Image forming apparatus

Abstract

The present disclosure relates to an image forming apparatus. An image forming apparatus includes a photosensitive member, a charging member, an exposure device, a developing device, a transfer member, a brush, a voltage application portion, and a control portion that controls a surface potential of the photosensitive member at a brush contact position. When a value obtained by subtracting a value of the surface potential of the photosensitive member in the brush contact position from a value of a brush voltage is defined as a contact position potential difference, the control portion controls the surface potential of the photosensitive member in the brush contact position so that the contact position potential difference changes from a first potential difference to a second potential difference in a predetermined direction, and then the contact position potential difference changes from the second potential difference to a third potential difference in the predetermined direction, the predetermined direction being either one of an increasing direction or a decreasing direction.

Description

TECHNICAL FIELD

[0001] The present application relates to an image forming apparatus using an electrophotographic method, such as a laser printer, a copier, and a facsimile apparatus. BACKGROUND

[0002] Image forming apparatuses using an electrophotographic method are widely used. In such image forming apparatuses, a process cartridge system is widely used in which a photosensitive drum and process components working together therewith are separable from a main body of the apparatus.

[0003] In recent years, in order to miniaturize the main body and the process cartridge of the image forming apparatus, a cleanerless system has been proposed (Japanese Laid-Open Patent Application No. 2003-91181). In the cleanerless image forming apparatus, there is no dedicated cleaning unit that removes and collects residual transfer toner remaining on the surface of the photosensitive drum after the transfer process. In the cleanerless image forming apparatus, the residual transfer toner remaining on the surface of the photosensitive drum is removed from the surface of the photosensitive drum by the developing component during the developing process, collected, and reused (cleaning at the same time as the developing).

[0004] However, in the cleanerless image forming apparatus, the cleaning unit that collects the residual transfer toner is not located downstream of the transfer portion and upstream of the charging portion in the rotation direction of the photosensitive drum. Therefore, the position on the photosensitive drum to which paper dust adheres during the transfer process becomes insufficiently charged during the charging process, and image defects such as blotchy missing ink can occur during the developing process.

[0005] Therefore, a configuration has been proposed in which a brush member (fixed brush) is placed downstream of the transfer portion and upstream of the charging portion in the rotation direction of the photosensitive drum to collect paper dust adhering to the surface of the photosensitive drum during the transfer process (Japanese Laid-Open Patent Application No. 2005-114754). Not only paper dust, but also residual transfer toner and toner on the non-image portion of the photosensitive drum (atomized toner) are accumulated on the brush member. If too much toner is accumulated on the brush member, the brush member can not hold the toner, and the toner can slip off the brush member and adhere to, for example, a charging member that is a charging component, resulting in a failure in charging.

[0006] On the contrary, a voltage can be applied to the brush member to make the toner more easily slip through. However, even when the brush member is conductive and a voltage is applied to the brush member in this way, because the brush member is in substantially constant contact with the photosensitive drum, the toner is collected and accumulated on the brush member. Therefore, in order to prevent the toner from being excessively accumulated on the brush member, it is necessary, for example, to periodically discharge the toner from the brush member and clean it.

[0007] Further improvements are required with respect to the brush member for collecting paper dust. For example, it is required to support cleaning of the brush member by discharging toner of a regular (normal) polarity (main charging polarity of the toner during the developing process) and a non-regular polarity (opposite polarity of the regular polarity) from the brush member. For example, when the potential difference between the voltage applied to the brush member and the surface potential of the photosensitive drum is changed to clean the brush member, if a large amount of toner is instantaneously discharged from the brush member, the large amount of toner can adhere to a charged member. For example, if toner adheres to a charging roller as a charged member, image defects can occur during the rotation period of the charging roller. Therefore, it is also required to address the problem caused by toner discharged from the brush member by the cleaning operation of the brush member. Furthermore, while the paper dust collecting brush in the cleanerless device suppresses image defects caused by the influence of paper dust collection, it can also cause image defects due to excessive toner accumulation. By way of example, at the instant when a paper sheet enters the roller nip portion between the transfer member and the drum (hereinafter referred to as "transfer nip portion") during feeding, the drum instantaneously changes from a state of being in contact with the transfer member to which a transfer voltage is applied to a state in which a paper sheet having electrical resistance is sandwiched between the drum and the transfer member. Therefore, at the instant when the paper sheet enters, the drum potential fluctuates in the transfer nip portion. When the potential fluctuation portion passes through the brush opposite portion, the charged toner accumulated in the brush is discharged into the potential fluctuation portion on the drum. The discharged toner is transferred to the paper sheet, which can cause image defects. Such image defects can be suppressed by controlling the potential of the transfer member, the brush voltage, or both to control the potential difference between the brush and the drum. In other words, by discharging toner accumulated in the brush by these controls during a period that does not affect the image, the occurrence of such defects can be suppressed.

[0008] For example, if the brush voltage cannot be freely changed due to a common power source, brush cleaning by controlling the brush potential can not be possible. Furthermore, from the viewpoint of miniaturization and cost reduction, it is desirable that the long side length of the transfer member be short (narrow width). In particular, when the long side length of the transfer member is narrower than the width of the paper sheet, when the paper sheet passes through the transfer portion, because the paper core is not pressed on the roller by the transfer portion, it is expected to have an effect of preventing paper dust from the paper core from adhering to the drum. However, in order to transfer toner in the image forming area, the length of the transfer member in the long side direction must be wider than the image forming area. When the long side length of the transfer member is shortened for this effect, brush cleaning using the transfer member cannot be performed on an area exceeding the width of the transfer member. Therefore, toner discharge and associated image defects can occur at the brush edge that is not cleaned by the transfer portion.

[0009] Accordingly, it is an object of the present application to improve the cleaning performance of a brush member positioned in contact with a photosensitive member. It is also an object of the present application to reduce the occurrence of image defects caused by a cleaning brush, while achieving miniaturization and cost reduction of a cleanerless image forming apparatus. SUMMARY

[0010] The above-mentioned object is achieved by an image forming apparatus according to the present application. In summary, the present application is an image forming apparatus including: a rotatable photosensitive member; a charging member configured to charge a surface of the photosensitive member at a charging portion; an exposure device that exposes the surface of the charged photosensitive member to light at an exposure position, and is configured to form an electrostatic latent image on the surface of the photosensitive member; a developing device that supplies toner of a normal polarity to the electrostatic latent image of the surface of the photosensitive member at a developing position, and is configured to form a toner image on the surface of the photosensitive member; a transfer member configured to transfer the toner image on the surface of the photosensitive member to a transfer material at a transfer position; a brush that contacts the surface of the photosensitive member at a brush contact position downstream of the transfer position and upstream of the charging position with respect to a rotation direction of the photosensitive member; a voltage application portion configured to apply a brush voltage to the brush; and a control portion configured to control a surface potential of the photosensitive member at the brush contact position, wherein toner remaining on the surface of the photosensitive member after transfer is collected by the developing device, and wherein when a value defined as a contact position potential difference, which is a value obtained by subtracting a value of the surface potential of the photosensitive member at the brush contact position from a value of the brush voltage, is a first potential difference, the control portion controls the surface potential of the photosensitive member at the brush contact position such that the contact position potential difference changes from the first potential difference to a second potential difference in a predetermined direction, which is either one of an increasing direction or a decreasing direction, and then the contact position potential difference changes from the second potential difference to a third potential difference in the predetermined direction.

[0011] To solve the above-mentioned problems, the present application has the following configuration. An image forming apparatus including: an image bearing member; a charging member configured to charge a surface of the image bearing member at a charging portion; an exposing member configured to expose the surface of the image bearing member to light to form an electrostatic latent image on the surface of the image bearing member charged by the charging member; a developing member configured to develop the electrostatic latent image formed on the surface of the image bearing member with a developer and form a developer image; a containing portion configured to contain the developer to be supplied to the developing member; a transferring member configured to transfer the developer image formed by the developing member to a recording material in a transfer portion; a contact member provided upstream of the charging portion and downstream of a transfer position with respect to a rotation direction of the image bearing member, and contacting the surface of the image bearing member in a first contact portion; a first applying member configured to apply a charging voltage to the charging member; a second applying member configured to apply a developing voltage to the developing member; a third applying member configured to apply a contact voltage to the contact member; a pre-exposing member configured to expose the surface of the image bearing member downstream of the first contact portion and upstream of the charging portion; and a control member configured to control, via the developing member, collection of toner remaining on the image bearing member, which is not transferred to the recording material by the transferring member, to the containing portion by controlling the developing voltage applied by the second applying member; wherein during a non-image forming operation, a section in which a potential difference is formed to generate an electrostatic force that moves the developer charged in a normal polarity from the contact member toward the image bearing member in the first contact portion is provided, and wherein before an area of the image bearing member in which the first contact portion is formed in the section by rotating the image bearing member moves to a second contact portion, the control member controls to switch a surface potential to be formed in the area such that a potential difference is formed to generate an electrostatic force that moves the developer charged in the normal polarity from the image bearing member toward the developing member.

[0012] Further features of the present application will become apparent from the following description of example embodiments with reference to the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a schematic cross-sectional view of an image forming apparatus.

[0014] Figure 2 is a timing chart showing the control of Embodiment 1.

[0015] Figure 3 is a timing chart showing the control of a modified example of Embodiment 1.

[0016] Figure 4 Parts (a) and (b) of are schematic views showing the behavior of toner accumulating on the brush.

[0017] Figure 5 Parts (a) and (b) are schematic diagrams illustrating changes in the brush's posture.

[0018] Figure 6 This is a timing diagram illustrating the control in Embodiment 2.

[0019] Figure 7 This is a schematic block diagram illustrating the control mode of the image forming apparatus.

[0020] Figure 8 This is a schematic block diagram showing the power supply configuration of the image forming apparatus.

[0021] Figure 9 This is a schematic diagram illustrating another example of how the surface potential of a photosensitive drum can be controlled.

[0022] Figure 10 This is a schematic cross-sectional view showing the image forming apparatus according to Embodiment 3.

[0023] Figure 11 This is a diagram illustrating routine cleaning control using the transfer roller in a comparative example with Example 3.

[0024] Figure 12 Parts (a) and (b) are diagrams illustrating the behavior of toner accumulation on the brush component in Example 3.

[0025] Figure 13 This is a diagram showing the lengths of the photosensitive drum and the components in contact with the photosensitive drum in Example 3.

[0026] Figure 14 This is a diagram of the brush cleaning control in Example 3.

[0027] Figure 15 This is a graph showing the relationship between the brush voltage at the brush contact area and the drum surface potential in Example 3.

[0028] Figure 16 This is a diagram of image defects caused by cleaning defects in Example 3.

[0029] Figure 17 This is a diagram of the brush cleaning control in Example 5. Detailed Implementation

[0030] The following is a more detailed description of the image forming apparatus according to the present invention, with reference to the accompanying drawings.

[0031] 1. Structure and operation of the image forming apparatus

[0032] Figure 1is a schematic cross-sectional view of an image forming apparatus 100 of the present embodiment. The image forming apparatus 100 in the present embodiment is a monochrome printer capable of forming a black monochrome image using an electrophotographic method (electrophotographic image forming process).

[0033] The image forming apparatus 100 has a photosensitive drum 1, which is a rotatable drum-type (cylindrical) photosensitive member (electrophotographic member) as an image carrier. In the present embodiment, the photosensitive drum 1 is a negatively charged organic photosensitive member. The photosensitive drum 1 has a photosensitive layer on a grounded aluminum drum-shaped substrate, and is driven at a designated process speed in the direction of the arrow R1 (clockwise direction) in the figure by a driving unit (not shown). In the present embodiment, the process speed corresponds to the peripheral speed (surface moving speed) of the photosensitive drum 1. Surrounding the photosensitive drum 1 are a charging roller 2, an exposure unit 4, a developing unit 3, a transfer roller 5, and a brush member 11, all of which are described below.

[0034] The charging roller 2, which is a roller-type charging member (contact charging member) as a charging member, contacts the photosensitive drum 1 with a predetermined pressing force to form a charged portion. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in the present embodiment) by the charging roller 2. During the charging process, a predetermined charging voltage (charging bias) is applied to the charging roller 2 by a charging power source (high-voltage power source) E1 (charging voltage application part) as a charging voltage application part. Figure 7 ) is applied to the charging roller 2.

[0035] In the present embodiment, the exposure unit 4, which is an exposure member, is a laser scanner unit. The exposure unit 4 outputs a laser beam corresponding to image information input from an external device such as a host computer, and performs scanning and exposure on the surface of the uniformly charged photosensitive drum 1. This exposure forms an electrostatic latent image (electrostatic image) on the surface of the photosensitive drum 1 according to the image information. The exposure unit 4 is not limited to a laser scanner unit, and for example, an LED array having a plurality of LEDs arranged along the rotation axis direction of the photosensitive drum 1 can also be used.

[0036] The latent image formed on the surface of the photosensitive drum 1 is developed (visualized) by supplying toner as a developer from the developing unit 3 as a developing member, thereby forming a toner image (developer image) on the surface of the photosensitive drum 1. In the present embodiment, a contact developing method is used as the developing method. The developing unit 3 has a developing roller 31 as a developer carrier (developing member), a toner supply roller 32 as a developing member, a developer chamber 33 that contains toner, and a developing blade 34 as a regulating member that controls the thickness of the toner layer on the developing roller 31. The toner supplied from the toner supply roller 32 to the developing roller 31 from the developer chamber 33 is charged to a predetermined polarity when it passes through the contact portion of the developing roller 31 and the developing blade 34. In the present embodiment, toner having a mean particle diameter of 6 μm and a negative normal charging polarity (normal polarity) is used as the developer, which is a single-component non-magnetic developer. In the present embodiment, a single-component non-magnetic contact developing method is employed as the developing method, but other developing methods, such as a two-component non-magnetic contact / non-contact developing method, or a magnetic developing method, can also be employed. The latent image formed on the surface of the photosensitive drum 1 is developed at the developing portion, which is the relative (contact) portion between the developing roller 31 and the photosensitive drum 1, where the toner carried by the developing roller 31 is supplied. During the developing process, a predetermined developing voltage (developing bias) is applied to the developing roller 31 by a developing power source (high voltage power source) E2 Figure 7 as a developing voltage application member (developing voltage application portion). In the present embodiment, the toner charged at the same polarity as that of the photosensitive drum 1 (negative polarity in the present embodiment) is attached to the developing portion of the photosensitive drum 1 after the charging process, where the charge is attenuated due to exposure (image portion) (reverse developing method).

[0037] A transfer roller 5 as a roller-type transfer member is positioned opposite the photosensitive drum 1. The transfer roller 5 is pressed against the photosensitive drum 1 to form a transfer portion, where the photosensitive drum 1 and the transfer roller 5 are pressed together. A transfer power source (high voltage power source) E3 Figure 7 as a transfer voltage application member (transfer voltage application portion) is connected to the transfer roller 5, and applies a predetermined voltage at a predetermined timing. The toner image formed on the surface of the photosensitive drum 1 is transferred to the surface of the recording material S fed between the photosensitive drum 1 and the transfer roller 5 in the transfer portion. During the transfer process, the transfer power source (high voltage power source) E3 Figure 7) A predetermined transfer voltage (transfer bias) that is a DC voltage of the opposite polarity (positive polarity in this embodiment) of the regular polarity of the toner is applied to the transfer roller 5. As the transfer roller 5, a roller having an elastic layer formed of an elastic member such as urethane rubber, EPDM (ethylene propylene diene rubber), or NBR (nitrile rubber) can be appropriately used. In particular, as the transfer roller 5, a roller having, for example, a foamed elastic layer formed of a foamed elastic member such as sponge rubber can be appropriately used.

[0038] The recording material S is stored in the cartridge 6. The recording material S stored in the cartridge 6 is fed out one sheet at a time from the cartridge 6 by the feeding unit 7, and then fed to the resistor roller pair 8. Then, in accordance with the timing at which the toner image formed on the surface of the photosensitive drum 1 reaches the transfer portion, the recording material S is fed to the transfer portion by the resistor roller pair 8.

