JP6108688B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

2. Description of the Related Art Conventionally, a tandem type image forming apparatus has an intermediate transfer member, a plurality of photosensitive drums provided in a row in contact with the intermediate transfer member, a developing unit, a primary transfer unit, and a secondary transfer unit. An image forming apparatus is known. In this image forming apparatus, the toner images formed on the respective photosensitive drums are sequentially superimposed and transferred (primary transfer) on the intermediate transfer belt when the developing unit comes into contact with the primary transfer unit. Further, the secondary transfer means collectively transfers (secondary transfer) the toner image that is primarily transferred to the intermediate transfer member and transferred onto a transfer material such as paper.
As such an image forming apparatus, as disclosed in Japanese Patent Application Laid-Open No. H10-228707, an apparatus that employs an ATVC (Active Transfer Voltage Control) control method as transfer control is known. ATVC performs constant current control of the primary transfer unit with a preset value, detects a change in resistance of the primary transfer unit based on a change in the generated voltage value at this time, and calculates the generated voltage value to calculate an image. It sometimes refers to setting the transfer voltage applied to the primary transfer means.
Further, recent image forming apparatuses employ a configuration in which the developing unit is detachably provided on the photosensitive drum in order to improve the durability of the developing unit. The developing means abuts on the photosensitive drum just before image formation and is separated immediately after the image formation is completed. That is, the uppermost developing means in the rotational direction of the intermediate transfer member comes into contact with the photosensitive drum in order and is separated from the photosensitive drum in order from the uppermost developing means.
In the image forming apparatus adopting such a configuration, ATVC is performed before the developing unit comes into contact with the photosensitive drum. This is to prevent the transfer current in ATVC from becoming unstable due to the phenomenon that toner adheres to a non-image portion that should originally be white by developing operation, that is, the effect of so-called fog toner.

JP 2001-125338 A

  In the conventional image forming apparatus, ATVC is independently performed in each image forming unit, and the developing unit in each image forming unit cannot be in contact with development on the photosensitive drum until ATVC is completed. As described above, when waiting for ATVC to end, the timing of developing contact is delayed, and as a result, the time until the first sheet is printed out after receiving the print command (First Print Out Time. FPOT) becomes long.

  Accordingly, an object of the present invention is to shorten FPOT while suppressing transfer failure.

The present invention is provided with a plurality of image carriers on which electrostatic latent images are formed, an intermediate transfer member that rotates along the plurality of image carriers, and an image that can be brought into contact with and separated from the image carrier. A plurality of developing means for visualizing the electrostatic latent image by supplying a developer onto the image carrier by contacting the image carrier in order from the upstream side to the downstream side in the rotation direction of the transfer body; A plurality of transfer units that are provided opposite to the image carrier through an intermediate transfer member and transfer the developer supplied onto the image carrier onto the intermediate transfer member, and a plurality of transfer units, respectively. A plurality of voltage applying means for applying a voltage; and the plurality of voltage applying means respectively applying a voltage to the plurality of transfer means in a state where the developing means is not in contact with the image carrier. Current of each current flowing through the transfer means A plurality of transfer voltage setting means for setting a transfer voltage value of a voltage applied by the plurality of voltage applying means to the plurality of transfer means when transferring the developer onto the intermediate transfer member, respectively. In the image forming apparatus, a second image carrier corresponding to a second image carrier that is second or later from the most upstream in the rotation direction of the intermediate transfer member among the plurality of image carrier members among the plurality of transfer voltage setting units. The transfer voltage setting unit sets the transfer voltage value, and the plurality of voltage application units apply the voltage of the transfer voltage value set by the second transfer voltage setting unit to the plurality of transfer units. The first developing means provided so as to be able to come into contact with and separate from the first image carrier that is the most upstream in the rotational direction among the plurality of image carriers is applied to the first developing means. First contact the first image carrier The second transfer voltage setting means can finish the setting of the transfer voltage value before the location on the intermediate transfer member corresponding to the location to reach the second image carrier. The second transfer voltage setting means starts an approaching operation to the first image carrier before setting the transfer voltage value.

