Image forming apparatus

Abstract

To prevent the occurrence of an image defect caused by a supply member peeling an insufficient amount of toner from a developing member.SOLUTION: An image forming apparatus 100 has an image carrier 1, a developing device 4, a developing voltage application unit E2, a supply voltage application unit E3, and a control unit 200. The control unit 200 can control the developing voltage application unit E2 and the supply voltage application unit E3 to execute a preliminary operation of forming a first potential difference and a second potential difference different from the first potential difference, while alternately switching them multiple times, between a developing member 42 and a supply member 43, while the developing member 42 and the supply member 43 are rotating in a non-image forming period during which developing is not performed.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a printer, a copying machine, or a facsimile machine that uses an electrophotographic or electrostatic recording method. [Background technology]

[0002] An image forming apparatus such as a printer using an electrophotographic system (electrophotographic process) has a developing device that develops an electrostatic latent image formed on an image carrier such as a photosensitive drum using toner as a developer. The developing device may be configured as an independent unit or as part of a process cartridge that is detachable from the main body of the image forming apparatus.

[0003] Such a developing device includes a developing roller as a developing member that supplies toner to an image carrier, and a supply roller as a supply member (supply / strip member) that supplies toner to the developing roller and strips toner from the developing roller. A potential difference may be provided between the developing roller and the supply roller.

[0004] Patent document 1 describes that while an electrostatic latent image is being developed, a voltage is applied to the supply roller to supply toner from the supply roller to the development roller, and after development and before the development roller stops rotating, a voltage is applied to the supply roller to strip toner from the development roller.

[0005] Furthermore, Patent Document 2 describes that when print image information longer than the circumferential length of the developing roller is detected, the potential applied to the supply roller is increased to the side that supplies toner to the developing roller. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-109242 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-237549 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, as the lifespan of developing devices (or process cartridges) has been extended, there has been a demand for an increase in the amount of toner that can be accommodated in the developing devices. However, when the capacity of the developing devices is increased in this way, the following problems may arise.

[0008] In other words, as the capacity of the developing device increases, the toner around the developing roller and supply roller tends to become compacted. In this state, the toner circulation is poor, making it difficult for the supply roller to expel the toner. This can prevent the supply roller from scraping off the toner on the developing roller, leaving a large amount of toner remaining on the developing roller. This can result in poor image quality.

[0009] SUMMARY OF THE INVENTION It is therefore an object of the present invention to prevent the occurrence of image defects caused by insufficient removal of toner from the developing member by the supplying member. [Means for solving the problem]

[0010] The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image forming apparatus including a rotatable image carrier, a developing device that develops an electrostatic latent image formed on the surface of the image carrier with toner, the developing device including a rotatable developing member that supplies toner to the electrostatic latent image, and a rotatable supply member that contacts the developing member and supplies toner to the developing member, a developing voltage application unit that applies a voltage to the developing member, a supply voltage application unit that applies a voltage to the supply member, and a control unit that can control the developing voltage application unit and the supply voltage application unit, wherein the control unit is capable of controlling the developing voltage application unit and the supply voltage application unit to perform a preparatory operation in which a first potential difference and a second potential difference different from the first potential difference are alternately switched multiple times between the developing member and the supply member while the developing member and the supply member are rotating during non-image formation when development is not being performed. [Effects of the Invention]

[0011] According to the present invention, it is possible to suppress the occurrence of image defects caused by insufficient removal of toner from the developing member by the supplying member. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Figure 2] FIG. 2 is a schematic block diagram illustrating a control configuration of the image forming apparatus. [Figure 3] FIG. 2 is a schematic cross-sectional view of the developing device. [Figure 4] FIG. 2 is a schematic cross-sectional view showing the state of toner in a developing device. [Figure 5] FIG. 10 is a timing chart showing the relationship between the potential of the developing roller and the potential of the supply roller during the preliminary operation. [Figure 6] FIG. 10 is a schematic diagram showing a control configuration in the second embodiment. [Figure 7] FIG. 4 is a schematic diagram of a light guide member of the toner amount sensor. [Figure 8] FIG. 2 is a schematic diagram illustrating a circuit configuration of a toner amount sensor. [Figure 9] FIG. 10 is a flowchart illustrating a method for calculating a toner deterioration degree. [Figure 10] FIG. 10 is a flowchart illustrating control of the preparatory movement in the second embodiment. [Figure 11] FIG. 10 is a schematic cross-sectional view of a process cartridge and a toner cartridge according to a third embodiment. [Figure 12] 5 is a schematic cross-sectional view showing the state of toner in the developing device after the toner cartridge has been replaced. FIG. [Figure 13] FIG. 11 is a flowchart illustrating control of the preparatory movement in the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[0014] [Example 1] <Overall Configuration and Operation of Image Forming Apparatus> The overall configuration and operation of an image forming apparatus of this embodiment will be described. Figure 1 is a schematic cross-sectional view of an image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem laser beam printer that employs an intermediate transfer system and is capable of forming full-color images using an electrophotographic system.

[0015] Image forming apparatus 100 has multiple image forming units, including four image forming units 10Y, 10M, 10C, and 10K that form images in yellow (Y), magenta (M), cyan (C), and black (K), respectively. These image forming units 10Y, 10M, 10C, and 10K are arranged in a row along the direction of movement of the image transfer surface of intermediate transfer belt 53 (described later). Elements having the same or corresponding functions or configurations for each color may be generally described by omitting the Y, M, C, or K suffixes to designate elements for a particular color. Furthermore, with respect to image forming apparatus 100 and its elements, "up" and "down" refer to up and down in the direction of gravity (vertical direction), but do not necessarily mean directly above or directly below, and also include above and below a horizontal plane passing through a reference position or element.

[0016] The image forming unit 10 is configured to include a photosensitive drum 1, a charging roller 2, an exposure device 3, a developing device 4, a cleaning device 5, etc. In this embodiment, the exposure device 3 is configured as a single unit that exposes the photosensitive drum 1 of each image forming unit 10. In this way, in this embodiment, the exposure device 3 is shared by the multiple image forming units 10, but it may also be provided for each image forming unit 10.

[0017] The photosensitive drum 1 is a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) and is an example of an image carrier. The photosensitive drum 1 is driven to rotate around its axis in the direction of arrow A1 in the drawing (counterclockwise direction) by a driving force transmitted from a drum drive motor D1 (FIG. 2), which is a driving source constituting a drive unit (drive device) serving as a driving means. In this embodiment, the photosensitive drum 1 is driven to rotate at a rotational speed such that the peripheral speed, which is the moving speed of the surface (outer circumferential surface), is 140 mm / sec, for example.

[0018] The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative in this embodiment) by a charging roller 2, a roller-type charging member serving as a charging means. In this embodiment, the charging roller 2 is a conductive roller with a conductive rubber layer provided on a metal core. The charging roller 2 is disposed so as to contact the surface of the photosensitive drum 1 with a predetermined pressure and rotates in accordance with the rotation of the photosensitive drum 1. During charging, a predetermined charging voltage (charging bias) is applied to the charging roller 2 by a charging power source E1 (FIG. 2) serving as a charging voltage application unit. In this embodiment, a DC voltage of, for example, −1250 V is applied to the charging roller 2 as the charging voltage, and the surface of the photosensitive drum 1 is uniformly charged to a surface potential (charging potential, dark potential) of approximately −600 V.

[0019] The surface of the charged photosensitive drum 1 is scanned and exposed by an exposure device (exposure unit) 3 as an exposure means, and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1. In this embodiment, the exposure device 3 is configured as a laser scanner, and irradiates the surface of the photosensitive drum 1 with laser light corresponding to an image signal while scanning it. As a result, an electrostatic latent image corresponding to the image signal is formed on the surface of the charged photosensitive drum 1. The image signal is input to the image forming apparatus 100 from an external device (not shown) in response to a request from a user. The external device is, for example, an image reading device (not shown) connected to an apparatus main body (hereinafter simply referred to as the "apparatus main body") 110 of the image forming apparatus 100, or a host device (not shown) such as a personal computer connected to the apparatus main body 110 so as to be able to communicate with it.

[0020] The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by the developing device 4, which serves as a developing means, by supplying toner as a developer, thereby forming a toner image (toner image, developer image) on the photosensitive drum 1. The developing device 4 deposits toner charged with the same polarity as the charge polarity of the photosensitive drum 1 onto portions of the surface of the photosensitive drum 1 where the charge has decayed due to exposure (image portions, exposed portions) to form a toner image (reverse development method). In this embodiment, the developing device 4 uses toner 90, which is a non-magnetic single-component developer, as the developer. In this embodiment, the normal charge polarity (normal polarity), which is the main charge polarity during development, is negative. The developing device 4 includes a developing roller 42, a supply roller 43, a regulating blade (developing blade) 44, etc. The developing roller 42 contacts the photosensitive drum 1 to form a developing section, and supplies toner charged with the normal polarity to the photosensitive drum 1 in the developing section. Details of the developing device 4 will be described later.

[0021] An intermediate transfer belt 53, which is an endless belt serving as an intermediate transfer body, is disposed facing the four photosensitive drums 1Y, 1M, 1C, and 1K. The intermediate transfer belt 53 is stretched and entrained around a plurality of tension rollers, including a tension roller 54, a drive roller 55, and a secondary transfer counter roller 56. The tension roller 54 applies a predetermined tension to the intermediate transfer belt 53. The drive roller 55 is driven to rotate by a driving force transmitted from a belt drive motor D2 (FIG. 2), which is a driving source constituting a drive unit serving as a driving means. The driving force transmitted from the drive roller 55 causes the intermediate transfer belt 53 to rotate (circumferentially move) in the direction of arrow A2 in the drawing (clockwise direction) at a peripheral speed substantially equal to that of the photosensitive drums 1. The secondary transfer counter roller 56 functions as an opposing member (counter roller) of a secondary transfer roller 52, which will be described later. Primary transfer rollers 51Y, 51M, 51C, and 51K, which are roller-type primary transfer members serving as primary transfer means, are arranged on the inner circumferential surface side of the intermediate transfer belt 53, corresponding to the respective photosensitive drums 1. The primary transfer rollers 51 press the intermediate transfer belt 53 toward the photosensitive drums 1, forming a primary transfer portion (primary transfer nip) T1, which is a contact portion between the photosensitive drums 1 and the intermediate transfer belt 53. The tension rollers other than the drive roller 55 and each primary transfer roller 51 are rotated in accordance with the rotation of the intermediate transfer belt 53.

[0022] At primary transfer portion T1, the toner image formed on photosensitive drum 1 is electrostatically transferred (primary transfer) onto a rotating intermediate transfer belt 53 serving as a transfer receiving member by the action of primary transfer roller 51. During primary transfer, a primary transfer voltage (primary transfer bias) of a polarity opposite to the normal polarity of the toner (positive polarity in this embodiment) is applied to primary transfer roller 51 by primary transfer power supply E5 (FIG. 2) serving as a primary transfer voltage application portion. For example, when a full-color image is formed, toner images of yellow, magenta, cyan, and black formed on photosensitive drums 1Y, 1M, 1C, and 1K are transferred sequentially onto intermediate transfer belt 53 in a superimposed state.

[0023] A secondary transfer roller 52, which is a roller-type secondary transfer member serving as a secondary transfer means, is disposed on the outer peripheral surface of the intermediate transfer belt 53 at a position facing the secondary transfer opposing roller 56. The secondary transfer roller 52 is pressed against the secondary transfer opposing roller 56 via the intermediate transfer belt 53, forming a secondary transfer portion (secondary transfer nip) T2, which is a contact portion between the intermediate transfer belt 53 and the secondary transfer roller 52. The secondary transfer roller 52 is driven to rotate in accordance with the rotation of the intermediate transfer belt 53. The secondary transfer roller 52 may also be configured to be driven to rotate by a driving force from a drive source. At the secondary transfer portion T2, the toner image formed on the intermediate transfer belt 53 is electrostatically transferred (secondary transfer) by the action of the secondary transfer roller 52 onto a recording material P, which is being nipped and transported between the intermediate transfer belt 53 and the secondary transfer roller 52 and serves as a transfer medium. During secondary transfer, a secondary transfer voltage (secondary transfer bias) of a polarity opposite to the normal polarity of the toner (positive polarity in this embodiment) is applied to the secondary transfer roller 52 by a secondary transfer power supply E6 (FIG. 2) serving as a secondary transfer voltage application unit. The secondary transfer opposing roller 56 is electrically grounded (connected to ground). Note that a secondary transfer voltage of the same polarity as the normal polarity of the toner may be applied to the inner secondary transfer roller corresponding to the secondary transfer opposing roller 56 in this embodiment, and the outer secondary transfer roller corresponding to the secondary transfer roller 52 in this embodiment may be electrically grounded. A sheet-like recording material (transfer material, recording medium, sheet) P, such as paper or a plastic sheet, is transported to the secondary transfer unit T2 at a predetermined timing by a feeding device (not shown) equipped with a recording material storage unit, feeding members, transport members, etc.

