Image forming apparatus

An embodiment of an image forming apparatus includes a first image forming unit including a photosensitive drum and a fur brush for cleaning toner on the photosensitive drum and a second image forming unit including a photosensitive drum and a fur brush for cleaning toner on the photosensitive drum. In at least one embodiment for image formation, the fur brush in the first image forming unit and the fur brush in the second image forming unit start at different timings.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to an electrophotographic image forming apparatus.

Description of the Related Art

An electrophotographic image forming apparatus uniformly charges a surface of an image-bearing member, such as a photosensitive drum, by charging means, then exposes it to form an electrostatic latent image, develops the electrostatic latent image with coloring toner, and forms a visible image (toner image). Then, the image forming apparatus transfers the formed toner image to a recording medium, such as a sheet of paper, directly or with an intermediate transfer member or other member disposed therebetween. Foreign matter remaining on the image-bearing member after the transfer, such as toner, is cleaned (removed) by a cleaning device, such as a cleaning blade. One known example of the cleaning device may be a configuration that uses a cleaning rotator, such as a fur brush, for cleaning foreign matter on the image-bearing member by rotating itself and rubbing the image-bearing member (Japanese Patent Laid-Open No. 2011-39427).

In a configuration in which a plurality of image-bearing members are provided with their respective fur brushes, when all the fur brushes are operated at the same timing, an electric power required for starting up the fur brushes is significantly large.

SUMMARY OF THE INVENTION

The present disclosure provides an image forming apparatus capable of reducing the intensive use of an electric power in starting up fur brushes.

The present disclosure provides an image forming apparatus including a first image forming portion, a second image forming portion, and a control portion. The first image forming portion includes a first image-bearing member, a toner image forming portion configured to form a first toner image on the first image-bearing member, and a first cleaning member being rotatable and configured to clean the first toner image on the first image-bearing member by rotation. The second image forming portion includes a second image-bearing member, a toner image forming portion configured to form a second toner image on the second image-bearing member, and a second cleaning member being rotatable and configured to clean the second toner image on the second image-bearing member by rotation. The control portion is configured to control a rotation start timing for each of the first and second cleaning members such that when an image forming operation starts after an image forming signal for forming an image on a recording medium is input, an output of a signal for starting the rotation of the first cleaning member and an output of a signal for starting the rotation of the second cleaning member are different.

According to other aspects of the present disclosure, one or more additional image forming apparatuses and one or more methods of using or controlling one or more image forming apparatuses are discussed herein. Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

A first embodiment of the present disclosure is described below with reference toFIGS. 1 to 6. First, a general configuration of an image forming apparatus in the present embodiment is described with reference toFIG. 1.

[Outline of Image Forming Apparatus]

FIG. 1is a diagram that illustrates an embodiment of the image forming apparatus in the present disclosure. As illustrated inFIG. 1, an image forming apparatus100is a full-color image forming apparatus using an electrophotographic technology. In the image forming apparatus100, image forming units200Y,200M,200C, and200K configured to form toner images of four colors are arranged. These four image forming units200Y,200M,200C, and200K have substantially the same configuration. In the following description, the configuration of the image forming unit200Y for yellow is described as a representative. For the other image forming units, the members having the same configurations and functions as those in the image forming unit200Y bear the same numerals and corresponding suffixes indicating their respective units. The toner images of four colors are made up of yellow (Y), magenta (M), cyan (C), and black (K) images.

The image forming unit200Y includes a photosensitive drum1Y as a rotationally drivable image-bearing member configured to bear a toner image, a charging device2Y, an exposing device3Y, a developing device4Y, a primary transfer roller5Y, and a cleaning device30Y. The surface of the photosensitive drum1Y is charged by the charging device2Y as charging means. The charged surface of the photosensitive drum1Y is exposed by the exposing device3Y as electrostatic latent image forming means based on image information, and an electrostatic latent image is formed thereon. The electrostatic latent image on the photosensitive drum1Y is developed as a toner image by the developing device4Y as developing means. The toner image on the photosensitive drum1Y is primarily transferred by the primary transfer roller5Y as primary transfer means at a primary transfer portion to an intermediate transfer belt8as an intermediate transfer member. Foreign matter remaining on the photosensitive drum1Y after the transfer, such as toner, is cleaned by the cleaning device30Y as cleaning means. The cleaning device30Y includes a fur brush6Y (cleaning rotator) configured to clean (remove) foreign matter on the photosensitive drum1Y and a cleaning blade7Y configured to remove foreign matter with attractive force reduced by the fur brush6Y.

The toner images of different colors formed by the image forming units200Y,200M,200C, and200K are transferred to the intermediate transfer belt8in an overlapping manner. The toner images transferred to the intermediate transfer belt8is made to arrive at a secondary transfer portion opposed a secondary transfer roller10by the intermediate transfer belt8rotationally driven in a direction indicated by the arrows inFIG. 1. The toner images on the intermediate transfer belt8are secondarily transferred to a recording medium12(a sheet of paper, a sheet material, such as a transparency, or the like) at the secondary transfer portion and are fixed on the recording medium12by a fixing device11as fixing means. Toner remaining on the intermediate transfer belt8after the secondary transfer (secondary transfer residual toner) is cleaned (removed) from the intermediate transfer belt8by an intermediate transfer belt cleaning device9as an intermediate transfer member cleaning portion.

Next, the elements in the above-described image forming unit200Y are described with reference toFIG. 2. In the following description, a configuration common to the image forming units is described without suffixes. A configuration specific to an image forming unit is described with a suffix.

In the present embodiment, the image forming apparatus100uses toner that is obtained by crushing and classifying a mixture in which a resin binder predominantly composed of polyester is kneaded with a pigment and that has an average particle diameter of approximately 6 μm. The toner is frictionally charged to negative polarity by rubbing with a magnetic carrier. The average charge amount of the toner attached to an electric potential at an exposure portion in the photosensitive drum1is approximately −30 μC/g.

The photosensitive drum1has a cylindrical shape with an axial length of 360 mm and an outside diameter of 84 mm and has a negatively chargeable organic photoconductor (OPC). Specifically, in the photosensitive drum1, a photosensitive layer including a photoconductive layer predominantly composed of an organic photoconductor is disposed on an electro-conductive base member. The OPC is typically a lamination in which a charge generation layer, charge transport layer, and surface protecting layer that are made of an organic material are laminated on a metal base member as an electro-conductive base member. In the present embodiment, a material described in Japanese Patent Laid-Open No. 2005-43806 is used in each layer. The photosensitive drum1is rotationally driven in a direction indicated by the arrow during image formation by a drum motor50(seeFIG. 4) as photoconductor driving means at a process speed (peripheral speed) of normally 300 mm/s.

