Image forming device

Abstract

To stably hold paper powder accumulated on a brush through paper feed to prevent an image defect caused by the paper powder.SOLUTION: An image forming apparatus controls a driving unit to make a transition, at a contact part where an image carrier and a brush member are in contact with each other, from a driving state in which the driving unit drives the image carrier in a state in which a first potential difference is formed between the brush member and the image carrier, to a stop state in which the driving unit stops the drive of the image carrier in a state in which a second potential difference is formed which has a smaller absolute value than that of the first potential difference.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, such as a laser printer, a copying machine, or a facsimile machine, which obtains a recorded image by transferring a toner image formed on an image carrier by electrophotography or the like onto a recording material. [Background technology]

[0002] Electrophotography is known as an image recording method used in image forming apparatuses such as printers and copiers. The electrophotography method is a method in which an electrostatic latent image is formed on a photosensitive drum (hereinafter referred to as drum) by a laser beam using an electrophotographic process, and a developer image is formed by developing a charged color material (hereinafter referred to as toner) into the electrostatic latent image. Then, the developer image is transferred to a recording material and fixed to form an image. In recent years, a cleanerless method has been proposed for the purpose of miniaturizing image forming apparatuses. The cleanerless method is a method in which the toner, which is a developer remaining on the surface of the drum after the transfer process, is removed from the drum, collected, and reused by simultaneously developing and cleaning the toner in a developing means. In the cleanerless method, since there is no cleaning means usually arranged on the drum, image defects may occur due to paper dust that adheres to the drum during the transfer process to the recording material.

[0003] Therefore, Patent Document 1 proposes a configuration in which a fixed brush is disposed downstream of the transfer unit in the drum rotation direction and upstream of the charging unit in order to collect paper dust that has adhered to the drum during the transfer process. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-65580 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 had the following problem: In a configuration in which a brush is in contact with a drum, speed fluctuations when starting and stopping the rotation of the drum can cause paper dust collected and held by the brush to fall onto the surface of the drum, and some of the fallen paper dust can slip through downstream of the brush, causing image problems.

[0006] SUMMARY OF THE PRESENTLY PREFERRED EMBODIMENTS An object of the present invention is to provide an image forming apparatus capable of stably retaining paper dust accumulated on a brush due to paper passing therethrough, thereby suppressing image defects caused by paper dust. [Means for solving the problem]

[0007] The above object is achieved by the image forming apparatus according to the present invention. In summary, a typical configuration of the present invention includes a rotatable image carrier, a drive unit for rotating the image carrier, a charging member for charging the surface of the image carrier in a charging unit facing the image carrier, an exposure unit for exposing the surface of the image carrier to light in order to form an electrostatic latent image on the surface of the image carrier charged by the charging member, a developing member for supplying a developer charged to a normal polarity to the surface of the image carrier to develop the electrostatic latent image into a developer image, a transfer member for contacting the image carrier to form a transfer unit and transferring the developer image from the image carrier to a transferee in the transfer unit, and a transfer unit for transferring the developer image from the image carrier to a transferee in the transfer unit, downstream of the transfer unit in the rotation direction of the image carrier, the developing device includes a brush member that forms a contact portion upstream of the charging portion and that contacts the image carrier at the contact portion, and a control portion that controls the driving portion, and is configured such that after the developer image formed on the surface of the image carrier is transferred to a transferee in the transfer portion, the developer remaining on the surface of the image carrier is collected by the developing member, and the control portion controls the driving portion to transition from a driving state in which the image carrier is driven in a state in which a first potential difference is formed between the brush member and the image carrier at the contact portion to a stop state in which driving of the image carrier is stopped in a state in which a second potential difference having an absolute value smaller than the first potential difference is formed. The control unit controls the brush member and the image carrier to change a potential difference between the brush member and the image carrier from the first potential difference to a third potential difference that is greater than the second potential difference, and to change the third potential difference to the second potential difference. The present invention is characterized by the above.

[0008] Also, the configuration of another embodiment of the present invention includes a rotatable image carrier, a drive unit that rotates and drives the image carrier, a charging member that charges the surface of the image carrier at a charging unit facing the image carrier, an exposure unit that exposes the surface of the image carrier to light in order 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 to a 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 unit and transfers the developer image from the image carrier to a transferee at the transfer unit, and a brush member that forms a contact unit downstream of the transfer unit and upstream of the charging unit in the rotation direction of the image carrier and contacts the image carrier at the contact unit, a brush voltage application unit that applies a brush voltage to the brush member; The driving unit and the brush voltage application unit. and a control unit that controls the developer image formed on the surface of the image carrier in the transfer unit to a transfer target body, and after the developer image formed on the surface of the image carrier in the transfer unit is transferred to a transfer target body, the developer remaining on the surface of the image carrier is collected by the developing member, and the control unit controls the developer image formed on the surface of the image carrier in the transfer unit to be collected by the developing member. The brush voltage is applied to the brush member; and A first potential difference is formed between the brush member and the image carrier, and the image carrier is stopped. 、 controlling the driving unit so as to transition to a driving state in which the image carrier is driven in a state in which a second potential difference having an absolute value larger than that of the first potential difference is formed; The control unit controls the brush member and the image carrier to change a potential difference between the brush member and the image carrier from the first potential difference to a third potential difference that is greater than the second potential difference, and to change the third potential difference to the second potential difference. The present invention is characterized by the above. Effect of the Invention

[0009] As described above, according to the present invention, paper dust accumulated on the brush due to paper passing can be stably retained, and image defects caused by paper dust can be suppressed. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is an explanatory diagram of an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a schematic diagram of a brush member in the first embodiment. [Diagram 3] FIG. 2 is a control block diagram according to the first embodiment. [Figure 4] FIG. 13 is a diagram illustrating control in Comparative Example 1. [Diagram 5] FIG. 4 is a diagram for explaining control in the first embodiment. [Figure 6] FIG. 4 is a diagram for explaining the posture of the brush in the first embodiment. [Figure 7] 5A to 5C are diagrams illustrating a change in brush posture and a state of paper dust in the first embodiment. [Figure 8] FIG. 11 is a diagram for explaining control in the second embodiment. [Figure 9] FIG. 11 is a diagram for explaining another mode of control in the second embodiment. [Figure 10] FIG. 11 is a diagram for explaining control in the third embodiment. [Figure 11] FIG. 13 is a diagram for explaining control in the fourth embodiment. [Figure 12] FIG. 13 is a diagram for explaining control in the fifth embodiment. [Figure 13] FIG. 11 is a diagram illustrating a control in another embodiment. [Figure 14] FIG. 11 is a diagram illustrating a control in another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiment of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the embodiment may be changed as appropriate depending on the configuration and various conditions of the device to which the invention is applied. In other words, the scope of the present invention is not limited to the following embodiment. EXAMPLES

[0012] 1. Image forming equipment 1 shows a schematic configuration of an embodiment of an image forming apparatus 100 according to the present invention. The image forming apparatus 100 of this embodiment is a monochrome laser beam printer that employs a cleanerless system and a contact charging system.

