Image forming apparatus

Abstract

To execute control of efficiently discharge a toner attached to a brush member in contact with a photoconductor drum to prevent an image defect.SOLUTION: A control unit controls such that the direction of an electric field generated in the first area of an image carrier forming a transfer part during image forming operations for a voltage applied to a brush member in a state in which the first area passes through a contact part, and the direction of an electric field generated in a second area of the image carrier forming the contact part for the voltage applied to the brush member during a transition from first operations in which the rotation speed of the image carrier is a first speed to second operations in which the rotation speed of the image carrier is a second speed different from the first speed during non-image forming operations different from the image forming operations, become different from each other.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an image forming apparatus using an electrophotographic method such as a laser printer, a copying machine, a facsimile machine, etc.

Background Art

[0002] As an image recording method used in an image forming apparatus such as a printer or a copying machine, an electrophotographic method is known. The electrophotographic method is a method of forming an electrostatic latent image on a photosensitive drum by a laser beam by using an electrophotographic process, and forming a developer image by developing a charged color material (hereinafter referred to as toner) on the electrostatic latent image. Then, image formation is performed by transferring and fixing the developer image onto a recording material.

[0003] A cleanerless method is known in which transfer residual toner remaining on the photosensitive drum without being transferred to the paper is recovered in the developing unit without using a cleaning member to recover the toner and the toner is reused. In Patent Document 1, in an image forming apparatus of the cleanerless method, since the surface of the photosensitive drum is not cleaned by a cleaning member, a configuration in which a brush member abuts on the photosensitive drum has been proposed as a means for recovering deposits adhering to the photosensitive drum.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, Patent Document 1 had the following problems: Toner that was not used for image formation, such as transfer residue toner remaining on the surface of the photosensitive drum, accumulated on the brush member that was in contact with the photosensitive drum. When toner accumulated on the brush member, the brush member could no longer hold the toner, and toner that passed through the brush member could adhere to the charging roller, causing image defects due to poor charging.

[0006] The present invention has been made in view of the above problems, and its purpose is to provide an image forming apparatus that suppresses image defects by performing control to efficiently eject toner adhering to a brush member that contacts a photosensitive drum. [Means for solving the problem]

[0007] Based on the above, the present invention is an image forming apparatus capable of performing an image forming operation to form an image on a transfer surface, comprising a rotatable image carrier and the surface of the image carrier and the charged part of form , The aforementioned In the charged part The surface of the image carrierThe device comprises a charging member that becomes charged, an exposure unit that exposes the surface of the image carrier to form an electrostatic latent image on the surface of the image carrier charged by the charging member, a developing member that supplies a developer charged with normal polarity to the surface of the image carrier to develop the electrostatic latent image as a developer image, a transfer member that contacts the image carrier to form a transfer section and transfers the developer image from the image carrier to a transfer object in the transfer section, a brush member that forms a contact section downstream of the transfer section and upstream of the charging section in the rotational direction of the image carrier and contacts the image carrier in the contact section, a voltage application unit that applies a voltage to the brush member, a drive unit that rotates the image carrier, and a control unit that controls the voltage application unit and the drive unit, wherein in the transfer section The device is configured such that, after the developer image formed on the surface of the image carrier is transferred to the transfer target, any developer remaining on the surface of the image carrier is recovered by the developing member, and the control unit controls the direction of the electric field generated in the first region of the image carrier where the transfer portion is formed when the first region of the image carrier passes the contact portion during the image forming operation, in response to the voltage applied to the brush member, and the direction of the electric field generated in the second region of the image carrier where the contact portion is formed in response to the voltage applied to the brush member before transitioning from a first operation where the rotation speed of the image carrier is a first speed to a second operation where the rotation speed of the image carrier is a second speed different from the first speed during a non-image forming operation different from the image forming operation. [Effects of the Invention]

[0008] By implementing control that efficiently ejects toner adhering to the brush component in contact with the photosensitive drum, image defects can be suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view of the image forming apparatus in Example 1. [Figure 2] This is a schematic diagram of the brush member in Example 1. [Figure 3]This is a control block diagram for Example 1. [Figure 4] This is an explanatory diagram illustrating the movement of toner passing through the brush member in Example 1. [Figure 5] This is an explanatory diagram regarding the force acting on the brush member in Example 1. [Figure 6] This is an explanatory diagram of the potential relationships during each operation in the printing process in Example 1. [Figure 7] This is a timing chart for the transition from the image formation operation to the stop operation of the photosensitive drum during startup in Example 1. [Figure 8] This is a schematic cross-sectional view of the brush member and photosensitive drum during control execution in Example 2. [Figure 9] This is a schematic cross-sectional view of the brush member and photosensitive drum during control execution in Example 3. [Modes for carrying out the invention]

[0010] The following describes in detail, with reference to the drawings, embodiments for carrying out this invention. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately modified depending on the configuration of the device to which the invention is applied and various conditions. In other words, the scope of this invention is not intended to be limited to the following embodiments. [Examples]

[0011] 1. Image forming apparatus Figure 1 shows a schematic configuration of one embodiment of the image forming apparatus 100 according to the present invention. The image forming apparatus 100 in this embodiment is a monochrome laser beam printer employing a cleanerless method and a contact charging method.

[0012] In the image forming apparatus 100 according to this embodiment, a cylindrical photosensitive member, that is, a photosensitive drum 1 is provided as an image carrier. Around the photosensitive drum 1, a charging roller 2 as charging means and a developing device 3 as developing means are provided. Further, an exposure device 4 as exposure means is provided between the charging roller 2 and the developing device 3 in the rotational direction of the photosensitive drum 1 in FIG. 1. Also, a transfer roller 5 as transfer means is pressed against the photosensitive drum 1.

[0013] The photosensitive drum 1 in this embodiment is a negatively chargeable organic photosensitive member. This photosensitive drum 1 has a photosensitive layer on a drum-shaped substrate of aluminum and is rotationally driven at a predetermined process speed in the direction of the arrow in the figure (clockwise direction) by a drive motor (drive unit) 110 as drive means (FIG. 3). In this embodiment, the process speed corresponds to the peripheral speed (surface movement speed) of the photosensitive drum 1 and is 140 mm / sec, and the outer diameter of the photosensitive drum 1 is 24 mm.

[0014] The charging roller 2 as a charging member contacts the photosensitive drum 1 with a predetermined pressing force to form a charging portion. Also, a desired charging voltage is applied by a charging high-voltage power supply E1 (FIG. 3) as charging voltage application means to uniformly charge the surface of the photosensitive drum 1 to a predetermined potential. In this embodiment, the surface of the photosensitive drum 1 is charged negatively by the charging roller 2. During the charging process, a predetermined charging voltage (charging bias) is applied to the charging roller 2 by the charging power supply E1. In this embodiment, a negative DC voltage is applied to the charging roller 2 as the charging voltage during the charging process. The charging voltage in this embodiment is, as an example, -1300 V. Thereby, in this embodiment, the surface of the photosensitive drum 1 is uniformly charged to a dark portion potential Vd of -700 V. Note that the charging roller 2 charges the surface of the photosensitive drum 1 by discharge occurring at at least one of the minute gaps between the charging roller 2 and the photosensitive drum 1 formed on the upstream side and the downstream side of the contact portion with the photosensitive drum 1 with respect to the rotational direction of the photosensitive drum 1. However, here, the contact portion between the charging roller 2 and the photosensitive drum 1 with respect to the rotational direction of the photosensitive drum 1 is described by assuming that it is a charging portion.

