Image formation device

Abstract

This image formation device is characterized in that: a control unit controls, so as to be executable, a first start control for starting rotation drive of a photoreceptor drum in a state where the potential difference between the voltage applied to a brush and the surface of the photoreceptor drum is a first potential difference, and a second start control for starting rotation drive of the photoreceptor drum in a state where the potential difference between the voltage applied to the brush and the surface of the photoreceptor drum is a second potential difference; the first potential difference and the second potential difference are potential differences formed such that an electrostatic force from the brush toward the surface of the photoreceptor drum acts on particles charged to a polarity opposite to a normal polarity of a toner; and the absolute value of the second potential difference is controlled to be larger than the absolute value of the first potential difference.

Description

Image forming device

[0001] The present invention relates to an electrophotographic image forming apparatus.

[0002] Some electrophotographic image forming apparatuses are cleanerless, in which residual toner remaining on the surface of the photosensitive drum after the transfer process is removed from the photosensitive drum by a developing unit, recovered, and reused. Since cleanerless image forming apparatuses lack a conventional blade for scraping residual toner from the surface of the photosensitive drum, paper dust adhering to the surface of the photosensitive drum during the transfer process cannot be removed, which can cause image defects. Patent Document 1 proposes a configuration in which a fixed brush is disposed downstream of the transfer unit and upstream of the charging unit in the rotation direction of the photosensitive drum, and the fixed brush removes the paper dust.

[0003] Japanese Patent Application Laid-Open No. 2007-65580

[0004] In a configuration in which a brush is in contact with a photosensitive drum, speed fluctuations when the photosensitive drum starts to rotate can cause paper dust collected and held by the brush to slip through downstream of the brush, which can cause image defects due to the paper dust that has slipped through adhering to the charging member.

[0005] An object of the present invention is to suppress image defects in an image forming apparatus having a brush that contacts the surface of a photosensitive drum.

[0006] The present invention provides an image forming apparatus having a rotatable photosensitive drum, charging means forming a charging portion between itself and the photosensitive drum and charging the surface of the photosensitive drum at the charging portion, developing means contacting the photosensitive drum to form a developing portion and supplying toner to the surface of the photosensitive drum charged by the charging means at the developing portion, transfer means contacting the photosensitive drum to form a transfer portion and transferring the toner supplied to the photosensitive drum to a transfer medium at the transfer portion, a brush contacting the surface of the photosensitive drum downstream of the transfer portion and upstream of the charging portion in the rotation direction of the photosensitive drum, application means applying a voltage to the brush, drive means rotating the photosensitive drum, and a control unit controlling the application means and the drive means, wherein the control unit is configured to perform a first start-up control to start rotating the photosensitive drum when a potential difference between the voltage applied to the brush and the surface of the photosensitive drum is a first potential difference, and a second start-up control that starts the rotation of the photosensitive drum when the potential difference between the voltage applied to the brush and the surface of the photosensitive drum is a second potential difference, wherein the first potential difference and the second potential difference are potential differences formed so that an electrostatic force acts from the brush toward the surface of the photosensitive drum on particles charged with a polarity opposite to the normal polarity of the toner, and the image forming apparatus is controlled so that the absolute value of the second potential difference is greater than the absolute value of the first potential difference.

[0007] In an image forming apparatus having a brush that contacts the surface of a photosensitive drum, image defects can be suppressed.

[0008] FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus according to a first embodiment. FIGS. 2(a) and 2(b) are schematic diagrams showing a brush member according to the first embodiment. FIG. 3 is a control block diagram according to the first embodiment. FIGS. 4(a) and 4(b) are schematic diagrams showing paper dust collection by the brush member according to the first embodiment. FIGS. 5(a) and 5(b) are schematic diagrams showing changes in the posture of the brush member according to the first embodiment. FIGS. 6(a) and 6(b) are schematic diagrams showing paper dust discharge from the brush member. FIG. 7 is a schematic diagram showing a black speckle image. FIG. 8 is a flowchart showing a second startup control and a paper dust collection sequence according to the first embodiment. FIGS. 9(a) to 9(c) are schematic diagrams showing a second startup control and a paper dust collection sequence according to the first embodiment. FIG. 10 is a diagram showing test results for the first embodiment. FIG. 11 is a diagram showing test results for the second embodiment.

[0009] The following describes in detail the embodiments of the present invention with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, voltages, speeds, densities, and other characteristics of the components described in the embodiments are merely examples for illustrative purposes and may be changed as appropriate depending on the configuration and various conditions of the device to which the invention is applied. The scope of the invention is not limited to the following embodiments.

[0010] (Example 1) 1. Image Forming Apparatus Figure 1 is a diagram showing the schematic configuration of an image forming apparatus of Example 1. The image forming apparatus 100 is a monochrome laser beam printer that employs a cleanerless system and a contact charging system. The image forming apparatus 100 is provided with a cylindrical rotatable photosensitive drum 1 as an image carrier. A charging roller 2 as charging means and a developing device 3 as developing means are provided around the photosensitive drum 1. In addition, an exposure unit 4 as exposure means is provided between the charging roller 2 and the developing device 3 in the rotation direction of the photosensitive drum 1 in Figure 1. In addition, a transfer roller 5 as transfer means is pressed against the photosensitive drum 1.