[0024] The recording material P onto which the toner image has been transferred is conveyed to a fixing device 6 serving as a fixing means. The fixing device 6 applies heat and pressure to the recording material P bearing the unfixed toner image, thereby fixing (melting and solidifying) the toner image onto the recording material P. The recording material P onto which the toner image has been fixed is discharged (output) to the outside of the apparatus main body 110 as an image-formed product.

[0025] Meanwhile, toner remaining on the surface of the photosensitive drum 1 after the primary transfer (primary transfer residual toner) is removed from the surface of the photosensitive drum 1 and collected by a cleaning device 5 serving as a photosensitive body cleaning means. The cleaning device 5 scrapes and collects the primary transfer residual toner from the surface of the rotating photosensitive drum 1 using a cleaning blade as a cleaning member provided to abut against the surface of the photosensitive drum 1. However, the image forming apparatus 100 may not have a dedicated cleaning device for cleaning the surface of the photosensitive drum 1, and may instead have a configuration in which the primary transfer residual toner is collected from the surface of the photosensitive drum 1 by the developing device 4 (cleanerless system). In addition, a belt cleaning device 7 serving as intermediate transfer body cleaning means is disposed on the outer peripheral surface side of the intermediate transfer belt 53. The belt cleaning device 7 is disposed downstream of the secondary transfer portion T2 and upstream of the primary transfer portion T1 (the most upstream primary transfer portion T1Y) in the movement direction of the surface of the intermediate transfer belt 53. Any deposits such as toner remaining on the surface of the intermediate transfer belt 53 after the secondary transfer (secondary transfer residual toner) are removed from the surface of the intermediate transfer belt 53 and collected by the belt cleaning device 7.

[0026] In this embodiment, in each image forming unit 10, the photosensitive drum 1 and the charging roller 2, developing device 4, and cleaning device 5 acting as process means thereon are integrated as a process cartridge 8. The process cartridge 8 is configured to be detachable from the apparatus main body 110. However, this is not limited to this, and for example, the developing device 4 may be configured to be detachable from the apparatus main body 110 substantially alone. In this embodiment, the apparatus main body 110 of the image forming apparatus 100 is the portion of the image forming apparatus 100 excluding the process cartridges 8.

[0027] FIG. 2 is a schematic block diagram showing the control configuration of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 has a control unit 200 that controls each unit of the image forming apparatus 100. The control unit 200 has a CPU 201 as a processing unit, which is a central element that performs calculations. The control unit 200 also has a main body storage unit 210, which serves as a storage unit (storage unit) for storing information and is composed of a ROM, RAM, non-volatile memory, etc. The ROM stores control programs, pre-calculated data tables, etc. The RAM stores information input to the control unit 200, detected information, calculation results, etc., and the non-volatile memory stores various setting information, etc. The CPU 200 and the main body storage unit 210 can transfer and read data to and from each other. The control unit 200 also has an input / output unit (not shown) for exchanging signals between the control unit 200 and each unit.

[0028] The control unit 200 is connected to various drive units such as a drum drive motor D1 and a belt drive motor D2. The control unit 200 is also connected to various power sources such as a charging power source E1, a developing power source E2 (described later), a supply power source E3 (described later), a regulating power source E4 (described later), a primary transfer power source E5, and a secondary transfer power source E6. The control unit 200 is also connected to an exposure device 3, various sensors, and the like. The control unit 200 is also optionally connected to an external device (not shown), such as an image reader or a personal computer. The control unit 200 can control the operation of each unit of the image forming apparatus 100 to perform image formation in response to an image signal input from the external device. The control unit 200 can also control the developing power source E2, the supply power source E3, and the like to perform a preparatory operation (described later).

[0029] Although not shown in the drawings, in this embodiment, the charging power supply E1, the developing power supply E2, the supply power supply E3, the regulating power supply E4, and the primary transfer power supply E5 are each provided independently for each image forming unit 10. However, at least one of these may be shared by multiple image forming units 10 (or all of the image forming units 10). Also, although not shown in the drawings, in this embodiment, the drum drive motor D1 is provided independently for each image forming unit 10. However, the drum drive motor D1 may be shared by multiple image forming units 10 (or all of the image forming units 10). Also, at least one drum drive motor D1 and the belt drive motor D2 may be shared.

[0030] The image forming apparatus 100 also executes a job (print job), which is a series of operations initiated by a single start instruction to form and output an image on one or more recording materials P. A job generally includes an image formation process, a pre-rotation process, a sheet-to-sheet process (when forming images on multiple recording materials P), and a post-rotation process. The image formation process is a period during which an electrostatic latent image of the image to be actually formed on the recording material P is formed, a toner image is formed, and the toner image is primarily and secondary transferred. This is referred to as the image formation period. More specifically, the timing of the image formation process differs depending on the location where the electrostatic latent image formation, toner image formation, primary transfer, and secondary transfer processes are performed. The pre-rotation process is a period during which preparatory operations are performed before the image formation process, from when a start instruction is input until the actual start of image formation. The sheet-to-sheet process is a period corresponding to the interval between recording materials P when image formation is performed continuously on multiple recording materials P (continuous image formation). The post-rotation process is a period during which a tidying-up operation (preparatory operation) is performed after the image formation process. Non-image formation time (non-image formation period) refers to a period other than image formation time, and includes the above-mentioned pre-rotation process, paper interval process, post-rotation process, and also the pre-multi-rotation process, which is a preparatory operation when the image forming device 100 is turned on or when it returns from a sleep state.

[0031] <Developing device> Next, the developing device 4 of this embodiment will be described. Figure 3 is a schematic cross-sectional view of the developing device 4 of this embodiment.

[0032] The general configuration of the developing device 4 will be described. The developing device 4 has a developing container (developing frame) 41, a rotatable developing roller 42 as a developing member (developer carrier), and a rotatable supply roller 43 as a supply member (supply scraping member). The developing device 4 also has a regulating blade 44 as a regulating member and a rotatable stirring member 47. The developing container 41 contains toner 90 as a developer. The developing roller 42 is rotatably provided so that a portion of it is exposed to the outside from a development opening, which is an opening provided in the developing container 41 that faces the photosensitive drum 1. By carrying the toner and rotating, the toner is transported from the inside of the developing container 41 to the outside. The supply roller 43 contacts the developing roller 42 to form a supply scraping portion F. By rotating, the supply roller 43 supplies toner to the developing roller 42 and scrapes toner from the developing roller 42 at the supply scraping portion F. The regulating blade 44 is provided so as to abut against the surface of the developing roller 42, and regulates the amount of toner carried by the developing roller 42 and passing through the development opening of the developing container 41. The stirring member 47 stirs and transports the toner. The developing roller 42 comes into contact with the photosensitive drum 1 to form a developing portion G. The developing roller 42 supplies toner charged to the normal polarity to the photosensitive drum 1 in the developing portion G. This will be explained in more detail below.

[0033] The developing container 41 forms a developing chamber 45 equipped with a developing roller 42, a supply roller 43, and a regulating blade 44, and a toner storage chamber 46 equipped with an agitator 47 and containing toner 90 to be supplied to the developing chamber 45. The developing chamber 45 and the toner storage chamber 46 are connected by a supply opening 41a, which is an opening. Toner 90 is supplied from the toner storage chamber 46 to the developing chamber 45 through this supply opening 41a. In this embodiment, the developing chamber 45 is disposed below the toner storage chamber 46 in the direction of gravity. The toner 90 is supplied from the toner storage chamber 46 to the developing chamber 45 by utilizing the conveying force of the agitator 47 as well as gravity.

[0034] The toner 90 supplied to the developing chamber 45 is supplied to the surface of the developing roller 42 by the supply roller 43 at a supply scraping section F, which is a contact point between the supply roller 43 and the developing roller 42. The toner 90 held on the developing roller 42 is then thinned by a regulating blade 44, which regulates the layer thickness (also referred to as "layer thickness" here). The regulating blade 44 functions as a regulating means for regulating the layer thickness of the toner 90 on the developing roller 42, and also as a developer charging means for applying a predetermined charge to the toner 90 on the developing roller 42. The thinned toner 90 is transported to a developing section G, which is a contact point between the photosensitive drum 1 and the developing roller 42, as the developing roller 42 rotates, and adheres to the surface of the photosensitive drum 1 in accordance with the electrostatic latent image formed on the surface of the photosensitive drum 1. Furthermore, the toner 90 remaining on the developing roller 42 without being used for development is scraped off by the supply roller 43 at a supply scraping portion F, which is a contact portion between the supply roller 43 and the developing roller 42, and is removed from the developing roller 42. The toner 90 removed from the developing roller 42 is stirred and mixed with the toner 90 in the developing device 4.

[0035] In this example, a negatively charged non-magnetic toner manufactured by suspension polymerization was used. However, the present invention is not limited to this, and toner manufactured by other polymerization methods, such as pulverization or emulsion polymerization, may also be used. The volume average particle size of the toner is preferably 5.0 to 8.0 μm. Note that the symbol "to" used in a numerical range includes the numerical values ​​before and after the range.

[0036] Here, the volume average particle diameter of the toner was measured using a precision particle size distribution measuring device, Multisizer 3, manufactured by Beckman Coulter, Inc. In this example, the volume average particle diameter of the toner was about 7.0 μm.

[0037] In this embodiment, all of the four color toners are toner particles containing a release agent and an organosilicon polymer on the surface of the toner particles. The organosilicon polymer is R-Si(O 1 / 2)3, where R represents an alkyl group or phenyl group having 1 to 6 carbon atoms, and the organosilicon polymer forms convex portions on the surface of the toner base particles. This creates a spacer effect between the surface of the toner base particles and components such as the developing roller 42, reducing adhesion. The convex portions are also characterized by surface contact with the surface of the toner base particles, which is expected to significantly inhibit the migration, detachment, and embedding of the convex portions. Therefore, even in a configuration in which the developing roller 42 is driven while spaced apart from the photosensitive drum 1, the toner can be used for a long period of time. Thus, in this embodiment, toner particles containing an organosilicon polymer on the surface of the toner base particles were used. However, this is not limited to this, and toner particles not containing an organosilicon polymer on the surface of the toner base particles may also be used.

[0038] Furthermore, additives (hereinafter also referred to as "external additives") such as a fluidizing agent and a cleaning aid may be added (externally added) to the toner in order to improve the fluidity, chargeability, cleaning properties, etc.

[0039] Examples of external additives include inorganic oxide particles such as silica particles, alumina particles, and titanium oxide particles; inorganic stearic acid compound particles such as aluminum stearate particles and zinc stearate particles; and inorganic titanic acid compound particles such as strontium titanate and zinc titanate. These may be used alone or in combination of two or more. These inorganic particles are preferably gloss-treated with a silane coupling agent, a titanium coupling agent, a higher fatty acid, a silicone oil, or the like to improve heat-resistant storage stability and environmental stability. The BET specific surface area of ​​the external additive is 10 m 2 / g or more, 450m 2 / g or less is preferable.

[0040] The BET specific surface area can be determined by a low-temperature gas adsorption method using a dynamic constant pressure method in accordance with the BET method (preferably the BET multipoint method). For example, a specific surface area measuring device (trade name: Gemini 2375 Ver. 5.0, manufactured by Shimadzu Corporation) is used to adsorb nitrogen gas onto the surface of a sample, and the BET multipoint method is used to measure the BET specific surface area (m 2 / g) can be calculated.

[0041] The total amount of these various external additives added is preferably 0.05 parts by mass or more and 5 parts by mass or less, and more preferably 0.1 parts by mass or more and 3 parts by mass or less, relative to 100 parts by mass of the toner. Various external additives may also be used in combination.

[0042] The developing roller 42 is a roller in which a conductive elastic rubber layer having a predetermined volume resistivity is provided on the outer periphery of a metal core, and furthermore, the surface of the developing roller 42 is configured to have a predetermined surface roughness. The developing roller 42 can be a single-layer roller or a multi-layer roller. For example, a single-layer roller can be used in which an elastic layer made of a rubber material such as silicone rubber, urethane rubber, or hydrin rubber is formed on a core. For example, a multi-layer roller can be used in which a surface layer is formed by coating the surface of an elastic layer with a silicone resin, urethane resin, polyamide resin, fluororesin, or the like.