[0039] The recording material S on which the toner image has been transferred is fed to the fixing unit 9 as a fixing member. In this embodiment, the fixing unit 9 employs a film heating method, having a fixing film 91 and a pressure roller 92 pressed against the fixing film 91. A fixing heater and a thermistor or the like for measuring the temperature of the fixing heater are arranged on the inner peripheral side of the annular fixing film 91. The fixing unit 9 fixes (melts and adheres) the toner image to the surface of the recording material S by heating and pressing the recording material S carrying the unfixed toner image while feeding it between the fixing film 91 and the pressure roller 92. The recording material S on which the toner image has been fixed is discharged (output) to the outside of the main body of the apparatus 110 (the outside of the apparatus) by the discharge roller pair 10, and stacked on the tray 15 provided on the upper portion of the main body of the apparatus 110.

[0040] The adhering material such as toner (residual transfer toner) that is not transferred to the recording material S and remains on the surface of the photosensitive drum 1 during the transfer process is removed from the surface of the photosensitive drum 1 in the subsequent process.

[0041] The residual transfer toner is mainly toner charged to the negative polarity, which is the regular polarity. However, the residual transfer toner includes toner charged to the positive polarity and toner charged to the negative polarity but not having sufficient charge. The residual transfer toner charged to the negative polarity again in the charging portion by discharge in the charging portion. With the rotation of the photosensitive drum 1, the residual transfer toner charged to the negative polarity again in the charging portion reaches the developing portion. As described above, an electrostatic latent image is formed on the surface of the photosensitive drum 1 that has reached the developing portion. The behavior of the residual transfer toner reaching the developing portion is described for the image portion (exposed portion) and the non-image portion (unexposed portion) of the surface of the photosensitive drum 1, respectively.

[0042] The residual transfer toner adhering to the non-image portion of the photosensitive drum 1 is removed from the photosensitive drum 1 in the developing portion by a potential difference between the potential of the non-image portion of the surface of the photosensitive drum 1 and the developing voltage, and is collected in the developer chamber 33. The potential of the developing voltage is set to a potential between the potential of the non-image portion of the surface of the photosensitive drum 1 and the potential of the image portion (exposed portion). The toner collected in the developer chamber 33 is used again for image formation.

[0043] The residual transfer toner adhering to the image portion (exposed portion) of the surface of the photosensitive drum 1 is not transferred from the photosensitive drum 1 to the developing roller 31 in the developing portion. This residual transfer toner, together with the toner supplied from the developing roller 31 to the photosensitive drum 1, constitutes a toner image, which is transferred to the recording material S in the transfer portion and removed from the photosensitive drum 1.

[0044] The configuration and operation of the brush member 11 as a component that removes paper dust will be described in detail below.

[0045] In the present embodiment, the photosensitive drum 1, the charging roller 2 as a processing member acting thereon, the developing unit 3, and the brush member 11 described later together constitute a process cartridge 14 that can be attached to and detached from the main body of the device 110.

[0046] The position in the rotation direction of the photosensitive drum 1 at which the charging process of the photosensitive drum 1 by the charging roller 2 is performed is a charging position Pl. In the present embodiment, the charging roller 2 charges the surface of the photosensitive drum 1 using discharge occurring in at least one minute air gap formed upstream and downstream of the contact portion between the charging roller 2 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1. However, for the sake of simplicity, the position on the photosensitive drum 1 at which the charging roller 2 contacts (i.e., the position on the photosensitive drum 1 at which the above-described charging portion is formed) can be considered to be the charging position Pl. More precisely, the charging position Pl can be defined as the position in the rotation direction of the photosensitive drum 1 between the most upstream and most downstream contact portions of the charging roller 2 and the photosensitive drum 1. An exposure position P2 is a position on the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 at which the photosensitive drum 1 is irradiated with light by the exposure unit 4. A developing position P3 is a position on the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 at which toner is supplied to the photosensitive drum 1 from the developing roller 31 (the position at which the developing roller 31 contacts) (i.e., the position on the photosensitive drum 1 at which the above-described developing portion is formed). A transfer position P4 is a position on the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 at which toner is transferred to the recording material S on the photosensitive drum 1 by the transfer roller 5 (the position at which the transfer roller 5 contacts) (i.e., the position on the photosensitive drum 1 at which the above-described transfer portion is formed). Further, a brush contact position P5 is a position on the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 at which paper dust is removed from the photosensitive drum 1 by the brush member 11 (the position at which the brush member 11 contacts) (i.e., the position on the photosensitive drum 1 at which the above-described brush contact portion is formed). The developing position P3, the transfer position P4, and the brush contact position P5 can also be provided at intermediate positions between the most upstream and most downstream positions in the rotation direction of the photosensitive drum 1.

[0047] 2. Control mode

[0048] Figure 7 Fig. 1 is a schematic block diagram showing a control portion of a key part of the image forming apparatus 100 in the present embodiment. The image forming apparatus 100 has a control portion 50. The control portion 50 has a CPU 51 as a central element that performs operation processing, a memory (storage element) 52 such as a ROM and a RAM as a storage part, and an input / output portion (not shown) that controls exchange of signals between elements connected to the control portion 50. The RAM stores sensor detection results, calculation results, and the like, and the ROM stores control programs, predetermined data tables, and the like.

[0049] The control section 50 is a control means that can comprehensively control the operations of the image forming apparatus 100. Each section of the image forming apparatus 100 is connected to the control section 50. In the present embodiment, for example, the charging power source El, the developing power source E2, the transfer power source E3, the brush power source E4 (described later), and the exposure unit 4 are connected to the control section 50. In the present embodiment, the transfer power source E3 is configured to be able to apply a positive polarity voltage and a negative polarity voltage to the transfer roller 5. The control section 50 can control the operations (ON / OFF and output values) of the above-described various power sources (bias supply means), the operation (ON / OFF and exposure amount) of the exposure unit 4, the timing of these operations, and the like, to perform the image forming and brush cleaning operations described below.

[0050] The image forming apparatus 100 can perform a print job (print operation, printout operation), which is a series of operations to form an image on a single or multiple recording materials S initiated by a single start instruction. In the present embodiment, the start instruction is input to the image forming apparatus 100 from an external device such as a personal computer. The print job generally has an image forming process (print process), a pre-rotation process, a paper interval process when an image is formed on multiple recording materials S, and a post-rotation process. The image forming process is a period during which an electrostatic latent image is actually formed on the photosensitive drum 1, a developed electrostatic latent image (toner image formation) is formed, a toner image is transferred, and a fixed toner image is formed, and the like. More precisely, the timing of image formation differs depending on the positions at which these processes of forming an electrostatic latent image, forming a toner image, transferring a toner image, and fixing a toner image are performed. The pre-rotation process is a period of preparation operations before the image forming process. The paper interval process (inter-image process) is a period corresponding to the time between two recording materials S when the image forming process is continuously performed on multiple recording materials S (during continuous image formation). The post-rotation process is a period of organization operations (preparation operations) performed after the image forming process. The non-image formation time is a period other than the image formation time, and includes the above-mentioned pre-rotation process, paper interval process, post-rotation process, and a multi-pre-rotation process, which is a preparation operation when the power source of the image forming apparatus 100 is turned on or when the apparatus returns from a sleep mode. The timing during image formation corresponds to the period of the positions on the photosensitive drum 1 through which the above-described electrostatic image is formed, a toner image is formed, a toner image is transferred, and a toner image is fixed. The timing for non-image formation corresponds to the period of each of the above-mentioned positions on the photosensitive drum 1. The image formation region on the photosensitive drum 1 is a region in which an image that is transferred to a recording material S and output from the image forming apparatus 100 can be formed, and the non-image formation region is a region other than the image formation region.

[0051] Figure 8is a schematic block diagram showing a power supply configuration that can be applied to the image forming apparatus 100 in the present embodiment. In Figure 7 the power supply configuration shown in Figure 8 is different from that in Figure 1 and 7 elements having the same or corresponding functions or configurations as those shown in Figure 1 and 7 are denoted by the same symbols as in Figure 8 the configuration in Figure 7 is different from that in Figure 8 In the configuration in Figure 8 the power supply for the developing roller 31, the developing blade 34, and the toner supply roller 32 is common. For example, a voltage of -380 V is applied to the developing roller 31, a voltage of -580 V is applied to the developing blade, and a voltage of -580 V is applied to the toner supply roller by the developing voltage E2, respectively. The charging power supply El (negative voltage source) applies a negative polarity voltage to the transfer roller 5 and the charging roller 2. In other words, the power supply for the transfer roller 5 and the charging roller 2 is common. A negative voltage is applied to the transfer roller 5, for example, to return toner and paper dust attached to the transfer roller 5 to the photosensitive drum 1 when they are attached to the transfer roller 5. The power supply E3 (positive voltage source) applies a positive polarity transfer voltage to the transfer roller 5. The current detection circuit 801 is used for current detection during constant current control. The switch 802 turns on / off the application of a negative voltage from the power supply El to the transfer roller 5. The control portion 50 sets the switch 802 to OFF during normal image forming control, and only the positive voltage from the power supply E3 is applied to the transfer roller 5. Figure 1 is not shown in Figure 8 In the present embodiment, a pre-exposure lamp can be provided. According to the configuration in Figure 8 the configuration of

[0052] 3. Brush member

[0053] Next, the configuration and operation of the brush member 11 in the present embodiment will be described.

[0054] As Figure 1As shown in FIG. 1, the present embodiment of the image forming apparatus 100 has a brush member 11, which is a paper dust removing member (collection member) as a paper dust removing part (paper dust removing mechanism). Paper dust is a fibrous foreign matter from paper, and is generally composed of pulp fibers (mainly cellulose) separated from paper, and can also include filler material separated from paper.

[0055] The brush member 11 is composed of bristle strings 11a, which are a plurality of bristles (substrates) that are a surface of the friction charging drum 1, and a base cloth 11b that supports the bristle strings 11a. The brush member 11 is arranged to form a brush contact portion (collection portion) that contacts the friction charging drum 1 downstream of a transfer position (transfer portion) P4 and upstream of a charging position (charging portion) PI in a rotation direction (moving direction of the surface) of the friction charging drum 1. The brush member 11 is supported by a support member (not shown) and arranged at a fixed position with respect to the friction charging drum 1, and slides on the surface of the friction charging drum 1 as the friction charging drum 1 moves. As described above, the brush contact position P5 is a position on the friction charging drum 1 that forms the above-described brush contact region in the rotation direction of the friction charging drum 1.

[0056] The brush member 11 collects (recovers) paper dust and other adherents that are transferred from the recording material S to the friction charging drum 1 at the transfer position P4, thereby reducing the amount of paper dust that moves in the rotation direction of the friction charging drum 1 to the charging position PI and the developing position P3 located downstream of the brush contact position P5.

[0057] In the present embodiment, the bristle strings 11a of the brush member 11 are made of electrically conductive nylon fibers, with nylon as a binding material and carbon mixed in as an electrically conductive material. However, the material of the bristle strings 11a of the brush member 11 is not limited thereto. For example, the material of the bristle strings 11a of the brush member 11 can be polyester or acrylic as a binding material, as long as the material is electrically conductive.

[0058] In the present embodiment, the length of the brush member 11 in a direction parallel to the circumferential direction of the friction charging drum 1 (hereinafter also referred to as the "short side direction") is set to 5 mm. However, the length of the brush member 11 in the short side direction is not limited thereto. The length of the brush member 11 in the short side direction can change depending on the amount of paper dust, which tends to increase as the life of the apparatus increases, for example, as the life of the image forming apparatus 100 and the process cartridge 14.

[0059] In the present embodiment, the bristle length of the brush member 11 is set to 5 mm. However, the bristle length of the brush member 11 is not limited thereto. However, when the brush member 11 is used to collect paper dust, it is necessary to ensure that the amount of penetration of the brush member 11 into the photosensitive drum 1 is above a certain amount. Therefore, if the bristle length of the brush member 11 is short, the contact pressure against the photosensitive drum 1 becomes strong, and the surface of the photosensitive drum 1 can be damaged by sliding. Therefore, it is desirable that the bristle length of the brush member 11 be 4 mm or longer. Although not limited thereto, the bristle length of the brush member 11 is generally 10 mm or less. The bristle length of the brush member 11 is the distance from the base cloth 11b to the front end of the bristle string 11a that is exposed from the base cloth 11b in the state of the brush member 11 itself (i.e., when no external force is applied to bend the bristle string 11a).

[0060] In the present embodiment, the length of the brush member 11 in the direction parallel to the direction of the rotation axis of the photosensitive drum 1 (hereinafter also referred to as the "longitudinal direction") is set to 230 mm. However, the length of the brush member 11 in the longitudinal direction is not limited thereto. The length of the brush member 11 in the longitudinal direction can be changed according to, for example, the maximum image forming width of the image forming apparatus 100.

[0061] In the present embodiment, the fineness of the brush member 11 is set to 2 d (meaning 2 g of fiber per 9000 m). "d" is an acronym for denier. However, the fineness of the brush member 11 is not limited thereto. However, when the fineness of the brush member 11 is high, each fiber becomes hard and the pressure of the brush member 11 against the photosensitive drum 1 becomes strong, which can damage the surface of the photosensitive drum 1 by friction. Therefore, it is desirable that the fineness of the brush member 11 be 6 d or less. Although not limited thereto, the fineness of the brush member 11 is generally 1 d or more.

[0062] In the present embodiment, the density of the brush member 11 is set to 240 kF / inch 2 (kF / inch 2 , which is a unit of brush density and indicates the number of filaments per square inch). However, the density of the brush member 11 is not limited thereto. However, when the brush member 11 is used to collect paper dust, a low density increases the likelihood of the paper dust sliding through. Therefore, the density should be 120 kF / inch 2 or more. Although not limited thereto, the density of the brush member 11 is generally 300 kF / inch 2 or less.

[0063] In the present embodiment, the penetration amount of the brush member 11 is set to 1.5 mm. However, the penetration amount of the brush member 11 is not limited thereto. When the brush member is used to collect paper dust, a small penetration amount of the brush member 11 into the photosensitive drum 1 increases the likelihood of the paper dust slipping through. Therefore, the penetration amount of the brush member 11 should be 1 mm or more. Although not limited thereto, the penetration amount of the brush member 11 is generally 3 mm or less. When the above-described bristle length is L1 and the shortest distance from the base cloth 11b of the brush member 11 fixed to the above-described support member to the photosensitive drum 1 is L2, the difference between L2 and L1 is the penetration amount of the brush member 11 into the photosensitive drum 1.

[0064] In the present embodiment, a brush voltage application member (brush voltage application portion), a brush power source (high voltage power source) E4 Figure 7 is connected to the brush member 11, and applies a predetermined voltage to the brush member 11 at a predetermined timing. In the present embodiment, a voltage mainly of a negative polarity is applied from the brush power source E4 to the brush member 11 in order to collect paper dust of a positive polarity adhering to the surface of the photosensitive drum 1 of a mainly negative polarity at the transfer position P4. In the present embodiment, the brush power source E4 applies a voltage in the range of -500 V to 0 V to the brush member 11.

[0065] In the present embodiment, the resistance of the brush member 11 is 1.0 x 10 5 Ω when measured as follows. That is, the brush member 11 is fixed to an aluminum cylinder, and the brush member 11 is advanced 1 mm in the length direction of the bristles of the brush member 11 from the front end of the bristle string 11a. The resistance of the brush member 11 is measured by applying a voltage of 50 V to the brush member 11 while the aluminum cylinder is rotated at 50 mm / sec. However, the resistance of the brush member 11 is not limited thereto, and a brush member 11 of a relatively high resistance of 1.0 x 10 8 Ω or less can be used.

[0066] 4. Brush cleaning operation

[0067] <Summary of brush cleaning operation>

[0068] Not only paper dust, but also residual transfer toner and toner (fog toner) on the non-image portion of the photosensitive drum 1 accumulate on the brush member 11. If too much toner accumulates on the brush member 11, the brush member 11 can not be able to hold the toner, and the toner can slip from the brush member 11 and adhere to the charging roller 2, resulting in charging failure.