[0011] The photosensitive drum 1 is a negatively charged organic photosensitive member. This photosensitive drum 1 has a photosensitive layer on a drum-shaped aluminum substrate, and is driven to rotate in the direction of arrow R (clockwise) in FIG. 3 by a drive motor 110 (as driving means) at a predetermined process speed. In Example 1, the outer diameter of the photosensitive drum 1 is 24 mm, and the process speed (peripheral speed (surface moving speed) of the photosensitive drum 1) is 140 mm / sec.

[0012] The charging roller 2 contacts the photosensitive drum 1 with a predetermined pressure, forming a charging portion between itself and the photosensitive drum 1, and charges the surface of the photosensitive drum 1. During charging, a predetermined charging voltage (charging bias) is applied to the charging roller 2 by a charging power source E1 (FIG. 3) serving as a charging voltage application means, thereby uniformly charging the surface of the photosensitive drum 1 to a predetermined potential. During charging, a negative DC voltage is applied to the charging roller 2 as the charging voltage, and the surface of the photosensitive drum 1 is uniformly charged to a negative dark potential Vd by the charging roller 2. In Example 1, the charging voltage is −1300 V, and the dark potential Vd of the photosensitive drum 1 is −700 V.

[0013] More specifically, the surface of the photosensitive drum 1 is charged by discharge occurring in at least one of the minute gaps between the photosensitive drum 1 and the charging roller 2, which are formed upstream and downstream of the contact point between the photosensitive drum 1 and the charging roller 2 in the rotation direction of the photosensitive drum 1. In the following explanation, the contact point between the charging roller 2 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 is considered to be the charging portion.

[0014] The exposure unit 4 is a laser scanner device that outputs laser light L corresponding to image information input from an external device 120 (FIG. 3) 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. The absolute value of the dark area potential Vd on the surface of the photosensitive drum 1, which has been uniformly charged, is reduced by exposure by the exposure unit 4 to become a light area potential Vl. In the first embodiment, the light area potential Vl is −100 V.

[0015] In the following description, the position on the surface of the photosensitive drum 1 that is exposed by the exposure unit 4 with respect to the rotation direction of the photosensitive drum 1 is referred to as the exposure portion (exposure position). Note that the exposure unit 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 used.

[0016] The image forming apparatus 100 uses a contact development method. The developing device 3 includes a developing roller 31 as a developer carrier, a toner supply roller as developer supply means, a developer storage chamber that stores toner, and a developing blade. The toner supplied from the developer storage chamber to the developing roller 31 by the toner supply roller is charged to a predetermined polarity by passing through a blade nip, which is the contact point between the developing roller 31 and the developing blade. The toner carried on the developing roller 31 is supplied from the developing roller 31 to the surface of the photosensitive drum 1 in the developing section in accordance with the electrostatic image.

[0017] In the following description, the contact point between the developing roller 31 and the photosensitive drum 1 is the developing portion with respect to the rotation direction of the photosensitive drum 1. The developing roller 31 is driven to rotate counterclockwise so that the photosensitive drum 1 and the developing roller 31 move in the same direction in the developing portion. The drive motor 110 (FIG. 3) serving as a drive means for driving the developing roller 31 may be a common motor with the drive motor 110 serving as a drive means 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 development voltage (development bias) is applied to the developing roller 31 by a development power source E2 (FIG. 3) serving as a development voltage application means. During development, a negative DC voltage is applied to the developing roller 31 as the development voltage. In Example 1, the development voltage is −380 V.

[0018] An image forming portion (exposed surface, image portion) is formed on the surface of the photosensitive drum 1, where the absolute value of the potential is reduced by being exposed to light after being uniformly charged. Toner charged with the same polarity as the charge polarity of the photosensitive drum 1 (negative polarity in Example 1) adheres to this exposed surface. This development method is called a reversal development method. In Example 1, the normal polarity, which is the charge polarity of the toner during development, is negative polarity.

[0019] The present invention can be applied to one-component non-magnetic contact development, two-component non-magnetic contact development, non-contact development, magnetic development, etc. The two-component non-magnetic contact development uses a two-component developer containing non-magnetic toner and magnetic carrier as the developer, and develops by bringing the developer (magnetic brush) carried on a developer carrier into contact with the photosensitive drum 1. The non-contact development is a method of developing by scattering toner from a developer carrier arranged opposite the photosensitive drum but without contact, onto the photosensitive drum. The magnetic development is a method of developing by magnetically carrying magnetic toner on a developer carrier incorporating a magnet as a magnetic field generating means, arranged opposite the photosensitive drum but without contact, using magnetic force. The toner in Example 1 has a median average particle size of 6 μm and a normal charge polarity of negative polarity.

[0020] The transfer roller 5 serving as the transfer means is preferably made of an elastic material such as polyurethane rubber, sponge rubber made of EPDM (ethylene propylene diene rubber), NBR (nitrile butadiene rubber), or the like. The transfer roller 5 is pressed against the photosensitive drum 1, and the photosensitive drum 1 and the transfer roller 5 come into contact to form a transfer section. During transfer, a predetermined transfer voltage (transfer bias) is applied to the transfer roller 5 by a transfer power supply E3 (FIG. 3) serving as a transfer voltage application means. During transfer, a DC voltage of the opposite polarity to the normal polarity of the toner (positive polarity in the first embodiment) is applied to the transfer roller 5 as the transfer voltage. The toner image is electrostatically transferred from the photosensitive drum 1 to the recording material P serving as the transfer recipient due to the action of the electric field formed between the transfer roller 5 and the photosensitive drum 1. In the first embodiment, the transfer voltage is +1000 V.