[0043] In this embodiment, the developing roller 42 is rotationally driven in the direction of arrow A3 in the figure (clockwise direction) by a driving force transmitted from a motor serving as a driving source. That is, the developing roller 42 is rotationally driven so that the surface (outer peripheral surface) of the developing roller 42 and the surface (outer peripheral surface) of the photosensitive drum 1 move in the forward direction at the opposing portion (contact portion) of the developing roller 42 and the photosensitive drum 1. In this embodiment, the developing roller 42 is driven by a driving force transmitted from the drum drive motor D1, but a dedicated driving source may be provided for the developing roller 42. Furthermore, in this embodiment, in order to obtain an appropriate image density, the developing roller 42 is rotationally driven at a rotational speed such that the moving speed (circumferential speed) of the surface of the developing roller 42 is, for example, 130% of the moving speed (circumferential speed) of the surface of the photosensitive drum 1.

[0044] The supply roller 43 is an elastic sponge roller with a conductive foam formed on the outer periphery of a metal core. The supply roller 43 is positioned so as to contact the developing roller 42 with a predetermined penetration depth. In this embodiment, the supply roller 43 has a urethane foam layer (an elastic foam layer formed from a urethane rubber foam), and the urethane foam layer contains an ionic conductive agent. In this embodiment, the supply roller 43 has a configuration in which an ionic conductive agent composed of a salt of a cation and an anion having a reactive functional group that reacts with an isocyanate group is chemically bonded to the urethane foam layer via the reactive functional group. For example, a supply roller 43 with such a configuration can be manufactured by foaming and curing a urethane composition containing an ionic conductive agent. By forming the urethane surface layer into an open-cell structure, toner can be contained inside the supply roller 43, enabling stable toner supply to the developing roller 42. In this embodiment, the electrical resistance of the supply roller 43 is 1×10 7 In this embodiment, in the supply stripping section F, the foamed elastic body that forms the surface layer of the supply roller 43 is compressed and crushed by the developing roller 42.

[0045] Here, a method for measuring the electrical resistance of the supply roller 43 will be described. The supply roller 43 is brought into contact with an aluminum sleeve having a diameter of 30 mm so that the penetration depth is 1.5 mm. By rotating this aluminum sleeve, the supply roller 43 is rotated at 30 rpm relative to the aluminum sleeve. Next, a DC voltage of -50 V is applied to the supply roller 43. At this time, a 10 kΩ resistive element is provided on the ground side, and the current is calculated by measuring the voltage across the element, and the electrical resistance value of the supply roller 43 is calculated.

[0046] In this embodiment, the cell diameter on the surface of the supply roller 43 is 50 to 1000 μm. Here, the cell diameter refers to the average diameter of foam cells in an arbitrary cross section, and can be determined as follows. First, the area of ​​the largest foam cell is measured from an enlarged image of the arbitrary cross section, and this area is converted into a diameter equivalent to a perfect circle to obtain the maximum cell diameter. Then, foam cells that are half or less of this maximum cell diameter are eliminated as noise, and the average value of the individual cell diameters converted in the same manner from the remaining individual cell areas is determined. The cell diameter refers to the average value determined in this manner.

[0047] In this embodiment, the supply roller 43 is driven to rotate in the direction of arrow A4 (clockwise direction) in the figure by a driving force transmitted from a motor serving as a drive source. In other words, the supply roller 43 is driven to rotate so that the surface (outer peripheral surface) of the supply roller 43 and the surface (outer peripheral surface) of the developing roller 42 move in opposite directions at the opposing portion (contact portion) of the supply roller 43 and the developing roller 42. In this embodiment, the supply roller 43 is driven by a driving force transmitted from the drum drive motor D1, but a dedicated drive source for the supply roller 43 may also be provided.

[0048] The regulating blade 44 is configured with a plate-shaped elastic member that is conductive and flexible. One end of the elastic member in the short direction is fixed to the developer container (frame) 41 and supported in a cantilevered manner. The other end of the elastic member in the short direction is a free end, which abuts against the surface (outer peripheral surface) of the developing roller 42. The regulating blade 44 is disposed so as to contact the surface (outer peripheral surface) of the developing roller 42 downstream of the opposing portion (contact portion) of the supply roller 43 and the developing roller 42 in the moving direction (rotating direction) of the surface of the developing roller 42. In this embodiment, a member made of SUS (stainless steel) is used as the elastic member of the regulating blade 44. In this embodiment, the regulating blade 44 abuts against the surface of the developing roller 42 at a side near the tip of the free end of the elastic member in the short direction, so that the tip faces upstream in the moving direction of the surface of the developing roller 42. That is, the regulating blade 44 is provided so as to be in a counter direction to the moving direction (rotating direction) of the surface of the developing roller 42.

[0049] In this embodiment, the agitating member 47 is configured to have a rotating shaft and a sheet-like agitating portion attached to the rotating shaft. The agitating member 47 is rotatably supported by the developing container 41. The agitating member 47 is driven to rotate in the direction of arrow A5 in the drawing (clockwise direction) by a driving force transmitted from a motor serving as a driving source. In this embodiment, the agitating member 47 is driven by a driving force transmitted from the drum driving motor D1, but a dedicated driving source for the agitating member 47 may also be provided.

[0050] <Bias applied to the developing device> A predetermined DC voltage is applied to the developing roller 42 by a developing power source E2 serving as a developing voltage application unit during image formation, etc. Furthermore, a predetermined DC voltage is applied to the supply roller 43 by a supply power source E3 serving as a supply voltage application unit during image formation, etc. Furthermore, a predetermined DC voltage is applied to the regulating blade 44 by a regulating power source E4 serving as a regulating voltage application unit during image formation, etc. Here, the voltage (potential) applied to the developing roller 42 is referred to as the developing voltage (developing bias), the voltage (potential) applied to the supply roller 43 is referred to as the supply voltage (supply bias), and the voltage (potential) applied to the regulating blade 44 is referred to as the regulating voltage (regulating bias).

[0051] In this embodiment, voltages corresponding to the temperature and humidity of the installation environment of the image forming apparatus 100 are applied to the developing roller 42, the supply roller 43, and the regulating blade 44. As an example, during image formation (development), a developing voltage of −450 V is applied to the developing roller 42, and a regulating voltage of −550 V is applied to the regulating blade 44. At this time, the potential difference between the regulating blade 44 and the developing roller 42 is such that toner charged to the normal polarity is urged from the regulating blade 44 toward the developing roller 42. In other words, the potential of the regulating blade 44 is greater toward the normal polarity of the toner than the potential of the developing roller 42. This stabilizes the intake of toner into the contact area between the regulating blade 44 and the developing roller 42, and stabilizes the application of charge to the toner by the regulating blade 44. Furthermore, in this embodiment, the image forming apparatus 100 is configured to be able to arbitrarily change the supply voltage applied to the supply roller 43. This allows the image forming apparatus 100 to variably control the potential difference between the supply roller 43 and the developing roller 42. As an example, in this embodiment, during image formation (development), a development voltage of −450 V is applied to the development roller 42, and a supply voltage of −550 V is applied to the supply roller 43. At this time, the potential difference between the supply roller 43 and the development roller 42 is such that toner charged to the normal polarity is urged (supplied) from the supply roller 43 side to the development roller 42 side. In other words, the potential of the supply roller 43 is greater than the potential of the development roller 42 toward the normal polarity of the toner. This allows the toner required for image formation (development) to be efficiently supplied to the development roller 42.

[0052] <Mechanism of uneven density caused by poor peeling> Next, a description will be given of the mechanism by which image defects occur due to insufficient removal of toner from the developing roller 42 by the supply roller 43. Figure 4 is a schematic cross-sectional view of the developing chamber 45 for explaining the behavior of toner in the developing chamber 45.

[0053] In this embodiment, the developing chamber 45 is located below the toner storage chamber 46 in the direction of gravity, and toner is supplied from the toner storage chamber 46 to the developing chamber 45 using not only the conveying force of the agitator 47 but also gravity. Therefore, when there is sufficient toner in the developing device 4, the developing chamber 45 is filled with toner, as shown in FIG. 4 . The supply roller 43 is in contact with the developing roller 42 with a certain amount of penetration. Therefore, the supply roller 43 expels toner near the position where the supply roller 43 is compressed by the developing roller 42, i.e., in the region upstream of the supply stripping portion F in the direction of rotation of the supply roller 43 (also referred to as the "V zone"). Furthermore, the supply roller 43 absorbs toner near the position where the supply roller 43 is released from the compression by the developing roller 42, i.e., in the region downstream of the supply stripping portion F in the direction of rotation of the supply roller 43 (also referred to as the "A zone"). As described above, when the developing chamber 45 is filled with toner, toner is virtually always present near the V zone. The toner near the V zone is compressed due to the weight of the toner in the toner storage chamber 46 acting from above. In this state, even if the supply roller 43 attempts to expel toner from the V zone, the compressed toner near the V zone makes it difficult to expel sufficient toner. If the V zone is not sufficiently expelled, the cells of the supply roller 43 become filled with toner, making it difficult to remove the toner from the developing roller 42. As a result, the amount of toner on the developing roller 42 may be partially excessive, resulting in uneven image density. This phenomenon is more likely to occur as the toner in the V zone becomes more compressed. Therefore, it is more likely to occur when the amount of toner in the developing device 4 is large, and it is also more likely to occur when the toner cohesion is high. This image defect (uneven density due to poor toner removal) is sometimes referred to as a "hazy image."

[0054] <Preparatory operations before image formation> Next, a preparatory operation before image formation in this embodiment will be described.

[0055] In this embodiment, the control unit 200 controls the developing device 4 (rotating the developing roller 42, the supply roller 43, and the agitator 47) to perform a preparatory operation to change the potential difference between the developing roller 42 and the supply roller 43 multiple times before image formation. The potential difference also includes a potential difference of approximately 0 V (approximately the same potential). In other words, by switching the potential difference between the developing roller 42 and the supply roller 43 before image formation, it is possible to vibrate and loosen the compacted toner around the developing roller 42 and the supply roller 43. This facilitates the toner discharge from the supply roller 43, making it easier for the supply roller 43 to scrape off the toner on the developing roller 42. The preparatory operation is typically performed after a job start command is input to the image forming apparatus 100 (control unit 200) before the operation of forming the first image of the job (the toner image to be transferred to one side (first side) of the first sheet of recording material P), more specifically, before the development of that image. This will be described in more detail below.

[0056] 5(a), (b), and (c) are timing charts showing specific examples of the transition of the potential (developing voltage) of the developing roller 42 and the potential (supply voltage) of the supply roller 43 during the preliminary operation.

[0057] In the example shown in FIG. 5A, a development voltage of −450 V is applied to the developing roller 42 during the preparatory operation. Also, in the example shown in FIG. 5A, a supply voltage of −550 V and a supply voltage of −450 V are alternately applied to the supply roller 43 every 1 second as a predetermined time. The potential difference between the developing roller 42 and the supply roller 43 is switched a total of 20 times. When a supply voltage of −550 V is applied to the supply roller 43, the potential difference between the supply roller 43 and the developing roller 42 is such that toner charged to the normal polarity is urged (supplied) from the supply roller 43 side to the developing roller 42 side. In other words, the potential of the supply roller 43 is greater than the potential of the developing roller 42 toward the normal polarity of the toner. On the other hand, when a supply voltage of −450 V is applied to the supply roller 43, the potential difference between the supply roller 43 and the developing roller 42 is approximately 0 V.

[0058] By switching the potential difference between the developing roller 42 and the supply roller 43 in this way, an electric field is formed between the supply roller 43 and the developing roller 42 every second. As a result, the toner in the V zone is subjected to a force that moves it from the supply roller 43 side to the developing roller 42 every second. By applying an intermittent force to the toner in the V zone, the toner vibrates and can loosen the compacted toner. By performing image formation in this state with the toner in the V zone loosened in the preliminary operation, the supply roller 43 can sufficiently expel the toner in the V zone, making it possible to suppress density unevenness caused by poor peeling.

[0059] In the example shown in FIG. 5(b), a supply voltage of −550 V is applied to supply roller 43 during the preliminary operation. Also, in the example shown in FIG. 5(b), a development voltage of −450 V and a supply voltage of −550 V are applied alternately to development roller 42 every second during the preliminary operation. The potential difference between development roller 42 and supply roller 43 is switched a total of 20 times. In this case, the electric field formed between development roller 42 and supply roller 43 is substantially the same as in the example shown in FIG. 5(a), and therefore the same effect as in the example shown in FIG. 5(a) can be obtained.

