JP4656600B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, or a facsimile.

An image forming apparatus capable of forming an image on both sides of a sheet, wherein the image is formed on one side of the sheet, and a part of the sheet on which the image is formed is transferred to the outside of the image forming apparatus. It is known that the sheet is discharged, and then the sheet is supplied again into the image forming apparatus to form an image on the back surface of the sheet (Patent Document 1).

Japanese Patent No. 3334481

  However, in the conventional technique, it is necessary to wait for the start of image formation on the other side of the sheet until preparation is completed in the image forming unit. Therefore, in a state where a part of the sheet is discharged to the outside of the apparatus, the sheet Sometimes stopped for a certain period of time. For this reason, there has been a problem that the user may mistakenly recognize that a sheet conveyance failure such as a sheet jam has occurred and pull out the sheet. In order to solve this problem, a technique is known in which a rotational load is applied to a pair of rolls that hold a sheet in a state where a part of the sheet is discharged outside the apparatus, thereby making it difficult for a user to pull out the sheet (Patent Document). 1). However, with this technology, the sheet is fixed in a state where a part of the sheet is discharged to the outside, so that when the user applies an excessive force to pull out the sheet, the sheet is broken or the device is destroyed. There was a problem that there was sometimes.

  The present invention solves the above problems, and a user conveys a sheet on which an image is formed on one side of the sheet and a part of the sheet is discharged outside the apparatus and waits for the start of an image forming form on the other side. An object of the present invention is to provide an image forming apparatus that is less likely to be mistaken for being defective.

In order to solve the above-described problems, the first feature of the present invention is that an image forming unit having a transfer unit that transfers a formed image to a sheet, and the sheet is conveyed to the transfer unit and discharged from a discharge port. After the main conveyance path and a part of the sheet on which the image is transferred on one side by the transfer unit are discharged from the discharge port of the main conveyance path, the sheet is reversed and the upstream side of the transfer unit in the main conveyance path A re-conveying path that re-conveys the sheet and a control unit that controls the conveyance of the sheet, and the image forming unit forms an image to be transferred onto one surface of the sheet and then transfers the sheet to the transfer unit. An image to be transferred to the other surface of the sheet until the image is re-conveyed, and the control means conveys the sheet in the main conveying path in order to transfer the image to one surface by the transfer unit. than the transport speed of, image on the other surface by the transfer unit In an image forming apparatus for controlling the conveyance of the sheet so as to have a transport mode to slow the transport speed for transporting the sheet re-conveying path in order to transfer the. Therefore, by controlling the conveyance of the sheet in this conveyance mode, the speed at which the sheet is re-conveyed to the image forming unit is slower than the sheet conveyance speed during normal image formation, and the sheet on which image formation has been performed on one side Can reach the image forming unit again. For this reason, it is possible to shorten the waiting time after the conveyance of the sheet is stopped in a state where a part of the sheet is discharged from the discharge port until the image forming unit completes preparation for image formation on the other side of the sheet. Thus, it is possible to make it difficult to cause a problem that the user inadvertently pulls out the sheet in the standby state.

Also, preferably, the control means, the time and the sheet on which the image on one surface by the transfer unit is transferred is conveyed again after passing through the transfer portion to the transfer portion, the other surface of the sheet Control is performed so that the time for forming the toner image to be transferred is substantially equal. Accordingly, the timing at which the sheet is re-conveyed to the image forming unit by the re-conveyance path substantially coincides with the timing at which the toner image transferred to the sheet is formed on the image carrier, and the image is satisfactorily formed on the back surface of the sheet. Is formed.

  Preferably, the sheet has a stopping means for temporarily stopping the sheet being re-conveyed, and the distance between the position of the front end of the sheet stopped by the stopping means and the discharge port is the longest. The length of the sheet is shorter than the length in the sheet conveying direction. Therefore, in order to synchronize the timing at which the image formed on the other surface is formed by the image forming unit and the timing at which the sheet is conveyed to the image forming unit, In the case where a sheet having an end that is long enough to be discharged from the discharge port of the housing is used, the time during which a part of the sheet is discharged from the discharge port and stopped can be shortened.

Preferably, the control means performs control so that the sheet on which the image is transferred on one side is re-divided into a plurality of times and upstream of the transfer section upstream of the main conveyance path. And Therefore, the number of times of stopping is increased by re-transporting the sheet in a plurality of times, and each stop time can be shortened. Therefore, it is possible to make it more difficult to cause a problem that the user misidentifies that the sheet is partially discharged from the discharge port and is stopped and is pulled out and is pulled out.

In order to solve the above problems, the second feature of the present invention is that an image forming unit having a transfer unit that transfers a formed image to a sheet, and a sheet is conveyed to the transfer unit from the discharge port. After the main conveyance path to be discharged and a part of the sheet on which the image is transferred on one side by the transfer unit are discharged from the discharge port of the main conveyance path, the main conveyance is performed from the discharge port side while reversing the sheet. re conveyed to the transfer section upstream of the road, and re-conveying path which the end of the transfer side of the sheet supplied to the transfer unit has a standby point to wait, and control means for controlling the conveyance of the sheet, The image forming means forms an image to be transferred to one side of the sheet and then transfers the image to be transferred to the other side of the sheet until the sheet is conveyed again to the transfer unit. formed, the control unit uses the image forming In the case where the length in the conveying direction of the sheet is longer than the length up to the waiting point from the discharge port in the re-feeding path to said main transport path for transferring an image on one surface by the transfer unit than the conveying speed for conveying the sheet in a first conveying mode to slow the transport speed for conveying the sheet in the re-conveying path for the transfer of images on the other surface by the transfer unit, used for image formation When the length in the conveyance direction of the sheet is shorter than the length from the discharge port to the standby point in the re-conveyance path, the sheet is transferred to the main conveyance path in order to transfer the image to one surface by the transfer unit. than the conveying speed for conveying a sheet to a second transport mode to increase the conveying speed for conveying the sheet in the re-conveying path for the transfer of images on the other surface by the transfer unit In an image forming apparatus for controlling the transmission.

