JP5084229B2 - Image forming apparatus and cleaning method - Google Patents

Description

  The present invention relates to an image forming apparatus for efficiently electrostatically cleaning an untransferred toner image remaining untransferred on a photosensitive drum or an intermediate transfer belt.

  An image forming apparatus has been put to practical use in which a toner image of different color separations is superimposed on an intermediate transfer belt for primary transfer, and then the toner image overlap is collectively transferred from the intermediate transfer belt to a recording material to form a full color image. . An image forming apparatus using an intermediate transfer belt includes a belt cleaning device that removes transfer residual toner that has not been secondarily transferred to a recording material and prepares for the next primary transfer. In addition, since it is difficult to remove the mechanical toner using a cleaning blade, an intermediate transfer belt having an elastic layer on the surface is desirably electrostatically cleaned using a conductive fur brush.

  However, the toner to be removed from the intermediate transfer belt by the belt cleaning device is not limited to untransferred toner that could not be electrically transferred to the recording material, that is, toner particles that are charged to the opposite polarity or uncharged toner particles. When the color patches of the respective color toners are formed on the intermediate transfer belt, the color patches are not secondarily transferred to the recording material. Therefore, it is necessary to remove the toner of normal charging polarity that constitutes the color patches. Further, in the recovery operation after the jam processing of the recording material is completed, it is necessary to remove a large amount of toner charged to the normal charging polarity that should have been secondarily transferred to the recording material from the intermediate transfer belt.

  In electrostatic cleaning using a conductive fur brush, the cleaning performance varies greatly depending on the charging polarity of the toner particles to be removed and the voltage to be applied. Therefore, it is necessary to optimize the voltage application according to these cases.

  Patent Document 1 discloses a belt cleaning device using a conductive fur brush. Here, in the recovery operation after jamming of the recording material, in order to remove a large amount of toner charged to a normal charging polarity, a voltage having a polarity opposite to that at the time of normal image formation is applied to the conductive fur brush. .

  Patent Document 2 shows a belt cleaning device using a pair of conductive fur brushes. Here, during normal image formation, toner particles charged to a polarity opposite to the normal charged polarity or uncharged toner particles by applying a voltage having the same polarity as the normal charged polarity of the toner to the upstream conductive fur brush Is removed from the intermediate transfer belt. Apply a voltage opposite to the normal charging polarity of the toner image to the downstream conductive fur brush, and contact the upstream conductive fur brush to transfer the toner particles charged to the normal charging polarity to the intermediate transfer. Removed from the belt. In the recovery operation after jamming of the recording material, the voltage applied to the upstream conductive fur brush is switched to a voltage having a polarity opposite to that in the normal state, that is, a voltage having a polarity opposite to the normal charging polarity of the toner. .

  Patent Document 3 discloses an image forming apparatus for performing a secondary transfer of an untransferred toner image from an intermediate transfer belt to a secondary transfer roller and cleaning the intermediate transfer belt in a recovery operation after the jam processing of the recording material. Here, a large amount of toner that should have been transferred to the recording material is transferred to the secondary transfer roller, and the toner is collected by a secondary transfer roller cleaning device provided on the secondary transfer roller.

  Patent Document 4 discloses a tandem-type full-color image forming apparatus that primarily transfers toner images of respective colors on an intermediate transfer belt in series. Here, a post charger using a corona discharger is disposed in front of the secondary transfer portion, and the charged state of each color toner image is adjusted to optimize for secondary transfer.

JP-A-2005-004079 JP 2005-308931 A JP 2002-174967 A JP 2004-246341 A

  In the image forming apparatuses of Patent Document 1 and Patent Document 2, all the toner charged with the same polarity as the voltage applied to the conductive fur brush passes through the conductive fur brush and remains on the surface of the intermediate transfer belt. A certain ratio of the toner particles primarily transferred to the intermediate transfer belt is charged to an uncharged or reverse polarity to the normal charged polarity (see FIG. 4). Further, when a high voltage is applied to the conductive fur brush, the amount of toner that contacts the conductive fur brush and is charged to the same polarity as the applied voltage increases. The toner remaining on the surface of the intermediate transfer belt in this way is mixed with the next toner image that is primarily transferred onto the intermediate transfer belt, and the quality (resolution and color purity) of the image formed on the recording material is lowered. I will let you.

  Therefore, in order to remove the toner particles that have passed through the conductive fur brush, after removing the toner particles charged to the normal charging polarity, the voltage applied to the conductive fur brush is set to the same as the normal charging polarity of the toner image. It is necessary to return to polarity. In this state, it is necessary to circulate the intermediate transfer belt once more to remove the uncharged or charged toner particles having a polarity opposite to the normal charging polarity. Therefore, it takes extra time for the recovery operation from the jam.

  In the image forming apparatus of Patent Document 3, a large amount of toner adheres to the secondary transfer roller, and if the cleaning is not performed for a long time, the toner remains on the surface, and the recording material to be secondarily transferred next time. Dirty the back side. A dedicated cleaning device including a large collection container needs to be provided on the secondary transfer roller, and there is a possibility that the toner may scatter around the secondary transfer roller. If the blade pressure is increased in order to improve the cleaning effect, the load on the secondary transfer roller is increased, causing uneven rotation, and the secondary transferred toner image may be disturbed.

  An object of the present invention is to provide an image forming apparatus capable of efficiently removing a large amount of untransferred toner adhering to an intermediate transfer belt or the like in a short time.

The image forming apparatus of the present invention includes an image carrier on which a surface carrying a charged toner image moves, a transfer device that transfers a toner image from the surface using a voltage having a polarity opposite to the charged polarity of the toner image, A first cleaning member that contacts the surface on the downstream side of the transfer device and applies a voltage of the same polarity as the charging polarity to remove residual toner on the surface; and on the downstream side of the first cleaning member A second cleaning member that contacts the surface and is applied with a voltage having a polarity opposite to the charging polarity to remove residual toner on the surface; and a toner image on the image carrier is removed from the surface by the transfer device. comprising a transfer operation to be transferred, and an execution unit capable of executing a non-transfer operation in which the toner image on the image bearing member is the surface in a state that is not transcribed to move from the surface by the transfer device, wherein When performing a transfer operation is to remove the toner of the image carried on body by applying the charging polarity opposite the polarity of voltage to the first cleaning member from the surface. And a charging unit that charges the toner on the image carrier to the charging polarity upstream of the transfer device, and the charging unit when performing the non-transfer operation than when performing the transfer operation. Control means for increasing the charging output of the toner, and when the non-transfer operation is executed, the control means identifies a toner loading amount of the toner on the image carrier and sets a predetermined threshold value. When the amount of applied toner is smaller than the above, the second cleaning member is applied with a voltage having a polarity opposite to the charged polarity. When the amount of applied toner exceeds a predetermined threshold, The voltage applied to the first cleaning member is increased as compared with the case where the amount of applied toner is less than the threshold value, and a voltage having the same polarity as the charging polarity is applied to the second cleaning member.

