JP2019184674A - Sheet conveyance device, and image formation device - Google Patents

Abstract

To provide a sheet conveyance device that can discharge the sheets in the device to the outside of the device as many as possible even if a conveyance failure occurs, and can reduce the residual sheets in the device.SOLUTION: A sheet conveyance device includes: a conveyance route for conveying sheets; a detection sensor that is disposed on the conveyance route and detects the conveyed sheets; a control unit that keeps the conveyance completion time from the start of sheet conveyance to the completion and controls the conveyance operation of the sheets on the basis of the detection result of the detection sensor; and a calculation unit that, on the basis of the information of the conveyance completion time held in the control unit, calculates a conveyance retry number showing the number of retry operations of executing the conveyance operation of the sheets again after the interruption of the conveyance of the sheets by the control unit.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus including the sheet conveying apparatus.

  Conventionally, in the conveyance of a paper during a printing operation in a paper conveyance device or an image forming apparatus, when a paper conveyed from a paper feeding unit in each device cannot be detected by a detection sensor, a paper feed failure that interrupts the printing operation is detected. The method is known. In this paper feed failure detection method, when the paper transported from the paper feed unit does not reach the detection sensor within a predetermined judgment time after the paper feed starts, the paper cannot be detected by the detection sensor. It is determined that a paper feed failure due to clogging (called jam or the like) has occurred.

  Further, in a paper transport device or an image forming apparatus, depending on the wear of a roller or the type of paper, the paper cannot be transported as expected due to slipping of the roller, and a paper transport failure may be detected. In this case, it is highly possible that the printing operation can be continued by continuing the paper transport operation. For this reason, even when a paper conveyance failure is detected, it is generally known to perform a retry operation for executing the paper conveyance operation again after a predetermined time without immediately interrupting the printing operation for the corresponding paper. ing.

  Also, in order to reduce the burden on the user who processes the paper remaining in each device when a paper conveyance failure is detected, the printing operation is performed after discharging the remaining paper that can be discharged from each device to the outside. Control for stopping is generally known. Further, in the apparatus that performs the above-described retry operation, a control method is known in which the sheets in the apparatus are discharged before the retry operation is started so that the order of image formation does not change.

  However, in the control for discharging the paper in the apparatus when the above-described paper feed failure is detected, the paper feed is performed at the path junction where the transport path from the paper feed unit and the transport path for backside printing join. There are cases where the paper from the unit and the paper being printed on the back side stay, and the paper being printed on both sides cannot be discharged from the apparatus.

  As a countermeasure when the paper during double-sided printing cannot be ejected from the device, paper is fed from the paper feed unit during double-sided printing in a device that cannot stop the paper in the transport path for double-sided printing. There has been proposed a control in which, when a defect is detected, the order of image formation is switched to discharge paper during double-sided printing (see, for example, Patent Document 1). In this control, the order of image formation is switched so that the reverse side printing of paper during duplex printing has priority over the retry operation, and the paper in the transport path for duplex printing is routed before the paper from the paper feed unit. Passing through the merging portion, retention of the sheet from the sheet feeding unit and the sheet during duplex printing at the path merging portion is suppressed.

  In addition, in an apparatus configured to be able to stop paper in the conveyance path for double-sided printing, the paper is fed in accordance with various conditions such as the cumulative driving time of the paper feeding device, the paper type of the paper, and the humidity around the device. There is known control for changing a value of a determination time for determining a paper defect and a number of times of executing a retry operation (retry count) (for example, see Patent Document 2). In this control, the probability that the paper can be conveyed from the paper feed unit to the detection sensor is increased, and the occurrence of paper feed failure in the paper feed unit is suppressed.

JP 2001-1000060 A JP 2008-127116 A

  However, in the method of controlling the number of retries in accordance with the various conditions described above, there are a wide variety of conditions that must be set in order to prevent the conveyance failure, so it is difficult to reliably suppress the conveyance failure. For example, even if they are the same paper type, there are a wide variety of types of paper such as high-quality paper and poor-quality paper, and it is difficult for the user to set the information accurately. For this reason, even if the driving time of each device is the same, the amount of paper dust is different, and even in the same paper type, a difference occurs in the transport amount due to a difference in quality paper, bad paper, or the like. Therefore, the conveyance failure cannot be reliably suppressed with the conveyance failure determination time and the number of retries calculated from the various set conditions. As a result, even if a paper transport retry operation is performed, the paper may remain at the position where the path junction is blocked on the transport path, and double-sided paper cannot be discharged outside the device, resulting in an increase in residual paper. There is.

  In order to solve the above-described problems, in the present invention, even in a retry operation when a conveyance failure occurs, paper conveyance in which the paper in the apparatus can be discharged out of the apparatus as much as possible and the residual paper in the apparatus can be reduced. An apparatus and an image forming apparatus are provided.

The paper transport device of the present invention includes a transport path for transporting paper, a detection sensor provided on the transport path for detecting the transported paper, and a transport completion time from the start of transport of the paper to completion. And the control unit that controls the sheet conveyance operation based on the detection result of the detection sensor, and the information on the conveyance completion time held in the control unit, after the conveyance of the sheet by the control unit is interrupted, A calculating unit that calculates the number of times of carrying out the retry, which represents the number of times of performing the retry operation for performing the carrying operation again;
Also, an image forming apparatus of the present invention includes the above-described sheet conveying device.

  According to the present invention, it is possible to provide a paper transport device and an image forming apparatus capable of reducing the residual paper in the apparatus during the retry operation.

FIG. 2 is a diagram illustrating a schematic configuration of a sheet conveying device and an image forming apparatus. FIG. 6 is a schematic diagram of a paper conveyance path. 2 is a functional block diagram of the image forming apparatus. FIG. 6 is a flowchart illustrating an example of sheet conveyance control for performing sheet feeding retry. FIG. 10 is a diagram for explaining a method of measuring an elapsed paper feeding time. FIG. 10 is a diagram for explaining a method of measuring an elapsed time of paper feeding when paper feeding is retried. FIG. 10 is a diagram for explaining a method for calculating the number of paper feed retries.

  Hereinafter, although the example of the form for implementing this invention is demonstrated, this invention is not limited to the following examples.