The charging device2is a contact charging roller and is configured to charge the photosensitive drum1by employing an electric discharge phenomenon occurring in a minute gap between the charging device2and the photosensitive drum1. A cored bar in the charging device2is subjected to an applied charging bias voltage having preset conditions. For example, in the case where the applied DC bias is set at −500 V and AC bias is set at a peak-to-peak bias higher than or equal to twice a discharge start voltage under that environment, the charging device2performs charging processing such that an image forming portion in the photosensitive drum1is uniformly charged to approximately −500 V. A charging potential in the charging processing by the charging device2is negative (has the negative polarity) and charges the photosensitive drum1to the negative side. The DC bias applied during image formation is not limited to −500 V and is set at an electric potential suited for satisfactory image formation in accordance with the environment and circumstances, such as times for which the photosensitive drum1and charging device2are used, lifespans, and the like, as appropriate. The charging device2is not limited to the contact charging roller and may be another configuration, such as a noncontact charging roller or a device that uses corona charging.

The exposing device3includes a semiconductor laser configured to perform image exposure on the photosensitive drum1with the surface uniformly charged by the charging device2based on image information. In the present embodiment, a potential of exposure with laser light is −200 V. The image forming unit200is provided with an electric potential measuring device (not illustrated) configured to measure the potential of the photosensitive drum1after the exposure and thus can check whether each of the charging potential and the exposure potential is actually a predetermined potential. In the present embodiment, the exposing device3is configured to perform image exposure by using the semiconductor laser. The exposing device3may be configured to perform image exposure by using another means, such as a light-emitting diode.

The developing device4includes a development container that stores two-component developer being a mixture of nonmagnetic toner and a magnetic carrier and a rotatable developing sleeve disposed at an opening portion in the development container. The developing sleeve has the functions of magnetically holding the developer in the development container by using a magnet fixed therein and of conveying the developer to a development portion being a gap portion between the developing sleeve and the photosensitive drum1. The axial length of the developing sleeve is 325 mm. The developing sleeve is connected to a high voltage power source configured to apply a development bias in which a direct-current voltage (−400 V) and an alternating-current voltage (Vp-p is 1600 V) are superimposed. By attaching toner to an electrostatic latent image by the development bias, developing processing is performed. The set value of the development bias is an example and may be set at a value adjusted in accordance with the charging potential or exposure potential for the photosensitive drum1as appropriate.

Next, the cleaning device30included in the image forming unit200is described in detail with reference toFIG. 2.FIG. 2is a cross-sectional view that illustrates the details of the cleaning device30. The cleaning device30includes the fur brush6, which has a brush shape, configured to scrape toner on the photosensitive drum1(image bearing member) and scrub the surface of the photosensitive drum1. The cleaning device30includes the cleaning blade7located downstream of the fur brush6in the rotational direction of the photosensitive drum1and configured to clean the surface of the photosensitive drum1. The cleaning device30houses the fur brush6and cleaning blade7inside a housing31.

The fur brush6has a rotating shaft with fibers implanted therein and, in the present embodiment, is produced by winding cloth with fibers implanted therein around a metal rotating shaft having a diameter of 12 mm. The fibers of the fur brush6in the present embodiment are bundles of 6-denier acrylic filaments and are implanted in a base material with a bristle implant density of 50 kF/inch2per filament. The fibers of the fur brush6have a length of 4.5 mm. The fur brush6is disposed in the image forming unit200such that the leading ends of the fibers enter the photosensitive drum1by approximately 0.4 mm.

The fur brush6is mounted such that the metal rotating shaft is grounded when it is mounted to the image forming apparatus. The photosensitive drum1and fur brush6are set such that both are rotated in the same direction at a contact nip portion where both are in contact with each other, as indicated by the arrows illustrated inFIG. 2. The rotation of the fur brush6is driven by a cleaning motor60as fur brush driving means and can be freely rotated by being controlled by a control portion40. In the present embodiment, the ratio of a peripheral speed of the fur brush6during steady rotation in which acceleration has been completed and the speed is constant to a peripheral speed of the photosensitive drum1during steady rotation is 110%. That is, the fur brush6and photosensitive drum1rotate at peripheral speeds at which the ratio of the peripheral speed of the fur brush6to that of the photosensitive drum1during steady rotation is 1.1. The peripheral speed at which the photosensitive drum1is in steady rotation is a speed at which images can be formed in the image forming apparatus100.

The fibers in the fur brush6are described in detail below. Each of the fibers in the fur brush6has a substantially circular cross-sectional shape and a surface shape having fine ridges and holes in places. The fine ridges provide the fur brush6with an increased area of a contact surface with foreign matter on the photosensitive drum1, and this leads to improved collecting performance. The cross-sectional shape of each of the fibers in the fur brush6is not limited to being circular and may be other shapes, such as oval, polygonal, or star shapes. It is useful that the cross-sectional shape of each of the fibers in the fur brush6may be selected in consideration of, in addition to the performance of colleting foreign matter, potential changes caused by contact with the surface layer of the photosensitive drum1, effects of rubbing on the surface layer of the photosensitive drum1, or other factors.

The fibers in the fur brush6in the cleaning device30are made of acrylic, which has characteristics of tending to become negative in the triboelectric series. The cleaning device30uses fibers that adjust resistance of the fibers by, for example, having a certain amount of carbon distributed in the fibers in the fur brush6and that possess electrical conductivity. The material that tends to be negatively charged is used in the fur brush6because an average charge amount in toner remaining on the photosensitive drum1in the image forming unit200can be of positive polarity (on the positive side). The state where the average charge amount in toner is on the positive side arises from the effects occurring when it passes through the primary transfer roller5and results from being able to switch from negative to positive in polarity caused by a significant decrease in the average charge amount in untransferred toner.

Thus, the use of the material that tends to become negative in the triboelectric series in the fibers in the fur brush6enables the cleaning device30to easily collet toner or the like that is made positive by the fur brush6. The use of the material that tends to become negative in the triboelectric series in the fibers in the fur brush6enables the cleaning device30to easily remove foreign matter from the surface of the photosensitive drum1and to assist the cleaning blade7in cleaning. The cleaning device30can perform discharging in which a negatively charged potential in the photosensitive drum1by causing the fur brush6to be in contact with the photosensitive drum1returns toward zero. The fibers in the fur brush6are not limited to acrylic and may be another material such as polyester, nylon, Teflon (registered trademark), or vinyl chloride. As the fibers in the fur brush6, a material that tends to become charged to polarity opposite to that of the charging potential of the toner and photosensitive drum1in the triboelectric series may be used in order to facilitate collecting negative toner or the like.

