JP4766091B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that transfers a toner image conveyed by a transfer belt onto a print medium by a transfer roller.

  As a conventional image forming apparatus, for example, an image forming apparatus described in Patent Document 1 is known. The image forming apparatus described in Patent Document 1 has a polarity opposite to the transfer voltage applied to the secondary transfer member in a time period before the recording medium enters the nip portion between the intermediate transfer member and the secondary transfer member in the printing operation. A reverse polarity voltage for cleaning is applied for a time T1. Thereafter, the image forming apparatus applies a cleaning same polarity voltage having the same polarity as the transfer voltage for a time T2. Further, the image forming apparatus applies a voltage having a polarity opposite to the transfer voltage to the secondary transfer member until the recording medium enters the nip portion between the intermediate transfer member and the secondary transfer member. According to the image forming apparatus as described above, the toner attached to the secondary transfer member can be moved to the intermediate transfer member, and the secondary transfer member can be cleaned. As a result, it is possible to prevent dirt from adhering to the back surface of the recording medium.

Incidentally, in recent years, in image forming apparatuses, with the demand for improving print quality, there has been an increasing demand for preventing the adhesion of dirt to paper. Therefore, the importance of cleaning the secondary transfer member is increasing.
JP 2006-350161 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that can more effectively clean toner attached to a secondary transfer member.

An image forming apparatus according to an aspect of the present invention forms an nip portion by facing an intermediate transfer member that conveys a toner image and the intermediate transfer member, and the toner that has been conveyed by the intermediate transfer member A secondary transfer member that transfers an image to a printing medium that passes through the nip portion, and a transfer voltage is applied to the secondary transfer member when the toner image is transferred, and the rear end of the toner image is placed at the nip portion. Voltage application means for applying a first cleaning voltage having a polarity opposite to that of the transfer voltage to the secondary transfer member after passing through the secondary transfer member, the secondary transfer member with respect to the intermediate transfer member, The voltage application means sets the time required for the secondary transfer member to make one rotation as a first time, and the voltage application means passes the nip portion after the rear end of the print medium passes through the nip portion. Until the intermediate transfer member stops When the second time is the second time and the second time is twice or more the first time, the intermediate transfer member after the rear end of the print medium has passed through the nip portion The switching between the second cleaning voltage having the opposite polarity to the first cleaning voltage and the first cleaning voltage is performed every first time until the first cleaning voltage is stopped .

(Copier configuration)
Hereinafter, a configuration of a copier equipped with an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of the copying machine 1.

  As shown in FIG. 1, the copying machine 1 includes an image reading unit 30 and an image forming unit 32. The image reading unit 30 reads an image of a document and generates image data. Since the image reading unit 30 is realized by a general scanner, further detailed description is omitted. The image forming unit 32 is an electrophotographic color printer configured to synthesize images of four colors (Y: yellow, M: magenta, C: cyan, K: black) in a so-called tandem system. is there. The image forming unit 32 has a function of forming an image on a sheet (print medium) based on the image data generated by the image reading unit 30, and includes the printing unit 2, the paper feeding unit 15, the fixing device 20, and a paper discharge. A tray 21 is provided.

  The paper feed unit 15 serves to supply paper one by one and includes a paper tray 16 and a paper feed roller 17. A plurality of sheets in a state before printing are stacked on the sheet tray 16. The paper feed roller 17 takes out the paper placed on the paper tray 16 one by one.

  The printing unit 2 forms a toner image on the paper supplied from the paper feeding unit 15, forms image forming units 22 Y, 22 M, 22 C, 22 K, primary transfer rollers 8 Y, 8 M, 8 C, 8 K, an intermediate transfer belt 11, A driving roller 12, a driven roller 13, a secondary transfer roller 14, a cleaning device 18, and a sensor 23 are included. The image forming units 22Y, 22M, 22C, and 22K include photosensitive drums 4Y, 4M, 4C, and 4K, chargers 5Y, 5M, 5C, and 5K, exposure devices 6Y, 6M, 6C, and 6K, and developing devices 7Y and 7M. , 7C, 7K, cleaners 9Y, 9M, 9C, 9K and erasers 10Y, 10M, 10C, 10K. Hereinafter, when the photosensitive drum, the charger, the exposure device, the developing device, the primary transfer roller, the cleaner, the eraser, and the image forming unit are collectively referred to, the photosensitive drum 4 and the charger are simply referred to. 5, an exposure device 6, a developing device 7, a primary transfer roller 8, a cleaner 9, an eraser 10, and an image forming unit 22, and each photosensitive drum, charger, exposure device, developing device, primary transfer roller , Cleaners, erasers, and image forming units, the photosensitive drums 4Y, 4M, 4C, 4K, the chargers 5Y, 5M, 5C, 5K, the exposure devices 6Y, 6M, 6C, 6K, and the developing device 7Y. , 7M, 7C, 7K, primary transfer rollers 8Y, 8M, 8C, 8K, cleaners 9Y, 9M, 9C, 9K, erasers 10Y, 10M, 10C, 10K, and image forming units 22Y, 22M, 22C, 22K That.

