Sheet transport device, image processing device, sheet transport method

Abstract

To provide a sheet transport device, an image processing device, and a sheet transport method that can prevent the next sheet after the sheet to be fed from being transported beyond the paper feed nip section. [Solution] The image forming apparatus 100 includes a paper feeding processing unit that performs a first paper feeding process by rotating the pickup roller 24, the paper feeding belt 25, and the separation roller 26 in a first direction D1, a second direction D2, and a fourth direction D4, respectively; a first determination processing unit that determines whether or not the leading edge of the document being transported by the first paper feeding process has passed through the paper feeding nip section 26A; and a lowering processing unit that lowers the lift plate 22 after the first determination processing unit has determined that the leading edge of the document has passed through the paper feeding nip section 26A, but before the first paper feeding process is completed.

Description

【Technical Field】 【0001】 The present invention relates to a sheet conveying device, an image processing device, and a sheet conveying method. 【Background Art】 【0002】 A sheet conveying device such as an ADF (Auto Document Feeder) for conveying a document is known. The sheet conveying device includes a sheet placement portion, a lift portion, a pickup roller, a conveying member, and a separation roller. The sheet is placed on the sheet placement portion. The lift portion is provided so as to be able to move up and down in the sheet placement portion, and lifts the sheet placed on the sheet placement portion. The pickup roller is provided above the sheet placement portion and rotates in a first direction capable of conveying the uppermost sheet among one or more sheets lifted by the lift portion in a predetermined conveying direction. The conveying member is provided so as to be able to contact the upper surface of the sheet on the downstream side of the pickup roller in the conveying direction, and rotates in a second direction capable of conveying the sheet conveyed by the pickup roller in the conveying direction. The separation roller forms a paper feed nip portion with the conveying member and rotates in a fourth direction opposite to a third direction capable of conveying the sheet conveyed by the pickup roller in the conveying direction. 【0003】 In the sheet conveying device, after the sheet placed on the sheet placement portion is lifted by the lift portion, a first paper feeding process for feeding the sheet is executed. In the first paper feeding process, the pickup roller, the conveying member, and the separation roller are rotated in the first direction, the second direction, and the fourth direction, respectively. The separation roller rotates in the fourth direction to separate other sheets attached to the sheet to be fed from the sheet to be fed. The first paper feeding process ends when the leading end of the sheet to be fed passes through a registration roller pair disposed on the downstream side of the paper feed nip portion in the conveying direction. 【0004】 Furthermore, a related technology is known in which a sheet transport device performs a second paper feeding process to feed the sheet after the sheet placed on the sheet placement section has been lifted by the lift section, and lowers the lift section while the second paper feeding process is being performed (see Patent Document 1). In the second paper feeding process, the pickup roller, the transport member, and the separation roller are rotated in the first, second, and third directions, respectively. [Prior art documents] [Patent Documents] 【0005】 [Patent Document 1] Japanese Patent Publication No. 2021-61581 [Overview of the Initiative] [Problems that the invention aims to solve] 【0006】 Incidentally, in the conventional sheet conveying device, when a small sheet such as a business card is fed by the first paper feeding process, the rear end of the sheet to be fed may pass the position where the pickup roller applies conveying force to the sheet before the first paper feeding process is completed. In this case, before the first paper feeding process is completed, the pickup roller applies conveying force to the next sheet. Here, if the next sheet reaches the paper feeding nip section along with the sheet to be fed, the next sheet may be conveyed beyond the paper feeding nip section after receiving the conveying force, which may prevent the sheet sensor, which is located downstream of the paper feeding nip section in the conveying direction, from detecting the rear end of the sheet to be fed. 【0007】 In contrast, in the sheet transport device relating to the above-mentioned related technology, the lift section is lowered during the execution of the second paper feeding process, so it is possible to disable the sheet transport function by the pickup roller before the rear end of the sheet to be fed passes the designated position. 【0008】 However, in the sheet transport device relating to the above-mentioned related technology, since the separation roller rotates in the third direction, if the next sheet is attached to the sheet being fed, it is not possible to separate the next sheet from the sheet being fed. 【0009】 The object of the present invention is to provide a sheet transport device, an image processing device, and a sheet transport method that can prevent the next sheet to be fed from being transported beyond the paper feed nip section. [Means for solving the problem] 【0010】 A sheet conveying device according to one aspect of the present invention comprises a sheet placement section, a lift section, a pickup roller, a conveying member, a separation roller, a paper feeding processing section, a first determination processing section, and a lowering processing section. A sheet is placed on the sheet placement section. The lift section is provided to be vertically movable on the sheet placement section and lifts the sheet placed on the sheet placement section. The pickup roller is provided above the sheet placement section and rotates the uppermost of the one or more sheets lifted by the lift section in a first direction that allows it to be conveyed in a predetermined conveying direction. The conveying member is provided downstream of the pickup roller in the conveying direction and is capable of contacting the upper surface of the sheet, and rotates the sheet conveyed by the pickup roller in a second direction that allows it to be conveyed in the conveying direction. The separation roller forms a paper feeding nip section with the conveying member and rotates the sheet conveyed by the pickup roller in a fourth direction opposite to the third direction that allows it to be conveyed in the conveying direction. The paper feeding unit performs a paper feeding process in which it rotates the pickup roller, the transport member, and the separation roller in the first, second, and fourth directions, respectively. The first determination unit determines whether the leading edge of the sheet being transported by the paper feeding process has passed the paper feeding nip. The lowering unit lowers the lift after the first determination unit has determined that the leading edge of the sheet in the transport direction has passed the paper feeding nip, but before the paper feeding process is completed. 