Image forming apparatus

Abstract

To accurately learn a state of deterioration of a photoreceptor.SOLUTION: An image forming apparatus has: a photoreceptor; charging means that electrostatically charges the photoreceptor; electric potential detection means that detects the charging electric potential of the photoreceptor; developing means that develops an electrostatic latent image on the photoreceptor; current detection means that detects a charging current flowing in the charging means; static eliminating means that eliminates static electricity before the photoreceptor is electrostatically charged; and control means including conversion means that converts the charging electric potential of the photoreceptor detected by the electric potential detection means into the electric potential of the photoreceptor at a developing position, and correction means that corrects a conversion formula converted by the conversion means. The correction means corrects the conversion formula converted by the conversion means into the charging electric potential of the photoreceptor at the developing position according to a result of the detection made by the current detection means.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] In an image forming apparatus using electrophotography, a technique is already known in which a potential sensor is used to detect the charged potential of a photoconductor, which is an image carrier, and the potential after exposure, and the photoconductor potential at the development position is predicted from the detection result. It is also known that a photoconductor deteriorates depending on the time of use and the environment. It is also known that after a predetermined amount of charge is applied to the photoconductor film, dark attenuation occurs, in which part of the charge is lost over time. In response to this, there is a technique for forming an image of uniform density, regardless of the cause of the dark attenuation in the photoconductor film, which fluctuates due to various causes.

[0003] For example, Patent Document 1 discloses an image forming apparatus having a rotatable photosensitive drum having a conductive substrate and a photosensitive film formed on the surface of the substrate, a charging means arranged in the vicinity of the photosensitive drum for charging the photosensitive film, an exposure means for irradiating the photosensitive film charged thereby with light to form an electrostatic latent image, a developing means arranged downstream of the exposure means along the rotation direction of the photosensitive drum for developing the electrostatic latent image, and a dark decay detection means for detecting fluctuations in the degree of dark decay of the photosensitive film, wherein the charging means changes the charging capacity of the charging means based on the fluctuations in the degree of dark decay detected by the dark decay detection means to change the potential of the photosensitive film directly below the charging means, thereby compensating for the fluctuations in the degree of dark decay.

[0004] Here, as the photoconductor deteriorates, the charge potential of the photoconductor decreases. One of the causes of this decrease is an increase in the dark attenuation of the photoconductor. Since the dark attenuation of the photoconductor changes, such as increasing, if the charge potential at the development position is predicted on the assumption that the amount of dark attenuation from the potential sensor position to the development position is constant, the surface potential of the photoconductor at the development position cannot be predicted correctly. In order to correctly predict the surface potential of the photoconductor at the development position, it is necessary to take into consideration the change in the dark attenuation of the photoconductor. Another cause of the decrease in the charge potential of the photoconductor is the decrease in charging ability due to deterioration of the charging roller, which is the charging means. The change in the dark attenuation of the photoconductor can be grasped by detecting the charging current of the charging means. Therefore, by utilizing both a potential sensor that measures the charge potential of the photoconductor and a means for detecting the current flowing through the charging means, the specific deterioration of the photoconductor can be accurately determined. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to make it possible to accurately determine the degree of deterioration of a photoconductor. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the invention of claim 1 is an image forming apparatus comprising a photoconductor, a charging means for charging the photoconductor, a potential detection means for detecting the charging potential of the photoconductor, a developing means for developing an electrostatic latent image on the photoconductor, a current detection means for detecting a charging current flowing through the charging means, a discharge means for discharging electricity before charging the photoconductor, and a control means including a conversion means for converting the charging potential of the photoconductor detected by the potential detection means into the potential of the photoconductor at a development position and a correction means for correcting the conversion formula used for conversion by the conversion means, wherein the correction means corrects the conversion formula used for conversion by the conversion means to the charging potential of the photoconductor at the development position based on the detection result of the current detection means. Effect of the Invention

[0007] According to the present invention, the deterioration degree of the photoconductor can be accurately determined. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 illustrates an overall configuration of a full-color copier. [Diagram 2] FIG. 2 is a diagram showing a configuration of an image forming unit. [Diagram 3] FIG. 4 is a diagram for explaining detection of a charging current. [Figure 4] 3A and 3B are diagrams illustrating a configuration of a charging roller that can be used in the present embodiment. [Diagram 5] FIG. 2 is a diagram showing a configuration of a photoconductor that can be used in the present embodiment. [Figure 6] FIG. 2 is a block diagram showing a part of an electric circuit of the full-color copying machine according to the embodiment. [Figure 7] FIG. 13 is a diagram showing the relationship between the deterioration state of the photoconductor and the charging means and the charging potential. [Figure 8] 11 is a diagram showing changes in charging potential at the potential sensor position and the development position with respect to the number of sheets passed on a new photoconductor and an aged photoconductor; [Figure 9] 13 is a graph showing the change in surface potential difference and charging current at the potential sensor position and the development position due to dark decay of a new photoconductor and an aged photoconductor in a paper feed test. [Figure 10] FIG. 4 is a diagram for explaining conversion and correction of the charging potential of the photoconductor at the development position based on the detection result of the charging current of the charging roller. [Figure 11A] FIG. 4 is a diagram showing a control flow in the present embodiment. [Figure 11B] FIG. 4 is a diagram showing a control flow in the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] <Embodiments of the present invention> DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

[0010] In addition, in each drawing for explaining the embodiments of the present invention, components such as parts and components having the same function or shape are given the same symbols as far as possible to distinguish them, and once they have been explained, their explanations will be omitted.

[0011] [Configuration of image forming device] An embodiment in which the present invention is applied to a full-color copying machine of a tandem intermediate transfer type as an image forming apparatus will be described.

[0012] 1 shows the overall configuration of a full-color copier. This full-color copier is composed of a main body 100, a paper feed table 200 on which the main body is placed, a scanner 300 attached to the main body of the copier, and an automatic document feeder (ADF) 400 attached to the scanner.

[0013] In the center of the main body, four image forming units 18Y, 18C, 18M, and 18Bk for Y, C, M, and Bk are arranged side by side to form a tandem image forming device 20. In this specification, the tandem image forming device 20 may be simply referred to as an image forming device. Each image forming unit of the tandem image forming device has a photoconductor 40Y, 40C, 40M, and 40Bk on which a toner image of each color Y, C, M, and Bk is formed, respectively.

[0014] An exposure device 21 is provided above the tandem image forming apparatus. The exposure device is composed of four laser diode (LD) type light sources prepared for each color, a polygon scanner consisting of a six-sided polygon mirror and a polygon motor, and lenses and mirrors such as an fθ lens and a long WTL arranged in the optical path of each light source. The laser light emitted from the LD according to the image information of each color is deflected and scanned by the polygon scanner and irradiated onto the photoconductor of each color.

[0015] An endless belt-like intermediate transfer belt 10 is installed below the tandem image forming apparatus. The intermediate transfer belt is wound around three support rollers 14, 15, and 16, and can be rotated clockwise in the figure. The support roller 14 is a drive roller that rotates the intermediate transfer belt. In addition, primary transfer rollers 82Y, C, M, and Bk are provided between the first support roller 14 and the second support roller 15 to face each photoconductor with the intermediate transfer belt sandwiched therebetween, as primary transfer means that transfers a toner image from the photoconductor of each color to the intermediate transfer belt.

