JP4442188B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile using an electrophotographic method, and more particularly to an image forming apparatus provided with an intermediate transfer member.

  In the image forming apparatus, the toner image primarily transferred from a latent image carrier such as a photosensitive member to an intermediate transfer member such as an intermediate transfer belt is secondarily transferred onto a recording medium such as transfer paper. Then, after the secondary transfer, the transfer residual toner remaining on the intermediate transfer member is removed from the intermediate transfer member by a cleaning means such as a cleaning blade that contacts the surface of the intermediate transfer member and scrapes the transfer residual toner. ing.

  In FIG. 1, 3 is an image carrier, 6a is a developing roller, 10 is a driving roller, 11 is a driven roller, 12 is an intermediate transfer member, 13 is a primary transfer roller, and 14 is a cleaning blade. FIG. 2A shows a state in which the cleaning blade 14 is in contact with the intermediate transfer body 12, and the toner T is deposited on the tip of the cleaning blade 14 by the thickness. When the cleaning blade 14 is separated from the intermediate transfer body 12 from this state as shown in FIG. 5B, a streak-like cleaning mark 24 (hereinafter referred to as a separation line) is generated. The width L of the spacing bar 24 is substantially equal to the thickness W of the cleaning blade 14.

As a result, there arises a problem that the separating stripe 24 overlaps with the toner image primarily transferred to the intermediate transfer body 12 in the next image forming process. Therefore, conventionally, the separation timing of the cleaning unit is controlled on the basis of the toner image primarily transferred onto the intermediate transfer body 12 so that the separation line of the cleaning unit does not enter the image area (Patent Document 1). reference).
JP 2000-231276 A JP 2002-82533 A

  FIG. 2 is a diagram showing a state in which the above-mentioned separating muscle 24 passes through the transfer position T1. FIG. (A) shows a state in which the separation stripe 24 remains on the intermediate transfer body 12 and the separation position C1 advances to the primary transfer position T1, and FIG. (B) shows the separation stripe 24 at the primary transfer position T1. FIG. (C) shows a state in which the separation line 24 passes through the primary transfer position T1, and the electrostatic latent image formed on the image carrier 3 is developed by the developing roller 6a.

  By the way, as a result of various experiments conducted by the present inventor, it has been found that the following problem occurs even if the separation line of the cleaning means does not enter the image area as described above. That is, as shown in FIG. 4B, when the separating stripe 24 is at the primary transfer position T1, the speed fluctuation of the image carrier 3 occurs, and when a latent image writing operation is performed on the image carrier 3, the image carrier 3 It has been found that density unevenness and color misregistration due to speed unevenness, so-called banding occurs. This is because if there is a separation line 24 (toner) between the intermediate transfer member 12 and the image carrier 3, the frictional force between them decreases, and as a result, the image carrier 3 slips and causes a speed fluctuation. It is due to that.

This phenomenon is particularly remarkable when there is a speed difference between the rotation of the image carrier 3 and the intermediate transfer member 12. FIG. 3 is a diagram showing experimental data obtained by measuring the speed fluctuation of the image carrier. In this experiment, the primary transfer bias is set to a general 300 V, and the toner images are transferred to the intermediate transfer member in the order of Bk (black), C (cyan), M (magenta), and Y (yellow). In FIG. 3, the vertical axis represents speed unevenness, the horizontal axis represents time,
(Rotation speed of the intermediate transfer member−rotation speed of the image carrier) / rotation speed of the image carrier × 100 (%). The minus sign indicates that the image carrier is faster than the intermediate transfer member. Here, the first large speed irregularity appears because of the disturbance of the signal that hits the belt joint of the encoder that detects the rotation, and is ignored because it does not directly indicate the disturbance of the rotation. According to this, it can be seen that significant speed unevenness occurs as shown by the arrows in FIG. 3 when the position of the separating stripe of the intermediate transfer member reaches the primary transfer position.

  Hereinafter, a case where the intermediate transfer member 12 has a higher peripheral speed than the image carrier 3 will be described. Generally, a frictional force and an electrostatic attraction force act between the image carrier 3 and the intermediate transfer member 12, and the image carrier 3 is driven to be pulled by the intermediate transfer member 12 by these two forces. However, if a separation line (toner) is locally present in the primary transfer region, the frictional force at that portion is rapidly reduced, and the force with which the intermediate transfer member 12 pulls the image carrier 3 is reduced. As a result, the image carrier is instantaneously slowed down. When a latent image is written on the image carrier at this time, the writing position is shifted and the above banding occurs.