[0013] The image forming apparatus 100 in this embodiment is provided with a cylindrical photosensitive member serving as an image carrier, that is, a photosensitive drum 1. A charging roller 2 serving as a charging means and a developing device 3 serving as a developing means are provided around the photosensitive drum 1. In addition, an exposure device 4 serving as an exposure means is provided between the charging roller 2 and the developing device 3 in the rotation direction of the photosensitive drum 1 in FIG. 1. A transfer roller 5 serving as a transfer means is pressed against the photosensitive drum 1.

[0014] The photosensitive drum 1 in this embodiment is a negatively charged organic photosensitive body. This photosensitive drum 1 has a photosensitive layer on a drum-shaped aluminum substrate, and is driven to rotate at a predetermined process speed in the direction of the arrow in the figure (clockwise direction) by a drive motor (drive unit) (FIG. 3) serving as drive means 110. In this embodiment, the process speed corresponds to the circumferential speed (surface moving speed) of the photosensitive drum 1, which is 140 mm / sec, and the outer diameter of the photosensitive drum 1 is 24 mm.

[0015] The charging roller 2, which is a charging member, contacts the photosensitive drum 1 with a predetermined pressure contact force to form a charging portion. A desired charging voltage is applied by a charging high-voltage power source E1 (FIG. 3) as a charging voltage application means, and the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential. In this embodiment, the surface of the photosensitive drum 1 is negatively charged by the charging roller 2. During charging, a predetermined charging voltage (charging bias) is applied to the charging roller 2 by the charging power source E1. In this embodiment, a negative DC voltage is applied to the charging roller 2 as a charging voltage during charging. The charging voltage in this embodiment is -1300V as an example. As a result, in this embodiment, the surface of the photosensitive drum 1 is uniformly charged to a dark potential Vd of -700V. More specifically, the charging roller 2 charges the surface of the photosensitive drum 1 by discharge generated in at least one of the small gaps between the charging roller 2 and the photosensitive drum 1 formed on the upstream side and downstream side of the contact portion with the photosensitive drum 1 with respect to the rotation direction of the photosensitive drum 1. However, in this case, it is assumed that the contact portion between the charging roller 2 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 is the charging portion.

[0016] In this embodiment, the exposure device 4, which is an exposure unit, is a laser scanner device, which outputs laser light corresponding to image information input from an external device such as a host computer, and scans and exposes the surface of the photosensitive drum 1. This exposure forms an electrostatic latent image (electrostatic image) corresponding to the image information on the surface of the photosensitive drum 1. In this embodiment, the absolute value of the dark area potential Vd of the surface of the photosensitive drum 1 formed by uniformly charging is reduced by exposure by the exposure device 4 to a light area potential Vl of -100V. Here, the position on the photosensitive drum 1 exposed by the exposure device 4 with respect to the rotation direction of the photosensitive drum 1 is the exposure area (exposure position). The exposure device 4 is not limited to a laser scanner device, and may be, for example, an LED array in which a plurality of LEDs are arranged along the longitudinal direction of the photosensitive drum 1.

[0017] In this embodiment, a contact development method is used as a development method. The development device 3 includes a development member, a development roller 31 as a developer carrier, a toner supply roller 32 as a developer supply means, a developer storage chamber 33 that stores toner, and a development blade 34. The toner supplied from the developer storage chamber 33 to the development roller 31 by the toner supply roller 32 passes through a blade nip that is a contact portion between the development roller 31 and the development blade 34, and is charged to a predetermined polarity. The toner carried on the development roller 31 moves from the development roller 31 to the photosensitive drum 1 in the development portion according to the electrostatic image. Here, the contact portion between the development roller 31 and the photosensitive drum 1 with respect to the rotation direction of the photosensitive drum 1 is the development portion. In this embodiment, the development roller 31 is rotationally driven in a counterclockwise direction so that the photosensitive drum 1 and the development roller 31 move in the forward direction in the development portion. The driving motor as the driving means 110 for driving the developing roller 31 may be a main motor common to the driving means 110 for the photosensitive drum 1, or separate driving motors may rotate the photosensitive drum 1 and the developing roller 31. During development, a predetermined developing voltage (developing bias) is applied to the developing roller 31 by a developing power source E2 (FIG. 3) as a developing voltage applying means. In this embodiment, a negative DC voltage is applied to the developing roller 31 as the developing voltage during development, and the developing voltage is set to -380V. In this embodiment, toner charged to the same polarity as the charging polarity of the photosensitive drum 1 (negative polarity in this embodiment) adheres to the exposure surface (image portion) which is the image forming portion on the photosensitive drum 1, the absolute value of the potential of which is reduced by exposure after being uniformly charged. This development method is called a reversal development 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 adopted, 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 be adopted. 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 the developer (magnetic brush) carried on the developer carrying member is brought into contact with the photosensitive drum 1 to perform development. The non-contact development method is a method in which toner is caused to fly onto the photosensitive member from the developer carrying member arranged opposite the photosensitive member in a non-contact manner to perform development.The magnetic development method is a method in which a magnetic toner is carried by a magnetic force on a developer carrier that has a magnet built in as a magnetic field generating means and is arranged opposite to the photoconductor in a contact or non-contact manner. In this embodiment, toner with a median average particle size of 6 μm and a normal negative charge polarity is used.

[0018] The transfer roller 5 as a transfer member may be preferably made of an elastic material such as polyurethane rubber, EPDM (ethylene propylene diene rubber), NBR (nitrile butadiene rubber), or other sponge rubber. The transfer roller 5 is pressed against the photosensitive drum 1 to form a transfer section where the photosensitive drum 1 and the transfer roller 5 are in pressure contact. During transfer, a predetermined transfer voltage (transfer bias) is applied to the transfer roller 5 by a transfer power source E3 (FIG. 3) as a transfer voltage application means. In this embodiment, during transfer, a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal polarity of the toner is applied to the transfer roller 5 as a transfer voltage. In this embodiment, the transfer voltage during transfer is +1000V, for example. Then, the toner image is electrostatically transferred from the photosensitive drum 1 to the recording material S by the action of the electric field formed between the transfer roller 5 and the photosensitive drum 1.

[0019] A transfer material S as a recording material stored in a cassette 6 is fed by a paper feed unit 7 in synchronization with the timing at which the toner image formed on the photosensitive drum 1 reaches the transfer section, and is conveyed to the transfer section through a pair of registration rollers 8. The toner image formed on the photosensitive drum 1 is transferred onto the transfer material S by a transfer roller 5 to which a predetermined transfer voltage is applied by a transfer high-voltage power supply E3.

[0020] The transfer material S after the toner image has been transferred is conveyed to a fixing device 9. The fixing device 9 is a film heating type fixing device equipped with a fixing film 91 incorporating a fixing heater (not shown) and a thermistor (not shown) for measuring the temperature of the fixing heater, and a pressure roller 92 for pressing against the fixing film 91. The transfer material S is heated and pressurized to fix the toner image thereon, and is then passed through a pair of paper discharge rollers 12 and discharged outside the machine.

