JP5338276B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  When forming an image on both sides of the recording material, the image forming apparatus secondarily transfers the surface toner image primarily transferred from the image carrier onto the intermediate transfer member onto the surface of the recording material, and the surface toner image is transferred to the surface of the recording material. Fix with a fixing device. Thereafter, the image forming apparatus reverses the recording material via the recording material reversal conveying mechanism and then conveys the recording material to the secondary transfer unit again, and the back-side toner image primarily transferred onto the intermediate transfer member is transferred to the back surface of the recording material. The toner image for the back surface is fixed by a fixing device. Further, the intermediate transfer member includes a seamless one and a seamless one. When an intermediate transfer member with a seam is used, an image cannot be formed at the position of the seam, so the number of image-formed sheets that can be discharged per unit time by the image forming apparatus (hereinafter referred to as productivity) decreases. There is a case.

In Patent Document 1, the length of the circulation path for reversing and circulating the recording material is an integral multiple of the circumference of the transfer belt having a seam.
In Patent Document 2, recording material feeding control is performed with respect to the transfer belt joint for each number of recording materials that can be arranged in the circumferential length of the transfer belt in accordance with the length of the recording material in the conveyance direction.
In Patent Literature 3, a reference signal is generated and scheduling for conveying a recording sheet is performed.
JP-A-11-160935 Japanese Patent Laid-Open No. 11-161039 JP 2001-265191 A

  The present invention provides an image forming apparatus with improved productivity when images are formed on both sides of a recording material.

Invention of the image forming apparatus according to claim 1 includes an image holding member for holding the toner image, it is formed in an endless shape having a seam, an intermediate transfer member the toner image is primarily transferred to the image carrier is held A secondary transfer portion that secondary-transfers the toner image primarily transferred to the intermediate transfer member to a recording material, and two images on one surface of the recording material when forming images on both sides of the recording material. After the next transfer, the recording material reversing paper feeding portion for reversing the recording material for secondary transfer to the other surface and refeeding to the transfer position of the secondary transfer portion, and the toner image on the one surface based on the position on the intermediate transfer member is primarily transferred, and a changing means for changing the timing at which the recording material reverse feed unit is refeeding the recording material to the transfer position of the secondary transfer portion The changing means is the intermediate transfer in which the toner image on the one surface is primarily transferred. Characterized in that than the number of the seam up to the present position on the intermediate transfer member the toner image of the other face from a position above is primarily transferred is one better in the case of two slow the timing And

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the position on the intermediate transfer member to which the toner image on the one surface is primarily transferred is the rotation of the intermediate transfer member. It is any one of the areas sequentially arranged from the seam in the direction.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect , the image holding body holds a toner image at the same position on the image holding body. .

According to the first aspect of the present invention, productivity when forming images on both sides of the recording material is improved. In addition, the recording material regardless of the number of seams existing from the position on the intermediate transfer body where the toner image on one side is primarily transferred to the position on the intermediate transfer body where the toner image on the other side is primary transferred. Productivity is improved when images are formed on both sides.

  According to the second aspect of the present invention, productivity when images are formed on both sides of the recording material is further improved.

According to the third aspect of the invention, the image quality of the image formed on the recording material is improved, and the productivity when forming images on both sides of the recording material is improved.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the accompanying drawings.
FIG. 1 shows an example of an image forming apparatus to which the present invention is applied. The image forming apparatus 1 forms an image on both surfaces of an image forming unit 2 that forms an image based on image data by an electrophotographic method, a paper feeding unit 3 that supplies paper (recording material) to the image forming unit 2 A recording material reversing paper feeding unit 4 that reverses the paper on which an image has been formed and feeds the paper again to the image forming unit 2.

  The paper feed unit 3 supplies the image forming unit 2 with a sheet having a size specified by the image data received by the image forming apparatus 1.

The image forming unit 2 includes C (cyan), M (magenta), Y (yellow), and K (black) image forming units 5C, 5M, 5Y, and 5K, an intermediate transfer member 10, and a secondary transfer unit. 11 and a fixing unit 12.
In each image forming unit, the surface of each photoconductor drum (image carrier) 6C, 6M, 6Y, 6K is scanned and exposed based on the image data to form an electrostatic latent image. The electrostatic latent images formed on the photosensitive drums 6C, 6M, 6Y, and 6K are developed as toner images of C, M, Y, and K, respectively, by the developing devices 7C, 7M, 7Y, and 7K. Thereafter, unless particularly distinguished, the image forming units 5C, 5M, 5Y, 5K are the image forming unit 5, the photosensitive drums 6C, 6M, 6Y, 6K are the photosensitive drum 6, and the developing devices 7C, 7M, 7Y and 7K are referred to as a developing device 7.

