command signal to the transfer bias power supply 512 at a predetermined timing. The transfer bias is transferred between the intermediate transfer belt 10 and the electrostatic latent image on the photoreceptor 40 at the transfer unit where the photoreceptor 40 faces the transfer device composed of the transfer roller 82 and the conveying belt unit. It is the voltage for forming the electric field.

The operation display unit 515 has a touch panel, numeric keys, etc., and displays images on the touch panel, and sends information input by the touch panel, numeric keys, etc. to the main control unit 500 .

The charging power source 516 applies a charging bias composed of a DC bias (charging DC bias) and an AC bias (charging AC bias) superimposed to the charging roller 70 . The charging power source 516 is provided with a current detection circuit 516a as detection means for detecting a DC component of the charging current flowing through the charging roller 70 (hereinafter referred to as "DC charging current"), and detects the current during the charging process. , and outputs the detection result (charging current value) to the main control unit 500 . Instead of or in addition to this, a current measuring circuit for detecting the current flowing through the base of the photoreceptor 40 may be provided to output the measurement result to the main controller 500 as the charging current value. The current detection circuit 516a may be incorporated in the charging power source 516. FIG.

The main control unit 500 functions as a predicting means for predicting the exposed portion potential VL of the photoreceptor, as will be described later. The main control section 500 also functions as a control device as control means for controlling other image forming conditions such as charging bias, developing bias, exposure conditions, and transfer bias.

The thickness of the photosensitive layer of the photoreceptor 40 described above is 3 to 5 [μm] for the undercoat layer 202, 0.1 to 1.0 [μm] for the charge generation layer 203, and 25 to 40 [μm] for the charge transport layer 204. ], and the thickness of the protective layer 205 is generally about 3 to 5 [μm]. The photoreceptor 40 inevitably has a film thickness variation of several μm due to the manufacturing process, resulting in a difference in capacitance. In addition, since the outermost layer wears due to friction with a cleaning blade or the like, the capacitance changes due to wear of the photosensitive layer after long-term use. Also, photoreceptor fatigue requires more current to clear traps in the photoreceptor. Due to this effect as well, the charging bias for obtaining the target potential of the exposed portion is different.

Therefore, in the present embodiment, the potential of the exposed portion of the photoreceptor is predicted, and the charging DC bias for obtaining the target potential of the exposed portion is calculated based on the predicted potential of the exposed portion of the photoreceptor. Calculation of the predicted value of the potential of the exposed portion of the photosensitive member will be described below.

[Acquisition of Static Elimination Unit Charging Current Value]
FIG. 6 is a timing chart of the acquisition operation of the static elimination unit charging current value (the DC charging current value for the static elimination unit of the photoreceptor).
In the following description, for the sake of simplification, the charging position by the charging roller 70, the static elimination position by the static elimination lamp 72, and the exposure position of the exposure light 76 by the exposure device are arranged as shown in FIG. A case will be described. That is, in the following description, when the charging position by the charging roller 70 is the position of 0°, the exposure position is arranged at the position where the photoreceptor 40 is rotated 90° counterclockwise in the drawing, and Description will be made on the assumption that the neutralization position is arranged at a position rotated by 270°. If the arrangement angle of each position with respect to the photoreceptor 40 is different from this example, the operation timing may be adjusted according to the arrangement angle.

First, the main controller 500 rotates the photoreceptor 40 and turns on the static elimination lamp 72, as shown in FIG. When the photoreceptor 40 reaches a predetermined rotational speed, only the charging AC bias is applied from the charging power supply 516 to the charging roller 70 (the charging DC bias is turned off). At this time, the charging roller 70 functions as a charge removing unit together with the charge removing lamp 72 , and the photoreceptor 40 is discharged by the charge removing light of the charge removing lamp 72 and the discharge of the charging roller 70 .

After rotating the photoreceptor 40 one turn or more to remove the charge from the entire surface of the photoreceptor, a predetermined charging DC bias (for example, -700 [V]) is applied from the charging power supply 516 to the charging roller 70 until the photoreceptor 40 makes at least one turn. Then, the DC charging current (charging current value of the neutralizing portion) at this time is detected. Although the image forming apparatus has a transfer device, the transfer bias is not applied when the DC charging current is detected because it disturbs the relationship between the photoreceptor potential and the DC charging current. This sensed DC charging current is stored in memory.

After the detection of the DC charging current (charging current value of the static elimination unit), the charging bias (charging DC bias and charging AC bias) is turned off. , the charge removing light of the charge removing lamp 72 is turned off. It is not necessary to turn on the exposure device when detecting the DC charging current (charging current value of the static elimination unit).

