JP2008233152A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus capable of preventing the lowering of printing speed caused by toner refreshing operation. <P>SOLUTION: The image forming apparatus has a plurality of image forming units including a photoreceptor and a developing means. In a first mode, an image is formed by bringing a plurality of photoreceptors into contact with a conveying belt. In a second mode, an image is formed by separating the photoreceptor A from the conveying belt and bringing the photoreceptor B into contact with the conveying belt. When judging that the refreshing operation is performed to the photoreceptor A, the refreshing operation is performed by separating the photoreceptor A from the conveying belt, and simultaneously the image is formed by bringing the photoreceptor B into contact with the conveying belt. In the refreshing operation, developer is forcibly stuck to the photoreceptor, and also the developer remaining on the photoreceptor is removed from the photoreceptor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that efficiently refreshes toner in an electrophotographic printer or the like that obtains a visualized image by superimposing a plurality of colors.

  Conventionally, in an image forming apparatus using an electrophotographic process, an electrostatic latent image corresponding to image data is formed on a photoreceptor, and then the electrostatic latent image is developed by a developing device to form a toner image. The toner image is transferred to a recording medium to form an image. The developing device includes a developing roller that faces the photoconductor, and the electrostatic latent image on the photoconductor is developed with toner at the development position. The developing device includes a developing sleeve that supplies toner to the surface of the photoreceptor, a toner supply device that supplies toner to the developing sleeve, and the like. When the photosensitive member on which the electrostatic latent image is formed passes through a portion facing the developing device to which a bias voltage is applied, the toner from the developing sleeve adheres to the electrostatic latent image, and the electrostatic latent image The image is visualized. After the transfer, residual toner remaining on the photoconductor is removed by a cleaning unit.

  In recent years, color printers often print originals in which color pages and monochrome pages are mixed. In one print job, the state is switched between a state where the Bk (black) M (magenta) C (cyan) Y (yellow) photoreceptor is pressed against the conveying belt and a state where only the Bk photoreceptor is pressed. FIG. 6 shows a configuration of a print engine of a conventional image forming apparatus. FIG. 6A is a diagram showing the configuration of an intermediate transfer belt type tandem color engine, in which a black image forming unit is arranged on the side close to the secondary transfer. FIG. 6B shows a black image forming unit arranged on the side farthest from the secondary transfer. FIG. 6C is a diagram showing the configuration of a direct transfer belt type tandem color engine, in which a black image forming unit is disposed on the belt near the sheet separation unit. FIG. 6D shows a black image forming unit arranged on the side farthest from the sheet separating portion on the belt.

  By the way, if a printing pattern having a low document printing rate is continued for a long period of time, the amount of toner that can be easily selected and developed in the developing device increases, and the image density decreases. The toner remaining on the developing sleeve without being subjected to the development increases the charge amount due to the bias voltage as the remaining period becomes longer, and causes problems such as fusion between the toners. Such toner is referred to as deteriorated toner. As a result, with the bias voltage applied during normal image formation, the toner is less likely to transfer to the photoreceptor, leading to a decrease in image density.

  In order to recover the deteriorated toner, toner refresh is executed. Apart from the normal operation mode, the quality-degraded toner is forcibly transferred to the peripheral surface of the photosensitive drum and removed, thereby removing the toner on the developing roller facing the peripheral surface of the photosensitive drum in the developing device. Run in refresh mode to refresh with fresh toner. In the refresh mode, the charge on the peripheral surface is adjusted so that toner is applied to substantially the entire surface for a predetermined length in the rotation direction on the peripheral surface of the photosensitive drum. That is, the printing rate is adjusted to 100%. As a result, the toner with reduced charging characteristics that is stuck on the developing roller is transferred to the peripheral surface of the photosensitive drum at a stroke. In the refresh mode, the quality-degraded toner transferred to the photosensitive drum is not transferred onto the paper but is collected by a predetermined cleaning device. By performing refresh mode operation, quality-deteriorated toner that has stagnated on the peripheral surface of the developing roller is updated with fresh toner in the developing device and refreshed, eliminating image density reduction and fogging. Is done.

