Image forming apparatus

Abstract

To apply an appropriate bias to a fur brush regardless of the cumulative usage of the fur brush, while preventing a charging failure of a photoreceptor caused by application of a bias to the fur brush.SOLUTION: An image forming apparatus 100 has a control unit 201 that can perform control to execute a setting operation of setting the value of a cleaning bias during image formation, on the basis of a result of detection performed by a detection unit 21 when a cleaning bias application unit E5 applies a plurality of test biases to a brush 62. When the surface potential of a photoreceptor 1 immediately before reaching a brush cleaning position Pe after passing through a transfer position Pd is defined as a potential before the brush, the control unit 201 performs control so that the potential before the brush of an area on the photoreceptor 1 passing through the brush cleaning position Pe when the plurality of test biases are applied to the brush 62 during the setting operation has a large value, on a side of the normal charge polarity of toner, compared to the potential before the brush of a non-image part on the photoreceptor during image formation.SELECTED DRAWING: Figure 11

Description

[Technical Field]

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

[0002] In conventional electrophotographic image forming apparatuses, a toner image formed on the surface of a photoreceptor through the processes of charging, exposure, and development is transferred directly to a recording material or transferred to the recording material via an intermediate transfer member. After the toner image transfer process from the photoreceptor to the receiving recording material or intermediate transfer member, untransferred toner (transfer residual toner), toner additives, discharge products, and other residues remain on the surface of the photoreceptor. Therefore, these must be removed from the surface of the photoreceptor prior to the next image formation process. Various methods for removing transfer residual toner and other residues from the surface of the photoreceptor have been used, including methods using a fur brush, a magnetic brush, and a cleaning blade. Among these, the method of scraping the photoreceptor surface with a cleaning blade to remove the transfer residual toner from the photoreceptor surface is widely used due to its relatively simple configuration and low cost.

[0003] In recent years, with the increasing speed and image quality of image forming apparatuses, the toner used has a lower melting point and is closer to a spherical shape, making it difficult to ensure cleaning performance with a cleaning blade alone.

[0004] One approach to address this issue is to use a cleaning assist device to assist the cleaning blade in removing residual toner from the photoreceptor. For example, a fur brush (brush roller) that contacts the surface of the photoreceptor is positioned upstream of the cleaning blade in the direction of movement of the photoreceptor surface (see Patent Document 1). By applying a bias to the fur brush, at least a portion of the residual toner can be removed from the photoreceptor surface before it reaches the cleaning blade. This allows the deposit of external additives (also referred to as an "external additive dam layer") formed near the contact point between the cleaning blade and the photoreceptor (also referred to as the "blade nip") to be stably maintained. As a result, the phenomenon of toner near the blade nip melting and adhering to the photoreceptor (also referred to as "toner fusion") is suppressed.

[0005] Thus, in order to meet the recent demand for higher speeds and longer lifespans of image forming apparatuses, the role of fur brushes as auxiliary cleaning means for improving the cleaning properties of photosensitive members has become increasingly important. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2023-26989 Summary of the Invention [Problem to be solved by the invention]

[0007] However, as the cumulative usage of the fur brush increases, the fibers tend to collapse (permanently deform) due to the influence of the components that penetrate and come into contact with the fur brush (such as the photosensitive element to be cleaned and the recovery element that recovers toner from the fur brush), causing the outer diameter of the fur brush to become smaller.When the outer diameter of the fur brush becomes smaller, the contact width between the photosensitive element and the fur brush in the direction of movement of the surface of the photosensitive element becomes smaller, and the contact resistance (electrical resistance) between the photosensitive element and the fur brush increases.

[0008] Therefore, if the bias voltage applied to the fur brush is fixed at a predetermined voltage, the current flowing through the fur brush decreases as the cumulative usage of the fur brush increases. As a result, the current (cleaning current) required for toner collection between the fur brush and the photoconductor ceases to flow, reducing the toner cleaning performance of the fur brush. When the toner cleaning performance of the fur brush decreases, toner can slip through the fur brush and destroy the external dam layer that has accumulated near the cleaning blade. This can cause toner near the blade nip to melt and result in toner fusion. On the other hand, if the bias voltage applied to the fur brush is set high in advance, anticipating a reduction in the outer diameter of the fur brush, excessive current may flow between the fur brush and the photoconductor during the initial stage of use. This can result in a phenomenon known as "positive memory" in the photoconductor. Positive memory is a phenomenon in which, when the normal charging polarity of a photosensitive member is negative, the photosensitive member becomes positive, which is the opposite polarity to the normal charging polarity, and the photosensitive member cannot be uniformly charged to the specified negative charging potential during the charging process, resulting in image defects such as uneven density in the image.

[0009] Therefore, the object of the present invention is to suppress poor charging of a photosensitive element caused by application of a bias to the fur brush, while making it possible to apply an appropriate bias to the fur brush regardless of the cumulative amount of use of the fur brush. [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 a rotatable photoconductor, a charging device that charges the surface of the photoconductor at a charging position, a charging bias applying section that applies a charging bias to the charging device to charge the surface of the photoconductor, a developing device that supplies toner to the surface of the photoconductor, a transfer device that transfers the toner from the surface of the photoconductor to a transfer recipient at a transfer position, a transfer bias applying section that applies a transfer bias to the transfer device to transfer the toner from the photoconductor to the transfer recipient, a cleaning blade that contacts the surface of the photoconductor at a blade cleaning position downstream of the transfer position and upstream of the charging position in the rotational direction of the photoconductor to remove toner from the surface of the photoconductor, a rotatable roller-shaped brush that contacts the surface of the photoconductor at a brush cleaning position downstream of the transfer position and upstream of the blade cleaning position in the rotational direction of the photoconductor to remove toner from the surface of the photoconductor, and a developing device that applies a toner to the surface of the photoconductor. and a control unit capable of controlling a setting operation to be performed during non-image formation, the setting operation setting the value of the cleaning bias based on the detection results of the detection unit when multiple test biases are applied to the brush by the cleaning bias application unit, wherein when the surface potential of the photosensitive body immediately before it first reaches the brush cleaning position after passing the transfer position is defined as a pre-brush potential, the control unit controls the pre-brush potential of an area on the photosensitive body that passes the brush cleaning position when the multiple test biases are applied to the brush during the setting operation to be a value larger toward the normal charging polarity of the toner than the pre-brush potential of a non-image area on the photosensitive body during image formation. [Effects of the Invention]

[0011] According to the present invention, it is possible to apply an appropriate bias to the fur brush regardless of the cumulative amount of use of the fur brush, while suppressing poor charging of the photosensitive member caused by application of a bias to the fur brush. [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 cross-sectional view of an image forming unit. [Figure 3] FIG. 2 is a schematic block diagram illustrating a control configuration of the image forming apparatus. [Figure 4] FIG. 2 is a schematic cross-sectional view of the periphery of a cleaning device. [Figure 5] 1A to 1C are schematic diagrams for explaining the process of toner fusion. [Figure 6] 10A and 10B are schematic diagrams for explaining the effect of suppressing toner fusion. [Figure 7] FIG. 10 is a graph showing changes in the outer diameter of the fur brush. [Figure 8] FIG. 10 is a graph showing changes in current flowing through a fur brush. [Figure 9] FIG. 10 is a graph showing changes in toner cleaning performance by a fur brush. [Figure 10] FIG. 4 is a graph showing the relationship between the cleaning bias and the potential of the photosensitive drum. [Figure 11] FIG. 10 is a flowchart showing a control procedure for a setting operation of a cleaning bias in the first embodiment. [Figure 12] FIG. 10 is a graph showing the relationship between the brush front potential and the positive conversion threshold value. [Figure 13] FIG. 10 is a graph showing a method for determining a voltage value of a cleaning bias. [Figure 14] 10A and 10B are timing charts of operations during image formation and setting operations. [Figure 15] FIG. 10 is a flowchart showing a control procedure for setting the cleaning bias in the second embodiment. [Figure 16]FIG. 10 is a schematic cross-sectional view of the periphery of a cleaning device in another example of an image forming apparatus. 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] 1. Overall configuration and operation of the image forming apparatus 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 four-color full-color printer that employs an intermediate transfer system and is capable of forming full-color images using an electrophotographic process.

[0015] Image forming apparatus 100 has multiple image forming units (stations): four image forming units 10Y, 10M, 10C, and 10K that form images of 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 7, which is disposed substantially horizontally, as described below. Elements in each image forming unit 10Y, 10M, 10C, and 10K that have the same or corresponding functions or configurations may be generally described by omitting the Y, M, C, or K suffixes to reference numerals indicating that the element is for one of the colors. Figure 2 is a schematic cross-sectional view showing one representative image forming unit 10. In this embodiment, the image forming unit 10 is configured to include photosensitive drums 1 (1Y, 1M, 1C, 1K), charging devices 2 (2Y, 2M, 2C, 2K), exposure devices 3 (3Y, 3M, 3C, 3K), developing devices 4 (4Y, 4M, 4C, 4K), primary transfer rollers 5 (5Y, 5M, 5C, 5K), cleaning devices 6 (6Y, 6M, 6C, 6K), etc., which will be described later.

[0016] The image forming apparatus 100 includes a photosensitive drum 1, a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) that serves as a first image carrier for carrying a toner image. The photosensitive drum 1 receives a driving force from a drum drive motor D1 (FIG. 3), a drive source constituting a drive device serving as a drive unit, and is driven to rotate at a predetermined peripheral speed (process speed) in the direction of arrow R1 (counterclockwise) in FIG. 1. 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 device 2 serving as a charging unit. During charging, a predetermined charging bias (charging voltage) is applied to the charging device 2 by a charging power supply (high-voltage power supply) E1 serving as a charging bias application unit. The charged surface of the photosensitive drum 1 is scanned and exposed by an exposure device 3 serving as an exposure unit in accordance with an image signal, forming an electrostatic latent image (electrostatic image) on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by the developing device 4 as a developing means, which supplies toner as a developer, and a toner image (toner image, developer image) is formed on the photosensitive drum 1. In this embodiment, toner charged with the same polarity as the charge polarity of the photosensitive drum 1 (negative polarity in this embodiment) adheres to the image portion (image portion) on the photosensitive drum 1, which has been uniformly charged and then exposed to light to reduce the absolute value of the potential (reverse development method). During development, a predetermined development bias (developing voltage) is applied to the developing sleeve 41 provided in the developing device 4 by a development power supply (high-voltage power supply) E2 as a development bias application unit. In this embodiment, the normal charge polarity of the toner during development, which is the normal charge polarity of the toner, is negative polarity (minus, negative).

[0017] An intermediate transfer belt 7, a rotatable intermediate transfer body formed of an endless belt, is disposed facing the four photosensitive drums 1Y, 1M, 1C, and 1K and serves as a second image carrier for carrying a toner image. The intermediate transfer belt 7 is stretched around a plurality of support rollers, including a drive roller 71, a tension roller 72, and a secondary transfer opposing roller 73, and is stretched with a predetermined tension. The intermediate transfer belt 7 rotates (circularly moves) in the direction of arrow R2 (clockwise direction) in FIG. 1 at a predetermined peripheral speed corresponding to the peripheral speed of the photosensitive drums 1, when a driving force is transmitted from a belt drive motor D2 (FIG. 3), which is a drive source constituting a drive device serving as a drive means, to rotate the drive roller 71. Primary transfer rollers 5Y, 5M, 5C, and 5K, which are roller-shaped primary transfer members (transfer devices) serving as primary transfer means, are disposed on the inner peripheral surface of the intermediate transfer belt 7 and correspond to the photosensitive drums 1Y, 1M, 1C, and 1K, respectively. The primary transfer roller 5 is pressed against the photosensitive drum 1 and contacts the photosensitive drum 1 via the intermediate transfer belt 7, forming a primary transfer nip T1, which is the contact point between the photosensitive drum 1 and the intermediate transfer belt 7. The primary transfer rollers 5, all of which are tension rollers other than the drive roller 71, are driven to rotate in accordance with the rotation of the intermediate transfer belt 7. The toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the rotating intermediate transfer belt 7 at the primary transfer nip T1 by the action of the primary transfer roller 5. During primary transfer, a predetermined primary transfer bias (primary transfer voltage), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the primary transfer roller 5 by a primary transfer power supply (high-voltage power supply) E3, which serves as a primary transfer bias application unit. For example, when forming a full-color image, the yellow, magenta, cyan, and black toner images formed on each photosensitive drum 1 are sequentially primary transferred onto the intermediate transfer belt 7 so that they are superimposed on top of each other.