Therefore, when image formation is performed on the other side of the sheet that is longer than the length of the re-conveying path and is partially discharged from the discharge port in the stopped state, the conveyance of the sheet is controlled in the first conveyance mode. By doing so, the speed at which the sheet is re-conveyed to the image forming unit becomes slower than the sheet conveying speed at the time of normal image formation, and the time for the sheet on which the image is formed on one side to reach the image forming unit is lengthened. be able to. For this reason, it is possible to shorten the waiting time for stopping the conveyance of the sheet in a state where a part of the sheet is discharged from the discharge port until preparation for image formation on the other side of the sheet is completed in the image forming unit. As a result, the problem that the user accidentally pulls out the sheet in the standby state is less likely to occur. Further, when image formation is performed on the other surface of the sheet that is shorter than the length of the re-conveying path and is not partially ejected from the ejection port in the stopped state, control is performed in the second conveyance mode. As a result, the speed at which the sheet is re-conveyed to the image forming unit becomes faster than the sheet conveying speed at the time of normal image formation, and the time until the entire sheet on which the image is formed on one side is pulled into the apparatus is reduced. It can be shortened, and the problem that the user accidentally pulls out the portion discharged from the sheet apparatus can be made difficult to occur.

In order to solve the above-mentioned problem, the third feature of the present invention is that it has a transfer portion that takes more time to form a color image than a monochromatic image and transfers the formed image to a sheet. An image forming unit; a main conveyance path that conveys the sheet to the transfer unit and ejects the sheet from a discharge port; and a part of the sheet on which an image is transferred on one surface of the transfer unit is ejected from the discharge port of the main conveyance path And a re-conveying path for re-conveying the sheet to the upstream side of the transfer unit while reversing the sheet, and a control unit for controlling the conveyance of the sheet. After the image to be transferred on one side is formed, the image to be transferred to the other side of the sheet is formed before the sheet is conveyed again to the transfer unit. in the case where the to, one surface in the transfer section Than the conveying speed for conveying the sheet on the main transport path for the transfer of images, the slower the transport speed for transporting the sheets in the re-conveying path for the transfer of images to the other face the transfer unit 1 And the other side of the transfer unit at a speed higher than the conveyance speed of conveying the sheet to the main conveyance path in order to form an image on one side of the transfer unit. The image forming apparatus controls the conveyance of the sheet so as to have a second conveyance mode for increasing the conveyance speed for conveying the sheet in the re-conveyance path in order to transfer the image to the sheet.

Therefore, when color image formation that requires time for image formation preparation on the other side is performed, the sheet conveyance speed is normally controlled in the first conveyance mode, so that the sheet is re-conveyed to the image forming unit. It is slower than the sheet conveying speed during image formation, and it is possible to lengthen the time for the sheet on which the image is formed on one side to reach the image forming unit. For this reason, it is possible to shorten the waiting time by stopping the conveyance of the sheet in a state where a part of the sheet is discharged from the discharge port until preparation for image formation on the other side of the sheet is completed in the image forming unit, Thereby, it can be made difficult to cause a problem that the user accidentally pulls out the sheet in the standby state. In addition, when performing monochromatic image formation in which the preparation for image formation on the other surface is completed in a shorter time than when forming a color image, the sheet is transferred to the image forming unit by controlling in the second conveyance mode. The re-conveying speed is faster than the sheet conveying speed during normal image formation. Therefore, it is possible to shorten the time from the completion of image formation preparation on the other side to the actual start of image formation on the other side, and the number of sheets on which double-sided image formation can be performed per unit time. Increase the productivity of double-sided image formation.

According to the present invention, when the image is formed on one side of the sheet and a part of the sheet is discharged to the outside of the apparatus and the user waits for the start of the image forming form on the other side, the user has poor conveyance. It is possible to provide an image forming apparatus that is less likely to be mistaken.

Next, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows an outline of an image forming apparatus 10 according to the first embodiment of the present invention. The image forming apparatus 10 includes a housing 12. In the housing 12, an image forming unit 16 having an image forming unit 17 that is a part for forming an image on a sheet, and a sheet supply for supplying the image to the image forming unit 17. -The conveyance part 50 is mounted.

  The housing 12 is provided with a discharge port 13 through which a sheet on which an image has been formed is discharged, and a discharge unit 14 through which the sheet discharged from the discharge port 13 is stocked.

  The image forming means 16 is of an electrophotographic type and is used as a latent image carrier on which a latent image is formed. The image forming means 16 is a drum-shaped photosensitive drum 18 and a uniform charging of the photosensitive drum 18. A charging device 20 composed of a charging roll, an optical writing device 22 for writing a latent image on the photosensitive drum 18 charged by the charging device 20 with a laser beam, and an optical writing device 22 formed on the photosensitive drum 18. A developing device 24 for developing the electrostatic latent image with toner to form a toner image, and the toner image formed on the surface of the photosensitive drum 18 by the developing device 24 are transferred, and the transferred toner image is transferred to the above-described toner image. An intermediate transfer device 30 that transfers to a sheet in the image forming unit 17, a cleaning device 40 that cleans toner remaining on the photosensitive drum 18, and an intermediate transfer device 30. The toner image transferred to the sheet, and a fixing device 44 for fixing to the seat.

  The developing device 24 includes a rotary unit 26 that rotates counterclockwise (counterclockwise in FIG. 1) about the rotation shaft 25, and yellow, yellow, magenta, and cyan that are attached to the rotary unit 26. ) And black (Black) toner images of four colors, respectively.