[0069] Therefore, in the present embodiment, the image forming apparatus 100 is configured to be able to perform a brush cleaning operation (brush cleaning control) to discharge toner from the brush member 11 at a predetermined timing during non-image formation. This can inhibit excessive accumulation of toner on the brush member 11.

[0070] In the present embodiment, the brush cleaning operation is executed in the post-rotation process which is an example of a non-image forming process. However, the brush cleaning operation can be executed at any non-image forming process, and can be executed in a pre-rotation process, a multi-pre-rotation process, an inter-sheet process, or the like. The brush cleaning operation is not limited to being executed in the post-rotation process or other processes each time a print job is executed. For example, the operation can be executed when any index value related to the amount of toner accumulated in the brush member 11 (the amount used by the brush member 11) such as the number of formed images, the number of times or the rotation time of the photosensitive drum 1, or the time for which a voltage is applied to the brush member 11 exceeds a predetermined threshold value.

[0071] <Control of the Present Embodiment>

[0072] Next, the brush cleaning operation of the present embodiment is explained. Figure 2 is a timing chart showing the operation of each part in the image forming apparatus 100 of the present embodiment when the brush cleaning operation is executed in the post-rotation operation until the operation of the image forming apparatus 100 is stopped after the image forming operation (e.g., a single-page print operation). This shows the time transition of the charging voltage applied to the charging roller 2 from the charging power supply El, the brush voltage applied to the brush member 11 from the brush power supply E4, and the transfer voltage applied to the transfer roller 5 from the transfer power supply E3. This also shows the surface potential of the photosensitive drum 1 after the transfer subjected to the transfer voltage, and the time transition of the difference between the brush voltage and the surface potential of the photosensitive drum 1 after the transfer. Figure 2 The operation shown in FIG. 20 is controlled by the control portion 50 by sending control signals to each power supply portion.

[0073] The surface potential of the photosensitive drum 1 is simply referred to as "drum potential", and the surface potential of the photosensitive drum 1 after the transfer is simply referred to as "post-transfer drum potential". Here, the post-transfer drum potential is more precisely the surface potential of the photosensitive drum 1 at the time of passing through the contact position P5, i.e., the surface potential of the photosensitive drum 1 at the contact position P5. However, the post-transfer drum potential can be represented by the surface potential of the photosensitive drum 1 after passing through the transfer position P4 and just before reaching the brush contact position P5. The toner charged in the negative polarity is also referred to as "negative toner", and the toner charged in the positive polarity is also referred to as "positive toner". In the present embodiment, the transfer voltage is controlled to be a constant voltage. The constant voltage control of the transfer voltage is control that adjusts the output voltage of the transfer power supply E4 so as to become substantially constant at a target voltage. The potential difference between the brush voltage and the post-transfer drum potential refers to the value (including the positive and negative signs) of the brush voltage minus the post-transfer drum potential, as described in detail below.

[0074] As Figure 2As shown in FIG. 1, during the image forming operation and the brush cleaning operation, a charging voltage of -1300 V is applied to the charging roller 2, and the drum potential is uniformly set to approximately -800 V in the rotation direction of the photosensitive drum 1. During the image forming operation and the brush cleaning operation, a brush voltage of -400 V, which is approximately between the drum potential of -800 V in the non-image portion and the drum potential of 0 to -100 V in the image portion, is applied to the brush member 11. Accordingly, the brush voltage should be set so that image defects due to discharge between the brush member 11 and the photosensitive drum 1 do not occur (i.e., the absolute value should be set to a voltage lower than the discharge threshold between the brush member 11 and the photosensitive drum 1). Furthermore, by setting the brush voltage to a potential approximately halfway between the drum potential of the non-image portion and the drum potential of the image portion, the following effects can be obtained. In other words, for both positive and negative polarity toners accumulated on the brush member 11, the toner can be removed from the brush member 11 to the photosensitive drum 1 by adjusting the drum potential. Furthermore, by setting the brush voltage in this way, the following effects can also be obtained. In other words, the brush voltage can be set to an electric potential relationship that allows negative toner (toner of a regular polarity) contained in the residual transfer toner to pass through the brush contact position P5 without adhering to the brush member 11 for the image portion, the drum potential of which is approximately 0 to -100 V. This can suppress excessive accumulation of toner on the brush member 11.

[0075] During the forming operation, a transfer voltage of approximately +1000 V is applied to the transfer roller 5. This transfer voltage during the image forming operation can be changed based on, for example, the type of recording material S or the detection result of the resistance of the transfer portion. After the transition to the post-rotation operation (brush cleaning operation), a transfer voltage of -400 V is applied to the transfer roller 5 as a voltage within a range that does not lower the absolute drum potential due to discharge for the drum potential of -800 V in the non-image portion. This widens the difference between the brush voltage and the post-transfer drum potential without lowering the absolute value of the post-transfer drum potential, and this potential difference expels positive toner that has accumulated on the brush member 11 from the brush member 11 to the photosensitive drum 1. Thereafter, a transfer voltage of +1000 V (corresponding to the transfer voltage during the image forming operation) is applied to the transfer roller 5. This operation lowers the absolute value of the post-transfer drum potential to approximately 0 V, thereby widening the difference between the brush voltage and the post-transfer drum potential to the opposite side of the above-mentioned potential difference, and expelling negative toner that can have accumulated on the brush member 11 from the brush member 11 to the photosensitive drum 1. According to Figure 2 The brush cleaning operation shown in FIG. 1, both regular polarity (main toner charging polarity during the developing process) and irregular polarity (polarity opposite to the regular polarity) toners can be disposed of, thereby improving the cleaning of the brush member 11 for collecting paper dust that is in contact with the photosensitive drum 1.

[0076] <Actions of the Present Embodiment>

[0077] Next, the actions of the brush cleaning operation in the present embodiment are further explained. By increasing the absolute value of the potential difference between the brush voltage and the drum potential, toner is discharged from the brush member 11 to the photosensitive drum 1. As Figure 4 (a) shows, if the drum potential is higher than the brush voltage with respect to the negative potential as the normal polarity (i.e., if the potential difference between the brush voltage and the post-transfer drum potential is positive), then positive toner is discharged from the brush member 11 to the photosensitive drum 1. On the other hand, as Figure 4 (b) shows, if the drum potential is lower than the brush voltage with respect to the negative potential as the normal polarity (i.e., if the potential difference between the brush voltage and the post-transfer drum potential is negative), then negative toner is discharged from the brush member 11 to the photosensitive drum 1. Thus, by changing the potential difference between the brush voltage and the drum potential to positive and negative, both negative and positive toner can be discharged from the brush member 11 to the photosensitive drum 1. In other words, the cleaning performance of the brush member 11 to collect paper dust can be improved.

[0078] In addition to the potential difference between the brush voltage and the drum potential, a gap can also be formed in the surface potential of the photosensitive drum 1 to more efficiently discharge toner from the brush member 11 to the photosensitive drum 1. This is explained using Figure 5

[0079] Figure 5 (a) is a schematic view showing the posture of the brush member 11 when the drum potential is set to -400 V with respect to the brush voltage of -400 V during the rotation drive operation of the photosensitive drum 1. Since the potential difference between the brush voltage and the photosensitive drum 1 is small, the electrostatic attraction force is small. Thus, the dynamic friction force between the brush member 11 and the photosensitive drum 1 causes the tips of the bristle strings 11a to flow in the rotation direction to the downstream of the photosensitive drum 1, but the overall posture of the brush member 11 changes little.

[0080] On the other hand, Figure 5 (b) is a schematic view showing the posture of the brush member 11 when the drum potential is set to -200 V with respect to the brush voltage of -400 V during the rotation drive operation of the photosensitive drum 1. Since the potential difference between the brush voltage and the photosensitive drum 1 is large, the electrostatic attraction force is large. Thus, the dynamic friction force between the brush member 11 and the photosensitive drum 1 causes the tips of the bristle strings 11a to flow in the rotation direction to the downstream of the photosensitive drum 1, and the overall posture of the brush member 11 changes greatly. Figure 5 ​In the case of (a), the electrostatic attraction force increases compared to the case of (b), and thus more of the tip of the fluff string 11a is attracted to the photosensitive drum 1. Therefore, the tip of the fluff string 11a is pulled to the downstream in the rotation direction of the photosensitive drum 1, and the entire brush member 11 is pulled to a posture located downstream in the rotation direction of the photosensitive drum 1. When the change in posture occurs in the entire brush member 11, the subsequent toner moves with the brush member 11. In other words, toner that is not in contact with the photosensitive drum 1, toner with low charge that is difficult to move by only the potential difference, or toner that is captured by paper dust on the brush member 11 and is difficult to discharge. When such toner comes into contact with or close to the photosensitive drum 1, it is discharged from the brush member 11 when it is subjected to a force from the brush member 11 side, thereby being discharged from the brush member 11 onto the photosensitive drum 1. Therefore, by utilizing not only the potential difference but also the change in posture of the brush member 11, toner accumulated on the brush member 11 can be efficiently discharged onto the photosensitive drum 1.

[0081] As mentioned above, the relative potential difference between the brush member and the drum potential, including the positive and negative signs, is important for the change in posture of the brush member 11. Therefore, here, the potential difference between the brush voltage and the drum potential refers to the relative potential difference between the brush voltage and the drum potential, including the positive and negative signs.

[0082] The negative toner discharged from the brush member 11 onto the photosensitive drum 1 passes through the charging position P1. This is because the force toward the photosensitive drum 1 is higher electrostatically than the force toward the charging roller 2 due to the potential difference between the charging voltage (-1300 V) and the drum potential (-800 V). Then, the negative toner is collected in the developing unit 3 due to the potential difference between the developing voltage (-400 V) and the drum potential (-800 V).

[0083] The positive toner discharged from the brush member 11 onto the photosensitive drum 1 is affected by discharge at the charging position P1, the charge polarity is reversed, and becomes negative toner, which is collected in the developing unit 3 in the same manner as the above-described negative toner.

[0084] However, Figure 2Further improvement of the brush cleaning operation shown in the above embodiment is possible. That is, when the amount of toner discharged from the brush member 11 is large, negative toner can not pass through the charging position P1 completely due to the potential difference between the charging voltage and the drum potential. Also, due to the influence of discharging at the charging position P1, positive toner can not be completely converted into negative toner. In either case, toner can adhere to the charging roller 2 and dirty the charging roller 2 with toner. The charging roller 2 to which toner adheres can not uniformly charge the surface of the photosensitive drum 1 in the rotation direction, resulting in abnormal discharging, which can cause a spot image defect on a halftone image (also referred to as a "white spot image" here). It is also desirable to address this problem. The following is a modified example of the present embodiment that addresses this problem.

[0085] <Control of the modified example>

[0086] Next, the brush cleaning operation in the modified example is explained.

[0087] Figure 3 is a timing chart showing the operation of each part of the image forming apparatus 100 according to the modified example when the brush cleaning operation is performed in the post-rotation operation until the operation of the image forming apparatus 100 is terminated after the image forming operation (e.g., one print operation). According to the timing chart in Figure 3 , the process is a process performed by the control portion 50 controlling the voltage output of each power supply portion. As in Figure 2 , the timing chart in Figure 3 shows the time transition of the charging voltage, the brush voltage, the transfer voltage, the post-transfer drum potential, and the potential difference between the brush voltage and the post-transfer drum potential. Figure 3 The operation shown in

[0088] Figure 3 The operation of each part of the photosensitive drum 1 in the modified example shown in Figure 2 is the same as that shown in

[0089] In the modification example, after the transition to the post-rotation operation (brush cleaning operation), at T1, the surface of the photosensitive drum 1 at the transfer position P4 is sequentially changed in the transfer voltage. At T2, the surface of the photosensitive drum 1 to which the transfer voltage changed by one step from T1 is applied moves in the rotation direction of the photosensitive drum 1 and reaches the brush contact position P5. Thereafter, the transfer voltage is changed from approximately +1000 V during the image forming operation to -400 V in steps. In other words, the potential difference between the brush voltage and the post-transfer drum potential is changed from -400 V to +400 V in steps. Then, at T3, the transfer voltage starts to change in the positive polarity direction from -400 V in steps. At T4, the surface of the photosensitive drum 1 to which the transfer voltage changed by one step from T3 is applied moves in the rotation direction of the photosensitive drum 1 and reaches the brush contact position P5. Thereafter, the transfer voltage is changed from -400 V to +1000 V in 10 steps. In other words, the potential difference between the brush voltage and the post-transfer drum potential is changed from +400 V to -400 V in 10 steps. At T5, the surface of the photosensitive drum 1 to which the final transfer voltage of +1000 V is applied in the brush cleaning operation in the modification example moves in the rotation direction of the photosensitive drum 1 and reaches the brush contact position P5.

[0090] The width of one step at which the transfer voltage is changed from the transfer voltage during image formation to -400 V is approximately the same as the width of one step at which the transfer voltage is changed from -400 V to +1000 V in 10 steps (140 V in the modification example). The number of steps at which the transfer voltage is changed from the transfer voltage during image formation to -400 V depends on the transfer voltage during image formation.

[0091] <Actions of the modification example>

[0092] Next, the actions of the brush cleaning operation in the modification example are explained. Here, in the case where the potential gap is formed in the photosensitive drum 1, by comparing Figure 2 the brush cleaning operation in Figure 3 the modification example with Figure 2 the brush cleaning operation in Figure 3 the modification example, the actions of the brush cleaning operation in the modification example are explained.

[0093] In the brush cleaning operation in Figure 2 the modification example, because of the sudden change in the drum potential, the posture of the brush member 11 is suddenly changed from the aforementioned posture in Figure 5 (a) to the posture in Figure 5 (b) or from the posture in Figure 5 (b) to the posture in Figure 5 (a). Therefore, the amount of toner instantaneously discharged from the brush member 11 to the photosensitive drum 1 increases.

[0094] On the other hand, Figure 3 During the brush cleaning operation, the posture of the brush component 11 is adjusted by gradually changing the drum potential. Figure 5 (a) The posture gradually changes to Figure 5 (b) posture or from Figure 5 (b) The posture gradually changes to Figure 5 The posture of (a). Therefore, in Figure 3 In the brush cleaning operation shown, sudden changes in the posture of the brush component 11 can be suppressed, so that whenever the gap in the drum potential passes through the brush contact position P5, the toner is gradually discharged from the brush component 11 onto the photosensitive drum 1.

[0095] Figure 3 The brush cleaning operation can also be adapted to both conventional polarity (the main charging polarity of the toner during the development process) and unconventional polarity (the polarity opposite to the conventional polarity) toners, thereby improving the cleaning of the brush component 11 positioned to contact the photosensitive drum 1 for collecting paper dust, thus improving the cleaning performance of the brush component 11 arranged to contact the photosensitive drum 1 for collecting paper dust.

[0096] Here, the gradual change in the potential difference between the brush voltage and the post-transfer drum potential more accurately means the following: For example, when the potential difference is as follows... Figure 2 As shown in the diagram, a rapid change of 800V takes approximately 100ms. Gradually changing the potential difference means that the potential difference should change much more slowly than the rapid change described above, thereby sufficiently reducing the amount of toner instantaneously discharged from the brush component 11 onto the photosensitive drum 1. For example, when the potential difference is as shown... Figure 3 When the change is shown, an 800V change over approximately 500ms to 3000ms is sufficient. In other words, a gradual change in the potential difference between the brush voltage and the post-transfer drum potential typically means a change at a rate of approximately 0.2V / ms to 2V / ms. When the potential difference between the brush voltage and the post-transfer drum potential changes gradually, a single-step change width should be set to achieve the aforementioned rate of change. For example, when the potential difference is as shown... Figure 3 As shown in the step-like change diagram, the width of each step change can be set to approximately 50V to 100V, and the change can be performed within 50ms to 100ms. Figure 2 In the brush cleaning operation shown, the amount of toner discharged from the brush component 11 can be increased, while... Figure 3 In the brush cleaning operation shown, the downtime may be prolonged because the potential difference at the brush contact point P5 changes gradually. Therefore, the conditions can be appropriately set considering the amount of toner discharged from the brush component 11. For example, when there is less toner contained in the brush component 11, the operation can be performed...Figure 2 The brush cleaning operation shown can be performed when there is a large amount of toner contained in the brush component 11. Figure 3 The brush cleaning operation is shown in the image. As an example, Figure 2 The brush cleaning operation can be performed during the intermittent operation of printing and recording materials S one sheet at a time, while Figure 3 The brush cleaning operation can be performed during continuous operation of multiple sheets of printing recording material S. Of course, the above conditions can be controlled by predicting and controlling the amount of residual transfer toner, etc.

