Paper sheet conveyance device and image forming system

Abstract

To stably stack paper sheets on a tray when transporting double-fed paper sheets to the tray.SOLUTION: A paper sheet conveyance device includes: a paper sheet discharge part that is mounted on an inlet side of a tray and discharges double-fed paper sheets onto the tray; an air blowing part that blows air from the lower side of the paper sheets that make up the double-fed paper sheets toward a direction along a tray placement surface when discharging the double-fed paper sheets onto the tray; and a control part that controls the air blowing part to vary the air volume based on a detection result obtained by a double-fed detection part that detects information regarding the double feeding.SELECTED DRAWING: Figure 3A

Description

[Technical Field]

[0001] The present invention relates to a paper transport device and an image forming system. [Background technology]

[0002] In the field of image forming devices, it is known that when a sheet is conveyed to a tray, air is blown from below the sheet in a direction along the loading surface of the tray (see Patent Document 1).

[0003] In the technology described in Patent Document 1, a blower unit is provided near the paper discharge unit (referred to as discharge means in Patent Document 1) that blows air from below the paper in a direction along the tray's loading surface. By blowing air onto the backside of the paper, the blower unit lifts the leading edge of the paper, preventing the paper from sticking together on the tray. In addition, by stopping the blowing operation of the blower unit just before the trailing edge of the paper passes through the paper discharge unit, the paper can be dropped to a predetermined position on the tray. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-57313 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technology described in Patent Document 1 does not anticipate discharging so-called overlapped sheets onto the tray. Therefore, if the blowing operation of the blowing unit is stopped just before the trailing edge of the first sheet of overlapped sheets passes through the paper discharge unit, the leading edge of the second sheet of overlapped sheets cannot be prevented from sagging, resulting in an unstable discharge state of the second sheet. As a result, the sheets may stick together on the tray or may be misaligned, making it difficult to stably stack the sheets on the tray.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a paper transport device and an image forming system that can stably stack papers on a tray when multiple-fed papers are discharged to the tray. [Means for solving the problem]

[0007] A paper transport device according to one aspect of the present invention comprises: a paper discharge unit provided on the entrance side of the tray and configured to discharge multi-fed paper sheets into the tray; an air blowing unit that blows air from below the sheets constituting the overlapped sheets in a direction along the loading surface of the output tray when the overlapped sheets are discharged onto the tray; The apparatus further includes a control unit that controls the blower unit to vary the air volume based on a detection result from a double feed detection unit that detects information about double feed.

[0008] An image forming system according to one aspect of the present invention includes: an image forming device that forms an image on a sheet; a paper feeder that is installed upstream of the image forming apparatus and feeds paper toward the image forming apparatus; The image forming apparatus further includes a paper transport device that is installed between the image forming apparatus and the paper feed device and transports the paper fed from the paper feed device to the image forming apparatus. [Effects of the Invention]

[0009] According to the present invention, when multiple fed sheets are conveyed to a tray, the sheets can be stably stacked on the tray. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing an image forming system according to this embodiment. [Figure 2A] FIG. 2A is a schematic diagram of multi-fed sheets positioned in a sheet feed path of a sheet feeder, as viewed from above. [Figure 2B] FIG. 2B is a schematic diagram of multi-fed sheets positioned in the sheet feed conveyance path of the sheet feeder, as viewed from the front. [Figure 3A]FIG. 3A is a schematic diagram showing how the multi-fed sheets are discharged onto the discharge tray by the discharge unit. [Figure 3B] FIG. 3B is a schematic diagram showing how the wind force of the blower fan is reduced at the second timing while the multi-fed sheets are being discharged. [Figure 4A] FIG. 4A is a schematic diagram showing how the air force of the blower fan is increased again at a third timing while multiple-fed sheets are being discharged. [Figure 4B] FIG. 4B is a schematic diagram showing how the wind force of the blower fan is reduced at the fourth timing while the multi-fed sheets are being discharged. [Figure 5] FIG. 5 is a schematic diagram showing how the blowing operation of the blower fan is stopped at a fifth timing while multiple-fed sheets are being discharged. [Figure 6] FIG. 6 is a control block diagram of the image forming system according to this embodiment. [Figure 7A] FIG. 7A is a diagram showing the relationship between the time after the start of the blowing operation of the blower fan and the air volume of the blower fan. [Figure 7B] FIG. 7B is a diagram showing the relationship between the time after the start of the blowing operation of the blower fan and the air volume of the blower fan. [Figure 8] FIG. 8 is a diagram showing the relationship between the time after the start of the blowing operation of the blower fan and the air volume of the blower fan. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present embodiment will be described below with reference to the drawings. In the specification and claims of this application, the upstream side refers to the upstream side in the paper transport direction, and the downstream side refers to the downstream side in the transport direction. In the drawings, "front" refers to the front direction, "rear" refers to the rear direction, "left" refers to the left direction, "right" refers to the right direction, "up" refers to the up direction, and "down" refers to the down direction.

