JP2011158852A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress upsizing of an image forming apparatus and a reduction in productivity of the apparatus, and also, secure the longer length in a conveying direction of a recording material capable of suppressing image deviation when an image is transferred. <P>SOLUTION: The image forming apparatus includes: a photoreceptor drum 11 on which a toner image is formed, and which rotates in a direction shown by an arrow A; and a transfer drum 21 which is arranged facing the photoreceptor drum 11, also, rotates in a direction shown by an arrow B, and configured to transfer the toner image to a paper S sandwiched between the transfer drum 21 and the photoreceptor drum 11 at a transfer position Pt facing the photoreceptor drum 11. Further, a transfer paper feed position Pi to supply the paper S to the transfer drum 21, and a transfer paper discharge position Po to discharge the paper S from the transfer drum 21 are provided. The transfer paper feed position Pi is located on the downstream side of the position Pt, the transfer paper discharge position Po is located on the downstream side of the position Pi, the transfer position Pt is located on the downstream side of the position Po. respectively, along the direction shown by the arrow B as the rotating direction of the transfer drum 21. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

The image forming apparatus includes a photoconductor that rotates while holding a toner image, and a transfer drum that rotates while holding a transfer material facing the photoconductor, and holds the toner image held on the photoconductor on the transfer drum. What is transferred to the transferred material is known.
As a conventional technique described in the publication, for example, when a four-color toner image sequentially formed and held on a photosensitive member is sequentially transferred for each color to a recording material held on a transfer drum, the recording material held on the transfer drum Is discharged after passing through the facing part of the photosensitive drum and the transfer drum four or five times depending on the length of the recording material in the conveying direction (see Patent Document 1).

JP-A-6-194968

  An object of the present invention is to secure a longer length in the conveyance direction of a recording material capable of suppressing the occurrence of image shift in image transfer while suppressing an increase in size and productivity of an image forming apparatus. And

  According to the first aspect of the present invention, an image holding member that is rotatably provided and holds an image, and an image that is rotatably provided opposite to the image holding member and is formed on the image holding member. A transfer member for transferring to a recording material sandwiched between the image holding body at a transfer position facing the holding body, a holding means for holding the recording material supplied to the transfer member on the transfer member, and a recording material The recording material is transferred to a transfer feeding position for supplying the recording material to the transfer member, and the recording material is sandwiched and conveyed, and the recording material is discharged from the transfer member. And a receiving section that receives the recording material discharged from the transfer discharge position, and a first path from the transfer feed position to the transfer position along the rotation direction of the transfer member, and the transfer The transfer part from the position The second path that reaches the transfer and discharge position along the rotation direction of the transfer member overlaps the portion that extends from the transfer and feed position to the transfer and discharge position along the rotation direction of the transfer member. An image forming apparatus characterized by the above.

According to a second aspect of the present invention, there is provided a delivery distance from the delivery position where the delivery unit sandwiches the recording material to the transfer feeding position, and the transfer delivery position from the transfer feeding position along the rotation direction of the transfer member. The sum of the distance between the paper-feeding and discharging to reach the transfer position from the transfer and discharging position to the transfer position along the rotation direction of the transfer member is set to be larger than the length in the conveyance direction of the recording material. The distance between the transfer and feed from the transfer position to the transfer and feed position along the rotation direction of the transfer member, the distance between the feed and discharge, and the receiving portion from the transfer and discharge position to the recording material. The image forming apparatus according to claim 1, wherein a sum of a receiving distance to a receiving position sandwiching the recording medium is set to be larger than a length in a conveyance direction of the recording material.
A third aspect of the present invention is the image forming apparatus according to the first or second aspect, wherein the receiving section also serves as a fixing section that fixes an image formed on the recording material.

  According to a fourth aspect of the present invention, there is provided an image holding body that is rotatably provided and holds an image, and an image that is rotatably provided facing the image holding body and formed on the image holding body. A transfer member for transferring to a recording material sandwiched between the image holding body at a transfer position facing the holding body, a holding means for holding the recording material supplied to the transfer member on the transfer member, and a recording material A transfer unit that sandwiches and conveys the recording material, and transfers the recording material toward a transfer sheet feeding position that is downstream in the rotation direction of the transfer member when viewed from the transfer position; An image forming apparatus including a receiving unit that receives a recording material discharged from a transfer discharge position that is downstream in the rotation direction of the transfer member as viewed from the position and upstream in the rotation direction of the transfer member as viewed from the transfer position. .

According to a fifth aspect of the present invention, the transfer distance from the transfer position where the transfer unit sandwiches the recording material to the transfer paper feed position, and the transfer discharge position from the transfer paper feed position along the rotation direction of the transfer member. The sum of the distance between the paper-feeding and discharging to reach the transfer position from the transfer and discharging position to the transfer position along the rotation direction of the transfer member is set to be larger than the length in the conveyance direction of the recording material. The distance between the transfer and feed from the transfer position to the transfer and feed position along the rotation direction of the transfer member, the distance between the feed and discharge, and the receiving portion from the transfer and discharge position to the recording material. The image forming apparatus according to claim 4, wherein a sum of a receiving distance to a receiving position sandwiching the recording medium is set to be larger than a length in a conveyance direction of the recording material.
A sixth aspect of the present invention is the image forming apparatus according to the fourth or fifth aspect, wherein the receiving section also serves as a fixing section that fixes an image formed on the recording material.

  According to a seventh aspect of the present invention, there is provided an image forming unit that forms a single color image or sequentially forms a plurality of color images for each color, and is rotatably provided to hold the image formed by the image forming unit. An image holding body and an image formed on the image holding body, which is rotatably provided facing the image holding body, are sandwiched between the image holding body at a transfer position facing the image holding body. A transfer member that transfers the recording material for each color, and a transfer unit that sandwiches and conveys the recording material, and delivers the recording material toward a transfer paper feeding position that is downstream in the rotation direction of the transfer member as viewed from the transfer position. The recording material is sandwiched and conveyed, and is discharged from a transfer discharge position that is downstream in the rotation direction of the transfer member as viewed from the transfer paper feed position and upstream in the rotation direction of the transfer member as viewed from the transfer position. The In the receiving portion for receiving the recording material, and in the transfer feeding position, the recording material supplied from the delivery portion is held by the transfer member, and the recording material held by the transfer member is formed by the image forming unit. The recording material passed through the transfer position as many times as the number of colors to be formed and passed through the transfer position as many times as the number of colors to be formed is received from the transfer member at the transfer discharge position. And an image forming apparatus including a control unit that causes the unit to discharge the image.

According to an eighth aspect of the present invention, the transfer distance from the transfer position where the transfer unit sandwiches the recording material to the transfer paper feed position, and the transfer paper discharge position along the rotation direction of the transfer member from the transfer paper feed position. The sum of the distance between the paper-feeding and discharging to reach the transfer position from the transfer and discharging position to the transfer position along the rotation direction of the transfer member is set to be larger than the length in the conveyance direction of the recording material. The distance between the transfer and feed from the transfer position to the transfer and feed position along the rotation direction of the transfer member, the distance between the feed and discharge, and the receiving portion from the transfer and discharge position to the recording material. 8. The image forming apparatus according to claim 7, wherein the sum of the receiving distance to the receiving position sandwiching the recording medium is set to be larger than the length of the recording material in the conveyance direction.
According to a ninth aspect of the present invention, in the image forming apparatus according to the eighth aspect, the receiving section also serves as a fixing section that fixes an image formed on the recording material.

According to the first aspect of the present invention, as compared with the case where the present configuration is not provided, an increase in the size of the image forming apparatus and a decrease in productivity are suppressed, and an occurrence of image shift in image transfer is suppressed. This makes it possible to ensure a longer length in the conveyance direction of the recording material.
According to the second aspect of the present invention, it is possible to more reliably suppress the image shift when the image is transferred to the recording material as compared with the case where the present configuration is not provided.
According to the third aspect of the present invention, the apparatus configuration can be simplified and the image transferred to the recording material can be prevented from being disturbed as compared with the case where the present configuration is not provided.
According to the fourth aspect of the present invention, compared with the case where the present configuration is not provided, the occurrence of image shift in image transfer is suppressed while suppressing the increase in size and productivity of the image forming apparatus. This makes it possible to ensure a longer length in the conveyance direction of the recording material.
According to the fifth aspect of the present invention, it is possible to more reliably suppress the image shift when the image is transferred to the recording material as compared with the case where the present configuration is not provided.
According to the sixth aspect of the present invention, the apparatus configuration can be simplified and the image transferred to the recording material can be prevented from being disturbed as compared with the case where the present configuration is not provided.
According to the seventh aspect of the present invention, compared to the case where the present configuration is not provided, the occurrence of image shift in image transfer is suppressed while suppressing the increase in size and productivity of the image forming apparatus. This makes it possible to ensure a longer length in the conveyance direction of the recording material.
According to the eighth aspect of the present invention, it is possible to more reliably suppress the image shift when transferring the image to the recording material, as compared with the case where the present configuration is not provided.
According to the ninth aspect of the present invention, the apparatus configuration can be simplified and the image transferred to the recording material can be prevented from being disturbed as compared with the case where the present configuration is not provided.