The intermediate transfer member 10 has a seam and is formed in an endless shape. The toner image developed on the photosensitive drum 6 is transferred by rotating while being in contact with the photosensitive drum 6.
The toner image transferred onto the intermediate transfer member 10 is sent to the transfer position of the secondary transfer unit 11 by the rotation of the intermediate transfer member 10.
The secondary transfer unit 11 transfers the toner image onto a sheet conveyed from the sheet feeding unit 3 and adjusted in timing with the toner image on the intermediate transfer member 10. The fixing unit 12 fixes the toner image on the paper to the paper. The paper on which the toner image is fixed by the fixing unit 12 is sequentially discharged to the paper discharge port 13.

When images are formed on both sides of the paper, the paper on which the toner image corresponding to the front surface (one surface) is fixed by the fixing unit 12 is not discharged to the paper discharge port 13, but in the direction of arrow a in FIG. And is conveyed to the recording material reversal sheet feeding unit 4.
The recording material reversal paper feeding unit 4 reverses the paper, adjusts the timing with the toner image corresponding to the back surface on the intermediate transfer body 10, and performs secondary transfer to form an image on the back surface (the other surface). Paper is fed again to the section 11. The secondary transfer unit 11 transfers the toner image corresponding to the back side to the sheet conveyed from the recording material reversal sheet feeding unit 4. The fixing unit 12 fixes the toner image on the paper to the paper. The paper on which the images are formed on both sides is sequentially discharged to the paper discharge port 13.

Next, the system configuration of the image forming apparatus will be described with reference to FIG. FIG. 2 is a diagram illustrating an example of a system configuration of the image forming apparatus 1.
The image forming apparatus 1 includes an image forming unit 2, a paper feeding unit 3, a recording material reversal paper feeding unit 4, and a control unit 8.
Since the configuration of the image forming unit 2, the paper feeding unit 3, and the recording material reversal paper feeding unit 4 have been described with reference to FIG. 1, the control unit 8 will be described here.
The control unit 8 is connected to the external device 100, each component of the image forming unit 2, the paper feed unit 3, and the recording material reversal paper feed unit 4. When receiving a request for outputting image data from the external device 100, the control unit 8 controls the image forming unit 5 so that the image forming unit 5 forms a toner image based on the image data. The external device 100 is a device that requests the image forming apparatus 1 to output image data. Specifically, the external device 100 is a personal computer, a facsimile, a scanner, or the like that requests image output. In addition, the image forming apparatus 1 includes an image reading device (not shown) that reads an image from a sheet on which an image to be output is formed. The image forming device 1 reads not only the image data received from the external device 100 but also the image reading device. Based on the image data, the image forming unit 5 can also be controlled so that the image forming unit 5 forms a toner image.