[0015] In this embodiment, the exposure device 4, which is an exposure unit, is a laser scanner device that outputs laser light corresponding to image information input from an external device such as a host computer and performs scanning exposure on the surface of the photosensitive drum 1. By this exposure, an electrostatic latent image (electrostatic image) corresponding to the image information is formed on the surface of the photosensitive drum 1. In this embodiment, the dark portion potential Vd on the surface of the photosensitive drum 1 formed by uniformly charging treatment decreases in absolute value when exposed by the exposure device 4 and becomes the bright portion potential Vl of -100V. Here, it is assumed that the position on the photosensitive drum 1 exposed by the exposure device 4 in the rotation direction of the photosensitive drum 1 is the exposure portion (exposure position). Note that the exposure device 4 is not limited to a laser scanner device, and for example, an LED array in which a plurality of LEDs are arranged along the longitudinal direction of the photosensitive drum 1 may be employed.

[0016] In this embodiment, a contact development method is used as the development method. The development apparatus 3 includes a developing member, a developing roller 31 as a developer carrier, a toner supply roller 32 as a developer supply means, a developer storage chamber 33 for storing toner, and a developing blade 34. The toner supplied from the developer storage chamber 33 to the developing roller 31 by the toner supply roller 32 is charged to a predetermined polarity by passing through the blade nip, which is the contact point between the developing roller 31 and the developing blade 34. The toner carried on the developing roller 31 moves from the developing roller 31 to the photosensitive drum 1 in the development section according to the electrostatic image. Here, the contact point between the developing roller 31 and the photosensitive drum 1 with respect to the rotation direction of the photosensitive drum 1 is considered to be the development section. In this embodiment, the developing roller 31 is driven to rotate counterclockwise in the development section so that the photosensitive drum 1 and the developing roller 31 move in the forward direction. The drive motor 110 for driving the developing roller 31 may be the same main motor as the drive motor 110 for the photosensitive drum 1, or separate drive motors may rotate the photosensitive drum 1 and the developing roller 31, respectively. During development, a predetermined developing voltage (developing bias) is applied to the developing roller 31 by a developing power supply E2 (Figure 3) which serves as a developing voltage application means. In this embodiment, during development, a negative polarity DC voltage is applied to the developing roller 31 as the developing voltage, resulting in a developing voltage of -380V. In this embodiment, toner charged with the same polarity (negative polarity in this embodiment) as the charging polarity of the photosensitive drum 1 adheres to the exposure surface (image area), which is the image forming area on the photosensitive drum 1, after it has been uniformly charged and then exposed, causing the absolute value of the potential to decrease. This developing method is called the inverse developing method. In this embodiment, the normal polarity, which is the charging polarity of the toner during development, is negative polarity. In this embodiment, a one-component non-magnetic contact development method is employed, but the present invention is not limited to this embodiment, and a two-component non-magnetic contact development method, a non-contact development method, a magnetic development method, etc., may also be employed. The two-component non-magnetic contact development method is a method in which a two-component developer comprising a non-magnetic toner and a magnetic carrier is used as the developer, and development is performed by bringing the developer (magnetic brush) supported on the developer carrier into contact with the photosensitive drum 1. The non-contact development method is a method in which toner is flown onto the photosensitive drum from a developer carrier positioned opposite the photosensitive drum in a non-contact manner, and development is performed.Furthermore, the magnetic development method is a method of developing a photoreceptor by supporting magnetic toner on a developer carrier containing a magnet as a means of generating a magnetic field, which is positioned opposite the photoreceptor, either in contact or not in contact with it. In this embodiment, a toner with a central average particle size of 6 μm and a normal charge polarity of negative polarity is used.

[0017] As the transfer roller 5, which serves as the transfer member, it is preferable to use one made of an elastic material such as polyurethane rubber, EPDM (ethylene propylene diene rubber), or NBR (nitrile butadiene rubber) sponge rubber. The transfer roller 5 is pressed toward the photosensitive drum 1, forming a transfer area where the photosensitive drum 1 and the transfer roller 5 are in contact. During transfer, a predetermined transfer voltage (transfer bias) is applied to the transfer roller 5 by the transfer power supply E3 (Figure 3), which serves as a transfer voltage application means. In this embodiment, during transfer, a DC voltage with the opposite polarity to the normal polarity of the toner (positive polarity in this embodiment) is applied to the transfer roller 5 as the transfer voltage. In this embodiment, this transfer voltage during transfer is, for example, +1000V. Then, due to the action of the electric field formed between the transfer roller 5 and the photosensitive drum 1, the toner image is electrostatically transferred from the photosensitive drum 1 to the recording material (transfer material) S.

[0018] As the toner image formed on the photosensitive drum 1 reaches the transfer section, the recording material S stored in the cassette 6 is fed by the paper feed unit 7, passes through the registration roller pair 8, and is transported to the transfer section. 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 E3.

[0019] After the toner image has been transferred, the recording material S is transported to the fuser 9. The fuser 9 is a film heating type fuser equipped with a fuser film 91 containing a fuser heater (not shown) and a thermistor (not shown) for measuring the temperature of the fuser heater, and a pressure roller 92 for pressing the recording material S onto the fuser film 91. The transfer material S is then heated and pressurized, fixing the toner image, and is discharged outside the machine by passing through the paper discharge roller pair 12.

[0020] Furthermore, any remaining toner on the photosensitive drum 1 that was not transferred to the transfer material S is removed by the following process.

[0021] The transfer residue toner contains a mixture of positively charged toner and negatively charged toner that does not have sufficient charge. The transfer residue toner is recharged to a negative polarity by discharge at the charging section of the charging roller 2. The transfer residue toner, which has been recharged to a negative polarity at the charging roller 2, reaches the developing section as the photosensitive drum 1 rotates. Here, there are two cases in which an electrostatic latent image is formed on the surface of the photosensitive drum 1 that has reached the developing section, forming an image forming section, and a non-image forming section where no electrostatic latent image is formed. The behavior of the transfer residue toner that has reached the developing section will be explained separately for the image forming section and the non-image forming section of the photosensitive drum 1.

[0022] The residual toner adhering to the image forming section of the photosensitive drum 1 is not transferred from the photosensitive drum 1 to the developing roller 31 in the developing section. Instead, it moves from the developing roller 31 to the transfer section along with the developed toner, is transferred to the transfer material S, and is used for image formation.

