Sheet conveyance device, and image formation system

Abstract

To prevent occurrence of jamming while guiding a first sheet and a second sheet which are multiply fed to a third conveyance path.SOLUTION: A sheet conveyance device (110) includes: a switching part (FL1) capable of switching a sheet conveyed to a first conveyance path (Ps12) by a conveyance part (110A) for conveying a sheet between a first position for guiding the sheet to a second conveyance path (Ps13), and a second position for guiding the sheet to a third conveyance path (Ps14); a multiple-feed detection part (for example, SN12) which is arranged on the upstream of the switching part in a sheet conveyance direction, and detects multiple-feed in which a subsequent second sheet is overlapped on the first sheet; and a control part for switching the switching part to a second position when the multiple-feed is detected by the multiple-feed detection part, and performs control to guide the first sheet and the second sheet to the second conveyance path. When the multiple-feed is detected by the multiple-feed detection part, the control part calculates a first time when the rear end of the second sheet passes through the switching part, and switches the switching part from the second position to the first position at the first time.SELECTED DRAWING: Figure 14

Description

[Technical Field]

[0001] The present invention relates to a sheet conveying device that conveys a sheet, and an image forming system. [Background technology]

[0002] For example, devices that feed sheets from a cassette or tray are provided with separation pads or separation rollers to separate sheets one by one, but due to sheet sticking or the like, double feeding can occur, where a subsequent sheet overlaps a preceding sheet and is conveyed. Such double feeding can cause poor image formation, jams, malfunctions, etc. For this reason, a device that stops conveyance when double feeding of sheets (paper) is detected has been proposed (see Patent Document 1).

[0003] However, stopping conveyance as in Patent Document 1 causes downtime, which may lead to a decrease in productivity. For this reason, a system has been proposed in which, when a double feed is detected, the double-fed sheets are discharged as is without image formation, and an image is formed on the next sheet (see Patent Document 2). Patent Document 2 also proposes discharging the double-fed sheets to a specific discharge tray other than the designated discharge tray. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-24506 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-333797 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, in order to switch and discharge a multi-fed sheet to a different discharge tray (discharge tray) as in Patent Document 2, a switching unit such as a flapper is used to switch the conveying path for the sheet. Then, when a sheet that is not a multi-fed sheet is subsequently conveyed, the switching unit must be returned to its original position. However, there is a problem in that, for example, two sheets that have been multi-fed differ in the timing at which the trailing edge of the second sheet passes through the switching unit depending on the amount of overlap (amount of misalignment) between them. In particular, if the switching unit is returned before the trailing edge of, for example, the second sheet that has been multi-fed passes through the switching unit, the second sheet may be caught between the switching unit and the guide and stopped, causing a subsequent sheet to collide with it and jam.

[0006] Therefore, an object of the present invention is to provide a sheet conveying device and an image forming system that can prevent jams from occurring while guiding overlapping first and second sheets to a third conveying path. [Means for solving the problem]

[0007] One aspect of the present invention is a sheet conveying device comprising: a conveying unit that conveys a sheet; a switching unit that can be switched between a first position that guides a sheet conveyed by the conveying unit along a first conveying path to a second conveying path and a second position that guides the sheet to a third conveying path; a multi-feed detection unit that is arranged upstream of the switching unit in the sheet conveying direction and detects multi-feeds in which a second sheet following a first sheet overlaps; and a control unit that, when a multi-feed is detected by the multi-feed detection unit, switches the switching unit to the second position and controls the first sheet and the second sheet to be guided to the second conveying path; and when a multi-feed is detected by the multi-feed detection unit, the control unit calculates a first time at which the trailing end of the second sheet passes the switching unit and switches the switching unit from the second position to the first position at the first time.

[0008] One aspect of the present invention is a sheet conveying device comprising: a conveying unit that conveys sheets; a switching unit that can be switched between a first position that guides a sheet conveyed by the conveying unit along a first conveying path to a second conveying path and a second position that guides the sheet to a third conveying path; a double feed detection unit that is arranged upstream of the switching unit in the sheet conveying direction and detects double feed in which a second sheet following a first sheet overlaps; a trailing end detection unit that is arranged upstream of the switching unit in the conveying direction and detects the trailing end of the second sheet; and a control unit that, when double feed is detected by the double feed detection unit, switches the switching unit to the second position and controls the first sheet and the second sheet to be guided to the second conveying path; and, when double feed is detected by the double feed detection unit, switches the switching unit from the second position to the first position in response to detection of the trailing end of the second sheet by the trailing end detection unit. [Effects of the Invention]

[0009] According to the present invention, it is possible to prevent the occurrence of a jam while properly guiding the overlapped first and second sheets to the third conveying path. [Brief explanation of the drawings]

[0010] [Figure 1] 1A is a block diagram showing a schematic configuration of an image forming system according to a first embodiment, and FIG. 1B is a schematic cross-sectional view showing a schematic configuration of an image forming system according to a first embodiment. [Figure 2] 1A is a schematic cross-sectional view showing the position of a sheet when a single-sided print job is performed in the image forming system according to the first embodiment, and FIG. 1B is a schematic cross-sectional view showing the position of a sheet when a double-sided print job is performed in the image forming system according to the first embodiment. [Figure 3] 1 is a schematic cross-sectional view showing a paper feeder according to a first embodiment. [Figure 4] 2 is a block diagram showing a control unit of the image forming system according to the first embodiment. FIG. [Figure 5] 2 is a block diagram showing a control unit of the paper feeder according to the first embodiment. FIG. [Figure 6] FIG. 2 is a block diagram showing a control function of the paper feeder according to the first embodiment. [Figure 7] 4 is a table illustrating a management table for a transport route in the paper feeder according to the first embodiment. [Figure 8] 5 is a diagram showing a sequence of transport control of the paper feeder according to the first embodiment. FIG. [Figure 9] 5 is a flowchart showing transport control of the paper feeder according to the first embodiment. [Figure 10] 6 is a flowchart showing multi-feed detection control of the paper feeding device according to the first embodiment. [Figure 11] 6 is a flowchart showing control for determining whether to switch paper transport paths in the paper feeder according to the first embodiment. [Figure 12] 5 is a flowchart showing flapper drive control of the paper feeder according to the first embodiment. [Figure 13] 10 is a time chart showing the relationship between the detected waveform of the double feed detection sensor and each time. [Figure 14] 1A is a diagram showing a case where the flapper can be switched after the multi-fed sheets have passed through the paper feeder, and FIG. 1B is a diagram showing a case where the flapper cannot be switched after the multi-fed sheets have passed through the paper feeder. [Figure 15] FIG. 10 is a schematic cross-sectional view showing a paper feeder according to a second embodiment. [Figure 16] 10 is a flowchart showing transport control of a paper feeder according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] First Embodiment A first embodiment for carrying out the present invention will be described below with reference to the drawings. In this first embodiment, an inkjet recording system is applied as an image forming system 1.

[0012] [Inkjet recording system] First, the schematic configuration of an image forming system 1 according to the first embodiment will be described with reference to FIGS. 1(a) and 1(b). FIG. 1(a) is a block diagram showing the schematic configuration of the image forming system according to the first embodiment. FIG. 1(b) is a schematic cross-sectional view showing the schematic configuration of the image forming system according to the first embodiment. The image forming system 1 is a sheet-fed inkjet recording system that produces recorded material by forming an ink image on a sheet (hereinafter also referred to as "paper") using two liquids: a reaction liquid and an ink. In this embodiment, "paper" refers to sheet-like plain paper, thin paper, thick paper, coated paper, etc., but is not limited to these and may also include other paper or sheets made of materials other than paper. In this embodiment, feeding a sheet is referred to as "paper feeding" and discharging a sheet is referred to as "paper discharge," but the material of the sheet is not necessarily limited to paper.

[0013] As shown in FIG. 1( a ), the image forming system 1 comprises six units: a paper feed section 100 , a print section 200 as an image forming apparatus, a fixing section 300 , a cooling section 400 , an inverting section 500 , and a paper ejection section 600 .

[0014] As shown in FIG. 1B, in this embodiment, sheet feeding unit 100, which serves as a feeding unit for feeding paper, is configured by connecting (linking) three sheet conveying devices, sheet feeding devices 110, 120, and 130. Sheet feeding device 110 is a unit having paper trays, and has a first sheet feeding tray 111, a second sheet feeding tray 112, and a third sheet feeding tray 113, which serve as three tiers of support units for holding various types of printing paper used in printing processes. Sheet feeding device 110 also has a paper output port 115, which can be used as a shelter for invalid paper, such as paper that cannot be properly conveyed to printing unit 200 due to a jam or paper that has been multi-fed during feeding. Similarly, sheet feeding device 120 has three tiers, first sheet feeding tray 121, second sheet feeding tray 122, and third sheet feeding tray 123, a paper output port 125, and a paper output tray 129. Similarly, the paper feeder 130 is further provided with three stages of a first paper feed tray 131, a second paper feed tray 132, a third paper feed tray 133, a paper discharge port 135, and a paper discharge tray 139.

[0015] The print unit 200 is a unit that prints a print image on a sheet of paper, and has an inkjet head 201 as an image forming unit. The inkjet head 201 constitutes an image forming unit that forms an image by performing a recording process (printing) in which ink is applied to the paper from above by a plurality of recording heads on the paper as it is transported.