[0060] In the example shown in FIG. 5(c), a development voltage of −450 V is applied to the developing roller 42 during the preparatory operation. Also, in the example shown in FIG. 5(c), a supply voltage of −350 V and a supply voltage of −450 V are alternately applied to the supply roller 43 every second during the preparatory operation. The potential difference between the developing roller 42 and the supply roller 43 is switched a total of 20 times. In this case, the strength of the electric field formed between the developing roller 42 and the supply roller 43 is substantially the same as in the example shown in FIG. 5(a), so the toner in the V zone can be loosened. However, in this case, the following other problem may occur. In this embodiment, the normal polarity of the toner is negative, so when the supply voltage is alternately switched between −350 V and −450 V, some positively charged toner is supplied to the developing roller 42. This is because when a supply voltage of −350 V is applied to the supply roller 43, the potential difference between the supply roller 43 and the developing roller 42 is such that toner charged with a polarity opposite to the normal polarity is urged (supplied) from the supply roller 43 to the developing roller 42. Because the positively charged toner on the supply roller 43 is not charged to the normal polarity, it tends to have an insufficient charge and weak adhesion to the developing roller 42. If the developing roller 42 is rotated in this state, the toner on the developing roller 42 may fall off the developing roller 42, which may cause toner contamination inside the image forming apparatus 100. This phenomenon is sometimes referred to as “toner falling.” Therefore, it is desirable that the supply voltage during the preparatory operation be the same value as the developing voltage during the preparatory operation or a value greater toward the normal polarity of the toner (negative polarity in this embodiment).

[0061] In this embodiment, during the preparatory operation, the same regulating voltage as during image formation is applied to the regulating blade 44. However, a configuration may be adopted in which no regulating voltage is applied to the regulating blade 44 during the preparatory operation, or a configuration in which a regulating voltage different from that during image formation is applied during the preparatory operation.

[0062] <Effects of this Example> The effects of this example will be described. Example 1-1 was configured to perform a preparatory operation in which the potential difference was switched as shown in FIG. 5(a). Example 1-2 was configured to perform a preparatory operation in which the potential difference was switched as shown in FIG. 5(b). Example 1-3 was configured to perform a preparatory operation in which the potential difference was switched as shown in FIG. 5(c). Comparative Example 1 was configured to apply a constant development voltage of −450 V to the developing roller 42 and a constant supply voltage of −550 V to the supply roller 43 during the preparatory operation. Then, in each configuration, a halftone image with a density of 25% was printed after the preparatory operation was performed, and the presence or absence of density unevenness due to poor peeling was confirmed. The results are shown in Table 1.

[0063] [Table 1]

[0064] In Examples 1-1 and 1-2, neither uneven density due to improper peeling nor toner falling from the developing roller 42 occurred.

[0065] In Example 1-3, density unevenness due to imperfect stripping did not occur, but toner sometimes fell off the developing roller 42. Note that, for example, in cases where suppression of density unevenness due to imperfect stripping can be prioritized, the configuration of Example 1-3 may be used. However, the configurations of Examples 1-1 and 1-2 are more preferable because they can suppress density unevenness due to imperfect stripping while suppressing toner falling off the developing roller 42.

[0066] In Comparative Example 1, density unevenness occurred due to poor peeling. This is thought to be because the toner in a compacted state around the developing roller 42 and the supply roller 43 could not be loosened by applying vibration. Note that in Comparative Example 1, toner did not fall off the developing roller 42.

[0067] As described above, in this embodiment, the control unit 200 can control the development power source E2 and the supply power source E3 to perform a preliminary operation in which, during non-image formation when development is not being performed, a first potential difference and a second potential difference different from the first potential difference are alternately switched multiple times between the development roller 42 and the supply roller 43 while the development roller 42 and the supply roller 43 are rotating. This reduces the compacted state of the toner around the supply roller 43 and the development roller 42, making it easier to expel the toner from the supply roller 43. As a result, the supply roller 43 can more easily strip the toner off the development roller 42, making it possible to suppress density unevenness caused by poor stripping.

[0068] In this embodiment, the potential difference between the developing roller 42 and the supply roller 43 is switched 20 times during the preliminary operation, but this is not limited to this number. This number can be set appropriately depending on, for example, the fluidity of the toner and the configuration of the developing device 4. Similarly, the predetermined time for applying each voltage (potential) is not limited to 1 second as in this embodiment and can be set appropriately depending on, for example, the fluidity of the toner and the configuration of the developing device 4. If this predetermined time is too short, the toner may not easily follow the change in the direction of the electric field, making it difficult to loosen the toner. If this predetermined time is too long, it may also be difficult to vibrate and loosen the toner. Although not limited to this, the predetermined time is preferably, for example, 0.5 seconds or more and 2 seconds or less. Furthermore, this predetermined time does not have to be constant during one preliminary operation or between multiple preliminary operations.

[0069] Furthermore, in this embodiment, during the preparatory operation, a supply voltage of, for example, −450 V and a supply voltage of −550 V are alternately applied to the supply roller 43. However, the value of the supply voltage during the preparatory operation is not limited to the value in this embodiment. For example, during the preparatory operation, a supply voltage of −450 V and a supply voltage of −650 V may be alternately applied to the supply roller 43. This increases the potential difference between the developing roller 42 and the supply roller 43 during the preparatory operation compared to this embodiment, thereby increasing the vibration applied to the toner in the V-zone compared to this embodiment. This potential difference can be appropriately set depending on, for example, the fluidity of the toner and the configuration of the developing device 4. Although not limited thereto, the potential difference at which the potential of the supply roller 43 increases toward the normal polarity of the toner relative to the potential of the developing roller 42 is preferably at least equal to or greater than the potential difference during image formation (typically, no more than three times the potential difference during image formation). Furthermore, if this potential difference is defined as the first potential difference, the second potential difference is preferably approximately 0 V (the developing roller 42 and the supply roller 43 are approximately at the same potential). As an example, the difference between the first potential difference and the second potential difference is preferably about 100 to 300 V. Note that the potential of the supply roller 43 may be alternately switched between the first potential difference and the second potential difference, each of which increases toward the normal polarity of the toner relative to the potential of the development roller 42.

[0070] Furthermore, for example, the number of times the potential difference between the developing roller 42 and the supply roller 43 is switched during the preliminary operation may be changed depending on the environment in which the image forming apparatus 100 is installed. As described above, the more compacted the toner in the V zone, the more likely it is that density unevenness due to poor stripping will occur. Therefore, for example, the higher the humidity environment, the more frequently the potential difference is switched. In addition to or instead of increasing the number of times the potential difference is switched, the potential difference may be increased as described above.

[0071] Furthermore, during the preparatory operation, the rotational speed (circumferential speed) of at least one of the developing roller 42 and the supply roller 43 may be made faster than during image formation, which is expected to improve the effect of loosening the toner around the developing roller 42 and the supply roller 43.

[0072] Although the present embodiment describes the preparatory operation being performed every time before image formation, the frequency of the preparatory operation is not limited to this. For example, if the image forming apparatus 100 has been left unused for a short time since the end of the previous image formation, the toner in the V zone may be less compacted, reducing the need for the preparatory operation. Therefore, the following configuration may be adopted. For example, the image forming apparatus 100 may be provided with a timer as a measuring unit for measuring the time (idle time) from the end of the previous image formation (e.g., when the developing device 4 is stopped) to the start of the current image formation (e.g., when a job start instruction is input or when the developing device 4 is started). If the idle time measured by the timer exceeds a predetermined threshold, the preparatory operation is performed before image formation. From a similar perspective, the number of times the potential difference between the developing roller 42 and the supply roller 43 is switched during the preparatory operation may be changed depending on the idle time. In this case, for example, the longer the idle time, the more frequently the potential difference may be switched. In this case, the potential difference may be increased as described above, in addition to or instead of increasing the number of times the potential difference is switched.

[0073] In addition, in this embodiment, the image forming apparatus 100 performs the preparatory operation between the input of the job start instruction and the start of the first image formation, but this is not limited to this. For example, the image forming apparatus 100 may perform an operation similar to the preparatory operation in this embodiment at a predetermined frequency (for example, at predetermined time intervals) while waiting for the job start instruction (while being left alone).

[0074] As described above, in this embodiment, the image forming apparatus 100 includes a rotatable image carrier (photosensitive drum) 1, a developing device 4 that develops an electrostatic latent image formed on the surface of the image carrier 1 with toner, the developing device 4 including a rotatable developing member (developing roller) 42 that supplies toner to the electrostatic latent image, and a rotatable supply member (supply roller) 43 that contacts the developing member 42 and supplies toner to the developing member 42, a developing voltage application unit (developing power source) E2 that applies a voltage to the developing member 42, and a supply member 43 that supplies a voltage to the supply member 43. The image forming apparatus includes a supply voltage application unit (power supply) E3 that applies a voltage to the developing member 42 and the supply voltage application unit E3, and a control unit 200 that can control the developing voltage application unit E2 and the supply voltage application unit E3. The control unit 200 can control the developing voltage application unit E2 and the supply voltage application unit E3 to perform a preparatory operation in which a first potential difference and a second potential difference different from the first potential difference are alternately switched multiple times between the developing member 42 and the supply member 43 while the developing member 42 and the supply member 43 are rotating during non-image formation (i.e., when development is not being performed). In this embodiment, the control unit 200 controls the preparatory operation to be performed between the input of a start instruction for a job in which images are formed on one or more recording materials P and output, and the start of development of the electrostatic latent image of the first image of the job. In this embodiment, the control unit 200 also controls the voltage applied to the supply member 43 to be a voltage greater toward the normal polarity of the toner than the voltage applied to the developing member 42 when at least one of the first potential difference and the second potential difference is formed. In this embodiment, when at least one of the first potential difference and the second potential difference is formed, the control unit 200 controls the voltage applied to the developing member 42 and the voltage applied to the supply member 43 so that they are substantially the same. In this embodiment, the developing device 200 has a developing chamber 45 in which the developing member 42 and the supply member 43 are provided, and a toner storage chamber 46 in which toner to be supplied to the developing chamber 45 is stored, and the developing chamber 45 is disposed below the toner storage chamber 46 in the direction of gravity.

[0075] Furthermore, the control unit 200 can control the preparatory operation to change the number of times the potential difference is alternately switched between the first potential difference and the second potential difference, based on information regarding the time from when rotation of the developing member 42 stopped upon completion of the previous job to when rotation of the developing member 42 started upon the start of the current job. In this case, the control unit 200 can control the preparatory operation so that the number of times is greater when the time indicated by the information is a second time that is longer than the first time than when the time indicated by the information is a first time. Furthermore, the control unit 200 can control the drive device that rotates at least one of the developing member 42 and the supply member 43 so that the rotation speed of at least one of the developing member 42 and the supply member 43 is faster during the preparatory operation than during image formation in which development is performed.

[0076] According to this embodiment, it is possible to prevent the occurrence of image defects caused by insufficient removal of toner from the developing member 42 by the supplying member 43.

[0077] [Example 2] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0078] <Outline of this Example> In this embodiment, the number of times the potential difference between the developing roller 42 and the supply roller 43 is switched during the preparatory operation is changed in accordance with the usage history information of the developing device 4.

[0079] As explained in the first embodiment, density unevenness due to improper stripping is more likely to occur the greater the amount of toner in the developing device 4, and the greater the degree of cohesion of the toner in the developing device 4. In other words, when the amount of toner in the developing device 4 is large, the toner in the V zone is more likely to become compacted due to its own weight. Furthermore, when the degree of cohesion of the toner is high, the toner in the V zone becomes less mobile. Therefore, in these cases, it becomes more difficult for the supply roller 43 to expel toner in the V zone, and density unevenness due to improper stripping is more likely to occur.

[0080] Therefore, in this embodiment, the control unit 200 controls the number of times the potential difference between the supply roller 43 and the developing roller 42 is switched during the preliminary operation depending on the amount of toner in the developing device 4 and the degree of deterioration of the toner in the developing device 4.

[0081] <Calculating remaining toner amount> Next, a configuration for detecting the amount of toner (remaining toner amount) in the developing device 4 in this embodiment will be described. Fig. 6 is a schematic diagram showing a configuration for detecting the amount of toner remaining in the developing device 4 in this embodiment. Fig. 7 is a schematic diagram of a light guiding member 18 that constitutes a toner amount sensor 20, which will be described later. Fig. 8 is a schematic diagram showing the circuit configuration of this toner amount sensor 20.