[0097] 5. Evaluation Test

[0098] Next, the results of the evaluation tests conducted to confirm the effectiveness of this embodiment and the modified example will be described.

[0099] First, an evaluation test on toner contamination of the charging roller 2 is conducted (hereinafter referred to as "Evaluation Test 1"). Evaluation Test 1 is conducted under the following conditions: Ten consecutive all-black images are printed using Xerox Vitality multipurpose printing paper (brand name, basis weight 75g) manufactured by Xerox Corporation as the recording material S at a temperature of 32.5°C and a relative humidity of 80% (high temperature and high humidity environment). Then, a post-rotation operation (brush cleaning operation) is performed. By continuously printing all-black images, more residual transfer toner is supplied to the brush component 11. Next, a halftone image with a 25% concentration is printed. If a large number of white spots appear in this halftone image during the rotation cycle of the charging roller 2, the image is judged as "X (bad)". If some white spots appear during the rotation cycle of the charging roller 2, the image is judged as "△ (slight, but potentially problematic)", and if virtually none appear, the image is judged as "○ (OK)".

[0100] After the above evaluation test 1, an evaluation test of the brush cleaning ability (also referred to as "evaluation test 2" here) was also performed. Evaluation test 2 was performed under the following conditions. As with evaluation test 1, 10 full-black images were printed in succession. After 10 were printed, the operation of the image forming apparatus 100 was forcibly stopped before entering the post-rotation operation, at which time the amount of toner accumulated on the brush member 11 was sucked up with the toner vacuum cleaner and its weight was measured to determine the "amount of toner attached before cleaning". Then, after cleaning the brush member 11 once and removing almost all of the toner from the brush member 11, 10 successive full-black images were printed and the post-rotation operation (brush cleaning operation) was performed. The amount of toner accumulated on the brush member 11 was then sucked up with the toner vacuum cleaner and its weight was measured to determine the "amount of toner attached after cleaning". Then, the value obtained by subtracting the "amount of toner attached after cleaning" from the "amount of toner attached before cleaning" was divided by the "amount of toner attached before cleaning", and multiplied by 100, to obtain a cleaning performance value (%). The higher this cleaning ability value, the less toner remains on the brush member 11, the more toner is expelled from the brush member 11, and the better the cleaning is performed.

[0101] The results of the above evaluation tests 1 and 2 for the present embodiment Figure 2 ) and the modified example Figure 3 ) are shown in Table 1.

[0102] [Table 1]

[0103]

[0104] From the results of evaluation test 1 in Table 1, it can be seen that in the brush cleaning operation shown in Figure 2 , because of the large potential gap of the photosensitive drum 1 as described above, the amount of toner instantaneously expelled from the brush member 11 onto the photosensitive drum 1 is large, and the charge roller 2 is contaminated with toner, resulting in some white speckled images. In contrast, in the brush cleaning operation shown in Figure 3 , as described above, toner is gradually expelled from the brush member 11 onto the photosensitive drum 1, so the charge roller 2 is not contaminated with toner and there are no white speckled images.

[0105] The results of evaluation test 2 in Table 1 also show that in the brush cleaning operation in Figure 2 , although the amount of toner instantaneously expelled is high, the value of the cleaning ability is relatively low (29%) because the number of times toner is expelled is low. On the other hand, in the brush cleaning operation in Figure 3 , although the amount of toner expelled in a single potential step is less than in Figure 2 , because the number of times toner is expelled is large, the value of the cleaning performance is high (83%).

[0106] According to the brush cleaning operation in the present embodiment, therefore, toner of a regular charging polarity (main charging polarity of toner during development) and toner of an irregular polarity (polarity opposite to the regular polarity) can be accommodated, and the cleaning performance of the brush member 11 for collecting paper dust can be improved. Particularly, according to the brush cleaning operation in the modified example of the present embodiment, the potential difference between the brush voltage and the post-transfer drum potential is changed stepwise (in the modified example, in a stepwise manner). This reduces the amount of toner instantaneously discharged from the brush member 11 onto the photosensitive drum 1 in the brush cleaning operation, inhibits toner contamination of the charging roller 2, and inhibits the occurrence of white spot images.

[0107] In the present embodiment and the modified example, the brush voltage is kept constant at -400 V, and the potential difference between the brush voltage and the post-transfer drum potential is changed by controlling the transfer voltage. However, the present application is not limited to this arrangement, and the potential difference between the brush voltage and the post-transfer drum potential can be changed by changing the post-transfer drum potential in other means. For example, the post-transfer drum potential can be controlled in the same manner as in the present embodiment or the modified example by controlling the charging voltage, by controlling the exposure of the exposure unit 3, or by controlling the exposure of a pre-exposure unit 13 (arranged to expose the photosensitive drum 1 in the rotational direction of the photosensitive drum 1 downstream of the transfer position and upstream of the brush contact position) (or by a combination of these means). Figure 9 ) of the exposure unit 3, or by controlling the exposure of a pre-exposure unit 13 (arranged to expose the photosensitive drum 1 in the rotational direction of the photosensitive drum 1 downstream of the transfer position and upstream of the brush contact position) (or by a combination of these means).

[0108] In the modified example, the potential difference between the brush voltage and the post-transfer drum potential is changed stepwise so as to change the potential difference between the brush voltage and the post-transfer drum potential stepwise, but the potential difference can be changed continuously. In this case, it can be changed substantially continuously in a linear manner or in a curved manner. While a plurality of potential steps as described above can be said to be advantageous in improving the cleaning performance, the stepwise change of the potential difference between the brush voltage and the post-transfer drum potential can have the effect of inhibiting toner contamination of the charging roller 2. In this case, for example, by increasing the number of times of repeated increase or decrease of the potential difference between the brush voltage and the post-transfer drum potential, the desired cleaning ability can be obtained as described below.

[0109] In the modified example, the voltage value of the transfer voltage applied by the constant voltage control is changed stepwise, but the transfer current flowing when the transfer voltage is applied by the constant current control can also be changed stepwise. The constant current control of the transfer voltage is control that adjusts the output voltage of the transfer power source E4 so that the current flowing in the transfer portion (transfer member) is substantially constant at a target voltage. As shown in FIG. 6, when the potential difference between the brush voltage and the post-transfer drum potential is changed sharply, the same applies. Figure 2

[0110] ​In the modification example, the potential difference between the brush voltage and the post-transfer drum potential is changed to gradually increase and then gradually decrease. However, the present application is not limited to this arrangement, and the method of changing the potential difference can be changed as needed. For example, the potential difference between the brush voltage and the post-transfer drum potential can gradually decrease and then gradually increase. The potential difference between the brush voltage and the post-transfer drum potential can be changed so that the potential difference between the brush voltage and the post-transfer drum potential gradually increases, then gradually decreases, then again gradually increases, and so on. The number of times the potential difference between the brush voltage and the post-transfer drum potential is repeatedly increased or decreased can be changed depending on the desired cleaning ability and other factors. As Figure 2 is shown in the modification example, the same applies when the potential difference between the brush voltage and the post-transfer drum potential is sharply changed.

[0111] The transfer voltage value (or the transfer current value) to be changed in steps can be adjusted in accordance with the endurance fluctuation and the environmental fluctuation, such as a change in the capacitance due to abrasion of the surface layer of the photosensitive drum 1 caused by repeated use, a change in the resistance of the transfer roller 5 due to repeated use and the environmental temperature and humidity, and so on. The same applies when the potential difference between the brush voltage and the post-transfer drum potential is sharply changed as shown in the modification example. This also applies to the adjustment of each control target when the post-transfer drum potential is changed by controlling the charging voltage, the exposure of the exposure unit 3, and the exposure of the pre-exposure unit 13 as described above. Figure 2

[0112] While the present embodiment and the modification example describe the effect of the brush member 11 for collecting paper dust, the present application is not limited to this. For example, a brush member for charging residual transfer toner to a predetermined polarity during an image forming operation and a brush member for collecting at least a part of the residual transfer toner during an image forming operation are examples. For these applications, it can be necessary to, for example, periodically discharge toner from the brush member and clean the brush member to prevent excessive accumulation of toner on the brush member. Therefore, by applying the present application to the brush member for these applications, the same effect as in the case of the brush member 11 for paper dust collection can be obtained. For example, not limited to the brush member for paper dust collection, toner contained in the brush member can fly if the brush member undergoes a large posture change. Therefore, for example, by applying the brush cleaning operation of the modification example to the brush member for other applications, the same effect as in the case of the brush member 11 for collecting paper dust can be obtained.

[0113] ​Thus, the image forming apparatus 100 according to the present application has a rotatable photosensitive member 1, a charging member 2 that charges a surface of the photosensitive member 1 at a charging position PI, and an exposure unit 4 that exposes the charged surface of the photosensitive member 1 at an exposure position P2 to form an electrostatic image on the surface of the photosensitive member 1. The image forming apparatus 100 according to the present application also has a developing unit 3 that forms a toner image on the surface of the photosensitive member 1 by supplying toner charged in a regular charge polarity to the electrostatic image on the surface of the photosensitive member 1 at a developing position P3, and a transfer member 5 that transfers the toner image on the surface of the photosensitive member 1 to a transfer body (a recording material S) at a transfer position P4. The image forming apparatus 100 according to the present application also has a brush member 11 that contacts the surface of the photosensitive member 1 at a brush contact position P5, which is located downstream of the transfer position P4 and upstream of the charging portion PI in a rotation direction of the photosensitive member 1, and a brush voltage application portion E4 that applies a brush voltage to the brush member 11. The image forming apparatus 100 according to the present application also has a control portion 50 that controls a surface potential of the photosensitive member 1 at the brush contact portion P5, and toner remaining on the surface of the photosensitive member 1 after the above-described transfer portion is collected by the developing unit 3. In the image forming apparatus 100 according to the present application, when a value of the brush voltage at the brush contact position P5 minus a value of the surface potential of the photosensitive member 1 is a contact position potential difference, the control portion 50 changes the contact position potential difference from a first potential difference to a second potential difference. Thereafter, the surface potential of the photosensitive member 1 at the brush contact position P5 is controlled so that the contact position potential difference changes from the second potential difference to a third potential difference. The control portion 50 can perform such control when a non-image forming portion on the photosensitive member 1 passes through the brush contact position P5.

[0114] In particular, in the present embodiment ( Figure 2 ), the control portion 50 changes the contact position potential difference from the first potential difference to the second potential difference in a predetermined direction, which is an increasing direction or a decreasing direction. Thereafter, the surface potential of the photosensitive member 1 at the brush contact position P5 is controlled so that the contact position potential difference changes from the second potential difference to the third potential difference in an opposite direction of the above-described predetermined direction. In the present embodiment, the control portion 50 controls the surface potential of the photosensitive member 1 at the brush contact position P5 so that the sign of the contact position potential difference is positive and negative.

[0115] In particular, in the modified example ( Figure 3), the control portion 50 changes the contact position potential difference from the first potential difference to the second potential difference in a predetermined direction, which is either an increasing direction or a decreasing direction. Thereafter, the control portion 50 controls the surface potential of the photosensitive member 1 at the brush contact position P5 so that the contact position potential difference changes from the second potential difference to the third potential difference in the predetermined direction. In the modified example, in addition to changing the contact position potential difference from the first potential difference to the third potential difference via the second potential difference in the predetermined direction, the control portion 50 changes the contact position potential difference from the fourth potential difference to the fifth potential difference in the opposite direction of the predetermined direction among the increasing and decreasing directions. Thereafter, the control portion 50 controls the surface potential of the photosensitive member 1 at the brush contact position P5 so that the contact position potential difference changes from the fifth potential difference to the sixth potential difference in the opposite direction. In the modified example, the control portion 50 controls the surface potential of the photosensitive member 1 at the brush contact position P5 so that the contact position potential difference changes stepwise. However, the control portion 50 can also control the surface potential of the photosensitive member 1 at the brush contact position P5 so that the contact position potential difference changes continuously. In the modified example, the control portion 50 controls the surface potential of the photosensitive member 1 at the brush contact position P5 so that the contact position potential difference is positive and negative.

[0116] The control portion 50 can control the surface potential of the photosensitive member 1 at the brush contact position P5 by controlling at least one of the voltage applied to the charging portion 2, the exposure of the photosensitive member 1 by the exposure unit 4, the voltage applied to the transfer portion 5, and the exposure of the surface of the photosensitive member 1 by the pre-exposure unit 13 provided to expose the surface of the photosensitive member 1 at a point downstream of the transfer position P4 and upstream of the brush contact position P5 in the rotation direction of the photosensitive member 1. In the present embodiment and the modified example, the image forming apparatus 100 has a transfer voltage application portion E3 that applies a transfer voltage to the transfer member 5, and the control portion 50 controls the transfer voltage application portion E3 to control the surface potential of the photosensitive member 1 at the brush contact position P5. In the present embodiment and the modified example, the brush member 11 removes and collects paper dust from the surface of the photosensitive member 1. In the present embodiment and the modified example, the charging member 2 contacts the surface of the photosensitive member 1 to charge the surface thereof.

[0117] As explained above, the present embodiment can improve the cleaning ability of the brush member 11 for collecting paper dust. Specifically, both the regular charging polarity (the main charging polarity of the toner during the developing process) and the irregular polarity (a polarity opposite to the regular polarity) toner can be accommodated, and the cleaning ability of the brush member 11 for collecting paper dust can be improved. Furthermore, according to the modified example of the present embodiment, both the cleaning ability of the brush member 11 and the suppression of image defects caused by toner contamination of the charging roller 2 can be achieved by cleaning the brush member 11 without toner contaminating the charging roller 2.

[0118] Next, other embodiments of the present application are described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatus in Embodiment 1. Therefore, elements of the image forming apparatus in this embodiment that have the same or corresponding functions or configuration examples as those of the image forming apparatus in Embodiment 1 are denoted by the same symbols as those of the image forming apparatus in Embodiment 1, and detailed explanation is omitted.

[0119] 1. Control of this embodiment

[0120] The brush cleaning operation in this embodiment is described below. Figure 6 is a timing chart showing the operation of each part in the image forming apparatus 100 of this embodiment when the brush cleaning operation is performed in the post-rotation operation until the image forming apparatus 100 stops the operation after the image forming operation (e.g., single-page printing operation). As in Figure 2 and 3 in Embodiment 1 and the modified example of Embodiment 1, the charging voltage, the brush voltage, the transfer voltage, the post-transfer drum potential, and the potential difference between the brush voltage and the post-transfer drum potential are shown. Figure 6 is shown. The operation shown in Figure 6 is controlled by the control section 50, which sends control signals to each power supply section. As in Embodiment 1 and the modified example of Embodiment 1, in this embodiment, the transfer voltage is controlled to be a constant voltage.

[0121] Figure 6 The operation of each part of the photosensitive drum 1 in this embodiment shown in Figure 2 and 3 is the same as that shown in

[0122] In this embodiment, first, after the transition to the post-rotation operation (brush cleaning operation), the post-transfer drum potential is changed in a stepwise manner to become equal to the brush voltage. Then, the transfer voltage is controlled so that the negative polarity potential difference between the brush voltage and the post-transfer drum potential gradually changes in the increasing direction. Thereafter, the post-transfer drum potential is changed so that it becomes equal to the brush voltage. Thereafter, the transfer voltage is controlled so that the positive polarity potential difference between the brush voltage and the post-transfer drum potential gradually changes in the increasing direction.