  The speed fluctuation of the image carrier 3 is further promoted by the image carrier cleaning means. Hereinafter, a case where a cleaning blade is used as the cleaning means will be described. The cleaning blade uses a stick-slip phenomenon to remove toner. Therefore, stress is always applied to the tip of the cleaning blade, and when the speed of the image carrier is decreased for a moment, the stress at the tip of the blade is released, which further promotes speed fluctuation.

  Further, at the primary transfer position T1, the electrostatic attraction force acts between the image carrier 3 and the intermediate transfer member 12 as described above, and the speed variation also depends on this force. That is, even if the frictional force due to the separating muscle 24 is reduced, if the electrostatic attraction force is large, the influence of the change can be reduced. On the contrary, if the electrostatic attraction force is weak, the speed fluctuation becomes large.

  In short, the above banding problem occurs when toner is present at the primary transfer position between the image carrier 3 and the intermediate transfer body 12 in the non-image area on the intermediate transfer body 12. Also occurs when the toner is separated from the intermediate transfer body 12. That is, as shown in FIG. 4A, the separation stripes 24 formed in the non-image area are subjected to the secondary transfer when the secondary transfer roller 15 contacts the intermediate transfer body 12 immediately before the secondary transfer. It adheres to the roller 15 side as a two-roller dirt stain 24 (see Patent Document 2). Then, when the secondary transfer onto the recording medium S is completed and the secondary transfer roller 15 is separated from the intermediate transfer body 12 as shown in FIG. 24 will adhere. When the two-roller roller smear line 24 comes to the primary transfer position, remarkable speed unevenness occurs as shown by the arrows in FIG.

  The present invention solves the above-mentioned conventional problems, and even if toner streaks adhere to a non-image area on the intermediate transfer member, it can reduce the speed fluctuation of the image carrier and prevent the occurrence of banding. An object is to provide an image forming apparatus.

Therefore, the image forming apparatus of the present invention includes a latent image forming unit that forms an electrostatic latent image on an image carrier, a developing unit that develops the electrostatic latent image into a toner image, and the toner image as an intermediate transfer member. A member that includes a primary transfer unit that transfers, and a secondary transfer unit that transfers the toner image transferred to the intermediate transfer member to a recording medium, and that performs a separation contact operation in a non-image area on the intermediate transfer member And an image carrier position corresponding to a primary transfer position of the intermediate transfer member separation position in the image forming apparatus for forming a latent image while the intermediate transfer member separation position of the member passes through the primary transfer position. Development operation is started on the image carrier corresponding to the non-image region upstream of the toner, toner is present in the non-image region of the image carrier, and electrostatic between the image carrier and the intermediate transfer member is performed. It is characterized by increasing the adsorption force .
The member that performs the separation and contact operation is a secondary transfer roller.
Further, the peripheral speeds of the image carrier and the intermediate transfer member are different at the primary transfer position.

  According to the present invention, even if toner streaks adhere to the non-image area on the intermediate transfer member, the speed fluctuation of the image carrier can be reduced and the occurrence of banding can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 6 is a diagram showing an embodiment of an image forming apparatus according to the present invention. Is an exposure device (latent image forming means), 6 is a developing device (developing means), 7 is a photoreceptor cleaner, 12 is an intermediate transfer member comprising an intermediate transfer belt, 13 is a primary transfer roller (primary transfer means), 14 Denotes a cleaning blade (intermediate transfer member cleaning means), 15 denotes a secondary transfer roller (secondary transfer means), 16 denotes a power supply device, 17 denotes a paper feed tray, 20 denotes a fixing device, and 21 denotes a paper discharge tray.