<Embodiments of Image Forming Apparatus and Paper Conveying Apparatus>
Hereinafter, a specific embodiment of a paper transport device capable of performing a transport retry operation for transporting paper again even when a transport failure occurs and an image forming apparatus including the paper transport layer will be described. To do. In the following description, as an example of the transport operation and the transport retry operation, a paper transport from the paper feed unit to the image forming unit, a retry operation in a so-called paper feed operation (hereinafter referred to as a paper feed retry operation) will be described. Furthermore, as an example of a paper transport device capable of transport operation and transport retry operation and an image forming apparatus, a paper transport device capable of performing the paper feed retry operation and an image forming apparatus will be described. However, the various operations relating to paper feeding described below can be similarly applied to the conveyance of paper other than paper feeding by appropriately replacing the configuration used for each conveyance.

[Configuration of Image Forming Apparatus]
FIG. 1 shows a schematic configuration of the sheet conveying device and the image forming apparatus. FIG. 2 is a schematic diagram of a sheet conveyance path from the sheet feeding unit to the sheet discharge outlet in the apparatus shown in FIG. In FIG. 1, the configuration of the paper transport device is included in the image forming apparatus, and the configuration including the paper transport path from the paper feeding unit to the paper discharge port in the image forming device corresponds to the paper transport device. . Further, in the following description, each roller provided in the image forming apparatus and the sheet conveying apparatus conveys the sheet with its rotational force by rotating with a pair of rotating members sandwiching the sheet therebetween, Below, a pair is abbreviate | omitted and it is called a roller. Each roller is connected to a driving motor (not shown) for rotating the roller, and the driving of each roller can be controlled by controlling each driving motor with a signal from the control unit.

  The image forming apparatus shown in FIG. 1 is, for example, a multi-function peripheral (MFP) 100 having the functions of a scanner, a color copier, and a color laser printer, and a paper supply for supplying image forming paper to the MFP 100. And a paper unit 133. In FIG. 1, the relay unit 140 and the post-processing device 150 are shown together with the MFP 100 and the paper feed unit 133.

  An image forming unit 130 is built in the casing of the MFP 100. Further, in the image forming apparatus, a paper feed unit 133 is attached to the lower part of the MFP 100. In the image forming apparatus, the image forming unit 130 includes an image forming unit 20, a fixing unit 30, and a sending unit 40. Each of these units functions as the image forming unit 130 of the MFP 100 and forms an image on a sheet based on the image data. The paper feed unit 133 includes a paper feed unit 10 and a manual feed tray 16. The paper supply unit 10 includes a paper storage unit 11 that stores a bundle of papers SH therein. In the paper feeding unit 133 illustrated in FIG. 1, two paper storage units 11 </ b> A and 11 </ b> B are illustrated as the paper storage unit 11.

As shown in FIG. 2, the sheet conveyance path 48 from the sheet feeding unit 133 to the sheet discharge outlet 42 includes a plurality of conveyance paths including a sheet feeding path 481, an image forming path 482, and a double-sided circulation path 483. Have. The paper feed path 481 is a path from the paper storage unit 11 (see FIG. 1) of the paper feed unit 133 and the manual feed tray 16 to the paper feed detection sensor 17 disposed in front of the image forming path 482. The image forming path 482 is a path from the paper feed detection sensor 17 to the path switching gate 41. The double-sided circulation path 483 is a path from the path switching gate 41 to the path merging unit 485 that is a merging point with the sheet feeding path 481.
In addition, a sheet switching threshold value 484 is set for the transport path 48. The sheet switching threshold value 484 is set as the distance from the path junction unit 485 to the sheet feed detection sensor 17.

  As shown in FIG. 1, an automatic document feeder (ADF) 110 is mounted on the upper surface of the casing of the MFP 100 so as to be openable and closable. Between MFP 100 and ADF 110, a scanner or the like (not shown) is built in the upper part of the casing of MFP 100.

  The MFP 100 shown in FIG. 1 is an in-body discharge type, and a discharge tray 46 is detachably installed in a gap DSP between the ADF 110 and the image forming unit 130, and paper is fed from the discharge outlet 42 to the discharge tray 46 in the gap DSP. Is discharged. A reversing tray 47 is installed above the paper discharge tray 46 in the gap DSP. When performing duplex printing, the paper on which the image is formed on the first surface (front surface) is reversed on the reverse tray 47. That is, the paper that has reached the reversing port 44 is once transported to a position where the front end exits from the reversing port 44 onto the reversing tray 47, and then the transport direction is reversed (switched back) so that the rear end of the first surface is It becomes the front end of the second surface and is drawn into the reversing port 44 again.

The relay unit 140 is installed so as to continue from the position where the paper discharge tray 46 is provided. The relay unit 140 receives a sheet from the paper discharge port 42 of the MFP 100 and relays the sheet to the post-processing device 150 for conveyance.
The post-processing device 150 performs post-processing on the paper received from the paper discharge port 42 via the relay unit 140 in response to an instruction from the MFP 100. This post-processing includes, for example, processing for aligning sheets into a bundle, processing for binding the bundle with staples, and the like.

  The post-processing device 150 includes a plurality of paper discharge trays. In the post-processing device 150 illustrated in FIG. 1, two paper discharge trays 151 and a paper discharge tray 152 are illustrated as the paper discharge trays. For example, sheets are stacked on the upper discharge tray 151 in the state when the sheets are delivered from the discharge outlet 42. The lower sheet discharge tray 152 is loaded with a bundle of sheets aligned or closed with staples.

In the paper feeding unit 133, the paper feeding unit 10 uses the paper feeding rollers 12 </ b> P, 12 </ b> R, 12 </ b> F, 13, 14, 15 from the paper storage unit 11 of the paper feeding unit 133 or the manual feed tray 16 to the MFP 100. The sheet SH is conveyed to the image forming unit 20 one by one. The size of the paper SH is, for example, A3, A4, A5, or B4. The paper storage unit 11 stores plain paper as a paper type, and the manual feed tray 16 can supply not only plain paper but also, for example, thin paper other than plain paper. Plain paper, basis weight predetermined range can be within the range of, for example, 60 to 100 / m ^2, thin paper has a basis weight of a predetermined value may be a smaller paper than for example 60 g / m ^2.