[0016] An intermediate transfer belt cleaning device 17 is provided downstream of the third support roller 16 to remove residual toner remaining on the intermediate transfer belt after image transfer. The intermediate transfer belt can be made of resin materials such as polyvinylidene fluoride, polyimide, polycarbonate, and polyethylene terephthalate, which are molded into seamless belts. These materials can be used as they are, or the resistance can be adjusted by adding a conductive material such as carbon black. In addition, these resins can be used as a base layer, and a surface layer can be formed by a method such as spraying or dipping to form a laminated structure.

[0017] A secondary transfer device 22 is provided below the intermediate transfer belt. The secondary transfer device is configured by stretching a secondary transfer belt 24, which is an endless belt, between two rollers 23, and is arranged by pressing the intermediate transfer belt against a third support roller 16, and transfers the image on the intermediate transfer belt to a transfer material. The secondary transfer belt can be made of the same material as the intermediate transfer belt.

[0018] A fixing device 25 that fixes the image on the transfer material is provided next to 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 transport function that transports the transfer material after image transfer to this fixing device. Of course, a transfer roller or transfer charger may be disposed as the secondary transfer device, and in such a case, it is necessary to provide a separate transfer material transport function.

[0019] In addition, below the secondary transfer device and the fixing device, a sheet inversion device 28 is provided, parallel to the above-mentioned tandem image forming device, which inverts and discharges the transfer material, or inverts and re-feeds the transfer material to form images on both sides of the transfer material.

[0020] When performing a copy operation using this full-color copier, an original is set on the document table 30 of the ADF. Alternatively, the ADF is opened and an original is set on the contact glass 32 of the scanner, and the ADF is closed to hold the original. Then, when the start switch on the operation display unit 515 (see FIG. 6 described later) is pressed, if an original is set on the ADF, the original is transported and moved onto the contact glass, and the scanner is then driven to travel on the first traveling body 33 and the second traveling body 34. On the other hand, if an original is set on the contact glass, the scanner is immediately driven to travel on the first traveling body 33 and the second traveling body 34.

[0021] Then, light is emitted from the light source on the first traveling body, and the light reflected from the surface of the document is further reflected toward the second traveling body, reflected by a mirror on the second traveling body, and enters the reading sensor 36 through an imaging lens 35, and the contents of the document are read. After that, the image forming operation starts in full color mode or black and white mode according to the mode setting on the operation unit, or according to the result of reading the document if the automatic mode selection is set on the operation unit.

[0022] When the full-color mode is selected, each photoconductor rotates counterclockwise in FIG. 1. Then, the surface of each photoconductor is uniformly charged by a charging roller, which is a charging device. Then, the photoconductor of each color is irradiated with a laser beam corresponding to the image of each color from an exposure device, and a latent image corresponding to the image data of each color is formed. As the photoconductor rotates, each latent image is developed with toner of each color by the developing device 60Y, C, M, Bk of each color. The toner images of each color are transferred sequentially onto the intermediate transfer belt as the intermediate transfer belt is transported, forming a full-color image on the intermediate transfer belt. After transfer, the photoconductor is photo-discharged by a discharge lamp, and the toner remaining after transfer is removed by a cleaning means.

[0023] On the other hand, one of the paper feed table paper feed rollers 42 is selected and rotated to feed the transfer material from one of the paper feed cassettes 44 provided in multiple stages on the paper feed table 43. Next, the transfer material is separated one by one by the separation roller 45 and placed in the paper feed path 46, and is conveyed by the conveyance roller 47 to be guided to the paper feed path 48 in the main body, and is stopped by being abutted against the registration roller 49. Alternatively, the paper feed roller 50 is rotated to feed the transfer material on the manual feed tray 51, and the transfer material is separated one by one by the separation roller 52 and placed in the manual feed path 53, and is also stopped by being abutted against the registration roller. Then, the registration roller is 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 toner image is transferred onto the transfer material by the secondary transfer device.

[0024] The transfer material onto which the toner image has been transferred is transported by the secondary transfer device and sent to the fixing device, where the toner image is fixed to the transfer material by applying heat and pressure, and then the sheet is switched by a switching claw 55 and discharged by discharge rollers 56 and stacked on a paper output tray 57. Alternatively, the sheet is switched by a switching claw and placed in a sheet inverting device 28, where it is inverted and fed again to the transfer position, an image is recorded on the back side as well, and then discharged by discharge rollers onto the paper output tray. Thereafter, when image formation on two or more sheets is instructed, the above-mentioned image forming process is repeated.

[0025] After the formation of a predetermined number of images is completed, post-image processing is performed and then the rotation of the photoconductor is stopped. In the post-image processing, the photoconductor is rotated one or more times with the charging bias and transfer bias turned off, and the charge on the surface of the photoconductor is removed by a discharging means at that time to prevent the photoconductor from being left in a discharged state and from being deteriorated.

[0026] When the black and white mode is selected, the support roller 15 moves downward, separating the intermediate transfer belt from the photoconductors Y, C, and M. Only the Bk photoconductor rotates counterclockwise in FIG. 1, the surface of the Bk photoconductor is uniformly charged by the charging roller, and a laser beam corresponding to the Bk image is irradiated to form a latent image, which is then developed with the Bk toner into a toner image. This toner image is transferred onto the intermediate transfer belt. At this time, the photoconductors and developing devices of the three colors other than Bk are stopped to prevent unnecessary consumption of the photoconductors and developer.

[0027] Meanwhile, a transfer material is fed from a paper feed cassette and conveyed by a registration roller in a timed manner to coincide 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 then processed through a paper discharge system according to a specified mode. Thereafter, when image formation on two or more sheets is instructed, the above-mentioned image forming process is repeated.

[0028] [Explanation of image forming unit] The configuration of the image forming unit is shown in Fig. 2. Around the photoconductor 40, which is an image carrier, an opening is provided to allow exposure light 76 from an exposure device to pass through. Arranged therein are a charging roller 70 as a charging member that uniformly charges the photoconductor, a developing device 60 that develops the electrostatic latent image formed on the photoconductor, a static elimination lamp 72 that eliminates static electricity from the surface of the photoconductor after the toner image has been transferred, and a brush roller 73 and a cleaning blade 75 for cleaning residual toner after transfer.

[0029] Further, potential sensor 71, which detects the surface potential of photoconductor 40, is disposed between the exposure device and development device 60 so as to be able to detect both the charging potential and the potential after exposure. In the present invention, photoconductor 40 is neutralized by neutralization lamp 72 after transfer, so that the charging current, which will be described below, can be detected even during printing or regardless of the image to be printed.

[0030] A solid lubricant 78 is in contact with the brush roller 74 arranged downstream of the cleaning blade 75, and the lubricant scraped off by the brush roller is applied to the photoreceptor by the application blade 80. Examples of solid lubricants 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 necessary. Solid lubricants can be produced by melting and solidifying lubricant particles or by compression molding.

[0031] The toner scraped off from the photoconductor by a brush roller or a cleaning blade made of polyurethane rubber is collected by a toner transport coil 79 and transported to a waste toner storage unit.

[0032] In this embodiment, the photoconductor which has been neutralized after transfer is cleaned, but the photoconductor which has been cleaned after transfer may be neutralized.

[0033] Fig. 3 is a diagram for explaining detection of charging current. As shown in Fig. 3, the charging roller 70 is connected to a charging power source 516, which is a high-voltage power source. In this embodiment, the charging power source 516 is provided with a current detection circuit 516a that detects the DC component of the charging current (hereinafter referred to as DC charging current) flowing through the charging roller 70. The charging power source 516 applies a charging bias to the charging roller 70 in which an AC component of the charging current (hereinafter referred to as AC charging current) is superimposed on the DC charging current, and detects the DC component of the charging current flowing through the charging roller 70.