[0082] As shown in Fig. 6, the developing device 4 is provided with a light-guiding member 18 that constitutes a toner amount sensor 20 serving as a remaining developer amount detection means. As shown in Fig. 7, the light-guiding member 18 has a light-emitting side light-guiding portion 18a and a light-receiving side light-guiding portion 18b. The light-emitting side light-guiding portion 18a guides light emitted from a light-emitting element 19a of a sensor portion 19 (described later) into the interior of the developing container 41 (the toner storage chamber 46 in this embodiment). The light-receiving side light-guiding portion 18b guides light that has passed through the light-emitting side light-guiding portion 18a and a spatial light path Q inside the developing container 41 to a light-receiving element 19b of the sensor portion 19 (described later).

[0083] As shown in FIG. 6, the device main body 110 is provided with a sensor unit 19 that constitutes the toner amount sensor 20. As shown in FIG. 8, the sensor unit 19 has a light-emitting element 19a as a light-emitting element that emits light and a light-receiving element 19b as a light-receiving element that receives the light emitted from the light-emitting element 19a. The sensor unit 19 also has a circuit board (not shown) on which the light-emitting element 19a and the light-receiving element 19b are provided. In this embodiment, an LED is used as the light-emitting element 19a, and a phototransistor is used as the light-receiving element 19b. The phototransistor is turned on by the light from the LED. The circuit board is also provided with a cable connector (not shown). The sensor unit 19 is connected to a control unit 200 provided in the device main body 110 via the cable connector and a cable (not shown).

[0084] Next, the arrangement of toner amount sensor 20 in this embodiment will be described. In this embodiment, toner amount sensor 20, which is composed of light guiding member 18 and sensor unit 19, is disposed on the side surface of toner storage chamber 46 of developing device 4. In this embodiment, toner amount sensor 20 (light guiding member 18 and sensor unit 19) is provided in the center of toner storage chamber 46 in the longitudinal direction (the direction of the rotational axis of developing roller 42). Toner inside toner storage chamber 46 may be distributed unevenly in the longitudinal direction of toner storage chamber 46, but the uneven distribution of toner is less in the center of toner storage chamber 46 in the longitudinal direction. Therefore, by providing toner amount sensor 20 (light guiding member 18 and sensor unit 19) in the center of toner storage chamber 46 in the longitudinal direction, the influence of uneven distribution of toner on the detection result of the remaining toner amount can be suppressed.

[0085] Next, a method for detecting the toner amount using toner amount sensor 20 will be described. In Fig. 8, a switch (not shown) is provided between light-emitting element 19a and power supply voltage Vcc1. When this switch is turned on, voltage is applied from power supply voltage Vcc1 to light-emitting element 19a, bringing light-emitting element 19a into a conductive state. Meanwhile, a switch (not shown) is also provided between light-receiving element 19b and power supply voltage Vcc2. When this switch is turned on, light-receiving element 19b is brought into a conductive state, and a current corresponding to the amount of light detected by light-receiving element 19b flows.

[0086] A power supply voltage Vcc1 and a current-limiting resistor R1 are connected to the light-emitting element 19a, and the light-emitting element 19a emits light in response to a current determined by the current-limiting resistor R1. The light emitted from the light-emitting element 19a passes through a spatial optical path Q and is received by the light-receiving element 19b. A power supply voltage Vcc2 is connected to the collector terminal of the light-receiving element 19b, and a detection resistor R2 is connected to the emitter terminal of the light-receiving element 19b. The light-receiving element 19b, which is a phototransistor, receives the light emitted from the light-emitting element 19a and outputs a signal (current) corresponding to the amount of light received. This signal is converted into a voltage by the detection resistor R2 and input to an A / D converter 202 (described later) of the control unit 200. That is, the light-receiving element 19b changes its output value according to the amount of toner contained in the toner storage chamber 46. Power is supplied to the toner amount sensor 20 from a power supply provided in the image forming apparatus 100.

[0087] As shown in FIG. 6 , the control unit 200 includes a CPU 201, an A / D conversion unit 202, a ROM 203, and a toner amount calculation unit 221. The A / D conversion unit 202 may be configured as part of the aforementioned input / output unit. The ROM 203 may be configured as part of the aforementioned main body storage unit 210. In this embodiment, the function of the toner amount calculation unit 221 is realized by the CPU 201 executing a program stored in the ROM 203. However, all or part of the function of the toner amount calculation unit 221 may be realized by a hardware circuit such as an ASIC (application-specific integrated circuit) or an FPGA (field programmable array). The process cartridge 8 is provided with a cartridge memory (hereinafter simply referred to as “memory”) 80 configured as a non-volatile memory serving as storage means (storage unit). An operation panel (operation unit) 300 provided in the apparatus main body 110 is connected to the control unit 200. The operation panel 300 is configured to include a display unit for displaying information to a user (operator) under the control of the control unit 200, and an input unit for inputting information to the control unit 200 in response to operations by the user (operator). The operation panel 300 may be configured to include a touch panel or the like that has the functions of a display unit and an input unit.

[0088] The toner amount calculation unit 221 of the control unit 200 determines whether the light receiving element 19b has received light from the light emitting element 19a based on the voltage level input to the control unit 200 by the toner amount sensor 20 and converted into a digital signal by the A / D conversion unit 202. The toner amount calculation unit 221 then calculates the length of time during which the toner amount sensor 20 detected light when the toner in the developing device 4 (in this embodiment, the toner storage chamber 46) was stirred by the stirring member 47 for a predetermined time. The ROM 203 of the control unit 200 stores toner amount determination information for determining (calculating, predicting, or estimating) the toner amount in advance as a table showing the relationship between the time and the toner amount. The toner amount calculation unit 221 then calculates the amount of toner in the developing device 4 based on the voltage level input to the control unit 200 by the toner amount sensor 20 and converted by the A / D conversion unit 202, and the information in the table.

[0089] More specifically, spatial light path Q of toner amount sensor 20 is set so as to intersect with the rotational trajectory of agitator 47 when viewed along the rotational axis of agitator 47 in toner storage chamber 46. The time during which spatial light path Q is blocked by toner transported by agitator 47 as agitator 47 makes one rotation, i.e., the time during which light receiving element 19b does not detect light from light emitting element 19a, varies depending on the amount of toner remaining in developing device 4. The intensity of light received by light receiving element 19b also varies depending on the amount of toner remaining in developing device 4.

[0090] In other words, when the remaining toner amount is low, the time that the spatial optical path Q is blocked by toner is short, so the time that the light receiving element 19b receives light is long and the light intensity of the light received by the light receiving element 19b is high. On the other hand, when the remaining toner amount is high, the time that the light receiving element 19b receives light is short and the light intensity of the light received by the light receiving element 19b is low. Therefore, the control unit 200 can determine the remaining toner amount level based on the light receiving time or light intensity of the light receiving element 19b.

[0091] In this embodiment, when image formation is performed, the toner amount T most recently detected by the toner amount sensor 20 at the end of image formation is calculated by the toner amount calculation unit 221, and this toner amount T is stored in the memory 80. The memory 80 also pre-stores the toner amount TM contained in the toner storage chamber 46 when the developing device 4 (process cartridge 8) is new, and the toner amount TL at the time of toner out. The toner amount TL at the time of toner out is a predetermined toner amount in the developing device 4 when the remaining toner in the developing device 4 has decreased to a level that recommends replacement of the developing device 4 (process cartridge 8). The toner amount TL at the time of toner out may be substantially 0 g, or may be a predetermined toner amount greater than 0 g. The toner amount calculation unit 221 calculates the remaining toner amount TJ [%] as toner amount information using the following formula (1): TJ[%]=(1-T / (TM-TL))×100 ···(1)

[0092] If the remaining toner amount TJ is greater than 0%, the control unit 200 determines that there is toner and controls the operation panel 300 to display the value of the remaining toner amount TJ. Furthermore, if the remaining toner amount TJ is less than or equal to 0%, the control unit 200 determines that there is no toner (toner out) and controls the operation panel 300 to display information (warning) urging the user to replace the process cartridge 8. The control unit 200 may also control an external device to display a similar display. Furthermore, the control unit 200 may also control the display of information related to the remaining toner amount TJ in response to an instruction (signal) input by a user (operator) through the operation panel 300 or an external device. Although the toner amount information is handled based on the remaining toner amount TJ in this embodiment, it may also be handled based on the amount of toner used. That is, when the remaining toner amount TJ is 0%, the amount of toner used is 100%, and when the remaining toner amount TJ is 100%, the amount of toner used is 0%, and the amount of available toner may be stored in advance in the memory 80.

[0093] The method for detecting / estimating the remaining toner amount is not limited to the optical detection method described above, and any other known method for detecting / estimating the remaining toner amount can be used. Examples include a capacitance detection method, a weight detection method, and a video count detection method. The capacitance detection method is as follows: Multiple electrodes, such as metal plates or conductive resin sheets extending in the longitudinal direction of two or more developing rollers, are arranged on the inner wall of the developing container, which serves as a frame. The capacitance between the metal plates or conductive resin sheets is measured, and the remaining toner amount is detected / estimated based on this capacitance. The weight detection method is as follows: For example, a load cell is provided to support the developing device from below. The remaining toner amount is detected / estimated by subtracting the weight of the developing device when it is empty from the weight measured by the load cell. The video count method is as follows: A video count, which correlates with the number of pixels in the image area (or the amount of toner applied to the image area), is measured based on image information related to image formation. Then, the amount of toner used is detected / estimated based on the value of the video count, and the amount of remaining toner is detected / estimated.

[0094] <Calculation of toner deterioration level> The toner in the developing device 4 rubs against the developing roller 42 and the regulating blade 44, and against the developing roller 42 and the supply roller 43, causing external additives to peel off, resulting in a decrease in fluidity and chargeability (also referred to here as "toner deterioration"). As the surface movement distance of the developing roller 42 increases, the number of times the toner rubs against the toner increases, and toner deterioration progresses, but the rate at which this progresses varies depending on the amount of toner in the developing device 4. Comparing a case where the amount of toner in the developing device 4 is large and a case where the amount of toner in the developing device 4 is small, even if the surface movement distance of the developing roller 42 is the same, the number of times the toner rubs against the toner increases, and toner deterioration progresses more quickly.

[0095] Next, a method for calculating the toner deterioration degree in this embodiment will be described. In this embodiment, the control unit 200 refers to the remaining toner amount TJ in the developing device 4 every time an image is formed on one sheet of recording material P (more specifically, one side of one sheet of recording material P). Then, the control unit 200 calculates the toner deterioration degree from the surface movement distance W of the developing roller 42 using a toner deterioration correction coefficient k corresponding to the remaining toner amount TJ.

[0096] As shown in FIG. 6, the control unit 200 has a developing roller surface movement distance calculation unit (hereinafter also simply referred to as a "distance calculation unit") 222 and a toner deterioration degree calculation unit 223. The distance calculation unit 222 measures the surface movement distance W of the developing roller 42. The toner deterioration degree calculation unit 223 calculates the toner deterioration degree from the surface movement distance W of the developing roller 42 using a toner deterioration correction coefficient k. In this embodiment, the functions of the distance calculation unit 222 and the toner deterioration degree calculation unit 223 are realized by the CPU 201 executing a program stored in the ROM 203. However, all or part of the functions of the distance calculation unit 222 and the toner deterioration degree calculation unit 223 may be realized by a hardware circuit such as an ASIC (application-specific integrated circuit) or an FPGA (field programmable array).

[0097] The distance calculation unit 222 measures the surface movement distance W based on the driving time Td of the developing device 4 (the rotation time of the developing roller 42, supply roller 43, and agitator 47), the process speed Ps of the image forming apparatus 100, and the peripheral speed ratio Sr of the developing roller 42 to the photosensitive drum 1. Here, the surface movement distance W is the distance that indicates how far a point on the surface of the developing roller 42 has moved due to the rotation of the developing roller 42. Furthermore, the process speed Ps of the image forming apparatus 100 is the movement speed (peripheral speed) of the surface of the photosensitive drum 1. Specifically, the surface movement distance W of the developing roller 42 is calculated by the following formula (2): W = Td × Ps × Sr (2)

[0098] Note that, as long as the information is about the surface movement distance of the developing roller 42, it is not limited to the above parameters, and the number of rotations of the developing roller 42 or the like may also be used.