The present invention also provides a transfer rotator, a first image carrier on which an electrostatic latent image is formed, and a downstream side of the first image carrier in the rotational direction of the transfer rotator, A second image carrier on which an electrostatic latent image is formed and a first image carrier that can be contacted and separated from the first image carrier and develop the electrostatic latent image on the first image carrier as a toner image. A first developing unit, a second developing unit that is capable of contacting and separating from the second image carrier and developing the electrostatic latent image on the second image carrier as a toner image, and the transfer rotation. A first transfer means provided opposite to the first image carrier through a body, for transferring the toner image on the first image carrier toward the transfer rotator, and the transfer A toner image on the second image carrier is provided to face the second image carrier through a rotator, and is transferred to the transfer rotator. A second transfer unit for applying a voltage, a first voltage applying unit for applying a voltage to the first transfer unit, a second voltage applying unit for applying a voltage to the second transfer unit, and the first transfer unit. In a state where the second developing unit is not in contact with the second image carrier, the current flowing through the second transfer unit when the second voltage applying unit applies a voltage to the second transfer unit. Transfer voltage setting means for setting a transfer voltage, which is a voltage applied by the second voltage applying means when the developer image is transferred to the transfer rotator based on the current value of In the apparatus, while the transfer voltage setting means is setting the transfer voltage, the transfer of the first developing means from the separated state to the contact state with respect to the first image carrier is started, and the transfer voltage setting means From the first developing means The attached developer attached to one image carrier moves from the first image carrier to the transfer rotator, and the attached developer moved onto the transfer rotator contacts the second image carrier. The transfer voltage setting means completes the setting of the transfer voltage before, and the transfer voltage setting means applies the set transfer voltage from the first voltage application means to the first transfer means, and the second voltage application means. It is characterized in that a blank is applied to the second transfer means .
The present invention also provides a transfer rotator, a first image carrier on which an electrostatic latent image is formed, and a downstream side of the first image carrier in the rotational direction of the transfer rotator, A second image carrier on which an electrostatic latent image is formed and a first image carrier that can be contacted and separated from the first image carrier and develop the electrostatic latent image on the first image carrier as a toner image. A first developing unit, a second developing unit that is capable of contacting and separating from the second image carrier and developing the electrostatic latent image on the second image carrier as a toner image, and the transfer rotation. A first transfer means provided opposite to the first image carrier through a body, for transferring the toner image on the first image carrier toward the transfer rotator, and the transfer A toner image on the second image carrier is provided to face the second image carrier through a rotator, and is transferred to the transfer rotator. A second transfer unit for applying a voltage, a first voltage applying unit for applying a voltage to the first transfer unit, a second voltage applying unit for applying a voltage to the second transfer unit, and the first transfer unit. In a state where the second developing unit is not in contact with the second image carrier, the current flowing through the second transfer unit when the second voltage applying unit applies a voltage to the second transfer unit. Transfer voltage setting means for setting a transfer voltage, which is a voltage applied by the second voltage applying means when the developer image is transferred to the transfer rotator based on the current value of In the apparatus, while the transfer voltage setting means is setting the transfer voltage, the transfer of the first developing means from the separated state to the contact state with respect to the first image carrier is started, and the transfer voltage setting means From the first developing means The attached developer attached to one image carrier moves from the first image carrier to the transfer rotator, and the attached developer moved onto the transfer rotator contacts the second image carrier. The transfer voltage setting unit completed the setting of the transfer voltage before, and the transfer voltage setting unit applied the set transfer voltage from the second voltage applying unit to the second transfer unit, and corrected the set transfer voltage. A voltage is applied from the first voltage application unit to the first transfer unit.

  According to the present invention, FPOT can be shortened while suppressing transfer failure.

Schematic sectional view showing a schematic configuration of an image forming apparatus according to the present embodiment Schematic sectional view showing a schematic configuration of an image forming unit according to the present embodiment The figure shown about the timing of image formation in a present Example The figure which shows the timing of image formation and ATVC in a prior art example The figure which shows the timing of image formation and ATVC in Example 1. The figure explaining the implementation timing of ATVC in Example 1 Diagram showing relationship between transfer current value and transfer voltage value The figure which shows the timing of image formation and ATVC in the modification of Example 1. The figure explaining the implementation timing of ATVC in the modification of Example 1 FIG. 3 is a schematic cross-sectional view illustrating a schematic configuration of an image forming apparatus according to a second embodiment. The figure which shows the relationship between the transfer voltage after ATVC in Example 2, and the number of paper passing.

  A schematic configuration of a printer (hereinafter simply referred to as an image forming apparatus) which is an embodiment of the electrophotographic image forming apparatus according to the present embodiment will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view illustrating a schematic configuration of the image forming apparatus according to the present embodiment. The image forming apparatus according to the present embodiment includes a paper feed cassette 2 that stores a transfer material 1 such as paper, an image forming station 8, a primary transfer roller 13 as a transfer unit, a fixing device 17, and an intermediate transfer belt as a transfer rotating member. 30 (intermediate transfer member) and a secondary transfer roller 34. The intermediate transfer belt 30 is formed of an endless belt and is supported by driving rollers 31 and 33 and a secondary transfer counter roller 32 so as to extend along the photosensitive drum 9 as an image carrier. It rotates in the direction of arrow R1 in FIG.

  The image forming apparatus according to the present exemplary embodiment includes image forming units that can form images corresponding to the respective colors of magenta M, cyan C, yellow Y, and black K. A so-called tandem configuration is employed, and magenta M, cyan C, yellow Y, and black K image forming units are provided in order from the upstream side in the rotation direction of the intermediate transfer belt 30. The four image forming units have the same configuration except that the image forming colors are different. Note that subscripts M, C, Y, and K for indicating an element provided for one of the colors will be described with reference numerals, but subscripts are not particularly required. Is omitted.

  The schematic configuration of the image forming unit according to this embodiment will be described with reference to FIG. FIG. 2 is a schematic cross-sectional view illustrating a configuration of an image forming unit that forms an image of magenta M as an example of the image forming unit. The image forming unit of magenta M includes an image forming station 8M and a primary transfer roller 13M (first transfer unit) provided opposite to the image forming station 8M via an intermediate transfer belt 30. The image forming station 8M includes a photosensitive drum 9M as a first image carrier, a charging roller 10M, an exposure device 11M, a developing device 12M as a first developing unit, and a cleaning device 14M.