  As shown in FIG. 6, the image forming apparatus 1 according to the present embodiment includes a paper discharge tray 21 formed on the upper part of the main body case 2 and a front cover 2 a that is openably and detachably inserted on the front surface. In the main body case 2, a developing device 6 having a plurality of developing cartridges, an image carrier 3 on which an electrostatic latent image is formed and developed to form a toner image, and a toner image on the image carrier 3 are transferred. An intermediate transfer unit, a control unit for controlling each drive motor and bias, a power supply device 16, a paper feed tray 17 for storing a recording medium, a fixing device 20 for fixing a toner image on the recording medium, and the like are disposed. A paper transport unit 19 for transporting the recording medium from the paper feed tray 17 to the fixing device 20 through the secondary transfer roller 15 is disposed in the front cover 2a. Each unit and device is configured to be detachable from the main body, and can be removed and repaired or replaced integrally during maintenance or the like.

  The photoreceptor 3 as an image carrier has a thin cylindrical conductive substrate and a photosensitive layer formed on the surface thereof. On the outer periphery of the photosensitive member 3, a charging device 4 for uniformly charging the photosensitive member 3 along the rotation direction, an exposure device 5 for forming an electrostatic latent image on the photosensitive member 3, an electrostatic latent A developing device 6 for developing an image, an intermediate transfer belt 12 for transferring a toner image on the photoreceptor 3, a photoreceptor cleaner 7 for cleaning the surface of the photoreceptor 3 after primary transfer, and the like are provided. Yes.

  The intermediate transfer unit is composed of a driving roller 10 and a driven roller 11 and an endless intermediate transfer belt 12. The intermediate transfer unit is wound around both rollers 10 and 11 and is driven in the direction of the arrow in the drawing to transfer the toner image on the photoreceptor 3. An intermediate transfer belt 12, a primary transfer roller 13 that is disposed on the back surface of the intermediate transfer belt 12 so as to face the photoreceptor 3 and primarily transfers the toner image on the photoreceptor 3 to the intermediate transfer belt 12, and intermediate transfer A transfer belt cleaning blade 14 that removes residual toner on the belt 12 and a drive roller 10 are arranged to face the four-color full-color toner image formed on the intermediate transfer belt 12 as a recording medium (paper or the like). ) And a secondary transfer roller 15 for secondary transfer.

  A power supply device 16 is disposed below the exposure device 5, and a paper feed cassette 17 is disposed at the bottom of the main body case 2. A recording medium in the paper feed cassette 17 is a pickup roller 18, a sheet material conveyance path. 19, the secondary transfer roller 15, and the fixing device 20 are conveyed to the paper discharge tray 21. The paper feed cassette 17 is attached to the front of the apparatus by a handle 17b so that it can be pulled out, and an auxiliary cassette 17a is attached so that it can be pulled out so as to protrude toward the rear of the apparatus so as to cope with a large paper size. Yes.

  In the image forming apparatus 1 configured as described above, when an image forming signal is input to the exposure device 5, the photoreceptor 3, the developing roller 6 a of the developing device 6, and the intermediate transfer belt 12 are controlled in accordance with the drive motor and bias control by the control unit. Is rotated, and first, the outer peripheral surface of the photoreceptor 3 is uniformly charged by the charging device 4. Thereafter, the exposure device 5 selectively exposes the surface of the photoreceptor 3 in accordance with the image information to form an electrostatic latent image. At this time, the developing device 6 rotates so that the developing roller 6 a of the developing cartridge comes into contact with the photoreceptor 3. As a result, a toner image of an electrostatic latent image is formed on the photoreceptor 3. The toner image formed on the photoreceptor 3 is transferred onto the intermediate transfer belt 12 by the primary transfer roller 13 to which a primary transfer voltage having a polarity opposite to the toner charging polarity is applied, and remains on the photoreceptor 3. The remaining toner is removed by the photoreceptor cleaner 7.

  In the full-color image forming apparatus, yellow Y, magenta M, cyan C, and black K developing cartridges 6Y, 6M, 6C, and 6K are detachably mounted on the developing device 6. In the image forming operation, the exposure device 5 selectively exposes the surface of the photoreceptor 3 in accordance with image information of the first color, for example, yellow Y, to form a yellow Y electrostatic latent image. At this time, the developing device 6 rotates so that the developing roller 6a of the yellow Y developing cartridge 6Y contacts the photoreceptor 3, and a yellow Y electrostatic latent image toner image is formed on the photoreceptor 3. Subsequently, the toner image is transferred onto the intermediate transfer belt 12 by the primary transfer roller 13 to which a primary transfer voltage having a polarity opposite to the charging polarity of the toner is applied.