[0023] Meanwhile, the residual toner adhering to the non-image-forming area of ​​the photosensitive drum 1 is recharged to its normal polarity, negative, by the charging unit. In the developing unit, the potential difference between the potential of the non-image-forming area of ​​the photosensitive drum 1 and the developing voltage causes the toner to be transferred to the developing roller 31 and recovered in the developer storage chamber 33. The toner recovered in the developer storage chamber 33 is then used again for image formation.

[0024] 2. Composition of brush components Next, the paper dust removal mechanism in this embodiment will be described. As shown in Figure 1, the image forming apparatus 100 in this embodiment has a brush member 10 (recovery member) which is a contact member that serves as a paper dust removal mechanism. In this embodiment, the image forming apparatus 100 has a brush member 10 that contacts the surface of the photosensitive drum 1 downstream of the transfer section and upstream of the charging section with respect to the rotation direction of the photosensitive drum 1, thereby forming a brush contact section (brush contact position). Here, the contact section between the brush member 10 and the photosensitive drum 1 with respect to the rotation direction of the photosensitive drum 1 is defined as the brush contact section (hereinafter referred to as the contact section).

[0025] Figure 2(a) is a schematic diagram of the brush member 10 in its standalone state, viewed along its longitudinal direction (approximately parallel to the rotation axis direction of the photosensitive drum 1). Figure 2(b) is a schematic diagram of the brush member 10 in contact with the photosensitive drum 1, viewed along its longitudinal direction.

[0026] The brush member 10 is composed of a fixed conductive brush 11 that is fixedly positioned. As shown in Figure 2, the brush member 10 is composed of multiple pile threads 11a made of conductive nylon 6, which are bristles that rub against the surface of the photosensitive drum 1, and a base fabric 11b that supports the pile threads 11a. As described above, this brush member 10 is positioned to contact the photosensitive drum 1 downstream of the transfer section and upstream of the charging section in the direction of movement (rotation) of the photosensitive drum 1.

[0027] The brush member 10 is positioned so that its longitudinal direction is approximately parallel to the rotation axis direction of the photosensitive drum 1. In addition to nylon, rayon, acrylic, polyester, or other materials may be used as the material for the conductive thread 11a.

[0028] As shown in Figure 2(a), when the brush member 10 is in a standalone state, that is, when no external force is applied to bend the conductive thread 11a, the distance from the base fabric 11b to the tip of the conductive thread 11a exposed is defined as L1. In this embodiment, L1 is 6.5 mm. The brush member 10 is positioned such that the tip of the conductive thread 11a penetrates the photosensitive drum 1, with the base fabric 11b fixed to a support member (not shown) installed at a predetermined position in the image forming apparatus 100 by fixing means such as double-sided tape. In this embodiment, the clearance between the support member and the photosensitive drum 1 is fixed. The shortest distance from the base fabric 11b of the brush member 10 fixed to the support member to the photosensitive drum 1 is defined as L2. In this embodiment, the difference between L2 and L1 is defined as the amount of penetration of the brush member 10 into the photosensitive drum 1. In this embodiment, the amount of penetration of the brush member 10 into the photosensitive drum 1 is 1 mm. Furthermore, in this embodiment, as shown in Figure 2(a), the length L3 of the brush member 10 in the circumferential direction (hereinafter referred to as the "short direction") of the photosensitive drum 1 is 5 mm when the brush member 10 is in a standalone state. Also, in this embodiment, the length of the brush member 10 in the longitudinal direction is 216 mm. This allows the brush member 10 to contact the entire image forming area (the area where a toner image can be formed) on the photosensitive drum 1 with respect to the rotation axis direction of the photosensitive drum 1. Also, in this embodiment, the thickness of the conductive thread 11a is 2 denier and the density is 240 kF / inch 2 (kF / inch 2 ( is a unit of brush density, indicating the number of filaments per square inch). The brush member 10 is supported by a support member (not shown) and is positioned in a fixed position relative to the photosensitive drum 1, and rubs against the surface of the photosensitive drum 1 as the photosensitive drum 1 moves.

[0029] The brush member 10 collects (recovers) attached materials such as paper dust that have been transferred from the recording material S to the photosensitive drum 1 in the transfer section, and reduces the amount of paper dust that moves downstream of the brush member 10 to the charging section and developing section in the direction of movement of the photosensitive drum 1.

[0030] In this embodiment, the length of the brush member 10 in the circumferential direction (hereinafter referred to as the short-side direction) of the photosensitive drum 1 is set to L3 = 5 mm, but it is not limited to this. For example, it may be changed as appropriate depending on the lifespan of the image forming apparatus or process cartridge. Needless to say, the longer the length of the brush member 10 in the short-side direction, the longer the paper dust can be collected.

[0031] In this embodiment, the longitudinal length of the brush member 10 is set to 216 mm, but it is not limited to this. For example, it may be changed as appropriate depending on the maximum paper feed width of the image forming apparatus 100.

[0032] In this embodiment, the fineness of the brush member 10 is set to 220T / 96F (meaning 96 strands of yarn with a thickness of 220g per 10,000m are bundled together), but it is desirable to determine this while considering the ease with which paper dust can pass through. If the fineness of the brush member 10 is too small, the force that blocks paper dust is weak, and the paper dust can easily pass through, which can hinder the charging of the photosensitive drum 1 by the charging roller 2 and cause image defects. On the other hand, if the fineness of the brush member 10 is too large, toner and fine paper dust cannot be collected, which can cause uneven density due to uneven toner adhesion along the length of the charging roller 2, or image defects due to poor charging at the paper dust adhesion points.

[0033] In this embodiment, the density of the brush member 10 is set to 240 kF / inch² (kF / inch² is the unit of brush density, indicating the number of filaments per square inch), but it is desirable to determine this considering toner passability and paper dust collection ability. That is, if the density of the brush member 10 is too high, the toner passability will deteriorate and the toner will stack (solidify), and problems may occur such as the stacked toner scattering and soiling the inside of the machine. Also, if the density of the brush member 10 is too low, the ability to collect paper dust will be weakened. Therefore, the thickness and density of the conductive thread 11a should be 1 to 6 denier and 150 to 350 kF / inch, respectively, from the viewpoint of paper dust collection ability. 2 It is preferable that this is the case. Furthermore, the length of the brush member 10 in the shorter direction is preferably 3 mm or more from the viewpoint of ensuring a long lifespan.

[0034] Furthermore, a brush power supply E4 (Figure 3) is connected to the brush member 10 as a means for applying the brush voltage. During image formation, a predetermined brush voltage (brush bias) is applied to the brush member 10 by the brush power supply E4. In this embodiment, a negative polarity DC voltage is applied to the brush member 10 as the brush voltage during image formation. In this embodiment, the brush voltage during image formation is, for example, -350V.