[0018] A secondary transfer roller 8, a roller-shaped secondary transfer member serving as a secondary transfer means, is disposed on the outer peripheral surface of the intermediate transfer belt 7, facing the secondary transfer opposing roller 73. The secondary transfer roller 8 is pressed against the secondary transfer opposing roller 73 and contacts the secondary transfer opposing roller 73 via the intermediate transfer belt 7, forming a secondary transfer portion (secondary transfer nip) T2, which is a contact portion between the intermediate transfer belt 7 and the secondary transfer roller 8. In this embodiment, the secondary transfer roller 8 is rotated in accordance with the rotation of the intermediate transfer belt 7. However, the secondary transfer roller 8 may be configured to be rotationally driven by a driving force transmitted from a driving source. The toner image formed on the intermediate transfer belt 7 is transferred (secondary transfer) by the action of the secondary transfer roller 8 onto the recording material P, which is being conveyed while being sandwiched between the intermediate transfer belt 7 and the secondary transfer roller 8, at the secondary transfer portion T2. During secondary transfer, a predetermined secondary transfer bias (secondary transfer voltage), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charge polarity of the toner, is applied to the secondary transfer roller 8 by a secondary transfer power supply (high-voltage power supply) E4, which serves as a secondary transfer bias application unit. The secondary transfer opposing roller 73 is electrically grounded (connected to ground). A roller corresponding to the secondary transfer opposing roller 73 in this embodiment may be used as a secondary transfer member, and a secondary transfer voltage of the same polarity as the normal charge polarity of the toner may be applied to it. In this case, the roller corresponding to the secondary transfer roller 8 in this embodiment may be used as a counter electrode and electrically grounded. Recording material (transfer material, recording medium, sheet) P, such as paper or plastic sheet, is stored in a recording material cassette 11, which serves as a recording material storage unit. The recording material P stored in the recording material cassette 11 is separated and fed one sheet at a time by a feed roller 12, which serves as a feeding unit. The recording material P is transported to a registration roller pair 14, which also serves as a transport unit, by a transport roller pair 13, which serves as a transport unit. Then, this recording material P is conveyed by a pair of registration rollers 14 to the secondary transfer portion T2 in synchronization with the toner image on the intermediate transfer belt 7.

[0019] The recording material P onto which the toner image has been transferred is transported to a fixing device 9 serving as a fixing means. The fixing device 9 heats and pressurizes the recording material P carrying the unfixed toner image by sandwiching it between a pair of fixing rotors and transporting it, thereby fixing (melting and adhering) the toner image to the surface of the recording material P. The recording material P onto which the toner image has been fixed is discharged (output) by a pair of discharge rollers 15 serving as a discharging means or the like onto a discharge tray (not shown) or the like provided outside the main body (outside the machine) of the image forming apparatus 100.

[0020] Meanwhile, deposits such as toner remaining on the photosensitive drum 1 after the primary transfer (primary transfer residual toner) are removed from the photosensitive drum 1 by a cleaning device 6 serving as cleaning means and collected. Also, deposits such as toner remaining on the intermediate transfer belt 7 after the secondary transfer (secondary transfer residual toner) are removed from the intermediate transfer belt 7 and collected by a belt cleaning device 74 serving as intermediate transfer body cleaning means.

[0021] Here, the position on the photosensitive drum 1 relative to the rotation direction of the photosensitive drum 1 where charging is performed by the charging device 2 is the charging position (charging portion) Pa. Furthermore, the position on the photosensitive drum 1 relative to the rotation direction of the photosensitive drum 1 where light is irradiated by the exposure device 3 is the exposure position (exposure portion) Pb. Furthermore, the position on the photosensitive drum 1 relative to the rotation direction of the photosensitive drum 1 where toner is supplied by the developing device 4 (the portion facing the developing sleeve 41) is the development position (developing portion) Pc. Furthermore, the position on the photosensitive drum 1 relative to the rotation direction of the photosensitive drum 1 where primary transfer of the toner image onto the intermediate transfer belt 7 is performed (corresponding to the above-mentioned primary transfer portion T1, which is the contact portion with the intermediate transfer belt 7) is the primary transfer position Pd. Furthermore, the position on the photosensitive drum 1 relative to the rotation direction of the photosensitive drum 1 where transfer residual toner is removed by a fur brush 62 (described later) of the cleaning device 6 is the brush cleaning position (brush cleaning portion) Pe. Furthermore, the position on the photosensitive drum 1 (contact portion with the cleaning blade 61) where the transfer residual toner is removed by a cleaning blade 61 (described later) of the cleaning device 6 in relation to the rotation direction of the photosensitive drum 1 is the blade cleaning position (blade cleaning portion) Pf. With respect to the rotation direction of the photosensitive drum 1, the charging position Pa, the exposure position Pb, the development position Pc, the primary transfer position Pd, the brush cleaning position Pe, and the blade cleaning position Pf are located in this order from upstream to downstream as viewed from the charging position Pa.

[0022] In this embodiment, the image forming unit 10 is provided with a pre-cleaning static eliminator 16 (FIG. 4), which will be described later.

[0023] FIG. 3 is a schematic block diagram showing the control configuration of the image forming apparatus 100 in this embodiment. The image forming apparatus 100 has a CPU 201 as a control unit (controller) that controls the image forming apparatus 100. The CPU 201 is connected to a RAM 202, which serves as a storage unit (storage unit) used as a working memory, and a ROM 203, which serves as a storage unit (storage unit) that stores programs executed by the CPU 201 and various data. The CPU 201 is also connected to a video controller 204 that processes image formation information input to the image forming apparatus 100. The video controller 204, which processes image information, processes image formation information input from an external device (not shown), such as a personal computer (PC) or an image reader, connected to the image forming apparatus 100. The CPU 201 controls each unit of the image forming apparatus 100 to form an image based on the image information processed and generated by the video controller 204. That is, the image forming apparatus 100 forms a toner image corresponding to the image information input to the CPU 201 on a recording material P and outputs (prints out) it.

[0024] The CPU 201 is connected to various power sources, such as a charging power source E1, a developing power source E2, a primary transfer power source E3, a secondary transfer power source E4, and a cleaning power source E5 (described later). The CPU 201 is also connected to various drive sources (drive devices), such as a drum drive motor D1 and a belt drive motor D2. The CPU 201 is also connected to various sensors, such as a current detection unit 21 (described later). The CPU 201 exchanges signals with these units to control the image forming operation and the setting operation of the cleaning bias (described later).

[0025] Although not shown in the drawings, in this embodiment, the charging power supply E1, the developing power supply E2, the primary transfer power supply E3, and the cleaning power supply E5 are provided independently for each image forming unit 10. However, at least one of these power supplies may be shared by all or some 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 photosensitive drum 1. However, the drum drive motor D1 may be shared by all or some of the photosensitive drums 1. Also, at least one of the drum drive motors may be shared with the belt drive motor.

[0026] The image forming apparatus 100 also executes a job (image output operation, print job), which is a series of operations that starts with a single start command and forms and outputs an image on one or more recording materials P. A job generally includes an image forming 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 forming process is a period during which electrostatic image formation, toner image formation, primary transfer of the toner image, and secondary transfer of the toner image are performed for the image that is actually formed and output on the recording materials P. This is referred to as the image formation period. More specifically, the timing of the image formation process differs depending on the positions where the electrostatic image formation, toner image formation, primary transfer of the toner image, and secondary transfer are performed. The pre-rotation process is a period from when a start command is input until the actual start of image formation, during which preparatory operations are performed before the image forming process. 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 tidying up operations (preparatory operations) are performed after the image forming 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.

[0027] 2.Detailed configuration of each part Next, we will explain in more detail the configuration of each part of the image forming apparatus 100. The cleaning device 6 and the pre-cleaning static eliminator 16 will be described in detail later.

[0028] <Charging device> In this embodiment, a corona charging device 2 is used as the charging means. The corona charging device 2 has a discharge electrode 2a and a grid electrode 2b. A high voltage is applied to the discharge electrode 2a and the grid electrode 2b, thereby uniformly charging the surface of the photosensitive drum 1 using a discharge phenomenon. In this embodiment, for example, during image formation, the discharge power supply E1a of the charging power supply E1 applies a voltage to the discharge electrode 2a so that a current of -1000 μA flows, and the grid power supply E1b of the charging power supply E1 applies a voltage of -600 V to the grid electrode 2b. This uniformly charges the surface of the rotating photosensitive drum 1 to a surface potential (charging potential, non-image area potential) of approximately -500 V. Note that the charging device 2 only needs to charge at least the image formation area (area where a toner image can be formed) on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1. In this embodiment, the charging device 2 charges almost the entire area of ​​the photosensitive drum 1 in the direction of the rotation axis. In this embodiment, the charging potential of the photosensitive drum 1 is negative, and the surface of the photosensitive drum 1 is charged to the negative polarity. The charging potential of the photosensitive drum 1 may be changed based on the environment, the state of the image forming apparatus 100, and the like, for example, in conjunction with the value of the developing bias.

[0029] The charging means is not limited to a corona charging type charging device. For example, a contact-type charging roller that contacts the surface of the photosensitive drum 1 may be used as the charging means. In this case, the surface of the photosensitive drum 1 is charged by utilizing the discharge phenomenon that occurs in the small gap between the photosensitive drum 1 and the charging roller. In this case, a charging bias of predetermined conditions is applied to the core of the charging roller. This charging bias can be an oscillating voltage in which a direct current component (DC bias) and an alternating current component (AC bias) are superimposed. For example, by setting the DC bias to -500 V and the AC bias to a peak-to-peak voltage value that is at least twice the discharge inception voltage when a DC voltage is applied in that environment, the surface of the photosensitive drum 1 can be uniformly charged to approximately -500 V.

[0030] <Exposure equipment> In this embodiment, a laser scanner was used as the exposure device 3. The exposure device 3 has a semiconductor laser as a light source, and performs image exposure based on image information on the photosensitive drum 1, the surface of which has been uniformly charged by the charging device 2. The surface potential (exposure potential, image area potential) of the photosensitive drum 1 formed by irradiating it with laser light by the exposure device 3 is approximately -200V.

[0031] In this embodiment, an example will be described in which the exposure means uses a semiconductor laser as a light source, but the exposure means may use other light sources such as an LED as a light source.

[0032] Furthermore, for example, by providing the image forming apparatus 100 with a potential measuring means capable of measuring the surface potential of the photosensitive drum 1 after exposure, it is possible to confirm whether the charging potential and exposure potential are actually at the specified potential.

[0033] <Developing device> In this embodiment, a developing device 4 employs a reversal development system using a two-component developer as a developing means. The developing device 4 includes a developer container 42 containing a two-component developer, which is a mixture of mainly non-magnetic toner particles (toner) and magnetic carrier particles (carrier). The developing device 4 also includes a developing sleeve 41 rotatably mounted at the opening of the developer container 42 as a developer carrier (developing member). In this embodiment, negatively charged toner (negative toner) was used as the toner. In this embodiment, the length of the developing sleeve 41 along its rotational axis is 325 mm. The developing sleeve 41 is rotated by a driving force transmitted from a drive motor serving as a drive source. The developing sleeve 41 may be driven by a dedicated drive source, or may be driven by a branched drive force transmitted from a drive source for another rotating member, such as the drive source for the photosensitive drum 1. In this embodiment, the developing sleeve 41 is rotated by a driving force transmitted from a drum drive motor D1. The developing sleeve 41 magnetically holds the developer in the developer container 42 by the action of a magnet (not shown) fixedly disposed inside the developing sleeve 41, and transports it to a developing section, which is a gap between the developing sleeve 41 and the photosensitive drum 1. In this embodiment, a developing bias, which is an oscillating voltage composed of a direct current (DC bias) and an AC component (AC bias) superimposed thereon, is applied to the developing sleeve 41 by a developing power supply E2. For example, a developing bias composed of a DC bias of -400 V superimposed on an AC bias with a Vpp of 1600 V is applied to the developing sleeve 41. This developing bias causes toner to adhere to the electrostatic latent image, thereby performing development. Note that the above setting value of the developing bias is merely an example, and the developing bias can be set to a value appropriately adjusted according to the charging potential and exposure potential of the photosensitive drum 1.