[0021] A recording material P stored in a cassette 6 is fed by a paper feed unit 7 in synchronization with the arrival of the toner image formed on the photosensitive drum 1 at the transfer section, and is transported to the transfer section via a pair of registration rollers 8. The toner image formed on the photosensitive drum 1 is transferred onto the recording material P by a transfer roller 5 to which a predetermined transfer voltage is applied by a transfer power source E3. After the toner image has been transferred, the recording material P is transported to a fixing device 9. The fixing device 9 is a film heating type fixing device that includes a fixing film 91 incorporating a fixing heater (not shown) and a thermistor (not shown) that measures the temperature of the fixing heater, and a pressure roller 92 that presses against the fixing film 91. The toner image is fixed on the recording material P by heating and pressurizing it, and the recording material P is then discharged outside the apparatus via a pair of paper discharge rollers 12.

[0022] Residual toner remaining on the photosensitive drum 1 without being transferred to the recording material P is removed in the following process. The residual toner is a mixture of toner that is positively charged and toner that is negatively charged but 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 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] 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 recording material P for image formation. Meanwhile, 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 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 development voltage, and is then collected in the developer storage chamber. The toner collected in the developer storage chamber is used again for image formation.

[0024] 3 , the image forming apparatus 100 has a control unit 150 that transmits and receives image data and commands to and from the external device 120 and controls the operation of each unit of the image forming apparatus 100. The control unit 150 has a CPU 151 and a memory 152. The control unit 150 controls the operation of the charging power supply E1, the developing power supply E2, the transfer power supply E3, the exposure unit 4, and the drive motor 110.

[0025] 2. Configuration of the Brush Member Next, the paper dust removal member will be described. The image forming apparatus 100 has a brush member 11 (contact member, collection member) as a paper dust removal member. The brush member 11 contacts the surface of the photosensitive drum 1 downstream of the transfer unit and upstream of the charging unit in the rotation direction of the photosensitive drum 1, forming a brush nip portion (brush contact portion, brush contact position). In the following description, the contact portion between the brush member 11 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 is considered to be the brush nip portion.

[0026] Fig. 2(a) is a schematic diagram of the brush member 11 in a standalone state, viewed along its longitudinal direction (substantially parallel to the rotational axis direction of the photosensitive drum 1), and Fig. 2(b) is a schematic diagram of the brush member 11 in contact with the photosensitive drum 1, viewed along its longitudinal direction.

[0027] The brush member 11 is a conductive brush fixed to the image forming apparatus 100. As shown in FIG. 2( b), the brush member 11 is composed 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 fabric 11b that supports the pile yarns 11a. The brush member 11 is disposed so as to contact the photosensitive drum 1 downstream of the transfer unit and upstream of the charging unit in the movement direction (rotation direction) of the photosensitive drum 1. The brush member 11 is disposed so that its longitudinal direction is approximately parallel to the rotational axis of the photosensitive drum 1. Note that the pile yarns 11a may be made of a material other than nylon, such as rayon, acrylic, or polyester.

[0028] 2A, when the brush member 11 is in a standalone state, i.e., when no external force is being applied to bend the pile yarns 11a, the length L1 of the pile yarns 11a extending from the base fabric 11b to their tips is used. The base fabric 11b is fixed to a support member 13 installed at a predetermined position in the image forming apparatus 100 by a fixing means such as double-sided tape. The position of the support member 13 and the length L1 of the pile yarns 11a are set so that when the base fabric 11b is fixed to the support member 13, the tips of the pile yarns 11a will penetrate into the photosensitive drum 1. In Example 1, L1 = 6.5 mm.

[0029] The clearance between the support member 13 and the photosensitive drum 1 is constant. The shortest distance from the base fabric 11b of the brush member 11 fixed to the support member 13 to the photosensitive drum 1 is defined as L2. The amount of penetration of the brush member 11 into the photosensitive drum 1 is defined as L4 = L1 - L2. In Example 1, L4 = 1 mm.

[0030] As shown in Figure 2(a), when the brush member 11 is in a standalone state, the length of the brush member 11 in the circumferential direction of the photosensitive drum 1 (hereinafter referred to as the "short direction") is L3. The length L3 of the brush member 11 in the short direction can be set depending on the life of the image forming apparatus 100 and the process cartridge. The longer L3 is, the longer the brush member 11 can collect paper dust, so from the perspective of long life, it is preferable that L3 be 3 mm or more. In Example 1, L3 = 5 mm.

[0031] The longitudinal length of the brush member 11 is set so that the brush member 11 contacts the entire image forming area (area where a toner image can be formed) on the photosensitive drum 1 with respect to the rotational axis direction of the photosensitive drum 1. The longitudinal length of the brush member 11 can be changed as appropriate depending on the maximum paper passing width of the image forming apparatus. In Example 1, the longitudinal length of the brush member 11 is 220 mm.