  The photosensitive drum 9M is made of a negative organic photo semiconductor, and is in contact with the intermediate transfer belt 30 so as to be rotatable in the direction of arrow R2 in FIG. The developing device 12M is provided so as to be able to contact and separate from the photosensitive drum 9M, and is in a contact state (solid line position in FIG. 1) and a separation state (dotted line position in FIG. 1) by a contact / separation mechanism (not shown). Is repeated, and is in contact (development contact) with the photosensitive drum 9 only during image formation.

  In this embodiment, the photosensitive drum 9M, the charging roller 10M, the developing device 12M, and the cleaning device 14M are integrally incorporated in the cartridge container 15M shown in FIG. 2, and constitute one cartridge as a whole. ing. This cartridge is configured to be detachable from the image forming apparatus main body. Therefore, for example, when the photosensitive drum reaches the end of its life, the photosensitive drum can be replaced with a new one by replacing the cartridge.

Next, the outline of the image forming process in this embodiment will be described with reference to FIGS. FIG. 3 is a diagram showing the timing of image formation in the present embodiment. First, when an image formation start signal is input to the image forming apparatus, the intermediate transfer belt 30 and the photosensitive drum 9 start to rotate. The charging roller 10 applies a DC voltage to charge the surface of the photosensitive drum 9 to a desired charging potential with a negative polarity. Then, the exposure device 11 irradiates laser light based on the image information, and forms an electrostatic latent image on the photosensitive drum 9 (on the image carrier).

  Further, the developing device 12 is contacted (development contact) with the photosensitive drum 9 on which the electrostatic latent image is formed, thereby supplying toner as a developer to visualize the electrostatic latent image on the photosensitive drum 9. A toner image (developer image) is formed. At this time, the developing device 12 develops on the photosensitive drum 9 immediately before image formation (toner image formation) in the order of cyan C, yellow Y, and black K from magenta M on the upstream side in the rotation direction R1 of the intermediate transfer belt 30. Abut. That is, as shown in FIG. 3, an image is formed in the contact state in order from the one arranged on the upstream side to the one arranged on the downstream side (image formation ON). Further, the image forming apparatus is sequentially separated from the upstream side to the downstream side to end image formation (image formation OFF).

  Thereafter, the toner image formed on the photosensitive drum 9 is electrostatically transferred (primary transfer) onto the intermediate transfer belt 30 by the primary transfer roller 13. At this time, a predetermined positive voltage is applied to the primary transfer roller 13 by a transfer power source 51 (voltage applying means) controlled by a transfer bias control means 50 (transfer voltage setting means). In FIG. 1, the illustration of the transfer bias control means 50 and the transfer power source 51 is omitted.

  Note that toner (residual toner) that is not transferred onto the intermediate transfer belt 30 and remains on the surface of the photosensitive drum 9 is removed by the cleaning device 14 and collected in a waste toner container (not shown). The photosensitive drum 9 whose surface has been cleaned in this way is used for the next image formation starting from charging by the charging roller 10.

  The above operation is similarly repeated in all the image forming stations 8. As a result, the magenta toner image, the cyan toner image, the yellow toner image, and the black toner image formed on each photosensitive drum (on the first image carrier and the second image carrier) are transferred onto the intermediate transfer belt 30. The primary transfer is performed in sequence on the intermediate transfer member and the transfer rotating member.

  Thereafter, the transfer material 1 such as paper stored in the paper feed cassette 2 is separated one by one by the pickup roller 18 and fed to the secondary transfer roller 34. The plurality of toner images formed on the intermediate transfer belt 30 are collectively transferred (secondary transfer) to the transfer material 1 fed at a predetermined timing by the secondary transfer roller 34. At this time, a predetermined positive voltage is applied to the secondary transfer roller 34 by the power source 35. After the secondary transfer, the transfer residual toner 22 remaining on the intermediate transfer belt 30 is removed by the second cleaning device 19 in FIG.

  Further, the transfer material 1 is conveyed to the fixing device 17, and the toner image is fixed on the transfer material 1 by being heated and pressed. The transfer material 1 on which the toner image is fixed is discharged out of the image forming apparatus, and a series of image forming processes is completed.

Example 1
The image forming apparatus according to the first embodiment performs ATVC at the time of primary transfer of a toner image, that is, when the toner image formed on each photosensitive drum 9 by the primary transfer roller 13 is transferred onto the intermediate transfer belt 30. Thus, the set transfer voltage is applied to the primary transfer roller 13. Hereinafter, ATVC will be described with reference to FIGS. FIG. 4 is a diagram showing the timing of image formation and ATVC in the conventional example. FIG. 5 is a diagram illustrating image formation and ATVC timing in the first embodiment. FIG. 6 is a diagram for explaining the ATVC execution timing in the first embodiment. As shown in FIGS. 4 and 5, in both the conventional example and the first embodiment, the time from when the print command is received until the ATVC control is started is T0, and ATVC performed in one image forming unit. The control time is Tb.