In the image forming apparatus according to the present invention, the voltage applied to the cleaning member is set at the time of normal image formation during a non-transfer operation such as a return operation after jamming processing of a recording material or a color patch cleaning for toner image density adjustment . Switching from the transfer residual toner image correspondence to the toner image on the image carrier during the non-transfer operation is switched. Then, the charging unit is used to shift the average charging state of the toner image on the image carrier to the normal charging polarity side, and the toner particles charged to the reverse polarity contained in the toner image on the image carrier Reduce the proportion of uncharged toner particles. Accordingly, the toner particles that pass through the cleaning member to which a voltage having a polarity opposite to the normal charging polarity is applied are reduced, and the electrostatic cleaning efficiency of the toner image on the image carrier by the cleaning member is increased.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. The image forming apparatus of the present invention is not limited to the limited configuration of the embodiments described below. Another embodiment in which a part or all of the configuration of each embodiment is replaced with the alternative configuration as long as the charged state of the untransferred toner image attached to the image carrier is adjusted to enhance the electrostatic cleaning effect. But it is feasible.

  In the first embodiment, a tandem image forming apparatus in which four photosensitive drums 1Y, 1M, 1C, and 1K are arranged along the intermediate transfer belt 5 will be described. However, the image forming apparatus of the present invention may be an image forming apparatus that transfers a toner image from one photosensitive drum having a plurality of color developing devices to an intermediate transfer belt. In addition, the image forming apparatus may perform not only the cleaning of the intermediate transfer belt but also the photosensitive drum and the like, and the present invention can also be applied to an electrostatic recording type image forming apparatus.

  In the first embodiment, the main part of the image forming apparatus related to the formation and transfer of a toner image will be described exclusively. However, the image forming apparatus includes a printer, various printing machines, and a copying machine in addition to necessary equipment and a casing. It can be adapted to various applications such as FAX machines and multifunction machines.

  In addition, about illustration of the structure of the image forming apparatus shown by patent documents 1-4, the detailed structure of each mounted apparatus, a general control flow, etc., illustration is partially omitted and detailed description is also abbreviate | omitted.

<Image forming apparatus>
FIG. 1 is a schematic explanatory diagram of the configuration of the image forming apparatus according to the first embodiment. As shown in FIG. 1, an image forming apparatus 100 according to the first embodiment includes four photosensitive drums 1Y, 1M, 1C, and 1K arranged along an endless belt-like intermediate transfer belt 5 to provide an electrophotographic full color. Perform image formation.

  The intermediate transfer belt 5 has a circumferential length of 900 mm, has elasticity on the surface, and is supported by being wound around a driving roller 21, a tension roller 22, and a secondary transfer inner roller 23. The intermediate transfer belt 5 is driven by a driving roller 21 driven by a motor (not shown) and circulates in the direction of arrow R5 at a process speed of 300 mm / second.

  In the horizontal portion of the intermediate transfer belt 5 positioned between the driving roller 21 and the tension roller 22, image forming portions Y, M, C, and K that respectively form yellow, magenta, cyan, and black toner images are disposed. The

  The image forming units Y, M, C, and K are configured in common except that the developers used in the developing devices 4Y, 4M, 4C, and 4K are yellow toner, magenta toner, cyan toner, and black toner. . Therefore, here, the image forming unit K will be described as a representative, and the other image forming units Y, M, and C will be understood by replacing the subscript K with Y, M, and C.

  In the image forming unit K, process devices such as a primary charger 3K, an exposure device 2K, a developing device 4K, and a cleaning device 7K are arranged around a photosensitive drum 1K that is a drum-shaped electrophotographic photosensitive member.

  The photosensitive drum 1K has an organic photoconductor layer (OPC) applied to the outer peripheral surface of an aluminum cylinder having a diameter of 80 mm. The photosensitive drum 1K is rotatably supported by flanges at both ends, and is rotated counterclockwise by transmitting a driving force from a driving motor (not shown) to one end. The photosensitive drum 1 </ b> K rotates in the direction of the arrow to form a black separated color toner image on the surface, and then primarily transfers the toner image to the intermediate transfer belt 5.

  The primary charger 3K is a conductive roller that is formed in a roller shape and contacts the surface of the photosensitive drum 1K. The primary charger 3K is charged with a charging bias voltage from a power source (not shown), and charges the rotating surface of the photosensitive drum 1K to a uniform negative potential.

  The exposure apparatus 2K scans a laser beam pulse-modulated with an image signal of black separation color with a polygon mirror, and forms an electrostatic latent image on the surface of the uniformly charged photosensitive drum 1K.

  The developing device 4K includes a toner storage unit 41 that stores black toner having a negative charge polarity, and a developing roller 42 that is provided at a position adjacent to the surface of the photosensitive drum 1K and is driven to rotate by a driving unit (not shown). Have. The developing roller 42 carries the toner pumped from the toner container 41 on the peripheral surface and conveys it to the surface of the photosensitive drum 1K, and applies a developing bias voltage from a developing bias power source (not shown) to attach the toner to the electrostatic latent image. . The developing device 4K uses the developing roller 42 to attach negatively charged black toner to the surface of the photosensitive drum 1K and develop the electrostatic latent image into a toner image.

  Inside the intermediate transfer belt 5, a primary transfer roller 6K that is in pressure contact with the photosensitive drum 1K via the intermediate transfer belt 5 is disposed. The primary transfer roller 6K is connected to a primary transfer bias power source (not shown), and is applied with a primary transfer bias voltage having a polarity (positive polarity) opposite to the toner charging polarity. The negatively charged toner image on the surface of the photosensitive drum 1 is responsive to the positive primary transfer bias voltage of the primary transfer roller 6K in the process of passing through the primary transfer portion T1 as the photosensitive drum 1K rotates. Primary transfer is performed on the intermediate transfer belt 5 in contact.

  In the image forming units Y, M, C, and K, the toner images of the respective separation colors are formed by adjusting the timing so that the heads of the toner images on the intermediate transfer belt 5 overlap each other at the primary transfer unit T1. The Each separation color toner image is primarily transferred to the intermediate transfer belt 5 at each primary transfer portion T <b> 1 and sequentially superposed thereon, whereby a full color toner image is formed on the intermediate transfer belt 5.

  The transfer residual toner that has not been transferred to the intermediate transfer belt 5 at the primary transfer portion T1 is conveyed to the cleaning device 7K as the photosensitive drum 1K rotates. The cleaning device 7K slides a rubber blade (not shown) on the surface of the photosensitive drum 1K, scrapes off the transfer residual toner and collects it in a container, and prepares the surface of the photosensitive drum 1K for the next toner image formation.