The cleaning blade7is made of urethane rubber and has an elastic force. The cleaning blade7in the present embodiment has an axial length of 340 mm and is in contact with the photosensitive drum1with a predetermined abutment pressure.

Next, the details of the removal of foreign matter on the photosensitive drum1by the cleaning device30are described. The cleaning device30weakens an attractive force to the photosensitive drum1by disturbing residues (foreign matter), such as toner (transfer residual toner), on the surface of the photosensitive drum1after a toner image is transferred by using the fur brush6. After weakening the attractive force of the foreign matter on the photosensitive drum1by using the fur brush6, the cleaning device30removes the foreign matter from the surface of the photosensitive drum1by using the cleaning blade7. The foreign matter removed from the surface of the photosensitive drum1is temporarily held on the fur brush6and then is transported to a scraper32being in contact with a circumferential surface of the fur brush6by rotation of the fur brush6. The foreign matter flies out of the fur brush6by a repulsive force of the fibers in the fur brush6elastically deformed by being in contact with the scraper32and falls on a conveying screw33or its vicinity. The foreign matter falling on the conveying screw33or its vicinity is conveyed in an axial direction of the photosensitive drum1by the conveying screw33, which extends along the rotational axial direction of the photosensitive drum1, passes through a collecting toner conveyance passage (not illustrated), and is collected by a toner collecting container (not illustrated).

The foreign matter removed by the fur brush6and cleaning blade7includes substances other than the transfer residual toner on the photosensitive drum1. The photosensitive drum1undesirably collects other substances, such as secondary transfer residual toner on the intermediate transfer belt8(on the intermediate transfer member), paper dust and filler containing paper fibers included in the recording medium12, calcium carbonate, or the like. Thus, the cleaning device30also cleans the secondary transfer residual toner and foreign matter such as components stemming from the recording medium12, together with the transfer residual toner on the photosensitive drum1. The secondary transfer residual toner and components stemming from the recording medium12on the intermediate transfer belt8should be cleaned by the intermediate transfer belt cleaning device9, but it is difficult to fully clean them. Foreign matter that has not been cleaned arrives at the photosensitive drum1.

When the components stemming from the recording medium12on the intermediate transfer belt8arrive at the cleaning blade7in the cleaning device30, they are caught in a contact portion between the cleaning blade7and the photosensitive drum1, and cleaning defects are likely to occur. Thus, it is useful to remove the components stemming from the recording medium12by using the fur brush6before they arrives at the cleaning blade7. When the intermediate transfer belt8is rotationally driven, the components stemming from the recording medium12may be conveyed to the photosensitive drum1from the intermediate transfer belt cleaning device9, and thus it is useful to drive the fur brush6in the cleaning device30.

Next, frictional charging the photosensitive drum1by the fur brush6is described. As previously described, in the present embodiment, the fur brush6is made of an acrylic fiber, and the photosensitive drum1is made of an OPC. Accordingly, the fur brush6is on the negative side in the triboelectric series with respect to the photosensitive drum1. Thus, if the photosensitive drum1comes into contact with the fur brush6too many times, the photosensitive drum1is charged to polarity opposite to that of the charging potential.

FIG. 3is a graph that illustrates a relationship between the time for which the fur brush6is driven (rubs) and the surface potential of the photosensitive drum1when the fur brush6is driven in a state where the photosensitive drum1is at rest.FIG. 3reveals that although the surface potential of the photosensitive drum1is substantially zero at a point in time before the fur brush6is driven, as the fur brush6is driven, the photosensitive drum1is charged to the positive side, which is opposite to the polarity of the charging potential. If the photosensitive drum1is charged at the positive side, it is difficult for the photosensitive drum1to be uniformly charged by the charging device2, and a potential difference locally arises on its surface. In this case, when image exposure light is emitted from the exposing device3, an electrostatic latent image with a different charging potential is formed locally, and when a development bias is applied by the developing device4, the amount of toner increases locally, and unevenness of image is likely to occur. Thus, it is useful that in a state where the photosensitive drum1is at rest, the fur brush6is not driven. In the following description, the state in which the photosensitive drum1is charged to polarity (positive) opposite to that of the charging potential (negative) is also described as being positively charged. The state in which the photosensitive drum1is charged to the same polarity as that of the charging potential (negative) is also described as being negatively charged.

When the fur brush6is new and near to its initial state, no contamination by transfer residual toner occurs, and the stiffness of the fibers is high and cleaning performance is high. Accordingly, the newer the fur brush6is, the more likely the photosensitive drum1is to be positively charged by the driving of the fur brush6.

In contrast, the more clogged the inside of the fur brush6is with toner, the less the effects on the charging potential of the photosensitive drum1by the driving of the fur brush6are. The effects on the charging potential of the photosensitive drum1by the driving of the fur brush6degraded by repeated use are also small. These phenomena are estimated to result from a change in the cleaning performance arising from a change in the driving torque of the fur brush6caused by a condition where toner is attached to the fur brush6or a change over time, such as an occurrence of a bend or twist in the fibers or shrinkage of an outer diameter of the fur brush6.

The intermediate transfer belt8is an endless belt, is rotationally driven in the direction indicated by the arrows inFIG. 1by a driving roller8A, and has a three-tier structure in which a resin layer, an elastic layer, and a surface layer are positioned in this order from the back side. In the present embodiment, examples of a resin material that forms the resin layer in the intermediate transfer belt8may include polyimide and polycarbonate. The resin layer has a thickness of 70 μm to 100 μm. Examples of an elastic material that forms the elastic layer in the intermediate transfer belt8may include urethane rubber and chloroprene rubber. The elastic layer has a thickness of 200 μm to 250 μm.

It is useful that the surface layer in the intermediate transfer belt8is made of a material that can reduce the attractive force of toner to the surface of the intermediate transfer belt8and that facilitates transferring a toner image to the recording medium12at the secondary transfer roller10. In the present embodiment, the surface layer in the intermediate transfer belt8may be made of a resin material of any one of polyurethane, polyester, epoxy resin, and other resins or elastic materials of any two or more of elastic rubber, elastomer, butyl rubber, and other elastic materials. The intermediate transfer belt8may use one kind or two or more kinds of powder and grains, including fluorocarbon polymers, as a material for reducing a surface energy and increasing lubricity and distribute it in the material forming the surface layer. In the case where the intermediate transfer belt8uses powder and grains of fluorocarbon polymers or the like, the powder and grains may have nonuniform particle and grain sizes.