Here, in the static elimination only by the static elimination light of the static elimination lamp 72, a residual potential remains on the photoreceptor 40, and the residual potential changes depending on the usage environment and the fatigue state of the photoreceptor. current value) may fluctuate. In order to suppress such fluctuations, in the present embodiment, static elimination is performed by combining the static elimination by the static elimination light and the static elimination by the discharge of the charging AC bias. current value). According to this, the photoreceptor potential after static elimination can be set to approximately 0 [V] without depending on the usage environment or the fatigue state of the photoreceptor. Fluctuations can be suppressed.

The reason why the photoreceptor potential after static elimination can be set to approximately 0 [V] will be described. When the charge potential of the photoreceptor 40 is lowered, the electric field applied to the photosensitive layer is reduced and the holes generated in the CGL cannot move. On the other hand, it is considered that the combined use of charge-eliminating light and charging AC bias allows the holes to move in the electric field of the charging AC bias, and in addition, the charge on the surface of the photoreceptor can be eliminated by discharging.

Even when static elimination is performed using both static elimination light and charging AC bias (discharge), the residual potential of the photosensitive member 40 is increased due to frequent use, or the photosensitive member may be affected by a low-temperature environment in which the moving speed of holes decreases. Under the conditions of use, it may not be possible to completely eliminate the charge to 0 [V] with only one turn of the photoreceptor. Therefore, the photosensitive member 40 may be rotated two or more rounds from the application of the charging AC bias, and the entire surface of the photosensitive member may be overlapped two or more times for neutralization. As a result, the photoreceptor can be satisfactorily neutralized to 0 [V] regardless of the usage conditions of the photoreceptor. In addition, when the photoreceptor is used frequently in a low temperature environment, the photoreceptor may be removed three or more times under usage conditions that make it more difficult to remove the static electricity. Also, the number of rotations of the photoreceptor may be increased.

[Relationship Between Surface Potential of Photoreceptor Before and After Charging During Acquisition of Static Elimination Unit Charging Current and Detected Current]
FIG. 8 shows the photoreceptor potential (pre-charging potential) after passing the static elimination position and before passing the charging position, and the photoreceptor potential after passing the charging position (post-charging potential) during the acquisition operation of the DC charging current (static elimination unit charging current). ) and the DC charging current (static elimination unit charging current). FIG. 8 shows the relationships when a photoreceptor with advanced fatigue is used.

As shown in FIG. 8, in the first round of static elimination, the photoreceptor potential (pre-charging potential) after static elimination by the static elimination light of the static elimination lamp 72 is less than 0 [V], and there is a residual potential. The photoreceptor potential (post-charging potential) after charge removal by discharging by applying the charging AC bias to the charging roller 70 approaches 0 [V]. At this time, the current detection circuit 516a is configured to detect the polarity side current for charging the photosensitive member, so the DC charging current (detection current) is not measured and is 0 [μA].

Since the transfer bias is turned off during the operation of predicting the charge potential, the sheet passes through the charge removal lamp 72 with the charge potential after the first round of charge removal. The photoreceptor surface is also irradiated with the charge-removing light from the charge-removing lamp 72 during the second cycle of charge-removal. The potential is approximately the post-charging potential of the first round of static elimination. Then, when the surface of the photoreceptor passes the charging position, the surface of the photoreceptor is subjected to a charging AC bias again, and the charge is further removed by the discharge. ] approach. Again, no charging DC bias is applied (0 [V]) and the DC charging current (sensed current) is not measured and is 0 [μA].

FIG. 8 shows the case where the photoreceptor is used after fatigue has progressed. While the photoreceptor is relatively new, the potential of the photoreceptor drops to approximately 0 [V] due to the discharge of the charging AC bias in the first round of charge elimination. Sometimes it becomes. Therefore, when the photoreceptor is relatively new, the rotation of the photoreceptor may be set to one rotation, and when the photoreceptor has been used for a predetermined period of time, the rotation of the photoreceptor may be two or more rotations. As a result, it is possible to shorten the operation of estimating the charging potential at the beginning of use of the photoreceptor. Since it is difficult to accurately predict the fatigue state of the photoreceptor, the number of rotations of the photoreceptor in the static elimination operation may be set to two from the beginning of the use of the photoreceptor.

In the present embodiment, the static elimination of the photosensitive member is performed by combining the static elimination by the static elimination light and the static elimination by the discharge of the charging AC bias. This is because, as described above, static elimination using only static elimination light leaves a residual potential on the photoreceptor 40 , and the residual potential fluctuates depending on the operating environment and the fatigue state of the photoreceptor 40 . By combining static elimination by static elimination light and static elimination by discharge of charging AC bias, the photoreceptor potential after static elimination can be set to approximately 0 [V] regardless of the usage environment and the fatigue state of the photoreceptor. In this way, after the static elimination operation, that is, before the DC charging current is detected, the photoreceptor potential is 0 [V]. By multiplying it, the accuracy of predicting the charging potential of the photoreceptor can be improved.