  ATVC (Active Transfer Voltage Control) control refers to a series of controls for setting a transfer voltage. First, constant current control is performed on the primary transfer roller 13 with a preset value. A change in resistance of the primary transfer roller 13 is detected based on a change in voltage value generated at this time. Then, a transfer voltage to be applied to the primary transfer roller 13 is set from a result of calculating the voltage value. This series of control is called ATVC control. ATVC is performed immediately before image formation in order to cope with durability fluctuation and environmental fluctuation of the resistance value of the primary transfer roller 13. In addition, when the toner adhering (adhering developer) adheres to the photosensitive drum 9, the voltage value generated by the constant current control becomes unstable. Therefore, ATVC has no toner on the photosensitive drum 9. Performed before development contact.

  As described above, the developing device 12 is provided so as to be able to contact and separate from the photosensitive drum 9. Then, the developing device 12 contacts the photosensitive drum 9 immediately before image formation in order from the most upstream image forming unit, and is sequentially separated immediately after the end of image formation. The reason why such a configuration is possible is to improve the durability of each member.

  As shown in FIG. 4, conventionally, ATVC is performed for each image forming unit, in order from the most upstream image forming unit, immediately before each developing device 12 develops and contacts each photosensitive drum 9. . Therefore, the ATVC control time is from the start of ATVC performed immediately before the most upstream magenta M developing device 12M contacts the photosensitive drum 9M to immediately before the most downstream black K developing device 12K contacts the photosensitive drum 9K. It was the time Ta until the end of ATVC to be carried out.

  As described above, in the conventional configuration, the developing device 12 in the image forming unit cannot be in contact with the photosensitive drum 9 until the ATVC in the image forming unit is completed. In other words, image formation in each image forming unit cannot be started until ATVC in each image forming unit is completed. As described above, when waiting for the end of ATVC, the timing of the contact state is delayed, and as a result, the time until the first sheet is printed out after receiving the print command (First Print Out Time. Below) , FPOT) becomes long. In other words, in order to shorten the FPOT, it is important to advance the timing of the contact state in the image forming unit.

  The image forming apparatus according to the first embodiment performs ATVC in only one image forming unit other than the most upstream image forming unit (that is, the second and subsequent image forming units), and feeds back the result to the other image forming units ( It is characterized in that it is configured to turn ON after ATVC in FIG. That is, ATVC is performed in one image forming unit to complete the setting of the transfer voltage value, and the voltage of the transfer voltage value is applied to all the primary transfer rollers 13. In the first embodiment, ATVC is performed only in the cyan C image forming unit that is second from the most upstream.

  The timing of performing ATVC is the intermediate transfer belt 30 corresponding to the position where the developing device 12M first contacts after the developing device 12M (first developing means) contacts the photosensitive drum 9M (first image carrier). This is before the upper portion reaches the photosensitive drum 9C (second image carrier). That is, as shown in FIG. 6, the developing device 12M at the uppermost stream makes development contact with the photosensitive drum 9M, and the fog toner 21M that moves and adheres to the intermediate transfer belt 30 reaches the second photosensitive drum 9C. Prior to contact, ATVC is performed in the cyan C image forming unit.

At this time, in the cyan C image forming portion, the developing device 12C is not in contact with development on the photosensitive drum 9C. Then, the transfer voltage set by ATVC performed in the cyan C image forming unit is applied to the primary transfer roller 13 of the other image forming unit. That is, the transfer power source 51M (first voltage application unit) applies the transfer voltage to the primary transfer roller 13M, and the transfer power source 51C (second voltage application unit) applies to the primary transfer roller 13C (second transfer unit). The transfer voltage is applied. By adopting such a configuration, the control time of ATVC is only the control time in one image forming unit, and thus the control time Tb is shorter than the conventional control time Ta.

  A transfer voltage that prevents the fog toner 21M from being transferred onto the intermediate transfer belt 30 as much as possible is set and applied to the primary transfer roller 13M of the most upstream image forming unit. The inventors of the present invention have examined that the amount of fog toner on the intermediate transfer belt 30 is in the range of 300 to 900V. In Example 1, 600V which is the center value was set as an initial voltage (voltage at the time of initial ON in FIG. 5).

  Next, a method for setting a transfer voltage in the ATVC implementation will be specifically described with reference to FIG. FIG. 7 is a diagram illustrating the relationship between the transfer current value and the transfer voltage value. First, the charging roller 10C charges the photosensitive drum 9C with a charging potential at the time of image formation in the image forming station 8C. Then, the transfer bias control means 50C (second transfer voltage setting means) controls the transfer power source 51C (second voltage application means) to thereby give a predetermined transfer potential to the primary transfer roller 13C (second transfer means). Apply to. Here, three types of transfer voltages Vft1, Vft2, and Vft3 shown in FIG. 7 are applied as predetermined voltages. Then, current value detection means (not shown) detects transfer current values Ift1, If2 and If3 flowing through the primary transfer roller 13C.

  Then, a target transfer voltage Vfttarget corresponding to the target transfer current Iftarget is calculated, and this is set as a transfer voltage in the ATVC implementation. In the first embodiment, this transfer voltage is also set as a transfer voltage in the magenta M, yellow Y, and black K image forming portions where ATVC is not performed. In the first embodiment, since the number of sheets passing through each image forming station 8 is assumed to be the same as a premise, the transfer voltage based on the result of ATVC performed in one image forming unit as described above is transferred to the other image forming units. It can be applied as it is.