1 is a diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment of the present invention. (A) is a figure for demonstrating the dimension and positional relationship of a transfer drum, a delivery part, and a receiving part, (b) is a figure for demonstrating the dimension of a paper. 6 is a timing chart for explaining an image forming operation by the image forming apparatus. FIG. 6 is a diagram for explaining a relationship between a sheet length and a first distance. FIG. 6 is a diagram for explaining a relationship between a sheet length and a second distance. It is a figure for demonstrating the dimension and positional relationship of a transfer drum, a delivery part, and a receiving part when the transfer position is arrange | positioned at the 1st rotation path | route side. It is a figure showing an example of other composition of an image forming device to which the present invention is applied.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating an example of a configuration of an image forming apparatus to which the exemplary embodiment is applied.
The image forming apparatus includes an image forming unit 10 that forms a toner image, a transfer unit 20 that transfers a toner image formed by the image forming unit 10 to a sheet S as an example of a recording material, and a sheet that is transferred by the transfer unit 20. Between the fixing unit 30 for fixing the toner image transferred to S, the delivery unit 40 for transferring the paper S conveyed from a paper storage unit (not shown) to the transfer unit 20, and between the transfer unit 20 and the fixing unit 30. A receiving unit 50 that receives the sheet S delivered from the transfer unit 20. The image forming apparatus according to the present embodiment further includes a control unit 100 as an example of a control unit that controls operations of the image forming unit 10, the transfer unit 20, the fixing unit 30, the delivery unit 40, the receiving unit 50, and the like. ing.

  Among these, the image forming unit 10 includes a photosensitive drum 11 as an example of an image carrier, a charging device 12 that charges the photosensitive drum 11, and an exposure device 13 that exposes the charged photosensitive drum 11. The rotary developing device 14 that develops the electrostatic latent image formed on the photosensitive drum 11 by charging and exposure with toner, and the cleaning device 15 that cleans the toner remaining on the photosensitive drum 11 are provided.

  The photosensitive drum 11 includes a photosensitive layer (not shown) having a negative charging polarity on the surface thereof, and is attached so as to rotate in the arrow A direction. The charging device 12, the exposure device 13, the rotary developing device 14, and the cleaning device 15 are arranged around the photosensitive drum 11 in this order along the arrow A direction.

The charging device 12 is a contact roller type discharging device in the present embodiment, and charges the photosensitive drum 11 while rotating together with the photosensitive drum 11.
The exposure device 13 forms an electrostatic latent image by selectively irradiating the surface of the charged photosensitive drum 11 with light. The exposure apparatus 13 of the present embodiment has a configuration in which a plurality of light emitting elements (for example, LEDs) are arranged along the axial direction of the photosensitive drum 11.

The rotary developing device 14 includes a rotating shaft 14A extending along the axial direction of the photosensitive drum 11, and yellow (Y), magenta (M), cyan (C), and black (K) disposed around the rotating shaft 14A. Development units 14Y, 14M, 14C, and 14K. Further, the rotary developing device 14 is configured to rotate in the direction of arrow C about the rotation shaft 14A, and at any position facing the photosensitive drum 11 (hereinafter referred to as a developing position), any one of the developing devices. The vessel stops. The rotary developing device 14 is configured to develop the electrostatic latent image formed on the photosensitive drum 11 formed by the exposure device 13 using toner of a developing device stopped at the developing position.
Each color developing device 14Y, 14M, 14C, 14K contains a two-component developer containing the corresponding color component toner and carrier. Although a two-component developer is used in this example, a one-component developer that does not include a carrier may be used.

  The cleaning device 15 removes toner remaining on the surface of the photosensitive drum 11 and adhering matters other than toner. The cleaning device 15 of the present embodiment is configured by a blade type cleaner.

  In addition, the transfer device 20 is disposed so as to be rotatable so as to face the photosensitive drum 11, and the transfer drum 21 that transfers the toner image on the photosensitive drum 11 to the paper S and the paper S on the transfer drum 21 are gripped. A leading edge gripper 22 and a trailing edge gripper 23 and a phase sensor 25 for detecting the phase of the rotating transfer drum 21 are provided. Here, the transfer drum 21 is configured to rotate in the direction of arrow B, which is the same direction as the direction of rotation of the photosensitive drum 11 (direction of arrow A), at a position facing the photosensitive drum 11.

  The transfer drum 21 as an example of the transfer member is made of a metal having a cylindrical shape. A transfer power source (not shown) is connected to the transfer drum 21, and a toner image formed on the photosensitive drum 11 is transferred between the photosensitive drum 11 and the transfer drum 21. A transfer bias for transferring to the paper S is supplied in a region facing the drum 21. In the following description, a region where the photosensitive drum 11 and the transfer drum 21 face each other is referred to as a transfer position Pt. In the transfer drum 21, for example, an elastic layer may be formed on the outer peripheral surface of the cylindrical metal.

  Further, the tip gripper 22 as an example of a holding unit is provided on the outer peripheral surface of the transfer drum 21 along the axial direction of the transfer drum 21. The leading edge gripper 22 grips the end of the sheet S in the traveling direction (referred to as the leading edge SS in the following description: see FIG. 2B), and holds the grip. It is configured to release.

  On the other hand, the rear end gripper 23 is provided on the outer peripheral surface of the transfer drum 21 at a position different from the front end gripper 22 along the axial direction of the transfer drum 21. The rear end gripper 23 holds an end portion (referred to as a rear end SE in the following description: see FIG. 2B, which will be described later) on the opposite side to the traveling direction side of the sheet S between the rear end gripper 23. In addition, it is configured to release the grip.

  The leading edge gripper 22 and the trailing edge gripper 23 are configured to rotate together with the transfer drum 21 as the transfer drum 21 rotates.

  The phase sensor 25 is disposed to face the outer peripheral surface of the transfer drum 21, and detects the mark (not shown) provided on the outer peripheral surface of the transfer drum 21 to detect the phase of the rotating transfer drum 21. Is supposed to measure.

  Further, the fixing unit 30 includes a heating roll 31 having a heating source (not shown) and rotatably installed, and a pressure roll 32 pressed against the heating roll 31.

  Moreover, the delivery part 40 is comprised by the roll pair which contacts and rotates. And in this Embodiment, one side of the roll pair which comprises the delivery part 40 becomes a drive roll, and the other is a driven roll driven by rotation of a drive roll. In the following description, the nip portion of the roll pair in the delivery unit 40 is referred to as a paper feed delivery position Pf.

  On the other hand, the receiving unit 50 is also configured by a pair of rolls that rotate in contact with each other. And in this Embodiment, one of the roll pair which comprises the receiving part 50 becomes a drive roll, and the other is a driven roll which follows the rotation of a drive roll. In the following description, the nip portion of the roll pair in the receiving unit 50 is referred to as a paper discharge receiving position Pe.

  Further, the image forming apparatus holds the paper S that is transported from the delivery unit 40 toward the outer peripheral surface of the transfer drum 21 and the paper S supplied to the transfer drum 21 on the outer peripheral surface of the transfer drum 21. A rotation path 62 for transporting the sheet S in a heated state, and a sheet discharge path 63 for transporting the sheet S from the outer peripheral surface of the transfer drum 21 toward the receiving unit 50. In the present embodiment, the paper S is supplied from the paper feed path 61 toward the transfer paper feed position Pi located downstream in the rotation direction of the transfer drum 21 as viewed from the transfer position Pt. In the present embodiment, the paper is discharged from the transfer paper discharge position Po that is located downstream in the rotation direction of the transfer drum 21 as viewed from the transfer paper feed position Pi and upstream in the rotation direction of the transfer drum 21 as viewed from the transfer position Pt. The paper S is discharged toward the paper path 63.