In the image forming apparatus 1 of the present embodiment, it is required to arrange the toner image from a specific position on the photosensitive drum 6 in order to keep the image quality of the image formed on the paper at a certain level. However, depending on the paper size specified by the image data, if the toner image is arranged from a specific position on the photosensitive drum 6, the productivity of the image forming apparatus 1 may be reduced. Therefore, the control unit 8 controls the image forming unit 5 to form a toner image from a specific position on the photosensitive drum 6 if the paper size designated by the image data is a predetermined paper size. . Further, as described above, since the toner image cannot be transferred onto the joint of the intermediate transfer member 10, the control unit 8 controls the intermediate transfer member 10 and the image forming unit 5 so as not to transfer the toner image onto the joint. To do.
Here, the control performed by the control unit 8 on the image forming unit 5 and the intermediate transfer body 10 in order to keep the image quality of the image formed on the paper at a certain level will be described with reference to FIG. FIG. 3 shows a position on the photosensitive drum 6 where development of the toner image is started when the number of toner images that can be arranged on the intermediate transfer member 10 (hereinafter referred to as the number of belt divisions) is 11, 5, and 7. 5 is a diagram illustrating an example of a relationship between the position of the toner image transferred to the intermediate transfer body 10 and the position of the toner image. Here, the number of belt divisions depends on the paper size.
In FIG. 3, the rectangle extending in the right direction is the toner image intermediate transfer member 10 developed in the rotational direction on the intermediate transfer member 10. In FIG. 3, the numbered figure arranged on the intermediate transfer member 10 represents a toner image transferred onto the intermediate transfer member 10. Further, an inverted triangular figure written in the information on the intermediate transfer member 10 represents a specific position on the photosensitive drum 6.
FIG. 3A shows a case where the paper size is a length corresponding to one rotation of the photosensitive drum 6 and the number of belt divisions is 11. In the case of FIG. 3A, since the paper size is a length corresponding to one rotation of the photosensitive drum 6, toner images developed from specific positions on the photosensitive drum 6 are sequentially arranged from the seam. Eleven toner images can be transferred. As described above, it is required to arrange the toner image from a specific position on the photosensitive drum 6 in order to keep the image quality of the image formed on the paper constant. In the case of FIG. 3A, since the toner image can be arranged at a specific position on the photosensitive drum 6, the image quality of the image formed on the paper can be kept at a certain level. Therefore, the control unit 8 controls the image forming unit 5 and the intermediate transfer member 10 so that the toner image is arranged on the intermediate transfer member 10 as shown in FIG.
FIG. 3B shows a case where the paper size is a length corresponding to two rotations of the photosensitive drum 6 and the number of belt divisions is five. In the case of FIG. 3B as well, since the paper size is a length corresponding to two rotations of the photosensitive drum 6, the photosensitive drum 6 produces a toner image developed from a specific position on the photosensitive drum 6. The toner images are sequentially arranged every two rotations, and five toner images can be transferred. Therefore, in the case of FIG. 3B as well, since the toner image can be arranged at a specific position on the photosensitive drum 6, the image quality of the image formed on the paper can be kept at a certain level.
However, when the number of belt divisions is 5, if the toner image is arranged in the area R indicated by hatching in the drawing, the seam is crossed, so that the toner image cannot be arranged in the area R. Therefore, when the number of belt divisions is 5, the control unit 8 controls the image forming unit 5 and the intermediate transfer member 10 so that the toner image is arranged on the intermediate transfer member 10 as shown in FIG.
FIG. 3C shows a case where the paper size is a length corresponding to 1.5 rotations of the photosensitive drum 6 and the number of belt divisions is seven. In the case of FIG. 3C, when a toner image is to be formed from a specific position on the photosensitive drum 6, after each toner image is formed, the photosensitive drum 6 must wait for 0.5 rotation. Therefore, the productivity of the image forming apparatus 1 is reduced. Therefore, in the case of FIG. 3C, regardless of a specific position on the photosensitive drum 6, the formation of the next toner image is started from the position where the toner image has been formed on the photosensitive drum 6. Yes. Even when the number of belt divisions is 7, if a toner image is arranged in the area R indicated by hatching in the drawing, the seam is crossed, so that the toner image cannot be arranged in the area R. Therefore, when the number of drum divisions is 7, the control unit 8 controls the image forming unit 5 and the intermediate transfer member 10 so that the toner image is arranged on the intermediate transfer member 10 as shown in FIG.
The relationship between the paper size and the rotational speed of the photosensitive drum 6 changes according to the diameter of the photosensitive drum 6. Further, the sheet size and the number of toner images that can be arranged on the intermediate transfer member 10 also vary depending on the peripheral length of the intermediate transfer member 10. Therefore, the relationship among the paper size, the number of rotations of the photosensitive drum 6 and the number of toner images that can be arranged on the intermediate transfer member 10 differs depending on each image forming apparatus, and is not restricted by this embodiment. Absent.

Again, the control part 8 is demonstrated based on FIG.
The control unit 8 selects a paper feeding unit mounted on the paper feeding unit 3 so as to feed a paper having a paper size specified by the image data, and the toner image transferred to the intermediate transfer member 10 is secondary. The paper feeding unit 3 is controlled so that the timing when the paper arrives at the transfer unit 11 coincides with the timing when paper is fed to the secondary transfer unit 11. Further, the control unit 8 controls the secondary transfer unit 11 and the fixing unit 12 so that an image is appropriately formed on the sheet.
Further, when forming images on both sides of the paper, the control unit 8 determines the timing at which the toner image corresponding to the back surface transferred to the intermediate transfer body 10 arrives at the secondary transfer unit 11 and the surface of the secondary transfer unit 11 on the surface. The recording material reversal sheet feeding unit 4 is controlled so that the timing at which the sheet on which the image has already been formed coincides with the timing of feeding. The timing at which the toner image corresponding to the back surface transferred to the intermediate transfer member 10 arrives at the secondary transfer unit 11 and the sheet on which the image has been formed on the surface are fed to the secondary transfer unit 11 controlled by the control unit 8. Details of the relationship with the timing will be described later.