[0034] 4 is a diagram showing the configuration of a charging roller that can be used in this embodiment. The charging roller 70 is composed of a core metal 101, which is a conductive support, a resin layer 102, and a gap retention member 103. The core metal is made of a metal such as stainless steel. If the core metal is too thin, the effects of deflection during cutting of the resin layer 102 or when pressed against the photoconductor 40 cannot be ignored, making it difficult to obtain the required gap accuracy. Furthermore, if the core metal 101 is too thick, the charging roller 70 may become large or heavy, so the diameter of the core metal is preferably about 6 to 10 mm.

[0035] The resin layer of the charging roller 70 is 10 4 ~10 9 A material having a volume resistivity of [Ωcm] is preferable. If the resistivity is too low, the charging bias is likely to leak if the photoconductor 40 has defects such as pinholes, and if the resistivity is too high, discharge does not occur sufficiently and a uniform charging potential cannot be obtained. The desired volume resistivity can be obtained by blending a conductive material with the base resin. As the base resin, resins such as polyethylene, polypropylene, polymethylmethacrylate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polycarbonate, etc. can be used. These base resins have good moldability and can be easily molded.

[0036] The conductive material is preferably an ion conductive material such as a polymeric compound having a quaternary ammonium base. Examples of polyolefins having a quaternary ammonium base include polyethylene, polypropylene, polybutene, polyisoprene, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-hexene copolymer, and other polyolefins having a quaternary ammonium base. In the present embodiment, polyolefins having a quaternary ammonium base are exemplified, but polymeric compounds other than polyolefins having a quaternary ammonium base may be used.

[0037] The ion conductive material is uniformly mixed with the base resin by using a twin-screw kneader, kneader, or other means. The mixed material can be easily molded into a roller shape by injection molding or extrusion molding on a core metal. The amount of the ion conductive material and base resin to be mixed is preferably 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 preferably 0.5 to 3 mm. If the resin layer is too thin, molding is difficult and there is 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 becomes large, resulting in a decrease in charging efficiency.

[0038] After the resin layer 102 is molded, the gap retention members 103, which have been molded in advance on both ends of the resin layer 102, are fixed to the core metal 101 by press-fitting, bonding, or a combination of both. After the resin layer 102 and the gap retention members 103 are integrated in this way, the outer diameter of the charging roller 70 is adjusted by cutting, grinding, or other processing, so that the phase of the runout of the resin layer 102 and the gap retention members 103 can be aligned, and the variation in the charging gap can be reduced.

[0039] The material of the gap retaining member 103 may be a resin such as polyethylene, polypropylene, polymethylmethacrylate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polycarbonate, or the like, as in the base material of the resin layer 102. However, since the gap retaining member 103 is brought into contact with the photosensitive layer, it is desirable to use a resin having a lower hardness than the resin layer 102 in order to prevent the photosensitive layer from being damaged. In addition, resins such as polyacetal, ethylene-ethyl acrylate copolymer, polyvinylidene fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer may also be used as resin materials that have excellent sliding properties and are unlikely to damage the photosensitive layer.

[0040] In addition, the resin layer 102 and the gap holding member 103 can be coated with a surface layer of several tens of μm to which toner and the like do not easily adhere. A gap is formed between the resin layer of the charging roller and the photoconductor by abutting the gap holding member against the outside of the image area of ​​the photoconductor. The charging roller has a gear attached to the end of the core metal that meshes with a gear formed on the photoconductor flange, and when the photoconductor rotates by the photoconductor drive motor, the charging roller also rotates in the same direction. Since the resin layer and the photoconductor do not come into contact with each other, the photosensitive layer in the image area will not be scratched even if a hard resin material and an organic photoconductor are used as the charging roller. In addition, if the gap is too wide, abnormal discharge occurs and uniform charging cannot be achieved, so the maximum gap must be kept to about 100 μm or less. When using a charging roller with a gap between the photoconductor and the charging roller, it is desirable to superimpose an AC voltage on a DC voltage as a charging bias.

[0041] Since the resin layer 102 and the gap retaining member are made of a resin material, it is easy to process and a high-precision charging roller can be manufactured. In addition, 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 attached to a metal core bar, and is in contact with the charging roller by its own weight, and removes dirt such as toner adhering to the charging roller surface while rotating with the rotation of the charging roller. The cleaning roller may be in constant contact with the charging roller, but it can also be configured to have a mechanism for contacting and separating the cleaning roller, to keep it separated from the charging roller normally and to periodically contact the charging roller as necessary to intermittently clean the charging roller surface. Note that the charging roller 70 described above is provided with a gap retaining member 103 and brings the surface of the photoconductor 40 and the resin layer 102 of the charging roller 70 close to each other, but a charging roller 70 that brings them into contact with each other can also be used.

[0042] Each developing device has the same configuration, and they are two-component developing devices that differ only in the color of toner they use. Each developing device for each color contains a two-component developer made of toner and carrier.

[0043] The developing device is composed of a developing roller 61 facing the photoconductor, screws 62 and 63 for transporting and stirring the developer, a toner concentration sensor 64, etc. The developing roller is composed of an outer rotatable sleeve and an inner fixed magnet. Depending on the output of the toner concentration sensor, the required amount of toner is replenished by the toner replenishing device.

[0044] The toner is composed mainly of a binder resin, a colorant, and a charge control agent, and other additives may be added as necessary. Specific examples of the binder resin include polystyrene, styrene-acrylic acid ester copolymer, polyester resin, etc. Colorants (e.g., yellow, magenta, cyan, and black) used in the toner may be those known for use in toners. The amount of colorant is preferably 0.1 to 15 parts by weight per 100 parts by weight of the binder resin.

[0045] Specific examples of the charge control agent include nigrosine dyes, chromium-containing complexes, and quaternary ammonium salts, which are used depending on the polarity of the toner particles. The amount of the charge control agent is 0.1 to 10 parts by weight per 100 parts by weight of the binder resin.

[0046] It is advantageous to add a fluidity imparting agent to the toner particles. As the fluidity imparting agent, fine particles of metal oxides such as silica, titania, alumina, etc., fine particles surface-treated with a silane coupling agent, titanate coupling agent, etc., fine polymer particles such as polystyrene, polymethyl methacrylate, polyvinylidene fluoride, etc. 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 added is preferably in the range of 0.1 to 7.0 parts by weight per 100 parts by weight of the toner particles.

[0047] The carrier is generally made of a core material itself or a core material with a coating layer. 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 material is preferably about 20 to 60 μm.

[0048] Materials used to form the carrier coating layer include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinyl ether substituted with a fluorine atom, and vinyl ketone substituted with a fluorine atom. The coating layer can be formed by applying a resin to the surface of the carrier core particles by spraying, dipping, or other methods, as in the conventional method.

[0049] 5 is a diagram showing the structure of a photoreceptor that can be used in this embodiment. One example of the photoreceptor 40 used in this embodiment is a laminated organic photoreceptor that is made up of a charge generating layer 203 and a charge transport layer 204, which are photosensitive layers formed on a conductive support 201. The conductive support 201 has a volume resistance of 10 -4 It is made of a material having a conductivity of 0.1Ωcm or less, for example, a pipe material such as aluminum, an aluminum alloy, nickel, or stainless steel, which has been surface-treated by cutting, polishing, etc. The charge generation layer 203 is a layer whose main component is a charge generation material.