  In the following description, a path from the transfer sheet feeding position Pi to the transfer sheet discharge path Po along the rotation direction B of the transfer drum 21 in the rotation path 62 is referred to as a first rotation path 621. Of the rotation paths 62, a path from the transfer sheet discharge path Po to the transfer sheet feeding position Pi along the rotation direction B of the transfer drum 21 is referred to as a second rotation path 622. Therefore, the transfer position Pt is located in the middle of the second rotation path 622.

As described above, in the rotation path 62, along the rotation direction B of the transfer drum 21, the transfer discharge position Po is downstream of the transfer paper feed position Pi, and the transfer position Pt is downstream of the transfer discharge position Po. The transfer paper feed position Pi is positioned on the downstream side of the transfer position Pt.
In the present embodiment, of the rotation path 62, the path from the transfer paper feed position Pi to the transfer position Pt via the transfer paper discharge position Po is the first path, and the transfer from the transfer position Pt to the transfer path Pt. The path from the paper feed position Pi to the transfer paper discharge position Po is the second path.

  2A is a diagram for explaining the dimensions and positional relationships of the transfer drum 21, the delivery unit 40, and the receiving unit 50 shown in FIG. 1, and FIG. 2B is a diagram for explaining the dimensions of the paper S. FIG. FIG.

  First, in FIG. 2A, the length in the rotation direction B of the outer peripheral surface of the transfer drum 21 is defined as a transfer drum peripheral length Ld. The distance from the transfer paper feed position Pi to the transfer paper discharge position Po along the rotation direction B, that is, the length of the first rotation path 621 is referred to as a paper feed / discharge distance Lx. The length from the transfer discharge position Po to the transfer position Pt along the rotation direction B is referred to as a discharge / transfer distance Ly. Further, the length from the transfer position Pt to the transfer paper feed position Pi along the rotation direction B is called a transfer paper feed distance Lz. Here, the sum of the sheet discharge transfer distance Ly and the transfer sheet feed distance Lz is the length of the second rotation path 622.

  Further, the distance from the paper feed delivery position Pf to the transfer paper feed position Pi, that is, the length of the paper feed path 61 is defined as the delivery distance Li, and the distance from the transfer paper discharge position Po to the paper discharge delivery position Pe, ie, the length of the paper discharge path 63. Let the length be the receiving distance Lo.

  On the outer peripheral surface of the transfer drum 21, the length from the paper feed delivery position Pf to the transfer position Pt via the transfer paper feed position Pi and the transfer paper discharge position Po is called a first distance L1 (= Li + Lx + Ly). . On the other hand, on the outer peripheral surface of the transfer drum 21, the length from the transfer position Pt to the paper discharge receiving position Pe via the transfer paper feed position Pi and the transfer paper discharge position Po is called a second distance L2 (= Lz + Lx + Lo). .

  FIG. 1 and FIG. 2A exemplify a case where the delivery distance Li and the reception distance Lo are the same length, and the paper discharge transfer distance Ly and the transfer paper feed distance Lz are the same length. As a result, the first distance L1 and the second distance L2 are equal. However, the present invention is not limited to this, and the delivery distance Li and the reception distance Lo may be made different, or the paper discharge transfer distance Ly and the transfer paper feed distance Lz may be made different. There may be a difference between the distance L1 and the second distance L2.

  Next, in FIG. 2B, the length in the traveling direction of the sheet S, that is, the length in the conveyance direction of the recording material is defined as a sheet length Ls. Further, the leading end of the sheet S in the traveling direction is referred to as a leading end SS, and the trailing end in the traveling direction is referred to as a trailing end SE.

Here, in the image forming apparatus of the present embodiment, the maximum value of the sheet length Ls of the sheet S that can be used for image formation is limited to be equal to or less than the transfer drum circumferential length Ld.
In the image forming apparatus according to the present embodiment, the maximum value of the sheet length Ls of the sheet S that can be used for image formation is less than the first distance L1 (Ls <L1) and less than the second distance L2 (Ls < L2). From the opposite viewpoint, the image forming apparatus according to the present embodiment has the first distance L1 and the second distance L2 so as to exceed the maximum value of the sheet length Ls of the sheet S that can be used for image formation. Is set. This reason will be described later.

Next, an image forming operation in the image forming apparatus shown in FIG. 1 will be described.
FIG. 3 shows a timing chart when the image forming apparatus shown in FIG. 1 is used and a full-color image including four colors of yellow, magenta, cyan and black is formed on the paper S. Here, FIG. 3 shows the passage of time, the passage of the paper S at the paper feed delivery position Pf, the transfer paper feed position Pi, the transfer paper discharge position Po, the transfer position Pt, and the paper discharge reception position Pe, and the development position. The relationship between the developing device to be arranged, the open / closed state of the front end gripper 22 and the rear end gripper 23, and the On / Off of the transfer bias supplied to the transfer position Pt is shown. In addition, in the paper feed delivery position Pf, the transfer paper feed position Pi, the transfer paper discharge position Po, the transfer position Pt, and the paper discharge reception position Pe shown in FIG. The case where it does not pass is shown at low level.
In FIG. 3, <1> indicates the first sheet S on which image formation is first performed, and <2> indicates the second sheet on which image formation is performed following the first sheet S. Paper S is shown.
In the initial state before the image forming operation is started, it is assumed that the yellow developing device 14Y is stopped at the developing position facing the photosensitive drum 11, as shown in FIG. In the initial state, the front end gripper 22 and the rear end gripper 23 are set to an open state, and the transfer bias is set to Off.

  As the image forming operation starts, the control unit 100 rotates the photosensitive drum 11 and the transfer drum 21 at predetermined peripheral speeds. At this time, the peripheral speeds of the photosensitive drum 11 and the transfer drum 21 are set so as to be constant speed or one of which is high within a range of 1% or less. Further, the control unit 100 rotates the roll pair configuring the delivery unit 40 and the roll pair configuring the receiving unit 50, respectively, at a predetermined peripheral speed. At this time, the peripheral speeds of the delivery unit 40 and the receiving unit 50 are set so as to be equal to the peripheral speed of the transfer drum 21. Then, as the transfer drum 21 starts rotating, a phase signal is input from the phase detection sensor 25 to the control unit 100. Here, in FIG. 3, a period in which the transfer drum 21 rotates once at the above-described peripheral speed is shown as a rotation period T of the transfer drum 21.

  Subsequently, the control unit 100 drives the charging device 12, the exposure device 13, and the developing device at the developing position (here, the yellow developing device 14Y). Accordingly, the photosensitive layer of the rotating photosensitive drum 11 is charged by the charging device 12 and then exposed by the exposure device 13, whereby an electrostatic latent image is formed on the photosensitive drum 11. Subsequently, the electrostatic latent image formed on the photosensitive drum 11 is developed by the yellow developing device 14Y, and a toner image corresponding to the electrostatic latent image is formed on the photosensitive drum 11. Thereafter, the yellow toner image formed on the photosensitive drum 11 moves toward the transfer position Pt as the photosensitive drum 11 further rotates.

  On the other hand, in response to the start of the image forming operation, the paper S is supplied from a paper storage unit (not shown). In response to a control signal from the control unit 100, the leading end SS of the first sheet S that is taken out and conveyed from the sheet storage unit reaches the sheet feeding position Pf (time t1). Next, the leading end SS of the first sheet S conveyed while being sandwiched by the delivery unit 40 reaches the transfer sheet feeding position Pi (time t2, first time). At this time, the control unit 100 causes the leading edge SS of the first sheet S to reach the transfer paper feeding position Pi as the leading edge gripper 22 attached to the transfer drum 21 reaches the transfer paper feeding position Pi. As described above, each unit is controlled based on the phase signal from the phase detection sensor 25. Then, the control unit 100 shifts the leading edge gripper 22 from the open state to the closed state as the leading edge SS of the first sheet S reaches the transfer paper feeding position Pi. As a result, the leading edge SS of the first sheet S is mechanically held on the transfer drum 21. Subsequently, in this example, the leading edge SS of the first sheet S held by the transfer drum 21 reaches the transfer discharge position Po (time t3, the first time), and then the first sheet S is transferred. The rear end SE passes through the paper feed delivery position Pf (time t4).

  Next, the leading edge SS of the first sheet S held by the transfer drum 21 reaches the transfer position Pt (time t5, first time). At this time, the control unit 100 adjusts the yellow toner image formation region on the photosensitive drum 11 as the leading end SS of the first sheet S held by the transfer drum 21 reaches the transfer position Pt. The exposure apparatus 13 is controlled based on the phase signal from the phase detection sensor 25 so that the leading end in the movement direction reaches the transfer position Pt. Then, the control unit 100 switches the transfer bias from Off to On as the leading edge SS of the first sheet S reaches the transfer position Pt. As a result, the image forming apparatus starts transfer of the yellow toner image onto the first sheet S.