[0012] An overview of an image forming system 10 according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing an image forming system 10 according to this embodiment.

[0013] As shown in Fig. 1, an image forming system 10 according to this embodiment is a system that forms an image on a sheet S and performs post-processing on the sheet S on which the image has been formed. The image forming system 10 includes a tandem image forming apparatus 12, which is an apparatus that forms an image on the sheet S by electrophotography. The image forming system 10 includes a paper feeder 14 installed upstream of the image forming apparatus 12, which is an apparatus that feeds the sheet S toward the image forming apparatus 12.

[0014] The image forming system 10 includes a paper transport device 16 installed between the image forming device 12 and the paper feed device 14, and the paper transport device 16 is a device that transports the paper S fed from the paper feed device 14 to the image forming device 12. The image forming system 10 includes a post-processing device 18 installed downstream of the image forming device 12, and the post-processing device 18 is a device that performs post-processing on the paper S on which an image has been formed.

[0015] Next, the configuration of the image forming apparatus 12 will be described with reference to FIG.

[0016] As shown in FIG. 1, the image forming apparatus 12 includes a box-shaped apparatus main body (apparatus main body for the image forming apparatus) 20, which constitutes the base frame of the image forming apparatus 12. An image forming section 22 that forms images by electrophotography is provided in the upper part of the apparatus main body 20. The image forming section 22 includes four image forming units 24Y, 24M, 24C, and 24K that form images using color toners of Y (yellow), M (magenta), C (cyan), and K (black) components based on image data included in a print job. The four image forming units 24Y, 24M, 24C, and 24K are arranged vertically.

[0017] The image forming units 24Y, 24M, 24C, and 24K for the Y, M, C, and K components have the same configuration. For ease of illustration and explanation, common components are denoted by the same reference numerals, and when distinguishing between them, the reference numerals are suffixed with Y, M, C, or K. In Figure 1, only the components of the image forming unit 24Y for the Y component are denoted by reference numerals, and the components of the other image forming units 24M, 24C, and 24K are not denoted by reference numerals.

[0018] The image forming unit 24 includes a photosensitive drum 26, a charging unit (not shown), an exposure unit (not shown), and a developing unit .

[0019] The photosensitive drum 26 is a negatively charged organic photosensitive body having an undercoat layer, a charge generation layer, and a charge transport layer laminated in that order on the circumferential surface of a conductive cylinder made of, for example, aluminum. The photosensitive drum 26 is rotated at a constant peripheral speed by a rotary motor (not shown). The charging unit uniformly charges the outer circumferential surface of the photosensitive drum 26 to a negative polarity. The exposure unit forms an electrostatic latent image on the outer circumferential surface of the photosensitive drum 26 by emitting a laser beam as a scanning light and scanning the outer circumferential surface of the photosensitive drum 26 while exposing it to light. The developing unit 28 adheres toner of each color component to the outer circumferential surface of the photosensitive drum 26, thereby visualizing the electrostatic latent image and forming a toner image on the outer circumferential surface of the photosensitive drum 26.

[0020] 1, a transfer unit 30 for transferring a toner image onto paper S is provided in the upper part of the device main body 20. The transfer unit 30 has an endless intermediate transfer belt 32 and a secondary transfer roller 34.

[0021] The intermediate transfer belt 32 extends in the vertical direction so as to face the multiple photosensitive drums 26, and is stretched over multiple support rollers (not shown). The intermediate transfer belt 32 circulates due to the rotation of the multiple support rollers. A primary transfer nip CN is formed between the outer circumferential surface of the intermediate transfer belt 32 and the outer circumferential surface of each photosensitive drum 26 to transfer a toner image from each photosensitive drum 26 to the intermediate transfer belt 32.

[0022] The secondary transfer roller 34 is disposed on the outer peripheral surface side of the intermediate transfer belt 32. The secondary transfer roller 34 rotates in cooperation with the intermediate transfer belt 32 while sandwiching the paper S. A secondary transfer nip TN for transferring a toner image from the intermediate transfer belt 32 to the paper S is formed between the outer peripheral surface of the secondary transfer roller 34 and the outer peripheral surface of the intermediate transfer belt 32.

[0023] When the intermediate transfer belt 32 passes through the primary transfer nip CN, the toner images on the photosensitive drums 26 are primarily transferred onto the intermediate transfer belt 32, one after the other, in a superimposed manner. Thereafter, when the paper S passes through the secondary transfer nip TN, the toner images on the intermediate transfer belt 32 are secondarily transferred onto the paper S, forming an image on the paper S.

[0024] 1, a fixing unit 36 ​​for fixing the toner image to the paper S is provided on the outlet side of the secondary transfer nip TN within the device main body 20. The fixing unit 36 ​​has a heating roller 38, a fixing roller 40, an endless fixing belt 42, and a pressure roller 44.