  Alternatively, when the specified number of copies is reached, the development bias is temporarily increased, and development is performed with a development bias higher than the setting until the development sleeve makes one revolution. The charged toner is increased more than necessary, and the deteriorated toner whose sufficient image density cannot be obtained is released. By renewing the toner on the developing sleeve and then returning it to the normal setting of the developing bias, a stable image quality can always be obtained. Alternatively, when non-image formation is performed, the toner is ejected onto the photoconductor to consume the toner, and the toner on the photoconductor is collected by the cleaning unit, thereby reducing and reducing image density reduction and image fogging during image formation. Alternatively, an electrostatic latent image is formed on the photosensitive member by a printing pattern having a high original printing ratio such as solid black, a large amount of toner is ejected on the photosensitive member side, and a toner image is formed on the photosensitive member. Is transferred to a recording medium, and toner is consumed. Below are some examples of prior art related to this.

  The “image forming apparatus” disclosed in Patent Document 1 performs a toner refresh process according to the degree of deterioration of toner on a developing sleeve of a copying machine or a printer. The photosensitive member is controlled to have a substantially zero potential, and a bias voltage having the same polarity as the toner is applied to the developing sleeve. Toner from the developing sleeve adheres to the photoreceptor, and a predetermined reference image is formed. The charge on the photoreceptor associated with the formation of the reference image is accumulated in the capacitor. The accumulated charge amount is measured by the control device. The degree of toner deterioration is determined based on the charge amount. Based on the determination result, a bias voltage higher than that during normal image formation is applied to the developing sleeve, and deteriorated toner on the developing sleeve is discharged onto the photoreceptor.

  The “image forming apparatus” disclosed in Patent Document 2 prevents image defects such as black spots by preventing defects due to dielectric breakdown from occurring on the surface of the photoreceptor. A polishing roller is disposed downstream of the transfer roller in the rotation direction of the photosensitive drum, and rubs the photosensitive drum. A cleaning blade is disposed downstream of the polishing roller in the rotation direction of the photosensitive drum, and removes toner remaining on the photosensitive drum. If the electrostatic latent image formed on the photosensitive drum is not used as a toner image, and a refresh process is performed to refresh the developer, the polarity of the charged charge of the toner is opposite to that of the toner. Is applied to the polishing roller.

The “image forming apparatus” disclosed in Patent Document 3 can normally operate in the refresh mode while suppressing damage to the photoreceptor due to dielectric breakdown. By supplying toner from the developing device to the photosensitive drum on which the electrostatic latent image is formed, a visible image along the electrostatic latent image is formed on the peripheral surface of the photosensitive drum. The operation in the refresh mode for refreshing the developer according to the deterioration of the developer in the developing device can be set separately from the operation in the normal mode. The control means for controlling the operation in the refresh mode controls the charge density per unit time of the quality deteriorated toner supplied from the developing device to the peripheral surface of the photosensitive drum.
JP 05-094072 A JP 2005-134776 JP 2006-308672 A

  However, the conventional toner refresh method has the following problems. Since toner refresh is executed during printing, the printing speed is reduced. Color printing is interrupted, the MCY photoreceptor is separated from the conveying belt, a toner refresh operation is performed, a color printing preparation operation is performed, and color printing is resumed, which takes time. In addition to a long processing time for switching between color printing and monochrome printing, the toner refresh operation is performed, so the printing speed is further reduced. Further, when the replacement time of the image forming unit is approaching, if the toner refresh is activated, the photoconductor and the toner are consumed unnecessarily, which may cause the replacement time to be advanced. Further, when the replacement time is approaching, even if refresh is performed, the effect is not so much.

  Depending on the arrangement of the image forming units, there may be a case where a paper gap is opened when switching between color printing and monochrome printing. For example, as shown in FIGS. 6B and 6D, when the CMYBk and the image forming unit are arranged in the order from the secondary transfer, the Bk image passes over the YMC image forming unit. For this reason, the YMC photoreceptor cannot be brought into pressure contact or separated during passage. Therefore, the toner refresh cannot be executed immediately. Alternatively, the print mode cannot be switched quickly after the toner refresh.

  An object of the present invention is to solve the above-described conventional problems and prevent a decrease in printing speed due to a toner refresh operation in an image forming apparatus.