[0016] The fixing unit 300 is a unit responsible for fixing the image printed by the printing unit 200 onto the paper, and includes a drying module 310 and a fixing module 320. The drying module 310 blows warm air onto the paper to reduce the liquid content of the ink adhering to the paper and improve the fixability of the ink to the paper. The fixing module 320 uses multiple heater units to heat the paper and fix the printed image to the paper. The fixing unit 300 also includes a paper outlet 301 that can be used as a shelter for invalid paper.

[0017] The cooling section 400 is a unit that controls the temperature to cool the paper that has been heated by the fixing section 300 back to room temperature, and uses a plurality of fan units to cool the paper.

[0018] The reversing unit 500 is a unit that switches back the transported paper and controls the reversal of the paper to switch whether the print side is to be the top or bottom when the paper is loaded onto the subsequent paper discharge unit 600. The reversing unit 500 also has a paper discharge port 501 that can be used as a shelter for invalid paper.

[0019] Paper discharge section 600 is a unit that stacks printed papers and controls paper discharge, and is configured by connecting (linking) three paper discharge devices 610, 620, and 630. Paper discharge device 610 has a paper discharge stacker 611 that supports and stacks printed papers. Paper discharge device 610 also has a paper discharge outlet 612 that can be used as a shelter for printed papers or invalid papers. Similarly, paper discharge device 620 is equipped with a paper discharge stacker 621 and a paper discharge outlet 622, and paper discharge device 630 is equipped with a paper discharge stacker 631 and a paper discharge outlet 632.

[0020] A print server 70 is connected to the image forming system 1, and print jobs are sent from the print server 70. Furthermore, the print server 70 can check the status of the image forming system 1, monitor print jobs, and perform maintenance control, and can comprehensively operate the various functions of the image forming system 1.

[0021] The inkjet head 201 in the printing unit 200 is a precision unit that requires precise control. For example, if a multi-feed occurs, in which multiple sheets of paper are transported overlapping each other, and the sheets are transported to the inkjet head 201, the distance between the inkjet head 201 and the multi-fed sheets may not be maintained properly, and the sheets may come into contact with the inkjet head 201. In such a case, there is a risk of damaging the inkjet head 201. To prevent damage to the inkjet head 201, it is necessary to remove the multi-fed sheets upstream of the printing unit 200 without transporting them there.

[0022] [Paper transport in image forming systems] Next, paper transport in the image forming system 1 will be described with reference to Figures 2(a) and 2(b). Figure 2(a) is a schematic cross-sectional view showing the position of paper when a single-sided print job is performed in the image forming system according to the first embodiment. Figure 2(b) is a schematic cross-sectional view showing the position of paper when a double-sided print job is performed in the image forming system according to the first embodiment.

[0023] 2(a), during the printing process of a single-sided print job, 20 sheets of paper, St1 to St20, are transported inside the image forming system 1. In detail, for example, assume that paper is fed from paper feed tray 131 of paper feed device 130 of paper feed unit 100. Then, the paper is transported from paper feed unit 100 to print unit 200, where it is printed, and then transported sequentially through each unit of fixing unit 300, cooling unit 400, and inverting unit 500. Then, the paper transported from inverting unit 500 is stacked as printed paper in paper output stacker 611 of paper output device 610 of paper output unit 600.

[0024] On the other hand, as shown in FIG. 2B, during the printing process of a double-sided print job, 33 sheets of paper, St1 to St33, are transported into the image forming system 1. Specifically, assume that paper is fed from paper feed tray 131 of paper feed device 130 of paper feed unit 100. Then, as with a single-sided print job, the paper is transported from paper feed unit 100 to print unit 200 and printed thereon. The paper is then transported sequentially through each unit, namely, fixing unit 300 and cooling unit 400. Here, the paper with only the front side printed is transported to the lower part of cooling unit 400, then transported sequentially through the lower part of fixing unit 300 and the lower part of print unit 200, and returned to paper feed device 110 of paper feed unit 100. The paper is flipped over midway through the lower part of fixing unit 300. The paper returned to paper feed device 110 of paper feed unit 100 is transported to print unit 200 for printing on the back side, i.e., the second side. Thereafter, the double-sided printed paper is transported in order through the fixing unit 300 , the cooling unit 400 and the reversing unit 500 , and is stacked in the paper discharge stacker 631 of the paper discharge device 630 of the paper discharge unit 600 .

[0025] In this embodiment, the position of the sheet to be controlled is calculated from the time elapsed since the start of conveyance. That is, the time of the sheet calculated by the control unit of one of the units upstream in the conveyance direction of the sheet is notified to the control unit of that unit as the time when the sheet arrives at the entrance of the unit. In this embodiment, the position (time) of the sheet is calculated by the control unit 150 of the sheet feeder 110, for example, as will be described later in the control description.

[0026] [Paper feeder configuration] Next, the configuration of sheet feeding device 110 of sheet feeding section 100 will be described with reference to Fig. 3. Fig. 3 is a schematic cross-sectional view showing a sheet feeding device according to the first embodiment. Since the three sheet feeding devices 110, 120, and 130 in sheet feeding section 100 of this embodiment each have the same configuration, only sheet feeding device 110 will be described, and descriptions of sheet feeding devices 120 and 130 will be omitted.

[0027] 3, the paper feeder 110 has three tiers of first to third paper feed trays 111 to 113 that support and stack various types of printing paper (blank paper) used in printing, as described above. Above the first to third paper feed trays 111 to 113, paper feed separators 111A, 112A, and 113A are provided as feeders for feeding the paper sheets supported therein one by one. Each of the paper feed separators 111A, 112A, and 113A has a paper feed belt 111a, 112a, and 113a that is driven by a motor (not shown) to suck and feed the topmost paper sheet floated by a fan (not shown). Furthermore, each of the paper feed separation units 111A, 112A, and 113A has a pair of separation rollers 111b, 112b, and 113b for separating the sheets of paper fed by the paper feed belts 111a, 112a, and 113a into individual sheets when multiple sheets are fed at once. The pair of separation rollers 111b, 112b, and 113b are configured with a general feed roller and a retard roller, but are not limited to this and may be of any type, such as a system using a separation pad.

[0028] Downstream of the separation roller pairs 11b, 112b, and 113b in the paper conveying direction V, are disposed multi-feed detection sensors SN11, SN12, and SN13 for detecting whether or not paper is being fed in multiple layers. These multi-feed detection sensors SN11, SN12, and SN13 sense the leading edge of the fed paper to determine whether multiple sheets of paper are being fed at the same time, and, if multiple sheets have been fed in multiple layers, to detect the degree of misalignment between the sheets. The detection of multi-feeds by these multi-feed detection sensors SN11, SN12, and SN13 will be described in detail later.

[0029] Next, the paper transport path in the paper feeder 110 will be described. The paper feeder 110 is provided with a horizontal path entrance EN2 that accepts paper transported from a device located upstream in the paper transport direction (i.e., paper feeder 120). The paper feeder 110 is also provided with a paper discharge outlet EX1 that discharges paper to a device located downstream in the paper transport direction V (i.e., printing unit 200). The paper feeder 110 is also provided with a duplex path entrance EN1 that accepts paper transported from a lower portion of the printing unit 200 for duplex printing. The paper feeder 110 is also provided with a paper discharge tray 119 that serves as a discharge support unit that is an evacuation destination for discharging and evacuating invalid paper, as will be described in detail later. That is, the paper discharge tray 119 supports a stack of paper that has been invalidated and discharged (ejected) due to, for example, double feeding. The paper feeder 110 is also provided with a paper discharge outlet 115 that allows paper to be discharged to the paper discharge tray 119. Similarly, the paper feeders 120 and 130 are also provided with the above-mentioned paper discharge ports 125 and 135 (see FIG. 1), and are configured so that paper can be discharged from these ports to a paper discharge tray (not shown).

[0030] The sheet feeding device 110 is provided with a plurality of transport paths that guide sheets by respectively connecting the horizontal path entrance EN2, the sheet discharge outlet EX1, the double-sided path entrance EN1, the sheet discharge outlet 115, and the first to third sheet feed trays 111 to 113. In addition, a plurality of transport roller pairs that transport sheets are arranged on these transport paths, and these transport roller pairs constitute a transport section 110A that transports sheets.

[0031] Specifically, the sheet feeding device 110 is provided with a first horizontal conveyance path Ps11, a second horizontal conveyance path Ps12 as the first conveyance path, and a third horizontal conveyance path Ps13 as the second conveyance path, which serve as horizontal paths connecting the horizontal path entrance EN2 to the sheet discharge outlet EX1. The first horizontal conveyance path Ps11, the second horizontal conveyance path Ps12, and the third horizontal conveyance path Ps13 are arranged in a horizontal line. The sheet feeding device 110 also has an error sheet discharge path Ps14 as the third conveyance path that branches off from an error bin branch P5 located between the second horizontal conveyance path Ps12 and the third horizontal conveyance path Ps13 and guides sheets to the sheet discharge outlet 115. This error bin branch P5 is provided with a flapper FL1 as a switching unit that can switch between a first position where the paper transported by the transport unit 110A along the second horizontal transport path Ps12 is guided to the third horizontal transport path Ps13, and a second position where the paper is guided to the error paper discharge path Ps14.