  The rotary unit 26 holds the developing units 27a to 27d at intervals of 90 ° and rotates by 90 ° to move the developing units 27a to 27d to a position where the latent image formed on the photosensitive drum 18 is developed. . The developing units 27a to 27d have developing rolls 28a to 28d, respectively, and these developing rolls 28a to 28d move so as to face the photosensitive drum 18, respectively. The developing rolls 28 a to 28 d are not in contact with the photosensitive drum 18, and a part of the outer periphery of each of the developing rolls 28 a to 28 d protrudes 2 mm from the outer periphery of the rotary portion 26 in the radial direction. A predetermined gap is formed between the photosensitive drum 18 and the latent image on the photosensitive drum 18 is developed with toner of each color.

  The intermediate transfer device 30 transfers an intermediate transfer belt 31 which is an endless intermediate transfer member used as an image carrier that holds a toner image on the surface, and a toner image on the photosensitive drum 18 to the intermediate transfer belt (primary transfer). ) A primary transfer roll 32, a wrap-in roll 33 and a wrap-out roll 34 that are positioned in the vicinity of the photosensitive drum 18 and hold the intermediate transfer belt 31 from the inside, and a toner image formed on the intermediate transfer belt 31. A secondary transfer roll 36 used as a transfer portion for transferring the toner image, a backup roll 35 for backing up the secondary transfer roll 36, an intermediate transfer cleaner 38 for cleaning the intermediate transfer belt 31, and the intermediate transfer belt 31. A brush backup roll 37 provided at a position facing the transfer cleaner 38;

The toner image on the photosensitive drum 18 is primary-transferred onto the intermediate transfer belt 31 by the primary transfer roll 32 in the order of, for example, yellow, magenta, cyan, and black. The intermediate transfer belt 31 transfers the primary-transferred toner image. It is conveyed toward the secondary transfer roll 36.

  The wrap-in roll 33 and the wrap-out roll 34 hold the intermediate transfer belt 31 so that the intermediate transfer belt 31 is wound around the photosensitive drum 18 in a wide area. A primary transfer nip which is a region where the toner contacts and a primary transfer position is formed.

  A secondary transfer roll 36 is in contact with the secondary transfer backup roll 35 with the intermediate transfer belt 31 interposed therebetween. A portion sandwiched between the secondary transfer roll 36 used as the transfer portion and the intermediate transfer belt 31 used as the image carrier described above is an image forming portion 17 that is a portion that forms an image on the sheet. The image forming unit 17 is a secondary transfer position where the toner image is transferred to the sheet, and is a secondary transfer nip portion. In the image forming unit 17, the secondary transfer roll 36 secondarily transfers the toner image primarily transferred to the intermediate transfer belt 31 to the sheet with the assistance of the secondary transfer backup roll 35.

  A brush roll 39 provided in the intermediate transfer body cleaner 38 is in contact with the brush back-up roll 37 with the intermediate transfer belt 31 interposed therebetween. The intermediate transfer body cleaner 38 rotates the brush roll 39 to scrape off the toner remaining on the surface of the intermediate transfer belt 31.

  The cleaning device 40 is in contact with the photosensitive drum 18 upstream of the charging device 20 in the rotation direction of the photosensitive drum 18, and a cleaning blade 41 that scrapes off toner remaining on the photosensitive drum 18 after temporary transfer. And a toner recovery bottle 42 for recovering the toner scraped off by the cleaning blade 41.

  The fixing device 44 includes a heating roll 45 and a pressure roll 46, fixes the toner image secondarily transferred to the sheet by the secondary transfer roll 36 and the secondary transfer backup roll 35, and a discharge roll described later. Transport toward 68.

  The sheet supply / conveyance unit 50 includes a main conveyance path 62 that conveys a sheet to the image forming unit 17 and discharges the sheet from the discharge port 13, a sheet supply unit 52 that supplies the sheet to the main conveyance path 62, and the image forming unit 17. After discharging a part of the sheet on which the image is formed on one surface from the discharge port 13 of the main conveyance path 62, the sheet is reversed and re-conveyed to the upstream side of the image forming unit 17 in the main conveyance path 62. A conveyance path 70. In addition, when the sheet conveyed from the main conveyance path 62 to the discharge roll 68 is temporarily stopped and conveyance to the re-conveyance path 70 is started, the position where the trailing edge of the sheet is located is the switchback point P. It is named.

  The sheet supply unit 52 includes two-stage sheet supply devices 53, 53. Each sheet supply device 53 includes a sheet supply cassette 54 that stores sheets, a pickup roll 56 that sends out sheets from the sheet supply cassette 54, and A feed roll 58 that conveys the sheet fed by the pickup roll 56 and a retard roll 60 that rolls the sheets one by one are provided.

  The main conveyance path 62 is a path for the sheet from each feed roll 58 to the discharge port 13, and the above-described feed roll 58 that forms the sheet supply unit 52 in order from the upstream in the sheet conveyance direction along the main conveyance path 62. A standby roll 64, a registration roll 66, the secondary transfer roll 36 described above, the fixing device 44 described above, and a discharge roll 68 are disposed. A first sensor 76 that detects that the leading edge and the trailing edge of the sheet pass through the fixing device 44 is provided at a position downstream of the fixing device 44 in the sheet conveyance direction and upstream of the discharge roll 68. It has been.

  The registration roll 66 sends the sheet to the image forming unit 17 in accordance with the timing at which the toner image formed on the intermediate transfer belt 31 is conveyed to the image forming unit 17.

  The discharge roll 68 is located in the vicinity of the discharge port 13 that discharges the sheet from the housing 12, and rotates forward and reverse, and forwardly rotates the sheet that has been transported along the main transport path 62. 14 to discharge. When image formation is performed on the back side of the sheet conveyed along the main conveyance path 62, the discharge roll 68 rotates in the reverse direction and sends the sheet to the re-conveyance path 70. The discharge roll 68 rotates forward when receiving a drive transmission from a fixing motor 106 described later, and rotates reversely when receiving a drive transmission from a reverse conveying motor 108 described later. In this embodiment, the discharge port 13 is used not only for discharging a part of a sheet on which an image is to be formed on the back side, but also for discharging a sheet on which image formation has been completed to the discharge unit 14. The second discharge port for discharging the sheet to the sheet discharge unit 14 is provided separately from the discharge port 13, and the discharge port 13 is used only for discharging a part of the sheet on which the image is formed on the back surface. It may be configured.