[0050] The charge generating material may be an inorganic or organic material, and representative examples thereof include monoazo pigments, disazo pigments, trisazo pigments, perylene pigments, perinone pigments, quinacridone pigments, quinone condensed polycyclic compounds, squaric acid dyes, phthalocyanine pigments, naphthalocyanine pigments, azulenium salt dyes, selenium, selenium-tellurium alloys, selenium-arsenic alloys, amorphous silicon, etc. These charge generating materials may be used alone or in combination of two or more.

[0051] The charge generating layer 203 can be formed by dispersing the charge generating material together with an appropriate binder resin using a solvent such as tetrahydrofuran, cyclohexanone, dioxane, 2-butanone, or dichloroethane using a ball mill, attritor, or sand mill, and applying the dispersion. The charge generating layer can be applied by a dip coating method, a spray coating method, a bead coating method or the like.

[0052] Examples of the binder resin that may be appropriately used include polyamide, polyurethane, polyester, epoxy, polyketone, polycarbonate, silicone, acrylic, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, polyacrylic, polyamide, etc. The amount of the binder resin is suitably 0 to 2 parts by weight per part of the charge generating material.

[0053] The thickness of the charge generating 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 the charge transport material and binder resin in a suitable solvent, applying the solution, and drying it. If necessary, a plasticizer, a leveling agent, etc. can also be added.

[0054] Among the charge transport materials, the low molecular weight charge transport materials include electron transport materials and hole transport materials. Examples of the electron transport materials include electron accepting substances such as chloranil, bromanil, 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]thiophen-4-one, and 1,3,7-trinitrodibenzothiophene-5,5-dioxide.

[0055] These electron transport materials may be used alone or in a mixture of two or more kinds. Examples of hole transport materials include electron donating substances such as 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 in a mixture of two or more kinds.

[0056] Examples of binder resins used in the charge transport layer together with the charge transport material include thermoplastic or thermosetting resins such as 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, and alkyd.

[0057] Examples of the solvent include tetrahydrofuran, dioxane, toluene, 2-butanone, monochlorobenzene, dichloroethane, and methylene chloride.

[0058] The thickness of the charge transport layer 204 may be appropriately selected within the range of 10 to 40 μm depending on the desired photoreceptor characteristics.

[0059] In the photoreceptor 40 of this embodiment, an undercoat layer 202 can also be formed between the conductive support 201 and the photosensitive layer. The undercoat layer 202 generally contains a resin as a main component, and considering that the photosensitive layer is applied thereon using a solvent, it is preferable that the resin has high resistance to dissolution in general organic solvents. Examples of such resins include water-soluble resins such as polyvinyl alcohol, casein, and sodium polyacrylate, alcohol-soluble resins such as copolymer nylon and methoxymethylated nylon, and curable resins that form a three-dimensional network structure, such as polyurethane, melamine, alkyd-melamine, and epoxy.

[0060] In addition, the undercoat layer 202 may contain fine powder of metal oxide such as titanium oxide, silica, alumina, zirconium oxide, tin oxide, indium oxide, etc., to prevent moire and reduce residual potential. The undercoat layer 202 can be formed using an appropriate solvent and coating method, similar to the above-mentioned photosensitive layer. Furthermore, it is also useful to use a metal oxide layer formed, for example, by a sol-gel method or the like, using a silane coupling agent, a titanium coupling agent, a chromium coupling agent, etc., as the undercoat layer 202. In addition, the undercoat layer 202 may be formed by anodizing Al2O3, or by forming an organic material such as polyparaxylylene (parylene), or an inorganic material such as SiO, SnO2, TiO2, ITO, CeO2, etc., by a vacuum thin film formation method. The thickness of the undercoat layer 202 is preferably 0 to 5 μm.

[0061] In the photoreceptor 40 of this embodiment, a protective layer 205 can be formed on the photosensitive layer as shown in FIG. 4(b) for the purpose of protecting the photosensitive layer and improving its durability. This protective layer 205 is configured by adding metal oxide particles such as alumina, silica, titanium oxide, tin oxide, zirconium oxide, and indium oxide to a binder resin for the purpose of improving wear resistance. Examples of the binder resin include styrene-acrylonitrile copolymer, styrene-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, olefin-vinyl monomer copolymer, chlorinated polyether, allyl, phenol, polyacetal, polyamide, polyamideimide, polyacrylate, polyarylsulfone, polybutylene, polybutylene terephthalate, polycarbonate, polyethersulfone, polyethene, polyethylene terephthalate, polyimide, acrylic, polymethylpentene, polypropylene, polyphenylene oxide, polysulfone, polyurethane, polyvinyl chloride, polyvinylidene chloride, and epoxy resins.

[0062] The amount of metal oxide particles added to the protective layer 205 is usually 5 to 30% by weight. If the amount of metal oxide particles is less than 5%, the wear is large and the effect of improving the wear resistance is small, resulting in poor durability. If the amount of metal oxide particles exceeds 30%, the increase in the bright area potential during exposure becomes significant, and the decrease in sensitivity cannot be ignored, which is undesirable. A normal coating method such as a spray method is adopted as a method for forming the protective layer 205. The thickness of the protective layer 205 is appropriately 1 to 10 [μm], preferably about 3 to 8 [μm]. If the thickness of the protective layer 205 is too thin, the durability is poor, and if the thickness of the protective layer 205 is too thick, not only the productivity during the production of the photoreceptor decreases, but also the increase in the residual potential over time increases. The particle diameter of the metal oxide particles added to the protective layer 205 is appropriately 0.1 to 0.8 [μm]. If the particle size of the metal oxide particles is too large, the surface of the protective layer becomes uneven, reducing the cleaning properties, and the exposure light is easily scattered by the protective layer, reducing the resolution and resulting in poor image quality.If the particle size of the metal oxide particles is too small, the abrasion resistance is poor.

[0063] Furthermore, a dispersion 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. The dispersion aid to be added can be any one used in paints, etc., and the amount of the dispersion aid is usually 0.5 to 4%, preferably 1 to 2%, based on the amount of the contained metal oxide fine particles, on a weight basis. Furthermore, by adding a charge transport material to the protective layer 205, the movement of charges in the protective layer can be promoted. The charge transport material to be added to the protective layer can be the same material as that of the charge transport layer.

[0064] 6 is a block diagram showing a part of the electric circuit of the full-color copier according to the embodiment. In the figure, a control section (main control section) 500 is responsible for driving and controlling each device of the full-color copier, and has a CPU (Central Processing Unit) 500a, a RAM (Random Access Memory) 500b as a data storage means, a ROM (Read Only Memory) 500c as a data storage means, etc. Then, based on the programs stored in the ROM 500c, it controls the driving of various devices and executes predetermined arithmetic processing.

[0065] A process motor 510, a developing bias power supply 511, a transfer bias power supply 512, a resist clutch 513, etc. are connected to the control unit (main control unit) 500. Also connected are an operation display unit 515, a charging power supply 516 that applies a voltage to the charging roller 70, a discharge device power supply (discharge lamp power supply) 517 for the discharge lamp 72, an optical writing control unit 518, an image information receiving unit 519, etc.

[0066] The image information receiving unit 519 receives image information sent from the scanner 300 and sends it to the control unit 500. The optical writing control unit 518 controls the driving of the exposure device 21 based on the image information sent from the control unit 500, thereby optically scanning the surface of the photoconductor 40. Note that, in this embodiment, the image information may be a copy of an original, but is not limited to this and may also include information from a printer, a facsimile, etc.