  In this example, after the leading edge SS of the first sheet S reaches the transfer position Pt, the trailing edge SE of the first sheet S passes the transfer feeding position Pi (time t6, first time). ). Then, the control unit 100 shifts the rear end gripper 23 from the open state to the closed state as the rear end SE of the first sheet S passes the transfer paper feeding position Pi. As a result, the first sheet S is wound around the transfer drum 21 by being held by the transfer drum 21 with the leading edge SS at the leading edge gripper 22 and the trailing edge SE at the trailing edge gripper 23. It will rotate in the state that was. In this example, the leading edge SS of the first sheet S held by the transfer drum 21 reaches the transfer sheet feeding position Pi (time t7, second time), and then after the first sheet S. The end SE passes the transfer / discharge position Po (time t8, first time).

  Thereafter, the leading end SS of the first sheet S held by the transfer drum 21 reaches the transfer discharge position Po (time t9, second time). In this example, the development of the yellow toner image on the photosensitive drum 11 is completed at time t9. Then, as the development of the yellow toner image is completed, the control unit 100 drives the rotary developing device 14 to switch the developing device disposed at the developing position (from the yellow developing device 14Y to the magenta developing device 14M). Switch to).

  Next, the trailing edge SE of the first sheet S held by the transfer drum 21 passes the transfer position Pt (time t10, first time). Then, the control unit 100 switches the transfer bias from On to Off as the trailing edge SE of the first sheet S passes the transfer position Pt. Thus, the image forming apparatus ends the transfer of the yellow toner image onto the first sheet S. Further, in this example, after the transfer of the yellow toner image to the first sheet S is completed, switching of the developing device disposed at the developing position (switching from the yellow developing device 14Y to the magenta developing device 14M) is performed. Is completed (time t11).

  Next, the leading end SS of the first sheet S held by the transfer drum 21 reaches the transfer position Pt (time t12, second time). At this time, the control unit 100 adjusts the magenta toner image formation region on the photosensitive drum 11 as the leading edge SS of the first sheet S held by the transfer drum 21 reaches the transfer position Pt. The exposure device 13 and the rotary developing device 14 are controlled so that the leading end in the moving direction reaches the transfer position Pt. Then, the control unit 100 switches the transfer bias from Off to On as the leading edge SS of the first sheet S reaches the transfer position Pt. As a result, the image forming apparatus starts transfer of the magenta toner image onto the first sheet S.

  In this example, after the leading edge SS of the first sheet S reaches the transfer position Pt, the trailing end SE of the first sheet S passes the transfer feeding position Pi (time t13, second time). ). In this example, the leading edge SS of the first sheet S held by the transfer drum 21 reaches the transfer sheet feeding position Pi (time t14, the third time), and then after the first sheet S. The end SE passes the transfer / discharge position Po (time t15, second time).

  Thereafter, the leading edge SS of the first sheet S held by the transfer drum 21 reaches the transfer discharge position Po (time t16, third time). In this example, the development of the magenta toner image on the photosensitive drum 11 is completed at time t16. Then, as the development of the magenta toner image is completed, the control unit 100 drives the rotary developing device 14 to switch the developing device disposed at the developing position (from the magenta developing device 14M to the cyan developing device 14C). Switch to).

  Next, the trailing edge SE of the first sheet S held by the transfer drum 21 passes the transfer position Pt (time t17, second time). Then, the control unit 100 switches the transfer bias from On to Off as the trailing edge SE of the first sheet S passes the transfer position Pt. As a result, the image forming apparatus ends the transfer of the magenta toner image to the first sheet S. In this example, after the transfer of the magenta toner image to the first sheet S is completed, switching of the developing device disposed at the developing position (switching from the magenta developing device 14M to the cyan developing device 14C) is performed. Is completed (time t18).

  Next, the leading edge SS of the first sheet S held by the transfer drum 21 reaches the transfer position Pt (time t19, third time). At this time, the control unit 100 adjusts the cyan toner image formation region on the photosensitive drum 11 as the leading end SS of the first sheet S held by the transfer drum 21 reaches the transfer position Pt. The exposure device 13 and the rotary developing device 14 are controlled so that the leading end in the moving direction reaches the transfer position Pt. Then, the control unit 100 switches the transfer bias from Off to On as the leading edge SS of the first sheet S reaches the transfer position Pt. As a result, the image forming apparatus starts transferring the cyan toner image onto the first sheet S.

  In this example, after the leading edge SS of the first sheet S reaches the transfer position Pt, the trailing edge SE of the first sheet S passes the transfer feeding position Pi (time t20, third time). ). In this example, the leading edge SS of the first sheet S held by the transfer drum 21 reaches the transfer sheet feeding position Pi (time t21, the fourth time), and then after the first sheet S. The end SE passes through the transfer discharge position Po (time t22, third time).

  Thereafter, the leading end SS of the first sheet S held by the transfer drum 21 reaches the transfer discharge position Po (time t23, fourth time). In this example, the development of the cyan toner image on the photosensitive drum 11 is completed at time t23. Then, the control unit 100 drives the rotary developing device 14 as the development of the cyan toner image is completed, and switches the developing device disposed at the developing position (from the cyan developing device 14C to the black developing device 14K). Switch to).

  Next, the trailing edge SE of the first sheet S held by the transfer drum 21 passes the transfer position Pt (time t24, third time). Then, the control unit 100 switches the transfer bias from On to Off as the trailing edge SE of the first sheet S passes the transfer position Pt. As a result, the image forming apparatus ends the transfer of the cyan toner image onto the first sheet S. Further, in this example, after the transfer of the cyan toner image to the first sheet S is completed, switching of the developing device disposed at the developing position (switching from the cyan developing device 14C to the black developing device 14K) is performed. Is completed (time t25).

  Next, the leading end SS of the first sheet S held by the transfer drum 21 reaches the transfer position Pt (time t26, fourth time). At this time, the control unit 100 adjusts the black toner image formation region on the photosensitive drum 11 as the leading edge SS of the first sheet S held by the transfer drum 21 reaches the transfer position Pt. The exposure device 13 and the rotary developing device 14 are controlled so that the leading end in the moving direction reaches the transfer position Pt. Then, the control unit 100 switches the transfer bias from Off to On as the leading edge SS of the first sheet S reaches the transfer position Pt. As a result, the image forming apparatus starts the transfer of the black toner image onto the first sheet S.

  In this example, after the leading edge SS of the first sheet S reaches the transfer position Pt, the trailing end SE of the first sheet S passes the transfer feeding position Pi (time t27, fourth time). ). In this example, the leading edge SS of the first sheet S held by the transfer drum 21 reaches the transfer sheet feeding position Pi (time t28, the fifth time), and then after the first sheet S. The end SE passes through the transfer discharge position Po (time t29, fourth time).

  Thereafter, the leading end SS of the first sheet S gripped by the transfer drum 21 reaches the transfer discharge position Po (time t30, fifth time). At this time, the control unit 100 shifts the leading edge gripper 22 from the closed state to the opened state as the leading edge SS of the first sheet S gripped by the transfer drum 21 reaches the transfer discharge position Po. Let As a result, the leading edge SS of the first sheet S is released from the transfer drum 21. In this example, the development of the black toner image on the photosensitive drum 11 is completed at time t30. Then, as the development of the black toner image is completed, the control unit 100 drives the rotary developing device 14 to switch the developing device disposed at the developing position (from the black developing device 14K to the yellow developing device 14Y). Switch to).

  Next, the trailing edge SE of the first sheet S held by the transfer drum 21 passes the transfer position Pt (time t31, fourth time). Then, the control unit 100 switches the transfer bias from On to Off as the trailing edge SE of the first sheet S passes the transfer position Pt. Thereby, the image forming apparatus ends the transfer of the black toner image onto the first sheet S. Accordingly, yellow, magenta, cyan, and black toner images are transferred onto the first sheet S in an overlapping manner. Further, in this example, after the transfer of the black toner image to the first sheet S is completed, switching of the developing device disposed at the developing position (switching from the black developing device 14K to the yellow developing device 14Y) is performed. Is completed (time t32).