[0099] FIG. 9 is a flowchart showing an example of a procedure for calculating the toner deterioration level in this embodiment. Here, the execution of the preparatory operation will be omitted from the description. When a job start instruction (print signal) is input, the control unit 200 starts the job operation and controls the developing device 4 to start driving (S101). Thereafter, the control unit 200 controls the image formation to start (S102). When the image formation for one sheet of recording material P is completed (S103), the toner deterioration level calculation unit 223 of the control unit 200 refers to the developing roller surface movement distance Wu during the image formation for one sheet of recording material P and the remaining toner amount TJ (S104). The developing roller surface movement distance Wu during the image formation for one sheet of recording material P is calculated by the distance calculation unit 222 of the control unit 200. The remaining toner amount TJ is calculated by the toner amount calculation unit 221 of the control unit 200 and stored in the memory 80. Then, the toner deterioration degree calculation unit 223 reads out the toner deterioration correction coefficient k corresponding to the remaining toner amount TJ, which is stored in the memory 80. The value of the toner deterioration correction coefficient k in this embodiment is shown in Table 2. In this embodiment, information indicating the relationship between the remaining toner amount TJ and the toner deterioration correction coefficient k as shown in Table 2 is set in advance and stored as a table in the memory 80. By setting the toner deterioration correction coefficient k to be larger as the remaining toner amount TJ decreases, it is possible to reflect the phenomenon in which toner deterioration progresses as the remaining toner amount TJ decreases.

[0100] [Table 2]

[0101] Then, the toner deterioration degree calculation unit 223 functions as a correction distance acquisition unit, and calculates the toner deterioration degree Hu by multiplying the developing roller surface movement distance Wu in forming an image on one sheet of recording material P by the toner deterioration correction coefficient k (S105). Specifically, the toner deterioration degree Hu is obtained by the following formula (3). Hu = k × Wu (3)

[0102] Next, the toner deterioration degree calculation unit 223 calculates the total cumulative toner deterioration degree Ht (S106) by adding (accumulating) the toner deterioration degree Hu to the cumulative toner deterioration degree Hr from the start of use (when the process cartridge 8 was new) stored in the memory 80. Specifically, the total cumulative toner deterioration degree Ht is calculated by the following formula (4). Ht = Hr + Hu (4)

[0103] Furthermore, the toner deterioration level calculation unit 223 calculates a toner deterioration life GJ as deterioration level information from the toner deterioration level threshold Wth and the total cumulative toner deterioration level Ht stored in the memory 80 (S107). Specifically, the toner deterioration life GJ is calculated by the following formula (5). GJ[%]=Ht / Wth×100 (5)

[0104] Then, the toner deterioration degree calculation unit 223 writes the total cumulative toner deterioration degree Ht as the cumulative toner deterioration degree Hr in the memory 80 (S108).

[0105] Here, when the toner deterioration life GJ=0%, it indicates that the developing device 4 is brand new. When the toner deterioration life GJ≧100% (i.e., when the total cumulative toner deterioration degree Ht exceeds the toner deterioration threshold Wth), it can be determined that the developing device 4 has reached the end of its life and it is time to replace the process cartridge 8.

[0106] The control unit 200 determines whether the toner deterioration life GJ is 100% or more (S109). If the control unit 200 determines in S109 that the toner deterioration life GJ is 100% or more, it controls the operation panel 300 to display information (a warning) urging the user to replace the process cartridge 8 (S110). The control unit 200 may also control an external device to display a similar message. The control unit 200 also controls the operation of the job to end (S111). On the other hand, if the control unit 200 determines in S109 that the toner deterioration life GJ is not 100%, it determines whether there is a next image formation for the job (S112), and if there is, it performs the next image formation (S102), and if there is not, it controls the operation of the job to end (S111).

[0107] <Preparatory movement control> Next, the control of the preparatory operation before image formation in this embodiment will be described. As mentioned above, density unevenness due to poor stripping is more likely to occur the greater the amount of toner in the developing device 4 and the greater the degree of cohesion due to toner degradation. In the configuration of this embodiment, the remaining toner amount TJ and toner degradation life GJ were set to different states, and the number of times the potential difference between the developing roller 42 and the supply roller 43 was changed to sufficiently suppress density unevenness due to poor stripping was determined through experiments. Table 3 shows the relationship between the determined remaining toner amount TJ and toner degradation life GJ and the number of times the potential difference was changed.

[0108] [Table 3]

[0109] In Example 1, the number of times the potential difference was switched during the preparatory operation was set to 20 times so as to sufficiently suppress density unevenness due to poor stripping throughout the entire period from the start of use of the developing device 4 (process cartridge 8) until the end of its life. However, as can be seen from Table 3, when the toner amount is low, for example, the potential difference was switched more times than necessary. For example, when the remaining toner amount TJ is 40% and the toner deterioration life is 60%, four times the potential difference would be sufficient, but in Example 1, it was set to 20 times. If the number of times the potential difference was switched during the preparatory operation is increased, the downtime before image formation begins will be longer, which may reduce usability.

[0110] Therefore, in this embodiment, when a job start instruction is input, the control unit 200 reads the toner amount T and cumulative toner deterioration level Hr stored in the memory 80 and calculates the remaining toner amount TJ and toner deterioration life GJ. The control unit 200 calculates the remaining toner amount TJ in the toner amount calculation unit 221 and calculates the toner deterioration life GJ in the toner deterioration level calculation unit 223. Then, the control unit 200 determines the number of times to switch the potential difference during the preparatory operation based on the calculated remaining toner amount TJ and toner deterioration life GJ, by referencing information indicating the relationship between the remaining toner amount TJ, toner deterioration life GJ, and the number of times the potential difference is switched. In this embodiment, information indicating the relationship between the remaining toner amount TJ, toner deterioration life GJ, and the number of times the potential difference is switched, as shown in Table 4, is preset and stored in the ROM 203 as a table. Note that a number of times the switching count is 0, which corresponds to no preparatory operation being performed. In this way, in this embodiment, the control unit 200 can control the preparatory operation to switch whether or not to perform it depending on the usage history information of the developing device 4 (the amount of toner in the developing device 4 and the degree of deterioration of the toner in the developing device 4).

[0111] [Table 4]

[0112] FIG. 10 is a flowchart outlining the job procedure in this embodiment, including the process for determining the number of times the potential difference is changed during the preparatory operation. When a job start instruction is input, the control unit 200 starts the job operation (S201), acquires the remaining toner amount TJ and the toner deterioration life GJ (S202), and determines the number of times the potential difference is changed during the preparatory operation from the table shown in Table 4 (S203). The control unit 200 then controls the preparatory operation to change the potential difference between the developing roller 42 and the supply roller 43 the determined number of times (S204). The control unit 200 then executes image formation (S205) and determines whether all image formation for the job has been completed (S206). If the control unit 200 determines in S206 that all image formation for the job has been completed, it controls the job operation to end (S207). On the other hand, if the control unit 200 determines in S206 that all image formation for the job has not been completed, it returns to the process of S205 and controls the image formation to be executed again.

[0113] <Effects of this Example> The effects of this example will now be described. Here, the occurrence of density unevenness due to poor stripping and the time required for the preparatory operation are compared between this example, the aforementioned Example 1-1 in which the number of times the potential difference was switched during the preparatory operation was fixed at 20 times, and Comparative Example 2 in which the number of times the potential difference was switched during the preparatory operation was fixed at 4 times. The results are shown in Table 5.

[0114] Consider Case 1, where the remaining toner amount TJ is 100% and the toner degradation life GJ is 80%. In this embodiment, the potential difference is switched 18 times during the preparatory operation, so 18 seconds are required before image formation, and density unevenness due to poor stripping can be suppressed. In Example 1-1, the potential difference is switched 20 times during the preparatory operation, so 20 seconds are required before image formation, and density unevenness due to poor stripping can be suppressed. On the other hand, in Comparative Example 2, the potential difference is switched 4 times during the preparatory operation, so 4 seconds are required before image formation, but density unevenness due to poor stripping may occur.

[0115] In Case 2, consider the case where the remaining toner amount TJ is 40% and the toner degradation life GJ is 60%. In this embodiment, the potential difference is switched four times during the preparatory operation, so 4 seconds are required before image formation, and the occurrence of density unevenness due to poor stripping can be suppressed. In Example 1-1, the potential difference is switched 20 times during the preparatory operation, so the occurrence of density unevenness due to poor stripping can be suppressed, but 20 seconds are required before image formation. In Comparative Example 2, the potential difference is switched four times during the preparatory operation, so 4 seconds are required before image formation, and the occurrence of density unevenness due to poor stripping can be suppressed.

[0116] [Table 5]

[0117] According to this embodiment, in both Case 1 and Case 2, it is possible to sufficiently suppress the occurrence of density unevenness due to poor peeling, while shortening the downtime that occurs before image formation according to the remaining toner amount TJ and toner degradation life GJ.

[0118] As described above, in this embodiment, the control unit 200 controls the number of times the potential difference between the developing member 42 and the supply member 43 is alternately switched between the first potential difference and the second potential difference during the preparatory operation based on toner amount information regarding the amount of toner in the developing device. In this embodiment, the control unit 200 controls the number of times to be alternately switched between the first potential difference and the second potential difference during the preparatory operation so that it is greater when the toner amount indicated by the toner amount information is a second toner amount that is greater than the first toner amount, than when the toner amount is the first toner amount. Also, in this embodiment, the control unit 200 controls the number of times to be alternately switched between the first potential difference and the second potential difference during the preparatory operation based on deterioration level information regarding the deterioration level of the toner in the developing device 4. In this embodiment, the control unit 200 controls the number of times to be alternately switched between the first potential difference and the second potential difference during the preparatory operation so that it is greater when the deterioration level indicated by the deterioration level information is a second deterioration level, in which the toner is more deteriorated than the first deterioration level, than when the deterioration level is the first deterioration level. In this embodiment, the control unit 200 acquires the deterioration level information based on information related to the rotation time of the developing member 42 and toner amount information related to the amount of toner in the developing device 4. In particular, in this embodiment, the control unit 200 controls the number of times the potential difference is alternately switched between the first potential difference and the second potential difference during the preliminary operation based on the toner amount information related to the amount of toner in the developing device 4 and the deterioration level information related to the deterioration level of the toner in the developing device 4.

[0119] In this way, in this embodiment, the number of times the potential difference between the developing roller 42 and the supply roller 43 is switched during the preliminary operation is changed depending on the amount of toner in the developing device 4 and the degree of deterioration of the toner in the developing device 4. This makes it possible to reduce the downtime that occurs before image formation while suppressing the occurrence of density unevenness due to improper stripping, thereby improving usability.

[0120] In this embodiment, the number of times the potential difference between the supply roller 43 and the development roller 42 is switched during the preliminary operation is changed depending on the amount of toner in the development device 4 and the degree of deterioration of the toner in the development device 4 as usage history information of the development device 4, but this is not limited to this. For example, at least one of the amount of toner in the development device 4 and the degree of deterioration of the toner in the development device 4 can be used as usage history information of the development device 4. Furthermore, for example, any index value correlated with the amount of use of the development device 4, such as the driving time or driving amount of the development device 4 (such as the rotation time and number of rotations of the development roller 42, the supply roller 43, and the agitation member 47), may also be used as usage history information of the development device 4.

[0121] [Example 3] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0122] <Outline of this Example> In this embodiment, unlike in Embodiments 1 and 2, image forming apparatus 100 is configured so that toner storage chamber 46 constituting developing device 4 can be removed from developing chamber 45 constituting developing device 4 and replaced. In this embodiment, image forming apparatus 100 is configured so that process cartridge 8 in Embodiments 1 and 2 is essentially detachable from apparatus main body 110, except that toner storage chamber 46 is detachable from developing chamber 45. Here, toner storage chamber 46 detachable from developing device 4 (process cartridge 8) is referred to as toner cartridge 8T, and the portion of process cartridge 8 excluding toner cartridge 8T is referred to as process cartridge main body 8P.

[0123] FIG. 11 is a schematic cross-sectional view showing the configuration of the process cartridge 8 in this embodiment. FIG. 11(a) shows the process cartridge main body 8P and the toner cartridge 8T separated, and FIG. 11(b) shows the process cartridge main body 8P and the toner cartridge 8T connected together. In this embodiment, the process cartridge 8 is configured so that the toner cartridge 8T can be separated, and when the toner in the toner storage chamber 46 runs out, image formation can be resumed by simply replacing the toner cartridge 8T of the process cartridge 8. The toner cartridge 8T is configured with a toner storage chamber 46 in which toner is stored and which is equipped with an agitator 47. The process cartridge 8 also includes the development chamber 46, which is equipped with a development roller 42, a supply roller 43, and a regulating blade 44.