The surface layer in the intermediate transfer belt8in the present embodiment has a thickness of 5 μm to 10 μm. The surface layer in the intermediate transfer belt8includes an additive conductive material for adjusting a resistance value, such as carbon black, and its volume resistivity is 1e8Ωcm to 1e14Ωcm. [Intermediate Transfer Belt Cleaning Device]

The intermediate transfer belt cleaning device9is disposed at a location opposed to a tension roller8B for stretching the intermediate transfer belt8and includes two fur brushes whose material and shape are the same as those of the fur brush6, and the two fur brushes are disposed along the rotational drive direction of the intermediate transfer belt8. Of the two fur brushes included in the intermediate transfer belt cleaning device9, an upstream fur brush9A is arranged on the upstream side in the rotational drive direction of the intermediate transfer belt8and applies a negative bias to secondary transfer residual toner on the intermediate transfer belt8. Of the two fur brushes included in the intermediate transfer belt cleaning device9, a downstream fur brush9B is arranged on the downstream side in the rotational drive direction of the intermediate transfer belt8with respect to the upstream fur brush9A and applies a positive bias to the secondary transfer residual toner on the intermediate transfer belt8. The upstream fur brush9A and downstream fur brush9B are disposed such that the leading ends of the fibers enter the intermediate transfer belt8by approximately 0.8 mm.

In the present embodiment, a voltage that enables an electric current of −50 μA to flow is applied to the upstream fur brush9A to collect the secondary transfer residual toner on the intermediate transfer belt8and cause the secondary transfer residual toner to be negatively charged. A voltage that enables an electric current of +55 μA to flow is applied to the downstream fur brush9B to collect the secondary transfer residual toner made negative by the upstream fur brush9A.

The intermediate transfer belt cleaning device9cleans the secondary transfer residual toner and the components stemming from the recording medium12on the intermediate transfer belt8by using the upstream fur brush9A and downstream fur brush9B. The intermediate transfer belt cleaning device9collects components such as toner attached to the upstream fur brush9A and downstream fur brush9B by using a scraper (not illustrated), as in the case of the cleaning device30. The scraper may not be used, and the intermediate transfer belt cleaning device9may include a metallic roller being in contact with each of the upstream fur brush9A and downstream fur brush9B. In this configuration, the intermediate transfer belt cleaning device9collects foreign matter on the upstream fur brush9A and downstream fur brush9B by employing a potential difference between the metallic roller and each of the upstream fur brush9A and downstream fur brush9B.

The image forming apparatus100can collect most of the foreign matter on the intermediate transfer belt8by using the intermediate transfer belt cleaning device9. Unfortunately, however, the intermediate transfer belt cleaning device9may be unable to fully collect the foreign matter, and some may remain on the intermediate transfer belt8. In the intermediate transfer belt cleaning device9, the scraper may be unable to fully remove the foreign matter on the upstream fur brush9A and downstream fur brush9B. In such a case, the intermediate transfer belt cleaning device9may eject the foreign matter attached to the upstream fur brush9A and downstream fur brush9B to the intermediate transfer belt8when the upstream fur brush9A and downstream fur brush9B are driven. The foreign matter ejected to the intermediate transfer belt8may be conveyed to the image forming unit200. As previously described, if the foreign matter is conveyed to the image forming unit200, the cleaning performance by the cleaning blade7may degrade, and this may lead to the occurrence of cleaning defects.

FIG. 4is a block diagram that illustrates a configuration of the control portion40for controlling the image forming apparatus100. As illustrated inFIG. 4, the control portion40includes a CPU41, which is a central processing unit for performing various control, a read-only memory (ROM)42configured to store programs executable by the CPU41and various data, and a random-access memory (RAM)43configured to temporarily retain results of computation by the CPU41and other data.

The CPU41controls a drum motor50configured to rotationally drive the photosensitive drum1and the cleaning motor60configured to rotationally drive the fur brush in each of the image forming units. The CPU41also controls a belt motor70as intermediate transfer belt driving means configured to rotationally drive the driving roller8A, which is configured to rotationally drive the intermediate transfer belt8. The CPU41also controls a belt cleaning motor80as intermediate transfer CLN driving means configured to rotationally drive the upstream fur brush9A and downstream fur brush9B included in the intermediate transfer belt cleaning device9. The CPU41emits driving OFF/ON signals to the motors in accordance with an executing program.

The CPU41controls an image formation high voltage applying portion51configured to control a charging voltage applied to the charging devices, a developing voltage applied to the exposing devices, and a transferring voltage applied to the primary transfer rollers. The CPU41also controls an intermediate transfer CLN high voltage applying portion81configured to apply a high-voltage potential to the intermediate transfer belt cleaning device9. The CPU41emits high-voltage OFF/ON signals to the high voltage applying portions.

In the image forming apparatus100in the present embodiment, the image forming unit200Y is nearest the intermediate transfer belt cleaning device9in the rotational drive direction of the intermediate transfer belt8. The distance from the intermediate transfer belt cleaning device9to the fur brush6Y in the image forming unit200Y along the intermediate transfer belt8and photosensitive drum1Y is 90 mm. That is, the sum of the distance traveled by a cleaned portion8a, which is in contact with the intermediate transfer belt cleaning device9at the initiation of driving of the intermediate transfer belt8, to when it arrives at the photosensitive drum1Y and the distance traveled by a surface1a, which is opposed to the cleaned portion8a, of the photosensitive drum1Y to when it arrives at the fur brush6Y is 90 mm. Because the process speed of the image forming apparatus100in the present embodiment is 300 mm/sec, the foreign matter from the intermediate transfer belt cleaning device9arrives at the fur brush6Y in 300 ms.

Each of the drum motor50and belt motor70in the present embodiment is a stepping motor and can make the photosensitive drum1and intermediate transfer belt8reach a steady rotation where both are stably driven in 200 ms from the initiation of the driving. The image forming apparatus100can also make the photosensitive drum1and intermediate transfer belt8reach the steady rotation in less than 200 ms. It is useful that both reach the steady rotation in not less than 100 ms to avoid a large peripheral speed difference between the photosensitive drum1and intermediate transfer belt8.

The cleaning motor60in the present embodiment is a DC motor. Thus, the time it takes the fur brush6to reach a steady rotation since a driving ON signal is transmitted from the CPU41to the cleaning motor60varies depending on the state of the fur brush6or product variation of DC motors used in the cleaning motor60. The time required to reach the steady rotation varies depending on the state of the fur brush6because the state where the fur brush6is in contact with the photosensitive drum1varies and the driving torque of the fur brush6varies depending on the state of the fur brush6.

Therefore, the CPU41sets the timing when it drives the fur brush6on the assumption that the cleaning motor60is a DC motor in which the driving torque of the fur brush6is high and the startup characteristics are not good. It is found that the time it takes the cleaning motor60in the present embodiment to reach a steady rotation from the initiation of rotation is 100 ms at maximum.