  The secondary transfer outer roller 24 pressed against the secondary transfer inner roller 23 via the intermediate transfer belt 5 forms a nip of the secondary transfer portion T2 between the secondary transfer outer roller 24 and the intermediate transfer belt 5. The secondary transfer outer roller 24 can be brought into contact with / separated from the intermediate transfer belt 5 by a moving mechanism (not shown). Except for the period related to the secondary transfer, the moving mechanism separates the secondary transfer outer roller 24 from the intermediate transfer belt 5 so that untransferred toner and dirt on the intermediate transfer belt 5 do not adhere to the secondary transfer outer roller 24. I have to.

  The secondary transfer inner roller 23 is connected to the ground potential, while the secondary transfer outer roller 24 is connected to a secondary transfer bias power source (not shown), and a secondary having a polarity opposite to the toner charging polarity (positive polarity). A transfer bias voltage is applied. In response to the electric field formed between the secondary transfer inner roller 23 and the secondary transfer outer roller 24 by the secondary transfer bias voltage, a negatively charged full color toner image on the intermediate transfer belt 5 is recorded on the recording material P. Secondary transfer.

  Cassettes 16 and 17 are arranged in the lower part of the image forming apparatus 100, and recording materials P having different sizes are stored. The recording material P is picked up one by one from the cassette 16 by the pickup roller 13 and waits at the registration roller 15. The registration roller 15 sends the recording material P to the secondary transfer portion T2 in time with the top of the toner image on the intermediate transfer belt 5. In the process in which the recording material P passes through the secondary transfer portion T2, the full color toner image carried on the intermediate transfer belt 5 is secondarily transferred to the recording material P, and the recording material P on which the full color toner image is secondarily transferred. Is conveyed to the fixing device 9.

  The fixing device 9 presses a pressure roller 9b with a predetermined pressure against a fixing roller 9a incorporating a heater to form a fixing nip. In the process of passing through the fixing nip of the fixing device 9, the full color toner on the recording material P is heated and pressurized and melted and fixed to the surface of the recording material P.

  The control unit 40, which is a microcomputer control device, controls such an image forming process by controlling each device, each unit, and each power source of the image forming device 100 in accordance with a stored control program.

  The secondary transfer roller 24 is composed of two or more layers including an elastic rubber layer and a coating layer, and the elastic rubber layer is composed of a carbon black dispersed foam layer having a cell diameter of 0.05 mm to 1.0 mm. . On the other hand, the surface coating layer is made of a fluororesin-based material having a thickness of 0.1 mm to 1.0 mm in which an ion conductive polymer is dispersed, and the surface roughness Rz> 1.5 μm in consideration of paper transportability. Is controlling.

  As the fluororesin material, tetrafluoroethylene (TFE), hexafluoropropylene copolymer (FEP), perfluoroalkoxy resin (PFA), polyvinylidene fluoride (PVDF), or the like can be employed. Examples of the ion conductive polymer used as the conductive agent include various (for example, styrene) copolymers with (meth) acrylates that bind a quaternary ammonium base to a carboxyl group. In addition, there are polymers that bind quaternary ammonium bases such as a copolymer of maleimide and methacrylate that binds to quaternary ammonium bases, and polymers that bind alkali metal salts of sulfonic acids found in sodium polysulfonate. There are also the following polymers in which at least a hydrophilic unit of an alkyl oxide is bonded in the branched chain. For example, polyethylene oxide, polyethylene glycol-polyamide copolymer, polyethylene-epichlorohydrin copolymer, polyether amide imide, block type polymer having polyether as a segment, and the like.

<Belt cleaning device>
FIG. 2 is a schematic explanatory diagram of the configuration of the belt cleaning device. As shown in FIG. 1, the residual transfer toner remaining on the intermediate transfer belt 5 without being secondarily transferred to the recording material P in the secondary transfer portion T2 is belt-cleaned as the intermediate transfer belt 5 circulates in the direction of arrow R5. It is conveyed to the device 30. The belt cleaning device 30 moves the toner electrostatically, removes it from the intermediate transfer belt 5 and collects it in the waste toner box 37, and prepares the intermediate transfer belt 5 for the next primary transfer.

As shown in FIG. 2, the belt cleaning device 30 includes a pair of conductive fur brushes 31 and 32 that are disposed to face the tension roller 22 with the intermediate transfer belt 5 interposed therebetween. The conductive fur brushes 31 and 32 are made by implanting conductive and fibrous hairs on a conductive shaft having a diameter of 8 mm so as to have an outer diameter of 20 mm. The pile length of the implanted hair is 6 mm, the material is nylon, the density is 100 kF, and the resistance is 5 × 10. ⁶ Ω.

  The belt cleaning device 30 can be moved from a position where the conductive fur brushes 31 and 32 are brought into contact with the intermediate transfer belt 5 to a position where the belt is separated by a moving mechanism (not shown). When the transfer residual toner on the intermediate transfer belt 5 is conveyed to the belt cleaning device 30, the control unit 40 causes the conductive fur brushes 31 and 32 to abut and perform cleaning.

  The conductive fur brush 31 (32) is in contact with the metal bias roller 33 (34) with an intrusion length of 1.5 mm. The conductive fur brush 31 (32) and the bias roller 33 (34) rotate in directions indicated by arrows, respectively. The rotation direction of the conductive fur brush 31 (32) is set to be opposite to the moving direction of the intermediate transfer belt 5 at the contact position with the intermediate transfer belt 5. The rotation direction of the bias roller 33 (34) is set to be in the same direction as the conductive fur brush 31 (32) at the contact position with the conductive fur brush 31 (32).

  A cleaning blade (scraper) 35 (36) is disposed in contact with the bias roller 33 (34) on the downstream side of the position in contact with the conductive fur brush 31 (32). The toner particles moved from the intermediate transfer belt 5 to the conductive fur brush 31 (32) are transferred to the bias roller 33 (34), and then transferred to the waste toner box (37: FIG. 1) by the cleaning blade 35 (36). It is scraped off.

  Cleaning bias power supplies 43 and 47 are switchably connected to the bias roller 33, and cleaning bias power supplies 44 and 48 are switchably connected to the bias roller 34. Since the tension roller 22 is connected to the ground potential, toner particles that can remove the conductive fur brush 31 (32) from the intermediate transfer belt 5 when the polarity of the cleaning bias voltage applied to the bias roller 33 (34) is switched. The charging polarity of switches.

  The control unit 40 switches the cleaning bias power supplies 43 and 47 according to the charging polarity of the toner particles to be removed from the intermediate transfer belt 5 by the conductive fur brush (upstream conductive fur brush) 31. Further, the cleaning bias power supplies 44 and 48 are switched according to the charging polarity of the toner particles to be removed from the intermediate transfer belt 5 by the conductive fur brush (downstream conductive fur brush) 32.