  In order to solve the above problems, in the present invention, the image forming apparatus includes a plurality of image forming units including a developing unit that supplies toner to a latent image formed on the surface of the photoconductor, and a visible image on the photoconductor. A transfer means for transferring the toner to the transport body, a refresh control means for forcing a toner to adhere to the photoreceptor and a refresh operation for removing the toner remaining on the photoreceptor from the photoreceptor, and a plurality of photoreceptors A mode control unit that switches between a first mode in which image formation is performed in contact with the conveyance body and a second mode in which image formation is performed by separating the photosensitive body A from the conveyance body and the photosensitive body B is in contact with the conveyance body; In response to the determination result of executing the refresh operation, the image forming in the second mode is performed simultaneously with the determination means for determining whether or not to execute the refresh operation. And the configuration and means for controlling the.

  Alternatively, whether or not to perform a refresh operation on the photoconductor A after an instruction to switch to the first mode and input an image is input during image formation in the second mode and before switching to the first mode. Depending on the determination means for determining whether or not to execute the refresh operation, the refresh operation is started at the timing when the refresh operation is completed before the image is being formed in the second mode and before switching to the first mode. Means for controlling to do.

  The determination means determines that the refresh operation is to be executed when the unit drive time or the toner consumption amount per unit drive amount of the image forming unit of the photoreceptor A is less than a predetermined amount from the refresh operation executed last time to the present time. Means are provided. The unit driving time is one rotation time of the photoconductor A. The unit driving amount is one rotation distance of the photoconductor A. Further, the determination means includes means for determining that the refresh operation is not executed when the total drive time of the image forming unit of the photosensitive member A exceeds a predetermined time. The total drive time is the cumulative rotation time of the photoconductor A.

  The determination means includes means for determining that the refresh operation is not executed when the total drive amount of the image forming unit of the photoreceptor A exceeds a predetermined amount. The total driving amount is the cumulative rotation distance of the photoconductor A. The determining means includes means for determining that the refresh operation is not executed when the total amount of toner consumed by the developing means corresponding to the photoreceptor A exceeds a predetermined amount. The plurality of image forming units are arranged in tandem along the rotation direction of the transport body.

  The image forming unit of the photosensitive member B further includes a secondary transfer unit that re-transfers the visible image transferred onto the carrier to the transfer medium at the secondary transfer position. It is located on the upstream side and at a position closest to the secondary transfer position among the plurality of photoconductors. The image forming unit is configured to be detachable integrally with the image forming apparatus main body. The image forming unit of the photoconductor B is disposed at a position closest to the fixing unit among the plurality of photoconductors in the rotation direction of the transport body.

  With the above-described configuration, the image forming apparatus can quickly execute toner refresh, and can immediately start the next printing after toner refresh.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to FIGS.

  The first exemplary embodiment of the present invention is an image forming apparatus that performs image forming by bringing the photosensitive member B into contact with the conveyance belt at the same time as performing the refresh operation by separating the photosensitive member A from the conveyance belt.

  Since the basic configuration of the image forming apparatus according to the first exemplary embodiment of the present invention is the same as that of a conventional apparatus, description of the apparatus configuration is omitted. The image forming unit may have an AIO unit configuration that can be integrally attached to and detached from the image forming apparatus main body. FIG. 1 is a flowchart illustrating a procedure of toner refresh processing in the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 2 is a flowchart showing a procedure of toner refresh determination data calculation processing. FIG. 3 is a flowchart showing the procedure of the toner refresh determination process. FIG. 4 is a diagram illustrating a state in which toner refresh is performed in a configuration in which the image forming unit of the photosensitive member B is disposed closest to the secondary transfer position on the upstream side of the secondary transfer position.

  The entire processing procedure will be described with reference to FIG. In step 1, it is checked whether 1 ms has elapsed. If not, wait. If it has elapsed, the other process 1 is executed in step 2. In step 3, toner refresh processing is executed. In step 4, the other process 2 is executed, and the process returns to step 1.

  The procedure of the toner refresh process will be described with reference to FIG. In step 5, a toner refresh determination data calculation process is executed. The toner refresh determination data calculation process calculates various data necessary for determining whether to perform toner refresh simultaneously with monochrome printing. In step 6, a toner refresh determination process is executed. In the toner refresh determination process, it is determined whether to perform toner refresh simultaneously with monochrome printing based on the calculated various data. In step 7, toner refresh execution processing is performed. In the toner refresh execution process, the toner refresh is actually executed during monochrome printing based on the determination result.