  In the image forming unit 130, the image forming unit 20 includes an image forming unit 21, a primary transfer roller 22, an intermediate transfer belt 23, a secondary transfer roller 24, and a photosensitive drum 25. In FIG. 1, as the image forming unit 21, four image forming units 21Y for forming each color of yellow (Y), magenta (M), cyan (C), and black (K), and image forming unit 21M are shown. The image forming unit 21C and the image forming unit 21K are illustrated. In FIG. 1, primary transfer rollers 22Y and 1D corresponding to the image forming unit 21Y, the image forming unit 21M, the image forming unit 21C, and the image forming unit 21K are used as the primary transfer roller 22 and the photosensitive drum 25, respectively. The secondary transfer roller 22M, the primary transfer roller 22C, and the primary transfer roller 22K, and the photosensitive drum 25Y, the photosensitive drum 25M, the photosensitive drum 25C, and the photosensitive drum 25K are illustrated.

  The image forming unit 20 forms an image on the paper SH sent from the paper supply unit 10. Specifically, in each of the four image forming units 21Y, 21M, 21C, and 21K, the photosensitive drums 25Y, 25M, 25C, and 25K are irradiated with laser light from the exposure unit 26. A pattern based on the image data is exposed on the surface of the substrate to form an electrostatic latent image.

  Each image forming unit 21 develops the electrostatic latent image with toner of each color of yellow (Y), magenta (M), cyan (C), and black (K). The obtained four color toner images are the same on the surface of the intermediate transfer belt 23 in order from the surface of the photosensitive drum 25 of each color by the electric field between the primary transfer roller 22 of each color and the photosensitive drum 25 of each color. It is transferred to the position. As a result, one color toner image is formed on the intermediate transfer belt 23.

  The color toner image receives an electric field between the intermediate transfer belt 23 and the secondary transfer roller 24 by passing through the nip portion between the intermediate transfer belt 23 and the secondary transfer roller 24 simultaneously with the paper SH. And transferred to the surface of the paper SH. Thereafter, the secondary transfer roller 24 conveys the paper SH to the fixing unit 30.

  The fixing unit 30 includes a fixing roller 31 and a pressure roller 32. The fixing unit 30 thermally fixes the toner image on the sheet SH conveyed from the image forming unit 20. Specifically, the heat of the heater in which the fixing roller 31 is built is applied to the paper SH that passes through the nip portion between the fixing roller 31 and the pressure roller 32, and the pressure roller 32 applies pressure to the heated portion. Add The toner image is fixed on the surface of the sheet SH by the heat from the fixing roller 31 and the pressure from the pressure roller 32. Thereafter, the pre-discharge roller 33 conveys the paper SH to the delivery unit 40.

  The delivery unit 40 includes a pre-discharge roller 33, a path switching gate 41, a discharge port 42, a discharge roller 43, a reverse port 44, a reverse roller 45, and a double-sided circulation path 483. The sending unit 40 conveys the paper SH conveyed from the fixing unit 30 via the pre-discharge roller 33 to the relay unit 140. Alternatively, the sending unit 40 switches the position of the path switching gate 41 so that the sheet SH conveyed from the fixing unit 30 via the pre-discharge roller 33 is conveyed to the reverse tray 47, and the front and rear ends of the sheet SH. Invert the edges.

  As shown in FIG. 2, the path switching gate 41 is a plate-like member whose one end is rotatably fixed between the paper discharge port 42 and the reversing port 44. The path switching gate 41 is provided so that the position of the other end can be moved by fixing one end of the path switching gate 41 to be rotatable. The path switching gate 41 moves the position of the other end to the sheet discharge port 42 side when conveying the sheet sent out by the pre-discharge roller 33 to the relay unit 140, and sets the path to the sheet discharge port 42 ( (Hereinafter referred to as “sending path”). Further, when the sheet is conveyed to the reversing port 44, the position of the other end is moved to the reversing port 44, and a path to the reversing port 44 (hereinafter referred to as “reversing path”) is formed.

  The paper discharge roller 43 is disposed inside the paper discharge port 42 and sends the paper SH that has moved along the path switching gate 41 from the paper discharge port 42 to the relay unit 140. The reversing roller 45 is disposed inside the reversing port 44 and is provided to be rotatable in both forward and reverse directions. The reversing roller 45 first rotates in the forward direction, and once the paper SH conveyed along the path switching gate 41 is sent out from the reversing port 44 and placed on the reversing tray 47. The reversing roller 45 rotates in the reverse direction before the rear end of the paper SH passes through the reversing roller 45, and draws the paper SH from the reversing tray 47 into the reversing port 44 and conveys it to the double-sided circulation path 483. .

In the double-sided circulation path 483, the paper SH conveyed from the reverse roller 45 by the conveyance roller 48a, the conveyance roller 48b, the conveyance roller 48c, and the conveyance roller 48d Is returned to the paper feed path 481 from the path merging unit 485.
Thereafter, the sheet SH is sent to the image forming unit 20 again. Then, the image forming unit 20 forms a toner image on the back surface (second surface) of the paper SH. The fixing unit 30 performs the heat treatment again on the sheet SH. The sending unit 40 forms a sending path by moving the path switching gate 41, and transports the paper SH from the paper discharge port 42 to the relay unit 140 by the paper discharge roller 43.

  The relay unit 140 relays the paper transported from the paper discharge port 42 to the post-processing device 150 using the transport roller 141, the transport roller 142, and the transport roller 143. The post-processing device 150 includes the paper discharge tray 151 and the paper discharge tray 152, the entrance transport roller 161, the sorting claw 162, the upper paper discharge roller 163, the transport roller group 164, the reverse roller 165, the post-processing unit 166, and A lower paper discharge roller 167.

  The entrance conveyance roller 161 receives the sheet from the relay unit 140 and draws the sheet into the post-processing device 150. The sorting claw 162 is a member whose one end is rotatably fixed and the other end is a claw-like or plate-like member. The sorting claw 162 is provided so that the other end can be moved up and down by swinging one end. When the paper drawn by the entrance transport roller 161 is sent out to the upper paper discharge roller 163, the sorting claw 162 moves the position of the other end downward to form a path to the upper paper discharge roller 163. Further, when the paper is sent to the post-processing unit 166, the sorting claw 162 moves the position of the other end upward to form a path to the transport roller group 164.