[0035] 3. Image output operation In this embodiment, the image forming apparatus 100 executes an image output operation (job), which is a series of operations to form an image on one or more recording materials S, in response to a single start instruction from an external device (not shown), such as a personal computer. A job generally includes an image forming process (printing process), a pre-rotation process, a paper-to-paper process when forming an image on multiple recording materials S, and a post-rotation process. The image forming process is the period during which the electrostatic image is actually formed on the photosensitive drum 1, the electrostatic image is developed (toner image formation), the toner image is transferred, and the toner image is fixed, and this period is referred to as the image forming time. More specifically, the timing of the image forming time differs depending on the position where these electrostatic image formation, toner image formation, toner image transfer, and toner image fixing are performed. The pre-rotation process is the period during which preparatory operations are performed before the image forming process. The paper-to-paper process is the period corresponding to the space between recording materials S when the image forming process is performed continuously on multiple recording materials S (continuous image forming). The post-rotation process is the period during which cleanup operations (preparatory operations) are performed after the image forming process. Non-image forming periods refer to periods other than image forming periods, and include the pre-rotation process, inter-paper process, post-rotation process, and pre-multi-rotation processes which are preparatory operations when the image forming apparatus 100 is powered on or when it returns from sleep mode.

[0036] 4. Control Modes Figure 3 is a schematic block diagram showing the control configuration of the main parts of the image forming apparatus 100 in this embodiment. The image forming apparatus 100 is equipped with a control unit 150. The control unit 150 includes a CPU 151 as a calculation control means, which is the central element for performing calculation processing; a memory (storage element) 152 such as ROM or RAM as a storage means; and an input / output unit (not shown) that controls the exchange of signals between the control unit 150 and various elements connected to it. Sensor detection results, calculation results, etc. are stored in the RAM, and a control program, a pre-determined data table, etc. are stored in the ROM.

[0037] The control unit 150 is a control means that comprehensively controls the operation of the image forming apparatus 100. The control unit 150 controls the transmission and reception of various electrical information signals and the timing of drives to execute a predetermined image forming sequence. Various parts of the image forming apparatus 100 are connected to the control unit 150. For example, in this embodiment, the control unit 150 is connected to the charging power supply E1, the developing power supply E2, the transfer power supply E3, the brush power supply E4, the exposure unit 4, the drive motor 110, and so on.

[0038] 5. Toner behavior relative to brush material Next, we will explain the behavior of the transfer residue toner passing through the brush member 10 using Figure 4. First, we will explain the relationship between the potential difference between the surface potential of the brush member 10 and the photosensitive drum 1 at the contact point and the polarity of the transfer residue toner.

[0039] As shown in Figure 4(a), if the proportion of toner R charged with the normal polarity (hereinafter referred to as normal polarity toner) is large in the transfer residue toner, and a potential relationship is generated in which an electric field is generated in a direction that causes the normal polarity toner R to adhere to the brush member 10, then toner will continue to accumulate on the brush member 10. On the other hand, as shown in Figure 4(b), if the proportion of normal polarity toner R in the transfer residue toner is large, and a potential relationship is generated in which an electric field is generated in a direction that prevents the normal polarity toner R from adhering to the brush member 10, then the normal polarity toner R will not be held by the brush member 10 and will pass through. Note that an electric field is generated in a direction that prevents the normal polarity toner R from adhering to the brush member 10, that is, a relationship is generated in which an electric field is generated that causes the normal polarity toner R to move in the direction of the photosensitive drum 1. In that case, the normal polarity toner R will pass through the contact area. This relationship remains the same even if the polarity of the toner is reversed, as only the polarity of the potential difference described above is reversed, and the resulting phenomenon is the same as described above. Therefore, in this embodiment, as will be described later, we will explain the control in the case where there is a large amount of normal polarity toner R in the remaining toner after transfer, but it can also be appropriately applied in the case where there is a large amount of toner charged with the opposite polarity (hereinafter referred to as reverse polarity toner).

[0040] As in this embodiment, under conditions where polarity reversal is unlikely, such as when the transfer bias applied to the transfer area is relatively low, the proportion of toner charged with the normal polarity tends to be high among the remaining toner after transfer. On the other hand, when polarity reversal is likely, such as when the transfer bias is too high, the proportion of toner with the reverse polarity tends to be high among the remaining toner after transfer.

[0041] In this embodiment, most of the residual toner is normal polarity toner with a weak negative charge, but some reverse polarity toner with a positive charge is also present due to discharge between the transfer bias in the transfer area and the surface potential of the photosensitive drum 1. Next, the behavior of normal polarity toner and reverse polarity toner at the contact point in the residual toner remaining on the surface of the photosensitive drum 1 will be described.

[0042] During image formation, the surface of the photosensitive drum 1 is charged to a dark area potential Vd of -700V. The image-forming area on the photosensitive drum 1 is exposed by the exposure device 4 and becomes a bright area potential Vl of -100V. The non-image-forming area on the photosensitive drum 1 also becomes approximately -100V due to the discharge between the transfer roller 5, to which a transfer voltage of +1000V is applied, and the photosensitive drum 1 as it passes through the transfer area. Therefore, the surface potential of the photosensitive drum 1 that reaches the contact area during image formation is approximately -100V. Of the remaining toner from the transfer, the normal polarity toner, which is negatively charged, is electrostatically attracted to the photosensitive drum 1 at the contact area due to the potential difference between the brush voltage (-350V) and the surface potential of the photosensitive drum 1 (approximately -100V), and passes through the contact area. On the other hand, among the remaining toner after transfer, the reverse-polarity toner that has been positively charged is electrostatically attracted to the brush member 10 at the contact point due to the potential difference between the brush voltage (-350V) and the surface potential of the photosensitive drum 1 after transfer (approximately -100V), and adheres to the brush member 10.

[0043] The negatively polarized toner that has passed through the charged section is sent to the developing section as the photosensitive drum 1 rotates. In the non-image forming section, the negatively polarized toner sent to the developing section moves to the developing roller 31 due to the potential difference between the dark area potential (Vd) and the developing bias (Vdc) on the surface of the photosensitive drum 1, and is collected by the developing device 3. On the other hand, in the image forming section, the negatively polarized toner sent to the developing section does not move to the developing roller 31 due to the potential difference between the bright area potential (Vl) and the developing bias (Vdc) on the surface of the photosensitive drum 1. This toner remains as toner in the image forming section and is sent to the transfer section as the photosensitive drum 1 rotates, and is transferred to the recording material S. As described above, the developing bias is set to a potential between the dark area potential Vd and the bright area potential Vl.

[0044] Furthermore, the image forming apparatus 100 may have a pre-exposure device as a static elimination means for static elimination treatment of the surface of the photosensitive drum 1 downstream of the transfer section and upstream of the charging section with respect to the rotation direction of the photosensitive drum 1. The pre-exposure device photo-eliminates the surface potential of the photosensitive drum 1 before it enters the charging section in order to generate a stable discharge in the charging section. Static elimination includes removing (attenuating) at least a portion of the charge. Here, the position exposed (static elimination treatment) by the pre-exposure device with respect to the rotation direction of the photosensitive drum 1 is assumed to be the static elimination section. It is more desirable to configure the surface of the photosensitive drum 1 downstream of the contact section and upstream of the charging section with respect to the rotation direction of the photosensitive drum 1 so that the toner that has passed through the contact section passes through the static elimination section and is stably charged to a negative polarity by a uniform discharge in the charging section.