Traditional image forming apparatuses typically start driving a fur brush and a photosensitive drum at the same time. However, if a driving shock occurs when an attempt to drive both at the same time is made, the fur brush may start rotating before the photosensitive drum starts being driven, the photosensitive drum may be much rubbed with the fur brush locally, an area charged to polarity opposite the charging potential (“memory”) may appear in the photosensitive drum. If the charging in the memory is slight, the image forming apparatus can recover the memory by idly rotating the photosensitive drum. If the photosensitive drum is idly rotated for a period of time required to recover the memory, the time for the idle rotation (down time) is taken before image formation starts, and this impairs usability.

To address this issue, in the present embodiment, the drum motor50and cleaning motor60are independent from each other, and both are independently controlled by the CPU41. The CPU41prevents the appearance of memory by controlling the drum motor50and cleaning motor60so as not to drive both at the same time. The details of the control of the drum motor50and cleaning motor60by the CPU41are described below.

FIG. 5is a flow chart that illustrates control processing when the CPU41performs drive control for the photosensitive drum1and fur brush6.FIG. 6is a sequence chart that illustrates behaviors of the drum motor50, cleaning motor60, and belt motor70when the CPU41performs the control in accordance with the flow chart illustrated inFIG. 5. The sequence chart inFIG. 6schematically illustrates timings when signals for turning-on electrical driving are input into the motors. Thus, real operations of each of the motors may differ by the order of several tens of microseconds depending on the status of the torque of an object to be driven. It is necessary for the image forming apparatus100to determine the timing when the driving of each of the motors starts while checking the real operations for driving the motors.

As illustrated inFIG. 5, the CPU41first starts driving the drum motor50and belt motor70(S101). In the processing at step S101, the CPU41outputs a driving ON signal to each of the drum motor50and belt motor70to start driving the drum motor50and belt motor70at the same time. In the image forming apparatus100, as illustrated inFIG. 6, the driving ON signal is output to each of the drum motor50and belt motor70, so that rotation of the photosensitive drum1and rotational drive of the intermediate transfer belt8start at the same time. The timing when the driving ON signal is output to each of the drum motor50and belt motor70and the rotation of the photosensitive drum1and rotational drive of the intermediate transfer belt8start at the same time is defined as first start timing A1. In the following description, the first start timing A1is used as the reference (0 ms) in the staring operation.

As previously described, the photosensitive drum1and intermediate transfer belt8are configured such that both reach a steady rotation in 200 ms since both start rotating. Thus, it is desirable that the fur brush6Y in the present embodiment start rotating after the time it takes the photosensitive drum1to start the steady rotation from the first start timing A1(=200 ms) or more elapses.

In the image forming apparatus100, as described above, foreign matter from the intermediate transfer belt cleaning device9arrives at the fur brush6Y in 300 ms. Thus, it is useful that the image forming apparatus100performs control such that the fur brush6Y can reach a steady rotation before 300 ms elapses from the initiation of rotational drive of the intermediate transfer belt8. As previously described, the fur brush6is configured such that it reaches the steady rotation in 100 ms from the initiation of rotation.

In consideration of the above, the CPU41determines the timing when it outputs the driving ON signal to the cleaning motor60. The CPU41proceeds to processing at step S102after the elapse of first time T1(=100 ms) from the processing at step S101. In the processing at step S102, the CPU41starts driving the belt cleaning motor80and starts applying a high voltage to the upstream fur brush9A and downstream fur brush9B by using the intermediate transfer CLN high voltage applying portion81. Then, the CPU41proceeds to processing at step S103after the elapse of second time T2(=100 ms) from the processing at step S102. In the processing at step S103, the CPU41starts rotation of the fur brush6by outputting a driving ON signal to the cleaning motor60.

In performing the processing at step S103, the CPU41outputs the driving ON signal to the cleaning motor60and starts rotation of all of the fur brushes6of the fur brushes6Y,6M,6C, and6K at the same time, as illustrated inFIG. 6. The timing when the driving ON signal is output to the cleaning motor60and all the fur brushes6start rotating is defined as second start timing A2.

In this way, after the elapse of the first time T1and second time T2from the processing at step S101, the CPU41performs the processing at step S103. Therefore, the CPU41can place a time interval equal to or longer than the time required to start a steady rotation of the photosensitive drum1(=200 ms) between the initiation of rotation of the photosensitive drum1and the initiation of rotation of the fur brush6. The CPU41starts rotation of the fur brush6Y at the point in time when 200 ms elapses from the initiation of rotational drive of the intermediate transfer belt8. Accordingly, the CPU41can make the fur brush6Y reach a steady rotation before the elapse of the time it takes foreign matter on the intermediate transfer belt8to arrive at the fur brush6Y from the initiation of rotational drive of the intermediate transfer belt8(=300 ms). The CPU41can rotate the fur brush6and photosensitive drum1at peripheral speeds at which the ratio of the peripheral speed of the fur brush6to that of the photosensitive drum1is always 1.1 or less by starting rotation of the fur brush6after the photosensitive drum1reaches the steady rotation. The first time T1and second time T2constitute a start waiting time in the present embodiment.

By executing the control at steps S101to S103, the CPU41prevents the photosensitive drum1and fur brush6from starting rotating at the same time. Thus, the image forming apparatus100can prevent the photosensitive drum1from being robbed with the fur brush6locally when each of the photosensitive drum1and fur brush6starts rotating and can reduce the appearance of memory on the photosensitive drum1.

After the processing at step S103, the CPU41ends the processing relating to the driving of the photosensitive drum1and fur brush6. After the elapse of third time T3, the CPU41performs various processing relating to image formation (S104). It is useful that the third time T3is a time required to stabilize the driving of the photosensitive drum1, fur brush6, and intermediate transfer belt8.

Next, control processing performed by the CPU41when it stops the photosensitive drum1and fur brush6is described with reference to the sequence chart inFIG. 6. As previously described, the cleaning motor60in the present embodiment is a DC motor and stops after it rotates by only the amount corresponding to moment of inertia during driving after it is electrically turned off. The cleaning motor60is configured such that 300 ms is needed as first stop time S1taken to stop in the state where the driving torque of the fur brush6is low and the moment of inertia of the DC motor is the largest.

As described above, the drum motor50is a stepping motor, and it stops after it rotates by only the amount corresponding to moment of inertia of the stepping motor after it is electrically turned off. The drum motor50in the present embodiment is configured such that 200 ms is needed as second stop time S2taken to stop the photosensitive drum1.