[0032] The density of the pile yarns 11a of the brush member 11 can be determined taking into consideration the toner passing ability and the paper dust collecting ability. If the density of the brush member 11 is too high, the toner passing ability will be impaired, causing the toner to accumulate (solidify), which may cause the accumulated toner to scatter and cause contamination inside the machine. Also, if the density of the brush member 11 is too low, the ability to collect paper dust will be weakened. The thickness and density of the pile yarns 11a should be 1 to 6 denier and 150 to 350 kF / inch, respectively, from the viewpoint of paper dust collecting ability. ２ The density unit is kF / inch. ２ indicates the number of filaments per square inch. In Example 1, the pile yarn 11a has a thickness of 2 denier and a density of 240 kF / inch. ２ is.

[0033] The fineness of the brush member 11 can be determined taking into consideration the ability of paper dust to pass through. If the fineness of the brush member 11 is too small, the force holding back paper dust is weak, making it easier for the paper dust to pass through. As a result, the paper dust that passes through may hinder the charging of the photosensitive drum 1 by the charging roller 2. Also, if the fineness of the brush member 11 is too large, it may not be able to adequately capture toner and fine paper dust. This may result in uneven density due to uneven toner adhesion in the longitudinal direction of the charging roller 2, or poor image quality due to insufficient charging in areas where paper dust has adhered. In Example 1, the fineness of the brush member 11 is 220T / 96F. This means that 96 strands of thread, each 220g thick, are bundled together per 10,000m.

[0034] The brush member 11 is supported by a support member 13 provided in the image forming apparatus 100, 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 rotates. The brush member 11 collects (recovers) deposits such as paper dust transferred from the recording material P to the photosensitive drum 1 at the transfer unit, and reduces the amount of paper dust that moves to the charging unit and the developing unit downstream of the brush member 11 in the rotation direction of the photosensitive drum 1.

[0035] The contact portion of the brush member 11 with the photosensitive drum 1 is referred to as a brush nip portion N. An application means for applying a voltage to the brush member 11 is connected to the brush member 11. In the first embodiment, the application means is common to the development power source E2 (FIG. 3). That is, the development power source E2 applies a voltage to the development roller 31 and the brush member 11. During image formation, a predetermined brush voltage (brush bias) is applied to the brush member 11 by the development power source E2. During image formation, a negative DC voltage is applied to the brush member 11 as the brush voltage. In the first embodiment, the brush voltage during image formation is −380 V.

[0036] 3. Image Output Operation In the first embodiment, the image forming apparatus 100 executes an image forming operation (print job) in response to an instruction from an external device 120 such as a personal computer. The job is a series of operations for forming an image on one or more recording materials P, and includes a pre-rotation process, an image forming process (printing process), a paper spacing process when forming images on multiple recording materials P, and a post-rotation process.

[0037] The pre-rotation process is a period in which a preparatory operation is performed before the image forming process.

[0038] The image forming process is a process of forming an electrostatic image on the photosensitive drum 1, developing the electrostatic image (forming a toner image), transferring the toner image, fixing the toner image, etc., and the image forming time refers to the period during which these processes are performed. Note that during image formation, the timing of forming the electrostatic image, forming the toner image, transferring the toner image, fixing the toner image, etc. varies.

[0039] The inter-sheet process is a period between the first recording material P and the second recording material P when the image forming process is performed continuously on a plurality of recording materials P (during continuous image formation).

[0040] The post-rotation process is a period in which an organizing operation (preparatory operation) is performed after the image forming process.

[0041] Non-image formation time refers to a period other than image formation time, and includes a pre-rotation process, a paper-to-paper process, a post-rotation process, and a pre-multi-rotation process, which is a preparatory operation when the image forming device 100 is turned on or when it returns from a sleep state.

[0042] 4. Image Defects Due to Paper Dust Discharge Paper dust from the recording material P adheres to the photosensitive drum 1 during transfer. The paper dust adhering to the photosensitive drum 1 is charged mainly to the same polarity as the transfer bias (opposite polarity to the toner) by the transfer voltage. The paper dust on the photosensitive drum 1 is physically collected by the brush member 11 on the upstream side of the brush nip portion N. Figure 4(a) shows a state in which paper dust F1 has been collected on the upstream side of the brush nip portion N of the brush member 11.

[0043] 5(a) and 5(b) are diagrams showing the posture of the brush member 11. Fig. 5(a) shows the posture of the brush member 11 when the photosensitive drum 1 is stopped, and Fig. 5(b) shows the posture of the brush member 11 when the photosensitive drum 1 is rotating. The posture of the pile yarns 11a of the brush member 11 is different when the photosensitive drum 1 is stopped and when it is rotating. This is because, when the photosensitive drum 1 rotates, the pile yarns 11a of the brush member 11 are pulled in the rotation direction due to frictional force exerted by the surface of the photosensitive drum 1.