【0011】 An image processing apparatus according to one aspect of the present invention comprises a sheet transport device and an image reading unit. The image reading unit reads an image of the sheet being transported by the sheet transport device. 【0012】 A sheet conveying method according to another aspect of the present invention is performed in a sheet conveying device comprising: a sheet mounting section on which sheets are placed; a lift section provided to be vertically movable in the sheet mounting section and lifting the sheets placed in the sheet mounting section; a pickup roller provided above the sheet mounting section and rotating in a first direction capable of conveying the uppermost of the one or more sheets lifted by the lift section in a predetermined conveying direction; a conveying member provided downstream of the pickup roller in the conveying direction and capable of contacting the upper surface of the sheet, and rotating in a second direction capable of conveying the sheet conveyed by the pickup roller in the conveying direction; and a separation roller forming a paper feeding nip section between itself and the conveying member and rotating in a fourth direction opposite to the third direction capable of conveying the sheet conveyed by the pickup roller in the conveying direction, and the method is performed in a sheet conveying device comprising: a paper feeding step; a determination step; and a descent step. In the paper feeding step, a paper feeding process is performed in which the pickup roller, the conveying member, and the separation roller are rotated in the first, second, and fourth directions, respectively. In the determination step, it is determined whether the leading edge of the sheet being transported by the paper feeding process has passed the paper feeding nip. In the lowering step, the lift is lowered after the determination step determines that the leading edge of the sheet in the transport direction has passed the paper feeding nip, but before the paper feeding process is completed. [Effects of the Invention] 【0013】 According to the present invention, it is possible to prevent the next sheet to be transported from being transported beyond the paper feeding nip section. [Brief explanation of the drawing] 【0014】 [Figure 1] Figure 1 is a block diagram showing the system configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] Figure 2 shows the configuration of the ADF and image reading unit of an image forming apparatus according to an embodiment of the present invention. [Figure 3] Figure 3 is a flowchart showing an example of a document conveyance process executed by an image forming apparatus according to an embodiment of the present invention. 【Embodiments for Carrying Out the Invention】 【0015】 Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following embodiments are an example of embodying the present invention and do not limit the technical scope of the present invention. 【0016】 [Configuration of Image Forming Apparatus 100] First, referring to FIG. 1, the configuration of an image forming apparatus 100 according to an embodiment of the present invention will be described. 【0017】 The image forming apparatus 100 is a multifunction device having a plurality of functions such as a facsimile function and a copy function, together with a scan function for reading an image from a document and a print function for forming an image based on image data. The image forming apparatus 100 is an example of the image processing apparatus of the present invention. Note that the image processing apparatus of the present invention may also be a scanner, a facsimile apparatus, a copy machine, or the like. 【0018】 As shown in FIG. 1, the image forming apparatus 100 includes an ADF (Auto Document Feeder) 1, an image reading unit 2, an image forming unit 3, a paper feeding unit 4, an operation display unit 5, a storage unit 6, and a control unit 7. 【0019】 The ADF 1 conveys a document (an example of a sheet of the present invention) to be read by the scan function. 【0020】 The image reading unit 2 realizes the scan function. Specifically, the image reading unit 2 reads an image from a document conveyed by the ADF 1. Further, the image reading unit 2 reads an image from a document placed on the document table 41 (see FIG. 2). 【0021】 The image forming unit 3 realizes the printing function. For example, the image forming unit 3 forms an image on a sheet supplied from the paper feeding unit 4 by an electrophotographic method. For example, the image forming unit 3 includes a photosensitive drum, a charging device, an optical scanning device, a developing device, a transfer device, a cleaning device, a fixing device, and a paper discharge tray. 【0022】 The paper feeding unit 4 supplies a sheet to the image forming unit 3. For example, the paper feeding unit 4 includes a paper feed cassette, a manual feed tray, a sheet conveyance path, and a plurality of conveyance rollers. 【0023】 The operation display unit 5 is the user interface of the image forming apparatus 100. The operation display unit 5 includes a display unit and an operation unit. The display unit displays various information according to a control instruction from the control unit 7. For example, the display unit is a display device such as a liquid crystal display. The operation unit inputs various information to the control unit 7 according to the user's operation. For example, the operation unit is an operation device including operation keys and a touch panel. 【0024】 The storage unit 6 is a non-volatile storage device. For example, the storage unit 6 is a flash memory. 【0025】 The control unit 7 comprehensively controls the image forming apparatus 100. As shown in FIG. 1, the control unit 7 includes a CPU 11, a ROM 12, and a RAM 13. The CPU 11 is a processor that executes various arithmetic processes. The ROM 12 is a non-volatile storage device in which information such as a control program for causing the CPU 11 to execute various processes is stored in advance. The RAM 13 is a volatile or non-volatile storage device used as a temporary storage memory (working area) for various processes executed by the CPU 11. The CPU 11 comprehensively controls the image forming apparatus 100 by executing various control programs stored in the ROM 12 in advance. 【0026】 Note that the control unit 7 may be a control unit provided separately from the main control unit that comprehensively controls the image forming apparatus 100. Further, the control unit 7 may be composed of an electronic circuit such as an integrated circuit (ASIC). 【0027】 [Configuration of ADF1 and image reading unit 2] Next, the configuration of the ADF1 and the image reading unit 2 will be described with reference to Figures 1 and 2. Here, Figure 2 is a cross-sectional view showing the configuration of the ADF1 and the image reading unit 2. 