  The re-conveying path 70 is a sheet conveying path from the discharge roll 68 to the standby roll 64, and conveys the sheet to the registration roll 66 while inverting the sheet on which the image is formed on the surface. Along this re-conveying path 70, in order from the upstream in the sheet conveying direction, the discharge roll 68, the first re-conveying roll 72 that conveys the sheet, the second re-conveying roll 74 that also conveys the sheet, and standby A roll 64 is disposed. Then, a second position for detecting that the leading edge of the sheet has passed through this position at a position downstream of the first re-conveying roll 72 and upstream of the second re-conveying roll 74. The sensor 78 is provided.

The standby roll 64 is an end point of the re-conveying path 70 and is provided at a position where the re-conveying path 70 and the main conveying path 62 are joined. The sheet conveyed along the re-conveying path 70 is
The end on the standby roll 64 side temporarily stops before reaching the standby roll 64. Then, at a predetermined timing, the standby roll 64, the first reconveying roll 72, and the second reconveying roll 74 are rotated, so that the sheet is supplied toward the registration roll 66. As described above, since the sheet conveyed along the reconveying path 70 is temporarily stopped at the position of the standby roll 64, the sheet conveyed to the registration roll 66 from the feed roll 58 of the sheet supply unit 52. This will not hinder the transport.

If the position of the end of the standby sheet on the standby roll 64 side is the standby point P2, the distance between the standby point P2 and the discharge port 13 is a sheet that can be used in the image forming apparatus 10. The length of the longest sheet in the sheet conveying direction is shorter than the length in the sheet conveying direction. Specifically, the distance from the standby point P2 to the discharge port 13 is 300 mm, and the length of the longest sheet in the conveyance direction is 431.8 mm. When this longest sheet is used, the rear end of the sheet protrudes from the discharge port 13 by a length of about 130 mm with the leading end of the sheet positioned at the standby point P2. On the other hand, when a sheet having a length in the conveyance direction shorter than 300 mm is used, the sheet is stored in the re-conveying path 70 in a state where the leading end portion of the sheet is positioned at the standby point P2, and the trailing end portion of the sheet extends from the discharge port 13. It does not protrude.

  According to the image forming apparatus 10 having the schematic configuration described above, the photosensitive drum 18 is uniformly charged by the charging device 20, and the charged photosensitive drum 18 is transferred from the optical writing device 22 to the charged photosensitive drum 18 based on the image signal. A light beam is emitted. The light beam from the optical writing device 22 exposes the surface of the photosensitive drum 18 to form a latent image. The latent image on the photosensitive drum 18 formed by the optical writing device 22 is developed into a yellow, magenta, cyan, and black toner image by the developing device 24, and is primarily transferred onto the intermediate transfer belt 31. Waste toner remaining on the photosensitive drum 18 after the primary transfer is scraped off and collected by the cleaning device 40.

  On the other hand, the sheet stored in the sheet supply cassette 54 is fed out by the feed roll 58, is turned by the retard roll 60, is guided to the main conveyance path 62, is temporarily stopped by the registration roll 66, and is subjected to the secondary transfer at a timing. Guided between the roll 36 and the secondary transfer backup roll 35. When the sheet is guided between the secondary transfer roll 36 and the secondary transfer backup roll 35, the toner image primarily transferred to the intermediate transfer belt 31 is imaged by the secondary transfer roll 36 and the secondary transfer backup roll 35. Secondary transfer is performed on the sheet by the forming unit 17. After the secondary transfer, the waste toner remaining on the intermediate transfer belt 31 is scraped off and collected by the intermediate transfer body cleaner 38.

  The sheet to which the toner image has been transferred is guided to the fixing device 44, and the toner image is fixed to the sheet by the heat and pressure of the heating roll 45 and the heating roll 45. The sheet having been fixed is conveyed toward the discharge unit 14 by the forward rotation of the discharge roll 68 until the trailing end reaches the switchback point P. When image formation is performed only on the front surface, the sheet is discharged from the discharge port 13 to the discharge unit 14 as it is. On the other hand, when image formation is performed on the back side, after the trailing edge of the sheet reaches the switchback point P, the discharge roll 68 starts reverse rotation at a predetermined timing, and the sheet is guided to the reconveying path 70. It is burned. Note that when the rear end of the sheet reaches the switchback point P, most of the sheet is in a state of protruding from the discharge port 13 to the discharge unit 14.

The sheet guided to the re-conveying path 70 is conveyed downward by the first re-conveying roll 72 and the second re-conveying roll 74, and after waiting for a predetermined time at the standby point P2, the back surface is intermediate. The paper is guided to the resist roll 66 in a state of being reversed in a direction facing the transfer belt 31. Then, the toner image is secondarily transferred to the back surface of the sheet guided to the registration roll 66 by the secondary transfer roll 36, the toner image is fixed by the fixing device 44, and discharged to the discharge unit 14 by the discharge roll 68. The

  FIG. 2 is an explanatory diagram showing a drive transmission system of the image forming apparatus 10. As shown in FIG. 2, the drive transmission system of the image forming apparatus 10 includes a developer motor 100 that rotationally drives the rotary portion 26 of the developing device 24, and an image carrier that rotationally drives the photosensitive drum 18 and the intermediate transfer belt 31. The body motor 102, the registration roll motor 104 for rotating the registration roll 66, the fixing motor 106 for rotating the pressure roll 46 of the fixing device 44, the first re-conveying roll 72 and the second And a reverse conveyance motor 108 that rotationally drives the re-conveyance roll 74.