In consideration of the above, the CPU41determines the timing when it outputs the driving OFF signal to each of the drum motor50and cleaning motor60. For example, to end an image forming operation and stop, the CPU41first outputs the driving OFF signal to the cleaning motor60. As illustrated inFIG. 6, the CPU41outputs the driving OFF signal to the cleaning motor60and stops rotation of all of the fur brushes6Y,6M,6C, and6K at the same time. The timing when the driving OFF signal is output to the cleaning motor60and a stopping operation for all the fur brushes6starts is defined as first stop timing A3. In the following description, the first stop timing A3is used as the reference (0 ms) in the stopping operation.

Next, because the first stop time S1(=300 ms) is needed to stop the fur brush6at maximum, the CPU41outputs the driving OFF signal to the drum motor50and belt motor70after the elapse of 300 ms or more from the first stop timing A3. In the present embodiment, the CPU41outputs the driving OFF signal to the drum motor50and belt motor70at the point in time when 400 ms elapses from the first stop timing A3. The timing when the driving OFF signal is output to the drum motor50and belt motor70and the stopping operation for the photosensitive drum1and intermediate transfer belt8starts is defined as second stop timing A4.

The CPU41can prevent a state where the fur brush6is rotating while the photosensitive drum1is at rest by starting the stopping operation for the photosensitive drum1at the second stop timing A4. Thus, the image forming apparatus100can prevent the photosensitive drum1from being rubbed with the fur brush6locally when the photosensitive drum1and fur brush6are at rest and can reduce the appearance of memory on the photosensitive drum1. In this way, the first stop time S1required to elapse from the first stop timing A3to the second stop timing A4constitutes a stop waiting time in the present embodiment.

As described above, the image forming apparatus100in the present embodiment starts rotation of the fur brush6after starting rotation of the photosensitive drum1. Thus, the image forming apparatus100can reduce the appearance of memory on the photosensitive drum1that would be caused by the fur brush6when the photosensitive drum1and fur brush6start rotating at the same time. That is, the image forming apparatus100can reduce the phenomenon in which the photosensitive drum1is charged by the fur brush6to polarity opposite the charging potential by the charging device2.

In the present embodiment, the CPU41is configured such that it outputs the driving ON signal to the cleaning motor60after the photosensitive drum1and intermediate transfer belt8reach a steady rotation. Other forms may also be used. If the fur brush6is driven for 100 ms or more in the state where the photosensitive drum1is at rest, the portion of the photosensitive drum1being in contact with the fur brush6is positively charged locally. If the peripheral speed difference between the peripheral speed of the fur brush6and that of photosensitive drum1is equal to or larger than a certain value, the photosensitive drum1is also positively charged.

The case where the photosensitive drum1is positively charged by being rubbed with the fur brush6rotating at a peripheral speed higher than that of the photosensitive drum1is described in detail below. An experiment on the relationship between the peripheral speed of the fur brush6with respect to that of the photosensitive drum1and the surface potential of the photosensitive drum1shows that the surface potential of the photosensitive drum1is positively charged to +15 V or more when the fur brush6rotates at a peripheral speed of 500% with respect to that of the photosensitive drum1. In the case where the fur brush6rotates at a peripheral speed of 450% with respect to that of the photosensitive drum1, the surface potential is positively charged to the order of +8 V. In contrast, in the case where the fur brush6rotates at a peripheral speed of 400% with respect to that of the photosensitive drum1, the surface potential of the photosensitive drum1is a potential of the order of −10 V to 0 V, and it is not substantially positively charged.

That is, during rotation of the fur brush6, including under acceleration and deceleration, when the peripheral speed of the fur brush6is always lower than 400% with respect to the peripheral speed of the photosensitive drum1, the image forming apparatus100can prevent the photosensitive drum1from being positively charged. Accordingly, the CPU41can start rotation of the fur brush6even before 200 ms elapses since rotation of the photosensitive drum1starts, at a timing at which the value of the ratio of the peripheral speed of the fur brush6to that of the photosensitive drum1is always less than 4.0. Specifically, the CPU41may be configured so as to perform the processing at step S103after the elapse of 150 ms since it performs the processing at step S101illustrated inFIG. 5. In this configuration, because the value of the ratio of the peripheral speed of the fur brush6to that of the photosensitive drum1is 2.5 at maximum, the fur brush6can be rotated within the range not larger than 4.0, which is the value of the peripheral-speed ratio where the surface potential of the photosensitive drum1is not positively charged. In this case, fourth time elapsed since the processing at step S101is performed (150 ms) constitutes the start waiting time. The value 4.0 of the ratio of the peripheral speed of the fur brush6to that of the photosensitive drum1constitutes a predetermined value.

With this configuration, the image forming apparatus100can properly rub the surface of the photosensitive drum1by using the fur brush6, can enhance the cleaning performance for the photosensitive drum1, and can prevent the cleaning blade7from being damaged by components stemming from the recording medium12. Because the image forming apparatus100can start rotation of the fur brush6before the photosensitive drum1reaches a steady rotation, the rise time required to start image formation can be reduced, and usability and productivity can be improved.

In rotation stopping operation, the image forming apparatus100may start a stopping operation for the photosensitive drum1before the fur brush6stops, at a timing at which the peripheral speed of the fur brush6is always lower than 400% with respect to that of the photosensitive drum1. With this configuration, the image forming apparatus100can reduce the fall time taken to complete image formation and can improve usability. In this case, fifth time elapsed from the initiation of the stopping operation for the fur brush6to the initiation of the stopping operation for the photosensitive drum1constitutes the stop waiting time.

Another control is described next with reference toFIGS. 7 and 8. In the above configuration, the fur brushes6Y,6M,6C, and6K start rotating at the same time and start their stopping operations at the same time. However, in the image forming apparatus100, components stemming from the recording medium12seldom reach the image forming units200C and200K, which are positioned on the downstream side in the rotational drive direction of the intermediate transfer belt8.

Specifically, of the total of foreign matter ejected from the intermediate transfer belt cleaning device9to the intermediate transfer belt8, approximately 60% attaches to the photosensitive drum1Y, and approximately 30% attaches to the photosensitive drum1M. That is, of the total of the foreign matter on the intermediate transfer belt8, approximately 90% attaches to the photosensitive drums1Y and1M, which are positioned on the upstream side in the rotation direction of the intermediate transfer belt8, and only approximately 10% arrives at the photosensitive drums1C and1K, which are positioned on the downstream side in the rotation direction. Thus, the foreign matter formed from the components stemming from the recording medium12on the intermediate transfer belt8affects the cleaning blades7C and7K little. Accordingly, in the present embodiment, the timing when the fur brush starts rotating is set for each of the image forming units.