【0028】 As shown in Figure 2, the ADF1 comprises a document placement section 21, a lift plate 22, a housing 23, a pickup roller 24, a paper feed belt 25, a separation roller 26, a pair of registration rollers 27, a plurality of transport roller pairs 28, and a document discharge section 29. The ADF1 also comprises a lift motor 30, a paper feed motor 31, a first sheet sensor 32, and a second sheet sensor 33, as shown in Figure 1. 【0029】 The document to be transported is placed on the document placement section 21. In the ADF1, the document placed on the document placement section 21 is transported in the transport direction D10 shown in Figure 2. The document placement section 21 is an example of a sheet placement section of the present invention. 【0030】 The lift plate 22 is provided in the document placement section 21 so as to be able to move up and down. Specifically, the lift plate 22 is supported so as to be able to swing at its downstream end in the transport direction D10, around an axis perpendicular to the transport direction D10. This allows the lift plate 22 to swing along the swing direction D11 shown in Figure 2. The lift plate 22 swings along the swing direction D11 by receiving driving force supplied from the lift motor 30. The lift plate 22 lifts one or more documents placed in the document placement section 21 until the uppermost document among the one or more documents comes into contact with the pickup roller 24. In Figure 2, each document lifted by the lift plate 22 is shown with a thick line. The lift plate 22 is an example of the lift section of the present invention. 【0031】 The housing 23 houses rollers and other components used for transporting documents. As shown in Figure 2, a document transport path 23A is formed inside the housing 23 to guide the document from the document placement section 21 to the document discharge section 29. In the ADF1, the document placed on the document placement section 21 is transported along the document transport path 23A. 【0032】 As shown in Figure 2, an opening 23B is provided at the bottom of the housing 23. The opening 23B exposes a portion of the document transport path 23A to the outside. At the opening 23B, the first imaging unit 42 of the image reading unit 2 (see Figures 1 and 2) reads the image of the document transported by the ADF 1. 【0033】 The pickup roller 24 is located above the document placement section 21. The pickup roller 24 receives a driving force supplied from the paper feed motor 31 and rotates in a first direction D1 (see Figure 2) that allows the uppermost document among the one or more documents lifted by the lift plate 22 to be transported in the transport direction D10 (an example of a predetermined transport direction in the present invention). By rotating in the first direction D1 while in contact with the document lifted by the lift plate 22, the pickup roller 24 can impart a transport force to the document that allows it to move in the transport direction D10. 【0034】 The paper feed belt 25 is provided in the document transport path 23A. The paper feed belt 25 is also provided so as to be able to contact the upper surface of the document downstream of the pickup roller 24 in the transport direction D10. The paper feed belt 25 receives driving force supplied from the paper feed motor 31 and rotates in a second direction D2 (see Figure 2) that allows the document transported by the pickup roller 24 to be transported in the transport direction D10. By rotating in the second direction D2 while in contact with the upper surface of the document, the paper feed belt 25 can impart a transport force to the document that allows it to move in the transport direction D10. The paper feed belt 25 is an example of a transport member of the present invention. Note that the transport member of the present invention is not limited to a belt-shaped member, but may also be a roller-shaped member. 【0035】 The separation roller 26 is positioned below the paper feed belt 25 and in contact with the paper feed belt 25. The separation roller 26 forms a paper feed nip section 26A (see Figure 2) with the paper feed belt 25. Receiving driving force supplied from the paper feed motor 31, the separation roller 26 rotates in a fourth direction D4 (see Figure 2), opposite to the third direction D3 (see Figure 2), which allows the original document conveyed by the pickup roller 24 to be conveyed in the conveying direction D10. By rotating in the fourth direction D4 while in contact with the underside of another document accompanying the original document being fed, the separation roller 26 can impart a conveying force to the other document that allows it to move in the opposite direction to the conveying direction D10. When the separation roller 26 is in contact with the underside of the original document being fed, the supply of driving force to the separation roller 26 is stopped by a torque limiter provided in the driving force transmission path from the paper feed motor 31 to the separation roller 26. In this case, the separation roller 26 receives the driving force supplied from the paper feed belt 25 via the document to be fed and rotates in the third direction D3. 【0036】 The registration roller pair 27 is located downstream of the paper feed nip section 26A in the document transport path 23A in the transport direction D10. The registration roller pair 27 receives driving force supplied from a transport motor (not shown) which is provided separately from the paper feed motor 31, and transports the document transported by the paper feed belt 25 in the transport direction D10. 【0037】 Multiple transport roller pairs 28 are provided along the transport direction D10 in the section downstream of the registration roller pair 27 in the document transport path 23A. Each transport roller pair 28 receives driving force supplied from the transport motor and transports the document in the transport direction D10. 【0038】 The document output unit 29 outputs the documents that have been transported along the document transport path 23A. 【0039】 The lift motor 30 is a motor that supplies driving force to the lift plate 22. 【0040】 The paper feed motor 31 is a motor that supplies driving force to the pickup roller 24, the paper feed belt 25, and the separation roller 26. 【0041】 The first sheet sensor 32 detects the original document at a first detection position P1 (see Figure 2) which is downstream of the paper feed nip section 26A in the transport direction D10 and upstream of the registration roller pair 27 in the transport direction D10. For example, the first sheet sensor 32 is a reflective type optical sensor. The first sheet sensor 32 is an example of the sheet sensor of the present invention. 【0042】 The second sheet sensor 33 detects the document at a second detection position P2 (see Figure 2) which is downstream of the registration roller pair 27 in the transport direction D10 and upstream of the second imaging unit 43 (see Figure 2) in the transport direction D10. For example, the second sheet sensor 33 is a reflective type optical sensor. 【0043】 As shown in Figures 1 and 2, the image reading unit 2 comprises a document table 41, a first imaging unit 42, and a second imaging unit 43. 