By adopting such a configuration, as shown in FIG. 5, as compared with the conventional configuration, it is made possible to accelerate the development contact start timing D _M of the most upstream image forming station 8M time T. As shown in FIGS. 4 and 5, the time from the receipt of the print command in the conventional example and that in the first embodiment to the start of the ATVC control is the same, and both are the time T0. Further, the control time of ATVC performed in one image forming unit in the conventional example and in the first embodiment is also the same, and both are Tb. In the conventional example, after ATVC in the most upstream magenta image forming unit is completed (the control time Tb has elapsed), the magenta developing device 12M starts an operation of approaching the photosensitive drum 9M. On the other hand, in the first embodiment, after the ATVC ends (control time Tb elapses) in the second cyan image forming unit from the most upstream, the operation of the cyan developing device 12C approaching the photosensitive drum 9C is started. To do. That is, in the first embodiment, while setting the transfer voltage in the ATVC control, the most upstream magenta developer (first developing means) 12M has already moved from the separated state to the contact state with respect to the photosensitive drum 9M. (Approaching action) has started. Thus, in Example 1, compared with the conventional to be able to advance the timing D _M of the development contact start at the most upstream portion, as a result, it is possible to shorten the FPOT.

In Example 1, the intervals of the development contact start timings D _M , D _C , D _Y , and D _K of the image forming stations 8M, 8C, 8Y, and 8K are all the same and set to 550 msec, so the time T is 550 msec. Therefore, in the first embodiment, the development contact start timing of the image forming station 8M can be made 550 msec earlier than before, and the FPOT can be shortened by 550 msec.

In the first embodiment, ATVC is performed only in the cyan C image forming unit that is second from the most upstream, but the present invention is not limited to this, and other than the magenta M image forming unit in the most upstream, other ATVC may be performed in the image forming unit. For example, as shown in FIGS. 8 and 9, ATVC may be performed only in the fourth black K image forming unit from the uppermost stream. FIG. 8 is a diagram illustrating the timing of image formation and ATVC according to a modification of the first embodiment. FIG. 9 is a diagram for explaining the implementation timing of ATVC according to a modification of the first embodiment.

  As shown in FIG. 9, before the fog toners 21M, 21C, and 21Y of the image forming stations 8M, 8C, and 8Y reach the intermediate transfer belt 30 at the position of the photosensitive drum 9K in the fourth black K image forming portion. The ATVC is performed in the black K image forming unit. In this case, as shown in FIG. 8, it is necessary to set the ATVC end timing before the image forming station 8M starts image formation. Then, an initial voltage at which the fog toners 21M, 21C, and 21Y are not transferred onto the intermediate transfer belt 30 as much as possible to the primary transfer rollers 13M, 13C, and 13Y of each image forming unit that has not yet performed ATVC (the initial ON in FIG. 8). Time voltage) is preset and applied.

By adopting such a configuration, as shown in FIG. 8, as compared with the conventional configuration, it is made possible to accelerate the development contact start timing D _M of the most upstream image forming station 8M time T ' . Since the intervals of the development contact start timings D _M , D _C , D _Y , and D _K of the image forming stations 8M, 8C, 8Y, and 8K are all the same and set to 550 msec, the time T ′ is 1650 msec. That is, the development contact start timing of the image forming station 8M can be made 1650 msec earlier than before, and the FPOT can be shortened by 1650 msec.

  As described above, in the first embodiment, the development contact start timing in the most upstream image forming station 8M can be advanced while suppressing the transfer failure. As a result, FPOT can be shortened.

(Example 2)
Next, an image forming apparatus according to the second embodiment will be described with reference to FIG. FIG. 10 is a schematic cross-sectional view illustrating a schematic configuration of the image forming apparatus according to the second embodiment. The image forming apparatus according to the second embodiment is implemented in that the transfer voltage applied to the primary transfer roller 13 that is not subjected to ATVC control is corrected according to the accumulated usage amount of the photosensitive drum acquired and stored by the storage unit. Different from Example 1. Since other configurations and operations are the same as those in the first embodiment, the same components are denoted by the same reference numerals and description thereof is omitted.

  When the cartridge is replaced, the drum film layer differs between the photosensitive drum of the image forming unit that performs ATVC and the photosensitive drum to which the transfer voltage is applied by feeding back the ATVC result. . In such a case, in the image forming unit that has received the feedback of the transfer voltage, a transfer memory or transfer failure may occur due to the transfer voltage being out of the allowable range. The transfer memory is a phenomenon in which fog toner is generated when the surface potential of the photosensitive drum is lowered.

A drum with a thick film layer such as a new drum has a small electrostatic capacity and a current does not easily flow. Conversely, a drum with a thin film layer such as a durable drum has a large capacitance and a current easily flows. Therefore, when the ATVC target current is the same, the transfer voltage of the durable drum is smaller than that of the new drum. That is, when the photosensitive drum of the image forming unit performing ATVC is a new drum and the photosensitive drum of the image forming unit not performing ATVC is a durable drum, a transfer voltage that is too high is applied to the photosensitive drum not performing ATVC. As a result, a transfer memory is generated. On the other hand, when the photosensitive drum of the image forming unit that performs ATVC is a durable drum and the photosensitive drum of the image forming unit that is not performing ATVC is a new drum, a transfer voltage that is too low is applied to the photosensitive drum that is not performing ATVC. As a result, a transfer failure occurs. In view of such circumstances, the second embodiment employs a configuration in which the transfer voltage applied to the primary transfer roller 13 that has not been subjected to ATVC control is corrected in accordance with the usage state of the photosensitive drum 9.