[0025] Heating roller 38 has a hollow cylindrical core and a heating device (not shown), such as a halogen lamp, provided inside the core. Fixing roller 40 is provided opposite heating roller 38. Fixing roller 40 has a hollow cylindrical core and a surface layer made of, for example, silicone rubber, provided on the outer circumferential surface of the core. Fixing belt 42 is stretched between heating roller 38 and fixing roller 40 and can rotate.

[0026] Pressure roller 44 is provided outside fixing belt 42 in a position facing fixing roller 40, and presses against fixing roller 40 with a predetermined fixing load. Pressure roller 44 has a hollow cylindrical core, an elastic layer made of, for example, silicone rubber provided on the outer surface of the core, and a surface layer made of, for example, PFA tubing provided on the surface of the elastic layer. In addition, a fixing nip FN is formed between fixing roller 40 and pressure roller 44 to transport paper S while applying heat and pressure.

[0027] The pressure roller 44 is rotated by the drive of a rotary motor, which causes the fixing belt 42 to rotate accordingly. As the fixing belt 42 rotates, the heating roller 38 and the fixing roller 40 also rotate accordingly. As a result, the paper S is conveyed while being heated and pressurized in the fixing nip FN, and the toner image that has not yet arrived can be fixed to the paper S.

[0028] As shown in FIG. 1 , a main transport path 46 is provided within the apparatus main body 20 for transporting the paper S transported from the paper transport device 16 toward the post-processing device 18. The main transport path 46 extends from the paper transport device 16 to the post-processing device 18. The main transport path 46 is a path for transporting the paper S transported from the paper transport device 16 toward the post-processing device 18 via the secondary transfer nip TN and the fixing nip FN. The main transport path 46 has multiple transport roller pairs, including a registration roller pair 48. Also, a reversing transport path 50 for reversing the paper S is provided below the main transport path 46 within the apparatus main body 20. The reversing transport path 50 is a path for transporting the paper S when a toner image is formed on the back side of the paper S. One end (the entrance end) of the reversing transport path 50 is connected to the main transport path 46 downstream of the fixing nip FN. The other end (the exit end) of the reversing transport path 50 is connected to the main transport path 46 upstream of the registration roller pair 48.

[0029] The paper S transported from the paper transport device 16 is transported by the main transport path 46 toward the secondary transfer nip TN via the secondary transfer nip TN and the fixing nip FN. At this time, the pair of registration rollers 48 corrects the inclination of the paper S and adjusts the transport timing of the paper S. Then, at the secondary transfer nip TN, the toner image on the intermediate transfer belt 32 is secondarily transferred all at once onto one side (front or back) of the paper S, and at the fixing nip FN, the toner image is fixed to the paper S. Thereafter, the paper S on which the image has been formed is transported to the post-processing device 18.

[0030] Next, the configuration of the sheet feeding device 14 will be described with reference to Figures 1, 2A, and 2B. Figure 2A is a schematic diagram of multi-fed sheets LS located on the sheet feed path 56 of the sheet feeding device 14, viewed from above. Figure 2B is a schematic diagram of multi-fed sheets LS located on the sheet feed path 56 of the sheet feeding device 14, viewed from the front.

[0031] 1, as described above, paper feeder 14 is a device that feeds paper S toward image forming device 12. In other words, paper feeder 14 is a device that feeds paper S to paper transport device 16. Paper feeder 14 has a box-shaped device main body (device main body for paper feeder) 52 installed upstream of image forming device 12, and device main body 52 forms a base frame of paper feeder 14.

[0032] A plurality of paper feed trays 54 for storing a plurality of sheets of paper S are provided within the device main body 52, and the plurality of paper feed trays 54 are arranged in vertical tiers. Each paper feed tray 54 stores a type of paper S that is preset based on basis weight, size, etc. Also provided within the device main body 52 is a paper feed transport path 56 for feeding paper from each paper feed tray 54 to the paper transport device 16.

[0033] As shown in FIGS. 1, 2A, and 2B, a multi-feed detection unit 58 that detects information related to multi-feeding of paper sheets S is provided on the outlet side of paper feed conveyance path 56 within device main body 52. ​​Multi-feeding of paper sheets S refers to multiple sheets of paper sheets S being conveyed while overlapping and misaligned. Information related to multi-feeding of paper sheets S includes whether or not multi-feeding of paper sheets S has occurred, the number of sheets of paper sheets S that make up multi-fed paper sheets (multi-fed paper sheets) LS, and the amount of overlap OA of the multi-fed paper sheets LS. Multi-feed detection unit 58 has a known configuration, for example, as shown in JP 2021-143069 A. Multi-feed detection unit 58 has a transmitting element (not shown) that transmits ultrasonic waves toward paper sheets S, and a receiving element (not shown) that receives ultrasonic waves that have passed through paper sheets S.