[0067] The process motor 510 is a motor that serves as a drive source for the photoconductor 40, the developing device 60, various rollers, etc. The rotational drive force of the process motor 510 is transmitted to the registration rollers 49 via a registration clutch 513. The control unit 500 connects the rotational drive force of the process motor 510 to the registration rollers 49 by turning on the registration clutch 513 at a predetermined timing.

[0068] The developing bias power supply 511 applies to the developing roller 61 a developing bias having the same polarity as the toner, an absolute value greater than the absolute value of the latent image potential VL, and less than the charging potential VD of the background portion of the photoconductor 40. For example, a developing bias of -550 [V] is applied under the conditions that the photoconductor background portion potential = -600 [V] and the electrostatic latent image potential = -30 [V]. The control unit 500 sends an output command signal to the developing bias power supply 511, thereby causing the developing bias power supply 511 to output the developing bias at a predetermined timing.

[0069] Furthermore, the control unit 500 sends an output command signal to the transfer bias power supply 512 at a predetermined timing, thereby causing the transfer bias power supply 512 to output a transfer bias. The transfer bias is a voltage for forming a transfer electric field between the intermediate transfer belt 10 and the electrostatic latent image on the photoconductor 40 in a transfer section where the photoconductor 40 faces a transfer device constituted by the transfer roller 82, a conveyor belt unit, etc.

[0070] Operation display unit 515 includes a touch panel, a numeric keypad, and the like, and displays images on the touch panel and sends information inputted via the touch panel, the numeric keypad, and the like to control unit 500. The operation display unit may also be simply called a display unit.

[0071] As described above, the charging power supply 516 applies a charging bias in which an alternating current AC is superimposed on a direct current DC to the charging roller 70, and detects a DC charging current which is a DC component of the charging current flowing through the charging roller 70. For this purpose, the charging power supply 516 is provided with a current detection circuit 516a which detects the current during charging, and the output of this circuit is sent to the control unit 500. Alternatively or in addition to this, a current measurement circuit which detects the current flowing through the base of the photoconductor 40 can be provided, and the output of this circuit can be sent to the control unit 500. In the present invention, the current detection circuit 516a may be built into the charging power supply 516.

[0072] The control unit 500 functions as a control device that controls the charging power source 516 and controls the charging bias applied to the charging roller.

[0073] The control unit 500 is connected to the potential sensor 71. The control unit 500 includes a conversion unit 500d that converts the surface potential (charged potential) of the photoconductor film measured by the potential sensor 71 into the potential of the photoconductor 40 at the development position, and a correction unit 500e that corrects the conversion equation used for the conversion by the conversion unit 500d. The details of the correction method and the like will be described later.

[0074] <Characteristic features of the present invention> Next, the configuration that characterizes the present invention will be described below. Before that, problems with the configuration according to the comparative example will be described first.

[0075] [Issues in the configuration of the comparative example] The potential sensor is located between the exposure device and the development device in the circumferential direction of the photoconductor, and the potential detected by the potential sensor is converted into the potential at the development position based on the pre-determined photoconductor characteristics (dark attenuation and light attenuation characteristics).The main factor that determines the lifespan of an organic photoconductor is the wear of the photosensitive layer, but on the other hand, the lifespan of photoconductors has been greatly improved due to technological developments such as protective layers.

[0076] In addition, image forming apparatuses are becoming faster, and large-volume printing is becoming mainstream. When image forming apparatuses are used in this way, the attenuation characteristics of the photoconductor change significantly, and the correct charging potential at the development position cannot be obtained from the detection result of the potential sensor using a conversion method that has been obtained in advance, and background scumming may occur.

[0077] Also, a configuration can be envisaged in which the potential at the development position is predicted by detecting the degree of change in dark attenuation by detecting the amount of potential drop from the initial reference potential of the photoconductor using a potential sensor. On the other hand, factors that cause the charge potential of the photoconductor to drop include not only an increase in dark attenuation of the photoconductor but also deterioration of the charging roller, which is the charging means. Therefore, it may not be possible to distinguish between an increase in dark attenuation due to fatigue of the photoconductor and a drop in charge potential due to deterioration of the charging means. When the charge potential drops due to deterioration of the photoconductor, dark attenuation increases. On the other hand, when the charge potential drops due to deterioration of the charging means, the dark attenuation of the photoconductor does not change, and therefore there is a problem that the charge potential at the development position cannot be accurately predicted.

[0078] [Detection of charging current] In order to accurately determine the deterioration of the photoconductor, it is necessary to be able to grasp the state of the charging means as described above. In response to this, the present invention has found that the characteristics of a charging means (charging roller) that has aged are different from the characteristics of a photoconductor that has aged, by detecting the charging current of the charging means, and has also been able to grasp the relationship between the dark decay of the photoconductor and the charging current. This will be explained in detail below.

[0079] FIG. 7 is a diagram showing the relationship between the deterioration state of the photoconductor and the charging means and the charging potential. FIG. 7 shows the relationship between the charging potential at the potential sensor position of the photoconductor when a bias of DC component voltage Vc=-700V and AC component voltage Vpp=2.3kV is applied to the charging roller, which is the charging means, and the charging current flowing through the charging roller at this time. In FIG. 7, the left graph shows the case of "Condition A: new charging, new photoconductor", the center graph shows the case of "Condition B: aged charging, new photoconductor", and the right graph shows the case of "Condition C: new charging, aged photoconductor". A new charging means that the charging roller is new, and an aged charging means that the charging roller is aged (deteriorated). A new photoconductor means that the photoconductor is new, and an aged photoconductor means that the photoconductor is aged (deteriorated). In this specification, new is defined as "not exceeding 10% of the lifespan," and aged or deteriorated is defined as "more than half of the lifespan."

[0080] Referring to Fig. 7, it can be seen that when the central charging roller is an aged product under condition B and when the photoconductor is an aged product under condition C, the amount of decrease in charging potential is about the same compared to when the photoconductor and charging roller are both new under condition A. It can also be seen that the charging current decreases when the charging roller is an aged product, as shown under condition B, and increases when the photoconductor is an aged product, as shown under condition C. Therefore, it can be seen from Fig. 7 that it is possible to distinguish whether the photoconductor or the charging roller has deteriorated by detecting the photoconductor potential and charging current.

[0081] Fig. 8 shows the change in the charging potential at the potential sensor position and the development position with respect to the number of sheets passed for a new photoconductor and an aged photoconductor. Note that when carrying out the paper passing test shown in Fig. 8, a surface potential meter was placed in place of the development device to measure the potential at the development position of the photoconductor.

[0082] As shown in this figure, for a new photoconductor, the difference in charge potential between the potential sensor position and the development position due to dark decay is small, and the change due to paper passing is also small. In contrast, for a worn-out photoconductor, the difference in charge potential between the potential sensor position and the development position is large due to increased dark decay, and this difference increases further as paper passes. In the paper passing test shown in this figure, the operation of the image forming apparatus was stopped after 7k (7000) sheets were passed, and the apparatus was left to rest without operation, and it was found to have recovered by the next day.

[0083] Figure 9 shows the change in surface potential difference between the potential sensor position and the development position and the charging current due to dark attenuation for a new photoconductor and an aged photoconductor in the paper feed test in Figure 8. Also, Figure 9(a) shows the relationship between the number of sheets passed and the dark attenuation and charging current in the case of a new photoconductor, and Figure 9(b) shows the relationship between the number of sheets passed and the dark attenuation and charging current in the case of an aged photoconductor.