  Next, the leading edge SS of the first sheet S released from the gripping of the transfer drum 21 by the leading edge gripper 22 reaches the paper discharge receiving position Pe (time t33). In this example, at the time t33, the leading end SS of the second sheet S conveyed from the sheet storage unit (not shown) reaches the sheet feeding / delivery position Pf. Then, the trailing edge SE of the first sheet S passes the transfer sheet feeding position Pi (time t34). Next, the leading edge SS of the second sheet S conveyed while being sandwiched by the delivery unit 40 reaches the transfer sheet feeding position Pi (time t35, first time). At this time, the control unit 100 causes the leading end SS of the second sheet S to reach the transfer feeding position Pi as the leading edge gripper 22 attached to the transfer drum 21 reaches the transfer feeding position Pi. Thus, each part is controlled. Then, the control unit 100 shifts the leading edge gripper 22 from the open state to the closed state as the leading edge SS of the second sheet S reaches the transfer feeding position Pi. As a result, the leading end SS of the second sheet S is mechanically held on the transfer drum 21.

  Thereafter, in this example, the trailing edge SE of the first sheet S held by the transfer drum 21 passes through the transfer discharge position Po (time t36, fifth time). At this time, the control unit 100 moves the trailing edge gripper 23 from the closed state to the opened state as the trailing edge SE of the first sheet S held by the transfer drum 21 reaches the transfer discharge position Po. And migrate. As a result, the trailing edge SE of the first sheet S is released from the transfer drum 21. Subsequently, in this example, the leading end SS of the second sheet S held by the transfer drum 21 reaches the transfer sheet discharge position Po (time t37, first time), and then the second sheet S is transferred. The rear end SE passes through the paper feed delivery position Pf (time t38, first time). In this example, the trailing edge SE of the first sheet S passes through the paper discharge receiving position Pe at time t38. The first sheet S that has passed through the paper discharge receiving position Pe, that is, the receiving unit 50 is nipped between the heating roll 31 and the pressure roll 32 in the fixing unit 30. Accordingly, the toner images of the respective colors transferred to the first sheet S are fixed by heating and pressurization and then discharged to a discharge stacking unit (not shown).

  Next, the leading end SS of the second sheet S held by the transfer drum 21 reaches the transfer position Pt (time t39, first time). At this time, the control unit 100 adjusts the yellow toner image formation region on the photosensitive drum 11 as the leading edge SS of the second sheet S held by the transfer drum 21 reaches the transfer position Pt. The exposure apparatus 13 is controlled so that the front end in the movement direction reaches the transfer position Pt. Then, the control unit 100 switches the transfer bias from Off to On as the leading edge SS of the second sheet S reaches the transfer position Pt. As a result, the image forming apparatus starts transferring the yellow toner image onto the second sheet S.

  In this example, after the leading end SS of the second sheet S reaches the transfer position Pt, the trailing end SE of the second sheet S passes the transfer feeding position Pi (time t40, first time). ). Then, the control unit 100 shifts the rear end gripper 23 from the open state to the closed state as the rear end SE of the second sheet S passes the transfer paper feeding position Pi. As a result, the second sheet S is wound around the transfer drum 21 by the leading end SS gripped by the leading end gripper 22 and the trailing end SE of the second sheet S by the trailing end gripper 23. It will rotate in the state that was.

  Thereafter, image formation is performed on the second sheet S and the third and subsequent sheets S in the same procedure as the first sheet S.

Here, the behavior of the sheet S in the above-described image forming operation will be described by taking the first sheet S as an example with reference to FIGS. 1 to 3.
First, in a period from time t1 to time t2, the first sheet S is conveyed through the sheet feeding path 61 while being sandwiched by the delivery unit 40.
Next, in a period from time t2 to time t4, the first sheet S is in a state where the leading end SS is gripped by the transfer drum 21 by the leading end gripper 22 and the other part is sandwiched by the delivery unit 40. The sheet is conveyed across the rotation path 62 and the sheet feeding path 61.
Subsequently, in a period from time t4 to time t6, the first sheet S straddles the rotation path 62 and the sheet feeding path 61 in a state where the leading edge SS is held by the transfer drum 21 by the leading edge gripper 22. Be transported.
Next, in the period from time t6 to time t30, the first sheet S is held by the transfer drum 21 with the leading edge SS held by the leading edge gripper 22 and the trailing edge SE by the trailing edge gripper 23, respectively. The rotation path 62 is conveyed.
Thereafter, in the period from time t30 to time t33, the first sheet S straddles the sheet discharge path 63 and the rotation path 62 in a state where the trailing edge SE is gripped by the transfer drum 21 by the trailing edge gripper 23. Be transported.
In the period from time t33 to time t36, the first sheet S is in a state where the trailing edge SE is gripped by the transfer drum 21 by the trailing edge gripper 23 and the other part is sandwiched by the receiving unit 50. The paper is conveyed across the paper discharge path 63 and the rotation path 62.
Finally, during the period from time t36 to time t38, the first sheet S is conveyed through the paper discharge path 63 while being sandwiched by the receiving unit 50.

  In the present embodiment, the transfer of the yellow, magenta, cyan, and black toner images at the transfer position Pt is performed within a period from time t5 to time t31. Here, at the time t5 when the transfer of the first yellow toner image is started, as described above, the sandwiching of the first sheet S by the delivery unit 40 has already been completed, and the first sheet The sheet S is conveyed while being held only on the transfer drum 21. On the other hand, at the time t31 when the transfer of the black toner image, which is the last color, is finished, as described above, the sandwiching of the first sheet S by the receiving unit 50 has not started, and the first sheet S Is conveyed while being held only on the transfer drum 21.

  4 is a diagram for explaining the relationship between the first distance L1 and the paper length Ls shown in FIG. 2, and FIG. 4A shows the first distance L1 larger than the paper length Ls. FIG. 4B shows a case (L1> Ls), and FIG. 4B shows a case where the first distance L1 is smaller than the paper length Ls (L1 <Ls). Note that, as described above, the first distance L1 is represented by the sum of the delivery distance Li, the paper feed / discharge distance Lx, and the discharge / transfer distance Ly (see FIG. 2A).

  For example, as shown in FIG. 4A, when L1> Ls, when the leading edge SS of the sheet S reaches the transfer position Pt in order to transfer the first color (yellow in the above example) toner image, this The trailing edge SE of the paper S passes through the paper feed delivery position Pf. That is, when L1> Ls, the sheet S is held only by the transfer drum 21 when the transfer of the first color toner image is started.

  On the other hand, for example, when L1 <Ls as shown in FIG. 4B, when the leading edge of the paper S reaches the transfer position Pt in order to transfer the toner image of the first color, The end SE does not pass through the paper feed delivery position Pf. That is, when L1 <Ls, the sheet S is held by the transfer drum 21 and sandwiched between the delivery units 40 at the time when the transfer of the first color toner image is started. After the transfer of the toner image is started and before the transfer of the first toner image is completed, the toner image is held only by the transfer drum 21.

  In the present embodiment, as described above, drive control is performed by the control unit 100 so that the peripheral speed of the transfer drum 21 and the peripheral speed of the roll pair constituting the delivery unit 40 are equal. However, the actual peripheral speeds are often not the same due to the processing accuracy, mounting accuracy, or driving accuracy of each member.

  Here, when L1> Ls as shown in FIG. 4A, the peripheral speed of the delivery section 40 is from the start to the end of the transfer of the first color toner image onto the paper S. Will not be affected. On the other hand, when L1 <Ls as shown in FIG. 4B, from the start of the transfer of the first color toner image to the paper S until the trailing edge SE of the paper S passes the delivery section 40. During this time, the sheet S is affected by the peripheral speed of the delivery unit 40, while the rear end of the sheet S passes through the delivery unit 40 until the transfer of the first color toner image is completed. The sheet S is not affected by the peripheral speed of the delivery unit 40. For this reason, when L1> Ls as in the present embodiment, the sub-scanning direction of the first color transfer image resulting from the change in the conveyance speed of the paper S during the transfer of the first color toner image. The expansion / contraction to is less likely to occur than when L1 <Ls. As a result, in this example, in the superimposed image formed on the paper S, a phenomenon (image shift) in which the yellow image is shifted in the sub-scanning direction with respect to the magenta, cyan, and black images is suppressed. .

  FIG. 5 is a diagram for explaining the relationship between the second distance L2 and the paper length Ls shown in FIG. 2, and FIG. 5A shows the case where the second distance L2 is larger than the paper length Ls. FIG. 5B shows a case where the second distance L2 is smaller than the paper length Ls (L2 <Ls). Note that, as described above, the second distance L2 is represented by the sum of the distance Lz between transfer and paper feed, the distance Lx between paper feed and paper discharge, and the receiving distance Lo (see FIG. 2A).