[0034] The configuration of the sheet transport device 16 according to this embodiment will be described with reference to FIGS. 1 and 3A to 6. FIG. 3A is a schematic diagram showing how the sheet discharge unit 66 discharges the multi-fed sheets LS onto the discharge tray 64. FIG. 3B is a schematic diagram showing how the air force of the blower fan 76 is reduced at a second timing T2 while the multi-fed sheets LS are being discharged. FIG. 4A is a schematic diagram showing how the air force of the blower fan 76 is increased again at a third timing T3 while the multi-fed sheets LS are being discharged. FIG. 4B is a schematic diagram showing how the air force of the blower fan 76 is reduced at a fourth timing T4 while the multi-fed sheets LS are being discharged. FIG. 5 is a schematic diagram showing how the blowing operation of the blower fan 76 is stopped at a fifth timing T5 while the multi-fed sheets LS are being discharged.

[0035] 1, the paper transport device 16 according to this embodiment is a device that transports paper S fed from the paper feed device 14 to the image forming device 12, as described above. The paper transport device 16 includes a box-shaped device main body (device main body for the paper transport device) 60, which constitutes a base frame of the paper transport device 16.

[0036] A main transport path 62 is provided within the device body 60 for transporting the paper S fed from the paper feed device 14 to the image forming device 12. The main transport path 62 extends in the left-right direction from the paper feed device 14 side to the image forming device 12 side. An entrance end of the main transport path 62 is connected to an exit end of the paper feed transport path 56 of the paper feed device 14. An exit end of the main transport path 62 is connected to an entrance end of the main transport path 46 of the image forming device 12.

[0037] As shown in FIGS. 1 and 3A to 5, a paper output tray 64 is provided on the top of the device main body 60 for placing (stacking) sheets S that make up multi-fed sheets LS. Also, a paper output unit 66 that outputs multi-fed sheets LS to the paper output tray 64 is provided on the entrance side of the paper output tray 64 on the top of the device main body 60. The paper output unit 66 has a paper output roller pair 68 that holds the multi-fed sheets LS, and a paper output motor 70 (see FIG. 6) that rotates the paper output roller pair 68. By driving the paper output motor 70 to rotate the paper output roller pair 68, the multi-fed sheets LS can be discharged from the paper output roller pair 68 to the paper output tray 64, as shown in FIGS. 3A to 5.

[0038] An air blower 72 that blows air is provided near the paper discharge unit 66 in the upper part of the device main body 60. When discharging the multi-fed sheets LS onto the paper discharge tray 64, the air blower 72 blows air from below the sheets S that make up the multi-fed sheets LS in a direction along the loading surface 64f of the paper discharge tray 64. The air blower 72 has an air blower pipe 74 with multiple blowing holes (not shown) that can blow air, and an air blower fan 76 (see FIG. 6) connected to the air blower pipe 74. By using the air blower fan 76 to blow air from the multiple blowing holes of the air blower pipe 74, an air layer can be created between the sheets S discharged from the paper discharge roller pair 68 and the sheets S on the paper discharge tray 64 or the loading surface 64f of the paper discharge tray 64.

[0039] As shown in FIG. 1, a reversing conveyance path 78 is provided within the device main body 60 to reverse the multi-fed sheets LS conveyed by the main conveyance path 62 and discharge them onto the discharge tray 64. The reversing conveyance path 78 extends vertically from the main conveyance path 62 side to the discharge roller pair 68 side. One end (the end on the entrance side) of the reversing conveyance path 78 is connected to the middle part of the main conveyance path 62. The other end (the end on the exit side) of the reversing conveyance path 78 is connected to the entrance side of the discharge roller pair 68. A conveyance path switching unit 80 (see FIG. 6) is provided at an appropriate position within the device main body 60 to switch the conveyance path for the sheets S (multi-fed sheets LS) from the main conveyance path 62 to the reversing conveyance path 78. The conveyance path switching unit 80 has the configuration of a known conveyance path switching unit that switches the conveyance path for the sheets S.

[0040] As shown in FIGS. 3A to 5, a paper sensor 82 is provided as a paper detection unit that detects paper S on the entrance side of the paper discharge roller pair 68 at the top of the device main body 60. The paper sensor 82 is a reflective or transmissive photosensor, and detects the presence or absence of paper S. The paper sensor 82 detects the leading edge of the first sheet S1, which is the leading sheet S of the multi-fed paper LS. The paper sensor 82 detects the trailing edge of the last sheet S of the multi-fed paper LS. When the multi-fed paper LS is made up of two sheets S, the paper sensor 82 detects the trailing edge of the second sheet S2, which is the last sheet S of the multi-fed paper LS.

[0041] In this embodiment, the timing at which the paper sensor 82 detects the leading edge of the first sheet S1 of the multi-fed sheets LS corresponds to the first timing T1 (see FIG. 7A) at which the first sheet S1 of the multi-fed sheets LS passes the pair of paper discharge rollers 68. The timing at which the paper sensor 82 detects the trailing edge of the last sheet S of the multi-fed sheets LS corresponds to the timing at which the trailing edge of the last sheet S of the multi-fed sheets LS passes the pair of paper discharge rollers 68. If the multi-fed sheets LS are made up of two sheets S, the timing at which the trailing edge of the second sheet S2 of the multi-fed sheets LS is detected corresponds to the fourth timing T4 (see FIG. 7A) at which the trailing edge of the second sheet S2 passes the pair of paper discharge rollers 68.