[0084] As can be seen from Figure 9, the change in the amount of dark decay and the change in charging current are in good agreement. Based on this result, it is possible to understand the change in dark decay using the detection results of the charging current, and understanding this leads to more accurate prediction of the potential of the photoconductor at the development position from the potential of the photoconductor at the potential sensor position.

[0085] From the above, the factors that cause the charge potential of the photoconductor to decrease include an increase in dark attenuation due to fatigue caused by the deterioration of the photoconductor through use, and deterioration of the charging roller or the like, which is the charging means. In addition, the change in the amount of dark attenuation and the change in charging current are in good agreement. When the dark attenuation characteristics of the photoconductor change, even if the detection result of the potential sensor is the same, a difference in the potential at the development position may occur. In order to understand the details of the occurrence of this difference, it is necessary to detect the charging current when the photoconductor is charged by the charging means.

[0086] In light of these, in the present invention, the potential at the development position of the photoconductor and the exposure potential are accurately grasped using a potential sensor. Additionally, in the present invention, the charging current when the photoconductor is charged by the charging means is also detected, and changes in the amount of dark attenuation are captured. Furthermore, in the present invention, the detection result is used to convert the detected potential of the potential sensor into the potential at the development position, and then this is corrected. In this way, even if the dark attenuation characteristics change, the potential at the development position can be predicted more accurately. First, the method for accurate prediction will be described in detail below.

[0087] [Conversion method and correction method in the present invention] In light of the above, in the present invention, a method of converting the detection result of the charging current of the charging roller into the charging potential of the photoconductor at the development position by a conversion means and correcting it by a correction means will be described below. Note that in this embodiment, the conversion means corresponds to conversion means 500d, and the correction means corresponds to correction means 500e. Also, the numerical values ​​etc. given below are merely examples, and the present invention is not limited to these.

[0088] Here, Fig. 10 is a diagram for explaining conversion and correction to the charging potential of the photoconductor at the development position based on the detection result of the charging current of the charging roller. Also, Fig. 10(a) shows a diagram for explaining acquisition of the initial value, Fig. 10(b) is a diagram for explaining a method of determining deterioration of the photoconductor, and Fig. 10(c) is a diagram for explaining the correction.

[0089] First, as shown in FIG. 10(a), the initial value of the photoconductor 40 when it is new is obtained. Specifically, the DC component of the charging bias (charging potential) is distributed, and the relationship between the potential and the current is obtained and approximated to a straight line. Specifically, the DC component of the charging bias is distributed, for example, as Vc=-500, -600, -700, and -800V. Then, the charging current [-μA] corresponding to these four charging biases is obtained. Then, the obtained charging current is approximated by a straight line. In this case, it is approximated by a straight line of y=0.107x-2.7228. Then, this straight line (approximation line) becomes the initial value, and is here called the straight line L.

[0090] Next, a method for determining deterioration of a photoconductor will be described with reference to FIG. 10(b). Note that the straight line L in FIG. 10(b) is the same as the straight line L obtained in FIG. 10(a). As described above, when a photoconductor deteriorates with use, the charging current tends to increase. When the charging roller deteriorates, the deterioration will follow the straight line L in FIG. 10(b) (along the arrow V). Here, if the measurement point where the charging current at a certain charging voltage is measured is point Q, the vertical distance from the straight line L is the current increase due to deterioration of the photoconductor. Note that this makes it possible to distinguish whether the deterioration is due to the photoconductor or the charging roller.

[0091] Then, by knowing the amount of current increase due to deterioration of the photoconductor, the conversion method (conversion formula) of the potential at the development position of the photoconductor (development position potential) can be obtained by formula (1) "development position potential [-V] = potential sensor position potential [-V] - (5 + (photoconductor charging) current increase [-μA] × 1.69)". As an example, when the potential sensor position potential is -569V and the current increase is -29.5μA, the development position potential is found to be -514V when formula (1) is applied, since "569 - (5 + 29.5 × 1.69) = 514". Note that this conversion method is performed by the conversion means 500d of the control unit (main control unit) 500.

[0092] Next, we will explain the method of correcting this calculated conversion formula. First, we obtained the relationship between the increase in charging current [μA] flowing through the photoconductor and the increase in dark attenuation [V]. Here, as mentioned above, the charging current increases when the photoconductor deteriorates with use. It is also known that there is a proportional relationship between the increase in charging current and the increase in dark attenuation of the photoconductor, so that the increase in the charging current flowing through the photoconductor increases, and the increase in dark attenuation increases.

[0093] Fig. 10(c) shows the obtained relationship between the increase in charging current of the photoconductor and the increase in dark decay. In this embodiment, the amount of dark decay when the current increase is 0 for a brand new photoconductor is 5V. Therefore, when a regression calculation is performed with an intercept of 5, the obtained relationship between the two is approximated by a straight line y=1.6892x+5 (the dashed straight line shown in Fig. 10(c)). Here, this approximation line is referred to as approximation line N.

[0094] Next, the correction of the above conversion formula will be explained. First, the relationship between the increase in the charging current of the photoconductor and the increase in dark attenuation can be found from the obtained approximation line N. Therefore, by inserting this into the above formula (1), the potential at the development position can be found, and the increase in dark attenuation can be corrected based on this result. Note that this correction is performed by the correction means 500e of the control unit (main control unit) 500.

[0095] [About control flow] 11A and 11B are diagrams showing a control flow (sometimes simply referred to as a flow) in an embodiment of the present invention. Using these diagrams, the control performed by the control unit 500 in the embodiment of the present invention will be described. For convenience of illustration, the control flow is shown separately in FIG. 11A and FIG. 11B. Also, the numerical values ​​and the like shown in the following flow are merely examples, and the present invention is not limited thereto.

[0096] First, for example, assume that a user intends to print early in the morning of a certain day and turns on the power of the image forming apparatus 20. In this embodiment, the time when the power is turned on is set as the start of the control flow (step S011 in FIG. 11A). After that, the control unit (main control unit) 500 judges whether the photoconductor 40 is new or not (step S021 in FIG. 11A). At this time, if the photoconductor 40 is new (Yes in step S021), the process proceeds to step S031. On the other hand, if the photoconductor 40 is not new (No in step S021), the process proceeds to step S041. Then, in step S031 in FIG. 11A, the initial value of the photoconductor 40 when it is new is acquired. The acquisition of the initial value is as described above in FIG. 10.

[0097] The electrostatic capacitance of the photoconductor varies from one to another, and the relationship between the charging potential and the charging current also varies accordingly. Therefore, in this embodiment, by acquiring the initial value (initial data) of the photoconductor actually used, the potential at the development position can be predicted more accurately from the potential at the potential sensor position, as described above.

[0098] At this time, the control unit 500 simultaneously detects the charging potential of the photoconductor 40 by the potential sensor 71 when the DC component of the charging bias Vc=-700V is applied, and detects the charging current of the charging roller 70, and corrects the dark attenuation (step S041 in FIG. 11A). This is done in order to be able to grasp the change in the dark attenuation of the photoconductor. The method of correction is as described above.

[0099] At this time, other adjustments are also made. In this embodiment, the subsequent adjustments are made after every 1k sheets (1000 sheets) of printing. The adjustments referred to here refer to process control (also called procon), which means a process control operation, and are intended to stabilize image density by adjusting image creation conditions such as the development bias, exposure amount, and target value of charging potential.