  In the present embodiment, an example in which toner refresh is executed simultaneously with monochrome printing in which the transfer belt and the black photosensitive member are always in pressure contact with each other will be described, but the present invention is not limited to monochrome printing. A configuration may be adopted in which the image forming units that are separated are refreshed with toner simultaneously with the printing using only the toner of the color corresponding to the photoconductor that is always in pressure contact.

  Next, a processing procedure for toner refresh determination data calculation will be described with reference to FIG. In step 11, it is confirmed whether the image forming unit is being driven. A specific example in which the image forming unit is being driven will be described later. If not, go to step 14. If the image forming unit is being driven, the drive amount or drive time is accumulated in step 12. The driving time is assumed to be the time when the photosensitive member is rotating, but may be the time when the developing roller is rotating or the time when the developing bias and the charging charger are on. The driving amount is a distance that the photosensitive member rotates, a distance that the developing roller rotates, or the like.

  In step 13, the accumulated driving amount or driving time is stored in the memory. If the time during which the toner is rotating is important as a factor for performing the toner refresh, the refresh determination is performed based on the rotation time. In step 14, in order to grasp the amount of toner consumed by the printing operation by driving the image forming unit, it is confirmed whether or not printing for one page has been completed. If printing has not ended, the process ends. When printing is completed, the toner amount consumed by the image forming unit is accumulated in step 15. In step 16, the accumulated toner consumption is stored in the memory.

  In this embodiment, the toner consumption amount is described as being accumulated at the timing of the end of printing for one page. However, it may be the timing of the end of image formation for each color, and the toner consumption amount periodically during image formation. May be confirmed. This process is basically performed in units of image forming units, but the calculation process may be performed for the entire image forming units that are separated from each other.

  Next, a processing procedure for toner refresh determination will be described with reference to FIG. In step 21, it is confirmed whether there is a monochrome printing request for the next page. If not, the process ends; In this embodiment, a process for confirming whether there is a monochrome printing request in which the transfer belt and the black photosensitive member are always in pressure contact will be described. However, the present invention is not limited to monochrome printing. Processing for confirming the presence / absence of a print request using only the toner of a color corresponding to the photoconductor that is always in pressure contact may be used.

  In step 22, it is determined whether toner refresh is necessary from the accumulation of drive amount or drive time and toner consumption amount. The cumulative driving amount or driving time is T, the toner consumption amount is M, the driving amount or driving time in printing corresponding to A4 is P (fixed value), and the toner refresh determination threshold (toner consumption amount in printing corresponding to A4) Is set to S (fixed value), and if the condition of S / P> M / T is satisfied, it is determined that the toner refresh is executed. Even if this inequality is not satisfied, if the condition of S / P> (M / T + α) is satisfied, it may be determined that the toner refresh is executed. α is a margin for condition determination.

  In addition to the above determination, when the replacement time of the image forming unit is approaching, it may be determined not to perform the determination process or to forcibly execute the toner refresh. Specifically, there are the following examples. When the total rotation time of the photoconductor in the image forming unit exceeds a certain value, it is determined that the replacement time is approaching. When the total rotation distance of the photoconductor in the image forming unit exceeds a certain value, it is determined that the replacement time is approaching. When the total toner consumption in the image forming unit exceeds a certain value, it is determined that the replacement time is approaching. In step 23, the determination result is stored in the memory.

  Next, the toner refresh execution process will be described with reference to FIG. In step 24, it is confirmed whether or not monochrome printing has actually started. End if not started. If it has been started, in step 25, it is confirmed whether or not toner refresh is performed with reference to the determination result stored in the toner refresh determination process. If “No”, the process ends. If “Yes”, in step 26, charging, exposure, development, and transfer are executed and toner refresh is executed in the same manner as in normal printing.

  Next, referring to FIG. 4, a state in which the toner refreshing is executed with the configuration in which the image forming unit of the photoconductor B is disposed closest to the secondary transfer position on the upstream side of the secondary transfer position. explain. As shown in FIG. 4A, during printing with only the black photoconductor, the other photoconductor is separated from the transfer belt and toner refresh is executed. When the toner refresh is completed, as shown in FIG. 4B, all the photosensitive members are brought into pressure contact with the transfer belt, and printing preparation is started. As shown in FIG. 4C, color printing of the next page can be started without a gap between sheets. In the case of the direct transfer method, toner refresh is executed in the same manner. At this time, the image forming unit of the photoreceptor B is disposed closest to the fixing unit.