After the static elimination operation of the photoreceptor is completed, the detection operation of the DC charging current (static elimination portion charging current) continues. The pre-charging potential before passing the charging position in the DC charging current detection operation is approximately 0 [V]. By applying a charging DC bias in addition to the charging AC bias to the charging roller 70, the photosensitive member is charged. In the example shown in FIG. 8, -700 [V] was applied to the charging roller 70 as the charging DC bias, and the photosensitive member was charged to -650 [V]. At this time, the amount of charge required to charge the photoreceptor from 0 [V] to -650 [V] is measured as a DC charging current (static elimination unit charging current) by the current detection circuit 516a, and is -65 [μA]. DC charging current was measured. The relationship between the charging potential of the photoreceptor and the DC charging current varies depending on the characteristics (fatigue and wear) of the photoreceptor used, the process speed of the image forming apparatus, and the like.

The DC charging current value cannot be converted into the potential of the photoreceptor 40 simply by detecting the DC charging current value. Conventionally, the film thickness of the photoreceptor 40 is predicted from, for example, the charging time of the photoreceptor and the rotation time of the photoreceptor, and the coefficient (characteristic value) corresponding to the electrostatic capacity of the photoreceptor 40 is detected. A method of predicting the charging potential of the photoreceptor by multiplying the value is known. However, even a new photoreceptor has film thickness variations within tolerance, and it is difficult to predict the film thickness of a photoreceptor that has been used and worn in an image forming apparatus. As a result, the accuracy of prediction of the photoreceptor potential obtained by the conventional method is low. Therefore, in this embodiment, the characteristic value of the photoreceptor 40 is acquired in the actual machine, and the charging potential of the photoreceptor is predicted from the acquired characteristic value of the photoreceptor and the detected DC charging current.

[Acquisition of Photoreceptor Characteristics]
FIG. 9 is a timing chart of the operation of acquiring photoreceptor characteristics.
First, the photosensitive member 40 is rotated and the static elimination lamp 72 is turned on. When the photoreceptor 40 reaches a predetermined rotational speed, a charging AC bias is applied from the charging power supply 516 to the charging roller 70, and the photoreceptor 40 is neutralized by light and discharge. After the photoreceptor 40 is rotated by one revolution or more from the application of the charging AC and the entire surface of the photoreceptor is neutralized, a predetermined charging DC bias is applied from the charging power source 516 until the photoreceptor 40 makes one revolution, and the DC charging current at this time is is detected by the current detection circuit 516a. This static elimination and charging cycle is repeated by changing the value of the charging DC bias applied from the charging power supply 516 . In the present embodiment, the charging DC bias uses five voltage levels of -400 [V], -500 [V], -600 [V], -700 [V], and -800 [V]. Although the image forming apparatus has a transfer device, the transfer bias is not applied when the DC charging current is detected because it disturbs the relationship between the photoreceptor potential and the charging current.

Since information about the residual potential is not required for obtaining the characteristics of the photoreceptor, the detection of the DC charging current in the operation of obtaining the characteristics of the photoreceptor is performed once around the photoreceptor in order to shorten the operation time. In addition, the photoreceptor charge removal before detection of the DC charging current may be performed for two or more rotations of the photoreceptor, or may be performed for one rotation of the photoreceptor in order to shorten the operation time. As will be described later, the photoreceptor characteristics acquired in this operation correspond to the amount of change in surface potential with respect to the amount of change in DC charging current (referred to as capacitance coefficient). This is because the residual potential does not change significantly in a short period of time, so even if some residual potential remains, it does not affect the calculation of the amount of change.

[Calculation of Photoreceptor Characteristics (Capacitance Coefficient)]
FIG. 10 plots the detected charging current [μA] on the horizontal axis and the applied charging DC bias×α [V] on the vertical axis. The horizontal axis represents the charging current I400 when −400 [V] is applied to the charging DC bias.
Although the actual charge potential of the photoreceptor 40 cannot be known, the difference in the charge potential of the photoreceptor 40 when the charging DC bias is -a [V] and -b [V] is given by the following (Equation 1). can be represented.
Difference in charging potential of photoreceptor = -(ab) x α [V] (Equation 1)

The above α takes a value of about 0.9 to 1.0, is determined by the characteristics of the photosensitive member 40 and the charging roller 70, and can be obtained in advance by experiments. Therefore, by obtaining the slope when plotting in FIG. 10, it is possible to know the amount of change in the charging potential of the photoreceptor with respect to the amount of change in the DC charging current.