Next, the control unit 8 will be described with reference to FIG. FIG. 4 is a diagram illustrating an example of a hardware configuration of the control unit 8.
The control unit 8 includes an input / output unit 84 that performs input / output of signals, a ROM 83 that stores a program (details will be described later) for calculating a timing at which the recording material reversal sheet feeding unit 4 performs refeeding, and the ROM 83. A central processing unit (CPU) 81 that reads and executes a stored program, and a RAM 82 that stores temporary data used when the program is executed.
Further, the changing means 85 shown in FIG. 5 is configured by calculation by the CPU 81 of the program stored in the ROM 83.

FIG. 5 is an example of a functional block diagram of the control unit 8 realized by the cooperation of the hardware such as the CPU 81 described above and the software stored in the ROM 83.
The control unit 8 includes a changing unit 85.
The changing unit 85 is connected to the external device 100 and the recording material reversing paper feeding unit 4. The changing unit 85 receives image data from the external device 100 and acquires the paper size when forming an image based on the image data from the image data. Next, the changing unit 85 calculates the number of belt divisions from the paper size.
Further, for example, a home position signal transmitted when the joint position comes to a position immediately before the photosensitive drum 6 and a specific position on the drum indicated by an inverted triangle in FIG. The position on the intermediate transfer body 10 where the toner image on the surface is arranged is calculated using the number of signal receptions.

When the image is to be formed on both sides, the changing unit 85 uses the calculated number of belt divisions and the position on the intermediate transfer body 10 where the toner image on the surface is disposed to change the sheet on which the image is formed on the surface to the secondary. The timing for refeeding to the transfer unit 11 is calculated. A method for calculating the refeed timing will be described later.
The changing unit 85 changes the timing at which the recording material reversal paper feeding unit 4 re-feeds to the calculated timing. As a result, the timing at which the toner image corresponding to the back surface transferred to the intermediate transfer body 10 arrives at the secondary transfer portion 11 and the timing at which the paper on which the image has been formed on the front surface are fed to the secondary transfer portion 11 Match and an image is formed on both sides of the paper.

Next, a case where the changing unit 85 changes the timing at which the recording material reversal paper feeding unit 4 refeeds will be described with reference to FIGS. 6 and 7.
FIG. 6 shows a region where a toner image can be arranged on the intermediate transfer member 10 when the number of belt divisions is 11, a position where a toner image on the front surface is arranged, and a position where a toner image on the back surface corresponding to the front surface is arranged. 4 schematically shows the timing at which the recording material reversal paper feeding unit 4 feeds paper again.
In FIG. 6, the toner image on the front surface is arranged at 1 position, and the toner image on the back surface corresponding to the front surface is arranged at 16 position. Similarly, a toner image on the front surface is arranged at the position 3 and a toner image on the back surface corresponding to the front surface is arranged at the position 18. Here, the toner image on the surface does not need to be transferred after the joint, and FIGS. 6 and 7 schematically illustrate the case where the image forming apparatus 1 is in a steady state.
At this time, the sheet is fed to the secondary transfer unit 11 for secondary transfer of the toner image arranged at the position 1, and then the sheet for transferring the toner image arranged at the position 16 to the sheet. Is the time (offset value) until the sheet is fed again to the secondary transfer unit 11. Accordingly, the recording material reversal sheet feeding unit 4 is configured to feed the sheet for forming the back side to the secondary transfer unit 11 after the sheet for forming the front side is fed to the secondary transfer unit 11. Refeeding may be performed so that the time becomes A. Even when the toner image on the front surface is arranged at the position 3 and the position 5 and the belt division number is 11, the recording material reversal sheet feeding unit 4 continues the sheet refeeding with the offset value as A. Thus, images can be formed on both sides of the paper.