[0042] 1, the multi-feed detection unit 58 may be provided on the entrance side of the main transport path 62 in the device body 60 of the paper transport device 16, instead of being provided on the exit side of the paper feed transport path 56 in the device body 52 of the paper feed device 14. The device body 60 of the paper transport device 16 may be configured integrally with the device body 52 of the paper feed device 14. In other words, the device body 60 of the paper transport device 16 and the device body 52 of the paper feed device 14 may be configured as a common device body.

[0043] The configuration of post-processing device 18 will be described with reference to FIG.

[0044] 1, as described above, post-processing device 18 is a device that performs post-processing on paper S on which an image has been formed. Post-processing device 18 includes a box-shaped device main body (device main body for post-processing device) 84, and device main body 84 constitutes a base frame of post-processing device 18.

[0045] A post-processing section 86 is provided within the device body 84 for performing post-processing such as stapling, cutting, and punching on the paper S on which an image has been formed. A paper output tray 88 is provided on the left side of the device body 84 for discharging the paper S that has been subjected to post-processing. A paper output tray 90 is provided above the paper output tray 88 on the left side of the device body 84 for discharging the paper S that has not been subjected to post-processing.

[0046] A paper discharge transport path 92 is provided within the device main body 84 for transporting the paper S transported from the image forming device 12 to a paper discharge tray 88 via a post-processing section 86. The entrance end of the paper discharge transport path 92 is connected to the exit end of the main transport path 62 of the image forming device 12. The exit end of the paper discharge transport path 92 is connected to the paper discharge tray 88 side.

[0047] A paper discharge transport path 94 is provided within the device main body 84 for transporting the paper S transported from the image forming device 12 to the paper discharge tray 90 without passing through the post-processing section 86. The entrance end of the paper discharge transport path 94 is connected to the exit end of the main transport path 62 of the image forming device 12. The exit end of the paper discharge transport path 94 is connected to the paper discharge tray 90 side.

[0048] The control configuration of the image forming system 10 according to this embodiment will be described with reference to Fig. 1 and Fig. 3A to Fig. 8. Fig. 6 is a control block diagram of the image forming system 10 according to this embodiment. Figs. 7A, 7B, and 8 are diagrams showing the relationship between the time after the start of the blowing operation of the blower fan 76 and the air volume of the blower fan 76.

[0049] 6, the image forming system 10 includes a control unit 96 that controls the image forming unit 22, transfer unit 30, fixing unit 36, paper feeder 14, paper discharge unit 66, air blower unit 72, transport path switching unit 80, post-processing unit 86, etc. The control unit 96 is responsible for controlling the entire image forming system 10. The control unit 96 includes a CPU (Central Processing Unit) 98, a ROM (Read Only Memory) 100, and a RAM (Random Access Memory) 102. The control unit 96 is connected to a storage unit 104, a communication unit 106, a double feed detection unit 58, a paper sensor 82, etc.

[0050] The CPU 98 controls the overall operation of the image forming system 10. The CPU 98 reads various control programs and setting data stored in the ROM 100, stores them in the RAM 102, and executes the programs to perform various arithmetic processing. The RAM 102 provides the CPU 98 with working memory space and stores temporary data. The CPU 98 also references various data stored in a storage unit 104 when performing various arithmetic processing. The storage unit 104 is configured, for example, from a non-volatile semiconductor memory or a hard disk drive.

[0051] The control unit 96 transmits and receives various data to and from an external device (e.g., a personal computer) connected to a communication network such as a LAN (Local Area Network) or WAN (Wide Area Network) via the communication unit 106. The control unit 96 receives, for example, a print job transmitted from an external device, and forms a toner image on the paper S based on image data (input image data) included in the print job. The communication unit 106 is configured, for example, by a communication control card such as a LAN card.

[0052] 1 and 6, when the multifeed detection unit 58 detects the occurrence of a multifeed as information relating to the multifeed of sheets S, the control unit 96 controls the transport path switching unit 80 to switch the transport path of the multifed sheets LS from the main transport path 62 to the reverse transport path 78. By switching the transport path of the multifed sheets LS from the main transport path 62 to the reverse transport path 78, the multifed sheets LS can be sent from the main transport path 62 to the reverse transport path 78 and transported to the paper discharge unit 66 by the reverse transport path 78.

[0053] The control unit 96 starts driving the paper discharge motor 70 of the paper discharge unit 66 before the multi-fed paper LS is transported to the paper discharge roller pair 68, on the condition that the multi-fed detection unit 58 has detected the occurrence of a multi-fed paper as information relating to the multi-fed paper S. By starting to drive the paper discharge motor 70, the multi-fed paper LS can be discharged to the paper discharge tray 64 by the paper discharge unit 66.