The upper paper discharge roller 163 is disposed in the vicinity of the upper paper discharge tray 151, and conveys the paper that has moved from the entrance conveyance roller 161 along the sorting claw 162 to the upper paper discharge tray 151. The transport roller group 164 transports the paper that has moved from the entrance transport roller 161 along the sorting claw 162 to the reverse roller 165 provided at the entrance of the post-processing unit 166.
The reversing roller 165 is disposed at the entrance of the post-processing unit 166 and can rotate in both forward and reverse directions. The reversing roller 165 first rotates in the forward direction, and feeds the paper from the transport roller group 164 to the post-processing unit 166. The post-processing unit 166 accumulates a predetermined number of sheets received from the reversing roller 165 to form a bundle, and performs post-processing such as alignment processing and stapling processing on the bundle. Next, the reverse roller 165 rotates in the reverse direction, pulls out the post-processed sheet bundle from the post-processing unit 166, and conveys it to the lower paper discharge roller 167. The lower discharge roller 167 is disposed in the vicinity of the lower discharge tray 152, and discharges a bundle of sheets conveyed from the post-processing unit 166 by the reverse roller 165 to the lower discharge tray 152.

[Transport route]
As described above, FIG. 1 and FIG. 2 show the sheet conveyance path in the sheet conveying apparatus and the image forming apparatus. As shown in FIGS. 1 and 2, in the MFP 100, not only the paper feeding unit 10 and the sending unit 40, but also the driving roller 23 </ b> R, the secondary transfer roller 24, the fixing roller 31, the pressure roller 32, and the paper discharge of the intermediate transfer belt 23. A part of the image forming unit 20 and the fixing unit 30 such as the front roller 33 functions as a sheet conveyance path.

  In the paper transport apparatus and the image forming apparatus shown in FIGS. 1 and 2, the transport path is configured as follows. First, three paths from the sheet storage units 11A and 11B and the manual feed tray 16 are connected to one sheet feeding path 481. The paper feed path 481 is connected to the image forming path 482 and passes through the image forming unit 20 and the fixing unit 30. Further, the image forming path 482 is connected to the sending unit 40, and the path switching gate 41 branches into two paths, a sending path and a reversing path. The path on the delivery path side is connected to the paper discharge tray 46 through the paper discharge port 42. Further, the path on the reverse path side is connected to the double-sided circulation path 483, and the double-sided circulation path 483 is further connected to the sheet feeding path 481 from the path junction 485.

  In addition to the rollers shown in FIGS. 1 and 2, a plurality of optical sensors such as a paper feed detection sensor 17 are installed on these transport paths. Each optical sensor detects the paper passing through the installation location. The optical sensor includes, for example, a light emitting unit and a light receiving unit. The light emitting unit emits light of a predetermined wavelength such as infrared rays, and the light receiving unit detects light of that wavelength. Then, while one sheet passes through the installation location of each optical sensor, the passing sheet blocks the light emitted from the light emitting unit in front of the light receiving unit or reflects it toward the light receiving unit. In this way, the sheet passing through the installation location of the optical sensor is detected by changing the output of the light receiving unit according to the blocking or reflection of the emitted light.

  The paper feed detection sensor 17 is provided in front of the registration roller 14 on the downstream side of the path junction 485. The registration roller 14 is generally in a stopped state, and temporarily stops the sheet conveyed from the paper feed path 481 by the registration roller 14. The registration roller 14 starts rotating at the timing indicated by the drive signal from the control unit, and sends the stopped paper to the image forming unit 20.

  A detection sensor 308 (see FIG. 3), which will be described later, is installed in the vicinity of the paper storage portions 11A and 11B, which are the starting ends of the transport path shown in FIG. 1, for detecting paper feed from the paper storage portions 11A and 11B. Yes. Based on the output of the detection sensor, it is possible to detect the start timing of paper feed. Further, based on the output of the detection sensor, it can be determined whether the paper feed roller 12P, the paper feed roller 12F, and the paper feed roller 12R are feeding each paper to the path at a normal timing. Instead of the paper feed start timing by the detection sensor, the paper feed start timing may be detected by detecting the opening / closing operation of the paper storage units 11A and 11B by the open / close detection unit 134 (open / close detection sensor). These detection sensors notify the control unit 300 (see FIG. 3), which will be described later, of the detection of paper that passes through the paper feeding unit 10, the sending unit 40, and the like. In response to this notification, the control unit determines whether the apparatus is operating normally without a jam or the like conveyance failure, and whether or not an abnormality has occurred in the sheet conveyance timing due to the jam or the like. .

  The paper conveyed from the paper feed path 481 and the paper conveyed from the double-sided circulation path 483 through the path junction 485 are detected by the paper feed detection sensor 17 to reach the registration roller 14. For this reason, it is preferable that the paper feed detection sensor 17 is disposed at a distance equal to or shorter than the length of one sheet from the registration roller 14 in the vicinity of the registration roller 14.

  Based on the output from the paper feed detection sensor 17, the control unit determines whether or not the paper has arrived at the registration roller 14 at a normal timing and whether or not the paper has been sent from the registration roller 14 at a normal timing. Further, the control unit can measure the size of the paper based on the output of the time required for sending each paper from the paper feed detection sensor 17.

  Further, the MFP 100 detects a sheet passing through the pre-discharge roller 33, the discharge roller 43, and the reversing roller 45, and detects the operation of each roller according to the passing timing, and the conveyance of the duplex circulation path 483. Other sensors such as a conveyance sensor that detects the paper passing through the roller 48a, the conveyance roller 48b, the conveyance roller 48c, and the conveyance roller 48d and detects the operation of each roller according to the passage timing may be provided.

[Block Diagram]
FIG. 3 shows a functional block diagram of MFP 100 of the image forming apparatus. The functional block diagram shown in FIG. 3 illustrates, as an example of an image forming apparatus, a control unit 300 that controls the entire MFP 100, an operation unit 316, a document reading unit 314 that reads a document and acquires image data, and In this example, an image processing unit 312 that executes various types of image processing, each motor drive circuit 304, each motor 306, each detection sensor 308, and a path switching SL 309 are provided. In the functional block diagram of the image forming apparatus shown in FIG. 3, an example in which the control unit 300 of the MFP 100 includes an MFP controller 301 that mainly controls image formation in the MFP 100 and an engine controller 302 that controls paper conveyance. Is shown.

  The operation unit 316 receives a job request and image data to be printed through a user operation or communication with an external electronic device, and transmits them to the MFP controller 301 of the control unit 300. The operation unit 316 includes an operation panel including push buttons, a touch panel, a display, and the like. The operation unit 316 controls the operation panel to display a GUI (Graphical User Interface) screen such as an operation screen or an input screen for various parameters. The display of the screen includes a message display indicating that a conveyance failure such as a jam has occurred on the paper being conveyed.