[0045] Next, the effect of toner accumulation on the brush member 10 on the image will be explained using Table 1. For image evaluation, Office70 (Canon, product name) was used as the transfer material S, and when 100 full-surface halftone images were printed, the occurrence of image defects was checked to determine how much toner accumulated on the brush member 10. Specifically, image defects refer to charging defects due to toner escaping caused by toner accumulation on the brush member 10, and development defects due to paper dust escaping. Charging defects are caused by toner escaping and adhering to the charging roller 2, etc. Development defects are caused by paper dust escaping and being collected by the developing device 3, which inhibits toner charging, resulting in low density, and the occurrence of streaks due to paper dust getting caught in the developing blade.

[0046] As shown in Table 1, in this embodiment, when the normal polarity toner accounts for the majority of the transfer residue toner, no image defects occurred when the potential relationship on the side passing through the transfer residue toner, i.e., the brush voltage, was set to the negative polarity side relative to the surface potential of the photosensitive drum 1. On the other hand, when the potential relationship was set such that the normal polarity toner adhered to the brush member 10, i.e., when the brush voltage was set to the positive polarity side relative to the surface potential of the photosensitive drum 1, image defects occurred.

[0047] [Table 1]

[0048] Based on the above results, in this embodiment, during the image forming operation, the potential relationship is controlled so that the residual toner passes through the contact area of ​​the brush member 10 on the photosensitive drum 1 without adhering to the brush member 10. This prevents the occurrence of image defects caused by excessive accumulation of toner on the brush member 10.

[0049] 6. Control of toner ejection from brush components As mentioned above, the transfer residue toner contains both normal polarity toner and reverse polarity toner charged with the opposite polarity to the normal polarity. Therefore, even if a potential relationship is formed at the contact point that allows normal polarity toner to pass through the transfer residue toner, which has a large proportion of normal polarity toner, reverse polarity toner may accumulate on the brush member 10. Thus, it is necessary to control the brush member 10 so that the toner adhering to it is periodically transferred (discharged) to the photosensitive drum 1 at appropriate timings.

[0050] Here, two methods can be considered for ejecting toner from the brush member 10 onto the surface of the photosensitive drum 1: one utilizing a potential difference and the other utilizing a change in the orientation of the brush member 10. In the method utilizing a potential difference, a potential relationship is created in which an electric field is generated in the direction that causes the toner to move from the brush member 10 towards the photosensitive drum 1, relative to the polarity of the main toner held in the brush member 10, thereby making it possible to eject toner from the brush member 10. This can be described as a method that utilizes electrical force.

[0051] On the other hand, the method that utilizes the change in the posture of the brush member 10 is a method that utilizes physical force. Specifically, this method involves intentionally causing a change in the posture of the brush member 10 by taking advantage of timings when there are fluctuations in the speed of the photosensitive drum 1, such as when the photosensitive drum 1 starts or stops, in order to remove toner adhering to the brush member 10.

[0052] When the drive is stopped, as shown in Figure 5(a), no force in the rotational direction of the photosensitive drum 1 is applied to the brush member 10, and only a reaction force is received from the photosensitive drum 1. Therefore, the brush member 10 is in a nearly perpendicular position to the photosensitive drum 1. In this state, if the drive is started without a potential difference between the brush member 10 and the photosensitive drum 1, as shown in Figure 5(b), the brush member 10 receives a static friction force μN (μ: coefficient of static friction, N: normal force) in the rotational direction of the photosensitive drum 1, and tilts to the downstream side in the rotational direction of the photosensitive drum 1, resulting in a change in posture between when the drive is stopped and when it is rotating. The same phenomenon occurs when the operation transitions from rotational driving to when the drive is stopped, changing from the posture in Figure 5(b) to the posture in Figure 5(a). By utilizing this change in posture, toner that is difficult to eject by electrical forces such as potential differences alone can be ejected. However, since the surface of the photosensitive drum 1 is often smooth, the static friction coefficient μ between it and the brush member 10 is small, so the movement of the brush member 10 is small due to the rotational drive / stopping operation of the photosensitive drum 1 alone. In this embodiment, the width of movement of the tip of the brush member 10 is about 100 μm.

[0053] Therefore, when the device is driven with a potential difference between the brush member 10 and the photosensitive drum 1, as shown in Figure 5(c), the brush member 10 receives an electrostatic attraction force proportional to the potential difference ΔV between the brush member 10 and the photosensitive drum 1, in addition to the static friction force μN, and assumes a posture that is tilted further downstream in the rotational direction than when there is no potential difference. Consequently, if there is a potential difference between the brush member and the photosensitive drum 1 when the drive is stopped and when the drive is rotating, the posture will change more significantly. In this embodiment, the tip of the brush member 10 moves by about 1 mm, and the amount of toner discharged increases. Even when the operation transitions from rotational driving to stopping, a similar phenomenon occurs where the posture changes from that in Figure 5(c) to that in Figure 5(a). By utilizing this change in posture, toner accumulated at the base of the brush member 10, which is farther from the photosensitive drum 1, can be discharged, even toner that is difficult to discharge by posture changes due to static friction alone, making it possible to discharge toner effectively.

[0054] Next, we will explain how to verify the effectiveness of toner ejection from the brush member 10. To verify the toner ejection effect, we used Office70 (Canon, product name) as the transfer material S and repeatedly performed intermittent printing of a full-surface halftone image using the image forming apparatus 100. We then checked for the occurrence of image defects after printing a total of 500 sheets. Furthermore, the amount of toner ejected using potential relationships and changes in the posture of the brush member 10 was confirmed by attaching a translucent polyester tape (manufactured by Nichiban Co., Ltd.) to the measurement target area on the photosensitive drum 1. Specifically, the toner ejected from the surface of the photosensitive drum 1 was transferred to the tape, and the density was quantified by the density when the peeled tape was attached to a backing paper. The density of the area where the tape was directly attached to the backing paper without being attached to the photosensitive drum 1, and the density of the area where the tape was attached to the measurement area and then to the backing paper were measured using a reflectance densitometer (Tokyo Denshoku Co., Ltd., TC-6MC-D), and the difference between these measured values ​​was recorded as the density. Therefore, a higher density value indicates a larger amount of toner has been ejected.

[0055] Figure 6 shows the potential relationships for Comparative Examples 1 and 2 and Example 1. In Comparative Example 1, the potential relationship between the brush member 10 and the photosensitive drum 1 is not changed from the start of operation until the operation stops, and the reverse polarity toner accumulated in the brush member 10 is not actively discharged. In other words, in Comparative Example 1, the potential relationship between the brush member 10 and the photosensitive drum 1 is always such that the normal polarity toner passes through the contact area.