  During this time, the transfer belt cleaning blade 14 and the secondary transfer roller 15 are separated from the intermediate transfer belt 12. A four-color full-color image is obtained by repeating this series of processes corresponding to the second color, the third color, and the fourth color of the image formation signal, thereby obtaining yellow Y, Magenta M, cyan C, and black K toner images are sequentially superimposed and transferred from the photoreceptor 3 onto the intermediate transfer belt 12. Note that the order of yellow Y, magenta M, cyan C, and black K is arbitrary.

  The recording medium on the paper feed tray 17 is conveyed from the pickup roller 18 to the secondary transfer roller 15 through the registration roller and the sheet material conveyance path 19 at the timing when the superimposed image of each color toner image reaches the secondary transfer roller 15. The secondary transfer roller 15 is pressed against the intermediate transfer belt 12 and a secondary transfer voltage is applied to transfer the toner image on the intermediate transfer belt 12 onto the recording medium. The recording medium onto which the toner image has been transferred in this manner is conveyed to the fixing device 20, and the toner image on the recording medium is heated and pressed by the fixing device 20 to be fixed. The toner remaining on the intermediate transfer belt 12 is removed by the cleaning blade 14.

  In the case of double-sided printing, the recording medium exiting the fixing device 20 is switched back so that its trailing edge is the leading edge, and is supplied again to the secondary transfer roller 15 via the double-sided printing conveyance path 22. The full-color toner image on the intermediate transfer belt 12 is transferred onto the recording medium, is heated and pressed again by the fixing device 20, and is discharged onto the paper discharge tray 21.

  In the developing device 6 of the present embodiment, the four developing cartridges 6Y, 6M, 6C, and 6K are detachably mounted as described above to form a four-color full-color image forming device, but a monochrome image forming device. As shown in FIG. 2, only the black K developing cartridge 6K is mounted and mounted, the developing cartridge 6K waits at the standby position (home position), and the black K developing cartridge 6K rotates and moves from the standby position during image formation. The electrostatic latent image on the photoreceptor 3 may be developed into a toner image at the position. This makes it possible to use the developing device 6 with the same design specifications for full color and mono color, and maintenance management and design compared to designing an image forming apparatus dedicated to full color and mono color by sharing full color and mono color. Manufacturing costs can be greatly reduced.

  7 to 9 are diagrams for explaining an embodiment of the present invention. FIG. 7 is a diagram showing an operation sequence, FIG. 8 is a diagram for explaining the control of FIG. 7, and FIG. FIG.

  FIG. 7 shows the vsync signal, the image signal, the color switching operation of the developing device, the developing operation, the primary transfer position, and the secondary transfer roller operation. This operation sequence will be described with reference to FIG. The surface of the image carrier 3 is uniformly charged by the charging device 4, and the image signal is turned on in synchronization with the vsync signal. First, the surface of the image carrier 3 is selectively selected according to the image information of the first color. Exposure is performed to form an electrostatic latent image. At this time, the developing device 6 rotates so that the first color developing roller 6a contacts the image carrier 3, and a toner image of the first color is formed on the image carrier 3, and then the primary transfer voltage. The toner image of the first color is transferred onto the intermediate transfer body 12 by the primary transfer roller 13 to which is applied.

  During this time, the transfer belt cleaning blade 14 and the secondary transfer roller 15 are separated from the intermediate transfer body 12. In a four-color full-color image, this series of processing is repeatedly executed corresponding to the second color, the third color, and the fourth color of the image formation signal, so that a toner image corresponding to the content of each image formation signal is obtained. From the image carrier 3, the images are sequentially superimposed and transferred onto the intermediate transfer body 12. The recording medium S is conveyed to the secondary transfer roller 15 at a timing when the superimposed image of each color toner image reaches the secondary transfer roller 15, and the secondary transfer roller 15 is pressed against the intermediate transfer belt 12 and 2. The next transfer voltage is applied, and the toner image on the intermediate transfer body 12 is transferred onto the recording medium S.