[0021] Moreover, the transfer residual toner remaining on the photosensitive drum 1 without being transferred to the transfer material S is removed in the following process.

[0022] The residual toner includes a mixture of positively charged toner and negatively charged toner that does not have a sufficient charge. The residual toner is charged negatively again by discharge at the charging section of the charging roller 2. The residual toner that has been charged negatively again by the charging roller 2 reaches the developing section as the photosensitive drum 1 rotates. Here, there are cases where 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 cases where a non-image forming section where no electrostatic latent image is formed is formed. The behavior of the residual toner that has reached the developing section will be explained separately for the image forming section and non-image forming section of the photosensitive drum 1.

[0023] The residual toner adhering to the 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 moves to the transfer portion together with the developed toner from the developing roller 31, where it is transferred to the transfer material S and used for image formation.

[0024] Meanwhile, the transfer residual toner adhering to the non-image forming portion of the photosensitive drum 1 is recharged to the normal negative polarity by the charging portion, and is transferred to the developing roller 31 in the developing portion due to the potential difference between the non-image forming portion potential of the photosensitive drum 1 and the developing voltage, and is collected in the developer storage chamber 33. The toner collected in the developer storage chamber 33 is used again for image formation.

[0025] 2. Brush component structure Next, the paper dust removing member in this embodiment will be described. As shown in Fig. 1, the image forming apparatus 100 in this embodiment has a brush member 10 (collection member) which is a contact member serving as the paper dust removing member. In this embodiment, the image forming apparatus 100 has the brush member 10 which contacts the surface of the photosensitive drum 1 downstream of the transfer section and upstream of the charging section in the rotation direction of the photosensitive drum 1 to form a brush contact section (brush contact position). Here, the contact section between the brush member 10 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 is considered to be the brush contact section (hereinafter referred to as the contact section).

[0026] Fig. 2(a) is a schematic diagram of the brush member 10 in a standalone state, as viewed along its longitudinal direction (substantially parallel to the direction of the rotation axis of the photosensitive drum 1). Fig. 2(b) is a schematic diagram of the brush member 10 in contact with the photosensitive drum 1, as viewed along its longitudinal direction.

[0027] The brush member 10 has a brush portion configured of a fixedly disposed conductive fixed brush 11. As shown in Fig. 2, the brush member 10 is configured of conductive nylon 6 pile yarns 11a, which are a plurality of bristles that rub against the surface of the photosensitive drum 1, and a base cloth 11b that supports the pile yarns 11a. As described above, the brush member 10 is disposed so as to come into contact with the photosensitive drum 1 downstream of the transfer unit and upstream of the charging unit in the moving direction (rotating direction) of the photosensitive drum 1.

[0028] The brush member 10 is disposed so that its longitudinal direction is substantially parallel to the direction of the rotation axis of the photosensitive drum 1. Note that, as the material of the conductive threads 11a, rayon, acrylic, polyester, etc. may be used in addition to nylon.

[0029] As shown in FIG. 2(a), when the brush member 10 is in a single state, that is, when no external force is applied to bend the conductive thread 11a, the distance to the tip of the conductive thread 11a exposed from the base fabric 11b is defined as L1. In this embodiment, L1 is 6.5 mm. The brush member 10 is arranged such that the base fabric 11b is fixed to a support member (not shown) installed at a predetermined position of the image forming apparatus 100 by a fixing means such as double-sided tape, and the tip of the conductive thread 11a penetrates into the photosensitive drum 1. In this embodiment, the clearance between the support member and the photosensitive drum 1 is fixed. And, 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 penetration amount of the brush member 10 into the photosensitive drum 1. In this embodiment, the penetration amount of the brush member 10 into the photosensitive drum 1 is 1 mm. In this embodiment, as shown in FIG. 2(a), when the brush member 10 is in a stand-alone state, the length L3 of the brush member 10 in the circumferential direction of the photosensitive drum 1 (hereinafter referred to as the "short direction") is 5 mm. In this embodiment, the length of the brush member 10 in the longitudinal direction is 216 mm. This allows the brush member 10 to come into contact with the entire image forming area (area where a toner image can be formed) on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1. In this embodiment, the conductive threads 11a have a thickness of 2 denier and a density of 240 kF / inch. 2 (kF / inch 2 (Filaments per square inch is a unit of brush density.) As described above, the brush member 10 is supported by a support member (not shown) and is disposed at 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.

[0030] The brush member 10 collects (recovers) adhesions such as paper dust that are transferred from the recording material S onto the photosensitive drum 1 at the transfer section, and reduces the amount of paper dust that moves to the charging section downstream of the brush member 10 in the movement direction of the photosensitive drum 1, and to the developing section.

[0031] In this embodiment, the length L3 of the brush member 10 in the circumferential direction of the photosensitive drum 1 (hereinafter, the short side direction) is set to 5 mm, but is not limited to this. For example, it may be changed appropriately depending on the life of the image forming apparatus or the process cartridge. It goes without saying that the longer the length of the brush member 10 in the short side direction, the longer the paper dust can be collected.

[0032] In this embodiment, the length of the brush member 10 in the longitudinal direction is set to 216 mm, but is not limited to this. For example, it may be changed appropriately according to the maximum paper passing width of the image forming apparatus 100.

[0033] In this embodiment, the fineness of the brush member 10 is 220T / 96F (meaning 96 bundles of threads each 220g thick per 10,000m), but it is desirable to determine this value taking into consideration the ability of paper dust to slip through. If the fineness of the brush member 10 is small, the force that blocks the paper dust is weak and the paper dust easily slips through, which may hinder the charging of the photosensitive drum 1 by the charging roller 2 and cause image defects. Also, if the fineness of the brush member 10 is too large, it may not be possible to collect toner or fine paper dust, which may result in 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 area.

[0034] The density of the brush member 10 in this embodiment is 240 kF / inch 2 (kF / inch 2 is a unit of brush density, indicating the number of filaments per square inch), but it is desirable to determine this taking into consideration toner passage and paper dust collection performance. In other words, if the density of the brush member 10 is too high, the toner passage will be impaired, causing the toner to stack (cluster), and the stacked toner may scatter and cause problems such as 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, from the perspective of paper dust collection performance, the thickness and density of the conductive threads 11a are set to 1 to 6 denier and 150 to 350 kF / inch, respectively. 2From the viewpoint of long life, the length of the brush member 10 in the short direction is preferably 3 mm or more.

[0035] Further, a brush power supply E4 (FIG. 3) serving as a brush voltage application means is connected to the brush member 10. 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, during image formation, a negative polarity DC voltage is applied to the brush member 10 as the brush voltage. In this embodiment, the brush voltage during image formation is, for example, −400 V.