【0044】 The document to be scanned is placed on the document tray 41. The document tray 41 is located on the upper part of the housing of the image forming apparatus 100. The ADF1 is provided so as to be openable and closable relative to the document tray 41 and also serves as a document cover that supports one side of the document placed on the first contact glass 411 (see Figure 2) of the document tray 41. 【0045】 As shown in Figure 2, the document glass 41 comprises a first contact glass 411, a second contact glass 412, and a guide member 413. The document on which the image is read by the first imaging unit 42 is placed on the first contact glass 411. When the ADF 1 is closed to the document glass 41, the second contact glass 412 and the guide member 413 face the opening 23B of the housing 23 and form part of the document transport path 23A. The second contact glass 412 transmits light emitted from the first imaging unit 42 toward the opening 23B and light reflected by the document. The guide member 413 guides the document downstream in the transport direction D10 from downstream of the second contact glass 412. 【0046】 The first imaging unit 42 is located below the first contact glass 411 and the second contact glass 412. The first imaging unit 42 is elongated in the depth direction of the paper in Figure 2 and is movably mounted along the left-right direction of the paper in Figure 2. The first imaging unit 42, positioned below the second contact glass 412, reads an image of the surface of the document being transported by the ADF 1. Specifically, the first imaging unit 42 comprises a CIS (Contact Image Sensor) and a housing that accommodates the CIS. The first imaging unit 42 outputs an analog signal corresponding to the image read from the surface of the document. The analog signal output from the first imaging unit 42 is converted into a digital signal (image data) by an analog front-end circuit (not shown) and input to the control unit 7. 【0047】 The second imaging unit 43 is located downstream of the registration roller pair 27 in the transport direction D10 on the document transport path 23A, and upstream of the transport roller pair 28 located at the uppermost position in the transport direction D10 among the multiple transport roller pairs 28. The second imaging unit 43 reads the image of the back side of the document being transported along the document transport path 23A. Specifically, the second imaging unit 43 is a CIS (Computer Identification System). The second imaging unit 43 outputs an analog signal corresponding to the image read from the back side of the document. The analog signal output from the second imaging unit 43 is converted into a digital signal (image data) by the analog front-end circuit and input to the control unit 7. 【0048】 In the image forming apparatus 100, after the document placed on the document placement section 21 is lifted by the lift plate 22, a first paper feeding process is performed to feed the document. In the first paper feeding process, the pickup roller 24, the paper feeding belt 25, and the separation roller 26 are rotated in the first direction D1, the second direction D2, and the fourth direction D4, respectively. The separation roller 26 rotates in the fourth direction D4 to separate other documents attached to the document to be fed from the document to be fed. The first paper feeding process is terminated when the second sheet sensor 33 detects that the leading edge of the document to be fed has passed the second detection position P2 (see Figure 2). 【0049】 Incidentally, in conventional image forming apparatuses, when a small-sized document such as a business card is fed by the first paper feeding process, the trailing edge of the document to be fed may pass the position P0 (see Figure 2) where the pickup roller 24 applies transport force to the document before the completion of the first paper feeding process. In this case, before the completion of the first paper feeding process, the pickup roller 24 applies transport force to the next document. Here, if the next document has reached the paper feeding nip section 26A along with the document to be fed, the next document may be transported beyond the paper feeding nip section 26A after the transport force is applied, which may interfere with the detection of the trailing edge of the document to be fed by the first sheet sensor 32. Note that the application position P0 is the position of the lower end on the outer circumference of the pickup roller 24. 【0050】 In contrast, a related technology is known in which a sheet transport device performs a second paper feeding process after the document placed on the document placement section 21 is lifted by the lift plate 22, and lowers the lift plate 22 while the second paper feeding process is being performed. In the second paper feeding process, the pickup roller 24, the paper feeding belt 25, and the separation roller 26 are rotated in the first direction D1, the second direction D2, and the third direction D3, respectively. In the sheet transport device according to this related technology, since the lift plate 22 is lowered while the second paper feeding process is being performed, it is possible to disable the document transport function of the pickup roller 24 before the trailing end of the document to be fed passes the designated position P0 (see Figure 2). 【0051】 However, in the sheet transport device relating to the above-mentioned related technology, the separation roller 26 rotates in the third direction D3, so if the next document is attached to the document being fed, it is not possible to separate the next document from the document being fed. 【0052】 In contrast, the image forming apparatus 100 according to the embodiment of the present invention can prevent the next document to be fed from being transported beyond the paper feeding nip section 26A, as will be explained below. 【0053】 [Configuration of Control Unit 7] Next, the configuration of the control unit 7 will be explained in more detail with reference to Figures 1 and 2. 【0054】 As shown in Figure 1, the control unit 7 includes a detection processing unit 51, a second determination processing unit 52, a paper feeding processing unit 53, a first determination processing unit 54, a stop processing unit 55, a lowering processing unit 56, and a setting processing unit 57. 【0055】 Specifically, the ROM 12 of the control unit 7 contains a document transport program that causes the CPU 11 to function as one of the aforementioned processing units. The control unit 7 then functions as one of the aforementioned processing units by executing the document transport program stored in the ROM 12. Here, a device comprising the ADF 1 and the control unit 7 is an example of the sheet transport device of the present invention. 【0056】 The document transport program may be recorded on a computer-readable recording medium such as a CD, DVD, or flash memory, and may be read from the recording medium and stored in a storage device such as the storage unit 6. Furthermore, some or all of the processing units included in the control unit 7 may be composed of electronic circuits. Also, the document transport program may be a program that causes multiple processors to function as individual processing units included in the control unit 7. 