  The drive of the developing device motor 100 is transmitted to the rotary unit 26, and the rotary unit 26 is rotated counterclockwise (counterclockwise in FIG. 1) about the rotation shaft 25 as a rotation center.

  The driving force of the image carrier motor 102 is transmitted to the photosensitive drum 18, and is transmitted to the intermediate transfer belt 31 via the photosensitive drum 18. The photosensitive drum 18 is rotated clockwise and the intermediate transfer belt 31 is moved. Rotate in the direction of the arrow shown in FIG.

  A registration roll 66 is connected to the registration roll motor 104 via a registration roll clutch 110. When the registration roll clutch 110 is in a state where drive transmission is possible, the registration roll motor 104 is driven. The resist roll 66 is transmitted to the resist roll 66 and rotates. Although the drive transmission system is not shown in FIG. 2, the driving of the registration roll motor 104 is also transmitted to the pickup roll 56 and the feed roll 58 of the sheet feeding device 53.

  The secondary transfer roll 36 and the heating roll 45 of the fixing device 44 are connected to the fixing motor 106. Further, a discharge roll 68 is connected to the fixing motor 106 via a discharge roll clutch 112. When the driving of the fixing motor 106 is transmitted to the discharge roll 68 via the discharge roll clutch 112, the discharge roll 68 rotates in the forward direction (the direction in which the sheet is discharged to the discharge portion 14).

  A first reconveying roll 72 is connected to the reverse conveying motor 108, and a second reconveying roll 74 is connected via the first reconveying roll 72. Further, the above-described discharge roll clutch 112 is connected to the reverse conveyance motor 108 via a double-sided clutch 114. Therefore, the discharge roll 68 is connected to the reverse conveyance motor 108 via the double-sided clutch 114 and the discharge roll clutch 112. When the rotation of the reverse conveyance motor 108 is transmitted to the discharge roll 68 via the double-sided clutch 114 and the discharge roll clutch 112, the discharge roll 68 rotates in the reverse direction (in the direction of feeding the sheet to the re-conveyance path 70). Rotate. Here, the reverse conveyance motor 108, the double-sided clutch 114, and the discharge roll clutch 112 are used as stopping means for temporarily stopping the sheet being conveyed through the re-conveying unit.

  FIG. 3 illustrates a control device 120 used as a control unit that controls the sheet supply / conveyance unit 50 of the image forming apparatus 10. This control device 120 re-conveys the image forming unit 17 to form an image on the other side, rather than the speed at which the sheet is conveyed on the main conveyance path 62 in order to form an image on one side by the image forming unit 17. Control means for controlling to have a transport mode for slowing the transport speed of transporting the sheet on the path 70, and moreover than the speed of transporting the sheet on the main transport path 62 in order to form an image on the surface by the image forming unit 17 The image forming unit 17 is a control unit that controls to have a conveyance mode in which the conveyance speed for conveying a sheet in the re-conveyance path 70 is increased in order to form an image on the back surface.

In FIG. 3, the control circuit 122 includes a CPU, and detection signals from the first sensor 76 and the second sensor 78 are input to the control circuit 122. In addition, a signal from the operation panel 124 in which whether or not to form a color image and the size of a sheet on which an image is formed is input by a user operation is also input to the control circuit 122. Here, the operation panel 124 includes those mounted on the housing 12 and those operated from an external terminal such as a personal computer. The control circuit controls the discharge roll clutch 112, the double-sided clutch 114, the fixing motor 106, and the reverse conveyance motor 108.

  A control flow when images are formed on both sides of the sheet by the control device 120 will be described with reference to FIGS. When double-sided image formation starts, first, a control mode used for image formation is selected from a plurality of control modes. In FIG. 4, when double-sided image formation is started, it is determined in step S10 whether or not color image formation is performed by an input from the operation panel 124. Here, color image formation means that toner images of four colors of yellow, magenta, cyan, and black developed by the developing devices 27a to 27d are superimposed on the surface of the intermediate transfer belt 31, and the superimposed toner images. The image is formed by so-called four-cycle printing in which the image is secondarily transferred to the sheet. In the single-color image formation, a current image of one color selected from four color toner images of yellow, magenta, cyan, and black developed by the developing devices 27a to 27d is transferred to a sheet to form an image. That means.

  If it is determined in step S10 that color image formation is being performed, whether or not the length in the conveyance direction of the sheet used for image formation is 300 mm or more is determined by input from the operation panel 124 in step S12. Is determined.

  If it is determined in step S12 that the sheet length is 300 mm or longer, the control in the one-batch / reverse low-speed mode is selected. As described above, when the length of the sheet is 300 mm or more, the trailing edge of the sheet protrudes from the discharge port 13 in a state where the leading edge of the sheet is positioned at the standby point P2.

  If it is determined in step S10 that color image formation is not being performed, in step S14, it is determined whether or not the length in the sheet conveyance direction is 216 mm or more. When the length of the sheet in the conveyance direction is 216 mm or more, the control in the 1 batch / reverse high speed mode is selected. When the length is not 216 mm or more, the control in the 2 batch mode is selected.

Here, one batch means that when image formation is performed on both surfaces of a plurality of sheets, image formation on the next sheet is performed after image formation on the front surface and back surface of a certain sheet is completed. On the other hand, the 2-batch process is to perform image formation on the front surfaces of two sheets, and then to perform image formation on the back surfaces of these two sheets when forming images on both sides of a plurality of sheets. Say. For example, when image formation is performed on both surfaces of two sheets in two batch processing, image formation is first performed on the surface of the first sheet, and then image formation is performed on the surface of the second sheet. Next, an image is formed on the back surface of the first sheet, and finally, an image is formed on the back surface of the second sheet.