  The control unit 300 includes a CPU, a RAM, and a ROM. The CPU controls the MFP controller 301, the engine controller 302, the operation unit 316 connected to the control unit 300, the document reading unit 314, and the image processing unit 312 according to the firmware. The RAM provides a work area when the CPU executes firmware to the CPU, and stores image data to be printed received by the operation unit 316. The ROM includes a non-writable semiconductor memory device in which information such as firmware is stored, a rewritable semiconductor memory device such as an EEPROM that provides a storage area for environment variables and the like to the CPU, an HDD, and the like.

  As the CPU executes various types of firmware, the MFP controller 301 controls other elements in the MFP based on operation information from the operation unit 316. For example, the MFP controller 301 displays an operation screen on the operation unit 316 and accepts an operation by the user. Then, the control unit 300 determines an operation mode such as an operation mode, a standby mode, and a sleep mode in accordance with a user operation, and notifies the MFP controller 301 of the operation mode according to each operation mode. Causes each element to execute the process. Specifically, when the operation unit 316 receives a print job from the user, the MFP controller 301 transfers the image data to be printed to the RAM of the control unit 300. Next, the MFP controller 301 designates the paper type and its feeding timing in accordance with the printing conditions from the control unit 300, provides the image data to the image forming unit, and supplies the surface of the fixing roller to the fixing unit. The temperature is specified, and the transfer destination and switching timing are specified in the delivery unit.

  Further, the MFP controller 301 monitors the operation state of each element of the MFP and the paper conveyance state, and when any failure is detected, the operation mode is appropriately changed to solve the failure. For example, when an abnormal delay in the sheet conveyance timing is detected through various sensors mounted on the image forming apparatus, the image forming process is interrupted and a message is displayed on the operation unit 316.

  Further, the control unit 300 controls an engine controller 302 for controlling driving of the image forming unit and the like together with the MFP controller 301. The engine controller 302 is controlled by the CPU of the control unit 300 executing dedicated firmware. The engine controller 302 controls the sheet transport operation in normal job processing by the control unit 300.

  The engine controller 302 of the control unit 300 controls each motor drive circuit 304, each motor 306, each detection sensor 308, and the path switching SL 309 according to the operation mode of the MFP controller 301 and the job conditions. The engine controller 302, the motor drive circuit 304, each motor 306, each detection sensor 308, and the path switching SL 309 are provided in the image forming unit 130 of the image forming apparatus.

  The motor drive circuit 304 drives each motor 306 in accordance with an instruction from the engine controller 302. Each motor 306 is connected to each transport roller on the paper transport path, and each motor on the paper transport path is rotated by driving of each motor 306, so that the paper moves from the paper feed unit to the image forming unit. In addition, the sheet is moved in the image forming unit, and the sheet is moved to the relay unit or the post-processing device.

The engine controller 302 includes a calculation unit 302a, a storage unit 302b, a time measurement unit 302c, a conveyance control unit 302d, and a determination unit 302e.
The time measuring unit 302c includes a timer and the like, and measures the paper feeding time from the discharge of the paper to the paper feeding unit until the detection sensor 308 is reached.
Based on information from the detection sensor 308, the calculation unit 302a calculates a paper position estimation and the number of paper feed retries described later.
The conveyance control unit 302d instructs the motor driving circuit 304 to convey the sheet, and instructs each motor driving circuit 304 to retry the paper feeding according to the calculated number of paper feeding retries.
The storage unit 302b includes a volatile memory and a non-volatile memory. The storage unit 302b measures the measurement time by the time measurement unit 302c, the paper feed retry history information, the transport speed used to calculate the number of retries, and the conditions for each paper type. Is retained.
The determination unit 302e determines whether or not the time measured by the time measurement unit 302c is equal to or shorter than a predetermined paper feed error determination time, arrival at each detection sensor 308, or the like.

  The detection sensor 308 outputs information on the arrival and passage of paper detected by various sensors provided in the conveyance path of the image forming apparatus to the conveyance control unit 302 d of the engine controller 302. The calculation unit 302a of the engine controller 302 estimates the paper position based on information from the detection sensor 308. Specifically, first, the conveyance control unit 302d of the engine controller 302 instructs the timing for picking up the paper to the paper feed roller of the paper feed unit. The time measuring unit 302c of the engine controller 302 measures the elapsed time from the time of pickup with a timer or the like every time the paper feed roller picks up the paper. A detection sensor 308 of the paper feed unit detects a conveyance state such as arrival or passage of each sheet, and outputs a detection signal to the conveyance control unit 302d of the engine controller 302. The transport controller 302d of the engine controller 302 monitors the paper transport state based on the detection signal from the detection sensor 308, and tracks the paper position on the transport path from the transport speed and elapsed time.

  A standard value (that is, a system speed) is defined for each operation mode for the sheet conveyance speed and the conveyance time, and is stored in the storage unit 302 b of the engine controller 302. The calculation unit 302a of the engine controller 302 calculates the moving distance and position information of the sheet based on the standard value of the conveyance time and the elapsed time from the pickup time. The calculation unit 302a of the engine controller 302 predicts the installation location of the detection sensor 308 through which the sheet passes next and the passage time thereof based on the position information. The calculation unit 302a of the engine controller 302 corrects the current position of the sheet from the error between the predicted time and the actual elapsed time at the detection sensor 308, and updates the position information with the corrected value. Then, the conveyance control unit 302d of the engine controller 302 uses the corrected position information to instruct the motor drive circuit 304 to drive the motor 306 according to the estimated sheet position, or to switch the path to the path switch SL309. Instructs the direction of the gate and the distribution claw and the timing for switching the direction.

  Further, when the determination unit 302e of the engine controller 302 detects an abnormal delay or the like in the conveyance timing based on the measurement time and position information and the output notified from the detection sensor 308, the conveyance of the paper such as a jam is performed. It is determined that a defect has occurred. As an event determined that the conveyance failure has occurred, for example, when the error between the passing time at the detection sensor 308 predicted from the position information and the actual passing time due to the output of the detection sensor 308 exceeds the allowable range, The case where the output of the passage cannot be obtained from the detection sensor 308 is included even if the allowable range is exceeded from the predicted passage time.

  If the determination unit 302e of the engine controller 302 determines that a conveyance failure has occurred, the MFP controller 301 interrupts job processing and executes purge processing. When it is determined that a conveyance failure has occurred, if the detection sensor 308 cannot detect a sheet conveyed from the sheet feeding unit, or if a so-called sheet feeding failure has occurred, the MFP controller 301 causes a retry described later. Processing is performed, and then purge processing is performed as necessary.