[0044] When the photosensitive drum 1 starts rotating from a stopped state, the orientation of the brush member 11 changes from the state shown in FIG. 5(a) to the state shown in FIG. 5(b), which can cause the paper dust F1 located in the position shown in FIG. 4(a) to move downstream in the direction of rotation. As a result, the paper dust F1 located in the position shown in FIG. 4(a) moves to the position shown in FIG. 4(b) as the paper dust F2. If the brush member 11 is repeatedly started with paper dust accumulated on it, this phenomenon of the paper dust located upstream of the brush nip moving toward the inside of the brush nip is likely to occur. The paper dust F2 located in the position shown in FIG. 4(b) has a weak holding force due to the small number of pile yarns 11a supporting it. Therefore, as shown in FIGS. 6(a) and 6(b), the paper dust F2 may be expelled from the brush member 11 during startup. FIG. 6(a) shows the photosensitive drum 1 stopped with the paper dust F2 held inside the brush nip. Fig. 6(b) is a diagram showing the movement of paper dust F2 when the start-up operation of the photosensitive drum 1 is performed in the state of Fig. 6(a). The paper dust F2 expelled from the brush member 11 may adhere to the charging roller 2 as shown in Fig. 6(b). In this case, charging failure may occur, and black spots B may appear on the recording material P as shown in Fig. 7. When the charging roller 2 rotates while the paper dust F2 remains adhered to it, black spots B appear with each rotation cycle of the charging roller 2.

[0045] 5. Brush Paper Dust Discharge Control Brush paper dust discharge control will now be described. The control unit 150 of the image forming apparatus 100 can execute first and second startup controls as startup controls for starting the rotation of the photosensitive drum 1. The first startup control is startup control for starting the rotation of the photosensitive drum 1 when the potential difference between the brush member 11 and the surface of the photosensitive drum 1 is a first potential difference. The second startup control is startup control for starting the rotation of the photosensitive drum 1 when the potential difference between the brush member 11 and the surface of the photosensitive drum 1 is a second potential difference. The first and second potential differences are potential differences formed so that an electrostatic force acts from the brush member 11 toward the surface of the photosensitive drum 1 on particles (e.g., paper dust) charged with a polarity opposite to the normal polarity (negative polarity in Example 1) of the toner. In Example 1, the absolute value of the second potential difference is greater than the absolute value of the first potential difference.

[0046] Specifically, the surface potential of the photosensitive drum 1 is equal to 0 V during the first startup control and the second startup control. The first brush voltage applied to the brush member 11 during the first startup control and the second brush voltage applied to the brush member 11 during the second startup control are both voltages of polarity opposite to the normal polarity (negative polarity) of the toner. The absolute value of the second brush voltage is greater than the absolute value of the first brush voltage. In Example 1, the first brush voltage is 150 V and the second brush voltage is 450 V. That is, the second brush voltage during the second startup control is greater toward the polarity opposite to the normal polarity of the toner than the first brush voltage during the first startup control. In Example 1, the power source that applies voltage to the brush member 11 is the same as the power source that applies voltage to the developing roller 31, so the voltage applied to the developing roller 31 is 150 V during the first startup control and 450 V during the second startup control.

[0047] The first startup control is executed in a pre-rotation step before the image forming operation begins. Therefore, the photosensitive drum 1, which has started to rotate by the first startup control, enters the image forming operation without stopping its rotation. On the other hand, the second startup control is executed in a post-rotation step, and the rotation of the photosensitive drum 1, which has started to rotate by the second startup control, is stopped after the second startup control ends.

[0048] Fig. 8 is a flowchart showing the sequence of the second startup control. Fig. 9(a) to Fig. 9(c) are diagrams showing the behavior of paper dust collected by the brush member 11 when the second startup control is executed.

[0049] When the second startup control is started, in step S1, the control unit 150 stops the rotational driving of the photosensitive drum 1 (FIG. 9A).

[0050] In step S2, the control unit 150 sets the voltage applied to the brush member 11 and the developing roller 31 to the second brush voltage of 450 V, and turns off (0 V) the voltage applied to the charging roller 2. At this time, since no charging bias is applied, no change occurs in the surface potential of the photosensitive drum 1.

[0051] In step S3, the control unit 150 starts (activates) the rotation of the photosensitive drum 1. Due to the change in posture of the brush member 11 caused by the activation and the second potential difference (450 V) between the brush member 11 and the surface of the photosensitive drum 1, the paper dust F2 of positive polarity that had been captured in the brush nip portion N is expelled.

[0052] In step S4, the control unit 150 determines whether a time corresponding to the distance between the brush unit and the developing unit has elapsed since the photosensitive drum 1 started rotating in step S3. The time corresponding to the distance between the brush unit and the developing unit is the time required for the portion of the surface of the photosensitive drum 1 that was in the brush unit when the photosensitive drum 1 started rotating to reach the developing unit. If the time corresponding to the distance between the brush unit and the developing unit has not elapsed (step S4: No), the control unit 150 returns to step S4. If the time corresponding to the distance between the brush unit and the developing unit has elapsed (step S4: Yes), the control unit 150 executes step S5. As a result, the discharged positive paper dust F2 passes through the charging roller 2 and the developing roller 31 ( FIG. 9B ). At this time, applying a voltage of 0 V or positive polarity to the charging roller 2 and the developing roller 31 can actively prevent the discharged positive paper dust F2 from adhering to the charging roller 2 and the developing roller 31. In Example 1, in step S2, the voltage applied to the charging roller 2 is turned off (0V), and the voltage applied to the developing roller 31 is set to 450V.