[0056] Next, in Comparative Example 2, the potential relationship between the brush member 10 and the photosensitive drum 1 is as follows: The potential is reversed between the region where the residual toner passes the contact area during the image forming operation and the region where the residual toner passes the contact area during non-image forming operations. In other words, in Comparative Example 2, the potential relationship is such that the normal polarity toner accumulated on the brush member 10 passes the contact area in the region where the residual toner passes the contact area, and the potential relationship is such that the normal polarity toner adheres to the photosensitive drum 1 during non-image forming operations. That is, in Comparative Example 2, the potential relationship is such that the reverse polarity toner is ejected onto the surface of the photosensitive drum 1. However, in Comparative Example 2, the timing for reversing the potential difference between the region where the residual toner passes the contact area and the contact area is excluded at the start and stop of operation. In other words, in Comparative Example 1, there is no timing at which the reverse polarity toner is electrically ejected at the contact area, while in Comparative Example 2, there is a timing at which the reverse polarity toner is electrically ejected at the contact area. Furthermore, in both Comparative Example 1 and Comparative Example 2, there is no relationship where the reverse polarity toner is electrically ejected at the contact point during rotational drive, when physical ejection occurs, or when stopped. Therefore, in both Comparative Example 1 and Comparative Example 2, the electrical ejection of the reverse polarity toner is not considered at all when the speed of the photosensitive drum 1 is switched, and in Comparative Example 2, ejection is considered only when rotating at a constant speed.

[0057] On the other hand, in Example 1, in addition to the conditions of Comparative Example 2, the potential relationship between the brush member 10 and the photosensitive drum 1 is reversed at the start and stop of the drive compared to the image forming operation. This configuration allows the reverse-polarity toner accumulated on the brush member 10 in the region where the transfer residue toner passes through the contact area to be discharged to the photosensitive drum 1 at the start and stop of the drive. In this case, the applied brush voltage was set to +150V.

[0058] In Comparative Example 1, Comparative Example 2, and Example 1, the polarity of the residual toner was adjusted by controlling the transfer voltage, and the toner ejection effect was confirmed when there was a large amount of toner with the correct polarity. The potential relationship between the brush member 10 and the photosensitive drum 1 in the region through which the residual toner passes the contact area was set to a potential relationship such that toner with the correct polarity passes through the contact area.

[0059] Next, Figure 7 shows the timing chart of the applied voltage in Example 1, from the start of driving the photosensitive drum 1 to the transition to the image forming operation, and from the transition from the image forming operation to the stop of driving the photosensitive drum 1.

[0060] From top to bottom, the diagram shows the ON / OFF switching of the rotation drive of the photosensitive drum 1 by the drive motor 110, the charging voltage applied to the charging roller 2 from the charging power supply E1, and the laser emission onto the photosensitive drum 1 by the laser scanner device 4, which is the exposure device. Next, the diagram shows the brush voltage (brush member potential) (A) applied to the brush member 10 from the brush power supply E4, the surface potential of the photosensitive drum 1 at the contact point (B), and the time progression of the difference between the brush voltage at the contact point and the surface potential of the photosensitive drum 1 ((A)-(B)).

[0061] When a print command is received before T1, a brush voltage is applied to the brush member 10 at T1 in Figure 7. In this embodiment, the brush voltage is set to +150V. With the brush voltage applied, the photosensitive drum 1 starts rotating at T2. Subsequently, at T3, a charging voltage of -1200V is applied to the charging roller 2 to charge the surface of the photosensitive drum 1. At T4, when the surface of the photosensitive drum 1, which was charged at T3, reaches the contact area, the brush voltage is switched from +150V to -350V. Up to T4, the potential difference between the surface potential of the brush member 10 and the photosensitive drum 1 formed at the contact area is equal to the brush voltage, so it is possible to control the ejection of toner from the brush member 10 by switching the brush voltage. In this embodiment, up to T4, an operation is performed to promote the ejection of negative polarity toner attached to the brush member 10. From T4 onward, a brush voltage of -350V is applied to the brush member 10 until the timing of T10 when the image forming operation is completed. During this time, a transfer bias is applied, and since this is the timing when the normal polarity toner reaches the contact area as residual toner, the brush voltage is set to the negative polarity to control the flow so that the residual toner passes through the contact area. Image formation starts at T5, and exposure for image formation is performed as appropriate. At T6, when the exposed surface of the photosensitive drum 1 reaches the contact area, the residual toner effectively reaches the contact area. At that time, as described above, a negative polarity brush voltage is already applied to the brush member 10, so the residual toner can pass through the contact area. Subsequently, image formation ends at T7, and at T8, when the exposed surface of the photosensitive drum 1 reaches the contact area at the timing of T7, the residual toner effectively no longer reaches the contact area. Since image formation ends at T8, the operation from T8 onwards is a post-rotation operation after the image formation operation. First, at T9, the charging voltage is turned OFF. At T10, when the surface of the photosensitive drum 1, whose charging voltage was turned OFF at T9, reaches the contact area, the brush voltage is switched from -350V to +150V. Subsequently, the drive motor 110 is turned OFF at T11. At this time, with a brush voltage of +150V applied, a positive potential difference is formed between the surface potential of the brush member 10 and the photosensitive drum 1 at the contact point.Therefore, due to the rotation stop operation of the photosensitive drum 1 and the effect of the above potential difference, reverse polarity toner can be actively ejected from the brush member 10. Then, at T12, the brush voltage is turned OFF.

[0062] Until timing T3, no surface potential has been formed at the contact point of the photosensitive drum 1, so adjustment of the surface potential of the photosensitive drum 1 is unnecessary. Between T3 and T12, it is certainly possible to control the pre-exposure device, transfer bias, etc., to adjust the surface potential of the photosensitive drum 1.

[0063] Next, Table 2 shows the results of determining toner ejection from the brush member 10 to the surface of the photosensitive drum 1 in Comparative Example 1, Comparative Example 2, and Example 1.

[0064] [Table 2]

[0065] From the results in Table 2, in Comparative Example 1, reverse polarity toner was ejected from the brush member 10 to the surface of the photosensitive drum 1 only during the start and stop of operation and the change in orientation, and the density of the ejection area was 10. This result indicates that some reverse polarity toner was ejected during the start and stop of operation and the change in orientation, even without considering electrical influences. However, in the judgment result for Comparative Example 1, sufficient toner accumulated on the brush member 10 at the 125th image, resulting in image defects.

[0066] Next, in Comparative Example 2, the ejection of reverse-polarity toner from the brush member 10 to the surface of the photosensitive drum 1 is first due to changes in posture at the start and stop of the drive, as in Comparative Example 1. In addition, it utilizes the reversal of the potential difference between the photosensitive drum 1 and the brush member 10 during non-image forming operations (excluding the start and stop of the drive). The ejection due to changes in posture resulted in a density of 10 at the ejection site, similar to Comparative Example 1. Furthermore, the density at the ejection site in the section utilizing the potential difference was 22, which is more than the ejection due to changes in posture alone. However, an image defect occurred at the 256th image, so it was judged as NG. The longer the ejection section utilizing the potential difference, i.e., the non-image forming operation, the greater the amount of toner ejected from the brush member 10, but the longer the rotation time of the photosensitive drum 1 during the non-image forming operation, the lower the productivity.