  The purge process is an operation of discharging a sheet that can continue to be transported from the transport path among the sheets being transported. In the purging process, the MFP controller 301 identifies a sheet that is positioned upstream from the sheet that cannot continue to be conveyed due to a jam or the like and that can continue to be conveyed as a purge target based on the position information of the sheet. Then, the MFP controller 301 determines the purge destination and the conveyance order for each identified sheet, and instructs the engine controller 302 to convey and discharge the identified sheet. As a result, the paper that can continue to be transported is removed from the transport path.

  Furthermore, when a conveyance failure is detected, the control unit 300 displays a message indicating that a conveyance failure has occurred on the screen of the operation unit 316. When the user opens and closes the exterior cover of the MFP 100 and performs a predetermined removing operation for removing the paper stopped on the transport path due to a jam or the like, the paper transport failure is eliminated. By canceling this conveyance failure, the suspended job is resumed.

[Retry processing]
Next, the retry process of the image forming apparatus will be described.
In order to relieve the user from the inconvenience of the predetermined removal work except the paper that is stopped on the transport path, the number of residual paper is reduced when the image forming apparatus interrupts the processing due to a jam or the like. It is preferable. If more sheets can be discharged when a conveyance failure occurs, the number of remaining sheets can be reduced, and the user's removal work can be reduced.

  In the image forming apparatus according to the present exemplary embodiment, the number of times the retry operation is performed when a paper conveyance failure occurs is determined by estimating the post-retry paper position from the retry history information. In this way, by determining the number of retry operations for paper conveyance, the number of residual paper in the image forming apparatus when a paper conveyance failure occurs is reduced. Further, the number of retry operations is determined to be the number of times that the sheet does not stay at the path junction 485 between the paper feed path 481 and the double-sided circulation path 483. As a result, it is possible to realize image formation that can reduce the residual paper in the machine at the time of poor feeding and reduce the burden of the user's removal work.

[flowchart]
FIG. 4 is a flowchart showing an example of paper conveyance control for performing paper feed retry. FIG. 4 is a flowchart for controlling a sheet feeding operation for conveying a sheet used for image formation from the sheet feeding unit to the image forming unit in the image forming apparatus, and a sheet feeding path from the sheet storage unit to the sheet feeding detection sensor. Represents the control of the paper transport process.

First, the transport controller of the engine controller of the controller starts feeding paper by rotating the paper feed roller in order to feed the paper one by one from the paper storage unit (step S101). Simultaneously with the start of paper feeding in step S101, the time measuring unit of the engine controller starts a paper feeding time measuring timer and starts measuring the paper feeding time (step S102).
The conveyance of the sheet by the sheet feeding roller in step S101 is executed for each sheet in accordance with a predetermined timing, for example, an interval from the preceding sheet (inter-sheet interval), a conveyance timing to the image forming unit, and the like.

  Next, in the determination unit of the engine controller, the control unit determines whether the elapsed time from the start of measurement (feed elapsed time) is equal to or shorter than a predetermined feed error determination time (step S103), and detects whether the sheet is fed. It is determined whether the sensor has been reached (step S104). Here, the paper feed elapsed time is an elapsed time counted after the timer is started by the rotation of the paper feed roller. If the paper has not reached the paper feed detection sensor (No in step S104), the determination unit performs step until the paper feed elapsed time in step S103 is equal to or longer than the paper feed error determination time (Yes in step S103). The comparison between the paper feed elapsed time and the paper feed error determination time in S103 is repeated. The determinations in step S103 and step S104 in the determination unit are performed every predetermined control cycle after the start of feeding in step S101.

  When the paper feed elapsed time is equal to or shorter than the paper feed error determination time (No in step S103) and the paper reaches the paper feed detection sensor (Yes in step S104), the time measuring unit of the engine controller The timer is stopped and the paper feed time measurement is stopped (step S105).

  Next, the control unit stores the time until the completion of feeding (feeding completion time) measured in step S105 in the storage unit of the engine controller (step S106), and stops the rotation of each feeding roller (step S107). ). The paper feed completion time is the time from the start of the timer until the detection sensor detects the paper. If no paper feed failure occurs, the paper feed operation is repeated until the end of the job along the above flow.

  Note that the paper feed error determination time in step S103 initially uses a standard value determined for each operation mode stored in the storage unit of the engine controller of the control unit. Then, after the paper feed completion time in step S106 is stored by continuous use, the paper feed completion time stored in step S106 is used as retry history information of the paper feed error determination time in step S103.

  As shown in FIG. 5, the elapsed time of paper feeding by the engine controller time measuring unit is measured from the paper feeding roller closest to the paper storage unit (paper feeding cassette) to the paper detection sensor. Time measurement is performed only during the period in which the leading edge position of the sheet (the leading edge position indicated by a solid line in FIG. 5) moves within this measurement section. Then, the elapsed paper feed time and the paper feed completion time are obtained from the time measurement from the start of rotation of the paper feed roller until the paper leading edge position reaches the paper detection sensor.

  In addition, as shown in FIG. 6, the elapsed time of feeding by the time measuring unit at the time of paper feeding retry is measured at the leading edge of the paper in the measuring section from the paper feeding roller on the paper container side to the paper detection sensor. Time measurement is performed only during a period in which the position (the leading end position of the paper indicated by the solid line in FIG. 6) moves. For this reason, the time measurement by the time measurement unit is suspended during a period in which the conveyance rollers such as the paper supply roller are stopped and the sheet is not moved. Then, the elapsed time of paper feeding and the time of completion of paper feeding are obtained from the sum of the time measurements during the period of paper movement from the start of rotation of the paper feed roller until the paper leading edge position reaches the paper detection sensor.

  Therefore, when no paper feed retry is performed because no paper feed error has occurred, the paper feed completion time is equal to or shorter than the paper feed error determination time. On the other hand, when a paper feed completion time is measured and stored after a paper feed error occurs and a paper feed retry is performed, the paper feed completion time is longer than the paper feed error determination time.