  For example, when L2> Ls as shown in FIG. 5A, when the trailing edge SE of the sheet S reaches the transfer position Pt in order to transfer the toner image of the last color (black in the above example), The leading edge SS of the paper S has not reached the paper discharge receiving position Pe. That is, when L2> Ls, the sheet S is held only on the transfer drum 21 when the transfer of the last color toner image is completed.

  On the other hand, for example, when L2 <Ls as shown in FIG. 5B, when the trailing edge SE of the paper S reaches the transfer position Pt in order to transfer the toner image of the last color, the paper S The leading edge SS has reached the paper discharge receiving position Pe. That is, when L2 <Ls, the sheet S is held only by the transfer drum 21 at the time when the transfer of the last color toner image is started, and the transfer of the last toner image is started. Then, before the transfer of the final toner image is completed, the toner image is held by the transfer drum 21 and is sandwiched by the receiving unit 50.

  In the present embodiment, as described above, drive control is performed by the control unit 100 so that the peripheral speed of the transfer drum 21 and the peripheral speed of the roll pair constituting the receiving unit 50 are equal. However, the actual peripheral speeds are often not the same due to the processing accuracy, mounting accuracy, or driving accuracy of each member.

  Here, when L2> Ls as shown in FIG. 5A, the sheet S has the peripheral speed of the receiving unit 50 from the start to the end of the transfer of the last toner image to the sheet S. It will not be affected. On the other hand, when L2 <Ls as shown in FIG. 5B, from the start of the transfer of the last color toner image to the paper S until the leading edge SS of the paper S passes through the receiving unit 50. While the sheet S is not affected by the peripheral speed of the receiving unit 50, while the leading edge SS of the sheet S passes through the receiving unit 50, the transfer of the last color toner image is completed. The sheet S is affected by the peripheral speed of the receiving unit 50. Therefore, when L2> Ls as in the present embodiment, the last color transfer image in the sub-scanning direction due to the change in the conveyance speed of the paper S during the transfer of the last color toner image. Is less likely to occur than when L2 <Ls. As a result, in this example, in the superimposed image formed on the paper S, a phenomenon (image shift) in which the black image is shifted in the sub-scanning direction with respect to the yellow, magenta, and cyan images is suppressed. .

  For the above reasons, in the image forming apparatus of the present embodiment, the maximum value of the sheet length Ls of the sheet S that can be used for image formation is less than the first distance L1 (Ls <L1) and less than the second distance L2. It is limited to (Ls <L2).

  Further, when a four-color full-color image is formed on the sheet S, as is apparent from FIGS. 1 to 3, the leading end SS is released after the transfer drum 21 starts to grip the leading end SS of one sheet S. In the meantime, the motor rotates 4 and a half times (more specifically, 4 times + Lx). During this time, in the rotation path 62 existing on the outer peripheral surface of the transfer drum 21, one sheet S passes through the first rotation path 621 from the transfer paper feed position Pi to the transfer paper discharge position Po five times. Then, the second rotation path 622 from the transfer paper discharge position Po to the transfer paper feed position Pi via the transfer position Pt is passed only four times.

  Here, FIG. 6 is a diagram for explaining the dimensions and positional relationships of the transfer drum 21, the delivery unit 40, and the receiving unit 50 when the transfer position Pt is arranged on the first rotation path 621 side. In the example shown in FIG. 6, along the rotation direction B of the transfer drum 21 in the rotation path 62, the transfer position Pt is downstream of the transfer paper feed position Pi, and the transfer discharge position is downstream of the transfer position Pt. The transfer paper feed position Pi is positioned downstream of the transfer paper discharge position Po.

  In FIG. 6, the transfer drum circumferential length Ld, delivery distance Li, and reception distance Lo are the same as those described with reference to FIG. A distance from the transfer paper feed position Pi to the transfer position Pt along the rotation direction B is referred to as a paper feed transfer distance La. The length from the transfer position Pt to the transfer discharge position Po along the rotation direction B is referred to as a transfer discharge distance Lb. Further, the length from the transfer / discharge position Po to the transfer / feed position Pi in the rotation direction B, that is, the length of the second rotation path 622 is referred to as a discharge / feed distance Lc. Here, the sum of the inter-paper transfer distance La and the inter-transfer paper discharge distance Lb is the length of the first rotation path 621. In the example shown in FIG. 6, the distance from the paper feed delivery position Pf to the transfer position Pt, that is, the sum of the delivery distance Li and the paper feed transfer distance La is the first distance L10 (the first distance shown in FIG. 2). The distance from the transfer position Pt to the paper discharge receiving position Pe, that is, the sum of the distance Lb between the transfer paper discharge and the reception distance Lo is a second distance L20 (second distance L2 shown in FIG. 2). To correspond). In the example shown in FIG. 6, since the positional relationship among the transfer paper feed position Pi, the transfer paper discharge position Po, and the transfer position Pt is different from that in FIG. 2, the paper feed paper discharge distance Lx shown in FIG. There is no paper discharge transfer distance Ly and transfer paper feed distance Lz. In the following description, it is assumed that the transfer drum circumferential length Ld, the delivery distance Li, and the reception distance Lo shown in FIGS. 2 and 6 are the same length, that is, in FIG. 2 and FIG. The diameter of 21 is the same.

  In the following, assuming the configuration shown in FIG. 6, when images of four colors of yellow, magenta, cyan, and black are sequentially transferred onto one sheet S, an image that is first transferred onto one sheet S In addition, the conditions necessary for suppressing the image shift (magnification fluctuation in the sub-scanning direction) of the image to be transferred last are examined. Here, in the former, when the leading edge SS of the paper S reaches the transfer position Pt in order to transfer the image of the first color (for example, yellow), the trailing edge SE of the paper S has already been delivered to the delivery unit 40 (feeding). It is necessary to pass through the paper delivery position Pf). In the latter case, when the trailing edge SE of the sheet S passes the transfer position Pt in order to transfer the image of the last color (for example, black), the leading end SS of the sheet S is moved to the receiving unit 50 (discharge receipt). It is required that the position Pe) has not been reached.

First, the first comparative embodiment based on the configuration shown in FIG. 6 will be described.
In the first comparative embodiment, the sheet S supplied to the transfer drum 21 from the delivery unit 40 (paper feed delivery position Pf) via the transfer paper feed position Pi passes the transfer position Pt for the first time (first). At this time, it is assumed that transfer of an image of the first color (for example, yellow) is started. In the first comparative embodiment, the sheet S supplied to the transfer drum 21 is the Xth time (X is the number of colors of the image transferred to the sheet S, and here, yellow, magenta, cyan, and black are used. After passing the transfer position Pt at X = 4), when passing the transfer discharge position Po for the first time (first time), it is released from the transfer drum 21 at the transfer discharge position Po, and the receiving section 50 (discharged paper) It is assumed that the sheet is conveyed toward the receiving position Pe).

  In the configuration shown in FIG. 6, when the method of the first comparative form is adopted, the sheet S passes through the transfer position Pt four times while being held by the transfer drum 21. For this reason, regarding the time required for image formation on one sheet S (the number of sheets S on which image formation is possible per unit time), the method of the present embodiment is adopted in the configuration shown in FIG. Become equivalent.

  When the method of the first comparative form is adopted in the configuration shown in FIG. 6, the sheet S is first supplied when it is first supplied to the transfer position Pt via the sheet feed delivery position Pf and the transfer sheet feed position Pi. The transfer of the color image is started. At this time, the length of the transport path (referred to as a pre-transfer transport path in the following description) of the sheet S from the paper feed delivery position Pf to the transfer position Pt at the start of transfer is the delivery distance Li and the paper feed transfer interval. The sum of distances La (Li + La), that is, the first distance L10.

  On the other hand, when the method of the present embodiment is adopted in the configuration shown in FIG. 2, the paper S is first supplied to the transfer position Pt via the paper feed delivery position Pf, the transfer paper feed position Pi, and the transfer paper discharge position Po. At that time, the transfer of the first color image is started. At this time, the length of the pre-transfer conveyance path of the paper S from the paper feed delivery position Pf to the transfer position Pt at the start of transfer is the delivery distance Li, the paper feed paper discharge distance Lx, and the paper discharge transfer distance Ly. The sum (Li + Lx + Ly), that is, the first distance L1.