This slope (the amount of change in the photoreceptor potential with respect to the amount of change in the DC charging current) is called the capacitance coefficient [V/μA]. Since this capacitance coefficient is proportional to the reciprocal of the capacitance of the photoreceptor 40, the thinner the photosensitive layer, the smaller the value. This capacitance coefficient reflects variations in the thickness of the photosensitive layer and changes in capacitance due to wear of the photosensitive layer during long-term use, and can be said to represent the characteristics of the photoreceptor. Also, photoreceptor fatigue requires more current to clear traps in the photoreceptor. Due to this effect as well, the capacitance coefficient, which is the amount of change in charging potential with respect to the amount of change in charging current, differs.

The main control unit 500 obtains a slope as a capacitance coefficient from the five-stage charging DC bias and the detected DC charging current value corresponding to each charging DC bias, and stores the obtained slope as a capacitance coefficient. stored in a storage means such as

[Calculation of Predicted Charging Potential of Photoreceptor Based on Static Elimination Unit Charging Current Value]
The main control unit 500 determines the charging potential of the photoconductor 40 based on the DC charging current value acquired by the DC charging current value acquisition operation for predicting the charging potential of the photoconductor 40 and the capacitance coefficient acquired by the photoconductor characteristic acquisition operation. Calculate potential predicted value. The following formula (2) can be used as a prediction formula for calculating the charging potential prediction value.
Predicted charging potential value = DC charging current detection value x capacitance coefficient + β (Equation 2)

Here, β is the residual potential after the photoreceptor 40 has been neutralized by light and discharge. is. The fact that it is not completely 0 is considered to be due to the influence of the distortion of the AC waveform of the high-voltage power supply, and is determined by the performance of the high-voltage power supply.

In the present embodiment, the photoreceptor potential after the photoreceptor is neutralized by light and discharge, i.e., before charging, is set to approximately 0 [V], so β can be set to 0 [V]. In the example of FIG. 8, assuming that the capacitance coefficient calculated by the above method is 10 [V/μA], the charge potential of the photoreceptor at this time is -65 [μA]× It can be predicted that 10 [V/μA]=-650 [V], which agrees with the known charging potential of -650 [V]. It should be noted that the main control unit 500 stores the calculated charging potential predicted value in storage means such as a memory.

[Acquisition of exposure area charging current value]
FIG. 11 is a timing chart of the acquisition operation of the exposure portion charging current value (DC charging current value for the exposed portion of the photoreceptor).
First, as shown in FIG. 11, the main control unit 500 rotates the photoreceptor 40 and lights the charge removal lamp 72 . When the photoreceptor 40 reaches a predetermined rotation speed, both the charging AC bias and the charging DC bias (charging bias) are applied to the photoreceptor 40 to perform charging processing.

When the photoreceptor rotates by 90° or more from the application of the charging bias, the exposure device is turned on to uniformly expose the photoreceptor 40, and the entire surface of the photoreceptor is exposed. At the timing when the photoreceptor rotates halfway after turning on the exposure device, the static elimination lamp 72 is turned off. Since the transfer bias is not applied, the charge removing lamp 72 is turned off, so that the surface potential of the photoreceptor before charging remains the potential of the exposed portion.

By detecting the DC charging current flowing through the charging roller 70 when charging the exposed portion potential, the amount of potential change from the exposed portion potential to the charged potential can be known. As described above, since the charging potential has already been predicted, if the amount of potential change from the exposed portion potential to the charging potential can be known, the exposed portion potential can be predicted.

After detecting the DC charging current during the charging process with respect to the exposed portion potential, the exposure device is turned off and the charge elimination lamp is turned on. Then, when the position on the photoreceptor where the charging bias is turned off passes the charge removing position, the photoreceptor 40 is stopped and the charge removing light is turned off.

When the operation of predicting the charging potential is performed, the charging current value (static elimination unit charging current value) when the surface potential of the photoreceptor is charged from 0 [V] to the charging potential is detected. On the other hand, when performing the operation of predicting the exposed portion potential, the charging current value (exposed portion charging current value) when the surface potential of the photosensitive member is charged from the exposed portion potential to the charging potential is detected. Although the photoreceptor surface potential (charging potential) after charging is the same, the photoreceptor surface potential before charging is different. Therefore, the detected DC charging current predicts the potential of the exposed area. It is smaller during operation. Since the difference between the two detection currents can be considered to correspond to the DC charging current value required to charge the photoreceptor from 0 [V] to the potential of the exposed area, the capacitance coefficient is calculated as the current difference. By multiplying, the potential of the exposed portion of the photoreceptor can be predicted.

For example, when -700 [V] is applied as a charging DC bias, -65 [μA] DC Assume that a charging current is detected. On the other hand, it is assumed that a DC charging current of -55 [μA] is measured during the operation of predicting the potential of the exposed portion (when charging the photosensitive member from the potential of the exposed portion to the charging potential). In this case, assuming that the separately calculated capacitance coefficient is 10 [V/μA], the exposed portion potential of the photosensitive member at this time is {-65 [μA]-(-55 [μA])}× It can be predicted that 10 [V/μA]=-100 [V].