[0123] In the modified example of Embodiment 1, regarding the discharge of the positive toner, which is the main discharge target in the brush cleaning operation, there is a period in which the absolute value of the potential difference between the brush voltage and the post-transfer drum potential changes in the decreasing direction. This is Figure 3period in which the potential difference between the brush voltage and the post-transfer drum potential is changed from +400 V to 0 V. In contrast, in the present embodiment, the potential difference between the brush voltage and the post-transfer drum potential is changed in a direction in which the absolute value thereof increases with respect to the discharge of the positive toner, which is the main discharge target in the brush cleaning operation. This is Figure 6 period in which the potential difference between the brush voltage and the post-transfer drum potential is changed from 0 V to +400 V. In addition, with respect to the discharge of the negative toner, there is also a period in which the absolute value of the potential between the brush voltage and the post-transfer drum potential is changed in an increasing direction. This is the period in which the potential difference between the brush voltage and the post-transfer drum potential is changed from 0 V to -400 V.

[0124] 2. Evaluation Tests

[0125] Next, the results of evaluation tests performed in order to confirm the effectiveness of the present embodiment are described. Here, Evaluation Tests 1 and 2 mentioned above were performed. The results of Evaluation Tests 1 and 2 for the present embodiment are shown in Table 2 together with the results for the modified example of Embodiment 1. The evaluation methods for Evaluation Tests 1 and 2 were the same as described above, but the case in which the spot white image in the rotation period of the charging roller 2 was better suppressed was judged to be "◎ (better)".

[0126] [Table 2]

[0127]

[0128] The results in Table 2 show that the present embodiment obtained better results than the modified example of Embodiment 1 for Evaluation Test 1 (toner contamination of the charging roller 2). In addition, in the present embodiment, similar results to the modified example of Embodiment 1 were obtained for Evaluation Test 2 (cleaning ability).

[0129] The results show that, in this example, contamination of the charging roller 2 with toner is further suppressed in the brush cleaning operation compared to the modified example of Example 1. This is considered to be because a smaller amount of toner is discharged from the brush member 11 onto the photosensitive drum 1 in this example than in the modified example of Example 1 for the following reasons. In this example, there is a period in which the absolute value of the potential difference between the brush voltage and the post-transfer drum potential gradually increases from the same post-transfer drum potential as the brush voltage, for both negative and positive toner. In particular, in this example, with regard to the discharge of positive toner, which is the main discharge target in the brush cleaning operation, the potential difference between the brush voltage and the post-transfer drum potential has a period in which its absolute value changes in the increasing direction, not the decreasing direction. Here, the greater the absolute value of the potential difference between the brush voltage and the post-transfer drum potential, the more favorable it is for discharge, but the absolute value should change from a small value to a large value. In other words, when the absolute value of the potential difference is smaller than it is larger, toner accumulated on the brush member 11 is preferentially selected from toner that is easy to move in terms of toner particle size, toner charge amount, and adhesion to the brush member 11, and moved onto the photosensitive drum 1. By gradually increasing the absolute value of the potential difference from a small value, a small amount of toner can be discharged from toner that is easily moved from the brush member 11 to the photosensitive drum 1. In contrast, if the absolute value of the potential difference is gradually decreased from a large value, the amount of toner that is instantaneously discharged onto the photosensitive drum 1 increases during the period in which the absolute value of the potential difference is large. In the modified example of Example 1, the potential difference between the brush voltage and the post-transfer drum potential is observed to change from +400 V to 0 V in the period in which the brush voltage is equal to the post-transfer drum potential. In contrast, in this example, there is no such period in which the potential difference between the brush voltage and the post-transfer drum potential is equal to 0 V. Therefore, in this example, the amount of toner that is instantaneously discharged can be further suppressed compared to the modified example of Example 1. Figure 3 In the modified example of Example 1, the potential difference between the brush voltage and the post-transfer drum potential is observed to change from +400 V to 0 V in the period in which the brush voltage is equal to the post-transfer drum potential. In contrast, in this example, there is no such period in which the potential difference between the brush voltage and the post-transfer drum potential is equal to 0 V. Therefore, in this example, the amount of toner that is instantaneously discharged can be further suppressed compared to the modified example of Example 1.

[0130] On the other hand, in this example, the transfer voltage must be adjusted so that the post-transfer drum potential is equal to the brush voltage. This is relatively easy if there is a component within the image forming apparatus 100 that measures the drum potential. However, if there is no component that measures the drum potential, it is necessary to set the transfer voltage so that the post-transfer potential is equal to the brush voltage, taking into account fluctuations in the drum potential due to environmental temperature and humidity, changes in the resistance of the transfer roller 5, and the capacitance of the photosensitive drum 1. In contrast, in the modified example of Example 1, it is not necessary to know the value of the transfer voltage at which the brush voltage and the post-transfer drum potential become the same level. Therefore, the control in the modified example of Example 1 is simpler than the control in this example.

[0131] Thus, in the present embodiment, the control portion 50 controls the surface potential of the photosensitive member 1 at the brush contact position P5 so that the contact position potential difference changes in a direction in which the absolute value of the contact position potential difference increases during a period in which the sign of the contact position potential difference becomes the opposite sign of the regular polarity of the toner.

[0132] As explained above, according to the present embodiment, it is possible to further suppress the instantaneous discharge of more toner from the brush member 11, and further suppress the contamination of the charging roller 2 with toner during the brush cleaning operation, compared to the modified example of Embodiment 1.

[0133] The present application has been explained in accordance with the specific embodiments described above. The dimensions, materials, shapes, and relative arrangements of the components described in the above embodiments should be changed in accordance with the configuration of the apparatus to which the present application is applied, and various other conditions. In other words, it is not intended to limit the scope of the present application to the above embodiments.

[0134] In the present embodiment, the printer is illustrated as an image forming apparatus, but the present application is not limited to this type of apparatus. The present application can be applied to other image forming apparatuses (such as a copier, a facsimile), or other image forming apparatuses (such as a multifunction machine that combines these functions), and the same effects as in the above embodiments can be obtained. In the present embodiment, the image forming apparatus is a monochrome image forming apparatus, but the present application can also be applied to a color image forming apparatus, and the same effects as in the above embodiments can be obtained. The color image forming apparatus can be a tandem type image forming apparatus equipped with a plurality of photosensitive members. The tandem type image forming apparatus is well known for an intermediate transfer method in which toner images are transferred from a plurality of photosensitive members to an intermediate transfer member by primary transfer to be transferred to a recording material by secondary transfer, and for a direct transfer method in which toner images are directly transferred from a plurality of photosensitive members to a recording material carried on a recording material carrier. In an image forming apparatus that uses an intermediate transfer member (intermediate transfer belt) as a transfer member, paper dust can adhere to the photosensitive member via the intermediate transfer member, so it is conceivable to provide a paper dust removal member to remove paper dust from the photosensitive member.

[0135] According to the present application, it is possible to improve the cleaning ability of a brush member positioned in contact with a photosensitive member.

[0136] [Image forming apparatus]

[0137] Figure 10is a schematic view of a configuration example of an image forming apparatus according to Embodiment 3. The image forming apparatus in Embodiment 3 is a monochrome printer. The image forming apparatus has a cylindrical photosensitive member or photosensitive drum 1 as an image carrier. Surrounding the photosensitive drum 1 is a charging roller 2 as a charging member and a developing unit 3. Between the charging roller 2 and the developing roller 3, there is an exposure unit 4 as an exposure member. Further, a transfer roller 5 as a transfer member is pressed against the photosensitive drum 1.

[0138] The photosensitive drum 1 is a negatively electrified organic photosensitive member. The photosensitive drum 1 has an outer diameter of, for example, 24 mm. The photosensitive drum 1 has a photosensitive layer on a drum-shaped substrate of aluminum that is grounded, and is driven by a driving unit (not shown) at a designated process speed in the direction of the arrow in the figure (clockwise direction). The process speed corresponds to the circumferential speed of the photosensitive drum 1 (the surface movement speed of the photosensitive drum 1).

[0139] The charging roller 2 contacts the photosensitive drum 1 with a predetermined contact force of pressure to form a charged portion. The charging roller 2 is subjected to a predetermined charging voltage by a charging high-voltage power supply 210 as a first member that applies a charging voltage, and the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential. The photosensitive drum 1 is charged to a negative polarity, for example, by the charging roller 2.

[0140] The exposure unit 4 is, for example, a laser scanner unit that outputs a laser beam L corresponding to image information input from an external device such as a host computer, and performs scanning and exposure on the surface of the photosensitive drum 1. This exposure forms an electrostatic latent image (electrostatic image) on the surface of the photosensitive drum 1 in accordance with the image information. The exposure unit 4 is not limited to a laser scanner device, but can employ, for example, an LED array that arranges a plurality of light emitting diodes (LEDs) along the long side direction of the photosensitive drum 1.

[0141] For example, a contact developing method is used as the developing method. The developing unit 3 has a developing roller 31 as a developer carrier, a toner supply roller 32 as a developer supply member, a developer chamber 33 that houses toner, and a developing blade 34. The toner supplied from the developer chamber 33 to the developing roller 31 as a developing member by the toner supply roller 32 is charged to a predetermined polarity when it passes through a contact portion with the developing blade 34. In Embodiment 3, for example, a conventional charged-polarity toner having a particle diameter of 6 μm and a negative polarity is used. Although a single-component non-magnetic contact developing method is employed in Embodiment 3, a two-component non-magnetic contact / non-contact developing method can also be employed, or a magnetic developing method can be employed.

[0142] In the developing portion between the developing roller 31 and the photosensitive drum 1, the electrostatic latent image formed on the photosensitive drum 1 (on the image bearer) is developed into a toner image (developer image) by the toner (developer) fed by the developing roller 31. At this time, as a second application member for applying a developing voltage, the developing roller 31 is applied with a developing voltage from a developing high-voltage power supply 220. In Embodiment 3, for example, the electrostatic latent image is developed by a reverse developing method. In other words, the electrostatic latent image is developed into a toner image by attaching charged toner having the same polarity as the polarity of the photosensitive drum 1 to the portion of the photosensitive drum 1 that has lost its charge after the charging process and exposure.

[0143] The transfer roller 5 can be appropriately made of an elastic member, such as a sponge rubber made of polyurethane rubber, EPDM (ethylene propylene diene rubber), NBR (nitrile rubber), or the like. The transfer roller 5 is pressed against the photosensitive drum 1 to form a transfer portion in which the photosensitive drum 1 and the transfer roller 5 are in pressure contact. The transfer roller 5 is connected to a transfer high-voltage power supply 230 as a fourth application member for applying a transfer voltage, and is applied with a predetermined voltage at a predetermined timing.

[0144] At the timing at which the toner image formed on the photosensitive drum 1 reaches the transfer portion, the recording material S stored in the paper cassette 6 is fed as a recording material by the paper feed unit 7, and is fed by the registration (hereinafter, simply referred to as “resistor”) roller pair 8 and fed to the transfer portion. The toner image formed on the photosensitive drum 1 is transferred onto the recording material S by the transfer roller 5, to which a predetermined transfer voltage is applied by the transfer high-voltage power supply 230. The image forming apparatus has a brush member 11 (collection member), which is a contact member as a paper dust removal mechanism. The brush member 11 is described below.

[0145] After the transfer of the unfixed toner image, the recording material S is fed to the fixing unit 9. The fixing unit 9 is a film fixing method fixing unit equipped with a fixing film 91 and a pressure roller 92. The fixing film 91 incorporates a fixing heater (not shown) and a thermistor (not shown) that measures the temperature of the fixing heater. The pressure roller 92 is pressed against the fixing film 91. The recording material S is heated and pressed by the fixing unit 9 to fix the toner image, and is discharged from the apparatus by the discharge roller pair 10.

[0146] The image forming apparatus is equipped with a control portion 200 that controls the entire image forming apparatus by controlling the above-described respective portions, including an image forming operation, a recording material S feed operation, a cleaning operation of the brush member 11 (hereinafter, referred to as “brush cleaning”), and the like. The control portion 200 has, for example, a CPU 200a that executes a program stored in a ROM 200b while using a RAM 200c as a temporary work area, the timing of which is controlled by a timer 200d.

[0147] [Removal of residual transfer toner]

[0148] The toner remaining on the photosensitive drum 1 without being transferred to the recording material S (hereinafter referred to as "residual transfer toner") is removed in the following process. The residual transfer toner is a mixture of positively charged toner and negatively charged toner that does not have sufficient charge. The residual transfer toner is recharged to a negative polarity by discharge in the charging portion. With rotation of the photosensitive drum 1, the residual transfer toner recharged to a negative polarity in the charging portion reaches the developing portion. Here, an electrostatic latent image is formed on the photosensitive drum 1 that has reached the developing portion. The behavior of the residual transfer toner that has reached the developing portion is described separately for the exposed portion (in other words, the image forming portion) and the non-exposed portion (in other words, the non-image forming portion) of the photosensitive drum 1.

[0149] (non-image forming portion (non-exposed portion))

[0150] The residual transfer toner attached to the non-image forming portion of the photosensitive drum 1 is transferred to the developing roller 31 in the developing portion by a potential difference between the potential of the non-image forming portion of the photosensitive drum 1 (hereinafter referred to as the non-image forming portion potential) and the developing voltage, and is collected (stored) in the developer chamber 33 as a storage portion. The toner collected in the developer chamber 33 is reused for image formation. In this way, the control portion 200 controls the developing voltage applied by the developing high voltage power supply 220 to collect the toner remaining on the photosensitive drum 1 without being transferred to the recording material S by the transfer roller 5 into the developer chamber 33 by the developing roller 31.

[0151] (image forming portion (exposed portion))

[0152] On the other hand, the residual transfer toner attached to the exposed portion (image forming portion) of the photosensitive drum 1 is not transferred from the photosensitive drum 1 to the developing roller 31 in the developing portion, but is transferred to the transfer portion together with the toner developed from the developing roller 31 and retransferred to the recording material S, where it is removed from the photosensitive drum 1.

[0153] [brush member 11]

[0154] Next, the paper dust removal mechanism of Embodiment 3 is described. As shown in FIG. 1, the image forming apparatus has a brush member 11 as a paper dust removal mechanism (collection member). The brush member 11 has a flock string as a plurality of bristles rubbing the surface of the photosensitive drum 1 and a base fabric supporting the flock string, as described in detail below. The brush member 11 is arranged to contact the photosensitive drum 1 downstream of the transfer portion and upstream of the charging portion in the moving direction (rotational direction) of the photosensitive drum 1. The brush member 11 is supported by a support member (not shown) and positioned at a fixed position with respect to the photosensitive drum 1, and slides on the surface of the photosensitive drum 1 as the photosensitive drum 1 moves. Figure 10 The brush member 11 is arranged to contact the photosensitive drum 1 downstream of the transfer portion and upstream of the charging portion in the moving direction (rotational direction) of the photosensitive drum 1. The brush member 11 is supported by a support member (not shown) and positioned at a fixed position with respect to the photosensitive drum 1, and slides on the surface of the photosensitive drum 1 as the photosensitive drum 1 moves.

[0155] The brush member 11 collects, along with toner, attached materials such as paper dust that is transferred from the recording material S to the photosensitive drum 1 in the transfer portion. The brush member 11 reduces the amount of paper dust that moves to the charging portion and the developing portion downstream of the brush member 11 in the moving direction (rotation direction) of the photosensitive drum 1. The brush member 11 uses the developing high-voltage power supply 220 as the third application member that applies the brush voltage. In other words, the second and third application members are common power supplies, and the same voltage as the developing voltage applied to the developing roller 31 is applied to the brush member 11 as the brush voltage. The brush cleaning control described below is not limited to the configuration in which the brush voltage is applied to the brush member 11 from the developing high-voltage power supply 220. The third application member that applies the brush voltage to the brush member 11 can be provided separately from the developing high-voltage power supply 220.

[0156] In Embodiment 3, nylon is used as the binding material of the bristle string of the brush member 11, and a carbon-mixed conductive nylon fiber is used as the conductive material, but these materials are not limited thereto. For example, even if the binding material is polyester or acrylic, it can be used in the same manner as long as it is conductive. The length of the brush member 11 in the diameter direction (hereinafter referred to as the short-side direction) of the photosensitive drum 1 is set to 5 mm, for example, but is not limited thereto. For example, it can be changed according to the amount of paper dust as the life of the image forming apparatus or the process cartridge increases.