FIG. 7is a flow chart that illustrates control processing when the CPU41performs drive control for the photosensitive drum1and fur brush6.FIG. 8is a sequence chart that illustrates behaviors of the drum motor50, cleaning motor60, and belt motor70when the CPU41performs the control in accordance with the flow chart illustrated inFIG. 7. In the present embodiment, the photosensitive drum1and intermediate transfer belt8are configured such that both reach a steady rotation in 500 ms since both start rotating. In the present embodiment, the fur brush6is configured such that it reaches a steady rotation in 100 ms since it starts rotating. The image forming apparatus100in the present embodiment is configured such that its process speed is 225 mm/sec and foreign matter from the intermediate transfer belt cleaning device9arrives at the fur brush6Y in 400 ms.

As illustrated inFIG. 7, the CPU41first starts driving the drum motor50and belt motor70(S201). In the processing at step S201, the CPU41outputs a driving ON signal to each of the drum motor50and belt motor70to start driving the drum motor50and belt motor70at the same time. In the image forming apparatus100, as illustrated inFIG. 8, the driving ON signal is output to each of the drum motor50and belt motor70, so that rotation of the photosensitive drum1and rotational drive of the intermediate transfer belt8start at the same time. The timing when the driving ON signal is output to each of the drum motor50and belt motor70and the rotation of the photosensitive drum1and rotational drive of the intermediate transfer belt8start at the same time is defined as first start timing B1. In the following description, the first start timing B1is used as the reference (0 ms) in the staring operation.

Next, the CPU41proceeds to the processing at step S202after the elapse of first time110(=100 ms) from the processing at step S201. In the processing at step S202, the CPU41starts driving the belt cleaning motor80and starts applying a high voltage to the upstream fur brush9A and downstream fur brush9B by using the intermediate transfer CLN high voltage applying portion81. Then, the CPU41proceeds to processing at step S203after the elapse of second time T11(=100 ms) from the processing at step S202. In the processing at step S203, the CPU41outputs a driving ON signal to the cleaning motor60and starts rotation of the fur brushes6Y and6M, which are near the intermediate transfer belt cleaning device9in the rotation direction of the intermediate transfer belt8.

In performing the processing at step S203, the CPU41outputs the driving ON signal to the cleaning motor60and starts rotation of the fur brushes6Y and6M at the same time, as illustrated inFIG. 8. The timing when the driving ON signal is output to the cleaning motor60and the fur brushes6Y and6M start rotating is defined as second start timing B2. In this way, after the elapse of the first time110and second time T11from the processing at step S201, the CPU41performs the processing at step S203.

Therefore, the CPU41can place a time interval equal to or longer than 200 ms between the initiation of rotation of the photosensitive drum1and the initiation of rotation of the fur brush6. In the case where the fur brushes6Y and6M start rotating at the second start timing B2, the value of the ratio of the peripheral speed of the fur brushes6Y and6M to that of the photosensitive drums1Y and1M is always at or below 2.5. That is, the CPU41can place a time interval equal to or longer than the time (=200 ms) required to achieve the state where the value of the ratio of the peripheral speed of the fur brushes6Y and6M to that of the photosensitive drums1Y and1M is always at or below a predetermined value before the initiation of the rotation of the fur brushes6Y and6M. Thus, even when the fur brushes6Y and6M rotate faster than the photosensitive drums1Y and1M, the image forming apparatus100can prevent the surface potential of the photosensitive drums1Y and1M from being positively charged by the fur brushes6Y and6M.

The CPU41starts rotation of the fur brush6Y at the point in time when 200 ms elapses from the initiation of rotational drive of the intermediate transfer belt8. Accordingly, the CPU41can make the fur brushes6Y and6M reach a steady rotation before the elapse of the time it takes components stemming from the recording medium12on the intermediate transfer belt8to arrive at the fur brush6Y from the initiation of rotational drive of the intermediate transfer belt8(=400 ms). Thus, the CPU41can increase the peripheral speed of the fur brush6Y up to a speed at which sufficient cleaning performance is achieved before foreign matter from the intermediate transfer belt cleaning device9arrives at the position of the fur brush6Y through the intermediate transfer belt8and photosensitive drum1. The first time T10and second time T11constitute a start waiting time in the present embodiment.

The CPU41proceeds to the processing at step S204after the elapse of third time T12(=100 ms). In the processing at step S204, the CPU41outputs a driving ON signal to the cleaning motor60and starts rotation of the fur brushes6C and6K, which are positioned on the downstream side in the rotation direction of the intermediate transfer belt8.

In performing the processing at step S204, the CPU41outputs the driving ON signal to the cleaning motor60and starts rotation of the fur brushes6C and6K at the same time, as illustrated inFIG. 8. The timing when the driving ON signal is output to the cleaning motor60and the fur brushes6C and6K start rotating is defined as third start timing B3. In this way, after the elapse of third time T12from the processing at step S203, the CPU41performs the processing at step S204.

By starting the rotation of the fur brushes6C and6K at the third start timing B3, the CPU41can make the peripheral speed of the photosensitive drums1C and1K at the third start timing B3higher than the peripheral speed of the photosensitive drums1Y and1M at the second start timing B2. That is, the CPU41can make the peripheral speed of the photosensitive drums1C and1K when the fur brushes6C and6K start rotating high and can more reliably prevent the surface potential of the photosensitive drums1C and1K from being positively charged. In the configuration according to the first embodiment, the surface potential of the photosensitive drums1C and1K is −9 V to +1 V. In the configuration according to the present embodiment, the surface potential of the photosensitive drums1C and1K can be −10 V to 0 V.

In the case where the fur brushes6C and6K start rotating at the third start timing B3, the value of the ratio of the peripheral speed of the fur brushes6C and6K to that of the photosensitive drums1C and1K is always at or below 2.5. Thus, even when the fur brushes6C and6K rotate faster than the photosensitive drums1C and1K, the image forming apparatus100can prevent the surface potential of the photosensitive drums1C and1K from being positively charged by the fur brushes6C and6K.

After the processing at step S204, the CPU41ends the processing relating to driving of the photosensitive drum1and fur brush6. After the elapse of fourth time T13, the CPU41executes control for stabilizing the driving of the photosensitive drum1and the driving of the intermediate transfer belt8(S205). Then, the CPU41performs various processing relating to image formation.

Next, control processing performed by the CPU41when it stops the photosensitive drum1and fur brush6is described with reference to the sequence chart inFIG. 8. As in the first embodiment, the cleaning motor60in the present embodiment is a DC motor and stops after it rotates by only the amount corresponding to moment of inertia during driving after it is electrically turned off. The cleaning motor60in the present embodiment is configured such that 300 ms is needed as first stop time S1taken to stop in the state where the driving torque of the fur brush6is low and the moment of inertia of the DC motor is the largest.