[0034] <Intermediate transfer belt> In this embodiment, an endless belt-like intermediate transfer belt 7 is used as the intermediate transfer body. In this embodiment, the intermediate transfer belt 7 has three layers, in this order from the back side (inner peripheral surface side) to the front side (outer peripheral surface side): a resin layer, an elastic layer, and a surface layer. Materials such as polyimide and polycarbonate are used as resin materials for the resin layer. The thickness of the resin layer is preferably 70 μm or more and 100 μm or less. Furthermore, materials such as urethane rubber and chloroprene rubber are used as elastic materials for the elastic layer. The thickness of the elastic layer is preferably 200 μm or more and 250 μm or less.

[0035] Furthermore, the material constituting the surface layer is preferably a material that can reduce the adhesion of toner to the surface of the intermediate transfer belt 7 and improve secondary transfer properties. For example, the base material may be one type of resin material such as polyurethane, polyester, or epoxy resin, or two or more types of elastic materials such as elastic rubber (elastic rubber, elastomer), butyl rubber, etc. Then, one or more types of powder or particles such as fluororesin, or particles with different particle sizes, that reduce surface energy and increase lubricity may be dispersed in the base material. The thickness of the surface layer is preferably 5 μm or more and 10 μm or less. In this embodiment, the intermediate transfer belt 7 is made by adding a conductive agent for adjusting electrical resistance, such as carbon black, to the belt, so that the volume resistivity is 1×10 8 Ω cm or more, 1×10 14 The resistance was adjusted to Ω·cm or less.

[0036] <Primary transfer roller> In this embodiment, the primary transfer means is a primary transfer roller 5, which is a roller formed by molding an elastic layer of hydrin rubber with adjusted electrical resistance around a metal shaft. The primary transfer roller 5 is positioned such that its center of rotation is offset approximately 2 mm downstream from the center of rotation of the photosensitive drum 1 in the direction of movement of the surface of the intermediate transfer belt 7, and is pressed toward the photosensitive drum 1 with a predetermined pressure. A primary transfer bias is applied to the primary transfer roller 5, transferring the toner image from the photosensitive drum 1 to the intermediate transfer belt 7. During this transfer, a small amount of carrier may be present on the photosensitive drum 1 in addition to the toner. Providing an elastic layer on the intermediate transfer belt 7 as described above reduces damage to the photosensitive drum 1 at the primary transfer portion T1, even if a hard object such as a carrier is sandwiched between the primary transfer portion T1 and the intermediate transfer belt 7.

[0037] <Toner> In this example, the toner is negatively charged by friction with the carrier. In this example, the carrier contains ferrite and has an average particle size of approximately 40 μm. The toner used in this example was a toner with an average particle size of approximately 6 μm, obtained by kneading a polyester-based resin binder with pigment and wax components, and then pulverizing and classifying the resulting mixture. In this example, multiple external components (external additives) were attached to the surface of the toner for purposes such as charge control, fluidity, and transferability improvement. In this example, in addition to silica and titanium oxide, inorganic fine particles with a primary particle average particle size of 30 nm to 300 nm, at least one of a cubic particle shape and a rectangular parallelepiped particle shape, and perovskite crystals were externally added. In this example, strontium titanate fine powder was externally added as the inorganic fine particles with perovskite crystals. The externally added component is preferably added in an amount of 0.05 parts by mass or more and 2.00 parts by mass or less per 100 parts by mass of the final toner particles before adding the externally added component to the toner particles, and in this example, 0.5 parts by mass of strontium titanate fine powder was externally added. It is more preferable that the strontium titanate used as the inorganic fine particles is a particle that has not been subjected to a sintering process.

[0038] Here, the average particle size (number average particle size) of the primary particles of the inorganic fine particles (external additive) can be determined by observing the inorganic fine particles present on the surface of toner particles using a scanning electron microscope. A Hitachi Ultra-High Resolution Field Emission Scanning Electron Microscope S-4800 (manufactured by Hitachi, Ltd.) can be used as the scanning electron microscope. Measurements can be performed after confirming the material of each particle through elemental analysis using an energy dispersive X-ray analyzer (manufactured by EDAX). For example, the number average particle size can be determined by measuring the major axis of the primary particles of 100 randomly selected inorganic fine particles in a field of view magnified up to 50,000 times. The observation magnification can be adjusted appropriately depending on the size of the inorganic fine particles.

[0039] The average particle size (weight average particle size) of the toner can be measured using a precision particle size distribution measuring device using the narrow hole electrical resistance method, "Coulter Counter Multisizer 3" (registered trademark, manufactured by Beckman Coulter, Inc.), equipped with a 100 μm aperture tube, and the accompanying dedicated software, "Beckman Coulter Multisizer 3 Version 3.51" (manufactured by Beckman Coulter, Inc.), for setting measurement conditions and analyzing measurement data, and can be calculated by analyzing the measurement data. Note that toner with an average particle size of 4 μm or more and 8 μm or less can be considered to be small particle size toner.

[0040] <Photosensitive drum> In this example, a negatively charged organic photoconductor (OPC) photosensitive drum 1 with a length of 360 mm in the direction of rotation axis and an outer diameter of 84 mm was used. In this example, the photosensitive drum 1 is configured by forming a photosensitive layer on a conductive substrate, the photoconductive layer being primarily composed of an organic photoconductor. An OPC typically comprises a conductive metal substrate, a charge generation layer made of organic materials, a charge transport layer, and a surface protection layer stacked in this order. In this example, the photosensitive drum 1 is configured with each layer made of materials described in, for example, Japanese Patent Application Laid-Open No. 2005-43806. In this example, a photosensitive drum 1 with the outermost layer surface hardened using, for example, an electron beam irradiation device (EC150 / 45 / 40mA, manufactured by Iwasaki Electric Co., Ltd.) was used.

[0041] The elastic deformation rate of the surface of the photosensitive drum 1 (for example, the photosensitive drum 1 of the type cured by the electron beam) is preferably 48% or more and 65% or less. The universal hardness value (HU) of the surface of this photosensitive drum 1 is 150 N / mm 2 More than 220N / mm 2 It is preferable that the elastic deformation ratio is less than the above range, or the universal hardness value (HU) is less than the above range, the surface of the photosensitive drum 1 is easily scratched, making it difficult to extend the life of the photosensitive drum 1. On the other hand, if the elastic deformation ratio is greater than the above range, or the universal hardness value (HU) is greater than the above range, the amount of scraping of the surface of the photosensitive drum 1 is too small, making it more likely that toner will melt onto the surface of the photosensitive drum 1.

[0042] In this embodiment, during image formation, the photosensitive drum 1 is normally rotated by a driving device at a process speed (peripheral speed) of 400 mm / s.

[0043] The universal hardness (HU) and elastic deformation rate of the surface of the photosensitive drum 1 were measured (obtained by performing a hardness test) using a Fischerscope H100V microhardness measuring device (manufactured by Fischer) under a temperature of 23°C and humidity of 50%RH. The Fischerscope H100V is a device that continuously measures hardness by contacting an indenter with the measurement target (the peripheral surface of the photosensitive drum 1), continuously applying a load to the indenter, and directly reading the indentation depth under the load. A Vickers square pyramidal diamond indenter with a facing angle of 136° was used as the indenter. The indenter was pressed against the peripheral surface of the photosensitive drum 1. The final load continuously applied to the indenter (final load) was 6 mN, and the time (holding time) for which the final load of 6 mN was applied to the indenter was 0.1 seconds. There were 273 measurement points.

[0044] 3.Cleaning device <Overall configuration and operation of the cleaning device> Next, the cleaning device 6 in this embodiment will be described in more detail. Figure 4 is a schematic cross-sectional view of the periphery of the cleaning device 6 in this embodiment.

[0045] The cleaning device 6 has a housing 66. The cleaning device 6 also has a fur brush (conductive fur brush roller) 62, which is a rotatable, conductive roller-shaped brush. The fur brush 62 functions as a toner scraping means (cleaning member) that scrapes toner off the photosensitive drum 1. The fur brush 62 also constitutes a cleaning auxiliary means (cleaning auxiliary member) that assists a cleaning blade 61 (described later) in removing toner from the surface of the photosensitive drum 1. The fur brush 62 is rotatably supported by the housing 66. The rotational axis of the fur brush 62 is approximately parallel to the rotational axis of the photosensitive drum 1. The fur brush 62 is disposed so as to abut against the surface of the photosensitive drum 1. In this embodiment, the fur brush 62 is disposed so that its penetration depth into the surface of the photosensitive drum 1 is 0.7 mm. Here, the penetration depth can be represented by the value obtained by subtracting the distance (shortest distance) between the base material on the rotational axis of the fur brush 62 (described later) and the photosensitive drum 1 from the length of the brush fibers (described later). The fur brush 62, while in contact with the surface layer of the photosensitive drum 1, receives a driving force from a driving motor as a driving source and is rotationally driven in the direction of arrow R3 (clockwise direction) in FIG. 4 at a predetermined rotational speed (the peripheral speed when the brush fibers are not deformed by an external force). In other words, the fur brush 62 is rotationally driven so as to move in the forward direction of the photosensitive drum 1 at the contact portion with the photosensitive drum 1. Note that the fur brush 62, which is a rotating member, may receive a driving force from a dedicated driving source, or may receive a branched driving force from a driving source of another rotating member, such as the driving source of the photosensitive drum 1. In this embodiment, the fur brush 62 is rotationally driven by a driving force transmitted from a drum driving motor D1. In this embodiment, the fur brush 62 is rotationally driven at a peripheral speed faster than the peripheral speed of the photosensitive drum 1 (the moving speed of the surface). In this embodiment, the fur brush 62 is rotationally driven at a peripheral speed that is 110% of the peripheral speed of the photosensitive drum 1.

[0046] The cleaning device 6 also has a cleaning blade (elastic cleaning blade) 61, which is a plate-like (blade-like) member made of an elastic material. The cleaning blade 61 functions as a toner scraping means (cleaning member) that scrapes toner off the photosensitive drum 1. The cleaning blade 61 is fixed to a support member 61a made of sheet metal or the like by adhesive or the like, and is supported by the housing 66 by the support member 61a being fixed to the housing 66. The longitudinal direction of the cleaning blade 61 is approximately parallel to the rotational axis direction of the photosensitive drum 1. The cleaning blade 61 is disposed so as to abut against the surface of the photosensitive drum 1 at a contact portion (blade cleaning position Pf) downstream in the rotation direction of the photosensitive drum 1 from a contact portion (brush cleaning position Pe) between the fur brush 62 and the photosensitive drum 1. In other words, the fur brush 62 is disposed so as to abut against the surface of the photosensitive drum 1 at a contact portion (brush cleaning position Pe) upstream in the rotation direction of the photosensitive drum 1 from a contact portion (blade cleaning position Pf) between the cleaning blade 61 and the photosensitive drum 1. The cleaning blade 61 is arranged so that the edge portion of the free end portion, which is one end portion in the width direction approximately perpendicular to the longitudinal direction of the cleaning blade 61 (the edge portion on the photosensitive drum 1 side), abuts against the photosensitive drum 1 with a predetermined pressure. The cleaning blade 61 also abuts against the photosensitive drum 1 in the counter direction to the rotation direction of the photosensitive drum 1 so that the free end portion is located upstream of the fixed end portion, which is the other end portion in the width direction of the cleaning blade 61, in the rotation direction of the photosensitive drum 1.