[0157] The bristle length of the brush member 11 is 5 mm, for example, but is not limited thereto. However, when the brush member 11 is used to collect paper dust, it is necessary to ensure a certain amount of penetration of the brush member 11 into the photosensitive drum 1, because if the bristle length is too short, the contact pressure against the photosensitive drum 1 becomes stronger, and the surface of the photosensitive drum 1 can be damaged by friction. Therefore, it is desirable for the bristle length of the brush member 11 to be 4 mm or more. The length of the brush member 11 in the long-side direction is set to 230 mm, for example, but is not limited thereto. For example, it can be changed according to the maximum paper width of the image forming apparatus. Here, the paper width refers to the length of the recording material S in the direction perpendicular to the feeding direction of the recording material S, in other words, in the long-side direction of the photosensitive drum 1. The image forming apparatus is capable of forming an image on recording material S of various paper widths, and the longest of the various paper widths is referred to as the maximum paper feeding width (maximum paper width).

[0158] The fineness of the brush member 11 is 2 d, for example, but is not limited thereto. Here, a fineness of 2 d means that each fiber weighs 2 g per 9000 m. However, a high fineness is not desirable because the fibers are hard and the contact pressure against the photosensitive drum 1 becomes stronger, and the surface of the photosensitive drum 1 can be damaged by friction. Therefore, a fineness of 6 d or less is desirable. The density of the brush member 11 is 240 kF / inch, for example, but is not limited thereto.2 However, it is not limited to this. Here, "kF / inch" 2 "" is a unit of brush density and indicates the number of filaments per square inch. However, when brush component 11 is used to collect paper dust, a low density increases the likelihood of paper dust slipping through. Therefore, 120 kF / inch is expected. 2 Or higher density.

[0159] The penetration depth of the brush component 11 is set, for example, to 1.5 mm, but is not limited thereto. However, when the brush component 11 is used to collect paper dust, the small penetration depth of the brush component 11 into the photosensitive drum 1 increases the possibility that the paper dust will slip through. Therefore, a penetration depth of 1 mm or more is desirable. The resistance of the brush component 11 is 1.0 x 10⁻⁶ when measured as follows. 5 Ω. That is, the brush component 11 is fixed to the aluminum cylinder such that the brush component 11 extends 1 mm from the tip of the bristles along the length direction of the bristles. The resistance of the brush component 11 is measured by applying a voltage of 50V to the brush component 11 while the aluminum cylinder rotates at a speed of 50mm / s. However, the resistance of the brush component 11 is not limited to this, and a resistance of approximately 1.0 x 10 Ω can be used. 8 A brush with high resistance of Ω.

[0160] [Brush cleaning control using the transfer roller]

[0161] Next, use Figure 11 This section explains an example of brush cleaning control during non-image forming operations. Brush cleaning control is performed by control section 200, which controls each of the application components mentioned above. Figure 11 The diagram illustrates brush cleaning control performed during the period between the image forming operation and its termination in a conventional image forming apparatus (hereinafter referred to as "post-rotation operation"). (i) shows the charging voltage applied to the charging roller 2 from the charging high-voltage power supply 210, and (ii) shows the brush voltage applied to the brush member 11 from a conventional brush high-voltage power supply (not shown). (iii) shows the transfer voltage applied to the transfer roller 5 from the transfer high-voltage power supply 230, and (iv) shows the surface of the photosensitive drum 1 after transfer (hereinafter referred to as "post-transfer") by the transfer roller 5 to which the transfer voltage (hereinafter referred to as "drum potential") is applied.

[0162] (v) Indicates the difference between the brush voltage and the post-transfer drum potential, i.e., the potential difference (brush voltage - post-transfer drum potential). Both horizontal axes indicate time.

[0163] For example, a charging voltage of -1300 V is applied to the charging roller 2, which uniformly charges the drum potential to approximately -800 V in the long-side direction. In addition, a value of, for example, -400 V, which is approximately an intermediate value between the drum potential of -800 V in the non-image forming portion and the drum potential of 0 to -100 V in the image forming portion, is applied to the brush member 11. This setting prevents image defects caused by discharge between the brush member 11 and the photosensitive drum 1. By taking the potential between the drum potential of the non-image forming portion and the drum potential of the image forming portion, the negative and positive polarity toners accumulated on the brush member 11 are discharged to the photosensitive drum 1 side by adjusting the drum potential. In addition, for the image forming portion in which the drum potential is approximately 0 to -100 V, the potential relationship is such that the negative polarity toner (hereinafter referred to as "negative toner") contained in the residual transfer toner is allowed to pass through the brush member 11 without being attached to it. This prevents toner from excessively accumulating on the brush member 11 (hereinafter referred to as "excessive accumulation").

[0164] After timing tl, when the operation is shifted from the image forming operation to the post-rotation operation, -400 V is applied to the transfer roller 5 as a voltage within a range in which the drum potential of -800 V in the non-image forming portion is not lowered due to discharge. This increases the difference between the brush voltage and the post-transfer drum potential without lowering the post-transfer drum potential, and the magnitude of the potential difference is such that the positive polarity toner (hereinafter referred to as "positive toner") accumulated in the brush member 11 is discharged to the photosensitive drum 1 side. Next, at timing t2, a transfer voltage of, for example, +1000 V is applied to the transfer roller 5 to lower the post-transfer drum potential to approximately 0 V. This increases the difference between the brush voltage and the post-transfer drum potential to the opposite side (-400 V) of the above-mentioned potential difference (+400 V), and the negative toner is discharged from the brush member 11 to the photosensitive drum 1 side. By the above operation, the positive toner and the negative toner accumulated in the brush member 11 are discharged onto the photosensitive drum 1.

[0165] [Action of brush cleaning control]

[0166] By increasing the potential difference between the brush member 11 and the drum potential, toner is discharged from the brush member 11 to the photosensitive drum 1. Figure 12 How toner is discharged from the brush member 11 to the photosensitive drum 1 is shown, with the vertical axis representing the potential and the horizontal axis representing the position. In Figure 12 In (a), the drum potential is -800 V and the brush voltage is -400 V, corresponding to timing tl to timing t2 in Figure 11 Thus, if the absolute value of the drum potential is higher than the absolute value of the brush voltage (|-800| V > |-400| V), the positive toner is discharged from the brush member 11 to the photosensitive drum 1. On the other hand, in Figure 12In (b), the drum potential is 0 V and the brush voltage is -400 V, which corresponds to timing t2 or later in (a). Therefore, if the absolute value of the drum potential is lower than the absolute value of the brush voltage (|0| V < |-400| V), the negative toner is discharged. Therefore, by changing the potential difference between the brush voltage of the brush member 11 and the drum potential to positive and negative with respect to the brush voltage, the negative and positive toners can be discharged. Figure 11

[0167] (Negative toner)

[0168] In the charging portion where the charging roller 2 contacts the photosensitive drum 1, due to the potential difference between the charging voltage (-1300 V) and the drum potential (-800 V), the electrostatic force applied to the negative toner is relatively larger toward the photosensitive drum 1 than toward the charging roller 2. Therefore, the negative toner discharged from the brush member 11 passes through the contact area between the photosensitive drum 1 and the charging roller 2 (hereinafter referred to as a charging contact area). The negative toner that has passed through the charging roller 2 due to the rotation of the photosensitive drum 1 is drawn toward the developing roller 31 and the developing portion. At the developing roller 31 and the photosensitive drum 1, due to the potential difference between the developing potential (-400 V) and the drum potential (-800 V), the electrostatic force applied to the negative toner is relatively larger than the force toward the developing roller 31. Therefore, the negative toner discharged from the brush member 11 is drawn by the developing roller 31 at the contact portion between the photosensitive drum 1 and the developing roller 31, and is collected in the developing unit (developer chamber 33).

[0169] (Positive toner)

[0170] Discharge occurs at the contact portion between the photosensitive drum 1 and the charging roller 2. The positive toner discharged from the brush member 11 is affected by this discharge and becomes a negative toner by being charged in a negative polarity, and is collected in the developing unit by the same process as the above-described negative toner.

[0171] As explained above, this brush cleaning control controls the drum potential via the transfer roller 5 by controlling the transfer voltage, and performs cleaning using the potential difference between the drum potential and the brush voltage. Therefore, cleaning is performed by this brush cleaning control only in the area corresponding to the length of the long side direction of the transfer roller 5 (hereinafter referred to as the width of the transfer roller 5).

[0172] ​In general, the transfer member only needs to have the width of the maximum image forming area, and from the viewpoint of reducing costs, the width should be as short as possible. Here, the image forming area refers to an area in which a toner image is formed in the width direction, and the maximum image forming area is an area in which the longest toner image is formed in the width direction, i.e., an area corresponding to the maximum paper width. On the other hand, the width of the opening of the developer chamber 33 in which the developing roller 31 is installed (hereinafter referred to as "developing opening width") should be longer than the maximum paper width. This is because if the developing opening width is wider than the image forming area but narrower than the paper width, a difference in toner concentration occurs at the boundary of the area on the paper (hereinafter referred to as the developing opening area) corresponding to the developing opening width. The amount of toner coated on the developing roller 31 differs between the developing opening area and the non-developing opening area. This is because the amount of toner coated on the photosensitive drum 1 in contact with the developing roller 31 also differs between the developing opening area and the non-developing opening area, and this is transferred to the paper. From the viewpoint of paper dust collection, the brush member 11 needs to be longer than the maximum paper width, and should be longer than the developing opening to prevent foreign matter from entering the developing opening portion.

[0173] [Configuration of Embodiment 3]

[0174] The length of each member in the long side direction in Embodiment 3 is shown in Figure 13 . Figure 13 The left side is a schematic view of the main part of the photosensitive drum 1 and the members in contact with the photosensitive drum 1, and the right side shows the relationship between the length of one end in the long side direction. In Embodiment 3, the recording material S is fed with the center in the width direction as a reference, and the members in contact with the photosensitive drum 1 are all arranged so that they are in line with respect to the center in the width direction. In Figure 10 the configuration shown in Figure 13 , the photosensitive drum 1, the charging roller 2 in contact with the photosensitive drum 1, the developing roller 31, the transfer roller 5, and the brush member 11 are shown so that the length relationship in the long side direction can be understood. However, the developing roller 31 shows the length of the developing opening portion of each roller on which there is toner (on the developing member). In Figure 13 , the length (width) of a letter-size paper sheet, which is assumed to be the maximum paper width, is also shown. For example, the width of the photosensitive drum 1 is 244 mm, and the width of the letter-size paper sheet (dotted line) is 216 mm. The charging roller 2 is longer than the letter-size paper sheet and shorter than the photosensitive drum 1, at 230 mm. The brush member 11 is 233 mm, which is longer than the charging roller 2 and shorter than the photosensitive drum 1. The transfer roller 5 is 215 mm, which is shorter than the letter-size paper sheet. The developing opening width of the developing roller 31 is 222 mm, which is longer than the letter-size paper sheet and shorter than the brush member 11.

[0175] In Embodiment 3, the long side length of the photosensitive drum 1 and each member in contact with the photosensitive drum 1 is in the order from short to long as the developing opening width in the developing roller 31, the brush member 11, the charging roller 2, and the transfer roller 5. In other words, there is a region in the vicinity of the end portion of the brush member 11 on the outside of the transfer roller 5 and on the inside of the developing opening portion of the developing roller 31. This region is defined as a region A. In the region A, the brush cleaning using the transfer roller 5 as described above cannot be performed, and the negative toner always accumulates on the brush member 11, as Figure 12 (a) shown. The position of the region A is shown in Figure 13

[0176] [Brush cleaning control in Embodiment 3]

[0177] The various types of potential control in Embodiment 3 are explained using Figure 14 The cleaning control in Embodiment 3 is performed by controlling the control portion 200 of each of the above-mentioned application members. Figure 14 The post-rotation operation after a single print operation in the image forming apparatus of Embodiment 3 is shown in (a) and (b). The process from the start of the rotation drive of the photosensitive drum 1 to the image forming operation is the same as in the conventional case. Figure 13 The horizontal axis in (a) and (b) shows time (ms), and the vertical axis shows the voltage or the like applied to each assembly. Specifically, (i) shows the charging voltage (V), and (ii) shows the brush / developer common voltage (V), in which the brush voltage and the developer voltage are common. (iii) indicates the surface potential of the photosensitive drum 1 (hereinafter referred to as the drum surface potential) (V) at the contact portion between the developing roller 31 and the photosensitive drum 1 (hereinafter referred to as the developing contact portion). (iv) shows the drum surface potential (V) at the contact region between the brush member 11 and the photosensitive drum 1 (hereinafter referred to as the brush contact region). (v) shows the potential difference (V) between the drum surface potential and the developing voltage at the developing portion. (vi) shows the potential difference (V) between the drum surface potential and the brush voltage at the brush contact region. The times (0, 1500, 1714, etc.) show examples at a processing speed of 139.67 mm / sec. Figure 14 For simplicity, the time required to switch the voltage applied to each member is not taken into account in (a) and (b), and thus it is assumed that the voltage is changed in a rectangular shape during the switching. The change in the drum surface potential is also outlined with a rectangle without taking into account the influence of natural decay and other factors. While these simplifications can cause the partial waveforms to not completely match the actual waveforms, the voltage switching order for each member remains the same, and what criteria should be specifically used to determine the switching timing will be appropriately described.

[0178] Figure 14 For simplicity, the time required to switch the voltage applied to each member is not taken into account in (a) and (b), and thus it is assumed that the voltage is changed in a rectangular shape during the switching. The change in the drum surface potential is also outlined with a rectangle without taking into account the influence of natural decay and other factors. While these simplifications can cause the partial waveforms to not completely match the actual waveforms, the voltage switching order for each member remains the same, and what criteria should be specifically used to determine the switching timing will be appropriately described.

[0179] ​​(Time slot 1)

[0180] The control following the transition from image forming control to rotation control at time t11 is as follows: Figure 14 The circled numbers 1 to 5 are described in chronological order. In the following text, time period circled number 1, etc., will be simply referred to as time period 1, etc. When switching to time period 1 at time t11, after the image forming operation is completed and the rotational operation begins, the common voltage of the developer and brush changes from -400V, which is the voltage during the image forming operation, to 150V. The charging voltage changes from -1300V to 0V, which is the voltage during the image forming operation. By changing the voltage applied in the brush contact portion (and the developing contact portion) and the charging portion, the photosensitive drum surface potential, which is -800V during image forming, changes from -800V to the positive side as the drum passes through the developing contact portion due to the discharge between the developing roller 31 and the photosensitive drum 1. For simplicity, Figure 14 The diagram illustrates the potential transition of each component when the developing voltage switches from -400V to 150V, specifically when the surface potential of the drum at the developing contact portion uniquely switches from -800V to 0V at the start of time period 1 (t11). However, in reality, the surface of the photosensitive drum may not switch at this timing, as potential switching takes time. A single contact between the developing roller 31 and the photosensitive drum 1 will not result in a potential of 0V; several contacts are required, and so on. Therefore, the absolute value of the surface potential of the drum before charging or after charging and passing through the developing section is less than -800V, but not necessarily 0V. Here, a necessary condition in the developing section is that backcontrast should be appropriately formed, which is the potential difference between the surface potential of the charged photosensitive drum and the developing voltage. In other words, the surface potential at the developing contact portion does not need to be 0V. The backcontrast is not limited to 150V and should be appropriately set. For simplicity of explanation, the following description assumes that the surface potential of the photosensitive drum is 0V before charging. The absolute value of the surface potential of the photosensitive drum after charging is even smaller due to the potential difference caused by the developing voltage and the brush voltage. In other words, as described above, the drum surface potential changes towards the positive side when it approaches 0V. Furthermore, as a result of this positive change, the surface potential of the drum that comes into contact with the charging roller 2 just before the charging voltage is switched at time t13 should be more positive than the common brush / developing voltage during time period 4.