[0067] On the other hand, in Example 1, the ejection of reverse polarity toner from the brush member 10 was performed using the potential difference and change in orientation at the start and stop of operation, in addition to the conditions of Comparative Example 2. The combined density of ejection using the potential difference in addition to the change in orientation at the start and stop of operation was 55. The judgment result was OK, as no image defects occurred even after 500 sheets were fed through.

[0068] The results obtained from Table 2 are summarized below. The method of reversing the potential difference between the brush member 10 and the photosensitive drum 1 for toner discharge from the brush member 10 is effective, as can be seen from the results of Comparative Example 1 and Comparative Example 2. However, comparing Comparative Example 2 with Example 1, the discharge capacity of Comparative Example 2 is insufficient. The toner discharged from the brush member 10 due to the potential difference is the toner attached to the brush bristles near the photosensitive drum 1, and has little effect on the toner accumulated in the area closer to the base, far from the photosensitive drum 1. On the other hand, in the case of toner discharge using only posture changes, although the toner accumulated in the area far from the photosensitive drum 1 also moves, the amount of toner discharged is reduced because no potential difference is formed to transfer to the photosensitive drum 1. Therefore, effective toner discharge can be achieved by using the posture change of the brush member 10 to move the entire toner attached to the brush member 10, as in Example 1, while creating a potential difference on the side from which the accumulated toner is discharged.

[0069] Based on the above, the configuration of Embodiment 1 is characterized by having the following: An image forming apparatus 100 capable of performing an image forming operation to form an image on a recording material S, comprising a rotatable photosensitive drum 1 and a charging roller 2 that charges the surface of the photosensitive drum 1 at a charging part facing the photosensitive drum 1. An exposure unit 4 that exposes the surface of the photosensitive drum 1 to form an electrostatic latent image on the surface of the photosensitive drum 1 charged by the charging roller 2. A developing roller 31 that supplies a developer charged with normal polarity to the surface of the photosensitive drum 1 to develop the electrostatic latent image as a developer image, and a transfer roller 5 that contacts the photosensitive drum 1 to form a transfer part and transfers the developer image from the photosensitive drum 1 to the recording material S at the transfer part. A brush member 10 that forms a contact part downstream of the transfer part and upstream of the charging part in the rotation direction of the photosensitive drum 1 and contacts the photosensitive drum 1 at the contact part, and a brush voltage application unit E4 that applies a brush voltage to the brush member 10. The system includes a drive motor 110 for rotating the photosensitive drum 1, and a control unit 150 for controlling the brush voltage application unit E4 and the drive motor 110. After the developer image formed on the surface of the photosensitive drum 1 in the transfer unit is transferred to the recording material S, the developer remaining on the surface of the photosensitive drum 1 is collected by the developing roller 31. The control unit 150 controls the direction of the electric field generated in the first region of the photosensitive drum 1 when the first region on which the transfer unit was formed passes the contact unit during the image formation operation, as follows: The direction of the electric field generated in the first region is different from the direction of the electric field generated in the second region of the photosensitive drum 1 which forms the contact unit at the timing when the rotation speed of the photosensitive drum 1 transitions from the first operation, which is the first speed, to the second operation, which is the second speed, during non-image formation operations. At this time, the photosensitive drum 1 may be controlled to rotate at a first speed during the image forming operation and to stop at a second speed, or it may be controlled to rotate at a second speed during the image forming operation after starting to rotate the photosensitive drum at the first speed. Furthermore, it is preferable to maintain the above-described relationship between the potential difference between the brush member 10 and the photosensitive drum 1 even after the photosensitive drum 1 has stopped, and it is preferable to maintain the above-described relationship between the potential difference between the brush member 10 and the photosensitive drum 1 before driving the photosensitive drum 1.

[0070] In this embodiment, the control unit 150 preferably controls the following at the timing when the first region of the photosensitive drum 1, on which the transfer portion is formed during the image formation operation, passes the contact portion: The direction of the electric field generated in the first region with respect to the brush voltage applied to the brush member 10 is controlled so that the developer charged with normal polarity moves from the brush member 10 to the surface of the photosensitive drum 1.

[0071] In the configuration described above, image defects can be suppressed by performing control to efficiently eject the toner adhering to the brush member 10 that contacts the photosensitive drum 1.

[0072] Furthermore, in this embodiment, the potential difference was reversed in the section where the remaining toner passes through the contact area, and at the start and stop of the drive, but this is not limited to the start and stop of the drive. For example, if there is a speed fluctuation between the photosensitive drum 1 and the brush member 10, a change in the posture of the brush member 10 will occur, so the potential relationship between the photosensitive drum 1 and the brush member 10 may be reversed when there is a speed fluctuation. For example, the ejection operation of this embodiment may be applied to configurations such as when the speed is reduced from the normal image formation mode speed (1 / 1 speed) to a low-speed mode such as the thick paper printing mode (1 / 2 speed), or vice versa. Also, in this embodiment, the brush member 10 was mainly used as a collection member for collecting paper dust, but it may of course also function as a collection member that temporarily collects toner and ejects the toner onto the surface of the photosensitive drum 1 at a certain timing. [Examples]

[0073] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are substantially the same as those described in Embodiment 1. Therefore, elements having the same or equivalent functions and configurations as those in the image forming apparatus of Embodiment 1 are denoted by the same reference numerals, and detailed descriptions are omitted.

[0074] Example 1 described an example that utilized the drive start and stop operations associated with a typical printing operation. In this example, while maintaining a potential relationship that discharges reverse polarity toner from the brush member 10 to the photosensitive drum 1, the operation is characterized by repeating the drive start and stop operations, as shown in Figure 8. In Example 1, discharge is performed once each at the start and stop of the drive for one printing operation, whereas in this example, the discharge operation can be performed multiple times, thereby increasing the amount of toner discharged in a single printing operation. The distance the photosensitive drum 1 is moved at one time should be considered in relation to the short side length of the brush member 10, and the effect can be obtained by moving it by approximately the same length as the short side length. Specifically, in this example, since the short side length L3 of the brush member 10 is 5 mm, the distance the surface of the photosensitive drum 1 is moved at one time is set to 5 mm. A movement distance of about 1 mm to 8 mm is preferable. In addition, the number of times it is moved should be sufficient to disperse the toner contained in the brush member 10. As an effect, performing it about 5 times resulted in effective toner discharge from the brush member 10. In this embodiment, five movements were performed when the photosensitive drum 1 stopped due to the post-rotation movement, which is a non-image forming operation. In addition, when the recording material S jammed, which is a condition in which a large amount of toner adheres to the brush member 10, the system was controlled to perform 10 movements.