[0032] The sheet feeding device 110 also has a duplex conveyance path Ps15 that guides sheets from the duplex path entrance EN1 to a horizontal path junction P4 located between the first horizontal conveyance path Ps11 and the second horizontal conveyance path Ps12. The sheet feeding device 110 also has a tray conveyance path Ps18 that guides sheets from the third sheet feeding tray 113 to the third sheet feeding tray junction P1. The sheet feeding device 110 also has a tray conveyance path Ps17 that guides sheets from the second sheet feeding tray 112 to the second sheet feeding tray junction P2. The sheet feeding device 110 also has a tray conveyance path Ps16 that guides sheets from the first sheet feeding tray 111 to the first sheet feeding tray junction P3.

[0033] In sheet feeding device 110 configured as described above, sheets fed from first sheet feeding tray 111 by sheet separation unit 111A are transported to sheet discharge outlet EX1 via tray transport path Ps16, duplex transport path Ps15, second horizontal transport path Ps12, and third horizontal transport path Ps13. Similarly, sheets fed from second sheet feeding tray 112 by sheet feeding unit 112A are transported to sheet discharge outlet EX1 via tray transport path Ps17, duplex transport path Ps15, second horizontal transport path Ps12, and third horizontal transport path Ps13. Similarly, sheets fed from third sheet feeding tray 113 by sheet feeding unit 113A are transported to sheet discharge outlet EX1 via tray transport path Ps18, duplex transport path Ps15, second horizontal transport path Ps12, and third horizontal transport path Ps13.

[0034] Furthermore, paper conveyed from the above-mentioned paper feeder 120 or paper feeder 130 (see FIG. 1) is conveyed to the paper discharge outlet EX1 via the horizontal path entrance EN2, the first horizontal conveyance path Ps11, the second horizontal conveyance path Ps12, and the third horizontal conveyance path Ps13. Furthermore, paper conveyed from the above-mentioned printing unit 200 (see FIG. 1) is conveyed to the paper discharge outlet EX1 via the double-sided path entrance EN1, the double-sided conveyance path Ps15, the second horizontal conveyance path Ps12, and the third horizontal conveyance path Ps13.

[0035] The above-mentioned flapper FL1 is driven by a flapper drive motor (not shown) and is initialized to guide paper from the second horizontal conveyance path Ps12 to the third horizontal conveyance path Ps13 (paper discharge outlet EX1) when the power is turned on or a print job starts. Then, suppose that the multi-feed detection sensors SN11, SN12, and SN13 serving as multi-feed detectors detect multi-feeding of paper in the tray conveyance paths Ps16, Ps17, and Ps18. In this case, the position of the flapper FL1 is switched from the first position to the second position, and the paper from the second horizontal conveyance path Ps12 is guided to the error discharge path Ps14 (paper discharge outlet EX115). Details of the switching control of this flapper FL1 will be described later.

[0036] [Control unit of image forming system] Next, the control unit 10 of the image forming system 1 will be described with reference to Fig. 4. Fig. 4 is a block diagram showing the control unit of the image forming system according to the first embodiment.

[0037] As shown in FIG. 4, the image forming system 1 is a controller unit that includes a control unit 10 that controls the input and output of sensor signals and device information and the execution of various control processes. For example, a program describing the processing content is stored in a ROM 13 or a HDD 14 and installed in the image forming system 1. A CPU 11 in the control unit 10 reads the program stored in the ROM 13 or the HDD 14 into a RAM 12 and executes it. The CPU 11 also controls all devices connected to a system bus 15. The RAM 12 functions as the main memory and work memory for the CPU 11. The ROM 13 stores a boot program that is executed when the power is turned on, and the HDD 14 stores the operating system and the control program for the device. The HDD 14 is also used for temporarily or long-term storage of large amounts of data.

[0038] Network 16 is connected to local area network 17 and handles input and output of data and device information with external devices. Alternatively, programs can be installed in ROM 13 or HDD 14 via Network 16. Device I / F 18 is an interface with printer engine 19 and inputs and outputs signals for operating and referencing various motors, sensors, inkjet heads, and other components connected to printer engine 19. Printer engine 19 is an inkjet output device that transports printing paper under control of control unit 10 and controls inkjet head 201 (see FIG. 1) to output images transferred from print server 70 onto the printing paper. Head control unit 20 controls inkjet head 201 of printer engine 19 via device I / F 18, and is responsible for controlling ink ejection for image formation and head retraction control when improper paper is detected. Transport control unit 21 controls transport motors and sensors for feeding printing paper from paper feed unit 100, transporting the paper in synchronization with the ink ejection timing of inkjet head 201, and discharging the paper to paper discharge unit 600.

[0039] Here, the case where the control unit 10 (controller unit) is configured as a single unit has been described. However, it is also possible to have a configuration in which there are multiple separate controller units, one for each of the paper feed unit 100, print unit 200, fuser unit 300, cooling unit 400, reversing unit 500, and paper discharge unit 600. In this case, a specific controller unit controls the other multiple controller units in an integrated manner.

[0040] [Paper feeder control unit] Next, the configuration of control unit 150 of sheet feeding device 110 will be described with reference to FIG. 5. FIG. 5 is a block diagram showing the control unit of the sheet feeding device according to the first embodiment. Note that in the case where sheet feeding devices 110, 120, and 130 of sheet feeding section 100 each have a separate control unit (controller unit), control unit 150 of sheet feeding device 110 will be described as one of these. In other words, sheet feeding devices 120 and 130 also have a control unit similar to control unit 150. With this configuration, it is possible to easily configure a system even when sheet feeding section 100 is used to connect three devices (units) in succession as the same sheet feeding unit (i.e., when three identical sheet feeding devices are connected).

[0041] As shown in FIG. 5, the sheet feeding device 110 is a controller unit that includes a control unit 150 that controls input and output of sensor signals and device information, and various control processes. For example, a program describing the processing contents is stored in a ROM 153 or a HDD 154 and installed in the sheet feeding device 110. The CPU 151 reads the program stored in the ROM 153 or the HDD 154 into a RAM 152 and executes it. The CPU 151 also comprehensively controls each device connected to a system bus 155. The RAM 152 functions as the main memory and work memory of the CPU 151. The ROM 153 stores a boot program that is executed when the power is turned on, and the HDD 154 stores the operating system and the control program of the device. The HDD 154 is also used for temporarily or long-term storage of large amounts of data.

[0042] The network 156 is connected to a local area network 157 and is responsible for inputting and outputting data and device information to and from the outside. Alternatively, a program can be installed in the ROM 153 or HDD 154 via the network 156. The unit I / F 158 is an interface with adjacent devices and, in this embodiment, is connected to (the control unit of) the connected sheet feeder 120. The controller I / F 160 is an interface with the controller and is connected to (the control unit of) the print unit 200 of the image forming system 1. The device control unit 161 controls the sheet feed fan for feeding sheets for printing from the first to third sheet feed trays 111 to 113, the transport motor for transporting sheets to downstream devices or the sheet discharge tray 119 (see FIG. 3), and sensors. The multi-feed detection sensors SN11, SN12, and SN13 detect multi-feeding of sheets fed by the sheet feed separation units 111A, 112A, and 113A, respectively, as described above. The flapper drive motor 162 drives the flapper FL1 to switch the position thereof.

[0043] [Paper feeder control function] Next, the control functions achieved by the control unit 150 of the sheet feeding device 110 performing various controls (processes) will be described with reference to FIG. 6. FIG. 6 is a block diagram showing the control functions of the sheet feeding device according to the first embodiment. The control units of the sheet feeding devices 120 and 130 also have functions similar to the control functions shown in FIG. 6. Each part as a software module shown in FIG. 6 is stored as a program on the HDD 154, loaded into the RAM 152, and executed by the CPU 151 to function.

[0044] The paper feeder management unit SS1 exchanges print job information and instruction responses with the printing unit 200 via the controller I / F 160, and performs overall control of each unit of the paper feeder 110. When a paper transport request (a request for paper feed or a request for paper transport during double-sided printing) is received from the printing unit 200, it issues a paper transport command to the transport control unit SS2. The transport control unit SS2 issues commands to the paper feed control unit SS3, the double feed detection unit SS4, and the transport path switching control unit SS5 according to the transport route in each of the transport paths described above. That is, the transport control unit SS2 issues commands to these control units and controls the transport of the paper to be fed or the paper transported from an adjacent device to the adjacent device downstream in the transport direction V (i.e., the printing unit 200) or the paper discharge port 115 according to the paper transport time.

[0045] The paper feed control unit SS3 controls the paper feed separation units 111A, 112A, and 113A to feed the sheets stacked in the paper feed trays 111, 112, and 113 one by one. The multi-feed detection unit SS4 senses the sheets fed from the paper feed trays 111, 112, and 113 using the multi-feed detection sensors SN11, SN12, and SN13, respectively. That is, the multi-feed detection sensors SN11, SN12, and SN13 detect whether or not sheets are being fed in a multi-feed state, and if so, how much the sheets are misaligned and overlapping in the conveying direction V. When a multi-feed of sheets is detected or when sheets being conveyed are invalid due to other errors, the conveying path switching control unit SS5 designates the sheets as invalid and switches the flapper FL1 to switch the conveying destination of the invalid sheets to the paper discharge port 115. This switching of the flapper FL1 is performed by driving the flapper drive motor 162.

[0046] [Transportation Route Management Table] Next, a transport route management table provided in control unit 150 of sheet feeding device 110 will be described with reference to Fig. 7. Fig. 7 is a table showing a transport route management table in the sheet feeding device according to the first embodiment.