[0047] The cleaning device 6 also has a collection roller 63, which is a rotatable, conductive roller-shaped member. The collection roller 63 functions as a collection means (collection member) that collects toner from the fur brush 62, and also functions as a voltage application member (conductive member) that applies a voltage to the fur brush 62. The collection roller 63 is rotatably supported by a housing 66. The rotational axis of the collection roller 63 is approximately parallel to the rotational axis of the fur brush 62. The collection roller 63 is disposed so as to contact the fur brush 62 downstream of the contact point between the fur brush 62 and the photosensitive drum 1 in the rotation direction of the fur brush 62. The contact point between the fur brush 62 and the collection roller 63 in the rotation direction of the collection roller 63 is the collection position Pg. While in contact with the fur brush 62, the collection roller 63 receives a driving force transmitted from a drive motor serving as a drive source and is rotationally driven in the direction of arrow R4 in FIG. 4 (counterclockwise direction) at a predetermined rotational speed (circumferential speed). That is, the collection roller 63 is rotationally driven so as to move in the forward direction of the fur brush 62 at the contact portion with the fur brush 62. The collection roller 63, which is a rotating member, may receive a driving force from a dedicated driving source, or may receive a branched driving force from a driving source of another rotating member, such as the driving source of the photosensitive drum 1 or the fur brush 62. In this embodiment, the collection roller 63 is rotationally driven by a driving force transmitted from the drum driving motor D1. In this embodiment, the collection roller 63 is rotationally driven at a circumferential speed that is faster than the circumferential speed of the fur brush 62. In this embodiment, the collection roller 63 is rotationally driven at a circumferential speed that is 105% of the circumferential speed of the fur brush 62.

[0048] The cleaning device 6 also has a scraper member 64, which is a plate-like (blade-like) member made of an elastic material. The scraper member 64 functions as a removal means (removal member) that removes toner from the collection roller 63. The scraper member 64 is supported by a housing 66. Like the cleaning blade 61, the scraper member 64 may be supported by the housing 66 via a support member. The longitudinal direction of the scraper member 64 is approximately parallel to the rotational axis of the collection roller 63. The scraper member 64 is positioned so as to abut against the surface of the collection roller 63 downstream of the contact point (collection position Pg) between the collection roller 63 and the fur brush 62 in the rotation direction of the collection roller 63. The contact point between the collection roller 63 and the scraper member 64 in the rotation direction of the collection roller 63 is the removal position Ph. The scraper member 64 is arranged so that an edge portion (edge ​​portion on the collection roller 63 side) of a free end portion, which is one end portion in a lateral direction approximately perpendicular to the longitudinal direction, abuts against the collection roller 63 with a predetermined pressure. The scraper member 64 also abuts against the collection roller 63 in a counter direction to the rotation direction of the collection roller 63 so that the free end portion is located upstream of the fixed end portion, which is the other end portion in the lateral direction, in the rotation direction of the collection roller 63.

[0049] The cleaning device 6 also has a conveying screw 65 as a conveying means. The conveying screw 65 is disposed below the scraper member 64 in the direction of gravity. The conveying screw 65 conveys the toner collected in the housing 66 along the rotational axis of the photosensitive drum 1, for example, from the front side to the back side of the paper surface in FIG. 4.

[0050] A cleaning power supply (high-voltage power supply) E5 serving as a cleaning bias application unit constituting a potential switching unit for the fur brush 62 is connected to the collection roller 63. The cleaning power supply E5 is capable of applying a cleaning bias (cleaning voltage) to the collection roller 63. A current detection unit (current detection circuit) 21 serving as a current detection unit detects the current flowing through the cleaning roller 63 (fur brush 62, cleaning power supply E5) when the cleaning power supply E5 applies a cleaning bias to the collection roller 63. The cleaning power supply E5 is also connected to a CPU 201. The CPU 201 controls the timing of applying the cleaning bias to the fur brush 62 and the value (potential, voltage value) of the cleaning bias applied to the fur brush 62. In this embodiment, the cleaning bias is applied under constant voltage control. The cleaning power supply E5 incorporates a voltage detection unit (not shown) serving as a voltage detection unit, and is capable of constant voltage control of the output voltage so that the voltage value detected by the voltage detection unit remains substantially constant. As will be described in detail later, in this embodiment, the CPU 201 controls the value (potential, voltage value) of the cleaning bias applied to the fur brush 62 based on the detection result of the current detection unit 21.

[0051] In this embodiment, when cleaning the toner on the surface of the photosensitive drum 1, a cleaning bias, which is a DC voltage of positive polarity (plus, positive), which is opposite to the normal charging polarity of the toner, is applied to the collection roller 63 by the cleaning power supply E5. The cleaning period is, more specifically, when the image formation area on the photosensitive drum 1, which is defined for the recording material P and is related to the direction of movement of the surface of the photosensitive drum 1, passes through the brush cleaning position Pe. As will be described in detail later, the fur brush 62 is made of a conductive material such as conductive fibers. When the fur brush 62 comes into contact with the collection roller 63 to which the cleaning bias is applied, the fur brush 62 assumes a potential whose absolute value is slightly smaller than that of the cleaning bias applied to the collection roller 63. In this way, the fur brush 62 assumes a positive potential, which is opposite to the normal charging polarity of the toner. As a result, the toner on the surface of the photosensitive drum 1 is not only mechanically captured by the fur brush 62 rubbing against the surface of the photosensitive drum 1, but also electrostatically captured. This further improves cleaning efficiency. In this way, at least a part of the toner on the surface of the photosensitive drum 1 is collected by the fur brush 62 before it reaches the cleaning blade 61 .

[0052] The toner that has moved from the surface of the photosensitive drum 1 to the fur brush 62 at the contact portion between the photosensitive drum 1 and the fur brush 62 moves to the collection roller 63 at the contact portion between the fur brush 62 and the collection roller 63 due to the potential difference between the fur brush 62 and the collection roller 63. In other words, the collection roller 63 has a potential that is slightly larger in absolute value than the fur brush 62 and that is opposite in polarity to the normal charging polarity of the toner. As a result, at least a portion of the toner collected by the fur brush 62 electrostatically moves to the collection roller 63. The toner that has moved to the collection roller 63 at the contact portion between the fur brush 62 and the collection roller 63 is scraped off the surface of the collection roller 63 by the scraper member 64 at the contact portion between the collection roller 63 and the scraper member 64. The toner scraped off the surface of the collection roller 63 by the scraper member 64 falls by gravity.

[0053] Furthermore, the toner on the surface of the photosensitive drum 1 that has not been collected by the fur brush 62 is scraped off from the surface of the photosensitive drum 1 by the cleaning blade 61 and is collected in the housing 66 .

[0054] The toner thus collected in the housing 66 is transported by the transport screw 65 disposed in the lower part (bottom) of the housing 66 and is discharged to the outside of the housing 66. Then, this toner is transported through a transport path (not shown) provided in the main body of the image forming apparatus 100 toward a collection container (not shown) provided in the main body of the image forming apparatus 100.

[0055] In this embodiment, the application of the cleaning bias to the recovery roller 63 is started in synchronization with the timing at which the driving of the charging device 2 (charging process of the surface of the photosensitive drum 1) starts after the rotation of the photosensitive drum 1 starts.

[0056] <Cleaning blade> The cleaning blade 61 in this embodiment is made of urethane rubber, has a length of 340 mm in the longitudinal direction, and is in contact with the photosensitive drum 1 with a predetermined contact pressure. From the viewpoint of cleaning performance, the preferred physical properties of the cleaning blade 61 are as follows: It is preferable that the hardness (IRHD) is in the range of 65° or more and 85° or less. It is also preferable that the coefficient of resilience in a 25°C environment is in the range of 15% or more and 60% or less. It is also preferable that the elongation at break in a tensile test is 300% or less. It is also preferable that the Young's modulus is 50 kg / cm. 2 More than 200kg / cm 2 It is preferable that the 100% modulus is in the range of 4.0 MPa or more and 9.0 MPa or less. It is more preferable that the hardness (IRHD) is in the range of 70° or more and 80° or less, the elongation at break in a tensile test is in the range of 250% or less, and the rebound resilience at 25°C is in the range of 15% or more and 35% or less.

[0057] The methods for measuring the above physical properties are as follows. The hardness (IRHD) of the prepared cleaning blade 61 was measured in accordance with JIS K 6253 using a Wallace hardness tester. The 100% modulus of the prepared cleaning blade 61 was measured in accordance with JIS K 6251 using a tensile tester (Unitron TS-3013) manufactured by Ueshima Seisakusho. The elongation at break in the tensile test was measured in accordance with JIS K 6251 using a tensile tester (Unitron TS-3013) manufactured by Ueshima Seisakusho. The rebound resilience of the prepared cleaning blade 61 was measured in an environment of 25°C in accordance with JIS K 6255 using a Lübke rebound resilience tester manufactured by Ueshima Seisakusho. The Young's modulus of the produced cleaning blade 61 was measured in accordance with JIS K 6251 using a tensile tester (Unitron TS-3013) manufactured by Ueshima Seisakusho.

[0058] <Fur Brush> The fur brush 62, which is a rotating member, is constructed by implanting fibers on a rotating shaft. In this embodiment, the fur brush 62 is manufactured by wrapping a fabric material (substrate) on which fibers are implanted around a metal rotating shaft having a diameter of 12.1 mm. As an example, the fibers (brush fibers) of the fur brush 62 are made of a bundle of acrylic monofilaments having a thickness of 6 denier, and are implanted at a density of 70 kF / inch. 2The fibers are implanted on the substrate at a density of 1 / 2 a fiber (fiber density per single fiber). As an example, the overall outer diameter of the fur brush 62 (when the brush fibers are not deformed by external force) is 21.4 mm. The length of the brush fibers, calculated by subtracting the diameter of the core (12.1 mm) and the thickness of the substrate (0.15 mm × 2) from the outer diameter, is 4.5 mm. In this embodiment, conductive fibers are used as the brush fibers, with the electrical resistance of the fibers adjusted by dispersing a certain amount of conductive particles such as carbon as a conductive agent in the fiber matrix. From the viewpoint of cleaning performance, the preferred physical properties of the fur brush 62 are as follows: The tensile strength of a single fiber (herein simply referred to as the "tensile strength of the brush fiber") at a temperature of 23°C and a humidity of 50% is preferably in the range of 50 cn / dtex or more and 80 cn / dtex or less. If the tensile strength of the brush fibers is less than 50 cn / dtex, the fibers may collapse early, making it difficult for the fur brush 62 to collect toner. If the tensile strength of the brush fibers exceeds 80 cn / dtex, the surface of the photosensitive drum 1 may be damaged in the circumferential direction. Furthermore, the electrical resistance of the fur brush 62 is preferably in the range of 10 Log Ω or more and 12 Log Ω or less under an environment of 23°C temperature and 50% humidity. If the electrical resistance is less than 10 Log Ω, excessive current may flow from the fur brush 62 to the photosensitive drum 1, which may cause positive memory. If the electrical resistance exceeds 12 Log Ω, it may become difficult for a sufficient current to flow through the fur brush 62, making it difficult for the fur brush 62 to collect toner.

[0059] The methods for measuring the above physical properties are as follows. The tensile strength of a single fiber of the brush fiber at a temperature of 23°C and humidity of 50% was measured in accordance with JIS L 1096:2010, Testing Methods for Woven and Knit Fabrics. The electrical resistance of the fur brush 62 was measured using a Canon-made device as follows: The fur brush 62 was brought into contact with a metal roller with a penetration depth of 1 mm, and the fur brush 62 was rotated while a voltage of +400 V was applied to the fur brush 62. The electrical resistance of the fur brush 62 was measured by detecting the current flowing through the fur brush 62.