【0057】 The detection processing unit 51 detects the size of the document placed on the document placement unit 21. 【0058】 For example, the ADF1 includes a pair of side cursors (not shown) that restrict the position of one or more documents placed on the document placement section 21 in the width direction perpendicular to the transport direction D10. The pair of side cursors are arranged opposite each other in the width direction. Each of the side cursors is provided to be movable along the width direction. The pair of side cursors restrict the position of one or more documents in the width direction by contacting both ends of the one or more documents placed on the document placement section 21 in the width direction. 【0059】 Furthermore, the ADF1 includes a signal output unit (not shown) that outputs an electrical signal corresponding to the distance between the pair of side cursors. 【0060】 The detection processing unit 51 determines the size of the document placed on the document placement unit 21 based on the electrical signal output from the signal output unit. 【0061】 The second determination processing unit 52 determines whether the length of the transport direction D10 of the document placed on the document placement unit 21 is greater than or equal to a predetermined specific value. 【0062】 The aforementioned specific value is set based on the distance from the designated position P0 (see Figure 2) to the second detection position P2 (see Figure 2) in the transport path of the document transported by the ADF1. Specifically, the aforementioned specific value is set to a value greater than the distance from the designated position P0 to the second detection position P2. 【0063】 For example, the second determination processing unit 52 determines, based on the detection result from the detection processing unit 51, whether the length of the transport direction D10 of the document placed on the document placement unit 21 is greater than or equal to the specified value. 【0064】 The second determination processing unit 52 may determine whether the length of the transport direction D10 of the document placed on the document placement unit 21 is greater than or equal to the specified value, based on the size of the document corresponding to the document placement unit 21, which has been set in advance by user operation. In this case, the control unit 7 does not need to include the detection processing unit 51. 【0065】 The paper feeding unit 53 performs the first paper feeding process (an example of the paper feeding process of the present invention) by rotating the pickup roller 24, the paper feeding belt 25, and the separation roller 26 in the first direction D1, the second direction D2, and the fourth direction D4, respectively. 【0066】 Specifically, the paper feeding unit 53 starts the first paper feeding process when the document placed on the document placement unit 21 is lifted by the lift plate 22. In other words, the paper feeding unit 53 drives the paper feeding motor 31. The paper feeding unit 53 also terminates the first paper feeding process when the second sheet sensor 33 detects that the leading edge of the document to be fed in the transport direction D10 has passed the second detection position P2 (see Figure 2). In other words, the paper feeding unit 53 stops the paper feeding motor 31. 【0067】 The first determination processing unit 54 determines whether the leading edge in the transport direction D10 of the document transported by the first paper feeding process has passed through the paper feeding nip section 26A (see Figure 2). 【0068】 For example, the first determination processing unit 54 uses the first sheet sensor 32 to determine whether the leading edge in the transport direction D10 of the document being transported by the first paper feeding process has passed through the paper feeding nip section 26A. In other words, the first determination processing unit 54 determines that the leading edge has passed through the paper feeding nip section 26A when the first sheet sensor 32 detects that the leading edge in the transport direction D10 of the document to be fed has passed through the first detection position P1 (see Figure 2). 【0069】 The first determination processing unit 54 may determine that the leading edge in the transport direction D10 of the document being transported by the first paper feeding process has passed the paper feeding nip section 26A when a predetermined specific time has elapsed since the start of the first paper feeding process. The specified time is set based on the time obtained by dividing the transport distance of the document from the position of the leading edge in the transport direction D10 of the document placed on the document placement section 21 to the paper feeding nip section 26A by the transport speed of the document by the pickup roller 24. 【0070】 The stop processing unit 55 temporarily stops the first paper feeding process when the first determination processing unit 54 determines that the leading edge of the document in the transport direction D10 has passed the paper feeding nip section 26A. In other words, the stop processing unit 55 temporarily stops the paper feeding motor 31. 【0071】 The lowering processing unit 56 lowers the lift plate 22 by a preset amount after the first determination processing unit 54 has determined that the leading edge of the document in the transport direction D10 has passed the paper feed nip section 26A, but before the first paper feeding process is completed. 【0072】 For example, the lowering unit 56 lowers the lift plate 22 while the first paper feeding process is stopped by the stop unit 55. The stop of the first paper feeding process by the stop unit 55 is released after the lowering of the lift plate 22 by the lowering unit 56 is completed. This makes it possible to avoid the trailing end of a document passing the designated position P0 between the time it is determined that the leading end of the document has passed the paper feeding nip 26A and the time the pickup roller 24 leaves the document, especially when the document is thick. 【0073】 Furthermore, the lowering processing unit 56 may lower the lift plate 22 when the first determination processing unit 54 determines that the leading edge of the document in the transport direction D10 has passed the paper feed nip unit 26A. In other words, the lowering processing unit 56 may lower the lift plate 22 while the pickup roller 24 is rotating. In this case, the control unit 7 does not need to include the stop processing unit 55. 【0074】 Here, the lowering processing unit 56 does not lower the lift plate 22 if the second determination processing unit 52 determines that the length of the document in the transport direction D10 is greater than or equal to the specified value. This prevents the lift plate 22 from lowering even when, at the end of the first paper feeding process, the trailing edge of the document to be fed has not passed the position P0 (see Figure 2) where the pickup roller 24 applies transport force to the document. 【0075】 The control unit 7 may also enable or disable the function of the lowering unit 56 according to predetermined user operations. In this case, the lowering unit 56 should lower the lift plate 22 regardless of the length of the transport direction D10 of the document, provided that its function is enabled. 