In the above description, the operation of estimating the charge potential of the photoreceptor 40 and the operation of estimating the potential of the exposed portion have been described separately. .

[Method for determining charging DC bias during image formation]
In the present embodiment, the charging DC bias applied during the operation for predicting the charging potential, the predicted charging potential of the photoreceptor calculated by Equation 2 above, and the above-described coefficient α are stored in the storage means. At the time of image formation, the main control unit 500 controls the charging DC bias stored in the storage unit, the predicted charge potential of the photoreceptor calculated from the above equation 2, the above coefficient α, and the charge potential at the time of image formation. A charging DC bias to be applied to the charging roller 70 is calculated from the target value. Let Vd1 be the charging DC bias applied during the operation for predicting the charging potential, Vy be the predicted value of the charging potential, and Vt be the target value of the charging potential during image formation. The bias Vd is obtained as follows.

That is, the following equations 3 and 4 are obtained from the relationship between the charging DC bias and the charging potential of the photosensitive member shown in equation (1).
(Vd1−Vd)×α=(Vy−Vt) (Formula 3)
Vd=[(Vy−Vt)/α]−Vd1 (Formula 4)

As a specific example, the charging DC bias Vd1 applied during the operation for predicting the charging potential is -700 [V], the predicted value Vy of the charging potential when -700 V is applied is -675 [V], and the charging potential during image formation. When the target value Vt of is −600 V, the charging DC bias Vd to be applied to the charging roller 70 during image formation is obtained in the following manner. That is, the charging DC bias Vd is Vd=(75/α)−700 [V] from the relationship of (−700−Vd)×α=−(675−600)=−75.

The predicted charging potential Vy=-675 [V] is obtained from the DC charging current value detected when the charging DC bias Vd1=-700 [V] is applied and the operation for obtaining the above photoreceptor characteristics. It is a value calculated from the obtained capacitance coefficient and the above (Equation 2).

The main control unit 500 controls the charging power supply 516 so as to achieve the calculated charging DC bias during image formation.

[Image Quality Adjustment Based on Predicted Value of Exposure Area Potential]
The main control unit 500 adjusts the developing bias applied to the developing roller and the amount of exposure based on the predicted value of the exposed portion potential stored in the storage means. Also, the image forming conditions such as the target value Vt of the charging potential during image forming are adjusted. By adjusting the target value Vt, the DC charging bias during image formation is also adjusted. Conventionally, a potential sensor is provided to detect the surface potential of the photoreceptor between exposure and development. I adjusted the imaging conditions. In this embodiment, the potential of the exposed portion of the photoreceptor can be grasped without providing a potential sensor, and the image forming conditions such as the target value Vt of the developing bias, the amount of exposure, and the charging potential can be adjusted. As a result, the number of parts can be reduced, and the size and cost of the device can be reduced.

In particular, in the present embodiment, the DC charging current when the surface of the photoreceptor is charged after the photoreceptor is neutralized by light and discharge, i.e., before the photoreceptor is charged, is set to approximately 0 [V]. Since the potential is predicted, the exposed portion potential can be predicted with high accuracy. Therefore, the image forming conditions can be adjusted satisfactorily, and a good image can be obtained.

Further, the detection error of the current detection circuit 516a can be canceled by obtaining the capacitance coefficient within the actual device. This is for the following reasons. Once the photoreceptor 40 is set in the main body, the combination of the photoreceptor 40 and the current detection circuit 516a is the same unless the photoreceptor 40 is replaced. Therefore, the charge potential [V ], the current detection error is cancelled.

In the present embodiment, the prediction of the potential of the exposed part, the correction of the charging voltage during image formation using the predicted result of the charged potential, and the correction of the image forming condition using the predicted result of the potential of the exposed part are the operations for obtaining the characteristics of the photosensitive member. run more frequently than As part of the so-called process control, it is executed first thing in the morning after power-on of the color copying machine and every 1000 copies during operation.

Prediction of the charged potential and the exposed portion potential requires only one current detection operation, so it can be completed in a short time. On the other hand, it takes time to obtain the capacitance coefficient because the current detection operation needs to be repeated. Therefore, in normal adjustment, only the charging potential and the exposed portion potential are predicted, and the capacitance coefficient is calculated only when it is determined that the calculation of the capacitance coefficient is necessary. The case where it is judged necessary is limited to the case where execution is truly necessary, which is lower in frequency than normal adjustment. This makes it possible to accurately predict the charged potential of the photosensitive member and the exposed portion potential in a short adjustment time. Cases where calculation of the capacitance coefficient is necessary include the following cases.