  In the normal image formation in which the toner image is secondarily transferred to the recording material P, the control unit 40 connects the cleaning bias power source 47 to the bias roller 33 and connects the cleaning bias power source 48 to the bias roller 34. As a result, the upstream conductive fur brush 31 is negatively charged and adsorbs positively charged toner particles and uncharged toner particles on the intermediate transfer belt 5. The downstream conductive fur brush 32 is positively charged and contacts the upstream conductive fur brush 31 to adsorb negatively charged toner particles.

  However, in the start-up process after the jam process, the cleaning bias power supply 43 is connected to the bias roller 33, and the upstream conductive fur brush 31 is charged to the positive polarity and charged to the negative polarity on the intermediate transfer belt 5. Toner particles are removed.

  For example, when +700 V is applied to the bias roller 33, a voltage of +600 V is induced in the conductive fur brush 31. At this time, the negatively charged toner particles on the intermediate transfer belt 5 are driven to an electric field of +600 V formed between the tension roller 22 having the ground potential and the conductive fur brush 31 to the conductive fur brush 31. Electrostatic transfer. The toner particles adhering to the conductive fur brush 31 are electrostatically transferred to the bias roller 33 by being driven by an electric field of +100 V formed between the conductive fur brush 31 and the bias roller 33.

<Post charger>
As shown in FIG. 1, a post charger 26 is disposed to face the intermediate transfer belt 5 between the driving roller 21 and the secondary transfer inner roller 23. The post charger 26 ensures the stability of the secondary transfer in the secondary transfer portion T2 by aligning the toner band charge amount between the four layers of toner images superimposed on the intermediate transfer belt 5.

  In other words, the separated color toner images formed independently by the image forming portions Y, M, C, and K and sequentially primary-transferred to the intermediate transfer belt 5 have different toner band charge amounts. Each transfer current is different. In general, when there is a difference of 10 μC / mg or more in the toner band charge amount of each separation color toner image, transfer of the separation color toner image that is secondarily transferred at a transfer current far from the optimum transfer current. Sex worsens.

  Therefore, a post charger 26 using a corona charger is disposed upstream of the secondary transfer portion T2, and a stretching roller 27 connected to the ground potential is disposed opposite to the post charger 26. Then, non-contact charging is performed by the post charger 26 to reduce the difference in the toner band charge amount of each separated color toner image.

  As shown in FIG. 2, the shield case of the post charger 26 is connected to the ground potential. The post charger 26 is arranged on the upstream side of the secondary transfer portion T2 shown in FIG. 1. In FIG. 2, for convenience of illustration, the post charger 26 is shown on the upstream side of the belt cleaning device 30, and the stretching roller 27 is not shown. . However, a dedicated corona charger that improves the cleaning efficiency of the belt cleaning device 30 without using the existing post charger 26 may be disposed at the position of the post charger 26 shown in FIG.

  The controller 40 controls the adjustment bias power supply 45 to apply the DC bias voltage and the AC bias voltage to the discharge electrode in a superimposed manner during normal image formation in which the toner image is secondarily transferred to the recording material P. Specifically, the adjustment bias power supply 45 is turned on immediately before the front end of the toner image passes through the post charger 26 and turned off when the toner image passes. However, when outputting a plurality of images in one job, the interval between sheets may be turned off. When the DC bias voltage was −1.0 kV and the AC bias voltage was Vpp = 5.8 kV (1.0 kHz), the current flowing in the direction of the intermediate transfer belt 5 was 20 μA. While preventing the toner particles charged to the negative polarity by the negative DC bias voltage from being dropped, the charged charge is moved between the toner images of the respective separated colors by the AC bias voltage to cancel the charge amount difference. In this way, as shown in Table 1, the separated toner band charge amounts of the respective separated color toner images are aligned to the latter half of −20 μC / g.

  However, in the start-up process after the jam process, the control unit 40 controls the adjustment bias power supply 45 to apply a higher negative DC bias voltage to the discharge electrode of the post charger 26. This induces the average toner band charge amount of each separated color toner image to a level exceeding −30 μC / g, thereby improving the efficiency of toner image removal by the upstream conductive fur brush 31.

<Patch detection control>
As shown in FIG. 1, the image forming apparatus 100 executes patch detection control so that an image obtained by normal image formation in which a toner image is secondarily transferred onto a recording material P is always suitable. In the patch detection control, a test pattern toner image called a patch of each separation color is formed and is primarily transferred to the intermediate transfer belt 5. Then, physical properties such as density and chromaticity are measured for each separation color patch on the intermediate transfer belt 5, and the image forming units Y, M, Image forming conditions in C and K are adjusted.

  A density detection sensor 25 is arranged to face the portion of the intermediate transfer belt 5 wound around the drive roller 21. The density detection sensor 25 is an optical sensor that detects reflected light by irradiating the patch with infrared light from a light source.

  The control unit 40 controls the image forming units Y, M, C, and K to form respective separation color patches on the photosensitive drums 1Y, 1M, 1C, and 1K, and arranges them on the intermediate transfer belt 5 to perform primary processing. Transfer.

  The control unit 40 measures the density of each separation color patch from the magnitude of the reflected light detected by the density detection sensor 25, and based on the measurement result, images such as exposure beam intensity, development bias voltage, and primary transfer bias voltage. Adjust the formation conditions. Thus, the relationship between the patch density and the image forming conditions is optimized so that an image with an appropriate density is always obtained.

  As an example of the image forming unit K, a suitable image density related to the image forming unit K is reproduced by adjusting the charging bias voltage in the primary charger 3K, the intensity of the exposure beam in the exposure device 2K, the developing bias voltage in the developing device 4K, and the like. Is done. In addition, when the toner stored in the developing device 4K is replenished, patch detection control is executed in order to match the image densities before and after replenishment.

  Maximum image density control is executed as a specific method of patch detection control. In maximum image density control, in order to cope with changes in toner characteristics due to durability and environmental changes, regular image patching is performed at the maximum image density between papers in the case of pre-rotation of image formation or in the case of large-scale continuous image formation. Form. Then, by detecting the output value of the density of the patch and changing the image forming condition for obtaining an appropriate density, the setting of the image forming condition according to the environment at that time is realized.

  That is, the maximum image density control is executed when the apparatus environment changes suddenly, when the initial density is set by the developer in the developing device 4K, or when the apparatus is started up after externally supplying or replacing the developer. By performing normal image formation under the image forming conditions determined by such maximum image density control, image control can be performed so as to achieve an appropriate density in all environments.

  At the time of maximum image density control, the control unit 40 stores data of a solid image having the maximum image density as a test exposure pattern serving as a patch. The surface of the photosensitive drum 1K uniformly charged by the primary charger 3K is exposed to the maximum image density by the exposure device 2K based on the solid image data to form a patch latent image. The patch latent image is developed with black toner stored in the developing device 4K to form a patch. A primary image patch is formed on the intermediate transfer belt 5 by performing primary transfer onto the intermediate transfer belt 5.