[0047] 7, the transport route management table records the relationship between time and branching and merging positions that a sheet passes through from the transport start position to the paper discharge outlet (error bin) at each position during transport, in order to manage the time it takes for the sheet to pass through these positions. Note that in this embodiment, the position of the transported sheet to be controlled is calculated based on the elapsed time from the start of transport.

[0048] This transport route management table stores information such as "Index No.", "junction position," and "transport time from transport start position to junction position." "Index No." is an identifier for uniquely identifying transport route information. "Junction position" is the name of the target junction position (P5) or junction position (P1, P2, P3, P4) (see FIG. 3). "Transport time from transport start position to junction position" is the transport time when the first paper feed tray 111, the second paper feed tray 112, the third paper feed tray 113, the duplex path entrance EN1, and the horizontal path entrance EN2 are set as the transport start position (0 mm). In other words, it is the time required to move from each transport start position to the junction position or junction position on the transport path for ejecting paper to the target paper ejection destination. In other words, this transport route management table stores information on the time it takes for the leading edge of a sheet of paper, which has been transported from each transport start position, to reach the "junction position." From the information in this transport route management table and the time at the transport start position notified by the control unit 10 of the print unit 200, it is possible to calculate the time at which the paper passes any point on the transport path.

[0049] [Paper feed sequence] Next, the overall sequence in the sheet feeding device 110 when feeding sheets one by one from the first to third sheet feeding trays 111 to 113 will be described with reference to Fig. 8. Fig. 8 is a diagram showing the sequence of transport control of the sheet feeding device according to the first embodiment.

[0050] 8, when the paper feeder management unit SS1 receives a transport request from the print unit 200, it initializes the flapper FL1 (moves it to its home position where it guides the paper to the paper exit EX1) and drives the paper feed fan, and then starts this sequence. The transport request includes information about the paper feed tray from which paper will be fed and the start time for paper transport.

[0051] First, in step S101, the sheet feeding device management unit SS1 notifies the transport control unit SS2 of a sheet feeding transport instruction. Next, in step S102, the transport control unit SS2 notifies the sheet feeding control unit SS3 of a sheet feeding start instruction. At this time, the sheet transport start time is also notified as information.

[0052] Next, in step S103, the paper feed control unit SS3 performs paper feed control in the paper feed separation unit of the specified paper feed tray. That is, it rotates the fan to float the paper, and when the paper transport start time arrives, it drives the paper feed belt to perform the paper feed operation. Next, in step S104, the paper feed control unit SS3 notifies the completion of paper feed. This notification can be made after step S105 without any problem.

[0053] Next, in step S105, the conveyance control unit SS2 issues a command to start double feed detection to the double feed detection unit SS4. At this time, the time when the leading edge of the fed paper passes the double feed detection sensor is also notified as information. Then, in step S106, the double feed detection unit SS4 performs the double feed detection control described below.

[0054] Next, in step SS107, the multi-feed detection unit SS4 notifies the result of the multi-feed detection. This notification includes whether or not a multi-feed occurred and the elapsed time from the leading edge of the paper when the multi-feed was detected. Then, in step S108, the transport control unit SS2 performs a paper transport path switching determination, which will be described later.

[0055] Next, in step SS109, the conveyance control unit SS2 notifies the conveyance path switching control unit SS5 of a paper conveyance path switching instruction as necessary. At this time, the switching start time of the switching flapper 117 and the return start time as the first time are notified as information. Next, in step S110, the conveyance path switching control unit SS5 performs flapper drive control, which will be described later. Then, in step S111, the conveyance path switching control unit SS5 notifies the conveyance control unit SS2 that the paper conveyance path switching has been completed.

[0056] When the transport to the paper discharge outlet EX1 or the paper discharge to the paper discharge outlet 115 is completed, the transport control unit SS2 notifies the paper feed device management unit SS1 of the completion of the paper feed transport in step S112. The paper feed transport process is carried out through the above sequence.

[0057] [Control of the paper feeder according to the first embodiment] Hereinafter, details of the control of the sheet feeding device according to this embodiment will be described using flowcharts. Note that in the following description, the control will be described as being executed by CPU 151 of control unit 150 of sheet feeding device 110, but the control may be executed by the CPU of the control unit of either device, and in particular, it may be executed by CPU 11 of control unit 10 of image forming system 1. In addition, in the following description, the first sheet that starts to be fed from the sheet feed tray will be referred to as sheet S1, the second sheet that is multi-fed following the first sheet will be referred to as sheet S2, and the sheet that is conveyed from an upstream device so as to follow sheet S1 or sheet S2 will be referred to as sheet S3.

[0058] (Transport control) First, the transport control of the paper feeder according to the first embodiment will be described with reference to FIG. 9. FIG. 9 is a flowchart showing the transport control of the paper feeder according to the first embodiment. In the following description of the flowchart, the actions of "instruction" and "notification" will be described as synonymous with setting a flag related to the processing to ON / OFF in the control unit 150 of paper feeder 110 or the control unit of another device. Regarding "instruction" and "notification," the setting of the flag can be used to start processing related to the set flag or to display on a display device (not shown) or the like.

[0059] As described above, when the transport control unit SS2 receives a paper feed transport instruction S101 from the paper feed device management unit SS1, transport control of this paper feed device is started. Then, first, as shown in FIG. 9, the CPU 151 drives the transport rollers of each unit in the transport unit 110A (S11). Next, the CPU 151 determines whether the paper feed transport instruction is an instruction to feed paper from the first to third paper feed trays 111 to 113, or an instruction to accept paper transported from an upstream device (i.e., another paper feed device or the printing unit 200) located upstream in the transport direction V (S12). If the instruction is to feed paper from the first to third paper feed trays 111 to 113, the process proceeds to step S13; if the instruction is to accept paper transport from an upstream device, the process proceeds to step S23.

[0060] In step S13, CPU 151 issues a paper feed start instruction. At this time, it transmits information to paper feed control unit SS3 (i.e., paper feed separation unit) such as "cassette ID: first paper feed cassette, paper transport start time: 12:10:30:000 milliseconds (hereinafter abbreviated as "30.000")." Upon receiving this, paper feed control unit SS3 performs processing for paper feed, and then starts paper transport from second paper feed tray 112 at "30.000," which is the paper transport start time.

[0061] Next, CPU 151 notifies multi-feed detection unit SS4 (i.e., multi-feed detection sensor) of a multi-feed detection start instruction (S14). At this time, if, for example, A3-size (420 mm long) paper is being transported at a speed of 1000 mm / s, the information transmitted is as follows: "Sensor ID: multi-feed detection sensor SN12, detection start time: '30:150', detection end time: '30:570'." The detection start time is determined by the fact that the leading edge of the fed paper passes multi-feed detection sensor SN12 150 msec after the paper is transported. The detection end time is determined by the 420 msec it takes for a 420 mm long paper sheet to pass (the detection time may be the length of the paper sheet or a different time). Upon receiving this instruction, multi-feed detection unit SS4 performs detection processing and then starts multi-feed detection at the detection start time of '30:150'. Details of multi-feed detection will be described later.

[0062] Next, CPU 151 determines whether the paper transport path switching determination time for paper S1 fed from the paper feed tray has arrived (S15). In this embodiment, the determination is made when the leading edge of paper S1 reaches the horizontal path junction (P4) position (605 msec after paper S1 starts to be transported from the second paper feed cassette (see FIG. 7)), and determines whether the arrival time is "30.605". If the arrival time has not arrived, the process is repeated until the arrival time arrives (No in S15). If the arrival time arrives (Yes in S15), the process proceeds to step S16. Then, in step S16, CPU 151 makes a paper transport path switching determination. Details of the control of this paper transport path switching determination will be described later.

[0063] Next, if the result of the paper transport path switching determination indicates that the paper transport path needs to be switched (Yes in S17), the CPU 151 proceeds to step S18, and if the result indicates that the paper transport path does not need to be switched (No in S17), the CPU 151 proceeds to step S27. In step S18, the CPU 151 issues a paper transport path switching instruction. At this time, based on the result of the paper transport path switching determination, information such as "switching start time: '30.615', return start time: '31.145'" is transmitted, and upon receiving this, the transport path switching control unit SS5 controls the switching of the flapper FL1.

[0064] Next, CPU 151 notifies paper feed device management section SS1 of the occurrence of a multi-feed (S19). The occurrence of a multi-feed is also notified to printing section 200 via paper feed device management section SS1. This notification may be made when the paper is discharged to paper discharge port 115, but by notifying earlier, it becomes possible to stop or switch the processing of subsequent paper or printing section 200 earlier.

[0065] Next, CPU 151 determines whether the sheets (here, overlapped sheets S1 and S2) have been discharged to discharge outlet 115 (S20). Completion of discharge may be determined from the time, or a sensor that monitors the transport of sheets may be provided nearby to monitor the passage of the trailing edge of sheet S2. The discharge completion time can be calculated by adding the length of the overlapped sheets (including the amount of misalignment, described below) to the time it takes for the leading edge of sheet S1 to reach discharge outlet 115 (which arrives 905 msec after sheet S1 starts to be transported from the second paper feed cassette (see FIG. 7)). If discharge is not complete (No in S20), the process is repeated until discharge is complete. If discharge is complete (Yes in S20), the process proceeds to step S21.