[When the photoreceptor is replaced]
As described above, since there is an individual difference in film thickness for each photoreceptor 40, it is necessary to calculate the capacitance coefficient when the photoreceptor 40 is replaced. In an image forming apparatus in which a customer engineer replaces the photoreceptor 40, when the customer engineer replaces the photoreceptor 40, the calculation operation of the capacitance coefficient may be manually executed. This manual execution instruction can be made using the operation display unit 515 . In an image forming apparatus in which a user replaces a process cartridge including a photoreceptor 40, new product information is stored in a memory mounted on the process cartridge, and calculation of the capacitance coefficient is automatically executed when the process cartridge is mounted on the main body. can also

[When the photoreceptor is used more than the specified amount]
As the photoreceptor 40 is used repeatedly, the photoreceptor layer of the photoreceptor 40 is gradually worn out, so that the capacitance changes. Therefore, it is desirable to memorize the rotation time of the photoreceptor 40, the number of output sheets, and the like, and to calculate the capacitance coefficient when the wear of the photoreceptor layer reaches an estimated amount. Since the progress of abrasion of the photosensitive layer is greatly affected by the composition of the photoreceptor 40 and the cleaning conditions, it may be appropriately set according to each apparatus. In addition to abrasion of the photosensitive layer, fatigue of the photoreceptor due to use over time may require more current to eliminate traps in the photoreceptor. Therefore, it is desirable to calculate the capacitance coefficient even in an apparatus using a photoreceptor in which the photoreceptor wears little, when the photoreceptor is used over a predetermined amount.

[When the usage environment changes]
From the experimental results, it has been found that even if the photoreceptor 40 is the same, the capacitance coefficient calculated varies depending on the environment in which it is used. This phenomenon does not mean that the electrostatic capacity of the photoreceptor 40 itself changes, but what is detected by the charging power supply (high voltage power supply) is the current flowing through the charging roller 70, which flows inside the photoreceptor. A current (a flow in which holes generated in the CGL cancel surface charges) has not been detected. For this reason, it is presumed that the relationship between the charging current and the charging potential varies due to the difference in the moving speed of the holes depending on the environment. The operating environment is monitored by a temperature and humidity sensor installed in the image forming apparatus, and if the capacitance coefficient has changed by a predetermined amount or more (for example, absolute humidity of 5 [g/m ³ ] or more) since the previous calculation of the capacitance coefficient, It is desirable to re-calculate the capacitance coefficient.

[When the high-voltage power supply is replaced due to failure, etc.]
Although this rarely occurs, since the capacitance coefficient is calculated based on the combination of the photoreceptor 40 and the current detection circuit 516a, if the charging power supply (high voltage power supply) is replaced due to a failure or other reason, the electrostatic capacity will be reduced. It is desirable to recalculate the capacity factor. In this case, the customer engineer has to replace the high-voltage power supply, so the customer engineer can do it manually.

In addition, in the present embodiment, the charge roller 70 removes the charge from the photoreceptor by discharging.

What has been described above is only an example, and each of the following aspects has a specific effect [first aspect]
In the first mode, a latent image formed by exposing the photoreceptor 40, which has been uniformly charged by a charging means (eg, charging roller 70), to light with an exposing means (eg, exposure device 21) is developed, and the latent image is obtained by development. An image forming apparatus (for example, a full-color copier) that transfers an image from a photoreceptor to a transfer material (for example, an intermediate transfer belt 10) and removes static electricity from the surface of the photoreceptor after transfer by a static elimination means (eg, a static elimination lamp 72). detection means (for example, a current detection circuit 516a) for detecting a charging current value (for example, a DC charging current value) when performing the charging process; and the exposure portion charging current value when the charging process is performed on the photoreceptor that has been subjected to the charge treatment and has been exposed by the exposure means without being discharged by the charge removal means, It is characterized by having control means (main control section 500) for controlling image forming conditions (for example, development bias, exposure amount).
In the conventional image forming apparatus, the charging potential of the photoreceptor is predicted from the charging current value detected by the detection means, and the charging bias is controlled based on the predicted charging potential to adjust the image quality. In this case, even if the charging potential of the photosensitive member can be predicted with high accuracy, image quality adjustment may not be performed appropriately. This is because even if the charged potential of the photoreceptor is the same, the exposed portion potential of the photoreceptor (the surface potential of the photoreceptor at the portion exposed by the exposing means) is not always the same. This is because the image quality cannot be adjusted according to the difference in the potential of the part.
In this embodiment, the static elimination portion charging current value when the photoreceptor that has been statically eliminated by the static elimination means is charged, and the photoreceptor that has been charged and has been exposed by the exposure means is not statically eliminated by the static elimination means. The image forming conditions are controlled based on the exposure portion charging current value when the charging process is performed.
From the static elimination unit charging current value, the potential from the surface potential of the photoreceptor that has been statically eliminated by the static elimination means (residual potential after static elimination) to the surface potential of the photoreceptor that has been charged by the charging process (charged potential) You can get the amount of change. Therefore, the photoreceptor is neutralized until the residual potential after static elimination becomes a known potential (for example, 0 V), or the residual potential after static elimination can be grasped by a known method (eg, the method disclosed in Patent Document 1). Thus, the charge potential of the photoreceptor can be obtained from the difference between the potential change amount obtained from the charge current value of the charge removing portion and the residual potential after the charge removal.
On the other hand, from the exposed portion charging current value, the surface potential of the exposed portion of the photoreceptor exposed by the exposure means (exposed portion potential) is converted to the surface potential of the photoreceptor after the exposed portion has been charged by the charging process (charged potential) can be obtained. Therefore, by grasping the charged potential of the photoreceptor, the exposed portion potential of the photoreceptor can be obtained from the difference between the potential change amount obtained from the exposed portion charging current value and the charged potential of the photoreceptor. The charging potential of the photoreceptor can be obtained from the charging current value of the static elimination unit, as described above. Therefore, the exposed portion potential of the photoreceptor can be obtained based on the static elimination portion charging current value and the exposed portion charging current value.
Therefore, according to this aspect, in which the image forming conditions are controlled based on the static elimination portion charging current value and the exposure portion charging current value, it is possible to control the image forming conditions based on the exposure portion potential of the photoreceptor. It is possible to adjust the image quality according to the difference in the potential of the exposed portion of the photoreceptor, which cannot be performed by controlling the image forming conditions based on the charging potential.