  In addition to the maximum image density control described here, there are various types of patch detection control. There is color misregistration control in which the color misregistration of each separation color patch formed on the intermediate transfer belt 5 is detected using a color misregistration sensor, and the exposure angle or the like in the exposure apparatus 2K is changed. When the developer contained in the developing device 4K is a two-component system, a solid image patch having a predetermined density setting is formed on the intermediate transfer belt 5, and toner is applied to the developing device 4K by detecting the density drop. There is also toner supply control for automatic supply. In some cases, a gradation image is formed as a patch, and gradation control is performed by measuring the chromaticity and density with a color sensor. In addition to such patch detection control, in order to update the toner in the developing device 4K, the toner may be discharged from the developing device 4K and transferred onto the intermediate transfer belt 5.

  In any case, the patches are primarily transferred onto the intermediate transfer belt 5, but these patches are removed by the belt cleaning device 30 without being secondarily transferred to the recording material P. At this time, the secondary transfer outer roller 24 is separated from the intermediate transfer belt 5 in order to avoid adhesion of patch toner. This is because if the toner adheres to the secondary transfer outer roller 24, it will be transferred to the recording material P during normal image formation.

  As will be described later, the belt cleaning device 30 efficiently collects the negatively charged toner constituting the patch with the charged polarity of the upstream conductive fur brush 31 opposite to that during normal image formation. It can be so.

<First Embodiment>
FIG. 3 is a flowchart of the cleaning control of the intermediate transfer belt using the belt cleaning device. FIG. 4 is an explanatory diagram of the charged state of the toner image primarily transferred to the intermediate transfer belt, FIG. 5 is an explanatory diagram of the relationship between the charging device applied voltage and the toner charge amount, and FIG. It is explanatory drawing of a relationship.

  As shown in FIG. 3 with reference to FIGS. 1 and 2, in the first embodiment, various settings and various controls different from normal image formation are executed in the return sequence operation after the jam processing and the patch detection control. .

  That is, when patch detection control is started (S11) while the intermediate transfer belt 5 is circulated (S11), the secondary transfer outer roller 24 is separated from the intermediate transfer belt 5 (S13). As a result, toner particles that are not transferred to the recording material P are prevented from being transferred or attached to the secondary transfer outer roller 24.

  Then, the circulation speed of the intermediate transfer belt 5 is decreased (S21). As a result, the contact density of the conductive fur brush 31 of the belt cleaning device 30 with respect to the surface of the intermediate transfer belt 5 is increased, and the toner particles that pass through the contact with the flocks are reduced.

  Then, the adjustment bias voltage applied to the post charger 26 is set to a negative polarity voltage higher than that in the case of normal image formation (S22). By non-contact charging using corona discharge, toner particles charged in reverse polarity and uncharged toner particles contained in the toner image on the intermediate transfer belt 5 are reduced. As a result, the toner passing through the conductive fur brush 31 charged to positive polarity (S23) is almost eliminated, and the recovery efficiency in the belt cleaning device 30 is further increased.

  Then, the cleaning bias power supply 43 is connected to the bias roller 33 to charge the conductive fur brush 31 to the positive polarity, and the cleaning bias power supply 48 is connected to the bias roller 34 to charge the conductive fur brush 32 to the positive polarity. (S23). That is, the charged state of the conductive fur brush 31 is reversed from that of normal image formation, and the belt cleaning device 30 is specialized in removing negatively charged toner particles on the intermediate transfer belt 5.

  On the other hand, if jamming of the recording material P occurs during normal image formation (NO in S12) (YES in S15), the conveyance of the recording material P and the circulation of the intermediate transfer belt 5 are stopped (S16), and the secondary material is secondary. The outer transfer roller 24 is separated (S17).

  When the operator detects that the jam processing has been completed (YES in S18), the head of the toner image on the intermediate transfer belt 5 is positioned upstream of the post charger 26 (S19). Circulation is resumed (S20).

  The following is the same as in the case of patch detection control. That is, the intermediate transfer belt 5 circulates at a slower speed than the normal image formation (S21), and the charging device 26 charges the untransferred toner image on the intermediate transfer belt 5 from the top with a negative corona discharge higher than normal. (S22). In the belt cleaning device 30, the upstream side conductive fur brush 31 is set to positive polarity, the downstream side conductive fur brush 32 is set to negative polarity, and the charging state is opposite to that of normal image formation. Clean the toner image. The upstream conductive fur brush 31 electrostatically moves normal negatively charged toner particles contained in the toner image to the flock and removes them from the intermediate transfer belt 5. The conductive fur brush 32 on the downstream side contacts the positively charged conductive fur brush 31 to remove toner particles charged to the positive polarity from the intermediate transfer belt 5.

  On the other hand, if the normal image formation (NO in S12) continues normally (NO in S15), the secondary transfer outer roller 24 is brought into contact with the intermediate transfer belt 5 (S30), and the second transfer to the recording material P is performed. Next transfer is performed. The intermediate transfer belt 5 circulates at a normal speed (S31), the post charger 26 is applied with a normal adjustment bias voltage (S32), and the conductive fur brushes 31 and 32 of the belt cleaning device 30 are charged normally. The state is set (S33).

By the way, in the return sequence operation after the jam processing, all separated color toner images are overlapped, and a toner image that is wider than the patch and has an amount of toner much larger than the patch is carried on the intermediate transfer belt 5. The toner loading amount of the intermediate transfer belt 5 reaches 1.5 to 2.0 mg / cm ² at the maximum, and the belt cleaning device 30 has to remove a large amount of toner as compared with the patch detection processing.

  In the first embodiment, by the above-described various settings different from the normal image formation, it is possible to process a toner amount that is significantly larger than that of the normal image formation by the same belt cleaning device 30. As one of them, the post charger 26 negatively charges the toner image on the intermediate transfer belt 5 to increase the electric field dependency of electrostatic cleaning.

  However, when the toner band charge amount is increased, the mirror force on the intermediate transfer belt 5 is increased. Therefore, the toner band charge amount is controlled so as not to exceed the limit value of the electrostatic cleaning capability of the belt cleaning device 30. There is a need.

  In order to assume a return sequence operation after the jam processing, a toner image was formed on the intermediate transfer belt 5 so as to overlap each separation color maximum density solid image in the full color mode and passed through the post charger 26. FIG. 4 shows a comparison between a case where an adjustment bias voltage for normal image formation is applied to the post charger 26 and a case where a high adjustment bias voltage applied to a return sequence operation after jam processing is applied.