  Note that parameters such as HV in each operation may be different from or the same as those during normal printing. Further, the image pattern of the visible image formed on the photosensitive member is a solid image pattern, but the image pattern is not limited to this. Such image data may be used as long as the mechanism refreshes only the area that needs to be consumed. The toner refresh is basically executed only for the image forming unit that needs to be refreshed. However, the image forming unit that is spaced apart may be refreshed. The width of the image in the main scanning direction is the maximum area width, but it may be a pattern in which only the area to be consumed is imaged. The actual operation time is the time taken to visualize an image pattern corresponding to the amount of toner that is insufficient.

  As described above, in the first exemplary embodiment of the present invention, the image forming apparatus performs the refresh operation by moving the photosensitive drum A away from the conveyance belt, and at the same time performs image formation by bringing the photosensitive drum B into contact with the conveyance belt. Therefore, the toner refresh can be performed quickly, and the next printing can be started quickly after the toner refresh.

  In the second embodiment of the present invention, after an instruction to form an image by switching to the first mode is input during image formation in the second mode, the photoconductor A is refreshed before switching to the first mode. It is determined whether or not to perform the operation, and refresh is performed at the timing when the refresh operation is completed before the image forming in the second mode and before switching to the first mode according to the determination result that the refresh operation is performed. An image forming apparatus that controls to start an operation.

  Since the basic configuration of the image forming apparatus according to the second exemplary embodiment of the present invention is the same as that of a conventional apparatus, description of the apparatus configuration is omitted. The procedure of the toner refresh process and the procedure of the toner refresh determination data calculation process are the same as those in the first embodiment. FIG. 5 is a flowchart illustrating a procedure of toner refresh determination processing in the image forming apparatus according to the second exemplary embodiment of the present invention.

  The toner refresh determination process will be described with reference to FIG. The requests are stacked on the memory so that a plurality of print requests from the controller can be received. In step 31, it is confirmed whether or not there is a color print request to be performed first among monochrome prints and among the stacked print requests. If not, go to step 32. In this embodiment, a process for confirming whether there is a request for monochrome printing in which the transfer belt and the black photosensitive member are always in pressure contact with each other will be described. However, the present invention is not limited to monochrome printing. Processing for confirming the presence / absence of a print request using only the toner of a color corresponding to the photoconductor that is always in pressure contact may be used.

  In step 32, it is determined whether toner refresh is necessary from the accumulation of drive amount or drive time and toner consumption amount, and the toner refresh execution time is calculated. The toner refresh execution time is a value obtained by converting (preparation operation required for toner refresh execution + image pattern length + post-processing) into time. The toner refresh necessity determination is the same as in the first embodiment. In step 33, the determination result and the toner refresh execution time are stored in the memory.

  Next, the toner refresh execution process will be described with reference to FIG. In step 34, it is confirmed whether or not toner refresh is performed with reference to the determination result stored in the toner refresh determination process. If “no”, the process ends. If “yes”, in step 35, the toner refresh execution time stored in the toner refresh determination process is compared with the time until the next color printing. If it is larger, the process ends. If the toner refresh execution time is shorter, the toner refresh in step 36 is executed. Step 36 is the same as that in the first embodiment.

  As described above, in the second embodiment of the present invention, the image forming apparatus is switched to the first mode after an instruction to switch to the first mode and to form an image is input during image formation in the second mode. Before, it is determined whether or not the refresh operation is to be performed on the photosensitive member A, and the image is being formed in the second mode and before switching to the first mode according to the determination result that the refresh operation is performed. Since the control is made so that the refresh operation is started at the timing when the refresh operation is completed, the toner refresh can be performed quickly, and the next printing can be started promptly after the toner refresh.

  The image forming apparatus of the present invention is optimal as an electrophotographic printer or the like that obtains a visualized image by superimposing a plurality of colors.