[0054] 3A, 6, and 7A, the control unit 96 controls the blower fan 76 of the blower unit 72 to vary the air volume based on the detection result from the double feed detection unit 58. When one of the detection results from the double feed detection unit 58 indicates that the double-fed sheets LS are made up of two sheets S1 and S2, the specific control of the blower fan 76 by the control unit 96 is as follows.

[0055] The control unit 96 controls the blower fan 76 to start blowing air and increase the air volume to a predetermined first air volume Qa based on a first timing T1 when the leading edge of the first sheet S1 of the multi-fed sheets LS passes the pair of paper discharge rollers 68. The control unit 96 also controls the blower fan 76 to decrease the air volume to a predetermined second air volume Qb based on a second timing T2 when the trailing edge of the first sheet S1 passes the pair of paper discharge rollers 68.

[0056] Here, the trailing edge of the first sheet S1 in the multi-fed sheets LS overlaps with the second sheet S2, and the sheet sensor 82 cannot detect the trailing edge of the first sheet S1. In other words, the control unit 96 cannot calculate the second timing T2 from the detection result of the sheet sensor 82. Therefore, the control unit 96 calculates the second timing T2 based on the first timing T1 and the size of the sheets S included in the print job. Specifically, the control unit 96 calculates the sheet passing time from when the leading edge of the first sheet S1 passes the pair of sheet discharge rollers 68 to when the trailing edge of the first sheet S1 passes the pair of sheet discharge rollers 68 based on the conveyance speed of the sheets S and the size of the sheets S included in the print job. The control unit 96 then calculates the second timing T2 by adding the sheet passing time to the first timing T1.

[0057] The control unit 96 controls the blower fan 76 so that the air volume of the blower fan 76 is increased again to a predetermined first air volume Qa after the rear end of the first sheet of paper S1 has passed through the pair of paper discharge rollers 68 and before the rear end of the second sheet of paper S2 has passed through the pair of paper discharge rollers 68.

[0058] Here, the control unit 96 determines a third timing T3 for again increasing the air volume of the blower fan 76 based on the overlap amount OA of the double-fed sheets LS (see FIG. 2A), the second timing T2, and the size of the sheets S. Specifically, the control unit 96 calculates the transport time for the predetermined length of the sheets S based on the transport speed of the sheets S and a predetermined length that is shorter than the length remaining after subtracting the overlap amount OA of the double-fed sheets LS from the sheet size of the sheets S. The control unit 96 then determines the third timing T3 by adding the transport time for the predetermined length of the sheets S to the second timing T2. The ratio of the predetermined length to the length remaining after subtracting the overlap amount OA of the double-fed sheets LS from the sheet size of the sheets S is set in advance. The control unit 96 may also calculate the overlap amount OA of the double-fed sheets LS based on the detection result from the double-feed detection unit 58 and the transport speed of the sheets S.

[0059] The control unit 96 controls the blower fan 76 to reduce the air volume of the blower fan 76 to a predetermined second air volume Qb based on a fourth timing T4 when the trailing edge of the second sheet S2 passes the pair of sheet discharge rollers 68. The control unit 96 may determine the fourth timing T4 based on the detection result from the sheet sensor 82. The control unit 96 may determine the fourth timing T4 based on the overlap amount OA of the multi-fed sheets LS, the first timing T1, the size of the sheets S, and the transport speed of the sheets S. The control unit 96 also controls the blower fan 76 to stop blowing air based on a fifth timing T5 when a predetermined time has elapsed since the trailing edge of the second sheet S2 passed the pair of sheet discharge rollers 68.

[0060] When the multi-fed sheets LS are made up of three or more sheets S, the control unit 96 controls the blower fan 76 in the same manner as described above. Specifically, the control unit 96 controls the blower fan 76 to increase the air volume of the blower fan 76 again before the trailing edge of the sheet S preceding the third or subsequent sheets S passes the pair of paper discharge rollers 68. The control unit 96 controls the blower fan 76 to decrease the air volume of the blower fan 76 based on the timing at which the trailing edge of the third or subsequent sheets S passes the pair of paper discharge rollers 68.

[0061] The control unit 96 may control the air blowing operation of the air blower fan 76 as shown in Fig. 7B instead of controlling the air blowing operation of the air blower fan 76 as shown in Fig. 7A. The configuration relating to the air blowing operation of the air blower fan 76 shown in Fig. 7B differs from the configuration relating to the air blowing operation of the air blower fan 76 shown in Fig. 7A in the following respects.

[0062] 7B, based on second timing T2, control unit 96 controls blower fan 76 to stop the blowing operation of blower fan 76 and reduce the air volume to zero. Based on third timing T3, control unit 96 controls blower fan 76 to resume the blowing operation of blower fan 76 and increase the air volume again to the predetermined first air volume Qa. Based on fourth timing T4, control unit 96 controls blower fan 76 to stop the blowing operation of blower fan 76 and reduce the air volume to zero.

[0063] Instead of controlling the air blowing operation of the blower fan 76 as shown in Fig. 7A, the control unit 96 may control the air blowing operation of the blower fan 76 as shown in Fig. 8. The configuration relating to the air blowing operation of the blower fan 76 shown in Fig. 8 differs from the configuration relating to the air blowing operation of the blower fan 76 shown in Fig. 7A in the following points.