[0060] <Recovery roller> In this embodiment, the recovery roller 63 is a solid metal roller made of SUS (stainless steel) and having an outer diameter of φ13 mm.

[0061] <Scraper component> The scraper member 64 may be made of a nylon sheet material, a polyurethane rubber blade, etc. In this embodiment, substantially the same material as the cleaning blade 61 described above is used.

[0062] 4. Pre-cleaning static elimination device In this embodiment, the image forming apparatus 100 has a pre-cleaning static eliminator 16 as a static eliminator that eliminates static on the surface of the photosensitive drum 1 that passes through the primary transfer position Pd and then enters the brush cleaning position Pe. In this embodiment, the pre-cleaning static eliminator 16 irradiates the surface of the photosensitive drum 1 with light to eliminate static on the surface of the photosensitive drum 1. The position on the photosensitive drum 1 where static elimination is performed (where light is irradiated) by the pre-cleaning static eliminator 16 in relation to the rotation direction of the photosensitive drum 1 is the pre-cleaning static eliminator position (pre-cleaning static eliminator) Pi. In other words, in relation to the rotation direction of the photosensitive drum 1, the pre-cleaning static eliminator position Pi is located downstream of the primary transfer position Pd and upstream of the brush cleaning position Pe.

[0063] In this embodiment, the pre-cleaning static eliminator 16 uses an LED as a static elimination light source. However, this is not limited thereto, and the pre-cleaning static eliminator 16 may use other static elimination light sources, such as a semiconductor laser. In this embodiment, the pre-cleaning static eliminator 16 controls the power supply to the light source using constant current control, with the current set to 50 mA. The pre-cleaning static eliminator 16 irradiates the surface of the photosensitive drum 1 with light (pre-cleaning exposure) to elimi- nate static electricity from the surface of the photosensitive drum 1. The pre-cleaning static eliminator 16 uniformly eliminates static electricity from the surface of the photosensitive drum 1 to approximately -50 V before the fur brush 62 electrostatically collects toner. As described above, the charged potential of the photosensitive drum 1 is approximately -500 V, and the exposed potential of the photosensitive drum 1 is approximately -200 V. "Static elimination" refers to the removal of at least a portion of the charge. The pre-cleaning static eliminator 16 only needs to eliminate static electricity from at least the image formation area on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1. In this embodiment, the pre-cleaning static eliminator 16 performs static elimination processing on almost the entire area of ​​the photosensitive drum 1 in the direction of the rotation axis.

[0064] Here, when a voltage of a polarity opposite to the normal charge polarity of the toner is applied to the fur brush 62 and a necessary current (cleaning current) flows between the fur brush 62 and the photosensitive drum 1, the toner is electrostatically collected from the photosensitive drum 1 by the fur brush 62. On the other hand, if the absolute value of the voltage applied to the fur brush 62 is too large, the charge polarity of the toner on the photosensitive drum 1 is reversed, making it difficult to electrostatically collect the toner from the photosensitive drum 1 by the fur brush 62. If the pre-cleaning static eliminator 16 is not provided, it may be difficult to collect the toner by the fur brush 62, for example, because the potential difference between the fur brush 62 and the photosensitive drum 1 is different between a solid black image area and a solid white image area (non-image area). In contrast, by providing the pre-cleaning static eliminator 16 in the image forming apparatus 100 as in this embodiment, the potential difference between the fur brush 62 and the photosensitive drum 1 is appropriately maintained, making it easier for the fur brush 62 to appropriately collect the toner.

[0065] However, the present invention is not limited to this, and the image forming apparatus 100 does not necessarily have to have the pre-cleaning static eliminator 16 .

[0066] 5. Suppression of toner fusion by fur brush and setting of cleaning bias The effect of the fur brush 62 in this embodiment in suppressing toner fusion will now be described. Fig. 5 is a schematic diagram for explaining the process by which toner fusion occurs. Fig. 6 is a schematic diagram for explaining the effect of the fur brush 62 in this embodiment in suppressing toner fusion.

[0067] As shown in Figure 5, the cleaning blade 61 in contact with the photosensitive drum 1 rubs against the photosensitive drum 1, causing the temperature to rise in the vicinity of the contact point ("blade nip") between the cleaning blade 61 and the photosensitive drum 1. As a result, the toner present in the vicinity of the blade nip melts and adheres to the photosensitive drum 1. Toner fusion is a phenomenon that occurs in this way.

[0068] Normally, a deposit of external additives ("external additive dam layer") (Figure 6) of the toner is formed near the blade nip, preventing the toner from entering the vicinity of the blade nip. As a result, the temperature rise of the toner is suppressed, and the occurrence of toner melting is suppressed.

[0069] However, the small particle size toner required for high image quality in recent years has high fluidity and is prone to destroying the external dam layer (Figure 5). In addition, as the process speed increases, the frictional heat generated by the friction between the cleaning blade 61 and the photosensitive drum 1 also tends to increase, making toner melting more likely to occur.

[0070] Therefore, in this embodiment, as shown in FIG. 6 , the fur brush 62 to which the cleaning bias is applied is positioned upstream of the cleaning blade 61 in the direction of movement of the surface of the photosensitive drum 1. This allows the fur brush 62 to collect the toner before it reaches the external dam layer. As a result, the external dam layer is stably maintained, suppressing the occurrence of toner fusion. In this embodiment, a cleaning bias of a polarity opposite to the normal charging polarity of the toner is applied to the conductive fur brush 62, and the toner is collected by the fur brush 62. In this embodiment, for example, in the initial stage of use of the fur brush 62, a cleaning bias of +400 V is applied to the fur brush 62, and a necessary current (cleaning current) is passed between the fur brush 62 and the photosensitive drum 1, allowing the fur brush 62 to collect the toner.

[0071] 7 is a graph showing the change in the outer diameter of the fur brush 62 as the cumulative usage of the fur brush 62 increases. As the cumulative usage of the fur brush 62 increases (after repeated use), the fibers tend to collapse (permanently deform) due to the influence of the components (photosensitive drum 1, collection roller 63) that have entered and are in contact with the fur brush 62, and the outer diameter of the fur brush 62 tends to decrease. As a result, the contact width between the photosensitive drum 1 and the fur brush 62 in the direction of movement of the surface of the photosensitive drum 1 decreases, and the contact resistance (electrical resistance) between the photosensitive drum 1 and the fur brush 62 increases.

[0072] 8 is a graph showing the relationship between the voltage value of the cleaning bias and the value of the current flowing through the fur brush 62. FIG. 8 shows an example in which the surface potential of the photosensitive drum 1 entering the brush cleaning position Pe is approximately -50 V. As shown in FIG. 8, when the value of the cleaning bias applied to the fur brush 62 is fixed at a predetermined voltage value, the value of the current flowing through the fur brush 62 decreases as the cumulative usage of the fur brush 62 increases. As a result, the current (cleaning current) required to collect toner no longer flows between the fur brush 62 and the photosensitive drum 1, and the toner cleaning ability of the fur brush 62 decreases.

[0073] FIG. 9 is a graph showing the relationship between the voltage value of the cleaning bias and the toner cleaning performance of the fur brush 62 when the fur brush 62 is in the early stages of use and when the cumulative usage of the fur brush 62 has increased. In FIG. 9, the vertical axis represents the amount of toner (optical density) remaining on the photosensitive drum 1 after passing the brush cleaning position Pe (before reaching the blade cleaning position Pf). FIG. 9 also shows an example in which the surface potential of the photosensitive drum 1 entering the brush cleaning position Pe is approximately -50 V. As shown in FIG. 9, when the same cleaning bias voltage is applied to the fur brush 62, the fur brush 62 with increased cumulative usage has a larger amount of toner slipping through the fur brush 62 than the fur brush 62 in the early stages of use. If the amount of toner that has slipped through the fur brush 62 increases, the toner that has slipped through can damage the external dam layer near the blade nip. As a result, the toner approaches the heated blade nip, melts, and adheres to the photosensitive drum 1, potentially causing toner fusion.

[0074] FIG. 10 is a graph showing the relationship between the voltage value of the cleaning bias applied to the fur brush 62 and the potential (post-brush potential) of the photosensitive drum 1 after passing the brush cleaning position Pe (before reaching the charging position Pa). FIG. 10 shows an example in which the surface potential of the photosensitive drum 1 entering the brush cleaning position Pe is approximately −50 V. As can be seen from FIG. 10 , if the voltage value of the cleaning bias applied to the fur brush 62 is set high in advance, assuming that the outer diameter of the fur brush 62 will become smaller, an excessive current may flow between the fur brush 62 and the photosensitive drum 1 in the initial stage of use of the fur brush 62. This is because, in the initial stage of use of the fur brush 62, the outer diameter of the fur brush 62 does not change and the contact resistance between the photosensitive drum 1 and the fur brush 62 is low. As a result, the surface potential of the photosensitive drum 1 after passing the brush cleaning position Pe becomes positive (+0 V or higher), which is the opposite polarity to the normal charging polarity of the photosensitive drum 1, and this may cause an image defect known as “positive memory” on the photosensitive drum 1.

[0075] 6. Control of cleaning bias in this embodiment In this embodiment, the cleaning bias is applied under constant voltage control. In this embodiment, the voltage value (target voltage, set voltage) of the cleaning bias is determined so as to allow a necessary current (cleaning current) to flow between the fur brush 62 and the photosensitive drum 1. The necessary cleaning current is determined in advance through experiments or the like and stored in the ROM 203. In this embodiment, a cleaning bias setting operation (also simply referred to as a "setting operation" herein) for setting (determining, adjusting) the voltage value of the cleaning bias is generally performed as follows: The voltage value of the cleaning bias is determined based on the current detection results when multiple test biases (test voltages) are applied to the fur brush 62. That is, multiple test biases are applied to the fur brush 62 under constant voltage control. The current detection unit 21 detects the currents that flow during this application. This allows the voltage-current characteristic (linear or curved) to be obtained. In this embodiment, the voltage-current characteristic obtained by applying multiple test biases to the fur brush 62 is a curve, so three or more test biases (six in this embodiment) are applied to the fur brush 62. Then, based on the voltage-current characteristics, a voltage value that provides the required cleaning current is calculated, and the voltage value of the cleaning bias can be changed so that the required cleaning current flows in response to changes in the contact resistance between the photosensitive drum 1 and the fur brush 62, etc.

[0076] The CPU 201 controls the setting operation so that it is executed when no image formation is taking place. The setting operation is typically executed in a pre-rotation process (such as when the power is turned on first thing in the morning). However, this is not limited to this, and the setting operation can be executed at any timing when no image formation is taking place. For example, the setting operation may be executed in a pre-rotation process for each job. Also, for example, the setting operation may be executed in an inter-sheet process for each predetermined number of sheets of image formation. Also, for example, the setting operation may be executed in a post-rotation process.

[0077] Here, in the setting operation, a plurality of test biases with different voltage values ​​are applied to the fur brush 62. In this embodiment, the plurality of test biases are preset so that they can be applied within a range including a voltage value that provides the necessary cleaning current regardless of the cumulative usage of the fur brush 62. For example, in this embodiment, the necessary cleaning current is approximately 10 μA, and the voltage value of the cleaning bias in the initial stage of use of the fur brush 62 is approximately +400 V. In this case, for example, the plurality of test biases are applied in increments of +200 V from near 0 V up to approximately +1000 V.

[0078] Therefore, if the conditions of the surface potential on the photosensitive drum 1 entering the brush cleaning position Pe when multiple test biases are applied to the fur brush 62 are the same as the conditions during normal image formation (also referred to here as "normal image formation conditions"), the following may occur: When the test bias is applied to the fur brush 62, the current flowing between the fur brush 62 and the photosensitive drum 1 becomes excessive, and the surface potential of the photosensitive drum 1 becomes positive, which is the opposite polarity to the normal charging polarity, and positive memory may occur. This is because if the surface potential of the photosensitive drum 1 entering the brush cleaning position Pe is near 0 V (approximately -50 V in this embodiment), the positification threshold, which will be described later, is low, and when a large current flows through the fur brush 62, a positive potential is likely to be formed on the surface of the photosensitive drum 1 (the potential is likely to be inverted) (FIG. 12).