Next, the toner remaining on the intermediate transfer belt 12 is removed by the cleaning blade 14. The cleaning blade 14 is brought into contact with the intermediate transfer body 12 after the trailing edge of the fourth color image has passed the cleaning blade position, and the leading edge of the first color image of the (second) image formed in the next step. Is separated from the intermediate transfer body 12 before reaching the cleaning blade position. By the separation contact of the cleaning blade 14, the toner image on which the fourth color is superimposed is transferred to the recording medium S, and the toner remaining on the intermediate transfer body 12 is removed by the cleaning blade 14.
more than

  When the cleaning blade 14 is separated from the intermediate transfer body 12, a separation stripe 24 is generated as shown in FIG. 8A. In this embodiment, a predetermined time t before the separation stripe 24 reaches the primary transfer position T1. In addition, the fog toner generated by the developing roller 6a is controlled to reach the primary transfer position T1. In other words, the developing bias is applied from the AC superimposed bias power supply 26 on the upstream side (relative to the rotation direction of the image carrier 3) of the position on the image carrier corresponding to the position of the separating stripe on the intermediate transfer member 12. ing. Accordingly, as shown in FIG. 8B, since the separating stripe 24 and fog toner always overlap at the primary transfer position, even if the separating stripe 24 passes through the primary transfer position T1, the intermediate carrier and the image carrier 3 are intermediate. There is no sudden fluctuation of the frictional force between the transfer bodies 12, and the speed unevenness of the image carrier 3 can be reduced. 8 is an example of non-contact development, but contact development may be used. In this case, fog toner is generated when the developing roller 6a is brought into contact with the image carrier 3.

  In FIG. 7, the image signal is turned on and image writing is started before the separation line 24 reaches the primary transfer position T <b> 1. However, the speed unevenness of the image carrier 3 due to the passage of the separation line 24 is reduced. Therefore, the image signal may be turned on and image writing may be started while the non-image area (the area where the transfer image is not formed) of the intermediate transfer body 12 including the separating stripe 24 passes through the primary transfer position T1. .

FIG. 9 is a diagram showing experimental data obtained by measuring the speed variation of the image carrier. In FIG. 9, the vertical axis represents speed variation, the horizontal axis represents time, and the speed variation is
(Rotation speed of the intermediate transfer member−rotation speed of the image carrier) / rotation speed of the image carrier × 100 (%). The minus sign indicates that the image carrier is faster than the intermediate transfer member. Here, the first large speed irregularity appears because of the disturbance of the signal that hits the belt joint of the encoder that detects the rotation, and it is ignored because it does not directly indicate the disturbance of the rotation.
According to FIG. 9, it can be seen that there is no or reduced speed unevenness at the position of the arrow when the separating line passes through the primary transfer position.

  10 to 11 are diagrams for explaining another embodiment of the present invention, FIG. 10 is a diagram illustrating an operation sequence, and FIG. 11 is a diagram illustrating measurement data.

  FIG. 10 shows the vsync signal, the image signal, the color switching operation of the developing device, the developing operation, the primary transfer position, and the secondary transfer roller operation. This operation sequence will be described with reference to FIG. The surface of the image carrier 3 is uniformly charged by the charging device 4, and the image signal is turned on in synchronization with the vsync signal. First, the surface of the image carrier 3 is selectively selected according to the image information of the first color. Exposure is performed to form an electrostatic latent image. At this time, the developing device 6 rotates and moves so that the first color developing roller 6 a contacts the image carrier 3, and a toner image of the first color is formed on the image carrier 3, followed by the primary transfer voltage. The toner image of the first color is transferred onto the intermediate transfer body 12 by the primary transfer roller 13 to which is applied.

  During this time, the transfer belt cleaning blade 14 and the secondary transfer roller 15 are separated from the intermediate transfer body 12. In a four-color full-color image, this series of processing is repeatedly executed corresponding to the second color, the third color, and the fourth color of the image formation signal, so that a toner image corresponding to the content of each image formation signal is obtained. From the image carrier 3, the images are sequentially superimposed and transferred onto the intermediate transfer body 12. The recording medium S is conveyed to the secondary transfer roller 15 at a timing when the superimposed image of each color toner image reaches the secondary transfer roller 15, and the secondary transfer roller 15 is pressed against the intermediate transfer belt 12 and 2. The next transfer voltage is applied, and the toner image on the intermediate transfer body 12 is transferred onto the recording medium S.