[0124] The method of detecting the toner amount T and the method of calculating the remaining toner amount TJ (first toner amount information) in this embodiment are the same as those in the second embodiment. When the remaining toner amount TJ = 0%, there is no toner in the toner cartridge 8T (toner storage chamber 46), and the amount of toner TL at the time of toner out remains in the developing chamber 46. The amount of toner TF stored in a new toner cartridge 8T is TF = TM - TL. TM is the amount of toner stored in the toner storage chamber 46 of a new process cartridge 8 (developing device 4). In other words, when a new toner cartridge 8T is installed in the process cartridge main body 8P (when the toner cartridge 8T is replaced), the amount of toner in the developing device 4 becomes TM. In this embodiment, the settings are TL = 30 g, TF = 150 g, and TM = 180 g.

[0125] <Calculating the degree of toner deterioration after replacing a toner cartridge> In a configuration in which the toner cartridge 8T is replaced while toner remains in the process cartridge 8, the toner in the developing device 4 after the toner cartridge 8T is replaced is not all new toner, but a mixture of degraded toner and new toner. Therefore, after replacement with a new toner cartridge 8T, the remaining toner amount returns to 100%, but the toner degradation degree does not return to 0%. In this embodiment, this fact is taken into consideration when calculating the toner degradation degree after replacement of the toner cartridge 8T.

[0126] A method for calculating the toner deterioration degree after replacing the toner cartridge 8T in this embodiment will be described. When the toner cartridge 8T is replaced, the control unit 200 calculates the total cumulative toner deterioration degree Ht from the cumulative toner deterioration degree Hr from the start of use of the process cartridge 8, the toner amount TL at the time of toner out (second toner amount information), and the toner amount TF of the new toner cartridge 8T, all of which are stored in the memory 80. Specifically, the total cumulative toner deterioration degree Ht is obtained by the following formula (6). The control unit 200 calculates the total cumulative toner deterioration degree Ht in the toner deterioration degree calculation unit 223. Ht = Hr × TL / (TL + TF) (6)

[0127] Furthermore, the toner deterioration level calculation unit 223 calculates the toner deterioration life GJ from the toner deterioration level threshold Wth and the total cumulative toner deterioration level Ht stored in the memory 80. Specifically, the toner deterioration life GJ is calculated by the following formula (7). GJ[%]=Ht / Wth×100 (7)

[0128] Then, the toner deterioration degree calculation unit 223 writes the total cumulative toner deterioration degree Ht into the memory 80 as the cumulative toner deterioration degree Hr.

[0129] Here is a specific calculation example. For example, consider a case where toner cartridge 8T is replaced when the toner deterioration life is 60% when the remaining toner amount TJ reaches 0%. When toner deterioration life GJ is 60%, the cumulative toner deterioration degree Hr is 0.6Wth. When toner cartridge 8T is replaced in this state, the total cumulative toner deterioration degree Ht will be as follows: Ht=0.6Wth×30 / (30+150)=0.1Wth

[0130] From the total cumulative toner deterioration degree Ht calculated here, the toner deterioration life GJ is calculated as follows: GJ[%]=0.1Wth / Wth×100=10%

[0131] Therefore, in this case, after the toner cartridge 8T is replaced, the remaining toner amount TJ will be 100%, but the toner deterioration life GJ will be 10%, and the toner will not return to a new condition. In this way, according to the method for calculating the toner deterioration degree of this embodiment, it is possible to obtain the toner deterioration life GJ that reflects the toner deterioration state when deteriorated toner and new toner are mixed.

[0132] <Preparatory movement control> In this embodiment, the control of the preparatory operation before image formation is the same as in the second embodiment.

[0133] <Effects of this Example> As described above, in this embodiment, the developing device 4 has a developing chamber 45 in which a developing member 42 and a supply member 43 are provided, and a toner storage chamber 46 in which toner to be supplied to the developing chamber 45 is stored, and a toner cartridge 8T equipped with the toner storage chamber 46 is detachably attached to a developing container 41 equipped with the developing chamber 45, and when the toner cartridge is replaced, the control unit 200 acquires second deterioration degree information regarding the deterioration degree of toner in the developing device 4 after the replacement based on first toner amount information regarding the amount of toner in the developing device 4 before the replacement, second toner amount information regarding the amount of toner in the developing device 4 after the replacement, and first deterioration degree information regarding the deterioration degree of toner in the developing device 4 before the replacement, and controls to change the number of times the potential difference between the developing member 42 and the supply member 43 is alternately switched between the first potential difference and the second potential difference during the preliminary operation based on the second toner amount information and the second deterioration degree information.

[0134] According to this embodiment, in a configuration in which the toner cartridge 8T of the process cartridge 8 is replaceable, the same effects as those of the second embodiment can be obtained.

[0135] In this embodiment, the toner storage chamber 46 is configured as a replaceable toner cartridge 8T, but the present invention is not limited to this. For example, the toner storage chamber 46 may be provided with a refill opening that is an openable opening, through which new toner can be refilled into the toner storage chamber 46. In this manner, the developing device 4 may be configured to be able to refill toner into the toner storage chamber 46. In this case, when toner is refilled into the toner storage chamber 46, the control unit 200 acquires second deterioration level information regarding the deterioration level of the toner in the developing device 4 after the refill based on first toner amount information regarding the amount of toner in the developing device 4 before the refill, second toner amount information regarding the amount of toner in the developing device 4 after the refill, and first deterioration level information regarding the deterioration level of the toner in the developing device 4 before the refill, and controls the controller 200 to change the number of times the potential difference is alternately switched between the first potential difference and the second potential difference during the preliminary operation based on the second toner amount information and the second deterioration level information.

[0136] [Example 4] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0137] <Outline of this Example> In this embodiment, as in the third embodiment, the image forming apparatus 100 is configured so that the toner cartridge 8T can be replaced with a new one for the developing device 4 (process cartridge 8). In the third embodiment, the toner deterioration degree of the toner remaining in the developing device 4 is used to calculate the toner deterioration degree after replacing the toner cartridge 8T. This calculation method assumes that the deteriorated toner remaining in the developing device 4 and the new toner in the toner cartridge 8T are sufficiently mixed. However, it has been found that when the toner cartridge 8T contains a large amount of toner, the deteriorated toner and the new toner may not be immediately mixed. In such a case, for example, when forming an image immediately after replacing the toner cartridge 8T, a discrepancy between the calculated toner deterioration life GJ and the actual degree of toner deterioration in the developing device 4 may result in uneven density due to poor toner removal.

[0138] For example, consider a case where toner cartridge 8T is replaced when the remaining toner amount TJ reaches 0% and the toner degradation life is 60%. In Example 3, the toner amount TL at the time of toner out is 30 g, and the toner amount TF in the new toner cartridge is 150 g, so the toner degradation life GJ is calculated to be 10%. However, immediately after replacing toner cartridge 8T, the state of the toner in developing device 4 is as shown in FIG. 12, with degraded toner remaining in developing chamber 45 and new toner remaining in toner storage chamber 46. In this state, the toner near zone V is degraded toner, and the weight of the new toner is acting on it, resulting in a state similar to 180 g of toner with a toner degradation life GJ of 60% remaining in developing device 4. In this case, in Example 3, the potential difference is switched 12 times during the preparatory operation (Table 4). However, this may not completely loosen the toner near zone V, resulting in uneven density due to poor toner removal. In order to fully suppress density unevenness due to poor peeling, it is actually necessary to switch the potential difference during the preliminary operation 16 times (Table 4).

[0139] The above problem can be solved by rotating the agitator 47 for a sufficiently long time after replacing the toner cartridge 8T to thoroughly mix the deteriorated toner in the developing chamber 45 with the new toner in the toner cartridge 8T. However, while the agitator 47 is rotating for a long time, image formation cannot be performed, which may result in a decrease in usability.

[0140] Therefore, in this embodiment, after replacing the toner cartridge 8T, the number of times the potential difference is switched during the preliminary operation can be appropriately set when the deteriorated toner in the developing chamber 45 and the new toner in the toner cartridge 8T are not mixed.

[0141] <Calculating the degree of toner deterioration after replacing a toner cartridge> A method for calculating the toner deterioration degree after replacing the toner cartridge 8T in this embodiment will be described. When the toner cartridge 8T is replaced, the control unit 200 calculates the total cumulative toner deterioration degree Ht from the cumulative toner deterioration degree Hr from the start of use of the process cartridge 8, the toner amount TL at the time of toner out, and the toner amount TF in the new toner cartridge, all of which are stored in the memory 80. Specifically, the total cumulative toner deterioration degree Ht is obtained by the following equation (8). The control unit 200 calculates the total cumulative toner deterioration degree Ht in the toner deterioration degree calculation unit 223. Ht = Hr × TL / (TL + TF) (8)

[0142] Furthermore, the toner deterioration level calculation unit 223 calculates a first toner deterioration life GJ1 (first deterioration level information) from the toner deterioration level threshold Wth and the total cumulative toner deterioration level Ht stored in the memory 80. Specifically, the first toner deterioration life GJ1 is calculated by the following formula (9). GJ1[%]=Ht / Wth×100 (9)

[0143] Next, the toner deterioration degree calculation unit 223 calculates the second toner deterioration life GJ2 (second deterioration degree information). Specifically, the second toner deterioration life GJ2 is calculated by the following formula (10). Hr in formula (10) is the cumulative toner deterioration degree Hr last stored in the memory 80 before the toner cartridge 8T was replaced. GJ2 [%] = Hr / Wth × 100 (10)

[0144] Then, the toner deterioration degree calculation unit 223 writes the total cumulative toner deterioration degree Ht as the cumulative toner deterioration degree Hr in the memory 80. In this embodiment, the toner deterioration degree calculation unit 223 also stores the calculated second toner deterioration life GJ in the memory 80. However, the cumulative toner deterioration degree Hr last stored in the memory 80 before the toner cartridge 8T is replaced may be held in the memory 80 so that the second toner deterioration life GJ can be calculated appropriately.

[0145] Here, the first toner deterioration life GJ1 is the same as the toner deterioration life GJ calculated in Example 3, and is calculated when the deteriorated toner in the developing chamber 45 and the new toner in the toner cartridge 8T are sufficiently mixed. On the other hand, the second toner deterioration life GJ2 is calculated when the deteriorated toner in the developing chamber 45 and the new toner in the toner cartridge 8T are not mixed.

[0146] <Preparatory movement control> In this embodiment, when a job start instruction is input, the control unit 200 reads the toner amount T and cumulative toner deterioration degree Hr stored in the memory 80 and calculates the remaining toner amount TJ and toner deterioration life GJ (first toner deterioration life GJ1, second toner deterioration life GJ2). Then, the control unit 200 refers to information indicating the relationship between the remaining toner amount TJ and toner deterioration life GJ and the number of times the potential difference is switched, in accordance with the calculated remaining toner amount TJ and toner deterioration life GJ (first toner deterioration life GJ1, second toner deterioration life GJ2), and determines the number of times the potential difference is switched during the preliminary operation. In this embodiment, the table referred to at this time is the same as that shown in Table 4 described in the second embodiment. This table is set in advance and stored in the ROM 203.

[0147] Here, the control unit 200 determines whether to use the first toner degradation life GJ1 or the second toner degradation life GJ2 as the toner degradation life GJ in the following manner. In this embodiment, the control unit 200 stores the post-replacement surface travel distance Wt, which is the integrated value of the surface travel distance Wu of the developing roller 42 since the replacement of the toner cartridge 8T, in the memory 80. Specifically, the distance calculation unit 222 of the control unit 200 integrates the post-replacement surface travel distance Wt and stores it in the memory 80. Then, when the post-replacement surface travel distance Wt is equal to or greater than a threshold value Wth2 previously set and stored in the memory 80, the control unit 200 sets GJ=GJ1 and refers to Table 4 to determine the number of times the potential difference is switched during the preparatory operation. On the other hand, when the post-replacement surface travel distance Wt is less than the threshold value Wth2, the control unit 200 sets GJ=GJ2 and refers to Table 4 to determine the number of times the potential difference is switched during the preparatory operation. As a result, if the surface travel distance Wt after replacement is equal to or greater than the threshold value Wth2, the number of switching operations can be determined assuming that the deteriorated toner in the developing chamber 45 and the new toner in the toner cartridge 8T are sufficiently mixed. On the other hand, if the surface travel distance Wt after replacement is less than the threshold value Wth2, the number of switching operations can be determined assuming that the deteriorated toner in the developing chamber 45 and the new toner in the toner cartridge 8T are not mixed. In this embodiment, Wth2 is set to 10920 mm. This is the surface travel distance of the developing roller 42 when the developing roller 42 rotates for 60 seconds. This threshold value Wth2 is a value determined by experimentally determining the time required for the deteriorated toner in the developing chamber 45 and the new toner in the toner cartridge 8T to be sufficiently mixed. Therefore, the value is not limited to this value and may be set appropriately depending on the configuration of the developing device 4.