[0053] In step S5, the control unit 150 applies −1000 V to the transfer roller 5. That is, after the photosensitive drum 1 starts to rotate, when a time corresponding to the time it takes for the photosensitive drum 1 to rotate through the angle between the contact portion (brush nip portion) between the brush member 11 and the photosensitive drum 1 and the developing portion has elapsed, a voltage of the same polarity as the normal polarity of the toner is applied to the transfer roller 5.

[0054] In step S6, the control unit 150 determines whether a time corresponding to the distance between the brush unit and the transfer unit has elapsed since the photosensitive drum 1 started to rotate. The time corresponding to the distance between the brush unit and the transfer unit is the time required for a portion of the surface of the photosensitive drum 1 that was in the brush unit when the photosensitive drum 1 started to rotate to reach the transfer unit. If the time corresponding to the distance between the brush unit and the transfer unit has not elapsed (step S6: No), the control unit 150 returns to step S6. If the time corresponding to the distance between the brush unit and the transfer unit has elapsed (step S6: Yes), the control unit 150 executes step S7. In step S7, the control unit 150 determines whether a time corresponding to one rotation of the transfer roller 5 has elapsed. If a time corresponding to one rotation of the transfer roller 5 has not elapsed (step S7: No), the control unit 150 returns to step S7. If a time corresponding to one rotation of the transfer roller 5 has elapsed (step S7: Yes), the control unit 150 executes step S8. As a result, the paper dust F2 is collected by the transfer roller 5 due to the potential difference between the surface potential (0 V) of the photosensitive drum 1 and the transfer voltage (FIG. 9C).

[0055] In step S8, the control unit 150 stops the rotation of the photosensitive drum 1, turns off the voltages applied to the brush member 11, the charging roller 2, and the developing roller 31, and ends the second startup control. That is, the control unit 150 ends the second startup control when the time equivalent to the time it takes for the photosensitive drum 1 to rotate to form the angle between the brush nip portion and the transfer portion has elapsed after the start of rotation of the photosensitive drum 1, and when the time it takes for the transfer roller 5 to make one rotation has elapsed.

[0056] In this way, by performing the second startup control, the paper dust F2 captured on the brush member 11 is collected on the transfer roller 5, and therefore, when the first startup control, which is executed during image formation, is executed, the paper dust F2 is moved from the brush member 11. This makes it possible to prevent image defects caused by the discharge of paper dust during image formation. Furthermore, even if paper dust F2 remains on the brush member 11 after the second startup control is executed, the brush voltage (150 V) of the first startup control is lower than the brush voltage (450 V) of the second startup control, so the paper dust is less likely to be discharged.

[0057] Paper dust discharge is more likely to occur if the brush member 11 is repeatedly started up while a certain amount of paper dust has accumulated on it due to paper passing. Therefore, in the first embodiment, the second startup control is executed when the total number of sheets passed through the image forming apparatus 100 exceeds a predetermined threshold. In the first embodiment, the threshold is set to 5,000 sheets. The threshold can be set appropriately depending on the operating environment of the image forming apparatus 100, the characteristics of the recording material P, and the like. In addition to the execution determination method based on counting up, in which the total number of sheets passed is counted and compared with the threshold, a countdown execution determination method may also be used, in which a predetermined value is used as a starting value and is subtracted for each sheet passed, and the second startup control is executed when the value reaches 0.

[0058] 6. Effects of the Invention A paper feed test conducted to confirm the effects of Example 1 will be described. The paper feed test was conducted under the following conditions: in an environment of a temperature of 15° C. and a relative humidity of 10% (low temperature and low humidity environment), Xerox Vitality Multipurpose paper, Letter size, with a basis weight of 75 g / m2 was used as the recording material P. ２ A two-sheet job was repeatedly executed to pass 10,000 sheets. The image was evaluated by counting the black speckled images that appeared on each sheet, and if there were three or more speckled images of 0.8 mm or larger, which have a significant visual impact, the image was judged as NG, and if there were fewer than that, it was judged as OK. The evaluation results for every 1,000 sheets are shown in Figure 10. If even one of the 1,000 sheets had an NG image, it was judged as NG.

[0059] In the comparative example, image NG occurred after 6,000 sheets or more were passed. In contrast, in Example 1, image NG was suppressed after 10,000 sheets were passed. This is because the paper dust that had entered the brush nip portion N was expelled by executing the second activation control during post-rotation and collected by the transfer roller 5, thereby suppressing the paper dust from being expelled from the brush member 11 during the first activation control during image formation.

[0060] In the first embodiment, the second start-up control during post-rotation is executed after the total number of sheets passed exceeds the threshold value (5,000 sheets). However, the second start-up control during post-rotation may be executed from the first sheet of paper passed. Also, the process of collecting paper dust by the transfer roller 5 may be omitted in the second start-up control. In this case, the paper dust F2 discharged from the brush nip portion N travels around the photosensitive drum 1 once and returns to the brush member 11, but the paper dust is captured at the position of paper dust F1 in FIG. 4A on the upstream side of the brush member 11. Therefore, compared to the case where the paper dust is at the position of paper dust F2 in FIG. 4B, the discharge of paper dust from the brush member 11 can be suppressed during the first start-up control.