  The charger 5 charges the peripheral surface of the photosensitive drum 4. The exposure apparatus 6 irradiates a laser under the control of a control unit (not shown in FIG. 1). As a result, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 4. That is, the charger 5 and the exposure device 6 serve as an electrostatic latent image forming unit that forms an electrostatic latent image on the peripheral surface of the photosensitive drum 4.

  The developing device 7 serves as a developing unit that applies toner to the photosensitive drum 4 and forms toner images on the peripheral surfaces of the plurality of photosensitive drums 4. More specifically, the developing device 7 contains toner and is negatively charged by stirring the toner. Then, the developing device 7 conveys the toner to the vicinity of the photosensitive drum 4 by the developing roller. At this time, the negatively charged toner moves from the developing roller to the photosensitive drum 4 under the influence of the electric field due to the electrostatic latent image. As a result, a toner image is formed on the peripheral surface of the photosensitive drum 4.

  The intermediate transfer belt 11 is stretched between the driving roller 12 and the driven roller 13, and the toner image formed on the photosensitive drum 4 is primarily transferred. The primary transfer roller 8 is disposed so as to be in contact with the inner peripheral surface of the intermediate transfer belt 11, and a toner formed on the photosensitive drum 4 by applying a primary transfer voltage from a voltage application unit (not shown). It plays the role of primary transfer of the image to the intermediate transfer belt 11. The cleaner 9 serves to collect the toner remaining on the peripheral surface of the photosensitive drum 4 after the primary transfer. The driving roller 12 is driven by the intermediate transfer belt 11 by being rotated by an intermediate transfer belt driving unit (not shown in FIG. 1). As a result, the intermediate transfer belt 11 conveys the toner image to the secondary transfer roller 14.

  The secondary transfer roller 14 is opposed to the intermediate transfer belt 11 to form a nip portion N, and the toner image conveyed by the intermediate transfer belt 11 is conveyed from the paper feeding portion 15 and passes through the nip portion N. Secondary transfer onto the paper to be printed. The secondary transfer roller 14 is always in pressure contact with the intermediate transfer belt 11. The cleaning device 18 removes the toner remaining on the intermediate transfer belt 11 after the secondary transfer of the toner image onto the paper. The sensor 23 is provided on the downstream side of the secondary transfer roller 14 and detects the presence / absence of a sheet passing through the secondary transfer roller 14 and the presence / absence of a toner image on the intermediate transfer belt 11.

  The sheet on which the toner image is secondarily transferred is conveyed to the fixing device 20. The fixing device 20 fixes the toner image on the paper by performing heat treatment and pressure treatment on the paper. Printed paper is placed on the paper discharge tray 21.

  Next, the control configuration of the copying machine 1 will be described with reference to the drawings. FIG. 2 is a control block of the copying machine 1. In FIG. 2, the image forming units 22Y, 22M, 22C, and 22K, the sensor 23, the image reading unit 30, the operation panel 34, the voltage applying unit 36, the intermediate transfer belt driving unit 38, the photoconductor driving unit 40, and the control unit 50 are illustrated. Are listed.

  The control unit 50 controls the entire copying machine 1 and is configured by a CPU, for example. The operation panel 34 is an input / output device that displays information such as a document size and the number of printed sheets and receives an input of a print instruction from a user, and is configured by a touch panel, for example.

  The voltage application unit 36 applies the secondary transfer voltage V3 to the secondary transfer roller 14 when transferring the toner image onto the sheet. The secondary transfer voltage V3 is a voltage for moving the negatively charged toner image from the intermediate transfer belt 11 to the sheet. Therefore, the secondary transfer voltage is a positive voltage at which the potential of the secondary transfer roller 14 is higher than the potential of the intermediate transfer belt 11.

  The intermediate transfer belt drive unit 38 is a motor connected to the drive roller 12, and rotates the intermediate transfer belt 11 by rotating the drive roller 12. The photoconductor drive unit 40 is a motor connected to the photoconductor drum 4 and rotates the photoconductor drum 4.

(Operation of copier 1)
The operation of the copying machine 1 configured as described above will be described below with reference to the drawings. FIG. 3 is a timing chart showing the operation of the copying machine 1. FIG. 4 is a timing chart of the image forming apparatus described in Patent Document 1.

  First, the operation of the image forming apparatus described in Patent Document 1 will be described. In the image forming apparatus described in Patent Document 1, the secondary transfer roller is in pressure contact with the intermediate transfer belt. Therefore, the toner remaining on the intermediate transfer belt after the transfer of the toner image onto the paper may adhere to the secondary transfer roller. Such contamination of the secondary transfer roller causes the back side of the paper to become dirty.