【0076】 The setting processing unit 57 sets the amount by which the lift plate 22 is lowered by the lowering processing unit 56, according to a predetermined setting operation. 【0077】 For example, the setting processing unit 57 displays a lowering amount setting screen on the operation display unit 5 in response to a predetermined user operation on the operation display unit 5, which accepts the setting operation. On the lowering amount setting screen, it is possible to arbitrarily set the lowering amount of the lift plate 22. For example, on the lowering amount setting screen, it is possible to set the lowering amount of the lift plate 22 in three stages: "large," "medium," and "small." This makes it possible to adjust the lowering amount of the lift plate 22 according to the thickness of the document being fed. 【0078】 Furthermore, if the amount of descent of the lift plate 22 has not been set by the setting operation, the lowering processing unit 56 only needs to lower the lift plate 22 by a preset initial descent amount. 【0079】 [Document transport processing] The sheet transport method of the present invention will be described below with reference to Figure 3, along with an example of the procedure for document transport processing performed by the control unit 7 in the image forming apparatus 100. Here, steps S11, S12, etc. represent the numbers of the processing procedures (steps) performed by the control unit 7. 【0080】 The detection processing unit 51 detects the size of the document placed on the document placement unit 21 when an instruction to execute an image reading process is received to read the image of the document being transported by the ADF 1. The second determination processing unit 52 determines, based on the detection result by the detection processing unit 51, whether the length of the transport direction D10 of the document placed on the document placement unit 21 is greater than or equal to the specified value. The control unit 7 executes the document transport process when the second determination processing unit 52 determines that the length of the transport direction D10 of the document is less than the specified value. In other words, the document transport process is executed when an instruction to execute the image reading process is received and the length of the transport direction D10 of the document placed on the document placement unit 21 is less than the specified value. 【0081】 <Step S11> First, in step S11, the control unit 7 drives the lift motor 30 to raise the lift plate 22 until the uppermost of the one or more documents placed on the document placement unit 21 comes into contact with the pickup roller 24. 【0082】 <Step S12> In step S12, the control unit 7 starts the first paper feeding process. That is, the control unit 7 drives the paper feeding motor 31. The process in step S12 is an example of the paper feeding step of the present invention and is performed by the paper feeding processing unit 53 of the control unit 7. 【0083】 <Step S13> In step S13, the control unit 7 determines whether the leading edge of the document being transported by the first paper feeding process has passed through the paper feeding nip section 26A (see Figure 2). The process in step S13 is an example of a determination step of the present invention and is performed by the first determination processing unit 54 of the control unit 7. 【0084】 Specifically, when the first sheet sensor 32 detects that the leading edge of the document has passed the first detection position P1 (see Figure 2), the control unit 7 determines that the leading edge has passed the paper feed nip section 26A. 【0085】 Here, if the control unit 7 determines that the leading edge of the document has passed through the paper feed nip section 26A (Yes side of S13), it proceeds to step S14. If the leading edge of the document has not passed through the paper feed nip section 26A (No side of S13), the control unit 7 waits in step S13 for the leading edge of the document to pass through the paper feed nip section 26A. 【0086】 <Step S14> In step S14, the control unit 7 stops the first paper feeding process. That is, the control unit 7 stops the paper feeding motor 31. The process in step S14 is performed by the stop processing unit 55 of the control unit 7. 【0087】 <Step S15> In step S15, the control unit 7 drives the lift motor 30 to lower the lift plate 22 by a preset amount of descent (the amount of descent set by the setting operation, or the initial amount of descent). The process in step S15 is an example of the descent step of the present invention and is performed by the descent processing unit 56 of the control unit 7. 【0088】 <Step S16> In step S16, the control unit 7 restarts the first paper feeding process after the completion of the processing in step S15. That is, the control unit 7 drives the paper feeding motor 31. The processing in step S16 is performed by the stop processing unit 55 of the control unit 7. 【0089】 <Step S17> In step S17, the control unit 7 determines whether the leading edge of the document being transported by the first paper feeding process has passed the registration roller pair 27 (see Figure 2). 【0090】 Specifically, the control unit 7 determines that the leading edge of the document has passed the registration roller pair 27 when the second sheet sensor 33 detects that the leading edge has passed the second detection position P2 (see Figure 2). 【0091】 Here, if the control unit 7 determines that the leading edge of the document has passed the registration roller pair 27 (Yes side of S17), it proceeds to step S18. If the leading edge of the document has not passed the registration roller pair 27 (No side of S17), the control unit 7 waits in step S17 for the leading edge of the document to pass the registration roller pair 27. 【0092】 <Step S18> In step S18, the control unit 7 terminates the first paper feeding process. That is, the control unit 7 stops the paper feeding motor 31. The process in step S18 is performed by the paper feeding processing unit 53 of the control unit 7. 【0093】 After the first paper feeding process is completed, the document fed is transported along the document transport path 23A by the registration roller pair 27 and the multiple transport roller pairs 28. The image of the front surface of the transported document is read by the first imaging unit 42. The image of the back surface of the transported document is read by the second imaging unit 43. 【0094】 <Step S19> In step S19, the control unit 7 determines whether the trailing end of the document being transported by the registration roller pair 27 has passed through the paper feed nip section 26A (see Figure 2). 【0095】 Specifically, when the first sheet sensor 32 detects that the trailing edge of the document has passed the first detection position P1 (see Figure 2), the control unit 7 determines that the trailing edge has passed the paper feed nip section 26A. 