[0100] Then, the flow thereafter moves to "1" in FIG. 11A and continues to the control flow shown in FIG. 11B.

[0101] Next, the control flow shown in Fig. 11B will be described. The control unit 500 proceeds to step S061. Then, when there is a print request from the user (Yes in step S061 in Fig. 11B), the control unit 500 proceeds to step S101 to start printing in the image forming apparatus 20. Steps after S101 will be described later.

[0102] On the other hand, if there is no print request from the user in step S061 (No in step S061 in FIG. 11B), the control unit 500 judges whether the printing job is completed (step S071 in FIG. 11B). At this time, if the printing job is completed (Yes in step S071 in FIG. 11B), the control unit 500 turns off the power of the image forming apparatus 20 (step S081 in FIG. 11B), for example, and the control flow ends (step S091 in FIG. 11B). On the other hand, if the printing job is not completed (No in step S071 in FIG. 11B), the control unit 500 returns to step S061 again and judges whether there is a print request.

[0103] Here, a case where the control unit 500 proceeds to step S101 of the control flow in FIG. 11B will be described.

[0104] When the control unit 500 proceeds to step S101, the image forming device 20 starts printing in response to a print command from the control unit 500. The control unit 500 then determines whether a predetermined time has elapsed since the image forming device 20 started printing (step S111 in FIG. 11B). Note that the predetermined time is 30 seconds, but this is merely an example. At this time, when the predetermined time has elapsed (if Yes in step S111 in FIG. 11B), the control unit 500 detects the charging current by the current detection circuit 516a (step S151 in FIG. 11B). In this step S151, the control unit 500 determines whether the charging current has changed by a predetermined value or more since the start of printing. Note that in this embodiment, a change of a predetermined value or more refers to, for example, a change of 5% or more.

[0105] On the other hand, if the predetermined time has not elapsed (No in step S111 in FIG. 11B), the control unit 500 judges whether printing has ended (S121 in FIG. 11B). Alternatively, when the control unit 500 detects the charging current in step S151, if the change in the charging current is not equal to or greater than a predetermined value (No in step S151 in FIG. 11B), the control unit 500 also judges whether printing has ended (step S121 in FIG. 11B). Note that if the change in the charging current is equal to or greater than a predetermined value in step S151 (Yes in step S151 in FIG. 11B), the control unit 500 proceeds to step S161.

[0106] Returning to the description of the control flow processed by the control unit 500, the control flow when the control unit 500 proceeds to step S131 after step S121 in Fig. 11B will be described first, and the control flow after step S161 will be described later.

[0107] Here, in step S131 of the control flow, the control unit 500 judges whether the image forming apparatus 20 has printed a predetermined number of sheets or more. Here, the predetermined number of sheets or more is, as an example, 1k sheets (1000 sheets). Then, if the predetermined number of sheets or more has been printed (Yes in step S131), the control unit 500 proceeds to step S141. On the other hand, if the predetermined number of sheets or more has been printed (No in step S131), the control unit 500 proceeds to "1" in the control flow, and the control flow again executes the process in step S061 shown in FIG. 11B. Steps from S061 onwards are as described above.

[0108] Then, the control unit 500 performs adjustment (process control) after the printing of the image forming apparatus 20 is completed (step S141 in FIG. 11B). In this step, the control unit 500 also simultaneously detects the charging potential of the photoconductor 40 by the potential sensor 71 when the DC component Vc of the charging bias of -700V is applied, and detects the charging current of the charging roller 70, and corrects the dark attenuation. The method of correction is as described above. After that, the control unit 500 moves to "1" in the control flow shown in FIG. 11B, so that the control flow executes the process of step S061 shown in FIG. 11B again. The control flow after step S061 is as described above.

[0109] In recent years, image forming devices have become faster and more durable, and so they are often used to continuously print several thousand sheets. In the present invention, the charging current is detected periodically (at predetermined intervals) during such continuous operation, and if the charging current changes by a predetermined amount or more, the image forming operation is interrupted and adjustment (process control) is performed. In this way, if the photoconductor has not deteriorated due to use, the image forming operation is not interrupted unnecessarily, and there is no decrease in productivity.

[0110] On the other hand, if the photoconductor has deteriorated due to use, the occurrence of abnormal images such as background stains can be prevented by adjusting it at appropriate intervals. The charging current can be constantly detected even during image formation, and there is no need to interrupt the image formation, so there is no decrease in productivity.

[0111] Furthermore, in the present invention, since the photoconductor 40 is neutralized by the neutralization lamp 72 after transfer, the charging current can be detected by the current detection circuit 516a even during printing or regardless of the image being printed.

[0112] Here, the control flow will be described again. Next, step S161 and subsequent steps shown in FIG. 11B will be described. First, in step S161, the control unit 500 determines whether the change (increase) in the charging current of the charging roller 70 from the initial value is equal to or greater than a predetermined value. Note that, in this case, equal to or greater than the predetermined value is defined as 50 [-μA] or more. Note that this numerical value is merely an example, and the present invention is not limited to this.

[0113] The deterioration of the photoconductor is greatly influenced not only by the number of sheets used but also by the way it is used. For example, when a large amount of printing is performed every day, the deterioration of the photoconductor is likely to progress. Therefore, in this embodiment, the change in the charging current is also added as a factor for determining the lifespan, so that the occurrence of problems such as background scumming can be prevented.

[0114] Then, when the change (increase) in the charging current is equal to or greater than a predetermined value (Yes in step S161 in FIG. 11B), the control unit 500 determines that the photoconductor 40 has reached the end of its life. The control unit 500 then, for example, displays on the operation display unit (display unit) 515 that the photoconductor needs to be replaced (step S171 in FIG. 11B), to prompt the user to replace the photoconductor. Thereafter, the power supply to the image forming apparatus 20 is turned OFF (step S181), and the control unit 500 ends the process (step S191). Note that in this embodiment, the target replacement (life) of the photoconductor is approximately 1.8 million sheets, based on the printing of A4 paper.

[0115] Thereafter, the user or the like replaces the photoconductor with a new one.

[0116] On the other hand, if the change (increase) in the charging current is not equal to or greater than the predetermined value (No in step S161 in FIG. 11B), the control unit 500 proceeds to step S201. When the control flow of the control unit 500 proceeds to the process of step S201, the charging current has changed by equal to or greater than the predetermined value since the start of printing, as described above. Therefore, in step S201 in FIG. 11B, the control unit 500 interrupts printing and performs adjustment.

[0117] In this step, the control unit 500 also simultaneously detects the charging potential of the photoconductor 40 by the potential sensor 71 when the DC component of the charging bias Vc=-700V is applied, and detects the charging current of the charging roller 70, and corrects the dark attenuation. The method of correction is as described above. The control unit 500 also performs other adjustments. Note that the image forming apparatus 20 may perform continuous printing of several k (several thousand) sheets or more, so the control unit 500 basically does not interrupt this and make adjustments.

[0118] After step S201, the control unit 500 returns to the process of step S111 again as shown in Fig. 11B. Then, the control unit 500 repeats the processes from step S111 onwards again, as described above.