  In view of this, the image forming apparatus described in Patent Document 1 is a process pre-process from the start of rotation of the photosensitive drum and the secondary transfer roller to the exposure of the photosensitive drum (hereinafter referred to as an exposure process). During this period, the cleaning process is performed. More specifically, as shown in FIG. 4, during the pre-process period, the voltage application unit alternately applies a negative cleaning voltage V1 and a positive cleaning voltage V2 to the secondary transfer roller. Yes. Accordingly, during the period when the negative cleaning voltage V1 is applied, the negatively charged toner attached to the secondary transfer roller moves from the secondary transfer roller to the intermediate transfer belt. Most toners are negatively charged, but some toners are positively charged. Therefore, during the period when the positive cleaning voltage V2 is applied, the positively charged toner attached to the secondary transfer roller moves from the secondary transfer roller to the intermediate transfer belt. By repeating the above operation, the toner adhering to the secondary transfer roller is removed.

  Incidentally, in recent years, in image forming apparatuses, with the demand for improving print quality, there has been an increasing demand for preventing the adhesion of dirt to paper. Therefore, the importance of cleaning the secondary transfer member is increasing.

  Therefore, in the image forming section 32 of the copying machine 1, as shown in FIG. 3, in addition to the period of the pre-process, the process from the end of the exposure process to the end of the rotation of the photosensitive drum 4 and the intermediate transfer belt 11 is completed. The cleaning process is also performed during the post-processing period. The operation of the image forming unit 32 will be described below with reference to the drawings.

  First, the outline of the operation of the image forming unit 32 will be described with reference to FIG. As shown in FIG. 3, the operation of the image forming unit 32 includes a pre-process, an exposure process, and a post-process.

  In the process pre-processing, the control unit 50 drives the charger 5, the eraser 10, the intermediate transfer belt driving unit 38, and the photosensitive member driving unit 40 (time t1 in FIG. 3). In the process preprocessing, the control unit 50 puts the photosensitive drum 4 into the photosensitive member driving unit 40 in a state where the charger 5 and the eraser 10 are operated in order to uniformly charge the peripheral surface of the photosensitive drum 4. Rotate by a predetermined number of revolutions The predetermined number of rotations is, for example, two rotations for color printing and one rotation for monochrome printing. Further, as shown in FIG. 3, the control unit 50 causes the voltage application unit 36 to alternately apply the cleaning voltages V <b> 1 and V <b> 2 to the secondary transfer roller 14 in the process pre-process so that the secondary transfer roller 14 Perform a cleaning process. The cleaning process will be described later.

  In the exposure process, the control unit 50 drives the exposure device 6 in addition to the charger 5, the eraser 10, the intermediate transfer belt driving unit 38, and the photosensitive member driving unit 40 at time t2. As a result, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 4. In the exposure process, the control unit 50 also applies the secondary transfer voltage V3 to the voltage transfer unit 14 to the secondary transfer roller 14 to perform secondary transfer of the toner image.

  In the process post-process, the control unit 50 removes the electric charge of the photosensitive drum 4 by the procedure described below after time t5. FIG. 5 is a view showing a state of the peripheral surface of the photosensitive drum 4 in the post-process processing. In FIG. 5, a portion indicated by a thick line on the photosensitive drum 4 is charged, and a portion indicated by a dotted line on the photosensitive drum 4 is not charged. Points A to F indicate positions where the primary transfer roller 8, the eraser 10, the cleaner 9, the charger 5, the exposure device 6, and the developing device 7 are provided.

  FIG. 5B is a diagram showing a state of the photosensitive drum 4 immediately after the exposure process is completed. A portion located at the point A at the time of FIG. In FIG. 5B, since the eraser 10 and the charger 5 are operating, only the portion of the photosensitive drum 4 between the eraser 10 (point B) and the charger 5 (point D) is not charged.

  As shown in FIG. 5C, when the photosensitive drum 4 rotates clockwise and the point X reaches the point D, it is not necessary to charge the photosensitive drum 4 any more. The drive of the device 5 is stopped. However, at this time, the eraser 10 is driven. Therefore, the portion of the photosensitive drum 4 that has passed the point B is in a state where the electric charge has been removed.

  As shown in FIG. 5D, when the photosensitive drum 4 rotates clockwise and the point X reaches the point B, the charge on the entire peripheral surface of the photosensitive drum 4 is removed. Therefore, the control unit 50 stops driving the photoconductor driving unit 40 and stops the rotation of the photoconductor drum 4. Furthermore, the control unit 50 also stops driving the eraser 10. As a result, the post-process processing ends (time t8).

  In addition, during the post-process, similarly to the pre-process, the control unit 50 alternately applies the cleaning voltages V1 and V2 to the voltage application unit 36 with respect to the secondary transfer roller 14, as shown in FIG. The secondary transfer roller 14 is cleaned by applying the cleaning force. This is the end of the outline of the operation of the image forming unit 32.

  Next, details of the cleaning process performed by the control unit 50 and the voltage application unit 36 of the image forming unit 32 will be described with reference to FIGS. 6 to 9 are flowcharts showing operations performed by the control unit 50 after the user issues a print instruction using the operation panel 34 until the printing of the image on the paper is completed.

  First, the user places a document on a platen glass (not shown), and uses the operation panel 34 to give a print instruction for printing an image of the document on paper (that is, copying the document). When receiving the print instruction, the control unit 50 causes the image reading unit 30 to read the image of the document, and obtains image data (step S1). Next, the control unit 50 performs predetermined image processing on the image data (step S2). Thereafter, the control unit 50 forms an image on the sheet based on the image data (step S3). Details of step S3 will be described below with reference to FIG.