[0079] Therefore, in this embodiment, the surface potential of the photosensitive drum 1 entering the brush cleaning position Pe when multiple test biases are applied to the fur brush 62 in the setting operation is set to a value greater on the side of the normal charging polarity of the toner (negative polarity in this embodiment) than the surface potential of the photosensitive drum 1 entering the brush cleaning position Pe during image formation. Note that the surface potential of the photosensitive drum 1 entering the brush cleaning position Pe can also be referred to as the surface potential of the photosensitive drum 1 immediately before it first reaches the brush cleaning position Pe after passing through the primary transfer position Pd. Here, the surface potential of the photosensitive drum 1 entering the brush cleaning position Pe or the surface potential of the photosensitive drum 1 immediately before it reaches the brush cleaning position Pe is also simply referred to as the "pre-brush potential."

[0080] In this embodiment, during image formation, a charging bias is applied to the charging device 2, a primary transfer bias is applied to the primary transfer roller 5, and the pre-cleaning exposure by the pre-cleaning static eliminator 16 is turned on. Therefore, during image formation, the pre-brush potential is approximately -50 V. In contrast, in this embodiment, during the setting operation, a charging bias is applied to the charging device 2, but a primary transfer bias is not applied to the primary transfer roller 5, and the pre-cleaning exposure by the pre-cleaning static eliminator 16 is not turned on. Therefore, the pre-brush potential when multiple test biases are applied to the fur brush 62 during the setting operation can be set to a value greater toward the normal toner charging polarity (negative polarity in this embodiment) than the pre-brush potential during image formation. For example, the pre-brush potential when multiple test biases are applied to the fur brush 62 during the setting operation is approximately -300 V. This pre-brush potential during the setting operation can be appropriately set in consideration of factors such as suppressing positive memory and the accuracy of determining the voltage value of the cleaning bias to obtain the required cleaning current. Typically, a range including the non-image portion potential formed by charging during image formation, for example, approximately -200V to -700V, is suitable. This makes it possible to prevent the current flowing between the fur brush 62 and the photosensitive drum 1 from becoming excessively large and causing positive memory. This is because by increasing the pre-brush potential toward the normal charging polarity of the toner and raising the positification threshold (described later), even if a large amount of current flows through the fur brush 62, it is difficult for a positive potential to be formed on the surface of the photosensitive drum 1 (the potential is difficult to invert) (FIG. 12).

[0081] In this embodiment, the means for increasing the pre-brush potential to the negative polarity side compared to the normal image forming conditions is to turn on the charging bias, turn off the primary transfer bias (0 V), and turn off the pre-cleaning exposure (light off), but this is not limited to this. Examples of other means include the following. For example, instead of turning off the primary transfer bias, the primary transfer bias can be increased toward the normal charging polarity side of the toner with respect to the value during image formation. In this case, the primary transfer bias can be made to have the same polarity (positive polarity) as during image formation but with a smaller absolute value, or can be made to have the opposite polarity (negative polarity) to that during image formation. Also, for example, instead of turning off the pre-cleaning exposure, the light amount (μJ / cm) of the pre-cleaning exposure can be increased. 2 ) can be made smaller than that during image formation. When either of the above means is used, the charging bias is ON. Note that, as an example will be described later, the value of the charging bias may be the same as that during image formation, or may be different. In addition, in a configuration in which the pre-cleaning static eliminator 16 is not provided, the primary transfer bias may be turned OFF (or increased toward the normal charging polarity of the toner relative to the value during image formation).

[0082] In this embodiment, during the setting operation, the developing bias is applied ON (typically the same developing bias as during image formation) in order to suppress adhesion of toner and carrier to the photosensitive drum 1. Since the developing bias often does not affect the surface potential of the photosensitive drum 1, it may be turned ON or OFF during the setting operation.

[0083] Furthermore, the relationship between the brush front potential during the setting operation and the brush front potential during image formation described above only needs to be established in at least the image formation area on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1. In this embodiment, the relationship between the brush front potential during the setting operation and the brush front potential during image formation described above is established in almost the entire area of ​​the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1.

[0084] Furthermore, in this embodiment, since the pre-cleaning static eliminator 16 is provided, the pre-brush potential during image formation is approximately the same value in the image portion and the non-image portion in the image forming area on the photosensitive drum 1 that has just passed the primary transfer position Pd. However, in a configuration where the pre-cleaning static eliminator 16 is not provided, the pre-brush potential during image formation may differ between the image portion and the non-image portion in the image forming area on the photosensitive drum 1 that has just passed the primary transfer position Pd. Therefore, more specifically, the pre-brush potential during image formation is represented by the surface potential of the non-image portion in the image forming area on the photosensitive drum 1 that has just passed the primary transfer position Pd.

[0085] 7. Control Procedure Next, an example of the procedure for the setting operation in this embodiment will be described with reference to the flowchart of FIG.

[0086] First, the CPU 201 controls the photosensitive drum 1 to be charged by applying a charging bias while the photosensitive drum 1 is rotating, without applying a primary transfer bias or turning on the pre-cleaning exposure light (S101). In this embodiment, the intermediate transfer belt 7 is rotating in contact with the photosensitive drum 1, the developing sleeve 41 is also rotating, and the same developing bias as during image formation is applied to the developing sleeve 41. Also, at this time, for example, a voltage is applied to the discharge electrode 2a so that a current of -1000 μA flows, and a voltage of -400 V is applied to the grid electrode 2b. As a result, the surface of the rotating photosensitive drum 1 is uniformly charged to a surface potential of approximately -300 V. As a result, the pre-brush potential becomes approximately -300 V.

[0087] FIG. 12 is a graph showing the relationship between the pre-brush potential and the threshold value of the cleaning current at which the surface potential of the photosensitive drum 1 becomes positive (also referred to here as the "positive potential threshold"). As described above, during normal image formation, the charging bias is applied, the primary transfer bias is applied, and the pre-cleaning exposure is turned on, and the pre-brush potential becomes approximately -50 V. In contrast, as described above, during the setting operation, the pre-brush potential becomes approximately -300 V. As shown in FIG. 12, the positive potential threshold can be increased by making the pre-brush potential during the setting operation larger toward the normal charging polarity of the toner than the pre-brush potential during image formation. This makes it possible to suppress the occurrence of positive memory.

[0088] Next, the CPU 201 controls the current detection unit 21 to detect the current flowing through the fur brush 62 while gradually changing the test bias applied to the fur brush 62 (for example, by 200 V) (S102). Next, the CPU 201 determines a voltage value of the cleaning bias that allows the cleaning current required for image formation to flow between the fur brush 62 and the photosensitive drum 1 based on the obtained relationship between the voltage value and the current value (voltage-current characteristics) (S104). Here, the CPU 201 interpolates the detected data to calculate a voltage value that provides a predetermined current value (required cleaning current). The CPU 201 also determines the voltage value of the cleaning bias by adjusting the potential difference between the brush front potential during the setting operation and the brush front potential during image formation. That is, the voltage value of the cleaning bias during image formation is determined by adding the difference (-250 V) between the brush front potential during the setting operation (-300 V) and the brush front potential during image formation (-50 V) to the voltage value calculated based on the detected data. 13 is a graph showing a method for determining the voltage value of the cleaning bias based on detection results obtained by applying multiple test biases. FIG. 13 shows the voltage-current characteristics when the pre-brush potential is −50 V (voltage-current characteristics obtained by shifting the obtained detection results by the difference in pre-brush potential). The CPU 201 stores the determined voltage value of the cleaning bias in the RAM 202 (S105). During image formation, the CPU 201 controls the application of the cleaning bias, which is constant-voltage controlled at the voltage value determined as described above, to the fur brush 62.

[0089] FIG. 14(a) is a timing chart showing the operation of each component during normal image formation, and FIG. 14(b) is a timing chart showing the operation of each component during setup operation. FIGS. 14(a) and 14(b) illustrate an example in which operation starts from a state in which the photosensitive drum 1 is stopped. As shown in FIG. 14(a), during image formation, application of the charging bias begins almost simultaneously with the start of rotation of the photosensitive drum 1 (t1). Thereafter, for example, application of the development bias, application of the primary transfer bias, turning on the pre-cleaning exposure light, and application of the cleaning bias begin (t2 to t5) in accordance with the timing when the charged area on the photosensitive drum 1 reaches the development position Pc, the primary transfer position Pd, the pre-cleaning charge discharging position Pi, and the brush cleaning position Pe. Note that application of the primary transfer bias, turning on the pre-cleaning exposure light, and application of the cleaning bias may begin, for example, almost simultaneously with the start of rotation of the photosensitive drum 1 or almost simultaneously with the start of application of the charging bias. On the other hand, as shown in Figure 14(b), during the setting operation, application of the charging bias begins almost simultaneously with the start of rotation of the photosensitive drum 1 (t1). Thereafter, application of the developing bias begins in time with the charged area on the photosensitive drum 1 reaching the developing position Pc (t2). Thereafter, application of the test bias begins after the charged area on the photosensitive drum 1 reaches the brush cleaning position Pe (t5). During the setting operation, application of the primary transfer bias and lighting of the pre-cleaning exposure are not performed.

[0090] The voltage value of the cleaning bias in the initial stage of use of the fur brush 62 may be a predetermined value. In this case, the setting operation can be performed when the cumulative usage amount of the fur brush 62 reaches a predetermined usage amount. For example, the image forming apparatus 100 may be provided with a counter (component counter) 205 ( FIG. 3 ) configured with a storage unit that stores an index value (usage history information) correlated with the cumulative usage amount of the fur brush 62. Any index value correlated with the cumulative usage amount of the fur brush 62 can be used as this index value. For example, this index value can be the number of images formed on a sheet, the rotation time or number of rotations (rotation distance) of the photosensitive drum 1 or the fur brush 62, etc. If the fur brush 62 is replaceable, this index value is reset to an initial value (e.g., 0) when the fur brush 62 is replaced, and the value after replacement is counted again. As an example, the counter 205 can accumulate and store the number of images formed on a sheet each time an image is formed on one side of the recording material P (it may also be configured to accumulate the number of sheets converted into a recording material of a predetermined size). Then, for example, when the count value of the counter 205 exceeds a predetermined count value during execution of a job, the CPU 201 can perform control so that the set operation is executed during the post-rotation process after image formation of the job is completed.

[0091] However, as described above, the setting operation can be performed at any timing during non-image formation, such as during the pre-rotation process after the image forming apparatus 100 is powered on, during the pre-rotation process at the start of a job, during the sheet interval process, or during the post-rotation process. The frequency with which the setting operation is performed can also be appropriately set depending on the configuration of the fur brush 62. For example, the setting operation can be performed every time the image forming apparatus 100 is powered on or at the start of a job, or when the count value of a necessity determination counter for determining whether the setting operation needs to be performed exceeds a predetermined threshold. This necessity determination counter can count any event suitable for setting the frequency with which the setting operation is performed, such as the elapsed time since the previous setting operation was performed, the number of times the job has been executed, or the number of times the power has been turned on.

[0092] 8. Test Results The results of a test verifying the effectiveness of this embodiment are described below. Two million images were formed in a high-humidity, high-temperature environment (30°C / 80%), and image defects due to toner fusion on the photosensitive drum 1 and positive memory were confirmed. As toner fusion on the photosensitive drum 1 progressed, white spots, where parts of the image were missing, appeared on the recording material P on which a solid black image was formed. If white spots of 2 mm or more appeared on the recording material P on which a solid black image was formed, among the 2 million images, the image was judged as poor (×); if no white spots appeared, the image was judged as good (◯). Furthermore, as positive memory progressed, density unevenness occurred in the halftone image. If the density difference on the recording material P on which the halftone image was formed was outside the allowable range, the image was judged as poor (×); if it was within the allowable range, the image was judged as good (◯). Furthermore, if either of the above image defects occurred, the test was discontinued. The tests were conducted for a case in which the setting operation was performed periodically according to this embodiment to adjust the cleaning bias voltage value (in this embodiment, performed once a day), and for Comparative Examples 1 and 2 in which the cleaning bias voltage value was fixed. In Comparative Example 1, the cleaning bias voltage value was fixed at +400 V, and in Comparative Example 2, the cleaning bias voltage value was fixed at +800 V. The configurations of the image forming apparatuses in Comparative Examples 1 and 2 are substantially the same as the image forming apparatus in this embodiment, except for the above points. The results are shown in Table 1.