[0066] In step S21, CPU 151 notifies conveyance control unit SS2 that the paper has been discharged to the error bin (paper discharge port 115). As a result, CPU 151 stops the paper discharge rollers (S22) and ends the conveyance control of paper feeder 110.

[0067] On the other hand, as described above, if in step S12 it is the receipt of paper transport from the upstream device, the process proceeds to step S23. When proceeding to step S23, CPU 151 determines whether the paper receipt time has arrived. If the receipt time has not arrived, the process is repeated until the receipt time arrives (No in S23), and if the receipt time arrives (Yes in S23), the process proceeds to step S24. When proceeding to step S24, CPU 151 receives paper S3 from the upstream device.

[0068] Next, CPU 151 determines whether the time for the sheet S3 received from the upstream device to pass through the error bin branch (P5) has arrived (S25). If the time has not yet arrived, the process is repeated until the time has arrived (No in S25). If the time has arrived (Yes in S25), the process proceeds to step S26.

[0069] In step S26, CPU 151 determines whether the conveying path is directed toward a downstream device (printing unit 200, or paper feeder 110 if it is paper feeder 120, or paper feeder 120 if it is paper feeder 130) located downstream in conveying direction V. In other words, it determines whether flapper FL1 is in the first position, which is the initial position. If the conveying path is directed toward the downstream device (Yes in S26), the process proceeds to step S27.

[0070] If switching of the paper transport path was not necessary in step S17 (No in S17), or if the transport path is directed toward the downstream device (Yes in S26), the process proceeds to step S27. Then, CPU 151 determines whether the paper (here, paper S1 or paper S3) has been discharged to the downstream device. Completion of paper discharge to the downstream device may be determined from the time, or a sensor that monitors paper transport nearby may be provided to monitor the passage of the trailing edge of paper S1 or S3. The paper discharge completion time can be calculated by adding the length of the paper being transported to the time it takes for the leading edge of the paper to reach paper output outlet EX1 (for example, the arrival of paper S1 705 msec after transport from the second paper cassette begins (see FIG. 7)). If paper discharge is not complete (No in S27), the process is repeated until paper discharge is complete. If paper discharge is complete (Yes in S27), the process proceeds to step S28. Then, in step S28, CPU 151 notifies conveyance control unit SS2 that the delivery of sheet S1 or sheet S3 to the downstream device has been completed normally, and then proceeds to step S22. As a result, CPU 151 stops the paper discharge rollers (S22) and ends conveyance control of sheet feeder 110.

[0071] On the other hand, in step S26, if the conveying path is not directed toward the downstream device (No in S26), that is, if the flapper FL1 has switched from the first position to the second position and the conveying path is directed toward the paper discharge outlet 115, the process proceeds to step S20. Note that this situation occurs when the previous sheets S1 and S2 are double-fed, and the amount of misalignment is large, so that sheet S3 conveyed from the upstream device reaches flapper FL1 before flapper FL1 can be returned, and flapper FL1 cannot be returned.

[0072] Even when the process proceeds to step S20 in this way, as described above, CPU 151 determines whether or not the sheets (sheets S1 to S3) have been discharged to the sheet discharge port 115 (S20). If the sheet discharge is not complete (No in S20), the process is repeated until the sheet discharge is complete. Then, if the sheet discharge is complete (Yes in S20), CPU 151 notifies conveyance control unit SS2 that the sheet discharge to the error bin (sheet discharge port 115) has been completed. This causes CPU 151 to stop the sheet discharge rollers (S22) and end conveyance control of sheet feeder 110.

[0073] In the transport control of the paper feeder 110 described above, the multiple transport rollers as the transport section 110A are driven or stopped collectively, but it is also possible to drive or stop only the necessary transport rollers sequentially based on the time when the paper arrives.

[0074] (Double feed detection control) Next, the multi-feed detection control of the paper feeder according to the first embodiment will be described with reference to Fig. 10 and Fig. 13. Fig. 10 is a flowchart showing the multi-feed detection control of the paper feeder according to the first embodiment. Fig. 13 is a time chart showing the relationship between the detection waveform of the multi-feed detection sensor and each time.

[0075] First, the relationship between the detection waveform of the multi-feed detection sensor and each time will be explained. As shown in Figure 13, the second sheet S2, which follows the first sheet S1, is transported overlapping with the first sheet S1, i.e., they are transported in a multi-feed state. When sheets S1 and S2 are transported misaligned, the detection start time Ts is the time when the leading edge of sheet S1 passes the multi-feed detection sensor, and the multi-feed occurrence time Td, which is the second time, is the time when the leading edge of sheet S2 reaches the multi-feed detection sensor. Note that with an ultrasonic multi-feed detection sensor, the detection waveform attenuates in the area where the sheets are transported overlapping, and it is determined that a multi-feed has occurred when it falls below a predetermined detection threshold. The multi-feed deviation time t, which corresponds to the deviation between the multi-fed sheets S1 and S2, can be calculated by subtracting the detection start time Ts from the multi-feed occurrence time Td. In other words, the multi-feed deviation time t is the length of time from when the leading edge of sheet S1 is detected until the multi-feed is detected, and corresponds to the transport time t' that is extended when the total transport length of the multi-fed sheets S1 and S2 is longer than the transport length of sheet S1. For example, if the detection start time Ts is "30:150" and the multi-feed occurrence time Td is "30:220," the sheets will have advanced 70 msec (i.e., 70 mm at a speed of 1000 mm / s) by the time the multi-feed is detected. This time difference is the multi-feed deviation time t, which corresponds to the amount of deviation of the multi-fed sheets.

[0076] Next, the multi-feed detection control of the paper feeding device according to the first embodiment will be described. When proceeding to step S14 (see FIG. 9) in the transport control of the paper feeding device described above, the multi-feed detection unit SS4 receives a multi-feed detection start instruction S105 from the transport control unit SS2, and the CPU 151 starts the detection control of this paper feeding device. Note that in this description, it is assumed that the received information is, for example, "sensor ID: multi-feed detection sensor SN12, detection start time: '30.150', detection end time: '30.570'".

[0077] 10, when the double feed detection control is started, first, the CPU 151 determines whether the double feed detection start time Ts ("30.150") has arrived (S31). If the detection start time Ts has not arrived (No in S31), the process is repeated until the detection start time Ts arrives, and if the detection start time Ts arrives (Yes in S31), the CPU 151 starts double feed detection (S32).

[0078] Next, CPU 151 determines whether or not a double feed has occurred (S33). If a double feed has not occurred (No in S33), the process proceeds to step S34; if a double feed has occurred (Yes in S33), the process proceeds to step S38. When proceeding to step S34, CPU 151 determines whether or not the double feed detection end time Te ("30.570") has arrived. If the detection end time Te has not arrived (No in S34), the process returns to step S33, and thereafter the process of steps S33 to S34 is repeated and the process waits. If the end time has arrived (Yes in S34), the process proceeds to step S35. Then, CPU 151 generates information that a double feed has not occurred (S35), ends the double feed detection (S36), notifies the detection result (S37), and ends control of the double feed detection.

[0079] On the other hand, if a double feed has occurred in step S33 (Yes in S33), the process proceeds to step S38, where CPU 151 acquires the double feed occurrence time Td. Then, CPU 151 generates information that a double feed has occurred (S35). This information includes a double feed deviation time t=70 msec, which corresponds to the extension of the conveyance length due to the simultaneous double feed. For example, the information generated may be "double feed occurred, double feed deviation time: 70 msec." Then, CPU 151 ends the double feed detection (S36), notifies the detection result (S37), and ends control of the double feed detection.

[0080] (Paper transport path switching decision control) Next, the control of determining whether to switch paper transport paths in the paper feeder according to the first embodiment will be described with reference to Fig. 11. Fig. 11 is a flowchart showing the control of determining whether to switch paper transport paths in the paper feeder according to the first embodiment.

[0081] When the process proceeds to step S16 (see FIG. 9) in the paper feeder transport control described above, CPU 151 starts paper transport path switching determination control and determines whether the multi-feed detection result indicates that a multi-feed has occurred (S41). If a multi-feed has not occurred (No in S41), the process ends. On the other hand, if a multi-feed has occurred (Yes in S41), the process proceeds to step S42.

[0082] First, the CPU 151 calculates the start time for switching the transport path (S42). For example, assume that switching the transport path requires 40 msec (30 msec flapper drive time + 10 msec margin). The time at which the leading edge of sheet S1 reaches the error bin branch position (P5) is "30.655" (655 msec after sheet S1 starts being transported from the second paper feed cassette (see FIG. 7)). The start time for switching the transport path is "30.615", which is the time at which the leading edge of sheet S1 reaches the error bin branch position (P5) minus 40 msec, which is the time required for switching the transport path.

[0083] Next, CPU 151 calculates the start time of returning the sheet to the transport path (S43). That is, it calculates the time when the trailing edge of subsequent sheet S2, of the overlapped sheets S1 and S2, passes through the error bin branch position (P5). Here, two examples will be explained. "Example 1" When transporting A3 paper, the double feed detection result is "Double feed detected, double feed deviation time: 0 msec" Paper length: 420mm (A3 size) Paper transport speed: 1000mm / s Double feed deviation time: 0 msec "Example 2" When transporting A3 paper, the double feed detection result is "Double feed detected, double feed deviation time: 70 msec" Paper length: 420mm (A3 size) Paper transport speed: 1000mm / s Double feed deviation time: 70 msec

[0084] In "Example 1," the time it takes for the leading edge of the paper to reach the error bin branch (P5) position (30.655) is added to the 420 msec transit time until the trailing edge of the paper passes through, resulting in "31.075." On the other hand, in "Example 2," it is necessary to add an additional 70 msec of double feed misalignment time to the time it takes for the trailing edge of A3 paper to pass through, resulting in "31.145."