  In step S3, the control unit 50 stands by while repeatedly determining whether or not the intermediate transfer belt driving unit 38 has started driving (step S11). If the pre-process is started and the intermediate transfer belt drive unit 38 starts driving, the process proceeds to step S12. On the other hand, if the pre-process is not started and the intermediate transfer belt drive unit 38 has not started driving, the process returns to step S11.

  When the intermediate transfer belt driving unit 38 is driven, the control unit 50 determines whether to execute color printing or monochrome printing (step S12). As described above, in the process preprocessing, the photosensitive drum 4 rotates once for monochrome printing and rotates twice for color printing. Therefore, the time required for the process pre-processing in color printing is different from the time required for the process pre-processing in monochrome printing. Therefore, in step S12, the control unit 50 determines whether to execute color printing or monochrome printing. When color printing is executed, the process proceeds to step S13. When monochrome printing is executed, the process proceeds to step S14.

  When color printing is executed, the control unit 50 calculates a time T3 during which the cleaning process can be performed when color printing is executed (step S13). As shown in FIG. 3, the time T3 during which the cleaning process can be performed is the time from when the photosensitive member driving unit 40 starts driving until the leading edge of the sheet reaches the nip portion N. 3 from time t1 to time t3. When the time T3 is calculated, the process proceeds to step S15.

  When monochrome printing is executed, the controller 50 calculates a time T3 during which the cleaning process can be performed when monochrome printing is executed (step S14). When the time T3 is calculated, the process proceeds to step S15.

  In step S15, the control unit 50 divides the time T3 by the time T1 required for the secondary transfer roller 14 to make one rotation to obtain the number of times of application n (step S15). The application number n indicates the number of times that the cleaning voltages V1 and V2 shown in FIG. 3 can be applied. More specifically, in the cleaning process, the controller 50 causes the secondary transfer roller 14 to make one rotation of a cleaning voltage V1 having a polarity opposite to the secondary transfer voltage and a cleaning voltage V2 having the same polarity as the secondary transfer voltage. The toner is alternately applied to the secondary transfer roller 14 every time T1 required for the above. Therefore, the controller 50 calculates how many times the cleaning voltages V1 and V2 can be applied in step S15. If the time T3 cannot be divided by the time T1, the decimal part of the number of times of application n is rounded down.

  Next, the control part 50 determines whether the application frequency n is 2 or more (step S16). That is, the control unit 50 determines whether or not the time T3 is twice or more the time T1. When the number of times of application n is 2 or more (when time T3 is twice or more of time T1), the process proceeds to step S17. When the number of times of application n is not 2 or more (when time T3 is not twice or more of time T1), the process proceeds to step S18.

  When the application number n is 2 or more, the control unit 50 executes the cleaning process 1 (step S17). Hereinafter, the cleaning process 1 will be described with reference to FIG.

  The control unit 50 causes the voltage application unit 36 to apply the cleaning voltage V1 to the secondary transfer roller 14 (step S41). The cleaning voltage V1 is a negative voltage having a polarity opposite to that of the secondary transfer voltage V3. Therefore, the negatively charged toner attached to the secondary transfer roller 14 moves from the secondary transfer roller 14 to the intermediate transfer belt 11 and is conveyed to the cleaning device 18 by the intermediate transfer belt 11.

  Next, the controller 50 determines whether or not the time T1 has elapsed since the cleaning voltage V1 was applied (step S42). In this process, the control voltage is applied to the entire peripheral surface of the secondary transfer roller 14 and the control unit 50 determines whether or not the entire peripheral surface of the secondary transfer roller 14 has been cleaned. If the time T1 has elapsed, the process proceeds to step S43. If the time T1 has not elapsed, the process returns to step S42.

  When the time T1 has elapsed, the control unit 50 subtracts one from the number of times of application n (step S43). Further, the control unit 50 determines whether or not the number of times of application n is 0 (step S44). When the number of times of application n is 0, the process proceeds to step S19 in FIG. If the application count n is not 0, the process proceeds to step S45.

  If the number of times of application n is not 0, the control unit 50 causes the voltage application unit 36 to apply the cleaning voltage V2 to the secondary transfer roller 14 (step S45). The cleaning voltage V2 is a positive voltage having the same polarity as the secondary transfer voltage V3. Therefore, the positively charged toner attached to the secondary transfer roller 14 moves from the secondary transfer roller 14 to the intermediate transfer belt 11 and is conveyed to the cleaning device 18 by the intermediate transfer belt 11.

  Next, the controller 50 determines whether or not the time T1 has elapsed since the cleaning voltage V2 was applied (step S46). In this process, the cleaning voltage V2 is applied to the entire peripheral surface of the secondary transfer roller 14 to determine whether or not the entire peripheral surface of the secondary transfer roller 14 has been cleaned. If the time T1 has elapsed, the process proceeds to step S47. If the time T1 has not elapsed, the process returns to step S46.