FIG. 7 shows an area where the toner image can be arranged on the intermediate transfer member 10 when the number of belt divisions is 5, the position where the front toner image is arranged, the position where the rear toner image is arranged, and the recording material reversal. The timing at which the sheet feeding unit 4 re-feeds is schematically shown.
FIG. 7A is a diagram showing a case where the changing unit 85 attempts to form images on both sides of the paper without changing the refeed timing of the recording material reversal paper feeding unit 4. In FIG. 7A, the control unit 8 arranges the toner image on the front surface at the position 1 and the toner image on the back surface at the position 8. Further, the control unit 8 arranges the toner image on the front surface at the position 3 and arranges the toner image on the back surface at the position 10. When the number of belt divisions is 5, assuming that the offset value is constant at A, the timing at which the toner image on the back surface arrives at the secondary transfer unit 11 when the toner image on the front surface is at the position 1 and the position 3 The timing at which the paper is re-fed coincides, and images can be formed on both sides of the paper. However, when the toner image on the front surface is disposed at the position 5, the timing at which the toner image on the back surface disposed at the position 12 arrives at the secondary transfer unit 11 and the sheet is re-fed to the secondary transfer unit 11. The timing does not coincide with each other, and images cannot be formed on both sides of the paper. Accordingly, when the offset value is constant at A, the surface toner image cannot be formed on both sides by disposing the surface toner image at the position 5, and therefore the control unit 8 places the surface toner image at the position 5. Is placed at position 7.
Even when the front toner image is arranged at position 9, the timing at which the back toner image arrives at the secondary transfer unit 11 and the timing at which the paper is re-fed to the secondary transfer unit 11 do not match. An image cannot be formed. Therefore, the control unit 8 arranges the toner image on the surface at the position 11 instead of the position 9. As described above, when the number of belt divisions is 5, when the number of seams from the position where the front toner image is arranged to the position where the rear toner image is arranged is two, the rear toner image is transferred to the secondary transfer unit 11. And the timing of refeeding the sheet to the secondary transfer unit 11 do not match. Therefore, if the changing unit 85 does not change the refeed timing of the recording material reversal sheet feeding unit 4, there is a position where the toner image on the front surface cannot be arranged. The nature will decline.

FIG. 7B is a diagram showing a case where the changing unit 85 changes the refeed timing of the recording material reversal sheet feeding unit 4 and attempts to form images on both sides of the sheet. As described with reference to FIG. 7A, when the number of seams from the position where the front toner image is arranged to the position where the rear toner image is arranged is two, the back toner image is transferred to the secondary transfer unit 11. The timing of arrival and the timing of refeeding the paper to the secondary transfer unit 11 do not match. In this case, the timing at which the re-fed paper is re-fed to the secondary transfer unit 11 is a earlier than the timing at which the toner image on the back side arrives at the secondary transfer unit 11. As described above, this is because the toner image formed from a specific position on the photosensitive drum 6 is transferred to the intermediate transfer member 10 in order to make the image quality constant, and therefore, the region R where the toner image cannot be arranged on the intermediate transfer member 10. This is because there exists.
Therefore, when the toner image on the front surface is arranged at the positions 5 and 9, the changing unit 85 sets A + a, which is a delay of the refeeding timing of the recording material reversal supply unit 4 by a. The timing at which the toner image arranged at the position 12 and the toner image arranged at the position 16 arrive at the secondary transfer unit 11 coincides with the timing at which the paper is re-fed. Can be formed. As a result, the position where the toner image on the surface cannot be arranged does not exist as shown in FIG. Therefore, according to this configuration, the productivity during double-sided printing is one-half that during single-sided printing.

Next, processing performed by the changing unit 85 will be described using a flowchart. FIG. 8 is a flowchart showing an example of processing executed by the changing unit 85.
First, the changing unit 85 obtains the paper size from the image data input from the external device 100, and calculates the number of belt divisions (step S10).
Further, for example, a home position signal transmitted when the position of the joint reaches the position immediately before the photosensitive drum 6 and a specific position on the drum indicated by an inverted triangle in FIG. 3 are transmitted, for example, immediately below. The position on the intermediate transfer body where the toner image on the surface is arranged is acquired using the number of times the signal is received (step S11).
Then, the changing unit 85 calculates the re-feeding timing from the offset value determination table using the number of belt divisions and the position where the toner image on the surface is arranged (step S12).