[0181] (Time slot 2)

[0182] The period 2 from timing t12 to timing t13 is the period from the timing at which the boundary between -800 V and 0 of the drum surface potential reaches the brush member 11 until the charging voltage is switched from 0 V to -1300 V. In other words, timing t12 is the timing at which the boundary between -800 V and 0 V of the drum surface potential reaches the brush member 11, indicated by a double dotted line. The charging voltage is switched after the drum surface potential in contact with the charging roller 2 becomes the positive side of the common brush / developer voltage in the period 4 described later. Figure 14 The transition of the potential of each member is shown when the drum surface potential of the developing contact portion is switched from -800 V to 0 at timing tll, which is the start of the period 1. However, if the switching of the drum surface potential takes time in actual control, it is necessary to delay the switching of the charging potential at the end of the period 2, and to switch it after the drum surface potential of the portion in contact with the charging roller 2 changes from the common brush / developer voltage to the positive side in the period 4. In Embodiment 3, as shown in FIG. 10, the case where the drum surface potential of the developing contact portion is switched from -800 V to 0 V when the developing voltage is switched from -400 V to 150 V is explained. Figure 14

[0183] (period 3)

[0184] At timing t13, which is the end of the period 2, the charging voltage is changed from 0 V to -1300 V, and the drum surface potential is charged from 0 V to -800 V at the portion in contact with the charging roller 2. The period from the switching of the charging voltage to the timing t14 when the boundary between 0 V and -800 V of the drum surface potential reaches the developing portion is defined as the period 3.

[0185] (period 4)

[0186] The period 4 from timing t14 to timing t15 is the period from the boundary between 0 V and -800 V of the drum surface potential reaching the developing portion until this boundary reaches the brush member 11. The solid arrow indicates that the boundary portion of the drum surface potential reaches the developing portion at timing t14 due to the switching of the charging voltage at timing t13. At timing t14, just after the start of the period 4, the brush / developer common voltage is switched from 150 V to -400 V. In the period 4, the relationship between the drum surface potential of the portion in contact with the brush member 11 and the brush voltage is the same as that in the period 1. Figure 12 ​(b) shows that the absolute value of the brush voltage (|-400| V) is greater than the absolute value of the drum potential (|0| V). Thus, the negative toner accumulated on the brush member 11 is discharged onto the photosensitive drum 1. At this time, when the same polarity brush voltage as the normal polarity of the toner is applied to the brush voltage, if the absolute value of the drum potential is less than the absolute value of the brush voltage, the negative toner is discharged onto the photosensitive drum 1. Thus, the voltage required as the brush voltage is appropriately set according to the photosensitive drum surface potential. In other words, as mentioned above, the surface potential of the photosensitive drum does not have to be 0 V. The negative toner accumulated on the brush member 11 should be set so that it is discharged onto the photosensitive drum 1. Figure 14 Period 4 of (vi) shows an image illustrating that the negative toner is discharged onto the photosensitive drum 1. On the other hand, the developing voltage at the developing roller 31 is -400 V, while the surface of the photosensitive drum at the portion where the drum contacts the developing roller 31 is -800 V, so the negative toner having the normal polarity is never developed on the photosensitive drum 1.

[0187] (Period 5)

[0188] Period 5 after timing t15 is a period after the boundary between 0 V and -800 V of the drum surface potential reaches the brush member 11. In other words, timing t15 is the timing when the boundary between 0 V and -800 V of the drum surface potential has reached the brush member 11, which is indicated by the double dotted line that has moved to the brush member 11. Since the drum surface potential (-800 V) of the brush contact area becomes more negative than the brush voltage (-400 V), the discharge of the negative toner from the brush member 11 onto the photosensitive drum 1 is completed. In period 4, the surface of the photosensitive drum 1 (hereinafter referred to as "drum surface") from which the negative toner has been discharged passes through the brush contact portion, contacts the charging roller 2, and then enters the developing contact portion. After timing t13, when period 3 starts, a charging voltage of -1300 V is applied to the charging roller 2. Thus, the drum surface from which the negative toner has been discharged is charged to -800 V by passing through the contact charging roller 2. When this surface contacts the developing roller 31 to which a voltage of -400 V is applied, the negative toner is collected on the developing roller 31 side due to the potential difference between the photosensitive drum 1 and the developing roller 31. Figure 14 Period 5 in (v) shows an image illustrating that the negative toner is collected on the developing roller 31. After enough toner is collected in period 5, the application of the voltage to each member and the operation of the driving system are terminated.

[0189] In Embodiment 3, for the sake of simplicity, the charging voltage is changed at timing t11 and the developing voltage is also changed when switching from image formation to post-rotation operation, but it is not limited thereto. For example, the charging voltage and the developing voltage can be changed stepwise, respectively. By so doing, the potential difference between the drum potential of the developing contact portion and the developing roller 31 can be controlled within a certain range to suppress the phenomenon that toner charged with positive polarity is discharged from the developing roller 31 onto the photosensitive drum 1.

[0190] Although Embodiment 3 assumes an image forming apparatus in which the photosensitive drum 1 and the developing roller 31 are always in contact with each other during driving of the image forming apparatus, the same control can be applied to an image forming apparatus equipped with a contact separation mechanism that can arbitrarily separate the two portions. In this case, the photosensitive drum 1 and the developing roller 31 should be separated from each other from period 1 to period 4 in Figure 14 and then be in contact with each other at period 5. This has the effect of discharging toner from the brush member 11 onto the photosensitive drum 1 at period 4 and collecting the toner with the developing roller 31 at period 5, and also prevents the atomized toner from being discharged from the developing roller 31 onto the photosensitive drum 1 during periods 1 to 4. The control portion 200 can keep the developing roller 31 in contact with the photosensitive drum 1 when the image forming apparatus is operated.

[0191] In Embodiment 3, the drum surface potential is changed by controlling the developing voltage applied to the developing roller 31 at the end of the developing roller operation, but it is not limited thereto. For example, an exposure unit for the photosensitive drum 1 can be installed downstream of the brush member 11 and upstream of the charging roller 2 in the rotation direction of the photosensitive drum 1 to change the potential of the photosensitive drum surface from -800 V to 0 V.

[0192] In Figure 14 , the control of the outside (region A) of the transfer roller 5 in which the transfer roller 5 has no influence on the drum surface potential is described, but it is not limited to this region. In the portion with the transfer roller 5, the drum surface potential after passing through the transfer portion can be adjusted by arbitrarily changing the voltage applied to the transfer roller 5. For example, if the transfer voltage is set to the same potential as the surface of the photosensitive drum 1 opposite the roller, the same operation as in Figure 14 can be performed in the portion with the transfer roller 5.

[0193] For example, when a negative voltage is applied to the transfer roller 5, the drum surface potential after passing through the transfer portion in the region where the transfer roller 5 exists in the longitudinal direction is charged to the negative side compared to the portion where the transfer roller 5 is not present. In addition to the control as shown in Figure 14 , the drum surface potential after passing through the transfer portion in the region where the transfer roller 5 exists in the longitudinal direction is charged to the negative side compared to the portion where the transfer roller 5 is not present. In addition to the control as shown in Figure 15 the brush voltage at the brush member 11 and the drum surface potential at the portion in contact with the brush member 11 during period 4 when a negative voltage is applied to the transfer roller 5 are shown. In Figure 15In this case, the horizontal axis indicates a coordinate (position) extending in the long direction, and the vertical axis indicates the brush voltage and the drum surface potential at that coordinate (position). In the region where the transfer roller 5 is not present, the brush voltage is -400 V and the drum surface potential is 0 V, which is the same as the voltage in the period 4. Figure 14 In contrast, in the portion where the transfer roller 5 is present (with the transfer roller), the photosensitive drum surface potential in the brush contact portion is charged to the negative side.

[0194] As described above, the control unit 200 controls the charging high voltage power supply 210 and the developing high voltage power supply 220 so that the developer collected by the brush member 11 is moved from the brush member 11 to the surface of the photosensitive drum 1 in the first contact portion where the brush member 11 contacts the photosensitive drum 1. The control unit 200 controls the charging high voltage power supply 210 and the developing high voltage power supply 220 so that the developer on the surface of the photosensitive drum 1 is collected from the surface of the photosensitive drum 1 into the developer chamber 33 by the developing roller 31 at the second contact portion where the developing roller 31 and the photosensitive drum 1 contact each other. The control unit 200 performs such brush cleaning control. The developer moved to the surface of the photosensitive drum 1 is moved from the surface of the photosensitive drum 1 to the developing roller 31 because the drum potential is at the first potential and the developing voltage is at the third voltage in the second contact portion.

[0195] More precisely, the control unit 200 switches the charging portion from the first voltage (-1300 V) to a second voltage (0 V) having an absolute value smaller than the first voltage to change the drum potential from the first potential (-800 V) to the second potential (0 V) by switching from the first potential (-800 V) to the second potential (0 V). At the same time, the control unit 200 switches the brush voltage as the developing voltage and the contact voltage from the third voltage (-400 V) to a fourth voltage (150 V) having an absolute value smaller than the third voltage. After the first boundary portion on the photosensitive drum 1 from the first potential to the second potential reaches the first contact portion due to the rotation of the photosensitive drum 1, the control unit 200 returns the drum potential from the second potential to the first potential by returning the charging voltage from the second voltage to the first voltage. After the first boundary portion reaches the second contact portion, the control unit 200 moves the developer from the brush member 11 to the surface of the photosensitive drum 1 by returning the developing voltage and the brush voltage from the fourth voltage to the third voltage.

[0196] The transfer of the developer from the brush member 11 to the surface of the photosensitive drum 1 is completed when the second boundary on the photosensitive drum 1, which changes from the second potential to the first potential due to the rotation of the photosensitive drum 1, reaches the first contact portion. The first voltage is a charging voltage when image formation occurs, and the third voltage is a developing voltage and a brush voltage when image formation occurs. In Embodiment 3, the brush cleaning control is performed after the image formation control is performed on the recording material S. The length of the transfer roller 5 in the long side direction, which is a direction perpendicular to the rotation direction, is shorter than the width of the recording material (for example, a letter-size paper), which has the longest width of the recording material on which image formation can be performed in the image forming apparatus, the longest width being the length in the long side direction.

[0197] [Action of Embodiment 3]

[0198] As mentioned above, when the drum surface potential is changed using the member in contact with the photosensitive drum 1, the boundary of the drum surface potential is in contact with each member with a time difference as the photosensitive drum 1 rotates. By making use of this, a time period (period 4) in which the drum surface potential of the brush contact portion is different from the drum surface potential of the developing portion is established. In this case, the drum surface potential of the brush contact portion should be positive when the regular polarity of the toner is negative, and the drum surface potential of the brush contact portion should be negative when the regular polarity of the toner is positive, compared to the drum surface potential of the developing portion. Further, during this time period (period 4), the brush / developer common voltage is set to the voltage between the drum surface potential of the brush contact portion and the drum surface potential of the developing portion. This causes the brush member 11 to discharge the toner charged with the regular polarity onto the photosensitive drum 1. On the other hand, a large amount of the regularly charged toner on the developing roller 31 is not developed on the photosensitive drum 1 in the developing contact portion. The toner discharged from the brush member 11 onto the photosensitive drum 1 is collected in the developing portion, thereby completing the cleaning of the brush member 11.

[0199] [Effect Description]

[0200] The following is a description of the results of a paper feeding test performed to confirm the effectiveness of Embodiment 3. The paper feeding test was performed under the following conditions. First, the length of the transfer roller 5 was trimmed in the long side direction to be shorter than the width of the recording material S to be fed. This is a process of confirming the effect of the brush cleaning control of Embodiment 3 on the area A in the brush member 11 outside the width of the transfer roller 5 and in which the cleaning control using the transfer roller 5 does not work.

[0201] As the recording material S, Xerox Vitality Multipurpose Paper (trademark, basis weight 75 g) manufactured by Xerox was used at a temperature of 32.5°C and a relative humidity of 80% (high-temperature high-humidity environment). Ten continuous prints were made on the recording material S to form a horizontal line image (an image in which a horizontal line having a width of 0.254 mm and a blank space having a width of 25.146 mm are repeated). Then, the cleaning operation shown in Figure 14 Example 2 was repeated five times.

[0202] The charging voltage during the paper feeding in Example 3 was usually -1300 V, but in this continuous 10-sheet feeding, it was set to -930 V. This was to supply a large amount of atomized toner to the brush member 11 by making the drum surface potential after passing through the charging roller 2 close to the developing voltage. Atomized toner is generated by also supplying toner to the non-image forming portions (marginal portions and blank areas in the horizontal line image) on the photosensitive drum 1 from the developing roller 31. When the charging voltage is -1300 V, the drum surface potential after passing through the charging roller 2 is -800 V, whereas when the charging voltage is -930 V, the drum surface potential after passing through the charging roller 2 is -430 V. The developing voltage was set to -400 V. When the charging voltage is -1300 V, the potential difference between the surface of the photosensitive drum and the developing voltage is 400 V. Due to this potential difference, the negative toner as the regular charging polarity is subjected to a force in the direction of being pushed toward the developing roller 31 from the photosensitive drum 1. On the other hand, even when the charging voltage is set to -930 V, the potential difference between the surface of the photosensitive drum and the developing voltage is 40 V, and the negative toner is subjected to a force from the photosensitive drum 1 in the direction of being pushed toward the developing roller 31. However, when the charging voltage is set to -930 V, the potential difference is smaller and the force to which the negative toner is subjected is smaller than when the regular charging voltage of -1300 V is applied. In addition to these conditions, a preparation operation in which the cleaning operation is not performed after the continuous 10-sheet horizontal line image passes was also prepared for comparison.

[0203] Next, a single horizontal line image was fed with and without the brush cleaning operation. In this paper feeding, the charging voltage was set to -1300 V. If toner stains appeared in a region A outside the width of the transfer roller 5 that is truncated in the long-side direction, in the vicinity of the one-week length of the photosensitive drum 1 from the leading end of the recording material S, then the brush cleaning was judged to be defective. A schematic view of a typical image of a cleaning defect is shown in Figure 16 . Figure 16The width of the transfer roller 5 (less than 215 mm), the width of the letter-size paper sheet (216 mm), the feeding direction of the recording material S, and the width direction of each member are also shown. This toner stain is transferred to the recording material S for the following reasons. Since 10 recording material S sheets are continuously fed with the charging voltage set to -930 V, negative toner accumulates in the brush member 11. If the subsequent cleaning is not effective enough, toner is discharged from the brush member 11 to the photosensitive drum 1 in response to fluctuations in the drum surface potential caused by the recording material S rushing into the transfer nip portion.

[0204] The results of the paper feeding test are shown in Table 3.

[0205] [Table 3]

[0206] With cleaning Without cleaning Cleaning defect No Yes

[0207] Table 3 shows the occurrence of cleaning defects with and without cleaning, with "Yes" when a cleaning defect occurs and "No" when a cleaning defect does not occur. No cleaning defects were observed in the case where the cleaning operation was performed in Embodiment 3, while cleaning defects occurred in the case where no cleaning operation was performed.

[0208] Based on this result, the brush cleaning operation of Embodiment 3 discharges toner charged with the regular polarity from the brush member 11 to the photosensitive drum 1, while preventing a large amount of toner charged with the regular polarity on the developing roller 31 from developing on the drum 1 in the developing contact portion. This allows the brush member 11 to be cleaned regardless of the presence or absence of the transfer roller 5 in the width direction. Therefore, it was found that it is possible to suppress the discharge of toner and the occurrence of associated image defects even at the edges of the brush member 11 that are not cleaned by the transfer roller 5.

[0209] According to the above-described Embodiment 3, it is possible to reduce the size and cost of the cleanerless image forming apparatus, while reducing the occurrence of image defects caused by the cleaning brush.

[0210] Next, Embodiment 4 is explained. The basic configuration and operation of the image forming apparatus according to Embodiment 4 are the same as those of the image forming apparatus according to Embodiment 3. Therefore, elements of the image forming apparatus in Embodiment 4 that have the same functions or configurations as those of the image forming apparatus of Embodiment 3 will be labeled using the same symbols as those of the image forming apparatus in Embodiment 3, and detailed explanations will be omitted.