  As shown in FIG. 4, the applied voltage of the post charger 26 is intended to negate the toner band charge amount of the toner image, so only a DC voltage is desirable. That is, the neutralization ability is reduced as compared with the application of the AC bias voltage, and the ratio of the polarity reversal particles and uncharged particles can be reduced to increase the toner band charge amount of the toner image.

  As shown in FIG. 5, when the applied voltage of the post charger 26 is increased to the negative polarity side, the toner band charge amount (toner charge amount) of the toner image on the intermediate transfer belt 5 irradiated with the corona discharge charged particles is Monotonically increasing.

  However, as shown in FIG. 6, if the toner band charge amount exceeds −50 μC / mg, the limit value of the total charge amount of electrostatic cleaning is exceeded, and the amount of toner passing through the belt cleaning device 30 increases. End up. Therefore, the toner band charge amount of the toner image that has passed through the post charger 26 needs to be set to −20 to −40 μC / mg.

In FIG. 6, as an index of the electrostatic cleaning performance of the belt cleaning device 30, the fog density that is the amount of toner on the intermediate transfer belt 5 that has passed through the belt cleaning device 30 is measured. The electrostatic cleaning performance changes according to the fur brush current of the conductive fur brush 31 adjusted by the cleaning bias voltage, and high electrostatic cleaning performance can be used in a low fog density range. The amount of applied toner on the intermediate transfer belt 5 is 0.3 mg / cm ^2, and the applied voltage of the post charger 26 is varied to induce the average toner band charge amount of the toner image to each value of −50 to −10 μC / mg. ing.

  As shown in FIG. 6, in particular, when the toner band charge amount is −20 to −30 μC / mg, a wide latitude of fog density with respect to the fur brush current can be secured, and the electrostatic cleaning performance of the belt cleaning device 30 is improved. However, if it is out of this range, the toner recovery rate by the belt cleaning device 30 is lowered if the toner band charge amount is too small or too large.

  When the toner band charge amount is too large, the toner particle adsorption force (so-called mirror power) to the intermediate transfer belt 5 becomes stronger than the electrostatic adsorption force to the conductive fur brush 31 and the electrostatic cleaning performance is deteriorated. If the toner band charge amount is too large, the cleaning bias voltage required for electrostatic cleaning becomes high, and the toner particles that are positively charged in contact with the conductive fur brush 31 to which a high voltage is applied increase.

  On the other hand, when the toner charge amount is too small, the electrostatic adsorption force of the toner particles is insufficient and the toner is not attracted to the conductive fur brush 31. Even in the case where the ratio of the toner particles charged to the opposite polarity and the uncharged toner particles contained in the toner image is large and the average toner band charge amount is small, the conductive fur brush 31 charged to the positive polarity is sufficiently recovered. The rate cannot be secured.

  However, all the toner particles that could not be collected by the upstream conductive fur brush 31 can be collected by the downstream conductive fur brush 32. At this time, the fur brush current of the downstream conductive fur brush 32 was 20 μA, and the fog density reflectance after passing through the fur brush 32 was 0.02 or less.

  The image forming apparatus 100 according to the first embodiment performs electrostatic cleaning using a post charger 26 upstream of the secondary transfer portion T <b> 2 that transfers a toner image from the intermediate transfer belt 5 to the recording material P and a conductive fur brush 31. A belt cleaning device 30 for performing

  Then, at the time of patch detection control on the intermediate transfer belt 5 and at the time of return operation after completion of jam processing, an untransferred toner image on the intermediate transfer belt 5 is transferred to a desired toner by the post charger 26 upstream of the secondary transfer portion T2. Induction to the charge amount. The secondary transfer outer roller 24 is detached from the intermediate transfer belt 5, and a cleaning bias voltage having a polarity opposite to that during normal image formation is applied to the conductive fur brush 31 to statically remove the untransferred toner image on the intermediate transfer belt 5. Clean the battery. As a result, a large amount of toner particles constituting the untransferred toner image can be collected by the same conductive fur brushes 31 and 32 as in the normal image formation.

  Further, as shown in FIGS. 4 to 6, the toner band charge amount (applied voltage of the post charger 26) and the electrostatic cleaning voltage (applied voltage of the bias rollers 33 and 34) are optimized, thereby further improving the efficiency. Thus, the untransferred toner image can be electrostatically cleaned.

  Further, the untransferred toner image of the portion that has stopped after passing through the post charger 26 when the jam occurs does not have the optimum band charge distribution shown in FIG. Therefore, in the return operation after the jam processing is completed, the intermediate transfer belt 5 is moved backward until the head of the untransferred toner image moves upstream of the post charger 26 (S19: FIG. 3). The non-transferred toner image is passed through the post charger 26 after switching the adjustment bias voltage, and the non-transferred toner image is guided to the optimum band charge distribution to improve the electrostatic cleaning property.

In addition to the return operation after the jam processing (YES in S18: FIG. 3), the patch detection control (YES in S12: FIG. 3) for forming the density patch on the intermediate transfer belt 5 also cleans the untransferred toner image. Cleaning control is applied. In the patch detection control, unlike the return operation after the jam processing is completed, the toner applied amount on the intermediate transfer belt is 0.5 to 0.6 mg / cm ^2, which is affected by the deterioration of the developer, but is substantially constant. It is also frequent. For this reason, the setting of the charging condition and electrostatic cleaning condition of the untransferred toner image is easier than the return operation after the jam processing is completed.

  Further, in the returning operation after the jam processing, a toner image with a loading amount greater than normal must be collected by electrostatic cleaning, so that the circulation speed of the intermediate transfer belt is made slower than that during normal image formation (S21: FIG. 3). Thus, the conductive fur brush 31 has a cleaning effect by adding a mechanical cleaning capability by scraping and scraping to an electrostatic cleaning capability by voltage switching.

  That is, the surface charge density is determined by setting the circulation speed of the intermediate transfer belt 5 to α times (0 <α <1) the speed v during normal image formation for the return operation and the patch detection control after the jam processing is completed. Becomes 1 / α times the normal value. The same is reflected in the charging polarity. That is, not only the electrostatic cleaning efficiency in the belt cleaning device 30 is improved, but also the non-contact charging efficiency in the post charger 26 upstream of the secondary transfer portion T2.

Second Embodiment
FIG. 7 is a flowchart of the control of the second embodiment, and FIG. 8 is an explanatory diagram of the relationship between the applied toner amount and the electrostatic cleaning performance. In the second embodiment, when the amount of applied toner is large in the control of the image forming apparatus 100 of the first embodiment, a negative cleaning bias voltage is applied to the conductive fur brush 32 on the downstream side. Since other configurations and controls (S15 to S22: FIG. 7) are the same as those in the first embodiment, detailed description thereof is omitted.