【0096】 Here, if the control unit 7 determines that the trailing edge of the document has passed through the paper feed nip section 26A (Yes side of S19), it proceeds to step S20. If the trailing edge of the document has not passed through the paper feed nip section 26A (No side of S19), the control unit 7 waits in step S19 for the trailing edge of the document to pass through the paper feed nip section 26A. 【0097】 <Step S20> In step S20, the control unit 7 determines whether or not a document remains on the document placement unit 21. 【0098】 For example, the control unit 7 uses a sensor (not shown) capable of detecting the presence or absence of a document in the document placement unit 21 to determine whether or not a document remains in the document placement unit 21. 【0099】 If the control unit 7 determines that there is still a document remaining in the document placement unit 21 (Yes in S20), it proceeds to step S11. If there is no document remaining in the document placement unit 21 (No in S20), the control unit 7 terminates the document transport process. 【0100】 Thus, in the image forming apparatus 100, the lift plate 22 is lowered during the execution of the first paper feeding process. Compared to the sheet transport device in the related technology described above, in which the lift plate 22 is lowered during the execution of the second paper feeding process, this makes it possible to separate the next document from the document being fed at the paper feeding nip section 26A when the next document is attached to the document being fed. Therefore, it is possible to prevent the next document following the document being fed from being transported beyond the paper feeding nip section 26A. 【0101】 [Notes on the invention] The following is an overview of the invention extracted from the above-described embodiments. Note that each configuration and processing function described below can be selected and combined as desired. 【0102】 <Note 1> A sheet mounting section on which a sheet is placed; a lift section provided to be vertically movable on the sheet mounting section and lifting the sheet placed on the sheet mounting section; a pickup roller provided above the sheet mounting section and rotating in a first direction capable of transporting the uppermost of the one or more sheets lifted by the lift section in a predetermined transport direction; a transport member provided downstream of the pickup roller in the transport direction and capable of contacting the upper surface of the sheet, and rotating in a second direction capable of transporting the sheet transported by the pickup roller in the transport direction; and a paper feeding nip section formed between the transport member and the pickup roller. A sheet conveying device comprising: a separation roller that rotates in a fourth direction opposite to a third direction that allows the sheet conveyed by the roller to be conveyed in the conveying direction; a paper feeding processing unit that performs a paper feeding process that rotates the pickup roller, the conveying member, and the separation roller in the first, second, and fourth directions, respectively; a first determination processing unit that determines whether the leading edge of the sheet in the conveying direction that is conveyed by the paper feeding process has passed the paper feeding nip unit; and a lowering processing unit that lowers the lift unit after the first determination processing unit has determined that the leading edge of the sheet in the conveying direction has passed the paper feeding nip unit, but before the paper feeding process is completed. 【0103】 <Note 2> The sheet conveying device according to Appendix 1, further comprising a second determination processing unit that determines whether the length of the sheet placed on the sheet placement unit in the conveying direction is greater than or equal to a predetermined specific value, wherein the lowering processing unit does not lower the lift unit when the second determination processing unit determines that the length of the sheet in the conveying direction is greater than or equal to the specific value. 【0104】 <Note 3> The sheet conveying device according to Appendix 2, further comprising a detection processing unit for detecting the size of the sheet placed on the sheet placing unit, and a second determination processing unit for determining whether the length of the sheet placed on the sheet placing unit in the conveying direction is greater than or equal to the specified value, based on the detection result by the detection processing unit. 【0105】 <Note 4> The sheet conveying device according to any one of the appendices 1 to 3, wherein the lowering processing unit lowers the lifting unit when the first determination processing unit determines that the leading edge of the sheet in the conveying direction has passed the paper feeding nip unit. 【0106】 <Note 5> A sheet conveying device according to any one of the appendices 1 to 3, comprising a stop processing unit that temporarily stops the paper feeding process when the first determination processing unit determines that the leading edge of the sheet in the conveying direction has passed the paper feeding nip unit, and the lowering processing unit lowers the lift unit while the paper feeding process is stopped. 【0107】 <Note 6> A sheet conveying device according to any one of the appendices 1 to 5, comprising a sheet sensor that detects the sheet downstream of the paper feeding nip in the conveying direction, wherein the first determination processing unit uses the sheet sensor to determine whether or not the leading edge in the conveying direction of the sheet being conveyed by the paper feeding process has passed the paper feeding nip. 【0108】 <Note 7> A sheet conveying device according to any one of the appendices 1 to 6, comprising a setting processing unit that sets the amount of descent of the lift section by the descent processing unit according to a predetermined setting operation. 【0109】 <Note 8> An image processing apparatus comprising a sheet transport device described in any of Appendix 1 to 7, and an image reading unit for reading an image of the sheet transported by the sheet transport device. 【0110】 <Note 9> A sheet mounting section on which a sheet is placed; a lift section provided to be vertically movable on the sheet mounting section and for lifting the sheet placed on the sheet mounting section; a pickup roller provided above the sheet mounting section and rotating in a first direction capable of transporting the uppermost of the one or more sheets lifted by the lift section in a predetermined transport direction; a transport member provided downstream of the pickup roller in the transport direction and capable of contacting the upper surface of the sheet, and rotating in a second direction capable of transporting the sheet transported by the pickup roller in the transport direction; and a paper feeding nip section formed between the transport member and the sheet transported by the pickup roller. A sheet conveying method performed with a sheet conveying device comprising: a separation roller that rotates in a fourth direction opposite to a third direction that allows the sheet to be conveyed in the conveying direction, the method comprising: a paper feeding step in which a paper feeding process is performed in