[0085] Next, CPU 151 obtains the subsequent sheet arrival time as the third time (S44). That is, the time when sheet S3, which is the succeeding sheet to sheets S1 and S2 that have been double-fed, arrives at the error bin branch position (P5) is obtained from the transport route management table (see FIG. 7). That is, when sheet S3 for double-sided printing is transported from duplex path entrance EN1 (i.e., print unit 200), the subsequent sheet arrival time is obtained as the transport time from the duplex path entrance EN1 to the error bin branch position (P5). Also, when sheet S3 is transported from horizontal path entrance EN2 (i.e., sheet feeder 120), the subsequent sheet arrival time is obtained as the transport time from the horizontal path entrance EN2 to the error bin branch position (P5).

[0086] Next, CPU 151 determines whether the acquired subsequent sheet arrival time is earlier than the transport path return time calculated in step S43 (S45). If the subsequent sheet arrival time is earlier than the transport path return time (Yes in S45), the process proceeds to step S46, and if not earlier (No in S45), the process proceeds to step S47.

[0087] In step S46, CPU 151 sets the transport path return start time to 0. By setting the transport path return start time to 0, flapper FL1 remains switched to switch the transport path to the paper discharge port 115 side (see S53 in FIG. 12, described later). In other words, the switching of flapper FL1 to return it to its original initial position, the first position, is stopped and it remains in the second position. This is because if flapper FL1 were to be returned, a jam would occur because the leading edge of the succeeding sheet S3 would have already passed flapper FL1 (error bin branch (P5) position) and entered error paper discharge path Ps14.

[0088] Thereafter, in step S47, CPU 151 generates paper transport path switching information. If the multifeed detection result is "multifeed occurred, multifeed deviation time: 70 msec," the paper transport path switching information becomes "switching start time: 30:615, return start time: 31:145." Then, once generation of the paper transport path switching information is complete, paper transport path switching determination control ends.

[0089] In this embodiment, control is performed assuming that the paper transport speed when double feed is detected and the paper transport speed when passing flapper FL1 are both 1000 mm / s, but if the speeds are different, the return start time can be calculated taking the speed difference into consideration. For example, if the paper transport speed when passing flapper FL1 is 1400 mm / s, the double feed deviation time can be calculated as 70 msec x 1000 / 1400 = 50 msec.

[0090] (Flapper drive control) Next, flapper drive control of the paper feeder according to the first embodiment will be described with reference to Figs. 12 and 14. Fig. 12 is a flowchart showing flapper drive control of the paper feeder according to the first embodiment. Fig. 14(a) is a diagram showing a case where the flapper can be switched after multiple sheets of paper have passed through the paper feeder. Fig. 14(b) is a diagram showing a case where the flapper cannot be switched after multiple sheets of paper have passed through the paper feeder.

[0091] When the process proceeds to step S18 (see FIG. 9) in the transport control of the paper feeder described above, the transport path switching control unit SS5 receives a paper transport path switching instruction notification S109 from the transport control unit SS2, and the CPU 151 starts flapper drive control of the paper feeder. Note that in this example, the paper transport path switching information received is "switching start time: '30.615', return start time: '31.145'".

[0092] When the flapper drive control is started, the CPU 151 first determines whether the switching start time ("30.615") has arrived (S51). If the switching start time has not arrived, the process is repeated until the switching start time arrives (No in S51). If the switching start time arrives (Yes in S51), the process proceeds to step SS52.

[0093] Next, CPU 151 switches flapper FL1 from its initial position, the first position, to the second position, i.e., switches the transport path along which sheets S1 and S2 are transported to the error bin side (S52). Next, CPU 151 determines whether the return start time is included in the information (S53). Here, a case where the return start time is not included in the information means that the paper transport path switching information notifies only the switching start time, such as "switching start time: '30.615', return start time: '0'." If the return start time is not included in the information (No in S53), this flapper drive control is terminated, and flapper FL1 remains in the second position and stops switching; that is, it does not switch to the downstream discharge side for discharging sheets to a downstream device.

[0094] In other words, if it is determined in step S45 (see FIG. 11) that the subsequent sheet arrival time is earlier than the transport path return time and subsequent sheet S3 arrives before the trailing edge of sheet S2 of the overlapped sheets passes through, the return start time is not included in the information (see S46). In this case, as shown in FIG. 14(b), the leading edge of subsequent sheet S3 reaches flapper FL1 before the trailing edge of sheet S2 of the overlapped sheets S1 and S2 passes through flapper FL1. If flapper FL1 were switched and returned to the first position at this timing, subsequent sheet S3 would be caught in flapper FL1 and a jam would occur. Therefore, the switching of flapper FL1 is stopped and flapper FL1 is not switched, and subsequent sheet S3 is also discharged to the discharge tray 119, thereby preventing a jam from occurring. In this embodiment, the conveying rollers are then stopped (see S22) and conveying control is terminated, but the sheets S1 and S2 that have been fed in duplicate, and the following sheet S3, may also be automatically fed in recovery.

[0095] On the other hand, in step S53, if the information includes the rewind start time (Yes in S53), the process proceeds to step S54. In step S54, the CPU 151 determines whether the rewind start time ("31.145") has arrived. If the rewind start time has not arrived (No in S54), the process is repeated until the rewind start time arrives, and if the rewind start time has arrived (Yes in S54), the process proceeds to step S55.

[0096] Then, the CPU 151 switches the flapper FL1 from the second position to the first position, which is the initial position, that is, switches the conveying path to the downstream paper discharge side (S55), and ends this flapper drive control.

[0097] In other words, this case is the case where the subsequent sheet arrival time is not earlier than the transport path return time, and it is determined that the subsequent sheet will arrive first after the trailing edge of sheet S2, one of the overlapped sheets, has passed through flapper FL1. Therefore, as shown in FIG. 14A, the leading edge of subsequent sheet S3 reaches flapper FL1 after the trailing edge of sheet S2, one of the overlapped sheets S1 and S2, has passed through flapper FL1. By switching flapper FL1 back to the first position at this timing, a jam will not occur if sheet S2 is caught in flapper FL1, or if subsequent sheet S3 is caught in flapper FL1. In other words, while sheets S1 and S2 can be ejected to the ejection tray 119 and subsequent sheet S3 can be conveyed to the downstream printing unit 200, jams can be prevented. Note that in this embodiment, the conveyance rollers are subsequently stopped (see S22) and conveyance control is terminated. However, the overlapped sheets S1 and S2 may be automatically fed by recovery.

[0098] [Summary of the first embodiment] As explained above, when sheets S1 and S2 are overlapped, sheets S1 and S2 may be misaligned, and the rear end of sheet S2 passes (reaches) flapper FL1 later than the rear end of sheet S1 due to the misalignment. However, in this sheet feeding device 110, when the multi-feed detection sensor detects multi-feeding, control unit 150 (i.e., CPU 151) calculates the conveyance path return start time at which the rear end of sheet S2 will pass flapper FL1. Then, at the conveyance path return start time, flapper FL1 is switched from the second position to the first position. This allows multi-fed sheets S1 and S2 to be appropriately guided to error discharge path St14, while switching flapper FL1 after the rear end of sheet S2 has passed flapper FL1, preventing jams from occurring.

[0099] Furthermore, when the multi-feed detection sensor detects a multi-feed, the control unit 150 switches the flapper FL1 from the second position to the first position according to the amount of deviation (multi-feed deviation time t) between the leading edge of the sheet S1 and the leading edge of the sheet S2 in the transport direction V. This allows the flapper FL1 to be switched after the trailing edge of the sheet S2 has passed the flapper FL1.

[0100] Furthermore, the control unit 150 calculates the return start time for the conveyance path by adding the length of time from when the double feed detection sensor detects the leading edge of the sheet S1 until the double feed is detected to the second time it takes for the trailing edge of the sheet S1 to pass the flapper FL1. That is, the control unit 150 adds the time from the detection start time Ts to the double feed occurrence time Td (double feed deviation time t) shown in Fig. 13 to the detection end time Te, and calculates this as the return start time for the conveyance path. This allows the time when the trailing edge of the sheet S2 passes the flapper FL1 to be calculated as the return start time for the conveyance path.

[0101] Furthermore, when sheet S3 is transported following sheet S2, if the subsequent sheet arrival time at which the leading edge of sheet S3 passes flapper FL1 is before the transport path return start time, control unit 150 halts switching of flapper FL1 at the transport path return start time. This prevents flapper FL1 from being switched after the leading edge of sheet S3 has passed flapper FL1, and prevents sheet S3 from being caught in flapper FL1 and causing a jam.

[0102] Furthermore, when flapper FL1 is in the first position in paper feeder 110, it can guide paper to third horizontal transport path Ps13, which transports paper to inkjet head 201, which forms an image. Inkjet head 201, which forms an image using an inkjet system, may be damaged if multiple sheets of paper are transported. However, in paper feeder 110, by appropriately switching flapper FL1 to prevent multiple sheets of paper from being transported to inkjet head 201, it is possible to prevent damage to inkjet head 201. In particular, in paper feeder 110, flapper FL1 can guide multiple sheets of paper to and discharge them into paper output tray 119, allowing invalid paper to be removed.