  The reversal low speed means that the image forming unit 17 forms an image on the other side more rapidly than the speed at which the sheet is conveyed on the main conveyance path 62 in order to form an image on one side. This means that the conveyance speed for conveying the sheet in the conveyance path 70 is slow. On the other hand, the reverse high speed is a re-conveying path for forming an image on the back surface in the image forming unit 17 rather than a speed at which the image forming unit 17 conveys a sheet on the main conveying path 62 in order to form an image on one side. 70 means that the sheet conveying speed is high.

  FIG. 5 shows a control flow of the image forming apparatus 10 when double-sided image formation is performed in the one-batch / reverse low-speed mode. When the control starts, in step S20, it is detected by the output of the first sensor 76 that the rear end portion of the sheet on which the image has been formed and passed through the fixing device 44 has reached the switchback point P.

  In the next step S22, the connection of the discharge roll clutch 112 is disconnected, the drive transmission from the fixing motor 106 to the discharge roll 68 is cut, and the forward rotation of the discharge roll 68 (the rotation in the direction in which the sheet is discharged to the discharge section 14). ) Stops, and the seat stops at a position where the rear end portion is at the switchback point S.

In the next step S24, the sheet stops for 2 seconds and waits with the rear end positioned at the switchback point P. In this state, the sheet is sandwiched between the discharge roll 68 and the roll facing the discharge roll 68, and most of the sheet protrudes to the discharge section 14. If the sheet is stopped for a long time in this state, the user may mistakenly recognize that a conveyance failure has occurred and pull out the sheet. However, in this control, since the time in which the seat is stopped is as short as 2 seconds, it is difficult for the user to misidentify.

  In the next step S26, at the timing when 2 seconds have passed since the sheet stopped, the double-sided clutch 114 and the discharge roll clutch 112 are in a state capable of transmitting drive, and the reverse conveying motor 108 rotates. To start. With the above operation, the rotation of the reverse conveyance motor 108 is transmitted to the discharge roll 68 via the double-sided clutch 114 and the discharge roll clutch 112, and the discharge roll 68 rotates in the reverse direction (the sheet is transferred from the discharge section 14 into the housing 12). Start rotation). Further, the rotation of the reverse conveyance motor 108 is transmitted to the first reconveying roll 72 and the second reconveying roll 74, and the first reconveying roll 72 and the second reconveying roll 74 are transferred to the sheet. Is rotated in the direction to convey the toner to the standby roll 64. At this time, the rotation speed of the discharge roll 68, the first re-conveying roll 72, and the second re-conveying roll 74 is controlled by controlling the rotational speed of the reverse conveying motor 108, so that the sheet conveying speed is a normal image. It is controlled to be 1/4 of the sheet conveyance speed at the time of formation. With the above operation, the sheet is conveyed along the reconveying path 70 at a speed that is ¼ of the conveying speed during normal image formation.

  In the next step S28, when it is detected by the output of the second sensor 78 that one end of the sheet has reached the standby point P2, the rotation of the reverse conveyance motor 108 is stopped, and one end of the sheet reaches the standby point P2. Stop in position and wait for 2 seconds in stop. In this state, the end on the side opposite to the end located on the standby point P <b> 2 of the sheet protrudes to the discharge unit 14. In this state, if the user has stopped for a long time, the user may mistakenly identify a conveyance failure and pull out the sheet. However, in this control, the sheet is in a stopped state for a short period of 2 seconds. User misidentification is unlikely to occur.

  In the next step S30, the reverse conveyance motor 108 is started at the timing when 2 seconds have elapsed since the sheet stopped at the standby point P2, and the discharge roll 68, the first re-conveyance roll 72, and the second re-conveyance roll 72 are started. The transport roll 74 starts to rotate. At this time, the rotation speed of the reverse conveyance motor 108 is controlled, and the rotation speeds of the discharge roll 68, the first re-conveyance roll 72, and the second re-conveyance roll 74 are the same as those when the sheet conveyance speed is normal image formation. Is controlled so as to be the same speed as the sheet conveyance speed. With the above operation, the sheet is conveyed to the main conveyance path 62 in a state where the back surface is reversed in the direction facing the intermediate transfer belt 31 side. Thereafter, the image forming unit 17 forms an image on the back surface of the sheet.

  FIG. 6 shows a control flow of the image forming apparatus 10 when double-sided image formation is performed in the one-batch / reverse high-speed mode. When the control starts, in step S40, it is detected by the output of the first sensor 76 that the rear end portion of the sheet on which the image has been formed and passed through the fixing device 44 has reached the switchback point P.

  In the next step S42, as soon as the trailing edge of the sheet arrives at the switchback point P, the fixing motor 106 is stopped, and the discharge of the sheet to the discharge unit 14 is stopped by stopping the rotation of the discharge roll 68. Then, the reverse conveyance motor 108 is started and the double-sided clutch 114 is in a state in which drive transmission is possible, so that the reverse rotation of the discharge roll 68, the first reconveyance roll 72, and the second reconveyance roll 74. And start rotating. At this time, the rotation speed of the discharge roll 68, the first re-conveying roll 72, and the second re-conveying roll 74 is controlled by controlling the rotational speed of the reverse conveying motor 108, so that the sheet conveying speed is a normal image. It is controlled to be twice the sheet conveyance speed at the time of formation. With the above operation, the sheet is conveyed along the re-conveying path 70 at a speed twice the conveying speed during normal image formation.

  In the next step S44, when it is detected by the output of the second sensor 78 that one end of the sheet has reached the standby point P2, the rotation of the reverse conveyance motor 108 is stopped, and one end of the sheet reaches the standby point P2. It stops in the state where it is located, and waits for 1 second in this stopped state.