[0119] As described above, this embodiment includes the photoconductor 40, charging means for charging the photoconductor 40, potential detection means 71 for detecting the charging potential of the photoconductor 40, developing means 60 for developing an electrostatic latent image on the photoconductor 40, current detection means 516a for detecting the charging current flowing through the charging means 70, charge removal means 72 for removing charge before charging the photoconductor 40, and control means 500 including a conversion means 500d for converting the charging potential of the photoconductor 40 detected by the potential detection means 71 into the potential of the photoconductor 40 at the development position and a correction means 500e for correcting the conversion formula used for conversion by the conversion means 500d, and the correction means 500e corrects the conversion formula used for conversion by the conversion means 500d to the charging potential of the photoconductor 40 at the development position based on the detection result of the current detection means 516a.

[0120] This allows the degree of deterioration of the photoconductor to be accurately determined.

[0121] As described above, in this embodiment, the control unit 500 simultaneously detects the charging potential of the photoconductor 40 by the potential detection unit 71 and detects the charging current by the current detection unit 516a.

[0122] This makes it possible to grasp the change in dark attenuation of the photoconductor, and also to accurately determine the degree of deterioration of the photoconductor.

[0123] As described above, in this embodiment, the control means 500 detects the charging current at predetermined time intervals during continuous image formation operation of the image forming device 20 using the current detection means 516a, and if there is a change in the detection result of the charging current by more than a predetermined amount, causes the image forming device 20 to interrupt image formation and performs adjustment using the potential detection means 71.

[0124] This allows adjustment (process control) to be performed at appropriate intervals, making it possible to prevent the occurrence of abnormal images such as background stains.

[0125] As described above, in this embodiment, when the photoconductor is replaced with a new one, the control unit obtains the initial values ​​of the charging potential and the charging current.

[0126] This makes it possible to obtain the initial value (initial data) of the photoconductor that is actually used, and further makes it possible to more accurately predict the potential at the development position from the potential at the potential sensor position.

[0127] As described above, in this embodiment, the control unit determines that the photoconductor has reached the end of its life when the amount of change in charging current from when it was new exceeds a predetermined value.

[0128] This makes it possible to prevent problems such as background staining from occurring.

[0129] As described above, in this embodiment, the current detection means 516a is a current detection circuit 516a, and the current detection circuit 516a is provided in the high voltage power supply 516 that applies a charging bias to the charging means .

[0130] This makes it possible to detect the charging current flowing through the charging roller.

[0131] The above description is merely an example, and the present invention provides unique effects for each of the following aspects.

[0132] [First aspect] The first aspect includes a photoconductor (e.g., photoconductor 40), a charging unit (e.g., charging roller 70) that charges the photoconductor, a potential detection unit (e.g., potential sensor 71) that detects the charging potential of the photoconductor, a developing unit (e.g., developing device 60) that develops an electrostatic latent image on the photoconductor, a current detection unit (e.g., current detection circuit 516a) that detects a charging current flowing through the charging unit, a static elimination unit (e.g., static elimination lamp 72) that eliminates static electricity before charging the photoconductor, and the and a control means (e.g., control unit 500) including a conversion means (e.g., conversion means 500d) that converts the charging potential of the photoconductor detected by the potential detection means into the potential of the photoconductor at the development position, and a correction means (e.g., correction means 500e) that corrects the conversion formula converted by the conversion means into the charging potential of the photoconductor at the development position, wherein the correction means corrects the conversion formula converted by the conversion means into the charging potential of the photoconductor at the development position based on the detection result of the current detection means.

[0133] [Second aspect] A second aspect of the present invention is characterized in that in the first aspect, the control means simultaneously detects the charging potential of the photoconductor by the potential detection means and detects the charging current by the current detection means.

[0134] [Third aspect] The third aspect is characterized in that, in the first or second aspect, the control means detects the charging current at predetermined time intervals during continuous image formation operation of an image forming device (e.g., image forming device 20) using the current detection means, and if there is a change in the detection result of the charging current by more than a predetermined amount, causes the image forming device to interrupt image formation and performs adjustment using the potential detection means.

[0135] [Fourth aspect] A fourth aspect is characterized in that in any one of the first to third aspects, when the photoconductor is replaced with a new one, the control means obtains initial values ​​of the charging potential and the charging current.

[0136] [Fifth aspect] A fifth aspect is characterized in that in any of the first to fourth aspects, the control means determines that the photosensitive member has reached the end of its life when an amount of change in charging current from when it was new exceeds a predetermined value.

[0137] [Sixth aspect] A sixth aspect is any one of the first to fifth aspects, characterized in that the charging means is a charging roller.

[0138] [Seventh aspect] A seventh aspect is characterized in that in any of the first to sixth aspects, the current detection means is a current detection circuit, and the current detection circuit is provided in a high-voltage power supply (e.g., a charging power supply 516) that applies a charging bias to the charging means. [Explanation of symbols]

[0139] 10: Intermediate transfer belt 18: Image forming unit 20: Tandem image forming device (image forming device) 21: Exposure equipment 22: Secondary transfer device 25: Fixing device 28:Sheet inversion device 40: Photoreceptor 60: Developing device 61: Developing roller 70: Charging roller 71: Potential sensor 72: Static electricity removal lamp 73,74: Brush roller 75: Cleaning blade 76: Exposure light 82: Primary transfer roller 100: Device body 101: Core 102: Resin layer 103: Gap retention member 201: Conductive support 202: Undercoat layer 203: Charge generating layer 204: Charge transport layer 205: Protective layer 300: Scanner 500: Control unit (main control unit) 510: Process motor 511: Development bias power supply 512: Transfer bias power supply 513: Resist Clutch 515: Operation display section (display section) 516: Charging power supply 516a: Current detection circuit 517: Static electricity removal device power supply (static electricity removal lamp power supply) 518: Optical writing control unit 519: Image information receiving unit [Prior art documents] [Patent documents]

[0140] [Patent Document 1] Japanese Patent Application Publication No. 7-43986

Claims

1. A photoconductor; A charging means for charging the photoconductor; A potential detection means for detecting a charging potential of the photoconductor; a developing means for developing the electrostatic latent image on the photoconductor; a current detection means for detecting a charging current flowing through the charging means; a charge removing means for removing electricity before the photoconductor is charged; a control means including a conversion means for converting the charging potential of the photoconductor detected by the potential detection means into a potential of the photoconductor at a development position, and a correction means for correcting a conversion formula used for conversion by the conversion means; The image forming apparatus according to claim 1, wherein the correction means corrects a conversion formula used by the conversion means to convert the charge potential of the photoconductor at the development position based on a detection result of the current detection means.

2. 2. The image forming apparatus according to claim 1, wherein said control means simultaneously detects the charging potential of said photoconductor by said potential detection means and detects the charging current by said current detection means.

3. the control means detects a charging current at predetermined time intervals during continuous image formation operations of the image forming apparatus by the current detection means; 2. The image forming apparatus according to claim 1, wherein when the detection result of the charging current changes by a predetermined amount or more, the image forming apparatus is caused to suspend image formation and adjustment is performed by the potential detection means.

4. 2. The image forming apparatus according to claim 1, wherein the control unit obtains initial values ​​of the charging potential and the charging current when the photoconductor is replaced with a new one.

5. 2. The image forming apparatus according to claim 1, wherein the control means determines that the photoconductor has reached the end of its service life when a change in charging current from when the photoconductor was new exceeds a predetermined value.

6. 2. The image forming apparatus according to claim 1, wherein the charging means is a charging roller.

7. The current detection means is a current detection circuit, 2. The image forming apparatus according to claim 1, wherein the current detection circuit is a high-voltage power supply that applies a charging bias to the charging means.

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