[0036] 3. Image output operation In this embodiment, the image forming apparatus 100 executes an image output operation (job), which is a series of operations for forming an image on a single or multiple 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-interval process in the case of forming an image on multiple recording materials S, and a post-rotation process. The image forming process is a period during which an electrostatic image is actually formed on the photosensitive drum 1, the electrostatic image is developed (a toner image is formed), the toner image is transferred, the toner image is fixed, and the image forming time refers to this period. More specifically, the timing during image formation differs depending on the positions at which the electrostatic image is formed, the toner image is formed, the toner image is transferred, the toner image is fixed, and the like. The pre-rotation process is a period during which a preparatory operation is performed before the image forming process. The paper-interval process is a period corresponding to the interval between recording materials S when the image forming process is performed continuously on multiple recording materials S (during continuous image formation). The post-rotation process is a period during which an arranging operation (preparatory operation) is performed after the image forming process. Non-image formation refers to periods other than image formation, and includes the above-mentioned pre-rotation process, paper interval process, post-rotation process, and also the pre-multiple-rotation process, which is a preparatory operation when the image forming apparatus 100 is turned on or when it returns from a sleep state.

[0037] 4. Control mode 3 is a schematic block diagram showing the control mode of the main parts of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 is provided with a control unit 150. The control unit 150 has a CPU 151 as an arithmetic control means which is a central element for performing arithmetic processing, a memory (storage element) 152 such as a ROM or RAM as a storage means, an input / output unit (not shown) for controlling the transmission and reception of signals between various elements connected to the control unit 150, and the like. The RAM stores the detection results of the sensors, the arithmetic results, and the like, and the ROM stores a control program, a data table obtained in advance, and the like.

[0038] The control unit 150 is a control unit that comprehensively controls the operation of the image forming apparatus 100. The control unit 150 executes a predetermined image formation sequence by controlling the transmission and reception of various electrical information signals and the timing of driving. Each unit of the image forming apparatus 100 is connected to the control unit 150. For example, in relation to this embodiment, 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 the like are connected to the control unit 150.

[0039] 5. Conventional forms of control Next, in order to facilitate understanding of various potential controls in this embodiment, a conventional control will be described with reference to FIG.

[0040] Fig. 4 is a timing chart showing the control of a single-sheet print job operation in a conventional image forming apparatus. From the top of Fig. 4, the chart shows ON / OFF 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 source E1, and laser emission onto the photosensitive drum 1 by the laser scanner device 4, which is an exposure device. Next, the chart shows the transfer voltage applied to the transfer roller 5 from the transfer power source E3, the surface potential of the photosensitive drum 1 at the contact portion after transfer that has received the transfer voltage, and the brush voltage applied to the brush member 10 from the brush power source E4. Then, the chart shows the surface potential of the photosensitive drum 1 at the contact portion, and the difference between the surface potential of the photosensitive drum 1 at the contact portion calculated from the brush voltage and the brush voltage at the bottom.

[0041] Fig. 4 is a timing chart relating to the control executed in performing the image forming operation. In Fig. 4, when a print instruction is received before T1, a pre-rotation operation executed before the image forming operation is started. At T1 during the pre-rotation operation, the photosensitive drum 1 starts to rotate and a voltage V0 is applied to the brush member. In this embodiment, a negative voltage is mainly applied as the brush voltage to collect the positive paper powder adhering to the photosensitive drum 1 at the transfer section, so a negative voltage is applied as the brush voltage even in the conventional configuration.

[0042] Next, at T2, a charging voltage is applied to the charging roller 2. At T3, when the charged surface on the surface of the photosensitive drum 1 reaches the transfer portion, a transfer voltage is applied to perform a resistance detection operation and the like. The transfer voltage at this time may be a voltage of the same polarity and smaller in absolute value than the transfer voltage of +1000V applied during the image forming operation, and in the conventional configuration and this embodiment, it is set to +700V as the voltage when no paper is passing. Then, at T4, the surface of the photosensitive drum 1 on which the post-transfer potential has been formed reaches the contact portion. The transfer voltage is changed between when no paper is passing and when paper is passing, but the setting is changed so that the transfer current flowing is the same depending on whether the recording material S is present or not. Therefore, the transfer voltage is controlled so that the post-transfer potential is approximately the same when no paper is passing and when paper is passing.

[0043] After the resistance detection operation is completed, the image forming operation is started. At T5, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 1. To this end, the surface of the photosensitive drum 1 is exposed by the laser scanner device 4. As a result, a developer image is formed on the photosensitive drum 1. To transfer the developer image to the recording material S at the transfer section, a transfer voltage during paper passage is applied at T6. The transfer voltage at that time is set to +1000V. After that, when the image forming operation is completed, the exposure is turned off at T7. Then, the operation proceeds to a post-rotation operation, and at T8, which is the timing when the surface of the photosensitive drum 1 that formed the exposed section at the timing of T7 reaches the transfer section, the transfer voltage is switched to a non-paper passing voltage. In this embodiment, the transfer voltage applied at T8 is the same as the non-paper passing voltage applied at T3, but is not limited to this.

[0044] Then, at T9, the charging voltage is turned off. After that, at T10, which is the timing when the surface of the photosensitive drum 1 that formed the charging portion at the timing of T9 reaches the exposure portion, the laser scanner device 4 performs forced light emission on the surface of the photosensitive drum 1, and the surface potential of the photosensitive drum 1 is reduced as much as possible. In FIG. 4, a diagram in which the potential is reduced to 0V is shown for the sake of simplicity. Then, at the timing when the surface of the photosensitive drum 1 that formed the exposure portion at the time of forced light emission reaches the transfer portion at T11, the transfer voltage is turned off. After that, after the timing of T12, the post-transfer potential formed at the contact portion becomes 0V. After that, the forced light emission is ended at T13, and in the conventional embodiment, at T14 when the surface potential of the photosensitive drum 1 after transfer is reduced, the rotational drive of the photosensitive drum 1 is stopped and the brush voltage is also turned off. In this embodiment, the feature is that the paper dust discharge suppression sequence of the brush member 10 is executed after the timing of T12. Hereinafter, the conventional embodiment is used as Comparative Example 1.

[0045] 6. Control of this embodiment Next, various types of potential control in this embodiment will be described with reference to FIG. 5. FIG. 5 is a diagram showing the control of a one-sheet print job operation in the image forming apparatus 100 of this embodiment, and the period from the start of rotational driving of the photosensitive drum 1 to time T12 (T12A in FIG. 5) is the same as that of the above-mentioned comparative example 1. This embodiment is characterized in that when the surface potential of the photosensitive drum 1 after transfer is reduced by forced emission at T12A, the brush voltage is reduced stepwise from V0 to V1 to V2 to OFF at the timings of T12A to T12B and T12C. Thereafter, the rotational driving of the photosensitive drum 1 is stopped at T14. By controlling as described above, when the driving of the photosensitive drum 1 is stopped, the electrostatic adsorption force generated between the photosensitive drum 1 and the brush member 10 can be gradually alleviated. In this embodiment, V0=-400V, V1=-200V, and V2=-100V are set, but it is preferable to apply voltages in the range of -500V to 0V. In addition, |V0-V1|>|V1-V2|, because the closer the timing of stopping the photosensitive drum 1, the smaller the voltage fluctuation, i.e., the smaller the electrostatic adsorption force, is, the more effective it is in retaining paper powder. On the other hand, if the electrostatic adsorption force is suddenly relaxed at the beginning when the photosensitive drum 1 is driven in a steady state, it may affect the posture of the brush member 10. Therefore, it may be better to relax the electrostatic adsorption force by gradually increasing the voltage fluctuation while maintaining the relationship |V0-V1|<|V1-V2|. Therefore, the relationship between V0, V1, and V2 may be adjusted as appropriate depending on the state of the brush member 10, etc.