which the pickup roller, the conveying member, and the separation roller are rotated in the first, second, and fourth directions, respectively; a determination step in which it is determined whether or not the leading edge of the sheet in the conveying direction that is conveyed by the paper feeding process has passed the paper feeding nip; and a lowering step in which the lift is lowered after it has been determined by the determination step that the leading edge of the sheet in the conveying direction has passed the paper feeding nip, but before the paper feeding process is completed. [Explanation of symbols] 【0111】 1 ADF 2 Image reading unit 3 Image forming unit 4 Paper feed section 5 Operation display section 6 Memory section 7 Control Unit 21 Manuscript Placement Section 22 Lift Plates 23 cabinets 24 Pickup Rollers 25 Paper feed belt 26 Separation rollers 26A Paper feed nip section 27 Resist Roller vs 28 Conveyor roller pair 29 Document output section 30 Lift Motors 31 Paper feed motor 32. First seat sensor 33. Second seat sensor 41 Manuscript stand 42 First Imaging Unit 43 Second Imaging Unit 51 Detection Processing Unit 52 Second Determination Processing Unit 53 Paper feed processing unit 54 First Determination Processing Unit 55 Stop Processing Unit 56 Downward Processing Unit 57 Configuration Processing Unit 100 Image forming apparatus

Claims

[Claim 1] A sheet mounting section on which the sheet is placed, A lift unit is provided in the sheet placement section so as to be able to move up and down, and lifts the sheet placed on the sheet placement section, A pickup roller is provided above the sheet placement section and rotates in a first direction capable of transporting the uppermost sheet among one or more sheets lifted by the lift section in a predetermined transport direction. A conveying member is provided downstream of the pickup roller in the conveying direction so as to be able to contact the upper surface of the sheet, and rotates in a second direction so as to be able to convey the sheet conveyed by the pickup roller in the conveying direction, A separation roller that forms a paper feeding nip section with the transport member and rotates in a fourth direction opposite to the third direction which allows the sheet transported by the pickup roller to be transported in the transport direction, A paper feeding processing unit that performs a paper feeding process by rotating the pickup roller, the transport member, and the separation roller in the first, second, and fourth directions, respectively, A first determination processing unit that determines whether the leading edge of the sheet being transported by the paper feeding process has passed the paper feeding nip section, A lowering processing unit lowers the lift section after the first determination processing unit determines that the leading edge of the sheet in the transport direction has passed the paper feed nip section, but before the paper feeding process is completed. A sheet transport device equipped with the following features. [Claim 2] The sheet is placed on the sheet placement section and the length in the transport direction of the sheet is determined to be equal to or greater than a predetermined specific value. The lowering unit, when the second determination unit determines that the length of the sheet in the transport direction is greater than or equal to the specified value, will not lower the lift unit. The sheet conveying device according to claim 1. [Claim 3] The sheet placement section includes a detection processing unit for detecting the size of the sheet placed on it, The second determination processing unit determines, based on the detection result by the detection processing unit, whether the length of the sheet placed on the sheet placement unit in the transport direction is greater than or equal to the specified value. The sheet conveying device according to claim 2. [Claim 4] The lowering unit lowers the lift unit when the first determination unit determines that the leading edge of the sheet in the transport direction has passed the paper feed nip unit. A sheet conveying device according to any one of claims 1 to 3. [Claim 5] The system includes a stop processing unit that temporarily stops the paper feeding process when the first determination processing unit determines that the leading edge of the sheet in the transport direction has passed the paper feeding nip unit. The lowering section lowers the lift section while the paper feeding process is stopped. A sheet conveying device according to any one of claims 1 to 3. [Claim 6] A sheet sensor is provided that detects the sheet downstream of the paper feeding nip section in the transport direction. The first determination processing unit uses the sheet sensor to determine whether the leading edge in the transport direction of the sheet being transported by the paper feeding process has passed the paper feeding nip section. A sheet conveying device according to any one of claims 1 to 3. [Claim 7] The system includes a setting processing unit that sets the amount of descent of the lift section by the descent processing unit according to a predetermined setting operation. A sheet conveying device according to any one of claims 1 to 3. [Claim 8] A sheet conveying device according to any one of claims 1 to 3, An image reading unit that reads an image of the sheet being transported by the sheet transport device, An image processing device equipped with the following features. [Claim 9] A sheet conveying method performed with a sheet conveying device comprising: a sheet placement section on which a sheet is placed; a lift section provided to be vertically movable on the sheet placement section and for lifting the sheet placed on the sheet placement section; a pickup roller provided above the sheet placement section and rotating in a first direction capable of conveying the uppermost of one or more sheets lifted by the lift section in a predetermined conveying direction; a conveying member provided downstream of the pickup roller in the conveying direction and capable of contacting the upper surface of the sheet, and rotating in a second direction capable of conveying the sheet conveyed by the pickup roller in the conveying direction; and a separation roller that forms a paper feeding nip section between itself and the conveying member and rotates in a fourth direction opposite to the third direction capable of conveying the sheet conveyed by the pickup roller in the conveying direction, wherein A paper feeding step in which the pickup roller, the transport member, and the separation roller are rotated in the first, second, and fourth directions, respectively, is performed. A determination step of determining whether the leading edge of the sheet being transported by the paper feeding process has passed the paper feeding nip section, A lowering step is performed to lower the lift section after the determination step determines that the leading edge of the sheet in the transport direction has passed the paper feed nip section, but before the paper feeding process is completed. A sheet transport method including the following.

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