3 is a flowchart illustrating a procedure of toner refresh processing in the image forming apparatus according to the first exemplary embodiment of the present invention. 6 is a flowchart illustrating a procedure of toner refresh determination data calculation processing in the image forming apparatus according to the first exemplary embodiment of the present invention. 6 is a flowchart illustrating a procedure of toner refresh determination processing and execution processing in the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 3 is a diagram illustrating a toner refresh processing method in the image forming apparatus according to the first exemplary embodiment of the present invention. 10 is a flowchart illustrating a procedure of toner refresh determination processing and execution processing in the image forming apparatus according to the second exemplary embodiment of the present invention. It is a figure which shows the structure of the tandem color engine of the conventional intermediate transfer belt system and a direct transfer belt system.

Claims (14)

  A plurality of image forming units including a developing unit that supplies toner to a latent image formed on the surface of the photosensitive member, a transfer unit that transfers a visible image on the photosensitive member to the conveying member, and the toner is forcibly applied to the photosensitive member. A refresh control means for executing a refresh operation for removing toner remaining on the photosensitive member from the photosensitive member, a first mode for forming an image by bringing a plurality of photosensitive members into contact with the conveying member, and the photosensitive member A. A mode control unit that switches between a second mode in which image formation is performed by bringing the photosensitive member B into contact with the conveying member away from the conveying member, a determining unit that determines whether or not to perform a refresh operation on the photosensitive member A, and An image forming apparatus comprising: a control unit configured to perform image formation in the second mode at the same time as performing the refresh operation according to a determination result of executing the refresh operation   A plurality of image forming units including a developing unit that supplies toner to a latent image formed on the surface of the photosensitive member, a transfer unit that transfers a visible image on the photosensitive member to the conveying member, and the toner is forced to the photosensitive member. A refresh control means for executing a refresh operation for removing toner remaining on the photosensitive member from the photosensitive member, a first mode for forming an image by bringing a plurality of photosensitive members into contact with the conveying member, and the photosensitive member A. A mode control unit that switches between the second mode in which image formation is performed by bringing the photosensitive member B into contact with the transport body away from the transport body, and during the image formation in the second mode, and subsequently switching to the first mode to form an image. After the instruction is input, before switching to the first mode, a determination unit that determines whether or not to perform a refresh operation on the photosensitive member A, and a determination result that the refresh operation is performed An image forming apparatus characterized by comprising a means for controlling so that the refresh operation until before switching even during the image formation and the first mode in the second mode starts the refresh operation in completed timing.   The determination unit executes the refresh operation when the unit driving time or the toner consumption amount per unit driving amount of the image forming unit of the photoreceptor A is less than a predetermined amount from the refresh operation executed last time to the present time. The image forming apparatus according to claim 1, further comprising a determination unit.   The image forming apparatus according to claim 3, wherein the unit driving time is one rotation time of the photoconductor A.   The image forming apparatus according to claim 3, wherein the unit driving amount is one rotation distance of the photoreceptor A.   6. The determination unit according to claim 1, further comprising a unit that determines that the refresh operation is not executed when a total drive time of the image forming unit of the photoconductor A exceeds a predetermined time. The image forming apparatus according to any one of the above.   The image forming apparatus according to claim 6, wherein the total driving time is a cumulative rotation time of the photoconductor A.   8. The method according to claim 1, wherein the determination unit includes a unit that determines that the refresh operation is not executed when the total drive amount of the image forming unit of the photosensitive member A exceeds a predetermined amount. The image forming apparatus according to any one of the above.   The image forming apparatus according to claim 8, wherein the total driving amount is a cumulative rotation distance of the photosensitive member A.   2. The determination unit according to claim 1, further comprising a unit that determines that the refresh operation is not executed when a total amount of toner consumed by the developing unit corresponding to the photosensitive member A exceeds a predetermined amount. The image forming apparatus according to any one of?   The image forming apparatus according to claim 1, wherein the plurality of image forming units are arranged in tandem along a rotation direction of the transport body.   The image forming unit of the photosensitive member B further includes a secondary transfer unit that re-transfers the visible image transferred onto the transport member to a transfer medium at a secondary transfer position. The image forming apparatus according to claim 1, wherein the image forming apparatus is disposed upstream of a next transfer position and at a position closest to the secondary transfer position among the plurality of photosensitive members. apparatus.   The image forming apparatus according to claim 1, wherein the image forming unit is configured to be detachable integrally with the main body of the image forming apparatus.   The image forming unit of the photoconductor B is disposed at a position closest to the fixing unit among the plurality of photoconductors in the rotation direction of the transport body. The image forming apparatus described.

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