  When the time T1 has elapsed, the control unit 50 subtracts one from the number of times of application n (step S47). Further, the control unit 50 determines whether or not the number of times of application n is 0 (step S48). When the number of times of application n is 0, the process proceeds to step S19 in FIG. If the number n of times of application is not 0, the process returns to step S41. By the operation as described above, the control unit 50 and the voltage application unit 36 apply the cleaning voltage V1 and the cleaning voltage V2 to the secondary transfer roller 14 alternately every time T1.

  In step S16, when the number of times of application n is not 2 or more, the controller 50 executes the cleaning process 2 (step S18). Hereinafter, the cleaning process 2 will be described with reference to FIG.

  The control unit 50 causes the voltage application unit 36 to apply the cleaning voltage V1 to the secondary transfer roller 14 (step S50). The cleaning voltage V1 is a negative voltage having a polarity opposite to that of the secondary transfer voltage V3. Therefore, the negatively charged toner attached to the secondary transfer roller 14 moves from the secondary transfer roller 14 to the intermediate transfer belt 11 and is conveyed to the cleaning device 18 by the intermediate transfer belt 11. Thereafter, the process proceeds to step S19 in FIG.

  In step S19, the control unit 50 determines whether or not the cleaning process is completed (step S19). In this process, the control unit 50 determines whether or not the time t3 in FIG. 3 has been reached. When the cleaning process is completed, the process proceeds to step S20. If the cleaning process has not been completed, the process returns to step S19.

  The controller 50 determines whether or not the time T4 has elapsed since the cleaning process was completed (step S20). In this process, the control unit 50 measures time T4 to determine whether or not the leading end of the toner image on the intermediate transfer belt 11 has reached the nip N at time t4 in FIG. . If the time T4 has elapsed, the process proceeds to step S21. If the time T4 has not elapsed, the process returns to step S20.

  When the time T4 has elapsed, the control unit 50 applies a positive secondary transfer voltage V3 to the secondary transfer roller 14 to the voltage application unit 36 (step S21). Since the toner image is negatively charged, it is attracted to the secondary transfer roller 14 side by the electric field from the secondary transfer roller 14. As a result, the toner image is secondarily transferred to the paper.

  Next, the control unit 50 determines whether or not the trailing edge of the sheet has passed through the nip portion N (step S22). In step S22, the control unit 50 detects the trailing edge of the sheet by the sensor 23 provided in the vicinity of the nip N, and determines whether or not the time t7 in FIG. If the trailing edge of the sheet has passed through the nip portion N, the process proceeds to step S23. If the trailing edge of the sheet has not passed through the nip portion N, the process returns to step S22.

  Next, the control unit 50 calculates a time T2 during which the cleaning process can be performed (step S23). The time T2 during which the cleaning process can be performed is the time from when the trailing edge of the paper passes through the nip portion N until the photosensitive drum 4 and the intermediate transfer belt 11 stop, and at time t7 in FIG. To time t8. When the time T2 is calculated, the process proceeds to step S24.

  Next, the controller 50 divides the time T2 by the time T1 required for the secondary transfer roller 14 to make one rotation to obtain the number of times of application n (step S24). The application number n indicates the number of times that the cleaning voltages V1 and V2 shown in FIG. 3 can be applied. More specifically, in the cleaning process, the controller 50 causes the secondary transfer roller 14 to make one rotation of a cleaning voltage V1 having a polarity opposite to the secondary transfer voltage and a cleaning voltage V2 having the same polarity as the secondary transfer voltage. The toner is alternately applied to the secondary transfer roller 14 every time T1 required for the above. Therefore, the controller 50 calculates how many times the cleaning voltages V1 and V2 can be applied in step S24. If the time T2 cannot be divided by the time T1, the decimal part of the number of times of application n is rounded down.

  Next, the control part 50 determines whether the application frequency n is 2 or more (step S25). That is, the control unit 50 determines whether or not the time T2 is twice or more than the time T1. When the number of times of application n is 2 or more (when time T2 is twice or more of time T1), the process proceeds to step S26. When the number of times of application n is not 2 or more (when time T2 is not twice or more of time T1), the process proceeds to step S27.

  When the application number n is 2 or more, the control unit 50 executes the cleaning process 1 (step S26). Hereinafter, the cleaning process 1 will be described with reference to FIG.

  The control unit 50 causes the voltage application unit 36 to apply the cleaning voltage V1 to the secondary transfer roller 14 (step S41). The cleaning voltage V1 is a negative voltage having a polarity opposite to that of the secondary transfer voltage V3. Therefore, the negatively charged toner attached to the secondary transfer roller 14 moves from the secondary transfer roller 14 to the intermediate transfer belt 11 and is conveyed to the cleaning device 18 by the intermediate transfer belt 11.

  Next, the controller 50 determines whether or not the time T1 has elapsed since the cleaning voltage V1 was applied (step S42). In this process, the control voltage is applied to the entire peripheral surface of the secondary transfer roller 14 and the control unit 50 determines whether or not the entire peripheral surface of the secondary transfer roller 14 has been cleaned. If the time T1 has elapsed, the process proceeds to step S43. If the time T1 has not elapsed, the process returns to step S42.