[0211] [Brush cleaning control in Embodiment 4]

[0212] The control of each type of potential control in Embodiment 4 is described below. The brush cleaning control in Embodiment 4 is also performed by the control section 200 controlling each of the application parts mentioned above. In Embodiment 3, after the image forming operation ends, the post-rotation operation (period 1 to period 5) shown in FIG. 10 is performed and the driving system operation is terminated. In the control shown in Embodiment 3, during continuous paper feeding, the brush member 11 is not cleaned from the start of feeding to the completion of the entire feeding. Therefore, when a large number of sheets are continuously fed, toner can accumulate in the brush member 11. Figure 14

[0213] In Embodiment 4, after a certain number of sheets have been fed and before the paper of the next sheet is fed (hereinafter referred to as "paper interval"), brush cleaning is performed. A specific control example is explained below. In Embodiment 4, during continuous paper feeding, brush cleaning is performed in the interval between papers, as shown in periods 1 to 5 in FIG. 11. Here, the paper interval refers to the space between the trailing end of the first recording material and the leading end of the second recording material when the second recording material is fed immediately after the first recording material and image formation is continuously performed. The paper interval can also be between the trailing end of the first toner image transferred to the first recording material and the leading end of the second toner image transferred to the second recording material. As shown in FIG. 11, in period 1, the brush member 11 is rotated in the direction opposite to the direction of rotation in the image forming operation. The brush member 11 is rotated in this direction to remove toner from the brush member 11. In period 2, the brush member 11 is rotated in the direction of rotation in the image forming operation. The brush member 11 is rotated in this direction to remove toner from the brush member 11. In period 3, the brush member 11 is rotated in the direction opposite to the direction of rotation in the image forming operation. The brush member 11 is rotated in this direction to remove toner from the brush member 11. In period 4, the brush member 11 is rotated in the direction of rotation in the image forming operation. The brush member 11 is rotated in this direction to remove toner from the brush member 11. In period 5, the brush member 11 is rotated in the direction opposite to the direction of rotation in the image forming operation. The brush member 11 is rotated in this direction to remove toner from the brush member 11. Figure 14 Figure 14

[0214] In this type of operation, the length of period 5 is noted. As explained in Embodiment 3, toner discharged from the brush member 11 onto the photosensitive drum 1 in period 4 is collected via the developing roller 31 once it reaches the developing section. If the next image forming operation is started before this collection operation is complete, toner remaining on the photosensitive drum 1 can be transferred to the recording material S, resulting in image defects. To suppress this, the control section 200 continues period 5 until the toner discharged from the brush member 11 is collected before starting the image forming section.

[0215] [Actions of Embodiment 4]

[0216] ​​​As described above, the brush cleaning operation is performed between sheets, so the brush can be cleaned frequently even when continuous feeding is performed, and the toner accumulation in the brush member 11 can be suppressed. In Embodiment 4, the brush cleaning operation is performed once every 5 sheets, for example, but is not limited to this frequency. The frequency at which the brush cleaning operation is performed during continuous image formation can be selected, for example, as follows. That is, a suitable number of sheets can be selected by taking into account factors such as the degree of toner accumulation in the brush member 11 due to continuous sheet feeding, the frequency of image defects due to toner accumulation, and the longer sheet feeding time due to the brush cleaning operation.

[0217] Therefore, in Embodiment 4, the brush cleaning control is performed between the end of image formation on the first recording material and the start of image formation on the second recording material, which is fed after the first recording material is fed while continuous image formation is performed. The control section 200 performs the brush cleaning control each time a predetermined number of images are formed in the continuous image formation operation.

[0218] According to the above-described Embodiment 4, the occurrence of image defects due to cleaning the brush can be reduced, while achieving the downsizing and cost reduction of the cleanerless image forming apparatus.

[0219] Embodiment 5 is described below. The basic configuration and operation of the image forming apparatus according to Embodiment 5 are the same as those of the image forming apparatus according to Embodiment 3. Therefore, elements of the image forming apparatus of Embodiment 5 that have the same functions or configurations as those of the image forming apparatus of Embodiment 3 are denoted by the same symbols as those of the image forming apparatus of Embodiment 3, and detailed explanations are omitted.

[0220] [Brush cleaning control in Embodiment 5]

[0221] Embodiment 5 performs the brush cleaning operation as a preparation operation (hereinafter referred to as "pre-rotation operation") before starting the image formation operation. The brush cleaning operation is performed using Figure 17 The control of various types of potential control in Embodiment 5 is explained. Figure 17 The image formation operation after the pre-rotation operation from the time of shutdown to timing t21 to timing t25 when the image formation operation is started in the image forming apparatus in Embodiment 5 is shown. Figure 17 (i) to 17(vi) are the same as Figure 14(i) to 14(iv) are the same. The horizontal axis shows time, and the vertical axis shows the voltage applied to each member, the drum surface potential of the brush contact portion and the developing portion, the drum surface potential of the brush contact portion in relation to the brush voltage, and the drum surface potential of the developing portion in relation to the developing voltage. The stop time until timing t21 is designated as period 1', and the periods are divided along the time series by the timing of switching the voltage applied to each member and the timing of switching the drum surface potential from period 1' to period 5' in order.

[0222] (periods 2' to 5')

[0223] In periods 2' to 5', the operations are the same as those of periods 2 to 5 in Embodiment 3, respectively, and thus detailed explanation is omitted. As in Embodiment 3, the toner held in the brush member 11 is discharged onto the photosensitive drum 1 in period 4', and the discharged toner is collected by the developing roller 31 in period 5'.

[0224] (means 1')

[0225] Period 1' indicates a stop time. No voltage is applied to each member (0 V), and the surface potential of the photosensitive drum 1 is 0 V. At timing t21 from period 1' to period 2', the drive system is activated. In addition, the brush / developer common voltage is switched from 0 V to 150 V. A potential difference is formed between the photosensitive drum 1 and the developing roller 31 in the developing portion, so that the toner charged in the regular charging polarity is pushed from the photosensitive drum 1 to the developing roller 31. This prevents the charged toner of the regular charging polarity, which occupies a large part of the toner present on the developing roller 31, from adhering to the photosensitive drum 1.

[0226] (period 5')

[0227] In period 5' from timing t24 to timing t25, the potentials of each member and the drum surface potentials are the same as during the image forming operation. After period 5' ends at timing t25, the process shifts to the continuous image forming operation. Period 5' is a period for collecting the toner discharged from the brush member 11. Therefore, the control portion 200 must continue period 5' until the toner collection is completed, and then shift to the image forming operation. Therefore, in Embodiment 5, the brush cleaning control is performed before the image formation on the recording material S is performed.

[0228] [Actions of Embodiment 5]

[0229] As described in Embodiment 3, the toner is supplied from the toner supply roller 32 to the developing roller 31 from the developer chamber 33, and is charged to a predetermined polarity (for example, a negative polarity, which is the regular charging polarity in Embodiment 5) when it passes through the contact portion with the developing blade 34. However, the charge that the toner has decays over time when the image forming operation is completed and the image forming apparatus is stopped. If the image forming apparatus is started up without the toner having sufficient charge, the following situation occurs. That is, the toner present on the developing roller 31 in the region extending from the developing blade 34 to the photosensitive drum 1 in the driving direction (rotational direction) does not contact the photosensitive drum 1 by the contact portion with the developing blade 34. Such toner is undercharged. Even if the potential relationship is such that the toner charged in the contact portion of the developing roller 31 with the photosensitive drum 1 at the regular polarity is pressed from the photosensitive drum 1 toward the developing roller 31, an amount of toner can be transferred from the developing roller 31 to the photosensitive drum 1. This occurs even if the potential relationship is such that the toner charged at the regular polarity is pressed toward the photosensitive drum 1 in the opposite direction. Such toner is referred to as start-up fog toner. By performing the brush cleaning operation during the pre-rotation operation, the brush contaminated with the start-up fog toner can be cleaned.

[0230] According to Embodiment 5 described above, it is possible to reduce the occurrence of image defects caused by the cleaning brush while achieving downsizing and cost reduction of the cleanerless image forming apparatus.

[0231] In Embodiments 5 to 5, the surface potential of the photosensitive drum 1 in the section of the surface of the photosensitive drum 1 onto which the toner held in the brush member 11 is discharged from the brush member 11 is controlled to a predetermined potential. The predetermined potential is controlled by controlling at least one of the charging high voltage power supply 210, the developing high voltage power supply 220, and the light intensity of the exposure unit 4 during that section. However, it is not limited to these. For example, a pre-exposure section (not shown) that is a pre-exposure member that equalizes the potential of the surface of the photosensitive drum 1 can be provided downstream of the first contact portion and upstream of the charging section. In this case, the potential of the surface of the photosensitive drum 1 at the first contact portion in that section can be controlled to a predetermined potential by controlling at least one of the charging high voltage power supply 210, the developing high voltage power supply 220, the pre-exposure unit, and the light intensity of the exposure unit 4 during that section.

[0232] The present application can reduce the size and cost of the cleanerless image forming apparatus while reducing the occurrence of image defects caused by the cleaning brush.

[0233] While the present application has been described with reference to example embodiments, it is to be understood that the application is not limited to the disclosed example embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. An image forming apparatus, comprising: Rotatable photosensitive component; The charging component is configured to charge the surface of the photosensitive component at the charging portion; An exposure apparatus that exposes the surface of a charged photosensitive element to light at an exposure location and is configured to form an electrostatic latent image on the surface of the photosensitive element; A developing apparatus that supplies toner charged with normal polarity to an electrostatic latent image on the surface of a photosensitive element at a developing position, and is configured to form a toner image on the surface of the photosensitive element. The transfer component is configured to transfer a toner image on the surface of the photosensitive component to the transfer material at the transfer location; The brush contacts the surface of the photosensitive element at the brush contact position, and the brush contact position is downstream of the transfer position and upstream of the charging position relative to the rotation direction of the photosensitive element. The voltage application section is configured to apply a brush voltage to the brush; as well as The control section is configured to control the surface potential of the photosensitive element at the brush contact point. The toner remaining on the surface of the photosensitive component after the transfer is collected by the developing equipment, and When the value obtained by subtracting the surface potential of the photosensitive element at the brush contact position from the value of the brush voltage is defined as the contact position potential difference, the control unit controls the surface potential of the photosensitive element at the brush contact position so that the contact position potential difference changes from a first potential difference to a second potential difference in a predetermined direction, and then changes from the second potential difference to a third potential difference in the predetermined direction, wherein the predetermined direction is either an increasing direction or a decreasing direction.

2. The image forming apparatus according to claim 1, wherein the control section controls the surface potential of the photosensitive element at the brush contact position, such that... (i) The contact position potential difference changes from a first potential difference to a third potential difference in the predetermined direction via a second potential difference. (ii) The contact position potential difference changes from a fourth potential difference to a fifth potential difference in the opposite direction, said opposite direction being either an increasing direction or a decreasing direction and opposite to said predetermined direction, and then... (iii) The contact position potential difference changes from the fifth potential difference to the sixth potential difference in the opposite direction.

3. The image forming apparatus according to claim 1, wherein the control section controls the surface potential of the photosensitive member at the brush contact position, such that the potential difference at the contact position changes in a stepwise manner.

4. The image forming apparatus according to claim 1, wherein the control section controls the surface potential of the photosensitive member at the brush contact position, such that the potential difference at the contact position changes continuously.

5. The image forming apparatus according to claim 1, wherein the control section controls the surface potential of the photosensitive member at the brush contact position, such that the sign of the potential difference at the contact position changes to positive and negative.

6. The image forming apparatus according to claim 1, wherein the control section controls the surface potential of the photosensitive member at the brush contact position to control at least one of the voltage applied to the charging member, the exposure of the photosensitive member by the exposure device, the voltage applied to the transfer member, and the exposure of the photosensitive member by the pre-exposure device, wherein the pre-exposure device is arranged downstream of the transfer position and upstream of the brush contact position relative to the rotation direction of the photosensitive member in order to expose the surface of the photosensitive member.

7. The image forming apparatus according to claim 1, further comprising a transfer voltage applying portion configured to apply a transfer voltage to the transfer member. The control section controls the surface potential of the photosensitive component at the brush contact position by controlling the transfer voltage application section.

8. The image forming apparatus according to claim 1, wherein the control portion controls the surface potential of the photosensitive member at the brush contact position such that during the period when the sign of the contact position potential difference becomes the opposite polarity to the normal polarity, the contact position potential difference changes in the direction of increasing the absolute value of the contact position potential difference.

9. The image forming apparatus of claim 1, wherein the brush removes and collects paper dust from the surface of the photosensitive element.

10. The image forming apparatus according to claim 1, wherein the charging member charges the surface of the photosensitive member by contacting the surface of the photosensitive member.

11. The image forming apparatus according to claim 1, wherein the brush has a substrate in contact with the surface of the photosensitive member, and The density of the brush substrate is 120 kF / inch. 2 Or larger.

12. An image forming apparatus, comprising: Image-carrying components; The charging component is configured to charge the surface of the image-bearing member at the charging portion; An exposure component is configured to expose the surface of an image carrier member to light in order to form an electrostatic latent image on the surface of the image carrier member charged by a charging component; The developing unit is configured to develop an electrostatic latent image formed on the surface of an image carrier member using a developer and to form a developer image; The receiving section is configured to receive the developer to be supplied to the developing unit; The transfer unit is configured to transfer the developer image formed by the developing unit to the recording material in the transfer section; The contact member is positioned upstream of the charging section and downstream of the transfer position relative to the rotation direction of the image carrier member, and contacts the surface of the image carrier member in the first contact section. The first applying component is configured to apply a charging voltage to the charging component; The second application component is configured to apply a developing voltage to the developing component; The third application component is configured to apply a contact voltage to the contact member; The pre-exposure component is configured to expose the surface of the image-bearing member downstream of the first contact portion and upstream of the charging portion; as well as The control unit is configured to control the collection of toner residue on the image carrier member that has not been transferred to the recording material by the transfer unit into the receiving portion by controlling the developing voltage applied by the second applying unit. During non-image forming operations, a section is provided to form a potential difference to generate an electrostatic force, which causes the developer charged with normal polarity in the first contact portion to move from the contact member toward the image-carrying member, and Until the region of the image carrier member forming the first contact portion in the section is moved to the second contact portion by rotating the image carrier member, the control unit controls the switching of the surface potential to be formed in the region, so as to form a potential difference to generate an electrostatic force that causes the developer charged with normal polarity to move from the image carrier member toward the developing member.

13. The image forming apparatus according to claim 12, wherein the second application member and the third application member share a common power source.

14. The image forming apparatus according to claim 12, wherein the collection of developer is performed before and after image formation on the recording material, or, in the case of performing continuous image formation, from the termination of image formation on the first recording material until the start of image formation on the second recording material, the second recording material being conveyed after the first recording material.

15. The image forming apparatus according to claim 14, wherein, in the case of performing continuous image forming, the control unit performs developer collection for image forming of each predetermined amount of recording material.

16. The image forming apparatus according to claim 12, wherein the length of the transfer member in the long side direction perpendicular to the rotation direction is shorter than the width of the recording material, the width of which in the long side direction is the longest of the recording materials to which the image forming apparatus can perform image forming.

17. The image forming apparatus according to claim 12, wherein during operation of the image forming apparatus, the developing member contacts the image carrying member.

18. The image forming apparatus according to claim 12, wherein the control member controls the surface potential of the image carrier member in the first contact portion of the segment to a predetermined potential by controlling at least one of the charging voltage of the first application member, the developing voltage of the second application member, and the light amount of the exposure member during the segment.

19. The image forming apparatus according to claim 18, wherein the control member controls the surface potential of the image carrier member in the first contact portion of the segment to a predetermined potential by controlling at least one of the charging voltage of the first application member, the developing voltage of the second application member, the light amount of the pre-exposure member, and the light amount of the exposure member during the segment.

20. The image forming apparatus according to claim 12, wherein the charging member charges the surface of the image carrier member by contacting the surface of the image carrier member.

21. The image forming apparatus of claim 12, wherein the contact member comprises a brush for collecting paper dust deposited on the surface of the image carrier member. The brush has a substrate that contacts the surface of the image-carrying component, and The density of the brush substrate is 120 kF / inch. 2 Or larger.

Images