[0093] [Table 1]

[0094] In Comparative Example 1, after forming 1 million images, an image defect due to toner fusion occurred. This is thought to be due to a decrease in the cleaning ability of the fur brush 62. In Comparative Example 2, after forming 200,000 images, an image defect due to positive memory occurred. This is thought to be due to excessive current flowing through the photosensitive drum 1. On the other hand, in this example, neither an image defect due to toner fusion nor an image defect due to positive memory occurred during the formation of 2 million images.

[0095] In this embodiment, multiple test biases are applied under constant voltage control during the setting operation. However, multiple test biases may also be applied under constant current control. At least one of the multiple test biases may be applied under constant voltage control, and at least one of the multiple test biases may be applied under constant current control. When the test biases are applied under constant current control, the voltage value generated when the test bias is applied is detected by a voltage detection unit (voltage detection circuit) serving as a voltage detection means. In other words, the cleaning bias can be determined based on the current or voltage detection results when multiple test biases (test voltages or test currents) are applied to the fur brush 62. It is sufficient to obtain a voltage-current characteristic (a straight line or a curve) corresponding to the electrical resistance of the fur brush 62 (more specifically, the contact resistance between the photosensitive drum 1 and the fur brush 62). Here, constant current control refers to control that adjusts the output of a power supply so that the current supplied to the target is approximately constant at a target current. Constant voltage control refers to control that adjusts the output of a power supply so that the voltage applied to the target is approximately constant at a target voltage.

[0096] In this embodiment, the cleaning bias is controlled to a constant voltage, but the present invention is not limited to this, and the cleaning bias may be controlled to a constant current. In this case, the setting operation can determine, for example, an initial voltage value when the cleaning bias is applied.

[0097] 9.Effects As described above, in this embodiment, the image forming apparatus 100 includes a rotatable photosensitive member (photosensitive drum) 1, a charging device 2 that charges the surface of the photosensitive member 1 at a charging position Pa, a charging bias application unit (charging power supply) E1 that applies a charging bias to the charging device 2 to charge the surface of the photosensitive member 1, a developing device 4 that supplies toner to the surface of the photosensitive member 1, a transfer device (primary transfer roller) 5 that transfers the toner from the surface of the photosensitive member 1 to a transferee (intermediate transfer belt) 7 at a transfer position (primary transfer position) Pd, a transfer bias application unit (primary transfer power supply) E3 that applies a transfer bias (primary transfer bias) to the transfer device 5 to transfer the toner from the photosensitive member 1 to the transferee 7, and a blade cleaning position Pf that is downstream of the transfer position Pd and upstream of the charging position Pa in terms of the rotation direction of the photosensitive member 1 and comes into contact with the surface of the photosensitive member 1 to remove the toner from the surface of the photosensitive member 1. The cleaning device includes a cleaning blade 61, a rotatable roller-shaped brush (fur brush) 62 that contacts the surface of the photosensitive member 1 at a brush cleaning position Pe that is downstream of the transfer position Pd and upstream of the blade cleaning position Pf in the rotation direction of the photosensitive member 1, and removes toner from the surface of the photosensitive member 1, a cleaning bias application unit (cleaning power supply) E5 that applies a cleaning bias of a polarity opposite to the normal charging polarity of the toner to the brush 62, a detection unit (current detection unit in this embodiment) 21 that detects the current flowing through the brush 62 or the voltage applied to the brush 62, and a control unit (CPU) 201 that can control the setting operation to be performed during non-image formation, which sets the value of the cleaning bias based on the detection results by the detection unit 21 when multiple test biases are applied to the brush 62 by the cleaning bias application unit E5. In this embodiment, when the surface potential of the photosensitive member 1 immediately before it first reaches the brush cleaning position Pe after passing the transfer position Pd is defined as the pre-brush potential, the control unit 201 controls the pre-brush potential of the area on the photosensitive member that passes the brush cleaning position Pe when multiple test biases are applied to the brush 62 during the setting operation so that it becomes a larger value toward the normal charging polarity of the toner than the pre-brush potential of the non-image area on the photosensitive member during image formation.

[0098] In this embodiment, the control unit 201 controls the brush 62 to apply multiple test biases when an area on the photoconductor that passed the charging position Pa when a charging bias is applied to the charging device 2 and that passed the transfer position Pd when no transfer bias is applied to the transfer device 5 passes the brush cleaning position Pe. In particular, in this embodiment, the image forming apparatus 100 has a pre-cleaning static eliminator 16 that performs a static elimination process to remove at least a portion of the charge on the surface of the photoconductor 1 at a pre-cleaning static elimination position Pi that is downstream of the transfer position Pd and upstream of the brush cleaning position Pe with respect to the rotation direction of the photoconductor 1, and the control unit 201 controls the brush 62 to apply multiple test biases when an area on the photoconductor that passed the charging position Pa when a charging bias is applied to the charging device 2, that passed the transfer position Pd when no transfer bias is applied to the transfer device 5, and that passed the pre-cleaning static elimination position Pi when no static elimination process is being performed by the pre-cleaning static eliminator passes the brush cleaning position Pe. In this embodiment, the pre-cleaning static eliminator 16 irradiates the surface of the photosensitive member 1 with light to eliminate static electricity.

[0099] As described above, according to this embodiment, it is possible to apply an appropriate cleaning bias to the fur brush 62 regardless of the cumulative usage amount of the fur brush 62 while suppressing the occurrence of positive memory on the photosensitive drum 1. This makes it possible to maintain stable toner cleaning performance by the fur brush 62 and suppress the occurrence of toner fusion on the photosensitive drum 1 for a long period of time.

[0100] [Example 2] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus 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.

[0101] 1. Overview of this Example In this embodiment, the potential in front of the brush (value of the charging bias) during the setting operation is changed based on the cumulative usage amount (usage history information) of the fur brush 62.

[0102] As the cumulative usage of the fur brush 62 increases, the outer diameter of the fur brush 62 decreases, increasing the contact resistance between the photosensitive drum 1 and the fur brush 62. This reduces the value of the current flowing between the fur brush 62 and the photosensitive drum 1. Therefore, during the setting operation, the brush front potential (charging bias value) is increased toward the normal charging polarity of the toner, thereby increasing the value of the current flowing between the fur brush 62 and the photosensitive drum 1. This improves the accuracy of determining the cleaning bias voltage value that provides the required cleaning current while suppressing the occurrence of positive memory in the photosensitive drum 1. Furthermore, the voltage value of at least one of the multiple test biases in the setting operation may be changed based on the cumulative usage of the fur brush 62. For example, the absolute value of at least one of the multiple test biases can be increased as the cumulative usage of the fur brush 62 increases. Typically, the absolute value of at least the largest test bias among the multiple test biases can be increased as the cumulative usage of the fur brush 62 increases, so as to include a voltage value that provides the required cleaning current.

[0103] 2. Control Procedure Next, an example of the procedure for the setting operation in this embodiment will be described with reference to the flowchart of FIG.

[0104] First, the CPU 201 acquires usage history information for the fur brush 62 from the counter 205 (S201). Here, the usage history information for the fur brush 62 is assumed to be the number of images formed since the fur brush 62 was replaced. Next, the CPU 201 calculates the value of the charging bias based on the usage history information for the fur brush 62 (S202). In this embodiment, as the cumulative usage amount of the fur brush 62 increases, the absolute value of the voltage value of the charging bias (the voltage applied to the grid 2b) is increased. As a result, as the cumulative usage amount of the fur brush 62 increases, the pre-brush potential is increased toward the normal toner charging polarity. In this embodiment, information indicating the relationship between the cumulative usage amount (usage history information) of the fur brush 62 and the voltage value of the charging bias is preset and stored in the ROM 203. The CPU 201 reads the charging bias setting corresponding to the acquired usage history information from the ROM 203 and uses it to control the charging power supply E1 (grid power supply unit E1b).

[0105] Next, the CPU 201 controls the photosensitive drum 1 to be charged by applying the charging bias determined as described above while the photosensitive drum 1 is rotating, without applying the primary transfer bias or turning on the pre-cleaning exposure light (S203). In this embodiment, the intermediate transfer belt 7 is rotating in contact with the photosensitive drum 1, the developing sleeve 41 is also rotating, and the same developing bias as during image formation is applied to the developing sleeve 41. Also, at this time, for example, in the early stages of use of the fur brush 62 (0 to 1 million images), a voltage is applied to the discharge electrode 2a so that a current of -1000 μA flows, and a voltage of -400 V is applied to the grid electrode 2b. This causes the surface of the rotating photosensitive drum 1 to be uniformly charged to a surface potential of approximately -300 V. As a result, the potential in front of the brush becomes approximately -300 V. On the other hand, when the cumulative usage of the fur brush 62 increases (when the number of images formed on more than 1 million sheets) a voltage is applied to the discharge electrode 2a so that a current of -1000 μA flows, and a voltage of -700 V is applied to the grid electrode 2b. As a result, the surface of the rotating photosensitive drum 1 is uniformly charged to a surface potential of approximately -600 V. As a result, the potential in front of the brush becomes approximately -600 V.

[0106] Next, the CPU 201 controls the current detection unit 21 to detect the current flowing through the fur brush 62 while gradually changing the test bias applied to the fur brush 62 (e.g., by 200 V each) (S204). At this time, the CPU 201 may also control the absolute value of at least one of the multiple test bias voltages to increase as the cumulative usage of the fur brush 62 increases. For example, the step width of the multiple test bias voltages may be increased. Alternatively or additionally, the number of multiple test bias voltages may be increased. Next, the CPU 201 determines a cleaning bias voltage value that allows the cleaning current required for image formation to flow between the fur brush 62 and the photosensitive drum 1 based on the obtained relationship between the voltage value and the current value (voltage-current characteristics) (S206). The method for determining this cleaning bias voltage value is the same as in the first embodiment. However, in this embodiment, the voltage value of the cleaning bias is determined by adjusting the potential difference between the pre-brush potential during the setting operation and the pre-brush potential during image formation, depending on the pre-brush potential during the setting operation that is changed as described above. The CPU 201 stores the determined voltage value of the cleaning bias in the RAM 202 (S207). Then, during image formation, the CPU 201 controls the cleaning bias to be applied to the fur brush 62 at the constant voltage controlled at the voltage value determined as described above.

[0107] As described above, in this embodiment, the image forming apparatus 100 includes a memory unit (counter) 205 that stores usage history information correlated with the cumulative usage amount of the brush 62, and the control unit 201 controls the pre-brush potential of the area on the photoconductor that passes through the brush cleaning position Pe when the multiple test biases during the setting operation are applied to the brush 62 based on the usage history information. In this embodiment, when the cumulative usage amount of the brush 62 indicated by the usage history information is a first usage amount, the control unit 201 controls the pre-brush potential of the area on the photoconductor that passes through the brush cleaning position Pe when the multiple test biases during the setting operation are applied to the brush 62 to be a first surface potential. When the cumulative usage amount of the brush 62 indicated by the usage history information is a second usage amount greater than the first usage amount, the control unit 201 controls the pre-brush potential of the area on the photoconductor that passes through the brush cleaning position Pe when the multiple test biases during the setting operation are applied to the brush 62 to be a second surface potential that is greater than the first surface potential and is closer to the normal charging polarity of the toner. The control unit 201 can also change the value of at least one of the multiple test biases based on the usage history information. For example, the control unit 201 can control the absolute value of the largest test bias among the multiple test biases when the usage history information indicates a first usage amount, so that the absolute value of the largest test bias among the multiple test biases is larger than the absolute value of the largest test bias among the multiple test biases when the usage history information indicates a second usage amount greater than the first usage amount. The control unit 201 can also control the difference between the test biases among the multiple test biases sequentially applied to the brush 62 to be a first difference when the usage history information indicates a first usage amount, and can control the difference between the test biases among the multiple test biases sequentially applied to the brush 62 to be a second difference greater than the first difference when the usage history information indicates a second usage amount greater than the first usage amount.In addition, the control unit 201 can control the number of multiple test biases to be a first number when the cumulative usage amount of the brush 62 indicated by the usage history information is a first usage amount, and can control the number of multiple test biases to be a second number greater than the first number when the cumulative usage amount of the brush 62 indicated by the usage history information is a second usage amount greater than the first usage amount.