  Further, when the method of the first comparative form is adopted in the configuration shown in FIG. 6, the sheet S is released at the transfer discharge position Po after the transfer of the last color image is completed at the transfer position Pt. Then, it is conveyed toward the paper discharge receiving position Pe. At this time, the length of the transport path (hereinafter referred to as a post-transfer transport path) of the sheet S from the transfer position Pt at the end of the transfer to the paper discharge receiving position Pe is the distance between the transfer paper discharge Lb and the reception. The sum of the distance Lo (Lb + Lo), that is, the second distance L20.

  On the other hand, when the method of the present embodiment is adopted in the configuration shown in FIG. 2, the sheet S passes through the transfer paper feed position Pi after the transfer of the last color image is completed at the transfer position Pt. Is released at the transfer paper discharge position Po and conveyed toward the paper discharge reception position Pe. At this time, the length of the post-transfer conveyance path of the paper S from the transfer position Pt at the end of the transfer to the paper discharge receiving position Pe is the distance between the transfer paper feed Lz, the paper feed paper discharge distance Lx, and the reception distance Lo. The sum (Lz + Lx + Lo), that is, the second distance L2.

  In the present embodiment, in the rotation path 62 of the transfer drum 21, the pre-transfer conveyance path and the post-transfer conveyance path partially overlap at a portion from the transfer paper feed position Pi to the transfer paper discharge position Po. On the other hand, in the first comparative embodiment, the pre-transfer conveyance path and the post-transfer conveyance path do not overlap in the rotation path 62 of the transfer drum 21.

  For this reason, in the first comparative embodiment, productivity equivalent to that in the present embodiment can be ensured, but on the other hand, both the pre-transfer conveyance path and the post-transfer conveyance path are limited to be shorter than in the present embodiment. End up. In other words, in the first comparative form, the maximum length of the paper length Ls of the paper S on which image formation is possible in a state where occurrence of image displacement is suppressed is smaller than that in the present embodiment. If the length of the pre-transfer conveyance path and the length of the post-transfer conveyance path in the first comparative embodiment are to be the same as those of the present embodiment, the transfer is performed to increase the transfer drum circumferential length Ld. The diameter of the drum 21 is increased, or the distance between the transfer section 40 and the transfer drum 21 and the distance between the transfer drum 21 and the reception section 50 are respectively increased in order to increase the transfer distance Li and the reception distance Lo. Is required.

Subsequently, a second comparative example based on the configuration shown in FIG. 6 will be described.
In the second comparative embodiment, the sheet S supplied to the transfer drum 21 from the delivery unit 40 (paper feed delivery position Pf) via the transfer paper feed position Pi passes the transfer position Pt for the first time (first). In this case, the transfer of the image is not started, and the transfer of the image of the first color (for example, yellow) is started when passing the transfer position Pt for the second time (again). In the second comparative embodiment, the sheet S supplied to the transfer drum 21 passes the transfer position Pt for the Xth time (here, X = 4 as described above), and then transferred and discharged for the first time (first). When the paper passes through the paper position Po, it is not released from the transfer drum 21 at the transfer paper discharge position Po, and further passes through the transfer position Pt (X + 1 time, at which time no image is transferred), and the second time (again ), The paper is released from the transfer drum 21 at the transfer paper discharge position Po and is conveyed toward the receiving unit 50 (paper discharge reception position Pe).

  In the configuration shown in FIG. 6, when the method of the second comparative form is adopted, the sheet S passes through the transfer position Pt six times while being held by the transfer drum 21. Therefore, regarding the time required for image formation on one sheet S (the number of sheets S on which image formation is possible per unit time), compared to the case where the method of the present embodiment is adopted in the configuration shown in FIG. As a result, productivity is lowered.

  Further, when the method of the second comparative form is adopted in FIG. 6, the sheet S is first supplied to the transfer position Pt via the paper feed delivery position Pf and the transfer paper feed position Pi, and then the transfer paper discharge position. The transfer of the image of the first color is started at the point in time when it passes Po and the transfer paper feed position Pi and is supplied to the transfer position Pt for the second time. At this time, the length of the pre-transfer conveyance path from the paper feed delivery position Pf to the transfer position Pt at the start of transfer is as follows: delivery distance Li, paper feed transfer distance La, transfer paper discharge distance Lb, paper discharge paper feed. The sum (Li + La + Lb + Lc + La) of the distance Lc and the distance La between paper feed and transfer. Accordingly, the length of the pre-transfer conveyance path in this case is longer than one transfer drum 21 or the transfer drum peripheral length Ld.

  On the other hand, when the method of the present embodiment is adopted in the configuration shown in FIG. 2, the length of the pre-transfer conveyance path is as follows: the delivery distance Li, the paper feed / discharge distance Lx, and the paper discharge / transfer distance Ly. (Li + Lx + Ly), that is, the first distance L1.

  In the configuration shown in FIG. 6, when the method of the second comparative form is adopted, after the transfer of the last color image is completed at the transfer position Pt, the sheet S is initially left at the transfer discharge position Po. Passed, further passed through the transfer paper feed position Pi and the transfer position Pt, and released to the transfer paper discharge position Po for the second time, is released from the transfer drum 21 and conveyed toward the paper discharge receiving position Pe. become. At this time, the length of the post-transfer conveyance path from the transfer position Pt at the end of transfer to the paper discharge receiving position Pe is as follows: transfer paper discharge distance Lb, paper discharge paper feed distance Lc, paper feed transfer distance La, This is the sum (Lb + Lc + La + Lb + Lo) of the distance Lb between transfer and discharge and the receiving distance Lo. Accordingly, the length of the post-transfer conveyance path in this case is larger than one transfer drum 21, that is, the transfer drum peripheral length Ld.

  On the other hand, when the method of the present embodiment is adopted in the configuration shown in FIG. 2, the length of the post-transfer conveyance path includes the distance Lz between the transfer and feeding, the distance Lx between the feeding and discharging, and the receiving as described above. The sum of the distance Lo (Lz + Lx + Lo), that is, the second distance L2.

  In the present embodiment, in the rotation path 62 of the transfer drum 21, the pre-transfer conveyance path and the post-transfer conveyance path partially overlap at a portion from the transfer paper feed position Pi to the transfer paper discharge position Po. On the other hand, in the second comparative embodiment, in the rotation path 62 of the transfer drum 21, the pre-transfer conveyance path and the post-transfer conveyance path overlap over the entire transfer drum circumferential length Ld.

  For this reason, in the second comparative embodiment, the length of the pre-transfer conveyance path and the length of the post-transfer conveyance path equivalent to those of the present embodiment can be ensured, but the productivity is reduced as compared with the present embodiment. It will be. That is, in the second comparative embodiment, the number of sheets S that can be image-formed and output per unit time in a state in which the occurrence of image displacement is suppressed is smaller than in this embodiment. If the productivity in the second comparative embodiment is to be the same as that of the present embodiment, the diameter of the transfer drum 21 is increased in order to extend the transfer drum circumferential length Ld, or the delivery distance Li In order to increase the receiving distance Lo, it is necessary to increase the distance between the transfer section 40 and the transfer drum 21 and the distance between the transfer drum 21 and the receiving section 50, respectively.

  In the present embodiment, the case where a four-color full-color image is formed on the paper S has been described with reference to FIG. 3. However, two or three colors are formed on the paper S using this image forming apparatus. An image can also be formed. For example, when a two-color image is formed on the sheet S, three and a half times (more concretely) from when the transfer drum 21 starts to grip the leading end SS of one sheet S to when the leading end SS is released. (Third round + Lx). Meanwhile, in the rotation path 62 existing on the outer peripheral surface of the transfer drum 21, one sheet S passes through the first rotation path 621 from the transfer paper feed position Pi to the transfer paper discharge position Po three times. The second rotation path 622 from the transfer paper discharge position Po to the transfer paper feed position Pi via the transfer position Pt is passed only twice. In addition, a single color (for example, black) image can be formed on the paper S by using this image forming apparatus. In this case, after the transfer drum 21 starts to grip the leading edge SS of one sheet S, it rotates two and a half times (more specifically, two revolutions + Lx) from when the leading edge SS is released. During this time, in the rotation path 62 existing on the outer peripheral surface of the transfer drum 21, one sheet S passes through the first rotation path 621 from the transfer paper feed position Pi to the transfer paper discharge position Po twice. The second rotation path 622 from the transfer paper discharge position Po to the transfer paper feed position Pi via the transfer position Pt is passed only once.