  As shown in FIG. 10, the image forming apparatus according to the second embodiment includes an engine control unit 40 and a controller 44. The engine control unit 40 includes a memory 41, a CPU (central processing unit) 42 that controls the operation of the image forming apparatus main body, a transfer power supply 51 that outputs a transfer voltage, a transfer bias control unit 50 that controls the transfer voltage, and a correction unit. As an ATVC correction means 43. The ATVC correction unit 43 adds a correction value to the transfer voltage value set by ATVC, which is the voltage applied to each primary transfer roller 13 in the image forming unit where ATVC has not been performed. The controller 44 converts image data from a PC (personal computer) 45 into video data and transfers it to the CPU 42 of the engine control unit 40.

  As shown in FIG. 10, the image forming apparatus according to the second embodiment includes a cartridge memory 16 as a storage unit in each image forming unit, and the cartridge memory 16 is connected to the CPU 42. Each cartridge memory 16 stores an accumulated number of image formation times of each image forming station 8 as an accumulated usage amount of each photosensitive drum 9. In the second embodiment, the definition of the count of the number of image formations is divided and counted according to the length of the sheet passing direction shown in Table 1. The detailed definition will be described below.

  Let L be the length in the paper passing direction. When L is a postcard (vertical) size and is A5 vertical or less, that is, when 148 [mm] ≦ L ≦ 210 [mm], the number of image formations is counted 0.5 times for one sheet of paper. . When L is larger than the A5 size and smaller than the A4 size, that is, when 210 [mm] <L ≦ 300 [mm], the number of image formations is 1.0 count per sheet. To do. When L is larger than the A4 size and smaller than the Legal size, that is, when 300 [mm] <L ≦ 356 [mm], the number of image formations is counted 1.5 times for one sheet. To do. However, when double-sided printing is performed on the same sheet, the number of image formation is doubled and counted. For example, when 148 [mm] ≦ L ≦ 210 [mm], the number of image formations is counted 1.0 for one sheet of paper to be printed on both sides.

  In Table 2 below, the correspondence relationship between the typical paper type and the length in the paper passing direction and the count of the number of image formations defined in the second embodiment is shown in more detail.

  Next, the post-ATVC transfer voltage value obtained when 20000 sheets are passed in a setting in which 2 sheets of A4 size paper are passed and paused (2 sheets intermittently) will be described with reference to FIG. FIG. 11 is a diagram illustrating the relationship between the transfer voltage value after ATVC and the number of sheets to be passed in the second embodiment.

As shown in FIG. 11, the transfer voltage value set after ATVC is 350V. When 10,000 sheets were passed, the transfer voltage value was 275 V, which was 75 V lower than the initial value. When 20000 sheets were passed, the transfer voltage value was reduced by 150V from the initial value to 200V. Accordingly, when the transfer voltage value is V _T1 and the number of sheets to be passed is P, the following formula 1 is obtained.

Next, the ATVC correction value ΔV is calculated. Assume that the transfer voltage set after ATVC of the image forming unit that has performed ATVC is V _ATVC , the number of sheets to be passed is P _ATVC , the transfer voltage of the image forming unit that receives feedback of ATVC is V _FB , and the number of sheets to be passed P _FB . The ATVC correction value ΔV can be determined based on the difference between the photosensitive drum 9C and the photosensitive drums 9M, 9Y, and 9K other than the photosensitive drum 9C (other than the second image carrier). That is, it can be obtained by the following formula 2.

For example, the number of sheets passed through the cyan C image forming unit that performed ATVC was 8000, and the number of sheets passed through the magenta M, yellow Y, and black K image forming units that fed back the ATVC results was 2000 and 7500, respectively. 12,000 sheets. In this case, the ATVC result of the cyan C image forming unit is V _C, and the ATVC correction values of the magenta M, yellow Y, and black K image forming units are ΔV _M , ΔV _Y , and ΔV _K. Moreover, the transfer voltage after ATVC corrected _{V M,} V Y, and _{V K.} From the above formulas 1 and 2, each value can be obtained as follows.

That is, under the above conditions, the transfer voltages V _M , V _Y , and V _K obtained by adding the correction values ΔV _M , ΔV _Y , ΔV _K to the transfer voltage V _C set by ATVC are used as the primary values of the image forming units. What is necessary is just to apply to the transfer rollers 13M, 13Y, and 13K.

  As described above, in the second embodiment, the development contact start timing in the most upstream image forming station 8 can be advanced while suppressing transfer defects. As a result, FPOT can be shortened. Furthermore, even if the film thickness of the photosensitive drum 9 in each image forming station 8 is different, it is possible to set a transfer voltage with high accuracy corresponding to each photosensitive drum, so that it is possible to suppress transfer memory and transfer defects. .