[0061] Although there is a possibility that paper dust discharged during the second startup control may adhere to the charge roller 2, in this test, no problems were observed in terms of images. This is because the charge roller 2 stops after the second startup control is executed during post-rotation, and then the charge roller 2 is driven to rotate during the first startup control during image formation operation, so the change in speed of the charge roller 2 causes the paper dust on the charge roller 2 to be shaken off. Also, some paper dust has the same polarity as the toner. When paper dust with the same polarity as the toner is discharged from the brush member 11, it becomes the same polarity as the voltage applied to the charge roller 2 during image formation operation, so it is unlikely to remain adhered to the charge roller 2 during image formation operation and is unlikely to cause image problems.

[0062] In addition, in the first embodiment, an example in which the second activation control is executed during the post-rotation has been shown, but the second activation control may be executed when activating the photosensitive drum 1 other than when activating the photosensitive drum 1 for the image forming operation, such as during pre-rotation, etc. This makes it possible to suppress the discharge of paper dust during the first activation control.

[0063] According to Example 1, the second start-up control is executed during post-rotation, and the voltage applied to the brush member 11 is increased to the opposite polarity to the toner than during the first start-up control, thereby suppressing image defects caused by paper dust being expelled from the brush member 11.

[0064] (Example 2) Next, Example 2 will be described. In Example 2, by controlling the potential of the photosensitive drum 1 during the second startup control, it is possible to obtain the same effect as Example 1 without using a large brush voltage. The basic configuration and operation of the image forming apparatus 100 in Example 2 are the same as those in Example 1. Elements having the same or corresponding functions or configurations as those in Example 1 are assigned the same reference numerals as those in Example 1, and detailed description thereof will be omitted.

[0065] 1. Brush Paper Dust Discharge Control As in the first embodiment, the first startup control is executed in the pre-rotation process before the image forming operation begins, and after the first startup control is executed, the photosensitive drum 1 enters the image forming operation without stopping its rotation. On the other hand, the second startup control is executed in the post-rotation operation, and the rotation of the photosensitive drum 1, which has been started by the second startup control, is stopped after the second startup control ends.

[0066] In the second embodiment, the voltages applied to the brush member 11 during the first startup control and the second startup control are equal, both 150 V. Furthermore, the second surface potential of the photosensitive drum 1 during the second startup control is higher on the side of the normal toner polarity (negative polarity in the second embodiment) than the first surface potential of the photosensitive drum 1 during the first startup control. Specifically, the first surface potential is 0 V, and the second surface potential is −300 V, which is the same polarity as the normal toner polarity. Therefore, the absolute value of the second potential difference between the brush voltage and the surface potential of the photosensitive drum 1 during the second startup control (450 V) is greater than the absolute value of the first potential difference between the brush voltage and the surface potential of the photosensitive drum 1 during the first startup control (150 V). This allows paper dust to be discharged from the brush nip portion N during the second startup control, while suppressing paper dust discharge during the first startup control.

[0067] After the second startup control, the voltage of the charging roller 2 is set to 0 V, the voltage of the developing roller 31 is set to 150 V to suppress adhesion of paper dust, and the voltage of the transfer roller 5 is set to −1000 V to collect paper dust on the transfer roller 5. Also, as in the first embodiment, the second startup control is executed after 5000 sheets have been passed.

[0068] 2. Effects of the Invention In order to confirm the effects of Example 2, a test similar to that of Example 1 was carried out. The evaluation results are shown in FIG. 11. In the comparative example, black spots occurred after 6,000 or more sheets were passed. In contrast, in Example 2, the occurrence of black spots was suppressed after 10,000 sheets were passed.

[0069] According to Example 2, the second start-up control is executed during post-rotation, and the potential difference between the brush voltage and the surface potential of the photosensitive drum during the second start-up control is made larger in the opposite polarity to the normal polarity of the toner than during the first start-up control, thereby suppressing image defects caused by the brush ejecting paper dust.

[0070] In the above embodiment, a configuration in which a toner image formed on the photosensitive drum 1 is transferred to a recording material P as a transfer target in a transfer unit has been described. However, the image forming apparatus to which the present invention is applicable is not limited to this configuration. For example, the present invention can also be applied to an image forming apparatus configured to primarily transfer a toner image to an intermediate transfer belt as a transfer target in a transfer unit, and then secondarily transfer the toner image from the intermediate transfer belt to a recording material P. Furthermore, in the above embodiment, a configuration in which the image forming apparatus 100 includes the photosensitive drum 1, the charging roller 2, and the developing device 3 has been described. However, the present invention can also be applied to a process cartridge-type image forming apparatus. In this case, a support member 13 supporting the brush member 11 that contacts the photosensitive drum 1 can be provided in the process cartridge having the photosensitive drum 1, and the brush member 11 can be fixed to the process cartridge. Furthermore, in the above embodiment, a common power supply is used to apply voltage to the brush member 11 and to the developing roller 31. However, a separate power supply may be provided to apply voltage to each. Furthermore, in the above embodiment, an example in which the present invention is applied to a cleanerless-type image forming apparatus has been described. That is, the image forming apparatus 100 is configured such that the developing device 3 removes the toner remaining on the surface of the photosensitive drum 1 without being transferred to a transfer medium. However, the present invention can also be applied to an image forming apparatus having a cleaner that comes into contact with the surface of the photosensitive drum 1 and scrapes off the toner remaining on the surface of the photosensitive drum 1.