[0046] Next, the action of the control of this embodiment on the change in the attitude of the brush member 10 when the photosensitive drum 1 rotates and stops will be described.

[0047] First, the attitude of the brush member 10 in the rotation direction of the photosensitive drum 1 due to the rotation drive of the photosensitive drum 1 will be described with reference to Fig. 6. Fig. 6(a) is a diagram showing the attitude of the brush member 10 when the photosensitive drum 1 is stopped. When the photosensitive drum 1 is stopped rotating, no tangential force acts on the brush member 10 in the rotation direction of the photosensitive drum 1, so there is little bristles falling downstream.

[0048] Fig. 6(b) is a diagram showing the attitude of the brush member 10 when the photosensitive drum 1 is rotationally driven with no brush voltage applied. When the photosensitive drum 1 is rotationally driven, a tangential force is generated in the brush member 10 in the rotation direction of the photosensitive drum 1, so that the brush member 10 falls more heavily downstream in the rotation direction of the photosensitive drum 1 than in Fig. 6(a).

[0049] Fig. 6(c) is a diagram showing the attitude of the brush member 10 when the photosensitive drum 1 is being rotated with a brush voltage applied. When a brush voltage is applied to the brush member 10, an electrostatic adsorption force is generated due to the potential difference between the surface of the photosensitive drum 1 and the brush voltage. As a result, in Fig. 6(c), compared to Fig. 6(b), the bristles in the downstream direction in the rotation direction of the photosensitive drum 1 due to the rotation of the photosensitive drum 1 become even more severe. The effect of the electrostatic adsorption force becomes greater as the potential difference between the brush voltage and the surface potential of the photosensitive drum 1 becomes larger.

[0050] In light of the above tendency, the change in posture of the brush member 10 under the control of Comparative Example 1 and this embodiment will be described.

[0051] In Comparative Example 1, as shown in FIG. 4, from T12 until the rotation of the photosensitive drum 1 is stopped, the potential difference between the surface potential of the photosensitive drum 1 after transfer and the brush voltage is almost equal to the brush voltage. Therefore, the brush falls significantly downstream as shown in FIG. 6(c). In Comparative Example 1, the rotation of the photosensitive drum 1 is stopped from this state and the brush voltage is turned OFF at the same time, returning to the state shown in FIG. 6(a). At this time, the posture of the brush member 10 changes abruptly from FIG. 6(c) to FIG. 6(a).

[0052] On the other hand, in this embodiment, the brush voltage is gradually reduced from time T12A to T14, when the photosensitive drum 1 stops rotating, and the potential difference between the surface potential of the photosensitive drum 1 and the brush voltage becomes smaller. Therefore, the posture of the brush member 10 gradually changes from FIG. 6(c) to FIG. 6(b). After that, when the rotation of the photosensitive drum 1 is stopped, the posture of the brush member 10 returns to FIG. 6(a). However, since the posture of the brush member 10 at this time changes from FIG. 6(b) to FIG. 6(a), the posture change is smaller than in Comparative Example 1.

[0053] Next, the results of a paper feed test conducted to confirm the effects of this embodiment will be described.

[0054] The paper passing experiment was carried out under the following conditions. In an environment with a temperature of 15°C and a relative humidity of 10% (low temperature and low humidity environment), 100 white images were printed continuously using CenturyStar paper (product name, manufactured by CENTURY PULP AND PAPER) as the recording material S. After printing was completed, the rotation of the photosensitive drum 1 was stopped once. Then, one white image was printed again. The speckled images that appeared on this one sheet were counted, and if there were 15 or more speckles of 0.8 mm or more in size that had a large visual impact, the paper dust collection ability was judged to be NG.

[0055] After carrying out the controls of Comparative Example 1 and Example 1, the above-mentioned paper feed test was carried out, and the results are shown in Table 1.

[0056] [Table 1]

[0057] From the results in Table 1, it can be seen that the number of spots in Comparative Example 1 exceeded 15, whereas the number of spots in Example 1 was less than 15, and thus the number of spots was clearly less than that in Comparative Example 1.

[0058] The behavior of the brush member 10 after collecting paper dust will be described with reference to Fig. 7. In the above paper feed test, paper dust gradually accumulates on the brush member 10 while 100 sheets are continuously printed, and as the dust accumulates, it becomes entangled and clumps together. Up to T12 (T12A) in Figs. 4 and 5 after 100 sheets have been fed, the state of paper dust accumulation on the brush member 10 of Comparative Example 1 is the same as that of Example 1. A conceptual diagram of the state of paper dust accumulation on the brush member 10 at T12 (T12A) is shown in Fig. 7(a).

[0059] In Comparative Example 1, the sudden change in the attitude of the brush member 10 caused by the transition from T12 to T14 in FIG. 4 causes the paper powder mass that had aggregated within the brush member 10 to break down, resulting in a large number of fine paper powder fibers adhering to the surface of the photosensitive drum 1. A conceptual diagram of this state is shown in FIG. 7(b). When the next print is started from this state, the large number of paper powder fibers that have broken down within the brush member 10 and adhered to the surface of the photosensitive drum 1 tend to slip through the contact area. As a result, the number of spots caused by the paper powder adhering to the surface of the photosensitive drum 1 increases during the printing operation of the first sheet immediately afterwards.

[0060] On the other hand, as described above, in Example 1, the change in the posture of the brush member 10 is smaller than in Comparative Example 1, so the paper powder lump that had aggregated within the brush member 10 is less likely to break down, and fine paper powder fibers are less likely to adhere to the photosensitive drum 1. A conceptual diagram of this state is shown in FIG. 7(c). In Example 1, even if the next print is started from this state, the paper powder lump within the brush member 10 remains held by the brush member 10. Therefore, little paper powder slips through the brush member 10 at the contact area. As a result, there are fewer spots caused by the paper powder that adheres to the surface of the photosensitive drum 1 during the printing operation of the first sheet immediately afterwards.

[0061] As described above, by executing the control of the first embodiment, the change in the posture of the brush member 10 when the rotational drive of the photosensitive drum 1 is stopped is reduced, and the paper dust accumulated on the brush member 10 is stably held. Therefore, image defects caused by the paper dust can be suppressed.