  When the time T1 has elapsed, the control unit 50 subtracts one from the number of times of application n (step S43). Further, the control unit 50 determines whether or not the number of times of application n is 0 (step S44). When the number of times of application n is 0, the process proceeds to step S28 in FIG. If the application count n is not 0, the process proceeds to step S45.

  If the number of times of application n is not 0, the control unit 50 causes the voltage application unit 36 to apply the cleaning voltage V2 to the secondary transfer roller 14 (step S45). The cleaning voltage V2 is a positive voltage having the same polarity as the secondary transfer voltage V3. Therefore, the positively charged toner attached to the secondary transfer roller 14 moves from the secondary transfer roller 14 to the intermediate transfer belt 11 and is conveyed to the cleaning device 18 by the intermediate transfer belt 11.

  Next, the controller 50 determines whether or not the time T1 has elapsed since the cleaning voltage V2 was applied (step S46). In this process, the cleaning voltage V2 is applied to the entire peripheral surface of the secondary transfer roller 14 to determine whether or not the entire peripheral surface of the secondary transfer roller 14 has been cleaned. If the time T1 has elapsed, the process proceeds to step S47. If the time T1 has not elapsed, the process returns to step S46.

  When the time T1 has elapsed, the control unit 50 subtracts one from the number of times of application n (step S47). Further, the control unit 50 determines whether or not the number of times of application n is 0 (step S48). When the number of times of application n is 0, the process proceeds to step S28 in FIG. If the number n of times of application is not 0, the process returns to step S41. By the operation as described above, the control unit 50 and the voltage application unit 36 apply the cleaning voltage V1 and the cleaning voltage V2 to the secondary transfer roller 14 alternately every time T1.

  In step S25, when the number n of times of application is not 2 or more, the control unit 50 executes the cleaning process 2 (step S27). Hereinafter, the cleaning process 2 will be described with reference to FIG.

  The control unit 50 causes the voltage application unit 36 to apply the cleaning voltage V1 to the secondary transfer roller 14 (step S50). The cleaning voltage V1 is a negative voltage having a polarity opposite to that of the secondary transfer voltage V3. Therefore, the negatively charged toner attached to the secondary transfer roller 14 moves from the secondary transfer roller 14 to the intermediate transfer belt 11 and is conveyed to the cleaning device 18 by the intermediate transfer belt 11. Thereafter, the process proceeds to step S28 in FIG.

  In step S28, the control unit 50 determines whether or not the intermediate transfer belt driving unit 38 is stopped (step S28). If the intermediate transfer belt drive unit 38 is stopped, the process proceeds to step S29. If the intermediate transfer belt drive unit 38 has not stopped, the process returns to step S28.

  When the intermediate transfer belt driving unit 38 is stopped, the control unit 50 determines that the post-process has been completed, and causes the voltage application unit 36 to apply a voltage of 0 V to the secondary transfer roller 14. That is, the control unit 50 causes the voltage application unit 36 to apply the cleaning voltages V1 and V2 to the secondary transfer roller 14 until the intermediate transfer belt driving unit 38 stops. This process is complete | finished above.

(effect)
According to the image forming unit 32, the cleaning process is performed in the post-process in addition to the pre-process. Therefore, the image forming unit 32 can more effectively remove the toner adhering to the secondary transfer roller 14 as compared with the image forming apparatus described in Patent Document 1 that performs the cleaning process only in the pre-process.

  The secondary transfer roller 14 is always in pressure contact with the intermediate transfer belt 11. Therefore, compared to the secondary transfer roller that is in pressure contact with the intermediate transfer belt only when the toner image is transferred, the toner easily adheres from the intermediate transfer belt 11 to the secondary transfer roller 14 of the image forming unit 32. Therefore, in the image forming unit 32, the amount of toner attached to the secondary transfer roller 14 can be more effectively reduced by performing the cleaning process in both the pre-process and the post-process.

  In the image forming unit 32, the secondary transfer roller 14 is always in pressure contact with the intermediate transfer belt 11. Therefore, the image forming unit 32 does not need a configuration for pressing or separating the secondary transfer roller 14 and the intermediate transfer belt 11 from each other. As a result, the manufacturing cost of the image forming unit 32 can be suppressed.

  In the pre-process and post-process, the cleaning voltages V1 and V2 are alternately applied, so that both positively charged toner and negatively charged toner are transferred from the secondary transfer roller 14 to the intermediate transfer belt 11. And can be moved. As a result, the image forming unit 32 can more effectively remove the toner attached to the secondary transfer roller 14.

  In the image forming unit 32, the cleaning process is performed in the time from when the trailing edge of the sheet passes through the nip portion N until the intermediate transfer belt 11 stops. However, the period for performing the cleaning process in the image forming unit 32 is not limited to this. More specifically, it is not necessary to apply the secondary transfer voltage V3 after the trailing edge of the toner image transferred to the sheet has passed through the nip portion N (after time t6 in FIG. 3). Therefore, the control unit 50 and the voltage application unit 36 perform the cleaning process at the second time T2 until the intermediate transfer belt 11 stops after the trailing edge of the toner image transferred onto the sheet passes through the nip portion N. You may go.