  In the storage of the paper feed completion time in step S106, a method of storing the paper feed completion times for a plurality of sheets in the nonvolatile memory of the storage unit of the engine controller for improving the prediction accuracy, or a plurality of sheets for reducing the memory area. Can be stored in a volatile memory of the storage unit of the engine controller, and various methods such as a method of writing only the average value into the nonvolatile memory can be employed. In addition, since the conveyance time varies depending on the conditions of the operation mode and the like, a separate paper feed completion time may be stored for each condition such as the conveyance speed, the paper type, and the paper feed tray. In addition, when storing the paper feed completion time for each paper storage unit of the paper feed unit, when the opening / closing detection unit provided in the paper feed unit detects the opening of the tray, the type of paper stored Therefore, the stored paper feed completion time may be reset. When the paper feed completion time is reset, the initial standard value determined for each operation mode can be used as the paper feed error determination time.

  If the paper does not reach the paper feed detection sensor (No in Step S104) and the elapsed paper feed time exceeds the paper feed error judgment time (No in Step S103), the determination unit of the engine controller performs this paper feed operation. It is determined that there is a paper feed error, and it is determined whether this paper feed error is the first time (step S108).

  If a paper feed error occurs for the first time (Yes in step S108), that is, if a paper feed error occurs during a paper feed operation other than the paper feed retry operation, the time measurement unit of the engine controller is used for paper feed time measurement. The timer is stopped and the paper feed time measurement is stopped (step S109). When the paper feeding error is not the first time (No in step S108), the calculation unit of the engine controller sets a retry count (step S116) described later.

Next, the calculation unit of the engine controller estimates the paper position (step S110). The paper position is estimated by the following method.
FIG. 7 shows a conceptual diagram of a method for calculating the number of paper feed retries.
When a paper feed error is detected, first, an estimated paper position Pes at the time of paper feed error detection is calculated from the following calculation formula (1).
Estimated paper position (Pes) = (Dfd / Tfd) × Tjm (1)
Dfd: Distance from paper feed roller to paper detection sensor (length of measurement section)
Tfd: stored paper feed completion time (see step S106)
Tjm: Feeding error judgment time

  By dividing the length of the measurement section (Dfd) by the paper feed completion time (Tfd), the estimated transport speed (in FIG. 7, the slope of the solid line indicating the leading edge position of the paper) is obtained. Then, by multiplying the estimated conveyance speed by the paper feed error determination time (Tjm), that is, by multiplying the paper feed elapsed time until the paper feed error is determined, the paper when the paper feed error determination time has elapsed Is calculated. Accordingly, it is possible to estimate the estimated sheet position (Pes) that indicates the position of the sheet when it is determined that a paper feed error has occurred. This estimated paper position (Pes) has the same meaning as the distance that the paper travels in one paper feeding operation. If there is no history information on the paper feed completion time (Tfd), for example, a predetermined time may be used as the provisional paper feed completion time used for the calculation.

  Next, the calculation unit of the engine controller is necessary for the paper to reach the paper feed detection sensor using the estimated paper position (Pes) calculated in step S110 described above and the following calculation formula (2). The number of paper feed retries (Nrt) is calculated, and the predicted paper position (Pex) after the retry is calculated using the following formula (3) (step S111).

Number of paper feed retries (Nrt) = round up ((Dfd−estimated paper position) / (estimated paper position)) (2)
Predicted paper position after retry (Pex) = estimated paper position + ((Dfd / Tfd) × Tjm × number of retries) (3)

In the above formula (2), by subtracting the estimated paper position (Pes) from the length (Dfd) of the measurement section, the length from which the paper movement is required in the paper feed retry operation, that is, the estimated paper position (Pes). The remaining distance to the paper feed detection sensor is obtained. Further, by dividing the remaining distance to the paper feed detection sensor by the estimated paper position (Pes; movement distance in one paper feed operation), the number of paper feed operations that the leading edge of the paper reaches the paper feed detection sensor is obtained. calculate. Since the number of sheet feeding operations may be calculated as a numerical value having a fractional part, the number of sheet feeding retries (Nrt) can be obtained by rounding up the numerical value to an integer.
Further, the distance traveled for each retry can be calculated by multiplying the estimated paper position (Pes; the distance traveled by a single paper feeding operation) by the number of retries. Therefore, in the above equation (3), the post-retry paper position (Pex) can be predicted by adding the distance traveled for each retry to the estimated paper position (Pes).

Next, the calculation unit of the engine controller compares the number of paper feed retries calculated in step S111 (hereinafter, the calculated number of retries) with the upper limit number of paper feed retries (step S112).
In step S111, the calculated retry count is obtained, and if the retry is repeated for this number of times, the image formation can be continued without interrupting the job or performing the purge process. However, it is preferable to set the upper limit number of retries in order to prevent a decrease in throughput and an increase in power consumption due to repeated retries more than necessary. The upper limit number of retries may be set to a predetermined number, or an arbitrary numerical value may be set by the user or the administrator from the operation unit or the like according to the use environment.

  Therefore, when the calculated retry count does not exceed the upper limit retry count (Yes in step S112), the calculation unit determines the calculated retry count to be the number of retries to be performed (step S113). On the other hand, when the calculation retry count exceeds the upper limit retry count (No in step S112), the calculation unit determines the upper limit retry count as the number of retry to be performed (step S114).

  However, if the retry count is the upper limit retry count, the post-retry paper position may not reach the paper feed detection sensor. Further, in this case, the paper advanced by the retry stays at the path junction between the paper feed path and the double-sided circulation path, and the paper waiting in the double-sided circulation path cannot be discharged out of the apparatus. there is a possibility. Therefore, the determination unit of the engine controller uses the predicted paper position after retry calculated in step S111 to determine whether the predicted paper position after the set number of retries can reach the paper feed detection sensor and the route merge. It is determined whether or not the part stays (step S115).

  If the retryed paper stays in the path junction (Yes in step S115), the determination unit determines that the paper feed is defective, and the conveyance control unit stops the paper feed roller without performing the paper feed retry operation. (Step S119), the paper feeding operation is terminated. On the other hand, if the paper after the retry does not stay in the path junction (No in step S115), the calculation unit sets the number of retries (step S116).

  In the setting of the number of retries in step S116, the calculated number of retries or the upper limit number of retries is set to the number of retries to be performed (hereinafter, set retry number). If the paper feed error is not the first time (No in step S108), in the setting of the number of retries in step S116, 1 is added to the number of retries performed, and the number of retries to be performed next is set. To do. As a result, the calculation unit sets the final number of retry operations, calculates the number of retry operations performed from the number of performed retry operations, and calculates the number of retry operations to be performed next (the number of performed retry operations). calculate.