  In the first embodiment, both the conductive fur brushes 31 and 32 are charged to the positive polarity, and the negatively charged toner particles on the intermediate transfer belt 5 are collected. The conductive fur brushes 31 and 32 were applied with a voltage in a range that did not cause a discharge to reverse the charged state of the toner particles on the intermediate transfer belt 5. This voltage is, for example, a voltage applied to the conductive fur brush 32 during normal image formation.

  That is, since the cleaning bias voltage applied to the upstream conductive fur brush 31 is made relatively low to prevent the toner particles from becoming positive on the intermediate transfer belt 5, the total charge amount collected by the conductive fur brush 31 is reduced. The limit value of was relatively low. The negative toner particles that passed through the conductive fur brush 31 beyond the limit value of the total amount of collected charges were electrostatically cleaned by the conductive fur brush 32 charged to the positive polarity on the downstream side.

On the other hand, in the second embodiment, as shown in FIG. 8, when the applied toner amount is less than 1.0 mg / cm ² (YES in S41), the same cleaning condition 2a as in the first embodiment is selected. (S42). However, when the applied toner amount is 1.0 mg / cm ² or more (NO in S41), a cleaning condition 2b different from the first embodiment is selected (S43).

  In the cleaning condition 2b, the cleaning bias voltage applied to the upstream conductive fur brush 31 is made relatively high, and the limit value of the collected total charge amount of the conductive fur brush 31 is made relatively high. On the other hand, the toner particles are likely to be positive on the intermediate transfer belt 5, so that the cleaning toner voltage applied to the downstream conductive fur brush 32 can be made negative so that the positive toner particles can be electrostatically cleaned. (S43).

  As shown in FIG. 2, when the completion of the jam processing is detected, the control unit 40 evaluates the image data of each separated color used for image formation, adds the amount of toner of each separated color, and adds the amount of toner on the intermediate transfer belt 5. The amount of applied toner is calculated. When the applied toner amount exceeds a preset threshold value, the cleaning bias power supply 43 is connected to the bias roller 33 and the cleaning bias power supply 44 is connected to the bias roller 34, contrary to the normal image formation. Connect to.

  Then, the upstream conductive fur brush 31 is charged with a positive polarity voltage higher than that of the first embodiment, and strongly strengthens the toner particles of the untransferred toner image that is negatively charged by the post charger 26. Adsorb. On the other hand, since the toner particles that are positively contacted with the conductive fur brush 31 increase, the conductive fur brush 32 on the downstream side adsorbs the positively charged toner particles that are negatively charged.

As shown in FIG. 8, the relationship between the amount of toner applied to the intermediate transfer belt 5 and the electrostatic cleaning performance of the belt cleaning device 30 was examined. The image forming conditions in the image forming portions Y, M, C, and K shown in FIG. 1 are adjusted to induce the toner band charge amount on the intermediate transfer belt 5 after passing through the post charger 26 to −35 μC / mg. A toner image having an applied amount of 0.2 to 2.2 mg / cm ² was formed.

  The intermediate transfer belt 5 was passed through the belt cleaning device 30 with the secondary transfer outer roller 24 being separated, and the ratio of the fog density reflectance before and after the passage was determined to evaluate the cleaning performance of the belt cleaning device 30.

As shown in FIG. 7, when the applied toner amount is 1.0 mg / cm ² or more, a sufficient electrostatic cleaning effect by the belt cleaning device 30 cannot be obtained. Even if a fur brush current equivalent to the total charge of the toner image passing every second is obtained by applying a high positive cleaning bias voltage, a portion where the fur brush current is not small is spent on the positive reversal of the toner particles on the intermediate transfer belt. It will be done.

Explaining in terms of phenomena, discharge through toner particles is likely to occur at the nip between the conductive fur brush 31 to which a high cleaning bias voltage is applied and the intermediate transfer belt 5. Since the toner particles become positive by discharge, when the applied toner amount is 1.0 mg / cm ² or more, the toner cannot be collected only by the positively charged conductive fur brush 31.

Therefore, in the second embodiment, when the applied toner amount is detected to be 1.0 mg / cm ² or more, the downstream conductive fur brush 32 has a negative polarity opposite to that of the upstream conductive fur brush 31. Apply the cleaning bias voltage.

The toner image that has passed through the conductive fur brush 31 charged to the positive polarity is estimated to be 10% or less of 2.2 mg / cm ² from FIG. 7, and the amount of applied toner is estimated to be 0.5 mg / cm ² or less. Is done. Therefore, by applying a relatively low negative polarity cleaning bias voltage to the downstream conductive fur brush 32, positively reversed toner particles can be efficiently recovered without causing negative reversal again. By collecting the positive toner that could not be collected by the upstream conductive fur brush 31, the total cleaning performance of the belt cleaning device 30 is dramatically improved.

  In this way, the toner image of any loading amount can be electrostatically cleaned efficiently by optimizing the toner charge amount and the applied voltage for electrostatic cleaning.

<Correspondence with Invention>
The image forming apparatus 100 includes an intermediate transfer belt 5 on which a surface carrying a charged toner image moves, and a secondary transfer outside that transfers the toner image from the surface using a voltage having a polarity opposite to the charging polarity of the toner image. A roller 24 and a conductive fur brush 31 that contacts the surface downstream of the secondary transfer outer roller 24 and is applied with a voltage having the same polarity as the charging polarity to remove residual toner on the surface. When the toner image is not transferred from the surface by the secondary transfer outer roller 24, a voltage having a polarity opposite to the charging polarity is applied to the conductive fur brush 31 to remove the untransferred toner on the surface. A post charger 26 is provided that charges the untransferred toner on the upstream side of the conductive fur brush 31 during the non-transfer, and shifts the charged state of the untransferred toner to the charging polarity side.

  The post charger 26 is disposed upstream of the secondary transfer outer roller 24 and also serves as means for adjusting the charged state of the toner image to be transferred by the secondary transfer outer roller 24. The controller 40 identifies the non-transfer time, reverses the polarity of the voltage applied to the conductive fur brush 31, and increases the charging output of the secondary transfer outer roller 24.

  The cleaning member of the image forming apparatus 100 is a conductive fur brush 31 that slidably rubs the surface of the rotationally driven conductive flocks. A conductive fur brush 32 to which a voltage having a polarity opposite to the charged polarity is applied when the transfer residual toner is removed by rubbing the surface on the downstream side of the conductive fur brush 31 is provided.

  The voltage applied to the conductive fur brush 31 at the time of non-transfer has a voltage value in a lower range than the cleaning efficiency starts to decrease with the increase of the cleaning current.

  The controller 40 identifies a toner loading amount of the untransferred toner at the time of non-transfer, and when the toner loading amount is larger than a predetermined threshold value, than when the toner loading amount is smaller than the threshold value. The voltage applied to the conductive fur brush 31 is increased, and a voltage having the same polarity as the charging polarity is applied to the conductive fur brush 32.