[0103] Second Embodiment Next, a second embodiment, which is a partial modification of the first embodiment, will be described with reference to Figs. 15 and 16. Fig. 15 is a schematic cross-sectional view showing a paper feeder according to the second embodiment. Fig. 16 is a flowchart showing transport control of the paper feeder according to the second embodiment. In the description of this second embodiment, the same reference numerals are used for parts similar to those in the first embodiment, and their description will be omitted.

[0104] In the first embodiment, the time when the rear end of sheet S2 of the multi-fed sheets passes through flapper FL1 is calculated. In contrast, in the second embodiment, a transport sensor SN4 is disposed on second horizontal transport path Ps12 as a rear end detector that detects the rear end of sheet S2.

[0105] 15, the sheet feeding device 110 according to the second embodiment is provided with a transport sensor SN4 that detects sheets passing through the second horizontal transport path Ps12. That is, the transport sensor SN4 is disposed upstream of the flapper FL1 (error bin branch P5) in the transport direction V, and downstream of the horizontal path junction P4 in the transport direction V. The transport sensor SN4 is configured to detect the trailing edge of the sheet S2 when the overlapped sheets S1 and S2 pass by. Note that, taking into consideration the response from when the transport sensor SN4 detects the trailing edge of the sheet S2 to when the flapper FL1 is driven, it is preferable to dispose the transport sensor SN4 a predetermined distance upstream from the flapper FL1.

[0106] [Control of the paper feeder according to the second embodiment] Next, control of the sheet feeding device according to the second embodiment, particularly the transport control according to the second embodiment, will be described with reference to Fig. 16. Note that the transport control according to the second embodiment is different from the transport control according to the first embodiment (see Fig. 9) in that steps S61 to S63 and steps S71 to S72 are changed, but the remaining processing is substantially the same.

[0107] As in the first embodiment, when the conveyance control unit SS2 receives a paper feed conveyance instruction S101 from the paper feeder management unit SS1, conveyance control of this paper feeder is started. Then, as shown in FIG. 16, first, the CPU 151 drives the conveyance rollers (S11). Next, the CPU 151 determines whether the paper feed conveyance instruction is an instruction to feed paper from one of the first to third paper feed trays 111 to 113, or an instruction to accept paper S3 conveyed from an upstream device (i.e., another paper feeder or the printing unit 200) located upstream in the conveyance direction V (S12). If the instruction is to feed paper from one of the first to third paper feed trays 111 to 113, the process proceeds to step S13; if the instruction is to accept paper conveyance from an upstream device, the process proceeds to step S23.

[0108] In step S13, CPU 151 issues a paper feed start instruction. At this time, it transmits information to paper feed control unit SS3 (i.e., paper feed separation unit) such as "cassette ID: first paper feed cassette, paper transport start time: 12:10:30:000 milliseconds (hereinafter abbreviated as "30.000")." Upon receiving this, paper feed control unit SS3 performs processing for paper feed, and then starts paper transport from second paper feed tray 112 at "30.000," which is the paper transport start time.

[0109] Next, CPU 151 notifies multi-feed detection unit SS4 (i.e., multi-feed detection sensor) of a multi-feed detection start instruction (S14). At this time, if, for example, A3-size (420 mm long) paper is being transported at a speed of 1000 mm / s, the information transmitted is as follows: "Sensor ID: multi-feed detection sensor SN12, detection start time: '30:150', detection end time: '30:570'." The detection start time is determined by the fact that the leading edge of the fed paper passes multi-feed detection sensor SN12 150 msec after the paper is transported. The detection end time is determined by the 420 msec it takes for a 420 mm long paper to pass through (the detection time may be the length of the paper, or any other time). Upon receiving this instruction, multi-feed detection unit SS4 performs detection processing and then starts multi-feed detection at the detection start time, '30:150'.

[0110] In the second embodiment, the CPU 151 determines whether the transport sensor SN4 has detected the leading edge of the sheet S1 (S61). If the leading edge of the sheet S1 has not been detected (No in S61), the process is repeated until the leading edge of the sheet S1 is detected. If the leading edge of the sheet S1 has been detected (Yes in S61), the process proceeds to step S62.

[0111] When the process proceeds to step S62, CPU 151 determines whether the multi-feed detection result from multi-feed detection unit SS4 indicates that a multi-feed has occurred (S62). If a multi-feed has occurred (Yes in S62), the process proceeds to step S63. If a multi-feed has not occurred (No in S62), the process proceeds to step S27. If a multi-feed has occurred and the process proceeds to step S63, it means that the leading edge of the multi-fed sheet S1 in step S61 has been detected by transport sensor SN4. Therefore, CPU 151 issues an instruction to switch flapper FL1, that is, in response to transport sensor SN4 detecting sheet S1, CPU 151 drives flapper FL1 to switch from the initial first position to the second position.

[0112] Next, CPU 151 notifies paper feed device management section SS1 of the occurrence of a multi-feed (S19). The occurrence of a multi-feed is also notified to printing section 200 via paper feed device management section SS1. This notification may be made when sheets S1 and S2 are discharged to paper discharge port 115, but by making the notification earlier, it becomes possible to stop or switch processing of subsequent sheet S3 or printing section 200 earlier.

[0113] Next, CPU 151 determines whether transport sensor SN4 has detected the rear end of sheet S2 of the overlapping sheets (S71). If the rear end of sheet S2 has not been detected (No in S71), the process is repeated until the rear end of sheet S2 is detected. If the rear end of sheet S2 has been detected (Yes in S71), the process proceeds to step S72.

[0114] Then, in step S72, CPU 151 issues an instruction to return flapper FL1. As a result, since transport sensor SN4 detects the rear end of sheet S2, which has shifted and passed later than sheet S1 due to the double feed, flapper FL1 can be returned from the second position to the first position when the rear end of sheet S2 passes flapper FL1. Therefore, sheet S2 will not be caught in flapper FL1, and a jam can be prevented.

[0115] Next, CPU 151 determines whether sheets S1 and S2 have been discharged to discharge outlet 115 (S20). Completion of discharge may be determined from the time, or a sensor that monitors the transport of sheets may be provided nearby to monitor the passage of the trailing edge of sheet S2. The discharge completion time can be calculated by adding the length of the overlapped sheets (including the amount of misalignment due to the overlapped feed) to the time it takes for the leading edge of sheet S1 to reach discharge outlet 115 (which occurs 905 msec after sheet S1 starts to be transported from the second paper feed cassette (see FIG. 7)). If discharge is not complete (No in S20), the process is repeated until discharge is complete. If discharge is complete (Yes in S20), the process proceeds to step S21.

[0116] In step S21, CPU 151 notifies conveyance control unit SS2 that the paper has been discharged to the error bin (paper discharge port 115). As a result, CPU 151 stops the paper discharge rollers (S22) and ends the conveyance control of paper feeder 110.

[0117] On the other hand, as described above, if in step S12 the paper sheet S3 is to be conveyed and accepted from the upstream device, the process proceeds to step S23. When proceeding to step S23, CPU 151 determines whether the paper acceptance time has arrived. If the acceptance time has not arrived, the process is repeated until the acceptance time arrives (No in S23), and if the acceptance time arrives (Yes in S23), the process proceeds to step S24. When proceeding to step S24, CPU 151 accepts paper sheet S3 from the upstream device.

[0118] Next, CPU 151 determines whether it is time for the paper to pass through the error bin branch (P5) (S25). If it is not time, the process is repeated until it is time (No in S25). If it is time (Yes in S25), the process proceeds to step S26.

[0119] In step S26, CPU 151 determines whether the conveying path is directed toward a downstream device (printing unit 200, or paper feeder 110 if it is paper feeder 120, or paper feeder 120 if it is paper feeder 130) downstream in conveying direction V. In other words, it determines whether flapper FL1 is in its initial position. If the conveying path is directed toward the downstream device (Yes in S26), the process proceeds to step S27.

[0120] If no double feed occurred in step S62 (No in S62) or if the conveyance path is directed toward the downstream device (Yes in S26), the process proceeds to step S27, where CPU 151 determines whether sheet S1 or sheet S3 has been discharged to the downstream device. Completion of sheet discharge to the downstream device can be determined from the time, or a sensor that monitors sheet conveyance nearby can be installed to monitor the passage of the trailing edge of sheet S1 or sheet S3. The sheet discharge completion time can be calculated by adding the length of the conveyed sheet to the time it takes for the leading edge of the sheet to reach sheet discharge outlet EX1 (705 msec after sheet S1 begins conveying from the second paper cassette (see FIG. 7)). If sheet discharge is not complete (No in S27), the process is repeated until sheet discharge is complete. If sheet discharge is complete (Yes in S27), the process proceeds to step S28. Then, in step S28, CPU 151 notifies conveyance control unit SS2 that the delivery of sheet S1 or sheet S3 to the downstream device has been completed normally, and then proceeds to step S22. As a result, CPU 151 stops the paper discharge rollers (S22) and ends conveyance control of sheet feeder 110.