[Second aspect]
In a second aspect, in the first aspect, the static elimination unit charging current value is a charging current value detected by the detection means when performing the charging process on the photoreceptor that has been subjected to the static elimination process of light and discharge. It is characterized by being
According to this, it is possible to detect the charging current value when the charging process is performed with respect to the state in which there is no residual potential on the surface of the photoreceptor (state of 0 [V]). Therefore, since the charging current value can be detected without being affected by the residual potential that may fluctuate depending on various conditions such as the environment and photoreceptor deterioration, the exposed portion potential of the photoreceptor can be predicted with higher accuracy.

[Third aspect]
A third aspect is the second aspect, wherein the charging means performs the charging process using a charging bias obtained by superimposing an AC bias on a DC bias, and the static elimination process of the discharge is performed by the charging means using the AC bias. and the detection means detects a DC current value of the charging current.
According to this, it is possible to remove charges from the surface of the photoreceptor by using the charging power source 516 that applies a charging bias to charging means such as the charging roller 70, and the charging power source 516 that applies a charging bias to the charging member. Apart from this, the cost increase of the apparatus can be suppressed as compared with the case of providing a power source for discharging the surface of the photoreceptor.

[Fourth aspect]
In a fourth aspect, in the second or third aspect, the static elimination unit charging current value performs the charging process on the photoreceptor that has undergone the photoreceptor orbiting the photoreceptor and has been subjected to the static elimination process of light and discharge two or more times. It is characterized in that it is a charging current value that is sometimes detected by the detecting means.
According to this, the surface of the photoreceptor can be brought into a state without a residual potential (state of 0 [V]) more reliably, so that the exposed portion potential of the photoreceptor can be predicted with higher accuracy.

[Fifth aspect]
According to a fifth aspect, in any one of the first to fourth aspects, the control means controls the static elimination portion charging current value, the exposure portion charging current value, and a characteristic value (for example, a capacitance coefficient α) of the photoreceptor. is used to predict the exposed portion potential of the photoreceptor, and the image forming conditions are controlled based on the predicted exposed portion potential of the photoreceptor.
According to this, it is possible to control the image forming conditions according to the difference in the exposed portion potential of the photoreceptor, and it is possible to perform the image quality adjustment according to the difference in the exposed portion potential of the photoreceptor.

[Sixth aspect]
A sixth aspect is characterized in that, in the fifth aspect, the control means executes the operation of acquiring the characteristic value of the photoreceptor when a specific condition is satisfied.
According to this, as described in the embodiment, the downtime can be suppressed as much as possible, and the decrease in prediction accuracy of the potential of the exposed portion can be suppressed.

[Seventh aspect]
A seventh aspect is characterized in that, in the sixth aspect, the case where the specific condition is satisfied includes the case where the photoreceptor is replaced.
According to this, as described in the above embodiment, since there are individual differences in photoreceptor characteristics due to manufacturing variations of the photoreceptor, when the photoreceptor is replaced, the characteristic values of the photoreceptor are acquired to perform exposure. Prediction accuracy of part potential can be maintained.