[0071] The present disclosure is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the present disclosure. Therefore, the following claims are appended to clarify the scope of the present disclosure. This application claims priority based on Japanese Patent Application No. 2023-121046, filed on July 25, 2023, the entire contents of which are incorporated herein by reference.

[0072] 1: photosensitive drum, 2: charging roller, 3: developing device, 4: exposure unit, 5: transfer roller, 11: brush member, 110: driving motor, 150: control unit, E2: developing power supply

Claims

1. An image forming apparatus having: a rotatable photosensitive drum; charging means forming a charging section between itself and the photosensitive drum and charging the surface of the photosensitive drum in the charging section; developing means contacting the photosensitive drum to form a developing section and supplying toner to the surface of the photosensitive drum charged by the charging means in the developing section; transfer means contacting the photosensitive drum to form a transfer section and transferring the toner supplied to the photosensitive drum to a transferee in the transfer section; a brush contacting the surface of the photosensitive drum downstream of the transfer section and upstream of the charging section in the rotation direction of the photosensitive drum; application means for applying a voltage to the brush; drive means for driving the photosensitive drum to rotate; and a control unit for controlling the application means and the drive means, wherein the control unit performs a first start-up control for starting the rotation drive of the photosensitive drum in a state in which the potential difference between the voltage applied to the brush and the surface of the photosensitive drum is a first potential difference; and a second start-up control that starts the rotational drive of the photosensitive drum when the potential difference between the voltage applied to the brush and the surface of the photosensitive drum is a second potential difference, wherein the first potential difference and the second potential difference are potential differences that are formed so that an electrostatic force acts from the brush to the surface of the photosensitive drum on particles charged with a polarity opposite to the normal polarity of the toner, and the image forming apparatus is controlled so that the absolute value of the second potential difference is greater than the absolute value of the first potential difference.

2. The image forming apparatus of claim 1, wherein the control unit controls so that the surface potential of the photosensitive drum in the first startup control and the second startup control is equal, the first brush voltage applied to the brush in the first startup control and the second brush voltage applied to the brush in the second startup control are voltages of opposite polarity to the normal polarity of the toner, and the absolute value of the second brush voltage is greater than the absolute value of the first brush voltage.

3. The image forming apparatus according to claim 2, wherein the control section controls the surface potential of the photosensitive drum to be 0 V during the first startup control and the second startup control.

4. An image forming apparatus as described in claim 1, wherein the control unit controls the voltages applied to the brush in the first startup control and the second startup control to be equal, and the second surface potential of the photosensitive drum in the second startup control to be greater on the side of the normal polarity of the toner than the first surface potential of the photosensitive drum in the first startup control.

5. The image forming apparatus according to claim 4, wherein said control section controls said first surface potential to be 0 V and said second surface potential to be a potential having the same polarity as the normal polarity of said toner.

6. An image forming apparatus according to any one of claims 1 to 5, wherein the control unit, after executing the first startup control, performs an image forming operation without stopping the rotational drive of the photosensitive drum.

7. The image forming apparatus according to any one of claims 1 to 5, wherein the control section stops the rotational driving of the photosensitive drum after executing the second startup control.

8. The image forming apparatus according to any one of claims 1 to 5, wherein said control section applies a voltage having the same polarity as the normal polarity of said toner to said transfer means in said second startup control.

9. An image forming apparatus as claimed in any one of claims 1 to 5, wherein in the second startup control, the control unit applies a voltage of the same polarity as the normal polarity of the toner to the transfer means at a point in time required for the part of the surface of the photosensitive drum that was at the contact point between the brush and the photosensitive drum to reach the developing unit after the photosensitive drum starts to rotate.

10. An image forming apparatus as described in claim 9, wherein the transfer means has a rotatable transfer roller, and the control unit terminates the second startup control when the time required for the part of the surface of the photosensitive drum that was in the contact area to reach the transfer area after the photosensitive drum starts to rotate has elapsed and when the time required for the transfer roller to make one rotation has elapsed from the time when the photosensitive drum starts to rotate.

11. An image forming apparatus according to any one of claims 1 to 5, wherein the control unit executes the second startup control when the total number of sheets passed through the image forming apparatus exceeds a predetermined threshold value.

12. The image forming apparatus according to any one of claims 1 to 5, wherein the control section executes the second startup control in a post-rotation operation carried out after an image forming operation.

13. An image forming device as described in any one of claims 1 to 5, wherein the control unit executes the first startup control when starting rotational driving of the photosensitive drum for an image forming operation, and executes the second startup control when starting rotational driving of the photosensitive drum for other purposes.

14. The image forming apparatus according to any one of claims 1 to 5, which is a cleanerless type image forming apparatus in which the developing means removes residual toner from the surface of the photosensitive drum that has not been transferred to the transfer medium from the surface of the photosensitive drum.

15. The image forming apparatus according to any one of claims 1 to 5, wherein the applying means applies a voltage to the brush and the developing means.

Images