[0062] The first embodiment has the following configuration. It includes a rotatable photosensitive drum 1, a drive motor 110 that rotates and drives the photosensitive drum 1, and a charging roller 2 that charges the surface of the photosensitive drum 1 at a charging portion facing the photosensitive drum 1. It also includes 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, and a developing roller 31 that supplies a developer charged to a normal polarity to the surface of the photosensitive drum 1 to develop the electrostatic latent image as a developer image. It also includes a transfer roller 5 that contacts the photosensitive drum 1 to form a transfer portion and transfers the developer image from the photosensitive drum 1 to a recording material S at the transfer portion. It includes a brush member 10 that forms a contact portion downstream of the transfer portion and upstream of the charging portion in the rotation direction of the photosensitive drum 1, and a control unit 150 that controls the drive motor 110.

[0063] After the developer image formed on the surface of the photosensitive drum 1 in the transfer portion 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 portion 150 executes the following control during the transition from a driving state in which the photosensitive drum 1 is driven to a stopped state in which the photosensitive drum 1 is stopped. After a first potential difference is formed between the brush member 10 and the photosensitive drum 1 in the contact portion, the control portion 150 controls the driving of the photosensitive drum 1 to be stopped in a state in which a second potential difference having an absolute value smaller than the first potential difference is formed.

[0064] In addition, the potential difference formed between the brush member 10 and the photosensitive drum 1 is controlled to be changed from the first potential difference to a third potential difference which is a potential difference between the first potential difference and the second potential difference, and then changed from the third potential difference to the second potential difference to stop driving the photosensitive drum 1.

[0065] With the above-mentioned configuration, paper dust accumulated on the brush member 10 due to paper passing can be stably held, and image defects caused by paper dust can be suppressed.

[0066] In addition, in the first embodiment, the brush voltage is turned off before the rotational drive of the photosensitive drum 1 is stopped. However, if the electrostatic adsorption force is sufficiently small that it has almost no effect on the posture change even if the brush voltage is set to V2, it is not necessarily required to turn it off before the rotational drive is stopped.

[0067] In the first embodiment, the brush voltage is switched three times before the rotation of the photosensitive drum 1 stops, but this is not limited to this. If the voltage is switched at least once, it is possible to obtain an effect compared to the conventional embodiment. The brush voltage may be switched three or more times.

[0068] In addition, in the first embodiment, the base of the photosensitive drum 1 is grounded, but this is not limited to this. For example, the surface potential of the photosensitive drum 1 after transfer may be controlled by switching the potential of the base using a high-voltage element or the like, so that the potential difference with the brush voltage is controlled to change stepwise.

[0069] In addition, in Example 1, the effect on paper dust was described, but since there is a risk that the toner contained in the brush member 10 will scatter if there is a large change in the posture of the brush member 10, the present invention is not necessarily limited to brush members 10 for collecting paper dust. EXAMPLES

[0070] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the embodiment 2 are the same as those of the image forming apparatus of the embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of the embodiment 1 are given the same reference numerals as those of the image forming apparatus of the embodiment 1, and detailed explanations are omitted.

[0071] 1. Control of this embodiment Next, various types of potential control in the second embodiment will be described with reference to Fig. 8. Fig. 8 is a diagram showing the control of a single sheet print job operation in the image forming apparatus 100 in the second embodiment, and the process from the start of rotational driving of the photosensitive drum 1 to T12A is the same as that in the first embodiment. In the second embodiment, when the surface potential of the photosensitive drum 1 after transfer is reduced by forced emission, the potential difference between the brush voltage and the surface potential of the photosensitive drum 1 is temporarily increased from T12A. Thereafter, at the timings of T12D, T12E, and T12F, the brush voltage is reduced from V0 to V1 to V2, and at T14, with the brush voltage OFF, the rotational driving of the photosensitive drum 1 is stopped.

[0072] When the control of the above-mentioned embodiment 2 was executed, the paper feed test was carried out in the same manner as in embodiment 1, and the results of comparison with embodiment 1 are shown in Table 2.

[0073] [Table 2]

[0074] By executing the control of the second embodiment, the number of spots can be further reduced compared to the first embodiment. The reason why the number of spots can be reduced is that the potential difference between the brush member 10 and the photosensitive drum 1 is intentionally increased once at T12A, thereby stabilizing the state of the paper dust held in the brush member 10. When the potential difference is increased, the electrostatic adsorption force between the brush member 10 and the photosensitive drum 1 increases temporarily. However, since the timing when the posture change is greatest is T14, which is the timing when the rotation of the photosensitive drum 1 stops, the effect of actively attracting the paper dust to the brush member 10 is greater than the increase in the electrostatic adsorption force caused by increasing the potential difference at the time of T12A. Therefore, it is considered that the second embodiment can create a state in which the brush member 10 is unlikely to spit paper dust onto the surface of the photosensitive drum 1 in advance.

[0075] In the second embodiment, the potential difference formed between the brush member 10 and the photosensitive drum 1 is changed from the first potential difference to a fourth potential difference which is greater than the second potential difference, and then changed from the fourth potential difference to the second potential difference, thereby controlling the driving of the photosensitive drum 1 to be stopped.

[0076] As described above, by executing the control of Example 2, the paper dust accumulated on the brush member 10 is stably retained, in comparison with Example 1, and the ejection of paper dust due to changes in the posture of the brush member 10 when the photosensitive drum 1 rotates can be further suppressed.

[0077] In addition, in the first and second embodiments, the brush voltage can be applied between -500V and 0V. However, in cases where only one voltage value can be applied due to the cost reduction of the device, the surface potential of the photosensitive drum 1 after the transfer may be changed in stages. That is, the surface potential of the photosensitive drum 1 may be changed in stages to change the potential difference between the brush voltage and the surface potential of the photosensitive drum 1 after the transfer. FIG. 9 shows a case where the exposure intensity of the laser scanner device 4 is changed in stages as an example of changing the surface potential of the photosensitive drum 1 after the transfer. After the forced emission of T10, exposure is performed under the condition of weak emission 1 at the timing of T10A, and exposure is performed under the condition of weak emission 2 at the timing of T10B. The timings of T12G and T12H show the corresponding potential difference between the brush member 10 and the photosensitive drum 1, and the post-transfer potential at the contact portion. The relationship of the exposure intensity in FIG. 9 shows a case where the forced emission is the strongest, followed by weak exposure 1 and weak exposure 2 in that order. By this control, the absolute value of the surface potential of the photosensitive drum 1 after transfer increases stepwise, and the potential difference with the brush voltage decreases stepwise. Therefore, the same effect as in the case of changing the brush voltage stepwise in the first and second embodiments can be obtained. In FIG. 9, the surface potential of the photosensitive drum 1 after transfer is controlled by changing the exposure intensity of the laser scanner device 4, but this is not limited to this. For example, the surface potential of the photosensitive drum 1 after transfer may be similarly controlled by combining the control of the charging voltage and the transfer voltage. It goes without saying that the same effect can be obtained by changing both the brush voltage and the surface potential of the photosensitive drum 1 after transfer and decreasing the potential difference between them stepwise. EXAMPLES

[0078] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the embodiment 3 are the same as those of the image forming apparatus of the embodiment 1. Therefore, in the image forming apparatus of the embodiment 3, elements having the same or corresponding functions or configurations as those of the image forming apparatus of the embodiment 1 are given the same reference numerals as those of the image forming apparatus of the embodiment 1, and detailed explanations are omitted.