[0064] As shown in FIG. 8, the control unit 96 controls the blower fan 76 so that the third air volume Qc of the blower fan 76, which is first increased based on the first timing T1, is greater than the first air volume Qa of the blower fan 76, which is increased again based on the third timing T3.

[0065] According to the configuration of the paper transport device 16 of this embodiment, the control unit 96 controls the blower fan 76 of the blower unit 72 to vary the air volume based on the detection result from the multi-feed detection unit 58. Therefore, when the multi-fed paper LS is discharged to the paper output tray 64, it is possible to stabilize the discharge state of the paper S by suppressing sagging of the leading edges of the paper S that make up the multi-fed paper LS. As a result, it is possible to suppress the paper S from sticking to each other on the paper output tray 64 and misalignment of the paper S.

[0066] Therefore, according to this embodiment, when the multi-fed sheets LS are discharged to the sheet discharge tray 64, the sheets S can be stably stacked on the sheet discharge tray 64.

[0067] According to the configuration of the paper transport device 16 of this embodiment, the control unit 96 controls the blower fan 76 to reduce the airflow rate of the blower fan 76 based on the second timing T2 when the trailing edge of the first paper S1 passes the pair of paper discharge rollers 68. The control unit 96 controls the blower fan 76 to increase the airflow rate again after the trailing edge of the first paper S1 passes the pair of paper discharge rollers 68 and before the trailing edge of the second paper S2 passes the pair of paper discharge rollers 68. This allows the first paper S1 to be placed (dropped) at a predetermined position on the paper discharge tray 64, and also makes it possible to sufficiently prevent the papers S1 and S2 from sticking together on the paper discharge tray 64.

[0068] In particular, when the air volume of the blower fan 76 is reduced based on the fourth timing T4 when the rear end of the second sheet S2 passes the pair of sheet discharge rollers 68, the second sheet S2 is placed (dropped) at a predetermined position on the sheet discharge tray 64. As a result, misalignment of the sheets S1 and S2 on the sheet discharge tray 64 can be sufficiently suppressed.

[0069] Therefore, according to this embodiment, when the multi-fed sheets LS are discharged to the sheet discharge tray 64, the sheets S can be stacked on the sheet discharge tray 64 more stably.

[0070] According to the configuration of the paper transport device 16 according to this embodiment, the paper transport device 16 has a reversing transport path 78 for reversing the multi-fed paper LS and discharging it onto the paper discharge tray 64. Therefore, the multi-fed paper LS is discharged onto the paper discharge tray 64 with the first sheet S1 overlapping the underside of the second sheet S2. As a result, the first sheet S1 is placed (dropped) onto a predetermined position on the paper discharge tray 64, and it is possible to sufficiently prevent the sheets S1 and S2 from sticking together on the paper discharge tray 64.

[0071] Therefore, according to this embodiment, when the multi-fed sheets LS are discharged to the sheet discharge tray 64, the sheets S can be stacked on the sheet discharge tray 64 more stably.

[0072] As described above, when the multi-fed sheets LS are made up of three or more sheets S, the control unit 96 controls the blower fan 76 to increase the air volume of the blower fan 76 before the trailing edge of the sheet S preceding the third or subsequent sheets S passes the pair of sheet discharge rollers 68. The control unit 96 controls the blower fan 76 to decrease the air volume of the blower fan 76 based on the timing at which the trailing edge of the third or subsequent sheets S passes the pair of sheet discharge rollers 68. Therefore, the third or subsequent sheets S are placed (dropped) in predetermined positions on the sheet discharge tray 64, and the sheets S on the sheet discharge tray 64 can be sufficiently prevented from sticking together.

[0073] Therefore, according to this embodiment, when multiple-fed sheets LS consisting of three or more sheets S are discharged to the sheet discharge tray 64, the sheets S can be stacked on the sheet discharge tray 64 more stably.

[0074] In the configuration of paper sheet transporting device 16 according to this embodiment, when the configuration for the blowing operation of blower fan 76 shown in Fig. 7B is adopted, control of blower fan 76 is simplified. Therefore, according to this embodiment, the control configuration of paper sheet transporting device 16 can be simplified.

[0075] 7B is employed in the configuration of paper transport device 16 according to this embodiment, the first sheet S1, which becomes heavy when overlapped with the second sheet S1, can be stably supported by air from the blower fan 76. Therefore, according to this embodiment, when multiple-fed sheets LS are conveyed to the paper output tray 64, the sheets S can be stacked more stably on the paper output tray 64.