(Stabilization operation)
The image forming unit 32 according to the embodiment performs a cleaning process in a pre-process and a post-process in a printing operation for printing an image on a sheet. However, the image forming unit 32 may perform the cleaning process in the pre-process and post-process when the toner image for the stabilization operation is formed on the intermediate transfer belt 11. The stabilization operation is to form a toner image of a predetermined pattern on the intermediate transfer belt 11 and observe the toner image in order to keep the quality of the image printed on the paper constant. This is an operation to adjust the condition. The stabilization operation is an operation automatically performed every time printing is performed on a predetermined number of sheets or every predetermined time.

  FIG. 10 is a timing chart showing the operation of the image forming unit 32. First, an outline of the operation of the image forming unit 32 in the stabilization operation will be described with reference to FIG. Similar to the image forming unit 32 in the printing operation, the operation of the image forming unit 32 in the stabilizing operation includes pre-process, exposure process, and post-process. The pre-process and post-process shown in FIG. 10 are the same as the pre-process and post-process shown in FIG.

  In the exposure process shown in FIG. 10, the control unit 50 drives the exposure device 6 in addition to the charger 5, eraser 10, intermediate transfer belt drive unit 38 and photoconductor drive unit 40 from time t <b> 12 to time t <b> 14. . As a result, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 4. Further, in the exposure process shown in FIG. 10, there is no need to secondary transfer the toner image. Therefore, the controller 50 performs the cleaning process of the secondary transfer roller 14 by causing the voltage application unit 36 to apply the cleaning voltage V1 to the secondary transfer roller 14 in the exposure process.

  Next, details of the cleaning process performed by the control unit 50 and the voltage application unit 36 of the image forming unit 32 in the stabilization operation will be described with reference to FIGS. 8, 9, and 11. FIG. 11 is a flowchart showing an operation performed by the control unit 50 in the stabilization operation. In FIG. 11, the same operations as those in FIG. 7 are denoted by the same reference numerals. Also, the following description will focus on differences from the operation of FIG. 7 in the operation of FIG.

  The stabilization operation is started, for example, by detecting that the control unit 50 has performed a predetermined number of prints since the previous stabilization operation. When the stabilization operation starts, the control unit 50 stands by while repeatedly determining whether or not the intermediate transfer belt driving unit 38 has started driving (step S11). If the pre-process is started and the intermediate transfer belt drive unit 38 starts driving, the process proceeds to step S113. On the other hand, if the pre-process is not started and the intermediate transfer belt drive unit 38 has not started driving, the process returns to step S11.

  When the intermediate transfer belt drive unit 38 is driven, the control unit 50 determines in the same manner as when it is determined that color printing is executed in the printing operation, and the process proceeds to step S113.

  The controller 50 calculates a time T13 during which the cleaning process can be performed when color printing is performed (step S113). The time T13 during which the cleaning process can be performed is the time from when the photosensitive member driving unit 40 starts driving until the leading edge of the toner image for the stabilizing operation reaches the nip N. 10 from time t11 to time t13. When the time T13 is calculated, the process proceeds to step S115.

  In step S115, the controller 50 divides the time T13 by the time T1 required for the secondary transfer roller 14 to make one rotation to obtain the number of times of application n (step S115). Since the application number n obtained in step S115 is the same as the application number n obtained in step S15 of FIG. 7, further explanation is omitted. The processing performed by the control unit 50 in steps S16 to S19 in FIG. 11 is the same as the processing performed by the control unit 50 in steps S16 to S19 in FIG.

  If the control unit 50 determines that the cleaning process is completed in step S19, the process proceeds to step S121. Next, the control unit 50 causes the voltage application unit 36 to apply a negative cleaning voltage V1 to the secondary transfer roller 14 (step S121 and time t13 in FIG. 10). Since the toner image is negatively charged, it is attracted to the intermediate transfer belt 11 side by the electric field from the secondary transfer roller 14. This prevents the toner from adhering to the secondary transfer roller 14.

  Next, the control unit 50 determines whether or not the trailing edge of the toner image has passed through the nip portion N (step S122). In step S122, the control unit 50 determines whether or not the time t15 in FIG. 10 has been reached based on the detection of the trailing edge of the toner image by the sensor 23 provided in the vicinity of the nip portion N. If the trailing edge of the toner image has passed through the nip portion N, the process proceeds to step S123. If the trailing edge of the toner image has not passed through the nip portion N, the process returns to step S122.

  Next, the control unit 50 calculates a time T12 during which the cleaning process can be performed (step S123). The time T12 during which the cleaning process can be performed is the time from when the trailing edge of the toner image passes through the nip portion N until the photosensitive drum 4 and the intermediate transfer belt 11 are stopped. This is the time from t15 to time t16. When the time T12 is calculated, the process proceeds to step S124.

  Next, the controller 50 divides the time T12 by the time T1 required for the secondary transfer roller 14 to make one rotation to obtain the number of times of application n (step S124). Since the application number n obtained in step S124 is the same as the application number n obtained in step S24 of FIG. 7, further description is omitted. The processing performed by the control unit 50 in steps S25 to S29 in FIG. 11 is the same as the processing performed by the control unit 50 in steps S25 to S29 in FIG.