[0079] 1. Control of this embodiment Next, various types of potential control in the third embodiment will be described with reference to Fig. 10. Fig. 10 is a diagram showing the control of a single sheet print job operation in the image forming apparatus 100 in the third embodiment, and the process from the start of rotational driving of the photosensitive drum 1 to T12A is the same as in the first and second embodiments. In the third embodiment, when the surface potential of the photosensitive drum 1 after transfer is reduced by forced emission, the brush voltage is continuously reduced from V0 to 0V (OFF) from T12J, and then the rotational driving of the photosensitive drum 1 is stopped.

[0080] When the control of the above-mentioned Example 3 was carried out, the paper feed test was carried out in the same manner as in Example 1, and the results of comparison with Example 1 are shown in Table 3.

[0081] [Table 3]

[0082] By executing the control of Example 3, it was possible to further reduce the number of spots compared to Example 1. The reason why the number of spots could be reduced is that the change in posture of the brush member 10 from T12J (from FIG. 6(c) to FIG. 6(b)) was more gradual when the brush voltage was reduced continuously as in Example 3 than when it was reduced stepwise. This is thought to be because the paper powder masses in the brush member 10 are less likely to crumble.

[0083] As described above, by executing the control of the third embodiment, the change in the posture of the brush member 10 during rotation of the photosensitive drum 1 can be further reduced compared to the first embodiment, and the paper dust accumulated on the brush member 10 can be stably held. EXAMPLES

[0084] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the embodiment 4 are the same as those of the image forming apparatus of the embodiment 1. Therefore, in the image forming apparatus of the embodiment 4, elements having the same or corresponding functions or configurations as those of the image forming apparatus of the embodiment 1 are given the same reference numerals as those of the image forming apparatus of the embodiment 1, and detailed explanations are omitted.

[0085] The fourth embodiment is characterized by implementing control that takes into consideration the ejection of toner adhering to the brush member 10. Specifically, a brush voltage having a polarity opposite to that of the brush voltage applied during the image forming operation is applied during the post-rotation.

[0086] Fig. 11 is a diagram showing the control of a one-sheet print job operation in the image forming apparatus 100 of the fourth embodiment, and the process from the start of rotational driving of the photosensitive drum 1 to T12A is the same as in the first, second and third embodiments. In the fourth embodiment, the brush voltage is switched from a negative voltage to a positive voltage at the timing of T12A in Fig. 11. Then, at the timings of T12K, T12L and T12M, the brush voltage is switched while gradually decreasing the positive voltage, and after the brush voltage is turned off, the rotational driving of the photosensitive drum 1 is stopped at T14.

[0087] By executing the control of the embodiment 4, it is possible to improve the toner discharge performance compared to the embodiment 1. The reason why the toner discharge performance can be improved is that the brush voltage is switched to a voltage of the opposite polarity by T12A, so that the toner of the opposite polarity accumulated during the image forming operation can be discharged during the post-rotation. Furthermore, since the brush voltage is switched in stages, the change in the posture of the brush member 10 is the same as that of the embodiment 1.

[0088] As described above, by executing the control of the fourth embodiment, the change in the posture of the brush member 10 during rotation of the photosensitive drum 1 can be maintained compared to the first embodiment, and further, the toner can be effectively discharged from the brush member 10.

[0089] Furthermore, the stepwise switching of the brush voltage in the fourth embodiment may be controlled in the same manner as in the configurations of the first and second embodiments. Specifically, in Fig. 11, the brush voltage is switched from -400V to +400V at the timing of T12A, and then changed to +200V at the timing of T12K, +100V at the timing of T12L, and 0V at the timing of T12M. Furthermore, the brush voltage is not limited to the values ​​described above. EXAMPLES

[0090] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the embodiment 5 are the same as those of the image forming apparatus of the embodiment 1. Therefore, in the image forming apparatus of the embodiment 5, elements having the same or corresponding functions or configurations as those of the image forming apparatus of the embodiment 1 are given the same reference numerals as those of the image forming apparatus of the embodiment 1, and detailed explanations are omitted.

[0091] Control during drive stop operations accompanying general printing operations has been described in the first, second, third, and fourth embodiments. In the present embodiment, control that can suppress the discharge of paper dust from the brush member 10 onto the surface of the photosensitive drum 1 also during drive start will be described.

[0092] 1. Control of this embodiment Next, various types of potential control in the fifth embodiment will be described with reference to Fig. 12. Fig. 12 is a diagram showing the control of a single sheet print job operation in the image forming apparatus 100 of the fifth embodiment, and is the same as in the first embodiment from T3 when the image forming operation starts to T14 when the rotational drive of the photosensitive drum 1 is stopped. In the fifth embodiment, the brush voltage is increased stepwise from V2 to V1 to V0 between T1 and T4, and then the image forming operation starts.

[0093] Next, the effect on the change in posture of the brush member 10 during the rotational operation of the photosensitive drum 1 in the case where the control up to T3 in the fifth embodiment is executed will be described with reference to FIG.

[0094] In the fifth embodiment, no brush voltage is applied when the photosensitive drum 1 starts to be driven. Therefore, no electrostatic attraction force is generated between the brush member 10 and the surface of the photosensitive drum 1, and the posture of the brush member 10 when the photosensitive drum 1 starts to be driven changes from Fig. 6(a) to Fig. 6(b). Subsequently, in the process of gradually switching the brush voltage from V2 to V1 to V0 at timings T1A and T1B, the posture of the brush member 10 changes from Fig. 6(b) to Fig. 6(c).

[0095] On the other hand, if the brush voltage is switched to V0 when the photosensitive drum 1 starts to be driven, the posture of the brush member 10 changes suddenly and significantly as shown in Fig. 6(a) to Fig. 6(c). Therefore, by controlling the brush voltage as in the fifth embodiment, the posture change of the brush member 10 can be made more gradual.

[0096] Considering the above, when the control of the fifth embodiment was executed, the paper feed test was carried out in the same manner as in the first embodiment, and the results of comparison with the first embodiment are shown in Table 4.

[0097] [Table 4]

[0098] By executing the control of Example 5, it was possible to further reduce the number of spots compared to Example 1. The reason why the number of spots could be reduced is considered to be that the paper powder lump in the brush member 10 became less likely to crumble by implementing the brush voltage control at the start of rotation of the photosensitive drum 1 of Example 5 in addition to the brush voltage control at the stop of rotation of the photosensitive drum 1 of Example 1.

[0099] As described above, by using the control of the fifth embodiment, the change in the posture of the brush member 10 during rotation of the photosensitive drum 1 can be reduced, and the paper dust accumulated on the brush member 10 can be held more stably.

[0100] Furthermore, in the fifth embodiment, the brush voltage is not applied when the rotational driving of the photosensitive drum 1 is started. However, for example, if the electrostatic adsorption force is sufficiently small and there is almost no effect on the attitude change even if the rotational driving of the photosensitive drum 1 is started by applying the brush voltage V2, the brush voltage may be applied when the rotational driving of the photosensitive drum 1 is started.