[Eighth aspect]
An eighth aspect is characterized in that, in the sixth or seventh aspect, the case where the specific condition is satisfied includes the case where the usage environment has changed by a predetermined amount or more.
According to this, as described in the above embodiment, the relationship between the charging current and the potential of the exposed portion changes depending on the usage environment. Therefore, when the usage environment changes, the characteristic value of the photosensitive member can be obtained. can maintain the prediction accuracy of the exposed portion potential.

[Ninth aspect]
A ninth aspect is characterized in that, in any one of the sixth to eighth aspects, the case where the specific condition is satisfied includes the case where the photoreceptor is used by a predetermined amount or more.
According to this, as described in the above embodiment, the electrostatic capacity of the photoreceptor changes when the photoreceptor wears out after being used for a long period of time. Photoreceptor fatigue also requires more current to clear traps in the photoreceptor. These change the relationship between the charging current and the potential of the exposed portion. By periodically acquiring the characteristic values of the photoreceptor, it is possible to maintain the accuracy of predicting the potential of the exposed portion.

[Tenth Aspect]
A tenth aspect is characterized in that, in any one of the sixth to ninth aspects, the case where the specific condition is satisfied includes the case where the detection means is replaced.
According to this, as described in the above embodiment, the characteristic value of the photoreceptor is obtained by combining the photoreceptor and the detection means (current detection circuit). It is desirable to reacquire the characteristic values of the photoreceptor in order to maintain the prediction accuracy of the potential of the part.

10: Intermediate transfer belt 11: Development bias power supply 18: Image forming unit 20: Tandem image forming device 21: Exposure device 22: Secondary transfer device 25: Fixing device 28: Sheet reversing device 40: Photoreceptor 60: Developing device 61: Developing roller 70 : Charging roller 72 : Eliminating lamps 73, 74 : Brush roller 75 : Cleaning blade 76 : Exposure light 82 : Primary transfer roller 100 : Apparatus body 101 : Metal core 102 : Resin layer 103 : Gap holding member 201 : Conductive Support 202 : Undercoat layer 203 : Charge generation layer 204 : Charge transport layer 205 : Protective layer 300 : Scanner 500 : Main controller 510 : Process motor 511 : Development bias power supply 512 : Transfer bias power supply 513 : Resist clutch 515 : Operation Display unit 516: charging power source 516a: current detection circuit 517: power source 518: optical writing control unit 519: image information receiving unit

Japanese Patent Application Laid-Open No. 2021-107910

Claims (10)

A latent image formed by exposing a photoreceptor uniformly charged by a charging means to light by an exposing means is developed, the image obtained by development is transferred from the photoreceptor to a transfer material, and the photoreceptor after transfer is transferred. An image forming apparatus for neutralizing the surface of the by a neutralizing means,
a detecting means for detecting a charging current value when performing the charging process;
a static elimination unit charging current value when the charging process is performed on the photoreceptor that has been statically eliminated by the static elimination means; and control means for controlling image forming conditions based on an exposure portion charging current value when performing the charging process. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the static elimination unit charging current value is a charging current value detected by the detection means when performing the charging process on a photoreceptor that has been subjected to the static elimination process of light and discharge. . In the image forming apparatus according to claim 2,
The charging means performs the charging process using a charging bias obtained by superimposing an AC bias on a DC bias,
The static elimination process of the discharge is performed by the charging means using the AC bias,
The image forming apparatus, wherein the detector detects a DC current value of the charging current. The image forming apparatus according to claim 2 or 3,
The static elimination unit charging current value is a charging current value detected by the detection means when performing the charging process on the photoreceptor that has been subjected to the photoreceptor and the static elimination process of light and discharge two or more times while rotating the photoreceptor. An image forming apparatus characterized by: The image forming apparatus according to any one of claims 1 to 4,
The control means predicts an exposed portion potential of the photoreceptor using the static elimination portion charging current value, the exposed portion charging current value, and the characteristic value of the photoreceptor, and based on the predicted exposed portion potential of the photoreceptor, An image forming apparatus that controls the image forming conditions. In the image forming apparatus according to claim 5,
The image forming apparatus, wherein the control unit executes the operation of acquiring the characteristic value of the photoreceptor when a specific condition is satisfied. The image forming apparatus according to claim 6,
The image forming apparatus, wherein the case where the specific condition is satisfied includes the case where the photoreceptor is replaced. The image forming apparatus according to claim 6 or 7,
The image forming apparatus, wherein the case where the specific condition is satisfied includes the case where the environment in which it is used has changed by a predetermined amount or more. The image forming apparatus according to any one of claims 6 to 8,
The image forming apparatus, wherein the case where the specific condition is satisfied includes the case where the photoreceptor is used by a predetermined amount or more. The image forming apparatus according to any one of claims 6 to 9,
The image forming apparatus, wherein the case where the specific condition is satisfied includes the case where the detection means is replaced.

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