  As described above, according to the image forming unit 32, it is possible to prevent the toner from adhering to the secondary transfer roller 14 even in the stabilization operation, similarly to the printing operation.

  Further, in the image forming unit 32, as shown in FIG. 10, while the toner image for the stabilization operation passes through the nip portion N (time t13 to time t15), the image forming unit 32 applies to the secondary transfer roller 14. A cleaning voltage V1 is applied. The cleaning voltage V1 is a negative voltage having a reverse polarity with respect to the secondary transfer voltage V3. Further, the toner image for the stabilization operation is negatively charged. Therefore, the toner image is attracted to the intermediate transfer belt 11 by the electric field generated by the cleaning voltage V1, and is not attracted to the secondary transfer roller 14. As a result, the image forming unit 32 prevents toner from adhering to the secondary transfer roller 14 in the stabilization operation.

1 is a diagram illustrating an overall configuration of a copier equipped with an image forming apparatus according to an embodiment of the present invention. 2 is a control block of the copier of FIG. 3 is a timing chart showing the operation of the copying machine according to the embodiment of the present invention. 5 is a timing chart of the image forming apparatus described in Patent Document 1. It is the figure which showed the mode of the surrounding surface of the photosensitive drum in a process post-process. 7 is a flowchart illustrating an operation performed by a control unit from when a user issues a print instruction using an operation panel to when printing of an image on a sheet is completed. 7 is a flowchart illustrating an operation performed by a control unit from when a user issues a print instruction using an operation panel to when printing of an image on a sheet is completed. 7 is a flowchart illustrating an operation performed by a control unit from when a user issues a print instruction using an operation panel to when printing of an image on a sheet is completed. 7 is a flowchart illustrating an operation performed by a control unit from when a user issues a print instruction using an operation panel to when printing of an image on a sheet is completed. 3 is a timing chart showing the operation of the image forming unit. It is the flowchart which showed the operation | movement which a control part performs in stabilization operation | movement.

Explanation of symbols

N nip part 1 copier 4Y, 4M, 4C, 4K photosensitive drum 11 intermediate transfer belt 14 secondary transfer roller 22Y, 22M, 22C, 22K image forming part 23 sensor 32 image forming part 36 voltage application part 38 intermediate transfer belt drive Unit 40 photoconductor driving unit 50 control unit

Claims (6)

An intermediate transfer member for conveying a toner image;
A secondary transfer member that forms a nip portion by facing the intermediate transfer member, and that transfers the toner image conveyed by the intermediate transfer member to a print medium that passes through the nip portion;
When transferring the toner image, a transfer voltage is applied to the secondary transfer member, and after the rear end of the toner image passes through the nip portion, a first cleaning voltage having a polarity opposite to the transfer voltage is applied to the secondary transfer member. Voltage application means for applying to the transfer member;
Equipped with a,
The secondary transfer member is always in pressure contact with the intermediate transfer member,
The voltage application means sets a time required for the secondary transfer member to make one rotation as a first time, and until the intermediate transfer member stops after the trailing edge of the print medium passes through the nip portion. When the second time is the second time and the second time is twice or more the first time, the intermediate transfer member after the rear end of the print medium has passed through the nip portion Switching between the second cleaning voltage having the opposite polarity to the first cleaning voltage and the first cleaning voltage every time the first cleaning voltage is stopped,
An image forming apparatus. The voltage applying means applies the first cleaning voltage to the secondary transfer member during a period from when the intermediate transfer member starts to rotate until the leading edge of the print medium reaches the nip portion. ,
The image forming apparatus according to claim 1 . The voltage application means sets a time required for the secondary transfer member to make one rotation as a first time, and the leading edge of the printing medium reaches the nip portion after the intermediate transfer member starts rotating. And when the third time is longer than twice the first time, the second cleaning voltage having the opposite polarity to the first cleaning voltage and the third time Alternately applying a first cleaning voltage every first time;
The image forming apparatus according to claim 2 . When the toner image for stabilization operation is conveyed to the nip portion by the intermediate transfer member, the voltage applying unit is configured to perform the first operation until the rear end of the toner image passes through the nip portion. Applying a cleaning voltage of 1 to the secondary transfer member;
The image forming apparatus according to any one of claims 1 to 3, characterized in. The voltage application means applies the first cleaning voltage to the secondary cleaning during a period from when the intermediate transfer member starts to rotate until the leading edge of the toner image for stabilization operation reaches the nip portion. Applying to the transfer member,
The image forming apparatus according to claim 4 . The voltage application means sets a time required for the secondary transfer member to make one rotation as a first time, and the leading end of the toner image for the stabilizing operation after the intermediate transfer member starts rotating. Assuming that the time until reaching the nip portion is the third time, and the third time is longer than twice the first time, the first polarity having the opposite polarity to the first cleaning voltage is used. Alternately applying the cleaning voltage of 2 and the first cleaning voltage every the first time;
The image forming apparatus according to claim 5 .

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