  Next, the toner remaining on the intermediate transfer belt 12 is removed by the cleaning blade 14. The cleaning blade 14 is brought into contact with the intermediate transfer body 12 after the rear end of the third color image has passed the cleaning blade position, and the front end of the first color image of the (second) image formed in the next step. Is separated from the intermediate transfer body 12 before reaching the cleaning blade position. By the separation contact of the cleaning blade 14, the toner image on which the fourth color is superimposed is transferred to the recording medium S, and the toner remaining on the intermediate transfer body 12 is removed by the cleaning blade 14.

  When the secondary transfer roller 15 is separated from the intermediate transfer body 12, a two-roller roller smear line 24 is generated as shown in FIG. 8A. In this embodiment, the two-roller roller smear line 24 is primary transferred. Control is performed so that the fog toner generated by the developing roller 6a reaches the primary transfer position T1 a predetermined time t before reaching the position T1. In other words, the developing bias is applied from the AC superimposing bias power source 26 on the upstream side (relative to the rotation direction of the image carrier 3) on the image carrier corresponding to the position of the two-roller stain on the intermediate transfer member 12. Like to do. Accordingly, as shown in FIG. 8B, at the primary transfer position, the two-roller roller smear line 24 and the fog toner always overlap each other. Therefore, even if the two-roller roller smear line 24 passes the primary transfer position T1, The frictional force between the image carrier 3 and the intermediate transfer member 12 is not rapidly changed, and the speed unevenness of the image carrier 3 can be reduced.

  FIG. 11 is a diagram showing experimental data obtained by measuring the speed variation of the image carrier. According to this, it can be seen that when the two-roller roller streak passes the primary transfer position, the speed unevenness is absent or reduced at the position of the arrow.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, the electrostatic latent image is formed on the image carrier by the exposure device, but the electrostatic latent image may be formed by a charging / writing device. It is defined as forming means. Although the intermediate transfer belt has been described in the above embodiment, it can be applied to an intermediate transfer drum, and in the present invention, these are defined as intermediate transfer members.

It is a figure for demonstrating generation | occurrence | production of the separation line which concerns on this invention. It is a figure which shows the state in which a separating muscle passes a transcription | transfer position. It is a figure for demonstrating the subject of this invention, and is a figure which shows the experimental data which measured the speed fluctuation | variation of the image carrier. It is a figure for demonstrating generation | occurrence | production of the 2 rolling-roller stain | pollution | contamination stripe | line according to this invention. It is a figure which shows the experimental data which measured the speed fluctuation | variation of the image carrier by the 2 rolling-roller stain | pollution | contamination streak. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. It is a figure for demonstrating one Embodiment of this invention, and is a figure which shows the outline | summary of an operation | movement sequence. It is a figure for demonstrating the control of FIG. It is a figure which shows the measurement data of embodiment of FIG. It is a figure for demonstrating other embodiment of this invention, and is a figure which shows the outline | summary of an operation | movement sequence. It is a figure which shows the measurement data of embodiment of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Image carrier, 5 ... Latent image formation means, 6 ... Developing means, 12 ... Intermediate transfer body 13 ... Primary transfer roller (primary transfer means), 14 ... Cleaning blade 15 ... Secondary transfer roller (secondary transfer) means)

Claims (4)

Latent image forming means for forming an electrostatic latent image on the image carrier;
Developing means for developing the electrostatic latent image into a toner image;
Primary transfer means for transferring the toner image to an intermediate transfer member;
Secondary transfer means for transferring the toner image transferred to the intermediate transfer member to a recording medium;
With
A member that performs a separation contact operation in a non-image area on the intermediate transfer member;
In the image forming apparatus for forming a latent image while the separation position on the intermediate transfer member of the member passes the primary transfer position,
The developing operation is started on the image carrier corresponding to the non-image area upstream of the image carrier position corresponding to the primary transfer position of the intermediate transfer body separation position, and the non-image area of the image carrier An image forming apparatus characterized in that toner is present in the toner to increase electrostatic attraction between the image carrier and the intermediate transfer member . The image forming apparatus according to claim 1, wherein the member that performs the separation and contact operation is an intermediate transfer member cleaning unit. The image forming apparatus according to claim 1, wherein the member that performs the separation and contact operation is a secondary transfer roller. 4. The image forming apparatus according to claim 1, wherein peripheral speeds of the image bearing member and the intermediate transfer member are different at the primary transfer position. 5.

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