  The intermediate transfer belt 5 is primary-transferred by superimposing a plurality of color toner images, and the post charger 26 is a corona discharge device that applies a voltage obtained by superimposing an AC voltage on a DC voltage to align the charging potentials of the toner images of a plurality of colors. It is. The control unit 40 applies a DC voltage in a range in which the peak of the toner band charge amount of the untransferred toner is induced to −20 to −30 μC / mg, which is higher than that in the case where the charging potential is equalized during the non-transfer. 26 is applied.

  The non-transfer time is a return operation after the jam processing of the recording material P on which the toner image is secondarily transferred from the intermediate transfer belt 5 is completed. When the completion of the jam processing is detected, the control unit 40 starts removing the untransferred toner after positioning the head of the toner image to the upstream side of the post charger 26.

  The control unit 40 makes the circulation speed of the intermediate transfer belt 5 at the time of non-transfer slower than that at the time of normal image formation.

  During the non-transfer, the color patch for adjusting the density of the toner image is primarily transferred to the intermediate transfer belt 5 and removed by the conductive fur brush 31 as the untransferred toner.

  The image forming apparatus 100 removes from the surface of the intermediate transfer belt 5 an untransferred toner image that is charged to the same polarity as the charged polarity of the toner image as a whole. The untransferred toner image is exposed to corona discharge to which a bias voltage having the same polarity as the charging polarity is applied, and toner particles charged to a polarity opposite to the charging polarity contained in the untransferred toner image are reduced. Then, a non-transferred toner image is electrostatically cleaned by rubbing the surface of a conductive fur brush 31 that is driven to rotate by applying a voltage having a polarity opposite to the charging polarity.

1 is a schematic explanatory diagram of a configuration of an image forming apparatus according to a first embodiment. It is a typical explanatory view of a configuration of a belt cleaning device. 6 is a flowchart of an intermediate transfer belt cleaning control using a belt cleaning device. FIG. 6 is an explanatory diagram of a charged state of a toner image primarily transferred to an intermediate transfer belt. It is explanatory drawing of the relationship between a charger application voltage and a toner charge amount. FIG. 6 is an explanatory diagram of a relationship between toner charge amount and cleaning performance. It is a flowchart of control of a 2nd embodiment. FIG. 6 is an explanatory diagram of a relationship between a toner loading amount and electrostatic cleaning performance.

Explanation of symbols

5 Image carrier (intermediate transfer belt)
1Y, 1M, 1C, 1K Photosensitive drums 2Y, 2M, 2C, 2K Exposure devices 4Y, 4M, 4C, 4K Development devices 6Y, 6M, 6C, 6K Primary transfer rollers 7Y, 7M, 7C, 7K Cleaning devices 16, 17 Cassette 21 Driving roller 22 Tension roller 23 Secondary transfer inner roller 24 Transfer device (secondary transfer outer roller)
25 Concentration detection sensor 26 Charging device (post charger)
30 Belt cleaning device 31, 32 Cleaning member (conductive fur brush)
33, 34 Bias roller 35, 36 Cleaning blade (scraper)
40 Control means (control unit)
43, 44, 47, 48 Cleaning bias power supply 45 Adjustment bias power supply P Recording material T1 Primary transfer portion T2 Secondary transfer portion

Claims (7)

An image carrier on which a surface carrying a charged toner image moves;
A transfer device for transferring the toner image from the surface using a voltage having a polarity opposite to the charging polarity of the toner image;
A first cleaning member that contacts the surface on the downstream side of the transfer device and is applied with a voltage having the same polarity as the charging polarity to remove residual toner on the surface ;
A second cleaning member that contacts the surface downstream of the first cleaning member and is applied with a voltage having a polarity opposite to the charging polarity to remove residual toner on the surface;
Transfer operation in which the toner image on the image carrier is transferred from the surface by the transfer device, and non-transfer in which the surface moves without the toner image on the image carrier being transferred from the surface by the transfer device and a performing unit capable of executing the operation,
When performing the non-transfer operation, in the image forming apparatus for removing the toner on the image carrier from the surface by applying a voltage having a polarity opposite to the charging polarity to the first cleaning member,
Charging means for charging the toner on the image carrier to the charging polarity upstream of the transfer device ;
When performing the non-transfer operation, and having a control means for increasing the charging output of the charging means than when performing the transfer operation,
When the non-transfer operation is executed, the control unit identifies a toner application amount of the toner on the image carrier, and when the toner application amount is smaller than a predetermined threshold value, A voltage having a polarity opposite to that of the charging polarity is applied to the cleaning member 2, but when the amount of applied toner is larger than a predetermined threshold, the amount of applied toner is smaller than when the amount of applied toner is smaller than the threshold. An image forming apparatus , wherein the voltage applied to the first cleaning member is increased and a voltage having the same polarity as the charging polarity is applied to the second cleaning member . The first cleaning member is an upstream conductive fur brush that slidably rubs the surface of electrically driven flocks that are driven to rotate,
The second cleaning member rubs the surface on the downstream side of the upstream conductive fur brush and applies a voltage having a polarity opposite to the charging polarity when removing the transfer residual toner during the transfer operation. the image forming apparatus according to claim 1, characterized in that the downstream conductive fur brush is. 3. The image according to claim 2 , wherein the voltage applied to the upstream conductive fur brush during the non-transfer operation is a voltage value in a lower range than the cleaning efficiency starts to decrease as the cleaning current increases. Forming equipment. The image carrier is an intermediate transfer belt on which toner images of a plurality of colors are superimposed and primarily transferred,
Before SL charging means is a corona discharge device for aligning the charging potential of the toner image of the plurality of colors is applied the voltage obtained by superimposing an AC voltage on a DC voltage,
In the non-transfer operation, the control means induces a peak of the toner band charge amount of the toner on the image carrier to be −20 μC / mg or more and −30 μC / mg or less, which is higher than the case where the charging potentials are made uniform. range image forming apparatus according to any one of claims 1 to 3 DC voltage, characterized in that for applying the corona discharge apparatus. The non-transfer operation is a return operation after completion of jam processing of a recording material on which a toner image is secondarily transferred from the intermediate transfer belt,
Upon detecting completion of the jam processing, the control means starts the non-transfer operation after positioning the head of the toner image to the upstream side of the corona discharge device and removes the toner on the image carrier. The image forming apparatus according to claim 4 . Wherein, the non-transfer operation when the intermediate transfer belt according to claim 4 or 5 image forming apparatus according to circulation rate characterized by slower than in the normal image formation. Wherein during non-transfer operation, and transferring the primary color patches on the intermediate transfer belt for adjusting the concentration of the toner image, and the second cleaning member and the first cleaning member as a toner on the image bearing member The image forming apparatus according to claim 4 , wherein the image forming apparatus is an operation for removing the image.

Images