  In the second embodiment, the correction value is determined according to the accumulated usage amount of the photosensitive drum 9. However, the correction value is not limited to this, and the correction value is determined based on the accumulated usage amount and toner consumption amount of the developing device 12. It may be configured. In this case, the ATVC correction value ΔV is determined based on the usage amount of the developing unit 12C (second developing unit), the usage amounts of the developing units 12M, 12Y, and 12K other than the photosensitive drum 9C (other than the second developing unit). Can be determined on the basis of the difference.

(Example 3)
Next, an image forming apparatus according to Embodiment 3 will be described. Also in the third embodiment, as in the first embodiment, in the process of changing the output voltage at the primary transfer roller 13 before the start of image formation, ATVC is performed only in one image forming section other than the most upstream image forming section. The result is fed back to another image forming unit. In the third embodiment, similarly to the first embodiment, ATVC is executed only in the second cyan image forming section from the most upstream in the rotation direction of the intermediate transfer belt 30.

In addition, in the third embodiment, ATVC is performed in all the image forming units while the image forming is not performed and the developing device 12 and the photosensitive drum 9 are separated from each other. Set the transfer voltage value. Here, “separating in a state where image formation is not performed” includes, for example, starting up when the image forming apparatus is turned on, during post-rotation after image formation, and during recovery during jamming. Here, a case where ATVC is performed during post-rotation after image formation will be described. Then, based on each transfer voltage value obtained in that case, the second correction unit included in the image forming apparatus according to the third embodiment sets a transfer set for an image forming station that has not yet performed ATVC immediately before the start of image formation. A correction value is added to the voltage value. Since other configurations and operations are the same as those in the first embodiment, the same components are denoted by the same reference numerals and description thereof is omitted.

Here, the result of ATVC at the time of post-rotation of each of the image forming stations 8M, 8Y, 8C, and 8K is _{M after} V _{, Y after} V _{, C after} V, and _{K after} V. Further, the ATVC correction values (second correction values) in the magenta M, yellow Y, and black K image forming portions that are not subjected to ATVC immediately before image formation are ΔV _M , ΔV _Y , and ΔV _K. In the third embodiment, the ATVC correction value is set to a transfer voltage value set based on a current value flowing through the primary transfer roller 13C (second transfer unit), and other than the primary transfer roller 13C (other than the second transfer unit). It is obtained by the difference from the transfer voltage value set based on the current value flowing through the object. That is, as shown in the following relational expression, the ATVC result V _{after C in} the rear rotation of the cyan C image forming station 8M, and the ATVC result V _{after M} in the rear rotation of the image forming stations other than the cyan C, It can be determined by the difference between _{Y after} V and _{K after} V.

As described in the first embodiment, the ATVC is performed only in the cyan C image forming unit immediately before the image formation, and the result is fed back to the magenta M, yellow Y, and black K image forming units in which ATVC is not performed. At this time, the second correction value of ATVC obtained in advance is used. The transfer voltage value set by the ATVC implementation of the cyan C image forming unit is set to V _{before C} , and the corrected transfer voltage value of the magenta M, yellow Y, and black K image forming units is set to V _{complementary M} , V _{complementary Y} , Assuming V _{complement K} , the following relational expression is obtained.

As described above, in the third embodiment, after the ATVC of the cyan C image forming unit, the transfer voltages V _{complement M} , V _{complement Y 1} , V V obtained by adding the correction values ΔV _M , ΔV _Y , ΔV _K to the _{C before} the transfer voltage V. _{The complementary K} may be applied to the primary transfer rollers 13M, 13Y, and 13K of each image forming unit.

  As described above, in the third embodiment, the development contact start timing in the most upstream image forming station 8 can be advanced while suppressing the transfer failure. As a result, FPOT can be shortened. Furthermore, by performing ATVC at a timing that does not affect FPOT, it is possible to accurately feed back the transfer voltage to an image forming unit that does not perform ATVC during image formation.

Photosensitive drum ... 9, developing unit ... 12, primary transfer roller ... 13, intermediate transfer belt ... 30, transfer bias control means ... 50, transfer power source ... 51

Claims (7)