[0075] From the above, in Example 2, image defects can be suppressed by implementing control to more efficiently eject the toner adhering to the brush member 10 that contacts the photosensitive drum 1. [Examples]

[0076] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in these embodiments are substantially the same as those described in Embodiments 1 and 2. Therefore, elements having the same or equivalent functions and configurations as those in the image forming apparatuses of Embodiments 1 and 2 are denoted by the same reference numerals, and detailed descriptions are omitted.

[0077] Examples 1 and 2 described embodiments that utilized the drive start and stop operations associated with general printing operations. In this embodiment, while maintaining a potential relationship that discharges reverse polarity toner from the brush member 10 to the photosensitive drum 1, the device is characterized by performing the same forward and reverse rotation operations as during printing, as shown in Figure 9. In Examples 1 and 2, discharge is performed by driving and stopping forward rotation, whereas in this embodiment, driving and stopping operations are performed in both the forward and reverse directions, so the change in the orientation of the brush member 10 in the reverse direction can also be utilized. Therefore, it is possible to increase the amount of toner discharged. In this embodiment, the toner discharge effect from the brush member 10 was enhanced by alternately performing forward rotation and reverse rotation of the photosensitive drum 1. Specifically, after rotating the photosensitive drum 1 in the forward direction, it was rotated in the reverse direction, and then rotated in the forward direction again. The number of forward and reverse rotations can be set as appropriate, but approximately two times is preferable. Furthermore, by making the second travel distance smaller than the first travel distance, an even greater toner ejection effect can be obtained. In other words, by making the first travel distance the largest, the amount of toner ejected can be increased. The toner ejected in the subsequent rotational movement passes through the contact area when the next photosensitive drum 1 starts up, making it possible to eject it more efficiently.

[0078] Based on the above, in Example 3, image defects can be suppressed by implementing control to more efficiently eject the toner adhering to the brush member 10 that contacts the photosensitive drum 1. [Explanation of Symbols]

[0079] 1 Photosensitive drum 2 Charging rollers 3. Developing device 4. Exposure apparatus 5 Transfer roller 10 Brush members 31 Developing roller 110 Drive motor

Claims

1. An image forming apparatus capable of performing an image forming operation to form an image on a transfer surface, A rotatable image carrier, A charging member that contacts the surface of the image carrier to form a charged portion, and charges the surface of the image carrier at the charged portion, An exposure unit that exposes the surface of the image carrier to form an electrostatic latent image on the surface of the image carrier which has been charged by the charging member, A developing member that supplies a developer charged with normal polarity to the surface of the image carrier to develop the electrostatic latent image as a developer image, A transfer member that contacts the image carrier to form a transfer portion, and in the transfer portion transfers the developer image from the image carrier to the transfer object, In the rotational direction of the image carrier, a contact portion is formed downstream of the transfer portion and upstream of the charging portion, and a brush member contacts the image carrier at the contact portion, A voltage application unit that applies voltage to the brush member, A drive unit for rotating the image carrier, The system comprises a voltage application unit and a drive unit, and a control unit that controls the voltage application unit and the drive unit. In the transfer section, after the developer image formed on the surface of the image carrier is transferred to the object to be transferred, the developer remaining on the surface of the image carrier is recovered by the developing member. The image forming apparatus is characterized in that the control unit controls the direction of the electric field generated in the first region with respect to the voltage applied to the brush member when the first region of the image carrier on which the transfer portion is formed passes the contact portion during the image forming operation, and the direction of the electric field generated in the second region of the image carrier forming the contact portion with respect to the voltage applied to the brush member before transitioning from a first operation in which the rotation speed of the image carrier is a first speed to a second operation in which the rotation speed of the image carrier is a second speed different from the first speed during a non-image forming operation different from the image forming operation.

2. An image forming apparatus that performs an image forming operation to form an image on a transfer surface, A rotatable image carrier, A charging member that charges the surface of the image carrier in a charging section facing the image carrier, An exposure unit that exposes the surface of the image carrier, which has been charged by the charging member, to form an electrostatic latent image on the surface of the image carrier, A developing member that supplies a developer charged with normal polarity to the surface of the image carrier to develop the electrostatic latent image as a developer image, A transfer member that contacts the image carrier to form a transfer portion, and in the transfer portion transfers the developer image from the image carrier to the transfer target, In the rotational direction of the image carrier, a contact portion is formed downstream of the transfer portion and upstream of the charging portion, and a brush member contacts the image carrier at the contact portion, A first voltage application unit configured to apply only a DC voltage to the charged member, A second voltage application unit configured to apply voltage to the brush member, A drive unit for rotating the image carrier, The system comprises a first voltage application unit, a second voltage application unit, and a control unit that controls the drive unit, In the transfer section, after the developer image formed on the surface of the image carrier is transferred to the object to be transferred, the developer remaining on the surface of the image carrier is recovered by the developing member. The image forming apparatus is characterized in that the control unit controls the direction of the electric field generated in the first region with respect to the voltage applied to the brush member when the first region of the image carrier on which the transfer portion is formed passes the contact portion during the image forming operation, and the direction of the electric field generated in the second region of the image carrier forming the contact portion with respect to the voltage applied to the brush member during the transition from a first operation in which the rotation speed of the image carrier is a first speed to a second operation in which the rotation speed of the image carrier is a second speed different from the first speed during a non-image forming operation different from the image forming operation.

3. The image forming apparatus according to claim 1 or 2, characterized in that the control unit controls the second speed to be slower than the first speed.

4. The image forming apparatus according to claim 1 or 2, characterized in that the control unit controls the second speed to be faster than the first speed.

5. The image forming apparatus according to claim 3, characterized in that the image carrier is controlled to rotate at the first speed during the image forming operation.

6. The image forming apparatus according to claim 4, characterized in that the image carrier is controlled to rotate at the second speed during the image forming operation.

7. The image forming apparatus according to claim 1 or 2, characterized in that the control unit controls the direction of the electric field generated in the first region with respect to the voltage applied to the brush member when the first region passes the contact portion during the image forming operation, such that the developer charged with the normal polarity moves from the brush member to the surface of the image carrier.

8. The image forming apparatus according to claim 1 or 2, characterized in that the interval for transitioning from the first operation to the second operation is an interval for transitioning from a first state in which the rotation of the image carrier has stopped to a second state in which the image carrier has been driven, or an interval for transitioning from the second state to the first state.

9. The image forming apparatus according to claim 1, characterized in that the control unit controls the direction of rotation of the image carrier when rotating the image carrier at the first speed and the direction of rotation of the image carrier when rotating the image carrier at the second speed to be in opposite directions.

10. The image forming apparatus according to claim 1 or 2, characterized in that the developer is a one-component developer.

11. The image forming apparatus according to claim 2, characterized in that the charging member is in contact with the surface of the image carrier in the charging portion.

12. The brush member comprises a base fabric and a yarn portion consisting of a plurality of threads extending from the base fabric, and the density of the threads in the brush member is 150 kF / inch ２ ~350kF / inch ２ The image forming apparatus according to claim 1 or 2, characterized in that it is the same as the image forming apparatus according to claim 1 or 2.

Images