  In the example shown in FIG. 3, after the leading edge SS of the first sheet S reaches the transfer position Pt at time t5, the transfer paper feeding position Pi is set to the trailing edge SE of the first sheet S at time t6. However, when the sheet length Ls of the sheet S is further shortened, the rear end SE of the first sheet S passes through the transfer sheet feeding position Pi, and then 1 is transferred to the transfer position Pt. It is also possible to reach the leading end SS of the sheet S. In order to realize this configuration, the maximum value of the sheet length Ls of the sheet S that can be used for image formation is determined by the distance (feeding) from the transfer paper feed position Pi to the transfer position Pt via the transfer paper discharge position Po. It is only necessary to limit the distance between the paper discharge distance Lx and the discharge paper transfer distance Ly). When this configuration is adopted, before the transfer of the first yellow toner image to the first sheet S is started, the rear end gripper 23 of the rear end SE of the first sheet S is used. The gripping can be completed.

  Further, in the present embodiment, the transfer drum 21 is mechanically held using the leading edge gripper 22 and the trailing edge gripper 23 without holding the sheet S using so-called electrostatic adsorption. It is not limited to this. For example, a mechanism for electrostatically attracting the sheet S to the transfer drum 21 may be provided in the transfer unit 20.

Further, in the present embodiment, the receiving unit 50 is arranged in the paper discharge path 63 provided between the transfer drum 21 and the fixing unit 30. However, the present invention is not limited to this.
FIG. 7 is a diagram showing an example of another configuration of the image forming apparatus to which the present invention is applied.
In the example illustrated in FIG. 7, the receiving unit 50 is not provided separately, and the fixing unit 30 also serves as the receiving unit 50. For this reason, the fixing nip constituted by the heating roll 31 and the pressure roll 32 constituting the fixing unit 30 functions as the paper discharge receiving position Pe.
In the image forming apparatus shown in FIG. 7 as well, the same effect as that of the image forming apparatus shown in FIG. 1 can be obtained by performing image formation in the same procedure as described with reference to FIG. Further, by not providing the receiving unit 50 independently, the configuration of the image forming apparatus can be simplified, and an unfixed toner image formed on the paper S passing through the paper discharge path 63 constitutes the receiving unit 50. It is also possible to suppress being disturbed by contact with the roll to be performed.

DESCRIPTION OF SYMBOLS 10 ... Image forming part, 11 ... Photosensitive drum, 12 ... Charging device, 13 ... Exposure device, 14 ... Rotary developing device, 15 ... Cleaning device, 20 ... Transfer part, 21 ... Transfer drum, 22 ... Tip gripper, 23 ... Rear end gripper, 25 ... phase sensor, 30 ... fixing unit, 40 ... delivery unit, 50 ... receiving unit, 61 ... feed path, 62 ... rotation path, 621 ... first rotation circuit, 622 ... second rotation path , 63 ... paper discharge path, 100 ... control unit, S ... paper, SS ... leading edge, SE ... trailing edge, Pf ... paper feed delivery position, Pi ... transfer paper feed position, Po ... transfer paper discharge position, Pt ... transfer position , Pe: paper discharge receiving position, Ld: transfer drum circumferential length, Lx: paper feed paper discharge distance, Ly: paper discharge transfer distance, Lz: transfer paper feed distance, Li: delivery distance, Lo: receiving distance, L1 ... first distance, L2 ... second distance, Ls ... paper length

Claims (9)

An image holder that is rotatably provided and holds an image;
An image formed on the image holding member is rotatably provided facing the image holding member, and is transferred to a recording material sandwiched between the image holding member at a transfer position facing the image holding member. A transfer member;
Holding means for holding the recording material supplied to the transfer member on the transfer member;
A transfer unit that sandwiches and conveys the recording material and delivers the recording material toward a transfer paper feeding position for supplying the recording material to the transfer member;
The recording material is sandwiched and conveyed, and a receiving unit that receives the recording material discharged from the transfer discharge position for discharging the recording material from the transfer member,
A first path from the transfer feeding position to the transfer position along the rotation direction of the transfer member, and a second path from the transfer position to the transfer discharge position along the rotation direction of the transfer member. The image forming apparatus is characterized in that the image forming apparatus overlaps with a portion extending from the transfer paper feed position to the transfer paper discharge position along the rotation direction of the transfer member. The delivery distance from the delivery position where the delivery unit sandwiches the recording material to the transfer paper feed position, and the distance between the paper delivery and delivery from the transfer paper feed position to the transfer paper delivery position along the rotation direction of the transfer member And the distance between the transfer and transfer distances from the transfer discharge position to the transfer position along the rotation direction of the transfer member is set to be larger than the length in the conveyance direction of the recording material,
The transfer paper feed distance from the transfer position to the transfer paper feed position along the rotation direction of the transfer member, the paper feed paper discharge distance, and the receiving unit sandwiches the recording material from the transfer paper discharge position. 2. The image forming apparatus according to claim 1, wherein the sum of the receiving distance to the receiving position is set to be larger than the length in the conveyance direction of the recording material.   The image forming apparatus according to claim 1, wherein the receiving unit also serves as a fixing unit that fixes an image formed on the recording material. An image holder that is rotatably provided and holds an image;
An image formed on the image holding member is rotatably provided facing the image holding member, and is transferred to a recording material sandwiched between the image holding member at a transfer position facing the image holding member. A transfer member;
Holding means for holding the recording material supplied to the transfer member on the transfer member;
A transfer unit that sandwiches and conveys the recording material, and delivers the recording material toward a transfer paper feeding position that is downstream in the rotation direction of the transfer member when viewed from the transfer position;
The recording material is sandwiched and conveyed, and the recording material is discharged from a transfer discharge position that is downstream in the rotation direction of the transfer member as viewed from the transfer feeding position and upstream in the rotation direction of the transfer member as viewed from the transfer position. An image forming apparatus including a receiving unit for receiving a material. The delivery distance from the delivery position where the delivery unit sandwiches the recording material to the transfer paper feed position, and the distance between the paper delivery and delivery from the transfer paper feed position to the transfer paper delivery position along the rotation direction of the transfer member And the distance between the transfer and transfer distances from the transfer discharge position to the transfer position along the rotation direction of the transfer member is set to be larger than the length in the conveyance direction of the recording material,
The transfer paper feed distance from the transfer position to the transfer paper feed position along the rotation direction of the transfer member, the paper feed paper discharge distance, and the receiving unit sandwiches the recording material from the transfer paper discharge position. 5. The image forming apparatus according to claim 4, wherein the sum of the receiving distance to the receiving position is set to be larger than the length in the conveyance direction of the recording material.   6. The image forming apparatus according to claim 4, wherein the receiving unit also serves as a fixing unit that fixes an image formed on the recording material. An image forming means for forming a single color image or sequentially forming a plurality of color images for each color;
An image holding member that is rotatably provided and holds an image formed by the image forming unit;
An image formed on the image carrier, which is rotatably provided facing the image carrier, is placed on a recording material sandwiched between the image carrier at a transfer position facing the image carrier, for each color. A transfer member to be transferred to,
A transfer unit that sandwiches and conveys the recording material, and delivers the recording material toward a transfer paper feeding position that is downstream in the rotation direction of the transfer member when viewed from the transfer position;
The recording material is sandwiched and conveyed, and the recording material is discharged from a transfer discharge position that is downstream in the rotation direction of the transfer member as viewed from the transfer feeding position and upstream in the rotation direction of the transfer member as viewed from the transfer position. A receiving part for receiving the material;
At the transfer feeding position, the recording material supplied from the delivery unit is held by the transfer member, and the recording material held by the transfer member is the same number of times as the number of colors formed by the image forming unit. And a control means for discharging the recording material passed through the transfer position only the same number of times as the number of colors to be formed from the transfer member to the receiving portion at the transfer discharge position. Including image forming apparatus. The delivery distance from the delivery position where the delivery unit sandwiches the recording material to the transfer paper feed position, and the distance between the paper delivery and delivery from the transfer paper feed position to the transfer paper delivery position along the rotation direction of the transfer member And the distance between the transfer and transfer distances from the transfer discharge position to the transfer position along the rotation direction of the transfer member is set to be larger than the length in the conveyance direction of the recording material,
The transfer paper feed distance from the transfer position to the transfer paper feed position along the rotation direction of the transfer member, the paper feed paper discharge distance, and the receiving unit sandwiches the recording material from the transfer paper discharge position. 8. The image forming apparatus according to claim 7, wherein the sum of the receiving distance to the receiving position is set to be larger than the length in the conveyance direction of the recording material.   The image forming apparatus according to claim 8, wherein the receiving unit also serves as a fixing unit that fixes an image formed on the recording material.

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