  In the next step S46, the reverse conveyance motor 108 is started at the timing when one second has elapsed since the sheet stopped at the standby point P2, and the discharge roll 68, the first re-conveyance roll 72, and the second re-conveyance roll 72 are started. The transport roll 74 starts to rotate. At this time, the rotation speed of the reverse conveyance motor 108 is controlled, and the rotation speeds of the discharge roll 68, the first re-conveyance roll 72, and the second re-conveyance roll 74 are the same as those when the sheet conveyance speed is normal image formation. Is controlled so as to be the same speed as the sheet conveyance speed. With the above operation, the sheet is conveyed to the main conveyance path 62 in a state where the back surface is reversed in the direction facing the intermediate transfer belt 31 side. Thereafter, the image forming unit 17 forms an image on the back surface of the sheet.

  In the one-batch / reverse high-speed mode described above, the sheet is made to wait while one end thereof is positioned at the waiting point P2 until the toner image to be transferred to the back surface of the sheet is formed on the intermediate transfer belt 31. However, the other end of the sheet does not protrude into the discharge unit 14, or the time for stopping at this position is short, and it is difficult to give the user a misconception that a sheet conveyance failure has occurred. Therefore, in order to shorten the time from when the toner image transferred to the back surface of the sheet is formed on the intermediate transfer belt 31 until the toner image is secondarily transferred to the back surface of the sheet, the sheet on which the image is formed on the front surface. The sheet is conveyed to the standby point P2 at a speed higher than the conveyance speed during normal image formation so that the sheet reaches the standby point P2 earlier.

  FIG. 7 shows a control flow of the image forming apparatus 10 when double-sided image formation is performed in the 2-batch mode. When the control starts, in step S50, it is detected by the output of the first sensor 76 that the trailing edge of the first sheet on which the image has been formed has reached the switchback point P.

  In the next step S52, as soon as the trailing edge of the first sheet arrives at the switchback point P, the fixing motor 106 is immediately stopped and the discharge roll 68 is stopped to discharge the sheet to the discharge unit 14. Stop. Then, the reverse conveyance motor 108 is started and the double-sided clutch 114 is in a state in which drive transmission is possible, so that the reverse rotation of the discharge roll 68, the first reconveyance roll 72, and the second reconveyance roll 74. And start rotating. At this time, the rotation speed of the discharge roll 68, the first re-conveying roll 72, and the second re-conveying roll 74 is controlled by controlling the rotational speed of the reverse conveying motor 108, so that the sheet conveying speed is a normal image. It is controlled to be twice the sheet conveyance speed at the time of formation. With the above operation, the first sheet is conveyed along the reconveying path 70 at a speed twice the conveying speed during normal image formation.

  In the next step S54, when it is detected by the output of the second sensor 78 that one end of the first sheet has reached the standby point P2, the rotation of the reverse conveyance motor 108 is stopped, and the first sheet is stopped. The sheet stops in a state where one end is positioned at the standby point P2, and waits in this stopped state. Since the sheet used for image formation in this mode has a length in the conveyance direction shorter than 216 mm, the entire sheet can be accommodated in the re-conveying path 70 even if one end is stopped at the standby point P2, and the other end. The part does not protrude into the discharge part 14.

  In the next step S56, it is detected from the output of the first sensor 76 that the trailing edge of the second sheet on which the image has been formed has reached the switchback point P.

  In the next step S58, when the trailing edge of the second sheet arrives at the switchback point P, the fixing motor 106 is immediately stopped, and the discharge roll 68 is stopped to discharge the second sheet. The discharge to the unit 14 is stopped. Then, the reverse conveyance motor 108 is started and the double-sided clutch 114 is in a state in which drive transmission is possible, so that the reverse rotation of the discharge roll 68, the first reconveyance roll 72, and the second reconveyance roll 74. And start rotating. At this time, the rotation speeds of the discharge roll 68, the first re-conveying roll 72, and the second re-conveying roll 74 are set so that the sheet conveying speed is the same as the sheet conveying speed during normal image formation. Be controlled. By this operation, conveyance of the first sheet waiting at the standby point P toward the registration roll 66 is started, and image formation on the back surface of this one sheet is started, and the switchback point P Conveyance of the second sheet positioned at the position toward the standby point P2 is started. At this time, the conveyance speed of the second sheet is equal to the conveyance speed during normal image formation.

  In the next step S60, when the first sheet on which the image is formed on the back surface reaches the discharge roll 68, the discharge roll 68 continues to rotate forward, so that the first sheet is fed to the discharge section 14. And discharged.

  In the next step S62, when it is detected by the output of the second sensor 78 that one end of the second sheet has reached the standby point P2, the rotation of the reverse conveying motor 108 is stopped, and the sheet has one end. It stops in the state located at the standby point P2, and waits for 1 second in the stopped state.

  In the next step S64, the reverse conveyance motor 108 is started at the timing when one second has elapsed since the second sheet stopped at the standby point P2, and the discharge roll 68, the first re-conveyance roll 72, and The second re-conveying roll 74 starts to rotate. At this time, the rotation speeds of the discharge roll 68, the first re-conveying roll 72, and the second re-conveying roll 74 are set so that the sheet conveying speed is the same as the sheet conveying speed during normal image formation. Be controlled. By this operation, the second sheet is conveyed to the main conveyance path 62 in a state where the back surface is reversed in the direction facing the intermediate transfer belt 31 side. Thereafter, the image forming unit 17 forms an image on the back side of the sheet, and the image formation on both sides of the two sheets is completed.

  As described above, the present invention can be used for an image forming apparatus.