[0101] In the fifth embodiment, the brush voltage is switched three times from when the photosensitive drum 1 starts to rotate until the image forming operation is performed, but this is not limited to this. The effect can be obtained by switching the brush voltage at least once. The brush voltage may also be switched three or more times.

[0102] In the fifth embodiment, the brush voltage can be applied between -500V and 0V. However, in cases where only one voltage value can be applied due to the cost reduction of the device, the surface potential of the photosensitive drum 1 after transfer may be changed in stages. That is, the surface potential of the photosensitive drum 1 may be changed in stages to change the potential difference between the brush voltage and the surface potential of the photosensitive drum 1 after transfer. For example, the surface potential of the photosensitive drum 1 after transfer may be controlled in a similar manner by combining the control of the charging voltage, the amount of laser exposure, and the transfer voltage. Needless to say, the same effect can be obtained by changing both the brush voltage and the surface potential of the photosensitive drum 1 after transfer and changing the potential difference between them in stages.

[0103] In addition, in the fifth embodiment, the brush voltage is increased stepwise, but it goes without saying that it may be increased continuously, contrary to the third embodiment. Furthermore, the control in the rotation stop operation of the photosensitive drum 1 in any one of the first, second, third, and fourth embodiments and the control in the rotation drive operation of the photosensitive drum 1 in the fifth embodiment may be combined and implemented. For example, as shown in FIG. 13, the second embodiment and the fifth embodiment may be combined and implemented, or as shown in FIG. 14, the first embodiment, the fourth embodiment, and the fifth embodiment may be combined and implemented. It goes without saying that the effect is further improved by implementing the control as shown in FIG. 13 and FIG. 14. In addition, V3, V4, and V5 in FIG. 14 are the same brush voltages in the pre-rotation operation and the post-rotation operation, but they may be different. In addition, the polarity of the brush voltage may be reversed according to the normal polarity of the toner. [Explanation of symbols]

[0104] 1 Photosensitive drum 2. Charge roller 3. Developing device 4. Exposure equipment 5 Transfer roller 11 Brush member 31 Developing roller 110 Drive motor

Claims

1. A rotatable image carrier; A drive unit that rotates and drives the image carrier; a charging member for charging a surface of the image carrier in a charging section facing the image carrier; an exposure unit for exposing the surface of the image carrier to light in order to form an electrostatic latent image on the surface of the image carrier charged by the charging member; a developing member for supplying a developer charged to a normal polarity to a surface of the image carrier to develop the electrostatic latent image into a developer image; a transfer member that contacts the image carrier to form a transfer portion and transfers the developer image from the image carrier to a transfer target at the transfer portion; a brush member that forms a contact portion downstream of the transfer portion and upstream of the charging portion in a rotation direction of the image carrier, the brush member being in contact with the image carrier at the contact portion; A control unit that controls the drive unit, the developer image formed on the surface of the image carrier in the transfer section is transferred to a transfer target body, and thereafter, the developer remaining on the surface of the image carrier is collected by the developing member; the control unit controls the drive unit to transition from a drive state in which the image carrier is driven in a state in which a first potential difference is formed between the brush member and the image carrier at the contact portion to a stop state in which driving of the image carrier is stopped in a state in which a second potential difference, the absolute value of which is smaller than that of the first potential difference, is formed at the contact portion; The control unit controls the potential difference formed between the brush member and the image carrier to change from the first potential difference to a third potential difference which is greater than the second potential difference, and then to change from the third potential difference to the second potential difference.

2. A rotatable image carrier; A drive unit that rotates and drives the image carrier; a charging member for charging a surface of the image carrier in a charging section facing the image carrier; an exposure unit for exposing the surface of the image carrier to light in order to form an electrostatic latent image on the surface of the image carrier charged by the charging member; a developing member for supplying a developer charged to a normal polarity to a surface of the image carrier to develop the electrostatic latent image into a developer image; a transfer member that contacts the image carrier to form a transfer portion and transfers the developer image from the image carrier to a transfer target at the transfer portion; a brush member that forms a contact portion downstream of the transfer portion and upstream of the charging portion in a rotation direction of the image carrier, the brush member being in contact with the image carrier at the contact portion; a brush voltage application unit that applies a brush voltage to the brush member; A control unit that controls the drive unit and the brush voltage application unit, the developer image formed on the surface of the image carrier in the transfer section is transferred to a transfer target body, and thereafter, the developer remaining on the surface of the image carrier is collected by the developing member; the control unit controls the drive unit to transition from a stopped state in which the image carrier is stopped with the brush voltage applied to the brush member and a first potential difference formed between the brush member and the image carrier at the contact unit, to a driven state in which the image carrier is driven with a second potential difference formed, the second potential difference having an absolute value greater than that of the first potential difference; The control unit controls the potential difference formed between the brush member and the image carrier to change from the first potential difference to a third potential difference which is greater than the second potential difference, and then to change from the third potential difference to the second potential difference.

3. The image forming apparatus according to claim 1 or 2, characterized in that the control unit controls the potential difference formed between the brush member and the image carrier to change from the first potential difference to a fourth potential difference which is a potential difference between the first potential difference and the second potential difference, and to change from the fourth potential difference to the second potential difference.

4. 4. The image forming apparatus according to claim 1, wherein the control unit controls the potential difference formed between the brush member and the image carrier so as to change stepwise from the first potential difference to the second potential difference.

5. 4. The image forming apparatus according to claim 1, wherein the control unit controls the potential difference formed between the brush member and the image carrier so as to change continuously from the first potential difference to the second potential difference.

6. A brush voltage application unit that applies a brush voltage to the brush member, 2. The image forming apparatus according to claim 1, wherein the control unit controls the brush voltage applied by the brush voltage application unit so that the first potential difference and the second potential difference are formed.

7. a charging voltage application unit that applies a charging voltage to the charging member, 7. The image forming apparatus according to claim 1, wherein the control unit controls the charging voltage application unit so that the first potential difference and the second potential difference are formed by controlling the surface potential of the image carrier at the contact portion.

8. A transfer voltage application unit that applies a transfer voltage to the transfer member, The image forming apparatus according to any one of claims 1 to 7, characterized in that the control unit controls the transfer voltage application unit so that the first potential difference and the second potential difference are formed by controlling the surface potential of the image carrier at the contact portion.

9. 9. The image forming apparatus according to claim 1, wherein the control unit controls the exposure unit so that the first potential difference and the second potential difference are formed by controlling the surface potential of the image carrier at the contact portion.

10. 10. The image forming apparatus according to claim 1, wherein the brush member is a paper dust removing member.

11. 11. The image forming apparatus according to claim 1, wherein the developer is a one-component developer.

12. 12. The image forming apparatus according to claim 1, wherein the image carrier and the charging member are in contact with each other in the charging section.

13. The brush member has a base fabric and a thread portion including a plurality of threads extending from the base fabric, and the density of the thread portion of the brush member is 150 to 350 kF / inch. ２ 13. The image forming apparatus according to claim 1, wherein

Images