As in the first embodiment, the drum motor50is a stepping motor, and it stops after it rotates by only the amount corresponding to moment of inertia of the stepping motor after it is electrically turned off. The drum motor50in the present embodiment is configured such that 200 ms is needed as second stop time S2taken to stop the photosensitive drum1.

In consideration of the above, the CPU41determines the timing when it outputs the driving OFF signal to each of the drum motor50and cleaning motor60. For example, to end an image forming operation and stop, the CPU41first outputs the driving OFF signal to the cleaning motor60. As illustrated inFIG. 8, the CPU41outputs the driving OFF signal to the cleaning motor60and stops rotation of all of the fur brushes6Y,6M,6C, and6K at the same time. The timing when the driving OFF signal is output to the cleaning motor60and a stopping operation for all the fur brushes6starts is defined as first stop timing B4. In the following description, the first stop timing B4is used as the reference (0 ms) in the stopping operation.

Next, because the first stop time S1(=300 ms) is needed to stop the fur brush6at maximum, the CPU41outputs the driving OFF signal to the drum motor50and belt motor70after the elapse of 300 ms or more from the first stop timing B4. In the present embodiment, the CPU41outputs the driving OFF signal to the drum motor50and belt motor70at the point in time when 400 ms elapses from the first stop timing B4. The timing when the driving OFF signal is output to the drum motor50and belt motor70and the stopping operation for the photosensitive drum1and intermediate transfer belt8starts is defined as second stop timing B5.

The CPU41can prevent a state where the fur brush6is rotating while the photosensitive drum1is at rest by starting the stopping operation for the photosensitive drum1at the second stop timing B5. Thus, the image forming apparatus100can prevent the photosensitive drum1from being rubbed with the fur brush6locally when the photosensitive drum1and fur brush6are at rest and can reduce the appearance of memory on the photosensitive drum1.

In this configuration, the image forming units200Y and200M, which are disposed on the upstream side in the rotational drive direction of the intermediate transfer belt8and in which the rotational drive of their fur brushes are started at the second start timing B2, constitute a first image forming unit. The image forming units200C and200K, which are disposed on the downstream side in the rotational drive direction with respect to the image forming units200Y and200M and in which the rotational drive of their fur brushes are started at the third start timing B3, constitute a second image forming unit. The number of units constituting the first image forming unit and the number of units constituting the second image forming units may not be the same. For example, the image forming unit200Y may constitute the first image forming unit, and the image forming units200M,200C, and200K may constitute the second image forming unit. As previously described, because approximately 30% of the components stemming from the recording medium12arrives at the image forming unit200M, it is useful that the first image forming unit and second image forming unit are configured as in the present embodiment.

In this way, the image forming apparatus100in the present embodiment first starts rotation of the fur brushes6Y and6M after starting rotation of the photosensitive drums1. Then, the image forming apparatus100starts rotation of the fur brushes6C and6K after starting rotation of the fur brushes6Y and6M. Accordingly, the image forming apparatus100can more reliably reduce the occurrence in which the photosensitive drums1C and1K are positively charged by the fur brushes6C and6K.

OTHER EMBODIMENTS

In the above-described embodiments, the image forming apparatus100starts rotation such that the fur brush6Y reaches a steady rotation after the rotational drive of the intermediate transfer belt8is started and before foreign matter on the intermediate transfer belt8arrives. Other forms may also be used. The fur brush6can sufficiently clean the photosensitive drum1when it rotates at a predetermined speed or more, even if the predetermined speed is below the peripheral speed in steady rotation. Thus, the image forming apparatus100may start rotation of the fur brush6Y at a timing that enables the fur brush6Y to be accelerated to a speed at which no cleaning defects occur after rotational drive of the intermediate transfer belt8is started and before foreign matter on the intermediate transfer belt8arrives.

In the above-described embodiments, the image forming apparatus100is configured such that the stopping operation for the photosensitive drum1is started after the stopping operation for the fur brush6is started. Other forms may also be used. The surface potential of the photosensitive drum1may be smaller than the potential change illustrated inFIG. 3, depending on the status of the fur brush6. Specifically, in the case where some toner is applied to the fur brush6, even when the photosensitive drum1is rubbed with the fur brush6, the occurrence in which it is positively charged can be reduced. Thus, by using a process for ejecting some toner from the developing device4to the fur brush6, the image forming apparatus100can avoid the photosensitive drum1from being positively charged even when the stopping operation for the photosensitive drum1is started before the stopping operation for the fur brush6is started.

The process for ejecting some toner from the developing device4to the fur brush6is described in detail below. The image forming apparatus100can eject some toner by repeating a series of operations of driving the developing sleeve in the developing device4for a short time and stopping it in the state where the charging potential and developing potential are 0 V. One example behavior of the developing device4may be repeating the operation of driving for 100 ms and stopping for 50 ms three times.

In the case where the toner is applied to the fur brush6, in the image forming apparatus100, even when the photosensitive drum1is at rest, the surface potential of the photosensitive drum1is not positively charged as long as the time for which the fur brush6is driven is at or below 300 ms. Thus, the image forming apparatus100can be configured such that the stopping operation for the photosensitive drum1is started before the stopping operation for the fur brush6is started. With this configuration, the image forming apparatus100can quickly stop the photosensitive drum1after image formation, and this leads to an extended life of the photosensitive drum1.

The image forming apparatus100in the above-described embodiments includes the fur brush6as a cleaning rotator. However, other forms may also be used. For example, a rotatable rolling member may also be used.

The image forming apparatus100in the above-described embodiments includes the drum motor50and cleaning motor60independently. Other forms may also be used. For example, the image forming apparatus100includes the drum motor50and cleaning motor60by using a single driving source. In this case, it is useful that the image forming apparatus100is configured such that the driving source is connected to a mechanism capable of switching power transmission, such as a clutch, to enable controlling the drum motor50and cleaning motor60independently.

The image forming apparatus100in the first and second embodiments is configured such that a toner image is transferred to the recording medium12by the secondary transfer roller10. Other forms may also be used. For example, the image forming apparatus100may be configured such that a toner image is transferred to the recording medium12by the primary transfer roller5in the image forming unit200.

The image forming apparatus according to the above-described embodiments is applicable to a copier, printer, facsimile machine, multifunction apparatus having the plurality of functions, and other similar apparatuses.

This application claims the benefit of Japanese Patent Application No. 2015-144847 filed Jul. 22, 2015, which is hereby incorporated by reference herein in its entirety.