[0108] As described above, according to this embodiment, by changing the brush front potential in accordance with the usage history information of the fur brush 62 during the setting operation, it is possible to improve the accuracy of determining the voltage value of the cleaning bias while suppressing the occurrence of positive memory.

[0109] [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.

[0110] In the above-described embodiment, the image forming apparatus did not include a means for discharging the surface of the photosensitive drum after it passed the pre-cleaning charge-removal position and before it reached the charging position. However, the image forming apparatus may include such a means. FIG. 16 is a schematic cross-sectional view of the cleaning device and its surroundings in another example of an image forming apparatus. In the image forming apparatus shown in FIG. 16, elements having the same or corresponding functions or configurations as those in the image forming apparatus of the above-described embodiment are described using the same reference numerals. The image forming apparatus 100 shown in FIG. 16 includes a pre-charge charge-removal device 17 as a charge-removal device for discharging the surface of the photosensitive drum 1 that enters the charging position Pa after passing the blade cleaning position Pf. In this example, the pre-charge charge-removal device 17 irradiates the surface of the photosensitive drum 1 with light to remove charge. The position on the photosensitive drum 1 where charge is removed (light is irradiated) by the pre-charge charge-removal device 17 relative to the rotational direction of the photosensitive drum 1 is the pre-charge charge-removal position (pre-charge charge-removal unit) Pj. That is, with respect to the rotation direction of the photosensitive drum 1, the pre-charge neutralization position Pj is located downstream of the blade cleaning position Pf and upstream of the charging position Pa. The pre-charge neutralization device 17 may have a configuration similar to that of the pre-cleaning neutralization device 16. By providing the pre-charge neutralization device 17 in the image forming apparatus 100, the surface potential of the photosensitive drum 1 entering the charging position Pa can be uniformly neutralized, facilitating stable and uniform charging at the charging position Pa. Because it is difficult to equalize the surface potential of the photosensitive drum 1 that has been made positive using the pre-charge neutralization device 17, it is desirable to suppress positive memory even in a configuration provided with the pre-charge neutralization device 17. In the image forming apparatus 100 shown in FIG. 16, the pre-charge neutralization device 17 neutralizes the surface of the photosensitive drum 1 during image formation and setup operations. In this way, the image forming apparatus 100 may have a pre-charge static eliminator 17 that performs a static elimination process to remove at least a portion of the charge on the surface of the photoconductor 1 at a pre-charge static elimination position Pj that is downstream of the blade cleaning position Pf and upstream of the charging position Pa in terms of the rotation direction of the photoconductor 1. This pre-charge static eliminator 17 may perform the static elimination process by irradiating the surface of the photoconductor 1 with light.

[0111] In the above-described embodiment, the rotatable roller-shaped brush is rotationally driven to move in the same direction as the photosensitive member at the contact portion with the photosensitive member, but this is not limited to this. For example, the rotatable roller-shaped brush may be rotationally driven to move in the opposite direction to the photosensitive member at the contact portion with the photosensitive member, so that it rotates at a speed different from the photosensitive member. Similarly, in the above-described embodiment, the collection member is rotationally driven to move in the same direction as the brush at the contact portion with the brush, but it may be rotationally driven to move in the opposite direction.

[0112] Furthermore, in the above-described embodiment, a configuration in which electricity is removed by light is used as the electricity removal means, but this is not limited to this, and it is also possible to use a configuration in which electricity is removed by AC discharge using a charger, or by dissipating charge to a conductive member in contact with the photosensitive member.

[0113] The present invention can also be applied to a configuration in which the normal charging polarity of the photosensitive member is positive. Even when the normal charging polarity of the photosensitive member is positive, the surface potential of the photosensitive member may become opposite to the normal charging polarity due to the application of a bias to the fur brush, which can cause the same problems as those in the above-described embodiment.

[0114] In addition to or instead of turning off the primary transfer bias in the above-described embodiment, the intermediate transfer belt may be separated from the photosensitive drum.

[0115] Furthermore, while the image forming apparatus in the above-described embodiment employs an intermediate transfer system, the present invention can also be applied to a direct transfer image forming apparatus. As is well known to those skilled in the art, a tandem image forming apparatus employing a direct transfer system has a recording material carrier formed of an endless belt or the like instead of the intermediate transfer member in the above-described embodiment. The toner image formed on the photosensitive member of each image forming station is then directly transferred to a recording material carried and transported on the recording material carrier, similar to the primary transfer in an intermediate transfer image forming apparatus. Applying the present invention in accordance with the above-described embodiment to such an image forming apparatus can achieve the same effects as those of the above-described embodiment.

[0116] Furthermore, in the above-described embodiment, the number of image forming units is four, but the present invention is not limited to this embodiment and can also be applied to an image forming apparatus having five or more (e.g., six) image forming units. Furthermore, in the above-described embodiment, the image forming apparatus is configured to use four colors of toner, Y, M, C, and K, but the present invention is not limited to this embodiment. The image forming apparatus may be configured to use a transparent toner or a metallic color toner in addition to Y, M, C, and K, or in place of any one of these colors.

[0117] Furthermore, in the above-described embodiment, the image forming apparatus is a color image forming apparatus having multiple image forming units, but the present invention can also be applied to, for example, a monochrome image forming apparatus having only one image forming unit. [Explanation of symbols]

[0118] 1 Photosensitive drum 2. Charging device 3 Exposure equipment 4. Developing device 5 Primary transfer roller 6 Cleaning Device 16 Pre-cleaning static eliminator 61 Cleaning blade 62 Fur Brush 63 Collection roller E1 charging power supply E5 Cleaning Power Supply 201 CPU

Claims

1. a rotatable photoreceptor; a charging device for charging the surface of the photoreceptor at a charging position; a charging bias applying section that applies a charging bias to the charging device to charge the surface of the photosensitive member; a developing device that supplies toner to the surface of the photoreceptor; a transfer device that transfers toner from the surface of the photoreceptor to a transfer target at a transfer position; a transfer bias applying unit that applies a transfer bias to the transfer device to transfer the toner from the photosensitive member to the transfer-receiving member; a cleaning blade that contacts the surface of the photoreceptor at a blade cleaning position downstream of the transfer position and upstream of the charging position in the rotation direction of the photoreceptor, and removes toner from the surface of the photoreceptor; a rotatable roller-shaped brush that contacts the surface of the photoreceptor at a brush cleaning position downstream of the transfer position and upstream of the blade cleaning position in the rotation direction of the photoreceptor, and removes toner from the surface of the photoreceptor; a cleaning bias applying unit that applies a cleaning bias having a polarity opposite to the normal charging polarity of the toner to the brush; a detection unit that detects a current flowing through the brush or a voltage applied to the brush; a control unit capable of controlling the setting operation of setting the cleaning bias value based on the detection result by the detection unit when the cleaning bias application unit applies a plurality of test biases to the brush so as to be executed during non-image formation; and When the surface potential of the photosensitive member immediately before it first reaches the brush cleaning position after passing the transfer position is defined as the pre-brush potential, the control unit controls the pre-brush potential of the area on the photosensitive member that passes the brush cleaning position when the multiple test biases during the setting operation are applied to the brush so that it becomes a larger value toward the normal charging polarity of the toner than the pre-brush potential of the non-image area on the photosensitive member during image formation.

2. The image forming apparatus of claim 1, wherein the control unit controls the brush so that the multiple test biases are applied to the brush when an area on the photosensitive element that passes the charging position when the charging bias is applied to the charging device and that passes the transfer position when the transfer bias is not applied to the transfer device passes the brush cleaning position.

3. a pre-cleaning static elimination device that performs static elimination processing to remove at least a part of the charges on the surface of the photosensitive member at a pre-cleaning static elimination position that is downstream of the transfer position and upstream of the brush cleaning position in the rotation direction of the photosensitive member; The image forming apparatus described in claim 1, characterized in that the control unit controls the brush so that the multiple test biases are applied to the brush when an area on the photosensitive body that passes the charging position when the charging bias is applied to the charging device, passes the transfer position when the transfer bias is not applied to the transfer device, and passes the pre-cleaning charge removal position when the charge removal process is not being performed by the pre-cleaning charge removal device passes the brush cleaning position.

4. 4. The image forming apparatus according to claim 3, wherein the pre-cleaning static eliminator performs the static elimination process by irradiating the surface of the photosensitive member with light.

5. a storage unit for storing usage history information correlated with the cumulative usage amount of the brush; The image forming apparatus according to claim 1, characterized in that the control unit controls the brush pre-potential of the area on the photosensitive element that passes through the brush cleaning position when the multiple test biases during the setting operation are applied to the brush based on the usage history information.

6. The image forming apparatus of claim 5, wherein the control unit controls the brush pre-potential of the area on the photosensitive body that passes through the brush cleaning position when the multiple test biases during the setting operation are applied to the brush so that it becomes a first surface potential when the cumulative usage amount of the brush indicated by the usage history information is a first usage amount, and controls the brush pre-potential of the area on the photosensitive body that passes through the brush cleaning position when the multiple test biases during the setting operation are applied to the brush so that it becomes a second surface potential that is larger than the first surface potential and is toward the normal charging polarity of the toner than the first surface potential when the cumulative usage amount of the brush indicated by the usage history information is a second usage amount that is larger than the first usage amount.

7. 6. The image forming apparatus according to claim 5, wherein the control unit controls the value of at least one of the plurality of test biases to be changed based on the usage history information.

8. The image forming apparatus according to claim 7, wherein the control unit controls the absolute value of the test bias having the largest absolute value among the plurality of test biases when the cumulative usage amount of the brush indicated by the usage history information is a second usage amount greater than the first usage amount, so that the absolute value of the test bias having the largest absolute value among the plurality of test biases is greater than the absolute value of the test bias having the largest absolute value among the plurality of test biases when the cumulative usage amount of the brush indicated by the usage history information is a second usage amount greater than the first usage amount.

9. The image forming apparatus of claim 7, wherein the control unit controls the difference between the test biases in the plurality of test biases applied sequentially to the brush to be the first difference when the cumulative usage amount of the brush indicated by the usage history information is a first usage amount, and controls the difference between the test biases in the plurality of test biases applied sequentially to the brush to be the second difference when the cumulative usage amount of the brush indicated by the usage history information is a second usage amount greater than the first usage amount.

10. The image forming apparatus of claim 7, wherein the control unit controls the number of the plurality of test biases to be a first number when the cumulative usage amount of the brush indicated by the usage history information is a first usage amount, and controls the number of the plurality of test biases to be a second number greater than the first number when the cumulative usage amount of the brush indicated by the usage history information is a second usage amount greater than the first usage amount.

11. 11. An image forming apparatus according to claim 1, further comprising a pre-charge charge eliminating device that performs a charge eliminating process to remove at least a portion of the charge on the surface of the photosensitive member at a pre-charge charge eliminating position that is downstream of the blade cleaning position and upstream of the charging position in the rotation direction of the photosensitive member.

12. 12. The image forming apparatus according to claim 11, wherein the pre-charge static eliminator performs the static elimination process by irradiating the surface of the photosensitive member with light.

Images