  Next, the determination unit of the engine controller determines whether the retry operation being performed is equal to or less than the set retry count (step S117). When the number of retry operations is less than or equal to the set number of retry operations (Yes in step S117), the transport controller of the engine controller stops the rotation of the paper feed roller and temporarily stops the paper feed operation (step S118). Thereafter, in order to perform a retry operation, the conveyance control unit starts rotation of the paper feed roller again and starts the paper feed operation (step S101). Thereafter, the paper feed retry operation is repeated until the paper reaches the paper feed detection sensor (Yes in Step S104) or until the number of execution retries exceeds the set number of retries (No in Step S112).

  When the number of execution retries exceeds the set number of retries (No in step S117), the determination unit of the engine controller determines that there is a paper feed failure, and the conveyance control unit does not perform the paper feed retry operation, The operation is stopped (step S119), and the paper feeding operation is terminated. Although not described in the flowchart of FIG. 4, when the calculated retry count exceeds the upper limit retry count (No in step S <b> 112), the determination unit determines that there is a paper feed failure and the conveyance control unit performs the paper feed retry. Without performing the operation, the paper feed roller may be stopped (step S119) to end the paper feed operation. In addition, even if the upper limit retry count is exceeded, the paper does not reach the paper feed detection sensor within the paper feed misjudgment time (No in step S104), and the determination unit determines that there is a paper feed failure (step S119). Discard without remembering time.

In the above-described flowchart, when the estimated paper position is calculated in step S110, the paper feed completion time (Tfd) is not stored, or the paper feed completion time (Tfd) is the paper feed error determination time (Tjm). If it is smaller than), the following exception handling may be performed.
If the paper feed completion time (Tfd) is not stored, the estimated paper position cannot be calculated. If no paper feed error has occurred before, no paper feed retry is performed and the paper feed completion time (Tfd) is shorter than the paper feed error determination time (Tjm). However, this is the position beyond the measurement section, that is, the position that has passed through the paper feed detection sensor. In these cases, the number of paper feed retries is set to 1 in step S116 as an exception for the calculation of the estimated paper position.

  In the above description, the paper transport operation (paper feed operation) in the paper feed unit is described as an example of the paper transport retry operation in the paper transport device and the image forming apparatus. Similar retry processing can also be applied to the sheet transport operation. For example, when the paper arrives at an arbitrary detection sensor provided on the transport path, the time measurement start point is measured, and the time until the paper reaches another arbitrary detection sensor is measured. A conveyance completion time corresponding to the paper completion time can be obtained. Then, the conveyance completion time between these arbitrary detection sensors can be used as retry history information, and the number of retries can be obtained by estimating the paper position after the retry based on this information.

  The present invention is not limited to the configuration described in the above-described embodiment, and various modifications and changes can be made without departing from the configuration of the present invention.

  DESCRIPTION OF SYMBOLS 10 Paper feed part, 11, 11A, 11B Paper storage part, 12F, 12P, 12R Paper feed roller, 14 Registration roller, 16 Manual feed tray, 17 Paper feed detection sensor, 20 Image forming part, 21, 21C, 21K, 21M, 21Y image forming unit, 22, 22C, 22K, 22M, 22Y primary transfer roller, 23 intermediate transfer belt, 23R driving roller, 24 secondary transfer roller, 25, 25C, 25K, 25M, 25Y photosensitive drum, 30 fixing unit , 31 Fixing roller, 32 Pressure roller, 33 Pre-discharge roller, 40 Delivery section, 41 Path switching gate, 42 Discharge port, 43 Discharge roller, 44 Reverse port, 45,165 Reverse roller, 46, 151, 152 Paper discharge tray, 47 reverse tray, 48 transport path, 48a, 48b, 48c, 48d , 141, 142, 143 Conveying roller, 100 MFP, 110 Automatic document feeder, 130 Image forming unit, 133 Paper feeding unit, 134 Open / close detection unit, 140 Relay unit, 150 Post-processing device, 161 Inlet conveying roller, 162 Sorting Claw, 163 Upper discharge roller, 164 transport roller group, 166 Post-processing unit, 167 Lower discharge roller, 301 MFP controller, 302 Engine controller, 302a calculation unit, 302b Storage unit, 302c Time measurement unit, 302d Transport control unit , 302e determination unit, 304 motor drive circuit, 306 motor, 308 detection sensor, 309 path switching SL, 312 image processing unit, 314 document reading unit, 316 operation unit, 481 paper feed path, 482 image formation path, 483 double-sided circulation Road, 484 sheet switch threshold, 485 path merging portion

Claims (8)

A transport path for transporting paper,
A detection sensor provided on the transport path for detecting the paper transported;
A control unit that holds a conveyance completion time from the start of conveyance of the paper to the completion thereof, and controls a conveyance operation of the paper based on a detection result of the detection sensor;
Based on the information on the completion time of conveyance held in the control unit, after the conveyance of the sheet by the control unit is interrupted, the number of conveyance retries indicating the number of times of performing the retry operation for performing the sheet conveyance operation again is calculated. A paper conveying device having a calculating unit. The control unit holds information on the time until the detection sensor detects the paper from the start of transport of the paper that has been transported previously or the start of the retry operation as the transport completion time,
The sheet conveying apparatus according to claim 1, wherein the calculation unit calculates the number of conveyance retries based on information on the conveyance completion time. The sheet conveying apparatus according to claim 1, wherein when the opening / closing detection unit that detects opening / closing of the sheet storage unit detects the opening of the sheet storage unit, the control unit resets the conveyance completion time held by the control unit. The said calculation part calculates | requires the said conveyance retry frequency by calculating | requiring the movement distance of the said paper from the said conveyance completion time, and estimating the position of the said paper after the said retry operation | movement from the said movement distance. Paper transport device. The control unit holds information on a predetermined upper limit retry count,
The sheet conveyance according to claim 1, wherein, when the conveyance retry count calculated by the calculation unit exceeds the upper limit retry count, the calculation unit sets the upper limit retry count to the conveyance retry count to be performed. apparatus. The paper transport device according to claim 5, wherein the upper limit retry count is set for each type of paper to be transported and each paper transport speed. A plurality of transport paths for transporting the paper;
A path merging unit where a plurality of the conveyance paths merge;
A sheet switching threshold set based on the position of the path merging portion and the position of the detection sensor, and the estimated position of the sheet after the retry operation for the number of times of the transport retry calculated The paper conveyance device according to claim 6, wherein the retry operation is not performed when the value is within a paper switching threshold value. An image forming apparatus comprising the sheet conveying device according to claim 1.

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