Here, the offset value determination table will be described with reference to FIG. FIG. 9 shows an example of the offset determination value table.
The offset value determination table in FIG. 9A has an offset initial value that is a reference for the timing of feeding the back surface for each number of belt divisions, and a difference value that is advanced or delayed from the offset initial value for each front surface arrangement position. ing. The changing unit 85 acquires the offset initial value and the difference value from the number of belt divisions and the position of the toner image on the surface. Then, the changing unit 85 calculates the offset value by adding the difference value to the offset initial value or subtracting the difference value from the offset initial value. Here, in this embodiment, the arrangement positions of the toner images on the surface are sequentially assigned to the toner images sequentially arranged from the seam as shown in FIG. 3, but are not limited to this embodiment. Absent.
For example, when the number of belt divisions is 5 and the arrangement position of the toner image on the surface is 1, the changing unit 85 calculates the offset value as A because the offset initial value is A and the difference value is 0. When the belt division number is 5 and the arrangement position of the toner image on the front surface is 4, the changing unit 85 calculates the offset value as A + D because the offset initial value is A and the difference value is D.
Further, as shown in FIG. 9B, the offset determination value table does not have an offset initial value but has an absolute value of the offset value for each arrangement position of the toner image on the surface. The offset value may be acquired from the arrangement position of the toner image.

The processing performed by the changing unit 85 that has calculated the offset value will be described again with reference to FIG. The changing unit 85 changes the refeed timing of the recording material reversal sheet feeding unit 4 to the offset value calculated in step 12 (step S13).
By this step, the recording material reversing paper feeding unit 4 performs the refeeding of the back surface with the changed offset value, so that the back side toner image transferred to the intermediate transfer body 10 arrives at the secondary transfer unit 11. And the timing at which the paper is re-fed, the images can be formed on both sides of the paper.

  As is apparent from the above description, according to the present embodiment, productivity is improved when the image forming apparatus 1 forms images on both sides of the paper. Further, in the case of a predetermined paper size, a toner image can be formed from a specific position of the photosensitive drum 6, so that the image quality of the image formed on the paper can be maintained at a certain level.

  The embodiment described above is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

1 is a diagram illustrating an example of an image forming apparatus to which the present invention is applied. 1 is a diagram illustrating an example of a system configuration of an image forming apparatus. FIG. 6 is a diagram illustrating an example of a relationship among a sheet size, a belt division number, and a position on a photosensitive drum. 3 is a diagram illustrating an example of a hardware configuration of a control unit 8. FIG. 3 is an example of a functional block diagram of a control unit 8. FIG. FIG. 6 is a diagram illustrating an example of timing for feeding a back sheet when performing duplex printing when the number of belt divisions is 11. FIG. 10 is a diagram illustrating an example of timing for feeding a back sheet when performing duplex printing when the number of belt divisions is 5. It is the flowchart which showed an example of the process which the control part 8 performs. It is a figure which shows an example of an offset value determination table.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 2 ... Image forming part 3 ... Paper feeding part 4 ... Recording material reversal paper feeding part 5C, 5M, 5Y, 5K ... Image forming unit 6C, 6M, 6Y, 6K ... Photosensitive drum 7C, 7M, 7Y , 7K ... developing device 8 ... control unit 10 ... intermediate transfer member 11 ... secondary transfer unit 12 ... fixing unit 13 ... discharge port 81 ... CPU
82 ... RAM
83 ... ROM
84 ... Input / output unit 85 ... Change means 100 ... External device

Claims (3)

An image carrier for holding a toner image;
An intermediate transfer member formed in an endless shape having a seam, to which a toner image held by the image carrier is primarily transferred;
A secondary transfer portion for secondary transfer of the toner image primarily transferred to the intermediate transfer member to a recording material;
When forming an image on both sides of the recording material, after the secondary transfer to one side of the recording material, the recording material is reversed and transferred to the secondary transfer unit for secondary transfer to the other side. A recording material reversing paper feed section that refeeds the position;
Based on the position on the intermediate transfer body on which the toner image on the one surface is primarily transferred, the recording material reversal paper feeding unit re-feeds the recording material to the transfer position of the secondary transfer unit. Changing means for changing ,
The changing means includes the seam existing from a position on the intermediate transfer body where the toner image on the one surface is primarily transferred to a position on the intermediate transfer body where the toner image on the other surface is primarily transferred. The image forming apparatus is characterized in that the timing is delayed in the case where the number is two as compared with the case where the number is one .   The position on the intermediate transfer member on which the toner image on the one surface is primarily transferred is any one of regions sequentially arranged from the joint in the rotation direction of the intermediate transfer member. Item 2. The image forming apparatus according to Item 1. The image forming apparatus according to claim 1 , wherein the image holding body holds a toner image at the same position on the image holding body.

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