1 is a cross-sectional view of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is an explanatory diagram illustrating a drive transmission system of the image forming apparatus according to the embodiment of the present invention. 1 is a block diagram illustrating a control device used in an image forming apparatus according to an embodiment of the present invention. 3 is a first flowchart illustrating an operation of the image forming apparatus according to the embodiment of the present invention. 6 is a second flowchart showing the operation of the image forming apparatus according to the embodiment of the present invention. 6 is a third flowchart showing the operation of the image forming apparatus according to the embodiment of the present invention. 10 is a fourth flowchart illustrating an operation of the image forming apparatus according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Housing | casing 13 Discharge port 14 Discharge part 16 Image forming means 17 Image forming part 18 Photosensitive drum 20 Charging apparatus 22 Optical writing apparatus 24 Developing apparatus 25 Rotating shaft 26 Rotary part 30 Intermediate transfer apparatus 31 Intermediate transfer belt 32 Primary transfer roll 33 Wrap-in roll 34 Wrap-out roll 35 Secondary transfer backup roll 36 Secondary transfer roll 37 Brush backup roll 38 Intermediate transfer body cleaner 39 Brush roll 40 Cleaning device 41 Cleaning blade 42 Toner recovery bottle 44 Fixing device 45 Heating roll 46 pressure roll 50 sheet supply / conveyance section 52 sheet supply section 53 sheet supply apparatus 54 sheet supply cassette 56 pickup roll 58 feed roll 60 retard roll 62 main conveyance path 64 standby roll 66 resist Roll 68 discharge roll 70 re-conveying path 72 first re-conveying roll 74 second re-conveying roll 76 first sensor 78 second sensor 100 developing device motor 102 image carrier motor 104 registration roll motor 106 fixing Motor 108 Reverse conveyance motor 110 Registration roll clutch 112 Discharge roll clutch 114 Double-sided clutch 120 Control device 122 Control circuit 124 Operation panel

Claims (6)

An image forming means having a transfer portion for transferring the formed image to the sheet ;
A main conveyance path for conveying a sheet to the transfer unit and discharging the sheet from a discharge port;
After a part of the sheet on which the image is transferred on one side in the transfer unit is discharged from the discharge port of the main transport path, the sheet is reversed and re-transported to the upstream side of the transfer unit in the main transport path. A re-conveying path;
Control means for controlling the conveyance of the sheet;
Have
The image forming unit forms an image to be transferred to the other side of the sheet after forming the image to be transferred to one side of the sheet and before the sheet is re-conveyed to the transfer unit,
Said control means, than said conveying speed for conveying the sheet in the main transport path for transferring an image on one surface by the transfer unit, the re-feeding to transfer images on the other surface by the transfer unit An image forming apparatus, wherein the conveyance of a sheet is controlled so as to have a conveyance mode in which a conveyance speed for conveying a sheet on a path is decreased. Wherein the control means, the time and the sheet on which the image on one surface by the transfer unit is transferred is conveyed again after passing through the transfer portion to the transfer portion, the toner image transferred to the other surface of the sheet The image forming apparatus according to claim 1 , wherein the image forming apparatus is controlled so as to be substantially equal to a time for forming the image. Having a stopping means for temporarily stopping the sheet being re-conveyed;
Eggplant distance between the position and the outlet of the conveying direction front end of the sheet is stopped by the stopping means, a sheet conveying direction of the longest sheet according to claim 1 or 2, wherein the shorter than the length Image forming apparatus. 2. The control unit according to claim 1, wherein the control unit performs control so that the sheet having the image transferred on one surface thereof is divided and re-transported to the upstream side of the transfer unit in the main transport path. 4. The image forming apparatus according to any one of 3 . An image forming means having a transfer portion for transferring the formed image to the sheet ;
A main conveyance path for conveying a sheet to the transfer unit and discharging the sheet from a discharge port;
After discharging a part of the sheet on which the image is transferred on one side in the transfer unit from the discharge port of the main conveyance path, the sheet is reversed and the upstream side of the transfer unit in the main conveyance path from the discharge port side is reversed. A re-conveying path having a standby point where an end of the transfer unit side of the sheet supplied to the transfer unit waits ,
Control means for controlling the conveyance of the sheet;
Have
The image forming unit forms an image to be transferred to the other side of the sheet after forming the image to be transferred to one side of the sheet and before the sheet is re-conveyed to the transfer unit,
The control unit is configured to transfer an image on one surface of the transfer unit when a length in a conveyance direction of a sheet used for image formation is longer than a length from the discharge port to the standby point in the re-conveyance path . than the conveying speed for conveying the sheet in the main transport path for transferring the first to slow the conveying speed for conveying the sheet in the re-conveying path for the transfer of images to the other surface of the transfer section In the transport mode and when the length of the sheet used for image formation in the transport direction is shorter than the length from the discharge port to the standby point in the re-transport path, an image is printed on one surface at the transfer unit. than the conveying speed for conveying the sheet on the main transport path for transfer, the second transport to increase the conveying speed for conveying the sheet re-conveying path for the transfer of images on the other surface by the transfer unit Image forming apparatus and controls the conveyance of the sheet so as to have a over de. Color image formation takes more time than monochromatic image formation,
An image forming means having a transfer portion for transferring the formed image to the sheet ;
A main conveyance path for conveying a sheet to the transfer unit and discharging the sheet from a discharge port;
After a part of the sheet on which the image is transferred on one side in the transfer unit is discharged from the discharge port of the main transport path, the sheet is reversed and re-transported to the upstream side of the transfer unit in the main transport path. A re-conveying path;
Control means for controlling the conveyance of the sheet;
Have
The image forming unit forms an image to be transferred to the other side of the sheet after forming the image to be transferred to one side of the sheet and before the sheet is re-conveyed to the transfer unit,
The image forming means, in the case of a color image forming, the than the conveying speed for conveying the sheet on the main transport path for transferring an image on one surface by the transfer portion, the other in the transfer section a first transport mode to slow the transport speed for transporting the sheet re-conveying path for the transfer of images to the surface, in the case of the monochromatic image formation, an image formed on one surface by the transfer unit A second conveyance mode in which the conveyance speed for conveying the sheet in the re-conveyance path is faster than the conveyance speed for conveying the sheet to the main conveyance path to transfer the image to the other surface in the transfer unit. An image forming apparatus that controls conveyance of a sheet so as to include:

Images