[0121] On the other hand, in step S26, if the conveying path is not directed toward the downstream device (No in S26), that is, if the flapper FL1 has been switched and the conveying path is directed toward the paper discharge outlet 115, the process proceeds to step S71. Note that this situation occurs when the previous sheets S1 and S2 are double-fed, and the amount of misalignment is large, so that sheet S3 conveyed from the upstream device reaches flapper FL1 before flapper FL1 can be returned, and flapper FL1 cannot be returned.

[0122] When the process proceeds to step S71 in this way, it is determined whether the transport sensor SN4 has detected the rear end of the sheet S3 that followed the overlapping sheets S1 and S2 (S71). If the rear end of the sheet S3 has not been detected (No in S71), the process is repeated until the rear end of the sheet S3 is detected, and if the rear end of the sheet S3 has been detected (Yes in S71), the process proceeds to step S72.

[0123] Then, in step S72, CPU 151 issues an instruction to return flapper FL1. As a result, since transport sensor SN4 detects the trailing edge of subsequent sheet S3 received from the upstream device in addition to the overlapped sheets S1 and S2, flapper FL1 can be returned from the second position to the first position when the trailing edge of sheet S3 passes flapper FL1. Therefore, sheet S3 will not be caught in flapper FL1, and a jam can be prevented.

[0124] Then, CPU 151 determines whether sheets S1 to S3 have been discharged to discharge outlet 115 (S20). If discharge is not complete (No in S20), the process is repeated until discharge is complete. If discharge is complete (Yes in S20), CPU 151 notifies conveyance control unit SS2 that discharge to the error bin (discharge outlet 115) has been completed. This causes CPU 151 to stop the discharge rollers (S22) and end conveyance control of sheet feeder 110.

[0125] In the transport control of the paper feeder 110 described above, the multiple transport rollers as the transport section 110A are driven or stopped collectively, but it is also possible to drive or stop only the necessary transport rollers sequentially based on the time when the paper arrives.

[0126] Furthermore, although the leading edge of the overlapped paper is detected by the transport sensor SN4, the leading edge of the paper passes at the same time as when there is no overlapped paper, so it may be determined by time.

[0127] [Summary of the second embodiment] As described above, when sheets S1 and S2 are overlapped, sheets S1 and S2 may be misaligned, and the rear end of sheet S2 passes (reaches) flapper FL1 later than the rear end of sheet S1 due to the misalignment. However, in this sheet feeding device 110, when the controller 150 (i.e., CPU 151) detects overlapping sheets S1 and S2 using the overlapping sheet detection sensor, it uses transport sensor SN4 to detect that the rear end of sheet S2 has passed through flapper FL1. Then, in response to the transport sensor SN4 detecting that the rear end of sheet S2 has passed through, flapper FL1 is switched from the second position to the first position. This allows overlapping sheets S1 and S2 to be appropriately guided to error discharge path St14, while switching flapper FL1 after the rear end of sheet S2 has passed through flapper FL1, preventing jams from occurring.

[0128] Furthermore, when sheet S3 is transported following sheet S2, the timing at which the leading edge of sheet S3 passes through flapper FL1 precedes the timing at which the trailing edge of sheet S2 passes through. In this case, control unit 150 switches flapper FL1 to the first position in response to detecting that the trailing edge of sheet S3 has passed through. This switches flapper FL1 after the trailing edge of sheet S3 has passed flapper FL1, preventing sheet S3 from being caught in flapper FL1 and causing a jam.

[0129] The other configurations, actions, and effects of the second embodiment are the same as those of the first embodiment, and therefore a description thereof will be omitted.

[0130] <Possibilities for other embodiments> In the first and second embodiments described above, when a multi-feed is detected in the sheet feeding device 110, the multi-fed sheets are discharged to the sheet output tray 119. However, the present invention is not limited to this, and any device may be used as long as it transports the multi-fed sheets to a location other than the location where normal sheets are transported. For example, the present invention may be applied to a portion of the fixing unit 300 that discharges invalid sheets toward the sheet output port 301. Similarly, the present invention may be applied to a portion of the reversing unit 500 that discharges invalid sheets toward the sheet output port 501. Furthermore, when the present invention is applied to the reversing unit 500 in this way, the destination of normal (non-invalid) sheets is the normal output tray, meaning that the device is not limited to transporting sheets to the image forming unit.

[0131] In the first and second embodiments, the "time" is used to manage the position of the paper. However, this is not limiting, and the "time" may be managed based on a time counted from some standard (for example, the time from when the power is turned on, the time from when the feed start command is issued, etc.). Furthermore, the position of the paper may be managed by coordinates on the device, and the time it takes for the paper to move may be calculated from the coordinates and the transport speed.

[0132] In the first embodiment, the time when the rear end of sheet S2 passes flapper FL1 (transport path return start time) is calculated based on the amount of deviation between double-fed sheets S1 and S2 (double-feed deviation time t (see FIG. 13)). However, the time when the rear end of sheet S2 passes flapper FL1 can be calculated in any way, for example, by detecting the leading edge of sheet S2 (double-feed occurrence time Td) and adding the time obtained by dividing the length of sheet S2 in the transport direction V by the transport speed.

[0133] Furthermore, the image forming system 1 described in the first and second embodiments is merely an example, and any system may be used as long as it has a configuration in which paper is transported and the transport path is switched by a switching unit. In particular, the image forming unit is not limited to an inkjet system, and may be, for example, an electrophotographic system.

[0134] The present disclosure can also be realized by providing a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that realizes one or more functions. [Explanation of symbols]

[0135] 1...Image forming system / 110...Paper feeding device (sheet conveying device) / 110A...Conveying section / 111...First paper feed tray (supporting section) / 111A...Separate paper feed section (feeding section) / 112...Second paper feed tray (supporting section) / 112A...Separate paper feed section (feeding section) / 113...Third paper feed tray (supporting section) / 113A...Separate paper feed section (feeding section) / 119...Paper discharge tray (discharge supporting section) / 150...Control section / 200...Printing section (image forming apparatus) / 201...Inkjet head (image forming (unit) / FL1...Flapper (switching unit) / Ps12...Second horizontal transport path (first transport path) / Ps13...Third horizontal transport path (second transport path) / Ps14...Error discharge path (third transport path) / S1...Paper (first sheet) / S2...Paper (second sheet) / S3...Paper (third sheet) / SN11, SN12, SN13...Double feed detection sensor (double feed detection unit) / SN4...Transport sensor (trailing edge detection unit) / t...Double feed deviation time (deviation amount) / Td...Double feed occurrence time (second time) / V...Transport direction

Claims

1. a conveying unit that conveys a sheet; a switching unit that is switchable between a first position where the sheet conveyed on the first conveying path by the conveying unit is guided to the second conveying path and a second position where the sheet is guided to the third conveying path; a multi-feed detection unit disposed upstream of the switching unit in the sheet conveyance direction, the multi-feed detection unit detecting a multi-feed in which a second sheet following a first sheet overlaps with the first sheet; a control unit that controls the switching unit to the second position when the double feed detection unit detects double feed, and guides the first sheet and the second sheet to the second conveying path, the control unit, when the double feed detection unit detects double feed, calculates a first time period during which the rear end of the second sheet passes through the switching unit, and switches the switching unit from the second position to the first position at the first time period. A sheet conveying device characterized by:

2. when the double feed detection unit detects double feed, the control unit switches the switching unit from the second position to the first position in accordance with an amount of deviation between the leading edge of the first sheet and the leading edge of the second sheet in the conveying direction.

2. The sheet transport device according to claim 1.

3. the control unit calculates the first time by adding a length of time from when the leading edge of the first sheet is detected by the double feed detection unit to when the double feed is detected, to a second time during which the trailing edge of the first sheet passes through the switching unit.

2. The sheet transport device according to claim 1.

4. when a third sheet is conveyed following the second sheet, if a third time at which a leading edge of the third sheet passes the switching unit is before the first time, the control unit cancels switching of the switching unit at the first time.

2. The sheet transport device according to claim 1.

5. the second conveying path is a conveying path for conveying a sheet to an image forming unit where an image is formed; 2. The sheet transport device according to claim 1.

6. the image forming unit forms an image by an inkjet method; 6. The sheet transport device according to claim 5.

7. a discharge support portion for supporting the discharged sheet; the third conveying path is a conveying path that conveys the sheet to the discharge support portion; 2. The sheet transport device according to claim 1.

8. a support portion that supports a plurality of sheets; a feeding unit that feeds the sheet supported by the support unit to the first conveying path, 2. The sheet transport device according to claim 1.

9. a conveying unit that conveys a sheet; a switching unit that is switchable between a first position where the sheet conveyed on the first conveying path by the conveying unit is guided to the second conveying path and a second position where the sheet is guided to the third conveying path; a multi-feed detection unit disposed upstream of the switching unit in the sheet conveyance direction, the multi-feed detection unit detecting a multi-feed in which a second sheet following a first sheet overlaps with the first sheet; a trailing edge detection unit disposed upstream of the switching unit in the conveying direction and configured to detect a trailing edge of the second sheet; a control unit that controls the switching unit to the second position when the double feed detection unit detects double feed, and guides the first sheet and the second sheet to the second conveying path, When the double feed detection unit detects double feed, the control unit switches the switching unit from the second position to the first position in response to detection of the trailing edge of the second sheet by the trailing edge detection unit. A sheet conveying device characterized by:

10. A sheet conveying device according to any one of claims 1 to 9; an image forming apparatus that forms an image on the sheet conveyed from the sheet conveying apparatus, An image forming system comprising:

Images