A plurality of image carriers on which electrostatic latent images are formed;
An intermediate transfer member that rotates along the plurality of image carriers;
The developer is supplied to the image carrier by contacting the image carrier in order from the upstream side to the downstream side in the rotation direction of the intermediate transfer member, provided so as to be able to contact and separate from the image carrier. A plurality of developing means for visualizing the electrostatic latent image;
A plurality of transfer means provided opposite to the image carrier through the intermediate transfer member and transferring the developer supplied onto the image carrier onto the intermediate transfer member;
A plurality of voltage applying means for applying a voltage to each of the plurality of transfer means;
Based on the current value of the current flowing through each of the plurality of transfer units when the plurality of voltage application units apply voltages to the plurality of transfer units in a state where the developing unit is not in contact with the image carrier. A plurality of transfer voltage setting means for respectively setting transfer voltage values of voltages applied by the plurality of voltage applying means to the plurality of transfer means when transferring the developer onto the intermediate transfer body;
In an image forming apparatus having
Of the plurality of transfer voltage setting means, a second transfer voltage setting means corresponding to a second image carrier that is second or later from the most upstream in the rotation direction of the intermediate transfer body among the plurality of image carriers. Set the transfer voltage value,
The plurality of voltage application units apply voltages of transfer voltage values set in the second transfer voltage setting unit to the plurality of transfer units, respectively.
Of the plurality of image carriers, a first developing unit provided so as to be able to come into contact with and separate from the first image carrier located on the most upstream side in the rotation direction is such that the first developing unit is the first image carrier. The timing at which the second transfer voltage setting means can finish the setting of the transfer voltage value before the location on the intermediate transfer member corresponding to the location where the first contact occurs first reaches the second image carrier. The image forming apparatus, wherein the second transfer voltage setting means starts an approaching operation to the first image carrier before setting the transfer voltage value. Storage means for acquiring and storing each usage amount of the plurality of image carriers;
Correction values determined respectively based on the difference between the usage amount of the second image carrier and the usage amount of an image carrier other than the second image carrier stored in the storage means are the second value. Correction means for adding each of the transfer voltage setting means to a transfer voltage value set based on a current value flowing through the second transfer means,
The image forming apparatus according to claim 1, further comprising: Storage means for acquiring and storing respective usage amounts of the plurality of developing means;
A correction value determined based on a difference between the usage amount of the second developing unit and the usage amount of a developing unit other than the second developing unit stored in the storage unit is set as the second transfer voltage. Correction means that the setting means adds to the transfer voltage value set based on the value of the current flowing through the second transfer means;
The image forming apparatus according to claim 1, further comprising: A transfer rotator,
A first image carrier on which an electrostatic latent image is formed;
A second image carrier disposed on the downstream side of the first image carrier in the rotation direction of the transfer rotator to form an electrostatic latent image; and
First developing means that is capable of contacting and separating from the first image carrier and developing the electrostatic latent image on the first image carrier as a toner image;
A second developing unit that is capable of contacting and separating from the second image carrier and developing the electrostatic latent image on the second image carrier as a toner image;
A first transfer means provided opposite to the first image carrier through the transfer rotator and for transferring a toner image on the first image carrier toward the transfer rotator; ,
A second transfer means provided opposite to the second image carrier through the transfer rotator and for transferring a toner image on the second image carrier toward the transfer rotator; ,
First voltage applying means for applying a voltage to the first transfer means;
Second voltage applying means for applying a voltage to the second transfer means;
In a state in which the second developing unit is not in contact with the second image carrier, the second voltage applying unit applies a voltage to the second transferring unit, whereby the second transferring unit is applied to the second transferring unit. A transfer voltage setting means for setting a transfer voltage, which is a voltage applied by the second voltage applying means when transferring the developer image toward the transfer rotator, based on a current value of a flowing current;
In an image forming apparatus having
While the transfer voltage setting unit is setting the transfer voltage, the first developing unit is moved from the separated state to the contact state with respect to the first image carrier,
The transfer voltage setting means moves the adhered developer attached to the first image carrier from the first developing means to the transfer rotator from the first image carrier, and onto the transfer rotator. The transfer voltage setting unit completes the setting of the transfer voltage before the moved adhered developer contacts the second image carrier, and the transfer voltage setting unit transfers the set transfer voltage from the first voltage application unit to the first image application unit. An image forming apparatus , wherein the first transfer unit is applied, and the second voltage application unit is applied to the second transfer unit . A transfer rotator,
A first image carrier on which an electrostatic latent image is formed;
A second image carrier disposed on the downstream side of the first image carrier in the rotation direction of the transfer rotator to form an electrostatic latent image; and
First developing means that is capable of contacting and separating from the first image carrier and developing the electrostatic latent image on the first image carrier as a toner image;
A second developing unit that is capable of contacting and separating from the second image carrier and developing the electrostatic latent image on the second image carrier as a toner image;
A first transfer means provided opposite to the first image carrier through the transfer rotator and for transferring a toner image on the first image carrier toward the transfer rotator; ,
The second image carrier is provided opposite to the second image carrier through the transfer rotator.
A second transfer means for transferring the upper toner image toward the transfer rotator;
First voltage applying means for applying a voltage to the first transfer means;
Second voltage applying means for applying a voltage to the second transfer means;
In a state in which the second developing unit is not in contact with the second image carrier, the second voltage applying unit applies a voltage to the second transferring unit, whereby the second transferring unit is applied to the second transferring unit. A transfer voltage setting means for setting a transfer voltage, which is a voltage applied by the second voltage applying means when transferring the developer image toward the transfer rotator, based on a current value of a flowing current;
In an image forming apparatus having
While the transfer voltage setting unit is setting the transfer voltage, the first developing unit is moved from the separated state to the contact state with respect to the first image carrier,
The transfer voltage setting means moves the adhered developer attached to the first image carrier from the first developing means to the transfer rotator from the first image carrier, and onto the transfer rotator. The setting of the transfer voltage is completed before the moved adhered developer contacts the second image carrier,
The transfer voltage setting unit applies the set transfer voltage from the second voltage application unit to the second transfer unit, and corrects the set transfer voltage from the first voltage application unit to the second transfer unit. and applying to the first transfer means images forming device. In the rotational direction of the transferring member, between said first image carrier and the second image bearing member, having a plurality of other image bearing members to claim 4 or claim 5, characterized in The image forming apparatus described. Said second image bearing member, an image forming apparatus according to any one of claims 4 to 6, characterized in that carrying the black developer image.

Images