[0148] FIG. 13 is a flowchart showing an outline of a job procedure in this embodiment including the determination process of the number of switching of the potential difference during the above-described preliminary operation. In the procedure of FIG. 13, for procedures similar to those in Embodiment 2 shown in FIG. 10, the same step numbers as in FIG. 10 are assigned, and the description thereof is omitted as appropriate. In this embodiment, the control unit 200 acquires the toner remaining amount TJ, the first toner deterioration life GJ1 and the second toner deterioration life GJ2, and the surface movement distance Wt after replacement in S202. Then, in this embodiment, the control unit 200 determines whether or not the surface movement distance Wt after replacement is equal to or greater than the threshold value Wth2 (S301). When the control unit 200 determines in S301 that Wt is equal to or greater than Wth2 (Wt≧Wth2), it determines to use the first toner deterioration life GJ1 as the toner deterioration life GJ (S302). On the other hand, when the control unit 200 determines in S302 that Wt is less than Wth2 (Wt<Wth2), it determines to use the second toner deterioration life GJ2 as the toner deterioration life GJ (S303). Also, in this embodiment, the control unit 200 determines the number of switching of the potential difference during the preliminary operation from the table shown in Table 4 based on the toner remaining amount TJ and the toner deterioration life GJ determined in S301 or S302 in S203. In this embodiment, the first toner deterioration life GJ1 and the second toner deterioration life GJ2 are acquired, and it is determined whether or not the surface movement distance Wt after replacement is equal to or greater than the threshold value Wth2, but the present invention is not limited thereto. For example, after determining whether or not the surface movement distance Wt after replacement is equal to or greater than the threshold value Wth2, the necessary toner deterioration life may be acquired.

[0149] <Effect of this embodiment> The effect of this embodiment will be described. Here, a case where the toner cartridge 8T is replaced in a state where the toner deterioration life when the toner remaining amount TJ reaches 0% is 60% is compared between this embodiment and Embodiment 3. After replacing the toner cartridge 8T with each configuration, a 25% density halftone image was printed, and the presence or absence of density unevenness due to peeling failure was confirmed. The results are shown in Table 6.

[0150]

Table 6

[0151] In the configuration of this embodiment, when forming an image immediately after replacing the toner cartridge 8T, the deteriorated toner in the developing chamber 45 and the new toner in the toner cartridge 8T are not sufficiently mixed. However, because the potential difference is switched 16 times during the preparatory operation, no uneven density due to poor stripping occurs. When image formation is then performed after driving the developing device 4 for 60 seconds, the potential difference is switched 12 times during the preparatory operation. However, because the deteriorated toner in the developing chamber 45 and the new toner in the toner cartridge 8T are sufficiently mixed, no uneven density due to poor stripping occurs.

[0152] Furthermore, in the configuration of Example 3, similar to this example, when forming an image immediately after replacing the toner cartridge 8T, the deteriorated toner in the developing chamber 45 and the new toner in the toner cartridge 8T are not sufficiently mixed. In Example 3, the potential difference is switched 12 times during the preparatory operation, which can result in uneven density due to poor stripping. For example, a low-temperature, low-humidity environment, in which toner tends to pack, can be cited as an example. When image formation is then performed after driving the developing device 4 for 60 seconds, the potential difference is switched 12 times during the preparatory operation, but the deteriorated toner in the developing chamber 45 and the new toner in the toner cartridge 8T are sufficiently mixed, so uneven density due to poor stripping does not occur.

[0153] As described above, in this embodiment, the control unit 200 controls the number of times the potential difference between the developing member 42 and the supply member 43 is alternately switched between the first potential difference and the second potential difference during the preparatory operation based on information regarding the rotation time of the developing member 42 after replacement of the toner cartridge T8. In this embodiment, the control unit 200 controls the number of times to be alternately switched between the first potential difference and the second potential difference more frequently when the rotation time indicated by the information regarding the rotation time of the developing member 42 after replacement is the second rotation time, which is shorter than the first rotation time, than when the rotation time is the first rotation time. Similarly, in a configuration in which toner can be replenished to the toner storage chamber 46, the control unit 200 can also control the number of times the potential difference is alternately switched between the first potential difference and the second potential difference during the preparatory operation based on information regarding the rotation time of the developing member 42 after the replenishment. In this case, the control unit 200 can control the number of rotations so that it is greater when the rotation time indicated by the information regarding the rotation time of the developing member 42 after the replenishment is a second rotation time that is shorter than the first rotation time than when the information indicates the first rotation time.

[0154] Thus, according to this embodiment, even if image formation is performed immediately after replacing the toner cartridge 8T when the deteriorated toner in the developing chamber 45 and the new toner in the toner cartridge 8T are not sufficiently mixed, it is possible to suppress the occurrence of uneven density due to poor peeling.

[0155] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

[0156] In the above-described embodiment, the developing device is configured such that the developing chamber is disposed below the toner storage chamber in the direction of gravity. As mentioned above, in such a configuration, the toner around the developing roller and the supply roller tends to become compacted when there is a large amount of remaining toner, making the effects of the present invention particularly pronounced. However, this is not limited to this, and the present invention can also be applied to a configuration in which the developing chamber is disposed horizontally next to the toner storage chamber, for example. Even in such a configuration, when there is a large amount of remaining toner, the toner around the developing roller and the supply roller tends to become compacted due to the conveying force of the agitator, etc. Therefore, the present invention is effective in such a configuration as well.

[0157] The developing device does not have to be detachable from the main body of the image forming apparatus. Alternatively, the toner cartridge may be detachable from a developing chamber fixedly disposed in the main body of the image forming apparatus. In this case, image formation may be performed while the toner cartridge remains attached to the developing device, or image formation may be performed after the toner cartridge is removed from the developing chamber after toner is replenished in the developing chamber. [Explanation of symbols]

[0158] 1 Photosensitive drum 4. Developing device 8 Process cartridge 8T Toner Cartridge 42 Developing roller 43 Supply roller 44 Regulatory Blade 53 Intermediate transfer belt 100 Image forming device 200 control section

Claims

1. a rotatable image carrier; a developing device that develops an electrostatic latent image formed on the surface of the image carrier with toner, the developing device including: a rotatable developing member that supplies toner to the electrostatic latent image; and a rotatable supplying member that contacts the developing member and supplies toner to the developing member; a developing voltage applying section that applies a voltage to the developing member; a supply voltage application unit that applies a voltage to the supply member; a control unit capable of controlling the developing voltage application unit and the supply voltage application unit; and The image forming apparatus is characterized in that the control unit is capable of controlling the development voltage application unit and the supply voltage application unit to perform a preliminary operation of forming a first potential difference and a second potential difference different from the first potential difference between the development member and the supply member by alternating multiple times while the development member and the supply member are rotating during non-image formation when the development is not being performed.

2. 2. The image forming apparatus according to claim 1, wherein the control unit controls the preparatory operation to be performed between the time when an instruction to start a job for forming and outputting an image on one or more recording materials is input and the time when the development of the electrostatic latent image of the first image of the job is started.

3. 2. The image forming apparatus according to claim 1, wherein the control unit controls the voltage applied to the supply member to be a voltage that is greater on the normal polarity side of the toner than the voltage applied to the developing member when at least one of the first potential difference and the second potential difference is formed.

4. The image forming apparatus according to claim 3, characterized in that the control unit controls the voltage applied to the developing member and the voltage applied to the supply member so that they are approximately the same when at least one of the first potential difference or the second potential difference is formed.

5. the developing device includes a developing chamber in which the developing member and the supply member are provided, and a toner storage chamber in which toner to be supplied to the developing chamber is stored; 2. The image forming apparatus according to claim 1, wherein the developing chamber is disposed below the toner storage chamber in the direction of gravity.

6. The image forming apparatus according to claim 2, characterized in that the control unit controls the number of times the potential difference is alternately switched between the first potential difference and the second potential difference during the preliminary operation based on information regarding the time from when the rotation of the developing member stops with the end of the previous job to when the rotation of the developing member starts with the start of the current job.

7. The image forming apparatus according to claim 6, characterized in that the control unit controls the number of times to be greater when the time indicated by the information is a second time that is longer than the first time than when the time indicated by the information is a first time.

8. The image forming apparatus according to claim 1, characterized in that the control unit controls a drive device that rotates at least one of the developing member or the supply member so that the rotation speed of at least one of the developing member or the supply member is faster during the preliminary operation than during image formation in which the development is performed.

9. The image forming apparatus according to claim 1, characterized in that the control unit controls the number of times the potential difference is alternately switched between the first potential difference and the second potential difference during the preliminary operation based on toner amount information regarding the amount of toner in the developing device.

10. The image forming apparatus according to claim 9, characterized in that the control unit controls the number of times to be greater when the toner amount indicated by the toner amount information is a second toner amount that is greater than the first toner amount than when the toner amount indicated by the toner amount information is a first toner amount.

11. The image forming apparatus according to claim 1, characterized in that the control unit controls the number of times the potential difference is alternately switched between the first potential difference and the second potential difference during the preliminary operation based on deterioration level information regarding the degree of deterioration of the toner in the developing device.

12. The image forming apparatus according to claim 11, characterized in that the control unit controls the number of times to be greater when the deterioration level indicated by the deterioration level information is a second deterioration level in which toner deterioration is more advanced than the first deterioration level, than when the deterioration level indicated by the deterioration level information is a first deterioration level.

13. 12. The image forming apparatus according to claim 11, wherein the control unit acquires the deterioration level information based on information relating to a rotation time of the developing member and toner amount information relating to an amount of toner in the developing device.

14. The image forming apparatus according to claim 1, characterized in that the control unit controls the number of times the potential difference is alternately switched between the first potential difference and the second potential difference during the preliminary operation based on toner amount information regarding the amount of toner in the developing device and deterioration level information regarding the degree of deterioration of the toner in the developing device.

15. the developing device has a developing chamber in which the developing member and the supply member are provided, and a toner storage chamber in which toner to be supplied to the developing chamber is stored, and a toner cartridge including the toner storage chamber is detachably attached to a developing container including the developing chamber; The image forming apparatus of claim 1, characterized in that when the toner cartridge is replaced, the control unit obtains second deterioration level information regarding the deterioration level of toner in the developing device after the replacement based on first toner amount information regarding the amount of toner in the developing device before the replacement, second toner amount information regarding the amount of toner in the developing device after the replacement, and first deterioration level information regarding the deterioration level of toner in the developing device before the replacement, and controls the image forming apparatus to change the number of times the potential difference is alternately switched between the first potential difference and the second potential difference during the preliminary operation based on the second toner amount information and the second deterioration level information.

16. The image forming apparatus according to claim 15, wherein the control unit controls the number of times the potential difference is alternately switched between the first potential difference and the second potential difference during the preliminary operation based on information regarding the rotation time of the developing member after the replacement.

17. The image forming apparatus according to claim 16, wherein the control unit controls the number of rotations so that the number of rotations is greater when the rotation time indicated by the information regarding the rotation time of the developing member after the replacement is a second rotation time that is shorter than the first rotation time than when the information regarding the rotation time of the developing member after the replacement is a first rotation time.

18. the developing device has a developing chamber in which the developing member and the supply member are provided, and a toner storage chamber in which toner to be supplied to the developing chamber is stored, and is configured to be able to replenish toner to the toner storage chamber; The image forming apparatus of claim 1, characterized in that when toner is replenished to the toner storage chamber, the control unit obtains second deterioration level information regarding the deterioration level of toner in the developing device after the replenishment based on first toner amount information regarding the amount of toner in the developing device before the replenishment, second toner amount information regarding the amount of toner in the developing device after the replenishment, and first deterioration level information regarding the deterioration level of toner in the developing device before the replenishment, and controls the number of times the potential difference is alternately switched between the first potential difference and the second potential difference during the preliminary operation based on the second toner amount information and the second deterioration level information.

19. The image forming apparatus according to claim 18, wherein the control unit controls the number of times the potential difference is alternately switched between the first potential difference and the second potential difference during the preliminary operation based on information regarding the rotation time of the developing member after the replenishment.

20. The image forming apparatus according to claim 19, characterized in that the control unit controls the number of rotations so that it is greater when the rotation time indicated by the information regarding the rotation time of the developing member after the replenishment is a second rotation time that is shorter than the first rotation time than when the information indicates the first rotation time.

Images