[0076] Although the present embodiment has been specifically described above, the present invention is not limited to the specific embodiment described above. Various modifications and changes to the specific examples described in the above embodiment are possible within the scope of the gist of the present invention as defined in the claims. [Industrial Applicability]

[0077] The present invention is useful as a paper transport device and an image forming system that can stably stack papers on a tray when multiple-fed papers are discharged to the tray. [Explanation of symbols]

[0078] 10. Image forming system 12 Image forming device 14 Paper feeder 16 Paper transport device 18 Aftertreatment device 20 Device body (device body for image forming device) 22 Image forming unit 24 Image forming unit 24Y Image Forming Unit 24M Image Forming Unit 24C Image Formation Unit 24K Image Forming Unit 26 Photosensitive drum 28 Development Unit 30 Transfer unit 32 Intermediate transfer belt 34 Secondary transfer roller 36 Fixing section 38 heated roller 40 Fixing roller 42 Fixing belt 44 Pressure roller 46 Main transport route 48 registration roller pair 50 Reversing conveyance path 52 Device body (device body for paper feeder) 54 Paper tray 56 Paper feed path 58 Double feed detector 60 Device body (device body for paper transport device) 62 Main transport route 64 Paper output tray 64f Placement surface 66 Paper output section 68 Paper ejection roller pair 70 Paper ejection motor 72 Blower 74 Air blast pipe 76 Blower fan 78 Reversing conveyance path 80 Conveyor path switching unit 82 Paper sensor (paper detection unit) 84 Device body (device body for post-processing device) 86 Post-processing section 88 Paper output tray 90 Paper output tray 92 Paper ejection path 94 Paper ejection path 96 Control Unit 98 CPU 100 ROM 102 RAM 104 Storage section 106 Communications Department

Claims

1. a paper discharge unit provided on the entrance side of the tray and configured to discharge multi-fed paper sheets into the tray; a blower that blows air from below the sheets of paper that constitute the multi-fed paper in a direction along the loading surface of the tray when the multi-fed paper is discharged onto the tray; a control unit that controls the blower unit to vary the air volume based on a detection result from a double feed detection unit that detects information about double feed. Paper transport device.

2. The control unit the air blowing unit is controlled so as to reduce the air volume based on the timing when the rear end of the first sheet of the multi-fed sheets passes through the paper discharge unit, and to increase the air volume again after the rear end of the first sheet of paper passes through the paper discharge unit and before the rear end of the second sheet of the multi-fed sheets passes through the paper discharge unit. The paper transport device according to claim 1 .

3. The control unit controlling the air blowing unit to increase the air volume based on the timing when the leading edge of the first sheet of paper passes through the paper discharge unit; The paper transport device according to claim 2 .

4. The control unit controlling the air blowing unit to reduce the air volume based on the timing when the rear end of the last sheet of the multi-fed sheets passes through the paper discharge unit; The paper transport device according to claim 3 .

5. The control unit calculating a timing at which the rear end of the first sheet of paper will pass through the paper discharge unit based on the timing at which the front end of the first sheet of paper passes through the paper discharge unit and the size of the sheet of paper; The paper transport device according to claim 2 .

6. The control unit determining the timing to increase the air volume of the air blower again based on the overlapping amount of the multi-fed sheets as information about the multi-fed sheets detected by the multi-fed detection unit, the timing when the rear end of the first sheet of paper passed through the paper discharge unit, and the size of the sheet; The paper transport device according to claim 2 .

7. The control unit When the overlapped sheets consist of two sheets of paper, the blower unit is controlled so that, based on the timing when the leading edge of the first sheet of the overlapped sheets passes the paper discharge section, the blower unit starts blowing air to increase the air volume, based on the timing when the trailing edge of the first sheet of paper passes the paper discharge section, the blower unit stops blowing air to decrease the air volume, after the trailing edge of the first sheet of paper passes the paper discharge section but before the trailing edge of the second sheet of the overlapped sheets passes the paper discharge section, the blower unit restarts blowing air to increase the air volume again, and based on the timing when the trailing edge of the second sheet of paper passes the paper discharge section, the blower unit stops blowing air to decrease the air volume. The paper transport device according to claim 1 .

8. the air volume of the air blower section that is initially increased after the leading edge of the first sheet of paper has passed through the air blower section is greater than the air volume of the air blower section that is increased again before the trailing edge of the second sheet of paper has passed through the paper discharge section; The paper transport device according to claim 3 .

9. a reversing conveyance path for reversing the multi-fed paper and discharging it onto the tray; The paper transport device according to claim 1 .

10. The control unit When the multi-fed sheets consist of three or more sheets of paper, the air blowing unit is controlled so as to increase the air volume after a sheet preceding the third or more sheets of paper has passed through the paper discharge unit and before the rear ends of the third or more sheets of paper pass through the paper discharge unit, and to decrease the air volume based on the timing when the rear ends of the third or more sheets of paper pass through the paper discharge unit. The paper transport device according to claim 4.

11. an image forming device that forms an image on a sheet; a paper feeder that is installed upstream of the image forming apparatus and feeds paper toward the image forming apparatus; a paper transport device according to any one of claims 1 to 10, which is installed between the image forming device and the paper feed device and transports the paper fed from the paper feed device to the image forming device; Imaging system.

Images